Characterization and application in XRF of HfO₂-coated glass monocapillary based on atomic layer deposition

Coating a glass monocapillary x-ray optics with high-density film is a promising way to improve transmission characteristics. For a long time, it has been a challenge to coat a high-density film in the inside of monocapillary with an extremely high length-to-diameter ratio. In this work, HfO_2 film is deposited on the inner wall of a tapered glass monocapillary with length 9.9 cm, entrance diameter 596.4 μm, and exit diameter 402.3 μm by atomic layer deposition. The coated and uncoated monocapillaries are studied by the transmission process of x-rays with energy from 5 keV to 100 keV and the x-ray fluorescence (XRF) spectra of a Mo sample are detected. Improved transmission characteristics have been obtained for the HfO_2-coated monocapillary. The energy upper limit of focused x-rays increases from 18.1 keV to 33.0 keV and the ‘penetration halo’ is suppressed to some extent. The XRF spectrum presents two stronger peaks at \sim 17.4 keV and \sim 19.6 keV which are considered as the characteristic x-rays of Mo K_\alpha and Mo K_\beta . These results reveal that more higher energy x-rays from the W x-ray tube are totally reflected on the inner wall of the HfO_2-coated glass monocapillary due to the increase of total reflection critical angle. This work is significant for more applications of monocapillary in higher energy x-ray field.