Reentrant first-order layering transitions in multilayer argon films on graphite

We report ellipsometric coverage--vapor-pressure isotherm measurements for argon on graphite over the temperature range 64 to 84 K, which resolve up to eight layers. We confirm previous observations that the first-order layering transitions broaden near 67 K. However, in the fourth and higher layers, condensation again becomes sharp and apparently first order in the range between about 73 K and a new series of layer critical points near 77 K. Thus the surface roughening transition is above 77 K and the behavior near 67 K represents disordering of only the top layer of the film.