Role of hydrogen in the initial stage of diamond heteroepitaxy on silicon

The reaction of atomic hydrogen with the C2H2-covered Si surface was studied using high-resolution electron-energy-loss spectroscopy (HREELS), thermal-desorption mass spectrometry (TDMS), and low-energy electron diffraction. We found that atomic hydrogen broke up the carbon-carbon bond in C2H2 and the Si-Si dimers on the Si surface, which led to the formation of C-H and Si-H bonds, respectively. When the C2H2-covered Si(100) surface was exposed to a filament-activated H-2/CH4 mixture, HREELS showed that the C-H stretching signal grew at the expense of the Si-H stretching signal. This observation was consistent with the replacement of the Si-H bond by - CH3, possibly following hydrogen abstraction from the Si-H bond by atomic hydrogen. TDMS analysis showed significant desorption of atomic hydrogen at both 650 and 750 K and a little desorption of CH2 and CH3 only at 650 K, although HREELS remained unchanged with annealing temperature. This showed that part of the hydrocarbon species on the Si surface existed as a stable network of hydrocarbon, which possibly was the initial stage of diamond formation on Si.