Applied Surface Science (v.253, #6)
fcc solid solution alloy films formed in immiscible Fe–Ag system and their mechanical behaviors by R.L. Zong; S.P. Wen; F. Zeng; Y. Gao; C. Song; B. He; F. Pan (2993-2998).
Fe–Ag alloy films were deposited by magnetron sputtering. Fe K edge X-ray absorption near-edge structure (XANES) was performed by synchrotron radiation to evidence the structure of the films. Annealing experiments were carried out to study their stability. The hardness and elastic modulus were measured by nanoindentation. The experimental and calculated XANES spectra both reveal that Fe atoms replace part of Ag atoms and supersaturated fcc Ag (Fe) solid solution alloy films are formed up to 38 at.% Fe. The solid solutions are stable and begin to precipitate at 400 °C The elastic modulus increases with the increase of Fe concentration and satisfies the rule of mixtures. The hardness of the as-deposited alloy film is larger than that calculated based on the rule of mixtures. The mechanism responsible for the enhancement of the hardness is discussed in terms of Labusch model of solid solution hardening.
Keywords: Fe–Ag alloy; Solid solution; XANES; Mechanical behavior;
Effects of hydrogen flux on the properties of Al-doped ZnO films sputtered in Ar + H2 ambient at low temperature by W.F. Liu; G.T. Du; Y.F. Sun; J.M. Bian; Y. Cheng; T.P. Yang; Y.C. Chang; Y.B. Xu (2999-3003).
Al-doped ZnO (AZO) transparent conductive thin films were grown by magnetron sputtering with AZO (98 wt.% ZnO, 2 wt.% Al2O3) ceramic target in Ar + H2 ambient at a relatively low temperature of 100 °C. To investigate the dependence of crystalline and properties of as-grown AZO films on the H2-flux, X-ray diffraction (XRD), X-ray photoemission spectrometer (XPS), Hall and transmittance spectra measurements were employed to analyze the AZO samples deposited with different H2-flux. The results indicate that H2-flux has a considerable influence on the transparent conductive properties of AZO films. The resistivity of 4.15 × 10−4 Ω cm and the average transmittance of more than 94% in the visible range were obtained with the optimal H2-flux of 1.0 sccm. Such a low temperature growing method present here may be especially useful for some low-melting point photoelectric devices and substrates.
Keywords: H2; Al-doped ZnO (AZO); Transparent conductive oxides; XPS; Low temperature deposition;
The effect of diffusion and overhangs/vacancies on the microstructure of zig-zag thin film by H.J. Qi; J.D. Shao; D.P. Zhang; K. Yi; Z.X. Fan (3004-3008).
Basing on some growth models of thin film, we have investigated the growth mechanism of glancing angle deposition (GLAD) film. The simulation verifies that the overhangs/vacancies also contribute to the columnar growth as well as the self-shadowing effect for GLAD thin film. Besides, we have studied the effect of the deposition rate, surface and bulk diffusions on the microstructure of thin film using the time-dependent Monte Carlo method. The results show that the surface and bulk diffusions can significantly enhance the packing density of thin film in GLAD growth, and the increase of the deposition rate induce the moderate decrease of the packing density.
Keywords: Simulation; Growth model;
The effect of covalent functionalization of carbon nanotube reinforcements on the atomic-level mechanical properties of poly-vinyl-ester-epoxy by M. Grujicic; Y.-P. Sun; K.L. Koudela (3009-3021).
The effect of covalent functionalization of (5,5)/(10,10)/(15,15) three-wall carbon nanotubes (3WCNTs) on the atomic-level mechanical properties of 3WCNT-reinforced vinyl ester epoxy polymer has been studied using molecular mechanics calculations. Inter- and intra-molecular atomic interactions in the 3WCNT + vinyl ester epoxy polymer system are represented using condensed-phased optimized molecular potential for atomistic simulation studies (COMPASS), an ab initio forcefield that enables an accurate and simultaneous prediction of various gas-phase and condensed-phase properties of organic and inorganic materials. The computational crystal consisting of a periodic array of infinitely long 3WCNTs surrounded by amorphous poly-vinyl-ester-epoxy is constructed using an in-house developed computer program and the amorphous cell tools by Accelrys. All the computations are carried out using Discover, a molecular statics/dynamics program from Accelrys.The results obtained show that covalent functionalization has a profound effect of the matrix-to-nanotube load transfer especially when the loads are applied in a direction orthogonal to the nanotube axis.
Keywords: Carbon nanotubes; Vinyl ester epoxy; Atomistic simulations; Functionalization;
A photoelectron spectroscopic study of the carburization of MoO3 by Ákos Koós; Albert Oszkó; Frigyes Solymosi (3022-3028).
MoO3 and Mo samples containing copper were treated with different hydrocarbon/hydrogen gas mixtures. The formation of Mo2C was followed by X-ray photoelectron spectroscopy (XPS). Spectra taken in the Mo 3d, C 1s, O 1s, Cu 2p and Cu KLL regions demonstrated that the treatment with the hydrocarbon/hydrogen gas mixtures led to the formation of Mo2C. From the comparison of the effects of various hydrocarbons on the XP spectra of Mo 3d we can state that the reduction of MoO3 starts at the lowest temperature for C2H6/H2 (600 K) followed by CH4/H2 (700 K) and C4H10/H2 (723 K). Binding energies of Mo 3d5/2 characteristic for Mo2C are measured in the range of 227.7–228.0 eV. These values were attained at 900 K for CH4/H2, at 800 K for C2H6/H2 and at 873 K for C4H10/H2. Addition of copper to MoO3 catalyzed its reduction and promoted the carburization process.
Keywords: Molybdenum oxide; Molybdenum carbide; Copper modified Mo catalysts; Carburization of MoO3; X-ray photoelectron spectroscopy;
Preparation of ZnO-doped Al films by spray pyrolysis technique by M.A. Kaid; A. Ashour (3029-3033).
Al-doped zinc oxide (AZO) thin films have been prepared by spray pyrolysis (SP) technique of zinc acetate and aluminium nitrate, and the effect of thickness on structural and optical properties has been investigated. The structural and optical characteristics of the AZO films were examined by X-ray diffraction (XRD) and double-beam spectrophotometry. These films, deposited on glass substrates at an optimal substrate temperature (T S = 450 °C), have a polycrystalline texture with a hexagonal structure. Transmission measurements showed that for visible wavelengths, the AZO films have an average transmission of over 90%. The optical parameters have been calculated. The dependence of the refractive index, n, and extinction coefficient, k, on the wavelength for the sprayed films is also reported. Optical band gap of AZO is 3.30 and 3.55 eV, respectively, depending on the film thicknesses.
Keywords: Aluminium-doped ZnO (AZO); Spray pyrolysis; XRD; Optical properties;
Formation of Ge islands from a Ge layer on Si substrate during post-growth annealing by I. Kovačević; B. Pivac; P. Dubček; H. Zorc; N. Radić; S. Bernstorff; M. Campione; A. Sassella (3034-3040).
We have deposited a 12 nm thick Ge layer on Si(1 0 0) held at 200 °C by thermal evaporation under high vacuum conditions. Upon subsequent thermal annealing in vacuum, self-assembled growth of nanostructural Ge islands on the Ge layer occurred. Atomic force microscopy (AFM) and grazing incidence small-angle X-ray scattering (GISAXS) were used to characterize such layers. GISAXS measurements evidenced the formation of cylinder shaped structures upon annealing at 700 °C, which was confirmed by AFM measurements with a very sharp tip. A Ge mass transport from the layer to the islands was inferred by X-ray reflectivity and an activation energy of 0.40 ± 0.10 eV for such a process was calculated.
Keywords: Ge nanostructures; X-ray reflectivity; Ge islands; Atomic force microscopy;
Smooth Nb surfaces fabricated by buffered electropolishing by Andy T. Wu; John Mammosser; Larry Phillips; Jean Delayen; Charles Reece; Amy Wilkerson; David Smith; Robert Ike (3041-3052).
It was demonstrated that smooth Nb surfaces could be obtained through buffered electropolishing (BEP) employing an electrolyte consisting of lactic, sulfuric, and hydrofluoric acids. Parameters that control the polishing process were optimized to achieve a smooth surface finish. The polishing rate of BEP was determined to be 0.646 μm/min which was much higher than 0.381 μm/min achieved by the conventional electropolishing (EP) process widely used in the superconducting radio frequency (SRF) community. Root mean square measurements using a 3D profilometer revealed that Nb surfaces treated by BEP were an order of magnitude smoother than those treated by the optimized EP process. The chemical composition of the Nb surfaces after BEP was analyzed by static and dynamic secondary ion mass spectrometry (SIMS) systems. SIMS results implied that the surface oxide structure of Nb might be more complicated than what usually believed and could be inhomogeneous. Preliminary results of BEP on Nb SRF single cell cavities and half-cells were reported. It was shown that smooth and bright surfaces could be obtained in 1800 s when the electric field inside a SRF cavity was uniform during a BEP process. This study showed that BEP is a promising technique for surface treatment on Nb SRF cavities to be used in particle accelerators.
Keywords: Surface property; Surface treatment; Particle accelerator; Niobium; Superconducting radio frequency cavity; Electropolishing;
Cobalt-induced polycrystalline silicon film growth by Joondong Kim; Alan M. Piwowar; Richard Nowak; Joseph A. Gradella; Wayne A. Anderson (3053-3056).
Cobalt (Co)-induced crystalline silicon (Si) growth was investigated. The Co catalyst reacted to dc magnetron sputtered Si at 600 °C forming a Co silicide layer. The polycrystalline Si (poly-Si) was epitaxially grown above the Co silicide template, which has a small lattice misfit to Si. Annealing followed to improve the Si crystallinity. X-ray diffraction was performed to trace Co silicide phase formation and transition. The Co-rich silicide phase transitioned to CoSi2 by annealing. The crystallinity of Si films was identified using reflection absorption Fourier transform-infrared spectroscopy, which detected unique peaks at 689 and 566 cm−1 after the annealing process. The thin poly-Si film was used to fabricate a Schottky diode to prove the electronic quality. A good quality Si thin film was achieved by the metal-induced Si growth.
Keywords: Metal-induced growth; Polycrystalline Si film; FT-IR; XRD; Photodiode;
Low-temperature CO gas sensors based on Au/SnO2 thick film by Shurong Wang; Yingqiang Zhao; Jing Huang; Yan Wang; Hongxia Ren; Shihua Wu; Shoumin Zhang; Weiping Huang (3057-3061).
A study on the low-temperature CO gas sensors based on Au/SnO2 thick film was reported. Au/SnO2 powders were prepared by a deposition–precipitation method. Thick films were fabricated from Au/SnO2 powders. X-ray diffraction (XRD), high-resolution transmission electron microscopy (HRTEM) and X–ray photoelectron spectroscopy (XPS) analyses were carried out for investigation of morphology and crystalline structure. Au/SnO2 thick film sensors exhibited high sensitivity to CO gas at relatively low operating temperature (83–210 °C). We also reported the effect of the calcination temperature of Au/SnO2 on the CO gas sensing behavior. The optimal calcination temperature of Au/SnO2 was 300 °C.
Keywords: Au/SnO2 thick film; Low-temperature CO gas sensors; Deposition–precipitation method; Calcination temperature;
Permeability of C60 films deposited on polycarbonatesyloxane to N2, O2, CH4, and He gases by V.A. Karachevtsev; A.M. Plokhotnichenko; V.A. Pashynska; A.Yu. Glamazda; O.M. Vovk; A.M. Rao (3062-3065).
In this study, we report on the gas permeability of non-polymerized and polymerized fullerene films (thickness about 0.5 μm) grown on an organic polymer substrate, polycarbonatesyloxane (PCS), using a high vacuum deposition method. The photopolymerized C60 films were prepared by a simultaneous thin film deposition and UV–vis irradiation method which was reported previously [V.A. Karachevtsev, P.V. Mateichenko, N.Y. Nedbailo, A.V. Peschanskii, A.M. Plokhotnichenko, O.M. Vovk, E.N. Zubarev, A.M. Rao, Carbon 42 (2004) 2091]. Raman spectroscopy revealed that ∼90% of the C60 molecules are covalently linked to neighboring C60 molecules in the photopolymerized film after 20 h of film deposition/irradiation. Permeability of the resulting membranes consisting of polymer PCS base and fullerene films to the N2, O2, CH4, and He gases has been investigated. Our experiments revealed that the gas permeability properties are dependent on the age of the membrane. In particular, the aged membrane exhibited an enhanced permeability for O2 and He gases in comparison to N2 and CH4, respectively.
Keywords: Fullerene film; Polycarbonatesyloxane; Membrane; Raman spectroscopy; Gas selectivity; Permeability;
Adsorption and decomposition of triethylsilane on Si(1 0 0) by J. Lozano; A. Brickman; S. Yeninas; D. Early; J.H. Craig (3066-3071).
The adsorption and decomposition of triethylsilane (TES) on Si(1 0 0) were studied using temperature programmed desorption (TPD), high resolution electron energy loss spectroscopy (HREELS), electron stimulated desorption (ESD), and X-ray photoelectron spectroscopy (XPS). TPD and HREELS data indicate that carbon is thermally removed from the TES-dosed Si(1 0 0) surface via a β-hydride elimination process. At high exposures, TPD data shows the presence of physisorbed TES on the surface. These species are characterized by desorption of TES fragments at 160 K. Non-thermal decomposition of TES was studied at 100 K by irradiating the surface with 600 eV electrons. ESD of mass 27 strongly suggests that a β-hydride elimination process is a channel for non-thermal desorption of ethylene. TPD data indicated that electron irradiation of physisorbed TES species resulted in decomposition of the parent molecule and deposition of methyl groups on the surface that desorbed thermally at about 900 K. Without electron irradiation, mass 15 was not detected in the TPD spectra, indicating that the production of methyl groups in the TPD spectra was a direct result of electron irradiation. XPS data also showed that following electron irradiation of TES adsorbed on Si(1 0 0), carbon was deposited on the surface and could not be removed thermally.
Keywords: Si(1 0 0); Triethylsilane; HREELS; TPD; ESD;
Non-contact AFM observation of the ( 3 × 3 ) to (3 × 3) phase transition on Sn/Ge(1 1 1) and Sn/Si(1 1 1) surfaces by Insook Yi; Ryuji Nishi; Yoshiaki Sugimoto; Seizo Morita (3072-3076).
The ( 3 × 3 ) to (3 × 3) phase transition in Sn/Ge(1 1 1)-( 3 × 3 )R30° and Sn/Si(1 1 1)-( 3 × 3 )R30° systems was investigated for the first time using a non-contact atomic force microscope (NC-AFM). Observations show the occurrence of the phase transition with small (3 × 3) domains on the Sn/Ge(1 1 1) surface at low temperatures of 78 and 6 K. However, no evidence was found to support the presence of the phase transition for the Sn/Si(1 1 1) system, even when the temperature was lowered to 6 K. The (3 × 3) domains present two patterns, one hexagonal and the other honeycomb, depending on the tip to sample distance.
Keywords: Sn/Ge(1 1 1); Sn/Si(1 1 1); Phase transition; Non-contact atomic force microscope (NC-AFM); Low temperature; ( 3 × 3 ) Phase; (3 × 3) Phase;
The preparation of nitrogen-doped TiO2−x N x photocatalyst coated on hollow glass microbeads by Chen Shifu; Liu Xuqiang; Liu Yunzhang; Cao Gengyu (3077-3082).
In this paper, the effective method for nitrogen-doped TiO2−x N x photocatalyst coated on hollow glass microbeads is described, which uses titanium tetraisopropoxide [Ti(iso-OC3H7)4] as the raw materials and gaseous ammonia as a heat treatment atmosphere. The effects of heat treatment temperature and time on the photocatalytic activity of TiO2−x N x /beads are studied. The photocatalyst is characterized by the UV–vis diffuse reflection spectroscopy, X-ray photoelectron spectroscopy (XPS), X-ray powder diffraction (XRD), Brunauer–Emmett–Teller (BET) analysis and scanning electron microscopy (SEM). The results show that when the TiO2−x N x /beads is heated at 650 °C for 5 h, the photocatalytic activity of the TiO2−x N x /beads is the best. Compared with TiO2, the photoabsorption wavelength range of nitrogen-doped TiO2−x N x red shifts of about 60 nm, and the photoabsorption intensity increases as well. The photocatalytic activity of the TiO2−x N x /beads is higher than that of the TiO2/beads under visible light irradiation. The presence of nitrogen neither influences on the transformation of anatase to rutile, nor creates new crystal phases. When the TiO2−x N x /beads is heated at 650 °C for 5 h, the amount of nitrogen-doped is 0.53 wt.% in the TiO2−x N x . As the density of TiO2−x N x /beads prepared is lower than 1.0 g/cm3, it may float on water surface and use broader sunlight spectrum directly.
Keywords: Nitrogen-doped; Titanium dioxide; Hollow glass microbeads; Coat; Photocatalyst;
Effect of fluence on the discoloration of marble cleaned with UV lasers by Jie Zhang; Andrew J. Birnbaum; Y. Lawrence Yao; Fen Xu; John R. Lombardi (3083-3092).
The effect of fluence level on the discoloration of marble surfaces after the removal of the encrustation by 355 nm laser pulses is comparatively studied. Considering the thermochemical reaction possibly occurring in the encrustation during laser irradiation, the mechanism responsible for the discoloration of the cleaned marble surface is analyzed. The reduction of iron oxides by graphite plays a key role in determining the final color of the cleaned marble surface. A two-dimensional laser ablative cleaning model including the reaction heat is applied to calculate the temperature distribution during laser heating. The kinetics of the thermochemical reaction is estimated based on the simulated temperature field. The occurrence of the thermochemical reaction is also verified indirectly with experiments. The marble surfaces before and after laser irradiation are characterized in terms of the chemical components through surface enhanced Raman spectroscopy. The surface color is measured with a chromameter using a 1976 CIE L * a * b * color system. The proposed mechanism is also applied to numerically analyze the severe discoloration of marble cleaned with laser pulses at 1064 nm.
Keywords: Laser cleaning; UV laser; Marble;
Investigation of metal nanoparticles produced by laser ablation and their catalytic activity by R.G. Song; M. Yamaguchi; O. Nishimura; M. Suzuki (3093-3097).
Polydiphenylsilylenemethylene (PDPhSM) thin films, which are difficult to fabricate by conventional methods because of their insolubility and high melting point, have been synthesized by using laser-ablated metal nanoparticles for the thermal ring-opening polymerization of 1,1,3,3-tetraphenyl-1,3-disilacyclobutane (TPDC) in this paper. TPDC was first evaporated on silicon substrates and then exposed to metal (Pt, Cu and Ag) nanoparticles deposition by laser ablation prior to heat treatment. The catalytic activity of Pt, Cu and Ag nanoparticles has been studied. The results showed that the mean diameter of Pt nanoparticles was the smallest, Cu nanoparticles the moderate and Ag nanoparticles the biggest, while the polymerization efficiency for Pt nanoparticles was the highest, Cu nanoparticles the moderate and Ag nanoparticles the lowest. In addition, the penetration behaviours of Pt, Cu and Ag nanoparticles into the TPDC monomer films during laser ablation were different due to the particle size or the chemical interaction between metal nanoparticles and TPDC molecules.
Keywords: Laser ablation; Metal nanoparticles; Catalytic activity; 1,1,3,3-Tetraphenyl-1,3-disilacyclobutane (TPDC); Polydiphenylsilylenemethylene (PDPhSM) thin films;
Deformation and motion by gravity and magnetic field of a droplet of water-based magnetic fluid on a hydrophobic surface by Hiroko Asakura; Akira Nakajima; Munetoshi Sakai; Shunsuke Suzuki; Yoshikazu Kameshima; Kiyoshi Okada (3098-3102).
Motion and deformation of a water-based magnetic fluid on a hydrophobic surface were investigated under gravity and a magnetic field. Surface energy and the resultant contact angle of the magnetic fluid depend on the surfactant concentration. The fluid viscosity is governed mainly by magnetite concentration. The front edge of the droplet moved under a weak external field. The rear edge required a higher external field for movement. The forces of gravity and the magnetic field for moving of the front edge are almost equal. However, those of the rear edge are different. The motion of magnetic fluids by an external field depends on concentrations of surfactants and magnetic particles, the external field, and experimental assembly.
Keywords: Magnetic fluid; Sliding angle; Contact angle; Magnetic field; Hydrophobic;
Effect of pulse parameters on the passive layer formation on pulse plated Ni–Co alloys by B. Tury; M. Lakatos-Varsányi; S. Roy (3103-3108).
From a chloride bath, Ni–Co alloys were pulse plated by varying the pulse parameters off-time and the peak current densities using a pulse generator that applies a square wave signal in order to examine the mechanism of the passive oxide layer formation on the deposited coatings in the frame of pulse parameters.Cyclic voltammetry and potential step measurements were carried out in order to characterise the electrochemical behaviour on the Ni–Co coatings at a selected electrode potential in an alkaline solution. Calculation of the oxide layer formation was evaluated from the total charge, determined by recorded current–time transients and from ICP-analysis of the samples. The most protective and compact oxide was formed on the sample that was deposited at low current densities and at high off-time.
Keywords: Ni–Co alloy; Passive layer; Pulse plating; Corrosion;
Cd0.5Zn0.5Se wide range composite thin films for solar cell buffer layer application by R.B. Kale; C.D. Lokhande; R.S. Mane; Sung-Hwan Han (3109-3112).
Cd0.5Zn0.5Se composite thin films were obtained on glass substrate using aqueous alkaline solution at low temperature using cadmium acetate and zinc acetate as Cd2+ and Zn2+ and Se2− ion sources. Different phases of individuals i.e. CdSe and ZnSe, spherical and needle shape surface morphology and good elemental chemical stoichiometric ratio were observed from X-ray diffraction, scanning electron microscopy (SEM) and energy dispersive X-ray analysis (EDX) studies, respectively. The band gap and electrical resistivity of the composite film were 2.35 eV and about 107 Ω cm, respectively.
Keywords: Composite thin films; XRD; SEM; AFM; Electrical resistivity;
Anisotropic emission in laser-produced aluminum plasma in ambient nitrogen by A.K. Sharma; R.K. Thareja (3113-3121).
We report on the dynamical expansion of pulsed laser ablation of aluminum in ambient pressure of nitrogen using images of the expanding plasma. The plasma follows shock model at pressures of 0.1 Torr and drag model at 70 Torr, respectively, with incident laser energy of 265 mJ. The plasma expansion shows unstable boundaries at 70 Torr and is attributed to Rayleigh–Taylor instability. The growth time of Rayleigh–Taylor instability is estimated between 0.09 and 4 μs when the pressure is varied from 1 to 70 Torr. The pressure gradients at the plasma–gas interface gives rise to self-generated magnetic field and is estimated to be 26 kG at 1 Torr ambient pressure using the image of the expanding plasma near the focal spot. The varying degree of polarization of Al III transition 4s 2S1/2–4p 2P°3/2 at 569.6 nm gives rise to anisotropic emission and is attributed to the self-generated magnetic field that results in the splitting of the energy levels and subsequent recombination of plasma leading to the population imbalance.
Keywords: Ablation; Shock wave; Rayleigh–Taylor instability; Self-generated magnetic field; Degree of polarization;
Analysis by using X-ray photoelectron spectroscopy for polymethyl methacrylate and polytetrafluoroethylene etched by KrF excimer laser by X.L. Zhu; S.B. Liu; B.Y. Man; C.Q. Xie; D.P. Chen; D.Q. Wang; T.C. Ye; M. Liu (3122-3126).
The C 1s, F 1s, and O 1s electron spectra for polymethyl methacrylate (PMMA) and polytetrafluoroethylene (PTFE) irradiated by KrF excimer laser with 248 nm wavelength were analyzed by the X-ray photoelectron spectroscopy (XPS) method. The results show that, after irradiation by the laser, the percentage of the carbon atoms of C–C bond decreases and the percentage of C＝O bond increases for PMMA, while for PTFE percentages of both C–C bond and CF2 group decrease drastically, respectively. Moreover, it was found that C–O bond and other complex carbon–oxygen groups appeared for PTFE. The photon-chemical processes associated with the energy level transitions, energy diversion, and dissociation of bonds in the interaction were theoretically analyzed based on the chemical structures of PTFE and PMMA. Our analyses can successfully explain that PMMA can be effectively etched by KrF excimer laser with 248 nm wavelength can efficiently etch the PMMA, but the surface of PTFE can only be modified by it.
Keywords: Excimer laser ablation; PTFE; PMMA; XPS spectrum; Mechanism of photo-polymer interaction;
Silanization and antibody immobilization on SU-8 by Manoj Joshi; Richard Pinto; V. Ramgopal Rao; Soumyo Mukherji (3127-3132).
SU-8, an epoxy based negative photoresist, has emerged as a structural material for microfabricated sensors due to its attractive mechanical properties like low Young's modulus and chemical properties like inertness to various chemicals used in microfabrication. It can be used to fabricate MEMS structures of high aspect ratio. However, the use of SU-8 in BioMEMS application has been limited by the fact that immobilization of biomolecules on SU-8 surfaces has not been reported. In this study, the epoxy groups on the SU-8 surface were hydrolyzed in the presence of sulphochromic solution. Following this, the surface was treated with [3-(2-aminoethyl) aminopropyl]-trimethoxysilane (AEAPS). The silanized SU-8 surface was used to incubate human immunoglobulin (HIgG). The immobilization of HIgG was proved by allowing FITC tagged goat anti-human IgG to react with HIgG. This process of antibody immobilization was used to immobilize HIgG on microfabricated SU-8 cantilevers.
Keywords: SU-8; AEAPS; Silanization; HIgG; Antibody immobilization;
Adsorption of BTSE and γ-GPS organosilanes on different microstructural regions of 7075-T6 aluminum alloy by J. Kim; P.C. Wong; K.C. Wong; R.N.S. Sodhi; K.A.R. Mitchell (3133-3143).
The adsorption of bis-1,2-(triethoxysilyl)ethane (BTSE) and γ-glycidoxypropyltrimethoxysilane (γ-GPS) on mirror-polished 7075-T6 aluminum alloy was studied with an emphasis on the different microstructural regions of the alloy surface, specifically the alloy matrix and the two main types of second-phase particles, as well as how the adsorption was affected by a heating pre-treatment and by changes in the pH of the γ-GPS solution. Surface characterizations were undertaken with scanning Auger microscopy (SAM), X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM) and time-of-flight secondary-ion mass spectrometry (TOF-SIMS). BTSE at its natural pH (4.3) adsorbed at all micro-regions of the air-oxidized surface, while γ-GPS at its natural pH (5.7) was largely ineffective. Adsorption of γ-GPS on all micro-regions was possible after adjusting the solution pH to a lower value (3.2), or by using the solution of natural pH after pre-treating the sample by heating at 200 °C for 15 min. TOF-SIMS measurements indicated that direct metal–O–Si covalent bonding occurred at each silane interface formed to the different micro-regions of the alloy surface, with Al–O–Si bonding being predominant in each case.
Keywords: Aluminum alloy; Silane coating; Surface microstructure; Auger electron spectroscopy; Time-of-flight SIMS;
On the growth of conversion chromate coatings on 2024-Al alloy by S.A. Kulinich; A.S. Akhtar; D. Susac; P.C. Wong; K.C. Wong; K.A.R. Mitchell (3144-3153).
The initial growth of chromate conversion coatings on aluminium 2024-T3 alloy has been investigated by scanning Auger microscopy, scanning electron microscopy and X-ray photoelectron spectroscopy. The coating initiation is shown to be influenced by the alloy microstructure. In agreement with previously proposed growth models, Cr(VI) to Cr(III) reduction begins on the Al–Cu–Fe–Mn intermetallic second-phase particles, which act as cathodic sites, and then over the entire Al matrix surface. The less noble Al–Cu–Mg second-phase particles demonstrate dual behaviour during the initial stage of coating; some dealloy, with formation of a Cu-rich sponge-like structure, while others show no evidence for etching during the first few seconds and coating deposits on them similar to the situation for the Al–Cu–Fe–Mn particles. XPS measurements show more Cr(III) at the very initial stage of nucleation and growth, whereas the amount of Cr(VI) in the coating increases with the length of the chromating treatment. This is discussed in relation to Raman spectroscopy measurements made in a separate study.
Keywords: Aluminium alloy; Conversion coating; Chromating; Surface microstructure; Auger electron spectroscopy;
Effects of water plasma immersion ion implantation on surface electrochemical behavior of NiTi shape memory alloys in simulated body fluids by X.M. Liu; S.L. Wu; Paul K. Chu; C.Y. Chung; C.L. Chu; K.W.K. Yeung; W.W. Lu; K.M.C. Cheung; K.D.K. Luk (3154-3159).
Water plasma immersion ion implantation (PIII) was conducted on orthopedic NiTi shape memory alloy to enhance the surface electrochemical characteristics. The surface composition of the NiTi alloy before and after H2O-PIII was determined by X-ray photoelectron spectroscopy (XPS) and atomic force microscopy (AFM) was utilized to determine the roughness and morphology of the NiTi samples. Potentiodynamic polarization tests and electrochemical impedance spectroscopy (EIS) were carried out to investigate the surface electrochemical behavior of the control and H2O-PIII NiTi samples in simulated body fluids (SBF) at 37 °C as well as the mechanism. The H2O-PIII NiTi sample showed a higher breakdown potential (E b) than the control sample. Based on the AFM results, two different physical models with related equivalent electrical circuits were obtained to fit the EIS data and explain the surface electrochemical behavior of NiTi in SBF. The simulation results demonstrate that the higher resistance of the oxide layer produced by H2O-PIII is primarily responsible for the improvement in the surface corrosion resistance.
Keywords: NiTi; Plasma immersion ion implantation; Water plasma immersion ion implantation; Electrochemical impedance spectroscopy;
Thermal spreading of WO3 onto zirconia support by Jorge Siqueira da Cruz; Marco A. Fraga; Silvana Braun; Lucia Gorenstin Appel (3160-3167).
This study focused on preparation of tungsten oxide supported on zirconia by thermal spreading. The prepared samples were characterized by infrared spectroscopy, UV–vis diffuse reflection spectroscopy, X-ray diffraction, and also by methanol dehydration reaction. It was observed that isolated octahedral tungsten dispersed species and dispersed polytungstate were formed on zirconia surface, although some WO3 that remained after the thermal treatment could also be detected. The presence of these species led to an increase of the number of Lewis sites and the generation of Brönsted acid sites. High calcination temperatures promoted the creation of Brönsted sites as a consequence of polytungstate species formation. The activity on methanol dehydration was also determined by the concentration of these species, whereas the isolated WO x species were found poorly active. The correlation observed between the catalytic performance and the tungsten dispersed species, as revealed by spectroscopic techniques, evidenced the occurrence of thermal spreading of WO3 on ZrO2. The results presented in this work show that WO3 thermal spreading on ZrO2 may be effectively accomplished as predicted by thermodynamics.
Keywords: Thermal spreading; Tungsten; Zirconia;
Humidity sensing properties of Pd2+-doped ZnO nanotetrapods by Xiaohua Wang; Jian Zhang; Ziqiang Zhu; Jianzhong Zhu (3168-3173).
Pd2+-doped ZnO nanotetrapods were prepared and studied for the humidity detection application. The humidity sensors developed were featured by combination of a quartz crystal microbalance (QCM) as a transducer and Pd2+-doped ZnO nanotetrapods as a sensing element. The ZnO nanotetrapods were synthesized by evaporating highly pure zinc pellets (99.999%) at 900 °C in air and PdCl2 was doped on by traditional solution mixing process. Then the mixed solution distributed onto the electrode surfaces of the quartz crystal at room temperature. Pd2+-doped ZnO nanotetrapods were characterized by X-ray diffraction (XRD) and scanning electron microscopy (SEM). The experimental results indicated that the response of the sensors varied with the different dosage PdCl2. Linear regression algorithm was used for evincing the highly linear behavior of the Pd2+-doped ZnO nanotetrapods sensor. In this humidity sensing system, the Pd2+-doped ZnO nanotetrapods sensing material coated on the gold electrode of QCM showed good sensitivity (∼74.24324 Hz/%RH (relative humidity)), reproducibility, linearity (R 2 = −0.98834), short response and recovery time (less than 5 s).
Keywords: ZnO nanotetrapods; PdCl2; Quartz crystal microbalance; Humidity sensor; Relative humidity; Doping;
Auger electron spectroscopy of Au/NiO x contacts on p-GaN annealed in N2 and O2 + N2 ambients by J. Liday; I. Hotový; H. Sitter; K. Schmidegg; P. Vogrinčič; A. Bonnani; J. Breza; G. Ecke; I. Vávra (3174-3180).
We have designed a promising contact scheme to p-GaN. Au/NiO x layers with a low concentration of O in NiO x are deposited on p-GaN by reactive dc magnetron sputtering and annealed in N2 and in a mixture of O2 + N2 to produce low resistivity ohmic contacts. Annealing has been studied of NiO x layers with various contents of oxygen upon the electrical properties of Au/NiO x /p-GaN. It has been found that the Au/NiO x /p-GaN structure with a low content of oxygen in NiO x layer provides a low resistivity ohmic contact even after subsequent annealing in N2 or O2 + N2 ambient at 500 °C for 2 min.Auger depth profiles and transmission electron microscopy (TEM) micrographs reveal that while annealing in O2 + N2 ambient results in reconstruction of the initial deposited Au/NiO x /p-GaN contact structure into a Au/p-NiO/p-GaN structure, annealing in N2 brings about reconstruction into Au/p-NiO/p-GaN and Ni/p-NiO/p-GaN structures. Hence, in both cases, after annealing in N2 as well as in O2 + N2 ambient, the ohmic properties of the contacts are determined by creation of a thin oxide layer (p-NiO) on the metal/p-GaN interface. Higher contact resistivities in the samples annealed in O2 + N2 ambient are most likely caused by a smaller effective area of the contact due to creation of voids.
Keywords: Gallium nitride; Nickel oxide; AES depth profiling; TEM; Low resistivity contact;
The role of Laplace pressure in the formation of the structure of thin layers based on silicon dioxide by F.N. Dultsev; I.P. Mikhailovskii (3181-3183).
Formation of the structure of thin layers deposited from the gas phase occurs not only during film deposition but also during the subsequent annealing. In the present work, porous films were deposited using the catalytic chemical vapor deposition (Cat-CVD) procedure. It was shown that the kinetics of a decrease in the film volume during annealing can be explained taking into account the role of Laplace pressure in the formed pores.
Keywords: Cat-CVD procedure; Porosity; Silicon dioxide;
Si growth effects on the formation of Er silicide nanostructures by Ting Ji; Junqiang Song; Wei Zhou; Qun Cai (3184-3189).
In this work, an ultra-high vacuum scanning tunneling microscopy has been utilized to study the effects of Si atoms to the formation and growth evolution of Er silicide nanostructures. Si evaporation is performed on the vicinal Si(0 0 1) surface as well as Er growth under different growth conditions: growth procedure, annealing temperature and duration time. The experimental results show that the Si evaporation performed at a high temperature plays a key role on the growth of Er silicide nanostructures. The deposited Si atoms become a significant source of the Si reactant and mainly affect the early growth stage of the nanostructures. It is also shown that Er atom is possibly another diffusing species during the growth of Er silicide nanostructures on the Si(0 0 1) surface.
Keywords: Scanning tunneling microscopy; Er silicide; Nanowire; Nanoisland; Si(001);
Nanosized multilayer films with concurrent photochromism and electrochromism based on Dawson-type polyoxometalate by Bingbing Xu; Lin Xu; Guanggang Gao; Yana Jin (3190-3195).
An inorganic–organic composite multilayer film constructed of poly(vinyl alcohol) (PVA) with Dawson-type phosphotungstate anion [P2W18O62]6− (P2W18) and poly(allylamine hydrochloride) (PAH) were fabricated on quartz, ITO, silicon and CaF2 substrates by a layer-by-layer self-assembly method. The film was provided with concurrent photochromism and electrochromism. IR spectra showed that the structure of the PVA was fully maintained in the multilayer film. And their photochromic and electrochromic properties were investigated by UV–vis spectra, cyclic voltammetry (CV), chronoamperometry (CA) measurement and X-ray photoelectron spectra (XPS). Atomic force microscopy (AFM) was used to investigate the surface topography. This study provides a new route to explore the possibility of application to polyoxometalate-based hybrid inorganic–organic materials.
Keywords: Photochromism; Electrochromism; Polyoxometalate; Layer-by-layer;
Control of nucleation site density of GaN nanowires by Chih-Yang Chang; S.J. Pearton; Ping-Jung Huang; Gou-Chung Chi; Hung-Ta Wang; Jau-Juin Chen; F. Ren; Kuei-Hsien Chen; Li-Chyong Chen (3196-3200).
The control of nucleation site size and density for Au catalyst-driven growth of GaN nanowires is reported. By using initial Au film thicknesses of 15–50 Å we have shown that annealing between 300 and 900 °C creates Au cluster size in the range 30–100 nm diameter with a cluster density from 300 to 3500 μm−2.Conventional optical lithography to create parallel Au stripes shoes that a minimum separation of ∼15 μm is needed to avoid overlap of wires onto neighboring lines with our growth conditions that yield wires of this same length. The GaN nanowires exhibit strong band-edge photoluminescence and total resistances of 1.2 × 108–5.5 × 106 Ω in the temperature range from 240 to 400 K, as determined for the temperature-dependent current–voltage characteristics.
Keywords: GaN; Nanowire;
SO2 adsorption capacity of K2CO3-impregnated activated carbon as a function of K2CO3 content loaded by soaking and incipient wetness by H. Fortier; C. Zelenietz; T.R. Dahn; P. Westreich; D.A. Stevens; J.R. Dahn (3201-3207).
The SO2 adsorption capacity of K2CO3-impregnated activated carbons, prepared by soaking carbon in large volumes of K2CO3 in solution of various concentrations, varies linearly with respect to the loading of K2CO3 on the carbon up to about 12% K2CO3 by weight. Above 12%, the capacity for SO2 levels out and then decreases. This suggests that at high loadings the K2CO3 either aggregates and/or blocks pores of the activated carbon. In contrast, the adsorption capacity of carbons prepared by repeatedly (maximum of three times total) loading K2CO3 via incipient wetness is much larger than that of the soaked samples, up to 70% more, when the loading of K2CO3 is greater than 12%. Static and dynamic adsorption, DSC, SEM, EDX and incipient wetness studies of the samples show that the impregnant aggregates but does not block carbon pores.
Keywords: Activated carbon; Impregnation; Adsorption; Differential scanning calorimetry; Scanning electron microscopy;
Study of magnesium and aluminum alloys absorption coefficient during Nd:YAG laser interaction by Nicolas Pierron; Pierre Sallamand; Simone Matteï (3208-3214).
In laser processes, the absorption factor of laser Nd:YAG by metals plays a very important role. In order to model laser welding, we need to know its evolution during the process. The theoretical calculation does not enable the prediction of the absorption factor in the case of a keyhole mode. It is difficult to predict the effect of plasma and recoil pressure on the shape of the keyhole. In this paper, an integrating sphere is used to determine the absorption factor during the laser process, which is carried out on two types of magnesium alloys (WE43 and RZ5) and an aluminum alloy. We obtain the evolution in time of the absorption factor according to different steps of the evolution of the keyhole.
Keywords: Laser; Nd:YAG; Absorption; Surface; Aluminum alloys; Magnesium alloys; Integrating sphere;
Relationships between surface compositions and properties of surfaces of mixed fumed oxides by V.M. Gun’ko; Y.M. Nychiporuk; V.I. Zarko; E.V. Goncharuk; O.A. Mishchuk; R. Leboda; J. Skubiszewska-Zięba; E. Skwarek; W. Janusz; G.R. Yurchenko; V.D. Osovskii; Y.G. Ptushinskii; V.V. Turov; P.P. Gorbik; J.P. Blitz; K. Gude (3215-3230).
Fumed oxides SiO2/Al2O3 (SA), SiO2/TiO2 (ST) and Al2O3/SiO2/TiO2 (AST) at different content of alumina and titania were investigated by one-pass temperature-programmed desorption (OPTPD) time-of-flight mass-spectrometry (TOFMS), Auger electron spectroscopy (AES), NMR, FTIR, thermally stimulated depolarization current (TSDC), microcalorimetry, adsorption of nitrogen, water, (dimethylamino)azobenzene (DMAAB) and metal ions (Pb(II) and Ni(II)). It was shown that all the studied adsorption/desorption and energetic properties of mixed fumed oxides depend strongly on the surface content of alumina C A l 2 O 3 s (shown as a surface content of aluminum, C Al s ) in SA and AST and titania C Ti O 2 s (shown as a surface content of titanium, C Ti s ) in ST and AST. Many of these properties demonstrate clear correlations with the C Al s and C Ti s values over the total range of alumina and titania content in the materials.
Keywords: Fumed SiO2/Al2O3; Fumed SiO2/TiO2; Fumed Al2O3/SiO2/TiO2; Auger electron spectroscopy; NMR; FTIR; One-pass temperature-programmed desorption time-of-flight mass-spectrometry; Nitrogen adsorption; Water adsorption/desorption; (Dimethylamino)azobenzene adsorption; Pb(II) adsorption; Ni(II) adsorption; Surface hydroxyls; Debye screening length;
Rapid synthesis of water-glass based aerogels by in situ surface modification of the hydrogels by Sharad D. Bhagat; Yong-Ha Kim; Young-Soo Ahn; Jeong-Gu Yeo (3231-3236).
The objective of the present research was to reduce the processing time of water-glass based aerogels synthesized via an ambient pressure drying. For this purpose we employed a co-precursor method for the surface modification in hydrogels using trimethylchlorosilane (TMCS) and hexamethyldisilazane (HMDS). The surface modification resulted in the displacement of pore water from the hydrogels and thereby absolutely avoiding the time-consuming solvent exchange step. The attachment of trymethylsilyl (―Si(CH3)3) groups to the silica surface was confirmed by the presence of Si―CH3 peaks at 2900, 1400, 1255 and 845 cm−1 in the Fourier Transform Infrared (FTIR) spectra. The differential thermal analysis (DTA) revealed that the aerogels maintain their hydrophobic behavior up to a maximum temperature of 500 °C above which they become hydrophilic. The physical and textural properties of the silica aerogels have been reported and the results have been discussed by taking into account the surface modification and the amounts of the pore water displaced out from the hydrogels.
Keywords: Silica aerogel; Water-glass; Surface modification; BET analysis; FE-SEM; FTIR; DTA;
Adsorption and manipulation of carbon onions on highly oriented pyrolytic graphite studied with atomic force microscopy by Jianfeng Zhou; Ziyong Shen; Shimin Hou; Xingyu Zhao; Zengquan Xue; Zujin Shi; Zhennan Gu (3237-3241).
Carbon onions produced by DC arc discharge method were deposited on highly oriented pyrolytic graphite (HOPG) surface and their adsorption and manipulation was studied using an atomic force microscopy (AFM). Well-dispersed adsorption of carbon onions on HOPG surface was obtained and aggregations of onions were not observed. The van der Waals interaction between the onion and HOPG surface and that between two onions, were calculated and discussed using Hamaker's theory. The manipulation of adsorbed onions on HOPG surface was realized using the AFM in both the raster mode and the vector mode. The controllability and precision of two manipulation modes were compared and the vector mode manipulation was found superior, and is a useful technique for the construction of nano-scale devices based on carbon onions.
Keywords: Atomic force microscopy (AFM); Carbon onions; Adsorption properties; Nano-scale manipulation;
Template preparation of Pt nanowire array electrode on Ti/Si substrate for methanol electro-oxidation by Guang-Yu Zhao; Cai-Ling Xu; Dao-Jun Guo; Hua Li; Hu-Lin Li (3242-3246).
Platinum (Pt) nanowire array electrode is obtained by dc electrodeposition of Pt into the pores of anodic aluminum oxide (AAO) template on Ti/Si substrate. Transmission electron microscope (TEM) examination shows all the nanowires have uniform diameter of about 30 nm. The brush shapes Pt nanowire array electrode can be seen clearly by field emission scanning electron microscope (FESEM). Pt nanowire array electrode gives the X-ray diffraction (XRD) pattern of face-centered cubic (fcc) crystal structure. The electro-oxidation of methanol on this electrode is investigated at room temperature by cyclic voltammetry. The results demonstrated that the Pt nanowire array electrode will have good potential applications in portable power sources.
Keywords: Portable power sources; AAO/Ti/Si; Pt nanowire array electrode; Electro-catalysis; Methanol oxidation;
Immobilization of poly(ɛ-caprolactone)–poly(ethylene oxide)–poly(ɛ-caprolactone) triblock copolymer on poly(lactide-co-glycolide) surface and dual biofunctional effects by Aiping Zhu; Ping Lu; Hao Wu (3247-3253).
Poly(ɛ-caprolactone)–poly(ethylene oxide)–poly(ɛ-caprolactone) (PCL–PEG–PCL) triblock copolymer was covalently immobilized onto poly(lactide-co-glycolide) (PLGA) surface with the precursor of photopolymerizable and biodegradable PCL–PEG–PCL diacrylates. Argon plasma technique was exploited to obtain hydrophilic PLGA surface (HPLGA). The surface properties were characterized by Water contact angle and X-ray photoelectron spectroscopy (XPS) techniques. PCL–PEG–PCL surface modified hydrophobic PLGA and hydrophilic PLGA results in different surface physicochemical properties. PCL–PEG–PCL modified hydrophobic PLGA surface (PLGA–PCL–PEG–PCL) demonstrates excellent inhibition of platelet adhesion and activation; while PCL–PEG–PCL modified hydrophilic PLGA surface (HPLGA–PCL–PEG–PCL) results in good cytocompatibility. The possible mechanism was discussed and the driven force was ascribed to the different assembly behavior of PCL–PEG–PCL on PLGA surface dependant on the hydrophilic/hydrophobic property of PLGA. This simple and effective surface engineering method is also suitable for the other biomaterials such as polyurethane (PU), silicon rubber and poly(ethylene terephthalate) (PET) to obtain the enhanced biocompatibility.
Keywords: PLGA; PCL–PEG–PCL diacrylates; Platelet adhesion; Smooth muscle cell; Assembly behavior;
Using response surface methodology for optimizing deposited partially stabilized zirconia in plasma spraying by Bor-Tsuen Lin; Ming-Der Jean; Jyh-Horng Chou (3254-3262).
This paper presents the application of the surface response methodology and fractional factorial experiment in developing a robust partially stabilized zirconia (PSZ) coating in plasma spraying processes. In this study, a two-step experimental design with a nonlinear regression model is proposed. After conducting a series of initial experiments in a controlled environment, significant factors for plasma spraying processes are selected to construct an appropriate response surface model for developing a robust performance for plasma spraying processes.The experimental results show that using a quadric response surface model with the proposed two-step design strategy is a simple, effective and efficient approach. In the optimized model, several response plots were generated to examine parameter effects on the profile hardness. Optimization of the PSZ performances in a plasma spray process has been performed.
Keywords: Response surface model; Fractional factorial design; Partially stabilized zirconia (PSZ); Plasma spraying; Analysis of variance;
New concept to remove heavy metals from liquid waste based on electrochemical pH-switchable immobilized ligands by Viel Pascal; Dubois Laetitia; Lyskawa Joël; Sallé Marc; Palacin Serge (3263-3269).
Absorption on resins is often used as secondary step in the treatment of water-based effluents, in order to reach very low concentrations. The separation of the trapped effluents from the resins and the regeneration of the resins for further use create wide volumes of secondary effluents coming from the washings of the resins with chemical reagents. We propose an alternative solution based on a “surface strategy” through adsorption phenomena and electrical control of the expulsion stage. The final goal is to limit or ideally to avoid the use of chemical reagents at the expulsion (or regeneration) stage of the depolluting process. Heavy metal ions were captured on active filters composed by a conducting surface covered by poly-4-vinylpyridine (P4VP). Due to pyridine groups those polymer films have chelating properties for copper ions. Our strategy for electrical triggering of the copper expulsion in aqueous medium is based on pH sensitive chelating groups. Applying moderate electro-oxidizing conditions generates acidic conditions in the vicinity of the electrode, i.e. “inside” the polymer film. This allows a “switch-off” of the complexing properties of the film from the basic form of pyridine to pyridinium. Interestingly, no buffer washing is necessary to restore (or “switch-on”) the complexing properties of the polymer film because the pH of the external medium is left unchanged by the electrochemical effect that affects only the vicinity of the electrode. Switch-on/switch-off cycles are followed and attested by IR spectroscopy and EQCM method.
Keywords: Heavy metals; Poly-4-vinylpyridine; Wastewater; pH-switchable;
Influence of glyphosate on the copper dissolution in phosphate buffer by C.F.B. Coutinho; M.O. Silva; S.A.S. Machado; L.H. Mazo (3270-3275).
The electrochemical behavior of copper microelectrode in phosphate buffer in the presence of glyphosate was investigated by electrochemical techniques. It was observed that the additions of glyphosate in the phosphate buffer increased the anodic current of copper microelectrode and the electrochemical dissolution was observed. This phenomenon could be associated with the Cu(II) complexation by glyphosate forming a soluble complex. Physical characterization of the surface showed that, in absence of glyphosate, an insoluble layer covered the copper surface; on the other hand, in presence of glyphosate, it was observed a corroded copper surface with the formation of glyphosate complex in solution.
Keywords: Copper dissolution; Passivation; Complex; Glyphosate;
Metal vapor vacuum-arc ion implantation effects on the adhesion and hardness of ion-beam deposited Cr/Cu films by Miao Yu; Jizhong Zhang; Dexing Li; Qingli Meng; Wenzhi Li (3276-3283).
Two groups of Cr/Cu multilayer films were deposited on surfaces of Si (1 0 0) crystal and Al2O3 ceramic, respectively. One group was prepared by both metal vapor vacuum-arc (MEVVA) ion implantation and ion beam assistant deposition (IBAD) technologies with different sputtering ion densities and deposition times. The other group was prepared only by IBAD. The morphologies of the Cr/Cu films and cross-section micrographs were observed by scanning electron microscopy (SEM). Nanohardness, modulus, and adhesive strength of the Cr/Cu films were measured by a nano-indenter. Continuous stiffness measurement (CSM) was used while measuring nanohardness and modulus of the samples. The experimental data indicate that the adhesive strength of the samples prepared with MEVVA ion implantation was about 3–3.5 times higher than one of the corresponding samples prepared without MEVVA ion implantation. The nanohardness and modulus of the Cr/Cu films were obviously affected by the test parameters and substrate kind.
Keywords: MEVVA; IBAD; Cr/Cu film; Nanohardness; Adhesion;
Depth control of a silicon structure fabricated by 100q keV Ar ion beam lithography by Noritaka Kawasegi; Noboru Morita; Shigeru Yamada; Noboru Takano; Tatsuo Oyama; Sadao Momota; Jun Taniguchi; Iwao Miyamoto (3284-3291).
Ion beam lithography of a silicon surface using an Ar ion beam with an ion energy in the order of hundreds of keV is demonstrated in this study. A specially designed ion irradiation facility was employed that enabled generation and irradiation with a highly accelerated and highly charged Ar ion beam. An ion-beam-induced amorphous layer on a silicon substrate can be selectively etched in hydrofluoric acid, whereas, a non-irradiated area is scarcely etched and, consequently, a concave structure can be fabricated on the irradiated area. To control the depth of the structure, parameters for dependence of the depth on ion irradiation were investigated. As a result, the depth of irradiated area can be controlled by the ion energy that is adjusted by the acceleration voltage and the ion charge. In addition, the etch resistance of the irradiated area increases with an increase in ion energy due to the crystalline layer formed on the surface. Simulation results reveal that the depth is strongly related to the defect distribution induced by ion irradiation. These results indicate the potential use of this method for novel three-dimensional lithography.
Keywords: Ion beam lithography; Three-dimensional fabrication; Maskless patterning; Highly charged ion bead; Ar; Silicon;
Improve the field emission uniformity of carbon nanotubes treated by ball-milling process by Zhejuan Zhang; Z. Sun; Yiwei Chen (3292-3297).
Carbon nanotubes (CNTs) deposited by chemical vapor deposition (CVD) were treated by ball milling. The morphologies and field emission properties of the treated CNTs depending on milling time were studied. The emission turn-on field is increased, and the field emission current density is reduced, when the milling time increased from 0.5 to 3 h. The as-deposited long CNTs were cut to short CNTs (∼1 h) and micro-particles (>1 h) with increasing of the milling time. It is found that the optimized milling time is 0.5–1 h, the treated CNTs showed excellent field emission properties, such as low turn-on field, high emission current density and uniform luminescence spots distribution.
Keywords: Flat panel display; Carbon nanotubes; Ball milling; Field emission property;
Interfacial differences in enhanced schottky barrier height Au/n-GaAs diodes deposited at 77 K by Andrew M. Herrero; A.M. Gerger; B.P. Gila; S.J. Pearton; Hung-Ta Wang; S. Jang; T. Anderson; J.J. Chen; B.S. Kang; F. Ren; H. Shen; Jeffrey R. LaRoche; Kurt V. Smith (3298-3302).
The use of cryogenic temperatures (∼77 K) during Au Schottky contact deposition onto n-GaAs produces an increase in barrier height from 0.73 eV for room temperature diodes to 0.82 eV. Not all Schottky metals show this enhancement—for example Pt and Ti do not show any significant change in barrier height whereas Au, Pd and Ni show increases between 7 and 18%. We used X-ray reflectivity to show that the main difference between Au deposited at 77 K and room temperature is a decreased metal roughness while the interfacial roughness between the Au and GaAs is basically the same. As the diodes are annealed to 300 °C both the difference in barrier height and interfacial roughness is lost. This is a simple method with potential for improving the performance of GaAs metal-semiconductor-field-effect-transistors (MESFETs).
Keywords: GaAs; Barrier height;
Preparation of well-adhered γ-Al2O3 washcoat on metallic wire mesh monoliths by electrophoretic deposition by Hong Sun; Xie Quan; Shuo Chen; Huimin Zhao; Yazhi Zhao (3303-3310).
Washcoat deposited on metallic wire mesh monoliths was prepared using γ-alumina powders by electrophoretic deposition under a relatively low electric voltage. The microstructure, phase structure and adhesion of washcoat were investigated by SEM, XRD, ultrasonic vibration and thermal shock. The results showed that the loading and adhesion of washcoat were affected obviously by the properties of suspension, such as the zeta potential and the amount of adding binders. A small quantity of aluminum isopropoxide could promote the cohesive affinity of washcoat in thermal shock. The adhesion of washcoat in ultrasonic vibration could be reinforced by increasing calcined temperature and adding a certain aluminum particles. It was also found that the washcoat immersed metal nitrate has excellent vibration-resistant ability.
Keywords: Wire mesh monoliths; Electrophoretic deposition; Alumina suspension; Adhesion;
Effects of organic modifiers on the size-controlled synthesis of hydroxyapatite nanorods by Aili Wang; Hengbo Yin; Dong Liu; Huixiong Wu; Yuji Wada; Min Ren; Yiqing Xu; Tingshun Jiang; Xiaonong Cheng (3311-3316).
Size-controlled synthesis of hydroxyapatite nanorods were carried out by chemical precipitation method using polyethylene glycol (MW 600), Tween 20, trisodium citrate, and d-sorbitol as organic modifiers and starting from calcium nitrate, phosphoric acid, and ammonia solution. The influence of the organic modifiers on the sizes of the resultant HAP nanorods was investigated under different synthesis temperatures. It was found that polyethylene glycol was beneficial to the formation of HAP nanorods with a larger aspect ratio (average length/average diameter) at high synthesis temperature, Tween 20 and trisodium citrate favored the formation of small-sized HAP nanorods, and d-sorbitol helped the formation of HAP nanorods with long length at low synthesis temperatures.
Keywords: Hydroxyapatite; Nanorods; Organic modifiers;
The influence of substrate temperature variation on tungsten oxide thin film growth in an HFCVD system by S. Pal; C. Jacob (3317-3325).
Tungsten oxide (WO3) thin films were deposited by a modified hot filament chemical vapor deposition (HFCVD) technique using Si (1 0 0) substrates. The substrate temperature was varied from room temperature to 430 °C at an interval of 100 °C. The influence of the substrate temperature on the structural and optical properties of the WO3 films was studied. X-ray diffraction and Raman spectra show that as substrate temperature increases the film tends to crystallize from the amorphous state and the surface roughness decreases sharply after 230 °C as confirmed from AFM image analysis. Also from the X-ray analysis it is evident that the substrate orientation plays a key role in growth. There is a sharp peak for samples on Si substrate due to texturing. The film thickness also decreases as substrate temperature increases. UV–vis spectra show that as substrate temperature increases the film property changes from metallic to insulating behavior due to changing stoichiometry, which was confirmed by XPS analysis.
Keywords: Tungsten oxide; Substrate temperature variation; Structural and optical properties;
Bioactivity of Mg-ion-implanted zirconia and titanium by H. Liang; Y.Z. Wan; F. He; Y. Huang; J.D. Xu; J.M. Li; Y.L. Wang; Z.G. Zhao (3326-3333).
Titanium and zirconia are bioinert materials lacking bioactivity. In this work, surface modification of the two typical biomaterials is conducted by Mg-ion-implantation using a MEVVA ion source in an attempt to increase their bioactivity. Mg ions were implanted into zirconia and titanium with fluences ranging from 1 × 1017 to 3 × 1017 ions/cm2 at 40 keV. The Mg-implanted samples, as well as control (unimplanted) samples, were immersed in SBF for 7 days and then removed to identify the presence of calcium and phosphate (Ca–P) coatings and to characterize their morphology and structure by SEM, XRD, and FT-IR. SEM observations confirm that globular aggregates are formed on the surfaces of the Mg-implanted zirconia and titanium while no precipitates are observed on the control samples. XRD and FT-IR analyses reveal that the deposits are carbonated hydroxyapatite (HAp). Our experimental results demonstrate that Mg-implantation improves the bioactivity of zirconia and titanium. Further, it is found that the degree of bioactivity is adjustable by the ion dose. Mechanisms are proposed to interpret the improvement of bioactivity as a result of Mg implantation and the difference in bioactivity between zirconia and titanium.
Keywords: Bioactivity; Titanium; Zirconia; Ion implantation; Hydroxyapatite; Magnesium;
Ce conversion and electrolysis surface treatments applied to A3xx.x alloys and A3xx.x/SiCp composites by A. Pardo; M.C. Merino; R. Arrabal; F. Viejo; J.A. Muñoz (3334-3344).
The influence of different variables (stirring, degreasing, oxidant additions, pH, Ce concentration, anion type, time and temperature of immersion) on the optimization of Ce conversion and electrolysis coatings on both A3xx.x alloys and aluminium metal matrix composites A3xx.x/SiCp was evaluated in 3.5 wt% NaCl at 22 °C using potentiodynamic polarization. Ce treated surfaces presented better corrosion behaviour in chloride media than original material surfaces without treatment. Both treatments preferentially covered the intermetallic compounds and SiCp. The electrolysis afforded a higher degree of protection than conversion treatment because the coating was more extensive. Coating microstructure was analysed by scanning electron microscopy (SEM), atomic force microscopy (AFM) and X-ray photoelectron spectroscopy (XPS).
Keywords: Aluminium; Composites; Cerium; Chemical conversion; Polarization;
Transparent conducting molybdenum-doped zinc oxide films deposited by RF magnetron sputtering by Xianwu Xiu; Zhiyong Pang; Maoshui Lv; Ying Dai; Lina Ye; Shenghao Han (3345-3348).
A new transparent conducting oxide (TCO) film with low resistivity and high transmittance in the visible range, molybdenum-doped zinc oxide (MZO), was successfully prepared by RF magnetron sputtering method on glass substrates at room temperature. The structural, electrical, and optical properties as a function of film thickness were investigated. All the samples have a preferred orientation with the (0 0 2) planes parallel to the substrates. The resistivity initially decreases and then shows an increase with the increase of the film thickness. When the thickness is 400 nm, the film has its best crystallinity and lowest resistivity 9.2 × 10−4 Ω cm with a Hall mobility of 30 cm2 V−1 s−1 and a carrier concentration of 2.3 × 1020 cm−3. The average transmittance in the visible range exceeds 84% for all thickness films.
Keywords: Molybdenum oxide; Zinc oxide; Magnetron sputtering; Transparent conducting oxides;
XPS analyses of lanthanides phosphates by B. Glorieux; R. Berjoan; M. Matecki; A. Kammouni; D. Perarnau (3349-3359).
XPS measurements were performed on lanthanide orthophosphates LnPO4 (Ln: La, Ce, Nd, Gd), and correlated with XRD and some EDS analyses. Single lanthanide phosphates LnPO4 and mixed lanthanide phosphates L n x L n ′ 1 − x P O 4 , all crystallized in a monoclinic structure similar to the monazite mineral. Results were examined qualitatively and quantitatively, by considering the Ln 3d lines, P 2p line and O 1s line.Ionic sputtering does not induce significant broadening nor an additional shift of the lanthanide peaks and does not have an effect on their chemical environments, except in the case of cerium. However, sputtering seems to significantly reduce the intensity of the O 1s and P 2p peaks, while Auger peaks of carbon and oxygen atoms interfere, respectively, with the 3d line of gadolinium and neodymium. Those phenomena are all the more important when the Nd and Gd content is weak and must be taken into account for a quantitative analysis of the spectra.The quantitative analyses reveal the expected results for single monazites. On mixed phosphates, the measured phosphorous and oxygen amounts are generally more valid for non-sputtered sample surfaces than for sputtered surfaces, while the calculated relative amount of lanthanides [Ln]/[Ln′] are correct in all the cases.One of the important goals of this work was to have a satisfactory value for the atomic ratio La/Gd, and particularly in the case of (La,Ce)PO4 and (La,Gd)PO4, to obtain good agreement between the calculated lanthanides ratio Nd/Gd and ratios estimated from XRD and EDS measurements.
Keywords: X-ray photoelectron spectroscopy; Monazite; Lanthanides; Phosphates;
Electrodeposition of n-type Bi2Te3−y Se y thermoelectric thin films on stainless steel and gold substrates by Luxia Bu; Wei Wang; Hui Wang (3360-3365).
Thermoelectric films of n-Bi2Te3−y Se y were prepared by potentiostatic electrodeposition technique onto stainless steel and gold substrates at room temperature. These films were used for morphological, compositional and structural analysis by environment scanning electron microscope (ESEM), energy dispersive spectroscopy (EDS) and X-ray diffraction (XRD). The effect of different substrates on the structure and morphology of Bi2Te3−y Se y films and relation between Se content in the electrodepositing solutions and in the films were also investigated. These studies revealed that Bi, Te and Se could be co-deposited to form Bi2Te3−y Se y semiconductor compound in the solution containing Bi3+, HTeO2 + and H2SeO3. The morphology and structure of the films are sensitive to the substrate material. The doped content of Se element in the Bi2Te3−y Se y compound can be controlled by adjusting the Se4+ concentration in the electrodepositing solution. X-ray diffraction analysis indicates that the films prepared at −40 mV versus saturated calomel electrode (SCE) exhibit strong (1 1 0) orientation with rhombohedral structure.
Keywords: Electrodeposition; Thin films; Bismuth telluroselenide;