Critical Angle Of Reflection Research Articles

Field and temperature dependence of the magnetization in ferromagnetic EuO thinfilms

Ferromagnetic EuO exhibits a metal–insulator transition showing a very largecolossal magneto-resistance. Recently, it became possible to grow epitaxial films ofEuO1−x on Si with spin polarization above 90%. The direct integration of EuO with Si will allowthe fabrication of model systems for studying devices in the field of spintronics. In order todetermine non-destructively the magnetic properties of thin films of EuO on Si, we havemeasured the critical angle of reflection by using polarized neutrons. The results confirmthat the magnetic moment in the films is consistent with the bulk value. In addition, weshow that the change of magnetization is not caused by repopulation of domains but bydomain rotation.

ナノシリコン層の歪み解析

A thin silicon nanooverlayer (SNOL) fabricated by oxidation and etch-back in a Separation by IMplantation of OXygen wafer was investigated by grazing incident X-ray diffraction at incident angles between 0.01° and 0.1° below the critical angle of total reflection (0.18°). We measured {220} reflections by probing the sample with respect to surface normal and found that the SNOL has finite domains under strain close to the surface. We also found that annealing the sample up to 1000°C significantly reduced inhomogeneous strain and increased the size of the domains in the surface region of the SNOL.

Observation of light transmission through randomly rough glass surfaces beyond the critical angle

In this series of experiments we study the transmission of laser light through a randomly rough interface between air and ground-glass diffusers. We verify the refractive index suppression predicted by Dogariu and Boreman [Opt. Lett.21, 701 (1996)]. We also observe and quantify transmission beyond the critical angle for total internal reflection defined by Snell's law. In particular, these results may be applied to the ANITA experiment, which detects astrophysical neutrino interactions via radio waves produced under the ice. These radio waves must pass through the rough surfaces of the Antarctic ice sheets and shelves.

The Effect of Thermal Barriers on Sound Wave Propagation

Sound propagation through regions of non-uniform temperature distribution in a gas is studied numerically. The main objective of this study is to determine the impact of temperature gradients on the sound wave parameters and to evaluate the effectiveness of using regions of hot gas as sound barrier. Such regions of hot gas (low acoustic impedance) can be generated by remotely depositing energy into a selected volume of gas, for example, by means of electrical discharge. Sound attenuation through the hot gas region is studied systematically for a range of sound wave and thermal field parameters by solving the two-dimensional unsteady compressible Euler's equations along with the ideal gas state equation using a finite volume scheme. Particular attention is given to the practical case when sound wavelength is comparable to the thickness of the thermal barrier. The present two-dimensional model indicates that considerable sound attenuation can be achieved at large incidence angles and a critical angle for total internal reflection is possible.

Seismic critical-angle reflectometry: A method to characterize azimuthal anisotropy?

Existing anisotropic parameter-estimation algorithms that operate with long-offset data are based on the inversion of either nonhyperbolic moveout or wide-angle amplitude-variation-with-offset (AVO) response. We show that valuable information about anisotropic reservoirs can also be obtained from the critical angle of reflected waves. To explain the behavior of the critical angle, we develop weak-anisotropy approximations for vertical transverse isotropy and then use Tsvankin’s notation to extend them to azimuthally anisotropic models of orthorhombic symmetry. The P-wave critical-angle reflection in orthorhombic media is particularly sensitive to the parameters [Formula: see text] and [Formula: see text] responsible for the symmetry-plane horizontal velocity in the high-velocity layer. The azimuthal variation of the critical angle for typical orthorhombic models can reach [Formula: see text], which translates into substantial changes in the critical offset of the reflected P-wave. The main diagnostic features of the critical-angle reflection employed in our method include the rapid amplitude increase at the critical angle and the subsequent separation of the head wave. Analysis of exact synthetic seismograms, generated with the reflectivity method, confirms that the azimuthal variation of the critical offset is detectable on wide-azimuth, long-spread data and can be qualitatively described by our linearized equations. Estimation of the critical offset from the amplitude curve of the reflected wave, however, is not straightforward. Additional complications may be caused by the overburden noise train and by the influence of errors in the overburden velocity model on the computation of the critical angle. Still, critical-angle reflectometry should help to constrain the dominant fracture directions and can be combined with other methods to reduce the uncertainty in the estimated anisotropy parameters.

Combining non-specular X-ray scattering and X-ray absorption spectroscopy for the investigation of buried layers

We will present a new approach for the structural investigation of buried layers and interfaces by non-specular grazing incidence X-ray scattering. By measuring and evaluating the distinct off-specularly scattered intensities which appear for grazing angles in the vicinity of the critical angle of total reflection as a function of the X-ray photon energy in the vicinity of an X-ray absorption edge, the atomic short-range order around the X-ray absorbing atom within the surface or interface region is accessible. We will apply this new technique for the investigation of metallic bilayers consisting of about 25 nm Cu on top of 175 nm Au on a glass substrate, and show that the Cu-atoms at the Cu–air (vacuum)-interface can be separated from those at the inner Cu–Au interface in an unambiguous way.

Giant Goos-Hänchen displacement enhanced by dielectric film in frustrated total internal reflection configuration

It is predicted that the Goos-Hänchen displacement in the usual frustrated total internal reflection configuration can be resonantly enhanced greatly by coating a dielectric thin film onto the surface of the first prism when the angle of incidence is larger than the critical angle for total reflection at the prism-vacuum interface and is smaller than but close to the critical angle for total reflection at the prism-film interface. Theoretical analysis shows that the displacement of transmitted beam is about half the displacement of reflected beam in the thick limit of the vacuum gap between the two prisms. This is to be compared with the relation in the usual symmetric double-prism configuration that the displacement of transmitted beam is equal to the displacement of reflected beam. Numerical simulations for a Gaussian incident beam of waist width of 100 wavelengths reveal that when the dielectric thin film is of the order of wavelength in thickness, both the reflected and transmitted beams maintain well the shape of the incident beam in the thick limit of the vacuum gap. So largely enhanced displacements would lead to applications in optical devices and integrated optics.

Strain Analysis of Silicon Nanolayers by Grazing Incidence X-ray Diffraction

Grazing incident X-ray diffraction was observed from a thin silicon nano scale overlayer fabricated by oxidation and etch-back in a separation by implantation oxygen wafer at incident angles between 0.01o and 0.1o below the critical angle of total reflection (0.18o). We measured {220} reflections by probing the sample with respect to surface normal and found that the silicon nano scale overlayer has finite domains under strain close to the surface. We also found that annealing the sample up to 1000oC significantly reduced inhomogeneous strain and increased the size of the domains in the surface region of the silicon nano scale overlayer.

Large and negative lateral displacement in an active dielectric slab configuration

We investigate the large negative lateral displacements of TE polarized light beams reflected from or transmitted through an active slab surrounded by transparent medium. The large negative displacements can be achieved when the incidence angle of the beam is less than but close to the critical angle for total reflection. It is also shown that both the reflectivity and transmissivity of the beam that correspond to the large negative displacements can be enhanced by active medium. These phenomena may lead to convenient measurements and interesting applications in optical devices.

Development of a multichannel parabolic guide for thermal neutron beam focusing

We have developed a multichannel parabolic guide for thermal neutron beam focusing. The guide was designed with multichannel structure, seven channels in the present case, to focus a neutron beam with wide cross section effectively. The multichannel structure is made with parabolically bent NiC/Ti supermirrors with critical reflection angles m = 3.0 and 3.6 times as much as that of nickel and thickness of 0.55 mm. The guide consists of two focusing devices with each length of 900 mm, which are separated by a gap of 150 mm for neutron beta decay experiments. The focal length of the guide is 995 mm away from the exit of the guide. The cross section of the guide is 90 × 20 mm 2 at the entrance and 52.3 × 12.1 mm 2 at the exit. The guide was installed at a thermal neutron beam line for neutron-induced prompt gamma-ray analysis (PGA) of JRR-3M in JAEA with straight supermirror guides with m = 3.0 . Focusing properties of the parabolic guide were measured at the focal point with a CCD imaging system and we obtained a gain of 9.6 and 4.1 in peak flux compared with those in cases of using the vacuum tube and the straight guide, respectively. The parabolic guide has been successfully used to enhance the efficacy of PGA and have also applied to neutron beta decay experiments.

Analysis of Evanescent Waves Scattering by a Single Particle in Total Internal Reflection Microscopy

Since its invention in the mid of eighties (1) Total Internal Reflection Microscopy (TIRM) has proven to be an effective technique to measure weak interactions between spherical colloidal particles and surfaces with a resolution of a few femtonewton. It is a single particle evanescent light scattering technique. In an experimental setup a laser beam is coupled into a prism and hits the glass-water interface with an angle slightly above the critical angle of total internal reflection. This generates an evanescent field near the interface that decays in the lower refractive index medium (water) with a characteristic penetration depth which depends on the angle of incidence. A colloidal particle that is dispersed in the medium will scatter light from the evanescent wave if it is in the vicinity of the surface. By registering a scattered intensity it is possible to deduce the particle- substrate distance. Compared to other methods for measure particle wall interactions like the surface force apparatus or the atomic force microscopy where a colloidal particle is attached to the tip, TIRM is the most sensitive technique because thermal fluctuations where limit the other methods in their resolution are exploited to determine the interaction potential. In this way forces in the order of a few femtonewton can be detected. TIRM has proven to be a valuable tool for the precise measurement of weak colloidal interactions as double layer forces, van der Waals forces, magnetic interactions and depletion forces. Review on TIRM can be found for example in (2,3). To compare experimental results with results of mathematical modeling an effective light scattering method is needed. For this purpose the Discrete Sources Method (DSM) has been chosen. The DSM is a well-known method for light scattering analysis, which has recently been applied for evanescent wave scattering (4). 1. Discrete Sources Method For the theoretical modeling the Discrete Sources Method (DSM) has been chosen. The DSM is a well-known method for the analysis of light scattering. It has recently been applied to the evanescent wave scattering (4). In frame of the DSM the mathematical statement can be presented as follows:

The new diffractometer for surface X-ray diffraction at beamline BL9 of DELTA

The experimental endstation of the hard X-ray beamline BL9 of the Dortmund Electron Accelerator is equipped with a Huber six-circle diffractometer. It is dedicated to grazing-incidence X-ray diffraction and X-ray reflectivity experiments on solid surfaces and thin films as well as to powder diffraction measurements. A new set-up for grazing-incidence X-ray scattering of liquids has been built up using a silicon mirror to reflect the incident X-ray to the liquid surface at angles of incidence around the critical angle of total reflection of the sample. X-ray reflectivity measurements of a polymer film and grazing-incidence X-ray diffraction measurements of an epitaxically grown Gd40Y60 film, an oxidized surface of Fe-15at.%Al alloy and aqueous salt solutions are presented and discussed.

Scarred resonances and steady probability distribution in a chaotic microcavity

We investigate scarred resonances of a stadium-shaped chaotic microcavity. It is shown that two components with different chirality of the scarring pattern are slightly rotated in opposite ways from the underlying unstable periodic orbit, when the incident angles of the scarring pattern are close to the critical angle for total internal reflection. In addition, the correspondence of emission pattern with the scarring pattern disappears when the incident angles are much larger than the critical angle. The steady probability distribution gives a consistent explanation about these interesting phenomena and makes it possible to expect the emission pattern in the latter case.

Local density profiles in thin films and multilayers from diffuse x-ray and neutron scattering

We develop a technique to determine local density profiles in conformally rough thin films and multilayers for which conventional reflectometry does not work. The main idea is to integrate the total scattered intensity for a given vertical momentum transfer over the parallel momentum transfer. Probing Fourier space globally results in a local probe in real space and the integrated intensity is proportional to the local reflectivity of the surface. We also discuss the influence of a finite range of integration as well as sample inhomogeneities, such as nonconformity of the roughness. This technique is limited to situations where the kinematic Born approximation is sufficient to describe the scattering process. However, in certain cases, the technique can be used in the vicinity of the critical angle of total external reflection as well.

In-plane strain distribution in the surface region of thin silicon overlayers on insulator

A thin silicon nano-overlayer (SNOL) fabricated by oxidation and etchback in a separation by implantation of oxygen wafer was investigated by grazing incident x-ray diffraction at incident angles between 0.01° and 0.1° below the critical angle of total reflection (0.18° ). We measured {220} reflections by probing the sample in depth and found that the SNOL has finite domains under strain close to the surface. We also found that annealing the sample up to 1000 °C significantly reduced inhomogeneous in depth strain and increased the size of the domains in the surface region of the SNOL.

Tunneling of X-ray photons through a thin film under total internal reflection conditions

Tunneling of 0.154-and 0.139-nm x-ray photons through a thin film under total internal reflection conditions has been experimentally demonstrated. The NiSi2 film 13 nm thick is deposited by magnetron sputtering on a polished Si substrate. A beam with an angular spread of 20″ is directed to the Si/NiSi2 interface from the inside through the lateral surface of a sample. A peak associated with tunneling of photons from Si to air through the NiSi2 film is observed at grazing angles of θ1 > 0.4θc, where θc is the critical angle of total internal reflection at the Si/NiSi2 interface. The integral intensity of tunneling peaks that is measured for various θ1 angles agrees with the calculations.

Extended-area optically induced organization of microparticles on a surface

To extend beyond the limited field of view associated with optical tweezers, we implement a new geometry for lensless optical trapping (“LOT”). A Ronchi ruling is imaged at a sample interface beyond the critical angle for total internal reflection imposing local structure upon the optical fields. Due to the resulting transverse optical gradients, more than one thousand microparticles spanning 1mm2 were organized into microchannels that are entirely optical in origin. A generalized approach is presented, allowing for either guiding or stable trapping, as a function of the relative intensity of the counterpropagating surface waves.

Calculation of grazing incidence EXAFS: Fresnel theory versus DWBA

The Fresnel theory with its numerous extensions is a well established method for the calculation of grazing incidence x-ray reflectivities for single surfaces and (multi-)layered systems. However, lateral surface correlations—which are always present e.g. for polycrystalline thin films—cannot be included in these calculations. Furthermore the application of the Fresnel theory is restricted to investigations of specular reflectivities, i.e. off specular reflectivities cannot be calculated. These limitations can be overcome by the application of the distortedwave Born approximation (DWBA). Simulations of grazing incidence reflection mode EXAFS spectra will be presented and the results obtained using different calculation procedures such as the Fresnel theory, the Névot–Croce model and the DWBA are compared. Furthermore, we will also prove the existence of a fine structure similar to EXAFS which can be observed in the region of diffusely scattered intensities. We will show that this new EXAFS technique is surface sensitive even for grazing angles above the critical angle of total reflection.

Structure of the magnetic trilayer system Fe/Pd/Fe epitaxially grown on GaAs(001)-4×6

The magnetic behaviour of ferromagnetic/non-ferromagnetic/ferromagnetic trilayers is strongly dependent on the nature of the interface between layers, the strain in the layers and the extent of any interdiffusion or reaction between layers and substrate. In this paper, results are presented from a polarization-dependent in situ XAFS study of Fe/Pd/Fe trilayers epitaxially grown on GaAs(001)-(4×6). Fe and Pd K-edge spectra were obtained both above and below the critical angle for total reflection. The structure of iron grown on the Ga-terminated 4×6 reconstructed surface of the GaAs(001) substrate, for thicknesses greater than 6 monolayers, is tetragonally distorted from its natural bcc structure with contracted and expanded lattice constants in the in-plane and out-of-plane directions, respectively. The intermediate Pd layer shows distortion from its natural fcc structure. Alloying at the interface with the underlying Fe is restricted to a depth of 0.5–1.0 monolayers (ML). The upper layer of Fe shows tetragonal distortion similar to the layers of Fe grown on GaAs(001)-4×6. However, the upper distortion is stronger. There is also evidence of alloy formation at the interface involving the underlying Pd with the thickness of the alloy region being 2–2.5 ML.

X-ray Optic Characteristics of Microchannel Plates Studied by X-ray Absorption Spectroscopy

The X-ray absorption spectra of white and black microchannel plates (MCPs) have been studied in the energy range from 80 to 250 eV. Data on the fine X-ray absorption near edge structure are presented. A new approach is described, which allows the effect of various treatments on the X-ray optic characteristics of MCPs to be studied. In particular, it is established that the thermal reduction of MCPs in hydrogen increases the critical reflection angle for long-wavelength X-rays in the channels.