Atmospheric Electron-induced X-ray Spectrometer (aexs) Instrument

Introduction: The progress in the development of the 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-tohigh 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. The AEXS system (Fig 1) consists of an electron microprobe encapsulated by the isolation membrane, and an EDX detection and analyzer system to determine the elemental abundance. Our initial, previously reported setup that was used for the demonstration of the ability of the transmitted electrons to excite 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 20keV electron gun 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 1 year and 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. The approach towards instrument development has been through 1) demonstrating the viability of microfabricated membranes, 2) assembling AEXS setups with increasingly integrated functional components, and 3) simulating the AEXS observational capabilities. This paper focuses on instrument assembly.