H. Raether

Bio: H. Raether is an academic researcher from University of Hamburg. The author has contributed to research in topics: Surface plasmon & Surface finish. The author has an hindex of 19, co-authored 33 publications receiving 7438 citations. Previous affiliations of H. Raether include Munich University of Applied Sciences.

Bestimmung optischer Konstanten von Festkörpern aus Energieverlusten mittelschneller Elektronen

Abstract: Elektronen konnen longitudinale Anregungen des festen Korpers erzeugen Sie ubertragen hierbei eine Energie ΔE=hω und einen Impuls ▄q auf die Kristallelektronen Die Anregungswahrscheinlichkeit ist proportional zu Im \(\left( { - \frac{1}{{ \in (\omega )}}} \right)\), wobei e(ω) die Dielektrizitats-konstante des festen Korpers darstellt Die Auswertung der Energieverlustspektren von Elektronen erlaubt daher die Bestimmung von e(ω) von isotropen sowie anisotropen Kristallen Beispiele fur die Anwendbarkeit dieser Methode werden fur Metalle, Isolatoren und Halbleiter gegeben Der q-Wert, der den Kristallelektronen ubertragen wird, kann mit der Ausdehnung der Brillouin Zone vergleichbar werden, so das die q-Abhangigkeit von e(ω, q) ins Spiel kommt Dieser Effekt wird an Graphit gezeigt

Messung der elastischen und unelastischen Streuverteilung mittelschneller (15–50-keV-) Elektronen mit Hilfe der Gegenfeldmethode

Abstract: Wenn man den gesamten Informationsgehalt eines Elektronen-Streudiagramms erfassen will, mus man sowohl die Winkel- als auch die Energieverteilung der gestreuten Elektronen messen. Eine hierfur geeignete Mesanordnung sollte daruber hinaus auch absolute Intensitatsmessungen gestatten. Fur solche absoluten Intensitatsmessungen von Streuverteilungen mittelschneller Elektronen beim Durchgang durch dunne Festkorperschichten von 100–500 A haben wir in unserem Institut eine Gegenfeldanlage aufgebaut. Das Schema dieser Apparatur ist in Abb. 1 dargestellt. Die Elektronen werden in einem ublichen Strahlerzeugungssystem auf 15–50 keV beschleunigt. Durch 2 Aperturblenden wird die Divergenz des Primarstrahles am Ort des Objektes auf 2 · 10−4 herabgesetzt. Aus der Elektronen-Streuverteilung wird durch einen feinen Spalt ein enges Strahlbundel ausgeblendet. Dieser Strahl durchlauft nun ein Gegenfeld. Die Elektronen, die das Bremspotential uberwinden konnen, erreichen den Auffanger und werden mit einem Gleichstromverstarker gemessen. Durch Variation des Bremspotentials mit Hilfe einer Zusatzspannung ΔU g erhalt man die integrale Energie Verteilung der Elektronen im ausgeblendeten Strahlbundel. Die Messung der Winkelverteilung bei festem Bremspotential erfolgt so, das das gesamte Auffangersystem auf einem Kreisbogen um das Objekt als Zentrum geschwenkt wird. Synchron mit dieser Schwenkbewegung wird der Auffangerstrom photographisch registriert.

Streuung am Objekt und Bildkontrast

Abstract: It has been recognized for more than 20 years (1) that one of the most important factors in the formation of electron microscope images is electron scattering. A number of papers have appeared (2) based on accepted theories of elastic and inelastic scattering. In order to obtain numerical results, approximations were made and in some cases the results were in fair agreement with experiments (3). We now believe that this agreement was only fair, due to the fact that the theoretical treatments were essentially based on statistical considerations where an average energy loss was used for the inelastic part of the scattering. During the last few years, quite an effort has been made, both experimental and theoretical, toward a better exploration of the inelastic process. As a result, we are now in a much better position to say something more definite about the factors contributing to the inelastic part of the electron scattering process and its role in image formation in electron microscopy.

Plasmonics for improved photovoltaic devices

Abstract: The emerging field of plasmonics has yielded methods for guiding and localizing light at the nanoscale, well below the scale of the wavelength of light in free space. Now plasmonics researchers are turning their attention to photovoltaics, where design approaches based on plasmonics can be used to improve absorption in photovoltaic devices, permitting a considerable reduction in the physical thickness of solar photovoltaic absorber layers, and yielding new options for solar-cell design. In this review, we survey recent advances at the intersection of plasmonics and photovoltaics and offer an outlook on the future of solar cells based on these principles.

Extraordinary optical transmission through sub-wavelength hole arrays

Abstract: The desire to use and control photons in a manner analogous to the control of electrons in solids has inspired great interest in such topics as the localization of light, microcavity quantum electrodynamics and near-field optics1,2,3,4,5,6. A fundamental constraint in manipulating light is the extremely low transmittivity of apertures smaller than the wavelength of the incident photon. While exploring the optical properties of submicrometre cylindrical cavities in metallic films, we have found that arrays of such holes display highly unusual zero-order transmission spectra (where the incident and detected light are collinear) at wavelengths larger than the array period, beyond which no diffraction occurs. In particular, sharp peaks in transmission are observed at wavelengths as large as ten times the diameter of the cylinders. At these maxima the transmission efficiency can exceed unity (when normalized to the area of the holes), which is orders of magnitude greater than predicted by standard aperture theory. Our experiments provide evidence that these unusual optical properties are due to the coupling of light with plasmons — electronic excitations — on the surface of the periodically patterned metal film. Measurements of transmission as a function of the incident light angle result in a photonic band diagram. These findings may find application in novel photonic devices.

Diamond-like amorphous carbon

Abstract: Diamond-like carbon (DLC) is a metastable form of amorphous carbon with significant sp3 bonding. DLC is a semiconductor with a high mechanical hardness, chemical inertness, and optical transparency. This review will describe the deposition methods, deposition mechanisms, characterisation methods, electronic structure, gap states, defects, doping, luminescence, field emission, mechanical properties and some applications of DLCs. The films have widespread applications as protective coatings in areas, such as magnetic storage disks, optical windows and micro-electromechanical devices (MEMs).

Surface plasmon resonance sensors: review

Abstract: Since the first application of the surface plasmon resonance (SPR) phenomenon for sensing almost two decades ago, this method has made great strides both in terms of instrumentation development and applications. SPR sensor technology has been commercialized and SPR biosensors have become a central tool for characterizing and quantifying biomolecular interactions. This paper attempts to review the major developments in SPR technology. Main application areas are outlined and examples of applications of SPR sensor technology are presented. Future prospects of SPR sensor technology are discussed.

High-impedance electromagnetic surfaces with a forbidden frequency band

Abstract: A new type of metallic electromagnetic structure has been developed that is characterized by having high surface impedance. Although it is made of continuous metal, and conducts dc currents, it does not conduct ac currents within a forbidden frequency band. Unlike normal conductors, this new surface does not support propagating surface waves, and its image currents are not phase reversed. The geometry is analogous to a corrugated metal surface in which the corrugations have been folded up into lumped-circuit elements, and distributed in a two-dimensional lattice. The surface can be described using solid-state band theory concepts, even though the periodicity is much less than the free-space wavelength. This unique material is applicable to a variety of electromagnetic problems, including new kinds of low-profile antennas.