Applied Surface Science (v.343, #C)

Synthesis of magnetic graphene oxide–TiO2 and their antibacterial properties under solar irradiation by Ying-Na Chang; Xiao-Ming Ou; Guang-Ming Zeng; Ji-Lai Gong; Can-Hui Deng; Yan Jiang; Jie Liang; Gang-Qiang Yuan; Hong-Yu Liu; Xun He (1-10).
Titanium dioxide (TiO2) has been intensively researched and increasingly used as antibacterial agent, but it suffers from separation inconvenience. Its effective removal from water after reaction while maintaining its high antibacterial activity becomes necessary. In this work, it was the first time the magnetic graphene oxide–TiO2 (MGO–TiO2) composites were prepared through a simple synthesis method. The results indicated that MGO–TiO2 exhibited a good antibacterial activity against Escherichia coli. MGO–TiO2 was found to almost completely inactivate the E. coli within 30 min under solar irradiation. The effect of inorganic ions present in E. coli suspension was also evaluated. Compared with other ions, HCO3 and HPO4 2− had a greater influence on the antibacterial property.
Keywords: Titanium dioxide; Graphene oxide; Antibacterial activity; Magnetic; Inorganic ions;

Effects of wood fiber surface chemistry on strength of wood–plastic composites by Sébastien Migneault; Ahmed Koubaa; Patrick Perré; Bernard Riedl (11-18).
Because wood–plastic composites (WPC) strength relies on fiber-matrix interaction at fiber surface, it is likely that fiber surface chemistry plays an important role in WPC strength development. The objective of the present study is to investigate the relationships between fiber surface chemical characteristics and WPC mechanical properties. Different fibers were selected and characterized for surface chemical characteristics using X-ray photoelectron spectroscopy (XPS) and infrared spectroscopy (FTIR). WPC samples were manufactured at 40% fiber content and with six different fibers. High density polyethylene was used as matrix and maleated polyethylene (MAPE) was used as compatibility agent. WPC samples were tested for mechanical properties and fiber-matrix interface was observed with scanning electron microscope. It was found WPC strength decreases as the amount of unoxidized carbon (assigned to lignin and extractives) measured with XPS on fiber surface increases. In the opposite case, WPC strength increases with increasing level of oxidized carbon (assigned to carbohydrates) on fiber surface. The same conclusions were found with FTIR where WPC strength decreases as lignin peaks intensity increases. Esterification reaction of fibers with MAPE occurs on polar sites of carbohydrates, such as hydroxyls (O―H). Thus, fibers with carbohydrates-rich surface, such as cellulose pulp, produced stronger WPC samples. Other factors such as mechanical interlocking and fiber morphology interfered with the effects of fiber surface chemistry.
Keywords: Wood-polymer composite; Wood surface chemistry; X-ray electron spectroscopy; Fiber-matrix adhesion; Mechanical properties;

Preparation of amine functionalized carbon nanotubes via a bioinspired strategy and their application in Cu2+ removal by Xiaoyong Zhang; Qiang Huang; Meiying Liu; Jianwen Tian; Guangjian Zeng; Zhen Li; Ke Wang; Qinsong Zhang; Qing Wan; Fengjie Deng; Yen Wei (19-27).
Amine functionalized carbon nanotubes were prepared via combination of mussel inspired chemistry and Michael addition reaction. These modified carbon nanotubes exhibited significant enhanced adsorption capacity toward copper ions.The environmental applications of carbon nanotubes (CNTs) have attracted great research attention since their first discovery. However, the performance of pristine CNTs for removal of heavy metal ions is greatly limited by their severe aggregation and lack of functional groups. In this work, a novel method has been developed for preparation of amine functionalized CNTs via combination of mussel inspired chemistry and Michael addition reaction. CNTs were first coated with polydopamine (PDA) through mussel inspired chemistry. And then commercial available agent polyethylene polyamine with a number of amine groups was further conjugated with PDA coated CNTs via Michael addition reaction. A series of characterization techniques have demonstrated that the amine functionalized CNTs have been successfully prepared. Furthermore, the adsorption application of thus amine functionalized CNTs for Cu2+ was examined. The effects of various parameters including pH solution, temperature, initial Cu2+ concentration and the adsorbent concentration were investigated. The data from experiments were analyzed by the Langmuir and Freundlich models of adsorption. Due to the universal of mussel inspired chemistry, the method described in this work should be a general strategy for surface modification of materials for environmental applications.
Keywords: Amine functionalized CNTs; Adsorption of heavy metal ions; Environmental application; Mussel inspired chemistry; Dopamine;

Biomolecule-assisted solvothermal synthesis of 3D hierarchical Cu2FeSnS4 microspheres with enhanced photocatalytic activity by Jiasong Zhong; Qingyao Wang; Daqin Chen; Leifeng Chen; Hua Yu; Hongwei Lu; Zhenguo Ji (28-32).
3D hierarchical Cu2FeSnS4 microspheres were successful synthesized by a novel environment-friendly solvothermal approach with the utilization of l-cystine, an amino acid, as a coordination agent and sulfur donor. The 3D hierarchical Cu2FeSnS4 exhibits high efficiency in the photodegradation of RhB under visible light illumination.In this work, we developed a novel environmentally friendly strategy toward solvothermal synthesis of 3D hierarchical Cu2FeSnS4 microspheres with the utilization of l-cystine, an amino acid, as a coordination agent and sulfur donor. The crystal structure, surface morphology and microstructure of the as-prepared products were investigated. The results showed that the 3D hierarchical Cu2FeSnS4 microspheres were composed of stannite nanosheets, and the average thickness of nanosheets was 100 nm. Moreover, the 3D hierarchical Cu2FeSnS4 exhibited high efficiency in the photodegradation of RhB under visible light illumination, suggesting a promising candidate for treatment of organic pollutants in waste water.
Keywords: Cu2FeSnS4; Microsphere; Solvothermal method; Photocatalytic;

Water adsorption on the clean and defective Cu2O(1 1 1) surfaces with different coverages was investigated using spin-polarized density functional theory.The interaction of water with solid surfaces plays an important role in many chemical reactions. The present work investigates water adsorption on the clean and defective Cu2O(1 1 1) surfaces using spin-polarized density functional theory. The results show that at low water coverage, only molecular H2O chemisorption is preferred on clean Cu2O(1 1 1) surface, and the water adsorption results in surface reconstruction. Up to 1 monolayer (ML), the adsorbed H2O molecules interact with the coordinatively unsaturated Cu atoms as well as the coordinatively unsaturated surface oxygen atoms via H-bonding. Up to 2 ML, the adsorbed H2O molecules interact with the coordinatively unsaturated surface oxygen atoms and the first layer adsorbed H2O molecules via H-bonding. Ordered surface layer structures are observed at 1 and 2 ML H2O adsorption. In contrast to the clean surface, the defect surface with oxygen vacancy favors dissociative H2O adsorption with the dissociated OH group bridging the surface Cu atoms and the H atom on the coordinatively saturated third layer O atom. The adsorption mechanisms are analyzed on the basis of the total density of states. It is found that wet electron states on the clean and H2O adsorbed Cu2O(1 1 1) surfaces might be important for their photocatalytic properties. Water adsorption on Cu2O surface is stronger than on MgO, Fe3O4, Fe2O3 and CeO2, while weaker than on Al2O3. The different H2O adsorption mechanisms on different metal oxides may benefit for new H2O-splitting metal oxides catalyst designing.
Keywords: Cuprous oxide; Water; Density functional theory; Adsorption; Photocatalytic;

High-temperature crack-healing behaviour and strength recovery of (MoNb)Si2 by Gaoming Zhu; Xiaohong Wang; Qiong Lu; Guangzhi Wu; Peizhong Feng (41-48).
(MoNb)Si2 materials were prepared using combustion synthesis and the vacuum hot-pressing technology. Cracks were introduced on the surface of polished materials using the Vickers indentation method. The crack-healing behaviour of (MoNb)Si2 materials were investigated with high-temperature oxidation in air. The results show that after annealing at 900 °C, 1200 °C and 1500 °C for 1 h, the crack-healing behaviour was observed in each case. The bending strength obviously decreased when the cracks were introduced, and the materials significantly recovered after the heat treatment. The crack-healed samples exhibited higher bending strengths than the original level after the 1200 °C treatment, e.g. 479 MPa versus 195 MPa of pure MoSi2. MoSi2 micro alloyed with niobium shows a high bending strength at room temperature and excellent crack-healing properties at high temperatures.
Keywords: Molybdenum disilicide; Crack healing; Strength recovery; Oxidation; Microstructure;

The evolution of chemical nature on U–0.79 wt.%Ti surface during vacuum annealing by Peng Shi; Lizhu Luo; Yawen Zhao; Xiaoguo Fu; Bingyun Ao; Bin Bai; Xiaolin Wang (49-55).
The evolution of the U–0.79Ti alloy surface character during vacuum annealing.The evolution of the oxide-overlayer's chemical nature on the surface of U–0.79 wt.%Ti alloy during vacuum annealing has been examined in situ by X-ray photoelectron spectroscopy (XPS). A specimen sheet of the alloy covered by oxide films is heated from room temperature to 700 °C in vacuum. It is found that the UO2+x outer oxide layer starts to be reduced to UO2 at 200 °C. Between 300 and 400 °C, an oxycarbide (UO x C y ) layer is observed due to the reaction between UO2 and carbon. Above 500 °C, UO x C y decomposes and the surface covered oxide layer starts to be reduced to the metallic state, meanwhile, a thermal driven segregation of Ti to the surface is also observed.
Keywords: U–Ti alloy; Vacuum annealing; XPS; Oxycarbide; Surface segregation;

In this paper, molecular dynamics method with the Tersoff–ZBL combined interatomic potential was adopted to study the dynamics of focused ion beam (FIB) milling and subsequent annealing. The Ga FIB induced damage and its recovery mechanism during subsequent annealing process were investigated in nanoscale time and space. To investigate the nanoscale damage during FIB milling with the ion energy of 0.5 keV, 1 keV and 2 keV, radial distribution function, bond length distribution, bond angle distribution, and common neighbour analysis (CNA) were calculated and analyzed under various ion doses. FIB irradiated silicon substrate with ion dose of 2 × 1014 ions/cm2 was annealed at various annealing temperatures from 1400 K to 2400 K. Molecular dynamics simulation illustrated that as a-Si region was surrounded by c-Si after implantation, the recrystallization lead to a c-Si regrowth processes both from bottom towards top surface and from periphery to centre. The damage area profiles by CNA represented a shortest recovery time of 2.0 ns at 2200 K. Both melting on the top surface and recrystallization at crystalline/amorphous interface have existed as annealing at 2400 K, which is near the melting point. Ga migrated together and moved towards the surface with the a-Si/c-Si interface.
Keywords: Focused ion beam (FIB); Annealing; Silicon; Gallium; Molecular dynamics (MD);

Effects of substrate temperature on the growth, structural and optical properties of NiSi/SiC core–shell nanowires by Najwa Binti Hamzan; Farah Nadiah Binti Nordin; Saadah Abdul Rahman; Nay Ming Huang; Boon Tong Goh (70-76).
In this paper we attempt to study the growth of NiSi/SiC core–shell nanowires on Ni-coated glass substrates by hot-wire chemical vapor deposition. The samples were prepared at different substrate temperatures of between 350 and 527 °C to investigate the growth of the nanowires. Ni nanoparticles were used as templates for initially inducing the growth of these core–shell nanowires at substrate temperature as low as 350 °C. The high density of the nanowires was clearly demonstrated at higher substrate temperatures of 450 and 527 °C. These core–shell nanowires were structured by single crystalline NiSi and amorphous SiC as the core and shell of the nanowires respectively. The amorphous SiC shell consisted of SiC nanocolumns within an amorphous matrix. The formation of these high density nanowires showed a noticeable suppression in photoluminescence emissions from the oxygen-related defects and superior optical absorption in visible and limited near infrared regions. The effects of substrate temperatures on growth, optical and structural properties of the nanowires are presented and discussed.
Keywords: Core–shell nanowires; NiSi; SiC; Photoluminescence; HWCVD;

Spreading-wetting method for highly reproducible tertiary growth of perfective bilayer TS-1 membranes by Xuguang Liu; Yong Liu; Lei Xu; Baoquan Zhang; Laibo Ma (77-87).
Spreading-wetting method is adopted to seed a support for tertiary growth of hydrophobic TS-1 membrane. It deposits the seed on the macro-hole of the support and results in a dispersive seed distribution. This enables a highly reproducible preparation of the perfective TS-1 membrane, revealed by SEM as a bilayer structure. An intermediate layer of the TS-1 membrane avoids the leaching of Al from the support and ensures the upper layer as the pure hydrophobic TS-1 membrane, proved by XRD, EDS, and water contact angle measurements. Another important advance about the TS-1 membrane is employing a Pd/SiO2 catalytic hydrocracking method to activate it at 593 K. Such a mild method favors maintaining that perfective macrostructure and hydrophobicity. Bearing the thermal stress, generated during the activation process, desires the TS-1 membrane with a sufficient thickness, gained by prolonging the crystallization time. This phenomenon is verified by gas permeation and ascribed with the membrane's mechanical properties.
Keywords: TS-1 membrane; Tertiary growth; Spreading-wetting; Catalytic hydrocracking; Hydrophobicity;

In this study, we report on the fabrication and characterization of periodic Ni and Ni-silicide nanocontact arrays on (1 1 0)Si substrates. From transmission electron microscopy and selected-area electron diffraction analysis, it is found that the epitaxial NiSi2 is the first and the only silicide phase formed in the nanoscale Ni contact/(1 1 0)Si sample after annealing at a temperature as low as 300 °C, demonstrating that the nanoscale Ni contact is more favorable for the epitaxial growth of NiSi2 phase on (1 1 0)Si. The orientation relationship between the epitaxial NiSi2 nanocontacts and the (1 1 0)Si substrate is identified as [1 1 0]NiSi2//[1 1 0]Si and ( 1 ¯ 1 1 ¯ )NiSi2//( 1 ¯ 1 1 ¯ )Si. For the samples annealed at higher temperatures, all the epitaxial NiSi2 nanocontacts formed on (1 1 0)Si are anisotropic in shape and elongated along the crystallographic 1 1 ¯ 0 directions. The observed results can be attributed to the higher surface area to volume ratio of Ni nanocontacts and the faster growth rate along the 〈1 1 0〉 directions than along other directions. The size and periodicity of the nanocontacts can be readily controlled by adjusting the diameter of the colloidal nanosphere template. The self-assembled approach proposed here will provide the capability to fabricate other highly-ordered metal silicide nanocontact arrays and may offer potential applications in constructing silicide-based nanodevices.
Keywords: Self-assembly; Ni silicide; Nanosphere lithography; (1 1 0)Si; Epitaxy; Nanocontact;

Aluminizing a Ni sheet was performed through severe plastic deformation induced by ball collisions. The Ni sheet was fixed in the center of a mechanically vibrated vial between two connected parts. The balls were loaded into the vial on both sides of the Ni disk. Al disks, which were fixed on the top and the bottom of the vial, served as the sources of Al contamination. During processing, the Ni sheet was subject to intense ball collisions. The Al fragments were transferred and alloyed to the surface of the Ni sheet by these collisions. The combined effects of deformation-induced plastic flow, mechanical intermixing, and grain refinement resulted in the formation of a dense, continuous nanostructured Al layer on the Ni surface on both sides of the sheet. The Al layer consisted of Al grains with an average size of about 40 nm. The Al layer was reinforced with nano-sized Ni flakes that were introduced from the Ni surface during processing. The local amorphization at the Ni/Al interface revealed that the bonding between Ni and Al was formed by mechanical intermixing of atomic layers at the interface. The hardness of the fabricated Al layer was 10 times that of the initial Al plate. The ball collisions destroyed the initial rolling texture of the Ni sheet and induced the formation of the mixed [1 0 0] + [1 1 1] fiber texture. The laminar rolling structure of the Ni was transformed into an ultrafine grain structure.
Keywords: Aluminizing; Mechanical alloying; Surface refinement; Nanostructured materials; Metal matrix composites; Texture;

In this work, perfectly organized triangular arrays of vertical nanopores are formed in an alumina matrix by combining a pre-patterning technique with the natural ability of alumina to form a triangular unit cell. More precisely, we imprinted a triangular array of indents on a thin layer of aluminum deposited on silicon substrates using nano-imprint lithography. During the anodization process, we forced the growth of pores in and in-between the indents obtaining a larger number of pores in the final alumina array than the initial number of indents patterned on the aluminum. Adapting the anodization conditions, a density multiplication by three was successfully achieved with a very good surface organization. The experimental details of the process are described in this paper. We studied in details the inner organization of the pores and we identified differences in their propagation between oxalic and orthophosphoric acid. The former showed a good surface propagation until 1500 nm in depth. On the contrary, the latter showed a perturbation in the organization at 450 nm: at this depth, the induced pores stopped whereas the indented ones rearranged into two or three. A longer shift in the initiation of the induced pores seemed to causes this poor propagation. A systematic study was performed to investigate the effect of the anodization conditions on the pores’ propagation. We demonstrate that the optimization of the orthophosphoric acid concentration and the applied voltage towards harder anodization conditions, i.e. to higher values, allows a better control of this self-assembling process and deeper order propagation until more than 1000 nm.
Keywords: Porous anodic alumina; Electrochemistry; Period multiplication; Surface arrangement; Pore propagation;

Fe-N x /C assisted chemical–mechanical polishing for improving the removal rate of sapphire by Li Xu; Chunli Zou; Xiaolei Shi; Guoshun Pan; Guihai Luo; Yan Zhou (115-120).
In this paper, a novel non-noble metal catalyst (Fe-N x /C) is used to improve the removal mass of sapphire as well as obtain atomically smooth sapphire wafer surfaces. The results indicate that Fe-N x /C shows good catalytic activity towards sapphire removal rate. And the material removal rates (MRRs) are found to vary with the catalyst content in the polishing fluid. Especially that when the polishing slurry mixes with 16 ppm Fe-N x /C shows the maximum MRR and its removal mass of sapphire is 38.43 nm/min, more than 15.44% larger than traditional CMP using the colloidal silicon dioxide (SiO2) without Fe-N x /C. Catalyst-assisted chemical–mechanical polishing of sapphire is studied with X-ray photoelectron spectroscopy (XPS). It is found that the formation of a soft hydration layer (boehmite, γ-AlOOH or γ-AlO(OH)) on sapphire surface facilitates the material removal and achieving fine surface finish on basal plane. Abrasives (colloid silica together with magnetite, ingredient of Fe-N x /C) with a hardness between boehmite and sapphire polish the c-plane of sapphire with good surface finish and efficient removal. Fe2O3, Fe3O4, pyridinic N as well as pyrrolic N group would be the catalytical active sites and accelerate this process. Surface quality is characterized with atomic force microscopy (AFM). The optimum CMP removal by Fe-N x /C also yields a superior surface finish of 0.078 nm the average roughness (Ra).
Keywords: Sapphire; Catalyst-assisted chemical–mechanical polishing; Non-noble metal catalyst; Material removal rate; Step-terrace structure;

A first-principles study on gas sensing properties of graphene and Pd-doped graphene by Ling Ma; Jian-Min Zhang; Ke-Wei Xu; Vincent Ji (121-127).
Sensitivity of pristine graphene (PG) and Pd-doped graphene (Pd-G) toward a series of small gas molecules (CO, NH3, O2 and NO2) has been investigated by first-principles based on density functional theory (DFT). The most stable adsorption configuration, adsorption energy, charge transfer, density of states and magnetic moment of these molecules on PG and Pd-G are thoroughly discussed. It is found that four gas molecules are weakly adsorbed on PG with low adsorption energy of 0.08–0.24 eV, and the electronic properties of PG are only sensitive to the presence of O2 and NO2 molecules. In contrast, doping graphene with Pd dopants significantly enhances the strength of interaction between adsorbed molecules and the modified substrate. The dramatically increased adsorption energy and charge transfer of these systems are expected to induce significant changes in the electrical conductivity of the Pd-G sheet. The results reveals that the sensitivity of graphene-based chemical gas sensors could be drastically improved by introducing the Pd dopants, so Pd-G is more suitable for gas molecules detection compared with PG.
Keywords: Gas sensitivity; Pd-doped graphene; Density functional theory;

Growth characteristics of graphene synthesized via chemical vapor deposition using carbon tetrabromide precursor by Taejin Choi; Hanearl Jung; Chang Wan Lee; Ki-Yeung Mun; Soo-Hyun Kim; Jusang Park; Hyungjun Kim (128-132).
A carbon tetrabromide (CBr4) precursor was employed for the chemical vapor deposition (CVD) of graphene, and the graphene growth characteristics as functions of the following key factors were then investigated: growth time, growth temperature, and the partial pressure of the precursor. The graphene was transferred onto a SiO2/Si substrate and characterized using transmission electron microscopy, Raman spectroscopy, and X-ray photoelectron spectroscopy, and the electrical properties were measured through the fabrication of field-effect transistors. Our results show that high yield and controllable growth are possible via CVD used with a CBr4 precursor. Thus, CBr4 precursor is a new alternative candidate for use in the mass production of graphene.
Keywords: Graphene; Carbon tetrabromide; Chemical vapor deposition; High yield; Bond dissociation energy;

Effect of laser surface melting on microstructure and corrosion characteristics of AM60B magnesium alloy by Cancan Liu; Jun Liang; Jiansong Zhou; Lingqian Wang; Qingbiao Li (133-140).
Surface modification of laser surface melting (LSM) was applied to the AM60B magnesium alloy using a 10 kW continuous-wave CO2 laser. The microstructure, composition and corrosion resistance of AM60B magnesium alloy after LSM treatment were investigated by using scanning electron microscopy (SEM), energy-dispersive spectroscopy (EDS), X-ray diffraction (XRD) and corrosion tests, respectively. Results showed that the LSM treatment produced a continuous and homogeneous modified layer with refined grains, enriched Al element and redistributed intermetallic compounds on AM60B alloy. The corrosion resistance of the AM60B alloy was enhanced by the LSM treatment. The enhancement of the corrosion resistance was mainly attributed to the reduced corrosion susceptibility of Al enriched α-Mg matrix and the barrier effect of uniformly distributed β-phase of the LSM modified layer.
Keywords: Magnesium alloy; Laser surface melting; Microstructure; Corrosion resistance;

Micro-dimple arrays play an important role in improving the performance and reliability of mechanical systems, and micro-dimples on the surfaces of piston rings and sliding bearings may reduce friction. Although many methods can be employed to create micro-dimples on cylindrical surfaces, it is still a challenge to generate micro-dimple arrays on cylindrical surfaces with high efficiency and low cost. In this paper, a patterned polydimethylsiloxane (PDMS) mask with good flexibility is introduced as a mask in through-mask electrochemical micromachining (TMEMM) for generating micro-dimple arrays on a cylindrical surface, in which thousands of micro-dimples can be fabricated in tens of seconds. In addition, the reusability of the PDMS mask is experimentally verified. To enhance removal of the product, the use of a pulsed current is introduced into TMEMM of micro-dimples. The experimental results show that the pulse duty cycle plays a significant role in enhancing the removal of product and improving the uniformity of the micro-dimple arrays. And the effect was weakened with increasing pulse duty cycle. Compared with duty cycles of 40, 60, and 80%, the highest current efficiency with a duty cycle of 20% is obtained at a frequency of 10 kHz. Finally, micro-dimple arrays with a diameter of approximately 110.6 μm and a depth of 11 μm are successfully generated on the cylindrical surface.
Keywords: Electrochemical micromachining; Micro-dimple arrays; Cylindrical surface; Pulsed current; PDMS mask; Reusability;

Synthesis and characterization of ZnO/Cu2O core–shell nanowires grown by two-step electrodeposition method by O. Messaoudi; H. Makhlouf; A. Souissi; I. Ben assaker; G. Amiri; A. Bardaoui; M. Oueslati; M. Bechelany; R. Chtourou (148-152).
ZnO/Cu2O core/shell nanowires have been grown by two-step electrodeposition method on ITO-coated glass substrates. The sample's morphology was explored by means of scanning electron microscopy (SEM). SEM images confirm the homogeneity of the nanowires and the presence of Cu2O shell on ZnO core. X-ray diffraction and Raman scattering measurements were used to investigate the purity and the crystallinity of the samples. Optical transmission measurements reveal an additional contribution at about 1.7 eV attributed to the type-II interfacial transition witch confirms the advantage of using the ZnO/Cu2O structure in photovoltaic application.
Keywords: ZnO/Cu2O core/shell; Electrochemical deposition; Type-II heterostructures; Raman scattering;

The effects of forming speed and temperature on the forming mechanism and mechanics of Cu50Zr25Ti25 metallic glass are studied using molecular dynamics simulations based on the second-moment approximation of the many-body tight-binding potential. These effects are investigated in terms of atomic trajectories, flow field, slip vectors, internal energy, radial distribution function, and elastic recovery of nanoimprint lithography (NIL) patterns. The simulation results show that a shear transformation zone (STZ) forms at the substrate surface underneath the mold during the forming process. The STZ area increases with mold displacement (D). The movement speed of substrate atoms underneath the mold increases with increasing D value. The movement directions of substrate atoms underneath the mold are more agreeable for a larger D value. The stick-slip phenomenon becomes more obvious with increasing D value and imprint speed. The substrate energy increases with increasing imprint speed and temperature. Great NIL pattern transfer is obtained with unloading at low temperatures (e.g., room temperature).
Keywords: Metallic glass; Forming; Mechanics; Mechanical properties; Molecular dynamics;

UV irradiated PVA–Ag nanocomposites for optical applications by Rishi Pal Chahal; Suman Mahendia; A.K. Tomar; Shyam Kumar (160-165).
The present paper is focused on the in-situ prepared Poly (vinyl alcohol)–Silver (PVA–Ag) nanocomposites and tailoring their optical properties by means of UV irradiation in such a way that these can be used for anti-reflective coatings and bandpass filters. The reflectance from these irradiated nanocomposites has been found to decrease leading to the increase in refractive index (RI), with increasing UV exposure time, in the entire visible region. Decrease in optical energy gap of PVA film from 4.92 to 4.57 eV on doping with Ag nanoparticles has been observed which reduces further to 4.1 eV on exposure to UV radiations for 300 min. This decrease in optical energy gap can be correlated to the formation of charge transfer complexes within the base polymer network on embedding Ag nanoparticles, which further enhances with increasing exposure time. Such complexes may also be responsible for increased molecular density of the composite films which corresponds to decrease in reflectance corroborating the observed results.
Keywords: UV irradiation; Optical energy gap; Refractive index; Anti-reflection coating;

Ionization of covalent immobilized poly(4-vinylphenol) monolayers measured by ellipsometry, QCM and SPR by Suji Uppalapati; Na Kong; Oscar Norberg; Olof Ramström; Mingdi Yan (166-171).
Covalently immobilized poly(4-vinylphenol) (PVP) monolayer films were fabricated by spin coating PVP on perfluorophenyl azide (PFPA)-functionalized surfaces followed by UV irradiation. The pH-responsive behavior of these PVP ultrathin films was evaluated by ellipsometry, quartz crystal microbalance (QCM) and surface plasmon resonance (SPR). By monitoring the responses of these films to pH in situ, the ionization constant of the monolayer thin films was obtained. The apparent pK a value of these covalently immobilized PVP monolayers, 13.4 by SPR, was 3 units higher than that of the free polymer in aqueous solution.
Keywords: Poly(4-vinylphenol); Monolayer; Perfluorophenyl azide; pH response; Ionization constant;

Superhydrophobic surfaces on the basis of hierarchical ZnO particles grafted by fluoroethylene-vinylether (FEVE) polymer derivative were prepared using a facile, mild and low-cost method. X-ray diffraction (XRD) and scanning electron microscope (SEM) revealed that the resulting ZnO particles via hydrothermal process exhibit micro–nano dual-scale morphology with high purity under a suitable surfactant amount and alkali concentration. The grafting of FEVE derivative was confirmed by Fourier transform infrared spectroscopy (FTIR) and energy-dispersive X-ray spectrometer (EDS), suggesting that hierarchical surface of ZnO particles was an imported monomolecular layer of fluorocarbon polymer. The obtained surface fabricated by drop-casting shows considerably high contact angle and good resistance to water immersion. The wetting behavior in this work was furthermore analyzed by theoretical wetting model. This work demonstrates that the sufficient low-wettable surface and high roughness both take a vital role in the superhydrophobic behavior.
Keywords: Superhydrophobicity; Hydrothermal process; Surface grafting; Contact angle; Wetting model;

Modification of TiO2 nanotubes by WO3 species for improving their photocatalytic activity by Hui Sun; Bohua Dong; Ge Su; Rongjie Gao; Wei Liu; Liang Song; Lixin Cao (181-187).
WO3/TiO2 nanotubular composite was synthesized at low temperature (383 K) by a novel approach. WO3 nanoparticles were loaded on anatase TiO2 nanotubes through the reaction between (NH4)6W7O24·6H2O and aqueous solution of HCl. The obtained products were characterized by transmission electron microscopy (TEM), X-ray diffraction (XRD) and UV–vis diffuse reflectance spectroscopy (UV-DRS). Degradation of methyl orange was employed to investigate the photocatalytic activity of the products. Results show that, among the samples with different concentrations of WO3, W10T with the atomic ratio W/Ti of 10% presents optimal degradation rate. This degradation rate is about 95% within 2 h under UV light irradiation, which is much higher than that of pure TiO2 nanotubes.
Keywords: WO3/TiO2 nanotubes; Photocatalytic activity; Hydrothermal; Ammonium paratungstate;

Modeling of the temperature field in the amorphous Ge2Sb2Te5 film induced by a picosecond laser with a body heat source by F.R. Liu; Z.K. Fan; Z. Zhu; J.F. Yang; X. Lin; F. Liu; N.X. Sun (188-193).
Three-dimensional body-heating finite element method simulation was carried out to study the temperature field of the amorphous Ge2Sb2Te5 film induced by picosecond laser pulse. In the model, the continuous medium heat conduction theory with semi-infinity heat conduction was employed together with the assumption of the Gaussian temporal and spatial profiles. The verification between the prediction and experiment showed that simulated results reasonably agreed with experimental observations. Based on the simulation, it showed that the maximum temperature appeared at the top surface center, and the variation of temperature field within the whole film followed the same trend. Characteristics of the temperature field between the thin and thick films were further compared. A relatively homogeneous temperature field along the thickness direction was obtained for the case of thin film where thermal equilibrium reaches quickly. The total absorbed energy by the Ge2Sb2Te5 film increased with the increase of film thickness, however, the predicted maximum temperature at the top surface center declines with the increment of film thickness, which is affected by thermal conduction.
Keywords: Phase-change material; Temperature field; Finite element model; Body heat source;

We introduce a simple method to synthesize localized surface plasmon resonance (LSPR) sensor chip of Ag NPs on the hydrogenated amorphous carbon by co-deposition of RF-Sputtering and RF-PECVD. The X-ray photoelectron spectroscopy revealed the content of Ag and C atoms. X-ray diffraction profile and atomic force microscopy indicate that the Ag NPs have fcc crystal structure and spherical shape and by increasing deposition time, particle sizes do not vary and only Ag NPs aggregation occurs, resulting in LSPR wavelength shift. Firstly, by increasing Ag NPs content, in-plan interparticles coupling is dominant and causes redshift in LSPR. At the early stage of agglomeration, out-plane coupling occurs and in-plane coupling is reduced, resulting a blueshift in the LSPR. By further increasing of Ag NPs content, agglomeration is completed on the substrate and in-plan coupling rises, resulting significant redshift in the LSPR. Results were used to implement biosensor application of chips. Detection of DNA primer at fM concentration was achieved based on breaking interparticles coupling of Ag NPs. A significant wavelength shift sensitivity of 30 nm and a short response time of 30 min were obtained, where both of these are prerequisite for biosensor applications.
Keywords: Ag NPs@a-C:H; RF-PECVD; LSPR biosensor chip; AFM; XPS; DNA primer;

Investigation of adhesion between molybdenum and polysilazane by XPS by Dodji Amouzou; Lionel Fourdrinier; Robert Sporken (202-206).

Forming ceria shell on Au-core by LSPR photothermal induced interface reaction by Y.H. Qu; F. Liu; Y. Wei; C.L. Gu; L.H. Zhang; Y. Liu (207-211).
A novel method for preparing core–shell structure of Au@ceria was presented, which is characterized with using photothermal effect from localized surface plasmon resonance (LSPR) to induce heat, and the heat can trigger the shell formation reactions confined on the surface of the Au nanoparticles (NPs). In short of the preparation procedure, aqueous sol of Au NPs, citric acid, ethylene glycol and cerous nitrate were irradiated with a Xe arc lamp, maintaining the temperature of the sol at 25 °C by cooling and stirring the sol. The Au NPs could generate heat from LSPR, and the heat induced polymerization reaction in the sol, resulting in cerium gel formation which enveloped each of the Au NPs, and the gel containing cerium formed only on the surface of the Au NPs. After calcination, Au@ceria was obtained. This method can be extended for preparing various core@shell nanocomposites in which metal cores possess LSPR effect and the shell formation can be induced by heat.
Keywords: Localized surface plasmon resonance (LSPR); Core–shell nanoparticle; Photothermal effect; Interface reaction; Au@ceria;