Low-energy Electron Spectra Research Articles

An experimental comparison of the K- and L-Auger electron spectra generated in the decays of 140Nd and 111In

The low-energy electron spectra generated in the decay of 140Nd have been measured using a combined electrostatic spectrometer adjusted to the 4, 7, and 35eV instrumental resolution. In order to estimate the therapeutic potential of low-energy electrons associated with the decay of 140Nd, similar experiments have been performed with 111In. Relative Auger electron intensity ratios per decay are: 111InK−Auger/140NdK−Auger=1.47(12), 111InL−Auger /140NdL−Auger=1.1(4), and 111InL−Auger [2.8–7keV]/140NdL−Auger [2.8–7keV]=0.24(11). The obtained K-Auger group intensity ratios have been compared with results of calculations. The good agreement found for the experimental and estimated values indicates that such information can be also derived using available nuclear and atomic data.The relative intensity of L-Auger electrons emitted within the 2.8–7keV interval is higher for 140Nd by a factor of about 4 compared to 111In. As the L-Auger emission is dominating relative to that of the K-Auger group, this implicates that any potential endotherapeutic strategy using 140Nd-labelled targeting vectors requires a maximum accumulation of the endoradiotherapeutical close to the cell nucleus or the DNA of the tumour cell.

A detailed experimental investigation of the low energy electron spectrum generated in the EC-decay of 6731Ga

A spectrum of the low energy electrons from the electron capture decay of 67Ga has been analyzed at the instrumental resolution 4, 7, and 14 eV in the region 570–10 400 eV using an electrostatic spectrometer. Energies and relative intensities of the LMM + LMN, KLL, KLM + KLN, and KMM + KMN Auger transitions have been determined with high accuracy and compared with results of available calculations. The measured absolute energies of the dominant KLL and KLM Auger lines have been found to be significantly higher than the semi-empirical values. Generally, worse agreement has been found between measured and calculated transition intensities. Relative intensities of the main spectrum components have been also determined to be: (LMM+LMN)/KLL/(KLM+KLN)/(KMM+KMN)=(27.5±2.3)/(60.1±4.6)/(14.5±1.0)/(1.00±0.07).

Low-energy magnetoplasmon excitations in semimetallic carbon nanotubes

The low-energy electron spectrum of semimetallic carbon nanotubes consists of two pairs of electron and hole subbands with linear dispersion intersecting at the Fermi level. An external perturbation such as a magnetic or electric field lifts the degeneracy of the subbands and opens a minigap at the band crossing. A quasi-one-dimensional massless Dirac-like Hamiltonian has been used to model the low-energy electron spectrum of this system as a function of the wave vector along the nanotube axis. Within this model, the plasmon dispersion formula is obtained for the arbitrary allowed angular- and linear-momentum transfer. The plasmon energies are calculated as a function of the transferred momentum and the nanotube radius when there is no transferred angular momentum. We show that both the low-frequency (quasiacoustic) and the high-frequency (optical) plasmon excitations are obtained in this system, depending on the position of the Fermi level with respect to the energy gap induced by the external perturbation. We calculate the phase velocity ${C}_{p}$ as a function of the Fermi level. Our results show that ${C}_{p}$ has kinks that are due to an increased density of states within the band. There is a discontinuity in the curve near which the minigap opens up.

The predicted 10.6 keV transition in 221Fr from the α-decay of 225Ac revealed

The low energy electron spectrum from the α-decay of 225Ac has been measured with 20 eV instrumental resolution using an electrostatic spectrometer and radioactive sources prepared by vacuum evaporation. The predicted 10.642(5) keV M1 + < 0.05% E2 nuclear transition in 221Fr have been revealed. Energies of 26.015(5), 36.660(5), 38.543(3) and 108.37(1) keV nuclear transitions in 221Fr have been essentially improved. Relative intensities of the measured conversion electron lines of these transitions have also been determined.

X-ray Spectroscopic Study of U6p,5f Electronic Levels in γ-UO3

The fine structures of X-ray photoelectron (XPE) spectra of low-energy electrons and conversion electron spectra of γ-UO3 (0-40 eV energy) were analyzed taking into account relativistic calculations based on the Xα discrete variation method of the electronic structure of uranium cluster [(UO2)O4]6- (D4h symmetry group) representing the closest coordination of uranium in γ-UO3. The theoretical and experimental data show that U5f electrons directly participate in the chemical bonding. The density of states of 5f valence electrons in uranium trioxide was calculated. At the same time, U6p electrons participate in formation of both inner and outer valence molecular orbitals, and the density of such 6p states in uranium trioxide was also calculated. The order of the inner valence molecular orbitals in the 13-40 eV range was determined, which is of particular importance for development of a procedure to evaluate the uranium-ligand bond distances in axial and equatorial directions in uranyl compounds using their X-ray photoelectron spectra in the range of inner group) representing the closest coordination of uranium in γ-UO3. The theoretical and experimental data showthat U5f electrons directly participate in the chemical bonding. The density of states of 5f valence electronsin uranium trioxide was calculated. At the same time, U6p electrons participate in formation of both inner andouter valence molecular orbitals, and the density of such 6p states in uranium trioxide was also calculated. The order of the inner valence molecular orbitals in the 13-40 eV range was determined, which is of particular importance for development of a procedure to evaluate the uranium-ligand bond distances in axial andequatorial directions in uranyl compounds using their X-ray photoelectron spectra in the range of innermolecular orbitals.

Excitation of plasmons by impact of slow ions on clean mono- and polycrystalline aluminum

Low-energy electron spectra have been measured for impact of slow (⩽10 keV) H +, H 2 +, He +, Ne +, Ne 2+, Ar + and Ar 2+ ions on atomically clean poly and monocrystalline aluminum surfaces. In these spectra broad peaks at 11 and 6.6 eV result from one-electron decay of Al bulk and surface plasmons, respectively. Their relative intensity has been studied for different angles of ion incidence and electron emission. “Direct” or “potential” excitation of plasmons can take place if the available ion neutralization energy E pot exceeds the sum of plasmon energy (15.3 and 10.9 eV for bulk and surface plasmons, respectively) and Al work function (4.3 eV). At our experimental conditions excitation of bulk plasmons was considerably stronger than of surface plasmons. Potential excitation of bulk plasmons shows a quasi-resonant dependence on E pot and is not significantly more important for multiply than for singly charged ions. With too small potential energy plasmons can only “indirectly” be excited by fast electrons from concomitant kinetic emission. For proton impact on Al(1 1 1), structures in the electron spectra which have earlier been ascribed to plasmon excitation are here explained by diffraction of electrons from kinetic emission which undergo multiple scattering in the uppermost surface layers before escape.

X-Ray Photoelectron Study of Thorium Silicate ThSiO4 · nH2O and Uranium Silicate USiO4·nH2O

The naturally occurring compounds of thorium ThSiO4, ThSiO4· nH2O, and (Th, Fe)SiO4 and uranium USiO4· nH2O have been studied by X-ray photoelectron spectroscopy in the range of electron binding energies from 0 to 1200 eV. The oxidation state of Th in the natural compounds is close to that in Th(OH)4; for uranium, it is similar to that in UO2. Based on the structure of the low-energy electron spectra it is assumed that the electrons of the filled Th6p- and O2s-atomic orbitals take an active part in chemical bonding. Fine structure was observed in the Th(U)6s-, 5d-, 5p-, 4f-, 4d-, and 4p 3/2 electron spectra of all substances under study. Mechanisms of fine structure formation are discussed and the fine structure parameters are correlated with the physicochemical properties of the compounds.

Spectroscopic characterization of the surface nanostructure of Ti during deposition on polycrystalline aluminium

Auger electron spectroscopy (AES), x-ray photoelectron spectroscopy (XPS), angle-resolved x-ray photoelectron spectroscopy (ARXPS), ion scattering spectroscopy (ISS) and factor analysis (FA) have been used to study the deposition of titanium on polycrystalline aluminium at room temperature. Analysis of AES and XPS spectra suggests the formation of a titanium aluminide alloy during the first steps of deposition. Application of FA to the low-energy Auger electron spectra allows the identification of three principal factors that can be attributed to metallic aluminium, metallic titanium and titanium aluminide, respectively. The ARXPS measurements are consistent with a two-stage mechanism for titanium growth: a first stage characterized by the formation of a uniform layer ∼4 ML thick of an intermetallic compound TiAlx (x = 1.5), followed by the formation of metallic titanium islands with an average thickness of 10 ML that grow over the TiAlx layer formed previously. Copyright © 1999 John Wiley & Sons, Ltd.

Superconducting GapΔc, the PseudogapΔp, and Pair Fluctuations aboveTcin OverdopedY1−xCaxBa2Cu3O7−δfrom Femtosecond Time-Domain Spectroscopy

The low-energy electronic excitation spectrum and gap structure in optimally doped and overdoped Y_{1-x}Ca_{x}Ba_{2}Cu_{3}O_{7-\delta} single crystals are investigated by real-time measurements of the quasiparticle relaxation dynamics with femtosecond optical spectroscopy. From the amplitude of the photoinduced reflectivity as a function of time, temperature and doping x we find clear evidence for the coexistence of two distinct gaps in the entire overdoped phase. One is a temperature-independent pseudogap $\Delta_{p}$ and the other is a T-dependent collective gap $\Delta_{c}(T)$ which has a BCS-like T-dependence closing at Tc. From quasiparticle relaxation time measurements above Tc we ascertain that fluctuations associated with the collective gap $\Delta_{c}(T)$ are limited to a few K, consistent with time-dependent Ginzburg-Landau theory and are distinct from the pseudogap whose presence is apparent well above Tc for all x.

The low-energy electron spectrum from the -decay of

The low-energy electron spectrum from the -decay of has been analysed in the region of 2.5-22.5 keV at the 20 eV instrumental resolution using a combined electrostatic spectrometer and a radioactive source prepared by vacuum evaporation. Energies , (?), , , , and have been determined for nuclear transitions in . Relative intensities of some conversion electron lines of these transitions have also been derived. For the 26.3 keV E1 and 43.4 keV transitions, the nuclear structure parameters , and the E2 admixture , respectively, have been obtained. Values of , , and were measured for the dominant , , and Auger transitions in Np, respectively.

Electron ejection from solids by heavy ions at high energies (1–100 MeV/u)

Results on electron emission from solids bombarded with swift heavy ions at high energies (from about 1 up to 100 MeV/u) are presented. Three different topics are discussed: (1) The ejection of high energy binary encounter electrons induced by argon ions. (2) Electron yields from thin carbon foil targets. (3) First results on high charge effects in low energy electron spectra from sputter cleaned carbon and the influence of controlled contamination by exposure to nitrogen.

The low-energy electron spectrum from the EC-decay of 57Co: 0eV up to 15keV

Abstract The low-energy electron spectrum from the 57Co decay has been examined in the region from 0 up to 15 keV at instrumental resolution ranging from 2 to 15 eV. Two electrostatic spectrometers and radioactive sources prepared by vacuum evaporation of 57Co onto Al foils were utilized. Relative intensities of the main spectrum components have been obtained as follows: (TSE+LLX+Shake-off)/LMM/KLL/KLM/KMM/K−14.4/L−14.4/MN−14.4=116±12/51±4/59.7±1.8/15.2±0.4/1.15±0.07/49.6±1.5/5.05±0.15/0.79±0.02 where TSE means “true secondary electrons”. Absolute and relative energies of the LMM, KLL, KLM, and KMM Auger transitions in Fe have also been determined, as well as their relative intensities with the exception of the LMM lines, the shapes of which were strongly distorted due to the inelastic electron scattering and probably also chemical effects. From the measured conversion electron lines of the 14.4 keV M1 transition in 57Fe, a transition energy of 14412.8±0.8 eV and the E2 admixture less than 8×10−6 were derived. Relative intensities of both the KL2,3(M4,5N1) Auger line group and the M4,5N1−14.4 conversion line were found to be lower by about 30% for the “oxide” state of decaying 57Co atoms than for the “metallic” state. Pronounced broadenings of narrow spectrum lines have been observed as a consequence of the oxidation of the 57Co sources in the laboratory atmosphere. Natural widths for most of the KLL, KLM, and KMM Auger lines and those of the K, L1, L2, L3, M1, M2, M3 and N1 atomic levels in 57Fe were also determined.

Study of Ni–Al interface formation

Auger electron spectroscopy (AES), electron energy loss spectroscopy (EELS) and factor analysis (FA) have been used to characterize the interface formation during the deposition of nickel on aluminum substrates at room temperature. The analysis of the shape of AES and EELS lines suggests the formation of a Ni–Al compound during the first stages of the deposition. Application of FA to the low-energy Auger electron spectra gives three principal factors that can be attributed to metallic aluminum, metallic nickel and nickel aluminide, respectively. These results, in addition to those on the evolution of the Ni LVV versus the Al LVV Auger intensity, are consistent with the formation of three monolayers of a Ni x Al compound with an average composition of x≈2, followed by a layer by layer growth of Ni on the Ni x Al interface.

Low-energy electron spectrum in copper oxides in the multiband p-d model

An exact diagonalization of the Hamiltonian in the p-d model of a CuO6 cluster was used to obtain dependences on the model parameters of the lowest-energy two-hole terms: the energy difference between the 2p orbitals of planar and apical oxygen Δ(apex)=e(2p)−e[2p(apex)], the crystal field parameter \(\Delta _d = \varepsilon _{3z^2 - r^2 } - \varepsilon _{x^2 - y^2 } \), and the ratio of the distances between the copper atom and the apical and planar oxygen atoms d(apex)/d(pl). In the limit of large d(apex)/d(pl) and Δd, our model is equivalent to the three-band p-d model and, in this case, large singlet-triplet splitting Δe⩾1 eV is also observed. As the parameters decrease, a singlet-triplet crossover is observed. Two mechanisms are identified for stabilization of the triplet term 3B1g(0) as the ground state. It is shown that for realistic values of the parameters, reduction of the p-d model to the three-band model is limited by the low energies of the current excitations because of the presence of the lower excited 3B1g and 1A1g cluster states. Intercluster hopping causes strong mixing of singlet and triplet states far from the G point. The results of the calculations are compared with data obtained by angle-resolved photoelectron emission in Sr2CuO2Cl2.

Self-Assembled Peptide Nanotubes from First Principles

Nanotubular structures made up of polypeptides have recently become available. We present a characterization of the structural and electronic properties of one such system within density functional theory with calculations using gradient-corrected exchange-correlation functionals. Comparison with data on natural amino acids, and with the predictions of empirical models, is drawn from the structural features. A large gap in the low-energy electronic excitation spectrum is predicted, and the presence of extended as well as localized states near the gap is found.

Precision investigations of the spectra of low-energy electrons from radioactive decay using an ESA50 combined electrostatic spectrometer

Methods for producing thin radioactive sources, for processing multiplet spectra and for the energy calibration of a spectrometer, which have been used in numerous precision investigations of low-energy K- and L-Auger electrons and conversion electrons, which are emitted in the radioactive decay of nuclei, using an ESA50 combined electrostatic spectrometer are described.

Low-energy Rydberg electron spectra from 64 MeV S q+ + He and C-foil collisions using zero-degree electron spectroscopy

Zero-degree electron spectra were measured with high resolution for 64 MeV S q+ ( q = 6, 11 to 13) ions on a He and C-foil target. Several peaks are observed in the electron energy range up to 2.5 eV for the 64 MeV S 12+ + He collision, in addition to a series of autoionization electrons produced by the Coster-Kronig transition 1 s 22p( 2P 3 2 )9l−1 s 22s ϵl′ . The charge state dependence of electron spectra for 64 MeV S 11+.12+.13+ + He and S 6+.12+.13+ + C were measured to identify the origin of the low energy electrons. No characteristic line is observed in the electron energy spectra following the 64 MeV S 13+ beam excitation with He. This indicates that the electron excitation and capture process that could produce the Li- and Be-like initial configurations resulting in autoionizing Coster-Kronig transitions does not occur during a collision between 64 MeV S 13+ ions and a He target at this collision energy. It is supposed that the electron spectra for S 11+ shows a series of autoionizing Coster-Kronig transitions of 1s 22p 27 l−1s 22s2p ϵl′, 1s 22p 29 l−1s 22s2p ϵl′ and 1s 22s2p9 l−1s 22s 2 ϵl′ for S 11+ ions, which are energetically possible.

Spectra of low-energy electrons excited by soft x rays

A study is made of the x-ray photoemission spectra of low-energy electrons (Ekin=0–30 eV) and its dependence on the way in which the potentials are applied to the entrance system of the analyzer. It is shown that under certain experimental conditions the spectrum consists solely of electrons emitted from the sample. The x-ray photoemission spectrum of pure silver is found to have a fine structure, which disappears when a surface layer of carbon or oxygen is deposited on the surface. The spectrum then takes on the “cascade” form. A possible interpretation of the fine structure is suggested in the framework of band theory.

Influence of geostationary spacecraft charging on measurements of low energy (0.05–20 keV) electron spectra

We find that the electron distributions measured from the Meteosat spacecraft in geosynchronous orbit have some characteristic spectral shapes associated with the different regions which the spacecraft passes through. Some of the temporal variations are associated with surface charging of the spacecraft, in particular when the spacecraft passes into the Earth's shadow. These charging events are well-known. In addition there is new evidence, from the distortion of the spectrum, that the spacecraft charges up to potentials of as much as 1 kV when an injection front passes over the spacecraft, even though it is still in sunlight.

Fragmentation processes of the core-excited NO molecule

Ionization and fragmentation processes of the NO molecule following the excitation of the nitrogen 1s electron have been studied by means of high-resolution mass-selective ion-yield measurements. The yields of and ions acquired with a quadrupole mass spectrometer (QMS) and a linear time-of-flight spectrometer (TOF) show surprising differences at the threshold region suggesting the selective attachment of the excited core electron to the centre during the dissociation of the ion. The fragmentation branching ratios corrected for the angular and kinetic energy effects are presented. The kinetic energy distributions of the and fragments have been extracted for a number of Rydberg states manifesting a significant dependence on l quantum number and energy of the primary excited Rydberg level. The lifetime of the core-excited state has been found from the shape of the low kinetic energy electron spectra acquired above the and thresholds.