nanoquebec 2007-06-05 08:02
纳米技术杂志5月份热点文章推荐（ 2007)
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[size=4][color=Green][b]Hierarchical magnetic assembly of nanowires[/b][/color][/size]
[color=Green]As top-down fabrication technologies approach physical limits and cost constraints, bottom-up strategies have gained considerable momentum. Although research efforts have been primarily focused on synthesis of nanostructures, rational assembly remains a significant hurdle, stunting the development of nanodevices.[/color]
[color=Green]This challenge in nanomanufacturing is crucial for the integration of nanostructures into existing silicon technologies and the incorporation of functional complexity. Methods for precise alignment and positioning are necessary for reproducibly interfacing nanowires to micro or macro components with reliable electrical contact. Complex structures including the cross-junction of nanowires are also needed to create heterostructures to perform logic functions and energy conversion, thus enabling higher-order operations from a small set of building blocks. Hierarchy assembly techniques must consequently be able to facilitate complex arrangements with both site-specific positioning and nanowire–nanowire junctions.[/color]
[color=Green] In our recent work, we demonstrated hierarchy assembly of nanowires using sequential alignments and radial field gradients. In sequential alignments, deposited nanowires were found to behave as ferromagnetic electrodes for subsequent nanowire alignments, resulting in both cross-junction and T-junction formation with excellent control over nanowire direction. Microfabricated ferromagnetic electrodes were also utilized for additional control, dominating dipole interactions among nanowires for an addressable nanowire assemblage.[/color]
[color=Green]Maturation of this technology could have significant implications for applications diverse as cell manipulation, sensors, spintronics and nano-electronics. Current efforts by the Nano Electrochemical Systems Laboratory at University of California, Riverside, include synthesis and assembly of multi-functional nanowires for bio and gas sensors, spintronics and thermoelectrics.[/color]
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[url=http://www.iop.org/EJ/abstract/-search=20020595.2/0957-4484/18/20/205305]Hierarchical magnetic assembly of nanowires[/url]
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[size=4][color=Green][b]Lab-in-a-drop[/b][/color][/size]
[color=Green]Self-assembly of colloidal nanocrystals makes it possible to obtain structures with a high level of ordering and enables construction of patterns that can be used in optoelectronics, photonics and biosensing. Thermodynamically driven self-organization processes allow large-scale production of nanowires or ordered 2D or 3D superlattices with very little infrastructural investment.[/color]
[color=Green]The technology was developed by researchers at the University of Reims Champagne-Ardenne (URCA). It is based on the fact that the nanocrystal properties that are essential to the arrangement process (including size, shape, surface protection and charge) can be controlled, along with the electronic structure of each nanocrystal. The researchers demonstrated that, under carefully selected conditions, the droplets of the aqueous solutions of water-solubilized CdSe/ZnS nanocrystal quantum dots and quantum rods are operating as a "lab-in-a-drop", in which a variety of nanostructures with desired properties may be produced.[/color]
[color=Green]The operation of the lab-in-a-drop may be controlled by external parameters, providing the fluorescent nanostructures of desired size, morphology and optical and energy transfer properties. Although a majority of the results were obtained with the CdSe/ZnS quantum dots and rods, similar nanocrystalline patterns may be produced in the aqueous suspensions of other nanocrystals. The entire process has been reported in Nanotechnology.[/color]
[color=Green]This work is a collaboration between URCA, Trinity College Dublin, Munich University and two Russian scientific centres, University of Informational Technologies, Mechanics and Optics, St Petersburg, and Shemyakin Institute of Bio-organic Chemistry, Russian Academy of Sciences, Moscow. Future work will include the development of self-healing polymers based on nanocrystal self-assembly and the application of designed nanostructures to biophotonics and to the engineering of energy harvesting and energy-transfer nano-devices operating in a FRET regime.[/color]
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[url=http://www.iop.org/EJ/abstract/-search=20576058.1/0957-4484/18/18/185602]Lab-in-a-drop[/url]
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[size=4][color=Green][b]N-type nanowire on p-type substrate: is there really a p-n junction?[/b][/color][/size]
[color=Green]When an n-type nanowire (NW) is placed on a p-type substrate, does it really form a standard p–n junction? A group of researchers from Harvard University suggest that the answer, in general, is "no". Especially for materials in which doping of both types (p and n) is difficult to achieve (e.g. ZnO, GaN), it's of paramount importance to answer this question.[/color]
[color=Green]The most common application for NW-substrate junctions today is the light-emitting diode (LED). The key challenge in creating NW light sources lies in their assembly rather than material synthesis. One aspect of this challenge, which has received considerable attention, deals with the geometric arrangement of NWs into large-scale patterns. The other aspect, which has received almost no attention, is the control of the interface properties resulting from making contact between NWs and planar surfaces. Semiconductor light sources derive their behaviour from the properties of the interface between two semiconductors: the p–n junction LED and the so-called double heterojunction laser are the most obvious examples.[/color]
[color=Green]In this study, in collaboration with the group of Prof. Venky Narayanamurti, also at Harvard University, the issue of p–n junction formation was addressed in the NW on-substrate geometry for the purpose of creating an ultraviolet NW LED and understanding the underlying physics affecting the luminescence properties and current-voltage characteristics, an aspect so far largely neglected in previous studies of such sytems. LEDs were assembled using n-type doped GaN NWs in contact with a p-type silicon substrate. The results show that, in general, junctions resulting from the intimate mechanical contact with a semiconductor substrate, due to Van der Waals type forces, are far from ideal compared with those epitaxially grown in planar systems, and practically form a tunnel junction rather than a standard p-n junction. [/color]
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[url=http://iop.org/EJ/abstract/0957-4484/18/23/235205]Electroluminescence from single nanowires by tunnel injection: an experimental study[/url]
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[size=4][b]A method to attach proteins to SWNTs for the treatment of cancer[/b][/size]
[color=Green]We are working to develop ways to functionalize single-walled carbon nanotubes (SWNTs) so that they can be used in medical applications. We're focusing on attaching proteins to the SWNTs for the targeting and treatment of cancer.[/color]
[color=Green]The problem we're seeking to solve is how to attach a protein to the SWNTs, and keep the SWNTs completely suspended and the protein biologically active. We chose horseradish peroxidase (HRP) as a model protein for this study because its activity can easily be measured in an enzyme activity assay. In our application we cannot covalently couple the protein to the SWNTs because previous studies have shown that this eliminates the strong optical absorption of the SWNTs, which is a property that must be retained in our application for cancer treatment.[/color]
[color=Green]The scientific core of our findings is that we have demonstrated that the sodium cholate suspension-dialysis method for the adsorption of HRP enzyme on SWNTs gives complete retention of the biological activity of the enzyme after adsorption. This indicates that adsorption of this enzyme onto the carbon nanotubes has not perturbed the biological function of this enzyme.[/color]
[color=Green]Besides the treatment of cancer, other possible applications of this work are:[/color]
[color=Green]• imaging of cancer tumors;[/color]
[color=Green]• any other type of medical treatment or imaging in which a nanoparticle needs to be complexed with a protein and the biological function of the protein must be retained;[/color]
[color=Green]• biosensors in which an enzyme or other protein is complexed with SWNTs. [/color]
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[url=http://iop.org/EJ/abstract/0957-4484/18/23/235601]Retentionof biological activity and near-infrared absorbance upon adsorption ofhorseradish peroxidase on single-walled carbon nanotubes[/url]
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[[i] 本帖最后由 nanoquebec 于 2007-06-04 19:04 编辑 [/i]]
伊绫曦 2008-10-22 15:18
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