期刊
ADVANCED SCIENCE
卷 8, 期 2, 页码 -出版社
WILEY
DOI: 10.1002/advs.202002541
关键词
h‐ BN; mechanical properties; molecular dynamics; nanoindentation; phase transitions
资金
- U.S. Department of Energy, Office of Science, Basic Energy Sciences, MSE Division [DE-SC0018924]
- US Army Research Office [W911NF2020116]
- U.S. Department of Energy's National Nuclear Security Administration [DE-NA0003525]
- U.S. Department of Energy (DOE) [DE-SC0018924] Funding Source: U.S. Department of Energy (DOE)
Understanding phase transformations in 2D materials is crucial for advancements in nanotechnology. Experiments and simulations have shown that applying local pressure can induce the formation of a diamond BN phase on h-BN, which remains metastable upon pressure release. Furthermore, the indentation stiffness of h-BN on SiO2 varies with pressure and number of layers, providing insights into the mechanical properties of 2D materials.
Understanding phase transformations in 2D materials can unlock unprecedented developments in nanotechnology, since their unique properties can be dramatically modified by external fields that control the phase change. Here, experiments and simulations are used to investigate the mechanical properties of a 2D diamond boron nitride (BN) phase induced by applying local pressure on atomically thin h-BN on a SiO2 substrate, at room temperature, and without chemical functionalization. Molecular dynamics (MD) simulations show a metastable local rearrangement of the h-BN atoms into diamond crystal clusters when increasing the indentation pressure. Raman spectroscopy experiments confirm the presence of a pressure-induced cubic BN phase, and its metastability upon release of pressure. angstrom-indentation experiments and simulations show that at pressures of 2-4 GPa, the indentation stiffness of monolayer h-BN on SiO2 is the same of bare SiO2, whereas for two- and three-layer-thick h-BN on SiO2 the stiffness increases of up to 50% compared to bare SiO2, and then it decreases when increasing the number of layers. Up to 4 GPa, the reduced strain in the layers closer to the substrate decreases the probability of the sp(2)-to-sp(3) phase transition, explaining the lower stiffness observed in thicker h-BN.
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