Changes in chemical bonding of diamond-like carbon films by atomic-hydrogen exposure

We have deposited unhydrogenated diamond-like carbon (DLC) films on Si substrate by pulsed laser deposition using KrF excimer laser, and investigated the effects of atomic-hydrogen exposure on the structure and chemical bonding of the DLC films by photoelectron spectroscopy (PES) using synchrotron radiation and Raman spectroscopy. The fraction of sp3 bonds at the film surface, as evaluated from C1s spectra, increased at a substrate temperature of 400 °C by atomic-hydrogen exposure, whereas the sp3 fraction decreased at 700 °C with increasing exposure time. It was found that the sp3 fraction was higher at the surfaces than the subsurfaces of the films exposed to atomic hydrogen at both the temperatures. The Raman spectrum of the film exposed to atomic hydrogen at 400 °C showed that the clustering of sp2 carbon atoms progressed inside the film near the surface even at such a low temperature as 400 °C.

Research Highlights
► The sp3 fraction at the DLC surface increases by atomic-hydrogen exposure at 400 °C.
► The sp3 fraction decreases at 700 °C with the exposure time.
► The sp3 fraction was higher at the surfaces than the subsurfaces.
► The sp2-carbon clustering progresses near the surface even at 400 °C.