High-temperature behaviour of supported graphene: electron-phonon coupling and substrate-induced doping

TL;DR

This study investigates how supported graphene's electronic properties change with temperature, revealing extremely weak electron-phonon coupling but significant substrate-induced doping effects driven by distance fluctuations.

Contribution

It provides the first detailed analysis of temperature-dependent electronic structure of supported graphene, highlighting substrate interactions as key to transport behavior.

Findings

Electron-phonon coupling in supported graphene is extremely weak.

Temperature causes significant changes in carrier type and density.

Fluctuations in graphene-substrate distance drive electronic structure variations.

Abstract

One of the salient features of graphene is the very high carrier mobility that implies tremendous potential for use in electronic devices. Unfortunately, transport measurements find the expected high mobility only in freely suspended graphen. When supported on a surface, graphene shows a strongly reduced mobility, and an especially severe reduction for temperatures above 200 K. A temperature-dependent mobility reduction could be explained by scattering of carriers with phonons, but this is expected to be weak for pristine, weakly-doped graphene. The mobility reduction has therefore been ascribed to the interaction with confined ripples or substrate phonons. Here we study the temperature-dependent electronic structure of supported graphene by angle-resolved photoemission spectroscopy, a technique that can reveal the origin of the phenomena observed in transport measurements. We show that the electron-phonon coupling for weakly-doped, supported graphene on a metal surface is indeed extremely weak, reaching the lowest value ever reported for any material. However, the temperature-dependent dynamic interaction with the substrate leads to a complex and dramatic change in the carrier type and density that is relevant for transport. Using ab initio molecular dynamics simulations, we show that these changes in the electronic structure are mainly caused by fluctuations in the graphene-substrate distance.