Surface Review and Letters

Based on the experimental maximum escape depth $S(W_{\mathrm{\text{p0}}}$, $Z)$ of rediffused electrons from atomic number $Z$ metal at incident energy of primary electron $W_{\mathrm{\text{p0}}}$, the relationship among $S(W_{\mathrm{\text{p0}}}$, $Z)$, $W_{\mathrm{\text{p0}}}$ and $Z$ in the energy range of 9.3keV$\leqq W_{\mathrm{\text{p0}}}\leqq$40keV was obtained and proved to be true by experimental data. According to the experimental results of rediffused electrons, the characteristics of secondary electron emission, relationships among parameters of rediffused electrons and the main processes of rediffused electrons emission, the formula for $W_{\mathrm{\text{p0}}}$ backscattering coefficient $\eta (W_{\mathrm{\text{p0}}}$, $Z$, $t)$ of $Z$ metal films with film thickness $t$ as a function of $t$, Z and was deduced, and the results were analyzed. It is concluded that the deduced formula for $\eta (W_{\mathrm{\text{p0}}}$, $Z$, $t)$ can be used to calculate $\eta (W_{\mathrm{\text{p0}}}$, $Z$, $t)$ in the energy range of 9.3keV$\leqq W_{\mathrm{\text{p0}}}\leqq$40keV. The secondary electron yield $\delta$ from thin films are applied in more and more fields such as electronic information technology, accelerator and space flight, and $\eta (W_{\mathrm{\text{p0}}}$, Z, $t)$ is an important parameter of $\delta$ from $Z$ metal films. So deducing the formula for $\eta (W_{\mathrm{\text{p0}}}$, $Z$, $t)$ in this study is necessary.

A gradient microstructure was generated on a low-carbon steel/Cr alloy through severe deformation by an impact peening and a recovery treatment. The microstructure was probed by scanning electron microscopy, energy disperse spectroscopy and x-ray diffraction. The microhardness, tensile strength and electrochemical corrosion resistance of the gradient microstructure surface were studied. The material with a fine grain gradient microstructure on the surface had increased microhardness, strength, ductility and corrosion resistance compared to a low-carbon steel standard. When a Cr solution was added, a hard (Fe,Cr)₇C₃ phase was generated, suggesting that Cr alloying plays important roles in these enhanced properties.

This paper reports the thermodynamic analysis of (Co–Cr) system using THERMO-calc package (basis for CALPHAD) and PBIN database. Calculations involve binary phase diagram, Gibb’s energy curve and activity curve at three different elevated temperatures 2125K, 2150K and 2175K. Induced miscibility gap is observed at particular concentration. Binary phase diagram shows variation in phases in prescribed alloy with increasing temperature and mole fraction concentration of $C_{\mathrm{\text{o}}}$. The total Gibbs energy decreases with increasing temperature showing the stability of Co–Cr system. Activity showed thorough fluctuation resulting in negative deviation from Raoult’s law ideal curve.

The synergistic effect of halide ions such as KCl, KBr and KI on the corrosion inhibition of mild steel in 1 N sulphuric acid by $\gamma$-2,c-6-diphenyl-t-3-methyl piperdin-4-ones with semicarbazone (01SC), $\gamma$-2,c-6-diphenyl-N-methyl-t-3-ethyl piperdin-4-ones with semicarbazone (02SC) and 2,6-diphenyl-t-3-ethyl piperdin-4-one with semicarbazone (03SC) has been examined by weight loss method, potentiodynamic polarization measurements and electrochemical AC impedance spectroscopy. Results show that substituted $\gamma$-2,c-6-diphenyl piperidin-4-ones with semicarbazone act as the perfect corrosion inhibitors and their inhibition efficiency increases with the addition of halide ions. The inhibitor (01SC) shows the inhibition efficiency of 78.28% (0.2mM) by using a weight loss method. The influence of I${}^{-}$, Br${}^{-}$ and Cl${}^{-}$ anions raises the inhibition efficiency of the substituted 2,6-diphenyl piperidin-4-ones with semicarbazone due to the synergistic effect. The synergistic effect of halide ions was formed in the following order: KI $>$ KBr $>$ KCl.

Cuprous oxide (Cu₂O) thin films were produced from metallic Cu targets on $\alpha$-Al₂O₃ (000$l$) substrate by radio frequency magnetron sputtering technology. Three batches of samples were deposited under various sputtering parameters by modulating substrate temperature, gas flow and sputtering power, respectively. The samples were characterized by X-ray diffraction and field-emission scanning electron microscopy. Through the experiment, the influences of the sputtering conditions were systematically investigated. It could be inferred that the crystallization extent and the crystal orientation in Cu₂O thin films mainly depend on the temperature exchange, which contribute to the variation of the film morphology. Moreover, the gas flow has an effect on the valence of the copper ion in the film and the sputtering power mainly affects the growth rate of the films. This research promotes a more specific scheme to deposit proper Cu₂O thin films with proper morphology and useful properties.

The Ni-P/TiN coating was used as bipolar plate by electroless plating on Ti. Surface morphology and phase structure of the coatings were characterized by SEM and XRD, respectively. Corrosion resistance of Ni-P and Ni-P/TiN coating was measured in the simulated solution of Proton exchange membrane fuel cells (PEMFCs). The interfacial contact resistance (ICR) was conducted by applied different forces. SEM images indicated that the particles of core–shell structure were formed on the surface of coating on Ti substrate. The core–shell structure was composed of TiN core and Ni-P electroless plating shell. Compared with Ni-P coatings, the Ni-P/TiN coating showed better corrosion resistance behaviors and low ICR (below 10m$\mathrm{\Omega }$ cm${}^{-2}$ under pressure of 200 N/cm${}^2)$. TiN particles and distribution of core–shell were in favor of the formation of coating and compact surface morphology. The good conductivity was attributed to the compact surface morphology of coating. The Ni-P/TiN coating showed excellent interfacial conductivity and good corrosion resistance at applied high potential in simulated solution of PEMFCs.

The effect of substrate temperature on growth of pulsed laser deposited copper oxide thin films has been investigated by employing Nd: YAG laser (532nm, 6ns, 10Hz) irradiation at a fluence of 8.2J/cm². XRD analysis reveals that copper oxide films deposited at room temperature are amorphous in nature, whereas films deposited at higher substrate temperatures are polycrystalline in nature. SEM and AFM analyses revealed that films deposited at substrate temperatures, ranging from room temperature to 300${}^{\circ }$C are comprised of large sized clusters, islands and particulates, whereas uniform films with an appearance of granular morphology and distinct bump formation are grown at higher substrate temperatures of 400${}^{\circ }$C and 500${}^{\circ }$C. The optical bandgap of deposited films is evaluated by UV-VIS spectroscopy and shows a decreasing trend with increasing substrate temperature. Four point probe analysis reveals that electrical conductivity of the deposited films increases with increase in the substrate temperature, and is maximum for highest growth temperature of 500${}^{\circ }$C. It is revealed that growth temperature plays a significant role for structure, texture, optical and electrical behavior of copper oxide thin films. The surface and structural properties of the deposited films are well correlated with their electrical and optical response.

The growth of biological systems like DNA, peptides and proteins are accredited to the self-assembly processes from the molecular level to the nanoscale. The flawless immobilization of DNA on any surface is quite an important step to the development of DNA-based biosensors. The present paper reports the use of atomic force microscopy to determine the mechanical properties of the as grown and annealed self-assembled monolayer (SAM) as well as the mutated DNA immobilized on the SAM. The SAM of alkane thiol (16-mercapto-1-hexadecanol) was developed on Au surface, which was then annealed and analyzed for its structural and mechanical properties. The surface coverage, height and monolayer’s order was studied as a function of incubation time and annealing time. Excessive annealing led to the defragmentation and desorption of SAM structures due to breaking of hydrocarbon bonds. AFM was employed to determine the detach separation, pull-off and work of adhesion of the as grown and annealed SAM.

The work reports the traces of graphene synthesized by Thermal-CVD technique over oxidized silicon substrates coated with nickel and cobalt catalysts under different pressures. Other process parameters like temperature, gas composition and time are kept constant during the growth. Effect of pressure on the nature of defects and structure of the graphene has been analyzed by Raman spectra. Effect of pressure on morphology has also been studied. It has been observed that the variation of pressure is responsible for any change in the structure and morphology of the graphene for a given catalyst. Formation of graphene and its defects has been explained with the help of two-step diffusion process.

It is a common and effective method to enhance the dielectric properties of BST ceramics by adding rare-earth elements. In this paper, it is important to analyze the cause of the high dielectric constant behavior of La-doped BST ceramics. The results show that proper rare earth La dopant ($0.2\le x\le 0.7$) may greatly increase the dielectric constant of BST ceramics, and also improve the temperature stability, evidently. According to the current–voltage ($J$–$V$) characteristics, the proper La-doped BST ceramics may reach the better semiconductivity, with the decrease and increase in La doping, the ceramics are insulators. By using the Schottky barrier model and electric microstructure model to find the surface or grain boundary potential barrier height, the width of the depletion layer and grain size do play an important role in impacting the dielectric constant.

The CH₃NH₃PbI₃ films were synthesized by a facile low-cost solution process and were used to fabricate photoconductive detectors. The perovskite photodetector is very sensitive to light, with a high responsivity of 5.51mA/W and a sensitivity of 50 at 5V under 350nm light illumination. The device exhibits the fast rise and decay processes with similar appearance, and the relaxation time constants are 270 and 300ms, respectively. The photo-current shows an evident saturation, without further increase for prolonging the illumination period. The perovskite photodetectors display high responsive performances to short-wavelength lights. This study is expected to provide a fundamental knowledge of perovskite photodetectors with high speed and repeatability for practical applications.

We have studied the effect of thickness on the structural, microstructural, electrical and magnetic properties of Ni films electrodeposited onto $n$-Si (100) substrates. A series of Ni films have been prepared for different potentials ranging from $-$1.6V to $-$2.6V. Rutherford backscattering spectrometry (RBS), X-ray diffraction (XRD), four point probe technique, atomic force microscopy (AFM) and vibrating sample magnetometry (VSM) have been used to investigate the physical properties of elaborated Ni thin films. From the analysis of RBS spectra, we have extracted the films thickness $t$ ($t$ ranges from 83nm to 422nm). We found that the Ni thickness, $t$ (nm), linearly increases with the applied potential. The Ni thin films are polycrystalline and grow with the $〈111〉$ texture. The lattice parameter $a$ (Å) monotonously decreases with increasing thickness. However, a positive strain was noted indicating that all the samples are subjected to a tensile stress. The mean grain sizes $D$ (nm) and the strain ${\epsilon }^{hkl}$ decrease with increasing thickness. The electrical resistivity $\rho$ ($\mu \mathrm{\Omega }.$cm) increases with $t$ for $t$ less than 328nm. The diffusion at the grain boundaries may be the important factor in the electrical resistivity. From AFM images, we have shown that the Ni surface roughness decreases with increasing thickness. The coercive field $H_C$, the squareness factor $S$, the saturation field $H_S$ and the effective anisotropy constant $K_{\mathrm{\text{1eff}}}$ are investigated as a function of Ni thickness and grain sizes. The correlation between the magnetic and the structural properties is discussed.

The depth profiles of residual stresses and lattice parameters in the surface layers of shot peened duplex stainless steel at elevated temperature were investigated utilizing X-ray diffraction analysis. At each deformation depth, residual stress distributions in both ferrite and austenite were studied by X-ray diffraction stress analysis which is performed on the basis of the sin${}^2\psi$ method and the lattice parameters were explored by Rietveld method. The results reveal that difference changes of depth residual compressive stress profiles between ferrite and austenite under the same annealing condition are resulted from the diverse coefficient of thermal expansion, dislocation density, etc. for different phases in duplex stainless steel. The relaxations of depth residual stresses in austenite are more obvious than those in ferrite. The lattice parameters decrease in the surface layer with the extending of annealing time, however, they increase along the depth after annealing for 16min. The change of the depth lattice parameters can be ascribed to both thermal expansion and the relaxation of residual stress. The different changes of microstructure at elevated temperature between ferrite and austenite are discussed.

In this work, we study the hydrophobic properties of silk fabrics by deposition of plasma-polymerized (pp) hexamethyldisiloxane (HMDSO) using low-pressure plasma-enhanced chemical vapor deposition. Recently, hydrophobic properties are under active research in textile industry. The effects of coating time and power on the HMDSO-coated silk fabrics are investigated. Water contact angle of pp-HMDSO-coated silk fabric surface is measured as a function of power and coating time. Fabric surface shows an enhancement in hydrophobicity after coating. Attenuated total reflectance-Fourier transform infrared spectroscopy reveals the surface chemistry, and scanning electron microscopy shows the surface morphology of the uncoated and HMDSO-coated fabrics, respectively. In the case of uncoated fabric, water droplet absorbs swiftly, whereas in the case of HMDSO-coated fabric, water droplet remains on the fabric surface with a maximum contact angle of 140${}^{\circ }$. The HMDSO-deposited silk surface is found to be durable after detergent washing. Common stains such as ink, tea, milk, turmeric and orange juice are tested on the surface of both fabrics. In HMDSO-coated fabrics, all the stains are bedded like ball droplet. In order to study the self-cleaning property, the fabric is tilted to 45${}^{\circ }$ angle; stain droplets easily roll off from the fabric.

In the International Space Station, urine is considered something to be treated. However, urine is mainly composed of water and urea, while they have been demonstrated as an excellent hydrogen carrier for sustainable energy supply. Through the simple chemical coprecipitation and hydrothermal reaction, the needle-like NiMoO₄ crystals were synthesized with the average width around 500nm and length up to 4$\mu$m. The resulted products were thoroughly characterized by scanning electron microscopy, energy dispersive X-ray spectrometry, X-ray diffraction, Fourier-transform infrared spectroscopy and ultraviolet–visible spectrum. The needle-like NiMoO₄ crystals exhibited excellent electrocatalytic oxidation toward urea at anode in alkali solution, leading to the increased performance of hydrogen evolution reaction at cathode with the lower electrochemical potential and energy consumption required to drive the reaction. The high electrocatalysis of the needle-like NiMoO₄ crystals toward urea oxidation reveals their great potential for future application to clean the urine/urea-rich wastewater and to produce hydrogen in space station and environmental wastewater.

A facile chemical reduction method was used to synthesize ZnO nanoparticles (NPs) in ethylene glycol solvent at two different calcination temperatures. As a result of variation in the calcination temperature, ZnO NPs with two different sizes were achieved. The NPs were investigated for their structural and optical characteristics using X-ray diffraction and ultraviolet (UV)–Vis spectroscopy. The synthesized ZnO NPs exhibited a hexagonal structure with sizes of 46 and 65nm. The synthesized NPs were then used to investigate dye photocatalytic behavior of products as a tunable UV detector for different skin types. The dye degradation and decolorization of methylene blue in the presence of ZnO NP, following UV radiation as a function of time, were studied at different pH levels. The optical absorption spectra were then taken every 15min for all samples. The UV–Vis spectroscopy spectra revealed that optical absorption of solution was decreased upon UV exposure as a function of time. Photocatalytic reaction indicated that the dye degradation and decolorization rate were accelerated with the increase of pH level. Therefore, a tunable UV detector for different skin types could be engineered by varying the pH level of solution to avoid human skin burning.