Surface Review and Letters

In situ titanium carbide reinforced iron-based composite coating was deposited on mild carbon steel using laser surface engineering (LSE) with ferrotitanium and graphite as precursor. The microstructure and phase constituents of the deposited coating were characterized. Formation mechanism of titanium carbide crystal in the composite coating was elucidated by correlating the morphology of titanium carbide and the thermal cycle experienced by the precursor during the laser treatment. It was demonstrated that titanium carbide was formed in situ as a result of the metallurgical reaction between ferrotitanium and graphite following a liquid-precipitation route. Different morphologies of titanium carbide crystal (dendrite and fishbone) correspond to the primary and eutectic titanium carbide respectively.

Nickel oxide (NiO) thin films were deposited on glass substrates by reactive direct current (DC) magnetron sputtering of a Ni target in an Ar/O₂ mixture. The effect of thickness (0.2 μm, 0.4 μm and 1 μm) on the structural and surface morphological properties of NiO thin films was investigated. These films were characterized by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR) and atomic force microscopy (AFM). The films were cubic NiO, with preferred orientation in the (111) direction at lower deposition time (10 mins). At higher deposition time (60 mins) the preferred orientation shifted to (200) plane. Electrochemical behavior of NiO thin films for different thickness samples were analyzed between the electrode potential ‑0.2 and 0.8 V vs scanning calomel electrode (SCE) in both anodic and cathodic directions and the current responses were measured.

(Bi_1-xCe_x)₂Ti₂O₇ thin films were grown on p-Si 〈100〉 substrates by chemical solution decomposition method. The relationship between the doping levels of cerium ions and the phase transition temperatures was studied. The doping of cerium ions could improve the phase stability of Bi₂Ti₂O₇, and the reason was comprehensively explained by the charge compensating theory. The doping of Ce ions enhances the crystallization temperature, which make the crystallization difficult, so the amount of cerium ions should be kept appropriate. The dielectric properties of (Bi_1-xCe_x)₂Ti₂O₇ thin films with different X values at different temperatures and different doping levels were listed, and the latent variation tendency was found. When the annealing temperature was 650–700°C and X = 0.12 or 0.16, the thin films showed better dielectric properties than the others.

A set of aluminium nitride (AlN) and oxidized AlN (AlNO) thin films were grown with the technique of direct current (dc) reactive magnetron sputtering. The main purpose of this investigation is to explore the influence of the oxygen on the structural properties of AlN and AlNO films. The crystalline properties and chemical identification of phases were studied by X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS), respectively. Electrical properties were analyzed from I-V measurements. It was found that films crystallized under the AlN würzite structure and presented a polycrystalline preferential growth along [0001] direction, perpendicular to substrate. Small amounts of secondary aluminium oxide phases were detected too. The oxide phases can induce defects, which can alter crystallinity of films.

The silicone rubber (SR) nanocomposites have been successfully prepared via the in situ hydrosilylation reaction in the presence of pristine ZnO and vinyl silane modified ZnO (SiVi@ZnO) nanoparticles. The structure of the pristine ZnO and SiVi@ZnO nanoparticles were analyzed by the Fourier transform infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS) and X-ray diffraction (XRD), respectively. The morphology, thermal stabilities, mechanical properties and thermal conductivity of the nanocomposites were also investigated. The results showed that the SiVi@ZnO nanoparticles exhibit a better dispersion in the silicone rubber than the pristine ZnO nanoparticles. The corresponding silicone rubber/SiVi@ZnO (SR/SiVi@ZnO) nanocomposites showed higher mechanical properties and thermal conductivity due to the better dispersion in silicone rubber matrix.

This study investigated the relationship and parameters interactions between five independent variables in laser percussion drilling of micro-hole. Experiments were conducted on single crystal silicon wafer with material thickness of 725 μm using femtosecond (fs) laser with wavelength of 775 nm and pulse duration of 200 fs. Laser power, focus position, number of pulses, workpiece temperature and assist liquid were selected as independent process variables. Taguchi L18 orthogonal array was applied to design the experiments. The drilling process was evaluated in terms of entrance hole diameter and exit hole diameter. The analysis of the variance (ANOVA) was used to determine the significant parameters that are affecting the entrance hole diameter and exit hole diameter. The result shows that laser power and focus position has highly significant effect on entrance hole diameter. The number of pulses, focus position and assist liquid however has highly significant effect on exit hole diameter.

A thin adhesion layer is required to glue Pt bottom electrodes of ferroelectric Pb(Zr,Ti)O₃ thin films to a SiO₂/Si wafer. Here we report the effect of adhesion layers, Ti and TiO₂, on the crystalline structure and surface properties of Pt electrode. The results show that the hillock formation is observed for the case of Ti glue layer, while the surface of Pt layer is flat and uniform with TiO₂ layer used instead. The crystallization in PZT thin films on Pt/TiO₂/SiO₂/Si substrate is investigated during post-deposition annealing. The perovskite phase is completely formed in the film annealed at 650°C for one hour.

Plasma polymerized thin films of aluminium/thin film/aluminium configuration were deposited at room temperature by a parallel plate capacitively coupled glow discharge reactor using N,N,3,5 tetramethylaniline (TMA) as a precursor. The infrared spectroscopic analyses revealed that plasma polymerized TMA (PPTMA) films contained an aromatic ring structure with NC and CH side groups, presence of C=O was also evident. The differential thermal analysis and thermogravimetric analysis of PPTMA thin film was thermally stable up to about 505 K. The scanning electron microscopy of PPTMA thin film showed a smooth, flawless and pinhole free surface. The capacitance and ac electrical conductance of PPTMA thin films were measured as functions of frequency (100 < f < 10⁵ Hz) and temperature (300 < T < 450 K). The electrical conductivity is more dependent on temperature in the low frequency region than that in the high frequency region. In PPTMA thin films the conduction may be dominated by hopping of carriers between the localized states at low temperatures and thermally excited at the high temperatures. The activation energies are estimated to be about 0.05 eV in the low temperature and 0.23 eV in the high temperature. Dielectric constant decreases with the increase of frequency and that decreases with the increase of temperature but dielectric loss increases with increasing frequency with a minimum in the low frequency region. The temperature-dependence of the Cole-Cole diagram shows the existence of distribution of dielectric relaxation times in the PPTMA thin films.

Titanium films of 120 nm thickness were magnetron sputtered on glass substrates at room temperature, and subsequently they were annealed under flowing oxygen atmosphere at different temperatures and time. Atomic force microscopy (AFM) was used to study topographic characteristics of the films, including nucleation, crystalline feature, grain size, clustering and roughening. The initial nucleation of titanium oxides has almost completed during annealing at 300°C for 120 min or 400°C for 30 min. Especially, we have already observed the preferential nucleation and grain growth of titanium oxides on locations that protrude from the surface, as opposed to deep grooves. It is confirmed by AFM characterization that both of annealing temperature and time can hasten the nucleation and grain growth of titanium oxides, but annealing time is less influential than its temperature. The typical crystal transfer from amorphous-like to crystalline state occurs at 300–400°C for 120 min during annealing, but the too low temperature of 200°C does not contribute to the crystal transfer. In addition, higher annealing temperature (600°C) leads to the transformation of crystal texture from globular-like to flaky type. Generally, higher annealing temperature or time can lead to higher film surface roughness through the grooving effect, but the roughness decreases with the increase of annealing time (at 400°C for 90–120 min).

Five compositions of the system As₂₅Se_75-xTl_x (x = 12, 16, 20, 24 and 28%) have been prepared using melt quench technique. Thin films of the same thickness (200 nm) were deposited by electron beam evaporation technique. Optical and other parameters of the films have been studied. The optical band gap E_op found to decrease by increasing the coordination number r and average number of bonds per atom N_av and by decreasing the heat of atomization H_s. Other parameters as an oscillator energy E_o, dispersion energy E_d and plasma frequency ω_p found to be affected by changing thallium content.

Ultra-thin Pb films with magic thicknesses of 2 monolayer (ML), 4 ML and 6 ML were prepared of atomically flat on the substrate of Si(111)-α-√3 × √3 (or SIC phase) at 145 K. Their surface morphologies and stability were studied by low temperature scanning tunneling microscopy and temperature-dependent angle resolved photoemission spectroscopy. We found that the well ordered SIC interface can lower the diffusion barrier and enhance the interface charge transfer, leading to different critical thickness compared to Pb/Si(111)-7 × 7 grown under same conditions. Enhanced thermal expansion coefficients were also observed in ultra-thin Pb films at low temperature.