To understand paths towards higher efficiency (η) for copper-indium-gallium-(sulfur)-selenide [CIG(S)Se] solar cells, we investigated a variety of absorber composition grading schemes for various back-side gallium (Ga), front-side sulfur (S), and double-graded Ga composition depth profiles in TCAD 1D/2D simulations. We fitted experimental results of a Back-Side Graded (BSG) solar cell with our TCAD models, prior to investigating other grading and interface schemes. The BSG solar cell was fabricated on a High Productivity Combinatorial (HPC™) platform based on sputtering Cu(In,Ga) followed by selenization. Our TCAD simulation methodology for optimizing CIG(S)Se solar cells started with a sensitivity analysis using 1D Solar-cell CAPacitance Simulator (SCAPS) [1] by selecting a typical range of key model parameters and analyzing the impact on η. We then used a 2D commercially-available Sentaurus simulation tool [2] to incorporate wavelength-dependent optical characteristics. As a result, we provide insight in the impact of grading schemes on efficiency for a fixed ‘material quality’ equal to an in-house BSG solar cell. We also quantify the effects of interface layers like MoSe2 at the Mo/CIG(S)Se interface, and an inverted surface layer at the CIG(S)Se/CdS interface.

Thin films (50 nm) of 2,5-di-4-biphenylthiophene (PPTPP), 5,5´-di-4-biphenylyl-2,2´-bithiophene (PPTTPP) and 4,4´-di-2,2´-bithienylbiphenyl (TTPPTT) were vapor-deposited on microstructured gold (source- and drain-) electrode arrays on thermal SiO2 as gate dielectric with underlying Si serving as gate electrode. The films were studied in their field-effect characteristics during film growth and subsequent to it. A decay of specific conductivity and of charge carrier mobility was observed in subsequent measurements. During annealing without an applied field the films recovered but showed a second decay as soon as an electric field was applied again for repeated characterization. Induced dipoles and subsequent structural changes as well as chemical interactions with the SiO2 interface are discussed as possible origins of these observations.

Graphene has been one of the hottest topics in materials science in the last years. Because of its special electronic properties graphene is considered one of the most promising materials for future electronics. However, in its pristine form graphene is a gapless semiconductor, which poses some limitations to its use in some transistor electronics. Many approaches have been tried to create, in a controlled way, a gap in graphene. These approaches have obtained limited successes. Recently, hydrogenated graphene-like structures, the so-called porous graphene, have been synthesized. In this work we show, based on ab initio quantum molecular dynamics calculations, that porous graphene dehydrogenation can lead to a spontaneous formation of a nonzero gap two-dimensional carbon allotrope, called biphenylene carbon (BC). Besides exhibiting an intrinsic nonzero gap value, BC also presents well delocalized frontier orbitals, suggestive of a structure with high electronic mobility. Possible synthetic routes to obtain BC from porous graphene are addressed.

With the development of applications involving high sensitivity ferromagnetic-ferroelectric laminates, a systematic analysis of the noise floor for magneto-electric (ME) laminated sensor has become crucial. We report and discuss the results of such an analysis on the noise floor of magnetostrictive-piezoelectric laminates in terms of the magnetic noise spectral density at room temperature. The noise floor of highly sensitive ME laminates with a JFET charge amplifier detection method has been studied. A good correlation was found between the theoretical and experimental noise curves within the measurement bandwidth. The dominating noise sources were found to include the dielectric loss noise, mechanical loss noise of the magneto-electric laminates and the noise sources of the charge amplifier. By using an appropriate low noise JFET charge amplifier, the noise contributions from the amplifier can be made negligible, enabling the measurement of the intrinsic noise of the ME laminates sensor. Thus, we have shown that at low frequencies, below the resonant frequency, the dielectric loss noise predominates with a one-per-root-frequency dependence whereas, around the resonance, the mechanical loss noise prevails over all other noise sources as expected from our theoretical analysis.

The Transition metal oxides such as TiO2 and CeO2 as catalyst and co-catalyst materials were studied for methanol oxidation. The metal oxide nanoparticles were impregnated into carbon aerogel and Pt-Ru/C (Tanaka) by modified sol-gel Pechini method and heat-treated at different temperatures. Crystal structure, particle size and composition of the catalyst particles were studied using XRD, TEM and EDS techniques. The electrochemical activity and stability of these catalyst materials were studied in acidic medium and the results were compared to their corresponding specific and active surface areas. The aerogel supported metal oxides were stable and proved for better methanol oxidation, while a significant synergetic effect in electro-oxidation is observed when the metal oxides were impregnated into the structure of Pt-Ru/C catalyst. The methanol-oxidation was further improved after heat treatment due to its improved structural and surface properties.

The availability of high-temperature stable surface acoustic wave (SAW) devices would enable realization of wireless sensors for monitoring high-temperature processes. One of the most promising substrate materials for SAW based high-temperature sensors is langasite (LGS, La3Ga5SiO14). It can be excited piezoelectrically up to its melting point at 1470 °C. However, gallium evaporation and degradation of the electrodes limit the application of LGS in SAW sensors for harsh environments to some extent.

The objectives of this work include the investigation of the gallium loss in the vicinity of the langasite surface in oxidizing, reducing and vacuum conditions at temperatures up to 900 °C. The gallium content in the vicinity of the LGS surface is not decreased after annealing the samples in air, while a significant gallium loss occurs in vacuum and reducing atmospheres (0.5 % H2/Ar). The latter results in a gallium oxide deficient region of 1.5 μm below the surface after annealing for 12 hours at 900 °C. The gallium loss is virtually completely suppressed after protecting the surface with a thin alumina film.

Further, thin-film electrodes based on platinum and platinum/rhodium are tested. While conventional platinum based electrodes are completely destroyed at 900 °C within hours due to agglomeration, alumina protected electrodes can be operated at least for several days at this temperature. After 400 hours at 700 °C, the alumina protected platinum electrodes show insignificant degradation. The influence of alumina passivation layers on the stability of the SAW devices is examined. Different electrode configurations are tested with respect to their long-term frequency stability at 650 °C.

Porous CoO/Mn2O3 Fischer-Tropsch (F-T) catalysts have been studied in CO hydrogenation. These CoO/Mn2O3 catalysts have been synthesized by incipient wetness impregnation method. These mesoporous catalysts have pore diameters of 2-25 nm and a surface area of 9.0 m2/g. The gas and liquid products have been analyzed by an online gas chromatograph. The solid products were characterized by gas chromatograph-mass spectroscopy. These microsize cobalt catalysts exhibit good activity with 72.1% CO conversion and they are very stable in a 48 h stream test at 280ºC. The selectivity to paraffins is above 95%. Few wax products were synthesized with a yield of less than 2%. The size effects of the cobalt catalysts have been studied by scanning electron microscopy.

The effect of mesogenic organic salts as reinforcing fillers for natural rubber has been investigated. The influence of cation size (thallium and sodium) and organic chain length (thallium (I) pentanoate and dodecanoate) on the vulcanization parameters, physical and mechanical characteristics and rheological behavior has also been analyzed. In general, the maximum torque of the vulcanizates increases in the presence of the salts and is clearly manifested in a sensible increase in tensile modulus and strength of the composites. The reinforcing effect of these salts is noticeable in the natural rubber matrix. The thallium (I) salts are more effective reinforcements than the sodium salt, and the length of the organic chain hardly has any influence on the mechanical properties. The composites based on the thallium (I) dodecanoate salt show a very peculiar rheological behavior with a “plateau” in the G’ and G” vs temperature graphics which is related with solid phase I, existing between 83.5 ºC and 127 ºC, characterized as a plastic condis phase. This issue is especially interesting for the fabrication of devices such as sensors to control, for instance, the security (resistance of a material) as a function of temperature.

This article presents an analysis of the heat generated by welding two different metals by friction. The welded samples were a DP600 steel and aluminum 6063. To perform this analysis it study the heat conducted in this system using Fourier’s Law and respective specific heat of each metal. We analyzed the integral equations that make up the model and the heat flow analysis to predict the optimal combination of alloys, in an ideal process.

We present here a report on a role of initial nitridation of Si(111) surface on GaN nanorod growth. High quality wurtzite GaN nanorods are grown by Molecular Beam Epitaxy on bare Si(111)-7x7, crystalline and amorphous silicon nitride at 750oC, under nitrogen rich conditions. Using in-situ reflection high energy electron diffraction and ex-situ X-ray photoelectron spectroscopy, field emission scanning electron microscopy and photoluminescence, the structural and chemical properties are monitored. In the first part of the study, we have optimized the conditions of the N2* RF plasma, for formation of crystalline and amorphous silicon nitride on Si(111)-7x7 surface. While in the second part, GaN nanorods are grown on clean and these modified Si(111) substrates. Anisotropic spots are observed by RHEED for GaN grown on clean Si and on the amorphous silicon nitride, while circular, sharp and intense RHEED spots have been observed for GaN grown on crystalline Si3N4. FESEM results show nanorod growth in all the three different conditions. However, GaN nanorods grown on crystalline Si3N4 surface are observed to be self aligned and oriented along <0001> direction, while those grown on amorphous silicon nitride and bare Si(111) surfaces show great disorder increasing, respectively. Overall, the results clearly demonstrate that high quality of dense and self aligned c-oriented GaN nanorods can be formed on Si(111) surface by modifying it by appropriate nitridation.

The authors present the technological routes used to build planar and vertical gate all-around (GAA) field-effect transistors (FETs) using both Si and SiGe nanowires (NWs) and the electrical performances of the as-obtained components. Planar FETs are characterized in back gate configuration and exhibit good behavior such as an ION/IOFF ratio up to 106. Hysteretic behavior and sub-threshold slope values with respect to surface and oxide interface trap densities are discussed. Vertical devices using Si NWs show good characteristics at the state of the art with ION/IOFF ratio close to 106 and sub-threshold slope around 125 mV/decade while vertical SiGe devices also obtained with the same technological processes, present an ION/IOFF ratio from 103 to 104but with poor dynamics which can be explained by the high interface traps density.

We use microwave (MW) absorption to induce rapid, uniform heating of the secondary high explosive octahydro-1,3,5,7-tetranitro-1,3,5,7-tetrazocine (HMX) for decomposition analysis in a fast kinetic regime (10-2 s). Because HMX alone is MW inactive, composites comprised of an HMX-polymeric binder system doped with a small mass fraction (<1 wt%) multiwalled carbon nanotubes or graphite, were fabricated. The dielectric properties were measured (real and imaginary permittivity between 1 – 18 GHz), which is necessary for describing the expected MW-materials interaction and predicted heating response. The real component of the relative dielectric permittivity ranged from 3 – 4 while the imaginary component was 0.01 – 0.07, depending on the amount of carbon dopant added. Dynamic temperature measurements of a similar explosive composite under MW exposure were accomplished using fiber-optic temperature measurement techniques, and can be reproducibly correlated to the amount of MW energy absorbed in the sample.

In this work we present the results of comparative study n- and p-doping of Ge:H and Ge0.96Si0.04 :H films deposited by LF PECVD at high deposition temperature (HT) Td=300°C and low deposition temperature (LT) Td=160°C. The concentration of boron and phosphorus in solid phase was measured by means of SIMS technique. Such parameters as spectral dependence of absorption coefficient, room temperature conductivity σRT and activation energy Ea for both intrinsic and doped films were obtained. The doping range studied in gas phase was for boron [B]gas= 0 to 0.15% and for phosphorus [P]gas= 0 to 0.2%. In general effect of deposition temperature on P and B doping has been demonstrated. For LT films changes of [P]gas=0.04% to 0.22% resulted in more than 2 orders increasing conductivity and reducing activation energy from Ea=0.28 to 0.16 eV. HT films in the range of [P]gas=0.04% to 0.2% demonstrated saturation of conductivity. HT films showed continuous reducing Ea with increase of [P]gas. In the case of boron doping both HT and LT films had a minimum of conductivity at certain values of [B]gas=0.05% (LT films) and 0.04% (HT films) and related maximums of activation energy Ea(max) at the same doping with Ea(max)=0.47 eV for HT and Ea(max)=0.53 eV for LT films. It suggests a compensation of electron conductivity in un-doped films for low B doping. Further raising [B]gas leads to reducing Ea and the smallest Ea=0.27 eV was obtained at [B]gas=0.18% for HT films and Ea=0.33 eV at [B]gas=0.14% for LH films.

Recent trend in thin film solar cells is to use earth abundant materials such as zinc and iron. Zinc phosphide (Zn3P2) has been has been explored as a choice for solar cell absorber and is currently reviving attention. Zinc phosphide is synthesized from earth-abundant constituents. We have already optimized zinc phosphide phase both in nanocrystalline and bulk thin film form. The purpose of this study is to study growth conditions at different temperatures. In this study, Trioctylphosphine (TOP) is used as a source of phosphorous which reacts with zinc and results in the growth of Zn3P2. The synthesized zinc phosphide phase has been characterized using SEM, EDS, XRD and XPS. We report a simple and repeatable process for synthesis of Zn3P2 phase.

The effect of exciplex dynamics on the device characteristics of organic semiconductor bilayer structures is explored. Exciplex formation, dissociation, and relaxation to the ground state are incorporated into a physics-based device model. The model is applied to both organic light emitting diodes and photovoltaic cells. In the examples, C 60and tetracene parameters are used for the electron and hole transport layers, respectively.

Two issues relating to the determination of junction position in thin film CdTe solar cells have been investigated. Firstly, the use of a focussed ion beam (FIB) milling as a method of sample preparation for electron beam induced current (EBIC) analysis is demonstrated. It is superior to fracturing methods. High quality secondary electron and combined secondary electron/EBIC images are presented and interpreted for solar cells with CdTe layers deposited by both close space sublimation (CSS) or RF sputtering. Secondly, it was shown that in an RF-sputtered CdTe device, while the photovoltaic junction was buried ~1.1 μm from the metallurgical interface, the shape of the external quantum efficiency (EQE) curve did not indicate the presence of a buried homo-junction. SCAPS modelling was used to verify that EQE curve shapes are not sensitive to junctions buried < 1.5μm from the CdTe/CdS interface.

In order to reduce the inherent uncertainty in kinetic theory models and promote their transition to become predictive methodologies, a multi-scale modeling approach is proposed and demonstrated in this work. KiValues of key materials properties such as point defect (vacancy and interstitial) migration enthalpies, as well as kinetic factors, such as dimer formation and defect recombination coefficients and self-interstitial atom – interstitial loop reaction rates, were obtained by ab initio/molecular dynamics calculations. A rate theory model was used to interpret the evolution of dislocation loops in irradiated molybdenum. Calculations of the dose dependence of average loop diameter were performed and compared to experimental measurements obtained from irradiations with high-energy electrons. The comparison demonstrates reasonable agreement between model-predicted and experiment-measured data.

We have investigated the effect of varying the film thickness on the surface orientation texturing in polycrystalline Si films obtained via mixed-phase solidification (MPS) of initially a-Si precursor films on SiO2. It is found that, for a given number of MPS exposure cycles, the degree of (100)-surface texturing is reduced as the film thickness is increased. We discuss how this trend can be accounted for by the previously proposed thermodynamic model of MPS, wherein a decreasing local solid/liquid interface curvature with increasing film thickness is identified as the primary cause for decreasing the influence which anisotropic solid-Si/SiO2 interfacial energies have on the survivability of the grains. This, in turn, leads to other factors becoming more significant in determining the grains that survive the MPS cycle, thereby reducing the degree of (100)-surface texturing in the resulting films.