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Sökning: LAR1:uu > Ahuja Rajeev > Övrigt vetenskapligt

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  • Löfås, Henrik, et al. (författare)
  • Computational Study of the Chaotic Behavior in Single-molecule Conduction
  • 2013
  • Ingår i: 2013 MRS Spring Meeting : Electrical Contacts to Nanomaterials and Nanodevices.
  • Konferensbidrag (övrigt vetenskapligt)abstract
    • Recently we have seen great advances in synthesis and fabrication of nanostructures. However, there is still no consensus on the conductance of small organic molecules, where different values of the conductance are often attributed to differences in metal-molecule interface structure or different molecular conformations[1,2]. Control and characterization of the metal-molecule interface during formation of the junction is in practice an impossible task. To get insight into this highly dynamic process, computer simulations are needed; here we are going to show a combination of ab-initio molecular dynamics (MD)-simulations and conductance calculations to address this problem.The conductance of a junction is mainly determined by the relative position of the energy level closest to the Fermi level of the electrodes and by the coupling of the corresponding electronic state to the electrodes[2]. These parameters are greatly influenced by the nature of the interaction and/or chemical bond between electrodes and the molecule. Information about the nature of this interaction and its variation with different binding sites can be extracted from the conduction spectra. Here we are using MD-simulations to get an unbiased set of geometries, thus mimicking the randomness of a real junction under thermal fluctuations. From the obtained geometries the zero-bias conductance is calculated and used for histograms to investigate the statistics of the junction.The obtained histograms for the thiol-bonded molecules are fitted with probability distributions for different Gaussian ensembles and we show that the interaction between the electrode and the molecule gives rise to quantum chaos in the junction. The effect of quantum chaos have earlier been found experimentally for quantum dots[3] and nanowires[4]. By removing the symmetry in the junction the chaotic behavior can be increased. We also compare the thiol anchoring groups with amines and we can see that the weaker coupling to the gold for the amines increases the conductance fluctuations in the junctions by one to two orders of magnitude. By tuning the ratio of the coupling between the electrodes and the molecular state we show, that the junction can be switched from a chaotic behavior to a case with a normal distributed conductance spectrum where only temperature fluctuations are present.[1] S. L. Bernasek, Angew. Chem. Int. Ed. 51, 9737 (2012).[2] A. Nitzan and M. A. Ratner, Science 300, 1384 (2003).[3] L. A. Ponomarenko, F. Schedin, M. I. Katsnelson, R. Yang, E. W. Hill, K. S. Novoselov, and A. K. Geim, Science 320, 356 (2008).[4] J. L. Costa-Krämer, N. García, P. García-Mochales, P. A. Serena, M. I. Marqués, and A. Correia, Phys. Rev. B 55, 5416 (1997).
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  • Scheicher, Ralph H., et al. (författare)
  • DNA sequencing with nanopores from an ab initio perspective
  • 2012
  • Ingår i: Journal of Materials Science. - 0022-2461. ; 47:21, s. 7439-7446
  • Forskningsöversikt (övrigt vetenskapligt)abstract
    • Advances in materials research means that we find ourselves at the verge of constructing nano-scale devices capable of electrically addressing individual molecules in order to identify or utilize their electrical or electromechanical properties. An important application in life sciences would be electromechanical translocation of a DNA molecule through a nanopore, between nano-scale electrodes, allowing to electrically read out the base sequence (genome). This approach promises to drastically lower the cost per genome, allowing for extensive application in medical diagnostics. Owing to the involved extremely small dimensions which require nanometer-resolution in the fabrication, atomistic modeling plays a crucial role in testing hypothetical device architectures for their performance in nucleobase distinction. First-principles simulations are ideally suited to explore the interactions involved in such scenarios and lay the foundation for electronic transport calculations. This role of computations is even more important here, since it is experimentally not possible to observe directly the kinetics occurring during translocation of a DNA molecule through a nanopore. Here, we provide a brief review of the state of the field, focusing on ab initio studies of nanopore-based DNA sequencing, in particular on the promising recent development regarding graphene nanopores and nanogaps.
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