Planar aromatic anchors control the electrical conductance of gold|molecule|graphene junctions

Abstract

Alkanethiol molecules with planar aromatic head groups were synthesised and assembled on gold surfaces. The conductance properties of the resulting monolayers were measured using conductive atomic force microscopy with Pt and graphene coated tips.

Pyrene-Terminated Self-Assembled Monolayers on Au Substrate: Molecular Organization and Charge Transport Properties

“…The somewhat lower packing density in the Pyr-C4S2 case compared to Pyr-C12 stems most likely from the shorter linker of the former film (less efficient "drive" for the selfassembly) and the disturbing effect of the S heteroatoms. Note that the relations between the packing densities of the Pyr-C12 and Pyr-C4S2 SAMs and that of the nonsubstituted monolayer (0.78 and 0.69, respectively) correlate well with the analogous parameter reported recently for pyrene-substituted alkanethiols on Au (0.74), 16 even though the absolute values of the packing densities in ref 16 are somewhat too high, which can be related to either the presence of a multilayer fraction or an overestimate by the technique (microbalance measurements).…”

“…The most prominent property of the respective monolayers was their rectification behavior with a rectification ratio of up to ∼10 2 at a bias voltage of 1 V. − The extent of this behavior depended on the substrate and varied noticeably at the intercalation of Li . However, whereas the charge transport data for the Pyr-C11 SAMs look entirely reliable, the complementary spectroscopic data, including the near-edge X-ray absorption fine structure (NEXAFS) spectra in particular, look not fully convincing in our opinion and cast therefore some doubt regarding the quality of these monolayers in context of the packing density, molecular orientation, and the state of the pyrenyl groups. , In addition, the most recent publication dealing with the electrical conductance of a family of alkanethiolate molecules with planar aromatic tail group does not report a pronounced asymmetry of the I–V curves in the case of pyrene …”

“…22,23 In addition, the most recent publication dealing with the electrical conductance of a family of alkanethiolate molecules with planar aromatic tail group does not report a pronounced asymmetry of the I−V curves in the case of pyrene. 16 To this end, we decided to revisit this system, taking a SAM of pyrene-substituted dodecanethiol (Pyr-C12; see Figure 1) on Au(111) as a representative test monolayer. Pyr-C12 has been used for the fabrication of photosensitive field-effect transistors made from semiconducting CNTs and noncovalently attached gold nanoparticles, 14 but the respective SAMs have not been characterized.…”

“…Pyrene serves as an important building block for semiconductors used in organic electronic devices, including organic light-emitting diodes, organic field-effect transistors, and organic solar cells . It represents also a useful element for nanofabrication and a versatile anchoring group for coupling of molecules and nanoobjects to graphene and carbon nanotubes (CNTs), − providing, e.g., a means to assemble molecular magnets on graphene and graphite as well as to couple Au nanoparticles to CNTs . An additional useful feature of pyrene is the possibility of its functionalization, , which, in particular, makes it possible to tune its highest occupied molecular orbital-lowest unoccupied molecular orbital (HOMO–LUMO) gap and fluorescence behavior .…”