Heating of a silicon single crystal introduces a surface roughness. Crystals are heated for periods of 45 sec in the temperature range from 560 to 1150°C. Using ellipsometry, Auger electron spectroscopy, mass spectroscopy and micrography it has been shown that the changes in the ellipsometric parameters are caused by surface roughness which in turn is strongly related to the sublimation of silicon during heating. The relation between surface roughness and temperature of the crystal during the heating is not linear.
Kono, S., Hanekamp, L. J., & van Silfhout, A. (1977). Effects on ellipsometric parameters caused by heat treatment of silicon (111) surface. Surface science, 65(2), 633-640. https://doi.org/10.1016/0039-6028(77)90471-X