Low-temperature adsorption microcalorimetry: Pb on MgO(100)

The heat of adsorption of Pb on an MgO(100) thin film at 190 K is measured calorimetrically as a function of coverage using a removable pyroelectric polymer ribbon as the heat-detecting element. This is the first demonstration that this versatile method of heat detection can be used for single-crystal adsorption calorimetry at cryogenic conditions. The results are compared to earlier measurements at room temperature. Similar to room temperature, the initial heat of adsorption at 190 K is similar to 100 kJ/mol. However, the heat of adsorption grows much more slowly with coverage toward the bulk heat of sublimation, consistent with a larger Pb island density (and smaller, flatter islands) at low temperature. Measurement of the sticking probability for Pb onto the MgO(100) thin film at temperatures down to 167 K are also consistent with this.