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Applied Surface Science (v.256, #8)

Structural, compositional and magnetic characterization of bulk V₂O₅ doped ZnO system by S. Karamat; R.S. Rawat; P. Lee; T.L. Tan; R.V. Ramanujan; W. Zhou (pp. 2309-2314).

This paper investigates the structural, compositional and magnetic properties of vanadium doped ZnO bulk samples prepared by solid state reaction technique. The Rietveld refinement analysis for XRD results of samples showed small change in lattice parameters for 3 and 5% vanadium doped ZnO samples indicating the substitution of Zn²⁺ ions by vanadium ions in ZnO lattice. Raman spectroscopy reveals the change in ZnO modes positions due to vanadium doping. The appearance of E₁ and E₂ modes showed that the wurtzite structure of ZnO is still maintained after doping of vanadium oxide. XPS analysis confirms the presence of the different elements and oxidation states of vanadium ions. M–H curves obtained from VSM showed weak ferromagnetism in the samples. The observation of ferromagnetic behavior indicates the formation of ZnVO phase with V²⁺ ion substitution in the ZnO lattice. XPS scans of the etched bulk samples confirmed the 2+ oxidation state of vanadium ions in our samples explaining the origin of ferromagnetism.

Keywords: PACS; 33.20.Fb; 36.20.KdRaman spectroscopy; XPS; V doped ZnO

Structure formation on the surface of alloys irradiated by femtosecond laser pulses by Lingling Ran; Shiliang Qu (pp. 2315-2318).

Laser-induced periodic surface structures with different spatial characteristics have been observed after multiple linearly polarized femtosecond laser pulse (120fs, 800nm, 1Hz to 1kHz pulse repetition frequency) irradiation on alloys. With the increasing number of pulses, nanoripples, classical ripples and modulation ripples with a period close to half of classical ripples have all been induced. The generation of second-harmonic has been supposed to be the main mechanism in the formation of modulation ripples.

Keywords: PACS; 42.62.−b; 61.80Ba; 81.65cf; 81.40Wx; 87.80MjFemtosecond laser pulse; Modulation ripples; SHG

Structural and magnetic properties of NiZn ferrite films with high saturation magnetization deposited by magnetron sputtering by Dangwei Guo; Xiaolong Fan; Guozhi Chai; Changjun Jiang; Xiling Li; Desheng Xue (pp. 2319-2322).

NiZn ferrite films with well-defined spinel crystal structure were in situ fabricated by radio frequency magnetron sputtering at room temperature. The microstructures and static magnetic properties of the films’ dependence on the partial pressure ratio of argon to oxygen gas were investigated. Scanning electron microscope images indicated that all the films consisted of particles nanocrystalline in nature and the sizes increase as the ratio increases in the range of 10–25nm. A large saturation magnetization (237.2emu/cm³) and a minimum of coercivity (68Oe) were obtained when the ferrite film was deposited in the ratio of 4:1. The complex permeability values ( μ = μ′ −iμ″) of the film were measured at frequency up to 5GHz. It was shown that the film exhibited a large real part of permeability μ′ of 18 and a very high resonance frequency f_r of 1.2GHz. The results suggested that the NiZn ferrite film as-deposited in the ratio of 4:1 may be promised as magnetic medium in the application of integrated circuits operating at microwave frequencies.

Keywords: Ferrite films; Soft magnetic property; Resonance frequency; Deposited at room temperature

Zinc oxide catalyzed growth of single-walled carbon nanotubes by Fenglei Gao; Lijie Zhang; Shaoming Huang (pp. 2323-2326).

We demonstrate that zinc oxide can catalyze the growth of single-walled carbon nanotubes (SWNTs) with high efficiency by a chemical vapor deposition process. The zinc oxide nanocatalysts, prepared using a diblock copolymer templating method and characterized by atomic force microscopy (AFM), were uniformly spaced over a large deposition area with an average diameter of 1.7nm and narrow size distribution. Dense and uniform SWNTs films with high quality were obtained by using a zinc oxide catalyst, as characterized by scanning electron microscopy (SEM), Raman spectroscopy, AFM, and high-resolution transmission electron microscopy (HRTEM).

Keywords: Zinc oxide; Nanoparticles; Catalyst

Synthesis of hollow carbon nitride microspheres by an electrodeposition method by Xinjiao Bai; Jie Li; Chuanbao Cao (pp. 2327-2331).

Hollow carbon nitride microspheres have been synthesized using a novel liquid phase electrodeposition technique. The microspheres are composed of numerous nanoparticles with size of about 5–30nm. The diameters of the spheres range from 800nm to 1.1μm, and shell thickness is about 80–250nm. This is the first attempt to synthesize carbon nitride with specific nanostructure by the electrodeposition method, which is proved to be facile and effective, and can be performed in an atmospheric environment and at a rather low temperature. The hollow carbon nitride may have potential applications as lubrication, catalysis, biomolecule adsorption, drug delivery, electronic materials, etc. in the future.

Keywords: Carbon nitride; Electrodeposition; Microsphere

Optimization of surface coating condition using vapor form of alkanethiol on Cu nano powders for the application of oxidation prevention by Mi-Ryn Seong; Jinhyeong Kwon; Gye-Young Lee; Dong-Kwon Kim; Young-Seok Kim; Caroline Sunyong Lee (pp. 2332-2336).

There has been a growing interest in metal nano powders recently, and researches on Copper (Cu) nano particles are actively pursued due to its good electrical conductivity and its low prices. However, its easiness to oxidation and corrosion has delayed its research progress in Cu nano particles to be applied in inkjet printed electronics and other related research area. To overcome these problems, new surface coating method on Cu nano particles has been developed using dry process instead of conventional wet coating method. Octanethiol was used as a dry coating material because it has sulfur at the end of monolayer to chemically bond to the surface of fresh non-oxidized Cu nano particles to prevent oxidation. Octanethiol does not bond to oxidized surface of Cu nano particles. Previously, bonding between octanethiol and Cu nano particles, more specifically bonding between Cu surface and Sulfur (S) was analyzed using X-ray Photoelectron Spectroscopy (XPS). As a result, S peak was detected on the coated Cu nano particles, indicating that octanethiol chain has been successfully coated on the surface of Cu nano particles.In this study, optimization of dry coating condition was studied by varying coating time and cycles. XPS was used to analyze the composition of coated material to monitor the change in amount of S and O peaks for each condition. It was found that as the amount of Sulfur increased, the amount of Oxygen decreased and vice versa. This finding indicates that dry coating has suppressed the formation of oxygen on the surface of Cu nano powders by surrounding Cu surface with Sulfur end of octanethiol chain. Based on these experiments, the optimum coating condition for suppressing Cu oxidation was found to be 5min and 6 cycles. For future work, the lifetime of octanethiol layer on the surface of Cu surface needs to be studied.

Keywords: Vapor coating; Octanethiol; Nano-sized copper; Sulfur; X-ray photoelectron spectroscopy

Deposition of durable thin silver layers onto polyamides employing a heterogeneous Tollens’ reaction by Torsten Textor; Moustafa M.G. Fouda; Boris Mahltig (pp. 2337-2342).

Tollens’ reaction is a well-known reaction employed in chemical analyses to detect reducing groups—basically aldehydes. If aldehydes are available in a solution these will reduce silver(I) ions to silver(0). The present paper describes an approach to use a heterogeneous Tollens’ reaction to establish thin layers of silver on polyamide surfaces. The polyamide surface is modified with aldehyde functions in a first step employing glutaraldehyde. The resulting polymer material is therefore equipped with reducing groups necessary for the reduction of silver in a next step. The polymer is subsequently treated with Tollens’ reagent yielding a yellow/brownish colour typical for the surface plasmon resonance of silver. The extend of the colouring – indicating the amount of silver deposited – varies with both the concentration of the Tollens’ reagent and the concentration of the glutaraldehyde solution used for the pre-treatment. The as-prepared samples not only show an excellent antimicrobial activity but also an enormous durability. Polyamide textiles that were treated with the described approach showed unchanged efficiency even after 30 laundry cycles.

Keywords: Tollens’ reagent; Antimicrobial activity; Glutaraldehyde; Silver; Polyamide

Electron beam evaporated LaF₃ thin films prepared by different temperatures and deposition rates by Guanghui Liu; Hongbo He; Yunxia Jin; Zhengxiu Fan (pp. 2343-2346).

LaF₃ thin films were prepared by electron beam evaporation with different temperatures and deposition rates. Microstructure properties including crystalline structure and surface roughness were investigated by X-ray diffraction (XRD) and optical profilograph. X-ray photoelectron spectroscopy (XPS) was employed to study the chemical composition of the films. Optical properties (transmittance and refractive index) and laser induce damage threshold (LIDT) at 355nm of the films were also characterized. The effects of deposition rate and substrate temperature on microstructure, optical properties and LIDT of LaF₃ thin films were discussed, respectively.

Keywords: LaF; ₃; films; Electron beam evaporation; Microstructure; Refractive index; LIDT

Highly water resistant surface coating by fluoride on long persistent Sr₄Al₁₄O₂₅:Eu²⁺/Dy³⁺ phosphor by Hom Nath Luitel; Takanori Watari; Toshio Torikai; Mitsunori Yada; Rumi Chand; Chao-Nan Xu; Kazuhiro Nanoka (pp. 2347-2352).

A novel and efficient method of providing moisture resistance of inorganic particles such as divalent europium activated strontium aluminate phosphors (Sr₄Al₁₄O₂₅:Eu²⁺/Dy³⁺) was developed by firing the phosphor in the presence of appropriate amount of ammonium fluoride at a temperature of 600–700°C. Scanning electron microscopy, X-ray diffraction, FT-IR, EDAX and Photoluminescence measurements were carried out to characterize the uncoated and coated samples. The pH measurements were carried out for the water resistivity measurements. The phosphor particles became coated with a moisture-impervious thin coating that did not suppress the luminescence of the phosphor and can withstand complete immersion in water for long periods of time, showing very high water resistivity.

Keywords: Phosphor; Fluoride coating; Water resistivity; Sr; ₄; Al; ₁₄; O; ₂₅; :Eu; ²⁺; /Dy; ³⁺

Spectra study and size control of cobalt nanoparticles passivated with oleic acid and triphenylphosphine by Yikun Su; Xing OuYang; Jiaoning Tang (pp. 2353-2356).

This paper compares the performance of two surfactants—triphenylphosphine (TPP) and oleic acid (OA) as a pair of capping agents in the synthesis of magnetic Co nanoparticles (NPs). Magnetic colloids of cobalt NPs are prepared by reducing solute cobalt chloride in the presence of stabilizing agents at a high temperature and characterized by TEM. Infrared spectra reveal that a chemical bond can be formed between O of CO band and Co atoms while a coordinate bond forms between P and Co atoms around the NPs on the surface. OA binds strongly to the particle surface during synthesis that hinders the particle from growing; the TPP reversibly coordinates neutral metal surface sites that favor rapid growth. We studied the influence of changing the TPP /OA concentration ratio on the particle size distribution and crystallinity of Co NPs. Our results indicate the presence of TPP /OA is able to control particle growth, stabilize the colloidal suspension and prevent the final product from oxidation by air.

Keywords: Nanomaterials; Magnetic materials; Spectra; Size control

Solvent effects for CO and H₂ adsorption on Cu₂O (111) surface: A density functional theory study by Zhijun Zuo; Wei Huang; Peide Han; Zhihong Li (pp. 2357-2362).

To investigate solvent effects, CO and H₂ adsorption on Cu₂O (111) surface in vacuum, liquid paraffin, methanol and water are studied by using density functional theory (DFT) combined with the conductor-like solvent model (COSMO). When H₂ and CO adsorb on Cu_cus of Cu₂O (111) surface, solvent effects can improve CO and H₂ activation. The H–H bond increases with dielectric constant increasing as H₂ adsorption on O_suf of Cu₂O (111) surface, and the H–H bond breaks in methanol and water. It is also found that both the structural parameters and Mulliken charges are very sensitive to the COSMO solvent model. In summary, the solvent effects have obvious influence on the clean surface of Cu₂O (111) and the adsorptive behavior.

Keywords: DFT; CO; H; ₂; Cu; ₂; O (1; 1; 1); Solvent effects; Adsorption

Surface morphology of organic thin films at various vapor flux by Gengxin Zhang; Brandon L. Weeks (pp. 2363-2366).

The surface morphology of the organic energetic material pentaerythritol tetranitrate (PETN) grown on silicon substrates has been investigated. The surface structure of the films reveal clearly differentiated morphologies which is dependent on the vapor flux. Dendrite crystals are formed with flux of 0.03nm/s while the morphology shows a transition from dendrite branches to grain growth as the flux is increased to 0.3nm/s. The deposition thickness did not show an obvious influence on the surface microstructure. Therefore, the deposition flux allows the production of PETN films with desired surface morphology in a controllable and reproducible way.

Keywords: PETN; Vacuum deposition; Morphology; Vapor flux; Surface diffusion

Cross-linked gelatin/nanoparticles composite coating on micro-arc oxidation film for corrosion and drug release by Xinhua Xu; Ping Lu; Meiqing Guo; Mingzhong Fang (pp. 2367-2371).

A composite coating which could control drug release and biocorrosion of magnesium alloy stent materials WE42 was prepared. This composite coating was fabricated on the surface of the micro-arc oxidation (MAO) film of the magnesium alloy, WE42, by mixing different degrees of cross-linked gelatin with well-dispersed poly(dl-lactide-co-glycolide) (PLGA) nanoparticles. The PLGA nanoparticles were prepared by emulsion solvent evaporation/extraction technique. Nano ZS laser diffraction particle size analyzer detected that the size of the nanoparticles to be 150–300nm. Scanning electron microscopy (SEM) and atomic force microscopy (AFM) was used to analyze the morphology of the nanoparticles and the composite coating. Potentiodynamic polarization and electrochemical impedance spectroscopy (EIS) were used to evaluate the corrosion behavior of the composite coating. Drug release was determined by ultraviolet–visible (UV–vis) spectrophotometer. The corrosion resistance of the composite coating was improved by preventing the corrosive ions from diffusing to the MAO films. The drug release rate of paclitaxel (PTX) exhibited a nearly linear sustained-release profile with no significant burst releases.

Keywords: Magnesium alloy; MAO; Nanoparticles; Gelatin; Drug release

Characterization of AISI 4140 borided steels by I. Campos-Silva; M. Ortiz-Domínguez; N. López-Perrusquia; A. Meneses-Amador; R. Escobar-Galindo; J. Martínez-Trinidad (pp. 2372-2379).

The present study characterizes the surface of AISI 4140 steels exposed to the paste-boriding process. The formation of Fe₂B hard coatings was obtained in the temperature range 1123–1273K with different exposure times, using a 4mm thick layer of boron carbide paste over the material surface. First, the growth kinetics of boride layers at the surface of AISI 4140 steels was evaluated. Second, the presence and distribution of alloying elements on the Fe₂B phase was measured using the Glow Discharge Optical Emission Spectrometry (GDOES) technique. Further, thermal residual stresses produced on the borided phase were evaluated by X-ray diffraction (XRD) analysis. The fracture toughness of the iron boride layer of the AISI 4140 borided steels was estimated using a Vickers microindentation induced-fracture testing at a constant distance of 25μm from the surface. The force criterion of fracture toughness was determined from the extent of brittle cracks, both parallel and perpendicular to the surface, originating at the tips of an indenter impression. The fracture toughness values obtained by the Palmqvist crack model are expressed in the form K_C( π/2)> K_C> K_C(0) for the different applied loads and experimental parameters of the boriding process.

Keywords: Boriding; Growth kinetics; Characterization; Diffusion model; Fracture toughness; Hard coatings; Residual stresses

Mechanical, tribological, and electrochemical behavior of Cr1−_xAl_xN coatings deposited by r.f. reactive magnetron co-sputtering method by J.E. Sanchéz; O.M. Sanchéz; L. Ipaz; W. Aperador; J.C. Caicedo; C. Amaya; M.A. Hernández Landaverde; F. Espinoza Beltran; J. Muñoz-Saldaña; G. Zambrano (pp. 2380-2387).

Chromium aluminum nitride (Cr1−_xAl_xN) coatings were deposited onto AISI H13 steel and silicon substrates by r.f. reactive magnetron co-sputtering in (Ar/N₂) gas mixture from chromium and aluminum targets. Properties of deposited Cr1−_xAl_xN coatings such as compositional, structural, morphological, electrochemical, mechanical and tribological, were investigated as functions of aluminum content. X-ray diffraction patterns of Cr1−_xAl_xN coatings with different atomic concentrations of aluminum (0.51< x<0.69) showed the presence and evolution of (111), (200), and (102) crystallographic orientations associated to the Cr1−_xAl_xN cubic and w-AlN phases, respectively. The rate of corrosion of the steel coated with Cr1−_xAl_xN varied with the applied power; however, always being clearly lower when compared to the uncoated substrate. The behavior of the protective effect of the Cr1−_xAl_xN coatings is based on the substitution of Cr for Al, when the power applied to the aluminum target increases. The mechanical properties were also sensitive to the power applied, leading to a maximum in hardness and a reduced elastic modulus of 30 and 303GPa at 350W and a monotonic decrease to 11 and 212GPa at 450W, respectively. Finally, the friction coefficient measured by pin-on disk revealed values between 0.45 and 0.70 in humid atmosphere.

Keywords: Co-sputtering; Hard coatings; Friction; Corrosion; Nanoindentation

In vitro remineralization of acid-etched human enamel with Ca₃SiO₅ by Zhihong Dong; Jiang Chang; Yan Deng; Andrew Joiner (pp. 2388-2391).

Bioactive and inductive silicate-based bioceramics play an important role in hard tissue prosthetics such as bone and teeth. In the present study, a model was established to study the acid-etched enamel remineralization with tricalcium silicate (Ca₃SiO₅, C₃S) paste in vitro. After soaking in simulated oral fluid (SOF), Ca–P precipitation layer was formed on the enamel surface, with the prolonged soaking time, apatite layer turned into density and uniformity and thickness increasingly from 250 to 350nm for 1 day to 1.7–1.9μm for 7 days. Structure of apatite crystals was similar to that of hydroxyapatite (HAp). At the same time, surface smoothness of the remineralized layer is favorable for the oral hygiene. These results suggested that C₃S treated the acid-etched enamel can induce apatite formation, indicating the biomimic mineralization ability, and C₃S could be used as an agent of inductive biomineralization for the enamel prosthesis and protection.

Keywords: Remineralization; Tricalcium silicate; Acidic-etching; Enamel

Theoretical investigations on multiple-reflection and Rayleigh absorption–emission–scattering effects in laser drilling by Kwan-Woo Park; Suck-Joo Na (pp. 2392-2399).

A fundamental study of laser drilling was performed with computational analysis. High power Q-switched diode-pumped laser drilling simulations were conducted on N-type silicon wafers. In the numerical model, the volume of fluid method was adopted to trace the free surface of the drilled-hole with the governing equations including continuity, momentum, and energy equation. The laser beam was considered as a surface heat flux with near-Gaussian distribution. The simulation model took into account the physical phenomena, taking place during drilling of the silicon wafer, such as the effects of recoil pressure producing a narrow and deep profile, Fresnel absorption transferring the energy from laser beam to workpiece, multiple-reflection raising the absorption of laser energy, and Rayleigh absorption–emission–scattering absorbing and distributing the entrance laser energy. In particular, a novel model for laser drilling was proposed from the view point of the transmitted, absorbed, emitted, and scattered light.

Keywords: Laser drilling; Ablation plume; Multiple-reflection; Rayleigh scattering

Super-hydrophobic nickel films with micro-nano hierarchical structure prepared by electrodeposition by Tao Hang; Anmin Hu; Huiqin Ling; Ming Li; Dali Mao (pp. 2400-2404).

Super-hydrophobic nickel films were prepared by a simple and low cost electrodepositing method. The surface morphologies of the films characterized by scanning electronic microscope exhibit hierarchical structure with micro-nanocones array, which can be responsible for their super-hydrophobic characteristic (water contact angle over 150°) without chemical modification. The wettability of the film can be varied from super-hydrophobic (water contact angle 154°) to relatively hydrophilic (water contact angle 87°) by controlling the size of the micro-nanocones. The mechanism of the hydrophobic characteristic of nickel films with this unique structure was illustrated by several models. Such micro-nanostructure and its special wettability are expected to be applied in the practical industry.

Keywords: Nickel films; Hydrophobic; Electrodepositing; Nanocones

Structural and optical characteristics of spin-coated ZnO thin films by M. Smirnov; C. Baban; G.I. Rusu (pp. 2405-2408).

Zinc oxide (ZnO) thin films were deposited onto glass substrates by spin-coating method, from a precursor solution containing zinc acetate, ethanol and ammonium hydroxide. After deposition, the films were heated at a temperature of 100°C in order to remove unwanted materials. Finally, the films were annealed at 500°C for complete oxidation. X-ray diffraction showed that ZnO films were polycrystalline and have a hexagonal (wurtzite) structure. The crystallites are preferentially oriented with (002) planes parallel to the substrate surface. The films have a high transparency (more than 75%) in the spectral range from 450nm to 1300nm. The analysis of absorption spectra shows the direct nature of band-to-band transitions. The optical bandgap energy ranges between 3.15eV and 3.25eV.Some correlations between the processing parameters (spinning speed, temperature of post deposition heat treatment) and structure and optical characteristics of the respective thin films were established.

Keywords: Zinc oxide; Spin-coating; Optical properties; Transparent films

Enhancement of field emission properties of graphite flakes by producing carbon nanotubes on above using thermal chemical vapor deposition by Wen-Ching Shih; Jian-Min Jeng; Ming-Hong Tsai; Jyi-Tsong Lo (pp. 2409-2413).

In order to improve the field emission properties of the graphite flakes, the carbon nanotubes (CNTs) are produced on above without the metallic catalyst using mixtures of C₂H₂ and H₂ gases by thermal chemical vapor deposition. We spin the graphite solution on the silicon wafer and dry it, then synthesize the CNTs on the graphite flakes. We change the synthetic time to obtain the optimal conditions for enhancement of field emission properties of graphite flakes. The experimental results show that the density and quality of the CNTs could be controlled significantly by the synthetic time. Besides, the field emission properties of the treated graphite flakes are also affected greatly by it. The emission current density of the treated graphite flakes reaches to 0.5mA/cm² at 3V/μm, and the turn-on field is decreased from 7.7 to 1.9V/μm after producing the CNTs on above.

Keywords: PACS; 79.70.+q; 85.45.Db; 85.45.FdGraphite flake; Carbon nanotube; Carbon nanoparticle; Thermal chemical vapor deposition; Field emission

The effect of back electrode on the formation of electrodeposited CoNiFe magnetic nanotubes and nanowires by F.E. Atalay; H. Kaya; V. Yagmur; S. Tari; S. Atalay; D. Avsar (pp. 2414-2418).

The electrodeposition of cobalt+nickel+iron alloy nanostructures in aqueous sulfate solution has been studied using vitreous templates placed on highly ordered porous anodic alumina oxide (AAO). During the deposition process some electrochemical bath parameters such as ion content, deposition voltage, pH and temperature of solution were kept constant. The morphological properties of the nanostructures were studied by scanning electron microscopy (SEM) and the chemical composition was determined by examination of the energy dispersive X-ray (EDX) spectra. The magnetic behaviour of the arrays was determined with a vibrating sample magnetometer (VSM). Voltammetric and galvanostatic results indicate that the back electrodes placed on AAO plays the main role in obtaining nanowire or nanotube structured material.

Keywords: PACS; 62.23.Hj; 61.46.Np; 81.07.−b; 81.15.Pq; 75.50.BbCoNiFe nanowires; CoNiFe nanotubes; Electrodeposition; Magnetic properties; Back electrode

Electronic properties of the surface of perylene tetracarboxylic acid dianhydride film upon deposition of the ultrathin conjugated layers of Pyronine B by Alexei S. Komolov; Eleonora F. Lazneva; Svetlana N. Akhremtchik (pp. 2419-2422).

Ultrathin conjugated layers of Pyronine B were thermally deposited in UHV on the surface of perylene tetracarboxylic acid dianhydride (PTCDA) film. The structure of unoccupied electron states located 5–20eV above the Fermi level ( E_F) and the surface potential were monitored during the Pyronine B overlayer deposition, using an incident beam of low-energy electrons according to the total current electron spectroscopy (TCS) method. Electronic work function of the PTCDA surface changed from 4.9±0.1eV, during the Pyronine B deposition due to the change of the contents of the surface layer, until it reached a stable value 4.6±0.1eV at the Pyronine B film thickness 8–10nm. The interface dipole corresponds to electron transfer from the Pyronine B overlayer to the PTCDA surface and the polarization in the Pyronine B overlayer was found confined within approximately 1nm near the interfaces. The edges of major bands of density of unoccupied electronic states (DOUS) of PTCDA substrate and of the Pyronine B overlayer were unaffected by the process of the interface formation. The major TCS spectral features of the Pyronine B film corresponding to the DOUS band edges were identified and the assignment of the π^*, σ^*(C–C) and σ^*(CC) character was suggested.

Keywords: PACS; Condensed matter; Electronic propertiesSurface electronic phenomena; Conjugated organic molecules; Organic film–organic film interface; Band alignment; Density of states

Metal and polymer melt jet formation by the high-power laser ablation by Jack J. Yoh; Ardian B. Gojani (pp. 2423-2427).

The laser-induced metal and polymer melt jets are studied experimentally. Two classes of physical phenomena of interest are: first, the process of explosive phase change of laser induced surface ablation and second, the hydrodynamic jetting of liquid melts ejected from a beamed spot. We focus on the dynamic link between these two distinct physical phenomena in a framework of forming and patterning of metallic and polymer jets using a high-power Nd:YAG laser. The microexplosion of ablative spot on a target first forms a pocket of hot liquid melt and then it is followed by a sudden volume change of gas–liquid mixture leading to a pressure-induced spray jet ejection into surrounding medium.

Keywords: PACS; 47.55.−t; 61.25.hk; 47.40.Rs; 52.38.Mf; 79.20.DsPhase change; Laser ablation; Melt jets; Interfacial instability; Laser beam impact

A comparative study of the physical properties of Sb₂S₃ thin films treated with N₂ AC plasma and thermal annealing in N₂ by M. Calixto-Rodriguez; H. Martínez; Y. Peña; O. Flores; H.E. Esparza-Ponce; A. Sanchez-Juarez; J. Campos-Alvarez; P. Reyes (pp. 2428-2433).

As-deposited antimony sulfide thin films prepared by chemical bath deposition were treated with nitrogen AC plasma and thermal annealing in nitrogen atmosphere. The as-deposited, plasma treated, and thermally annealed antimony sulfide thin films have been characterized by X-ray diffraction (XRD), energy dispersive X-ray spectroscopy, scanning electron microscopy, atomic force microscopy, UV–vis spectroscopy, and electrical measurements. The results have shown that post-deposition treatments modify the crystalline structure, the morphology, and the optoelectronic properties of Sb₂S₃ thin films. X-ray diffraction studies showed that the crystallinity of the films was improved in both cases. Atomic force microscopy studies showed that the change in the film morphology depends on the post-deposition treatment used. Optical emission spectroscopy (OES) analysis revealed the plasma etching on the surface of the film, this fact was corroborated by the energy dispersive X-ray spectroscopy analysis. The optical band gap of the films ( E_g) decreased after post-deposition treatments (from 2.36 to 1.75eV) due to the improvement in the grain sizes. The electrical resistivity of the Sb₂S₃ thin films decreased from 10⁸ to 10⁶Ω-cm after plasma treatments.

Keywords: PACS; 81.40.−z; 81.65.−bSb; ₂; S; ₃; Thin film; Plasma treatment; Chemical bath deposition

Local electrical characteristics of passive films formed on stainless steel surfaces by current sensing atomic force microscopy by T. Souier; F. Martin; C. Bataillon; J. Cousty (pp. 2434-2439).

A current sensing atomic force microscope was used to study the topography and the local electronic properties of the passive film formed on a duplex ferrite–austenite stainless steel (Uranus 50). Comparison of current maps with topography AFM images reveals that the passive film covering austenite and ferrite phases exhibits different properties. On freshly formed passive film, a high and homogenous resistance (typically 10GΩ for 1V) characterises the film on austenite grains while current maps of the passive layer covering the ferrite grains show a high density of spots (few 100MΩ for 1V). Besides the current maps, local I– V curves acquired on austenite show wider band gap energy than the ones obtained on ferrite grains. Finally, the conductivity difference in passive films covering ferrite and austenite grains is discussed.

Keywords: Stainless steel; Passive film; Conducting atomic force microscopy; Semiconductor

Two component silicone modified epoxy foul release coatings: Effect of modulus, surface energy and surface restructuring on pseudobarnacle and macrofouling behavior by S.K. Rath; J.G. Chavan; Savita Sasane; Jagannath; M. Patri; A.B. Samui; B.C. Chakraborty (pp. 2440-2446).

Two component silicone modified epoxy resin based low surface energy and non-toxic foul release coatings were developed. Silicone modified epoxy resin with 15 and 30% silicone content was used as component A and a polyether diamine (Jeffamine-500) was used as the component B. Free standing films were prepared by casting a mixture of components A and B in stoichiometric proportions. The surface composition, surface topography and wetting properties of the coatings were studied by angle resolved X-ray photoelectron spectroscopy (XPS), atomic force microscopy (AFM) and contact angle goniometry respectively. The mechanical properties of the cured films were evaluated by tensile measurements as well as dynamic mechanical analysis. Pseudobarnacles made of aluminium studs were attached to the coated panels and adhesion tests were carried out by a pseudobarnacle tester. Coated panels were exposed in Mumbai harbor for fouling studies for a period of 90 days. Surface restructuring studies of the coatings upon immersion in seawater were carried out by measuring the changes in advancing and receding contact angles by contact angle goniometry. The effect of surface energy, modulus and surface restructuring of the coatings on the macrofouling and pseudobarnacle adhesion properties has been discussed in detail.

Keywords: Foul release; Pseudobarnacle; Low surface energy; Macrofouling

Nanostructured WO₃ thin film as a new anode material for lithium-ion batteries by Wen-Jing Li; Zheng-Wen Fu (pp. 2447-2452).

Nanostructured WO₃ thin film has been successfully fabricated by radio-frequency magnetron sputtering method and its electrochemistry with lithium was investigated for the first time. The reversible discharge capacity of WO₃/Li cells cycled between 0.01V and 4.0V was found above 626mAh/g during the first 60 cycles at the current density 0.02mA/cm². By using X-ray diffraction, X-ray photoelectron spectroscopy, transmission electron microscopy and selected-area electron diffraction measurements, the reversible conversion of WO₃ into nanosized metal W and Li₂O was revealed. The high reversible capacity and good recyclability of WO₃ electrode made it become a promising cathode material for future rechargeable lithium batteries.

Keywords: WO; ₃; Anode materials; Lithium-ion batteries; Magnetron sputtering

Defects related room temperature ferromagnetism in p-type (Mn, Li) co-doped ZnO films deposited by reactive magnetron sputtering by C.W. Zou; H.J. Wang; M.L. Yi; M. Li; C.S. Liu; L.P. Guo; D.J. Fu; T.W. Kang (pp. 2453-2457).

We report on the defects related room temperature ferromagnetic characteristics of Zn0.95–_xMn_xLi_0.05O ( x=0.01, 0.03, 0.05 and 0.08) thin films grown on glass substrates using reactive magnetron sputtering. By increasing the Mn content, the films exhibited increases in the c-axis lattice constant, fundamental band gap energy, coercive field and remanent magnetization. Comparison of the structural and magnetic properties of the as-deposited and annealed films indicates that the hole carriers, together with defects concentrations, play an important role in the ferromagnetic origin of Mn and Li co-doped ZnO thin films. The ferromagnetism in films can be described by bound magnetic polaron models with respect to defect-bound carriers.

Keywords: Ferromagnetism; Thin films; Reactive magnetron sputtering; ZnO

The photoacoustic spectroscopic investigations of the surface preparation of ZnSe crystals with the use of the optimization methods by Ł. Chrobak; M. Maliński; J. Zakrzewski; K. Strzałkowski (pp. 2458-2461).

This paper shows results of the photoacoustic (PA) spectral studies, with the microphone detection, of a series of ZnSe crystals with differently prepared surfaces. All samples exhibited the surface absorption connected with defects states located on their surfaces. The quality of the surface preparation is expressed by the surface absorption coefficient spectra of the samples times the thickness of a damaged layer. In this paper both theoretical and experimental photoacoustic amplitude and phase spectra as also the corresponding computed surface and volume optical absorption coefficient spectra of the samples with differently prepared surfaces are presented and discussed. The procedure of computations of the volume and surface absorption spectra with the use of the optimization method is presented in the paper too.

Keywords: PACS; 78.20.Ci; 78.55.Et; 81.05.Dz; 82.80.Kq; 96.12.Kz; 02.60.PnII–VI semiconductors; ZnSe; Surface states; Photoacoustics; Numerical optimization

Influence of diluent compositions on the porous structure of methacrylate derivatives of aromatic diols and divinylbenzene by Beata Podkościelna; Barbara Gawdzik (pp. 2462-2467).

Synthesis and properties of the new aromatic tetrafunctional methacrylate monomer 2,7-(2-hydroxy-3-methacryloyloxypropoxy)naphthalene are presented. This monomer was applied for the synthesis of porous microspheres. It was copolymerized with divinylbenzene in the presence of pore-forming diluents, decan-1-ol and toluene. Influence of diluents composition on their porous structures was studied. Porous structures of the obtained microspheres in dry (from nitrogen adsorption–desorption measurements) and swollen (the inverse size exclusion chromatography method) states were compared with those synthesized from isomeric 2,3-(2-hydroxy-3-methacryloyloxypropoxy)-naphthalene and divinylbenzene.

Keywords: Polymeric microspheres; Methacrylate monomers; Naphthalene-2,7-diol; Copolymerization; Porous structure; Swelling

Temperature-dependent ferroelectric and dielectric properties of Bi_3.25La_0.75Ti₃O₁₂ thin films by Shan-Tao Zhang; Zhong Chen; Chong Zhang; Guo-Liang Yuan (pp. 2468-2473).

To investigate temperature-dependent ferroelectric and dielectric properties of ferroelectric films, Bi_3.25La_0.75Ti₃O₁₂ (BLT) thin films were prepared on Pt-coated silicon substrates by pulsed laser deposition. The ferroelectric and dielectric behaviors have been studied in a wide temperature range from 80K to room temperature. The saturated polarization ( P_sat) decreases with decreasing temperature and decreasing electric field, whereas remnant polarization ( P_r) shows a more complex temperature dependence. These results, which can be well explained based on a temperature-dependent charged defects–domain wall interaction model, might be helpful for further understanding the domain switching behavior. Based on these results, an alternative way to investigate temperature-dependent ferroelectric fatigue is proposed and experimentally carried out. The measured fatigue rate is found to be linearly dependent on temperature, consistent with the report on Pb(Zr,Ti)O₃ films. Temperature-dependent dielectric measurements of the films further confirm the above explanation.

Keywords: PACS; 77.84.Dy; 77.80.Dj; 68.65.+gFerroelectric; Thin films; Temperature; Domain switching

Characterisation of wettability in gas diffusion layer in proton exchange membrane fuel cells by V. Parry; E. Appert; J.-C. Joud (pp. 2474-2478).

This paper presents a detailed study of the wetting properties of three fuel cell gas diffusion layers (GDLs) having different morphologies and different contents of hydrophobic agent. An internal contact angle to water at temperature representative of PEM fuel cell operating conditions was directly obtained using the Washburn method with 66° C water as test liquid. These results show that the surface of the carbon fibres is hydrophilic under fuel cell operating conditions. Surface energy values of the GDL fibres, determined by a combination of the Washburn method and the Owens–Wendt two parameters theory, were found to be low, indicating that GDLs are wet very poorly by most liquids. About 40% of the total surface free energy values was related to a polar component allowing dipole–dipole and hydrogen bonding interactions with water. The origin of this polar character is discussed.

Keywords: PACS; 82.47.Gh; 68.08.Bc; 68.35.MdWetting; Contact angle; Surface energy; PEM fuel cell; Gas diffusion layer

Study on tribological behavior and cutting performance of CVD diamond and DLC films on Co-cemented tungsten carbide substrates by Dongcan Zhang; Bin Shen; Fanghong Sun (pp. 2479-2489).

The tribological behaviors of diamond and diamond-like carbon (DLC) films play a major role on their machining and mechanical applications. In this study, diamond and diamond-like carbon (DLC) films are deposited on the cobalt cemented tungsten carbide (WC–Co) substrate respectively adopting the hot filament chemical vapor deposition (HFCVD) technique and the vacuum arc discharge with a graphite cathode, and their friction properties are evaluated on a reciprocating ball-on-plate tribometer with counterfaces of silicon nitride (Si₃N₄) ceramic, cemented tungsten carbide (WC) and ball-bearing steel materials, under the ambient air without lubricating condition. Moreover, to evaluate their cutting performance, comparative turning tests are conducted using the uncoated WC–Co and as-fabricated CVD diamond and DLC coated inserts, with glass fiber reinforced plastics (GFRP) composite materials as the workpiece. The as-deposited HFCVD diamond and DLC films are characterized with energy-dispersive X-ray spectroscopy (EDX), scanning electron microscope (SEM), X-ray diffraction spectroscopy (XRD), Raman spectroscopy and 3D surface topography based on white-light interferometry. Furthermore, Rocwell C indentation tests are conducted to evaluate the adhesion of HFCVD diamond and DLC films grown onto WC–Co substrates. SEM and 3D surface topography based on white-light interferometry are also used to investigate the worn region on the surfaces of diamond and DLC films. The friction tests suggest that the obtained friction coefficient curves that of various contacts exhibit similar evolution tendency. For a given counterface, DLC films present lower stable friction coefficients than HFCVD diamond films under the same sliding conditions. The cutting tests results indicate that flank wear of the HFCVD diamond coated insert is lower than that of DLC coated insert before diamond films peeling off.

Keywords: HFCVD; Diamond film; DLC film; WC–Co substrate; Tribological behavior; Cutting performance

A versatile method for the preparation of end-functional polymers onto SiO₂ nanoparticles by a combination of surface-initiated ATRP and Huisgen [3+2] cycloaddition by J.C. Chen; W.Q. Luo; H.D. Wang; J.M. Xiang; H.F. Jin; F. Chen; Z.W. Cai (pp. 2490-2495).

A versatile method was developed for the chain-end functionalization of the grafted polymer chains for surface modification of nanoparticles with functionalized groups through a combination of surface-initiated atom-transfer radical polymerization (ATRP) and Huisgen [3+2] cycloaddition. First, the surface of SiO₂ nanoparticles was modified with poly(methyl methacrylate) (PMMA) brushes via the “grafting from” approach. The terminal bromides of PMMA-grafted SiO₂ nanoparticles were then transformed into an azide function by nucleophilic substitution. These azido-terminated PMMA brushes on the nanoparticle surface were reacted with alkyne-terminated functional end group via Huisgen [3+2] cycloaddition. FTIR and¹H NMR spectra indicated quantitative transformation of the chain ends of PMMA brushes onto SiO₂ nanoparticles into the desired functional group. And, the dispersibility of the end-functional polymer-grafted SiO₂ nanoparticles was investigated with a transmission electron microscope (TEM).

Keywords: Surface modification; Atom-transfer radical polymerization (ATRP); Cu-catalyzed Huisgen [3; +; 2] cycloaddition; Chain-end functionalization

Fabrication and characterization of La-doped HfO₂ gate dielectrics by metal-organic chemical vapor deposition by Liu-Ying Huang; Ai-Dong Li; Wen-Qi Zhang; Hui Li; Yi-Dong Xia; Di Wu (pp. 2496-2499).

La-doped HfO₂ gate dielectric thin films have been deposited on Si substrates using La(acac)₃ and Hf(acac)₄ (acac=2,4-pentanedionate) mixing sources by low-pressure metal-organic chemical vapor deposition (MOCVD). The structure, thermal stability, and electrical properties of La-doped HfO₂ films have been investigated. Inductive coupled plasma analyses confirm that the La content ranging from 1 to 5mol% is involved in the films. The films show smaller roughness of ∼0.5nm and improved thermal stability up to 750°C. The La-doped HfO₂ films on Pt-coated Si and fused quartz substrates have an intrinsic dielectric constant of ∼28 at 1MHz and a band gap of 5.6eV, respectively. X-ray photoelectron spectroscopy analyses reveal that the interfacial layer is Hf-based silicate. The reliable value of equivalent oxide thickness (EOT) around 1.2nm has been obtained, but with a large leakage current density of 3A/cm² at V_g=1 V+ V_fb. MOCVD-derived La-doped HfO₂ is demonstrated to be a potential high- k gate dielectric film for next generation metal oxide semiconductor field effect transistor applications.

Keywords: La-doped HfO; ₂; MOCVD; High-; k; gate dielectric; Mixing precursors

Superhydrophilic stability enhancement of RF co-sputtered Ti_xSi1−_xO₂ thin films in dark by M. Mirshekari; R. Azimirad; A.Z. Moshfegh (pp. 2500-2506).

Ti_xSi1−_xO₂ compound thin-film systems were deposited by reactive RF magnetron co-sputtering technique. The effect of Ti concentration on the hydrophilicity of Ti_xSi1−_xO₂ compound thin films was studied and it was shown that the films with Ti_0.6Si_0.4O₂ composition possess the best hydrophilic property among all the grown samples. Surface ratio and average roughness of the thin films were measured by atomic force microscopy (AFM). Surface chemical states and stoichiometry of the films were determined by X-ray photoelectron spectroscopy (XPS). In addition, XPS revealed that the amount of Ti–O–Si bonds in nanometer depth from the surface of the Ti_0.6Si_0.4O₂ films was the maximum, which resulted in the most stable superhydrophilic property. According to XRD data analysis for the pure TiO₂ films, the polycrystalline anatase phase was formed with an average grain size of about 15nm. Moreover, amorphous phase was also formed for the Ti_xSi1−_xO₂ compound systems due to presence of silicon in the films. Finally, optical properties of the films such as transmission, reflection and band gap energy were investigated using UV–vis spectrophotometry. It was found that the transmittance of the films was decreased with increasing Ti concentration in the films.

Keywords: PACS; 82.30.Rs; 81.20.FwTitania–silica; Hydrophilicity; Contact angle measurement; XPS

Room-temperature ferromagnetism of the amorphous Cu-doped ZnO thin films by Jing Qi; Daqiang Gao; Li Zhang; Yinghu Yang (pp. 2507-2508).

Amorphous copper-doped ZnO thin films (ZnO:Cu) prepared on glass substrates by the radio-frequency magnetron co-sputtering have been investigated. Magnetic measurements indicated that the amorphous ZnO:Cu thin films were ferromagnetic at room temperature and the saturation magnetization was much higher than that of the polycrystalline films. X-ray diffraction results showed there was no Cu₂O phase in amorphous ZnO:Cu films, which might be the reason for the high magnetic moment of the films. On the other hand, the high saturation magnetization of the amorphous ZnO:Cu films could also attribute to that there was no limit of solid solubility of Cu in amorphous ZnO solvent. The X-ray photoelectron spectroscopy study of the amorphous ZnO:Cu thin films reveal that copper was in Cu²⁺ chemical state.

Keywords: Diluted magnetic semiconductors; Ferromagnetism; ZnO

Plasma enhanced CVD of SiO_xC_yH_z thin film on different textile fabrics: Influence of exposure time on the abrasion resistance and mechanical properties by Giuseppe Rosace; Roberto Canton; Claudio Colleoni (pp. 2509-2516).

In order to improve textile fabric abrasion resistance, in this work a SiO_xC_yH_z thin film was realized by low pressure plasma chemical vapour deposition (PCVD) at room temperature, using hexamethyldisiloxane (HMDSO) as precursor compound. To test changes in the performance properties of the surface finished samples as a function of the type of the substrate, the deposition was carried out on different textile fabrics. The polymerization processes were followed by weight measurements of textile fabrics. It was found that, after PCVD, a significantly lower fabric weight loss was observed on treated samples after rubbing than on the untreated samples. The morphology, elemental composition and type of chemical bonding present in the film applied on textile fabrics were also investigated using electron scanning microscopy (SEM), energy dispersive X-ray (EDX) and infrared spectroscopy techniques (FT-IR (ATR)). The results showed a substantial enhancement of wear resistance for the surfaces modified with the presented process, while tensile and tearing strength were adversely affected.

Keywords: Textile fabric; Plasma polymerization; Hexamethyldisiloxane; Abrasion resistance; Mechanical properties

Morphological effect of MoS₂ nanoparticles on catalytic oxidation and vacuum lubrication by Kun Hong Hu; Xian Guo Hu; Xiao Jun Sun (pp. 2517-2523).

The closed layered MoS₂ nano-balls and the opened layered MoS₂ nano-slices were prepared by decomposing MoS₃ in hydrogen atmosphere. The obtained MoS₂ nanoparticles were respectively used as catalysts for S²⁻ oxidation into SO₄²⁻ and lubricating fillers in polyoxymethylene (POM) plastic. Only basal surface could be found in the closed layered MoS₂ nano-balls, which represented very low catalytic efficiency for S²⁻ oxidation into SO₄²⁻. However, the opened layered MoS₂ nano-slices were of both basal surface and rim-edge surface and showed excellent catalytic properties. Moreover, it was shown that MoS₂ nano-balls could improve the self-lubrication of POM plastic in vacuum. However, MoS₂ nano-slices led to the obvious degradation of POM, implying it is not a proper additive for POM. The high activity of MoS₂ nano-slices for catalyzing S²⁻oxidation and degrading POM was ascribed to their small sizes and partly wedge-like shapes, which led to a considerable increase in the rim sites. The weak catalysis and excellent lubrication of MoS₂ nano-balls were resulted from its closed structure and chemical inertness.

Keywords: MoS; ₂; nanoparticles; Catalytic properties; Tribological properties; Morphological effect

Surface modification of poly(dimethylsiloxane) for microfluidic assay applications by Christine Séguin; Jessica M. McLachlan; Peter R. Norton; François Lagugné-Labarthet (pp. 2524-2531).

The surface of a poly(dimethylsiloxane) (PDMS) film was imparted with patterned functionalities at the micron-scale level. Arrays of circles with diameters of 180 and 230μm were functionalized using plasma oxidation coupled with aluminum deposition, followed by silanization with solutions of 3-aminopropyltrimethoxy silane (3-APTMS) and 3-mercaptopropyltrimethoxy silane (3-MPTMS), to obtain patterned amine and thiol functionalities, respectively. The modification of the samples was confirmed using X-ray photoelectron spectroscopy (XPS), gold nanoparticle adhesion coupled with optical microscopy, as well as by derivatization with fluorescent dyes. To further exploit the novel surface chemistry of the modified PDMS, samples with surface amine functionalities were used to develop a protein assay as well as an array capable of cellular capture and patterning. The modified substrate was shown to successfully selectively immobilize fluorescently labeled immunoglobulin G (IgG) by tethering Protein A to the surface, and, for the cellular arrays, C2C12 rat endothelial cells were captured. Finally, this novel method of patterning chemical functionalities onto PDMS has been incorporated into microfluidic channels. Finally, we demonstrate the in situ chemical modification of the protected PDMS oxidized surface within a microfluidic device. This emphasizes the potential of our method for applications involving micron-scale assays since the aluminum protective layer permits to functionalize the oxidized PDMS surface several weeks after plasma treatment simply after etching away the metallic thin film.

Keywords: Poly(dimethyl siloxane); Silanization; Microfluidics; Protein assays

Oriented single crystalline TiO₂ nano-pillar arrays directly grown on titanium substrate in tetramethylammonium hydroxide solution by Xiang Dong; Jie Tao; Yingying Li; Hong Zhu (pp. 2532-2538).

Oriented single crystalline titanium dioxide (TiO₂) nano-pillar arrays were directly synthesized on the Ti plate in tetramethylammonium hydroxide (TMAOH) solution by one-pot hydrothermal method. The samples were characterized respectively by means of field-emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM), high-resolution transmission electron microscopy (HRTEM), and X-ray diffraction (XRD). Results showed that the TiO₂ nano-pillar with a tetrahydral bipyramidal tip grew vertically on the titanium substrate. HRTEM and Raman results confirmed that the TiO₂ nano-pillar arrays were single crystalline anatase. The controls of morphology, size, and orientation of the nano-pillar could be achieved by varying the solution concentration and hydrothermal temperature. Furthermore, the special morphology of the TiO₂ nano-pillar arrays was caused by the selectively absorption of the tetramethylammonium (TMA) through hydrogen bonds on the lattice planes parallel to (001) of anatase TiO₂. Less grain boundaries and direct electrical pathway for electron transferring were crucial for the superior photoelectrochemical properties of the single anatase TiO₂ nano-pillar arrays. This approach provides a facile in situ method to synthesize TiO₂ nano-pillar arrays with a special morphology on titanium substrate.

Keywords: TiO; ₂; Nano-pillar arrays; One-step synthesis; Hydrothermal

UV laser ablation of intraocular lenses: SEM and AFM microscopy examination of the biomaterial surface by E. Spyratou; I. Asproudis; D. Tsoutsi; C. Bacharis; K. Moutsouris; M. Makropoulou; A.A. Serafetinides (pp. 2539-2545).

Several new materials and patterns are studied for the formation and etching of intraocular lenses (IOLs), in order to improve their optical properties, to reduce the diffractive aberrations and to decrease the incidence of posterior capsular opacification. The aim of this study is to investigate the use of UV ( λ=266nm) laser pulses to ablate the intraocular lenses materials, and thus to provide an alternative to conventional surface shaping techniques for IOLs fabrication. Ablation experiments were conducted using various polymer substrates of hydrophobic acrylic IOLs and PMMA IOLs. We investigated the ablation efficiency and the morphology of the ablated area by imaging the surface modification with atomic force microscopy (AFM) and scanning electron microscopy (SEM). The morphological appearance of IOL samples reveals the effect of a photochemical and photothermal ablation mechanism.

Keywords: UV polymer ablation; Intraocular lenses; AFM; SEM

Solid-phase photocatalytic degradation of polystyrene plastic with goethite modified by boron under UV–vis light irradiation by Guanglong Liu; Duanwei Zhu; Wenbing Zhou; Shuijiao Liao; Jingzhen Cui; Kang Wu; David Hamilton (pp. 2546-2551).

A novel photodegradable polyethylene-boron-goethite (PE-B-goethite) composite film was prepared by embedding the boron-doped goethite into the commercial polyethylene. The goethite catalyst was modified by boron in order to improve its photocatalytic efficiency under the ultraviolet and visible light irradiation. Solid-phase photocatalytic degradation of the PE-B-goethite composite film was carried out in an ambient air at room temperature under ultraviolet and visible light irradiation. The properties of composite films were compared with those of the pure PE films and the PE-goethite composite films through performing weight loss monitoring, scanning electron microscope (SEM) analysis, FT-IR spectroscopy and X-ray photoelectron spectroscopy (XPS). The photo-induced degradation of PE-B-goethite composite films was higher than that of the pure PE films and the PE-goethite composite films under the UV-irradiation, while there has been little change under the visible light irradiation. The weight loss of the PE-B-goethite (0.4wt.%) composite film reached 12.6% under the UV-irradiation for 300h. The photocatalytic degradation mechanism of the composite films was briefly discussed.

Keywords: Soild-phase; Photocatalytic degradation; Polyethylene; Boron; Goethite

Crystallization-dependent magnetic properties of Mn_1.56Co_0.96Ni_0.48O₄ thin films by Y.Q. Gao; Z.M. Huang; Y. Hou; J. Wu; Z.Q. Li; J.H. Chu (pp. 2552-2556).

The effects of magnetic property dependence of the Mn_1.56Co_0.96Ni_0.48O₄ (MCN) films on crystallization are investigated in the growth temperature of 450–750°C. With the growth temperature increase, both the crystalline quality and the grain size improve. The MCN films exhibit paramagnetic to ferromagnetic transition and the paramagnetic parts fit to the modified Curie–Weiss law. The ferromagnetic couplings of the magnetic ions in the MCN films enhance at elevated growth temperature. The saturation magnetization at 5K increases with increasing growth temperature, but coercive field decreases monotonously. The magnetic properties of the MCN films strongly depend on their microstructures.

Keywords: PACS; 72.80.Ga; 75.70.−iTransition metal oxide; Thin films; Crystallization-dependent; Magnetic properties

Preparation and properties of ZnO nanostructures by electrochemical anodization method by Shuanghu He; Maojun Zheng; Lujun Yao; Xiaoliang Yuan; Mei Li; Li Ma; Wenzhong Shen (pp. 2557-2562).

ZnO thin films with diverse nanostructures, including nanodot, nanowire and nanoflower, have been fabricated on zinc foils by a simple and rapid electrochemical anodization method. The ZnO thin films reveal very strong visible emission that is ascribed to the transition between V_OZn_i and valence band. Under the dc or ac electric field, the electroinduced surface wettability conversion from the superhydrophobic to hydrophilic state was observed and the generation of surface defective sites on ZnO films under electric field was used to explain the transition mechanism. This work provides a simple and rapid method for synthesizing different ZnO nanostructures in large scale, and electric field can be used to modulate the wettability of ZnO nanostructures.

Keywords: PACS; 81.07.−b; 82.45.Aa; 78.67.−n; 78.55.Et; 68.08.BcDiverse ZnO nanostructures; Electrochemical anodization; Strong visible emission; Electrowettability; Near superhydrophobic

LiFePO₄ thin films grown by pulsed laser deposition: Effect of the substrate on the film structure and morphology by V. Palomares; I. Ruiz de Larramendi; J. Alonso; M. Bengoechea; A. Goñi; O. Miguel; T. Rojo (pp. 2563-2568).

Well crystallized and homogeneous LiFePO₄/C (LFPO) thin films have been grown by pulsed laser deposition (PLD). The targets were prepared by the sol–gel process at 600°C. The structure of the polycrystalline powders was analyzed with X-ray powder diffraction (XRD) data. The XRD patterns were indexed having a single phase olivine structure (Pnma). LFPO thin films have been deposited on three different substrates: aluminum (Al), stainless steel (SS) and silicon (Si) by pulsed laser deposition (PLD). The structure of the films was analyzed by X-ray diffraction (XRD), Raman spectroscopy, scanning electron microscopy (SEM), transmission electron microscopy (TEM) and atomic force microscopy (AFM). It is found that the crystallinity of the thin films depends on the substrate temperature which was set at 500°C. When annealed treatments were used, secondary phases were found, so, one step depositions at 500°C were made.Stainless steel is demonstrated to be the best choice to act as substrate for phosphate deposition. LiFePO₄ thin films grown on stainless steel plates exhibited the presence of carbon, inducing a slight conductivity enhancement that makes these films promising candidates as one step produced cathodes in Li-ion microbatteries.

Keywords: LiFePO; ₄; Pulsed laser deposition; Conductive substrates

Adsorption isotherms and kinetics of methylene blue on a low-cost adsorbent recovered from a spent catalyst of vinyl acetate synthesis by Zhengyong Zhang; Zebiao Zhang; Y. Fernández; J.A. Menéndez; Hao Niu; Jinhui Peng; Libo Zhang; Shenghui Guo (pp. 2569-2576).

A regenerated activated carbon used as catalyst support in the synthesis of vinyl acetate has been tested as a low-cost adsorbent for the removal of dyes. After a thorough textural characterization of the regenerated activated carbon, its adsorption isotherms and kinetics were determined using methylene blue as model compound at different initial concentrations. Both Langmuir and Freundlich isotherm models were developed and then compared. It was found that the equilibrium data were best represented by the Langmuir isotherm model. The kinetic data were fitted to pseudo-first-order, pseudo-second-order and intraparticle diffusion models, and it was found that the best fitting corresponded to the pseudo-second-order kinetic model. The results showed that this novel adsorbent had a high adsorption capacity, making it suitable for use in the treatment of methylene blue enriched wastewater.

Keywords: Regenerated activated carbon; Spent catalyst; Basic dye; Adsorption isotherm; Kinetic

Regular and reverse nanoscale stick-slip behavior: Modeling and experiments by Fakhreddine Landolsi; Yuekai Sun; Hao Lu; Fathi H. Ghorbel; Jun Lou (pp. 2577-2582).

We recently proposed a new nanoscale friction model based on the bristle interpretation of single asperity contacts. The model is mathematically continuous and dynamic which makes it suitable for implementation in nanomanipulation and nanorobotic modeling. In the present paper, friction force microscope (FFM) scans of muscovite mica samples and vertically aligned multi-wall carbon nanotubes (VAMWCNTs) arrays are conducted. The choice of these materials is motivated by the fact that they exibit different stick-slip behaviors. The corresponding experimental and simulation results are compared. Our nanoscale friction model is shown to represent both the regular and reverse frictional sawtooth characteristics of the muscovite mica and the VAMWCNTs, respectively.

Keywords: Nanoscale friction; Dynamic modeling; Stick-slip behavior

Electrochemical characterization of surface complexes formed on Cu and Ta in succinic acid based solutions used for chemical mechanical planarization by Christopher M. Sulyma; Dipankar Roy (pp. 2583-2595).

Open-circuit potential measurements, cyclic voltammetry and Fourier transform impedance spectroscopy have been used to study pH dependent surface reactions of Cu and Ta rotating disc electrodes (RDEs) in aqueous solutions of succinic acid (SA, a complexing agent), hydrogen peroxide (an oxidizer), and ammonium dodecyl sulfate (ADS, a corrosion inhibitor for Cu). The surface chemistries of these systems are relevant for the development of a single-slurry approach to chemical mechanical planarization (CMP) of Cu lines and Ta barriers in the fabrication of semiconductor devices. It is shown that in non-alkaline solutions of H₂O₂, the SA-promoted surface complexes of Cu and Ta can potentially support chemically enhanced material removal in low-pressure CMP of surface topographies overlying fragile low-k dielectrics. ADS can suppress Cu dissolution without significantly affecting the surface chemistry of Ta. The data analysis steps are discussed in detail to demonstrate how the D.C. and A.C. electrochemical probes can be combined in the framework of the RDE technique to design and test CMP slurry solutions.

Keywords: Copper; CMP; Impedance spectroscopy; Rotating disc; Surfactant; TantalumPACS; 68.08.−p; 68.43.−h; 81.20.−n; 81.65.−b; 82.45.Bb

Study on the surface erosion route to the fabrication of TiO₂ hollow spheres by Liu Lei; Cui Yuming; Li Bo; Zhou Xingfu; Ding Weiping (pp. 2596-2601).

Anatase-type TiO₂ hollow spheres with a diameter of ∼1μm and shell thickness of ∼150nm are successfully fabricated via the surface erosion route. Study shows the repeated dissolution–crystallization process governing the formation process of TiO₂ hollow spheres, i.e., the dissolution of titanium powder and crystallization of TiO₂ on the surface of titanium, then the dissolution of surface TiO₂ and the recrystallization and assembly of TiO₂ nanoparticles on the gas–liquid interface of the gas bubble template finally makes the formation of TiO₂ hollow spheres with the depletion of titanium.Three-dimensional (3D) architecture of TiO₂ hollow sphere has many excellent and interesting performances that attract significant attention nowadays. In this paper, a simple surface erosion approach to the fabrication of TiO₂ hollow spheres via the hydrothermal process has been developed. The morphologies and the phase were characterized by scanning electron microscopy (SEM) and X-ray diffractometer (XRD). The results indicate that the anatase-type TiO₂ hollow spheres with a diameter of ∼1μm are successfully synthesized. The shell thickness of TiO₂ hollow spheres is ∼150nm and the size of hollow cavity is ∼600nm. By the control experiments, the influence of ammonium fluoride and hydrogen peroxide on the hollow spherical structures was studied. Hydrogen peroxide acts as both the oxidant and the bubble generator, ammonium fluoride is crucial for the erosion and dissolution of titanium, the detailed dissolution–crystallization mechanism for the formation of TiO₂ hollow spheres was also proposed.

Keywords: Titanium powder; TiO; ₂; hollow sphere; Ammonium fluoride; Surface erosion; Assembly

Pitfalls in measuring work function using photoelectron spectroscopy by M.G. Helander; M.T. Greiner; Z.B. Wang; Z.H. Lu (pp. 2602-2605).

Accurate measurement of work function is essential in many areas of research and development. Despite the importance of photoelectron spectroscopy as a technique for measuring work function, there has been relatively little discussion in the literature of how to conduct accurate measurements. We review the basic technique of measuring work function using ultraviolet photoelectron spectroscopy and discuss several common sources of error related to the experimental setup. In particular, the sample-detector geometry is found to be a key experimental parameter; accurate results are only obtained when the sample is perpendicular to the electron detector. In addition, we demonstrate that photoelectron work function values correspond to the minimum work function “patch” on a non-uniform surface, in contrast to the average work function measured by other techniques, such as the Kelvin probe method.

Keywords: Ultraviolet photoelectron spectroscopy; Work function; Secondary electron cut-off; Fermi level

Effects of annealing treatment on the formation of CO₂ in ZnO thin films grown by metal-organic chemical vapor deposition by Gaolin Zheng; Anli Yang; Hongyuan Wei; Xianglin Liu; Huaping Song; Yan Guo; Caihong Jia; Chunmei Jiao; Shaoyan Yang; Qinsheng Zhu; Zhanguo Wang (pp. 2606-2610).

Post-growth annealing was carried out on ZnO thin films grown by metal-organic chemical vapor deposition (MOCVD). The grain size of ZnO thin film increases monotonically with annealing temperature. The ZnO thin films were preferential to c-axis oriented after annealing as confirmed by X-ray diffraction (XRD) measurements. Fourier transformation infrared transmission measurements showed that ZnO films grown at low temperature contains CO₂ molecules after post-growth annealing. A two-step reaction process has been proposed to explain the formation mechanism of CO₂, which indicates the possible chemical reaction processes during the metal-organic chemical vapor deposition of ZnO films.

Keywords: ZnO; Metal-organic chemical vapor deposition; Infrared absorption; Surface

Synthesis of hollow silver spheres using poly-(styrene-methyl acrylic acid) as templates in the presence of sodium polyacrylate by Aili Wang; Hengbo Yin; Chen Ge; Min Ren; Yumin Liu; Tingshun Jiang (pp. 2611-2615).

Hollow silver spheres were successfully prepared by reducing AgNO₃ with ascorbic acid and using negatively charged poly-(styrene-methyl acrylic acid) (PSA) spheres as templates in the presence of sodium polyacrylate as a stabilizer. Firstly, silver cations adsorbed on the surface of PSA spheres via electrostatic attraction between the carboxyl groups and silver cations were reduced in situ by ascorbic acid. The silver nanoparticles deposited on the surface of PSA spheres served as seeds for the further growth of silver shells. After that, extra amount of AgNO₃ and ascorbic acid solutions were added to form PSA/Ag composites with thick silver shells. In order to obtain compact silver shells, the as-prepared PSA/Ag composites were heated at 150°C for 3h. Then hollow silver spheres were prepared by dissolving PSA templates with tetrahydrofuran.

Keywords: Silver; Hollow silver spheres; Poly-(styrene-methyl acrylic acid); Sodium polyacrylate

Characterization of laser waveguides in Nd:CNGG crystals formed by low fluence carbon ion implantation by Liang-Ling Wang; Yong-Gui Yu (pp. 2616-2619).

We report on Nd:CNGG active planar waveguides produced by 6.0MeV carbon ion implantation at fluence from 1×10¹⁴ ions/cm² to 8×10¹⁴ ions/cm². The refractive index profiles, which were reconstructed according to the measured dark mode spectroscopy, showed that the refractive indices had negative changes in the surface region, forming typical barrier waveguide. The width of waveguide structure induced by carbon ion implantation is ∼3.8μm. The typical barrier-shaped distribution may be mainly due to the nuclear energy deposition of the incident ions into the substrate. By performing a modal analysis on the observed TE modes, it was found that the TE₀ and TE₁ modes can be well-confined inside the waveguide.

Keywords: PACS; 42.82.Et; 61.80.JhWaveguide; Ion implantation; Nd:CNGG crystal

Preparation and the optical nonlinearity of surface chemistry improved titania nanoparticles in poly(methyl methacrylate)–titania hybrid thin films by Xiujing Sun; Xiangjun Chen; Guanghua Fan; Shiliang Qu (pp. 2620-2625).

With 800-nm, 120-fs laser pulses, optical nonlinearity has been studied in a series of thin films containing poly(methyl methacrylate) (PMMA), filled with surfactant acetylacetone (Acac) capped TiO₂ nanoparticles, which were synthesized by a simple in situ sol–gel/polymerization process, assisted by spin coating and multi-step baking. The resulting nanohybrid thin films have highly optical transparency and demonstrate a unique nonlinear optical (NLO) response. The highest nonlinear refractive index ( n₂) is observed up to 6.55×10⁻²cm²GW⁻¹ in the nanohybrid thin film of 60wt% Ti(OBu)₄ in PMMA, with a negligible two-photon absorption (TPA), as confirmed by the Z-scan technique. The titanium precursor loading combined with the nature of the capping molecules are used to influence the ability of nanoparticles to nonlinear optical response. Indeed, the ligands at the nanoparticles’ surface can not only control the extent of the interaction between the organic molecules and the embedded nanoparticles but also influence the optical nonlinearities of nanoparticles.

Keywords: PACS; 82.35.NPNanohybrid thin film; Surface improvement; Optical nonlinearity

Microstructure of microwave dielectricthin films by RF magnetron sputtering by Feng Shi; Chuanwen Cui (pp. 2626-2629).

The article describes the microstructure and morphological properties of microwave dielectric ceramic thin films. These thin films were successfully prepared on SiO₂ (110) single-crystal substrates by radio frequency magnetron-sputtering system. The microstructure and morphology of the thin films were characterized by X-ray diffraction, scanning electron microscopy, atomic force microscopy, and transmission electron microscopy. The results show that the main phase is Ba_0.5Sr_0.5Nb₂O₆,which has a tetragonal perovskite structure, a long strip pattern, and uniform crystal-grain size of about 2–3μm in length when annealed under 1150°C for 30min in an O₂ atmosphere. These thin films are of excellent crystallization quality, with a polycrystalline and dense structure.

Keywords: Microwave dielectric ceramic; Thin films; Radio frequency magnetron-sputtering; Microstructure

Synthesis of Mn doped ZnO nanoparticles with biocompatible capping by Sharda; K. Jayanthi; Santa Chawla (pp. 2630-2635).

Free standing nanoparticles of ZnO doped with transition metal ion Mn have been prepared by solid state reaction method at 500°C. X-ray diffraction (XRD) analysis confirmed high quality monophasic wurtzite hexagonal structure with particle size of 50nm and no signature of dopant as separate phase. Incorporation of Mn has been confirmed with EDS. Bio-inorganic interface was created by capping the nanoparticles with heteromultifunctional organic stabilizer mercaptosuccinic acid (MSA). The surface morphological studies by scanning electron microscopy (SEM) showed formation of spherical particles and the nanoballs grow in size uniformly with MSA capping. MSA capping has been confirmed with thermo gravimetric analysis (TGA) and FTIR. Photoluminescence (PL) studies show that the ZnO:Mn²⁺ particles are excitable by blue light and emits in orange and red. Occurrence of room temperature ferromagnetism in Mn doped ZnO makes such biocompatible luminescent magnetic nanoparticles very promising material.

Keywords: Transition metal ion; Mercaptosuccinic acid; Photoluminescence; Capping

Effect of micro and nanoparticle inorganic fillers on the field emission characteristics of photosensitive carbon nanotube pastes by J.H. Kim; H.S. Lee; J.C. Goak; Y.H. Seo; K.B. Kim; K.S. Park; N.S. Lee (pp. 2636-2642).

We successfully fabricated field emitter arrays of carbon nanotube (CNT) dots of 10μm diameter with excellent field emission properties by using photosensitive CNT paste. The CNT paste was investigated in terms of morphologies, current –voltage properties, and luminous uniformities by varying the mixing ratios of micro and nanoparticle inorganic fillers and the amount of CNTs added into the paste. The 3:1 mixing of micro and nanoparticle fillers and the addition of 5% CNTs in the paste brought about the best field emission characteristics of dot-patterned CNT field emitter arrays.

Keywords: Field emission; Carbon nanotube; Photosensitive paste; Inorganic filler; Nanoparticle; Luminous uniformity

Synthesis, field emission and glucose-sensing characteristics of nanostructural ZnO on free-standing carbon nanotubes films by Dan Bai; Zhi Zhang; Ke Yu (pp. 2643-2648).

Free-standing multiwall carbon nanotubes (MWNTs) films were coated, using chemical vapor deposition method, with a thin layer of nanostructural ZnO. The morphology and crystal structure of the as-grown products were characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD) and Raman scattering analyses. Field emission (FE) results demonstrated that the needle-like and spherical ZnO–MWNTs composite structure films possessed good performance with a turn-on field of 1.3, 2.2Vμm⁻¹ and a threshold field of 2.6, 4.5Vμm⁻¹, respectively. The glucose-sensing characteristic has also been studied. The multi-layer electrode (PDDA/GOx/ZnO/MWNTs) exhibited significant electrocatalysis to the oxidation and reduction of H₂O₂ than the PDDA/GOx/MWNTs electrode, which provided wide potential applications in clinical, environmental, and food analysis.

Keywords: PACS; 81.05.Dz; 81.05.Uw; 85.45.Db; 82.47.RsZinc oxide nanomaterials; Multiwall carbon nanotubes film; Field emission; Biosensors

Complete filling of 41nm trench pattern using Cu seed layer deposited by SAM-modified electroless plating and electron-beam evaporation by W.K. Han; G.H. Hwang; S.J. Hong; H.H. An; C.S. Yoon; J.H. Kim; M.J. Lee; G. Hong; K.S. Park; S.G. Kang (pp. 2649-2653).

To overcome the limitation of the sputtered Cu seed layer in electroplating of Cu interconnects imposed by the shadow effect, a new method for depositing a Cu seed layer on a 41nm trench pattern based on combination of electroless plating (ELP) and electron-beam (E-Beam) evaporation was developed. A Cu seed layer formed by ELP alone was too thin to be used for electroplating due to its high resistivity. To solve this problem, an additional Cu layer was deposited on top of the trench by E-Beam evaporator to enhance the electrical conductivity of the Cu seed layer. The electrical resistivity of the resulting Cu layer was reduced to 4.8μΩcm, which was sufficient for the conductive seed layer for electroplating the 41nm trench pattern. The gap-filling capability also improved and there were no voids or seams in the 41nm trench pattern. The proposed method can be an effective solution for fabrication of a conductive seed layer to fill a 41nm trench pattern by electroplating.

Keywords: Electroplating; Self-assembled monolayer; Gap-filling capability; 41; nm trench pattern

Heterogeneous nucleation and growth of silver nanoparticles on unmodified polystyrene spheres by in situ reduction by Shaochun Tang; Lan Chen; Sascha Vongehr; Xiangkang Meng (pp. 2654-2660).

The in situ reduction growth of Ag nanoparticles (NPs) on unmodified polystyrene (PS) spheres is investigated via controlling Ag nucleation and growth rates by continuous dripping addition of reductant solution in the absence of surfactants. The sub-micro PS spheres were coated by a uniform coverage of Ag NPs with several shapes like elongated islands, spherical particles, and particle aggregates. The reaction temperature and reductant concentration are demonstrated to influence the crystal structure, distribution, and stability of the Ag NPs on the PS substrates. The heterogeneous nucleation and growth of Ag NPs on PS spheres are found to depend on the inhibition of in-solution reduction and homogeneous nucleation.

Keywords: Silver; Nucleation; In situ reduction; Crystal growth; Composite particles

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Applied Surface Science (v.256, #8)

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Applied Surface Science (v.256, #8)