Hidenobu Ohta

Ar Ion Effect on Mechanical Properties of Carbon Nitride Films Prepared by Ion-Beam-Assisted Deposition

Carbon nitride (CN) films have been prepared by ion-beam-assisted deposition. Carbon was evaporated by electron beam and N and Ar ions were bombarded simultaneously from one ion source. To clarify the role of Ar ion bombardment, CN films were prepared on Si(001) substrates. The Ar/N2 ratio was varied between 0 and 2. Mechanical properties were measured in terms of hardness, friction coefficient and wear. The films prepared under Ar/N2 ratio of 1 showed the highest hardness and best wear resistance. The XPS analysis of the CN films showed two distinct bond components that correspond to C–N sp2, and C–N sp3 bond. CN films with Ar/N2 ratio of 1.0 mainly consisted of C–N sp2 bond structure. TEM observation, shows that the simultaneous bombardment of Ar ion promotes two-dimensional network of C–N chemical bonds that are formed similar to stacked graphite-like sheets with a columnar alignment perpendicular to the substrate surface (nanotube-like structure). This is advantageous from the mechanical strength point of view, however, excess bombardment of Ar ion prevents the formation of nanotube-like structure. The variation of the mechanical properties is due to the structural change obtained by simultaneous bombardment of Ar ions.

Relationship between Tribological Properties and Microstructures in Carbon Nitride Thin Films Prepared by Ion-Beam-Assisted Deposition. Effect of Ar Ion Assist.

Carbon nitride (C-N) thin films have been prepared by ion-beam-assisted deposition. The correlation of the influence of the Ar ion assist in the tribological properties and microstructure of C-N films were investigated. The ion-beam gas ratio (Ar/N2 ratio) was changed between 0 and 2. The tribological properties were measured by pin-on-disc type tribotester. The microstructure of the C-N thin films was investigated by X ray photoelectron spectroscopy (XPS) and transmission electron microscopy (TEM). The friction coefficients were 0.15-0.20 irrespective of the ion-beam gas ratio and frictional materials. However, the film which formed under condition of Ar/N2 =1.0 showed excellent wear resistance. It also showed highest hardness of 21 GPa in this experiment. By the XPS analysis and TEM observation, microstructure of C-N thin film changed from amorphous to three dimensional crystalline-like structure by Ar ion adddtion. Consequently, it shows that the addition of Ar ion was very effective for improvement of mechanical properties when C-N thin film was formed by ion-beam-assisted deposition.

Synthesis of B-C-N Thin Films by Ion-Beam-Assisted Deposition and Their Mechanical Properties

B-C-N films have been synthesized by an ion-beam-assisted deposition technique, in which boron and carbon were evaporated by electron beam and a mixed nitrogen and argon ion beam was simulataneously irradiated onto silicon (100) substrates. The ratio of argon ions to nitrogen ions was varied by the flow rate ratio of Ar and N2 gases fed into the ion source. In this experiment, the influence of the ratio on the mechanical properties and the microstructure were investigated. Nano indentation studies show the maximum hardness up to 23 GPa at the gas ratio of 25.50 %. The films prepared under the appropriate conditions indicated low friction coefficients of 0.04-0.08 against a sapphire ball and excellent wear resistance. The existence of a cubic B-C-N like phase in the film, which has been predicted as one of new hard materials, was revealed by various micro-structural analyses. It was concluded that the excellent mechanical properties prepared at the optimum gas ratio could be attributed to the appearnce of the new cubic like phase.