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  • 1
    Electronic Resource
    Electronic Resource
    Localization of a magnesium .delta.-sheet within a lead stearate Langmuir-Blodgett multilayer by x-ray reflectivity measurement (1993)
    s.l. : American Chemical Society
    Langmuir 9 (1993), S. 208-210 
    Details
    ISSN: 1520-5827
    Source: ACS Legacy Archives
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1021/la00025a040
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  • 2
    Electronic Resource
    Electronic Resource
    Depth-resolved measurement of lattice relaxation in Ga1−xInxAs/GaAs strained layer superlattices by means of grazing-incidence x-ray diffraction (1993)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 74 (1993), S. 2381-2387 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The state of relaxation in two different superlattices (SLs) of a system with large lattice mismatch, Ga0.8In0.2As/GaAs grown on GaAs [001] by molecular beam epitaxy, has been investigated by surface-sensitive grazing-incidence diffraction (GID). The SL is squeezed between the substrate and a thick GaAs top layer. The thickness of individual GaInAs layers ta (active layer) is the same in both samples, while the GaAs barrier thickness tb is different. We have studied the influence of the thickness ratio tb/ta on the state of relaxation for different distances from the sample surface. We find that for thick barriers the whole SL remains coherently strained and for the thinner barrier thickness the SL is partially relaxed against the the GaAs top layer. The GID technique was applied for the first time to obtain depth resolution of the lateral lattice parameter in a SL. It is demonstrated to be especially well suited for SL systems with a small difference of the average electron density between the sublayers. The scattering contrast is improved by measuring the intensity as a function of the exit angle ("rod scans'') from the "weak'' (200) Bragg reflection. Comparing computer simulations with the measured variation of the scattering contrast between GaAs and GaInAs layers obtained from different "information depths'' and at different angular positions of the in-plane rocking curves, the state of relaxation can quantitatively be evaluated. On the basis of these results we propose two models for the partial relaxation of the SL into the state of strain-reduced domains. We believe that the partial relaxation is due to the elastic field interaction between the GaInAs layers accross the GaAs barriers, if tb is small.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.354724
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  • 3
    Electronic Resource
    Electronic Resource
    Investigations of semiconductor superlattices by depth-sensitive x-ray methods (1993)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 74 (1993), S. 146-152 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Focusing on the structure determination of a GaInAs/InP superlattice (SL), the potential of grazing incidence diffraction (GID) to resolve structure parameters on a microscopic scale is compared to x-ray reflectivity and conventional x-ray diffraction (XRD) measurements. Usually, information on the density profile perpendicular to the surface is obtained by x-ray reflectivity and on lattice mismatch by XRD. Since the penetration depth of x rays is much larger than the total thickness of the SL these methods measure parameters averaged over the whole structure. Furthermore, the depth sensitivity of both methods is small in the case of extremly high thickness ratios of the sublayers within the SL period. These disadvantages can be overcome using GID geometry for which the information depth can be reduced by keeping the angle of incidence αi and exit αf of the x-ray beam with respect to the surface in the range close to the critical angle of total external reflection αC. This enables a depth-selective structure determination. As an example measurements and computer simulations corresponding to the three different methods of a lattice-matched (GaIn)As/InP SL are presented. The periodic length of the present SL and the thickness of the top layer was determined by all three methods to monolayer accuracy.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.354130
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  • 4
    Electronic Resource
    Electronic Resource
    Determination of the anharmonicity constant of GaAs by means of the Bijvoet relation of the weak (666) reflection. Erratum (1994)
    Copenhagen : International Union of Crystallography (IUCr)
    Acta crystallographica 50 (1994), S. 780-780 
    Details
    ISSN: 1600-5740
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1107/S010876819409991X
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  • 5
    Electronic Resource
    Electronic Resource
    Extreme asymmetric X-ray Bragg reflection of semiconductor heterostructures near the edge of total external reflection (1990)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 23 (1990), S. 228-233 
    Details
    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: Synchrotron radiation has been used to measure the rocking curves from a (GaIn)(AsP) single layer grown on an InP (100)-oriented substrate. For angles of incidence ΦB = (ΘB − φ) ≤ 0.7° measured at the Bragg angle ΘB (φ is the angle between the diffracting lattice plane and the surface), the rocking curve (RC) is very strongly influenced by total external reflection (TER). This causes a decrease in the full width at half-maximum (FWHM) and an asymmetrical shape for the RC for small ΦB. Both of these effects are due to the Bragg-angle shift from the actual incident angle Φ which is not considered in the conventional dynamical theory. In this paper the essential influence of TER on any thin-layer rocking curve is investigated using a numerical solution of the extended dynamical theory. The pattern can be interpreted up to ΦB ≥ ΘC (ΘC is the angle of TER) by semiempirical incorporation of the results of the extended theory with the coupling formalism of Barrels, Hornstra & Lobeek [Acta Cryst. (1986). A42, 539–545].
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1107/S0021889890001704
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  • 6
    Electronic Resource
    Electronic Resource
    Determination of the anharmonicity constant of GaAs by means of the Bijvoet relation of the weak (666) reflection (1993)
    Copenhagen : International Union of Crystallography (IUCr)
    Acta crystallographica 49 (1993), S. 822-825 
    Details
    ISSN: 1600-5740
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1107/S0108768193003842
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  • 7
    Electronic Resource
    Electronic Resource
    Grazing incidence diffraction of X-rays in semiconductor heterostructures: Application of the integral mode (1990)
    Springer
    The European physical journal 80 (1990), S. 347-352 
    Details
    ISSN: 1434-6036
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract The grazing incidence diffraction (GID) of X-rays enables to characterize thin subsurface layers in semiconductor heterostructures having a thickness smaller than 100 nm. The dynamical theory of X-ray diffraction is extended for the case of identical in plane lattice parameters at the heterointerface. Especially the variation in the specular diffracted (220) Bragg intensity measured with open detector (integral mode) is evaluated in dependence on the grazing angle Φ0 of the primary beam with respect to the (001) surface. Using a parallel beam an oscillation behaviour occurs at the high angle side Θ c 〈 Φ0≦0.50(Θ c is the angle of total external reflection) of the diffraction curveI(Φ0) which can be related to the thickness of the perfect crystalline part of the epilayert K . Having an incident beam divergence and a small difference in the effective refractive indices of the layer and the substrate the oscillations are almost leveled. They are further visible in case of a minute inclination of the (220) lattice plane with respect to the surface normal. In the interval 0 〈 Φ0〈Θ c the slope of the integral curve depends on the thickness of the subsurface layert A which does not contribute to the Bragg diffraction. The integral mode is sensitive for layers of about 0〈t A 〈15 nm and 15〈t K 〈80 nm. The proposed theory working principally for multilayer structures is presently suplicated to interpret GID curves ofA III B v heterostructures.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01323515
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  • 8
    Electronic Resource
    Electronic Resource
    Structural properties of high-quality sputtered Fe films on Al2O3(1120) and MgO(001) substrates (1994)
    Springer
    Applied physics 59 (1994), S. 659-665 
    Details
    ISSN: 1432-0630
    Keywords: 81.15.Cd ; 68.55.Jk ; 61.10.-i
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Abstract High-quality thin Fe films were deposited on MgO(001) and Al2O3(1120) substrates in the thickness range from 7 to 50 nm. The structural properties have been studied by out-of-plane and in-plane X-ray scattering experiments. From the out-of-plane measurements the electron density profile was determined together with interface and surface roughness parameters. Fe on Al2O3 grows along the [110]-direction with a structural coherence length comprising about the total film thick ness and a very small mosaicity. From in-plane scattering experiments a three-domain structure was observed. On MgO(001) substrates Fe grows in the [001]-direction, with the Fe [100]-axis parallel to the MgO [110]-axis. On both substrates, the Fe films exhibit a very small surface and interface roughness, indicative for a high quality of the sputtered samples.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00331928
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  • 9
    Electronic Resource
    Electronic Resource
    Migration ofTrichobilharzia ocellata schistosomula in the duck and in the abnormal murine host (1991)
    Springer
    Parasitology research 77 (1991), S. 642-644 
    Details
    ISSN: 1432-1955
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Abstract The migration ofTrichobilharzia ocellata schistosomula in the duck host and the accidental mouse host was studied by the detection of [75Se]-methionine in radiolabelled cercariae using autoradiography of compressed host tissues and by the recovery of schistosomula following the mincing and incubation of host tissues. Exposure via duck feet (30 min) and mouse tails (60 min) resulted in low infection rates: 3.9% in the duck and 3.1% in the mouse. However, when mice were infected via the abdominal skin using the ring method, 25% of the cercariae were recovered in the skin. In the duck, schistosomula left the skin within 3 days post-infection (p.i.) and were detected in the lungs between days 2 and 4 p.i. Thereafter, only few radioactive foci were found in the liver, kidney and intestine. In the mouse, schistosomula were detected in the lungs within 10 h and for up to 6 days p.i., and some foci were detected in the liver and intestine on days 2–5 p.i. On days 3–4 p.i., 36% of the detectable parasites in the mouse (91 foci in 10 mice) had migrated from the skin to other organs. Living schistosomula could be extracted from mouse skin and lungs only until day 4 p.i. The schistosomula ofT. ocellata migrate faster within their vertebrate hosts than do those ofSchistosoma mansoni, indicating that the former may use other transformation and immune-evasion mechanisms.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00931029
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  • 10
    Electronic Resource
    Electronic Resource
    A comparison of X-ray methods for structure refinement of Langmuir-Blodgett multilayers (1992)
    Weinheim : Wiley-Blackwell
    Acta Polymerica 43 (1992), S. 206-209 
    Details
    ISSN: 0323-7648
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Description / Table of Contents: Die Möglichkeiten und Grenzen der Strukturaufklärung an Langmuir-Blodgett Filmen mittels symmetrischer Reflexion von Röntgenstrahlen werden anhand des Beispiels einer Stearinsäure-Multischicht beschrieben. Drei verschiedene Techniken der Elektronendichteprofil-Bestimmung werden verglichen: eine Fourier-Methode, eine Patterson-Methode und Modellrechnungen. Dabei wird die Bedeutung der a priori-Information bei der Auswahl des günstigsten Strukturmodells hervorgehoben.
    Notes: The possibilities and limits of structure refinement of Langmuir-Blodgett films by means of symmetrical reflection of X-rays are described using the example of a stearic acid multilayer. Three different techniques for the determination of the electron density profile from reflectivity data are compared: a Fourier method, a Patterson method, and model calculations. The important role of the a priori information for finding the best structure model is outlined.
    Additional Material: 6 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/actp.1992.010430404
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