Precursor configurations and post-rupture evolution of Ag–CO–Ag single-molecule junctions

Abstract

ut. 8., Hungary Experimental correlation analysis and first-principles theory are used to probe the structure and evolution of Ag-CO-Ag single-molecule junctions, both before the formation, and after the rupture of the junctions. Two dimensional correlation histograms and conditional histograms demonstrate that prior to the single-molecule bridge configuration the CO molecule is already bound parallel to the Ag single-atom contact. This molecular precursor configuration is accompanied by the opening of additional conductance channels compared to the single-channel transport in pure Ag monoatomic junctions. To investigate the post-rupture evolution of the junction we introduce a cross-correlation analysis between the opening and the subsequent closing conductance traces. This analysis implies that the molecule is bound rigidly to the apex of one electrode, and so the same single-molecule configuration is re-established as the junction is closed. The experimental results are confirmed by ab initio simulations of the evolution of contact geometries, transmission eigenvalues and scattering wavefunctions.

Alternative types of molecule-decorated atomic chains in Au–CO–Au single-molecule junctions

“…All these imply that Au–CO–Au single-molecule junctions are usually not preceded by clean Au monoatomic contacts or atomic chains. There is rather a so-called precursor configuration with higher conductance (A2 region), similarly to our previous report on Ag–CO junctions [ 27 ]. We interpret these precursor configurations by the binding of a CO molecule to the side of a single-atom contact, which opens additional conductance channel(s) compared to the single-channel transport in pure Au monoatomic contacts and atomic chains.…”

“…We note here, that the selected data sets obtained by this technique are not distinct, because the length of a given trace can be longer than the average in more regions (positive correlation). More details on the method can be found in [ 19 , 26 – 27 ].…”

“…To identify them we carry out a statistical analysis going far beyond the simple conductance histogram approach. By combining conditional conductance histograms, two-dimensional correlation histograms (2DCH) [ 25 – 27 ] and two dimensional conductance–displacement histograms (2DCDH) [ 19 , 21 – 22 ] we are able to narrow down the possible configurations formed during the process of breaking. The comparison of our results with calculations of [ 29 – 31 ] implies that the CO molecule can be either incorporated to gold atomic chains (bridge geometry), or can bind next to the chain (atop geometry).…”

Transition from Tunneling Leakage Current to Molecular Tunneling in Single-Molecule Junctions

“…Conductance-Distance Measurement of Single-Molecule OAE2 Junctions Typical conductance-distance curves of the OAE2 molecule from MCBJ experiments in solution 24,34,35 are shown in Figure 2A (see Figure 1B and Experimental Procedures for details). Both opening and closing curves [36][37][38] display clear plateaus at around 10 À3 G 0 (where G 0 is the conductance quantum, which equals 2e 2 /h). A sudden conductance drop to the molecular plateau followed by discrete G 0 steps was observed in the opening process (blue curves in Figure 2A), which suggests the pulling of a gold atomic contact and formation of an initial nanogap from the inevitable snap-back after final rupture of the gold-gold atomic chain.…”

Universal 1/f type current noise of Ag filaments in redox-based memristive nanojunctions

“…(i) STM based Ag/AgI/PtIr resistive switching nanojunctions 57,58 were created in the same manner as the sibling Ag/Ag 2 S/PtIr structures. The photosensitive AgI thin films were formed directly before the measurements on identical substrate structures by exposing the latter to iodine vapor at 40°C and ambient pressure for 30 seconds in a dark chamber following the method of Kumar et al 59 Noise measurements were also carried out on atomic scale Ag nanojunctions lacking any resistive switching media by utilizing either (ii) notched Ag wires and the mechanically controllable break-junction (MCBJ) technique 60 or (iii) lithographically designed Ag nanobridges and current controlled electromigration. 61 The initial structure of the latter method consisted of two-terminal Ag constrictions of 100 nm width, 400-1000 nm length and 40 nm thickness evaporated onto standard, nonswitching SiN x substrates.…”