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August 30, 2010

A six degree of freedom nanomanipulator design based on carbon nanotube bundles updated version

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There was previous coverage on a research paper for making a six degree of freedom atomic scale manipulation using carbon nanotube bundles The designs can support the 9 tooltips designed by Freitas and Merkle.

There is now an updated copy of the paper in the Journal of Nanotechnology. The paper is available with free registration for 30 days. (8 page pdf)

Scanning probe imaging and manipulation of matter is of crucial importance for nanoscale science and technology. However, its resolution and ability to manipulate matter at the atomic scale is limited by rather poor control over the fine structure of the probe. In the present paper, a strategy is proposed to construct a molecular nanomanipulator from ultrathin single-walled carbon nanotubes. Covalent modification of a nanotube cap at predetermined atomic sites makes the nanotube act as a support for a functional 'tooltip' molecule. Then, a small bundle of nanotubes (three or four) with aligned ends can act as an extremely high aspect ratio parallel nanomanipulator for a suspended molecule, where protraction or retraction of individual nanotubes results in controlled tilting of the tooltip in two dimensions. Together with the usual scanning probe microscopy three degrees of freedom and augmented with rotation of the system as a whole, the design offers six degrees of freedom for imaging and manipulation of matter with the precision and freedom so much needed for advanced nanotechnology. A similar design might be possible to implement with other high aspect ratio nanostructures, such as oxide nanowires.



As an alternative to carbon nanotubes, other atomically precise structural elements could be used. Recent examples include silica (0.3–0.4 nm) and titania (0.4–0.5 nm) nanowires. Such structures may even possess certain advantages over carbon nanotubes, such as piezo- or ferroelectricity, as well as there being fewer competing sites of possible covalent functionalization, making the assembly of complex architectures easier. Finally, besides stiff nanotubes and nanowires, more flexible chainlike structures might be utilized in future designs to build bendable manipulators. Fullerene carbyne composite chains are one possible example.

The present paper describes a class of nanoscale parallel manipulators based on carbon nanotube bundles. The manipulators offer precise control over the position and orientation of individual molecules, thanks to the well-defined structure of constituent nanotubes and to the two additional degrees of freedom that such systems provide, compared to regular scanning probes. An important step is the choice of carbon nanotube type so as to achieve tip functionalization at predictable atomic sites. Functional molecules can then be attached by either strong covalent C–C bonds or reversible dative bonds between substitutional B and N atoms in the parts of the assembly. The designs have been demonstrated to be thermodynamically feasible, and pathways that might eventually lead to their practical implementation have been suggested. In particular, techniques to extract ultrathin carbon nanotubes from zeolite pores, or some alternative methods of free-standing ultrathin nanotube synthesis, would be desirable. Although manipulators such as those described above can be expected to substantially improve the spatial resolution of scanning probe microscopy, the true diversity of potential applications comes from the various kinds of functional molecules that they can support. Even without the possibility to actuate individual nanotubes, rigid locking of the molecules in place will enable improved control over their position and orientation, making this approach far superior to single-nanotube imaging and manipulation in terms of both versatility and precision. Here, designs that can support all nine tooltips from the minimal toolset for positionally controlled diamond mechanosynthesis have been provided. If built, they may serve as stepping stones from current scanning probe technology towards more efficient autonomous positioning systems required for high-throughput deterministic manipulation of matter at the atomic scale, ultimately leading to the much anticipated prospects of machine-phase diamond and graphitic nanotechnology. Although the research into application of carbon nanotubes in scanning probe technologies appears to have slowed down due to practical difficulties, hopefully the benefits from the present proposal can outweigh these and trigger further attempts to advance the needed prerequisite techniques, or stimulate the exploration of other possible ways to produce the proposed tools, possibly including some of the alternatives suggested in this paper.


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