The Winner Takes It All: Carbon Supersedes Hexagonal Boron Nitride with Graphene on Transition Metals at High Temperatures

TL;DR

This paper reveals that avoiding carbon during high-temperature processing is crucial for fabricating high-quality hexagonal boron nitride on transition metals, and demonstrates a method for converting h-BN to graphene via surface reactions.

Contribution

It establishes the importance of carbon exclusion in h-BN fabrication and introduces a surface reaction-assisted conversion technique to produce graphene on Pt(111).

Findings

Carbon presence leads to graphene formation on metals.

High-temperature annealing affects h-BN quality depending on pyrolysis temperature.

Excluding carbon results in cleaner, higher-quality h-BN layers.

Abstract

The production of high-quality hexagonal boron nitride (h-BN) is essential for the ultimate performance of two-dimensional (2D) materials-based devices, since it is the key 2D encapsulation material. Here, a decisive guideline is reported for fabricating high-quality h-BN on transition metals: It is crucial to exclude carbon from h-BN related process. Otherwise carbon prevails over boron and nitrogen due to its larger binding energy, thereupon forming graphene on metals after high-temperature annealing. We demonstrate the surface reaction-assisted conversion from h-BN to graphene with high-temperature treatments. The pyrolysis temperature Tp is an important quality indicator for h-BN/metals. When the temperature is lower than Tp, the quality of h-BN layer is improved upon annealing. While the annealing temperature is above Tp, in case of carbon-free conditions, the h-BN disintegrates and nitrogen desorbs from the surface more easily than boron, eventually leading to clean metal surfaces. However, once the h-BN layer is exposed to carbon, graphene forms on Pt(111) in the high-temperature regime. This not only provides an indispensable principle (avoid carbon) for fabricating high-quality h-BN materials on transition metals, but also offers a straightforward method for the surface reaction-assisted conversion from h-BN to graphene on Pt(111).