Conformation-dependent conductance through a molecular break junction

Abstract

Ab initio molecular dynamics simulations have been performed of a gold-1,4-benzenedithiol (BDT)-gold nanojunction under mechanical stress. For three different pulling rates between 10 and 40 m s(-1), it is found that the nanowire always ruptures between the second and third Au atom from the thiol sulfur. Larger rupture forces and longer extensions are required at higher pulling rates and vice versa. The electrical conductance was calculated along a pulling trajectory using the DFT-NEGF method to study the effect of thermal and stress-induced structural changes on the electrical transport properties. While the mechanically induced stretching of the junction is seen to lower the time-averaged conductance, thermal conformational changes are capable of altering the conductance by one order of magnitude. No single geometric quantity could be identified as the main contributor to the conductance fluctuations. Small modulations, however, can be explained in terms of C=C double bond vibrations in the BDT molecule. The dependence of the conductance on different geometric variables has further been investigated systematically by performing constrained geometry optimizations along a number of angle and dihedral coordinates. The largest changes in the conductance are observed when the Au-S-C angle and the Au-S-C-C dihedral are simultaneously constrained.

Nanomechanics of Bidentate Thiolate Ligands on Gold Surfaces

“…The pronounced inter est in these particular hybrid molecule-metal junctions and interfaces is due to a multitude of potential applications such as tailoring the properties of surfaces [3][4][5][6][7], chemical anchors for molecular electronics applications [8][9][10], or coating agents for the stabilization of gold nanoparticles [11,12]. Only lately, it has been realized that the consid eration of the mechanical properties of these moleculemetal hybrids becomes a crucial design factor [13][14][15][16][17][18][19][20][21][22][23][24] for nanoscale devices.…”

Unexpected Magnetic Properties of Gas-Stabilized Platinum Nanostructures in the Tunneling Regime

“…Manipulation of the contact structure could also result in changes of conductance, Kondo effect and magnetic ordering. [15][16][17] Here, we study atomic contacts of Pt fabricated using the break junction technique. 18,19 Pt films for break junctions were deposited using e-beam evaporation from targets containing less than 1 ppm magnetic impurities.…”

“…Furthermore, the possibility of a spin structure where the strength and time scale of the magnetic interactions are controlled at the atomic scale via electromagnetic fields could be the electronic equivalent to optical devices in quantum computing. Manipulation of the contact structure could also result in changes of conductance, Kondo effect, and magnetic ordering. − …”

High thermopower of mechanically stretched single-molecule junctions

“…The geometrical dependence of thermoelectricity in Au-BDT-Au junctions is inferred in the Δ V – t profiles. TR and TD tendencies clearly suggest accompanying roles of the mechanical stretching along specific directions, which results in molecular tilting toward an upright conformation and elongation of the Au-S bond lengths of BDT in a Au-hollow or -top geometry, to weaken the electrode-molecule electronic coupling that leads to steady decrease in G and meanwhile inducing gradual shift of HOMO toward or away from E F , respectively 33 34 35 36 . On the other hand, the rapid increase in both G and Δ V of RI indicates a drastic change in the Fermi alignment: E gap lowered for more than 0.5 eV and Γ L,R decreased by up to 0.05 eV.…”