AN ULTRAHIGH-VACUUM SINGLE-CRYSTAL ADSORPTION MICROCALORIMETER

The design of an ultrahigh vacuum microcalorimeter enabling calorimetric heats of adsorption to be obtained on single crystal surfaces as a detailed function of coverage is discussed. The system comprises a pulsed supersonic molecular beam source, an ultrathin metal single crystal, and remote infrared temperature sensing. Sticking probabilities and coverages are determined pulsewise by the King and Wells method, and heat capacity calibrations are conducted in situ by laser beam pulsing. Results for CO and O2 on Ni{110} demonstrate excellent sensitivity to adsorption of approximately 10(-13) moles of gas (approximately 0.01 monolayer). The heat capacity of the calorimeter is 4.2-mu-J K-1.