Using a combination of complementary in situ X-ray photoelectron spectroscopy and X-ray diffraction, we study the fundamental mechanisms underlying the chemical vapor deposition (CVD) of hexagonal boron nitride (h-BN) on polycrystalline Cu. The nucleation and growth of h-BN layers is found to occur isothermally, i.e., at constant elevated temperature, on the Cu surface during exposure to borazine. A Cu lattice expansion during borazine exposure and B precipitation from Cu upon cooling highlight that B is incorporated into the Cu bulk, i.e., that growth is not just surface-mediated. On this basis we suggest that B is taken up in the Cu catalyst while N is not (by relative amounts), indicating element-specific feeding mechanisms including the bulk of the catalyst. We further show that oxygen intercalation readily occurs under as-grown h-BN during ambient air exposure, as is common in further processing, and that this negatively affects the stability of h-BN on the catalyst. For extended air exposure Cu oxidation is observed, and upon re-heating in vacuum an oxygen-mediated disintegrationof the h-BN film via volatile boron oxides occurs. Importantly, thisdisintegration is catalyst mediated, i.e., occurs at the catalyst/h-BNinterface and depends on the level of oxygen fed to this interface.In turn, however, deliberate feeding of oxygen during h-BN depositioncan positively affect control over film morphology. We discuss theimplications of these observations in the context of corrosion protectionand relate them to challenges in process integration and heterostructureCVD.
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