Showing papers on "Total external reflection published in 1995"
TL;DR: It is shown that diffuse-scattering experiments within the region of total external reflection can be explained quantitatively using the distorted-wave Born approximation for layer systems.
Abstract: In this paper it is shown that diffuse-scattering experiments within the region of total external reflection can be explained quantitatively using the distorted-wave Born approximation for layer systems. Three Si/Ge samples with different degrees of complexity were investigated. The simultaneous analysis of the specular reflected intensity and the diffuse scattering leads to one consistent set of interface and layer parameters, which is able to fit both the shapes and the locations of all dynamic peaks in the off-specular scans and the characteristics of the reflected intensity. Therefore the distorted-wave Born approximation seems to give a correct and complete description of the diffuse scattering in the region of total external reflection.
105 citations
TL;DR: The first observation of a true geometrical focus of X-rays well beyond the exit of a paraboloidally tapered glass monocapillary is reported.
Abstract: The first observation of a true geometrical focus of X-rays well beyond the exit of a paraboloidally tapered glass monocapillary is reported. An intensity gain of 250 +/- 20 into a 6 x 9 mum pinhole for 8 keV X-rays and transmission efficiencies of more than 90% below 20 keV were observed.
42 citations
TL;DR: In this article, x-ray diffraction measurements from GaAs surface gratings are performed using a three-crystal diffractometer and compared with model calculations based on a dynamical scattering theory.
Abstract: In this work x-ray-diffraction measurements from GaAs surface gratings are presented. The experiments were performed using a three-crystal diffractometer. Measurements in the region of total external reflection (small incidence angles) for five samples were done and compared with model calculations based on a dynamical scattering theory. The theory is able to explain all experiments quantitatively. Mesoscopic grating parameters as well as microscopic surface roughnesses of the samples were obtained from fits of the data. For three samples scanning-electron-microscope pictures were taken. The analysis of these pictures leads to the same mesoscopic parameters as obtained from x-ray diffraction.
38 citations
23 citations
TL;DR: In this article, a multilayer mirror with 50 W/Si bilayers with different thicknesses on the Si substrate has a smooth reflectivity of up to 32% in the whole energy range from 5 to 22 keV at a grazing incidence angle of 0.32° which is considerably larger than using total external reflection.
Abstract: X‐ray multilayer supermirrors for the energy range up to 20 keV have been theoretically studied and experimentally measured with synchrotron radiation. A multilayer mirror with 50 W/Si bilayers with different thicknesses on the Si substrate has a smooth reflectivity of up to 32% in the whole energy range from 5 to 22 keV at a grazing incidence angle of 0.32° which is considerably larger than using total external reflection.
22 citations
Journal Article•
20 citations
TL;DR: In this article, the authors investigated the X-ray diffraction is determined by the amplitude and the wavelength of the surface acoustic waves of a LiNbO/sub 3/ crystal modulated by surface acoustic wave.
Abstract: Space-time modulation of an X-ray beam is investigated by total external reflection on a YZ-cut of a LiNbO/sub 3/ crystal modulated by surface acoustic waves. It is shown that the X-ray diffraction is determined by the amplitude and the wavelength of the surface acoustic waves. Both experimental and theoretical studies have revealed the possibility of fabricating X-ray optical elements based on space-time modulation by controlling the wavelength and the pulse modulation of the surface acoustic waves. These experiments were carried out at CNRS (Grenoble, France) using a rotating copper anode. >
14 citations
TL;DR: In this article, the in-plane structure of the liquid surface yields a peak in the diffuse scattering at the specular position, and the data were analyzed simultaneously, which leads to a consistent set of interface parameters.
Abstract: X-ray diffraction measurements within the region of total external reflection from a thin wetting film of liquid CCl4 on a Si/SiO2 substrate are presented. The in-plane structure of the liquid surface yields a peak in the diffuse scattering at the specular position. Since there is no way to separate specular and off-specular contributions, the data were analysed simultaneously, which leads to a consistent set of interface parameters. Although the obtained power spectral density function of the liquid surface is very similar to that used in the case of free capillary waves, a modified cut-off has to be introduced. The difference results from the constrained thin-film geometry and is therefore caused by the interaction with the underlying substrate.
12 citations
TL;DR: In this paper, the free surface of a C 12 E 5 + water mixture at a mass fraction of the surfactant of 0.4 was measured at a temperature of T = 23.82°C and the typical Bragg pattern for hexagonal symmetry was observed when the angle of incidence of the beam is larger than the critical angle of total external reflection, α c.
Abstract: X-ray reflectivity measurements of the free surface of a C 12 E 5 + water mixture at a mass fraction of the surfactant of 0.4 are presented. This system forms a hexagonal LC-phase at ambient temperatures. At a temperature of T = 23.82°C the typical Bragg pattern for hexagonal symmetry is no longer observed when the angle of incidence of the beam is larger than the critical angle of total external reflection, α c . If the angle of incidence is smaller than α c , well-pronounced reflexes are observed at the same temperature. This shows that the anisotropic phase is stable to higher temperatures at the surface as compared to the bulk.
11 citations
Patent•
20 Apr 1995
TL;DR: In this paper, the authors proposed a method of delivering guided radiation via a first transparent medium having a first refractive index into a second transparent medium with a second one having a smaller one.
Abstract: A method of delivering guided radiation arriving via a first transparent medium having a first refractive index into a second transparent medium having a second refractive index that is smaller than the first refractive index, comprising: providing a transparent radiation delivery waveguide capable of admitting concentrated radiation and having a longitudinal axis and a third refractive index substantially equal to or greater than the first refractive index and adapted to guide the radiation along the longitudinal axis. The waveguide having a tapered radiation delivery portion of non-circular cross-sectional shape. Mounting the waveguide in optical contact with the first transparent medium so that the radiation delivery portion projects inside the second transparent medium.
7 citations
TL;DR: In this article, the in-plane structure of arsenic adatoms on an Si (111) surface of the 1 × 1 structure was determined using X-ray fluorescence signals observed from a sample in ultra-high vacuum at a synchrotron source.
Abstract: Grazing-angle diffraction of X-rays by crystal planes normal to a surface generates dynamical (lattice-modulated) standing waves, which are used in this paper to determine the in-plane structure of arsenic adatoms on an Si (111) surface of the 1 × 1 structure. The X-ray field, formed by the interference of the incident, specular-reflected and Bragg-diffracted beams above the surface, has two components with and without intensity modulation in the direction of the reciprocal-lattice vector parallel to the surface. The two components behave differently as a function of X-ray glancing incidence angle on the surface in the vicinity of the critical angle for total external reflection. This property has been exploited to determine the ordering of the As atoms accurately using X-ray fluorescence signals observed from a sample in ultra-high vacuum at a synchrotron source. The data show highly ordered As atoms occupying the threefold-coordinated sites on the bulk-like Si (111) surface. Displaced arsenic positions are not supported by the observation. The conclusion is fairly insensitive to the vertical height of the overlayer atoms used in the analysis, in accordance with the slow variation of the field profile along the surface normal. The grazing-angle X-ray standing-wave method allows model-independent determination of the registry of foreign atoms at a crystal surface with a positional accuracy of a few hundredths of an A.
TL;DR: In this article, the sensitivity to x-ray beam energy of structure measurements using X-ray standing waves (XSW) generated under conditions of total external reflection has been determined and the optical properties of the system were examined in a theoretical analysis to identify possible energy-dependent components such as surface roughness.
Abstract: The sensitivity to x‐ray beam energy of structure measurements using x‐ray standing waves (XSW) generated under conditions of total external reflection has been determined. To this end, the optical properties of the system were examined in a theoretical analysis to identify possible energy‐dependent components such as surface roughness. The analysis shows that, provided surface roughness is small (Debye–Waller factor less than 10 A) and the energy range covered in the XSW measurements lies within several keV, its contribution can be accounted for satisfactorily by a simple Debye–Waller factor. In addition, a series of XSW measurements were made on Langmuir–Blodgett films of manganese arachidate (C20:0) on a gold mirror surface at three incident x‐ray beam energies in the 7–11.2 keV range. The XSW data were analyzed to account for the Debye–Waller factor. No obvious dependence on incident x‐ray energy was found. These results demonstrate that the contribution of surface roughness to the x‐ray fluorescence ...
TL;DR: In this article, single quantum wells were grown by means of a low-pressure metal-organic chemical vapour deposition technique on GaAs(001), their nominal thickness was varied among 0.7, 2, 3 and 4 monolayers and they were buried under a thick GaAs top layer.
Abstract: InAs single quantum wells were grown by means of a low-pressure metal-organic chemical vapour deposition technique on GaAs(001). Their nominal thickness was varied among 0.7, 2, 3 and 4 monolayers and they were buried under a thick GaAs top layer. The samples were investigated by means of the grazing incidence X-ray diffraction using the weak (200) in-plane reflection. Depth resolution was obtained setting the angle of incidence and exit alpha i and alpha f, respectively, smaller or larger than the critical angle of total external reflection alpha c. Owing to the high sensitivity near the surface the collected rod scans show pronounced thickness oscillations for alpha i> alpha c. The thickness and the In-content, which control the scattering power of the single quantum wells were evaluated via simulation using the kinematic approach to X-ray diffraction. Partial relaxation occurs whenever the single quantum wells' thickness exceeds one monolayer. It is explained by the appearance of strain-reduced and non-tetragonally deformed islands built after the two- to three-dimensional transition of the growing mode.
TL;DR: In this paper, X-ray reflectivity and characteristic fluorescence yield from investigated ions excited by the primary beam give a unique opportunity for determination of the ion position in the organic system in the direction normal to the surface.
TL;DR: The high sensitivity of the change in the interference pattern with respect to small changes in the refractive index in the vicinity of the critical angle is theoretically proved and experimentally confirmed.
Abstract: An interferometer is investigated in which the interacting beams undergo total internal reflection from a boundary surface with a variable relative refractive index. The high sensitivity of the change in the interference pattern with respect to small changes in the refractive index in the vicinity of the critical angle is theoretically proved and experimentally confirmed.
TL;DR: In this article, the ambiguity of Mossbauer spectra measured under total external reflection conditions due to the increase of the number of parameters which should be determined can be compensated by measuring a series of experimental spectra.
Abstract: An ambiguity of Mossbauer spectra measured under total external reflection conditions due to the increase of the number of parameters which should be determined can be compensated by measuring a series of experimental spectra. The interpretation of all experimental data must be done by means of numerical modeling (or fitting). The method enables us to study phase transformations within a layer of about 10 nm thickness.
TL;DR: In this article, the Kolmogorov growth model was used to explain the film thickness as a function of time in the growing process of liquid films on top of silicon wafers.
Abstract: X-ray scattering experiments of liquid films on top of solid substrates were performed. With a short pulse disturbance, caused by a temperature difference between the substrate and the vapour in the X-ray cell, the wetting film thickness is reduced. Afterwards the time dependence of the growing film is monitored by X-ray reflectivity measurements in the region of total external reflection. We have examined CCl4- and CCl3Br-films on top of silicon wafers and CCl3Br on glass/gold and glass/silver substrates. The film thickness as function of time is explained by the Kolmogorov growth model. From the data we obtain rather long time constants and the dimensiond=2 of the growing process
TL;DR: Using a newly developed reflectometer, the authors measured the reflectivity at the silicon [ital K] edge for different silicon compounds and determined the binding energy of core excitons at the [ital L] edge.
Abstract: Using a newly developed reflectometer we have measured the reflectivity at the silicon [ital K] edge for different silicon compounds Combining these measurements with silicon [ital L] edge reflectivity measurements carried out on a different reflectometer we determined the binding energy of core excitons at the [ital L] edge The results show that it is possible to carry out reflectivity measurements with the resolution necessary for the determination of the exciton parameters Comparison with literature values shows that a rigid Kramers--Kronig analysis is not needed when the angle of incidence is well below the critical angle of total external reflection
23 Jun 1995
TL;DR: In this paper, simple reflection techniques for optical parameter determination of isotropic or anisotropic multilayers on a lower refractive index substrate are presented, in case of weak absorption in at least one of the layers characteristic minima appear in the angular dependence of the reflectivity by computer fit of which the layer refractive indices and thicknesses can be determined.
Abstract: Simple reflection techniques for optical parameter determination of isotropic or anisotropic multilayers on a lower refractive index substrate are presented here. In case of weak absorption in at least one of the layers characteristic minima appear in the angular dependence of the reflectivity by computer fit of which the layer refractive indices and thicknesses can be determined. In case of a monolayer the achieved accuracy is better than the third and fourth decimal in the real and imaginary part of the refraction index, respectively. The fit of bi-layers has lower accuracy, but has the advantage of refractive index determination of non-absorbing layer(s) in the presence of a weakly absorbing auxiliary layer. Comparison between measured refractive indices by reflectometric and optical waveguiding methods shows agreement within 0.001.© (1995) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.
31 Jan 1995
TL;DR: In this article, the effect of boundary reflection on the time-resolved transmittance through slabs of scattering and absorbing media simulating biological tissues was investigated using a pulsed diode laser of 784 nm and an optical oscilloscope.
Abstract: Time-resolved spectroscopy in the near-infrared wavelength range is a promising technology for the development of optical tomography to measure the profiles of oxygenation state in living tissues. Many investigators have reported the experimental results of time-resolved reflectance and transmittance of ultra-short light pulses incident on tissue samples and phantoms. However, none of them has reported the effect of the boundary reflection which takes place at the interface between the sample and air because of the difference in the refractive indices. This paper describes the effect of the boundary reflection on the time- resolved transmittance through slabs of scattering and absorbing media simulating biological tissues. Time-resolved measurement was carried out by using a pulsed diode laser of 784 nm and an optical oscilloscope. The samples were latex microsphere suspension in water with or without the addition of ink. The cells containing the suspension were equipped with uncoated or anti-reflection coated glass windows to see the effect of the boundary reflection. The measured results were compared with the Monte Carlo simulation results which incorporated the boundary reflection. It has been found that the boundary reflection broadens the transmitted pulse width, and that the neglecting of the boundary reflection leads to an overestimation of the scattering coefficients.© (1995) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.
TL;DR: In this article, the angular distribution of X-rays propagating in the film at very small angles was investigated and a simple explanation and corresponding expressions for the peak positions are in good agreement with the experimental results.
02 Aug 1995
TL;DR: In this paper, an overview of the recent results in dynamical diffraction theory of surface guided electromagnetic waves (SGEW) in chiral liquid crystals (CLC) is presented.
Abstract: Excitation and propagation of surface guided electromagnetic waves (SGEW) of optical wave range in chiral liquid crystals (CLC) are theoretically examined in the framework of dynamical diffraction theory and an overview of the recent results in this field are presented. Unusual polarization properties and propagation diagram of SGEW are discussed. In the general case, the polarization properties of SGEW correspond to elliptical polarizations and are dependant on the SGEW propagation direction orientation relative to the director at the CLC surface, the SGEW frequency, and the film thickness. It is underlined that a qualitative difference related to the excitation and attenuation of SGEW in semi-infinite CLC and CLC films exists. The SGEW attenuation does not vanish even in nonabsorbing CLC films if total internal reflection at one of the film boundaries is absent. For CLC films, along with the conventional excitation of SGEW by means of attenuated total external reflection, it is possible to excite SGEW by a beam incident at the film from the side of a boundary where total internal reflection is absent. The above mentioned SGEW properties are illustrated by the results of calculations for typical experimental situations.© (1995) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.
TL;DR: In this article, the mean intensity of a point source as a function of propagation range and statistical parameters of a surface is derived for the presence of rough dielectric interfaces with total internal reflection.
Abstract: Wave propagation in the presence of a rough dielectric interface with total internal reflection is studied theoretically using the Kirchhoff approximation. An approximate expression valid when the surface is smooth enough is obtained for the mean intensity of a point source as a function of propagation range and statistical parameters of a surface. It is shown that if the characteristic angle of incidence is close to the angle of total internal reflection, small irregularities of interface can drastically change the reflectivity and, consequently, the signal level far away from the source. As an example, far beyond the horizon propagation of radiowaves in the presence of elevated irregular reflecting layers in the atmosphere is discussed.
20 Jun 1995
TL;DR: In this paper, the concept of multilayer coated reflectors has been proposed to extend useful reflectivity to higher energies, and a new deposition process which does not involve the use of vacuum, is performed at a relatively low temperature, can be scaled up to large surface areas and to curved substrates, is low cost, and results in ultra thin, ultra smooth, uniform, high density films with sharp interfaces.
Abstract: X-ray optics typically rely on total external reflection and for hard x rays, the critical angle in any material becomes very small. This in turn leads to vanishingly small projected areas. To extend useful reflectivity to higher energies, the concept of multilayer coated reflectors has been proposed. Such hard x-ray multilayer structures require the capability to deposit ultra- thin (of the order of ten angstrom), ultra-smooth (of the order of a few angstroms rms), uniform, alternating films of high Z and low Z materials, with sharp interfaces and no interdiffusion between the layers. Standard vapor phase deposition processes such as evaporation and sputtering cannot achieve all the above goals. We have developed a new deposition process which does not involve the use of vacuum, is performed at a relatively low temperature, can be scaled up to large surface areas and to curved substrates, is low cost, and results in ultra thin, ultra smooth, uniform, high density films with sharp interfaces. This is optimal for the construction of multilayer x-ray optical components. This process is also capable of depositing films of high melting point noble metals such as iridium and osmium which cannot be deposited by evaporative procedures. The surface characterization and x-ray reflectivity of the films are presented.