Highly ordered self-assembled monolayers (SAMs) can be considered as functional building blocks for molecular electronics. Aromatic SAMs can be converted into a highly stable monolayer, i.e., carbon nanomembranes, via electron irradiation induced cross-linking. Here, we report the electronic transport characteristics of the pristine SAM of 4′-nitro-1,1′-biphenyl-4-thiol (NBPT) and the amino-terminated cross-linked monolayer prepared on Au/mica and Au/Si substrates with the use of a conductive probe atomic force microscope (CP-AFM) and a eutectic Ga–In (EGaIn) top electrode. The amino-terminated cross-linking monolayer exhibits a lower friction compared to the non-crosslinked SAM, as electron irradiation leads to the enhancement of both molecular rigidity and hydrophilicity. The electron irradiation effect on junction conductance was also directly observed by CP-AFM. Quantitative measurements and statistical analysis were performed by applying current–voltage spectroscopy in CP-AFM and EGaIn methods. Both methods demonstrate that the cross-linking of a NBPT–SAM leads to a decrease of conductance by more than one order of magnitude, which is attributed to a partial loss of aromaticity of the SAM as well as a partial decoupling of molecules from the Au substrate. Transition voltages were found to be significantly reduced for the cross-linked monolayer. The surface roughness effect on the transport characteristics has been addressed based on a comparison between two junction platforms.
Investigation of electronic transport through ultrathin carbon nanomembrane junctions by conductive probe atomic force microscopy and eutectic Ga–In top contacts
Xianghui Zhang, Emanuel Marschewski, Paul Penner, André Beyer, Armin Gölzhäuser; Investigation of electronic transport through ultrathin carbon nanomembrane junctions by conductive probe atomic force microscopy and eutectic Ga–In top contacts. J. Appl. Phys. 7 August 2017; 122 (5): 055103. https://doi.org/10.1063/1.4995533
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