Vibrational Properties in Highly Strained Hexagonal Boron Nitride Bubbles

Abstract

Hexagonal boron nitride (hBN) is widely used as a protective layer for few-atom-thick crystals and heterostructures (HSs), and it hosts quantum emitters working up to room temperature. In both instances, strain is expected to play an important role, either as an unavoidable presence in the HS fabrication or as a tool to tune the quantum emitter electronic properties. Addressing the role of strain and exploiting its tuning potentiality require the development of efficient methods to control it and of reliable tools to quantify it. Here we present a technique based on hydrogen irradiation to induce the formation of wrinkles and bubbles in hBN, resulting in remarkably high strains of ∼2%. By combining infrared (IR) near-field scanning optical microscopy and micro-Raman measurements with numerical calculations, we characterize the response to strain for both IR-active and Raman-active modes, revealing the potential of the vibrational properties of hBN as highly sensitive strain probes.

Excitons under strain: light absorption and emission in strained hexagonal boron nitride

“…1. We found a large shift and split of the E 2g mode in agreement with Raman measurements and previous calculations [15,24]. The shift of the phonon frequencies depends on the strain and the phonon mode: under compression, the acoustic modes have their energies lowered; under stretch, the acoustic modes have their energies increased.…”

“…For large strain we found that only one valley contributes to the luminescence spectra, and the spectra return to a shape similar to the equilibrium one but shifted at lower energies. This prediction could be verified by means of luminescence measurements in highly strained h-BN [24].…”

Homogeneous Spatial Distribution of Deuterium Chemisorbed on Free-Standing Graphene

“…One of the most effective spectroscopy techniques for determining the thickness, doping, strain, lattice deformation, and defects in 2D materials is the Raman technique, widely used in graphene [ 25 , 39 , 40 ], in nanoporous graphene [ 19 , 20 ], and other 2D systems [ 41 , 42 , 43 , 44 , 45 , 46 , 47 ].…”

Strain Quantum Sensing with Spin Defects in Hexagonal Boron Nitride

“…The bubbles generated during the transfer process are typically 10 to 40 nm high, and 1 to 4 μm large (see Supporting Information for the atomic force microscopy images of bubbles 1 and 2 in Figure 3a), leading to much smaller strains than in voluntarily created bubbles. 32,33 Note that since the bubbles in Figures 2b and 3a are not necessarily gas-filled, but can be created by particles remaining on the stripline before the h-BN transfer, their form does not necessarily show spherical or radial symmetry (e.g., bubble1, which displays a triangular pyramidal form). Finally, Si ions were used to implant h-BN nanosheets and create VB − centers.…”

“…For the E 2g mode, the frequency shift is linearly dependent on external strains, 36 with a shift rate Δ = −∂ω/∂ε in under in-plane strain ε in = ε xx + ε yy equal to 27.9 cm −1 /%, which has been determined by previous reports analyzing the vibration response of h-BN sheets to external strain. 32 We performed Raman mapping on a 15 μm × 15 μm area (Figure 3a) by recording the Raman spectrum for each 348 nm × 348 nm pixel. Automatic Lorentz fitting was done to determine the peak position for each spectrum, while the Raman frequency probed on flat regions was used to calculate the Raman shift (see Supporting Information).…”