Appearance potential spectroscopy (APS) was introduced in the early seventies as a relatively simple surface sensitive analytical technique. Later, various processes involved in APS signal formation have been investigated, making use of sophisticated experimental set-ups. In this way, APS became a possible tool for studying electron transport processes in the surface region of solids.
In the experimental part of the submitted work that represents a considerable extension of the previously obtained results, ultrathin layers were deposited by in situ evaporation on polycrystalline substrates. Ti, Cr,
Mn and Ni were chosen as substrates and deposits in a series of overlayer experiments. The L3, Lz and L, (if possible) subshell signal intensities have been measured as a function of the overlayer thickness. Auger spectra have also been taken to monitor the cleanliness of the substrates and the overlayers. The discrete model of the APS signal formation according to Eckertova, instead of the common exponential model, offered the possibility of fitting the experimental results. Its parameters represent the probabilities of the basic types of electron interactions related to one atomic layer. Approximate values of these quantities have been calculated.