Two alternative chemical etchings (aqueous solution of bromine and bromine methanol solution) have been here tested to replace the KCN etching step in Cu-rich CuInSe2 based solar cells fabrication process. This new oxidative etch aims also at smoothing and thinning the as-grown films. This directly affects the interface between the absorber and the CdS buffer, interface which causes problems for Cu-rich solar cells. We present here the effect of these two alternative etchings on both the absorber surface and the solar cells parameters: whereas the bromine methanol etching destroys the solar cell, the aqueous solution of bromine leads to an improvement of the device through reduced interface and tunneling enhanced recombination.

We fabricated ferroelectric (Pb,La)(Zr,Ti)O3 (PLZT) capacitors with Sn:In2O3 (ITO) top electrodes using chemical solution deposition. Then, the effects of a thin conductive ITO buffer layer between the Pt bottom electrode and PLZT thin film were investigated in combination with top electrode (ITO/PLZT/ITO/Pt). The H2 degradation resistance of ITO/PLZT/ITO/Pt capacitors with a 3- and 28-nm-thick buffer layer was improved to 78 and 85%, respectively, from 60% without a buffer layer. The time-of-flight secondary ion mass spectrometry profiles indicated the intensity of H ion increased after 45 min forming gas (3% H2/balance N2) annealing.

Thermal emission plays a critical role in a wide variety of applications, including adjusting radiative losses in photovoltaics and selective solar absorbers, as well as enhancing the emission of high energy photons for thermophotovoltaics and photon-enhanced thermionic emission. In this work, we consider the benefit to thermal emission associated with replacing conventional mirrors with meta-mirrors following Generalized Snell’s Law. By reflecting light at a different angle than incident, they can couple internally guided thermal radiation modes to the escape cone, ideally starting from any internally-guided angle. We illustrate the concept with two meta-mirror structures: a graded index material and a xylophone structure. Even without optimization, angle-averaged selective thermal emission is significantly enhanced compared to the planar case at selected wavelengths. Furthermore, the central wavelength and bandwidth of the enhancement can be matched with the requirements of each application.

In this study, we fabricated Mg2Si from metal Mg and Si with different particle sizes (425 - 300, 300 - 180, and 75 μm or less) using spark plasma sintering (SPS) equipment. Additionally, the Mg2Si formation was investigated. A sieved Si powder was mixed with metal Mg powder in an inert gas (Ar) atmosphere. The mixture was placed in a graphite die while still in an Ar atmosphere and subjected to SPS at 923 K and 1113 K. The obtained sintering bodies were Mg2Si particles with a size of about 5 μm. Then, the sintered bodies were evaluated by X-ray diffraction (XRD). As a result, it was confirmed that generation of Mg2Si increased with decreasing Si particle size.

Wrinkle-less graphene films are obtained through roll-to-roll microwave plasma chemical vapor deposition by using flexible copper/polyimide (Cu/PI) webs. Raman spectra suggests that the average domain size of the obtained graphene on the flexible Cu/PI is almost the same compared to the graphene on a Cu web that includes wrinkles. Also, by utilizing the flexible Cu/PI webs, the compressive strains decreased. The sheet resistances of graphene deposited on the Cu/PI are (1∼5)×104Ω, which is two orders of magnitude lower than those of graphene deposited on the Cu webs. Our results suggest that the controlling the expansion of web material an important technology to improve graphene transparent conductive properties.

Various promising applications such as acoustic cloaking, sub-wavelength imaging, acoustic wave manipulation, transmission or reflection control etc. are feasible because of the ability of manipulating sounds and vibrations using artificially engineered “Acoustics meta-materials”. Recent works on space-coiling acoustic metamaterials show their extreme constitutive parameters like large refractive index, double negativity and zero mass density. Three dimensional structures have a wide application in sub-wavelength broadband acoustic wave suppression due to huge attenuation. Here we report the study of propagated and transmitted wave through 3D acoustic metamaterials structure using finite element method. Our simulations on 3D structure show a huge absorption/damping over few hundreds kilohertz frequency range.

Nano-phase separation is of great relevance for functional materials like thermoelectrics. Indeed, nano-domains in CoSb-based half-Heusler thermoelectrics have been found to reduce the lattice heat conductivity, which increases the figure of merit. Within this context, we studied the configurational energy in the alloy CoTi0.5Sc0.5Sb by means of first-principle calculations. We consider structures formed by Ti (Sc) nano-domains. In recent publications we have showed that these domains are the most stable atomic configurations. In this work we found that for a given concentration the electronic density of states is considerably modified as the volume of the domains are increased.

The effect of Ti addition on the density and microstructure development of MoSiBTiC alloy was investigated. Two kinds of MoSiBTiC alloys with the composition of Mo-5Si-10B-10Ti-10C (10Ti alloy) and Mo-5Si-10B-15Ti-10C (15Ti alloy) (at. %) were prepared by conventional arc-melting. The primary phase of as-cast 10Ti and 15Ti alloys was (Ti,Mo)C, and there were two eutectic phases of Moss + (Ti,Mo)C and Moss + T2 + (Ti,Mo)C in the alloys. In addition, 10Ti alloy had a Moss + T2 + (Mo,Ti)2C eutectic. There was no Moss + T2 + (Mo,Ti)2C eutectic in the 15Ti alloy, and thus it is apparent that the (Mo,Ti)2C formation was suppressed by 5 at. % Ti addition. The volume fraction of (Ti,Mo)C increased and thus the density reduced from 8.78 to 8.43 g/cm3 with the Ti addition. In all constituent phases, Ti concentration increased while Mo concentration decreased. In spite of the changes, hardness, Young’s modulus and shear modulus were hardly changed. Therefore, Ti addition seems to be effective to further lower the density without deteriorating mechanical properties of the MoSiBTiC alloy.

Electrochemical performance of hybrid supercapacitor (HSC) utilizing surface sculpted Li4Ti5O12 (LTO) insertion electrode having nanoplatelet-like morphology and activated carbon (AC) electrode is investigated for energy storage application. Cyclic voltammetry (CV) at variable scan rates 0.5 to 60 mV.s-1 in the 0-3.2 V range show pseusocapacitive behavior and fast rate of current change indicating rapid Faradaic kinetics. Nyquist impedance study show charge transfer resistance due to kinetic effects of electron transfer and Li+ de-intercalation process at the LTO anode. Low capacity (0.2 C-1C) charge-discharge (CD) curves show high Coulomb efficiency with marginal reduction at high 5-10 C rates due to irreversibility of adsorbed PF6 anions at the electrolyte-AC interface. Galvanostatic CD cycling tests over 50 cycles at different C-rates show decline in storage capacity due to electrode polarization effects. Reduction, broadening and shift of the Raman line at 678 cm-1 from Ti-O bonds in TiO6 octahedra after cycling indicates Li insertion reactions in functioning of hybrid supercapacitor. The hybrid supercapacitor cells have shown energy density, 29 Wh.kg-1 and power density, 350 W.kg-1.

Susceptibility to external stress corrosion cracking (ESCC) of API X52 pipeline steel in calcareous soil containing different moisture content has been investigated using slow strain rate tests (SSRT). This type of soil is common of the state of Campeche Mexico and has a pH around 8. The results indicate that X52 pipeline steel was susceptible to external SCC only in the saturated calcareous soil, showing some micro cracks in the gage section of the SSR specimen. It was observed that some micro cracks were found at the bottom of micro-pits. Which indicate that first develop a pit and this evolved with time and micro-strain like a crack. Few micro cracks were observed as initiation of SCC close to surface failure. The mechanism of SCC may be influenced by formation and rupture film of carbonates.

Oxidation tests of Cr containing Co-based superalloys with compositions of Co-20at.%Ni-9at.%Al-9at.%W-x at.%Cr (x = 2, 4, 6, 8 and 10) have been carried out at 1173 and 1273 K in air. Oxidation resistance is improved upon alloying with Cr not only at 1173 K but also at 1273 K. The weight gain of the 10at.%Cr alloy oxidized at 1173 K is similar to that of the 5th generation Ni-based superalloy of TMS-173. Alloying with Cr is efficient to improve oxidation resistance, however, the shape of γ’ precipitates is rounded and the alignment of the precipitates along the <100> direction becomes less pronounced upon alloying with Cr.

Zinc oxide (ZnO) is a crystalline material with diverse morphology, large bandgap and high visible light transparency. All of these characteristics make ZnO a suitable material for applications in optical devices such as photovoltaic cells and photodiodes. Regarding photovoltaic applications, it is necessary to grow ZnO on a transparent conducting oxide (TCO) substrate. In this work, vertically aligned 1-dimensional ZnO have been synthesized on a TCO substrate through chemical vapor deposition (CVD). Although ZnO is capable of being synthesized at lower temperatures through the use of Zn powder precursor, oxidation of precursor remains a significant limiting factor to control dimensional characteristics of the synthesized product.

In our work we have developed a method by which ZnO is synthesized under lower temperatures through the prevention of precursor oxidation and control of Zn vapor fluid dynamics. Partial pressure of Zn vapor—a significant factor in the morphology and quality of product—is controlled and maintained during growth. The morphology and crystal structure of the synthesized ZnO is characterized by scanning electron microscopy (SEM) and x-ray diffraction (XRD). We also demonstrate the fabrication of dye-sensitized solar cell (DSSC) with synthesized 1-dimensional ZnO, as a photoelectrode, and compare the photovoltaic characteristics of two devices fabricated under same conditions, except for the photoelectrode utilized.

The paper presents complex research of the structure and electrophysical properties of thin films on the basis of Cr2O3, V2O5 and SiO2 oxides compounds. The paper studies binary compounds films of Cr2O3 -V2O5 and Cr2O3 - V2O5 -SiO2 films. The method of electron-beam evaporation is used for the films deposition; glass is used as the substrate. The films structure is studied by the methods of slow electron diffraction, infrared spectroscopy, and electron paramagnetic resonance. The films composition is determined by the X-ray microanalysis.

In the course of studies the following regularities have been established:

- dependence of the films structure on their composition;

- dependence of electrophysical films properties on the their composition;

- dependence of volt-ampere characteristics on the films composition (memory effect);

- high film stability to the effect of electron flow and radiation in the discharge plasma.

ZnO nanorods were synthesized by recrystallization of ZnO thin films during multiannealing process. It was found that the obtained ZnO nanorods showed well-controlled grown direction. The periodical oxygen introducing between reducing annealing processes was effective to help on the oxidization reaction, result in the ZnO nanorods growth significantly. With controlling the annealing parameters, the morphologies of ZnO nanorods could be also controlled. The low-temperature (less than 420°C) initial reducing annealing process contributed to control the density of ZnO nanorods. The multi-annealing processes could reduce the ZnO thin film to produce ZnO nanorods efficiently. The structural, optical and electrical properties of the ZnO nanorods were investigated. Finally, the obtained ZnO nanorods used as photoelectrodes demonstrated in a dye-sensitized solar cell, the overall conversion efficiency of 3.65% was achieved.

The TRISO (tristructural isotropic) coated fuel particle is made of a uranium oxide kernel coated with three layers of pyrolytic carbon and one of silicon carbide. This fuel, originally used in High Temperature Reactors, has been proposed as accident tolerant fuel for Light Water Reactors after the accident in Fukushima. Although this fuel is capable of retaining fission products within the particle up to 1600°C, little is known on the origin of this temperature limit. Therefore, in order to increase the safety of this type of fuel, it is necessary to understand the origin of the degradation of the materials that compose this fuel. We have studied the effect of temperature on the microstructure and diffusion of silver in pyrolytic carbon coatings produced by fluidized bed chemical vapor deposition. Samples were heat treated at 1000°C, 1400°C and 1700°C for 200 hrs. under inert atmosphere. The effect of temperature on the microstructure and silver diffusion behavior were analyzed by Raman spectroscopy, X-Ray diffraction, optical microscopy, SEM and TEM. We observed that the microstructure of PyC changed drastically above 1400°C, showing the increase in anisotropy and the re-orientation of the graphene planes. The diffusion of silver appears to be also correlated with this change in microstructure.

Generally, the electrodes are regarded as free electron gases when we calculate the transport characteristics of nanostructure materials or devices. In three dimensional electrodes, there are little electron correlation. However, in low-dimensional electrodes, electron correlation becomes much larger than that in three dimensional ones. Recently, nanotechnology has made much progress to fabricate two-dimensional (2D) electrodes easily and precisely. As a result, we must consider whether two-dimensional electrodes can be regarded as free electron gases. In this study, we investigate the electron energy spectrum of 2D electrodes, taking into consideration the electron correlation. These results suggest that the free electron model is justified only at the Fermi momentum and that we should not regard 2D electrodes as free electron gases without careful consideration under high electric field and/or high temperature.

Bifunctional electrocatalysts, which facilitate the oxygen reduction reaction (ORR) and oxygen evolution reaction (OER), are vital components in advanced metal-air batteries. Results are presented for carbon-free, nanocrystalline, rod-like, Mn-Co oxide/PEDOT bifunctional electrocatalysts, prepared by template-free sequential anodic electrodeposition. Electrochemical characterization of synthesized electrocatalysts, with and without a conducting polymer (PEDOT) coating, was performed using cyclic voltammetry (CV) and linear sweep voltammetry (LSV). In addition, microstructural characterization was conducted using SEM, TEM, STEM and XPS. Mn-Co oxide/PEDOT showed improved ORR/OER performance relative to Mn-Co oxide and PEDOT. On the basis of rotating disk electrode (RDE) experiments, Mn-Co oxide/PEDOT displayed the desired 4-electron transfer oxygen reduction pathway. Comparable ORR activity and superior OER activity relative to commercial Pt/C were observed.

Depending on their application temperature thermoelectric (TE) materials are classified in three main categories; as low (up to 250°C), intermediate (up to 550°C) and high (above 600°C) temperature. Currently, Skutterudites (CoSb3) based materials have shown promising results in the intermediate temperature range (300-500°C). This family of material is highly suitable for automotive, marine transportation and industrial power generation applications to recover the waste heat from the exhaust and generate electricity. Conventional TE modules need p- and n-type semiconductor materials and for the skutterudite family, iron (Fe) has proven to be among the best candidates for the substitution of cobalt sites. Additionally, rare earths are introduced as rattlers in the crystal cages of the skutterudite to decrease the thermal conductivity, thus improving the figure of merit ZT of the TE material. For practical application for device fabrication, stability of these materials is of great importance. Compositional stability is being addressed as the material decomposes above certain temperature. Temperature dependent x-ray diffraction study was performed on Fe substituted, Yb-filled skutterudites, using Beam Line I711 at MAX LAB, to observe the crystal structure as a function of temperature. Diffraction patterns were collected from room temperature up to 500°C by utilizing Huber furnace. The results show success in filling process showing almost 80% reduction of the thermal conductivity from bulk. Additionally the thermal expansion coefficient value was within the average value for skutterudites which proves practical application of this powder for industrial applications.

Nanogenerators (NGs) have great potential to solve the problems of energy depletion and environmental pollution. Here, two types of flexible nanogenerators (FNGs) based on graphene oxide (GO) and multiwall carbon nanotubes (MW-CNTs) are presented. The peak output voltage and current of GO based FNG reached up to 2 V and 30 nA, respectively, under 15 N force at 1 Hz. Moreover, the output voltage could be improved to 34.4 V when the frequency was increased to 10 Hz. It was also found the output voltage increased from 0.1 V to 2.0 V using a released GO structure. The other FNG was made by MW-CNTs mixed with ZnO nanoparticles (NPs). Its output voltage and power reached up to 7.5 V and 18.75 mW, respectively, which is much larger than that of bare ZnO based FNG. Furthermore, a peak voltage of 30 V could be gained by stamping one’s foot on the FNG. Finally, a modified NG was fabricated using four springs and two flexible layers. As a result, the voltage and power reached up to 9 V and 27mW, respectively. These works may bring out broad applications in energy harvesting.

VO2 is one of the very few natural materials that can be used to modulate terahertz (THz) radiations. A 100-nm thick VO2, when in its metallic phase, has a charge density of more than ∼ 1015 cm-2 which will strongly reflect and absorb the THz radiation; while in its insulator state, the charge density is lowered by several orders of magnitude to be THz transparent. Therefore, exploiting the metal-insulator transition of VO2 is a potential approach to modulate or even switch THz radiation for THz optics. Here we report that VO2 epitaxial thin films on sapphire substrate exhibits 85% amplitude modulation depth in a broad bandwidth, while this value can be improved to 95% when VO2 film is coated on both sides of a substrate. We further demonstrate that with wafer bonding, 4-layered VO2 thin films exhibit a transmittance as low as -20 dB to -30 dB at their metallic state, enough for switching applications. We also report our proof-of-concept demonstration of THz spatial light modulator that exhibits amplitude modulation as large as 96%, -30 dB pixel-to-pixel crosstalk, and a broad THz bandwidth.