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arXiv · 2609.23447

Sapphire-Side hBN Formation by Ni--Cr-Mediated Growth in a Stacked Ni--Cr/Boron/Sapphire Configuration: Effect of Boron Supply

Donghoi Kim·Aelim Ha·Soohyung Park·Young Duck Kim·Chinkyo Kim
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Abstract

Metal-mediated growth provides an effective route to high-quality hexagonal boron nitride (hBN), but hBN formation on the metal does not necessarily ensure hBN formation on an adjoining dielectric substrate. Here, we investigate this distinction using a vertically stacked Ni--Cr/boron/sapphire configuration operated at 1550~$^\circ$C under atmospheric pressure, with the relative boron supply varied at fixed Ni:Cr = 8:2. hBN is detected by Raman spectroscopy on the gas-exposed alloy surface throughout the investigated Alloy:B range, whereas sapphire-side hBN appears only at the higher relative boron supplies of Alloy:B = 24:1 and 18:1, as confirmed by both Raman spectroscopy and XRD. The hBN (002) reflection further narrows as the boron supply increases from 24:1 to 18:1, corresponding to an increase in the apparent c-axis coherent length from approximately 86 to 143~nm. Additional crystalline reflections also emerge only under these higher-boron conditions. These results identify boron supply as a key parameter governing the transition from alloy-side hBN formation to concurrent sapphire-side hBN growth. Once formed, sapphire-side hBN occurs within a substantially reconstructed and chemically modified Al/O-rich sapphire environment rather than as a uniform film on an intact substrate. To our knowledge, this study provides the first demonstration of successful sapphire-side hBN formation by Ni--Cr-mediated growth.

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Donghoi Kim, Aelim Ha, Soohyung Park, Young Duck Kim, Chinkyo Kim. 2026-09-20. Sapphire-Side hBN Formation by Ni--Cr-Mediated Growth in a Stacked Ni--Cr/Boron/Sapphire Configuration: Effect of Boron Supply. https://arxiv.org/abs/2609.23447

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