Scintillators are widely utilized for radiation detections in many fields, such as nondestructive inspection, medical imaging, and space exploration. Lead halide perovskite scintillators have ...recently received extensive research attention owing to their tunable emission wavelength, low detection limit, and ease of fabrication. However, the low light yields toward X‐ray irradiation and the lead toxicity of these perovskites severely restricts their practical application. A novel lead‐free halide is presented, namely Rb2CuBr3, as a scintillator with exceptionally high light yield. Rb2CuBr3 exhibits a 1D crystal structure and enjoys strong carrier confinement and near‐unity photoluminescence quantum yield (98.6%) in violet emission. The high photoluminescence quantum yield combined with negligible self‐absorption from self‐trapped exciton emission and strong X‐ray absorption capability enables a record high light yield of ≈91056 photons per MeV among perovskite and relative scintillators. Overall, Rb2CuBr3 provides nontoxicity, high radioluminescence intensity, and good stability, thus laying good foundations for potential application in low‐dose radiography.
A new lead‐free halide Rb2CuBr3 scintillator with 1D crystal structure is presented. It exhibits self‐trapped exciton emission with a large Stokes shift (0.91 eV). Thus, it has near‐unity photoluminescence quantum yield (98.6%) and a high radioluminescence light yield of ≈91 056 photons per MeV.
An X‐ray detector with high sensitivity would be able to increase the generated signal and reduce the dose rate; thus, this type of detector is beneficial for applications such as medical imaging and ...product inspection. The inorganic lead halide perovskite CsPbBr3 possesses relatively larger density and a higher atomic number in contrast to its hybrid counterpart. Therefore, it is expected to provide high detection sensitivity for X‐rays; however, it has rarely been studied as a direct X‐ray detector. Here, a hot‐pressing method is employed to fabricate thick quasi‐monocrystalline CsPbBr3 films, and a record sensitivity of 55 684 µC Gyair−1 cm−2 is achieved, surpassing all other X‐ray detectors (direct and indirect). The hot‐pressing method is simple and produces thick quasi‐monocrystalline CsPbBr3 films with uniform orientations. The high crystalline quality of the CsPbBr3 films and the formation of self‐formed shallow bromide vacancy defects during the high‐temperature process result in a large µτ product and, therefore, a high photoconductivity gain factor and high detection sensitivity. The detectors also exhibit relatively fast response speed, negligible baseline drift, and good stability, making a CsPbBr3 X‐ray detector extremely competitive for high‐contrast X‐ray detections.
The hot‐pressing fabrication method for quasi‐monocrystalline CsPbBr3 thick film and the performance of their X‐ray detection are introduced. The high crystalline quality of CsPbBr3 films and the formation of self‐formed shallow bromide vacancy defects during the high‐temperature process result in a large µτ product and therefore high photoconductivity gain factor and record‐high detection sensitivity.
Abstract
Atomic-resolution Cs-corrected scanning transmission electron microscopy revealed local shifting of two oxygen positions (O
I
and O
II
) within the unit cells of a ferroelectric (Hf
0.5
Zr
...0.5
)O
2
thin film. A reversible transition between the polar
Pbc
2
1
and antipolar
Pbca
phases, where the crystal structures of the 180° domain wall of the
Pbc
2
1
phase and the unit cell structure of the
Pbca
phase were identical, was induced by applying appropriate cycling voltages. The critical field strength that determined whether the film would be woken up or fatigued was ~0.8 MV/cm, above or below which wake-up or fatigue was observed, respectively. Repeated cycling with sufficiently high voltages led to development of the interfacial nonpolar
P
4
2
/
nmc
phase, which induced fatigue through the depolarizing field effect. The fatigued film could be rejuvenated by applying a slightly higher voltage, indicating that these transitions were reversible. These mechanisms are radically different from those of conventional ferroelectrics.
Abstract
The resistive switching effect in memristors typically stems from the formation and rupture of localized conductive filament paths, and HfO
2
has been accepted as one of the most promising ...resistive switching materials. However, the dynamic changes in the resistive switching process, including the composition and structure of conductive filaments, and especially the evolution of conductive filament surroundings, remain controversial in HfO
2
-based memristors. Here, the conductive filament system in the amorphous HfO
2
-based memristors with various top electrodes is revealed to be with a quasi-core-shell structure consisting of metallic hexagonal-Hf
6
O and its crystalline surroundings (monoclinic or tetragonal HfO
x
). The phase of the HfO
x
shell varies with the oxygen reservation capability of the top electrode. According to extensive high-resolution transmission electron microscopy observations and ab initio calculations, the phase transition of the conductive filament shell between monoclinic and tetragonal HfO
2
is proposed to depend on the comprehensive effects of Joule heat from the conductive filament current and the concentration of oxygen vacancies. The quasi-core-shell conductive filament system with an intrinsic barrier, which prohibits conductive filament oxidation, ensures the extreme scalability of resistive switching memristors. This study renovates the understanding of the conductive filament evolution in HfO
2
-based memristors and provides potential inspirations to improve oxide memristors for nonvolatile storage-class memory applications.
Metal halide perovskites and derivatives exhibit a high sensitivity and low detection limit as direct X‐ray detectors. Inorganic 2D bismuth halide perovskites are promising for X‐ray detections, but ...have not been reported. Moreover, the quantitative relationship between the structural dimensionality of A3B2X9 perovskites and their compositions has never been investigated, and the underlying mechanism is unclear. Here, the key structural descriptors for 2D A3B2X9 perovskite derivatives are reported: i) octahedral factor μ, 0.377 < μ < 0895; ii) tolerance factor t, 0.8 < t < 1.06; iii) (rA‐0.55)/t < 1.48 Å. Accordingly, a new 2D A3B2X9 perovskite derivative, Rb3Bi2I9, with high X‐ray attenuation coefficients is found. The assembled X‐ray detector exhibits a high μτ product of 2.51 × 10−3 cm2 V−1, good sensitivity for 159.7 μC Gyair−1 cm−2, and a record low detection limit of 8.32 nGyair s−1 among all direct and indirect perovskite X‐ray detectors. The device also exhibits good stability toward external bias and continuous gamma ray radiations (480 000 Gy). This work provides crystal structural insights to rationally design 2D perovskites for new types of radiation detectors.
The key structural descriptors are reported for 2D A3B2X9 perovskite derivatives. By following the above designing rules, Rb3Bi2I9 is assembled into an X‐ray detector, exhibiting a low detection limit of 8.32 nGyair s−1 and suppressed ions migration. The inorganic composition also guarantees excellent stability toward continuous radiation from the 60Co source.
Electrochemical nitrate reduction reaction (NO3RR) offers a new pathway for low-temperature green ammonia synthesis. It is widely known that copper and its copper oxide catalysts are selective for ...NO3RRs, although the role played by their oxidation state in catalysis is not fully understood. Here, we found that in situ electrochemical reduction modulates the oxidation state of copper facilitating in situ loading of Cu2O active sites on island-like copper, and investigated the effect of cuprous oxide on nitrate reduction. We found that the improvement of ammonia yield (Faraday efficiency: 98.28%, selectivity: 96.6%) was closely related to the generation of Cu2O, which exceeded the performance of the state-of-the-art catalysts available today. The presence of a multilayer structure of the material was demonstrated by X-ray photoelectron spectroscopy combined with ion beam sputtering. Using operando Raman spectroscopy, we monitored the reduction process of the catalyst surface oxide species at the applied potential. Density functional theory (DFT) calculations indicated that the stable presence of Cu(I) effectively promotes the conversion of *HNOH to *HNHOH. We optimized the model building for DFT calculations and established relatively more reliable reaction paths, which provided a strong support for a further understanding of the reaction mechanism of NO3RR.
Through oxygen profile engineering, we fabricated W/AlOx/Al2O3/Pt bilayer memristors with a 250-nm feature size. The AlOx fabricated by sputtering serves as an oxygen vacancy source, whereas the ...Al2O3 deposited by atomic layer deposition acts as a dominant resistive switching (RS) layer. Our devices show forming-free RS behaviors with high speed (28 ns), uniform resistance distribution, large on/off ratio (~103@100K, ~103@298K, and ~80@400K), and good retention. Besides, temperature stability with record high endurance from cryogenic to high-temperature (108@100K, 1010@298K, and 107@400K) is demonstrated, to the best of our knowledge.
Abstract
X-ray detectors are broadly utilized in medical imaging and product inspection. Halide perovskites recently demonstrate excellent performance for direct X-ray detection. However, ionic ...migration causes large noise and baseline drift, limiting the detection and imaging performance. Here we largely eliminate the ionic migration in cesium silver bismuth bromide (Cs
2
AgBiBr
6
) polycrystalline wafers by introducing bismuth oxybromide (BiOBr) as heteroepitaxial passivation layers. Good lattice match between BiOBr and Cs
2
AgBiBr
6
enables complete defect passivation and suppressed ionic migration. The detector hence achieves outstanding balanced performance with a signal drifting one order of magnitude lower than all previous studies, low noise (1/
f
noise free), a high sensitivity of 250 µC Gy
air
−1
cm
–2
, and a spatial resolution of 4.9 lp mm
−1
. The wafer area could be easily scaled up by the isostatic-pressing method, together with the heteroepitaxial passivation, strengthens the competitiveness of Cs
2
AgBiBr
6
-based X-ray detectors as next-generation X-ray imaging flat panels.
2D ‐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. ‐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 ‐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 PbBr64− 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.
A ‐oriented 2D EPZPbBr4 (EPZ = 1‐ethylpiperazine) perovskite with minimized tilting and interlayer distance is designed through A‐site stereo‐hindrance engineering. The piperazine functional group pushes Pb─Br─Pb closer to a straight line (maximum Pb─Br─Pb angle ≈180°), suppressing the tilting and electron–phonon coupling. The EPZPbBr4 X‐ray detector exhibits specific detectivity of 1.23 × 108 µC Gy−1 cm−1 A−1/2.
PDF
