Surface Review and Letters

In this study, Al–Ti–Co was used to improve the surface performance of pure Ti. Laser cladding is an important surface modification technique, which can be used to improve the surface performance of pure Ti. Laser cladding of the Al–Ti–Co + TiB₂ pre-placed powders on pure Ti can form ceramics reinforced the composite coating, which improved the wear resistance of the substrate. Characteristics of the composite coating were investigated using X-ray diffraction (XRD), scanning electron microscopy (SEM), microhardness and wear tests. And the laser-cladded coating can also have major dilution from the substrate. Due to the action of the fine grain strengthening and the phase constituent, the wear resistance and microhardness of pure Ti surface were greatly improved.

Tantalum (Ta) films deposited on glass substrates have been prepared by a direct current magnetron sputtering method, and buckling patterns induced by residual compressive stress are investigated in detail. When the film thickness increases, the buckling morphologies evolve from straight-sided buckle network to wavy or wormlike wrinkles gradually, and finally change into telephone cord buckles. The geometrical parameters of the buckling patterns are found to increase linearly with the film thickness. Based on the geometrical parameters of the buckling patterns, the mechanical properties of the Ta films are also discussed in the frame of continuum elastic theory.

In this article, titanium oxide nanotube arrays (TiO₂–NTAs) were fabricated by anodic oxidation in an ethylene glycol (EG) electrolyte solution containing 0.25 wt.% NH₄F. By varying anodized time and annealed temperature, the obtained nanotube arrays behaved different photocatalytic (PC) activities and photocurrent properties. These samples were characterized by scanning electronic microscope (SEM), X-ray powder diffraction (XRD). It was indicated in SEM images that TiO₂ nanotube manifests highly ordered structure which, however, has been completely destroyed when the temperature comes to 800°C. XRD manifested that TiO₂ nanotubes with various kinds of length all possessed anatase crystallite when annealed at 500°C; meanwhile, with certain length, TiO₂–NTAs annealed at series calcination temperature range of 300–600°C also presented anatase crystallite, which is gradually enhanced with the increment of temperature. At 700°C, mixed structure was observed which was made up of proportions of overwhelming anatase and toothful rutile. Methyl blue (MB) degradation and photocurrent measurement testified that TiO₂–NTAs under 4 h oxidation and 3 h of 600°C calcination manifested the highest activity and photocurrent density.

Nanosized and highly reactive Mg₄Ta₂O₉ were successfully synthesized by aqueous sol–gel method compared with conventional solid-state method. Ta-Mg-citric acid solution was first formed and then evaporated resulting in a dry gel for calcination in the temperature ranging from 600°C to 800°C for crystallization in oxygen atmosphere. The crystallization process from the gel to crystalline Mg₄Ta₂O₉ was identified by thermal analysis and phase evolution of powders was studied using X-ray diffraction (XRD) technique during calcinations. Particle size and morphology were examined by transmission electron microscopy (TEM) and high resolution scanning electron microscopy (HR-SEM). The results revealed that sol–gel process showed great advantages over conventional solid-state method and Mg₄Ta₂O₉ nanopowders with the size of 20–30 nm were obtained at 800°C.

Influence of surfactants on the corrosion properties of chromium-free electroless nickel deposit were investigated on AZ91D magnesium alloy. The corrosion tests were carried out by immersion test (1 M HCl) and electrochemical polarization test (3.5 wt% NaCl). The surfactants in the electroless nickel bath increases the corrosion resistance properties of the deposit on the magnesium alloy. In addition, smoothness and amorphous plus nano-crystalline phase were increased and accounted for the significant corrosion resistance. As a consequence, the corrosion potential moved towards the positive direction and the corrosion current density decreased. The immersion tests also provided the same trend as that of electrochemical polarization test. On the whole, the study concluded that corrosion resistance was enhanced by including a surfactant in the electroless deposits on magnesium alloy.

Near-stoichiometric and stoichiometric Cu(InAl)Se₂ (CIAS) thin films have been prepared by successive ionic layer adsorption and reaction (SILAR) onto well-cleaned substrates. energy dispersive X-ray analysis (EDAX) spectra of the prepared thin films enabled to determine the film composition, stoichiometry nature, type of conductivity, lattice constants, volume of the unit cell and density of CIAS thin films. The estimated compositional, structural and electrical parameters are presented and discussed in this paper in detail.

In agreement with experimental results relative to acetylene and deuterated-acetylene molecules on copper, a quantitative study relative to electronic density of states and tunneling current in terms of voltage is carried out within the context of inelastic electron tunneling spectroscopy. Our starting point is regarding the corresponding differential tunneling conductance as a function of the tunneling voltage. In particular, as a relevant figure of merit, the first derivative of the above conductance is determined. A numerical computation relative to this figure of merit is also carried out.

Reactive plasma sprayed coatings were prepared on carbon steel substrates with Ti and B₄C as starting materials. Two kinds of gases (Ar and N₂) were used as feeding gases for powders, respectively. 10 wt.% Cr was added in the powders as binder to increase the bond strength of the coating. The phases, microstructure, micro-hardness and corrosion polarization behavior in 3.5 wt.% NaCl solution of the two coatings were studied. The results show that TiN-TiB₂ coatings were prepared under both conditions. The two coatings have typically laminated structure. However, the coating prepared with Ar as feeding gas has higher porosity and some unmelted Cr particles. It also contains certain content of titanium oxides. The microhardness of coating prepared with Ar as feeding gas is lower due to its higher porosity, unmelted Cr particles and some amounts of TiO₂. The corrosion resistance of TiN-TiB₂ coating prepared with Ar as feeding gas in 3.5 wt.% NaCl solution is worse than that of the coating prepared with N₂ as feeding gas. Yet the corrosion resistance of reactive plasma sprayed TiN-TiB₂ coating is improved greatly compared with that of carbon steel. The thermodynamic analysis of reactive plasma spraying process is also discussed.

A quantitatively kinetic model has been established to address the self-assembly of the ring shaped nanostructures upon the droplet epitaxy via kinetic Monte Carlo simulations. The theoretical predictions about the temperature and As flux dependences of the self-assembly of the ring shaped nanostructures were in well agreement with recent experiments. It was found that the morphological evolution of the ring shaped nanostructures was attributed to the cooperation of the enhanced diffusion barriers of free Ga atoms in the inner ring region and the effects of the surface reconstruction around the Ga droplets during the arsenization step.

Magnetoelectric (ME) coupling in layered structures of magnetostrictive and piezoelectric phases are mediated by mechanical deformation and depends strongly on the interface conditions. Ni-lead zirconium titanate-Ni trilayers with neither electrodes nor bonding layers have been derived by electroless deposition. The structure of the electroless deposited Ni layer was characterized by X-ray diffraction. The cross-section of the Ni/PZT layers was investigated using scanning electron microscopy. The value of ME voltage coefficient (α_E,31) increases as the interface roughness increases. The maximum of α_E,31 for the Ni/PZT/Ni trilayers polarized after electroless deposition is higher than that for the Ni/PZT/Ni trilayers polarized before electroless deposition. It is essential to optimize the interface and the polarization to obtain higher ME voltage coefficient.

In this paper, a new calculated method of image fractal dimension (IFD) of true color image has been presented in order to solve the problem that laser scanning profilimeter, applied to measuring fractal characteristic of rough surface, has too small scanning field to obtain three-dimensional coordinates of larger area surface. The method can also characterize indirectly surface profile by quantifying roughness of true color surface built in terms of connecting endpoint of the vector with three components of red, green and blue. The correctness and feasibility of the IFD method have been verified by scanning test on rough surface using larger-scale laser profilimeter. Comparison between conventional dimension theory presented in previous study and IFD proposed in the paper has shown that IFD method has the advantage of simplification, convenience and large scanning capacity, and is progressing in the field of surface configuration investigation. Furthermore, fractal characteristic of binary image, grey-scale image as well as true color image is researched to probe their physical nature. Comparison among IFD of three kinds of image implies that, IFD of true color image is largest, IFD of grey-scale image is second largest, and IFD of binary image varying within the range of 1–2 is the smallest. From the phenomena, it is indicated that: (i) IFD of binary image is dimension of curved line; (ii) for IFD of grey-scale image, only effect of luminance is considered; (iii) for IFD of true color image, contribution of hue, saturation and luminance is sufficiently considered, and therefore it is just "complete" IFD.

The 0.65Ba(Mg_1/3,Nb_2/3)O₃-0.35BaTiO₃ thin films was deposited on glass/aluminum substrates by using spray pyrolysis method. The effect of annealing temperature on perovskite phase and crystalline structure analysis of the BMN-BT films was performed on an X-ray diffraction (XRD). Surface morphology, roughness and particle size of the BMN-BT thin films was characterized with atomic force microscopy (AFM) and scanning electronic microscopy (SEM). Polarization hysteresis measurements was performed at different temperatures. From the P–E hysteresis loops one can observe the best temperature that led to improved properties of dielectric constant, polarization and piezoelectric coefficients were 600°C.

In this work, the p-type doping of the S_A type stepped Ge(100) surface by a diborane (B₂H₆) gas flow has been simulated by the possible dissociation and adsorption models. The most probable dissociation model of B₂H₆ and adsorption models of the fragments of B₂H₆ on the stepped Ge(100) surface have been determined by the local minimum total energy and/or binding energy calculations based on the Density functional (B3LYP/6-3g) and Hartree–Fock (HF/STO-3g) theories, respectively. The present calculations have shown that, the step region (for both up and down terraces) of the stepped Ge(100) surface has the most attractive sites for BH₃ molecules determined to be the first dissociation fragments of B₂H₆ by an external energy of ~ 1.3 eV. It has been found that, at the first step of the adsorption, BH₃ can dissociate to BH₂ and BH fragments on the stepped Ge(100) surface. While BH₃ and BH₂ products prefer to be attached to a single surface Ge atom, BH is bridged between two adjacent surface Ge atoms. According to the present optimization calculations, the p-type doping process of the stepped Ge(100) surface has started with the adsorption of BH₃ on the electron deficient site (buckled down) of the Ge dimer bond close to the step edge and ended with the substitutional occupation of the Ge site in the layers of the surface by B atom. The beginning of the p-type doping of the stepped Ge(100) surface has been illustrated by the electronic states of B appeared in the optical energy gap of Ge very close to the edge of the HOMO.