Conductance quantum

In the presence of specifically adsorbed ions, e.g., for halides at potentials E > Epzc, the trend changes and the position of the 1 G0 peaks shifts to higher values than the quantum conductance unit. The up-shifts follow the order of adsorption strength, Cl- < Br < I-. 

The conductance of MWCNTs is quantized. The experimental setup to measure the conducting properties involved the replacement of an STM tip with a nanotube fiber that was lowered into a liquid metal to establish the electrical contact. The conductance value observed corresponded to one unit of quantum conductance (Go = 2e /h = 12.9 kQ ). This value may reflect the conductance of the external tube because, for energetic reasons, the different layers are electrically insulated [150]. Finally, the conductance of semiconductor nanotubes depends on the voltage applied to the gate electrode their band gap is a function of their diameter and helicity [145] and the ON/OFF ratio of the transistors fabricated with semiconductor nanotubes is typically 10 at room temperature and can be as high as 10 at... 

Within the Landauer approach, the computation of the quantum conductance is thus traced back to the knowledge of the electronic structure—i.e., the Hamiltonian—of the target system molecule+leads . The best-developed implementations of the Landauer framework employ tight-binding Hamilto-... 

The zero-bias conduction in this case is given by the quantum conductance unit / nh). 

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]. 

Fig. 11.8 Magic numbers for Ag nanowires for the thinning process (changes in cross section) and the fractional quantum conductance (Reproduced from Ref. [27] with kind permission of The American Physical Society)...

The structural symmetry of CNTs leads to quantization of states such that the electric conduction takes places through two electronic modes. Electronic conductivity measurements of individual SWCNTs as well as MWCNTs confirm their quantum conductance [172,173]. The conductivity of individual CNTs can be tailored by application of external voltage. This leads to a controllable metallic-semiconductor transition of CNTs by varying the applied voltage [174]. This is similar to the operating principal of field-effect transistor (FET), where the applied gate voltage controls the channel... 

Product brochures, Hysol and Quantum Conductive Adhesives, Leadframe Die Attach, Dexter Electronic Materials, Industry, Calif, www.dexelec.com. May 2001. 

Sanvito S, Kwon Y K, Tomanek D and Lambert C L (2000) Fractional quantum conductance in carbon nanotubes, Phys Rev Lett 84 1974-1977. 

Xie, X.F., Yan, J.W., Liang, J.H. et al. (2013) Measurement of the quantum conductance of germanium by an electrochemical scanning tunneling microscope break junction based on a jump-to-contact mechanism. Chemistry - An Asian Journal, 8, 2401-2406. 

Curvature effects are shown to distinguish carbon nsuiotubes from graphitic carbon in qualitative ways. In particular, bonding geometries and magnetic moments are found to be sensitively dependent on curvature. Furthermore, our work also reveals that use of full orbital basis set is necessary for realistic calculations of quantum conductance of carbon nwotubes. 

In this section we describe a state-of-the-art formalism to efficiently calculate the quantum conductivity of SWCNs and present results using this formalism and compare them with available experiments. We also show that inclusion of full basis set enables structural relaxation and quantum conductivity calculations using the same Hamiltonian, providing a consistent approach for the treatment of SWCNs. 

Andriotis, A. N., Menon, M. (2001). Greens function embedding approach to quantum conductivity of single wall carbon nanotubes. Journal of Chemical Physics, 115, 2737. 

Using bosonization procedures and real-time path integral techniques, the quantum conductance of a rigid (i.e., no lattice distortion) ID quantum wire has been computed. Analytical theories predict that, in the presence of even a single defect, the conductance of a strictly ID quantum wire would vanish at 0 K. Bosonization of this system yields an equivalent spin-boson model with an infinite number of tight-binding states, which turns out to be the same model as for CTCs discussed in... 

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