PULSED DESORPTION-KINETICS USING MICROMACHINED MICROHOTPLATE ARRAYS

We demonstrate a technique for obtaining desorption kinetics parameter s by applying temperature pulses to small samples. In these experiment s 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 el ements are 100 mumX200 mum and have a mass of 0.4 mug. A metal film is deposited on the microhotplate array surface. After exposing the samp le to a gas species of interest, a sequence of temperature pulses of c ontrolled duration is applied to the array elements. The desorption si gnal from each pulse is recorded using a mass spectrometer. For each t emperature, the desorption time constant is determined. A simple Arrhe nius plot of desorption time constant versus inverse temperature yield s directly the activation energy for desorption and the rate constant prefactor or frequency factor. The results are independent of the pump ing speed of the vacuum system. The technique is demonstrated for adso rbed CO on platinum using temperature pulses that range over nearly fo ur orders of magnitude in duration.