One dimensional photonic crystal 1D-PhC silicon waveguide resonators with quality factor, Q∼105, are demonstrated at mid-infrared wavelengths between 2 um to 5 um. Silicon has several advantages for mid-infrared applications including its broad mid-infrared transmission spectrum which extends out to 9 um, CMOS compatible fabrication processing, and ease of electronic-photonic integration. The proposed resonators are composed of photonic crystal cavities with optimized (i) lattice parameter a, (ii) cavity width w and (iii) hole radius r. Finite difference time domain (FDTD) simulations are used to adjust these three parameters, a, w, and r, to select a resonant frequency of interest within the mid-infrared spectral range. Due to the high quality factor Q, these PhC silicon waveguide resonators have much higher sensitivity as chemical sensors and have the potential to replace bulky instruments such as an FTIR.

This work investigates scanning laser annealing used for ultra-shallow junction (USJ) activation. We investigate the laser system via simulation to determine the peak temperature achieved in the active area during processing. We employed the Sentaurus TCAD software by Synopsys to perform a 2D simulation of a laser scans across the active area of the device, solving the heat equation in both time and space. An absorber layer is deposited on the wafer surface to enhance the absorption of incident energy and reduce SOI reflectivity. An effective absorption coefficient of α=8000cm-1 was calculated for the absorber layer, calibrated with the experimental laser intensity. This absorption coefficient correctly predicts the silicon temperature as a function of power with any arbitrarily defined scan speed. To investigate the role of dopant activation, an SOI wafer was implanted with arsenic 25 keV, dose 3e15 /1.5e15 cm-2 and laser annealed in areas of target temperatures ranging from 850-1300°C. The sheet resistance was measured using 4-point probe showing sheet resistance improvement with increasing laser temperature. The extracted temperature cycle from the 2D heat simulation was used as an equivalent millisecond RTA in a full 3D process simulation to study dopant distribution and activation using Sentaurus Process Kinetic Monte Carlo (KMC), considering the effect of dopants, dopant clusters, and point defects. The results of this simulation demonstrate deactivation of arsenic above 1050°C, which is inconsistent with Hall measurements that suggest increasing laser temperature will increase mobility and activation. The results are analyzed versus the expected trends and suggest future improvements needed to the KMC model or the laser temperature profiles in order to describe activation kinetics in millisecond anneals within SOI.

The metallic binary-alloy fuel Uranium-Zirconium is important for the use of the new generation of advanced fast reactors. Uranium-Zirconium goes through a phase transition at higher temperatures to a (gamma) Body Centered Cubic (BCC) phase. The BCC high temperature phase is particularly important, since the BCC phase corresponds to the temperature range in which the fast reactors will operate. A semi-empirical MEAM (Modified Embedded Atom Method) potential is presented for Uranium-Zirconium. The physical properties of the Uranium-Zirconium binary alloy were reproduced using Molecular Dynamics (MD) simulations and Monte Carlo (MC) simulations with the MEAM potential. This is a large step in making a computationally acceptable fuel performance code.

Aiming the understanding of how the application to devices is affected by the presence of oxygen in semiconductor nanostructures, Al/Ge-nanowires Schottky devices were fabricated without any previous treatment to remove the native oxide from nanowires' surface, originated during the growth process. Electronic transport properties of these devices were investigated and it was observed that interface states originated from the disordered oxide layer effectively pinned the Fermi level at the Ge surface, affecting Schottky barriers. Numerical calculations were made to complement this study agreeing with experiments.

We explore a model of heat transport between two heat reservoirs mediated by a quantum particle. The reservoirs are modeled as ensembles of harmonic modes linearly coupled to the mediator. The steady state heat current, as well as the thermal conductance are obtained for arbitrary coupling strength and will be analyzed for the cases of weak and strong coupling regimes. It is shown that the violation of the virial theorem – the imbalance between the average potential and kinetic energy of the mediator – can be considered as a measure of the coupling strength that takes into account all the relevant factors. The dependence of the thermal conductance on the coupling strength is non-monotonic and displays a maximum. Temperature dependence of the heat conductance may reach a plateau at intermediate temperatures, similar to the classical plateau at high temperatures. We will discuss the origin of Fourier’s law in a chain of macroscopically large, but finite subsystems coupled by the quantum mediators. We will also address the origin of the anomalously large heat current between the scanning tunneling microscope tip and the substrate in deep vacuum which was found in recent experiments.

Development of devices storing and delivering high-energy power such as supercapacitors is necessary to assist intermittent sources of energy. Most of the commercial systems are carbon-based, but due to their high surface charge, oxides offer a valuable alternative for high-rate energy storage. Among them, layered transition metal oxides with mixed valence properties present both good electronic and ionic conductivities suitable for application to electrochemical applications intermediate between capacitors and batteries. This work focuses on lamellar oxide bronzes based on cobalt MxCoO2 and vanadium MxV2O5 (M = H, Li, Na or K). A low temperature synthesis leads to high specific area particles (above 100 m2/g). Hydrated and anhydrous NaxCoO2 are promising cathode materials for aqueous supercapacitors, with a high capacity of more than 100 mAh/g obtained under 20 mV/s for the hydrated NaxCoO2. The MxV2O5 bronzes appear to be good candidates for organic supercapacitors, especially the LixV2O5 bronze, which shows a high stable capacity above 100 mAh/g (at 20 mV/s ie a charging time of 125 s).

We have improved bio-inspired Moth eye nanostructures to enhance the scintillator materials external quantum efficiency significantly. As a proof of concept, we have demonstrated very high light output efficiency enhancement for Lu2SiO5:Ce3+ (LSO:Ce) film in large area. The X-ray mammographic instrument was employed to demonstrate the light output enhancement of the Lu2SiO5:Ce thin film with bio-inspired Moth eye-like nano photonic structures. Our work could be extended to other thin film scintillator materials and is promising to achieve lower patient dose, higher resolution image of human organs and even smaller scale medical imaging.

Promoting a sense of societal connectedness is critical in today’s engineering educational environment. The NAE’s Grand Challenges for Engineering point to broad human concerns — sustainability, health, vulnerability, and joy of living — and human connectivity as the future of engineering problem solving. Engineering studies, however, are often presented in a completely decontextualized manner, with an emphasis on technical content that is free of any human meaning. As a result, students may have difficulty identifying either personal or societal value in their learning tasks. Through their course design, instructors can help students situate themselves and their engineering learning experiences within the larger human system. Studying technologies and technological development within the broader societal context may, in turn, offer significant benefits to student motivation and engagement in learning. In this paper, we report findings from a three-year investigation of the effects of disciplinary integration on student motivation and learning engagement in introductory materials science courses. The quantitative results show that integrating materials science with humanities provides for increased student motivation and cognitive engagement in learning. Compared to students in non-integrated project-based courses, students in integrated project-based courses show higher intrinsic motivation and task value. In addition to these motivational gains, students in the integrated materials science-history course report significantly higher use of critical thinking strategies in their project work, indicating that an emphasis on societal context may help students cognitively engage in their engineering studies. Our findings also indicate that women in the integrated materials-history course report higher intrinsic motivation, task value, self-efficacy, and critical thinking strategy use compared to women in the non-integrated materials course. Overall, our research suggests that putting human contexts at the center of engineering learning can help students build a sense of societal relatedness that promotes better learning.

Studies have demonstrated that the reinforcement of polymeric matrices using nanofiller can results with better thermo-physical properties of polymer. Carbon nanofiber (CNF) is a unique quasi-one dimensional nanostructure with large numbers of edges and defects compared to carbon nanotube (CNT). Further the availability in large quantity along with lower cost makes them an important nanomaterial for future technology. We have previously used CNF in different thermoplastic polymers. In this study CNFs were used with water soluble thermoplastic aliphatic polyster polylactic acid (PLA) and studied their thermal and mechanical properties. Thermal analysis using Thermogravimetric Analysis showed enhanced thermal stability of the polymer at higher nanotube loading (>1 wt%) and decrease of thermal stability at higher loading (>10 wt%). Crystallization thermogram of PLA was modified heavily with the addition of nanofibers changing clearly from one stage to two stage crystallization. In addition, CNF facilitates the crystallization of PLA resulting in an increase of its crystallization. The mechanical testing showed the steady increase of modulus of the composites with the nanofiber content within the range of study which can be regarded as due to the change in interface property of the composites.

The ferroelectric properties of anisotropically strained SrTiO3 films are analyzed by detailed measurements of the complex dielectric constant as function of temperature, frequency, bias voltage and electric field direction. The strain induces a relaxor-ferroelectric phase that persists up to room temperature. However, transition temperature and ferroelectric properties strongly depend on the orientation of the electric field and therefore on the amount of structural strain in the given electric field direction. Frequency and time dependent relaxation experiments reveal the presence and properties of polar nanoregions with randomly distributed directions of dipole moments in the film.

This study provides a recipe of a 2-step selenization and sulfurization method for high strain point (HSP) glass to improve the quality of Cu(In, Ga)(S, Se)2 (CIGSSe). The recipe is distinguished by slow selenization growth before sulfurization growth at the high temperature of 580 °C. We used proto-type HSP glass instead of standard soda lime glass (SLG) to tolerate this higher temperature process. The provided slow selenization recipe improved an averaged relative efficiency by 14 percent compared to a rapid selenization recipe. We confirmed the improvement of the quality of CIGSSe which was characterized by the high crystal quality, the smooth surface, the uniform depletion layer and reduced defects as measured by XRD, SEM, EBIC and Admittance spectroscopy.

Environmental concerns emphasize the urgent need for the development of biodegradable polymers. In this study, poly (lactic acid) (PLA), being a biodegradable polymer matrix, was used together with poly (ethylene glycol) (PEG) to enhance its low toughness. In addition, the deterioration in mechanical properties owing to plasticization was tried to be overcome by addition of nanofiller. As nanofiller, two nanotubular halloysite (HNT) types, one local (ESAN HNT) and an imported one (Nanoclay HNT) supplied by Aldrich, were used. As the first step, characterization and purification of local HNT was performed. In the second step, plasticized and unplasticized PLA matrix composites containing 3, 5 and 10 wt % were prepared and their morphological and mechanical analysis were performed. Upon the addition of both ESAN HNT (local HNT) and Nanoclay HNT (imported HNT) no improvement was observed in the basal spacing of the clay layers owing to poor interaction between the matrix and the surface of the nanotubes which should be modified for better dispersion.

Thin films of Transition Metal Oxides (TMOs) were deposited by reactive sputtering of pure transition metal targets in Argon-Oxygen gas mixture at elevated substrate temperature for efficient energy consumption. The atomic composition and thickness of the TMO films was determined by Rutherford Backscattering Spectroscopy (RBS). Optical transmittance and reflectance spectrum of the films on quartz substrate was measured with thin film measuring system at room temperature and slightly elevated temperature. The surface morphology and structure of the TMO films was determined with Atomic Force Microscope (AFM).

The accuracy and robustness of new Buckingham potentials for the pyrochlores Gd2Ti2O7 and Gd2Zr2O7 is demonstrated by calculating and comparing values for a selection of point defects with those calculated using a selection of other published potentials and our own ab inito values. Frenkel pair defect formation energies are substantially lowered in the presence of a small amount of local cation disorder. The activation energy for oxygen vacancy migration between adjacent O48f sites is calculated for Ti and Zr pyrochlores with the energy found to be lower for the non-defective Ti than for the Zr pyrochlore by ∼0.1 eV. The effect of local cation disorder on the VO48f → VO48f migration energy is minimal for Gd2Ti2O7, while the migration energy is lowered typically by ∼43 % for Gd2Zr2O7. As the healing mechanisms of these pyrochlores are likely to rely upon the availability of oxygen vacancies, the healing of a defective Zr pyrochlore is predicted to be faster than for the equivalent Ti pyrochlore.

In addition to graphene, 2D transition-metal chalcogenides as, e.g., MoS2 and WS2 nanostructures are promising materials for applications in electronics and mechanical engineering. Though the structure of these materials causes a highly inert surface with a low defect concentration, defects and edge effects can strongly influence the properties of these nanostructured materials. Therefore, a basic understanding of the interplay between electronic and mechanical properties and the influence of defects, edge states and doping is needed. We demonstrate on the basis of atomistic quantum-chemical simulations of a circular MoS2 platelet, how the mechanical deformation can vary the electronic properties and other device characteristics of such a system.

An isothermal, physics-based model was developed in COMSOL multiphysics software to simulate the galvanostatic discharge performance of LixC6/Liquid Electrolyte/ Liy(NiaCobMnc)O2 dual lithium-ion insertion cell at 298 K. Modeling results are compared with experimental data to provide further insight into design and optimization of these cells for advanced electric vehicles.

Antireflection with broadband and wide angle properties is important for a wide range of applications on photovoltaic cells and display. The SiOx shell layer provides a natural antireflection from air to the Si core absorption layer. In this work, we have demonstrated the random core-shell silicon nanowires with both broadband (from 400nm to 900nm) and wide angle (from normal incidence to 60°) antireflection characteristics within AM1.5 solar spectrum. The graded index structure from the randomly oriented core-shell (Air/SiOx/Si) nanowires may provide a potential avenue to realize a broadband and wide angle antireflection layer.

Large-area Cu2ZnSnS4 (CZTS) thin films were deposited by low-cost spray pyrolysis technique on Mo-coated soda-lime glass (SLG) substrates at varied substrate temperatures of 563-703°K. Deposition conditions were optimized to obtain best quality films and effect of post deposition thermal processing of the as-deposited films under H2S ambient were investigated. Structural, morphological, and compositional characterization of as-deposited and H2S treated CZTS absorber layers were carried out by x-ray diffraction (XRD), Raman spectroscopy, scanning electron microscopy (SEM) and energy dispersive x-ray analysis (EDX). Optical and electrical properties were measured by UV-Vis spectroscopy, van der Pauw, and Hall-effect measurements. Films grown at ∼360°C substrate temperature showed superior optoelectronic properties, improved stoichiometry and smoother morphology compared to films grown at much higher or lower temperatures. Film properties were significantly improved after the H2S processing. Our results show that large area high quality CZTS films can be fabricated by low-cost spray pyrolysis technique for high throughput commercial production of CZTS based heterojunction solar cells.

Polypyrrole (pPy) conducting polymer films embedded with MnO2 nanoparticles have been synthesized by electrochemical polymerization and anodic oxidation processes. MnO2 nanoparticles coexist in the hydrated Mn(II) and Mn(IV) states and undergo valence state change along side pPy anion doping-dedoping contributing to the system pseudocapacitance. Increased density of sequestered MnO2 nanoparticles in pPy significantly improves charge storage properties as shown by increased electrodic specific capacitance from 200 to 620 Fg-1 based on cyclic voltammetry studies. MnO2 nanoparticle dispersion in open porous pPy microstructure is affected by current density in excess of 4 mA.cm-2 used in synthesis and results in MnO2 particle agglomeration that excludes open surface access reducing specific capacitance. Charge-discharge studies show stable capacitance retention for ∼1000 cycles. The redox performance of MnO2-pPy composite electrodes is suitable for application in the high energy density supercapacitors.

The tolerance of photovoltaic performances of Cu(In,Ga)Se2-based (CIGSe) solar cells prepared from 3-stage grown absorbers to cadmium sulfide (CdS) buffer layer thickness was investigated. We focus on the influence of the maximum Cu content y = [Cu]/([In]+[Ga]) reached during the co-evaporation process on this tolerance. By increasing the duration of the 2nd stage we varied ymax from 0.93±0.11 up to 1.06±0.12. Although final Cu content and CIGSe surface morphology seem to be similar for all absorbers, the photovoltaic performance of cells with higher maximum Cu content are better; moreover they tolerate much thinner CdS buffers (down to 10 nm-thick) without open circuit voltage or fill factor loss. Cells with lower ymax exhibit more erratic performance and J(V,T) measurements show a specific voltage distribution for thin CdS. From these results it appears possible to decrease the CdS buffer layer thickness if it is deposited on adapted absorbers.