Surface Review and Letters

Reduced graphene oxide (RGO)/TiO₂ nanocomposite coating was synthesized using electrophoretic co-deposition (EPD) of graphene oxide and TiO₂ colloidal suspension. Direct assembly by EPD facilitated the transformation from GO to RGO and resulted in RGO/TiO2 films on Cu substrate. The prepared samples were characterized by X-ray diffraction, field emission scanning electron microscopy, Fourier transform infrared spectroscopy and Raman spectroscopy. The obtained results proved the presence of titania nanoparticles and RGO planes in the nanocomposite coatings and the reduction of GO during EPD process. Methylene blue photodegradation experiments showed that the degradation efficiency and the reduction rate of the contact angle increased in nanocomposite coatings by 12% and 15%, respectively. There is a direct correlation between the amount of RGO in the coating and the improvement of the photocatalytic activity and wettability.

Surface roughness and taper angle of an abrasive waterjet machined surface of 7075 Aluminum metal matrix composite were deliberately studied. Response surface methodology design of experiments and analysis of variance were used to design the experiments and to identify the effect of process parameters on surface roughness and taper angle. The jet traverse speed and jet pressure were the most significant process parameters which influence the surface roughness and taper angle, respectively. Increasing the pressure and jet traverse speed results in increasing the surface roughness and taper angle. At the same time, decreasing the standoff distance and jet traverse speed possibly enhances both the responses. The optimal process parameters of 1mm as standoff distance, 192MPa as water pressure and 30mmmin${}^{-1}$ as jet traverse speed were identified to obtain the minimum value of surface roughness and taper angle. Based on the optimal parameters, the confirmation test was conducted. The mathematical equation was obtained from the experimental data using regression analysis; it was observed that the error was less than 5% of the experimentally measured values.

CrCuN coatings were deposited using double target co sputtering by DC pulsed magnetron reactive sputtering. The Cu content increases from 0.7at.% to 5.5at.% with the increase of Cu target current from 0.08 to 0.24A. The influence of Cu content on preferred orientation and properties of CrCuN coatings was investigated. The results show that CrCuN coatings are mainly composed of CrN phase. Except for the coating containing 4.2at.% Cu, the other CrCuN coatings show CrN(111) preferred orientation. All the coatings have loose structure, which is chiefly responsible for unsatisfactory hardness. The oriented growth plays an important role in the change of coating hardness with Cu content.

Undoped and europium doped ZnO films were electrodeposited from precursor solution on indium tin oxide (ITO) surfaces. Undoped ZnO nanorods were successfully obtained and grown under diffusion control perpendicularly ($c$ axis) on the ITO surface. The X-ray diffraction (XRD) analysis showed a wurtzite structure with sizes of the hexagonal unit cell: $a=3.2045$Å $=b$ and $c=5.2033$Å. After insertion of Eu${}^{3+}$ into the ZnO matrix, XRD analysis shows a shift of preferential peak to lower angles (2$\theta )$ indicating that a dislocation occurs into the unit cell with modification of its parameters. The grain sizes of doped ZnO decrease with increasing Eu${}^{3+}$ rate. Scanning electron microscopy (SEM) images show a clear change of morphological structure from nanorods to a nanosheet structure. Photoluminescence tests clearly showed an improvement in emission bands and the corresponding intensities are important in Eu${}^{3+}$ doped ZnO.

This work aims at synthesis and characterization of 2,2${}^{\prime }$-dibenzimidazolyl butane as an effective corrosion inhibitor of mild steel in sulfuric acid solution. A simple and efficient method for its synthesis in described. The chemical structure and surface morphology of 2,2${}^{\prime }$-dibenzimidazolyl butane were characterized by mass spectrometry (MS), Fourier transform infrared (FTIR), Raman, ¹H, ${}^{13}$C NMR spectroscopy and transmission electron microscopy (TEM). Its thermal decomposition and its variation in mass was studied by thermogravimetric analysis (TGA) coupled with differential thermal analysis (DTA). The molecular mass of 2,2${}^{\prime }$-dibenzimidazolyl butane was determined to be at 290g/mol and its degradation was achieved at 455^∘C. Then, the corrosion inhibition efficiency of 2,2${}^{\prime }$-dibenzimidazolyl butane was studied with various concentrations in 0.5 M H₂SO₄ solution for mild steel by the potentiodynamic polarization and the electrochemical measurements. According to the results of electrochemical impedance spectroscopy, the inhibition efficiency decreased with concentration and reached its maximum (95.5%) at 100ppm. The polarization measurements showed that the prepared inhibitor acts as a cathodic type inhibitor. The mass loss tests are in accordance with the results of electrochemical measurements.

Al_xGa${}_{1-x}$N films were grown on Si/N-treated sapphire substrate by atmospheric pressure metalorganic vapor phase epitaxy (AP-MOVPE) in a home-made vertical reactor. This process can be considered as randomly in situ epitaxial lateral overgrowth (ELO) technology. The growth firstly begins by three-dimensional (3D) mode and is completed in two-dimensional (2D) growth mode as shown by real time in situ laser $(\lambda =632.8$nm$)$ reflectometry measurements and confirmed by scanning electron microscopy (SEM) images. Secondary ion mass spectroscopy (SIMS) measurements evidence Al composition pulling effect in the Al_xGa${}_{1-x}$N layer. The Si/N treatment technique is compared to conventional Al_xGa${}_{1-x}$N growth techniques. The results of high-resolution X-ray diffraction (HRXRD), photoluminescence (PL) measurements and SEM images agree well on the fact that the Si/N treatment produces Al_xGa${}_{1-x}$N layers with comparable qualities of Al_xGa${}_{1-x}$N layers grown on high temperature GaN template but with much higher qualities than Al_xGa${}_{1-x}$N layers grown on low temperature AlN nucleation layer. Moreover, the Si/N treatment technique permits the growth of high quality Al_xGa${}_{1-x}$N layers with appreciable thicknesses with respect to the others techniques.

An energy dissipation model was raised, including the influence of film properties, counterpart, contact stress and adhesion strength between film and substrate. A new plastic deformation-tendency index was introduced. The new index was more appropriate in predicting the wear behavior of a-C films than hardness and H/E. Particularly, the critical value of the new index existed for film failure in the friction test. Realizing the limitation of the model, some improvement directions of the model were also discussed in this study.

The nonalloyed steels are very cost-effective, but their usefulness in numerous applications is imbedded due to low mechanical strength. The strength of several steels can be improved by nitriding; however, nonalloyed steels are not suitable. They can be nitrided by introducing special nitriding alloys (like chromium, aluminum, etc.) during manufacturing or some interlayer deposition, but it is quite expensive. The aim of this study is to improve nitriding capability of nonalloyed steels without any additional treatment. This is done by using alloyed stainless steel active screen in active screen plasma treatment, which provides an adequate amount of chromium to form stable and hard nitrides. The processed samples are characterized by X-ray diffraction, scanning electron microscope, energy dispersive spectroscopy, pin-on-disc wear tester, hardness tester and potentiodynamic polarization test.

SU-8 is becoming increasingly important for fabrication of lab-on-a-chip devices due to its excellent chemical stability, mechanical, and optical properties. To form a complete SU-8 device, O₂ plasma-assisted thermal bonding has been used to bond SU-8 layers. O₂ plasma treatment is critical and has a significant influence on the fabrication quality of SU-8 devices. However, to the best of our knowledge, there is no work which analyzed O₂ plasma treating process for SU-8 material in depth and systematically. In this study, the influence of O₂ plasma treatment on the water contact angle and bonding strength for both un-crosslinked and crosslinked SU-8 layer was investigated in detail. The etching effect of SU-8 layer was also studied. The leakage test demonstrated that there is no gas leakage in the bonded SU-8 layer up to 0.65Mpa which indicates the practicability of the proposed SU-8 bonding method.

In this study, a surface-sensitive Auger Electron Spectroscopy (AES) was used to comprehensively characterize titanium-oxynitride coatings on metals for high efficient solar absorbers. Primary information obtained from the AES is chemical composition, but chemical state of the elements may also be estimated. Corroborative information about the coating’s structure was obtained from the estimate of Cu, Al and Ti oxidation state vs depth, also derived from the AES data. Ti/(O $+$ N) concentration ratios vs depth in TiO_XN_Y layer of the coatings on the Al and Cu substrate were also determined. Physical Vapor Deposition (PVD) was used to prepare TiO_XN_Y multilayered on Al and Cu substrates. Individual layer’s depth was in submicron domain. Deposition procedure and corresponding deposition parameters are presented. Optical properties (emittance, absorptance) of the coatings on both substrate types were also measured to confirm that coatings performed well their intended function (i.e. spectral selectivity).

The effects of underwater friction stir welding (UFSW) on mechanical properties, strain hardening behavior, and formability of dissimilar materials of AA5052-O and AA6061-T6 welded joints were investigated. The mechanical properties of the UFSW joints exhibited higher strength and higher joint efficiency than the conventional friction stir welded joints (CFSW). The maximum joint efficiency of 73% has been attained for UFSW joints, which is due to the effect of welding atmosphere. The hardness of the stir zone (SZ) and heat affected zone (HAZ) are also obtained higher for the UFSW joints. Moreover, the hardening capacity, strain hardening exponent and formability of the UFSW joints were greatly improved over the CFSW joints. The improvement in mechanical properties of the UFSW joints is mainly due to faster cooling rate during welding. The microstructural characteristics revealed the formation of fine grains in the UFSW joints compared to the CFSW joints.

This study carried out to examine electrocatalytic activity of Ni–Mn–Sn alloy foams for oxygen evolution reaction (OER) in alkaline media. As the first step, Ni–Mn–Sn alloy foams were prepared of sulfate bath on copper substrate. Next, after optimization of electrodeposition condition by cyclic voltammetry (CV) test, foams were electrodeposited at different current densities 100, 120, 140 and 180mA⋅cm${}^{-2}$. Then, they were characterized by field emission scanning electron microscopy (FE-SEM) along with energy disperse x-ray spectroscopy (EDS) to investigate surface morphologies and chemical compositions. According to FE-SEM results, it was revealed that formation of foam like structures were due to the presence of dynamic hydrogen bubbles template (DHBT). To survey their structure, grazing incidence X-ray diffractometer (GIXRD) analysis was performed. The resulted diffraction pattern determined not only FCC nickel structure of foams, but also mixed phases composed. Following this, Ni–Mn–Sn alloy foams were placed in 0.1 M KOH and related CV tests were applied to measure their electrocatalytic activity for OER. This study demonstrated good electrocatalytic activity for Ni–Mn–Sn alloy foams by showing favorable oxygen evolution overpotenitals and Tafel slopes.

Raw single-walled carbon nanotubes (SWCNTs) were oxidized by using sulfuric acid and nitric acid at 3:1 ratio to produce oxygen functional groups attached to SWCNTs surfaces. Then, the oxidized SWCNTs are coated with zinc oxide and silver nanoparticles by chemical precipitation route to synthesize ZnO/Ag-SWCNTs nanocomposite material. The nanocomposite sample was analyzed via zeta potential analyzer, ultraviolet-visible (UV-Vis) spectrophotometer, field emission scanning electron microscopy (FESEM), energy dispersive X-ray spectroscopy (EDS), X-ray diffraction (XRD), and Raman spectroscopy to investigate colloidal stability, optical, morphological, and structural properties. The SWCNT properties were found to be changed after the addition of ZnO/Ag nanoparticles. Hence, the new ZnO/Ag-SWCNTs nanocomposite is a good candidate for photocatalyst applications and biological applications.

Nickel(II) phthalocyanine-tetrasulfonic acid tetrasodium salt (NiTsPc) thin films were deposited on glass substrates at different substrate temperatures ($T_s$) by chemical spray pyrolysis (CSP) technique. The substrate temperature varied from 110^∘C to 310^∘C in 50^∘C steps. The substrate surface temperature is the main parameter that determines the film morphology and properties of the thin films. The structural properties of the deposited NiTsPc thin films were investigated by X-ray diffraction (XRD) and from the obtained results, it was shown that depositing thin films using 210^∘C as $T_s$ results in higher crystallinity. Atomic force microscope (AFM) was employed to obtain the surface topography and to calculate the roughness and grain size. The smoothest thin film surface was obtained when using at 160^∘C, while the highest roughness was obtained at 310^∘C. The optical properties were investigated by ultraviolet visible (UV-Vis) spectrophotometer and fluorescence spectrophotometer. From the absorption spectra recorded in the wavelength range 190–1100nm, two absorption bands were observed, which are known as Soret and Q-band. By observing the absorption spectrum, it can be concluded that the deposited thin films at 110^∘C–310^∘C have direct energy gap. From Tauc plot relation, the energy gap ($E_g$) was calculated. The values of the energy gap were between 3.05 and 3.14eV. It was observed that different $T_s$ highly affects the structural and optical properties of the deposited thin films. The crystallinity, grain size, roughness and the optical properties were strongly affected by the different substrate temperatures.

In this study, the influences of electrolytic gas generation on the surface of aluminum as a cushioning media against cavitation bubbles were experimentally investigated. The electrolytic gas evolution was controlled by applying electric current to the metal with different polarity and current densities. The surface of the metal specimen was either polarized anodically or cathodically while simultaneously being subject to vibratory cavitation. It was revealed that the surface damage behavior was mainly dependent on the current densities applied to the metal. It was apparent that a moderate current density range of between $-1\times 10^{-3}$ and $-7.5\times 10^{-3}$ A/cm² applied cathodically can produce electrolytic gas evolution to cushion the cavitation bubbles sufficiently. However, application of a too a high current density (greater than $-1\times 10^{-3}$ A/cm${}^2)$ may lead to cathodic corrosion of Al alloys.