Controlled Lay-By-Layer Etching of CVD Grown Multilayer h-BN Single Crystal

Being a 2D insulator with alternating sp2 hybridized B and N atoms in a honeycomb structure, Hexagonal Boron Nitride(hBN) not only have uniqure properties like high transparency, large thermal conductivity, high mechanical strength and superior chemical inertness by itself, but also be able to promote other 2D materials’ performance when serving as the ultra-smooth dielectrilayer.[1,2] Since CVD process is established as the most effective way to grow large area hBN materials, it is critical to understand and control the growth process so as to making them ready for the large scale industrial applications. Etching of 2D materials should provide a scalable route for fabrication of highly desired various nanostructures such as nanoribbons with controlled termination providing a simple and direct way for 2D material property design, such as controlling the band gap and optical properties. [3,4] However, it is often easy to initiate the etching, but difficulty the control the location, shape, and size of the etching pattern. Previously reported etching patterns for 2D materials can be generally divided into four different categories: domain, boundary, fractal, and adlayer etching. [3-6] These etching patterns may co-exist in the etching process, but the dominant pattern depends on competition between various factors such as atmosphere, temperature, substrate, time etc. Layer number increase can often be achieved by increase the reaction temperature, time, and precursor concentration.While the layer number reducing after the multilayer hBN growth process remain challenging. Here we use the as-grow multilayer hBN single crystal from CVD process for controllable etching experiment, then both temperature related hydrogen etching and electronic energy related e-beam etching will be used to remove single layer of as-grown multilayer hBN. References Lu, G.; Wu, T; Yuan, Q.; Wang, H.; Wang, H.; Feng Ding, F.; Xie, X.; Jiang, M. Synthesis of large single-crystal hexagonal boron nitride grains on Cu–Ni alloy. Nat. Commun. 2014, 6, 6160. Liu, Z.; Gong, Y.; Zhou, W.; Ma, L.; Yu, J.; Idrobo, J. C.; Jung, J.; MacDonald, A.H.; Vajtai, R.; Lou, J.; Ajayan, P.M. Ultrathin high-temperature oxidation-resistant coatings of hexagonal boron nitride. Nat. Commun. 2013, 4, 2541. Vlassiouk, I.; Regmi, M.; Fulvio, P.; Dai, S.; Datskos, P.; Eres, G.; Smirnov, S. Role of hydrogen in chemical vapor deposition growth of large single-crystal graphene. ACS nano 2011, 5, 6069-6076. Wang, L.; Wu, B.; Jiang, L.; Chen, J.; Li, Y.; Guo, W.; Hu, P.; Liu, Y. Growth and Etching of Monolayer Hexagonal Boron Nitride. Adv. Mater. 2015, 27, 4858–4864. Rong, Y.; He, K.; Pacios, M.; Robertson, A. W.; Bhaskaran, H.; Warner, J. H. Controlled Preferential Oxidation of Grain Boundaries in Monolayer Tungsten Disulfide for Direct Optical Imaging. ACS Nano, 2015, 9, 3695–3703. Stehle, Y.; Sang, X.; Unocic, R.; Voylov, D.; Jackson, R.; Smirnov, S.; Vlassiouk, I., Anisotropic etching of hexagonal boron nitride and graphene: question of edge terminations Nano letters, 2017, 17 (12), 7306-7314