The magnetic and transport properties of films based on discontinuous layers of Ni81Fe19 (Py) embedded in Al2O3 were investigated. In films with nominal Py thicknesses 6 and 8 angstrom superparamagnetic particles with median diameters D-med = 2.8 and 3.1 nm and distribution widths sigma(D)= 1.2 and 1.3 nm were formed. Current voltage (IU) curves were measured with the current perpendicular to the film plane. The analyses show that the charge transport occurs via tunneling; with the charging energy supplied by thermal fluctuations at high temperature, T >= 100 K, and by the electric field at low temperature, T < 10 K. The separation of the two regimes allows independent estimates of the mean charging energy < EC > approximate to 40 meV for both samples; from the resistance R versus T analyzed in an effective-medium model at high temperature and from I versus U at 4 K. In order to obtain a consistent description of the transport properties, the size distributions must be included to account for the deviation from the single size behavior R similar to exp(E-C/k(B)T) at high T. The scaling parameter in the relation I proportional to (U/U-th-1)(gamma), where U-th is the threshold for conduction, is estimated to gamma approximate to 2 at 4 K. The superparamagnetic relaxation of the particles becomes blocked below a temperature T approximate to 20 K respective 30 K for 6 and 8 angstrom. The magnetic field (B) dependence of the resistance R(B) displays a single maximum of the ratio MR = [R(B)-R(2 T)]/R(2 T) in zero field at room temperature and a characteristic splitting of the peak at 4 K, attributed to the blocking. The maxima, approximate to 0.9% for 6 angstrom and 1.1% for 8 angstrom, are positioned at fields about a factor of two to three higher than the coercive fields of the samples.

We have built a model where we use a wound as a probe of the dielectric properties of skin. In this way one is able to infer information about skin dielectric properties in situ. We introduce the notion of a skin electrochemical capacitor. This gives good agreement with recent measurements for the electric potential landscape around a wound. Possible diagnostic consequences are briefly touched upon.

A theory of coherent excitation of a localized state on an adatom by two-photon photoemission spectroscopy(TR-2PPE) is presented within a microscopic model and the time-dependent formalism. Coherent oscillation and incoherent population decay of the excitation are obtained, and are shown to attain well-defined lifetime constants only in the long-delay limit. In addition, we have found a competing excitation channel via electron transfer. The theory is applied to Cs/Cu (111), which reproduces a few qualitative features observed in recent experiments. The effect of atomic motion on the 2PPE spectra, which manifests dominantly as a redshift in the spectrum, has been analysed.

In the scanning tunnelling microscopy of metal surfaces, electrons tunnelling inelastically emit light via the decay of coupled plasmons of the tip and the sample. We present an experimental study of the influence of the tip shape in light emission for a double tip system which is specially suitable to isolate the influence of the tip shape from other features in fluorescence spectra. Model calculations for various tip shapes show qualitative agreement with the experimental features, emphasizing the importance of tip shape in light emission.

The deexcitation probability of localized electronic states in metals has been studied regarding the influence of the degree of localization. Results show that localization reduces the probability of deexcitation, thus increasing the lifetime, as a consequence of the mismatch between the momentum spectrum of a highly localized state and the excitation spectrum of the electron gas. The energy dependence of the probability is only slightly affected by the localization of the state.

We study small identical magnetic particles embedded in a non-magnetic medium with their centers lying in a two-dimensional regular lattice. Within the approximation of the Weiss molecular field due to the magnetic dipole moments of the neighboring particles on the spins of a central particle, we derive general expressions for magnetization and magnetic susceptibility of the system. As an application, we discuss the ordering for a square lattice.

Electronic absorption spectrum in the near IR region (Qy band) of LH I of Rhodopsirillum rubrum and LH 11 of Rhodopseudomonas acidophila is calculated using an electrodynamical point dipole approximation. The model uses the geometrical arrangement and the properties of individual chromophores made available from recent structural and spectroscopic determinations and is found to accurately predict not only the resonance frequencies, but also the shape of the Qy band of the absorption spectrum.

We study a square lattice of small magnetic particles in a non-magnetic medium. We use the Weiss Molecular Field approximation to derive expressions for magnetic ordering temperature. For the magnetization normal to the lattice plane, we get long range antiferromagnetic ordering For inplane magnetization, we find that the moments of the particles order in ferromagnetic chains while the neighboring chains are antiferromagnetically ordered relative to each other.

The effect of the density of states on the lifetime of low-energy electrons in metals has been studied using a golden rule approach. Simple approximations to the real density of states of metals have been used allowing analytical results, which show that the free-electron scaling (E-E-F)(-2) Of the lifetime is affected above the onset of d-electron contributions. Hence, in noble metals a scaling with (E-E-F-omega(d))(-2), where omega(d) is the energy distance from the Fermi energy to the top of the d band, appears once d electrons can be excited. In ferromagnetic Co, the ratio between the lifetimes of majority and minority spin electrons is found energy independent below the threshold for the excitation of majority d electrons while this ratio increases with energy above that point.

The applicability of density-functional theory is extended to the area of van der Waals interactions between macroscopic bodies, in particular between two parallel surfaces. It is shown how the strength and the asymptotic form, including the van der Waals planes for the surfaces can be calculated with the electronic densities and the static image planes of the interacting objects as the only input. The calculation is carried out easily in a simple density-functional scheme, suggesting the possibility of extensions to the description of forces between more generally shaped macroscopic bodies, including the sample and tip in scanning-force microscopy.

Light emission during the interaction of slow singly-charged clusters with solid surfaces is studied theoretically. More precisely, we consider positive ions of Ag n clusters (n = 1...5) impinging on silver surfaces. In such systems, the charge transfer process involved during the cluster-surface interaction is mainly resonant capture. However, photon emission due to radiative capture is also a possible charge transfer channel. Our simple theoretical model including both processes allows us to calculate the light spectra and the total photon yield for the different cluster sizes, n. Our results show that light emission strongly depends on the electronic level dynamics of the clusters in front of the surface, providing a tool for electronic structure analysis of atoms, clusters and solid surfaces.

We calculate the attractive van der Waals force in a model system consisting of a sphere and a semi-infinite slab representing the tip and sample in an atomic force microscopy experiment. The objective of the calculation is to establish estimates of the errors involved when using Hartmann's approximation scheme [Phys. Rev. B 42, 1541 (1990)], which accounts for tip and sample geometry by treating them as a set of piecewise parallel planes. Neglecting retardation effects, we can evaluate the electromagnetic stress tensor and the van der Waals force exactly in the model system. Comparing the results with those obtained within the Hartmann scheme we find that the difference is not larger than 5-10% in practice in an atomic force microscopy experiment, and 25% in a worst-case situation. The accuracy of Hartmann's scheme is, however, to some extent the result of canceling errors, since the maximum stress is overestimated while the tip-sample interaction area is underestimated.

Photon emission due to the radiative neutralization of slow Ag3+, Ag4+ and Ag5+ clusters impinging on a silver surface is studied theoretically. The photon spectra and the total photon yield are calculated by using two different sets of experimental data for the ionization potential. The features of the photon spectra such as energy of the emitted photons and frequency at which the emission is maximum strongly depends on the experimental ionization potential chosen as input. Consequently, we propose light emission as a complementary experimental tool to study the electronic properties and, in particular, the ionization potential of such clusters.

This chapter discusses the classical optical response of a superlattice (SL) in terms of the macroscopic dielectric functions of its constituents. It provides a detailed description of the elementary excitations in the SL, including collective excitations—such as plasmons and polaritons. The chapter also briefly reviews the effect of nonlocal dielectric functions. The first GaAs/GaAlAs SL represents a milestone in material engineering through the use of molecular beam epitaxy technology. It consists of a periodic repetition of alternating layers of lattice-matched GaAs and Ga1-x AlxAs. The properties of the bulk materials are often retained in the direction perpendicular to stacking, whereas if the layer width is less than the Bohr radius for the bulk material, novel quantum mechanical confinement effects are obtained. The band structure of a metallic SL is very different from those of the constituents, if the layer thickness is only one or a few atomic layers thick.

The discovery of the fullerenes in 1985 by Kroto, Heath, O'Brien, Curl and Smalley and the development of a method for production of macroscopic amounts in 1990 by Kratschmer, Lamb, Fostiropoulos and Huffman opened a new area of carbon research with possible production of new materials with unique properties. The field has developed further later on with discoveries of nanotubes, metal filled nanotubes, carbon onions and more recently metal covered fullerenes. All these new discoveries show how cluster science opens approaches to the area of meososcopic physics. The general trend is here in the direction from small to large contrary to the general trend of modern mesoscopic physics or micro-electronics where the movement is from large to small. It is especially fascinating how the whole area of fullerene research was initiated by problems in astrophysics. Originally Kratschmer and Huffman had the intention to explain an observed strong extinction from interstellar dust and produced in experiments special carbon soot with a characteristic optical absorption known as ''the camel hump smoke''. This paper gives a short overview of some of our more recent theoretical work of the electronic properties of C-60, metal covered C-60 and nanotubes. In addition some results are also presented of optical properties of metal covered C-60 as a function of metal coverage.

In the frame of the self-energy formalism, the interaction of STEM electrons with a cylindrical surface is studied. The surface modes of cylindrical interfaces so obtained are proven to fulfil certain sum rules. A general expression for the energy loss probability valid for any beam direction nonparallel to the cylinder axis is presented. In all the cases the so-called begrenzung effect is found.

The fabrication of silicon nitride components by pressure slip casting has been studied. Simple as well as more complicated shapes such as spin test discs, with homogeneous microstructure, were produced using this technique.Prior to casting in a full-scale pressure casting machine, fundamental studies of the casting behaviour of the slips were conducted using filter pressing experiments. Due to the coarse pore structure of the polymeric mould material used special attention was given to the slip proper ties in order to avoid slip penetration into the mould and to obtain an adequate consolidation. Parameters like the degree of particle interaction and solid content as well as the pressure schedule were investigated.Partially flocculated slips were found to give considerably faster castings and the obtained bodies sintered to nearly full density without deformations In pressure casting of spin test discs with stabilized slips, optimization of the pressure schedule was required to avoid cracking caused by stress gradients.

After the discovery of the C60 molecule a lot of attention has been given to its optical and collective properties. The latest development in fullerene related research was the synthesis of coaxial carbon sheets called carbon or nano tubes and also spherical concentric graphitic shells called carbon onions. With a model describing the collective dynamics of electrons we may gain insight in the physics of the collective resonances. Based on a simple equation of motion for the induced density in a carbon particle we demonstrate the existence of a rich spectrum of collective resonances for both carbon onions and carbon tubes.

In the frame of the self-energy formalism, the energy loss spectrum for STEM electrons moving close to a sphere coupled to a planar surface is studied. As an application the problem of the coupling between a small metallic particle and a large supporting surface is studied, as well as its dependence on both the size of the particle and the dielectric nature of the support. The coupling between both surfaces is found to be relevant only for particles of radius less than upsilonomega-1, where omega is the energy transfer and upsilon is the electron velocity. This result is explained in terms of the range of the Coulomb interaction. Our results are in qualitative agreement with recent experimental data.