EFFECTS OF SUBSTRATE-TEMPERATURE ON CHEMICAL-STRUCTURE OF AMORPHOUS-CARBON FILMS

Amorphous carbon thin films were prepared at 30, 200, and 450-degrees-C by magnetron sputtering of a graphite target. The surface structure and chemical bonding (sp2/sp3) of the carbon films were characterized by scanning tunneling microscopy (STM) and Raman spectroscopy. STM images show that graphite microcrystallites of 20-40 angstrom in size are present at the surfaces of all the films and the number of the microcrystallites increases with increasing substrate temperature. The microcrystallites often contain structural defects. Raman measurements show that increasing the substrate temperature results in an increase in the sp2-bonded fraction of carbon atoms and a decrease in the microstructural defects. These results indicate that the microstructural changes are correlated with changes in the chemical bonding ratio (sp3/sp3) and no diamond microcrystallites are present in the amorphous carbon. A three-dimensional atomic structure of the graphite microcrystallites is discussed in terms of turbostratic graphite.