Pulsed desorption kinetics using micromachined microhotplate arrays

Abstract

We demonstrate a technique for obtaining desorption kinetics parameters by applying temperature pulses to small samples. In these experiments we use an array of micromachined hotplates, each with a temperature range from 300 to 1300 K and a thermal response time of 5 ms. Array elements are 100 μm×200 μm and have a mass of 0.4 μg. A metal film is deposited on the microhotplate array surface. After exposing the sample to a gas species of interest, a sequence of temperature pulses of controlled duration is applied to the array elements. The desorption signal from each pulse is recorded using a mass spectrometer. For each temperature, the desorption time constant is determined. A simple Arrhenius plot of desorption time constant versus inverse temperature yields directly the activation energy for desorption and the rate constant prefactor or frequency factor. The results are independent of the pumping speed of the vacuum system. The technique is demonstrated for adsorbed CO on platinum using temperature pulses that range over nearly four orders of magnitude in duration.