Citation: | Li SS, Fang YN, Wang JF. Control of light–matter interactions in two-dimensional materials with nanoparticle-on-mirror structures. Opto-Electron Sci 3, 240011 (2024). doi: 10.29026/oes.2024.240011 |
[1] | Xia FN, Wang H, Xiao D et al. Two-dimensional material nanophotonics. Nat Photonics 8, 899–907 (2014). doi: 10.1038/nphoton.2014.271 |
[2] | Grigorenko AN, Polini M, Novoselov KS. Graphene plasmonics. Nat Photonics 6, 749–758 (2012). doi: 10.1038/nphoton.2012.262 |
[3] | Schaibley JR, Yu HY, Clark G et al. Valleytronics in 2D materials. Nat Rev Mater 1, 16055 (2016). doi: 10.1038/natrevmats.2016.55 |
[4] | Pei JJ, Liu X, del Águila AG et al. Switching of K-Q intervalley trions fine structure and their dynamics in n-doped monolayer WS2. Opto-Electron Adv 6, 220034 (2023). doi: 10.29026/oea.2023.220034 |
[5] | Xia FN, Wang H, Jia YC. Rediscovering black phosphorus as an anisotropic layered material for optoelectronics and electronics. Nat Commun 5, 4458 (2014). doi: 10.1038/ncomms5458 |
[6] | Dai S, Fei Z, Ma Q et al. Tunable phonon polaritons in atomically thin van der Waals crystals of boron nitride. Science 343, 1125–1129 (2014). doi: 10.1126/science.1246833 |
[7] | Kang K, Lee KH, Han YM et al. Layer-by-layer assembly of two-dimensional materials into wafer-scale heterostructures. Nature 550, 229–233 (2017). doi: 10.1038/nature23905 |
[8] | Sierra JF, Fabian J, Kawakami RK et al. Van der Waals heterostructures for spintronics and opto-spintronics. Nat Nanotechnol 16, 856–868 (2021). doi: 10.1038/s41565-021-00936-x |
[9] | Ming T, Chen HJ, Jiang RB et al. Plasmon-controlled fluorescence: beyond the intensity enhancement. J Phys Chem Lett 3, 191–202 (2012). doi: 10.1021/jz201392k |
[10] | Yang JL, Wang HJ, Zhu ZW et al. In situ Raman probing of hot-electron transfer at gold–graphene interfaces with atomic layer accuracy. Angew Chem Int Ed 61, e202112749 (2022). doi: 10.1002/anie.202112749 |
[11] | Lu RT, Konzelmann A, Xu F et al. High sensitivity surface enhanced Raman spectroscopy of R6G on in situ fabricated Au nanoparticle/graphene plasmonic substrates. Carbon 86, 78–85 (2015). doi: 10.1016/j.carbon.2015.01.028 |
[12] | Gong SH, Alpeggiani F, Sciacca B et al. Nanoscale chiral valley-photon interface through optical spin-orbit coupling. Science 359, 443–447 (2018). |
[13] | Luo Y, Shepard GD, Ardelean JV et al. Deterministic coupling of site-controlled quantum emitters in monolayer WSe2 to plasmonic nanocavities. Nat Nanotechnol 13, 1137–1142 (2018). doi: 10.1038/s41565-018-0275-z |
[14] | Schuknecht F, Kołątaj K, Steinberger M et al. Accessible hotspots for single-protein SERS in DNA-origami assembled gold nanorod dimers with tip-to-tip alignment. Nat Commun 14, 7192 (2023). doi: 10.1038/s41467-023-42943-7 |
[15] | Paria D, Roy K, Singh HJ et al. Ultrahigh field enhancement and photoresponse in atomically separated arrays of plasmonic dimers. Adv Mater 27, 1751–1758 (2015). doi: 10.1002/adma.201404312 |
[16] | Benz F, Schmidt MK, Dreismann A et al. Single-molecule optomechanics in “picocavities”. Science 354, 726–729 (2016). doi: 10.1126/science.aah5243 |
[17] | Liu DJ, Wu TT, Zhang Q et al. Probing the in-plane near-field enhancement limit in a plasmonic particle-on-film nanocavity with surface-enhanced Raman spectroscopy of graphene. ACS Nano 13, 7644–7654 (2019). doi: 10.1021/acsnano.9b00776 |
[18] | Hou SY, Tobing LYM, Wang XL et al. Manipulating coherent light–matter interaction: continuous transition between strong coupling and weak coupling in MoS2 monolayer coupled with plasmonic nanocavities. Adv Opt Mater 7, 1900857 (2019). doi: 10.1002/adom.201900857 |
[19] | Xu YH, Hu HT, Chen W et al. Phononic cavity optomechanics of atomically thin crystal in plasmonic nanocavity. ACS Nano 16, 12711–12719 (2022). doi: 10.1021/acsnano.2c04478 |
[20] | Mertens J, Eiden AL, Sigle DO et al. Controlling subnanometer gaps in plasmonic dimers using graphene. Nano Lett 13, 5033–5038 (2013). doi: 10.1021/nl4018463 |
[21] | Tserkezis C, Esteban R, Sigle DO et al. Hybridization of plasmonic antenna and cavity modes: extreme optics of nanoparticle-on-mirror nanogaps. Phys Rev A 92, 053811 (2015). doi: 10.1103/PhysRevA.92.053811 |
[22] | Baumberg JJ, Aizpurua J, Mikkelsen MH et al. Extreme nanophotonics from ultrathin metallic gaps. Nat Mater 18, 668–678 (2019). doi: 10.1038/s41563-019-0290-y |
[23] | Sigle DO, Mertens J, Herrmann LO et al. Monitoring morphological changes in 2D monolayer semiconductors using atom-thick plasmonic nanocavities. ACS Nano 9, 825–830 (2015). doi: 10.1021/nn5064198 |
[24] | Chen W, Zhang SP, Kang M et al. Probing the limits of plasmonic enhancement using a two-dimensional atomic crystal probe. Light Sci Appl 7, 56 (2018). doi: 10.1038/s41377-018-0056-3 |
[25] | Huh JH, Lee J, Lee S. Comparative study of plasmonic resonances between the roundest and randomly faceted Au nanoparticles-on-mirror cavities. ACS Photonics 5, 413–421 (2018). doi: 10.1021/acsphotonics.7b00856 |
[26] | Ruan QF, Shao L, Shu YW et al. Growth of monodisperse gold nanospheres with diameters from 20 nm to 220 nm and their core/satellite nanostructures. Adv Opt Mater 2, 65–73 (2014). doi: 10.1002/adom.201300359 |
[27] | Liu LF, Krasavin AV, Zheng JS et al. Atomically smooth single-crystalline platform for low-loss plasmonic nanocavities. Nano Lett 22, 1786–1794 (2022). doi: 10.1021/acs.nanolett.2c00095 |
[28] | Han XB, Wang K, Xing XY et al. Rabi splitting in a plasmonic nanocavity coupled to a WS2 monolayer at room temperature. ACS Photonics 5, 3970–3976 (2018). doi: 10.1021/acsphotonics.8b00931 |
[29] | Huang SX, Ming T, Lin YX et al. Ultrasmall mode volumes in plasmonic cavities of nanoparticle-on-mirror structures. Small 12, 5190–5199 (2016). doi: 10.1002/smll.201601318 |
[30] | Xomalis A, Chikkaraddy R, Oksenberg E et al. Controlling optically driven atomic migration using crystal-facet control in plasmonic nanocavities. ACS Nano 14, 10562–10568 (2020). doi: 10.1021/acsnano.0c04600 |
[31] | Cui XM, Lai YH, Ai RQ et al. Anapole states and toroidal resonances realized in simple gold nanoplate-on-mirror structures. Adv Opt Mater 8, 2001173 (2020). doi: 10.1002/adom.202001173 |
[32] | Huang H, Wang H, Li SS et al. WS2−flake-sandwiched, Au-nanodisk-enabled high-quality Fabry−Pérot nanoresonators for photoluminescence modulation. ACS Nano 16, 14874–14884 (2022). doi: 10.1021/acsnano.2c05769 |
[33] | Wang CY, Chen HY, Sun LY et al. Giant colloidal silver crystals for low-loss linear and nonlinear plasmonics. Nat Commun 6, 7734 (2015). doi: 10.1038/ncomms8734 |
[34] | Ramasubramaniam A. Large excitonic effects in monolayers of molybdenum and tungsten dichalcogenides. Phys Rev B 86, 115409 (2012). doi: 10.1103/PhysRevB.86.115409 |
[35] | Schneider C, Glazov MM, Korn T et al. Two-dimensional semiconductors in the regime of strong light–matter coupling. Nat Commun 9, 2695 (2018). doi: 10.1038/s41467-018-04866-6 |
[36] | Liu XZ, Galfsky T, Sun Z et al. Strong light–matter coupling in two-dimensional atomic crystals. Nat Photonics 9, 30–34 (2015). doi: 10.1038/nphoton.2014.304 |
[37] | Törmä P, Barnes WL. Strong coupling between surface plasmon polaritons and emitters: a review. Rep Prog Phys 78, 013901 (2015). doi: 10.1088/0034-4885/78/1/013901 |
[38] | Kleemann ME, Chikkaraddy R, Alexeev EM et al. Strong-coupling of WSe2 in ultra-compact plasmonic nanocavities at room temperature. Nat Commun 8, 1296 (2017). doi: 10.1038/s41467-017-01398-3 |
[39] | Qin J, Chen YH, Zhang ZP et al. Revealing strong plasmon–exciton coupling between nanogap resonators and two-dimensional semiconductors at ambient conditions. Phys Rev Lett 124, 063902 (2020). doi: 10.1103/PhysRevLett.124.063902 |
[40] | Zheng D, Zhang SP, Deng Q et al. Manipulating coherent plasmon–exciton interaction in a single silver nanorod on monolayer WSe2. Nano Lett 17, 3809–3814 (2017). doi: 10.1021/acs.nanolett.7b01176 |
[41] | Wen JX, Wang H, Wang WL et al. Room-temperature strong light–matter interaction with active control in single plasmonic nanorod coupled with two-dimensional atomic crystals. Nano Lett 17, 4689–4697 (2017). doi: 10.1021/acs.nanolett.7b01344 |
[42] | Liu RM, Zhou ZK, Yu YC et al. Strong light-matter interactions in single open plasmonic nanocavities at the quantum optics limit. Phys Rev Lett 118, 237401 (2017). doi: 10.1103/PhysRevLett.118.237401 |
[43] | Akselrod GM, Ming T, Argyropoulos C et al. Leveraging nanocavity harmonics for control of optical processes in 2D semiconductors. Nano Lett 15, 3578–3584 (2015). doi: 10.1021/acs.nanolett.5b01062 |
[44] | Sun JW, Hu HT, Zheng D et al. Light-emitting plexciton: exploiting plasmon–exciton interaction in the intermediate coupling regime. ACS Nano 12, 10393–10402 (2018). doi: 10.1021/acsnano.8b05880 |
[45] | Zhu GP, Shi XQ, Huang GY et al. Highly polarized light emission of monolayer WSe2 coupled with gap-plasmon nanocavity. Adv Opt Mater 10, 2101762 (2022). doi: 10.1002/adom.202101762 |
[46] | Li CY, Wang QF, Diao H et al. Enhanced photoluminescence of monolayer MoSe2 in a double resonant plasmonic nanocavity with Fano resonance and mode matching. Laser Photonics Rev 16, 2100199 (2022). doi: 10.1002/lpor.202100199 |
[47] | Zhao WJ, Wang SF, Liu B et al. Exciton–plasmon coupling and electromagnetically induced transparency in monolayer semiconductors hybridized with Ag nanoparticles. Adv Mater 28, 2709–2715 (2016). doi: 10.1002/adma.201504478 |
[48] | Li ZW, Liu CX, Rong X et al. Tailoring MoS2 valley-polarized photoluminescence with super chiral near-field. Adv Mater 30, 1801908 (2018). doi: 10.1002/adma.201801908 |
[49] | Wen T, Zhang WD, Liu S et al. Steering valley-polarized emission of monolayer MoS2 sandwiched in plasmonic antennas. Sci Adv 6, eaao0019 (2020). doi: 10.1126/sciadv.aao0019 |
[50] | Sun JW, Hu HT, Pan D et al. Selectively depopulating valley-polarized excitons in monolayer MoS2 by local chirality in single plasmonic nanocavity. Nano Lett 20, 4953–4959 (2020). doi: 10.1021/acs.nanolett.0c01019 |
[51] | Kim S, Lim YC, Kim RM et al. A single chiral nanoparticle induced valley polarization enhancement. Small 16, 2003005 (2020). doi: 10.1002/smll.202003005 |
[52] | Li SS, Wang H, Wang J et al. Control of light–valley interactions in 2D transition metal dichalcogenides with nanophotonic structures. Nanoscale 13, 6357–6372 (2021). doi: 10.1039/D0NR08000D |
[53] | Huang JN, Akselrod GM, Ming T et al. Tailored emission spectrum of 2D semiconductors using plasmonic nanocavities. ACS Photonics 5, 552–558 (2018). doi: 10.1021/acsphotonics.7b01085 |
[54] | Park KD, Jiang T, Clark G et al. Radiative control of dark excitons at room temperature by nano-optical antenna-tip Purcell effect. Nat Nanotechnol 13, 59–64 (2018). doi: 10.1038/s41565-017-0003-0 |
[55] | Lo TW, Chen XL, Zhang ZD et al. Plasmonic nanocavity induced coupling and boost of dark excitons in monolayer WSe2 at room temperature. Nano Lett 22, 1915–1921 (2022). doi: 10.1021/acs.nanolett.1c04360 |
[56] | Luo Y, Liu N, Li XZ et al. Single photon emission in WSe2 up 160 K by quantum yield control. 2D Mater 6, 035017 (2019). doi: 10.1088/2053-1583/ab15fe |
[57] | Tran TN, Kim S, White SJU et al. Enhanced emission from interlayer excitons coupled to plasmonic gap cavities. Small 17, 2103994 (2021). doi: 10.1002/smll.202103994 |
[58] | Zhou Y, Scuri G, Wild DS et al. Probing dark excitons in atomically thin semiconductors via near-field coupling to surface plasmon polaritons. Nat Nanotechnol 12, 856–860 (2017). doi: 10.1038/nnano.2017.106 |
[59] | Zhang XX, Cao T, Lu ZG et al. Magnetic brightening and control of dark excitons in monolayer WSe2. Nat Nanotechnol 12, 883–888 (2017). doi: 10.1038/nnano.2017.105 |
[60] | Jadczak J, Glazov M, Kutrowska-Girzycka J et al. Upconversion of light into bright intravalley excitons via dark intervalley excitons in hBN-encapsulated WSe2 monolayers. ACS Nano 15, 19165–19174 (2021). doi: 10.1021/acsnano.1c08286 |
[61] | Qi PF, Dai YC, Luo Y et al. Giant excitonic upconverted emission from two-dimensional semiconductor in doubly resonant plasmonic nanocavity. Light Sci Appl 11, 176 (2022). doi: 10.1038/s41377-022-00860-2 |
[62] | Mueller NS, Arul R, Kang GW et al. Photoluminescence upconversion in monolayer WSe2 activated by plasmonic cavities through resonant excitation of dark excitons. Nat Commun 14, 5726 (2023). doi: 10.1038/s41467-023-41401-8 |
[63] | Rahaman M, Zahn DRT. Plasmon-enhanced Raman spectroscopy of two-dimensional semiconductors. J Phys Condens Matter 34, 333001 (2022). doi: 10.1088/1361-648X/ac7689 |
[64] | Cong X, Liu XL, Lin ML et al. Application of Raman spectroscopy to probe fundamental properties of two-dimensional materials. npj 2D Mater Appl 4, 13 (2020). doi: 10.1038/s41699-020-0140-4 |
[65] | Chen C, Chen XL, Yu HY et al. Symmetry-controlled electron–phonon interactions in van der Waals heterostructures. ACS Nano 13, 552–559 (2019). doi: 10.1021/acsnano.8b07290 |
[66] | Lee JU, Woo S, Park J et al. Strain-shear coupling in bilayer MoS2. Nat Commun 8, 1370 (2017). doi: 10.1038/s41467-017-01487-3 |
[67] | Zhang SS, Huang JQ, Yu Y et al. Quantum interference directed chiral Raman scattering in two-dimensional enantiomers. Nat Commun 13, 1254 (2022). doi: 10.1038/s41467-022-28877-6 |
[68] | Xu HX, Aizpurua J, Käll M et al. Electromagnetic contributions to single-molecule sensitivity in surface-enhanced Raman scattering. Phys Rev E 62, 4318–4324 (2000). doi: 10.1103/PhysRevE.62.4318 |
[69] | Zhang YX, Chen W, Fu T et al. Simultaneous surface-enhanced resonant Raman and fluorescence spectroscopy of monolayer MoSe2: determination of ultrafast decay rates in nanometer dimension. Nano Lett 19, 6284–6291 (2019). doi: 10.1021/acs.nanolett.9b02425 |
[70] | Chen SY, Li P, Zhang C et al. Extending plasmonic enhancement limit with blocked electron tunneling by monolayer hexagonal boron nitride. Nano Lett 23, 5445–5452 (2023). doi: 10.1021/acs.nanolett.3c00404 |
[71] | Chen SY, Weng SR, Xiao YH et al. Insight into the heterogeneity of longitudinal plasmonic field in a nanocavity using an intercalated two-dimensional atomic crystal probe with a ~7 Å resolution. J Am Chem Soc 144, 13174–13183 (2022). doi: 10.1021/jacs.2c03081 |
[72] | Wen BY, Wang JY, Shen TL et al. Manipulating the light–matter interactions in plasmonic nanocavities at 1 nm spatial resolution. Light Sci Appl 11, 235 (2022). doi: 10.1038/s41377-022-00918-1 |
[73] | Zhu WQ, Esteban R, Borisov AG et al. Quantum mechanical effects in plasmonic structures with subnanometre gaps. Nat Commun 7, 11495 (2016). doi: 10.1038/ncomms11495 |
[74] | Savage KJ, Hawkeye MM, Esteban R et al. Revealing the quantum regime in tunnelling plasmonics. Nature 491, 574–577 (2012). doi: 10.1038/nature11653 |
[75] | Zhang C, Li DY, Zhang GD et al. Switching plasmonic nanogaps between classical and quantum regimes with supramolecular interactions. Sci Adv 8, eabj9752 (2022). doi: 10.1126/sciadv.abj9752 |
[76] | Wang P, Krasavin AV, Nasir ME et al. Reactive tunnel junctions in electrically driven plasmonic nanorod metamaterials. Nat Nanotechnol 13, 159–164 (2018). doi: 10.1038/s41565-017-0017-7 |
[77] | Zhang C, Hu HT, Ma CM et al. Quantum plasmonics pushes chiral sensing limit to single molecules: a paradigm for chiral biodetections. Nat Commun 15, 2 (2024). doi: 10.1038/s41467-023-42719-z |
[78] | Shao L, Wang XM, Xu HT et al. Nanoantenna-sandwiched graphene with giant spectral tuning in the visible-to-near-infrared region. Adv Opt Mater 2, 162–170 (2014). doi: 10.1002/adom.201300313 |
[79] | Cobas E, Friedman AL, van’t Erve OMJ et al. Graphene as a tunnel barrier: graphene-based magnetic tunnel junctions. Nano Lett 12, 3000–3004 (2012). doi: 10.1021/nl3007616 |
[80] | Turunen M, Brotons-Gisbert M, Dai YY et al. Quantum photonics with layered 2D materials. Nat Rev Phys 4, 219–236 (2022). doi: 10.1038/s42254-021-00408-0 |
[81] | Koperski M, Nogajewski K, Arora A et al. Single photon emitters in exfoliated WSe2 structures. Nat Nanotechnol 10, 503–506 (2015). doi: 10.1038/nnano.2015.67 |
[82] | Branny A, Kumar S, Proux R et al. Deterministic strain-induced arrays of quantum emitters in a two-dimensional semiconductor. Nat Commun 8, 15053 (2017). doi: 10.1038/ncomms15053 |
[83] | Darlington TP, Carmesin C, Florian M et al. Imaging strain-localized excitons in nanoscale bubbles of monolayer WSe2 at room temperature. Nat Nanotechnol 15, 854–860 (2020). doi: 10.1038/s41565-020-0730-5 |
[84] | Li SS, Chui KK, Shen FH et al. Generation and detection of strain-localized excitons in WS2 monolayer by plasmonic metal nanocrystals. ACS Nano 16, 10647–10656 (2022). doi: 10.1021/acsnano.2c02300 |
[85] | Mendelson N, Ritika R, Kianinia M et al. Coupling spin defects in a layered material to nanoscale plasmonic cavities. Adv Mater 34, 2106046 (2022). doi: 10.1002/adma.202106046 |
[86] | Xu XH, Solanki AB, Sychev D et al. Greatly enhanced emission from spin defects in hexagonal boron nitride enabled by a low-loss plasmonic nanocavity. Nano Lett 23, 25–33 (2023). doi: 10.1021/acs.nanolett.2c03100 |
[87] | Parzefall M, Szabó Á, Taniguchi T et al. Light from van der Waals quantum tunneling devices. Nat Commun 10, 292 (2019). doi: 10.1038/s41467-018-08266-8 |
[88] | McKeever J, Boca A, Boozer AD et al. Experimental realization of a one-atom laser in the regime of strong coupling. Nature 425, 268–271 (2003). doi: 10.1038/nature01974 |
[89] | Guselnikova O, Lim H, Kim HJ et al. New trends in nanoarchitectured SERS substrates: nanospaces, 2D materials, and organic heterostructures. Small 18, 2107182 (2022). doi: 10.1002/smll.202107182 |
[90] | Lawless J, McCormack O, Pepper J et al. Spectral tuning of a nanoparticle-on-mirror system by graphene doping and gap control with nitric acid. ACS Appl Mater Interfaces 15, 38901–38909 (2023). doi: 10.1021/acsami.3c05302 |
[91] | Iranzo DA, Nanot S, Dias EJC et al. Probing the ultimate plasmon confinement limits with a van der Waals heterostructure. Science 360, 291–295 (2018). doi: 10.1126/science.aar8438 |
[92] | Sun Z, Gu J, Ghazaryan A et al. Optical control of room-temperature valley polaritons. Nat Photonics 11, 491–496 (2017). doi: 10.1038/nphoton.2017.121 |
[93] | Dufferwiel S, Lyons TP, Solnyshkov DD et al. Valley-addressable polaritons in atomically thin semiconductors. Nat Photonics 11, 497–501 (2017). doi: 10.1038/nphoton.2017.125 |
[94] | Chen YJ, Cain JD, Stanev TK et al. Valley-polarized exciton–polaritons in a monolayer semiconductor. Nat Photonics 11, 431–435 (2017). doi: 10.1038/nphoton.2017.86 |
[95] | Qiu L, Chakraborty C, Dhara S et al. Room-temperature valley coherence in a polaritonic system. Nat Commun 10, 1513 (2019). doi: 10.1038/s41467-019-09490-6 |
[96] | Lundt N, Dusanowski Ł, Sedov E et al. Optical valley Hall effect for highly valley-coherent exciton–polaritons in an atomically thin semiconductor. Nat Nanotechnol 14, 770–775 (2019). doi: 10.1038/s41565-019-0492-0 |
[97] | Liu XZ, Yi J, Yang S et al. Nonlinear valley phonon scattering under the strong coupling regime. Nat Mater 20, 1210–1215 (2021). doi: 10.1038/s41563-021-00972-x |
[98] | Chen H, Jiang ZH, Hu HT et al. Sub-50-ns ultrafast upconversion luminescence of a rare-earth-doped nanoparticle. Nat Photonics 16, 651–657 (2022). doi: 10.1038/s41566-022-01051-6 |
[99] | Chen YL, Zheng JP, Zhang LL et al. Inversion of the chiroptical responses of chiral gold nanoparticles with a gold film. ACS Nano 18, 383–394 (2024). doi: 10.1021/acsnano.3c07475 |
[100] | Yang LL, Yuan Y, Fu BW et al. Revealing broken valley symmetry of quantum emitters in WSe2 with chiral nanocavities. Nat Commun 14, 4265 (2023). doi: 10.1038/s41467-023-39972-7 |
[101] | Wang DQ, Yang AK, Wang WJ et al. Band-edge engineering for controlled multi-modal nanolasing in plasmonic superlattices. Nat Nanotechnol 12, 889–894 (2017). doi: 10.1038/nnano.2017.126 |
Highly confined electromagnetic field in the nanogap. (a) Simulated scattering cross-sections of a Au NSoM structure. The schematic of the structure is given in the inset. The diameter of the Au NS is 100 nm. The refractive index of the spacer is taken as a constant (1.45) for simplicity. The thickness is 1 nm. The propagating direction of the excitation light is set to be parallel to the substrate. (b) Contours of the electric field intensity enhancement along the different axes at the resonance wavelength marked by the star in (a). (c) Simulated scattering cross-sections with an in-plane excitation, where the propagating direction of the excitation light is perpendicular to the substrate. (d) Corresponding electric field intensity enhancement at the resonance wavelength marked by the star in (c).
Plasmon modes in the nanogap. (a) Schematic of a flat-junction NPoM configuration, with a facet width of w. (b) Antenna modes ln and gap modes smn in the NPoM structure, which can be adjusted with the facet width w. The shaded area shows an experimentally accessed facet range. (c) Charge distributions for the l1, s11, and s02 modes. (d) Schematic showing the interactions between the antenna and gap modes. The plasmon modes in the nanogap are the hybridization (jn) of the antenna and gap modes. (e) Extinction cross-sections of a faceted spherical gold nanoparticle in the NPoM structure. The diameter is 80 nm and the spacer thickness is varied from 0.6 to 1.4 nm. Figure reproduced with permission from: (b) ref.23, Copyright 2014 American Chemical Society; (c–e) ref.21, Copyright 2015 American Physical Society.
Construction of NPoM structures. (a–e) Plasmonic nanoparticles for the construction of NPoM structures: Au NSs (a), Au nanorods (b), Ag NCs (c), Au nanoplates (d), and Au nanodisks (e). (f) High-resolution transmission electron microscopy (TEM) cross-sectional image of a SLG-sandwiched NPoM structure. (g) Average count profile across the local area as indicated in the white box in (f). The values of brightness were extracted from the high-resolution TEM image in (f) for analysis. (h) Dark-field scattering spectra and images (insets) of the structure before and after Raman measurements. (i, j) Effect of the mirror quality: Au nanorod-on-(rough gold mirror) (i) and Au nanorod-on-(ultrasmooth gold mirror) (j). GNR: gold nanorod. The surface root-mean-square roughness of the single-crystalline gold microflake (GMF) in (j) is ~ 0.2 nm, which is much lower than that of the deposited gold film in (i). The ultrasmooth gold mirror endows the nanocavities with significantly enhanced quality factors and scattering intensities. Figure reproduced with permission from: (a) ref.25, Copyright 2017 American Chemical Society; (b, i, j) ref.27, Copyright 2022 American Chemical Society; (c) ref.28, Copyright 2018 American Chemical Society; (d, e) ref.31, Copyright 2020 Wiley-VCH GmbH; (f–h) ref.17, Copyright 2019 American Chemical Society.
Plasmon–exciton coupling in the extreme gap. (a) Schematic of the coupled harmonic oscillator model. (b) Schematic of a NCoM structure with a MoS2 monolayer. The insets show the TEM image of an individual Ag NC (left) and the cross-sectional schematic of the structure (right). (c) Dependences of the optical mode volume (red) and coupling strength (blue) on the thickness of the spacer. The strong coupling regime is shaded in yellow. (d) Electric field enhancement at different spacer thicknesses. Figure reproduced with permission from: (b–d) ref.18, Copyright 2019 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
Strong coupling. (a, b) Schematics of NPoM cavities constructed from WSe2 flakes. The layer numbers of the WSe2 flakes are 1 (a) and 12 (b), respectively. (c) Dark-field scattering spectra of the individual NPoMs, showing mode splitting for WSe2 multilayer. The mode splitting was reproduced by FDTD simulations (dashed line), with two eigen-frequencies (ω±) of the hybrid system and a Rabi splitting energy (ℏΩ) exceeding 140 meV. Only a single-plasmon peak was observed in the WSe2 monolayer structure, where ωp denotes the angular frequency of the plasmon resonance. (d) Schematic and scanning electron microscopy (SEM) image of a plasmonic nanocavity sandwiched with WS2 monolayer. (e) PL (red) and scattering (cyan) spectra of the hybrid system in the strong coupling regime. Figure reproduced with permission from: (a–c) ref.38, under the terms of the Creative Commons CC BY license; (d, e) ref.39, Copyright 2020 American Physical Society.
PL enhancement in the weak coupling regime. (a) PL spectra from a MoS2 monolayer on a Si/SiO2 substrate (blue) and in the nanocavity (red). The intensity is measured per unit of excitation power and per unit of integration time. The inset shows the normalized spectra for the two cases along with the scattering spectrum for a typical structure (gray). (b) Schematic of the MoS2 monolayer-sandwiched NCoM structure. The Ag NC is wrapped with PVP and separated from an ultrasmooth gold film by an alumina layer and a MoS2 monolayer. (c) Circularly polarized PL spectra under the right circularly polarized (σ+) excitation. The degree of circular polarization, defined as ρ = (I(σ+) − I(σ−))/(I(σ+) + I(σ−)), was used to evaluate the valley modulation. I(σ+) and I(σ−) are the measured right-handed and left-handed components of the PL emissions, respectively. A high degree of circular polarization up to 48.7% was obtained. (d) Schematic showing the valley-dependent emissions owing to the chiral Purcell effect. The decay rate of the excitons in the –K (γ−K) valley is much larger than that in the K (γK) valley, leading to enhanced left-handed PL emissions. The intervalley scattering process is denoted using the parameter (γs) with a similar expression to the decay rate of the excitons. Figure reproduced with permission from: (a) ref.43, Copyright 2015 American Chemical Society; (b–d) ref.50, Copyright 2020 American Chemical Society.
Plasmonic enhancement for the detection of new exciton complexes. (a) PL spectra from a MoS2 monolayer on Si/SiO2 (black) and a MoS2 monolayer in the nanocavity containing a 65 nm Ag NC (red). The B exciton emissions are largely enhanced. (b) Schematic showing the bright (X0) and dark excitons (XD) in the WSe2 monolayer at the K valley (left) and the coupling between the gap plasmon mode of NSoM and the out-of-plane dipole of the dark excitons (right). (c) PL spectra obtained from the unetched WSe2-NSoM (top) and etched WSe2-NSoM (bottom). The insets show the corresponding nanostructures. The PL peak related to the dark excitons is clearly seen in the etched structure. (d) Schematic of a WS2/MoS2 heterostructure inserted in a NPoM cavity. A thin h-BN flake acts as a spacer to adjust the resonance wavelength to match the interlayer emissions. The type II band alignment is shown in the right panel, forming the interlayer excitons (IX). (e) PL spectra from the coupled (red) and uncoupled structures (blue). Figure reproduced with permission from: (a) ref.53, Copyright 2017 American Chemical Society; (b, c) ref.55, Copyright 2022 American Chemical Society; (d, e) ref.57, Copyright 2021 Wiley-VCH GmbH.
Excitonic upconverted emissions. (a) Schematic of the plasmonic nanocavity. The WSe2 monolayer is separated from the Au NCs with an organic adhesive layer, i.e., poly(allylamine hydrochloride)/poly(sodium 4-styrenesulfonate) (PAH-PSS), to avoid the hot carrier injection from the plasmonic nanoparticles. (b) Energy diagram showing the photon upconversion process of the 2D excitons. The electrons in the ground state (g) are excited through the absorption of a photon with energy (
Surface-enhanced Raman scattering. (a) Schematic (top) and cross-sectional TEM image (bottom) of a 1L MoS2-NPoM structure. The inset in the bottom panel shows the enlarged image of the marked area (red square). (b) Atomic displacements of the A1g,
Quantum tunneling through the atomic spacer. (a) Measured (Exp.
2D material-gapped nanocavities for nanoscale light sources. (a) Schematic of WSe2 monolayer coupled to a Au NCoM array for single-photon emissions. The inset shows the cross-sectional view of the structure. The WSe2 monolayer is separated from the Au NCs and the Au film by a 2 nm Al2O3 layer (grey shading in the inset) on each side to prevent quenching and short-circuiting of the nanoplasmonic gap mode. (b) Simulated (dashed line), measured (grey solid line) extinction spectra, and emission spectrum (red solid line) of an individual quantum emitter. (c) Second-order photon-correlation function g(2)(τ) recorded under pulsed excitation, indicating single-photon emissions. (d) Single-photon purity values at zero delay time for 15 quantum emitters. (e) Schematic showing an electroluminescence device. A PVP-coated Ag NC is separated from a Au film by a graphene (top) and h-BN (bottom) stacking. (f, g) Measured spatial (f) and spectral (g) photon distributions. The inset in (f) shows a line-cut of the emission spot, featuring a linewidth of ~ 460 nm. Figure reproduced with permission from: (a–d) ref.13, Copyright 2018 The Author(s), under exclusive licence to Springer Nature Limited; (e–g) ref.87, Copyright 2019 The Author(s), under a Creative Commons Attribution 4.0 International License.