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Diamond has an ultrawide bandgap with excellent physical properties, such as high critical electric field, excellent thermal conductivity, high carrier mobility, etc. Diamond with a hydrogen-terminated (H-terminated) surface has a negative electron affinity (NEA) and can easily produce surface electrons from valence or trapped electrons via optical absorption, thermal heating energy or carrier transport in a PN junction. The NEA of the H-terminated surface enables surface electrons to emit with high efficiency into the vacuum without encountering additional barriers and promotes further development and application of diamond-based emitting devices. This article reviews the electron emission properties of H-terminated diamond surfaces exhibiting NEA characteristics. The electron emission is induced by different physical mechanisms. Recent advancements in electron-emitting devices based on diamond are also summarized. Finally, the current challenges and future development opportunities are discussed to further develop the relevant applications of diamond-based electron-emitting devices. [ABSTRACT FROM AUTHOR]

Graphene has broad prospects for application in photonic devices. However, its zero-band gap limits its nonlinear optical (NLO) properties, and thus, its application. In this study, we synthesized reduced graphene oxide modified by Mn-doped semiconductor CdS nanoparticles (RGO/CdS:Mn) via a solvothermal method to study the development of NLO properties of graphene. The structures, morphologies and basic physical properties of RGO, CdS, RGO/CdS, and RGO/CdS:Mn were characterized. The third-order optical nonlinearities were tested by the Z-scan technique using a mode-locked Nd:YAG laser operating at 532 nm with a 30 ps pulse width. The results showed that the nonlinear susceptibility and saturation absorption of RGO/CdS:Mn were 15.3 and 26 times higher than those of RGO, respectively. The mechanism of the enhancement was analyzed based on the charge transfer between and within the components, and Mn doping produced trapping effect. The significantly improved optical nonlinearity of RGO/CdS:Mn lays a foundation for its applications in photonic devices. [ABSTRACT FROM AUTHOR]

Myocardial perfusion (MP) PET imaging plays a key role in risk assessment and stratification of patients with coronary artery disease. In this work, we proposed a patch-based artificial neural network (ANN) fusion approach that integrates information from the ML and the post-smoothed ML reconstruction to improve MP PET imaging. The proposed method was applied to images reconstructed from different noise levels to enhance quantification and task-based MP defect detection. Using the XCAT phantom, we simulated three MP PET imaging cases, one with normal perfusion and the other two with non-transmural and transmural regionally reduced perfusion of the left ventricular (LV) myocardium. The proposed ANN fusion technique was quantitatively evaluated in terms of the noise versus bias and noise versus contrast tradeoff, and compared with the post-smoothed ML reconstruction. Using the channelized Hotelling observer, we evaluated the detectability of the non-transmural and transmural defects through the receiver operating characteristic analysis. The quantitative results demonstrated that the ANN enhancement method reduced bias and improved contrast while reaching comparable noise to what the post-smoothed ML reconstruction achieved. Moreover, the ANN fusion technique significantly improved the defect detectability of both the non-transmural and transmural defects. In addition to the simulation study, we further evaluated the proposed method using patient data. Compared with the post-smoothed ML reconstruction, the ANN fusion improved the tradeoff between noise and the mean value on the LV myocardium, indicating its potential clinical application in MP PET imaging. [ABSTRACT FROM AUTHOR]

The first Schottky diodes based on n-CdMnTe crystals with pronounced rectifying properties are investigated. It is shown that the I–V characteristics of the diodes fabricated by printing colloidal graphite can be described by the Sah–Noyce–Shockley theory of generation–recombination in the space charge region. Exponential increase of forward current with voltage is limited by a relatively low barrier height at the graphite/CdMnTe contact (∼ 0.4 eV) and a significant series resistance of the crystal bulk (∼ 106 Ω at room temperature). Tunneling due to high concentration of uncompensated impurities in investigated Cd0.9Mn0.1Te crystals (7 × 1017 cm−3) does not allow increasing the reverse bias voltage to the values needed for the operation of x- and γ-ray detectors. High concentration of uncompensated donors is interpreted by the fact that a certain part of the Mn atoms does not substitute for Cd but plays a role of over-stoichiometric impurities. In the case of the presence of a thin intermediate insulator layer in the graphite/CdMnTe contact, a rapid increase in the current for both polarities of high voltage due to the Frenkel–Poole emission is observed. The obtained results shed light on the problems of technology of growing and post-processing CdMnTe crystals regarded as a prospective material for x- and γ-ray detectors. [ABSTRACT FROM AUTHOR]

This paper presents an analysis of the local electric field in hexagonal boron nitride (h-BN) by introducing a modified parameter. Based on the determination of the modified parameter of h-BN, the revised Lorenz equation is developed. Then the permittivity at high temperature and in the microwave frequency is investigated. In addition, this equation is derived for evaluating the temperature coefficient of the permittivity of h-BN. The analyses show that the permittivity increases with increasing temperature, which is mainly attributed to the positive temperature coefficient of the ionic polarizability. [ABSTRACT FROM AUTHOR]

In this work, the thermal phase separation and annealing optimization of ZrSiO4 thin films have been carried out. Following annealing optimization, the frequency-dependent electrical characteristics of the Al/ZrSiO4/p-Si/Al MOS capacitors were investigated in detail. The chemical evolution of the films under various annealing temperatures was determined by Fourier transform infrared spectroscopy (FTIR) measurements. The phase separation was determined by x-ray diffraction (XRD) measurements. The electrical parameters were determined via the capacitance–voltage (C–V), conductance–voltage (G/ω) and leakage-current–voltage (Ig–Vg). The results demonstrate that zirconium silicate formations are present at 1000 °C annealing with the SiO2 interfacial layer. The film was in amorphous form after annealing at 250 °C. The tetragonal phases of ZrO2 were obtained after annealing at 500 °C. When the temperature approaches 750 °C, transitions from the tetragonal phase to the monoclinic phase were observed. The obtained XRD peaks after 1000 °C annealing matched the crystalline peaks of ZrSiO4. This means that the crystalline zirconium dioxide in the structure has been converted into a crystalline silicate phase. The interface states increased to 5.71 × 1010 and the number of border traps decreased to 7.18 × 1010 cm−2 with the increasing temperature. These results indicate that an excellent ZrSiO4/Si interface has been fabricated. The order of the leakage current varied from 10−9 Acm−2 to 10−6 Acm−2. The MOS capacitor fabricated with the films annealed at 1000 °C shows better behavior in terms of its structural, chemical and electrical properties. Hence, detailed frequency-dependent electrical characteristics were performed for the ZrSiO4 thin film annealed at 1000 °C. Very slight capacitance variations were observed under the frequency variations. This shows that the density of frequency-dependent charges is very low at the ZrSiO4/Si interface. The barrier height of the device varies slightly from 0.776 eV to 0.827 eV under frequency dispersion. Briefly, it is concluded that the devices annealed at 1000 °C exhibit promising electrical characteristics. [ABSTRACT FROM AUTHOR]

With the first-principles method based on the density functional theory (DFT), we study the effect of defects on Cu-doped CdS. A single Cd vacancy, S vacancy or Cd interstitial is inserted into the Cd34Cu2S36 crystal structure, respectively. Band structures and the density of states (DOS) are calculated to investigate the effect of various defects on the electronic structures, which are considered to be associated with magnetic properties and optical properties. It turns out that the Cd vacancy, S vacancy and Cd interstitial have a significant influence on the ferromagnetic (FM) stability and optical properties. These results provide an approach to utilize Cu-doped CdS-based materials used as spintronics and optoelectronic devices efficiently. [ABSTRACT FROM AUTHOR]

Polycrystalline Sb2Te3−xSex samples were synthesized by the solid-state reaction method. The structural analysis showed that up to the maximal concentration of Se, the samples possess rhombohedral crystal symmetry (space group ). The increase of Se content increases the resistivity of the samples. The variation of phonon frequencies, observed from the Raman spectroscopic study, depicts an anomalous behaviour around . The sample Sb2Te2.8Se0.2 also shows maximum Seebeck coefficient, carrier concentration and thermoelectric power factor. The nature of the scattering mechanism controlling the thermopower data has been explored. The thermoelectric properties of the synthesized materials have been analyzed theoretically in the frame of the Boltzmann equation approach. [ABSTRACT FROM AUTHOR]