Multilayer phase diagram of CF₄ adsorbed on graphite

Layer transitions in CF₄ adsorbed on graphite are studied by vapor-pressure isotherm measurements in the range one to eight layers and 52 K <T<104 K, using an ellipsometric technique to measure the coverage on a single surface. A maximum of two layers adsorb below 71 K. Above 71 K we observe for the first time the condensation of a double-layer (third and fourth), which splits into separate layers above a triple point at 75 K. The fifth layer appears at 80 K, the sixth at 87 K, and at least eight discrete layers are seen over several kelvin above the bulk melting point at 89.5 K. The slopes of the layer chemical potentials versus temperature yield estimates of the locations of phase transitions and of entropy differeneces.