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F Bianco, S Pezzini, [K Watanabe](https://orcid.org/0000-0003-3701-8119), [T Taniguchi](https://orcid.org/0000-0002-1467-3105), F Fabbri

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[Scanning electron irradiation of hexagonal boron nitride: an efficient procedure for quenching undesired defects emissions monitored by <i>in-situ</i> room temperature cathodoluminescence](https://mdr.nims.go.jp/datasets/b83eb92f-30f8-4855-a804-993cbe07fc30)

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Scanning electron irradiation of hexagonal boron nitride: an efficient procedure for quenching undesired defects emissions monitored by in-situ room temperature cathodoluminescence2D Materials     PAPER • OPEN ACCESSScanning electron irradiation of hexagonal boronnitride: an efficient procedure for quenchingundesired defects emissions monitored by in-situroom temperature cathodoluminescenceTo cite this article: F Bianco et al 2025 2D Mater. 12 025026 View the article online for updates and enhancements.You may also likeSurface versus bulk: behavior ofphotoexcited charge carriers in GeSSepideh Khanmohammadi, KaterynaKushnir Friedman, Catherine Tran et al.-Valley emission and upconversion inisotopically engineered monolayer WS2under resonant excitationRahul Kesarwani, Vaibhav Varade, ArturSlobodeniuk et al.-Ionically gated transistors based on two-dimensional materials for neuromorphiccomputingKe Xu and Susan K Fullerton-Shirey-This content was downloaded from IP address 144.213.253.16 on 02/04/2025 at 03:12https://doi.org/10.1088/2053-1583/adc119/article/10.1088/2053-1583/adc13e/article/10.1088/2053-1583/adc13e/article/10.1088/2053-1583/adc27d/article/10.1088/2053-1583/adc27d/article/10.1088/2053-1583/adc27d/article/10.1088/2053-1583/adb8c3/article/10.1088/2053-1583/adb8c3/article/10.1088/2053-1583/adb8c32D Mater. 12 (2025) 025026 https://doi.org/10.1088/2053-1583/adc119OPEN ACCESSRECEIVED28 January 2025REVISED12 February 2025ACCEPTED FOR PUBLICATION10 March 2025PUBLISHED26 March 2025Original content fromthis work may be usedunder the terms of theCreative CommonsAttribution 4.0 licence.Any further distributionof this work mustmaintain attribution tothe author(s) and the titleof the work, journalcitation and DOI.PAPERScanning electron irradiation of hexagonal boron nitride: anefficient procedure for quenching undesired defects emissionsmonitored by in-situ room temperature cathodoluminescenceF Bianco1, S Pezzini1, K Watanabe2, T Taniguchi3 and F Fabbri1,∗1 NEST, Istituto Nanoscienze—CNR, Scuola Normale Superiore, Piazza San Silvestro 12, 56127 Pisa, Italy2 Research Center for Electronic and Optical Materials, National Institute for Materials Science, 1-1 Namiki, Tsukuba 305-0044, Japan3 Research Center for Materials Nanoarchitectonics, National Institute for Materials Science, 1-1 Namiki, Tsukuba 305-0044, Japan∗ Author to whom any correspondence should be addressed.E-mail: filippo.fabbri@nano.cnr.itKeywords: hexagonal boron nitride, in-situ cathodoluminescence, emission quenching, deep level emissionSupplementary material for this article is available onlineAbstractRecently, layered materials have become an interesting platform for quantum optics andnanophotonics. Among them, hexagonal boron nitride (hBN) has attracted a widespread interestdue to its peculiar defect-related luminescence properties. In particular, the possible generationand tailoring of color centers by particle irradiation are becoming pivotal aspects for nextgeneration quantum optics and photonics. In this work, we use in-situ cathodoluminescencehyperspectral analysis to investigate the effect of fast-scanning, low-voltage electron irradiation ondeep level emissions in the ultraviolet (UV) range. The quenching of the UV band (UVB) andchanges in the width of the near-band-edge UV luminescence of hBN are investigated as a functionof the irradiation time. This quenching is assigned to the electron beam dissociation of in-planecarbon dimer, responsible for such emission, with a concurrent substitutional carbon atomsreconfiguration in donor acceptor pair with a spatial separation in the hBN lattice, that can beoptically inactive or can emit in a different optical range, as demonstrated by the intensity decreaseof below-bandgap excitation photoluminescence emissions. A possible mechanism of the UVBquenching is also the change of the charge state of the in-plane carbon dimer, that causes a lightemission in a different optical range. In addition, ex-situ analyzes reveal an important side effect ofprolonged electron irradiation, such as the 40 nm thick deposition of tetrahedral amorphouscarbon on top of the hBN flake. This is a clear evolution of the well-established electron beaminduced surface contamination due to the adsorption of carbonic species.1. IntroductionWith the growing interest in quantum opticsapplications [1–4], hexagonal boron nitride (hBN)has emerged as a promising platform for high-yield,room-temperature single-photon emitters (SPEs)based on color centers [5–10]. The generation andtuning of color centers with SPE properties in hBNcan be achieved through various approaches [8, 11–18]. Among these, irradiation with charged particleshas shown several advantages [7, 11, 19], includ-ing spatial localization [20–22] and the creation ofhigh-formation-energy point defects, such as theboron vacancy [9, 23–26].Electron irradiation offers the highest spatial loc-alization of radiative centers [20–22]. The color cen-ters generated by this technique depend on irradi-ation parameters, with light emissions spanning fromblue to infrared by varying factors such as accelerat-ing voltage, beam current, or irradiation time [20–22,27]. Recently, cathodoluminescence (CL) has facil-itated studies of SPE-related color centers in hBN[20, 23, 28–32]. Notably, recent research has demon-strated the potential of CL for in-situ monitoring© 2025 The Author(s). Published by IOP Publishing Ltdhttps://doi.org/10.1088/2053-1583/adc119https://crossmark.crossref.org/dialog/?doi=10.1088/2053-1583/adc119&domain=pdf&date_stamp=2025-3-26https://creativecommons.org/licenses/by/4.0/https://creativecommons.org/licenses/by/4.0/https://orcid.org/0000-0002-6372-8889https://orcid.org/0000-0003-4289-907Xhttps://orcid.org/0000-0003-3701-8119https://orcid.org/0000-0003-1142-0441mailto:filippo.fabbri@nano.cnr.ithttps://doi.org/10.1088/2053-1583/adc1192D Mater. 12 (2025) 025026 F Bianco et alof localized activation of blue-emitting color centersthrough spot-mode electron beam irradiation [33,34]. CL is one of themost versatile experimental toolsfor studying and monitoring the optical properties ofhBN [12, 35–41]. Typically conducted at cryogenictemperatures, CL can excite near-band-edge (NBE)emissions of hBN (5.8 eV, 215 nm) in the deep ultra-violet (UV) region [36, 38]. Furthermore, CL hasbeen used to unambiguously identify hBN crystal-line phases [42] and detect UV emission at 300 nm(4.1 eV), which is modulated by the twist angle ofstacked hBN multilayers [31, 43]. Finally, CL analysisis important for the CL is also critical for identifyingunique optical features in hBNmicrostructures, suchas bubbles and wrinkles [39, 44, 45].In this study, we present an efficient and rapidprocedure involving large-area, fast-scanning, low-voltage electron irradiation to suppress undesireddefect-related radiative recombination. This processis monitored via in-situ CL hyperspectral analysis.Prolonged irradiation leads to a monotonic quench-ing of deep-level UV emissions and a concurrent nar-rowing of NBE UV emissions in hBN. The quench-ing of the UV band (UVB) is attributed to the elec-tron beam-induced dissociation of in-plane carbondimers, into different configurations of the donoracceptor pair of substitutional carbon atoms withdifferent spatial separations in the hBN lattice, thatcan be optically inactive or emits light in a differ-ent optical range. An additional mechanism of theUVB quenching is the positively or negatively char-ging of the in-plane carbon dimer, that would cause alight emission in a different optical range. This hypo-thesis is supported by the observed decrease in below-bandgap excitation photoluminescence (PL) emis-sions. Ex-situ Raman and atomic force microscopy(AFM) analyzes reveal a notable side effect of pro-longed large-area, low-voltage electron irradiation:the deposition of a 40 nm thick layer of tetrahed-ral amorphous carbon. This outcome highlights theevolution of surface contamination induced by elec-tron beam exposure due to the adsorption of carbon-aceous species.2. ResultsFigure 1 illustrates the schematic setup of the exper-iment, which combines CL measurements and elec-tron irradiation, conducted at room temperature. Thefirst step of the experiment is a CL hyperspectralmap-ping of the hBN flake of interest. Specifically, themapping is performed using an acceleration voltageof 5 keV and an electron beam current of 150 pA.The hyperspectral map is a 1024 × 1024 array ofspectral acquisitions across the selected area, with anacquisition time of 1 s per spectrum. A represent-ative CL spectrum for a 400 nm-thick hBN flake isshown in figure 1. The thickness of the hBN flake isprecisely measured using AFM, as detailed in figureS1, confirming a thickness of 400 nm. The CL spec-trum reveals several light emission peaks: an asym-metric emission at 5.83 eV (212nm) and a broad bandcentered at 3.73 eV (332 nm). Additional peaks are setat 2.91 eV (426 nm) and 1.92 eV (646 nm) which areidentified as second-order diffraction of the 5.83 eVand 3.73 eV radiative recombination processes.The sharp peak at 5.83 eV corresponds to theNBE phonon-assisted recombination in hBN at roomtemperature [46] This emission arises from s-like freeexcitons [38, 40, 47]. The low-energy tail of this peakis attributed to the D series, which represents radi-ative recombination associated with extended struc-tural defects, such as stacking faults [48], dislocations[49] or grain boundaries [47]. The broad emissionband at 3.73 eV, commonly referred to as the UVB,is attributed to radiative transitions involving impur-ities and their phonon replicas [38, 50].The second step of the experiment involves irradi-ating the hBN flake, as indicated by the blue square infigure 1. For this step, an accelerating voltage of 5 kVand a beam current of 90 pA are used to irradiate a30 µm × 30 µm area. During irradiation, the elec-tron beam scans the area at the maximum availablescan rate of 2MHz per frame, as provided by the scan-ning electron microscope (SEM). This ensures spatialhomogeneity of the irradiation dose. The 5 kV accel-erating voltage is selected to maximize the numberof scattering events within the hBN flake (as suppor-ted by the Monte Carlo simulation shown in figureS2). Additionally, this irradiation condition keeps thesystemwithin the dynamic charging regime, enablingvaluable secondary electron (SE) imaging [51–54].Importantly, at low accelerating voltages, the processoccurs at energy levels far below the knock-on energythreshold (120 keV) of the hBN lattice atoms [55].Consequently, the irradiation does not generate newcrystalline defects.The third step of the experiment involves acquir-ing a CL hyperspectral map of the same area analyzedin Step 1. Steps 2 and 3 are then repeated, consistentlyinvolving the same area. The hBN flake is irradiatedfor a total of 60min, divided into two sessions: an ini-tial 15 min round, followed by a 45 min round.The SE imaging of the hBN flake is shown infigure 2(a). When increasing the irradiation time, itis possible to distinguish the exposed area by a localchange in the SE contrast. It is worth noting that the15 min low-voltage irradiation (figure 2(b)) changesthe SE contrast homogeneously in the treated area.Increasing the irradiation time to 60min (figure 2(c))causes two main effects: the appearance of severalbright contrast lines and a charging striping effect inthe adjacent area. Using the standard formula for theSE contrast (C) of an object, we can perform a more22D Mater. 12 (2025) 025026 F Bianco et alFigure 1. Sketch of the process steps of the experiment combining room temperature CL measurements and electron irradiation.In step 1, the CL hyperspectral map of the pristine hBN flake is collected. The inset presents a representative CL spectrum, wherethe NBE and UVB emissions are indicated. In step 2, electron irradiation of a small area is carried out. In this particular case, thebeam continuously scans with a fast rate. In step 3, the CL map is collected again using the same magnification and number ofspectra as the initial map. Steps 2 and 3 are then repeated increasing the irradiation time in the same area.quantitative analysis of the effect of electron irradi-ation on the SE contrast [56]:C=(IOBJ − IBGIBG)× 100where IOBJ is the average SE intensity of the of thearea of interest, and IBG is the average SE intensityof the background. The SE contrast of the exposedarea increases by 37% after 15min of irradiation. Thisenhanced brightness is attributed to negative char-ging within the irradiated region [51]. After 60 minof irradiation, the SE contrast in the irradiated area isonly 16%brighter than the background. This reducedincrease in dynamic charging, combined with thepresence of a dark frame surrounding the irradi-ated region and several brighter lines, indicates sur-face contamination of the hBN, likely caused by theadsorption of carbonaceous species. Additionally, thecharge striping effect results in a 65% increase in SEcontrast in the adjacent area. The preferential char-ging observed to the right of the irradiated regionis attributed to the beam’s scanning direction, whichprogresses from left to right [53].The CL spectra of hBN as a function of increasingelectron irradiation time are shown in figure 3(a). Theprimary evolution of the CL lineshape with irradi-ation time is characterized by a decrease in the intens-ity of the UVB band. Furthermore, the full width athalf maximum (FWHM) of the NBE emission nar-rowswith increasing irradiation time. Specifically, thepristine hBN exhibits an FWHM of 450 meV, whichdecreases to 420 meV after 15 min of irradiation andreaches a minimum of 360 meV after 60 min. CLintegrated intensity and FWHM of the NBE and thesecond order diffraction bands as function of the irra-diation time are reported in figure S3.The evolution of the integrated CL intensities ofthe UVB and NBE emissions, along with their intens-ity ratio as a function of irradiation time, is shown infigure 3(b). The UVB emission is identified as a com-plex convolution of multiple radiative recombinationprocesses. A detailed deconvolution of the UVB band,presented in figure S4, reveals three distinct com-ponents. Two of these bands, located at 4.03 eV and3.86 eV, are attributed to the zero-phonon line (ZPL)of carbon defects and its corresponding phonon32D Mater. 12 (2025) 025026 F Bianco et alFigure 2. SEM micrograph, obtained with an Everhart–Thornley detector, of the analyzed flake before and after each irradiationstep: (a) pristine, (b) after 15 min, and (c) after 60 min.Figure 3. (a) Representative CL spectra of the hBN flat area: pristine (red line), after 15 min of irradiation (green line), and after60 min (blue line). For clarity, the CL spectra are shifted vertically every 30 cps. (b) CL integrated intensity of the UVB (blackcircles) and NBE (black squares) bands and the UVB/NBE integrated intensity ratio (red symbols) as function of the irradiationtime. UVB/NBE integrated intensity ratio maps, acquired in the same area: (c) pristine hBN, (d) of 15 min irradiated and (e)60 min irradiated, respectively.replica [57, 58]. An additional emission at 3.43 eV isreported, probably related to a donor–acceptor pair[59]. The integrated intensity of the UVB emissiondecreases by 20% after 15 min of irradiation anddeclines by an additional 20% following 60 min ofirradiation. In contrast, the integrated intensity of theNBE recombination exhibits a peak after 15 min ofirradiation, with an increase of 3.2%. However, thisintensity subsequently decreases by 6% after 60 minof irradiation. To illustrate the evolution of UVBand NBE emission intensities with increasing elec-tron irradiation time, we present the CL mapping ofthe UVB/NBE integrated intensity ratio for the dif-ferent irradiation steps in figures 3(c)–(e), respect-ively. The UVB/NBE ratio is widely recognized as akey indicator of defect density [40, 47]. The intensityratio is not uniform across the analyzed area, indicat-ing a spatially inhomogeneous distribution of defectdensity. Nevertheless, the primary effect of electronirradiation is a consistent, homogeneous decrease in42D Mater. 12 (2025) 025026 F Bianco et alFigure 4. (a) Below-bandgap excitation PL analysis, before (defined as pristine, red line) and after (defined as irradiated, cyanline) the electron irradiation process. (b) Raman spectra collected in the irradiation area before (red line) and after (cyan line) the60 min irradiation process. The black dashed line highlight the presence of amorphous carbon Raman modes.the UVB/NBE integrated intensity ratio over time(figure 3(b)).To investigate the origin of theUVBband quench-ing, we performed ex-situ optical and structural ana-lyzes. Recent studies have shown that below-bandgapexcitation PL analysis can offer valuable insights intothe presence of deep levels within the hBN bandgap[44]. Specifically, it has been shown that the PL emis-sion between 1.8 eV and 2.5 eV originates from radi-ative recombination involving the same deep levelsresponsible for the CL emission observed between3.0 eV and 4.5 eV [44]. The PL spectra of the hBNflake before and after the 60 min irradiation pro-cess are shown in figure 4(a). Due to the ex-situnature of the investigation, only the PL spectrum ofthe 60 min irradiated sample is presented. The irra-diation process results in a significant decrease inluminescence intensity across the entire energy range.Notably, the PL spectra consist of multiple emis-sions, with theirGaussian deconvolutions provided infigure S5.The most prominent effect of the irradiation pro-cess is the substantial quenching of the broad emis-sion at 2.03 eV, which decreases by 66%. This quench-ing is considerably more severe than the intensityreductions observed for the 2.33 eV and 1.88 eV com-ponents, which decrease by 44% and 47%, respect-ively. The below-bandgap excitation PL analysis con-firms the irradiation-induced modifications to thedeep-level emissions previously identified in the CLanalysis, as shown in figure 3.Raman spectroscopy has been employed toidentify possible structural changes in the irradiatedarea by analyzing the hBNRamanmode FWHM. TheRaman peak, which is conventionally investigatedin hBN, is at 1365 cm−1. This mode is attributedto the in-plane atom vibrations (E2g mode) [60].Figure 4(b) presents the Raman spectra before irradi-ation (defined as pristine, red line), and after irradi-ation and exposure to the lab environment (definedas irradiated, cyan line). The careful analysis of theE2g mode FWHM shows that the irradiation processcauses a broadening of the peak from 8.3 cm−1 to8.7 cm−1. This broadening is an indication of thedegradation of the crystalline quality of the hBN lat-tice. The Raman spectrum after irradiation presentsalso the appearance of an additional broad bandsat 1575 cm−1 and at 1350 cm−1 superimposed tothe hBN Raman mode. These modifications to theRaman spectrum can be attributed to the surfacecontamination by hydrocarbon species [61] and theconsequent modification of such species by the elec-tron beam irradiation. In fact, the broad mode at1575 cm−1 and at 1350 cm−1 can be assigned to theG and D modes of amorphous carbon. The Ramanlineshape can indicate the presence of partially recrys-tallized tetrahedral amorphous carbon (ta-C) [62,63]. This attribution is manly supported by theRaman shift of the G mode at 1575 cm−1 and theD/G intensity ratio equal to 0.5. In fact, The increaseof theD peak intensity in ta-C is due to an increase ofthe sp2 bonds cause by electron beam irradiation [64,65]. In our case, the 60 min electron irradiation pro-cess provides enough energy to transform the hydro-carbon contaminants in ta-C and then to enhance thecrystallinity of the deposited layer. The Raman intens-ity maps of the hBN and G modes are reported infigure S5 in order to highlight the spatial localizationof the Gmode in the irradiated area. An actual trendin the Raman analysis of particles irradiated hBN isreporting a defect activated Raman modes (grapheneD peak like) of hBN [66–68]. While the authors of52D Mater. 12 (2025) 025026 F Bianco et althese works have attributed these Raman modes todefect-activated modes of hBN, our data suggeststhat these Raman modes appear to be related to thepresence of amorphous carbon, deposited during theirradiation processes [7, 21, 69]. The morphologicalanalysis of the irradiated area, carried out by AFM,reveals the presence of a 43 nm thick amorphouscarbon layer as reported in figure S7.3. DiscussionThe UVB quenching observed in both PL and CLexperiments indicates a reduction in the concentra-tion of defects that facilitate radiative recombinationwithin the hBN bandgap. This effect can be attributedto two possiblemechanisms: electron beam annealingof the irradiated region of the hBN flake or the elec-tron beam-induced dissociation of defects respons-ible for the UVB emission. To evaluate the potentialfor electron beam annealing, we estimated the localtemperature increase caused by electron beam irra-diation by comparing two well-established models:the modified Vine-Einstein model [70, 71] and theBaker-Sexton model [72]. The temperature increaseis estimated to be 85 K using the Vine-Einsteinmodel and 115 K using the Baker-Sexton model. Allparameters and formulas used for these temperatureestimations are provided in table S1. However, theestimated temperature increase is likely insufficient tomodify the radiative defects responsible for the UVBemission. Notably, high-temperature annealing pro-cesses (T⩾ 1273K) are typically required to eliminateradiative defects in hBN [73, 74]. Therefore, we attrib-ute the dissociation of defects by the electron beam asthe most probable cause of the UVB emission reduc-tion. Similar effects have been reported for low energyelectron beam irradiation in C-doped hBN [34], Mg-doped GaN thin film [75, 76], GaN quantum wells[77] and diamond films [78–80]. To clarify the disso-ciation process occurring during electron irradiation,it is essential to identify the origin of the UVB band.Several studies have attributed the UVB emission tocarbon-containing defects [30, 81–85]. In particu-lar, recent works have addressed the in-plane carbondimer (CBCN) as the defect originating the 4.1 eVZPLemission [57, 58, 86–89]. The in-plane carbon dimerhas a formation energy of approximately 2 eV [58].Consequently, the energy delivered by electron beamirradiation (250 eV across the entire thickness of thehBN flake, as shown in figure S2, for a single irra-diation event) is sufficient to cause the dissociationof this defect. This energy is delivered through mul-tiple scattering events, that occurs during the long-time irradiation process.The in-plane carbon dimer dissociation may leadto a different configuration of carbon substitutionalcenters. The most probable configuration is thedonor–acceptor pair composed of a carbon atomin boron position and in nitrogen position (CBCN-DAP). These configurations are energetically favored,considering the energy provided by the scatteringevents with the electron beam [86]. These particu-lar configurations present radiative recombination inthe range of the second order diffraction of the UVBor outside of the optical range analyzed in this work[86]. The atomistic model of the evolution of the in-plane carbon dimer is presented in figure 5, report-ing the possible configuration of the CBCN-DAP withdifferent spatial separation. The calculated ZPL of thedifferent configuration of the (CBCN-DAP) are repor-ted in table S2. A possible change of the charge stateof the CBCN center is a possible mechanism for thequenching of the UVB. In fact, the ZPL of the pos-itively and negatively charged carbon dimer falls inan optical range not analyzed in the present work. Inparticular, the positively charged CBCN is expected topresent a light emission at 1.055 eV while the negat-ively charged one should emit light at 0.442 eV [86].The SE contrast analysis, reported in figure 2, suggeststhe negative charge state of the CBCN donor acceptorpair.The possible rise of amorphous carbon inducedartifacts, affecting the in-situ CL analysis, is reportedin figure S8.4. ConclusionsIn conclusion, we demonstrate an efficient andrapid method for suppressing undesired defect-related radiative recombination in hBN throughlarge-area, fast-scanning, low-voltage electron irradi-ation, monitored via in-situ CL hyperspectral ana-lysis. Prolonged irradiation leads to a monotonicquenching of deep-level UV emissions and a concur-rent narrowing of NBEUV emissions. The quenchingof the UVB is ascribed to the electron beam-induceddissociation of in-plane carbon dimers, into differentconfigurations of the donor acceptor pair of substitu-tional carbon atoms, that can be optically inactive oremits light in a different optical range. An additionalmechanism of the UVB quenching is the change ofthe charge state of the CBCN center, that causes a lightemission in a different optical range. This interpreta-tion is further supported by the observed reduction inex-situ below-bandgap excitation PL emissions.Additionally, ex-situ Raman and AFM analyzesreveal a significant side effect of prolonged electronirradiation: the formation of a 40 nm thick layer oftetrahedral amorphous carbon. This result under-scores the evolution of electron beam-induced surfacecontamination, caused by the adsorption of carbon-aceous species, observed by SE contrast modificationduring the in-situ CL analysis.62D Mater. 12 (2025) 025026 F Bianco et alFigure 5. Atomistic model of the evolution of the in-planer carbon dimer under electron beam irradiation, (B in blue, N in pinkand C in grey) with the possible configuration of the donor acceptor pair with different spatial separation (indicated asred-highlighted atoms). The blue arrows indicate the hopping of the carbon atoms in the different site of the hBN lattice.5. Experimental methodsWe obtain the hBN flake via standard micro-mechanical exfoliation from bulk single crystals [44,82].The CL measurements and sample irradiationprocesses are carried out in a CL dedicated AttolightRosa SEMmicroscope. The specimen is left overnightin vacuum for an effective degassing of the SEMchamber. The electron irradiation is carried out withan accelerating voltage of 5 kV and a beam current of91 pA, keeping the electron beam scanning over thearea of interest at a frequency of 2 MHz/frame. Thetotal dose in the first round of irradiation (15 min) is177 mC cm−2 and 708 mC cm−2 during the 60 minirradiation.The integrated intensity of the NBE is evaluatedbetween 6.25 eV and 5 eV, while for the UVB emis-sion, the integrated intensity is obtained between 5 eVand 3.2 eV.The SEM images are taken in-situ with a standardEverhart–Thornley detector for SEs. The CL meas-urements are carried out at room temperature, withan accelerating voltage of 5 kV and a beam currentof 150 pA. The CL signal is sent to a spectrometerby means of an objective (NA = 0.71) placed in theelectron microscope. The system is equipped with a600 l mm−1 diffraction grating and a Peltier-cooledcharge-coupled device.AFM measurements are performed using aDimension Icon AFM (Bruker) operating in PeakForce mode and using a ScanAsyst probe.Raman and PL experiments are carried out witha Renishaw InVia system, equipped with a confocalmicroscope, a 473 nm excitation laser and a 2400line/mmgrating. TheRamanmeasurements are takenwith the following parameters: excitation laser power1 mW, 10 s acquisition time for each spectrum and aspot size of 800 nm (100X objective with NA= 0.85).The PL experiments are carried out with the sameparameters, except for an acquisition of 30 s.Data availability statementThe data that support the findings of this study areopenly available at the following URL/DOI: https://10.5281/zenodo.14671078.AcknowledgmentF F wants to thank C Blaga, N Tappy and Professor AFontcuberta i Morral for the scientific discussions. FB, S P and F F thank Dr C Coletti from the IstitutoItaliano di Tecnologia for the access to the micro-Raman facility. K W and T T acknowledge supportfrom the JSPS KAKENHI (Grant Numbers 21H05233and 23H02052), the CREST (JPMJCR24A5), JST7https://10.5281/zenodo.14671078https://10.5281/zenodo.146710782D Mater. 12 (2025) 025026 F Bianco et aland World Premier International Research CenterInitiative (WPI), MEXT, Japan.Conflict of interestThe authors declare no conflict of interest.ContributionsK.W. and T.T. provided the hBN crystals. S.P. exfoli-ated the hBN flakes. F.B. carried out themicro-Ramanand PL spectroscopies measurements. F.F. carried outthe in-situ CL spectroscopic measurements and theAFM analysis. F. F. and F. B. analyzed and interpretedthe data. F.F. conceived the idea of the experiment,coordinated research efforts and wrote the paper. Allauthors participated in reviewing the manuscript.ORCID iDsF Bianco https://orcid.org/0000-0002-6372-8889S Pezzini https://orcid.org/0000-0003-4289-907XKWatanabe https://orcid.org/0000-0003-3701-8119F Fabbri https://orcid.org/0000-0003-1142-0441References[1] Caldwell J D, Aharonovich I, Cassabois G, Edgar J H, Gil Band Basov D N 2019 Photonics with hexagonal boron nitrideNat. Rev. Mater. 4 552–67[2] Turunen M, Brotons-Gisbert M, Dai Y, Wang Y, Scerri E,Bonato C, Jöns K D, Sun Z and Gerardot B D 2022 Quantumphotonics with layered 2D materials Nat. Rev. Phys. 4219–236[3] Moon S, Kim J, Park J, Im S, Kim J, Hwang I and Kim J K2023 Hexagonal boron nitride for next-generation photonicsand electronics Adv. 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Introduction 2. Results 3. Discussion 4. Conclusions 5. Experimental methods References