Showing papers on "Secondary electrons published in 2009"

Injection and Trapping of Tunnel Ionized Electrons into Laser Produced Wakes

Abstract: A method, which utilizes the large difference in ionization potentials between successive ionization states of trace atoms, for injecting electrons into a laser-driven wakefield is presented. Here a mixture of helium and trace amounts of nitrogen gas was used. Electrons from the K shell of nitrogen were tunnel ionized near the peak of the laser pulse and were injected into and trapped by the wake created by electrons from majority helium atoms and the L shell of nitrogen. The spectrum of the accelerated electrons, the threshold intensity at which trapping occurs, the forward transmitted laser spectrum, and the beam divergence are all consistent with this injection process. The experimental measurements are supported by theory and 3D OSIRIS simulations.

Dependence of electronic properties of epitaxial few-layer graphene on the number of layers investigated by photoelectron emission microscopy

Abstract: We used spectroscopic photoemission and low-energy electron microscopy to investigate the electronic properties of epitaxial few-layer graphene grown on 6H-SiC(0001). Photoelectron emission microscopy (PEEM) images using secondary electrons (SEs) and $\text{C}\text{ }1s$ photoelectrons can discriminate areas with different numbers of graphene layers. The SE emission spectra indicate that the work function increases with the number of graphene layers and that unoccupied states in the few-layer graphene promote SE emission. The $\text{C}\text{ }1s$ PEEM images indicate that the $\text{C}\text{ }1s$ core level shifts to lower binding energies as the number of graphene layers increases, which is consistent with the reported thickness dependence of the Dirac point energy.

The Physics of the FIR-Radio Correlation: I. Calorimetry, Conspiracy, and Implications

Abstract: (Abridged) The far-infrared (FIR) and radio luminosities of star-forming galaxies are linearly correlated over a very wide range in star formation rate, from normal spirals like the Milky Way to the most intense starbursts. Using one-zone models of cosmic ray (CR) injection, cooling, and escape in star-forming galaxies, we attempt to reproduce the observed FIR-radio correlation over its entire span. We show that ~2% of the kinetic energy from supernova explosions must go into primary CR electrons and that ~10 - 20% must go into primary CR protons. Secondary electrons and positrons are likely comparable to or dominate primary electrons in dense starburst galaxies. We discuss the implications of our models for the magnetic field strengths of starbursts, the detectability of starbursts by Fermi, and cosmic ray feedback. Overall, our models indicate that both CR protons and electrons escape from low surface density galaxies, but lose most of their energy before escaping dense starbursts. The FIR-radio correlation is caused by a combination of the efficient cooling of CR electrons (calorimetry) in starbursts and a conspiracy of several factors. For lower surface density galaxies, the decreasing radio emission caused by CR escape is balanced by the decreasing FIR emission caused by the low effective UV dust opacity. In starbursts, bremsstrahlung, ionization, and Inverse Compton cooling decrease the radio emission, but they are countered by secondary electrons/positrons and the decreasing critical synchrotron frequency, which both increase the radio emission. Our conclusions hold for a broad range of variations on our fiducial model.

Collisional heating as the origin of filament emission in galaxy clusters

Abstract: It has long been known that photoionization, whether by starlight or other sources, has difficulty in accounting for the observed spectra of the optical filaments that often surround central galaxies in large clusters. This paper builds on the first of this series in which we examined whether heating by energetic particles or dissipative magnetohydrodynamic (MHD) wave can account for the observations. The first paper focused on the molecular regions which produce strong H2 and CO lines. Here we extend the calculations to include atomic and low-ionization regions. Two major improvements to the previous calculations have been made. The model of the hydrogen atom, along with all elements of the H-like iso-electronic sequence, is now fully nl-resolved. This allows us to predict the hydrogen emission-line spectrum including excitation by suprathermal secondary electrons and thermal electrons or nuclei. We show how the predicted H i spectrum differs from the pure-recombination case. The second update is to the rates for H0–H2 inelastic collisions. We now use the values computed by Wrathmall et al. The rates are often much larger and allow the ro–vibrational H2 level populations to achieve a thermal distribution at substantially lower densities than previously thought. We calculate the chemistry, ionization, temperature, gas pressure and emission-line spectrum for a wide range of gas densities and collisional heating rates. We assume that the filaments are magnetically confined. The gas is free to move along field lines so that the gas pressure is equal to that of the surrounding hot gas. A mix of clouds, some being dense and cold and others hot and tenuous, can exist. The observed spectrum will be the integrated emission from clouds with different densities and temperatures but the same pressure P/k=nT. We assume that the gas filling factor is given by a power law in density. The power-law index, the only free parameter in this theory, is set by matching the observed intensities of infrared H2 lines relative to optical H i lines. We conclude that the filaments are heated by ionizing particles, either conducted in from surrounding regions or produced in situ by processes related to MHD waves.

Imaging single atoms using secondary electrons with an aberration-corrected electron microscope

Abstract: A new type of scanning electron microscope with aberration correction allows a resolution of 0.1 nm. The instrument also allows for simultaneous imaging of atoms on the surface and in the bulk of a sample, which represents a real breakthrough in the field. Aberration correction has embarked on a new frontier in electron microscopy by overcoming the limitations of conventional round lenses, providing sub-angstrom-sized probes1,2,3,4,5,6,7,8. However, improvement of spatial resolution using aberration correction so far has been limited to the use of transmitted electrons both in scanning and stationary mode, with an improvement of 20–40% (refs 3–8). In contrast, advances in the spatial resolution of scanning electron microscopes (SEMs), which are by far the most widely used instrument for surface imaging at the micrometre–nanometre scale9, have been stagnant, despite several recent efforts10,11. Here, we report a new SEM, with aberration correction, able to image single atoms by detecting electrons emerging from its surface as a result of interaction with the small probe. The spatial resolution achieved represents a fourfold improvement over the best-reported resolution in any SEM (refs 10–12). Furthermore, we can simultaneously probe the sample through its entire thickness with transmitted electrons. This ability is significant because it permits the selective visualization of bulk atoms and surface ones, beyond a traditional two-dimensional projection in transmission electron microscopy. It has the potential to revolutionize the field of microscopy and imaging, thereby opening the door to a wide range of applications, especially when combined with simultaneous nanoprobe spectroscopy.

Breakdown of a Space Charge Limited Regime of a Sheath in a Weakly Collisional Plasma Bounded by Walls with Secondary Electron Emission

Abstract: A new regime of plasma-wall interaction is identified in particle-in-cell simulations of a hot plasma bounded by walls with secondary electron emission. Such a plasma has a strongly non-Maxwellian electron velocity distribution function and consists of bulk plasma electrons and beams of secondary electrons. In the new regime, the plasma sheath is not in a steady space charge limited state even though the secondary electron emission produced by the plasma bulk electrons is so intense that the corresponding partial emission coefficient exceeds unity. Instead, the plasma-sheath system performs relaxation oscillations by switching quasiperiodically between the space charge limited and non-space-charge limited states.

Self-sputtering far above the runaway threshold: an extraordinary metal-ion generator

Abstract: When self-sputtering is driven far above the runaway threshold voltage, energetic electrons are made available to produce "excess plasma" far from the magnetron target. Ionization balance considerations show that the secondary electrons deliver the necessary energy to the "remote" zone. Thereby, such a system can be an extraordinarily prolific generator of usable metal ions. Contrary to other known sources, the ion current to a substrate can exceed the discharge current. For gasless self-sputtering of copper, the usable ion current scales exponentially with the discharge voltage.

Theoretical and experimental investigations of electron emission in C6+ + H2O collisions

Abstract: Theoretical differential and total cross sections for the direct ionization process of water vapour by 6 MeV/u C6+ ions are compared to new experimental measurements performed by the dedicated apparatus already used for measuring the energy and angular distributions of secondary electrons emitted from water vapour by fast heavy-ion impact [D. Ohsawa, H. Kawauchi, M. Hirabayashi, Y. Okada, T. Homma, A. Higashi, S. Amano, Y. Hashimoto, F. Soga, Y. Sato, Nucl. Instr. and Meth. B 227 (2005) 431]. In the present work, ab initio calculations have been carried out in the first Born approximation by using an accurate molecular wave function for describing the initial bound state of the target. The calculated cross sections exhibit good agreement with the present experimental measurements and compare relatively well to the existing semi-empirical results over the entire angular and energy ranges investigated here. Free from any adjustable parameter, the proposed theoretical approach describes in detail the complete kinematics of the water molecule ionization process by highly energetic carbon ions, and could therefore be easily used for modelling the heavy charged-particle transport in the biological matter.

Different modes of electron heating in dual-frequency capacitively coupled radio frequency discharges

Abstract: A systematic study of different modes of electron heating in dual-frequency capacitively coupled radio frequency (CCRF) discharges is performed using a particle-in-cell simulation. Spatio-temporal distributions of the total excitation/ionization rates under variation of gas pressure, applied frequencies and gas species are discussed. Some results are compared qualitatively with an experiment (phase resolved optical emission spectroscopy) operated under conditions similar to a parameter set used in the simulation. Different modes of electron heating are identified and compared with α- and γ-mode operation of single-frequency CCRF discharges. In this context the frequency coupling and its relation to the ion density profile in the sheath are discussed and quantified. In light gases the ion density in the sheath is time modulated. This temporal modulation is well described by an analytical model and is found to affect the excitation dynamics via the frequency coupling. It is shown that the frequency coupling strongly affects the generation of beams of highly energetic electrons by the expanding sheath and field reversals caused by the collapsing sheath. The role of secondary electrons at intermediate and high pressures is clarified and the transition from α- to γ-mode operation is discussed. Depending on the gas and the corresponding cross sections for excitation/ionization the excitation does not generally probe the ionization as is usually assumed.

A novel highly sensitive gas ionization sensor for ammonia detection

Abstract: A novel highly sensitive gas ionization sensor for ammonia detection in ambient air is introduced in this paper. Carbon nanotubes (CNTs) grown on silicon substrate were incorporated to fabricate a gas ionization sensor. Application of a positive bias to the CNTs generates electric fields sufficiently to field-ionize passing gas-phase molecular and initiate a prebreakdown current. When the CNTs film is configured as the cathode, secondary electrons repelled away from the CNTs tips into the gap spacing make more ionizing collisions and also initiate a prebreakdown current. By monitoring the prebreakdown current, the gas ionization sensor was demonstrated to be capable of ionizing and detecting the ammonia and with a linear response over the entire range from 1 to 160 ppm ammonia in air. The sensitivity mechanism of the gas ionization sensor was also discussed in detail. The sensitivity and selectivity of the gas ionization sensor to the gases is not only dependent on its ionization energy but also its electric dipole moment. The novel CNTs-based gas ionization sensor described here exhibits high accuracy, repeatability and stability. The sensor is promising for use in various fields.

Understanding imaging modes in the helium ion microscope

Abstract: Recent investigations are gaining us a better understanding of the nature of the beam-sample interactions in the helium ion microscope and what they mean for the image information provided In secondary electron (SE) imaging, for example, the surface sensitivity is attributed to the low SE-II fraction Voltage contrast imaging shows the ability to see both buried structures and to probe the conductance to ground of surface contacts It is found, however, that the prominence of these two types of contrast varies oppositely with beam energy, yielding information about the nature of the interactions that gives rise to them Transmission ion imaging can yield information about material density, atomic number, grain structure, and electronic structure It is possible to capture the top-side SE signal, bright field signal, and dark field signal from a given sample simultaneously The detection of diffraction contrast is under investigation

Ion-induced electron production in tissue-like media and DNA damage mechanisms

Abstract: This work is the first stage in the development of an inclusive approach to calculation of the DNA damage caused by irradiation of biological tissue by ion/proton beams. The project starts with an analysis of ionization caused by the projectiles and the characteristics of secondary electrons produced in tissue-like media. We consider interactions with the medium on a microscopic level and this allows us to obtain the energy spectrum and abundance of secondary electrons as functions of the projectile’s kinetic energy. The physical information obtained in this analysis is related to biological processes responsible for the DNA damage induced by the projectile. In particular, we consider double strand breaks of DNA caused by secondary electrons and free radicals, and local heating in the ion’s track. The heating may enhance the biological effectiveness of electron/free radical nteractions with the DNA and may even be considered as an independent mechanism of DNA damage. Numerical estimates are performed for the case of carbon-ion beams. The obtained dose-depth curves are compared with results of the MCHIT model based on the GEANT4 toolkit.

Damage induced to DNA by low-energy (0-30 eV) electrons under vacuum and atmospheric conditions.

Abstract: In this study, we show that it is possible to obtain data on DNA damage induced by low-energy (0-30 eV) electrons under atmospheric conditions. Five monolayer films of plasmid DNA (3197 base pairs) deposited on glass and gold substrates are irradiated with 1.5 keV X-rays in ultrahigh vacuum and under atmospheric conditions. The total damage is analyzed by agarose gel electrophoresis. The damage produced on the glass substrate is attributed to energy absorption from X-rays, whereas that produced on the gold substrate arises from energy absorption from both the X-ray beam and secondary electrons emitted from the gold surface. By analysis of the energy of these secondary electrons, 96% are found to have energies below 30 eV with a distribution peaking at 1.4 eV. The differences in damage yields recorded with the gold and glass substrates is therefore essentially attributed to the interaction of low-energy electrons with DNA under vacuum and hydrated conditions. From these results, the G values for low-energy electrons are determined to be four and six strand breaks per 100 eV, respectively.

A compact vapor source of conductive target material sputtered by 3-keV ions at 0.05-Pa pressure

Abstract: A vapor source is developed its 80-mm-diameter and 15-mm-thick flat target being positioned on the bottom of a 120-mm-diameter and 70-mm-deep hollow cathode, isolated from the cathode and sputtered by 1–4-keV argon ions. A permanent magnet induces an axially symmetric heterogeneous magnetic field, the field induction on the target surface reaching 20 mT and the field lines of force being diverging from the target surface and crossing the cathode surface. The cathode bombardment by 1–3-keV secondary electrons emitted by the target results in an increase of the electron emission current in the cathode circuit and enables to reduce the argon pressure down to 0.05 Pa. It allows a collisionless transport of the sputtered metal atoms to a substrate thus keeping their initial energy amounting to tens of electronvolts. A higher energy of deposited atoms improves quality of coatings, for instance of Ti3SiB2 films, their deposition rate on a substrate distanced at 0.1–0.2 m from the target amounting to 10–20 µm/h at 1-A current in the target circuit and 3-keV energy of sputtering ions. This value is one order of magnitude higher in comparison with the target sputtering in a planar magnetron discharge by 300–500-eV argon ions at the same 1-A current in the target circuit.

Ionization processes in the atmosphere of Titan: I. Ionization in the whole atmosphere

Abstract: Context. The Cassini probe regularly passes in the vicinity of Titan, revealing new insights into particle precipitation thanks to the electron and proton spectrometer. Moreover, the Huygens probe has revealed an ionized layer at 65 km induced by cosmic rays. The impact of these different particles on the chemistry of Titan is probably very strong. Aims. In this article, we compute the whole ionization in the atmosphere of Titan: from the cosmic rays near the ground to the EUV in the upper atmosphere. The meteoritic layer is not taken into account. Methods. We used the transTitan model to compute the electron and EUV impact, and the planetocosmics code to compute the influence of protons and oxygen ions. We coupled the two models to study the influence of the secondary electrons obtained by planetocosmics through the transTitan code. The resulting model improves the accuracy of the calculation through the transport of electrons in the atmosphere. Results. The whole ionization is computed and studied in details. During the day, the cosmic ray ionization peak is as strong as the UV-EUV one. Electrons and protons are very important depending the precipitation conditions. Protons can create a layer at 500 km, while electrons tend to ionize near 800 km. The oxygen ion impact is near 900 km. The results shows few differences to precedent models for the nightside T5 fly-by of Cassini, and can highlight the sources of the different ion layers detected by radio measurements. Conclusions. The new model successfully computes the ion production in the atmosphere of Titan. For the first time, a full electron and ion profile has been computed from 0 to 1600 km, which compares qualitatively with measurements. This result can be used by chemical models.

Analysis of the fluorescence emission from atmospheric nitrogen by electron excitation, and its application to fluorescence telescopes

Abstract: A microscopic analysis of the processes involved in the fluorescence emission of nitrogen molecules induced by electronic collisions is carried out for a large range of incident energies (eV to GeV) and pressures (Pa to atmospheric conditions). The contribution of secondary electrons to that fluorescence is calculated by means of detailed Monte Carlo simulations. For this purpose, a novel analytical approximation of the energy spectrum of secondary electrons is used. The results of the simulations are shown to be useful for the interpretation of available experimental data. For instance, they account for the pressure dependence of the fluorescence observed in laboratory experiments. The conditions under which emitted fluorescence is proportional to deposited energy are also studied. Finally, these calculations provide an absolute value of the fluorescence yield consistent with available experimental data.

Radiation damage in biological material: Electronic properties and electron impact ionization in urea

Abstract: Radiation damage is an unavoidable process when performing structural investigations of biological macromolecules with X-rays. In crystallography this process can be limited through damage distribution in a crystal, while for single molecular imaging it can be outrun by employing short intense pulses. Secondary electron generation is crucial during damage formation and we present a study of urea, as model for biomaterial. From first principles we calculate the band structure and energy loss function, and subsequently the inelastic electron cross-section in urea. Using Molecular Dynamics simulations, we quantify the damage and study the magnitude and spatial extent of the electron cloud coming from an incident electron, as well as the dependence with initial energy.

Monte Carlo model of electron energy degradation in a CO2 atmosphere

Abstract: [1] A Monte Carlo model has been developed to study the degradation of ≤1000 eV electrons in an atmosphere of CO2, which is one of the most abundant species in Mars' and Venus's atmospheres. The e-CO2 cross sections are presented in an assembled set along with their analytical representations. Monte Carlo simulations are carried out at several energies to calculate the “yield spectra,” which embodied all the information related to the electron degradation process and can be used to calculate “yield” (or population) for any inelastic process. The numerical yield spectra have been fitted analytically, resulting in an analytical yield spectra. We have calculated the mean energy per ion pair and efficiencies for various inelastic processes, including the double and dissociative double ionization of CO2 and negative ion formation. The energy distribution of the secondary electrons produced per incident electron is also presented at few incident energies. The mean energy per ion pair for CO2 is 37.5 (35.8) eV at 200 (1000) eV, compared to the experimental value 32.7 eV at high energies. Ionization is the dominant loss process at energies above 50 eV with a contribution of ∼50%. Among the excitation processes, 13.6 eV and 12.4 eV states are the dominant loss processes consuming ∼28% energy above 200 eV. Around and below ionization threshold, 13.6 eV, 12.4 eV, and 11.1 eV, followed by 8.6 eV and 9.3 eV, excitation states are important loss processes, while below 10 eV, vibrational excitation dominates.

Monte Carlo calculations of electron transport in silicon and related effects for energies of 0.02-200 keV

Abstract: We present results of systematic Monte Carlo calculations of electron transport in silicon for the wide energy range of 0.02–200 keV, obtained in the frame of a single model using verified input data. The results include characteristics of electron transport, such as backscattering coefficients, ranges, transmission, and deposited-energy distributions, which are quantities of importance for electron-beam applications. The calculations of the spatial and temporal evolution of the electron-initiated cascades of secondary electrons yield a better understanding of the electron and ion track structures and related effects in silicon.

Nanoscale Chemical Imaging by Scanning Tunneling Microscopy Assisted by Synchrotron Radiation

Abstract: Nanoscale chemical imaging using scanning tunneling microscopy is demonstrated with a core-level excitation of the probed element by a synchrotron radiation light. Pronounced element-specific contrasts were observed in the spatial resolution of approximately 10 nm on checkerboard-patterned Ni and Fe samples in differential photoinduced current images taken with the scanning tunneling microscopy tip under the synchrotron radiation irradiation whose photon energies are above and below the Ni (Fe) L absorption edge. The local detection of the photoinduced secondary electrons through the surface barrier lowered by the proximate tip and/or via the tunneling process probably plays an important role in achieving the high-spatial resolution.

Comparison of secondary electron emission in helium ion microscope with gallium ion and electron microscopes

Abstract: To evaluate secondary electron (SE) image characteristics in helium ion microscope, Si surfaces with a rod and step structures is scanned by 30 keV He and Ga ion beams and 1 keV electron beam. The topographic sensitivity of He ions is in principle higher than that for scanning electron microscope (SEM) because of the stronger dependency of SE yield versus incident angle for He ions. As shrinking to sub nm patterns, the pseudo-images constructed from line profile of SE intensity by the electron beam lose their sharpness, however, the images for the He and Ga ion beams keep clearness due to darkening the bottom corners of the pattern. Here, the sputter erosion for Ga ions must be considered. Furthermore, trajectories of emitted SEs are simulated for a rectangular Al surface scanned by the beams to study voltage contrast, where positive and negative voltages are applied to the small area of the sample. Both less high energy component in the energy distribution of SEs and dominant contribution of direct SE excitation by a projectile He ion keep a high voltage contrast down to a sub nm sized area positively biased against the zero-potential surroundings.

200 MeV silver ion irradiation induced structural modification in YBa2Cu3O7−y thin films at 89 K: An in situ x-ray diffraction study

Abstract: We report in situ x-ray diffraction (XRD) study of 200 MeV Ag ion irradiation induced structural modification in c-axis oriented YBa2Cu3O7−y (YBCO) thin films at 89 K. The films remained c-axis oriented up to a fluence of 2×1013 ionscm−2, where complete amorphization sets in. The amorphous ion tracks, the strained region around these tracks, and irradiation induced point defects are shown to control the evolution of the structure with ion fluence. Secondary electrons emanating from the ion paths are shown to create point defects in a cylindrical region of 97 nm radius, which corresponds to their maximum range in the YBCO medium. The point defects are created exclusively in the CuO basal planes of fully oxygenated YBCO, which has not been possible, by other techniques including low energy ion irradiation and thermal quenching. The point defects led to a faster decrease in the integral intensity of XRD peaks at very low fluences of irradiation (Φ≤3×1010 ionscm−2) than what can be expected from amorphous tra...

Stochastic spatial energy deposition profiles for MeV protons and keV electrons

Abstract: With the rapid advances being made in novel high-energy ion-beam techniques such as proton beam writing, single-ion-event effects, ion-beam-radiation therapy, ion-induced fluorescence imaging, proton/ion microscopy, and ion-induced electron imaging, it is becoming increasingly important to understand the spatial energy-deposition profiles of energetic ions as they penetrate matter. In this work we present the results of comprehensive yet straightforward event-by-event Monte Carlo calculations that simulate ion/electron propagation and secondary electron ($\ensuremath{\delta}$ ray) generation to yield spatial energy-deposition data. These calculations combine SRIM/TRIM features, EEDL97 data and volume-plasmon-localization models with a modified version of one of the newer $\ensuremath{\delta}$ ray generation models, namely, the Hansen-Kocbach-Stolterfoht. The development of the computer code DEEP (deposition of energy due to electrons and protons) offers a unique means of studying the energy-deposition/redistribution problem while still retaining the important stochastic nature inherent in these processes which cannot be achieved with analytical modeling. As an example of an application of DEEP we present results that compare the energy-deposition profiles of primary MeV protons and primary keV electrons in polymethymethacrylate. Such data are important when comparing proximity effects in the direct write lithography processes of proton-beam writing and electron-beam writing. Our calculations demonstrate that protons are able to maintain highly compact spatial energy-deposition profiles compared with electrons.

Sensitivity of scanning electron microscope width measurements to model assumptions

Abstract: The most accurate width measurements in a scanning electron microscope (SEM) require raw images to be corrected for instrumental artifacts. Corrections are based on a physical model that describes the sample-instrument interaction. Models differ in their approaches or approximations in the treatment of scattering cross sections, secondary electron generation, material properties, scattering at the surface potential barrier, etc. Corrections that use different models produce different width estimates. We have implemented eight models in the Java Monte Carlo simulator for secondary electrons (JMONSEL) SEM simulator. Two are phenomenological models based on fitting measured yield versus energy curves. Two are based on a binary scattering model. Four are variants of a dielectric function approach. These models are compared to each other in pairwise simulations in which the output of one model is fit to the other by using adjustable parameters similar to those used to fit measured data. The differences in their edge position parameters is then a measure of how much these models differ with respect to a width measurement. With electron landing energy, beam width, and other parameters typical of those used in industrial critical dimension measurements, the models agreed to within ±2.0 nm on silicon and ±2.6 nm on copper in 95% of comparisons.

Numerical Optimization of a Multistage Depressed Collector With Secondary Electron Emission for an X-band Gyro-BWO

Abstract: A three-stage depressed collector was previously designed and simulated to recover the kinetic energy of the spent electron beam in an X-band gyrotron backward wave oscillator (gyro-BWO) by using the 3-D particle-in-cell code MAGIC. The geometry of the depressed collector was optimized using a genetic algorithm to achieve the optimum overall recovery efficiency for specific parameters of the spent beam. In this paper, secondary electron emissions were simulated, and a few emission models were compared to investigate the effects of the secondary electrons on the overall recovery efficiency and the backstreaming of the electrons from the collector region. The optimization of the shape and dimensions of each stage of the collector using a genetic algorithm achieved an overall recovery efficiency of more than 80% over the entire operating regime of the Gyro-BWO, with a minimized backstreaming of 1.4%. The heat distribution on the collector was calculated, and the maximum heat density on the electrodes was approximately 195 W/cm2, hence avoiding the generation of ?hot spots?.

Secondary Electron Generation in Electron-beam-irradiated Solids: Resolution Limits to Nanolithography

Abstract: We have investigated the secondary electron generation in electron-beam-irradiated solids by means of a Monte Carlo simulation. The slow secondary electron energy was found to be independent of the position and the incident energy of the electron beam, and the electron beam broadening in thin films due to secondary electrons was found to be at least 5 – 10 nm, setting limits to the nanolithographic resolution.

On the inverse Compton scattering interpretation of the hard X-ray excesses in galaxy clusters: the case of Ophiuchus

Abstract: Context. Populations of high energy electrons can produce hard X-ray (HXR) emission in galaxy clusters by up-scattering CMB photons via the inverse Compton scattering (ICS) mechanism. However, this scenario has various astrophysical consequences. Aims. We discuss here the consequences of the presence of a population of high energy particles for the multi-frequency emissivity of the same clusters and the structure of their atmospheres. Methods. We derive predictions for the ICS HXR emission in the specific case of the Ophiuchus cluster (for which an interesting combination of observational limits and theoretical scenarios have been presented) for three main scenarios producing high-E electrons: primary cosmic ray model, secondary cosmic rays model and neutralino DM annihilation scenario. We further discuss the predictions of the Warming Ray model for the cluster atmosphere. Under the assumption to fit the HXR emission observed in Ophiuchus, we explore the consequences that these electron populations induce on the cluster atmosphere. Results. We find that: i) primary electrons can be marginally consistent with the available data provided that the electron spectrum is cutoff at E 30 and E 90 MeV for electron spectral index values of 3.5 and 4.4, respectively; ii) secondary electron models from pp collisions are strongly inconsistent with the viable gamma-ray limits, cosmic ray protons produce too much heating of the intracluster (IC) gas and their pressure at the cluster center largely exceeds the thermal one; iii) secondary electron models from DM annihilation are also strongly inconsistent with the viable gamma-ray and radio limits, and electrons produce too much heating of the IC gas at the cluster center, unless the neutralino annihilation cross-section is much lower than the proposed value. In that case, however, these models no longer reproduce the HXR excess in Ophiuchus. Conclusions. We conclude that ICS by secondary electrons from both neutralino DM annihilation and pp collisions cannot be the mechanism responsible for the HXR excess emission; primary electrons are still a marginally viable solution provided that their spectrum has a low-energy cutoff at E 30−90 MeV. We also find that diffuse radio emission localized at the cluster center is expected in all these models and requires quite low values of the average magnetic field (B ∼ 0.1−0.2 μG in primary and secondary-pp models; B ∼ 0.055−0.39 μG in secondary-DM models) to agree with the available observations. Finally, the WR model (with B ∼ 0.4−2.0 μG) offers, so far, the most accurate description of the cluster in terms of the temperature distribution, heating and pressure and multifrequency spectral energy distribution. Fermi observations of Ophiuchus will provide further constraints to this model.

Difference of Spur Distribution in Chemically Amplified Resists upon Exposure to Electron Beam and Extreme Ultraviolet Radiation

Abstract: In chemically amplified resists, acid generators are sensitized mainly by secondary electrons upon exposure to an electron beam (EB) or extreme ultraviolet (EUV) radiation. Therefore, the reaction mechanisms of EB and EUV resists are analogous. In addition to the difference in the absorption coefficients and related phenomena, the major difference between EB and EUV resists is the energy spectrum of secondary electrons generated by incident radiation. Both an EB and EUV radiation generate ion pairs through ionization in resist films. The space that an ion pair occupies is called a spur. When spurs overlap, the electron dynamics changes and affects the chemical yield and distribution. In this study, the distribution of intermediate species in EB and EUV resists was investigated by a Monte Carlo simulation. The difference between their spur distributions and its effects were clarified. To calculate the acid distribution in chemically amplified resists, the single-spur model is generally sufficient for EB resists, while the multispur model is required for EUV resists.