Xianglong Zhao

A General Synthetic Approach to Interconnected Nanowire/Nanotube and Nanotube/Nanowire/Nanotube Heterojunctions with Branched Topology

Heterojunctions between nanotubes (NTs) and nanowires (NWs) could provide building blocks for nanoelectronics and nanophotonics, with other applications in barcodes, optical readout, biomolecular separation, catalysis, selfassembly, and magnetic manipulation. Although hybrid NWs (metal/polymer, semiconductor/semiconductor, 9] metal/semiconductor, and metal/metal ), hybrid NTs (metal/metal), NT/NW heterojunctions, and tree-like nano-heterojunctions have beenmade, the corresponding studies demonstrated limited control over the geometry and complexity of the nano-heterojunctions, which ultimately are central to the design of building blocks for nanocircuits, nanodevices, and nanosystems. Herein we show a general synthetic approach to various branched two-segment NW/NT and three-segment NT/NW/NT heterojunctions, based on a combinatorial process of electrodepositing NWs within the branched channels of anodic aluminum oxide (AAO) templates, selectively etching part of the electrodeposited NWs, and growing NTs on the ends of the NWs. The NWs can be metallic or semiconducting, while the NTs can consist of carbon, silicon, and silica; the two NT segments in threesegment NT/NW/NT nanoarchitectures can comprise either the same or different materials. This approach enables excellent control over the geometry, chemical composition, and complexity of the hetero-nanoarchitectures that can be the framework for nanoscale devices and systems. Figure 1 shows schematic depictions of the basic heteronanoarchitectures we have made, which consist of various NT and NW segments placed combinatorially in a Y-shaped topology. The synthesis scheme follows a typical buildingblock concept in which a set of different nanoscale components (NTs and NWs of different materials with distinct properties, in linear and branched topologies) can be connected in a predetermined fashion inside the branched

Color Fine-Tuning of CNTs@AAO Composite Thin Films via Isotropically Etching Porous AAO Before CNT Growth and Color Modification by Water Infusion

[*] Prof. G. Meng, Dr. X. Zhao, Dr. Q. Xu, Dr. F. Han Key Laboratory of Materials Physics Anhui Key Laboratory of Nanomaterials and Nanostructures Institute of Solid State Physics, Chinese Academy of Sciences P. O. Box 1129, Hefei 230031 (PR China) E-mail: gwmeng@issp.ac.cn Prof. Q. Huang Key Laboratory of Ion Beam Bioengineering Institute of Plasma Physics, Chinese Academy of Sciences Hefei 230031 (P. R. China)

Gap-tunable Ag-nanorod arrays on alumina nanotip arrays as effective SERS substrates

Large area arrays of length-tunable alumina nanotips on the joints of hexagonally patterned conical-pores in an anodic aluminum oxide (AAO) template are achieved via a repeated process of anodizing Al foil for pore growth downwards and phosphoric acid etching for pore-widening. By top-view sputtering Ag on the alumina nanotip arrays, hexagonally patterned arrays of Ag-nanorods (Ag-NRs) on the alumina nanotips and uniformly distributed Ag-nanoparticles (Ag-NPs) on the upper rim of the inner surface of the conical-pores are obtained and they exhibit strong surface-enhanced Raman scattering (SERS) activity due to the high density of sub-10 nm gaps between the nearest neighboring Ag-NRs and between the adjacent Ag-NPs. The resultant nanostructures are tailored to attain an optimal SERS enhancement factor of ∼3.2 × 107 by tuning the Ag-sputtering duration. SERS measurements demonstrate that the as-fabricated large-scale Ag-nanostructures can serve as highly sensitive and reproducible SERS substrates. Finite element method calculation also confirms that the fabricated substrates possess excellent SERS activity. By modifying the Ag-NR arrays with mono-6-thio-β-cyclodextrin, the SERS detection limit of PCB-77 (a congener of polychlorinated biphenyls (PCBs)) reaches 10−6 M, showing potential in SERS-based rapid detection of trace PCBs, a kind of global environmental hazardous material.

Macroporous Inverse Opal-like MoxC with Incorporated Mo Vacancies for Significantly Enhanced Hydrogen Evolution

The hydrogen evolution reaction (HER) is one of the most important pathways for producing pure and clean hydrogen. Although platinum (Pt) is the most efficient HER electrocatalyst, its practical application is significantly hindered by high-cost and scarcity. In this work, an MoxC with incorporated Mo vacancies and macroporous inverse opal-like (IOL) structure (MoxC-IOL) was synthesized and studied as a low-cost efficient HER electrocatalyst. The macroporous IOL structure was controllably fabricated using a facile-hard template strategy. As a result of the combined benefits of the Mo vacancies and structural advantages, including appropriate hydrogen binding energy, large exposed surface, robust IOL structure and fast mass/charge transport, the synthesized MoxC-IOL exhibited significantly enhanced HER electrocatalytic performance with good stability, with performance comparable or superior to Pt wire in both acidic and alkaline solutions.

A generic approach to nanocables via nanochannel-confined sequential electrodeposition

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.

Spontaneous perpendicular exchange bias effect in L10-MnGa/FeMn bilayers grown by molecular-beam epitaxy

We report on the spontaneous perpendicular exchange bias effect in as-grown L10-MnGa/FeMn bilayers. An FeMn layer with different thicknesses is introduced as an antiferromagnetic layer to couple with single-crystalline ferromagnetic L10-MnGa, which is epitaxially grown on a GaAs (001) substrate by molecular-beam epitaxy. The perpendicular exchange bias shows a strong dependence on both the thickness of the FeMn layer and the measurement temperature. A large spontaneous perpendicular exchange bias up to 8.9 kOe is achieved in L10-MnGa/FeMn bilayers at 5 K without any external magnetic treatment. The corresponding effective interfacial exchange energy Jeff is estimated to be 1.4 mJ/m2. The spontaneous perpendicular exchange bias effect in the (001) textured L10-MnGa/FeMn bilayers paves the way for spintronic devices based on exchange biased perpendicularly magnetized materials.

ERRATUM: Nanocontainers made of Various Materials with Tunable Shape and Size

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.