OBSERVATION OF A CHEMICAL-REACTION USING A MICROMECHANICAL SENSOR

We describe a new form of calorimeter designed for use in gaseous and vacuum environments which can sense chemical reactions with an estimated sensitivity limit of approximate to 1 pJ. The device is based on a micromechanical Si lever coated with a thick layer of Al upon which a sample in the form of a thin layer is fixed or deposited. Heat fluxes are detected by measuring the cantilever deflection induced by the differential thermal expansion of the lever (bimetallic effect) using the optical position sensor from a force microscope. The limit of sensitivity to local temperature changes is approximate to 10(-5) K at 300 K. Using this technique the catalytic conversion of H-2 + O-2 to form H2O over a thin Pt overcoated layer is observed to exhibit self-sustained oscillations in the reaction rate on the macroscopic scale.