Intra- and inter-atomic auger processes in collisions of low energy He++, He+, He* (23,S, 21 S) and Li+ with Li covered W(110) surfaces

Electron spectra from He⁺⁺, He⁺ and Li⁺ (10 to 1500 eV) ions colliding under grazing incidence with Li covered W (110) surfaces are reported. The results are compared with those obtained from thermal collisions of (2³ S; 2¹ S) metastable He atoms. In these collisions 1s vacancies are either produced during the collision event (energetic He⁺ (Li ⁺) collisions) or are brought into the collision (slow He⁺⁺ (He⁺, He*) collisions). Population of the 2s orbitals by two electrons produces states which decay by intraatomic Auger processes: we observe autoionization of He** (2s ²) and Li** (1s 2s ²) as well as autodetachment of He^?* (1s 2s ²). Alternatively the 1s-holes in the projectile or target (Li) can be filled by Auger processes involving one or two surface electrons. The processes leading to electron emission are studied as a function of the Li coverage in the submonolayer region (0≦Θ_Li≦1Ml) and as a function of the projectile energy. It is concluded that with one or two 1s vacancies present in the projectile the double capture of two surface electrons constitutes an important process responsible for electron emission of low work function surfaces.     

Towards a miniaturized non-radioactive electron emitter with proximity focusing

Most state of the art gas sensor systems based on atmospheric pressure ionization, such ion mobility spectrometers use radioactive beta-sources (e.g. ³H or ⁶³Ni) to provide free electrons with high kinetic energy to initiate a chemical gas phase ionization of the analytes to be detected. Here, we introduce a non-radioactive electron emitter which generates free electrons at atmospheric pressure. Therefore, electrons are generated in a vacuum by field emission and accelerated towards a 300 nm thin 1 mm² silicon nitride membrane separating the vacuum from atmospheric pressure. Electron currents of about a few hundred microamps can be reached. High energetic electrons of about 10 keV can easily penetrate the membrane without significant loss of kinetic energy. The concept of proximity focusing avoids complex electron lenses to focus the electron beam onto the membrane. The used field emitter tips are made of multi-walled carbon nanotubes. Another benefit of our system is that no insulated power supply operating at high voltage is needed, as necessary for thermo emitters. Here, we show a first prototype of a proximity focused electron gun with field emitting carbon nanotubes. The system is coupled to our drift tube ion mobility spectrometer for validation. Ion mobility spectra similar to those of a ³H ionization source were achieved.     

Electrophysical properties of poly(<Emphasis Type="Italic">N</Emphasis>-vinylcarbazole)-carbon nanotubes composite films

The specific features of charge carrier transport in poly(N-vinylcarbazole) films doped with single-wall carbon nanotubes have been investigated. The mobilities of electrons and holes in ITO-polymer composite-Al samples have been determined by the time-of-flight method and by measuring the voltage-current characteristics of steady-state currents. According to the time-of-flight experiments, in the films of a poly(N-vinylcarbazole)-0.26 wt % single-wall carbon nanotubes composite, the drift mobility of electrons lies within (1.2–4.5) × 10^?6 cm²/(V s) and exceeds the mobility of holes by a factor of 5. The shape of the transient current suggests the dispersion character of transport of electrons and holes. With an increase in the concentration of single-wall nanotubes from 0.26 to 0.43 wt %, the conductivity of the composite films increases by two orders of magnitude; that is, the threshold of conductivity percolation has been achieved. A simple model is proposed to describe the transport of charge carriers in the polymer system under study.     

Visualization of electron correlation in a series of helium S states

Electron correlation has been studied for a series of helium S states represented by a variety of wavefunctions, the best of which are accurate Hylleraas—Kinoshita functions. The states studied are the ground state, the lowest excited ¹S and ³S states, and the (2s)² and (2p)² doubly-excited ¹S states. Primary data is obtained from graphs of the conditional probability density as a function of the radial distance r₂ and the interelectronic angle θ₁₂, given that r₁ is fixed at various distances. Such graphs make clear the extent to which characteristics such as angular and radial correlations, and Fermi and Coulomb holes, are consequences of the relative motion of electrons in two-electron atoms.     

Electrochemical Generation of Hot Electrons in Fully Aqueous Solutions at Tetrahedral Amorphous Carbon Thin Film Electrodes and Electrochemiluminescence Immunoassay of Serum Amyloid A

Electrochemistry of hot electrons in fully aqueous solutions at tetrahedral amorphous carbon thin film electrodes is discussed. The generation of these highly reducing chemical species was confirmed by normal pulse voltammetry and several electrochemiluminescent systems. Electron transfer into pre-existing solvent cavities was observed at approximately −2.65 V vs. Ag/AgCl (sat.). Electrogenerated hot electrons were utilized as chemiluminescent mediators in heterogeneous sandwich immunoassay of Serum Amyloid A. The calibration curve was linear over four orders of magnitude and the detection limit was 85 ng L⁻¹ that demonstrates the efficiency of hot electron generation at this electrode material.     

Size effects in the conduction electron spin resonance of anthracite and higher anthraxolite

Electron paramagnetic resonance spectroscopy of conduction electrons, i.e. Conduction Electron Spin Resonance (CESR), is a powerful tool for studies of carbon samples. Conductive samples cause additional effects in CESR spectra that influence the shape and intensity of the signals. In cases where conduction electrons play a dominant role, whilst the influence of localized paramagnetic centres is small or negligible, the effects because of the spins on conduction electrons will dominate the spectra. It has been shown that for some ratios of the bulk sample sizes (d) to the skin depth (δ), which depend on the electrical conductivity, additional size effects become visible in the line asymmetry parameter A/|B|, which is the ratio of the maximum to the absolute, minimum value of the resonance signal. To study these effects the electrical direct current–conductivity and CESR measurements are carried out for two amorphous bulk coal samples of anthracite and a higher anthraxolite. The observed effects are described and discussed in terms of the Dyson theory. Copyright © 2015 John Wiley & Sons, Ltd.     

Localized moments in the superconducting Li1+xTi2−xO4 spinel system

Electron spin resonance (ESR) and magnetic-susceptibility measurements on the Li_1+xTi_2?xO₄ spinel system ($\text{0 ≤ x ≤}\text{1}\text{3}$) indicate the presence of two types of localized moments in this material. In both cases, an unpaired electron is trapped as a Ti³⁺ ion in a crystal field that is predominantly octahedral, but with a strong tetragonal component. This type of crystal field cannot arise in the stoichiometric spinel. We propose two types of defect in the title spinel system: an oxygen vacancy and a hydroxyl ion. Unpaired electrons are trapped as Ti³⁺ ions adjacent to these defects, and it is argued that the strong tetragonal field is associated with the formation of a static (TiO)⁺ ion by a displacement of the titanium ion from the defect. Spin relaxation occurs via a thermal ionization of the trapped electron that appears to be associated with a static-dynamic transition in the titanium-ion displacement.     

First-Principles Calculations of Magnetism in Nanoscale Carbon Materials Confining Metal with <Emphasis Type="Italic">f</Emphasis> Valence Electrons

The f electrons in the unfilled shell of actinide and lanthanide display complex bonding behavior and the hybridized sp electrons in carbon could show spin polarization in finite nanostructures. Correspondingly, materials combining these two features exhibit abundant magnetic properties. In this paper, we outline our first-principles calculations on various nanoscale carbon materials confining U and Gd which are representative actinide and lanthanide, respectively. The complex interaction between f electrons and sp electrons make the induced magnetic property sensitive to metal specie and carbon confinement. Specially, (1) The magnetism could be suppressed by stronger adsorption with vacancy sites on graphene and adjusted by varying the valence state of some endohedral metallofullerenes (EMFs). (2) The magnetic coupling between metal and carbon structures could be promoted by large curvature when confinement site is carbon nanotubes and altered by the adatom defect on fullerene cages. (3) Untrivial magnetic property with large net spin and asymmetric spin distribution is obtained by confining U atom and Gd atom in one fullerene as a heteronuclear EMF. These results contribute to a systematic understanding of the magnetism in nanoscale carbon materials confining metal with f valence electrons.     

Gas phase 1,3-deoxystannylation reactions of γ-substituted organotin alcohols utilizing chemical ionization mass spectrometry

The gas phase 1,3-deoxystannylation reactions of γ-substituted organotin alcohols have been studied by methane and isobutane chemical ionization mass spectrometry. It was found that γ-hydroxybutyltributyltin and γ-hydroxybutyldibutyltin chloride undergo the 1,3-deoxystannylation reaction to a greater extent than the corresponding 1,4-deoxystannylation using the δ-substituted analogues of the above named compounds. This result substantiates the unusual reactivity of γ-substituted organotin alcohols under gas phase protonolysis conditions.The electronic factors affecting the stabilization of the transition state were ascertained with γ-phenyl-γ-hydroxypropyltrimethyltin derivatives, in which the γ-phenyl group was substituted with groups such as H, p-OMe, p-Me, p-Cl, p-F, m-OMe, m-Me, m-Cl and m-CF₃. We observed a reasonably linear Hammett relationship when plotting the log [P ? 17]_x⁺/[P ? 17]_H⁺ vs. σ⁺ with rho (ρ) equal to ?1.0.Thus electron-donating groups stabilize the [P ? 17]⁺ ion and carbon—tin sigma (σ) electrons can either, by a neighbouring group effect, attack the nucleofugic center, or the carbonium ion can attack the carbon—tin σ electrons to form the trimethyltin cation and a cyclopropane derivative. Consequently, we propose that a two-step mechanism for the 1,3-deoxystannylation reaction is operating in the gas-phase with this type of compound. The factors contributing to this gas phase reaction will be discussed.     

Trans-membrane electron transfer in red blood cells immobilized in a chitosan film on a glassy carbon electrode

We have studied the trans-membrane electron transfer in human red blood cells (RBCs) immobilized in a chitosan film on a glassy carbon electrode (GCE). Electron transfer results from the presence of hemoglobin (Hb) in the RBCs. The electron transfer rate (k _s) of Hb in RBCs is 0.42 s^?1, and <1.13 s^?1 for Hb directly immobilized in the chitosan film. Only Hb molecules in RBCs that are closest to the plasma membrane and the surface of the electrode can undergo electron transfer to the electrode. The immobilized RBCs displayed sensitive electrocatalytic response to oxygen and hydrogen peroxide. It is believed that this cellular biosensor is of potential significance in studies on the physiological status of RBCs based on observing their electron transfer on the modified electrode.

Theoretical and empirical calculations of the carbon chemical shift in terms of the electronic distribution in molecules

The principles of the theoretical calculations of the carbon atom screening constant are reviewed. The Independent Electron, SCF? MO and Valence Bond formulae are briefly discussed, and the relative importance of the different terms involved in an approximate decomposition of σ¹³C are pointed out. The variations of the excitation energy ΔE, the mean distance between the nucleus and 2p electrons, and the electronic charges and bond orders with the structure are presented. The nature of the steric effect is also explained. In a second part the various empirical correlations which make an evaluation of δ¹³C from structural and physical properties possible are shown. The actual substituent parameters of the main classes of compounds are listed and worked examples given to make the use of the tables easier. The correlations between δ¹³C and the electronic charge, electronegativity, Hammett-Taft constants, electric field effects, geometrical parameters, spectroscopic data (electronic transitions, screening of other nuclei) and pH are also discussed with a view to appraising the carbon screening.     

Near-IR photorefractive composites based on oxidized single-wall carbon nanotubes

The photoelectric, nonlinear optical, and photorefractive characteristics of polymer composites made from unplasticized polyvinylcarbazole (PVK) and single-wall carbon nanotubes containing surface oxygen groups (at C:O ratio of 77.8:22.2%) were analyzed. The dependences of the quantum efficiency of charge-carrier generation on the applied electric field E measured at 1064 and 1550 nm coincide and are approximated by the Onsager equation expanded to the E ⁴ term, at π₀ = 0.012 and r ₀ = 9.8 Å. The third-order optical nonlinearity determined by the EFISH technique at a nanotube content of 0.26 wt % is 2 × 10⁵ pm²/V² or 2.3 × 10^?29 C⁴ m/J³ in SI units. The pattern of photorefractive kinetic curves indicates that the mean free path of holes is longer than the mean range of electrons. The photorefractive net gain coefficient of the signal beam measured at 1064 nm in a field of E = 170 V/μm is Γ ? α = 55 cm^?1 (α = 10 cm^?1 is the optical absorption coefficient at 1064 nm). At 1550 nm, the net gain coefficient measured in a field of E = 265 V/μm is Γ ? α = 55.7 cm^?1 (α = 3.3 cm^?1 at 1550 nm). In the presence of oxygen groups, there is no transfer of electrons photogenerated in carbon nanotubes to the external acceptor C⁶⁰. This effect can be associated with an increase in the ionization potential of nanotubes by almost 0.8 eV as a result of oxidation.     

Novel diapocarotenoid dications with VIS/NIR absorption

Isoprenoid acyclic polyene carbodications with 6, 14 and 18 π electrons have been synthesized and characterized in comparison with previously prepared dicyclic C₄₀-carotenoid dications. An equation correlating λ_max (400-1100 nm region) and the number of sp² hybridized carbon atoms in the dication is presented.     

Radioluminescence of methylcyclohexane in the glassy state

The radioluminescence of pure, frozen methylcyclohexane (MCH) has been investigated. λ-Irradiation of MCH at 77 K produces at least three negative species—trapped electrons, e^-_t, and two types of anions, which are formed in the reactions of electrons with radicals, R^-, and with stable radiolysis products, P^-. It is shown that the radiothermoluminescence (RTL) emission is due to the recombination of e_t-(RTL peak at 90 K) and R^-, P^- (RTL peak at 95 K) with cations. The intensity-dose dependence of the RTL peaks has been interpreted using a simple kinetic model.     

The role of photoejected electrons in the delayed fluorescence of indole derivatives in frozen aqueous solutions at 77°K

A delayed fluorescence emission of biphotonic nature with the triplet state intermediary is observed from indole ring in low temperature water glasses or in polycrystalline ices. Electron scavengers like Cd²⁺ ions are shown to quench the D.F. emission. A mechanism involving “mobile” electrons or electrons in different solvation states is discussed.     

Temperature effects on positronium formation and inhibition: a contribution to the elucidation of early spur processes. I. Glycerol/water mixtures

In order to elucidate the mechanism of positronium (Ps) formation in liquids, the effect of temperature, T, on the inhibiting properties of various solutes has been investigated in glycerol/water mixtures. Whereas the inhibition constants of Cl^? and I^? are found to increase markedly with T, that of CH₃NO₂ is T insensitive and that of NO₃^? diminishes with T. These findings are consistent with our previous model, according to which Ps would be formed via two pathways, either through the quasi-free entities or by the reaction of localized, not yet fully solvated, electrons and positrons. The increase with T of the Ps yield is found to be due to the fraction arising from the latter reaction. The results confirm Cl^? and I^? react with e_loc⁺, while CH₃NO₂ and NO₃^? scavenge quasi-free electrons. Regarding the behaviour of the inhibition constants of these latter solutes, a provisional explanation is given: CH₃NO₂ would scavenge epithermal electrons while NO₃^? would react with electrons at a lower energy state, in competition with the localization process. Hot Ps atoms are not likely to be involved.     

Angle and spin resolved Auger and photoelectron spectroscopy on Rb-layers by means of circularly polarized VUV radiation

Normal incidence circularly polarized VUV radiation with energies around 23 eV creates spin polarized photoelectrons from thick layers of Rb on Pt(111) and thus excites oriented 4p hole states. The preferential spin direction of the Auger electrons and its dependence upon the emission angle has been measured and is compared with the corresponding angular dependence of the primary photoelectron spin polarization also measured. Since the CVV Auger decay relates to as ² pair of valence electrons, the cross comparison of results for photoelectrons and Auger electrons studies the questions on whether photoemission and Auger decay occur in sequence, assuming an independent two step model, and whether the valences-electrons couple to a singlet state configuration.     

The rotational spectrum and heavy-atom-planar structure of propargyl benzene (3-phenyl-1-propyne)

The microwave rotational spectrum of propargyl benzene has been studied and its stable conformation has coplanar carbon atoms. This planar structure is confirmed independently by the value of its P_cc second moment consistent with only a pair of H atoms out of the plane, by its rotational spectrum obeying a- and b-type and not c-type selection rules, by its display of spectra of nine rather than six distinguishable monosubstituted ¹³C isotopomers, by the absence of tunneling splittings, and by the insensitivity of P_cc to ¹³C isotopic substitution. This conformation is also observed in its isoelectronic analogue, benzyl cyanide. The structure is stabilized by an effective hydrogen bond between an ortho C-H and the π electrons of the triple bond.     

Doubly excited1 P 0 resonances in He

Doubly excited¹ P ⁰ autoionizating states in He below then=2 threshold of He⁺ ions are calculated by use of a method of complex-coordinate rotation. Hylleraas type wave functions are used to calculate resonance parameters for intrashell states (the two electrons occupy the same shell), and products of Slater-orbitals are used for intershell states (the two electrons occupy different shells). A total of 15 resonances below then=2 He⁺ thresholds are reported in this work. This includes six members in the 2snp ₊ (2≦n≦7) series, five members in the 2snp _? (3≦n≦7) series, and four members in the 2pnd (3≦n≦6) series. Comparisons are made with other theoretical calculations and with experimental observations.     

Reactivity of plasma-treated SiO2 against O2: An EPR study

During plasma treated of SiO₂ (dehydrated at 700°C in high vacuum) electrons become trapped at the surface and in the bulk. The captured electrons from the well known E_í centre, an F-like electron centre with the unpaired electron mainly in an s-type orbital, and CO₂^? which comes from carbon impurities. Adsorption of O₂ (partial pressure 5 × 10^-3 torr ? po₂ ? 10 ^?1 torr) gives O₂^? species that depend on the adsorption temperature, characterized by the following g-values: g₁ = 2.069, g₂ = 2.000m T_ads = 300 K; g₁ = 2.039, g₂ = 2.007, g₃ = 2.002, T_ads = 77 K.