APbI3-A2AgBiI6 Double-Layer Perovskite Film for a Self-Powered and High-Stability X-ray Detector

The development of lead halide perovskite X-ray detectors has promising applications in medical imaging and security inspection but is hindered by poor long-term stability and drift of the dark current and photocurrent. Herein, we design a (Cs0.05MA0.65FA0.3)PbI3-(Cs0.1MA1.3FA0.6)AgBiI6 double-layer perovskite film to assemble a self-powered flat-panel X-ray detector. The demonstrated X-ray detector achieves an outstanding self-powered sensitivity of 80 μC Gyair-1 cm-2 under a 0 V bias. More importantly, owing to the inhibition of the phase transition process and ion migration of (Cs0.05MA0.65FA0.3)PbI3 by the (Cs0.1MA1.3FA0.6)AgBiI6 layer, the device exhibits excellent continuous operating stability with a retention rate of 99% dark current and photocurrent over X-ray pulses of up to 4000 s and excellent long-term stability without a loss of the original response current after 150 days in an air environment. The strategy of double-layer perovskites improves the stability and sensitivity of devices, which paves a path for the industrial application of lead halide perovskite X-ray detectors.

Aging CsPbBr3 Nanocrystal Wafer for Ultralow Ionic Migration and Environmental Stability for Direct X-ray Detection

The outstanding photoelectric properties of perovskites demonstrate extreme promise for application in X-ray detection. However, the soft lattice of the perovskite results in severe ionic migration for three-dimensional materials, limiting the operation stability of perovskite X-ray detectors. Although ligand-decorated nanocrystals (NCs) exhibit significantly higher stability than three-dimensional perovskites, defects remaining on the interface of NCs could still trigger halide migration under a high bias due to the incomplete ligand decoration. Furthermore, it is still challenging to realize sufficient thickness of absorption layers based on NCs for X-ray detectors through traditional methods. Herein, we develop a centimeter-size and millimeter-thick wafer based on CsPbBr3 NCs through isostatic pressing for X-ray detectors, in which the interfacial defects of NCs are remedied by CsPb2Br5 during aging of wafer in ambient humidity. The wafer shows outstanding sensitivity (200 μC Gyair-1 cm-2) and ultralow dark current drift (1.78 × 10-8 nA cm-1 s-1 V-1 @ 400 V cm-1). Moreover, it shows storage stability with negligible performance degradation for 60 days in ambient humidity. Thus, aging perovskite NC wafers for X-ray detection holds huge potential for next-generation X-ray imaging plates.

Stereo-Hindrance Engineering of A Cation toward <110>-Oriented 2D Perovskite with Minimized Tilting and High-Performance X-Ray Detection

2D <100>-oriented Dion-Jacobson or Ruddlesden-Popper perovskites are widely recognized as promising candidates for optoelectronic applications. However, the large interlayer spacing significantly hinders the carrier transport. <110>-oriented 2D perovskites naturally exhibit reduced interlayer spacings, but the tilting of metal halide octahedra is typically serious and leads to poor charge transport. Herein, a <110>-oriented 2D perovskite EPZPbBr4 (EPZ = 1-ethylpiperazine) with minimized tilting is designed through A-site stereo-hindrance engineering. The piperazine functional group enters the space enclosed by the three [PbBr6 ]4- octahedra, pushing Pb─Br─Pb closer to a straight line (maximum Pb─Br─Pb angle ≈180°), suppressing the tilting as well as electron-phonon coupling. Meanwhile, the ethyl group is located between layers and contributes an extremely reduced effective interlayer distance (2.22 Å), further facilitating the carrier transport. As a result, EPZPbBr4 simultaneously demonstrates high µτ product (1.8 × 10-3 cm2 V-1 ) and large resistivity (2.17 × 1010 Ω cm). The assembled X-ray detector achieves low dark current of 1.02 × 10-10 A cm-2 and high sensitivity of 1240 µC Gy-1 cm-2 under the same bias voltage. The realized specific detectivity (ratio of sensitivity to noise current density, 1.23 × 108 µC Gy-1 cm-1 A-1/2 ) is the highest among all reported perovskite X-ray detectors.

Evaluation of a Large Area, 83 μm Pixel Pitch Amorphous Selenium Indirect Flat Panel Detector

Dual-layer detectors provide a low-cost solution to improved material decomposition and lesion differentiation in X-ray imaging, while eliminating motion artifacts from multiple exposures. Most designs utilize two indirect detectors with scintillators designed for low-energy and higher-energy detection and separated by a copper filter to harden the beam for high energy detection. To improve the performance of the bottom detector and lower dose requirements, we have previously proposed an alloyed amorphous selenium photodetector to achieve improved resolution and absorption at green wavelengths, better suited to high-performance scintillators such as CsI:Tl. In this work, we demonstrate a baseline prototype for the bottom layer-a continuous, large area 83 μm pixel pitch flat panel indirect detector with well-established amorphous selenium as the photodetector-and verify the architecture's performance and detector design. We characterize lag, noise-power spectrum, detective quantum efficiency, and modular transfer function of the detector, and show resolution up to 6 lp/mm when operated at an applied bias of 150 V. This provides a starting point for evaluating the alloyed selenium materials, and shows promise for this detector in the future dual-layer design.

Interface-Tension-Assisted Temperature-Gradient Crystallization of High-Quality MAPbBr3 Perovskite Single Crystals with Low Defect Densities

Comprehensive understanding and precise manipulation of the crystallization process for organic-inorganic hybrid perovskite materials are crucial for advancing perovskite single-crystal optoelectronic technology. In this study, we theoretically and experimentally investigated the influence of interface tension on the synthesis of perovskite single crystals. On the basis of the understanding of the nucleation and growth mechanisms, we developed a polydimethylsiloxane-assisted temperature-gradient growth technique to prepare high-quality MAPbBr3 single crystals. Using this technique, we harvested some high-quality MAPbBr3 single crystals, with the narrowest reported full width at half-maximum (0.00806°) of X-ray diffraction rocking curve, the longest carrier lifetime of 1002 ns, and an ultralow trap-state density of 4.25 × 109 cm-3. Furthermore, the X-ray detector fabricated using our MAPbBr3 single crystal exhibited a high sensitivity of 7275 μC Gy1- cm2 and a low minimum detection limit of 0.67 μGy s-1. This paper presents a novel method to control the crystallization and growth processes of high-quality perovskite single crystals.

Macroscopic Piezoelectricity of Halide Perovskite Single Crystals and Their Highly Sensitive Self-Powered X-ray Detectors

The FAxMA1-xPbI3 single crystal has excellent semiconductor photoelectric performance and good stability; however, there have been conflicting opinions regarding its macroscopic piezoelectricity. Here, the FAxMA1-xPbI3 (x = 0-0.1) single crystals (FAx SCs) exhibit a high macroscopic piezoelectric d33 coefficient of over 10 pC/N. The single crystal transforms from a tetragonal ferroelectric phase to a cubic paraelectric phase at x = 0.1-0.125. Furthermore, the fully polarized MAPbI3 and FA0.05 SCs were applied to prepare self-powered X-ray detectors with vertical structures. The sensitivity of the detector reaches 5.1 × 104 μC·Gy-1·cm-2 under a 0 V bias voltage, and its detection limit is as low as 50 nGy/s. This work provides an approach to designing self-powered and high-quality detectors with piezoelectric semiconductors.

Perovskite-Based X-ray Detectors

X-ray detection has widespread applications in medical diagnosis, non-destructive industrial radiography and safety inspection, and especially, medical diagnosis realized by medical X-ray detectors is presenting an increasing demand. Perovskite materials are excellent candidates for high-energy radiation detection based on their promising material properties such as excellent carrier transport capability and high effective atomic number. In this review paper, we introduce X-ray detectors using all kinds of halide perovskite materials along with various crystal structures and discuss their device performance in detail. Single-crystal perovskite was first fabricated as an active material for X-ray detectors, having excellent performance under X-ray illumination due to its superior photoelectric properties of X-ray attenuation with μm thickness. The X-ray detector based on inorganic perovskite shows good environmental stability and high X-ray sensitivity. Owing to anisotropic carrier transport capability, two-dimensional layered perovskites with a preferred orientation parallel to the substrate can effectively suppress the dark current of the device despite poor light response to X-rays, resulting in lower sensitivity for the device. Double perovskite applied for X-ray detectors shows better attenuation of X-rays due to the introduction of high-atomic-numbered elements. Additionally, its stable crystal structure can effectively lower the dark current of X-ray detectors. Environmentally friendly lead-free perovskite exhibits potential application in X-ray detectors by virtue of its high attenuation of X-rays. In the last section, we specifically introduce the up-scaling process technology for fabricating large-area and thick perovskite films for X-ray detectors, which is critical for the commercialization and mass production of perovskite-based X-ray detectors.

Photon counting-energy integrating hybrid flat panel detector systems for image-guided interventions: an experimental proof-of-concept

OBJECTIVE

Current C-arm x-ray systems equipped with scintillator-based flat panel detectors (FPDs) lack sufficient low-contrast detectability and spectral, high-resolution capabilities much desired for certain interventional procedures. Semiconductor-based direct-conversion photon counting detectors (PCDs) offer these imaging capabilities, although the cost of full field-of-view (FOV) PCD is still too high at the moment. The purpose of this work was to present a hybrid photon counting-energy integrating flat panel detector design as a cost-effective solution to high-quality interventional imaging. &#xD;&#xD;Approach: In the proposed hybrid detector design, the central scintillator and thin-film transistor elements in the FPD are replaced with a semiconductor PCD module to upgrade the imaging capabilities of the C-arm system while preserving the full FOV coverage. The central PCD module can be used for high-quality 2D and 3D region-of-interest imaging with improved spatial- and temporal-resolution as well as spectral resolving capability. An experimental proof-of-concept was conducted using a 30x2.5 cm^2 CdTe PCD and a 40x30 cm^2 CsI(Tl)-aSi(H) FPD. &#xD;&#xD;Main Results: Phantom and in vivo animal studies show 1) improved visualization of small stent wires in both 2D and 3D images due to the better spatial resolution of the PCD; 2) dual-energy angiography imaging capability by using the spectral PCD; 3) better conspicuity of small peripheral iodinated vessels (contrast-to-noise ratio improvement range: [29%, 151%]); 4) the central PCD outputs can be fused seamlessly with the surrounding scintillator detector outputs to provide full field imaging: a post-processing chain was developed by leveraging the PCD's spectral information to match the image contrast of PCD images to the surrounding scintillator detector, followed by spatial filtering of the PCD image to match noise texture and spatial resolution. &#xD;&#xD;Significance: The hybrid FPD design provides a cost-effective option to upgrade C-arm systems with spectral and ultra-high resolution capabilities without interfering with the clinical need for full FOV imaging.

Ultrasound-Assisted Crystallization Enables Large-Area Perovskite Quasi-Monocrystalline Film for High-Sensitive X-ray Detection and Imaging

In recent years, halide perovskites have shown great application potential in X-ray detection due to their superior optoelectronic properties and high X-ray attenuation coefficient. However, the large-area perovskite fabrication for high performance X-ray detectors remains extremely challenging. Herein, ultrasound-assisted crystallization combined with hot-pressing method is proposed to prepare large-area (10 cm × 10 cm) and high-quality quasi-monocrystalline thick film of a mixed-cation perovskite MA_0.42 FA_0.58 PbI₃ . The rapid ultrasound-assisted crystallization provides more homogeneous nucleation, which is essential to the fabrication of large-area and uniform perovskite microcrystalline film. Furthermore, the post hot-pressing treatment is implemented to fuse the crystal boundaries, rearrange the crystal grains and eliminate the voids between crystals, resulting in a quasi-monocrystalline film. After the hot-pressing treatment, the carrier mobility and the carrier mobility-lifetime product increased about 13-fold (from 1.8 cm² s^-1 V^-1 to 23.5 cm² s^-1 V^-1 ) and 18 times (from 8.4 × 10^-6 cm² V^-1 to 1.5 × 10^-4 cm² V^-1 ) respectively. As a result, a high-performance MA_0.42 FA_0.58 PbI₃ quasi-monocrystalline X-ray detector was achieved with an impressively high sensitivity (1.16 × 10⁶ μC Gy_air ^-1 cm^-2 ) and low detection limit (37.4 nGy_air s^-1 ), demonstrating the potential of the ultrasound-assisted crystallization and hot-pressing strategy from an industrial perspective. This article is protected by copyright. All rights reserved.

Printable Perovskite Diodes for Broad-Spectrum Multienergy X-Ray Detection

Multienergy X-ray detection is critical to effectively differentiate materials in a variety of diagnostic radiology and nondestructive testing applications. Silicon and selenium X-ray detectors are the most common for multienergy detection; however, these present poor energy discrimination across the broad X-ray spectrum and exhibit limited spatial resolution due to the high thicknesses required for radiation attenuation. Here, an X-ray detector based on solution-processed thin-film metal halide perovskite that overcomes these challenges is introduced. By harnessing an optimized n-i-p diode configuration, operation is achieved across a broad range of soft and hard X-ray energies stemming from 0.1 to 10's of keV. Through detailed experimental and simulation work, it is shown that optimized Cs_0.1 FA_0.9 PbI₃ perovskites effectively attenuate soft and hard X-rays, while also possessing excellent electrical properties to result in X-ray detectors with high sensitivity factors that exceed 5 × 10³ µ C   G y Vac - 1   cm - 2 $\mu {\rm{C}}\;{{\bf Gy}}_{{\rm{Vac}}}^{ - 1}\;{\rm{c}}{{\rm{m}}^{ - 2}}$ and 6 × 10⁴ µC Gy^-1 cm^-2 within soft and hard X-ray regimes, respectively. Harnessing the solution-processable nature of the perovskites, roll-to-roll printable X-ray detectors on flexible substrates are also demonstrated.

Structural and Scintillation Properties of Ce3+:Gd3Al3Ga2O12 Translucent Ceramics Prepared by One-Step Sintering

Cerium-doped gadolinium aluminum gallium garnet (Ce³⁺:Gd₃Al₃Ga₂O₁₂, Ce³⁺:GAGG) ceramic is a promising scintillation material. In this study, Ce³⁺:Gd₃Al₃Ga₂O₁₂ scintillation ceramics were prepared by the one-step sintering of commercially available Gd₂O₃, Al₂O₃, Ga₂O₃, and CeO₂ powders in a flowing oxygen atmosphere at 1600 °C by solid-phase reaction sintering. For all the Ce³⁺:Gd₃Al₃Ga₂O₁₂ ceramic samples doped with different amounts of Ce³⁺ doping, dense ceramics were obtained. The structure, photoluminescence, and scintillation properties of the Ce³⁺:Gd₃Al₃Ga₂O₁₂ ceramics have been investigated. The average grain size of samples sintered at 1600 °C is about 2 μm. The X-ray excitation luminescence peak is around 560 nm, which is consistent with that of Ce³⁺:Gd₃Al₃Ga₂O₁₂ single crystals, matching well with the computed tomography X-ray detector's response sensitivity. The light yield is higher compared to the standard reference sample-lutetium yttrium orthosilicate single crystal.

Benefits of using removable filters in dual-layer flat panel detectors

OBJECTIVE

Existing dual-layer flat panel detectors (DL-FPDs) use a thin scintillator layer to preferentially detect low-energy x-rays, followed by a permanent Cu filter to absorb residual low-energy x-rays, and finally, a thicker scintillator layer to preferentially detect high-energy x-rays. The image outputs of the two scintillator layers can be jointly processed for dual-energy (DE) planar and cone-beam CT imaging. In clinical practice, a given FPD is often used for not only DE imaging but also routine single-energy (SE) imaging. With the permanent Cu layer, the total x-ray absorption is unsatisfactory for SE imaging since more than 30% of x-rays can be lost in the Cu layer. The purpose of this work was to demonstrate the benefits of using a removable filter material in DL-FPDs for SE and DE imaging applications.&#xD;&#xD;Approach: The proposed detector contains a removable filter between the two scintillator layers. The filter can be either a chamber filled with a liquid high-Z material or a removable solid filter. When DE imaging is not clinically indicated, the DL-FPD can switch to a high-efficiency SE imaging mode by retracting the filter from the inter-scintillator space. For commonly available filter materials (iodine, gadolinium, and Cu), their optimal area densities were theoretically calculated for both water-bone decomposition and water-iodine decomposition DE imaging tasks. Preliminary experimental studies were also performed to compare the SE performance of the proposed DL-FPD with the existing DL-FPD with the permanent Cu filter and study the stability of the liquid filter on a rotating gantry.&#xD;&#xD;Main Results: The optimal filter material was found to be an iodine solution (approximately 350 mg/cm2). With this liquid filter in place, the proposed DL-FPD has equivalent or better DE imaging performance compared with the existing DL-FPD with the Cu filter. When the filter is removed from the inter-scintillator space for SE imaging, the total x-ray absorption efficiency of the proposed DL-FPD ranges from 73% (100 kVp) to 54% (140 kVp), compared with 51% (100 kVp) to 41% (140 kVp) for the existing DL-FPD with a permanent 1 mm Cu filter.&#xD;&#xD;Significance: The removable filter provides a boost to the total x-ray absorption efficiency of DL-FPDs for SE imaging without compromising DE imaging. This can facilitate the adoption of DL-FPDs in clinical x-ray imaging systems that usually perform more SE imaging procedures than DE imaging series.

Timepix3: Compensation of Thermal Distortion of Energy Measurement

The Timepix3 is a hybrid pixellated radiation detector consisting of a 256 px × 256 px radiation-sensitive matrix. Research has shown that it is susceptible to energy spectrum distortion due to temperature variations. This can lead to a relative measurement error of up to 35% in the tested temperature range of 10 °C to 70 °C. To overcome this issue, this study proposes a complex compensation method to reduce the error to less than 1%. The compensation method was tested with different radiation sources, focusing on energy peaks up to 100 keV. The results of the study showed that a general model for temperature distortion compensation could be established, where the error in the X-ray fluorescence spectrum of Lead (74.97 keV) was reduced from 22% to less than 2% for 60 °C after the correction was applied. The validity of the model was also verified at temperatures below 0 °C, where the relative measurement error for the Tin peak (25.27 keV) was reduced from 11.4% to 2.1% at -40 °C. The results of this study demonstrate the effectiveness of the proposed compensation method and models in significantly improving the accuracy of energy measurements. This has implications for various fields of research and industry that require accurate radiation energy measurements and cannot afford to use power for cooling or temperature stabilisation of the detector.

CsPbBr3-DMSO merged perovskite micro-bricks for efficient X-ray detection

Inorganic perovskite wafers with good stability and adjustable sizes are promising in X-ray detection but the high synthetic temperature is a hindrance. Herein, dimethyl sulfoxide (DMSO) is used to prepare the CsPbBr3 micro-bricks powder at room temperature. The CsPbBr3 powder has a cubic shape with few crystal defects, small charge trap density, and high crystallinity. A trace amount of DMSO attaches to the surface of the CsPbBr3 micro-bricks via Pb-O bonding, forming the CsPbBr3-DMSO adduct. During hot isostatic processing, the released DMSO vapor merges the CsPbBr3 micro-bricks, producing a compact and dense CsPbBr3 wafer with minimized grain boundaries and excellent charge transport properties. The CsPbBr3 wafer shows a large mobility-lifetime (μτ) product of 5.16 × 10-4 cm2·V-1, high sensitivity of 14,430 μC·Gyair-1·cm-2, low detection limit of 564 nGyair·s-1, as well as robust stability in X-ray detection. The results reveal a novel strategy with immense practical potential pertaining to high-contrast X-ray detection.

Electronic Supplementary Material

Supplementary material (further details of the characterization, SEM images, AFM images, KPFM images, schematic illustration, XRD patterns, XPS spectra, FTIR spectra, UPS spectra, and stability tests) is available in the online version of this article at 10.1007/s12274-023-5487-3.

Timepix3: Temperature Influence on Radiation Energy Measurement with Si Sensor

The Timepix3 readout ASIC chip is a hybrid pixelated radiation detector, designed at CERN, which contains a 256 px × 256 px matrix. Each of the 65,536 radiation-sensitive pixels can record an incoming particle, its energy deposition or time of arrival and measure them simultaneously. Since the detector is suitable for a wide range of applications from particle physics, national security and medicine to space science, it can be used in a wide range of temperatures. Until now, it has to be calibrated every time to the operating point of the application. This paper studies the possibility of energy measurement with Timepix3 equipped with a 500 m thick silicon sensor and MiniPIX readout interface in the temperatures between 10 ∘C and 70 ∘C with only one calibration. The detector has been irradiated by X-ray fluorescence photons in the energy range from 8 keV to 57 keV, and 31 keV to 81 keV photons from the ¹³³Ba radioactive source. A deviation of 5% in apparent energy value may occur for a 10 ∘C change in temperature from the reference point, but, with the next temperature change, it can reach up to -30%. Moreover, Barium photons with an energy of 81 keV appear as deposited energy of only 55 keV at a detector temperature of 70 ∘C. An original compensation method that reduces the relative measurement error from -30% to less than 1% is presented in this paper.

Copper-based metal halides for X-ray and photodetection

Copper-based metal halides have become important materials in the field of X-ray and photodetection due to their excellent optical properties, good environmental stability and low toxicity. This review presents the progress of research on crystal structure/morphology, photophysics/optical properties and applications of copper-based metal halides. We also discuss the challenges of copper-based metal halides with a perspective of their future research directions.

Comparative Analysis of Multilayer Lead Oxide-Based X-ray Detector Prototypes

Lead oxide (PbO) photoconductors are proposed as X-ray-to-charge transducers for the next generation of direct conversion digital X-ray detectors. Optimized PbO-based detectors have potential for utilization in high-energy and dynamic applications of medical X-ray imaging. Two polymorphs of PbO have been considered so far for imaging applications: polycrystalline lead oxide (poly-PbO) and amorphous lead oxide (a-PbO). Here, we provide the comparative analysis of two PbO-based single-pixel X-ray detector prototypes: one prototype employs only a layer of a-PbO as the photoconductor while the other has a combination of a-PbO and poly-PbO, forming a photoconductive bilayer structure of the same overall thickness as in the first prototype. We characterize the performance of these prototypes in terms of electron-hole creation energy (W_±) and signal lag-major properties that define a material's suitability for low-dose real-time imaging. The results demonstrate that both X-ray photoconductive structures have an adequate temporal response suitable for real-time X-ray imaging, combined with high intrinsic sensitivity. These results are discussed in the context of structural and morphological properties of PbO to better understand the preparation-fabrication-property relationships of this material.

Dark Current Modeling for a Polyimide-Amorphous Lead Oxide-Based Direct Conversion X-ray Detector

The reduction of the dark current (DC) to a tolerable level in amorphous selenium (a-Se) X-ray photoconductors was one of the key factors that led to the successful commercialization of a-Se-based direct conversion flat panel X-ray imagers (FPXIs) and their widespread clinical use. Here, we discuss the origin of DC in another X-ray photoconductive structure that utilizes amorphous lead oxide (a-PbO) as an X-ray-to-charge transducer and polyimide (PI) as a blocking layer. The transient DC in a PI/a-PbO detector is measured at different applied electric fields (5-20 V/μm). The experimental results are used to develop a theoretical model describing the electric field-dependent transient behavior of DC. The results of the DC kinetics modeling show that the DC, shortly after the bias application, is primarily controlled by the injection of holes from the positively biased electrode and gradually decays with time to a steady-state value. DC decays by the overarching mechanism of an electric field redistribution, caused by the accumulation of trapped holes in deep localized states within the bulk of PI. Thermal generation and subsequent multiple-trapping (MT) controlled transport of holes within the a-PbO layer governs the steady-state value at all the applied fields investigated here, except for the largest applied field of 20 V/μm. This suggests that a thicker layer of PI would be more optimal to suppress DC in the PI/a-PbO detector presented here. The model can be used to find an approximate optimal thickness of PI for future iterations of PI/a-PbO detectors without the need for time and labor-intensive experimental trial and error. In addition, we show that accounting for the field-induced charge carrier release from traps, enhanced by charge hopping transitions between the traps, yields an excellent fit between the experimental and simulated results, thus, clarifying the dynamic process of reaching a steady-state occupancy level of the deep localized states in the PI. Practically, the electric field redistribution causes the internal field to increase in magnitude in the a-PbO layer, thus improving charge collection efficiency and temporal performance over time, as confirmed by experimental results. The electric field redistribution can be implemented as a warm-up time for a-PbO-based detectors.

Efficient Eco-Friendly Flexible X-ray Detectors Based on Molecular Perovskite

Next-generation wearable electronics requires mechanical robustness. In addition to the previously reported eco-friendliness, low cost, and light weight of molecular perovskites, flexibility is also a desired merit for their practical use. Here we design a flexible X-ray detector based on a novel molecular perovskite, DABCO-CsBr₃ (DABCO = N-N'-diazabicyclo[2.2.2]octonium), which is the missing link between metal-free molecular perovskites A(NH₄)X₃ (A = divalent organic ammoniums) and conventional metal halide based ABX₃ (B = divalent metal cations) perovskites. DABCO-CsBr₃ inherits its band nature from A(NH₄)X₃, while it exhibits a stronger stopping power. DABCO-CsBr₃ shows potential for high-performance ionizing radiation detectors due to low dark current, low ion migration, and an efficient mobility-lifetime (μτ) product. Finally, a molecular-perovskite-based flexible X-ray detector is demonstrated on the basis of the DABCO-CsBr₃/poly(vinylidene fluoride) composite, with a sensitivity of 106.7 μC Gy_air^-1 cm^-2. This work enriches the molecular perovskite family and highlights the promise of molecular perovskites for the next-generation eco-friendly and wearable optoelectronic devices.

All-Vacuum-Deposited Perovskite X-ray Detector with a Record-High Self-Powered Sensitivity of 1.2 C Gy-1 cm-3

Highly sensitive X-ray detection is crucial in, for example, medical imaging and secure inspection. Halide perovskite X-ray detectors are promising candidates for detecting highly energetic radiation. In this report, we describe vacuum-deposited Cs-based perovskite X-ray detectors possessing a p-i-n architecture. Because of the built-in potential of the p-i-n structure, these perovskite X-ray detectors were capable of efficient charge collection and displayed an exceptionally high X-ray sensitivity (1.2 C Gy_air^-1 cm^-3) under self-powered, zero-bias conditions. We ascribe the outstanding X-ray sensitivity of the vacuum-deposited CsPbI₂Br devices to their prominent charge carrier mobility. Moreover, these devices functioned with a lowest detection limit of 25.69 nGy_air s^-1 and possessed excellent stability after exposure to over 3000 times the total dose of a chest X-ray image. For comparison, we also prepared traditional spin-coated CH₃NH₃-based perovskite devices having a similar device architecture. Their volume sensitivity was only one-fifth of that of the vacuum-deposited CsPbI₂Br devices. Thus, all-vacuum deposition appears to be a new strategy for developing perovskite X-ray detectors; with a high practical deposition rate, a balance can be reached between the thickness of the absorbing layer and the fabrication time.

A polycrystalline diamond micro-detector for X-ray absorption fine-structure measurements

The microminiaturization of detectors used to record the intensity of X-ray beams is very favorable for combined X-ray experimental techniques. In this paper, chemical-vapor-deposited (CVD) polycrystalline diamond film was used to fabricate a micro-detector owing to its well controlled size, good thermostability, and appropriate conductivity. The preparation process and the main components of the CVD diamond micro-detector are described. The external dimensions of the packaged CVD diamond micro-detector are 15 mm × 7.8 mm × 5.8 mm. To demonstrate the performance of the detector, K-edge X-ray absorption fine-structure (XAFS) spectra of Cr, Fe, Cu, and Se foils were collected using the CVD diamond micro-detector and routine ion chamber. These XAFS measurements were performed at beamline 1W2B of Beijing Synchrotron Radiation Facility, covering an energy range from 5.5 to 13.5 keV. By comparison, it can be seen that the CVD diamond micro-detector shows a more excellent performance than the routine ion-chamber in recording these XAFS spectra. The successful application of the CVD diamond micro-detector in XAFS measurements shows its feasibility in recording X-ray intensity.

The X-ray Sensitivity of an Amorphous Lead Oxide Photoconductor

The photoconductor layer is an important component of direct conversion flat panel X-ray imagers (FPXI); thus, it should be carefully selected to meet the requirements for the X-ray imaging detector, and its properties should be clearly understood to develop the most optimal detector design. Currently, amorphous selenium (a-Se) is the only photoconductor utilized in commercial direct conversion FPXIs for low-energy mammographic imaging, but it is not practically feasible for higher-energy diagnostic imaging. Amorphous lead oxide (a-PbO) photoconductor is considered as a replacement to a-Se in radiography, fluoroscopy, and tomosynthesis applications. In this work, we investigated the X-ray sensitivity of a-PbO, one of the most important parameters for X-ray photoconductors, and examined the underlying mechanisms responsible for charge generation and recombination. The X-ray sensitivity in terms of electron–hole pair creation energy, W_±, was measured in a range of electric fields, X-ray energies, and exposure levels. W_± decreases with the electric field and X-ray energy, saturating at 18–31 eV/ehp, depending on the energy of X-rays, but increases with the exposure rate. The peculiar dependencies of W_± on these parameters lead to a conclusion that, at electric fields relevant to detector operation (~10 V/μm), the columnar recombination and the bulk recombination mechanisms interplay in the a-PbO photoconductor.

Sb2Se3 film with grain size over 10 µm toward X-ray detection

Direct X-ray detectors are considered as competitive next-generation X-ray detectors because of their high spatial resolution, high sensitivity, and simple device configuration. However, their potential is largely limited by the imperfections of traditional materials, such as the low crystallization temperature of α-Se and the low atomic numbers of α-Si and α-Se. Here, we report the Sb₂Se₃ X-ray thin-film detector with a p-n junction structure, which exhibited a sensitivity of 106.3 µC/(Gy_air·cm²) and response time of < 2.5 ms. This decent performance and the various advantages of Sb₂Se₃, such as the average atomic number of 40.8 and μτ product (μ is the mobility, and τ is the carrier lifetime) of 1.29 × 10^-5 cm²/V, indicate its potential for application in X-ray detection.

A High-Sensitivity Flexible Direct X-ray Detector Based on Bi2O3/PDMS Nanocomposite Thin Film

The characteristics of mechanical flexibility, low health risk, and simple processing of polymer nanocomposite materials make them potentially applicable as flexible X-ray detectors. In this study, we report on a high sensitivity, environmentally friendly, and flexible direct X-ray detector using polymer nanocomposite material consisting of bismuth oxide (Bi₂O₃) nanoparticles and polydimethylsiloxane (PDMS). This detector was realized by printing patterned Ag electrodes on the polymer nanocomposite material. The response of PDMS to X-rays was verified for the first time, and the effect of doping different contents of Bi₂O₃ nanoparticles on the performance of the device was tested. The optoelectronic performance of the optimized detector indicated a high sensitivity (203.58 μC Gy_air⁻¹ cm⁻²) to low dose rate (23.90 μGy_air s⁻¹) at a 150 V bias voltage and the X-ray current density (J_X-ray) was 10,000-fold higher than the dark current density (J_dark). The flexible direct X-ray detector could be curled for 10,000 cycles with slight performance degradation. The device exhibited outstanding stability after storage for over one month in air. Finally, this device provides new guidance for the design of high-performance flexible direct X-ray detectors.

Charge Sharing and Charge Loss in High-Flux Capable Pixelated CdZnTe Detectors

Cadmium zinc telluride (CdZnTe) detectors are known to suffer from polarization effects under high photon flux due to poor hole transport in the crystal material. This has led to the development of a high-flux capable CdZnTe material (HF-CdZnTe). Detectors with the HF-CdZnTe material have shown promising results at mitigating the onset of the polarization phenomenon, likely linked to improved crystal quality and hole carrier transport. Better hole transport will have an impact on charge collection, particularly in pixelated detector designs and thick sensors (>1 mm). In this paper, the presence of charge sharing and the magnitude of charge loss were calculated for a 2 mm thick pixelated HF-CdZnTe detector with 250 μm pixel pitch and 25 μm pixel gaps, bonded to the STFC HEXITEC ASIC. Results are compared with a CdTe detector as a reference point and supported with simulations from a Monte-Carlo detector model. Charge sharing events showed minimal charge loss in the HF-CdZnTe, resulting in a spectral resolution of 1.63 ± 0.08 keV Full Width at Half Maximum (FWHM) for bipixel charge sharing events at 59.5 keV. Depth of interaction effects were shown to influence charge loss in shared events. The performance is discussed in relation to the improved hole transport of HF-CdZnTe and comparison with simulated results provided evidence of a uniform electric field.

The 1-Megapixel pnCCD detector for the Small Quantum Systems Instrument at the European XFEL: system and operation aspects

The X-ray free-electron lasers that became available during the last decade, like the European XFEL (EuXFEL), place high demands on their instrumentation. Especially at low photon energies below 1 keV, detectors with high sensitivity, and consequently low noise and high quantum efficiency, are required to enable facility users to fully exploit the scientific potential of the photon source. A 1-Megapixel pnCCD detector with a 1024 × 1024 pixel format has been installed and commissioned for imaging applications at the Nano-Sized Quantum System (NQS) station of the Small Quantum System (SQS) instrument at EuXFEL. The instrument is currently operating in the energy range between 0.5 and 3 keV and the NQS station is designed for investigations of the interaction of intense FEL pulses with clusters, nano-particles and small bio-molecules, by combining photo-ion and photo-electron spectroscopy with coherent diffraction imaging techniques. The core of the imaging detector is a pn-type charge coupled device (pnCCD) with a pixel pitch of 75 µm × 75 µm. Depending on the experimental scenario, the pnCCD enables imaging of single photons thanks to its very low electronic noise of 3 e^- and high quantum efficiency. Here an overview on the EuXFEL pnCCD detector and the results from the commissioning and first user operation at the SQS experiment in June 2019 are presented. The detailed descriptions of the detector design and capabilities, its implementation at EuXFEL both mechanically and from the controls side as well as important data correction steps aim to provide useful background for users planning and analyzing experiments at EuXFEL and may serve as a benchmark for comparing and planning future endstations at other FELs.

High-Performance X-ray Detector Based on Single-Crystal β-Ga2O3:Mg

X-ray detection plays an important role in medical imaging, scientific research, and security inspection. Recently, the β-Ga₂O₃ single-crystal-based X-ray detector has attracted extensive attention due to its excellent intrinsic properties such as good absorption for X-ray photons, a high breakdown electric field, high stability, and low cost. However, developing a high-performance β-Ga₂O₃-based X-ray detector remains a challenge because of the large dark current and the high oxygen vacancy concentration in the crystals. In this paper, we report a high-performance Mg-doped β-Ga₂O₃ single-crystal-based X-ray detector with a sandwich structure. The reduced dark current enables the detector to have a high sensitivity of 338.9 μC Gy^-1 cm^-2 under 50 keV X-ray irradiation with a dose rate of 69.5 μGy/s. The sensitivity is 16-fold higher than that of the commercial amorphous selenium detector. Furthermore, the reduced oxygen vacancy concentration can improve the response speed (<0.2 s) of the detector. The present studies provide a promising method to obtain the high performances for the X-ray detector based on β-Ga₂O₃ single crystals.

Single Crystal CdSe X-ray Detectors with Ultra-High Sensitivity and Low Detection Limit

CdSe single crystals (SCs), with a relatively high atomic number, large X-ray absorption coefficients, and high carrier mobility, are expected to provide high-performance detection for X-ray. However, the difficulty of growing high-quality CdSe SC has severely limited its application in X-ray detection. In this work, we develop an unconstrained physical gas phase method and in situ annealing process to grow high-quality CdSe SCs under unconstrained conditions. Using this method, CdSe SCs exhibit natural exposure planes, ultrahigh resistivity of 5.43 × 10¹² to 1.29 × 10¹³ Ω cm and high μτ product of 1.3 × 10^-2 to 1.5 × 10^-2 cm² V^-1. It is also observed that CdSe SC X-ray detectors exhibit a record sensitivity of 2.08 × 10⁵ μC Gy_air^-1 cm^-2 and a low detection limit of 85 nGy_air s^-1, which are both desired in medical diagnostics. Moreover, those devices with different crystal directions provide anisotropic X-ray detection performance. Our findings pave a new avenue to exploit high-performance CdSe SC X-ray detectors.

Characterization of the Uniformity of High-Flux CdZnTe Material

Since the late 2000s, the availability of high-quality cadmium zinc telluride (CdZnTe) has greatly increased. The excellent spectroscopic performance of this material has enabled the development of detectors with volumes exceeding 1 cm³ for use in the detection of nuclear materials. CdZnTe is also of great interest to the photon science community for applications in X-ray imaging cameras at synchrotron light sources and free electron lasers. Historically, spatial variations in the crystal properties and temporal instabilities under high-intensity irradiation has limited the use of CdZnTe detectors in these applications. Recently, Redlen Technologies have developed high-flux-capable CdZnTe material (HF-CdZnTe), which promises improved spatial and temporal stability. In this paper, the results of the characterization of 10 HF-CdZnTe detectors with dimensions of 20.35 mm × 20.45 mm × 2.00 mm are presented. Each sensor has 80 × 80 pixels on a 250-μm pitch and were flip-chip-bonded to the STFC HEXITEC ASIC. These devices show excellent spectroscopic performance at room temperature, with an average Full Width at Half Maximum (FWHM) of 0.83 keV measured at 59.54 keV. The effect of tellurium inclusions in these devices was found to be negligible; however, some detectors did show significant concentrations of scratches and dislocation walls. An investigation of the detector stability over 12 h of continuous operation showed negligible changes in performance.

Large and Dense Organic-Inorganic Hybrid Perovskite CH3NH3PbI3 Wafer Fabricated by One-Step Reactive Direct Wafer Production with High X-ray Sensitivity

Lead halide perovskites with good optoelectronic properties and high attenuation of high-energy radiation are great candidates for X-ray radiation detectors. Large area, dense, and thick films or wafers are a prerequisite for these applications. In this paper, a one-step heat-assisted high-pressure press method is developed to directly prepare a large (the largest has a diameter of 80 mm) and thickness- and shape-controlled phase-pure organic-inorganic hybrid CH₃NH₃PbI₃ wafer of densely packed large microcrystals from raw powder materials. Meanwhile, this method uses no solvent to achieve essentially 100% material utilization. The obtained wafers show good ambipolar carrier mobilities of ∼20 cm² V^-1 s^-1 and a μτ product as high as 3.84 × 10^-4 cm² V^-1. Under an X-ray source using an acceleration voltage of 40 kV, the perovskite wafer-based X-ray detector shows an X-ray sensitivity as large as 1.22 × 10⁵ μC Gy_air^-1 cm^-2 under a 10 V bias, the highest reported for any perovskite material. The method provides a convenient strategy for producing large perovskite wafers with good optoelectronic properties, which will facilitate the development of large perovskite devices.

Flexible Inkjet-Printed Triple Cation Perovskite X-ray Detectors

Flexible direct conversion X-ray detectors enable a variety of novel applications in medicine, industry, and science. Hybrid organic-inorganic perovskite semiconductors containing elements of high atomic number combine an efficient X-ray absorption with excellent charge transport properties. Due to their additional cost-effective and low-temperature processability, perovskite semiconductors represent promising candidates to be used as active materials in flexible X-ray detectors. Inspired by the promising results recently reported on X-ray detectors that are based on either triple cation perovskites or inkjet-printed perovskite quantum dots, we here investigate flexible inkjet-printed triple cation perovskite X-ray detectors. The performance of the detectors is evaluated by the X-ray sensitivity, the dark current, and the X-ray stability. Exposed to 70 kVp X-ray radiation, reproducible and highly competitive X-ray sensitivities of up to 59.9 μC/(Gy_aircm²) at low operating voltages of 0.1 V are achieved. Furthermore, a significant dark current reduction is demonstrated in our detectors by replacing spin-coated poly(3,4-ethylenedioxythiophene)/poly(styrenesulfonate) (PEDOT:PSS) with sputtered NiO_x hole transport layers. Finally, stable operation of a flexible X-ray detector for a cumulative X-ray exposure of 4 Gy_air is presented, and the applicability of our devices as X-ray imaging detectors is shown. The results of this study represent a proof of concept toward flexible direct conversion X-ray detectors realized by cost-effective and high-throughput digital inkjet printing.

High spatial resolution inorganic scintillator detector for high-energy X-ray beam at small field irradiation

Purpose

Small field dosimetry for radiotherapy is one of the major challenges due to the size of most dosimeters, for example, sufficient spatial resolution, accurate dose distribution and energy dependency of the detector. In this context, the purpose of this research is to develop a small size scintillating detector targeting small field dosimetry and compare its performance with other commercial detectors.

Method

An inorganic scintillator detector (ISD) of about 200 µm outer diameter was developed and tested through different small field dosimetric characterizations under high‐energy photons (6 and 15 MV) delivered by an Elekta Linear Accelerator (LINAC). Percentage depth dose (PDD) and beam profile measurements were compared using dosimeters from PTW namely, microdiamond and PinPoint three‐dimensional (PP3D) detector. A background fiber method has been considered to quantitate and eliminate the minimal Cerenkov effect from the total optical signal magnitude. Measurements were performed inside a water phantom under IAEA Technical Reports Series recommendations (IAEA TRS 381 and TRS 483).

Results

Small fields ranging from 3 × 3 cm², down to 0.5 × 0.5 cm² were sequentially measured using the ISD and commercial dosimeters, and a good agreement was obtained among all measurements. The result also shows that, scintillating detector has good repeatability and reproducibility of the output signal with maximum deviation of 0.26% and 0.5% respectively. The Full Width Half Maximum (FWHM) was measured 0.55 cm for the smallest available square size field of 0.5 × 0.5 cm², where the discrepancy of 0.05 cm is due to the scattering effects inside the water and convolution effect between field and detector geometries. Percentage depth dose factor dependence variation with water depth exhibits nearly the same behavior for all tested detectors. The ISD allows to perform dose measurements at a very high accuracy from low (50 cGy/min) to high dose rates (800 cGy/min) and was found to be independent of dose rate variation. The detection system also showed an excellent linearity with dose; hence, calibration was easily achieved.

Conclusions

The developed detector can be used to accurately measure the delivered dose at small fields during the treatment of small volume tumors. The author's measurement shows that despite using a nonwater‐equivalent detector, the detector can be a powerful candidate for beam characterization and quality assurance in, for example, radiosurgery, Intensity‐Modulated Radiotherapy (IMRT), and brachytherapy. Our detector can provide real‐time dose measurement and good spatial resolution with immediate readout, simplicity, flexibility, and robustness.

Rubidium Doping to Enhance Carrier Transport in CsPbBr3 Single Crystals for High-Performance X-Ray Detection

The direct band gap CsPbBr₃ perovskite is regarded as a promising alternative for low-cost and high-performance X-ray radiation detectors. Despite the fact that CsPbBr₃ nanocrystals have been shown to be good scintillators in the indirect conversion mode, the direct X-ray conversion with CsPbBr₃ single crystals is expected to yield higher spatial resolution. Here, rubidium (Rb) doping is demonstrated to be an efficient approach to improve carrier transport and X-ray detection performance in the direct-conversion X-ray detectors based on Cs_(1-x)Rb_xPbBr₃ single crystals. Electrical properties' characterizations as combined with X-ray photoelectron spectroscopy (XPS) measurements have revealed that Rb doping in Cs_(1-x)Rb_xPbBr₃ single crystals can enhance the atomic interaction and orbital coupling between Pb and Br atoms, leading to an enhancement of carrier transport and X-ray detection performance. X-ray detectors based on a small amount (0.037%) of Rb-doped Cs_(1-x)Rb_xPbBr₃ single crystals exhibited a high X-ray sensitivity of 8097 μC Gy_air^-1 cm^-2. This work offers a feasible strategy to improve the X-ray detection performance by chemical doping in all-inorganic perovskite X-ray detectors.

Ammonium Fluoride Passivation of CdZnTeSe Sensors for Applications in Nuclear Detection and Medical Imaging

Cadmium zinc telluride selenide (Cd_1−xZn_xTe_1−ySe_y or CZTS) is one of the emerging CdTe-based semiconductor materials for detecting X- and gamma-ray radiation at or near room temperature (i.e., without cryogenic cooling). Potential applications of CZTS sensors include medical imaging, X-ray detection, and gamma-ray spectroscopy. Chemical passivation of CZTS is needed to reduce the conductivity of Te-rich surfaces, which reduces the noise and improves the device performance. In this study, we focus on the effect of surface passivation of CZTS using a 10% aqueous solution of ammonium fluoride. The effects of the chemical treatment were studied on the leakage current, charge transport measured as the electron mobility-lifetime (µτ) product, and the spectral resolution measured as the full-width at half-maximum (FWHM) of specific peaks. After passivation, the leakage current increased and began to decrease towards pre-passivation levels. The energy resolutions were recorded for eight applied voltages between −35 V and −200 V. The results showed an average of 25% improvement in the detector’s energy resolution for the 59.6 keV gamma peak of Am-241. The electron µτ product was unchanged at 2 × 10⁻³ cm²/V. These results show that ammonium fluoride is effective for chemical passivation of CZTS detectors.

Controllable Cs xFA1- xPbI3 Single-Crystal Morphology via Rationally Regulating the Diffusion and Collision of Micelles toward High-Performance Photon Detectors

Cs _xFA_{1- x}PbI₃ single crystals are expected to provide more excitement in optoelectronic applications, including photodetector, laser, light-emitting diode, etc. Herein, we aim to gain an in-depth understanding of the growth mechanisms of perovskite single crystal with various morphologies in view of microscopic dynamics by the combination of component, structure, and solvent engineering. A sequence of Cs _xFA_{1- x}PbI₃ (0 ≤ x ≤ 0.14) perovskite single crystals with a dodecahedron morphology and tunable aspect ratio can be obtained by means of a solution-processed uniform-cooling approach. The optimized Cs_0.1FA_0.9PbI₃ single crystals prepared in γ-butyrolactone mixed with dimethyl sulfoxide are theoretically and experimentally demonstrated to have superior performances, e.g., extremely higher long-term stability, lower trap density, and higher mobility. The broadband absorption, i.e., 300-910 nm, enables its application in near-infrared detection (880 nm), and the corresponding detector demonstrates higher responsivity at different light intensities and a fast photocurrent response (τ₁ = 11 μs, τ₂ = 10 μs). Equally important, we also explore the application of optimized Cs_0.1FA_0.9PbI₃ single crystals with a tunable aspect ratio in an X-ray detector and the extremely high sensitivity (2772.1 μC Gy_air^-1 cm^-2 under a bias of 150 V) demonstrates their good potential for radiation detection.

High-Performance Surface Barrier X-ray Detector Based on Methylammonium Lead Tribromide Single Crystals

Hybrid methylammonium lead tribromide (MAPbBr₃) perovskite has attracted great attention in ionization radiation detection. However, the charge collection remains a challenge. Here, fast response and high-sensitivity X-ray detection based on MAPbBr₃ single crystals with a surface barrier Schottky diode has been achieved at room temperature. The Schottky surface barrier can overcome the large leakage current at a high electrical field, enabling us to reduce the noise and increase the charge collection efficiency. This surface barrier device has been demonstrated a 3 times improvement over the photoconductor based X-ray detector, which enables usage in nuclear medicine, especially for X-ray imaging technology.

Enhanced X-ray Sensitivity of MAPbBr3 Detector by Tailoring the Interface-States Density

An important factor for the high performance of light-harvesting devices is the presence of surface trappings. Therefore, understanding and controlling the carrier recombination of the organic-inorganic hybrid perovskite surface is critical for the device design and optimization. Here, we report the use of aluminum zinc oxide (AZO) as the anode to construct a p-n junction structure MAPbBr₃ nuclear radiation detector. The AZO/MAPbBr₃/Au detector can tolerate an electrical field of 500 V·cm^-1 and exhibit a very low leakage current of ∼9 nA, which is 1 order of magnitude lower than that of the standard ohmic contact device. The interface state density of AZO/MAPbBr₃ contact was reduced from 2.17 × 10¹⁰ to 8.7 × 10⁸ cm^-2 by annealing at 100 °C under an Ar atmosphere. Consequently, a photocurrent to dark current ratio of 190 was realized when exposed to a green light-emitting diode with a wavelength of 520 nm (∼200 mW·cm^-2). Simultaneously, a high X-ray sensitivity of ∼529 μC·Gy_air^-1 cm^-2 was achieved under 80 kVp X-ray at an electric field of 50 V·cm^-1. These results demonstrate the use of surface engineering to further optimize the performance of MAPbBr₃ detectors, which have many potential applications in medical and security detection with low radiation dose brought to the human body.

The Adaptive Gain Integrating Pixel Detector at the European XFEL

The Adaptive Gain Integrating Pixel Detector (AGIPD) is an X-ray imager, custom designed for the European X-ray Free-Electron Laser (XFEL). It is a fast, low-noise integrating detector, with an adaptive gain amplifier per pixel. This has an equivalent noise of less than 1 keV when detecting single photons and, when switched into another gain state, a dynamic range of more than 104 photons of 12 keV. In burst mode the system is able to store 352 images while running at up to 6.5 MHz, which is compatible with the 4.5 MHz frame rate at the European XFEL. The AGIPD system was installed and commissioned in August 2017, and successfully used for the first experiments at the Single Particles, Clusters and Biomolecules (SPB) experimental station at the European XFEL since September 2017. This paper describes the principal components and performance parameters of the system.

An all-diamond X-ray position and flux monitor using nitrogen-incorporated ultra-nanocrystalline diamond contacts

Diamond X-ray detectors with conducting nitrogen-incorporated ultra-nanocrystalline diamond (N-UNCD) films as electrodes were fabricated to measure X-ray beam flux and position. Structural characterization and functionality tests were performed for these devices. The N-UNCD films grown on unseeded diamond substrates were compared with N-UNCD films grown on a seeded silicon substrate. The feasibility of the N-UNCD films acting as electrodes for X-ray detectors was confirmed by the stable performance in a monochromatic X-ray beam. The fabrication process is able to change the surface status which may influence the signal uniformity under low bias, but this effect can be neglected under full collection bias.

A Silicon-on-Insulator-Based Dual-Gain Charge-Sensitive Pixel Detector for Low-Noise X-ray Imaging for Future Astronomical Satellite Missions

In this paper, we report on the development of a monolithic active pixel sensor for X-ray imaging using 0.2 µm fully depleted silicon-on-insulator (SOI)-based technology to support next generation astronomical satellite missions. Detail regarding low-noise dual-gain SOI based pixels with a charge sensitive amplifier and pinned depleted diode sensor structure is presented. The proposed multi-well sensor structure underneath the fully-depleted SOI allows the design of a detector with low node capacitance and high charge collection efficiency. Configurations for achieving very high charge-to-voltage conversion gain of 52 µV/e⁻ and 187 µV/e⁻ are demonstrated. Furthermore, in-pixel dual gain selection is used for low-noise and wide dynamic range X-ray energy detection. A technique to improve the noise performance by removing correlated system noise leads to an improvement in the spectroscopic performance of the measured X-ray energy. Taken together, the implemented chip has low dark current (44.8 pA/cm² at −30 °C), improved noise performance (8.5 e⁻ rms for high gain and 11.7 e⁻ rms for low gain), and better energy resolution of 2.89% (171 eV FWHM) at 5.9 keV using ⁵⁵Fe and 1.67% (234 eV FWHM) at 13.95 keV using ²⁴¹Am.

Signal and noise characteristics of a CdTe-based photon counting detector: Cascaded systems analysis and experimental studies

Recent advances in single photon counting detectors (PCDs) are opening up new opportunities in medical imaging. However, the performance of PCDs is not flawless. Problems such as charge sharing may deteriorate the performance of PCD. This work studied the dependence of the signal and noise properties of a cadmium telluride (CdTe)-based PCD on the charge sharing effect and the anti-charge sharing (ACS) capability offered by the PCD. Through both serial and parallel cascaded systems analysis, a theoretical model was developed to trace the origin of charge sharing in CdTe-based PCD, which is primarily related to remote k-fluorescence re-absorption and spatial spreading of charge cloud. The ACS process was modeled as a sub-imaging state prior to the energy thresholding stage, and its impact on the noise power spectrum (NPS) of PCD can be qualitatively determined by the theoretical model. To validate the theoretical model, experimental studies with a CdTe-based PCD system (XC-FLITE X1, XCounter AB) was performed. Two x-ray radiation conditions, including an RQA-5 beam and a 40 kVp beam, were used for the NPS measurements. Both theoretical predictions and experimental results showed that ACS makes the NPS of the CdTe-based PCD flatter, which corresponds to reduced noise correlation length. The flatness of the NPS is further boosted by increasing the energy threshold or reducing the x-ray energy, both of which reduce the likelihood of registering multiple counts from the same incidenting x-ray photon.

Infrared LED Enhanced Spectroscopic CdZnTe Detector Working under High Fluxes of X-rays

This paper describes an application of infrared light-induced de-polarization applied on a polarized CdZnTe detector working under high radiation fluxes. We newly demonstrate the influence of a high flux of X-rays and simultaneous 1200-nm LED illumination on the spectroscopic properties of a CdZnTe detector. CdZnTe detectors operating under high radiation fluxes usually suffer from the polarization effect, which occurs due to a screening of the internal electric field by a positive space charge caused by photogenerated holes trapped at a deep level. Polarization results in the degradation of detector charge collection efficiency. We studied the spectroscopic behavior of CdZnTe under various X-ray fluxes ranging between 5 × 10 5 and 8 × 10 6 photons per mm 2 per second. It was observed that polarization occurs at an X-ray flux higher than 3 × 10 6 mm - 2 ·s - 1 . Using simultaneous illumination of the detector by a de-polarizing LED at 1200 nm, it was possible to recover X-ray spectra originally deformed by the polarization effect.

High-speed X-ray imaging pixel array detector for synchrotron bunch isolation

A wide-dynamic-range imaging X-ray detector designed for recording successive frames at rates up to 10 MHz is described. X-ray imaging with frame rates of up to 6.5 MHz have been experimentally verified. The pixel design allows for up to 8-12 frames to be stored internally at high speed before readout, which occurs at a 1 kHz frame rate. An additional mode of operation allows the integration capacitors to be re-addressed repeatedly before readout which can enhance the signal-to-noise ratio of cyclical processes. This detector, along with modern storage ring sources which provide short (10-100 ps) and intense X-ray pulses at megahertz rates, opens new avenues for the study of rapid structural changes in materials. The detector consists of hybridized modules, each of which is comprised of a 500 µm-thick silicon X-ray sensor solder bump-bonded, pixel by pixel, to an application-specific integrated circuit. The format of each module is 128 × 128 pixels with a pixel pitch of 150 µm. In the prototype detector described here, the three-side buttable modules are tiled in a 3 × 2 array with a full format of 256 × 384 pixels. The characteristics, operation, testing and application of the detector are detailed.

X-ray characterization of a multichannel smart-pixel array detector

The Voxtel VX-798 is a prototype X-ray pixel array detector (PAD) featuring a silicon sensor photodiode array of 48 × 48 pixels, each 130 µm × 130 µm × 520 µm thick, coupled to a CMOS readout application specific integrated circuit (ASIC). The first synchrotron X-ray characterization of this detector is presented, and its ability to selectively count individual X-rays within two independent arrival time windows, a programmable energy range, and localized to a single pixel is demonstrated. During our first trial run at Argonne National Laboratory's Advance Photon Source, the detector achieved a 60 ns gating time and 700 eV full width at half-maximum energy resolution in agreement with design parameters. Each pixel of the PAD holds two independent digital counters, and the discriminator for X-ray energy features both an upper and lower threshold to window the energy of interest discarding unwanted background. This smart-pixel technology allows energy and time resolution to be set and optimized in software. It is found that the detector linearity follows an isolated dead-time model, implying that megahertz count rates should be possible in each pixel. Measurement of the line and point spread functions showed negligible spatial blurring. When combined with the timing structure of the synchrotron storage ring, it is demonstrated that the area detector can perform both picosecond time-resolved X-ray diffraction and fluorescence spectroscopy measurements.

Pixelated transmission-mode diamond X-ray detector

Fabrication and testing of a prototype transmission-mode pixelated diamond X-ray detector (pitch size 60-100 µm), designed to simultaneously measure the flux, position and morphology of an X-ray beam in real time, are described. The pixel density is achieved by lithographically patterning vertical stripes on the front and horizontal stripes on the back of an electronic-grade chemical vapor deposition single-crystal diamond. The bias is rotated through the back horizontal stripes and the current is read out on the front vertical stripes at a rate of ∼ 1 kHz, which leads to an image sampling rate of ∼ 30 Hz. This novel signal readout scheme was tested at beamline X28C at the National Synchrotron Light Source (white beam, 5-15 keV) and at beamline G3 at the Cornell High Energy Synchrotron Source (monochromatic beam, 11.3 keV) with incident beam flux ranges from 1.8 × 10(-2) to 90 W mm(-2). Test results show that the novel detector provides precise beam position (positional noise within 1%) and morphology information (error within 2%), with an additional software-controlled single channel mode providing accurate flux measurement (fluctuation within 1%).

Novel X-ray Communication Based XNAV Augmentation Method Using X-ray Detectors

The further development of X-ray pulsar-based NAVigation (XNAV) is hindered by its lack of accuracy, so accuracy improvement has become a critical issue for XNAV. In this paper, an XNAV augmentation method which utilizes both pulsar observation and X-ray ranging observation for navigation filtering is proposed to deal with this issue. As a newly emerged concept, X-ray communication (XCOM) shows great potential in space exploration. X-ray ranging, derived from XCOM, could achieve high accuracy in range measurement, which could provide accurate information for XNAV. For the proposed method, the measurement models of pulsar observation and range measurement observation are established, and a Kalman filtering algorithm based on the observations and orbit dynamics is proposed to estimate the position and velocity of a spacecraft. A performance comparison of the proposed method with the traditional pulsar observation method is conducted by numerical experiments. Besides, the parameters that influence the performance of the proposed method, such as the pulsar observation time, the SNR of the ranging signal, etc., are analyzed and evaluated by numerical experiments.