Laser directed lithography of asymmetric graphene ribbons on a polydimethylsiloxane trench structure

Abstract

Recently, manipulating heat transport by asymmetric graphene ribbons has received significant attention, in which phonons in the carbon lattice are used to carry energy. In addition to heat control, asymmetric graphene ribbons might also have broad applications in renewable energy engineering, such as thermoelectric energy harvesting. Here, we transfer a single sheet of graphene over a 5 μm trench of polydimethylsiloxane (PDMS) structure. By using a laser (1.77 mW, 1 μm diameter spot size, 517 nm wavelength) focusing on one side of the suspended graphene, a triangular shaped graphene ribbon is obtained. As the graphene has a negative thermal expansion coefficient, local laser heating could make the affected graphene area shrink and eventually break. Theoretical calculation shows that the 1.77 mW laser could create a local hot spot as high as 1462.5 °C, which could induce an asymmetric shape structure. We also find the temperature coefficient (−13.06 cm⁻¹ mW) of suspended graphene on PDMS trench substrate is ten times higher than that reported on SiO₂/Si trench substrate. Collectively, our results raise the exciting prospect that the realization of graphene with asymmetric shape on thermally insulating substrate is technologically feasible, which may open up important applications in thermal circuits and thermal management.