Search

The negatively charged boron vacancy ( V B - ) in hexagonal boron nitride (hBN) is currently considered an intriguing quantum object for testing and developing quantum technologies on two-dimensional van der Waals materials. This article presents results from photoinduced electron spin echo (ESE)-detected electron spin resonance (ESR) and electron–nuclear double-resonance (ENDOR) spectroscopy at the W-band (ν = 94 GHz), focusing on the interactions of the V B - electron spin with the three nearest nitrogen nuclei (14N, I = 1). The lines in the ENDOR spectrum are due to both hyperfine and quadrupole interactions for MS = ± 1 levels and only quadrupole interactions for MS = 0 levels. We show that significant hyperfine interaction with the three nearest nitrogen atoms, despite the high magnetic field, results in a mixing of the hyperfine sublevels for MS = 0. We show that significant hyperfine interaction with the three nearest nitrogen atoms, despite the high magnetic field, results in mixing of the hyperfine sublevels. This mixing shifts the 14N Larmor frequency from its nominal value defined as ν L = g N μ N B / h . This shift observed through ENDOR experiments can be understood using spin-Hamiltonian formalism within the second-order perturbation theory. These findings enhance an understanding of electron–nuclear interactions in hBN. [ABSTRACT FROM AUTHOR]

The distinct spin, optical, and coherence characteristics of solid-state spin defects in semiconductors have positioned them as potential qubits for quantum technologies. Both bulk and two-dimensional materials, with varying structural properties, can serve as crystalline hosts for color centers. In this study, we conduct a comparative analysis of the spin–optical, electron–nuclear, and relaxation properties of nitrogen-bound vacancy defects using electron paramagnetic resonance (EPR) and electron–nuclear double resonance (ENDOR) techniques. We examine key parameters of the spin Hamiltonian for the nitrogen vacancy (NV−) center in 4H-SiC: D = 1.3 GHz, Azz = 1.1 MHz, and CQ = 2.53 MHz, as well as for the boron vacancy (VB−) in hBN: D = 3.6 GHz, Azz = 85 MHz, and CQ = 2.11 MHz, and their dependence on the material matrix. The spin–spin relaxation times T2 (NV− center: 50 µs and VB−: 15 µs) are influenced by the local nuclear environment and spin diffusion while Rabi oscillation damping times depend on crystal size and the spatial distribution of microwave excitation. The ENDOR absorption width varies significantly among color centers due to differences in crystal structures. These findings underscore the importance of selecting an appropriate material platform for developing quantum registers based on high-spin color centers in quantum information systems.

The distinct spin, optical, and coherence characteristics of solid-state spin defects in semiconductors have positioned them as potential qubits for quantum technologies. Both bulk and two-dimensional materials, with varying structural properties, can serve as crystalline hosts for color centers. In this study, we conduct a comparative analysis of the spin–optical, electron–nuclear, and relaxation properties of nitrogen-bound vacancy defects using electron paramagnetic resonance (EPR) and electron–nuclear double resonance (ENDOR) techniques. We examine key parameters of the spin Hamiltonian for the nitrogen vacancy ( N V − ) center in 4H-SiC: D = 1.3 GHz, Azz = 1.1 MHz, and CQ = 2.53 MHz, as well as for the boron vacancy ( V B − ) in hBN: D = 3.6 GHz, Azz = 85 MHz, and CQ = 2.11 MHz, and their dependence on the material matrix. The spin–spin relaxation times T2 ( N V − center: 50 µs and V B − : 15 µs) are influenced by the local nuclear environment and spin diffusion while Rabi oscillation damping times depend on crystal size and the spatial distribution of microwave excitation. The ENDOR absorption width varies significantly among color centers due to differences in crystal structures. These findings underscore the importance of selecting an appropriate material platform for developing quantum registers based on high-spin color centers in quantum information systems. [ABSTRACT FROM AUTHOR]

Spin defects in hexagonal boron nitride (hBN) are emerging as promising platforms for quantum sensing applications. In particular, the negatively charged boron vacancy ( V B - ) centers have been engineered in bulk hBN and few-layer hBN flakes, and employed for sensing. Here, we investigate the engineering of V B - spin defects in boron nitride nanotubes (BNNTs). The generated spin defects are distributed along and around the BNNTs. Moreover, in contrast to hBN flakes, the spins in BNNTs exhibit a directional response relative to the direction of a surrounding magnetic field, which is consistent with the tubular geometry. The unique geometry of BNNTs allows for a more controlled and predictable placement of spin defects compared to bulk hBN, paving the way for innovative sensing applications with high spatial resolution and optomechanical studies of spin defects in hBN.

Designing atomically defective adsorbents with high specific surface area has emerged as a promising approach to improve sorption properties. Herein, hierarchical porous boron nitride nanosheets with boron vacancies (Bv-BNNSs) were in-situ synthesized via a one-step ZnCl 2 -assisted strategy. Being benefitted from the dual-functional template of zinc salt, highly-active boron vacancies and abundant hierarchical pores were simultaneously generated in the Bv-BNNSs framework. By employing the boron vacancies engineering strategy, the morphological and electronic structures were controllably tuned. Meanwhile, the specific surface area was improved to as high as 1104 m2/g. Owning to the abundance of accessible surface active-sites, the sorption capacity to antibiotic tetracycline (TC) on Bv-BNNSs was boosted by 38% compared to the pristine boron nitride nanosheets (BNNSs). Detailed fitting results showed that TC sorption on Bv-BNNSs obeyed the pseudo-second order kinetic equation and the Freundlich isotherm model. The pi − pi interaction with a multi-layered stacking form was proposed as the dominated sorption mechanism. Furthermore, DFT calculations verified that the interaction energy between Bv-BNNSs and TC was enhanced. The high activity, excellent selectivity, and remarkable durability of the Bv-BNNSs nanomaterial suggest the great potential in practical wastewater treatment. [ABSTRACT FROM AUTHOR]

Dielectric breakdown in 2D insulating films for future logic device technology is not well understood yet, in contrast to the extensive insight we have in the breakdown of bulk dielectric films, such as HfO2 and SiO2. In this letter, we investigate the stochastic nature of breakdown (BD) in hexagonal boron nitride (h-BN) films using ramp voltage stress and examine the BD trends as a function of stress polarity, area, and temperature. We present evidence that points to a non-Weibull distribution for h-BN BD and use the multi-scale physics-based simulations to extract the energetics of the defects that are precursors to BD, which happens to be boron vacancies. [ABSTRACT FROM AUTHOR]

Optically active point defects in semiconductors have received great attention in the field of solid-state quantum technologies. Hexagonal boron nitride, with an ultra-wide band gapEg= 6 eV, containing a negatively charged boron vacancy (VB-) with unique spin, optical, and coherent properties presents a new two-dimensional platform for the implementation of quantum technologies. This work establishes the value ofVB-spin polarization under optical pumping with λ ext = 532 nm laser using high-frequency ( ν mw = 94 GHz) electron paramagnetic resonance (EPR) spectroscopy. In optimal conditions polarization was found to be P ≈ 38.4%. Our study reveals that Rabi oscillations induced on polarized spin states persist for up to 30-40 μ N. These results have fundamental importance for understanding the spin properties of boron vacancy.C q = 180 kHz related to nuclear quadrupole moment of 14 N. These results have fundamental importance for understanding the spin properties of boron vacancy., (© 2024 IOP Publishing Ltd.)

We compare and contrast the physisorption behavior of imidazolium and butyltrimethylammonium based ionic liquids (ILs) on mono-vacant nitrogen and boron defective hexagonal boron nitride nanoflakes (h-BNNF) using M06-2X/cc-pVDZ level of theory. The presence of defects on the nanoflakes results in an increase in IL binding energy by ~ 1–27 kcal/mol partly due to the lowering of the energy band in the defective nanoflakes. Imidazolium based ILs adsorb energetically more favorably on h-BNNF-V B than on h-BNNF-V N while butyltrimethylammonium based ILs prefer to adsorb on h-BNNF-V N . Upon adsorption of imidazolium ILs on the nanoflakes, an increase in both HOMO and LUMO orbital energies is observed - resulting in net increase in HOMO-LUMO energy gap (E g ) value and chemical hardness (η). On the other hand, the adsorption of butyltrimethylammonium ILs leads to an increase in HOMO energy and a decrease in LUMO energy of the h-BNNF-V B nanoflake thereby lowering the E g and η values of defective nanoflakes. The absorption spectra of mono-vacant surfaces undergo shifts upon IL adsorption. The first absorption peak at 296 nm is red-shifted while the second absorption peak at 421 nm is blue-shifted. The magnitude of the first absorption peak for the h-BNNF-V B …IL complexes follow the order of h-BNNF-V B …[Btma][Y] > h-BNNF-V B… [Bmim][Y] (Y = BF 4 − , PF 6 − , Tf 2 N − ) consistent with greater binding energies and energy gaps of imidazolium based complexes in comparison to their butyltrimethylammonium counterparts. Generally, it is concluded that the modulation of opto-electronic properties of IL-functionalized h-BNNF surfaces is largely provided by the defects and to a lesser extent by the choice of IL. [ABSTRACT FROM AUTHOR]

Detecting magnetic noise from small quantities of paramagnetic spins is a powerful capability for chemical, biochemical, and medical analysis. Quantum sensors based on optically addressable spin defects in bulk semiconductors are typically employed for such purposes, but the 3D crystal structure of the sensor inhibits sensitivity by limiting the proximity of the defects to the target spins. Here we demonstrate the detection of paramagnetic spins using spin defects hosted in hexagonal boron nitride (hBN), a van der Waals material that can be exfoliated into the 2D regime. We first create negatively charged boron vacancy (V B - ) defects in a powder of ultrathin hBN nanoflakes (<10 atomic monolayers thick on average) and measure the longitudinal spin relaxation time ( T 1 ) of this system. We then decorate the dry hBN nanopowder with paramagnetic Gd 3+ ions and observe a clear T 1 quenching under ambient conditions, consistent with the added magnetic noise. Finally, we demonstrate the possibility of performing spin measurements, including T 1 relaxometry using solution-suspended hBN nanopowder. Our results highlight the potential and versatility of the hBN quantum sensor for a range of sensing applications and make steps toward the realization of a truly 2D, ultrasensitive quantum sensor.

Negatively charged boron vacancies (V B ) in hexagonal boron nitride (hBN) have recently gained interest as spin defects for quantum information processing and quantum sensing by a layered material. However, the boron vacancy can exist in a number of charge states in the hBN lattice, but only the -1 state has spin-dependent photoluminescence and acts as a spin-photon interface. Here, we investigate the charge state switching of V - ) in hexagonal boron nitride (hBN) have recently gained interest as spin defects for quantum information processing and quantum sensing by a layered material. However, the boron vacancy can exist in a number of charge states in the hBN lattice, but only the -1 state has spin-dependent photoluminescence and acts as a spin-photon interface. Here, we investigate the charge state switching of V B defects under laser and electron beam excitation. We demonstrate deterministic, reversible switching between the -1 and 0 states (V B - ⇌ V B 0 + e - ), occurring at rates controlled by excess electrons or holes injected into hBN by a layered heterostructure device. Our work provides a means to monitor and manipulate the V B charge state, and to stabilize the -1 state which is a prerequisite for spin manipulation and optical readout of the defect.

Abstract: First principle calculations for a hexagonal (graphene-like) boron nitride (g-BN) monolayer sheet in the presence of a boron-atom vacancy show promising properties for capture and activation of carbon dioxide. CO2 is found to decompose to produce an oxygen molecule via an intermediate chemisorption state on the defect g-BN sheet. The three stationary states and two transition states in the reaction pathway are confirmed by minimum energy pathway search and frequency analysis. The values computed for the two energy barriers involved in this catalytic reaction after enthalpy correction indicate that the catalytic reaction should proceed readily at room temperature. [Copyright &y& Elsevier]

Negatively charged boron vacancies ( V B - ) in hexagonal boron nitride (hBN) exhibit a broad emission spectrum due to strong electron-phonon coupling and Jahn-Teller mixing of electronic states. As such, the direct measurement of the zero-phonon line (ZPL) of V B - has remained elusive. Here, we measure the room-temperature ZPL wavelength to be 773 ± 2 nm by coupling the hBN layer to the high- Q nanobeam cavity. As the wavelength of cavity mode is tuned, we observe a pronounced intensity resonance, indicating the coupling to V B - . Our observations are consistent with the spatial redistribution of V B - emission. Spatially resolved measurements show a clear Purcell effect maximum at the midpoint of the nanobeam, in accord with the optical field distribution of the cavity mode. Our results are in good agreement with theoretical calculations, opening the way to using V B - as cavity spin-photon interfaces.

First-principles calculations were carried out to calculate the formation energy, migration barrier and electronic properties of a resistive memory model based on hexagonal boron nitride (h-BN) in the presence of an active metal and a boron vacancy (V B) using density functional theory (DFT). Following the benchmark of the exchange correlation functional and the calculated parameters of monolayer h-BN, a model of a multilayer h-BN vertical stack with distribution states of SW-5577 defects was proposed. For four active metal dopants (Ti, Ag, Cu and Ni), a preference towards substitution sites (S1) with the lowest dopant formation energies (DFEs) was identified, which enhanced the formation of adjacent V B , especially for the nearest neighbour. Furthermore, a low concentration of Ti dopant in the closest location to the initial position of the migration path would drastically reduce the migration barrier of the V B between layers. Finally, Ti dopants with two and three V B neighbours in the same layer significantly improved the conductivity and the formation of conducting channels because of the improvement of charge distribution in the resistance model, which was demonstrated by DOS plots, band-decomposed charge density and Bader charge. Our present work can provide theoretical guidance for the rational design and device optimization of h-BN-based RRAM devices. • A multilayer vertical stack with SW-5577 defects was proposed for theoretical calculation of h-BN based RRAM. • A preference towards substitution site (S1) with the lowest DFEs was identified for Ti, Ag, Cu and Ni dopants. • The closest Ti dopant to the initial position would drastically reduce the migration barrier of the V B between layers. • The increase in the number and spatial distribution of V B is beneficial to the surrounding electron localization. [ABSTRACT FROM AUTHOR]

Coherent coupling of defect spins with surrounding nuclei along with the endowment to read out the latter are basic requirements for an application in quantum technologies. We show that negatively charged boron vacancies (V B - ) in hexagonal boron nitride (hBN) meet these prerequisites. We demonstrate Hahn-echo coherence of the V B - spin with a characteristic decay time T coh = 15 μs, close to the theoretically predicted limit of 18 μs for defects in hBN. Elongation of the coherence time up to 36 μs is demonstrated by means of the Carr-Purcell-Meiboom-Gill decoupling technique. Modulation of the Hahn-echo decay is shown to be induced by coherent coupling of the V B - spin with the three nearest 14 N nuclei via a nuclear quadrupole interaction of 2.11 MHz. DFT calculation confirms that the electron-nuclear coupling is confined to the defective layer and stays almost unchanged with a transition from the bulk to the single layer.

[Display omitted] • Thermal NaBH 4 treatment is used to update the surface properties of ɑ-MnO 2. • BV is in situ formed via the wash-away of B dopant during dye elimination process. • BV transforms DO into ROS without extra energy input. • Strong acidity, free Mn3+ site and large pore contribute to adsorptive dye removal. • The treated MnO 2 shows excellent Pb2+ adsorption capacity especially in acid matrix. Oxygen vacancy (OV), one frequently designed structural anion defect, can transport active oxygen species towards multi-phase pollutant oxidation by activating oxygen molecules or chemical oxidants. However, dissolved oxygen (DO), a desirable oxidant source for water organics degradation, is very difficult to be directly utilized by OV-abundant metal oxides without extra heat or light input. To solve this problem, in this study another anion defect, i.e. , boron vacancy (BV), was successfully incorporated into ɑ-MnO 2 via a two-step method, i.e. , thermal NaBH 4 treatment for boron doping followed by in situ wash-away of boron during organic dye elimination process. The NaBH 4 -modified ɑ-MnO 2 exhibited much higher Rhodamine B (RhB) elimination than the original one. BV is capable of transforming DO into 1O 2 , OH and O 2 − radicals at 30 °C and without extra energy input, completely mineralizing RhB into inorganic carbon. Besides, NaBH 4 -induced strong acid sites, free Mn3+ species and large pore size contributed to adsorptive RhB removal. For the original ɑ-MnO 2 , surface lattice oxygen was the key oxidant for dye degradation. Malachite Green, Congo Red, Orange I and Methyl Blue were further tested as target substrates. The NaBH 4 -treated ɑ-MnO 2 presented superiority over the pristine sample in adsorptive Pb2+ removal as well. [ABSTRACT FROM AUTHOR]

W-doped ZrB 2 ceramics were hot-pressed at 1800–2100 °C by using W additive. The effects of W doping on the densification, microstructure, and high temperature strength of ZrB 2 ceramics were investigated. The reaction between ZrB 2 and W resulted in the formation of WB, ZrB and boron vacancies in ZrB 2 -x. The solid solution formed by dissolving WB in ZrB 2 -x has core-shell structure, inhibited the grain growth and densification of ZrB 2 ceramics. (W,Zr)B converted to liquid promoted densification at 2100 °C, and dissolved the oxygen from the surface of ZrB 2 powders. The ZrB 2 ceramics with 3–10 vol% W exhibited fine microstructures and high grain boundary strength. The cleaning boundary produced by WB significantly improved the flexural strength of ZrB 2 ceramics at 25–1600 °C. (Zr,W)B precipitated from vacancy-rich (Zr,W)B 2-x solid solution under tensile stress at 1600 °C. • The solid solution formed by dissolving WB in ZrB 2 -x inhibited the densification of ZrB 2 ceramics. • WB dissolved the oxygen from ZrB 2 powders and markedly improved strength of ZrB 2 ceramics. • (Zr,W)B precipitated from vacancy-rich (Zr,W)B 2-x solid solution under tensile stress at 1600 °C. [ABSTRACT FROM AUTHOR]