In the wide world of 2D materials, hexagonal boron nitride (hBN) holds a special place due to its excellent characteristics. In addition to its thermal, chemical and mechanical stability, hBN demonstrates high thermal conductivity, low compressibility, and wide band gap around 6 eV, making it promising candidate for deep ultraviolet optoelectronic devices. Furthermore, its excellent insulating properties with a dielectric constant lower than 2 and its large electrical bandgap, combined with diffusion barrier properties against migration of metals into semiconductors render it interesting for based substrates gate dielectrics for transistors and interconnects, and electronic packaging insulators.
 
Vapor-phase processes like Chemical Vapor Deposition can achieve large scale coverage, but selfstanding hexagonal boron nitride crystals provide exfoliated nanosheets of unrivaled purity and crystal quality which are still preferred for demanding applications. In this context, to achieve high quality and large h-BN nanosheets (BNNSs), we propose novel synthesis ways by the Polymer Derived Ceramics route involving polyborazylene as precursor, combined with sintering techniques. [1,2] These promising approaches allow synthesizing pure and well-crystallized h-BN single crystals, which can be easily exfoliated into BNNSs with lateral size over hundreds of microns. Here we present recent investigations on how to optimize processes. Structural studies were led by TEM and Raman spectroscopy. Both methods evidence a very high crystalline quality attested by the LWHM value, 7,6 cm-1, as the best reported in literature. [3] More original characterizations were performed by cathodoluminescence and XPS to prove the high BNNSs purity from both structural and chemical point of view. As a final application purpose, physical measurements have confirmed that derived BNNSs exhibit an interesting dielectric constant of 3.9 associated with a dielectric strength of 0.53 V/nm.

References
[1] S. Yuan, S. Linas, C. Journet, P. Steyer, V. Garnier, G. Bonnefont, A. Brioude, B. Toury, Scientific Reports, 6 (2016) 20388
[2] Y. Li, V. Garnier, C. Journet, J. Barjon, A. Loiseau, I. Stenger, A. Plaud, B. Toury, P. Steyer, Nanotechnology 30 (2019) 035604 
[3] Y. Li, V. Garnier, P. Steyer, C. Journet, B Toury, ACS Applied Nano Materials, 2020, doi.org/10.1021/acsanm.9b02315