Nano Res.[探测]│南京航空航天大学郭万林院士团队聂日明教授课题组:溶液法 Pb₂SbS₂I₃薄膜实现单次曝光双能 X 射线成像

X 射线成像因其非侵入式的内部结构可视化能力，被广泛应用于医疗诊断、安检与工业无损检测等场景。然而，常规 X 射线成像往往缺乏能量分辨能力：不同材料对不同能量 X 射线的吸收差异被“压缩”到单一灰度信号中，导致材料区分度受限。

为提升材料区分能力，双能 X 射线成像（DEXI）通过获取低能与高能两类信息实现能量维度的互补。但现有 DEXI 方案通常依赖多次曝光或复杂、昂贵的能量分辨读出（如光子计数体系），在成本、结构复杂度与可扩展性方面仍存在掣肘。此外，在常见 X 射线管的轫致辐射谱中，低能（软）X 射线成分客观存在，却往往在常规探测中被高能信号“淹没”，难以被有效提取并用于成像。

本工作提出一种“探测式滤光片”思路：在现有探测器前端引入一层可直接探测软 X 射线的吸收层，一方面将软 X 射线信息从混合信号中分离出来，另一方面允许高能 X 射线穿透并由后端常规探测器继续采集，从而在单次曝光中获得互补的能量信息。

我们首次将金属硫卤化物 Pb₂SbS₂I₃应用于 X 射线探测，利用其较高的原子序数与密度，在约 20 μm 厚度下即可实现对 <10 keV 软 X 射线的强吸收，同时对高能 X 射线保持较高透过性。基于溶液法制备的 Pb₂SbS₂I₃ 直接型软 X 射线探测器在低偏压下表现出优异综合性能：灵敏度可达 9669 μC·Gy_air⁻¹·cm⁻²，最低检测限低至 71 nGy_air·s⁻¹，并具备毫秒级响应（0.7 ms/1.6 ms，上升/下降）。进一步地，将 Pb₂SbS₂I₃ 前端层与后端钙钛矿/商用探测器协同集成，可在不改变后端探测器工作方式的前提下实现单次曝光双能成像示范，为在现有成像体系中“捡回”软 X 射线信息提供了模块化、低成本的实现路径。

本研究第一作者为南京航空航天大学博士研究生朱冰鉴，通讯作者包括郭万林院士、张助华教授、聂日明教授和雷威教授，工作由南京航空航天大学与东南大学团队联合完成。

Figure 1. Design Rationale for the Dual-Energy X-Ray Detector. (a) Simulated bremsstrahlung spectra of a conventional gold-target X-ray tube under various tube voltages (40–100 kV). (b) The proportion of soft X-rays (below 10 keV) generated at different tube voltages. (c) X-ray energy ranges suitable for detecting different materials. (d) Schematic of the conceptual imaging process for a conventional single-layer X-ray detector and our proposed dual-layer detector architecture.

Figure 2. Structural and Chemical Characterization of Pb₂SbS₂I₃ for Soft X-Ray Absorption. (a) Simulated X-ray absorption characteristics of Pb₂SbS₂I₃. (b) The ability of Pb₂SbS₂I₃ with various thickness to absorb X-rays. (c) XRD pattern of the optimized Pb₂SbS₂I₃ film. (d) High resolution XPS spectrum of Pb 4f. (e) High resolution XPS spectrum of S 2p. (f) Raman spectrum of Pb₂SbS₂I₃. (g) HRTEM image at 10 nm scale showing well-defined lattice fringes in Pb₂SbS₂I₃. (h) HRTEM image at 2 nm scale, showing lattice spacings of 0.55 nm horizontally and 0.30 nm diagonally. (i) EDS maps showing the uniform distribution of Pb, Sb, S, and I in the Pb₂SbS₂I₃ film, along with BF and HAADF-STEM images at 250 nm scale.

Figure 3. Device Structure Characterization of Pb₂SbS₂I₃. (a) Kelvin probe force microscopy (KPFM) surface potential mapping of Pb₂SbS₂I₃. (b) UV-Vis absorption spectrum of Pb₂SbS₂I₃. Inset: Tauc plot analysis indicating a bandgap of 2.15 eV. (c) Ultraviolet photoelectron spectroscopy (UPS) of Pb₂SbS₂I₃. Inset: magnified region indicating an onset of 1.08 eV. (d) Schematic energy level diagram of the device structure. (e) Cross-sectional device structure schematic of the X-ray detector. (f) Comparison of normalized photocurrent response of Pb₂SbS₂I₃ and normal detectors with and without an Al filter to block soft X-rays.

Figure 4. Device Performance of Pb₂SbS₂I₃-based X-ray Detectors. (a) Minimum detection limit for the optimized 1.3 mol/L device. (b) Response time measurements showing a rise time of 0.7 ms and fall time of 1.6 ms. (c) Performance comparison with existing soft X-ray detectors. (d) Setup for resolution testing using stepwise scanning across a metal edge. (e) Edge spread function (ESF). Line spread function (LSF). (f) Modulation transfer function (MTF) plot showing a resolution of 7.2 lp/mm at 20% contrast threshold. (g) Radiation stability test after 20 minutes of high-energy X-ray exposure. (h) Stability testing under continuous unencapsulated X-ray exposure at 20 kV and 100 µA.

Figure 5. Enhanced Dual-Energy Imaging with Pb₂SbS₂I₃-based Soft X-ray Detection. (a) Normalized current response line plots for X-ray imaging with and without a Pb₂SbS₂I₃ detector. The left plot represents the conventional X-ray detector image without Pb₂SbS₂I₃ detector while the right plot includes the Pb₂SbS₂I₃ detector. (b) Schematic of rail-guided dual-detector imaging system. (c) Line plot of signal intensity along the center line of a scanned leaf structure. (d) Comparison of Pb₂SbS₂I₃ and normal detector images of a leaf. (e) Dual-energy imaging results for a composite leaf and nail object, showing the soft X-ray detector image (left), hard X-ray detector image (middle), and a dual-energy subtraction image (right), with color mapping distinguishing the leaf in green and the nail in blue.

聂日明教授为南京航空航天大学教授、博士生导师，主要从事空天能源与探测相关研究，包括钙钛矿/金属硫族-卤族化合物器件、光电探测器与 X 射线探测等方向。

招生信息：课题组招收钙钛矿/金属硫族-卤族化合物太阳能电池方向硕士研究生 2–3 名、博士研究生 1–2 名，并招收博士后及研究助理若干名；联系邮箱：rmnie@nuaa.edu.cn。