PHOTOELECTRON-SPECTROSCOPY OF THE TIN DICHALCOGENIDES SNS2-XSEX INTERCALATED WITH COBALTOCENE

Single crystals of the n-type semiconducting tin dichalcogenides SnS2−xSex, (x = 0, 0.3, 0.5, 1.3, 1.85, 2), which have a two-dimensional layered structure, have been intercalated with cobaltocene to give the series of compounds SnS2−xSex(CoCp2)o.33, where Cp =η5-C5H5. Photoelectron spectroscopy has been employed to investigate the electronic changes upon intercalation, especially the electron transfer from the guest to the host. X-ray photoelectron spectroscopy (XPS) has revealed mixed oxidation states for both tin [Sn(ll), Sn(lV)] and cobalt [Co(I), Co(II), Co(III)]. Of the three cobalt species observed by XPS, two have been unambiguously identified as CoCp2and [CoCp2]+, whereas the third cobalt species has only been tentatively assigned to a Co(η5-C5H5)(η4-C5H5R) complex, in which cobalt is formally in the oxidation state Co(I). Ultraviolet photoelectron spectroscopy (UVPES) shows that the intercalates are either semiconducting (x = 0, 0.3, 0.5, 1.3) or metallic (x = 1.85, 2), whereas all the hosts are n-type semiconductors. An impurity-band model is presented as a possible qualitative explanation for this transition through the series. © 1990, American Chemical Society. All rights reserved.