SSLS

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SSLS

SINGAPORE SYNCHROTRON LIGHT SOURCE

MAKES LIGHT WORK FOR YOU

SINGAPORE SYNCHROTRON LIGHT SOURCE

Electromagnetic Metamaterials — Availability and Spectral Coverage of a New Class of Micro/Nanofabricated Composite Materials H. O. Moser*, B. D. F. Casse , M. Bahou, J. W. Lee , P. D. Gu and L. K. Jian

Characterization of the EM3 Structures Microfabrication of Electromagnetic Metamaterials 1 3

Singapore Synchrotron Light Source (SSLS), National University of Singapore, 5 Research Link, Singapore 117603. *[email protected]

Electroplati ng

AZ P4620

Project Outline

Si

Development of a new kind of artificial materials, referred to as electromagnetic metamaterials (EM3), which possess superior electromagnetic properties that cannot be found in naturally occurring materials. EM3 refers to materials having simul-taneously negative permittivity ε and permeability μ. Veselago, in his pioneering paper in 1967 [1], predicted that such materials would exhibit a plethora of unusual effects such as a negative index of refraction, a reverse Doppler, Čerenkov and Goos-Hänchen effects. EM3 are expected to provide new functionalities and enhancements to future optical and optoelectronics devices such as high-speed circuits, high-resolution imaging systems and higher capacity optical data storage systems. The nextgeneration EM3, based on miniaturization technologies, will also impact areas such as telecommunications, information technology, life sciences and military applications.

Au Cr

4 Cr etch

2 5

Laser writing

Au etch Figure 3: The resonance frequencies at which the composite materials (rod-split-rings structures) show EM3 behavior.

LIGA and Assembled THz Multilayer Structures (Scale bar 20 μm)

1

5

X-ray exposure

Hot embossing

X-rays Gold absorber

Background

2.1 mm x 2.1 mm microchip

In the 1990’s Sir John Pendry and co-workers devised recipes for obtaining a negative permittivity [2] and permeability [3] by a combination of metallic rods and split ring resonators. Pendry’s inspiring work led to a resurgence of effort in fabricating electromagnetic metamaterials with first demonstrations in the GHz range [4]. More recently, micro-/nanofabrication has been exploited to push the useful resonance frequency by more than 4 orders of magnitude into the THz range, thus reaching already near infrared telecommunications frequencies around 194 THz (~1.55 μm) [5–8]. SSLS has been using its LiMiNT facility (Lithography for Micro-/Nanotechnology) since 2003 to manufacture the nextgeneration EM3, thus producing the first microelectromagnetic metamaterials in the THz range (2.28–2.7 THz) and nanoelectro-magnetic metamaterials at frequencies up to 187.5 THz [6]. LiMiNT is a one-stop shop comprising the full LIGA† process cycle for micro-/nanomanufacturing in a class 1000 cleanroom. Present developments at SSLS aims to reach even higher resonance frequencies by reducing the geometric dimensions of the structures further, to improve isotropy of the materials by means of tilted X-ray exposure, and to produce copious amounts of high-quality samples by X-ray lithography and, later on, hot embossing.

Graphite membrane Resist

(Scale bar 100 μm)

Substrate

Figure 1: 2.1 x 2.1 mm2 microchip containing about 400 rod-split-rings structures embedded in a plastic matrix (AZ P4620).

2

Development

3

4

Resist stripping

Electrodeposition

Nanofabrication of Electromagnetic Metamaterials 1

3

Metal deposition via sputtering Au

Figure 4: Illustration of the LIGA Process

PMMA Glass

2

E-beam

4 Lift-off

(Scale bar 200 μm)

SU8 Chip produced by LIGA

Methods and Materials

Figure 5: Metal structures embedded in SU8 chip, produced by the LIGA process (left). Several chips stacked together to form EM3 slab (right). [Note that the spacing of the layers has been exaggerated for illustration purposes]

The microstructures were patterned by means of a Heidelberg DWL 66 laser writer, and the nanostructures by means of an FEI Sirion SEM equipped with the Nabity Nanometer pattern Generator System (NPGS). X-ray lithography was employed for batch processing of larger quantities of EM3 on 4˝ wafer format. The resonance fre-quency at which the composite materials (rod-splitrings structures) show EM3 behavior is determined by means of IR Fourier transform spectroscopy at the Bruker IFS 66 v/S of SSLS’ ISMI beamline.

References [1] V. G. Veselago, Sov. Phys. Usp.,10:509, 1968. [2] J. B. Pendry, A. J. Holden , W. J. Stewart , and I. Youngs, Phys. Rev. Lett. 76, 4773 (19 96); J. Phys. Condens. Matter 10, 4785 (1998). [3] J. B. Pendry, A. J. Holden , D. J. Robbins, W. J. Stewart, IEEE Trans. Microwave Theory and Tech. 47, 2075(1999).

Nanostructures on glass (Scale bar 1 μm) Figure 2: 500 × 500 μm2 array containing 250,000 rod-split-ring structures. †

LIGA is the German acronym for X-ray Lithography (Lithographie), Electrodeposition (Galvanoformung) and Molding (Abformung).

[4] D. R. Smith, W. J. Padilla, D. C. Vier, S. C. Nemat-Nasser, and S. Schultz, Phys. Rev. Lett. 84, 4184(2000). [5] H. O. Moser, B. D. F. Casse, O. Wilhelmi, and B. T. Saw, Phys. Rev. Lett., 94(6):063901, (2005). [6] B. D. F. Casse, H. O. Moser, M. Bahou, L. K. Jian, and P. D. Gu, Nanoelectronics, 2006 IEEE Conference on Emerging Technologies, 10–13 Jan 2006, pages: 328–331. [7] Stefan Linden, Christian Enkrich, Martin Wegener, Jianfeng Zhou, Thomas Koschny, and Costas M. Soukoulis Science 306, 1351 (2004). [8] S. Zhang, W. Fan, N. C. Panoiu, K. J. Malloy, R. M. Osgood, and S. R. J. Brueck, Phys. Rev. Lett. 95, 137404 (2005).

Acknowledgments Work performed at SSLS under A*STAR/MOE RP3979908M, A*STAR 0121050038, NUS Core C-380-003-003001 grants. The authors would like to thank Stephen Inglis for his contributions to the microtechnology processes.

SSLS

MAKES LIGHT WORK FOR YOU

SINGAPORE SYNCHROTRON LIGHT SOURCE

SSLS

MAKES LIGHT WORK FOR YOU

SINGAPORE SYNCHROTRON LIGHT SOURCE