Anomalous Pressure Characteristics of Defects in Hexagonal Boron Nitride Flakes

Xue, Yongzhou; Hui, Wang; Tan, Qinghai; Zhang, Jun; Yu, Tongjun; Ding, Kan; Jiang, Desheng; Dou, Xiuming; Shi, Junjie; Sun, Bo

doi:10.1021/acsnano.8b02970

Cited by 60 publications

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References 49 publications

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“…These emitters have matched PL-CL spectra but large strain variations among them. The observed spectral tunability (121 meV) between this class of emitters can be due to strain, consistent with previous reports 10, 33 and our first principle modeling (see SI S10). We note that emitter E 10 at 554 nm could be part of this same class, even though the strain variation is not more than 1.5% compared to E 6 ; similar emitters can be seen in Fig.…”

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Revealing multiple classes of stable quantum emitters in hexagonal boron nitride with correlated optical and electron microscopy

et al. 2020

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Single photon emitters (SPEs) in solids have emerged as promising candidates for quantum photonic sensing, 1-3 communications, 4, 5 and computing. 6, 7 Defects in hexagonal boron nitride (hBN) exhibit high-brightness, room-temperature quantum emission, 8-10 but their large spectral variability and unknown local structure significantly challenge their technological utility. Here, we directly correlate hBN quantum emission with the material's local strain using a combination of photoluminescence (PL), cathodoluminescence (CL) and nanobeam electron diffraction. Across 40 emitters and 15 samples, we observe zero phonon lines (ZPLs) in PL and CL ranging from 540-720 nm. CL mapping reveals that multiple defects and distinct defect species located within an optically-diffraction-limited region can each contribute to the observed PL spectra. Local strain maps indicate that strain is not required to activate the emitters and is not solely responsible for the observed ZPL spectral range. Instead, four distinct defect classes are responsible for the observed emission range. One defect class has ZPLs near 615 nm with predominantly matched CL-PL responses; it is not a straintuned version of another defect class with ZPL emission centered at 580 nm. A third defect class at 650 nm has low visible-frequency CL emission; and a fourth defect species centered at 705 nm has a small, ∼10 nm shift between its CL and PL peaks. All studied defects are stable upon both electron and optical irradiation. Our results provide an important foundation for atomic-scale optical characterization of color centers, as well as a foundation for engineering defects with precise emission properties. 1 arXiv:1901.05952v2 [cond-mat.mtrl-sci]

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“…13 and Ref. 10,33). More examples of such Type-iii emitters in panel (c) also show predominantly shifted spectral responses between their PL and CL ZPLs.…”

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confidence: 90%

Revealing multiple classes of stable quantum emitters in hexagonal boron nitride with correlated optical and electron microscopy

et al. 2020

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“…Initial reports on tuning of hBN emitters employed voltage‐controlled Stark shift devices and hydrostatic pressure. [ 11 ] Strain‐based tuning of hBN defects has also been investigated using either the application of surface acoustic waves [ 12 ] or mechanical deflection of solid beams that translated vertical displacements to primarily horizontal strain tensors. [ 13 ] However, contribution from both vertical and horizontal strain components in previous studies has precluded direct analysis of the in‐plane response to strain, which is especially critical for 2D materials.…”

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confidence: 99%

Strain‐Induced Modification of the Optical Characteristics of Quantum Emitters in Hexagonal Boron Nitride

et al. 2020

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favorable quantum efficiencies. [8] However, the emitters have been shown to be susceptible to environmental influences, which lead to extreme inhomogeneity in their emission properties, [9] including a broad, continuous spectral range of zero phonon lines spanning from the deep ultraviolet to the near infrared. [10] Consequently, reliable tuning methods for controlling the emission properties are paramount for their implementation in quantum photonic applications.Initial reports on tuning of hBN emitters employed voltage-controlled Stark shift devices and hydrostatic pressure. [11] Strainbased tuning of hBN defects has also been investigated using either the application of surface acoustic waves [12] or mechanical deflection of solid beams that translated vertical displacements to primarily horizontal strain tensors. [13] However, contribution from both vertical and horizontal strain components in previous studies has precluded direct analysis of the in-plane response to strain, which is especially critical for 2D materials. In this work, we employ high degrees of tensile strain to tune the emission of hBN SPEs and achieve record tuning magnitudes for a layered material of up to 20 nm (65 meV). Unlike all previous reports, we take advantage of large-area (approximately few square millimeters) ultrathin hBN films (≈10 nm) that host a variety of SPEs. [14] These samples are amenable to the direct application of tensile strain (as is detailed below), and we report both red and blue spectral shifts, relating our results to modifications of the defect energy level manifold and corresponding coupling to the bulk phonon bath. We demonstrate a rotation of the optical dipole in select SPEs, suggesting the presence of a second excited state. A theoretical model to describe strain tuning the emission frequency of SPEs in hBN is fully derived and further expanded to suggest that dipole rotation occurs via the influence of this additional energy level. The ability to tune emission frequency and additional photophysical characteristics of emitters offers a promising route to tailor lightmatter interactions in these systems. [15] Strain experiments were performed on hBN films grown by chemical vapor deposition (CVD) on a copper foil to a thickness of ≈7 nm. [14a] Additional characterization and properties of the hBN films can be found elsewhere. [14a] The films were transferred from the copper foil using a polymer-assisted (poly(methyl methacrylate) (PMMA) wet-transfer process to a poly(dimethylsiloxane) (PDMS) slab of 2.7 cm in length and ≈200 µm thick (cf. Experimental Section). The hBN/PDMS slab was secured in a mechanical straining device and mounted for optical characterization via confocal microscopy, as shown in Figure 1a. The PDMS slab was subject to varying degrees of Quantum emitters in hexagonal boron nitride (hBN) are promising building blocks for the realization of integrated quantum photonic systems. However, their spectral inhomogeneity currently limits their potential applications. Here, tensile strain is app...

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“…We further argue that the observed pressure responses of PL and Raman cannot be explained by Br vacancies. The effect of hydrostatic pressure on point-defect states or luminescent centers has been investigated in many semiconductors 51,52,53,54,55,56 . The consensus is that localized states such as Br vacancies are very stable under hydrostatic pressure, especially if they are already deep level states.…”

Section: The Observation Of Raman Difference and Identification Of Csmentioning

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Revealing the Origin of Luminescence Center in 0D Cs₄PbBr₆ Perovskite

et al. 2019

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Zero dimensional perovskite Cs4PbBr6 has attracted considerable attention recently not only because of its highly efficient green photoluminescence (PL), but also its two highly debated opposing mechanisms of the luminescence: embedded CsPbBr3 nanocrystals versus intrinsic Br vacancy states. After a brief discussion on the root cause of the controversy, we provide sensitive but noninvasive methods that can not only directly correlate luminescence with the underlying structure, but also distinguish point defects from embedded nanostructures. We first synthesized both emissive and non-emissive Cs4PbBr6 crystals, obtained the complete Raman spectrum of Cs4PbBr6 and assigned all Raman bands based on density functional theory simulations. We then used correlated Raman-PL as a passive structure-property method to identify the difference between emissive and non-emissive Cs4PbBr6 crystals and revealed the existence of CsPbBr3 nanocrystals in emissive Cs4PbBr6. We finally employed a diamond anvil cell to probe the response of luminescence centers to hydrostatic pressure. The observations of fast red-shifting, diminishing and eventual disappearance of both green emission and Raman below Cs4PbBr6 phase transition pressure of ~3 GPa is compatible with CsPbBr3 nanocrystal inclusions as green PL emitters and cannot be explained by Br vacancies. The resolution of this long-lasting controversy paves the way for further device applications of low dimensional perovskites, and our comprehensive optical technique integrating structure-property with dynamic pressure response is generic and can be applied to other emerging optical materials to understand the nature of their luminescent centers.

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Anomalous Pressure Characteristics of Defects in Hexagonal Boron Nitride Flakes

Cited by 60 publications

References 49 publications

Revealing multiple classes of stable quantum emitters in hexagonal boron nitride with correlated optical and electron microscopy

Revealing multiple classes of stable quantum emitters in hexagonal boron nitride with correlated optical and electron microscopy

Strain‐Induced Modification of the Optical Characteristics of Quantum Emitters in Hexagonal Boron Nitride

Revealing the Origin of Luminescence Center in 0D Cs₄PbBr₆ Perovskite

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Anomalous Pressure Characteristics of Defects in Hexagonal Boron Nitride Flakes

Cited by 60 publications

References 49 publications

Revealing multiple classes of stable quantum emitters in hexagonal boron nitride with correlated optical and electron microscopy

Revealing multiple classes of stable quantum emitters in hexagonal boron nitride with correlated optical and electron microscopy

Strain‐Induced Modification of the Optical Characteristics of Quantum Emitters in Hexagonal Boron Nitride

Revealing the Origin of Luminescence Center in 0D Cs4PbBr6 Perovskite

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Revealing the Origin of Luminescence Center in 0D Cs₄PbBr₆ Perovskite