Graphene-metal interactions beyond Van der Waals forces

Abstract

With extraordinary properties, graphene has been applied in various studies to explore new phenomena, new understandings, and new applications. With only one atomic layer thick and all its atoms are on the surface, graphene's properties could be altered by being brought into contact with any arbitrary surfaces, and similarly the close presence of graphene contact could change the properties of that surface as well. This thesis aims to provide insights into graphene-metal interactions by analyze novel phenomena and develop practical applications. First, we modified the graphene-copper interface to prevent the growths of thicker graphene islands in order to grow a uniform bilayer graphene (2LG), by introducing the concept of interface adhesive energy. To characterize the different types of 2LG better, we developed a machine-learning-assisted Raman analysis tool and confirmed that our FM-mode-grown 2LG is of quasi-AB-stacking.

Taking advantage of the better mechanical properties of 2LG, a support-free, Marangoni-driven graphene transfer technique was developed. Next, we utilize the stability of Sn-graphene-Cu interfaces to develop an approach that allows for more reliable low-temperature bonding technology. The proposed bonding scheme inherently solves both high bonding temperature and interfacial diffusion issues. Specifically, the lowering of bonding temperature is achieved by introducing nano-cone features in the surface of the Cu side. A one-atomic-thick graphene interlayer on the Cu does not prevent the bonding between Cu and Sn, while preventing the atom diffusion to form the intermetallic compounds that are harmful for the reliability of the bonding. Finally, we examined graphene-metal interactions for the modification of optical properties in the graphene-aluminum and graphene-tin systems.

The Sn nanodot arrays have a light-trapping effect on graphene, therefore, increases graphene absorption from <2% to >15% in spectral regime of [lambda] = 900-2000 nm. On the contrary, a counter-intuitive transmittance enhancement is observed in graphene-Al hetero-films. We find that the relative transmittance enhancement reaches up to 27% for 370nm incident light on an interface of graphene and 10nm-thick aluminum. These two examples reveal the fascinating aspect of how the interface between graphene and metal could bring about unexpected property alterations in either of the layer or the whole system together.