Photoelectron spectromicroscopy study of a misfit layer compound, and its interaction with Cs

Misfit layer compounds are built of alternating MX and TX$_2$ layers, where M is e.g.~Sn or Pb, T is a transition metal, and X is S or Se. We have studied surfaces of (PbS)$_{1.13}$TaS$_2$ and their interaction with Cs, using the photoelectron microscopy beamline at MAX-lab, Sweden. By imaging the sample using emission from the Pb 5$d$ and Ta 5$d$ core levels, we resolved domains terminated by either PbS or TaS$_2$ layers. Imaging by Cs 4$d$ emission revealed larger sticking of Cs on the PbS terminated domains. Further information was obtained by measuring high-resolution spectra from different domains, before and after Cs deposition. We found that the PbS layers react with the Cs, while the TaS$_2$ layers are more inert. The results also indicated presence of substitutional defects. Cs intercalation of the kind observed in TaS$_2$ polytypes was not observed.