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 Gyair-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 nGyair 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.

High Stability Electron Field Emitters Synthesized via the Combination of Carbon Nanotubes and N2-Plasma Grown Ultrananocrystalline Diamond Films.

An electron field emitter with superior electron field emission (EFE) properties and improved lifetime stability is being demonstrated via the combination of carbon nanotubes and the CH4/N2 plasma grown ultrananocrystalline diamond (N-UNCD) films. The resistance of the carbon nanotubes to plasma ion bombardment is improved by the formation of carbon nanocones on the side walls of the carbon nanotubes, thus forming strengthened carbon nanotubes (s-CNTs). The N-UNCD films can thus be grown on s-CNTs, forming N-UNCD/s-CNTs carbon nanocomposite materials. The N-UNCD/s-CNTs films possess good conductivity of σ = 237 S/cm and marvelous EFE properties, such as low turn-on field of (E0) = 3.58 V/µm with large EFE current density of (J(e)) = 1.86 mA/cm(2) at an applied field of 6.0 V/µm. Moreover, the EFE emitters can be operated under 0.19 mA/cm(2) for more than 350 min without showing any sign of degradation. Such a superior EFE property along with high robustness characteristic of these combination of materials are not attainable with neither N-UNCD films nor s-CNTs films alone. Transmission electron microscopic investigations indicated that the N-UNCD films contain needle-like diamond grains encased in a few layers of nanographitic phase, which enhanced markedly the transport of electrons in the N-UNCD films. Moreover, the needle-like diamond grains were nucleated from the s-CNTs without the necessity of forming the interlayer that facilitate the transport of electrons crossing the diamond-to-Si interface. Both these factors contributed to the enhanced EFE behavior of the N-UNCD/s-CNTs films.

Electron field emission enhancement of vertically aligned ultrananocrystalline diamond-coated ZnO core-shell heterostructured nanorods.

Enhanced electron field emission (EFE) behavior of a core-shell heterostructure, where ZnO nanorods (ZNRs) form the core and ultrananocrystalline diamond needles (UNCDNs) form the shell, is reported. EFE properties of ZNR-UNCDN core-shell heterostructures show a high emission current density of 5.5 mA cm(-2) at an applied field of 4.25 V µm(-1) , and a low turn-on field of 2.08 V µm(-1) compared to the 1.67 mA cm(-2) emission current density (at an applied field of 28.7 V µm(-1) ) and 16.6 V µm(-1) turn-on field for bare ZNRs. Such an enhancement in the field emission originates from the unique materials combination, resulting in good electron transport from ZNRs to UNCDNs and efficient field emission of electrons from the UNCDNs. The potential application of these materials is demonstrated by the plasma illumination measurements that lowering the threshold voltage by 160 V confirms the role of ZNR-UNCDN core-shell heterostructures in the enhancement of electron emission.

Microplasma illumination enhancement of vertically aligned conducting ultrananocrystalline diamond nanorods.

Vertically aligned conducting ultrananocrystalline diamond (UNCD) nanorods are fabricated using the reactive ion etching method incorporated with nanodiamond particles as mask. High electrical conductivity of 275 Ω·cm-1 is obtained for UNCD nanorods. The microplasma cavities using UNCD nanorods as cathode show enhanced plasma illumination characteristics of low threshold field of 0.21 V/µm with plasma current density of 7.06 mA/cm2 at an applied field of 0.35 V/µm. Such superior electrical properties of UNCD nanorods with high aspect ratio potentially make a significant impact on the diamond-based microplasma display technology.