Graphene Films with Large Domain Size by a Two-Step Chemical Vapor Deposition Process

TLDR

Graphene’s exceptional properties make it attractive for many applications, and recent work has shown that large‑area graphene can be synthesized by CVD of methane on copper foils. This study investigates how growth temperature, methane flow, and partial pressure influence graphene growth rate, domain size, and coverage, and proposes a two‑step CVD process to produce films with domains spanning hundreds of square microns. The authors employ a two‑step CVD on copper, varying temperature and methane flow, and characterize the resulting films with Raman spectroscopy, SEM, and TEM to assess growth kinetics and domain morphology. The two‑step CVD yields surface‑mediated, polycrystalline graphene with domains up to hundreds of square microns, rotated by 13–30°, and films with larger domains exhibit carrier mobilities up to 16,000 cm² V⁻¹ s⁻¹ at room temperature.

Abstract

The fundamental properties of graphene are making it an attractive material for a wide variety of applications. Various techniques have been developed to produce graphene and recently we discovered the synthesis of large area graphene by chemical vapor deposition (CVD) of methane on Cu foils. We also showed that graphene growth on Cu is a surface-mediated process and the films were polycrystalline with domains having an area of tens of square microns. In this paper we report on the effect of growth parameters such as temperature, and methane flow rate and partial pressure on the growth rate, domain size, and surface coverage of graphene as determined by Raman spectroscopy, and transmission and scanning electron microscopy. Based on the results, we developed a two-step CVD process to synthesize graphene films with domains having an area of hundreds of square microns. Scanning electron microscopy and Raman spectroscopy clearly show an increase in domain size by changing the growth parameters. Transmission electron microscopy further shows that the domains are crystallographically rotated with respect to each other with a range of angles from about 13 degrees to nearly 30 degrees. Electrical transport measurements performed on back-gated FETs show that overall films with larger domains tend to have higher carrier mobility, up to about 16,000 cm2 V-1 s-1 at room temperature.