Showing papers on "Auger published in 2009"
TL;DR: In this article, the Auger coefficient for wurtzite InGaN is calculated from first-principles density-functional and many-body perturbation theory.
Abstract: We report Auger recombination rates for wurtzite InGaN calculated from first-principles density-functional and many-body-perturbation theory. Two different mechanisms are examined—inter- and intra-band recombination—that affect different parts of the emission spectrum. In the blue to green spectral region and at room temperature the Auger coefficient can be as large as 2×10−30 cm6 s−1; in the infrared it is even larger. Since Auger recombination scales with the cubic power of the free-carrier concentration it becomes an important nonradiative loss mechanism at high current densities. Our results indicate that Auger recombination may be responsible for the loss of quantum efficiency that affects InGaN-based light emitters.
346 citations
TL;DR: The first experimental observation of a striking convergence of Auger recombination rates in nanocrystals of both direct- and indirect-gap semiconductors is reported, which is in contrast to a dramatic difference in the Auger decay rates in respective bulk solids.
Abstract: We report the first experimental observation of a striking convergence of Auger recombination rates in nanocrystals of both direct- (InAs, PbSe, CdSe) and indirect-gap (Ge) semiconductors, which is in contrast to a dramatic difference (by up to 4-5 orders of magnitude) in the Auger decay rates in respective bulk solids. To rationalize this finding, we invoke the effect of confinement-induced mixing between states with different translational momenta, which diminishes the impact of the bulk-semiconductor band structure on multiexciton interactions in nanocrystalline materials.
294 citations
TL;DR: In this paper, the Auger recombination coefficient in In0.1Ga0.9N/GaN quantum wells, emitting at 407 nm, has been determined from large signal modulation measurements on lasers in which these quantum wells form the gain region.
Abstract: The Auger recombination coefficient in In0.1Ga0.9N/GaN quantum wells, emitting at 407 nm has been determined from large signal modulation measurements on lasers in which these quantum wells form the gain region. A value of 1.5×10−30 cm6 s−1 is determined for the Auger coefficient at room temperature, which is used to analyze the reported efficiency characteristics of 410 nm In0.1Ga0.9N/GaN quantum wells light emitting diodes. The calculated efficiencies agree remarkably well with the measured ones. It is apparent that Auger recombination is largely responsible for limiting device efficiencies at high injection currents.
139 citations
TL;DR: In this paper, a systematic X-ray photoelectron spectroscopy (XPS) study of the Ni silicides produced by annealing of sputtered thin films is presented, focusing on both the core level peaks and Auger peaks.
Abstract: This paper presents a systematic X-ray photoelectron spectroscopy (XPS)study of the Ni silicides Ni3Si, Ni31Si12, Ni2Si, NiSi and NiSi2 produced by annealing of sputtered thin films. The in situ XPS study focuses on both the core level peaks and Auger peaks. The peak positions, shapes, satellites as well as Auger parameters are compared for different silicides. The factors that influence the Ni core level peak shifts are discussed. The Ni 2p3/2 peak shape and satellites are correlated with the valence band structure. The effect of argon ion etching on surface composition and chemical states is also investigated.
58 citations
Patent•
25 Sep 2009
TL;DR: A helical auger turbine and hydrokinetic device for use with electrical generators for producing electricity was proposed in this article, where the turbine blade support connection is included for connecting the central shaft to a support structure.
Abstract: A helical auger turbine and hydrokinetic device for use with electrical generators for producing electricity. The auger turbine includes a generally helical turbine blade rotatably mounted on a central shaft, which may be tapered at each end, and a flange extending perpendicularly to an edge of the turbine blade. At least one turbine blade support connection is included for connecting the central shaft to a support structure. An electrical generator may be powered by the helical auger turbine, that can be used in a tidal water flow. The helical auger turbine can operate a high pressure pump connected to a hydraulic accumulator for storing pressurized hydraulic fluid from the high pressure pump. An electrical generator can be operated by hydraulic fluid delivered from the hydraulic accumulator at times of slow water flow. A plurality of helical auger turbines can be horizontally oriented under water, tethered to legs of an ocean platform such as an oil rig secured to the seabed.
50 citations
TL;DR: The calculations reveal that the final two-hole valence states can be delocalized over both ammonia molecules, and this interpretation is also applicable to the solid phase since the same features have been observed, but not assigned, in the Auger spectrum of solid ammonia.
Abstract: Valence and core level photoelectron spectra and Auger electron spectra of ammonia in pure clusters have been measured. The Auger electron spectra of gas-phase ammonia, pure ammonia clusters and ammonia in aqueous solution are compared and interpreted via ab initio calculations of the Auger spectrum of the ammonia monomer and dimer. The calculations reveal that the final two-hole valence states can be delocalized over both ammonia molecules. Features at energies pertaining to delocalized states involving one, or more, hydrogen bonding orbitals can be found in both the ammonia cluster Auger electron spectrum and in that of the liquid solvated molecule. The lower Coulombic repulsion between two delocalized valence final state holes gives higher kinetic energy of the Auger electrons which is also observed in the spectra. This decay path—specific to the condensed phase—is responsible for more than 5% of the total cluster Auger intensity. Moreover, this interpretation is also applicable to the solid phase since the same features have been observed, but not assigned, in the Auger spectrum of solid ammonia.
30 citations
TL;DR: Aqueous potassium chloride has been studied by synchrotron-radiation excited core-level photoelectron and Auger electron spectroscopy and through ab initio calculations for microsolvated clusters, these subunits have been assigned as potassium ions and the surrounding water molecules.
Abstract: Aqueous potassium chloride has been studied by synchrotron-radiation excited core-level photoelectron and Auger electron spectroscopy. In the Auger spectrum of the potassium ion, the main feature comprises the final states where two outer valence holes are localized on potassium. This spectrum exhibits also another feature at a higher kinetic energy which is related to final states where outer valence holes reside on different subunits. Through ab initio calculations for microsolvated clusters, these subunits have been assigned as potassium ions and the surrounding water molecules. The situation is more complicated in the Auger spectrum of the chloride anion. One-center and multicenter final states are present here as well but overlap energetically.
29 citations
Journal Article•
TL;DR: In this article, the Auger recombination rates for wurtzite InGaN calculated from the first principles density-functional and many-body perturbationtheory were reported.
Abstract: Materials Department, University of California, Santa Barbara, CA 93106-5050(Dated: April 22, 2009)We report Auger recombination rates for wurtzite InGaN calculated from first principles density-functional and many-body-perturbationtheory. Two different mechanisms are examined – inter- andintra-band recombination – that affect different parts of the emission spectrum. In the blue to greenspectral region and at room temperature the Auger coefficient can be as large as 2×10
28 citations
TL;DR: This work simulates the wave packet dynamics of electrons in the hydrogenated diamond nanoparticle C197H112 to understand how core ionization and subsequent Auger decay lead to bond breaking in large systems, and finds that surface core ionizations cause emission of carbon fragments and protons through a direct Auger mechanism.
Abstract: To understand how core ionization and subsequent Auger decay lead to bond breaking in large systems, we simulate the wave packet dynamics of electrons in the hydrogenated diamond nanoparticle C_(197)H_(112). We find that surface core ionizations cause emission of carbon fragments and protons through a direct Auger mechanism, whereas deeper core ionizations cause hydrides to be emitted from the surface via remote heating, consistent with results from photon-stimulated desorption experiments [Hoffman A, Laikhtman A, (2006) J Phys Condens Mater 18:S1517–S1546]. This demonstrates that it is feasible to study the chemistry of highly excited large-scale systems using simulation and analysis tools comparable in simplicity to those used for classical molecular dynamics.
28 citations
TL;DR: The data strikingly reveal that the flux is lost rather than diverted, indicating that the two-step interpretation of photoionization followed by Auger emission is insufficient to fully describe the core-photoionization process.
Abstract: We have used cold target recoil ion momentum spectroscopy to study the continuum correlation between the photoelectron of core-photoionized neon and the subsequent Auger electron. We observe a strong angular correlation between the two electrons. Classical trajectory Monte Carlo calculations agree quite well with the photoelectron energy distribution that is shifted due to the potential change associated with Auger decay. However, a striking discrepancy results in the distribution of the relative angle between Auger and photoelectron. The classical model predicts a shift in photoelectron flux away from the Auger emission direction, and the data strikingly reveal that the flux is lost rather than diverted, indicating that the two-step interpretation of photoionization followed by Auger emission is insufficient to fully describe the core-photoionization process.
20 citations
TL;DR: In this paper, a quantum theory of a laser-assisted Auger process in atoms excited by an ultra-short (attosecond) electromagnetic pulse in the field of a few-cycle strong laser pulse is presented.
Abstract: A quantum mechanical theory of a laser-assisted Auger process in atoms excited by an ultra-short (attosecond) electromagnetic pulse in the field of a few-cycle strong laser pulse is presented. It is based on the non-stationary Schrodinger equation, which describes the photoionization of an inner atomic shell and the decay of the created vacancy, while the Auger electron is treated in the strong field approximation. As an example, the photoionization of the Ne 1s shell with the subsequent KLL Auger transition is considered. The spectra and angular distributions of photoelectrons and Auger electrons are calculated and discussed. The photoelectron spectra show a typical picture of streaking in the laser field. In contrast, the Auger electron spectrum contains sideband structure, which is however, different from the conventional equidistant sideband structure, which had been discussed for longer pulses and smaller Auger electron energies. The predicted sideband structure strongly depends on the delay time between the laser pulse and the x-ray pulse. It is sensitive to the carrier-envelope phase as well. A simplified description of the Auger electron spectra in laser-assisted Auger decay, which gives the sideband structure in close agreement with the results of the exact theory, is suggested.
TL;DR: In this paper, the effect of Auger coefficient on the efficiency and output power of InGaN light-emitting diodes was investigated numerically and it was found that the electron current leakage and nonuniform hole distribution are the possible mechanisms responsible for the efficiency droop at high injection current.
Abstract: The Auger recombination is recently proposed as one of the possible origins for the deteriorated internal quantum efficiency of InGaN light-emitting diodes. The Auger recombination behavior is quite different under widely varied Auger coefficients. The effect of Auger coefficient on the efficiency and output power is investigated numerically. The simulation results indicate that the Auger recombination with large Auger coefficient greatly decreases the efficiency in the whole current range under study. It is found that the electron current leakage and nonuniform hole distribution are the possible mechanisms responsible for the efficiency droop at high injection current.
TL;DR: In this paper, the importance of radiative and Auger carrier losses in InGaN/GaN quantum wells is investigated and numerical estimates indicate that the resulting losses constitute an important intrinsic loss process.
Abstract: Fully microscopic many-body models are used to study the importance of radiative and Auger carrier losses in InGaN/GaN quantum wells. Since the usual direct bandto-band Auger losses are too small to explain the experimentally observed droop of the external quantumefficiency in such structures, phonon assisted Auger processes are discussed. First numerical estimates indicate that the resulting losses constitute an important intrinsic loss process in InGaN/GaN quantum wells (© 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)
TL;DR: In this paper, an ab initio formalism for the quantum dynamics of Auger decay by laser-dressed atoms which are inner-shell ionized by extreme ultraviolet (XUV) light is devised.
Abstract: We devise an ab initio formalism for the quantum dynamics of Auger decay by laser-dressed atoms which are inner-shell ionized by extreme ultraviolet (XUV) light. The optical dressing laser is assumed to be sufficiently weak such that ground-state electrons are neither excited nor ionized by it. However, the laser has a strong effect on continuum electrons which we describe in strong-field approximation with Volkov waves. The XUV light pulse has a low peak intensity and its interaction is treated as a one-photon process. The quantum dynamics of the inner-shell hole creation with subsequent Auger decay is given by equations of motion (EOMs). For this paper, the EOMs are simplified in terms of an essential-states model which is solved analytically and averaged over magnetic subshells. We apply our theory to the M_4,5 N_1 N_2,3 Auger decay of a 3d hole in a krypton atom. The orbitals are approximated by scaled hydrogenic wave functions. A single attosecond pulse produces 3d vacancies which Auger decay in the presence of an 800nm laser with an intensity of 10^13 W / cm^2. We compute the Auger electron spectrum and assess the convergence of the various quantities involved.
TL;DR: In this article, the authors analyzed mid-infrared diode lasers with type-II W active regions using a fully microscopic many-body theory and found that the Auger carrier losses are dominant over radiative losses even at low temperatures.
Abstract: Mid-infrared diode lasers with type-II “W” active regions are analyzed using a fully microscopic many-body theory. The Auger carrier losses are found to dominate over radiative losses even at low temperatures. The experimentally observed strong temperature-dependent increase in Auger losses is shown to be a consequence of thermal gain reduction causing increased threshold carrier densities. Good agreement between theory and experiment is demonstrated for temperature-dependent photoluminescence spectra as well as threshold loss currents.
TL;DR: In this article, the fragmentation of the CH42+ dication, formed upon C1s inner shell ionization and the following Auger electron decay, has been studied by means of Auger-ion and Auger ion-ion coincidence spectroscopies at three different kinetic energies of the Auger electrons, which correspond to the three main configurations of the dication.
Abstract: The fragmentation of the CH42+ dication, formed upon C1s inner shell ionization and the following Auger electron decay, has been studied by means of Auger electron–ion and Auger electron–ion–ion coincidence spectroscopies at three different kinetic energies of the Auger electron, which correspond to the three main configurations (1t2−2, 1t2−12a1− 1 and 2a1− 2) of the dication. For each ion pair detected in coincidence with the Auger electron, the dynamics of the dissociation is discussed. The results show that the fragmentation process is stepwise and mainly occurs via the formation and dissociation of the CH3+ intermediate. The orientation of the methyl ion, induced by a dipole moment during the first step of the fragmentation, is suggested to play a key role. Moreover, the experiments together with ab initio CAS calculations of the equilibrium geometries of the methane dication and the methyl cation provide information on the structure of the intermediate methyl ion.
Patent•
23 Dec 2009
TL;DR: In this article, a rotary mud drill is used to produce a drill hole up to the location of the aberrations, and an auger is inserted into the drill hole to fill the holes.
Abstract: The invention provides a system for adapting an HVAC system in an existing building for utilizing geothermal energy, the system comprising an incoming flux of geothermal energy; a plurality of heat exchange surfaces adapted to receive the incoming flux of geothermal energy; and an interface between the HVAC system and the heat exchange surfaces, said interface adapted to transfer the geothermal energy to the system. Also provided is a method for repairing aberrations in drill borings, the method comprising using a rotary mud drill system to produce a drill hole up to the location of the aberrations; removing the rotary mud drill from the drill hole; inserting an auger into the drill hole to a point directly above the location of the aberrations; actuating the auger; introducing loose substrate into the drill hole; allowing the substrate to contact the auger; and lifting and lowering the auger along longitudinally extending regions of the drill hole defining the aberrations for a time and in substrate amounts sufficient to fill the aberrations. The invention also provides a system which facilitates rotating drill bits at an rpm which are multiples faster than their associated drill strings.
TL;DR: In this paper, a theoretical model of the secondary electron emission yield (γ) from a MgO layer is developed based on the Auger neutralization of ions, resulting in an analytical expression of γ in terms of the ionization energy Ei for the density of states in the valence band, being an exponentially decaying function of the energy deviation from the band characteristic energy of 7.88 eV.
Abstract: A theoretical model of the secondary electron emission yield (γ) from a MgO layer is developed based on the Auger neutralization of ions, resulting in an analytical expression of γ in terms of the ionization energy Ei for the density of states in the valence band, being an exponentially decaying function of the energy deviation from the band characteristic energy of 7.88 eV. The analytical expression recovers the previously known empirical formulation of γ∼(Ei−2φ) for the work function φ. Results of the theoretical model agree well with the measured data in terms of the data trend.
Patent•
29 Apr 2009
TL;DR: In this article, a vertical mixer for mixing bulk material is described, which includes cutting knives positioned on an outside edge of the flighting for cutting bulk material during rotation of the auger.
Abstract: A vertical mixer for mixing bulk material is disclosed. The vertical mixer includes an auger having an auger post and flighting including upper flighting and a lower flight. In one example, the auger comprises cutting knives positioned on an outside edge of the flighting for cutting bulk material during rotation of the auger. The auger also includes an angled knife connected to an outside edge of the flighting and oriented so that a blade of the angled knife is positioned at an angle suitable for allowing the angled knife to at least partially cut loosened bulk material that may be bridging in the mixing chamber thereby at least partially preventing or reducing bridging in the mixing chamber and allowing the bulk material to fall towards the floor of the mixing chamber and increasing the cutting action of the cutting knives.
TL;DR: The one-center approach for molecular Auger decay is applied to predict the angular distribution of Auger electrons from rotating and fixed-in-space molecules and a parametrization for the molecular frame Auger electron angular distribution is suggested.
Abstract: The one-center approach for molecular Auger decay is applied to predict the angular distribution of Auger electrons from rotating and fixed-in-space molecules. For that purpose, phase shifts between the Auger decay amplitudes have been incorporated in the atomic model. The approach is applied to the resonant Auger decay of the photoexcited C 1s -> 2 pi resonance in carbon monoxide. It is discussed how the symmetry of the final ionic state is related to features in the angular distributions and a parametrization for the molecular frame Auger electron angular distribution is suggested. The angular distribution of Auger electrons after partial orientation of the molecule by the sigma ->pi-excitation process is also calculated and compared to available experimental and theoretical data. The results of the one-center approach are at least of the same quality as the available theoretical data even though the latter stem from a much more sophisticated method. As the one-center approximation can be applied with low computational demand even to extended systems, the present approach opens a way to describe the angular distribution of Auger electrons in a wide variety of applications.
Dissertation•
01 Jan 2009
TL;DR: In this paper, the carrier dynamics in double-cap quantum dots (DC-QDs) grown on InP(113)B were investigated, yielding an emission wavelength of about 1.55μm at room temperature.
Abstract: The carrier dynamics in InAs double-cap quantum dots (DC-QDs) grown on InP(113)B are investigated. The shape of these QDs can be controlled during the growth, yielding an emission wavelength of the system of about 1.55 μm at room temperature. The DC-QD dynamics is studied by time-resolved photoluminescence experiments at low temperature for various excitation densities. A simplified dynamic model is developed, yielding results consistent with experimental data. This analysis yields the determination of the Auger coefficients and the intradot relaxation time in this system.
TL;DR: In this article, it was shown that the shake-off mechanism is not sufficient to model direct double Auger decay of a hole in Ar and suggests an important contribution from the knock-out mechanism.
Abstract: Simultaneous two-electron emission upon $2p$ core-electron excitation in Ar has been studied using a state-of-the-art multielectron coincidence method. Simultaneous two-electron emission effectively populates Rydberg-excited ${\text{Ar}}^{2+}$ states, in which the excited electron behaves as a spectator of the direct double Auger decay of the core hole. This observation constitutes experimental evidence that the shake-off mechanism is not sufficient to model direct double Auger decay of a $2p$ hole in Ar and suggests an important contribution from the knock-out mechanism.
TL;DR: In this paper, the fine structure of the carbon layer inside and outside these domains has been studied by small spot Auger electron spectroscopy (AES), high resolution transmission electron microscopy (HRTEM), AFM and lateral force microscopy.
TL;DR: A direct comparison of the energies, widths, and relative intensities of the final OCS(2+) states with theoretical calculations has been achieved and the angular distributions of some selected Auger electrons have been measured in coincidence with the photoelectron at two different photon energies.
Abstract: The selectivity of the photoelectron−Auger electron coincidence technique has been used to isolate the S L3MM contribution to the L2,3MM Auger spectrum in OCS. In this way, a direct comparison of the energies, widths, and relative intensities of the final OCS2+ states with theoretical calculations has been achieved. Moreover, the angular distributions of some selected Auger electrons have been measured in coincidence with the photoelectron at two different photon energies. In contrast with the results of noncoincidence measurements, the coincidence angular distributions show a significant asymmetry and a dependence on the photon energy and OCS2+ final state.
TL;DR: In this article, a constructive solid geometry model for a sample geometry, which is complex in elemental distribution, as well as in topographical configuration and a ray-tracing technique in the calculation procedure of electron flight steps that across the different element zones is presented.
Abstract: Simulation of contrast formation in Auger electron imaging of surfaces is helpful for analyzing scanning Auger microscopy/microanalysis (SAM) images. In this work, we have extended our previous Monte Carlo model and the simulation method for calculation of scanning electron microscopy (SEM) images to SAM images of complex structures. The essentials of the simulation method are as follows. (1) We use a constructive solid geometry modeling for a sample geometry, which is complex in elemental distribution, as well as in topographical configuration and a ray-tracing technique in the calculation procedure of electron flight steps that across the different element zones. The combination of the basic objects filled with elements, alloys, or compounds enables the simulation to a variety of sample geometries. (2) Sampled Auger signal electrons with a characteristic energy are generated in the simulation following an inner-shell ionization event, whose description is based on the Castani’s inner-shell ionization cr...
TL;DR: Wethekam et al. as mentioned in this paper presented a theoretical analysis of experimental data on ion fractions and polar angular distributions for He atoms and ions produced during grazing scattering of keV neutral He atoms from an atomically clean and flat Al(111) surface.
Abstract: We present a theoretical analysis of experimental data on ion fractions and polar angular distributions for He atoms and ions produced during grazing scattering of keV neutral He atoms from an atomically clean and flat Al(111) surface. The discussion focuses on the mechanism of Auger ionization for which we have recently presented the first quantitative treatment by an ab initio method [S. Wethekam, Diego Valdes, R. C. Monreal, and H. Winter, Phys. Rev. B 78, 033105 (2008)]. Auger ionization, the inverse process of Auger neutralization, is a dynamical process that converts kinetic energy from the projectile to electronic excitations. We calculate Auger ionization rates and perform molecular-dynamics and Monte Carlo simulations of trajectory and charge state of scattered projectiles. We achieve quantitative agreement with experimental ion fractions and angular distributions. This demonstrates that Auger ionization is an efficient mechanism of ionization. We also discuss the sensitivity of the results on the theoretical input used in the simulations and give an estimate on the contribution of resonant processes.
TL;DR: In this paper, the $KLL$ Auger spectrum of atomic aluminum has been recorded applying electron impact for the creation of $1s$ core hole states, and experimental results are compared to predictions obtained with ab initio calculations for spectral structures.
Abstract: The $KLL$ Auger spectrum of atomic aluminum has been recorded applying electron impact for the creation of $1s$ core hole states. The experimental results are compared to predictions obtained with ab initio calculations for spectral structures.
TL;DR: In this paper, the Auger coefficient was shown to scale with the cubic power of the free-carrier concentration, and it becomes an important non-radiative loss mechanism at high current densities.
Abstract: We report Auger recombination rates for wurtzite InGaN calculated from first principles density-functional and many-body-perturbation theory. Two different mechanisms are examined -- inter- and intra-band recombination -- that affect different parts of the emission spectrum. In the blue to green spectral region and at room temperature the Auger coefficient can be as large as 2x10^-30cm^6s^-1; in the infrared even larger. Since Auger recombination scales with the cubic power of the free-carrier concentration it becomes an important non-radiative loss mechanism at high current densities. Our results indicate that Auger recombination may be responsible for the loss of quantum efficiency that affects InGaN-based light emitters.
TL;DR: In this paper, the Auger transitions to different repulsive doubly charged molecular ion states are separated by measuring the angular resolved photoelectrons and Auger electrons in coincidence in the molecular fixed frame.
Abstract: The Auger transitions to different repulsive doubly charged molecular ion states are separated by measuring the angular resolved photoelectrons and Auger electrons in coincidence in the molecular fixed frame. The separation is achieved by comparing the experimental Auger-electron angular distributions at different kinetic-energy release values with theoretical curves calculated for different final dicationic states.