Applied Surface Science (v.322, #C)

The environmental stability of solution processed Al-doped ZnO (AZO) thin films was enhanced by functionalizing the film surface with a thin self-assembled molecular layer. Functionalization of AZO films was performed using two types of molecules having identical 12-carbon alkyl chain termination but different functional groups: dodecanethiol (DDT) and dodecanoic acid (DDA). Surface modified AZO films were examined using electrical resistivity measurements, contact angle measurements and quantitative nanomechanical property mapping atomic force microscopy. The hydrophobic layer inhibits the penetration of oxygen and water into the AZO's grain boundaries thus significantly increasing the environmental stability over unmodified AZO. Surface modified AZO films using DDT exhibited lower electrical resistivity compared to DDA functionalized AZO films. Our study demonstrates a new approach for improving the physical properties of oxide based nanoparticulate films for device applications.
Keywords: Al-doped ZnO; Nanoparticulate thin films; Solution process; Surface modification; Environmental stability;

Non-vacuum electron-beam carburizing and surface hardening of mild steel by I.A. Bataev; M.G. Golkovskii; A.A. Losinskaya; A.A. Bataev; A.I. Popelyukh; T. Hassel; D.D. Golovin (6-14).
In this paper, we study the structure, microhardness, and tribological properties of surface layers of mild (0.19% C) steel, which was formed by electron-beam cladding with an iron–graphite powder mixture followed by quenching and tempering. A 1.4 MeV electron beam that was extracted into air was used. Cladding of steel with the iron–graphite mixture at a beam current of 24 and 26 mA formed a hypoeutectic cast iron layer (2.19% C) and a hypereutectoid steel (1.57% C) layer, which were 2.0 and 2.6 mm thick, respectively. The microhardness of the surface-quenched and tempered steel and cast iron layers was 7 and 8 GPa, respectively. Electron-beam quenching of the surface layers of hypoeutectic cast iron was accompanied with multiple cracking. During the quenching of the 1.57% C steel layer, crack formation was not observed. In friction tests against fixed and loose abrasive particles, the surface layers of hypereutectoid steel and hypoeutectic cast iron that were produced by electron-beam cladding and quenching had lower wear rates than mild steel after pack carburizing, quenching, and tempering. In the sliding wear tests, the cast iron clad layer, which was subjected to electron-beam quenching and tempering, exhibited the highest wear resistance. Electron-beam treatment can be used to harden local areas of large workpieces. It is reasonable to treat clad layers of high-carbon steel with electron-beam quenching and tempering. To prevent multiple cracking, white cast iron layers should not be quenched.
Keywords: Electron beam; Carburizing; Surface hardening; Microstructure; Wear resistance;

Morphological variation of highly porous Ni–Sn foams fabricated by electro-deposition in hydrogen-bubble templates and their performance as pseudo-capacitors by Kai Zhuo; Myung-Gi Jeong; Myung Sik Shin; Woo Won Chun; Jong Wook Bae; Pil Jin Yoo; Chan-Hwa Chung (15-20).
Ni–Sn alloy foams with different morphologies for pseudo-capacitor applications have been prepared by electro-deposition involving a hydrogen evolution reaction. The morphology depends upon the composition of electrolytes and the electro-deposition temperature. Among the several different structures of Ni–Sn foams, one that has been prepared at 45 °C represents the best electro-chemical performance of 1313 F g−1 at 1 A g−1 and it retained up to 91% of its initial performance even after 5000 cycles of charge–discharge. This Ni–Sn foam has a planar dendrite structure with bundles of flower-like tubes, providing highly porous foam with an extremely large surface area.
Keywords: Ni–Sn foams; Pseudo-capacitor; Electro-deposition; Hydrogen-bubble template;

Reduction of V2O5 thin films deposited by aqueous sol–gel method to VO2(B) and investigation of its photocatalytic activity by Olivier Monfort; Tomas Roch; Leonid Satrapinskyy; Maros Gregor; Tomas Plecenik; Andrej Plecenik; Gustav Plesch (21-27).
A way of preparation of VO2(B) thin films by reduction of V2O5 films synthesized from an aqueous sol–gel system has been developed and photocatalytic properties of the obtained films were studied. The reduction was performed by annealing of the V2O5 film in vacuum as well as in H2/Ar atmosphere, which was followed by temperature dependent XRD. It has been shown that the reduction is influenced by the layered-structure of the vanadium oxides. It is a two-step process, where the mixed-valence vanadium oxide V4O9 is first formed before reaching the VO2(B) phase. The film microstructure was characterized by SEM and AFM and the valence states of vanadium in VO2(B) films were evaluated by XPS. The VO2(B) polymorph shows an energy band-gap around 2.8 eV and it exhibits photocatalytic properties. It was measured by following the degradation of rhodamine B under UVA as well as metalhalogenide lamp irradiation, which has similar spectral distribution as natural sunlight. The VO2(B) films show distinct photoactivities under both lamps, although they were found to be more active under the UVA irradiation. The film annealed under reducing hydrogen atmosphere, which exhibits higher granularity and surface roughness, shows higher photoactivity than the vacuum-annealed film.
Keywords: Sol–gel; Vanadium oxides; VO2(B); Film; XRD; Photocatalysis;

Freestanding membrane composed of micro-ring array with ultrahigh sidewall aspect ratio for application in lightweight cathode arrays by Lanlan Wang; Hongzhong Liu; Weitao Jiang; Wei Gao; Bangdao Chen; Xin Li; Yucheng Ding; Ningli An (28-34).
A freestanding multilayer ultrathin nano-membrane (FUN-membrane) with a micro-ring array (MRA), in which the dimension of each micro-ring is 3 μm in diameter, 2 μm in height and sub-100 nm in sidewall thickness is successfully fabricated, as shown in the SEM image of figure (a). Due to the MRA with ultrahigh aspect ratio of dielectric-metal sidewall, the FUN-membrane can be transferred to either rigid or flexible substrate to be used as the cathode for lightweight display panel, as shown in the schematic of figure (b).A freestanding multilayer ultrathin nano-membrane (FUN-membrane) with a micro-ring array (MRA) is successfully fabricated through the controllable film deposition. Each micro-ring of FUN-membrane is 3 μm in diameter, 2 μm in height and sub-100 nm in sidewall thickness, demonstrating an ultrahigh sidewall aspect ratio of 20:1. In our strategy, a silica layer (200 nm in thickness), a chromium transition layer (5 nm-thick) and a gold layer (40 nm-thick), were in sequence deposited on patterned photoresist. After removal of the photoresist by lift-off process, a FUN-membrane with MRA was peeled off from the substrate, where the gold layer acted as a protecting layer to prevent the MRA from fracture. The FUN-membrane was then transferred to a flexible polycarbonate (PC) sheet coated with indium tin oxide (ITO) layer, which was then used as a flexible and lightweight cathode. Remarkably, the field emission effect of the fabricated FUN-membrane cathode performs a high field-enhancement factor of 1.2 × 104 and a low turn-on voltage of 2 V/μm, indicating the advantages of the sharp metal edge of MRA. Due to the rational design and material versatility, the FUN-membrane thus could be transferred to either rigid or flexible substrate, even curved surface, such as the skin of bio-robot's arm or leg. Additionally, the FUN-membrane composed of MRA with extremely high aspect ratio of insulator-metal sidewall, also provides potential applications in optical devices, lightweight and flexible display devices, and electronic eye imagers.
Keywords: Freestanding ultrathin nano-membrane; Electronic transport in nanoscale materials and structures; Field emitters and array;

Photocatalytic efficiency of reusable ZnO thin films deposited by sputtering technique by R. Ahumada-Lazo; L.M. Torres-Martínez; M.A. Ruíz-Gómez; O.E. Vega-Becerra; M.Z. Figueroa-Torres (35-40).
The photocatalytic activity of ZnO thin films with different physicochemical characteristics deposited by RF magnetron sputtering on glass substrate was tested for the decolorization of orange G dye aqueous solution (OG). The crystalline phase, surface morphology, surface roughness and the optical properties of these ZnO films were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), atomic force microscopy (AFM) and UV–visible spectroscopy (UV–Vis), respectively. The dye photodecolorization process was studied at acid, neutral and basic pH media under UV irradiation of 365 nm. Results showed that ZnO films grow with an orientation along the c-axis of the substrate and exhibit a wurtzite crystal structure with a (002) preferential crystalline orientation. A clear relationship between surface morphology and photocatalytic activity was observed for ZnO films. Additionally, the recycling photocatalytic abilities of the films were also evaluated. A promising photocatalytic performance has been found with a very low variation of the decolorization degree after five consecutive cycles at a wide range of pH media.
Keywords: Sputtering; Decolorization; Orange G; UV-light; Photocatalysis; pH media.;

In vitro biocompatibility response of Ti–Zr–Si thin film metallic glasses by J.L. Ke; C.H. Huang; Y.H. Chen; W.Y. Tsai; T.Y. Wei; J.C. Huang (41-46).
In this study, the bio-electrochemical response of the Ti–Zr–Si thin film metallic glasses (TFMGs) in simulated body fluid with different contents of titanium is measured via potentiostat. According to the results of bio-corrosion potential and current, as well as the polarization resistance, it is concluded that the Ti66Zr25Si9 TFMGs possess the highest bio-electrochemical resistance. With increasing content of titanium, the corrosion resistance becomes progressively higher. The passive current results reveal that amorphous alloys can form a more protective and denser passive film on the metallic glass surface than the crystalline materials. In addition, the mechanical performance of the Ti–Zr–Si TFMGs is better than the crystalline counterparts. As a result, the Ti-based TFMGs are considered to be potential materials for bio-coating applications.
Keywords: Ti; Metallic glass; Biomaterials; Electrochemical; Corrosion;

The corrosion behaviour of a type 316L (UNS S31603) stainless steel (SS) expansion joint in a simulated leaching solution of sediment on blast furnace gas pipeline in a power plant is investigated by using dynamic potential polarization curves, electrochemical impedance spectroscopy (EIS), optical microscope, atomic force microscope (AFM) and Scan Kelvin Probe (SKP). Severe general corrosion accompanied by pitting corrosion occurs on the type 316L SS surface in this solution. As the immersion period increases, the charge transfer resistance R ct decreases, the dissolution rate accelerates, the surface roughness increases and the surface potential difference enhances significantly. Then eight corrosion-resistant materials are tested, the corrosion rates of type 254SMo SS, type 2507 SS and TA2 are relatively minor in the solution. The corrosion resistance properties of TA2 is most excellent, indicating it would be the superior material choice for blast furnace gas pipeline.
Keywords: High acidified chloride solution; Blast furnace gas pipeline; Corrosion; Stainless steel; TA2.;

Replication of rose petal surfaces using a nickel electroforming process and UV nanoimprint lithography by Sang-woo Ryu; Soyoung Choo; Hak-Jong Choi; Chae-Hyun Kim; Heon Lee (57-63).
In this research, we replicate the hierarchical structures of rose petals by using poly urethane acrylate (PUA) nanomolding technology. After a molding process, we use a PUA replica as the mother mold for nickel electroforming processes. By replicating the original rose petal hierarchical structure, we obtain the rose petal effect with nickel substrates. In order to make a negative-patterned nickel stamp, a second PUA replication was done using the first PUA mother mold and a nickel electroforming process was performed. Using these, the hierarchical structure of rose petals was imprinted in perfluoropolyether (PFPE), which exhibited the petal effect.
Keywords: Rose petal effect; PUA nanomolding; Nickel electroforming; PFPE UV nanoimprint lithography;

A modified solid electrolyte interface (SEI) on a graphite negative electrode with a fluoroethylene carbonate (FEC) additive was prepared by narrow-range cycling in a cell formation process. The SEI surface properties were investigated by extreme high-resolution scanning electron microscopy (XHR-SEM) under low acceleration voltage and X-ray photoelectron spectroscopy (XPS). A linkage structure of submicron-sized particles on the SEI film layer largely developed by narrow-range cycling in the formation process; these particles were mainly composed of the inorganic component (P―F bonding states, LiP x O y F z ) from the FEC. The application of narrow-range cycling with an FEC additive in the formation process improves the cycling performance and Coulombic efficiency of the cell. It is suggested that the SEI layer modified with FEC-derived SEI components on the graphite anode electrode by narrow-range cycling in the formation process, could improve the cell performance.
Keywords: Solid electrolyte interface; Formation process; Narrow-range cycling; Fluoroethylene carbonate; Linkage structure; Cyclability;

Rod-shaped hydroxyapatite with mesoporous structure as drug carriers for proteins by Wandong Zhang; Yamin Chai; Xianghua Xu; Yonglan Wang; Nana Cao (71-77).
Rod-shaped hydroxyapatite (HAp) with mesoporous structure was synthesized by a hydrothermal method using Pluronic block co-polymer F127 as the template. The rod-shaped HAp was then tested as protein drug carriers by investigating their protein adsorption/release properties. Bovine serum albumin (BSA) and lysozyme (LSZ) were used as the model drugs. Various instrumental methods were used to characterize the structure, morphology, texture and protein drug adsorption/release properties of the samples. The amounts of BSA or LSZ adsorbed onto the rod-shaped HAp and their release profiles were evaluated in a simulated body fluid (SBF). The synthesized rod-shaped HAp had irregular mesostructures with lengths of 75–125 nm and diameters of about 25 nm. The rod-shaped HAp exhibited a higher loading capacity for BSA than for LSZ in the SBF. This adsorption behavior can be explained by the morphology of the rod-shaped HAp, which grew along the c-axis, leading to an a(b)-plane area that is larger than the c-plane area. Consequently, the number of positive charges on the surface of the rod-shaped HAp increased relative to the number of negative charges. The BSA release rate in SBF was slower than that of LSZ which is a result of the HAp surface properties.
Keywords: Hydroxyapatite; Mesoporous; Proteins; Drug delivery;

Dissolution behaviour of model basalt fibres studied by surface analysis methods by T. Förster; C. Scheffler; E. Mäder; G. Heinrich; D.A. Jesson; J.F. Watts (78-84).
New concepts of surface modifications aimed at the enhancement of alkali resistance of basalt fibres require research work on chemical composition of interacting surface layers as well as knowledge about fundamental processes of basaltic glass dissolution. Therefore, two model basalt fibres manufactured out of subalkaline and alkaline rock material were leached in NaOH solution at a temperature of 80 °C for up to 11 days. The formation of a corrosion shell was observed in both cases and was analyzed by SEM/EDX. The model fibres out of subalkaline rocks show dissolution kinetic, which is two-staged, whereas the more alkaline fibre reflects a linear one. The complex composition of basalt fibre is detected by EDX and XPS. The surface of basalt fibres is rich in Si and Al. XPS high resolution spectra provide information on oxidation state of iron.
Keywords: Basalt fiber; Dissolution kinetics; XPS; EDX;

Chemical and microstructural transformations in lithium iron phosphate battery electrodes following pulsed laser exposure by Adrian H.A. Lutey; Maurizio Fiorini; Alessandro Fortunato; Alessandro Ascari (85-94).
Multi-layer lithium iron phosphate (LFP) battery electrodes are exposed to nanosecond pulsed laser radiation of wavelength 1064 nm. Test parameters are chosen to achieve characteristic interaction types ranging from partial incision of the active coating layers only to complete penetration of the electrodes with high visual cut quality. Raman spectroscopy is performed on unexposed regions and at points approaching each incision, highlighting changes in chemical composition and microstructure in the heat affected zone (HAZ). Thermogravimetric analysis is performed on the unexposed electrode active materials to distinguish the development of compositional changes under conditions of slow heating below the melting and sublimation temperatures. A brief theoretical description of the physical phenomena taking place during laser exposure is provided in terms of direct ablation during each laser pulse and vaporization or thermal degradation due to conductive heat transfer on a much longer time-scale, with characteristics of the HAZ reported in terms of these changes. For all laser exposures carried out in the study, chemical and microstructural changes are limited to the visible HAZ. Some degree of oxidation and LFP olivine phase degradation is observed in the cathode, while the polycrystalline graphite structure becomes less ordered in the anode. Where complete penetration is achieved, melting of the cathode active layer and combustion of the anode active layer take place near the cut edge due to thermal conduction from the metallic conductive layers. The presented results provide insight into the effects of laser processing on LFP electrode integrity.
Keywords: Laser cutting; Raman spectroscopy; Lithium ion; LiFePO4; Graphite;

Piezoelectric nanogenerator based on a flexible carbon-fiber/ZnO–ZnSe bilayer structure wire by Chunlei Liu; Weiguang Zhang; Jianbo Sun; Jing Wen; Qing Yang; Huixin Cuo; Xinzhi Ma; Mingyi Zhang (95-100).
The pin-shaped ZnO–ZnSe nanowire arrays on the surface of a carbon fiber (CF/ZnO–ZnSe) were synthesized via two-step hydrothermal method. Based on a single CF/ZnO–ZnSe on a polymer substrate, a flexible nanogenerator device was fabricated which produced high-output current about 333 μA when the device was subjected to a −0.55% tensile strain and the current was enhanced by as much as 66%. The superior piezoelectric performance is derived from the piezopotential in ZnO nanowire arrays induced by the compressive strain or tensile strain, which lowers or raises the barrier height and increases or decreases the current density at the ZnO–ZnSe heterojunction interface. This kind of CF/ZnO–ZnSe bilayer structure has a great potential for nanogenerator device and this result opens up the path for practical applications of piezoelectric nanogenerator.
Keywords: Carbon–fiber/ZnO–ZnSe; Nanogenerator; Piezoelectric; High-output current;

Polyvinylidene fluoride (PVDF) membrane and PVDF membrane with phenolphthalein polyethersulfone (PES-C) addition were prepared via thermally induced phase separation (TIPS) method by using diphenyl carbonate (DPC) and dimethyl acetamide (DMAc) as mixed diluents. The effects of coagulation temperature and pre-evaporation time on structure and properties of membranes were studied. The changes of sewage flux in MBR and the attenuation coefficient of sewage flux were investigated. The resistance distributions of PVDF and PVDF/PES-C membranes were compared by resistance analysis. Membrane composition and structure were characterized by ATR-FTIR, TGA, SEM and AFM. The foulant on membranes was analyzed by FTIR. The contact angle of PVDF/PES-C membrane was lower than that of PVDF membrane. A thinner skin layer and a porous cellular support layer formed in PVDF/PES-C membrane and resulted in a higher porosity and pure water flux. The pure water flux and porosity of PVDF/PES-C membrane increased with rising coagulation temperature and decreased with extending pre-evaporation time. The flux attenuation coefficient, the cake layer resistance and internal fouling resistance of PVDF/PES-C membrane in MBR were smaller than those of PVDF membrane in MBR. The FTIR spectrum of foulant on membrane indicated that the foulant on PVDF/PES-C membrane was mostly composed of protein and polysaccharide, while the foulant on pure PVDF membrane included biopolymer clusters besides protein and polysaccharide.
Keywords: Polyvinylidene fluoride (PVDF); Phenolphthalein polyethersulfone (PES-C); Membrane; Resistance; Foulant;

CeO2 thin films were deposited on Si (1 1 1) substrates by laser molecular-beam epitaxy (LMBE). The thermal stability and surface behaviors of CeO2/Si samples were investigated by X-ray photoelectron spectroscopy during in-situ vacuum annealing. Temperature dependency of surface compositions was identified. At the temperature from 700 K to 1000 K, CeO2 was reduced gradually, but incomplete transformation of CeO2 to Ce2O3 was found even when the sample was annealed at 1000 K for an hour. When the sample was exposed to oxygen ambience, the enhanced thermal stability of the partially reduced surface was revealed by the slight variation of Ce3d and Ce4d spectra. Si2p peak at 102.7 eV was detected on the top surface after the whole heating treatments, while not for the sub-surface during sputtering till to the interface. The Si signal at the outmost surface is induced by surface segregation due to the decreasing solid solubility of Si atoms in CeO2 matrix with the decreasing temperature. At the interface, Si2p peaks at 99.9 eV with the presence of Ce4d peaks at 122.2 eV and 125.6 eV are attributed to the formation of cerium silicates with Ce–Si–O matrix during annealing due to interfacial reactions, which are supposed to stabilize the partially reduced ceria system.
Keywords: CeO2 thin films; Thermal stability; Vacuum annealing; Solid-state reaction;

Feature extraction plays a great important role in image processing and pattern recognition. As a power tool, multifractal theory is recently employed for this job. However, traditional multifractal methods are proposed to analyze the objects with stationary measure and cannot for non-stationary measure. The works of this paper is twofold. First, the definition of stationary image and 2D image feature detection methods are proposed. Second, a novel feature extraction scheme for non-stationary image is proposed by local multifractal detrended fluctuation analysis (Local MF-DFA), which is based on 2D MF-DFA. A set of new multifractal descriptors, called local generalized Hurst exponent (Lh q ) is defined to characterize the local scaling properties of textures. To test the proposed method, both the novel texture descriptor and other two multifractal indicators, namely, local Hölder coefficients based on capacity measure and multifractal dimension D q based on multifractal differential box-counting (MDBC) method, are compared in segmentation experiments. The first experiment indicates that the segmentation results obtained by the proposed Lh q are better than the MDBC-based D q slightly and superior to the local Hölder coefficients significantly. The results in the second experiment demonstrate that the Lh q can distinguish the texture images more effectively and provide more robust segmentations than the MDBC-based D q significantly.
Keywords: Image stationarity; Local multifractal detrended fluctuation analysis; Local generalized Hurst exponent; Image segmentation; Noise;

Tuning the grade of graphene: Gamma ray irradiation of free-standing graphene oxide films in gaseous phase by Ludovic F. Dumée; Chunfang Feng; Li He; Francois-Marie Allioux; Zhifeng Yi; Weimin Gao; Connie Banos; Justin B. Davies; Lingxue Kong (126-135).
A direct approach to functionalize and reduce pre-shaped graphene oxide 3D architectures is demonstrated by gamma ray irradiation in gaseous phase under analytical grade air, N2 or H2. The formation of radicals upon gamma ray irradiation is shown to lead to surface functionalization of the graphene oxide sheets. The reduction degree of graphene oxide, which can be controlled through varying the γ-ray total dose irradiation, leads to the synthesis of highly crystalline and near defect-free graphene based materials. The crystalline structure of the graphene oxide and γ-ray reduced graphene oxide was investigated by x-ray diffraction and Raman spectroscopy. The results reveal no noticeable changes in the size of sp2 graphitic structures for the range of tested gases and total exposure doses suggesting that the irradiation in gaseous phase does not damage the graphene crystalline domains. As confirmed by X-ray photoemission spectroscopy, the C/O ratio of γ-ray reduced graphene oxide is increasing from 2.37 for graphene oxide to 6.25 upon irradiation in hydrogen gas. The removal of oxygen atoms with this reduction process in hydrogen results in a sharp 400 times increase of the electrical conductivity of γ-ray reduced graphene oxide from 0.05 S cm−1 to as high as 23 S cm−1. A significant increase of the contact angle of the γ-ray reduced graphene oxide bucky-papers and weakened oxygen rich groups characteristic peaks across the Fourier transform infrared spectra further illustrate the efficacy of the γ-ray reduction process. A mechanism correlating the interaction between hydrogen radicals formed upon γ-ray irradiation of hydrogen gas and the oxygen rich groups on the surface of the graphene oxide bucky-papers is proposed, in order to contribute to the synthesis of reduced graphene materials through solution-free chemistry routes.
Keywords: Radiation chemistry; Gamma irradiation; Solution-free chemistry; Graphene oxide reduction and graphene bucky-papers;

The surface-enhanced Raman scattering (SERS) activity of the gold nanostars with vimineous branches has been investigated by using rhodamine 6G (R6G) as the Raman active probe. The colloidal gold nanostars have two intense localized surface plasmon resonance (LSPR) peaks in the visible and infrared ranges, respectively. Besides the visible LSPR dependent local field effect induced Raman signal enhancement, the SERS ability also greatly depends on the infrared absorption from the plasmon resonance along the aligned branches. Whether increasing the peak intensity or wavelength of the infrared absorption leads to the efficient improvement of SERS. These correlations between plasmonic absorption and SERS indicate that the lightning rod effect and creation of hot spots have been enhanced with the length and number of gold branches.
Keywords: Gold nanostars; Surface-enhanced Raman scattering (SERS); Localized surface plasmon resonance (LSPR); Absorption spectrum;

Here, the thermal stability of Ag(Al) films in air has been explored by the evolutions of surface morphology and optic-electric properties with annealing temperatures. The results show that the thermal stability of Ag films in air has been improved significantly by adding Al forming Ag(Al) films deposited on glass substrates by co-evaporation. In this experiment, optic-electric properties of Ag(Al) films are stable annealed between 400 and 600 °C for 1 h in air. Until the annealing temperature up to 700 °C, the slight agglomeration appeared in surface only results in the dramatic drop of surface reflectance. It is further found the evident concentration gradient of as-deposited film promotes mostly the distribution of Al gradually uniform and relays Ag agglomeration, meanwhile some Ag gently agglomerates in surface. After achieving a balance, the slight Ag agglomeration is formed in surface.
Keywords: Ag(Al) films; Co-evaporation; Annealing in air; Retardation; Agglomeration;

Solvothermal synthesis and characterization of ceria with solid and hollow spherical and multilayered morphologies by Lei He; Junping Li; Zhihai Feng; Dongfeng Sun; Tingyu Wang; Ruixing Li; Yaohui Xu (147-154).
Ceria powders with different morphologies were synthesized using a facile template-free solvothermal process combined with calcination. The influence of solvothermal temperature and time on the powder was studied. Solid spheres, hollow spheres, and multilayered structures were controlled by adjusting the solvothermal conditions. The possible mechanisms for the formation of the precursors under the solvothermal conditions employed and the evolution of the powder from solid spherical to multilayered structures were discussed. Ethylene glycol played a key role in the morphology evolution of the powder. Cerium catalyzed the Guerbet-like reaction and reacted with ethylene glycol to produce ceria (CeO2), Ce(HCOO)3, and Ce(OH)CO3. The redox-assisted dissolution–recrystallization process significantly contributed to the morphology transformation from solid spheres to multilayered structures. Moreover, the samples synthesized at different temperatures for 24 h possessed excellent adsorption capacities towards the removal of acid orange 7 when compared with commercial ceria.
Keywords: Ceria; Solvothermal; Multilayer structure; Morphology; Adsorption.;

Water dispersible, non-cytotoxic, cross-linked luminescent AIE dots: Facile preparation and bioimaging applications by Meiying Liu; Xiqi Zhang; Bin Yang; Fengjie Deng; Zhen Li; Junchao Wei; Xiaoyong Zhang; Yen Wei (155-161).
Fluorescent organic nanoparticles have attracted great current research interest due to their superior properties as compared with small organic dyes and fluorescent inorganic nanoparticles. However, fluorescent organic nanoparticles based on conventional organic dyes often result in significant fluorescence decrease due to the notorious aggregation-caused quenching effect. On the other hand, these fluorescent organic nanoparticles obtained from self-assembly are normally not stable in diluted solution. Therefore, the development of novel fluorescent organic nanoparticles which could overcome these limitations is highly desirable for their practical biomedical applications. In this work, water dispersible, non-cytotoxic and cross-linked luminescent polymeric nanoparticles based on aggregation induced emission dyes were prepared via one pot emulsion polymerization. These cross-linked luminescent polymeric nanoparticles emitted strong red fluorescence and were highly stable in diluted aqueous solution, making them highly potential for various biomedical applications.
Keywords: Aggregation-induced emission; Fluorescent organic nanoparticles; Cross-linked; Emulsion polymerization; Cell imaging;

Functionalized hybrid nanofibers to mimic native ECM for tissue engineering applications by Priyadharsini Karuppuswamy; Jayarama Reddy Venugopal; Balchandar Navaneethan; Ashang Luwang Laiva; Sreepathy Sridhar; Seeram Ramakrishna (162-168).
Nanotechnology being one of the most promising technologies today shows an extremely huge potential in the field of tissue engineering to mimic the porous topography of natural extracellular matrix (ECM). Natural polymers are incorporated into the synthetic polymers to fabricate functionalized hybrid nanofibrous scaffolds, which improve cell and tissue compatibility. The present study identified the biopolymers – aloe vera, silk fibroin and curcumin incorporated into polycaprolactone (PCL) as suitable substrates for tissue engineering. Different combinations of PCL with natural polymers – PCL/aloe vera, PCL/silk fibroin, PCL/aloe vera/silk fibroin, PCL/aloe vera/silk fibroin/curcumin were electrospun into nanofibrous scaffolds. The fabricated two dimensional nanofibrous scaffolds showed high surface area, appropriate mechanical properties, hydrophilicity and porosity, required for the regeneration of diseased tissues. The nanofibrous scaffolds were characterized by Scanning electron microscope (SEM), porometry, Instron tensile tester, VCA optima contact angle measurement and FTIR to analyze the fiber diameter and morphology, porosity and pore size distribution, mechanical strength, wettability, chemical bonds and functional groups, respectively. The average fiber diameter of obtained fibers ranged from 250 nm to 350 nm and the tensile strength of PCL scaffolds at 4.49 MPa increased upto 8.3 MPa for PCL/silk fibroin scaffolds. Hydrophobicity of PCL decreased with the incorporation of natural polymers, especially for PCL/aloe vera scaffolds. The properties of as-spun nanofiber scaffolds showed their potential as promising scaffold materials in tissue engineering applications.
Keywords: Electrospinning; Polycaprolactone; Natural polymers; Nanofibers; Tissue engineering;

Surface modification of yttria stabilized zirconia via polydopamine inspired coating for hydroxyapatite biomineralization by Norhidayu Muhamad Zain; Rafaqat Hussain; Mohammed Rafiq Abdul Kadir (169-176).
Yttria stabilized zirconia (YSZ) has been widely used as biomedical implant due to its high strength and enhanced toughening characteristics. However, YSZ is a bioinert material which constrains the formation of chemical bonds with bone tissue following implantation. Inspired by the property of mussels, the surface of YSZ ceramics was functionalized by quinone-rich polydopamine to facilitate the biomineralization of hydroxyapatite. YSZ discs were first immersed in 2 mg/mL of stirred or unstirred dopamine solution at either 25 or 37 °C. The samples were then incubated in 1.5 simulated body fluid (SBF) for 7d. The effect of coating temperature for stirred and unstirred dopamine solutions during substrate grafting was investigated on the basis of chemical compositions, wettability and biomineralization of hydroxyapatite on the YSZ functionalized surface. The results revealed that the YSZ substrate grafted at 37 °C in stirred solution of dopamine possessed significantly improved hydrophilicity (water contact angle of 44.0 ± 2.3) and apatite-mineralization ability (apatite ratio of 1.78). In summary, the coating temperature and stirring condition during grafting procedure affected the chemical compositions of the films and thus influenced the formation of apatite layer on the substrate during the biomineralization process.
Keywords: Yttria stabilized zirconia; Hydroxyapatite; Polydopamine; Biomineralization;

Composition-controlled optical properties of colloidal CdSe quantum dots by Delele Worku Ayele; Wei-Nien Su; Hung-Lung Chou; Chun-Jern Pan; Bing-Joe Hwang (177-184).
A strategy with respect to band gap engineering by controlling the composition of CdSe quantum dots (QDs) is reported. After the CdSe QDs are prepared, their compositions can be effectively manipulated from 1:1 (Cd:Se) CdSe QDs to Cd-rich and then to Se-rich QDs. To obtain Cd-rich CdSe QDs, Cd was deposited on equimolar CdSe QDs. Further deposition of Se on Cd-rich CdSe QDs produced Se-rich CdSe QDs. The compositions (Cd:Se) of the as-prepared CdSe quantum dots were acquired by Energy-dispersive X-ray spectroscopy (EDX). By changing the composition, the overall optical properties of the CdSe QDs can be manipulated. It was found that as the composition of the QDs changes from 1:1 (Cd:Se) CdSe to Cd-rich and then Se-rich CdSe, the band gap decreases along with a red shift of UV–vis absorption edges and photoluminescence (PL) peaks. The quantum yield also decreases with surface composition from 1:1 (Cd:Se) CdSe QDs to Cd-rich and then to Se-rich, largely due to the changes in the surface state. Because of the involvement of the surface defect or trapping state, the carrier life time increased from the 1:1 (Cd:Se) CdSe QDs to the Cd-rich to the Se-rich CdSe QDs. We have shown that the optical properties of CdSe QDs can be controlled by manipulating the composition of the surface atoms. This strategy can potentially be extended to other semiconductor nanocrystals to modify their properties.
Keywords: CdSe quantum dots (QDs); Surface state; Carrier recombination; Selenium-rich QDs; Optical properties; Controlled composition.;

Influence of surface defects on the tensile strength of carbon fibers by F. Vautard; J. Dentzer; M. Nardin; J. Schultz; B. Defoort (185-193).
The mechanical properties of carbon fibers, especially their tensile properties, are affected by internal and surface defects. In order to asses in what extent the generation of surface defects can result in a loss of the mechanical properties, non-surface treated carbon fibers were oxidized with three different surface treatment processes: electro-chemical oxidation, oxidation in nitric acid, and oxidation in oxygen plasma. Different surface topographies and surface chemistries were obtained, as well as different types and densities of surface defects. The density of surface defects was measured with both a physical approach (Raman spectroscopy) and a chemical approach (Active Surface Area). The tensile properties were evaluated by determining the Weibull modulus and the scale parameter of each reference, after measuring the tensile strength for four different gauge lengths. A relationship between the tensile properties and the nature and density of surface defects was noticed, as large defects largely control the value of the tensile strength. When optimized, some oxidation surface treatment processes can generate surface functional groups as well as an increase of the mechanical properties of the fibers, because of the removal of the contamination layer of pyrolytic carbon generated during the carbonization of the polyacrylonitrile precursor. Oxidation in oxygen plasma revealed to be a promising technology for alternative surface treatment processes, as high levels of functionalization were achieved and a slight improvement of the mechanical properties was obtained too.
Keywords: Carbon fibers; Tensile strength; Surface defects; Atomic force microscopy (AFM); Raman spectroscopy; Active surface area (ASA);

Sorption of Cd2+ on mercapto and amino functionalized palygorskite by Xuefeng Liang; Jun Han; Yingming Xu; Lin Wang; Yuebing Sun; Xin Tan (194-201).
Sorption of Cd2+ on PAL, PAL-SH and PAL-NH2 involved different mechanisms. For pristine palygorskite, Cd2+ reacted with surface hydroxyl groups to form surface complexation; for mercapto functionalized palygorskite, the complexation of Cd2+ with mercapto groups existed in addition to the complexation with surface hydroxyl groups; for amino functionalized palygorskite, surface precipitation of Cd2+ with OH― and CO2 to form CdCO3 played an important role in the sorption process except complexation with amino and hydroxyl groups.Mercapto and amino functionalized palygorskite samples were prepared by nanotexturization method, respectively, and applied for the sorption of Cd2+ from aqueous solution to investigate the sorption mechanism and assess the application potential for the remediation of Cd polluted water and soils. The samples before and after sorption were characterized through XRD, FTIR, 29Si CP/MAS NMR and XPS. The sorption thermodynamics, kinetics and mechanisms of Cd2+ sorption on mercapto and amino functionalized palygorskite were studied. Langmuir isotherm was proved to describe the sorption data better and pseudo second order kinetic model could fit the sorption kinetic processes well. Functionalization increased the sorption amounts significantly compared to pristine palygorskite. The positive enthalpy change confirmed that the sorption process was endothermic. The positive entropy changes revealed that sorption of Cd2+ was driven by entropy changes. Combined the results of analyses of the diffraction peaks by XRD, vibration modes of functional groups by FTIR, chemical shifts by 29Si CP/MAS NMR and binding energies of key elements by XPS, the sorption mechanisms were complexation with mercapto or amino groups, and surface precipitation of CdCO3.
Keywords: Palygorskite; Mercapto; Amino; Cadmium; Sorption;

We report the use of molecular layer deposition (MLD) for depositing 3-aminopropyltriethoxysilane (APTES) on a silicon dioxide surface. The APTES monolayer was characterized using spectroscopic ellipsometry, contact angle goniometry, and atomic force microscopy. Effects of reaction time of repeating pulses and simultaneous feeding of water vapor with APTES were tested. The results indicate that the synergistic effects of water vapor and reaction time are significant for the formation of a stable monolayer. Additionally, increasing the number of repeating pulses improved the APTES surface coverage but led to saturation after 10 pulses. In comparing MLD with solution-phase deposition, the APTES surface coverage and the surface quality were nearly equivalent. The hydrolytic stability of the resulting films was also studied. The results confirmed that the hydrolysis process was necessary for MLD to obtain stable surface chemistry. Furthermore, we compared the pH sensing results of Si nanowire field effect transistors (Si NWFETs) modified by both the MLD and solution methods. The highly repeatable pH sensing results reflected the stability of APTES monolayers. The results also showed an improved pH response of the sensor prepared by MLD compared to the one prepared by the solution treatment, which indicated higher surface coverage of APTES.
Keywords: SAMs; MLD; Si nanowires FETs; Hydrolysis stability; pH sensing;

Characterisation of coloured TiO x /Ti/glass systems by Ł. Skowroński; M. Trzcinski; A.J. Antończak; P. Domanowski; M. Kustra; W. Wachowiak; M.K. Naparty; T. Hiller; A. Bukaluk; A.A. Wronkowska (209-214).
Display OmittedThis paper presents a study of the optical properties, microstructure and chemical composition of titanium oxide layers deposited on Ti film using gas injection magnetron sputtering (GIMS). The samples are examined by means of spectroscopic ellipsometry, atomic force microscopy and X-ray photoelectron spectroscopy. The investigation is complemented by colorimetric measurements. The influence of deposition time on the thickness of dielectric layers has been found. A comprehensive analysis of effective dielectric functions of titanium and titanium oxide films is presented. The thickness of titanium oxide film ranges from 13 nm to 54 nm and directly determines the colour of a sample from gold to blue, respectively.
Keywords: Titanium oxides; GIMS; Interference colours; Dielectric function; Spectroscopic ellipsometry;

Nanocrystalline materials of pure and doped ZnO with La/Ce metals have been successfully synthesized using sol gel method. The prepared materials were characterized by standard analytical techniques, i.e., XRD, SEM, EDX, UV–vis Spectroscopy and FTIR. The (XRD) analysis showed that the obtained particles are present in partial crystalline nature with Hexagonal wurtzite phase and exhibit no other impurity phase. The EDX and (SEM) images depicted that La and Ce metals has been successfully loaded on the surface of ZnO. FTIR of La doped ZnO showed an additional absorption band at 910 cm−1, characteristic of La–O absorption band indicating the incorporation of dopant into the ZnO lattice in addition to a broad and strong absorption band in the region of 410–580 cm−1 due to Zn–O stretching. The UV–vis absorption spectra of synthesized particles indicate that the doping of La and Ce metals into the ZnO lattice shift the absorption band towards the visible region. Thermal analysis measurement of the synthesized sample showed that the thermal stability of pure ZnO is decreased due to increase in dopant concentration. The photocatalytic activity of the synthesized particles was studied by measuring the change in concentration of three different chromophoric dyes as a function of irradiation time. The photocatalytic activity of doped ZnO was found to increase with increase in dopant concentration of Ce from 0 to 2.0% and La from 0 to 0.9%. A further increase in dopant concentration led to decrease in the degradation rate of dyes.
Keywords: Doped ZnO; Degradation; Sol–gel; Dyes; Photocatalysis; Visible light;

The interface characteristics of graphene/n-type Si samples using X-ray photoelectron spectroscopy (XPS) measurements are investigated. XPS makes it possible to extract a reliable Schottky barrier value. For graphene/n-type Si samples with (without) sulfide treatment, the Schottky barrier height is 0.86 (0.78) eV. The Schottky barrier height was increased from 0.78 to 0.86 eV, indicating that sulfide treatment is effective in passivating the surface of Si (owing to the formation of Si–S bonds). To determine the Fermi-level pinning/unpinning at the graphene/n-type Si interfaces with sulfide treatment, an analysis is conducted according to the Schottky–Mott limit and the actual work function of graphene is examined with the Kelvin probe. It is shown that the Fermi energy level is unpinned and the Schottky barrier value is dependent on the work function of graphene. Investigation of graphene/n-type Si interfaces is important, and providing the other technique for surface potential control is possible.
Keywords: Graphene; Si; Schottky barrier height; Work function;

A bio-ceramic composite coating was fabricated on ZK60 magnesium (Mg) alloy using combined micro-arc oxidation (MAO) with electrophoretic deposition (EPD) technique. The MAO coating as the basal layer was produced in alkaline electrolyte with (n-MAO coating) and without (MAO coating) the addition of CeO2 and ZrO2 nano-particles, respectively. A hydroxyapatite (HA) coating as the covering layer was deposited on the n-MAO coating to improve the biological properties of the coating (n-MAO/EPD composite coating). The morphology and phase composition of three treated coatings were investigated by scanning electron microscope (SEM) and X-ray diffraction (XRD). The corrosion resistance of these coatings was evaluated with potentiodynamic polarization tests and immersion tests in simulated body fluid (SBF) at 36.5 ± 0.5 °C. The XRD spectra showed that the CeO2 and ZrO2 peaks can be collected in the n-MAO coating, and HA particles exists in the n-MAO/EPD composite coating. The results of corrosion tests indicated that the n-MAO/EPD composite coating owned increased bioactivity and long-term protective ability compared with the MAO coating and the n-MAO coating. Thus Mg alloy coated with the n-MAO/EPD composite coating should be more suited as biodegradable bone implants.
Keywords: Magnesium alloy; Micro-arc oxidation; Electrophoresis deposition; Potentiodynamic polarization; Corrosion resistance;

A comparative study of nitrogen plasma effect on field emission characteristics of single wall carbon nanotubes synthesized by plasma enhanced chemical vapor deposition by Avshish Kumar; Shama Parveen; Samina Husain; Javid Ali; Mohammad Zulfequar; Harsh; Mushahid Husain (236-241).
Vertically aligned single wall carbon nanotubes (SWCNTs) with large scale control of diameter, length and alignment have successfully been grown by plasma enhanced chemical vapor deposition (PECVD) system. The nickel (Ni) as catalyst deposited on silicon (Si) substrate was used to grow the SWCNTs. Field emission (FE) characteristics of the as grown SWCNTs were measured using indigenously designed setup in which a diode is configured in such a way that by applying negative voltage on the copper plate (cathode) with respect to stainless steel anode plate, current density can be recorded. To measure the FE characteristics, SWCNTs film pasted on the copper plate with silver epoxy was used as electron emitter source. The effective area of anode was ∼78.5 mm2 for field emission measurements. The emission measurements were carried out under high vacuum pressure of the order of 10−6  Torr to minimize the electron scattering and degradation of the emitters. The distance between anode and cathode was kept 500 μm (constant) during entire field emission studies. The grown SWCNTs are excellent field emitters, having emission current density higher than 25 mA/cm2 at turn-on field 1.3 V/μm. In order to enhance the field emission characteristics, the as grown SWCNTs have been treated under nitrogen (N2) plasma for 5 min and again field emission characteristics have been measured. The N2 plasma treated SWCNTs show a good enhancement in the field emission properties with emission current density 81.5 mA/cm2 at turn on field 1.2 V/μm. The as-grown and N2 plasma treated SWCNTs were also characterized by field emission scanning electron microscope (FESEM), high resolution transmission electron microscope (HRTEM), Raman spectrometer, Fourier transform infrared spectrometer (FTIR) and X-ray photoelectron spectroscopy (XPS).
Keywords: Single wall carbon nanotube; Plasma enhanced chemical vapor deposition; Field emission; Scanning electron microscope; Raman spectrometer; Fourier transform infrared spectrometer;

Molecular organization in the thin films of gallium(III) phthalocyanine chloride and its μ-(oxo)dimer: Optical spectroscopy and XPS study by Tamara V. Basova; Vitaly G. Kiselev; Florian Latteyer; Heiko Peisert; Thomas Chassé (242-248).
Molecular arrangement in the thin films of gallium(III) phthalocyanine chloride (PcGaCl) and its μ-(oxo)dimer (μ-(oxo)bis[phthalocyaninato] gallium(III), (PcGa)2O) has been studied using complementary spectroscopic techniques: viz., X-ray photoelectron and optical (polarized Raman and UV-vis) spectroscopies, as well as atomic force microscopy. The former films grown by physical vapor deposition on ITO substrates transformed into the films of the latter μ-(oxo)dimer upon thermal annealing at 300 °C under controlled environmental conditions. The polarized Raman spectroscopy revealed that both films are well organized, and the mean tilt angle between the molecular planes and the substrate surface increases from 53 ± 5° (PcGaCl) to 85 ± 5° ((PcGa)2O). All intense bands in the experimental Raman spectra of PcGaCl and (PcGa)2O were assigned using density functional theory calculations. The theoretically predicted wavenumbers are in a good agreement with the experimental values.
Keywords: Thin films; Metal phthalocyanines; Molecular orientation; Vibrational spectroscopy; X-ray photoelectron spectroscopy;

The efficient charge transfer at the interface of g-C3N4/Bi2O2CO3 hetrojunction composites leads to an effective photoexcited electron–hole separation and promotes the photocatalytic activity.Novel composite photocatalyst g-C3N4/Bi2O2CO3 has been synthesized by a simple mixed-calcinations method. The photocatalysts were characterized by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), and diffuse reflection spectroscopy (DRS). The g-C3N4/Bi2O2CO3 composites showed high efficiency for the degradation of Rhodamine B (RhB) under visible light. The optimum photocatalytic activity of g-C3N4/Bi2O2CO3 with molar ratio of 1:2 under visible light irradiation was almost 3.1 and 14.2 times as high as those of the pure g-C3N4 and Bi2O2CO3, respectively. The enhancement of visible light photocatalytic activity in g-C3N4/Bi2O2CO3 should be assigned to the effective separation and transfer of photogenerated charges originating from the well-matched overlapping band-structures. The supposed photocatalytic mechanism was verified by the result of photoluminescence spectroscopy (PL) and active species trapping experiments.
Keywords: g-C3N4; Bi2O2CO3; Visible-light irradiation; Rhodamine B;

Magnetic properties of novel superparamagnetic iron oxide nanoclusters and their peculiarity under annealing treatment by Marin Tadic; Slavko Kralj; Marko Jagodic; Darko Hanzel; Darko Makovec (255-264).
The aim of this work is to present the magnetic properties of novel superparamagnetic iNANOvative™|silica nanoparticle clusters. A TEM analysis showed that these nanoparticle clusters, approximately 80 nm in size, contained an assembly of maghemite nanoparticles in the core and an amorphous silica shell. The maghemite nanoparticles in the core were approximately 10 nm in size, whereas the uniform silica shell was approximately 15-nm thick. The number of magnetic nanoparticles that were densely packed in the core of the single nanocluster was estimated to be approximately 67, resulting in a high magnetic moment for the single nanocluster of m nc  ∼ 1.2 × 106 μ B. This magnetic property of the nanoparticle cluster is advantageous for its easy manipulation using an external magnetic field, for example, in biomedical applications, such as drug delivery, or for magnetic separation in biotechnology. The magnetic properties of the iNANOvative™|silica nanoparticle clusters were systematically studied, with a special focus on the influence of the magnetic interactions between the nanoparticles in the core. For comparison, the nanoparticle clusters were annealed for 3 h at 300 °C in air. The annealing had no influence on the nanoparticles’ size and phase; however, it had a unique effect on the magnetic properties, i.e., a decrease of the blocking temperature and a weakening of the inter-particle interactions. We believe that this surprising observation is related to the thermal decomposition of the organic surfactant on the surfaces of the nanoparticles’ at the high annealing temperatures, which resulted in the formation of amorphous carbon inside the nanocluster.
Keywords: Maghemite; Surface effects; Superparamagnetism (SPION); Self-assembly nanoparticles; AC susceptibility; Inter-particle interactions;

Titania nanotube-Cd0.65Zn0.35S nanocomposite (Cd0.65Zn0.35S-TiO2) was synthesized from titanate nanotubes for ion change of Cd2+ and Zn2+ followed by hydrothermal sulfuration treatment using thiourea as sulfur source. The Cd0.65Zn0.35S-TiO2 with enhanced crystallinity of TiO2 nanotube can be obtained by increasing hydrothermal temperature from 90 °C to 120 °C. And further increasing hydrothermal temperature to 150 °C, TiO2 nanotubes collapse and transform into irregular shaped particles. The photocatalytic activity for hydrogen production of the prepared Cd0.65Zn0.35S-TiO2 with different hydrothermal temperature was investigated under visible-light irradiation. The result shows that the Cd0.65Zn0.35S-TiO2 with hydrothermal temperature of 120 °C presents the highest hydrogen evolution rate and photostability, which can be attributed to a rapid charge transfer at the interface between Cd0.65Zn0.35S and TiO2 nanotube due to the increased crystallinity and unique 1-D nanotubular structure of TiO2.
Keywords: Titania nanotube; Cd0.65Zn0.35S; Hydrothermal sulfuration; Good crystallinity; Hydrogen production;