Multiple Bioimaging Applications Based on the Excellent Properties of Nanodiamond: A Review.

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.

A Review on the Progress of Optoelectronic Devices Based on TiO2 Thin Films and Nanomaterials.

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.

First-principles screening of surface-charge-transfer molecular dopants for n-type diamond.

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 of2.60×1013cm-2and9.20×1012cm-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.

A Review on Optoelectronical Properties of Non-Metal Oxide/Diamond-Based p-n Heterojunction.

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.

Photoluminescence and Electrical Properties of n-Ce-Doped ZnO Nanoleaf/p-Diamond Heterojunction.

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.

Enhanced Photoluminescence and Electrical Properties of n-Al-Doped ZnO Nanorods/p-B-Doped Diamond Heterojunction.

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.

A Review on the Properties and Applications of WO3 Nanostructure-Based Optical and Electronic Devices.

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.

Excellent optoelectronic applications and electrical transport behavior of the n-WO3nanostructures/p-diamond heterojunction: a new perspective.

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-WO3nanorods/p-diamond heterojunction at high temperatures were studied by Wanget al(2017Appl. Phys. Lett.110052106), 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-WO3nanostructures/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.

Review on the Properties of Boron-Doped Diamond and One-Dimensional-Metal-Oxide Based P-N Heterojunction Optoelectronic.

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.

Negative Differential Resistance of n-ZnO Nanorods/p-degenerated Diamond Heterojunction at High Temperatures.

In the present study, an n-ZnO nanorods (NRs)/p-degenerated diamond tunneling diode was investigated with regards to its temperature-dependent negative differential resistance (NDR) properties and carrier tunneling injection behaviors. The fabricated heterojunction demonstrated NDR phenomena at 20 and 80°C. However, these effects disappeared followed by the occurrence of rectification characteristics at 120°C. At higher temperatures, the forward current was increased, and the turn-on voltage and peak-to-valley current ratio (PVCR) were reduced. In addition, the underlying mechanisms of carrier tunneling conduction at different temperature and bias voltages were analyzed through schematic energy band diagrams and semiconductor theoretical models. High-temperature NDR properties of the n-ZnO NRs/p-degenerated diamond heterojunction can extend the applications of resistive switching and resonant tunneling diodes, especially in high-temperature, and high-power environments.

Improved electrical transport properties of an n-ZnO nanowire/p-diamond heterojunction.

A heterojunction of n-ZnO nanowire (NW)/p-B-doped diamond (BDD) was fabricated. The rectifying behavior was observed with the turn on voltage of a low value (0.8 V). The forward current at 5 V is 12 times higher than that of a larger diameter n-ZnO nanorod (NR)/p-BDD heterojunction. The electrical transport behaviors for the comparison of n-ZnO NWs/p-BDD and n-ZnO NRs/p-BDD heterojunctions are investigated over various bias voltages. The carrier injection process mechanism for ZnO NWs/BDD is analyzed on the basis of the proposed equilibrium energy band diagrams. The ZnO NWs/BDD heterojunction displays improved I-V characteristics and relatively high performance for the electrical transport properties.

Aligned ZnO nanorod arrays growth on GaN QDs for excellent optoelectronic applications.

Uniformly aligned ZnO nanorod (NR) arrays grown on GaN quantum dots (QDs) as preferred nucleation sites are imperative for designing field emission emitters, ultraviolet photodetectors and light-emitting diodes for a wide range of new optoelectronic applications. In a recent study (2015 Nanotechnology 26 415601), Qi et al reported a novel method of fabricating ZnO NRs arrays with uniform shape, the density of which is easily tunable by adjusting the density of GaN QDs. This approach opens a door to obtaining a combination of 0D and 1D structures for optoelectronic applications.