Ulrike Eigenthaler

Planar Metamaterial Analogue of Electromagnetically Induced Transparency for Plasmonic Sensing

We experimentally demonstrate a planar metamaterial analogue of electromagnetically induced transparency at optical frequencies. The structure consists of an optically bright dipole antenna and an optically dark quadrupole antenna, which are cut-out structures in a thin gold film. A pronounced coupling-induced reflectance peak is observed within a broad resonance spectrum. A metamaterial sensor based on these coupling effects is experimentally demonstrated and yields a sensitivity of 588 nm/RIU and a figure of merit of 3.8.

Nanoscale imaging using deep ultraviolet digital holographic microscopy

A deep ultraviolet off-axis digital holographic microscope (DHM) is presented. The microscope has been arranged with as least as possible optical elements in the imaging path to avoid aberration due to the non-perfect optical elements. A high resolution approach has been implemented in the setup using oblique illumination to overcome the limitation introduced by the optical system. To examine the resolution of the system a nano-structured template has been designed and the result confirms the submicron and nanoscale resolution of the arranged DHM setup.

Plasmon energy mapping in energy-filtering transmission electron microscopy

In this paper, we demonstrate the two-dimensional mapping of plasmon energies by energy-filtering transmission electron microscopy. The maps are obtained from a series of energy-filtered images in the plasmon energy region. Examples are shown for a nano-crystalline Si-B-C-N ceramic. This material contains SiC and Si(3)N(4) grains as well as intergranular regions composed of hexagonal BN (h-BN) and turbostratic carbon (t-C). The different phases can be clearly identified by their specific plasmon energies. An energy resolution of < or =0.1eV is achieved. In addition, the plasmon map of an amorphous carbon film is used to visualize the non-isochromaticity of the Corrected Omega filter (90 degrees filter) of the SESAM2. A procedure is proposed for the correction of the non-isochromaticity.

Interfaces in semiconductor/metal radial superlattices

Semiconductor/metal radial superlattices are produced by the roll-up of inherently strained InGaAs∕Ti∕Au as well as InAlGaAs∕GaAs∕Cr films. Cross sections of the obtained structures are prepared and investigated in detail by diverse transmission electron microscopy as well as microanalysis techniques. Special attention is paid to the interfaces of the semiconductor/metal hybrid superlattice. The study reveals amorphous, noncrystalline layers for the semiconductor/metal as well as for the metal/semiconductor interface. The chemical analysis suggests that the observed interlayers are oxides giving rise to a semiconductor/oxide/metal/oxide superlattice rather than a pure semiconductor/metal superlattice.

Rapid prototyping of Fresnel zone plates via direct Ga+ ion beam lithography for high-resolution x-ray imaging

A significant challenge to the wide utilization of X-ray microscopy lies in the difficulty in fabricating adequate high-resolution optics. To date, electron beam lithography has been the dominant technique for the fabrication of diffractive focusing optics called Fresnel zone plates (FZP), even though this preparation method is usually very complicated and is composed of many fabrication steps. In this work, we demonstrate an alternative method that allows the direct, simple, and fast fabrication of FZPs using focused Ga(+) beam lithography practically, in a single step. This method enabled us to prepare a high-resolution FZP in less than 13 min. The performance of the FZP was evaluated in a scanning transmission soft X-ray microscope where nanostructures as small as sub-29 nm in width were clearly resolved, with an ultimate cutoff resolution of 24.25 nm, demonstrating the highest first-order resolution for any FZP fabricated by the ion beam lithography technique. This rapid and simple fabrication scheme illustrates the capabilities and the potential of direct ion beam lithography (IBL) and is expected to increase the accessibility of high-resolution optics to a wider community of researchers working on soft X-ray and extreme ultraviolet microscopy using synchrotron radiation and advanced laboratory sources.

Optimizing the fabrication of diffractive optical elements using a focused ion beam system

In the past, UV lithography has been used extensively for the fabrication of diffractive optical elements (DOEs). The advantage of this technique is that the entire structure can be written at one time, however, the minimum feature size is limited to about 1 μm. Many 1-d and 2-d periodic grating structures may not need such fine details but it is essential for diffractive optics with circular structures. This is because the spacing between features typically decreases towards the edge of the element resulting in the smallest feature falling well below 1 μm. 1-d structures such as sub-wavelength gratings will also have smaller feature sizes throughout the structure. In such cases, advanced techniques such as Focused Ion Beam and Electron-beam Lithography are required for the fabrication of finer structures. In this paper, we present results of DOEs fabricated with a focused ion beam system (Nova Nanolab 600 from FEI) directly on a single mode fibre tip. The ability to write DOEs directly on fibre tip is of great importance in fields such as endoscopy and optical trapping. The DOE itself, transforms the laser beam to a phase and intensity profile that matches the requirement. Because it is located directly on the fibre, no extra alignment is required. In addition, the system becomes more compact, which is especially important for applications in the field of endoscopy. The main goal of the present work was to develop the most accurate method for creating the desired pattern (that is, the DOE structure) into an actually working element. Different exposure strategies for writing test structures directly with the ion beam on the fibre tip have been tested and carefully evaluated. The paper will present in detail the initial fabrication and optical test results for blazed and binary structures of 1-d and circularly symmetric Fresnel axicons on optical fibres.

Different approaches to increase resolution in DHM

Different approaches to increase the resolution in digital holographic microscopy (DHM) are presented. A high resolution approach has been implemented in the off axis Deep UV DHM setup using oblique illumination to overcome the limitation introduced by the optical system and the theoretical resolution limit of 250 nm (according to Abbe criterion) has been verified, experimentally. A two view DHM system operating in the visible wavelength is also introduced to increase the resolution and contrast in 3D imaging of complex biological samples.

Effect of surface orientation on intrinsic island formation on SrTiO3 surfaces

Intrinsic islands were formed on Nb-doped SrTiO3 (100) and (111) surfaces by high-temperature annealing (1200°C) under oxygen atmosphere. The influence of surface orientation on the chemical composition and structure of islands was investigated by using Auger electron spectroscopy, energy-dispersive X-ray spectroscopy as well as electron diffraction in a transmission electron microscope. For a given island size, the same compositional profiles were observed for both surface orientations. While the bigger islands (with a height of several 100 nm) contain almost only Sr as cations, the smaller islands (with a height of few 10 nm) also contain Ti. Identical lattice-plane distances in all islands point to a distinct crystal structure for islands growing on (001) and (111) surfaces.