Control on arrangement of AgI clusters incorporated into zeolite LTA

AgI clusters were incorporated into Li, Na, and K-form LTA zeolites with a loading number of four AgI molecules per -cage. The X-ray powder diffraction (XRD) patterns and optical absorption spectra of the samples were obtained. The XRD patterns indicate that the sizes of the clusters and their arrangements depend on the type of alkali-cations. AgI clusters with different sizes, i.e., (AgI)_n and (AgI)_8–n (5n7), are arrayed alternatively in Na-form LTA conforming to the space group of P2₁3. AgI-loaded Li-form LTA also conformed to the space group of P2₁3, although (AgI)_n clusters seem to be distributed disorderly. On the contrary, (AgI)₄ cluster is in each cage in K-form LTA conforming to the space group of or . The optical spectra showed that Li and Na-form LTAs include (AgI)_n (5 n), and that K-form LTA includes (AgI)₄ cluster in each cage.     

Morphological and structural characterizations of CrSi2 nanometric films deposited by laser ablation

The structure and morphology of chromium disilicide (CrSi₂) nanometric films grown on 〈1 0 0〉 silicon substrates both at room temperature (RT) and at 740 K by pulsed laser ablation are reported. A pure CrSi₂ crystal target was ablated with a KrF excimer laser in vacuum (∼3 × 10⁻⁵ Pa). Morphological and structural properties of the deposited films were investigated using Rutherford backscattering spectrometry (RBS), grazing incidence X-ray diffraction (GID), X-ray reflectivity (XRR), scanning (SEM) and transmission electron microscopy (TEM). From RBS analysis, the films’ thickness resulted of ∼40 nm. This value is in agreement with the value obtained from XRR and TEM analysis (∼42 and ∼38 nm, respectively). The films’ composition, as inferred from Rutherford Universal Manipulation Program simulation of experimental spectra, is close to stoichiometric CrSi₂. GID analysis showed that the film deposited at 740 K is composed only by the CrSi₂ phase. The RT deposited sample is amorphous, while GID and TEM analyses evidenced that the film deposited at 740 K is poorly crystallised. The RT deposited film exhibited a metallic behaviour, while that one deposited at 740 K showed a semiconductor behaviour down to 227 K.     

Release time calculations for the SPES direct UCx target

A Direct Target for a mid-term RIB ISOL-type facility is being developed at LNL, in the framework of the R&D for the SPES project [1]. Using a 40 MeV proton beam impinging on a UCx thick target of 2.5 g/cm³ density, a production rate of 10¹³ in target fissions per second is expected [2]. The crucial point, when short-lived isotopes are produced in the target, is to build systems (target + ion source) with good release properties and high efficiency. Monte Carlo simulations were performed using the GEANT4 toolkit [3] and the RIBO code [4] in order to optimize our target geometry and to estimate the average release time.     

Thermal expansion behaviors of hcp and fcc Co nanowire arrays

The lattice parameters of as-prepared and annealed Co nanowires with hcp and fcc structures have been measured using the in situ high-temperature x-ray diffraction method. The hcp and fcc Co nanowires have been fabricated within the porous anodic alumina membranes by a direct-current electrodeposition technique. The results indicate that the variational quantity of the interplanar spacing for hcp Co nanowire arrays is bigger than that for fcc Co nanowire arrays in spite of as-prepared and annealed samples. The structural difference between hcp and fcc Co nanowires results in the different thermal expansion behaviors.     

Fine structure effects and phase transition of Xe nanocrystals in Si

We report on an X-ray diffraction study performed on Xe agglomerates obtained by ion implantation in a Si matrix. At low temperature, Xe nano-crystals were formed in Si with different average sizes according to the preparation procedure. High resolution diffraction spectra were detected as a function of the temperature, in the range 15–300 K, showing evidence of fine structure effects in the growth mode of the Xe nanocrystals. We report the first experimental observation of fcc crystalline agglomerates with a lattice parameter expanded by the epitaxial condensation on the Si cavities, whereas for small agglomerates randomly oriented evidence of a contracted lattice was found. For these nanocrystals, a solid-to-liquid transition temperature, size dependent, was detected; above the transition temperature, a fluid phase was observed. Neither overpressurized clusters were detected at any temperature, nor preferential binary size distribution as reported for a metal matrix.     

Shear modulus and compliance in the range of the dynamic glass transition for metallic glasses

High-resolution synchrotron-radiation powder diffraction experiments were performed to observe structural changes induced by hydrogen loading in rapidly-quenched Ti-Zr-Ni alloy ribbons with dominant icosahedral character. Lattice expansion effects due to hydrogen storage in Ti-Zr-Ni quasicrystals as well as phonon and phason disorder coefficients are obtained from an analysis of diffraction linewidths. Received: 26 August 1997 / Revised: 8 January 1998 / Accepted: 10 February 1998     

pH-dependent kinetics of MgCl2 adsorption under a fatty-acid Langmuir film

The effect of subphase pH (5.5 and 10.5) on the structure of behenic-acid monolayers was investigated during Mg²⁺ adsorption by means of Grazing Incidence X-ray Diffraction (GIXD) and Brewster Angle Microscopy (BAM). The final phase corresponding to an ion superlattice commensurate to the behenic-acid cell is pH-independent. In contrast, the sequence of phases evidenced from the initial L₂-phase to this final state presents at pH 10.5 an additional stage associated to a film condensation toward the L' ₂-phase. The structures of the intermediate states preceding the superstructure nucleation are slightly different, both with a short-range fatty-acid order. Finally, a laser light effect that could result from visible light absorption by the inorganic complexes is evidenced in the final state as well as in the intermediate phases.     

Pressure-induced phase transitions of lanthanide monoarsenides LaAs and LuAs with a NaCl-type structure

By use of synchrotron radiation the powder X-ray diffraction of lanthanide monoarsenides LaAs and LuAs with a NaCl-type structure has been studied up to 60 GPa at room temperature. First-order phase transitions with the crystallographic change were found at around 20 GPa for LaAs, and 57 GPa for LuAs. The high-pressure form of LaAs is a tetragonal structure and can be viewed as a distorted CsCl-type structure. The atoms in the tetragonal structure are located at La: 0, 0, 0; As: 1/2, 1/2, 1/2. The space group is P4/mmm. The structural change to the tetragonal structure occurs with the volume collapse of about 10%. The structure of these high-pressure phases of LuAs is unknown. The volume vs. pressure curves for LaAs and LuAs are fitted by a Birch equation of state. The bulk moduli of both arsenides are 92±6 GPa for LaAs and 85±3 GPa for LuAs. The high-pressure structural behavior of LaX (X=P, As and Sb) and LnAs (Ln=lanthanide) with the NaCl-type structure is discussed.     

Structural and optical properties of thermal evaporated magnesium phthalocyanine (MgPc) thin films

X-ray powder diffraction (XRD) of MgPc indicated that the material in the powder form is polycrystalline with monoclinic structure. Miller indices, h k l, values for each diffraction peak in XRD spectrum were calculated. Thermal evaporation technique was used to deposit MgPc thin films. The XRD studies were carried out for MgPc thin films where the results confirm the amorphous nature for the as-deposited films. While, polycrystalline films orientated preferentially to (1 0 0) plane with an amorphous background were obtained for films annealed at 623 K for 3 h. Optical properties of MgPc thin films were characterised by using spectrophotometric measurements of transmittance and reflectance in the spectral range from 190 to 2500 nm. The refractive index, n, and the absorption index, k, were calculated. According to the analysis of dispersion curves, the parameters, namely; the optical absorption coefficient (α), molar extinction coefficient (?_molar), oscillator energy (E_os), oscillator strength (f), and electric dipole strength (q²) were also evaluated. The recorded absorption measurements in the UV-vis region show two well defined absorption bands of phthalocyanine molecule; namely the Q-band and the Soret (B-band). The Q-band showed its splitting characteristic (Davydov splitting), and ΔQ was obtained as 0.15 eV. The analysis of the spectral behaviour of the absorption coefficient (α), in the absorption region revealed indirect transitions. The transport and the near onset energy gaps were estimated as respectively 2.74 ± 0.02 and 1.34 ± 0.01 eV.     

Structural phase transition of ScSb and YSb with a NaCl-type structure at high pressures

By use of synchrotron radiation, powder X-ray diffraction of ScSb and YSb with a NaCl-type structure has been studied up to 45 GPa at room temperature. A first-order phase transition from the NaCl-type (B1) to a CsCl-type structure (B2) began to occur at around 28 GPa for ScSb and at around 26 GPa for YSb. Crystal data of the high-pressure phase of both antimonides are obtained. The high-pressure structural behavior of ScSb and YSb is similar to that of heavier LnSb (Ln=Dy-Lu). The B1-B2 transition for ScSb and YSb can be understood according to the rigid sphere model. The bulk moduli of ScSb and YSb are about 58 GPa at ambient pressure.     

The Al-Pd-Mn quasicrystalline approximant -phase revisited

A detailed investigation of the Fourier space of several Al-Pd-Mn samples with composition Al-72.6 at. %, Pd-22.9 at. %, Mn-4.5 at. % is reported. In the phase diagram of the Al-Pd-Mn ternary alloy, this composition corresponds to the so-called ξ' phase which was described as an icosahedral quasicrystalline approximant. By re-examining the Fourier space by means of X-ray diffraction (powder patterns and single crystal precession patterns), complex structures in close relation with the ξ'-phase have been observed. These long-range order complex structures are described as resulting from a periodic perturbation of the ξ' structure along the c direction. Two states with periodicities c (3 + τ) and c (5 + τ) have been observed in this study (τ: golden mean). Structural models based on periodic arrangements of “defects” layers separating layers of phase are proposed. These two states are certainly intermediate states between the phase and the metastable decagonal quasicrystalline phase. Received 11 April 2002 / Received in final form 24 June 2002 Published online 17 September 2002     

Interplay between the local structural disorder and the length of structural coherence in stabilizing the cubic phase in nanocrystalline ZrO2

The atomic-scale structure of three nanocrystalline ZrO₂ samples obtained by different techniques and possessing a different length of structural coherence has been studied using high-energy X-ray diffraction and the atomic pair distribution function technique. The studies reveal that all samples show a monoclinic-like local atomic ordering. Only when the length of structural coherence exceeds 1 nm the atomic arrangement evolves into a cubic-type one. The result underlines the importance of both the local structural disorder and the length of structural coherence, i.e. the spatial extent of longer-range atomic order, in stabilizing the technologically important cubic zirconia at room temperature.     

Structure and dielectric properties of (Na0.50Bi0.50)1−xBaxTiO3: 0≤x≤0.10

Solid solution of (1−x)Na_0.5Bi_0.5TiO₃-xBaTiO₃ is investigated in the composition range 0.00≤x≤0.10. It is shown that the system exhibits rhombohedral structure up to x=0.055 and then becomes ‘nearly cubic’ for x≥0.06. Temperature dependent dielectric measurements reveals three peaks in the imaginary part of the dielectric constant for compositions exhibiting rhombohedral as well as ‘nearly cubic’ structures. The first of these three peaks exhibits Vogel-Fulcher type relaxation behaviour.     

Strain relaxation of epitaxial SiGe layer and Ge diffusion during Ni silicidation on cap-Si/SiGe/Si(0 0 1)

Strain relaxation of the epitaxial SiGe layer and Ge diffusion during nickel silicidation by rapid thermal annealing the structure of Ni(≅14 nm)/cap-Si(≅26 nm)/Si_0.83Ge_0.17/Si(0 0 1) at the elevated annealing temperatures, T_A, were investigated by X-ray diffraction analyses of high-resolution ω-2θ scan and reciprocal space mapping. The analyses showed a much larger strain relaxation at a lower T_A and a reduction in Ge content in the SiGe layer of Ni/SiGe/Si(0 0 1) after thermal annealing compared to the case of cap-Si/SiGe/Si(0 0 1). The results indicate that the strain relaxation of the SiGe layers in NiSi/SiGe/Si(0 0 1) is related to the phenomena of NiSi agglomeration and penetration into the SiGe layer during silicidation at elevated anneal temperatures ≥750 °C. At elevated T_A ≥ 750 °C, Ge diffused into the intact cap-Si area during silicidation.     

Optical and electrical properties of PbTe films grown by laser induced evaporation of pressed PbTe pellets

A simple and cheap method has been developed for the deposition of lead telluride thin films on glass substrates by pulsed Nd:YAG laser evaporation of lead telluride pellets made of high purity Pb and Te powders.Preliminary characterization of the crystallographic and optical properties of the films has been performed as a function of the substrate temperature.The influence of deposition conditions on the sheet resistance of these thin films has been studied. Both deposition temperature, nitrogen pressure during deposition, and addition of Ga and As impurities in the source pellets have been considered.     

Extension of the resonant scattering technique to liquid crystals without resonant element

We report X-ray resonant scattering experiments performed on the prototype liquid-crystalline compound MHPOBC doped with a chemical probe containing a resonant atom (selenium). We determined directly for the first time the microscopic 3- and 4-layer structure of the ferrielectric subphases ( SmC_FI1^* and SmC_FI2^*) present in MHPOBC. Despite the low fraction of the selenium probe, the resonant signal is strong enough to allow an unambiguous determination of the basic structure of the ferrielectric subphases. These experiments demonstrate that the resonant scattering technique can be extended to liquid crystalline materials without resonant element and may stimulate new studies. A non-resonant Bragg reflection was also found in the SmC_FI1^* phase in pure MHPOBC, consistent with the 3-layer distorted model, but never detected before.     

Comparison of focusing optics for femtosecond X-ray diffraction

We characterize and compare four different types of focusing optics for hard X-rays, suitable for femtosecond X-ray diffraction experiments, usinga tabletop femtosecond laser-based plasma source. We demonstrate a 23 μmfocus with a toroidally bent Ge single crystal. A maximum flux of 7× 10⁸ photons/(s mm²) is generated in a 32 μm focus using a multi-layer mirror. An elliptical glass capillary yields the highest number of photons per Bragg angle [2× 10⁵ photons/(s mrad)]. The largest number of photons[3× 10⁶ photons/s] per second is obtained in the 105 μm focus of a poly-capillary optical lens system. All numbers are given for characteristic Cu K _α photons.This revised version was published online in May 2005. The Article Category was removed.This revised version was published online in August 2005 with a corrected cover date.     

Phase analysis of TaN/Ta barrier layers in sub-micrometer trench structures for Cu interconnects

The resistance behavior of TaN/Ta diffusion barrier bilayers has been investigated. The dependence of the Ta-phase on the TaN layer thickness was examined by means of X-ray micro-diffraction and resistivity measurements. Furthermore, the influence of the geometry of a damascene trench structure on the Ta-phase of the deposited TaN/Ta barrier bilayers has been studied and compared to the results obtained with blanket wafers. The influence of the Ta-phase on the via resistance of Cu interconnects is discussed.     

Synthesis and structure of the monolayer hydrate K0.3CoO2·0.4H2O

The monolayer hydrate (MLH) K_0.3CoO₂·0.4H₂O was synthesized from K_0.6CoO₂ by extracting K⁺ cations using K₂S₂O₈ as an oxidant and the subsequent intercalation of water between the layers of edge-sharing CoO₆ octahedra. A hexagonal structure (space group P6₃/mmc) with lattice parameters a=2.8262(1) Å, c=13.8269(6) Å similar to the MLH Na_0.36CoO₂·0.7H₂O was established using high-resolution synchrotron X-ray powder diffraction data. The K/H₂O layer in the K-MLH is disordered, which is in contrast to the Na-MLH. At low temperatures metallic and paramagnetic behavior was found.     

Synthesis and structure of aluminum substituted MoSi2

Mo(Si_1−xAl_x)₂ compositions have been prepared by a modified SHS route under pressure. The compositional phase analysis indicates a body centered tetragonal C11_b phase below x<0.05 substitution, above which a biphasic region of C11_b and C40 structure coexists. Occurrence of pure hexagonal C40 phase is observed for x>0.1. The aluminum substitution leads to a continuous increase in the lattice parameters in both these structures. In the biphasic region, redistribution of aluminum concentration takes place with the evolution of aluminum rich C40 phase as indicated by energy dispersive X-ray analysis and supported by micro-hardness measurements.