Ni–Mo–S Ternary Chalcogenide Thin Film for Enhanced Hydrogen Evolution Reaction

Catalysis Letters - Transition metal dichalcogenides (TMDs) hold a great promise to replace Pt-based catalysts for hydrogen evolution reaction (HER). Among those, MoS2 has been the center of...     

Gallium oxide films deposition by RF magnetron sputtering; a detailed analysis on the effects of deposition pressure and sputtering power and annealing

In this study, gallium oxide (Ga₂O₃) thin films were deposited on sapphire and n-Si substrates using Ga₂O₃ target by radio frequency magnetron sputtering (RFMS) at substrate temperature of 300 °C at variable RF power and deposition pressure. The effects of deposition pressure and growth power on crystalline structure, morphology, transmittance, refractive index and band gap energy were investigated in detail. X-ray diffraction results showed that amorphous phase was observed in all the as-deposited thin films except for the thin films grown at low growth pressure. All the films showed conversion to poly-crystal β-Ga₂O₃ phase after annealing process. When the deposition pressure increased from 7.5 mTorr to 12.20 mTorr, change in the 2D growth mode to 3D columnar growth mode was observed from the SEM images. Annealing clearly showed formation of larger grains for all the thin films. Lower transmission values were observed as the growth pressure increases. Annealing caused to obtain similar transmittance values for the thin films grown at different pressures. It was found that a red shift observed in the absorption edges and the energy band gap values decrease with increasing growth pressure. For as-deposited and annealing films, increasing sputtering power resulted in the increase refractive index.     

Giant stretchability of thin gold films on rough elastomeric substrates

Stretching metallic conductors to large deformations while maintaining a low and constant electrical resistance is one of the main challenges in stretchable electronics technologies. Here, we report the conservation of conductivity for deformations of up to 100% in 80 and 500 nm thick gold films deposited on rough polydimethylsiloxane (PDMS) substrates. The roughness is produced by curing PDMS on sand-blasted or surface-etched masters. Under stretching, roughness creates a fine-scale inhomogeneous stress state within the film and a non-percolating crack pattern develops, preserving the conductivity. Compared to smooth surfaces, the strain corresponding to electrical failure is increased by a factor >50. By combining the roughness effect with prestretching of the substrate during deposition, a fine-scale random wrinkling morphology develops and the stretchability is enhanced even further. The stretchability is finally improved by increasing the thickness of the film. These synergistic effects can be explained based on fracture mechanics arguments. Finally, a high number of large deformation cycles can be accommodated without electrical failure.     

Nonlinear buckling finite element analysis of stiffened B–Al plates

Nonlinear buckling behavior of stiffened composite B–Al plates was analyzed by means of finite element analysis (FEA) method. In the method, the composite material was taken as B matrix into which Al fibers were embedded in different configurations. The laminated B–Al material in the form of rectangular plates was subjected to lateral compressive loading. It is observed that stiffeners have significant effect on the buckling behavior of plates under compressive loading and for various geometrical configurations. The stiffeners used in the modeling are one-sided and have rectangular cross-sections. It is found that there are physically important loading intervals and the critical buckling modes make transitions back and forth between stable and unstable states. Bifurcation buckling regions resulting from various configurations of fiber orientations and different plate aspect ratios are determined. The whole analysis is performed by using ANSYS finite element computations. Only the buckling patterns of stiffened plate configurations under simply supported boundary conditions are studied. Distributions of compressive stresses (σ_x) vs in-plane contractions (u) and compressive stresses (σ_x) vs out-of plane deflections (δ) are obtained. Nonlinear analysis of the C2 fiber configuration yields the safest critical buckling stress amongst C1, C2, C3 and C4 configurations. It is concluded that FEA method for the nonlinear buckling analysis generates accurate results.