A Synchrotron Radiation Study of the Formation of CuxSey and NaxCuySez Thin Films on Cu Substrates; Cl2-Induced Out-Diffusion of Na

In this paper we study the growth of CuxSey and NaxCuySez thin films on polycrystalline Cu substrates. The investigation took place in situ by means of photoemission spectroscopy with synchrotron radiation, in UHV. Deposition of elemental Se with a dense flux on a polycrystalline Cu substrate at RT and subsequent heating to 100°C causes the formation of a thick Cu2-xSe film (with x equal or very close to zero). A phase transition of this copper selenide occurs by annealing at 200°C. Deposited Na on the Cu2-xSe film is diffused into the bulk, resulting in the formation of a NaxCuySez compound. Exposure to Cl2 at 120°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–deintercalation from TX2 layer compounds.