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太赫兹散射式扫描近场光学显微镜(scattering-type scanning near-field optical microscopy, s-SNOM)在生物纳米成像、太赫兹纳米光谱学、纳米材料成像以及极化激元的研究中有着广泛的应用前景. 原子力显微镜探针作为太赫兹s-SNOM的重要组成部分, 起着近场激发、探测、增强等关键作用. 但是在测量过程中, 探针与样品的相互作用会影响测量结果. 本文通过仿真和实验, 分别揭示了太赫兹s-SNOM中探针与样品相互作用对近场激发、近场探测以及太赫兹近场频谱的影响. 首先, 研究了探针激发的近场的波矢权重分布, 发现波矢主要集中在105 cm–1量级, 与一般的太赫兹激元的波矢相差2—3个数量级, 这表明太赫兹近场很难激发太赫兹激元. 其次, 通过理论和实验研究, 发现金属针尖会干扰石墨烯圆盘结构的表面近场, 这表明太赫兹近场系统在探测结构的近场分布具有局限性; 最后研究了探针对近场频谱的影响, 发现探针长度和悬臂长度是影响近场频谱的重要参数, 可以通过增大探针长度或者悬臂长度的方法来减小探针对近场频谱的影响.Terahertz scattering scanning near-field optical microscopy (s-SNOM), as an important means to break through the limits of conventional optical diffraction, can achieve super-resolution imaging on a nanoscale and has a wide range of applications in biological nano-imaging, terahertz nano-spectroscopy, nanomaterials imaging, and the study of polarized excitations. As an important component of the terahertz s-SNOM, the atomic force microscope tip plays a key role in implementing the near-field excitation, detection, and enhancement. However, the tip-sample interaction can greatly affect the results. In this paper, the effects of tip-sample interaction on near-field excitation, near-field detection, and terahertz near-field spectrum in terahertz s-SNOM are revealed through simulations and experiments. First, the wave vector coupling weight of the near field excited by the tip is investigated, and it is found that the wave vector is concentrated mainly on the order of 105 cm–1, which differs from that of the general terahertz excitations by 2 to 3 orders of magnitude, indicating that the terahertz near field is difficult to excite terahertz excitations. Secondly, through theoretical and experimental studies, it is found that the metal tip interferes with the surface near-field of the graphene disk structure, which indicates the limitations of the terahertz s-SNOM in probing the near-field distribution of the structure. Finally, the influence of the tip on the near-field spectrum is studied. It is found that the tip length and cantilever length are important parameters affecting the near-field spectrum, and the influence of the tip on the near-field spectrum can be reduced by increasing the tip length or cantilever length.
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Keywords:
- tip-sample interactions /
- terahertz near-field spectrum
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图 2 (a)近场耦合权重; (b)石墨烯色散曲线
Fig. 2. (a) Near-field coupling weight; (b) graphene dispersion curves.
图 3 (a)石墨烯圆盘结构的仿真模型示意图; (b), (c) 在0.1和1 THz石墨烯圆盘结构表面的|Ez|分布图
Fig. 3. (a) Schematic diagram of simulation of graphene disk; (b), (c) electric field |Ez| contour of graphene disk at 0.1 and 1 THz.
图 4 石墨烯圆盘结构的太赫兹近场成像 (a)石墨烯圆盘的AFM形貌图; (b)−(d)石墨烯圆盘的太赫兹近场一阶、二阶、三阶成像
Fig. 4. THz near-field imaging of graphene disk: (a) AFM topography of graphene disk; (b)−(d) THz near-field imaging of graphene disk with 1st, 2nd, 3rd harmonics.
图 5 不同长度探针的仿真结果 (a)时域谱; (b)频域谱; (c)仿真模型
Fig. 5. Simulation results of tips of different length: (a) Time domain signal; (b) frequency domain signal; (c) schematic diagram of simulation.
图 6 不同长度悬臂的探针的仿真结果 (a)时域谱; (b)频域谱; (c)仿真模型; (d)长悬臂探针的时域谱; (e)长悬臂探针的频域谱
Fig. 6. Simulation results of tips of different cantilever length: (a) Time domain signal; (b) frequency domain signal; (c) schematic diagram of simulation; (d) time domain signal of long cantilever tip; (e) frequency domain signal of long cantilever tip.
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[1] Alonso-Gonzalez P, Nikitin A Y, Gao Y, Woessner A, Lundeberg M B, Principi A, Forcellini N, Yan W, Velez S, Huber A J, Watanabe K, Taniguchi T, Casanova F, Hueso L E, Polini M, Hone J, Koppens F H L, Hillenbrand R 2017 Nat. Nanotechnol. 12 31
Google Scholar
[2] Soltani A, Kuschewski F, Bonmann M, Generalov A, Vorobiev A, Ludwig F, Wiecha M M, Cibiraite D, Walla F, Winnerl S, Kehr S C, Eng L M, Stake J, Roskos H G 2020 Light Sci. Appl. 9 97
Google Scholar
[3] Stinson H T, Sternbach A, Najera O, Jing R, Mcleod A S, Slusar T V, Mueller A, Anderegg L, Kim H T, Rozenberg M, Basov D N 2018 Nat. Commun. 9 1
Google Scholar
[4] Yang Z, Tang D, Hu J, Tang M, Zhang M, Cui H L, Wang L, Chang C, Fan C, Li J, Wang H 2020 Small 17 2005814
Google Scholar
[5] Shigekawa H, Yoshida S, Takeuchi O 2014 Nat. Photonics 8 815
Google Scholar
[6] McLeod A S, Kelly P, Goldflam M D, Gainsforth Z, Westphal A J, Dominguez G, Thiemens M H, Fogler M M, Basov D N 2014 Phys. Rev. B 90 085136
Google Scholar
[7] Babicheva V E, Gamage S, Stockman M I, Abate Y 2017 Opt. Express 25 23935
Google Scholar
[8] Chen X, Liu X, Guo X, Chen S, Hu H, Nikulina E, Ye X, Yao Z, Bechtel H A, Martin M C, Carr G L, Dai Q, Zhuang S, Hu Q, Zhu Y, Hillenbrand R, Liu M, You G 2020 ACS Photonics 7 687
Google Scholar
[9] Mooshammer F, Plankl M, Siday T, Zizlsperger M, Sandner F, Vitalone R, Jing R, Huber M A, Basov D N, Huber R 2021 Opt. Lett. 46 3572
Google Scholar
[10] Zhang Z, Hu M, Zhang X, Wang Y, Zhang T, Xu X, Zhao T, Wu Z, Zhong R, Liu D, Wei Y, Gong Y, Liu S 2021 Appl. Phys. Express 14 102004
Google Scholar
[11] Zayats A V, Smolyaninov, I I 2003 J. Opt. A-Pure and Appl. Op. 5 S16
Google Scholar
[12] Fei Z, Andreev G O, Bao W, Zhang L M, McLeod A S, Wang C, Stewart M K, Zhao Z, Dominguez G, Thiemens M, Fogler M M, Tauber M J, Castro-Neto A H, Lau C N, Keilmann F, Basov D N 2011 Nano Lett. 11 4701
Google Scholar
[13] Fei Z, Rodin A S, Andreev G O, Bao W, McLeod A S, Wagner M, Zhang L M, Zhao Z, Thiemens M, Dominguez G, Fogler M M, Castro Neto A H, Lau C N, Keilmann F, Basov D N 2012 Nature 487 82
Google Scholar
[14] Fei Z, Goldflam M D, Wu J S, Dai S, Wagner M, McLeod A S, Liu M K, Post K W, Zhu S, Janssen G C A M, Fogler M M, Basov D N 2015 Nano Lett. 15 8271
Google Scholar
[15] Luo W, Cai W, Xiang Y, Wu W, Shi B, Jiang X, Zhang N, Ren M, Zhang X, Xu J 2017 Adv. Mater. 29 1701083
Google Scholar
[16] Duan J, Capote-Robayna N, Taboada-Gutierrez J, Alvarez-Perez G, Prieto I, Martin-Sanchez J, Nikitin A Y, Alonso-Gonzalez P 2020 Nano Lett. 20 5323
Google Scholar
[17] Zhang Y, Hu C, Lyu B, Li H, Ying Z, Wang L, Deng A, Luo X, Gao Q, Chen J, Du J, Shen P, Watanabe K, Taniguchi T, Kang J H, Wang F, Zhang Y, Shi Z 2020 Nano Lett. 20 2770
Google Scholar
[18] Venuthurumilli P K, Wen X L, Iyer V, Chen Y P, Xu X F 2019 ACS Photonics 6 2492
Google Scholar
[19] Gerber J A, Berweger S, O'Callahan B T, Raschke M B 2014 Phys. Rev. Lett. 113 055502
Google Scholar
[20] Carney P S, Deutsch B, Govyadinov A A, Hillenbrand R 2012 ACS Nano 6 8
Google Scholar
[21] 段嘉华, 陈佳宁 2019 物理学报 68 110701
Google Scholar
Duan J H, Chen J N 2019 Acta Phys. Sin. 68 110701
Google Scholar
[22] Zhang J, Chen X, Mills S, Ciavatti T, Yao Z, Mescall R, Hu H, Semenenko V, Fei Z, Li H, Perebeinos V, Tao H, Dai Q, Du X, Liu M 2018 ACS Photonics 5 2645
Google Scholar
[23] Ahn J S, Kihm H W, Kihm J E, Kim D S, Lee K G 2009 Opt. Express 17 2280
Google Scholar
[24] Neuman T, Alonso-González P, Garcia-Etxarri A, Schnell M, Hillenbrand R, Aizpurua J 2015 Laser Photonics Rev. 9 637
Google Scholar
[25] Cvitkovic A, Ocelic N, Hillenbrand R 2007 Opt. Express 15 8550
Google Scholar
[26] Maissen C, Chen S, Nikulina E, Govyadinov A, Hillenbrand R 2019 ACS Photonics 6 1279
Google Scholar
[27] Siday T, Hale L L, Hermans R I, Mitrofanov O 2020 ACS Photonics 7 596
Google Scholar
[28] Mastel S, Lundeberg M B, Alonso-Gonzale P, Gao Y, Watanabe K, Taniguchi T, Hone J, Koppen F H L, Nikitin A Y, Hillenbrand R 2017 Nano Lett. 17 6526
Google Scholar
[29] Siday T, Natrella M, Wu J, Liu H, Mitrofanov O 2017 Opt. Express 25 27874
Google Scholar
[30] Moon K, Park H, Kim J, Do Y, Lee S, Lee G, Kang H, Han H 2015 Nano Lett. 15 549
Google Scholar
[31] Moon K, Do Y, Park H, Kim J, Kang H, Lee G, Lim J H, Kim J W, Han H 2019 Sci. Rep. 9 169158
Google Scholar
[32] Wang Y Y, Hu M, Zhang Z C, Zhang T Y, Gong S, Wang W, Liu S G 2019 44th International Conference on Infrared, Millimeter, and Terahertz Waves (IRMMW-THz) Maison de la Chimie, France, September 1−6, 2019 pp1,2
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