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John O | June 2017

Researchers use graphene to tune functionality of molecular devices


a team of researchers from the national physical laboratory (npl) in london (u.k.) and the university of bern (switzerland) have demonstrated the stability of multi-layer, graphene-based molecular devices to the single molecule limit, which opens the door to smaller, high-performance devices in a range of applications.

 


researchers have demonstrated graphene-based molecular devices.
(national physical laboratory)

 

according to a report on the npl website, “the findings represent a major step change in the development of graphene-based molecular electronics, with the reproducible properties of covalent contacts between molecules and graphene (even at room temperature) overcoming the limitations of current state-of-the-art technologies based on coinage metals.”

 

the adsorption of specific molecules allows the graphene-based devices to be tunable by modifying the electrical resistance.

 

in the past, it was difficult to understand how the adsorption of an individual molecule would impact the device properties, but researchers used a low-noise experimental technique to measure electrical current through a single molecule attached to graphite or multi-layered graphene electrodes.

 

“they demonstrated that variations on the graphite surface are very small and that the nature of the chemical contact of a molecule to the top graphene layer dictates the functionality of single-molecule electronic devices,” the article continued.

 

the research was recently published in science advances. the abstract read:

 

“an open challenge for single-molecule electronics is to find stable contacts at room temperature with a well-defined conductance. common coinage metal electrodes pose fabrication and operational problems due to the high mobility of the surface atoms. we demonstrate how molecules covalently grafted onto mechanically robust graphite/graphene substrates overcome these limitations.

 

“to this aim, we explore the effect of the anchoring group chemistry on the charge transport properties of graphite-molecule contacts by means of the scanning tunneling microscopy break-junction technique and ab initio simulations.

 

“molecules adsorbed on graphite only via van der waals interactions have a conductance that decreases exponentially upon stretching the junctions, whereas the molecules bonded covalently to graphite have a single well-defined conductance and yield contacts of unprecedented stability at room temperature.

 

“our results demonstrate a strong bias dependence of the single-molecule conductance, which varies over more than one order of magnitude even at low bias voltages, and show an opposite rectification behavior for covalent and noncovalent contacts.

 

“we demonstrate that this bias-dependent conductance and opposite rectification behavior is due to a novel effect caused by the nonconstant, highly dispersive density of states of graphite around the fermi energy and that the direction of rectification is governed by the detailed nature of the molecule/graphite contact.

 

“combined with the prospect of new functionalities due to a strongly bias-dependent conductance, these covalent contacts are ideal candidates for next-generation molecular electronic devices.”

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