Scanning electron irradiation of hexagonal boron nitride: an efficient procedure for quenching undesired defects emissions monitored by in-situ room temperature cathodoluminescence

Recently, layered materials have become an interesting platform for quantum optics and nanophotonics. Among them, hexagonal boron nitride (hBN) has attracted a widespread interest due to its peculiar defect-related luminescence properties. In particular, the possible generation and tailoring of color centers by particle irradiation are becoming pivotal aspects for next generation quantum optics and photonics. In this work, we use in-situ cathodoluminescence hyperspectral analysis to investigate the effect of fast-scanning, low-voltage electron irradiation on deep level emissions in the ultraviolet (UV) range. The quenching of the UV band (UVB) and changes in the width of the near-band-edge UV luminescence of hBN are investigated as a function of the irradiation time. This quenching is assigned to the electron beam dissociation of in-plane carbon dimer, responsible for such emission, with a concurrent substitutional carbon atoms reconfiguration in donor acceptor pair with a spatial separation in the hBN lattice, that can be optically inactive or can emit in a different optical range, as demonstrated by the intensity decrease of below-bandgap excitation photoluminescence emissions. A possible mechanism of the UVB quenching is also the change of the charge state of the in-plane carbon dimer, that causes a light emission in a different optical range. In addition, ex-situ analyzes reveal an important side effect of prolonged electron irradiation, such as the 40 nm thick deposition of tetrahedral amorphous carbon on top of the hBN flake. This is a clear evolution of the well-established electron beam induced surface contamination due to the adsorption of carbonic species.