Valence-band spectra of BEDT-TTF and TTF-based magnetic charge-transfer salts

Abstract

The electronic structure of BEDT-TTF bis(ethylenedithio)tetrathiafulvalene, and TTF, tetrathiafulvalene, based ferrimagnetic insulating and paramagnetic semiconducting charge-transfer salts have been studied by x-ray emission spectroscopy (XES) and photoelectron spectroscopy (XPS). The counterions for the salts are the d-transition-metal complex anions [Cr(NCS)(4)(phen)](-), [Cr(NCS)(4)(Me(2)phen)](-) and [Cr(NCS)(4)(isoq)(2)](-) where Me(2)phen=4, 7-dimethyl-1, 10-phenanthroline, phen=1, 10-phenanthroline), and isoq=isoquinoline=C9H7N. The distribution of partial and total density of states was determined by comparing the XES spectra of the constituents (carbon and nitrogen Kalpha and Cr L-2,L-3) with XPS valence-band spectra on the binding-energy scale. Splitting in the XPS N 1s and S 2p spectra was attributed to contributions from nonequivalent atoms, i.e., N in the NCS and phen based ligands, S in NCS and BEDT-TTF. Cr L-XES measured at the L-2-threshold display an unusually high L-2 to L-3 intensity ratio, which is discussed in terms of Coster-Kronig transitions and a different excitation of L-3 and L-2 levels at the L-2 threshold.