  We performed a comprehensive angle-resolved photoemission spectroscopy study
of the electronic band structure of LaOFeAs single crystals. We found that
samples cleaved at low temperature show an unstable and highly complicated band
structure, whereas samples cleaved at high temperature exhibit a stable and
clearer electronic structure. Using \emph{in-situ} surface doping with K and
supported by first-principles calculations, we identify both surface and bulk
bands. Our assignments are confirmed by the difference in the temperature
dependence of the bulk and surface states.
