Single Electron Emission Research Articles

Ionization of metallic clusters via multi-plasmon excitation

Theoretical study of the ionization of sodium clusters by an intense laser pulsewith a photon energy close to the surface plasmon resonance is presented. Theproposed model describes the resonance channel of cluster ionization viaexcitation of a multi-plasmon collective electron state that can subsequently decaythrough a single electron emission. The method of separation of the centreof mass coordinate from other electronic degrees of freedom has beenemployed to take into account the highly excited electronic states. Theautoionization decay rate of the multi-plasmon excited state together with theenergy and angular distributions of outgoing electrons has been obtained.

Molecular Photonics and Electronics

Molecular Photonics and Electronics

Two-center continuum approximation with correct boundary conditions for single-electron emission ine−+H2collisions

A two-center continuum approximation with correct boundary conditions in the entrance and exit channels is introduced to study the $(e,2e)$ reaction for ${\mathrm{H}}_{2}$ targets. The case of impact of fast projectiles for highly asymmetric coplanar geometries is investigated. The influence of the description of the ejected electron on triple differential cross sections is analyzed. Particular attention is paid to the relevance of the screening of the nuclei of the target produced by the nonejected electron. The model, which implies relatively small computational effort, gives a good representation of absolute experimental data.

Excitation spectra of free fullerene clusters

In this work we study the single electron emission from fullerene clusters upon the impact of low-energy electrons. The calculations of the quantum ground states of the fullerene are performed within the Hartree–Fock and the jellium shell model. The interaction between the incoming projectile and knocked out electrons is described on the basis of random phase approximation with exchange, which leads to the concept of screening of the inter-electronic interaction. We compare the results of the calculations with available experimental data for the ionization of C 60 by electron impact and show that neglect of polarization leads to results at variance with experimental finding.

Electron Emission Induced by Collisional Ionization of Ne by p, p- and Alpha Particles

The single electron emission from helium and lithium target atoms have been extensively studied by Sahoo et al. [Phys. Rev. A62, 022716 (2000)]. In the present work, we calculate the single ionization of Ne in encounter with protons, anti-protons, and alpha particles using the method same as Sahoo et al. We find out the total and differenti al ionization cross sections covering wide range of impact energy. The dependence of the cross sectional values on the projectile charges (-1, +1, +2) is analyzed. The present results are found to be encouraging when compared with existing experimental as well as theoretical findings.

Performance characterization of twisted undulator

A special two-period insertion device is considered in terms of useful properties of spontaneous emission. General idea of the geometry can be interpreted as helical transformation applied to an original linear undulator structure to provide superimposed fast and slow transverse oscillations of the electron beam. Periodic sextupolar focusing effect of the device is calculated analytically. Three-dimensional hybrid magnetic design is treated numerically on the base of traditional and specially modified feasible structures. Main properties of the spontaneous emission of single electron were studied using a derived analytical form and numerical computations. The following features of the radiation are outlined: (i) reduction of relative content of higher odd harmonics as the “slow” imposed helical field increases; (ii) radiation enhancement as the number of helical turns increases; (iii) spectral line splitting and intensity adjustment; and (iv) opposite directions of circular polarization for adjacent spectral lines. In particular, unlike most insertion devices this structure does not require any magnetic readjustments or electromagnetic switching to provide opposite polarization. Potential technical advantages in application for single pass superradiant free electron lasers are also discussed.

Differential Net- and Multiple-Ionization Cross Sections in Fast Highly-Charged Ion Collisions with Atoms

We have calculated doubly differential cross sections (DDCS) for electron emission in 3.6 MeV/amu Au53+ collisions with neon and argon atoms in the continuum distorted wave with eikonal initial state approximation. DDCS for a given final charge state of the recoil ion are extracted from the differential ionization probabilities by use of a binomial analysis. Our results are in very good agreement with experimental data for net- and single-electron emission, when the calculations are based on the optimized potential method to describe the target atom. By contrast, artificial structures in the low-energy continuum are found if a Hartree–Fock–Slater model potential is used for argon targets.

Origin of structures in the low-energy single-electron continuum in calculations for ion collisions from argon

Doubly differential cross sections for inclusive single-electron emission in $3.6 {\mathrm{M}\mathrm{e}\mathrm{V}/\mathrm{a}\mathrm{m}\mathrm{u}\mathrm{}\mathrm{Au}}^{53+}+\mathrm{Ar}$ collisions are calculated in the continuum distorted wave with eikonal initial-state approximation. Previously observed structures in the low-energy continuum are traced back to a known deficiency of the Hartree-Fock-Slater target potential that has been used in the work [R. Moshammer et al., Phys. Rev. Lett. 83, 4721 (1999)]. The structures do not occur, if the argon atom is described in terms of the optimized potential method, in which the electronic exchange interaction is treated exactly.

Long-lived high-spin states of small anions:6Πstate ofCO−

Stimulated by recent mass spectrometric observations, we have investigated several high-spin states of ${\mathrm{CO}}^{\mathrm{\ensuremath{-}}}$ to identify the observed anionic state. We follow a general construction principle for long-lived anionic states of small molecules: A possibly long-lived anionic state possesses several ``equivalent'' valence electrons bound to a positively charged ion core. Applying this idea to ${\mathrm{CO}}^{\mathrm{\ensuremath{-}}},$ we have found a ${}^{6}\ensuremath{\Pi}$ state which is stable with respect to both single-electron emission and dissociation. Since all different decay channels are spin forbidden, this state is long-lived, and will be observable in a mass spectrometer.

Two- and three-body effects in single ionization of Li by 95-MeV/uAr18+projectiles: Analogies with photoionization

Cross sections for single electron emission have been measured in collisions of 95-MeV/u ${\mathrm{Ar}}^{18+}$ projectiles with atomic Li for electron energies ranging from 3 to 1000 eV and angles ranging from $25\ifmmode^\circ\else\textdegree\fi{}$ to $155\ifmmode^\circ\else\textdegree\fi{}.$ Models based on the Born approximation are introduced to separate two- and three-body effects in the angular distributions of the ejected electrons. Both experiment and theory provide information about the separability of the two- and three-body effects. The high projectile velocity and the use of the Li target are shown to be essential for the present analysis. The emission of the $1s$ electron is attributed mainly to three-body effects. The cross section for three-body collisions rapidly decreases with the electronic energy transfer involving a power law with an exponent of $\ensuremath{-}3.5.$ Consequently, two-body effects dominate at high electron emission energies. Remarkably large contributions from two-body collisions were also observed for the low-energy emission of the $2s$ electrons. Demonstrating the analogy in ionization by photons and ions, the two- and three-body processes are associated with Compton scattering and photoabsorbtion, respectively.

Two- and Three-Body Effects in Single Ionization of Li by95MeV/uAr18+Ions: Analogies with Photoionization

Cross sections for single electron emission have been measured in collisions of $95\mathrm{MeV}/\mathrm{u}{\mathrm{Ar}}^{18+}$ with atomic Li for electron energies 5--1000 eV and angles 25\ifmmode^\circ\else\textdegree\fi{}--155\ifmmode^\circ\else\textdegree\fi{}. The high projectile velocity made possible the separation of two- and three-body processes in the angular distributions of the ejected electrons. Low-energy emission of the $2s$ electrons is found to be significantly influenced by two-body effects and, furthermore, the node in the Li $2s$ wave function manifests itself in the angular spectra. Emission of $1s$ electrons is attributed mainly to three-body effects. The two- and three-body processes are associated with Compton scattering and photoabsorption, respectively.

Measurement of multiple-electron emission in single field-emission events

Thermal and field electron emission from a modified electron microscope W source were measured with an energy-dispersive counting system. Thermal-emission spectra were consistent with random emission of single electrons, while field-emission spectra were consistent with multiple-electron emission in random events. As many as 11 electrons were detected in isolated random field-emission events.

High-field single electron emission rates and their influence on the Paschen characteristics in compressed gases

By means of a newly developed statistical avalanche counting technique which enables high-field, single electron emission rates (SEERS) to be measured from unsparked freshly prepared surfaces having various thicknesses of oxide film, it is established for the first time that SEERS increases, for a given electric field, with an increase in the bulk modulus (hardness) of the material cathodes; also remarkably the thicker the oxide layer, the higher the SEERS. These trends are reflected in the Paschen sparking characteristics which show that the gaseous electric strength decreases with increase in the bulk modulus and increase of oxide layer thickness of the cathode material; and thus the increase in SEERS. This former trend is opposite to that established more than forty years ago. Other hitherto unobserved phenomena like a gas pressure effect, switching from a low to a high electron emission mode and vice versa, the influence of deliberate sparking and the total absence of spark conditioning are reported. Analysis of SEERS by the more successful Richardson-Schottky rather than the Fowler-Nordheim equation shows that the low electric field intensification factors derived increase with the bulk modulus of the cathode material and ultimately are determined by the polishing procedure.

Single Atom Electron Emission from the Silicon Tip Coated by Calcium Fluoride with Samarium Dopant Ions

We present the first experimental results of the studying of field electron emission from sharp silicon tips covered by thin dielectric CaF 2 layers containing Sm dopant ions. Some indications on the resonant tunneling of electrons from sharp silicon tip through dopant samarium ions inside the coating have been observed, which can be regarded as an implementation of one-atom electron source of a new type, based on dielectric coating of emitting tip.

New trends in radiation imaging: CsI-based gaseous detectors

A new class of radiation imaging detectors is described. They combine thin solid converters and gaseous electron multipliers. CsI or CsI-coated films provide an efficient means for UV, X-ray and thermal neutron conversion. The latter is followed by the emission of single photoelectrons or multiple secondary electrons in the eV range. The surface conversion and the electron multiplication close to the radiation impact location guarantee an accurate localization, fast response and low occupancy, regardless of the angle of incidence. A low gas pressure permits the operation at very intense radiation flux, with a low sensitivity to ionizing background. The article briefly reviews the new technique and its potential applications.

On some factors affecting discharge conditions in micro-strip gas chambers

We describe the results of an investigation on the influence of geometricla parameters on the maximum gain that can be attained in a micro-strip gas chamber. Single electron emission from the cathode was confirmed to be a precursor of discharge, particularly for gas mixtures with a high fraction of quencher, confirming our previous observations. In contradiction however with the results of a theoretical model proposed in earlier work, we found that the maximum gain is obtained in a narrow range of cathode strip width. This suggests the presence of other mechanisms initiating a discharge, such as photon- or ion-initiated feedback. The influence of strongly ionising irradiation on discharge conditions has also been investigated; we have observed an increasing probability of discharge in detectors irradiated with α particles, releasing around 1 MeV in the gas, as compared to 6 keV X-rays. This results in a reduction by a factor of 2 of the maximum gain at which a MSGC can be safely operated, a concern for the use of micro-strip chambers in vertex detectors for colliders where low energy, heavily ionizing particles and thermal neutrons are produced together with minimum ionizing particles.

Ion-induced electron emission from solid surfaces: information content of the electron number statistics

Measured electron number statistics resulting from the impact of singly and multiply charged atomic, cluster and fullerene ions on atomically clean metal (polycrystalline gold) and insulator (lithium fluoride) surfaces depend in a characteristic manner on the given projectile-target combinations and projectile impact energies. Comparison with model statistics delivers, apart from the respective total electron yields, further information on the total numbers and single-electron emission probabilities of the complete electron ensemble taking part in the emission process. For potential emission induced by slow multicharged ions on gold, the present analysis provides new insights on hollow atom formation and decay in front of the surface, in excellent agreement with recently calculated hollow atom autoionization rates.

Emittance measurements at the ESRF

A new method of electron beam imaging is operating routinely at the ESRF. It uses the x-ray beam from an undulator. The white beam is monochromatized by a Si 400 Bragg reflection at 30 keV. The monochromatic beam is projected onto a fluorescent screen and imaged by a CCD camera. The emittance of the electron beam is deduced from the image size measured by the CCD camera and the independent knowledge of the beta function at the source point. This technique has measured emittances in the range of 0.2–20 nm rad with a precision of 20%. The principal limitation appears to be the single electron emission angular pattern which limits the minimum detectable emittance to 0.1 nm rad. This diagnostic has been routinely used for more than 1000 h. It is fully automated, resulting in a permanent display of the values of horizontal and vertical emittances without intervention by any operator.

Noise suppression in semiconductor p-i-n junctions: Transition from macroscopic squeezing to mesoscopic Coulomb blockade of electron emission processes.

We analyse noise suppression properties of a constant-current driven p-i-n heterojunction. It is shown that the junction capacitance and temperature determine the minimum measurement time required for obtaining sub-Poissonian electron injection. As the capacitance of the junction is reduced, the noise spectrum develops a «regulated single electron emission peak» at the single electron charging frequency, indicating regulation of the individual thermionic emission events and therefore a transition from macroscopic squeezing to Coulomb blockade regime

Search for an M0 transition in 170Yb.

We have examined the suggestion that an M0 transition occurs between the 2819.6-keV ${0}^{\mathrm{\ensuremath{-}}}$ level of $^{170}\mathrm{Yb}$ and the ${0}^{+}$ ground state by internal-conversion electron emission. Gamma rays, internal-conversion electrons, and internal ${\mathit{e}}^{+}$${\mathit{e}}^{\mathrm{\ensuremath{-}}}$ pairs were detected from the ${\mathrm{\ensuremath{\beta}}}^{+}$ and electron capture decay of two-day $^{170}\mathrm{Lu}$ (${0}^{+}$). At an upper limit of 2\ifmmode\times\else\texttimes\fi{}${10}^{\mathrm{\ensuremath{-}}8}$ electron per $^{170}\mathrm{Lu}$ decay, no evidence was obtained for M0 decay of the 2819.6-keV level of $^{170}\mathrm{Yb}$ by single-electron emission.