A novel process of electroless Ni-P plating with plasma electrolytic oxidation pretreatment

A novel Ni based coating - plasma electrolytic oxidation (PEO) pre-treatment followed by electroless nickel (EN) plating - has been developed to produce pore free Ni coatings on AZ91 magnesium alloy. The application of the PEO film between the nickel coating and the substrate acts as an effective barrier and catalytic layer for the subsequent nickel plating. The potentiodynamic tests indicated that the corrosion current density of the PEO + EN plating on AZ91 decreased by almost two orders of magnitudes compared to the traditional EN coating. Salt fog spray testing further proved this improvement. More importantly, the new technique does not use Cr⁺⁶ and HF in its pretreatment, therefore is a much environmentally friendlier process.     

Laser ablation and micropatterning of thin TiN coatings

Laser ablation of thin TiN films deposited on steel substrates has been studied under wide-range variation of irradiation conditions (pulsewidth, wavelength, energy density and spot size). It has been demonstrated that both picosecond (150–300 ps) and nanosecond (5–9 ns) laser pulses were suitable for controllable ablation and microstructuring of a 1-μm-thick TiN film unlike longer 150-ns pulses. The ablation rate was found to be practically independent of the wavelength (270–1078 nm) and pulsewidth (150 ps–9 ns), but it increased substantially when the size of a laser spot was reduced from 15–60 μm to 3 μm. The laser ablation technique was applied to produce microstructures in the thin TiN films consisting of microcraters with a typical size of 3–5 μm in diameter and depth less than 1 μm. Tests of lubricated sliding of the laser-structured TiN films against a steel ball showed that the durability of lubricated sliding increased by 25% as compared to that of the original TiN film. Received: 28 July 1999 / Accepted: 17 April 2000 / Published online: 20 September 2000     

Strong ultraviolet and violet photoluminescence from Si-based anodic porous alumina films

We have investigated photoluminescence (PL) from Si-based anodic porous alumina films formed by real-time controlled anodization of electron-beam evaporated Al films. As-anodized samples show three strong PL bands at 295, 340, and 395 nm. These bands blueshift and their intensities decrease after the samples are annealed. When the annealing temperature increases to 1000 °C, the blueshift becomes specially pronounced and meanwhile the structures of the films develop toward crystalline Al₂O₃. Based on discussions on the thermal annealing behaviors of the PL and PL excitation spectra, we suggest that optical transitions in oxygen-related defects, F⁺ (oxygen vacancy with one electron) centers, are responsible for the observed ultraviolet and violet PL. Received: 24 July 2000 / Accepted: 24 February 2001 / Published online: 3 May 2001     

Stress anisotropy in circular planar magnetron sputter deposited molybdenum films and its annealing effect

As part of the program to develop a free-standing thin-film filter for soft X-ray optics application, stress anisotropy in the molybdenum films deposited by dc circular planar magnetron sputtering were studied by X-ray diffraction (XRD) as a function of sputtering argon gas pressure over a range of 0.8–1.5 Pa. Surface morphology of the films has been investigated by optical microscopy and scanning tunneling microscopy (STM). It is found that, for the film deposited at 0.8 Pa pressure, the stresses are more compressive in the tangential than in the radial direction; the highest compressive stress exists in the center area. The film deposited at 1.5 Pa pressure has the highest stress anisotropy, and the stresses are less tensile in the tangential than in the radial direction. Annealing in vacuum is more effective in reducing tensile stress and stress anisotropy in the tensile stressed film than in the compressively stressed film. Received: 14 September 2001 / Accepted: 21 January 2002 / Published online: 5 July 2002 RID="*" ID="*"Corresponding author. Fax: +86-21/6598-6323, E-mail: ygwu@mail.tongji.edu.cn     

Intrinsic stress of ultrathin epitaxial films

The present article focuses on the stress developing during the deposition of ultrathin epitaxial films in the thickness range of a few atomic layers. The studied systems exhibit the three well-known modes of film growth: Stranski–Krastanow mode [Ge/Si(001), Ge/Si(111), Ag/Si(111)], Frank–Van der Merwe mode [Fe/MgO(001)] and Volmer–Weber mode [Ag/mica(001), Cu/mica(001)]. The experimental results demonstrate the important role of the misfit strain as well as the contribution of surface stress effects as mechanisms for the stress in single atomic layers. Received: 26 April 1999 / Accepted: 25 June 1999 / Published online: 6 October 1999     

AFM studies of surface morphologies of sputtered SrTiO3 films and annealed MgO substrates

3 films on single-crystal MgO(100) substrates. Meanwhile, surface morphologies of as-polished and post-annealed MgO(100) substrates are investigated as well. Effects of the miscut (or misorientation) of the substrate surface on morphologies and growth mechanisms are discussed. For comparison, a typical surface morphology and growth mechanism of the spiral island structure in sputtered PrBa₂Cu₃O_7-δ films on MgO(100) substrates are presented. Received: 27 March 1998     

Characterization of defect type and dislocation density in double oxide heteroepitaxial CeO2/YSZ/Si(001) films

In order to qualitatively and quantitatively analyze the structural defects including the defect types and their concentrations in oxide heteroepitaxial films, a new X-ray rocking-curve width-fitting method was used in the case of doubleCeO₂/YSZ/Si (YSZ=yttria-stabilized ZrO₂) films that were prepared by pulsed laser deposition. Two main defect types, angular rotation and oriented curvature, were found in both CeO₂ and YSZ. Dislocation densities of CeO₂ and YSZ, which were obtained from the angular rotations, are functions of the YSZ thickness. A distinct two-step correlation between dislocation densities of CeO₂ and YSZ was found that as the dislocation density of YSZ is higher than 2.4×10¹¹ cm^-2, the dislocation density of CeO₂ shows a high sensitivity with that of YSZ compared with the low relativity in lower dislocation density (<2.4×10¹¹ cm^-2). In addition, YSZ always has higher dislocation densities and oriented curvatures than CeO₂ in each specimen, which can be attributed to the smaller mosaic domain sizes in YSZ than in CeO₂ as observed by high-resolution transmission electron microscopy. Received: 12 August 2002 / Accepted: 14 August 2002 / Published online: 4 December 2002 RID="*" ID="*"Corresponding author. Fax: +81-3/5734-3369, E-mail: chun_hua_chen@hotmail.com     

Microstructure and Corrosion Performance of Oxide Coatings on Aluminium by Plasma Electrolytic Oxidation in Silicate and Phosphate Electrolytes

Ceramic coatings are fabricated on pure aluminium by plasma electrolytic oxidation （PEO） in three kinds of electrolyte systems [E1： 0.05M NaOH＋0.033M Na2SiO3, E2： 0.025M NaOH＋0.008M （NAPO3）6 and E3： 0.025M NaOH＋0.066M Na2SiO3＋0.008M （NAPO3）6]. The voltage-time responses show that the PEO process of E2 has the highest discharging voltage, which results in the biggest pores and heaviest cracks on the surfaces. X-ray diffraction results show that coatings produced in E1 and E3 are mainly composed of γ-Al2O3 and mullite, while coatings produced in E2 are mainly composed of a-Al2O3. After PEO treatment the corrosion resistance of aluminium is improved significantly and the coatings produced in E3 perform the best corrosion resistance.     

Determination of molecular orientation in ultrathin liquid crystal. films on solid substrates using X-ray absorption spectroscopy

42 H₆₀O₆, HBT) deposited on a (111)-oriented Au single crystal and a polycrystalline indium tin oxide (ITO) substrate has been carried out using X-ray absorption spectroscopy. Films of thicknesses between 2 nm and 15 nm were prepared in UHV by evaporation of HBT [which exhibits a discotic liquid crystalline (LC) bulk phase] from a Knudsen cell. Thickness and composition of the HBT films were determined using X-ray photoelectron spectroscopy (XPS). For the thinnest films with thicknesses in the monolayer regime, the orientational analysis reveals a pronounced orientation of the disc-shaped HBT molecules parallel to the Au surface. For thicker films, a significantly reduced anisotropy is observed with the molecular plane oriented more normal to the Au surface. In the case of the ITO-substrates, no significant differences were observed between different thickn esses and the average orientation of the molecular planes was predominantly normal to the surfaces, as for the thicker films on the Au substrate. Received: 1 March 1997/Accepted: 24 April 1997     

A theoretical study on various models for the domain boundaries in epitaxial GaN films

Various domain boundaries that are found in epitaxial Wurtzite GaN films were studied by molecular dynamics simulation. The Ewald summation algorithm and Keating potential model are adopted to calculate the long-range Coulomb interaction and the short-range bonding force in the semiconductor system, respectively. The research results show that the domain formation energies of (100) and (110) boundaries are significantly different. The latter ones have general quite higher formation energies than the formers. The like-atom (i.e. atoms of the same kind) bonding domain boundaries (LABDB) have higher formation energies than their counterparts of unlike-atom (i.e. atoms of different kinds) bonding domain boundaries (UABDB) in all GaN (100) and (110) interfaces. The UABDB structures are all stable while most of the LABDB are unstable. The advantage and the limitation of Keating potential model in Molecular Dynamics simulation for covalent crystal are discussed. Received: 7 April 1999 / Accepted: 1 November 1999 / Published online: 8 March 2000     

Characterization of heat-treated CN films fabricated by dual-facing-target sputtering for soft X-ray multilayer mirrors

The structural characterization of heat-treated CN films fabricated by dual-facing-target sputtering for soft X-ray multilayer mirrors was performed by means of X-ray diffraction (XRD), Raman spectroscopy (RS) and X-ray photoelectron spectroscopy (XPS). The XRD analyses indicate a graphization process in the CN films during thermal annealing. The Raman analyses imply that the primary bonding in the CN films is sp². In other words, the formation of the sp³ bonding in the CN films can be suppressed effectively by doping with N atoms, and thus the thickness expansion resulting from the changes in the density of CN films during annealing can be decreased considerably. This result is also clarified by the increased conductivity measured. The XPS results give the information of the existence of the strong covalent bonding between N and C atoms, which can slow down the tendency of the structural relaxation during annealing. These results suggest that CN films suitable for soft X-ray multilayers used at high-temperature environments can be obtained by reactive dual-facing-target sputtering. With the low-angle X-ray diffraction measurements, we do observe the enhanced thermal stability of CoN/CN multilayers. Received: 2 October 1998 / Accepted: 21 April 1999 / Published online: 23 September 1999     

Beam delivery of femtosecond laser radiation by diffractive optical elements

Received: 4 February 1998/Accepted: 22 April 1998     

Correlation between density and structure. in boron nitride thin films by X-ray diffraction

* _ion=100 eV. Above E^* _ion the average density (deduced from X-ray reflectivity) shows a strong increase, indicating the sudden appearance of the cubic boron nitride phase consistent with the sp³ concentration deduced from IR absorption spectroscopy. The in-plane X-ray diffraction shows that this cubic phase consists of small nanocrystals of 70 Å linear size. Received: 26 November 1996/Accepted: 27 January 1997     

Electrodeposition of diamond-like carbon (DLC) films on Ti

Diamond-like carbon films (DLC) were deposited on titanium substrates in acetonitrile and N,N-dimethyl formamide (DMF) liquids by the liquid-phase electrodeposition technique at ambient pressure and temperature. The applied voltage between the electrodes was high (1200 V) due to the use of resistive organic liquids. The surface morphology was examined by Atomic Force Microscopy (AFM) and Scanning Electron Microscopy (SEM). Corrosion performance of the coatings was investigated by potentiodynamic polararization tests in phosphate buffer saline solution. Raman spectroscopy analysis of the films revealed two broad bands at approximately 1360 cm⁻¹ and 1580 cm⁻¹, related to D and G-band of DLC, respectively. The coated Ti was tested in a ball-on-plate type wear test machine with Al₂O₃ balls. The films presented a low friction coefficient (about 0.1), and the films deposited from DMF presented the best wear resistance.     

Synthesis of carbon nitride films by low-power inductively coupled plasma-activated transport reactions from a solid carbon source

Thin films of carbon nitride were prepared by low-power inductively coupled plasma chemical vapor deposition from a solid carbon source by utilizing transport reactions. The maximum deposition rate achieved was 10 nm/min and depended mainly on the substrate position in the reactor. The nitrogen fraction in the films was not so sensitive to the process parameters and was at about 0.5 for all experiments as measured by Auger electron spectroscopy (AES) and elastic recoil detection (ERD) analysis. The chemical bonding structure studied by Fourier transform infrared (FTIR) spectroscopy and X-ray photoelectron spectroscopy (XPS) showed the presence of triple, double and single bonds between carbon and nitrogen atoms. Received: 12 May 1999 / Accepted: 12 May 1999 / Published online: 24 June 1999     

Synthesis and tribological behaviors of diamond-like carbon films by electrodeposition from solution of acetonitrile and water

Diamond-like carbon (DLC) films were prepared on silicon substrates by liquid phase electrodeposition from a mixture of acetonitrile and deionized water. The deposition voltage was clearly reduced owing to the presence of deionized water in the electrolyte by changing the basic properties (dielectric constant and dipole moment) of the electrolyte. Raman spectra reveal that the ratio of sp³/sp² in the DLC films is related to the concentration of acetonitrile. The surface roughness and grain morphology determined by atomic force microscopy are also influenced by the concentration of the acetonitrile. The UMT-2 universal micro-tribometer was used to test the friction properties of the DLC films obtained from electrolytes with different concentration. The results convey that the DLC film prepared from the electrolyte containing 10 vol.% acetonitrile has the better surface morphology and friction behavior comparing with the other. In addition the growth mechanism of the film was also discussed.     

Angular-dependent photoemission studies of indium tin oxide surfaces

Indium tin oxide (ITO) surfaces were treated by solvent cleaning, by plasma of oxygen, argon, nitrogen and by argon ion (Ar⁺) sputtering. Angular-dependent X-ray photoelectron spectroscopy (ADXPS) and ultraviolet photoelectron spectroscopy (UPS) were used to determine the chemical composition, the chemical states and the work function after each treatment. It was found that oxygen plasma and nitrogen plasma chemically reacted with the ITO surfaces. Yet little etching of the surface can be observed after plasma treatments. Among all treatments, oxygen-plasma-treated ITO achieved the highest work function of 4.40 eV, whereas Ar⁺-sputtered ITO surface had the lowest work function of 3.90 eV. The stoichiometry of the ITO surface is shown to be the major controlling factor of the ITO work function. Received: 7 February 2000 / Accepted: 28 March 2000 / Published online: 13 September 2000     

The incorporation of Nickel and Phosphorus dopants into Boron-Carbon alloy thin films

5 C) alloy thin films grown by plasma-enhanced chemical vapor deposition have been examined. The Ni-doped boron–carbon alloys were grown using closo-1,2-dicarbadodecaborane (C₂B₁₀H₁₂) as the boron–carbon source compound and nickelocene(Ni(C₅H₅)₂) as the nickel source. The phosphorus-doped alloys were grown using the single-source compound: dimeric chloro-phospha(III)-carborane ([C₂B₁₀H₁₀PCl]₂). Nickel doping increased the conductivity, relative to undoped B₅C, by six orders of magnitude from 10^-9 to 10^-3 (Ω cm)^-1 and transformed the material from a p-type semiconductor to an n-type. Phosphorus doping decreased the conductivity, relative to undoped B₅C, by two orders of magnitude and increased the band gap from 0.9 eV for the undoped material to 2.6 eV. Infrared absorption spectra of the nickel- and phosphorus-doped B₅C alloys were relatively unchanged from those of undoped B₅C. X-ray diffraction suggests that the phosphorus-doped material may be a different polytype from the Ni-doped and undoped B₅C alloys. Received: 23 April 1997/Accepted: 3 November 1997     

Corrosion behavior and protective ability of Zn and Zn-Co electrodeposits with embedded polymeric nanoparticles

The anodic behavior, corrosion resistance and protective ability of Zn and alloyed Zn-Co (∼3 wt.%) nanocomposite coatings were investigated in a model corrosion medium of 5% NaCl solution. The metallic matrix of the layers incorporates core-shell nano-sized stabilized polymeric micelles (SPMs) obtained from poly(ethylene oxide)-b-poly(propylene oxide)-b-poly(ethylene oxide) block co-polymers. The protective properties of the composite coatings were evaluated using potentiodynamic polarization technique, polarization resistance measurements and powder X-ray diffraction. The sizes and distribution of the stabilized polymeric micelles in the starting electrolytes used as well as in the metal matrices of the layers were investigated using scanning and transmission electron microscopy. The results obtained are compared to those of electrodeposited Zn and Zn-Co (∼3 wt.%) alloy coatings at identical conditions and demonstrate the enhanced protective characteristics of the Zn nanocomposites during the investigating period. The influence of the SPMs on the corrosion resistance of the nanocomposite layers is commented and discussed.     

Electrical characterization of impurity-free disordering-induced defects in n-GaAs using native oxide layers

Defects created in rapid thermally annealed n-GaAs epilayers capped with native oxide layers have been investigated using deep-level transient spectroscopy (DLTS). The native oxide layers were formed at room temperature using pulsed anodic oxidation. A hole trap H0, due to either interface states or injection of interstitials, is observed around the detection limit of DLTS in oxidized samples. Rapid thermal annealing introduces three additional minority-carrier traps H1 (E_V+0.44 eV), H2 (E_V+0.73 eV), and H3 (E_V+0.76 eV). These hole traps are introduced in conjunction with electron traps S1 (E_C-0.23 eV) and S2 (E_C-0.45 eV), which are observed in the same epilayers following disordering using SiO₂ capping layers. We also provide evidence that a hole trap whose DLTS peak overlaps with that of EL2 is present in the disordered n-GaAs layers. The mechanisms through which these hole traps are created are discussed. Capacitance–voltage measurements reveal that impurity-free disordering using native oxides of GaAs produced higher free-carrier compensation compared to SiO₂ capping layers. Received: 12 March 2002 / Accepted: 15 July 2002 / Published online: 22 November 2002 RID="*" ID="*"Corresponding author. Fax: +61-2/6125-0381, E-mail: pnk109@rsphysse.anu.edu.au