Surface Review and Letters

Adhesion strength is one of the important properties that reflects the quality of a plasma electrolytic oxidation (PEO) coating. Scratch testing can be considered as an appropriate technique to evaluate the adhesion strength of PEO coatings on magnesium, titanium, and aluminum substrates. The scratch test is usually performed either under a constant or a progressively increasing normal load, where the critical load is used as a measure of adhesion strength of the coatings. In this review paper, the effect of different factors such as duration of coating processing, electrolyte composition, and processing current density, as well as different additives to the electrolyte bath, was studied on the adhesion strength of PEO coatings formed on magnesium, titanium, and aluminum substrates. It is understood that an optimum increase in process time and input energy leads to a corresponding increase in thickness of the PEO dense oxide layer and, consequently, an increase in critical load and adhesion strength. Moreover, the electrolyte composition and additives were found to affect the coating microstructure and composition and, subsequently, the coating adhesion strength.

This paper deals with the effect of yttrium doping on the structural and optical properties of zinc sulphide (ZnS) nanoparticles with nanoparticulated mesoporous. The morphology of the nanoparticles is determined by FESEM and it shows that the particles are spherical shape. HRSEM images show that particle size and agglomerated nature of the samples are augmented when doping concentration increases. Transmission electron microscope images probe the spherical shape of the nanoparticles as well as small number of inter particle mesoporous with intra-particles. The selected area electron diffraction images validate the crystalline and cubic nature of the synthesized samples. The presence of intra-particles is corroborated by XRD and FTIR spectra. X-ray diffraction’s results also confirm that the synthesized nanoparticles are crystallized in zinc blende structure. The diffuse reflectance spectra indicate that 5wt.% of yttrium-doped zinc sulphide shows higher reflectance than the undoped ZnS. Thus photoluminescence studies suggest that 5wt.% of yttrium-doped ZnS sample may be used for the development of supersensitive ultraviolet detector.

We fabricated 25 Au/$n$-GaP/Al Schottky devices and investigated the influence of high electron irradiation, which has 12MeV on the devices, at room temperature. The X-ray diffraction patterns, scanning electron microscopic images and Raman spectra of a gallium phosphide (GaP) semiconductor before and after electron irradiation have been analyzed. Furthermore, some electrical measurements of the devices were carried out through the current–voltage ($I$–$V$) and capacitance–voltage ($C$–$V$) measurements. From the $I$–$V$ characteristics, experimental ideality factor $n$ and barrier height $\mathrm{\Phi }$ values of these Schottky diodes have been determined before and after irradiation, respectively. The results have also been analyzed statically, and a gauss distribution has been obtained. The built-in potential $V_{\mathrm{\text{bi}}}$, barrier height $\mathrm{\Phi }$, Fermi level $E_F$ and donor concentration $N_d$ values have been determined from the reverse bias $C$–$V$ and $C^{-2}-V$ curves of Au/$n$-GaP/Al Schottky barrier diodes at 100kHz before and after 12MeV electron irradiation. Furthermore, we obtained the series resistance values of Au/$n$-GaP/Al Schottky barrier diodes with the help of different methods. Experimental results confirmed that the electrical characterization of the device changed with the electron irradiation.

Silicon carbon nitride (SiCN) films were prepared on silicon substrate by reactive magnetron sputtering of a sintered silicon carbide target in a mixture of argon, nitrogen and acetylene. Detailed studies including energy dispersive spectrometer, atomic force microscope, X-ray diffraction, Fourier transformed infrared spectrometry and $C$–$V$ measuring instrument were performed. The as-deposited SiCN films do not exhibit obvious crystalline phase, and the SiCN films annealed at 600${}^{\circ }$C show SiC crystal and graphite carbon. The SiCN films mainly consist of Si–N, Si–C, Si–O, C–C, C$\equiv$N, Si–H_n and N–H_n bonds, and increasing C₂H₂ flow rate promotes the formation of C–C, N–H_n and Si–N bonds. The SiCN film with low dielectric constant of 3.8 and compact structure was successfully prepared.

Polyethylene terephthalate (PET) films with thickness 40$\mu$m are irradiated with 3keV argon ion beams with different fluence ranging from $0.5\times 10^{18}$ions.cm${}^{-2}$ to $2\times 10^{18}$ions.cm${}^{-2}$ using locally designed broad ion source. The changes in the PET structure are characterized using X-ray diffraction (XRD), Fourier transform infrared (FTIR) and scanning electron microscope (SEM) techniques. The XRD patterns show that the peak intensity decreases with irradiation and the particle size decreases from 65.75 Å for the un-irradiated to 52.80 Å after irradiation. The FTIR indicates partial decrease and reduction in the intensity of the bands due to the degradation of the polymer after ion irradiation. The optical energy band gap decreases from 3.14eV to 3.05eV and the number of carbon cluster increases from 119 to 126 after ion irradiation. The results show a slight increase in the electrical conductivities and the dielectric constant ($\epsilon$). The results indicate the effectiveness of using PET films as capacitors and resistors in industrial applications.

Fretting fatigue life is traditionally estimated by experiment. The objective of this work is to introduce a special approach for estimation of axial fretting fatigue life at elevated temperatures from plain fatigue test based on the critical distance theory. The method uses Fatemi–Socie parameter as a multiaxial criterion to compute the stress multiaxiality on focus path. This method considers only elastic behavior for materials, and two characteristic diagrams are obtained from plain fatigue tests on two U-shaped and V-shaped notched specimens. The results showed reasonable agreement between the predictions by the proposed method and the experiments for ambient temperature. For elevated temperatures, the results indicated that the predicted fretting fatigue life was considerably overestimated in the low cycle fatigue (LCF) regime and underestimated in the high cycle fatigue (HCF) region with respect to experimental measurements. The reason for such discrepancy is believed to be due to the complex behavior of AL 7075-T6, which exhibits at elevated temperatures because of the problems such as aging, oxidation and reduction of strength.

Sb-doped silicon nanocrystals (Si–NCs) films were fabricated by magnetron co-sputtering combined with rapid-thermal annealing. The effects of Sb content on the structural and electrical properties of the films were studied. The dot size increased with the increasing Sb content, and could be correlated to the effect of Sb-induced crystallization. The variation in the concentration of Sb shows a significant impact on the film properties, where as doped with 0.8at.% of Sb exhibited major property improvements when compared with other films. By employing Sb-doped Si–NCs films as emitter layers, Si–NCs/monocrystalline silicon heterojunction solar cells were fabricated and the effect of the Sb doping concentration on the photovoltaic properties was studied. It is found that the doping level in the Si–NCs layer is a key factor in determining the short-circuit current density and power conversion efficiency (PCE). With an optimized doping concentration of 0.8at.% of Sb, a maximal PCE of 7.10% was obtained. This study indicates that the Sb-doped Si–NCs can be good candidates for all-silicon tandem solar cells.

We present here an ab initio study for the energetic, electronic, magnetic and optical structures of the graphene sheet with and without the adsorption of M atom (M $=$ C, N, O, F, Cl). The calculations are preformed using the full-potential linearized augmented plane wave (FP-LAPW) within the generalized gradient approximation (GGA) to describe the exchange-correlation potential. The calculations show that N prefers the bridge site, while C, O, F and Cl prefer the top site above the graphene sheet. The calculated M-graphene bond length is found to be inversely proportional to the adsorption energy. The hybridization between sp-states of the graphene sheet and M adatom is determined by the analysis of the partial and local density of states (PDOS and TDOS). In case of O and F as adsorbed atoms, graphene sheets show a wide energy band-gap and some significant magnetic moments. The optical properties of the studied sheets are performed in different radiation regions using the real and imaginary parts of the dielectric function. We think that the energetic, electronic, optical and magnetic properties of the M-graphene sheets are governed by two main factors; the number of unpaired valence electrons and the electronegativity of the M atom.

We carry out first-principles calculations based on density functional theory and non-equilibrium Green’s function to investigate the electronic transport properties of a diarylethene-based molecule sandwiched between two Au electrodes. This molecular switch can be reversed between open and close forms by using light stimulation. We analyze the switch behavior of these two forms through the current–voltage curves, transmission spectra and molecular projected self-consistent Hamiltonian. It has been found that the current of the close form is significantly larger than the open form, and there is a large and stable switch ratio in a wide bias window. This result indicates that this molecule can become one of the good candidates for optical molecular switch in the future.

The purpose of this paper is to present the corrosion behavior of the Cryorolled (CR) material and its Friction Stir Welded joints. Due to the thermal cycles of Friction Stir Welding (FSW) process, the corrosion behavior of the material gets affected. Here, the cryorolling process was carried out on AA2219 alloy and CR material was joined by FSW process using four different pin tool profiles such as cylindrical, threaded cylindrical, square and hexagonal pin. The FSW joints were analyzed by corrosion resistance with the help of potentiodynamic polarization test with 3.5% NaCl solution. From the analysis, it is found that CR AA2219 material exhibits good corrosion resistance compared to the base AA2219 material, and also a hexagonal pin profile FSW joint exhibits high corrosion resistance. Among the weld joints created by four different tools, the lowest corrosion resistance was found in the cylindrical pin tool FSW welds. Further, the corroded samples were investigated through metallurgical investigations like OM, Transmission Electron Microscopy (TEM), Energy-Dispersive X-ray Spectroscopy (EDX) and X-Ray Diffraction (XRD). It was found that the amount of dissolution of Al₂Cu precipitate was present in the weld nugget. The amount of dissolution of Al₂Cu precipitate is higher in the weld nugget produced by hexagonal pin tool. This is due to the enhancement of the corrosion resistance.

This paper reports an electrochemical route for carbonitriding 316L stainless steel in molten salts. Carbonitriding process was accomplished in molten alkaline chloride (LiCl/KCl) with the addition of KNO₂ at 480${}^{\circ }$C using a three-electrode system in which a carbon sheet was the counter electrode. The carbonitriding layer of 316L stainless steel obtained by potentiostatic electrolysis was analyzed by several physical techniques. The results showed that a compact layer with a thickness of about 7$\mu$m formed after the treatment. According to X-ray diffraction analysis, chromium nitride and carbide formed on the surface of carbonitriding layer. The microhardness of the carbonitriding layer is HV 336, as compared to HV 265 for the substrate.

A simple and sensitive Pb${}^{2+}$ sensor is developed based on label-free 17E DNAzyme and unmodified Au nanoparticles. On this basis, Pb${}^{2+}$ concentration can be judged according to the color variation of Au nanoparticles. The detection limit is 100nM and linear range is 100nM–16$\mu$M. It can serve as a measurement tool for Pb${}^{2+}$ rapid detection, which provides reference for the development of sensors in environmental monitoring and food safety.

In order to enhance the corrosion resistance of mooring chain, the composite coatings are carried out on the surface of 22MnCrNiMo steel for mooring chain by double-pulsed electrodeposition technology using centrifugal force in the rotating device. The microstructure and anti-corrosion performance of the composite coatings have been investigated experimentally. This paper mainly focuses on the experimental work to determine the structural characteristics and corrosion resistance of composite coatings in the presence of nano-SiC. The results show that the presence of nano-SiC has a significant effect on the preparation of composite coating during the process. The surface of the coating becomes compact and smooth at a moderate concentration of nano-SiC particles. Furthermore, the best corrosion resistance of the composite coatings can be obtained when the concentration of nano-SiC particles is 2.0g.L${}^{-1}$ after salt spray treatment.

Copper indium gallium selenide (CIGS) is currently most efficient thin film solar technology in use but it is faced with problems of material scarcity and toxicity. An alternative earth abundant and non-toxic materials consisting of Cu₂ZnSnS₄ (CZTS) have been investigated as a replacement for CIGS. In this work, CZTS thin films deposited by low cost co-electrodeposition, at a potential of $-$1.2V, coupled with chemical bath techniques at room temperature and then annealed under sulphur rich atmosphere were investigated. CZTS thin film quality determination was carried out using Raman spectroscopy which confirmed formation of quality CZTS film, main Raman peaks at 288cm${}^{-1}$ and 338cm${}^{-1}$ were observed. Electrical characterization was carried out using four-point probe instrument and the resistivity was in the order of $\sim 10^{-4}\mathrm{\Omega }$-cm. The optical characterization was done using UV-VIS-NIR spectrophotometer. The bandgaps of the annealed CZTS film ranged from 1.45 to 1.94eV with absorption coefficient of order $\sim 10^4$cm${}^{-1}$ in the visible and near infrared range of the solar spectrum were observed.

Sol–gel method has been employed to prepare Ni–Zn ferrite with chemical formula Ni${}_{1-x}$Zn_xFe₂O₄ where $x=$ 0, 0.1, 0.2, 0.3, 0.4 and 0.5. The structural Ni–Zn ferrite was studied via the X-ray diffractometer (XRD) pattern. X-ray analysis showed that there is a small shift in peaks towards shorter angles which increases with the concentration of zinc. Experimental values of lattice constant was varied from 8.34 of Ni ferrite to 8.397nm for Ni–Zn ferrite. The crystallite size of Ni ferrite was 83nm which is decreasing with substituted Zn to it and became 43nm at $4x=0.5$. Therefore, the superparamagnetic behavior appears with substitution of Zn to Ni ferrite. The saturation magnetization, remiensis, coersivity, magnetic moment and anisotropy constant were calculated according to hysteresis loop using the result of vibrating sample magnetometer (VSM). The effect of cation distribution appeared clearly through the saturation magnetization value which was 46.8emu/gm for nickel ferrite and increased to an optimum value (59.64emu/gm) at $x=0.3$.

Mo alloying Fe-based coating was fabricated on the surface of Q235 steel by using 6 kW fiber laser. The effects of Mo additions on the microstructure, microhardness and wear resistance of the cladding layer were studied by means of optical microscopy (OM), scanning electron microscope (SEM), X-ray diffraction (XRD), energy dispersive spectrometer (EDS), Vickers hardness tester and M-200 ring block wear tester. Research results showed that the microstructure of Mo-free cladding layer mainly consisted of matrix and eutectic structure. The matrix was martensite and retained austenite. The eutectic structure mainly consisted of M₂(B,C) and M₇(C,B)₃ type of eutectic borocarbides. With the increase of Mo content, there was no significant change in the matrix. However, the eutectic structure was transformed from M₂(B,C)- and M₇(C,B)₃-type borocarbides into M₂(B,C)-, M₇(C,B)₃- and M${}_{23}$(C,B)₆-type borocarbides. When the content of Mo is 4.0wt.%, the Mo₂C-type carbide appear on the matrix, and parts of the borocarbide networks are broken. The change of microhardness of the cladding layer was not obvious with the increase of Mo content. But the increase of Mo content increases the wear resistance of the cladding layer. The wear resistance of cladding layer with 4.0wt.% Mo is 2.4 times as much as the cladding layer which is Mo-free.