Direct tuning of graphene work function via chemical vapor deposition control

Qinke Wu,Young Jae Song,Dong-Jin Yun,Seong Heon Kim,Taegeun Yoon

doi:10.1038/s41598-020-66893-y

Abstract

Besides its unprecedented physical and chemical characteristics, graphene is also well known for its formidable potential of being a next-generation device material. Work function (WF) of graphene is a crucial factor in the fabrication of graphene-based electronic devices because it determines the energy band alignment and whether the contact in the interface is Ohmic or Schottky. Tuning of graphene WF, therefore, is strongly demanded in many types of electronic and optoelectronic devices. Whereas study on work function tuning induced by doping or chemical functionalization has been widely conducted, attempt to tune the WF of graphene by controlling chemical vapor deposition (CVD) condition is not sufficient in spite of its simplicity. Here we report the successful WF tuning method for graphene grown on a Cu foil with a novel CVD growth recipe, in which the CH4/H2 gas ratio is changed. Kelvin probe force microscopy (KPFM) verifies that the WF-tuned regions, where the WF increases by the order of ~250 meV, coexist with the regions of intrinsic WF within a single graphene flake. By combining KPFM with lateral force microscopy (LFM), it is demonstrated that the WF-tuned area can be manipulated by pressing it with an atomic force microscopy (AFM) tip and the tuned WF returns to the intrinsic WF of graphene. A highly plausible mechanism for the WF tuning is suggested, in which the increased graphene-substrate distance by excess H2 gases may cause the WF increase within a single graphene flake. This novel WF tuning method via a simple CVD growth control provides a new direction to manipulate the WF of various 2-dimensional nanosheets as well as graphene.

Highlights

Based on the Raman spectroscopy analysis, it was confirmed that the graphene grown by the new CVD recipe is same as a conventional CVD-grown graphene on a Cu foil, in terms of its intrinsic properties
We developed a novel work function (WF) tuning method for graphene grown on a Cu foil by changing the CH4:H2 gas ratio in a CVD growth
It was demonstrated that the WF-tuned regions, in which the WF increases by the order of ~250 meV, coexist with the regions of the intrinsic WF within a single graphene flake in Kelvin probe force microscopy (KPFM)

Summary

Introduction

Raman and X-ray photoelectron spectroscopy (XPS) confirmed that the graphene grown with the CVD recipe of high H2 gas portion has considerably increased WF, while its chemical structure is almost same as that of a conventional graphene. To investigate the WF properties of the graphene grown on a Cu foil with the new CVD recipe, we performed XPS, a representative surface analysis technique to explore the electronic structure including WF.

Results

Conclusion