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O: Fachverband Oberflächenphysik

O 89: Methods: other (experimental)

O 89.2: Vortrag

Donnerstag, 17. März 2011, 17:30–17:45, WIL B321

Microcalorimetry Based on Thermally Induced Deformations of Ultra-thin Single Crystals — •Christian Punckt¹, Pablo Sanchez Bodega², and Harm Hinrich Rotermund² — ¹Dept. of Chem. and Biolog. Engineering, Princeton University, Princeton, NJ 08544 — ²Dept. of Physics and Atmospheric Science, Dalhousie University, Halifax, NS B3H 3J5, Canada

We show that ultra-thin metal foils can be used to measure the heat of adsorption of molecular species with a sensitivity of a few nJ by monitoring their thermally induced mechanical deformation. A platinum foil with a thickness of 300 nm and 4 mm diameter has a heat capacity of 10 µJ/K. As carbon monoxide (CO) adsorbes on its surface, about 30 µJ of adsorption heat per monolayer are released. Therefore even the adsorption of fractions of a monolayer increases the foil temperature sufficiently, such that thermo-elastic stress leads to buckling of the foil. In order to detect this deformation, we set up an imaging interferometer capable of measuring deflections of a few tens of nanometers. We observe that adsorption of CO and oxygen causes a significant mechanical response of the Pt foil. Additionally, we can detect heat release during the oxidation of CO on the platinum catalyst. Fronts and pulses of deformation are found which we relate to reaction patterns on the catalyst surface. Our work provides a proof-of-concept for the direct measurement of adsorption heat based on a simple chemo-thermo-mechanical mechanism that operates in a wide temperature and pressure range. The system can be calibrated using continuous or pulsed laser light.