Electrolysis: processes – compositions used therein – and methods – Electrolytic erosion of a workpiece for shape or surface... – With control responsive to sensed condition
Reexamination Certificate
2001-07-24
2004-03-23
Phasge, Arun S. (Department: 1741)
Electrolysis: processes, compositions used therein, and methods
Electrolytic erosion of a workpiece for shape or surface...
With control responsive to sensed condition
C205S662000, C205S664000, C219S061400, C219S162000
Reexamination Certificate
active
06709566
ABSTRACT:
TECHNICAL FIELD
The present invention relates to nanotube shaping. In particular, the invention relates to a nanotube that exhibits a controllably shaped or “made-to-order” geometric contour and to a method for shaping a nanotube material having a layered structure.
BACKGROUND
Microfabrication represents a high-priority research area within a wide range of fields such as electronics, mechanical devices, chemical processes and biological systems. As a result, a number of techniques have been developed to shape the contour of microscopic, three-dimensional solid articles. Such techniques include both additive and subtractive processes, often involving lithographic techniques. However, lithographic techniques are usually insufficient to produce nanometer-sized features. In addition, the accuracy and precision formation of nanometer-sized features is strongly dependent on both the crystallographic structure of the material to be shape as well as the technique employed. Thus, it is evident that only certain techniques may be employed to shape articles of a certain material when high accuracy and close tolerances are required.
Carbon nanotubes are attractive candidates for a host of applications due to their unique mechanical and electrical properties. For example, carbon nanotubes have found use in catalytic reactions, see Freemantle (1996), “Filled Carbon Nanotubes Could Lead to Improved Catalysts and Biosensors,”
Chemical & Engineering News
74:62-66, electrodes, see Britto et al. (1996), “Carbon Nanotube Electrode For Oxidation of Dopamine,”
Bioelectrochemistry and Bioenergetics
41:121-125, nanoscale electronics, see Collins et al. (1997), “Nanotube Nanodevice,”
Science
278:100-103, nanoscale mechanical systems, see Iijima (1998), Proc. IEEE Eleventh Annual International Workshop on Micro Elector Mechanical Systems (IEEE, Heidelberg, Germany) 520-525, and scanned probe microscope and electron field emission tips, see Dai et al. (1996), “Nanotubes as Nanoprobes in Scanning Probe Microscopy,”
Nature
384:147-150 and deHeer et al. (1995), “A Carbon Nanotube Field-Emission Electron Source,”
Science
270:1179-1180. In addition, a number of patents describe various processes that alter the material characteristics of carbon nanotubes, such as functionalization of nanotube surfaces, see, e.g., U.S. Pat. No. 6,203,814 to Fisher et al., or encapsulation of materials in carbon nanotubes, see, e.g., U.S. Pat. No. 5,916,642 to Chang.
Carbon nanotubes have found use as probes for sensing and manipulating microscopic environments and structures. For example, U.S. Pat. No. 6,159,742 to Lieber et al. describes a carbon-based tip that may be used to reveal chemical characteristics of a sample for scanning probe microscopy. The tip is described as having a structure of the formula: X—(L—M)
n
in which n is 1 to 100, X is a carbon-based nanotube having a first end and a second end, L is a linking group bonded at the first end of the carbon-based nanotube, and M is a molecular probe bonded to the linking group. The second end of the carbon-based nanotube X is adapted for attachment to a cantilever configured for microscopy. The linking group L may be a functional moiety such as an amino, amido, carbonyl, carboxyl, alkyl, aryl, ether, or ester group. While this patent describes the attachment of a nanotube to another solid article, the nanotube itself is not controllably shaped.
Similarly, U.S. Pat. No. 6,239,547 to Uemura et al. describes a method for forming an electron-emitting source in which the carbon nanotubes are fixed to a substrate. This method involves preparing a paste by dispersing, in a conductive viscous solution, a plurality of needle-like structures each made of an aggregate of carbon nanotubes. A pattern of this paste is formed on the substrate. Non-needle-like portions are removed to a predetermined degree from the surface of the pattern through laser irradiation or plasma processing, to at least partially expose the needle-like structures. As a result, an electron-emitting source in which the carbon nanotubes are fixed to the substrate is formed. Thus, while this subtractive method allows a nanotube to be attached to a substrate so that the needle-like structure of the nanotube is exposed, the material removal process does not controllably shape the nanotube.
Thus, for use as probes or other applications, it would be desirable to control or shape nanotube geometry. Although recent progress has been made in the growth of nanotubes at pre-selected sites, see Kong et al. (1998), “Synthesis of Individual Single-Walled Carbon Nanotubes on Patterned Silicon Wafers,”
Nature
395:878-881, and the modification of nanotube ends through chemical etching, see Tsang et al. (1994), “A Simple Chemical Method of Opening and Filling Carbon Nanotubes,”
Nature
372:159-162, fine control over nanotube shaping has not been possible. When nanotubes are grown, they exhibit a substantially constant cross-sectional dimension along their longitudinal axis. Therefore, while it is possible to grow a plurality of nanotubes of differing diameters, each nanotube exhibits only one diameter. Similarly, known chemical etching techniques do not provide adequate control over the shaping of the contour of a nanotube. While chemical etching removes material from nanotube, targeted material removal from a specific location on the nanotube is currently beyond the capability of those skilled in the art. Often, nanotubes comprising a layered material undergo uncontrolled exfoliation when exposed to an etchant.
There is therefore a need for a method of shaping nanotubes to exhibit a desired or made-to-order contour, particularly nanotubes having a layered structure.
SUMMARY OF THE INVENTION
Accordingly, it is an object of the present invention to overcome the above-mentioned disadvantages of the prior art by providing a method for the controllable shaping of nanotubes to exhibit a desired contour.
It is another object of the invention to provide nanotubes that exhibit a controllably shaped contour.
Additional objects, advantages and novel features of the invention will be set forth in part in the description that follows, and in part will become apparent to those skilled in the art upon examination of the following, or may be learned through routine experimentation upon practice of the invention.
In one embodiment, the invention relates to a method for shaping a nanotube through the use of a shaping electrode to remove material from a portion of the nanotube so that the nanotube is controllably shaped to exhibit a desired contour. The material removal is carried out while the nanotube and the shaping electrode are under a potential difference. Typically, the potential difference is no more than about 10 volts. However, the potential difference is preferably no more than about 5 volts and is optimally about 0.5 to about 3.0 volts. In addition, it is preferred that the potential of the nanotube is at or near ground.
Depending on the potential difference, material removal may take place when the shaping electrode contacts the nanotube or when the shaping electrode is sufficiently close to the nanotube. Thus, material removal may not require contact between the shaping electrode and the nanotube. In some instances, material removal can be carried out by first placing a shaping electrode in contact with the nanotube when the shaping electrode and the nanotube do not exhibit a sufficient potential difference for material removal from the nanotube, and then controllably increasing the potential difference between the electrode and the nanotube to remove material from a portion of the nanotube, thereby shaping the nanotube to exhibit a desired contour. In other instances, the shaping electrode is placed in a noncontacting yet shaping spatial relationship with the nanotube when the shaping electrode and the nanotube do not exhibit a sufficient potential difference for material removal and then controllably increasing the potential difference between the electrode and the nanotube to remove material from a portion of a na
Cumings John P.
Zettl Alex K.
Phasge Arun S,.
Reed & Eberle LLP
Wu Louis L.
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