Hexagonal boron nitride: a review on selfstanding crystals synthesis towards 2D nanosheets

Hexagonal boron nitride (hBN) is emerging as essential for 2D material-based technologies. New optoelectronic applications require high crystal quality hBN with low defect density and contamination. While vapor-phase processes like chemical vapor deposition can produce large-area hBN thin films, self-standing hexagonal boron nitride crystals provide exfoliated nanosheets of very high quality. The synthesis of these selfstanding hBN crystals prior to the exfoliation process is the focus of this review. Theses syntheses are described with emphasis on crystal size, purity, and defects. These considerations are based on various recently developed physical studies, including optical characterizations such as luminescence measurements highlighting the crystallinity and structural defects of hBN crystals.