Showing papers on "Free electron model published in 2004"
TL;DR: A combination of electron lifetime measurement in nanoparticles as a function of the Fermi level position at high resolution in the potential scale with a new model to describe this dependence provides a powerful tool to study the microscopic processes and parameters governing recombination in dye-sensitized solar cells.
Abstract: A combination of electron lifetime measurement in nanoparticles as a function of the Fermi level position at high resolution in the potential scale with a new model to describe this dependence provides a powerful tool to study the microscopic processes and parameters governing recombination in dye-sensitized solar cells. This model predicts a behavior divided in three domains for the electron lifetime dependence on open-circuit voltage that is in excellent agreement with the experimental results: a constant lifetime at high photovoltage, related to free electrons; an exponential increase due to internal trapping and detrapping and an inverted parabolla at low photovoltage that corresponds to the density of levels of acceptor electrolyte species, including the Marcus inverted region.
858 citations
TL;DR: In this paper, a superposition of the free and trapped electron spectra was obtained by subtracting the electron spectrum from the transient absorption spectrum, and the spectrum of trapped holes was obtained.
Abstract: Reactive species, holes, and electrons in photoexcited nanocrystalline TiO2 films were studied by transient absorption spectroscopy in the wavelength range from 400 to 2500 nm. The electron spectrum was obtained through a hole-scavenging reaction under steady-state light irradiation. The spectrum can be analyzed by a superposition of the free-electron and trapped-electron spectra. By subtracting the electron spectrum from the transient absorption spectrum, the spectrum of trapped holes was obtained. As a result, three reactive speciestrapped holes and free and trapped electronswere identified in the transient absorption spectrum. The reactivity of these species was evaluated through transient absorption spectroscopy in the presence of hole- and electron-scavenger molecules. The spectra indicate that trapped holes and electrons are localized at the surface of the particles and free electrons are distributed in the bulk.
437 citations
TL;DR: A model describing the free-electron generation in transparent solids under high-intensity laser irradiation that follows the nonstationary energy distribution of electrons on ultrashort time scales as well as the transition to the asymptotic avalanche regime for longer irradiations.
Abstract: We develop a model describing the free-electron generation in transparent solids under high-intensity laser irradiation. The multiple rate equation model unifies key points of detailed kinetic approaches and simple rate equations to a widely applicable description, valid on a broad range of time scales. It follows the nonstationary energy distribution of electrons on ultrashort time scales as well as the transition to the asymptotic avalanche regime for longer irradiations. The role of photoionization and impact ionization is clarified in dependence on laser pulse duration and intensity.
272 citations
TL;DR: In this article, the optical absorption edge covers a wide energy range from the intrinsic band gap of InN of about 0.7 to about 1.7 eV which is close to the previously accepted band gap.
Abstract: InN films with free electron concentrations ranging from mid-1017 to mid-1020 cm−3 have been studied using optical absorption, Hall effect, and secondary ion mass spectrometry. The optical absorption edge covers a wide energy range from the intrinsic band gap of InN of about 0.7 to about 1.7 eV which is close to the previously accepted band gap of InN. The electron concentration dependence of the optical absorption edge energy is fully accounted for by the Burstein–Moss shift. Results of secondary ion mass spectrometry measurements indicate that O and H impurities cannot fully account for the free electron concentration in the films.
222 citations
TL;DR: A microscopic theory for the interplay between light and matter is presented and it is shown how the slow light can provide an effective magnetic field acting on the electrically neutral fermions, a direct analogy of the free electron gas in an uniform magnetic field.
Abstract: We investigate the effect of slow light propagating in a degenerate atomic Fermi gas. In particular we use slow light with an orbital angular momentum. We present a microscopic theory for the interplay between light and matter and show how the slow light can provide an effective magnetic field acting on the electrically neutral fermions, a direct analogy of the free electron gas in an uniform magnetic field. As an example we illustrate how the corresponding de Haas-van Alphen effect can be seen in a neutral gas of fermions.
148 citations
TL;DR: In this paper, the authors report on the study of plasma edge absorption of InN epilayers with free electron concentration ranging from 3.5×1017 to 5×1019cm−3.
Abstract: We report on the study of plasma edge absorption of InN epilayers with free electron concentration ranging from 3.5×1017to5×1019cm−3. Together with the previously reported data, the wide range variation of effective mass cannot be explained by Kane’s two band k∙p model alone. We show that the combination of Kane’s two band k∙p model, band renormalized effect due to electron–electron interaction, and electron–ionized impurity interaction can provide an excellent description. The effective mass of the free electron at the bottom of the conduction band was found to be m*=0.05m0, which is in good agreement with the very recent theoretical calculation.
128 citations
TL;DR: In this paper, the reduced density matrix describing an interval of N sites in an infinite chain of free electrons is investigated and a commuting operator is found for arbitrary filling and also for open chains.
Abstract: The properties of the reduced density matrix describing an interval of N sites in an infinite chain of free electrons are investigated. A commuting operator is found for arbitrary filling and also for open chains. For a half filled periodic chain it is used to determine the eigenfunctions for the dominant eigenvalues analytically in the continuum limit. Relations to the critical six-vertex model are discussed.
124 citations
TL;DR: In this article, the femtosecond time-resolved near-infrared spectra of TiO2 and Pt/TiO2 powders were measured at the wavelength region of 0.9−1.5 μm with the direct absorption method.
Abstract: Femtosecond time-resolved near-infrared spectra of TiO2 and Pt/TiO2 powders are measured at the wavelength region of 0.9−1.5 μm with the direct absorption method. Broad absorption bands of charge carriers, mainly free and trapped electrons, are observed for TiO2 and Pt/TiO2. The absorption band shape changes with a time constant of 160 fs after the photoirradiation, which most probably reflects the trapping of the generated free electrons. Population decay curves of the carriers after 1 ps, obtained for three different pump light powers, are well-explained by the second-order decay kinetics with a common second-order rate constant, indicating nongeminate recombination of the electron−hole pairs. When Pt is loaded to TiO2, an additional decaying process of 2.3 ps is observed. This decay component represents the transfer of generated electrons from TiO2 to Pt, which is consistent with the known increase of overall catalytic activities by the Pt cocatalyst.
95 citations
TL;DR: By solving the Bethe-Salpeter equation for the electron-holes Green function for crystalline anthracene, this work finds the lowest absorption peak generated by strongly bound excitons or by a free electron-hole pair, depending on the polarization direction being parallel to the short or the long molecular axis, respectively.
Abstract: By solving the Bethe-Salpeter equation for the electron-hole Green function for crystalline anthracene we find the lowest absorption peak generated by strongly bound excitons or by a free electron-hole pair, depending on the polarization direction being parallel to the short or the long molecular axis, respectively. Both excitations are shifted to lower energies by pressure. The physical difference of these excitations is apparent from the electron-hole wave functions. Our findings are a major contribution to solve the long-standing puzzle about the nature of the lowest optical excitations in organic materials.
83 citations
TL;DR: In this paper, the authors calculate the skin depth of indium tin oxide (ITO) films and related materials as a result of free electron absorption within the visible spectrum using the simple Drude model, and discuss the consequences of finite skin depth for the transparency of current spreading layers for light emitting diode (LED) applications.
Abstract: In this article we calculate the skin depth of indium tin oxide (ITO) films (and related materials) as a result of free electron absorption within the visible spectrum using the simple Drude model. We also discuss the consequences of finite skin depth for the transparency of current spreading layers for light emitting diode (LED) applications. Low sheet resistances are highly desirable for these layers, but the free electron density n in ITO cannot be increased much beyond 2
79 citations
TL;DR: In this article, the phase difference between a s and a p-polarized wave at different wavelengths, 632.8 nm and 1.15 μm, was used to measure the temperature of a metal film and its environment.
TL;DR: It is found that inclusion of the electron gas in the model slows down the Coulomb explosion, and suggests that by using ultrashort exposures, structural information may be collected before the sample is destroyed due to radiation damage.
Abstract: A microscopic sample placed into a focused x-ray free electron laser beam will explode due to strong ionization on a femtosecond time scale. The dynamics of this Coulomb explosion has been modeled by Neutze et al. [Nature (London) 406, 752 (2000)] for a protein, using computer simulations. The results suggest that by using ultrashort exposures, structural information may be collected before the sample is destroyed due to radiation damage. In this paper a method is presented to include the effect of screening by free electrons in the sample in a molecular dynamics simulation. The electrons are approximated by a classical gas, and the electron distribution is calculated iteratively from the Poisson-Boltzmann equation. Test simulations of water clusters reveal the details of the explosion dynamics, as well as the evolution of the free electron gas during the beam exposure. We find that inclusion of the electron gas in the model slows down the Coulomb explosion. The hydrogen atoms leave the sample faster than the oxygen atoms, leading to a double layer of positive ions. A considerable electron density is located between these two layers. The fact that the hydrogens are found to explode much faster than the oxygens means that the diffracting part of the sample stays intact somewhat longer than the sample as a whole.
TL;DR: In this article, the photon emission from high-charged heavy ions was studied and it was shown that high-Z$ ions provide a unique tool for improving the understanding of the electron-electron and electron-photon interaction in the presence of strong fields.
Abstract: Recent progress in the study of the photon emission from highly-charged heavy ions is reviewed. These investigations show that high-$Z$ ions provide a unique tool for improving the understanding of the electron-electron and electron-photon interaction in the presence of strong fields. Apart from the bound-state transitions, which are accurately described in the framework of Quantum Electrodynamics, much information has been obtained also from the radiative capture of (quasi-) free electrons by high-$Z$ ions. Many features in the observed spectra hereby confirm the inherently relativistic behavior of even the simplest compound quantum systems in Nature.
TL;DR: In this article, the authors used the high-gain free-electron laser logistic equation to describe the field evolution from spontaneous emission to saturation in the self-amplified spontaneous-emission regime.
Abstract: We use the high-gain free-electron laser logistic equation to describe the field evolution from spontaneous emission to saturation in the self-amplified spontaneous-emission regime. The model we present is capable of including the effects of diffraction, beam qualities, and pulse propagation.
TL;DR: In this article, a double quantum dot (2qd) system connected in a series with electrodes is studied by means of nonequilibrium Green functions and using the equation of motion method, in which all electron correlations in the 2qd are treated exactly.
Abstract: Coherent electronic transport through a double quantum dot (2qd) system connected in a series with electrodes is studied by means of nonequilibrium Green functions and using the equation of motion method, in which all electron correlations in the 2qd are treated exactly. For moderate Coulomb interactions we predict features in a conductance characteristics resulting from transmission through triplet states, which can be strongly activated for larger source-drain voltages. The analysis of the spin-spin correlation functions shows strong antiferromagnetic correlations arising from transport through the singlet state and a reduction of the total magnetic moment. However, when the transmission channel corresponding to the triplet state becomes activated the antiferromagnetic correlations are much weaker, the spins behave as free electrons spins and strongly fluctuate. We speculate that this effect can be seen in wide range of a gate voltage for a double electron occupancy of the 2qd.
TL;DR: In this article, the authors investigated the charge dependence of surface plasma resonance (SPR) on 2 nm octanethiol-protected Au nanoparticles and showed that the peak position of the SPR bands as a function of charge can be precisely calculated by simple Mie theory without any adjustable parameters but by using the number of remaining free electrons in the particle and the experimentally determined dielectric constant for the protecting layer of octanithiol.
Abstract: Charge dependence of surface plasma resonance (SPR) was investigated on 2 nm octanethiol-protected Au nanoparticles. Remarkably, if assuming that each Au-thiol bond localizes one free electron, the observed variations in peak position of the SPR bands as a function of charge can be precisely calculated by simple Mie theory without any adjustable parameters but by using the number of the remaining free electrons in the particle and the experimentally determined dielectric constant for the protecting layer of octanethiol. Additionally, the variations in line-width of the SPR bands can also be quantitatively described by the phenomenological damping law ΔΓ = AvF/R with A = 1.2, a value that suggests a strong chemical-interface damping effect that is consistent with a strong metal−thiol bonding. In the calculations, Perdew's classic spherical jellium model is used to account for the electron spill-out effect. Altogether, these results not only strongly support recent findings by Dickson and co-workers (Phys. ...
TL;DR: In this article, a photo-thermo-refractive glass (PTRG) was used for volume hologram recording, and a system of balance equations was derived which describes the processes of generation of electrons in a conduction band of these glass matrix by photoionization of Ce3+ and trapping of electrons by both silver ions Ag+ and hole centers (Ce3+)+.
TL;DR: In this article, the authors used a 266 nm line of a Nd:YAG laser to increase the conductivity of SnO 2 sol-gel films at low temperature, at the expense of increased bandgap energy.
Abstract: Photoconductivity of SnO 2 sol-gel films is excited, at low temperature, by using a 266 nm line—fourth harmonic—of a Nd:YAG laser. This line has above bandgap energy and promotes generation of electron-hole pairs, which recombines with oxygen adsorbed at grain boundary. The conductivity increases up to 40 times. After removing the illumination on an undoped SnO 2 film, the conductivity remains unchanged, as long as the temperature is kept constant. Adsorbed oxygen ions recombine with photogenerated holes and are continuously evacuated from the system, leaving a net concentration of free electrons into the material, responsible for the increase in the conductivity. For Er doped SnO 2 , the excitation of conductivity by the laser line has similar behavior, however after removing illumination, the conductivity decreases with exponential-like decay.
TL;DR: In this article, the three-body recombination (two free electrons and a proton scattering into one free electron and a hydrogen atom: e+e+p{yields} H+e) in strong magnetic fields was investigated.
Abstract: Using a classical Monte Carlo method, we have computed the three-body recombination (two free electrons and a proton scattering into one free electron and a hydrogen atom: e+e+p{yields} H+e) in strong magnetic fields. The proton is allowed its full motion whereas the motion of the electron is given by the guiding center approximation. We investigate recombination for temperatures and fields similar to those used in recent experiments that generated anti-hydrogen. When the proton has the same temperature as the electrons, the recombination rate for the more elaborate equations of motion is roughly 60% larger than for the B{yields}{infinity} approximation. The recombination rate decreases as the proton speed approaches the electron thermal speed; the variation of this rate has implications for the directionality of the anti-atoms formed in recent experiments. We report on several properties of the atoms formed by three-body recombination in strong magnetic fields.
TL;DR: In this paper, a small electron pocket composed of a metallic and parabolic surface-state band of Si(1.1) 3 × 3 -Ag was investigated by high-resolution angle-resolved photoemission spectroscopy (ARPES) and scanning tunneling spectroscopic (STS), and the effective mass (m*) was extracted by a new method, two-dimensional fitting to the band dispersion.
Metz1
TL;DR: A theoretical approach to calculate differential and total ionization cross sections of polyatomic molecules by fast electron impact using the distorted wave Born approximation without exchange by employing the independent electron model.
Abstract: In this paper, we present a theoretical approach to calculate differential and total ionization cross sections of polyatomic molecules by fast electron impact. More exactly, we have studied the ionization of ammonia (NH3) and methane (CH4) molecules, and previous results concerning the H2O molecule ionization are reported for comparison. The calculations are performed in the distorted wave Born approximation without exchange by employing the independent electron model. The molecular target wave functions are described by linear combinations of atomic orbitals. To describe the interaction between the inactive target electrons and the slow ejected electron, we have introduced a distortion via an effective potential calculated for each molecular orbital. The present theoretical calculations agree well with a large set of existing experimental data in terms of multiple differential and total cross sections.
TL;DR: It is shown that Ti-O has a covalent component and that the Sr-O bond is mainly ionic, and the role of Ti 3d electrons inTi-O bonding is also discussed.
Abstract: Accurate low-order Fourier coefficients of the crystal potential of SrTiO 3 are measured by quantitative convergent-beam electron diffraction. The accuracy in the corresponding derived X-ray structure factors is about 0.1% for the strong low-order reflections (sin θ/λ < 0.3 A -1 ). This accuracy is better than for conventional X-ray diffraction and equivalent to the accuracy of the X-ray Pendellosung method. Combination of these structure factors with high-order X-ray diffraction measurements allows accurate bonding information to be obtained from a multipole model fitted to the experimental data. It is shown that Ti-O has a covalent component and that the Sr-O bond is mainly ionic. The role of Ti 3d electrons in Ti-O bonding is also discussed.
TL;DR: In this paper, the Faddeev-Watson-Lovelace (FWL) treatment, in a second-order approximation, and an active electron model have been applied to calculate the singleelectron capture differential cross sections from K-, L- and M-shells of many-electron atoms by protons at medium and high (but nonrelativistic) impact energies.
Abstract: The Faddeev–Watson–Lovelace (FWL) treatment, in a second-order approximation, and an active electron model have been applied to calculate the single-electron capture differential cross sections from K-, L- and M-shells of many-electron atoms by protons at medium and high (but non-relativistic) impact energies. The radial part of the wavefunction for the active electron was obtained by constructing suitable bases from merging hyperbolic cosine functions with Slater-type radial ones. Converting the Schrodinger-like equation obtained from Hartree–Fock theory gives the effective potential, which is experienced by the active electron in the target atom. A simple analytic radial function composed of a Coulomb and a Yukawa potential was fitted to the effective potential. Near-the-shell two-body T-matrices, electronic–nuclear and inter-nuclear partial amplitudes are calculated to obtain the electron capture differential cross sections between various shells of the target atom and the ground state of atomic hydrogen formed. Theoretical results are compared with the available experimental data on helium, neon and argon atoms at different energies.
TL;DR: In this paper, the reduced density matrix describing an interval of N sites in an infinite chain of free electrons is investigated and a commuting operator is found for arbitrary filling and also for open chains.
Abstract: The properties of the reduced density matrix describing an interval of N sites in an infinite chain of free electrons are investigated. A commuting operator is found for arbitrary filling and also for open chains. For a half filled periodic chain it is used to determine the eigenfunctions for the dominant eigenvalues analytically in the continuum limit. Relations to the critical six-vertex model are discussed.
TL;DR: In this article, the dynamics of charge and spin carriers and coherent phonons as well as magnetic order in III-V ferromagnetic semiconductors were investigated using ultrafast optical techniques.
Abstract: We use ultrafast optical techniques to investigate the dynamics of charge and spin carriers and coherent phonons as well as magnetic order in III-V ferromagnetic semiconductors. We observe a rich array of dynamical phenomena that are absent in traditional nonmagnetic semiconductors or metallic ferromagnets. Very short charge and spin lifetimes of the photoinjected carriers (∼2ps) and multi-level charge decay dynamics are observed, which are attributed to a large density of mid-bandgap states introduced during low temperature molecular beam epitaxy (LT-MBE) growth and highly p-type Mn doping. During the very short free carrier lifetime, the coercivity of the system is seen to be reduced. We attribute this photo-induced ‘softening’ to the transient modification of carrier-mediated ferromagnetic exchange coupling between Mn spins. After the photogenerated free electrons are trapped by defects, periodic oscillations appear in differential reflectivity due to the coherent generation of acoustic phonon...
TL;DR: In this paper, the topology of the Fermi surface of a crystal lattice has been studied and the properties of the crystal topology have been discussed, and the authors showed that the behavior of band electrons under the influence of external electric and magnetic fields depends strongly on the topological topology.
Abstract: The topological aspect of the dynamics of electrons in a crystal (band electrons) and of crystal lattice vibrations (phonons) is discussed. The main features of the dynamics of conduction electrons in metals are connected with the shape of their Fermi surface, which is different from that for free electrons. It is demonstrated that the behavior of band electrons under the influence of external electric and magnetic fields depends strongly on the topology of the Fermi surface. Various examples of such a dependence (calculation of the periods of quantum oscillations, magnetic breakdown, features of the magnetoresistance, Bloch oscillations) are adduced and discussed. The features of the dynamics of phonons are manifested in singularities of the density of vibrational states (van Hove singularities), which are directly related to a change in the topology of the constant-frequency surfaces. The presence of a topological invariant that changes by a jump upon a change in topology of the constant-frequency surface is pointed out. The origin of the so-called phase transition of order two and a half is discussed.
TL;DR: In this article, a dynamical model of local dust charging is presented, which shows that rapid local heating of electrons by the high-power radio wave results in parameter-sensitive modifications of the average dust charge and free-electron density.
Journal Article•
TL;DR: In this article, a novel mechanism of hole-assisted energy absorption by dielectric materials interacting with ultrashort laser pulses of moderate intensity (below damage threshold) is proposed.
Abstract: A novel mechanism of hole-assisted energy absorption by dielectric materials interacting with ultrashort laser pulses of moderate intensity (below damage threshold) is proposed. The analytical theory of multiphoton absorption is generalized to the cases of hole-assisted processes in laser fields of arbitrary polar- ization. Numerical simulations of the non-stationary Schrodinger equation in one-dimensional model systems are performed to gauge the validity of the analytical theory. Large (up to several orders of magnitude) enhance- ments of the multiphoton transition rates are found both numerically and analytically. The applicability of the analytical theory is confirmed up to relatively high Keldysh parameters.We also describe a second novel mech- anism of energy absorption: laser-assisted electron avalanche in dielectric materials. Unlike the traditional ava- lanche, in this process, collisional excitation of new electrons to the conduction band occurs without heating the already free electrons to energies above the bandgap energy. This process should dominate for ultra-short laser pulses which do not give enough time for the development of the traditional avalanche.
TL;DR: In this article, a formalism is developed for calculating the neutrino ionization cross sections for H, He, Ne, and Ar. This formalism was based on the use of spin-independent atomic wave functions and should very accurately describe the ionization spectra for H. The accuracy is considerably reduced for the Xe case though, where the spin dependence in the wave functions is non-negligible.
Abstract: For neutrinos of $\mathcal{O}(10\text{ }\mathrm{k}\mathrm{e}\mathrm{V})$ energies, their oscillation lengths are less than a few hundred meters, thereby suggesting the fascinating idea of oscillation experiments of small geometrical size. To help in evaluating this idea, a formalism is developed for calculating the neutrino ionization cross sections for H as well as the noble atoms. This formalism is based on the use of spin-independent atomic wave functions and should very accurately describe the ionization spectra for H, He, Ne, and Ar. The accuracy is considerably reduced for the Xe case though, where the spin dependence in the wave functions is non-negligible. Nevertheless, even for Xe the results remain qualitatively correct. In all cases, the atomic ionizations cross section per electron is found to be smaller than the neutrino cross section off free electrons, approaching it from below as the energy increases to the 100 keV region. At the 10--20 keV range though, the atomic binding effects in the cross sections and the spectra are very important and increasing with the atomic number. They are canceling out though, when total ionization cross section ratios, like ${\ensuremath{
u}}_{\ensuremath{\mu}}/{\ensuremath{
u}}_{e}$ or ${\overline{\ensuremath{
u}}}_{\ensuremath{\mu}}/{\overline{\ensuremath{
u}}}_{e}$, are considered.