Recombination Spectra Research Articles

Fermi liquid effects and quasiparticle mass renormalization in a system of two-dimensional electrons with strong interaction

The dependence of the quasiparticle Fermi energy on the electron density is investigated by analyzing the radiative recombination spectra of two-dimensional electrons with photoexcited holes bound at remote acceptors. In this way, the electron-density dependence of the renormalized mass of quasiparticles is determined. It is established that, as the electron density decreases (the parameter rs increases to 4.5), the density-of-states effective mass of quasiparticles increases by 35% as compared to the cyclotron mass of the electron. It is shown that, in a perpendicular magnetic field, the concept of quasiparticles in a two-dimensional Fermi liquid is applicable not only near the Fermi level but also deeply below the Fermi surface, even to the bottom of the quantum-confinement subband, because the broadening of excitations remains considerably smaller than their energy.

Optical signatures of valence-band mixing in positive trion recombination spectra of double quantum dots

We consider optical signatures of valence band mixing in positive trion and exciton complexes in vertically stacked InGaAs quantum dots. We use the configuration interaction method and an axially symmetric four-band Luttinger-Kohn Hamiltonian (KL) that allows for heavy-hole and light-hole band mixing due to spin-orbit interaction. A scalar effective hole mass model is also included for comparison. We found essential differences (i.e., different recombination patterns) between the KL and separated-bands model spectra. In the weak-coupling regime for KL model, we obtained a good agreement with experimentally observed X patterns in contrast to the scalar effective mass model.

Sub-bandgap analysis of boron doped InSe single crystals by constant photocurrent method

Sub-bandgap absorption properties of indium selenide doped with boron atoms within a range of [B]=0–1.8at.% have been investigated. From the absorption coefficient spectra measured by using constant photocurrent method (CPM) at 300K, we observed that the disorder in the structure increases. The calculated Urbach parameters, quantifying the disorder, vary from 17 to 53meV, as [B] is increased from 0 to 1at.%. Also the calculated optical gaps decrease from 1.28eV to 1.17eV for the same range of [B]. From temperature dependent dark conductivity measurements, the characteristic activation energies are calculated to range from 0.25 to 0.18eV for vertical (to c-axis) direction; to stay almost constant for parallel (c-axis) direction. At a temperature of 12K, the absorption coefficient spectra by using CPM and the radiative recombination spectra by photoluminescence (PL) have been taken for the samples with [B]=0 and 0.5at.%. Three main PL bands are observed at photon energies of ∼1.24, 1.306 and 1.337eV. The PL bands are interpreted by corresponding absorption bands detected at 12K and at the photon energies of ∼1.24, ∼1.31 and ∼1.35eV.

Experimental recombination rate coefficients of B-like carbon and B-like neon

In this paper, we present recombination rate coefficients for astrophysically relevant B-like C and B-like Ne ions, recently measured at the CRYRING electron cooler. The investigated energy ranges covered the dielectronic recombination resonances of 2s–2p (△n = 0) core excitations for both the ions. The experimental rate coefficients are compared with the results from AUTOSTRUCTURE calculation. Temperature-dependent plasma rate coefficients from 103 to 106 K are obtained from the recombination spectra by convolution with Maxwell–Boltzmann energy distributions. The experimental plasma rate coefficients of B-like C show good agreement with the calculations at high temperatures, while at low temperatures, the calculated results severely underestimate the plasma rate coefficients. In the case of B-like Ne, the agreement between experimental and calculated results is rather good (within the experimental uncertainties) over the presented temperature range.

Does atomic polarizability play a role in hydrogen radio recombination spectra from Galactic H II regions?*This paper is dedicated to the memory of my esteemed senior colleague Professor Eduard Hintz (1929–2012), in appreciation of invaluable insights provided into atomic processes in the edge plasma of the tokamak.

Since highly excited atoms, which contribute to the radio recombination spectra from Galactic H II regions, possess large polarizabilities, their lifetimes are influenced by ion (proton)–induced dipole collisions. It is shown that, while these ion–radiator collisional processes, if acting alone, would effectively limit the upper principal quantum number attainable for given plasma parameters, their influence is small relative to that of electron impacts within the framework of line broadening theory. The present work suggests that ion–permanent dipole interactions (Hey et al 2004 J. Phys. B: At. Mol. Opt. Phys. 37 2543) would also be of minor importance in limiting the occupation of highly excited states. On the other hand, the ion–induced dipole collisions are essential for ensuring equipartition of energy between atomic and electron kinetic distributions (Hey et al 1999 J. Phys. B: At. Mol. Opt. Phys. 32 3555; 2005 J. Phys. B: At. Mol. Opt. Phys. 38 3517), without which Voigt profile analysis to extract impact broadening widths would not be possible. Electron densities deduced from electron impact broadening of individual lines (Griem 1967 Astrophys. J. 148 547; Watson 2006 J. Phys. B: At. Mol. Opt. Phys. 39 1889) may be used to check the significance of the constraints arising from the present analysis. The spectra of Bell et al (2000 Publ. Astron. Soc. Pac. 112 1236; 2011 Astrophys. Space Sci. 333 377; 2011 Astrophys. Space Sci. 335 451) for Orion A and W51 in the vicinity of 6.0 and 17.6 GHz are examined in this context, and also in terms of a possible role of the background ion microfield in reducing the near-elastic contributions to the electron impact broadening below the predictions of theory (Hey 2012 J. Phys. B: At. Mol. Opt. Phys. 45 065701). These spectra are analysed, subject to the constraint that calculated relative intensities of lines, arising from upper states in collisional–radiative equilibrium, should be consistent with those obtained from Voigt profile analysis. It is shown that the experimental technique yields an excellent temperature diagnostic for the H II regions. On the other hand, strong evidence is not obtained, from those spectra which satisfy the above constraint on intensity, to indicate that the electron impact broadening theory requires substantial correction. The main grounds for attempting a revision of theory to allow for the influence of the ion microfield during the scattering processes on the upper and lower states of each line thus still appear to have a stronger theoretical (Hey 2007 J. Phys. B: At. Mol. Opt. Phys. 40 4077) than experimental basis.

Experimental rate coefficients of F5+recombining into F4+

Recombination spectra of F 5+ producing F 4+ have been investigated with high-energy resolution, using the CRYRING heavy-ion storage ring. The absolute recombination rate coefficients are derived in the centre-of-mass energy range of 0−25 eV. The experimental results are compared with intermediate-coupling AUTOSTRUCTURE calculations for 2s−2p (� n = 0) core excitation and show very good agreement in the resonance energy positions and intensities. Trielectronic recombination with 2s 2 −2p 2 transitions are clearly identified in the spectrum. Contributions from F 5+ ions in an initial metastable state are also considered. The energy-dependent recombination spectra are convoluted with Maxwell-Boltzmann energy distribution in the 10 3 −10 6 K temperature range. The resulting temperature-dependent rate coefficients are compared with theoretical results from the literature. In the 10 3 −10 4 K range, the calculated data significantly underestimates the plasma recombination rate coefficients. Above 8 × 10 4 K, our AUTOSTRUCTURE results and plasma rate coefficients from elsewhere show agreement that is better than 25% with the experimental results.

Radiative recombination and optical gain spectra in biaxially strainedn-type germanium

We calculate band-to-band radiative transition rate spectra in pure Ge as functions of applied tensile strain, heavy doping, charge injection density, and temperature. Direct and indirect phonon-assisted transitions are considered. Deformation potential theory is adopted to describe the conduction and valence near-gap edges. Biaxial strain has required appropriate treatment of system anisotropy through the evaluation of the mass tensor components for the different bands involved in the studied transitions. Population distribution in the $\ensuremath{\Gamma}$ and $L$ conduction valleys and in the valence states near $\ensuremath{\Gamma}$ have been evaluated accordingly considering the degeneracy condition of the sample, induced by high doping and high injection charge density. Also the effect of strain on the dipole matrix elements have been properly taken into account. The energy-resolved near-infrared spontaneous recombination spectra and the TE and TM polarized absorption/gain spectra have been obtained for a broad range of $n$-type doping, strain values, and excitation densities. We conclude that, despite the free carrier losses, net gain values as high as 6000 cm${}^{\ensuremath{-}1}$, are achievable for doping density and strain values reported in the literature.

저온수열합성방법에 의해 성장한 ZnO 나노로드의 전구체 몰농도 변화에 따른 특성 연구

In this research, we investigated the effect of mole concentration of precursor on morphological, structural and optical properties of ZnO nanorods. ZnO nanorods were hydrothermally grown on c-plane sapphire substrates in aqueous solution which contains zinc nitrate hexahydrate and hexamethylenetetramine at 90 o C in the precursor range of 0.01 M to 0.025 M. With the increase of mole concentration, length and diameter of ZnO nanorods increased. In all the conditions, the growth direction of rods was longitudinally c-axis direction. From the strong emission peak at 380 nm of PL spectra at room temperature, we could confirm that the crystal quality of ZnO nanorods is good to emit radiative recombination spectra.

Effective conductance method for the primordial recombination spectrum

As atoms formed for the first time during primordial recombination, they emitted bound-bound and free-bound radiation leading to spectral distortions to the cosmic microwave background. These distortions might become observable in the future with high-sensitivity spectrometers, and provide a new window into physical conditions in the early universe. The standard multilevel atom method habitually used to compute the recombination spectrum is computationally expensive, impeding a detailed quantitative exploration of the information contained in spectral distortions thus far. In this work it is shown that the emissivity in optically thin allowed transitions can be factored into a computationally expensive but cosmology-independent part and a computationally cheap, cosmology-dependent part. The slow part of the computation consists in pre-computing temperature-dependent effective ``conductances,'' linearly relating line or continuum intensity to departures from Saha equilibrium of the lowest-order excited states ($2s$ and $2p$), that can be seen as ``voltages.'' The computation of these departures from equilibrium as a function of redshift is itself very fast, thanks to the effective multilevel atom method introduced in an earlier work. With this factorization, the recurring cost of a single computation of the recombination spectrum is only a fraction of a second on a standard laptop, more than four orders of magnitude shorter than standard computations. The spectrum from helium recombination can be efficiently computed in an identical way, and a fast code computing the full primordial recombination spectrum with this method will be made publicly available soon.

Very deep spectroscopy of the bright Saturn nebula NGC 7009 – II. Analysis of the rich optical recombination spectrum

[Abridged] We present a critical analysis of the rich optical recombination spectrum of NGC 7009, in the context of the bi-abundance nebular model proposed by Liu et al. (2000). The observed relative intensities are compared with the theoretical predictions based on high quality effective recombination coefficients, now available for the recombination line spectrum of a number of heavy element ions. The possibility of plasma diagnostics using the optical recombination lines (ORLs) of heavy element ions is discussed in detail. Plasma diagnostics based on the N II and O II recombination spectra both yield electron temperatures close to 1000 K, which is lower than those derived from the collisionally excited line (CEL) ratios by nearly one order of magnitude. The very low temperatures yielded by the O II and N II ORLs indicate that they originate from very cold regions. The C^{2+}/H^+, N^{2+}/H^+, O^{2+}/H^+ and Ne^{2+}/H^+ ionic abundance ratios derived from ORLs are consistently higher, by about a factor of 5, than the corresponding values derived from CELs. In calculating the ORL ionic abundance ratios, we have used the newly available high quality effective recombination coefficients, and adopted an electron temperature of 1000 K, as given by the ORL diagnostics and as a consequence presumably representing the physical conditions prevailing in the regions where the heavy element ORLs arise. A comparison of the results of plasma diagnostics and abundance determinations for NGC 7009 points to the existence of "cold", metal-rich (i.e. H-deficient) inclusions embedded in the hot, diffuse ionized gas, first postulated by Liu et al. (2000).

Plasma diagnostics for planetary nebulae and H ii regions using the N ii and O ii optical recombination lines

We carry out plasma diagnostic analyses for 123 planetary nebulae (PNe) and 42 H II regions using the N II and O II optical recombination lines (ORLs). New effective recombination coefficients for the N II and O II optical recombination spectra are used. These data were calculated under the intermediate coupling scheme for a number of electron temperature (Te) and density (Ne) cases. We used a new method to determine the Te and Ne for the nebular sample, combining the ORLs with the most reliable measurements for each ion and the predicted intensities that are based on the new atomic data. Uncertainties of the derived Te and Ne are estimated for each object. The diagnostic results from heavy element ORLs show reasonable agreement with previous calculations in the literature. We compare the electron temperatures derived from the N II and O II ORLs, Te(ORLs), and those from the collisionally excited lines (CELs), Te(CELs), as well as the hydrogen Balmer jump, Te(H I BJ), especially for the PNe with large abundance discrepancies. Temperatures from He I recombination lines, Te(He I), are also used for comparison if available. For all the objects included in our sample, Te(ORLs) are lower than Te(H I BJ), which are in turn systematically lower than Te(CELs). Nebulae with Te(He I) available show the relation Te(ORLs) < Te(He I) < Te(H I BJ) < Te(CELs), which is consistent with predictions from the bi-abundance nebular model postulated by Liu et al. (2000).

Profile Measurement of Ion Temperature and Toroidal Rotation Velocity with Charge Exchange Recombination Spectroscopy Diagnostics in the HL-2A Tokamak

This paper deals with the profile measurement of impurity ion temperature and toroidal rotation velocity that can be achieved by using the charge exchange recombination spectrum (CXRS) diagnostics tool built on the HL-2A tokamak. By using CXRS, an accurate impurity ion temperature and toroidal plasma rotation velocity profile can be achieved under the condition of neutral beam injection (NBI) heating. Considering the edge effect of the line of CVI 529.06 nm (n = 8∼7), which contains three lines (active exciting spectral line (ACX), passivity exciting spectral line (PCX) and electron exciting spectral line (ICE)), and using three Gaussian fitted curves, we obtain the following experimental results: the core ion temperature of HL-2A device is nearly thousands of eV, and the plasma rotation velocity reaches about 104 m · s−1. At the end of paper, some explanations are presented for the relationship between the curves and the inner physical mechanism.

Spectroscopy above the ionization threshold: Dissociative recombination of the ground vibrational level of ${\rm N}_{\rm 2}^{\rm + }$N2+

Comprehensive theoretical calculations are reported for the dissociative recombination of the lowest vibrational level of the N(2)(+) ground state. Fourteen dissociative channels, 21 electron capture channels, and 48 Rydberg series including Rydberg states having the first excited state of the ion as core are described for electron energies up to 1.0 eV. The calculation of potential curves, electron capture and predissociation widths, cross sections and rate constants are described. The cross sections and rate constants are calculated using Multichannel Quantum Defect Theory which allows for efficient handling of the Rydberg series. The most important dissociative channel is 2(3)Π(u) followed by 4(3)Π(u). Dissociative states that do not cross the ion within the ground vibrational level turning points play a significant role in determining the cross section structure and at isolated energies can be more important than states having a favorable crossing. By accounting for autoionization, the interactions between resonances, between dissociative states, and between resonances and dissociative states it is found that the cross section can be viewed as a complex dissociative recombination spectrum in which resonances overlap and interfere. The detailed cross section exhibits a rapid variation in atomic quantum yields for small changes in the electron energy. A study of this rapid variation by future high resolution storage ring experiments is suggested. A least squares fit to the calculated rate constant from the ground vibrational level is 2.2(+0.2)/(-0.4) × 10(-7) × (T(e)/300)(-0.40) cm(3)/sec for electron temperatures, T(e), between 100 and 3000 K and is in excellent agreement with experimentally derived values.

Low Temperature Photoluminescence Signature of Stacking Faults in 6H-SiC Epilayers Grown on Low Angle Off-Axis Substrates

The radiative recombination spectra of 6H-SiC epilayers grown on low angle (1.4° off-axis) substrates have been investigated by low temperature photoluminescence spectroscopy. Four different types of stacking faults have been identified, together with the presence of 3C-SiC inclusions. From the energy of the momentum-conserving phonons, four excitonic band gap energies have been found with Egx equal to 2.837, 2.698, 2.600 and 2.525 eV. These photoluminescence features, which give a rapid and non-destructive approach to identify stacking faults in 6H-SiC, provide a direct feedback to improve the material growth.

Negative trion emission spectrum in stacked quantum dots: External electric field and valence band mixing

We study the negatively charged exciton trion in stacked quantum dots by the configuration interaction method. We discuss the trion recombination spectrum in an external electric field ($F$) and look for the effects of the valence band mixing leading to the antibonding-hole ground-state formation in the quantum dot molecule. We find that the antibonding-hole ground state produces a distinct modification of the trion emission for strongly coupled dots inverting the intensities of recombination lines in the principal avoided crossing appearing in the spectrum within the range of low $F$. This avoided crossing is very similar to the one observed for the neutral exciton only with a shift of the anticrossing centra on the scale of $F$. The exciton and trion emission spectra are distinctly different for weak interdot tunnel coupling, for which the effects of the antibonding-hole ground state are less evident for both the exciton and the trion. In particular for both the bonding and the antibonding-hole ground states the dissociation of the negative trion ground state appears as a two-stage process with a characteristic shape of the recombination line as observed experimentally.

Identification of a silicon vacancy as an important defect in 4H SiC metal oxide semiconducting field effect transistor using spin dependent recombination

A spin dependent recombination (SDR) spectrum observed in a wide range of SiC metal oxide semiconducting field effect transistors (MOSFETs) has previously been only tentatively linked to a silicon vacancy or vacancy related defect. By resolving hyperfine interactions in SDR detected spectra with 13C nuclei, we provide an extremely strong argument identifying the SDR spectrum with a silicon vacancy. Since the silicon vacancy spectrum dominates the SDR response in a wide variety of SiC MOSFETs, silicon vacancies are quite important traps in this technology.

MD2-5 An Investigation of DME HCCI Combustion Using Spectroscopic Analysis(MD: Measurement and Diagnostics,General Session Papers)

In order to control the ignition timing and overall combustion rate of HCCI, it is important to have a firm understanding of the chemical reactions of fuel because HCCI can be characterized as controlled chemical auto-ignition process. One technique that can be employed to gain a better understanding of the HCCI combustion process is chemiluminescence, which is the light emission from the excited state of intermediates or radicals. The objective of this study is to experimentally investigate the correlation between chemiluminescence of the active species, which play important role in the ignition, and HCCI combustion characteristics for providing the way to control auto-ignition process. In addition, a combination of experimental and computational results is employed. The experiments were conducted using optical accessible engine, photo-multiplier and band-pass filters. Senkin application of the CHEMKIN-II kinetics rate code was used for computation. As the result, there was a precise correlation between the rate of heat release and chemiluminescence intensity of OH (307.4 nm) and all band (350-700 nm) by tracing the in-cylinder mass-averaged. The start timing of emitting luminescence in OH coincided with H_2O_2 dissociation, and the peak timing of emitting luminescence in all band corresponded to the CO-O recombination spectrum.

Features of structural reorganization in bulk III–V compounds induced by weak magnetic fields

The long-term transformations of defect structure in GaP, GaAs and InP single crystals treated with pulsed weak magnetic fields are obtained. The treatments were performed in two regimes, namely, single-pulse (τ=30ms) and multi-pulse (τ=1.2ms) ones, at varying magnitude of magnetic induction. The defect structure transformations were inferred from the radiative recombination spectra in the 0.6–2.5μm range at 77–300K as well as Raman scattering and morphology investigations. A possible mechanism of observed modifications related to the electron spin transformation is discussed.

The Multiple Continuum Components in the White-Light Flare of 16 January 2009 on the dM4.5e Star YZ CMi

The white light during M dwarf flares has long been known to exhibit the broadband shape of a T~10,000 K blackbody, and the white light in solar flares is thought to arise primarily from Hydrogen recombination. Yet, a current lack of broad wavelength coverage solar-flare spectra in the optical/near-UV prohibits a direct comparison of the continuum properties to determine if they are indeed so different. New spectroscopic observations of a secondary flare during the decay of a megaflare on the dM4.5e star YZ CMi have revealed multiple components in the white-light continuum of stellar flares, including both a blackbody-like spectrum and a hydrogen recombination spectrum. One of the most surprising findings is that these two components are anti-correlated in their temporal evolution. We combine initial phenomenological modeling of the continuum components with spectra from radiative-hydrodynamic models to show that continuum veiling gives rise to the measured anti-correlation. This modeling allows us to use the components' inferred properties to predict how a similar spatially resolved, multiple-component white-light continuum might appear using analogies to several solar flare phenomena. We also compare the properties of the optical stellar flare white light to Ellerman bombs on the Sun.

The effects of quantum interference between direct and resonant photorecombination of H-like Ar17+ ions

The multiconfiguration Dirac–Fock method has been used to study interference effects between direct and resonant photorecombination (i.e. radiative and dielectronic recombination) from the ground state 1s2S1/2 of H-like Ar17+ ions via doubly excited 2s21S0, 2s2p 3P0, 1, 2, 1P1 and 2p23P0, 1, 2, 1D2, 1S0 resonances of He-like Ar16+ ions combined with the Fano parameterization technique. In order to produce total photorecombination spectra, it is necessary to calculate the energy levels of the 1s of H-like Ar17+ ions, 1s2, 1s2l and 2l2l′ (l,l′ =0, 1) of He-like Ar16+ ions, the radiative and nonradiative properties of the doubly excited states of He-like Ar16+ ions, and the direct and resonant photorecombination cross sections from the 1s state of H-like Ar17+ ions into the ground state 1s2 and the single excited states of 1s2l (l=0, 1) of He-like Ar16+ ions, in detail. Based on good agreement between the present calculations and other available experimental and theoretical results, the interference profile determined by the so-called Fano parameters q and ρ2 is also shown. The results indicate that interference effects are remarkable at some resonances, especially near the doubly excited 2s2p 1P1 state of He-like Ar16+ ions, and strongly influence the intensity of the wing of the nonresonant background in the photorecombination of H-like Ar17+ ions through comparison between the final Fano and total radiative recombination to dielectronic recombination spectra.