Characterization of organic ultra-thin films by Penning ionization electron spectroscopy during layer-by-layer preparation: TFTCNQ, TMTSF and their charge transfer complex

Abstract Using Penning ionization electron spectroscopy, which provides information on the local distribution of individual orbitals exposed outside the outermost surface layer, ultra-thin films (one to several monolayers) of tetrafluorotetracyanoquinodimethane (TFTCNQ) and tetramethyltetraselenafulvalene (TMTSF) were characterized during layer-by-layer vacuum deposition onto a graphite substrate. The changes in the molecular orientation and electronic state were sensitively detected. Further, a monolayer of TFTCNQ was vacuum-deposited alternately with that of TMTSF. The charge-transfer reactions between them and also between TFTCNQ and the substrate were confirmed on the basis of the change in the electronic state.