Surface Review and Letters

A two-dimensional computational fluid dynamics (CFD) model was developed to study the load-bearing capacity of asymmetric texture under the state of fluid lubrication. The effects of asymmetric parameter H and the Reynolds number Re on hydrodynamic load-bearing capacity of the oil film were discussed. It was found that a decrease in asymmetric parameter H may significantly improve the load-bearing capacity, but an increase in Reynolds number Re may reduce this effect. For example, with a Re at 20, the load-bearing capacity increases by 73.44% with the H varying from 4 to 0.2. However, with a Re at 160, it has only an increase of 4.68% at the same conditions. In addition, the numerical results also showed that the load-bearing capacity will increase with the increase of Re in certain texture.

Bismuth Telluride (Bi₂Te₃) films were deposited by a simple and cost-effective galvanostatic electrodeposition process from a solution containing bismuth tri-nitrate penta-hydrate and tellurium dioxide of different concentration ratios in 1 M nitric acid onto gold sputtered silicon substrate at various current densities. The effect of distinct current densities, electrolyte concentrations and electrodes distances on the microstructure and the thermoelectric properties of Bi₂Te₃ films were investigated. X-Ray diffraction (XRD) and field emission scanning electron microscope (FESEM) analysis ensured a high density, homogenous and near stoichiometric film. The surface morphology, crystalline structure and grain size were correlated with the applied current density. A prominent orientation (110) was observed for all the films and the grain size was acquired from 21 to 45 nm. The Seebeck measurement affirmed n-type semiconductor behavior of the deposited films. Enhancement in carrier mobility without significant change of the carrier concentration and Seebeck coefficient was achieved by tuning the electrodes distance. The thermoelectric film has a maximum measured Seebeck coefficient of –61.215 μV/K and a very high electrical conductivity of 2.13 × 10³ Ω^-1 ⋅ cm^n-1. The maximum calculated power factor was 8.2 μW⋅K^-2 ⋅ cm^-1.

In this paper, we investigated indium-tin-oxide (ITO) thin films on glass substrates deposited by RF magnetron sputtering using ceramic target to find the optimal condition for fabricating optoelectronic devices. The structural, electrical and optical properties of the ITO films prepared at various substrate temperatures were investigated. The results indicate the grain size increases with substrate temperature increases. As the substrate temperature grew up, the resistivity of ITO films greatly decreased. The ITO film possesses high quality in terms of electrode functions, when substrate temperature is 480°C. The resistivity is as low as 9.42 × 10^-5 Ω•cm, while the carrier concentration and mobility are as high as 3.461 × 10²¹ atom∕cm³ and 19.1 cm²∕V⋅s, respectively. The average transmittance of the film is about 95% in the visible region. The novel ITO/np-Silicon frame, which prepared by RF magnetron sputtering at 480°C substrate temperature, can be used not only for low-cost solar cell, but also for high quantum efficiency of UV and visible lights enhanced photodetector for various applications.

In this work, we studied the effect of rapid thermal oxidation process on the structural and surface morphology of silicon nanocrystal-based heterostructures. PLD technique was employed in combination with rapid thermal oxidation process to form multilayers heterostructures. Results show the dependence of the surface roughness and structure on the oxidation temperature. Best surface morphology was achieved at 723 K oxidation temperature, at which, the X-ray diffraction result ensured the formation of the Cu₂O phase at (111) and (002) diffraction plain with uniform porous surface.

In this paper, stearic acid/Zn²⁺ monolayer were formed at air–water interface and then multilayers were deposited onto a glass slide by Langmuir–Blodgett method. After annealing at 300°C for 0.25 h and 550°C for 2 h, ZnO thin films were fabricated. The optimized parameters for monolayer formation and multilayers deposition were determined by the surface pressure-surface area (Π-A) isotherm and transfer ratio (t.r.), respectively. The results of X-ray diffraction showed that multilayers changed into ZnO thin films with hexagonal structure and of high crystallization after annealing at high temperature. The observation of SEM images indicated that ZnO thin films had a uniform and flat surface with compact arrangement.

Effect of the tempering on the microstructures and tribological properties of the laser alloying coatings is investigated. Laser alloying of the T-Co50/TiC mixed powders on a 45 steel substrate can form a hard composite coating, which increased the micro-hardness and wear resistance of the substrate greatly. Such laser alloying coating was investigated by means of a scanning electron microscope (SEM) and a transmission electron microscope (TEM). Experimental results indicate that the tempering is able to remove the accumulation of the residual stress in a certain extent, improving the plastic and toughness properties of such coating; moreover, tempering also improves greatly the formation mechanism, making the coating have enough ability of the intensity transfer, which is beneficial in preventing the crack propagation of the interface in such coating, leading to an improvement of the wear resistance.

Direct current electrodeposition of Co–P alloy coatings were carried out using gluconate bath and they were characterized by employing techniques like XRD, FESEM, DSC and XPS. Broad XRD lines demonstrate the amorphous nature of Co–P coatings. Spherical and rough nodules are observed on the surface of coatings as seen from FESEM images. Three exothermic peaks around 290, 342 and 390°C in DSC profiles of Co–P coatings could be attributed to the crystallization and formation of Co₂P phase in the coatings. As-deposited coatings consist of Co metal and oxidized Co species as revealed by XPS studies. Bulk alloy P(P^δ-) as well as oxidized P(P⁵⁺) are present on the surface of coatings. Concentrations of Co metal and P^δ- increase with successive sputtering of the coating. Observed microhardness value is 1005 HK when Co–P coating obtained from 10 g L^-1NaH₂PO₂ is heated at 400°C that is comparable with hard chromium coatings.

The semiconductor SnO₂ is an important material to be used in different fields as the monitoring of air pollution, toxic gas and other applications as solar cells, optoelectronic devices, etc. The simulation method such as the generalized gradient approximation (GGA) of SnO₂ is very interesting in determining its lattice parameters with accuracy in comparison with the experimental data. The GGA simulation method and the one established by Becke and Johnson mBJ are useful for predicting the electronic properties related to the charge distribution of SnO₂ compound. The calculated density of states and the charge density are well confirmed owing to the experimental results related to the electron energy loss spectroscopy (EELS) technique, very sensitive to the characterization of materials.

Porous titania coatings with Ca and P elements were synthesized by plasma electrolytic oxidation (PEO). The treatment was carried out in an electrolyte containing calcium acetate monohydrate and disodium phosphate dodecahydrate (Ca/P = 5), and 4–20 μm micropores were prepared on the coatings by applied pulse frequencies of 200–1000 Hz. The surface structure, chemical composition of the TiO₂ coatings, and time-dependent variation of electric currents were studied. The result revealed that the coating micropores, which could be controlled in size, increased with higher frequency, and the coatings mainly consisted of anatase and rutile phases with varying fractions. Based on our experiment, the formation mechanism of micropores and phases of the PEO coatings was further discussed in details.

Thin film of tin oxide (SnO₂) was prepared on p-type polished silicon wafer by ultrasonic spray pyrolysis technique using SnCl₄ precursor solution to fabricate nanospherical n-SnO₂/p-Si heterojunction photoelectric device. Deposition of film was achieved at 400°C substrate temperature. The self-made ultrasonic spray pyrolysis system is very cheap and convenient. The microstructural, optical and electrical properties of the SnO₂ film were characterized by XRD, SEM, XPS, UV-VIS spectrophotometer, four point probe and Hall effect measurement, respectively. The SnO₂ film has the nanospherical particles. The electrical properties of heterojunction were investigated by I–V measurement, which reveals that the heterojunction shows strong rectifying behavior under a dark condition. The ideality factor and the saturation current density of this diode are 4.27 and 2.52 × 10^-6 A/cm², respectively. And the values of I_F/I_R (I_F and I_R stand for forward and reverse current, respectively) at 5 V is found to be as high as 248. The SnO₂/p-Si heterojunction device exhibits obvious photovoltaic effect. Under an AM1.5 illumination condition, the open-circuit voltage (V_oc), short-circuit current density (J_SC), fill factor (FF) of the device are 150 mV, 3.9 × 10^-3 mA/cm² and 20.58%, respectively. High photocurrent is obtained under a reverse bias when the crystalline quality of SnO₂ film is good enough to transmit the light into p-Si. Under 6.3 mW/cm² illumination, when the reverse bias is -5 V, the photocurrent gain is as high as 86.

Micro-arc oxidation (MAO) coatings were prepared on closed-cell aluminum foams. The microstructure, elemental distribution and phase composition of the MAO coatings were analyzed by scanning electron microscopy (SEM), energy-dispersive spectroscopy (EDS) and X-ray diffraction (XRD), respectively. The corrosion resistances and compressive properties of the uncoated and coated aluminum foams were studied by electrochemical polarization test and mechanical test, respectively. The results show that the MAO coatings cover the surfaces of closed-cell aluminum foams. The average thickness of the MAO coatings is 7 μm. The MAO coatings are mainly composed of γ-Al₂O₃ phase. The corrosion resistances of the closed-cell aluminum foams are improved by MAO treatment. The as-received foams show a low corrosion potential (-1.36 V), on contrary, the MAO coated foams get an increase corrosion potential (-0.78 V). But the MAO coated foams show the marginal variation in compressive strengths when the thickness of the coatings could be negligible compared with the total thickness of the foams.