Preparation and performance of a CsI scintillation screen with a double-period structure based on an oxidized silicon micropore array template.

A structured double-period CsI scintillation screen was successfully developed to improve its detection efficiency based on an oxidized silicon micropore array template with a period value on the order of micro-scale. The structure comprises a main structure along with a sub-structure. The main structure with a period of 8 µm was arranged in a square array consisting of square columnar scintillator units. The micropore walls between the main structure units were purposely fabricated from a SiO2-Si-SiO2 layered structure. The pore walls in commonly used single-structure with a period of 4 µm use the same layered structure composition to obtain a fair comparison. The thickness of both Si and the SiO2 layers was around 0.4 µm. The unique feature of the double structure lies in the even separation of each unit within the main structure into four square columnar scintillator sub-units. These four sub-units within each sub-structure were isolated solely by SiO2 layers with a thickness of approximately 0.8 µm. As a result, the X-ray-induced optical luminescence intensity of the double-structure screen exhibited a 31% increase compared to the corresponding single-structure scintillation screen. In X-ray imaging, a spatial resolution of 109 lp/mm was achieved, which closely matched the results obtained with the single-structure CsI screen. Furthermore, the detective quantum efficiency also displayed a notable improvement.

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.

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.

Influence of the thickness of a SiO2 reflective layer on the performance of a structured CsI(Tl) scintillation screen based on an oxidized Si micropore array template in X-ray imaging.

To obtain better light guidance and optical isolation effects under a limited microcolumn wall thickness, the influence of the thickness of a SiO2 reflective layer on the performance of a structured CsI(Tl) scintillation screen based on an oxidized Si micropore array template in X-ray imaging was simulated. The results show that the SiO2 reflective layer should maintain a certain thickness to achieve good light-guide performance. However, if the template is entirely composed of SiO2, the light isolation performance of the microcolumn wall will be slightly worse. The results provide a basis for optimizing the thickness of SiO2 reflective layer.

Influence of Si wall thickness of CsI(Tl) micro-square-frustums on the performance of the structured CsI(Tl) scintillation screen in X-ray imaging.

To improve the detection efficiency of the structured scintillation screen with CsI(Tl) micro-square-frustums based on oxidized Si micropore array template in the case of a period as small as microns, the influence of Si wall thickness of the CsI(Tl) micro-square-frustums on the performance of the structured screen in X-ray imaging was investigated. The results show that when CsI(Tl) at the bottom of the screen is structured, the detective quantum efficiency (DQE) improves at almost all spatial frequency as the top thickness of the Si wall tSi decreases. However, when CsI (Tl) at the bottom of the screen is not structured, the DQE becomes better at low-frequency and worse at high-frequency as tSi decreases. The results can provide guidance for optimizing tSi according to the comprehensive requirements of detection efficiency and spatial resolution in X-ray imaging.

Performance of a CsI(Tl) scintillation screen with a dual-periodic structure based on an oxidized silicon micropore array template in X-ray imaging.

To address the reduction in the detection efficiency of a structured CsI(Tl) scintillation screen when its structure period reaches the order of microns, a dual-periodic structure of the screen is proposed. The special feature of the dual structure is that each unit of the primary structure is divided equally into either four or nine square column-shaped scintillation sub-units. The sub-units are separated only by SiO2 layers to form a secondary structure. The results show that the performance of a dual-structure CsI(Tl) screen in X-ray imaging is much better than that of a corresponding single-structure screen.

Influence of silicon wall thickness on the performance of structured CsI(Tl) scintillation screen based on oxidized silicon micropore array template in X-ray imaging.

The influence of silicon wall thickness on the performance of structured CsI(Tl) scintillation screen based on oxidized silicon micropore array template in X-ray imaging was simulated using Geant4 Monte Carlo simulation code in terms of light output (LO), modulation transfer function (MTF) and detective quantum efficiency (DQE). The results show that when the thickness of the silicon wall is less than 0.5 µm, the increase in the bottom light output (BLO) of the screen and the decrease in the spatial resolution of the X-ray imaging system using the screen become more significant as the thickness decreases. At low spatial frequency, the thicker the silicon wall, the lower the DQE. However, the DQE with a thick silicon wall can exceed the DQE with a thin silicon wall at high spatial frequency. All the results provide the quantitative relation between the silicon wall thickness of the structured CsI(Tl) scintillation screen and the quality of the X-ray imaging.

Simulated performances of pixelated CsI(Tl) scintillation screens with different micro-column shapes and array structures in X-ray imaging.

The performances of the pixelated CsI(Tl) scintillation screens based on oxidized silicon micro-pore array templates with different CsI(Tl) micro-column shapes and array structures in X-ray imaging were simulated using the Geant4 Monte Carlo simulation code. The shapes of the micro-columns include square, hexagonal and circular, and the array structures include square and hexagonal arrangements. The pitch size of the pixelated CsI(Tl) scintillation screens was set to 4 µm, and the incident X-ray energy was set to 20 keV. The ratios of the number of scintillation photons that propagate along the CsI(Tl) micro-columns to the total number of scintillation photons of the micro-columns gradually decrease with the increase in total reflection time on the lateral surfaces of the micro-columns. However, these ratios are closely related to the shapes of the micro-columns and the incident positions of X-ray on the cross-sections of the micro-columns, especially for the circular micro-column. The sequence of bottom light outputs stimulated by a uniform flood field of X-ray from high to low corresponds to the circular, square and hexagonal CsI(Tl) micro-columns with the same cross-section areas. In addition, all spatial resolutions in terms of modulation transfer functions (MTFs) for the pixelated CsI(Tl) scintillation screens with square and hexagonal array structures are over 100 lp/mm. However, the resolution for the pixelated screen with the hexagonal array structure is approximately 8.5% higher than that for the screen with the square array structure. Moreover, the former screen has a higher detective quantum efficiency (DQE) than the latter screen at the same thickness. The pixelated CsI(Tl) scintillation screen with circular micro-column and hexagonal array structure in X-ray imaging has superior performance compared to other pixelated screens in this work.

Sol-Gel Template Synthesis and Characterization of Lu2O3:Eu3+ Nanowire Arrays.

Uniform Lu2O3:Eu3+ nanowire arrays were successfully prepared by the sol-gel process using anodic aluminum oxide (AAO) templates. The as-synthesized nanowires are homogeneous, highly ordered, and dense and have a uniform diameter of ~300 nm defined by the AAO templates. The X-ray diffraction and selected area electron diffraction results show that the Lu2O3:Eu3+ nanowires have a polycrystalline cubic structure, and the crystallite size of the Lu2O3:Eu3+ nanowires is confined by the AAO template. The nanowires within the AAO template showed good photoluminescence and X-ray-excited optical luminescence performances for Lu2O3:Eu3+. The emission peaks were attributed to the 5D0 → 7FJ transitions of Eu3+ (J = 0, 1, 2, 3).

Development of ZnO-based nanorod arrays as scintillator layer for ultrafast and high-spatial-resolution X-ray imaging system.

Under excitation of high-energy and low-flux density of X-ray beam, a 1-µm system spatial resolution was initially achieved by using an 18-µm thickness ZnO nanorod array as the scintillator layer in X-ray imaging beamline at Shanghai Synchrotron Radiation Facility. The decay time measurements indicated the ultraviolet and visible emissions of the arrays were subnanosecond and nanosecond, respectively. Through hydrogen annealing treatment, the ultraviolet luminescence was intensively enhanced and the visible luminescence was remarkably suppressed simultaneously. In conclusion, it can be determined that the ZnO-based nanorod arrays are the decent candidates for applications in ultrafast and high-spatial-resolution X-ray imaging systems.