Unexpected hole doping of graphene by osmium adatoms

TL;DR

This study reveals that osmium adatoms uniquely hole-dope graphene by acting as electron acceptors, contrasting with other metallic adatoms, and exhibit low charge-doping efficiency with surface diffusion effects.

Contribution

It demonstrates the unexpected hole doping effect of osmium adatoms on graphene and analyzes their behavior as charged impurity scatterers with low doping efficiency.

Findings

Osmium adatoms shift graphene's charge neutrality point positively.

Osmium acts as an electron acceptor, unlike other metallic adatoms.

Charge neutrality point varies non-monotonically with temperature.

Abstract

The electronic transport of monolayer graphene devices is studied before and after \emph{in situ} deposition of a sub-monolayer coating of osmium adatoms. Unexpectedly, and unlike all other metallic adatoms studied to date, osmium adatoms shift the charge neutrality point to more positive gate voltages. This indicates that osmium adatoms act as electron acceptors and thus leave the graphene hole-doped. Analysis of transport data suggest that Os adatoms behave as charged impurity scatterers, albeit with a surprisingly low charge-doping efficiency. The charge neutrality point of graphene is found to vary non-monotonically with gate voltage as the sample is warmed to room temperature, suggesting that osmium diffuses on the surface but is not completely removed.