Micro-Raman spectroscopy for stress analysis on large area diamond/Ti6Al4V electrodes

摘要

Residual stress in boron doped diamond films grown on perforated and non-perforated titanium alloy substrates (Ti6Al4V) have been investigated. Diamond films were deposited at 870 K and 6.5 X 10~3 Pa by the conventional hot filament chemical vapor deposition technique (HFCVD) using a gas mixture of methane 1.0 vol. percent in hydrogen. For controlling the B/C ratio it was necessary an additional H_2 line that passed through a bubbler containing B_2O_3 dissolved in methanol. Large substrates with a geometric area of 12 cm~2 were fixed in a rotation mechanism that improves the film uniformity. Perforated substrates were obtained from laser machining and promoted an increase of approximately 30 percent on surface geometric area when compared with similar non-perforated sample. Scanning electron microcopy (SEM) has evidenced a faceted polycrystalline grains with orientation (111) and (100) of approximately 1 (mu)m in size for a film thickness of 1.5 (mu)m. From micro-Raman analyses, the stresses were evaluated in many points on samples surface by using the summation method. The contribution of the pure diamond and the non-diamond phases was also analyzed. These results were imperative for comparing the total residual stress in perforated and non-perforated samples and show a good agreement for both of them. Higher compressive stress values are associated with perforated sample that presented lower amount of sp~3 bond. The relative higher concentration of non-diamond phase among the crystalline grains can help the structure relaxing promoting a decrease of intrinsic stress. Total stress result in both samples was compressive but in the samples edges the values are higher due to the thermal component to be a dominant contribution in this region.