He. Brauer et al., ELECTRONIC-STRUCTURE OF PURE AND ALKALI-METAL-INTERCALATED VSE2, Physical review. B, Condensed matter, 58(15), 1998, pp. 10031-10045
The valence bands of the layered compound VSe2 and the related interca
lation compounds NaxVSe2, KxVSe2, and CsxVSe2 have been investigated b
y means of angle-resolved photoelectron spectroscopy, and compared to
self-consistent linear augmented plane-wave (LAPW) band calculations.
The intercalation compounds were prepared in situ by deposition of Na,
K, and Ca on VSe2 cleavage surfaces. The intercalation was monitored
by core-level spectroscopy, and although K was found to intercalate mo
re slowly than Na and Cs, estimated alkali concentrations of x = 0.2-0
.3 were reached for all three alkali metals. Additional depositions ma
inly seemed to increase the intercalation depth. Good agreement betwee
n LAPW calculations and valence-band spectra was found, in particular
for the dispersion along the layers. Normal-emission spectra, obtained
at different photon energies, indicated vanishing perpendicular dispe
rsion, but in spectra measured under variation of the emission angle s
ome band-edge signatures were seen, which suggests that some perpendic
ular dispersion remains, in accordance with the LAPW calculations. The
lack of dispersion in the normal-emission spectra could be due to int
ercalation induced structural transformations, leading to stacking dis
order. Also correlation effects may contribute. The rigid-band model i
s found inadequate, except as a crude approximation, for describing th
e changes during the initial phase of intercalation. It might be used
to describe the continued intercalation, however, under condition that
the intercalation modified bands are used. The need for studies that
probe both electronic and crystallographic structure (including defect
s) is stressed. [SO163-1829(98)08536-1].