Reflectance anisotropy spectroscopy (RAS) has become a powerful surfac
e characterization tool in semiconductor physics. To clarify the origi
ns of RAS spectra model systems are currently being studied. Kerr we s
tudy the temperature dependence of the RAS spectrum of the Si(001) sur
face. The intensity of the positive RAS peak at 4.3 eV is found to pro
vide a direct measure of the (2 x 1):(1 x 2) domain ratio, while the b
road negative trough centered on about 3 eV shows variation of fine sh
ape as well as intensity with temperature. The origins of these featur
es are discussed.