Synchrotron Radiation Studies of Hydrocarbon Treated Silicon Surfaces and Diamond Nucleation
Abstract
Synchrotron radiation has been employed to study the surface chemistry of diamond nucleation and growth on Si substrates. Diamond films were grown by filament -assisted chemical vapor deposition on both atomically clean and diamond-polished Si surfaces. The surface chemistries of well-defined adamantane-, neopentane-, and methane-dosed Si surfaces were also studied along with carbon films grown by synchrotron radiation induced chemical vapor deposition. In all studies, combinations of valence-band and core-level photoemission, Auger, and near edge X-ray absorption fine structure spectroscopies were used to investigate the chemistry of the C/Si surface. Methane (30 K), neopentane (85 K) and adamantane (85 K) were determined to adsorb molecularly on the 7 x 7 reconstructed Si surface. Conversely, the adamantane and neopentane adlayers desorb at ~205 and 115 K for heating rates of ~1 K/min. The methane adlayer desorbed below 100 K. Si(2p) core-level photoelectron spectra of the thermally reacted surfaces showed chemically shifted components of 0.48 +/- 0.05, 1.00 +/- 0.05, and 1.50 +/- 0.05 eV with respect to the Si bulk component indicating the formation of Si(C) _{rm n} (n = 1-3) surface species. When the adamantane-dosed Si(111)-7 x 7 surface was irradiated with broadband synchrotron radiation, the chemistry of the adamantane adlayer was found to depend on the energy of the excitation beam. With energies greater than the C(1s) binding energy (284 eV), the adamantane -dosed surface reacted to form a thin SiC layer. In contrast, when the surface was irradiated with lower energy broadband synchrotron radiation (<284 eV), only the adamantane in direct contact with the Si surface dissociated. A fraction of the remaining adlayer reacted with the surface to form adamantyl-Si surface complexes. At larger adamantane coverages (1.0 times 10^ {16} molecules/cm^2), high energy (>284 eV) broadband synchrotron radiation promotes the formation of an amorphous hydrogenated carbon film. In the diamond deposition studies, Raman spectroscopy and atomic force microscopy were used as well to complement the vacuum surface characterization techniques. Within three minutes of deposition, a carbon rich SiC layer, at least 25 A thick, developed. At early stages of growth (<10 min. of deposition), no differences were observed between the cleaned and diamond polished surfaces. With additional deposition, a 20-30 A thick amorphous carbon overlayer was deposited on the originally clean Si surface. The amorphous carbon layer did not promote diamond nucleation. In contrast, ~500 A diamond films were deposited within 45 to 60 minutes on the diamond polished surfaces. Two types of nuclei were observed on the diamond-polished surfaces following 20 minutes of deposition by atomic force microscopy: (1) large (200-300 nm in diameter) nuclei, randomly distributed on the surface, and (2) smaller (50-100 nm) nuclei that show a preference for forming along the scratches. Atomic force micrographs of the originally clean surface show the formation of carbon islands.
- Publication:
-
Ph.D. Thesis
- Pub Date:
- 1993
- Bibcode:
- 1993PhDT.......276S
- Keywords:
-
- SILICON SURFACES;
- Chemistry: Analytical; Physics: Condensed Matter; Chemistry: Physical