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.