Three-Terminal Junctions of Carbon Nanotubes: Synthesis,Structures, Properties and Applications

We summarize recent studies on the fabrication methods, structures and properties of three-terminal junctions of carbon nanotubes (NTs). Then, we present topological classifications of planar Y- and T-junctions of single-walled NTs. Finally, we discuss possible applications of these junctions.     

Electronic structure of carbon nanotubes modified by alkali metal atoms

The electronic structure and parameters of the energy band structure of (n, 0)-type nanotubes modified by alkali metal atoms (Li, Na) and intercalated by potassium atoms are studied. The quantum-chemical semiempirical MNDO method and a model of the covalent cyclic cluster built in via ionic bonding are used to model infinitely long nanotubes. The electronic density of states of modified nanotubes is found. It is shown that semiconductor-metal transitions can occur in semiconductor nanotubes and that semimetal nanotubes can undergo metal-metal transitions.     

Basic configuration of a single-wall carbon nanotube <Emphasis Type="Italic">Y</Emphasis> junction of <Emphasis Type="Italic">D</Emphasis><Subscript>3<Emphasis Type="Italic">h</Emphasis></Subscript> symmetry: Structure and classification

The structure of single-wall carbon nanotube Y junctions of symmetry D_3h containing topological defects in the form of six heptagons or three octagons located immediately in the junction region of each pair of nanotubes forming the Y junctions is investigated, and their classification is suggested. It is shown that the pairs of heptagons in a Y junction formed by nanotubes of the “zigzag” type can be arranged in two ways and can be transformed into one another by using the (6, 7, 7, 6) ? (7, 6, 7, 6) Stone-Wales transformation and that the octagon and pairs of heptagons in a Y junction formed by nanotubes of the “armchair” type can be transformed into one another by introducing or removing a C₂ cluster. A method for constructing such Y junctions is suggested.     

A new class of MO<Subscript>2</Subscript> dioxide nanotubes (M=Si,Ge, Sn,Pb) composed of “square” lattices of atoms: Their structure and energy characteristics

New dioxide nanotubes are described. These nanotubes are rolled up of a “square” lattice of atoms differing from the conventional hexagonal lattice isoelectronic to graphite. The dependence of the strain energy on the nanotube diameter D departs from a 1/D² behavior, and the optimum shape at the same diameter corresponds to “zigzag” tubelenes. Two-layer nanotubes consisting of an MO₂ layer bonded to a carbon nanotube (CNT) are characterized by a considerably lower strain energy, which points to the possibility of using CNTs as a template for the synthesis of such MO₂ nanotubes.     

Rectification properties of carbon nanotube "Y-junctions"

Quantum conductivity of single-wall carbon nanotube Y-junctions is calculated. The current versus voltage characteristics of these junctions show asymmetry and rectification, in agreement with recent experimental results. Furthermore, rectification is found to be independent of the angle between the branches of these junctions, indicating this to be an intrinsic property of symmetric Y-junctions. The implications for the Y-junction to function as a nanoscale molecular electronic switch are investigated.     

Bigraphene nanomeshes: Structure,properties, and formation

New carbon structures of nanomeshes have been considered, which are formed from bilayer graphene by cutting hexagonal holes in it. Edges of these holes by joining chemically active atoms, transforming into folds of graphene, form a closed structure of sp ₂ hybridized C atoms. The structure and electron properties of several typical nanomeshes, which are superlattices made of joined nanotube and bigraphene fragments, have been studied. Their stability and essential difference of the electronic band structure from those of their analogs-monolayer graphene nanomeshes—have been demonstrated.     

Erratum to: Several Articles in JETP Letters

JETP Letters - An Erratum to this paper has been published: https://doi.org/10.1134/S002136402234001X     

Features of 30° Moiré Graphene Bilayers with Folded Holes

New nanomeshes with closed holes based on bilayer graphene twisted by 30° are studied. It is found that such structures can have different electronic characteristics (from semiconducting to metallic) depending on the shape of holes. Comparison with the single-layer graphene meshes having holes of similar shapes demonstrates a significant difference of their electronic spectra. The meshes with triangular “folded” holes turn out to be nonmagnetic in contrast to the single-layer meshes with the same holes. The spectra of 30° bilayer graphene nanomeshes exhibit numerous peaks in the electron density of states within a wide energy range. This makes such structures promising for applications in photovoltaics and optoelectronics. Features of 30° Moiré Graphene Bilayers with Folded Holes.