Lateral doping inhomogeneities as revealed by μ-NEXAFS and μ-PES

The photoemission electron microscope (PEEM) based techniques mu-NEXAFS and mu-PES have been recently installed at the BESSY HE-TOM beam lines as novel techniques for material analysis. The ability of these novel techniques for the analysis of semiconductors and thin films is demonstrated by studies of UHV cleaved MoTe2 (0001) surfaces as well as by studies of thin films of a conductive (pyrrole based) polymer and of sublimated WO3 - films. For all these systems we provide evidence for lateral inhomogeneities which cause a lateral varying work function. It is caused be either coagulated intercalated oxygen contaminants, by a nonhomogeneous distribution of the counter-ions, and by clustering of sodium exposed to the clean surface of a WO3 film, respectively. These examples demonstrate the ability of the PEEM to resolve lateral doping inhomogeneity and the need of a combination of the spectroscopic techniques to differentiate between the individual contrast mechanisms.