Applied Surface Science (v.300, #C)
Editorial Board (ii).
Preparation and corrosion resistance of pulse electrodeposited Zn and Zn–SiC nanocomposite coatings by M. Sajjadnejad; A. Mozafari; H. Omidvar; M. Javanbakht (1-7).
Pure Zn and Zn matrix composite coatings containing nano-sized SiC particles with an average size of 50 nm were prepared from the zinc sulfate bath. The effects of the pulse frequency, maximum current density and duty cycle on the amount of particles embedded were examined. Electron microscopic studies revealed that the coating morphology was modified by the presence of SiC nanoparticles. In the presence of SiC nanoparticles deposit grows in outgrowth mode resulting in a very rough and porous microstructure. However, at very low and very high duty cycles a smooth and pore free microstructure was obtained. Corrosion resistance properties of the coatings were studied using potentiodynamic polarization technique in 1 M NaCl solution. It was established that presence of well-dispersed nanoparticles significantly improves corrosion resistance of the zinc by filling gaps and defects between zinc flakes and leading to a smoother surface. However, presence of the SiC nanoparticles led to a mixed microstructure with fine and coarse zinc flakes in some coatings, which presented a weak corrosion behavior. Incorporation of SiC nanoparticles enhanced hardness of the Zn coatings by fining deposit structure and through the dispersion hardening effect.
Keywords: Corrosion; Nanocomposite coating; Potentiodynamic polarization; Zinc; Electrodeposition;
Surface modification of polypropylene nonwoven fabrics via covalent immobilization of nonionic sugar-based surfactants by Zhirong Xin; Shunjie Yan; Jiaotong Ding; Zongfeng Yang; Binbin Du; Shanshan Du (8-15).
Amphiphilic N-alkyl-1-amino-1-deoxy-D-glucitol (C n AG, n = 8, 12) were successfully prepared. Polypropylene nonwoven fabrics (PPNWF) were grafted with glycidyl methacrylate (GMA) via a technique of UV-induced graft polymerization combined with plasma pre-treatment, and then PPNWF-g-GMA was used for the covalent immobilization of C n AG. The surface graft polymerization was confirmed by ATR-FTIR and XPS, respectively. Effect of grafting parameters, e.g., acetone content, monomer concentration and UV irradiation time on the grafting density of GMA was investigated. And the hemocompatibility of the modified PPNWF was evaluated by protein adsorption and platelet adhesion. It was founded that the C n AG-modified substrates greatly suppressed protein adsorption and platelet adhesion compared with the native and pGMA-grafted PPNWF.
Keywords: Polypropylene nonwoven fabrics (PPNWF); Sugar-based surfactant; Photografting polymerization; Amphiphilicity; Hemocompatibility;
Robustness of tungsten single atom tips to thermal treatment and air exposure by Cristian Vesa; Radovan Urban; Jason L. Pitters; Robert A. Wolkow (16-21).
Experiments aimed at assessing the robustness of nitrogen-etched, single-atom tips (SATs) prepared using W(1 1 1) single crystal wire were performed. Our experiments showed that single-atoms tips sustain minimal damage when exposed to atmospheric conditions and can be readily and quickly nitrogen-etched to single-atom tips thereafter. The SATs can be annealed at temperatures up to 1100 °C with minimal shape changes. Moreover, annealing temperatures in excess of 1200 °C resulted in an apex faceting which may prove important in further single-atom tip creation. Procedures for warming of the SATs from operating temperatures of 80 K were also evaluated to determine conditions that limit tip contamination. These results show that SATS could be fabricated in a dedicated vacuum system and subsequently transferred to other instruments where they would undergo a brief conditioning procedure to recover the single-atom apex configuration prior to being subjected to operating conditions.
Keywords: Field ion microscopy; Single atom tip; Gas field ion source; Faceting; Gas assisted etching;
Controlled short-linkage assembly of functional nano-objects by Shilpi Chaudhary; Tripta Kamra; Khan Mohammad Ahsan Uddin; Olesia Snezhkova; H. Surangi N. Jayawardena; Mingdi Yan; Lars Montelius; Joachim Schnadt; Lei Ye (22-28).
In this work, we report a method that allows the deterministic, photo-controlled covalent assembly of nanoparticles directly on surface. As a model system, we study the conjugation of molecularly imprinted polymer (MIP) nanoparticles on a glass surface and confirm that the immobilized nanoparticles maintain their molecular recognition functionality. The glass slide was first modified with perfluorophenylazide and then used to bind MIP nanoparticles under UV irradiation. After each step the surface was analyzed by water contact angle measurement, fluorescence microscopy, scanning electron microscopy, and/or synchrotron-based X-ray photoelectron spectroscopy. The MIP nanoparticles immobilized on the glass surface remained stable and maintained specific binding for the template molecule, propranolol. The method developed in this work allows MIP nanoparticles to be directly coupled to a flat surface, offering a straightforward means to construct robust chemical sensors. Using the reported photo conjugation method, it is possible to generate patterned assembly of nanoparticles using a photomask. Since perfluorophenylazide-based photochemistry works with all kinds of organic material, the method developed in this work is expected to enable immobilization of not only MIPs but also other kinds of organic and inorganic–organic core–shell particles for various applications involving photon or electron transfer.
Keywords: Molecular imprinting; Nanoparticles; Photocoupling; X-ray photoelectron spectroscopy; Immobilization;
Synergistic enhancement in the capacitance of nickel and cobalt based mixed oxide supercapacitor prepared by electrodeposition by Biplab Sarma; Rupashree S. Ray; Swomitra K. Mohanty; Mano Misra (29-36).
A simple and versatile electrodeposition method was adopted to prepare nickel oxide (NiO) and cobalt oxide (Co2O3) based mixed oxide supercapacitor material. The mixed electrode was fabricated by electrodeposition of Co2O3 on to NiO substrate at various potentials of 0.8, 1.0 and 1.2 V vs Ag/AgCl reference electrode. The NiO substrate was prepared by simple air oxidation of Ni foil at two temperatures of 500 and 700 °C for 2 and 6 h. Ni-foil/Co2O3 electrode materials were also synthesized by electrodeposition of Co2O3 on to Ni foil under similar deposition conditions for comparative study. The morphology, phase and oxidation states of the composite electrodes were studied using SEM, EDAX and XPS methods. The overall emphasis of this work is to demonstrate the effect of mixed transition oxides in their bulk forms on the supercapacitance behavior of the electrode material. It was indeed observed that NiO/Co2O3 composite electrode showed significant improvement in supercapacitance behavior in their mixed oxide architecture. Cyclic voltammetric (CV) studies revealed that the NiO/Co2O3 composite electrode could attain a very high level of specific capacitance (>400 F g−1) at a scan rate of 20 mV s−1, together with excellent rate capabilities. More than 50% retention in capacitance was also observed after 200 continuous CV cycles demonstrating promising stability of the electrode material. On the other hand, specific capacitance observed in the case of Ni-foil/Co2O3 electrodes was drastically reduced compared to the NiO/Co2O3 electrodes. It has been emphasized that the synergistic effect, due to the presence of multiple transition oxides, enhanced the overall capacitance behavior of the electrode material. Further, it was also observed that higher the oxidation temperature of the Ni substrates, lower was the specific capacitance for the NiO/Co2O3 electrode. The oxidation time, however, did not alter the capacitance significantly for the electrode material.
Keywords: NiO; Co2O3; Supercapacitance; Electrodeposition; Cyclic voltammetry; Redox;
Influence of pH on cephalexin adsorption onto SBA-15 mesoporous silica: Theoretical and experimental study by María S. Legnoverde; Sandra Simonetti; Elena I. Basaldella (37-42).
Cephalexin adsorption from aqueous solutions using SBA-15 mesoporous silica as adsorbent and the influence of pH solution on drug adsorption were studied. In order to have a better knowledge about the way the drug molecules interact with the inorganic matrix, the adsorption process was estimated by applying the computational chemistry software YAeHMOP (Yet Another extended Hückel Molecular Orbital Package). A strong correlation between the theoretical calculations and the experimental results was established, showing that the adsorbate–adsorbent interaction is pH dependent. Calculated cephalexin horizontal adsorption energy was almost 9 eV more stable than the one corresponding to vertical adsorption, and also the lowest enthalpy of contact and the maximum adsorption percent were found for the cationic cephalexin–silica system. Cephalexin adsorption through the NH3 + group is 8 eV stronger than the molecule adsorption through the COO− group. In agreement with these theoretical predictions, experimental results indicate that the electrostatic attraction between CPX ions and the surface of mesoporous silica is favored at pH values between 2 and 2.56, the maximum being for cephalexin adsorption obtained at pH 2.3.
Keywords: Mesoporous materials; Adsorption; Computer modeling and simulation;
Polymethyl methacrylate-co-methacrylic acid coatings with controllable concentration of surface carboxyl groups: A novel approach in fabrication of polymeric platforms for potential bio-diagnostic devices by Samira Hosseini; Fatimah Ibrahim; Ivan Djordjevic; Leo H. Koole (43-50).
The generally accepted strategy in development of bio-diagnostic devices is to immobilize proteins on polymeric surfaces as a part of detection process for diseases and viruses through antibody/antigen coupling. In that perspective, polymer surface properties such as concentration of functional groups must be closely controlled in order to preserve the protein activity. In order to improve the surface characteristics of transparent polymethacrylate plastics that are used for diagnostic devices, we have developed an effective fabrication procedure of polymethylmetacrylate-co-metacrylic acid (PMMA-co-MAA) coatings with controlled number of surface carboxyl groups. The polymers were processed effectively with the spin-coating technique and the detailed control over surface properties is here by demonstrated through the variation of a single synthesis reaction parameter. The chemical structure of synthesized and processed co-polymers has been investigated with nuclear magnetic resonance spectroscopy (NMR) and matrix-assisted laser desorption time-of-flight mass spectrometry (MALDI-ToF-MS). The surface morphology of polymer coatings have been analyzed with atomic force microscopy (AFM) and scanning electron microscopy (SEM). We demonstrate that the surface morphology and the concentration of surface –COOH groups (determined with UV–vis surface titration) on the processed PMMA-co-MAA coatings can be precisely controlled by variation of initial molar ratio of reactants in the free-radical polymerization reaction. The wettability of developed polymer surfaces also varies with macromolecular structure.
Keywords: Co-polymer; Spin-coating; Surface functional groups; Diagnostic device;
Preparation and characterization of fly ash cenospheres supported CuO–BiVO4 heterojunction composite by Jin Zhang; Hao Cui; Bing Wang; Chuang Li; Jianping Zhai; Qin Li (51-57).
Novel fly ash cenospheres supported CuO–BiVO4 heterojunction composites (CuO–BiVO4/FACs) were prepared by modified metalorganic decomposition and impregnation methods. The as-prepared samples were characterized by X-ray diffraction (XRD), scanning electron microscope (SEM), X-ray photoelectron spectra (XPS), and UV–vis diffused reflectance spectroscopy (DRS) techniques. The XPS and SEM analyses indicated that Cu was present as CuO dispersed on the surface of BiVO4. The DRS spectra revealed that the composites had improved optical adsorption in the visible light region, and the composites exhibited enhanced photocatalytic activity for methylene blue (MB) degradation under visible light irradiation. It was found that the 5 wt% CuO-loaded composite showed the highest photocatalytic activity for MB dye wastewater treatment. FACs, a by-product generated in coal-firing power plants, were used as a low cost support which favored phase separation after the reaction owing to their low density.
Keywords: BiVO4; CuO; Heterojunction; Fly ash cenospheres (FACs); Photocatalysis; Visiblelight;
Catalytic oxidation of NO with O2 over FeMnO x /TiO2: Effect of iron and manganese oxides loading sequences and the catalytic mechanism study by Mengying Zhang; Caiting Li; Long Qu; Mengfan Fu; Guangming Zeng; Chunzhen Fan; Jinfeng Ma; Fuman Zhan (58-65).
FeMnO x /TiO2 with different iron and manganese oxides adding orders were prepared through isovolumetric impregnation and tested for catalytic oxidation of NO with O2. It was found that the sample obtained from one-step impregnation method had better catalytic activity. The excellent activity was attributed to higher surface area, lower crystalline of manganese oxides, abundant Mn3+, Fe3+ and chemisorbed oxygen species on the surface. Furthermore, effects of loading sequences on FeMnO x /TiO2 catalysts were investigated. The study showed that Fe and Mn would affect each other and change the surface physicochemical properties of FeMnO x /TiO2 when they were loaded step-by-step. In addition, the inhibiting effect of H2O on catalytic activity was reversible while the conversion of NO recovered to 40% when SO2 was cut off. XPS analysis between used and fresh catalysts revealed the electron transfer between Fe n+ and Mn n+ ions in FeMnO x /TiO2. Possible reaction mechanism was put forward by comprehensive analysis of XPS and FT-IR results.
Keywords: NO oxidation; FeMnO x /TiO2; Loading sequences; Mechanism;
Study on antibacterial activity of chemically synthesized PANI-Ag-Au nanocomposite by Pandi Boomi; Halliah Gurumallesh Prabu; Paramasivam Manisankar; Sundaram Ravikumar (66-72).
Pristine polyaniline (PANI), PANI-Ag, PANI-Au and PANI-Ag-Au nanocomposites have been successfully synthesized by chemical oxidative polymerization method using aniline as monomer, ammonium persulphate as oxidant and metal (Ag, Au and Ag-Au) colloids. UV-Vis analysis exhibited surface Plasmon resonances of Ag, Au, Ag-Au nanoparticles. FT-IR spectra revealed the shift in peak position of N-H stretching. X-ray diffraction (XRD) results confirm the presence of Ag, Au and Au-Ag nanoparticles. HR-TEM images show nanosizes of Ag, Au, Ag-Au and the incorporation of such nanoparticles into the PANI matrix. Pristine PANI, PANI-Ag, PANI-Au and PANI-Ag-Au nanocomposites were tested for antibacterial activity by agar well diffusion method. PANI-Ag-Au nanocomposite exhibited higher antibacterial activity against both gram-positive [Streptococcus sp. (MTCC 890), Staphylococcus sp. (MTCC 96)] and gram-negative bacteria [Escherichia coli (MTCC 1671) and Klebsiella sp. (MTCC 7407)] when compared with PANI-Ag nanocomposite, PANI-Au nanocomposite and pristine PANI. The novelty of this study is the polymer-bimetal synthesis and its antibacterial potential.
Keywords: Polyaniline; Chemical synthesis; Composite materials; Nanostructure; Characterization; Antibacterial activity.;
Surface structure deduced differences of copper foil and film for graphene CVD growth by Junjun Tian; Baoshan Hu; Zidong Wei; Yan Jin; Zhengtang Luo; Meirong Xia; Qingjiang Pan; Yunling Liu (73-79).
Graphene was synthesized on Cu foil and film by atmospheric pressure chemical vapor deposition (CVD) with CH4 as carbon source. Electron backscattered scattering diffraction (EBSD) characterization demonstrates that the Cu foil surface after the H2-assisted pre-annealing was almost composed of Cu(1 0 0) crystal facet with larger grain size of ∼100 μm; meanwhile, the Cu film surface involved a variety of crystal facets of Cu(1 1 1), Cu(1 0 0), and Cu(1 1 0), with the relatively small grain size of ∼10 μm. The different surface structure led to the distinctive influences of the CH4 and H2 concentrations on the thickness and quality of as-grown graphene. Further data demonstrate that the Cu foil enabled more nucleation densities and faster growth rates at the initial growth stages than the Cu film. Our results are beneficial for understanding the relationship between the metal surface structure and graphene CVD growth.
Keywords: Graphene CVD growth; Cu foil/film; Surface structure; Crystal facet; Growth dynamics;
Beeswax–chitosan emulsion coated paper with enhanced water vapor barrier efficiency by Weiwei Zhang; Huining Xiao; Liying Qian (80-85).
For lipid–hydrocolloid emulsion based film, the increase of lipid amount would improve its water vapor barrier property, but also reduce the mechanical strength of the film in the meantime thus leading to a compromised lipid content in the film. However, when the emulsion is coated on paper surface, more lipid could be used for emulsion preparation to enhance the moisture resistance without considering the weakened strength of the film induced by lipid, because the mechanical properties of emulsion coated paper is mainly governed by the strength of base paper instead of the coating layer. In this study, beeswax–chitosan emulsion was first prepared and then coated on paper surface to improve paper's water vapor barrier and water resistance properties. The range and variance analysis of orthogonal test design showed that the order of priorities of the factors accordingly was beeswax solid content, drying temperature and chitosan concentration. The effect of drying temperature on water vapor transmission rate (WVTR) and water contact angle of coated paper was further investigated using 1.2 wt% chitosan and 96% beeswax solid content in the coating layer. The results indicated that water vapor barrier property was in accordance with the density of the coating layer. Atomic force microscope (AFM) was also used to characterize the surface morphology and explain the hydrophobicity of beeswax–chitosan coated paper. It was found that surface beeswax particles melted to wrinkle at high drying temperatures, while roughness values maintained at micro-scale over the temperature range investigated.
Keywords: Beeswax–chitosan emulsion; Coating; WVTR; Contact angle;
Direct laser interference patterning of polystyrene films doped with azo dyes, using 355 nm laser light by M.F. Broglia; S. Suarez; F. Soldera; F. Mücklich; C.A. Barbero; R. Bellingeri; F. Alustiza; D. Acevedo (86-90).
The generation of line-like periodic patterns by direct laser interference patterning (DLIP) of polystyrene films (PS) at a wavelength of 355 nm has been investigated. No structuration is achieved in plain PS due to the weak absorption of the polymer at 355 nm. On the other hand, patterning is achieved on films doped (PSd) with an azo dye (2-anisidine → 2-anisidine) which is incorporated in the polymer solution used for film preparation. Periodic micro-structures are generated. DLIP on PSd results in the swelling of the surface at low fluences, while at high laser intensities it causes the ablation of the regions at the interference maxima positions. The results contrast with the usual process of DLIP on PS (at shorter wavelengths, like 266 nm) where only ablation is detected. The results suggest that decomposition of the azo dye is the driving force of the patterning which therefore differ from the patterning obtained when plain PS is irradiated with laser light able to be absorbed by the aromatic ring in PS (e.g. 266 nm). The biocompatibility of these materials and adhesion of cells was tested, the data from in vitro assays shows that fibroblast cells are attached and proliferate extensively on the PSd films.
Keywords: Laser interference; Polystyrene films; Periodic microstructures; Azo dye;
O2 activation on the outer surface of carbon nanotubes modified by encapsulated iron clusters by Dongwei Ma; Shuanwen Jia; Dongqiu Zhao; Zhansheng Lu; Zongxian Yang (91-97).
Based on first-principle calculations, this study shows that the confined small Fe cluster inside the SWCNT can significantly modify the electronic structure of the carbon surface. This drastically facilitates the activation of the adsorbed O2 molecule. The calculated energy barrier (less than 0.8 eV) of the rate-determining step for the O2 dissociation indicates that the process can proceed readily at room temperature.Using first-principles calculations, the structural, magnetic, and electronic properties of the (6, 6) single-walled carbon nanotubes (SWCNT) with the confined small Fe cluster are systematically studied. We find that Fe–C interactions can induce the transfer of the electrons from the confined Fe to the carbon surface of the SWCNT considerably, and consequently the reduction of the local work function of the region in contact with the Fe. The charging of the carbon surface and the reduction of the work function make the adsorption of the O2 molecule much more energetically favorable on the outer surface of the SWCNT. Furthermore, the energy barrier of the rate-determining step, i.e., the approaching of the O2 towards the modified carbon surface, for the O2 dissociation is less than 0.8 eV, indicating that the process can proceed readily at room temperature.
Keywords: First-principles calculation; Carbon nanotube; Iron cluster; Charge transfer; O2 activation;
Gas sensing properties and in situ diffuse reflectance infrared Fourier transform spectroscopy study of trichloroethylene adsorption and reactions on SnO2 films by Zhenxin Zhang; Kaijin Huang; Fangli Yuan; Changsheng Xie (98-103).
The detection of trichloroethylene has attracted much attention because it has an important effect on human health. The sensitivity of the SnO2 flat-type coplanar gas sensor arrays to 100 ppm trichloroethylene in air was investigated. The adsorption and surface reactions of trichloroethylene were investigated at 100–200 °C by in-situ diffuse reflection Fourier transform infrared spectroscopy (DIRFTS) on SnO2 films. Molecularly adsorbed trichloroethylene, dichloroacetyl chloride (DCAC), phosgene, HCl, CO, H2O, CHCl3, Cl2 and CO2 surface species are formed during trichloroethylene adsorption at 100–200 °C. A possible mechanism of the reaction process is discussed.
Keywords: Trichloroethylene; In situ DRIFTS; Flat-type coplanar gas sensor arrays; SnO2 films;
Quantification of surface-anchored RAFT chain transfer agent on silica particles by Zongqiang Duan; Zhenyuan Qu; Fenglin Hu; Yunxia Yang; Guorong Chen; Hong Xu (104-110).
Surface-initiated RAFT polymerization has received much attention in the fabrication of spherical brushes. The grafting density of surface-anchored RAFT chain transfer agents (SA-RAFT CTA) exerts great influence on the properties of the resulting spherical brushes. In this paper, we proposed a modified measurement approach named fitting method to determine the grafting density of SA-RAFT CTA by means of UV–vis spectrometry using about 100-nm silica particles (SiPs) as model materials. On the basis of an in-depth investigation on the UV absorption and scattering characteristics of SiPs, the background absorption of SiPs in RAFT CTA modified SiPs (SiP@RAFT) was accurately identified by fitting method and the error introduced by the scattering interference of SiPs was greatly suppressed. With such improvement, the present method exhibits a much higher accuracy and sensitivity (the detection limit is 2.6 μmol/g), which makes it an ideal method for SA-RAFT CTA quantification, especially for particles with a relatively large size. The present method was successfully applied in the study of RAFT CTA immobilization kinetics and the synthesis of spherical poly(tert-butyl ester) brushes (SiP@P(t-BA)) with tunable brush thickness.
Keywords: Silica particles; RAFT chain transfer agent; Quantification; UV–vis spectrometry; Fitting; Grafting density;
Tribological properties of adaptive phosphate composite coatings with addition of silver and molybdenum disulfide by Cancan Liu; Lei Chen; Jiansong Zhou; Huidi Zhou; Jianmin Chen (111-116).
Adaptive phosphate composite coatings with addition of solid lubricants of molybdenum disulfide (MoS2) and silver (Ag) using aluminum chromium phosphate as the binder were fabricated on high-temperature steel. The tribological properties of phosphate composite coatings were evaluated from room temperature (RT) to 700 °C. The phase composition and microstructure were investigated according to the characterization by power X-ray diffraction (XRD), Raman spectroscopy and scanning electron microscopy (SEM). The results show that the composite coating with the Ag/MoS2 mass ratio of 2:1 exhibits the stable and low friction coefficients from RT to 700 °C and relative low wear rates at all testing temperatures. The tribo-chemical reaction between Ag and MoS2 occurred in the rubbing process to form silver molybdates compounds lubricating film. The temperature-adaptive tribological properties were attributed to the formation of lubricating films composed of lubricants silver, MoS2 and silver molybdates phases on the worn surfaces of the composites coatings in a wide-temperature range.
Keywords: Adaptive coating; Silver molybdate; Phosphate composites; Tribological properties;
Enhancement of dynamic wetting properties by direct fabrication on robust micro–micro hierarchical polymer surfaces by Donghui Chu; Akihiko Nemoto; Hiroshi Ito (117-123).
Understanding evaporation phenomena on hierarchical surfaces is of crucial importance for the design of robust superhydrophobic polymer structures for various applications. This fabrication method enables precise control of the dimensions to elucidate the dynamic wetting behavior affected by geometric parameters. That behavior exhibits three distinct evaporation modes: a constant contact line (CCL), a constant contact angle (CCA), and mixed mode during the droplet evaporation. The droplet evaporation results show that the sticky CCL mode and the Cassie–Wenzel transition can be prevented by engineering hierarchy integration. Moreover, the CCL–CCA transition point time scale exhibits remarkable dependence on surface dimensions such as the area fraction and solid–liquid contact line. Finally, the fabricated hierarchical structures indicate remarkable superhydrophobic properties, static contact angle above 160° and low sliding angle under 10°, with good durability in terms of aging effect and mechanical robustness for 2 months.
Keywords: Polymethylmethacrylate (PMMA); Superhydrophobic; Evaporation; Geometric parameter;
Development of FePt–Si–N nanocomposite thin films for magnetic recording by Jing Liu; Y.P. Zeng; H.Y. Yu; D.L. Jiao; Z.G. Zheng; Z.W. Liu; G.Q. Zhang (124-128).
Nanocomposite FePt–Si–N thin films consisting of magnetic L10 FePt nanograins and non-magnetic Si–N matrix for high density recording medium are developed in this work. The (Fe x Pt100-x )100-y Si y –N films (x = 50–65 and y = 0–10) were fabricated on Si (100) substrates by dc reactive magnetron sputtering followed by vacuum annealing. The maximum value of coercivity around 15.3 kOe was obtained in the film with atom ratio Fe:Pt = 55:45. To achieve a high coercivity, the concentrations of Si and N also have to be properly controlled. Doping Si–N improves the coercivity of FePt film through weakening the exchange coupling interaction. Si and N also play an important role in reducing average grain size of the magnetic particles and smoothing the surface of the films. Transmission electron microscopy demonstrated the nanogranular structure consisting of FePt nanoparticles embedded in the amorphous Si–N matrix.
Keywords: FePt; Magnetic recording; Magnetron sputtering; Nanocomposite magnetic film;
Effect of electrodeposition conditions on the properties of Cu–Si3N4 composite coatings by Maryam Eslami; Hassan Saghafian; Farhad Golestani-fard; Alain Robin (129-140).
Cu–Si3N4 composite coatings were obtained by co-electrodeposition under DC conditions from a copper sulphate bath containing suspended Si3N4 particles. The effect of some electroplating parameters such as surfactant (SDS) concentration, stirring rate, and particle concentration on microstructural and mechanical properties of the coatings was investigated. The incorporation of Si3N4 particles into the copper matrix resulted in the production of coatings with finer copper grains. The incorporation of Si3N4 particles also led to a change of the preferred growth orientation of copper grains from (2 0 0) to (2 2 0) crystal face. Cu–Si3N4 composite coatings presented lower friction coefficient and wear loss than pure copper deposit due to the increased hardness related to grain refinement strengthening and dispersion strengthening.
Keywords: Electrodeposition; Copper matrix composite coating; Si3N4; Microstructure; Wear resistance;
Influence of consumed power on structural and nano-mechanical properties of nano-structured diamond-like carbon thin films by Neeraj Dwivedi; Sushil Kumar; Ishpal Rawal; Hitendra K. Malik (141-148).
Mixed Ar–C2H2 plasma was characterized by VI probe for estimating the actual consumed power (CP) in the plasma and its effect on diamond-like carbon (DLC) thin films deposited at different CPs in the range 16–85 W. The structural properties of the films were examined using variety of spectroscopic and microscopic techniques, such as Fourier Transform Infrared spectroscopy, X-ray Photoelectron Spectroscopy, Micro-Raman Spectroscopy and Atomic Force Microscopy. The film deposited at 36 W CP showed the formation of nano-structure, creation of optimum sp3/sp2 bonding ratio and excellent nano-mechanical properties with the maximum hardness of ∼28.2 GPa. However, the nano-mechanical properties of the films got altered with the variation of CP, which is attributed to the changes seen in the structural properties. These findings show that high quality DLC films with higher hardness can be deposited by monitoring and controlling the process parameters of the plasma.
Keywords: Plasma deposition; VI probe; XPS; Nanoindentation; DLC;
Accelerated formation of sodium depletion layer on soda lime glass surface by corona discharge treatment in hydrogen atmosphere by Keiga Kawaguchi; Hiroshi Ikeda; Daisuke Sakai; Shiro Funatsu; Keiichiro Uraji; Kiyoshi Yamamoto; Toshio Suzuki; Kenji Harada; Junji Nishii (149-153).
Formation of a sodium depletion layer on a soda lime glass surface was accelerated efficiently using a corona discharge treatment in H2 atmosphere. One origin of such acceleration was the preferential generation of H+ with a larger mobility at an anode needle end with a lower applied voltage than that in air. The second origin was the applied voltage across the glass plate during the corona discharge treatment, which was estimated theoretically as 2.7 times higher than that in air. These two effects doubled the depletion layer thickness compared with that in air.
Keywords: Corona discharge; Silicate glass; Alkali; Proton; Hydrogen;
Electrodeposited polymer encapsulated nickel sulphide thin films: frequency switching material by Sumanta Jana; Nillohit Mukherjee; Biswajit Chakraborty; Bibhas Chandra Mitra; Anup Mondal (154-158).
Polyvinylpyrrolidone encapsulated NiS thin films were synthesized electrochemically. The light induced frequency switching study of the synthesized material was carried out and it was observed that the films performed well as a switching device under 1 Sun illumination. This pulse generation within an insulating polymer encapsulated semicondctor matrix (PVP NiS) might be due to surface covering which leads to reduction of recombination process.Polyvinylpyrrolidone (PVP) encapsulated nickel sulfide (NiS) thin films have been synthesized electrochemically from aqueous solution of hydrated nickel chloride (NiCl2, 6H2O), thioacetamide (CH3C(S) NH2) (TAA) and polyvinylpyrrolidone (PVP). Surface modification of nickel sulfide (NiS) thin films was achieved by this polymer encapsulation. X-ray diffraction (XRD), high resolution transmission electron microscope (HRTEM), field emission scanning electron microscopy (FESEM) and Energy dispersive X-radiation (EDAX) techniques were used for the characterization of thin films. Infrared spectroscopy (IR) confirmed the formation of polymer encapsulated semiconductor. Frequency switching generation study shows that the encapsulated material could be used as a frequency switching device that generates a frequency ∼ 50 Hz under 1 Sun illumination. Encapsulation with PVP causes surface modification that reduces the surface states and barrier height. As a result, the width of the depletion region decreases. So the number of electron-hole pairs increases. Consequently, the number of excitons and exciton related emission increases and this leads to reduction of recombination process and shows photo induced frequency switching phenomenon.
Keywords: Thin film; Nickel sulphide; Electrodeposition; Exciton generation; Frequency switching.;
Exfoliated graphite/titanium dioxide nanocomposites for photodegradation of eosin yellow by Thabile Ndlovu; Alex T. Kuvarega; Omotayo A. Arotiba; Srinivasan Sampath; Rui W. Krause; Bhekie B. Mamba (159-164).
An improved photocatalyst consisting of a nanocomposite of exfoliated graphite and titanium dioxide (EG-TiO2) was prepared. SEM and TEM micrographs showed that the spherical TiO2 nanoparticles were evenly distributed on the surface of the EG sheets. A four times photocatalytic enhancement was observed for this floating nanocomposite compared to TiO2 and EG alone for the degradation of eosin yellow. For all the materials, the reactions followed first order kinetics where for EG-TiO2, the rate constant was much higher than for EG and TiO2 under visible light irradiation. The enhanced photocatalytic activity of EG-TiO2 was ascribed to the capability of graphitic layers to accept and transport electrons from the excited TiO2, promoting charge separation. This indicates that carbon, a cheap and abundant material, can be a good candidate as an electron attracting reservoir for photocatalytic organic pollutant degradation.
Keywords: Photocatalysis; Nanocomposite; Photodegradation; Visible light; Exfoliated graphite; Water pollution;
Enhanced capacitive performance of TiO2 nanotubes with molybdenum oxide coating by Dongsheng Guan; Xianfeng Gao; Jianyang Li; Chris Yuan (165-170).
Alpha-phase MoO3 is electrochemically deposited on well-aligned TiO2 nanotubes which are synthesized by anodic oxidation. The morphology, composition and electrochemical behaviors of MoO3-coated and bare TiO2 nanotubes are studied. The former deliver greatly higher capacitance than the latter and their performance can be readily optimized by varying MoO3 deposition cycles. The large areal capacitance of 209.6 mF cm−2 at a scan rate of 5 mV s−1 is firstly achieved for TiO2 nanotube array electrode. In addition, the coated TiO2 nanotubes show significantly more capacitance than a dense MoO3 film. For example, they exhibit a capacitance up to 74.9 F g−1 at 5 mV s−1 in 1 M KCl solution, while the dense film only shows a capacitance of 32.3 F g−1 under same conditions. Such improvement is found ascribed to MoO3 with high pseudocapacity and TiO2 nanotubes with large surface area allowing efficient MoO3 nanoparticle loading and rapid charge transfer. This nanostructured electrode with features of facile synthesis and excellent performance is believed as a potential candidate for supercapacitor applications.
Keywords: TiO2 nanotube; MoO3; Anodic oxidation; Electrodeposition; Supercapacitor;
Effect of microwave irradiation on selective heating behavior and magnetic separation characteristics of Panzhihua ilmenite by Wei Zhao; Jin Chen; Xiaodong Chang; Shenghui Guo; C. Srinivasakannan; Guo Chen; Jinhui Peng (171-177).
The influences of microwave irradiation on the surface characteristics of Panzhihua ilmenite were systematically investigated. The crystal structures, surface morphology and surface chemical functional groups of ilmenite were characterized before and after microwave irradiation and magnetic separation for different microwave treatment times by using various methods, such as XRD, SEM, and FT-IR, respectively. XRD analysis showed that the microwave treated ilmenite has the strongest peaks of phase more than that of raw samples, indicates that the crystalline compound of ilmenite increased with the microwave irradiation time. SEM analysis showed the micro-cracking appeared at many grain boundaries of ilmenite after being pretreated by microwave treatment. The separations of ilmenite from gangue minerals were completed and the micro-fissure within ilmenite minerals were also formed, which could be attributed to the microwave selective heating characteristics of the different minerals and compounds, and the thermal stresses were caused by the uniform heat rate disturbed under microwave irradiation. The mineral processing results showed that the magnetic separation characteristics and properties of microwave treated ilmenite samples were better than that of microwave untreated ilmenite samples. It was concluded that microwave irradiation can be applied effectively and efficiently to the irradiation processes of Panzhihua ilmenite.
Keywords: Microwave irradiation; Ilmenite; Crystalline compound; Structure;
Enhancement and stability of photoluminescence from Si nanocrystals embedded in a SiO2 matrix by H2-passivation by Yanli Li; Peipei Liang; Zhigao Hu; Shuang Guo; Qinghu You; Jian Sun; Ning Xu; Jiada Wu (178-183).
Si nanocrystals embedded in SiO2 (Si-NCs/SiO2) with efficient light emission were prepared by N2-annealing of amorphous SiO x (a-SiO x ) and subsequent H2-passivation, and the effects of passivation on the photoluminescence (PL) from Si-NCs/SiO2 were studied. The H2-passivation was performed in a mixed gas of 5% H2 + 95% N2 at temperatures ranging from 400 to 700 °C for varied times, which is effective for passivating dangling bonds and enhancing luminescence. The PL intensity increases with passivation time, shortly followed by a saturation that depends on the passivation temperature. The H2-passivation also results in a red shift of PL spectra. The effects of H2-passivation show nearly complete reversibility as revealed by the emitted luminescence. Subsequent heating of the passivated samples in N2 has an effect of depassivation which regenerates dangling bonds and the regenerated dangling bonds can also be passivated. Si-NCs/SiO2 are found to exhibit stable behaviors in passivation and depassivation processes after three cycles of passivation and depassivation treatments.
Keywords: Si nanocrystal; Photoluminescence; Stability; Passivation; Depassivation;
Fabrication and characterization of stable superhydrophobic surface with good friction-reducing performance on Al foil by Peipei Li; Xinhua Chen; Guangbin Yang; Laigui Yu; Pingyu Zhang (184-190).
A lotus-leaf-like hierarchical structure was successfully created on Al foil by a facile three-step solution–immersion method. As-obtained etched-immersed Al/STA rough surface contains interconnected convex–concave micro-structure and uniformly distributed nano-sheets that endow the surface with excellent superhydrophobicity (WCA: 164.2°; WSA: below 5°). Besides, the as-prepared etched-immersed Al/STA superhydrophobic surface on Al foil exhibits good friction-reducing ability and stable superhydrophobicity.A lotus-leaf-like hierarchical structure with superhydrophobicity was created on Al foil by a facile three-step solution–immersion method involving etching in hydrochloric acid solution and immersing in hot water as well as surface-modification by stearic acid (denoted as STA). As-prepared etched-immersed Al/STA rough surface was characterized by means of scanning electron microscopy and X-ray photoelectron spectroscopy. Moreover, the water contact angles and water sliding angles of as-prepared etched-immersed Al/STA rough surface were measured, and the friction-reducing performance and self-cleaning ability of the as-prepared surface were also evaluated. Results indicate that the etched-immersed Al/STA rough surface consists of interconnected convex–concave micro-structure and uniformly distributed nano-sheets. Besides, it exhibits stable superhydrophobicity and good friction-reducing ability. Namely, it has a contact angle of water as high as 164.2° and a water sliding angle lower than 5°, while it retains good friction-reducing ability during extended sliding and possesses good self-cleaning ability as well. This demonstrates that the etched-immersed Al/STA rough surface may favor the applications of Al and its alloys in various industrial fields.
Keywords: Aluminum; Superhydrophobic surface; Stability; Friction-reducing performance; Self-cleaning ability;
Studies of potassium-promoted nickel catalysts for methane steam reforming: Effect of surface potassium location by Tadeusz Borowiecki; Andrzej Denis; Michał Rawski; Andrzej Gołębiowski; Kazimierz Stołecki; Jaromir Dmytrzyk; Andrzej Kotarba (191-200).
The effect of potassium addition to the Ni/Al2O3 steam reforming catalyst has been investigated on several model systems, including K/Al2O3 with various amounts of alkali promoters (1–4 wt% of K2O), a model catalyst 90%NiO-10%Al2O3 promoted with potassium and a commercial catalyst. The potassium surface state and stability were investigated by means of the Species Resolved Thermal Alkali Desorption method (SR-TAD). The activity of the catalysts in the steam reforming of methane and their coking-resistance were also evaluated. The results reveal that the beneficial effect of potassium addition is strongly related to its location in the catalysts. The catalyst surface should be promoted with potassium in order to obtain high coking-resistant catalysts. Moreover, the catalyst preparation procedure should ensure a direct interaction of potassium with the Al2O3 support surface. Due to the low stability of potassium on θ-Al2O3 this phase is undesirable during the preparation of a stable steam reforming catalyst.
Keywords: Steam reforming of methane; Ni-K catalyst; SR-TAD method; Resistance to coking;
NH3-TPD-MS study of Ce effect on the surface of Mn- or Fe-exchanged zeolites for selective catalytic reduction of NO x by ammonia by M. Stanciulescu; P. Bulsink; G. Caravaggio; L. Nossova; R. Burich (201-207).
The selective catalytic reduction (SCR) of NO x with NH3 is considered to be a promising technique for the efficient reduction of highly detrimental NO x emitted from diesel engine vehicles to N2. This study was focused on a series of catalysts with ZSM-5 as support, prepared by Mn- or Fe-exchange followed by wet impregnation of Ce, or Fe or Mn. These catalysts were characterized by temperature-programmed desorption coupled with a mass spectrometer using ammonia (NH3-TPD-MS). Specifically, NH3-TPD-MS was used as a means of identifying the various strengths of acid sites and their relative abundance in an attempt to explain the effect of the catalyst surface acid sites on DeNO x activity. Acid sites with adsorption energies ranging from 47.0 to 75.6 kJ/mol were detected for all of the catalysts. For the same concentration of exchanged metal it was found that the DeNO x activity depends strongly on the type of metal. Furthermore, the acid site strength and distribution depend on the active metal and correlate with the observed DeNO x catalyst activity. Additionally, SEM metal mapping images confirmed the presence of well dispersed active metal on the surface of all catalysts. The catalysts with bimetallic active phase were stable and demonstrated high NO x conversion over a broad temperature range. Impregnation of metal-exchanged zeolites with Ce enhanced the low temperature NO x conversion. Observed differences of activity between the various catalysts of this study may be due to the formation of new ammonia activation sites. The ammonia desorption profile during the elevation of temperature was correlated to the DeNO x activity.
Keywords: Zeolite acidity; Catalyst acidity; DeNO x ; NH3-SCR; NH3-TPD; Aftertreatment;
Phosphorus diffusion in germanium following implantation and excimer laser annealing by Chen Wang; Cheng Li; Shihao Huang; Weifang Lu; Guangming Yan; Maotian Zhang; Huanda Wu; Guangyang Lin; Jiangbin Wei; Wei Huang; Hongkai Lai; Songyan Chen (208-212).
We focus our study on phosphorus diffusion in ion-implanted germanium after excimer laser annealing (ELA). An analytical model of laser annealing process is developed to predict the temperature profile and the melted depth in Ge. Based on the heat calculation of ELA, a phosphorus diffusion model has been proposed to predict the dopant profiles in Ge after ELA and fit SIMS profiles perfectly. A comparison between the current–voltage characteristics of Ge n+/p junctions formed by ELA at 250 mJ/cm2 and rapid thermal annealing at 650 °C for 15 s has been made, suggesting that ELA is promising for high performance Ge n+/p junctions.
Keywords: Excimer laser annealing (ELA); Phosphorous implantation; Diffusion model; Germanium; Junction;
Retraction notice to “Effect of hydrogenation vs. re-heating on intrinsic magnetization of Co doped In2O3” [Appl. Surf. Sci. 257 (2) (2010) 585–590] by A. Samariya; R.K. Singhal; Sudhish Kumar; Y.T. Xing; S.C. Sharma; P. Kumari; D.C. Jain; S.N. Dolia; U.P. Deshpande; T. Shripathi; E. Saitovitch (213).