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Energetic proton precipitation from the magnetosphere plays an important role in the magnetosphere‐ionosphere‐thermosphere coupling and energy transfer. Proton precipitation causes hydrogen emissions, such as Hβ (486.1 nm), and also triggers the excitation of other emission lines such as the blue‐line (427.8 nm) and the green‐line (557.7 nm). In light of the growing availability of ground‐based proton auroral measurements in recent years, we revisit the proton auroral modeling in this study, with more focus on the application for interpreting ground observations. An accurate simulation of these optical emissions requires a comprehensive understanding of particle transport and collisions in the upper atmosphere, where the simultaneous consideration of precipitating protons, newly generated energetic hydrogen atoms, and secondary electrons is critical. For this purpose, we couple a 3D Monte‐Carlo proton transport model and an electron transport model. The integrated model framework can compute the emission rates of most major auroral emission lines/bands resulting from proton precipitation, along with self‐consistent calculation of the ionospheric electron density variations. The model results show improved agreement with ground optical observations in terms of the Hβ yield and the green‐to‐Hβ ratio compared to previous model studies. Our new model is a valuable tool for quantifying excitation and ionization due to proton aurora. It has the potential to leverage ground observations to infer precipitating conditions at high altitudes and even for studying magnetospheric activity. Plain Language Summary: The terrestrial auroral display is caused by the collision of energetic particles from space with the Earth's atmosphere. Both energetic electrons and protons can enter the atmosphere and cause auroras, but their transport processes are different. The proton can exchange its charge with atmospheric neutral particles in a collision and become a neutral hydrogen atom, and the hydrogen atom can become a proton again in another collision with atmospheric particles. Both the protons and the hydrogens can ionize the atmospheric neutrals and produce secondary electrons. To model the proton‐induced auroras, the three components, protons, hydrogens, and secondary electrons, must be considered together with their different trajectories and transport in the atmosphere. In this study, we present such a coupled proton‐hydrogen‐electron transport model and simulate the resulting proton auroral intensities. The model results show reasonable agreement with existing ground‐based observations. Key Points: We present a model of coupled proton‐hydrogen‐electron transport in the atmosphere and the resulting auroral excitation and ionizationThe model results show improved agreement with the Hbeta yield reported in existing observations compared to previous modelsOur model can simulate the 557.7 nm emission in proton auroras. The modeled green‐to‐Hbeta ratio is compatible with the existing observation [ABSTRACT FROM AUTHOR]

Secondary electron yield (SEY) is a dominant factor in determining the multipactor threshold. In this study, we analyzed the secondary roughness effect of surface microstructures for plastic dielectric on SEY reduction and multipactor mitigation. A single ridge waveguide (SRW) operating in Ku-band, filled with polytetrafluoroethylene (PTFE) or polyimide (PI), was designed with a dielectric–metal multipactor gap. By employing a femtosecond laser, periodic microstructures were fabricated on PTFE and PI surfaces to suppress SEY. The SEY peak values of PTFE and PI decreased from 2.05 to 1.40 and 1.37 to 1.07 by the porous surface. The surface morphologies and cross-sectional images of the porous PTFE and PI demonstrated the existence of secondary roughness structures. Via simulation, we obtained multipactor thresholds of 8496 W, 12 374 W, and 9397 W for the SRWs filled with untreated PTFE surface, ideal porous surface (without secondary roughness), and real porous surface (with secondary roughness). Similar works were implemented for the PI-filled SRWs, resulting in simulated multipactor thresholds of 7640 W, 11 327 W, and 9433 W. The results indicate that the multipactor effect may not be effectively suppressed under the influence of secondary roughness structures such as plastic velvet and foam. Besides, simulation works indicated that the radio frequency electric field could extract secondary electrons from the microstructures, weakening the mitigation effect of microstructures on multipactor. The impact of surface charging on electron motion was also analyzed by considering energy distribution. It was suggested that the surface microstructures of plastic dielectrics lead to a decrease in the surface charge density and the electrostatic field strength, weakening the self-extinguishing effect and lowering the multipactor threshold. This study provides an in-depth analysis of the effect of secondary roughness on SEY and multipactor for organic dielectrics, which makes significant sense for the further investigation of dielectric multipactor. [ABSTRACT FROM AUTHOR]

We conducted developmental experiments using avalanche photodiode (APD) for electron measurements applicable in future space plasma explorations. Electrons with energies of 10 eV to a hundred keV could be detected by applying "floating" voltages up to +5 kV to APD to achieve wide‐energy electron measurements. We detected 10‐eV electrons from an electron source as energized electrons of an energy of approximately 5 (5.01) keV due to the 5‐keV electrostatic acceleration (=Source energy: 0.01 keV + Acceleration energy: 5 keV; hereafter, (0.01 + 5) keV) with an energy resolution of ∼4.6 keV by simplified assumption and calculation based on peak energy and full width at half maximum of the pulse height distribution. The energy resolution for (5 + 0)‐keV electrons, ∼5.3 keV in our experiments, was equivalent to the previous results. On the other hand, we concluded that for (5 + 5) keV, the energy resolution was significantly improved to 1.3 keV compared with that for (5 + 0) keV. For (1 + 5)‐keV electrons, the energy distribution showed a broadening toward lower energies than that for (6 + 0) keV because the backscattered electrons produced secondary electrons at the APD chassis surface, which were accelerated to 5 keV by the floating voltage to be detected by the APD. We verified that the floating‐mode APD can contribute to space plasma measurements as a detector with characteristics different from those of microchannel plates. This is the first achievement to establish advanced in‐situ observation techniques based on APD for wide‐energy (a few eV to a hundred keV) electron measurements in space. Key Points: We conducted fundamental developments of floating‐mode avalanche photodiode (APD) for reducing lowermost measurable energy of electrons in spaceExperimental results indicate that the floating‐mode APD applied by +5 kV as floating voltage can detect 10‐eV electronsWe identified contaminations by secondary electrons that were produced by backscattered electrons and accelerated by the floating voltage [ABSTRACT FROM AUTHOR]

Multipactor is a common discharge phenomenon occurring in space microwave systems. The surface microstructure has been verified to be effective in mitigating multipactor. In this work, we design a square coaxial low-pass filter (SCLPF) with dielectric sheets loaded to check the multipactor dependence on the structure parameters of the loaded dielectric sheets, and further model groove structures on the sensitive area surface to lower the risk of multipactor. Simulation results indicate that the SCLPF loaded with alumina and PTFE exhibits favorable operational characteristics, and the multipactor threshold is significantly improved after introducing the surface grooves. Then, we investigate the effects of three typical groove parameters, groove depth, groove number, and aspect ratio, on the multipactor threshold of the SCLPF device. The results show that the multipactor threshold rises at first as the groove number and groove depth increase, and then the threshold reaches a saturation status. For a deeper analysis of multipactor, we discuss how the grooves shelter the secondary electrons, and further mitigate the electron avalanche. Furthermore, the mechanisms of threshold saturation under the effect of groove parameters are analyzed in detail, and a contour map for the multipactor threshold of PTFE-loaded SCLPFs is given, which makes significant sense for predicting the multipactor threshold of the devices with its sensitive surface being grooved. The regularity of modulating the multipactor threshold by the groove structures obtained in this study is of engineering significance for suppressing multipactor in microwave devices in practical applications. [ABSTRACT FROM AUTHOR]

Exploiting advanced patterning strategies and materials to achieve smaller sizes and higher precision is urgently and constantly pursued. In this work, to suppress the radiolytic low-energy secondary electron diffusion and accompanying unpredictable defects, we demonstrate a patterning control strategy to realize high-precision nanoscale fabrication through a quenching mechanism and achieve significant resolution and roughness enhancement in ∼10 nm patterning. [Display omitted] Nanopatterning is a well-established approach to fabricating nanostructures in electronics and optics, and exploiting patterning strategy to achieve smaller feature sizes and higher precision is urgently and constantly pursued. State-of-the-art extreme ultraviolet lithography and electron beam lithography have proven to produce smaller sizes. However, for such energetic radiation-based approaches, the serious diffusion behavior of the radiolytic low-energy secondary electrons will result in unpredictable defects in the unexposed matrix, limiting the ultimate resolution and hindering its potential in sub-10 nm patterning. Herein, we report significant progress in high-resolution patterning via suppressing of residues caused by secondary electron diffusion, and 10 nm line-space nanostructures are achieved by utilizing a free radical quencher in patterning a highly sensitive zirconium-containing photoresist. Lithography evaluation combined with theoretical calculation reveals this novel radical quencher approach can effectively suppress undesired electronic excitation and ionization reactions, thereby significantly improving resolution and edge roughness. By inhibiting secondary electron-induced active species, this quenching mechanism is found to increase the onset dose and effectively narrow the energy deposition; thus improving the patterning contrast and facilitating the acquisition of straight lines with sharp edges. This work provides a new perspective on active species diffusion control for higher precision nanoscale fabrication. [ABSTRACT FROM AUTHOR]

The energy-dependence of the secondary electron yield by electron impact on clean materials is shown, through comparisons with both experimental data and previous semi-empirical models, to be described well by a log-normal distribution. The maximum yield and corresponding energy are calculated in terms of the fit parameters. The function also agrees with the 'universal curve' obtained by expressing the experimental data in terms of the position and magnitude of maximum yield. The positron- and ion-induced secondary electron yields also exhibit a log-normal dependence and this is used to extend their energy ranges without prior knowledge of the position and magnitude of their maxima. In addition to their intrinsic usefulness, the results provide further support for the statistical description of inelastic processes advanced by Laricchia et al. (2018). [ABSTRACT FROM AUTHOR]

In this study, a three-dimensional microchannel model of a single hollow-core glass fiber was constructed and the Finite Integral Technique and Monte Carlo method were combined to comprehensively simulate the electron multiplication process in a single channel under DC mode. The electron dynamic trajectory in DC electron emission mode was achieved. The effects of different structural parameters and applied bias voltage on the electron gain and the most probable exit energy at the output end of MCP were investigated. The results show that the electrons with a certain initial current can be continuously and stably multiplied in the channel under DC mode and eventually reach a stable value because of the space charge effect; additionally, the electron gain increases with the increase in the bias angle and DC bias voltage and decreases with the increase in the penetration depth of the MCP output electrode. The electron gain at the output end of the MCP increases with the length-to-diameter ratio under the normalized voltage but shows a maximum value under the constant voltage. The simulation results are consistent with the reported experimental trend and theoretical analyses. The method provides data support for the optimal structural design of the microchannel plate. [ABSTRACT FROM AUTHOR]

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Multipactor is a common discharge phenomenon occurring in space microwave systems. The surface microstructure has been verified to be effective in mitigating multipactor. In this work, we design a square coaxial low-pass filter (SCLPF) with dielectric sheets loaded to check the multipactor dependence on the structure parameters of the loaded dielectric sheets, and further model groove structures on the sensitive area surface to lower the risk of multipactor. Simulation results indicate that the SCLPF loaded with alumina and PTFE exhibits favorable operational characteristics, and the multipactor threshold is significantly improved after introducing the surface grooves. Then, we investigate the effects of three typical groove parameters, groove depth, groove number, and aspect ratio, on the multipactor threshold of the SCLPF device. The results show that the multipactor threshold rises at first as the groove number and groove depth increase, and then the threshold reaches a saturation status. For a deeper analysis of multipactor, we discuss how the grooves shelter the secondary electrons, and further mitigate the electron avalanche. Furthermore, the mechanisms of threshold saturation under the effect of groove parameters are analyzed in detail, and a contour map for the multipactor threshold of PTFE-loaded SCLPFs is given, which makes significant sense for predicting the multipactor threshold of the devices with its sensitive surface being grooved. The regularity of modulating the multipactor threshold by the groove structures obtained in this study is of engineering significance for suppressing multipactor in microwave devices in practical applications.

Under X-ray irradiation, a printed circuit board trace with a positive bias voltage within an electronic enclosure could generate a secondary electron collection effect. This effect is attributed to box internal electromagnetic pulses and can result in the collection of nearby secondary electrons outside the trace and generate a secondary electron current. A secondary electron collection effect model is established based on yield models of secondary and backscattered electrons as well as motion models of the primary, secondary, and backscattered electrons. Compared with the existing models, the results obtained through this model are more accurate. The results show that an increase in bias voltage and X-ray fluence could enhance the secondary electron current and an increase in X-ray fluence could significantly change the waveform of the current, which includes advancing the first peak time and delaying the maximum peak because of the space-charge-limited effect. The influence of a biased trace on an adjacent unbiased trace depends on the secondary electron collection distance. Moreover, if two adjacent traces have opposite bias voltages, the secondary electron current of the positively biased trace could be enhanced whereas that of the negatively biased trace could be weakened. [ABSTRACT FROM AUTHOR]

In this study, a three-dimensional microchannel model of a single hollow-core glass fiber was constructed and the Finite Integral Technique and Monte Carlo method were combined to comprehensively simulate the electron multiplication process in a single channel under DC mode. The electron dynamic trajectory in DC electron emission mode was achieved. The effects of different structural parameters and applied bias voltage on the electron gain and the most probable exit energy at the output end of MCP were investigated. The results show that the electrons with a certain initial current can be continuously and stably multiplied in the channel under DC mode and eventually reach a stable value because of the space charge effect; additionally, the electron gain increases with the increase in the bias angle and DC bias voltage and decreases with the increase in the penetration depth of the MCP output electrode. The electron gain at the output end of the MCP increases with the length-to-diameter ratio under the normalized voltage but shows a maximum value under the constant voltage. The simulation results are consistent with the reported experimental trend and theoretical analyses. The method provides data support for the optimal structural design of the microchannel plate.

This paper presents current research trends in advanced electron microscopy techniques for materials science. The survey is based on the special issue of Materials Transactions published in October 2019 (Vol. 60, No. 10). Advanced electron microscopy has been applied extensively to characterize various materials. The recent development and extension of analyses of electric fields and the collective motions of secondary electrons by in situ electron holography are discussed in detail. [ABSTRACT FROM AUTHOR]

We report direct observation by electron holography of the spin polarization of electrons in a vacuum region around a charged SiO2 wire coated with Pt-Pd. Irradiating the SiO2 wire with 300 keV electrons caused the wire to become positively charged due to the emission of secondary electrons. The spin polarization of these electrons interacting with the charged wire was observed in situ using a phase reconstruction process under an external magnetic field. The magnetic field of the spin-polarized electrons was simulated taking into account the distribution of secondary electrons and the effect of the external magnetic field., (© The Author(s) 2023. Published by Oxford University Press on behalf of The Japanese Society of Microscopy.)

Surface adsorption of N2 molecules is a critical factor to limit the reduction of secondary electron (SE) yield (SEY) in many fields of applied physics. On the basis of the Polanyi potential theory, we describe a multi-layer N2 physical adsorption model to arrange the distribution of N2 molecules adsorbed on a Cu (110) surface. Considering six scattering types, we used a Monte Carlo method to develop a three-dimensional numerical model that simulated the scattering processes between electrons and adsorbed molecules. Thus, the SEY of a surface covered by an adsorbed layer could be obtained by statistical analysis of the final SE states. We found that the maximum of total SEY decreased exponentially with increasing N2 pressure between 0 and 0.1 Torr and decreased linearly with increased adsorbed layer thickness between 0 and 10 nm. The reduction in SEY was due mainly to the elastic scattering of large scattering angle and ionization of energy consumption in the scattering processes of electrons and adsorbed molecules. Accordingly, our model and results provide a powerful tool to fully understand the microcosmic mechanism of the SE emission of a metal surface with adsorbed layer.

Determination of the thickness of a nanometer thin film is an important topic in the nanostructure characterization field. Currently, the X-ray photoelectron spectroscopy and the ellipsometer have been used to analyze the film thickness. This work proposes another thickness measurement method based on secondary electron (SE) and backscattered electron (BE) yields which are produced by an electron beam with a certain energy. Through comprehensively analyzing a lot of simulated data of the ratio of SE to BE yields at different primary energies and overlayer thicknesses for a variety of overlayer/substrate structures, a semiempirical formula was obtained for the film thickness determination (up to 5 nm). According to the formula, the film thickness can be obtained based on the measured ratio of SE to BE yields. A specific example shows a good agreement is reached between the simulated and experimental measurements in the case of the Be/Pt systems. [ABSTRACT FROM AUTHOR]

Focused ion beam (FIB) – scanning electron microscopy (SEM) serial sectioning tomography has become an important tool for three‐dimensional microstructure reconstruction of solid oxide fuel cells (SOFC) to obtain an understanding of fabrication‐related effects and SOFC performance. By sequential FIB milling and SEM imaging a stack of cross‐section images across all functional SOFC layers was generated covering a large volume of 3.5·104 μm3. One crucial step is image segmentation where regions with different image intensities are assigned to different material phases within the SOFC. To analyze all relevant SOFC materials, it was up to now mandatory to acquire several images by scanning the same region with different imaging parameters because sufficient material contrast could otherwise not be achieved. In this work we obtained high‐contast SEM images from a single scan to reconstract all functional SOFC layers consisting of a Ni/Y2O3‐doped ZrO2 (YDZ) cermet anode, YDZ electrolyte and (La,Sr)MnO3/YDZ cathode. This was possible by using different, simultaneous read‐out detectors installed in a state‐of‐the‐art scanning electron microscope. In addition, we used a deterministic approach for the optimization of imaging parameters by employing Monte Carlo simulations rather than trial‐and‐error tests. We also studied the effect of detection geometry, detecting angle range and detector type. [ABSTRACT FROM AUTHOR]

Purpose: Liquid water being the major constituent of the human body, is of fundamental importance in radiobiological research. Hence, the knowledge of electron‐water interaction physics and particularly the secondary electron yield is essential. However, to date, only very little is known experimentally on the low energy electron interaction with liquid water because of certain practical limitations. The purpose of this study was to gain some useful information about electron emission from water using a Monte Carlo (MC) simulation technique that can numerically model electron transport trajectories in water. Methods: In this study, we have performed MC simulations of electron emission from liquid water in the primary energy range of 50 eV–30 keV by using two different codes, i.e., a classical trajectory MC (CMC) code developed in our laboratory and the Geant4‐DNA (G4DNA) code. The calculated secondary electron yield and electron backscattering coefficient are compared with experimental results wherever applicable to verify the validity of physical models for the electron‐water interaction. Results: The secondary electron yield vs. primary energy curves calculated using the two codes present the same generic curve shape as that of metals but in rather different absolute values. G4DNA underestimates the secondary electron yield due to the application of one step thermalization model by setting a cutoff energy at 10 eV so that the low energy losses due to phonon excitations are omitted. Our CMC code, using a full energy loss spectrum to model electron inelastic scattering, allows the simulation of individual phonon scattering events for very low energy losses down to 10 meV, which then enables the calculated secondary electron yields much closer to the experimental data and also gives quite reasonable energy distribution curve of secondary electrons. Conclusions: It is concluded that full dielectric function data at low energy loss values below 10 eV are recommended for modeling of low energy electrons in liquid water. [ABSTRACT FROM AUTHOR]

With the development of industrial civilization, advanced manufacturing technology has attracted widespread concern, including in the aerospace industry. In this paper, we report the applications of ultra-thin atomic layer deposition nanofilm in the advanced aerospace manufacturing industry, including aluminum anti-oxidation and secondary electron suppression, which are critical in high-power and miniaturization development. The compact and uniform aluminum oxide film, which is formed by thermal atomic layer deposition (ALD), can prevent the deep surface oxidation of aluminum during storage, avoiding the waste of material and energy in repetitive production. The total secondary electron yield of the C/TiN component nanofilm, deposited through plasma-enhanced atomic layer deposition, decreases 25% compared with an uncoated surface. The suppression of secondary electron emission is of great importance in solving the multipactor for high-power microwave components in space. Moreover, the controllable, ultra-thin uniform composite nanofilm can be deposited directly on the complex surface of devices without any transfer process, which is critical for many different applications. The ALD nanofilm shows potential for promoting system performance and resource consumption in the advanced aerospace manufacturing industry.

Scanning/transmission electron microscopy (STEM) is a powerful characterization tool for a wide range of materials. Over the years, STEMs have been extensively used for in situ studies of structural evolution and dynamic processes. A limited number of STEM instruments are equipped with a secondary electron (SE) detector in addition to the conventional transmitted electron detectors, i.e. the bright-field (BF) and annular dark-field (ADF) detectors. Such instruments are capable of simultaneous BF-STEM, ADF-STEM and SE-STEM imaging. These methods can reveal the 'bulk' information from BF and ADF signals and the surface information from SE signals for materials <200 nm thick. This review first summarizes the field of in situ STEM research, followed by the generation of SE signals, SE-STEM instrumentation and applications of SE-STEM analysis. Combining with various in situ heating, gas reaction and mechanical testing stages based on microelectromechanical systems (MEMS), we show that simultaneous SE-STEM imaging has found applications in studying the dynamics and transient phenomena of surface reconstructions, exsolution of catalysts, lunar and planetary materials and mechanical properties of 2D thin films. Finally, we provide an outlook on the potential advancements in SE-STEM from the perspective of sample-related factors, instrument-related factors and data acquisition and processing., (© The Author(s) 2024. Published by Oxford University Press on behalf of The Japanese Society of Microscopy. All rights reserved. For commercial re-use, please contact reprints@oup.com for reprints and translation rights for reprints. All other permissions can be obtained through our RightsLink service via the Permissions link on the article page on our site–for further information please contact journals.permissions@oup.com.)

This article describes a neural network system for predicting the secondary electron yield of metallic materials. For bulk metals, experimental values are used as training data. Due to the strong correlation between the secondary electron yield and the work function, deep learning predicts the secondary electron yield with relatively high accuracy even with a small amount of training data. Our approach demonstrates the importance of the work function in predicting the secondary electron yield. For the secondary electron yield of thin metal films on metal substrates, deep learning predictions are generated using training data obtained by Monte Carlo simulations. The accuracy of the secondary yield predictions of thin films on substrates could be improved by adding experimental values of bulk metals to the training data., (© The Author(s) 2023. Published by Oxford University Press on behalf of The Japanese Society of Microscopy. All rights reserved. For permissions, please e-mail: journals.permissions@oup.com.)

We measured the yield of Auger electrons emitted through Coster–Kronig transitions from Rydberg states 1 s 2 p ( 3 P) nl (n = 7 , 8) and 1 s 2 2 p ( 2 P) nl (n = 5 , 6 , 7) of emergent atomic ions C q + under irradiation of 3.5-MeV/atom C+ and C 2 + ions on thin C foil targets. The Auger electron yields are suppressed for C 2 + irradiation compared with C+ irradiation and the relative yield becomes larger as n increases. Thus, amount of scattered electrons having lower relative energy in the projectile rest frame becomes larger. The results obtained in this study support the influence of projectile velocity on the cluster effect of secondary electron yields. [ABSTRACT FROM AUTHOR]

The main component of magnetically selected cesium frequency standard is electron multiplier. Its working principle is to magnify cesium beam signal by emitting secondary electron through surface of material. Magnesium oxide (MgO) has been adopted due to its excellent capability to emit secondary electron. There are many ways to prepare MgO thin film, including evaporation, pulsed laser deposition and MOCVD. It has been studied that doping can be used to enhance its emission capability and decrease its working potential of the thin film. In this paper, Ti-doped MgO thin films were deposited by magnetron sputtering method. Titanium metal and MgO ceramic were co-sputtered in oxygen containing argon ambient with DC and RF power source, respectively. XRD results show that the deposited film has the texture of (100) and (110) orientation. The ratio of Ti/Mg were consistent in XPS and EDS. SEM and AFM show that the film is polycrystalline. Electron multiplier device was assembled, and the secondary electron emission coefficient of the Ti-doped MgO film is greater than that of the undoped one, especially 36% higher at low primary electron energy of 200 eV which is meaningful to cesium atomic frequency standard. [ABSTRACT FROM AUTHOR]

Highlights • Simulations reveal relaxation of keV electrons in metals toward equilibrium. • Faster electrons cause less radiation damage in femtosecond XFEL experiments. • Significant amount of secondary electrons generated near the Fermi surface. • Demonstrates quantum H-theorem in nonequilibrium statistical mechanics. Abstract Collisional relaxation of high-energy primary electrons (PEs) and generation of secondary electrons (SEs) in a metal are simulated self-consistently by the quantum Boltzmann equation taking into account dynamic screening. An efficient scheme to evaluate the multi-dimensional integral in the collision term is introduced, which enables one to compute time evolutions of nonequilibrium energy distribution functions over an energy range up to a few keV until the whole system reaches thermal equilibrium. Numerical results reveal that rapid energy loss of PEs by plasmon excitation occurs in an early stage, followed by a cascade excitation of SEs near the Fermi level. The overall energy distribution eventually converges to the equilibrium Fermi distribution of partially degenerate electron gas, corroborating the quantum-mechanical H -theorem; time evolutions of the corresponding nonequilibrium entropies are also simulated. The electron temperature and total number of SEs in the final state are consistent with thermodynamic values predicted from the initial energy density of PEs. The number of SEs excited during an early stage (initial 10 fs) turns out smaller for higher PE energies; this feature would bear relevance to an estimation of transient radiation damage in a metallic sample irradiated by an intense femtosecond x-ray laser pulse. [ABSTRACT FROM AUTHOR]