Professor Bo W. Laursen, Head of Nano Science Center, Department of Chemistry, University of Copenhagen, Copenhagen, Denmark

Getting Into Contact With Molecules

A major challenge for measurements of molecular conductance and the fabrication of molecular electronic devices is the formation of reliable contacts to the molecules. This contact problem has troubled molecular electronic for decades. However, graphene materials may offer a possible solution to this problem.

Vertical devices based on self-assembled molecular monolayers (SAMs) or Langmuir Blodgett (LB) films deposited between top and bottom electrodes are very attractive architectures for molecular electronics. However, this device layout in general suffers from ill-defined junctions when vapor deposited metal top-contacts are applied.^[1] A promising solution to this top-contact problem is the application of graphene materials as the actual contacts or as protective interlayers between molecules and metals.  

      Deposition of a dense LB film of single layer graphene oxide flakes is shown by x-ray reflectometry to provide an efficient protection of fragile molecular LB films from vapor deposited titanium-gold top electrodes.^[2] Large are thin films (≈5 nm thickness) of reduced graphene oxide (rGO) can be deposited as top contacts to molecular SAM’s grown in lithography defined micro wells on an array of bottom electrodes (Figure 1). The conductive rGO film complete a devices with two molecular junctions in series (junction I), or after vapor deposition of a metal cross wire a well-defined permanent monolayer device (junction II).^[3] In this way rGO is demonstrated to function as both a protective layer and as soft electrodes for molecular devices. The transparency of the rGO film is further exploited to fabricate a light switchable electronic device (junction I) from a SAM of photo chemical active molecules.^[4]

Figure 1. Ultra-thin films of reduced graphene oxide may serve as transparent top electrodes and connector for a device with two molecular junctions in series (junction I) or as a protective inter layer between molecules and vapor deposited top contacts (junction II).

1. Hansen et al, Nano Letters, ” Structure of the Buried Metal-Molecule Interface in Organic Thin Film Devices “, 2009, 9, 1052-1057.
2. Petersen et al, ACS Nano, ” Graphene Oxide as a Mono Atomic Blocking Layer “, 2012, 6, 8022–8029.
3. Li et al, Advanced Materials, ” Solution-Processed Ultrathin Chemically Derived Graphene Films as Soft Top Contacts for Solid-State Molecular Electronic Junctions“, 2012, 24, 1333–1339.
4. Li et al., Advanced Materials,“Ultrathin Reduced Graphene Oxide Films as Transparent Top-Contacts for Light Switchable Solid-State Molecular Junctions”, 2013, 25, 4164–4170.

Host: Professor Kim Daasbjerg, iNANO & Dept. of Chemistry, Aarhus University, Denmark

Coffee, tea and bread will be served in front of the auditorium from 10:00.