Single-Molecule Junctions with Highly Improved Stability

Abstract

Single-molecule junctions (SMJs) have been fabricated using layers generated by diazonium electroreduction. This process immobilizes the molecule and creates a direct C-Au covalent bond between the molecule and the electrode. As a result, rigid oligomers of variable length, mainly perpendicular to the surface, are formed. The oligomers are based on porphyrin derivatives in their free base or cobalt complex forms. The conductance of the grafted oligomers has been studied by means of the scanning-tunneling-microscopy break-junction (STM-bj) technique and G(t) measurements, and the lifetime of the single-molecule junctions has been investigated. The conductance histograms indicate that charge transport in the porphyrins is relatively efficient and influenced by the presence of the cobalt center. With both systems, random telegraph G(t) signals are easily recorded showing SMJ on off states. The SMJs then stabilize and exhibit a surprisingly long lifetime around 10 s, and attenuation plots, obtained by both G(t) and STM-bj conductance measurements, give identical attenuation values. This work shows that highly stable SMJs can be prepared using diazonium grafting approach.

Room‐Temperature Spin‐Dependent Transport in Metalloporphyrin‐Based Supramolecular Wires

“…Even longer lifetimes can be observed using more stable molecule‐electrode contact chemistry. [ 36 , 37 , 38 ] After that, the current abruptly drops to the initial tunneling value due to the spontaneous breakdown of the junction. The formation of mechanically stable molecular junctions is confirmed through an induced STM tip vertical pulling during the blinking lifetime and a subsequent analysis of the current decay trace.…”

Smart Eutectic Gallium–Indium: From Properties to Applications

“…So far, the mature methods to measure the characteristics of molecular junctions include mechanically controllable break junctions (MCBJ), [84,176,177] scanning tunneling microscope break junctions (STM-BJ), [178,179] EGaIn-based molecular tunneling junctions (MTJs), [180,181] to name a few. [161,182] Currently, the most common way of incorporating EGaIn in ME devices is to measure the current-voltage characteristics of a molecular layer by either constructing a cone-shaped EGaIn tip or by using microfluidic channels filled with EGaIn as a top electrode to complete the MTJ.…”

Mechanically Tuned Thermopower of Single‐Molecule Junctions

“…In this study, SMJs were created between a Au(111) electrode and a Au tip of a scanning tunneling microscope (STM) using the BJ technique [ 34–36 ] and the relationship between the thermopower and the tip–electrode separation distance (i.e., nanogap distance) of SMJs was analyzed. The nanogap distance between the Au tip and the Au electrode, in which a single molecule is embedded, could be mechanically adjusted with atomic‐scale precision using the BJ technique, thereby modulating the junction electronic structure and thermopower.…”

“…[11,[17][18][19][20][21][22][23][24][25][26][27][28][29][30] However, the tuning of SMJ thermopower [19,21,24,25,27,28] has proven more difficult due to the large variation of the thermopower value itself within a sample, compared to the electric conductance. [30][31][32][33] In this study, SMJs were created between a Au(111) electrode and a Au tip of a scanning tunneling microscope (STM) using the BJ technique [34][35][36] and the relationship between the thermopower and the tip-electrode separation distance (i.e., nanogap distance) of SMJs was analyzed. The nanogap distance between the Au tip and the Au electrode, in which a single molecule is embedded, could be mechanically adjusted with atomic-scale precision using the BJ technique, thereby modulating the junction electronic structure and thermopower.…”