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We analyze a new type of the plasmon mode in nanosize semiconductor crystals. Rotational dipole plasmon resonance, in which only angular degrees of freedom are excited, prevails in the optical spectra of photodoped nanocrystals. Such a collective mode differs basically from surface plasmon resonances in typical photoabsorption spectra of metallic nanoclusters and can be described as an excited state in a finite Fermi system as well as a rotational motion of a quantum liquid. We demonstrate that such dipole oscillations are harmonic, which makes it possible to identify them as a plasmon resonant excitation.

A mechanism of angular-momentum transfer between photoelectrons and Auger electrons is applied to Auger electron emission in process of photoionization of deep inner atomic shells followed by Auger decay. This mechanism proofs to be the leading contribution to distortion of angular distribution of the Auger electrons and highlights important features of postcollision interaction effect in the inner shells photoionization. The theory developed is applied to the photoionization of $n{s}^{2}$ shells of noble gases. Calculations show the noticeable influence of angular-momentum transfer on the Auger-electron angular distribution in a number of cases. Photoionization processes suitable for experimental observation of the proposed effect are discussed.

The ground state properties of an multi-exciton (ME) complex localized in a nanoscale semiconductor quantum dot (QD) have been studied. The calculations have been performed using the envelope function approximation for electron and hole motion in the QD. The many-body quantum mechanical treatment of the electron-hole dynamics was done within the Density Functional Theory approach. The ground state energy dependencies upon QD radius, number of electron-hole pairs, QD dielectric function and effective masses of electron and holes have been analyzed. It is demonstrated that when multi-exciton complex is strongly localized within the QD, the physical properties of the system are determined by a single parameter, the ratio of QD and free exciton radii, and its binding energy is given by the function of this parameter multiplied by the binding energy of an isolated exciton in bulk semiconductor.

Electron-ion coincidence experimental data obtained following argon 1s photoionization are reported. Slow photoelectrons were measured in coincidence with Ar+ and Ar2+ ions, and the beta angular di ...

The kinetics of vertical electron transport in a semiconductor superlattice is considered taking into account partial localization of electrons. The time dependences of photoemission currents from samples based on a strained semiconductor superlattice calculated by numerically solving the kinetic equation are in good agreement with experimental data. Comparison of the theory with experiment makes it possible to determine the characteristic electron localization and thermoactivation times, the diffusion length, and losses of photoelectrons in the superlattice.

A concrete mechanism of angular-momentum transfer in photoionization process is proposed for electron photoemission from deep inner atomic shells. It is demonstrated that the leading contribution to angular-momentum transfer is provided by postcollision interaction of the photoelectrons and Auger electrons. The standard theoretical approach to postcollision interaction has been considerably improved by taking into account angular-momentum transfer. The theory developed is applied to the photoionization of $1{s}^{2}$ shell in Ar. Calculations show the noticeable influence of angular-momentum transfer on the photoelectron angular distribution.

We study the optical properties of nanosize two-component Fermi systems. The photoabsorption spectra in Fermi systems containing not more than 102 pairs of oppositely charged particles are calculated. The main focus is on the role of collective plasmon excitations. The dependences of the position of the plasmon resonance on the number of particles and the ratio of their masses in the system are investigated.

The dependence of the properties of finite two-component Fermi systems containing two types of oppositely charged particles on the ratio of their masses has been studied. A theoretical model for the quantum-mechanical description of a system containing a finite number of pairs of particles has been proposed on the basis of the Hartree-Fock approximation and the random-phase approximation with exchange. A method that makes it possible to exclude the motion of the center of mass of the system from the spectrum of excited states has been developed in the random-phase approximation with exchange. This method has been used to calculate the binding energies and static dipole polarizabilities of systems containing 8, 20, and 40 pairs of oppositely charged particles at various ratios of their masses.

Electro-physical parameters of super-thin basalt fiber (STBF) from Armenian basalt rocks are measured before and after hydrochloric acid treatment. It is shown that specific resistance and dielectric parameters of super-thin basalt fiber change essentially after hydrochloric acid treatment. The temperature dependence of these parameters was studied too. The probable cause of the change is an increase in the total amount of pores and modification of the share of pores of various sizes in STBF, followed by an increase of absorption of water molecules from the ambient medium. The results (in both alternating and direct electric fields) are interpreted within the framework of the dipole-relaxation mechanism of the polarization of water molecules in STBF pores.

A classical approach to the description of angular momentum transfer between the Auger electron and photoelectron in post-collision interaction is worked out. The results of the classical approach coincide with the quantum mechanical ones at the photoionization threshold. Besides, the approach developed provides a description of angular momentum transfer beyond the photoionization threshold. In particular, it is suitable in the energy region of comparable velocities of two emitted electrons.

We consider the double ionization (DI) of a helium atom by fast protons and study the role of electron correlations in this process. We develop a quantum-mechanical approach that takes into account the interaction of the emitted electrons in continuum and the dynamical charge screening of the ejected particles, which depends on their ejection kinematics. The interaction of the emitted electrons between themselves and with the core is described in the model of approximate 3C functions, while the dynamical charge screening is described by introducing effective charges of the emitted electrons and the ion core, which are determined by the particle momenta. The derived closed analytical expressions for the differential ionization cross sections have been applied to the case of a coplanar particle ejection geometry at various momenta q transferred to the atom. Analysis of our calculations has shown that the developed model describes adequately the available experimental data. Including the dynamical charge screening has a significant effect on the DI cross section and improves considerably the agreement between theory and experiment.

Attenuation of light in light guides is a well understood phenomenon from the point of view of the basic underlying physics. Particularly in the case of light guides having a macroscopic cross section, ray trace modeling captures all of the key physics and makes it possible to accurately predict the decay of radiant flux as a function of length in the guide. Unfortunately, in typical applications in the field of illuminating engineering, such calculations are prohibitively difficult for two primary reasons. First, the precise bi-directional reflectance distribution function for the internal surfaces may not be readily available. Second, the precise angular distribution of luminous intensity, as a function of position on the input aperture, may also not be easily quantified. This paper presents a surprisingly simple and accurate general model for describing the flux attenuation with distance in a general light guide. The model has only two free parameters, and therefore measurement of decay at just...

Theoretical study of the ionization of sodium clusters by an intense laser pulse with a photon energy close to the surface plasmon resonance is presented. The proposed model describes the resonance channel of cluster ionization via excitation of a multi-plasmon collective electron state that can subsequently decay through a single electron emission. The method of separation of the centre of mass coordinate from other electronic degrees of freedom has been employed to take into account the highly excited electronic states. The autoionization decay rate of the multi-plasmon excited state together with the energy and angular distributions of outgoing electrons has been obtained.

The correlation function between two emitted electrons has been calculated as a function of their momentum difference for double ionization of 1s2s excited He atoms by fast ion impact. A simple quantum mechanical approach is developed to take into account the dynamics of two-electron ejection as well as the effects of electron exchange and correlated electron motion in the final state. A clear difference between the correlation functions of the excited and ground state targets is reported.

We study electron-electron correlation effects in double ionization of He and Ne by 3.6 MeV/amu Au53+ impact by analysing the correlation function for back-to-back emission of electrons with equal energy. For this particular emission pattern we find the correlation function to be sensitive to the target while without selection of this pattern no significant dependence on the initial state is observed. Therefore, this method may open the possibility to sensitively map correlated many-electron bound states.

The correlation function for the process of double ionization of the He atom by ion impact is calculated. A simple quantum mechanical approach is developed to take into account the dynamics of two-electron ejection as well as the effects of correlated motion of electrons in the final state and electron exchange. The reasonable agreement with the available experimental data shows that our approach can describe the most essential features of electron correlation in the correlation function.

A theoretical study of the inelastic scattering of low-energy electrons from metallic clusters is presented. We calculate the total inelastic electron scattering cross section using the standard jellium model and the methods of quantum many-body theory. Many-electron correlations for collective excitations of the cluster target are taken into account within the random-phase approximation with exchange (RPAE). The polarization interaction between the projectile and the cluster electronic system is described using the Dyson equation. We report resonance maxima in the energy dependence of the total inelastic cross section in the energy region above the surface plasmon frequency. This resonance effect is connected with the process of electron capture to quasi-discrete levels localized in the field of the target cluster and simultaneous excitation of the surface plasmon. This process can explain experimentally observed resonance behaviour of the electron attachment cross section in the projectile energy range e

We have applied the dynamical jellium model for metal clusters, which treats simultaneously the vibrational modes of the ionic jellium background in a cluster, the quantized electron motion and the interaction between the electronic and the ionic subsystems beyond the adiabatic approximation, for the calculation of widths of electron excitations in metal clusters caused by multiphonon transitions, and investigated their temperature dependences. We have also estimated the decay time and the energy relaxation time of electron excitations in metal clusters.

We have developed a dynamic jellium model for metallic clusters, which treats simultaneously the vibrational modes of the ionic jellium background in a cluster, the quantized electron motion and the interaction between the electronic and the ionic subsystems beyond the adiabatic approximation. Using this model, we have calculated the widths of electron excitations in metal clusters in the vicinity of the plasmon resonance caused by the multiphonon transitions and investigated their temperature dependence. We estimated the decay time and the energy relaxation time of electron excitations in metal clusters.

New calculations of the low-energy free-electron attachment cross section to neutral and charged metallic clusters are reported. We include all the bound states of the negative ion as well as Rydberg series of neutral cluster targets as possible final states for attachment and calculate the electron attachment cross sections. The influence of the dynamic core polarization on the capture process is studied. Quadrupole contributions are found to play a more important role than in the optical spectra as cluster size increases.

We demonstrate that the electron energy loss spectrum in collision with metal clusters or fullerenes depends strongly on the scattering angle of the electron. This results from the fact that the excitation probability of the surface plasmon modes of different multipolarity is correlated with the scattering angle of the electron. We derive the kinematic conditions under which the plasmon excitation with the given angular momentum dominates in the cross section. We perform our treatment in the resonance plasmon approximation and also in the random phase approximation with exchange using the wavefunctions of the Hartree-Fock jellium model. We compare the predictions of these two quite different approaches for the cluster and report their qualitative agreement. Theoretical results are compared with the available experimental data for the electron-fullerene collision. Reasonable agreement between theoretical and experimental results is reported.

We present the results of the many-body treatment of the bremsstrahlung (BrS) process in collisions of fast electrons with metal clusters. We concentrate our attention on the range of photon frequencies characteristic for plasmon excitations in clusters. The dynamic polarizability of a cluster in this frequency range is very large and it determines the value and behaviour of the cross section of the process as a function of various parameters. When calculating the cross section of the process, we treat the dynamic response of the cluster in the random-phase approximation with exchange, using wavefunctions of the Hartree-Fock jellium model and also in the resonance plasmon approximation. The latter approach is well applicable for the treatment of collective excitations of electrons in clusters. We analyse the spectral and angular distributions of the emitted photons, as well as the collision velocity dependence of the cross section for small sodium clusters and demonstrate that collective electron excitations determine the main features of the BrS cross section.

In this paper we suggest the many-body treatment for the inelastic scattering of fast electrons on metal clusters. The accurate many-body theory for this process is necessary because electrons in the cluster experience collective excitations during the collision. We perform our calculation in the random phase approximation with exchange using the wavefunctions of the Hartree-Fock jellium model and also in the plasmon resonance approximation. The latter approach is appropriate to treat collective excitations in clusters. We analyse the differential and total inelastic scattering cross sections and elucidate the relative importance of collective electron excitations and single-electron transitions in the formation of the inelastic scattering cross section on metal clusters. We perform this calculation for the magic sodium clusters Na20 ,N a 40 ,N a 58 and Na92. Theoretical results are also compared with the experimental data available for electron collisions with the Na8 ,N a 20 and Na40 clusters. We report some discrepancy between theoretical and experimental results.

We consider the radiative process in collisions of electrons with metal clusters and fullerenes and demonstrate that the plasmon resonance structure manifests itself the photon emission spectrum. This effect occurs because the cross section of this process is mainly determined by the dynamical polarizability of the cluster. We suggest a new method of description of the photon emission in the vicinity of a plasmon resonance. Our consideration is applicable to any polarizable system possessing a collective giant resonance. We also demonstrate that the collision velocity dependence of the cross section has a pronounced maximum. The absolute maximum of the radiation intensity occurs at the collision velocity determined by the cluster radius and the frequency of the plasmon resonance.

It is shown that the main contribution to the elastic cross section of fast electrons on metal clusters and fullerenes results from scattering on the frozen cluster potential, which is determined by the electron density distribution of the ground state of the target cluster. The specific shape of the electron distribution in fullerenes and metal clusters manifests itself in the diffraction behaviour of the elastic differential cross section. The analysis of the total elastic cross section dependence upon projectile velocity, the number of atoms in the cluster and its size is provided. The cross section of elastic scattering on a cluster surpasses the sum of the individual scattering cross sections on the equivalent number of isolated atoms. This occurs because of the coherent interaction of the projectile electron with electrons delocalized in the cluster volume. We have demonstrated that collective electron excitations sensitive to the many-electron correlations dominate inelastic scattering. The surface plasmon resonances can be observed in the differential cross section for inelastic scattering. We found a condition for the quadrupole and higher multipole plasmon excitations to contribute relatively little to the electron energy loss spectrum. The results obtained have been compared with experimental data for the electron - fullerene collision. Reasonable agreement between theoretical and experimental results is reported. We have also demonstrated that plasmon excitations provide the main contribution to the total inelastic cross section over a wide energy range. We have calculated the dependence of the total inelastic cross section on collision energy and compared the result obtained with the experimental data available, giving an interpretation for the plateau region in the cross section as caused by plasmon excitations rather than the cluster fragmentation process. We have shown that the single-particle jellium approximation fails to describe this experiment. Our analysis is performed for metal clusters and fullerenes, However, it can also be applied to other polarizable systems, possessing plasmon or giant collective resonances.

Atomic inner-shell photoionization followed by double Auger decay is investigated. The focus of our study is the effect of post-collision interaction (PCI) on the photoelectron energy distribution. A semi-classical approach is employed to describe the PCI distortion of the photoelectron line shapes associated with both direct and cascade double Auger decays. This approach is shown to be valid at low photoelectron energies, whereas for large incident photon energies it reduces to the eikonal approximation. The theory is applied to the case of Ar $2p$ photoionization spectra and good agreement with available experimental data is achieved.

Optimized AlInGaAs/AlGaAs superlattice with strained quantum wells has been developed, fabricated and studied. The choice of hetero‐layer composition and thicknesses is based on calculations of Sl’s band energy spectrum, photoabsorption spectrum and transport properties. Electron emission from the developed photocathodes demonstrates maximal polarization above 90%.

We study the process of low-energy electron capture by the ${\text{SF}}_{6}$ molecule. Our approach is based on the model of Gauyacq and Herzenberg [J. P. Gauyacq and A. Herzenberg, J. Phys. B 17, 1155 (1984)] in which the electron motion is coupled to the fully symmetric vibrational mode through a weakly bound or virtual $s$ state. By tuning the two free parameters of the model, we achieve an accurate description of the measured electron attachment cross section and good agreement with vibrational excitation cross sections of the fully symmetric mode. An extension of the model provides a limit on the characteristic time of intramolecular vibrational relaxation in highly excited $\text{SF}_{6}{}^{\ensuremath{-}}$. By evaluating the total vibrational spectrum density of $\text{SF}_{6}{}^{\ensuremath{-}}$, we estimate the widths of the vibrational Feshbach resonances of the long-lived negative ion. We also analyze the possible distribution of the widths and its effect on the lifetime measurements, and investigate nonexponential decay features in metastable $\text{SF}_{6}{}^{\ensuremath{-}}$.

New photocathode for highly polarized electron emission has been developed, fabricated and studied. Polarized electron source is based on short‐period strained AlInGaAs/AlGaAs superlattice grown by MBE method. Deformation of AlInGaAs quantum well results in 85 meV energy splitting between heavy hole and light hole minibands. Electron emission from the developed photocathode demonstrates maximal polarization of 92% with quantum efficiency of 0.85%.

Resonance enhancement of the quantum efficiency of new polarized electron photocathodes based on a short‐period strained superlattice structures is reported. The superlattice is a part of an integrated Fabry‐Perot optical cavity. We demonstrate that the Fabry‐Perot resonator enhances the quantum efficiency by the order of magnitude in the wavelength region of the main polarization maximum. The high structural quality implied by these results points to the very promising application of these photocathodes for spin‐polarized electron sources.

Many-particle effects in two-component systems composed of two types of oppositely charged fermions are studied. The influence of mass ratio of the particles on physical properties of microscopic electron–hole droplets is investigated. We offer a theoretical model describing a quantum-mechanical system of a finite number of electron–hole pairs coupled by Coulomb interaction. The model is based on the Hartree–Fock approximation and the Random Phase Approximation with Exchange (RPAE). Within our theoretical approach we exclude center-of-mass motion from the spectrum of excited states of the system. Using our model we calculate the binding energies, static dipole polarizabilities and photoabsorption cross sections for the systems containing different numbers of particles with various ratios of electron and hole masses.

The relaxation time of optical excitations in simple metal clusters is calculated. The relaxation mechanism arises from electron-phonon transitions from the optically excited electron state to all possible excited states. The electronic excitations are described in the random-phase approximation with exchange within the jellium model. The phonon spectrum is associated with the thermal fluctuations of the ionic background, which is described in the liquid drop model. Calculated relaxation times are in a good agreement with available experimental data. The asymptotic limit of these rates in very large clusters is estimated within an analytical model that describes the decay, into particle-hole excitations, of the dipole collective state associated with the center-of-mass motion.

In this work we treat inelastic scattering of fast electrons on metal clusters in the range of transferred energies above the ionization threshold. We demonstrate that in this energy range many-electron collective excitations, namely, the volume plasmons, provide dominating contribution to the differential cross section resulting in its resonance behavior. The volume-plasmon resonances excited in the cluster during the collision decay via the ionization process. We determine the resonance frequency and the autoionization width of the volume plasmon excitations. In order to elucidate the role of plasmon excitations, we calculate the differential cross section of the process using two different approaches. We calculate the cross section in the random-phase approximation using the Hartree-Fock wave functions as a basis and accounting simultaneously for all singleparticle and collective excitations in the cluster. We compare the results of this approach with those obtained in the plasmon resonance approximation. PACS number~s!: 36.40.Gk

We consider a photon emission in collisions of electrons with atoms and clusters under the conditions when the radiation of atomic electrons gives significant or even dominating contribution to the total spectrum. This occurs, for example, when the frequency of the emitted photon is comparable with the energy of giant collective or plasmon resonance in an atom or cluster. We consider the manifestation of the effect for atomic and solid targets demonstrating the significant role of the photon self-absorption and electron energy loss in a solid target. We present results of recent calculations of the cross sections of the process for a number of targets. Theoretical results are compared with the available experimental data.

The results of experimental and theoretical studies of spin polarized electron transport in semiconductor SL used for photoemitter application are presented. The experimental study is based on the time resolved measurements of electron emission from the cathode after its photoexcitation by fs laser pulse. The response and spin relaxation times have been determined by means of measured time dependent intensity and polarization of electron emission. We also performed theoretical calculations of photocathode pulse response and compared the obtained results with experimental data. Our analysis testifies the presence of partial electron localization in SL. Electron capture by localized states leads to unavoidable losses of quantum efficiency and polarization.

Optimal photocathode performance requirements and recent developments of highly efficient emitters of polarized electrons are reviewed.