Photoluminescence of hexagonal boron nitride: effect of surface oxidation under UV-laser irradiation

TL;DR

This study investigates how UV laser irradiation affects the photoluminescence of hexagonal boron nitride, revealing surface defect dynamics and the role of oxygen in defect healing and surface chemistry changes.

Contribution

It provides new insights into the effects of surface oxidation on UV-induced fluorescence and defect formation in hexagonal boron nitride.

Findings

Surface fluorescence bands are linked to nitrogen vacancies and impurities.

Oxygen adsorption quenches vacancy-related fluorescence and prevents boron deposition.

Vacuum irradiation creates vacancies and elemental boron, while oxygen-rich environments heal defects.

Abstract

We report on the UV laser induced fluorescence of hexagonal boron nitride (h-BN) following nanosecond laser irradiation of the surface under vacuum and in different environments of nitrogen gas and ambient air. The observed fluorescence bands are tentatively ascribed to impurity and mono (VN), or multiple (m-VN with m = 2 or 3) nitrogen vacancies. A structured fluorescence band between 300 nm and 350 nm is assigned to impurity-band transition and its complex lineshape is attributed to phonon replicas. An additional band at 340 nm, assigned to VN vacancies on surface, is observed under vacuum and quenched by adsorbed molecular oxygen. UV-irradiation of h-BN under vacuum results in a broad asymmetric fluorescence at ~400 nm assigned to m-VN vacancies; further irradiation breaks more B-N bonds enriching the surface with elemental boron. However, no boron deposit appears under irradiation of samples in ambient atmosphere. This effect is explained by oxygen healing of radiation-induced surface defects. Formation of the oxide layer prevents B-N dissociation and preserves the bulk sample stoichiometry.