Osamu Takai

XPS structural characterization of hydrogenated amorphous carbon thin films prepared by shielded arc ion plating

Hydrogenated amorphous carbon (a-C:H) thin films were synthesized by shielded arc ion plating. Structural characterization of the a-C:H films was performed using Raman, infrared and X-ray photoelectron spectroscopy (XPS). It is concluded that XPS is useful for estimating sp2 and sp3 carbon networks in the a-C:H films by analyzing the peak positions and FWHM (full width at half maximum) values of XPS C 1s spectra.

Effects of deposition pressure on structure and hardness of amorphous carbon nitride films synthesized by shielded arc ion plating

Amorphous carbon nitride (a-C:N) films were synthesized by shielded arc ion plating (SAIP) at the wide pressure range of 0.01-30 Pa. It is essential to prepare a-C:N films at pressures below 0.1 Pa or apply negative voltages to substrates at pressures below 1 Pa for fabricating hard films. Appropriate N 2 + ion bombardment increases compressive stresses and promotes formation of fourfold coordinated carbon micro-networks in a-C:N films. N/C ratios of these hard films were <0.26 and N atoms substituted for C sites in amorphous carbon networks. On the other hand, in order to raise N/C ratios of a-C:N films, it is necessary to prepare the films at as high a pressure as possible. The maximum N/C ratio was 0.51 at 30 Pa with no substrate bias. Even this value is much lower than 1.33 of hypothetical C 3 N 4 . CN radicals were remarkably formed in the plasma at higher pressures and related to nitrogen concentrations in a-C:N films. CN radicals were considered to act as precursors of aromatic plain carbon-nitrogen networks, and a-C:N films prepared at higher pressures were very soft. Conclusively, three-dimensional carbon nitride structures with high hardnesses and high nitrogen concentrations have not achieved at the same time by such PVD processes as SAIP.

Tribological properties of a-C : N and a-C films prepared by shielded arc ion plating

Abstract Amorphous carbon nitride (a-Cxa0:xa0N) and amorphous carbon (a-C) thin films that rarely contained hydrogen were synthesized on Si(1xa00xa00) wafers by means of shielded arc ion plating. Nanomechanical properties of these films were studied in relation to substrate bias voltage. The a-C film prepared at a DC bias voltage of 100xa0V showed a maximal hardness of 35 GPa, whereas the film deposited at −500xa0V had a minimal hardness of 7 GPa. Wear resistance was excellent for films with hardness greater than 20 GPa when rubbed with a diamond tip at a contact force of 20xa0μN. Hardness of the a-Cxa0:xa0N films, remained in the range of 10–14 GPa, independent of the bias voltage. However, the wear resistance of the a-Cxa0:xa0N films was much better than that of the hard a-C films. In particular, the a-Cxa0:xa0N film prepared at −300xa0V was so wear resistant that the film did not wear at all.

Nanoindentation studies on amorphous carbon nitride thin films prepared by shielded arc ion plating

Three types of amorphous carbon-based thin films, a-C:N, a-C:Ar and a-C:N:Ar thin films, were prepared by shielded arc ion plating (SAIP) at various substrate bias voltages. SAIP uses a shielding plate set between target and substrate, which traps macroparticles flowing from the target and avoids their deposition on the substrate. This simple shielding method results in smooth surfaces of the deposited films. Nanohardness and nano-wear-resistance of these synthesized films were measured with a nanoindentation system. The a-C:Ar films were the hardest, possessing maximum hardness of 35 GPa. The a-C:N films and a-C:N:Ar films showed excellent wear resistance.

Amorphous Carbon Nitride Hard Coatings by Multistep Shielded Arc Ion Plating

Hard amorphous carbon nitride (a-C:N) films fabricated by shielded arc ion plating break into pieces because of the large compressive stresses in the films when the film thicknesses are more than 200 nm. In the application of these films to practical hard coatings, the development of a technique to grow thicker films (over 1 µ m) is necessary. In this study, we developed a multistep ion plating technique to grow thick hard multilayer films. We formed a-C:N multilayers with a total thickness of more than 1 µ m on Si (100) and high speed steel (SKH9) substrates by stacking hard and soft films alternately in order to relax the large compressive stress in the hard film. The multilayers are extremely hard (Knoop hardness: 3200) and neither break into pieces nor peel off substrates spontaneously.

Wear-Resistant Thin Films of Amorphous Carbon Nitride Prepared by Shielded Arc Ion Plating

Amorphous carbon nitride (a-C:N) thin films were synthesized by means of shielded arc ion plating using a graphite target and pure nitrogen gas. The mechanical properties and chemical structures of these a-C:N films were studied through nanoindentation and X-ray photoelectron spectroscopic analysis. Nanohardness of the a-C:N film prepared at a substrate bias voltage of 0 V was ≈10 GPa. It was increased to 13–14 GPa when the substrate was biased negatively in the range of -100 to -500 V. The a-C:N film prepared at a bias of -300 V was particularly wear-resistant such that the film did not wear at all when rubbed with a diamond tip at a contact force of 20 µN. This highly wear-resistant a-C:N film was found to contain almost equal amounts of two C-N phases: β-C3N4-like and graphitelike phases.

Field emission properties of amorphous carbon nitride thin films prepared by arc ion plating

Abstract Amorphous carbon nitride thin films (a-C:N) were deposited by means of shielded arc ion plating (SAIP) using nitrogen and graphite as an operating gas and a carbon source, respectively. In the applied field strength range of up to 20 V/μm, electron field emission properties of these films were characterized and compared with those of amorphous carbon (a-C) thin films prepared using an argon plasma by the same SAIP apparatus. The a-C:N films showed better characteristics, that is, lower threshold field strengths and higher maximum emission current densities, than the a-C films. Among all of the fabricated a-C:N films, the film with a N concentration of 23%, prepared using a nitrogen arc plasma at a pressure of 1 Pa with applying a sample bias voltage of −100 V, showed the lowest threshold field of approximately 13 V/μm and the highest emission current density of near 2 μA/cm2 at a field strength of 20 V/μm. However, the best results obtained on the a-C films were a threshold field of approximately 16 V/μm and an emission current density of less than 0.1 μA/cm2 at the same field strength. The characteristics of the a-C:N films depended not only on the N concentration but also on the chemical bonding state of nitrogen in the a-C:N networks. The C-N phase distinguished by the N1s XPS peak at 400.5 eV plays a crucial role in field emission of the a-C:N.

Deposition of carbon nitride thin films by arc ion plating

Abstract Amorphous carbon nitride thin films are deposited by cathodic arc ion plating at the dc current of 60 A and the nitrogen pressure of 1 Pa with various negative bias voltages. Structure, chemical composition and chemical bonding states are analyzed by using X-ray diffraction, Raman spectroscopy, X-ray photoelectron spectroscopy and infrared spectroscopy. The deposition rate and the N:C ratio change with bias voltage. The N:C ratio decreases with negative bias voltages. Application of negative bias on the substrate is effective to increase the film hardness. The maximum hardness is obtained at about −300 V. By this negative bias the three dimensional C–N bonding develops and the film becomes hard.