Graphene – projects

Back to graphene.

Quantum dots in graphene

We study quantum confinement of Dirac particles in gate-defined quantum dots in graphene, in part motivated by the prospect of highly coherent spin qubits. The two-dimensional graphene is first etched into a quasi-one-dimensional nano-ribbon, so that a transport gap is formed. Then barriers are formed via local electrostatic gates on top of the ribbon. In this way we can form single and double quantum dots. (Nano Letters 10, 1623, 2010; Phys. Rev. B 80, 121407, 2009)

DNA translocation through graphene nanopores

A holy grail in single-molecule experiments based on nanopores is to resolve individual bases in a DNA molecule as it passes through the pore. What is required is a pore in an atomically thin membrane. As a first step, we transfer graphene using a novel “wedging” technique onto a TEM support and drill a hole in the graphene using a focussed electron beam. We observe a temporary step in the ionic conductance through the pore when a single ds-DNA molecule translocates through it. (Nano Letters 10, 3163, 2010, Nano Letters 10, 1912, 2010) (collaboration C. Dekker en H. Zandbergen)

Gate-induced band gap in bilayer graphene

Single layer graphene and undoped bilayer graphene (with Bernal stacking) are zero-gap semiconductors. This makes it difficult to confine the particles or cretae transistors in such materials. We fabricate bilayer graphene devices with a local top gate and global back gate, so that we can apply an electric field perpendicular to the layers. We observe that the electric field induces a bandgap in bilayer graphene, as predicted. When placing the Fermi level inside the bandgap, transport is suppressed by several orders of magnitude at low temperature. (Nature Mat. 7, 151, 2007) (collaboration A. Morpurgo)

Induced superconductivity in graphene

We fabricated mesoscopic superconducting junctions by contacting a graphene layer by two closely spaced superconducting electrodes. We observed a supercurrent that is carried by either electrons in the conduction band or by holes in the valence band, tuneable by gate voltage. This supercurrent persists at the Dirac point. The observations demonstrate the presence of time reversal symmetry in graphene and phase coherent electronic transport at the Dirac point. (Nature 446, 56 (2007). (collaboration A. Morpurgo)