Plasma-enhanced chemical vapor deposition of amorphous Si on graphene

TL;DR

This study compares RF and VHF plasma-enhanced chemical vapor deposition methods for coating graphene with amorphous silicon, highlighting differences in graphene integrity and resulting material properties.

Contribution

It demonstrates that VHF plasma preserves graphene's crystalline quality while depositing thin Si layers, unlike RF plasma which causes amorphization.

Findings

VHF plasma maintains graphene's high crystalline quality.

RF plasma causes amorphization of graphene.

Post-annealing transforms amorphous Si into polycrystalline film.

Abstract

Plasma-enhanced chemical vapor deposition of thin a-Si:H layers on transferred large area graphene is investigated. Radio frequency (RF, 13.56 MHz) and very high frequency (VHF, 140 MHz) plasma processes are compared. Both methods provide conformal coating of graphene with Si layers as thin as 20 nm without any additional seed layer. The RF plasma process results in amorphization of the graphene layer. In contrast, the VHF process keeps the high crystalline quality of the graphene layer almost intact. Correlation analysis of Raman 2D and G band positions indicates that Si deposition induces reduction of the initial doping in graphene and an increase of compressive strain. Upon rapid thermal annealing the amorphous Si layer undergoes dehydrogenation and transformation into a polycrystalline film whereby a high crystalline quality of graphene is preserved.