Synchrotron radiation study of the formation of CuxSey and NxCuySez thin films on Cu substrates; Cl-2-induced out-diffusion of Na

In this paper we study the growth of CuxSey and NaxCuySez thin films on pol ycrystalline Cu substrates. The investigation took place ist situ by means of photoemission spectroscopy with synchrotron radiation, in UHV. Depositio n of elemental Se with a dense flux on a polycrystalline Cu substrate at RT and subsequent heating to 100 degrees C causes the formation of a thick Cu 2-xSe film (with x equal or very close to zero). A phase transition of this copper selenide occurs by annealing at 200 degrees C. Deposited Na on the Cu2-xSe film is diffused into the bulk, resulting in the formation of a Nax CuySez compound. Exposure to Cl-2 at 120 degrees C causes the out-diffusion of Na to the surface, where NaCl is formed. The Na diffusion in and out of the copper selenide film is analogous to alkali intercalation-deintercalat ion from TX2 layer compounds.