Carbon nanotubes and graphene
Quantum confinement in low dimensional carbon nanostructures
There is much interest in carbon-based electronic systems with reduced dimensionality due to their potential as future electronic devices on the nanometer scale. Transport properties as well as thermal properties of these one and two-dimensional carbon nanostructures are our primary interests.
Carbon nanotubes
Carbon nanotubes (CNT) are cylindrical structures made of carbon with unique mechanical and electronic properties. A CNT can be thought of as a sheet of graphite (a hexagonal lattice of carbon) rolled into a cylinder. These are large mesoscopic molecules with high aspect ratios. They could be as long as millimeters with sub-nanometer diameters. These intriguing nanostructures have sparked a lot of excitement in the last two decades.
The physical properties of carbon nanostructures are still being discovered and debated with interest. What makes it so interesting and difficult at the same time is that nanotubes have a very broad range of electronic, thermal, and structural properties that change depending on the different types of nanotubes. These properties are usually defined by the diameter, length, and chirality during their growth.
Different kinds of carbon nanotubes (CNT) exist. They can be single walled nanotubes (SWNTs) or have a multiple wall structure (cylinders inside a larger cylinder-MWNTs). They could exhibit metallic or semiconducting behavior that is predetermined during the growth process.
We are interested in studying electronic and thermal properties of SWCT in the mesoscopic quantum regime aimed at understanding the nature of quasi-one-dimensional nanostructures, the manifestation of quantum mechanical effects in confined geometries, and the possibilities for their applications in manufactured nano-electronic devices. We are focusing on a design, fabrication and measurement of nano-device architectures made out of SWCNTs for studying fundamental quantum problems in solid state physics and materials and their potential applications.
We currently employ ambient CVD growth techniques in our lab to produce SWCNT on Si substrates for further fabrication of nano-device architectures.
AFM image of SWCNT grown via CVD on Si substrate. Diameter of the tube is 1.4 nm as seen from the cross section (line scan).
Graphene
Graphene - a single atomic
layer of graphite crystal that was believed to be unstable in a “freestanding”
form has been recently produced and measured. This two-dimensional form of
carbon densely packed into the hexagonal benzene-ring structure exhibits high
crystal quality and ballistic transport at room temperature. It is expected to
be stable at very high temperatures up to few thousands degrees Celsius and at
the same time be as hard as diamond similar to a one dimensional carbon wires
(carbon nanotubes).
Graphene is often thought of as rolled out single carbon shell. The graphene 2D system is an exciting playground for researchers because it makes an excellent material for device fabrication due to its planar geometry and perfect crystal structure. Its electronic properties can be tuned and changed by simply applying an external potential. Graphene shows rich quantum mechanical effects. For example, in the presence of a magnetic field, an unconventional Quantum Hall Effect (QHE) that persists even to room temperature at sufficiently high magnetic fields. This contrasts with conventional QHE found only in high quality semiconductor samples like AlGaAs/GaAs heterostructure 2D systems at low temperatures.
We are interested in pursuing number of exciting projects to study this new material in various temperature regimes with the use of conventional transport techniques as well as local scanning probe techniques (SPM) that will allow for local study of its electronic properties.
Optical image of the flake produced by mechnical exfoliation techique on Si/SO2 substrate with thickness of the thermal oxide being roughly 300 nm. Size of the flake to the left of the mark LE is approximately 4 x 18 micron.
