Tianyou Zhai

A Comprehensive Review of One-Dimensional Metal-Oxide Nanostructure Photodetectors

One-dimensional (1D) metal-oxide nanostructures are ideal systems for exploring a large number of novel phenomena at the nanoscale and investigating size and dimensionality dependence of nanostructure properties for potential applications. The construction and integration of photodetectors or optical switches based on such nanostructures with tailored geometries have rapidly advanced in recent years. Active 1D nanostructure photodetector elements can be configured either as resistors whose conductions are altered by a charge-transfer process or as field-effect transistors (FET) whose properties can be controlled by applying appropriate potentials onto the gates. Functionalizing the structure surfaces offers another avenue for expanding the sensor capabilities. This article provides a comprehensive review on the state-of-the-art research activities in the photodetector field. It mainly focuses on the metal oxide 1D nanostructures such as ZnO, SnO2, Cu2O, Ga2O3, Fe2O3, In2O3, CdO, CeO2, and their photoresponses. The review begins with a survey of quasi 1D metal-oxide semiconductor nanostructures and the photodetector principle, then shows the recent progresses on several kinds of important metal-oxide nanostructures and their photoresponses and briefly presents some additional prospective metal-oxide 1D nanomaterials. Finally, the review is concluded with some perspectives and outlook on the future developments in this area.

Single-Crystalline CdS Nanobelts for Excellent Field-Emitters and Ultrahigh Quantum-Efficiency Photodetectors

The single crystalline CdS nanobelts were synthesized by an improved vapor-liquid-solid (VLS) process. Field emission measurements show that the nanostructures have a low turn-on field of 3.7 V&m-1 at a current density of 10 μA cm-1, a low threshold field of 9.3 V μm cm-1 and a high enhancement factor of 1298. When assembled into nanoscale visible light photodetectors, the CdS nanobelts showed good sensitivity and wavelength selectivity. The results imply that the present CdS nanobelts are excellent candidates for applications in high-performance field emitters and photodetectors.

Centimeter‐Long V2O5 Nanowires: From Synthesis to Field‐Emission, Electrochemical, Electrical Transport, and Photoconductive Properties

Adv. Mater. 2010, 22, 2547–2552 2010 WILEY-VCH Verlag G One-dimensional nanostructures have attracted considerable attention due to their importance in basic scientific research and potential technologic applications. Among them, vanadium pentoxide (V2O5) nanowires have been extensively studied in recent years because of their prospective applications in chemical sensors, field-emitters, catalysts, lithium-ion batteries, actuators, and electrochromic or other nanodevices. Several different approaches have been explored for the synthesis of V2O5 nanowires, such as thermal evaporation methods, hydrothermal/solvothermal syntheses, sol–gel techniques, and electrodeposition. However, the nanowires synthesized by these methods have typical lengths in the micrometer range (most of them are shorter than 10mm);moreover, if one canmake centimeter-long V2O5 nanowires, which should be much more useful compared to short wires for some specific purposes, such as field-emission (FE), device interconnects, and reinforcing fibers in composites. Herein, we fabricated high-quality single-crystalline centimeter-long V2O5 nanowires ( 80–120 nm in diameter, several centimeters in length; aspect ratio >10–10) using an environmental friendly hydrothermal approach without dangerous reagents, harmful solvents, and surfactants. The FE, electrochemical and electrical transport, and photoconductive properties of the synthesized V2O5 nanowires were then investigated in detail. Our results suggest a high potential of utilizing these novel nanowires in field-emitters, lithium-ion batteries, interconnects, and optoelectronic devices. The representative morphologies of the V2O5 nanowires were investigated by FE scanning electron microscopy (SEM), as shown in Figure 1a. Other SEM images (see the Supporting Information, Fig. S1) also confirm the high-yield fabrication of smooth and straight nanowires of 80–120 nm in diameter. Large portions of the nanowires are usually several millimeters or even up to several centimeters in length (inset of Fig. 1a), resulting in an aspect ratio of 10–10. To the best of our knowledge, this is the first time that such ultra-long V2O5 nanowires have been obtained. An X-ray diffraction (XRD) pattern of the sample is shown in Figure 1b. All the diffraction peaks can be indexed to an orthorhombic V2O5 phase with the lattice parameters of a1⁄4 11.54 A, b1⁄4 3.571 A, and c1⁄4 4.383 A, in good agreement with the literature values (Joint Committee on Powder Diffraction Standards (JCPDS) Card, no. 89-0612). No characteristic peaks of any impurities are detected in this pattern. Figure S2 (Supplementary Information) depicts a room temperature micro-Raman spectrum of the ultralong V2O5 nanowires. The peaks, located at 145, 197, 285, 305, 407, 480, 525, 694, and 990 cm , can be assigned to the Raman signature of V2O5. [18,19] A predominant low-wavelength peak at 145 cm 1 is attributed to the skeleton bent vibration (B3g mode), while the peaks at 197 and 285 cm 1 derive from the bending vibrations of OC V OB bond (Ag and B2g modes). The bending vibration of V OC (Ag mode), the bending vibration of V OB V bond (Ag mode), the stretching vibration of V OB V bond (Ag mode), and the stretching vibration of V OC bond (B2g mode) are regarded at about 305, 407, 525, and 694 cm , respectively. The layered structure of V2O5 is stacked up from distorted trigonal bipyramidal atoms that share edges to form (V2O4)n zigzag double chains along the [001] direction and are cross-linked along the [100] direction through the shared corners. The mode of a skeleton bent, corresponding to the peak at 145 cm , provides an evidence for the layered structure of V2O5. Furthermore, the narrow peak centered at 990 cm , corresponding to the stretching of vanadium atoms connected to oxygen atoms through double bonds (V1⁄4O), is also an additional clue to the layer-type structure of V2O5. [22,23] The detailed microstructures of V2O5 nanowires were further studied by transmission electron microscopy (TEM). Figure 2a shows a TEM image of V2O5 nanowires, which demonstrates that the V2O5 nanowires have uniform diameters throughout their entire lengths. An X-ray energy-dispersive spectrum (EDS) acquired from an individual nanowire exhibits strong V and O peaks. The atomic ratio of V and O is close to the 2:5

Fabrication of High-Quality In2Se3 Nanowire Arrays toward High-Performance Visible-Light Photodetectors

The synthesis of high-quality In2Se3 nanowire arrays via thermal evaporation method and the photoconductive characteristics of In2Se3 individual nanowires are first investigated. The electrical characterization of a single In2Se3 nanowire verifies an intrinsic n-type semiconductor behavior. These single-crystalline In2Se3 nanowires are then assembled in visible-light sensors which demonstrate a fast, reversible, and stable response. The high photosensitivity and quick photoresponse are attributed to the superior single-crystal quality and large surface-to-volume ratio resulting in fewer recombination barriers in nanostructures. These excellent performances clearly demonstrate the possibility of using In2Se3 nanowires in next-generation sensors and detectors for commercial, military, and space applications.

Ultrahigh-performance solar-blind photodetectors based on individual single-crystalline In2Ge2O7 nanobelts

[∗] Dr. L. Li , Dr. T. Y. Zhai , Dr. X. S. Fang , Prof. Y. Bando , Prof. D. Golberg International Center for Materials Nanoarchitectonics (MANA) National Institute for Materials Science (NIMS) Namiki 1–1, Tsukuba, Ibaraki, 305–0044 (Japan) E-mail: LI.Liang@nims.go.jp; ZHAI.Tianyou@nims.go.jp; FANG.Xiaosheng@nims.go.jp Prof. P. S. Lee , Dr. C. Y. Yan School of Materials Science and Engineering Nanyang Technological University (NTU) (Singapore) Dr. M. Y. Liao , Prof. Y. Koide Sensor Materials Center, NIMS Namiki 1–1, Tsukuba, Ibaraki, 305–0044 (Japan) E-mail: Meiyong.Liao@nims.go.jp

High‐Performance Blue/Ultraviolet‐Light‐Sensitive ZnSe‐Nanobelt Photodetectors

Single-crystalline zinc selenide (ZnSe) nanobelts were fabricated via the ethylenediamine (en)-assisted ternary solution technique and subsequent thermal treatment. Individual ZnSe nanobelts were assembled into nanoscale devices, showing a high spectral selectivity and photocurrent/immediate-decay ratio and a fast time response, justifying effective utilization of the ZnSe nanobelts as blue/UV-light-sensitive photodetectors.

ZnO Hollow Spheres with Double‐Yolk Egg Structure for High‐Performance Photocatalysts and Photodetectors

Inspired by opening soft drink cans, a one-pot method to prepare ZnO hollow spheres with double-yolk egg (DEH) architectures is developed. The bubble-assisted Ostwald ripening is proposed for the formation of these novel structures. Uniqueness of DEHs morphology led to greatly enhanced photocatalytic activity and photodetector performance. The newly developed synthetic concept and the obtained novel morphologies should pave the way towards the design and fabrication of other similar materials with enhanced properties for microelectronics, optoelectronics, and other applications.

Morphology-dependent stimulated emission and field emission of ordered CdS nanostructure arrays.

Highly ordered CdS nanostructure arrays were successfully fabricated via a simple two-step metal-organic chemical vapor deposition process. Both stimulated emission and field-emission measurements were carried out in an attempt to understand the correlation between the morphologies, alignments, and emission performances of five ordered CdS nanostructure array types (well-aligned truncated nanocones, nanorods, cleft nanorods, quasi-aligned nanowires, and nanowires). The 1D CdS nanostructures of various types displayed notable differences in stimulated and field-emission performances. The stimulated emission strongly correlated with the structure alignment: the better the alignment, the lower the threshold. Both of the alignments and aspect ratios greatly affected the field-emission properties; the CdS emitters of higher aspect ratio and better alignment exhibited better field-emission performance. Thus the well-aligned CdS nanorod arrays had the lower threshold for stimulated emission, and quasi-aligned nanowire arrays produced the higher field-emission current and possessed the lower turn-on fields.

Low-cost fully transparent ultraviolet photodetectors based on electrospun ZnO-SnO2 heterojunction nanofibers.

Electrospun ZnO-SnO2 heterojunction nanofibers are demonstrated to be promising candidates for easily assembled fully transparent high-performance photodetectors.

Flexible Ultraviolet Photodetectors with Broad Photoresponse Based on Branched ZnS‐ZnO Heterostructure Nanofilms

The application of nanofilm networks made of branched ZnS-ZnO nanostructures as a flexible UV photodetector is demonstrated. The fabricated devices show excellent operational characteristics: tunable spectral selectivity, widerange photoresponse, fast response speed, and excellent environmental stability.