Consider a photoelectron spectroscopy setup with the following definition of geometry Z Electron detector hv e- Crystal The angle 0 describes how far the detector is off-normal (0 = 0 is normal to the sample) The angle o describes the azimuthal angle of the detector with respect to the photons incoming angle. Depending on the type of sample and sample surface the following statements can be made: When measuring core levels by XPS increasing 0 will When measuring core levels by XPS changing o will When measuring the valence band of a two dimensional surface structure with UPS increasing 0 will When measuring the valence band of a two dimensional surface structure with UPS changing o will