Thin layers of bis(arene) transition metal (TM) compounds have been formed in situ in ultra-high vacuum by depositing Cr or V metal on top of a film of benzene (Bz) or toluene (Tol) ice at 100 K on a graphite substrate. The species thus formed are Cr(C6H6)2, V(C6H6)2, or Cr(C6H5-CH3)2 (termed CrBz2, VBz2, or Cr(Tol)2), and the valence structures have been examined using electron energy loss and ultraviolet photoemission spectroscopies (ELS and UPS). The reaction is “clean” in that there is no indication of side reactions or unwanted by-products, although a small coverage of unreacted TM atoms appears unavoidable. A simple ring substituent (CH3) remains intact during the reaction. Thus, it should be possible to synthesize and study species that are not readily available (or cannot easily be made) in bulk form or that have too low vapor pressure to allow easy in situ deposition. Data have been obtained for VBz2 and Cr(Tol)2, the valence structures of which have not previously been studied in detail using UPS and ELS. Although deeper-lying arene orbitals are essentially unperturbed by formation of the bis(arene)TM sandwich, subtle differences in the TM-related orbitals have been observed and discussed in comparison to CrBz2 with the aid of density functional theory. In the case of VBz2, clear evidence is seen for a molecular reorientation during annealing, based on the ELS polarization dependence. Electron transfer between an adsorbed bis(arene)TM and graphite depends on the occupancy of the highest occupied molecular orbital (HOMO) and on its energy relative to the Fermi level (EF). The small amount of unreacted TM resulting from in situ synthesis causes a large decrease in work function, which shifts the adsorbate HOMO to below EF and thus impedes electron transfer to highly oriented pyrolytic graphite. This is an obstacle to forming doping layers by this method.
Jump to Content
View Cart
RSS
This Publication
Scitation
SPIN
Scitopia
Google Scholar
PubMed