Title : Enhancement of properties of HfO2-coated glass monocapillary
The glass monocapillary X-ray optics works based on total external reflection of X-rays. And a glass monocapillary with inner high-density film coating is expected to improve the transmission characteristics. Here ~150 nm HfO2 film is deposited on the inner wall surface of the tapered glass monocapillary with entrance diameter 596.4 μm, exit diameter 402.3 μm and length 9.9 cm by atomic layer deposition (ALD). The full energy spectrum and the light intensity gain of X-rays focused by monocapillary before and after coating are measured and calculated. As one of the theoretical advantages, energy broadening of focused X-rays is observed by using HfO2-coated glass monocapillary. The highest energy of X-ray is improved from ~18 keV to ~33 keV and the light intensity gain of X- rays between 16 keV and 20 keV reaches 2.5, which is the result of more higher energy X-rays from the W X-ray tube being totally reflected on the inner wall of the HfO2-coated glass monocapillary due to the increase of total reflection critical angle. In addition, HfO2-coated glass monocapillary shows ability to suppress the ‘penetration halo’ because of the absorption of more high energy X-rays by the HfO2 film. Besides that, ~50 nm HfO2 film is deposited on the inner wall surface of another tapered glass monocapillary with entrance diameter 459 μm, exit diameter 374 μm and length 5 cm also by ALD. The ~50 nm HfO2-coated monocapillary is used in X-ray fluorescence (XRF) experimental system. Comparing the two energy spectra of sample Mo obtained by uncoated and coated monocapillaries, the energy spectrum of HfO2-coated monocapillary appears two new peaks at ~17.4 keV and ~19.6 keV. It’s because that the X-rays focused by HfO2-coated monocapillary is higher than the absorption edge of Mo and the characteristic peaks of Mo are excited, which also indicates the extension of the energy range of the X-rays focused by HfO2-coated monocapillary.
Audience take away:
• Highly homogeneous thin film (several angstrom) can be deposited on the surfaces of flat and curved substrates by ALD.
• High-density film coated capillary can be used in micro-XRF to excite higher energy characteristic peaks of the sample.
• High-density film coated capillary can be used in X-ray microscope to obtain high resolution.