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Applied Surface Science (v.258, #6)

Editorial Board (pp. ii).

Contents (pp. i-ii).

Preface (pp. 1895-1895).

Enhanced emission of Er³⁺ from alternately Er doped Si-rich Al₂O₃ multilayer film with Si nanocrystals as broadband sensitizers by Xiao Wang; Zuimin Jiang; Fei Xu; Zhongquan Ma; Run Xu; Bin Yu; Mingzhu Li; Lingling Zheng; Yongliang Fan; Jian Huang; Fang Lu (pp. 1896-1901).

► The intensity of Er³⁺ PL from the multilayer film is much higher than that of the monolayer film. ► The enhancement of Er³⁺ PL might be due to the energy transfer from Si nanocrystals to Er³⁺ ions ► A nonmonotonic temperature dependence from the Er:Si:Al₂O₃ multilayer film. ► Good perspectives for the development of Er-doped waveguide amplifiers operating at high temperature.Alternately Er doped Si-rich Al₂O₃ (Er:SRA) multilayer film, consisting of alternate Er–Si-codoped Al₂O₃ (Er:Si:Al₂O₃) and Si-doped Al₂O₃ (Si:Al₂O₃) sublayers, has been synthesized by co-sputtering from separated Er, Si, and Al₂O₃ targets. The dependence of Er³⁺ related photoluminescence (PL) properties on annealing temperatures over 700–1100°C was studied. The maximum intensity of Er³⁺ PL, about 10 times higher than that of the monolayer film, was obtained from the multilayer film annealed at 950°C. The enhancement of Er³⁺ PL intensity is attributed to the energy transfer from the silicon nanocrystals in the Si:Al₂O₃ sublayers to the neighboring Er³⁺ ions in the Er:Si:Al₂O₃ sublayers. The PL intensity exhibits a nonmonotonic temperature dependence: with increasing temperature, the integrated intensity almost remains constant from 14 to 50K, then reaches maximum at 225K, and slightly increases again at higher temperatures. Meanwhile, the PL integrated intensity at room temperature is about 30% higher than that at 14K.

Keywords: PACS; 78.20.−e; 78.55.−m; 78.67.Bf; 81.15.CdErbium doping; Silicon rich Al; ₂; O; ₃; Silicon nanocrystals

Phase transition in Ising, XY and Heisenberg magnetic films by R. Masrour; M. Hamedoun; A. Benyoussef (pp. 1902-1909).

► The phase transition and magnetic properties of diluted thin and semi-infinite film is studied. ► The reduced critical temperature of the ferromagnetic system is studied as function of the thickness of the thin film. ► The magnetic phase diagrams and the percolation threshold are obtained. ► The critical exponent n is obtained.The phase transition and magnetic properties of a ferromagnet spin- S, a disordered diluted thin and semi-infinite film with a face-centered cubic lattice are investigated using the high-temperature series expansions technique extrapolated with Padé approximants method for Heisenberg, XY and Ising models. The reduced critical temperature of the system τ_c is studied as function of the thickness of the thin film and the exchange interactions in the bulk, and within the surfaces J_b, J_s and J_⊥, respectively. It is found that τ_c increases with the exchange interactions of surface. The magnetic phase diagrams ( τ_c versus the dilution x) and the percolation threshold are obtained. The shifts of the critical temperatures T_c( l) from the bulk value ( T_c(∞)/ T_c( l)−1) can be described by a power law l−^λ, where λ=1/ υ is the inverse of the correlation length exponent.

Keywords: PACS; 75.70.Ak; 71.70.Gm; 77.80.BhPhase transition; Magnetic properties; Diluted thin film; Exchange interactions; Magnetic phase diagrams; Percolation threshold; Critical exponents

Preparation and size control of highly monodisperse vinyl functionalized silica spheres by Jianbo Yin; Tiansong Deng; Gengmin Zhang (pp. 1910-1914).

► Silica spheres functionalized by vinyl groups are prepared in a one-step reaction in aqueous solution. ► Our method guarantees a good monodispersity and reliable controllability of the silica spheres. ► The size of the silica spheres could be controlled by adjusting the reaction temperature.Vinyl functionalized silica spheres (VFSSs) are prepared by one-step reaction using the aqueous solution of organosilane. The synthetic method is effective and reproducible with one process used. The VFSSs could self-assemble into three-dimensional (3D) fcc photonic crystals. Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) observations revealed that the VFSSs were highly monodisperse and their surfaces were sufficiently smooth. The size of the VFSSs could be controlled by adjusting the reaction temperature. The sphere size reached its minimum, 394nm, around 45°C and became larger when the temperature was either elevated or lowered. The maximum sphere size, 515nm, was obtained around 15°C. This work is expected to extend to the preparation and size control of other kinds of hybrid silica spheres.

Keywords: Silica sphere; Monodisperse; Temperature; Photonic crystal

Self-healing coatings containing microcapsule by Zhao Yang; Zhang Wei; Liao Le-ping; Wang Si-jie; Li Wu-jun (pp. 1915-1918).

► The microcapsules containing epoxy resins were synthesized successfully. The size is around 100μm. ► The microcapsules basically exhibit good storage stability at temperature below 200°C. ► Cracks in coating were successfully healed when epoxy resin was released from microcapsules.Effectiveness of epoxy resin filled microcapsules was investigated for healing of cracks generated in coatings. Microcapsules were prepared by in situ polymerization of urea–formaldehyde resin to form shell over epoxy resin droplets. Characteristics of these capsules were studied by 3D measuring laser microscope, particle size analyzer, Fourier-transform infrared spectroscopy (FTIR) and differential scanning calorimeter (DSC) to investigate their surface morphology, size distribution, chemical structure and thermal stability, respectively. The results indicate that microcapsules containing epoxy resins can be synthesized successfully. The size is around 100μm. The rough outer surface of microcapsule is composed of agglomerated urea–formaldehyde nanoparticles. The size and surface morphology of microcapsule can be controlled by selecting different processing parameters. The microcapsules basically exhibit good storage stability at room temperature, and they are chemically stable before the heating temperature is up to approximately 200°C. The model system of self-healing coating consists of epoxy resin matrix, 10wt% microencapsulated healing agent, 2wt% catalyst solution. The self-healing function of this coating system is evaluated through self-healing testing of damaged and healed coated steel samples.

Keywords: Self-healing coating; Microcapsule; Epoxy resin; Healing test

Analysis of laser-generated ultrasonic force source at specimen surface and display of bulk wave in transversely isotropic plate by numerical method by Jijun Wang; Yunfei Shi; Lizhong Lu; Guidong Xu; Baiqiang Xu (pp. 1919-1923).

• A generation model of laser ultrasonic wave in transversely isotropic plate. • The full acoustic field of laser ultrasonic bulk wave in transversely isotropic plate. • The features of laser-generated ultrasound waveforms in anisotropic specimen.Taking into account the effects of thermal diffusion and optical penetration, as well as the finite width and duration of the laser source, the laser-generated ultrasonic force source at surface vicinity is presented. The full acoustic fields of laser-generated ultrasonic bulk wave are obtained and displayed in transversely isotropic plate. The features of laser-generated ultrasound bulk waves are analyzed. The features of laser-generated ultrasonic bulk wave are in good agreement with the theoretical results (the phase velocity surfaces), demonstrating the validity of this simulation. The numerical results indicate that the features of laser-generated ultrasound waveforms in anisotropic specimen, different from the case in isotropic materials, have a close relation with the propagating plane and propagation direction. This method can provide insight to the generation and propagation of laser-generated ultrasonic bulk wave in transversely isotropic material.

Keywords: PACS; 42.62−b; 43.35+d; 02.70.DhLaser ultrasound; Finite element method; Full field display; Transversely isotropic plate

Self-organization of ripples on Ti irradiated with focused ion beam by H.X. Qian; W. Zhou (pp. 1924-1928).

• Ripple is observed on Ti irradiated with focused ion beam even at normal incidence. • Ripple orientation is progressively influenced by the ion beam direction with incidence angle increasing. • The morphological evolution from the well-developed straight ripples to the curved ones is observed.30keV focused Ga⁺ ions were used to raster the metallographically polished surface of commercially pure Ti (CP Ti) at various FIB incidence angles over a wide range of doses (10¹⁶–10¹⁸ions/cm²) at room temperature. The sputtered surfaces were observed in situ using FIB imaging and later carefully characterized ex situ under scanning electron microscope (SEM) and atomic force microscope (AFM). Ripples were observed on the irradiated surfaces even at the normal FIB incidence angle. The ripple evolution is analyzed as functions of surface diffusion, surface crystallographic orientation, ion dose and incidence angle. It is found that the ripple orientation was progressively influenced by the ion beam direction with incidence angle increasing and in some cases curved ripples or fragmented rods viewed from different angles occurred at high ion doses. The morphological evolution from the well-developed straight ripples to the curved ones is never observed. The formation of ripples is attributed to the competition between the formation of ripples due to anisotropic surface diffusion and the formation of incidence-angle dependent ripples determined by Bradley–Harper (BH) model.

Keywords: PACS; 79.20.Rf; 68.35.Fx; 81.65.CfRipple; Focused ion beam; Ti; Surface diffusion

Effects of TiN coating on the corrosion of nanostructured Ti–30Ta– xZr alloys for dental implants by Won-Gi Kim; Han-Cheol Choe (pp. 1929-1934).

► Electrochemical characteristics of a titanium nitride (TiN)-coated/nanotube-formed Ti–30Ta– xZr (x=3, 7 and 15wt%) alloys for biomaterials have been researched by using the magnetic sputter and electrochemical methods. ► The interspace between the nanotubes was approximately 20, 80 and 200nm for Zr contents of 3, 7 and 15wt %, respectively. ► The corrosion resistance of the TiN-coated on the anodized Ti–30Ta– xZr alloys was higher than that of the un-treated Ti alloys, indicating a better protective effect.Electrochemical characteristics of a titanium nitride (TiN)-coated/nanotube-formed Ti–Ta–Zr alloy for biomaterials have been researched by using the magnetic sputter and electrochemical methods. Ti–30Ta– xZr ( x=3, 7 and 15wt%) alloys were prepared by arc melting and heat treated for 24h at 1000°C in an argon atmosphere and then water quenching. The formation of oxide nanotubes was achieved by anodizing a Ti–30Ta– xZr alloy in H₃PO₄ electrolytes containing small amounts of fluoride ions at room temperature. Anodization was carried out using a scanning potentiostat, and all experiments were conducted at room temperature. The microstructure and morphology of nanotube arrays were characterized by optical microscopy (OM), field emission scanning electron microscopy (FE-SEM) and X-ray diffraction (XRD). The TiN coatings were obtained by the radio-frequency (RF) magnetron sputtering technique. The depositions were performed from pure Ti targets on Ti–30Ta– xZr alloys substrates. The corrosion properties of the specimens were examined using potentiodynamic test in a 0.9% NaCl solution by using potentiostat. The microstructures of Ti–30Ta– xZr alloys were changed from an equiaxed to a needle-like structure with increasing Zr content. The interspace between the nanotubes was approximately 20, 80 and 200nm for Zr contents of 3, 7 and 15wt%, respectively. The corrosion resistance of the TiN-coated on the anodized Ti–30Ta– xZr alloys was higher than that of the untreated Ti alloys, indicating a better protective effect.

Keywords: Nanotube; TiN coating; Corrosion behaviour; Biomaterials

Morphology and photoluminescence of ultrasmall size of Ge quantum dots directly grown on Si(001) substrate by Wang Ke-Fan; Zhang Yang; Zhang Weifeng (pp. 1935-1939).

► Sub-10-nm domelike Ge QDs with uniform size were obtained directly on the Si(001) surface. ► Their density is the highest one among the Ge QDs grown directly on Si surface. ► Two metastate QDs, pyramid-to-dome and multiheaded dome, were observed due to no post-annealing. ► The QDs own a very strong non-phonon peak with a large blue shift of 0.19eV at 14K.High density and ultrasmall size of Ge quantum dots (QDs) have been achieved directly on Si(001) (2×1) reconstruction surface. Their detailed morphology was observed by atomic force microscope (AFM) and shows that small pyramids, small domes, huts, and multi-headed large domes coexist in the film grown at 400°C, while small domes and multi-headed large domes formed at 450°C. Their low temperature photoluminescence (PL) showed that a very strong non-phonon (NP) peak with a large blue shift of 0.19eV at 14K, which can be attributed to their very high areal density, 5.2×10¹¹cm⁻², and sub-10-nm mean size, 7.6±2.3nm.

Keywords: Ge quantum dots; Molecular beam epitaxy; Atomic force microscope; Photoluminescence

Research on tribological behaviors of composite Zn/ZnS coating under dry condition by Kang Jia-jie; Wang Cheng-biao; Wang Hai-dou; Xu Bin-shi; Liu Jia-jun; Li Guo-lu (pp. 1940-1943).

► The composite Zn/ZnS coating was successfully prepared by a novel combined method. ► ZnS and Zn could combine to take role of friction-reducing and wear-resisting. ► The composite Zn/ZnS coating possessed excellent tribological properties under dry sliding condition.A composite Zn/ZnS coating was prepared by a novel compound technology-combining high velocity arc spraying and low temperature ion sulfurizing in this paper. The surface and cross-section morphologies were observed by scanning electron microscopy (SEM). The X-ray diffraction (XRD) pattern for the Zn/ZnS coating implies that it mainly consists of Zn and ZnS. The nanohardness and elastic modulus were measured by a nano-indentation tester. The tribological behaviors were investigated on a ball-on-disk wear tester under dry condition. The results showed that the friction coefficient and worn depth of the composite Zn/ZnS coating were low and stable, indicating that it had excellent friction-reduction and anti-wear properties under dry condition.

Keywords: High velocity arc spraying method; Low temperature ion sulfurizing; Composite Zn/ZnS coating; Tribological behavior

Microstructure and tribological properties of WS₂/MoS₂ multilayer films by Zhu Li-na; Wang Cheng-biao; Wang Hai-dou; Xu Bin-shi; Zhuang Da-ming; Liu Jia-jun; Li Guo-lu (pp. 1944-1948).

► The WS₂/MoS₂ multilayer film has a smooth appearance. ► The WS₂/MoS₂ multilayer film has high yield strength. ► The alternating structure of WS₂ and MoS₂ layers shows an effective synergistic role. ► The WS₂/MoS₂ multilayer film has better anti-friction and wear resistance properties under both room and high temperature.In this paper, a novel method, namely, magnetron sputtering and low temperature ion sulfurizing combined technique was used to fabricate the solid lubrication WS₂/MoS₂ multilayer films. Scanning Electron Microscopy (SEM) was used to observe the surface and worn scar morphologies. X-ray diffraction (XRD) was utilized to analyze the phase structure. The nano-hardness and elastic modulus of WS₂/MoS₂ multilayer films were surveyed by the nano-indentation tester. The friction and wear test were conducted on a ball-on-disk wear tester under dry sliding condition. The results obtained showed that the WS₂/MoS₂ multilayer films exhibited a lower friction coefficient and better wear-resistance when compared with single WS₂ film and original 1045 steel.

Keywords: Magnetron sputtering; Low temperature ion sulfurizing; WS; ₂; /MoS; ₂; multilayer films; Microstructure; Tribological properties

BiOCl nanowire with hierarchical structure and its Raman features by Ye Tian; Chuan Fei Guo; Yanjun Guo; Qi Wang; Qian Liu (pp. 1949-1954).

► Synthesis the BiOCl nanowire with hierarchical structure. ► Clarify the formation mechanism of BiOCl nanowire with hierarchical structure. ► Find the new Raman band induced by surface/interface effect in the BiOCl nanowire with hierarchical structure.BiOCl is a promising V–VI–VII-compound semiconductor with excellent optical and electrical properties, and has great potential applications in photo-catalysis, photoelectric, etc. We successfully synthesize BiOCl nanowire with a hierarchical structure by combining wet etch (top-down) with liquid phase crystal growth (bottom-up) process, opening a novel method to construct ordered bismuth-based nanostructures. The morphology and lattice structures of Bi nanowires, β-Bi₂O₃ nanowires and BiOCl nanowires with the hierarchical structure are investigated by scanning electron microscope (SEM) and transition electron microscope (TEM). The formation mechanism of such ordered BiOCl hierarchical structure is considered to mainly originate from the highly preferred growth, which is governed by the lattice match between (110) facet of BiOCl and (220) or (002) facet of β-Bi₂O₃. A schematic model is also illustrated to depict the formation process of the ordered BiOCl hierarchical structure. In addition, Raman properties of the BiOCl nanowire with the hierarchical structure are investigated deeply.

Keywords: PACS; 64.70.Nd; 62.23.Kn; 68.37.Lp; 81.10.Dn; 81.07.BcBiOCl nanowire; Hierarchical nanostructures; Crystal growth; Raman properties

Oxidation of Zn in UHV environment at low temperature by Suttinart Noothongkaew; Hideki Nakajima; Anusorn Tong-on; Worawat Meevasana; Prayoon Songsiriritthigul (pp. 1955-1957).

► PES is suitable for in situ measurements of ultra thin oxide films. ► Below 110°C, thickness of ZnO increases with time first and then saturates. ► The saturated thickness appears to increase with oxidation temperature. ► The oxidation rate conforms to a two-stage logarithmic equation.Thermal oxidation of polycrystalline Zn foils at 5×10⁻⁷Torr oxygen pressure and at room temperature, 50°C, 70°C, 90°C and 110°C was studied. In situ photoemission spectroscopy using synchrotron light with photon energy of 57eV was used to monitor the formation of ZnO and to determine the thickness of the oxide overlayer. At the initial oxidation, the oxidation rate follows a two-stage logarithmic equation and later trends to saturate at a certain thickness depending on the oxidation temperature. The saturated thickness was found to increase with the oxidation temperature. The two-stage oxidation process may be governed by two kinds of space charge presumably formed in the thin oxide overlayer.

Keywords: ZnO; Oxidation of Zn; Photoemission spectroscopy; Synchrotron radiation

Solution route to SnO₂ crystals with controllable morphology by Y.Q. Guo; R.Q. Tan; Y. Li; W.J. Song (pp. 1958-1963).

► SnO₂ crystals with various morphologies were hydrothermally fabricated under mild conditions. ► Various self-assembled hierarchical structures of SnO₂ were obtained by varying the solvent and the introduction of polyethylene glycol. ► A formation mechanism of oriented attachment assisted by PEG was proposed for SnO₂ microspheres assembled by cone-like nanocrystals. ► This simple method provides an alternative approach for potential large-scale synthesis of SnO₂ nanostructures with tailored morphology.SnO₂ crystals with various morphologies were prepared by a facile hydrothermal method in the simple solution systems of SnCl₂ and SnCl₄, respectively. This process was carried out under mild conditions and required no high-temperature heat treatment. The morphological evolution with the preparation conditions was investigated. Various self-assembled hierarchical structures including microspheres assembled with nanoparticles, oriented nanocones, and flower-like, cabbage-like structures consisting of single-crystalline nanosheets were obtained by varying the solvent and the introduction of polyethylene glycol. A possible mechanism for the formation of the spherical hierarchically structures assembled by cone-like nanocrystals was proposed.

Keywords: SnO; ₂; Morphology; Hierarchical structure; Solution

Diverse nanowires activated self-scrolling of graphene nanoribbons by Dan Xia; Qingzhong Xue; Keyou Yan; Cheng Lv (pp. 1964-1970).

► A simple method of synthesizing NW/CNS core/shell composite nanostructures. ► The successful process of GN self-scrolling depends on the NW radiuses. ► The formed CNSs exhibit a tubular structure similar to that of MWCNTs. ► The long GNs self-scrolling onto NWs have potential to prevent the NWs from corrosion.Diverse nanowires (NWs) activating the self-scrolling of planar graphene (GN) nanoribbons have been studied by using molecular dynamics (MD) simulations. Once the NWs’ radiuses reach a threshold, all the seven NWs, acting as an external force, can initiate the conformational change of the GN nanoribbons, and finally form the core/shell composite NWs. Our simulation found that van der Waals (vdW) force plays an important role in the process of forming core/shell composite NWs. This preparation method of the core/shell composite NWs will open a further development of a broad new class of metal/GN core/shell composite NWs with enhanced properties. And these core/shell structures can be the building blocks of functional nanodevices with unique mechanical, electrical, or optical properties.

Keywords: Graphene nanoribbon; Nanowire; Self-scrolling; Core/shell composite nanowire; Molecular dynamics simulation

Fabrication of a graphene field effect transistor array on microchannels for ethanol sensing by Bangdao Chen; Hongzhong Liu; Xin Li; Congxiang Lu; Yucheng Ding; Bingheng Lu (pp. 1971-1975).

► Fabrication of back-gated graphene FET arrays on microchannels was investigated. ► The IDS changed immediately by more than 17% when the device was exposed to an ethanol atmosphere. ► The SU-8 microchannels served as gas flow passages that helped the ethanol vapor reach the sensitive region. ► This work provides a convenient way of constructing back-gated graphene FETs for sensing applications.A new approach to the fabrication of back-gated graphene FET (field effect transistor) arrays on microchannels was investigated. Narrow walls fabricated on a substrate with SU-8 (a negative photoresist), with top metal electrodes were pressed onto another silicon/SiO₂ substrate with predeposited graphene pieces such that the electrodes came into contact with graphene pieces and formed the source and drain contact. The SU-8 narrow walls with the top metal layer were fabricated by the conventional lift-off process. The graphene pieces were reduced chemically from graphite oxide. The I_DS changed immediately by more than 17% when the device was exposed to an ethanol atmosphere. The current recovered very well after the ethanol gas was pumped out. The SU-8 microchannels served as gas flow passages that helped the ethanol vapor reach the sensitive region of the device: the graphene channel. This work provides a convenient way of constructing back-gated graphene FETs for sensing applications. This method could potentially be scaled up for mass production.

Keywords: PACS; 81.05.Uw; 85.30.TvNarrow walls; Graphene; FET; MEMS; Sensor

Molecular structure and optical properties of PTFE-based nanocomposite polymer–metal coatings by A.V. Rahachou; A.A. Rogachev; M.A. Yarmolenko; Jiang Xiao-Hong; Liu Zhu Bo (pp. 1976-1980).

► For PTFE+Cu and PTFE+Ag coatings the molecular organization of PTFE component is similar to pure PTFE coatings. ► The filling metallic nanoclusters of Ag or Cu to PTFE matrix leads to form the well-oriented, solid and pore-free layers at the less thickness of a coating. ► The molecules of the PTFE component are off-oriented of thin PTFE+Mo coatings.The molecular organization of polytetrafluoroethylene (PTFE) thin coatings with incorporated Ag, Cu, and Mo nanoparticles that are deposited from an active gas component has been studied. Polyethylene terephtalate film coated by aluminium served as a substrate. The active gas component was produced by electron beam dispersion of original components in vacuum. The effect of metal particle size and its nature on the molecular structure of coatings have been investigated. Dichroism of thin nanocomposite coatings has been examined by polarized Fourier transform infrared spectroscopy using an attenuated total reflection unit. The morphology of the coatings has been analyzed by transmission (TEM), atomic-force (AFM), and scanning electron (SEM) microscopy. It is found that introduction of a metal (Ag or Cu) yields oriented layers at a lesser efficient thickness of a coating. The surface plasmon resonance of such structures was studied by measuring optical absorption of the coatings in the ultraviolet and visible ranges. The results show that the composite coatings containing Ag clusters are diameter less than 30nm and absorb within the short-wave range from 400 to 550nm.

Keywords: Electron beam deposition; Molecular structure; Nanocomposite coatings; Plasmon absorption

Fabrication of Zr and Zr–N surface alloying layers and hardness improvement of Ti–6Al–4V alloy by plasma surface alloying technique by Xiuyan Li; Bin Tang; Jiaorong Ye (pp. 1981-1984).

► A very thick Zr diffusing layer was formed in the surface of Ti–6Al–4V alloy substrate after Zr surface alloying by plasma surface alloying technique. ► Zr and Zr–N surface alloying layers all enhance the surface hardness of Ti–6Al–4V alloy, but Zr–N surface alloying layer results in greater improvement in hardness, up to 1370HK at the subsurface. ► Element Zr has obviously different diffusing characteristics in Ti–6Al–4V substrate for Zr and Zr–N surface alloying.Titanium alloys are very attractive materials because they have high specific strength, excellent corrosion and erosion resistance in many active environments. However, their low hardness values and poor tribological properties require improvement of their surface properties. The present study is concerned with the fabrication of Zr and Zr–N alloying layers in the surfaces of Ti–6Al–4V substrates by plasma surface alloying technique. The microstructure, chemical composition and hardness of the surface alloying layers were analyzed to understand the mechanisms of surface alloying and hardness improvement. The Zr and Zr–N surface alloying layers formed were homogeneous and compact, in which the surface alloying elements all displayed gradient distributions. The Zr and Zr–N surface alloying layers all enhanced the surface hardness of Ti–6Al–4V alloy. Zr–N surface alloying resulted in greater improvement in hardness and the maximum microhardness of (1.37±0.04)×10³HK was obtained at the subsurface, which was much higher than that of the untreated Ti–6Al–4V alloy. The Zr–N surface alloying layer consisted of an outer nitride layer and an inner diffusion zone of Zr and N, and its very high hardness owed to the formation of the nitride layer. The mechanism of hardness improvement of Zr surface alloyed Ti–6Al–4V alloy was solid solution strengthening.

Keywords: Plasma surface alloying; Ti–6Al–4V alloy; Hardness; Microstructure

First-principles study of electron transport in Si atom wires under finite bias voltage by Hiroyuki Kusaka; Nobuhiko Kobayashi (pp. 1985-1990).

Display Omitted► Ab initio calculations of quantum transport in Si atom wires at finite bias voltages. ► The Lippmann–Schwinger equation is solved in the framework of DFT. ► Three channels contribute to the transport at the bias voltage. ► The current through the vacuum region is enhanced for the single-atom wire.We have theoretically analyzed electron transport in wires consisting of one to three Si atoms at a finite bias voltage using a first-principles method. The electronic states and transport properties are calculated in the framework of density functional theory using the Lippmann–Schwinger equation in the Laue representation. We analyzed the transport properties of Si wires between metallic electrodes and elucidated the effects of metallic contacts on a Si atom wire, the characteristics of conduction channels, and their dependence on the bias voltage. The conduction channels are analyzed using eigenchannel decompositions, and it is found that the three channels contributing to the transport are almost open in the bias window under a finite bias voltage.

Keywords: Si; Nanowire; Quantum transport; Density functional theory

Synthesis and gas sensing characteristic based on metal oxide modification multi wall carbon nanotube composites by Hongzhong Liu; Hui Ma; Weiman Zhou; Weihua Liu; Zheng Jie; Xin Li (pp. 1991-1994).

► ZnO/MWCNT, SnO₂/MWCNT and TiO₂/MWCNT as electron transport interface. ► Introduction of MO nano-particles makes MWCNT showing variety morphology. ► MO/MWCNT composite are better than pure MWCNT film in electron transportation. ► The TiO₂/MWCNTs composite is superior to the others in electron transportation.A new type of gas sensing material based on metal oxide modification multi wall carbon nanotube (MO/MWCNT) composites is presented since the interface between the composites enhance the carrier density so as to improve the gas sensitivity. Three kinds of MO/MWCNT composite materials, such as ZnO/MWCNT, SnO₂/MWCNT and TiO₂/MWCNT, have been acquired in situ growth using catalytic pyrolysis method. The MO nano particles have decorated on side of MWCNTs, whereas the introduction of SnO₂ nano particles makes part of MWCNT showing two-dimensional form of carbon nano-wall structure. Among four kinds of cathode of ZnO/MWCNTs, SnO₂/MWCNTs, TiO₂/MWCNTs and pure MWCNT composite film, TiO₂/MWCNTs composite has the lowest threshold electric field required to draw current of 12μA has been found to be ∼1.2V/μm, and also TiO₂/MWCNTs composite has the highest sensitivity of 16% to ethanol. The TiO₂/MWCNTs composite is superior to the others both in vacuum electron transportation and gas sensitivity.

Keywords: PACS; 81.05.Uw; 81.07.−b; 81.15.Gh; 81.16.−cMutli wall carbon nanotube; Metal oxide; Composite materials; Gas sensitivity; Field emission property

Dynamic wettability of wood surface modified by acidic dyestuff and fixing agent by Shuangying Wei; Junyou Shi; Jiyou Gu; Di Wang; Yanhua Zhang (pp. 1995-1999).

► The contact angles θ-values decreased significantly with the extension of time. ► The initial contact angles ( θ_i) decreased with the moisture contents of veneers increasing. ► When moisture contents were same, the θ variation of rare veneers was minimal, the fixed was maximal. ► K-values of these gluing interfaces all decreased with moisture contents increasing. ► Wetting model describing dynamic wetting process was established on the basis of these variations.Acidic dyestuffs can bring brilliant colors to the wood and fixing agents can avoid the color loss. They could change the surface wettability of wood, which impact the gluing process of veneers. In condition of the higher moisture content of wood, the rare veneers, the veneers dyed by acidic dyestuffs and the dyed veneers fixed by Chitosan were glued respectively by one-component wet-curing isocyanate adhesive and the contact angles ( θ) of the different gluing interfaces were measured. The dynamic wettability of these gluing interfaces was characterized by both the contact angle θ and the spreading–penetration parameter ( K) calculated by θ. The results showed that the θ-values decreased significantly with the extension of time and the initial contact angles ( θ_i) decreased with the moisture contents of veneers increasing, but the variation of the balance contact angles ( θ_e) was reversed with θ_i. When the moisture contents of veneers were same, the variation of θ of the rare veneers was minimal and the variation of θ of the fixed veneers was maximal. The K-values of these gluing interfaces all decreased significantly with the moisture contents of veneers increasing, but the variations of K were different. The wetting model describing the dynamic wetting process was established on the basis of these variations.

Keywords: Dynamic wettability; Dyed and fixed wood; Contact angle; θ; Spreading–penetration parameter; K; Wetting model

Process optimization studies of 10-Hydroxycamptothecin (HCPT)-loaded folate-conjugated chitosan nanoparticles by SAS-ionic crosslink combination using response surface methodology (RSM) by Xiuhua Zhao; Ru Jiang; Yuangang Zu; Ying Wang; Qi Zhao; Baishi Zu; Dongmei Zhao; Meixiang Wang; Zhiqiang Sun (pp. 2000-2005).

► Preparation of HCPT nanoparticles by supercritical antisolvent (SAS) method. ► 10-Hydroxycamptothecin (HCPT)-loaded folate-conjuated chitosan nanoparticles by SAS-ionic crosslink combination method using response surface methodology (RSM). ► FA–HCPT–CSNPs used in drug carrier systems could have potential value in HCPT-sensitive tumors.10-Hydroxycamptothecin (HCPT) is a well-established topoisomerase I inhibitor of a broad spectrum of cancers. However, poor aqueous solubility, low instability, and toxicity to normal tissues have limited its clinical development. A novel HCPT-containing drug carrier system was developed to overcome these disadvantages. The response surface methodology was used to optimize the process of preparing HCPT–chitosan nanoparticles (HCPT–CSNPs) by the SAS-ionic crosslink (supercritical antisolvent SAS) combination method; the resulting HCPT–CSNPs were then conjugated with folate for specific targeting. A central composite design, composed of four independent variables, namely, chitosan concentration, TPP concentration, HCPT nanoparticle concentration, and crosslink time, was applied in the modeling process. The mean particle size and drug entrapment efficiency (DEE) of HCPT–CSNPs were chosen as response variables. The interactive effects of the four independent variables on the response variables were also studied. Nanoparticle characteristics such as morphology, DEE, and mean particle size were investigated. The optimum conditions for preparing HCPT–CSNPs were determined as follows: folate-coupled chitosan concentration 2.46mg/ml, TPP concentration 7.73mg/ml, HCPT nanoparticle concentration 0.48mg/ml, and crosslinking time 47.4min. Optimum conditions for preparing desired HCPT–CSNPs with a mean particle size of 173.5nm and entrapment efficiency of 77.3% were obtained. The resulting folate-conjugated HCPT–CSNPs (FA–HCPT–CSNPs) reveal that the amount of folate conjugation was 197.64mg/g CS. FA–HCPT–CSNPs used in drug carrier systems could have potential value in HCPT-sensitive tumors.

Keywords: 10-Hydroxycamptothecin (HCPT); Response surface method (RSM); Chitosan; Target; SAS; Ionic crosslink

Dynamics of water adsorption on TiO₂ monitored by work function spectroscopy by Ana G. Silva; Nenad Bundaleski; Augusto M.C. Moutinho; Orlando M.N.D. Teodoro (pp. 2006-2009).

► New features on water adsorption dynamics. ► Highly reduced 2×1 TiO₂ surface effects on water adsorption. ► New adsorption sites suggested.Water adsorption dynamics on two TiO₂ (110) rutile surfaces at room temperature has been investigated using the work function (WF) change as a function of time. The first surface was prepared in a standard way using sputtering/annealing cycles, whereas the second one was long term annealed at 620K in moderate vacuum conditions (the residual gas pressure of about 1×10⁻⁷mbar) and cleaned afterwards. The WF change show striking difference as compared to those obtained for highly reduced TiO₂ (110) rutile or the (2×1) reconstructed surfaces. For the first kind of surface we show that the observed adsorption dynamics can be qualitatively explained by the present understanding of the water adsorption on non-reconstructed TiO₂ (110) rutile surface according to which the bridging oxygen vacancies and Ti rows are the main adsorption sites. Although generally similar to the former results, water adsorption dynamics on the second kind of the surface has an additional feature that can be only explained by a new adsorption site, which we suggest to be due to (2×1) reconstructed regions coexisting with the non-reconstructed TiO₂ (110) surface.

Keywords: Work function; Titanium dioxide; Hydroxyls

The fabrication and photoresponse of ZnO/diamond film heterojunction diode by J. Huang; L.J. Wang; K. Tang; J.J. Zhang; Y.B. Xia; X.G. Lu (pp. 2010-2013).

► The study on the fabrication of ZnO/diamond heterojunction diode and its application for UV detectors.Boron-doped p-type freestanding diamond (FSD) films were prepared by hot filament chemical vapor deposition (HFCVD) method. The effect of B/ C ratio on the electrical properties of FSD films was investigated by Hall effect measurement system. A ZnO/diamond heterojunction diode was fabricated successfully by depositing n-type ZnO films on the p-type FSD substrate by radio-frequency (RF) magnetron sputtering method. The wavelength dependent photoresponse properties of the heterojunction diode were investigated by studying the effect of light illumination on current–voltage ( I– V) characteristics and photocurrent spectra at room temperature. The diode showed a significant discrimination between ultraviolet (UV) and the visible light under reverse bias conditions and photoresponse of the device was approximately linear related to the increasing reverse bias voltages.

Keywords: Diamond; ZnO; Heterojunction diode; Ultraviolet

A molecular dynamics simulation study on resonance frequencies comparison of tunable carbon-nanotube resonators by Jeong Won Kang; Oh Kuen Kwon (pp. 2014-2016).

► Tunable gigahertz-resonators, which is based on the application of a telescoped carbon-nanotube. ► These can be used repeatedly and operate at a single frequency or have a relatively narrow frequency range. ► The frequency bandwidth of our cantilevered type design can exceed that of the bridged type.We investigated tunable gigahertz-resonators, which is based on the application of a telescoped double-walled carbon-nanotube that can be used repeatedly and operate at a single frequency or have a relatively narrow frequency range, via classical molecular dynamics simulations of a double-walled carbon-nanotube. Two types of telescoped double-walled carbon-nanotube resonators were compared with each other; one was bridge-type and another was cantilever-type, and one side was connected to a position controller in order to achieve a telescoped carbon-nanotube. The frequency bandwidth of our cantilevered type design can exceed that of the bridged type. Our simulations showed that such a system can tune it up its resonance frequency by controlling the length of oscillating carbon-nanotube resonator.

Keywords: PACS; 61.46.+w; 66.30.Pa; 83.10.RsNanotube tuner; Nanotube resonator; Molecular dynamics

Preparation of electrochemical sensor for lead(II) based on molecularly imprinted film by Zhihua Wang; Yaxin Qin; Chu Wang; Lijun Sun; Xiaole Lu; Xiaoquan Lu (pp. 2017-2021).

► A high selective voltammetric sensor for lead(II) is prepared. ► Using schiff-base as assembling monomer of imprinted membrane is a new try. ► The stability and the life of imprinted membrane are improved by storing into lead ion solution. ► The redox process of lead ion on the imprinted electrode is controlled by surface reaction.A high selective voltammetric sensor for Pb²⁺ was introduced. The feasibility of utilizing strong interactions between Schiff bases and metal ion to prepare the molecularly imprinted polymers (MIPs) electrochemical sensor for Pb²⁺ in aqueous solutions was studied. Some parameters affecting sensor response were optimized and then a calibration curve was plotted. A dynamic linear range of 3.00×10⁻⁷ to 5.00×10⁻⁵mol/L was obtained. The redox process of Pb²⁺ on the imprinted electrode is controlled by surface reaction. The stability and the life of imprinted membrane were improved by storing into diluted Pb²⁺ ion solution. The proposed method was applied to determination of Pb²⁺ in the Yellow River.

Keywords: Schiff base; Molecularly imprinted polymer; Self-assembled; Electrochemical sensor

Molecular dynamics simulation of nano-scale interfacial friction characteristic for different tribopair systems by En-Qiang Lin; Li-Sha Niu; Hui-Ji Shi; Zheng Duan (pp. 2022-2028).

► We examine microstructural and temperature evolutions of Cu/Fe and Cu/Ag tribopairs. ► Plastic deformation, amorphization and atom mixing are observed for both tribopairs. ► For Cu/Fe, amorphous Cu recrystallizes into bcc structure on Fe surface. ► Two peak values appear in temperature profile and shift into Cu Part during sliding. ► For Cu/Ag, flatter temperature profile appears with no shift of peak value position.3D non-equilibrium molecular dynamics (NEMD) simulations using embedded atom potentials method (EAM) are performed to identify the dynamics processes of atomic-scale interfacial friction taking places in metal tribopairs. A block–block sliding simulation model for soft-to-hard (Cu/Fe) and soft-to-soft (Cu/Ag) tribopairs with is built. The microstructural evolution and temperature variation of the two tribopairs are analyzed at different sliding speeds. The results show that the average temperature of the two different tribopairs both increases rapidly during the transient sliding period. The different microstructural changes for the two tribopairs, including extensive plastic deformation, mechanical mixing and material transfer are observed when the temperature rapidly increases. The characteristics of the friction effects for the two tribopairs are also revealed by analyzing the friction force evolution as a function of time and velocity.

Keywords: Molecular dynamics; Sliding friction; Embedded atom potential; Microstructural changes; Thermal effect

A newly investigated approach for the control of tunnel resistance of nanogaps using field-emission-induced electromigration by Kazutoshi Takiya; Yusuke Tomoda; Watari Kume; Shunsuke Ueno; Takato Watanabe; Junichi Shirakashi (pp. 2029-2033).

► A newly investigated approach by field-emission-induced electromigration was reported. ► Wide range control of the tunnel resistance of the nanogaps was achieved. ► Average power during the process using a current source could be successfully suppressed.We report a newly investigated approach for the control of the tunnel resistance of nanogaps using field-emission-induced electromigration (“activation”), in order to decrease the power consumption during the process. The method is demonstrated by applying a bias current to initial nanogaps using a current source. As a result, a wide range control of the tunnel resistance of the nanogaps was achieved by performing the current-source-based activation. Furthermore, the average power could be successfully suppressed in comparison with that of the voltage-source-based activation. These results indicate that the current-source-based activation is suitable for the tuning of the tunnel resistance of nanogaps.

Keywords: Nanogap; Electromigration; Current source; Field emission current; Average power; Moving atom

Anchoring of alkyl chain molecules on oxide surface using silicon alkoxide by Ayumi Narita; Yuji Baba; Tetsuhiro Sekiguchi; Iwao Shimoyama; Norie Hirao; Tsuyoshi Yaita (pp. 2034-2037).

► Chemical bonds between octadecyl-trietoxy-silane (ODTS) molecules and sapphire surfaces are formed through silicon alkoxide. ► One Si–O bond in the molecule is perpendicular to the surface. ► ODTS SAMs are formed on the sapphire surface.Chemical states of the interfaces between octadecyl-triethoxy-silane (ODTS) molecules and sapphire surface were measured by X-ray photoelectron spectroscopy (XPS) and near edge X-ray absorption fine structure (NEXAFS) using synchrotron soft X-rays. The nearly self-assembled monolayer of ODTS was formed on the sapphire surface. For XPS and NEXAFS measurements, it was elucidated that the chemical bond between silicon alkoxide in ODTS and the surface was formed, and the alkane chain of ODTS locates upper side on the surface. As a result, it was elucidated that the silicon alkoxide is a good anchor for the immobilization of organic molecules on oxides.

Keywords: Octadecyl-triethoxy-silane; Sapphire single crystal; Synchrotron radiation; X-ray photoelectron spectroscopy; Near edge X-ray absorption fine structure

A simple method to prepare miniature quartz fiber boats with superhydrophobicity by Z.X. Jiang; X.Q. Cheng; J. Li; W.J. Qiu; S.A. Guan; W. Dong; Z.Y. Ma; Y.D. Huang (pp. 2038-2042).

► A novel quartz fiber with superhydrophobic property was prepared by the combination of rough surfaces and low surface energy material treatment. ► The quartz fiber boats can not only float freely on a water surface but also exhibit large loading capacities, and the highest loading weight, 10.19g, is achieved. ► The striking loading capacities of these boats are attributed to the air trapped around the fiber surface.According to the reformed Cassie–Baxter equation, a superhydrophobic quartz fiber bundle boat was fabricated from mimicking the lotus leaf venation using chemical surface modifications and roughness introductions. Water contact angles as high as 165.8° were achieved for quartz fiber cloths. The loading capacities of the miniature boats made from the superhydrophobic quartz fiber bundles were measured. The highest loading weight, 10.19g, was obtained by the boats with 2.0mm spacing distance between fiber bundles. The striking loading capacities were believed to stem from the air film surrounding the superhydrophobic surfaces of the boats. The results of this study presented new applications of artificial hydrophobic surfaces in areas of aquatic devices.

Keywords: Quartz fiber bundle; Miniature boat; Loading capacity; Superhydrophobic surface

Ion irradiation induced Al–Ti interaction in nano-scaled Al/Ti multilayers by M. Milosavljević; N. Stojanović; D. Peruško; B. Timotijević; D. Toprek; J. Kovač; G. Dražič; C. Jeynes (pp. 2043-2046).

► Ar ion irradiation induces chemical reaction in Al/Ti multilayers at room temperature. ► Reaction is triggered by thermal spikes and enhanced by chemical driving forces. ► The resulting structure has a graded composition of metals and intermetallics. ► The applied processing is interesting for nanoalloying of multilayered structures.Interactions induced in Al/Ti multilayers by implantation of Ar ions at room temperature were investgated. Initial structures consisted of (Al/Ti)×5 multilayers deposited by d.c. ion sputtering on Si(100) wafers, to a total thickness of ∼250nm. They were irradiated with 200keV Ar⁺ ions, to the fluences from 5×10¹⁵ to 4×10¹⁶ions/cm². It was found that ion irradiation induced a progressed intermixing of the multilayer constituents and Al–Ti nanoalloying for the highest applied fluence. The resulting nanocrystalline structure had a graded composition with non-reacted or interdiffused Al and Ti, and γ-AlTi and AlTi₃ intermetallic phases. Most intense reactivity was observed around mid depth of the multilayers, where most energy was deposited by the impact ions. It is presumed that Al–Ti chemical reaction is triggered by thermal spikes and further enhanced by chemical driving forces. The applied processing can be interesting for fabrication of tightly bond multilayered structures with gradual changes of their composition and properties.

Keywords: PACS; 61.80.−x; 61.46.−w; 61.72. WwAl/Ti multilayers; Ion irradiation; Nanoalloying; Intermetallic phases

Surface characterization of self-assembled N–Cu nanostructures by Lucila J. Cristina; Juan C. Moreno-López; Silvano J. Sferco; Mario C.G. Passeggi Jr.; Ricardo A. Vidal; Julio Ferrón (pp. 2047-2051).

► N₂⁺ implantation and annealing of a Cu(001) surface. ► N diffuses to the surface and reacts to form c(2×2) Cu–N nanostructures. ► N atoms locates on the four-fold hollow site of the Cu(001) surface above it. ► DFT calculations estimate N height above the surface to be 0.25Å. ► The appearance of a gap, consistent with the semiconductor character of Cu₃N, is apparent in the N–Cu sample.We report on the process of low energy N₂⁺ implantation and annealing of a Cu(001) surface. Through AES we study the N diffusion process as a function of the substrate temperature. With STM and LEIS we characterize the surface morphology and the electronic structure is analyzed with ARUPS. Under annealing (500< T<700K) N migrates to the surface and reacts forming a Cu_xN compound that decomposes at temperatures above 700K. LEIS measurements show that N locates on the four-fold hollow sites of the Cu(001) surface in a c(2×2) arrangement. Finally, a gap along the [001] azimuthal direction is determined by ARUPS. DFT calculations provide support to our conclusions.

Keywords: PACS; 71.15.Mb; 68.49.−h; 68.37.Ef; 62.23.St; 61.05.−aCopper nitride; Nanostructures; Self-assembling; LEIS; STM; Surface spectroscopy

Surface modification of Al–12.6Si alloy by high current pulsed electron beam by Y. Hao; B. Gao; G.F. Tu; H. Cao; S.Z. Hao; C. Dong (pp. 2052-2056).

► The microstructure and wear property of HCPEB-treated Al–12.6Si alloy are first researched. ► The eutectic structure disappears and a supersaturated solid solution of Al forms in remelted layer. ► Relative wear resistance of HCPEB-treated sample surface is improved by a factor of 2.5.The paper investigates the microstructure and property modifications of Al–12.6Si alloy induced by high current pulsed electron beam (HCPEB) treatment. The scanning electron microscope (SEM) results show a fine and equiaxed grain structure of several micrometers is obtained on the top surface of the melted layer. Underneath the top surface, a remelted layer with about 10μm thickness is obtained and a supersaturated solid solution of Al is formed in the remelted layer. XRD analysis shows that the relative strength of diffraction peaks of Al (111) and Si (111) crystal planes is increased after HCPEB treatment. As a result, relative wear resistance of HCPEB-treated sample is significantly improved by a factor of 2.5 due to fine grain strengthening and solid solution strengthening. Therefore, the HCPEB treatment has a good application future in treating Al–Si alloys.

Keywords: Al–12.6Si alloy; High current pulsed electron beam; Remelted layer; Supersaturated solid solution; Wear resistance

Low energy Ar-ion bombardment effects on the CeO₂ surface by G.D. Wang; D.D. Kong; Y.H. Pan; H.B. Pan; J.F. Zhu (pp. 2057-2061).

► Ar⁺ bombardment of the CeO₂ surface causes the appearance of the reduced oxidation state Ce³⁺. ► The reduction of CeO₂ is attributed to a preferential sputtering of oxygen from the surface. ► The thickness of the oxygen depletion layer induced by Ar⁺ bombardment can be quantitatively determined.The structure and electronic properties of epitaxial grown CeO₂(111) thin films before and after Ar⁺ bombardment have been comprehensively studied with synchrotron radiation photoemission spectroscopy (SRPES). Ar⁺ bombardment of the surface causes a new emission appearing at 1.6eV above the Fermi edge which is related to the localized Ce 4f¹ orbital in the reduced oxidation state Ce³⁺. Under the condition of the energy of Ar ions being 1keV and a constant current density of 0.5μA/cm², the intensity of the reduced state Ce³⁺ increases with increasing time of sputtering and reaches a constant value after 15min sputtering, which corresponds to the surface being exposed to 2.8×10¹⁵ions/cm². The reduction of CeO₂ is attributed to a preferential sputtering of oxygen from the surface. As a result, Ar⁺ bombardment leads to a gradual buildup of an, approximately 0.69nm thick, sputtering altered layer. Our studies have demonstrated that Ar⁺ bombardment is an effective method for reducing CeO₂ to CeO2−_x and the degree of the reduction is related to the energy and amount of Ar ions been exposed to the CeO₂ surface.

Keywords: PACS; 73.20.−rAr; ⁺; bombardment; Synchrotron radiation; Cerium oxide; Preferential sputtering

A study of TiMoN nano-multilayer coatings deposited by CFUBMSIP using DC and HIPIMS power by Shicai Yang; Xiaoying Li; K.E. Cooke; D.G. Teer (pp. 2062-2067).

► TiMoN nano-multilayer hard coatings have been deposited by CFUBMSIP using (i) 4 off DC powered magnetrons; and, (ii) 3 off DC powered +1HIPIMS powered magnetrons. ► The mechanical and tribological properties of the coatings were evaluated using scratch adhesion, Fischerscope hardness and pin on disc wear tests. The elemental compositions, crystalline phases and cross sectional microstructures of the coatings were studied using glow discharge optical emission spectroscopy (GDOES), X-ray Diffraction (XRD), and Transmission Electron Microscopy (TEM) respectively. ► The properties of the coatings deposited using the combined HIPIMS and DC powered CFUBMSIP are similar to those of the coatings deposited using exclusively DC powered CFUBMSIP in terms of hardness, adhesion, wear friction and microstructures. ► The nanoscale TiMoN multilayer is found to be formed as TiN face centred cubic (fcc) with no non-fcc MoN based phases identified, suggesting that epitaxial growth of MoN follows the fcc TiN with a bi-layer period of approximately 10nm.TiMoN nano-multilayer hard coatings have been deposited using the closed field unbalanced magnetron sputter ion plating (CFUBMSIP) technique. In one set of experiments, standard DC power supplies were used on four magnetrons in the CFUBMSIP system (4DC magnetrons). The second set of experiments was also in the same magnetic field configuration of CFUBMSIP, but three magnetrons were as again powered with standard DC whilst one magnetron with Ti target was supplied by a high power impulse magnetron sputtering (HIPIMS) power generator (3DC+1HIPIMS magnetrons). Two elemental titanium sputtering targets and two of molybdenum were used to produce the TiMoN nano-multilayer coatings. Analysis of the coatings was carried out to investigate the differences in terms of properties, compositions and microstructures of the coatings deposited by these two sets of experiments. It was found that the coatings deposited by both sets of the experiments exhibited similar properties of high hardness, good adhesion and exceptional wear resistance, with a lower sliding friction than more commonly used hard coatings including TiN, CrN, TiAlN, CrTiAlN etc. Although the initial TiN coating as formed at the coating-substrate interface using the process of 3DC+1HIPIMS magnetrons appeared to show a less oriented microstructure in comparison with that of the coating produced by the process using 4DC magnetrons, the compositions and cross sectional microstructures of the bulk of the coatings did not show significant differences, as observed by the cross sectional Transmission Electron Microscopy microstructures of these two types of TiMoN coatings.

Keywords: PACS; 68.37.Lp; 61.72.−y; 84.40.Fe; 81.15.Cd; 81.15.−ZTEM; Microstructure; Magnetron; Sputtering; Deposition

Numerical modeling and experimental investigation of TiC formation on titanium surface pre-coated by graphite under pulsed laser irradiation by A. Chehrghani; M.J. Torkamany; M.J. Hamedi; J. Sabbaghzadeh (pp. 2068-2076).

► A numerical model for carbonizing titanium surface by pulsed laser is developed. ► Higher pulse durations lead to significant increasing in the microhardness value. ► The hardness values of the processed layer increased up to 10 times of the Ti. ► The maximum microhardness of the layer experimentally obtained is 1717Hv.A model for carbonization of titanium surface by pulsed Nd:YAG laser was developed. The Ti substrate was covered with a relatively thick graphite layer prior to be processed under the laser beam. The experiments were performed at 15J pulse energy with various pulse durations and overlapping factor to validate the results obtained from the numerical calculations. The model results such as temperature gradient, surface temperature, and the cooling rate were correlated with the micro-hardness of the alloyed layer. Higher pulse durations and overlapping factors which lead to the heat input increasing will result in significant rising in the micro-hardness values. The hardness values of the processed layer partially containing TiC, increased up to 10 times of the Ti substrate.

Keywords: Laser surface alloying; Pulsed Nd:YAG laser; Titanium surface carbonization; Numerical modeling

Effect of chemisorption structure on the interfacial bonding characteristics of graphene–polymer composites by Cheng Lv; Qingzhong Xue; Dan Xia; Ming Ma (pp. 2077-2082).

► A simple method of investigating the interfacial bonding characteristics between graphene and polymer. ► Besides the interfacial bonding energy, the shear force depends on the mechanical interlocking between the graphene and polymer. ► The suitable structure of chemical groups to the graphene surface may be an effective way to significantly improve the load transfer between the graphene and polymer.The influence of the chemical functionalization of graphene on the interfacial bonding characteristics between graphene and polymer was investigated using molecular mechanics and molecular dynamics simulations. In this study, three chemical functionalization, (a) phenyl groups, (b) –C₆H₁₃ and(c) –C₂H₄(C₂H₅)₂, which have the same number of carbon atoms, were chosen to investigate the influence of the structure of functionalized groups on the bonding energy and shear stress in the graphene–polyethylene (PE) composites. Our simulations indicated that, the interfacial bonding energy between the graphene modified by –C₆H₁₃ groups and PE matrix has the strongest enhancement, but the shear force between the graphene modified by –C₂H₄(C₂H₅)₂ groups and PE matrix is the strongest in the graphene–polymer composites. Therefore, the suitable structure of chemical groups to the graphene surface may be an effective way to significantly improve the load transfer between the graphene and polymer when graphene is used to produce nanocomposites.

Keywords: Graphene–polymer composites; Simulation; Chemical functionalization

Surface phenomena of HA/TiN coatings on the nanotubular-structured beta Ti–29Nb–5Zr alloy for biomaterials by Eun-Ju Kim; Yong-Hoon Jeong; Han-Cheol Choe; William A. Brantley (pp. 2083-2087).

► Surface phenomena of HA/TiN coatings on the nanotubular structured beta Ti–29Nb–5Zr alloy for biomaterials have been investigated by several experimental methods. ► The nanotubular structure was formed by anodizing. ► Hydroxyapatite (HA)/titanium nitride (TiN) films were deposited on Ti–29Nb–5Zr alloy specimens using a magnetron sputtering system. ► The Ti–29Nb–5Zr alloy substrate had small grain size and preferred orientation along the drawing direction. ► The HA/TiN coating was stable with a uniform morphology at the tips of the nanotubes.Surface phenomena of HA/TiN coatings on the nanotubular-structured beta Ti–29Nb–5Zr alloy for biomaterials have been investigated by several experimental methods. The nanotubular structure was formed by anodizing the Ti–29Nb–5Zr alloy in 1M H₃PO₄ electrolytes with 1.0wt.% NaF at room temperature. Hydroxyapatite (HA)/titanium nitride (TiN) films were deposited on Ti–29Nb–5Zr alloy specimens using a magnetron sputtering system. The HA target was made of human tooth-ash by sintering at 1300°C for 1h, and the HA target had an average Ca/P ratio of 1.9. The HA/TiN depositions were performed, using the pure HA target, on Ti–29Nb–5Zr alloy following the initial deposition of a TiN buffer layer coating. Microstructures and nanotubular morphology of the coated alloy specimens were examined by FE-SEM, EDX, XRD, and XPS. The Ti–29Nb–5Zr alloy substrate had small grain size and preferred orientation along the drawing direction. The HA/TiN coating was stable with a uniform morphology at the tips of the nanotubes.

Keywords: Ti–29Nb–5Zr alloy; Nanotubular structure; HA/TiN coating; Magnetron sputtering

Surface characteristics of TiN/ZrN coated nanotubular structure on the Ti–35Ta– xHf alloy for bio-implant applications by Byung-Hak Moon; Han-Cheol Choe; William A. Brantley (pp. 2088-2092).

► We investigated the surface characteristics of the TiN/ZrN-coated nanotubular structure on Ti–35Ta– xHf ternary alloys for bio-implant applications. ► The highly ordered, high aspect ratio, and nanotubular morphology surface oxide layers can be formed on the ternary titanium alloys by anodization. ► The TiN and ZrN coatings formed on the nanotubular surfaces were uniform and stable. ► The top of the nanotube layers was uniformly covered with the ZrN film compared to the TiN film when the Ti–35Ta– xHf alloys had high Hf content.In this study, we investigated the surface characteristics of the TiN/ZrN-coated nanotubular structure on Ti–35Ta– xHf ternary alloys for bio-implant applications. These ternary alloys contained from 3wt.% to 15wt.% Hf contents and were manufactured in an arc-melting furnace. The Ti–35Ta– xHf alloys were heat treated in Ar atmosphere at 1000°C for 24h, followed by water quenching. Formation of the nanotubular structure was achieved by an electrochemical method in 1M H₃PO₄ electrolytes containing 0.8wt.% NaF. The TiN coating and ZrN coating were subsequently prepared by DC-sputtering on the nanotubular surface. Microstructures and nanotubular morphology of the alloys were examined by FE-SEM, EDX and XRD. The microstructure showed a duplex (α′′+β) phase structure. Traces of martensite disappeared with increasing Hf content, and the Ti–35Nb–15Hf alloy had an entirely equiaxed structure of β phase. This research has shown that highly ordered, high aspect ratio, and nanotubular morphology surface oxide layers can be formed on the ternary titanium alloys by anodization. The TiN and ZrN coatings formed on the nanotubular surfaces were uniform and stable. The top of the nanotube layers was uniformly covered with the ZrN film compared to the TiN film when the Ti–35Ta– xHf alloys had high Hf content.

Keywords: Nanotube; TiN coating; ZrN coating; Magnetron sputtering; Biomaterials

Fabrication of functionally gradient nanocomposite coatings by plasma electrolytic oxidation based on variable duty cycle by M. Aliofkhazraei; A. Sabour Rouhaghdam (pp. 2093-2097).

► Si₃N₄ content in the layer increases with the increase of its concentration in bath. ► Microhardness of layers increases with weight percentage of nanoparticulates. ► Coatings fabricated with lower rate of variable duty cycle has higher microhardness. ► Microhardness profile of the coatings showed different zones.Plasma electrolytic oxidation (PEO) was applied on the surface of commercially pure titanium substrates in a mixed aluminate-phosphate electrolyte in the presence of silicon nitride nanoparticles as suspension in the electrolyte in order to fabricate nanocomposite coatings. Pulsed current was applied based on variable duty cycle in order to synthesize functionally gradient coatings (FGC). Different rates of variable duty cycle (3, 1.5 and 1%/min), applied current densities (0.06–0.14A/cm²) and concentrations of nanoparticles in the electrolyte (2, 4, 6, 8 and 10gl⁻¹) were investigated. The nanopowder and coated samples were analyzed by atomic force microscope, scanning electron microscope and transmission electron microscope. The influence of different rates of variable duty cycle (or treatment times) on the growth rate of nanocomposite coatings and their microhardness values was investigated. The experimental results revealed that the content of Si₃N₄ nanoparticulates in the layer increases with the increase of its concentration in the plasma electrolysis bath. Nanocomposite coatings fabricated with lower rate of variable duty cycle have higher microhardness with smoother microhardness profile.

Keywords: Plasma electrolytic oxidation; Functionally gradient coatings; Nanocomposite; Pulse current

Approaches to the manufacture of layered nanocomposites by Yan Zhang; Julian R.G. Evans (pp. 2098-2102).

► Review what is likely to become a new generation of nanocomposites based on layered reinforcement of mineral platelets that mimic natural structures. ► Review methods to produce layered nanocomposites. ► Rapid production of layered montmorillonite and layered double hydroxides in the quest for high levels of ordering in the timescales acceptable for production operations.Clay–polymer nanocomposites, resulting from industrial research, have emerged as a new class of material because a low addition of clay in a polymer matrix causes dramatic improvement in mechanical and barrier properties. They represent the low volume fraction (<4vol.%) end of the composition range. The question now is: what will emerge from attempts to explore the high volume fraction (>60vol.%) end? Naturally occurring materials, such as nacre, show that a combination of a high platelet content in a polymer with a layered structure is strong and tough (4–10MPam^1/2), even if the reinforcement, aragonite in this case, is inherently brittle (∼1MPam^1/2). This achievement of nature has inspired the synthesis of materials to mimic the nacre structure using high aspect ratio reinforcements of high elastic modulus such as smectite clay tactoids. Preliminary successes were based on layer-by-layer assembly methods and it will be interesting to find out whether sufficient order can be obtained in composites assembled by more rapid manufacturing pathways. We are interested in the factors affecting dispersion, orientation and intercalation of platelets and here we survey the strategies that have been adopted in order to create organized structures of layered nanocomposites.

Keywords: Nacre; Layered nanocomposites; Layered-double-hydroxide; Montmorillonite; Filtration; Self-assembly

Photocatalytic thin films containing TiO₂:N nanopowders obtained by the layer-by-layer self-assembling method by L. Rojas-Blanco; M.D. Urzúa; R. Ramírez-Bon; F.J. Espinoza Beltrán (pp. 2103-2106).

► In this work were synthesized by high-energy ball milling TiO₂–N and immobilized these powders on glass slides for layer-by-layer method using polyethylenimine. ► We studied the effect of the milling time on the characteristics of material. ► We concluded that the grain size of the samples decreases, UV–Vis spectroscopy showed shift in the onset of light absorption. ► The TiO₂–N samples had higher photocatalytic activity than undoped, which was assigned to the effect of introducing N atoms and XPS results confirm it.In this work, TiO₂–N powders were synthesized by high-energy ball milling, using commercial titanium dioxide (TiO₂) in the anatase phase and urea to introduce nitrogen into TiO₂ in order to enhance their photocatalytic properties in the visible spectral region. Several samples were prepared by milling a mixture of TiO₂–urea during 2, 4, 8, 12 and 24h and characterized by spectroscopic and analytical techniques. X-ray diffraction (XRD) results showed the coexistence of anatase and high-pressure srilankite TiO₂ crystalline phases in the samples. Scanning electron microscopy (SEM) revealed that the grain size of the powder samples decreases to 200nm at 24h milling time. UV–Vis diffuse reflectance spectroscopic data showed a clear red-shift in the onset of light absorption from 387 to 469nm as consequence of nitrogen doping in the samples. The photocatalytic activity of the TiO₂–N samples was evaluated by methylene blue degradation under visible light irradiation. It was found that TiO₂–N samples had higher photocatalytic activity than undoped TiO₂ samples, which could be assigned to the effect of introducing N atoms and XPS results confirm it. Using polyethylenimine (PEI), transparent thin films of TiO₂–N nanoparticles were prepared by layer-by-layer self assembly method. UV–visible spectrophotometry was employed in a quantitative manner to monitor the adsorbed mass of TiO₂ and PEI after each dip cycle. The adsorption of both TiO₂ and PEI showed a saturation dip time of 15min.

Keywords: Photocatalysis; Titanium oxide; Nitrogen doping; Layer by layer; Srilankite

Soft X-ray photoemission study of nitrogen diffusion in TiN/HfO:N gate stacks by E. Martinez; C. Gaumer; S. Lhostis; C. Licitra; M. Silly; F. Sirotti; O. Renault (pp. 2107-2112).

► The post nitridation anneal of HfO:N induces nitrogen diffusion towards the Si substrate. ► Defects in the high- k are removed by incorporation of oxygen during this anneal. ► After gate fabrication and without anneal, nitrogen is trapped inside the HfO:N. ► After gate fabrication and anneal, nitrogen diffuses from the gate and high- k towards the Si substrate.The impact of HfO:N post nitridation anneal (PNA) and gate fabrication on the physico-chemical properties of the TiN/HfO:N/SiO₂/Si stack are investigated using Soft X-ray Photoelectron Spectroscopy (S-XPS) and Vacuum UltraViolet Spectroscopic Ellipsometry (VUV-SE). Defects created in the high- k during plasma nitridation are passivated by PNA under O₂. Both oxygen and nitrogen diffusion is observed towards the bottom SiO₂/Si interface together with a regrowth of the SiO₂. These defects play a major role regarding nitrogen diffusion during gate fabrication. Without PNA, no diffusion is observed because O and N atoms are trapped inside the high- k. With PNA and simultaneous defects passivation, nitrogen from both metal gate and high- k diffuses towards the bottom SiO₂/Si interface.

Keywords: Metal/high-; k; stack; TiN; HfO:N; Nitrogen; Diffusion; S-XPS; VUV-SE

Nano-image profiles transferred by near field phase-shifting lithography precisely simulated by finite element method and fabricated by Fu-Der Lai (pp. 2113-2116).

► High precision nano-image profiles transferred by near field phase-shifting mask lithography at various exposure-energy-intensities are simulated by the finite element method (FEM). ► The transferred energy-intensity distribution in the photoresist during the NFPSM process can be accurately simulated by the FEM. ► The nano-image profile with the nano-linewidth of 98nm and the highness of 360nm is simulated and fabricated. ► The fabricated nano-imaging profile precisely fits the simulation results.The operating frequency of the SAW filters is limited by the gap width but not the line width. The narrow gap width is required for the high operating frequency SAW filters. Therefore, in this study, high precision nano-image profiles transferred by near field phase-shifting mask (NFPSM) lithography at various exposure-energy-intensities (EEIs) are simulated by the finite element method (FEM). The transferred energy-intensity distribution (TEID) in the photoresist during the NFPSM process (at the wavelength of 248nm) can be accurately simulated by the FEM. The TEID at the interface between the mask and the photoresist is also simulated. The fabricated pattern widths clearly match the simulation results. The study of the simulated image profiles shows that they are dependent on the EEI. The greater the EEI is, the narrower the width and the shorter the height of the image profile. The nano-linewidth of 60nm is simulated and fabricated. The fabricated nano-imaging profile precisely fits the simulation results. Therefore, any expected nano-image profile can easily be fabricated by way of the simulation.

Keywords: Nano-image profile; Finite element method; Near field phase-shifting lithography

Characterization of diamond films deposited on Re substrate by magnetic field-assisted hot filament chemical vapor deposition by Xiaobin Wu; Zhiming Yu; Xiaolong You; Mengkun Tian; Yilun Gong (pp. 2117-2120).

► Boron doped diamond films on rhenium substrate by hot-filament vapor chemical deposition (HFCVD) are synthesized successfully. ► The result shows that the low threshold field of the sample is 3.3V/μm. ► Also the total emission current density at 6.2V/μm increases from 6.3 to 21.5μA/cm². ► The results infer that the electron conduction in the boron doped diamond films is improved and the electron emission is enhanced. ► The thickness of the diamond film with the period magnetic field-assisted is about 2900 nm after 4 hour deposition. ► From the observed results, it is clear that the diamond films deposited with the period magnetic field-assisted leads to improvement of its field emission characterstic.A periodically magnetic field (PMF) was used in a hot-filament chemical vapor deposited (HFCVD) for diamond growth on the rhenium substrate. The morphology, band structures and crystalline structure of the film were analyzed by the scanning electron microscopy (SEM), Raman spectroscopy and X-ray diffractometer (XRD), respectively. The results show that the thickness of the diamond film is about 2900nm by 4h deposition with magnetic field-assisted. There is no interlayer between diamond film and the rhenium substrate. The result shows that the turn on voltage of the sample is enhanced from 3.3 to 2.6V/μm with the PMF. Also the total emission current density at 6.2V/μm increased from 6.3 to 21.5μA/cm².

Keywords: PACS; 72.15.Eb; 73.61.At; 73.63.Bd; 74.25.NfMagnetic fields; Field emission; Chemical vapor deposition; Diamond film

Bias drop and phonon emission in molecular wires by Kenji Hirose; Hiroyuki Ishii; Nobuhiko Kobayashi (pp. 2121-2123).

► Formulation of electron–phonon coupling in the ab initio transport calculations. ► Bias drop and screening of electric field in molecular wires. ► Elastic and inelastic scattering effects in the electron transport.Using the recursion-transfer-matrix (RTM) method combined with the non-equilibrium Green's function (NEGF) method and density-functional theory, we perform ab initio calculations for the electron transport of molecular wires bridged between electrodes. We present an effective potential of molecular wire under a finite bias voltage and discuss the phonon emission and local heating due to inelastic electron–phonon coupling effects. We find that it is strongly dependent on contact conditions. When the contacts to electrodes are bad, excitation phonon modes at contacts become dominant for the energy dissipation.

Keywords: Electron–phonon coupling; Local heating; Molecular wire; Ab initio transport calculation; Density-functional-theory

The study of magnetic properties and microstructures of nano-size FePt islands on amorphous carbon film by C.L. Shen; P.C. Kuo; G.P. Lin; K.T. Huang; S.C. Chen (pp. 2124-2128).

► The surface energy difference caused the FePt films to form island shapes. ► The thickness of FePt films must be reduced to below 2.5nm, so as to obtain island-shaped FePt films. ► A nano-size island FePt film can reduce the exchange coupling and increase the recording density.This work focuses on the formation mechanisms of nano-island FePt film on commercial copper grids covered with an amorphous carbon film. FePt films of different thickness (1–7.5nm) were deposited on amorphous carbon film and then post-annealed at 700°C for 30min. The configuration of the film was changed during the annealing process due to the surface energy difference between the amorphous carbon films and FePt alloy. We have prepared nanometer-size island-shaped FePt films on the amorphous carbon films and investigated their magnetic properties and microstructures. A discontinuous nano-size island magnetic film can reduce the exchange coupling of the media and increase the recording density.

Keywords: FePt; Magnetic recording media; Nano-island; Surface energy; Self-assembled

Electrochemical and surface behavior of hydyroxyapatite/Ti film on nanotubular Ti–35Nb– xZr alloys by Yong-Hoon Jeong; Han-Cheol Choe; William A. Brantley (pp. 2129-2136).

► The electrochemical and surface behavior of hydroxyapatite (HA)/Ti films on the nanotubular Ti–35Nb– xZr (x=3, 5, 7, 10wt.%) alloys were investigated. ► The Ti–35Nb– xZr alloys showed a solely β phase microstructure that resulted from the addition of Zr. ► The nanotubular structure formed with a diameter of about 200nm, and the HA/Ti thin film was deposited on the nanotubular structure. ► The HA/Ti thin film-coated nanotubular Ti–35Nb– xZr alloys showed good corrosion resistance in 0.9% NaCl solution.In this paper, we investigated the electrochemical and surface behavior of hydroxyapatite (HA)/Ti films on the nanotubular Ti–35Nb– xZr alloy. The Ti–35Nb– xZr ternary alloys with 3–10wt.% Zr content were made by an arc melting method. The nanotubular oxide layers were developed on the Ti–35Nb– xZr alloys by an anodic oxidation method in 1M H₃PO₄ electrolyte containing 0.8wt% NaF at room temperature. The HA/Ti composite films on the nanotubular oxide surfaces were deposited by a magnetron sputtering method. Their surface characteristics were analyzed by field-emission scanning electron microscopy (FE-SEM), energy-dispersive X-ray spectroscopy (EDS) and an X-ray diffractometer (XRD). The corrosion behavior of the specimens was examined through potentiodynamic and AC impedance tests in 0.9% NaCl solution. From the results, the Ti–35Nb– xZr alloys showed a solely β phase microstructure that resulted from the addition of Zr. The nanotubular structure formed with a diameter of about 200nm, and the HA/Ti thin film was deposited on the nanotubular structure. The HA/Ti thin film-coated nanotubular Ti–35Nb– xZr alloys showed good corrosion resistance in 0.9% NaCl solution.

Keywords: Hydroxyapatite; EB-PVD; Ti–35Nb–; x; Zr alloy; Corrosion behavior; Nanotubular oxide

Effects of substrate temperature upon the properties of ZnMgTe layer grown by MOVPE by K. Saito; Y. Inoue; Y. Hayashida; T. Tanaka; Q.X. Guo; M. Nishio (pp. 2137-2140).

► Mg composition increases with decreasing substrate temperature. ► Improvement of optical quality with decreasing substrate temperature was observed. ► There is narrow range of optimal substrate temperature for obtaining smooth surface. ► ZnTe-and MgTe-like longitudinal optical phonon modes were observed.The effects of substrate temperature upon the optical property, composition and surface morphology have been investigated on nominally undoped Zn1−_xMg_xTe layers grown on (100) ZnTe substrates by atmospheric pressure metal organic vapor phase epitaxy (MOVPE). It was found that Mg composition increases with decreasing substrate temperature. The result of low temperature photoluminescence (PL) measurement suggests that the optical quality of Zn1−_xMg_xTe layers becomes better with decreasing substrate temperature. On the other hand, there is a narrow range of optimal substrate temperature for a smooth surface morphology. For all the layers, a two-mode behavior with ZnTe- and MgTe-like longitudinal optical phonon modes was confirmed by Raman scattering.

Keywords: ZnMgTe; MOVPE; Substrate temperature; Optical properties; Surface morphology

Effect of gas diffusion layer and membrane properties in an annular proton exchange membrane fuel cell by I. Khazaee; M. Ghazikhani; M. Nasr Esfahani (pp. 2141-2148).

► Investigation a new geometry of the PEM fuel cell. ► Investigation the effect of GDL properties on the performance. ► Investigation the effect of membrane properties on the performance. ► Understanding the many interacting, complex electrochemical and transport phenomena that cannot be studied experimentally.A complete three-dimensional and single phase computational dynamics model for annular proton exchange membrane (PEM) fuel cell is used to investigate the effect of changing gas diffusion layer and membrane properties on the performances, current density and gas concentration. The proposed model is a full cell model, which includes all the parts of the PEM fuel cell, flow channels, gas diffusion electrodes, catalyst layers and the membrane. Coupled transport and electrochemical kinetics equations are solved in a single domain; therefore no interfacial boundary condition is required at the internal boundaries between cell components. This computational fluid dynamics code is used as the direct problem solver, which is used to simulate the two-dimensional mass, momentum and species transport phenomena as well as the electron- and proton-transfer process taking place in a PEMFC that cannot be investigated experimentally. The results show that by increasing the thickness and decreasing the porosity of GDL the performance of the cell enhances that it is different with planner PEM fuel cell. Also the results show that by decreasing the thickness of the membrane the performance of the cell increases.

Keywords: Fuel cell; Annular; Numerical modeling; Current density; Gas concentration; Material properties

Local field emission of electrons from an individual boron nanowire at nanometer electrode separation by C.D. Zhang; J.M. Cai; M. Gao; H.L. Lu; Q. Zou; J.F. Tian; H. Hu; C.M. Shen; H.M. Guo; H.J. Gao (pp. 2149-2152).

The field emission of individual β-rhombohedral boron nanowire was studied by ultrahigh vacuum four-probe scanning tunneling microscopy (STM) system for the first time. ► A reproducible and stable emission current is obtained, which is comparable to carbon nanotubes. ► The field emission properties were also studies at nanoscale electrode distance. ► An obvious deviation was observed when the electrodes getting too close. This deviation is tentatively assumed to due to the invalidation of free electron cloud approximation in FN theory.The field electron emission properties of an individual β-rhombohedral boron nanowire ( β-r BNW) with electrode separation at nanoscale have been studied by ultrahigh vacuum four-probe scanning tunneling microscope (STM) system. A reproducible and stable emission current can be obtained. The maximal emission current density of individual boron nanowire is about 5×10⁴A/cm² at a low bias voltage (80V). An obvious deviation from the Fowler–Nordheim (FN) theory appears, when the electrode separation reduced below 120nm. This deviation is tentatively assumed to due to the invalidation of free electron cloud approximation in FN theory.

Keywords: Field emission; Single boron nanowire; Nanoscale electrode separation; Fowler–Nordheim (FN) theory

Field-emission-induced electromigration method for the integration of single-electron transistors by Shunsuke Ueno; Yusuke Tomoda; Watari Kume; Michinobu Hanada; Kazutoshi Takiya; Jun-ichi Shirakashi (pp. 2153-2156).

► Simple and easy method for the integration of Ni-based SETs was developed. ► The integration of two SETs with similar electrical properties was achieved. ► The charging energy of the integrated SETs was simultaneously controlled.We report a simple and easy method for the integration of planar-type single-electron transistors (SETs). This method is based on electromigration induced by a field emission current, which is so-called “activation”. The integration of two SETs was achieved by performing the activation to the series-connected initial nanogaps. In both simultaneously activated devices, current–voltage ( I_D– V_D) curves displayed Coulomb blockade properties, and Coulomb blockade voltage was also obviously modulated by the gate voltage at 16K. Moreover, the charging energy of both SETs was well controlled by the preset current in the activation.

Keywords: Electromigration; Field emission current; Nanogap; Single-electron transistor; Integration

1-D modeling of ion transport in rectangular nanofluidic channels by Liu Kun; Ba Dechun; Gu Xiaoguang; Du Guangyu; Lin Zeng; Liu Xinghua; Wang Zhixue; Xiao Songwen (pp. 2157-2160).

► Simplified models are established to describe transport in 1-D nanofluidic channels. ► Flow velocity distribution in the nanofluidic channels can be predicted. ► Electric potential can be controlled by adjusting the parameters in the channels. ► The solution flow rate can be controlled by adjusting the solution character.Based on the continuity hypothesis of fluid, 1-D mathematical models of ions’ transport in the rectangular nanofluidic channels are established by using the Poisson–Boltzmann (PB) equation and the modified Navier–Stokes (N–S) equations. The deduced equations are solved with MATLAB software. The results show that the distribution of the electric potential and the flow field could be predicted by the parameters, such as conductivity, surface charge density, solution concentration and channel height. The relationships between the parameters and the flow characteristics of the solution are also discussed. The research will help to the accurate manipulation of the solution in the nanofluidic channels.

Keywords: Nanofluidics; Electric double layer; Ion transport; Electric potential distribution; Flow field distribution

Synchrotron radiation photoelectron spectroscopy study of metal-oxide thin film catalysts: Pt–CeO₂ coated CNTs by I. Matolínová; R. Fiala; I. Khalakhan; M. Vorokhta; Z. Sofer; H. Yoshikawa; K. Kobayashi; V. Matolín (pp. 2161-2164).

► Pt–CeO₂ catalyst films prepared by rf sputtering deposition exhibit high concentration of Pt²⁺ and Pt⁴⁺ ions. ► Ce reveals mixed 4+ and 3+ oxidation states. ► CNT substrate enhances reducibility of the catalyst.The interaction of Pt with CeO₂ layers was investigated by using high resolution hard X-ray photoelectron spectroscopy. Pt doped CeO₂ layers were deposited simultaneously by rf-magnetron sputtering on a SiO₂/Si substrate and carbon nanotubes (CNTs) grown on a carbon diffusion layer of a polymer membrane fuel cell. In the case of the CNT support photoelectron spectra showed the formation of ionic platinum rich cerium oxide with Pt^2+,4+ species, and with the Pt²⁺/Pt⁴⁺ ratio strongly dependent on the amount of platinum. Ce reveals 4+/3+ mixed valent character with Ce³⁺ concentration increasing with Pt content. In the case of the SiO₂/Si substrate the film revealed Ce⁴⁺ and Pt⁴⁺ species only.

Keywords: Cerium oxide; Platinum; Magnetron sputtering; Hard X-ray photoelectron spectroscopy

Simulations of structures of amorphous Si_xC1−_x films by Huiqing Lan; Yang Wang; Can Liu (pp. 2165-2168).

► Molecular dynamics is used to predict structures of Si_xC1−_x films. ► The sp³/sp² ratio of the films increases with an increase in silicon contents. ► But the stiffness of the films decreases with increasing silicon contents. ► Moreover, silicon atoms are almost surrounded by carbon atoms.Amorphous Si_xC1−_x films possess the potential to improve wear performance in humid atmospheres and at higher temperatures. But some experimental work on the films showed that silicon contents greatly influenced their microstructures and mechanical properties. Therefore, simulations of molecular dynamics were carried out to predict structures of the Si_xC1−_x films at different silicon contents. The results show that the sp³/sp² ratio of all the films increases, but the stiffness of the films is decreasing with an increase in silicon contents. Moreover, silicon atoms are almost surrounded by carbon atoms, which is in agreement with the experiments.

Keywords: PACS; 68.55.agMolecular dynamics; Structures; Amorphous films; Structure; Silicon

Electrodeposition of Sb₂Se₃ on indium-doped tin oxides substrate: Nucleation and growth by Xuezhao Shi; Xin zhang; Yuan Tian; Chengmin Shen; Chunming Wang; Hong-Jun Gao (pp. 2169-2173).

► In this paper, antimony selenide (Sb₂Se₃) was prepared onto (indium-doped tin oxides) ITO substrate using electrodeposition method. ► The deposition mechanism of antimony and selenium on ITO substrate were investigated. ► Nucleation and growth mechanism of Sb₂Se₃ was discussed according to chronoamperometry (CA) data. ► Electrochemical behavior of antimony onto Sb₂Se₃ was investigated. ► Morphology and crystalline structure of Sb₂Se₃ were measured using SEM and XRD.The mechanisms related to the initial stages of the nucleation and growth of antimony selenide (Sb₂Se₃) semiconductor compounds onto the indium-doped tin oxides (ITO) coated glass surface have been investigated using chronoamperometry (CA) technique. The fabrication was conducted from nitric acid bath containing both Sb³⁺ and SeO₂ species at ambient conditions. No underpotential deposition (UPD) of antimony and selenium onto ITO substrate was observed in the investigated systems indicating a weak precursor–substrate interaction. Deposition of antimony and selenium onto ITO substrate occurred with large overvoltage through 3D nucleation and growth mechanism followed by diffusion limited growth. FE-SEM and XRD results show that orthorhombic phase Sb₂Se₃ particles with their size between 90 and 125nm were obtained and the atomic ratio for antimony and selenium was 2:2.63 according to the EDX results.

Keywords: Nucleation and growth; Antimony triselenide (Sb; ₂; Se; ₃; ); Electrodeposition; ITO antimony

Effects of hydrogen etching process on the structural and optical properties of nano-crystalline diamond films by Linjun Wang; Jian Huang; Qingkai Zeng; Ke Tang; Run Xu; Jijun Zhang; Yiben Xia (pp. 2174-2176).

► Hydrogen etching method was used to improve the quality of nano-crystalline diamond films. ► The grain size and surface roughness decreased with increasing the duration of hydrogen etching. ► The optical transmittance increased obviously while increasing the duration of hydrogen etching. ► The X-ray transmittance at 258eV reached 53.3% under 4h hydrogen etching.In this work, hydrogen etching method is applied to improve the quality of nano-crystalline diamond (NCD) films grown from hot-filament assisted chemical vapor deposition (HFCVD) system. From the characteristics of the structure and optical property, the grain size and surface roughness decrease while the optical transmission increase obviously under certain deposition parameters (gas pressure and substrate temperature) and longer etching time. Soft X-ray transmission measurements by synchrotron radiation are also carried out on the NCD films. The result shows that the X-ray transmission has an obvious improvement when the NCD film is fabricated from the hydrogen etching method. And the transmittance reaches 53.3% at X-ray photon energy of 258eV, which has met the requirement for X-ray mask materials.

Keywords: PACS; 68.55.−a; 81.07.Bc; 78.20.−eNano-crystalline diamond film; Optical properties; Plasma etching

The electrical, optical and magnetic properties of Si-doped ZnO films by J.T. Luo; X.Y. Zhu; G. Chen; F. Zeng; F. Pan (pp. 2177-2181).

► The resistivity of the ZnO films can significantly decrease by Si-doped. ► The bandgap of the film increases to 3.52eV when Si concentration is of 6%. ► Yellow emission enhances due to the increase of extrinsic impurity or defects. ► The maximum magnetic moment of 2.6μ_B/Si is obtained.In this paper, the influences of Si-doping on electrical, optical and magnetic properties of ZnO films have been systematically investigated. It is found that the resistivity of the films decreases from 3.0×10³ to 6.2×10^–2Ωcm with Si-doping due to the increase of carrier concentration. The bandgap of ZnO films increases from 3.28 to 3.52eV with increasing of Si concentration, which is found to be due to the collective effects of bandgap narrowing and Burstein–Moss effect induced by high carrier concentration. With increase of Si concentration, the near band edge (NBE) emission decreases due to the deterioration of crystal quality, while the yellow emission enhances due to the increase of extrinsic impurity or defects. The additional Si-doping has a profound influence on the enhancement of magnetic property and the maximum magnetic moment of 2.6μ_B/Si is obtained. The ferromagnetic ordering is seen to be correlated with carrier concentration and structural defects.

Keywords: PACS; 68.55.Ln; 73.61.Ga; 75.70.−i; 78.66.HfZnO films; Si doping; Electrical property; Photoluminescence; Ferromagnetism

Fabrication of nested elliptical KB mirrors using profile coating for synchrotron radiation X-ray focusing by Chian Liu; G.E. Ice; W. Liu; L. Assoufid; J. Qian; B. Shi; R. Khachatryan; M. Wieczorek; P. Zschack; J.Z. Tischler (pp. 2182-2186).

► A detailed description of the fabrication process of the first-ever synchrotron hard X-ray Montel/nested elliptical KB mirror using a profile coating technique and flat Si substrates. ► Demonstrated excellent figure-precision of sub-nm rms height-error of profile-coated elliptical KB mirrors. ► Provided an economic solution of fabricating KB mirrors with a very precise elliptical surface profile at the small corner area of Montel optics for synchrotron hard X-rays.This paper describes fabrication methods used to demonstrate the advantages of nested or Montel optics for micro/nanofocusing of synchrotron X-ray beams. A standard Kirkpatrick-Baez (KB) mirror system uses two separated elliptical mirrors at glancing angles to the X-ray beam and sequentially arranged at 90° to each other to focus X-rays successively in the vertical and horizontal directions. A nested KB mirror system has the two mirrors positioned perpendicular and side-by-side to each other. Compared to a standard KB mirror system, Montel optics can focus a larger divergence and the mirrors can have a shorter focal length. As a result, nested mirrors can be fabricated with improved demagnification factor and ultimately smaller focal spot, than with a standard KB arrangement. The nested system is also more compact with an increased working distance, and is more stable, with reduced complexity of mirror stages. However, although Montel optics is commercially available for laboratory X-ray sources, due to technical difficulties they have not been used to microfocus synchrotron radiation X-rays, where ultra-precise mirror surfaces are essential. The main challenge in adapting nested optics for synchrotron microfocusing is to fabricate mirrors with a precise elliptical surface profile at the very edge where the two mirrors meet and where X-rays scatter. For example, in our application to achieve a sub-micron focus with high efficiency, a surface figure root-mean-square (rms) error on the order of 1nm is required in the useable area along the X-ray footprint with a ∼0.1mm-diameter cross section. In this paper we describe promising ways to fabricate precise nested KB mirrors using our profile coating technique and inexpensive flat Si substrates.

Keywords: PACS; 81.15.Cd; 41.50.+h; 42.82.CrProfile coating; X-ray optics; KB mirrors; Sputter deposition

In situ study on the electronic structure of graphene grown on 6H–SiC(0001¯) with synchrotron radiation photoelectron spectroscopy by Chaoyang Kang; Jun Tang; Limin Li; Haibin Pan; Pengshou Xu; Shiqiang Wei; Xiufang Chen; Xiangang Xu (pp. 2187-2191).

► We examine the electronic structures of the graphene grown on 6H–SiC(0001¯). ► The LEED results showed the several reconstructions of 6H–SiC and the anisotropic graphene layers. ► The C 1s core levels showed that the interface interaction was weak. ► The existence of Si clusters was confirmed by Si 2p core levels. ► The valence band spectra indicated that both of σ and π bonds existed.Low energy electron diffraction (LEED) and synchrotron radiation photoelectron spectroscopy (SRPES) were used to study the synthesis process and detailed electronic structures of graphene produced by thermal decomposition of 6H–SiC(0001¯) in ultrahigh vacuum (UHV). The LEED results showed that as annealing temperature increased, different reconstructions of 6H–SiC(0001¯) appeared and the anisotropic graphene layers were produced finally. The results of C 1s core levels indicated that the component, which was assigned to graphene emerged and the interface interaction between graphene and the substrate was weak. The existence of Si clusters was confirmed by Si 2p core levels and perhaps these clusters led to rough epitaxial graphene surface. The results of valence band spectra showed that at high annealing temperature both of σ and π bonds existed in the grown graphene layers.

Keywords: PACS; 73.22.Pr; 32.30.Rj; 87.15.Pc; 68.65.PqSynchrotron radiation photoelectron spectroscopy; 6H–SiC; Graphene; Electronic properties

Microwave excitation and readout of nano- and micron scale cantilevers by Ling Hao; Stefan Goniszewski; Jie Chen; John Gallop (pp. 2192-2195).

► Microwave near-field allows cantilever excitation on a scale less than microwave λ. ► We show that at room temperature our system displacement sensitivity ∼70fm/Hz^1/2. ► Measured force between near-field probe and cantilever agreed with theory. ► The dependence of mechanical resonator Q on pressure accurately measured. ► We have demonstrated passive cantilever mode cooling from 300K to 80K.We show that a microwave near-field coaxial resonator system allows mechanical cantilever excitation on a scale much shorter than the microwave wavelength. Thermal noise is observed in the unexcited system, enabling room temperature displacement sensitivity of ∼70fm/Hz^1/2. The measured force between near-field probe and cantilever varies with separation, in excellent agreement with theory. Uniquely, optical excitation and read-out lasers are also included. The dependence of mechanical resonator quality factor on ambient air pressure has been accurately measured. We have demonstrate passive cantilever mode cooling from 300K to 80K by frequency detuning the microwave resonator and propose pulsed cooling operation to enable several high-sensitivity applications.

Keywords: Near-field microwave microscope; Cantilever; MEMS; NEMS

Supramolecular architecture of organic molecules: PTCDA and CuPc on a Cu(111) substrate by M.C. Cottin; J. Schaffert; A. Sonntag; H. Karacuban; R. Möller; C.A. Bobisch (pp. 2196-2200).

Display Omitted► PTCDA and CuPc are consecutively evaporated onto a Cu(111) substrate. ► Molecular phases after an annealing step are studied by LT-STM and LEED. ► Molecular phases include a highly ordered (HO) and a disordered mixed molecular phase.► HO phase seems to be thermodynamically favored. ► HO mixed molecular phase can be tailored from prepatterned dense PTCDA domains.We report on the molecular self-assembly of a highly ordered mixed molecular structure of copper–phthalocyanine (CuPc) and 3,4,9,10–perylene–tetracarboxylic–dianhydride (PTCDA) on Cu(111) starting from dense PTCDA domains. Low temperature scanning tunneling microscopy (LT-STM) data reveal the surface structure as the CuPc coverage is stepwise increased. A highly ordered mixed phase as well as a disordered mixed phase can be found, where the highly ordered mixed phase seems to be thermodynamically favored. Low energy electron diffraction (LEED) measurements aid the STM analysis. Tentative models for the formation of the highly ordered mixed phase are given.

Keywords: LT-STM; PTCDA; CuPc; Mixed molecular structures; LEED

In-situ study on thermal decomposition of 1,3-disilabutane to silicon carbide on Si(100) surface by Hae-geun Jee; Sang-Hun Nam; Jin-Hyo Boo; Seong Kyu Kim; Soon-Bo Lee (pp. 2201-2205).

► Si(100) surface was exposed to DSB vapor at a temperature less than 100K and analyzed by the RIS technique. ► Based on the Residual Gas Analysis (RGA) and RIS spectrum, 2 and 89amu masses were used in Temperature Programmed Desorption for hydrogen and DSB, respectively. Also, based on adspecies identified by RIS and TPRIS at various temperatures, we suggest the decomposition reaction path from DSB to SiC. ► Each carbon peaks were deconvoluted with three species of molecular DSB, graphitic, and carbidic carbon.The intermediates of thermal decomposition of 1,3-disilabutane (SiH₃CH₂SiH₂CH₃, DSB) to form SiC on Si(100) surface were in situ investigated by reactive ion scattering (RIS), temperature programmed reactive ion scattering (TPRIS), temperature programmed desorption (TPD), and auger electron spectroscopy (AES). DSB as a single molecular precursor was exposed on Si(100) surface at a low temperature less than 100K, and then the substrate was heated up to 1000K. RIS, TPD, and AES investigations showed that DSB adsorbed molecularly and decomposed to SiC via some intermediates on Si(100) surface as substrate temperature increasing. Between 117 and 150K molecularly adsorbed DSB desorbed partially and decomposed to CH₄Si₂, which is the first observation on Si(100) surface, and further decomposed to CH₄Si between 150 and 900K. CH₄Si lost hydrogen and formed SiC over 900K.

Keywords: 1,3-Disilabutane; Thermal decomposition; RIS and TPRIS; TPD; AES

Growth, microstructure, and mechanical properties related to modulation period for ZrAlN/ZrB₂ superlattice coatings by Y.B. Kang; D.J. Li; H.Y. Wang; J.Y. Yan; S. Zhang; X.Y. Deng (pp. 2206-2210).

► ZrAlN/ZrB₂ multilayer has potential on quality in protective coatings. ► Modulation period gives a significant contribution to its properties. ► There is a critical modulation period for the hardest multilayer. ► The effects are related to interfacial nature and layer nonacrystalline.ZrAlN/ZrB₂ multilayered superlattice coatings with modulation periods ranging from 20nm to 60nm were grown in magnetron sputtering chamber. X-ray diffraction (XRD), scanning electron microscopy (SEM) and nanoindention were employed to investigate the influence of modulation period on microstructure and mechanical properties of the multilayers. The sharp interfaces and nanoscale multilayered modulation were confirmed by SEM and XRD. The coating with modulation period of 40nm and modulation ratio of 1:3 showed a marked polycrystalline structure with the strong mixture of ZrAlN (111), ZrB₂ (001) and ZrB₂ (101) textures. Meanwhile, it also possessed the highest hardness (36.4GPa), elastic modulus (477GPa), critical fracture load (76.48mN), and lower residual stress, compared to those with other modulation periods and monolithic coatings.

Keywords: Multilayer; Sputtering; Superlattice; Hardness; Residual stress

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Applied Surface Science (v.258, #6)

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Applied Surface Science (v.258, #6)