Changes in work function due to charge transfer in chemisorbed layers

In a simple tight-binding model well suited to transition and noble metals, we calculate the work function change due to adsorption of alkali metals. A decrease is found to be caused by ionic bonds formed on the surface through charge transfer between the two metals. The local density of states and the number of electrons in the substrate and the chcmisorbed layer are evaluated for various alkali metals and coverages. The method is applicable in both the high and low coverage limits in contrast to existing theories.     

Applying electrohydrodynamic atomization to enhance mass transfer of metal salts from an aqueous phase towards ionic liquids

In this work a two coaxial nozzles configuration is used to investigate whether electro hydrodynamic atomization of an ionic liquid in combination with an aqueous metal salt solution could enhance the removal of metal salts. The technique was evaluated for the removal of manganese (II), cobalt (II) calcium and sodium chloride. Good metal salt extraction was observed for the water-presaturated ionic liquid, tetraoctylammonium oleate, at an applied electrical potential of 5 kV, which was slightly lower compared to mechanical mixing, but a higher separation factor was obtained between the transition metals and the alkali and earth alkali metals.     

A Monte-Carlo calculation of the secondary electron emission of normal metals: I. The model

A model is proposed to describe the secondary electron emission (SEE) of pure normal metals. The various types of collisions suffered by an electron travelling in the solid are analyzed. The dielectric theory is used to account for the collisions with the jellium, including surface effects in an approximate way. The different damping mechanisms for plasmons are reviewed and their influence on SEE is emphasized. The elastic and ionizing collisions with the ionic cores are described by a randium model. The relative importance of each of the above processes for the SEE of normal metals is discussed.     

A model for the metal-non-metal transition in metal-molten-salt solutions

Summary We outline a theory for the metal-non-metal transition occurring in solutions of alkali metals in molten alkali halides as governed by a balance between the binding of ionic clusters by localized electrons and the excess free energy of an ionic assembly screened by metallic electrons. In the model the transition is driven by the composition dependence of the screening length. The theory is amenable to an analytic solution within the mean spherical approximation when Thomas-Fermi screening is used and the ions are described by charged hard spheres.     

On the electronic potential and ionic relaxation at metal surfaces

Some results, obtained by a simple method which gives the main effect of the ions on the surface potential of metals, are advanced. A general expression is given for the change in the surface dipole barrier. The ionic relaxation of (110) and (111) faces of Al are obtained self-consistently, tending to support one of the two current interpretations of LEED diagrams.     

Interatomic forces in the b.c.c. transition metals

Using information obtained from X-ray scattering data, a model for the charge density in the transition metals is constructed. In this model the charge density is given by the sum of the charges situated at the ionic and bond centre sites. Within this framework, expressions for the second order elastic constants and the phonon frequencies in the cubic transition metals are obtained. These quantities have been calculated with and without the bond charge contributions for iron. The comparison with the experimental results shows that the introduction of bond charges, and hence angularity in the force-fields, in iron leads to distinctly better agreement with experiment. From a study of the elastic constants of the other b.c.c. transition metals some observations as to the nature of the angular force fields are made.     

Optical properties of the surface transition-metal structures in fluoride ionic crystals and peculiarities of their formation during thermal diffusion

The possibility of forming surface films with an elevated concentration of an impurity metal during high-temperature diffusion has been analyzed for a wide series of ionic crystals: LiF with Co, Ni, Mg, Ca, Ba, and Sr impurities; NaF with Co, Mn, Mg, Ca, and Sr; MgF₂ with Co and Ni; and CaF₂ with Co. It is established that films are formed only on alkali halide crystals with impurities of transition metals and are not formed on alkaline earth fluorides with transition metals, as well as on alkali halide crystals activated with other divalent cationic impurities. The dynamics of the increase and decrease in the intensity of centers related to impurity-vacancy dipoles during thermal diffusion is shown. The mechanisms of film formation are explained in terms of the features of growth and structure of ionic crystals with cationic impurities and on the basis of isomorphism rules.     

Observation of localized d states in metals

By application of the perturbed γ-ray distribution method combined with heavy-ion reactions and recoil implantation techniques, we have found an experimental was of producing and investigating localized 3d and 4d states in metals. 3d and 4d ions in sp metal hosts, in particular in alkali metals, exhibit the phenomena of large orbital magnetism, extremely small spin fluctuation rates, well defined ionic ground states, mixed valence, and crystal field splittings smaller than theLS coupling. These results upset long standing assumptions about the nature of d states in metals and their magnetic instabilities due to interaction of d orbitals with conduction electrons. If magnetic, the d states of 3d and 4d ions cannot be described by one electron approaches based on Anderson type models but required an analysis based on ionic configurations. The tendencies towards reduced magnetism can be well reproduced by increasing spin fluctuations which gives new insight into antiferromagnetic d-sp exchanges and the Kondo problem for d ions in sp metals. Localized ionic d states, large orbital effects, small crystal fields, and mixed valence-these new phenomena for d ions in sp metals exhibit common basic features with stable and unstable 4f and 5f systems but reflect qualitative differences to the spin dominated magnetism of 3d ions in Cu, Ag, Au and in d metal hosts.     

The plasticity of pure single crystals

The theory of the work-hardening curve of a pure single crystal is discussed. An outline is given of the experimental methods available for the study of the mechanism of plastic deformation and work hardening. An attempt is made to correlate existing theories of work hardening. The theory is illustrated by discussions of copper, of other face-centred cubic metals, of the diamond and sphalerite structures, of hexagonal close-packed metals, of ionic face-centred cubic crystals and of body-centred cubic metals.     

Effect of correlations on electron momentum density in liquid metals

A scheme to calculate the electron momentum density in simple liquid metals, with the effect ofboth electron correlations and ionic potentials included, is given. This scheme is applied to the case of liquid aluminium. The results are substantially different from calculations considering only the ion potentials, and also from the results for a homogeneous electron gas of corresponding density.     

Calculation of energy characteristics of the metal surface taking into account the lattice relaxation effects

Within the framework of the electron-density functional theory method, a self-consistent calculation of the shift of two near-surface ionic planes in different metals has been carried out. The effect of the near-surface lattice relaxation on the surface energy of metals and on the electron work function from these metallic surfaces has been investigated. To describe the arising strong inhomogeneity of the electronic system in the near-surface region, gradient corrections have been taken into account for the kinetic and exchange-correlation energy. To calculate the effect of electron-ion interaction on the energy characteristics of the surface, the Heine-Abarenkov pseudopotential has been used.     

The volume dependent total energy of metals and the ionic radii

The cohesive energies, lattice constants and compressibilities for a number of metals are correlated with the ionic radii through second order pseudo-potential theory. The model yields reasonable results not only for simple metals of arbitrary valency, but for transition elements with no more than 5 d-electrons.     

A new theory of compressible ions — structures of the alkali halides

Ions in ionic crystals are considered to exist in compressible space-filling polyhedral cells analogous to the Wigner-Seitz cell in metals. Repulsion arises from the compression energy of the ions written as a surface integral over the ionic cells. Two adjustable parameters are introduced per ion with the provision that the same parameters can be used in any crystal of any structure in which the ion occurs. The 18 parameters for the 5 alkali and 4 halogen ions have been determined from PV data on the 20 alkali halides. The important successes of the theory are: (i) All the twenty alkali halides are correctly predicted to occur in their observed structures (ii) The thermal transition in CsCl is explained (iii) The pressure transitions in the alkali halides are predicted well (iv) The calculated values of the variation of transition pressures with temperature agree well with experiment. These results are much better than those obtained by earlier theories.     

Theory of electron spin resonance of magnetic ions in metals

Reviewed at both a relatively elementary and more advanced level is the interpretative theory of the electron spin resonance of magnetic ions in metals. The various theoretical possibilities are illustrated by experimental examples wherever possible. Initially the development is based upon the Bloch-Hasegawa equations. The relationship of the advanced theory to this more elementary theory is emphasized. Multimagnetic-impurity experiments, the skin depth problem, the analysis of exchange, hyperfine and crystal field parameters, Redfield theory, ionic and virtual bound state models and the Kondo effect, all in relation to E.S.R. in metals, are each covered in some detail. A discussion of some outstanding problems and projections for the future are also included.     

Photochemistry of solid C60 with tunable infrared radiation

60 with trains of picosecond infrared (IR) pulses, tuned over the 8–15 μm range, is studied. At some specific wavelengths, white-light emission as well as ejection of ionic species from the solid is observed. The spectral characteristics of the white-light emission resemble those of a black body. The mass distribution of the ejected ionic species shows substantial amounts of C₆₀ coalescence products. Unexpectedly, all these processes only occur at wavelengths where solid C₆₀ is relatively transparent. No white-light emission nor ejection of ionic species is observed when being resonant with an IR-allowed transition of C₆₀. It is concluded that regular C₆₀ is not the chromophore for the observed processes, and that sequential absorption of single photons by a strong absorber that is dilute in the crystal takes place. Plausible chromophores are sites that are intercalated with alkali metals. Accumulation of energy at these sites leads to fullerene coalescence in the solid, ion ejection, and white-light emission, ultimately resulting in the destruction of the C₆₀ molecules. Received: 14 April 1998/Accepted: 22 April 1998     

Magnetic 4d systems studied by implanted ions

By application of the perturbed -ray distribution method following heavy-ion reactions and recoil implantation techniques, we have found an experimental way of producing and investigating magnetic 4d states in metals. Strong 4d magnetism has been found for 4d ions in alkali metal hosts and in Pd hosts. In alkali metals, 4d ions reflect the phenomena of well-defined ionic ground states, orbital magnetism, mixed valence, and crystal field splittings smaller than theLS coupling. Magnetic 4d states in alkali metals cannot be described by one-electron approaches based on Anderson-type models, but requires an analysis in terms of many electron ionic configurations exhibiting basic features common to the physics of stable and unstable f stales in metals. In contrast, the local moment formation of 4d and 3d ions in Pd is governed by inter-atomic interactions of the magnetic d states with host d-band electrons, giving rise to spin magnetic behavior of the 4d impurity and to strong spin polarizations of the 4d electrons of the Pd host. Thus, the magnetism and electronic structure of 4d ions in metals exhibit qualitative differences in alkali metal hosts compared to Pd. The existence of magnetic 4d systems strongly depends on the 4d ion species and the host matrix, and on spin fluctuation rates or the corresponding Kondo temperatures. The results can be directly compared to theoretical work and also to the magnetic behavior of 3d ions in sp metal hosts and in hosts with d-band electrons.     

Highly charged ions in field evaporating 4d-transition metals

An energy-focused time-of-flight atom-probe has been employed in a search for high ionic charges obtained in field-evaporating Zr, Nb, Mo, Rh, Pd and Ag, the 4d-transition metals. Although no new higher charges than the already established ones are found for these metals the maximum abundance of the highest charge is determined in each case. An empirical rule predicting the limits of the charge of field-evaporating ions is proposed.     

Determination of Complexed and Ionic Metal in Aqueous Solution. Determination of Stability Constants at Low Concentrations and Kinetic Studies of Complex Formation Using Accelerated Electrodeposition

Metal speciation has become one of the most important areas of concern for today's analysts. Metal complexes can be more readily assimilated by living systems than inorganic forms of the same metals. Conventional atomic absorption spectroscopy is the most widely used technique for the determination of trace metals. By using atomic absorption spectroscopy in conjunction with accelerated electroplating it is possible to distinguish between ionic metal and organically bound or complexed metals in solution.