Atmospheric Electron Induced X-Ray Spectrometer (AEXS) Development

The progress in the development of the Atmospheric Electron X-ray Spectrometer (AEXS) is described. The AEXS is a surface analysis tool based on excitation of characteristic X-ray fluorescence (XRF) spectra from samples in ambient atmospheres using a focused electron beam. Operation in ambient atmospheres with moderate-to-high spatial resolution in comparison to similar instruments is obtained through the use of a thin electron transmissive membrane to isolate the vacuum of the electron probe, obviating the need for the samples to be drawn into the probe vacuum. Our initial setup consisted of an actively pumped chamber from within which the electrons were transmitted -not a portable instrument. The instrument that has been assembled and used to acquire XRF spectra in our laboratory during the past two years consists of a 20 keV electron tube sealed with a SiN membrane and requires no active pumping -a big step towards the development of a stand-alone instrument. The microprobe was used to perform elemental analysis of NIST and USGS standards, with good agreement with the certified composition for samples in up to about 90 Torr-cm thick atmosphere, and for resolving the composition of mm-sized mineral grains in inhomogeneous samples, a big improvement over the several cm-scale spatial resolution of the APXS instrument that flew on NASA's MER mission.