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 $[\mathrm{Cr}(\mathrm{NCS}{)}_{4}(\mathrm{phen}){]}^{\ensuremath{-}},$ $[\mathrm{Cr}(\mathrm{NCS}{)}_{4}({\mathrm{Me}}_{2}\mathrm{phen}){]}^{\ensuremath{-}}$ and $[\mathrm{Cr}(\mathrm{NCS}{)}_{4}(\mathrm{isoq}{)}_{2}{]}^{\ensuremath{-}}$ where ${\mathrm{Me}}_{2}\mathrm{phen}=4,$ 7-dimethyl-1, 10-phenanthroline, $\mathrm{phen}=1,$ 10-phenanthroline), and $\mathrm{isoq}=\mathrm{isoquinoline}={\mathrm{C}}_{9}{\mathrm{H}}_{7}\mathrm{N}.$ The distribution of partial and total density of states was determined by comparing the XES spectra of the constituents (carbon and nitrogen $K\ensuremath{\alpha}$ and Cr ${L}_{2,3})$ 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.