SUPERFLUIDITY AND FILM STRUCTURE IN HE-4 ADSORBED ON GRAPHITE

We have completed a torsional-oscillator study of superfluidity in thi n films of He-4 adsorbed on the basal plane of graphite for coverages from 1 1/2 to 7 atomic layers. In contrast to superfluidity in films a dsorbed on amorphous substrates, we find several different regimes of superfluid behavior. Superfluidity in the second layer shows an anomal ous temperature dependence and is destroyed by solidification of the h im. The superfluid film appears to coexist with a two-dimensional surf ace gas for low coverages in the third layer. Evidence of a phase tran sition, which may be the reconstruction of an underlying layer, appear s just above the completion of the third layer. Modulation of the supe rfluid signal with coverage is seen through the completion of the sixt h layer.