Plasmonic bowtie antennas made of doped silicon can operate as plasmonic resonators at terahertz (THz) frequencies and provide large field enhancement close to their gap. We demonstrate both experimentally and theoretically that the field confinement close to the surface of the antenna enables the detection of ultrathin (100 nm) inorganic films, about 3750 times thinner than the free space wavelength. Based on model calculations, we conclude that the detection sensitivity and its variation with the thickness of the deposited layer are related to both the decay of the local THz field profile around the antenna and the local field enhancement in the gap of the bowtie antenna. This large field enhancement has the potential to improve the detection limits of plasmon-based biological and chemical sensors.

© 2012 OSA

1. R. Ulbricht, E. Hendry, J. Shan, T. F. Heinz, and M. Bonn, “Carrier dynamics in semiconductors studied with time-resolved terahertz spectroscopy,” Rev. Mod. Phys.83(2), 543–586 (2011). [CrossRef]
2. A. J. Huber, F. Keilmann, J. Wittborn, J. Aizpurua, and R. Hillenbrand, “Terahertz near-field nanoscopy of mobile carriers in single semiconductor nanodevices,” Nano Lett.8(11), 3766–3770 (2008). [CrossRef] [PubMed]
3. B. M. Fischer, H. Helm, and P. U. Jepsen, “Chemical recognition with broadband THz spectroscopy,” Proc. IEEE95(8), 1592–1604 (2007). [CrossRef]
4. P. Haring Bolivar, M. Brucherseifer, M. Nagel, H. Kurz, A. Bosserhoff, and R. Büttner, “Label-free probing of genes by time-domain terahertz sensing,” Phys. Med. Biol.47(21), 3815–3821 (2002). [CrossRef] [PubMed]
5. H. Sun, Y. J. Ding, and I. B. Zotova, “THz spectroscopy by frequency-tuning monochromatic THz source: from single species to gas mixtures,” IEEE Sens. J.10(3), 621–629 (2010). [CrossRef]
6. N. Shimizu, K. Kikuchi, T. Ikari, K. Matsuyama, A. Wakatsuki, S. Kohjiro, and R. Fukasawa, “Absorption spectra of smoke emitted from heated nylon fabric measured with continuous-wave sub-terahertz spectrometer,” Appl. Phys. Express4(3), 032401 (2011). [CrossRef]
7. D. L. Jeanmaire and R. P. Van Duyne, “Surface raman spectroelectrochemistry: Part I. Heterocyclic, aromatic, and aliphatic amines adsorbed on the anodized silver electrode,” J. Electroanal. Chem. Interfacial Electrochem.84(1), 1–20 (1977). [CrossRef]
8. M. Moskovits, “Surface-enhanced Raman spectroscopy: a brief retrospective,” J. Raman Spectros.36(6-7), 485–496 (2005). [CrossRef]
9. S. J. Lee, Z. Guan, H. Xu, and M. Moskovits, “Surface-enhanced raman spectroscopy and nanogeometry: the plasmonic origin of SERS,” J. Phys. Chem. C111(49), 17985–17988 (2007). [CrossRef]
10. A. Hartstein, J. R. Kirtley, and J. C. Tsang, “Enhancement of the infrared absorption from molecular monolayers with thin metal overlayers,” Phys. Rev. Lett.45(3), 201–204 (1980). [CrossRef]
11. E. Johnson and R. Aroca, “Surface-enhanced infrared spectroscopy of monolayers,” J. Phys. Chem.99(23), 9325–9330 (1995). [CrossRef]
12. A. Pucci, F. Neubrech, D. Weber, S. Hong, T. Toury, and M. Lamy de la Chapelle, “Surface enhanced infrared spectroscopy using gold nanoantennas,” Phys. Status Solidi, B Basic Res.247(8), 2071–2074 (2010). [CrossRef]
13. F. Neubrech, A. Pucci, T. W. Cornelius, S. Karim, A. García-Etxarri, and J. Aizpurua, “Resonant plasmonic and vibrational coupling in a tailored nanoantenna for infrared detection,” Phys. Rev. Lett.101(15), 157403 (2008). [CrossRef] [PubMed]
14. K. Berdel, J. Gómez-Rivas, P. Haring Bolívar, P. de Maagt, and H. Kurz, “Temperature dependence of the permittivity and loss tangent of high-permittivity materials at terahertz frequencies,” IEEE Trans. Microw. Theory Tech.53(4), 1266–1271 (2005). [CrossRef]
15. M. Theuer, R. Beigang, and D. Grischkowsky, “Sensitivity increase for coating thickness determination using THz waveguides,” Opt. Express18(11), 11456–11463 (2010). [CrossRef] [PubMed]
16. J. Saxler, J. Gómez-Rivas, C. Janke, H. P. M. Pellemans, P. Haring Bolívar, and H. Kurz, “Time-domain measurements of surface plasmon polaritons in the terahertz frequency range,” Phys. Rev. B69(15), 155427 (2004). [CrossRef]
17. T. H. Isaac, W. L. Barnes, and E. Hendry, “Determining the terahertz optical properties of subwavelength films using semiconductor surface plasmons,” Appl. Phys. Lett.93(24), 241115 (2008). [CrossRef]
18. H. Tao, S. C. Strikwerda, M. Liu, J. P. Mondia, E. Ekmekci, K. Fan, D. L. Kaplan, W. J. Padilla, X. Zhang, R. D. Averitt, and F. G. Omenetto, “Performance enhancement of terahertz metamaterials on ultrathin substrates for sensing applications,” Appl. Phys. Lett.97(26), 261909 (2010). [CrossRef]
19. B. You, J.-Y. Lu, J.-H. Liou, C.-P. Yu, H.-Z. Chen, T. A. Liu, and J. L. Peng, “Subwavelength film sensing based on terahertz anti-resonant reflecting hollow waveguides,” Opt. Express18(18), 19353–19360 (2010). [CrossRef] [PubMed]
20. J. Gómez Rivas, M. Kuttge, H. Kurz, P. H. Bolívar, and J. A. Sanchez-Gil, “Low frequency active surface plasmon optics on semiconductors,” Appl. Phys. Lett.88(8), 082106 (2006). [CrossRef]
21. A. Berrier, R. Ulbricht, M. Bonn, and J. G. Rivas, “Ultrafast active control of localized surface plasmon resonances in silicon bowtie antennas,” Opt. Express18(22), 23226–23235 (2010). [CrossRef] [PubMed]
22. V. Giannini, A. Berrier, S. A. Maier, J. A. Sánchez-Gil, and J. G. Rivas, “Scattering efficiency and near field enhancement of active semiconductor plasmonic antennas at terahertz frequencies,” Opt. Express18(3), 2797–2807 (2010). [CrossRef] [PubMed]
23. M. Pelton, J. Aizpurua, and G. Bryant, “Metal-nanoparticle plasmonics,” Laser Photon. Rev.2(3), 136–159 (2008). [CrossRef]
24. E. D. Palik, Handbook of optical constants of solids, Elsevier (1998).
25. S. Adachi, Handbook on physical properties of semiconductors, Vol. 1 (Kluwer, 2004).
26. F. Le, D. W. Brandl, Y. A. Urzhumov, H. Wang, J. Kundu, N. J. Halas, J. Aizpurua, and P. Nordlander, “Metallic nanoparticle arrays: a common substrate for both surface-enhanced Raman scattering and surface-enhanced infrared absorption,” ACS Nano2(4), 707–718 (2008). [CrossRef] [PubMed]

ACS Nano

• F. Le, D. W. Brandl, Y. A. Urzhumov, H. Wang, J. Kundu, N. J. Halas, J. Aizpurua, and P. Nordlander, “Metallic nanoparticle arrays: a common substrate for both surface-enhanced Raman scattering and surface-enhanced infrared absorption,” ACS Nano2(4), 707–718 (2008). [CrossRef] [PubMed]

Appl. Phys. Express

• N. Shimizu, K. Kikuchi, T. Ikari, K. Matsuyama, A. Wakatsuki, S. Kohjiro, and R. Fukasawa, “Absorption spectra of smoke emitted from heated nylon fabric measured with continuous-wave sub-terahertz spectrometer,” Appl. Phys. Express4(3), 032401 (2011). [CrossRef]

Appl. Phys. Lett.

• T. H. Isaac, W. L. Barnes, and E. Hendry, “Determining the terahertz optical properties of subwavelength films using semiconductor surface plasmons,” Appl. Phys. Lett.93(24), 241115 (2008). [CrossRef]
• H. Tao, S. C. Strikwerda, M. Liu, J. P. Mondia, E. Ekmekci, K. Fan, D. L. Kaplan, W. J. Padilla, X. Zhang, R. D. Averitt, and F. G. Omenetto, “Performance enhancement of terahertz metamaterials on ultrathin substrates for sensing applications,” Appl. Phys. Lett.97(26), 261909 (2010). [CrossRef]
• J. Gómez Rivas, M. Kuttge, H. Kurz, P. H. Bolívar, and J. A. Sanchez-Gil, “Low frequency active surface plasmon optics on semiconductors,” Appl. Phys. Lett.88(8), 082106 (2006). [CrossRef]

IEEE Sens. J.

• H. Sun, Y. J. Ding, and I. B. Zotova, “THz spectroscopy by frequency-tuning monochromatic THz source: from single species to gas mixtures,” IEEE Sens. J.10(3), 621–629 (2010). [CrossRef]

IEEE Trans. Microw. Theory Tech.

• K. Berdel, J. Gómez-Rivas, P. Haring Bolívar, P. de Maagt, and H. Kurz, “Temperature dependence of the permittivity and loss tangent of high-permittivity materials at terahertz frequencies,” IEEE Trans. Microw. Theory Tech.53(4), 1266–1271 (2005). [CrossRef]

J. Electroanal. Chem. Interfacial Electrochem.

• D. L. Jeanmaire and R. P. Van Duyne, “Surface raman spectroelectrochemistry: Part I. Heterocyclic, aromatic, and aliphatic amines adsorbed on the anodized silver electrode,” J. Electroanal. Chem. Interfacial Electrochem.84(1), 1–20 (1977). [CrossRef]

J. Phys. Chem.

• E. Johnson and R. Aroca, “Surface-enhanced infrared spectroscopy of monolayers,” J. Phys. Chem.99(23), 9325–9330 (1995). [CrossRef]

J. Phys. Chem. C

• S. J. Lee, Z. Guan, H. Xu, and M. Moskovits, “Surface-enhanced raman spectroscopy and nanogeometry: the plasmonic origin of SERS,” J. Phys. Chem. C111(49), 17985–17988 (2007). [CrossRef]

J. Raman Spectros.

• M. Moskovits, “Surface-enhanced Raman spectroscopy: a brief retrospective,” J. Raman Spectros.36(6-7), 485–496 (2005). [CrossRef]

Laser Photon. Rev.

• M. Pelton, J. Aizpurua, and G. Bryant, “Metal-nanoparticle plasmonics,” Laser Photon. Rev.2(3), 136–159 (2008). [CrossRef]

Nano Lett.

• A. J. Huber, F. Keilmann, J. Wittborn, J. Aizpurua, and R. Hillenbrand, “Terahertz near-field nanoscopy of mobile carriers in single semiconductor nanodevices,” Nano Lett.8(11), 3766–3770 (2008). [CrossRef] [PubMed]

Opt. Express

• M. Theuer, R. Beigang, and D. Grischkowsky, “Sensitivity increase for coating thickness determination using THz waveguides,” Opt. Express18(11), 11456–11463 (2010). [CrossRef] [PubMed]
• B. You, J.-Y. Lu, J.-H. Liou, C.-P. Yu, H.-Z. Chen, T. A. Liu, and J. L. Peng, “Subwavelength film sensing based on terahertz anti-resonant reflecting hollow waveguides,” Opt. Express18(18), 19353–19360 (2010). [CrossRef] [PubMed]
• A. Berrier, R. Ulbricht, M. Bonn, and J. G. Rivas, “Ultrafast active control of localized surface plasmon resonances in silicon bowtie antennas,” Opt. Express18(22), 23226–23235 (2010). [CrossRef] [PubMed]
• V. Giannini, A. Berrier, S. A. Maier, J. A. Sánchez-Gil, and J. G. Rivas, “Scattering efficiency and near field enhancement of active semiconductor plasmonic antennas at terahertz frequencies,” Opt. Express18(3), 2797–2807 (2010). [CrossRef] [PubMed]

Phys. Med. Biol.

• P. Haring Bolivar, M. Brucherseifer, M. Nagel, H. Kurz, A. Bosserhoff, and R. Büttner, “Label-free probing of genes by time-domain terahertz sensing,” Phys. Med. Biol.47(21), 3815–3821 (2002). [CrossRef] [PubMed]

Phys. Rev. B

• J. Saxler, J. Gómez-Rivas, C. Janke, H. P. M. Pellemans, P. Haring Bolívar, and H. Kurz, “Time-domain measurements of surface plasmon polaritons in the terahertz frequency range,” Phys. Rev. B69(15), 155427 (2004). [CrossRef]

Phys. Rev. Lett.

• F. Neubrech, A. Pucci, T. W. Cornelius, S. Karim, A. García-Etxarri, and J. Aizpurua, “Resonant plasmonic and vibrational coupling in a tailored nanoantenna for infrared detection,” Phys. Rev. Lett.101(15), 157403 (2008). [CrossRef] [PubMed]
• A. Hartstein, J. R. Kirtley, and J. C. Tsang, “Enhancement of the infrared absorption from molecular monolayers with thin metal overlayers,” Phys. Rev. Lett.45(3), 201–204 (1980). [CrossRef]

Phys. Status Solidi, B Basic Res.

• A. Pucci, F. Neubrech, D. Weber, S. Hong, T. Toury, and M. Lamy de la Chapelle, “Surface enhanced infrared spectroscopy using gold nanoantennas,” Phys. Status Solidi, B Basic Res.247(8), 2071–2074 (2010). [CrossRef]

Proc. IEEE

• B. M. Fischer, H. Helm, and P. U. Jepsen, “Chemical recognition with broadband THz spectroscopy,” Proc. IEEE95(8), 1592–1604 (2007). [CrossRef]

Rev. Mod. Phys.

• R. Ulbricht, E. Hendry, J. Shan, T. F. Heinz, and M. Bonn, “Carrier dynamics in semiconductors studied with time-resolved terahertz spectroscopy,” Rev. Mod. Phys.83(2), 543–586 (2011). [CrossRef]

Other

• E. D. Palik, Handbook of optical constants of solids, Elsevier (1998).
• S. Adachi, Handbook on physical properties of semiconductors, Vol. 1 (Kluwer, 2004).

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