Comparison of Thermal Behavior of Vacuum-Crushed, Air-Crushed, and Mechanically Polished Silicon Surfaces by Electron Paramagnetic Resonance

Surfaces of Si produced by crushing in vacuum, in air, and by mechanical polishing have been studied by monitoring the EPR signal at $g=2.0055\mathrm{}$, arising from such specimens. Effects of heat treatment in vacuum to 400°C are similar for both samples crushed in air and samples that have been fine-polished, but annealing behavior differs markedly for samples crushed in high vacuum (${10}^{-9\mathrm{}}$ Torr). The polished samples have a surface stress which drops rapidly with annealing from the initial value of 16 000 dyn ${\mathrm{cm}}^{-1\mathrm{}}$ at room temperature to 2000 dyn ${\mathrm{cm}}^{-1\mathrm{}}$ after 125°C, and thereafter slowly to below 400 dyn ${\mathrm{cm}}^{-1\mathrm{}}$ after 400°C. Detailed comparisons of effects of heat on line intensity, shape, and width indicate that the surfaces produced by mechanical polishing and by crushing in air are essentially similar. Surface stresses do not appear to have a significant effect on the resonance signal. The principal effect of the various treatments, as monitored by EPR, is to produce extra surface area, in the form of cleavage surfaces on fissures and fragments, contaminated by atmosphere in the case of specimens processed in air.