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ABSTRACT: We present a surface-enhanced Raman scattering (SERS) substrate featured by large-scale homogeneously distributed Ag nanoparticles (Ag-NPs) with sub-10 nm gaps assembled on a two-layered honeycomb-like TiO(2) film. The two-layered honeycomb-like TiO(2) film was achieved by a two-step anodization of pure Ti foil, with its upper layer consisting of hexagonally arranged shallow nano-bowls of 160 nm in diameter, and the lower layer consisting of arrays of about fifty vertically aligned sub-20 nm diameter nanopores. The shallow nano-bowls in the upper layer divide the whole TiO(2) film into regularly arranged arrays of uniform hexagonal nano-cells, leading to a similar distribution pattern for the ion-sputtered Ag-NPs in each nano-cell. The lower layer with sub-20 nm diameter nanopores prevents the aggregation of the sputtered Ag-NPs, so that the Ag-NPs can get much closer with gaps in the sub-10 nm range. Therefore, large-scale high-density and quasi-ordered sub-10 nm gaps between the adjacent Ag-NPs were achieved, which ensures homogeneously distributed 'hot spots' over a large area for the SERS effect. Moreover, the honeycomb-like structure can also facilitate the capture of target analyte molecules. As expected, the SERS substrate exhibits an excellent SERS effect with high sensitivity and reproducibility. As an example, the SERS substrate was utilized to detect polychlorinated biphenyls (PCBs, a kind of persistent organic pollutants as global environmental hazard) such as 3,3',4,4'-pentachlorobiphenyl (PCB-77) with concentrations down to 10(-9) M. Therefore the large-scale Ag-NPs with sub-10 nm gaps assembled on the two-layered honeycomb-like TiO (2) film have potentials in SERS-based rapid trace detection of PCBs.
Nanotechnology 09/2012; 23(38):385705. · 3.98 Impact Factor
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ABSTRACT: We report on the synthesis of multi-segment nanowire (NW) junctions of Au(1-x)Ge(x) and Ge inside the nanochannels of porous anodic aluminum oxide template. The one-dimensional heterostructures are grown with a low-temperature chemical vapor deposition process, assisted by electrodeposited Au nanowires (AuNWs). The Au-catalyzed vapor-liquid-solid growth process occurs simultaneously in multiple locations along the nanochannel, which leads to multi-segment Au(1-x)Ge(x)/Ge heterojunctions. The structures of the as-grown hybrid NWs, analyzed by using transmission electron microscopy and energy-dispersive X-ray spectroscopy elemental mapping, show clear compositional modulation with variable modulation period and controllable junction numbers. Remarkably, both GeNW and Au(1-x)Ge(x)NW segments are single crystalline with abrupt interfaces and good crystallographic coherences. The electronic and transport properties of individual NW junctions are measured by using a multi-probe scanning tunneling microscope, which confirms the semiconducting nature of Ge segments and the metallic behavior of Au(1-x)Ge(x) segments, respectively. The high yield of multiple segment NW junctions of a metal-semiconductor can facilitate the applications in nanoelectronics and optoelectronics that harness multiple functionalities of heterointerfaces.
ACS Nano 12/2011; 6(1):831-6. · 10.77 Impact Factor
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ABSTRACT: We report on the synthesis of multi-segment nanowire (NW) junctions of Au1–xGex and Ge inside the nanochannels of porous anodic aluminum oxide template. The one-dimensional heterostructures are grown with a low-temperature chemical vapor deposition process, assisted by electrodeposited Au nanowires (AuNWs). The Au-catalyzed vapor–liquid–solid growth process occurs simultaneously in multiple locations along the nanochannel, which leads to multi-segment Au1–xGex/Ge heterojunctions. The structures of the as-grown hybrid NWs, analyzed by using transmission electron microscopy and energy-dispersive X-ray spectroscopy elemental mapping, show clear compositional modulation with variable modulation period and controllable junction numbers. Remarkably, both GeNW and Au1–xGexNW segments are single crystalline with abrupt interfaces and good crystallographic coherences. The electronic and transport properties of individual NW junctions are measured by using a multi-probe scanning tunneling microscope, which confirms the semiconducting nature of Ge segments and the metallic behavior of Au1–xGex segments, respectively. The high yield of multiple segment NW junctions of a metal–semiconductor can facilitate the applications in nanoelectronics and optoelectronics that harness multiple functionalities of heterointerfaces.Keywords: germanium; gold; multiple segment hybrid nanowires; electrodeposition; chemical vapor deposition
12/2011;
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ABSTRACT: Large-scale Ag nanosheet-assembled micro-hemispheres, with sufficient hot spots on their surfaces, have been achieved on an indium tin oxide substrate via electrodeposition. Surface-enhanced Raman scattering (SERS) measurements demonstrate that the Ag nanosheet-assembled micro-hemispheres can serve as sensitive and reproducible SERS substrates.
Chemical Communications 03/2011; 47(9):2709-11. · 6.17 Impact Factor
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ABSTRACT: We report on the controlled growth of germanium (Ge) nanostructures in the form of both nanowire (NW) and nanotube (NT) with ultrahigh aspect ratios and variable diameters. The nanostructures are grown inside a porous anodic aluminum oxide (AAO) template by low-temperature chemical vapor deposition (CVD) assisted by an electrodeposited metal nanorod catalyst. Depending on the choice of catalytic metals (Au, Ni, Cu, Co) and germane (GeH(4)) concentration during CVD, either Ge NWs or NTs can be synthesized at low growth temperatures (310-370 °C). Furthermore, Ge NWs and NTs with two or more branches can be grown from the same stem while using AAO with branched channels as templates. Transmission electron microscopy studies show that NWs are single crystalline and that branches grow epitaxially from the stem of NWs with a crystalline direction independent of diameter. As-grown NTs are amorphous but can crystallize via postannealing at 400 °C in Ar/H(2) atmosphere, with a wall thickness controllable between 6 and 18 nm in the CVD process. The yield and quality of the NTs are critically dependent on the choice of the catalyst, where Ni appears the best choice for Ge NT growth among Ni, Cu, Co, and Au. The synthesis of structurally uniform and morphologically versatile Ge nanostructures may open up new opportunities for integrated Ge-nanostructure-based nanocircuits, nanodevices, and nanosystems.
Nano Letters 03/2011; 11(4):1704-9. · 13.20 Impact Factor
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ABSTRACT: A highly sensitive and selective fluorescence ratiometric sensor membrane for 2,3,3'-trichlorobiphenyl has been achieved, via depositing polypyrrole nanotubes (PPyNTs, the fluorescence indicator) in nano-porous anodic aluminium oxide (NPAAO) template and subsequently immobilizing fluorescein isothiocyanate (as an internal reference) onto the inner walls of the PPyNTs embedded in the NPAAO.
Chemical Communications 02/2011; 47(13):3808-10. · 6.17 Impact Factor
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Angewandte Chemie International Edition 02/2011; 50(9):2036-40. · 13.45 Impact Factor
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ABSTRACT: Silicon, being in the same group in the periodic table as carbon, plays a key role in modern semiconductor industry. However, unlike carbon nanotube (NT), progress remains relatively slow in silicon NT (SiNT) and SiNT-based heteroarchitectures, which would be the fundamental building blocks of various nanoscale circuits, devices, and systems. Here, we report the synthesis of linear and branched crystalline SiNTs via porous anodic aluminum oxide (AAO) self-catalyzed growth and postannealing, and the connection of crystalline SiNTs and gold nanowires (AuNWs) via a combinatorial process of electrodepositing AuNWs with predesired length and location in the channels of the AAO template and subsequent AAO self-catalyzed and postannealing growth of SiNTs in the remaining empty channels adjacent to the AuNWs. Using the approach, a large variety of two-segment AuNW/SiNT and three-segment SiNT/AuNW/SiNT heteronanostructures with both linear and branched topologies have been achieved, paving the way for the rational design and fabrication of SiNT-based nanocircuits, nanodevices, and multifunctional nanosystems in the future.
ACS Nano 11/2010; 4(12):7105-12. · 10.77 Impact Factor
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Advanced Functional Materials 09/2010; 20(21):3791 - 3796. · 10.18 Impact Factor
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Advanced Materials 05/2010; 22(24):2637-41. · 13.88 Impact Factor
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ABSTRACT: Large-scale arrays of aligned ZnO hexagonal nanorods with planar ends have been achieved on a bare native n-type (100) Si substrate via a simple electrochemical deposition in Zn(NH3)4(NO3)2 solution with a pure Zn sheet as the anode without using any catalysts, additives, and additional seed crystals. The ZnO hexagonal nanorods grow from the single-crystal seeds self-formed in the initial stage of the electrochemical deposition. The diameters and the lengths of the ZnO nanorods can be tailored by adjusting the electrolyte concentration and the electrodeposition duration. Field-emission measurements show that the ZnO nanorods with smaller diameters exhibit lower turn-on field and higher current density. The well-aligned ZnO hexagonal nanorods (on Si substrate) with tunable size and field emission performance may have potentials in the future of nanotechnology.
11/2009;
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Guowen Meng,
Fangming Han,
Xianglong Zhao,
Bensong Chen,
Dachi Yang,
Jianxiong Liu, Qiaoling Xu,
Mingguang Kong,
Xiaoguang Zhu,
Yung Joon Jung,
Yajun Yang,
Zhaoqin Chu,
Min Ye,
Swastik Kar,
Robert Vajtai,
Pulickel M Ajayan
Angewandte Chemie International Edition 07/2009; 48(39):7166-70. · 13.45 Impact Factor
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ABSTRACT: We report a facile, economic, and generic way to mono- and multisegment metallic nanowires (MNWs) of various pure metals (e.g., Au, Pt, Pd, Cu, Ni, and Co) and their alloys with both linear and branched topologies, by merely infiltrating aqueous solutions of metal chloride salts into Au-coated native porous anodic aluminum oxide template with Al foil on its outside edge. Redox reactions of two galvanic cells where the Al foil acts as the anode are responsible for the formation of the MNWs. Redox reaction of the top galvanic cells on the surrounding Al foil leads to the formation of metal atoms on the Al foil surface, which subsequently diffuse away from the Al foil and into the nanochannels. Simultaneously, redox reaction of the bottom galvanic cell where the Au layer serves as a cathode results in the formation of metal atoms on the top surface of the bottom Au layer, followed by crystal nucleus formation and growth upward the channels to form short MNWs. With the elongation of the infiltration duration, the diffusing metal atoms coming from the top galvanic cells reach the tips of the growing MNWs, and combine with those on the MNW tips coming from the bottom galvanic cell, resulting in longer MNWs under the nanochannel geometrical confinement. The approach enables excellent control over the composition, location, length, and diameter of the individual segments and the topology of the overall NWs that are promising for many applications in nanotechnology.
06/2009;
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ABSTRACT: A low-frequency mechanical spectroscopy approach for liquids was proposed for studying conformational transition of polymer chains in concentrated solutions. The technique is applied to aqueous solutions of a poly(ethylene oxide)-poly(propylene oxide)-poly(ethylene oxide) (PEO-PPO-PEO) triblock copolymer in order to determine if chain conformation is altered in response to temperature. Two transitions are revealed by mechanical spectra and verified by differential thermal analysis with increasing temperature, which may be related to the unimer-to-micelle transition and the phase separation, respectively. The transitions are also found to be much dependent on the concentration of the solution and the addition of NaCl. Moreover, it reveals that the PEO blocks play a more important role in the micellar crystallization process. This study may be helpful in understanding the dynamics of polymer chains in concentrated solutions.
The Review of scientific instruments 01/2009; 79(12):126105. · 1.52 Impact Factor
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ABSTRACT: Anelastic spectroscopy is used to study the composition dependence of the damping and molecular relaxation dynamics in miscible poly(ethylene oxide) (PEO)/poly(methyl methacrylate) (PMMA) blends above the glass transition temperature. The ultrahigh damping peak of the relaxation type is shown to be associated with the liquid-liquid transition of PMMA. A higher PEO concentration leads to a higher damping performance and a lower transition temperature. The decreasing activation energy with increasing PEO concentration indicates a drastic increase in molecular mobility. Moreover, the relaxation time reveals a transition from the Vogel–Fulcher–Tamman behavior to the Arrhenius behavior due to the intermolecular guest-host interactions.
Applied Physics Letters 08/2008; · 3.84 Impact Factor
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ABSTRACT: Bismuth nanotubes (BiNTs) were synthesized by electrodeposition inside the nanochannels of an anodic aluminum oxide template coated with a thin mesh-like Au layer onto one planar surface side. By tuning the Au layer thickness and current density during electrodeposition, BiNTs with a predesigned wall thickness and with a wall thickness variation along the axis were achieved. Measurements of resistance−temperature demonstrate that BiNTs show a semiconducting electronic transport behavior, and the resistance of BiNTs with thinner walls shows a larger temperature dependence than that of BiNTs with thick walls. Our approach could be used to build other materials that can be obtained via electrodeposition into nanotubes with a designed wall thickness that might have potential in future nanotechnology.
05/2008;
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ABSTRACT: Compound nanowires (NWs) of Si-related materials, such as SiC, Si 3N 4, and Zn 2SiO 4 have been synthesized in high yield via a simple thermal evaporation, chemical reaction, and deposition process using porous silicon as the Si element source. The vapor-solid growth mechanism of NWs plays a main role in the formation of the as-prepared Si-related NWs. Photoluminescence (PL) measurements reveal that SiC NWs emit an ultraviolet light at 364 nm, Si 3N 4 NWs shows a broad PL spectrum with a maximum at 495 nm, and Zn 2SiO 4 NWs reveals a green emission at about 510 nm. These Si-related NWs have potential in both composites and optoelectronic nanodevices.
05/2008;
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ABSTRACT: We have exploited a generic method for nanocables, consisting of two materials that can be obtained via electrodeposition, by first electrodepositing the cable “shells” on the interior walls of nanochannels inside anodic aluminum oxide template with one planar surface side coated with a thin meshlike Au layer and then filling the cavities inside the shells by electrodeposition again to achieve the cable “cores.” The method has been demonstrated for the nanocables of Cu-Bi (Cu shell and Bi core) and Bi-Cu (Bi shell and Cu core). Nanocables of other two materials with tunable shell thickness and inner core diameter can be achieved by modulating the Au-layer thickness, and might have potential in the future nanotechnology.
Applied Physics Letters 03/2008; · 3.84 Impact Factor
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ABSTRACT: The internal friction and relative modulus are measured for a copolymer–micellar system EO37PO56EO37 at different concentrations. At concentration above ∼21.5 wt%, we have evidenced the presence of two first-order phase transitions, corresponding to the sol–gel transition and the gel–sol transition, respectively. The former is related to the micelle crystallization, while the latter is due to the formation of worm-like micelles. It is found that the formation of crystalline phase strongly depends on the interpenetration and entanglement of the PEO chains. Our work confirms that internal friction technique is sensitive to structural changes of micellar systems.
Physica B: Condensed Matter.
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ABSTRACT: Ternary CoNiP nanowire (NW) arrays have been synthesized by electrochemical deposition inside the nanochannels of anodic aluminum oxide (AAO) template. The CoNiP NWs deposited at room temperature present soft magnetic properties, with both parallel and perpendicular coercivities less than 500 Oe. In contrast, as the electrolyte temperature (Telc) increases from 323 to 343 K, the NWs exhibit hard magnetic properties with coercivities in the range of 1000–2500 Oe. This dramatic increase in coercivities can be attributed to the domain wall pinning that is related to the formation of Ni and Co nanocrystallites and the increase of P content. The parallel coercivity (i.e. the applied field perpendicular to the membrane surface) maximum as high as 2500 Oe with squareness ratio up to 0.8 is achieved at the electrolyte temperature of 328 K. It has been demonstrated that the parallel coercivity of CoNiP NWs can be tuned in a wide range of 200–2500 Oe by controlling the electrolyte temperature, providing an easy way to control magnetic properties and thereby for their integration with magnetic-micro-electro-mechanical systems (MEMS).
Journal of Crystal Growth 310(15):3579-3583. · 1.73 Impact Factor
