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We report on an apparent low-energy nanoscale electronic inhomogeneity in ${\mathrm{FeSe}}_{0.4}{\mathrm{Te}}_{0.6}$ due to the distribution of selenium and tellurium atoms revealed through unsupervised machine learning. Through an unsupervised clustering algorithm, characteristic spectra of selenium- and tellurium-rich regions are identified. The inhomogeneity linked to these spectra can clearly be traced in the differential conductance and is detected both at energy scales of a few electron volts as well as within a few millielectronvolts of the Fermi energy. By comparison with angle-resolved photoemission spectroscopy, this inhomogeneity can be linked to an electronlike band just above the Fermi energy. It is directly correlated with the local distribution of selenium and tellurium. There is no clear correlation with the magnitude of the superconducting gap, however, the height of the coherence peaks shows a significant correlation with the intensity with which this band is detected, and hence with the local chemical composition.

A central mystery in high temperature superconductivity is the origin of the so-called "strange metal," i.e., the anomalous conductor from which superconductivity emerges at low temperature. Measuring the dynamic charge response of the copper-oxides, $\chi''(q,\omega)$, would directly reveal the collective properties of the strange metal, but it has never been possible to measure this quantity with meV resolution. Here, we present the first measurement of $\chi''(q,\omega)$ for a cuprate, optimally doped Bi$_2$Sr$_2$CaCu$_2$O$_{8+x}$ ($T_c=91$ K), using momentum-resolved inelastic electron scattering. In the medium energy range 0.1-2 eV relevant to the strange metal, the spectra are dominated by a featureless, temperature- and momentum-independent continuum persisting to the eV energy scale. This continuum displays a simple power law form, exhibiting $q^2$ behavior at low energy and $q^2/\omega^2$ behavior at high energy. Measurements of an overdoped crystal ($T_c=50$ K) showed the emergence of a gap-like feature at low temperature, indicating deviation from power law form outside the strange metal regime. Our study suggests the strange metal exhibits a new type of charge dynamics in which excitations are local to such a degree that space and time axes are decoupled., Comment: 21 pages, 8 figures

Making a large-gap topological insulator Although of interest to basic research, topological insulators (TIs) have not yet lived up to their technological potential. This is partly because their protected surface-edge state usually lives within a narrow energy gap, with its exotic transport properties overwhelmed by the ordinary bulk material. Reis et al. show that a judicious choice of materials can make the gap wide enough for the topological properties to be apparent at room temperature. Numerical calculations indicate that a monolayer of Bismuth grown on SiC(0001) is a two-dimensional TI with a large energy gap. The researchers fabricated such a heterostructure and characterized it using scanning tunneling spectroscopy. The size of the experimentally measured gap was consistent with the calculations. Science , this issue p. 287

The influence of the discharge cavity dimensions on the properties of the spherical plasma formed in a fast discharge was studied experimentally. The passage of a current pulse with an amplitude of 30–40 kA and a rise rate of ~1012 A/s (a fast discharge) through a spherical ceramic (Al2O3) cavity with an inner diameter of 11 mm filled with argon at a pressure of 80 Pa results in the formation of a 1- to 2-mm-diameter spherical plasma with an electron temperature of several tens of electronvolts and a density of 1018–1019 cm–3. It is shown that an increase in the inner diameter of the discharge cavity from 11 to 21 mm leads to the fourfold increase in the formation time of the spherical plasma and a decrease in the average ion charge. A decrease in the cavity diameter to 7 mm makes the spherical plasma unstable.

To realize the fundamental limits of photovoltaic device efficiency, solar absorbers must exhibit strong absorption and abrupt absorption onsets. Ideally, onsets to maximum absorption (α > 105 cm–1) occur over a few tenths of an electronvolt. First-principles calculations predict CuTaS3 represents a potentially new class of materials with such absorption characteristics. Narrow metallic d bands in both the initial and final states present high joint densities of states and, therefore, strong absorption. Specifically, a mixture of metal d (Cu1+, d10) and S p characterizes states near the valence band maximum, and metal d (Ta5+, d0) dominates near the conduction band minimum. Optical absorption measurements on thin films confirm the abrupt onset to strong absorption α > 105 cm–1 at Eg + 0.4 eV (Eg = 1.0 eV). Theoretical CuTaS3 solar cell efficiency is predicted to be 28% for a 300 nm film based on the metric of spectroscopic limited maximum efficiency, which exceeds that of CuInSe2. This sulfide may offer n...

A method is reported for a simple, yet reliable, calculation of electron inelastic mean free paths in condensed phase insulating and conducting materials, from the very low energies of hot electrons up to the high energies characteristic of electron beams. Through a detailed consideration of the energy transferred by the projectile in individual and collective electronic excitations, as well as ionizations, together with the inclusion of higher order corrections to the results provided by the dielectric formalism, inelastic mean free paths are calculated for water, aluminum, gold and copper in excellent agreement with the available experimental data, even at the elusive very low energy region. These results are important due to the crucial role played by low energy electrons in radiobiology (owing to their relevant effects in biodamage), and also in order to assess the not yet elucidated disagreement between older and recent measurements of low energy electron mean free paths in metals (which are relevant for low energy electron transport and effects in nanostructured devices)., 5 pages, 4 figures

The determination of the neutrino mass is still an open issue in particle physics. The calorimetric measurement of the energy released in a nuclear beta decay allows measuring the whole energy, except the fraction carried away by the neutrino: due to the energy conservation, a finite neutrino mass m ν causes the energy spectrum to be truncated at Q-m ν , where Q is the transition energy of the decay. The electron capture of 163 Ho (Q ~ 2.5 keV) is an ideal decay, due to the high fraction of events close to the endpoint (i.e., the maximum energy of the relaxation energy spectrum). In order to achieve enough statistics, a large number of detectors (~10 4 ) are required. Superconducting microwave microresonators are detectors suitable for large-scale multiplexed frequency-domain readout, with theoretical energy and time resolution on the order of electronvolts and microseconds, respectively. Our aim is to develop arrays of microresonator detectors applicable to the calorimetric measurement of the energy spectrum of 163 Ho. Currently, a study aimed at the selection of the best design and material for the detectors is in progress. In order to obtain low-Tc detectors, with Tc ranging between ~0.5 and 2 K, different Ti/TiN (titanium nitride) multilayer films were produced. The reduced Tc was obtained by superposing thin layers of stoichiometric TiN to pure Ti layers, and the Tc was tuned by varying the ratio between the thickness of the layers. In this contribution, a comparison between the measurements (critical temperature, gap parameter, and X-ray energy spectra) made with stoichiometric and substoichiometric TiN and Ti/TiN multilayer film microresonators is presented.

This paper reports on the development and testing of a novel, highly efficient technique for the injection of very rare species into electron beam ion traps (EBITs) for the production of highly charged ions (HCI). It relies on in-trap laser-induced desorption of atoms from a sample brought very close to the electron beam resulting in a very high capture efficiency in the EBIT. We have demonstrated a steady production of HCI of the stable isotope 165Ho from samples of only 1012 atoms (∼300 pg) in charge states up to 45+. HCI of these species can be subsequently extracted for use in other experiments or stored in the trapping volume of the EBIT for spectroscopic measurements. The high efficiency of this technique extends the range of rare isotope HCIs available for high-precision atomic mass and spectroscopic measurements. A first application of this technique is the production of HCI of the synthetic radioisotope 163Ho for a high-precision measurement of the QEC-value of the electron capture in 163Ho within the "Electron Capture in Holmium" experiment [L. Gastaldo et al., J. Low Temp. Phys. 176, 876-884 (2014); L. Gastaldo et al., Eur. Phys. J.: Spec. Top. 226, 1623-1694 (2017)] (ECHo collaboration) ultimately leading to a measurement of the electron neutrino mass with an uncertainty on the sub electronvolt level.

There are significant differences between the atomic orbital energies listed in the evaluated photon data library EPDL97 and values published elsewhere. In particular, comparisons with the values adopted by the National Institute of Standards and Technology (NIST) show discrepancies up to several hundred electron volts. Although the uncertainties in the EPDL97 atomic orbital energies were recognised by the original authors, the library has subsequently been widely adopted as a primary source of photon transport and atomic relaxation data. We compare experimentally measured X-ray fluorescence spectra with fits using the EPDL97 and NIST line energies. Our results strongly favour the NIST energies for K-shell and L-shell fluorescent X-rays and show that the EPDL97 atomic orbital energy values should not be used for applications, such as X-ray fluorescence, where atomic relaxation phenomena are important. Copyright © 2012 John Wiley & Sons, Ltd.

Molecular dynamics computer simulations are employed to investigate the effect of the kinetic energy and impact angle on the ejection process from a free-standing graphene of thickness between 1 and 16 layers. The target is bombarded by C60 projectiles with kinetic energy between 5 and 40 keV and the impact angle ranging between 0° and 80°. The yields, kinetic energies, and ejection directions of atoms are monitored. Computer simulations are used to point to optimal conditions when a soft ejection of unfragmented molecules may occur, which may be invaluable information for the development of secondary ion mass spectrometry based on a transmission geometry.

A short survey is given on mass units and recommendations on the proper use of the notations mass and weight.Whereas mass is an inertial physical quantity in classical mechanics, weight is a force due to the gravitational field and depending on the geographic situation.

A methodology for characterizing the transient response of 4H-SiC MOSFETs has been developed. The method combines new physical models, simulation techniques, and experiment to provide insight into the details of MOSFET time-dependent dynamics. A new physical model for generation-recombination between interface traps and channel electrons was derived, facilitating the analysis of trap dynamics in the energy, space, and time domains. A set of algorithms was developed, which enabled these rates to be incorporated into the drift-diffusion model so that their effect on the switching of 4H-SiC MOSFETs could be numerically evaluated. The correlation of simulated and experimental dc and transient drain current allowed the extraction of the density and the effective capture cross sections of interface traps. It was found that states near the band edge would become occupied much more quickly and had a much larger effective capture cross section than those that were several tenths of an electronvolt away from the band edge. This has led to the conclusion that the fast traps with large capture cross sections are likely to be interface states, whereas the traps with the smaller capture cross sections are a combination of midgap interface states and oxide traps. The observation of trap dynamics suggests that improvements in long-term device stability can be achieved by reducing oxide traps, whereas short-term stability can be improved by the reduction of interface traps.

An intense positron beam, for application in nanophase characterization, is now under construction at the 1 MW PULSTAR nuclear reactor at North Carolina State University (NCSU). A tungsten converter/moderator is used, allowing positrons to be emitted from the surface with energies of a few electron volts. These slow positrons will be extracted from the moderator and formed into a beam by electrostatic lenses and then injected into a solenoidal magnetic field for transport to one of three experimental stations, via a beam switch. To optimize the performance of the beam and to predict the slow-positron intensity, a series of simulations were performed. A specialized Monte-Carlo routine was integrated into the charged-particle transport calculations to allow accounting for the probabilities of positron re-emission and backscattering from multiple-bank moderator/converter configurations. The results indicate that either a two-bank or a four-bank tungsten moderator/converter system is preferred for the final beam design. The predicted slow-positron beam intensities range from nearly 7×108 to 9×108e+/s for the two-bank and the four-bank systems, respectively.

In the course of Rutherford’s effort to develop a plausible model of the atomic nucleus, he postulated the existence of a particle having the same mass as the hydrogen nucleus but having no electrical charge whatsoever. He conceived of this neutral particle—essentially a bound-state of a proton and an electron—in order to account for isotopes having identical atomic charges but different atomic weights (e.g. helium-3 and helium-4). Just a few years later, Rutherford’s hypothetical particle was discovered by one of his students.

Band gap modification for small-diameter (approximately 1 nm) silicon nanowires resulting from the use of different species for surface termination is investigated by density functional theory calculations. Because of quantum confinement, small-diameter wires exhibit a direct band gap that increases as the wire diameter narrows, irrespective of surface termination. This effect has been observed in previous experimental and theoretical studies for hydrogenated wires. For a fixed cross-section, the functional group used to saturate the silicon surface significantly modifies the band gap, resulting in relative energy shifts of up to an electronvolt. The band gap shifts are traced to details of the hybridization between the silicon valence band and the frontier orbitals of the terminating group, which is in competition with quantum confinement.

An extremely low-lying nuclear isomer in 229Th is still to be established in spite of efforts made since the first postulation of the isomer in 1976. To study such an extremely low-lying nuclear isomer, we have built an entirely new device that is based on the well-established atomic spectroscopic technique: Hollow-cathode discharge. The isomer in question is expected to be populated by the process NEET through atomic excited states if it exists in an energy range of electron volt. After switching off the discharge, we will measure alphas from the isomer, photons from the isomer itself and photons from atomic states to which the isomer is expected to decay by the inverse NEET. Our experiment is under way at Oarai using the world’s radiochemically purest 229Th sample.

We have measured the kinetic energy release distributions for unimolecular C 2 loss from singly and multiply charged endohedral La@C 80 z + and La@C 80 z + ions for charge states z = 1–3. Using finite heat bath theory, we deduce the dissociation energies for loss of C 2 . The charge state z has no statistically significant effect on the dissociation energies. The dissociation energies of endohedral fullerene ions are larger than those of the corresponding empty fullerene ions by a few tenths of an electron volt, but the differences are barely statistically significant. The small differences also imply that the complexation energies of La@C n z + and La@C n − 2 z + are identical within the experimental errors, for n = 80 and 82 and all charge states.

The plasma surface treatment and ion implantation were utilized to improve the stability of charge storage in the SiO 2 film electret. It was found that the SiO 2 films treated by argon plasma with the arcing at 700 V for 15 min, or implanted by 150 keV (kilo electron volt) Ar + with a dose of 2 × 10 11 cm −2 , after being negatively charged, showed a remnant negative potential as large as 90% of the primary value after being stored in a glass container with desiccant for 10 days. It was also found that after being negatively charged at room temperature and aged at 200–350 °C for several times, the SiO 2 films implanted by 150 keV Ar + had a relatively high remnant potential and it did not decay significantly even after being heated at the aging temperature of 200–350 °C in room atmosphere for 60 min.

The necessity of a three-dimensional simulation of the extraction has been accepted for electron cyclotron resonance ion sources (ECRIS) as well as for negative ion sources. For an ECRIS, the magnetic hexapole together with the solenoidal mirror field defines a minimum B structure which confines the plasma. Depending on the magnetic flux density distribution, the plasma density in front of the extraction electrode might be non-homogeneous. In H−-sources, magnetic filter fields are used to separate electrons with different energies or to separate electrons from negative ions. These magnetic filters influence the ions as well. Besides these asymmetry effects other quantities have to be considered, namely the correct formulation of initial conditions of all present charged particles. For ECRIS the initial conditions for ions are assumed to be in the electronvolt range, whereas it can be in the kilo electronvolt range for laser ion sources. Another quantity of interest is the electron energy and the distribut...

Collisional interactions represent a major source of decoherence for a gas of Rydberg atoms. We investigate the irreversible dephasing of coherently excited Rydberg wavepackets due to decoherence in collisions with ambient rare gas atoms. We show that the rate of decoherence provides a sensitive tool for measuring quasi-elastic electron-atom (or molecule) collisions at energies extending down to micro electron volts. We present proof of principle calculations for n ≃ 388 potassium Rydberg atoms in an ambient gas of xenon atoms.

In this, the hundredth year since Einstein first postulated the existence of photons, the successful application of wave - particle duality to matter has seen an explosion of activity in the field of atom optics and Bose - Einstein condensation (BEC). This article provides a brief introduction to atom optics, illustrated with applications taken from experiments using helium atoms in long-lived (metastable) excited states. Metastable helium atoms store the greatest amount of energy (∼20 electron volts) in any atomic or molecular system. They behave like nano-hand grenades, making it easy to detect single atoms, opening up promising applications as well as fundamental studies of the quantum statistical properties of atomic systems.

The Tera Electronvolt Superconducting Linear Accelerator (TESLA) is the only linear electron–positron collider project based on superconductor technology for particle acceleration. In the first stage with 500 GeV center-of-mass energy an accelerating field of 23.4 MV / m is needed in the superconducting niobium cavities which are operated at a temperature of 2 K and a quality factor Q0 of 1010. This performance has been reliably achieved in the cavities of the TESLA Test Facility (TTF) accelerator. The upgrade of TESLA to 800 GeV requires accelerating gradients of 35 MV / m . Using an improved cavity treatment by electrolytic polishing, it has been possible to raise the gradient to 35– 43 MV / m in single cell resonators. Here we report on the successful transfer of the electropolishing technique to multi-cell cavities. Presently 4 nine-cell cavities have achieved 35 MV / m at Q0⩾5×109, and a fifth cavity could be excited to 39 MV / m . In two high-power tests it could be verified that EP-cavities preserve their excellent performance after welding into the helium cryostat and assembly of the high-power coupler. One cavity has been operated for 1100 h at the TESLA-800 gradient of 35 MV / m and 57 h at 36 MV / m without loss in performance.

Extremely large ion-induced electron emission (IIEE) yields, γ, defined as the number of emitted electrons per incident projectile, were previously reported by us for impingement of sub-mega electron volt light (H) and heavy (N and Ar) ions onto hydrogenated, boron-doped diamond surfaces. γ was found to decrease rapidly with increasing ion dose, presumably because of ion-damage related modification of the emitting material. In this work, we compare γ for molecular impingement (H 2 + , N 2 + ) to that of the atom ion impingement (H + , N + ) with the individual species having the same velocity. It is found that (i) the maximal IIEE yields (extrapolated to 0 dose) per atom for molecular impingement is smaller by 15–20% than that measured for the corresponding single ions. Yet they are still extremely large. (ii) The decay rates of γ per atom for molecular impingement are faster than those measured for the corresponding single ions, yet they still saturate at very high γ values. The present results bear on the physics of ion–solid interactions and on the applicability of diamond for the detection and counting of single ion and molecule.

Direct measurements of the kinetic energy of Ne atoms adsorbed on activated carbon (AC) at submonolayer coverage, is reported. The electronvolt spectrometer of the ISIS neutron source that utilizes the neutron Compton scattering technique, was employed. The specific adsorption area of the AC was ∼3000 m2/g. The momentum distribution of adsorbed Neon was measured at 12 K. The kinetic energy of Ne was found to be 66.3±6.2 K, and is much higher than that of solid neon, at the same temperature, being 45.8±4.8 K. This result is considered to be an evidence for the occurrence of a confinement effect of Ne atoms within the pores of the AC. The result was also used for deducing the average pore size of the AC adsorber assumed to have slit shaped pores.

This chapter focuses on principles of physics that are needed for the study of the release of nuclear energy and its conversion into thermal and electrical form. A limited number of basic forces exist—gravitational, electrostatic, electromagnetic, and nuclear. Associated with each of these is the ability to do work. Thus energy in different forms may be stored, released, transformed, transferred, and “used” in both natural processes and man-made devices. It is often convenient to view nature in terms of only two basic entities—particles and energy. Even this distinction can be removed, because the matter can be converted into energy and vice versa. The addition of thermal energy to a substance causes an increase in temperature. Electromagnetic radiation arising from electrical devices, atoms, or nuclei may be considered to be composed of waves or of photons. Matter can be converted into energy and vice versa according to Einstein's formula. The energy of nuclear fission is millions of times as large as that from chemical reactions. Energy is fundamental to all human endeavors and survival.

A search for solar axions has been performed using an axion helioscope which is equipped with a 2.3m-long 4T superconducting magnet, PIN-photodiode X-ray detectors, and a telescope mount mechanism to track the sun. In addition, a gas container to hold dispersion-matching gas has been developed and a mass region up to m_a=0.27eV was newly explored. From the absence of any evidence, analysis sets a limit on axion-photon coupling constant to be $g_{a\gamma\gamma}, Comment: 12 pages, 6 PostScript figures, accepted for publication in Phys. Lett. B

Systematic studies of electron interaction with perfluorinated targets carried out recently in our laboratory revealed a distinct increase of the total cross section, Q tot , over the impact energy range from a dozen or so to several tens of electronvolts. A likely reason for this striking feature is a significant contribution of elastic processes in this energy range. The ratio of the total ionization electron-scattering cross section to the total cross section can be expressed with a simple regression formula. That formula was used to estimate the GeH 4 ionization cross section.

The effect of dose and energy on postannealing defect formation for high energy (mega-electron-volt) phosphorus implanted silicon has been studied using etch pit studies and transmission electron microscopy (TEM). Previous work has shown that after annealing there is a strong dependence of dislocation density threading to the surface on the implanted phosphorus dose and energy. A superlinear increase in threading dislocation density (TDD) with implant energy between 180 and 1500 keV is observed for a dose of 1×1014 cm−2. In addition as a function of ion fluence, there is a maximum in the threading dislocation density at a dose of 1×1014 cm−2 followed by a rapid decrease in TDD. Both the superlinear increase in TDD with increasing energy and the rapid decrease with increasing dose have been further investigated by TEM. A TEM study of these higher doses revealed formation of a strong bimodal loop distribution with small loops averaging

The perplexing problem of the extremely large activation energy for nucleation Uac∼106 eV, which, as was shown by Landauer, appears in the Merz thermal-fluctuational theory of ferroelectric switching, is examined. Such enormous values of Uac are a result of the combined contribution of the energy of the depolarization field and the surface energy of the nucleus. While the depolarizing field term can be reduced by a redistribution of free charges, the surface energy term alone is too large (greater than 104 eV) for thermal-fluctuation-aided nucleation to be possible. This conclusion contradicts the numerous observations of a rapid increase in the number of repolarization nuclei with temperature, which suggest that the actual activation energy is on the order of an electron volt. This article is devoted to the problem of how the surface energy of a nucleus can be compensated. It is assumed that repolarization nuclei form by a fluctuon mechanism, and it is shown how this assumption can help in resolving the ...

Recent decades have seen a revival of the interest in studies of the transport and localization of charge carriers in molecular solids, stimulated by several current and emerging applications of these materials. Of particular interest to the matter of this paper is the situation when a molecular system consisting of nonpolar molecules is doped with polar guest species. In this case, permanent dipole moment of the dopant molecules modifies locally the polarization energy, the changes resulting in the appearance of local states in the vicinity of the dopant. Earlier calculations of the author demonstrated that the presence of dipoles in non-polar molecular lattices may result in creation of traps as deep as several tenths of an electronvolt. While the earlier papers considered the effect of isolated dipoles (thus reflecting the situation in nearly-perfect molecular crystals), this contribution will report on results of similar calculations performed on systems mimicking molecularly doped polymers and molecular glasses in which the concentration of dopants is so high that the dipoles cannot be treated as isolated.

Direct measurements of the kinetic energies of He atoms adsorbed on active carbon fibre (ACF), at submonolayer coverage, are reported. The electronvolt spectrometer (eVs) of the ISIS neutron source, that utilizes the neutron Compton scattering technique, was employed. The specific adsorption area of the ACF was 3000 m2 g-1. The momentum distribution of adsorbed helium was measured at 4.6 K and 10.2 K and the average kinetic energy Ks was found: 54.3±3.0 K. This value is 30% higher than that estimated by assuming slit-shaped pores of dimensions ~0.7 nm together with a nearly monolayer coverage on a graphitic type adsorber.

We have successfully produced single-atom W , HfC , and ZrC tips using the field-induced buildup technique. The cold field emission characteristics of these tips were studied with particular emphasis on the emission stability and the energy distribution of the emitted electrons. W tips were the least stable. Reaction with acetylene improved the emission stability for all these tips. We observed multiple peaks in the energy distributions of emitted electrons from single-atom HfC and ZrC tips. The separations between the peaks are in the order of half electron volt. Possible origin of the multiple peaks is discussed.

Operation of quadrupole mass filters in higher zones of stability is described with an emphasis on the potential for elemental mass spectrometry. The higher zones allow a resolution at half height of up to 9000 on atomic ions and make possible unit resolution on ions with kinetic energies up to several thousand electron volts. The theory of quadrupole operation is briefly reviewed. Operation of quadrupoles in the third stability region with Mathieu parameters (a,q)≈(3,3) and the second stability region with (a,q)≈(0.02, 7.55) is described in detail. Previously unpublished data showing the variation of resolution with ion energy are presented. The variation of transmission with resolution is compared with previous calculations and with new calculations presented here.

The charge-transfer rate coefficient for the reaction ${\mathrm{Si}}^{4+}+\mathrm{H}\stackrel{\ensuremath{\rightarrow}}{e}\mathrm{products}$ was measured at an equivalent temperature of $4.6\ifmmode\times\else\texttimes\fi{}{10}^{3} \mathrm{K}$ using a laser-induced plasma ion source and ion storage. The rate coefficient is $4.54(0.48)\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}12} {\mathrm{cm}}^{3}{\mathrm{}\mathrm{s}}^{\mathrm{\ensuremath{-}}1}$ and is at least an order of magnitude smaller than the available theoretical values.

The time-dependent local-density approximation (TDLDA) is applied to the optical response of conjugated carbon molecules in the energy range of 0--30 eV, with calculations given for carbon chains, polyenes, retinal, benzene, and C{sub 60}. The major feature of the spectra, the collective {pi}-{pi}{sup *} transition, is seen at energies ranging from below 2 to 7 eV and is reproduced by the theory to a few tenths of an electron volt with a good account of systematic trends. However, there is some indication that TDLDA predicts too much fragmentation of the strength function in large molecules. Transition strengths are reproduced with a typical accuracy of 20%. The theory also predicts a broad absorption peak in the range of 15--25 eV, and this feature agrees with experiment in the one case where quantitative data is available (benzene).

We found that anthraquinone diffuses along a straight line across a flat, highly symmetric Cu(111) surface. It can also reversibly attach one or two CO 2 molecules as “cargo” and act as a “molecule carrier,” thereby transforming the diffusive behavior of the CO 2 molecules from isotropic to linear. Density functional theory calculations indicated a substrate-mediated attraction of ∼0.12 electron volt (eV). Scanning tunneling microscopy revealed individual steps of the molecular complex on its diffusion pathway, with increases of ∼0.03 and ∼0.02 eV in the diffusion barrier upon attachment of the first and second CO 2 molecule, respectively.

The kinetic model for electron-capture detection (ECD) has recently been expanded to include excited states. Multiple electron affinities for C6F6, anthracene and tetracene have been reported in the literature. The temperature dependence of the ECD response is calculated using these values and the expanded two state model. Activation energies and pre-exponential terms for kinetic rate constants are determined. The pre-exponential terms for thermal electron attachment are compared with the maximum value calculated from the DeBroglie wavelength of the electron and the probability for stabilization. Temperature data from different methods of electron collection are compared. A general procedure for the determination of electron affinities from ECD data is presented. The following ECD electron affinities are reported: C6Cl6, 1.17±0.02 and 0.71±0.02; C6F5Cl, 0.96±0.03 and 0.82±0.02; C6F5NO2, 1.52±0.02; C6H5NO2, 1.00±0.01 and m-hydroxyacetophenone, 0.74±0.02 (all values in electron volts, eV).

Quantitative measurements of line parameters in the spectrum of η Carinae are presented for both the broad and narrow line components. A total of 655 spectral features were measured in the spectral range 3850 A to 11000 A, giving a comprehensive view of the behavior of atomic transitions ranging from a few to tens of electron volts. The spectrum on the phase of maximum intensity in the high excitation lines (1995) is compared with that on minimum intensity (June 1992), showing that at this phase the high excitation lines disappear but the broad components of low excitation lines strengthens. We reject a number of previous line identifications and propose several new ones, including FeII, [FeII], [FeIII], [NII], and the near-infrared CaII triplet. Some lines commonly used to diagnose density, temperature, chemical composition, and reddening were found to be blended, urging a revision of the results based on previous data. The existence of double-peaked lines, suggested in previous papers, is ruled out. In the case of hydrogen lines, the apparent double-peaks are shown to be real absorption components. The velocity field in the inner 2" around the central star shows additional components previously unknown. The phases of high and low excitation in η Carinae are discussed in light of a recently proposed binary system. We suggest a temperature T ~ 16000 K for the primary star, what indicates that it is close to the beginning of the core helium-burning evolutionary stage.

One of the still uncertain and debated questions about Jupiter is the origin of its excess heat. Understanding the source of such heat will certainly shed some light on the physics of the interior of the planet and on scenarios of its formation. Recent measurements of sound velocities in Jupiter show substantial disagreement with the existing models for the Jovian interior. Analysis of these measurements suggests that helium (He) sedimentation (through H-He phase separation) is plausible in the planet's interior, contrary to what is believed from numerical calculations of H-He mixture at conditions prevailing in Jupiter's deep interior. This signals the need for a revision of the existing models of Jupiter and allows for new models to be explored. While He sedimentation might help shift the calculated sound velocities toward the observed ones, we find that it cannot explain the excess heat. Here, we analyze the consequences of deuterium (D) sedimentation on Jupiter's excess heat and discuss its effects on the sound profiles. Such a sedimentation is assumed to have occurred in the early stages of planet formation (here the core-instability model) through planetesimal vaporization in the deeper parts of the envelope. Our interest in investigating D sedimentation resulted from the recent extrapolations of D-D, D-T, D-3He, and p-D fusion to electron volt temperatures, which indicate that D-D fusion largely dominates the other reactions under conditions thought to prevail in the interior of early Jupiter. We find that with a modest degree of interior stratification of D (5%-15% of the total D of the planet), D-D burning naturally explains the excess heat given off by the planet. For our model to operate, we find that D sedimentation must occur during the early stages of planet formation (core-instability scenario) when interior temperatures of 16-18 eV where available. Our model is applied to the family of the Jovian planets as a whole.

The charge-transfer reactions of ground state Ti4+ (3p(6), S-1) with Ar and N-2 were studied in a quadrupole r.f. ion trap at the mean collision energy of 4.55 eV. The rate coefficients were measured to be 1.06(0.14) x 10(-9) cm(3)/s for Ti4+ with Ar at an equilibrium temperature of 1.6 x 10(4) K and 7.45(0.38) x 10(-10) cm(3)/s for Ti4+ with N-2 at an equilibrium temperature of 1.3 x 10(4) K. Both results are comparable with the Langevin rate coefficients. (C) 1998 Elsevier Science B.V. All rights reserved.

This manuscript reports electrochemical and angle-resolved X-ray photoelectron spectroscopy measurements of surface-bound porphyrazine monolayers in which the molecule-surface distance and molecular orientation of the porphyrazine are controlled through the design of the adsorbates. This system has allowed us to probe the importance of molecule-surface interaction in determining the shift in reduction potential upon binding to a gold surface. This quantity currently is in theoretical dispute, with one computation indicating that a porphyrazine/porphyrin exhibits an extremely large covalent binding energy ( approximately 10 eV) to a gold surface, whereas a more recent one finds the binding energy to be only a fraction of an electronvolt. Our study indicates that the shift in reduction potential upon surface binding is not a discontinuous function of the molecule-surface distance, as would be the case if covalent interaction of the porphyrazine core with the gold surface were controlling, but rather varies smoothly. This, therefore, rules out the possibility that the large potential shift seen for a porphyrazine whose macrocyclic core lies approximately 3.9 A above the gold surface, relative to one that lies approximately 8.9 A above the surface, DeltaDeltaE = 340 mV, is caused by direct covalent binding of the pi-system to the metal surface.

Using a time-resolved, mass analyzed, pulsed field ionization technique it is shown that molecules excited to energies within several electron volts above their lowest ionization thresholds can survive for several microseconds. These observations are consistent with the recent observations of efficient dissociative electron attachment to molecules excited to energies above their ionization thresholds.

The possibilities of obtaining information about interband scattering processes from electron energy-loss spectra, taken in a VG601UX scanning transmission microscope, are investigated. With the help of precise simulations of the zero-loss peak it is feasible to process, extract and analyse data in the electron volt regime. The accuracy of the results is restricted predominantly by instrumental limitations. It is possible to extract band gaps of > 2 eV (e.g. for GaN) correctly. In the case of band gaps between 1 and 2eV (i.e. in GaAs), the uncertainty is larger, since the tail of the zero-loss peak interferes with the interband losses, and further refinements in the data analysis as well as the measurement techniques are discussed. ‘Band-gap mapping’ in the VG601UX can be carried out with a spatial resolution of a few nanometres.

The charge-transfer rate coefficient for the reaction Si(3+)(3s(sup 2)S) + He yields products is measured by means of a combined technique of laser ablation and ion storage. A cylindrical radio-frequency ion trap was used to store Si(3+) ions produced by laser ablation of solid silicon targets. The rate coefficient of the reaction was derived from the decay rate of the ion signal. The measured rate coefficient is 6.27(exp +0.68)(sub -0.52) x 10(exp -10)cu cm/s at T(sub equiv) = 3.9 x 10(exp 3)K. This value is about 30% higher than the Landau-Zener calculation of Butler and Dalgarno and is larger by about a factor of 3 than the recent full quantal calculation of Honvault et al.

Molecular dynamics simulations were performed of the energy dissipation of incident atoms after impact onto a 3D FCC lattice with energies in the range 2 - 3 keV. The interactions between atoms were described using the Lennard-Jones potential parameterized for copper. The impacting directions were and . The results for low energies, of a few electron volts, show that the energy of the impacting atom was dissipated via focused collision sequences (focusons). With increasing energy, cascading bow waves were generated by the focusons, in the close-packed (111) planes only, and carried away the energy of the focusons while, in the high-energy range of a few kiloelectron volts, most of the energy was confined to the lower-index (100) or (110) planes. The structure of these planes was disrupted by secondary focusons generated in these planes, and sputtering occurred when these focusons reach the surface of the substrate. Backward focusons were observed in the low-energy impact case and appeared to be the main reason for the reflection of the impacting ion.

A component of neutral particles with hyper-thermal velocity has recently been observed in the flux from a new type of beam source for production of excited alkali atoms, the so called open diffusion source. The hyper-thermal component is probed with a time-of-flight technique and is found to consist of fast atoms with translational energies of several hundreds of electronvolts. They are formed in charge transfer reactions in the gas phase with cross sections of the order of 4000 - 8000 , which shows that highly electronically excited atoms are involved in the reaction.

This paper gives a brief outline of the theory and practice of kinetic energy measurements made on the electronvolt spectrometer at the ISIS spallation neutron source. The usefulness of the technique is illustrated by measurements made on as a function of temperature and density, on mixtures as a function of concentration and on liquid neon. Future developments and applications are discussed.

Occupied and unoccupied electronic distributions of quasicrystalline have been studied mainly using soft-x-ray emission and absorption spectroscopy measurements. The partial distributions are adjusted in the binding energy scale in order to gain insight into the electronic interactions in this material. Interaction between Al states and Ru 4d states near the Fermi level and between Al and Cu 3d states in the middle of the occupied band is shown. At the Fermi level a significant pseudo-gap is observed in the Al 3p and 3s - d distributions. In the unoccupied band, the Ru and Cu d - s-like states are in interaction with the Al p states. The Ru and Cu states retain a slight d-like character at the energies of the conduction edges that suggests faint charge transfer to Ru atoms. Far from the Fermi level, the Ru and Cu states are strongly hybridized to s states. Adjustment of Al 3p and Al p distributions at the same intensity at the Fermi level points to a significant low intensity of the density of Al p conduction states over a few electronvolts from the Fermi level.

This paper reports measurements of absolute differential cross sections for the direct scattering of oxygen atoms by He, Ne, Ar, Kr, Xe, ${\mathrm{H}}_{2}$, ${\mathrm{N}}_{2}$, ${\mathrm{O}}_{2}$, CO, ${\mathrm{CO}}_{2}$, ${\mathrm{H}}_{2}$O, ${\mathrm{SO}}_{2}$, ${\mathrm{NH}}_{3}$, ${\mathrm{CH}}_{4}$, ${\mathrm{CF}}_{4}$, and ${\mathrm{SF}}_{6}$ targets. The measured cross sections include contributions from all elastic and inelastic processes that result in a fast neutral oxygen atom product. Cross sections are presented for 0.5- and 1.5-keV projectile energies over the laboratory angular range 0.2\ifmmode^\circ\else\textdegree\fi{}--5\ifmmode^\circ\else\textdegree\fi{}. When compared in the center-of-mass reference frame, these cross sections exhibit a high degree of similarity in both amplitude and angular dependence. The cross sections for ${\mathrm{N}}_{2}$, CO, ${\mathrm{CO}}_{2}$, and ${\mathrm{H}}_{2}$O are inverted using a partial-wave analysis to yield empirical interaction potentials, which can then be used to extrapolate the measurements down to lower energies. Using these potentials, cross sections are evaluated at 0.1 keV. \textcopyright{} 1996 The American Physical Society.