Second-layer phase compressed monolayers

Before discussing compressed monolayers with their even richer behavior than the submonolayer regime we note that the experimental determination of the coverage gets more difficult due to possible second-layer adsorption [90, 93]. Thus, the coverages marking a phase boundary may differ between various experimental techniques and groups (see the discussion in Section I.C). 

Figure 48. Semilogarithmic plot of the isothermal compressibility of N2 on boron nitride at 60.8 K as a function of the coverage in units of the complete /3 monolayer. The peak sequence starting at low coverages is attributed to the fluid to commensurate solid F-C and commensurate solid to reentrant fluid C-RF transitions and finally to second-layer growth RF-B (instead of a transition from the reentrant fluid to an incommensurate solid phase). (Adapted from Fig. 5 of Ref. 1.)...

Beyond a compression to about 1.4 monolayers, evidence for a second-layer fluid on top of the incommensurate monolayer solid is found in the calorimetric study [112] (see the phase diagram. Fig. 49). A second-layer... 

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