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High-temperature annealing has been regarded as an effective technology to improve the performance of Ga2O3-based solar-blind photodetectors (SBPDs). However, as a metastable phase, ε-Ga2O3 thin film may undergo phase transformation during post-annealing. Therefore, it is necessary to investigate the effect of the phase transition and the defect formation or desorption on the performance of photodetectors during post-annealing. In this work, the ε-Ga2O3 thin films were grown on c-plane sapphire with a two-step method, carried out in a metal-organic chemical vapor deposition (MOCVD) system, and the ε-Ga2O3 metal-semiconductor-metal (MSM)-type SBPDs were fabricated. The effects of post-annealing on ε-Ga2O3 MSM SBPDs were investigated. As a metastable phase, ε-Ga2O3 thin film undergoes phase transition when the annealing temperature is higher than 700 °C. As result, the decreased crystal quality makes an SBPD with high dark current and long response time. In contrast, low-temperature annealing at 640 °C, which is the same as the growth temperature, reduces the oxygen-related defects, as confirmed by X-ray photoelectron spectroscopy (XPS) measurement, while the good crystal quality is maintained. The performance of the SBPD with the post-annealing temperature of 640 °C is overall improved greatly compared with the ones fabricated on the other films. It shows the low dark current of 0.069 pA at 10 V, a rejection ratio (Rpeak/R400) of 2.4 × 104 (Rpeak = 230 nm), a higher photo-to-dark current ratio (PDCR) of 3 × 105, and a better time-dependent photoresponse. These results indicate that, while maintaining no phase transition, post-annealing is an effective method to eliminate point defects such as oxygen vacancies in ε-Ga2O3 thin films and improve the performance of SBPDs. [ABSTRACT FROM AUTHOR]

In this study, an Ag-doped Ni(OH)2 (Ag:Ni(OH)2) thin film is fabricated by solution process with Ag concentration of 2% at 200 °C and applied to threshold switching selector devices. X-ray photoelectron spectroscopy and high-resolution transmission electron microscopy analysis confirm that the matrix contains 72% Ni(OH)2 and 28% NiO, while the Ag is doped as ion state. As the processing temperature increases, the Ni(OH)2 matrix changes to NiO, and the doped Ag tends to metal state. Selector devices with Pt bottom and top electrodes were fabricated and measured. Compared with a Pt/Ag:NiO/Pt device, which shows non-volatile resistive switching characteristics, bi-directional threshold switching behavior is demonstrated in the Pt/Ag:Ni(OH)2/Pt device. The selectivity is larger than 104. The high/low resistance state cycles have been measured by half-bias pulse stimulation without obvious deterioration. Since Ag ion in Ni(OH)2 matrix shows fast diffusion, a thin Ag filament could be formed at low voltage, which then disperses and fractures after the voltage is removed. It corresponds to the main mechanism of bi-directional threshold switching. For the Pt/Ag:NiO/Pt device, the formation of thicker Ag filaments at higher electric fields leads to non-volatile resistive switching. [ABSTRACT FROM AUTHOR]

The ε-Ga2O3 p–n heterojunctions (HJ) have been demonstrated using typical p-type oxide semiconductors (NiO or SnO). The ε-Ga2O3 thin film was heteroepitaxial grown by metal organic chemical vapor deposition (MOCVD) with three-step growth method. The polycrystalline SnO and NiO thin films were deposited on the ε-Ga2O3 thin film by electron-beam evaporation and thermal oxidation, respectively. The valence band offsets (VBO) were determined by x-ray photoelectron spectroscopy (XPS) to be 2.17 eV at SnO/ε-Ga2O3 and 1.7 eV at NiO/ε-Ga2O3. Considering the bandgaps determined by ultraviolet-visible spectroscopy, the conduction band offsets (CBO) of 0.11 eV at SnO/ε-Ga2O3 and 0.44 eV at NiO/ε-Ga2O3 were obtained. The type-II band diagrams have been drawn for both p–n HJs. The results are useful to understand the electronic structures at the ε-Ga2O3 p–n HJ interface, and design optoelectronic devices based on ε-Ga2O3 with novel functionality and improved performance. [ABSTRACT FROM AUTHOR]

In this work, MIL-100(Fe)-decorated mesoporous carbon powders (MC@MIL-100(Fe)) were prepared by in situ growth of MIL-100(Fe) on the surface of ZIF-8 framework-based mesoporous carbons (MC). The hybrid material was characterized using SEM equipped with EDS mapping for morphology investigation, X-ray photoelectron spectroscopy for chemical valence analysis, and X-ray diffraction for crystal structure determination. The developed sensor separated from the traditional bismuth film decoration, and simultaneously, MC@MIL-100(Fe) was applied for the first time to electrochemically detect trace amounts of Pb(II) and Cd(II). The fabricated MC@MIL-100(Fe)-based electrochemical sensor showed excellent response to the target analytes at –0.55 and − 0.75 V for lead and cadmium ions, respectively. By adjusting some measurement parameters, that is, the loading concentration of MC@MIL-100(Fe), acidity of the HAc-NaAc buffer (ABS), deposition potential, and deposition time, the analytical performance of the proposed electrochemical sensor was examined by exploring the calibration curve, repeatability, reproducibility, stability, and anti-interference under optimized conditions. The response current of the proposed MC@MIL-100(Fe) electrochemical sensor showed a well-defined linear relationship in the concentration ranges of 2–250 and 2–270 μg·L−1 for Cd(II) and Pb(II), respectively. In addition, the detection limits of the sensor for Cd(II) and Pb(II) were 0.18 and 0.15 μg L−1, respectively, which are well below the World Health Organization (WHO) drinking water guideline value. The MC@MIL-100(Fe) can be potentially used as an electrochemical platform for monitoring heavy metals in surface water, with satisfactory results. [Display omitted] • A noval heavy metal ion sensor based on MC@MIL-100 (Fe) was developed. • The incorporation of MC material reduced the background current of the detection. • The LOD of the sensor for Pb(II) and Cd(II) as low as 0.15 and 0.18 μg·L−1. • MC@MIL-100 (Fe) based sensor is expected to be used in actual water samples. [ABSTRACT FROM AUTHOR]

In the present work, hematite–boron-carbonitride (Fe 2 O 3 –BCN) nanosheets were synthesized by a simple hydrothermal reaction and the following high temperature treatment. The morphology, structure and chemical composition of the as-prepared material were carefully characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD), and X-ray photoelectron spectroscopy (XPS). The Fe 2 O 3 –BCN nanosheets were used to modified on the surface of the glassy carbon electrode to fabricate an electrochemical sensor for lead ions (Pb(II)) via differential pulse anodic stripping voltammetry (DPASV). At the same time, the influence of the modification concentration, solution acidity, deposition potential and deposition time on response peak current of Pb(II) at the Fe 2 O 3 –BCN-based electrochemical sensor was well investigated. Under the optimized conditions, the electrochemical signal and concentration of Pb(II) show two-stage linear relationship in the range of 0.5 – 40 μg/L and 40 –140 μg/L, with a limit of detection (LOD) of 0.129 μg/L. The Fe 2 O 3 –BCN-based electrochemical sensor shows excellent selectivity and anti-interference ability in the anti-interference experiments and actual sample analysis experiments, revealing its broad application in environmental monitoring of Pb(II). Fe 2 O 3 –BCN nanosheet-based electrochemical sensor was fabricated for sensitive determination of trace lead(II) in aqueous environmental samples with detection limit lower than 0.129 μg/L. [Display omitted] • 2D Fe 2 O 3 –BCN composite was easily synthesized via a hydrothermal method. • A noval Fe 2 O 3 –BCN-based electrochemical sensor was fabricated for Pb(II) detection. • The sensor show high sensitivity and good selectivity. • The sensor has a broad linear range with a low LOD of 0.129 μg/L. [ABSTRACT FROM AUTHOR]