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

Abstract The production of high‐quality hexagonal boron nitride (h‐BN) is essential for the ultimate performance of 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 the 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. The surface reaction‐assisted conversion from h‐BN to graphene with high‐temperature treatments is demonstrated. The pyrolysis temperature T_p is an important quality indicator for h‐BN/metals. When the temperature is lower than T_p, the quality of the h‐BN layer is improved upon annealing. While the annealing temperature is above T_p, 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).