Influence of Molecular Organization on the Electrical Characteristics of π-Conjugated Self-Assembled Monolayers

Abstract

Two new thiol compounds with σ-π-σ structure were synthesized and self-assembled on gold substrates. The morphology and the structural characterization of SAMs assessed by infrared spectroscopy, contact angle, XPS, electrochemistry and scanning tunneling microscopy (STM) show the formation of monolayers. SAMs with a terthiophene (3TSH) core as conjugated system are much better organized compared to those with a naphthalene carbodiimide (NaphSH) core as demonstrated by the cyclic voltammetry and STM studies. The surface concentration of 3TSHand NaphSH is respectively three and six times lower than ordered SAMs of pure alkyl chains.A large number of I/V characteristics have been studied either by STS measurements on gold substrates or by C-AFM on gold nanodots. Transition Voltage Spectroscopy (TVS) was used to clearly identify the transport in these partially organized monolayers. The chemical nature of the conjugated system, donor for 3TSH and acceptor for NaphSH, involves an opposite rectification associated to the asymmetrical coupling of the molecular orbitals and the electrodes. The conductance histograms show that the 3TSH junctions are less dispersed than those of NaphSH junctions. This is explained by a better control of the molecular organization in the molecular junctions.

Fluorinated benzalkylsilane molecular rectifiers

“…In this configuration, the forward bias condition corresponds to a positive potential applied at the fluorinated end of the molecules. The eutectic liquid metal EGaIn was utilized as a soft top-contact because its use is non-damaging, reproducible, and well-studied in this context22233132333435363738. A schematic of the device structure used in this study is included in Fig.…”

Synthesis and characterization of thiophene-based push-pull chromophores for tuning the electrical and optical properties of surfaces with controlled SAM formation

“…. 21 To bring out LUMO position, IPES spectrum with subtracted background signal is plotted in SI (see Fig. S1).…”

An important impact of the molecule–electrode coupling asymmetry on the efficiency of bias-driven redox processes in molecular junctions

“…A coupling asymmetry Γ s > Γ t has been concluded in ref. 41 after a detailed analysis of the transport data in CP-AFM junctions. In CP-AFM setups such an asymmetry appears to be plausible because one can expect that t s > t t , given the fact that a stable molecule-tip chemical bond is hard to imagine; normally, charge transport only occurs by applying a loading force at the CP-AFM tip.…”