Surface Review and Letters

In the present communication, by means of the frequency-dependent plane wave expansion method, we theoretically demonstrate the photonic band structures of a new type of two-dimensional (2D) annular photonic crystals (PCs) called 2D ternary superconductor PCs created by square and triangular lattices. Our idea is based on the appearance of the interfacial layer through a number of experimental works. We mainly investigate the maximization of the photonic band gap (PBG) using two types of ternary superconductor PCs. Type I in which an interfacial layer of Nb low temperature superconductor (LTSC) is encircled by cylindrical rods and a background material of two different dielectric materials. Type II is composed of cylindrical rods of Nb enclosed with an interfacial layer and a background material of the same dielectric materials used in type I. With the calculated photonic band structures, it can be found that the PBG can be significantly enlarged using the ternary structures more than the conventional (binary) structures. In addition, the different distributions of the constituent materials of the ternary structures have a distinct effect on the width of the PBGs.

Co–Sn–Co multi-layer films with various Sn-layer thicknesses have been deposited by using the electrodeposition technique. The deposition was performed at room temperature on gold coated silicon substrates. The thickness of Sn layer was kept $\sim$4.5, 2.5, 1.5 and 1$\mu$m, while the thickness of each Co layer was fixed to $\sim$0.75$\mu$m. The Sn layer was sandwiched between two Co layers. The total thickness of the films was $\sim$6, 4, 3, 2.5$\mu$m, respectively. The intended ratio of Sn was about 25 at.% while Co was about 75 at.%. The separation inside the Sn-layer has been observed at higher Sn-layer thicknesses with increasing reflow temperature. It may be due to the combined effect of thermal stress arising during cooling from elevated reflow temperatures and solidification shrinkage in the thick Sn layer due to the formation of IMC CoSn₂. However, 1$\mu$m has been found to be a critical thickness, which remains intact when sandwiched between two cobalt layers. The structure of these multi-layer films was studied as a function of temperature. It has been observed from X-ray diffraction (XRD) that the as-deposited films exhibit strong peaks belonging to elemental Co and Sn. At temperatures of 270–290^∘C, CoSn₂ begins to appear and grow at the interfaces and in the middle of Sn layer with the decrease in elemental Sn. However, sufficient amount of Co is still present in pure form as is evident by the XRD and field emission scanning electron microscopy images at all temperatures. This study confirms that only one reaction product, viz. CoSn₂, formed in as-deposited during reflow at temperatures 270–290^∘C for a fixed time of 10min, although several other stable IMCs, e.g. Co₃Sn₂, CoSn, CoSn₂, CoSn₃ exist in the Co–Sn system at 250^∘C according to phase diagram. It is not uncommon that all the thermodynamically stable IMCs do not form in the system due to kinetic reasons. Accordingly, the formation of IMCs through interfacial reaction has been discussed in this paper.

In this paper, back-propagation (BP) neural network model with 8 hidden layers and 10 neurons was utilized to estimate corrosion behaviors of Ni-TiN coatings, deposited through pulse electrodeposition. Effects of plating parameters, namely, pulse frequency, TiN concentration and current density, on Ni-TiN coatings weight losses were discussed. Results indicated that pulse frequency, TiN concentration and current density had significant effects on weight losses of Ni-TiN coatings. Maximum mean square error of BP model was 9.10%, and this verified that the BP neural network model could accurately estimate corrosion behavior of Ni-TiN coatings. The coating fabricated at pulse frequency of 500Hz, TiN particle concentration of 8g/L and current density of 4A/dm² consisted of fine grains and compact oxides, demonstrating that the coating displayed best corrosion resistance in this corrosion test. Concentrations of Ti and Ni in Ni-TiN coating prepared at pulse frequency of 500Hz, TiN particle concentration of 8g/L and current density of 4A/dm² were 18.6at.% and 55.4at.%, respectively.

Well-oriented TiO₂ nanorod (NR) arrays were fabricated directly on conductive side of F/SnO₂ substrates via hydrothermal technique. The effect of growth time on the TiO₂ NR thin film was examined. Field emission scanning electron microscope revealed that NRs exhibited a tetragonal structure with square top facets. Thickness measurements indicated that the thicknesses of the samples increased from 0.234$\mu$m to 1.544$\mu$m as the growth time was extended. The investigation of XRD indicates that the TiO₂ films are single-crystalline type of rutile. The effect of growth time on optical and electrical properties has been studied. With optimum growth time, dye sensitized solar cell (DSSC) efficiency of 1.48% could be reached using 1.544$\mu$m long TiO₂ NR arrays as electrode.

Nylon ($N$), Glass-filled nylon (GFN) composites and hybrid graphene oxide blended GFN (GO-GFN) nanocomposites plates were prepared by blending and subsequent injection molding process. Mechanical tests were conducted to study the tensile property, flexural property and hardness of nylon, GFN and GO-GFN system. The fabricated plates were subjected to abrasive wear testing in Pin-on-disc tribometer. The pin used is aluminium oxide (Al₂O₃) ceramic tool. The coefficient of friction, frictional force and loading variations were observed and studied to analyze the susceptibility of nylon, GFN and GO-GFN nanopolymer composites for abrasive wear conditions. This experimental study confirmed the enhancement in the abrasive wear resistance behavior of GO-GFN hybrid nanocomposites.

The nano-SiC/Ni–P composite coatings (nSNCCs) were fabricated on the surface of Glass substrates with the assistance of different electromagnetic fields. Then, the deposition rates of the nSNCCs were calculated by the weighing method. Morphology, chemical composition and crystal structure were characterized by SEM, EDS and X-ray diffraction (XRD), respectively. Experimental results show that the nSNCCs are all built by the accretion of spherical co-deposition product of Ni solid solution and nano-SiC particulates. Moreover, at the same plating time, the deposition rates of the nSNCCs increase with the increasing magnetic strength, and reach the peak by 17.5g/h$\cdot$m${}^{-2}$. Meanwhile, the spherical particle size and the spaces between spherical co-deposition decrease, which result in the formation of the dense layers. The addition of magnetic fields in preparation process not only promotes the deposition of the nSNCCs, but also has a great influence on the orientation of the deposited products, which is favorable for the formation of a compact and uniform composite coating.

Zinc Oxide thin films were deposited on glass substrates by sol–gel spin coating method. Zinc acetate dihydrate, 2-methoxyethanol and monoethanolamine were used as precursor, solvent and stabilizer, respectively. Zinc acetate dihydrate was used with different molar concentrations of 0.15, 0.25 and 0.5 M. Optical properties of ZnO thin films such as dielectric constants, absorption coefficient, Urbach energy and optical band gap energy were calculated by spectroscopic ellipsometry (SE) method. The effect of zinc acetate concentration on optical properties of ZnO thin films is investigated. ZnO thin film with Zn concentration of 0.25 M had the highest optical band gap. Wemple DiDomenico oscillator model was used for calculation of the energy of effective dispersion oscillator, the dispersion energy, the high frequency dielectric constant, the long wavelength refractive index and the free carrier concentration.

AlCrTiSiN coatings were deposited on YT14 cemented carbide using cathodic arc ion plating (CAIP) method. The surface and cross-section morphologies, chemical composition, phases, surface roughness, and binding energies of chemical elements of obtained coatings were analyzed using a field emission scanning electron microscopy (FESEM), energy dispersive spectroscopy (EDS), X-ray diffractometer (XRD), atomic force microscopy (AFM), X-ray photoelectron spectroscopy (XPS), respectively, and its mechanical properties were characterized using a scratch tester and nanoindentation tester. The friction-wear behaviors of AlCrTiSiN coatings at 700^∘C, 800^∘C and 900^∘C were investigated using a high temperature wear test, the distributions of chemical elements on the worn tracks were analyzed using a plane scan analysis of EDS, and the high temperature wear mechanisms were also discussed. The results show that the chemical elements are uniformly distributed on the AlCrTiSiN coating with the surface roughness of 105nm, which is composed of faced centered cubic (FCC)–(Cr, Al)N, body-centered cubic (HCP)–AlN and Si₃N₄ amorphous phases. The interfacial bonding strength, microhardness and elastic modulus of AlCrTiSiN coating is 26.15N, 25.789GPa, and 251.364GPa, respectively. The average coefficient of friction (COF) of AlCrTiSiN coatings at 600^∘C, 700^∘C and 800^∘C is 1.06, 0.73, and 0.97, respectively, of which friction performance is the best at 700^∘C. The wear mechanism of AlCrTiSiN coating at 600^∘C, 700^∘C and 800^∘C is adhesive wear $+$ fatigue wear, abrasive wear $+$ oxidation reaction, and adhesive wear $+$ fatigue wear, respectively.

The paper demonstrates four different polymer substrate microchannels are fabricated by CO₂ laser machine. The four different polymer substrates are Polymethyl-methacrylate (PMMA), Polycarbonate (PC), Polystyrene (PS) and Polyethylene Terephthalate (PET), respectively. A number of microchannels are obtained and all roughness is measured. The four different polymer substrate microchannels are processed with different processing parameters. Laser power is set from 4W to 32W and laser cutting speed is set from 5mm/s to 30mm/s. The results show the roughness of PS substrate microchannel is lower than that of other three polymer substrate microchannels at the same parameters. When laser power is below 4W, the roughness of four polymer substrates are similar. The roughness of different polymer substrate microchannels decreases with the increase of laser power. The roughness of different polymer substrate microchannels also happens to change with increase of laser cutting speed.

Metal oxide-carbon composites (MOCCs) derived from sodium alginate gels were prepared through a facile and green ionic gelation method. Various polyvalent cations (Mn${}^{2+}$, Fe${}^{3+}$, and Zn${}^{2+})$ were used to crosslink sodium alginate to produce gels, following which the gels were carbonized under nitrogen flow to yield MOCCs. X-ray diffraction, scanning electron microscopy, and Raman spectra can character the as-prepared materials’ structural and morphological characters and thermogravimetric analysis. The electrochemical behavior of the as-prepared materials was studied by applying to cyclic voltammetry, galvanostatic charge–discharge measurements, and electrochemical impedance spectroscopy in 6M KOH electrolyte. The highest specific capacitance (161F g${}^{-1}$ at 0.5A g${}^{-1})$ was obtained for the Fe oxide-doped carbon material (MOCC-Fe), which displayed a good life cycle with only a 10% capacitance decline after 2000 cycles.

We report on the influence of stirring of electrolyte (glycerol$+$ H₂O $+$ NaCl) on anodic growth of Ni-Ti-O nanopores (NPs) on nearly equiatomic NiTi alloy at different applied voltages. The results show that anodization is a diffusion-controlled process. The stirring has little influence on the NP diameter, but shortens its length. High stirring speed of electrolyte yields high Ni content in the NPs, which is promising in electrocatalysis, biosensor, supercapacitor, and other related fields.

High-entropy alloys (HEAs) have recently received significant attention in the materials science community. Some of these alloys can display a good combination of mechanical properties. The perfect dense and smooth coatings of AlFeCrNiMo HEA have been deposited by direct current magnetron sputtering method. The coatings possess single BCC crystal structure. The thickness of the coatings increases with increasing deposited time and plasma power. The coatings display excellent high hardness and Young’s modulus. The corrosion resistance of all coatings in acidic and salt media is better than that of 201 stainless steel. It is expected that the HEA coatings have very broad application prospects.

Titanium dioxide (TiO${}_2)$ nanoparticles have been synthesized by the cost effective Sol–Gel technique. Characteristics of TiO₂ nanoparticles were investigated by X-ray diffraction and Fourier Transform Infrared spectroscopy. The Eosin Y dye and dye extracted from Hibiscus tea have been successfully used in fabrication of the dye sensitized solar cell. The photovoltaic performance of the dye sensitized solar cell indicates that the short circuit photo current, open circuit voltage and efficiency of the DSSC using Eosin Y dye is 10 times more compared to the DSSC using the Hibiscus dye.

In this study, the effect of copper ion (Cu${}^{2+}$) was investigated on the film formation rate of Ti-based nanoceramic conversion layer on a ST12 type mild steel. At the first step, the film formation properties of the Ti conversion layer were characterized using DC polarization technique and FE-SEM micrographs. In the next step, concentration of Cu ion was optimized in the Ti solution bath, and finally, the rate of Ti ion (Ti${}^{4+}$) consumption in the conversion solution bath, with and without Cu ion, was detected by spectrophotometric technique using a dye-metal indicator. It was revealed that the addition of Cu ion to the Ti solution bath could increase the precipitation rate of Ti-based compounds on the mild steel substrate, leading to increment of film formation rate of the conversion layer.

BiFe${}_{1-x}$Cr_xO₃ ($x$BFCO, $x=0.01$, 0.02, 0.03, 0.04, 0.05) thin films were successfully fabricated onto Pt(111)/TiO₂/SiO₂/Si substrate via a solgel process. The correlation between microstructure and insulating, ferroelectric properties of $x$BFCO thin films are investigated. The leakage behavior for all the thin films is in accordance with the Ohmic conduction and FN Tunneling emission during low and high electric field region, respectively. Compared with the pure BFO, all the thin films with Cr${}^{3+}$ doping possess reduced leakage current density by 1–2 orders of magnitude, with the lowest value approximately 10${}^{-4}$ at 200kV/cm. Moreover, the 0.04BFCO thin film exhibits the maximum remanent polarization ($P_r$) value of 29.8$\mu$C/cm² with a great fatigue behavior, which could be ascribed to the absence of impurity phase and reduced leakage current.

Undoped and magnesium-doped zinc oxide thin films were prepared by the sol–gel method. Results from X-ray diffraction indicated that the films exhibited a hexagonal wurtzite structure and were highly oriented along the $c$-axis. The intensity of the (002) diffraction peak increased with increasing the Mg doping concentration. Also, Mg doping inhibited the growth of crystallite size which decreased from 46nm to 38nm with doping concentration. Morphological studies by atomic force microscopy (AFM) indicated the uniform thin film growth and the decreasing of grain size and surface roughness with Mg doping. Optical analysis showed that the average transmittance of all films was above 90% in the visible range and Mg doping has significantly enhanced the bandgap energy of ZnO. Two Raman modes assigned to $E_{2L}$ and $E_{2H}$ for the ZnO wurtzite structure were observed for all films. UV emission peak and three defect emission peaks in the visible region were observed by photoluminescence measurements at room temperature. The intensity ratio of UV emission to the visible emission increased with the Mg concentration. Photocurrent measurements revealed that all films presented the photoresponses with $n$-type semiconducting behavior and their generated photocurrents were reduced by Mg doping. The prepared thin films of high quality with improved properties by Mg doping could be proposed to workers in the field of optoelectronic devices for using them as a strong candidate.