Selected Electron Energy Research Articles

Cross sections for electron scattering by methanol in the intermediate-energy range

We present an experimental study on electron scattering by methanol (CH${}_{3}$OH). More specifically, differential, integral, and momentum-transfer cross sections for elastic electron scattering in the 100- to 1000-eV energy range are reported. Experimentally, angular distributions of the energy-selected electrons are measured and converted to absolute cross sections using the relative-flow technique. Relative-flow rates measured using the method of pressure decrease are applied for this purpose. The influence of the adsorption-desorption of methanol vapor on the surfaces inside of the gas-handling manifold is also studied. The possibility of dimerization of methanol at low pressures is investigated and disregarded based on the experimental evidence and also on a molecular-dynamics-simulation study. Electron-methanol collision cross sections are also calculated using the independent-atom model at the static-exchange-polarization and static-exchange-polarization-absorption levels of approximation. The comparison of our measured results of cross sections with other experimental and theoretical data available in the literature and with the present calculated data is encouraging.

Advantages of Energy Selective Secondary Electron Detection in SEM

Extended abstract of a paper presented at Microscopy and Microanalysis 2010 in Portland, Oregon, USA, August 1 – August 5, 2010.

Ecological optimization of energy selective electron (ESE) heat engine

The ecological performance optimization of an energy selective electron (ESE) heat engine operated at maximum power regime and the intermediate regime (i.e. between maximum power operation and reversible operation) is carried out in this paper by using finite time thermodynamics. In the analyses, the analytical formulae for the entropy generation rate and the ecological function of the ESE heat engine are derived for the two operation regimes, respectively. The performance characteristic curves are obtained by numerical examples. The influence of the resonance widths on the ecological performance of the ESE heat engine at intermediate regime is discussed. The ecological performances are analyzed and compared with the power and efficiency characteristic. It is shown that, when the working point is changed from the maximum power point to the maximum ecological function point, the efficiency increases and the entropy generation rate decreases mostly with only a small power output drop. The results obtained herein have theoretical significance for the understanding of thermodynamic performance of the micro-nano devices.

Energy selective scanning electron microscopy to reduce the effect of contamination layers on scanning electron microscope dopant mapping

We demonstrate that energy selective scanning electron microscopy can lead to substantial dopant contrast and resolution improvements (compared to standard SEM) when the energy selection is carried out based on Monte Carlo modelled secondary electron spectra in combination with detector transfer modelling.

Spatially correlated erbium and Si nanocrystals in coimplanted SiO2 after a single high temperature anneal

We present a study of silicon (Si) and erbium (Er) coimplanted silica (SiO2) in which we observe, by combining high resolution scanning transmission electron microscopy and selective electron energy loss spectroscopy (EELS), a high spatial correlation between silicon nanocrystals (Si-NCs), Er, and oxygen (O) after a single high temperature (1100 °C) anneal. The observation of a spatial overlap of the EELS chemical maps of dark field (DF) images at the Er N4,5, Si L2,3, and O K edges is concomitant with an intense room temperature infrared luminescence around 1534 nm. We suggest that these observations correspond to Er–O complexes within an amorphous silicon (a-Si) shell at the Si-NC/SiO2 interface. The presence of a crystalline phase at the Si-NC center, verified by high resolution electron micrographs and DF diffraction contrast images and the low solubility of Er in crystalline Si (c-Si) would tend to suggest a preferential Er agglomeration toward the Si-NC/SiO2 interface during formation, particularly when high concentrations of both Si and Er are obtained in a narrow region of the SiO2 after coimplantation. The absence of narrow Stark related features in the Er emission spectrum at low temperature and an inhomogeneous broadening with increasing temperature, which are characteristic of Er confined by an amorphous, rather than a crystalline host further support these hypotheses. After comparing the luminescence to that from a SiO2:Er control sample prepared in exactly the same manner but without Si-NCs, we find that, despite the observed spatial correlation, only a small fraction (∼7%) of the Er are sensitized by the Si-NCs. We ascribe this low fraction to a combination of low sensitizer (Si-NC) density and Auger-type losses arising principally from Er ion-ion interactions.

Energy selective electron heat pump with transmission probability

The electron transport through an energy transmission spectrum between two reservoirs with different temperatures and chemical potentials is studied. The heat flow carried by the electrons is obtained. Taking into account the radiative heat leaks between the two electron reservoirs, the performance parameters of the heat pump are derived by numerical calculation. The performance characteristic curves of the heat pump are plotted. The influence of the heat leaks, the position of resonance energy level and the width of the level on the operation performance of the heat pump is analyzed. When the width of resonance energy level is infinitely small, the coefficient of performance may reach the value of Carnot heat pump.

Absolute cross-sections and kinetic-energy-release distributions for electron-impact ionization and dissociation of CD 2 +

Absolute cross-sections have been measured for electron-impact dissociative excitation and ionization of \({\rm CD}_{3}^{+} / {\left( {{\rm CH}_{3}^{+} } \right)}\) leading to formation of singly-charged fragments (CD 2 + , CH+, C+, H 2 + and D+). The animated crossed-beams method is applied in the energy range from the reaction threshold up to 2.5 keV. The maximum cross-sections are found to be (14.0±1.0)×10-17 cm2, (6.5± 0.7)×10-17 cm2, (3.3± 0.3)×10-17 cm2, (1.1±0.1)×10-17 cm2 and (14.0± 1.3)×10-17 cm2 for CD 2 + , CH+, C+, H 2 + and D+, respectively. Individual contributions for dissociative excitation and dissociative ionization are determined for each product as they are indispensable for plasma modelling, diagnostics and data analysis in fusion experiments. Conforming to the scheme recently used in the CD 4 + study, the cross-sections are presented in analytic forms suitable for their implementation in plasma simulation codes. Kinetic-energy-release distributions are determined for each product at selected electron energies.

Optimum performance analysis of an energy selective electron refrigerator affected by heat leaks

An energy selective electron (ESE) refrigerator with heat leaks is established in a one-dimensional system. Based on the theory of electronic transport, the expressions of the heat flux into hot and cold electron reservoirs are derived. When the heat leaks between two electron reservoirs via phonons are taken into account, the cooling rate, coefficient of performance (COP) and input power are obtained. The performance characteristic curves such as the cooling rate versus the COP, the cooling rate and the COP versus the center position of the resonance energy level are plotted by numerical calculation. The influence of the center position and width of the resonance energy level on the performance of the ESE refrigerator is analyzed in detail. Lastly, the influence of heat leaks and average temperature on the performance of the ESE refrigerator is discussed. The results obtained here have theoretical significance for understanding the thermodynamic performance of the practical ESE refrigerator.

Performance characteristics of an energy selective electron refrigerator with double resonances

This paper establishes the energy selective electron (ESE) engine with double resonances as a refrigerator in one dimensional (1D) system. It consists of two infinitely large electron reservoirs with different temperatures and chemical potentials, and they are perfectly thermally insulated from each other and interaction only via a double ‘idealized energy filter’ whose widths are all finite. Taking advantage of the density of state and Fermi distribution in the 1D system, the heat flux into each reservoir may then be calculated. Moreover, the coefficient of performance may be derived from the expressions for the heat flux into the hot and cold reservoirs. The performance characteristic curves are plotted by numerical analysis. The influences of the resonances widths, the energy position of resonance and the space of two resonances on performance of the ESE refrigerator are discussed. The results obtained here have theoretical significance for the understanding of thermodynamic performance of the micro–nano devices.

A Rapid Synthesis of Oriented Palladium Nanoparticles by UV Irradiation

Palladium nanoparticles of average size around 8 nm have been synthesized rapidly by UV irradiation of mixture of palladium chloride and potassium oxalate solutions. A rod-shaped palladium oxalate complex has been observed as an intermediate. In the absence of potassium oxalate, no Pd nanoparticles have been observed. The synthesized Pd nanoparticles have been characterized by powder X-ray diffraction (XRD), transmission electron microscopy (TEM), selective area electron diffraction and energy dispersive analysis by X-rays (EDAX) analyses. XRD analysis indicates the preferential orientation of catalytically active {111} planes in Pd nanoparticles. A plausible mechanism has been proposed for the formation of anisotropic Pd nanoparticles.

Landau cooling in metal–semiconductor nanostructures

An electron-cooling principle based on Landau quantization is proposed for nanoscale conductor systems. Operation relies on energy-selective electron tunnelling into a two-dimensional electron gas in quantizing magnetic fields. This quantum refrigerator provides significant cooling power (∼10−9 W at a few kelvin for realistic parameters) and offers a unique flexibility thanks to its tunability via the magnetic-field intensity. The available performance is only marginally affected by nonidealities such as disorder or imperfections in the semiconductor. Methods for the implementation of this system and its characterization are discussed.

Superconducting proximity effect inPb∕Agnanocomposites

We show that the superconducting transition temperature $({T}_{C})$ of a two-component system consisting of a random distribution of Pb and Ag nanoparticles, with sizes less than their respective coherence lengths, is governed essentially by proximity effect. The microstructure of the nanodispersed two-phase system has been studied using in-lens secondary electron and energy selective backscattered electron detectors. The theory of the superconducting proximity effect as previously applied to bilayers and multilayers can be suitably modified to include the ratio of the volume fraction of the superconducting and the normal metal components so as to explain the observed variation in ${T}_{C}$ in such nanocomposites with varying metal composition. Interestingly, Pb behaves as a weak-coupling superconductor in the random Pb-Ag nanocomposite.

A crossed-beam experiment for electron impact ionization and dissociation of molecular ions: its application to CO+

A crossed electron–ion beam experimental set-up has been upgraded for the study of electron impact ionization and dissociation of molecular ions by means of ionic product detection. Both the experimental set-up and the data analysis procedures are described in detail for the estimation of (i) absolute cross sections, (ii) kinetic energy release distributions (KERD) and (iii) anisotropies of angular distributions. Absolute cross sections are obtained separately for dissociative excitation (DE) and for dissociative ionization (DI). A double focusing magnetic field analyser is used for the observation of product velocity distributions, in the laboratory frame, at selected electron energies. The KERD in the centre of mass frame is calculated from the measured velocity distribution as well as the anisotropy of the angular distribution with respect to the initial orientation of the molecular ions. Results are reported for dissociative ionization and dissociative excitation of CO+ to C+ and O+ fragments in the energy range from about 5 eV to 2.5 keV. Absolute cross sections for DE at maximum, i.e. for an electron energy around 35 eV, are found to be (9.69 ± 2.08) × 10−17 cm2 and (6.24 ± 1.33) × 10−17 cm2, for C+ and O+, respectively, and the corresponding threshold energies are found to be (8.5 ± 0.5) eV and (14.8 ± 0.5) eV. The DE process leading to C+ production is seen to dominate at low electron energies. For DI, the absolute cross section is found to be (12.56 ± 2.38) × 10−17 cm2 around 125 eV and the corresponding threshold energy is (27.7 ± 0.5) eV. KERDs, which extend from 0 to 24 eV both for C+ and O+, exhibit very different shapes at low electron energy but similar ones above 100 eV, confirming the role observed respectively for DE and DI. The groups of states contributing to the different processes are identified by comparing present energies thresholds values and the KERDs with theoretical values. Anisotropies are estimated to be in the range 3–6% for both C+ and O+.

Formation of multi-charged Kr ions through photoionization of 2p electrons studied with a coincidence technique

Multi-charged Kr ions have been measured using monochromatized undulator radiation combined with a coincidence technique. The coincidence measurements between multi-charged ions and energy-selected Auger electrons have clarified decay processes, as follows. The Auger final states formed through L 3M 45M 45 decays turn significantly into Kr 4+ and those through L 3M 23M 45 decays generate Kr 5+ mainly. The Auger decays of L 3M 23M 23 types yield Kr 6+ dominantly. These findings are consistent with the consideration on energy levels of Kr ions.

Angular‐resolved elastic peak electron spectroscopy: experiment and Monte Carlo calculations

AbstractElastic peak electron spectroscopy (EPES) is widely applied for determining the inelastic mean free path (IMFP) of electrons, which is of crucial importance for quantitative electron spectroscopy. For this reason, it is highly desirable to verify the reliability of the EPES method for a variety of elements and different experimental geometries. In the present work, elastically backscattered electrons from Au, Ag, Cu, Fe and Si were measured at different experimental geometries (fixed incidence angle along the surface normal and various emission angles) for selected electron energies: 200, 500 and 1000 eV. The experimental angular distributions of elastically backscattered electrons were compared to the Monte Carlo (MC) calculations by the conventional and the reverse simulations.Agreement between the results of conventional, reverse MC calculations and the experimental values of electron backscattering intensity was obtained. Application of the procedure for the surface‐excitation corrections resulted in better agreement between the simulated and the experimental data. Larger values of deviation were observed for grazing emission angles, indicating inaccuracy of the correcting procedure and the values of the material parameter, independent of the electron energy and the geometry of measurement. Copyright © 2006 John Wiley & Sons, Ltd.

Formation mechanisms of multi-charged Kr ions through 2p shell photoionization using a coincidence technique

Multiply charged Kr ions have been measured using monochromatized undulator radiation combined with a coincidence technique. Above the L3 ionization threshold, photoionization has yielded multi-charged ions in a variety of charge states, which range mainly 3+ through 7+. The charge state distribution obtained using a pulse field technique is close to the spectra previously measured with different techniques, and is slightly different from that obtained by calculation. The coincidence measurements between multi-charged ions and energy-selected Auger electrons have disentangled complex decay processes. The Auger final states formed through L3M45M45 decays turn significantly into Kr4+ and those through L3M23M45 decays generate Kr5+ mainly. The Auger decays of L3M23M23 types yield Kr6+ dominantly. These findings are consistent with the consideration of energy levels of Kr ions; higher energy states turn into more highly-charged ions.

Analysis of film response to electron beams using a laser scanner system developed in the laboratory

An optical scanner system, which incorporates a He–Ne laser, photodiode detectors, and a platform for placing film, was built in the laboratory. The laser system operates at the green wavelength of 543.5 nm and functions as a scanning densitometer for measurement of optical changes in a film resulting from irradiation .The central axis electron depth dose of selected electron energies 10,12 and 14 MeV were analysed using Kodak X-Omat and Kodak Extended Dose Range (EDR2) films. The Kodak X-Omat film is routinely used for high-energy electron dose distributions in radiation therapy. The electron depth–dose measured with X-Omat film was found to agree well with standard depth–dose curves in water, obtained using an ion chamber. Conversely, the recently introduced Kodak EDR2 showed an energy dependence for electron beams, the percentage depth–dose curve shifting towards the surface for 12 and 14 MeV electron beams compared to that in water.

Calculation of the yield of Xe i+ photoions upon the decay of M 45 vacancies through intermediate states in coincidence with energy-selected Auger electrons

A theoretical model is proposed for calculating the yield of photoions detected in coincidence with energy-selected Auger electrons. This model provides a correct explanation for experimental data on the yield of photoions upon ionization of the M 45 shell of xenon atoms. In the framework of the proposed model, the intermediate-coupling approximation is used to calculate both the structure of the terms of the N −2 two-hole states generated through the M 45 NN Auger decays and the probabilities of branching due to decays of these states into three-hole states upon the Auger, Coster—Kronig, and super-Coster—Kronig transitions. The probabilities of branching for subsequent branches of the cascade decay are calculated in the configuration-average approximation. The results of these calculations are in good agreement with the experimental data.

Intensity modulated radiation therapy with electrons using algorithm based energy/range selection methods

Background and purposeIn recent years photon intensity modulated radiation therapy (IMRT) has gained attention due to its ability to improve conformity of dose distributions. A potential advantage of electron-IMRT is that the dose fall off in the depth dose curve makes it possible to modulate the dose distribution in the direction of the beam by selecting different electron energies. This paper examines the use of a computer based energy selection in combination with the IMRT technique to optimise the electron dose distribution. Materials and methodsOne centimetre square electron beamlets ranging from 2.5 to 50MeV were pre-calculated in water using Monte Carlo methods. A modified IMRT optimisation tool was then used to find an optimum mix of electron energies and intensities. The main principles used are illustrated in some simple geometries and tested on two clinical cases of post-operated ca. mam. ResultsIt is clearly illustrated that the energy optimisation procedure lowers the dose to lung and heart and makes the dose in the target more homogeneous. Increasing the energy at steep gradients compensates for lack of target coverage at beam edges and steep gradients. Comparison with a clinically acceptable four segment plan indicates the advantage of the used electron IMRT technique. ConclusionsUsing an intensity optimised mix of computer selected electron energies has the potential to improve electron treatments for mastectomy patients with good target coverage and reduced dose to normal tissue such as lung and heart.

Information depth for elastic-peak electron spectroscopy

We present a formalism for calculating the information depth (ID) for elastic-peak electron spectroscopy (EPES) in which a measurement is made of the intensity of elastically backscattered electrons for an amorphous or polycrystalline material and a selected electron energy. IDs and a related quantity, the mean penetration depth (MPD) for the detected electrons, were computed from Monte Carlo simulations and a simple single-scattering model for two elemental solids, copper and gold, at energies between 100 and 10,000 eV for a common EPES measurement configuration. Similar calculations were made as a function of emission angle for an electron energy of 1000 eV. The IDs and MPDs from the Monte Carlo simulations were generally smaller than found from the single-scattering model. The deviations are due in part to neglect of multiple scattering in the analytical model and often to strong variations of the differential cross section for elastic scattering for scattering angles within the acceptance solid angle of the analyzer. Reasonable agreement was found between the computed IDs for gold at an energy of 1000 eV (corresponding to detection of 90% and 95% of the total detected EPES signal) and values estimated from EPES experiments in which Au overlayers were deposited on a Ni substrate. Computed MPDs for copper and gold at energies between 100 and 10,000 eV were found to be smaller than mean escape depths for Auger electrons from these solids, but generally not by as much as expected from the single-scattering model for EPES and from neglect of elastic scattering of the Auger electrons. Multiple-elastic scattering is significant in EPES, and Monte Carlo simulations provide a convenient means for determining the IDs and MPDs for different materials, electron energies, and measurement configurations.