Atmospheric electron-induced X-ray spectrometer (AEXS) development

The progress in the development of the atmospheric electron X-ray spectrometer (AEXS) described. The AEXS is a surface analysis tool based on the excitation of characteristic X-ray and luminescence spectra at ambient pressure using an electron beam. In situ operation for the AEXS is obtained through the use of a thin electron transmissive membrane to isolate the vacuum of the electron source from the ambient atmosphere, resulting in rapid spectrum acquisition, nondestructive evaluation of surfaces, and moderate-to-high variable spatial resolution in comparison to similar portable instruments. The applications of the instrument for NASA planetary exploration include determination of elemental abundance and identification of minerals suspect of past biological activities, through correlation of X-ray and optical luminescence data. The proof-of-principle for the instrument is being demonstrated through 1) simulation of observational capabilities for the instrument, 2) characterization of the effect of thin membranes on the properties of the excitation beam, and 3) assembly and characterization of a membrane-encapsulated prototype instrument. The observational capabilities for the instrument are simulated through acquisition of X-ray and luminescence spectra using the scanning electron microscope (SEM), cathodoluminescence (CL) spectrometer, and an environmental chamber that was constructed in our laboratory to simulate the effect of Mars planetary atmosphere. The effect of the membrane is determined by comparing the spectra acquired from metal and mineral samples with and without the membrane intersecting the excitation beam, and from samples in the laboratory ambient and in the environmental chamber. The comparison isolates the effect of membrane and atmosphere interactions, which determine performance limits for AEXS in situ operation. A breadboard vacuum-encapsulated stand-alone instrument requiring no vacuum apparatus support is being assembled in our laboratory.