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The growth and properties of hexagonal boron nitride (hBN) have recently attracted much attention due to applications in graphene-based monolayer thick two dimensional (2D)-structures and at the same time as a wide band gap material for deep-ultraviolet device (DUV) applications. The authors present their results in the high-temperature plasma-assisted molecular beam epitaxy (PA-MBE) of hBN monolayers on highly oriented pyrolytic graphite substrates. Their results demonstrate that PA-MBE growth at temperatures ∼1390 °C can achieve mono- and few-layer thick hBN with a control of the hBN coverage and atomically flat hBN surfaces which is essential for 2D applications of hBN layers. The hBN monolayer coverage can be reproducible controlled by the PA-MBE growth temperature, time and B:N flux ratios. Significantly thicker hBN layers have been achieved at higher B:N flux ratios. The authors observed a gradual increase of the hBN thickness from 40 to 70 nm by decreasing the growth temperature from 1390 to 1080 °C. However, by decreasing the MBE growth temperature below 1250 °C, the authors observe a rapid degradation of the optical properties of hBN layers. Therefore, high-temperature PA-MBE, above 1250 °C, is a viable approach for the growth of high-quality hBN layers for 2D and DUV applications. [ABSTRACT FROM AUTHOR]