Marking the Graphene Era in Disseminating the Redefined SI

TL;DR

This paper reviews the development of quantum Hall effect standards using graphene, highlighting synthesis methods and their impact on metrological applications in redefining SI units.

Contribution

It provides a comprehensive overview of graphene-based quantum Hall resistance standards and compares different synthesis techniques for metrological suitability.

Findings

Exfoliated graphene shows the highest mobilities for quantum Hall applications.

Graphene-based QHE devices are rapidly becoming accessible for metrology.

Various synthesis methods impact the quality and applicability of graphene in standards.

Abstract

The history of quantum Hall standards stretches several decades and mostly begins with the use of GaAs given that 2D electron systems exhibit interesting quantum phenomena. At the end 2000s, research in 2D materials like graphene became prevalent. The QHE was observed and quickly became accessible to metrologists. QHR devices were becoming graphene-based, with fabrications performed by chemical vapor deposition (CVD), epitaxial growth, and the exfoliation of graphite. Given the many methods of available graphene synthesis, efforts to find an optimal synthesis method for metrological purposes were underway. Exfoliated graphene was widely known to exhibit the highest mobilities due to its pristine crystallinity. It was a primary initial candidate as far as metrological testing was concerned.