Substrate-Induced Modulation of Quantum Emitter Properties in 2D Hexagonal Boron Nitride: Implications for Defect-Based Single Photon Sources in 2D Layers

Abstract

Quantum emitters (QEs) based on deep-level defects in hexagonal boron nitride (hBN) layers are promising alternatives to other qubit-candidates in three-dimensional wide bandgap semiconductors. The two-dimensional (2D) form factor of hBN allows the possibility of near-deterministic placement of quantum emitters and an ease of property-tuning via different means, such as application of strain. However, the 2D nature of hBN also results in a unique set of challenges, including a sensitivity of the QEs to their environment that can influence their different properties, such as their emission frequencies and brightness. In particular, although observed experimentally, theoretical works thus far have ignored substrate-induced modulation of hBN's QE properties. As a result, to date, the magnitude of substrate effects and the underlying mechanism(s) involved in the modulation of QE properties remain unknown. In our density functional theory-based work, we use silicon dioxide as a prototype substrate to demonstrate that the substrate effects can indeed have a significant impact on ground-and excited-state properties of defects responsible for quantum emission. Our analysis shows large structural distortions at the defect sites due to substrate interactions, resulting in significant changes in quantum emission frequencies. These calculations reveal that accounting for substrate effects is critical to the successful use of hBN in quantum sensing and quantum computing.

Color Centers in Hexagonal Boron Nitride Nanosheet-Based Heterojunctions: Implications for Quantum Emitters and Ultrathin Sensors

“…Second, it is possible that the PL spectrum of V B –1 in hBN can be tuned by environmental screening, including the surrounding hBN layers, adsorbates, substrates, and substrate-induced strain. − Figure c shows the strain effect on the ZPL of V B –1 in hBN obtained by the HSE06 functional, and the relationship between the ZPL energy with strain ε (%) can expressed by 1.7923–0.0830ε, which means that the compressive strain can increase the ZPL energy. The compressive strain effect is equivalent to the pressure dependence of the ZPL energy.…”

“…The most recent experimental and theoretical investigations related to the substrate effects also find that the substrate plays a key role in tuning the PL spectra. − According to a few experimental investigations, compared with dielectric substrates or alumina, a gold substrate reduces the energy range of the color center with a ZPL at ∼2.1 eV in few-layer hBN nanostructures with a lateral size of 50–200 nm, and ozone treatments can reduce the ZPL line width and inhibit background emission . Furthermore, carbon-related defects have different ZPL energies and phonon sidebands in 50 nm and 10-layer hBN films, and DFT calculations with a quantum-embedding approach demonstrate that the screening of density–density Coulomb interactions between the defect orbitals is the dominant dielectric effect of the surrounding hBN layers .…”

“…52 Furthermore, carbon-related defects have different ZPL energies and phonon sidebands in 50 nm and 10-layer hBN films, and DFT calculations with a quantumembedding approach demonstrate that the screening of density−density Coulomb interactions between the defect orbitals is the dominant dielectric effect of the surrounding hBN layers. 53 The other DFT calculations with the PBE functional show that the SiO 2 substrate can increase the ZPL of the V N N B color center by 0.22 eV, due to the interaction between the V N N B defect and hydrogen atom of the passivated SiO 2 , which is represented by a seven-layer β-cristobalite (111) slab, 54 but the real SiO 2 substrate is amorphous (Figure 1). Therefore, the screening effects of the SiO 2 substrate on vacancy-related and carbon-related color centers in hBN are still elusive, and the more reasonable atomic structure of the SiO 2 substrate and advanced computational method with many-body effects should be developed in the future.…”

Site-Specific Integration of Hexagonal Boron Nitride Quantum Emitters on 2D DNA Origami Nanopores

“…Opto-structural characterization through AFM imaging and single-molecule fluorescence microscopy confirms the site-specific integration of these solid-state optical probes with structural DNA molecules. The further modulation of QEs can be achieved by changing the pH of the buffer, the buffer composition (e.g., organic solvent), and the substrate of the sample . This scalable generation of QE-functionalized nanopores can be implemented for single-molecule biosensing and sequencing schemes based on high-parallel optical readouts.…”

“…The further modulation of QEs can be achieved by changing the pH of the buffer, 58 the buffer composition (e.g., organic solvent), 25 and the substrate of the sample. 59 This scalable generation of QE-functionalized nanopores can be implemented for single-molecule biosensing and sequencing schemes based on high-parallel optical readouts. Multi-color hBN NPs offer the potential for multiplexed detection by exciting nanopores with multiple laser wavelengths without increasing the number of integrated probes.…”