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The wide band gap semiconductor Ga2O3 has become an excellent UV detection material due to its suitable band gap, high crystalline quality and thermal stability. In this paper, the microstructure of Ga2O3 with different thicknesses is characterized and the solar-blind detection performance of Ga2O3/p-Si heterojunctions are further investigated. XRD and UV–VIS demonstrate that Ga2O3 sputtered for 20 min is amorphous with a band gap of 4.98 eV, as the sputtering time increases, Ga2O3 grows along the (002) crystal plane and the band gap increases. XPS reveals that the lattice oxygen content in the Ga2O3 increases with the sputtering time, however, the Ga3+ content reaches a peak in Ga2O3 sputtered for 1.5 h. And the increasing of the binding energy between Ga-O in Ga2O3/p-Si heterojunctions accelerates response speed. Electrical experiments show that the heterojunction consisting of sputtered 1.5 h Ga2O3 and p-Si reaches a higher PDCR, with a value of 6684 at 5.7 V. Meanwhile, the rise and decay time of the heterojunction are 0.13 s and 0.14 s at 0 V, and the decay time gradually increases from 0.1 to 0.7 s with increasing the applied voltage. However, insertion of 20 nm Si-doped Ga2O3 as a hole-blocking layer at the interface of p-Si and Ga2O3 remarkably declines the decay time under various applied biases and causes no obvious damage to the photo current of the heterojunction. [ABSTRACT FROM AUTHOR]

Based on first-principles calculations and the Wannier-function-based tight-binding method, we investigate the topological electronic properties of designed noncentrosymmetric transition metal monochalcogenide superlattices AX/BX (A, B = Cr, Mo, W, A ≠B; X = Se, Te). Here, we mainly consider time-reversal symmetry (TRS) MoTe/WTe and MoSe/WSe and TRS broken CrTe/WTe and CrTe/MoTe, which are the Weyl and magnetic Weyl semimetals, respectively. The considered systems are nodal line semimetals with nodal lines on three mirror planes of the Brillouin zone of hexagonal lattice in the absence of spinâ€"orbit coupling (SOC). When considering the SOC, each nodal line opens a gap except for some pairs of Weyl points (WPs) on the kz ≠0 planes and the number of WPs is material-dependent. We identify the termination-dependent Fermi arc connection patterns on the (001) and (00 1 ˉ ) surfaces for four Weyl semimetal superlattices AX/BX. These results provide a theoretical basis to realize the possible applications of these superlattice materials in future topological electronic devices. [ABSTRACT FROM AUTHOR]

This paper presents a feasibility study of a gamma-ray imager using a hybrid collimation (HC) scheme. This detector is based on the use of a multiple pinhole collimator and a position sensitive scintillation detector with Anger logic readout. A pixelated semiconductor detector, located between the collimator and the scintillation detector, is used as a scattering detector. For gamma-rays scattered in the first detector and then stopped in the second detector, an image can be built up based on the joint probability of their passing through the collimator and falling into a broadened conical surface, defined by the detected Compton scattering event. Since these events have a much smaller angular uncertainty, they provide more information per photon compared with using solely the mechanical or electronic collimation. Therefore, the overall image quality can be improved. This feasibility study used a theoretical approach based on analyzing the resolution-variance tradeoff in images reconstructed using maximum a posteriori (MAP) algorithms. The effect of the detector configuration, Doppler broadening, the energy resolution of the scattering detector and mechanical aperture design are studied. The results showed that the combined collimation leads to a significant improvement in image quality at energies below 300 keV. However, due to the mask penetration, the performance of such a detector configuration is worse than a standard Compton camera above this energy. Index Terms--Compton-scattering, hybrid collimation.

Recent measurements of the performance of the newly available multi-pixel Hybrid Photodiode (M-HPD) have demonstrated their particular value in the detection of very low light-level signals in the visible region. The single and multiple photo-electron response characteristics of these devices is unmatched by any other room-temperature device. This characteristic, coupled with their speed of response and the availability of an internally-generated trigger signal when one or more of the pixels detect an event, makes them particularly interesting as possible photo-detectors for fast plastic scintillators and, in particular, as detectors for reading out scintillating fibres. The results of tests made when Minimum Ionising Particles (MIPs) pass through single and multi-clad plastic scintillating fibres have confirmed the usefulness of these devices in particle-tracking applications. The technique used to read-out 61 channels of data is described along with a way to view as many as 2000 fibres with just two 61-pixel MHPDs. Finally, an outline concept for a new high energy gamma-ray telescope is described. This could use multiple planes of scintillation fibres read-out by M-HPDs.

We have investigated the structural phase transition of FeCo and FeNi nanoparticles by molecular dynamics (MD) simulation using the generalized embedded atom potential (GEAM). It is found that the phase varies with the atomic compositions and annealing processes. By using the Honeycutt and Andersen index (HA index), bond order parameters (BOP) and pair correlation function (PCF), we found that a BCC to defective icosahedra phase transition occurs in the FeCo nanoparticle when Co composition is increased to about 60 at %. In the FeNi nanoparticle, three phases have been identified, namely, the BCC phase, the mixed BCC/FCC phase, and the multilayer defective icosahedral phase, which correspond to the Ni compositions of 0-20 at %, 20-70 at %, and 70-100 at %, respectively. Our simulations have well reproduced the phase transition points and most of the phases observed in recent experiments. [ABSTRACT FROM AUTHOR]

Based on semiempirical generalized embedded atom method (GEAM), we carried out molecular dynamics and Monte Carlo simulations to study the structural properties of FeCo and FeNi nanoparticles. It is found that these two kinds of nanoparticles possess a new stable quasicore-shell structure, no matter whether they are in molten or condensed state and whether they are prepared by annealing or quenching. In FeCo (FeNi) nanoparticles of various sizes and atom compositions, the quasicore-shell structure is always preferred, with the shell formed only by Fe atoms and the core formed by randomly distributed Co(Ni) and Fe atoms. We have also investigated the formation mechanism of the quasicore-shell structure by energy difference analysis of the pure and doped icosahedra structure of FeCo and FeNi nanoparticles. [ABSTRACT FROM AUTHOR]

The results of a feasibility study for a high-resolution PET detector system are presented. The detector is based on the use of etched LSO scintillation crystals viewed from just one end. We have demonstrated that this configuration yields Depth-of-Interaction (DOI) information whilst also preserving good energy and coincidence-time resolution. A prototype detector was built using a 4x4 crystal array coupled to 61-pixel hybrid photodiodes. The measurements demonstrate a DOI resolution of 5~7mm FWHM in a 30mm deep detector. The signal level was measured to be in the range 250 to 600 photoelectrons depending on the location of the 511 keV energy deposit in the crystal. A resolving-time of less than 5ns FWHM was estimated based on indirect measurements. The technique depends on the assumption that all of the events detected above a selected threshold value are, in fact, full-energy deposits. The validity of this assumption and the impact of the photons scattered in the object have been studied using a Monte Carlo simulation of the proposed small animal PET imager.