Surface Review and Letters

The adsorption of small organic molecules on silicon surfaces has been long a subject of investigations, as it provides the fundamental basis of silicon-based technologies in many fields. Several approaches were used, both theoretical and experimental, on many types of adsorbate-substrate systems aiming at determining preferential sites and geometries of adsorption, stable configurations, transition barriers, adsorption mechanisms, electronic structures among others. The research efforts, though, did not always bring to conclusive arguments and on some systems investigations are still going on following the evolution of the experimental techniques and computational methods. In this review, two case studies are reported: benzene and methanol on Si(100)2$\times$1, i.e. examples of a molecular and a dissociative adsorption. The adsorption of benzene on Si(100)2$\times$1 is still an open case, as it may adsorb in di-$\sigma$ or tetra-$\sigma$ bonded configurations, but contrasting evidences have been reported so far, on which of the two is the most stable one and the debate is still open. The adsorption of methanol is less controversial and it is widely accepted it is dissociative with breakage of the O–H at low coverages. But also in this case, investigations are going on to elucidate the adsorption mechanism.

This work examines the performance of the Cu₂SnS₃ (CTS) solar cells using the solar cell capacitance simulator (SCAPS) approach. The performance of the CTS solar cell was evaluated in terms of $V_{\mathrm{\text{oc}}}$, $J_{\mathrm{\text{sc}}}$, fill factor and efficiency. The structural parameter variation of CTS solar cell has been studied in terms of buffer and absorber layer thickness, bandgap, effect of temperature on total efficiency of the solar cell. Increasing the thickness of the CdS buffer layer decreases the efficiency of the simulated solar cell. A significant increase in the efficiency of the solar cell to 20.36% was obtained with a simulated buffer layer thickness to 10nm. In terms of the CTS absorber layer thickness, the efficiency of the solar cell increases by increasing the thickness of absorber layer. By setting the thickness of CTS to 4.0$\mu$m, the efficiency obtained is 20.36%. It is observed that an increase in the bandgap can enhance the efficiency of the solar cell. In the performed simulation, an 0.9eV bandgap resulted in a 11.58% cell efficiency and a 1.25eV bandgap resulted in 21.96% cell efficiency. In terms of temperature, the efficiency of 20.36% was obtained at 300K, and as the temperature increases, cell efficiency will decrease.

In this study, porous silicon (PS) samples were prepared on $n$-type silicon (100) wafers by electrochemical etching method, varying the current density from 20 to 100mA/cm² and keeping constant HF concentration (10%) and etching time of 15min. Then, Ag thin films, which have 10, 50 and 100nm film thicknesses, were deposited on PS layers by using thermal evaporation to investigate the influence of Ag film thickness on structural and optical properties of PS. The structural and optical properties of PS and Ag deposited PS layers have been investigated by XRD, FE-SEM, Raman and photoluminescence (PL) spectroscopy. FE-SEM XRD and Raman analyzes indicate that average pore size and porosity of PS layers increase with the increasing current density. Further, Ag nanoparticles have embedded in pore channel. PL measurement reveals that higher porosity of PS would be better to form the Ag–PS nano-composite material leading to stronger PL band. The PL spectra of PS and Ag–PS samples indicate that PL bands show blue shift with increasing current density and film thickness. Consequently, it has been found that the structural and optical properties of PS depend on current density and Ag film thickness individually.

In this research paper, total 246 individual microfluidic devices have been fabricated by maskless lithography, hot embossing lithography and direct bonding technique. The effect of surface area to volume ratio on the surface-driven capillary flow of different liquids has been experimentally investigated in these microfluidic devices fabricated by polymethylmethacrylate (PMMA). Also, the individual effects of liquid viscosity and surface wettability on the surface-driven capillary flow of different liquids are experimentally investigated. The polystyrene particles of 10$\mu$m diameters have been separated from the aqueous microparticle suspensions in the microfluidic lab-on-a-chip systems with 100% separation efficiency. Also, the polystyrene particles of 5$\mu$m diameters have been separated from a different set of aqueous microparticle suspensions in the microfluidic lab-on-a-chip systems with 100% separation efficiency. The individual designs of the microfluidic lab-on-a-chip systems are a novel approach in this research paper. The effect of surface area to volume ratio on the separation time is experimentally investigated as another novel approach of this research paper.

Aluminum (Al) alloy ships are vulnerable to both damage from chlorine ions in seawater environments and cavitation-erosion due to fast relative motion of metal and liquid resulting from lightweight and high-speed vessels moving through seawater. These corrosive processes cause damage to the hulls of ships, resulting in large economic losses. Recently, cavitation peening technology to improve the durability of a material has been in development. The technology works by forming compressive residual stress on the surface layer of the material in order to improve fatigue strength and fatigue life. In this study, we performed a water cavitation peening (WCP) on a 5083-O Al alloy for ships by applying an ultrasonic piezoelectric effect and cavitation effect, as described in ASTM-G32. From these experiments, we determined an optimum WCP duration, 2.5min, for sufficient cavitation resistance characteristics. This timing improved cavitation resistance by 48.68% compared to the untreated condition. A comprehensive comparison of all of results revealed that the optimum WCP duration was 3min with respect to the point of cavitation and corrosion resistance.

Al₂O₃ insulator layer was deposited by atomic layer deposition (ALD) technique on p-type Si $〈111〉$ and the Al/Al₂O₃/p-Si metal/insulator/semiconductor (MIS) structures were fabricated. The current–voltage ($I-V$) characteristics of these structures were investigated in two different temperatures. The main electrical parameters such as the ideality factor ($n$), zero bias barrier height (${\mathrm{\Phi }}_{Bo(I-V)}$), and series resistance ($R_s$) values were found for 300 and 400K. The energy density distribution profiles of the interface state density ($N_{ss}$) were determined from the $I-V$ characteristics. In addition, the capacitance–voltage ($C-V$) and conductance–voltage ($G/w-V$) characteristics of devices were investigated in the frequency range 50–1000kHz at room temperature. Frequency-dependent electrical characteristics such as doping acceptor concentration ($N_A$), energy difference between the valance band edge and bulk Fermi level ($E_F$), diffusion potential ($V_{\text{D}}$), barrier height (${\mathrm{\Phi }}_{B(C-V)}$), the image force barrier lowering ($\mathrm{\Delta }{\mathrm{\Phi }}_B$), maximum electric field ($E_m$), and $R_s$ values were determined using $C-V$ and $G/w-V$ plots. In addition, the $N_{ss}$ values were performed using Hill–Coleman method. According to experimental results, the locations of $N_{ss}$ and $R_s$ have an important effect on $I-V$, $C-V$ and $G/w-V$ plots of MIS structure.

S30432 steels were processed by multistep shot peening treatment. The refined microstructures, including domain size, microstrain, domain size distribution and texture were characterized by X-ray diffraction (XRD) line profile analysis method, respectively. The results demonstrate that in the deformed layers, a gradient structure is formed after shot peening. The domain size reaches 25nm at the surface, then it decreases as the depth increases, but microstrain (0.0027) is the largest at the surface. The domain size distributions at different depths calculated by Rietveld method are consistent with domain size variation along the depth. There are no strong textures after shot peening treatment. The change of microhardness along the depth is in accordance with the gradient microstructure. It is expected that this work can offer useful information for characterizing the microstructure of shot peened materials.

The film of poly (N-vinylcarbazole) (PVK) polymers and its composite film of PVK/C${}_{60}$ were prepared successfully by spin-coating method at speed of 1200rms for 30s. Atomic force microscopy (AFM), UV–Vis absorption spectroscopy and the photoluminescence (PL) were used to investigate the film structure and optoelectronic properties. The PL quench was observed for the PVK/C${}_{60}$ composite film. The current increased near three orders of magnitude under illumination for PVK/C${}_{60}$ composite film comparing with that in the dark through $I-V$ measurement, which resulted from the electron transfer from PVK to C${}_{60}$.

The possibility of deposition of Fe–TiC nanocomposite on the surface of carbon steel substrate with the laser coating method had been investigated. Mechanical milling was used for the preparation of raw materials. The mixture of milled powders was used as a coating material on the substrate steel surface and a CO₂ laser was used in continuous mode for coating. Microstructural studies were performed by scanning electron microscopy. Determinations of produced phases, crystallite size and mean strain have been done by X-ray diffraction. The hardness and wear resistance of coated samples were measured. The results showed that the in situ formation of Fe–TiC nanocomposite coating using laser method is possible. This coating has been successfully used to improve the hardness and wear resistance of the substrate so that the hardness increased by about six times. Coated iron and titanium carbide crystallite sizes were in the nanometer scale.

Al- and N-polar AlN have been grown by metalorganic vapor phase epitaxy (MOVPE) with the assistance of In dopant and characterized by in situ interferometry, ellipsometry, scanning electron microscopy, atomic force microscopy, and X-ray diffractometry. The growth of Al-polar AlN is faster with smoother surfaces than the N-polar ones, which is explained by theoretical calculations. The surfactant effect of In is confirmed by improving the growth rate and surface flatness without getting into the epilayer. Additionally, In is also favorable for reducing the density of dislocations and improving the crystalline quality, especially that of Al-polar AlN. The results suggest that using In surfactant to grow the Al-polar AlN epilayer leads to a better crystal quality under proper pre-growth treatments, low- and high-temperature AlN growth conditions.

In the present paper, the influences of different double layer on wear and scratch performances of commercially pure Titanium (CP-Ti) were investigated. TiO₂/SiO₂ and SiO₂/TiO₂ double layer coatings were deposited on CP-Ti by sol–gel dip coating process and calcined at 750${}^{\circ }$C. The phase structure, cross-sectional morphology, composition, wear track morphologies, adhesion properties, hardness and roughness of uncoated and coated samples were characterized with X-ray diffraction, scanning electron microscopy (SEM), nano-indentation technique, scratch tester and 3D profilometer. Also, the tribological performances of all samples were investigated by a pin-on-disc tribo-tester against Al₂O₃ ball. Results showed that hardness, elastic modulus and adhesion resistance of double layer coated samples were higher than untreated CP-Ti. It was found that these properties of TiO₂/SiO₂ double layer coatings have higher than SiO₂/TiO₂ double layer coating. Additionally, the lowest friction coefficient and wear rates were obtained from TiO₂/SiO₂ double layer coatings. Therefore, it was seen that phase structure, hardness and film adhesion are important factors on the tribological properties of double layer coatings.

NiCrBSi alloy coatings are widely used in wear and corrosion protection at higher temperature. As a primary hard phase forming element, B element can effectively improve the coating hardness. In this study, the low coefficient of friction of BN with three ratios (10%, 20%, and 30%) was added in order to reduce the wear rate and provide additional B element. The NiCrBSi/h-BN composite coatings were successfully prepared on a cast-iron substrate using supersonic air-plasma spray technology. The phase constitution, microstructure characterization, and microhardness of the coatings before and after oxyacetylene flame remelting were investigated by means of scanning electron microscope (SEM), X-ray diffraction, and energy dispersive analysis of X-ray techniques, respectively. The wear resistance of composite coatings was also tested in this paper. It was found that the microstructure was well refined by remelting treatment and this was beneficial for the adherence between the coating and the substrate, which was nearly 33MPa. The wear resistance of the NiCrBSi alloy coating was also improved with the increasing component of h-BN in remelted samples. When the h-BN content reached 30%, the friction coefficient decreased to 0.38 for the remelted coating. The effect of the remelting process on the anti-abrasive property and extension of the material’s wear life was quite important.

In this research, the electrochemical impedance spectroscopy (EIS) and Tafel analysis were utilized to study the hot corrosion performance at 700${}^{\circ }$C of air plasma-sprayed (APS) yttria-stabilized zirconia (YSZ) coatings with a NiCrAlY bond coat grown by high velocity oxygen fuel spraying (HVOF), deposited on an INCONEL 625 substrate, in contact with corrosive solids salts as vanadium pentoxide V₂O₅ and sodium sulfate Na₂SO₄. The EIS data were interpreted based on proposed equivalent electrical circuits using a suitable fitting procedure performed with Echem Analyst^TM Software. Phase transformations and microstructural development were examined using X-ray diffraction (XRD), with Rietveld refinement for quantitative phase analysis, scanning electron microscopy (SEM) was used to determinate the coating morphology and corrosion products. The XRD analysis indicated that the reaction between sodium vanadate (NaVO${}_3)$ and yttrium oxide (Y₂O${}_3)$ produces yttrium vanadate (YVO${}_4)$ and leads to the transformation from tetragonal to monoclinic zirconia phase.

Structural and magnetic properties of Zn${}_{1-x}$Ni_xO thin films and diluted magnetic semiconductors have been investigated. This sample has been synthesized using a spray pyrolysis technique with a stoechiometric mixture of zinc acetate (C₄H₆O₄Zn$\cdot$2H₂O) and Nickel acetate (C₄H₆O₄Ni$\cdot$ 2H₂O) on a heated glass substrate at 450${}^{\circ }$C. The films were characterized by X-ray diffraction (XRD), UV–Vis spectrophotometry and Hall Effect measurements. These films of ZnO crystallized in the hexagonal Wurtzite structure. The optical study showed that the band-gap energy was increased, from 3.3eV to 3.5eV, with increasing the Ni concentration. The film resistivity was affected by Ni-doping, and the best resistivity value 1.15$\times$10${}^{-2}$ ($\mathrm{\Omega }$ cm) was obtained for the film doped with 2 at.% Ni. The electronic structure and optical properties of the Wurtzite structure Zn${}_{1-x}$Ni_xO were obtained by first-principles calculations using the Korringa–Kohn–Rostoker method combined with the coherent potential approximation (CPA), as well as CPA confirm our results.

In this work, the structural properties of the zinc sulfide (ZnS) films have been investigated using X-ray diffraction (XRD) analysis which show an enhancement in the crystallite degree after doping with copper (Cu). Good matching between the ZnS and porous silicon (PS) structure was noted from the atomic force microscope (AFM) results. The reflectivity gave a clear observation of anti-reflected coating improvement for PS layer and more enhancements after the ZnS deposition. The optical properties show a blue shift in the bandgap for the ZnS deposited with higher substrate temperature and a red shift after doped with different elements. For ZnS/PS heterojunction, the electrical resistivity has been increased after PS layer formed and changed with the variation of the pore size and it was much higher after ZnS deposited on the PS. However, use of ZnS:Cu/PS photodetector showed much higher output current at the ultraviolet (UV) region compared to ZnS/PS. The ZnS:Cu/PS photodetector showed higher output current value than that of the ZnS/PS leading to improvement in the quantum efficiency of 42%.

This study investigated the preparation of graphene oxide from mildly oxidized graphite through ultrasonic exfoliation. Both the original and produced materials were analyzed by ultraviolet–visible spectrophotometer, X-ray diffraction and atomic force microscopy. The results indicated that the exfoliation yield of graphene oxide was proportional to the input ultrasonic energy. In addition, a two-stage exfoliation phenomenon was observed in the exfoliation of mildly oxidized graphite with both ultrasonic homogenizer and cleaner. It also was found that increasing the content of [$O$] in a C–H₂SO₄–[$O$] reaction system was the most simple and direct method to increase the oxidation degree of graphite oxide.

The influence of applied voltage on the plasma electrolytic borocarburizing (PEB/C) layer of Q235 low-carbon steel in high-concentration borax solution was investigated. XRD and XPS spectra of PEB/C layer confirmed that the modified boride layer mainly consisted of Fe₂B phase, and the FeB phase only exists in the loose top layer. The applied voltage on Q235 steel played a key role in determining the properties of hardened layers. The thickness and microhardness of boride layers increased with the increase of the applied voltage, which led to superior corrosion and wear resistances of Q235 low-carbon steel. The diffusion coefficient ($D)$ of boride layer at 280, 300 and 330V increased with borocarburizing temperature and ranged from $0.062\times 10^{-12}$m²/s to $0.462\times 10^{-12}$m²/s. The activation energy ($Q)$ of boride layer growth during PEB/C treatment was only 52.83$\mathrm{\text{kJ}}\cdot {\mathrm{\text{mol}}}^{-1}$, which was much lower than that of the conventional boriding process.

Chloride ions in seawater can destroy the passive state films on the exposed surface of aluminum (Al) alloy ships. This shortens hull lifespan and increases the maintenance costs of ships. Recently, the water cavitation peening (WCP) technology has been adopted to form compressive residual stress on surfaces to improve resistance to cavitation. This study was conducted to investigate corrosion damage prevention by applying the WCP technology to 5083-O Al alloy for ships; the optimum WCP duration and corrosion protection potential range for maintaining corrosion resistance were determined. We found that the optimum WCP duration was 2.5min by performing a potentiostatic experiment, and the optimum corrosion protection potential range was $-1.30$V–$-0.75$V for ICCP system.