Solving the 'Micro-to-Macro' Spatial Scale Problem with Milliprobe X-ray Fluorescence/X-ray Spectrum Imaging

摘要

Milliprobe x-ray fluorescence (mXRF) with x-ray spectrum imaging (XSI) enables elemental mapping over centimeter lateral distances with a resolution of 40.150 μm. While highly complementary to classic elemental mapping scanning electron microscopy/energy dispersive x-ray spectrometry (SEM/EDS), mXRF has several advantages: (1) The lack of electron bremsstrahlung in the XRF spectrum, except for the elastic scattering of the primary continuum, means that the inherent detection sensitivity of mXRF is better. (2) The broad continuum excitation of mXRF enables sensitive access to secondary x-rays with photon energies in the range 10 keV to 40 keV, which are either not efficiently excited or are completely inaccessible with SEM. (3) The range of penetration of x-rays (with minimal sideways scatter) is typically 10 to 100 times the range of an electron beam, enabling deeper probing into the specimen or even viewing the specimen through protective covering such as glass or plastic. (4) The vacuum requirements of mXRF are much less than even environmental SEM, and primary excitation and secondary detection can occur through an atmospheric gas path if required. The scale of mXRF-XSI mapping is particularly useful for attacking problems that require following compositional structures over a wide spatial scale, the classic "micro-to-macro" spatial scale challenge.