X-ray photoemission measurements were performed on YBa2Cu3O7-x thin fi
lms in order to understand the origin and nature of various features a
ppearing in O 1s spectra before and after sputtering. The peak appeari
ng at 528.8 eV is totally intrinsic and is assigned to the bulk. Peak
appearing at about 531.2 eV which has been a subject of controversy, e
xtrinsic or intrinsic in origin, is shown to entirely originate from t
he unstable surface layer of YBa2Cu3O7-x which is non-superconducting
at room temperature under UHV environment. The peak at 530.4 arises be
cause of the change in the environment of oxygen atoms present in this
non-superconducting layer on sputtering.