THERMOGRAVIMETRIC ANALYSIS OF SELECTED CONDENSED MATERIALS ON A QUARTZ-CRYSTAL MICROBALANCE

Employing a quartz crystal microbalance and a quadrupole mass spectrom eter in a vacuum chamber, thermogravimetric analyses (TGA) and mass sp ectrometer analyses have born performed at low temperature (90-190 K) on depositions of ammonia, acetone, methanol. toluene, isopropyl alcoh ol, water, para-xylene, and selected combinations of these materials. Deposition of a single species yielded a TGA curve characteristic of a pure substance. Homogeneous binary mixtures, like methanol and water, exhibited a desorption curve which contained structure in addition to that observed for the pure materials. Sequential layering of one mate rial on top of another also altered the TGA response, suggesting subst antial interlayer interactions, and the TGA curve shape was found to b e a function of the top-layer thickness for the water-on-methanol syst em. Backfilling the chamber with nitrogen or argon at a pressure of 1 Torr increased the apparent desorption temperature of water by about 2 0 K. (C) 1995 American Vacuum Society.