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.

(Na,K)NbO3 is a promising candidate for lead-free piezoelectric materials. (Na1-xKx)NbO3 films (x = 0.3–0.7) were epitaxially grown on a (100)SrTiO3 substrate via pulsed laser deposition. The effects of substrate temperature and oxygen pressure during deposition on the crystallinity of the films were examined: both parameters affected the mosaic spread of the crystallites and the formation of an impurity phase. In this study, the optimum conditions for the preparation of highly crystalline films were a substrate temperature of 800 °C and oxygen pressure of ∼60 Pa. The lattice constants parallel and perpendicular to the substrate surface responded differently to changes in x: the constant parallel to the surface increased with increasing x, while the constant perpendicular to the surface was maximized at x = 0.5. The difference in the dependence of the lattice constants could be explained by the elastic distortion of the lattice.

Metal Nickel(Ni) fill becomes the challeng in integrating silicide-last process into CMOS advanced technology with further contact size scaling. In this work, the specific contact resistivity (ρc) of cold titanium(Ti)/Si was investigated by the cross-bridge Kelvin resistor(CBKR) method and compared with that of Ni(Pt)Si/Si. The cold Ti/n+-Si showed comparable contact resistance(ρc∼3x10-8Ω·cm2) to Ni(Pt)Si/ n+-Si, while a larger ρc(7.5x10-1Ω·cm2) for cold Ti formed on B+ doped Si substrates. The cold Ti/Si interface was also discussed. Our results furnish a fresh perspective on the solutions to the metal fill challeng for silicide-last process.

For CdTe there is no real distinction between defects and impurities exists when non-shallow dopants are used. These dopants act as beneficial impurities or detrimental carrier trapping centers. Unlike Si, the common assumption that the trap energy level Et is around the middle of the band-gap Ei, is not valid for thin film CdTe. Trap energy levels in CdTe band-gap can distributed with wide range of energy levels above EF. To identify the real role of traps and dopants that limit the solar cell efficiency, a series of samples were investigated in thin film n+-CdS/p-CdTe solar cell, made with evaporated Cu as a primary back contact. It is well known that process temperatures and defect distribution are highly related. This work investigates these shallow level impurities by using temperature dependent current-voltage (I-V-T) and temperature dependent capacitance-voltage (C-V-T) measurements. I-V-T and C-V-T measurements indicate that a large concentration of defects is located in the depletion region. It further suggests that while modest amounts of Cu enhance the cell performance by improving the back contact to CdTe, the high temperature (greater than ∼100°C) process condition degrade device quality and reduce the solar cell efficiency. This is possibly because of the well-established Cu diffusion from the back contact into CdTe. Hence, measurements were performed at lower temperatures (T = 150K to 350K). The observed traps are due to the thermal ionization of impurity centers located in the depletion region of p-CdTe/n+-CdS junction. For our n+-CdS/p-CdTe thin film solar cells, hole traps were observed that are verified by both the measurement techniques. These levels are identical to the observed trap levels by other characterization techniques.

This paper shows a new semiconductor bonding technology for mechanically stacked multi-junction solar cells. Our strategy is the combination of conductive nanoparticle alignments and the van der Waals bonding technique. With this method, reasonably low bonding resistances and minimal optical absorption losses were simultaneously attained for the use of mechanically stacked solar cells. We examined a GaInP(Eg-1.89 eV)/GaAs (Eg-1.42 eV)/InGaAsP (Eg-1.15 eV) three-junction solar cell fabricated with this bonding method. As a result, the total efficiency of 22.5% was achieved, which was in good agreement with the theoretically predicted value. These results suggested that our bonding method is highly useful to fabricate high-efficiency mechanically stacked multi-junction solar cells.

The sorption processes for hydrogen and carbon dioxide are of considerable, and growing interest, particularly due to their relevance to a society that seeks to replace fossil fuels with a more sustainable energy source. X-ray diffraction allows a unique perspective for studying structural modifications and reaction mechanisms that occur when gas and solid interact. The fundamental challenge associated with such a study is that experiments are conducted while the solid sample is held under a gas pressure. To date in-situ high gas pressure studies of this nature have typically been undertaken at large-scale facilities such as synchrotrons or on dedicated laboratory instruments. Here we report high-pressure XRD studies carried out on a multi-purpose diffractometer. To demonstrate the suitability of the equipment, two model studies were carried out, firstly the reversible hydrogen cycling over LaNi5, and secondly the structural change that occurs during the decomposition of ammonia borane that results in the generation of hydrogen gas in the reaction chamber. The results have been finally compared to the literature. The study has been made possible by the combination of rapid X-ray detectors with a reaction chamber capable of withstanding gas pressures up to 100 bar and temperatures up to 900 °C.