Institute of Electron Physics

We present a new extended version of the R -matrix method for the calculation of continuum properties in which non-orthogonal orbitals are extensively used for describing both the target states and the R -matrix basis functions. In particular, a B -spline basis is used for the description of continuum states in the inner region and the target states may be obtained from independent calculations. This leads to a generalized eigenvalue problem but has the advantage of requiring much smaller bases for accurate representation of target wavefunctions and to achieve convergence in the close-coupling expansion. The present approach and its code are both applicable to a general atom and their efficiency for low-energy scattering processes is demonstrated by calculating the photoionization of Li. A detailed analysis of the resonance structure is given. Very good agreement with experimental data has been obtained, and considerable improvement in the description of resonances has been achieved in comparison with the standard R -matrix calculations.

Abstract A review of recent applications of Raman spectroscopy as a fast, sensitive, and non-destructive technique for exploring II–VI semiconductor nanocrystals fabricated by various methods (colloidal chemistry, Langmuir–Blodgett method, diffusion-limited growth) is presented. Specific size-related features revealed in the nanocrystal Raman spectra (phonon confinement, surface phonons) are analysed, as well as more complicated size effects for ultrasmall nanocrystals (NCs) related to the activation of the phonon density of states modified by surface reconstruction. Similarities and differences of the Raman scattering in II–VI and III–V or elemental (Si) semiconductor NCs are briefly analysed. Implementation of resonant conditions and application of infrared absorption analysis, complementary to the Raman spectroscopy—resulting in the observation of phonon modes ‘silent’ in conventional Raman scattering processes—are discussed. Furthermore, Raman spectroscopy is employed for fast and efficient assessment of the composition of matrix-embedded ternary II–VI nanocrystals, as well as more complicated multimode quaternary II–VI systems. Selective probing of electronic and vibrational spectra of different parts of heterogeneous NCs (such as core–shell systems) by tuning the excitation wavelength in resonant Raman scattering is considered. The analysis of phonon spectra is applied to the quantitative estimation of strain in the core and shell, and degree of interface intermixing, as well as to checking the surface oxidation. The above approaches and phenomena are further explored in more complex compound NCs beyond II–VI, such as CuInS 2 /ZnS. Recent results in the field of surface- and tip-enhanced Raman spectroscopy and surface-enhanced infrared absorption are analysed showing the perspectives of Raman spectroscopy as a tool for investigation of single-nanocrystal phonon spectra.

A velocity map imaging/ion time-of-flight spectrometer designed specifically for pump-probe experiments combining synchrotron and laser radiations is described. The in-house built delay line detector can be used in two modes: the high spatial resolution mode and the coincidence mode. In the high spatial resolution mode a kinetic energy resolution of 6% has been achieved. The coincidence mode can be used to improve signal-to-noise ratio for the pump-probe experiments either by using a gate to count electrons only when the laser is present or by recording coincidences with the ion formed in the ionization process.

The higher film coverage and better device performance is achieved for film spin-coated in air and then annealed in vacuum.

The valence photoelectron spectra of the aromatic amino acids phenylalanine, tyrosine, tryptophan and 3-methylindole in the gas phase have been investigated by soft X-ray radiation. The photoemission spectra of the outer valence regions are similar to previously reported He I spectra, although relative peak intensities are different due to the different photon energy. The spectral range has been extended to the inner valence region and new information has been obtained. The photofragmentation mass spectra of the aromatic amino acids were measured after ionization by noble gas resonance radiation at energies from 8.4 to 21.2 eV. The main peak in the mass spectra of phenylalanine corresponds to loss of the aromatic functional group, while for tyrosine and tryptophan it is due to the loss of the carboxylic and amino groups. Lower photon energies lead to ‘softer’ ionization, with reduced fragmentation and increased parent ion signal.

Resonant Raman scattering spectra of glass-embedded CdSi-^Se^ nanocrystals are measured and complemented with and optical absorption as well as photoluminescence data. The selectivity of the resonant Raman process not only for the size, but also for the composition of nanocrystals within the ensemble, is directly observed in the dependence of phonon band frequency, linewidth and shape on the excitation wavelength.

Reactions of highly excited atoms (A ** ) with molecules (BC) \begin{aligned} \text{A$^{**}$}+\text{BC}{\rightarrow}\text{A$^{+}$}+\text{B}+\text{C$^{-}$}, \label{eq1} \end{aligned} are studied. It is theoretically shown that the cross section for (1) can be approximately expressed in terms of that for dissociative attachment of electrons to molecules BC, namely, \begin{aligned} \mathrm{e}+\text{BC}{\rightarrow}\text{B}+\text{C$^{-}$}. \end{aligned} The rate constants and the angular distributions of the products for some reactions including \begin{aligned} \text{K$_{\text{r}}$$^{**}$}+\text{CCl$_{4}$}{\rightarrow}\text{K$_{\text{r}}$$^{+}$}+\text{CCl$_{3}$}+\text{Cl$^{-}$}, \label{eq2} \end{aligned} are predicted. The rate constant for reaction (2) is found to be of the order of the magnitude 10 -7 cm 3 /sec. Together with the results of the previous papers (M. Matsuzawa: J. chem. Phys. 55 (1971) 2685; J. Phys. Soc. Japan 32 (1972) 1088) it is pointed out that the measurements of reactions of highly excited atoms with molecules give useful information on the inelastic scattering of a slow electron by the molecules.

Abstract The Raman spectra of CdS 1− x Se x nanocrystals, embedded in a borosilicate glass matrix, are studied, CdS‐like and CdSe‐like LO phonon frequencies being used to determine the nanocrystal composition. The Raman lineshape is analyzed taking account of confinement‐related phonons with nonzero wavevector, surface phonon modes, glass matrix pressure and disorder effects.

A phenomenological complex optical potential is used to investigate the elastic and inelastic scattering of electrons by Ca, Sr, Ba and Yb atoms in the energy range E<or=200 eV. The values of adjustable parameters in the polarization potential were found using known electron affinity to the Ca, Sr, Ba and Yb atoms. It is also shown that peaks near elastic thresholds in cross sections, which have been found in experiments, arise from 2D shape resonances at energies equal to 0.87 eV, 0.60 eV, 0.34 eV and 0.89 eV and with widths equal to 0.98 eV, 0.68 eV, 0.13 eV and 0.89 eV for Ca, Sr, Ba and Yb, respectively. Comparisons with experimental data and other theoretical results are given.

The low-energy electron collision with neutral oxygen has been investigated using a modified R-matrix method based on the B-spline representation of the scattering orbitals. Integral cross sections for elastic scattering and for excitation of the 3P-1D, 3P-1S and 1D-1S transitions are presented in the energy region from threshold to 30 eV. Accurate representation of target wavefunctions has been obtained on the basis of the non-orthogonal orbitals. Both the correlation and relaxation effects are shown to be important. The close-coupling expansion consists of the 26 spectroscopic bound and autoionizing target states. A calculation with 26 spectroscopic states and 17 pseudo-states has also been carried out to check the effect of coupling to the continuum. The present results for the elastic scattering are in excellent agreement with the measurements, but large discrepancies with the existing experimental data are found for the 3P-1D and 3P-1S transitions. The excitation cross sections agree well with the recent R-matrix calculation with pseudo-states by Thomas et al (Thomas M R J, Bell K L and Berrington K A 1997 J. Phys. B: At. Mol. Opt. Phys. 30 4599) except for lower energies about 5-7 eV of threshold.

Ejected-electron excitation functions for the lowest-lying (3p54s2)2P3/2 and (3p54s2)2P1/2 autoionizing states in potassium have been measured for incident-electron energies from threshold to 500 eV and 200 eV, respectively, with improved energy resolution. Strong resonances have been observed and well resolved in the excitation functions of both states near their excitation thresholds. R-matrix (close-coupling) calculations were performed to analyse and tentatively assign these features. A remarkable similarity between the spectrum of the core-excited negative-ion potassium states and the excited states of atomic argon is noted.

The development of nephrocalcinosis and the time course of changes in kidney function, especially proximal tubular function, were studied in young male rats fed a high-phosphorus diet. The animals were fed a purified diet with a phosphorus content of either 0.5% (normal phosphorus diet) or 1.5% (high-phosphorus diet). In the group fed the high-phosphorus diet, nephrocalcinosis was found in 4 of 42 rats after 1 d of feeding and in all rats of this group at 3 d. The degree of nephrocalcinosis gradually increased with time. Upon histological observation by electron microscopy, vacuoles, lysosomes and swelling of microvilli in the proximal tubules were observed in rats fed the high-phosphorus diet after 1 d of feeding. Giant lysosomes with deposition of calcium and deposition of hydroxyapatite in mitochondria were observed in the proximal tubules of rats fed the high-phosphorus diet at 3 d. Albumin concentration in the urine of these rats was significantly increased at 3 d. The activity of N-acetyl-beta-D-glucosaminidase in the urine was also significantly increased after 1 d of feeding the high-phosphorus diet, and then reached a plateau. The beta 2-microglobulin concentration in the urine of rats fed the high-phosphorus diet was significantly increased at 14 d, and increased more toward 21 d. We concluded that nephrocalcinosis and injury to the proximal tubules are rapidly induced in rats fed a high-phosphorus diet.

The inner shell ionization of pyrimidine and some halogenated pyrimidines has been investigated experimentally by X-ray photoemission spectroscopy (XPS) and theoretically by density functional theory (DFT) methods. The selected targets-5-Br-pyrimidine, 2-Br-pyrimidine, 2-Cl-pyrimidine, and 5-Br-2-Cl-pyrimidine-allowed the study of the effect of the functionalization of the pyrimidine ring by different halogen atoms bound to the same molecular site, or by the same halogen atom bound to different molecular sites. The theoretical investigation of the inductive and resonance effects in the C(1s) ionization confirms the soundness of the resonance model for a qualitative description of the properties of an aromatic system. Moreover, the combination of the experimental results and the theoretical analysis provides a detailed description of the effects of the halogen atom on the screening of a C(1s) hole in the aromatic pyrimidine ring.

Systematic calculations of energies and decay rates for the 2p53snl core-excited states (with n<or=7) in Na have been performed using a configuration-interaction method, including spin-orbit interaction and core-polarization correlation through a semi-empirical model core potential. Data obtained extend and clarify considerably the classification of lines in the existing photoabsorption and ejected-electron spectra of Na. Lifetime determination included radiative decay to the bound 2p6nl levels and to the lower core-excited states as well as autoionization. Both correlational and relativistic effects play an important role, as expected, but in addition it was found that the non-orthogonality of bound and continuum orbitals, being a result of core excitation, is also very important in evaluating of autoionization rates. The predicted lifetimes are analysed with respect to their 'quasimetastability', which has recently attracted great attention in atomic spectroscopy and in the construction of XUV lasers.

A graph theoretic color image segmentation algorithm is proposed, in which the popular normalized cuts image segmentation method is improved with modifications on its graph structure. The image is represented by a weighted undirected graph, whose nodes correspond to over-segmented regions, instead of pixels, that decreases the complexity of the overall algorithm. In addition, the link weights between the nodes are calculated through the intensity similarities of the neighboring regions. The irregular distribution of the nodes, as a result of such a modification, causes a bias towards combining regions with high number of links. This bias is removed by limiting the number of links for each node. Finally, segmentation is achieved by bipartitioning the graph recursively according to the minimization of the normalized cut measure. The simulation results indicate that the proposed segmentation scheme performs quite faster than the traditional normalized cut methods, as well as yielding better segmentation results due to its region-based representation.

Recent communication equipment such as mobile and cellular phones, radio systems, pagers, LANs, have demanded high performance components. Among these components, the last generation of SAW filters and signal processing devices, presenting low loss, flexible frequency and phase response characteristics, control of spurious, and so forth, have played a major role in designing new equipment and redesigning existing systems. The highest frequency obtainable with SAW technology in practical devices is limited to a couple of GHz, usually due to restrictions in the fabrication process involved and SAW propagation characteristics. The pseudo-SAW and the shear horizontal mode, presenting phase velocities circa 40% superior than the SAW and low attenuation along certain directions, have permitted the construction of devices operating at higher frequencies. The high velocity pseudo-SAW, with phase velocities about 100% higher than the SAW and low attenuation in many materials along certain directions, extends the high operating limit of SAW devices even further. In this paper the major characteristics of this new type of wave are reviewed. Extended topics such as: the boundary function magnitude behavior, the relationship between the "growing tilted bulk-like partial waves" and the bulk slowness, the number of roots (uncoupling of modes), and the Poynting vector behavior with depth are explored, enlightening the solution and behavior of this new type of high velocity pseudo-SAW.

An experimental technique for measuring the cross sections of direct and dissociative ionization of N2, O2, H2O, and CO2 molecules by electron impact in the near-threshold energy range is described. The setup used in the experiments allows mass separation of ions with a monopole mass spectrometer. It is shown that such a setup can be used to advantage in separation experiments. For incident electron energies between 7 and 35 eV, the energy dependences of the cross sections of generation of parent ions and ion fragments due to parent molecule dissociation are obtained.

This work is devoted to the study of the adsorption of strontium, yttrium, and zirconium ions by the strong acid cation exchange resin Dowex HCR-s/s. The adsorption of strontium, yttrium, and zirconium ions in batch and dynamic conditions from individual solutions of the studied elements, as well as from their mixture, was studied. It was shown that the dependences of the adsorption of strontium, yttrium, and zirconium ions on agitation time fit well with the pseudo-first-order and Elovich equations. Equilibrium adsorption of all three cations can be described with Langmuir's theory. Column adsorption has shown that Dowex HCR-s/s adsorb all three investigated cations from the acidic medium. The inductively coupled plasma mass spectrometry (ICP-MS) proves that separation of these cations using Dowex HCR-s/s is possible only in highly dilute solutions at a concentration of 10 ng/ml of each element. The basis of separation will be a higher rate of adsorption of tetravalent zirconium, compared with strontium and yttrium. As the concentration of the investigated elements increases to 100 ng/ml, all three cations are adsorbed by the resin in equal amounts and can be separated only using special eluents, such as Ca-EDTA.

Statistical static timing analysis (SSTA) is emerging as a solution for predicting the timing characteristics of digital circuits under process variability. For computing the statistical max of two arrival time probability distributions, existing analytical SSTA approaches use the results given by Clark in [8]. These analytical results are exact when the two operand arrival time distributions have jointly Gaussian distributions. Due to the nonlinear max operation, arrival time distributions are typically skewed. Furthermore, nonlinear dependence of gate delays and non-gaussian process parameters also make the arrival time distributions asymmetric. Therefore, for computing the max accurately, a new approach is required that accounts for the inherent skewness in arrival time distributions. In this work, we present analytical solution for computing the statistical max operation.1 First, the skewness in arrival time distribution is modeled by matching its first three moments to a so-called skewed normal distribution. Then by extending Clark's work to handle skewed normal distributions we derive analytical expressions for computing the moments of the max. We then show using initial simulations results that using a skewness based max operation has a significant potential to improve the accuracy of the statistical max operation in SSTA while retaining its computational efficiency.

We show that the data for the total cross section and for the real part of the elastic amplitude indicate the presence of a hard pomeron in πp and Kp elastic scattering at t=0, compatible with that observed in deep inelastic scattering. We show that such a hard pomeron is also compatible with pp and p̄p data, provided one unitarises it at high energy.