Surface Review and Letters

In this work, TiO₂ nanotube thin films were prepared by using the anodization technique. Different electrolytes solutions were used to specify the optimum condition. Annealing in air at different temperatures of (400, 500, and 600)${}^{\circ }$C at constant time of 1h was achieved for all films. The structure (XRD, SEM, EDX, and AFM), and optical (UV–Visible spectroscopy, PL spectroscopy, and Spectral Response) properties of nanotube TiO₂ films were investigated and analyzed for different electrolyte solutions. XRD analysis of all deposited films has confirmed the formation of polycrystalline-tetragonal phase (anatase, and rutile) with increase in crystalline size and, annealing temperatures. SEM measurements of TiO₂ films show nanotube shapes with outer diameter of (80–130) nm. EDX analysis confirmed the stoichiometry ratio between Ti and O to be 1:2 to produce TiO₂ film. PL measurement results show two peaks: one located at UV-region pointing to energy band gap (Eg) for TiO₂ nano films; the second one is located at visible region pointing to impurities on films. Spectral response measurements show photocurrent peaks centered at UV-region (355nm). Then, TiO₂ films were deposited with different electrolyte solution for photoelectrocatalytic (PEC) application. The higher response to UV-light was received by using TiO₂ film grown by anodization technique with (HNO${}_3+$HF) electrolyte solution.

Aluminum and its alloys are widely used in our daily life because of their desirable physical properties. Improving the quality of Al-alloys surface layers is required for industrial applications. Nd: YAG pulsed Nanosecond Laser was used in irradiating aluminum 1100 alloy to study the surface morphology and hardness properties. Scanning Electron Microscope (SEM) images reveal the presence of small holes with different diameters that are produced by the irradiation of Aluminum alloy surfaces with different laser power densities. The diameters of the produced holes are decreased gradually by increasing the laser power density. Minimum diameter of about 1.84$\mu$m is obtained after irradiating the aluminum surface with 1256.04MW/cm² at which semi-periodic holes-like pattern were produced. An increase in the Vickers microhardness values was obtained until the maximum value of 28 HV was reached at laser power density of 750.16MW/cm². After reaching the maximum value, a fast decrease in the microhardness values was observed. Such changes in microhardness values maybe attributed to the lattice disorder and the change in the defect density produced by laser irradiation.

In the present work, Zinc Sulphide (ZnS) thin films deposited by resistive heating technique on BK-7 glass substrate. Optical and structural characterizations of ZnS films have been carried out along with the post-deposition annealing at different temperatures. The thickness of the film is monitored by quartz crystal monitor and found to be 500nm. Fourier transform infrared (FTIR) spectroscopy provides the qualitative analysis of ZnS film before and after annealing at different temperatures. The optical investigation shows that the as-deposited and annealed ZnS film display the high optical transmittance of (64–68%) in the visible/near infrared region. The optical energy gaps of present as-deposited and annealed ZnS film vary in the range of 3.32–3.18eV with the change in annealing temperature.

Due to the study of marine corrosion of mild steel, in order to simulate the corrosion conditions of enamel coatings in seawater, enamel coatings applied on mild steel were immersed in 3.5wt.% NaCl liquor and the related corrosion features and behavior of enamel were analyzed by X-ray diffraction (XRD), scanning electron microscopy (SEM) and evaluated by electro-chemical method such as potentiodynamic polarization testing. Under the appropriate heat treatment system, the enamel coatings sintered on the same kind of mild steel at different temperatures were studied: all enamel samples were within the temperature range from 710${}^{\circ }$C to 830${}^{\circ }$C, the heat treating process at the microstructural level was evaluated and correlated with corrosion resistance properties. All the enamel coatings were characterized and it was observed that the enamel coatings that showed excellent corrosion resistance when sintered at a temperature of 810${}^{\circ }$C can offer a better physical barrier than other temperatures because of their better bonding force and dense microstructure with less pores.

The Schottky barrier type Ni/$n$-GaAs contacts fabricated by us were thermally annealed at 600${}^{\circ }$C and 700${}^{\circ }$C for 1min. The apparent barrier height ${\mathrm{\Phi }}_{\mathrm{\text{ap}}}$ and ideality factor of the diodes were calculated from the forward bias current–voltage characteristic in 60–320K range. The ${\mathrm{\Phi }}_{\mathrm{\text{ap}}}$ values for the nonannealed and 600${}^{\circ }$C and 700${}^{\circ }$C annealed diodes were obtained as 0.80, 0.81 and 0.67eV at 300K, respectively. Thus, it has been concluded that the reduced barrier due to the thermal annealing at 700${}^{\circ }$C promises some device applications. The current preferentially flows through the lowest barrier height (BH) with the temperature due to the BH inhomogeneities. Therefore, it was seen that the ${\mathrm{\Phi }}_{\mathrm{\text{ap}}}$ versus ${(2kT)}^{-1}$ plots for the nonannealed and annealed diodes showed the linear behavior according to Gaussian distributions.

The development of new corrosion-resistant coatings is often challenging, but strongly driven by the potential benefits such coatings hold. A nanostructured Ta₂N coating was deposited on a Ti–6Al–4V substrate in an Ar–N atmosphere using a double cathode glow discharge plasma method with the aim being to improve its corrosion resistance in oral environments. The microstructure of the coating was investigated by a range of methods including XRD, SEM-EDS and TEM. The as-deposited coating exhibited densely packed fibrous structure and the individual fibers were composed of equiaxed grains with an average grain size $\sim 13$nm, arranged along the longitudinal axis of the individual fibers. The electrochemical behavior of the Ta₂N nanocrystalline coating was characterized in artificial saliva containing different NaF concentrations by a range of electrochemical techniques, including potentiodynamic measurement, EIS, capacitance and PZFC measurements. It was shown that the coating possessed superior corrosion resistance compared to uncoated Ti–6Al–4V, because its passive film exhibited higher stability against the fluoride ion attack.

The use of NPs in the health care field is increasing. Before their biological application, investigating the toxicities of both n-type ZnO nanoparticles (NPs) and nitrogen-doped (“p-type”) NPs is important. Using L929 cells, the cell viability, oxidative stress, apoptosis induction, inflammatory responses, and cellular uptake were assayed 24h after the addition of n-type ZnO NPs and nitrogen-doped NPs (which act as p-type) (25$\mu$g/mL). The ZnO NPs were fabricated using a gas evaporation method. Increased H₂O₂ generation and decreased levels of glutathione were more evident in with n-type than in those treated with nitrogen-doped (“p-type”) ZnO NPs. Caspase-3/-7 activity was higher in cells treated with n-type ZnO NPs than in those treated with nitrogen-doped (“p-type”) NPs. Elevated levels of TNF-$\alpha$ and IL-1$\beta$ were observed in cell culture supernatants: IL-1$\beta$ levels were higher in n-type ZnO NPs than nitrogen-doped (“p-type”) NPs. The cellular Zn uptake of n-type ZnO NPs was higher than nitrogen-doped (“p-type”) NPs. These findings show that n-type ZnO NPs have higher cytotoxicity than nitrogen-doped (“p-type”) ZnO NPs. This may be due to a reductive effect of n-type ZnO NPs that induces higher free radical production, reactive oxygen species (ROS) generation, and cellular uptake of this type of ZnO NPs.

Brucite/TiO₂ composite particle was prepared with Titanium dioxide (TiO₂), coating on brucite particles’ surfaces by mechano-chemical method. X-ray diffraction (XRD), scanning electron microscope (SEM) and infrared spectra were used to investigate the microstructures, morphologies of the composite and the reaction mechanism. The results show that the ground extent of brucite as well as the mixed particles of brucite and TiO₂ should keep at a suitable state. The hiding power and whiteness of the composite particles are 17.24g/m² and 96.88%, respectively, presenting its similarity to TiO₂ in pigment properties. TiO₂ coats evenly on the surfaces of brucite through surface dehydroxylation reaction during mechano-chemical method.

Plasma nitriding of AISI 5140 low alloy steel was carried at pressures ranging from 100Pa–500Pa for 4h with hollow cathode discharge assistance. The treated samples were characterized by optical microscope, microhardness tester, X-ray diffraction and electrochemical workstation. The results show that the compound layer is about 5$\mu$m in thickness and the depth of surface hardening layer is about 240$\mu$m for the sample nitrided at 100Pa for 4h. The hardness value of nitrided surface is about 830HV${}_{0.1}$, which is about 2.9 times higher than that (290HV${}_{0.1}$) of the substrate. There is no obvious difference in the thickness of compound and diffusion layers, surface microhardness and phase composition of nitrided layers in comparison with that of samples nitrided at pressure 300 and 500Pa used by conventional plasma nitriding. But plasma nitriding with low pressure can effectively reduce the assumption of nitriding gas and amount of exhausted emission.

The composite of a nanocrystalline SnO₂ thick film deposited on an Al-doped ZnO ceramic substrate was firstly proposed. This study also provided a simple, fast and cost effective method to prepare SnO₂ thick film and Al-doped ZnO ceramic as well as the final composite. The crystal structure, morphology, composition, pore size distribution and gas sensitivity of the composite were investigated by means of X-ray diffraction, scanning electron microscopy, transmission electron microscopy, energy dispersive spectroscopy, Barrett–Joyner–Halenda analysis and gas sensitive measurement system. Results indicated that the composite was fully porous consisted of SnO₂, ZnO and ZnAl₂O₄ crystal phases. The macrosized pores generated in the composite could enhance the gas infiltration into the sensing layers effectively. In this way, combining a high gas-transporting-capability and a nanocrystalline SnO₂ thick film, the composite showed very impressive performance. The gas sensitivity of the composite was high enough for ethanol vapor with different concentrations, which was comparable to other kinds of reported SnO₂ gas sensors, while showing two straight lines with a turning point at 1000ppm. Finally, the gas sensitive mechanism was proposed based on the microstructure and composition of the composite.

Liquid meniscuses were prepared by spraying silicone oil drops with different sizes onto clean glass slides. Metal (iron) films with varied thicknesses were then deposited on the liquid meniscuses by direct current magnetron sputtering. The fracture and wrinkle behaviors of the films resulting from residual stresses are investigated in detail. It is found that cracks nucleate and propagate in the film during deposition owing to the thermal expansion of the liquid substrate. Subsequent cooling of the system creates a high compressive stress, resulting in the formation of various wrinkles in the film. The initiation and shape of the cracks are closely related to the film thickness and oil drop size. The wrinkle morphologies are dependent on the stress anisotropy induced by the liquid meniscus and crack edge.

In this study, an infiltrated Al/SiC composite was fabricated by the pressureless vibration method. Porous silicon carbide preforms with the pore size of 10, 20 and 30ppi were used as the reinforcement. The molten aluminum–magnesium alloy was infiltrated into the preforms at 650${}^{\circ }$C and 850${}^{\circ }$C. The investigation showed complete infiltration at 650${}^{\circ }$C, but infiltration at 850${}^{\circ }$C broke the oxidation layer and improved the composite quality. Scaning electron microscopy (SEM) micrographs showed the creation of a good interface and connection between the matrix and the reinforcement. EDS analysis also showed spinel phase (MgAl₂O${}_4)$ had been formed in the interface. This phase was formed due to a reaction against Al₂O₃ in the reinforcements and MgO. The possibility of the formation of MgAl₂O₄ phase and the wettability between the metal matrix and ceramic reinforcement was enhanced with increasing the temperature.

We found that quantization of the scanning tunneling microscope (STM) current becomes apparent as the size of a quantum corral (QC) decreases and the corral thickness increases. It is shown that STM current images provide the position dependence of the conduction channels and local density of states (LDOS) images provide the spatial distribution of differential conductance channels. We clarified for the first time that there exist fractal structures in the QC size dependence of the $I$–$V$ characteristic and in that of the LDOS. LDOS images also exhibit a fractal structure as a function of bias voltage. These results demonstrate fractal structures in energy space and real space. For an extremely large QC, we found that the $I$–$V$ curve becomes Ohmic and the LDOS converges to a constant corresponding to the bulk two-dimensional density of states.

The aim of this work is to study the solution concentration effect on the SnO₂ thin film properties, which were deposited on glass substrates by spin coating technique and annealed for one hour at 500${}^{\circ }$C. X-ray diffraction (XRD) spectra show that the films deposited at various solution concentrations (0.5mol/L, 0.7mol/L and 1mol/L) are polycrystalline with a tetragonal rutile type. Grains have two preferred orientations along the directions (110) and (101) corresponding to 2$\theta$ equal to 26.74${}^{\circ }$ and 34.11${}^{\circ }$, respectively. We have also noted that the grain size changes between 109nm and 178nm. However, the film coated at 10 deposition cycles and 0.7mol/L solution concentration has a minimum arithmetic average roughness of 0.376 nm. The optical transmittance of the films in the visible spectrum was in the range of 77–84% and the optical band gap gradually decreases with the decrease of the solution concentration from 4.11eV to 3.56eV.

Oxygen-deficient tin oxide thin films were prepared by radiofrequency magnetron sputtering with a sintered non-stoichiometric tin oxide ceramic target under an atmosphere of various ratios of O₂/Ar from pure Ar to 1:1. X-ray diffraction analysis showed that the thin films were polycrystalline with relatively strong (1 1 0), (1 0 1) and (2 1 1) diffraction peaks. Scanning electron microscopy observation revealed that the thin films prepared at different O₂/Ar ratios were all of relatively dense and homogeneous structure. With increasing O₂/Ar ratio, the grain size of the films decreased slightly, and their chemical composition became close to the stoichiometric SnO₂; but the deposition rate as well as film thickness increased first and then decreased sharply. It was revealed that the main defect in obtained films was oxygen vacancy (V_O), and as the O₂/Ar ratio increased, the concentration of V_O fell down monotonously, which would lead to an increased electrical resistivity.