Halide perovskites and perovskite related materials for particle radiation detection.

Radiation detectors are widely used in physics, materials science, chemistry, and biology. Halide perovskites are known for their superior properties including tunable bandgaps and chemical compositions, high defect tolerance, solution-processable synthesis of films and crystals, and high carrier diffusion length. Recently, halide perovskites have attracted enormous interest as particle radiation detectors for both charged (α and ß) and uncharged (neutrons) particles. Solid-state detectors based on single crystal perovskites can detect α particles and thermal neutrons with energy-resolved spectra. Halide perovskite scintillators are also able to detect ß particles and fast neutrons. In this review, we briefly introduce the fundamentals of radiation detection and summarize the recent progress on halide perovskite detectors for particle radiation.

Role of the Metal-Semiconductor Interface in Halide Perovskite Devices for Radiation Photon Counting.

Halide perovskites are promising optoelectronic semiconductors. For applications in solid-state detectors that operate in low photon flux counting mode, blocking interfaces are essential to minimize the dark current noise. Here, we investigate the interface between methylammonium lead tri-iodide (MAPbI3) single crystals and commonly used high and low work function metals to achieve photon counting capabilities in a solid-state detector. Using scanning photocurrent microscopy, we observe a large Schottky barrier at the MAPbI3/Pb interface, which efficiently blocks dark current. Moreover, the shape of the photocurrent profile indicates that the MAPbI3 single-crystal surface has a deep fermi level close to that of Au. Rationalized by first-principle calculations, we attribute this observation to the defects due to excess iodine on the surface underpinning emergence of deep band-edge states. The photocurrent decay profile yields a charge carrier diffusion length of 10-25 µm. Using this knowledge, we demonstrate a single-crystal MAPbI3 detector that can count single γ-ray photons by producing sharp electrical pulses with a fast rise time of <2 µs. Our study indicates that the interface plays a crucial role in solid-state detectors operating in photon counting mode.

Thiol-Epoxy "Click" Chemistry to Engineer Cytocompatible PEG-Based Hydrogel for siRNA-Mediated Osteogenesis of hMSCs.

Thiol-epoxy "click" chemistry is employed for the first time to engineer a new cytocompatible PEG-based hydrogel system in aqueous media with the ability to encapsulate human mesenchymal stem cells (hMSCs) and control their fate for tissue regeneration. Cells were easily encapsulated into the hydrogels and exhibited high cell viability over 4 weeks of culture regardless of the presence of siRNA, complexed with polyethylenimine (PEI) in the form of siRNA/PEI nanocomplexes, indicating the biocompatibility of the developed hydrogel. Loading pro-osteogenic siNoggin in the hydrogel significantly enhanced the osteogenesis of encapsulated hMSCs, demonstrating the potential application of this system in tissue engineering.

Critical Role of Interface and Crystallinity on the Performance and Photostability of Perovskite Solar Cell on Nickel Oxide.

Hybrid perovskites are on a trajectory toward realizing the most efficient single-junction, solution-processed photovoltaic devices. However, a critical issue is the limited understanding of the correlation between the degree of crystallinity and the emergent perovskite/hole (or electron) transport layer on device performance and photostability. Here, the controlled growth of hybrid perovskites on nickel oxide (NiO) is shown, resulting in the formation of thin films with enhanced crystallinity with characteristic peak width and splitting reminiscent of the tetragonal phase in single crystals. Photophysical and interface sensitive measurements reveal a reduced trap density at the perovskite/NiO interface in comparison with perovskites grown on poly(3,4-ethylene dioxy thiophene) polystyrene sulfonate. Photovoltaic cells exhibit a high open circuit voltage (1.12 V), indicating a near-ideal energy band alignment. Moreover, photostability of photovoltaic devices up to 10-Suns is observed, which is a direct result of the superior crystallinity of perovskite thin films on NiO. These results elucidate the critical role of the quality of the perovskite/hole transport layer interface in rendering high-performance and photostable optoelectronic devices.

Graphene-aluminum nitride NEMS resonant infrared detector.

The use of micro-/nanoelectromechanical resonators for the room temperature detection of electromagnetic radiation at infrared frequencies has recently been investigated, showing thermal detection capabilities that could potentially outperform conventional microbolometers. The scaling of the device thickness in the nanometer range and the achievement of high infrared absorption in such a subwavelength thickness, without sacrificing the electromechanical performance, are the two key challenges for the implementation of fast, high-resolution micro-/nanoelectromechanical resonant infrared detectors. In this paper, we show that by using a virtually massless, high-electrical-conductivity, and transparent graphene electrode, floating at the van der Waals separation of a few angstroms from a piezoelectric aluminum nitride nanoplate, it is possible to implement ultrathin (460 nm) piezoelectric nanomechanical resonant structures with improved electromechanical performance (>50% improved frequency×quality factor) and infrared detection capabilities (>100× improved infrared absorptance) compared with metal-electrode counterparts, despite their reduced volumes. The intrinsic infrared absorption capabilities of a submicron thin graphene-aluminum nitride plate backed with a metal electrode are investigated for the first time and exploited for the first experimental demonstration of a piezoelectric nanoelectromechanical resonant thermal detector with enhanced infrared absorptance in a reduced volume. Moreover, the combination of electromagnetic and piezoelectric resonances provided by the same graphene-aluminum nitride-metal stack allows the proposed device to selectively detect short-wavelength infrared radiation (by tailoring the thickness of aluminum nitride) with unprecedented electromechanical performance and thermal capabilities. These attributes potentially lead to the development of uncooled infrared detectors suitable for the implementation of high performance, miniaturized and power-efficient multispectral infrared imaging systems.