Conjugated Thiol Linker for Enhanced Electrical Conduction of Gold−Molecule Contacts

Abstract

Single-molecule electrical conduction studies are used to evaluate how the molecular linking unit influences the tunneling efficiency in metal-molecule-metal (m-M-m) junctions. This work uses conducting-probe atomic force microscopy (CP-AFM) to compare the molecular conduction of two π-bonded molecules: one with a single thiol linker, and another with a conjugated double thiol linker at both ends of the molecules. The results demonstrate that the molecule with conjugated double thiol linkers displays higher conduction in gold-molecule-gold junctions than nonconjugated single thiol-gold contacts. IntroductionIn recent years, improving the electrical conduction of molecular wires by using conjugated molecules has been a major focus in molecular electronics. However, the conduction of the molecule can become very large, so the metal-moleculemetal (m-M-m) contacts can dominate the response. Recent experimental 1-9 and theoretical [10][11][12][13][14][15] work has demonstrated the importance of metal-molecule contacts to the efficiency of charge transfer through m-M-m junctions. Particularly, for alkanethiol-based junctions, metal-molecule contact resistance decreased up to 2 orders of magnitude when chemically bonded contacts were used instead of nonbonded (mechanical) contacts. 1 Unlike electrical conduction studies on saturated molecules, fewer experimental studies address how the contacts effect conduction through conjugated molecular systems. This work demonstrates that the efficiency of charge transport through π-bonded molecules forming m-M-m junctions with thiol linking units between the metals and the molecule can be improved by using conjugated double thiol linkers at both ends of the molecule. This knowledge should be useful for the design and fabrication of more-efficient electrical and optical devices with potential use in molecular electronics.This work compares electrical conduction measurements for gold-molecule-gold tunnel junctions containing two different types of gold-molecule contacts: single gold-sulfur-Arsulfur-gold and double gold-S 2 C-Ar-CS 2 -gold contacts at both ends of the molecule, where Ar is a biphenyl moiety. The gold-S 2 C-Ar-CS 2 -gold contacts are postulated to provide two points of contact with each gold electrode and better conjugation to the molecule's π-system than the single goldsulfur-Ar-sulfur-gold contact. The junctions are formed using

Orbital Interaction Mechanisms of Conductance Enhancement and Rectification by Dithiocarboxylate Anchoring Group

“…The computed current is four orders of magnitude larger than the experimental one. 15 Our I-V curves qualitatively reproduce the experimental conductance enhancement although theoretically predicted increase in conductivity (∼ 2.1) is larger than the experimentally observed amplification factor (∼ 1.4). 15 The conductance enhancement is clearly shown in the transmission spectra.…”

Probing charge transfer dynamics in self-assembled monolayers by core hole clock approach

“…These moieties were addressed both individually and as a molecular assembly on conductive substrates, bonded over a dedicated anchor group. The most popular experimental strategies included the use of conducting probe atomic force microscopy and scanning tunneling microscopy [5][6][7][8][9][10][11][12][13], break junction techniques [14][15][16][17][18][19], in-wire junctions [18], mercury drop approach [20][21][22][23][24], and liquid metal eutectic Ga-In top contact [25]. A widely used approach is to study a particular series of molecules in a dedicated experiment, varying certain parameters such as the length of molecular chain [4], its conformation [26][27][28][29], character of the anchor group (groups) [13], or the work function of the substrate [7,13].…”

Conductance and application of organic molecule pairs as nanofuses

“…67 For high conductivity, a strong-coupling regime is required. In this case, it has been described that linkers based on nitrogen, [68][69][70][71][72][73][74][75] sulphur, [76][77][78][79][80][81][82] phosphorus, 83 or carbon 84 can be used to carry out measurements of conductivity values.…”