Penetration of hydrogen atoms and termination of dangling bonds in amorphous carbon films

The various properties of amorphous carbon (a-C) films have been extensively studied with the expectation of a wide range of applications, such as tribological coatings, etching masks, and so forth. One of the general issues of a-C is how to terminate dangling bonds. In this study, to clarify the reaction of H atoms in the a-C films, a penetration of H atoms and termination of dangling bonds were investigated using an in-situ electron spin resonance (ESR) measurement system. 50 or 100 nm-thick a-C films were grown by a plasma-enhanced chemical vapor deposition system. The H radical irradiation for 5 minutes under 100 Pa, 30 sccm of H$_{\mathrm{2}}$ flow rate, and 50 W of microwave power, and the in-situ ESR spin density measurement were repeated alternately. The spin densities decreased from 0 to 15 minutes, then saturated. Converting to areal density, they decreased by the same amount regardless of the film thickness. This means that the H atoms penetrated to a certain depth and inactivated the defects. Calculating based on the initial defect density, it corresponds to terminating the whole defects in the 5 nm-thick regions. This result indicates that the dangling bonds in the a-C surface can be terminated by H atoms at room temperature.