Huanyao Cun

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).