Abstract-Sub-nanometer thin oxide film sensing with localized surface phonon polaritons

Gubbin, Virginia D Wheeler, Alexander J. Giles, Vincenzo Giannini, Stefan A. Maier, Simone De Liberato, Joshua D Caldwell

https://pubsdc3.acs.org/doi/10.1021/acsphotonics.7b01482


Chemical sensing methods based on surface polaritonic resonances stem from their intense near fields and resultant sensitivity to changes in local refractive index. Polar dielectric crystals (e.g. SiC, hBN) support surface phonon polaritons (SPhPs) from the mid-infrared to terahertz range with mode volumes and quality factors exceeding the best case scenario attained by plasmonic counterparts, making them strong candidates for resonant surface-enhanced infrared spectroscopy (SEIRA). We report on the behaviour of SPhP resonances of SiC nanopillars following the incorporation of sub- and nanometric coatings of Al2O3 and ZrO2 obtained by atomic layer deposition. Concurrent anomalous red and blue-shifts of SPhP resonances were observed upon deposition of sub-nanometric Al2O3 films, with shift direction dictated by the mode position relative to the ordinary longitudinal optic (LO) phonon of Al2O3. These concurrent shifts, which are attributed to coupling to the Berreman mode of the Al2O3 layer, persist for thicker films and are correctly predicted by numerical calculations employing the measured Al2O3 permittivity. Deposition of ZrO2, whose phonon resonances are detuned from the SPhPs, also led to anomalous blue-shifts of transverse and longitudinal SPhP resonances around 900 cm-1 for films up to ≈ 1.5 nm, reversing to the canonical red-shift for thicker layers. These anomalous shifts were not reproduced numerically using the measured ZrO2 permittivity and suggest the existence of a localized surface state, which when modelled as a simple Lorentz oscillator, provide semi-quantitative agreement with experimental results. In addition, predicted shifts for thicker ZrO2layers may thus provide a tool for real-time monitoring of ultrathin film growth.

Abstract-Terahertz All-Dielectric Magnetic Mirror Metasurfaces

Zhijie Ma, Stephen M. Hanham, Pablo Albella, Binghao Ng, Hsiao Tzu Lu, Yandong Gong, Stefan A. Maier and Minghui Hong

http://pubs.acs.org/doi/abs/10.1021/acsphotonics.6b00096?journalCode=apchd5

We demonstrate an all-dielectric metasurface operating in the terahertz band that is capable of engineering a reflected beam's spatial properties with high efficiency. The metasurface is formed from an array of silicon cube resonators which simultaneously support electric and magnetic dipolar Mie resonances. By controlling the interference between these modes, the amplitude and phase of a reflected wave can be arbitrarily controlled over a sub-wavelength area. We demonstrate the flexibility and utility of this metasurface by optimizing the surface to produce several reflected beam types including vortex and Bessel beams; the latter being useful for diffraction-free point-to-point terahertz communications. Additionally, we show theoretically and experimentally how the metasurface can produce an all-dielectric magnetic mirror in the terahertz band.

Abstract-Terahertz Waves: Perfect Extinction of Terahertz Waves in Monolayer Graphene over 2-nm-Wide Metallic Apertures

1. Hyeong-Ryeol Park¹, 
2. Seon Namgung¹,
3. Xiaoshu Chen¹, 
4. Nathan C. Lindquist²,
5. Vincenzo Giannini³, 
6. Yan Francescato³,
7. Stefan A. Maier³ and
8. Sang-Hyun Oh^1,*

Article first published online: 12 MAY 2015

DOI: 10.1002/adom.201570031

© 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

http://onlinelibrary.wiley.com/doi/10.1002/adom.201570031/abstract

For enhanced light–matter interactions with 2D materials, ultra-small metallic nanogaps can be utilized. As shown in the image from S.-H. Oh and co-workers, light incident from below is strongly confined within these annular gaps and efficiently funneled through for extraordinarily large transmission. On page 667, by placing monolayer graphene at the exit of these gaps (the right side is covered with graphene), this enhanced transmission is blocked since the graphene absorbs 99% of the strongly confined waves.

Abstract-High-order localized spoof surface plasmon resonances and experimental verifications

• Zhen Liao,
• Yu Luo,
• Antonio I. Fernández-Domínguez,
• Xiaopeng Shen,
• Stefan A. Maier
• & Tie Jun Cui

http://www.nature.com/srep/2015/150410/srep09590/full/srep09590.html

We theoretically demonstrated and experimentally verified high-order radial spoof localized surface plasmon resonances supported by textured metal particles. Through an effective medium theory and exact numerical simulations, we show the emergence of these geometrically-originated electromagnetic modes at microwave frequencies. The occurrence of high-order radial spoof plasmon resonances is experimentally verified in ultrathin disks. Their spectral and near-field properties are characterized experimentally, showing an excellent agreement with theoretical predictions. Our findings shed light into the nature of spoof localized surface plasmons, and open the way to the design of broadband plasmonic devices able to operate at very different frequency regimes.

Abstract-Perfect Extinction of Terahertz Waves in Monolayer Graphene over 2-nm-Wide Metallic Apertures

1. Hyeong-Ryeol Park¹, 
2. Seon Namgung¹,
3. Xiaoshu Chen¹, 
4. Nathan C. Lindquist²,
5. Vincenzo Giannini³, 
6. Yan Francescato³,
7. Stefan A. Maier³ and
8. Sang-Hyun Oh^1,*

Article first published online: 7 JAN 2015

http://onlinelibrary.wiley.com/doi/10.1002/adom.201400546/abstract

DOI: 10.1002/adom.201400546

© 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

High carrier mobility and tunability in graphene enable fundamental studies for plasmonics and various applications. Despite its versatility, however, single-layer graphene (SLG) suffers from poor coupling efficiency to electromagnetic waves, presenting a major challenge for photonic applications. Compared with visible or infrared radiation, terahertz (THz) waves exhibit higher absorption in SLG due to Drude-like intraband transitions, but the wavelength-to-SLG size mismatch becomes even more dramatic. Here, we experimentally demonstrate 99% extinction of THz wave transmission when SLG covers the openings of 2-nm-wide (≈λ/1 000 000) slits through a metal film. By resonantly coupling THz waves through annular nanogaps, the extremely localized fields lead to near-perfect extinction and strong absorption in SLG. Atomic-layer lithography is used to produce these nanometer-wide, millimeter-long gaps over an entire 4-in. wafer. Furthermore, by integrating these devices with an ionic liquid, enhanced intraband absorption in the SLG leads to 80% modulation of THz waves with an operational voltage as low as 1.5 V.

Abstract-Broadband Terahertz Sensing on Spoof Plasmon Surfaces

Binghao Ng , Stephen M. Hanham , Jianfeng Wu ,Antonio I. Fernández-Domínguez , Norbert Klein ,Yun Fook Liew , Mark B.H. Breese , Minghui Hong, and Stefan A. Maier

ACS Photonics, Just Accepted Manuscript

DOI: 10.1021/ph500272n

Publication Date (Web): September 2, 2014

Copyright © 2014 American Chemical Society

http://pubs.acs.org/doi/abs/10.1021/ph500272n


In this paper, we show that broadband spectral data can be experimentally extracted from corrugated metallic surfaces consisting of a linear array of subwavelength grooves supporting tightly confined spoof plasmons. Using a combination of the scattering edge coupling method and short-time Fourier transform, we are able to discern the group velocity characteristics of a spoof plasmon pulse which in turn allows for the extraction of broadband dispersion data from 0.4 THz to 1.44 THz in a single measurement. Refractive index sensing of various fluids is demonstrated at microlitre volume quantities by monitoring changes in not only the dispersion relation but also the frequency dependent attenuation of the spoof plasmons. This gives information about both the real and imaginary part of the refractive index of an analyte, indicating the potential for spoof plasmon surfaces to fully characterise substances in the terahertz regime. Lastly, we show that the strong electromagnetic field confinement near the effective spoof plasmon frequency allows for surface enhanced absorption spectroscopy, demonstrated here with α-lactose monohydrate powder. This allows us to take a more spectroscopic approach to THz sensing whereby substances can be uniquely identified by their spectral fingerprints. The enhanced light-matter interactions that occur in the vicinity of the spoof plasmon surface allows for a more efficient use of the limited power of current terahertz sources. Together with the ability to integrate spoof plasmon surfaces with microfluidics and to freely design its electromagnetic properties, we believe that these surfaces can be a very versatile platform on which chip-scale terahertz sensing can be performed.

Abstract-Free-standing terahertz chiral meta-foils exhibiting strong optical activity and negative refractive index

Jianfeng Wu¹, Binghao Ng², Shuvan P. Turaga¹, Mark B. H. Breese^1,3, Stefan A. Maier², Minghui Hong⁴, Andrew A. Bettiol¹, and Herbert O. Moser^5
1Department of Physics, Center for Ion Beam Applications (CIBA), National University of Singapore, 2 Science Drive, Singapore 
²Department of Physics, Imperial College, London SW7 2AZ, United Kingdom 
³Singapore Synchrotron Light Source (SSLS), National University of Singapore, 5 Research Link, 117603 Singapore 
⁴Department of Electrical and Computer Engineering, National University of Singapore, 4 Engineering Drive 3, 117576 Singapore 
⁵Karlsruhe Institute of Technology (KIT), Network of Excellent Retired Scientists (NES), and Institute of Microstructure Technology (IMT), Postfach 3640, 76021 Karlsruhe, Germany 

http://apl.aip.org/resource/1/applab/v103/i14/p141106_s1?isAuthorized=no

A chiral meta-foil consisting of a self-supported square array of interconnected conjugated rosettes is demonstrated at terahertz frequencies. It exhibits strong optical activity and circular dichroism. Negative refractive index with a figure-of-merit as high as 4.2 is achieved, attributed to its free-standing nature. Experimental results are in good agreement with numerical simulation. Free-standing chiral meta-foils provide a unique approach to create a completely all-metal chiral metamaterial, which can be flexibly integrated into optical setups while eliminating dielectric insertion losses.

© 2013 AIP Publishing LLC

Abstract-Active control of electromagnetically induced transparency analogue in terahertz metamaterials

http://www.nature.com/ncomms/journal/v3/n10/full/ncomms2153.html

Jianqiang Gu, Ranjan Singh, Xiaojun Liu, Xueqian Zhang, Yingfang Ma,, Shuang Zhang,  Stefan A. Maier, Zhen Tian, Abul K. Azad,, Hou-Tong Chen,Antoinette J. Taylor,Jiaguang Han, Weili Zhang

Recently reported metamaterial analogues of electromagnetically induced transparency enable a unique route to endow classical optical structures with aspects of quantum optical systems. This method opens up many fascinating prospects on novel optical components, such as slow light units, highly sensitive sensors and nonlinear devices. In particular, optical control of electromagnetically induced transparency in metamaterials promises essential application opportunities in optical networks and terahertz communications. Here we present active optical control of metamaterial-induced transparency through active tuning of the dark mode. By integrating photoconductive silicon into the metamaterial unit cell, a giant switching of the transparency window occurs under excitation of ultrafast optical pulses, allowing for an optically tunable group delay of the terahertz light. This work opens up the possibility for designing novel chip-scale ultrafast devices that would find utility in optical buffering and terahertz active filtering