engleski

Elastic properties of diamond(oid) wires

Molecular wire is an ultimate molecular electronic device and as such has been attracting considerable attention [1]. Recently a theoretical study has shown [2] an unusually high conductivity of polyyne-based ( ) molecular wire when anchored on Au(111) surface. However, the electronic properties are not the only intriguing properties of one-dimensional carbon-based structures. We undertook a theoretical study of mechanical properties of (quasi) one-dimensional molecular wires built from the sp3-hybridized carbon atoms. The simplest diamondoid wire (DW) is formed by infinite extension of rod-shaped diamondoids having their long axes perpendicular to their diamond (110) lattice planes [3]. According to Balaban and Schleyer notation [4] they form the series [121] (tetramantane), [1212] (pentamantane), ... etc. and [...1212...] would stand for the simplest infinite DW. When looked along its long axis a hexagonal tube is seen and a hexagon may thus be used as its graphical symbol. It is then not difficult to imagine thicker DWs of the same type. The vibrational density of states for practically any finite [12...] system can easily be obtained semi-empirically (AM1) ( calculations with more advanced and time-consuming methods are currently under way ). The normal coordinate analysis reveals the kind of distortions that are described by low-frequency normal modes. It also furnishes the force constants associated with these modes which gives some idea about the rigidity of the diamondoids against the corresponding deformations. The vibrational problem for an infinite DW [...12...] here considered as a polymer chain is solved by employing either empirical potentials or valence force field derived from the DFT calculations of finite systems. The elastic properties of [...12...] microscopically derived from the calculated sound wave velocities are then compared with the analogous properties of carbon nanotubes [5, 6]. [1] Chemical Physics 281 (2002), special issue on processes in molecular wires. [2] Ž. Crljen and G. Baranović (2006) submitted. [3] J.E. Dahl, S.G. Liu and R.M.K. Carlson, Science 299 (2003) 96. [4] A.T. Balaban and P. von Rague Schleyer, Tetrahedron 34 (1978) 3599. [5] G. Overney, W. Zhong and D. Tomanek, Z. Phys. D 27 (1993) 93. [6] V.N. Popov, V.E. van Doren and M. Balkanski, Phys. Rev. B 61 (2000) 3078.

diamond; nanowires

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