Researchers at the University of Southampton have successfully deposited monolayer graphene shapes onto silicon photonic devices that were prepared by Mellanox as part of the LEAF-2D project. Each shape is deposited with a single laser pulse that is just 190 fs in duration, via the Laser Induced Forwards Transfer (LIFT) method. Monolayer graphene can be grown uniformly over large areas by Chemical Vapour Deposition (CVD), but many device designs call for the graphene to be deposited only at particular locations. Laser transfer methods such as LIFT allow the location and shape of deposition to be directly controlled by modifying the laser beam’s intensity profile. This works a bit like an old-fashioned typewriter… In this analogy the donor material (large area, CVD grown, monolayer graphene transferred onto a nickel carrier) is like the ink ribbon. The laser is then like the typebar (with a character moulded onto its face) that strikes the ribbon and transfers ink to the page (the silicon photonic device). In these latest results the spatial intensity profile of the laser beam is controlled using a Digital Micromirror Device (DMD). This allows digital control over the shape of the deposited material (the shape of the character moulded onto the typebar), with features down to the micron scale.
In the background of the images you can see waveguides that are part of the silicon photonic device design. The darker region in the middle is a semi-transparent red/black colour mapping of the intensity of the Raman ‘2D’ peak – i.e. it shows (in red) where the graphene has been deposited. The shape of the deposited graphene is controlled by the pattern that is displayed on the DMD (shown on the left and by the dashed red outline of the cross and by the transparent blue leaf shape). In the top right of each image a full Raman spectrum is shown (recorded at the position of the green circle). The transferred material exhibits the expected Raman peaks for monolayer graphene, with a small ‘D’ peak (leftmost) indicating that the transferred graphene is of high quality.