Synthesis and Nanotribology of Superhard Carbon Nitride Films

采用自行研制的保护弧离子镀工艺，成功地合成了非晶态氮化碳(a-C：N)薄膜。本研究对a-C：N薄膜作为新型超硬涂层的应用进行了基础性研究。用红外光谱和X射线光电子能谱对薄膜的化学成分和成键状态进行了表征。用摩擦显微镜观察了薄膜的纳米力学性能。我们改变了氮气气压和衬底偏压作为沉积参数。随着氮气压力的增加，氮气组成增加，达到N/C组成比0.45。而C-C和C-N键分别变为类石墨态和类绒毛状，具有二维平面网状结构。施加负衬底偏压会在生长的薄膜表面引发离子轰击，从而导致薄膜中sp3键态的形成。A…然而，过多的负偏压既提高了sp^3键态的图形化，同时也降低了氮的组成。在高氮压条件下，由于离子在弧光等离子体中的平均自由程较短，减小了负偏压的影响。利用摩擦显微镜测量了在不同氮气压力和负衬底偏压下制备的a-C：N薄膜的纳米硬度。所有样品的薄膜厚度均为150 nm。纳米硬度随着氮气压力和负衬底偏压的增加而降低。这一结果与高氮压使薄膜中的C-N键而不是3D的C-N网络变为类毛状态，以及衬底负偏压过大使薄膜中的碳网络处于类sp^2键态的事实相一致。最硬的a-C：N薄膜表现出比广泛用作硬涂层材料的TiN薄膜更高的纳米硬度。利用摩擦显微镜对其纳米磨损性能进行了研究。用Vercobich型金刚石针尖在低载荷下扫描薄膜表面1μm×1μm的区域，用原子力显微镜观察该区域的磨损深度。纳米碳膜的耐磨性能远优于已被应用于耐磨涂层的类金刚石碳膜。这些结果表明，本研究合成的a-C：N薄膜在摩擦学相关领域具有一定的应用价值。较少

We have succeeded to synthesize amorphous carbon nitride (a-C : N) thin films by using the shielded arc ion plating process developed by ourselves. In this study, fundamental investigations were performed in order to apply the a-C : N thin films as novel super hard coatings. Chemical compositions and bonding states of the deposited films were characterized both by infrared spectroscopy and by X-ray photoelectron spectroscopy. The nanomechanical properties were made clear by using Triboscope.<Chemical Bonding States>We varied a nitrogen gas pressure and a substrate bias as deposition parameters. As increasing the nitrogen pressure, the nitrogen composition increased up to the N/C composition ratio of 0.45. However the C-C and C-N bonds became graphite-like and piligine-like states, respectively, which had 2D plane network structures. Applying negative substrate biases invoked ion bombardments on the growing film surfaces, which caused formation of the sp^3 bonding states in the films. A … More n excess of the negative bias, however, raised both a graphitation of the sp^3 bonding states and a decrease in the nitrogen composition at the same time. In the condition of the high nitrogen pressure, the effect of the negative bias was reduced due to the short mean free path of the ions in the arc plasma. Thus the sp hybridizing ratio and the N/C composition ratio was able to control by the nitrogen gas pressure and the negative substrate bias.<Nanomechanical Properties>By using Triboscope, we measured nanohardness of the a-C : N films prepared at various nitrogen gas pressures and negative substrate biases. The film thickness was unified at 150 nm for all samples. The nanohardness was degraded with increase both in the nitrogen pressure and in the negative substrate bias. This result was consistent with the fact that the high nitrogen pressure makes the C-N bonds in the films be the piligine-like states instead of the 3D C-N networks, and that the excess of the negative substrate bias makes the carbon networks in the films sp^2-like bonding states. The hardest a-C : N thin film showed a nanohardness greater than the TiN film which is widely used as hard coating materials. The nano-wear property was also investigated by Triboscope. After a region of 1μm x 1μm on the film surface was scanned by a Vercobich-type diamond tip in a low load, the wear depth of the region was observed by an atomic force microscope. The nano-wear property was much more excellent than that of the diamondlike carbon films which have been already applied as wear-resistant coatings. From these results, the a-C : N thin films synthesized in this study was proved to be useful in the fields related in tribology. Less