Abrupt changes in the graphene on Ge(001) system at the onset of surface melting

TL;DR

This study investigates how the quality and morphology of CVD-grown graphene on Ge(001) change abruptly near 930°C due to incomplete surface melting, revealing the importance of this transition for graphene quality.

Contribution

It uncovers the role of incomplete Ge surface melting at 930°C in causing abrupt changes in graphene's properties and morphology.

Findings

Abrupt change in graphene quality at 930°C.

Incomplete Ge surface melting influences graphene growth.

High-quality graphene requires near-melting Ge surface.

Abstract

By combining scanning probe microscopy with Raman and x-ray photoelectron spectroscopies, we investigate the evolution of CVD-grown graphene/Ge(001) as a function of the deposition temperature in close proximity to the Ge melting point, highlighting an abrupt change of the graphene's quality, morphology, electronic properties and growth mode at 930 degrees. We attribute this discontinuity to the incomplete surface melting of the Ge substrate and show how incomplete melting explains a variety of diverse and long-debated peculiar features of the graphene/Ge(001), including the characteristic nanostructuring of the Ge substrate induced by graphene overgrowth. We find that the quasi-liquid Ge layer formed close to 930 degrees is fundamental to obtain high-quality graphene, while a temperature decrease of 10 degrees already results in a wrinkled and defective graphene film.