Role of solvents in the electronic transport properties of single-molecule junctions

Abstract

SummaryWe report on an experimental study of the charge transport through tunnel gaps formed by adjustable gold electrodes immersed into different solvents that are commonly used in the field of molecular electronics (ethanol, toluene, mesitylene, 1,2,4-trichlorobenzene, isopropanol, toluene/tetrahydrofuran mixtures) for the study of single-molecule contacts of functional molecules. We present measurements of the conductance as a function of gap width, conductance histograms as well as current–voltage characteristics of narrow gaps and discuss them in terms of the Simmons model, which is the standard model for describing transport via tunnel barriers, and the resonant single-level model, often applied to single-molecule junctions. One of our conclusions is that stable junctions may form from solvents as well and that both conductance–distance traces and current–voltage characteristics have to be studied to distinguish between contacts of solvent molecules and of molecules under study.

Environmental Control of Single‐Molecule Junction Evolution and Conductance: A Case Study of Expanded Pyridinium Wiring

“…Break junction experiments were performed in the past in the solvent environment mainly to avoid contamination and to promote the molecular junction ( Figure 1a)formation. [27,28] Later as uitable solvent was used to realize electrochemical gating between several single-molecule conductance states in ON/OFF switches for molecular electronics. [20,29,30] Thee nvironmental control was also essential for the achievement of high rectification ratio in single-molecule diodes [4] and the notion of solvent gating was introduced.…”

Environmental Control of Single‐Molecule Junction Evolution and Conductance: A Case Study of Expanded Pyridinium Wiring

“…Break junction experiments were performed in the past in the solvent environment mainly to avoid contamination and to promote the molecular junction (Figure 1 a) formation [27, 28] . Later a suitable solvent was used to realize electrochemical gating between several single‐molecule conductance states in ON/OFF switches for molecular electronics [20, 29, 30] .…”

Single Level Tunneling Model for Molecular Junctions: Evaluating the Simulation Methods

“…Experimentally single state junction has been achieved by attaching electroactive group like ferrocene or conjugate organic molecules as the single electronic active state with alkane molecule as insert molecular linker to adjust the coupling of the electronic state with electrode. Function and special transport behaviors have been observed like, rectification 14 , Coulomb blockade and Kondo effect 15,16 through utilization of experimental techniques such as scanning tunneling microscope (STM), mechanical controllable break junctions (MC-BJ) 17 , conducting probe atomic force microscope (CP-AFM) 18 and liquid junction techniques like eutectic indium gallium (EGaIn) or mercury drop junctions 19,20 . Theoretical analysis based on SLM depends on the mathematical modeling of the experimental I-V plot where coupling strength (Γ) and energy offset (ε0) can be obtained and cross compared to spectroscopy measurement like ultraviolet photoelectron spectroscopy (UPS) or ab initio calculation 21 The currentvoltage (I-V) relation in single level model is described by Landauer formula (Eq 1) with single level transmission function 9,11 (1.…”

“…The current voltage (I-V) analysis using Eq 1 as the first recognized SLM expression in tunneling junction analysis achieves to unveil various features of the molecular junctions. For example, Luka-Guth et al studied the role played by the solvent in electronic transport in molecular junction, the junction analysis help them to make a reasonable conclusion on differentiated solvent conductance with that of molecular junction 17 . On the other hand, Zotti et al revealed the effect of anchoring group in molecular junction by examining the influence of moleculemetal contact interaction in molecule junction 24 .…”