Keywords: MEMS/NEMS, Nanosensors & Nanoactuatuators, Nanomaterials
Abstract: The first concept of multi-source Computed Tomography (CT) systems originated in the 1980s, and opened the way to innovative system concepts in X-ray and computed tomography. Multi-source CT systems offer promising opportunities in system performance. In addition, multi-source X-ray radiographic systems are widely studied, namely for X-ray stereographic imaging, X-ray tomosynthesis imaging, and inverse-geometry imaging. One significant benefit of the multi-source X-ray technology is the ability to fabricate the source array in various two- dimensional configurations. The more complicated distributive source topologies are designed to improve the sampling of projection data, to further improve both in-plane and depth imaging resolution within the constraints of the limited-angle acquisition of projection data. In multi-source systems, the X-ray sources are arranged in an array format, and each source is launched individually. However, current X-ray generators are not suited for these systems because of their large size, huge power requirement, and slow response. This talk will focus on the field emission X-ray technology that enables to the realization of multi-source CT systems.

Keywords: Modeling & Simulation, Nanomaterials, Nanoelectronics: Emerging material and device challenges in futuristic systems
Abstract: Heat dissipation and thermal management is a rising concern for nanoelectronic devices and threatens to curtail their adoption in integrated circuits, sensors, and energy converters. Joule heating due to dissipation in the channel region of nanoelectronic devices causes increased temperature and may lead to mobility degradation and long-term reliability issues. Here we study thermal transport and cross-plane thermal boundary conductance in a variety of “beyond graphene” 2D materials and few-layer stacks on several amorphous and crystalline substrates using a combination of first principles methods and Boltzmann transport of phonons. We employ machine learning to accelerate the discovery of 2D-substrate pairings with enhanced thermal conductance. Beyond that, we couple electronic and thermal transport to study dissipation in field effect MOS transistors and show that heat dissipation is non-uniform and that self-heating reduces mobility. We find that judicious selection of the number of layers and substrate can significantly reduce the deleterious effects of Joule heating.

Keywords: Modeling & Simulation, Nanoelectronics: Emerging material and device challenges in futuristic systems, Nanomaterials
Abstract: Ultrawide bandgap (UWBG) materials (e.g., diamond, gallium oxide, boron nitride, and aluminum nitride) possess exquisite materials, electronic, and thermal properties. Atomistic materials and TCAD device modeling and simulations are prime accelerators for understanding the exquisite capabilities of UWBG materials, which can therefore guide future experimental UWBG device design. In this study, we explore several electronic properties of UWBG materials and heterointerfaces (i.e., UWBG semiconductor – UWBG semiconductor heterointerfaces and UWBG semiconductor – metal heterointerfaces) using Density Functional Theory (DFT) first-principle approaches in Synopsys Quantum ATK. TCAD device simulations were also performed using Synopsys Sentaurus TCAD, where Transfer Length Method (TLM) current-voltage (I-V) simulations were performed to extract specific contact resistivity values, which could assist in down-selecting materials needed to form compatible Schottky and/or Ohmic contacts for future UWBG-based devices. All UWBG materials and device simulations were performed using multi-level parallelization on high-performance computing workstations (> 16 cores) provided by NGSC. Comprehensively, these atomistic materials and TCAD device simulation results show promise for developing the next generation of high-performance UWBG devices and systems for emerging Department of Defense (DoD) applications (e.g., RF, power electronics, and high-temperature environments).

Keywords: Modeling & Simulation, Nano-optics, Nano-photonics & Nano-optoelectronics, Nanometrology & Characterization
Abstract: Nanoparticles exhibit optical and infrared sensitivity useful in optoelectronics, spectroscopy, and sensing. Capacitative and conductive coupling induces dipolar and charge transfer plasmon modes in nanoscale dimers. Optical and infrared activity of these hybridized modes are exquisitely sensitive to geometric features of the nanoscale dimer. This study examined spectra for 7 to 8-nanometer dimers with symmetric or asymmetric radii using discrete dipole approximation. Variations in optical and infrared activity were attributable to field localization due to geometry-induced hybridization. Methods herein are useful guides to design dimers for optoelectronic, spectroscopic, and sensing applications.

Keywords: Modeling & Simulation, Nanoelectronics: Emerging material and device challenges in futuristic systems, Nanomaterials
Abstract: With its potential for high-power, high-voltage applications, β-Ga2O3 has garnered much attention due to its large energy bandgap of ~4.8 eV, high theoretical breakdown field of ~8 MV/cm and the availability of shallow donors and native substrates for n-type device fabrication. The material features a much higher Baliga’s figure-of-merit compared to 4H-SiC and GaN. Functional devices, such as diodes and MOSFETs, have already been demonstrated using β-Ga2O3. Recently, various groups have conducted numerical simulations on β-Ga2O3, focusing on fundamental material properties, carrier (electron) scattering mechanisms, and terminal characteristics using first-principles as well as commercial TCAD simulations. In a previous work, we reported the calculation of electron mobility in the bulk form of β-Ga2O3, where the presence of low crystal symmetry induces multiple phonon modes. With the dominance of polar optical phonon (POP) scattering mechanism, however, a 50 meV of POP energy was found to be good enough for the Fröhlich scattering model. For low electrical fields at 300K, we reported an electron mobility of ~110 cm2/V∙s, which matched very well with the experimental findings. Motivated by this work, we have extended our efforts and developed a comprehensive three-dimensional Monte Carlo device simulation platform that enables us to obtain the current-voltage characteristics in scaled devices. In this work, we will present the various features of this modeling framework, which couples atomistic bandstructure calculation with a quantum-corrected electron transport module. There is a plan to further augment the simulator by incorporating the effects of lattice heating, which has been identified as a reliability factor in the use of this material system. We plan to present simulation results on the effects of dynamic trapping of electrons and the localization of unintentional charges (e.g., as observed in single-event upsets), breakdown voltage and carrier transport processes at/near the breakdown voltage, as well as the generation of internal heating in scaled β-Ga2O3 MOSFETs.

Keywords: Modeling & Simulation, Nanomaterials
Abstract: As many times before, the scaling is facing a roadblock as current materials and device architectures are reaching its fundamental limits. In parallel to the material-device limitations, we are also on the brink of the architecture revolution as Von Neumann's architecture cannot follow the continuously increasing memory capacity and ever-rising workloads. Even though the path forward (comprised of in-memory-computing, monolithic integration, 3D stacking, and intelligent functional interconnects) is not fully clear, it will be enabled by functional energy-efficient materials and material-device engineering. Adoption of the new materials and devices can be accelerated and achieved only by understanding and diagnosing its properties and its evolution with lifetime. Here, this will be accomplished utilizing a modelling platform GinestraTM [1] which enables a modelling-augmented metrology and defect-centric device engineering. The Ginestra TM modelling framework is comprised of two main interconnected parts that cover the charge (e/h) and material transport, as well as the stress-induced material modifications enabling us to evaluate and predict device reliability and variability.

We will look at binary-oxide-based ferroelectrics (the most efficient memory material) and oxide-semiconductor materials and devices. We'll review what challenges they need to overcome to be integrated into logic and memory architectures [2]. We will look in detail at the material phases, defects, vacancies, material changes, and underlying physical mechanisms governing those functional materials' variability, reliability, and integrity [2-3]. Only understanding the underlying physical mechanism can help us engineer novel superior devices of the future. Lead by this principle, we will show how we can modify the free energy, engineer and integrate non-volatile anti-ferroelectric devices that fulfil many requirements of the novel memory architectures.

In the second part, we will delve into the reliability features of the alternative channel materials, particularly 3D stacking-ready oxide semiconductors, and investigate the details of their density of states, mobility, and reliability. We will analyse physical mechanism and device reliability governed by channel defects, develop an ALD-grown IGZO channel material, and integrate it into a double-gated transistor test vehicle. Finally, interface-engineered IGZO-based transistors with high mobility and superior reliability (low PBTS) will be presented [4,5].

Keywords: Nanometrology & Characterization
Abstract: Material studies with imaging have been actively employed over the past few decades for fabrication and characterization applications in the nanotechnology field. This paper presents an automated analysis method for detecting the nanoscale and microscale structures and determining their sizes from scanning electron microscope (SEM) images. The MATLAB-based numerical image processing techniques introduced in this work can accurately detect the edges of material and device structures or their defects from the varying monochromatic contrast of different imaged materials. This proposed image processing technique can precisely compute the centroid, area, perimeter, and other relevant dimensional parameters of the structure of interest. The algorithm encompasses image binarizing with adaptive thresholding, grayscale conversion, and filtering to isolate the specific desired structures. We showed the detection of voids in a Ge2Sb2Te5 nanodevice and computed the centroid, area, and perimeter for each detected void. We compared the voids’ area calculated using MATLAB image processing with those computed in GoExplore and ImageJ tools to validate the image processing method presented in this work. We repeated the detection procedures of various types of circular and elliptical voids and hexagonal structures from the SEM images from published works to evaluate the efficacy of the detection method. With minimal adjustment of the image processing parameters, the top view plane of all structures could be identified accurately. This study opens up new possibilities for finite element method analysis in materials research with exact modeling of the geometries of materials and devices utilizing the automated and precise evaluations of multiple complex structures from SEM images.

Keywords: Nanometrology & Characterization
Abstract: The ultrafast dynamics of the antiferrodistortive (AFD) phase transition in perovskite SrTiO3 is monitored via time-domain Brillouin scattering. Using femtosecond optical pulses, we initiate a thermally driven tetragonal-to-cubic structural transformation and detect the crystal phase through changes in the frequency of Brillouin oscillations (BO) induced by propagating acoustic phonons. Coupling the measured BO frequency with a spatiotemporal heat diffusion model, we demonstrate that, for a sample kept in the tetragonal phase, deposition of sufficient thermal energy induces a rapid transformation of the heat-affected region to the cubic phase. The initial phase change is followed by a slower reverse cubic-to-tetragonal phase transformation occurring on a time scale of hundreds of picoseconds. We attribute this ultrafast phase transformation in the perovskite to a structural resemblance between atomic displacements of the R-point soft optic mode of the cubic phase and the tetragonal phase, both characterized by anti-phase rotation of oxygen octahedra. The structural relaxation time exhibits a strong temperature dependence consistent with the prediction of the equation of motion describing collective oxygen octahedra rotation based on the energy landscape of the phenomenological Landau theory of phase transitions. Evidence of such a fast structural transition in perovskites can open up new avenues in information processing and energy storage sectors.

Keywords: Nanometrology & Characterization, Nanofabrication, Nanorobotics & Nanomanufacturing
Abstract: The pull-off (adhesive) force of the tip of an atomic force microscope relies on the bluntness of the tip. The DMT (Derjaguin, Muller, and Toporov) and model JKR (Johnson, Kendall, and Roberts) model are used to estimate this adhesive force. Which to use depends on the Tabor transition parameter. However, the process of determining this parameter has its caveats. Hence, this paper investigates the difference between estimating the pull-off force using the two models for non-integer values of tip bluntness. It was found that the sharper the tip the more it is sensitive to the pull-off force. Moreover, the difference between the two models becomes more pronounces the more spherical it is.

Keywords: Nanometrology & Characterization, Nanomaterials, Fundamentals and applications of nanotubes, nanowires, quantum dots and other low dimensional materials
Abstract: Raman thermometry has gained immense popularity for probing the thermal properties of nanostructured materials due to its excellent spatial resolution and lack of contact error; however, it has a key weakness in its temperature resolution. In this work, we aim to improve the temperature resolution of Raman thermometry through training neural networks to track the locations, widths, and relative heights of multiple peaks at once. We find that in training a multilayer perceptron on 13 pixel values representing the Raman peak of silicon, the variance and standard deviation in thermal conductivity predictions can be reduced as compared to those resulting from the predominant method of tracking the peak location as it shifts with temperature. We expect that this work may contribute to greater accuracy of thermal measurements from non-contact Raman-based techniques and thereby improve the consensus on the thermal properties of 2D materials.

Keywords: Modeling & Simulation
Abstract: Increases in power density in nanoscale devices and the use of different material systems exacerbates local self-heating and can affect device performance and reliability in various ways. In this work, we examine the role of self-heating effects on the high-energy tail of the distribution function in fully-depleted SOI devices. We find that, due to self-heating, the tail of the distribution function extends to higher energy at cryogenic temperatures as opposed to the isothermal case, thus raising the question of reliability concerns due to hot-carriers degradation in these devices.

Keywords: Modeling & Simulation, Nanoelectronics: Emerging material and device challenges in futuristic systems
Abstract: The aggressive scaling of the metal oxide semi- conductor field effect transistors (MOSFET) has led to various issues such as the higher off-state leakage current and Sub- threshold swing (SS). At room temperature, the minimum SS for MOSFETs is 60 mV/dec. For the deep submicron regime, MOSFET is therefore unsuitable. To get around MOSFET limitations, a novel device structure is being researched. In this work, we demonstrate a novel tunnel field-effect transistor (TFET) structure, which uses SiGe and GaAs materaial. The proposed device is based on a double gate structure, utilising SiGe as a source material and GaAs for channel and drain region to enhance the performance of the proposed device and is being referred as Pocket Doped SiGe/GaAs Tunnel FET (PD- SiGe/GaAs TFET). The use of SiGe and n-type pocket at the source has significantly enhanced the ON state performance and GaAs at channel and drain terminals has reduced the ambipolarity of the proposed device. A comparative analysis of the proposed TFET with the conventional Silicon based TFET device has shown significant improvement in ON current (ION ), ION /IOFF ratio, SS and cut-off frequency (fT). The proposed device shows ≈ 1.75x10^3 times increase in ION , 3.5 x10^4 times in ION /IOFF, 54 times in cut-off frequency, 68% improvement in SS

Keywords: Modeling & Simulation, Nanoenergy, Environment & Safety, Nanoelectronics: Emerging material and device challenges in futuristic systems
Abstract: CuBi2O4 (CBO) has recently emerged as a promising photovoltaic material. In this paper, we investigated the performance of a new heterojunction solar cell structure with graphene oxide (GO) as the hole transport material (HTM) through numerical modeling and simulation. Our proposed Au/GO/CBO/CdS/ZnO/ITO/Al device configuration achieved ~23% efficiency using only 600 nanometer thick CBO photo-absorber film. Various parameters, including thickness of the absorber layer, bulk and interfacial defect densities were varied to analyze their dependence on the device performance. The optimized cell exhibited an open-circuit voltage (Voc) of 1.343 V, a short-circuit current density (Jsc) of 22.32 mA/cm2, 75.53% fill factor (FF), and 23.24% power conversion efficiency (PCE).

Keywords: Modeling & Simulation
Abstract: This paper presents the interface trap effects on the subthreshold operation of cryogenic ultra-thin body and box fully depleted silicon-on-insulator (UTBB FDSOI) and that the back-gate technique dynamically modulates the DC characteristics and guarantees no degradation of the analog performance in the subthreshold regime. Besides the characterization from TCAD simulation, a proposed model, including the interface trap, can demonstrate the front/back gatedependent subthreshold characteristics and its implementation in an industrial compact model. The proposed model is verified through the SPICE results.

Keywords: Quantum, Neuromorphic & Unconventional Computin, modeling & simulation
Abstract: The complexity of multi-state devices (e.g., memristors, ferroelectric RAMs (FERAMs) hinder the creation of their unified physics-based model. Data-driven approaches, such as machine learning (ML), are increasingly favoured to address this challenge. In this study, we demonstrate the dynamic modelling of a synaptic ZnO/Ta2O5 Solid Electrolyte-FET by transforming its characteristics into a multivariate time-series problem based on which a Long-Short Term Memory model of the device is constructed. Our method can also be applied to other multi-state devices to accelerate the development time of Neuromorphic Computing Systems.

Keywords: Modeling & Simulation, Nanomaterials, Quantum, Neuromorphic & Unconventional Computing
Abstract: Progress in the field of spin orbit torque (SOT) technology within two-dimensional van der Waals (2D vdW) materials has not only pushed the boundaries of spintronic devices to atomic scales but has also unveiled unconventional torque phenomena and innovative spin-switching mechanisms. The diversity of SOT effects observed in numerous 2D vdW materials begs the question which material might be best suited for realistic applications. A systematic and fast screening approach to identify materials optimal for torque device performance is desirable to guide experimental explorations. However, such a screening process has not yet been developed. The challenge in the screening process is that full Non-Equilibrium Function Theory Spin Torque calculations are computationally expensive and cannot easily be scaled to larger disordered systems. Simpler and faster DFT calculations may be able to guide the selection of materials faster. We develop a figure of merit that relates DTF-based results to spin orbit torque to rapidly search through materials. As such we employ a combination of density functional theory and non-equilibrium Green's function methods to compute SOT properties in various 2D vdW bilayer heterostructures. Our investigation leads to the identification of three high SOT systems: WTe2/CrSe2, MoTe2/VS2, and NbSe2/CrSe2.

Keywords: Nano-biomedicine, MEMS/NEMS, Nanofabrication
Abstract: This paper reports on the development of nanoelectrodes for electrically stimulating neurospheres. The nanoelectrodes were fabricated using self-assembled microsphere beads and Au coating, which were integrated within a cell-culture chamber. The viability and differentiation of the cells within the neurospheres under electrical stimulation have been studied for the first time. It has been found that the optimal electrical stimulation voltage is 20 mV for high viability and neuron differentiation of the cells in neurospheres.

Keywords: Nano-biomedicine, Nanofabrication, Nanosensors & Nanoactuatuators
Abstract: This paper reports on a novel chemical factor-free process to modulate or control cellular processes in stem cells. Specifically, we have shown that Adipose Derived Stem Cells (ADSCs) can be differentiated into neuronal lineage by only applying electrical stimulation delivered via micromachined penetrating nanoelectrodes and have compared this novel methodology to the conventional differentiation of ADSCs achieved using chemical growth factors and other reagents.

Keywords: Nano-biomedicine, Nanosensors & Nanoactuatuators, Nano-optics, Nano-photonics & Nano-optoelectronics
Abstract: Nanoparticle labels enable colorimetric point-of-care devices for rapid, low-cost diagnosis and health monitoring. Accurate interpretation of colorimetric assays relies on reliable perception of differences in quantitative color attributes such as hue, chromaticity, and saturation. This study examined interactions between physical factors such as nanoparticle shape, illumination, and sample environment, and biological factors affecting color vision deficit and optical signal processing that influenced perceived color difference. Comparing measurements and simulation supported a rational framework to design and implement nanoscale spheroids that maximized perceptual color differences for both normal and colorblind observers in colorimetric biomedical point-of-care assays.

Keywords: Nanoelectronics: Emerging material and device challenges in futuristic systems, Nanomaterials, DNA Nanotechnology
Abstract: Despite the strong interest in DNA electronics, the electronic properties of the blueprint of life remain controversial and difficult to precisely determine due to the lack of a reliable single or a few molecules based electrical measurement platform and both intrinsic and extrinsic factors effecting the electron transport characteristics in DNA (Endres et al., 2004). Among a variety of electrical probing of a DNA molecule, nanometer scale separated metallic electrodes separations can be used convenient means of electrical measurement platform for molecular junctions constructed from self-assembling DNA strands (Mahapatro et al,. 2009; Iqbal et al., 2005). Here, we propose a nanowire based nanogap electronic test beds for direct electrical measurement of DNA molecular junctions. Electric-field assisted assembly of Au-Ag-Au nanowires, in which a short silver segment serves the sacrificial layer, was used to precisely align a single nanowire between a pair gold microelectrodes photolithograpically defined on a Si-wafer. The sacrificial layer was selectively etched to create nanogap (~100-150 nm) electrode pairs from each of the aligned nanowire. Chemisorption of thiolated DNA molecules on the surface of wire and then bridging the gap in the wire by capturing a single Au-nanoparticle (200 nm) were followed to build on-chip two DNA molecular junctions linked in series by a single gold nanoparticle. The nanoparticle capture was performed by AC dielectrophoresis under 10 mM pH7 histidine buffer to keep the salinity low and prevent the DNA monolayers on the both side of the nanowire.

Keywords: Nanomaterials, Modeling & Simulation, Nano-fluidics and integrated bio-chips
Abstract: Recent advancements in nanofabrication and low-dimensional materials have enabled synthetic pores to mimic the high ion selectivity and optimized transport systems of biological channels, offering a wide range of potential applications. Nanopores in two-dimensional (2D) solid-state membranes like graphene and transition metal dichalcogenides (TMDs) are particularly promising due to their minimal resistance to ion translocation and robust stability. We have investigated ionic transport through biomimetic subnanometer (sub-nm) pores of graphene and “Janus” MoSSe using all-atom molecular dynamics (MD) simulations. The charged edge sites of these arbitrarily shaped pores can be obtained by optoelectronic control in experiments. For graphene sub-nanometer (sub-nm) pores, cations (K+) are adsorbed on the same side of the pore and cation translocation is observed when an incoming cation replaces one of the adsorbed ions. Anions (Cl-) are mostly repelled by the pore edge charges, resulting in high ion selectivity. This selectivity depends on both pore size and edge charges. We have further explored the energy landscape during the ion translocation to understand the underlying mechanisms and developed a physical model based on the thermionic emission formalism to reproduce the I−V characteristics. "Janus" MoSSe sub-nm pore membrane exhibits an internal electric field because of the charge imbalance between S and Se atoms on each side of the membrane. Under forward bias, K+ ions are adsorbed on either side of the membrane (Figure 1a), while under reverse bias, all ions are adsorbed on the same side. This difference in ion adsorption profiles in response to the polarity of external biases results in asymmetric I-V characteristics. This asymmetry is a direct consequence of the charge inequality between S and Se atoms and is unique to the MoSSe sub-nm pores. Two-step and three-step ion transports are observed in MoSSe pore membranes during cation translocation (Figures 1b and 1c) which resembles trapping-assisted ion transport seen in graphene. Energy calculations and statistical analysis of total translocation time further shed light on the impact of the internal electric field and high biases on the ion transport mechanism. Additionally, increasing the number of MoSSe layers raises the barrier for cation translocations, providing an effective way to control ionic currents.

Keywords: Modeling & Simulation
Abstract: We present a fully-atomistic theoretical framework to model valence change memory (VCM) cells. The model consists of three steps: (1) calculating the activation energies of relevant chemical processes using Density Functional Theory (DFT) calculations, (2) performing Kinetic Monte Carlo (KMC) simulations to obtain the structure of the conductive filament at given voltage and temperature, and (3) performing Quantum Transport calculations to obtain the conductance and the current through the device (Fig 1). [1] The model successfully emulates the switching mechanism in HfO2-based VCM cells based on the creation and rupture of the conductive filament made of oxygen vacancies. Furthermore, we demonstrate that the current flows through uncoordinated hafnium atoms neighbouring oxygen vacancies. A newer version of the model includes the effects of Joule heating, allowing for a more realistic description of the resistive switching, closer to the experimental data. Finally, we apply the model to study some distinctive types of switching occurring in VCMs, such as interfacetype switching in SrTiO3-based memristors and unipolar switching in NiO-based memristors.

Keywords: Modeling & Simulation, Nanorobotics & Nanomanufacturing, Nanomaterials
Abstract: We propose a mechanism of VIA generation based on threshold switching effects known earlier in the physics of solid-state memories and dielectric breakdowns of gate oxides. Our consideration shows that such VIA generation becomes possible under moderate electric fields around 105 V/cm and evolves along the nucleation scenario, whose sensitivity to minute variations in chemical composition opens venue to purposely tweaking VIAs parameters and technology. We provide experimental results that can serve as proof of our concept.

Keywords: Modeling & Simulation, Nanomaterials, Nanoelectronics: Emerging material and device challenges in futuristic systems
Abstract: Despite their potential for miniaturization, electronic devices made of 2D materials face thermal management challenges due to their reduced dimensionality, which can limit their efficiency and lifespan. Low thermal boundary conductance (TBC) is one major limiting factor in realizing efficient heat transfer to the substrate. Due to the roughness at the interface, the adhesion of 2D materials to their substrates tend to be weak, resulting in low TBC. Therefore, to improve heat flow from the 2D material, we need to discover novel ways of increasing TBC. In this study, we have used a numerical model combined with first-principles DFPT simulations to investigate a possible method to increase TBC using an electrostatic field due to gate voltage. Our study shows that electrostatic pressure can be used to effectively enhance TBC for an interface formed by a 2D material and a rough substrate. We find that electrostatic pressure can improve TBC by more than 300 % when an electric field of 3 V/nm is applied. This is due to an improvement in the vdW spring coupling constant, which shows a more than two-fold increase when a substrate roughness of 1.6 nm and correlation length of 10.8 nm, 2D-material's bending stiffness of 1.5 eV, and adhesion energy of 0.1 J/m^2 were used. We show that TBC is enhanced more when the substrate has a large roughness and small correlation length, and the 2D material has a large bending stiffness. This is because a stiff 2D sheet resist bending when voltage/pressure is applied, thus causing it to press more on the roughness peaks, resulting in a tremendous increase in the coupling constants at the peaks in the atomically rough surface of the substrate. However, a flexible 2D material can easily bend to conform to the topography of the rough substrate when voltage/pressure is applied, which makes the coupling constants across the interface more uniform. Here we show that TBC is enhanced more when adhesion is weak because a weak vdW bond is easily compressed by external pressure. Therefore, our study provides valuable information that can be applied in designing electronic devices with efficient heat management by using gate voltage, substrate roughness combined with the mechanical properties.

Keywords: Modeling & Simulation, Nanomaterials, Nano-optics, Nano-photonics & Nano-optoelectronics
Abstract: Conjugated polymers (CP) are frequently doped to modulate their transport and optical properties. Doping alters the intrinsic Gaussian density of states (DOS) by adding Coulomb energy and inducing an exponential tail. Changes in transport or optical properties are mainly tracked back to changes in DOS and carrier hopping rates. Conductivity shows a power-law like increase and the Seebeck coefficient a decrease with carrier concentration. This results in a trade-off between transport properties with doping. However, their modification with doping is still not well understood. Here we show that capture transport and optical properties of doped CPs, by developing a tight-binding Hamiltonian that includes dopant-induced energetic disorder (DID) via Coulomb interactions. We utilize perturbation theory to calculate transition rates between wavefunctions from the calculated eigenenergies and eigenfunctions. With the obtained transition rates, we solve Pauli master equation for occupational probabilities to compute transport properties of doped CPs. Additionally, we capture optical absorption features by simply simulating the joint DOS and IR absorption features via simulated AC conductivity. We anticipate our work to significantly contribute to understanding of underlying transport and optical physics of doped CPs.

Keywords: Modeling & Simulation, Nanoelectronics: Emerging material and device challenges in futuristic systems
Abstract: We present our work on the modeling and simulation of the transport charactristics of nanosheets, with special emphasis being placed on efficient computational methods for the analysis of the quantum transport properties.

Keywords: Modeling & Simulation
Abstract: A major advantage of ultra-wide band gap (UWBG) materials for power electronic applications are the predicted high breakdown voltages limited by avalanche breakdown due to impact ionization. However, experimental data on the impact ionization coefficients in these new class of materials is limited. Theoretical calculations of ionization coefficients using Monte Carlo methods are highly influenced by the choice of deformation potential scattering rates, which in turn are dependent on the phonon deformation potentials used as inputs. Hence, to understand the limits of performance of these materials, we report on first principles theoretical calculations of the high field transport properties of UWBG materials using a combination of ab initio calculations of the electronic and phononic structure coupled with particle based full-band Cellular Monte Carlo (CMC) [1] high field transport simulation. The electronic structure of the UWBG materials of interest are computed from DFT using Quantum Espresso [2] where the norm-conserving BLYP unctional was used. The DFT results were then used as the basis for GW calculations using BerkeleyGW [3], to provide accurate bandgaps and excited state (i.e. conduction band) electronic structure. Figure 1 shows the GW electronic structure calculated for three UWBG materials, diamond, cubic BN (c-BN) and wurzite AlN. Cubic BN was considered as it is closely lattice matched to diamond, allowing UWBG heterostructures of the two. Phonon dispersions are calculated from DFPT (density functional perturbation theory) using Quantum Espresso. Wavevector dependent deformation potentials are computed using EPW (electron-phonon using Wannier) [4] using the DFPT phonon dispersion and eigenvectors together with the GW wavefunctions. The calculated electronic structure, phonon dispersion and anisotropic electron-phonon deformation potentials are input into the CMC code, where the fully anisotropic scattering rates are computed from time dependent perturbation theory including defect scattering in addition to electron-phonon scattering. Figure 2 shows a comparison of the energy averaged electron-phonon scattering rates for the three materials. We calculate the band-to-band impact ionization scattering rate directly from the GW electronic structure, using a screened Coulomb interaction based on the full band frequency-dependent Lindhard dielectric function. Figure 3 shows a comparison of the calculated impact ionization rates for the three materials. Interestingly, the hole initiated rate for AlN is quite low due to the narrow width of the valence band (Fig. 1), which prevents holes from reaching threshold. Based on these scattering mechanisms as input, transport quantities such as the velocity-field characteristics and impact ionization coefficients as a function of field are calculated from full band Cellular Monte Carlo (CMC) simulation. One important observation is that while the critical field depends strongly on the material bandgap, the relative magnitude of the deformation potential plays an important role as well. Figure 4 shows the simulated impact ionization coefficient using full band CMC (related to the number of electron-hole pairs generated per unit length due to impact ionization) versus inverse electric field for diamond compared to prior Monte Carlo simulations and experiment [5]. Lower values of the deformation potential for holes in diamond lead to more energetic electron and hole populations which favor impact ionization, hence reducing the breakdown field. In the talk, we compare different approximations of the deformation potential in relation to the simulated impact ionization coefficients and their impact on breakdown for diamond, AlN and BN. The impact of other scattering processes due to defects such as ionized impurities on the high field properties are also under investigation. We also simulate transport at UWBG interfaces between diamond and BN and the potential for heterojunction transistors.

Keywords: Education in nanotechnology
Abstract: Much has changed since Feynman complained that "Social science is an example of a science which is not a science... They follow the forms... but they don't get any laws." The social sciences, particularly economics, have made huge strides in being able to provide both the data and analytic tools that can help people make sound, evidence-based decisions about their lives. But not all analysis or data is created equal. In this talk, I’ll explain how you can use free, readily available public data to improve your and your boss’s lives, and why it is that high quality, reliable economic data collection should probably not be shrunk down to 20 people living in North Dakota running web scraping / AI tools and publishing the data.