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At least 1,729 records · Page 96
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DOE OSTI2014

Diffusion-driven precipitate growth and ripening of oxygen precipitates in boron doped silicon by dynamical x-ray diffraction

X-ray Pendellösung fringes from three silicon single crystals measured at 900 °C are analyzed with respect to density and size of oxygen precipitates within a diffusion-driven growth model and compared with TEM investigations. It appears that boron doped (p+) material shows a higher precipitate density and a higher strain than moderately (p-) boron crystals. In-situ diffraction reveals a diffusion-driven precipitate growth followed by a second growth regime in both materials. An interpretation of the second growth regime in terms of Ostwald ripening yields surface energy values (around 70 erg/cm{sup 2}) similar to published data. Further, an increased nucleation rate by a factor of ∼13 is found in the p+ sample as compared to a p- sample at a nucleation temperature of 450 °C.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2014

Temperature, pressure, and size dependence of Pd-H interaction in size selected Pd-Ag and Pd-Cu alloy nanoparticles: In-situ X-ray diffraction studies

In this study, in-situ X-ray diffraction has been carried out to investigate the effect of temperature and pressure on hydrogen induced lattice parameter variation in size selected Pd-Ag and Pd-Cu alloy nanoparticles. The nanoparticles of three different mobility equivalent diameters (20, 40, and 60 nm) having a narrow size distribution were prepared by gas phase synthesis method. In the present range of temperature (350 K to 250 K) and pressure (10{sup −4} to 100 millibars), no α (H/Pd ≤ 0.03) ↔ β (H/Pd ≥ 0.54) phase transition is observed. At temperature higher than 300 °C or pressure lower than 25 millibars, there is a large difference in the rate at which lattice constant varies as a function of pressure and temperature. Further, the lattice variation with temperature and pressure is also observed to depend upon the nanoparticle size. At lower temperature or higher pressure, size of the nanoparticle seems to be relatively less important. These results are explained on the basis of the relative dominance of physical absorption and diffusion of H in Pd alloy nanoparticles at different temperature and pressure. In the present study, absence of α ↔ β phase transition points towards the advantage of using Pd-alloy nanoparticles in applications requiring long term and repeated hydrogen cycling.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2014

Nano-scale characterization of GaAsP/GaAs strained superlattice structure by nano-beam electron diffraction

Distribution of lattice strain in a GaAsP/GaAs superlattice with a periodicity of 10 nm thickness, deposited on a 100 nm GaAs basal layer has been measured by nano-beam electron diffraction. The superlattice on the (001) plane of the basal GaAs layer shows a constant lattice strain from the bottom to the top layers, whereas the superlattice on the basal GaAs surface sloped by 16° from the (001) plane shows a variation of the lattice strain and crystal orientation. The difference of the strain distributions was discussed from the viewpoint of average strain. This tilt was explained by an atomistic model.

36 MATERIALS SCIENCE↗
DOE OSTI2014

The structural organization of N-methyl-2-pyrrolidone + water mixtures: A densitometry, x-ray diffraction, and molecular dynamics study

A combined approach of molecular dynamics simulations, wide angle X-ray scattering experiments, and density measurements was employed to study the structural properties of N-methyl-2-pyrrolidone (NMP) + water mixtures over the whole concentration range. Remarkably, a very good agreement between computed and experimental densities and diffraction patterns was achieved, especially if the effect of the mixture composition on NMP charges is taken into account. Analysis of the intermolecular organization, as revealed by the radial and spatial distribution functions of relevant solvent atoms, nicely explained the density maximum observed experimentally.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2014

Thermal equation of state of solid naphthalene to 13 GPa and 773 K: In situ X-ray diffraction study and first principles calculations

In a wide range of P-T conditions, such fundamental characteristics as compressibility and thermoelastic properties remain unknown for most classes of organic compounds. Here we attempt to clarify this issue by the example of naphthalene as a model representative of polycyclic aromatic hydrocarbons (PAHs). The elastic behavior of solid naphthalene was studied by in situ synchrotron powder X-ray diffraction up to 13 GPa and 773 K and first principles computations to 20 GPa and 773 K. Fitting of the P-V experimental data to Vinet equation of state yielded T 0 = 8.4(3) GPa and T' = 7.2 (3) at V0 = 361 Å(3), whereas the thermal expansion coefficient was found to be extremely low at P > 3 GPa (about 10(-5) K(-1)), in agreement with theoretical estimation. Such a diminishing of thermal effects with the pressure increase clearly demonstrates a specific feature of the high-pressure behavior of molecular crystals like PAHs, associated with a low energy of intermolecular interactions.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2014

Synthesis and single crystal x-ray diffraction study of a Schiff base derived from 4-acylpyrazolone and 2-aminophenol

The title compound, (Z)-1-(3-chlorophenyl)-4[1((2hydroxyphenyl)amino)propylidene] -3-methyl-1H-pyrazol-5(4H)-one was synthesized by refluxing compound 1-(m-chlorophenyl)-3-methyl-4-propionyl-5-pyrazolone, with 2-aminophenol in ethanol. The compound crystallizes in the orthorhombic crystal system with space group Pca2{sub 1} having unit cell parameters: a = 26.2993(8), b = 7.0724(2) and c = 18.7170(5)Å. The structure contains two crystallographically independent molecules, A, and, B, in the asymmetric unit cell. The crystal structure was solved by direct method using single crystal X-ray diffraction data collected at room temperature and refined by full-matrix least-squares procedures to a final R- value of 0.049 for 5207 observed reflections.

36 MATERIALS SCIENCE↗
DOE OSTI2014

Experimental investigation of a relativistic magnetron with diffraction output on a repetitive short pulse generator

An experimental investigation of a relativistic Magnetron with Diffraction Output (MDO) on a short voltage pulse generator, which has maximum repetition rate of 100 Hz and plateau of 2.5 ns, is detailed in this paper. Compared to the conversional solid cathode, a direct Density Modulation Cathode is capable for desired microwave radiation. When applied voltage is 200 kV and axial magnetic field is ∼0.12 T, the MDO radiates 120 MW of microwave with 2.3 GHz of central frequency. Power conversion efficiency reaches 22%. Pulse duration is 3 ns. At repetition rates of 50 Hz and 100 Hz, output microwave powers range from 90 MW to 120 MW. Life time is up to 10{sup 4} shots.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2014

High-resolution X-ray diffraction analysis of Al{sub x}Ga{sub 1−x}N/In{sub x}Ga{sub 1−x}N/GaN on sapphire multilayer structures: Theoretical, simulations, and experimental observations

The work presents a comparative study on the effects of In incorporation in the channel layer of AlGaN/GaN type-II heterostructures grown on c-plane sapphire by Plasma Assisted Molecular Beam Epitaxy. The structural characterizations of these samples were performed by High-Resolution X-Ray Diffraction (HRXRD), X-ray Reflectivity (XRR), Field Emission Scanning Electron Microscopy, and High Resolution Transmission Electron Microscopy. The two-dimensional electron gas in the AlGaN/GaN and AlGaN/InGaN interface was analyzed by electrochemical capacitance voltage and compared with theoretical results based on self-consistent solution of Schördinger–Poisson equations. The carrier profile shows enhanced confinement in InGaN channel (1.4393 × 10{sup 13} cm{sup −2} compared to 1.096 × 10{sup 13} cm{sup −2} in GaN). On the basis of HRXRD measurements, the stress-strain of the layers was examined. The c- and a-lattice parameters of the epilayers as well as in-plane and out-of plane strains were determined from the ω-2θ for symmetric scan and ω-Xθ (X represents the coupling coefficient) for asymmetric scan. Strain, tilt, and correlation lengths were calculated from Williamson–Hall plots, whereas stress was examined from modified plot of the same data assuming Uniform Stress Deformation Model. Moreover, the twist angle was measured from skew symmetric scan of (102), (103), and (105) plane along with (002) symmetric plane. The composition and strain/relaxation state of the epilayers were observed in detail by reciprocal space mapping (RSM). The symmetric (002) triple axis RSM and asymmetric (105 and 114) double axis RSM of grazing incidence and exit geometry were carried out on each sample. The defect density was measured from HRXRD curves of skew symmetric (002) and (102) reflection plane. The Al and In mole fraction and strain states of the layers were calculated by fitting the experimental curves with computer simulations and compared with theoretical findings based on elastic theory. The thicknesses of the layers and roughness of the interfaces were measured from simulation of the nominal structure by fitting with XRR experimental curves. The HRXRD measured thicknesses of the layers were further confirmed by cross sectional electron micrographs.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2014

Time-, frequency-, and wavevector-resolved x-ray diffraction from single molecules

Using a quantum electrodynamic framework, we calculate the off-resonant scattering of a broadband X-ray pulse from a sample initially prepared in an arbitrary superposition of electronic states. The signal consists of single-particle (incoherent) and two-particle (coherent) contributions that carry different particle form factors that involve different material transitions. Single-molecule experiments involving incoherent scattering are more influenced by inelastic processes compared to bulk measurements. The conditions under which the technique directly measures charge densities (and can be considered as diffraction) as opposed to correlation functions of the charge-density are specified. The results are illustrated with time- and wavevector-resolved signals from a single amino acid molecule (cysteine) following an impulsive excitation by a stimulated X-ray Raman process resonant with the sulfur K-edge. Our theory and simulations can guide future experimental studies on the structures of nano-particles and proteins.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2014

Composition determination of quaternary GaAsPN layers from single X-ray diffraction measurement of quasi-forbidden (002) reflection

GaAsPN layers with a thickness of 30 nm were grown on GaP substrates with metalorganic vapor phase epitaxy to study the feasibility of a single X-ray diffraction (XRD) measurement for full composition determination of quaternary layer material. The method is based on the peak intensity of a quasi-forbidden (002) reflection, which is shown to vary with changing arsenic content for GaAsPN. The method works for thin films with a wide range of arsenic contents and shows a clear variation in the reflection intensity as a function of changing layer composition. The obtained thicknesses and compositions of the grown layers are compared with accurate reference values obtained by Rutherford backscattering spectroscopy combined with nuclear reaction analysis measurements. Based on the comparison, the error in the XRD defined material composition becomes larger with increasing nitrogen content and layer thickness. This suggests that the dominating error source is the deteriorated crystal quality due to the nonsubstitutional incorporation of nitrogen into the crystal lattice and strain relaxation. The results reveal that the method overestimates the arsenic and nitrogen content within error margins of about 0.12 and about 0.025, respectively.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2014

Bi-O covalency in PbTiO{sub 3}-BiInO{sub 3} with enhanced ferroelectric properties: Synchrotron radiation diffraction and first-principles study

High-T{sub C} ferroelectric (1 − x)PbTiO{sub 3}-xBiInO{sub 3} shows a sustainable spontaneous polarization in tetragonal phase by amount of BiInO{sub 3} augmented. It is rare and interesting that weak ferroelectric In{sup 3+} substitution does not reduce ferroelectricity as most of BiMeO{sub 3} materials. To understand this abnormality behavior, the structure and the cation displacements are studied by means of synchrotron radiation diffraction. The cation displacements of A-site atoms and B-site atoms exhibit a coupling property. Their sustainedly increasing trend is quantitatively associated with spontaneous polarization. Moreover, the structure, the valence electron density distributions, electron localization function, and Bader analysis have been researched on the chemical bond in (1 − x)PbTiO{sub 3}-xBiInO{sub 3} through first-principles calculations here. Although In atoms substitution reduces the covalency degree, this loss is offset by enhanced covalency between Bi-O bonds. The crucial role of Bi atom substitution not only contributes to enhance the covalency but also promotes the polarization.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2014

Neutron diffraction study on very high elastic strain of 6% in an Fe{sub 3}Pt under compressive stress

An Fe{sub 3}Pt alloy with degree of order 0.75 exhibits a second-order-like martensitic transformation from a cubic structure to a tetragonal one at about 90 K; its tetragonality c/a changes nearly continuously from 1 to 0.945 on cooling from 90 K to 14 K. We have investigated the change in lattice parameters in a single crystal of the Fe{sub 3}Pt alloy at 93 K under compressive stresses, σ, applied in the [001] direction by neutron diffraction. The tetragonality c/a has decreased continuously from 1 to 0.907 with an increase in |σ| up to |σ| = 280 MPa; the corresponding lattice strain in the [001] direction, due to the continuous structure change, increases from 0% to 6.1%. When the stress of 300 MPa is reached, c/a has changed abruptly from 0.907 to 0.789 due to a first-order martensitic transformation.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2014

Neutron diffraction studies for realtime leaching of catalytic Ni

The leaching of Al from intermetallic samples of Nickel Aluminium alloys to form Raney-type nickel catalysts is widely used in the hydrogenation industry, however, little is known of the leaching process itself. In this study, the leaching of Al was measured in realtime, in situ, using the high-flux powder neutron diffractometer, D20, at the Institut Laue-Langevin. Despite the liberation of hydrogen and effervescent nature of the reaction the transformation of the dry powder phases into Raney-type Ni was determined. Samples produced by gas-atomisation were found to leach faster than those produced using the cast and crushed technique. Regardless of processing route of the precursor powder, the formation of spongy-Ni occurs almost immediately, while Ni{sub 2}Al{sub 3} and NiAl{sub 3} continue to transform over longer periods of time. Small-angle scattering and broadening of the diffraction peaks is an evidence for the formation of the smaller Ni particles. Understanding the kinetics of the leaching process will allow industry to refine production of catalysts for optimum manufacturing time while knowledge of leaching dynamics of powders produced by different manufacturing techniques will allow further tailoring of catalytic materials.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2014

Direct observation of intrinsic piezoelectricity of Pb(Zr,Ti)O{sub 3} by time-resolved x-ray diffraction measurement using single-crystalline films

Lead zirconate titanate, Pb(Zr,Ti)O{sub 3} or PZT, is one of the most widely investigated ferroelectric and piezoelectric materials due to its superior properties. However, the intrinsic properties of PZT have not been directly measured due to the lack of fabrication of single crystals even though a basic understanding of intrinsic properties has been of interest developing lead-free piezoelectric materials. We demonstrated the direct observation of the intrinsic piezoelectric property by means of the detection of electric-field induced crystal lattice distortion of thick Pb(Zr{sub 0.35}Ti{sub 0.65})O{sub 3} single-crystalline films with single polar-axis orientation and negligible residual strain using the time-resolved X-ray diffraction (XRD) together with the polarization response. Consequently, the effective converse piezoelectric response was experimentally revealed; hence, the electrostrictive coefficient, which is the conversion coefficient between the electrical and mechanical response, was determined. The obtained effective electrostrictive coefficient was 5.2–6.3 × 10{sup −2} m{sup 4}/C{sup 2}, which agrees with theoretical prediction.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2014

Epitaxial polymorphism of La{sub 2}O{sub 3} on Si(111) studied by in situ x-ray diffraction

The phase formation of La{sub 2}O{sub 3} epitaxial films during growth on Si(111) is investigated by synchrotron-based in situ grazing incidence x-ray diffraction and high resolution transmission electron microscopy. We find that first a 2–4 nm thick cubic bixbyite La{sub 2}O{sub 3} layer grows at the interface to Si(111) substrate, followed by a hexagonal La{sub 2}O{sub 3} film. Hence, to keep a cubic on cubic heteroepitaxy and to achieve high quality epitaxial nanostructures or multi-layers, the thickness of the interfacial La{sub 2}O{sub 3} layer has to be restricted to 2 nm. The larger formation energy of the cubic phase can only partially be compensated by the biaxial strain in the epitaxial film based on density functional perturbation theory. Hence, the stabilization of the cubic phase is not due to bulk strain but could be related to a lower surface or interface free energy, or to kinetic effects.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2014

Boron phosphide under pressure: In situ study by Raman scattering and X-ray diffraction

Cubic boron phosphide, BP, has been studied in situ by X-ray diffraction and Raman scattering up to 55 GPa at 300 K in a diamond anvil cell. The bulk modulus of B{sub 0} = 174(2) GPa has been established, which is in excellent agreement with our ab initio calculations. The data on Raman shift as a function of pressure, combined with equation-of-state (EOS) data, allowed us to estimate the Grüneisen parameters of the TO and LO modes of zinc-blende structure, γ{sub G}{sup TO }= 1.26 and γ{sub G}{sup LO }= 1.13, just like in the case of other A{sup III}B{sup V} diamond-like phases, for which γ{sub G}{sup TO }> γ{sub G}{sup LO }≅ 1. We also established that the pressure dependence of the effective electro-optical constant α is responsible for a strong change in relative intensities of the TO and LO modes from I{sub TO}/I{sub LO} ∼ 0.25 at 0.1 MPa to I{sub TO}/I{sub LO} ∼ 2.5 at 45 GPa, for which we also find excellent agreement between experiment and theory.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2014

Highly constrained ferroelectric [BaTiO{sub 3}]{sub (1−x)Λ}/[BaZrO{sub 3}]{sub xΛ} superlattices: X-ray diffraction and Raman spectroscopy

We report an x-ray diffraction (XRD) and a Raman-scattering investigation of ferroelectric/paraelectric superlattices [BaTiO{sub 3}] {sub (1−x)Λ}/[BaZrO{sub 3}]{sub xΛ} for which the composition varied, 0.15 ≤ x ≤ 0.85, while the superlattice (SL) modulation period Λ was kept constant at about 100 Å. The samples were epitaxially grown by pulsed laser deposition on MgO substrates buffered with La{sub 0.5}Sr{sub 0.5}CoO{sub 3}. Based on the XRD analysis and on polarized Raman spectra, we have showed that the large strain in SLs induced ferroelectricity in BaZrO{sub 3} (BZ) for all SLs, a material that is paraelectric in the bulk form at any temperature and in the single film. The induced polar axis in BZ layers is perpendicular to the plane of substrate while BaTiO{sub 3} (BT) layers exhibit in-plane polar orientation. Raman spectroscopy revealed a lattice ordering in SLs due to the misfit strain generated by the large lattice mismatch between the alternating BZ and BT layers. This strain induced a huge upward frequency of the lowest E(1TO) soft mode from 60 cm{sup −1} in the BT single film to 215 cm{sup −1} in the SL with x = 0.85. These results show that in spite of relatively large periodicity of SLs, they are highly constrained and the variation of BZ ratio allowed modifying strains between layers. The temperature dependence of the Raman spectra for BT{sub 0.3Λ}/BZ{sub 0.7Λ} and BT{sub 0.7Λ}/BZ{sub 0.3Λ} samples revealed giant shift of the ferroelectric phase transition. The phase transition temperature was found to be upshifted by about 300 °C with respect to BT single crystal.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2014

In-situ neutron diffraction study of martensitic variant redistribution in polycrystalline Ni-Mn-Ga alloy under cyclic thermo-mechanical treatment

The influences of uniaxial compressive stress on martensitic transformation were studied on a polycrystalline Ni-Mn-Ga bulk alloy prepared by directional solidification. Based upon the integrated in-situ neutron diffraction measurements, direct experimental evidence was obtained on the variant redistribution of seven-layered modulated (7M) martensite, triggered by external uniaxial compression during martensitic transformation. Large anisotropic lattice strain, induced by the cyclic thermo-mechanical treatment, has led to the microstructure modification by forming martensitic variants with a strong 〈0 1 0〉{sub 7M} preferential orientation along the loading axis. As a result, the saturation of magnetization became easier to be reached.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗