Surface Nitridation of Amorphous Carbon by Nitrogen Ion Beam Irradiation
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Surface Nitridation of Amorphous Carbon by Nitrogen Ion Beam Irradiation Chihiro Iwasaki, Masami Aono, Nobuaki Kitazawa, and Yoshihisa Watanabe Department of Materials Science and Engineering, National Defense Academy, Kanagawa 239-8686, Japan ABSTRACT Amorphous carbon was irradiated with a nitrogen ion beam and changes in composition and tribological properties after surface nitridation have been studied. The nitrogen ion beam energy was varied from 0.1 to 2.0 keV under the constant ion current density. Composition and chemical bonding states near the surface were analyzed by X-ray photoelectron spectroscopy (XPS). Tribological properties were studied by a pin-on-disk type tribotester. XPS studies show that the nitrogen concentration near the surface increases after nitrogen ion irradiation. The depth profiles of nitrogen in the irradiated specimens display that the nitrogen concentration near the surface is maximized after 0.2 to 0.7 keV ion irradiation. From the pin-on-disk testing, it is found that the friction coefficient of amorphous carbon increases after irradiation by 1.5 keV nitrogen ions, while the friction coefficient does not change drastically after irradiation by 0.2 keV ions.
INTRODUCTION Since it was predicted that crystalline carbon nitride (β-C3N4) would be comparable with or harder than diamond [1], various attempts have been made to synthesize this hypothesized material using different techniques, such as laser ablation deposition [2], ion beam assisted deposition [3], reactive sputtering [4], hot-filament chemical vapor deposition. [5] In addition to the deposition methods, nitrogen ion irradiation into carbon materials has been proposed as an effective technique for preparation of carbon nitride (CNx). [6] Hoffman et al irradiated graphite and diamond by 500 eV nitrogen ions in the temperature range from room temperature to 800 K and studied effects of irradiation temperature, post-irradiation annealing and ion dose. According to their results, it is found that the nitrogen concentration increases and implanted nitrogen is present in three different bonding states of nitrogen and carbon. [6-8] Galán et al studied X-ray photoelectron spectroscopy of CNx films grown by nitrogen ion implantation on graphite and hydrogenated amorphous carbon in the ion energy region from 250 to 5000 eV. [9] They found that higher nitrogen concentration is obtained by consecutive implanting from higher to lower energies and the N1s line shape is composed of four chemical species. Husein et al prepared CNx films by implanting amorphous carbon films with nitrogen using plasma immersion ion implantation and conventional ion beam implantation. [10] Raman spectra show that the structure of implanted CNx films becomes more amorphous compared with the as-deposited films. Recently, the present authors irradiated bulk amorphous carbon using a nitrogen ion beam to form CNx layers. [11] Amorphous carbon shows unique properties, such as isotropic mechanical properties and non-cleavage, compared with graphite. In the p
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