Temperature dependence of the phase diagram of Cl/Ag(100)

Using low-energy electron diffraction, we have determined the coverage at which overlayers of Cl adsorbed on Ag(100) order into a c(2×2) structure for sample temperatures ranging from 300 to 500 K. We find no evidence for a variation in the critical coverage ${\theta }_o$ over this temperature range. However, experimental uncertainties in the values of ${\theta }_0$ are too large to rule out the small variation predicted by an interacting-hard-square model with only next-nearest-neighbor repulsions. We find that the addition of modest third-neighbor repulsions to the model improves agreement of transfer-matrix scaling calculations with experimental measurements.