Recently, organometal halide perovskites (OHPs) have achieved significant advancement in photovoltaics, lightemitting diodes, X-ray detectors, and transistors. However, commercialization and practical applications were hindered by the notorious ion migration issue of OHPs. Here, we report a simple solvent-based surface passivation strategy with organic halide salts (methylammonium bromide (MABr) and phenylethylammonium bromide (PEABr)) to suppress the ion migration of MAPbBr 3 single crystals. The surface passivation effect is evidenced by the stronger photoluminescence (PL) intensity and extended PL lifetime. Using the pulse voltage and continuous voltage current−voltage measurements, we found that single crystals with surface passivation showed negligible hysteresis on the surface due to the suppression of ion migration. As a result, the dark current stability of coplanar structure devices was significantly improved. Moreover, the vertical structure X-ray detectors with PEABr treatment exhibited a high sensitivity of 15 280 μC Gy air −1 cm −2 and a low detection limit of 87 nGy air s −1 under 5 V bias. The proposed technology would be a versatile tool to improve the performance of perovskite photoelectronic devices.

High-resolution spatial data have become increasingly available with modern data collection techniques and efforts. However, it is often inappropriate to use the default geographic units to perform spatial analysis due to unstable estimates with small areas (e.g. cancer rates for census blocks or tracts). Regionalization is aggregating small units into relatively larger areas while optimizing a homogeneity measure (such as the sum of squared differences). For exploratory spatial analysis, regionalization may help remove spurious data variation through aggregation and discover hidden patterns in data (such as areas of unusually high cancer rates). Towards this goal, this research introduces several improvements to a recent group of regionalization methods -REDCAP (Guo 2008) and conducts evaluation experiments with synthetic data sets to assess and compare the capability of regionalization methods for exploratory spatial analysis. One of the major improvements is the integration of a local empirical Bayes smoother (EBS) with the regionalization methods. We generate a large number of synthetic data sets with controlled spatial patterns to evaluate the performance of both new and existing methods. Evaluation results show that the new methods (integrated with EBS) perform significantly better than their original versions and other methods (including the EBS method on its own) in terms of detecting the true patterns in the synthetic data sets.

High-performance self-powered photodetectors based on GaN microwire array/Si heterojunctions show a broadband photoresponse with high EQE, responsivity and detectivity at zero bias.

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GaN nano/microwires, due to their large surface-tovolume ratio and the reduced dimensionality, have been widely used in high-performance ultraviolet (UV) photodetectors (PDs). However, there has been a fundamental trade-off between the photocurrent gain and the speeds of PDs, which have limited their practical applications. In this work, highly ordered GaN microwire array based Schottky UV PDs have been fabricated, and optimizing Si doping concentrations can entirely improve the performances of the devices. The results show that output photocurrent increases monotonously as increasing doping concentration, while the dark current experiences a decrease followed by an increase, resulting in an optimized value under a certain doping concentration. At doping concentration of 1 × 10 18 cm −3 with 2.2 mW cm −2 illuminating intensity, the sensitivity, responsivity, and detectivity of the devices are greatly enhanced by 1.84 × 10 4 %, 163%, and 2103%, respectively. Meanwhile, the time-dependent response in Si-doped device possesses fast response time (τ on < 10 ms and τ off < 10 ms) at this optimum concentration, compared with that of undoped one (τ on = 70 ms and τ off = 90 ms). The effective advances in the devices are attributed to the increased Schottky barrier height by Si doping and the intensive oxygen molecules adsorption and desorption processes in microwire surface. This study offers a design guideline for the optimum doping concentration for obtaining high performances in microwire-based PDs.

The corrosion behavior of 2205 DSS in HCl solutions containing sulfide were investigated using mass loss test, electrochemical measurements, scanning Kelvin probe, scanning electron microscope (SEM) and X-ray photoelectron spectroscopy (XPS). The results showed that Na2S had significant effect on corrosion behavior of 2205 DSS in dilute HCl solutions. Slight Na2S can prevent the passive film from localized attacking of Cl- in HCl solution with a concentration lower than 0.1 mol/L. However, when the concentration of HCl solution higher than 0.137 mol/L, Na2S addition will tremendously promote corrosion. The intergranular corrosion combined surficial active dissolution of 2205 DSS could happen in HCl + Na2S solution.

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