[Show abstract][Hide abstract] ABSTRACT: Tin oxide (SnO2) is a promising wide bandgap semiconductor for next generation ultraviolet (UV) non-polar optoelectronic devices applications. The development of SnO2-based optoelectronic devices is obsessed by its low exciton emission efficiency. In this study, quantum confined SnO2 nanocrystals have been fabricated via pulsed laser ablation in water. The SnO2 quantum dots (QDs) possess high performance exciton emission at 297‒300 nm light in water. The exciton emission intensity and wavelength can be slightly tuned by laser pulse energy and irradiation time. Optical gain has been observed in SnO2 QDs. Therefore, SnO2 QDs can be a promising luminescence material for the realization of deep UV nano-emitter and lasing devices.
Full-text · Article · Feb 2015 · Journal of Materials Science and Technology -Shenyang-
[Show abstract][Hide abstract] ABSTRACT: Surface-enhanced Raman spectroscopy (SERS) is a fast analytical technique for trace chemicals; however, it requires the active SERS-substrates to adsorb analytes, thus limiting target species to those with the desired affinity for substrates. Here we present networked polyacrylic acid sodium salt (PAAS) film entrapped Ag-nanocubes (denoted as Ag-nanocubes@PAAS) as an effective SERS-substrate for analytes with and without high affinity. Once the analyte aqueous solution is cast on the dry Ag-nanocubes@PAAS substrate, the bibulous PAAS becomes swollen forcing the Ag-nanocubes loose, while the analytes diffuse in the interstices among the Ag-nanocubes. When dried, the PAAS shrinks and pulls the Ag-nanocubes back to their previous aggregated state, while the PAAS network “detains” the analytes in the small gaps between the Ag-nanocubes for SERS detection. The strategy has been proven effective for not only singleanalytes but also multi-analytes without strong affinity for Ag, showing its potential in SERS-based simultaneous multi-analyte detection of both adsorbable and non-adsorbable pollutants in the environment.
[Show abstract][Hide abstract] ABSTRACT: Galvanic reduction (GR) is a classic reaction. In simple terms, metals can reduce less reactive (or more noble) metal ions, while the opposite-metals reduce more reactive (or less noble) metal ions-should not occur. However, recently we found that anti-galvanic reduction (AGR) occurred to thiolated gold and silver nanoparticles. However, the essential issue whether the occurrence of AGR requires the assistance of reductive thiolate ligands or not still remained unanswered. In this work, by using a novel protocol (chemical reduction and physical ablation), we synthesized surfactant- and ligand-free gold nanoparticles. We found that these as-prepared nanoparticles can reduce silver ions and copper ions, thus illustrating that AGR is not dependent on reductive ligands. Further experiments demonstrated that AGR is applicable to other metal (such as Pt and Pd) nanoparticles and that the AGR process is size-dependent. Finally, it was found that the Raman scattering signals of Rhodamine 6G are distinctly enhanced on the gold nanoparticles that had been reacted with silver ions, which indicates the use of AGR for tuning the property of nanoparticles.
Full-text · Article · Apr 2014 · Chemistry - An Asian Journal
[Show abstract][Hide abstract] ABSTRACT: We present a facile approach for the controlled fabrication of well-aligned arrays of Ge nanotubes (GeNTs) with tunable sizes and hierarchical branches inside the pre-designed nanochannels of porous anodic aluminum oxide (AAO) templates. Metal salts, such as nickel nitrate, silver nitrate, cobalt nitrate and copper sulphate are pre-decorated on the inner wall of the AAO nanochannels as catalyst precursors, where they are reduced into nickel, silver, cobalt, and copper clusters, and provide nucleation sites for subsequent Ge growth. GeNTs are formed by confining the Ge growth on the inner walls of the porous AAO template in a low temperature (300–380 °C) chemical vapor deposition process. The as-grown GeNTs have open ends with tailored wall thickness (between 10 and 26 nm), diameter (between 80 and 248 nm), and geometrical configuration (e.g., linear, Y-branching, multi-branching, and various multiple-generation branching). The GeNT formation process is sensitive to the choice of the catalyst precursor. Nickel salts lead to a uniform wall thickness of GeNTs compared with copper, silver, and cobalt salts. And GeNTs grown with copper salts as catalysts are polycrystalline, while nickel, silver and cobalt salts assisted GeNTs are amorphous though they can crystallize via post-annealing at 400 °C in Ar/H2 atmosphere. These open-end hollow nanotubes with tunable sizes and hierarchical branches can serve as nanoscale containers or pipes to deliver fluids and molecular species, and are excellent building blocks for the construction of large-scale nanofluidic systems.
No preview · Article · Aug 2013 · Journal of Materials Chemistry
[Show abstract][Hide abstract] ABSTRACT: Nanocontainers have great potentials in targeted drug delivery and nanospace-confined reactions. However, the previous synthetic approaches exhibited limited control over the morphology, size and materials of the nanocontainers, which are crucial in practical applications. Here, we present a synthetic approach to multi-segment linear-shaped nanopores with pre-designed morphologies inside anodic aluminium oxide (AAO), by tailoring the anodizing duration after a rational increase of the applied anodizing voltage and the number of voltage increase during Al foil anodization. Then, we achieve nanocontainers with designed morphologies, such as nanofunnels, nanobottles, nano-separating-funnels and nanodroppers, with tunable sizes and diverse materials of carbon, silicon, germanium, hafnium oxide, silica and nickel/carbon magnetic composite, by depositing a thin layer of materials on the inner walls of the pre-designed AAO nanopores. The strategy has far-reaching implications in the designing and large-scale fabrication of nanocontainers, opening up new opportunities in nanotechnology applications.
[Show abstract][Hide abstract] 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.
[Show abstract][Hide abstract] 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.
[Show abstract][Hide abstract] 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.
Full-text · Article · Mar 2011 · Chemical Communications
[Show abstract][Hide abstract] ABSTRACT: Filling the pores: A two-layer anodized alumina template consists of two sorts of parallel pores-through-pores and capped-pores. By selectively filling only the through-pores by various techniques, and then wet-chemically etching the walls between the capped-pores, a generic synthetic approach to aluminsheathed nanocables with cores of different structures and materials such as nanowires (see picture) and nanotubes has been developed.
Full-text · Article · Feb 2011 · Angewandte Chemie International Edition
[Show abstract][Hide abstract] 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.
Full-text · Article · Feb 2011 · Chemical Communications
[Show abstract][Hide abstract] 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).
[Show abstract][Hide abstract] 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.
[Show abstract][Hide abstract] ABSTRACT: A facile and economic approach has been developed for the synthesis of coaxial nanocables with AuNi alloy nanowires as inner solid cores and NiO as outer shells by infiltrating a gold-coated anodic aluminum oxide (AAO) template, with ring-shaped Al foil on its outer edge, with a mixed aqueous solution of NiCl2 and HAuCl4 to form AuNi/Ni nanocables, and subsequent immersion in an aqueous NaOH solution to oxidize the Ni sheath during template removal. The formation of the AuNi/Ni nanocables in the channels of the AAO template could be ascribed to the reduction of the Ni2+ ion complexes adhering on the AAO channel walls and the redox reactions of two galvanic cells in which the surrounding Al foil acts as the anode. The approach enables excellent control over the shell thickness and the chemical composition of the AuNi/NiO nanocable by tuning the composition of the mixed solution. The AuNi/NiO nanocables have potentials in nanodevices and nanosystems.
No preview · Article · Sep 2010 · Berichte der deutschen chemischen Gesellschaft
[Show abstract][Hide abstract] ABSTRACT: A large variety of interconnected nanowire/nanotube (NW/NT) and nanotube/nanowire/nanotube (NT/NW/NT, see picture) hybrid architectures with branched topology have been prepared using a combinatorial process of electrodepositing nanowires in the branched channels of anodic aluminum oxide templates, selectively etching part of the deposited nanowires, and growing nanotubes in the remaining empty channels on the ends of the nanowires.
[Show abstract][Hide abstract] 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.
Preview · Article · Jun 2009 · Chemistry of Materials
[Show abstract][Hide abstract] 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.
No preview · Article · Mar 2008 · Applied Physics Letters