Revealing the Role of Anchoring Groups in the Electrical Conduction Through Single‐Molecule Junctions

Abstract

A combined experimental and theoretical study is presented revealing the influence of metal-molecule coupling on electronic transport through single-molecule junctions. Transport experiments through tolane molecules attached to gold electrodes via thiol, nitro, and cyano anchoring groups are performed. By fitting the experimental current-voltage characteristics to a single-level tunneling model, we extract both the position of the molecular orbital closest to the Fermi energy and the strength of the metal-molecule coupling. The values found for these parameters are rationalized with the help of density-functional-theory-based transport calculations. In particular, these calculations show that the anchoring groups determine the junction conductance by controlling not only the strength of the coupling to the metal but also the position of the relevant molecular energy levels.

A Molecular Platinum Cluster Junction: A Single-Molecule Switch

“…In the case of C 18 , the energy alignment seems to be considerably affected by the binding geometry. In the hollow geometry, the HOMO-1 (which is delocalized throughout the whole chain and gives the main contribution to the transmission 20 ) is shifted down in energy compared to the top position (as has also been observed for other thiolated molecules 31 ), yielding a difference in the conductance of one order of magnitude between the two geometries. Notice also the presence of the HOMO (localized on the S atoms) very close to the Fermi level, clearly visible as a bump in the transmission curve for the top geometry.…”

Light‐Induced Switching of Tunable Single‐Molecule Junctions

“…For the characterization of the conducting molecular states the level broadening Γ of the conductance channel and the molecular level E 0 were plotted against the transmission T in semi‐logarithmic histograms 2. All data were normalized to achieve better comparability.…”

Characterizing the Metal–SAM Interface in Tunneling Junctions

“…[6][7][8][9][10][11][12][13][14][15][16][17][18] Recent studies of singlemolecule break junctions have been interpreted to indicate that the presence of covalent Au−C σ-bonds-formed using trimethyltin (-SnMe 3 )-terminated n-alkyl groups, 19,20 and SnMe 3 -terminated aromatics [19][20][21] or trimethylsilyl (TMS)-terminated conjugated systems 22 -increases rates of charge transport across these junctions by approximately a factor of 10-100, relative to amine or thiolate anchoring groups. One possible inference from the increase is that the Au−C σ-bond, and the absence of resistive anchoring heteroatoms, increases "conductivity" (although the meaning of this word is not entirely clear for tunneling junctions).…”