Quartz oscillator study of monolayer 4He and 3He-4He mixture films adsorbed on solid H2

The superfluid transition in submonolayer and monolayer He-4 films and He-3-He-4 mixture films on solid H-2 has been studied using a quartz crystal microbalance technique. Kosterlitz-Thouless (KT) transitions were observed in submonolayer He-4 films with density greater than 0.062 +/- 0.002 Angstrom(-2). We determine a binding energy of He-4 to 0.241 Angstrom(-2) H-2 of -15.7 K in the presence of approximate to 1 monolayer of He-4, At several He-4 coverages, a range of submonolayer He-3 coverages was studied (n(3) less than or equal to 0.0567 Angstrom(-2)). With each increase in the He-3 coverage, the KT transition temperature decreased. For the higher coverage mixture films studied (n(4) greater than or equal to 0.0726 Angstrom(-2)) we observed an apparent second decoupling of the film from the quartz oscillator frequency in addition to the KT transition. We have studied the coverage dependence of this new feature.