Analyses of ion-exchanged glass optical waveguides by means of secondary ion mass spectroscopy: Condensation of impurity halide ions at the surface

We analyzed the chemical composition of K⁺-exchanged glass optical waveguides (OWGs) by secondary ion mass spectroscopy. Extensive condensation of impurity halide ions took place at the surface of the OWGs in the ion-exchanging and annealing processes. The condensation of Cl ions is likely a cause of the abnormal behavior observed for soda-lime glass OWGs; that is, a guided mode having appeared during the annealing did not disappear even after long annealing. Moreover, it was suggested that a space charge layer was formed at the OWG surfaces owing to the condensation of the halide ions.     

Ion Flux from the Cathode Region of a Vacuum Arc

This paper reviews the properties of the cathode ion flux generated in the vacuum arc. The structure and distribution of mass erosion from individual cathode spots and the characteristics of current carriers from the cathode region at moderate arc currents are described. An appreciable ion flux (～10% of total arc current) is emitted from the cathode of a vacuum arc. This ion flux is strongly peaked in the direction of the anode, though some ion flux may be seen even at angles below the plane of the cathode surface. The observed spatial distribution of the ion flux is expressed quite well as an exponential function of solid angle. The ion flux is quite energetic, with average ion potentials much larger than the arc voltage, and generally contains a considerable fraction of multiply-charged ions. The average ion potential and ion multiplicity increase significantly for cathode materials with higher arc voltages, but decrease with increasing arc current for a particular material. The main theories concerning ion acceleration in cathode spots are the potential hump theory (PH), which assumes that all ions are created at the same potential, and the gas dynamic theory (GD), which assumes that all ions are created with the same flow velocity. Experimental data on the potentials and energies of individual ions indicates that these theories in their original forms are not quite correct, however extensions or modifications of the PH and GD theories seem very likely to be able to predict correct values for the charge states, potentials, and energies of individual ions.     

Ion flux from the cathode region of a vacuum arc

The properties of the ion flux generated in a vacuum arc are reviewed. The structure and distribution of mass erosion from individual cathode spots and the characteristics of current carriers from the cathode region at moderate arc currents are described. An appreciable ion flux (~10% of the total arc current) is emitted from the cathode of a vacuum arc. This ion flux is strongly peaked in the direction of the anode, although some ion flux may be seen even at angles below the plane of the cathode surface. The observed spatial distribution of the ion flux is expressed quite well as an exponential function of the solid angle. The ion flux is quite energetic, with average ion potentials much larger than the arc voltage, and generally contains a considerable fraction of multiply charged ions. The average ion potential and ion multiplicity increase significantly for cathode materials with higher arc voltages but decrease with increasing arc current for a particular material. The main theories concerning ion acceleration in cathode spots are the potential hump theory and the gas dynamic theory. Experimental data indicate that these theories serve reasonably well when used to predict the mean values of the charge state, ion potential, and ion energies for the ion flux, but are quite insufficient when compared with the results for the potentials and energies of individual ions     

Surface double layer on (001) surfaces of alkali halide crystals: a scanning force microscopy study

In this Letter we consider the surface double layer on (001) surfaces of UHV cleaved and annealed alkali halide crystals (KCl, NaCl), which we studied with dynamic scanning force microscopy and Kelvin probe force microscopy. Kelvin images show bright and round patches at corner sites and steps. Images with atomic resolution always show kinks at the latter step sites. Our findings are in perfect agreement with the long-standing picture that, due to the presence of divalent impurity ions, the surface carries a net negative surface charge originating from negative cation vacancies at kinks.     

Potential energy of an isolated gold atom on the (100) surface of alkali halide crystals

The energy of an isolated gold atom on the (100) surface of several alkali halide crystals (NaCl, NaF, KCl, KBr) is calculated as a function of distance above the crystal surface. The calculations include dispersion, electrostatic and repulsive potentials and are performed by direct summation over near neighbours and integration over the rest of the crystal. Detailed potential maps of the (100) surface as seen by a gold adatom are obtained, preferred adsorption sites are identified, and surface quantities such as adsorption energies, minimum energy barriers for diffusion and vibrational frequencies are computed. The effects of relaxations of the (100) surface ions due to both the presence of the surface and the presence of the adatom are examined. Both are found to be significant. Some comparison with experimental results is made.     

Positive ion emission during the interaction of dissociated gases with alkali-halide crystals

Radical-recombination emission (RRE) from the surfaces of a number of alkali-halide crystals has been studied in an atmosphere of nitrogen, hydrogen, and oxygen. It is found that RRE of positive ions in an atmosphere of atomic hydrogen is much greater than from atmospheres of either nitrogen or oxygen. The kinetics of positive ion emission have also been investigated. It is found that the emission intensity is proportional to the surface coverage by chemisorbed atoms. The experimental data are consistent with the assumption that RRE is due to sputtering of alkali-metal ions (which together with a halide form the matrix of the crystal lattice) during surface atomic recombination reactions.     

Interionic potentials and force constant models for rocksalt structure crystals

It is suggested that the observed departure from the Cauchy relation in alkali halide structure crystals is due to ionic deformations. Interionic forces may then be taken to be central and a comparison between lattice dynamical models and interionic potential models becomes possible. In this paper attention is restricted to MgO, NaCl, LiF and KI for all of which (i) an isotropic (breathing) deformation can account for the difference C₄₄–C₁₂ and (ii) only the negative ion need be considered deformable. The interionic potential is assumed to consist of Coulombic and van der Waals terms, which are taken as known, and short range repulsive terms with an exponential dependence on separation. The constants in these repulsive terms are determined from the force constants of the lattice dynamical models. Satisfactory agreement with measured cohesive energies can be achieved only if the charge on the ions is very close to the electronic charge (2e in the case of MgO). This leads to a sacrifice in accuracy of the lattice dynamical models but this is shown to be small so that reasonable compatibility between the two sets of models is thus demonstrated. The interionic potentials are compared with those of other workers.     

Direct ToF-SIMS analysis of organic halides and amines on TLC plates

It has been reported that: “direct analysis of thin layer chromatography (TLC) plates with secondary ion mass spectrometry (SIMS) yields no satisfactory results” (J. Chromatogr. A 1084 (2005) 113-118). While this statement appears to be true in general, we have identified two important classes of compounds, organic halides and amines, that appear to yield to such direct analyses. For example, five organic halides with diverse structures were eluted on normal phase TLC plates. In all cases the halide signals in the negative ion time-of-flight secondary ion mass spectrometry (ToF-SIMS) spectra were notably stronger than the background signals. Similarly, a series of five organic amines with diverse structures were directly analyzed by positive ion ToF-SIMS. In all but one of the spectra characteristic, and sometimes even quasi-molecular ions, were observed. Most likely, the good halide ion yields are largely a function of the electronegativity of the halogens. We also propose that direct analysis of amines on normal phase silica gel is facilitated by the acidity, i.e., proton donation, of surface silanol groups.     

Ideal multipole ion traps from planar ring electrodes

We present designs for multipole ion traps based on a set of planar, annular, concentric electrodes which require only rf potentials to confine ions. We illustrate the desirable properties of the traps by considering a few simple cases of confined ions. We predict that mm-scale surface traps may have trap depths as high as tens of electron volts when parameters of a magnitude common in the field are chosen. Under similar conditions, micromotion amplitudes in a 2D ion crystal as low as tens of nanometers could be realized. Several example traps are studied, and the scaling of those properties with voltage, frequency, and trap scale, for small numbers of ions, is derived. Applications of these traps include quantum information science, frequency metrology, and cold ion–atom collisions.     

Nuclear quadrupolar relaxation in ionic crystals

The nuclear quadrupolar relaxation time of alkali halide crystals is investigated by the Heitler-London approximation. We use the Slater determinant which is constructed by the Hartree-Fock wave functions of the free ions. The charge distribution around an ion is not spherically symmetrical because of mutual overlap of the atomic wave functions of nearest-neighbor ions. Moreover, the charge distribution around an ion changes its shape during thermal vibrations of the ions, because the degree of the overlap depends upon the distance apart of the ions. Therefore, the quadrupolar interaction in alkali halide lattices is the resultant of a combination of the thermal vibration with the charge overlap. As illustrations of the theory, we have computed the quadrupolar relaxation time of the ³⁹K and the ³⁵Cl nuclei in the KCl crystal, and the ²³Na nucleus in the NaCl crystal. The theoretical results are in good agreement with those of experiments. We have also computed the ratio of the quadrupolar relaxation time of the metal nucleus to that of the halogen nucleus for some alkali halide crystals. After computing the same ratio by the covalent model and the deformation model, we have compared these results with the available experimental data. Finally, by using the same overlap model as that mentioned previously, we have developed a formula which gives the chemical shift of ionic crystals.     

Interionic potentials in alkali halides and their use in simulations of the molten salts

After an outline of work on rare-gas systems, which serves as a target for parallel work on alkali halides, and an initial brief survey of those parts of this parallel work for which results have been obtained, interionic potential models for alkali halides are considered in some detail. The rigid ion potentials of Fumi and Tosi are discussed and then a major part of the section is devoted to deriving a new set of polarizable ion potentials, which incorporate the ideas behind the lattice dynamical shell model. Extensions which include many-body terms in the potentials are considered briefly and finally the information which can be obtained from alkali halide diatomic molecules is discussed.

In the third section methods of computer simulation for ionic liquids are outlined, concentrating on the molecular dynamics method, and some of the properties which can be obtained by analysing the ion trajectories are listed. Results from simulations, including some new work on LiF, NaCl and RbI, are reviewed.     

Stabilization of LiBH4 superionic phase by halide doping and H disordering

We performed first-principles density-functional theory calculations to investigate the structural properties and the effect of halide ion doping to the superionic-conducting, high-temperature phase and the effect of halide doping on the phase of LiBH₄. It is computationally demonstrated that the superionic phase is stabilized owing to the halide doping with the large ions which fill the interlayer space of the superionic phase. The H-disordered phase is observed in the structure and is found to contribute to the stabilization of the superionic phase.     

MeV-ion-induced defects in organic crystals

We present scanning force microscope images of crater-like defects induced by MeV atomic ions incident on single-crystal L-valine surfaces. For grazing incidence ions, the craters are elongated alongthe ion azimuth of incidence and are followed by raised tails in the surface above the ion track. Craters formed by off-normal ions are wider than craters formed by nrmally incident ions. The crater volume is highly nonlinear in (dE/dx)_e. We discuss our observations qualitatively in terms of thermal-spike and pressure-pulse/shock-wave models for the sputtering of organic solids.     

ESCA-studies of the surface film formed on stainless steels by exposure to 0.1 M NaCl solution at various controlled potentials

After immersion in a 0.1 M NaCl solution for 1 h at various controlled potentials, the surface films formed on two commercial stainless steels, 18–12 and 29-4-2, have been studied using a surface analysis technique ESCA (Electron Spectroscopy for Chemical Analysis) combined with ion etching. The influence of controlled potential in the lower region, between the OCP and the critical pitting potential, on the structure and chemical composition of the passive film is in limited agreement with the prior work. At higher controlled potentials above the pitting potential, the surface films consist of two components: the passive film and corrosion products. Changes to both oxidized chromium and metallic iron form major differences in the depth profiles in comparison with the previous results with the passive film. At higher controlled potentials oxidized alloying elements tend to the higher oxidation states on the outermost part of surface together with a possibility of enhanced adsorption of chloride ions. There is a great amount of oxidized molybdenum and chloride ions mainly from the corrosion products on the surface at higher applied potential. Their contents increase with the controlled potential.     

LaOBr1-xClx:Tb3+晶体中Tb3+的4f75d1激发态的能级分裂

在室温和78K下对六种LaOBr1-xClx:Tb3+(x=0、0.2、0.4、0.6、0.8、1.0)粉末样品的4f75d1激发谱进行了研究,在78K下观察到了Tb3+离子的4f75d1激发态的能级分裂。利用点电荷模型计算得到了LaOBr1-xClx:Tb3+晶体中Tb3+的4f75d1激发态能级的分裂值。考虑到LaOBr1-xClx:Tb3+化合物的共价性等因素,三个因子α=0.32,β=0.67-1.08,γ=0.32-0.40相应地引入到Akm展开式中与O.X.La有关的各项中。计算得到的能级分裂值和实验值相差小于20cm-1。     

Synthesis of periodic plasmonic microstructures with copper nanoparticles in silica glass by low-energy ion implantation

Ion implantation was used to locally modify the surface of silica glass to create periodic plasmonic microstructures with Cu nanoparticles. Nanoparticles were synthesized by Cu-ion irradiation of the silica glass at the ion energy of 40 keV, dose of 5×10¹⁶ ions/cm² and current density of 5 μA/cm². This procedure involves low-energy ion implantation into the glass through a mask placed at the surface. Formation of nanoparticles was observed by optical spectroscopy and atomic force microscopy. The presented results clearly demonstrate how the low-energy ions can be used for the fabrication of photonic microstructures on dielectric surfaces in a single-step process.     

丙酮化学发光反应中卤素离子敏化效应的研究

本文报导了丙酮化学发光反应中卤素离子的敏化效应,对其敏化机理进行了探讨,并研究卤素离子敏化效应的分析应用。     

STM and AFM observations of damage produced by swift Ne and Kr ions in graphite

Radiation damage of highly oriented pyrolitic graphite (HOPG) samples have been investigated following irradiation with 215 MeV Ne and 209 MeV Kr ions, available at U-400 cyclotron, Dubna. A freshly cleaved HOPG surface was irradiated perpendicularly to the sample surface (c plane). A low ion irradiation dose was used (10¹² ions/cm²) in order to avoid damage overlap. Scanning tunneling microscopy (STM) and atomic force microscopy (AFM) are useful methods allowing direct observation of surface defects. The observations were made after irradiation without any further sample preparation. The experimental results are compared to computer simulations (TRIM code) and primary knonked-on atomic spectrum calculations (LET code). Clear distinction can be made between surface features attributed to nuclear stopping effects and defects owing to electronic stopping mechanisms.