Defects and impurities in amorphous semiconductors and in liquid electrolytes

Amorphous (a-) semiconductors like a-Si:H and the chalcogenide glasses possess a general tendency to establish an overall equilibrium between the electronic system and the lattice with its dopant and defect sites. In the present paper the chemical interactions which establish these equilibria within the bulk of the a-semiconductor lattices are compared to chemical interactions in liquid electrolytes, particularly to those in H₂O. These considerations reveal close similarities between autocompensation doping in a-semiconductors and acid/base reactions in H₂O. The effects of light and field-effect induced defect formation, on the other hand, are shown to be related to the phenomenon of electrolysis in H₂O. The consideration of these analogies further emphasizes the roles of charge-carrier localization and that of H-diffusion in promoting dopant and defect equilibration reactions in a-semiconductors.     

Twin walls in anorthoclase are enriched in alkali and depleted in Ca and Al

Abstract

Composition profiles have been measured in transformation twin walls of the albite type in anorthoclase. Regions close to the walls between two twin domains are enriched in K and Na and depleted in Ca and Al. Microanalysis experiments show high mobility of alkali cations close to twin boundaries. Twin walls are generated via the displacive phase transition C2/m?C[lbar] in Al, Si disordered feldspar, and the chemical heterogeneity is a fingerprint for the subsequent diffusion of alkali and earth alkali ions during the cooling history of the sample.     

Patterns and Symmetries in the Visual Cortex and in Natural Images

As borders between different entities, lines are an important element of natural images. Indeed, the neurons of the mammalian visual cortex are tuned to respond best to lines of a given orientation. This preferred orientation varies continuously across most of the cortex, but also has vortex-like singularities known as pinwheels. In attempting to describe such patterns of orientation preference, we are led to consider underlying rotation symmetries: Oriented segments in natural images tend to be collinear; neurons are more likely to be connected if their preferred orientations are aligned to their topographic separation. These are indications of a reduced symmetry requiring joint rotations of both orientation preference and the underlying topography. This is verified by direct statistical tests in both natural images and in cortical maps. Using the statistics of natural scenes we construct filters that are best suited to extracting information from such images, and find qualitative similarities to mammalian vision. PACS84.35+i 89.70.+c 87.57.Nk     

Clustering phenomena in radioactive and stable nuclei and in heavy-ion collisions

A theory for clustering formation in nuclei and in heavy-ion collisions has been worked out in terms of the quantum-mechanical fragmentation process. Treating the mass fragmentation and relative separation coordinates as weakly coupled, the spontaneous cluster-decay of radioactive nuclei has been considered as a two-step process of clustering formation and tunnelling of the confining nuclear interaction barrier. This model has also been applied to “stable” nuclei, lighter than lead. The effects of adding more and more neutrons to collidingN =Z,A = 4n nuclei are studied for theα-clustering transfer phenomenon.     

Spin-canting and transverse relaxation in maghemite nanoparticles and in tin-doped maghemite

The magnetic properties of maghemite nanoparticles and tin-doped maghemite have been studied by ⁵⁷Fe and ¹¹⁹Sn Mössbauer spectroscopy at temperatures from 6 to 300 K with and without applied magnetic fields. The low-temperature ⁵⁷Fe spectra of both samples, obtained in a field of 4 T, can be described in terms of A-site and B-site components with perfect ferrimagnetic order and a strongly canted component, which seems to have its main contribution from B-site ions. At higher temperatures, the components with strong canting are influenced by transverse relaxation, which results in significant line broadening, a reduction of the magnetic hyperfine splitting and a reduction in the relative areas of lines 2 and 5. The ¹¹⁹Sn spectra show a very broad distribution of magnetic hyperfine fields at low temperatures. When the sample was exposed to applied magnetic fields the distribution became narrower. The spectra show that the direction of the hyperfine field of a large fraction of the tin ions in maghemite is antiparallel to the applied field, but a minor fraction of the tin ions have canted hyperfine fields.     

DNA dynamics and organization in sub-micron scale: Bacterial chromosomes and plasmids in vivo and in vitro

Decades of research have witnessed that the mechanical properties of DNA and the associated protein interactions are crucial to the structural organizations and dynamic behaviors of bacterial DNA molecules. Packaged in a restricted cellular space and respective compositions, the entropic force due to confinement is a major factor driving the basal structural formation of the bacterial chromosome and the distribution of plasmids. The dynamic responses of the DNA-protein interactions also modulate the DNA organization when the cellular functions proceed. In this review, we survey the in-vivo and in-vitro evidence and the current understandings of the cellular phenomena of DNA molecules in the sub-micron scale of the bacterial cellular environment. The physical nature and constraints of DNA in cells and the related biological factors, especially the effects induced by gene expressions, are also discussed. We anticipate that by the methodological advances in vivo and in vitro as well as their combinations, the fundamental insights of the coupling from the physical environment and DNA-protein interactions on bacterial DNA dynamics and organization may be revealed.     

Uncertainty in prediction and in inference

The concepts of uncertainty in prediction and inference are introduced and illustrated using the diffraction of light as an example. The close relationship between the concepts of uncertainty in inference and resolving power is noted. A general quantitative measure of uncertainty in inference can be obtained by means of the so-called statistical distance between probability distributions. When applied to quantum mechanics, this distance leads to a measure of the distinguishability of quantum states, which essentially is the absolute value of the matrix element between the states. The importance of this result to the quantum mechanical uncertainty principle is noted. The second part of the paper provides a derivation of the statistical distance on the basis of the so-called method of support.     

Maximum-Entropy and Stability in Statistics and Thermodynamics

The object of the present paper is first to study the role of maximum-entropy principle based on Shannon's entropy in generating stable distribution in statistics and characterizing stable thermal equilibrium state in thermodynamics. The second is to show the nonuniqueness of Shannon's entropy in the study of the stable distribution in statistics and stable equilibrium state in thermodynamics.     

Tyrosyl Fluorescence Decays and Rotational Dynamics in Tyrosine Monomers and in Dipeptides

Picosecond time-correlated single-photon counting was used to measure fluorescence lifetimes and fluorescence anisotropy decays of tyrosine and the tyrosine–alanine and tyrosine–leucine dipeptides. After excitation of tyrosine at 287 nm two emitting species were observed, one at 303 nm with a lifetime of 3.3 ns and another at 340 nm with a lifetime of 360 ps. The rotational correlation time of tyrosine at 303 nm is 38 ps in water at pH 7 and depends linearly on viscosity with a slope of 44 ps/cP, consistent with Stokes–Einstein–Debye theory. We calculated a value of 45 ns for the radiative lifetime of tyrosine, yielding a fluorescence quantum yield of 0.07. The dipeptides Tyr–Ala and Tyr–Leu exhibit two- or three-exponential decays. The amplitudes of the decay components for three-exponential fits correlate closely with the populations of rotamers in these peptides as determined by NMR. The quenching of dipeptide fluorescence is shown to depend on the solvent polarity, strongly supporting the hypothesis that tyrosyl fluorescence in peptides is quenched by charge transfer. The rotational correlation times of tyrosine, Tyr–Ala, and Tyr–Leu increase linearly with the van der Waals volumes. However, rotational relaxation is somewhat faster than expected from Stokes–Einstein–Debye theory with stick boundary conditions.     

Advection and dispersion in time and space

Previous work showed how moving particles that rest along their trajectory lead to time-nonlocal advection–dispersion equations. If the waiting times have infinite mean, the model equation contains a fractional time derivative of order between 0 and 1. In this article, we develop a new advection–dispersion equation with an additional fractional time derivative of order between 1 and 2. Solutions to the equation are obtained by subordination. The form of the time derivative is related to the probability distribution of particle waiting times and the subordinator is given as the first passage time density of the waiting time process which is computed explicitly.     

Photothermal and electrooptic nonlinearities in ZnSe and ZnTe and their application in bistable devices

In this paper we present results on ZnSe and ZnTe optically bistable elements in connection with electrooptic effects. The behaviour of optical hysteresis under an applied electric field is studied and the electrical characteristics under illumination with monochromatic laser radiation are investigated. Influences of optical bistability on the photocurrent are measured and an attempt is made to explain the unusual behaviour of the current with respect to the absorbed amount of light, namely a switching down in photocurrent when the absorptive switching takes place. Towards this aim we report here for the first time on spatially resolved measurements of photoconductivity in ZnSe to investigate the influence of Schottky contacts on photothermal electrooptic bistability. Furthermore, we report also to our knowledge for the first time on the influence of the 3D-Stank effect on optical bistability.     

Fermions and disorder in ising and related models in two dimensions

The aspects of phase transitions in the two-dimensional Ising models modified by quenched and annealed site disorder are discussed in the framework of fermionic approach based on the reformulation of the problem in terms of integrals with anticommuting Grassmann variables.     

Modeling of Cu gettering in p- and n-type silicon and in poly-silicon

Based on experimental findings we set up calculations of numerical modeling of gettering efficiencies for Cu in various silicon wafers. Gettering efficiencies for Cu were measured by applying a reproducible spin-on contamination in the 10¹² atoms/cm² range, followed by a thermal treatment to redistribute the metallic impurity. Subsequently, the wafers were analyzed by a novel wet chemical layer-by-layer etching technique in combination with inductively coupled plasma mass spectrometry. We investigated p/p+ and n/n+ epitaxial wafers with different doping levels and different substrate-doping species. We have also investigated gettering efficiencies of phosphorus-diffused p- and n-type wafers. Heavilyboron doped silicon exhibited a gettering efficiency of ∼100%, while gettering by n+ silicon occurred for doping levels >3×10¹⁹ atoms/cm³ only. In another set of experiments we investigated the dependence of the gettering efficiency of p-type wafers with poly-silicon back sides for different cooling rates and Cu spiking levels. A strong dependence on both parameters was found. Cu gettering in p/p+ epitaxial wafers was modeled by calculating the increased solubility of Cu in p+ silicon compared to non-doped silicon taking into account the Fermi-level effect, which stabilizes donors in p+ silicon, and the pairing reaction between Cu and B. Calculated gettering efficiencies were in very good agreement with experimental results. Gettering in n+ silicon was similarly modeled in terms of pairing reactions and the Fermi-level effect. But, for n-type silicon, many experimental uncertainties existed; thus, we applied our expressions to solubility data of Hall and Racette to obtain the unknown parameters. The empirical calculations were in good agreement even with results on n/n+ wafers. For phosphorus-diffused wafers we had to consider an excess vacancy concentration of 1.2–5.5 times the equilibrium concentration to explain the experimental findings by the model. Gettering by poly-silicon back sides was simulated by solving the time-dependent diffusion equation with boundary conditions that take into account different surface reaction rates of silicon point defects. Using this advanced model, the experimentally measured gettering efficiencies were reproduced within the uncertainty of the measurement. Received: 3 September 2001 / Accepted: 4 September 2001 / Published online: 20 December 2001     

Zip and velcro bifurcations in competition models in ecology and economics

During the last six years or so, a number of interesting papers discussed systems with line segments of equilibria, planes of equilibria, and with more general equilibrium configurations. This note draws attention to the fact that such equilibria were considered previously by Miklós Farkas (1932–2007), in papers published in 1984–2005. He called zip bifurcations those involving line segments of equilibria, and velcro bifurcations those involving planes of equilibria. We briefly describe prototypical situations involving zip and velcro bifurcations.

     

沉积岩中的分形及其在石油勘探和开发中的应用

介绍了沉积岩的分形性质，简述了沉积岩中的分形在石油勘探和开发中的应用．     

屋顶花园种植的金银花、竹荪中铅和镉含量及其评价

采用火焰原子吸收光谱法测定屋顶花园种植金银花、竹荪中Pb、Cd的含量。该法简单、快速、灵敏度高,准确性好。回收率在93.6%—96.7%之间,相对标准偏差小于5%。实验结果表明:金银花中Pb、Cd的平均含量范围分别为16.46—16.60、0.19—0.23mg/kg,竹荪中Pb、Cd的平均含量范围分别为11.07—14.62、5.54—5.48mg/kg。     

Mass and Charge in Brane-World and Non-Compact Kaluza-Klein Theories in 5 Dim

In classical Kaluza-Klein theory, with compactified extra dimensions and without scalar field, the rest mass as well as the electric charge of test particles are constants of motion. We show that in the case of a large extra dimension this is no longer so. We propose the Hamilton-Jacobi formalism, instead of the geodesic equation, for the study of test particles moving in a five-dimensional background metric. This formalism has a number of advantages: (i) it provides a clear and invariant definition of rest mass, without the ambiguities associated with the choice of the parameters used along the motion in 5D and 4D, (ii) the electromagnetic field can be easily incorporated in the discussion, and (iii) we avoid the difficulties associated with the splitting of the geodesic equation. For particles moving in a general 5D metric, we show how the effective rest mass, as measured by an observer in 4D, varies as a consequence of the large extra dimension. Also, the fifth component of the momentum changes along the motion. This component can be identified with the electric charge of test particles. With this interpretation, both the rest mass and the charge vary along the trajectory. The constant of motion is now a combination of these quantities. We study the cosmological variations of charge and rest mass in a five-dimensional bulk metric which is used to embed the standard k = 0 FRW universes. The time variations in the fine structure constant and the Thomson cross section are also discussed.