Heat capacity and sticking probability measurements ofHe4submonolayers adsorbed on evaporated Ag films: Bose statistics in two dimensions

We have measured the heat capacity of submonolayers of ${}_{}{}^4{}_{}{}^{}\mathrm{He}$ adsorbed on Ag films between 1.7 and 3.3 K. Good fits to the results are obtained with a model of a noninteracting two-dimensional Bose gas. The sticking probability for room-temperature ${}_{}{}^4{}_{}{}^{}\mathrm{He}$ atoms on cold Ag has been measured as a function of substrate temperature and ${}_{}{}^4{}_{}{}^{}\mathrm{He}$ coverage. The sticking probability is 4% at low coverage, and abruptly drops to 1% for coverages above 0.5 monolayer.