Jianxia Gao

Cyclic Voltammetry Studies of Sputtered Nitrogen Doped Diamond-Like Carbon Film Electrodes

The conductive nitrogen-doped diamond-like carbon film (N-DLC) of about 0.14 m in thickness was deposited on highly conductive silicon wafer (111) with DC magnetron sputtering system. The electrochemical characteristics of the film have been studied with cyclic voltammetry (CV). The N-DLC film electrodes compare very favorably with conventional carbon based electrodes such as glassy carbon. The N-DLC film electrode exhibits a low double-layer capacitance, a large electrochemical potential window, and a relatively high electrochemical activity toward ferricyanide reduction. In addition, the electrode exhibits catalytic activity for Cl2/Cl as well as durability to high anodic potential, and a high signal for the trace analysis of Pb 2 . These characteristics demonstrate great promise of the N-DLC film as a novel electrode material for electrochemical analysis.

Stripping Voltammetric Analysis of Heavy Metals at Nitrogen Doped Diamond-Like Carbon Film Electrodes

Conductive nitrogen doped diamond-like carbon (N-DLC) film electrodes were used to investigate the possibility of detecting heavy metals such as lead, copper and cadmium by differential pulse anodic stripping voltammetry (DPASV) in the absence of mercury film. The preconcentration conditions (deposition potential, deposition time) and solution pH were optimized for the determination of lead in aqueous solution. A linear dependence of lead stripping current peak within the concentration (5 10 7 to 2 10 6 MP b 2 ) and deposition time (30 to 300 s at 1.00 V vs. SCE) was obtained. A multi-elemental analysis (Pb 2 ,C d 2 and Cu 2 ) illustrated that the N-DLC film electrode provided a significant stripping response for determination of multi-metals simultaneously. The present novel electrode showed great promise for the analysis of heavy metals.

Impedance study on electrochemical characteristics of sputtered DLC films

Diamond-like carbon (DLC) films with different structure were deposited on highly electrically conductive silicon substrates (SiO ySi), using d.c. magnetron sputtering deposition process. Their structure and electrochemical behavior in a 0.5 M H SO 2 24 solution were studied with micro-Raman spectroscopy, electrochemical impedance spectroscopic analysis and film impedance spectroscopy. The combined polarization resistance of silicon coated with DLC film increased to approximately 10 –10 V cm , 68 2

Photografting of argon plasma-treated graphite/PEEK laminate to enhance its adhesion

Graphite/PEEK laminates were treated by argon plasma followed by air aging and then photografting of α- glycidyl ω- acrylate bisphenol A(GABA) to improve their adhesion characteristics. The effects of plasma time and power and photografting time on the epoxy bonded single lap shear joints between graphite/PEEK laminates were investigated. An optimum photografting time was found at which the single lap shear strength was optimized to 37 MPa compared to 28 MPa and 7 MPa obtained with air-aged argon plasma activated and pristine samples, respectively. Argon plasma treatment followed by air aging of graphite/PEEK laminate introduces surface peroxides and hydroperoxides and these when cleaved with ultraviolet (UV) light in the presence of the GABA monomer results in covalent grafting of the latter to PEEK/graphite laminate surface. The epoxy functionality of the GABA monomer then reacts with the epoxy adhesive. X-ray photoelectron spectroscopy (XPS) confirms the appearance of surface peroxides and hydroperoxides on air-aged argon plasma treated samples and disappearance of the same with UV irradiation. With UV irradiation of the air-aged argon plasma treated samples, XPS indicates the appearance of ester groups. Without the grafting monomer, UV irradiation in air cleaves the peroxide and causes oxidation resulting in the formation of surface esters. In the presence of the grafting monomer, UV irradiation results in covalent bonding of the monomer to the peroxide/hydroperoxide through the acrylate functionality resulting in increased concentration of ether linkages as confirmed by our XPS data; the ester functionality present in the grafted monomer caused the appearance of the ester peak in the XPS spectrum.

Surface characterization of nickel alloy plasma-treated by O2/CF4 mixture

The micro- or nano-structured mold used for polymer embossing typically must be coated with an anti-adhesion material to reduce its interaction with the embossing. The mold is typically made by nickel sulphamate electroforming. For the anti-adhesion coating to adhere to the mold, the nickel mold surface must be clean and preferably unoxidized or possess reactive groups suitable for covalent bonding with the anti-adhesion coating. The effectiveness of plasma cleaning using mixtures of oxygen (O2) and tetrafluoromethane (CF4) with varying ratios versus liquid-only cleaning was investigated. To simulate the nickel mold, Ni200 alloy was used. Plasma treatment using mixtures of O2 and CF4 was found to be more effective in cleaning the Ni200 surface than liquid-only cleaning or pure O2 or pure CF4 plasma treatment. Using a 1 : 1 O2 /CF4 mixture plasma, the contact angles of water, glycerol and diiodomethane on Ni200 were the lowest and the calculated surface energy was the highest among the investigated treatments. From X-ray photoelectron spectroscopy (XPS), the amount of organic contamination on Ni200 was significantly reduced with plasma treatment. For liquid-only cleaned samples, metallic nickel, NiO and Ni(OH)2 are present on the surface. With pure O2 or pure CF4 or 1 : 1 O2 /CF4 mixture plasma, both oxidation and fluorination occur and the surface contains combinations of NiF2, Ni(OH)2, Ni(OH)F, Ni2O3 and NiO15F instead (without metallic nickel and NiO). The proportions of these different compounds vary according to the O2/CF4 ratio; O/Ni ratio is highest for pure O2 plasma treatment, whilst F/Ni is highest for pure CF4 plasma treatment.

Compositional depth profile analysis of coatings on hard disks by X-ray photoelectron spectroscopy and imaging

A hard disk medium is typically composed of several layers including the magnetic recording layer, a buffer layer, as well as a wear protective layer. In the work presented here, the hard disks analysed have a total of five layers with the uppermost layer being the lubricant. The second layer is diamond like coating and this is followed by the magnetic layer consisting of an alloy of cobalt and other elements. The fourth layer is a buffer composed of an alloy of chromium, vanadium and molybdenum with the final layer being a nickel transition layer doped with phosphorus. These multilayers were subjected to numerous etchings by argon ions. The chemical structures of these layers were analysed with an X-ray photoelectron spectroscope (XPS) after each etching. Combining the XPS spectra with XPS imaging it is possible to determine the depth distribution of elements in the hard disk coating. In addition, it is also shown that XPS imaging can be employed to monitor the thickness of all multilayers.

MICROSTRUCTURE AND ELECTROCHEMICAL BEHAVIOR OF SPUTTERED DIAMOND-LIKE CARBON FILMS

Diamond-like carbon (DLC) films with different structure were deposited on highly electrically conductive silicon substrates (SiO2/Si), using dc magnetron sputtering deposition process. Their structure and electrochemical behavior in 0.5 MH2SO4 solution were studied with micro-Raman spectroscopy, electrochemical impedance spectroscopic (EIS) analysis and film impedance. The double layer capacitance on the DLC films was about 0.571 - 3.91 μF-cm-2. The capacitance increased with the increased Raman spectrum intensity ratio ID/IG and accelerated at around 2.25 of the ratio. The results suggest that the potential of DLC films as electrode materials for electrochemical analysis.

Structure of post-annealed ferroelectric PbZrxTi1-xO3 and SrBi2Ta2O9 thin films

In order to fabricate good quality ferroelectric thin films, PbZrxTi(1-x)O3 (PZT) and SrBi2Ta2O9 (SBT) films were fabricated on SiO2/Si(100) substrates and on Pt/Ti/SiO2/Si(100) substrates by pulsed laser excimer deposition (PLD). X-ray diffraction, Rutherford backscattering analysis, and atomic force microscopy were used to characterize the structural properties of the samples, which were post-annealed at different temperatures. The results showed that the PZT and SBT films fabricated on Pt/Ti/SiO2/Si(100) substrates and annealed at 700 degreesC exhibited optimum properties

Low temperature deposition of tantalum diffusion barrier by filtered cathodic vacuum arc

Tantalum (Ta) diffusion barrier films were deposited on un-patterned and patterned silicon substrates at ambient temperature and without substrate bias by filtered cathodic vacuum arc (FCVA). The films were characterized by atomic force microscopy, scanning electron microscopy, x-ray diffraction, x-ray photoelectron spectroscopy, four-point resistivity probe and surface profilometer. It was found that the Ta film was 750 A thick and free of C and O except for surface contamination. The film morphology was smooth and uniform with root-mean-square roughness of ~0.82 A. The Ta film was polycrystalline β phase with a mean grain size of ~3 nm and possessed a dense microstructure, which are ascribed to the high energy of the condensing species in FCVA. It was shown that the Ta filling of the trenches (0.33 μm wide, 1 : 1 aspect ratio) was very conformal and quite uniform. Also, it was preliminarily found that at the Ta film was effective against diffusion of Cu into Si at 600°C.

GROWTH AND STRUCTURAL STUDY OF NANOCRYSTALLINE TITANIUM OXIDE AND ZIRCONIUM OXIDE THIN FILMS DEPOSITED AT LOW TEMPERATURES

Titanium oxide and zirconium oxide thin films were deposited at low temperatures (not exceeding 350°C) by off-plane filtered cathodic vacuum arc (FCVA). The film structures were studied by XRD and Raman spectra. For titanium oxide thin films, amorphous structure remains up to 230°C, and anatase film with the crystallite size of 16 nm is observed at 330°C as confirmed by XRD and Raman analysis. For zirconium oxide, the film structure develops from amorphous at room temperature to polycrystalline state at 150°C and above. Moreover, for the crystallized films, preferred orientation is along [-111] direction. At 150°C the films possess nano-sized crystallites (less than 15 nm). For these two kinds of metal oxide thin films, surface roughness both increases with the growth temperature.