M. Bahou

Towards three-dimensional and multilayer rod-split-ring metamaterial structures by means of deep x-ray lithography

Presently existing THz electromagnetic metamaterials were mostly produced as planar single layer structures, either deposited on a substrate or embedded in a polymer matrix, and patterned by a primary pattern generator such as an electron beam writer or a laser writer. Some attempts to produce more voluminous structures were made using ultraviolet photolithography and a stacking process. We explore deep x-ray lithography and subsequent stacking of chips to fabricate, with good yield, substantial quantities of rod-split-ring structures that come closer to three dimensions than before. Samples were characterized layer-by-layer using Fourier transform interferometry in the far infrared.

Multivariate analysis techniques in the forensics investigation of the postblast residues by means of Fourier transform-infrared spectroscopy.

Fourier transform-infrared (FT-IR) spectroscopy has gained considerable attention among the forensic scientists because it shows high sensitivity and selectivity and offers near real time detection of analyzed samples. However, the amount of obtained information due to complexity of the measured spectra forces the use of additional data processing. Application of the multivariate statistical techniques for the analysis of the FT-IR data seems to be necessary in order to enable feature extraction, proper evaluation, and identification of obtained spectra. In this article, an attempt to develop a feasible procedure for characterization of spectroscopic signatures of the explosive materials in the remnants after explosion has been made. All spectra were derived after analysis of samples from debris after especially prepared and performed blasts with the use of three various highly explosive materials: C-4, 2,4,6-trinitrotoluene (TNT), and pentaerythritol tetranitrate (PETN). Two well-known multivariate statistical methods, hierarchical cluster analysis (HCA) and principal component analysis (PCA), were tested in order to classify the samples into separate classes using a broad wavelength data range (4000-600 cm(-1)) on collected spectra sets. After many trials it seems that PCA is the best choice for the mentioned earlier tasks. It was found that only three principal components carry over 99.6% of variance within the sample set. The results show that FT-IR spectroscopy in combination with multivariate methods is well-suited for identification and differentiation purposes even in quite large data sets, and for that reason forensic laboratories could employ these methods for rapid screening analysis.

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.

All-metal self-supported THz metamaterial--the meta-foil.

Modern metamaterials face functional constraints as they are commonly embedded in or deposited on dielectric materials. We provide a new solution by microfabricating a completely free-standing all-metal self-supported metamaterial. Using upright S-string architecture with the distinctive feature of metallic transverse interconnects, we form a locally stiff, globally flexible space-grid. Infrared Fourier transform interferometry reveals the typical double-peak structure of a magnetically excited left-handed and an electrically excited right-handed pass-band that is maintained under strong bending and heating, and is sensitive to dielectrics. Exploiting UV/X-ray lithography and ultimately plastic moulding, meta-foils can be mass manufactured cost-effectively to serve as optical elements.

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%

THz meta-foil – a platform for practical applications of metamaterials

The meta-foil, an all-metal fully self-supported locally stiff and globally flexible metamaterial, is presented. Its architecture is based on an array of parallel S-strings interconnected by transverse metal rods that are periodically repeated along the strings. For the present samples, this period is about once or twice the length of an S, which is 31 µm. The resonance frequency of the left-handed pass-band is 3.2 THz or somewhat higher depending on geometry. The meta-foil is manufactured by UV or X-ray lithography-based microfabrication. In the end, it may be produced cost-effectively by plastic moulding. The physical function is explained by numerical simulation and equivalent circuit theory. The spectra are measured by Fourier transform infrared spectroscopy. Maximum transmission is achieved at normal incidence with a cosine-square-like decrease with incidence angle. A change of geometrical parameters alters the resonance frequency as expected. The spectra are also rather sensitive to surrounding dielectrics, indicating a sensor capability. As the meta-foil can be bent, a cylindrical hyperlens set-up is discussed as a forthcoming application to sub-wavelength resolution imaging.

Making and measuring nanostructures: Nanoscience and technology at the Singapore synchrotron light source

Synchrotron radiation facilities are natural places for nanoscience and technology as they may be used for both micro-and nanomanufacturing and the analytic characterization of nanoscale samples. The Singapore Synchrotron Light Source is conducting work in both fields. Examples given refer to the micro-and nanomanufacturing of the first electromagnetic metamaterials for the THz spectral range, the measurement of thin-film parameters such as thickness, density, and roughness in organic and inorganic nanoscale layer systems via X-ray reflectometry; the study of the atomic structure of the so-called carbon nanomesh that is formed through annealing of a SiC wafer at 1100°C by means of high-resolution X-ray photoemission spectroscopy; and the investigation of the chemical states of nanographite via X-ray absorption spectroscopy.

Deep X-Ray Lithography in the Fabrication Process of a 3D Diffractive Optical Element

We present first results of the fabrication process of a diffractive optical element (DOE) using deep X‐ray lithography. The DOE forms the core of our proposed fast parallel‐processing infrared Fourier transform interferometer (FPP FTIR) that works without moving parts and may allow instantaneous spectral analysis only limited by detector bandwidth. Design and specifications of the DOE are discussed. A fabrication process including deep X‐ray lithography (DXRL) on stepped substrates is introduced.

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.