Structure of an inert layer of He4 adsorbed on mesoporous silica

We have studied the structure of inert layer 4He adsorbed on mesoporous silica (FSM-16), by the vapor pressure and heat capacity measurements. The heat capacity shows a Schottky-like peak due to the excitation of a part of localized solid to fluid. We analyzed the heat capacity over a wide temperature region based on the model including the contribution of the localized solid and excited fluid and clarified that the excited fluid coexists with the localized solid at high temperature. As the areal density approaches the value at which superfluid appears (n_C), the fluid amount is likely to go to zero, suggesting a possibility that the inert layer is solidified just below n_C.