Surface Review and Letters

The synthesis of hard composite coating on titanium alloy by laser cladding of Al/Fe/Ni+C/Si₃N₄ pre-placed powders has been investigated in detail. SEM result indicated that a composite coating with metallurgical joint to the substrate was formed. XRD result indicated that the composite coating mainly consisted of γ-(Fe, Ni), FeAl, Ti₃Al, TiC, TiNi, TiC_0.3N_0.7, Ti₂N, SiC, Ti₅Si₃ and TiNi. Compared with Ti-3Al-2V substrate, an improvement of the micro-hardness and the wear resistance was observed for this composite coating.

Many surface related properties, such as surface roughness, surface tension and reflection etc are heavily dependent on the surface morphology of materials. Patterned surfaces may have significant effects on these properties. In this paper, we compare wrinkles produced atop three different types of shape memory materials, namely, shape memory alloy, shape memory polymer and shape memory hybrid. We show the advantages and disadvantages of them in terms of the processing techniques and the resultant wrinkle patterns.

The chemical vapor deposition (CVD) process has been used to synthesize gallium nitride (GaN) nanostructures using Pt-coated n-type Si(100) as the substrate, and NH₃ gas and Ga₂O₃ powder as the reaction agents. The surface morphologies of the prepared GaN nanostructures obtained by field emission scanning electron microscopy (FE-SEM) show a large number of GaN nanowires and nanorods on the Si substrates. The synthesized nanostructures are hexagonal as determined from XRD analysis and show a turn-on field of 5 v/μm at 10 μA/cm².

CdS thin layers of 250 nm thick doped with zero, 0.1, 0.2 and 0.3 weight percents iron were deposited on glass substrates by modified flash evaporation technique in vacuum at the pressure of 5 × 10⁻⁶ mbar. The structure of the films was investigated by X-ray diffractometry. It was revealed that the films had hexagonal structure with (002) preferred orientation. Field emission scanning electron microscopy (FESEM) was employed to study the surface morphology of the prepared samples. It was found from FESEM images that the Fe-doped CdS film showed more surface uniformity. Optical absorption data of the films were used to measure the band gap of the films. It was found that the band gap of the samples decreased upon increasing the Iron concentration. Photoluminescence (PL) spectra of the CdS:Fe thin films were used to study most prominent excitation peaks within the energy range (1.6–2.6 eV). The variation in peak energy was observed upon increasing the Fe content in the films.

Ternary rare earth oxides are expected to be more promising high-k dielectric materials than conventional binary rare earth oxides due to higher band gap, higher permittivity and good interfacial stability. In the present study, the band alignment and atom thermal diffusion of LaYbO₃, a new ternary rare earth oxide, are studied by X-ray photoelectron spectrum (XPS) and angle-resolved XPS, respectively. The band gap value for LaYbO₃ crystalline film rises to 6.7 eV compared with 6.2 eV for amorphous film. Valence (ΔE_v) and conduction band (ΔE_c) offset are ΔE_v = 3.5 eV, ΔE_c = 1.6 eV for the amorphous film and ΔE_v = 3.3 eV, ΔE_c = 2.3 eV for the crystalline film. From elemental depth profile through high-k layer and silicon substrate, it is shown that La atom tends to diffuse into silicon substrate and piles up at oxide/silicon interface at high annealing temperature ~1000°C.

ZnO:Al (AZO) transparent conductive films used for solar cells were prepared by DC magnetron sputtering technology. The influence of substrate temperature on the electrical and optical properties of the films was studied. Further, the AZO films prepared were etched in diluted hydrochloric acid. The film surface morphology after etching for different time was researched.

A pulsed Nd:YAG laser was used to modify the surface properties of Mg alloy (AZ31B) for wear application with Al-Si as precursor material. Highly refined microstructure consisting of Mg₂Si, Mg, Al₁₂Mg₁₇ and Al₂O₃ was obtained. Phase constituent was correlated with thermodynamic calculation by employing Thermocalc™. The evolution of phase amount in the coatings was associated with the laser processing parameters. Due to the presence of highly refined microstructure and hard intermetallic reinforcements, substantial improvement of microhardness has been found in the coating region.

In situ synthesized TiC reinforced composite coating was fabricated by laser cladding of Al-Ni-Cr-C powders on titanium alloys, which can greatly improve the surface performance of the substrate. In this study, the Al-Ni-Cr-C laser-cladded composite coatings have been researched by means of X-ray diffraction, scanning electron microscope (SEM) and electron probe micro-analyzer (EPMA). There was a metallurgical combination between the Al-Ni-Cr-C laser-cladded coating and the Ti-6Al-4V substrate, and the micro-hardness of the Al-Ni-Cr-C laser-cladded coating was in the range of ~1200–1450 HV_0.2, which was ~3–4 times higher than that of Ti-6Al-4V substrate. Furthermore, the reinforcement of theAl-Ni-Cr-C laser-cladded coating were mainly contributed to the action of the TiC, Ti₃Al, Cr₇C₃, Al₈Cr₅ phases and the solution strengthening.

ZnO thin films were prepared onto the glass substrates by the sol–gel spin coating method for various Zn concentrations and at different spin rates. The influence of concentration of zinc and spin rate on the structural and optical properties of the ZnO thin films were investigated. It was observed that the zinc concentration and spin rate influence the grain size and morphology of the ZnO thin films. The optical band gap energy was found to increase with decrease of Zn concentration and increase in spin speed. The photoluminescence peaks show green radiation at ~485 nm. It was also observed that the enrichment of zinc and variation in spin speed influence the intensity of luminescence peaks.

Nanocrystals of maghemite (γ-Fe₂O₃) have been prepared at the interface of organic-aqueous layer by the reaction of ferric acetylacetonate in toluene with sodium hydroxide in aqueous solution. The nanocrystals of γ-Fe₂O₃ formed at the interface of the organic-aqueous layer have been confirmed by X-ray diffraction (XRD) pattern. The sample has been characterized morphologically by scanning electron microscopy (SEM), transmission electron microscopy (TEM) and atomic force microscopy (AFM) techniques. Magnetic hysteresis loop and zero-field cooling measurements exhibited superparamagnetism behavior for γ-Fe₂O₃ nanocrystals.

The isomeric effects on the adsorption geometry of di-halobenzene (C₆H₄X₂; X = F, Cl, Br, I) and pentacene (C₂₂H₁₄) on the idealized non-interacting substrate are analyzed both qualitatively and quantitatively by means of Monte Carlo simulations. The shape of pentacene isomers and the relative positions of halogen atoms in di-halobenzene may be important in determination of the favored adsorption geometry, contributing to the thermodynamic and chemical factors affecting the determination of the adsorbate geometry for these system. These simple methods may be applied to any planar molecules to quantify the contributions to the adsorption geometry that arises solely from the topological or geometrical isomeric differences in the molecules of interest.

The structural, elastic and electronic properties of chalcopyrite compound CuInSe₂ and CuGaSe₂ have been investigated using the full-potential linearized muffin-tin orbital method (FP-LMTO) within the frame of density functional theory (DFT). In this approach, the local density approximation is used for the exchange-correlation potential using Perdew–Wang parametrization. The equilibrium lattice parameters, bulk modulus, transition pressure, elastic constants and their related parameters such as Poisson's ratio, Young modulus, shear modulus and Debye temperature were calculated and compared with available experimental and theoretical data. They are in reasonable agreement. In this paper the electronic properties are treated with GGA + U approach, which brings out the important role played by the d-state of noble metal (Cu) and give the correct nature of the energy band gap. Our obtained results show that both compounds exhibit semi-conductor behaviour with direct band gap.