Structural relaxation in Ag-Ni nanoparticles: Atomistic modeling away from equilibrium

The out-of-equilibrium structural relaxation of Ag-Ni nanoparticles containing about 1000--3000 atoms was investigated computationally by means of molecular dynamics trajectories in which the temperature is decreased gradually over hundreds of nanoseconds. At low silver concentration of 10--30\%, the evolution of chemical ordering in Ni$_{\rm core}$Ag$_{\rm shell}$ nanoparticles with different surface arrangements is found to proceed spontaneously and induce some rounding of the nickel core and its partial recristallization. Fast cooling of an initially hot metal vapor mixture was also considered, and it is shown to disfavor silver aggregation at the surface. Silver impurities are also occasionally produced but remain rare events under the conditions of our simulations.

Micro-Concentrated Photovoltaics Based on Cu(In,Ga)Se2 Microcells: An Optical Study

Micro-concentrated Cu(In,Ga)Se2 (μCPV-CIGSe) solar cells offer the potential to reduce the consumption of raw materials to a great extent while maintaining high efficiencies. A theoretical model of μCPV-CIGSe solar cells, consisting of hexagonally spaced micro-CIGSe solar cells embedded in the low-index dielectric matrix and micro-sized lenses placed right on top, is proposed for optical study. It is discovered that micro-lenses enable to effectively concentrate the incident light due to the inherent nanojet phenomenon, and the μ-CIGSe absorbers trap the penetrated light within absorbers arising from wave-guided modes. The two effects co-contribute to an optimized absorption for μCPV-CIGSe solar cells with a μ-CIGSe absorber diameter of 800 nm and a pitch of 1500 nm. Short-circuit current density reaches 36.5 mA/cm2 and accounts for 98.8% compared to their plain counterparts without lenses, corresponding to an absorber material saving by a factor of 3/4. Notably, a large contacting area between lenses and CIGSe solar cells are recommended for an improved angular tolerance. Those findings will recommend design principles for further experiments.

Morphology of metallic foams synthetized by plasma electrolysis deposition

The aim of our work is to understand the mechanism governing the growth of metallic foams synthetized by plasma electrolysis deposition. This paper reports the influence of the applied voltage on the morphology and microstructure of copper and gold foams. The evolution of strands morphology and size is investigated by field emission scanning electronic microscopy (FE-SEM). The role of the voltage in the growth of metallic foams is then discussed. Finally, the crystalline structure of the strands is determined by transmission electronic microscopy (TEM) and selected area electron diffraction.

Significant effect of SDS on the optimum operating temperature of ZnO nanosheets gas-sensitive materials

Many methods have been used to reduce the operational energy consumption of ZnO gas-sensitive material effectively. In this paper, different morphologies of ZnO nanomaterials are respectively prepared in the anionic hydrophilic surfactant sodium lauryl sulfate (SDS) with different concentrations as soft templates by hydrothermal method. The influence of SDS concentrations is investigated on the morphology of materials under the conditions of a weak alkali environment with the same pH, and their gas sensitivity after annealing with the same temperature and time. The morphologies and phase structures of all samples are characterized by FESEM and XRD, and their gas-sensitive properties are analyzed by CGS-1TP. Interestingly, the experimental results show that the optimal working temperature of ZnO gas-sensitive materials containing low concentration SDS is reduced by nearly 55% than that of containing 10 times this concentration, and its sensitivity is also slightly improved. The possible mechanism by which the SDS concentration affects the gas sensitivity of the material is also proposed.

Tuning the optoelectronic properties of AZO thin films for silicon thin film solar cell applications

Al-doped ZnO (AZO) thin films are deposited using dc magnetron sputtering and the process conditions are optimized to obtain TCE with desirable properties suitable for photovoltaic applications. In the course, the effects of deposition parameters such as growth temperature, deposition time and plasma power density on the structural and optoelectronic properties were investigated using suitable characterization techniques. XRD analysis of the deposited films at different process conditions showed a strong c-axis preferred orientation. The surface roughness of the deposited films was examined using AFM analysis. Elemental analysis was carried out using XPS. The resistivity and sheet resistance of the thin films decreased with increase in temperature, deposition time and power density. The optimized films deposited at 250°C resulted in electrical resistivity of 6.23 x10-4 Ωcm, sheet resistance of 9.2 Ω/□ and exhibited an optical transmittance of >85% in the visible range. FOM calculations were carried out to analyze the suitability of deposited thinfilms for thin film amorphous silicon solar cell applications. The photo gain of optimized intrinsic a-Si:H layer was in the range of 104, whereas no photo gain was observed in doped a-Si:H layers. The thin film solar cell fabricated using the optimized AZO film as TCE exhibited power conversion efficiency of 6.24% when measured at AM 1.5 condition.

Tailored TiO2 Nanorod Arrays for Dye Sensitized Solar Cell Applications

A TiO2 layer using titanium (IV) butoxide on fluorine doped tin oxide (FTO) substrate is used as a seed layer for the growth of 2D-TiO2 arrays (TRA). TRAs with length of ~1 to 2 µm were grown on seed layer (SL) by two step method. In the first step TiO2 SLs were deposited by sol-gel assisted spin coating method and the second step involved the typical hydrothermal technique to grow rutile TRAs. Most of the TRAs grown on FTO substrate without SL were randomly oriented and TRAs with 0.025M SL was oriented vertically from the substrate. Whereas TRAs grown on 0.05M SL showed hierarchical nanoflower clusters composed of a bunch of TRAs as petals blooming to all directions from the core. The XRD pattern showed all the three TRAs to be crystallized in a tetragonal rutile phase. Photo Luminescence spectra revealed that the TRAs on 0.05M SL have comparatively low intense blue emission band, predicting the suppressed electron-hole recombination rate. The power conversion efficiency of the dye sensitized solar cell (DSSC) with TRAs grown on 0.05M SL was recorded as 3%, which is 3 times greater than that without SL and 1.6 times greater than that with 0.025M SL in our observations.

Nanostructured LaFeO3 /Si Thin Films Grown by Pulsed Laser Deposition

The orthorhombic LaFeO3 thin films grown by pulsed laser deposition on silicon showed nano-structuration of their surface and preferential crystallographic exposed facets, depending on the deposition temperature. The LaFeO3 film deposited at 850°C has two types of grain termination, flat or tip-like, corresponding to two different growth directions, respectively [110] and [200]. Due to the shape of the termination, the same {110} facets are exposed. The LaFeO3 is iron deficient and consequently contains oxygen vacancies, the exact chemical formula being LaFe0.82O3-delta.

Fast growth of pure V2O5 nanoparticles by low-cost hydrothermal process

Vanadium pentoxide (V2O5) nanorods were successfully grown through an easy, quick and clean hydrothermal method using vanadium oxide sols (V2O5.1,6H2O) as precursor. Structurals studies based on the X-ray diffraction and Raman spectroscopy revealed that the synthesized nanomaterials are pure divanadium pentoxide with an orthorhombic phase. The morphological properties and the particle size of the developed V2O5 nanoparticles were investigated by scanning electron microscopy (SEM) and high resolution transmission electron microscope (HRTEM). The results show that the as-grown samples consist of a large amount of one-dimensional V2O5 nanorods with the widths approximately 52 nm and the lengths are up to several hundred nanometers. The effects of different growth conditions, such as hydrothermal duration and stirring temperature of the precursor on the formation of the nanorods has been recorded. Moreover, the structural and morphological properties of the resulting nanopowders have been experimentally studied. Time-dependent experiments showed that V2O5.1,6H2O were dehydrated progressively and transformed into orthorhombic V2O5 single-crystalline nanorods. It has been established that high stirring temperature of the precursor is benefical for the formation of V2O5 nanorods and minimizes the duration time of the heat treatment. Hence the adjusted parameters (time and temperature) appears to be the key element to achieving the desired nanomaterial with defined forms.

Enhanced photocatalytic performance of Molybdenum disulfide-copper oxide nanoparticles photoanodes

In this paper, the molybdenum disulfide (MoS2)/copper oxide (CuO) heterostructure is introduced in a very simple way for photoelectrochemical application. MoS2 multilayers were prepared by sonication method and decorated with copper oxide nanoparticles through its thin film deposition layer and heating in argon atmosphere. SEM, TEM, AFM, absorption and Raman analyses were employed to characterize the nanostructures. The results show that the presence of copper oxide nanoparticles reduces the recombination rate of photogenerated electron-holes in MoS2 multilayers and produces a significant photocurrent compared to the individual MoS2 electrode. Such a proposed structure demonstrates a high potential for photoelectrochemical applications.

Phase-shifting digital holography with an unknown reference beam

In digital holography, errors of the reference field degrade the quality of the reconstructed object field. In this paper, we propose an effective method in phase-shifting digital holography in which the reference field does not need to be known and perfect. The unknown complex amplitudes of both reference and object fields are derived simultaneously. The method employs only five digital holograms and a single execution of a phase retrieval algorithm. So, the required measurements and algorithm executions in this method are fewer than those in other methods; it suggests a simpler and faster method. The effectiveness of the suggested method is indicated by simulation, under noise-free and noisy conditions. Moreover, the capability of the method to extract full information about the phase singularities in both fields is demonstrated.