This paper investigates the influence of the interface between a gold or silver metal electrode and an n-alkyl SAM (supported on that electrode) on the rate of charge transport across junctions with structure Met(Au or Ag) TS /A(CH 2 ) n H//Ga 2 O 3 /EGaIn by comparing measurements of current density, J(V), for Met/AR = Au/thiolate (Au/SR), Ag/thiolate (Ag/SR), Ag/carboxylate (Ag/O 2 CR),and Au/acetylene (Au/CtCR), where R is an n-alkyl group. Values of J 0 and β (from the Simmons equation) were indistinguishable for these four interfaces. Since the anchoring groups, A, have large differences in their physical and electronic properties, the observation that they are indistinguishable in their influence on the injection current, J 0 (V = 0.5) indicates that these four Met/A interfaces do not contribute to the shape of the tunneling barrier in a way that influences J(V).

As an organic nanostructure, self-assembled monolayers (SAMs) play a central role in many aspects of nanotechnology, including molecular electronics. In this work, we show that SAMs based on N-heterocyclic carbenes on a Au(111) substrate offer a high level of crystallinity and also exhibit the highest possible packing density. As a result of this structural optimization, defect concentrations were reduced by 2–3 orders of magnitude and thermal stability was ∼100 K higher than those of any other SAMs on Au. The conductivity of these SAMs is ∼4 orders of magnitude lower than that of standard alkanethiols of comparable length, which together with very low defect concentration and high thermal stability makes them a highly interesting material for potential application in organic thin film transistors. The self-assembly of such dense, highly crystalline, and notably stable structures is associated with strong C–Au bonding and the rational design of assembled molecules, resulting in the high mobility of both adsorbate and substrate atoms, as confirmed by the size of the molecular domains and the adsorbate-driven modification of the Au(111) substrate, respectively.

Self-assembled monolayers (SAMs) of the homologous series of biphenyl-substituted fatty acids on Ag(111) in the form of (C 6 H 4 ) 2 −(CH 2 ) n −COO/Ag (BPnCOO/Ag, n = 1−4) were studied using infrared reflection absorption spectroscopy (IRRAS), X-ray photoelectron spectroscopy (XPS), and scanning tunneling microscopy (STM). The combination of spectroscopic (IRRAS and XPS) and microscopic analyses (STM) revealed that depending on the parity of the parameter n, which defines the length of the short aliphatic linker, two types of structures are formed by the BPnCOO/Ag. For n = even, highly ordered and stable SAMs are formed in a very short time. For n = odd, the respective monolayers have a disordered liquidlike structure with more canted orientation of the molecular backbone and the anchoring carboxylic group, which results in lower packing density and film thickness compared to the even-numbered SAMs. By comparing obtained results with former odd−even effects reported for analogous SAMs based on thiols and selenols, a common, qualitative model relating the odd−even effect to the monolayer stability and structure is discussed. Our results demonstrate that for BPnCOO/Ag, this odd−even effect is particularly strong and fully controls the ability of molecules to form highly ordered structures. This observation seems to be of key importance for the design of SAMs based on the carboxylic group, which, for correctly designed molecules, forms much better two-dimensionally ordered structures compared to commonly used thiols.

The structure of analogous SAMs chemisorbed on an Ag substrate via a -SH or -COOH binding group is reported. Our observations indicate that COOH binding groups can be considered as a promising alternative for the current standard based on the sulfur binding groups, particularly when 2D ordering, SAM fabrication time and stability under ambient conditions are of great importance.