Alkali doping of graphene: the crucial role of high temperature annealing

TL;DR

This study demonstrates that high-temperature annealing significantly enhances lithium doping efficiency in graphene, achieving an order of magnitude higher charge carrier density compared to non-annealed samples.

Contribution

It reveals the crucial role of high-temperature annealing in increasing lithium doping levels in graphene, a factor previously underappreciated.

Findings

Doping saturation at 2×10^{13} e^-/cm^2 without annealing

Annealing at 900 K increases doping saturation to 2×10^{14} e^-/cm^2

High-temperature annealing improves doping efficiency in graphene

Abstract

The doping efficiency of lithium deposited at cryogenic temperatures on epitaxial and CVD monolayer graphene has been investigated under ultra-high vacuum conditions. Change of charge carrier density was monitored by gate voltage shift of the Dirac point and by Hall measurements, in low and high doping regimes. It was found that pre-annealing the graphene greatly enhanced the maximum levels of doping that could be achieved: doping saturated at $\Delta n = 2\times 10^{13}$ e$^-$/cm$^2$ without annealing, independent of sample type or previous processing; after a 900 K anneal, the saturated doping rose one order of magnitude to $\Delta n = 2\times 10^{14}$ e$^-$/cm$^2$.