Applied Surface Science (v.325, #C)

Degradation of microcystin-LR by highly efficient AgBr/Ag3PO4/TiO2 heterojunction photocatalyst under simulated solar light irradiation by Xin Wang; Motoo Utsumi; Yingnan Yang; Dawei Li; Yingxin Zhao; Zhenya Zhang; Chuanping Feng; Norio Sugiura; Jay Jiayang Cheng (1-12).
A novel photocatalyst AgBr/Ag3PO4/TiO2 was developed by a simple facile in situ deposition method and used for degradation of mirocystin-LR. TiO2 (P25) as a cost effective chemical was used to improve the stability of AgBr/Ag3PO4 under simulated solar light irradiation. The photocatalytic activity tests for this heterojunction were conducted under simulated solar light irradiation using methyl orange as targeted pollutant. The results indicated that the optimal Ag to Ti molar ratio for the photocatalytic activity of the resulting heterojunction AgBr/Ag3PO4/TiO2 was 1.5 (named as 1.5 BrPTi), which possessed higher photocatalytic capacity than AgBr/Ag3PO4. The 1.5 BrPTi heterojunction was also more stable than AgBr/Ag3PO4 in photocatalysis. This highly efficient and relatively stable photocatalyst was further tested for degradation of the hepatotoxin microcystin-LR (MC-LR). The results suggested that MC-LR was much more easily degraded by 1.5 BrPTi than by AgBr/Ag3PO4. The quenching effects of different scavengers proved that reactive h+ and •OH played important roles for MC-LR degradation.
Keywords: Microcystin-LR; Methyl orange; AgBr/Ag3PO4; TiO2; Photocatalysis;

HfO2/GeO x N y /Ge gate stacks with sub-nanometer capacitance equivalent thickness and low interface trap density by in situ NH3 plasma pretreatment by Yan-Qiang Cao; Jun Chen; Xiao-Jie Liu; Xin Li; Zheng-Yi Cao; Yuan-Jie Ma; Di Wu; Ai-Dong Li (13-19).
The native oxides on Ge substrates can be transformed into GeO x N y by in situ NH3 plasma pretreatment. The interfacial and electrical properties of HfO2 caps gate stacks on Ge with and without ultrathin GeO x N y barrier layers have been investigated thoroughly. HfO2/GeO x N y /Ge stacking structure shows a sharp and flat interface between HfO2 and Ge substrates without recognized interfacial layer. In situ NH3 plasma pretreatment effectively improves the electrical properties such as higher accumulation capacitance, smaller frequency dispersion, and lower interface trap density (D it) than without NH3 plasma pretreatment. It is ascribed to that fact that the GeO x N y barrier layer between HfO2 and Ge substrates shows better thermal stability and suppresses the Ge outdiffusion. The 3-nm-thick HfO2 gate stacks on Ge with 60 s NH3 plasma pretreatment exhibit a capacitance equivalent thickness of 0.96 nm and a leakage current density of 1.12 mA/cm2 at +1 V gate bias with acceptable D it value of 3.42 × 1012  eV−1  cm−2. These results indicate that the surface nitridation by in situ NH3 plasma pretreatment may be a promising approach for the realization of high quality Ge-based transistor devices.
Keywords: In situ NH3 plasma; Surface nitridation; Ge-based transistor; Electrical property;

Oxidation and microstructure evolution of Al–Si coated Ni3Al based single crystal superalloy with high Mo content by Xiaolu Tu; Hui Peng; Lei Zheng; Wenyan Qi; Jian He; Hongbo Guo; Shengkai Gong (20-26).
A Si modified aluminide (Al–Si) coating was prepared on a Ni3Al based single crystal superalloy with high Mo content by high-activity pack cementation. Cyclic oxidation test at 1150 °C was carried out and the microstructure evolution of the coating was investigated. The results show that the oxidation resistance of the substrate was greatly increased by applying an Al–Si coating. During oxidation, outward diffusion of Mo was effectively blocked due to its high affinity with Si. Besides, a layered structure was formed as a result of the elements inter-diffusion. An obvious degradation of the Al–Si coating was observed after 100 h oxidation. Possible mechanisms related to the oxidation and elements inter-diffusion behaviours were also discussed.
Keywords: Superalloy; Al–Si coating; Pack cementation; Cyclic oxidation; Inter-diffusion;

Phase transition, effective mass and carrier mobility of MoS2 monolayer under tensile strain by Sheng Yu; Hao D. Xiong; Kwesi Eshun; Hui Yuan; Qiliang Li (27-32).
We report a computational study on the impact of tensile strain on MoS2 monolayer. The transition between direct and indirect bandgap structure and the transition between semiconductor and metal phases in the monolayer have been investigated with tensile strain along all direction configurations with both x-axis and y-axis components ɛ xy (ɛ x and ɛ y ). Electron effective mass and the hole effective mass are isotropic for biaxial strain ɛ xy  =  ɛ x  =  ɛ y and anisotropic for ɛ xy with ɛ x  ≠  ɛ y . The carrier effective mass behaves differently along different directions in response to the tensile strain. In addition, the impact of strain on carrier mobility has been studied by using the deformation potential theory. The electron mobility increases over 10 times with the biaxial strain: ɛ x  =  ɛ y  = 9.5%. Also, the mobility decreases monotonically with the increasing temperature as μ  ∼  T −1. These results are very important for future nanotechnology based on two-dimensional materials.
Keywords: Strain effect; Two-dimensional materials; MoS2 monolayer; Mobility enhancement; Phase transition;

Atomistic spectrometrics of local bond-electron-energy pertaining to Na and K clusters by Maolin Bo; Yan Wang; Yongli Huang; Yonghui Liu; Can Li; Chang Q. Sun (33-38).
Consistency between density functional theory calculations and photoelectron spectroscopy measurements confirmed our predications on the undercoordination-induced local bond relaxation and core level shift of Na and K clusters. It is clarified that the shorter and stronger bonds between under-coordinated atoms cause local densification and local potential well depression and shift the electron binding-energy accordingly. Numerical consistency turns out the energy levels for an isolated Na (E 2p  = 31.167 eV) and K (E 3p  = 18.034 eV) atoms and their respective bulk shifts of 2.401 eV and 2.754 eV, which is beyond the scope of conventional approaches. This strategy has also resulted in quantification of the local bond length, bond energy, binding energy density, and atomic cohesive energy associated with the undercoordinated atoms.
Keywords: Na and K nanoclusters; XPS; DFT; Binding energy; BOLS;

Enhanced nano-mechanical and wear properties of polycarbosilane derived SiC coating on silicon by Jonaki Mukherjee; Sujan Ghosh; Arnab Ghosh; Ashok Ranjan; Arvind K. Saxena; Probal K. Das; Rajat Banerjee (39-44).
Liquid Polycarbosilane derived β-SiC and α-SiC coating was deposited at three differently moderate high temperatures by CVD method on Silicon wafers. The nano-mechanical properties such as hardness, reduced Young's modulus, elastic recovery and plasticity index of the coatings were evaluated and compared at different deposition temperature. It was observed that with the increase in deposition temperature the nano-mechanical property of the coating enhances, the reason being the increase in crystallinity along with good adherence at higher temperature. Moreover the tribological properties of the coated samples show similar trends with increase in deposition temperature although it were found to be much better for the β-SiC than that of the α-SiC coated samples. All the coated samples shows brittle mode of failure during tribological testing. It was found that the 900 °C deposited film has better nano-mechanical as well as good tribological properties compared to other temperature of deposition due to better crystallinity and adherence. Thus the enhanced mechanical and tribological properties of this coating can be used as protective films on silicon for application in micrometers and other micro devices.
Keywords: Polycarbosilane; SiC; Nanoindentation; Scratch;

Highly sensitive surface enhanced Raman scattering substrates based on Ag decorated Si nanocone arrays and their application in trace dimethyl phthalate detection by Zewen Zuo; Kai Zhu; Lixin Ning; Guanglei Cui; Jun Qu; Ying Cheng; Junzhuan Wang; Yi Shi; Dongsheng Xu; Yu Xin (45-51).
Wafer-scale three-dimensional (3D) surface enhancement Raman scattering (SERS) substrates were prepared using the plasma etching and ion sputtering methods that are completely compatible with well-established silicon device technologies. The substrates are highly sensitive with excellent uniformity and reproducibility, exhibiting an enhancement factor up to 1012 with a very low relative standard deviation (RSD) around 5%. These are attributed mainly to the uniform-distributed, multiple-type high-density hot spots originating from the structural characteristics of Ag nanoparticles (NPs) decorated Si nanocone (NC) arrays. We demonstrate that the trace dimethyl phthalate (DMP) at a concentration of 10−7  M can be well detected using this SERS substrate, showing that the AgNPs-decorated SiNC arrays can serve as efficient SERS substrates for phthalate acid esters (PAEs) detection with high sensitivity.
Keywords: Surface-enhanced Raman scattering (SERS); Three-dimensional substrate; Silicon nanocone array; Hot spots; Trace detection;

The insights of synergistic effect between chromium oxides and ceria supported on Ti-PILC were studied for NO oxidation. The aim of this study was to investigate the role of chromium oxides and ceria and their synergistic effect in textural properties, redox performance and surface species over the Cr1−x Ce x /TP catalysts. These catalysts were investigated in detail by means of Brunauer–Emmertt–Teller (BET) surface area analysis, X-ray diffraction (XRD), transmission electron microscope (TEM), temperature-programmed reduction of H2 (H2-TPR), temperature-programmed desorption (NO-TPD, O2-TPD), photoluminescence spectra (PL), X-ray photoelectron spectroscopy (XPS) and in situ diffuse reflectance infrared Fourier transform spectroscopy (in situ DRIFTS). It has been found that CrO x were beneficial to adsorb and activate NO to form NO+ and then generate nitrates while ceria were inclined to activate O2 via oxygen vacancies to produce nitrates. Besides, the results of in situ DRIFTS further demonstrated that surface species were associated with not only reaction atmosphere but also reaction temperature. Hence, a possible reaction model was tentatively proposed.
Keywords: Selective catalytic oxidation; Nitric oxide removal; Synergistic effect; Surface species; In situ DRIFTS;

Structural and mechanical properties of nanocrystalline Zr co-sputtered a-C(:H) amorphous films by A. Escudeiro; N.M. Figueiredo; T. Polcar; A. Cavaleiro (64-72).
The aim of this study was to investigate the effect of Zr as alloying element to carbon films, particularly in respect to film structure and mechanical properties. The films were deposited by magnetron sputtering in reactive (Ar + CH4) and non-reactive (Ar) atmosphere with different Zr contents (from 0 to 14 at.%) in order to achieve a nanocomposite based films. With an increase of Zr content a broad peak was observed in X-ray diffraction spectra suggesting the presence of nanocrystalline (nc) ZrC phase for the coatings with Zr content higher than 4 at.%. The application of Scherrer formula yielded a grain sizes with a dimension of 1.0–2.2 nm. These results were supported by X-ray photoelectron spectroscopy showing typical charge transfer at Zr―C nanograins and carbon matrix interface. The nc-ZrC phase was also observed by transmission electron microscopy. The hardness of the coatings was approximately independent of Zr content. However, the Young modulus increased linearly. The residual stress of the coatings was strongly improved by the presence of nc-ZrC phase embedded in the a-C matrix. Finally, the incorporation of H into the matrix led to denser and harder films.
Keywords: Nanocrystalline ZrC; Amorphous carbon; XPS; ZrC/a-C(:H);

New type of organic/gold nanohybrid material: Preparation, properties and application in catalysis by Alexander G. Majouga; Elena K. Beloglazkina; Evgeniy A. Manzheliy; Dmitriy A. Denisov; Evgeniy G. Evtushenko; Konstantin I. Maslakov; Elena V. Golubina; Nikolay V. Zyk (73-78).
Microcrystals of 1,4-bis(terpyridine-4′-yl)benzene (BTB) adsorb gold nanoparticles (AuNPs) with an average size of 15 nm or 25 nm from the solution forming an organic–gold composite with ∼20 wt% of Au. The composite with 15 nm nanoparticles was characterized by thermal gravimetric analysis (TGA), transition electron microscopy (TEM), atomic force microscopy (AFM) and X-ray photoelectron spectroscopy (XPS). Gold nanoparticles are uniformly distributed on the organic surface and retain the same size and shape distribution even after heating at 600 °C which removes the organic matrix of 1,4-bis(terpyridine-4′-yl)benzene and effectively deposits nanoparticles onto solid substrate (mica). The catalytic activity of composites was demonstrated using a model reaction of the reduction of 4-nitrophenol to 4-aminophenol. The values of the apparent rate constants at 295 K, ca. 1.9 × 10−3  s−1 for the Au(15 nm)–BTB and 7.2 × 10−4  s−1 for the Au(25 nm)–BTB, obtained using UV–vis spectroscopy, are comparable to those reported for other catalytic systems based on supported Au nanoparticles. The catalytic activity is found to be size-dependent; the bigger nanoparticles show lower activity and longer reaction induction period. Au–BTB catalyst can be recovered from the reaction mixture and used again.
Keywords: Gold nanoparticles; Terpyridine; Organic supported catalyst; 4-Nitrophenol reduction;

Micro arc oxidation (MAO) is an effective method to improve the corrosion resistance of magnesium alloys. In order to reveal the influence of alloying element Ca and CaCO3 electrolyte on the formation process and chemical compositions of MAO coatings on binary Mg-1.0Ca alloy, anodic coatings after different anodizing times were prepared on binary Mg-1.0Ca alloy in a base solution containing 3 g/L sodium hydroxide and 15 g/L sodium phytate with and without addition of CaCO3. The coating formation was studied by using scanning electron microscope (SEM), energy dispersive X-ray spectroscopy (EDS) and X-ray diffraction (XRD). The results show that Mg-1.0Ca alloy is composed of two phases, the Mg phase and Mg2Ca phase. After treating for 5 s, the coating began to develop and was preferentially formed on the area nearby Mg2Ca phase, which may be resulted from the intrinsic electronegative potential of the Mg phase than that of Mg2Ca phase. Anodic coatings unevenly covered the total surface after 20 s. After 80 s, the coatings were uniformly developed on Mg-1.0Ca alloy with micro pores. During MAO process, some sodium phytate molecules are hydrolyzed into inorganic phosphate. CaCO3 has minor influence on the calcium content of the obtained MAO coatings.
Keywords: Magnesium-calcium alloys; Micro arc oxidation; Microstructure; Formation process;

Photocatalytic carbon–carbon bond formation with concurrent hydrogen evolution on the Pt/TiO2 nanotube by Jian Wang; Pengju Yang; Baoyue Cao; Jianghong Zhao; Zhenping Zhu (86-90).
The photocatalytic H2-production from water by using different aliphatic alcohols as sacrifice agent, over Pt/TiO2 nanotube, has been studied. The rate of H2-production over Pt/TiO2 showed the following trend: methanol > ethanol > i-propanol > n-propanol > sec-butanol > tert-butanol. Moreover, it was found that the aliphatic alcohols after photocatalytic reaction, including ethanol, n-propanol, i-propanol, sec-butanol and tert-butanol, were successfully coupled to corresponding dihydric alcohol such as 2,3-butanol, pinacol, 3,4-hexanediol, 3,4-dimethyl-3,4-hexanediol and 2,5-dimethyl-2,5-hexanediol. The effect of reaction condition on the C―C coupling of alcohols was also investigated, and the possible mechanism of C―C coupling depend on whether α-C radicals oxidized by hole or •OH can fast strip from the TiO2 surface.
Keywords: TiO2; Photocatalysis; Aliphatic alcohol; H2-production; C―C coupling;

Biosensing interfaces consisting of linker molecules (COOH or NH2) and charged, antifouling moieties ((―SO3− and N+(Me)3) for biosensing applications were prepared for the first time by the in situ deposition of mixtures of aryl diazonium cations on indium tin oxide (ITO) electrodes. A linker molecule is required for the attachment of biorecognition molecules (e.g., antibodies, enzymes, DNA chains, and aptamers) close to the transducer surface. The attached molecules improve the biosensing sensitivity and also provide a short response time for analyte detection. Thus, the incorporation of a linker and antifouling molecules is an important interfacial design for both affinity and enzymatic biosensors. The reductive adsorption behavior and electrochemical measurement were studied for (1) an individual compound and (2) a mixture of antifouling zwitterionic molecules together with linker molecules [combination 1: 4-sulfophenyl (SP), 4-trimethylammoniophenyl (TMAP), and 1,4-phenylenediamine (PPD); combination 2: 4-sulfophenyl (SP), 4-trimethylammoniophenyl (TMAP), and 4-aminobenzoic acid (PABA)] of aryl diazonium cations grafted onto an ITO electrode. The mixture ratios of SP:TMAP:PPD and SP:TMAP:PABA that provided the greatest resistance to non-specific protein adsorptions of bovine serum albumin labeled with fluorescein isothiocyanate (BSA–FITC) and cytochrome c labeled with rhodamine B isothiocyanate (RBITC–Cyt c) were determined by confocal laser scanning microscopy (CLSM). For the surface antifouling study, we used 2-[2-(2-methoxyethoxy) ethoxy]acetic acid (OEG) as a standard control because of its prominent antifouling properties. Surface compositions of combinations 1 and 2 were characterized using X-ray photoelectron spectroscopy (XPS). Field-emission scanning electron microscopy (FE-SEM) was used to characterize the morphology of the grafted films to confirm the even distribution between linker and antifouling molecules grafted onto the ITO surfaces. Combination 1 (SP:TMAP:PPD) with a ratio of 0.5:1.5:0.37 exhibited the best antifouling capability with respect to resisting the nonspecific adsorption of proteins.
Keywords: Biosensor; Indium tin oxide; Anti-biofouling coating; Zwitterionic molecules;

Averaged over wavelength range from 500 to 1600 nm at normal incidence, the reflection losses of silicon wafer as master mold are reduced from original 35% to only 0.2% after integrating surface moth-eye structures, and glass slide suppresses the reflection from 7.5% to near 0.4% after incorporating polymer-based moth eyes on double side by replica molding that enables transferring moth eyes from master mold of silicon onto any substrate. An outstanding anti-reflective property out to large incident angles is realized with the average reflection below 0.5% until 50°, below 2.5% at 60° and below 7.5% at 70°, which holds promise for solar cell application.
Keywords: Antireflection; Moth-eye; Replica molding; Broadband; Quasi-omnidirection; Solar cell;

VUV treatment combined with mechanical strain of stretchable polymer foils resulting in cell alignment by R.-A. Barb; B. Magnus; S. Innerbichler; T. Greunz; M. Wiesbauer; R. Marksteiner; D. Stifter; J. Heitz (105-111).
Cell-alignment along a defined direction can have a direct effect on the cell functionality and differentiation. Oriented micro- or nanotopographic structures on cell culture substrates can induce cell-alignment. Surface chemistry, wettability, and stiffness of the substrate are also important material features as they strongly influence the cell–substrate interactions. For improved bio-compatibility, highly elastic polyurethane (PU) foils were exposed to the vacuum-UV (VUV) light of a Xe2 * excimer lamp at 172 nm in a nitrogen containing atmosphere (N2 or NH3). The irradiation resulted in a change in the chemical surface composition. Additionally, the formation of regular parallel microgrooves was observed on the irradiated surfaces after strong uni-axial deformation (i.e., more than about 50% strain) of the photo-modified PU foils. Cell seeding experiments demonstrated that the VUV modified polymer foils strongly enhance cell adhesion and proliferation. Cells seeded onto microgrooves aligned their shapes and elongated in the direction of the grooves. A similar effect was observed for cells seeded on photo-modified PU foils subjected to cyclic mechanical stretching at lower strain levels (i.e., typically 10% strain) without groove-formation. The cells had also here an elongated shape, however they not always align in a defined direction relative to the stretching.
Keywords: Vacuum-UV irradiation; Biocompatible polymer foils; Strain-induced microgrooves; Alignment of biological cells;

Effect of oxygen vacancy on enhanced photocatalytic activity of reduced ZnO nanorod arrays by Chao Wang; Di Wu; Peifang Wang; Yanhui Ao; Jun Hou; Jin Qian (112-116).
Partially reduced ZnO nanorod arrays (NRAs) were synthesized in a reducing reagent of NaBH4. The NaBH4 treatment substantially increased the density of oxygen vacancies. The ZnO NRAs with a partially reduced surface exhibited much higher photocatalytic activity. The improvement of activity was ascribed to the introducing oxygen vacancies. The increased surface oxygen vacancy decreased the surface recombination centers, and improved the charge separation efficiency, thus enhances the photocatalytic activity.Partially reduced ZnO nanorod arrays (NRAs) were synthesized in a reducing reagent of NaBH4. The NaBH4 treatment substantially increased the density of oxygen vacancies. The obtained materials were characterized by a field emission scanning electron microscopy, X-ray diffractometer, X-ray photoelectron spectroscopy and UV–vis absorption spectra. The photocatalytic activity of the resulting samples was evaluated by degradation of methylene blue (MB) under UV light irradiation. The ZnO NRAs with a partially reduced surface exhibited enhanced photocatalytic activity. The improvement was ascribed to the introducing oxygen vacancies in ZnO by NaBH4 treatment. The increased surface oxygen vacancy decreased the surface recombination centers, and improved the charge separation efficiency, thus enhances the photocatalytic activity. Furthermore, we found that moderate treatment enhanced photocatalytic activity. However, with longer time of treatment, bulk oxygen vacancies appeared, which would cause a reduced activity.
Keywords: ZnO nanorod arrays; NaBH4; Oxygen vacancies; Photocatalysis; Visible light;

ZnO/Er2O3 core–shell nanorod arrays: Synthesis, properties and growth mechanism by Jun Yang; Yongqian Wang; Tingting Jiang; Yinchang Li; Xiande Yang (117-123).
In this study, we demonstrated large-scale ZnO/Er2O3 core–shell nanorod arrays, which were successfully synthesized by a facile and simple electrodeposition method. The effect of varying the amount of Er2O3 in the range from 0.2 g to 1.0 g on morphology of ZnO nanorod arrays has been thoroughly investigated. The results indicate that the growth pattern of all the ZnO/Er2O3 shell–core nanorod arrays were along c-axis and perpendicular to the substrate as before, even more vertical. Photoluminescence measurement was carried out and the PL peaks at 382 nm, 438 nm and 462 nm were observed, which are considered to be due to free excitons and donor-bound excitons, respectively. The ZnO/Er2O3 core–shell nanorods exhibited improved optical property, which can be attributed to the enhanced donor density by the covered Er2O3. Finally, a possible growth mechanism of the ZnO nanostructures is discussed. The electrochemical deposition of ZnO/Er2O3 core–shell nanorod arrays including two stages, namely nucleation and growth process.
Keywords: ZnO nanorod arrays; Electrodeposition; Er2O3; Core–shell; Growth mechanism;

Microscopic and spectroscopic investigation of an explanted opacified intraocular lens by V. Simon; T. Radu; A. Vulpoi; C. Rosca; D. Eniu (124-131).
The investigated polymethylmethacrylate intraocular lens explanted an year after implantation presented a fine granularity consisting of ring-like grains of about 15 μm in diameter. In order to evidence the changes occurred on intraocular lens relative to morphology, elemental composition and atomic environments, microscopic and spectroscopic analyses were carried out using scanning electron microscopy (SEM), Fourier transform infrared (FTIR), energy-dispersive X-ray (EDS), and X-ray photoelectron (XPS) spectroscopies. The results revealed that the grains contain hydroxyapatite mineral phase. A protein layer covers the lens both in opacified and transparent zones. The amide II band is like in basal epithelial cells. The shape and size of the grains, and the XPS depth profiling results indicate the possibility of a cell-mediated process involving lens epithelial cells which fagocitated apoptotic epithelial cells, and in which the debris derived from cell necrosis were calcified. To the best of our knowledge, this is the first investigation on explanted intraocular lenses using XPS depth profiling in order to examine the inside of the opacifying deposits.
Keywords: Intraocular lens; Calcification; Epithelial cells; SEM; XPS depth profiling.;

Penetration treatment of plasma spray SUS316L stainless steel coatings by molten MnO–SiO2 oxides by Jin Wang; Nobuya Shinozaki; Zhensu Zeng; Nobuaki Sakoda; Naotaka Fukami (132-138).
A study of the penetration treatment of plasma sprayed SUS316L stainless steel coatings by molten MnO–SiO2 oxides with near-eutectic composition was performed. The penetration treatment was introduced at 1353 K for 5, 20, and 45 min, and the effectiveness of the penetration and the underlying mechanisms of interfacial reactions are discussed on the basis of structural observation (EPMA), high-temperature wetting measurements and further supported by a thermodynamic calculation and analysis. The results indicated that at 1353 K, the MnO–SiO2 oxides could infiltrate into the stainless steel coating within a depth of approximately 100 μm within 5 min due to the very good wettability of the stainless steel coating by molten MnO–SiO2 oxides. The oxide could further penetrate to the coating/substrate interface when the treatment was extended to 20 min. During the penetration into the coating, a reaction between the MnO–SiO2 oxides and adjacent stainless steel particles occurred, which produced MnCr2O4 crystalline particles characterized by a spinel structure. As a result, a variation of the MnO–SiO2 oxides composition was observed.
Keywords: SUS316L stainless steel coating; MnO–SiO2 oxides; MnCr2O4 spinel;

Surface porosity and pore size distribution of sensing material greatly influence performance parameters such as sensitivity, reproducibility and response time of sensors. Various approaches have been employed to generate surface porosity having varying pore size distribution. This paper presents our results on pulsed laser irradiation based surface microstructuring of sintered zinc oxide (ZnO) pellets leading to generation of enhanced surface porosity. ZnO targets have been surface treated using a frequency doubled nanosecond pulsed Nd:YAG laser at laser fluence levels ranging between 2 and 9 J/cm2. Our observations establish that laser irradiation provides an effective technique for generation of surface macro porosity in case of ZnO pellets. Also, extent of surface porosity and the mean pore size could be controlled by appropriately varying the incident laser fluence. Such laser treated ZnO surfaces with enhanced surface porosity and large size pores can serve as potential candidate for humidity sensors with high sensitivity and fast response time, particularly in high humidity range.
Keywords: ZnO; Macro porosity; Humidity sensor; Laser irradiation;

Morphologies of high-aspect-ratio silicon grooves fabricated by using femtosecond laser irradiation and selective chemical etching of hydrofluoric acid (HF) were studied. Oxygen was deeply doped into silicon under femtosecond laser irradiation in air, and then the oxygen-doped regions were removed by HF etching to form high-aspect-ratio grooves. After HF etching, periodic nano-ripples which were induced in silicon by femtosecond laser were observed on the groove sidewalls. The ripple orientation was perpendicular or parallel to the laser propagation direction (z direction), which depended on the relative direction between the laser polarization direction and the scanning direction. The formation of nano-ripples with orientations perpendicular to z direction could be attributed to the standing wave generated by the interference of the incident light and the reflected light in z direction. The formation of nano-ripples with orientations parallel to z direction could be attributed to the formation of self-organized periodic nanoplanes (bulk nanogratings) induced by femtosecond laser inside silicon. Materials in the tail portion of laser-induced oxygen doping (LIOD) regions were difficult to be etched by HF solution due to low oxygen concentration. The specimen was etched further in KOH solution to remove remaining materials in LIOD regions and all-silicon grooves were fabricated.
Keywords: Silicon groove; Chemical selective etching; Femtosecond laser; Laser microprocessing;

Fabrication of hierarchical structures for stable superhydrophobicity on metallic planar and cylindrical inner surfaces by Xiuqing Hao; Li Wang; Danhui Lv; Quandai Wang; Liang Li; Ning He; Bingheng Lu (151-159).
Recently, the construction of stable superhydrophobicity on metallic wetting surfaces has gained increasing attention due to its potential wide applications. In this paper, we propose an economic fabricating method, which not only is suitable for metallic planar surfaces, but also could be applied onto cylindrical inner surfaces. It mainly involves two steps: etching micro-concaves by a movable mask electrochemical micromachining (EMM) technique and fabricating nanopillars of ZnO by a hydrothermal method. Then the influences of surface morphology on the static and dynamic behaviors of water droplets are investigated. The energy loss during impact on the surfaces is quantified in terms of the restitution coefficient for droplets bouncing off the surfaces. For hierarchical structures with excellent superhydrophobicity (contact angle ≈180° and sliding angle ≤1°), the droplet bounces off the surface several times, superior to the droplet's response on single nanopillars (contact angle ≈165.8° and sliding angle ≈6.29°) where droplet bounces off only for limited a number of times, and even far better than the dynamics of a liquid droplet impinging on microstructures (contact angle ≈132.1° and sliding angle >90°) where droplet does not rebound and remains pinned. The highest elasticity is obtained on the hierarchical surface, where the restitution coefficient can be as large as 0.94. The fabricating method is then applied onto the cylindrical inner surface and the wetting behavior is confirmed to be consistent with the planar surface. This method, which can be generalized to any kind of solid electroconductive metal or other surfaces with different shapes, could find wide practical applications in self-cleaning surfaces, chemical industry, microfluidic devices, mechanical engineering and aviation.
Keywords: Superhydrophobic; Electrochemical micromachining; ZnO; Droplet bouncing; Cylindrical inner surface;

Enhanced corrosion protective PANI-PAA/PEI multilayer composite coatings for 316SS by spin coating technique by Junaid Ali Syed; Hongbin Lu; Shaochun Tang; Xiangkang Meng (160-169).
In the present study, polyaniline-polyacrylic acid/polyethyleneimine (PANI-PAA/PEI) composite coatings with a multilayer structure for corrosion protection of 316 stainless steels (316SS) were prepared by an alternate deposition. Spin coating combined with heating assists removal of residual water that result in a linear increase in thickness with layer number (n). The combination of PANI-PAA composite with PEI and their multilayer structure provides a synergistic enhancement of corrosion resistance properties as determined by electrochemical measurements in 3.5% NaCl solution. Importantly, the PANI-PAA/PEI coating with an optimized layer number of n  = 20 shows improved corrosion protection. The superior performance was attributed to the formation of an interfacial oxide layer as well as the multilayer structure that extend the diffusion pathway of corrosive ions.
Keywords: Polyaniline; Polyacrylic acid; Composites; Spin coating; EIS; Corrosion;

Formation and optical properties of Ge films grown on Si(1 1 1) substrates using nanocontact epitaxy by Kazuki Tanaka; Yoshiaki Nakamura; Shuto Yamasaka; Jun Kikkawa; Takenobu Sakai; Akira Sakai (170-174).
Ge thin films were epitaxially grown on Si(1 1 1) substrates using ultrathin SiO2 film technique called nanocontact epitaxy. The key to this technique was the use of high density spherical nanodots (NDs) as seed crystals for the epitaxial growth of the Ge films. The seed crystal NDs were elastically strain-relaxed without misfit dislocations so that highly crystalline Ge thin films could be formed. The Ge films were ≈140 nm in thickness and were composed of island-shaped domains with flat Ge(1 1 1) surfaces. The domains had an average size of ≈1 μm and flat surfaces with root mean square of a surface roughness of ≈3 nm. The films had a photoluminescence peak at 0.8 eV, which meant that the films were highly crystalline.
Keywords: Nanodot; Ge; Epitaxy; Si; Thin film;

Polyamide (PA) incorporated CdSe–CdS films were deposited using sorption–diffusion method. A single precursor – K2SeS2O6 was used as both sulfur and selenium source. In aqueous solution, SeS2O6 2− diffused into the polymer where it reacted with Cd2+ ions to form cadmium chalcogenide particles. Crystallinity of the composite material was analyzed via XRD and both CdSe and CdS were detected within the material at all deposition conditions of temperature and SeS2O6 2− – chalcogenization – exposure time. A complex surface speciation was obtained using XPS analysis. Formation of the protonated amide species was observed in combination with the adsorbed SO4 2− on the surface of the polymer confirming that SeS2O6 2− and its decomposition products hydrolyzed to form cadmium chalcogenides and H2SO4. A significant red shift in UV–vis spectrum was observed with the increasing chalcogenization time of PA, whereas Cd2+ solution temperature had very little effect on the apparent thickness and the optical properties of the composite materials. SEM surface analysis revealed sub-micron particles deposited on top of the PA–CdSe–CdS composite materials in continuous overlapping films, showing a possible dual crystal growth mechanism.
Keywords: Mixed cadmium chalcogenides; Polyamide; Sorption–diffusion; XRD; XPS; SEM;

Ion beam induced chemical and morphological changes in TiO2 films deposited on Si(1 1 1) surface by pulsed laser deposition by R.R. Mohanta; V.R.R. Medicherla; K.L. Mohanta; Nimai C. Nayak; S. Majumder; V. Solanki; Shikha Varma; Komal Bapna; D.M. Phase; V. Sathe (185-191).
We have investigated TiO2 films prepared by pulsed laser deposition method on Si(1 1 1) surface using X-ray diffraction (XRD), Raman Spectroscopy, X-ray Photoelectron Spectroscopy (XPS), Atomic Force Microscopy (AFM) and ion beam sputtering techniques. Our XRD data along with Raman indicated that the deposited TiO2 is in anatase phase. The binding energy position of Ti 2p also supports the anatase phase formation. AFM topography of as deposited film indicates the formation of non uniform TiO2 growth with the formation of voids on Si(1 1 1) substrate. After sputtering with argon ion beam, surface erosion occurs and voids have disappeared. The Ti 2p core level of sputtered TiO2 exhibits the formation of Ti2O3, TiO and pure Ti on the surface. High binding energy shoulder of O 1s peak becomes sharp after sputtering. Ti LMM Auger peaks become broader after sputtering but no shift in kinetic energy is observed.
Keywords: Thin films; Ion beam irradiation; X-ray Photoelectron Spectroscopy; Atomic Force Microscopy; Pulsed laser deposition;

The stress-induced martensitic transformation occurring in sputter-deposited Ni48.1Ti51.9 and Ni43.4Ti49.6Cu7 interlayers, integrated in a W-S-C/Ni–Ti(–Cu) bilayer design, was investigated by transmission electron microscopy, after these bilayers were subjected to different sliding conditions. Martensitic bands across the interlayers were formed depending on the sliding direction with their shape and distribution a function primarily of both applied normal load and grain size.The Ni48.1Ti51.9 interlayer (lateral grain size of ∼3 μm) showed well oriented and ordered martensitic bands extended through the interlayer thickness under low load (5 N). At a higher load (18 N) the growth of these bands was limited by the stabilised martensite formed as a consequence of the high compressive stress, at the interface with the substrate.The Ni43.4Ti49.6Cu7 interlayer (lateral grain size of ∼650 nm) exhibited no significant evidence of stabilised martensite under different loading conditions. The martensitic transformation was limited by the smaller grain size and most of the stress was relaxed by elastic and, to some extent, pseudo-elastic deformation of the austenitic phase. Grain boundaries were found to stop the growth of martensitic bands, thus limiting the activation of the martensitic transformation into the neighbouring grains during sliding.The grain refinement caused a change in the capability of the interlayer to relax shear and compressive stresses. Such a change was found to affect the formation of the WS2-rich tribolayer on the W-S-C sliding surface, and consequently the shear stress transmitted down throughout the bilayers thickness. Accordingly, different levels of deformation were observed on the top layer.
Keywords: Martensitic transformation; Grain boundary; Shape memory alloys; Self-lubricant; Transmission electron microscopy (TEM);

In this study we determine the optimal parameters for surface modification using the laser surface melting of powder-metallurgy processed, vanadium-rich, cold-work tool steel. A combination of steel pre-heating, laser surface melting and a subsequent heat treatment creates a hardened and morphologically modified surface of the selected high-alloy tool steel. The pre-heating of the steel prior to the laser surface melting ensures a crack- and pore-free modified surface. Using a pre-heating temperature of 350 °C, the extremely fine microstructure, which typically evolves during the laser-melting, became slightly coarser and the volume fraction of retained austenite was reduced. In the laser-melted layer the highest values of microhardness were achieved in the specimens where a subsequent heat treatment at 550 °C was applied. The performed thermodynamic calculations were able to provide a very valuable assessment of the liquidus temperature and, especially, a prediction of the chemical composition as well as the precipitation and dissolution sequence for the carbides.
Keywords: Pre-heating; Laser surface melting; Cold-work tool steel; Powder metallurgy; Cracking;

Ce0.2Co0.2Ti mixed oxide catalyst was synthesized by a facile sol–gel method and the catalytic activity was evaluated through NO oxidation. The catalyst was characterized by XRD, Raman, TEM, H2-TPR, O2-TPD and XPS. The results showed that Ce0.2Co0.2Ti exhibited high catalytic activity of NO oxidation with maximum conversion of 76% at 300 °C under the condition of 400 ppm NO, 8% O2 and 30 000 h−1 GHSV. The high activity was ascribed to the strong interaction between Ce and Co, which resulted in small particle, excellent redox and large amount of chemisorbed oxygen. These features were favorable for the high catalytic performance of NO oxidation.
Keywords: NO oxidation; Ce–Co–Ti catalyst; Interaction; Sol–gel method;

Laser-induced oxidation of titanium substrate: Analysis of the physicochemical structure of the surface and sub-surface layers by Arkadiusz J. Antończak; Łukasz Skowroński; Marek Trzcinski; Vasyl V. Kinzhybalo; Łukasz K. Łazarek; Krzysztof M. Abramski (217-226).
This paper presents the results of the analysis of the complex chemical structure of the layers made on titanium in the process of the heating of its surfaces in an atmospheric environment, by irradiating samples with a nanosecond-pulsed laser. The study was carried out for electroplated, high purity, polycrystalline titanium substrates using a Yb:glass fiber laser. All measurements were made for samples irradiated in a broad range of accumulated fluence, below the ablation threshold. It has been determined how the complex index of refraction of both the oxynitride layers and the substrate vary as a function of accumulated laser fluence. It was also shown that the top layer of the film produced on titanium, which is transparent, is not a pure TiO2 as had been supposed before. The XPS and XRD analyses confirmed the presence of nitrogen compounds and the existence of nonstoichiometric compounds. By sputtering of the sample's surface using an Ar+ ion gun, the changes in the concentration of individual elements as a function of the layer's cross-section were determined. Lastly, an analysis of the surface morphology has also been carried out, explaining why the layers crack and exfoliate from their substrate.
Keywords: Laser surface oxidation; Laser color marking; Titanium oxynitride; Fiber laser;

Single-site SBA-15 supported zirconium catalysts. Synthesis, characterization and toward cyanosilylation reaction by Wei Xu; Bo Yu; Ying Zhang; Xi Chen; Guofang Zhang; Ziwei Gao (227-234).
Ligand-modified signal-site SBA-15 supported zirconium catalysts were synthesized by SOMC method and characterized by a variety of techniques. The zirconium surface complexes show high catalytic efficiency for cyanosilylation of benzaldehyde.A successive anchoring of Zr(NMe2)4, cyclopentadiene and a O-donor ligand, 1-hydroxyethylbenzene (PEA), 1,1′-bi-2-naphthol (Binol) or 2,3-dihydroxybutanedioic acid diethyl ester (Tartrate), on dehydroxylated SBA-15 pretreated at 500 °C for 16 h (SBA-15-500) was conducted by SOMC strategy in moderate conditions. The dehydoxylation of SBA-15 was monitored by in situ Fourier transform infrared spectroscopy (in situ FT-IR). The ligand-modified SBA-15-500 supported zirconium complexes were characterized by in situ FT-IR, 13C CP MAS-NMR, X-ray photoelectron spectroscopy (XPS), inductively coupled plasma mass spectrometry (ICP-MAS) and elemental analysis in detail, verifying that the surface zirconium species are single-sited. The catalytic activity of these complexes was evaluated by cyanosilylation of benzaldehyde. The results showed that the catalytic activity is dependent strongly on the structure of surface species and the configuration of the ligands.
Keywords: Surface organometallic chemistry; SBA-15; Surface zirconium complex; Cyanosilylation;

The effects of 3 MeV proton irradiation for fluences of 3.5 × 1010  cm−2 to 3.1 × 1012  cm−2 on structure and electrical conductivity of multi-walled carbon nanotubes (MWCNTs) film were investigated. The pristine and the irradiated MWCNTs films were characterized using scanning electron microscopy (SEM), Raman spectroscopy, X-ray photoelectron spectroscopy (XPS), Fourier transform infrared spectroscopy (FTIR), elemental analysis (EA) and electron paramagnetic resonance (EPR) spectroscopy in order to investigate the effects of irradiation on their structure. Electrical conductivity of the MWCNTs films was characterized before and after irradiation. SEM analysis reveals that the proton irradiation for the high fluence (more than 3.6 × 1011  cm−2) leads to evident changes in morphology of the MWCNTs film, such as forming uneven film surface, curve, shrinkage and fragmentation of nanotubes. Based on Raman, XPS, FTIR and EA analyses, it is confirmed that the 3 MeV protons with high fluence (more than 3.6 × 1011  cm−2) can damage the structure of the MWCNTs, including increase of the disorder and the formation of functional groups. EPR spectroscopy shows that the electrons delocalized over carbon nanotubes increase with increasing irradiation fluence, implying that the MWCNTs film might be sensitive to ionizing radiation to some extent. With increasing the irradiation fluence, the electrical conductivity of the MWCNTs film decreases due to the structural and morphological damage.
Keywords: Proton irradiation; Multi-walled carbon nanotubes; Structure; Electrical conductivity;

Control over surface coverage while fabricating efficient silver nanocube (AgNC) based SERS substrates is crucial to develop an enhanced electromagnetic field. These substrates with tunable surface coverages made it possible to demonstrate the dependence of the SERS enhancement on the surface coverage and to quantify the enhancement factors (EFs) in the SERS enhancement obtained in various surface coverages of AgNC monolayers. It was found that the EFs apparently increased with the increase of nanocube surface coverage. These results indicate that electromagnetic filed (EM) enhancement is the main factor for SERS activity. In addition to the effects of surface coverage of AgNCs on the SERS enhancement, the effects of surface plasmon resonance (SPR) on SERS enhancement reveal an interesting dependence of SERS intensity on the close degree between surface plasmon resonance (SPR) and laser wavelength.
Keywords: Surface-enhanced Raman scattering; Silver nanocube; Monolayer; Surface coverage; Surface plasmon resonance;

Carbon nanofilms are directly grown on silicon substrates by plasma-enhanced hot filament chemical vapor deposition in methane environment. It is shown that the nanofilms are composed of aligned carbon nanoflakes by extensive investigation of experimental results of field emission scanning electron microscopy, micro-Raman spectroscopy and transmission electron microscopy. In comparison with the graphene-like films grown without plasmas, the carbon nanoflakes grow in an alignment mode and the growth rate of the films is increased. The effects of the plasma on the growth of the carbon nanofilms are studied. The plasma plays three main effects of (1) promoting the separation of the carbon nanoflakes from the silicon substrate, (2) accelerating the motion of hydrocarbon radicals, and (3) enhancing the deposition of hydrocarbon ions onto the substrate surface. Due to these plasma-specific effects, the carbon nanofilms can be formed from the aligned carbon nanoflakes with a high rate. These results advance our knowledge on the synthesis, properties and applications of graphene-based materials.
Keywords: Carbon nanoflakes; Chemical vapor deposition; Plasma; Polarization;

Effect of growth pressure on the characteristics of β-Ga2O3 films grown on GaAs (1 0 0) substrates by MOCVD method by Yuanpeng Chen; Hongwei Liang; Xiaochuan Xia; Rensheng shen; Yang Liu; Yingmin Luo; Guotong Du (258-261).
The β-Ga2O3 films were grown on GaAs (1 0 0) substrates by metal-organic chemical vapor deposition method. The influences of growth pressure on the surface morphology, crystal quality and electrical properties of β-Ga2O3 films were investigated using FE-SEM, XRD and leakage current measurements. It was found that the growth pressure could obviously influence the preferred orientation and growth rate of the β-Ga2O3 films prepared from 2000 Pa to 10,000 Pa. At the growth pressure of 5000 Pa, we obtained β-Ga2O3 film with relatively high resistance. According to the XRD phi-scan results, the in-plane epitaxial relationship could be confirmed as β-Ga2O3 [0 1 0]||GaAs 〈0 1 1〉 and β-Ga2O3 [0 0 1]||GaAs 〈0 1 1〉. In addition, the effect of growth pressure on the parasitic gas-phase reaction was studied to explain the changes of growth rate.
Keywords: β-Ga2O3 film; Growth pressure; Preferred orientation; MOCVD;

Corrigendum to “The poisoning effect of Na and K on Mn/TiO2 catalyst for selective catalytic reduction of NO with NH3: A comparative study” [Appl. Surf. Sci. 317 (2014) 111–116] by Rui-tang Guo; Qing-shan Wang; Wei-guo Pan; Wen-long Zhen; Qi-lin Chen; Hong-lei Ding; Ning-zhi Yang; Chen-zi Lu (262).