Bifunctional Au-nanorod@Fe3O4 nanocomposites: synthesis, characterization, and their use as bioprobes

Membrane gas separation technology has been rapidly growing for industrial applications such as air separation, carbon dioxide (CO₂) separation from natural gas production, hydrogen separation, etc. Needs for CO₂ separation are increasing as carbon capture technology has been recognized as an essential part when combating the global warming issue. Membrane gas separation technology deals with mass transport phenomena through the membrane engineered on a sub-nanoscale controlling transport properties of small gas molecules such as CO₂, N₂, O₂, H₂, etc. In this review, we will report on the recent developments in capture technologies utilizing various membranes including nano-engineered thermally rearranged (TR) polymers. TR polymer membranes show high gas permeability as well as good separation properties, especially in CO₂ separation processes such as from post-combustion flue gas and natural gas sweetening.     

Antiproton-hydrogen scattering at low-eV energies

In the scattering of negative particles other than the electron by atoms at lab-frame energies around 10 eV, an elastic process termed “brickwall scattering” might lead to a high probability for scattering angles around 180°. For an antiproton slowing in hydrogen, this backward scattering would result in the loss of nearly all of its energy in a single collision, since it and a hydrogen atom have nearly the same mass. Such energy loss would have a significant effect on the energy distribution of antiprotons at energies where capture by the protons of hydrogen is possible and might, thereby, affect the capture rate and the distribution of capture states. In the semiclassical treatment of the problem with an adiabatic potential energy, brickwall scattering is indeed present, and with a substantial cross section. However, this model appears to underestimate inelastic processes. Based on calculations for negative muons on hydrogen atoms, these processes appear to occur for about the same impact parameters as brickwall scattering and thus substantially reduce its effect.     

The method of concentration pulses for studying hydrogen transport in solids

The method of concentration pulses is designed for investigating the kinetics of hydrogen transport in complex diffusion systems and allows one to choose the most probable transport model and determine the rate constants of processes influencing the kinetics, e.g., diffusion, adsorption, and desorption, capture to traps, etc. We describe the idea of the method, its experimental realization, and a procedure for processing the results which allows one to choose the most probable model and determine the desired rate constants. Zh. Tekh. Fiz. 69, 99–103 (January 1999)     

Electroweak radiative corrections to muon capture

Electroweak radiative corrections to muon capture on nuclei are computed and found to be sizable. They enhance the capture rates for hydrogen and helium by 2.8% and 3.0%, respectively. As a result, the value of the induced pseudoscalar coupling, g(P)(exp), extracted from a recent hydrogen 1S singlet capture experiment is increased by about 21% to g(P)(exp)=7.3+/-1.2 and brought into good agreement with the prediction of chiral perturbation theory, g(P)(theory)=8.2+/-0.2. Implications for helium capture rate predictions are also discussed.     

Physical applications of muon catalysis: Muon capture in hydrogen

Results of theoretical and experimental research on capture of negative muons in hydrogen are reported with an emphasis on the accompanying phenomenon of muon catalysis in hydrogen and subtleties of the experimental method. A conclusion is drawn that precise determination of the capture rate is important for refining the standard model.     

Defect passivation using ultrasound treatment: fundamentals and application

Ultrasonic vibrations introduced into semiconductor thin-films can trigger defect reactions, which are beneficial for electronic materials and devices. This type of semiconductor processing is assigned as ultrasound treatment (UST). The UST technology was initially developed in compound semiconductors and recently successfully applied to Si-based materials. The analysis of UST effects is performed within a general scenario of three-step point-defect gettering comprised of the (a) release, (b) diffusion, and (c) capture of the defects. As a demonstrating vehicle of UST mechanisms, the experimental data on ultrasonically enhanced diffusion of atomic hydrogen in thin polycrystalline Si films are discussed. UST applied to plasma-hydrogenated films improves the homogeneity of recombination and transport properties. Ultrasound promotes a passivation of grain boundary defects as revealed using scanning photoluminescence spectroscopy, contact potential difference with nano-scale resolution, and sheet resistance measurements. The results favor a model of trap-limited hydrogen diffusion facilitated by ultrasound. Illustrative examples of the UST application for electronic devices are presented. Received: 1 March 1999 / Accepted: 28 March 1999 / Published online: 14 June 1999     

Effect of electrons of the multiply charged ion core on single-electron capture

The population of various electronic states of particles that arise during the capture of a single electron in hydrogen and helium atoms, as well as hydrogen molecules, by Ar³⁺ and Ne³⁺ ions with an energy of several kiloelectronvolts was studied by collision spectroscopy, viz., precision analysis of kinetic energy variation for ions formed as a result of interaction between ions and atoms. It is shown that single-electron capture in many cases is a multielectron process accompanied by the rearrangement of a multiply charged ion core. It is found that the triply charged Ne³⁺ ions formed as a result of ionization of Ne atoms by electron impacts are formed mainly in metastable states. The population of excited states of particles during their multiple ionization should be taken into account in determining the characteristics of various particles by the appearance potential method. Collision spectroscopy can be used for analyzing the metastable ion impurities in ionic beams.     

Modeling of radiation-induced charge trapping in MOS devices under ionizing irradiation

The numerical model of the radiation-induced charge trapping process in the oxide layer of a MOS device under ionizing irradiation is developed; the model includes carrier transport, hole capture by traps in different states, recombination of free electrons and trapped holes, kinetics of hydrogen ions which can be accumulated in the material during transistor manufacture, and accumulation and charging of interface states. Modeling of n-channel MOSFET behavior under 1 MeV photon irradiation is performed. The obtained dose dependences of the threshold voltage shift and its contributions from trapped holes and interface states are in good agreement with experimental data.     

Cross sections of electron capture and electron capture ionization versus the impact parameter in collisions of a proton with multielectron atoms

The absolute differential cross sections of scattering of hydrogen atoms resulting from an electron capture and an electron capture ionization are measured for collisions of 4.5- and 11-keV protons with argon and xenon atoms. The range of scattering angles is 0°–2°. From the scattering differential cross section found experimentally, the probabilities of single-electron capture and electron capture ionization as a function of the impact parameter are calculated. The dependences of the incident particle scattering angle on the impact parameter (deviation function) for interactions with Ar and Xe atoms are calculated in terms of classical mechanics using the Moliére—Yukawa potential to describe the interaction of atomic particles. Analysis is given to the probabilities of electron capture and electron capture ionization versus the impact parameter and to the distribution of the electron density on different electron shells in a target atom versus a distance to the core. It is concluded that only electrons from the outer shell of the target atom are involved in the process of electron capture ionization. The cross section of electron capture ionization is calculated in the proton energy range 5–20 keV.     

Anomalous bumpy structures in the capture cross sections of antiprotons by helium

We investigate the state-specified capture process of antiprotons by helium. Freezing one of the two electrons, we reduce this four-body rearrangement problem into a three-body problem. The capture cross sections are calculated by solving the Chew-Goldberger-type integral equation. Differing from the capture of antiprotons by hydrogen atoms, the bumpy structures are revealed in the total angular momentum dependent capture cross sections. Further analysis shows that the bumps arise from the partial channel closing due to the removal of the energy degeneracy in the antiprotonic helium.     

Micromechanical modelling of coupled crystal plasticity and hydrogen diffusion

Hydrogen transport behaviour in metals is greatly influenced by the mechanical stress and the underlying microstructural features. In this work, a micromechanical model based on coupled crystal plasticity and hydrogen diffusion is developed and applied to model hydrogen diffusion and storage in a polycrystalline microstructure. Particular emphasis is laid on mechanical influences on hydrogen transport, invoked by internal stresses and by trapping of dislocations generated by plastic strains. First, a study of a precharged material is carried out where hydrogen is allowed to redistribute under the influence of mechanical loading. These simulations demonstrate to which extent hydrogen migrates from regions with compressive strains to those with tensile strains. In the next step, the influence of plastic prestraining on hydrogen diffusion is analysed. This prestraining produces internal residual stresses in the microstructure, that mimic residual stresses introduced into components during cold working. Lastly, a series of permeation simulations is performed to characterise the influence of hydrogen trapping on effective diffusivity. It is shown that the effective diffusivity decreases with stronger traps and the effect is more prominent at a larger predeformation, because the trapped hydrogen concentration increases considerably. The reduction of effective diffusivity with plastic deformation agrees very well with experimental findings and offers a way to validate and parameterise our model. With this work, it is demonstrated how micromechanical modelling can support the understanding of hydrogen transport on the microstructural level.     

The hydrogen bond under pressure

The hydrogen bonds are quite pervasive in several classes of materials. Its parameters are known to show systematic variations with hydrogen bond length, and pressure variable is thus a natural way for studying hydrogen bonded substances. In this article, we review the unifying features as obtained through several experimental and theoretical investigations. Amongst other things, it is examined whether the observed pressure-induced variations in parameters of hydrogen bonds are consistent with the co-relations known on different chemical substances at normal pressure. In particular, the controversies on variations of O–H and H- - -O pairs with pressure and symmetrization of hydrogen bond have been resolved. The effects of close packing promoted by pressure such as formation of muli-centered hydrogen bonds and steric repulsions and the way the hydrogen bonds counter these in different ways are also examined.     

Formation of exotic atoms by direct capture and via transfer from hydrogen

Exotic atoms like muonic atoms can be formed either by direct capture, often called Coulomb capture, or by muon transfer from a muonic hydrogen atom. The first estimates for the formation predicted, for both mechanisms, probabilities approximately proportional to the charge numberZ. The experiments did not confirm such a simpleZ-dependence. In direct capture, it turned out that the chemical bond played a decisive role, at least for lighter elements. In the formation via transfer, surprising data were obtained not only for heteroatomic molecules but also for noble gases. Whereas for direct capture, a model is able to reproduce quite satisfactorily a great number of measured capture ratios, including those in hydrogen compounds, the formation via transfer seems to put completely different and more fundamental questions.     

Quantum statistical effects in nuclear reactions,fission, and open quantum systems

Quantum diffusion equations with time-dependent transport coefficients are derived from generalized non-Markovian Langevin equations. Generalized fluctuation-dissipation relations and analytical formulas for calculating friction and diffusion coefficients in nuclear processes are obtained. The asymptotics of the transport coefficients and of the correlation functions are investigated. The problem of correlation decay in quantum dissipative systems is studied. A comparative analysis of diffusion coefficients for the harmonic and inverted oscillators is performed. The role of quantum statistical effects during passage through a parabolic potential barrier is investigated. Sets of diffusion coefficient assuring the purity of states at any time instant are found in cases of non-Markovian dynamics. The influence of different sets of transport coefficients on the rate of decay from a metastable state is studied in the framework of the master equation for reduced density matrices describing open quantum systems. The approach developed is applied to investigation of fission processes and the processes of projectile-nuclei capture by target nuclei for bombarding energies in the vicinity of the Coulomb barrier. The influence of dissipation and fluctuation on these processes is taken into account in a self-consistent way. The evaporation residue cross sections for asymmetric fusion reactions are calculated from the derived capture probabilities averaged over all orientations of the deformed projectile and target nuclei.     

Influence of impurities on short range electron transport in GaAs

The influence of Cr impurities on muonium atom formation in GaAs has been studied using muon spin relaxation techniques with alternating electric fields. The results suggest that electron transport to and capture by the muon is suppressed by capture/scattering on intervening Cr centers. The length scale involved is estimated to be about 3x10(-6) cm. This offers an opportunity to study electron transport to positive centers in semiconductors on a microscopic scale.     

Overview: The constructive role of noise in fluctuation driven transport and stochastic resonance

Random noise is typically thought of as the enemy of order rather than as a constructive influence. Recent work has shown however that under certain circumstances, noise and Brownian motion can facilitate transmission of information via a mechanism know as stochastic resonance, and help systems use chemical energy and nonequilibrium fluctuations to drive directed motion via fluctuation driven transport. In this focus issue we have collected several articles that capture the flavor of these developing fields and point the way to new directions for research. (c) 1998 American Institute of Physics.     

Negative muon capture in very light atoms

The transition rates for unbound muons to be captured into atomic bound states are calculated as functions of (1) incident muon center-of-mass energy, (2) muon principal quantum number n, and (3) muon (final) angular momentum l, for the hydrogen, helium, and lithium atoms. These rates reflect differences in electron binding energies. At muon energies of several hundred electron volts, lithium K-shell electrons are more likely to be ejected than the L-shell electron, while this behavior is reversed for energies ? 10 eV. However, in each case when the capture rate is folded with a muon stopping power function, the result is that more than half of the unbound muons are absorbed above 75 eV. Implications for experiments which look at muon transfer processes are noted.     

Triazole and triazole derivatives as proton transport facilitators in polymer electrolyte membrane fuel cells

Some basic aspects pertaining to the application of triazole and its derivatives as proton transport facilitators for membranes for high temperature fuel cell operations are investigated. Performance as proton transport facilitators is studied for compounds in their native solid state and as a dopant in a polymer membrane. Some key parameters which influence the proton transport in the system are the proton affinity, pKa or acidity, activation energy and the ease of formation of hydrogen bonding network. Theoretical calculations of the proton affinity of the compounds are presented. The effect of proton affinity of the compound on the activation energies for proton transport is investigated. Proton conductivity is measured for acid doped triazoles in both pellet form (powder triazole mixed with acid) and in composite forms wherein the acid group is contained in a polymer matrix. The effect of formation of a hydrogen bonding network by the triazoles and its impact on the proton conductivity are studied. Also, the effect of ion exchange capacity (IEC) of the host polymeric electrolytes and loading of triazoles in the composites were investigated.