Ion Beam Analysis of the Surface of Volatile Liquids and Solids

Surfaces play an especially important role in the chemistry of high vapor pressure material.

U. K. KriegerA., T. Huthwelker A,B., C. DanielB., Th. PeterA. and W. A. LanfordB.

A. Institute for Atmospheric and Climate Science (IACETH), ETH Zürich, Hönggerberg HPP, Ch-8093, Zürich, Switzerland

B. Physics Department, University at Albany, Albany, New York 12222

Surfaces play an especially important role in the chemistry of high vapor pressure material. Measurement of elemental or isotopic concentration profiles on such materials would provide key data for understanding the microscopic mechanism underlying their physical chemistry. However, such measurements present a significant analytical challenge. Most modern profiling methods rely on either sputtering or ion energy loss to derive depth information. Ion beam analysis might seem incompatible with the high vapor pressures associated with these materials. However, we have demonstrated that a simple modification of a conventional ion beam analysis chamber allows these materials to be studied. This approach provides for the first time in situ quantitative concentration profiles for volatile liquids or solids held at controlled ambient pressures up to a few hPa and opens up whole new avenues to the study of this important class of materials.

Our interest in this analytical problem arose from open questions in atmospheric chemistry where important chemical reactions occur in the bulk or on the surface of atmospheric particles (aerosols). These reactions affect the atmosphere's life-protection functions, including shielding from UV radiation and regulation of the global temperature. Common aerosol materials on which such reactions occur include ice and aqueous sulfuric acid droplets. The pressure range of the chamber described here allows the study of aerosol materials under conditions similar to those encountered in the atmosphere.

The experimental chamber is described in the following publication:

RBS Analysis of trace gas uptake on ice.

T. Huthwelker, U. K. Krieger, U. Weers, Th. Peter and W. A. Lanford, Presented at the International Conference on Ion Beam Analysis, Cairns, Australia, July 15-20, 2001 (submitted for publication).