Surface Review and Letters

This paper describes a simple and economic approach for fabrication of surface wettability gradient on poly(butyl acrylate – methyl methacrylate) [P (BA–MMA)] and poly(butyl acrylate – methyl methacrylate – 2-hydroxyethyl methacrylate) [P (BA–MMA–HEMA)] films. The (meth)acrylate copolymer [including P (BA–MMA) and P (BA–MMA–HEMA)] films are hydrolyzed in an aqueous solution of NaOH and the transformation of surface chemical composition is achieved by hydrolysis in NaOH solution. The gradient wetting properties are generated based on different functional groups on the P (BA–MMA) and P (BA–MMA–HEMA) films. The effects of both the surface chemical and surface topography on wetting of the (meth)acrylate copolymer film are discussed. Surface chemical composition along the materials length is determined by XPS, and surface topography properties of the obtained gradient surfaces are analyzed by FESEM and AFM. Water contact angle system (WCAs) results show that the P (BA–MMA–HEMA) films provide a larger slope of the gradient wetting than P (BA–MMA). Moreover, this work demonstrates that the gradient concentration of chemical composition on the poly(meth) acrylate films is owing to the hydrolysis processes of ester group, and the hydrolysis reactions that have negligible influence on the surface morphology of the poly(meth) acrylate films coated on the glass slide. The gradient wettability surfaces may find broad applications in the field of polymer coating due to the compatibility of (meth) acrylate polymer.

Chalcogenide films can be used in thin-film solar cells due to their high photoelectric conversion efficiencies. It was difficult to identify one abnormal phase with high X-ray diffraction (XRD) intensity and preferred orientation in the samples for preparing chalcogenide films by spin-coating and co-reduction on soda-lime glass ($\mathrm{\text{Na}}{}_2\mathrm{\text{O}}\cdot \mathrm{\text{CaO}}\cdot 6{\mathrm{\text{SiO}}}_2$) substrates. The raw materials and reductant are metal chlorides and hydrazine hydrate respectively. In order to identify this phase, a series of experiments were done under different conditions. The phases of obtained products were analyzed by XRD and the size and morphology were characterized by scanning electron microscope (SEM) and atomic force microscopy (AFM). From the experimental results, first it was proved that the abnormal phase was water-soluble by water immersion experiment, then it was identified as NaCl crystal through XRD, energy dispersive spectrometer (EDS) and SEM. The cubic NaCl crystals have high crystallinity with size lengths of about 0.5–2$\mu$m and show a $<$100$>$ preferred orientation. The reaction mechanism of NaCl crystal was proposed as follows: The NaCl crystal was formed by reaction of Na₂O and HCl in a certain experimental conditions.

The present study investigates the effect of titania particles on the micro-hardness, wear resistance, corrosion resistance and friction of electroless Ni–P–TiO₂ composite coatings deposited on mild steel substrates at different annealing temperatures. The experimental results confirmed that the amount of TiO₂ particles incorporated in the coatings increases with increase in the concentration of particles in the electroless bath. In presence of TiO₂ particles, hardness, wear resistance and corrosion resistance of the coating improve significantly. At higher annealing temperature, wear resistance increases due to formation of hard Ni₃P phase and incorporation of titania particles in the coated layer. Charge transfer resistance and corrosion current density of the coatings reduce with an increase in TiO₂ particles, whereas corrosion potential increases. Microstructure changes and composition of the composite coating due to heat treatment are studied with the help of scanning electron microscopy (SEM), energy dispersive X-ray analysis (EDXA) and X-ray diffraction (XRD) analysis.

Modification of solidification structures by applying electric current has been the subject of interest in recent years. However, the exact relationships between the dendrite growth parameters and the current density are not yet clear. The dendrite tip geometry is an important growth parameter which can be characterized using the dendrite tip radius and the universal amplitude coefficient. In this paper, the dendrite tip shape was investigated in the absence and presence of an electric field using a transparent model material, i.e. the succinonitrile–acetone alloy. The results showed that both dendrite tip radius and universal amplitude coefficient increased by increasing the applied current density. The increase in the tip radius was attributed to the Joule heat produced at the solid–liquid interface which reduced the interface undercooling. The increase in the universal amplitude coefficient was postulated to be due to the changes in the distribution coefficient of the alloy system which would result in higher solute concentration in front of the solid–liquid interface. Owing to the increased universal amplitude coefficient, more prominent dendritic fins were observed at dendrites tips under electric current.

Samples of AISI 201 austenitic stainless steel were produced by plasma nitriding at 350${}^{\circ }$C, 390${}^{\circ }$C, 420${}^{\circ }$C, 450${}^{\circ }$C and 480${}^{\circ }$C for 5h. Systematic characterization of the nitrided layer was carried out in terms of micrograph observations, phase identification, chemical composition depth profiling, surface microhardness measurements and electrochemical corrosion tests. The results show that the surface hardness and the layer thickness increased with increasing temperature. XRD indicated that a single S-phase layer was formed during low temperature ($\le$420${}^{\circ }$C), while Cr₂N or CrN phase was formed besides S-phase when nitrided at 450${}^{\circ }$C and 480${}^{\circ }$C. The specimen treated at 390${}^{\circ }$C presents a much enhanced corrosion resistance compared to the untreated substrate. The corrosion resistance deteriorated for samples treated above 450${}^{\circ }$C due to the formation of chromium nitrides.

In this paper, effect of oxygen (O${}^{+}$) ion irradiation on the properties of polycrystalline cubic structure CdTe thin films has been investigated. CdTe thin films were irradiated with O${}^{+}$ ions of energy 80keV at different fluence ranging from $1\times 10^{15}$ to $5\times 10^{16}$ ion/cm² at room temperature. At $1\times 10^{15}$ ion/cm² O${}^{+}$ ions fluence, the CdTe structure was maintained while XRD peaks of cubic phase were shifted toward lower angles. At $5\times 10^{16}$ ion/cm² O${}^{+}$ ions fluence, cubic structure of CdTe thin films was transformed into hexagonal structure. In addition, electrical resistivity and optical bandgap were decreased with increasing O${}^{+}$ ion beam irradiation.

In this paper, we have electrodeposited copper on polypyrrole surface. Results show that at high applied cathodic potential ($>$$-$1.8V), copper electrodeposition occurs with difficulties. The amount of electrodeposited copper is low (1.32%) and it is limited by the low polypyrrole conductivity. At this potential, poor conductivity is caused by its insulating state. However, at an applied cathodic potential of $-$1.2V, the polypyrrole exhibits a relatively high conductivity and copper particles are electrodeposited with large amounts (12.44%) on polypyrrole/silicon system. At high applied cathodic potential, the SEM images show clearly dispersed grains of copper, but polypyrrole surface is less occupied. At an applied cathodic potential of $-$1.2V, the SEM image shows that polypyrrole surface is homogenously more occupied with copper. After copper deposition, the Cu/PPy/Si system is used to catalyze the hydrogen reaction. It was found that, once the deposited copper is present with considerable amounts, the proton reduction occurs easily. As for the polypyrrole conductivity, it was found that electrodeposited copper onto PPy/Si surface affect the total conductivity.

A silver-loaded one-dimensional (1D) vertical ZnO nanowires (NWs) array synthesized by a facile seed mediated hydrothermal-RF magnetron sputtering method has been investigated for the fabrication of a highly stable and reproducible acetylene (C₂H₂) gas sensor. Successful immobilization of silver nanoparticles (NPs) as a sensitizer on the ZnO NWs array significantly enhanced the C₂H₂ sensing properties and showed a stable sensing performance. The grown structure exhibited high response magnitude (30.8 at 1000ppm), short response time (43s) and excellent selectivity at 220${}^{\circ }$C. The enhanced performance can probably be accounted for the effect of combining the highly orientated ZnO NWs and catalytically active silver-based network. The superior sensing features toward C₂H₂ along with broad detection range (1–1000ppm), outstanding stability and excellent reproducibility indicate that the sensor is a promising candidate for practical applications.

The dense ceramic coatings based on alumina with hardness of 1100$\pm$25 HV${}_{0.3}$ and porosity of less than 1% have been prepared by multi-chamber detonation sprayer (MCDS) with a barrel length of 500mm. The intermetallic compound of type FeAl was revealed in the area of the coating that adjoins the substrate.

Bamboo charcoal (BC) accompanied silver (Ag) nanocomposite is synthesized through sol–gel method. The produced BC/Ag nanocomposite was surface modified by air and oxygen plasma treatments. Silver ions (Ag${}^{+}$) will serve to improve the antibacterial activity as well as the surface area of BC. Plasma treatment has improved the surface functional groups, crystalline intensity and antibacterial activity of the prepared nanocomposite. Scanning electron microscopy (SEM) and X-ray diffraction (XRD) studies show that Ag nanoparticles have good agreement with BC and the particle size has a mean diameter of 20–40nm. We observe the carboxyl functional groups in Fourier transform infrared spectroscopy (FTIR) after the oxygen plasma treatment. Moreover surface area and adsorption were analyzed by using the Brunauer, Emmett and Teller (BET) surface area ($S_{\mathrm{\text{BET}}}$) and UV–Vis spectroscopy.

Sintering characteristics and microwave dielectric properties of Mg₄Ta₂O₉–5wt% B₂O₃ ceramics were investigated. With the sintering temperature increasing in the range of 1100${}^{\circ }$C–1350${}^{\circ }$C, the apparent density, ${\epsilon }_r$ and $Q\cdot f$ values increased firstly and then saturated at 1250${}^{\circ }$C with excellent microwave properties: ${\epsilon }_r\sim 12.1$, $Q\cdot f\sim 77,575$GHz and ${\tau }_f\sim -40$ppm/${}^{\circ }$C. Compared to the pure MT ceramics, the B₂O₃ additives effectively decreased the sintering temperature of MT ceramics and had no detrimental effect on the properties of the MT ceramics due to the liquid phase effect.

The color of Tectona grandis wood is an attribute that favors its commercialization, however, wood color from fast-growth plantation trees is clear and lacks uniformity. The aim of this work is to characterize steamed teak wood by means of the Fourier transform infrared spectroscopy (FTIR) and $L^{\ast }{a}^{\ast }{b}^{\ast }$ color systems. Two moisture conditions (green and 50%) and two grain patterns (flat and quarter) of boards were analyzed through the application of different steaming times (0, 3, 6, 9, 12, 15 and 18h). The FTIR results showed that the bands at 1158, 1231, 1373 and 1419cm${}^{-1}$ did not show any change with steaming, whereas the bands at 1053, 1108, 1453, 1506, 1536, 1558, 1595, 1652, 1683, 1700 and 1733cm${}^{-1}$ presented a decrease in the intensity with the steaming time. The band at 1318cm${}^{-1}$ was the only one that increased. Lightness ($L^{\ast }$) was the most affected parameter, followed by yellowness ($b^{\ast }$), while redness ($a^{\ast }$) showed the smallest change. Surface color change ($\mathrm{\Delta }{E}^{\ast }$) presented the lowest value between 3h and 6h of steam-drying in the boards with flat grain, whereas for boards with quarter grain, the smallest $\mathrm{\Delta }{E}^{\ast }$ value was obtained after 18h of steaming.

Surface functional modification of NiTi electrode with noble Pt and Pd metal has been successfully carried out by simple and cost effective electro-spark deposition technique (ESD). Thin-film X-ray diffraction (TF-XRD), scanning electron microscopy (SEM), energy dispersive X-ray analysis (EDX) and cyclic voltammetry (CV) have been carried out in order to investigate the structure, morphology, chemical composition and electrochemical behavior of the modified electrode surface. The modified Pt/NiTi and Pd/NiTi electrode surface exhibit a circular splash pattern with a tiny amount of Pt ($\sim$5.30 at.% Pt) and Pd ($\sim$5.71 at.% Pd) existence. The electrochemical results demonstrate that the Pt/NiTi and Pd/NiTi electrode possess an improved electro-catalytic activities toward methanol (MeOH), ethanol (EtOH) and ethylene glycol (EG) oxidation in alkaline media in comparison with the bare NiTi electrode. In acidic environments, the Pt/NiTi electrode exhibits even much better catalytic activities than the pure Pt sheet electrode due to the bi-functional mechanism. In the same way, the electro-catalytic activity of the modified Pd/NiTi electrode is also slightly larger than that of the pure Pd sheet electrode in alkaline environment. The electro-spark surface modification approach is rapid and environmentally-benign, being attractive to widen the application of traditional surface modification technique in the field of material surface/interface design and functionalization.

Copper (Cu) nanowire arrays embedded in anodic aluminium oxide films (AAO) on aluminium substrate have been synthesized by alternating current electrochemical deposition. Two-step anodization process has been performed to get the through-hole AAO with ordered nanochannels in 0.3M oxalic acids at DC voltages 30, 40, 50 and 60V, respectively. Structural characterization of the Cu nanowires has been analyzed by scanning electron microscopy (SEM) and X-ray diffraction (or) X-ray diffractometer (XRD). Our SEM analysis has revealed that the diameters of vertically oriented Cu nanowires are 15, 25, 45 and 60nm and the length of Cu nanowires having high packing density is about 15$\mu$m. XRD measurement has indicated that polycrystalline Cu nanowires prefer growth orientation along the (111) direction. Optical measurements show that reflection of the Cu nanowires/AAO on aluminium reduces with decreasing diameter of the Cu nanowires. This effect can be associated with increased light scattering from metal nanoparticles near their localized plasmon resonance frequency depending on the size and shape of the nanoparticles.

Zinc oxide (ZnO) and aluminum (Al) doped ZnO nanostructures with and without surfactant have been successfully prepared via sol-gel route. The effect of the surfactant glyoxalic acid and various concentration of Al on the structural property of ZnO was analyzed by X-ray powder diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR). The morphology of the samples was recorded using field emission scanning electron microscopy. The uniform distribution of ZnO nanostructures with hexagonal facets is facilitated by the surfactant and the grain growth is further inhibited by the increase in concentration of Al. The ethanol (0–300ppm) sensing characteristics of the as-prepared samples were systematically investigated at room temperature. Surfactant-assisted ZnO/Al:ZnO nanostructures show higher sensitivity of 94% at room temperature than ZnO/Al:ZnO nanostructures without surfactant. Faster response at 68s and recovery at 50s is also achieved by the samples. The surfactant-assisted ZnO nanostructures exhibit sharp selective detection towards ethanol when compared to the samples without surfactant. The enhanced ethanol sensing property may be ascribed to the larger surface area which is due to uniform and smaller crystallite size of the surfactant-assisted sample.

Hydrogen cyanide (HCN) adsorption on graphene doped with 5d transition metal (TM) is investigated by the first principles based on density functional theory. It is observed that Hg atom cannot be doped into graphene due to saturated valence electron configurations of 5d¹⁰6s². Three kinds of HCN adsorption configurations are investigated, in which H, C and N in HCN are close to the adsorption site, respectively. The most stable adsorption configuration is obtained by total energy optimization. HCN adsorption can be studied by adsorption energy and electron density difference. HCN can only be physisorbed on Ir, Pt and Au-doped graphenes, while chemisorption is observed for Lu, Hf, Ta, W, Re and Os-doped graphenes. The band structure is calculated by B3LYP and Generalized gradient approximation (GGA) functionals. It is observed from B3LYP method that the conductivity of Lu, Hf, Re and Os-doped graphenes does not obviously change before and after HCN adsorption. Ta and W-doped graphenes change from semiconductor to metal after adsorption of HCN molecule. The results indicate that Ta and W-doped graphenes may be a promising sensor for detecting HCN. This study provides a useful basis for understanding of a wide variety of physical properties on graphene.

Localized strain accumulation and related defects strongly affect the performance of optoelectronic detectors. However, characterizing distribution of the localized strain and defects still challenges usability and spatial resolution of many measurements. In current study, the defects and surface strain accumulation of In${}_{\mathrm{\text{0.83}}}$Al${}_{\mathrm{\text{0.17}}}$As/In${}_{\mathrm{\text{0.83}}}$Ga${}_{\mathrm{\text{0.17}}}$As multilayer detectors are investigated using low-frequency atomic force acoustic microscope (AFAM) and Raman spectroscopy. With AFAM, the strain accumulation and defects can be easily identified and measured with spatial resolution as good as that of atomic force microscope (AFM).