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  • 1
    Electronic Resource
    Electronic Resource
    s.l. : American Chemical Society
    Langmuir 9 (1993), S. 208-210 
    ISSN: 1520-5827
    Source: ACS Legacy Archives
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    Amsterdam : Elsevier
    Physica B: Physics of Condensed Matter 198 (1994), S. 249-252 
    ISSN: 0921-4526
    Source: Elsevier Journal Backfiles on ScienceDirect 1907 - 2002
    Topics: Physics
    Type of Medium: Electronic Resource
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  • 3
    Electronic Resource
    Electronic Resource
    Amsterdam : Elsevier
    Physica B: Physics of Condensed Matter 198 (1994), S. 256-258 
    ISSN: 0921-4526
    Source: Elsevier Journal Backfiles on ScienceDirect 1907 - 2002
    Topics: Physics
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  • 4
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 110 (1999), S. 8104-8111 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Langmuir-Blodgett (LB) multilayer systems are found to be inhomogeneous in morphology and structure. The most characteristic feature of these multilayer films is the appearance of three-dimensional domains in which the molecules arrange themselves as a result of the film transfer onto the substrate. A series of lead arachidate (PbA2) LB multilayers have been prepared as model systems to study the dependence of film morphology on the pH value in the subphase. Atomic force microscopy (AFM) and two different x-ray scattering methods [specular (XSR) and diffuse (XDS) x-ray reflectometry] have been used to investigate the intrinsic interface properties, such as the vertical electron density profile and lateral distribution of head groups and chains, as well as the microscopic description of the interface structure, thus providing an overall picture of the investigated multilayers. With AFM, discrete height variations of domains with minimum step widths of one double layer independent of the salt concentration in the films were observed. The lateral domain size shows a dependence on pH. It was found to be maximum at pH=4.2 (pure acid) but minimum at pH 7.0 (maximum salt content). The AFM pictures were treated by a statistical analysis to extract quantities that can be compared with the x-ray results. A considerable number of Bragg maxima were observed in XSR. The vertical correlation length LZ was calculated from the angular width of Bragg maxima along 2θ and was found to vary with pH value. It follows, in general, the tendency of the domain sizes, being maximum at pH=4.8 and minimum at pH=7.0, respectively. The lateral correlation length LX has been evaluated via XDS from the half widths Δω measured by rocking the sample across a fixed 2θ. It decreases for increasing pH. LX was compared with the respective quantity of the AFM analysis. Estimated by XDS, the correlation lengths for inner interfaces and domains complement one another with the lateral length scales resulting from AFM analysis of the surface. © 1999 American Institute of Physics.
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  • 5
    Electronic Resource
    Electronic Resource
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 73 (1998), S. 806-808 
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The depth dependent strain relaxation in photolithographically defined and reactive ion etched Si/SiGe quantum wire and dot arrays is determined by high resolution grazing incidence x-ray diffraction. The laterally periodic structures were aligned along two orthogonal [110] and [1¯10] directions on the (001) surface. By recording reciprocal space maps around the (220) and (2¯20) reciprocal lattice points, the shape and in-plane strain could be determined independently of each other. Using triple axis diffractometry and changing the effective penetration depth of the x-ray radiation between 5 and 300 nm the strain relaxation in the wires and dots could be determined depth resolved. © 1998 American Institute of Physics.
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  • 6
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 78 (1995), S. 3144-3148 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: A lattice matched {InP/GaInAs}30/InP[001] superlattice containing an enlarged quantum well (EQW) was investigated by means of grazing incidence x-ray diffraction (GID) using synchrotron radiation. The in-plane (220) rocking curve was measured choosing a grazing angle for the incident beam with respect to the surface, αi. At the angular position of maximum intensity we recorded the intensity distribution of the reflected beam normal to the surface (rod scan) using a position sensitive detector. The rod contains information about the density variation towards the surface normal. Instead of a single superlattice Bragg peak we found a double peak which can be explained by the phase shift of the partial x-ray waves scattered at the two superlattices sandwitching the EQW. For fixed αithe intensity ratio of the two peaks is a measure of the EQW thickness. An additional advantage of the GID technique is that this ratio can be modified by changing the penetration depth of the probing x-ray beam into the sample. This is performed by keeping αi smaller or larger than the critical angle for total external reflection. The EQW thickness and its position below the surface is determined by simulation of the recorded rod scans using the kinematic approach of the GID. Both quantities are obtained with monolayer accuracy. © 1995 American Institute of Physics.
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  • 7
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 74 (1993), S. 2381-2387 
    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.
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  • 8
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 74 (1993), S. 146-152 
    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.
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  • 9
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 81 (1997), S. 2601-2606 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The depth profile of the chemical composition in InxGa1−xAs single quantum wells (SQWs), epitaxially grown onto a GaAs[001] substrate and covered by a GaAs cap layer, has been determined by use of grazing incidence diffraction (GID). This method allows the scattering signal from the SQW to be enhanced and the scattering depth to be tailored. The coherently illuminated area is large, due to the small incident angle αi; this makes GID a unique technique for investigating buried thin layers over a lateral length scale of several microns. In the case of very thin SQWs the measurements could be described assuming a Gaussian-like distribution of the In content with depth. The broad In profile seen using this method is in contrast with the sharp monolayer signal achieved by photoluminescence measurements. This can be explained by the assumption of a terracelike In distribution and the very different lateral integration length of both experiments. For thicker SQWs we could verify that at least one of the two interfaces is not sharp but shows a gradient in the chemical composition. © 1997 American Institute of Physics.
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  • 10
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 66 (1995), S. 4845-4846 
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: 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. © 1995 American Institute of Physics.
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