# Fileset

[s42004-023-00899-1.pdf](https://mdr.nims.go.jp/filesets/80746e53-be43-48b5-a691-d613011fc746/download)

## Creator

Chunhui Dai, Derek Popple, Cong Su, Ji-Hoon Park, [Kenji Watanabe](https://orcid.org/0000-0003-3701-8119), [Takashi Taniguchi](https://orcid.org/0000-0002-1467-3105), Jing Kong, Alex Zettl

## Rights

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

## Other metadata

[Evolution of nanopores in hexagonal boron nitride](https://mdr.nims.go.jp/datasets/5f9435ce-2f46-4d37-9920-12492f5741c7)

## Fulltext

Evolution of nanopores in hexagonal boron nitrideARTICLEEvolution of nanopores in hexagonal boron nitrideChunhui Dai1,2,3, Derek Popple 2,3,4, Cong Su 1,2,3, Ji-Hoon Park 5, Kenji Watanabe 6,Takashi Taniguchi 6, Jing Kong 5 & Alex Zettl 1,2,3✉The engineering of atomically-precise nanopores in two-dimensional materials presentsexciting opportunities for both fundamental science studies as well as applications in energy,DNA sequencing, and quantum information technologies. The exceptional chemical andthermal stability of hexagonal boron nitride (h-BN) suggest that exposed h-BN nanopores willretain their atomic structure even when subjected to extended periods of time in gas or liquidenvironments. Here we employ transmission electron microscopy to examine the timeevolution of h-BN nanopores in vacuum and in air and find, even at room temperature,dramatic geometry changes due to atom motion and edge contamination adsorption, fortimescales ranging from one hour to one week. The discovery of nanopore evolution con-trasts with general expectations and has profound implications for nanopore applications oftwo-dimensional materials.https://doi.org/10.1038/s42004-023-00899-1 OPEN1 Department of Physics, University of California at Berkeley, Berkeley, CA 94720, USA. 2Materials Sciences Division, Lawrence Berkeley National Laboratory,Berkeley, CA 94720, USA. 3 Kavli Energy NanoSciences Institute at the University of California at Berkeley and the Lawrence Berkeley National Laboratory,Berkeley, CA 94720, USA. 4Department of Chemistry, University of California at Berkeley, Berkeley, CA 94720, USA. 5Department of Electrical Engineeringand Computer Science, Massachusetts Institute of Technology, Cambridge, MA 02142, USA. 6 International Centre for Materials Nanoarchitectonics,National Institute for Materials Science, Tsukuba, Japan. ✉email: azettl@berkeley.eduCOMMUNICATIONS CHEMISTRY |           (2023) 6:108 | https://doi.org/10.1038/s42004-023-00899-1 | www.nature.com/commschem 11234567890():,;http://crossmark.crossref.org/dialog/?doi=10.1038/s42004-023-00899-1&domain=pdfhttp://crossmark.crossref.org/dialog/?doi=10.1038/s42004-023-00899-1&domain=pdfhttp://crossmark.crossref.org/dialog/?doi=10.1038/s42004-023-00899-1&domain=pdfhttp://crossmark.crossref.org/dialog/?doi=10.1038/s42004-023-00899-1&domain=pdfhttp://orcid.org/0000-0002-3189-1948http://orcid.org/0000-0002-3189-1948http://orcid.org/0000-0002-3189-1948http://orcid.org/0000-0002-3189-1948http://orcid.org/0000-0002-3189-1948http://orcid.org/0000-0002-7198-0259http://orcid.org/0000-0002-7198-0259http://orcid.org/0000-0002-7198-0259http://orcid.org/0000-0002-7198-0259http://orcid.org/0000-0002-7198-0259http://orcid.org/0000-0003-4776-5206http://orcid.org/0000-0003-4776-5206http://orcid.org/0000-0003-4776-5206http://orcid.org/0000-0003-4776-5206http://orcid.org/0000-0003-4776-5206http://orcid.org/0000-0003-3701-8119http://orcid.org/0000-0003-3701-8119http://orcid.org/0000-0003-3701-8119http://orcid.org/0000-0003-3701-8119http://orcid.org/0000-0003-3701-8119http://orcid.org/0000-0002-1467-3105http://orcid.org/0000-0002-1467-3105http://orcid.org/0000-0002-1467-3105http://orcid.org/0000-0002-1467-3105http://orcid.org/0000-0002-1467-3105http://orcid.org/0000-0003-0551-1208http://orcid.org/0000-0003-0551-1208http://orcid.org/0000-0003-0551-1208http://orcid.org/0000-0003-0551-1208http://orcid.org/0000-0003-0551-1208http://orcid.org/0000-0001-6330-136Xhttp://orcid.org/0000-0001-6330-136Xhttp://orcid.org/0000-0001-6330-136Xhttp://orcid.org/0000-0001-6330-136Xhttp://orcid.org/0000-0001-6330-136Xmailto:azettl@berkeley.eduwww.nature.com/commschemwww.nature.com/commschemThere is rapidly growing interest in local atomic-structureengineering of two-dimensional (2D) materials such asgraphene1,2, MoS23,4, and hexagonal boron nitride (h-BN)5–13. Nanopores, ranging in size from just one missing atomto dozens or even hundreds of missing atoms, can have profoundeffects on the chemical14, mechanical15,16, and electro-opticalproperties of the material17–19. Nanopore technology couldreshape various fields ranging from energy conversion andstorage20 to water purification14 to quantum datatechnologies15,17,21–24.Of particular interest is h-BN, for which nanopores with highlyreproducible shapes and sizes, with atomically precise edges, canbe readily created5–13. Bulk h-BN is also especially chemically andthermally stable (even in an oxidizing environment)25, suggestinghighly stable nanopore configurations. Edge defects are found toeffectively tune the band gap of h-BN26, which enables thecreation of highly reactive sites for hydrogen evolution reactionand facilitates the development of hydrogen-based greenenergy20. Channels formed in monolayer h-BN can serve asultrasensitive solid-state nanopore sensors for DNA sequencingand advanced DNA-based information storage devices27.Vacancy-related defects in monolayer17, multilayer23, andinterfacial24 h-BN forms serve as controllable, efficient quantumemitters setting the stage for optically based quantum datatransfer and computation technologies.Various techniques have been employed to achieve nanoporesin h-BN, including laser irradiation28, focused ion beam(xenon29,30, nitrogen30, argon30, and helium ions31), and con-densed electron beam (e-beam)5,7,11–13,15,32. Among these tech-niques, condensed electron beam irradiation in a TEM or ascanning transmission electron microscope (STEM) stands out asthe most precise and controllable tool due to its capability forselective knock-on energy transfer coupled with in situ atomic-scale imaging12,13,32. In h-BN, the nanopore shape (e.g., trian-gular, hexagonal, or otherwise) can be precisely tuned by selectingthe temperature or irradiation dose during the electron irradia-tion process5,7.Many of the predicted nanopore properties for h-BN (andrelated 2D materials) depend sensitively on the pore size and edgegeometry12,33. Therefore, it is critical to understand nanoporestability. Nanopore instability in graphene has been previouslyinvestigated34,35. However, because of the highly stable nature ofbulk h-BN, it has generally been assumed that the atomic con-figuration of h-BN nanopores would be equally stable21,22,especially under the relatively mild environmental conditions ofthe air at room temperature. In this report, we show that thisconventional wisdom is wrong. We present an investigation of theevolution of nanopores in h-BN under different environmentalconditions (vacuum and air, at room temperature). A condensedelectron beam in a TEM system is used to create nanopores inmono- and multilayer h-BN. The nanopores are characterized byTEM immediately after being created, and exactly the samenanopores are again characterized via TEM after the sample isstored in a vacuum or air for selected time periods ranging fromone hour to 1 week. TEM is used for this study because it has ashorter imaging acquisition time than STEM, and we therebyminimize undesirable imaging-induced nanopore changes. Wefind that nanopores in both monolayer and multilayer h-BN arehighly stable in a vacuum but not in the air. Even at room tem-perature, the atomic configuration of h-BN nanopores evolves inthe air spontaneously and dramatically within one hour. Thesefindings suggest additional work on stabilizing the nanopores isrequired to employ them for reliable and stable devices.Results and discussionThree types of h-BN are used in this study: monolayer h-BN, AA’stacked multilayer h-BN, and Bernal stacked (AB) multilayerh-BN. The monolayer and AB stacked multilayer h-BN are syn-thesized by a chemical vapor deposition (CVD) process asdescribed in the methods and refs. 36,37. As stated in our earlierwork37, the AB stacking order is achieved by employing low-pressure CVD on transition metals, iron or copper, and has beenconfirmed by selected area electron diffraction. A wet transferprocess is used to transfer the membranes onto holey siliconnitride TEM grids37 (see Supplementary Fig. S1). AA’ stackedmultilayer h-BN is directly exfoliated from crystals grown inJapan and dry transferred onto a TEM grid38. After transferring,the suspended membranes are imaged and irradiated by an 80 kVe-beam in a TEM system (JEOL 2010) to create the nanopores.Figure 1a schematically shows the electron irradiation-inducednanopore formation process in suspended h-BN membranes. Asreported in previous work7,12,13,32, the nanopore preferably startsfrom a boron (B) vacancy, as B has a lower knock-on thresholdcompared to nitrogen (N). Then the adjacent N and B atoms areknocked off alternatively, forming a larger triangular nanoporeterminated by nitrogen zigzag edges5. Figure 1b shows thus-formed triangular nanopores with various sizes in monolayerFig. 1 Schematics and TEM images showing the formation of nanopores in h-BN. a Schematic of nanopore formation process in mono- or multi-layer h-BNusing a condensed electron beam. A single boron vacancy is formed initially, and the nanopore grows into a larger nanopore. The electron beam is operatedat 80 kV with a beam current of 40A/cm2. b TEM image of triangular nanopores formed in CVD-grown monolayer h-BN. c TEM image showing theformation of incomplete nanopores, i.e., pits and striping of layers in an exfoliated AA’ stacked multilayer h-BN. The patterns shown in the TEM image arethe edges of the nanopore pits. Due to the AA’ stacking order, anti-directional triangular nanopores are formed in interlayers, leading to the loss of triangulargeometry in the membrane. The membrane thickness is around ~10 nm. The inset shows schematically the AA’ stacking configuration, where each atomicsite has an N stacked over a B or a B stacked over an N. Upper layer atoms are drawn smaller for clarity. d TEM image of incomplete nanopores (pits) formedin Bernal (AB) stacked multilayer h-BN. The membrane thickness is around ~10 nm. The nanopores preserve the triangular geometry as in monolayer BN.The inset shows schematically the AB stacking configuration. As in the inset to c, upper layer atoms are drawn smaller for clarity.ARTICLE COMMUNICATIONS CHEMISTRY | https://doi.org/10.1038/s42004-023-00899-12 COMMUNICATIONS CHEMISTRY |           (2023) 6:108 | https://doi.org/10.1038/s42004-023-00899-1 | www.nature.com/commschemwww.nature.com/commschemh-BN. In multilayer BN, the electron beam may interact withadjacent layers, leading to more complex incomplete nanopores,i.e., pits10. In AA’ stacked h-BN, all the B and N in the adjacentlayers are alternatingly stacked together (Fig. 1c inset), losing thethree-fold symmetry of the lattice37. As a result, the nanoporeshape is not deterministic. Figure 1c shows incomplete nanoporesformed on the surface of an AA’ stacked h-BN. No preferredshape is observed. In contrast, for AB stacked h-BN, only half ofthe lattice sites are stacked in the form of B on N or N on B37(Fig. 1d inset), which allows the vacancies to preserve p3 sym-metry as in the monolayer. Figure 1d shows incomplete nano-pores formed on the surface of an AB-stacked h-BN. Thetriangular outlines can still be clearly identified. For the detailedstudy of nanopore evolution presented below, we use nanoporesformed in monolayer and AB stacked multilayer h-BN, whichhave triangular geometry and allow us to clearly track geometrychanges.Evolution of nanopores in monolayer hBN. Figure 2 presentsthe nanopores’ geometry change in monolayer h-BN 1 h aftertheir creation in a vacuum. Once the nanopores are created andimaged by an 80 kV TEM e-beam, the samples are withdrawnfrom the electron beam region and are stored at room tempera-ture in a vacuum (Fig. 2a–c) or air with relative humidity ~40%(Fig. 2d–i). After 1 h, the same samples are returned to thevacuum and imaged to evaluate any spontaneous geometricalchanges. To avoid unnecessary electron irradiation, a differentarea on the sample grid is first used for focusing. Once focused,the TEM viewing window is returned to precisely the same ori-ginal nanopore region for secondary rapid structuralcharacterization.For nanopores that see only vacuum, the triangular nanoporeremains intact, even for nanopores in close proximity to oneother (examples are indicated by the red circles in Fig. 2b, c). Forstorage in air, both the adjacent nanopores (Fig. 2d–f) and theseparated nanopores (Fig. 2g–i) are unstable, even at theminimum timescale of 1 h. The adjacent nanopores with a sharednarrow edge (Fig. 2e, highlighted by the red circle) have merged,growing into an enlarged triangular nanopore (Fig. 2f, highlightedby the red circle). Separated nanopores are also unstable in theair. As shown in Fig. 2g, h, even though the large and smallFig. 2 Evolution of nanopores in monolayer h-BN after being stored in vacuum or air for 1 h. a–c are for vacuum and d–i are for air. a, d, g The schematicsare generic representations of the geometries of the nanopores (and do not necessarily represent a scaled atomic mapping to the TEM images below). Thegreen triangles represent the original geometry of the nanopores. d, g The red arrows show the merging direction of the nanopores, and the gray areasshow the newly extended pore regime. a Schematics and b, c TEM images showing the defects b before and c after being stored in a vacuum for 1 h.b Initially, the sample supports suspended zigzag edges around large nanopores and smaller triangular nanopores (highlighted by the red circles). c Theseparate or adjacent distinct triangular nanopores are stable in a vacuum and preserve their original form. d–i Schematics and TEM images showing thedeformation processes of d–f adjacent nanopores and g–i separate nanopores after being stored in air for 1 h. e TEM image of the two adjacent triangularnanopores (highlighted by the red circle). f The adjacent triangular nanopores are unstable in the air and merge into a larger triangular nanopore. h TEMimage highlights three groups of nanopores (indicated by the red circles) with a separation from 1 to 5 nm. i The two separated nanopores have, uponexposure to air for 1 h, merged into a single nanopore, as shown schematically in (g). Orange arrows depict the flow of time.COMMUNICATIONS CHEMISTRY | https://doi.org/10.1038/s42004-023-00899-1 ARTICLECOMMUNICATIONS CHEMISTRY |           (2023) 6:108 | https://doi.org/10.1038/s42004-023-00899-1 | www.nature.com/commschem 3www.nature.com/commschemwww.nature.com/commschemtriangular nanopores are separated by up to ~5 nm, a vacancypathway is spontaneously formed between the two nanopores,making the two nanopores join into one (Fig. 2i). Theseobservations indicate that the N-terminated edges of thenanopores are extremely unstable in the air. Unlike previouslyreported electron beam stimulated migration of such nanopores7,the spontaneous deformation processes here observed aredominated by apparent etching/erosion of the atoms on the edgeof the nanopores rather than the diffusion of atoms within thelattice. This erosion-like process is conjectured to be caused bythe reaction between the nanopore edge atoms with danglingbonds and the oxygen or other related gas molecules in the air.Evolution of nanopores in multilayer hBN. To further examinethe evolution of nanopores in h-BN, we conducted an experimenton AB-stacked multilayer h-BN at a longer time scale. Figure 3ashows the initial nanopores formed on a 10-nm thick AB-stackedh-BN membrane. The detailed nanopore formation processes areshown in supplementary Fig. S2. Both incomplete nanopores (i.e.,nanopore pits that penetrate only some of the h-BN layers) andlarge through-pores can be observed. Also, the nanopores are alltriangular in shape with clear edges. After being stored in the airfor 1 week, these nanopores experience dramatic changes(Fig. 3b). First, almost no triangular incomplete nanoporesremain at the same location. Second, the thinner membraneregions near the edges of the large pores are eroded (Fig. 3b,indicated by the red arrow). As a result, all the sharp edges of thetriangular nanopores drilled through the membrane becomerounded. Third, the incomplete nanopores can also erode nor-mally to the surface, transforming a previously finite-depth pitinto a round nanopore entirely piercing the membrane (Fig. 3b,highlighted by the red circles). These observations confirm acontinuing longer-term evolution of the h-BN nanopore sub-jected to air.Surface contamination spreading. Figure 4 presents anothernanopore evolution phenomenon: that of surface contaminationspreading. Figure 4a, c shows the initial nanopores with differentsizes formed in the h-BN membranes. The dominant con-taminants on the h-BN are presumably inevitable Poly(methylmethacrylate) (PMMA) residuals left from the wet transferprocess39. But there this a clear boundary to a very clean regimethat has no apparent contamination residuals (Fig. 4a, c, high-lighted by the dashed white lines). Following initial nanoporecreation and imaging, these two samples are stored in a vacuumor in the air for 15 h, respectively. In a vacuum, there is almost nochange in the majority of the nanopores, and almost all of theoriginally clean area remains contamination free (a few spots ofnew contamination are highlighted by arrows in Fig. 4b). Incontrast, the h-BN sample stored in air experiences significantlymore change (Fig. 4d). When subjected to air, large portions ofthe originally clean area outlined in Fig. 4c become highly con-taminated (Fig. 4d). The new contamination appears to benucleated at edges of the existing patches of contamination,which apparently present preferential sites for molecule attach-ment. In the air more and more surface contaminants are builtup, thereby “spreading” the surface contamination. This spread-ing can sometimes entirely obscure an original nanopore (Fig. 4d,indicated by the arrows). Overall, the air environment can sig-nificantly facilitate not only erosion but also contaminationexpansion processes and can quickly render, in a matter of hours,a well-engineered nanopore configuration in h-BN whollyineffective.ConclusionsIn conclusion, this work finds that different nanopores formed inmono- and multi-layer h-BN are stable in a vacuum but undergodramatic changes in the air. In the air, nanopores can grow insize, which inevitably involves both boron and nitrogen removalat the pore edges. Existing nanopores can also be overrun byexpanding surface contamination that primarily originates fromadjacent patches of surface contamination. Notably, we do notobserve any obvious changes to pristine regions (atomicallyperfect regions with no nanopores or contamination present) ofFig. 3 Longer-term evolution of nanopores in Bernal stacked multilayerh-BN stored in air. a Triangular complete nanopores and incompletenanopores (i.e., pits) are created using a condensed electron beam inmultilayer h-BN. The electron beam is condensed to a 10–20 nm diameterwith a beam current of ~40 A/cm2. The overall nanopore formation processtakes ~2 h. The thickness of the membrane is ~10 nm. The red arrowindicates the thin fringes near the large pores. The red circles highlight thepits partially etched area on the surface of the membrane. b After beingstored in the air for one week, most of the triangular incomplete nanoporesare unrecognizable. The sharp triangular edges near the pores are eroded,leading to a rounded nanopore. The red arrow indicates the eroded edges.Also, some incomplete nanopores are further etched into the h-BNmembrane and form new nanopores, as highlighted by the red circles. Theorange arrow indicates the flow of time.ARTICLE COMMUNICATIONS CHEMISTRY | https://doi.org/10.1038/s42004-023-00899-14 COMMUNICATIONS CHEMISTRY |           (2023) 6:108 | https://doi.org/10.1038/s42004-023-00899-1 | www.nature.com/commschemwww.nature.com/commschemsuspended monolayer or multilayer h-BN, in a vacuum or in anair environment. This is key to the excellent stability of bulkh-BN. We also surmise that h-BN nanopores covered by at leastone monolayer of pristine h-BN will be relatively immune to thespontaneous reconfiguration of the defect within, perhaps pro-viding a simple pathway to the stabilization of, for example, tai-lored quantum emitters. This study also raises the importance ofstudying nanopores stabilities in other two-dimensional materialsfor advancing both fundamental understanding and applications.Moreover, the reaction at the edge sites of BN nanopores in theair suggests a useful direction to further investigate the reactionmechanism with different gas molecules.MethodsMonolayer hBN synthesis. The monolayer hBN is synthesized on a copper foilusing a CVD process. The quartz tube in the CVD system is first heated to 1070 °Cunder a flow of 10 sccm of hydrogen (H2) gas. The reaction chamber is maintainedin this condition for 10 min to stabilize the temperature. Next, borazine andhydrogen are flowed into the reaction chamber at 0.6 sccm and 10 sccm, respec-tively, to grow the monolayer hBN. To ensure high-quality monolayer hBN, thefurnace is cooled down quickly to room temperature.AB stacked multilayer hBN synthesis. The AB stacked hBN used in this work issynthesized on iron (Fe) foil using a low-pressure (LP)-CVD system, which con-sists of two heating zones. Ammonia-borane power is used as a solid B and Nprecursor. During the synthesis, the foil is first annealed for 1 h at 1100 °C under aflow of 100 sccm H2 and 300 sccm argon (Ar). To grow the AB stacked multilayerhBN. Ar gas is turned off, and the H2 gas flow rate is maintained at 100 sccm.Totally, 100 mg of ammonia borane loaded in the separate quartz tube upstream ofthe reaction tube is heated to 80 °C to initiate the film growth. After 1 h synthesis,the precursor and main reaction tube are both quickly cooled to room temperature.The H2 gas flow rate is reduced to 10 sccm during the cooling process.TEM for nanopore formation and imaging. The nanopores in h-BN are preparedusing a JEOL 2010 TEM operated at 80 kV. The vacuum system is operated in the10−9 torr range. To form nanopores, the electron beam is condensed to a 10–20 nmdiameter at spot size 3, alpha= 3, with a beam current of ~40 A/cm2. In amonolayer hBN, it takes around 2-3 minutes (electron dose:1.5–2.2 × 1021 electrons/cm2) to form one pore in a newly exposed layer. In mul-tilayer hBN, the nanopore formation time varies according to the membranethickness. For a 10 nm thick hBN, it could take two to three hours (electron dose:0.9–1.3 × 1023 electrons/cm2) to form a pore. To acquire images, the beam isexpended to reduce the beam current down to ~3 A/cm2 at spot 3.Data availabilityAll data are available in the main text or the supplementary materials.Received: 17 December 2022; Accepted: 8 May 2023;References1. Schneider, G. F. et al. DNA translocation through graphene nanopores. NanoLett. 10, 3163–3167 (2010).2. Drndić, M. Sequencing with graphene pores. Nat. Nanotechnol. 9, 743–743(2014).3. Sapkota, B. et al. High permeability sub-nanometre sieve composite MoS2membranes. Nat. Commun. 11, 2747 (2020).4. Thiruraman, J. P., Masih Das, P. & Drndic, M. Stochastic ionic transport insingle atomic zero-dimensional pores. ACS Nano 14, 11831–11845 (2020).5. Pham, T. et al. Formation and dynamics of electron-irradiation-induceddefects in hexagonal boron nitride at elevated temperatures. Nano Lett. 16,7142–7147 (2016).6. Xu, X. et al. Creating quantum emitters in hexagonal boron nitridedeterministically on chip-compatible substrates. Nano Lett. 21, 8182–8189 (2021).7. Alem, N. et al. Vacancy growth and migration dynamics in atomically thinhexagonal boron nitride under electron beam irradiation. Phys. Status Solidi 5,295–297 (2011).8. Gao, X. et al. Femtosecond laser writing of spin defects in hexagonal boronnitride. ACS Photonics 8, 994–1000 (2021).9. Alem, N. et al. Atomically thin hexagonal boron nitride probed by ultrahigh-resolution transmission electron microscopy. Phys. Rev. B 80, 155425 (2009).10. Alem, N. et al. Subangstrom edge relaxations probed by electron microscopyin hexagonal boron nitride. Phys. Rev. Lett. 109, 205502 (2012).11. Dogan, M. et al. Electron beam-induced nanopores in Bernal-stackedhexagonal boron nitride. Appl. Phys. Lett. 117, 023102 (2020).12. Gilbert, S. M. et al. Fabrication of subnanometer-precision nanopores inhexagonal boron nitride. Sci. Rep. 7, 15096 (2017).13. Kotakoski, J., Jin, C. H., Lehtinen, O., Suenaga, K. & Krasheninnikov, A. V.Electron knock-on damage in hexagonal boron nitride monolayers. Phys. Rev.B 82, 113404 (2010).14. Tsukanov, A. A., & Shilko, E. V. Molecular dynamics of water and ionsfiltration through rectangular nanopores in boron nitride nanosheets. in AIPConference Proceedings (Vol. 2167, p. 020372). (AIP Publishing LLC, 2019,November).15. Liu, K. et al. Geometrical effect in 2D nanopores. Nano Lett. 17, 4223–4230(2017).16. Nicolaï, A. et al. Molecular dynamics investigation of polylysine peptidetranslocation through MoS2 nanopores. J. Phys. Chem. B 123, 2342–2353 (2019).17. Tran, T. T., Bray, K., Ford, M. J., Toth, M. & Aharonovich, I. Quantumemission from hexagonal boron nitride monolayers. Nat. Nanotechnol. 11,37–41 (2016).18. Zheng, X. et al. Spatial defects nanoengineering for bipolar conductivity inMoS2. Nat. Commun. 11, 3463 (2020).19. Dogan, M. & Cohen, M. L. Magnetism and interlayer bonding in pores ofBernal-stacked hexagonal boron nitride. Phys. Chem. Chem. Phys. 24,20882–20890 (2022).20. Uosaki, K. et al. Highly efficient electrochemical hydrogen evolution reactionat insulating boron nitride nanosheet on inert gold substrate. Sci. Rep. 6, 32217(2016).Fig. 4 TEM images showing the relative stability of surfacecontamination in a vacuum and the spreading of surface contamination inthe air for monolayer h-BN with nanopores. a, b Sample always in avacuum. The white dashed lines outline the boundary between the cleanregion (interior to the boundary) and the high surface contaminated region(exterior to the boundary). After 15 h in a vacuum, the boundary has notchanged, and the nanopores present are largely unmolested (white arrowsidentify two representative nanopores). c, d Evolution of sample in air. Thewhite dashed line in c outlines the initial boundary between clean (interior)and contaminated (exterior) regions; the same white dashed line isreproduced in (d). The red dashed dot line in d) shows the new contaminationboundary after 15 h storage in air. The surface contamination has substantiallyprogressed inward and has totally overrun the two nanopores identified withwhite arrows. The orange arrows depict the flow of time.COMMUNICATIONS CHEMISTRY | https://doi.org/10.1038/s42004-023-00899-1 ARTICLECOMMUNICATIONS CHEMISTRY |           (2023) 6:108 | https://doi.org/10.1038/s42004-023-00899-1 | www.nature.com/commschem 5www.nature.com/commschemwww.nature.com/commschem21. Zhou, Z. et al. DNA translocation through hydrophilic nanopore in hexagonalboron nitride. Sci. Rep. 3, 3287 (2013).22. Liu, S. et al. Boron nitride nanopores: highly sensitive DNA single‐moleculedetectors. Adv. Mater. 25, 4549–4554 (2013).23. Gottscholl, A. et al. Initialization and read-out of intrinsic spin defects in a vander Waals crystal at room temperature. Nat. Mater. 19, 540–545 (2020).24. Su, C. et al. Tuning colour centres at a twisted hexagonal boron nitrideinterface. Nat. Mater. 21, 896–902 (2022).25. Su, C. et al. Waterproof molecular monolayers stabilize 2D materials. Proc.Natl Acad. Sci. USA 116, 20844–20849 (2019).26. Lyalin, A., Nakayama, A., Uosaki, K. & Taketsugu, T. Theoretical predictionsfor hexagonal BN based nanomaterials as electrocatalysts for the oxygenreduction reaction. Phys. Chem. Chem. Phys. 15, 2809–2820 (2013).27. He, Y., Tsutsui, M., Zhou, Y. & Miao, X. S. Solid-state nanopore systems: frommaterials to applications. NPG Asia. Materials 13, 1–26 (2021).28. Hou, S. et al. Localized emission from laser-irradiated defects in 2D hexagonalboron nitride. 2D Mater. 5, 015010 (2017).29. Glushkov, E. et al. Engineering optically active defects in hexagonal boronnitride using focused ion beam and water. ACS Nano 16, 3695–3703 (2022).30. Kianinia, M., White, S., Fröch, J. E., Bradac, C. & Aharonovich, I. Generationof spin defects in hexagonal boron nitride. ACS Photonics 7, 2147–2152(2020).31. Gilbert, S. M., Liu, S., Schumm, G. & Zettl, A. Nanopatterning hexagonalboron nitride with helium ion milling: towards atomically-thin,nanostructured insulators. MRS Adv. 3, 327–331 (2018).32. Meyer, J. C., Chuvilin, A., Algara-Siller, G., Biskupek, J. & Kaiser, U. Selectivesputtering and atomic resolution imaging of atomically thin boron nitridemembranes. Nano Lett. 9, 2683–2689 (2009).33. Zhang, J. et al. Point defects in two-dimensional hexagonal boron nitride: aperspective. J. Appl. Phys. 128, 100902 (2020).34. Zan, R., Ramasse, Q. M., Bangert, U. & Novoselov, K. S. Graphene reknits itsholes. Nano Lett. 12, 3936–3940 (2012).35. Lee, J. et al. Stabilization of graphene nanopore. Proc. Natl Acad. Sci. USA 111,7522–7526 (2014).36. Tavakoli, M. M. et al. Monolayer hexagonal boron nitride: an efficient electronblocking layer in organic photovoltaics. Adv. Funct. Mater. 31, 2101238(2021).37. Gilbert, S. M. et al. Alternative stacking sequences in hexagonal boron nitride.2D Mater. 6, 021006 (2019).38. Wang, L. et al. One-dimensional electrical contact to a two-dimensionalmaterial. Science 342, 614–617 (2013).39. Lin, Y. C. et al. Graphene annealing: how clean can it be? Nano Lett. 12,414–419 (2012).AcknowledgementsThis work was supported primarily by the Director, Office of Science, Office of BasicEnergy Sciences, Materials Sciences and Engineering Division, of the US Department ofEnergy under contract no. DE-AC02-05-CH11231, within the Nanomachines Program(KC1203), which provided for the design of the project, device fabrication, and TEMcharacterization. This work was also supported in part by the Director, Office of Science,Office of Basic Energy Sciences, Materials Sciences and Engineering Division, of the USDepartment of Energy under contract no. DE-AC02-05-CH11231, within the van derWaals Heterostructures Program (KCWF16), which provided for the growth of selectedhexagonal boron nitride. J.H.P. and J.K. acknowledge the support from the U.S. ArmyResearch Office (ARO) MURI project under grant number W911NF-18-1-04320431 andthe US Army Research Office through the Institute for Soldier Nanotechnologies at MIT,under cooperative agreement No. W911NF-18-2-0048.Author contributionsC.D. and A.Z. conceived the idea; C.D., J.H.P., K.W., and T.T. synthesized the materials;C.D., D.P., and C.S. conducted TEM experiments; A.Z. and J.K. supervised the project;and all authors contributed to the discussion of the results and writing of the paper.Competing interestsThe authors declare no competing interests.Additional informationSupplementary information The online version contains supplementary materialavailable at https://doi.org/10.1038/s42004-023-00899-1.Correspondence and requests for materials should be addressed to Alex Zettl.Peer review information Communications Chemistry thanks Si-Young Choi and theother anonymous reviewers for their contribution to the peer review of this work. A peerreview file is available.Reprints and permission information is available at http://www.nature.com/reprintsPublisher’s note Springer Nature remains neutral with regard to jurisdictional claims inpublished maps and institutional affiliations.Open Access This article is licensed under a Creative CommonsAttribution 4.0 International License, which permits use, sharing,adaptation, distribution and reproduction in any medium or format, as long as you giveappropriate credit to the original author(s) and the source, provide a link to the CreativeCommons license, and indicate if changes were made. The images or other third partymaterial in this article are included in the article’s Creative Commons license, unlessindicated otherwise in a credit line to the material. If material is not included in thearticle’s Creative Commons license and your intended use is not permitted by statutoryregulation or exceeds the permitted use, you will need to obtain permission directly fromthe copyright holder. To view a copy of this license, visit http://creativecommons.org/licenses/by/4.0/.© The Author(s) 2023ARTICLE COMMUNICATIONS CHEMISTRY | https://doi.org/10.1038/s42004-023-00899-16 COMMUNICATIONS CHEMISTRY |           (2023) 6:108 | https://doi.org/10.1038/s42004-023-00899-1 | www.nature.com/commschemhttps://doi.org/10.1038/s42004-023-00899-1http://www.nature.com/reprintshttp://creativecommons.org/licenses/by/4.0/http://creativecommons.org/licenses/by/4.0/www.nature.com/commschem Evolution of nanopores in hexagonal boron nitride Results and discussion Evolution of nanopores in monolayer hBN Evolution of nanopores in multilayer hBN Surface contamination spreading Conclusions Methods Monolayer hBN synthesis AB stacked multilayer hBN synthesis TEM for nanopore formation and imaging Data availability References References Acknowledgements Author contributions Competing interests Additional information