AVS 50th International Symposium
    Surface Science Tuesday Sessions
       Session SS-TuP

Paper SS-TuP2
Studying Surface Phenomena by Pulsed Heating of Microdevices

Tuesday, November 4, 2003, 5:30 pm, Room Hall A-C

Session: Poster Session
Presenter: O.C. Thomas, National Institute of Standards and Technology
Authors: O.C. Thomas, National Institute of Standards and Technology
R.E. Cavicchi, National Institute of Standards and Technology
S. Semancik, National Institute of Standards and Technology
Correspondent: Click to Email
MEMS microheater devices have been operated with periodic (2-40 Hz), short duration (5ms) temperature pulses to investigate the relationship between surface adsorbate concentrations and surface electronic behavior of high surface area, oxide films. Tin oxide films were grown by CVD on microscale (40 µm X 100 µm), thermally isolated bridge structures that possess embedded polysilicon heaters and surface electrodes. These structures permit the rapid thermal cycling and real time conductometric measurement of the deposited oxide films. In air devoid of reducing analyte, the application of short, high temperature (500°C, 5 ms) heating pulses results in the generation of surface bound O@super -@ from surface adsorbed O@sub 2@, and as a consequence a tin oxide film that is both highly resistive and highly sensitive to reducing gases. Exposure of such a film to trace concentrations of reducing gas results in large conductometric changes (from 1x10@super -7@ @OMEGA@@super -1@ in dry air to 2.5x10@super -4@ @OMEGA@@super -1@ in 10 ppm MeOH; measured at 25 °C). In the presence of reducing gases, the heating pulses activate the titration of the surface bound O@super -@ by the reducing species. Modulating the period between heating pulses from 25 ms to 500 ms reveals an increase in room temperature conductance, which is interpreted in terms of the adsorption dynamics of the reducing species. Results on a number of reducing gases show conductance vs. period profiles, which may be explained in terms of both molecular adsorption dynamics and stoichiometric capacity for reduction. These results provide a basis for analyte recognition and a level of mechanistic insight about interfacial transduction processes.