The Department of Theoretical Physics has multidisciplinary character and specializes in a wide range of physics problems such as condensed matter physics, stochastic processes like turbulence, particle and space physics, as well as the definition of electronic properties of nanostructures. It uses various methods for tackling the given tasks. The following part of this short Departmental presentation focuses on the theme of carbon nanostructures.
Carbon compounds are one of the most studied nanomaterials today. These structures have unique properties within solid substances. The geometric structure of these compounds strongly influences their physical properties. These may also be affected by electromagnetic fields. Carbon nanotubes and fullerenes are among the most interesting and popular nanostructures. Carbon nanotubes were first isolated and described by Ijima in 1991 and fullerene C60 was first discovered as early as 1985. This discovery was awarded the Nobel Prize. The diameter of carbon nanotubes is expressed in nanometres, whereas their length can reach up to several micrometres and they are 100 times stronger than steel. Depending on their diameter they may have the properties of metals or semiconductors without the requirement for additional doping. The width of the forbidden band gap of semiconductor nanotubes depends on their diameter and chirality. One can imagine the smallest semiconductor devices being constructed from carbon nanomaterials. Some other carbon compound structures such as cones and fullerenes made of the graphene honeycomb lattice also have similar properties. To obtain such structures it is necessary to create one or several topological defects (e.g. pentagons or heptagons) in the hexagonal lattice of graphene, or deform it for example by rolling the lattice (see picture 1).
Topological defects evoke changes in the geometry of carbon materials that may exhibit strong effect on their electronic properties. Twelve pentagons in the graphene lattice together with 20 hexagons form the fullerene C60 molecule. Fullerenes have interesting properties that could be used in various areas of nanoindustry. Fullerene C60 can be grouped to ferromagnetic materials such as iron or cobalt, or iron-cobalt alloy, that can make thin films with the required magnetic properties. Some fullerene compounds show superconductive characteristics. Interesting properties are also found in nanotubes and fullerenes (see picture 2), in which the outer layer is charged positively and inner layer negatively as a result of different Fermi levels in separate nanostructures, and also of interactions between individual layers.
In the future carbon nanoparticles may be helpful in the development of technologies utilizing solar energy, as well as in microelectronics and nanomedicine. Our group from the Department of Theoretical Physics has been participating actively in research into the electronic properties of carbon nanostructures, as attested by our publications in renowned international journals and our winning the award for the best theoretical result in 2007 at the Joint Institute for Nuclear Research in Dubna, Moscow Region. Our Department has collaborated with this Research Institute for many years.
Picture 2 – A
Picture 2 – B