A ‘hot wall epitaxy’ is applied to grow PbTe thin films on sapphire substrates with BaF2 buffer layer deposited by molecular beam epitaxy (MBE). The microstructural and strain state characteristics of PbTe layer were examined with high resolution X-ray diffraction techniques. The epilayer is composed of two (111)PbTe‖(0001)Al2O3 epitaxially oriented domain variants. The domains are azimuthally rotated and their interfacial directions relative to the substrate are [011̄]PbTe‖21̄1̄0Al2O3 and [1̄54̄]PbTe‖21̄1̄0Al2O3, respectively. Another possible alignment of the domain variant corresponds to 31̄2̄PbTe‖31̄2̄0Al2O3 orientation. The strain state analysis of PbTe layer points to its relaxation via domain formation and high dislocation density generation in the lattice. Despite the domains formation the measured mobility of electron carriers is approximately 1600 cm2/V s and 30 000 cm2/V s at 300 K and 77 K, respectively. The theoretical analysis of the measured electrical properties indicates that the scattering by acoustic and optical phonons is the factor affecting the conduction process.

The nanostructured powder prepared by critical CO2 extraction of the urea-assisted wet chromia gel mixture at 373K in vacuum was studied by X-ray diffraction techniques. Thermoanalytical methods showed the presence of the lattice water molecules in the resulting phase corresponding to a chemical formula CrOOH·2H2O. The CrOOH·2H2O nanocrystals of 3–5nm in diameter were observed in transmission electron microscopy and their structure was derived from the Rietveld analysis in which the disorder contribution to the X-ray scattering was implemented. The structural model shows that the hexagonal unit cell of α-CrOOH undergoes monoclinic distortion with half of the O−2 anions and OH− groups being replaced by bonded water molecules in the three-dimensional packing resulting in half of the sites in regular Cr+3 octahedra being vacant. Further examination of the quasi-crystalline disordered state of the CrOOH·2(H2O) nanocrystals was performed by model independent method of Radial Distribution Function (RDF). This complementary technique is sensitive to the molecular composition and allows to assess the average atomic (or electron) density distribution and the spacings of the atomic arrangements in the nearest neighbor shells comprising the range of the crystalline order in the structure of this material.

A comparative study of the nucleation of In enriched islands in In0.2Ga0.8As/GaAs multilayers grown on top of GaAs or AlAs buffers deposited on GaAs substrates with various miscut parameters was performed by using X-ray diffraction, transmission electron microscopy (TEM) and atomic force microscopy (AFM) techniques. Experimental results showed that the evolution of the self-assembly strongly depends on the miscut parameters and the morphology of the buffer/multilayer interface. For the samples with the same nominal strain misfit between the bilayers the nucleation is enhanced for the larger initial miscut on the substrate and the degree of the lateral ordering across the interface is promoted by the morphology of the underlying AlAs buffer layer.

LPOMVPE-grown In 0.2 Ga 0.8 As/GaAs multilayers on GaAs substrates with miscut values of 0°, 0.3° and 2° around the [100] azimuthal direction were investigated by employing X-ray diffraction techniques complemented by atomic force microscopy (AFM) and transmission electron microscopy (TEM). The step-terrace structure evolving on the interfaces upon deposition strongly depends on the initial substrate morphology. The initiation of island nucleation, and both lateral and vertical ordering are related to the interfacial morphological parameters. Finite element analysis (FEA) is performed to elucidate the interplay between structural and strain relaxation processes.

Reciprocal space mapping in non-coplanar diffraction geometry using a triple-crystal diffractometer is applied to study strained In0.2Ga0.8As/GaAs multilayer. The modelling accounts for the measured integrated intensities of the satellites in the simulation of the reciprocal space map to provide compositional profile of In distribution in the nucleated islands on the interfaces. Theoretical approach to calculate the intensity in this unconventional geometry is discussed.

A comparative study of the nucleation of In enriched islands in In Ga As yGaAs multilayers grown on top of GaAs or AlAs 0.2 0.8 buffers deposited on GaAs substrates with various miscut parameters was performed by using X-ray diffraction, transmission electron microscopy(TEM) and atomic force microscopy (AFM) techniques. Experimental results showed that the evolution of the self-assembly strongly depends on the miscut parameters and the morphology of the buffer ymultilayer interface. For the samples with the same nominal strain misfit between the bilayers the nucleation is enhanced for the larger initial miscut on the substrate and the degree of the lateral ordering across the interface is promoted by the morphology of the underlying AlAs buffer layer. 2002 Elsevier Science B.V. All rights reserved.

Mesoporous chromia acrogels with a surface area of 484-735 m(2) g(-1), a pore volume of 0.4-0.9 cm(3) g(-1) and a pore diameter of 3-9 nm were prepared by urea-assisted homogeneous precipitation from an aqueous Cr(NO3)(3) solution, followed by continuous supercritical extraction with CO2 under different conditions (pressure and time) after replacement of the water with a hexane/2-butanol mixture. The texture and chemistry of the aerogels transformed by heating in air or an inert atmosphere and the structure of the nanoparticles were characterized by means of N-2-adsorption isotherms, AA, HRTEM, FTIR, a variety of thermoanalytical methods (TPD, DSC, TGA, TPO-TPK) and X-ray diffraction in combination with structure modeling. At the CO2 extraction stage, a pressure of about 400 bars was critical for production of aerogels with surface areas > 700 m(2) g(-1). The fresh chromia aerogels consisted of closely packed almost globular, 3- to 5-nm nanoparticles with a structure analogous to that of monoclinic alpha-CrOOH, in which half of the 0 atoms and OH groups were replaced with coordinately bonded water molecules. After dehydration at 550-600 K, the materials retained their texture, being converted to faceted 3- to 5-nm nanoparticles, consisting of two-dimensional fragments (clusters) of alpha-CrOOH crystals built on [Cr(OH)(3)O-3] octahedra without bonding along the Z-axis. The texture of dehydrated chromia, aerogels was stable at temperatures up to 650 K in air and up to 773 K in an inert atmosphere. At higher temperatures, the material underwent a glow transition, yielding microcrystalline 50-nm particles with the well-defined structure of alpha-Cr2O3 and a surface area < 200 m(2) g(-1). (C) 2002 Elsevier Science B.V. All rights reserved.

The investigation of the initial stages of nucleation of In-enriched islands in In0.2Ga0.8As/GaAs multilayers grown on top of GaAs or AlAs buffers deposited on GaAs substrates with a miscut of 2° in the vicinity of the [100] azimuthal direction was performed by using X-ray diffraction and transmission electron microscopy techniques. Simulation of the reciprocal space maps relied on the modelling of the strain field resulting from the compositional profile of the nucleated islands, the substrate and buffer morphology. Consideration of both thickness dependent vertical strain gradients and lateral strain gradients on the interfaces and their effect on the intensity patterns near the superlattice peaks and lateral satellites is elaborated. The observed skew vertical correlation of the islands can vary with the increasing number of interfaces.

A strained superlattice composed of five bilayers of In0.2Ga0.8As/GaAs grown on a (001) GaAs substrate was studied via comparison of the measured high-resolution reciprocal space maps near to the various substrate Bragg peaks with the theoretically modelled intensity distributions. Fourier synthesis was used to describe the strain field and the morphology of the nucleated islands. Modelling, which explains the presence of the side intensity maxima, shows that the lateral compositional variation produces domains with enriched In concentration surrounded by In depleted regions. The distribution of the strain field in both substrate and the multilayer suggests that the compositional modulation promotes nucleation of the islands with a skew vertical correlation on the subsequent interfaces.

Simulated intensity maps from perfect crystals are compared with experimental ones collected with high-resolution Philips MRD and Bede D-3 diffractometers employing a four-reflection Bartels monochromator and two-reflection analyser optics with the sample set in dispersive and non-dispersive configurations, respectively. The patterns resulting from the instrumental monochromator and analyser optical elements, as well as from the wavelength dispersion of the conventional x-ray source, are elaborated. The convolution of the intensity maps with the instrumental function based on two-dimensional integration and on the interactive graphical method are discussed. The latter approach is convenient and facilitates the convolution of the model simulations for comparison with experiment.

X-ray techniques were employed to characterize the interfacial region in the Si-on-sapphire heterostructure. Strained interfacial layer is formed at the top of the sapphire substrate. Application of the biaxial strain model to the strain-stress relation transformed to the actual crystal system attached to the sapphire surface (01 (1) over bar2) allowed to derive the strain/stress tenser at the interface. In this mismatched heterostructure the wafer aquires an overall curvature and the elastic anisotropicity, in particular that of the sapphire substrate, has a detrimental effect on the surface topography of the Si epilayers. The bending profile visualized in the laser light interference patterns reflects the strain/stress distribution determined for the interfacial layer.

Surface sensitive grazing incidence diffraction (GID) is used to study the interface between silicon and sapphire. A thin crystalline layer of aluminium silicate with a lateral lattice parameter slightly different from sapphire is found and quantified by model calculations. We demonstrate that in GID, very thin interface layers can be investigated for which the sensitivity for measuring small Bragg angle differences, Δθ, is enhanced by a factor of about 25 by the projection of Δθ into the plane perpendicular to the sample surface. The accuracy of the lattice parameter determination is thereby improved by at least one order of magnitude.

The interfacial region at the substrate, the morphology of the interface and the surface were studied for a number of Si-on-saphire (SOS) samples using X-ray scattering techniques, transmission electron microscopy (TEM) and scanning electron microscopy (SEM). A strained interfacial layer is formed in this high misfit system. The dislocations created in this layer and at the interfacial steps accommodate the elastic strain buildup. The misfit relaxation is accompanied by the misorientation of the epilayer with respect to the substrate, which itself depends on the substrate miscut parameters and the thickness of the epilayer. The observed azimuthal rotation of the epilayer miscut is attributed to the effect of the anisotropic microtwinning evolving with the increasing epilayer thickness. This azimuthal rotation is reflected by the step morphology on the surface of the epilayers.

The characterization of the AlAs\GaAs multilayers based on the modelling of the X-ray scattering is discussed. The structural parameters regarding the thickness of the bilayer components and the vertical and lateral variations (interface roughness) were assessed from low and high angle scan modes. The diffuse scattering analysis showed that both lateral and vertical correlation of the interface roughness develops in this LPOMVPE grown system.

A combination of experimental techniques: high-resolution X-ray diffraction (HXRD), high-resolution cross-sectional electron microscopy (HREM), X-ray photoelectron spectroscopy (XPS) and Auger electron spectroscopy (AES) were employed to elucidate the interfacial microstructure in Si-on-sapphire system. The observed structural features and their role in the strain relieving mechanism at the interface are discussed. Chemical analysis shows that to some extent bonds like in aluminosilicates and SiO2 are formed in the interfacial layer.

Characteristics of the interface roughness in a low-pressure organometallic vapour phase epitaxy (LPOMVPE) grown AlAs/GaAs multilayer are studied by grazing-incidence x-ray scattering. Quantitative results are obtained by comparing experimental and theoretically calculated diffuse scattering maps. These corroborate with the features resolved by atomic force microscopy. The observed morphological features are discussed in the following sections.

Strain distribution in Si-on-sapphire (SOS) heterostructure was assessed using the experimentally determined in-plane and out-of-plane strain values. The calculation is performed in the frame of the biaxial strain model. Similar strain distributions were observed for the SOS samples obtained from different sources.

The interface in Si-on-sapphire studied by transmission electron microscopy (TEM) and X-ray diffraction techniques showed that the complicated interfacial structure is associated with arrays of microtwins and stacking faults as well as interfacial dislocations. The networks of dislocations were found to have non-rational line directions. The elastic strain in the heterostructure is accommodated by these defects and crystallite misorientations at the interface.

X-ray anomalous scattering measured with a high-resolution triple-crystal diffractometer was analysed in terms of different models of microdefects present in the bulk of InP crystal. The observed broadening of the Laue reflections is consistent with the formation of large aggregations of dislocation loops belonging to {111}〈110〉 system. The complete simulation of the diffuse intensity including both Huang and Stokes-Wilson regions in comparison with the experimental data revealed that these aggregations consist of vacancy loops occupying predominantly the (111) plane and that the rest of the {111} planes are occupied by the interstitial loops.

HgBa2CuO4+δand CaxLa1−xBa1.75−xLa0.25+xCu3O7±δsuperconducting systems were structurally investigated employing Rietveld analysis. The doping of holes in Hg compounds was done by oxygenation and reduction methods. In Ca–La–Ba–Cu–O system the doping of holes was introduced via cation cosubstitution of Ca+2for La+3and La+3for Ba+2, so that the nominal charge of non-copper cations remained constant (=7.25). The electronic structure was assessed by calculating Madelung site potentials. It was found that the difference ΔVAof Madelung potentials on the apical and planar oxygen sites correlates with Tcsimilar to the trends reported in the literature. Based on ΔVA}$ analysis it was possible to separate the intrinsic `chemical pressure' effect on Tcfrom the one caused by electron density redistribution in Ca–La–Ba–Cu–O system upon cosubstitution.