TY - JOUR

T1 - Planar aromatic anchors control the electrical conductance of gold|molecule|graphene junctions

AU - O'Driscoll, Luke J.

AU - Jay, Michael

AU - Robinson, Benjamin

AU - Sadeghi, Hatef

AU - Wang, Xintai

AU - Penhale-Jones, Becky

AU - Bryce, Martin R.

AU - Lambert, Colin

PY - 2023/4/21

Y1 - 2023/4/21

N2 - The synthesis of a family of alkanethiol molecules with planar aromatic head groups, designed to anchor molecules effectively to graphene electrodes, is reported. Characterisation of self-assembled monolayers of these molecules on a gold surface via conductive atomic force microscopy shows that when an aromatic head group is present, the conductance Ggraphene obtained using a graphene coated probe is higher than the conductance GPt obtained using a platinum (Pt) probe. For Pt probe and graphene probe junctions, the tunnelling decay constant of benzyl ether derivatives with an alkanethiol molecular backbone is determined as β = 5.6 nm−1 and 3.5 nm−1, respectively. The conductance ratio Ggraphene/GPt increases as the number of rings present in the aromatic head unit, n, increases. However, as the number of rings increases, the conductance path length increases because the planar head groups lie at an angle to the plane of the electrodes. This means that overall conductance decreases as n increases. Density functional theory-based charge transport calculations support these experimental findings. This study confirms that planar aromatic head groups can function as effective anchoring units for graphene electrodes in large area molecular junctions. However, the results also indicate that the size and geometry of these head groups must be considered in order to produce effective molecular designs.

AB - The synthesis of a family of alkanethiol molecules with planar aromatic head groups, designed to anchor molecules effectively to graphene electrodes, is reported. Characterisation of self-assembled monolayers of these molecules on a gold surface via conductive atomic force microscopy shows that when an aromatic head group is present, the conductance Ggraphene obtained using a graphene coated probe is higher than the conductance GPt obtained using a platinum (Pt) probe. For Pt probe and graphene probe junctions, the tunnelling decay constant of benzyl ether derivatives with an alkanethiol molecular backbone is determined as β = 5.6 nm−1 and 3.5 nm−1, respectively. The conductance ratio Ggraphene/GPt increases as the number of rings present in the aromatic head unit, n, increases. However, as the number of rings increases, the conductance path length increases because the planar head groups lie at an angle to the plane of the electrodes. This means that overall conductance decreases as n increases. Density functional theory-based charge transport calculations support these experimental findings. This study confirms that planar aromatic head groups can function as effective anchoring units for graphene electrodes in large area molecular junctions. However, the results also indicate that the size and geometry of these head groups must be considered in order to produce effective molecular designs.

U2 - 10.1039/D2NA00873D

DO - 10.1039/D2NA00873D

M3 - Journal article

C2 - 37056609

VL - 5

SP - 2299

EP - 2306

JO - Nanoscale Advances

JF - Nanoscale Advances

SN - 2516-0230

IS - 8

ER -