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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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Angewandte Chemie International Edition 02/2011; 50(9):2036-40. · 13.45 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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ABSTRACT: Arrays of Au hierarchical micro/nanotowers have been achieved on Au-coated silicon planar substrate, via electrochemical deposition in a mixed aqueous solution of PVP and HAuCl4 under appropriate electrodeposition conditions. The Au hierarchical micro/nanotower arrays have exhibited distinct surface-enhanced Raman scattering (SERS) effect due to the enhanced local electromagnetic field in the vicinity of the sharp nanotips of the towers and the gaps between the neighboring nanotowers. More importantly, the SERS effect has been further improved significantly via decorating Ag nanoparticles on the surfaces of the Au hierarchical micro/nanotowers due to the Ag nanoparticle hot spots themselves and the hot spots formed at the interfaces between the Ag nanoparticles and the Au micro/nanotowers. These Ag-nanoparticle-decorated Au hierarchical micro/nanotower arrays have shown potential applications as sensitive and robust SERS substrates in monitoring environmental pollutants, such as 3,3′,4,4′-tetrachlorobiphenyl (PCB-77).
01/2011;
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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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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: 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
