Substituent Effect on the Mechanical Properties of Au−N Nanojunctions

Abstract

We report on the calculated binding energies and rupture forces of a series of ortho-substituted pyrazines bonded to gold nanoclusters. This system is proposed as a model for the 4,4-bipyridine-gold nanojunction to assess the effect of the substituent on the mechanical stability and the rupture modes of such nanojunction. The present results show that although there is a definite trend to a reduced rupture force for a more electron withdrawing substituent on the pyrazine molecule, this dependence is small, allowing for the construction of nanojunctions with different transport properties but similar mechanical stabilities. A clear-cut correlation is found between the rupture force of the nanojunction and the pK a value of the structurally related pyridines, providing with a simple empirical way of predicting the stability of the system. The possibility of attaching the molecule to the cluster through a monatomic gold chain is also explored, with the finding that the Au-Au rupture at the chain is a possible mechanism when the chain is at least two atoms long.

Quantitative Evaluation of Metal−Molecule Contact Stability at the Single-Molecule Level

“…Furthermore, back calculations of E B from eq with F = 0 N yield E B ∼ 0.69 and 0.71 eV for BDA and ABT junctions, respectively. Here, it should be pointed out that this E B of BDA is in excellent accordance with the theoretical bond strength recently reported. , These values are about 0.3 eV lower than that obtained for BDT junctions, reflecting the relatively weak Au−NH 2 coordinate bonds . As a consequence, it is concluded that Au−NH 2 contacts provide relatively lower thermal stability that brings about 5 orders of magnitude difference in the room temperature stability when employed in metal−molecule−metal junctions compared to Au−S contacts.…”

Role of metal contacts in the mechanical properties of molecular nanojunctions: Comparativeab initiostudy of Au/1,8-octanedithiol and Au/4,4-bipyridine

“…This feature, combined with the high vertical fragmentation energy of the Au 2 -Au 3 ͑2.43 eV͒ and Au 4 -Au 5 ͑1.90 eV͒ bonds, suggests the existence of conjugation in the bonds of the monatomic Au chain for the 4 , 4Ј BPD nanojunction. Similar results in terms of bond distances, vertical fragmentation energies and bond order have been reported by our research group 43 for the mechanical stretching of a pyrazine molecule attached to a small Au cluster via a planar monatomic chain of 3, 4, or 5 Au atoms.…”

“…7,33 Something similar can be stated on other equivalent Au-N systems, as it is the case of the nanojunction involving the pyrazine molecule 7,43 and ortho substituted pyrazines molecules. 43,44 In this paper, we will study comparatively from first principles calculations, the 1,8-octanedithiol and 4 , 4Ј-bipyridine molecular nanojunctions involving Au electrodes. The analysis will focus on the stability of such systems when subjected to mechanical stretching.…”

Anchoring sites to the STM tip can explain multiple peaks in single molecule conductance histograms

“…The potential use of single molecules as components of electronic devices has promoted a profusion of experimental [1][2][3][4][5][6][7][8][9][10] and theoretical [11][12][13][14][15][16][17] work. Besides the obvious advantages in miniaturization of such devices, the chemical versatility of molecules allows the exploration of new device design methods based on controlling the function through chemical tailoring.…”