A novel way of engineering DNA molecules involves substituting the imino proton of each base pair with a metal ion to obtain M-DNA with altered electronic properties. We report the first direct evidence of metalliclike conduction through 15 microm long M-DNA. In contrast, measurements on B-DNA give evidence of semiconducting behavior with a few hundred meV band gap at room temperature. The drastic change of M-DNA conductivity points to a new degree of freedom in the development of future molecular electronics utilizing DNA, such as creating all-DNA junction devices for use as nanoelectronic building blocks.
Electronic transport measurements were performed on Y-junction carbon nanotubes. These novel junctions contain a large diameter tube branched into smaller ones. Independent measurements using good quality contacts on both individual Y junctions and many in parallel show intrinsic nonlinear transport and reproducible rectifying behavior at room temperature. The results were modeled using classic interface physics for a junction with an abrupt change in band gap due to the change in tube diameter. These Y-junction tubes represent new heterojunctions for nanoelectronics.
A possible mechanism of the laser-field-induced superionic transition in the near-surface region is proposed theoretically in ionic-electronic materials, i.e. , mixed conductors. The laser field does not expose ions immediately but via intermediate interaction with conduction electrons and induces many nonequilibrium defects in the Ag sublattice. These processes cause the decreasing of activation energy of stable Frenkel defects and, consequently, the decreasing of the superionic transition temperature.
I. BV. I. aODUtmIONHegels' law that quantitative changes lead to change of some quality is embodied in the process of modification of crystal properties as the crystal becomes more and more imperfect. Given a small concentration of defects in a solid, it is possible to examine their contribution to its features by means of expansion in a perturbation series of a suSciently small parameter. However, in a crystal with many defects, the disordering of the structure becomes considerable, to the extent that a lot of properties of the constituent particles become liquidlike. A situation where the number of allowable sites is much greater than the number of particles may occur at lower temperatures than the ordinary superionic transition temperature in superionic conductors (SIC's). In SIC's a phase transition of the ionic subsystem to a liquidlike state often follows the melting of one of the ionic sublattices. Frenkel defects randomly occupy the numerous fine local minima of the potential. These minima are closely connected with the diffusion paths of mobile ions. The transition of a crystal into the superionic state takes place due to the stepwise growth in the concentration of Frenkel defects (in a cation-type conductor) stemming from their interaction with each other through the mediation of the lattice distortion' and the direct Coulomb interaction.The role of electrons in the superionic transition is considered to be important. In AgI-family materials their influence is neglected usually, because of the relatively low concentration of conduction electrons in comparison with the concentration of mobile ions (10 cm ), while articles exist where the electron-electron correlations are assumed to be responsible for formation of the superionic state. ' In a mixed SIC, such as the Ag chalcogenides (Ag2S, Ag2Se, AgzTe), the electronic conductivity plays an essential part in the total conductivity of the crystal and the electron-electron and electron-ion interaction effects also are indubitably important.As was discussed by Bondarev and Kuklov, the formation of a superionic state near the surface in an ionic crystal is preferable to inside the crystal, on account of the presence of an electric double layer. In Ref. 5 the possibility of inducing the superionic state was suggested by application of an external static electric field, which leads to decrease in the surface barrier for ionic diffusion.In this paper, we discuss a credible mechanism of inducing a superionic state in the region near the surface of a mixed SIC with...
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