US20030082092A1

US20030082092A1 - Carbon nanoloop

Info

Publication number: US20030082092A1
Application number: US10/016,758
Authority: US
Inventors: Nyles Nettleton
Original assignee: Sun Microsystems Inc
Current assignee: Sun Microsystems Inc
Priority date: 2001-10-30
Filing date: 2001-10-30
Publication date: 2003-05-01

Abstract

The present invention relates to the field of carbon, and in particular to making a carbon nanoloop. According to one embodiment, this nanoloop is made using nanomanipulators or some exotic chemistry. According to another embodiment, depending upon the cross-sectional structure of the nanoloop, it can be a conductor, an insulator, or a semi-conductor, such that two nanoloops with the same chirality exhibit the same mechanical, electrical, and magnetic properties.

Description

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to the field of carbon and in particular to making a carbon nanoloop.

Portions of the disclosure of this patent document contains material that is subject to copyright protection. The copyright owner has no objection to the facsimile reproduction by anyone of the patent document or the patent disclosure as it appears in the Patent and Trademark Office file or records, but otherwise reserves all rights whatsoever.

2. Background Art

Carbon

Carbon is a non-metallic chemical that is known by several names depending on its purity, and its interaction with other chemicals. Elemental carbon is one such form that has three profiles, viz.: diamond, graphite, and carbon black which includes charcoal, coal, lampblack, and coke. Each of the three profiles have their own physical characteristics. While diamond and graphite, on one hand, are crystalline in structure (yet differ in physical properties because the arrangements of the carbon atoms in their structures are dissimilar), carbon black, on the other hand, is amorphous. While pure diamond is the hardest naturally occurring substance known, it is a poor conductor of electricity. Graphite, on the other hand, is a soft, slippery solid that is a good conductor of both heat and electricity. Each of the amorphous forms of black carbon have their own characteristics, and hence, each has its own particular applications.

Carbon also comes in an aromatic compound form. In this form there are three known profiles, viz.: diamond, graphite, and fullerene. Fullerenes is a class by itself and contains such elements as buckyball or C ₆₀, and buckytube or nanotube. Essentially, they are any class of closed, hollow, aromatic carbon compounds made up of 12 pentagonal and differing numbers of hexagonal faces consisting of an even number of carbon atoms ranging from 32 to as many as 600 atoms.

Buckyball (C ₆₀)

Found only as early as 1985, a buckyball contains 60 carbon atoms (C ₆₀) joined together by single or double bonds to form a hollow sphere with 12 pentagonal and 20 hexagonal faces resembling a soccer ball. FIG. 1 shows the molecular structure of a buckyball, which is also known by its more celebrated name of Buckminsterfullerene after the American architect R. Buckminster Fuller. C₆₀is an extremely stable compound since every carbon vertex (the junction of one pentagon and two hexagon) is identical, resulting in an equal distribution of bonding strains which makes it withstand very high temperatures and pressures. Even though C₆₀can react with a wide variety of elements, its spherical structure is left intact. This means that C₆₀can not only withstand high temperatures and pressures, but also withstand external forces like stresses caused when it reacts with other elements. The unique structure as well as properties of C₆₀suggests potential uses as superconductors, lubricants, industrial catalysts, and drug-delivery systems ( e.g., targeted cancer therapy).

Buckytube (Nanotube)

The buckytube was accidentally discovered in the resultant soot left behind from an electrical discharge between two carbon electrodes. A buckytube is a single-molecule structure similar in construction to a buckyball, but tubular and of variable length. Currently, a nanotube comes in two forms, viz.: single and multi-walled carbon nanotube. A multi-walled nanotube is several concentric tubes of carbon (or graphite sheets) nested within each other, while a single walled nanotube is a single sheet of graphite rolled up into just one tube. A nanotube ends in a cap section, which is usually hemispherical in shape. While the thickness of a multi-walled nanotube ranges in the tens of nanometers, the typical diameter of a single-walled nanotube is a couple of nanometers across. In spite of the microscopic size, a nanotube has exceptional strength due to the strong bond that connects every carbon atom to its neighbors. Depending on the manner in which this tube is cultivated and the substrate on which it is grown, novel structures, such as “nanobrushes” 200 can be observed and are shown in FIG. 2. A nanotube has unique electrical, mechanical, and magnetic properties depending on the way it is rolled and due to the characteristics of carbon itself.

Electrical Properties

Depending on the way the tube is rolled, a nanotube can be a semi-conductor or a resistor of electric current, and has commercial applications in nanoscale wires, resistors, transistors, and sensors. Since a carbon nanotube conducts electric current via the ballistic transport mechanism rather than via conductance, every electron that enters one end of the nanotube leaves out the other end. This means that a nanotube can function as a superconductor, or a semi-conductor. The basic resistance between a nanotube and a conductive metal attached to its end is constant at 12.7 K ohms. This characteristic of the nanotube can be used to measure a precise resistance of 12.7 K ohms in an electric circuit by using it as a resistor in series or in parallel to other resistors made of carbon nanotubes with conductive metals on the ends. A complete description of using a carbon nanotube as an electrical resistor is contained in co-pending U.S. patent application “Use Of Carbon Nanotubes As Electrical Resistors”, Ser. No. ______ filed on ______, and assigned to the assignee of this patent. A small diameter of carbon nanotube is also very favorable for field emission, the process by which a device emits electrons when an electric field or voltage is applied to it. The use of nanotubes as field emitters is important in several industries, including lighting and displays, and electron microscopy.

Mechanical Properties

Since each carbon atom is strongly bonded to three other atoms in each graphite sheet, the sheet is very strong in certain directions. In numerous experiments where a rod of graphite is compressed along its length, the rod remains straight as the compression increases, before flipping into a curve at the Euler limit. This means that a carbon nanotube will bend over to surprisingly large angles, before it starts to ripple and buckle, and then finally develop kinks as well. The amazing thing about a carbon nanotube is that these deformations are elastic (as opposed to plastic) which disappear completely when the load or stress is removed. This mechanical property of the carbon nanotube allows it to be used as a strain gauge to measure a precise strain in another material when attached firmly to the other material. A complete description of using a carbon nanotube as a strain gauge by altering its physical shape is contained in co-pending U.S. patent application “Carbon Nanotubes As A Strain Gauge”, Ser. No. ______ filed on ______, and assigned to the assignee of this patent.

Magnetic Properties

A carbon nanotube is used to demonstrate the AharonovBohm effect which is a fundamental actuality in quantum physics. In the AharonovBohm effect a beam of quantum particles like electrons are split in two partial beams that pass on either side of a region containing a magnetic field. These partial beams are then recombined to form an interference pattern. This pattern can be changed by altering the magnetic field in between it, even though the pattern does not actually come in contact with the magnetic field. By observing the interference pattern, one can demonstrate that a single electron does not choose a particular path but behaves as an extended wave that follows both paths simultaneously. This pattern shifts as the magnetic field changes, returning to the original pattern when the magnetic flux has changed by the quantum of magnetic flux, Φ ₀=h/e, where h is the Planck constant and e is the charge on the electron. Since a nanotube is a cylindrical conductor when it is placed in a magnetic field with its axis parallel to the field, the electrons can propagate in either clockwise or anti-clockwise directions. These “two” paths interfere resulting in a periodic modulation of the electrical resistance as the magnetic flux through the tube is changed. This effect is quite robust and can be observed even if the electron transport in the nanotube is diffusive.

SUMMARY OF THE INVENTION

BRIEF DESCRIPTION OF THE DRAWINGS

These and other features, aspects and advantages of the present invention will become better understood with regard to the following description, appended claims and accompanying drawings where: [0019]
FIG. 1 is an illustration of a buckyball. [0020]
FIG. 2 is an illustration of “nanobrushes”. [0021]
FIG. 3A is an illustration of a nanoloop according to the present invention. [0022]
FIG. 3B shows different illustrations of a nanoloop. [0023]

DETAILED DESCRIPTION OF THE INVENTION

The invention relates to the field of carbon, and in particular to making a carbon nanoloop. In the following description, numerous specific details are set forth to provide a more thorough description of embodiments of the invention. It is apparent, however, to one skilled in the art, that the invention may be practiced without these specific details. In other instances, well known features have not been described in detail so as not to obscure the invention. [0024]
A carbon nanoloop is a variation of a carbon nanotube, where instead of the ends of the tube terminating in a cap section, the end caps are joined together forming a continuous loop. FIG. 3A is one illustration of a nanoloop which is a toroidal shaped structure similar to a nanotube in cross section. Having a continuous closed looped form, this shape can be changed to other interesting closed looped shapes, some of which are shown in FIG. 3B. Further, since a nanotube can be either single or multi-walled, a nanoloop can also be either single or multi-walled. A complete description of single and multi-walled nanotubes is contained in co-pending U.S. patent application “Carbon Nanotubes As A Strain Gauge”, Ser. No. ______ filed on ______, and assigned to the assignee of this patent. A carbon nanoloop displays characteristics similar to a carbon nanotube, and include electrical, mechanical, and magnetic properties that may be used commercially. These properties as well as their commercial applications have been discussed in the background section. [0025]
Growth of Carbon Nanoloops [0026]
Since carbon nanoloops are made out of carbon nanotubes whose ends touch each other, one possibility is to take carbon nanotubes and mechanically join its ends to form loops. Another possibility is to use a chemical process whereby the two ends of a carbon nanotube can be made to join without altering the chemical form of the carbon nanotube. [0027]
Thus, a new shape to a carbon nanotube namely a carbon nanoloop is described in conjunction with one or more specific embodiments. The invention is defined by the following claims and their full scope of equivalents. [0028]

Claims

We claim:

1. A new shape to the existing carbon nanotube shape comprising:

constructing a toroidal structure from said carbon nanotube.

2. Said toroidal structure of claim 1 is either single or multi-walled.

3. Said toroidal structure of claim 1 is an electrical conductor, an electrical resistor, or an electrical insulator depending on the way the loop is rolled.