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Showing papers on "Free electron model published in 2001"


Journal ArticleDOI
TL;DR: In this article, the authors used ab initio band structure calculations in the local density approximation to determine the optical properties and the electronic structure of the bulk SrTiO3 in a dedicated scanning transmission electron microscope, vacuum ultraviolet spectroscopy and spectroscopic ellipsometry.
Abstract: Valence electron-energy loss spectroscopy (VEELS) in a dedicated scanning transmission electron microscope, vacuum ultraviolet spectroscopy and spectroscopic ellipsometry, and ab initio band structure calculations in the local density approximation have been used to determine the optical properties and the electronic structure of SrTiO3 Assignments of the interband transitions in the electronic structure of bulk SrTiO3 have been determined quantitatively by comparison of VEELS spectra with vacuum ultraviolet spectra and with the ab initio calculated densities of states The experimentally determined indirect band gap energy is 325 eV, while the direct band gap energy is 375 eV The conduction bands in SrTiO3 correspond to the bands composed of mainly Ti 3d t2g and eg states, followed at higher energies by the bands of Sr 4d t2g and eg states, and free electron like states dominating at energies above 15 eV The upper valence band (UVB) contains 18 electrons in dominantly O 2p states, hybridized with Ti and Sr states, and has a bandwidth of 5 eV The interband transitions from the UVB to the Ti 3d bands and to the Sr 4d bands give rise to the transitions spanning from the indirect band gap energy of 325 eV up to 15 eV The lower valence band contains 12 electrons in Sr 4p and O 2s states which are separated by 2 eV, while having a bandwidth of 5 eV The interband transitions from the Sr 4p to the Ti 3d and Sr 4d bands give rise to transition energies spanning from 15 to 24 eV Interband transitions from the O 2s band to the conduction bands appear at 26 eV A very narrow band at −33 eV below the top of the valence band is composed of Sr 4s and Ti 3p states and contains eight electrons

766 citations


Journal ArticleDOI
TL;DR: In this article, the Schrodinger equation and the corre-sponding wave equation in electrodynamics are compared to the corresponding equations of photonic crystals, and it is inferred from the few photonic crystal that appear in nature, in contrast to ubiqui-tous semiconductor materials, that these differences have an adisadvantageous effect on the likelihood of the formation ofphotonic bandgaps.
Abstract: In semiconductors electrons propagate in a periodic poten-tial, which originates from the atomic lattice. This modifiesthe dispersion relation of free electrons and a band structurewith a bandgap occurs in the case of semiconductors. Theincorporation of electrically active defects allows the manipu-lation of the electronic properties, which gave birth to a largevariety of electronic devices. There are distinct electrical andelectro-optical properties of the different semiconductormaterials, the dominant and most studied semiconductorbeing silicon.For more than ten years, the optical analogues to electronicsemiconductors, the so-called photonic crystals, have been thesubject of intense international research efforts. Photoniccrystals are materials with a periodically varying index ofrefraction. This allows the control of the propagation of elec-tromagnetic waves, similar to electrons in a semiconductorcrystal. By analogy with semiconductors, the periodicity of theunderlying lattice structure is of the same order of magnitudeas the wavelength of the electromagnetic radiation.Despite the far-reaching analogies between electronicwaves in semiconductors and electromagnetic waves in pho-tonic crystals, there are pronounced differences between thetwo as is noticeable from the corresponding equations of mo-tion. Electrons are described by a scalar wavefield. In con-trast, the electromagnetic field is vectorial by nature. Further-more, the time-independent Schrodinger equation allowssolutions with negative energy eigenvalues, whereas the corre-sponding wave equation in electrodynamics contains only thesquare of the eigenfrequencies, hence negative eigenvaluesare excluded from the outset. It may be inferred from the fewphotonic crystals that appear in nature, in contrast to ubiqui-tous semiconductor materials, that these differences have adisadvantageous effect on the likelihood of the formation ofphotonic bandgaps. From the multitude of the optical phe-nomena only, for example, the colorful speckles of opals, somecrystallites on the wings of butterflies and the spine of the sea-mouse

324 citations


Journal ArticleDOI
13 Sep 2001-Nature
TL;DR: The diffraction of free electrons from a standing light wave is reported—a realization of the Kapitza–Dirac effect as originally proposed.
Abstract: In their famous 1927 experiment, Davisson and Germer observed the diffraction of electrons by a periodic material structure, so showing that electrons can behave like waves. Shortly afterwards, Kapitza and Dirac predicted that electrons should also be diffracted by a standing light wave. This Kapitza-Dirac effect is analogous to the diffraction of light by a grating, but with the roles of the wave and matter reversed. The electron and the light grating interact extremely weakly, via the 'ponderomotive potential', so attempts to measure the Kapitza-Dirac effect had to wait for the development of the laser. The idea that the underlying interaction with light is resonantly enhanced for electrons in an atom led to the observation that atoms could be diffracted by a standing wave of light. Deflection of electrons by high-intensity laser light, which is also a consequence of the Kapitza-Dirac effect, has also been demonstrated. But the coherent interference that characterizes wave diffraction has not hitherto been observed. Here we report the diffraction of free electrons from a standing light wave-a realization of the Kapitza-Dirac effect as originally proposed.

208 citations


01 May 2001
TL;DR: In this article, the Kapitza-Dirac effect was shown to be present in free electrons from a standing light wave, which is a realization of the k-drac effect as originally proposed by Davisson and Germer.
Abstract: In their famous 1927 experiment, Davisson and Germer observed the diffraction of electrons by a periodic material structure, so showing that electrons can behave like waves. Shortly afterwards, Kapitza and Dirac predicted that electrons should also be diffracted by a standing light wave. This Kapitza-Dirac effect is analogous to the diffraction of light by a grating, but with the roles of the wave and matter reversed. The electron and the light grating interact extremely weakly, via the 'ponderomotive potential', so attempts to measure the Kapitza-Dirac effect had to wait for the development of the laser. The idea that the underlying interaction with light is resonantly enhanced for electrons in an atom led to the observation that atoms could be diffracted by a standing wave of light. Deflection of electrons by high-intensity laser light, which is also a consequence of the Kapitza-Dirac effect, has also been demonstrated. But the coherent interference that characterizes wave diffraction has not hitherto been observed. Here we report the diffraction of free electrons from a standing light wave-a realization of the Kapitza-Dirac effect as originally proposed.

145 citations


Journal ArticleDOI
TL;DR: In this paper, a fluid-kinetic hybrid electron model for electromagnetic simulations of finite-β plasmas is developed based on an expansion of the electron response using the electron-ion mass ratio as a small parameter.
Abstract: A fluid–kinetic hybrid electron model for electromagnetic simulations of finite-β plasmas is developed based on an expansion of the electron response using the electron–ion mass ratio as a small parameter. (Here β is the ratio of plasma pressure to magnetic pressure.) The model accurately recovers low frequency plasma dielectric responses and faithfully preserves nonlinear kinetic effects (e.g., phase space trapping). Maximum numerical efficiency is achieved by overcoming the electron Courant condition and suppressing high frequency modes. This method is most useful for nonlinear kinetic (particle-in-cell or Vlasov) simulations of electromagnetic microturbulence and Alfvenic instabilities in magnetized plasmas.

133 citations


Journal ArticleDOI
Hajime Mase1
TL;DR: In this article, the authors developed a prediction model for multi-directional random wave transformation, which is based on an energy balance equation with an energy dissipat-tation.
Abstract: The purpose of this paper is to develop a prediction model for multi-directional random wave transformation. The wave prediction model is based on an energy balance equation with an energy dissipat...

128 citations


Journal ArticleDOI
TL;DR: The characteristics of planar diode electron emission in 2D space with the emphasis on the transition region between the beam and vacuum are investigated and increased current density "wings" are observed near the beam edges in a 2D finite element, electrostatic ray-tracing code.
Abstract: There is, at present, no analytic solution that extends Child-Langmuir space-charge-limited emission beyond 1D. Herein, we investigate the characteristics of planar diode electron emission in 2D space with the emphasis on the transition region between the beam and vacuum. Current density above that predicted by Child-Langmuir is observed near the beam edges in a 2D finite element, electrostatic ray-tracing code. The properties of these increased current density "wings" are examined and then discussed in terms of their applications to cathodes which have large reservoirs of free electrons.

107 citations


Journal ArticleDOI
TL;DR: The time evolution of the carrier density reveals nongeminate electron-ion recombination within hundreds of picoseconds at high ion concentration.
Abstract: We examine the transport properties and the dynamics of free electrons in n-hexane by means of femtosecond spectroscopy using an ultraviolet pump pulse to create the electrons and a THz electromagnetic pulse as a probe. The complex dielectric response of the photogenerated electrons is determined over a broad range of frequencies, from which we infer the electron scattering time and density through the Drude model. The time evolution of the carrier density reveals nongeminate electron-ion recombination within hundreds of picoseconds at high ion concentration.

92 citations


Journal ArticleDOI
TL;DR: In this paper, a self-consistent model to describe vibrational, electronically excited states and free electron kinetics has been applied to study N 2 expansion through a converging-diverging conic nozzle.
Abstract: A self-consistent model to describe vibrational, electronically excited states (master equations) and free electron kinetics (Boltzmann equation) has been applied to study N 2 expansion through a converging-diverging conic nozzle. Strong departures from equilibrium can be observed for both vibrational, electronically excited states and electron energy distributions. In particular, the role of electronically excited states of nitrogen molecules and free electrons has been investigated. The strong interaction between these two systems, by means of inelastic and superelastic collisions, influences not only the internal state kinetics, but also the macroscopic quantities such as Mach number and gas temperature profile

90 citations


Journal ArticleDOI
TL;DR: In this article, the authors used the laser photoelectron attachment (LPA) method to investigate dissociative electron attachment to carbon tetrachloride in the electron energy range 0 E ≤ 173 meV with very high resolution (energy width 1 meV).

79 citations


Journal ArticleDOI
TL;DR: In this article, the conduction of free electrons along a low-dimensional channel at low temperatures, using surface-state electrons on liquid helium in novel microelectronic devices, is studied.
Abstract: We present measurements of the conduction of nondegenerate free electrons along a low-dimensional channel at low temperatures, using surface-state electrons on liquid helium in novel microelectronic devices. Above 1 K, the electrons form an ideal classical Drude conductor. Below 1 K, Coulomb interactions produce electronic spatial order, leading to strong non-Ohmic effects and negative differential conductivity. Evidence is presented for self-organized current filaments in the channel, created by a nonequilibrium phase transition. Periodic conductance oscillations suggest an anisotropic spatial order with lines of electrons along the channel edges.

Journal ArticleDOI
Abstract: The transport properties, particularly free carrier density and mobility, of SiC are usually determined by the Hall effect. Raman spectroscopy has been shown to yield transport parameters similar to the Hall effect. The analysis of the longitudinal optical plasmon coupled (LOPC) modes in doped SiC provides such information. In the case of damped plasmons in n-type 4H–SiC, changes in the carrier concentration result in a frequency shift of the LOPC mode, which appears close to the A1(LO) phonon mode. The validity of this approach for different free carrier concentrations (plasma frequencies) and mobilities (plasmon damping constants) is analyzed. The theoretical results obtained show that reliable estimation of the free carrier density can be obtained from the frequency shift of the LOPC mode for low carrier concentrations. At such a carrier concentration a reliable correlation between the Raman shift of the LOPC mode and the plasma frequency is established, without noticeable influence of the plasmon damping constant. However, when the free electron concentration increases, a non-negligible influence of the plasmon damping constant on the Raman frequency shift of the LPOC mode is observed. Therefore reliable transport data can only be obtained by a full line-shape analysis. These results are confirmed by the experimental results obtained on n-type 4H–SiC bulk samples with free electron concentration between 1×1017 and 5×1018 cm−3. © 2001 American Institute of Physics.

Journal ArticleDOI
TL;DR: In this paper, a concept of mixed exciton-trion states is formulated theoretically and proved experimentally for II-VI semiconductor quantum wells with a two-dimensional electron gas.
Abstract: A concept of mixed exciton-trion states is formulated theoretically and proved experimentally for II-VI semiconductor quantum wells with a two-dimensional electron gas. The concept considers the resonances of neutral excitons and charged excitons (trions) as mixed (with each other) via their interaction with free electrons. Reflectivity spectra of modulation-doped ZnSe/(Zn,Mg)(S,Se) and CdTe/(Cd,Mg)Te quantum wells are analyzed. A good qualitative agreement of the experimental results with model calculations is achieved.

Journal ArticleDOI
TL;DR: In this paper, the Boltzmann equation describing electron flow in semiconductor devices is considered, and the collision operator models the scattering processes between free electrons and phonons in thermal equilibrium.

Journal ArticleDOI
TL;DR: In this article, a hybrid model with fully gyrokinetic ions and a zero-inertia fluid model for the electrons is presented, where the electron fluid equations are derived from moments of the drift kinetic equation, taking the small mass ratio limit, but with finite electron temperature.
Abstract: This paper describes the formulation of a hybrid model with fully gyrokinetic ions and a zero-inertia fluid model for the electrons. The electron fluid equations are derived from moments of the drift kinetic equation, taking the small mass ratio limit, but with finite electron temperature. This model eliminates the inertial Alfven wave and any physics relating to electron transit motion, making it useful for studying low frequency, high β (β≫me/mi) electromagnetic turbulence as well as kinetic magnetohydradynamics (MHD) physics including kinetic ballooning and toroidal Alfven eigenmodes. Electromagnetic effects (δB⊥) are included through the parallel ion and electron current. A predictor-corrector scheme for the fluid part that is consistent with the gyrokinetic ion part has been developed. Here we derive the model equations, derive the linear kinetic-fluid theory in a three-dimensional shearless slab, and compare the simulation results with the linear theory.

Journal ArticleDOI
TL;DR: In this article, the authors showed that the free electron concentration is always higher on the (0 0 0 % 1)N face of the GaN single crystal than on the 0 0 0 1)Ga face.

Book
01 Jan 2001
TL;DR: In this paper, the free electron model of metals is used to measure electronic properties of alloys, including electron transport properties in crystal metals, amorphous metals and quasicrystals.
Abstract: 1. Introduction to electron theory of metals 2. Bonding styles and the free electron model 3. Electrons in a metal at finite temperatures 4. Periodic lattice and lattice vibrations in crystals 5. Conduction electrons in a periodic potential 6. Electronic structure of pure elements in periodic table 7. Principles of measuring electronic structure related phenomena 8. Electronic structure calculations 9. Electronic structure of alloys 10. Electron transport properties in periodic systems (I) 11. Electronic transport properties in crystal metals (II) 12. Superconductivity 13. Magnetism, electronic structure and electron transport properties in magnetic metals 14. Electronic structure of strongly correlated electron systems 15. Electronic structure and electron transport properties of liquid metals, amorphous metals and quasicrystals.

Journal ArticleDOI
TL;DR: In this paper, the authors point out that this model neglects the variation of the wave function in the plane of the interface and show that oscillations of wave function parallel to the interface increase its rate of decay.
Abstract: Electron tunneling in solids is usually envisioned in terms of a simple barrier model based on free electrons tunneling through a region of homogeneous potential. We point out that this model neglects the variation of the wave function in the plane of the interface and show that oscillations of the wave function parallel to the interface increase its rate of decay perpendicular to the interface. This simple observation has important implications for spin-dependent tunneling and may explain why $``s$ electrons'' seem to tunnel much more readily than $``d$ electrons.''

Journal ArticleDOI
TL;DR: In this article, the spin dependent tunnel conductance of ballistic ferromagnet/tunnel barrier/two-dimensional electron gas (FM/I/2DEG) junctions and double junctions for different barrier strengths was calculated using free electron approximation.
Abstract: Using free electron approximation, we calculated the spin dependent tunnel conductance of ballistic ferromagnet/tunnel barrier/two-dimensional electron gas (FM/I/2DEG) junctions and FM/I/2DEG/I/FM double junctions for different barrier strengths. We find that a tunnel barrier improves spin injection considerably. For sufficiently strong barriers, it is predicted that the tunnel conductance ratio between spin up and spin down channels is, in first approximation, equal to the ratio between their Fermi velocities in the FM. For single junctions, this results in a significant current polarization (similar to 10%). This corresponds to a relative resistance change of several percent between parallel and antiparallel magnetization of the two FM electrodes, respectively, for the double junction. In the weak barrier regime, the magnitude and sign of the current polarization are strongly dependent on the (controllable) electron density in the 2DEG.

Journal ArticleDOI
TL;DR: The Schrodinger equation was originally postulated in 1926 as having a solution of the one electron atom. But, as the principal quantum number n⪢1, the eigenfunctions become nonsensical as mentioned in this paper.

Journal ArticleDOI
TL;DR: In this paper, the authors present an analysis of a Smith-Purcell system in which a thin current sheet of electrons moves above a grating surface in the direction perpendicular to the grating grooves.
Abstract: We present an analysis of a Smith–Purcell system in which a thin current sheet of electrons moves above a grating surface in the direction perpendicular to the grating grooves. We develop a consistent theory for evolution of the electromagnetic field and electron distribution in the exponential growth regime starting from the initial electron noise and the incoming amplitude. The dispersion relation for the complex growth rate for this system is a quadratic equation.

Journal ArticleDOI
TL;DR: In this paper, the angular-dependent Stokes parameters for the X-ray emission were calculated for the recombination of a free electron into the K-shell of Bi83+ projectiles.

Journal ArticleDOI
TL;DR: In this paper, a study of dc resistance and infrared reflectance changes induced in epitaxial Cu(1/0/0) films by adsorbed oxygen was conducted, and it was shown that standard surface resistivity models based on free electrons and point scatterers are inadequate.

Journal ArticleDOI
TL;DR: In this paper, the electronic structure of the Hg-chalcogenides HgTe and HgSe was studied by means of high resolved photoemission along the ΓΣ K -direction with the aim of investigating prototype materials for the inverted band structure model in detail.

Journal ArticleDOI
01 Aug 2001-EPL
TL;DR: In this paper, the decay rate of Bloch electrons may be minimal at an arbitrary k∥ (hot spots ), and the prefactor is determined by the electron's group velocity, rather than by its quasimomentum.
Abstract: Tunneling of Bloch electrons through a vacuum barrier introduces new physical effects in comparison with the textbook case of free (plane wave) electrons. For the latter, the exponential decay rate in the vacuum is minimal for electrons with the parallel component of momentum k∥ = 0, and the prefactor is defined by the electron momentum component in the normal to the surface direction. However, the decay rate of Bloch electrons may be minimal at an arbitrary k∥ (hot spots ), and the prefactor is determined by the electron's group velocity, rather than by its quasimomentum. We illustrate this by first-principles calculations for (110) Pd surface.

Journal ArticleDOI
TL;DR: The observation of sub-Poisson intensity fluctuations in the coherent spontaneous harmonic radiation generated by an infrared free-electron laser in a photon counting experiment using a well-defined ensemble of electron pulses constitutes the first observation of a nonclassical state of the radiation field generated by a beam of free electrons.
Abstract: We report the observation of sub-Poisson intensity fluctuations in the coherent spontaneous harmonic radiation generated by an infrared free-electron laser in a photon counting experiment using a well-defined ensemble of electron pulses These observations constitute the first observation of a nonclassical state of the radiation field generated by a beam of free electrons The fluctuations observed in the experiment are smaller than those expected from semiclassical radiation theory, and larger than those expected from electron shot noise

Journal ArticleDOI
TL;DR: In this paper, a finite-difference time-domain method is developed to treat a nearly free-electron metal by rewriting the timedomain Maxwell's equations into three coupled partial differential equations for three vector functions.
Abstract: A finite-difference time-domain method is developed to treat a nearly-free-electron metal by rewriting the time-domain Maxwell's equations into three coupled partial differential equations for three vector functions. The method is used to calculate the band structures of two-dimensional metallic photonic crystals, and the numerical results are compared with those obtained by other methods. The new time-stepping formulae are also used to investigate the defect modes by calculating the transmission spectrum.


Journal ArticleDOI
TL;DR: A coherent x-ray generation scheme is proposed which involves characteristics of free electron lasers and atomic high harmonic generation schemes, and thousands of harmonics of the laser radiation field are shown to coherently amplify along the interaction length.
Abstract: A coherent x-ray generation scheme is proposed which involves characteristics of free electron lasers and atomic high harmonic generation schemes. A thin solid layer or any other periodic atomic structure with limited dimensions is exposed to a short, superintense laser pulse. The electrons are extracted from the layer due to the extreme force and penetrate periodically through the ionic structure. Consequently, thousands of harmonics of the laser radiation field are shown to coherently amplify along the interaction length. The small signal gain of the generated x-ray radiation exceeds that arising from the multiphoton Compton process in plasmas and is competitive with that in the leading x-ray free electron lasers.

Journal ArticleDOI
TL;DR: In this paper, the first observation of cyclotron resonances in alkali feldspars, using highly sensitive optical detection methods, has been reported, and a near isotropic effective electron mass value of m * e = 0.79m e has been determined.
Abstract: We report the first observation of cyclotron resonances in alkali feldspars, using highly sensitive optical detection methods. In Na-feldspar (NaAlSi 3 O 8 ), a near isotropic effective electron mass value of m * e = 0.79m e has been determined. The significance of this measurement in terms of the optical transition energies of shallow donor centres is considered.