Koumei Baba

Synthesis and properties of TiO2 thin films by plasma source ion implantation

Plasma source ion implantation was used to prepare anatase type photocatalytic TiO2 films on silicon wafer and quartz glass from titanium tetraisopropoxide as a precursor. RF power was used to produce a glow discharge plasma. High negative voltage pulses of −20 kV, repetition rate 100 Hz and 1 kHz were applied to the substrate holder to accelerate ions from the plasma. After the deposition, the films were annealed for 1 h in air at a constant temperature from 673 to 1023 K. The films were analyzed by XRD, XPS and Raman spectroscopy. The photocatalytic property of TiO2 films was evaluated by examining the decomposition of an aqueous solution of methylene blue under UV irradiation. XPS and Raman results showed that the deposited films consisted of Ti, O and C and an amorphous carbon structure. The color of the films changed from black to colorless and transparent after annealing at a temperature above 723 K. XPS results showed that the composition of the films annealed at 873 K was stoichiometric TiO2. The formation of a single phase anatase type TiO2 crystalline was confirmed for the films annealed between 723 and 923 K by XRD and Raman measurements. The films annealed at 973 K were a mixture of anatase and rutile type crystals. The film annealed at 973 K had the highest photocatalytic activity for the decomposition of aqueous solution of methylene blue.

Deposition and characterization of Ti- and W-containing diamond-like carbon films by plasma source ion implantation

Abstract Ti and W-containing diamond-like carbon (DLC) films were prepared on silicon wafer substrate by a process combining reactive magnetron sputtering with plasma source ion implantation (PSII). Ti and W were deposited by r.f. magnetron sputtering of a metal target and PSII using hydrocarbon gas. Ar/C 2 H 2 mixed gas was introduced into the discharge chamber. The negative high voltage pulse (−10 kV, 100 Hz, 100 μs) superposed on a d.c. voltage of −0.5 kV was applied to the substrate holder. The structure of the films changed from metal containing amorphous DLC, to a composite of metal containing DLC and metal carbides with increasing metal content in the films. The sheet resistivity of the films was decreased abruptly with increasing metal content in the films. The tribological properties of the films were improved by W doping.

Preparation and properties of nitrogen and titanium oxide incorporated diamond-like carbon films by plasma source ion implantation

Abstract Nitrogen and titanium oxide incorporated diamond-like carbon (DLC) films were deposited by a plasma source ion implantation on silicon wafer and quartz glass. Pure acetylene gas was used as a working gas for plasma. Additional nitrogen and titanium tetraisopropoxide gases were fed into acetylene plasma to prepare nitrogen and titanium oxide incorporated DLC films. The plasma was generated by a radio frequency glow discharge. Ions were accelerated from the plasma by a high-voltage pulse (−20 kV, 100 Hz, 50 μs) applied directly to the substrates. The surface morphology was observed by a scanning electron microscope (SEM) and an atomic force microscope (AFM). The compositional and structural characterization of the films was carried out using X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and Raman spectroscopy. The hardness of the films was measured by an indentation method. The sheet resistivity of the films was measured by a four-point probe method. The results showed that all of the N incorporated and unincorporated films were amorphous and showed typical Raman spectra of DLC films. The XPS and the FT-IR spectra indicated the formation of C–N, CN and CN valence bonds. XPS measurement for titanium oxide incorporated films revealed the existence of Ti–C, Ti–O, C–C bonding in the DLC films. The hardness of the nitrogen and titanium oxide incorporated films decreased with the amount of incorporated species. The sheet resistivity of the films decreased abruptly with increasing nitrogen and titanium oxide contents in the films.

Ion implantation into inner wall surface of millimeter size diameter steel tube by plasma source ion implantation

Abstract Nitrogen and carbon ions were implanted into the inner wall surface of 304 austenitic type stainless steel and Ni tubes with inner diameters of 0.9, 2 and 1.6 mm, by a plasma source ion implantation (PSII). These 30 mm long substrate tubes were fixed to an alumina ceramic tube in a vacuum chamber, fed with nitrogen and acetylene gases. A 2.45 GHz microwave was supplied to an antenna in the alumina ceramic tube and plasma was produced by a coaxial electron cyclotron resonance (ECR) discharge in this tube. A negative high voltage pulse of 15 kV (1 kHz, 10 μs) was applied to the steel and Ni tubes to extract ions from the generated plasma. The compositional and structural characterizations of the implanted surfaces were carried out using Auger electron spectroscopy and Raman spectroscopy. The results showed that uniform nitrogen ion implantation into the millimeter size inner wall surface of metal tubes was achieved by the PSII. Carbon implantation and subsequent diamond like carbon (DLC) coating was confirmed for the inner wall surface treated by acetylene PSII.

Pulsed laser deposition of carbon nitride thin films from graphite targets

Abstract Carbon nitride thin films were synthesized on Si(100) substrates by a pulsed Nd:YAG laser deposition. The laser beam is incident on the high-purity graphite targets. The films are grown using an energy density 3.8 J cm−2 at a laser repetition rate of 10 Hz. The nitrogen gas pressure in the chamber is 10.0 Pa. Morphology features of the films have been obtained by employing the technique of scanning electron microscopy. Auger electron spectroscopy has been used to obtain compositional information about the films. The N C composition ratio was found to vary from zero to 0.32 depending on deposition conditions. IR absorption spectra show two characteristic bands: a broad band composed of the graphite G-band and disordered D-band of carbon, and another associated with CN triple bonds. Raman spectra have also been used to characterize the films.

ADHESIVE AND CORROSION-RESISTANT ZIRCONIUM OXIDE COATINGS ON STAINLESS STEEL PREPARED BY ION BEAM ASSISTED DEPOSITION

Abstract To improve the adhesion and corrosion resistance in ceramic and steel systems, zirconium oxide films were deposited on austenitic type 316L stainless-steel substrates by using the ion beam assisted deposition (IBAD) method, in which ZrO 2 evaporation and energetic Ar and/or O 2 ion bombardment at 250 eV were carried out simultaneously. To study the influence of the film thickness on the performance of coatings, thin (0.2–0.4 μm) and thick (2–3 μm) films were prepared. The film structure was investigated by X-ray diffractometry. The adhesion was evaluated by a tensile pull-off tester, showing that IBAD treatments could provide a remarkable potential to enhance the adhesion. The corrosion behavior was determined by potentio-dynamic polarization measurements. It was found that excellent corrosion-protection ability of zirconium oxide coatings on stainless steel was achieved after IBAD treatments. The mechanism for explaining the results has been discussed in terms of the surface observation and X-ray photoelectron spectroscopy studies.

Pulsed laser deposition of tungsten carbide thin films on silicon (100) substrate

Abstract A method of synthesizing tungsten carbide (WC) thin films by a pulsed YAG laser deposition is investigated. WC thin films are deposited on silicon (100) substrates by using WC5%Co alloy targets. Glancing angle X-ray diffraction shows that the strong peaks of W 2 C appear at the substrate temperature of 500°C. Beside the strong peaks of W 2 C, weak peaks of WC and W 3 Co 3 C appear at the substrate temperature of 650°C. Auger electron spectroscopy shows that the almost stoichiometric WC films are deposited at the methane gas pressure of 1.0 Pa. Morphological features of the samples have been obtained by employing the technique of scanning electron microscopy. X-ray photoelectron spectroscopy has been used to obtain structural and compositional information about the samples.

The effects of Ti implantation on corrosion and adhesion of TiN coated stainless steel

Abstract Thin titanium nitride (TiN) films of 40 and 70 nm in thickness were deposited on austenitic-type 304 stainless steel substrates by a rf ion plating process, and these specimens were irradiated with 70 kV titanium ions at a fluence of 1 × 10 17 /cm 2 by use of MEVVA IV metallic ion source at room temperature. After that TiN films of 2 μm were deposited by the same method. The results of X-ray photoelectron spectroscopy and Auger electron spectroscopy revealed that implanted titanium penetrated into the substrate and interfacial mixing was verified. The adhesion strength was estimated by a scratch test. It was found that ion implantation can enhance the adhesion strength between the film and the substrate. The corrosion resistance of the specimens was evaluated in aqueous solutions of sulfuric acid by an electrochemical method. Titanium implantation was extremely effective in suppressing the anodic dissolution of stainless steel.

Ion-beam-assisted deposition of aluminium and aluminium alloy coatings for corrosion protection

Abstract Ion-beam-assisted deposition (IBAD) was used for depositing pure aluminium coatings on low carbon steel in order to study the corrosion properties as a function of the energy of the incident argon ions, the ion-to-atom arrival ratio and the angle of ion incidence. With theoretical considerations about the localized corrosion behaviour of substrate-coating systems it is possible to evaluate the porosity, the relative number of coating defects and their mean diameter. Their dependence on the process parameters gives an insight into the initial stages of film growth and shows that the energy deposition in the near-surface region is the most important factor for modifying coating defects and therefore the corrosion properties of the steel-aluminium system. The modification potential of each parameter of IBAD is studied in comparison to pure vapour deposition for the corrosion in acetate buffer. In chloride-containing aqueous solutions the depassivation behaviour of aluminium can be improved by use of alloying elements. Aluminium and magnesium were deposited on inert glass substrates; the magnesium concentration and the bombarding energy were varied. The resulting alloys have equilibrium potentials less noble than pure aluminium and increased passive regions. The passive region decreases with increasing magnesium concentration. From glancing-angle X-ray diffraction measurements it can be seen that structural changes influenced by the ion beam go parallel with changes in the localized corrosion behaviour.

Synthesis and corrosion properties of silicon nitride films by ion beam assisted deposition

Abstract Silicon nitride films SiNx were deposited on 316L austenitic stainless steel substrates by silicon evaporation and simultaneous nitrogen ion irradiation with an acceleration voltage of 2 kV. In order to study the influence of the nitrogen content on changes in stoichiometry, structure, morphology, thermal oxidation behaviour and corrosion behaviour, the atom to ion transport ratio was systematically varied. The changes of binding states and the stoichiometry were evaluated with XPS and AES analysis. A maximum nitrogen content was reached with a Si N transport ratio lower than 2. The films are chemically inert when exposed to laboratory atmosphere up to a temperature of more than 1000°C. XRD and SEM measurements show amorphous and featureless films for transport ratios Si N from 1 up to 10. The variation of the corrosion behaviour of coated stainless steel substrates in sulphuric acid and hydrochloric acid shows a minimum at medium transport ratios. This goes parallel with changes in porosity and adhesion. Additional investigations showed that titanium implantation as an intermediate step improves the corrosion resistance considerably.