Monolayer Boron Nitride: Hyperspectral Imaging in the Deep Ultraviolet

Area of Science:

• Materials Science
• Optics
• Condensed Matter Physics

Background:

• Two-dimensional (2D) materials and heterostructures are extensively researched for their optical properties.
• Hexagonal boron nitride (hBN), despite its prevalence, has been underexplored in its thinnest forms due to its ultrawide bandgap and deep-ultraviolet microscopy challenges.

Purpose of the Study:

• To investigate the optical response and luminescence properties of exfoliated few-layer and monolayer hexagonal boron nitride (hBN).
• To explore the potential of deep-ultraviolet hyperspectral imaging for characterizing hBN.

Main Methods:

• Hyperspectral imaging was performed at deep-ultraviolet wavelengths (around 200 nm) at low temperatures.
• Exfoliated flakes of hexagonal boron nitride (hBN) with thicknesses ranging from one to few layers were analyzed.

Main Results:

• Direct-gap emission was observed in monolayer hexagonal boron nitride (hBN) at approximately 6.1 eV.
• Photoluminescence signals were found to be intense in few-layer hBN, unlike transition metal dichalcogenides.
• Near-unity radiative efficiency was identified in indirect-gap multilayer hBN.

Conclusions:

• This study demonstrates the feasibility of deep-ultraviolet hyperspectral imaging for characterizing ultrathin hBN.
• The findings reveal distinct luminescence behaviors in monolayer and multilayer hBN, highlighting the importance of layer number and band structure on optical properties.