X-ray diffraction analysis of the surface acoustic wave propagation in langatate crystal

X-ray diffraction on a langatate crystal (La₃Ga_5.5Ta_0.5O₁₄, LGT) modulated by a Λ=12 μm Rayleigh surface acoustic wave (SAW) was studied in a double axis X-ray diffractometer scheme at the BESSY synchrotron radiation source. SAW propagation in the crystal causes sinusoidal modulation of the crystal lattice and the appearance of diffraction satellites on the rocking curves, with their number, angular positions, and intensities depending on the wavelength and amplitude of acoustic vibrations of the crystal lattice. Strong absorption of X-ray radiation in LGT enables the observation of the diffraction spectra extinction at certain SAW amplitudes. X-ray diffraction spectra analysis makes it possible to determine SAW amplitudes and wavelengths, to measure the power flow angles, and investigate the diffraction divergence in acoustic beam in LGT.     

Purity of rubrene single crystals

Liquid chromatography connected with mass spectroscopy reveals that the oxidized form of rubrene is the major impurity in commercial powder of rubrene as well as in rubrene single crystals. One form of rubrene impurity can be transformed into the other. In solution, rubrene undergoes photo-oxidation completely until the red color of the rubrene solution disappears. Single crystals, due to compact packing of molecules and the required molecular shape change during oxidation, oxidize only on the surface.     

Er<Superscript>3+</Superscript> as glass structure modifier of Ga–Ge–S chalcogenide system

Er³⁺ clustering phenomenon in Ga–Ge–S chalcogenide system is studied using Raman spectroscopy. The Raman spectra from 10 to 500 cm⁻¹ for glasses (100−y)[15Ga₂S₃–85GeS₂]–yEr₂S₃ (y=0.08−5.00 mol. %) have been analyzed. To reveal the influence of the chemical composition on the glass structure the intensity of the peak corresponding to Ge–Ge (Ga–Ga) homopolar bonds has been examined. The peak intensity increase with Er₂S₃ concentration change in the region 0<C(Er₂S₃)<2 mol. % has been interpreted in terms of the sulphur deficiency in the glass resulting in the formation of S₃Ge–GeS₃ (S₃Ga-GaS₃) structural units. The further increase in concentration beyond 2 mol. % reduces the sulphur deficiency, which can be attributed to the formation of the ternary compound Er₃GaS₆. The structural units Er₃GaS₆ contain a large mol. fraction of Er³⁺ or, in other words, Er³⁺ clusters. The data obtained from the low-frequency Raman spectra (boson band) indicate strong variations of the medium-range order (MRO) in the glasses induced by Er³⁺. The observed behavior of the MRO size (the correlation length) with increasing of Er₂S₃ concentration provides for additional evidence of the Er³⁺ clustering.     

Origin of the defect states at ZnS/Si interfaces

Electrical characterisation of silicon surfaces contaminated by a zinc-sulphide overlayer has been carried out by forming Schottky diodes on the silicon after the ZnS has been etched off. The techniques include current-voltage, capacitance-voltage, and deep-level transieni spectroscopy. The Schottky diodes show clear memory of the presence of the ZnS overlayer and the electrical characteristics are far from ideal. Five deep levels in the sub-surface region of the silicon are detected, corresponding to the Zn⁺, Zn⁺⁺, S^–, S^–– states and probably to a Zn–B complex (p-type). Diffusion of the zinc and sulphur into the silicon is therefore confirmed and this diffusion is thought to create a compensated layer at the interface. These impurity states control the electrical characteristics of the surface in these diodes.     

Real-time X-ray diffraction measurements of structural dynamics and polymorphism in diindenoperylene growth

We investigate the temperature-dependent polymorphs in diindenoperylene (DIP) thin films on sapphire and silicon oxide substrates using in situ X-ray scattering. On both substrates the DIP unit cell is very similar to the high-temperature phase of bulk crystals, with the substrate stabilising this structure well below the temperature where a phase transition to a low-temperature phase is observed in the bulk. Lowering the substrate temperature for DIP growth leads to a change in molecular orientation and an additional polymorph appears, with both these effects being more pronounced on sapphire as compared to silicon oxide. Using real-time reciprocal-space mapping we observe an expansion of the in-plane unit cell during DIP growth, which may be due to changes in molecular orientation as well as strain in the first monolayers. Electronic Supplementary Material  The online version of this article () contains supplementary material, which is available to authorized users.     

Maximum excitation energy in fusion-evaporation reactions from light particle multiplicity measurements in32S+58Ni at 25 MeV/A

By using two 4 detector systems for charged particles and neutrons, we measured the evaporated light particles emitted in coincidence with evaporation residues (ER) produced in the reaction³²S+⁵⁸Ni atE(³²S) 820 MeV. From the analysis of the light particle multiplicities as a function of the ER velocity, we extracted the maximum excitation energy reached in fusion evaporation reactions for the studied system.Supported by the European Community Programme Human Capital and Mobility     

Flattop operation of the ILC accelerating cryomodule

A 500 GeV center-of-mass International Linear Collider (ILC), currently under R&D development, is foreseen as the next-generation high-energy physics (HEP) instrument [1]. The achievement of a 31.5 MV/m average operational accelerating gradient in a single cryomodule is a proof of principle for the ILC project. However, individual cavity performance may have a large spread in operating gradients, up to 20% of the nominal value [2, 3]. In case of cavities performing below the average, the design parameters could be achieved by tweaking the RF distribution accordingly. We present a simple theoretical analysis of the ILC cryomodule operation with a gradient spread. The difference in the gradients breaks the synchronism of a transient processes in each cavity and causes nonuniform acceleration along the bunch train. A proper solution was found to maintain flattop operation of the accelerating module. Finally, we perform numerical efficiency estimations for the proposed RF distribution scheme based on real data of the gradient spread of actual cavities. The text was submitted by the authors in English.     

The use of linear superconducting electron accelerator for subcritical reactor driving

At the National Science Centre, Kharkiv Institute of Physics and Technology (NSC KIPT) the possibility of creating an installation with a subcritical reactor driven by an electron accelerator is examined. To obtain the maximal stream of neutrons from a neutron-producing target at a minimal density of energy emission, the electron energy should be in the range of 100–200 MeV and the size of the target should be as large as possible. Other important requirements are beam continuity with time and long-term stability of the accelerator parameters. The variants of using the superconducting linear accelerator on the basis of a TESLA accelerating structure as of subcritical reactor driver are considered. The basic design parameters and characteristics of this installation are presented. The text was submitted by the authors in English.     

Enhanced magnetization of nanoparticles of Mg x Fe(3? x )O4 (0.5≤ x ≤1.5) synthesized by combustion reaction

For the first time nanocrystalline magnetic particles of Mg _x Fe_(3−x)O₄ with x ranging from 0.5 to 1.5 have been synthesized by a combustion reaction method using iron nitrate Fe(NO₃)₃.9H₂O, magnesium nitrate Mg(NO₃)₂.6H₂O, and urea CO(NH₂)₂ as fuel without intermediate decomposition and/or calcining steps. X-ray diffraction patterns of all systems showed broad peaks consistent with cubic inverse spinel structure of MgFe₂O₄. The absence of extra reflections in the diffraction patterns of as-prepared materials ensures the phase purity. The mean crystallite sizes determined from the prominent (311) peak of the diffraction using Scherrer’s equation and transmission electron microscopy micrographs were c.a. 40 nm with spherical morphology. Fourier transform infrared spectra of the as-prepared material showed traces of organic and metallic salt by-products; however, these could be removed by washing with deionized water. Typical hysteresis curves were obtained for all specimens in magnetic field up to 14 T between 4 and 340 K. The saturation magnetization was 48.3 emu/g and 31.3 emu/g, 44.8 emu/g, and 28.4 emu/g for x=1.0 and 0.8 at 4 K and 340 K, respectively. The saturation magnetization, M _s , of nanoparticles of the MgFe₂O₄ specimen is about 50% higher when compared to the bulk. The enhanced magnetization measured in our nanoparticles MgFe₂O₄ specimens may be attributed to the uncompensated magnetic moment of iron ions between the A- and B-sites, i.e., changes in the inversion factor. Our magnetization results of MgFe₂O₄ specimens are comparable to the existing data for the same compound but with different particle size and prepared by different synthesis methods.     

Magnetotransport properties of La<Subscript>0.67</Subscript>Ca<Subscript>0.33</Subscript>MnO<Subscript>3</Subscript> with different grain sizes

The magnetotransport and magnetoresistive (MR) properties of manganese-based La_0.67Ca_0.33MnO₃ perovskite with different grain sizes are reported. The electrical resistivity was measured as a function of temperature in magnetic fields of 0.5 and 1 T. The insulator–metal transition temperature, T _IM, shifted to a higher temperature with the application of the magnetic field. In zero field, T _IM is almost constant (∼271 K) for all samples except for the sample with the largest grain size, where T _IM=265 K. The temperature dependence of resistivity was fitted with several equations in the metallic (ferromagnetic) region and the insulating (paramagnetic) region. The density of states at the Fermi level, N(E _F), and the activation energy of electron hopping were estimated by fitting the resistivity versus temperature curves. The ρ–T ² curves are nearly linear in the metallic regime, but the ρ–T ^2.5 curves exhibit a deviation from linearity. The variable range hopping model and small polaron hopping model fit the data well in the high-temperature region, indicating the existence of the Jahn–Teller distortion that localizes the charge carriers. MR was found to increase with an increase in the magnetic field, an effect which is attributed to the intergrain spin tunneling effect.     

Structural and electrical properties of iron molybdenum phosphate glasses

Summary  Iron molybdenum phosphate glasses [xMoO₃ · (0.6 -x)P₂O₅ · 0.4Li₂O] :yFe₂O₃ with 0 ≤x ≤ 0.6 andy = 0.03 (mol%) prepared in ambient atmosphere using the melt quenching technique were studied by using DC electrical conductivity,⁵⁷Fe M?ssbauer and infrared spectroscopies. The DC conductivity depends on the MoO₃ concentrationx. It was observed that, with increasingx, the ratio Fe²⁺ /(Fe³⁺ + Fe²⁺) and the DC conductivity increase. Infrared spectroscopy and X-ray powder diffraction indicate that a Li₂ MoO₄ crystalline phase is present for high MoO₃ content samples (x = 0.5, 0.6). This work was partly sponsored by FINEP, CNPq (Brazilian agencies) and UECE (Universidade Estadual do Cearà).     

Electronic and structural properties of graphene-based transparent and conductive thin film electrodes

We demonstrate that graphene-based transparent and conductive thin films (GTCFs), fabricated by thermal reduction of graphite oxide, have very similar electronic and structural properties as highly oriented pyrolytic graphite (HOPG). Electron spectroscopy results suggest that the GTCFs are also semi-metallic and that the individual graphene sheets of the film are predominantly oriented parallel to the substrate plane. These films may therefore be considered as a technologically relevant analogue to HOPG electrodes, which cannot be easily processed into thin films.     

Non-stoichiometric oxide and metal interfaces and reactions

We have employed a combination of experimental surface science techniques and density functional calculations to study the reduction of TiO₂(110) surfaces through the doping with submonolayer transition metals. We concentrate on the role of Ti adatoms in self doping of rutile and contrast the behaviour to that of Cr. DFT+U calculations enable identification of probable adsorption structures and their spectroscopic characteristics. Adsorption of both metals leads to a broken symmetry and an asymmetric charge transfer localised around the defect site of a mixed localised/delocalised character. Charge transfer creates defect states with Ti 3d character in the band gap at ∼1-eV binding energy. Cr adsorption, however, leads to a very large shift in the valence-band edge to higher binding energy and the creation of Cr 3d states at 2.8-eV binding energy. Low-temperature oxidation lifts the Ti-derived band-gap states and modifies the intensity of the Cr features, indicative of a change of oxidation state from Cr³⁺ to Cr⁴⁺. Higher temperature processing leads to a loss of Cr from the surface region, indicative of its substitution into the bulk.     

Electronic structure and self-assembling processes in platinum metalloporphyrins: photoemission and AFM studies

The main goal of this paper is to investigate the electronic structure of valence band and core levels as well as surface topography of pristine tetraphenylporphyrin and Pt-based compounds Pt-TPP(p-COOH₃)₄, Pt-TPP(m-OCH₃)₄, PtCl₂-TPP(m-OCH₃)₄ thin films. The electronic structure of various Pt-based metalloporphyrins which were investigated in dependence on their chemical structure and spectra were measured by high-resolution X-ray photoelectron spectroscopy (XPS) of valence band and Pt4f, Pt4d, C1s, O1s, N1s core levels. Results of atomic force microscopy (AFM) studies of topography and self-assembling processes in thin films of porphyrines are presented and discussed.     

Evidence for formation of Se molecular clusters during precipitation of CdSe<Subscript>1−<Emphasis Type="Italic">x</Emphasis></Subscript>S<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript> nanoparticles in glass

While studying the effect of thermal treatment at 625–700°C on the formation of borosilicate glass-embedded CdSe or CdSe_1−x S _x nanocrystals, pronounced bands at 323 and 646 cm⁻¹ were observed in the Raman spectra. They are assigned to Se₂ clusters on the base of their frequency positions, widths, intensities, and resonance behavior. The precipitation of Se₂ molecular clusters in borosilicate glass is shown to occur when the heat treatment temperature and/or duration are beyond the range, most suitable for the formation of CdSe or CdSe-rich CdSe_1−x S _x nanocrystals.     

Entrance channel effects on preequilibrium emission and incomplete fusion in Promptly Emitted Particle model

In intermediate energy heavy ion collision prompt particles emitted in the early stages of the reaction affect the properties of the incompletely fused composite. We have studied the entrance channel effects on preequilibrium proton emission and various observables, like temperature, residual velocity, and linear momentum transfer of the incompletely fused residue, in the framework of Promptly Emitted Particle (PEP) model. The calculated preequilibrium proton energy spectra for Oxygen and Sulphur induced reactions on various targets have been confronted with the respective experimental data and the agreement between the two has been found to be quite satisfactory. Proton multiplicity has been found to decrease/increase with the increase in target/projectile mass. Residual velocity and linear momentum transfer have been found to have weak dependance on target mass. With the increase in incident energy, the calculation predicts a tendency towards limiting the temperature of the residue for all the target masses. The limiting temperature has been found to decrease with increase in the mass of the residue which is in accordance with the experimental observations.One of the authors (S.D) is thankful to R. Auble and his collaborators at Oak Ridge National Laboratory, for providing the experimental data. The authors would also like to thank Dr. S.K. Basu for his help in running the code PACE2.     

Influence of pre-fission neutron emission on fission fragment angular distribution for the system209Bi +16O

The data of fission fragment anisotropies measured for the system¹⁶O +²⁰⁹Bi in the centre of mass energy region of 73 to 95 MeV have been compared with the saddle point statistical model calculations. The corrections to the nuclear temperature and the spin distribution arising due to pre-fission neutron emission have been made. While the resultant calculations reproduce very well the data in the near- and sub-barrier energy regions, they deviate from the data at higher energies. This observation is similar to what was already reported for¹⁶O +²⁰⁸Pb system.     

Mechanism of enhanced yield of light particles in compound nucleus formation: Diffusion description

In the formation of a compound nucleus the evolution of a dinuclear system is considered. The enhanced yield of light particles for some reactions is explained by the dynamic reasons. The role of quantum and thermal fluctuations is discussed. The results of the previous paper are confirmed.Authors wish to thank Prof. V.V. Volkov for his active attention and comments.