X-ray study of molecular oxygen adsorbed on graphite

Melting and Wetting Behavior in Oxygen Films

“…The system of oxygen on exfoliated graphite has received considerable attention and much of the phase diagram is well understood. 1 Our interest here is focused on melting and possible wetting behavior. In an extensive series of experiments we have measured the magnetic susceptibility and heat capacity of oxygen films on Grafoil exfoliated graphite from submonolayer to multilayer coverages.…”

Magnetic and melting transitions of oxygen monolayers and multilayers physisorped on exfoliated graphite

“…Fluid I, which is a higher-temperature phase, is considered to be a normal liquid phase, while in fluid II a very broad peak was observed in the XRD measurement in this coverage region. 7,8,10 The structure of fluid II in this coverage region is not clear. The observed anisotropy of suggests at least that in fluid II the molecular axis does not have a random distribution though the translational symmetry may be almost lost.…”

“…[7][8][9][10][11][12][22][23][24][25] The melting temperature of the ␦ phase is increased from Tϭ25.5 to 31.8 K as the coverage increases from Cϭ1.0 to 1.2. The previous LEED experiments proposed the existence of a phase above the melting temperature of the ␦ phase, which is believed to be a 2D solid with molecular axis disorder.…”

“…This means the density of the phase is not changed with coverage, which is consistent with the XRD experiments. 8 The LEED experiment reported previously two different monolayer phases in the phase, that is, 1 and 2 phases and found the transition temperature at Tϭ18 K between the 1 and 2 phases. 27 However, we could not observe any anomaly of in this temperature region.…”

“…These temperatures are considered the melting temperatures of first and second layers, respectively, as proposed by XRD measurements. 8,9 Namely, in the XRD model there is the phase between these temperatures, which consists of a solid first layer and a fluid second layer. The coverage dependence of the changes of at Tϭ38.4 and 39.0 K is consistent with this model as described later.…”