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.
Highlights
Hexagonal boron nitride, a wide-gap layered material,[1] features a marked chemical inertness[2,3] and mechanical robustness.[4]
We hypothesize that protons with kinetic energies of ∼10−30 eV penetrate through Hexagonal boron nitride (hBN) for ∼10 nm and that the formation of wrinkles or bubbles depends on where H2 remains caged
To form thinner bubbles, instead, we irradiated some samples with deuterium ions, which are known to penetrate less through hBN with respect to protons,[43] and we measured bubble thicknesses as thin as ∼0.5 nm; see Supporting Figure S4
Summary
Hexagonal boron nitride (hBN), a wide-gap layered material,[1] features a marked chemical inertness[2,3] and mechanical robustness.[4]. We report on a method to mechanically deform hBN based on the low-energy hydrogen (H) or deuterium (D) ion irradiation of multilayer flakes. Depending on the flake thickness, H/D-ion treatments lead to the formation of nano/micrometric bubbles or wrinkles. Unlike methods based on the deposition of ultrathin films,[30] the proposed technique permits the formation of wrinkles and bubbles with a high density and on flakes with virtually unrestricted size. In. addition, we can control the thickness of the bubbles from a few layers to tens of layers by tuning the energy or changing the isotope of the ion beam. With the support of numerical modeling of the strain distribution, we extract the Grüneisen parameters of hBN and, by performing linearly polarized Raman spectroscopy, its shear deformation potential
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