  We studied the resonant diffraction signal from stepped surfaces of SrTiO3 at
the Ti 2p -> 3d (L2,3) resonance in comparison with x-ray absorption (XAS) and
specular reflectivity data. The steps on the surface form an artificial
superstructure suited as a model system for resonant soft x-ray diffraction. A
small step density on the surface is sufficient to produce a well defined
diffraction peak, showing the high sensitivity of the method. At larger
incidence angles, the resonant diffraction spectrum from the steps on the
surface resembles the spectrum for specular reflectivity. Both deviate from the
XAS data in the relative peak intensities and positions of the peak maxima. We
determined the optical parameters of the sample across the resonance and found
that the differences between the XAS and scattering spectra reflect the
different quantities probed in the different signals. When recorded at low
incidence or detection angles, XAS and specular reflectivity spectra are
distorted by the changes of the angle of total reflection with energy. Also the
step peak spectra, though less affected, show an energy shift of the peak
maxima in grazing incidence geometry.
