Measuring X-ray fundamental parameters with superconducting transition-edge sensor microcalorimeters with a laser calibration system with comparisons to theory

X-ray fundamental parameters exist for each element and characterise them in terms of emission energies, spectral line shape, intensities, etc. These reference data are critical for a range of industrial and scientific purposes. Specifically, the semi-conductor industry needs new high accuracy X-ray data as novel elements are used and circuits get smaller requiring more precise data for imaging. Some X-ray emission energies are known to 1 ppm, others to well over 100 ppm, or not existing/traceable to the S.I at all. These issues are emphasised in the soft X-ray regime.

We have made measurements of the L-lines of Ga, Ge, Se, and As, and some of their compounds using a superconducting transition-edge sensor microcalorimeter. Calibrating X-ray energies to the S.I. is performed with a laser calibration system where discrete 405 nm (3.06 eV) laser photons are counted providing a dense calibration curve. An optical setup with a cryogenic steerable mirror focusses the laser beam onto single sensors in an array of 256. Stimulating sensors individually eliminates cross-talk and permits measurements at the ppm level. These measurements support traceable standards for materials and semiconductor analysis.

Ab initio multiconfiguration Dirac-Hartree-Fock calculations are performed for comparison. The pairing of high accuracy, high resolution, X-ray data with state-of-the-art atomic physics provides insight into theoretical atomic physics questions such as anomolous asymmetries and intensity ratios.