Molecular beam static secondary ion mass spectrometry for surface analysis

The chemistry at surfaces is playing an increasing role in understanding the fate of chemicals in the environment and in technologies that utilize surface coatings and thin films. Understanding the chemistry of the very top monolayer has been hampered by the difficulty in probing only this region (without penetrating into the bulk of the solid). We have developed two unique technologies that enable static secondary ion mass spectrometry to be used in this application. Pulsed extraction sample neutralization overcomes the sample charging problems commonly encountered with electrically non-conducting samples, and our molecular anion primary beam heightens sensitivity for molecular compounds. We are also combining these with ion trap mass spectrometry to improve sensitivity and permit multiple stages of mass spectrometry to be performed. This provides increased specificity and the ability to gain a more complete understanding of the chemical environment at the surface. As one example, we have shown that the oxidation/reduction chemistry of the surface of mineral samples can be characterized using probe molecules and static SIMS. The technique is also being applied to detection of trace levels of herbicides and pesticides, for detection and characterization of hazardous wastes, and as a possible method of air sampling via chemically selective surfaces.