2D Multilayered Perovskite Ferroelectric with Halogen Bond Induced Interlayer Locking Structure toward Efficient Self-Powered X-Ray Detection.

Due to the built‐in electric field induced by spontaneous polarization in hybrid perovskite (HP) ferroelectrics, the devices based on them exhibit excellent performance in self‐powered photodetection. However, most of the self‐powered photodetector are made of lead‐based HP ferroelectrics and have a relatively narrow photoresponse waveband. Although lead‐free HPs solve the problem of lead toxicity, their optoelectronic performance is inferior to that of lead‐based HPs and photoresponse waveband is limited by its optical band gap, which hinders their further application. To solve this problem, herein, a lead‐free HP ferroelectric (HDA)BiI5 (HDA is hexane‐1,6‐diammonium) with large spontaneous polarization shows an enhanced photocurrent and achieves x‐ray‐ultraviolet–visible‐near‐infrared (x‐ray‐UV–Vis–NIR) photoresponse through the ferro‐pyro‐phototronic (FPP) effect. The ferroelectric, pyroelectric, and photovoltaic characteristics coupled together in a single‐phase (HDA)BiI5 ferroelectric is an effective way to improve the performance of the devices. What is particularly attractive is that the FPP effect not only improves the optoelectronic performance of (HDA)BiI5, but also achieves broadband photoresponses beyond its optical absorption range. Especially, the current boosting with an exceptional contrast of ~1100% and 2400% under 520 and 637 nm, respectively, which is associated with FPP effect. Meanwhile, single crystal self‐powered photodetector based on (HDA)BiI5 also exhibit significant FPP effects even under high‐energy x‐ray, which owns an outstanding sensitivity of 170.7 μC Gy−1 cm−2 and a lower detection limit of 266 nGy s−1 at 0 V bias. Therefore, it is of great significance to study the coupling of multiple physical effects and improve device performance based on lead‐free HP ferroelectrics.image

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.

Quasi-2D DJ type perovskites theoretically offer excellent properties for X-ray detection, but they often face issues such as phase segregation and small crystal size. In this study, we synthesized large single crystals of quasi-2D DJ type perovskite (3AMPY)(MA)Pb2Br7 using temperature-controlled crystallization. The resulting X-ray detector exhibited high resistivity (1.78 × 109 Ω cm), a carrier mobility-lifetime (μτ) product of 9.32 × 10-4 cm2 V-1, a dark current of 5.6 × 10-8 A cm-2 V-1, and a sensitivity of 129.86 μC Gy-1 cm-2. These results demonstrate the potential of quasi-2D DJ type perovskites for high-performance X-ray detection and provide insights into improving crystal growth for optoelectronic applications.

Summary form only given. Measurements have been made on 4-mm-diameter gas proportional straw tubes with lengths up to 1 m, operating with a gas mixture tailored for both efficient X-ray detection and high-rate operation. Using a new high-bandwidth shaping amplifier, which has an impulse response of about 3.5 ns full width at half maximum (FWHM), a clear picture of signal reflections from the end of anode wire has been obtained. Electronic noise levels resulting from the various modes of anode wire termination, and the lowest signal levels that can be used to satisfy high-rate operation and efficient particle or transition radiation photon detection have been determined. >

A new X-ray image intensifier(Toshiba J-type I.I.)has been developed in response to the digital X-ray image requirements of recent diagnostic systems. In the J-type I.I., the input phosphor screen(450-μm thick, CsI)has been deposited directly on the input window. Since there is no space between the input window and phosphor screen, the scattering of X-rays at the input window is reduced. Consequently, the X-ray detection efficiency over a wide range of X-ray tube operating voltages is also improved. Our studies have shown that the 10-mm contrast ratio is 24(for a 9 inch I.I.). Using International Electrotechnical Commission(IEC)Standard methods, we have concluded that the detective quantum efficiency(DQE)is 70%. We have also compared the characteristics of the J-type I.I.with those of the conventional G-type I.I. using the DFP-2000A DF system(TOSHIBA). The main results are enumerated below. (1)The veiling-glare fraction(VGF)was about 5% less for the J-type I.I. (2)The resolution quality was the same for both types of I.I. (3)Noise was less for the J-type I.I.because of the improvement in DQE. (4)The signal to noise ratio was higher for the J-type I.I.because of the reduction of noise. (5)Receiver operating characteristic(ROS)analysis showed that signal detectability was better for the J-type I.I.

van der Waals heterostructures formed by vertically stacking two-dimensional (2D) crystals can not only harness the already fascinating properties of their constituent monolayers but also extend them due to the coupled interlayer interactions. With their emerged interlayer and intralayer excitons, 2D transition metal dichalcogenides (TDMC) crystals and their heterostructures have drawn growing attention for the applications of nanoelectronics, optoelectronics and nanophotonics. Yet, there are few studies on how interlayer and interfacial interactions influence the thermal transport in TDMC heterostructures which is critical for heat management. In this work, we investigate the lateral and out-of-the-plane thermal conductivity (κ) of four prototype TDMC heterostructures (bilayer MoS2 and WS2, heterobilayer MoS2/WS2 and superlattice MoS2/WS2) by solving the phonon Boltzmann transport equation from first-principles. The calculated room-temperature lateral κ of bilayer MoS2 and WS2 are 61.13 W m−1 K−1 and 87.52 W m−1 K−1, respectively, in reasonable agreement with literature experiments. The weak interlayer interactions in the heterobilayer MoS2/WS2 help preserve the high lateral thermal transport (70.01 W m−1 K−1) of its constituent monolayer. In the superlattice MoS2/WS2, there exist strong interlayer and interfacial interactions between the alternating MoS2 and WS2 monolayer which reduce the lateral κ to be 7.22 W m−1 K−1 by a factor of 10. The greatly reduced lateral κ of the superlattice mainly arises from the low phonon relaxation time, which indicates the existence of strong interfacial anharmonic phonon scattering. This work aims at uncovering the physics of emerged thermal transport properties in TDMC heterostructures and helps advance their applications in heat management among nanoelectronics and optoelectronics.

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 Cs0.1 FA0.9 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 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.

Metal-halide perovskite single crystals (SCs) are promising candidates for next-generation X-ray detectors. X-ray detectors fabricated using perovskite FAPbI3 SCs exhibit high detection sensitivity. However, two pressing issues still need to be addressed for practical applications: the orientation-controlled growth and environmentally friendly acquisition of high-quality FAPbI3 SCs. In this study, large high-quality perovskite FAPbI3 SC rods (SCRs) with unique orientation are grown using a biomass-derived green solvent. Owing to the high carrier mobility and large bulk resistivity of the oriented FAPbI3 SCRs, the SC detectors realize a record high X-ray detection sensitivity (2.16 × 105 µC Gy-1 cm-2) and high sensitivity to dark current density ratio (1.93 × 109Gy-1 s). Furthermore, the detectors exhibit both ultralow dark and X-ray current drifts, as well as a detection limit of 2 nGy s-1. These characteristics enable the detectors to achieve high-resolution X-ray imaging, even at dose rates as low as 12 nGy s-1. This study not only contributes a new technical solution for low-dose X-ray detection, but also establishes a new approach for the low-cost and environmentally friendly production of core materials for X-ray detectors.

Many recent computed tomography (CT) dose reduction approaches belong to one of three categories: statistical reconstruction algorithms, efficient x-ray detectors, and optimized CT acquisition schemes with precise control over the x-ray distribution. The latter category could greatly benefit from fast and accurate methods for dose estimation, which would enable real-time patient-specific protocol optimization. The authors present a new method for volumetrically reconstructing absorbed dose on a per-voxel basis, directly from the actual CT images. The authors' specific implementation combines a distance-driven pencil-beam approach to model the first-order x-ray interactions with a set of Gaussian convolution kernels to model the higher-order x-ray interactions. The authors performed a number of 3D simulation experiments comparing the proposed method to a Monte Carlo based ground truth. The authors' results indicate that the proposed approach offers a good trade-off between accuracy and computational efficiency. The images show a good qualitative correspondence to Monte Carlo estimates. Preliminary quantitative results show errors below 10%, except in bone regions, where the authors see a bigger model mismatch. The computational complexity is similar to that of a low-resolution filtered-backprojection algorithm. The authors present a method for analytic dose reconstruction in CT, similar to the techniques used in radiation therapy planning with megavoltage energies. Future work will include refinements of the proposed method to improve the accuracy as well as a more extensive validation study. The proposed method is not intended to replace methods that track individual x-ray photons, but the authors expect that it may prove useful in applications where real-time patient-specific dose estimation is required.

Early on, crystallography was a domain of mineralogy and mathematics and dealt mostly with symmetry properties and imaginary crystal lattices. This changed when Wilhelm Conrad Röntgen discovered X-rays in 1895, and in 1912, Max von Laue and his associates discovered that X-ray irradiated salt crystals would produce diffraction patterns that could reveal the internal atomic periodicity of the crystals. In the same year, the father-and-son team, Henry and Lawrence Bragg successfully solved the first crystal structure of sodium chloride and the era of modern crystallography began. Protein crystallography (PX) started some 20 years later with the pioneering work of British crystallographers. In the past 50–60 years, the achievements of modern crystallography and particularly those in PX have been due to breakthroughs in theoretical and technical advancements such as phasing and direct methods; to more powerful X-ray sources such as synchrotron radiation; to more sensitive and efficient X-ray detectors; to ever faster computers and to improvements in software. The exponential development of PX has been accelerated by the invention and applications of recombinant DNA technology that can yield nearly any protein of interest in large amounts and with relative ease. Novel methods, informatics platforms and technologies for automation and high-throughput have allowed the development of large-scale, high-efficiency macromolecular crystallography efforts in the field of structural genomics. Very recently, the X-ray free-electron laser sources and its applications in PX have shown great potential for revolutionizing the whole field again in the near future.

Weak interlayer interactions and nearly temperature independent electrical transport in p-type 1T′-MoTe2/Sb2Te3 superlattice-like films

2D perovskite single crystals (SCs) demonstrate significant potential for developing low-cost, stable, and low dose X-ray detection. However, the large interlayer spacing in 2D perovskite results in low carrier mobility, limiting the sensitivity enhancement of X-ray detection. Herein, a tandem detector is designed and assembled for the first time to solve the critical issue of low carrier transport efficiency in 2D perovskite SCs. The tandem SC detector establishes efficient cross-layer charge transport channels through a "layered synchronous collection" strategy, enabling a "short-range transport" mechanism. The unique "longitudinal short-range transport" reduces carrier transport distance and then decreases recombination and trap capture, thus significantly enhanced carrier collection efficiency. Consequently, these detectors not only maintain low dark current but also exhibit a higher response current than single-junction counterparts, resulting in superior X-ray detection performance. Specifically, the tandem SC detectors achieved a high sensitivity of 5218 µC Gy-1 cm-2, a low detection limit of 2.2 n Gy s-1, and a short response time of 1.8ms. Furthermore, the tandem detectors retain original response after continuous X-ray irradiation with a high dose of 2.4Gy. The combination of high stability and sensitivity enables the tandem SC detectors achieved high-definition imaging at 12.5 lp mm-1.

The accurate calculation of characteristic peak intensity is essential for interpreting X-ray spectra in electron microprobe analysis. Conventionally, the measured intensity from a standard of known composition is used as a reference to simplify the calculation. However, if no such standard is available, then all factors influencing X-ray generation and X-ray detection efficiency must be included. If the intensity and energy distribution of the background radiation can also be calculated, the investigator can simulate an entire spectrum from an assumed composition, gaining powerful benefits in setting up an experiment and in confirming the results. The study presented here demonstrates a fast method of spectrum simulation, suitable for energy-dispersive spectroscopy (EDS), and assesses the accuracy using 309 spectra from samples of known composition. These include K, L, and M lines from elements of atomic number 6-92, excited by beam energies in the range of 5-30 keV. The RMS error between 360 measured and calculated peak intensities was found to be 7.1%. Central to the method is the use of the ratio of peak intensity/total background intensity, which allows spectra to be compared from instruments of differing collection efficiency, thereby easing the collection of data over a wide range of conditions.

Quantum noise is an important factor influencing the quality of the images obtained by X-ray phase contrast imaging because it induces a random fluctuation on the intensity. In this paper, a method is reported to analyze the noise characteristics of hard X-ray differential phase contrast imaging, and the relationship between the quantum noise and images is determined by numerical simulation. The results show that the mean square deviations of the refractive and scattering images are inversely proportional to the visibility of moir fringe. That is to say, the higher visibility of moir fringe leads to the lower mean square deviations of the refractive and scattering images. Therefore, in the case of ensuring an enough X-ray detection efficiency, the improvement in the visibility of moir fringe will be beneficial to obtaining high-quality phase contrast images and the effective reduction of X-ray exposure dose.

The accurate calculation of characteristic peak intensity is essential for interpreting X-ray spectra in electron microprobe analysis. Conventionally, the measured intensity from a standard of known composition is used as a reference to simplify the calculation. However, if no such standard is available, then all factors influencing X-ray generation and X-ray detection efficiency must be included. If the intensity and energy distribution of the background radiation can also be calculated, the investigator can simulate an entire spectrum from an assumed composition, gaining powerful benefits in setting up an experiment and in confirming the results. The study presented here demonstrates a fast method of spectrum simulation, suitable for energydispersive spectroscopy (EDS), and assesses the accuracy using 309 spectra from samples of known composition. These include K, L, and M lines from elements of atomic number 6–92, excited by beam energies in the range of 5–30 keV. The RMS error between 360 measured and calculated peak intensities was found to be 7.1%. Central to the method is the use of the ratio of peak intensity/total background intensity, which allows spectra to be compared from instruments of differing collection efficiency, thereby easing the collection of data over a wide range of conditions.