Quantitative measurement of the deformation of ultra-thin platinum foils during adsorption and reaction of CO and O2

An ultra-thin self-supporting Pt-foil with a thickness of 300 nm and 4 mm diameter has a heat capacity of only 10 μJ/K. Thus, even small amounts of heat deposited within the thin metal foil cause a significant temperature increase. During the adsorption of, for example, CO heat in the order of 30 μJ/ML is released into the metal. If the rim of a Pt(1 1 0) single crystal foil is rigidly mounted on a substrate, a temperature increase of the foil induced by adsorption and reaction of CO and O2 causes thermo-elastic stress. This will lead to macroscopic deformations of the metal foil. To quantify these deformations an imaging Michelson-interferometer was set up, capable to detect small deflections of the ultra-thin Pt catalyst down to 10-20 nm. Adsorption of CO and O2 causes a clear mechanical response of the Pt foil. Depending on sample temperature and partial pressures of the reactants fronts and pulses of deformation were found. The system can be calibrated by using continuous and chopped laser light. The optical properties of the catalytic surface change in the presence of adsorbates. This complicates the analysis, but can be avoided in an improved setup.