P. D. Gu

Free-standing THz electromagnetic metamaterials.

Using micromanufactured S-shaped gold strings suspended in free space by means of window-frames, we experimentally demonstrate an electromagnetic meta-material (EM(3)) in which the metallic structures are no longer embedded in matrices or deposited on substrates such that the response is solely determined by the geometrical parameters and the properties of the metal. Two carefully aligned and assembled window-frames form a bi-layer chip that exhibits 2D left-handed pass-bands corresponding to two different magnetic resonant loops in the range of 1.4 to 2.2 THz as characterized by Fourier transform interferometry and numerical simulation. Chips have a comparably large useful area of 56 mm(2). Our results are a step towards providing EM(3) that fulfill the common notions of a material.

Infrared Spectro/Microscopy at SSLS — Edge Effect Source in a Compact Superconducting Storage Ring

Singapore Synchrotron Light Source (SSLS) is commissioning its new beamline for Infrared Spectro/Microscopy (ISMI). The infrared light is extracted from the edge region of dipole D1 of the compact superconducting electron storage ring Helios 2. The nominal source point is located at half the maximum field, i.e., at 2.25 T. The end station comprises both, a medium and a high resolution Fourier transform infrared spectrometer (FTIR), the former featuring an infrared microscope as well as a UHV chamber for catalysis experiments. Synchrotron Radiation Workshop (SRW) calculations and a preliminary experimental evaluation of ISMI show the capability of this beamline to deliver a bright flux of photons in the Far and Mid infrared spectral regions.

Fabrication of 2D and 3D Electromagnetic Metamaterials for the Terahertz Range.

This paper addresses the 2D and 3D micro- and nanofabrication of ElectroMagnetic MetaMaterials (EM3) for the terahertz range. EM3 refers to artifbial composite materials which consist of a collection of repeated metal elements designed to have a strong response to applied electromagnetic felds, so that near resonance both the effective permittivity and magnetic permeability µ become simultaneously negative. This unusual situation leads to exotic consequences such as a negative index of refraction and an inverse Doppler and Cerenkov effect. EM3 fabricated so far have been mostly two-dimensional and in this respect are highly anisotropic. By anisotropic, it is inferred that the response of the system depends on the direction of illumination. The anisotropic nature of the metamaterials impedes eventual real-life applications of the negative media as it places constraints on the impinging electromagnetic waves. Ways of producing three-dimensional (3D) or more isotropic EM3 by means of tilted x-ray exposures will be introduced. Basic geometry tells us that if the structures are inclined at 30-45°, this would lead to an improvement of the coupling of the vector by 50-70%

Free‐space Electromagnetic Metamaterials From The Far Infrared To The Visible

The development of electromagnetic metamaterials by micro/nanomanufacturing at SSLS has led to matrix‐embedded or substrate‐supported rod‐split‐ring‐based samples reaching left‐handed pass‐bands at 216 THz or 1.39 μm and to free‐space S‐string bi‐layer chips at 2.2 THz. Potential applications of metamaterials range from sub‐wavelength resolution imaging over invisibility cloaking to advanced antennae and are relevant to fields including microscopy, lithography, electromagnetic shielding, and telecommunication.

Quantitative investigation of phase retrieval from X-ray phase-contrast tomographic images

X-ray phase-contrast tomographic microimaging is a powerful tool to reveal the internal structure of opaque soft-matter objects that are not easily seen in standard absorption contrast. In such low Z materials, the phase shift of X-rays transmitted can be important as compared to the absorption. An easy experimental set up that exploits refractive contrast formation can deliver images that are providing detailed structural information. Applications are abundant in fields including polymer science and engineering, biology, biomedical engineering, life sciences, zoology, water treatment and filtration, membrane science, and micro/nanomanufacturing. However, available software for absorptive contrast tomography cannot be simply used for structure retrieval as the contrast forming effect is different. In response, CSIRO has developed a reconstruction code for phase-contrast imaging. Here, we present a quantitative comparison of a micro phantom manufactured at SSLS with the object reconstructed by the code using X-ray images taken at SSLS. The phantom is a 500 μm thick 800 μm diameter cylindrical disk of SU-8 resist having various eccentric cylindrical bores with diameters ranging from 350 μm to 40 μm. Comparison of these parameters that are well known from design and post-manufacturing measurements with reconstructed ones gives encouraging results.

Towards large area THz electromagnetic metamaterials

Up to date, electromagnetic metamaterials (EM3) have been mostly fabricated by primary pattern generation via electron beam or laser writer. Such an approach is time-consuming and may have limitations of the area filled with structures. Especially, electron beam written structures are typically confined to areas of a few 100×100 μm2. However, for meaningful technological applications, larger quantities of good quality materials are needed. Lithography, in particular X-ray deep lithography, is well suited to accomplish this task. Singapore Synchrotron Light Source (SSLS) has been applying its LIGA process that includes primary pattern generation via electron beam or laser writer, X-ray deep lithography and electroplating to the micro/nano-manufacturing of high-aspect ratio structures to produce a variety of EM3 structures. Starting with Pendrys split ring resonators, we have pursued structure designs suitable for planar lithography since 2002 covering a range of resonance frequencies from 1 to 216 THz. More recently, string-like structures have also been included. Latest progress made in the manufacturing and characterization of quasi 3D metamaterials having either split ring or string structures over areas of about ≈1 cm2 extension will be described.

Towards 3D Electromagnetic Metamaterials in the THz Range

SSLS has been using its lithography‐based micro/nanofabrication facility LiMiNT (Lithography for Micro and Nanotechnology) and its infrared spectro/microscopy facility ISMI to develop and characterize the first electromagnetic metamaterials having their spectral response in the THz range. Derived from Pendry’s nested‐split‐ring resonator design, these structures require micro/nanofabrication in order to have resonances in the THz range. They exhibit a negative refractive index and hold promise of sub‐diffraction limit imaging. Besides the reduction of the size of the resonating structures to extend the spectral range towards the visible, outstanding issues include the production of high‐aspect‐ratio resonators that are sensitive for the magnetic field in any direction (3D sensitivity) and the capability to produce copious amounts of the electromagnetic metamaterials with a good yield. In this paper, we shall report on first results of 3D EM3 structures made by inclined exposures.

Research Frontiers at SSLS

Singapore Synchrotron Light Source operates five experimental facilities for micro/nanomanufacturing and the characterization of materials and processes. Highlights of results include THz electromagnetic metamaterials, the elucidation of C bonds in the so‐called carbon nanomesh, and the high precision determination of the geometric parameters and the density of thin layers in multilayer systems.

Shaping And Characterising Materials — Recent Results From Singapore Synchrotron Light Source

SSLS offers facilities for micro/nanofabrication and the analytical characterization of devices, materials and processes. Selected applications are presented including the manufacturing of electromagnetic metamaterials for the THz spectral range up to the near infrared, core‐hole clock spectroscopy of the charge transfer from BBB and BFF molecules to an Au electrode, and the characterization of Co and ITO thin films.

NanoElectromagnetic Metamaterials Approaching Telecommunications Frequencies

Arrays of gold Rod-Split-Ring-Resonators with structural details down to sub 100 nm, and exhibiting electromagnetic metamaterial (EM3) behavior near telecommunications frequencies, have been produced by nanofabrication. Samples were characterized at the Singapore Synchrotron Light Source ISMI (Infrared Spectro/MIcroscopy) facility using Bruker Optics’ IFS 66v/S Fourier transform interferometer and Hyperion 2000 Microscope powered by synchrotron radiation. Oblique incidence transmission spectra were measured and revealed a spectral resonance around 190 THz. The present work extends the frequency range in which EM3are available, thereby opening up opportunities for new applications in the telecommunications frequency regime.