Surface Review and Letters

TiB₂ films deposited using various deposition techniques are used to increase the wear lifetime of industrial components. The performance of TiB₂ films is dependent on the coating–substrate adhesion. In this study, the fatigue behavior of TiB₂ films was investigated using the multi-mode scratch method. Films of TiB₂ were deposited on silicon wafers and AISI M2 steel substrates at different frequencies by pulsed-dc closed field unbalanced magnetron sputtering (CFUBMS). The microstructures of the films were investigated using SEM techniques, and the hardness was measured using a microhardness tester. A multi-mode operation was used for sliding-fatigue, like multi-pass scratching in the same track at different fractions of critical load (bidirectional sliding) and a standard mode using progressive load operation. It was observed that the films deposited at low frequencies had higher adhesion strength and microhardness, and a denser microstructure.

Diamond-like carbon nanostructures were prepared using Plasma enhanced chemical vapor deposition (PECVD). Temperature dependence of self-assembly of carbon nanostructures is noted. Carbon and silicon exhibit significant lattice mismatch and during the self-assembly, stacking of carbon atoms takes place which results in conic projections. The carbon nanostructures were prepared at 600°C and 100 W RF power and were subjected to a cooling treatment. Argon and Methane were used as reactant gases. The formation of nanostructures did not use any catalyst. The surface morphology and roughness analysis was carried by Atomic Force microscopy. The nanocones were characterized by X Ray Diffractometer and Raman Spectroscopy.

Nano copper-based catalysts were prepared by co-precipitation method and the performance of catalytic hydrogenation for methyl 3-hydroxypropionate (MHP) to 1, 3-propanediol (1, 3-PDO) on the nano catalysts were studied under a high-pressure microcontinuum fixed-bed reactor. The effects of structure, texture, and composition of the catalysts on the catalytic performance were investigated by characterizing the catalysts with XRD, TG–DTG, SEM, and N₂ adsorption/desorption analysis technique. The results showed that addition of promoters enhanced the activity and selectivity of copper-based catalysts, which promoted the dispersion of the active components effectively and stabilized the active center of the catalysts. Especially, the copper-based catalyst of loaded P could restrain side-reaction effectively and improve selectivity obviously, the conversion of MHP and the selectivity of 1, 3-PDO could be 91.30% and reach 90.15%, respectively.

Photoluminescence, photoabsorption, and X-ray photoelectron spectroscopic study revealed that an optical transition of porous silicon from red-shift to blue-shift, and Si-2p binding energy transition from low to high at a critical anodization temperature, 343 K. Possible origin for the reverse variations happening at temperature below and above the critical temperature is discussed.

In this paper, theoretical study on the surface phonon–polariton (SPP) modes of wurtzite (α-) structure indium nitride (InN) semi-infinite crystal is presented. Based on an anisotropy model, the surface polariton (SP) dispersion curve of α-InN is simulated. The characteristics of this dispersion curve are discussed. The relevant experimental information by attenuated total reflection method is given. For comparison, the SP dispersion curve of cubic (β-) structure InN simulated based on isotropy model is also presented. Due to optical anisotropic, the SP dispersion curve of α-InN exhibits an extra branch as well as an extra SPP mode as compared to α-InN. In addition, the SPP mode of α-InN is found to be 4 cm^-1 smaller than that of β-InN.

In this paper, an optical microscopy study of orderly structures, namely bands, which are observed in a nearly free sustained copper (Cu) film system, is presented. The band is composed of a large number of parallel key-formed domains with different width w but nearly uniform length L. This study shows that the morphologies of the Cu films are very susceptible to the deposition rate, i.e. with the increase in the deposition rate f, the bands with rectangular domains first become irregular gradually and then disappear completely. The experiment indicates that the growth mechanism of the orderly patterns can be explained in terms of the relaxation of the internal stress in the films, which is related to the characteristic boundary condition of the films on the liquid substrates and the nearly zero adhesion of the solid–liquid interface.

A significant enhancement in light extraction from colloidal ZnO QD films was observed on an addition of a layer of two-dimensional photonic crystal (2D-PC) structure. The PCs with a rectangular-lattice air-hole array pattern with the period of 1.4 μm and the hole-size of 400 nm were fabricated by UV-nanoimprint lithography (UV-NIL). Unlike the commonly utilized electron-beam lithographic technique, the UV-NIL process can make patterns over a large area with high throughput. The resultant colloidal zinc oxide (ZnO) QD films with a PC pattern add-on had nearly double the output power, as measured from the top of the film.

The NiCoCrAlYTa coating was prepared on Ni-based single crystal super-alloys by low pressure plasma spraying (LPPS). The phases and microstructures for the coatings were characterized by X-ray diffraction and scanning electron microscopy, and the fracture toughness and micro-hardness for both coatings and substrate were also investigated. The relationship between coating properties and oxidation was analyzed. The result shows that elementary distribution of NiCoCrAlYTa coatings, which consists of γ-Ni, β-NiAl, γ'-Ni₃Al, and CrCoTa phases, is much homogeneous. The composition changes with depth from the surface to substrate for the coatings. The micro-hardness of coatings is 350.8 HV_0.3 and fracture toughness is 2.73 MPa m^1/2. The oxidation resistance of coatings excelled than Ni-based single crystal super-alloys.

Single-phase CuInSe₂ films were grown by high vapor selenization of CuIn alloy precursors within a partially closed graphite box. The CuIn precursors were prepared using Cu_xIn_y alloy targets with different composition rates under low vacuum level by a homemade sputtering system. The Cu and In composition rates of the used targets are 11:9, 10:10, and 9:11, respectively. The metallic precursor films were selenized using a two-step temperature profile, i.e. at 250°C and 400–500°C, respectively. The influence of the temperature at the second selenization step on the quality of the CIS absorbing layers was investigated. The CIS films were characterized by X-ray diffractometry, scanning electron microscopy, energy dispersive X-ray analysis, and Raman spectroscopy. The deposited CIS absorbers selenized at a high temperature of 500°C for 30 min exhibited a single-phase chalcopyrite structure with a preferential orientation in the (112) direction. These layers display uniform, large, and densely packed crystals with a grain size of about 3–5 μm. Cadmium sulfide buffer layer was manufactured by chemical bath deposition method. Bilayers ZnO/ZnO:Al were prepared by RF magnetron sputtering deposition. CIS solar cells with an efficiency of about 6.5% were produced without antireflective films. The method to fabricate CIS solar cells by a combination of the low vacuum sputtering deposition and the graphite box selenization process has provided a simple control process and shown a promising potential for developing high efficient and low-cost CuInSe₂ solar cells.

The electrical and microstructural properties of a series of ZnO-based thick film varistors (TFVs) doped with 0.00, 0.02, 0.04, 0.06, 0.08, and 0.10 mol% Y₂O₃ were studied. It was found that sample doped with 0.08 mol% Y₂O₃ showed the highest potential gradient of 3159.4 V/mm with a leakage current of 36.4 μA and a nonlinear exponent of 13.1. The ZnO grain size decreased with increasing Y₂O₃ content, which was the origin for the increase in potential gradient. Raman spectra results showed that the tensile stress increased linearly with Y₂O₃ doping. Larger tensile stress was considered to result from the lattice distortion and inevitably influenced the grain boundary characteristics. While the Y₂O₃ doping concentration was beyond 0.08 mol%, the effect of residual stress on electrical properties was much more remarkable than that of grain size, leading potential gradient to be weakened. As a result, high potential gradient of ZnO-based TFVs could be obtained with Y₂O₃ doping concentration of 0.08 mol% and qualified as excellent candidates for high voltage varistor application.

The thick ceramic coatings were prepared on 6061 aluminum alloys by microarc oxidation in a silicate electrolyte. The morphology and phase constituent of the coatings with different thickness were studied by scanning electron microscope, and X-ray diffraction. Scratch and thermal shock tests were employed to evaluate the adhesion between the coating and alloy substrate. The maximum microhardness and its position away from alloy/coating interface increases with increasing the coating thickness. The critical scratch force for the coating break was about 55 N in the 50 μm thick coating. Thermal shock resistance of the coatings depend on their thickness and thinner coating has better thermal shock resistance. The coated alloy with 50 μm thick coating can be subjected to 50 times thermal cycles of heating up to 500°C followed by quenching into water.

The focus of this study is to synthesize a new calixarene derivative namely calix[6]arene (C21) and to test its performance as corrosion inhibitor of C38 steel in molar HCl at 308 K. Polarization and weight loss measurements were used. Weight loss tests show that C21 retards until to stop corrosion phenomenon at 5 × 10^-5M. C21 is an excellent inhibitor and its inhibition efficiency increases with its concentration to reach 100% since 5 × 10^-5M. Polarization curves revealed that C21 affects both cathodic and anodic domains by decreasing current densities and then it may be classified as a mixed type inhibitor. The calixarene tested is adsorbed on the surface according to the Langmuir adsorption isotherm. Free enthalpy of adsorption reveals that C21 acts from chemisorption onto the steel surface.

In the current study, a multilayered polyester composite based on betelnut fiber mats is fabricated. The adhesive wear and frictional performance of the composite was studied against a smooth stainless steel at different sliding distances (0–6.72 km) and applied loads (20–200 N) at 2.8 m/s sliding velocity. Variations in specific wear rate and friction coefficient were evaluated at two different orientations of fiber mat; namely parallel (P–O) and normal (N–O). Results obtained were presented against sliding distance. The worn surfaces of the composite were studied using an optical microscope. The effect of the composite sliding on the stainless steel counterface roughness was investigated. The results revealed that the wear performance of betelnut fiber reinforced polyester (BFRP) composite under wet contact condition was highly dependent on test parameters and fiber mat orientation. The specific wear rate performance for each orientation showed an inverse relationship to sliding distance. BFRP composite in N–O exhibited better wear performance compared with P–O. However, the friction coefficient in N–O was higher than that in P–O at lower range of applied load. The predominant wear mechanism was debonding of fiber with no pullout or ploughing. Moreover, at higher applied loads, micro- and macrocracking and fracture were observed in the resinous region.

Pure poly(vinylidene fluoride) (PVDF) membrane and PVDF composite membranes modified by three kinds of inorganic nanoparticles (SiO₂, Al₂O₃, and TiO₂) were made using a phase inversion method and characterized by pure water flux, retention efficiency of Bovine serum albumin (BSA), flux reduction coefficient, and scanning electron microscope (SEM). The results of flux reduction coefficient illustrated that PVDF membrane modified by nanoparticles had better antifouling property in the order of TiO₂, Al₂O₃, SiO₂. The Lewis acid–base properties of the nanoparticle materials were measured by inverse gas chromatography (IGC). The Lewis acid number, K_a, and Lewis base number, K_b, had the following order K_{a TiO2} < K_{a Al2O3} < K_{a SiO2}, and K_{b TiO2} > K_{b Al2O3} > K_{b SiO2}. The experimental results indicated that PVDF membrane modified by nanoparticles with relatively strong base exhibited excellent antifouling performance.

The role of artificial polarization in two different applications of the title color center, namely optical properties of F_A2:Sr²⁺ center and adsorbate–substrate interactions, is investigated by using quantum mechanical CI-singles and DFT ab initio methods. Clusters of variable sizes were embedded in the simulated Coulomb field that closely approximate the Madelung field of the host surface, and ions that were the nearest neighbors to the defect site were allowed to relax to equilibrium. The sensitivity of the calculated transition energies (Stokes shifts) of F_A2:Sr²⁺ center as well as related optical properties, such as optical–optical conversion efficiency, relaxed excited states of the defect-containing surface, orientational destruction of the point defect, recording sensitivity, the Glasner–Tompkins empirical rule, and the artificial polarization were examined. The dependence of NO and ON adsorption energies at RbCl (001) surface on artificial polarization were also examined, and the results were explained in terms of electrostatic potential curves. The coadsorption of NO molecules, and the charge transfer reactions between the NO molecules and the paramagnetic chlorine vacancy on RbCl surface were considered.

In order to protect carbon/carbon (C/C) composites from oxidation at 1700°C, a MoSi₂–SiC–Si/MoSi₂ coating was prepared on the surface of these composites by a simple and effective method. The MoSi₂–SiC–Si inner layer was obtained by pack cementation, and the MoSi₂ outer layer was prepared by slurry coating using silicon-sol as the caking agent. The microstructures of the as-prepared coating were examined by X-ray diffraction and scanning electron microscope. Oxidation test shows that, the as-received coating can protect C/C composites from oxidation for more than 107 h at 1700°C in air. The excellent anti-oxidation ability of this coating is attributed to its dense structure and the formation of the SiO₂ film on the coating surface during oxidation.

Up to fourth moment distribution of carbide nanocrystallites produced by duplex treatments of surface nanocrystallization and pulsed plasma electrolytic carbonitriding on AISI 1010 mild steel was investigated by the means of figure analysis with high precision. Skewness and kurtosis study of the Gaussian distribution have been studied and the effect of duty cycle of pulsed current has been determined. The usage of lower duty cycles of pulsed current is more suitable for achieving lower sizes of carbide nanocrystallites. Surface roughness of treated samples was measured and it has been observed that there is an optimum level of duty cycle of pulsed current for surface roughness increasing (difference between two measured data).

Surface crack of CeF₃ films generated by thermal stress were characterized by scanning electron microscopy and atom force acoustic microscopy (AFAM). Low frequency (8–18 kHz) acoustic response of films and cracks was measured by AFAM. The low frequency acoustic response is similar to what had been got at several MHz or even higher frequency. It was found that surface elastic properties of CeF₃ films can be easily qualitatively measured by low frequency AFAM.

The MoS₂ particles were coated with Al₂O₃ ratio varying from 5 to 50 wt.% content. Ni–MoS₂/Al₂O₃ composite coatings were prepared by means of pulse electrodeposition. The dependence of preferential orientation index and corrosion properties of these composite coatings was investigated in relation to the Al₂O₃ ratio in MoS₂/Al₂O₃ particles. Polarization measurements have been used to evaluate corrosion resistance performance of coating. The Ni–MoS₂/50 wt.%Al₂O₃ coatings showed the highest corrosion resistance compared with Ni–MoS₂/5 wt.%Al₂O₃, Ni–MoS₂/10 wt.%Al₂O₃, and Ni–MoS₂/30 wt.%Al₂O₃ coatings. Thus, it is understood that the increase of ratio of Al₂O₃ in MoS₂/Al₂O₃ composite particle improves the corrosion efficiency of coating. These Al₂O₃ act as inert physical barriers to the initiation and development of corrosion defect, hence improve the corrosion resistance of the coating.

K-shell X-ray emission was observed in the neutralization process of Ar¹⁶⁺ interacting with beryllium and molybdenum at slow speed (less than Bohr velocity). The K-shell X-ray emission came from the metastable component of Ar¹⁶⁺ beam with the configuration (1s2s) produced from electron cyclotron resonance ion source. The intensity ratio of K_β X-ray emission to K_α X-ray emission (I_Kβ/I_Kα) in the neutralization process decreased when the kinetic energy of the projectile increased. This is closely related to the flight time the projectiles spend above the surface, which is dominated by both the work function of the metal and the normal velocity component of the incident ions to the surface according to the classical over-barrier model. As the relation between I_Kβ/I_Kα and the above-flight time shows, the longer time above the surface the larger ratio due to the above-surface contribution. Furthermore, the smaller work function leads to the smaller contribution from the above surface.

In this paper, we reported a comparative study of process and structural characterization of cadmium sulfide (CdS) and zinc sulfide (ZnS) thin films by chemical bath deposition (CBD) technique. Their deposition process is similar which clearly shows three different growth phases, a none-film one, a quasi-linear one, and a saturation one. And the growth rate of CBD-CdS is higher than that of CBD-ZnS. Through calculating the activation energy of reaction, we can conclude that the rate determining step of CBD-CdS in the deposition process is a chemical one, in contrast with the CBD-ZnS in which the determining step can be a diffusion step. The XRD analysis of the as-deposited films shows that the CBD-CdS films present cubic and hexagonal mixed structure and CBD-ZnS films are in cubic ZnS structure. The deposition time significantly influenced the crystal structure of CdS thin film. Transmission measurement shows that when the wavelength is below 500 nm, the optical transmission of CBD-ZnS film is higher than that of CBD-CdS film. Optical transmission of both CBD-ZnS and CBD-CdS films is about 90% when the wavelength is over 600 nm. The band gap (Eg) value of CBD-CdS is about 2.41 eV and that of CBD-ZnS is about 3.51 eV.

Microstructure of WC reinforced Ni-based self-fluxing alloy composite coating sprayed and fused by oxy-acetylene flame was investigated by scanning electron microscopy and energy dispersive X-ray Spectrometry, X-ray diffraction, and transmission electron microscopy. The wear performance of the coating was studied by a MLS-225 wet sand rubber wheel abrasive wear tester at various loads and sizes of abrasive particles. Also, the wear resistance of the coating was compared with uncoated ASTM1020 steel. The results indicated that the coating is bonded metallurgically to the substrate and has a homogeneous microstructure composed of both coarse WC and fine carbide and boride grains such as Cr₇C₃, Cr₂₃C₆, and Ni₂B which disperse uniformly in the matrix of γ-Ni solid solution and Ni₃B. The worn mass loss of the coating and ASTM1020 steel both increased with the load and size of abrasive particles, also, the coating has exhibited excellent abrasive wear resistance compared with ASTM1020 steel.

Combining hybrid nanostructures of metal nanoparticles (NPs) and carbon nanotubes could afford a novel strategy to prepare promising nanomaterials for the highly sensitive sensors and imaging science applications. Conventional acid oxidation process was used to obtain carboxylic acid bound multi-walled carbon nanotubes (MWNTs) which was further acylated with thionyl chloride to give acyl chloride functionalized MWNTs. Thiol functionalized MWNTs were synthesized by amidation reaction of the acylated MWNTs with cysteamine. Further, gold nanoparticles (GNPs) were successfully fabricated on the tube walls to yield the CNT/Au hybrid. Fourier transform infrared spectroscopy and energy dispersive X-ray studies were used to characterize the surface chemical functionalities and composition of MWNTs, respectively. Evidence for the attachment of GNPs to thiol functionalized MWNTs was obtained from ultraviolet–visible absorption spectra. In addition, TEM images provided a vivid image of uniform decoration of GNPs on the nanotube sidewalls.

The dielectric properties of Ba_0.6Sr_0.4TiO₃ (BST) thin films deposited using SrRuO₃ (SRO) materials as bottom electrode were compared with those of the films grown using La_0.5Sr_0.5CoO₃ (LSCO) materials as bottom electrode. X-ray diffraction scanning revealed that the two kinds of films could be epitaxially grown in pure single-oriented perovskite phases and atomic force microscopy showed that the root mean square roughness of BST/SRO films were similar to BST/LSCO films. The dielectric properties of the BST/SRO and BST/LSCO thin films were measured at 10 kHz and 300 K with a parallel-plate capacitor configuration. Compared with BST/LSCO, the dielectric tunability for BST/SRO films slightly decreased, while the loss decreased synchronously. The figure of merit factor value increases from 25.67 for BST/LSCO films to 48.76 for BST/SRO films under an applied voltage of 6 V. The leakage current density of the thin films at a positive voltage of 2 V decreases from 2.41 × 10^-7A/cm² for BST/LSCO to 8.41 × 10^-8A/cm² for BST/SRO. This phenomenon is ascribed to the smaller strain induced in BST/SRO materials.

The transmission of 60 keV O⁺ ions through Al₂O₃ nanocapillaries target in a series of different tilted angles was measured. The capillaries with diameters of 50 nm and 30 nm respectively, and 10 μm in length were used. Our results indicate the existence of guiding effect when ions through the capillary and a significant dependence of the ion transmission on the diameters of the capillaries.