Optimization of SiO₂ reflective layer thickness for improving the performance of structured CsI scintillation screen based on oxidized Si micropore array template in X-ray imaging

Abstract

Structured scintillation screen based on oxidized Si micropore array template can effectively improve the spatial resolution of X-ray imaging. The purpose of this study is to investigate the effect of SiO2 layer thickness on the light guide and X-ray imaging performance of CsI scintillation screen when the structural period is as small as microns. Cylindrical micropores with a period of 4.3 µm, an average diameter of 3.3 µm and a depth of about 40 µm were prepared in Si wafers. SiO2 layer was formed on the pore walls after thermal oxidation. Increasing SiO2 layer thickness would be beneficial to the propagation of scintillation light along the cylindrical channels. What was not previously anticipated was that the pore size gradually shrank as the SiO2 layer thickened. The pore shrinkage would reduce the filling rate of CsI in the templates and thus would reduce the production of scintillation light. The structured CsI scintillation screens with different SiO2 layer thicknesses were fabricated by filling CsI scintillator into the oxidized silicon micropore array template. The morphology, crystallinity, X-ray excited optical luminescence, and X-ray imaging performance of the screens were studied. The results show that the spatial resolutions of X-ray images measured using the structured CsI scintillation screens with different SiO2 layer thicknesses are close to each other, and they are all about 110 lp/mm. However, the X-ray excited optical luminescence of the screen and detective quantum efficiency of X-ray imaging vary with the thickness of the SiO2 layer. The optimal thickness is about 350 nm.

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“…This groundbreaking technology finds application in a myriad of fields, including medical imaging, nondestructive inspection, industrial testing, and material sciences. − Consequently, the pursuit of “better scintillators” to facilitate superior quality X-ray indirect imaging has garnered immense attention. Recent studies have unveiled that “nanophotonic scintillators”, achieved by two-dimensional periodic etching on scintillators or materials atop them, harbor the capacity to manipulate the optical field response on a scale commensurate with the wavelength of light at the scintillator exit surface. − This can engender substantial enhancements in scintillation yield and spectral response. − However, it must be accentuated that these studies have predominantly centered on bolstering the photon output of scintillators with the pivotal facet of improving signal reception quality warranting further meticulous exploration. It should be noted that the periodic subwavelength structure on the scintillators, responsible for modulating the input light signal, is, in essence, an encoding mechanism within the spatial frequency domain.…”