First principles calculations of mechanical propierties of 4,4-´bipyridine attached to Au monoatomic nanowires

P. VÉLEZ; S. A. DASSIE; E. P. LEIVA

Busan, Korea

Congreso; 56th ANNUAL MEETING OF THE INTERNACIONAL SOCIETY ELECTROCHEMISTRY: “Electrochemistry for the Next Generation”; 2005

The electromechanical properties of single molecules have been recently the subject of novel research[1-3]. Among these publications, it is worth mentioning the work of Xu  et al[2], who measured the conductance and the spring constant of a single molecule bonded to two electrodes and the dependence of the conductance on the applied force. These authors performed electromechanical measurements of 1,8-octanedithiol, and 4,4’- bipyridine covalently attached to two electrodes during mechanical stretching. Conductance and force histograms were constructed from a large number of experimental curves. The force histograms revealed pronounced peaks with a force quantum characteristic of 0.8±0.2 nN  for 4,4’- bipyridine, which was assigned to the Au-N bond. While in the case of the thiol the breaking of the Au-Au bond is expected on the basis of the Au-S bond strength, this is not so clear in the case of the Au-N  interaction. On the other hand, the measured values of conductance show discrete steps, that correlated with the sawtooth behavior found in the force. While abundant work can be found in the literature for the calculation of conductance for systems involving nanowires[3], this is not the case for the forces. In the present work we present density functional calculations for the forces occurring in nanowires consisting of a bipyridine molecule located between two pieces of monoatomic gold nanowires. The geometry of the system was optimized for different forces applied. In all cases the calculated   maximum forces were close to 1 nN, which if of the order of the experimental value, and smaller than that corresponding to the rupture of the Au-Au chain (1.5-1.6 nN). However, the present calculations show that when the 4,4’-bypiridine is attached to the wire, the maximum force required to break the Au-Au bond may be lowered to values close to that obtained to break the N-Au bond.     References [1] X. Xiao, B. Xu, and N. Tao,, Nano Letters 4 (2004)267. [2]B. Xu, X. Xiao and N. Tao, J. Am. Chem.. Soc. 125(2003)16164. [3]S. Hou, J. Zhang, R. Li, J. Ning, R. Han, Z. Shen, X. Zhao, Z. Xue and Q. Wu, Nanotechnology, 16(2005)239.