Electrical properties and mechanical stability of anchoring groups for single-molecule electronics

Abstract

SummaryWe report on an experimental investigation of transport through single molecules, trapped between two gold nano-electrodes fabricated with the mechanically controlled break junction (MCBJ) technique. The four molecules studied share the same core structure, namely oligo(phenylene ethynylene) (OPE3), while having different aurophilic anchoring groups: thiol (SAc), methyl sulfide (SMe), pyridyl (Py) and amine (NH2). The focus of this paper is on the combined characterization of the electrical and mechanical properties determined by the anchoring groups. From conductance histograms we find that thiol anchored molecules provide the highest conductance; a single-level model fit to current–voltage characteristics suggests that SAc groups exhibit a higher electronic coupling to the electrodes, together with better level alignment than the other three groups. An analysis of the mechanical stability, recording the lifetime in a self-breaking method, shows that Py and SAc yield the most stable junctions while SMe form short-lived junctions. Density functional theory combined with non-equlibrium Green’s function calculations help in elucidating the experimental findings.

Transition from Strong to Weak Electronic Coupling in a Single-Molecule Junction

“…The top panel of Fig. 4(a) shows that the average level alignment is around 0.6-0.9 eV, consistent with values previously found at room temperature [20,21]. For the CB I-V's we extract ϵ 0 directly from the position of the step or linear onset in the current (ϵ 0 ¼ eV gap =4).…”

“…4(b) shows the histogram of the total electronic coupling of junction 2 in the strong coupling regime extracted from the single-level model fit of the I-V's. The average electronic coupling is about 10 meV, again consistent with previous room temperature measurements [20,21]. In the case of the CB I-V's we extract the electronic coupling from the formula I sat ¼ ðG 0 =eÞπΓ, where I sat is the saturation current at a bias beyond the resonance (eV ≫ 2ϵ 0 þ Γ) [3]; the histogram in the bottom panel of Fig.…”

“…The histograms show a clear conductance peak indicating the formation of molecular junctions. We find that the average conductance of OPE3 at room temperature, defined as the maximum of the peak, is G ¼ 1.5 × 10 −4 G 0 , comparable to the value found in previous studies [16][17][18][19][20][21]37], and that the peak width corresponds to 1 order of magnitude. The conductance histogram, built from low temperature measurements, shows a similar average conductance value and peak width.…”

“…We study oligo(phenyleneethynilene) (OPE3) molecules [13][14][15][16][17][18][19][20][21] terminated with acetyl-protected thiol anchoring groups for Au nanoelectrodes [22][23][24]. We perform low-bias conductance measurements of the OPE3 molecules at room (T ∼ 300 K) and at cryogenic temperatures (T ∼ 10 K).…”

Study on Semiconductor Properties of Acetylide-Thiourea Fabricated onto Interdigitated Electrodes (Ides) Platform Towards Application In Gas Sensing Technology

“…3 various chemical substitutions can lead to various electrical functions which can open up new possibilities in electronic devices that have never been offered [6]. Electron hoping within single molecular junction is determined by charge instillation barriers at the electrodemolecule surface [7], which in turn characterised by the energy configuration between the electrode Fermi level and a single discrete energy level of molecules, known to be either the highest occupied molecular orbital (HOMO) or the lowest unoccupied molecular orbital (LUMO) levels [8]. Thus, noteworthy efforts have been given to attain modulation of the HOMO-LUMO molecules with external stimulus such as electric field, light, and mechanical forces, for understanding and controlling the unique electrical characteristics of single-molecule junctions [9].…”