Adsorption of CF₄ on graphite preplated with a monolayer of CF₃Cl

We report a study of the adsorption of CF₄ on graphite preplated with a monolayer of CF₃Cl, using infrared reflection absorption spectroscopy combined with ellipsometry. The saturated vapor pressure of CF₃Cl is nearly 3 orders of magnitude smaller than that of CF₄ at the same temperature, so the main control variables are the temperature and the pressure (or chemical potential) of CF₄, together with the initial coverage of CF₃Cl. The temperature range covered is 60–105 K. We find that, if the initial monolayer of CF₃Cl is liquid, CF₄ continuously displaces CF₃Cl by substitution in the monolayer. If the initial monolayer of CF₃Cl is solid, due to either lower temperature or compression, CF₄ condenses as a second layer on the top of the CF₃Cl layer, with only slight mixing with the original layer. This behavior persists to multiple layers of CF₄.