Your Clean Graphene is Still Not Clean

TL;DR

This paper reveals that graphene, often considered clean after high-temperature treatment, can still be coated with a thin, diffusing hydrocarbon layer, impacting atomic fabrication processes and our understanding of surface cleanliness.

Contribution

The study provides direct evidence that heated graphene surfaces can retain a dynamic hydrocarbon layer, challenging assumptions about surface cleanliness post-heating.

Findings

Graphene can be coated with a thin hydrocarbon layer despite high-temperature cleaning.

Hydrocarbon contamination on graphene is dynamically diffusing and not fully removed by heating.

Implications for e-beam atomic fabrication and surface cleaning strategies.

Abstract

Efforts aimed at scaling fabrication processes to the level of single atoms, dubbed atom-by-atom fabrication or atomic fabrication, invariably encounter the obstacle of atomic scale cleanliness. When considering atomic fabrication, cleanliness of the base material and purity of the source reservoir from which atomic structures will be built are invariable constraints imposed by laws of physics and chemistry. As obvious as such statements may be, and regardless of the inevitable consequences for successful atomic fabrication, there is a poignant lack of understanding of the "dirt" (contamination/impurities). Here, we examine hydrocarbon contamination on graphene. Graphene has formed the base substrate for many e-beam-based atomic fabrication studies and many strategies for cleaning graphene have been presented in the literature. One popular method is heating to high temperatures (>500 {\deg}C). It is usually inferred that volatile hydrocarbons evaporate into the microscope vacuum system leaving behind pristine graphene. Here, we show through direct image intensity analysis that what appears to be clean graphene can be coated with a thin layer of dynamically diffusing hydrocarbons. This result holds significant implications for approaches to e-beam based atomic fabrication, updates the conceptual model of e-beam induced hydrocarbon deposition, and may extend to hot surfaces generally.