Early stage of CVD graphene synthesis on Ge(001) substrate

TL;DR

This study investigates the initial stages of graphene growth on Ge(001) during CVD, identifying a carbon precursor phase and its evolution into graphene domains, revealing surface restructuring processes involved.

Contribution

It provides detailed insights into the early nucleation process of graphene on Ge(001), highlighting the precursor phase and surface morphology changes.

Findings

Identification of a carbon precursor phase with varied size and order.

Observation of initial hexagonal structure signatures in aggregates.

Correlation between surface restructuring and graphene domain growth.

Abstract

In this work we shed light on the early stage of the chemical vapor deposition of graphene on Ge(001) surfaces. By a combined use of microRaman and x-ray photoelectron spectroscopies, and scanning tunneling microscopy and spectroscopy, we were able to individuate a carbon precursor phase to graphene nucleation which coexists with small graphene domains. This precursor phase is made of C aggregates with different size, shape and local ordering which are not fully sp2 hybridized. In some atomic size regions these aggregates show a linear arrangement of atoms as well as the first signature of the hexagonal structure of graphene. The carbon precursor phase evolves in graphene domains through an ordering process, associated to a re-arrangement of the Ge surface morphology. This surface structuring represents the embryo stage of the hills-and-valleys faceting featured by the Ge(001) surface for longer deposition times, when the graphene domains coalesce to form a single layer graphene film.