The Heat Capacity of 4He Monolayers Adsorbed on Evaporated Gold

The specific heat of 4He condensed on an evaporated gold surface has been measured for coverages between 0.007 and 0.096 A−2 and temperatures between 0.4 and 3.0 K. There are at least two types of physisorption site on the gold surface with binding energies −83 ± 7 and −94 ± 7 K. For coverages below 0.06 A−2 (∼0.5 monolayers), the 4He is a two-dimensional classical gas at sufficiently high temperatures. At lower temperatures and higher coverages, the 4He forms condensed phases, including liquids, solids commensurate with the gold lattice, and incommensurate solids. The phase diagram of 4He/evaporated gold is similar to that for 4He/graphite, but the phase boundaries are shifted and not well defined, nor is the diagram as rich in structure.