Table of contents

From a deterministic point of view of quantum theory the Schrödinger equation, considered as an equation of motion, is defined within an area of instability formed by two potential minima. This view can be related to the renormalization group theory of critical phenomena, and the location of two nontrivial fixed points can be defined with respect to those two potential minima.

The renormalization group theory parameter: d, the dimensionality of space, defines the transition between classical and quantum theory. For a system in which d ≧ 4, classical mechanics applies, and for d < 4, quantum mechanics applies. Whereas the classical potential defining an equation of motion has one potential minimum (at the Gaussian fixed point), the quantum potential defining an equation of motion has two potential minima (at the nontrivial fixed points).

An analogy exists between systems based on wave mechanics and those based on lattice systems. The underlying dynamics of that potential, the minimization of which results in an equation formally equivalent to the Schrödinger equation, can, in this formal analogy, be identified with the underlying dynamics of the exchange energy at the vertex of a lattice. There is thus a mathematical global similarity underlying the behavior of these two distinct theoretical frameworks which describes both. The principal and angular momentum quantum numbers of electron systems in this analogy are equivalent to the dimensionality of space, d, and the dimensionality of spin space, n, in the general theory of critical phenomena.

The general theory describes the phase transitions of electron (wave mechanical) systems, and also a "Mendeleev's table" based on the d and n parameters constructed for those electron systems, in analogy with such a table for lattice systems.

We present details of a display type photoelectron spectrometer, based on the principal of mirror-electron-microscopy employing an electrostatic projection lens system, which is capable of imaging photoelectrons as a linear function of their parallel wavevector throughout the entire Brillouin zone. The photocurrent is amplified onto a phosphor screen via a channel electron multiplier array. The very low light levels are then picked up with a specially developed CCD camera so that the digitized image can be both position and energy analysed. The system has the advantage over existing display type analysers in that the image is a rectilinear mapping of k_||-space independent of both photon energy used or binding energy of the electronic states selected. It is possible to energy select various states at or below the Fermi energy with a retarding field analyser to a resolution of 0.3 eV.

The performance of this electrostatic lens system is demonstrated by imaging the photoelectron distribution from the valence band states of a clean Cu(001) surface. Analysis of the results shows good agreement with the energy band diagram of copper and with results obtained by conventional angle-resolved photoelectron spectroscopy.

The electrofission cross section of ²³²Th was measured between 5.6 and 32 MeV. The data analysis indicates a concentration of E2-fission strength (∼ 8% of an E2-energy weighted sum rule) near the fission barrier of ²³²Th, in agreement with electro- and photofission angular distribution results found in the literature. The E2-fission probability deduced from the data (in the energy region of the Giant Quadrupole resonance - GQR), is comparable to the fission probabilities of both the Giant Dipole Resonance and the compound nucleus, indicating that in the decay of the GQR a statistical equilibrium is probably reached.

Electron excitation rates for the ground state to n = 2 and 3 S and P levels in He-like ions between F VIII and Mn XXIV have been determined by interpolating recent R-matrix and distorted wave calculations for O VII, Mg XI, Ca XIX and Fe XXV. Results are presented in the form of polynomial fits in log T_e to the effective collision strengths (γ) for each transition. The fits may be used to estimate values of γ accurate to between 10 and 20% over a temperature range approximately equal to log T_max ± 0.8 dex, where T_max is the temperature of maximum fractional abundance in ionisation equilibrium of the relevant species.

The problem of K-shell vacancy creation by 2pσ-2pπ rotational coupling is considered in the presence of other inelastic channels. The effect of these channels is described through appropriate decay widths of rotationally coupled states. By varying only the decay strength of the 2pσ state in a very limited range, numerical solution of the corresponding coupled equations for several collision systems with Z₁ ∼ Z₂ ⩽ 10 (Z being the nuclear charge) shows good agreement with experimental data on the impact-parameter dependence of the K-shell vacancy production probability.

K-vacancy fractions as well as cross sections for creation and quenching of K-vacancies have been measured for O, F, Mg, Si, and S projectiles moving through solid Fe, Co, Ni and Gd at velocities ranging from 1.5v₀ to 10.5v₀. Two different techniques were used, i.e., the beam-X-ray and the probe-layer method, respectively. Based on comparisons with semiempirical estimates a number of different K-shell processes were identified. Direct Coulomb ionization and excitation and electron capture dominate at high velocities, whereas collision-perturbed deexcitation and quasi-molecular effects are important at low velocities. Distinct level-swapping effects are observed for O and F in Fe. The present data provide the basis for an investigation of the origin of the transient magnetic field in a recent paper.

Fluorescence from SiO matrix isolated in argon has been investigated in the wavelength region 120-300 nm. Fluorescence emission spectra from the valence states, A¹Π, E¹Σ⁺ and G¹Π, revealed that nearly all radiation comes from one channel at 305 nm, which was analysed as originating from the b³Π-X¹Σ⁺ transition. Contrary to the A¹Π and G¹Π states, the E¹Σ⁺ state also decays radiatively, although weakly, through two other channels situated in the vicinity of 305 nm. These two channels were believed to originate from the a³Σ⁺-X¹Σ⁺ and e³Σ^--X¹Σ⁺ transitions.

The autoionization region of mercury was investigated with spin- and angle-resolved photoelectron spectroscopy between the Hg⁺ (5d⁹ 6s²)²D_5/2 and Hg⁺ (5d⁹ 6s²)²D_3/2 thresholds. Spin-polarization parameters A and ξ and intensity were measured separately for the photoelectrons corresponding to the two final ionic states accessible (²S_1/2, ²D_5/2) as function of the radiation wavelength. The data are dominated by structure due to autoionization resonances and differ quantitatively for the two peaks in the photoelectron spectra. The results are compared with earlier measurements below the ²D_5/2-threshold.

For the first time solutions of binaphthyl-derivatives, menthylesters of a helical skeleton of the cyclophane type and combinations of these structure units have been measured in an absorption type CD experiment between 200 nm and 160 nm using synchrotron radiation as a continuum light source. Assignments of exciton chirality were made according to the CD exciton coupling mechanism. In the case of the well known ¹B_b transition the combined units neither do change their chirality nor do they develop strong exciton coupling between themselves. Below 200 nm two new transitions had been accessed: CD data allow to distinguish between the X → C and the X → D transition which strongly overlap in the absorption spectra. By comparison of acetonitril and hexafluoro-iso-propanol solution data they could be determined as a Rydberg transition and a molecular valence transition, the latter showing a bisignate CD Cotton effect.

High resolution far ultraviolet (1200-2000 Å) spectra of 17 cool giant and supergiant stars have been obtained using the IUE satellite of ESA, NASA and UK. We have measured the line intensities, wavelengths and widths of approximately 200 EUV emission lines in these spectra, using a least squares gaussian fitting technique. Line identification has been obtained in about one third of the cases. The measured values are organized in a database in order to facilitate updating and investigation of interrelations with stellar atmospheric parameters.

The observations include lines from C I, C II, C IV, S I, O I, O IV, Si II, Si IV, N V, Al III, Fe II and Mg II. These lines are mostly formed by radiative processes in the extremely rarefied plasma in the outer stellar atmospheres, and occasionally involve highly excited energy levels of the atoms and ions. The temperature of formation ranges from about 5 × 10³ to 10⁵K, corresponding to different depth levels in the atmosphere, and the lines serve as a valuable tool for probing the physical conditions in these regions. We may also get new information on atomic processes that take place under conditions that are never duplicated in the laboratory. The present data may therefore give important contributions both to astrophysics and to atomic physics.

Well resolved photoelectron spectra of the HCl inner valence shell have been obtained with monochromatized synchrotron radiation in the 30-90 eV photon energy range. They show the limiting case of the "complete breakdown" of the molecular orbital picture when ionization takes place in the inner valence shell of HCl. The photoelectron data have been analyzed in comparison with the results obtained from X-UV absorption, L₂₃-MM Auger and photon spectroscopy.

A systematic study of the reproducibility of the VUV continuum emitted from a laser-produced samarium-plasma source driven by a 10-Hz Q-switched Nd: YAG laser is reported, and its possible use with a conventional scanning monochromator in absorption spectroscopy is demonstrated.

A new simplified equation, describing low-frequency, short-wavelength acoustic gravity waves in the atmosphere, is deduced.

Using the unrestricted Hartree-Fock scheme in the framework of pseudocluster calculation developed by us earlier, the Coulomb gap is investigated for compensated doped semiconductors in deep nonmetallic regime. For given degree of compensation, we obtain a power law behavior of the Coulomb gap Δ_c ∝ P^ν, where P is the donor concentration and ν ≃ 1/3. Above the Coulomb gap the excitation spectrum exhibits a sharp threshold. Relation between the present quantum mechanical treatment and the classical treatment is discussed.

Muon spin precession spectra are observed in transverse field geometry at all temperatures, including the antiferromagnetic state. This unique behaviour is a consequence of the chemical and magnetic structure of FeSn. The observed precession signals contain two components, one at a frequency corresponding to the external field and, in an intermediate temperature range, a second one corresponding to a field at the muon of 0.21 T extrapolated to 0 K.

We apply the surface Green function matching (SGFM) method to the study of the electronic states of surfaces and interfaces. We use empirical tight binding Hamiltonians to describe the ideal (100) GaAs-Ge interfaces and the corresponding free surfaces. Electronic band structures and local densities of states are calculated and discussed, with emphasis on the practical aspects of SGFM as a computational technique.

Heavy fermions compounds show highly unusual properties. The most striking one is probably superconductivity. Triplet superconductivity has been suggested. Here we want to suggest that singlet superconductivity is possible. We first emphasize that heavy fermions are due to quasi localized f-electrons. Thus we show that magnetic correlations are important in this heavy Fermi liquid. Even in the non magnetic case, magnetic interactions as measured for instance by the paramagnetic Curie temperature, are greater than the Kondo temperature. This point, using a Fermi liquid theory, suggests that singlet superconductivity is likely in these compounds.

The magnetic phase diagram of Fe_1-xAl_x alloys has been calculated. The short range comositional order was included. Two different models were used. The reentrant spin glass phenomenon has been obtained for the better of them. The effects of clustering were also discussed.

In GaSb/AlSb multi quantum well structures (MQW) we previously observed a quantum size induced direct to indirect band structure transition at well widths around 40 Å. Using time resolved optical spectroscopy, we investigated the time dependence of the quantum well emission as a function of the well width. The life time of the quantum well emission changes by two orders of magnitude if the well width of 40 Å is exceeded. This verifies the direct to indirect cross-over in the GaSb/AlSb system

An all optical Time-of-Flight method is used to study transport properties of laser pulse generated ambipolar carrier systems. Exciting carrier pulses at the front of Si wafers and probing the carrier density by a thin layer at the back yields a high temporal and spatial resolution.

The evaluation with a simple hydrodynamical and a kinetic model yields the mobility and the distribution function as a function of space and time at different temperatures.

The most important feature of surface generated ambipolar carriers is the motion in a nonequilibrium state over relatively large distances, though no electric field is applied. The moving carriers are identified as free excitons showing the classical mobility μ(T) ∼ T^–1.5 by scattering with acoustic phonons via the deformation potential.

The majority optical cross section and the concentration of levels with optical response induced by boron implantation at 10¹⁰ ions/cm² in GaAs, have been obtained using the technique labelled Optical Isothermal Transient Spectroscopy, OITS, in an energy range between 0.8 eV and 1.4 eV. The experimental optical data measured at different annealing temperatures, show only the presence of the EL2 and EL6 electron trap levels. The optical behaviour found is in complete agreement with the existence of an interaction between these two deep levels, EL2 and EL6. Besides, this interaction has been found to be the origin of the U-band in the DLTS spectra and of the anomalous dependence of the level concentration on the annealing temperature deduced from the OITS and DLTS spectra.

We have enhanced the flipping ratio of spin-polarised-neutron near-critical-angle reflectivity measurements by sandwiching thin (few atomic layers) magnetic films (area 2 cm²) between non-magnetic materials, thereby producing interference in the neutron wave field within the sandwich structure. A strongly spin dependent reflectivity is observed for a 12 Å polycrystalline Fe film at 300 K but no spin dependence is observed for ultrathin f.c.c. Fe films at 300 K.

The subject of this contribution is multiphoton interaction of laser light in the blue and green spectral ranges with cleaved and polished (111) surfaces of BaF₂ in ultrahigh vacuum and air. We claim that photoemission and laser-induced non-thermal desorption of positive ions are triggered by nonlinear absorption of some order between two and five. Photoemission and ion desorption yields are strongly wavelength dependent and display conspicuous resonance structures, with striking similarities between electron and ion yield spectra. Cluster calculations are performed in an attempt to understand the origin of these resonances. They predict the existence of occupied surface states near the middle of the bandgap together with a high density of resonances in the upper half of the bandgap. Measurements of the surface second harmonic generation in air showed a similar wavelength dependence as the electron yield in vacuum. The transition from pure second harmonic generation to plasma discharge was studied and evidence is presented that the discharge is ignited by resonant multiphoton absorption in adsorbed gas molecules.

Recent experimental results of spin-polarized electron emission following photoexcitation of the valence orbitals of adsorbed rare-gas atoms are presented. As light source we employed the circularly polarized synchrotron radiation from the storage ring BESSY (Berlin). As detection technique served angle- and spin-resolved electron spectroscopy. The resolution of the experimental method is demonstrated by the example of photoemission from Ar on Pt(111), where a doublet feature with a splitting of only 90 meV could be resolved, which is hardly discernible in intensity spectroscopy. Below the threshold for direct photoemission narrow electronic resonances have been observed, resulting from discrete np → n's excitations in the adsorbate. For the system Xe on Ir(111) the dependence of the resonance features on the coverage from the sub-monolayer regime up to the 3D-crystal is discussed.

The electronic structure of the valence band and the core levels nearest to it was investigated for Cd_1-xCa_xF₂, Cd_1-xPb_xF₂ and Cd_1-xMn_xF₂(0 ⩽ x ⩽ 1) crystals with the fluorite structure. UPS (hv₁ = 21.2 eV and hv₂ = 40.8 eV) and XPS experiments were carried out for all of these crystals and obtained results are compared with the available results of the electronic structure calculation. The results present how the nearest to the valence band-core levels of the cations contribute to the density of states distribution in the valence band of ternary alloys. The measured energy shift of the core levels of the anion with the change of the ternary crystal composition is treated as corresponding to the appearance of the local structure in the crystal.

Some details of the chemical and electronic structure of tri-p-dimethylaminophenyl carbonium chloride, or Crystal violet (CV), have been studied by Ultra Violet Photoelectron Spectroscopy (UPS) and X-Ray Photoelectron Spectroscopy (XPS, or ESCA). Thin films consisting of either the salt, CV⁺Cl^-, or metastable neutral molecules, CV⁰, have been studied. Valence band spectra of ultra thin solid films of crystal violet are compared with the UPS spectra of N,N-dimethylaninile (NNDMA) and p-methyl-N,-N-dimethylaniline (p-M-NNDMA) in the gas phase. Preliminary MNDO and VEH calculations are used to interpret the spectra.

Polarized reflection spectra of orthorhombic indium bromide has been measured in 2-30 eV region by using the synchrotron radiation. From 2 to 15 eV, structure in the spectra comes from the transition from the valence bands of Br 4p and In 5s. At about 20 eV, sharp doublet structure due to In 4d N_IV,V levels has been observed with several fine structures. Analysis of the intensity ratio of the doublet peaks reveals that the effect of the exchange interaction is significant in this d⁹p manifold.

The Σ-CO species in the system CO-Ni(100), identified as a genuine co-adsorption state by Goodman et al. some years ago, has been investigated with IR reflection-absorption spectroscopy and with photoemission. The data reveal that only Σ-CO is present at low temperatures; the state is weakly adsorbed and shows a strong similarity to CO adsorbed on copper surfaces. Photoemission selection rules indicate a non-normal bonding geometry.

Many body effects in 3d core photoemission (3d-XPS) and 2p core photoabsorption (L₃-XAS) spectra in insulating La compounds, La₂O₃ and LaF₃, are studied theoretically by using the Anderson model with a filled valence band. A unified picture is proposed to explain the two-peak structure of 3d-XPS and the single-peak structure of L₃-XAS in these materials. It is shown that in the final state of L₃-XAS the Coulomb interactions U_fd (between 4f and 5d electrons) and - U_dc (between a 5d electron and a core hole) are essentially important in addition to the Coulomb interaction - U_fc (between a 4f electron and a core hole).

Ce 3d core X-ray photoemission (3d-XPS), 3d core photoabsorption (3d-XAS), 3d core resonant photoemission (3d-RXPS) and bremsstrahlung isochromat spectra (BIS) in a mixed valent insulator CeO₂ and typical metallic mixed valent Ce compounds such as CeRh₃ are studied theoretically on the basis of the Anderson model. By assuming that the weight of 4f⁰ configuration in the ground state, the 4f-valence band mixing and the 4f-4f Coulomb interaction for CeO₂ are considerably larger than those for metallic Ce compounds, a remarkable difference in 3d-XPS and an apparent similarity in 3d-XAS between the two systems are consistently explained. Furthermore differences in 3d-RXPS and in BIS between the two systems expected from the present analysis are predicted. A preliminary discussion about the effect of 4f-core hole and 4f-4f exchange interactions on core absorption spectra in mixed valent systems is also presented.

Using a time resolved magnetic modulated fluorescence technique a specific decay channel for highly excited singlet excitons (until 40 eV) has been discovered consisting of: autoionization in an excited electron-hole pair, slowing down of the "hot" electron of the pair by excitation of triplet excitons charge carrier geminate recombination retarded by transient complexes between Frenkel excitons and charges. The connection of this process with exciton fission in two triplet or two singlet excitons is mentioned.

Two new techniques for the observation of image potential states are discussed, i.e., two-photon photoemission with the image potential state as intermediate and resonant second harmonic generation with the image state as final state. Presently, two-photon photoemission provides the best energy and momentum resolution for probing image states. It is possible to achieve high enough population densities to study electron-electron interaction. An overview of experimental results is given and the prospects for observing two-dimensional electron gas phenomena are discussed.

The formation of point defects in alkali halides by monochromatic radiation was investigated over a wide range of photon energies from the near UV exciton region to the hard X-ray region near the K-edge of bromine (from about 5 eV to 14 keV). The spectral dependence of the production efficiency was measured using monochromatic X-rays and VUV radiation as well as turnable monochromatic beams of synchrotron radiation. F center production efficiencies of the order of one keV/F-center were obtained for KBr and KCl. The yield dropped sharply in regions of strongest absorption such as in the exciton bands. An increase in F-center production efficiency was observed for KBr at the K-edge of bromine (13.4 keV). In the soft X-ray region (50-1500 eV) the F-center generation curves were strongly influenced by the X-ray absorption depth and proximity of the surface.

We have studied chemically adsorbed glycine on the hydrophilic surface of the oxidized surface of silicon. A stable adsorbate layer is formed, which consists of zwitterionic glycine molecules. Most importantly, these zwitterionic molecules have a tendency for orientation in a direction perpendicular to the substrate surface, with COO^- groups away from the surface and the NH₃⁺ groups toward the surface.

Photoemission measurements at hv values covering the 5p excitation edges in solid Eu and Yb, allow to obtain information on the electron states in the rare earth divalent metals, and to identify a very efficient decay channel for the 5p core hole which accounts for the 5p near edge structures in the optical absorption spectra.

We present and discuss carbon K soft X-ray emission spectra of Highly Ordered Pyrolytic Graphite (HOPG) and LiC₆, stage 1 Li intercalated graphite. These measurements allow us to observe the filling of the carbon π states by the electrons from the donor alkali atoms. By fitting the shape of these donor-filled π states with simple models, we can determine several parameters describing the electronic density of states near the Fermi energy in this material. In addition knowing the charge transfer, and measuring the area under the donor-filled π states allows us to evaluate the intensity enhancement seen in X-ray emission near the Fermi energy relative to the rest of the π band.

A modified many angle reflection method based on the use of synchrotron radiation has been applied to study the optical constants of GaAs and GaP in the spectral range from 14 to 26eV. Experimental data on the energy dependence of the density of unoccupied band states have been obtained from the imaginary part of permittivity, where transitions from the 3d-core levels of Ga atoms can be observed. The experiment has been found in a good agreement with theoretical ab initio calculations of the density of p-states in both investigated materials.

Energy distributions of the 4f partial states in lanthanide-copper compounds, RCu₆ (R = Ce, Pr, Nd and Sm) and Ce_xLa_1-xCu₆ (x = 0, 0.2, 0.5, 0.8 and 1.0), have been measured by means of 4d-4f resonant photoemission. Main 4f peaks shift toward the high binding energy and the 4f partial density of states near the Fermi edge decreases successively in the order of CeCu₆, PrCu₆ and NdCu₆. In SmCu₆, an appreciable magnitude of the 4f feature is observed near the Fermi edge in addition to the main feature occurring above 4 eV indicating the coexistence of Sm²⁺ and Sm³⁺ ions in this compound. The main 4f feature in Ce_xLa_1-xCu₆ can be approximated by a Lorentzian shape. The location of the 4f peak and its width are dependent on the concentration of 4f electrons. The shape of the ³D₁ line of the lanthanum ion as observed in partial yield spectra varies with the concentration of lanthanum ions.