Yanjuan Xiang

Gold nanorod-seeded growth of silver nanostructures: From homogeneous coating to anisotropic coating

Single crystalline gold nanorods (Au NRs) dominated by {110} side facets were employed as seeds to tailor the deposition of Ag. Apart from homogeneous coating, anisotropic coating of Ag was observed and resulted in an orange slice-like shape for the Au@Ag nanocrystal. Different growth rates for the {110} side facets were responsible for this shape: among the four {110} facets, two of the neighboring {110} facets grew more quickly and another two grew more slowly, thus inducing the anisotropic deposition of Ag around the Au NR. This growth behavior is believed to be a consequence of competition between the strong stabilization of cetyltrimethylammomium bromide (CTAB) molecules to the {110} facets of Ag and minimization of the overall surface energy. Although the reason for the anisotropic coating remains to be clarified, our results lead to one important conclusion: The interaction of CTAB and metal can be utilized to tune the shapes of bimetallic structures.

Well-Controlled Synthesis of Au@Pt Nanostructures by Gold-Nanorod-Seeded Growth

Pt nanodots were formed on Au nanorods (NRs) by using a simple seed-mediated growth. Their density and distribution on the Au NR can be finely tuned by varying the reaction parameters. At lower Pt/Au ratios, the Pt nanodots mainly appear at endcaps and side edges of the Au rod. At higher Pt/Au ratios, they distribute homogeneously over the whole Au rod. The obtained Pt nanostructure is a single crystal owing to the epitaxial growth of Pt on the Au rod. Due to the unique surface plasmon resonance (SPR) features of the Au NRs, the Au core/Pt shell (Au@Pt) nanostructures also exhibit well-defined and red-shifted longitudinal SPR bands in the visible and near-infrared region. The position and intensity can be regulated by the thickness and amount of the Pt shell. At a thinner Pt thickness, the Au@Pt NRs show higher dielectric sensitivity than the corresponding Au NRs. It thus opens up the potential of Pt nanostructures for SPR-based sensing.

Enhanced Optical Responses of Au@Pd Core/Shell Nanobars

A Pd nanoshell was epitaxially grown on a Au nanorod (NR) via simple seed-mediated growth. Compared with the cylindrical shape of the Au NR, the Au core/Pd shell (Au@Pd) nanorods change to a rectangular shape due to the disappearance of {110} facets. The Au NRs exhibit a strong longitudinal surface plasmon resonance (LSPR). As Pd is deposited, damping and broadening occur to the LSPR band. Interestingly, the LSPR band maximum first shows a small red-shift (ca. 40 nm) which then is followed by a blue-shift as the amount of Pd is increased. A thickness-dependent LSPR feature of the Pd shell is believed to contribute to the shift. At a thinner Pd thickness, the Au@Pd nanobars exhibit a well-defined LSPR band in the visible and near-infrared region, which demonstrates a higher dielectric sensitivity than that of the corresponding Au NRs. It thus opens up the potential of Pd nanostructures for SPR-based sensing. Investigations on the surface-enhanced Raman scattering (SERS) indicate that the SERS activities of the Au@Pd nanobars at thicknesses smaller than 2.5 nm mainly originate from the Au cores; thus, the SERS activities can be improved by tuning the aspect ratio of the Au core and/or the Pd shell thickness.

A simple route to scalable fabrication of perfectly ordered ZnO nanorod arrays

ZnO nanorod arrays with perfect order and uniformity were prepared using a simple, low-cost, commonly available and scalable nanosphere lithography for patterning gold catalyst particles and a successive bottom-up growth technique in a tube furnace chemical vapor deposition system. Each rod in the arrays had perfect surface facets, sharp edges and uniform size. For all of the rods, their sides were oriented the same. This bottom-up assembly method may accelerate the use of ZnO nanorods in real device applications.

Growth of ZnO hexagonal nanoprisms

We show the success of large-scale growth of ZnO hexagonal nanoprisms on silicon substrates by a two-staged mechanism. In the first stage, the catalyst nanoparticles assisted the nucleation via the vapour–liquid–solid (VLS) mechanism to form polyhedral nanoparticles. In the second stage, the nanoprism was grown up by anisotropic homoepitaxy, layer by layer, on the c-face of the polyhedral nanoparticle. The surface of the nanoprism consists of the ultraflat {0001} and planes. The nanoprism is 200–500 nm in width and controllably sized in length, of high crystalline quality and excellent optical quality. This nanoprism would be an interesting building block for highly efficient nanolasers.

Template-free synthesis of helical hexagonal microtubes of indium nitride

Single crystalline indium nitride (InN) helical microtubes with a hexagonal hollow cross section have been synthesized in bulk quantities by nitriding indium oxide powder in ammonia flux. As-prepared InN microtubes grow along the [0001] direction with typical outer diameters of 1–3μm, wall thickness of 50–80nm and lengths up to hundreds of microns. The InN microtubes exhibit both right-handed and left-handed helicities with helical angles ranging from zero to about 30°. Variation of helicity can be observed in a single tube. A number of observations demonstrate that the growth of the tubular structure occurs by the spiraling of the warped InN nanobelts. Photoluminescence spectrum of the microtubes presents a strong emission peak centered at 700nm at room temperature.

Electrochemical fabrication and structure of NixZn1−x alloy nanowires

NixZn1?x alloy nanowires were successfully prepared by the templated electrodeposition technique. The morphology and the microstructures of as-deposited nanowires were examined by scanning electron microscope, x-ray diffraction, transmission electron microscope and electron diffraction. It is demonstrated that the content of magnetic element Ni in the nanowires can be easily adjusted by changing the ingredients of the electrolyte, the deposited current density and the deposited voltage, which is critical to tune the magnetic property of the nanowires. X-ray diffraction and electron diffraction analysis indicate that the NixZn1?x nanowires exhibit different structures with the variation in the quantity of nickel in the nanowires. It is expected that these heterogeneous alloy nanowires will have a potential application in nanoscale giant-magnetoresistance devices.

Growth of ultrafine ZnS nanowires

Ultrafine ZnS nanowires have been grown successfully through thermal evaporation of zinc powder and sulfur powder at 580 and 90??C respectively. The nanowires are mainly in the range of 5?12?nm in diameter, and several microns in length. X-ray diffraction and high-resolution transmission electron microscope analysis shows that the ZnS nanowires are of wurtzite structure and have two different growth directions of [001] and []. The growth mechanism is discussed in detail.

Efficiently producing single-walled carbon nanotube rings and investigation of their field emission properties

Single-walled carbon nanotube (SWNT) rings with a diameter of about 100 nm have been prepared by thermally decomposing hydrocarbon in a floating catalyst system. These rings appeared to consist mostly of SWNT toroids. High resolution transmission electron microscopy showed that these rings were composed of tens of SWNTs with a tightly packed arrangement. The production of SWNT rings was improved through optimizing various growth parameters, such as growth temperature, sublimation temperature of the catalyst, different gas flows and different catalyst components. The growth mechanism of the SWNT rings is discussed. In the field emission measurements we found that field emission from a halved ring is better than that from a whole SWNT ring, which contributed to the better emission from two opened ends of the nanotubes of the halved SWNT ring.

Anodizing behavior of aluminum foil patterned with SiO2 mask

SiO 2 -Patterned anodic aluminum oxide (AAO) is fabricated on the surface of aluminum (Al) foil by combining both photolithography and anodizing technique. Tilted pores and ridge-like features on the Al surface are observed under the SiO 2 mask by scanning electron microscopy characterization. A mechanism based on the deflection of electric field due to the existence of SiO 2 barrier on Al surface has been proposed to explain the observed anodizing behavior. Moreover, large-scale ordered metallic Al patterns are also revealed by removing the AAO film and SiO 2 mask.