Synthesis, characterization and photoluminescence of tin oxide nanoribbons and nanowires

In this work we report the successful formation of tin oxide nanowires and tin oxide nanoribbons with high yield and by using simple cheap method. We also report the formation of curved nanoribbon, wedge-like tin oxide nanowires and star-like nanowires. The growth mechanism of these structures has been studied. Scanning electron microscope was used in the analysis and the EDX analysis showed that our samples is purely Sn and O with ratio 1:2. X-ray analysis was also used in the characterization of the tin oxide nanowire and showed the high crystallinity of our nanowires. The mechanism of the growth of our1D nanostructures is closely related to the vapor–liquid–solid (VLS) process. The photoluminescence PL measurements for the tin oxide nanowires indicated that there are three stable emission peaks centered at wavelengths 630, 565 and 395 nm. The nature of the transition may be attributed to nanocrystals inside the nanobelts or to Sn or O vacancies occurring during the growth which can induce trapped states in the band gap.     

Large hexagonal arrays of aligned ZnO nanorods

Large-scale truly periodic arrays of vertically aligned zinc oxide nanorods were grown on pre-patterned and pre-annealed gold dots on a-plane sapphire substrates via the vapor–liquid–solid mechanism. Periodic arrays of triangular gold islands were first patterned on the a-plane sapphire substrates by the nanosphere self-assembly technique. Zinc has been found to be an effective interfacial modifier between gold and sapphire to form single catalytic dots from triangular islands. The successful fabrication of zinc oxide nanowires in truly periodic arrays opens up the possibility of achieving enhanced room-temperature ultraviolet lasing and photonic crystal based devices and sensors. PACS 81.07.Bc; 81.10.-h; 81.16.Nd     

Si-based materials and devices for light emission in silicon

We report on the fabrication and performances of extremely efficient Si-based light sources. The devices consist of MOS structures with erbium (Er) implanted in the thin gate oxide. The devices exhibit strong 1.54 μm electroluminescence (EL) at 300 K with a 10% external quantum efficiency, comparable to that of standard light-emitting diodes using III–V semiconductors. Er excitation is caused by hot electrons impact and oxide wearout limits the reliability of the devices. Much more stable light-emitting MOS devices have been fabricated using Er-doped silicon rich oxide (SRO) films as gate dielectric. These devices show a high stability, with an external quantum efficiency reduced to 1%. In these devices, Er pumping occurs by energy transfer from the Si nanostructures to the rare-earth ions. Finally, we have also fabricated MOS structures with Tb- and Yb-doped SiO₂ which show room temperature EL at 540 nm (Tb) and 980 nm (Yb) with an external quantum efficiency of a 10% and 0.1%, respectively.     

Fabrication and characterization of β-Ga2O3 optical nanowires

Monoclinic gallium oxide (β-Ga₂O₃) nanowires with lengths of tens of micrometers and diameters ranging from 100 to 250 nm are synthesized using simple physical evaporation based on vapor–liquid–solid (VLS) mechanism. The as-synthesized straight β-Ga₂O₃ nanowires show excellent diameter uniformity and sidewall smoothness, making them suitable for optical wave-guiding. Light from a fiber taper is launched into the nanowire by means of evanescent coupling. Measured propagation loss of the nanowire at 633 nm wavelength is on the order of 10 dB/mm. Favorable mechanical strength of these nanowires for elastic bending is also observed. Our results suggest that β-Ga₂O₃ nanowires are promising building blocks for micro- and nanophotonic circuits and devices.     

Fabrication of substrate-free double-side emitting flexible device based on silver nanowire-polymer composite electrode

Flexible light emitting diodes are a promising component for future electronic devices, but require a simple structure and fast fabrication method. Organic light emitting diodes are a viable option as they are lightweight, thin, and flexible. However, they currently have costly fabrication procedures, complicated structures, and are sensitive to water and oxygen, which hinder widespread application. Here, we present a novel approach to fabricate flexible light emitting devices by employing Ag nanowire/polymer composite electrodes and ZnS phosphor particles. The composite electrode was fabricated using inverted layer processing, and used as both a bottom electrode and a dielectric layer. The high mechanical stability of the composite allowed the device to be free standing and mechanically flexible, eliminating the need for any additional support. Using Ag nanowires in both the top and bottom electrodes made a double-sided light emitting device that could be applied to wearable lightings or flexible digital signages.     

多波长飞秒激光激发下GaAs纳米线SHG特性研究

本文基于有限元法研究了直立生长于GaAs衬底的GaAs纳米线的光场响应和光场增强性质. 实验使用多个波长的飞秒激光脉冲激发GaAs纳米线, 测得了较高效率的二次谐波信号, 并首次使用宽带超连续飞秒脉冲 (1000–1300 nm) 在纳米线上获取了宽带、无杂散荧光噪声的二次谐波信号. 这种高效的二次谐波产生过程主要归因于纳米结构引起的局域场增强效应. 本文阐明了GaAs纳米线的二次谐波倍频特性, 这些结果对于其在纳米光学中的光器件、 光集成等领域的进一步研究和实际应用具有很好的参考价值. 关键词： GaAs纳米线 二次谐波 飞秒激光     

Hierarchical nanowires for high-performance electrochemical energy storage

Nanowires are promising candidates for energy storage devices such as lithium-ion batteries, su- per（：apa.citors and lithium-air batteries. However, simple-structured nanowires have some limitations hence the strategies to make improvements need to be explored and investigated. Hierarchical nanowires with enhanced periormanee have been considered as an ideal candidate for energy storage due to the novel structures and/or synergistic properties. This review describes some of the recent progresses in the hierarchical nanowire merits, classification, synthesis and performance in energy storage applieat, ions. Herein we discuss the hierarchical nanowires based on their structural design from three major categories, including exterior design, interior design and aligned nanowire assembly. This review also briefly outlines the prospects of hierarchical nanowires in morphology control, property enhancement and application versatility.     

Elastic and plastic deformations of nickel nanowires under uniaxial compression

Using atomistic molecular dynamics simulation with a Sutton–Chen many body potential, we studied the structural evolution and deformation mechanisms of nickel nanowires under homogeneous uniaxial compressions. Nickel nanowires with helical multi-shell structure and fcc-like crystalline structures have been considered. Elastic and plastic behaviors of nickel nanowires under compression were observed and their elastic limits were determined. Our simulations show that the nickel nanowires with helical multi-shell structure have greater yield strength than that of macroscopic solid. Above elastic limit, the plastic deformation of the nanowires shows behavior that is associated with superplasticity. The final atomic structures for the two kinds of nanowires are resemblant crystalline-like.     

Fabrication of nanowires and nanostructures: combining template synthesis with patterning methods

We report on different approaches that we have adopted and developed for the fabrication of nanowires and nanostructures. Methods based on template synthesis and on self organization seem to be the most promising for the fabrication of nanomaterials and nanostructures due to their easiness and low cost. The development of a supported nanoporous alumina template and the possibility of using this template to combine electrochemical synthesis with lithographic methods open new ways for the fabrication of complex nanostructures. The numerous advantages of the supported template and its compatibility with microelectronic processes make it an ideal candidate for further integration into large-scale fabrication of various nanowire-based devices.     

Modified solution-processible fabrication of metallic photonic crystals with template removal

High-temperature annealing and pre-annealing lift-off procedures are employed to improve the solutionproeessible technique for the fabrication of one- （1D） and two-dimensional （2D） metallic photonic crystals （MPCs） based on colloidal gold nanoparticles. This enables the successful fabrication of gold nanowires or nanocylinder array structures with the photoresist template removed completely, which is crucial for the application of MPCs in biosensors and optoelectronic devices. Microscopic measurements show homogeneous 1D and 2D photonic structures with an area as large as 100 mm2. Plasmonic resonance of the gold nanostructures and its coupling with the resonance mode of the planar waveguide underneath the photonic structures are observed, implying the excellent optical properties of this kind of MPCs based on the improved fabrication technique.     

Dilute magnetic semiconductor nanowires

Semiconductor materials form the basis of modern electronics, communication, data storage and computing technologies. One of today’s challenges for the development of future technologies is the realization of devices that control not only the electron charge, as in present electronics, but also its spin, setting the basis for future spintronics. Spintronics represents the concept of the synergetic and multifunctional use of charge and spin dynamics of electrons, aiming to go beyond the traditional dichotomy of semiconductor electronics and magnetic storage technology. The most direct method to induce spin-polarized electrons into a semiconductor is by introducing appropriate transition-metal or rare-earth dopants producing a dilute magnetic semiconductor (DMS). At the same time the seamless integration of future spintronic devices into nanodevices would require the fabrication of one-dimensional DMS nanostructures in well-defined architectures. In this review we focus on recent advances in the synthesis of DMS nanowires as well discussing the structural, optical and magnetic properties of these materials. PACS 75.75.+a; 81.07.Vb; 68.65.La     

2D planar field emission devices based on individual ZnO nanowires

2D planar field emission devices based on individual ZnO nanowires were achieved on Si/SiO₂ substrate via a standard e-beam lithography method. The anode, cathode and ZnO nanowires were on the same substrate; so the electron field emission is changed to 2D. Using e-beam lithography, the emitter (cathode) to anode distance could be precisely controlled. Real time, in situ observation of the planar field emission was realized in a scanning electron microscope. For individual ZnO nanowires, an onset voltage of 200 V was obtained at 1 nA. This innovative approach provides a viable and practical methodology to directly implement into the integrated field emission electrical devices for achieving “on-chip” fabrication.     

Issues in the realization of strained-layer quantum well optoelectronic devices

Ion-beam processing is the ideal complement to modern lattice-mismatched (strained-layer) heteroepitaxy for optoelectronic device fabrication. Bandstructure engineering of optoelectronic devices through the use of lattice strain is presented, and the effects of ion-beam processing on III–V strained-layer heteroepitaxial structures are summarized. Representative results from ion-implanted optoelectronic devices are presented to illustrate these principles.     

Fabrication of Micro -Optical Devices by a Femtosecond Laser

Femtosecond laser is a perfect laser source for materials processing when high accuracy and small structure size are required. Due to the ultra short interaction time and the high peak power, the process is generally characterized by the absence of heat diffusion and, consequently molten layers. Various induced structures have been observed in materials after the femtosecond laser irradiation. Here, we report on fabrication of micro-optical devices by the femtosecond laser. 1) formation of optical waveguide with internal loss less than 0.5dB/cm in the wavelength region from 1.2 to 1.6 mm, by translating a silica glass perpendicular to the axis of the focused femtosecond laser beam; 2) nano-scale valence state manipulation of active ions inside transparent materials; 3) space-selective precipitation and control of metal nanoparticles inside transparent materials; The mechanisms and applications of the femtosecond laser induced phenomena were also discussed.     

Trench-template fabrication of indium and silicon nanowires prepared by thermal evaporation process

In this study, we report on the trench-template assisted fabrication of nanowires for thermally evaporated indium and silicon thin films on quartz substrate. Length of the nanowires is completely dependent on the length of the trench, whereas the diameter of the nanowires is dependent on the thickness of the thin film. The diameter of nanowire increases from 200 nm to 1 μm when the thickness was increased from 15 to 60 nm. It is observed that nanowires diameter is invariably controlled by material deposition thickness. Average crystallite sizes for 60 nm indium and silicon deposition inside the trench are 120 and 35 nm, respectively. Nanowire surface plasmon peak shift as compared to the same thickness untemplated continuous thin film is more for thinner nanowires. This technique of nanowire fabrication is shown to be versatile in nature.     

Refit Silver Nanostructures Using a Convergent Electron Beam

Using a superionic conductor AgI thin film and a direct current electric field, we synthesize silver nanowires in diameter of about lOOnm. In order to refit the prepared nanowires, the samples are irradiated by a convergent electron beam （200 k V） inside a transmission electron microscope to prepare new small silver nanostructures. The new nanostructures are investigated in situ by high-resolution transmission electron microscope. This electron- induced crystal growth method is useful for technical applications in fabrication of nanodevices.     

Large-scale fast production of amorphous Si-Al-O nanowires under ambient conditions

A novel approach to the large-scale and fast production of free-standing nanowires and microwires under ambient conditions is reported. The method is based on the interaction of a high power laser beam with a commercial ceramic substrate under a high-pressure gas jet under ambient conditions. Large quantities of amorphous Si-Al oxide nanowires were produced and characterized. An explanation for the growth of the nanowires based in the vapor–liquid–solid (VLS) mechanism is proposed . PACS 81.05.Je; 81.07.b     

Multiple air-gap filters and constricted mesa lasers – material processing meets the front of optical device technology

Real three-dimensional material structures enable enormous perspectives in the functionality of advanced electronic and optoelectronic III/V semiconductor devices. We report on the technological implementation of surface-micromachined III/V semiconductor devices for optoelectronic applications. Considering fabrication technology, the general principles can be reduced to three fundamental process steps: deposition of a layered heterostructure on a substrate, vertical structurization and horizontal undercutting by selectively removing sacrificial layers. Very useful quality-control elements for precise process control are presented. The basic principles are applied and illustrated in detail by presenting two selected optoelectronic examples. (i) The fabrication technology of buried mushroom stripe lasers is shown. Bent waveguides on homogeneous grating fields are used to obtain chirped gratings, enabling a high potential to tailor specific performances. Excellent optical properties are obtained. (ii) The fabrication technology of vertical optical cavity based tunable single- or multi-membrane devices including air gaps is shown. Record optical tuning characteristics for vertical cavity Fabry–Pérot filters are presented. Single parametric wavelength tuning over 142 nm with an actuation voltage of only 3.2 V is demonstrated. PACS 85.60.-q; 87.80.Mj; 68.65.Ac     

Properties of Schottky barrier photodiodes based on InGaN/GaN MQW structures

The characterization and fabrication of Schottky barrier photodiodes based on InGaN/GaN multiple-quantum well structures in the active region are presented. These devices allow photodetection based on nitrides from the visible (VIS) to the ultraviolet (UV) ranges to be covered, and offer an alternative to InGaN bulk devices. Indium concentrations in the 8 to 14% range have been used. It has also been shown that in these devices the envelope average electric field in the depletion region can be tailored as a result of the huge polarization fields present in wells and barriers. As a consequence, two different device operation modes, as a function of voltage bias, are possible. By proper well and barrier design, charge accumulation can be produced at the boundaries of the active region and a large responsivity for photons with energies close to the barrier bandgap is found. Photodetectors show a rather sharp detection edge with a contrast of more than four orders of magnitude, reaching peak responsivities in the 0.1–1.0 A/W range. Self-consistent simulations and a discussion on the electric fields in the active regions are also presented.