Synthesis of Single-Crystalline Silicon Nitride Nanobelts Via Catalyst-Assisted Pyrolysis of a Polysilazane

Recently, one-dimensional nanostructures have attracted extensive attention since they are potentially important for both applications and fundamental research. In this paper, we report the synthesis of ultra-long single crystal Si₃N₄ nanobelts via catalyst-assisted pyrolysis of polymeric precursors. The obtained products contain both α- and β-Si₃N₄ nanobelts, which are 50–100 nm in thickness, 400–1000 nm in width, and a few hundreds of micrometers to several millimeters in length. Different from previous techniques for synthesizing one-dimensional structures, the current nanobelts are synthesized through confined crystallization of an amorphous phase. A solid–liquid–gas–solid reaction/crystallization growth mechanism is proposed. The formation of nanobelts instead of nanowires is attributed to the anisotropy growth at an earlier stage.     

Synthesis of ultra-thin nanobelt-like vanadium-oxide and its abnormal optical-electrical properties

The transport and optical response can be easily modulated in low-dimensional structures which makes them potential candidates for future technologies. Therefore, a variety of 2-dimensional nanostructures of different metal oxides were designed for a large number of applications such as energy storage, transparent electrodes, solar cells, etc. In this study, ultra-thin vanadium-oxide nanobelts were fabricated by the chemical exfoliation method (a top-down approach), and their structure, electrical, and optical properties were investigated. The nanobelts exhibited excellent structural and morphological stability even at high temperatures. Surprisingly, the metal-insulator transition was absent in vanadium oxide nanobelts, contrary to 3-dimensional vanadium dioxide structures (metal-insulator transition around 68 °C). The electrical behavior of 2-dimensionally structured vanadium oxide nanobelts was well described by thermally activated transport phenomena. The optical band gap was estimated to be ～2.1 eV. The unique morphology (nanobelt-like) and unusual electrical-optical properties make this material a worthy candidate for applications in the electronic industry.     

A novel method for designing carbon nanostructures: Tailoring-induced self-scrolling of graphene flakes

Design and fabrication of functional carbon nanostructures is a challenging but meaningful mission for scientists to propel the development of nanotechnology, such as nanopharmacology, nanobiology and nanofluidic manipulation. In order to fabricate the carbon nanostructures, using forced-field-based molecular dynamics simulations, we proposed a feasible method to obtain the carbon nanostructures through tailoring-induced self-scrolling of graphene flakes. And the shapes of the carbon nanostructures could be regulated by controlling the tailoring patterns. We also analyzed the mechanism for the tailoring-induced self-scrolling of graphene flakes. By analyzing the scrolling process in detail, it was found that the van der Waals interactions were responsible for the formation of the carbon nanostructures. In addition, we also found that the tailoring could also induce the scrolling of Boron Nitride flakes, and this indicates that the tailoring might provide an universal method for self-assembly of two dimensional materials. This work is expected to trigger further studies on the design of nanostructures and the applications of these nanostructures in functional nanodevices.     

Ordered macroporous bimetallic nanostructures: design, characterization, and applications

Ordered porous metal nanomaterials have current and future potential applications, for example, as catalysts, as photonic crystals, as sensors, as porous electrodes, as substrates for surface-enhanced Raman scattering (SERS), in separation technology, and in other emerging nanotechnologies. Methods for creating such materials are commonly characterized as "templating", a technique that involves first the creation of a sacrificial template with a specific porous structure, followed by the filling of these pores with desired metal materials and finally the removal of the starting template, leaving behind a metal replica of the original template. From the viewpoint of practical applications, ordered metal nanostructures with hierarchical porosity, namely, macropores in combination with micropores or mesopores, are of particular interest because macropores allow large guest molecules to access and an efficient mass transport through the porous structures is enabled while the micropores or mesopores enhance the selectivity and the surface area of the metal nanostructures. For this objective, colloidal crystals (or artificial opals) consisting of three-dimensional (3D) long-range ordered arrays of silica or polymer microspheres are ideal starting templates. However, with respect to the colloidal crystal templating strategies for production of ordered porous metal nanostructures, there are two challenging questions for materials scientists: (1) how to uniformly and controllably fill the interstitial space of the colloidal crystal templates and (2) how to generate ordered composite metal nanostructures with hierarchical porosity. This Account reports on recent work in the development and applications of ordered macroporous bimetallic nanostructures in our laboratories. A series of strategies have been explored to address the challenges in colloidal crystal template techniques. By rationally tailoring experimental parameters, we could readily and selectively design different types of ordered bimetallic nanostructures with hierarchical porosity by using a general template technique. The applications of the resulting nanostructures in catalysis and as substrates for SERS are described. Taking the ordered porous Au/Pt nanostructures as examples for applications as catalysts, the experimental results show that both the ordered hollow Au/Pt nanostructure and the ordered macroporous Au/Pt nanostructure exhibit high catalytic ability due to their special structural characteristics, and their catalytic activity is component-dependent. As for SERS applications, primary experimental results show that these ordered macroporous Au/Ag nanostructured films are highly desirable for detection of DNA bases by the SERS technique in terms of a high Raman intensity enhancement, good stability, and reproducibility, suggesting that these nanostructures may find applications in the rapid detection of DNA and DNA fragments.     

Functional micro/nanostructures: simple synthesis and application in sensors, fuel cells, and gene delivery

In order to develop new, high technology devices for a variety of applications, researchers would like to better control the structure and function of micro/nanomaterials through an understanding of the role of size, shape, architecture, composition, hybridization, molecular engineering, assembly, and microstructure. However, researchers continue to face great challenges in the construction of well-defined micro/nanomaterials with diverse morphologies. At the same time, the research interface where micro/nanomaterials meet electrochemistry, analytical chemistry, biomedicine, and other fields provides rich opportunities to reveal new chemical, physical, and biological properties of micro/nanomaterials and to uncover many new functions and applications of these materials. In this Account, we describe our recent progress in the construction of novel inorganic and polymer nanostructures formed through different simple strategies. Our synthetic strategies include wet-chemical and electrochemical methods for the controlled production of inorganic and polymer nanomaterials with well-defined morphologies. These methods are both facile and reliable, allowing us to produce high-quality micro/nanostructures, such as nanoplates, micro/nanoflowers, monodisperse micro/nanoparticles, nanowires, nanobelts, and polyhedron and even diverse hybrid structures. We implemented a series of approaches to address the challenges in the preparation of new functional micro/nanomaterials for a variety of important applications This Account also highlights new or enhanced applications of certain micro/nanomaterials in sensing applications. We singled out analytical techniques that take advantage of particular properties of micro/nanomaterials. Then by rationally tailoring experimental parameters, we readily and selectively obtained different types of micro/nanomaterials with novel morphologies with high performance in applications such as electrochemical sensors, electrochemiluminescent sensors, gene delivery agents, and fuel cell catalysts. We expect that micro/nanomaterials with unique structural characteristics, properties, and functions will attract increasing research interest and will lead to new opportunities in various fields of research.     

One-Dimensional Nanostructures and Devices of II–V Group Semiconductors

The II–V group semiconductors, with narrow band gaps, are important materials with many applications in infrared detectors, lasers, solar cells, ultrasonic multipliers, and Hall generators. Since the first report on trumpet-like Zn₃P₂ nanowires, one-dimensional (1-D) nanostructures of II–V group semiconductors have attracted great research attention recently because these special 1-D nanostructures may find applications in fabricating new electronic and optoelectronic nanoscale devices. This article covers the 1-D II–V semiconducting nanostructures that have been synthesized till now, focusing on nanotubes, nanowires, nanobelts, and special nanostructures like heterostructured nanowires. Novel electronic and optoelectronic devices built on 1-D II–V semiconducting nanostructures will also be discussed, which include metal–insulator-semiconductor field-effect transistors, metal-semiconductor field-effect transistors, and p–n heterojunction photodiode. We intent to provide the readers a brief account of these exciting research activities.     

Synthesis of Tapered CdS Nanobelts and CdSe Nanowires with Good Optical Property by Hydrogen-Assisted Thermal Evaporation

The tapered CdS nanobelts and CdSe nanowires were prepared by hydrogen-assisted thermal evaporation method. Different supersaturation leads to two different kinds of 1D nanostructures. The PL measurements recorded from the as-prepared tapered CdS nanobelts and CdSe nanowires show only a bandgap emission with relatively narrow full-width half maximum, which means that they possess good optical property. The as-synthesized high-quality tapered CdS nanobelts and CdSe nanowires may be excellent building blocks for photonic devices.     

Atomic layer deposition for nanofabrication and interface engineering

Atomic layer deposition (ALD) provides a tool for conformal coating on high aspect-ratio nanostructures with excellent uniformity. It has become a technique for both template-directed nanofabrications and engineering of surface properties. This Feature Article highlights the application of ALD in selected fields including photonics, SERS and energy materials. Specifically, the topics include fabrication of plasmonic nanostructures for the SERS applications, fabrication of 3-D nanoarchitectured photoanodes for solar energy conversions (dye-sensitized solar cells and photoelectrochemical cells), and coating of electrodes to enhance the cyclic stability and thus device life span of batteries. Dielectric coating for tailoring optical properties of semiconductor nanostructures is also discussed as exemplified by ZnO nanowires. Future direction of ALD in these applications is discussed at the end.     

Tuning the peak position of subwavelength silica nanosphere broadband antireflection coatings

Subwavelength nanostructures are considered as promising building blocks for antireflection and light trapping applications. In this study, we demonstrate excellent broadband antireflection effect from thin films of monolayer silica nanospheres with a diameter of 100 nm prepared by Langmuir-Blodgett method on glass substrates. With a single layer of compact silica nanosphere thin film coated on both sides of a glass, we achieved maximum transmittance of 99% at 560 nm. Furthermore, the optical transmission peak of the nanosphere thin films can be tuned over the UV-visible range by changing processing parameters during Langmuir-Blodgett deposition. The tunable optical transmission peaks of the Langmuir-Blodgett films were correlated with deposition parameters such as surface pressure, surfactant concentration, ageing of suspensions and annealing effect. Such peak-tunable broadband antireflection coating has wide applications in diversified industries such as solar cells, windows, displays and lenses.     

防紫外线织物的研究

由于大气污染、臭氧层变薄甚至出现空洞，紫外线辐射严重损坏人体皮肤、因此，开发防紫外线纺织品势在必行。文中介绍了纺织品防紫外线辐射的原理，阐述了防紫外线纺织品的加工方法和特点，并探讨了防紫外线纺织品的发展趋势。     

Promising electrode material of Fe3O4 nanoparticles decorated on V2O5 nanobelts for high-performance symmetric supercapacitors

Bundled V₂O₅ nanobelts decorated with Fe₃O₄ nanoparticles (F3V nanostructures) were successfully synthesized to develop a low-cost electrode material for energy storage applications. The synthesized samples were subjected to structural, morphological and electrochemical studies. The Fe₃O₄ nanoparticles decorated over bundled V₂O₅ nanobelts exhibited better electrochemical properties than the pristine Fe₃O₄ nanoparticles and V₂O₅ nanobelts. The electrochemical behavior of the fabricated electrodes was investigated in an electrolyte of 3 M KOH, demonstrated an exceptional specific capacity values of 750.1, 660.3, and 1519 F g^–1 for V₂O₅, Fe₃O₄, and F3V respectively at a current density of 15 A g^–1. The assembled F3V symmetric supercapacitor (SSC) device exhibited an excellent specific capacitance of 93 F g^–1 at a current density of 0.5 A g^–1, delivering energy and power densities of 13 Wh.kg^–1 and 1530 W kg^–1, respectively, and superior long-term cycling stability of ～84% capacity retention over 5000 galvanostatic charge–discharge cycles. These findings demonstrate the extraordinary electrochemical characteristics of the F3V nanostructures, indicating their potential use in energy storage applications.     

氧化亚铜在太阳能电池、光催化领域的研究进展

作为半导体光电功能材料,Cu2O薄膜和纳米材料由于具有独特的能带结构和优异的性能,在电子信息、能源、环境保护等领域具有重要的应用前景。介绍了Cu2O薄膜与纳米材料的制备方法及其在太阳能电池和光催化领域的应用。分析了目前存在的问题,并提出今后研究的对策。     

Facile synthesis of boron carbide elongated nanostructures via a simple in situ thermal evaporation process

Boron carbide elongated nanostructures such as nanowires, nanobelts and nanosheets have been synthesized via a low-cost and simple in situ thermal evaporation process using commercially available B₄C powders as the main precursor. Heat treatments were done in the temperature range of 1400-1600 °C in the presence of Co nanoparticles (and NiCl₂ in some experiments) as the catalyst material. The growth mechanism of the nanostructures was proposed to be a cooperative growth procedure including surface diffusion, vapor-liquid-solid (VLS) and solid-liquid-solid (SLS) growth mechanisms. The final product, containing some of the initial B₄C particles and as-synthesized elongated nanostructures may be potentially applicable as an excellent reinforcing phase in composite materials. Moreover, nanostructures with right angle junctions were obtained from the sidewalls of the graphite boats, which may be operative in MEMS and NEMS devices. The samples have been characterized by scanning electron microscopy, transmission electron microscopy, X-ray diffraction and photoluminescence spectroscopy.     

难溶有机药物阿莫西林纳米结构的制备

在表面活性剂SDS的辅助下,运用简单的化学沉淀法制备了三种阿莫西林纳米结构.运用扫描电镜和红外光谱对制备的阿莫西林进行了形貌、尺寸和化学结构的表征.实验发现通过调节阿莫西林钠溶液的pH值,可以得到阿莫西林纳米和微米颗粒纳米带和纳米纤维,在一定程度上实现了这一难溶有机药物的可控生长.     

Synthesis of Ceramic Nanocomposite Powders with in situ Formation of Nanowires/Nanobelts

A significant challenge in synthesizing nanowire/nanobelt-reinforced ceramic nanocomposites is to uniformly disperse these reinforcements. Here, we report the synthesis of amorphous silicon carbonitride powders containing in situ- formed single-crystal Si₃N₄ nanowires and nanobelts via the catalyst-assisted pyrolysis of a polymeric precursor. The nanowires/nanobelts are uniformly dispersed within the powder matrix. The ratio of nanomaterials to powder can be controlled by tailoring the experimental conditions. The novel powders could be useful for fabricating nanowire/nanobelt-reinforced ceramic nanocomposites.     

Nanoindentation and nanoscratching studies of amorphous carbon films

Hydrogen-free amorphous carbon (a-C) films prepared by RF magnetron sputtering were deposited on Si substrates in thin films, at various negative bias voltages V_b (i.e. Ar-ion energies), and in thick layered-structure films with alternative values of V_b. The main purposes of this work are to present preliminary results concerning the effect of Ar-ion bombardment during deposition on the elastic properties of thin a-C films with Ar⁺ energies in the range 30–200 eV, and the adhesion failure which limits their thickness and usefulness for practical applications, and the enhancement of hardness and scratch resistance of sputtered a-C films developed in a layered structure. The results show a significant improvement in the elastic properties of layered structure films and their stability. The combination of high hardness and relative low elastic modulus which the layered films exhibit make them more resistant to plastic deformation during contact, as confirmed by scratch testing.     

Rapid thermal pyrolysis of interferometrically patterned resist

In recent years pyrolysis of interferometrically-patterned photoresists has produced three-dimensionally nanopatterned, electrically conductive carbon films with applications from energy storage to biological sensing. We investigate here conditions for rapid thermal pyrolysis that drastically reduce film processing time (from hours to minutes) while preserving the films’ unique nanoscale morphology, film adhesion, and electrochemical properties. We specifically show that heating rate dramatically affects nanoscale morphology, while reducing atmosphere composition, dwell time, and dwell temperature impact the electrochemical performance of these rapidly pyrolyzed nanostructures. Accelerated processing with rapid thermal pyrolysis may facilitate the expanded applicability and rapid fabrication of these promising nanostructured materials.     

Synthesis and Characterization of Several α-Silicon Nitride Nanostructures

Silicon nitride (Si₃N₄) nanowires and nanobelts have been successfully prepared via direct crystallization of amorphous Si₃N₄ nanoparticles under high temperature in a N₂ flow. The products were characterized by X-ray powder diffraction, scanning electron microscopy, transmission electron microscopy, high-resolution electron microscopy, and electron diffraction. They are pure α-phase hexagonal single-crystal structures. The nanowires are long and smooth; nanobelts are long and twisted. In our samples, there exist some special nanostructures, such as wire-inserted hexagonal nanosheet and hollow-chain-shaped structure. The different growth modes were understood upon the observations and characterization of those microstructures. The solid–liquid–solid growth mechanism is also discussed.     

Ordering in thin films of block copolymers: Fundamentals to potential applications

The ordering of block copolymers in thin films is reviewed, starting from the fundamental principles and extending to recent promising developments as templates for nanolithography which may find important applications in the semiconductor industry. Ordering in supported thin films of symmetric and asymmetric AB diblock and ABA triblock copolymers is discussed, along with that of more complex materials such as ABC triblocks and liquid crystalline block copolymers. Techniques to prepare thin films, and to characterise ordering within them, are summarized. Several methods to align block copolymer nanostructures, important in several applications are outlined. A number of potential applications in nanolithography, production of porous materials, templating, and patterning of organic and inorganic materials are then presented. The influence of crystallization on the morphology of a block copolymer film is briefly discussed, as are structures in grafted block copolymer films.     

Fabrication and spectroscopic investigation of branched silver nanowires and nanomeshworks

Wide wavelength ranges of light localization and scattering characteristics can be attributed to shape-dependent longitude surface plasmon resonance in complicated nanostructures. We have studied this phenomenon by spectroscopic measurement and a three-dimensional numerical simulation, for the first time, on the high-density branched silver nanowires and nanomeshworks at room temperature. These nanostructures were fabricated with simple light-induced colloidal method. In the range from the visible to the near-infrared wavelengths, light has been found effectively trapped in those trapping sites which were randomly distributed at the corners, the branches, and the junctions of the nanostructures in those nanostructures in three dimensions. The broadened bandwidth electromagnetic field enhancement property makes these branched nanostructures useful in optical processing and photovoltaic applications.