Laser has been used to cut to shape and deposit graphene on a target substrate in a single step process, potentially lowering device fabrication time and cost. Graphene patches with diameters as small as 30 micrometers were transferred onto technologically relevant substrates.
The preferred method for production of large-area graphene is chemical vapour deposition (CVD), which allows roll-to-roll scalable production of good quality material. CVD is widely used to create graphene films and devices for industrial and research applications. The CVD process is most commonly restricted to growth on catalytic substrates, such as thin copper films.
In order to produce finished devices, such as field effect transistors, graphene needs to be transferred onto a technologically usable substrate, most commonly a silicon or silica wafer. The common methods of transferring graphene involve polymer intermediary overlayers, application of lithographic masking layers and chemical etching, steps that increase process complexity and reduce the quality of the pristine graphene. Laser-induced localized transfer bypasses all these steps, simplifying device fabrication.
Image: Graphene transferred by laser. Image from Praeger et al, Appl. Surf. Sci. 533, 147488 (2020). CC BY 4.0 license.
Laser-induced transfer utilizes high power femtosecond laser pulses to “peel” graphene off a substrate. A possible explanation for the underlying physical mechanism is thermal expansion of the substrate, in this case nickel metal, which leads to a rupture of the graphene sheet at the edges of the laser-illuminated area. The research team, joining forces from the UK, Greece, Spain and Israel, having published their results in the journal Applied Surface Science, believes that laser transfer has the potential to eliminate many time-consuming lithographic processing steps, allowing precise, direct application of 2D materials with complex shapes to specific locations on a device, although they acknowledge that the process should be further refined to improve on the quality of the transferred material.
Image: Sequence of illustrations showing the laser transfer process. Image from Praeger et al, Appl. Surf. Sci. 533, 147488 (2020). CC BY 4.0 license.