Light emission properties of mechanical exfoliation induced extended defects in hexagonal boron nitride flakes

Abstract

Recently hBN has become an interesting platform for quantum optics due to the peculiar defect-related luminescence properties. Concomitantly, hBN was established as the ideal insulating support for realizing 2D materials device, where, on the contrary, defects can affect the device performance. In this work, we study the light emission properties of hBN flakes obtained by mechanical exfoliation with particular focus on extended defects generated in the process. In particular, we tackle different issues as the light emission in hBN flakes of different thicknesses in the range of hundreds of nanometers, revealing a higher concentration of deep level emission in thinner area of the flake. We recognize the effect of crystal deformation in some areas of the flake with an important blue-shift (130 meV) of the room temperature near band edge emission of hBN and the concurrent presence of a novel emission at 2.36 eV related to the formation of array of dislocations. We studied the light emission properties by means of cathodoluminescence and sub-bandgap excitation photoluminescence of thickness steps with different crystallographic orientations, revealing the presence of different concentration of radiative centers. CL mapping allows to detect buried thickness steps, invisible to the SEM and AFM morphological analysis.

Engineering Multicolor Radiative Centers in hBN Flakes by Varying the Electron Beam Irradiation Parameters

“…The standard FWHM of the hBN, provided by the supplier, is ≈8.2 cm −1 as recently reported [ 54 ]. This agreement indicates that the exfoliation protocol, employed for the preparation of the flake, does not cause any worsening of the material crystallinity [ 55 ]. As expected, the electron irradiation dramatically affects the local crystallinity of hBN.…”

“…In the case of the 15 keV and 20 keV processes, the hBN Raman mode suffers a decrease in intensity and a broadening of the FWHM. In particular, the FWHM increases up to 13.6 cm −1 and 10.2 cm −1 for the 15 keV and 20 keV processes, respectively, indicating a worsening of the crystallinity of hBN [ 55 ]. It is worth mentioning that no previous works, to the best of our knowledge, has correlated the appearance of light emitting color centers by low-energy electron irradiation with the hBN crystallinity in terms of the FWHM of the hBN E 2g peak [ 44 , 45 , 46 ].…”

“…The broad band composed of the 610 nm and the 660 nm peaks appears in areas having a high degree of crystalline disorder, as demonstrated by the broadening or the complete disappearance of the Raman peak. Therefore, the possible attributions to crystalline defects can be multiple, however, an intense double peak at around 610 nm with a shoulder at 660 nm has been localized at thickness step in mechanically exfoliated hBN flakes [ 55 ]. This emission has been recently attributed to substitutional boron atoms [ 60 ] or boron vacancy [ 61 , 62 , 63 ] in hBN grown with chemical vapor deposition.…”

Encapsulation of the Graphene Nanoribbon Precursor 1,2,4-trichlorobenzene in Boron Nitride Nanotubes at Room Temperature

“…In most cases, the Raman spectrum was buried under the photoluminescence background originating from color centers present in defective or strained boron nitride structures. [20] The 355 nm laser excitation generated the weakest photoluminescence (Figure 2). The BNNT sample shows the well known E 2g mode of BNNTs at 1358 cm −1 .…”

Encapsulation of the Graphene Nanoribbon Precursor 1,2,4‐Trichlorobenzene in Boron Nitride Nanotubes at Room Temperature

“…In most cases, the Raman spectrum was buried under the photoluminescence background originating from color centers present in defective or strained boron nitride structures. [ 20 ] The 355 nm laser excitation generated the weakest photoluminescence ( Figure ). The BNNT sample shows the well‐known E 2g mode of BNNTs at 1358 cm −1 .…”