Surface elemental analysis in ambient atmosphere using electron-induced x-ray fluorescence

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 that was used for the demonstration of the ability of the transmitted electrons to excite the XRF spectra in the external atmosphere consisted of an actively pumped chamber from within which the electrons were transmitted—not a portable instrument. The AEXS instrument that has been assembled in our laboratory during the past year consists of a miniature 20 keV electron microprobe that is vacuum sealed with a thin SiN membrane and requires no active pumping—a big step towards the development of a stand-alone instrument. The microprobe has been in operation for over one year and is used for performing rapid elemental analysis of NIST and USGS traceable metal and mineral standards, with good agreement with the certified composition for samples in up to about 90 Torr cm thick external atmospheres.