Reflectivity measurements of thin SiO2 layers in the soft-X-ray region

Energy and angular dependent reflectivity measurements of differently prepared SiO₂ layers were made in the soft X-ray region in order to study differences in their optical and electronic behaviour caused by the technological process. The optical constants of the layers were determined by fitting the angular dependent reflectivity data with a multilayer model which takes into account the roughness of all interfaces. Detailed knowledge of the polarization level of the primary beam from the synchrotron radiation source is needed for reliable results. The energy dependent reflectivity measurements indicate that high-pressure dry-oxidized layers have a more perfect structure than normal dry-oxidized layers. Independent on the deposition process the Si SiO₂ interface roughness amounts to ± 1 nm. The Si_2p-XANES of Si and SiO₂ were detected.     

Zum asymmetrischen Bragg-Fall der Röntgenstrahlinterferenzen am Realkristall Besonderheiten als Folge der Extinktion und Möglichkeit zur röntgenografischen Charakterisierung des Versetzungsnetzwerkes

The asymmetrical Bragg case of X-ray diffraction on a thick real crystal is theoretically investigated on a layer model containing dynamically diffracting mosaic blocks. By means of this theory the experimental dependence of the integrated reflectivity R_i on the asymmetry angle α deviation from the kinematical formula may be understood as a result of extinction- and absorption processes inside the mosaic crystal. Thus the remarkably thick surface layers or surface protuberances assumed by Mathieson and in previous papers for the interpretation of the experimental R_i(α) become needless or they are considerably thinner. respectively, indeed. – On the base of the represented theory the determination of special (model-dependent) characteristics of the dislocation network is possible via absolute R_i(α)-measuring values.     

Characterization of heterointerfaces in GaAs/MnAs/MnZn-ferrite structures

We have grown GaAs epitaxial films on MnZn-ferrite substrates using MnAs buffer layers and investigated their heterointerfaces with glazing incidence-angle X-ray reflectivity and X-ray photoelectron spectroscopy. It has been found that the heterointerfaces for this structure are quite abrupt and the roughness at the GaAs/MnAs and MnAs/MnZn-ferrite interfaces are 1.1 and 0.2 nm, respectively. We also found that the diffusion of atoms through the GaAs/MnAs interface into the GaAs film is negligible. These results indicate that the MnAs buffer layer for the GaAs/ferrite structure is chemically stable and promising for the application to the future magnetic electronics.     

Optical investigations of germanium nanoclusters – Rich SiO2 layers produced by ion beam synthesis

In this work, refractive index and extinction coefficient spectra of germanium nanoclusters – rich SiO₂ layers have been determined using variable angle spectroscopic ellipsometry (VASE) in the 250–1000 nm range. The samples were produced by Ge⁺ ion implantation into SiO₂ layers on Si substrates and subsequent annealing at temperatures from 700 to 1100 °C. It is known from previous investigations of similar samples that the Ge nanoclusterization process starts already at 800 °C and spherical Ge nanocrystallites 5–8 nm in diameter are observed in the SiO₂ layers after annealing for 1 h at even higher temperatures of 1000–1100 °C. Rutherford backscattering spectrometry (RBS) was employed to measure the Ge atom concentration depth profiles in the studied samples. The RBS results helped us choose realistic models for the VASE analysis which were necessary for a proper interpretation of the VASE data. It has been found that the refraction index value for the SiO₂/Si layer increases after Ge implantation. This effect can be explained by a defect-dependent compaction of ion-bombarded layers. A band’s tail in the extinction coefficient spectra for all the samples is observed which originates from a strong ultraviolet absorption band at 6.8 eV due to a Germanium Oxygen-Deficiency Center (GeODC) and/or a Ge-E’center in SiO₂. The annealing process results in the emergence of weaker extinction coefficient bands in the 400–600 nm region, associated with direct band-to-band transitions in Ge nanostructures. Transformation of these bands, including their blue-shift with the increasing annealing temperature could be explained via a quantum-confinement mechanism, by size and structural changes in Ge nanostructures.     

Fabrication of Multilayer Films on the Basis of Lysozyme Protein and Precipitant (Iodide and Potassium) Ions on a Silicon Substrate by the Modified Langmuir–Schaefer Method

Multilayer structures, consisting of successive lysozyme layers and layers of iodide and potassium ions, have been formed on a silicon substrate by the modified Langmuir–Schaefer method; the use of this technique implies preliminary preparation of a crystallization protein solution containing an oligomeric phase. The multilayer structure has been characterized by methods of X-ray reflectivity and total external reflection X-ray standing waves (TER XSW). The data obtained indicate the formation of a dense lysozyme film (3 nm thick) and layers of potassium and iodide ions, adjacent to this film.     

Magnetic properties and sensitized visible and NIR luminescence of DyIII and EuIII coordination polymers by energy transfer antenna ligands

Two coordination polymers, {[Ln(2-stp)(4,4′-bipy)(H₂O)].(H₂O)}, [Ln = Dy (1) and Eu (2), 2-stp = 2-sulfoterephthalate and 4,4′-bipy = 4,4′-bipyridine] have been characterized by solid state UV-vis, FTIR spectra, X-ray single crystal diffraction and solid state photoluminescence. Variable-temperature magnetic susceptibility and isothermal magnetization as function of external magnetic field is also studied for both complexes. After ligand-mediated excitation, both complexes show the characteristic visible and NIR luminescence of the corresponding Ln^III ions (Ln = Dy, Eu) which is due to efficient energy transfer from the ligands to the central Ln^III ions via an antenna effect. The indirect energy transfer in both complexes has been investigated and discussed in detail.     

Studies on crystal growth,optical and electrical characterization of pure and Dy-doped bismuth silicate single crystals

(0.5 mol%) Dysprosium (Dy) doped bismuth silicon oxide (BSO) single crystals were grown by the Czochralski technique under air atmosphere. Detailed analysis of Dy-doped BSO with pure BSO has been studied through optical analysis. The absorption edges of pure and Dy-doped BSO crystals are found to be 405 nm and 415 nm, respectively. The shift in the absorption edge is contributed to the defect centers created in the crystal with Dy-doping. The shifts observed in the Raman spectra on doping Dy are found to be lower, when compared with the pure BSO crystal. This effect can be correlated to the lattice distortion induced by the Dy doping. The oxide formation and intrinsic defects in the BSO crystal have been identified by photoluminescence analysis. Dielectric measurements reveal that higher permeability value in the BSO sample is due to the presence of charged defects, which can be related to the space charge polarization. There is a slight decrease in dielectric constant on doping with Dy. The piezoelectric value explains the defects formed in the crystal. On poling, d₃₃ value of BSO and Dy-doped BSO are 32 pC/N and 40 pC/N, respectively.     

Features of the magnetic state of the layered Fe-V nanostructure of the superconductor-ferromagnet type

The magnetic state of the V(39 nm)/20 [V(3 nm)/Fe(3 nm)] nanostructure has been investigated by polarized neutron reflectometry in the temperature range from 1.6 to 30 K in magnetic fields from 0.2 to 15 kOe. The data obtained indicate that the superconductivity of vanadium layers may affect magnetic ordering both over the depth of the structure and in its plane.     

Magnetic susceptibility of sodium rare-earth fluorites Na0.5 − x R 0.5 + x F2 + 2x (R = Dy, Ho, Er, Tm, Yb) and some ordered phases

Magnetic properties of the nonstoichiometric phases with the fluorite-type “defect” structure Na_0.4 R _0.6F_2.2 (R = Ho, Er, Tm, Yb) and Na_0.35Dy_0.65F_2.3 have been studied as well as some ordered phases with different distortions of the initial fluorite lattice (NaHo₂F₇, Na₇Tm₁₃F₄₆, NaYb₂F₇, and Na₇Yb₁₃F₄₆) and Na_1.5Dy_1.5F₆ with the gagarinite-type structure (NaCaYF₆). Magnetic susceptibility χ was measured with the aid of the Faraday balance in the temperature range from 20 to 300 K. The crystals with R= Dy, Ho, Er, Tm are paramagnetic; their temperature dependence χ is described by the Curie-Weiss law. It is shown that in the temperature range studied, magnetic susceptibility does not depend on the degree of order of Dy, Ho, Er, and Tm ions in the structure. Below 80 K, the temperature dependence of magnetic susceptibility of the the Yb³⁺-containing phases differs from the analogous dependence χ of an ideal paramagnetic crystal, which is assumed to be caused by the interaction of the crystalline field with Yb³⁺ ions.     

Microstructural and magnetic characterization of Nd2Fe17 ball milled alloys

Microstructural and magnetic changes induced by ball milling in Nd₂Fe₁₇ alloy have been investigated. X-ray and neutron powder diffraction studies have shown that the main crystalline phase present in the as-cast Nd₂Fe₁₇ compound is the rhombohedral Th₂Zn₁₇-type crystal structure. Contrary to other materials, the crystal structure does not change after milling, and the crystal lattice parameters slightly increases while the induced strain is less than 0.1%. It has been observed from SEM and TEM images that the microstructure consists of agglomerates of nanoparticles with a mean size around 20 nm, and from magnetic measurements a broadening of the temperature range in which ferromagnetic to paramagnetic transition takes place.     

Microstructure of eutectic composites Ln 1?x Ln′ x MnO3 (Ln = Eu or Tb; Ln′ = Y or Ho) near the transition between the orthorhombic structure and hexagonal structures

Multiferroic crystals Ln _{1 ? x} MnO₃ (Ln = Eu or Tb; Ln?? = Y or Ho) have been grown by floating-zone melting; the compositions of these crystals are close to the point of concentration transition from the orthorhombic structure to the hexagonal phase. Scanning microscopy has revealed that the crystal boules have a regular lamellar structure in the form of alternating layers of the orthorhombic and hexagonal phases; this structure is typical of the materials obtained by the directional solidification of eutectic composites. The local chemical and phase compositions and the unit-cell parameters of the phases have been determined. The microstructure and morphology of the lamellar structures are described for different growth conditions. The mutual orientation of the crystallographic axes of the orthorhombic and hexagonal phases in the neighboring layers has been determined by electron backscatter diffraction. The orientational features are considered from the point of view of the crystal structure of both phases.     

The (−)-gossypol-2,4-pentanedione (1:2) inclusion complex

(–)-Gossypol and 2,4-pentanedione form an inclusion complex in a one-to-two molar ratio. The compound crystallizes in the tetragonal P4₁2₁2 space group and has unit cell dimensions of a=b = 10.9966(7) Å and c = 60.213(4) Å. Both solvent molecules are in the enol form and occupy two distinct cavities within the structure. The first cavity is formed between pairs of gossypol naphthalene rings and contains a pair of symmetry-related solvent molecules that each accept a hydrogen bond from one of the surrounding gossypol molecules. The four molecules together form a wedge-shaped assembly that is repeated throughout the cell. The assemblies stack to form columns, and adjacent columns are aligned parallel to form layers. Neighboring layers are oriented at 90° angles, which accounts for the fourfold symmetry of the space group. The second solvent cavity is located in isolated pockets that form between the layers. These solvent molecules also accept hydrogen bonds from the surrounding gossypol molecules. Although many gossypol solvates have been reported, this structure is unusual in a number of features. It is the first report of a chiral non-conglomerate gossypol solvate. It is also the only known chiral gossypol inclusion complex to not lose appreciable amounts of solvent when removed from its mother liquor.     

Czochralski growth and characterization of Dy: La3Ga5.5Nb0.5O14 single crystals

Dysprosium (Dy) doped La₃Ga_5.5Nb_0.5O₁₄ single crystals were grown by the traditional Czochralski method along z‐axis. The structure of the crystal has been studied by X‐ray powder diffraction method, and the unit‐cell parameters are calculated to be a=8.22070 Å, c=5.12533 Å and V=299.965 ų. The segregation coefficient of Dy³⁺ in La₃Ga_5.5Nb_0.5O₁₄ crystal was measured by X‐ray fluorescence analysis. For 1 mol% doping level in the melt, the distribution coefficient of Dy³⁺ was determined to be 0.341 wt%. Specific heat, thermal expansion and transmission spectrum of Dy: La₃Ga_5.5Nb_0.5O₁₄ single crystals have been measured. The fluorescence spectra of Dy³⁺: La₃Ga_5.5Nb_0.5O₁₄ crystals were measured at room temperature, and there were four emission transitions occurring at 479, 576, 662 and 754 nm, respectively. The fluorescent lifetimes measurement results show 1.0% Dy: La₃Ga_5.5Nb_0.5O₁₄ possesses shorter fluorescence decay time (303.4 μs) than does 1.0%Dy:LGS (436.12 μs). (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Nonlinear Optical Properties of Isomorphic Family of Crystals with Yttrium-Aluminium Borate (YAB) Structure

The second harmonics generation of Nd-laser radiation (λ = 1.06 microns) of the isomorphic family of crystals with yttrium-aluminium borate (YAB) structure — RAl₃(BO₃)₄ (R = Y, Sm, Eu, Gd, Dy, Er, Ho, Tu) — investigated using the powder method and the theoretical calculation of SHG–coefficients — are reported. The refraction indices (for λ = 5481 Å) and optical sign for all studied YAB-type crystals are determined with the help of the immersion method. All studied crystals possess PM direction and oee-interaction. The SH-intensity is of KDP order of magnitude, with reasonable correlation of experimental and theoretical data. Theoretical analysis of the contributions of different ions to the integral d magnitude has shown identical signs for all ion species in YAB structure type.     

Study of magnetic metal periodic structures by X-Ray and electron microscopy methods

Complex studies of magnetic periodic metallic systems based on Dy/Gd layers have been carried out by X-ray diffraction, resonance X-ray reflectometry, transmission electronic microscopy, and energydispersve microanalysis. The application of these methods and joint analysis of their results provide an effective approach to study of the structure and determination of the parameters of individual layers and interfaces and their structural quality with a high degree of reliability.     

Optical Absorption Spectra of Czochralski-grown (Dy1-xGdx)3O12Ga5O12 and Dy3(Ga1-yAly)5O12 Garnets Relating Unstable Spiral-shape Growth

Optical absorption has been measured from 700 to 1300 nm for garnet single crystals by substituting Dy or Ga for Gd or Al of Dy³Ga₅O₁₂ grown by the Czochralski method, and a suppression of unstable spiral-shape growth on Dy₃Ga₅O₁₂ by the substitution was discussed relating the absorption spectra. The total absorption in the single crystals at the wavelength corresponding to the radiation from Ir crucible was decreased relatively with the increase of Gd or Al content. The decrease of this absorption in the single crystals is one of the causes to suppress the unstable spiral-shape growth.     

Optical constants of semiconducting amorphous TiS2

Absorption edge, index of refraction and reflectivity were measured on a-TIS₂, which is liquid at room temperature. Optical constants ?₁ and ?₁ in the 0.05–5 eV region were derived using the Kramers-Kronig analysis.     

X-ray diffraction study of short-period AlN/GaN superlattices

The structure of short-period hexagonal GaN/AlN superlattices (SLs) has been investigated by X-ray diffraction. The samples have been grown by metalorganic vapor-phase epitaxy (MOVPE) in a horizontal reactor at a temperature of 1050°C on (0001)Al₂O₃ substrates using GaN and AlN buffer layers. The SL period changes from 2 to 6 nm, and the thickness of the structure varies in a range from 0.3 to 1 μm. The complex of X-ray diffraction techniques includes a measurement of θ-2θ rocking curves of symmetric Bragg reflection, the construction of intensity maps for asymmetric reflections, a measurement and analysis of peak broadenings in different diffraction geometries, a precise measurement of lattice parameters, and the determination of radii of curvature. The thickness and strain of separate SL layers are determined by measuring the θ-2θ rocking curves subsequent simulation. It is shown that most SL samples are completely relaxed as a whole. At the same time, relaxation is absent between sublayers, which is why strains in the AlN and GaN sublayers (on the order of 1.2 × 10^?2) have different signs. An analysis of diffraction peak half-widths allows us to determine the densities of individual sets of dislocations and observe their change from buffer layers to SLs.     

Spectral and magnetic properties of macroacyclic and macrobicyclic Schiff base RE complexes

IR spectroscopic, electrospray ionization mass spectrometry, TG-DTA, structure and magnetic properties of the gadolinium(III), samarium(III) and dysprosium(III) macroacyclic tripodal Schiff base, C₂₇H₂₇N₄O₃C_l3Gd(Dy, Sm) as well as gadolinium(III) and erbium(III) cryptate C₃₉H₄₇MN₉O₆ (MGd, Er) complexes are reported. The positions of ν(CN) stretching bonds indicate that the azomethine group nitrogen is coordinated to the rare earth ion. The [1:1] ligand to metal proportion in all macrocyclic and mocrobicyclic Schiff base complex samples has been confirmed by both electron ionization and electron spray molecular spectroscopy spectra. A TG-DTA analysis has indicated the presence of two water molecules in the inner-sphere of the macrobicyclic complex and confirmed that there is no water coordination of the metal ion in the macroacyclic complex. The near neighborhood of cation ions in the complexes of both types and their structure have been proposed on the basis of the above data. The temperature dependence of the EPR spectra integrated intensity has made it possible to reveal magnetic interactions in the spin system of these compounds.     

Stress,Strain, and Symmetry of Pseudomorphically Grown Epitaxial Layers

The complete stress and strain tensors and the point symmetry of pseudomorphically grown epitaxial layers are calculated from the epitaxial relationship and the elastic constants of the deposit material. The angle misalignment of crystallographic directions in the deposit due to the strain is also calculated and results are given for the epitaxial systems CaF₂/Si(100) and CaF₂/Si(111).