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Surface charge transfer doping (SCTD) is an alternative approach to achieving n-type doped diamonds since the n-type bulk doping of diamonds remains a challenge, but so far efficient diamond n-type SCTD has not been achieved. Here we provide a comprehensive study of the n-type SCTD of the diamond by using first-principles calculations based on the density functional theory. Taking the principle that ionization potentials of the dopants must be higher than those of the diamond, we screened a series of molecules that may be suitable for diamond n-type SCTD doping. Methyl viologen and benzyl viologen provide the largest amount of transfer electron among the common n-type SCTD dopants for the oxygen and fluorine terminated (100) surface diamond, with the electron areal densities of 2.60 × 10 13 cm − 2 and 9.20 × 10 12 cm − 2 , respectively. It is indicated that the transferred electron amount is positively correlated with the difference between the ionization potentials of the dopants and the electron affinity of the diamond, while the density of dopants also has a positive impact with a decreasing trend. The present work provides a useful understanding of the physical mechanism for the n-type SCTD of diamonds, and benefits the development of n-type SCTD diamond materials. [ABSTRACT FROM AUTHOR]

Nanodiamonds (NDs) are emerging as a promising candidate for multimodal bioimaging on account of their optical and spectroscopic properties. NDs are extensively utilized for bioimaging probes due to their defects and admixtures in their crystal lattice. There are many optically active defects presented in NDs called color centers, which are highly photostable, extremely sensitive to bioimaging, and capable of electron leap in the forbidden band; further, they absorb or emit light when leaping, enabling the nanodiamond to fluoresce. Fluorescent imaging plays a significant role in bioscience research, but traditional fluorescent dyes have some drawbacks in physical, optical and toxicity aspects. As a novel fluorescent labeling tool, NDs have become the focus of research in the field of biomarkers in recent years because of their various irreplaceable advantages. This review primarily focuses on the recent application progress of nanodiamonds in the field of bioimaging. In this paper, we will summarize the progress of ND research from the following aspects (including fluorescence imaging, Raman imaging, X-ray imaging, magnetic modulation fluorescence imaging, magnetic resonance imaging, cathodoluminescence imaging, and optical coherence tomography imaging) and expect to supply an outlook contribution for future nanodiamond exploration in bioimaging. [ABSTRACT FROM AUTHOR]

Titanium dioxide (TiO2) is a kind of wide-bandgap semiconductor. Nano-TiO2 devices exhibit size-dependent and novel photoelectric performance due to their quantum limiting effect, high absorption coefficient, high surface-volume ratio, adjustable band gap, etc. Due to their excellent electronic performance, abundant presence, and high cost performance, they are widely used in various application fields such as memory, sensors, and photodiodes. This article provides an overview of the most recent developments in the application of nanostructured TiO2-based optoelectronic devices. Various complex devices are considered, such as sensors, photodetectors, light-emitting diodes (LEDs), storage applications, and field-effect transistors (FETs). This review of recent discoveries in TiO2-based optoelectronic devices, along with summary reviews and predictions, has important implications for the development of transitional metal oxides in optoelectronic applications for researchers. [ABSTRACT FROM AUTHOR]

The hydrothermal approach has been used to fabricate a heterojunction of n-aluminum-doped ZnO nanorods/p-B-doped diamond (n-Al:ZnO NRs/p-BDD). It exhibits a significant increase in photoluminescence (PL) intensity and a blue shift of the UV emission peak when compared to the n-ZnO NRs/p-BDD heterojunction. The current voltage (I-V) characteristics exhibit excellent rectifying behavior with a high rectification ratio of 838 at 5 V. The n-Al:ZnO NRs/p-BDD heterojunction shows a minimum turn-on voltage (0.27 V) and reverse leakage current (0.077 μA). The forward current of the n-Al:ZnO NRs/p-BDD heterojunction is more than 1300 times than that of the n-ZnO NRs/p-BDD heterojunction at 5 V. The ideality factor and the barrier height of the Al-doped device were found to decrease. The electrical transport behavior and carrier injection process of the n-Al:ZnO NRs/p-BDD heterojunction were analyzed through the equilibrium energy band diagrams and semiconductor theoretical models. [ABSTRACT FROM AUTHOR]

N-TiO 2 nanorod clusters (Ncs)/p-degenerated boron-doped diamond (n-TiO 2 Ncs/p-DBDD) film heterojunction was prepared by hydrothermal method, and the photoelectric properties depending on temperature dependence were tested. Three distinct emission peaks of 402 nm, 429 nm and 454 nm were detected by the photoluminescence (PL) test under 355 nm ultraviolet light and excited in the blue-green region light. The heterojunction exhibited good rectification characteristics and thermal stability from room temperature to 180 °C. The forward current first decreases and then increases with increasing temperature. The 160 °C is considered to be the ideal high temperature for the best performance of the heterojunction, with the rectification ratio reaching 20.667. The carrier transport mechanisms and tunneling process of n-TiO 2 Ncs/p-DBDD heterojunction with temperature are analyzed in detail through the established band structure diagram. This study provides an effective way method for the potential development of high-temperature stable optoelectronic devices. [Display omitted] • Tested the high-temperature (RT-180 °C) electrical performance of n-TiO 2 Ncs/p-DBDD heterojunction devices for the first time. • The heterojunction exhibited good rectification characteristics and thermal stability from room temperature to 180 ° C. • The 160 °C is considered to be the ideal high-temperature for the best performance of the heterojunction, with the rectification ratio reaching 20.667. • he mechanism for the enhanced optical and electrical properties of this heterojunction is revealed. • This work provides a new path for the design and application of diamond-based devices. [ABSTRACT FROM AUTHOR]

Nanostructured n-type metal oxides/p-type boron-doped diamond heterojunctions have demonstrated a typical rectification feature and/or negative differential resistance (NDR) potentially applied in wide fields. Recently, the fabrication and electronic transport behavior of n-WO3 nanorods/p-diamond heterojunction at high temperatures were studied by Wang et al (2017 Appl. Phys. Lett. 110 052106), which opened the door for optoelectronic applications that can operate at high-temperatures, high-power, and in various harsh environments. In this perspective, an overview was presented on the future directions, challenges and opportunities for the optoelectronic applications based on the n-WO3 nanostructures/p-diamond heterojunction. We focus, in particular, on the prospects for its high temperature NDR, UV photodetector, field emission emitters, photocatalyst and optical information storage for a wide range of new optoelectronic applications. [ABSTRACT FROM AUTHOR]

In the past decades, even though the performance of electronic devices based on MoS 2 has reached a very high level, the service life, failure rate and stability of the devices often deteriorate with the increase of temperature when they work in high temperature or harsh environment. In this work, n-MoS 2 NSs/p-type boron-doped diamond (BDD) film heterojunction was fabricated by sol–gel method to investigate the temperature dependence of the optoelectronic transport behavior of the device, and the electrical properties of the heterojunction device at high temperature (RT-180 °C) were tested. The heterojunction presented all rectification characteristics from room temperature to 180 °C and exhibited good thermal stability. With the increase in temperature, the rectification ratio reached the maximum at 120 °C and turned into backward diodes at 160 °C and 180 °C. The mechanism of the current and rectification ratio of n-MoS 2 NSs/p-BDD heterojunction changing with temperature was mainly attributed to the decrease of tunneling current caused by the shift of Fermi level of the two semiconductors at high temperature. The heterojunction undergoes a transition from tunneling current to thermal excitation current, and the shift of Fermi level to the valence band of n-MoS 2 provides support for the transition to reverse diode. In accordance with the carrier transport behavior following ohmic laws, the current conduction of composite tunneling and the space charge limitation under different bias voltages and temperatures were also discussed, which provides theoretical and experimental basis for optimizing the design of new photoelectric devices in the field of high temperature optoelectronics. [Display omitted] • Tested the high-temperature (RT-180 °C) electrical performance of n-MoS 2 NSs/p-BDD heterojunction devices. • The n-MoS 2 NSs/p-BDD heterojunction presented all rectification characteristics from RT to 180 °C and exhibited good thermal stability. • The rectification ratio of n-MoS 2 NSs/p-BDD heterojunction reached the highest value at 120 °C and transformed into backward diode at 160 °C and 180 °C. [ABSTRACT FROM AUTHOR]

The dielectric properties and the role of grain boundaries in polycrystalline tetracene were studied at pressures of up to 21.3 GPa using in situ impedance spectroscopy measurements. Two anomalous changes in some of the electrical parameters (resistance, relaxation frequency and relative permittivity) were found at 6.0 and 19.0 GPa, which were related to the structural rearrangement and condensation reaction processes, respectively. Within this pressure range, grain boundaries play an important role in polycrystalline tetracene's conduction mechanism. Based on first-principles calculations, it was found that the variation in bulk resistance under pressure was mainly caused by a change of band gap. Intermolecular interactions are more sensitive to pressure than intramolecular interactions. The decrease in the relative permittivity under pressure indicates the existence of space charge polarization of the interface layer in addition to electronic polarization. [ABSTRACT FROM AUTHOR]

Highlights: [•] We report the epitaxial growth of ZnO nanorods (NRs) on diamond by thermal vapor transport method. [•] The epitaxial behaviors of ZnO NRs strongly depend on the selected diamond facets. [•] The n-ZnO NR/p-diamond heterojunctions are constructed. [•] A negative differential resistance is presented for the junction with degenerated p-type diamond. [ABSTRACT FROM AUTHOR]

Abstract: Zinc oxide (ZnO) nanorods grown on chemical vapor deposited diamond films by thermal vapor transport method have been investigated. In the initial growth status, the semi-spherical ZnO nuclei were preferably deposited near the growth steps on the terraces and the boundaries of diamond grains. With increasing the growth time, the [0001] orientated ZnO nanorods appeared and further covered the whole diamond film. It is found that the size of diamond grains would determine the diameter of ZnO nanorods. The electron field emission properties of the ZnO nanorods/diamond system have been significantly improved with respect to pure diamond film. The feature of the ZnO nanorods grown on diamond films played an important role in further enhancing the electron field emission performances. [Copyright &y& Elsevier]

Tungsten oxide (WO3) is a wide band gap semiconductor with unintentionally n-doping performance, excellent conductivity, and high electron hall mobility, which is considered as a candidate material for application in optoelectronics. Several reviews on WO3 and its derivatives for various applications dealing with electrochemical, photoelectrochemical, hybrid photocatalysts, electrochemical energy storage, and gas sensors have appeared recently. Moreover, the nanostructured transition metal oxides have attracted considerable attention in the past decade because of their unique chemical, photochromic, and physical properties leading to numerous other potential applications. Owing to their distinctive photoluminescence (PL), electrochromic and electrical properties, WO3 nanostructure-based optical and electronic devices application have attracted a wide range of research interests. This review mainly focuses on the up-to-date progress in different advanced strategies from fundamental analysis to improve WO3 optoelectric, electrochromic, and photochromic properties in the development of tungsten oxide-based advanced devices for optical and electronic applications including photodetectors, light-emitting diodes (LED), PL properties, electrical properties, and optical information storage. This review on the prior findings of WO3-related optical and electrical devices, as well as concluding remarks and forecasts will help researchers to advance the field of optoelectric applications of nanostructured transition metal oxides. [ABSTRACT FROM AUTHOR]

This review is mainly focused on the optoelectronic properties of diamond-based one-dimensional-metal-oxide heterojunction. First, we briefly introduce the research progress on one-dimensional (1D)-metal-oxide heterojunctions and the features of the p-type boron-doped diamond (BDD) film; then, we discuss the use of three oxide types (ZnO, TiO2 and WO3) in diamond-based-1D-metal-oxide heterojunctions, including fabrication, epitaxial growth, photocatalytic properties, electrical transport behavior and negative differential resistance behavior, especially at higher temperatures. Finally, we discuss the challenges and future trends in this research area. The discussed results of about 10 years' research on high-performance diamond-based heterojunctions will contribute to the further development of photoelectric nano-devices for high-temperature and high-power applications. [ABSTRACT FROM AUTHOR]

Alkali metal azides can be used as starting materials for the synthesis of polymeric nitrogen, a potential material of high energy density. In this letter, we report the ionic transport behavior in sodium azide under high pressure by in situ impedance spectroscopy and density functional theory calculations. The ionic transportation consists of ion transfer and Warburg diffusion processes. The ionic migration channels and barrier energy were given for the high-pressure phases. The enhanced ionic conductivity of the γ phase with pressure is because of the formation of space charge regions in the grain boundaries. This ionic conduction and grain boundary effect in NaN3 under pressures could shed light on the better understanding of the conduction mechanism of alkali azides and open up an area of research for polymeric nitrogen in these compounds and other high-energy-density polynitrides. [ABSTRACT FROM AUTHOR]

Diamond holds promise for optoelectronic devices working in high-frequency, high-power and high-temperature environments, for example in some aspect of nuclear energetics industry processing and aerospace due to its wide bandgap (5.5 eV), ultimate thermal conductivity, high-pressure resistance, high radio frequency and high chemical stability. In the last several years, p-type B-doped diamond (BDD) has been fabricated to heterojunctions with all kinds of non-metal oxide (AlN, GaN, Si and carbon-based semiconductors) to form heterojunctions, which may be widely utilized in various optoelectronic device technology. This article discusses the application of diamond-based heterostructures and mainly writes about optoelectronic device fabrication, optoelectronic performance research, LEDs, photodetectors, and high-electron mobility transistor (HEMT) device applications based on diamond non-metal oxide (AlN, GaN, Si and carbon-based semiconductor) heterojunction. The discussion in this paper will provide a new scheme for the improvement of high-temperature diamond-based optoelectronics. [ABSTRACT FROM AUTHOR]

Proton-conducting BaZrO3-doped electrolytes are considered as potential high temperature proton conductors due to their high ionic conductivity and electrical efficiency in the operating temperature range of solid oxide fuel cells. However, doping leads to a decrease in grain boundary conductivity and greatly limits its applications. Here, the charge transport properties of sub-micro and nano-BaZrO3 electrolytes were studied by in situ high-pressure impedance measurements and first-principles calculations. Mixed ionic-electronic conduction was found in both samples in the whole pressure range. Pressure-induced negative capacitance in the tetragonal phase of nano-BaZrO3 was observed, which was related to the space charge layer of grain boundaries as well as the electrostrictive strain of grains. The enhanced electrostrictive effect was attributed to the existence of polar nano-domains in nano-BaZrO3. Furthermore, the coincident imaginary part of impedance and modulus peaks on the frequency scale indicated a non-localized carrier conduction in the tetragonal phase of nano-BaZrO3. The grain boundary conductivity of nano-BaZrO3 was enhanced by four orders of magnitude, and the impedance response changed from a constant phase element to an ideal capacitance, which was accompanied by the cubic to tetragonal phase transition. At a switching frequency of 0.1 Hz, the real part of the dielectric function of nano-BaZrO3 increases sharply with frequencies from negative to positive values, exhibiting a plasma-like Drude behavior. Our results provide insight into the optimization and application of BaZrO3-based proton conductors in solid oxide fuel cells. [ABSTRACT FROM AUTHOR]

The n-type Ce:ZnO (NL) grown using a hydrothermal method was deposited on a p-type boron-doped nanoleaf diamond (BDD) film to fabricate an n-Ce:ZnO NL/p-BDD heterojunction. It shows a significant enhancement in photoluminescence (PL) intensity and a more pronounced blue shift of the UV emission peak (from 385 nm to 365 nm) compared with the undoped heterojunction (n-ZnO/p-BDD). The prepared heterojunction devices demonstrate good thermal stability and excellent rectification characteristics at different temperatures. As the temperature increases, the turn-on voltage and ideal factor (n) of the device gradually decrease. The electronic transport behaviors depending on temperature of the heterojunction at different bias voltages are discussed using an equilibrium band diagram and semiconductor theoretical model. [ABSTRACT FROM AUTHOR]

The heavier alkaline-earth hydrides AeH2 (Ae = Ca, Sr, and Ba) are considered as promising materials for hydrogen energy storage. Pressure-induced structural changes in AeH2 materials could improve hydrogen transport properties and result in a better understanding of the structure-property relationship. In this work, pressure evolution of carrier transport properties of SrH2 was investigated using impedance spectroscopy measurements at room temperature and first-principles calculations. The pressure-induced structure phase transition from a Pnma phase to a P63/mmc phase was accompanied by a transition from pure electronic conduction to mixed ionic-electronic conduction, which was related to the ionic migration barrier energy. In the P63/mmc phase, the H− ionic and electronic resistances of bulk and grain boundaries were distinguished, respectively. The total resistance of SrH2 decreased by about four orders of magnitude after the phase transition. This work provides critical insight into the structure-conduction relationship and the role of grain boundaries in the transport process of alkaline-earth hydrides under high pressure. [ABSTRACT FROM AUTHOR]

The parallel ultrafine SiO2 nanowires coated with amorphous SiO2 have been synthesized by a thermal evaporation method. The samples have been systematically studied by X-ray powder diffraction, Raman spectroscopy, scanning electron microscope, high-resolution transmission electron microscopy, selective area electron diffraction, and photoluminescence. The results show that the synthesized nanowire consists of a composite structure of the amorphous shell and the nanometer-sized crystalline core which has a monoclinic structure. The diameter of the internal one-dimensional crystal structure is about 10 nm. Furthermore, the luminous performance of SiO2 nanowires coated with amorphous SiO2 reveals a stable and strong yellow-red emission band. The products might be suitable for optoelectronic semiconductor application. [ABSTRACT FROM AUTHOR]

Hydrangea‐like ZnO nanospheres were fabricated on Al substrates via a facile hydrothermal method with only one step. Scanning electron microscopy, energy‐dispersive spectroscopy, X‐ray diffraction, X‐ray photoelectron spectroscopy, and photoluminescence were used to investigate their morphology, component, structure, and optical properties. The hierarchical nanospheres are fabricated by 2D nanosheets with the shape of 3D sphere. By adjusting the reaction time, the formation process was monitored. The photocatalytic activity of ZnO nanospheres was also investigated for their dye degradation, and they exhibit good photocatalytic ability to congo red, with the degradation rate of 98.4%. Besides, they have universal catalysis effect on methyl orange. [ABSTRACT FROM AUTHOR]

CuO nanoplates (NPs) have been prepared on ZnO nanorods (NRs) to form heterostructure by a simple photodeposition method at room temperature. The morphology, composition, and structure of the as‐prepared CuO NPs/ZnO NRs heterostructure were analyzed by SEM, TEM, XPS, and XRD. UV/Vis absorption spectrum indicates that the CuO NPs/ZnO NRs heterostructure exhibits a strong absorption in both the UV and visible light region. Photocurrent response results and the photoluminescence spectrum confirm that the CuO NPs/ZnO NRs heterostructure could promote the separation of photogenerated carriers. The photocatalytic ability of the as‐prepared samples was evaluated by degrading methyl orange. Moreover, the possible growth and photocatalytic mechanisms of the CuO NPs/ZnO NRs heterostructure were discussed. [ABSTRACT FROM AUTHOR]

Abstract: Boron doped ZnO nanorods were fabricated by hydrothermal technique on silicon substrate covered with a ZnO seed layer. It is found that the concentration of boric acid in the reaction solution plays a key role in varying the morphology and properties of the products. The growth rate along the [0001] orientation (average size in diameter) of the doped ZnO nanorods decreased (increased) with the increase of boric acid concentration. Based on the results of XRD, EDX and XPS, it is demonstrated that the boron dopants tend to occupy the octahedral interstice sites. The photoluminescence of the ZnO nanorods related to boron doping are investigated. [Copyright &y& Elsevier]

• Scaly-like hollow SnSe nanotubes (NTs) were synthesized by a green and rapid solution method. • Light utilization efficiency is improved due to unique scaly-like hollow structure and large surface area of the SnSe NTs. • SnSe NTs infrared photodetector can realize efficient and stable IR light detection free of the external power. [Display omitted] SnSe nanotubes (NTs) have been successfully synthesized via a simple solution method. The as-synthesized tubular crystals with orthorhombic structure are composed of numerous scaly nanosheets which distributed hierarchically. The average diameter of the SnSe NTs is roughly 180 nm and length primarily concentrate in the range of 1–3 µm. It was found that Se nanowires were served as a template and as an only source of Se ion for the formation of SnSe NTs. Furthermore, a novel self-powered infrared photodetector (IRPD) established on the SnSe NTs with desirable detection performance was fabricated. Exposed to IR illumination of 830 nm, the SnSe NTs IRPD displays a maximal photocurrent density of 46.46 nA/cm2 and a rapid photoresponse, together with the rise time and decay time approach up to 0.174 s and 0.349 s, respectively. Meanwhile, it can be recognized that the SnSe NTs IRPD remain consistent and repeatable at zero voltage. Moreover, a plausible mechanism for IR detection based on the SnSe NTs IRPD are also discussed. [ABSTRACT FROM AUTHOR]