Quantum wires, one-dimensional

Superlattice and low-dimensional physics are some of the most interesting subjects in solid-state physics. A challenging problem in this field is the formation of quantum wire and quantum box structures by using ultra-high technology such as MBE, MOCVD (metallorganic chemical vapor deposition), and related frontier microprocessing. However, this problem has not yet been solved. Poly silane is probably a perfect quantum wire in itself The absorption spectrum of polysilane clearly shows the characteristics of a one-dimensional quantum wire. Even a quantum box or a one-dimensional superlattice can be formed by chemical polymerization, which may be the simplest way. 

Campos V. B., das Sarma S. and Stroscio M. A. (1992), Phonon-confinement effect on electron energy loss in one-dimensional quantum wires , Phys. Rev. B 46, 3849-3853. 

In the previous sections we have considered the hybridization of Frenkel and Wannier-Mott excitons in two-dimensional (quantum wells) and one-dimensional (quantum wires) geometries. For the sake of completeness, in this subsection we shall briefly and qualitatively discuss the zero-dimensional (0D) case that corresponds to a quantum dot geometry. We have in mind a configuration where a semiconductor QD is located near a small size organic cluster or is just covered by a thin shell of an organic material. 

In principle, the low-dimensional semiconductors are divided into the two-dimensional quantum wells and superlattices, the one-dimensional quantum wires, and the zero-dimensional quantum dots. In the following, we list the most common fabrication methods for each of these systems. 

First experiments and calculations revealed the electronic properties of carbon nanotubes to be in parts rather extraordinary. The small diameter, for instance, causes the occurrence of quantum effects. The tubes behave like a quasi-one-dimensional molecular wire, which is very useful for some electronic apphcations. However, the electronic properties of nanotubes are also related to those of the two-dimensional graphene as the first formally result from the roUing up of the latter. Changes and unexpected phenomena then arise, for example, from the curvature of the graphene lattice. 

More fundamentally, in the ballistic phonon regime at low enough temperatures, one-dimensional (ID) wires should manifest the quantization of the thermal conductance for the lowest energy modes [3,4]. Here K = JIAT is the thermal conductance with AT as the temperature difference. The fundamental quantum of thermal conductance is V klTI3h where is the Boltzmann constant, h is Planck s constant, and T is the temperature. This value is universal, independent not only of the conducting material, but also of the particle statistics, i.e., the quantum conductance is the same for bosons and fermions [3]. 

Nanometer sized semiconductor dusters, expected to have properties different from those of molecular and bulk semiconductors of the same composition, represent a new class of materials. Interest in their preparation and potential applications as photocatalysts and device components used in quantum electronics and nonlinear optics is growing rapidly. Isolated, so-called nanophase semiconductors can be considered as zero and one dimensional quantum dots and quantum wires. Their electronic, optical, and photochemical properties change with cluster size. Wider electronic band gaps and new absorption maxima in the electronic spectra have been observed as the size of these materials decreases and have been interpreted as quantum size effects. For example, as the dimensions of the semiconductor particle are reduced, a shift to higher energy in the absorption spectrum relative to that of the bulk is generally observed. 

In conclusion, wc have shown the interesting information which one can get from electrical resistivity measurements on SWCNT and MWCNT and the exciting applications which can be derived. MWCNTs behave as an ultimate carbon fibre revealing specific 2D quantum transport features at low temperatures weak localisation and universal conductance fluctuations. SWCNTs behave as pure quantum wires which, if limited in length, reduce to quantum dots. Thus, each type of CNT has its own features which are strongly dependent on the dimensionality of the electronic gas. We have also briefly discussed the very recent experimental results obtained on the thermopower of SWCNT bundles and the effect of intercalation on the electrical resistivity of these systems. 

The methodology used to answer these questions can be classified as either semi-empirical or based on first principles. The confined structure is assumed to be two-dimensional (2D = quantum well), one-dimensional (lD = quantum wire) or zero-dimensional (0D = quantum dot). 

Figure 1 2 6. The Fermi surface of the second (red) and third subband (black) of a 2D superlattice of quantum wires near the type (III) ETT where the third suhhand changes from the one-dimensional (left panel) to two-dimensional (right panel) topology. Going from the left panel to the right panel the chemical potential EF crosses a vHs singularity at Ec associated with the change of the Fermi topology going from EF>EC to EF

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