Nuclear excitation in atomic processes

We have introduced a model of two indistinguishable quantum oscillators (IQO) and examined several processes of nuclear excitations in atomic transitions. These processes are: (i) nuclear excitation in an electron transition, (ii) radiationless transitions in muonic atoms, (iii) nuclear excitation in positron-electron annihilation, and (iv) inelastic photoelectric effect. Predictions of our IQO model for these processes are in very good agreement with the available experimental data.     

Quantitative investigations of atomic processes on metal surfaces at atomic resolution

Using the atomic resolution of the field-ion microscope (FIM) and the single-atom identification capability of the time-of-flight atom-probe field-ion microscope, fundamental properties of solid surfaces can be investigated at atomic level. Atomic structures of many surface planes are fully resolved. The chemical composition of a surface can be determined with a single atomic layer spatial resolution. Several interactions of single surface atoms, which are basic to the understanding of many surface phenomena, such as the atom to substrate surface interaction, the adatom-adatom interaction, the adatom-impurity atom interaction, the adatom-plane edge interaction, etc. can all be studied in atomic details. The charge distribution of a single atom, as manifest in its dipole moment and polarizability, can also be studied. Great advantages of FIM investigations include the availability of atomically perfect surface planes, which can be prepared by field evaporation process, and the capability of a direct observation of the atomic images. Although some electronegative atoms cannot be imaged, the surface conditions and the state of the atoms can be characterized by the atom-probe. Basic principles and results of these single-atom FIM studies are presented and discussed.     

Diffusion and elementary atomic processes at steeped surfaces

The mobility of atoms at and near lattice step edges plays an important role in epitaxial growth and surface morphology of thin films, and the dynamic behavior of surfaces at elevated temperature. We summarize our recent FIM studies on how atoms move and bind at step edges, how atoms can descend and ascend lattice steps, how in-layer atoms can move up to the upper terrace, and how these atomic processes are related to various growth structures in thin film epitaxy.     

Photo- and thermally stimulated relaxation processes in pre-irradiated atomic solids

Atomic and electronic relaxation processes in pre-irradiated atomic solids are considered using preliminary irradiated by an electron beam solid Ar as an example. The results of real-time-correlated study are presented for the first time with an accent on recently found anomalous low-temperature sputtering of Ar atoms from the surface. The experiments were performed using a set of activation spectroscopy methods—thermally stimulated exoelectron emission (TSEE) thermally stimulated luminescence (TSL) in combination with measurements of the sputtering yield. Solid evidence of thermally induced charge recombination mechanism is obtained. Mechanism of energy transfer based on the crowdion model is discussed. Photo-stimulated sputtering from pre-irradiated rare gas solids (RGS) is predicted.     

Molecular views and measurements of hemostatic processes using atomic force microscopy

Hemostasis and thrombosis are highly complex and coordinated interfacial responses to vascular injury. In recent years, atomic force microscopy (AFM) has proven to be a very useful approach for studying hemostatic processes under near physiologic conditions. In this report, we review recent progress in the use of AFM for studying hemostatic processes, including molecular level visualization of plasma proteins, protein aggregation and multimer assembly, and structural and morphological details of vascular cells under aqueous conditions. AFM offers opportunities for visualizing surface-dependent molecular and cellular interactions in three dimensions on a nanoscale and for sensitive, picoNewton level, measurements of intermolecular forces. AFM has been used to obtain molecular and sub-molecular, resolution of many biological molecules and assemblies, including coagulation proteins and cell surfaces. Surface-dependent molecular processes including protein adsorption, conformational changes, and subsequent interactions with cellular components have been described. This review outlines the basic principles and utility of AFM for imaging and force measurements, and offers objective perspectives on both the advantages and disadvantages. We focus primarily on molecular level events related to hemostasis and thrombosis, particularly coagulation proteins, and blood platelets, but also explore the use of AFM in force measurements and surface property mapping.     

Effect of matrix components on chromium atomization processes in graphite furnace atomic absorption spectrometry

The effect of various organic and inorganic matrix components on chromium atomization in graphite furnace atomic absorption spectrometry is studied. The results are explained on the basis of chromium's atomization mechanisms. The two predominant mechanisms are the thermal dissociation of the oxide and of the carbide. Losses through molecular volatilization reduce the sensitivity when chromium chelate complexes are atomized. In this case, the atomization mechanism consists of the thermal dissociation of the chelate. The formation of chromium carbide from the carbon residue produced by decomposition of the organic solvents leads to a loss of sensitivity.     

Visualization of atomic processes on ruthenium dioxide using scanning tunneling microscopy.

The visualization of surface reactions on the atomic scale provides direct insight into the microscopic reaction steps taking place in a catalytic reaction at a (model) catalyst's surface. Employing the technique of scanning tunneling microscopy (STM), we investigated the CO oxidation reaction over the RuO2(110) and RuO2(100) surfaces. For both surfaces the protruding bridging O atoms are imaged in STM as bright features. The reaction mechanism is identical on both orientations of RuO2. CO molecules adsorb on the undercoordinated surface Ru atoms from where they recombine with undercoordinated O atoms to form CO2 at the oxide surface. In contrast to the RuO2(110) surface, the RuO2(100) surface stabilizes also a catalytically inactive c(2 x 2) surface phase onto which CO is not able to adsorb above 100 K. We argue that this inactive RuO2(100)-c(2 x 2) phase may play an important role in the deactivation of RuO2 catalysts in the electrochemical Cl2 evolution and other heterogeneous reactions.     

Post-adiabatic approach to atomic and molecular processes: The van der Waals interactions of some open shell systems

Summary Various properties of post-adiabatic representations of multichannel Schrödinger equations are described in the general context of adiabatic and classical path approximations as used in atomic and molecular physics. The van der Waals interactions of fluorine, chlorine, and oxygen atoms with rare gases, hydrogen, methane, and hydrogen halides are considered: it is found that in some of these systems, the first-order post-adiabatic scheme exhibits a smaller coupling than the adiabatic representation, thus providing an appropriate choice of the basis functions for a decoupling approximation.     

Determination of lead in plants in controlling phytoremediation processes using slurry sampling electrothermal atomic absorption spectrometry

The comparative determination of lead in plant samples by two atomic spectrometric techniques is reported. At first, slurry sampling electrothermal atomisation atomic absorption spectrometry (ETAAS) was applied. The results obtained were compared with those found after a wet digestion procedure by flame atomic absorption spectrometry (FAAS) or ETAAS. The accuracy of the studied methods was checked using a certified reference material (CL???1 CRM, Cabbage Leaves). The recovery of lead was 90% for slurry sampling ETAAS, and 86.6% for liquid sampling ETAAS. The advantages of the slurry sampling ETAAS method are the simplicity of sample preparation and very good sensitivity.     

锂电池电极过程的原位电化学原子力显微镜研究进展

随着人类对能源的使用与存储需求不断增加,高能量密度和高安全性能的二次锂电池体系正在被不断地开发与完善.深入理解充放电过程中锂电池内部电极/电解质界面的电化学过程以及微观反应机理,有利于指导电池材料的优化设计.原位电化学原子力显微镜将原子力显微镜的高分辨表界面分析优势与电化学反应装置相结合,能够在电池运行条件下实现对电极/电解质界面的原位可视化研究,并进一步从纳米尺度上揭示界面结构的演化规律与动力学过程.本文总结了原位电化学原子力显微镜在锂电池电极过程中的最新研究进展,主要包括基于转化型反应的正极过程、固体电解质中间相的动态演化以及固态电池界面演化与失效分析.     

AFS-230E双道原子荧光光度计测定蔬菜中的砷和汞

采用湿法消解蔬菜样品,用AFS-230E型双道原子荧光光度计测定蔬菜中的As、Hg重金属含量。在最佳实验条件下,As、Hg元素的工作曲线相关系数(r)分别为0.9992、0.9996,检出限分别为0.0119ug/L、0.0139ug/L,回收率分别为：91.6%~101.50%,89.8%~97.3%,相对标准偏差（RSD%,n=7）分别为1.39%、0.52%,该法可供各地测定该类蔬菜中As、Hg等重金属元素含量的参考。     

Study of processes in the hydride generation atomic absorption spectrometry of antimony,arsenic and selenium

Studies of the decomposition rate of the reducing agent sodium tetrahydroborate in alkaline and acidic media and of the reaction rate of the formation of the hydrides under the usual analytical conditions are described. The stripping of the hydrides with different lengths of the stripping coil, with different amounts of hydrogen in the carrier gas and with sodium hydroxide added during and after the stripping process are discussed. Some evidence for the existence of an intermediate during the decomposition reaction of the sodium tetrahydroborate is given. The role of temperature, hydrogen and oxygen during the atomization of the hydrides in an electrically heated quartz cuvette is discussed. Under certain conditions, antimony atoms form dimers or elemental antimony precipitates in the heated cuvette.     

Free-atom formation processes in premixed fuel-rich and stoichiometric oxygen-acetylene flames employed in atomic emission and absorption spectroscopy

Detailed observations on the atomic and molecular absorption and emission spectra of the various zones of premixed oxyacetylene flames are presented. Spatial flame profile data for both the natural flame species and those formed when solutions of metallic salts are nebulized into the flame are interpreted in terms of: (a) the relative concentrations of reactive intermediate and stable species in the various zones; (b) the mechanism of free-atom formation from aerosol droplets; and (c) free-atom depopulation processes. The results of this study clearly show that the striking enhancement in atomic spectra observed in either absorption or emission for many elements in the fuel-rich oxyacetylene flame originate in the favorable chemical environment provided by the interconal zone for the formation and existence of free-atoms.     

An atomic absorption method for continuous analytical monitoring of metal and alloy refining processes

Atomic absorption spectrometry is discussed as a method of measurement for the investigation and continuous analytical monitoring of metal and alloy refining processes by electron beam melting. The theoretical dependence of the absorbance on the density of the atom flow of the component under investigation emanating from the melt surface is derived. In addition, the paper describes the use of this method for the continuous determination of the iron content in a vanadium melt and measurements of the evaporation rate of iron and its thermodynamic activity in the vanadium melt at high temperature.     

Discharge on boiling in a channel: Effect of channel geometry on the performance characteristics of determining metals in a liquid flow by atomic emission spectrometry

Discharge on boiling in a channel was studied as a new atomization and excitation source for spectrochemical analysis in a flow of electrolyte solutions. The discharge arises between the liquid walls of a vapor lock formed in the channel of a dielectric membrane because of the rapid Joule heating of the liquid in the channel. The effect of channel geometry on the reproducibility of the integrated light intensity was studied. The background radiation spectrum was measured over the range 220–900 nm, and the possibility of determining alkali and alkaline earth metals in a flow was studied. The parameters of linear calibration equations and the detection limits for these metals are given.     

Energetics of surface atomic processes and effects on growth of ultrathin films and nanoislands

Real surfaces of a crystal, especially those of nanometer in size, have many steps and all types of lattice imperfections. Moreover, there are atoms of different atomic environments: adatoms sit at a flat terrace, kink-site atoms sit in kink sites, and step-edge atoms of various coordination numbers sit in different step-edge sites. Using field-ion and atom-probe field-ion microscopy, it is possible to measure site specific binding energies of these surface atoms, and determine the mechanisms and activation energies of the various elementary surface atomic processes, i.e. surface diffusion. For kink-site atoms, our measurements with several metals find the binding energy to be equal to the cohesive energy of these metals. Atoms at other sites have slightly smaller binding energies. However, they are not proportional to the coordination numbers of the atoms, as assumed in many calculations. Such information will not only shed light on the binding mechanisms of solids, but is also needed for understanding the mechanisms of growth phenomena, such as crystal growth and epitaxial growth of thin films and nanoislands.     

The oscillator strength in atomic absorption spectroscopy

The role of the oscillator strength, f, in the theory of atomic absorption is investigated. For a pure natural broadened absorption line, the peak absorption coefficient α_o is independent of the oscillator strength. The peak absorption coefficient becomes dependent on f only through additional broadening processes such as Doppler or collisional broadening. The peak cross section for resonance absorption, α₀/N₁, for a closed transition with equal statistical weights is given by σ₀ = 2πXXX² = ( )/[cn(ω₀)] (where XXX = and n(ω₀) is the spectral mode density of the radiation field at the resonance frequency ω₀) and physically represents the cross-sectional area per allowed mode of the radiation field per unit time per unit frequency interval, multiplied by a lineshape factor 2/π.A summary is presented of some recent determinations of oscillator strengths of atomic absorption lines, based on lifetime measurements made in this laboratory. The results are used to revise values of the theoretical characteristic mass for Ag, Al, Au, Ca, Cu, Mo, Na, Ti and V used in absolute analysis by graphite furnace atomic absorption spectroscopy.     

Investigation of corrosion processes on cleavage edges of potash-lime-silica glasses by atomic force microscopy

Corrosion phenomena on surfaces of potash-lime-silica glass with medieval composition have been imaged in-situ using AFM in combination with a home built sample holder and a commercial liquid cell. Measurements under ambient atmosphere lead to pit corrosion. Sample preparation and measurement performed under liquids such as isobutanol inhibit the corrosion process. Addition of water (10 vol%) induces the formation of a leached layer, where the network modifiers such as K and Ca are exchanged by hydrogen-bearing species. During the measurements interactions of the tip with the sample surface have been observed.