We have used low-energy electron microscopy to study the etching of la
rge terraces on Si(001) with molecular oxygen. By imaging the etching
process in situ, and comparing the results to detailed kinetic models,
we determine and quantify the dominant mechanisms by which oxygen att
acks the surface. We find that the etch rate follows an Arrhenius form
with an activation energy of 2.0 +/- 0.4 eV, significantly lower than
estimates reported in modulated beam investigations. [S0031-9007(98)0
7716-3].