Electric heating – Metal heating – By arc
Reexamination Certificate
2002-11-21
2003-12-09
Heinrich, Samuel M. (Department: 1725)
Electric heating
Metal heating
By arc
Reexamination Certificate
active
06660959
ABSTRACT:
TECHNICAL FIELD
The present invention relates generally to new manufacturing processes for machining (i.e. removing material) at the nano-scale. The invention specifically relates to methods and devices for machining a workpiece at the nanoscale level using carbon nanotubes as the machining tool.
BACKGROUND OF THE INVENTION
Conventional machining and micro
ano fabrication processes transfer energy into small spatial regions to remove material from a workpiece. For instance, traditional cutting with a lathe transfers energy from a tool to a workpiece through the cutting edge of the tool and focused ion beam machining transfers energy to a workpiece with a narrow beam of ions that strike the workpiece's surface. To achieve nanoscale machining, which is the removal of material near the atomic scale (1 nm-100 nm), energy must be concentrated spatially with nearly atomic resolution and also sufficient to break bonds in crystal lattices. If the energy is too excessive, then nearby atoms will also be effected and nanoscale resolution cannot be attained. Therefore, to achieve nanoscale machining, energy should be within specific limits and spatially controlled to attain patterns.
Current micromachining processes can be categorized as either parallel techniques, which simultaneously remove material from a workpiece at many locations, or serial techniques, which sequentially remove material from a single location. Common parallel techniques include surface micromachining, bulk micromachining, and laser micromachining. Common serial techniques include mechanical cutting, micro electro discharge machining (EDM), electron beam machining, ion beam machining, and laser beam machining. Parallel techniques are well suited to economically fabricating parts with 2-D geometry in batches. Serial techniques are more suitable for complex 3-D micromachining, but cannot be used for fabricating batches of parts.
Both parallel and serial micromachining techniques require a shape-generation mechanism. In parallel techniques, the shape-generating mechanism is usually a mask used during lithography. In e-beam, ion-beam, and laser micromachining, the shape-generating mechanism is the column and tip of the energy beam. In micro EDM, the electrode is the shape-generating mechanism. The physical processes that produce the shape-generating mechanism limit the resolution and size of the geometry that can be machined. Most micromachining processes are limited to feature sizes and resolution exceeding 1 &mgr;m. For instance, electrodes for micro EDM are commonly manufactured using wire electro discharge grinding (WEDG). WEDG can produce cylindrical electrodes with diameters down to about 5 &mgr;m. Consequently, the minimum feature-size producible with micro EDM is also on the order of 5 &mgr;m.
Because of the limits in current micro- and nano-machining processes, there is a need in the art for an entirely new approach for nano-machining desired workpieces. The present invention relates to a nanotool with nanostructures less than 100 nm in size, and to methods of using the nanotool to remove material from a workpiece in desired two-dimensional (2D) and three-dimensional (3D) patterns. Nanotubes, which are carbon structures with diameters varying from 2 nm to 100 nm and lengths up to several microns, are used for shape generation and machining due to their unique physical properties for nano-machining via electrical discharges or electron emission. The present invention employs electron beams emitted from carbon nanotubes as a source of energy with nanoscale resolution and manufactures patterns by either using a predetermined pattern of nanotubes, or by relative motion between the workpiece and nanotubes.
The natural size of nanotubes and the inherent precision in their fabrication processes enable the manufacture of nano-scale tools for both serial and parallel nano-machining. For serial nano-machining, a single nanotube may be grown on an electrode. For parallel nano-machining, a 2D pattern of nanotubes may be grown on a conductive electrode substrate. The methods and devices of the present invention enable nano-machining by improving resolution and reducing minimum machined feature sizes by two to three orders of magnitude in comparison to conventional micro- and nano-machining technologies.
SUMMARY OF THE INVENTION
In accordance with the purposes of the present invention as described herein, in one aspect the present invention provides a method for machining a nanometer-scale pattern on a surface of an electrically conductive workpiece, comprising the steps of placing a nanotool in substantial proximity to the conductive workpiece surface, creating an electrical potential difference between the nanotool and the workpiece surface to cause an electron beam to emit from the nanotool and strike the conductive workpiece surface, resulting in evaporation of nanoscale quantities of material from the workpiece surface, and applying a vacuum to remove evaporated material from the workpiece surface. The electric field potential established to cause the electron beam to emit from the nanotool will typically be at least 1 V/&mgr;m. The nanotool may comprise at least one nanotube supported on an electrically conductive base. The method of the present invention may include the further step of exciting the workpiece to a threshold energy prior to contacting the workpiece with the electron beam to evaporate material therefrom.
In one embodiment of the method of the present invention, the workpiece or the nanotool may be moved relative to one another to remove material from the workpiece in accordance with a predetermined pattern. The nanotool may comprise a single nanotube supported by an electrically conductive base, or may comprise a plurality of substantially aligned nanotubes supported on the base. The plurality of nanotubes may be confined to one or more patterned regions of the electrically conductive base. It will be appreciated that for some applications this feature obviates the need to move either workpiece or nanotool relative to one another to machine the corresponding pattern into the workpiece.
Nanotubes suitable for the present invention include carbon nanotubes. However, it will be appreciated that any substance capable of forming a nanotube for emitting an electron beam in response to an electrical field may be used, such as tungsten, nickel, and the like. The nanotubes of the present invention may be single-walled or multi-walled nanotubes, and typically have a diameter of from about 1 to about 100 nanometers.
The nanotool conductive base may be fabricated from any suitably electrically conductive metal or polymer, including but not limited to materials selected from the group consisting of silicon nitride, titanium nitride, tungsten carbide, tantalum nitride, porous silicon, nickel, cobalt, gold, aluminum, polycrystalline diamond, and any combination thereof.
The conductive workpiece may be fabricated from any suitably conductive metal or polymer, and may be selected from materials including, but not limited to, the group consisting of aluminum, copper, silver, gold, polymethylmethacrylate, and any combination thereof. The workpiece may be deposited as a thin film on a substrate, with the thin film having a depth of up to 5 microns. The workpiece substrate may be fabricated from any material which is substantially transparent to a laser beam. It will be appreciated that this feature allows use of a laser to heat the workpiece from a first surface, while the nanotool of the invention is used to remove material from the obverse surface of the workpiece. The substrate may be fabricated from materials selected from the group consisting of, but not limited to, single-crystal quartz, amorphous quartz, silicon, and any combination thereof.
Excitation of the workpiece to a threshold energy may be achieved by heating. The workpiece may be heated by localized heating, by radiative heating, by conductive heating, by resistive heating, or any combination thereof. In one embodiment of the method of the present inve
Menguc M. Pinar
Rao Apparao M.
Vallance Robert Ryan
Heinrich Samuel M.
King & Schickli PLLC
University of Kentucky Research Foundation
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