Exfoliation of boron nitride nanosheets from ammonia with Density Functional Theory calculations

In recent years, the quest for efficient thermal management materials has become increasingly crucial and pressing to ensure enhanced thermal performance, life cycle, reliability, and safety in modern electronic devices. High quality boron nitride nanosheets (BNNs) represent an ideal platform for this purpose due to their excellent thermally conductivity, electrically insulation, chemical and thermal stabilities, and strong resistance to oxidation even at elevated temperatures. High-quality BNNs with a thinner and larger lateral dimension, and less defects are desired but their efficient production still remains a major challenge. In this work, we examined various experimental conditions for the exfoliation of commercially acquired hexagonal boron nitride into BNNs and showed both experimental and theoretical evidences of efficient exfoliation in the presence of an aqueous ammonia solution under supercritical fluid conditions. Morphology and structure of the resulting BNNs were characterized by powder X-ray diffraction (XRD), field-emission scanning and transmission electron microscopy (SEM and TEM), and FT-IR. Our quantum molecular dynamics simulation further identified critical points for optimizing pressure and temperature to achieve favorable exfoliation conditions. Density Functional Theory calculation also showed that boron site of h-BN is favorable for NH₂ attachment while nitrogen site is favorable for OH attachment at dangling bonds of 2D h-BN.