# Fileset

[kikkawa-et-al-2025-observation-of-boron-vacancy-concentration-in-hexagonal-boron-nitride-at-nanometer-scale.pdf](https://mdr.nims.go.jp/filesets/a0bda6a3-b54b-4797-8d31-ec5566534df4/download)

## Creator

[Jun Kikkawa](https://orcid.org/0000-0003-0659-1844), [Chikara Shinei](https://orcid.org/0000-0003-4926-8641), [Jun Chen](https://orcid.org/0000-0003-4272-2653), Yuta Masuyama, Yuichi Yamazaki, Teruyasu Mizoguchi, [Koji Kimoto](https://orcid.org/0000-0002-3927-0492), [Takashi Taniguchi](https://orcid.org/0000-0002-1467-3105), [Tokuyuki Teraji](https://orcid.org/0000-0002-7731-0547)

## Rights

[Creative Commons BY Attribution 4.0 International](https://creativecommons.org/licenses/by/4.0/)

## Other metadata

[Observation of Boron Vacancy Concentration in Hexagonal Boron Nitride at Nanometer Scale](https://mdr.nims.go.jp/datasets/8e579ef2-edbd-4452-b0e1-e62f814daa8c)

## Fulltext

Observation of Boron Vacancy Concentration in Hexagonal Boron Nitride at Nanometer ScaleObservation of Boron Vacancy Concentration in Hexagonal BoronNitride at Nanometer ScaleJun Kikkawa,* Chikara Shinei, Jun Chen, Yuta Masuyama, Yuichi Yamazaki, Teruyasu Mizoguchi,Koji Kimoto, Takashi Taniguchi, and Tokuyuki TerajiCite This: https://doi.org/10.1021/acs.nanolett.5c02988 Read OnlineACCESS Metrics & More Article Recommendations *sı Supporting InformationABSTRACT: Negatively charged boron vacancy (VB−) ensembles in hexagonalboron nitride (h-BN) have attracted considerable attention as a promisingplatform for quantum sensing. Current challenges include the experimentalvalidation of the spatial distribution and electronic states of optically active VB−and optically inactive neutral boron vacancy (VB0) defects. To address theseissues, we employ electron energy loss spectroscopy (EELS) combined withscanning transmission electron microscopy (STEM) using monochromated 30-keV electrons, effectively reducing background interference. This approachunveils distinct spectral peaks at 2.5 and 1.9 eV, corresponding to VB− and VB0defects, respectively. Furthermore, we achieve nanometer-scale concentrationmapping for VB− and VB0 defects, advancing insights into spin defectconfigurations crucial for optimizing quantum sensor performance.KEYWORDS: hexagonal boron nitride, boron vacancy, electron energy loss spectroscopy, scanning transmission electron microscopy,frist-principles simulationQ uantum sensors hold considerable potential formeasuring a wide range of physical and chemicalproperties, providing exceptional resolution and precision.1,2Ensembles of color centers (i.e., point defects caused byvacancies and impurities) in hexagonal boron nitride (h-BN)are promising platforms for next-generation quantum sensorsas post negatively charged nitrogen-vacancy (NV−) ensemblesin diamond.3,4 h-BN is a two-dimensional material with a widebandgap at ∼ 6 eV,5,6 and has the advantages of easyintegration into quantum devices, high photon extractionefficiency, and photon wavelength diversity.7,8 Negativelycharged boron vacancies (VB−), antisite nitrogen vacancies(NBVN), and carbon-based defects are color centers generatingluminescence at ∼1.5,9−13 ∼2.0,14,15 and ∼4.1 eV,16−20respectively. In particular, the VB− centers exhibit spin-dependent photon emission at room temperature, a desirableproperty for quantum sensing.9−13 The spatial VB− distributionuniformity, VB− concentration, and the distance betweenindividual VB− defects are fundamental properties, in additionto the crystallinity and purity of h-BN, for determining spatialresolution and sensitivity in quantum sensors. Ion or electronirradiation on h-BN generates VB− defects,9−13 and cansimultaneously generate neutral born vacancies (VB0) andother types of defects,21−27 which coexist with intrinsicimpurity-related defects.14−20,28 Direct observations haveshown that electron and He+ ion irradiation preferentiallygenerate VB defects rather than VN defects.25−27 However, thedistribution, concentration, and spacing of VB− and VB0 defectsare as yet not fully understood because of the absence of astandardized measurement method at the nanometer scale,especially for optically inactive VB0. Furthermore, despite thefirst-principles simulations of the electronic structures of VB−and VB0 defects,17,29−31 experimental validation remainsnecessary. Therefore, it is crucial to measure the arrangementand electronic states of VB− and VB0 defects.Electron energy loss spectroscopy (EELS) combined withscanning transmission electron microscopy (STEM) enablesprobing the subgap states of lattice defects and the chemicalbonding states at defect sites.32−35 However, measuring thedetailed EELS spectral structure from point defects in bulkcrystals presents a significant challenge, because of the lowconcentration of point defects (≲ 103 ppm) and the weaknessof EELS signals compared with other intrinsic signals. Threetypes of background intensity can hinder the detection ofEELS signals of defect states. The first is the tail of the zero-loss peak (ZLP, i.e., elastic scattering peak), whose signal canbecome dominant even in several eV region in EELS. A smallerenergy spread of the incident electrons evaluated with fullwidth at half-maximum (fwhm) or more appropriately at 10−nReceived: June 6, 2025Revised: August 19, 2025Accepted: August 19, 2025Letterpubs.acs.org/NanoLett© XXXX American Chemical SocietyAhttps://doi.org/10.1021/acs.nanolett.5c02988Nano Lett. XXXX, XXX, XXX−XXXThis article is licensed under CC-BY 4.0Downloaded via NATL INST FOR MATLS SCIENCE (NIMS) on August 27, 2025 at 01:31:35 (UTC).See https://pubs.acs.org/sharingguidelines for options on how to legitimately share published articles.https://pubs.acs.org/action/doSearch?field1=Contrib&text1="Jun+Kikkawa"&field2=AllField&text2=&publication=&accessType=allContent&Earliest=&ref=pdfhttps://pubs.acs.org/action/doSearch?field1=Contrib&text1="Chikara+Shinei"&field2=AllField&text2=&publication=&accessType=allContent&Earliest=&ref=pdfhttps://pubs.acs.org/action/doSearch?field1=Contrib&text1="Jun+Chen"&field2=AllField&text2=&publication=&accessType=allContent&Earliest=&ref=pdfhttps://pubs.acs.org/action/doSearch?field1=Contrib&text1="Yuta+Masuyama"&field2=AllField&text2=&publication=&accessType=allContent&Earliest=&ref=pdfhttps://pubs.acs.org/action/doSearch?field1=Contrib&text1="Yuichi+Yamazaki"&field2=AllField&text2=&publication=&accessType=allContent&Earliest=&ref=pdfhttps://pubs.acs.org/action/doSearch?field1=Contrib&text1="Teruyasu+Mizoguchi"&field2=AllField&text2=&publication=&accessType=allContent&Earliest=&ref=pdfhttps://pubs.acs.org/action/doSearch?field1=Contrib&text1="Koji+Kimoto"&field2=AllField&text2=&publication=&accessType=allContent&Earliest=&ref=pdfhttps://pubs.acs.org/action/doSearch?field1=Contrib&text1="Koji+Kimoto"&field2=AllField&text2=&publication=&accessType=allContent&Earliest=&ref=pdfhttps://pubs.acs.org/action/doSearch?field1=Contrib&text1="Takashi+Taniguchi"&field2=AllField&text2=&publication=&accessType=allContent&Earliest=&ref=pdfhttps://pubs.acs.org/action/doSearch?field1=Contrib&text1="Tokuyuki+Teraji"&field2=AllField&text2=&publication=&accessType=allContent&Earliest=&ref=pdfhttps://pubs.acs.org/action/showCitFormats?doi=10.1021/acs.nanolett.5c02988&ref=pdfhttps://pubs.acs.org/doi/10.1021/acs.nanolett.5c02988?ref=pdfhttps://pubs.acs.org/doi/10.1021/acs.nanolett.5c02988?goto=articleMetrics&ref=pdfhttps://pubs.acs.org/doi/10.1021/acs.nanolett.5c02988?goto=recommendations&?ref=pdfhttps://pubs.acs.org/doi/10.1021/acs.nanolett.5c02988?goto=supporting-info&ref=pdfhttps://pubs.acs.org/doi/10.1021/acs.nanolett.5c02988?fig=tgr1&ref=pdfpubs.acs.org/NanoLett?ref=pdfhttps://pubs.acs.org?ref=pdfhttps://pubs.acs.org?ref=pdfhttps://doi.org/10.1021/acs.nanolett.5c02988?urlappend=%3Fref%3DPDF&jav=VoR&rel=cite-ashttps://pubs.acs.org/NanoLett?ref=pdfhttps://pubs.acs.org/NanoLett?ref=pdfhttps://acsopenscience.org/researchers/open-access/https://creativecommons.org/licenses/by/4.0/https://creativecommons.org/licenses/by/4.0/https://creativecommons.org/licenses/by/4.0/(n ≥ 1) of the ZLP,36 is required to reduce the contribution ofthe ZLP tail. The second is EELS signals, which can appear ataround several eVs owing to the generation of Cherenkovradiation.37 This radiation can be reduced or ignored bylowering the energy of incident electrons or by using a thinnerspecimen.32,33,38 The third is detector noise. It is veryimportant to reduce readout noise in addition to gain noiseso that weak signals are not buried in their noise.In this study, to measure electronic states of VB− and VB0defects in h-BN by EELS, we use monochromated 30-keVelectrons, reducing the fwhm of the ZLP to 40 meV,39 andsuppressing Cherenkov radiation.32,33,38,40 To detect scatteredelectrons in EELS, we use a charge-coupled-device (CCD)camera with a high-sensitivity scintillator optimized for 30-keVelectrons,39 and the readout noise reduction scheme.41,42 EELSin combination with first-principles simulations revealed a highpeak at 2.5 eV with enhanced intensity appearing at theshoulder position of 1.9 eV, which are respectively assigned tosignals from VB− and VB0 defects. Furthermore, we obtain theconcentration maps for VB− and VB0 defects at the nanometerscale.h-BN single crystals were grown using a temperaturegradient method at a high pressure,43 and their flakes withthicknesses of 30−200 nm were prepared using a tape-peelingmethod (details of the specimen preparation and experimentalmethods are described in Supporting Information). The h-BNflakes were dispersed on a holey carbon-film-supported coppergrid and then irradiated with a 40-keV nitrogen ion (N2+) beamalong the c-axis at a total dose of 1 × 1015 cm−2 at roomtemperature,11 as shown in Figure 1a. Figure 1b shows thephotoluminescence (PL) spectra of the pristine and irradiatedh-BN flakes at room temperature with an incident photonenergy of 2.33 eV. PL occurs with a peak maximum at 1.53 eV(=810 nm) only after the irradiation, indicating the formationof optically active VB− defects, as observed in previousstudies.9−13 Figure 1c shows the optically detected magneticresonance (ODMR) spectrum of the irradiated h-BN flake.ODMR occurs at a microwave frequency of ∼3.5 GHz afterthe irradiation, corresponding to a ground state zero-fieldsplitting between spin states ms = 0 and ms = ±1 for VB− in h-BN.4,9 Figure 1d displays the EELS spectra of the pristine andirradiated h-BN flakes below 6.2 eV. Two characteristic EELSintensities appear in the subgap region only for the irradiatedh-BN flake as indicated by the arrows (Figure 1d). One is anasymmetric signal centered at ∼2.5 eV and the other is acontinuous intensity distribution ranging from 3.8 to 5.9 eV.These EELS intensities reflect the density of states (DOS) ofthe defect levels introduced by the irradiation. The asymmetric2.5 eV signal was more clearly observed in flakes thicker than∼100 nm. In the range of 6−30 eV, there is no markeddifference in EELS profiles between the pristine and irradiatedh-BN flakes (Figure S1a). In addition, no marked changes wereobserved at the N K edge after the irradiation; only a slightlyasymmetric broadening of the peak at 191.8 eV was detected atthe B K edge (Figures S1b and S1c), suggesting the formationof nitrogen vacancies (see details in Supporting Informa-tion).44 We also observed cathodoluminescence (CL) atapproximately 4.1 eV (Figure S2), which occurred dependingon the measurement position for both pristine and irradiatedflakes. This indicates the presence of carbon-related defects inthe original h-BN crystal.16−20 As the energy levels associatedwith these defects lie outside the energy range of interest (i.e.,1.5−3.5 eV), it is appropriate to focus exclusively on the VB−and VB0 defects hereafter (see details in SupportingInformation).To identify fine structures of the 2.5 eV asymmetric signal inFigure 1d, we conducted EELS with a high energy resolution(i.e., fwhm of the ZLP, 40 meV). By scanning the electronprobe in steps of 3.6 nm in 143 nm-square areas in theirradiated h-BN flake, we obtained 1600 single EELS spectra.By summing the single spectra and subtracting the backgroundintensity mainly due to the ZLP tail with a power-low fit(Figure S3), we found that the asymmetric 2.5 eV signal iscomposed of four characteristic intensities, as shown in Figure1e. The high intensity peak P2 locates at 2.5 eV, overlappingwith relatively low intensity peaks labeled P1 at 1.9 eV, P3 at2.9 eV, and P4 at 3.45 eV. The appearance of the intense signalat 2.5 eV in EELS is consistent with the maximum absorptionat ∼2.6 eV in PL excitation measurements for VB− defects in h-BN.10 Note that the asymmetric 2.5 eV signal is weaker thanintrinsic bulk signals. For instance, the EELS intensity of the2.5 eV signal (i.e., integrated intensity in the range of 1.34−3.34 eV) is approximately 10−1 of that of optical phonons (i.e.,integrated intensity in the range of 0.13−0.28 eV), despite the13-fold difference in integration range (Figure S4).To understand the fine structures of the 2.5 eV asymmetricsignal in Figure 1e, we conducted first-principles simulations(details of the calculation methods are described in SupportingInformation). Figures 2a−2c show the electronic DOS valuesof h-BN crystals without defects, with a VB− defect, and with aVB0 defect, respectively (see Figure S5 for a wider energyrange). Occupied and unoccupied states are filled and blank,while up- and down-spin states are displayed in the upper andlower side, respectively. The three DOS diagrams are alignedwith the 2s levels (Figure S5). The positions of VBM andCBM in Figures 2b and 2c denote those for the perfect crystalFigure 1. (a) Illustration of N2+ ion irradiation of h-BN flake. (b) PLspectra of pristine and irradiated h-BN flakes. (c) ODMR spectrum ofirradiated h-BN flake. (d) EELS spectra of pristine and irradiated h-BN flakes. The inset optical microscopy and annular dark-field STEMimages in (b) and (d) respectively show the h-BN flakes on a holey a-C film. (e) EELS spectrum after subtraction of the ZLP tail for theirradiated h-BN flake in (b), revealing four characteristic intensitypeaks labeled P1−P4. Row data (solid circle) and smoothed profile(solid line).Nano Letters pubs.acs.org/NanoLett Letterhttps://doi.org/10.1021/acs.nanolett.5c02988Nano Lett. XXXX, XXX, XXX−XXXBhttps://pubs.acs.org/doi/suppl/10.1021/acs.nanolett.5c02988/suppl_file/nl5c02988_si_001.pdfhttps://pubs.acs.org/doi/suppl/10.1021/acs.nanolett.5c02988/suppl_file/nl5c02988_si_001.pdfhttps://pubs.acs.org/doi/suppl/10.1021/acs.nanolett.5c02988/suppl_file/nl5c02988_si_001.pdfhttps://pubs.acs.org/doi/suppl/10.1021/acs.nanolett.5c02988/suppl_file/nl5c02988_si_001.pdfhttps://pubs.acs.org/doi/suppl/10.1021/acs.nanolett.5c02988/suppl_file/nl5c02988_si_001.pdfhttps://pubs.acs.org/doi/suppl/10.1021/acs.nanolett.5c02988/suppl_file/nl5c02988_si_001.pdfhttps://pubs.acs.org/doi/suppl/10.1021/acs.nanolett.5c02988/suppl_file/nl5c02988_si_001.pdfhttps://pubs.acs.org/doi/suppl/10.1021/acs.nanolett.5c02988/suppl_file/nl5c02988_si_001.pdfhttps://pubs.acs.org/doi/suppl/10.1021/acs.nanolett.5c02988/suppl_file/nl5c02988_si_001.pdfhttps://pubs.acs.org/doi/suppl/10.1021/acs.nanolett.5c02988/suppl_file/nl5c02988_si_001.pdfhttps://pubs.acs.org/doi/suppl/10.1021/acs.nanolett.5c02988/suppl_file/nl5c02988_si_001.pdfhttps://pubs.acs.org/doi/suppl/10.1021/acs.nanolett.5c02988/suppl_file/nl5c02988_si_001.pdfhttps://pubs.acs.org/doi/suppl/10.1021/acs.nanolett.5c02988/suppl_file/nl5c02988_si_001.pdfhttps://pubs.acs.org/doi/suppl/10.1021/acs.nanolett.5c02988/suppl_file/nl5c02988_si_001.pdfhttps://pubs.acs.org/doi/10.1021/acs.nanolett.5c02988?fig=fig1&ref=pdfhttps://pubs.acs.org/doi/10.1021/acs.nanolett.5c02988?fig=fig1&ref=pdfhttps://pubs.acs.org/doi/10.1021/acs.nanolett.5c02988?fig=fig1&ref=pdfhttps://pubs.acs.org/doi/10.1021/acs.nanolett.5c02988?fig=fig1&ref=pdfpubs.acs.org/NanoLett?ref=pdfhttps://doi.org/10.1021/acs.nanolett.5c02988?urlappend=%3Fref%3DPDF&jav=VoR&rel=cite-as(Figure 2a). As shown in Figures 2b and 2c, subgap statesbetween VBM and CBM differ largely depending on whetherthe charge of VB is − 1 or zero. The diagonal components ofthe dielectric tensor perpendicular and parallel to the c-axis arewritten as εxx = ε1,xx + iε2,xx(=εyy) and εzz = ε1,zz + iε2,zz,respectively. Figures 2e−2g show the imaginary parts ε2,xx andε2,zz for the perfect crystal, the VB− defect, and the VB0 defect,respectively (see Figure S6 for a wider energy range and realparts). The imaginary parts represent absorption. Note thatε2,xx for the VB− defect is intense with fine structures denoted asA−F in the 2.0−4.0 eV range (Figure 2f). This indicates thatelectronic excitations at 2.0−4.0 eV in the ab-plane directionare dominant compared with those along the c-axis. For the VB0defect, ε2,xx has a relatively low intensity and fine structuresdenoted as G−J in the 0.5−2.5 eV range (Figure 2g), whereasthere is no characteristic intensity in ε2,xx and ε2,zz for theperfect crystal because of the absence of subgap states (Figure2e). The A−F peaks in Figure 2f and the G−J peaks in Figure2g originate from the electron excitations between subgapstates, A−F in Figure 2b and G−J in Figure 2c. The lossfunction L when the electron incident direction is parallel tothe c-axis and the convergence angle α = 0 is calculated as45ÄÇÅÅÅÅÅÅÅÅÅÅÅikjjjjjy{zzzzzÉÖÑÑÑÑÑÑÑÑÑÑÑ= +L Im12ln 1zzzzxx E22θE = ΔE/2E0 in nonrelativistic form, where E0 (=30 keV) andΔE respectively represent the incident energy and energy lossof the primary electron: θE = 4.2 × 10−2 mrad for ΔE = 2.5 eV.Considering that the electron probe used in STEM−EELS hasα (≠0), β is approximately replaced with β* = +2 2 tocalculate L (details are described in Supporting Information).Figures 2h−2j show L for the perfect crystal, the VB− defect, andthe VB0 defect, respectively. The profile of L mainly reflects thatof ε2,xx. The A′−F′ peaks in Figure 2i and the G′−J′ peaks inFigure 2j reflect the A−F peaks in Figure 2f and the G−J peaksin Figure 2g, respectively. This is because ε2,xx in L becomesdominant when θE ≪ β and also because ε2,zz is originallysmall. Reflecting the intensities of ε2,xx in L for the VB− and VB0defects (Figures 2f and 2g), the intensity of L for the VB− defect[L (VB−)] in the range including the A′−F′ peaks (Figure 2i) ishigher than that L for the VB0 defect [L (VB0)] in the rangeincluding the G′−J′ peaks (Figure 2j). Figures 2i and 2j alsosuggest that the EELS intensity in the 4−6 eV range in Figure1d originates from other types of defects and partly from theVB− defects. Figure 3 shows plots of L (VB−) and L (VB0) withcoefficients of 0.16 and 0.84, respectively, and their linearcombination, 0.16 L (VB−) + 0.84 L (VB0), where L was plottedso that the linear combination profile matched the smoothedEELS spectrum (Figure 1e) (see Figure S8 for the method ofdetermining the coefficients). The good agreement betweenFigure 2. First-principles simulations. [(a)−(c)] DOS values of h-BN crystals without defects, with a VB− defect, and with a VB0 defect, respectively.The filled and blank areas are the occupied and unoccupied states, respectively. The upper and lower sides are the up- and down-spin states,respectively. [(e)−(g)] Imaginary parts of dielectric function, ε2,xx (solid line) and ε2,zz (dashed line) for perfect crystal in (e), VB− in (f), and VB0 in(g). Intensities in ε2,xx denoted by A−F in (f) and G−J in (g) originate from electron excitations indicated by A−F in (b) and G−J in (c),respectively. [(h)−(j)] Loss functions (L) for perfect crystal in (h), VB− in (i), and VB0 in (j). Intensities in L denoted by A′−F′ in (i) and G′−J′ in(j) predominantly reflect the intensities in ε2,xx denoted by A−F in (f) and G−J in (g).Nano Letters pubs.acs.org/NanoLett Letterhttps://doi.org/10.1021/acs.nanolett.5c02988Nano Lett. XXXX, XXX, XXX−XXXChttps://pubs.acs.org/doi/suppl/10.1021/acs.nanolett.5c02988/suppl_file/nl5c02988_si_001.pdfhttps://pubs.acs.org/doi/suppl/10.1021/acs.nanolett.5c02988/suppl_file/nl5c02988_si_001.pdfhttps://pubs.acs.org/doi/suppl/10.1021/acs.nanolett.5c02988/suppl_file/nl5c02988_si_001.pdfhttps://pubs.acs.org/doi/10.1021/acs.nanolett.5c02988?fig=fig2&ref=pdfhttps://pubs.acs.org/doi/10.1021/acs.nanolett.5c02988?fig=fig2&ref=pdfhttps://pubs.acs.org/doi/10.1021/acs.nanolett.5c02988?fig=fig2&ref=pdfhttps://pubs.acs.org/doi/10.1021/acs.nanolett.5c02988?fig=fig2&ref=pdfpubs.acs.org/NanoLett?ref=pdfhttps://doi.org/10.1021/acs.nanolett.5c02988?urlappend=%3Fref%3DPDF&jav=VoR&rel=cite-asthe linear combination and the EELS spectrum enables theassignment of the origin of the P1−P4 peaks in EELS andreveals the concentration ratio of the VB0 defects to theVB−defects, VB0/VB− is 5.3 as the average value within themeasured 143 nm-square area. The intense P2 peak in EELScorresponds to the A′ and B′ peaks in L (VB−), and, thus, theelectron excitations A and B in Figure 2b. The P3 and P4 peakscorrespond to the C′ and E′ peaks in L (VB−), whereas the P1peaks correspond to the I’ peak in L (VB0). The finding that theoptically inactive VB0 coexists with the optically active VB−implies that adjusting the charge state from 0 to − 1 canincrease the VB− concentration through electron injection.22,46Figure 4 shows a schematic unifying our understanding fromthe results of PL, EELS, and first-principles simulations in thisstudy and PL excitation in a previous study for VB−.10 Asillustrated in the DOS schematics of the ground state for VB−(Figure 4), the 1.53 eV PL occurs as an electronic relaxationprocess after the 2.5 eV excitation (i.e., absorption in EELS andPL excitation) between the occupied and unoccupied defectstates. The remaining energy of approximately 1 eV isattributed to nonradiative relaxation.To evaluate the absolute concentrations of VB− and VB0 byEELS, we utilize the vacancy concentration in the supercell forfirst-principles simulations, which is 13889 ppm for both VB−and VB0. Using the integrated intensities for VB− and VB0 (i.e., VB−+ VB0) in the range of 1.0−3.0 eV and the π-plasmon in the lossfunctions and those in the EELS spectrum, we estimated theaverage concentration of VB− + VB0 as approximately 2000 ppm(details are given in Figure S9). We assumed that the intensityratio of VB to the π plasmon in EELS is proportional to the VBconcentration. Then, the average VB− and VB0 concentrations areapproximately estimated as 300 and 1700 ppm, using thecoefficients 0.16 and 0.84 (Figure 3), respectively. The averageVB− concentration can be evaluated directly using the integratedintensities for VB− in the range of 2.3−3.0 eV, resulting in 300ppm as well (details are given in Figure S10). By implementingthis method for the original 1600 single spectra from the 143nm-square area (i.e., 40 × 40 pixels), we obtained theconcentration map of VB− and its histogram, as shown inFigures 5a and 5b, respectively. The VB− concentration is nearlyuniform without significant segregation (Figure 5a). TheGaussian fit in Figure 5b provides the center and standarddeviation of 330 ± 33 ppm, which is close to the average valueof 300 ppm estimated above. Figures 5c and 5d respectivelyshow the map of the concentration ratio of VB0 to VB− (i.e., VB0/VB−) and its histogram, where the VB0/VB− ratio at each pixel wasobtained using the integrated intensities in the ranges of 1.7−2.0 eV for VB0 and 2.3−2.6 eV for VB− (Figure S8a). The VB0/VB−map represents the distribution of the charge state ratio (i.e., 0to − 1). The negative values of the VB0/VB− ratio for severalpixels are due to the excess removal of ZLP tail signals and thelow signal-to-nose ratio. The Gaussian fit in Figure 5d givesVB0/VB−=5.0 ± 1.7, which closely matches the average VB0/VB−=5.3 obtained after integrating the 1600 single spectradescribed above. By multiplying the VB− map (Figure 5a) andthe VB0/VB− map (Figure 5c), we also obtained theconcentration map of VB0 and its histogram as shown inFigures 5e and 5f, respectively. The Gaussian fit in Figure 5fprovides the center and standard deviation of 1647 ± 648ppm, which is close to the average value of 1700 ppmestimated above. Figures 5g−5i show plots of typical singleEELS spectra at 1 pixel (3.6 nm-square areas) in Figure 5c withthe VB0/VB− values of 1.4, 5.0, and 7.1, respectively. Thesmoothed line profiles certainly reveal the increase in P1intensity at ∼ 1.9 eV from Figures 5g to 5i. Regarding thespatial resolution of the maps (Figure 5), the diameter andscan step of the electron probe we used were 0.6−0.7 and 3.6nm, respectively, whereas the effective diameter consideringthe delocalization of EELS around 2.5 eV was estimated to be8 nm.37 Thus, the maps in Figure 5 are blurred byapproximately 2 × 2 pixels compared with the actual intensitydistribution.Finally, we briefly discuss the quantitative aspects of theconcentration maps in Figure 5. The primary concern lies inthe comparison between the electron arrival time interval Δt atthe electron probe position in STEM−EELS and the lifetime τfrom the excited state back to the ground state for VB− and VB0.In this study, Δt was 1.3 ns (i.e., the probe current of ∼120pA) and the exposure time at each pixel was 0.6 s in Figure 5.The excited state for VB− returns to the ground statepredominantly via a singlet metastable state.31,47 The lifetimeof this metastable state is approximately 10−30 ns at roomtemperature, making τ longer than this,47−50 whereas thelifetime of VB0 remains unknown. This suggests the potential forunderestimating the VB− concentration during EELS measure-ment at each pixel. The measurement was probably performedwith a certain fraction of VB− in the metastable state, specificallywith a reduced concentration of VB−. Reducing the probeFigure 3. Plots of the loss function L for VB− (blue) and VB0 (green) inFigure 2 with factors of 0.16 and 0.84, respectively, their linearcombination (magenta), and smoothed EELS spectrum (black) inFigure 1e.Figure 4. Schematic of the 2.5 eV electron excitation (i.e., absorption)and 1.5 eV luminescence accompanied by nonradiative decay at theVB− defect in h-BN, illustrated in the DOS schematic of the groundstates.Nano Letters pubs.acs.org/NanoLett Letterhttps://doi.org/10.1021/acs.nanolett.5c02988Nano Lett. XXXX, XXX, XXX−XXXDhttps://pubs.acs.org/doi/suppl/10.1021/acs.nanolett.5c02988/suppl_file/nl5c02988_si_001.pdfhttps://pubs.acs.org/doi/suppl/10.1021/acs.nanolett.5c02988/suppl_file/nl5c02988_si_001.pdfhttps://pubs.acs.org/doi/suppl/10.1021/acs.nanolett.5c02988/suppl_file/nl5c02988_si_001.pdfhttps://pubs.acs.org/doi/10.1021/acs.nanolett.5c02988?fig=fig3&ref=pdfhttps://pubs.acs.org/doi/10.1021/acs.nanolett.5c02988?fig=fig3&ref=pdfhttps://pubs.acs.org/doi/10.1021/acs.nanolett.5c02988?fig=fig3&ref=pdfhttps://pubs.acs.org/doi/10.1021/acs.nanolett.5c02988?fig=fig3&ref=pdfhttps://pubs.acs.org/doi/10.1021/acs.nanolett.5c02988?fig=fig4&ref=pdfhttps://pubs.acs.org/doi/10.1021/acs.nanolett.5c02988?fig=fig4&ref=pdfhttps://pubs.acs.org/doi/10.1021/acs.nanolett.5c02988?fig=fig4&ref=pdfhttps://pubs.acs.org/doi/10.1021/acs.nanolett.5c02988?fig=fig4&ref=pdfpubs.acs.org/NanoLett?ref=pdfhttps://doi.org/10.1021/acs.nanolett.5c02988?urlappend=%3Fref%3DPDF&jav=VoR&rel=cite-ascurrent to below 1 pA and increasing the exposure time wouldresolve this issue, although it is expected to result in a lowersignal-to-noise ratio of the spectrum, making measurementsmore challenging. Alternatively, when the τ of VB0 iscomparable to that of VB−, the VB0/VB− ratio can be consideredquantitative despite the underestimation of the respectiveabsolute densities. In any case, the optimization of EELSconditions and a more precise quantitative evaluation of bothrelative and absolute densities remain future challenges.In summary, in this study, we investigated the intricatecharacteristics of optically active VB− and optically inactive VB0defects in nitrogen-ion irradiated h-BN by STEM−EELS withmonochromated 30-keV electrons and first-principles simu-lations. EELS played a pivotal role in identifying the subgapstates resulting from the irradiation, distinguishing distinctspectral peaks at 2.5 and 1.9 eV corresponding to VB− and VB0defects, respectively. The concentrations of VB− and VB0 defectswere estimated as approximately 300 and 1700 ppm onaverage, respectively. We also accomplished the concentrationmapping of these defects at the nanometer scale, whichrevealed their near-uniform distribution without significantsegregations. As a future challenge, it is necessary to optimizeEELS conditions by considering the lifetime τ to avoid theunderestimation of defect concentration. Such optimization isimperative for precise quantitative assessments, as it providesindispensable insights that are vital for the future application ofh-BN in quantum technology sectors.■ ASSOCIATED CONTENT*sı Supporting InformationThe Supporting Information is available free of charge athttps://pubs.acs.org/doi/10.1021/acs.nanolett.5c02988.Details of experimental method, first-principles simu-lations, other possible defects, loss function calculation,and additional figures (PDF)■ AUTHOR INFORMATIONCorresponding AuthorJun Kikkawa − National Institute for Materials Science,Tsukuba 305-0044, Japan; orcid.org/0000-0003-0659-1844; Email: kikkawa.jun@nims.go.jpAuthorsChikara Shinei − National Institute for Materials Science,Tsukuba 305-0044, JapanJun Chen − National Institute for Materials Science, Tsukuba305-0044, JapanYuta Masuyama − National Institutes for Quantum Scienceand Technology, Takasaki 370-1292, JapanYuichi Yamazaki − National Institutes for Quantum Scienceand Technology, Takasaki 370-1292, JapanTeruyasu Mizoguchi − Institute of Industrial Science, TheUniversity of Tokyo, Tokyo 153-8505, Japan; orcid.org/0000-0003-3712-7307Koji Kimoto − National Institute for Materials Science,Tsukuba 305-0044, Japan; orcid.org/0000-0002-3927-0492Takashi Taniguchi − National Institute for Materials Science,Tsukuba 305-0044, Japan; orcid.org/0000-0002-1467-3105Tokuyuki Teraji − National Institute for Materials Science,Tsukuba 305-0044, JapanComplete contact information is available at:https://pubs.acs.org/10.1021/acs.nanolett.5c02988Figure 5. Concentration maps of vacancies in the irradiated h-BN flake. The VB− map in (a) and its histogram in (b). The VB0/VB− ratio map in (c)and its histogram in (d). The VB0 map in (e) and its histogram in (f). All maps have the same area. The centers and standard deviations for Gaussianfits in the histogram are 300 ± 33 ppm, 5.0 ± 1.7, and 1647 ± 648 ppm in (b), (d), and (f), respectively. [g−h] Typical single EELS spectra at 1pixel (3.6 nm-square areas) with the VB0/VB− ratios of 1.4, 5.0, and 7.1 in (g), (h), and (i), respectively.Nano Letters pubs.acs.org/NanoLett Letterhttps://doi.org/10.1021/acs.nanolett.5c02988Nano Lett. XXXX, XXX, XXX−XXXEhttps://pubs.acs.org/doi/10.1021/acs.nanolett.5c02988?goto=supporting-infohttps://pubs.acs.org/doi/suppl/10.1021/acs.nanolett.5c02988/suppl_file/nl5c02988_si_001.pdfhttps://pubs.acs.org/action/doSearch?field1=Contrib&text1="Jun+Kikkawa"&field2=AllField&text2=&publication=&accessType=allContent&Earliest=&ref=pdfhttps://orcid.org/0000-0003-0659-1844https://orcid.org/0000-0003-0659-1844mailto:kikkawa.jun@nims.go.jphttps://pubs.acs.org/action/doSearch?field1=Contrib&text1="Chikara+Shinei"&field2=AllField&text2=&publication=&accessType=allContent&Earliest=&ref=pdfhttps://pubs.acs.org/action/doSearch?field1=Contrib&text1="Jun+Chen"&field2=AllField&text2=&publication=&accessType=allContent&Earliest=&ref=pdfhttps://pubs.acs.org/action/doSearch?field1=Contrib&text1="Yuta+Masuyama"&field2=AllField&text2=&publication=&accessType=allContent&Earliest=&ref=pdfhttps://pubs.acs.org/action/doSearch?field1=Contrib&text1="Yuichi+Yamazaki"&field2=AllField&text2=&publication=&accessType=allContent&Earliest=&ref=pdfhttps://pubs.acs.org/action/doSearch?field1=Contrib&text1="Teruyasu+Mizoguchi"&field2=AllField&text2=&publication=&accessType=allContent&Earliest=&ref=pdfhttps://orcid.org/0000-0003-3712-7307https://orcid.org/0000-0003-3712-7307https://pubs.acs.org/action/doSearch?field1=Contrib&text1="Koji+Kimoto"&field2=AllField&text2=&publication=&accessType=allContent&Earliest=&ref=pdfhttps://orcid.org/0000-0002-3927-0492https://orcid.org/0000-0002-3927-0492https://pubs.acs.org/action/doSearch?field1=Contrib&text1="Takashi+Taniguchi"&field2=AllField&text2=&publication=&accessType=allContent&Earliest=&ref=pdfhttps://orcid.org/0000-0002-1467-3105https://orcid.org/0000-0002-1467-3105https://pubs.acs.org/action/doSearch?field1=Contrib&text1="Tokuyuki+Teraji"&field2=AllField&text2=&publication=&accessType=allContent&Earliest=&ref=pdfhttps://pubs.acs.org/doi/10.1021/acs.nanolett.5c02988?ref=pdfhttps://pubs.acs.org/doi/10.1021/acs.nanolett.5c02988?fig=fig5&ref=pdfhttps://pubs.acs.org/doi/10.1021/acs.nanolett.5c02988?fig=fig5&ref=pdfhttps://pubs.acs.org/doi/10.1021/acs.nanolett.5c02988?fig=fig5&ref=pdfhttps://pubs.acs.org/doi/10.1021/acs.nanolett.5c02988?fig=fig5&ref=pdfpubs.acs.org/NanoLett?ref=pdfhttps://doi.org/10.1021/acs.nanolett.5c02988?urlappend=%3Fref%3DPDF&jav=VoR&rel=cite-asAuthor ContributionsJ.K. and T. Teraji conceived and directed the project. T.Taniguchi made the h-BN crystal. Y.M. and Y.Y. conducted thenitrogen-ion irradiation. J.K. conducted EELS experiments andanalyses. C.S., Y.Y., and J.C. measured PL, ODMR, and CLspectra, respectively. T.M. conducted first-principles simula-tions. All authors have discussed the experimental andsimulated results. J.K. wrote the manuscript with the supportof all the authors.NotesThe authors declare no competing financial interest.■ ACKNOWLEDGMENTSJ.K. thanks Y. Moronaga (NIMS) for specimen preparationsand J. Inoue (NIMS) for fruitful discussion. This work waspartly supported by JSPS KAKENHI Grant Nos. JP22H01959and JP23H02052 and World Premier International ResearchCenter Initiative (WPI), MEXT, Japan.■ REFERENCES(1) Taylor, J. M.; Cappellaro, P.; Childress, L.; Jiang, L.; Budker, D.;Hemmer, P. R.; Yacoby, A.; Walsworth, R.; Lukin, M. D. High-Sensitivity Diamond Magnetometer with Nanoscale Resolution. Nat.Phys. 2008, 4 (10), 810−816.(2) Aslam, N.; Pfender, M.; Neumann, P.; Reuter, R.; Zappe, A.;Fávaro de Oliveira, F.; Denisenko, A.; Sumiya, H.; Onoda, S.; Isoya,J.; et al. Nanoscale Nuclear Magnetic Resonance with ChemicalResolution. Science 2017, 357 (6346), 67−71.(3) Tetienne, J. P. Quantum Sensors Go Flat. Nat. Phys. 2021, 17(10), 1074−1075.(4) Gottscholl, A.; Diez, M.; Soltamov, V.; Kasper, C.; Krauße, D.;Sperlich, A.; Kianinia, M.; Bradac, C.; Aharonovich, I.; Dyakonov, V.Spin Defects in hBN as Promising Temperature, Pressure andMagnetic Field Quantum Sensors. Nat. Commun. 2021, 12 (1), 4480.(5) Watanabe, K.; Taniguchi, T.; Kanda, H. Direct-BandgapProperties and Evidence for Ultraviolet Lasing of Hexagonal BoronNitride Single Crystal. Nat. Mater. 2004, 3 (6), 404−409.(6) Cassabois, G.; Valvin, P.; Gil, B. Hexagonal Boron Nitride Is anIndirect Bandgap Semiconductor. Nat. Photonics 2016, 10 (4), 262−266.(7) Maciaszek, M.; Razinkovas, L.; Alkauskas, A. Thermodynamicsof Carbon Point Defects in Hexagonal Boron Nitride. Phys. Rev.Mater. 2022, 6 (1), 014005.(8) Kim, S. H.; Park, K. H.; Lee, Y. G.; Kang, S. J.; Park, Y.; Kim, Y.D. Color Centers in Hexagonal Boron Nitride. Nanomaterials 2023,13 (16), 2344.(9) Gottscholl, A.; Kianinia, M.; Soltamov, V.; Orlinskii, S.; Mamin,G.; Bradac, C.; Kasper, C.; Krambrock, K.; Sperlich, A.; Toth, M.;et al. Initialization and Read-out of Intrinsic Spin Defects in a van derWaals Crystal at Room Temperature. Nat. Mater. 2020, 19 (5), 540−545.(10) Kianinia, M.; White, S.; Fröch, J. E.; Bradac, C.; Aharonovich, I.Generation of Spin Defects in Hexagonal Boron Nitride. ACSPhotonics 2020, 7 (8), 2147−2152.(11) Suzuki, T.; Yamazaki, Y.; Taniguchi, T.; Watanabe, K.; Nishiya,Y.; Matsushita, Y.; Harii, K.; Masuyama, Y.; Hijikata, Y.; Ohshima, T.Spin Property Improvement of Boron Vacancy Defect in HexagonalBoron Nitride by Thermal Treatment. Appl. Phys. Express 2023, 16(3), 032006.(12) Zabelotsky, T.; Singh, S.; Haim, G.; Malkinson, R.;Kadkhodazadeh, S.; Radko, I. P.; Aharonovich, I.; Steinberg, H.;Berg-Sørensen, K.; Huck, A.; et al. Creation of Boron Vacancies inHexagonal Boron Nitride Exfoliated from Bulk Crystals for QuantumSensing. ACS Appl. Nano Mater. 2023, 6 (23), 21671−21678.(13) Sarkar, S.; Xu, Y.; Mathew, S.; Lal, M.; Chung, J.-Y.; Lee, H. Y.;Watanabe, K.; Taniguchi, T.; Venkatesan, T.; Gradecǎk, S. IdentifyingLuminescent Boron Vacancies in h-BN Generated Using ControlledHe+ Ion Irradiation. Nano Lett. 2024, 24 (1), 43−50.(14) Tran, T. T.; Bray, K.; Ford, M. J.; Toth, M.; Aharonovich, I.Quantum Emission from Hexagonal Boron Nitride Monolayers. Nat.Nanotechnol. 2016, 11 (1), 37−41.(15) Martínez, L. J.; Pelini, T.; Waselowski, V.; Maze, J. R.; Gil, B.;Cassabois, G.; Jacques, V. Efficient Single Photon Emission from aHigh-Purity Hexagonal Boron Nitride Crystal. Phys. Rev. B 2016, 94(12), 121405.(16) Silly, M. G.; Jaffrennou, P.; Barjon, J.; Lauret, J. S.; Ducastelle,F.; Loiseau, A.; Obraztsova, E.; Attal-Tretout, B.; Rosencher, E.Luminescence Properties of Hexagonal Boron Nitride: Cathodolu-minescence and Photoluminescence Spectroscopy Measurements.Phys. Rev. B 2007, 75 (8), 085205.(17) Weston, L.; Wickramaratne, D.; Mackoit, M.; Alkauskas, A.;Van de Walle, C. G. Native Point Defects and Impurities inHexagonal Boron Nitride. Phys. Rev. B 2018, 97 (21), 214104.(18) Mackoit-Sinkevicǐene,̇ M.; Maciaszek, M.; Van de Walle, C. G.;Alkauskas, A. Carbon Dimer Defect as a Source of the 4.1 eVLuminescence in Hexagonal Boron Nitride. Appl. Phys. Lett. 2019,115 (21), 212101.(19) Jara, C.; Rauch, T.; Botti, S.; Marques, M. A. L.; Norambuena,A.; Coto, R.; Castellanos-Águila, J. E.; Maze, J. R.; Munoz, F. First-Principles Identification of Single Photon Emitters Based on CarbonClusters in Hexagonal Boron Nitride. J. Phys. Chem. A 2021, 125 (6),1325−1335.(20) Plo, J.; Pershin, A.; Li, S.; Poirier, T.; Janzen, E.; Schutte, H.;Tian, M.; Wynn, M.; Bernard, S.; Rousseau, A.; et al. IsotopeSubstitution and Polytype Control for Point Defects Identification:The Case of the Ultraviolet Color Center in Hexagonal BoronNitride. Phys. Rev. X 2025, 15 (2), 021045.(21) Gale, A.; Li, C.; Chen, Y.; Watanabe, K.; Taniguchi, T.;Aharonovich, I.; Toth, M. Site-Specific Fabrication of Blue QuantumEmitters in Hexagonal Boron Nitride. ACS Photonics 2022, 9 (6),2170−2177.(22) Gale, A.; Scognamiglio, D.; Zhigulin, I.; Whitefield, B.;Kianinia, M.; Aharonovich, I.; Toth, M. Manipulating the ChargeState of Spin Defects in Hexagonal Boron Nitride. Nano Lett. 2023,23 (13), 6141−6147.(23) Bozanic, A.; Petravic, M.; Fan, L. J.; Yang, Y. W.; Chen, Y.Direct Observation of Defect Levels in Hexagonal BN by Soft X-RayAbsorption Spectroscopy. Chem. Phys. Lett. 2009, 472 (4), 190−193.(24) Peter, R.; Bozanic, A.; Petravic, M.; Chen, Y.; Fan, L. J.; Yang,Y. W. Formation of Defects in Boron Nitride by Low Energy IonBombardment. J. Appl. Phys. 2009, 106 (8), 083523.(25) Jin, C.; Lin, F.; Suenaga, K.; Iijima, S. Fabrication of aFreestanding Boron Nitride Single Layer and Its Defect Assignments.Phys. Rev. Lett. 2009, 102 (19), 195505.(26) Cretu, O.; Ishizuka, A.; Yanagisawa, K.; Ishizuka, K.; Kimoto, K.Atomic-Scale Electrical Field Mapping of Hexagonal Boron NitrideDefects. ACS Nano 2021, 15 (3), 5316−5321.(27) Liang, H.; Chen, Y.; Loh, L.; Cheng, N. L. Q.; Litvinov, D.;Yang, C.; Chen, Y.; Zhang, Z.; Watanabe, K.; Taniguchi, T.; et al. Site-Selective Creation of Blue Emitters in Hexagonal Boron Nitride. ACSNano 2025, 19 (15), 15130−15138.(28) Exarhos, A. L.; Hopper, D. A.; Patel, R. N.; Doherty, M. W.;Bassett, L. C. Magnetic-Field-Dependent Quantum Emission inHexagonal Boron Nitride at Room Temperature. Nat. Commun. 2019,10 (1), 222.(29) Attaccalite, C.; Bockstedte, M.; Marini, A.; Rubio, A.; Wirtz, L.Coupling of Excitons and Defect States in Boron-Nitride Nanostruc-tures. Phys. Rev. B 2011, 83 (14), 144115.(30) Zhang, H.; Lan, M.; Tang, G.; Chen, F.; Shu, Z.; Chen, F.; Li,M. Discrete Color Centers in Two-Dimensional Hexagonal BoronNitride Induced by Fast Neutron Irradiation. J. Mater. Chem. C 2019,7 (39), 12211−12216.(31) Ivády, V.; Barcza, G.; Thiering, G.; Li, S.; Hamdi, H.; Chou, J.-P.; Legeza, Ö.; Gali, A. Ab Initio Theory of the Negatively ChargedNano Letters pubs.acs.org/NanoLett Letterhttps://doi.org/10.1021/acs.nanolett.5c02988Nano Lett. XXXX, XXX, XXX−XXXFhttps://doi.org/10.1038/nphys1075https://doi.org/10.1038/nphys1075https://doi.org/10.1126/science.aam8697https://doi.org/10.1126/science.aam8697https://doi.org/10.1038/s41567-021-01338-5https://doi.org/10.1038/s41467-021-24725-1https://doi.org/10.1038/s41467-021-24725-1https://doi.org/10.1038/nmat1134https://doi.org/10.1038/nmat1134https://doi.org/10.1038/nmat1134https://doi.org/10.1038/nphoton.2015.277https://doi.org/10.1038/nphoton.2015.277https://doi.org/10.1103/PhysRevMaterials.6.014005https://doi.org/10.1103/PhysRevMaterials.6.014005https://doi.org/10.3390/nano13162344https://doi.org/10.1038/s41563-020-0619-6https://doi.org/10.1038/s41563-020-0619-6https://doi.org/10.1021/acsphotonics.0c00614?urlappend=%3Fref%3DPDF&jav=VoR&rel=cite-ashttps://doi.org/10.35848/1882-0786/acc442https://doi.org/10.35848/1882-0786/acc442https://doi.org/10.1021/acsanm.3c03395?urlappend=%3Fref%3DPDF&jav=VoR&rel=cite-ashttps://doi.org/10.1021/acsanm.3c03395?urlappend=%3Fref%3DPDF&jav=VoR&rel=cite-ashttps://doi.org/10.1021/acsanm.3c03395?urlappend=%3Fref%3DPDF&jav=VoR&rel=cite-ashttps://doi.org/10.1021/acs.nanolett.3c03113?urlappend=%3Fref%3DPDF&jav=VoR&rel=cite-ashttps://doi.org/10.1021/acs.nanolett.3c03113?urlappend=%3Fref%3DPDF&jav=VoR&rel=cite-ashttps://doi.org/10.1021/acs.nanolett.3c03113?urlappend=%3Fref%3DPDF&jav=VoR&rel=cite-ashttps://doi.org/10.1038/nnano.2015.242https://doi.org/10.1103/PhysRevB.94.121405https://doi.org/10.1103/PhysRevB.94.121405https://doi.org/10.1103/PhysRevB.75.085205https://doi.org/10.1103/PhysRevB.75.085205https://doi.org/10.1103/PhysRevB.97.214104https://doi.org/10.1103/PhysRevB.97.214104https://doi.org/10.1063/1.5124153https://doi.org/10.1063/1.5124153https://doi.org/10.1021/acs.jpca.0c07339?urlappend=%3Fref%3DPDF&jav=VoR&rel=cite-ashttps://doi.org/10.1021/acs.jpca.0c07339?urlappend=%3Fref%3DPDF&jav=VoR&rel=cite-ashttps://doi.org/10.1021/acs.jpca.0c07339?urlappend=%3Fref%3DPDF&jav=VoR&rel=cite-ashttps://doi.org/10.1103/PhysRevX.15.021045https://doi.org/10.1103/PhysRevX.15.021045https://doi.org/10.1103/PhysRevX.15.021045https://doi.org/10.1103/PhysRevX.15.021045https://doi.org/10.1021/acsphotonics.2c00631?urlappend=%3Fref%3DPDF&jav=VoR&rel=cite-ashttps://doi.org/10.1021/acsphotonics.2c00631?urlappend=%3Fref%3DPDF&jav=VoR&rel=cite-ashttps://doi.org/10.1021/acs.nanolett.3c01678?urlappend=%3Fref%3DPDF&jav=VoR&rel=cite-ashttps://doi.org/10.1021/acs.nanolett.3c01678?urlappend=%3Fref%3DPDF&jav=VoR&rel=cite-ashttps://doi.org/10.1016/j.cplett.2009.03.030https://doi.org/10.1016/j.cplett.2009.03.030https://doi.org/10.1063/1.3253576https://doi.org/10.1063/1.3253576https://doi.org/10.1103/PhysRevLett.102.195505https://doi.org/10.1103/PhysRevLett.102.195505https://doi.org/10.1021/acsnano.0c10849?urlappend=%3Fref%3DPDF&jav=VoR&rel=cite-ashttps://doi.org/10.1021/acsnano.0c10849?urlappend=%3Fref%3DPDF&jav=VoR&rel=cite-ashttps://doi.org/10.1021/acsnano.5c03423?urlappend=%3Fref%3DPDF&jav=VoR&rel=cite-ashttps://doi.org/10.1021/acsnano.5c03423?urlappend=%3Fref%3DPDF&jav=VoR&rel=cite-ashttps://doi.org/10.1038/s41467-018-08185-8https://doi.org/10.1038/s41467-018-08185-8https://doi.org/10.1103/PhysRevB.83.144115https://doi.org/10.1103/PhysRevB.83.144115https://doi.org/10.1039/C9TC03695Dhttps://doi.org/10.1039/C9TC03695Dhttps://doi.org/10.1038/s41524-020-0305-xpubs.acs.org/NanoLett?ref=pdfhttps://doi.org/10.1021/acs.nanolett.5c02988?urlappend=%3Fref%3DPDF&jav=VoR&rel=cite-asBoron Vacancy Qubit in Hexagonal Boron Nitride. npj Comput.Mater. 2020, 6 (1), 41.(32) Asano, T.; Tezura, M.; Saitoh, M.; Tanaka, H.; Kikkawa, J.;Kimoto, K. Nanoscale Observation of Subgap Excitations in β-Si3N4with a High Refractive Index Using Low-Voltage MonochromatedSTEM: A New Approach to Analyze the Physical Properties ofDefects in Dielectric Materials. Appl. Phys. Express 2022, 15 (7),076501.(33) Yamashita, S.; Fukushima, S.; Kikkawa, J.; Arai, R.; Kanitani, Y.;Kimoto, K.; Kudo, Y. Local Defect and Mid-Gap State Analysis ofGaN Using Monochromated EELS Combined with Nanodiffractionand Atomic-Resolution Imaging. APL Mater. 2024, 12 (3), 031101.(34) Wang, S.; March, K.; Ponce, F. A.; Rez, P. Identification ofPoint Defects Using High-Resolution Electron Energy Loss Spec-troscopy. Phys. Rev. B 2019, 99 (11), 115312.(35) Browning, N. D.; Pennycook, S. J. Direct ExperimentalDetermination of the Atomic Structure at Internal Interfaces. J.Phys. D: Appl. Phys. 1996, 29 (7), 1779.(36) Kimoto, K.; Kothleitner, G.; Grogger, W.; Matsui, Y.; Hofer, F.Advantages of a Monochromator for Bandgap Measurements UsingElectron Energy-Loss Spectroscopy. Micron 2005, 36 (2), 185−189.(37) Egerton, R. F. Electron Energy-Loss Spectroscopy in the ElectronMicroscope; Springer Science+Business Media, LLC: 2011.(38) Chen, C. H.; Silcox, J. Calculations of the Electron-Energy-LossProbability in Thin Uniaxial Crystals at Oblique Incidence. Phys. Rev.B 1979, 20 (9), 3605−3614.(39) Kikkawa, J.; Taniguchi, T.; Kimoto, K. Nanometric PhononSpectroscopy for Diamond and Cubic Boron Nitride. Phys. Rev. B2021, 104 (20), L201402.(40) Laturia, A.; Van de Put, M. L.; Vandenberghe, W. G. DielectricProperties of Hexagonal Boron Nitride and Transition MetalDichalcogenides: From Monolayer to Bulk. npj 2D Mater. Appl.2018, 2 (1), 6.(41) Haruta, M.; Fujiyoshi, Y.; Nemoto, T.; Ishizuka, A.; Ishizuka,K.; Kurata, H. Extremely Low Count Detection for EELS SpectrumImaging by Reducing CCD Read-out Noise. Ultramicroscopy 2019,207, 112827.(42) Haruta, M.; Kikkawa, J.; Kimoto, K.; Kurata, H. Comparison ofDetection Limits of Direct-Counting CMOS and CCD Cameras inEELS Experiments. Ultramicroscopy 2022, 240, 113577.(43) Taniguchi, T.; Watanabe, K. Synthesis of High-Purity BoronNitride Single Crystals under High Pressure by Using Ba−BNSolvent. J. Cryst. Growth 2007, 303 (2), 525−529.(44) McDougall, N. L.; Partridge, J. G.; Nicholls, R. J.; Russo, S. P.;McCulloch, D. G. Influence of Point Defects on the near EdgeStructure of Hexagonal Boron Nitride. Phys. Rev. B 2017, 96 (14),144106.(45) Browning, N. D.; Yuan, J.; Brown, L. M. TheoreticalDetermination of Angularly-Integrated Energy-Loss Functions forAnisotropic Materials. Philos. Mag. A 1993, 67 (1), 261−271.(46) Fraunié, J.; Clua-Provost, T.; Roux, S.; Mu, Z.; Delpoux, A.;Seine, G.; Lagarde, D.; Watanabe, K.; Taniguchi, T.; Marie, X.; et al.Charge State Tuning of Spin Defects in Hexagonal Boron Nitride.Nano Lett. 2025, 25 (14), 5836−5842.(47) Clua-Provost, T.; Mu, Z.; Durand, A.; Schrader, C.; Happacher,J.; Bocquel, J.; Maletinsky, P.; Fraunié, J.; Marie, X.; Robert, C.; et al.Spin-Dependent Photodynamics of Boron-Vacancy Centers inHexagonal Boron Nitride. Phys. Rev. B 2024, 110 (1), 014104.(48) Baber, S.; Malein, R. N. E.; Khatri, P.; Keatley, P. S.; Guo, S.;Withers, F.; Ramsay, A. J.; Luxmoore, I. J. Excited State Spectroscopyof Boron Vacancy Defects in Hexagonal Boron Nitride Using Time-Resolved Optically Detected Magnetic Resonance. Nano Lett. 2022,22 (1), 461−467.(49) Whitefield, B.; Toth, M.; Aharonovich, I.; Tetienne, J.-P.;Kianinia, M. Magnetic Field Sensitivity Optimization of NegativelyCharged Boron Vacancy Defects in hBN. Adv. Quantum Technol.2025, 8 (4), 2300118.(50) Lee, W.; Liu, V. S.; Zhang, Z.; Kim, S.; Gong, R.; Du, X.; Pham,K.; Poirier, T.; Hao, Z.; Edgar, J. H.; et al. Intrinsic High-Fidelity SpinPolarization of Charged Vacancies in Hexagonal Boron Nitride. Phys.Rev. Lett. 2025, 134 (9), 096202.Nano Letters pubs.acs.org/NanoLett Letterhttps://doi.org/10.1021/acs.nanolett.5c02988Nano Lett. XXXX, XXX, XXX−XXXGhttps://doi.org/10.1038/s41524-020-0305-xhttps://doi.org/10.35848/1882-0786/ac6e28https://doi.org/10.35848/1882-0786/ac6e28https://doi.org/10.35848/1882-0786/ac6e28https://doi.org/10.35848/1882-0786/ac6e28https://doi.org/10.1063/5.0178995https://doi.org/10.1063/5.0178995https://doi.org/10.1063/5.0178995https://doi.org/10.1103/PhysRevB.99.115312https://doi.org/10.1103/PhysRevB.99.115312https://doi.org/10.1103/PhysRevB.99.115312https://doi.org/10.1088/0022-3727/29/7/013https://doi.org/10.1088/0022-3727/29/7/013https://doi.org/10.1016/j.micron.2004.11.001https://doi.org/10.1016/j.micron.2004.11.001https://doi.org/10.1103/PhysRevB.20.3605https://doi.org/10.1103/PhysRevB.20.3605https://doi.org/10.1103/PhysRevB.104.L201402https://doi.org/10.1103/PhysRevB.104.L201402https://doi.org/10.1038/s41699-018-0050-xhttps://doi.org/10.1038/s41699-018-0050-xhttps://doi.org/10.1038/s41699-018-0050-xhttps://doi.org/10.1016/j.ultramic.2019.112827https://doi.org/10.1016/j.ultramic.2019.112827https://doi.org/10.1016/j.ultramic.2022.113577https://doi.org/10.1016/j.ultramic.2022.113577https://doi.org/10.1016/j.ultramic.2022.113577https://doi.org/10.1016/j.jcrysgro.2006.12.061https://doi.org/10.1016/j.jcrysgro.2006.12.061https://doi.org/10.1016/j.jcrysgro.2006.12.061https://doi.org/10.1103/PhysRevB.96.144106https://doi.org/10.1103/PhysRevB.96.144106https://doi.org/10.1080/01418619308207156https://doi.org/10.1080/01418619308207156https://doi.org/10.1080/01418619308207156https://doi.org/10.1021/acs.nanolett.5c00654?urlappend=%3Fref%3DPDF&jav=VoR&rel=cite-ashttps://doi.org/10.1103/PhysRevB.110.014104https://doi.org/10.1103/PhysRevB.110.014104https://doi.org/10.1021/acs.nanolett.1c04366?urlappend=%3Fref%3DPDF&jav=VoR&rel=cite-ashttps://doi.org/10.1021/acs.nanolett.1c04366?urlappend=%3Fref%3DPDF&jav=VoR&rel=cite-ashttps://doi.org/10.1021/acs.nanolett.1c04366?urlappend=%3Fref%3DPDF&jav=VoR&rel=cite-ashttps://doi.org/10.1002/qute.202300118https://doi.org/10.1002/qute.202300118https://doi.org/10.1103/PhysRevLett.134.096202https://doi.org/10.1103/PhysRevLett.134.096202pubs.acs.org/NanoLett?ref=pdfhttps://doi.org/10.1021/acs.nanolett.5c02988?urlappend=%3Fref%3DPDF&jav=VoR&rel=cite-as