CHEMICAL AND MORPHOLOGICAL MODIFICATIONS OF SILICON-WAFERS TREATED BYULTRASONIC IMPACTS OF POWDERS - CONSEQUENCES ON DIAMOND NUCLEATION

The mechanical enhancement of diamond nucleation on silicon wafers by the use of ultrasonic impacts of different abrasive powders in various liquid media is investigated via surface-enhanced Raman spectroscopy (SERS), atomic-force microscopy (AFM) and scanning electron microscopy (SEM). The growth of diamond nuclei is carried out in a bell-jar micr owave-assisted plasma set-up. The nucleation densities obtained are co mpared to those resulting from a highly oriented pyrolitic graphite (H OPG) substrate, a virgin silicon wafer and a silicon wafer previously in-situ etched by a hydrogen plasma. The results are analyzed in terms of free carbon formation, surface morphology and particle implantatio n. The role of the morphological aspect is seen to be negligible compa red with the chemical role. When non-diamond powders are used, the nuc leation density is seen to depend on the amount of amorphous carbon ph ases formed in the physical sites (defects, stresses), at the silicon surface. When diamond powder is used, nucleation density up to 1.5 x 1 0(10) cm(-2) is obtained. It is attributed to an implantation of the d iamond particles occurring during the ultrasonic impacts. On the HOPG substrate, a low and non-uniform crystal density, related to the distr ibution of scratches on the surface, is obtained. This highlights the role played by carbon phases, located at highly defective regions, in promoting diamond nucleation.