Abstract
One of the main challenges to upscale the fabrication of molecular devices is to achieve a mechanically stable device with reproducible and controllable electronic features that operates at room temperature1,2. This is crucial because structural and electronic fluctuations can lead to significant changes in the transport characteristics at the electrode-molecule interface3,4. In this study, we report on the realization of a mechanically and electronically robust graphene-based molecular junction. Robustness was achieved by separating the requirements for mechanical and electronic stability at the molecular level. Mechanical stability was obtained by anchoring molecules directly to the substrate, rather than to graphene electrodes, using a silanization reaction. Electronic stability was achieved by adjusting the π-π orbitals overlap of the conjugated head groups between neighbouring molecules. The molecular devices exhibited stable current-voltage (I-V) characteristics up to bias voltages of 2.0 V with reproducible transport features in the temperature range from 20 to 300 K.
Highlights
Layered materials have found a wide range of applications,[1] ranging from high power battery cells[2] tosensors[3,4,5] and optoelectronics circuit components.[1,6]
Transport through strongly coupled molecules is expected to be heavily influenced by the electrode geometry, edge termination and crystallographic structure, leading to a large variability in the shape of the current-voltage characteristics.[22]
We propose a new strategy to achieve stable and reproducible graphene-based molecular junctions by separating the strong mechanical anchoring from the electronic pathways
Summary
Layered materials have found a wide range of applications,[1] ranging from high power battery cells[2] to (bio-)sensors[3,4,5] and optoelectronics circuit components.[1,6] In particular for electronic and optoelectronic purposes they have generated considerable interest, being used as building block for transistors,[7] photodetectors,[8] artificial neurons[9] and memristors for non-volatile random-access memory and neuromorphic computing.[10,11,12] Due to its unique mechanical,[13] optical[14] and electronic[15] properties, graphene is, in this context, an appealing electrode material for planar molecular devices.[16,17,18,19]. The high similarity between successive IV curves is observed at all temperatures This behaviour highlights the high electronic and mechanical stability of the devices, in stark contrast to the behaviour of junctions based on molecule C (Fig. 1d). The plot shows that the current remains fairly constant over the entire temperature range for various bias voltage values, and in particular in the high temperature region between 150 K and 300 K This observation suggests that charge transport though these graphene-molecule-graphene junctions remains coherent up to 300 K. On the other hand, no delocalized orbitals are formed and transport occurs via the poorly conducting silane groups These calculations demonstrate the crucial role of π − π stacked head groups in the transport, and rationalize the large difference in current observed experimentally for the two molecules
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