The Absorption Spectrum of UF6, from 2000 to 4200 Å

The absorption spectrum of UF₆ between 3400 and 4200 Å, is well-documented,^(1–3) but the region below 3400 Å has not been studied in any detail. We present here a spectrum of UF₆ between 2000 and 4200 Å that shows significant structure below 3400 Å. The absorption in this region must be observed at very low pressures and relatively short path lengths.     

Data analysis method to achieve sub‐10 pm spatial resolution using extended X‐ray absorption fine‐structure spectroscopy

Obtaining sub‐10 pm spatial resolution by extended X‐ray absorption fine structure (EXAFS) spectroscopy is required in many important fields of research, such as lattice distortion studies in colossal magnetic resistance materials, high‐temperature superconductivity materials etc. However, based on the existing EXAFS data analysis methods, EXAFS has a spatial resolution limit of π/2Δk which is larger than 0.1 Å. In this paper a new data analysis method which can easily achieve sub‐10 pm resolution is introduced. Theoretically, the resolution limit of the method is three times better than that normally available. The method is examined by numerical simulation and experimental data. As a demonstration, the LaFe_1–xCr_xO₃ system (x = 0, 1/3, 2/3) is studied and the structural information of FeO₆ octahedral distortion as a function of Cr doping is resolved directly from EXAFS, where a resolution better than 0.074 Å is achieved.     

Lattice imaging of close-packed structures by high resolution electron microscopy: ABO3 perovskite polytypes

Lattice imaging technique of high resolution electron microscopy has been employed to examine 4H, 6H and 9R ABO₃ perovskite polytypes. The lattice images can be correlated with the lattice periodicity and the stacking sequence of AO₃ layers and BO₆ octahedra. The study shows the utility and validity of the lattice imaging technique for the study of relatively close-packed systems. Commonwealth Visiting Professor, University of Oxford (1974–75).     

Kontrastreiche und von Aufladungsstörungen freie Abbildung hochisolierender Oberflächen mittels Sekundärelektronen

The apparent secondary electron yield from metal surfaces (Au, W, Al, Zn, Ag, Ni and Cu) with a polymeride layer of varying thickness was measured. It was found that even with a layer thickness of as much as 40 Å and a primary energy of 25 kev there were clearly noticeable differences in emission from the various substances. This effect can be used for the electron emission microscopy of specimens consisting of insulating materials. In some cases, satisfactory images of such specimens could not be obtained in a reproducible way if other methods, e.g. Cevales' partial evaporation method were applied. If a carbon layer 30 Å in thickness was evaporated onto the insulating specimen surface byBradley's procedure, well contrasted images free from disturbances by surface charges could be obtained from specimens such as glass, thermally etched A1₂O₃ and other minerals. In these images, a resolution limit of 800 Å was attained.     

The ferroelectric phase transition in tridymite type BaAL2O4 studied by electron microscopy

The paraelectric-ferroelectric (PE-FE) phase transition in stuffed tridymite BaAl₂O₄ was studied in situ by transmission electron microscopy. Electron diffraction revealed that the PE and FE phases have hexagonal symmetry. The PE-FE phase transition is accompanied by a doubling of the cell dimensions in the a-b plane. The transition is reversible, takes place over a wide temperature range (400–670 K.) and the interfaces related to the transition have a fluctuating character. The crystal structure of the high temperature PE phase was determined by high resolution electron microscopy. The structures of the PE phase (space group P6₃22, a≈ 5.22 Å, c ≈ 8.8 Å) and of the FE phase (space group P6₃, a= 10.4469(1)Å, c = 8.7927(1)Å) differ mainly by the configuration of the Al-O strings oriented along the c-axis. In the PE phase all the strings are equivalent whereas straight and corrugated strings alternate in an ordered manner in the FE phase resulting in doubling of the a and b cell parameters. Translation and orientation domains due to the decrease of the translation and point symmetry were frequently observed.     

Oxidation of iron within the scanning electron microscope: Oxide crystallite growth kinetics during the oxidation of iron in CO2

The growth of magnetite (Fe₃O₄) on a polycrystalline iron substrate has been continuously followed in situ in the S.E.M. at 500°C in 13.3 N m^?2 CO₂. Medium resolution (250 Å) micrographs of the same area have been taken at time intervals over periods of oxidation in excess of 200 hr. Successive layers of oxide crystallites grow according to the same logarithmic rate law, but the overall thickening rate of the oxide film conforms to the parabolic rate law. A theoretical analysis of this situation suggests that the dominant factor determining the overall growth kinetics is the frequency of oxide nucleation steps. It can be shown that the basic logarithmic growth of individual oxide crystallites could lead to a variety of overall growth processes, depending upon the conditions required for nucleation.     

Observations of four-wave mixing processes in barium vapour

Emission at fifty discrete wavelengths is observed when Ba I is excited by two laser beams, a dye laser tuned to the λ 7911 Å intercombination line, 6s²¹S₀-6s6p ³P₁ and a ruby laser. The wavelengths range from 2312 Å to 8027 Å. Most of the emission lines can be attributed to four-wave mixing processes in barium.     

Ordered arrays of myoglobin adsorbed on the surfactant modified surface by scanning tunneling microscopy

Myoglobin molecules were deposited on a surfactant sodium dodecyl sulfate modified HOPG surface and imaged in air with a high resolution scanning tunneling microscope (STM) for the first time. STM images exhibit not only ordered arrays of the surfactant molecules but also regular two-dimensional arrays of myoglobin molecules. From STM images, the myoglobin molecule can be described as an ellipsoid-shaped pattern for the tertiary structure. In this study the dimensions of a myoglobin molecule were determined approximately as 43.0 × 36.2 × 8 ų, which are in good agreement with the known data from X-ray analysis, except for the height of a molecule which cannot be estimated from STM.     

Saturated absorption experiments using a free running CW dye laser

The hyperfine structure of some new iodine lines has been observed over the tuning range of Rhodamine 6G (5800–6200 Å), using a free running, single mode cw dye laser. The resolution obtained in this experiment allowed to calculate the hyperfine constants of the excited state (³π₀⁺) of iodine with an accuracy of 2% for the quadrupole coupling constant and 50% for the magnetic one.     

Use of grazing incidence X-ray diffraction for the study of nitrogen implanted stainless steels

The identification of Fe, Ni and Cr nitrides formed by nitrogen-ion implantation (4×10¹⁷ N⁺ cm^-2, 50 keV) in austenitic steels is performed by X-ray diffraction under very low glancing angles (0.00 ⩽ i ⩽ 1.5°). Spectra obtained with increasing angles i permit the investigation of layers with depths varying from 20 to more than 1000 Å. This non-destructive technique allows the surface to be controlled at each step of the treatments. Spectra were recorded on polished steel prior to and after implantation, with or without electrochemical attack. A 100 Å martensitic layer formed during the mechanical polishing is observed on the austenitic substrate. This layer is destroyed by an anodic attack before implantation of the samples. After implantation a CrN or carbonitride overlayer of a few tens of Å in thickness, may be observed. In the subjacent layers several iron and nickel nitrides are present, mainly ϵ-Fe₂N-Fe₃N, ς-Fe₂N and Ni₃N.     

Magnetooptical,optical, and magnetotransport properties of Co/Cu superlattices with ultrathin cobalt layers

We investigated the field dependences of the magnetization and magnetoresistance of superlattices [Co(t _x, Å)/Cu(9.6 Å)]30 prepared by magnetron sputtering, differing in the thickness of cobalt layers (0.3 Å ≤ t _Co ≤ 15 Å). The optical and magnetooptical properties of these objects were studied by ellipsometry in the spectral region of hω= 0.09–6.2 eV and with the help of the transverse Kerr effect (hω= 0.5–6.2 eV). In the curves of an off-diagonal component of the tensor of the optical conductivity of superlattices with t _Co = 3–15 Å, a structure of oscillatory type (“loop”) was detected in the ultraviolet region, resulting from the exchange splitting of the 3d band in the energy spectrum of the face-centered cubic structure of cobalt (fcc Co). Based on magnetic experiments and measurements of the transverse Kerr effect, we found the presence of a superparamagnetic phase in Co/Cu superlattices with a thickness of the cobalt layers of 3 and 2 Å. The transition from superlattices with solid ferromagnetic layers to superparamagnetic cluster-layered nanostructures and further to the structures based on Co and Cu (t _Co = 0.3–1 Å) with a Kondo-like characteristics of the electrical resistivity at low temperatures is analyzed.     

Atomic structure of a 1<Emphasis Type="Italic">T</Emphasis>-TiSe<Subscript>2</Subscript> surface layer from photoelectron and Auger electron holography data

A three-dimensional (3D) reconstruction of the atomic structure of the (100) surface of a 1T-TiSe₂ layered dichalcogenide crystal has been performed from X-ray photoelectron and Auger electron diffraction data. The diffraction patterns of the emission of Auger electrons of Se(LMM) selenium and photoelectrons of Ti2p titanium have been considered as holographic diagrams. Being processed with the scattering pattern extraction algorithm using the maximum entropy method (SPEA-MEM), they provide individual 3D images of the nearest environment of selenium and titanium atoms in the TiSe₂ lattice. Using reconstructed 3D images, the positions of 128 atoms in the 2 × 2 × 1.5-nm region of the surface layer of TiSe₂ have been determined. The structure of the surface has a 1T polytype. Interatomic distances in the layer and van der Waals gap are larger than the respective parameters in the bulk of the crystal. It is assumed that titanium layers in two Se-Ti-Se upper surface structural units are displaced along the [001] axis. The structure of the surface layer can be described by a unit cell of the P3 space group with the parameters a = 3.85 Å and c = 14.4 Å.     

A new one-dimensional hybrid material lattice: AC conductivity and structural characterization of [C<Subscript>7</Subscript>H<Subscript>12</Subscript>N<Subscript>2</Subscript>][CdCl<Subscript>4</Subscript>]

The present paper reports the synthesis, crystal structure, ¹³C and ¹¹¹Cd cross-polarization magic-angle spinning nuclear magnetic resonance(CP-MAS-NMR) analysis and ac conductivity for a new organic–inorganic hybrid salt, [C₇H₁₂N₂][CdCl₄]. The compound crystallizes in the triclinic system, space group P\( \overline 1 \), with unit cell dimensions: a?=?7.1050(3) Å, b?=?8.9579(3) Å, c?=?9.4482(3) Å, α?=?81.415(1)°, β?=?89.710(2)°, γ?=?85.765(1)°, V?=?592.97(4) Å³, and Z?=?2. The asymmetric unit is composed of one-2,4-diammonium toluene cation and one [CdCl₄]^2? anion. The Cd atom is in a slightly distorted octahedra coordination environment. Its structure can be described by infinite chains of CdCl₆ octahedron linked to organic cations by a strong charge-assisted N–H???Cl interactions in order to build organic–inorganic layers staked along \( \left[ {0\overline 1 1} \right] \) direction. The solid state ¹³C CP-MAS-NMR spectra has shown seven isotropic resonances, confirming the existence of seven non-equivalent carbon atoms, which is consistent with crystal structure determined by X-ray diffraction. As for ¹¹¹Cd MAS-NMR, it has shown one cadmium site with isotropic chemical shift observed at 167.2 ppm. The complex impedance of the compound has been investigated in the temperature range of 403–460 K and in the frequency range of 200 Hz–5 MHz. The impedance plots have shown semicircle arcs at different temperatures and an electrical equivalent circuit has been proposed to explain the impedance results. The circuits consist of the parallel combination of bulk resistance R _p and constant phase elements.     

Structure of 4,4′-butane-(1,4,7-three-p-tolylsulphonyl-1,4,7-three amine) diphthalonitrile

Abstract

The crystal structure of the title compound, C₄₁ H₃₅ N₇ O₆ S₃ was determined as monoclinic by single crystal X-Ray diffraction technique. The molecular structure was identified by IR, ¹H-NMR, ¹³C-NMR and elemental analysis. The crystal parameters of this compound are as follows: monoclinic P 2 1/n, a = 12.694(2) Å, b = 26.204(2) Å, c = 13.005(2) Å, β = 102.95(2)°, V = 4216.02(1) Å.³, Z = 4, Dx = 1.289 g/cm³, F(000) = 1704, λ (MoKα) = 0.71070 Å, μ = 0.2 mm^?1. The structure was solved by SHELXS-97 and refined by SHELXL-97. R = 0.06 for 3178 observed reflections with I > 2σ (I).     

Preparation of highly oriented poly-diacetylene films with ion beam irradiation

Abstract

Substituting metallic or rare-earth atoms or removing O in the superconductor YBa₂Cu₃O₇ usually has a strong effect on the superconducting properties. We have made extensive XAFS studies on Co, Fe, Ni, Zn, Gd, and Pr substituted materials including some thin film samples. In nearly all cases, significant distortions are found. Although the lattice constant change is small (< 0.05 Å) the local distortions can be significant larger (～ 0.1 to 0.3 Å). The observed large local distortions of the lattice together with a change in the charge distribution at a site indicate that the interior of the unit cell is easily distorted. The correlation of a strong Tc suppression with large local distortions suggests that distortions of the nearby layers must play a significant role in models for superconductivity in high Tc materials.     

Ferromagnetic ordering in the MMnF6 series (M = Ni,Cu, Zn,Pd)

Neutron diffraction experiments performed on MMnF₆ compounds (M = Ni, Cu, Zn, Pd) have shown that both NiMnF₆ and ZnMnF₆ crystallize in the rhombohedral R$\text{3}$ space group with a cationic ordering, whereas PdMnF₆ shows cationic disordering (R$\text{3}$c, a = 5.46 Å, α = 54.45°). CuMnF₆ has a monoclinic distortion derived from the MnF₃ structural type (a = 8.57 Å, b = 4.85 Å, c = 13.46 Å, β = 92.12°). The magnetic properties can be correlated with the structure: the R$\text{3}$ ordered compounds show a ferromagnetic behavior (T_C(NiMnF₆) = 39 K; T_C(ZnMnF₆) = 9.5 K; T_C(CdMnF₆) = 8 K), while the other two have an antiferromagnetic ordering.     

Radial scanning diagnostics of bremsstrahlung and line emission in T-10 plasma

The paper describes the scanning spectroscopic diagnostics designed for measurement of line integrated plasma radiation in two visible spectral ranges. This diagnostic system is aimed at measuring the bremsstrahlung absolute values and profile with high spatial resolution. The bremsstrahlung absolute values are used to determine the value and radial distribution of effective plasma ion charge Z _eff(r) in T-10 discharges. The importance of Z _eff measurement is due to its strong influence on plasma heating, confinement, and stability. The spatial distribution of emission for one of the chosen spectral lines is measured simultaneously with bremsstrahlung. The spatial resolution of measurements is ~1 cm, and the temporal resolution is up to 10 ms. The spectral equipment and methods for its calibration are described. Examples of line integrated brightness distribution in a “continuum window” of 5236 ± 6 Å and brightness of the lines C⁵⁺ (5291 Å), He¹⁺ (4686 Å), and D_β (4861 Å) are given. Flattening of the bremsstrahlung brightness profile in the central region of the plasma column in some discharges with sawtooth oscillations in the T-10 is observed. The measured effective ion charge profiles in ohmic discharges with high plasma density and low discharge currents demonstrate accumulation of light impurities at the column axis; as a consequence, quenching of sawtooth oscillations in some discharges is observed. The developed diagnostics provides necessary data for investigation of heat, particle, and current transport in the plasma of the T-10. Successful application of the obtained data on Z _eff(r) for investigation of geodesic acoustic modes of plasma oscillations in the T-10 should be specially noted.     

Long-wave X-ray radiation mirrors

Problems of obtaining mirrors for long-wave length (200-20 Å) X-radiation are discussed. Results of the investigation of roentgenooptical characteristics of multilayer periodical C-Re, C-W and C-Ta structures with periods 60–80 Å have been analyzed. The layer thickness of the heavy elements varied from 3 to 25 Å. The following characteristics have been recorded in the wavelength range λ = 50–80 Å; reflection coefficient up to 20%, resolution λ/Δλ = 7–14, width of the angular dependence R(θ)Δθ ≈ 2°. The number of effectively reflecting pairs of layers, N_max = 17, has been determined from the position of secondary diffraction maxima.