From Growth Surface to Device Interface: Preserving Metallic Fe under Monolayer Hexagonal Boron Nitride

Abstract

We investigate the interfacial chemistry between Fe catalyst foils and monolayer hexagonal boron nitride (h-BN) following chemical vapour deposition and during subsequent atmospheric exposure, using scanning electron microscopy, X-ray photoemission spectroscopy, and scanning photoelectron microscopy. We show that regions of the Fe surface covered by h-BN remain in a reduced state during exposure to moist air for ~40 hours at room temperature. This protection is attributed to the strong interfacial interaction between h-BN and Fe, which prevents the rapid intercalation of oxidizing species. Local Fe oxidation is observed on bare Fe regions and close to defects in the h-BN film (e.g. domain boundaries, wrinkles, and edges), which over the longer-term provide pathways for slow bulk oxidation of the Fe. We further confirm that the interface between h-BN and reduced Fe can be recovered by vacuum annealing at ~600 °C, although this is accompanied by the creation of defects within the h-BN film. We discuss the importance of these findings in the context of integrated manufacturing and transfer-free device integration of h-BN, particularly for technologically important applications where h-BN has potential as a tunnel barrier such as magnetic tunnel junctions.S.C. and L.D. acknowledge EPSRC Doctoral Training Awards. H.S. acknowledges a research fellowship from the Japanese Society for the Promotion of Science (JSPS). S.H. acknowledges funding from ERC grant InsituNANO (no. 279342). This research was partially supported by the EUFP7 Work Programme under grant GRAFOL (project reference 285275) and EPSRC under grant GRAPHTED (project reference EP/ ACS Applied Materials & Interfaces Research Article K016636/1). R.S.W. acknowledges a Research Fellowship from St. John’s College, Cambridge, and a Marie Skłodowska-Curie Individual Fellowship (Global) under grant ARTIST (no. 656870) from the European Union’s Horizon 2020 research and innovation programme