HEAT-CAPACITY, ADSORPTION-ISOTHERMS, AND QUASI-ELASTIC NEUTRON-SCATTERING MEASUREMENTS OF BILAYER DEUTERIUM HYDRIDE ADSORBED ON GRAPHITE

Bilayer films of deuterium hydride (HD) adsorbed on exfoliated graphit es have been studied using heat capacity, adsorption isotherms, and qu asielastic neutron scattering (QENS) measurements. The second layer of HD shows solid (S), liquid (L), and gaseous (G) [vapor (V)] phases, w ith two-dimensional (2D) characteristics. We determined the S-L-V trip le line at T-t(2D)=8.44 K, and the L-V critical temperature at T-c(2D) =11.45 K. QENS identified the L phase and measured its translation dif fusion coefficient D-T(approximate to 10(-5) cm(2) s(-1) at 9.25 K). I sosteric heats, latent heat, and entropy change at melting, and solid Debye temperatures are calculated. The results are used to construct a general graph of critical and triple points of adsorbed gases as a fu nction of their quantum parameter.