Carbon nanotube quantum dot
Encyclopedia
A carbon nanotube quantum dot (CNT QD) is a small region of a carbon nanotube
in which electron
s are confined.
to a gate electrode, dragging the valence band
of the CNT down in energy, thereby causing electrons to pool in a region in the vicinity of the electrode. Experimentally this is accomplished by laying a CNT on a silicon dioxide
surface, sitting on a doped
silicon wafer. This can be done by chemical vapor deposition
using carbon monoxide
. The silicon wafer serves as the gate electrode. Metallic leads can then be laid over the nanotube in order to connect the CNT QD up to an electrical circuit.
is often used to study the CNT QD. The CNT QD is modelled as an Anderson-type model, which can be reduced by Schrieffer-Wolff transformation to an effective Kondo-type model at low temperature.
Carbon nanotube
Carbon nanotubes are allotropes of carbon with a cylindrical nanostructure. Nanotubes have been constructed with length-to-diameter ratio of up to 132,000,000:1, significantly larger than for any other material...
in which electron
Electron
The electron is a subatomic particle with a negative elementary electric charge. It has no known components or substructure; in other words, it is generally thought to be an elementary particle. An electron has a mass that is approximately 1/1836 that of the proton...
s are confined.
Formation
A CNT QD is formed when electrons are confined to a small region within a carbon nanotube. This is normally accomplished by application of a voltageVoltage
Voltage, otherwise known as electrical potential difference or electric tension is the difference in electric potential between two points — or the difference in electric potential energy per unit charge between two points...
to a gate electrode, dragging the valence band
Valence band
In solids, the valence band is the highest range of electron energies in which electrons are normally present at absolute zero temperature....
of the CNT down in energy, thereby causing electrons to pool in a region in the vicinity of the electrode. Experimentally this is accomplished by laying a CNT on a silicon dioxide
Silicon dioxide
The chemical compound silicon dioxide, also known as silica , is an oxide of silicon with the chemical formula '. It has been known for its hardness since antiquity...
surface, sitting on a doped
Doping (semiconductor)
In semiconductor production, doping intentionally introduces impurities into an extremely pure semiconductor for the purpose of modulating its electrical properties. The impurities are dependent upon the type of semiconductor. Lightly and moderately doped semiconductors are referred to as extrinsic...
silicon wafer. This can be done by chemical vapor deposition
Chemical vapor deposition
Chemical vapor deposition is a chemical process used to produce high-purity, high-performance solid materials. The process is often used in the semiconductor industry to produce thin films. In a typical CVD process, the wafer is exposed to one or more volatile precursors, which react and/or...
using carbon monoxide
Carbon monoxide
Carbon monoxide , also called carbonous oxide, is a colorless, odorless, and tasteless gas that is slightly lighter than air. It is highly toxic to humans and animals in higher quantities, although it is also produced in normal animal metabolism in low quantities, and is thought to have some normal...
. The silicon wafer serves as the gate electrode. Metallic leads can then be laid over the nanotube in order to connect the CNT QD up to an electrical circuit.
Electronic structure
The CNT QD has interesting properties as a result of the strong correlation between the confined electrons. In addition to this the electrons possess orbital angular momentum, as is characteristic of CNT electrons. Spin-orbit coupling has also been shown to be significant in these systems. These properties are often probed by connecting the nanotube to two metallic leads and measuring the conductance of the system.Carbon nanotube quantum dots and many-body systems
The CNT QD connected to metallic leads constitutes a genuine many-body system, due to the electron correlations. Therefore, Wilson's Numerical renormalization groupNumerical renormalization group
The Numerical Renormalization Group is a technique devised by Kenneth Wilson to solve certain many-body problems where quantum impurity physics plays a key role. It is an inherently non-perturbative procedure, which was originally used to solve the Kondo model...
is often used to study the CNT QD. The CNT QD is modelled as an Anderson-type model, which can be reduced by Schrieffer-Wolff transformation to an effective Kondo-type model at low temperature.