SCANNING-TUNNELING-MICROSCOPY AND SPECTROSCOPY OF NA INTERCALATION INVSE2

We have used an ultrahigh vacuum variable-temperature scanning tunneli ng microscope to study in situ Na intercalation in 1T-VSe2. At room te mperature the clean surface showed large flat areas and a trigonal ato mic arrangement. Tunneling spectroscopy revealed the known state at 10 0 mV below E-F. At 60 K the clean surface showed a 4 x 4 charge densit y wave and the spectra showed a CDW gap Delta approximate to 80 mV. Wh en evaporating less than or equal to 1 ML Na at room temperature, the intercalated Na were distributed non-uniformly, giving bright areas of increased topographic height where Na was intercalated. In the interc alated material the VSe2 state was seen in the tunneling spectra, and was slightly shifted towards E-F. Preliminary spectroscopy of the inte rcalated material at 60 K showed two different types of spectra. One t ype showed the VSe2 peak clearly, but had no sign of the CDW gap, whil e the other type showed a gap structure but did not resolve the VSe2 s tate. Presently, we can not tell whether these different spectra origi nate from the differences in the intercalated and non-intercalated are as or not.