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Nanoscale light field imaging with graphene
Communications Materials volume 3 , Article number: 40 ( 2022 ) Cite this article 2075 Accesses 14 Altmetric Metrics details
Modern nano-optics and nanophotonics rely heavily on the precise formation of nanostructured light fields. Accurate and deterministic light field formation and characterization are indispensable for device operation as well as for revealing the underlying physical mechanisms involved. Despite a significant progress made in detection of scattered light with extremely high precision down to 1 nm resolution, there are only a limited number of techniques for direct subwavelength light mapping which do not rely on measurements of light scattering, fluorescence, or non-linear light conversion. Hence, techniques for direct conversion of light to electrical signals with precise and non-destructive imaging of nanoscale light would be of great benefit. Here, we report a nanoscale light field imaging approach based on photodetection with a p-n junction that is induced and moved inside a graphene probe by gate voltage, formed by a set of external electrodes. The spatial resolution of this electrical scanning technique is determined by p-n junction width, reaching ~ 20 nm. The developed approach is demonstrated with mapping the electric field distribution of a plasmonic slot-waveguide at telecom wavelengths. Our method provides a non-invasive nanoscale light field imaging that ensures extremely high spatial resolution and precision. Similar content being viewed by others Real-space imaging of acoustic plasmons in large-area graphene grown by chemical vapor deposition Strong in-plane scattering of acoustic graphene plasmons by surface atomic steps Large-area nanoengineering of graphene corrugations for visible-frequency graphene plasmonsIntroduction. Nanoscale light manipulation and characterization are two pillars of modern nano-optics 1 , 2 , 3 . Recently, a significant progress in this field has been realized through the use of plasmonic structures 4 and their assemblies 5 , 6 , 7 , superlenses 8 , 9 , plasmonic waveguides 10 , graphene plasmonics 11 , 12 , and optical phononics 13 . At the same time, most often the light field imaging and characterization still rely on microscopy methods: detection of scattered propagating optical fields that are subject to the diffraction limit, thus limiting the spatial resolution to a fraction of the light wavelength 14 . The resolution of light field imaging can be significantly improved by utilizing optical near-fields 15 . Unfortunately, the near-field optical microscopy suffers from the fundamental six-power scaling of scattered power with the probe size 16 that limits the resolution in practice for direct light mapping to the level of 50 nm at optical wavelengths 17 , 18 . The archetypal near-field microscopy is also inherently invasive as the detected optical fields are scattered by a probe immersed in an interrogated optical (near) field. Moreover, the workhorse of modern near-field optical characterization, scattering scanning near-field optical microscopy (s-SNOM) with pseudo-heterodyne interferometric detection 17 , utilizes demodulation of detected signals at high harmonics to suppress the background, a very efficient approach that however introduces inevitably image distortions when fields with different spatial frequencies are being imaged. It should be mentioned that there have been developed various electron microscopies, such as electron energy-loss spectroscopy (EELS) and cathodoluminescence (CL) microscopy, that provide information on the optical response of nanostructures with unmatched, down to sub-nanometre, spatial resolutions by making use of tightly focused electron beams 18 . The optical information is deduced by analyzing spatial maps of correspondingly electron energy loss spectra or spectra of emitted radiation, mapping the efficiency of resonant excitation of hybrid polariton modes, and relating the efficiency maps to the mode spatial distributions. The electron microscopies provide thereby indirect access to the optical information, and one has to use elaborate data treatment to extract this information and mainly that associated with resonant excitations 18 . Indirect methods of light imaging using scattered fields can also achieve extremely high spatial resolution down to 1 nm. For example, mapping of Brownian motion of a dye particle was used to image fluorescent profile of a single hot spot with 1 nm resolution 19 , surface-enhanced Raman scattering can be used to evaluate electric fields with high spatial resolution of 5 nm, see review 20 , backscattered light can be used to determine optical oscillation patterns of plasmon modes with the help of s-SNOM achieving resolution of <10 nm 21 . However, these indirect methods (while providing extremely high spatial resolution) are often invasive and rely on certain assumptions which allow one to translate measured parameters to light field maps. Here we describe a conceptually different direct and virtually non-invasive method of nanoscale light-field imaging with a lateral resolution of ~20 nm. The method is based on the photoelectric effect in a p-n junction induced in graphene. The position of such p-n junction can be very accurately controlled by an external gate voltage. The graphene surface defines the plane of optical field imaging and should thus be placed near a nanostructure generating nanoscale light fields to be characterized. As a practical example, we measure the electric field profile of a strongly confined plasmonic slot-waveguide mode at telecom wavelengths. The experimentally obtained mode profile is found to be in excellent agreement with numerical simulations. Our method provides a practical way of nanoscale light field imaging with extremely high spatial resolution and precision. It should be emphasized that, in terms of the optical information made available, our approach is similar to conventional near-field microscopy techniques 15 , 17 , but, being radically different in the operation principle, allows one to circumvent the aforementioned fundamental limitation in the achievable spatial resolution. It is worth stressing that light field imaging discussed in this work is concerned with non-destructive mapping of optical fields with direct conversion of light to electrical signals. The limitations of our method in the presented form are connected to the complex fabrication procedures and limited geometries which can be probed. We believe that these limitations can be overcome with technique development. Nanoscale mapping of light fields with grapheneThe concept of nanoscale mapping of light fields with the help of graphene is illustrated in Fig. 1 (here we consider one-dimensional light field imaging for simplicity). A graphene sheet is placed in the region of interest and electrically connected with source and drain contacts. It is important that the source and drain contacts are made from the same material and are kept at the same temperature to avoid thermopower parasitic signals. Gate dielectric is deposited on top of graphene, and two parallel metallic gates are fabricated on top of the dielectric, defining the orientation of a p-n junction and, thus, the scanning direction (parallel and perpendicular to the gate electrodes, respectively). Note that the two-dimensional light imaging with this concept is, in principle, feasible, but would require a more complex gating arrangement.  a Schematics of a p-n junction induced in graphene by gating of a plasmonic waveguide. b Fermi energy in initially doped graphene calculated in the presence of a gate voltage applied to one side of the waveguide. c A graphene p-n junction position as a function of gate voltage applied to one side of a waveguide. d Electric field of a p-n junction induced in graphene. When the area between the two gating contacts is exposed to light—an additional electrical signal is observed in graphene. Here, it is worth mentioning that graphene absorption in the visible and near-infrared light is ~ 2.3% at normal incidence 22 and at the level of 0.01–0.1 dB·μm −1 for confined plasmonic modes propagating along the graphene layer 23 , so that the influence of graphene on light field distributions can be neglected. There are several phenomena that could contribute to the electrical signal: the photoelectric 24 , thermoelectric 25 , and bolometric 26 effects. While the bolometric effect should be zero in non-biased graphene 26 , both the photoelectric and thermoelectric effects could, in general, contribute to the electrical signal induced by light illumination and provide the possibility for the electrical detection of light fields. It is often assumed that the thermoelectric effect yields the largest contribution 26 . However, in the case when the source and the drain are kept at the same temperature and made of the same material, it is possible to show that the total thermoelectric contribution is exactly zero for metals 27 (see also Supplementary Note 1 ). The exception to this rule is a discontinuity in temperature derivative 28 or dependence of the mean free path of electrons on the wavevector 27 . For semiconductors, the situation is more complicated and the contribution of the thermoelectric effect could be non-zero. In the following, we will assume that the main contribution to the photo-electrical signal in our case comes from the photoelectric effect, which requires the presence of a p-n junction in graphene to separate electrons and holes produced during light absorption. The above consideration suggests the following method of nanoscale light field imaging. Initially, doped graphene (e.g., p -doped) is gated by the gating contact with a positively applied voltage V G2 while the other contact is connected to ground ( V G1 = 0) in such a way that a p-n junction is formed in the area where the light is present (see Fig. 1a ). A non-zero photoelectric current is thereby generated, with the current being proportional to the electric field intensity at the position of the p-n junction where the electron–hole pairs produced by light are separated due to the electric field applied. Variation of Fermi energy across a p-n junction induced in graphene in our geometry (Fig. 1b ) was calculated for the 30 nm-thin hafnia dielectric separator using the established methodology 29 , 30 (see also Supplementary Note 2 ). A change in the gating voltage causes a lateral displacement of the p-n junction location within the graphene sheet (Fig. 1c ). Moving the p-n junction, where the photoelectric signal is generated, across the gap between the gating electrodes allows one to accurately map the light field distribution across the gap. Note that the described field mapping approach, contrary to scanning near-field microscopy 15 , does not involve any moving parts and is thereby amenable to a very precise control of the scanning coordinate. The lateral size of p-n junction can be estimated from the built-in electric field distribution (Fig. 1d ) and, for the 30 nm-thin hafnia separator, is ~ 20 nm, which is close to the previously reported values 29 , 30 . It is worth mentioning that the calculated width of the p-n junction (Supplementary Note 2 ) changes around 40% for different gating voltages applied. However, the width was reasonably constant (~20 nm) in the region of the fast changes of the studied waveguide mode. In addition, Supplementary Note 2 calculates the “photo-active” width of the p-n junction in which electric fields are large enough to separate electron–hole pairs produced by light and which defines the spatial resolution of the technique. The calculated “photo-active” width (and hence the resolution of our technique) was below 20 nm for all gating voltages applied. Finally, we extracted the experimental spatial resolution of our technique from the measured data as described in Supplementary Note 6 . This spatial resolution of light field mapping was also around 20 nm. This resolution can be easily improved by decreasing the thickness of a dielectric separator or lowering the temperature (see Supplementary Note 2 ) or using advanced gating electrode geometries. Nanoscale light field imaging in plasmonic slot waveguidesFor the experimental demonstration of our imaging approach, we have conducted the nanoscale electric field mapping of the gap surface plasmon (GSP) mode supported by a plasmonic slot waveguide. The plasmonic slot waveguide configuration, apart from allowing to squeeze the mode field down to nm-sized lateral dimensions 31 , has the advantage of fully exploiting the available dielectric space and thus making the best out of the confinement-loss trade-off 10 . It has been widely used in plasmon-empowered nanophotonics for demonstrating diverse ultra-compact components, ranging from branched and cross-shaped resonators 31 to high-speed fibre-coupled electro-optical 32 and ultrafast energy-efficient all-optical 33 modulators. The plasmonic slot waveguide configuration used for the demonstration of light field imaging with graphene (Fig. 2a ) was designed to operate at telecom wavelengths 34 . To fabricate the device, two pieces of graphene flakes were wet transferred on the silicon substrate that has a 1500 nm oxide layer on the top. Note that the dielectric silica layer should be sufficiently thick to minimize leakage of the GSP mode into the high refractive index silicon substrate. Graphene flakes were etched into two 4 µm-wide strips to serve as two detectors or as a modulator and a detector (see “Methods”). Then, a 30 nm-thick high refractive index dielectric (hafnium oxide) layer was deposited via electron beam evaporation above graphene strips to electrically isolate the graphene strips from the plasmonic waveguide structure used also for graphene gating. Hafnia was previously demonstrated to be a reliable dielectric layer for graphene gating with low voltages due to supercapacitance effect 35 , 36 . Next, a 100 nm-thick silver waveguide structure with a 300 nm slot between the two strips was fabricated using electron beam lithography and lift-off process. During this procedure, 100 nm-thick silver contacts to the graphene flakes and the waveguide legs were also fabricated (Fig. 2b ). The slot waveguide incorporates a 90° bend to enhance the visibility of the out-coupled (relatively weak) radiation as compared to that specular-reflected at the input coupler by using crossed polarizers (Supplementary Note 3 ). To efficiently interface free-space propagating (normal to the surface) radiation with the GSP mode supported by the slot plasmonic waveguide, two dipole nano-antennas with back reflectors 34 were fabricated near the waveguide terminations (inset in Fig. 2b ). Finally, a 1.5 µm-thick layer of polymethyl methacrylate (PMMA) was used to cover the whole configuration in order to encapsulate the device and avoid oxidization.  a Schematics of the antenna-coupled plasmonic waveguide device. Two pieces of graphene work separately for the optical modulation and electrical detection of the waveguide mode. b A microscope image of one device. Inset shows an enlarged picture of the nano-antenna and the reflector taken by scanning electron microscope. c An experimental setup. A lamp and CCD camera were used to locate the sample. A NIR camera was used to detect input and output signals and to measure the light modulation under gating. An optical chopper and lock-in was used to achieve electrical detection of light in the waveguide. The optical excitation of the resulting waveguide configuration involved a focused (40× objective with NA = 0.65) incident 1550-nm laser beam polarized parallel to the in-coupling antenna. The detection of the out-coupled radiation was performed in the cross-polarized configuration (Fig. 2c ). Using InGaAs short-wave infrared (SWIR) camera, we controlled the excitation of the waveguide mode by monitoring the input and output light intensities (Supplementary Fig. 6b ). At the same time, we were able to measure a photo-current induced in graphene (between the source and drain contacts) as a function of the gate voltage in the presence/absence of light. This was performed using either light modulation with an optical chopper and lock-in detection, which provided the photocurrent response due to the GSP mode absorption by graphene, or direct measurements of the photocurrent with a source metre, which gave the dark and light responses. The gating characteristics of graphene were determined by applying the same gate voltage to both waveguide sides G1 and G2 with a graphene strip being grounded (Fig. 3a ). The range of applied gate voltages was determined by supercapacitor gating property of e-beam evaporated HfO 2 35 , 36 . The ratio of the maximum and minimum values of the graphene sheet resistance was above 4 which suggests good quality of the graphene used. It is worth noting that the graphene was initially p -doped as the Dirac peak is shifted to the positive voltage (Fig. 3a ). We also verified that the graphene strips interact with the GSP waveguide mode by realizing the modulation of output light intensity with graphene being gated to achieve the Pauli blocking effect 37 . By applying a 1 Hz square-wave gate signal with 6 V amplitude and 1 V offset to both sides of the waveguide, we observed a 12% modulation of the transmitted output light (Supplementary Fig. 6e ). This modulation level corresponds to the modulation depth of 0.12 dB·μm −1 , which is significantly larger than those obtained previously with hybrid graphene plasmonic waveguide modulators 23 , 35 , and assigned to strong change in graphene absorption due to Pauli blocking. It is worth noting that these measurements allowed us to establish that Fermi level in graphene reaches half of the excitation energy (conditions for the Pauli blocking) at the applied gate voltage of 5.5 V.  a The resistance of graphene as a function of the gate voltage applied to both G1 and G2 contacts for a sample with a 30 nm HfO 2 dielectric layer. b A photovoltage measured between the source and drain of graphene as a function of the gate voltage G2 when the contact G1 is grounded. The photovoltage was measured with an optical chopper and lock-in amplifier. c A photovoltage (drain voltage in open circuit) and d a photocurrent (drain current in a short circuit) as a function of the gate voltage G2 with and without light input through the waveguide, measured directly with a source metre. Both the source and the G1 contact were connected to the ground. e Dependence of the photocurrent on the drain bias voltage of graphene with and without illumination. Both source and G1 are connected to ground, and 0.4 V gate voltage is applied to G2. f Linear dependence of the photovoltage on the incident light power with a fixed gate voltage of 0.4 V applied to G2 and G1 contact being grounded. The data for a , b and c – f were measured on two different samples with the same geometry. The main result of our work, electrical mapping of light intensity with the help of graphene, was obtained with the gate voltage being applied to the contact G2 (while the contact G1 was grounded) to form a p-n junction in graphene underneath, which could then be moved by adjusting the gate voltage (see Fig. 1c ). Using the input laser light at the wavelength of 1550 nm and power of 0.5 mW, the corresponding photovoltage was measured (at zero applied bias between the source and drain contacts) with lock-in detection (chopping at 800 Hz) as a function of the gate voltage applied to G2 (Fig. 3b ). The photovoltage being near zero for the gate voltages below 0.2 V (not large enough to induce p-n junction in graphene at the places with light fields) is seen to increase sharply for larger gate voltages, reaching the maximum value of ~ 5 µV at 0.4 V gate voltage. The drain photovoltage measured as a function of the gate voltage (Fig. 3b ) allowed us to restore the electromagnetic field profile of the GSP mode excited in the plasmonic slot waveguide as described in “Discussion”. Note that the maximum gate voltage applied and thereby maximum of the p-n junction displacement was restricted by the electric breakdown of the dielectric. We have also measured both the photovoltage and photocurrent dependencies on the gate voltage directly with a source metre (i.e., without using the lock-in detection) under the light and dark conditions (i.e., with and without the incident light). Two representative runs (demonstrating the repeatability of measurements) are displayed for the light and dark photovoltages (Fig. 3c ) and photocurrents (Fig. 3d ) signals. Both light and dark photovoltages show a non-zero limit at negative voltages which is associated with the contact voltages. At the same time, the difference between the dark and light photovoltages (the yellow curve in Fig. 3c ) follows the same behaviour as that observed with the lock-in measurements (Fig. 3b ). The light and dark photocurrents measured at the conditions of zero applied bias voltage (Fig. 3d ) behave similarly to the corresponding photovoltages (Fig. 3c ). The dark current and voltage dependencies connected by the Ohm’s law reflect the gating characteristics of graphene strips (Supplementary Note 4 and Supplementary Fig. 7 ). Besides, both light and dark photocurrents show a linear dependence on the bias voltage between the source and the drain (from −10 to 20 µV) provided the gate voltage applied to the contact G2 is constant (Fig. 3e ). Finally, the photovoltage was measured to depend linearly on the incident light power (Fig. 3f ) as one would expect for the photo-response governed by the photoelectric effect. It is worth mentioning that linear photoresponse could also be observed for thermoelectric effect at some conditions 25 , 38 . Calculations of the thermoelectric contribution in the linear approximation for our structures are provided in Supplementary Note 7 . Light propagation and field distribution in our device were modelled with finite difference time domain (FDTD) simulations (Lumerical) for the experimental geometry and conditions (Supplementary Note 5 ), revealing details of the GSP mode propagation and attenuation in the waveguide (Fig. 4a ). The simulated power transmission ratio P out / P in was 0.12%, which is close to the experimentally measured ratio of 0.1%. To get more accurate values of electric field distribution of the studied GSP mode, we employed the two-dimensional (2D) mode analysis using the finite-element method (FEM) implemented in COMSOL software (“Methods”). The 2D distribution of electric field magnitude in the waveguide cross-section (Fig. 4b ) represents a typical GSP mode field profile in a slot waveguide, with the electric field component E x (across the slot and in the graphene plane) being strong and weakly varying (Fig. 4c ) resembling the electrostatic field distribution in a capacitor.  a Simulated electric field distribution excited by a laser beam (wavelength of 1550 nm) that falls onto the input antenna (taken in the plane of the waveguide at the half-height of the waveguide and calculated with the help of Lumerical FDTD solutions). b Simulated electric field distribution in the cross-section of the plasmonic slot waveguide calculated with the help of Comsol software. c The line-scan of the norm of electric field calculated at the graphene position. d Comparison of the simulated field profile in the plasmonic slot waveguide (the red solid line) with the reconstructed profile obtained with a p-n junction moved in graphene by gating (the blue circles). The main contribution to the photo-response in our geometry comes from photoelectric effect in the p - n junction induced in graphene by the gating voltage as discussed above. In order to recover the mode profile along the graphene from the photovoltage dependence on the gate voltage (Fig. 3b ), one should verify linearity of the photo-response with respect to the mode power (Fig. 3f ) and correlate the position of the graphene p-n junction and the gating voltage applied to contact G2 (Fig. 1c ). With this information at hand, we were able to plot the intensity of the (GSP mode) electric field component in graphene plane as a function of the p-n junction position, obtaining thereby the GSP mode field profile in the plasmonic slot waveguide. Excellent agreement between the calculated and reconstructed plasmonic mode intensity profiles (Fig. 4d ) demonstrates the success of electrical mapping of optical field intensity using graphene. The possible reason for a disagreement of profiles at large gating voltages (that were needed to move the p-n junction in graphene to the middle of the waveguide) is connected to larger leakage currents inside the dielectric which break simple capacitance relation between the applied voltage and the induced charges in the graphene sheet. It is worth adding that the thermoelectric effect was often claimed to be the main contributor to the generated by light signals in hybrid graphene/plasmonic systems 25 , 38 . However, the calculations of the thermoelectric contribution in the linear approximation for our structures (provided in Supplementary Note 7 ) were not able to describe the measured data. The spatial resolution of this mapping depends on the properties of the p-n junction induced in graphene. The spatial resolution of our measurements was extracted from comparison of the measured field profile with the calculated field distribution in Supplementary Note 6 . This comparison yielded the Gaussian apparatus function with width of 9.5 nm and the resolution at the full width at half maximum of the response function of 22 nm. Since we applied the gating voltages of ~ 1 V, which is much smaller than 5.5 V necessary to achieve Pauli blocking in our devices, this implies that Pauli blocking did not affect the light absorption in the induced graphene p-n junction. Using the FDTD modelling we estimated the maximal photo-current produced in the graphene p-n junction under our experimental conditions as ~ 3 nA, which is close to the observed photocurrents (Supplementary Note 5 ). Finally, it is worth stressing again that graphene does not significantly perturb electromagnetic field distributions due to small light absorption. Our light-field imaging method is especially useful for characterization of strongly confined optical modes supported by planar nanophotonic circuitry, since it allows natural integration of intermediate graphene monolayers and gate electrodes (which, potentially, can also be made from graphene, thus, making the whole system even less invasive). An addition of a graphene layer to a nanostructure is not a difficult process: it requires several additional steps in the fabrication procedure or one transfer step if we apply graphene to a ready-made structure. The measurement procedure then requires only simple optics and a source metre and, hence, is open to many researchers. In our work, we have demonstrated only one-dimensional (1D) imaging of plasmonic light fields. We note that electric gates, necessary for implementation of our method, could have other symmetry, e.g., we can use circular nanoparticles and circular gates, x–y gates, or we can place studied nanoparticles (even made of dielectric) inside the plasmonic slot waveguide and compare the field profiles with and without nanoparticles. We can also envisage a creation of complex moving p-n junction by a proper electron illumination. Even at the simplest 1D realization described in our work, our technique is already capable of achieving what none of existing microscopy technique can achieve and we have no doubts that it can be developed further. We have suggested and experimentally realized the electromagnetic field mapping based on the photo-detection with a p-n junction induced and moved inside graphene by an external gate voltage. The spatial resolution of this electrical, rather than mechanical, scanning technique is determined by the p-n junction width of ~20 nm which can further be improved by decreasing the thickness of the gating dielectric. The developed approach is demonstrated with mapping the electric field distribution of a strongly confined plasmonic slot-waveguide mode at telecom wavelengths, resulting in the mode profile found in excellent agreement with numerical simulations. Importantly, the developed configuration exhibited also good electro-optical modulation characteristics, featuring the modulation depth of 0.12 dB·μm −1 at the gate voltage amplitude of 6 V. Our method of non-invasive light mapping provides a fresh paradigm in nanoscale optical characterization that ensures extremely high spatial resolution and precision, offering at the same time promising opportunities for nanoscale plasmonic on-chip devices. FabricationTo fabricate the devices, a piece of graphene grown on copper by a chemical vapour deposition process was transferred on a Si substrate with top 1.5 µm thick SiO 2 layer using a standard wet-transfer method: a layer of PMMA was firstly spin-coated on the graphene, and then the copper underneath was etched in an ammonium persulfate solution. The floating membrane was then moved to deionized water with the help of a clean Si chip to remove the ammonium persulfate residue. Finally, the PMMA/graphene membrane was fished with the substrate. After that, it was left to dry for 24 h, and after drying, it was baked in a hot plate at 170 °C (improving adhesion between graphene and substrate) for 15 min and then bathed in acetone for 10 min to remove the PMMA. The sample was then put in isopropanol solvent for 10 min to clean residual acetone and dried with a nitrogen gun. The area with good graphene quality was located by optical microscopy. Electron beam lithography and O 2 :Ar plasma etch were used to define two graphene stripes on the substrate. The dielectric layer pattern was defined by electron beam lithography. Then, 30 nm hafnium oxide was deposited on the substrate above two graphene stripes with the help of electron beam evaporation, which was performed by Moorfield deposition system at a speed of 0.6 Å/s. After the lift-off procedure, the sample was cleaned with isopropanol alcohol (IPA) and deionized water. The waveguide structure and contacts pattern were again defined by a third electron beam lithography, using a 210 nm thick layer of PMMA and a high-resolution 100 kV beam. The exposed areas were developed at 5 °C in methyl isobutyl ketone:IPA mixture with ratio 1:3 for 40 s and then IPA for 20 s. 1 nm Cr as adhesion layer and 100 nm Ag were evaporated with Moorfield electron beam deposition system, with a high deposition rate of 0.9 nm·s −1 for the silver deposition. After the final lift-off, the waveguide structures were imaged with a scanning electron microscope (SEM). Then, the whole device was spin-coated by a 1.5 µm thick PMMA layer to protect silver from oxidation. More details on sample fabrications, measurement procedures, and results can be found in ref. 39 . COMSOL simulationsMode analysis was performed using FEM implemented in RF module of COMSOL software (version 5.3). As can be seen in Fig. 4b , edges of silver electrodes were rounded with a 20 nm radius of curvature to avoid artificial singularities and influence of mesh discretization, which should better represent the fabricated geometry. All material properties were the same as in 3D FDTD simulations, and graphene layer was assumed to have no influence on the mode profile and, thus, not included into simulations. A standard triangular mesh was applied, with a maximum mesh element size of 10 nm inside silver and (190 nm)/ n everywhere else, where n stands for the refractive index of correspondent material. The mesh of the line, corresponding for the position of graphene, was refined to decrease the mesh size down to ~1 nm. The whole simulation domain size was 14 × 14 µm 2 , with perfect electric conductor boundary conditions. The convergence of simulations was verified by varying the meshing and domain size. We also verified the waveguide light profile with the help of an alternative FDTD software 39 . Data availabilityThe data that support the findings of this study are available from the corresponding author ANG upon reasonable request. Novotny, L. & Hecht, B. Principles of Nano-Optics (Cambridge University Press, 2019). Zayats, A. V., Smolyaninov, I. I. & Maradudin, A. A. Nano-optics of surface plasmon polaritons. Phys. Rep. 408 , 131–314 (2005). 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Download references AcknowledgementsWe acknowledge the support from the EU Graphene Flagship grant Core 3 (881603) and Graphene NOWNANO CDT programme funded by EPSRC grant EP/L01548X/1. F.S. was funded by European Graphene Flagship Project ERC Synergy grant Hetero2D. S.I.B. acknowledges the support from the Villum Kann Rasmussen Foundation. V.A.Z. acknowledges the financial support from Villum Fonden (Grant No. 16498). Author informationAuthors and affiliations. Department of Physics and Astronomy, University of Manchester, Oxford Road, Manchester, M13 9PL, UK Tongcheng Yu, Francisco Rodriguez, Vasyl G. Kravets, Konstantin S. Novoselov & Alexander N. Grigorenko National Graphene Institute, University of Manchester, Oxford Road, Manchester, M13 9PL, UK Fred Schedin Centre for Nano Optics, University of Southern Denmark, Campusvej 55, DK-5230, Odense, Denmark Vladimir A. Zenin & Sergey I. Bozhevolnyi Department of Materials Science and Engineering, National University of Singapore, Singapore, 117574, Singapore Konstantin S. Novoselov You can also search for this author in PubMed Google Scholar ContributionsA.N.G. conceived the project. A.N.G., S.I.B., and K.S.N. guided the project. T.Y., F.R., F.S., and V.G.K. made the samples and characterized them. T.Y. and F.R. performed optical measurements. S.I.B., V.A.Z., and T.Y. performed the modelling of waveguide modes. A.N.G. and K.S.N. contributed to the theory of p-n junctions. All authors contributed to discussions and manuscript preparation. Corresponding authorCorrespondence to Alexander N. Grigorenko . Ethics declarationsCompeting interests. The authors declare no competing interests. Peer reviewPeer review information. Communications Materials thanks the anonymous reviewers for their contribution to the peer review of this work. Primary Handling Editor: Aldo Isidori. 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Sign up for the Nature Briefing newsletter — what matters in science, free to your inbox daily.  Nonlinear optics at nanoscale: frequency conversion at interracesJun 19, 2023 Laura Rodríguez i Suñé, Presentation date: 19th June 2023 Author: Laura Rodríguez i Suñé Title: Nonlinear optics at nanoscale: frequency conversion at interraces Supervisors: Cojocaru, Crina; Trull Silvestre, José Francisco Presentation date: 19th June , 2023 Link to text: https://upcommons.upc.edu/handle/2117/402164 Abstract: The use of semiconductors, metals, or ordinary dielectrics in the process of fabrication of nanodevices is at the front edge of nowadays technology. In the last decade an impressive technological progress has been made towards the miniaturization process, giving birth to the field of nanotechnology. Currently, nanostructures are routinely fabricated and integrated in different photonic devices for a variety of purposes and applications. At the nanoscale, light-matter interaction can display new phenomena, different from those occurring in homogeneous materials or even micrometer-scale optical structures and devices. This scenario makes conventional approximations to the dynamics of light-matter interactions to break down and new strategies must be sought in order to study, understand, and ultimately harness the performance of subwavelength nonlinear optical materials. This is the case of nonlinear interactions and in particular, of nonlinear frequency conversion, a fundamental physical process that lies on the basis of many modern disciplines, from bioimaging in nanomedicine to material characterization in material science and nanotechnology. Nonlinear photonics also holds great promise in laser physics with applications in information technology for optical signal processing and in the development of novel coherent light sources. Thus, a deep understanding of the specific aspects of light-matter interaction at the nanoscale is crucial if one is to properly engineer nanodevices. In this thesis we report comparative experimental and theoretical studies of nonlinear frequency conversion in different strategic materials for photonics having nanoscale dimensions. We start our study with homogeneous layers and project our results to nanostructures, where second and third harmonic conversion efficiencies drastically decrease compared to typical nonlinear optics working conditions. We have developed novel experimental set-ups capable of measuring second and third harmonic generation efficiencies arising from semicondutors, conductive oxides and metal nanolayers and nanostructures. Our experimental approach allows us to estimate very low conversion efficiencies, and it is designed to perform an exhaustive study of harmonic generation by analyzing the nonlinear signals as a function of incident angle, wavelength and polarization, important parameters that determine and distinguish the origin of the nonlinear process. At the nanoscale phase matching conditions and even absorption no longer play a primary or significant role, and new linear and nonlinear sources become relevant, including magnetic dipole and electric quadrupole (surface) nonlinearities arising from both free and bound electrons, as well as nonlocal effects, convection, and hot electrons nonlinearities, associated with free electron dynamics, pump depletion, and phase-locking. We have performed numerical simulations based on a unique microscopic hydrodynamic model that considers all these contributions to the nonlinear polarization. By comparing experimental results with numerical simulations we are able to identify and distinguish the different mechanisms that trigger the harmonic generated signals at visible and UV wavelengths, while extracting basic physical properties of the material. With this knowledge we are able to make a step forward and predict conversion efficiencies in complex structures which are specifically designed to enhance harmonic generation. The capability to efficiently generate harmonics at the nanoscale will have an enormous impact in the fields of nanomedicine and nanotechnology, since it would allow one to realize much more compact devices and to interrogate matter in extremely confined volumes. ● Postdoc fellows ● Graduate students ● Visiting scholars ● Undergraduate students ● Lab alumni ● Photo gallery  Xiulin Ruan, Professor, Purdue University Faculty Scholar, ASME Fellow [ Curriculum Vita ] Professor Ruan received his B.S. and M.S. in Engineering Thermophysics from Tsinghua University in 2000 and 2002, respectively. He received an M.S. in Electrical Engineering and Ph.D. in Mechanical Engineering from the University of Michigan at Ann Arbor, in 2006 and 2007 respectively. Subsequently, he joined Purdue as an assistant professor. He was promoted to associate professor with tenure in 2013 and full professor in 2017. Dr. Ruan received many awards, including NSF CAREER Award in 2012, Air Force Summer Faculty Fellowship in 2010, 2011, and 2013, ASME Heat Transfer Division Best Paper Award in 2015, College of Engineering Early Career Research Excellence Award in 2016, School of Mechanical Engineering Outstanding Graduate Student Mentor Award in 2016, B.F.S. Schaefer Award in 2017, University Faculty Scholar in 2017, College of Engineering Research Award in 2022, College of Engineering Outstanding Graduate Student Mentor Award in 2022, SXSW Innovation Award for Sustainability in 2023, Brillouin Medal from the International Society of Phononics in 2023, and Time Magazine's "Best Inventions of 2023". He currently serves as an associate editor for the ASME Journal of Heat Transfer. Office: FLEX 1081C and BRK 1270 Phone: 765-494-5721 (FLEX), 765-494-6603 (BNC) e-mail: [email protected]  Dr. Dudong Feng Dr. Dudong Feng received his PhD from Georgia Institute of Technology in December 2021 and joined our group as a postdoc fellow in early 2022. Email: [email protected]  Dr. Xiaojie Liu Dr. Xiaojie Liu received her PhD from Northeastern University in December 2022 and joined our group as a prestigeous Gilbreth Postdoctoral Fellow in early 2023. Xiaojie is also co-advised by Profs. Jianguo Mei and Tian Li. Email: [email protected] Abdulaziz Alkandari, PhD student Abdulaziz received his MS from Penn State University, before joining our group as a PhD student. He is co-advised by Prof. Thomas Beechem. Office: Flex Lab Phone: Email: [email protected] Khalid Alhammadi, PhD student Khalid received his MS from Northeastern University in 2022, before joining our group as a PhD student. Office: Flex Lab Phone: Email: [email protected]  Abdulrahman Aljwirah, PhD student Abdulrahman received his BS from Saginaw Valley State University in 2019 and MS from Northeastern University in 2021, before joining our group as a PhD student. Office: Flex Lab Phone: Email: [email protected]  Emily Barber, PhD student Emily received her B.S. in Mechanical Engineering from the University of Georgia in 2021 and subsequently joined our group as an MS student. She received MS in 2023 and continued to pursue PhD with our group. Her PhD is co-advised by Prof. Travis Horton. She is a recipient of the NSF Graduate Fellowship in 2021, Purdue Mechanical Engineering Fellowshipship in 2021, Third Prize of the Purdue Moonshot Competition in 2021, and South by Southwest (SXSW) Innovation Award for Sustainability in 2023. Office: Flex Lab Phone: Email: [email protected]  Daniel Carne, PhD student Daniel received his B.S. and M.S. from the Oklahoma State University in 2019 and 2021 respectively, before joining our group as a PhD student. Daniel received the Lambert Teaching Fellowship. Office: Flex Lab Phone: Email: [email protected]  Ziqi Fang, combined BS-MS student (will continue PhD) Ziqi received his B.S. from the School of Mechanical Engineering at Purdue University in 2022, and joined our group as an MS student. Office: Flex Lab Phone: Email: [email protected]  Andrea received her B.S. in Mechanical Engineering from the University of Akron in 2019 and then joined our group. She is co-advised by Professor George Chiu. Her current research involves nanomaterials, additive manufacturing, sustainable energy, and bioengineering. She is a recipient of NSF Graduate Research Fellowship in 2019-2022, Purdue Doctoral Fellowship for 2022-2024, Outstanding Graduate Mentor Award during Purdue SURF in 2020, South by Southwest (SXSW) Innovation Award for Sustainability in 2023, and Time Magazine "Best Inventions of 2023".  Ziqi Guo, PhD student Ziqi received his B.S. in Energy and Power Engineering from the Huazhong University of Science and Technology in 2021 and subsequently joined our group. He is a recipient of the Purdue Ross Fellowship in 2021, the Heat Transfer Division K-9 Session Presentation Award at the 2023 ASME Summer Heat Transfer Conference. He is co-advised by Prof. Guang Lin. Office: Flex Lab Phone: Email: [email protected]  Orlando G. Rivera Gonzalez, PhD student Orlando received his B.S. from the University of Puerto Rico, Mayaguez. He is a recipient of the NSF Graduate Research Fellowship in 2022-2025 and Purdue's Ross Fellowship in 2021-2022. He is co-advised by Prof. Justin Weibel. Office: Flex Lab Phone: Email: [email protected]  Zherui received his B.S. in Energy and Power Engineering from the Huazhong University of Science and Technology in 2019 and then joined our group. His current research involves atomistic level simulations and machine learning. He is a recipient of Purdue's Ross Fellowship in 2019-2020, Bilsland Dissertation Fellowship for 2023-2024, Best Presentation Award at 2021 MRS Fall Meeting, Best Poster Award at the 2022 Hawkins Poster Session.  Ioanna Katsamba, PhD student Ioanna received her B.S. and M.S. in Mechanical Engineering and Manufacturingfrom from the University of Cyprus in 2017 and 2019 respectively. Her research interest is in transport phenomena in nanomaterials additive manufacturing and processing. She received an Outstanding Graduate Mentor Award for SURF 2021, the Lambert Teaching Fellowship for 2023-2024, and the Stevenson Scholarship in 2023. Office: Phone: Email: [email protected]  Krutarth Khot, PhD student Krutarth received his B.S. from Indian Institute of Technology Gandhinagar. He received Heat Transfer Division K-9 Session Presensation Award at 2023 ASME IMECE. Office: Flex Lab Phone: Email: [email protected]  Andrew Witty, MS student (start in summer 2024) Andrew is currently a senior in Purdue ME and a student-athelet in the Purdue swimming team. He will join our group as an MS student in summer 2024. He received the Cordier Fellowship. Office: Flex Lab Phone: Email: 
Richard Smith
 Vignesh Gouthaman  Dedeepya Valluripally  Dr. Xiangyu Li received his B.S. from Tsinghua University and PhD from Purdue with our group. He subsequently joined MIT as a postdoctoral fellow. His PhD dissertation topic was "Nanoparticle composites for thermal conductive and radiative applications". While at Purdue Xiangyu received the Ross Fellowship. Victoria Zhao  Josephh Peoples  Emily Barber Ziqi Fang Tingting Du  Yanhua Cheng  MULTISCALE MODELING OF QUANTUM TRANSPORT IN 2D MATERIAL BASED MOS TRANSISTORSThe emergence of beyond-graphene 2D materials has opened up the possibility of using them as alternative channel material for metal oxide semiconductor (MOS) based transistors. Since such atomically thin devices offer excellent electrostatic integrity, 2D materials pave the way for downscaling the transistor channel length below deca-nanometer, where the wave nature of electron gets manifested. In order to explore the plethora of 2D materials one needs to develop a multi-scale modeling methodology, which enables estimation of intrinsic performance of MOS transistors from the crystallographic information of the materials. In this thesis we have developed such modeling framework for two different types of transistors (MOSFET and tunnel-FET) involving three different 2D materials. First, the ballistic transport in monolayer Germanane MOSFETs is investigated for high-performance applications. Our approach is based on a self-consistent quantum ballistic transport model within the framework of the nonequilibrium Green’s function formalism and relies on DFT (density functional theory)calibrated single-band and a two-band k · p Hamiltonian for n and p-type channels respectively. We found that, even for a gate length scaled down to 3 nm, the ON current (ION) in n- and p-MOSFETs for a fixed OFF current IOFF = 100 nA/μm is as high as ∼890 and 700 μA/μm, respectively. For longer channel lengths,the p-MOSFET can outperform the n-MOSFET in terms of ION requirements, as the direct source-to-drain tunneling gets suppressed. Second, we employ the same methodology to assess the intrinsic performance limit of monolayer GeSe based TFET for low-power applications. We first study the electronic band structure by regular and hybrid density functional theory and develop two band k · p Hamiltonian for the material, which is then used for transport calculation. We also find that the complex band wraps itself within the conduction band and valence band edges and thus signifies efficient band to band tunneling (BTBT) mechanism. Keeping the OFF-current fixed at 10 pA/μm we investigate different static and dynamic performance metrics (ONcurrent, energy and delay) under three different constant-field scaling rules: 40, 30 and 20 nm/V. Our study shows that monolayer GeSe-TFET is scalable till 8 nm while preserving ON/OFF current ratio higher than 104. Third, we study the anisotropic dissipative quantum transport in Phosphorene based MOSFET in armchair and zigzag directions. Here the transport equations rely on DFT-calibrated two-band k · p Hamiltonian and the treatment of electron phonon scattering is done under the self-consistent Born approximation (SCBA). We investigate in detail the effect of different acoustic and optical phonon modes on the drain current of n and p channel device. We find that optical phonon modes are largely responsible for degradation of ON- current apart from p channel armchair MOSFET where acoustic phonon modes play a stronger role. Also, electron-phonon scattering is more pronounced in zigzag direction. However, the diffusive ON-current of p-MOSFET in a particular direction is higher than n-MOSFET. Further calculations reveal that complex band structure along armchair direction has wrapping between conduction and valence band edges whereas it shows multiple band crossings along zigzag direction. This suggests that band to band tunneling in Phosphorene TFET is least affected by phonon assisted tunneling (PAT) along the armchair direction. Indeed, we find that electron-phonon scattering is observed only in the near vicinity of the OFF current. Researcher: Madhuchhanda Brahma (2019) QUANTUM-DRIFT-DIFFUSION FORMALISM BASED COMPACT MODEL FOR LOW EFFECTIVE MASS CHANNEL MOSFETWith the passage of time the semiconductor research community around the globe has progressed from a nearly four decades of dominating Silicon research to look for newer transistor materials, in the pursuit of more operating speed along with reduced power, area and cost. Low effective mass materials like III-V compounds are the best examples of such transistor materials. In order to use those materials in real life transistor design and electronic applications, an engineer must have a set of mathematical models ready to use – which accurately predict various electronic characteristics of the devices. Therefore the development of canonical compact models for low effective mass channel material transistors is of prime importance for bringing these wonder materials into real life use. Compact modeling is necessarily the art of translating the highly cumbersome and complicated physics within an electronic device into a set of predictable, portable, robust and computationally efficient analytical equations – that can be used in real-time circuit design. Existing compact models on low effective mass channel materials have a number of critical limitations, e.g. dealing with only symmetric oxide thickness, excessive use of unphysical approaches and empirical fitting parameters etc. Through our work – for the first time a fully physical, robust, portable compact model of low effective mass channel Common Double Gate MOSFET has been proposed and implemented. This compact model is a combination of accurate yet computationally efficient Surface Potential Equation (SPE) having analytical solution of coupled Schrodinger-Poisson equation; a Quantum Drift-Diffusion (QDD) based current transport and terminal charge model along with inclusion of DIBL effect. Due to enormous quantum confinement, the quasi-Fermi levels of each energy sub-band remains distant from each other because the carriers remain in the thermal equilibrium in their respective sub-bands. This segregation in quasi-Fermi levels, caused by strong quantum confinement, severely affects the transport in the semiconductor channel – thus changing the transport from normal Drift-Diffusion as in Silicon MOSFETs to QDD in low effective mass channel MOSFETs. The model development starts with a couple of rightfully logical assumptions, which are compensated in subsequent stages to the best possible extent. The wave-function corresponding to a particular sub-band in the channel is derived only under flat-band condition. It is used throughout in model development, and in the last stage the model is compensated by introducing an analytically derived correction factor. Individual sub-band energies are also derived initially under ground-state, and in later stages their bias dependence is addressed through perturbation technique. While modeling the transport, channel charge density for an individual sub-band is shown to be varying linearly with sub-band energy along the channel, resulting into a square law current versus channel charge density model. The uniqueness of the proposed model lies in its precise handling of multiple issues like asymmetry in oxide layer thickness, wave function penetration, bias dependent diffusivity, Quantum Drift-Diffusion transport, multi-sub-band carrier occupancy and wide range of material effective mass, device thickness along with input voltages – without ever using a single unphysical polynomial fitting or empirical constant, while preserving the mathematical lucidity of industry standard Silicon MOSFET models. The proposed model is validated against numerical TCAD simulation for various device geometries, oxide asymmetries, material properties and successfully implemented in professional circuit simulator through its verilog-A interface. Through this work, the fundamental Quantum Drift-Diffusion transport is for the first time introduced into circuit simulation, which earlier was limited within device simulation only – thus opening the possibility of designing circuits using low effective mass materials. Researcher: Ananda Sankar Chakraborty (2019) ATOMISTIC STUDY OF CARRIER TRANSMISSION IN HETERO-PHASE MoS2 STRUCTURESIn recent years, the use of first-principles based atomistic modeling technique has become extremely popular to gain better insights on the various locally modulated electronic properties of nano materials and structures. Atomistic modeling offers the benefit of predicting crystal structures, visualizing orbital distribution and electron density, as well as understanding material properties which are hard to access experimentally. The single layer MoS2 has emerged as a suitable choice for the next generation nano devices, owing to its distinctive electrical, optical and mechanical properties like, better electrostatics, increased photo luminescence, higher mechanical flexibility, etc. The real- ization of decananometer scale digital switches with the single layer MoS2 as the channel may provide many significant advantages such as, high On/Off current ratio, excellent electrostatic control of the gate, low leakage, etc. However, there are quite a few critical issues such as, forming low resistance source/drain contacts, achieving higher effective mobility, ensuring large scale controlled growth, etc. which need to be addressed for successful implementation of the atomically thin transis- tors in integrated circuits. Recent experimental demonstration showing the coexistence of metallic and semiconducting phases in the same monolayer MoS2, has attracted much attention for its use in ultra-low contact resistance-MoS2 transistors. Howbeit, the elec- tronic structures of the metallic-to-semiconducting phase boundaries, which appear to dictate the carrier injection in such transistors, are not yet well understood. In this work, we first develop the geometrically optimized atomistic models of the 2H- 1T′ hetero-phase structures with two distinct phase boundaries, β and γ. We then apply density functional theory to calculate the electronic structures for those optimized geome- tries. Furthermore, we employ non equilibrium Green’s function formalism to evaluate the transmission spectra and the local density of states in order to assess the Schottky barrier nature of the phase boundaries. Nonetheless, the symmetry of the source-channel and drain-channel junction, is a unique property of a metal-oxide semiconductor field effect transistor (MOSFET), which needs to be preserved while realizing sub-10 nm channel length devices using advanced technology. Employing experimental-findings-driven atomistic modeling technique, we demonstrate that such symmetry might not be preserved in an atomically thin phase-engineered MoS2- based MOSFET. It originates from the two distinct atomic patterns at phase boundaries (β and β*) when the semiconducting phase (channel) is sandwiched between the two metallic phases (source and drain). Next, using first principles based quantum transport calculations we demonstrate that, due to the clusterization of “Mo” atoms in 1T′ MoS2, the transmission along the zigzag direction is significantly higher than that in the armchair direction. Moreover, to achieve excellent impedance matching with various metal contacts (such as, “Au”, “Pd”, etc.), we further develop the atomistic models of metal-1T′ MoS2 edge contact geometries and compute their resistance values. Other than the charge carrier transport, analysing the heat transport across the channel is also crucial in designing the ultra-thin next generation transistors. Hence, in this thesis work, we have investigated the electro-thermal transport properties of single layer MoS2, in quasi ballistic regime. Besides the perfect monolayer in its pristine form, we have also considered various line defects which have been experimentally observed in mechanically exfoliated MoS2 samples. Furthermore, a comprehensive study on the phonon thermal conductivity of a suspended monolayer MoS2, has been incorporated in this thesis. The studies presented in this thesis could be useful for understanding the carrier transport in atomically thin devices and designing the ultra-thin next generation transistors. Researcher: Dipankar Saha (2017) FIRST PRINCIPLES STUDY OF 2D MATERIAL METAL CONTACTMoore’s law falls short of down-scaling the technology nodes in the sub decananometer regime and producing effective high performance logic devices. So, the ITRS trend expects to conceptualize novel device structure such as extremely thin Silicon on insulator (ETSOI), multi gate FETs (MuGFETs) or FinFETs and explore new 2D materials as a suitable channel materials for FET’s. Post the exfoliation of monolayer graphene, many 2D materials are being utilized to replace the bulk silicon as the channel material, viz., TMD’s, black phosphorous etc. Though semiconductive atomically-thin layered materials based FET may provide exceptional electrostatic integrity, yet the ON current in the experimental devices are low in comparison to the required one. Significant Schottky barrier height (SBH) at the metal-semiconductor interface at source/drain terminals is identified as one of the possible reasons for low values of ON current. Many techniques are demonstrated experimentally as well as novel 2D materials are explored with an aim to lessen the SBH and enhance the values of ON current. Nonetheless, the interface chemistry leading to the reduction of SBH is not probed effectively since accessing this phenomena experimentally at atomic level is in altogether quite challenging. Thereby, in the present thesis, a comprehensive and thorough study is done to develop a theoretical perspective of various 2D material – metal interface by employing Density Functional Theory (DFT) which is efficaciously applied earlier to study the graphene-metal contact. The study is organized by following entirely a systematic approach: creation of optimized geometry for the interface, estimation of an equilibrium interlayer distance, analysis of potential barrier at the interface, exploration of charge transfer and interface dipole, investigation of orbital hybridization and finally evaluating the SBH. Exchange correlation functions, pseudopotentials and basis sets are chosen appropriately and very carefully for each interface structure to produce the precise electronic structures. Firstly we outline our methodology to study a 2D material-metal contact. The first application of our methodology is for an interface formed between the metal (gold, palladium and titanium) and puckered honeycomb monolayer of black phosphorous (i.e. phosphorene). Following it, we analyze a graphene inserted MoS2-metal interface (titanium, silver, ruthenium, gold and platinum), ranging from metal with low work function to high work function. Furthermore, we continue our study for p-type niobium doped MoS2 and its contact with gold. Apart from p type TMD, n-type chlorine doped WS2 and its contact with gold and palladium is also examined for this study. Doping graphene with BN is one among the possible choices to open band gap in pristine graphene. In the next part we study these materials and analyze various defects such as stone-wales and vacancy on the performance of boron-nitride embedded graphene nanoribbon transistor. Researcher : Anuja Chanana (2016) COMPACT MODELING OF SHORT CHANNEL COMMON DOUBLE GATE MOSFET ADAPTED TO GATE-OXIDE THICKNESS ASYMMTERYCompact Models are the physically based accurate mathematical description of the circuit elements, which are computationally efficient enough to be incorporated in circuit simulators so that the outcome becomes useful for the circuit designers. Since the multi-gate MOSFETs have appeared as replacements for bulk-MOSFETs in sub-32nm technology nodes, efficient compact models for these new transistors are required for their successful utilization in integrated circuits. Existing compact models for common double-gate (CDG) MOSFETs are based on the fundamental assumption of having symmetric gate oxide thickness. In this work we explore the possibility of developing models without this approximation, while preserving the computational efficiency at the same level. Such effort aims to generalize the compact model and also to capture the oxide thickness asymmetry effect, which might prevail in practical devices due to process uncertainties and thus affects the device performance significantly. However solution to this modeling problem is nontrivial due to the bias-dependent asymmetric nature of the electrostatic. Using the ‘single implicit equation based Poisson solution’ and the ‘unique quasi-linear relationship between the surface potentials’, previous researchers of our laboratory have reported the ‘core’ model for such asymmetric CDG MOSFET. In this work effort has been put to include Non-Quasistatic (NQS) effects, different small-geometry effects, and noise model to this ‘core’, so that the model becomes suitable for practical applications. It is demonstrated that the quasi-linear relationship between the surface potentials remains preserved under NQS condition, in the presence of all small geometry effects. This property of the device along with some other new techniques is used to develop the model while keeping the mathematical complexity at the same level of the models reported for the symmetric devices. Proposed model is verified against TCAD simulation for various device geometries and successfully implemented in professional circuit simulator. The model passes the source/drain symmetry test and good convergence is observed during standard circuit simulations. Researcher : Neha Sharan (2014) INVESTIGATION OF ELECTRO-THERMAL AND THERMOELECTRIC PROPERTIES OF CARBON NANOMATERIALSDue to the aggressive downscaling of the CMOS technology, power and current densities are increasing inside the chip. The limiting current conduction capacity (106 Acm-2) and thermal conductivity (201 Wm-1K-1 for Al and 400 Wm-1K-1 for Cu) of the existing interconnects materials has given rise to different electro-thermal issues such as hot-spot formation, electromigration, etc. Exploration of new materials with high thermal conductivity and current conduction has thus attracted much attention for future integrated circuit technology. Among all the elemental materials, carbon nanomaterials (graphene and carbon nanotube) possess exceptionally high thermal (600-7000 Wm-1K-1) and current ~ 108 – 109 Acm-2) conduction properties at room temperature, which makes them potential candidate for interconnect materials. At the same time development of efficient energy harvesting techniques are also becoming important for future wireless autonomous devices. The excess heat generated at the hot-spot location could be used to drive an electronic circuit through a suitable thermoelectric generator. As the Seebeck coefficient of graphene is reported to be the highest among all elementary semiconductors, exploration of thermoelectric properties of graphene is very important. This thesis investigates the electrothermal and thermoelectric properties of metallic single walled carbon nanotube (SWCNT) and single layer graphene (SLG) for their possible applications in thermal management in next generation integrated circuits. A closed form analytical solution of Joule-heating equation in metallic SWCNTs is thus proposed by considering a temperature dependent lattice thermal conductivity (κ) on the basis of three-phonon Umklapp, mass-difference and boundary scattering phenomena. The solution of which gives the temperature profile over the SWCNT length and hence the location of hot-spot (created due to the self-heating inside the chip) can be predicted. This self-heating phenomenon is further extended to estimate the electromigration performance and mean-time-to-failure of metallic SWCNTs. It is shown that metallic SWCNTs are less prone to electromigration. To analyze the electro-thermal effects in a suspended SLG, a physics-based flexural phonon dominated thermal conductivity model is developed, which shows that κ follows a T1.5 and T-2 law at lower (less than 300) K and higher temperature respectively in the absence of isotopes (C13 atoms). However in the presence of isotopic impurity, the behavior of κ sharply deviates from T-2 at higher temperatures. The proposed model of κ is found to be in excellent match with the available experimental data over a wide range of temperatures and can be utilized for an efficient electro-thermal analysis of encased/supported graphene. By considering the interaction of electron with in-plane and flexural phonons in a doped SLG sheet, a physics-based electrical conductance (σ) model of SLG under self-heating effect is also discussed that particularly exhibits the variation of electrical resistance with temperature at different current levels and matches well with the available experimental data. To investigate the thermoelectric performance of a SLG sheet, analytical models for Seebeck effect coefficient (SB) and specific heat (Cph) are developed, which are found to be in good agreement with the experimental data. Using those analytical models, it is predicted that one can achieve a thermoelectric figure of merit (ZT) of ~ 0.62 at room temperature by adding isotopic impurities (C13 atoms) in a degenerate SLG. Such prediction shows the immense potential of graphene in waste-heat recovery applications. Those models for σ, κ, SB and Cph are further used to determine the time evolution of temperature distribution along suspended SLG sheet through a transient analysis of Joule-heating equation under the Thomson effect. The proposed methodology can be extended to analyze the graphene heat-spreader theory and interconnects and graphene based thermoelectrics. Researcher : Rekha Verma (2013) EXPLORATION OF REAL AND COMPLEX DISPERSION RELATIONSHIP OF NANOMATERIALS FOR NEXT GENERATION TRANSISTOR APPLICATIONSTechnology scaling beyond Moore’s law demands cutting-edge solutions of the gate length scaling in sub-10 nm regime for low power high speed operations. Recently SOI technology has received considerable attention, however manufacturable solutions in sub-10 nm technologies are not yet known for future nanoelectronics. Therefore, to continue scaling in sub-10 nm region, new one (1D) and two dimensional (2D) “nano-materials” and engineering are expected to keep its pace. However, significant challenges must be overcome for nano-material properties in carrier transport to be useful in future silicon nanotechnology. Thus, it is very important to understand and modulate their electronic band structure and transport properties for low power nanoelectronics applications. This thesis tries to provide solutions for some problems in this area. In recent times, one dimensional Silicon nanowire has emerged as a building block for the next generation nano-electronic devices as it can accommodate multiple gate transistor architecture with excellent electrostatic integrity. However as the experimental study of various energy band parameters at the nanoscale regime is extremely challenging, usually one relies on the atomic level simulations, the results of which are at par with the experimental observations. Two such parameters are the band gap and effective mass, which are of pioneer importance for the understanding of the current transport mechanism. Although there exists a large number of empirical relations of the band gap in relaxed Silicon nanowire, however there is a growing demand for the development of a physics based analytical model to standardize different energy band parameters which particularly demands its application in TCAD software for predicting different electrical characteristics of novel devices and its strained counterpart to increase the device characteristics significantly without changing the device architecture. The first part of this work reports the analytical modeling of energy band gap and electron transport effective mass of relaxed and strained Silicon nanowires in various crystallographic directions for future nanoelectronics. The technology scaling of gate length in beyond Moorefs law devices also demands the SOI body thickness, Tsi–> The investigations on ultrathin body materials also call for a need to explore new 2D materials with finite band gap and their various nanostructures for future nanoelectronic applications in order to replace conventional Silicon. In the third part of this report, we have investigated the electronic and dielectric properties of semiconducting layered Transition metal dichalcogenide meterials (MX2) (M = Mo, W; X = S, Se, Te) which has recently emerged as a promising alternative to Si as channel materials for CMOS devices. Five layered MX2 materials (except WTe2) in their 2D sheet and 1D nanoribbon forms are considered to study the real and imaginary band structure of those MX2 materials by atomistic simulations. Studying the complex dispersion properties, it is shown that all the five MX2 support direct BTBT in their monolayer sheet forms and offer an average ON current and subthreshold slope of 150 µA/µm and 4 mV/dec, respectively. However, only the MoTe2 support direct BTBT in its nanoribbon form, whereas the direct BTBT possibility in MoS2 and MoSe2 depends on the number of layers or applied uniaxial strain. WX2 nanoribbons are shown to be non-suitable for efficient TFET operation. Reasonably high tunneling current in these MX2 shows that these can take advantage over conventional Silicon in future tunnel field effect transistor applications. Researcher : Ram Krishna Ghosh (2013) POISSON's SOLUTION AND LARGE-SIGNAL MODELING FOR INDEPENDENT DOUBLE GATE MOSFETIndependent double gate (IDG) metal oxide semiconductor field effect transistor (MOSFET) has received considerable attention in recent years owing to its ability to modulate threshold voltage and transconductance dynamically. Due to the asymmetric nature of electrostatic, developing efficient compact models for such devices is a daunting task in comparison to the symmetric double gate transistor. The thesis tries to provide solutions for some problems in this area. The modeling of the long channel potential by solving the one-dimensional Poisson equation (PE) is the most fundamental step towards developing surface-potential-based core compact models for such transistors. Previous techniques used for solving the one-dimensional Poisson equation rigorously for the long channel asymmetric and independent double gate transistors result in potential models that involve multiple inter-coupled implicit equations. As these equations need to be solved self-consistently, such potential models are clearly inefficient for compact modeling. This work reports a different rigorous technique for solving the same Poisson equation by which one can obtain the potential profile of a generalized independent double gate transistor that involves a single implicit equation. The proposed Poisson solution is shown to be at-least five times computationally more efficient for circuit simulation than the previous solutions. Developing efficient models for terminal charges is another crucial step towards compact modeling. In this work we show the limitations of the traditional charge linearization techniques for modeling terminal charges of the IDG MOSFETs. We propose a new charge linearization technique in order to model the terminal charges and transcapacitances of the IDG MOSFETs. We report two different types of quasi-static large signal models for the long channel device. In the first type, the terminal charges are expressed as closed form functions of source and drain end inversion charge densities and found to be accurate when the potential distribution at source end of the channel is hyperbolic in nature. The second type, which is found to be accurate in all regimes of operations, is based on quadratic spline collocation technique and requires the input voltage equation to be solved two more times apart from the source and drain end. Proposed model has been successfully implemented in professional circuit simulator. Voltage controlled oscillators (VCOs) based on metal oxide semiconductor (MOS) varactors have become an integral part of RF communication circuits. An independently controlled double gate based MOS capacitor can bring out new functionalities, which could be interesting for RF circuit applications. For the first time, this work, explores the characteristics of MOS capacitor controlled by independent double gates by numerical simulation and analytical modeling for its possible use in RF circuit design as a varactor. By numerical simulation it is shown how the quasi-static and non-quasi-static characteristics of the first gate capacitance could be tuned by the second gate biases. Analytical solution of complete (considering both electron and hole concentration) Poisson equation (PE) is proposed. A new set of input voltage equations (IVEs) for independent double gate MOSFET are proposed by solving the governing bipolar Poisson equation rigorously. The proposed IVEs, involve the Legendre’s incomplete elliptic integral of the first kind andJacobian elliptic functions and are valid from accumulation to inversion regimes. As Legendre’s incomplete elliptic integral of first kind and Jacobian elliptic functions are computationally expensive, hence I also propose a semi-empirical solution using previous analytical solution of the PE for IDG MOS capacitor considering only electron/hole. Proposed models, which are valid from accumulation to inversion, are shown to have excellent agreement with numerical simulation for practical bias conditions. Researcher : Pankaj Kumar Thakur (2013) COMPACT MODELING OF ASYMMETRIC/INDEPENDENT DOUBLE GATE MOSFETFor the past 40 years, relentless focus on Moore’s Law transistor scaling has provided ever-increasing transistor performance and density. In order to continue the technology scaling beyond 22nm node, it is clear that conventional bulk-MOSFET needs to be replaced by new device architectures, most promising being the Multiple-Gate MOSFETs MuGFET). Intel in mid 2011 announced the use of bulk Tri-Gate FinFETs in 22nm high volume logic process for its next-gen IvyBridge Microprocessor. It is expected that soon other semiconductor companies will also adopt the MuGFET devices. As like bulk- MOSFET, an accurate and physical compact model is important for MuGFET based circuit design. Compact modeling effort for MuGFET started in late nineties with planar double gate MOSFET (DGFET), as it is the simplest structure that one can conceive for MuGFET devices. The models so far proposed for DG MOSFETs are applicable for common gate symmetric DG (SDG) MOSFETs where both the gates have equal oxide thick- nesses. However, for practical devices at nanoscale regime, there will always be some amount of asymmetry between the gate oxide thicknesses due to process variations and uncertainties, which can affect device performance significantly. At the same time, Independently controlled DG (IDG) MOSFETs have gained tremendous attention owing to its ability to modulate threshold voltage and transconductance dynamically. Due to the asymmetric nature of the electrostatic, developing efficient compact models for asymmetric/independent DG MOSFET is a daunting task. In this thesis effort has been put to provide some solutions to this challenge. We propose simple surface-potential based compact terminal charge models, applicable for Asymmetric Double gate MOSFETs (ADG) in two configurations 1) Common-gate 2) Independent-gate. The charge model proposed for the common-gate ADG (CDG) MOSFET is seamless between the symmetric and asymmetric devices and utilizes the unique so-far-unexplored quasi-linear relationship between the surface potentials along the channel. In this model, the terminal charges could be computed by basic arithmetic operations from the surface potentials and applied biases, and can be easily implemented in any circuit simulator and extendable to short-channel devices. The charge model proposed for independent ADG (IDG) MOSFET is based on a novel piecewise linearization technique of surface potential along the channel. We show that the conventional “charge linearization techniques that have been used over the years in advanced compact models for bulk and double-gate (DG) MOSFETs are accurate only when the channel is fully hyperbolic in nature or the effective gate voltages are same. For other bias conditions, it leads to significant error in terminal charge computation. We demonstrate that the amount of nonlinearity that prevails between the surface potentials along the channel for a particular bias condition actually dictates if the conventional charge linearization technique could be applied or not. We propose a piecewise linearization technique that segments the channel into multiple sections where in each section, the assumption of quasi-linear relationship between the surface potentials remains valid. The cumulative sum of the terminal charges obtained for each of these channel sections yield terminal charges of the IDG device. We next present our work on modeling the non-ideal scenarios like presence of body doping in CDG devices and the non-planar devices like Tri-gate FinFETs. For a fully depleted channel, a simple technique to include body doping term in our charge model for CDG devices, using a perturbation on the effective gate voltage and correction to the coupling factor, is proposed. We present our study on the possibility of mapping a non-planar Tri-gate FinFET onto a planar DG model. In this framework, we demon- strate that, except for the case of large or tall devices, the generic mapping parameters become bias-dependent and an accurate bias-independent model valid for geometries is not possible. An efficient and robust “Root Bracketing Method” based algorithm for computation of surface potential in IDG MOSFET, where the conventional Newton-Raphson based techniques are inefficient due to the presence of singularity and discontinuity in input voltage equations, is presented. In case of small asymmetry for a CDG devices, a simple physics based perturbation technique to compute the surface potential with computational complexity of the same order of an SDG device is presented next. All the models proposed show excellent agreement with numerical and Technology Computer-Aided Design (TCAD) simulations for all wide range of bias conditions and geometries. The models are implemented in a professional circuit simulator through Verilog-A, and simulation examples for different circuits verify good model convergence. Researcher : J. Srivatsava (2013) IMPACT OF ENERGY QUANTIZATION ON SINGLE ELECTRON TRANSISTOR DEVICES AND CIRCUITSAlthough scaling of CMOS (Complementary Metal Oxide Semiconductor) technology has been predicted to continue for another decade, novel technological solutions are required to overcome the fundamental limitations of the decananometer MOS transistors. Single Electron Transistor (SET) has attracted attention mainly because of its unique Coulomb blockade oscillations characteristics, ultra low power dissipation and nano-scale feature size. Despite the high potential, due to some intrinsic limitations (e.g., very low current drive) it will be very difficult for SET to compete head-to-head with CMOS’s large-scale infrastructure, proven design methodologies, and economic predictability. Nevertheless, the characteristics of SET and MOS transistors are quite complementary. SET advocates low-power consumption and new functionality (related to the Coulomb blockade oscillations), while CMOS has advantages like high-speed driving and voltage gain that can compensate the intrinsic drawbacks of SET. Therefore, although a complete replacement of CMOS by single-electronics is unlikely in the near future, it is also true that combining SET and CMOS one can bring out new functionalities, which are un-mirrored in pure CMOS technology. As the hybridization of CMOS and SET is gaining popularity, silicon SETs are appearing to be more promising than metallic SETs for their possible integration with CMOS. SETs are normally studied on the basis of the classical Orthodox Theory, where quantization of energy states in the island is completely ignored. Though this assumption greatly simplifies the physics involved, it is valid only when the SET is made of metallic island. As one cannot neglect the quantization of energy states in a semiconductive island, it is extremely important to study the effects of energy quantization on hybrid CMOS-SET integrated circuits. The main objective of this thesis is to understand energy quantization effects on SET by numerical simulations, develop simple analytical models that can capture the energy quantization effects, analyze the effects of energy quantization on SET logic inverter, and finally, develop a CAD framework for CMOS-SET co-simulation and to study the effect on energy quantization on hybrid circuits using that framework. In this work the widely accepted SIMON Monte Carlo (MC) simulator for single electron devices and circuits is used to study the effect of energy quantization. So far SIMON has been used to study SETs having metallic island. In this work, for the first time, we have shown how one can use SIMON to analyze SET island properties having discrete energy states. It is shown that energy quantization mainly changes the Coulomb Blockade region and drain current of SET devices and thus affects the noise margin, power dissipation, and the propagation delay of SET logic inverter. A new model for the noise margin of SET inverter is proposed, which includes the energy quantization term. Using the noise margin as a metric, the robustness of SET inverter is studied against the effects of energy quantization. An analytical expression is developed, which explicitly defines the maximum energy quantization (termed as “Quantization Threshold”) that an SET inverter logic circuit can withstand before its noise margin falls below a specified tolerance level. It is found that SET inverter designed with CT : CG = 0.366 (where CT and CG are tunnel junction and gate capacitances respectively) offers maximum robustness against energy quantization. Then the effects of energy quantization are studied for Current biased SET (CBS), which is an integral part of almost all hybrid CMOS-SET circuits. It is demonstrated that energy quantization has no impact on the gain of the CBS characteristics though it changes the output voltage levels and oscillation periodicity. The effects of energy quantization are further studied for two circuits: Negative Differential Resistance (NDR) and Neurone Cell, which use CBS. A new model for the conductance of NDR characteristics is also formulated that includes the energy quantization term. A novel CAD framework is then developed for CMOS-SET co-simulation, which uses MC simulator for SET devices along with conventional SPICE. Using this framework, the effects of energy quantization are studied for some hybrid circuits, namely, SETMOS, multiband voltage filter, and multiple valued logic circuits. It is found that energy quantization degrades the performance of hybrid circuit, which could be compensated by properly tuning the bias current of SET devices. Though this study is primarily done by exhaustive MC simulation, effort has also been put to develop first order compact model for SET that includes energy quantization effects. Finally it is demonstrated that one can predict the SET behavior under energy quantization with reasonable accuracy by slightly modifying the existing SET compact models that are valid for metallic devices having continuous energy states. Researcher : Surya Shankar Dan (2009) Compact modeling is necessarily the art of translating the highly cumbersome and complicated physics within an electronic device into a set of predictable, portable, robust and computationally efficient analytical equations – that can be used in real-time circuit design. Existing compact models on low effective mass channel materials have a number of critical limitations, e.g. dealing with only symmetric oxide thickness, excessive use of unphysical approaches and empirical fitting parameters etc. Through our work – for the first time a fully physical, robust, portable compact model of low effective mass channel Common Double Gate MOSFET has been proposed and implemented. This compact model is a combination of accurate yet computationally efficient Surface Potential Equation (SPE) having analytical solution of coupled Schrodinger-Poisson equation; a Quantum Drift-Diffusion (QDD) based current transport and terminal charge model along with inclusion of DIBL effect. Due to e normous quantum confinement, the quasi-Fermi levels of each energy sub-band remains distant from each other because the carriers remain in the thermal equilibrium in their respective sub-bands. This segregation in quasi-Fermi levels, caused by strong quantum confinement, severely affects the transport in the semiconductor channel – thus changing the transport from normal Drift-Diffusion as in Silicon MOSFETs to QDD in low effective mass channel MOSFETs. The model development starts with a couple of rightfully logical assumptions, which are compensated in subsequent stages to the best possible extent. The wave-function corresponding to a particular sub-band in the channel is derived only under flat-band condition. It is used throughout in model development, and in the last stage the model is compensated by introducing an analytically derived correction factor. Individual sub-band energies are also derived initially under ground-state, and in later stages their bias dependence is addressed through perturbation technique. While modeling the transport, channel charge density for an individual sub-band is shown to be varying linearly with sub-band energy along the channel, resulting into a square law current versus channel charge density model. The uniqueness of the proposed model lies in its precise handling of multiple issues like asymmetry in oxide layer thickness, wave function penetration, bias dependent diffusivity, Quantum Drift-D iffusion transport, multi-sub-band carrier occupancy and wide range of material effective mass, device thickness along with input voltages – without ever using a single unphysical polynomial fitting or empirical constant, while preserving the mathematical lucidity of industry standard Silicon MOSFET models. The proposed model is validated against numerical TCAD simulation for various device geometries, oxide asymmetries, material properties and successfully implemented in professional circuit simulator through its verilog-A interface. Through this work, the fundamental Quantum Drift-Diffusion transport is for the first time introduced into circuit simulation, which earlier was limited within device simulation only – thus opening the possibility of designing circuits using low effective mass materials. Researcher: Ananda Sankar Chakraborty (2019) Structures for nanoscale DRAM memories - PhD thesis
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Joint School of Nanoscience and Nanoengineering Doctor of Philosophy in Nanoengineering degree
About the Doctor of Philosophy in NanoengineeringThe Ph.D. program in Nanoengineering features coursework, laboratory rotations and extensive dissertation research involving engineering at the nanoscale. It’s designed for students with a strong academic track record who seek advanced-level education and training to pursue careers in academia, industrial or government organization that utilize nanotechnology. Students will have the opportunity to work in one or more of the following research areas: nanobiology, nanomaterials, nanometrology, nanobioelectronics, nanoenergy, and computational nanotechnology. Program Contacts
Admission RequirementsIn addition to the application materials required by NC A&T State University Graduate School, applicants must submit a personal statement indicating their interest in the program, research interests and potential faculty advisors, as well as a current Curriculum Vitae. Students may be admitted for the Fall term only. Applications will continue to be reviewed until May 31, 2021 . The application deadline for the Ph.D. is July 1, 2021 for general admission. Qualified applicants will have an engineering or science bachelor’s degree. .accordion-icon-plus { fill:none; stroke-width:2; stroke-miterlimit:10; } Degree RequirementsTotal credit hours: 60 (post baccalaureate)
Qualifying ExaminationThe Qualifying Examination is given to assess student competence in a broad range of relevant subject areas. The Qualifying Examination is given once each semester (Fall and Spring) and is held on two consecutive days. Only students with unconditional status and in good academic standing may take the Qualifying Examination. Students must take the Qualifying Examination by the end of the second semester of enrollment. In case of failure to pass in this first attempt, students will have the opportunity to take the exam in the following semester. Failure to pass the Qualifying Examination by the end of the third enrolled semester or the second attempt will result in termination from the program. Preliminary Oral ExaminationThe Preliminary Oral Examination is conducted by the student’s dissertation committee and is a defense of the student’s dissertation proposal. Students must have successfully completed the qualifying examination to be eligible for the Preliminary Oral Examination. Passing this exam satisfies requirements for Ph.D. candidacy. Failure of the examination may result in dismissal from the doctoral program. The student’s Advisory Committee may permit one re-examination. At least one full semester must elapse before the re-examination. Failure on the second attempt will result in dismissal from the doctoral program. Admission to Ph.D. CandidacyA student will be admitted to candidacy upon successful completion of the Qualifying Examination and Preliminary Oral Examination. Dissertation ResearchA student may not register for dissertation credits before passing their Qualifying Examination. No more than 18 dissertation credits are counted toward the total credit hours requirement for the degree. Final Oral Dissertation DefenseThe Final Oral Dissertation Defense is conducted by the student’s dissertation committee. This examination is the final dissertation defense presentation that is scheduled after a dissertation is completed. The examination may be held no earlier than six months after admission to candidacy. Failure on the examination may result in dismissal from the doctoral program. The student’s Advisory Committee may permit one re-examination. At least one full semester must elapse before the re-examination. Failure on the second attempt will result in dismissal from the doctoral program. Submission of DissertationUpon passing the Ph.D. Final Oral Dissertation Defense, the Ph.D. student must have the dissertation approved by each member of the student’s dissertation committee. The approved dissertation must be submitted to The Graduate College by the deadline given in the academic calendar, and must conform to the Graduate College’s guidelines for theses and dissertations. Program-Specific Academic Policies
.accordion-icon-plus { fill:none; stroke-width:2; stroke-miterlimit:10; } Course DescriptionsNano 701: simulation and modeling methods in nanoscience and nanoengineering. This course covers first principles quantum based methods, classical atomistic simulation methods interatomic potentials, modeling of bulk nanostructure metals, carbon nanotubes, soft matter and multiscale modeling techniques. Prerequisite: NONE 3 (3:0) NANO 702: Fundamentals of Nanoengineering: Physical PrinciplesThis course is an introduction to physical principles involved at the nanoscale due to quantum size effects, and energy band structure engineering for nanoelectronic devices. NANO 703: Fundamentals of Nanoengineering: Chemical-Biochemical PrinciplesThis course covers chemical and bio-chemical principles involved in design, synthesis, assembly, and performance of nanomaterials and devices. Also studied are the structure and function of biomolecules and their specific roles in nano-biomolecular interactions and signaling pathways, as well as application of chemical biological detection methods at the micro and nanoscales. NANO 704: Fundamentals of NanomaterialsThe course introduces fundamentals of nanomaterials, brings in knowledge on frontiers of the rapidly developing interdisciplinary field of nanomaterials and help to develop skills to understand and communicate in the field of nano-engineering. NANO 711: Introduction to NanoprocessingThis course introduces students to the field of nanoprocessing including basic fabrication and processing techniques to construct nanostructures and nanomaterials through both “bottom up” and “top down” strategies. Basic nanostructure characterization techniques are integrated as a start. NANO 721: NanobioelectronicsThis course introduces the emerging areas where biology, medicine, nanofabrication and electronics coverage. The course addresses fundamental concepts and current applications of biofabrication and bioelectronic devices such as biosensors, DNA electronics, protein based devices, analytical electrochemistry, biomolecular electronics, single molecule physics, BioNano machines, and biofuel cells. A special emphasis is placed on problem-based learning targeting current issues in nanobioelectronics. Prerequisite: NANO 702 or NANO 703 or consent of instructor 3 (3:0) NANO 731: Introduction to Nanomodeling and ApplicationsThis graduate level course provides an introduction to nanomodeling and applications for students with background in engineering, physical, mathematical, and biological sciences focusing on atomistic and molecular dynamics modeling. Prerequisite: NANO 701 or consent of instructor. 3 (3:0) NANO 741: Colloidal and Molecular Self-AssemblyThis course offers an introduction to self-assembly in soft matter and the associated thermodynamic and chemical principles. Topics are covered from a materials-oriented perspective and include colloidal crystals, liquid crystals, surfactants and micelles, polymers and block copolymers, and biomolecule assembly. NANO 761: Introduction of Nano EnergyThe student will conduct advanced research of interest to the student and the instructor. A written proposal which outlines the nature of the project must be submitted for approval. This course is only available to project option students NANO 785: Special Topics in NanoengineeringThis course is designed to allow the introduction of potential new courses on a trial basis or special content courses on a once only basis at the Master’s level. The topic of the course and title are determined prior to registration. Prerequisite: Consent of the instructor. 3 (3:0) NANO 794: Master’s Supervised ResearchThis course is supervised research under the mentorship of a faculty member. It is not intended to serve as the project nor thesis topic of the master’s student Prerequisite: Master’s level standing. 3 (3:0) NANO 796: Master’s ProjectThe student will conduct advanced research of interest to the student and the instructor. A written proposal which outlines the nature of the project must be submitted for approval. This course is only available to project option students. Prerequisite: Master’s level standing with project option. 3 (3:0) NANO 797: Master’s ThesisMaster of Science thesis research will be conducted under the supervision of the thesis committee chairperson leading to the completion of the Master’s thesis. This course is available only to thesis option students and can be repeated. NANO 799: Continuation of Master’s ThesisThis is a continuation of NANO 797. This course is for master’s students who have completed all required credit hour requirements. Prerequisite: Completion of all Thesis Credits. 3 (3:0) NANO 811: Polymeric Materials EngineeringThis course introduces polymer fundamentals, synthesis, structure and properties, and processing with an emphasis on applying basic knowledge in nanoengineering applications. NANO 812: Process Modeling in CompositesThis course provides an overview of composites, composite manufacturing processes followed by transport equations, constitutive laws and their characterization in composite processing. Process modeling applications to specific composite manufacturing processes involving short fibers, continuous and woven fibers for processing with thermoplastic and reactive thermoset resin systems are discussed. Transport issues in the processing of polymer nanocomposites are briefly discussed. NANO 821: Advanced NanosystemsThis course is designed to teach advanced nanosystems, which are a result of hierarchical assembly and integration of diverse and heterogeneous components including materials, molecules and components at the nanoscale. This course discusses the fundamental concepts and current trends in such advanced nanosystems with examples from nanoelectronic/photonic devices, organic-inorganic assemblies, biomimetic devices, bio-nano machines, biofuel cells etc. A special emphasis is placed on problem-based learning targeting current issues in nanosystem integration. Prerequisite: NANO 721 or consent of instructor. 3 (3:0) NANO 823: Compound Semiconductor and Nanostructure DevicesThis course covers physics of compound semiconductors, application of Schrodinger equation to nanoscale structures; heteroepitaxy layered and self-assembled nanostructures. The course also discusses strain and bandgap engineering, materials and device options for advanced optoelectronic devices at the nanoscale. Prerequisite: NANO 702 or consent of instructor. 3 (3:0) NANO 825: Thin Film Technology for Device FabricationThe course provides a fundamental understanding of the thin film deposition techniques and epitaxial growth of semiconductor materials. High vacuum technology and application of the deposition processes to the fabrication of heterostructure devices are also covered NANO 831: Advanced Nanomodeling and ApplicationsThis graduate level course is an advanced level treatment of atomistic and molecular modeling at nanoscale with a focus on the principles and background theory of the modeling methods and applications of relevance to crystalline, amorphous, ceramic, cementitious, and bio systems. Prerequisite: NANO 731 or consent of the instructor. 3 (3:0) NANO 841: Intermolecular and Surface ForcesThis course covers the theory and principles of forces between molecules, particles, and surfaces typically relevant at micrometer and nanometer length scales. Topics include: detailed treatment of dispersion, polar, and electrostatic interactions; solvation, hydration and steric forces; adhesion and surface tension; and relevance to real material systems. Prerequisite: Basic courses in thermodynamics recommended. 3 (3:0) NANO 851: Computational Nanoscale Modeling LaboratoryThis is a laboratory rotation course to expose and educate the students on computational modeling analysis and enabling technologies available for nanoscale modeling. Prerequisite: Student in Nanoengineering/Nanoscience Ph.D. program 1 (0:1) NANO 852: Nanoelectronics LaboratoryThis is a laboratory rotation course to expose and educate the students on the equipment and tools available in the nanoelectronics laboratory. NANO 853: Nano-Bio Electronics LaboratoryThis is a laboratory rotation course to expose and educate the students on the equipment and tools available in the nano-bio electronics laboratory. NANO 854: Nanomaterials LaboratoryThis is a laboratory rotation course to expose and educate the students on the equipment and tools available in the nanomaterials laboratory. NANO 855: Advanced Nano LaboratoryA practical and more hand-on oriented laboratory course of energy storage material and device. The laboratory course will provide hands-on experiences with the specific topics regarding advanced nanomaterials such as battery anode and cathode material for energy storage application. Student will learn how to design and synthesize energy storage material for battery and how to assemble its device and finally how to evaluate batter performance. NANO 861: Advanced Nano Energy SystemAn advanced and more practical oriented course of energy storage material and system. The course will be specifically touching on what are the advanced nanomaterials on energy storage application, how to design the material and how to fabricate its device through state-of-the-art equipment. Furthermore, the course will provide how to elucidate the failure mechanism using a nanoscale fundamental analysis. NANO 885: Special Topics NanoengineeringThis course is designed to allow the introduction of potential new courses on a trial basis or special content courses on a once only basis at the doctoral level. The topic of the course and title are determined prior to registration. NANO 994: Doctoral Supervised ResearchThis is supervised research under the mentorship of a member of the graduate faculty. It is not intended to serve as the dissertation topic of the doctoral student. The student receives a Pass/Fail and no letter grade is given upon completion Prerequisite: Doctoral level standing. 3 (3:0) NANO 997: Doctoral DissertationThis represents the supervised research leading to the dissertation for the doctoral student. The student receives a Pass/Fail grade only after the completion of the final Ph.D. oral defense. Prerequisite: Passed NANO 995 and consent of the advisor. 3 (3:0) NANO 999: Continuation of DissertationThis course is for doctoral students who have completed all required dissertation credit hours. This can be repeated by the students as required. The student receives a Pass/Fail and no letter grade given upon completion. Prerequisite: Completion of all dissertation credits in nanoengineering. 1 (1:0) Mechanical Engineering
Ph.D. in Mechanical EngineeringThe Doctor of Philosophy in Mechanical Engineering prepares students for careers in research and academia. Our collaborative faculty are investigating a diverse range of research areas like additive manufacturing, air quality, cellular biomechanics, computational design, DNA origami, energy conversion and storage, nanoscale manufacturing, soft robotics, transdermal drug delivery, transport phenomena, machine learning, and artificial intelligence. Interested? Visit our research pages for more information, including faculty areas of expertise and research videos.
I’d like more information. View the degree requirements in the handbook. Doctor of Philosophy in Mechanical EngineeringStudents typically complete the Ph.D. degree requirements in three to five years. Early in the program, students focus on course-work that enhances their knowledge as they prepare to conduct research. Within one year, students must pass the departmental qualifying exam, an oral exam that tests research skills and knowledge of a core mechanical engineering subject area. Student research forms the core of the Ph.D. program. Research involves active student-directed inquiry into an engineering problem, culminating in a written thesis and oral defense. Ph.D. Financial SupportThe majority of full-time Ph.D. students accepted through the standard application process receive fellowships that cover full tuition, the technology fee, and a stipend for living expenses for up to five years, as long as sufficient progress is made toward degree completion. These awards are sufficient to cover all expenses for the year (including summers). Students are required to pay for health insurance, the transportation fee, the activity fee, books, and course supplies. Off-campus housing is available within walking distance of campus. At least one year of residency is required for the Ph.D. We offer two ways to enter the Ph.D. program.  Advanced entry Ph.D.The advanced entry Ph.D. is for students with an M.S. in an engineering discipline or equivalent field. Direct Ph.D.The direct Ph.D. is for students entering the program with a B.S. in an engineering discipline or equivalent field. For a comprehensive overview of the programs, including degree requirements, please consult the most recent handbook Ph.D. candidate Remesh Shrestha, co-advised by Professors Sheng Shen and Maarten de Boer, explains his research to create polymer nanowires that have high thermal conductivity: Other Ph.D. programs and partnershipsApply here (by these deadlines). For spring 2023 For fall 2022 The application for fall entry opens in October. More informationPh.D. employment stats Ph.D. enrollment and completion stats [pdf]  Nanoscale Infrared Near-Field Spectroscopy, PHD thesis by Florian HuthFlorian Huth, Pre-doctoral Researcher at the Nanooptics Group at nanoGUNE, receives his PhD at the University of the Basque Country (UPV/EHU) after the defense of his thesis project on Monday 25 May 2015. Hir research work, entitled Nanoscale Infrared Near-Field Spectroscopy ", has been developed under the supervision of the Nanooptics Group Leader and Ikerbasque Research Professor Dr. Rainer Hillenbrand. An international committee including leading researchers in the field was selected to assess the research project:
The defense consisted of a presentation by the candidate of the main aspects of the research project followed by a long discussion about the questions that each one of the members of the committee raised around the research works that have been carried out during the whole PhD period. After its final deliberation, the committee decided to award the candidate the Doctor Degree with the highest mention existing at the Spanish University (cum laude). After the defense, we had a little interview with Dr. Huth and we asked him to explain us a bit more about his project: Which was the subject of your thesis? My thesis is focused on Nano-FTIR, an innovating technology to increasing the spatial resolution of infrared spectroscopy to enable spectroscopic analysis of nanoscale objects. Why did you choose this subject? Because nanotechnology experiences a huge interest in the recent years, creating a demand for novel ultrahigh-resolution techniques such as nano-FTIR. Which metodology or techniques did you use? We improved existing technologies such as IR-spectroscopy and Near-field spectroscopy to develop the nano-FTIR system. Which have been the main conclusions? The developed Nano-FTIR system achieves >100 times better spatial resolution compared to standard IR-spectroscopy and could be proven to work with a large variety of materials including semiconductors, polymers and organic samples. What could be the contribution of your research for present or future nanotechnologies? The new high-resolution analytical capabilities of Nano-FTIR could help understanding and improving a manifold of different material-systems, from nanoscale electronics to molecular biology, or even the nanostructure of stardust. How do you feel now that you have finished the thesis? Which are your plans for the future? It has been a great experience and honor to work here in this amazing scientific environment. In the future I will continue to work for Neaspec GmbH , a company that was co-founded by Rainer Hillenbrand, my thesis supervisor. My duties there will be mostly related to the development and improvement of the nano-FTIR system, which is already commercially available since very recently. Related newsQuantum hardware to be developed at cic nanogune, summer’24 interns are here, nanogune joins pint of science donostia 2024, research positions and industry, hand in hand, niklas friedrich gets rsef-epj+ award for best experimental phd thesis.  Nanoscale AdvancesIntroduction to photocatalytic materials for clean energy, renewable chemicals production, and sustainable catalysis.  * Corresponding authors a Department of Physics and Astronomy, Condensed Matter Theory, Materials Theory Division, Uppsala University, Uppsala 75120, Sweden E-mail: [email protected] b Department of Physics, Indian Institute of Technology Ropar, Rupnagar, Punjab 140001, India c Department of Chemistry, Catalysis Research Laboratory, Indian Institute of Technology Ropar, Rupnagar, Punjab 140001, India E-mail: [email protected] A graphical abstract is available for this content 
Article information Download CitationPermissions.  R. Ahuja and R. Srivastava, Nanoscale Adv. , 2024, Advance Article , DOI: 10.1039/D4NA90075H This article is licensed under a Creative Commons Attribution 3.0 Unported Licence . You can use material from this article in other publications without requesting further permissions from the RSC, provided that the correct acknowledgement is given. Read more about how to correctly acknowledge RSC content . Social activitySearch articles by author. This article has not yet been cited. Advertisements Nanoscale Biomolecular Mapping in Cells and Tissues with Expansion MicroscopyThe ability to map the molecular organization of cells and tissues with nanoscale precision would open the door to understanding their biological functions as well as the mechanisms that lead to pathologies. Though recent technological advances have expanded the repertoire of biological tools, this crucial ability remains an unmet need. Expansion Microscopy (ExM) enables the 3D, nanoscale imaging of biological structures by physical magnifying cells and tissues. Specimens, embedded in a swellable hydrogel, undergo uniform expansion as covalently anchored labels and tags are isotropically separated. ExM thereby allows for the inexpensive nanoscale imaging of biological samples on conventional light microscopes. In this thesis, I describe the development of a method called Expansion FISH (ExFISH) that uses ExM to enable the nanoscale imaging of RNA throughout cells and tissues. A novel chemical approach covalently retains endogenous RNA molecules in the ExM hydrogel. After expansion, RNA molecules can be interrogated with in situ hybridization. ExFISH opens the door for the investigation of the nanoscale organization of RNA molecules in various contexts. Applied to the brain, ExFISH allows for the precise localization of RNA in nanoscale neuronal compartments such as dendrites and spines. Furthermore, the optical homogeneity of expanded samples enables the imaging of RNA in thick-tissue sections. ExFISH also supports multiplexed imaging of RNA as well as signal amplification techniques. Finally, this thesis describes strategies for the multiplexed characterization of biological specimens. Taken together, these approaches may find applications in developing an integrative understanding of cellular and tissue biology. Asmamaw "Oz" Wassie completed a BS in Biological Engineering at MIT. As a PhD student in Biological Engineering, and funded by a Hertz Foundation Fellowship, he is pursuing new physical, chemical, and biological methods for controlling and observing neural processes. Thesis Committee:
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 PhD Thesis : Self Assembled photonic-plasmonic crystals for light control at the nanoscale Related PapersUI Conference oluwagbemiga shoewu This paper examines and employs the application of optical communication in solving physics-inspired engineering problem and periodic structure in plasmonics and photonics with inspired electromagnetic waves. The optical properties of the material (gold) such as dielectric function are employed and modelled i.e., the frequency-dependent dielectric function as well as other optical properties through the quantummechanical approach to visualise the behaviour of the real-and imaginary parts of the optical properties (dielectric function) of the material of interest. The essential equations and its associated supplementary variable equations are neatly analogous with the starting point being Maxwell's equations. This is a justification that demonstrates the visceral uniformity and flexibility of the calculated supplementary, essential and diagonalised forms from Maxwell's equations.  Robert Lipton Analytic representation formulas and power series are developed describing the band structure inside non-magnetic periodic photonic three-dimensional crystals made from high dielectric contrast inclusions. Central to this approach is the identification and utilization of a resonance spectrum for quasiperiodic source-free modes. These modes are used to represent solution operators associated with electromagnetic and acoustic waves inside periodic high contrast media. A convergent power series for the Bloch wave spectrum is recovered from the representation formulas. Explicit conditions on the contrast are found that provide lower bounds on the convergence radius. These conditions are sufficient for the separation of spectral branches of the dispersion relation for any fixed quasi-momentum. ESAIM: Mathematical Modelling and Numerical Analysis Antoine Bourgeade , Brigitte Bidégaray-fesquet Physica Status Solidi (b) Nguyen Ha Quang Progress In Electromagnetics Research M asep suhendi We studied electromagnetic wave propagation in a system that is periodic in both space and time, namely a discrete 2D transmission line (TL) with capacitors modulated in tandem externally. Kirchhoff’s laws lead to an eigenvalue equation whose solutions yield a band structure (BS) for the circular frequency ω as function of the phase advances kxa and kya in the plane of the TL. The surfaces ω(kxa, kya) display exotic behavior like forbidden ω bands, forbidden k bands, both, or neither. Certain critical combinations of the modulation strength mc and the modulation frequency Ω mark transitions from ω stop bands to forbidden k bands, corresponding to phase transitions from no propagation to propagation of waves. Such behavior is found invariably at the high symmetry X and M points of the spatial Brillouin zone (BZ) and at the boundary ω = (1/2)Ω of the temporal BZ. At such boundaries the ω(kxa, kya) surfaces in neighboring BZs assume conical forms that just touch, resembling a South Ame... Physical Review B Vladimir Kuzmiak Pablo Benitez A detailed analysis is presented of the modes of a class of spatiotemporal photonic crystal. The structure analyzed is a perfect dielectric with periodic variation of {\epsilon} in a single spatial direction, as well as periodic variation in time. Analytic solutions are presented for {\epsilon} being separated in both variables, that is {\epsilon}(z,t)={\epsilon}0{\epsilon}r(z){\epsilon}t(t), and dispersion diagrams are presented. Karl Brommer Applied Physics Letters Ilya Shadrivov Loading Preview Sorry, preview is currently unavailable. You can download the paper by clicking the button above. RELATED PAPERSInTech eBooks Yurii Lozovik Journal of the Optical Society of America B Muhammad Faryad Boris Malomed Optical and Quantum Electronics Frank Placido Remy Ndangali Acta Acustica united with Acustica Catherine Potel Physical Review E Sajeev John Andrea Dunbar Mathematische Nachrichten Alessandro Veltri , L. Pezzi Michael V Davidovich International Journal of Applied Electromagnetics and Mechanics André Nicolet Microwave and Optical Technology Letters Didier Felbacq Gregory Morozov Optics letters Victor Sanchez Morcillo , Muriel Botey Zeitschrift für angewandte Mathematik und Physik P. Zhevandrov Valentin Freilikher MRS Proceedings Ilya Vitebskiy Marian Marciniak Siam Journal on Applied Mathematics Peter Kuchment Physica A: Statistical … Youssef El Hassouani Sonia Fliss
The Ohio State University
 Alumni earn awards in research, service, mentoring Tapajyoti Ghosh is helping to pave the way for more efficient, reliable, and affordable renewable energy systems. A former member of the Bhavik Bakshi group and a National Renewable Energy Laboratory Researcher IV Environmental Engineer, his work was highlighted on MIT's homepage ("Evaluating the global energy system," https://bit.ly/Ghosh-MIT ) and featured in National Renewable Energy Laboratory (NREL) News ("Renewable energy is green, but we can make it greener: Code-based life cycle assessments confront environmental impacts of renewable energy technologies from cradle to grave," https://bit.ly/Ghosh-MIT ).  Karen Hendricks, '71 BSAt Ohio State's 435th Commencement ceremony in December 2023, Karen Hendricks received an Ohio State University Distinguished Service Award for her efforts as an Ohio State University Trustee, volunteer on the New Koffolt Labs Committee, and philanthropist. Hendricks, one of very few women studying engineering in the late 1960s, is a former CEO of Baldwin Piano Company and Procter & Gamble executive whose guidance and support has benefited countless students and faculty. She inspired other Ohio State women in their engineering careers and in their choosing to also serve their alma mater.  |
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Interest in nanoscale heat and mass transport has been augmented through current trends in nanotechnology research. The theme of this dissertation is to characterize electric charge, mass and thermal transport at the nanoscale using a fundamental molecular simulation method, namely molecular dynamics. This dissertation reports simulations of
Wolpert_PhD_Thesis.pdf 4.98 MB (No. of downloads : 1309) PDF of dissertation: Description ... This dissertation examines the mechanisms affecting the temperature dependence of device current in nanoscale systems, and proposes a set of techniques for (i) detecting the temperature dependence, (ii) controlling and exploiting the temperature ...
In this thesis, nanoscale engineering is introduced to tackle major challenges in current technologies, especially in remote epitaxy, and to propose new strategies to assemble or integrate a broad range of mixed-dimensional heterostructures that are distinct from the vdW heterostructure counterparts.
the nanoscale By Alexandre Reily Rocha A thesis submitted for the degree of Doctor of Philosophy School of Physics Trinity College Dublin January 2007. x. ... gamble when without knowing each other I decided to be his first PhD student and he decided to be my supervisor. We started off quite literally under a rail bridge
This thesis presents reliability techniques that make designing in sublithographic and nanometer scale practically feasible. Considerable amount of research and work is devoted to continue feature size scaling and also invent new nanoscale electronic devices that can potentially replace the conventional lithpgraphic-based designs.
considered to develop the mechanism. In this thesis, results from a computational investiga-tion of porous low-k SiCOH etching in fluorocarbon plasmas, damage during cleaning of CFx polymer etch residue in Ar/O2 and He/H2 plasmas, NH3 plasma pore sealing and low-k deg-radation due to water uptake, will be discussed.
2021. Dr. Yves Mermoud. Thermoelectric Effects in Nanoscale Devices. 2021. Dr. Oliver Braun. Nanoprinted Quantum DOT/Graphene Infrared Photodetectors, and their Temperature-Dependent Mechanism of Charge Carrier Transfer. 2020. Dr. Matthias Grotevent. Nanojunctions from molecules to graphene nanoribbons : optical characterization and transport ...
Nanoscale light manipulation and characterization are two pillars of modern nano-optics 1,2,3.Recently, a significant progress in this field has been realized through the use of plasmonic ...
Thus, a deep understanding of the specific aspects of light-matter interaction at the nanoscale is crucial if one is to properly engineer nanodevices. In this thesis we report comparative experimental and theoretical studies of nonlinear frequency conversion in different strategic materials for photonics having nanoscale dimensions.
This thesis details research undertaken at the Experimental Solid State group within the Department of Physics at Imperial College London between October 2011 and October 2014. The work presented in this thesis is a product of my own work, except where specific reference is made to the work of others. The material presented in this thesis
Her PhD dissertation title was "Nanoscale energy transport in photovoltaic and thermoelectric nanomaterials". While at Purdue Kelly received the Winkelman Fellowship, Best Student Presentation Award (1st Place) at the Nanostructured Thin Films Conference, a conference within the 2012 SPIE Optics and Photonics Conference, Cordier Fellowship, and ...
Phd Thesis. MULTISCALE MODELING OF QUANTUM TRANSPORT IN 2D MATERIAL BASED MOS TRANSISTORS. ... However as the experimental study of various energy band parameters at the nanoscale regime is extremely challenging, usually one relies on the atomic level simulations, the results of which are at par with the experimental observations. ...
Completion of at least 9 credit hours of 600 or higher level coursework as advised relevant to a NSE Nanoscale Engineering track. Nine (9) credit hours of seminar/external courses. Fifteen (15) credit hours of Ph.D. dissertation research. Students admitted with an appropriate Master's degree shall complete 36 credit hours of academic coursework ...
This thesis is divided into four parts. First part - Background, introduces the reader into the problematic of DRAM structures, principle of their operation, their evolution and current issues ...
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About the Doctor of Philosophy in Nanoengineering. The Ph.D. program in Nanoengineering features coursework, laboratory rotations and extensive dissertation research involving engineering at the nanoscale. It's designed for students with a strong academic track record who seek advanced-level education and training to pursue careers in ...
express my deep and sincere gratitude to my extraordinary thesis ad-visors, Dr. Eduard Alarc on and Dr. Albert Cabellos-Aparicio. Their profound dedication and tireless work shaped this PhD thesis and inspired me throughout its development. Whenever I felt lost, their wise guidance served as a lighthouse that pointed me to the right di-rection.
The Doctor of Philosophy in Mechanical Engineering prepares students for careers in research and academia. Our collaborative faculty are investigating a diverse range of research areas like additive manufacturing, air quality, cellular biomechanics, computational design, DNA origami, energy conversion and storage, nanoscale manufacturing, soft robotics, transdermal drug delivery, transport ...
Nanoscale Infrared Near-Field Spectroscopy, PHD thesis by Florian Huth. 26/05/2015. Florian Huth, Pre-doctoral Researcher at the Nanooptics Group at nanoGUNE, receives his PhD at the University of the Basque Country (UPV/EHU) after the defense of his thesis project on Monday 25 May 2015. Hir research work, entitled Nanoscale Infrared Near-Field ...
Chen's research interests center on nanoscale transport and energy conversion phenomena, and their applications in energy storage, conversion, and utilization. He has made important ... Professor Chen has supervised ~90 MS and PhD students thesis and over 60 post-docs. More than 40 of his PhD students and post-docs are in academia. He is an
Introduction to Photocatalytic Materials for Clean Energy, Renewable Chemicals production, and Sustainable Catalysis R. Ahuja and R. Srivastava, Nanoscale Adv., 2024, Advance Article , DOI: 10.1039/D4NA90075H This article is licensed under a Creative Commons Attribution 3.0 Unported Licence. You can use material from this article in other publications without requesting further permissions ...
ExM thereby allows for the inexpensive nanoscale imaging of biological samples on conventional light microscopes. In this thesis, I describe the development of a method called Expansion FISH (ExFISH) that uses ExM to enable the nanoscale imaging of RNA throughout cells and tissues.
This thesis is devoted to studying the interaction of classical and quantum light states with photonic nanostructures in different configurations. Two main scenarios are explored: the first one consists of a photonic nanostructure interacting with a quantum emitter, such as a molecule or a quantum dot. We analyze the asymmetry in the Fano ...
Bacterial biofilm is a structured community of bacterial cells enclosed in a self-produced polymeric matrix and adherent to an inert or living surface, which allows a protected mode of growth and survival in a hostile environment.
Hannah Zierden, '15 BS. Assistant Professor Hannah Zierden (University of Maryland Chemical and Biomolecular Engineering) was named a 2024 Emerging Investigator by Nanoscale Journey and Outstanding Young Engineer by the Maryland Academy of Sciences. Her research focuses on advancing specialized nanotechnologies for female reproductive health. As an undergrad, Zierden worked in the David Wood ...