Lateral size selection of liquid exfoliated hexagonal boron nitride nanosheets

Hexagonal boron nitride (h-BN) is of great importance in imaging, thermal and quantum applications in the mid-infrared regions (most of which are size related) for its natural hyperbolic properties. Liquid exfoliation is a promising production approach, however it is limited by the wide range of nanosheet length and thickness. Here we demonstrate a simple and effective method to sort the exfoliated nanosheets according to their lateral sizes. The process uses a combination of low-rate and high-rate configurations to separate the lateral lengths ranging from 1 to 3 μm. In contrast to Raman spectroscopy, infrared results exhibit intensive dependence on the nanosheet length, where the E(1u) phonon frequency and intensity ratio of E(1u) to A(2u) modes are significantly sensitive to the nanosheet length owing to the large anisotropy between the in-plane and out-of-plane axes.