Frequency of the surface collective mode for submonolayer (open symbols) and saturated (solid symbols) films vs temperature in the low-temperature region. Lines connect successive spectra in temperature scans.
Lattice constant vs chemical potential along isothermal pressure scans at temperatures between 109 and 180 K. The lattice constant (or mean nearest-neighbor distance) is calculated from the frequency as described in the text. Chemical potential is measured relative to its value at coexistence with bcc bulk.
Expanded plot of lattice constant vs chemical potential in the IC2 region between 140 and 170 K.
monolayer phase diagram in the intensive variables chemical potential and temperature. Solid symbols are measured layer condensation points. Open symbols are measured (centers of) phase transitions. monolayer; IC1 and IC2 are incommensurate solid phases; monolayer; bulk; centered cubic bulk. Chemical potential is measured relative to monolayer—bcc bulk coexistence (extrapolated).
Measured widths of the layer condensation step (crosses with error bars). The fitted line has the power law dependence of the 2D Ising model with critical temperature of 156 K.
Phase diagram in the variables areal density and temperature based on our data. monolayer; IC1 and IC2 are incommensurate solid phases; monolayer; vapor; bulk; centered cubic bulk. The melting transition is presented as a first-order coexistence region, but this actually may be a region of rapid density change in a continuous transition. The IC2 region presumably terminates in the vicinity of 210 K. The liquid-vapor coexistence region is based solely on the measured critical temperature of 156 K. By coincidence, the saturated film transition from C to IC1 and the bulk transition from monoclinic to bcc occur at nearly the same temperature.
Lattice constant vs temperature: comparison with x-ray data. The lines are interpolated from our data for submonolayer (left) and saturated monolayer (right) films. Crosses are data points. The solid symbols are x-ray data for saturated films and open symbols are x-ray data for nominally submonolayer films: triangles are from Refs. 2 and 3, circles are from Ref. 4.
Spreading pressure at saturation vs temperature calculated from our data. This is a direct measure of the resistance to displacement by a second adsorbate in the absence of mutual solubility.
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