Facile synthesis of mesoporous core-shell TiO2 nanostructures from TiCl3

The present study reports the synthesis and formation process of mesoporous core-shell TiO₂ nanostructures by employing a glucose-assisted solvothermal process using water-ethanol mixture as solvent and subsequent calcination process at 550 °C for 4 h. X-ray diffraction, field emission scanning electron microscopy, transmission electron microscopy and nitrogen adsorption-desorption analysis were used to investigate the structural properties of these nanostructures. By optimizing the preparation conditions, especially the contents of water and ethanol in the mixture solvent, mesoporous core-shell TiO₂ nanostructures were obtained. These mesoporous nanostructures have anatase phase and exhibit the superior photocatalytic activity. This synthesis route is facile due to the usage of stable and low-cost Ti precursor such as TiCl₃ and is thus applicable for large-scale production.     

Large-scale synthesis of ZnO flower-like and brush pen-like nanostructures by a hydrothermal decomposition route

In this present report, large-scale ZnO flower-like and brush pen-like nanostructures have been synthesized by a simple hydrothermal decomposition route. The flower-like nanostructure is composed of tens of radially oriented hexagonal nanorods. Field emission scanning electron microscopy was used to investigate the formation process of the brush pen-like nanostructures which ultimately lead to the formation of ZnO nanonunchakus. This facile low-cost controllable growth procedure holds promise in the future large-scale synthesis of ZnO nanostructures for many important applications in nano-/micro-scale devices. Room-temperature PL spectra from the ZnO flower-like and brush pen-like structures reveal weak UV emission and strong green emission.     

Morphological syntheses of ZnO nanostructures under microwave irradiation

ZnO nanostructures with flower-, rod-, and flake-like morphologies have been controllably synthesized using Zn(acac)₂·H₂O (acac = acetylacetonate) as a single-source precursor through a facile and fast microwave-assisted method. The morphologies of ZnO nanostructures can be systematically adjusted by using various surfactants. The ZnO products are characterized by X-ray diffraction, scanning electron microscopy, transmission electron microscopy, and selected area electron diffraction. The results show that all ZnO nanostructures are of single-crystalline nature with hexagonal wurtzite structure. The possible formation mechanism for these ZnO nanostructures is proposed and their photoluminescence properties are also investigated.     

Synthesis of doped ZnS one-dimensional nanostructures via chemical vapor deposition

ZnS one-dimensional (1D) nanostructures doped with Mn or Cd have been rapidly synthesized in large scale via a chemical vapor deposition process. Using Zn and S as precursors and MnCl₂ or Cd as doping source, the doped ZnS 1D nanostructures were obtained. X-ray diffraction (XRD), field-emission scanning electron microscopy (FE-SEM) and transmission electron microscopy (TEM) were employed to characterize the as-synthesized ZnS nanostructures. The catalytically grown ZnS 1D nanostructures, including nanowires and nanoribbons, are tens of micrometers in length. All the products are wurtzite ZnS in structure and preferentially grow along the [001] direction. The room temperature photoluminescence properties of these doped ZnS nanostructures are presented.     

Hyperfine interactions in graphene and related carbon nanostructures

Hyperfine interactions, magnetic interactions between the spins of electrons and nuclei, in graphene and related carbon nanostructures are studied. By using a combination of accurate first principles calculations on graphene fragments and statistical analysis, I show that both isotropic and dipolar hyperfine interactions in sp2 carbon nanostructures can be accurately described in terms of the local electron spin distribution and atomic structure. A complete set of parameters describing the hyperfine interactions of 13C and other nuclear spins at substitution impurities and edge terminations is determined. These results permit the design of graphene-based nanostructures allowing for longer electron spin coherence times which are required by spintronics and quantum information processing applications. Practical recipes for minimizing hyperfine interactions in carbon nanostructures are given.     

High-resolution mapping of electron-beam-excited plasmon modes in lithographically defined gold nanostructures

We demonstrate the use of high-resolution electron beam lithography to fabricate complex nanocavities with nanometric spatial and positional control. The plasmon modes of these nanostructures are then mapped using electron energy-loss spectroscopy in a scanning transmission electron microsope. This powerful combination of patterning and plasmon mapping provides direct experimental verification to theoretical predictions of plasmon hybridization theory in complex metal nanostructures and allows the determination of the full mode spectrum of such cavities.     

Low dimensional silver nanostructures: synthesis, growth mechanism, properties and applications

This work presents a review of the recent advances on the low-dimensional (LD) silver nanostructures (e.g., one-dimensional nanorods and nanowires, and two-dimensional nanoplates and nanodisks). First, the methods, either physical or chemical, for the synthesis of silver LD nanostructures are introduced. Then, the use is discussed of advanced experimental techniques (e.g., transmission electron microscope, high-resolution transmission electron microscope, scanning electron microscope, atomic force microscope, ultraviolet-visible and Raman spectra) and theoretical techniques at different time and length scales from quantum mechanics (e.g., ab initio simulation and density function theory) to molecular dynamics method for understanding the principles of governing particle growth, as well as discrete dipolar approximate method for understanding the optical properties of different shapes and sizes of silver LD nanostructures. Subsequently, the functional applications of the LD silver nanostructures in different areas such optical, electronic, and sensing, particularly for those related to surface plasma resonance are summarized based on the recent findings. Finally, some perspectives and comments for future investigation of silver nanostructures are also briefly discussed.     

Synthesis of rose-like boron nitride particles with a high specific surface area

Novel rose-like BN nanostructures were synthesized on a large scale via a two-step procedure. The products were characterized by X-ray diffraction, scanning electron microscopy, transmission electron microscopy, Fourier transform infrared spectroscopy, X-ray photoelectron spectrometer and nitrogen porosimetry. The results show that the obtained rose-like nanostructures are composed of a large amount of h-BN crystalline flakes and have a surface area of 90.31 m²/g. A mechanism was proposed to explain the formation process of the rose-like BN nanostructures.     

The influence of source material composition on morphology and optical properties of ZnO nanostructures

We investigated the influence of the composition of the source materials on the morphology and optical properties of ZnO nanostructures. The source materials consisted of a mixture of ZnO and carbon, or ZnO, carbon, and another metal oxide (In2O3, MnO2, or V2O5). The addition of a different metal oxide to the source materials is a commonly used method to achieve doping and/or alteration of the morphology of ZnO nanostructures. For each metal oxide additive, we investigated the influence of different forms of carbon (graphite, carbon nanofibers, and single wall carbon nanotubes). Obtained nanostructures were studied using scanning electron microscopy, transmission electron microscopy, energy dispersive X-ray spectroscopy, selected area electron diffraction, and photoluminescence. The morphology and the optical properties of the obtained nanostructures were strongly dependent on the source material composition. Possible reasons for observed differences are discussed.     

Homogeneity of Ge-rich nanostructures as characterized by chemical etching and transmission electron microscopy

The extension of SiGe technology towards new electronic and optoelectronic applications on the Si platform requires that Ge-rich nanostructures be obtained in a well-controlled manner. Ge deposition on Si substrates usually creates SiGe nanostructures with relatively low and inhomogeneous Ge content. We have realized SiGe nanostructures with a very high (up to 90%) Ge content. Using substrate patterning, a regular array of nanostructures is obtained. We report that electron microscopy reveals an abrupt change in Ge content of about 20% between the filled pit and the island, which has not been observed in other Ge island systems. Dislocations are mainly found within the filled pit and only rarely in the island. Selective chemical etching and electron energy-loss spectroscopy reveal that the island itself is homogeneous. These Ge-rich islands are possible candidates for electronic applications requiring locally induced stress, and optoelectronic applications which exploit the Ge-like band structure of Ge-rich SiGe.     

ZnO四足和多足纳米结构的制备和光致发光性能研究

采用简单的热蒸发法,在没有使用载气和催化剂的情况下成功制备出ZnO四足和多足纳米结构。采用场发射扫描电镜、X射线衍射、高分辨透射电子显微镜和荧光分光光度计研究了ZnO纳米结构的形貌、结构和光致发光性能。结果表明所合成的ZnO是由具有六方纤锌矿结构的四足和多足纳米结构组成,足部呈棒状并沿[0001]方向生长。提出了四足和多足ZnO纳米结构的生长机制。在室温下的光致发光光谱中,494nm处出现一个较强的绿色发射峰,391nm处出现一个较弱的紫外发射峰。     

Shape‐Controlled 3D Periodic Metal Nanostructures Fabricated via Nanowelding

A novel method for fabricating 3D metallic nanostructures to be used in polarized color filters based on nanoimprint lithography, electron‐beam evaporation, and nanowelding is proposed. The shape of the nanostructures can be controlled by adjusting the temperature for the nanowelding process. Ag nanowires deposited on polymer patterns are accumulated by the nanowelding process to build up diverse 3D nanostructures. The morphologies of the fabricated 3D nanostructures are analyzed using scanning electron microscopy, atomic force microscopy, and focused ion beam; the heating temperature is varied from 90 to 130 °C in steps of 10 °C. In order to analyze the recrystallization phenomenon after welding, transmission electron microscopy is utilized. The 3D metallic nanostructure has different morphologies and optical properties corresponding to welding temperature conditions and accumulated layer thicknesses. Based on preliminary experimental results, the process parameters are optimized and a polarized color filter is fabricated. Optical characteristics of the filter are evaluated using polarizer and spectrometer. Through this work, it is shown that the proposed method is an effective way to realize various 3D metallic nanostructures for special optical properties, therefore the method based on nanowelding can be utilized in fabrication of functional metamaterials, optical filters, biosensors, and others.     

Dendritic and epitaxial growths of ZnO particle-rod and rod-rod nanostructures with quasi-one-dimensional and two-dimensional configurations

Quasi-one-dimensional and two-dimensional ZnO nanostructures have been fabricated through thermal evaporation approach. The microstructures of the ZnO nanostructures have been studied using scanning electron microscopy and high-resolution electron microscopy. Quasi-one-dimensional ZnO nanostructures are formed by dendritic growths of ZnO nanoparticles from the stem nanorods surfaces, forming particle-rod nanostructures. While epitaxial growths of branch nanorods from the stem nanorods configure two-dimensional ZnO nanostructures. The epitaxial growth orientation relationship can be described as [2? 110]_R1 || [2? 110]_R2 and (0001) _R1 || (011?0)_R2. The growth mechanism of the quasi-one-dimensional and two-dimensional ZnO nanostructures has been discussed.     

Controlled growth of novel doorframe-like ITO nanostructures and their photoluminescence properties

This paper describes a thermal evaporation method that generated large-scale novel doorframe-like ITO nanostructures by regularly switching flow rate of the carried gas. Their morphology and microstructures were determined by scanning electron microscopy, high-resolution transmission electron microscopy, energy-dispersive X-ray spectroscopy and photoluminescence spectroscopy. The as-synthesized doorframe-like nanostructures are single crystal with diameters ranging from hundreds of nm to about 1 μm. The growth direction of the doorframe-like nanostructures are < 100> and < 011> and the growth process follows a self-catalytic vapor-liquid-solid mechanism. The PL spectrum of the doorframe-like nanostructures shows two emission bands around 418 and 505 nm, which is probably resulted from oxygen vacancies, oxygen-indium vacancy pairs and impurity level, respectively.     

Synthesis, characterization, and hydrophobic properties of Bi2S3 hierarchical nanostructures

Novel Bi₂S₃ hierarchical nanostructures self-assembled by nanorods are successfully synthesized in mild benzyl alcohol system under hydrothermal conditions. The hierarchical nanostructures exhibit a flower-like shape. X-ray diffraction (XRD), X-ray photoelectron spectra (XPS), scanning electron microscopy (SEM), transmission electron microscopy (TEM), high-resolution transmission electron microscopy (HRTEM), and selected area electron diffraction (SAED) were used to characterize the as-synthesized samples. Meanwhile, the effect of various experimental parameters including the concentration of reagents and reaction time on final product has been investigated. In our experiment, PVP plays an important role for the formation of the hierarchical nanostructures and the possible mechanism was proposed. In addition, Bi₂S₃ film prepared from the flower-like hierarchical nanostructures exhibits good hydrophobic properties, which may bring nontrivial functionalities and may have some promising applications in the future.     

Ag+-assisted heterogeneous growth of concave Pd@Au nanocubes for surface enhanced Raman scattering (SERS)

AgNO3 is often used in the preparation of Au nanostructures since Ag-based substances (AgBS) can selectively be adsorbed on Au(100) and significantly modulate the growth of Au nanocrystals.High-index-faceted Au nanostructures have demonstrated excellent performance in catalysis and surface enhanced Raman scattering (SERS),thus attracting the interest of many researchers in the past several decades.Herein,high-index-faceted Pd@Au concave nanocubes (CNCs) were prepared using AgBS as growth-directing agents in the heterogeneous growth of Au on Pd nanocubes (NCs).During the growth of Pd@Au CNCs,Au atoms are initially deposited on the Pd{100} facets leading to the formation of thin Au shells,and then AgBS are quickly adsorbed on the formed Au(100),favoring the growth along 〈111〉 and the formation of Pd@Au CNCs.Transmission electron microscopy (TEM),high resolution transmission electron microscopy (HRTEM),energy dispersive spectroscopy (EDS),high angle annular dark field (HAADF),and scanning transmission electron microscopy EDS (STEMEDS) were used to systematically investigate the growth of Pd@Au CNCs.We also demonstrated that the high-index-faceted Pd@Au CNCs exhibited excellent SERS performances.     

Silver nanocrystals of various morphologies deposited on silicon wafer and their applications in ultrasensitive surface-enhanced Raman scattering

Silver nanostructures with dendritic, flower-like and irregular morphologies were controllably deposited on a silicon substrate in an aqueous hydrogen fluoride solution at room temperature. The morphology of the Ag nanostructures changed from dendritic to urchin-like, flowerlike and pinecone-like with increasing the concentration of polyvinyl pyrrolidone (MW = 55,000) from 2 to 10 mM. The Ag nanostructures were characterized by transmission electron microscopy, high-resolution transmission electron microscopy, scanning electron microscopy, energy-dispersive X-ray, and X-ray diffraction. Through a series of time-dependent morphological evolution studies, the growth processes of Ag nanostructures have been systematically investigated and the corresponding growth mechanisms have been discussed. In addition, the morphology-dependent surface-enhanced Raman scattering of as-synthesized Ag nanostructures were investigated. The results indicated that flower-like Ag nanostructure had the highest activity than the other Ag nanostructures for Rhodamine 6G probe molecules.     

Controllable synthesis of self-assembled Cu2S nanostructures through a template-free polyol process for the degradation of organic pollutant under visible light

Cu₂S nanostructures were fabricated by polyol method and then characterized by X-ray diffractometer, scanning electron microscopy, transmission electron microscopy (TEM) and high resolution TEM. The morphologically different Cu₂S nanostructures such as vertically nanorod arrays, nanoflowers assembled by nanorod arrays, nanoparticles and nanowires, can be successfully synthesized under different experimental conditions. The growth mechanism for the different nanostructures is proposed. The photocatalytic activity of the prepared samples was evaluated based on the degradation of organic pollutant, active brilliant red X-3B (X-3B), under visible light. Among the Cu₂S nanostructures, self-assembled nanoflowers have the highest photocatalytic activity. In addition, the prepared Cu₂S nanostructures are found to be able to decolorize X-3B with iron ions for the formation of Fenton reagent. This study provides a more choice to prepare self-assembled nanostructures for the application of environmental pollution control.     

Self-catalytic growth and photoluminescence properties of ZnS nanostructures

Mass production of uniform wurtzite ZnS nanostructures has been achieved by a H₂-assisted thermal evaporation technique. X-ray diffraction (XRD) analyses, scanning electron microscopy (SEM) and high-resolution transmission electron microscopy (HRTEM) observations show that the ZnS nanostructures consist of nanobelts, nanosheets with a hexagonal wurtzite structure. The as-synthesized nanobelts have a length of several tens of micrometers and a width of several hundreds of nanometers. Self-catalytic vapor-liquid-solid (VLS) growth and vapor-solid (VS) growth are proposed for the formation of the ZnS nanostructures because neither a metal catalyst nor a template was introduced in the synthesis process. Room-temperature photoluminescence measurement indicates that the synthesized ZnS nanostructures have a strong emission band at a wavelength of 443 nm, which may be attributed to the presence of various surface states.     

Large-scale synthesis and characterization of fan-shaped rutile TiO2 nanostructures

Large-scale fan-shaped rutile TiO₂ nanostructures have been synthesized by means of a simple hydrothermal method using only TiCl₄ as titanium source and chloroform/water as solvents. The physicochemical features of the fan-shaped TiO₂ nanostructures are characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), selected-area electron diffraction (SAED), nitrogen absorption-desorption, diffuse reflectance ultraviolet-visible spectroscopy (UV-vis) and Fourier transform infrared spectroscopy (FTIR). Structural characterization indicates that the fan-shaped TiO₂ nanostructures are composed of several TiO₂ nanorods with diameters of about 5 nm and lengths of 300-350 nm. The average pore size and BET surface area of the fan-shaped TiO₂ nanostructures are 6.2 nm and 59 m²/g, respectively. Optical adsorption investigation shows that the fan-shaped TiO₂ nanostructures possess optical band gap energy of 3.11 eV.