keV Electron Irradiation Research Articles

10 keV electron irradiation of methane ices at ocean world surface temperatures

The surface environmental conditions of many of the icy ocean worlds in the Solar System are outside of the thermal stability field of methane ice. However, mechanisms may exist that entrain or trap methane within water ice that arrives at the surface via plume eruptions or resurfacing events. At the surface, the ice grains may experience charged particle irradiation that could lead to the production of new complex hydrocarbons. We investigated the irradiation products of 12CH4 versus 13CH4, the temperature dependence of CH4 radiation processing and product stability, and the temperature stability of CH4 when mixed with H2O in a cryogenic vacuum environment. Significantly, methane ice experimentally encased in water ice was irradiated at 100 K in an ultra-high vacuum environment and produced similar radiation-formed secondary phases as pure methane ice irradiated at 20 K. The methane radiation products produced outside of the methane ice thermal stability field, while encased in a water ice film, were most notably 13CO2 and a candidate hydrocarbon feature. Evidence for complex hydrocarbons, such as C2H6, was observed during warming and sublimation of the sample.

Effect of electron irradiation on perovskite films and devices for novel space solar cells

Perovskite solar cells (PSCs) are considered as one of the strong contenders for next-generation space solar cells due to their advantages of high efficiency, low cost, high specific power, and remarkable irradiation resistance compared with those of silicon-based and III-V compound solar cells. At present, one focuses on the irradiation effects of perovskite solar cells, but there are a few studies on the irradiation damage mechanism of the core perovskite film. To advance the spatial application of perovskite solar cells, this study conducts a comprehensive examination of the performance fluctuations exhibited by mixed-cation perovskite films and solar cells under electron irradiation. Initially, the Monte Carlo method is employed to simulate and predict the effect of electron irradiation on perovskite solar cells. Subsequently, in conjunction with the microstructure characterization and the comparison of optical/electrical performance of perovskite films before and after irradiation, the irradiation damage mechanism of film is elucidated and the electron irradiation reliability of perovskite solar cells is evaluated. The research demonstrates that mixed-cation perovskite film and solar cells exhibit outstanding resistance to electron irradiation. Even when exposed to 100 keV electron irradiation with a cumulative fluence of 5×10<sup>15</sup> e·cm<sup>–2</sup>, the PSCs maintain an average power conversion efficiency of 17.29%, retaining approximately 85% of their initial efficiency. This study provides sound theoretical and experimental evidence for designing the irradiation-resistant reinforcement of new-generation space solar cells, contributing to the improvement of their operational performance and reliability in space applications.

Calculation of Precision Measure and Effect of the Sample Crystallographic Orientation on the Charge Kinetics of MgO Single Crystals Subjected to keV Electron Irradiation

Calculation of Precision Measure and Effect of the Sample Crystallographic Orientation on the Charge Kinetics of MgO Single Crystals Subjected to keV Electron Irradiation

Comparing the radiolytic oxidation of sulfur and chloride within ice on Europa and Mars

The surface of Europa is heavily irradiated by high-energy particles with the energy ranges of 1–100 MeV for primary electrons and ∼10 keV for secondary electrons. These irradiations may cause oxidation of surface materials, such as chlorides and sulfur-bearing species, through reactions with oxidative radicals formed by dissociation of H2O ice. Similar irradiation-induced oxidation could have occurred in near-surface ice on Mars. However, most of previous experiments simulated ∼10 keV electron irradiation onto ice materials on Europa and Mars, and few studies have investigated the oxidation of chlorides and sulfur by MeV electron irradiation. Here we performed laboratory experiments on MeV electron irradiation, as well as 10 keV electron and UV irradiations, onto mixtures of H2O ice and chlorides, or elemental sulfur, at low temperatures. Our experimental results indicate selective oxidation of sulfur against chlorides, with negligible formation of oxychlorides on irradiation of H2O ice and chloride mixtures, regardless of experimental conditions (temperature, electron energy, or presence of oxidants in ice). Sulfate is effectively formed by the electron irradiation. This selective oxidation may be caused by the different stabilities of atoms within irradiated H2O ice. If sulfate on Europa's surface is transported into the subsurface ocean, this could provide energy sources for possible chemoautotrophic life in the ocean. On Europa, sulfur would be one of key elements in redox chemistry on the surface and possibly in the subsurface ocean.

Solute atom mediated crystallization of amorphous alloys

We propose a new mechanism of crystallization of amorphous alloy which is mediated by additional solute atoms produced by electronic excitation. For a freestanding Pd-19at%Si amorphous alloy film, electron irradiation causes subtle structural change. By contrast, extensive crystallization of Pd-19at%Si amorphous alloy sandwiched by amorphous (a-) SiOx films, i.e., a-SiOx/a-Pd-Si/a-SiOx, occurred by 75 keV and 200 keV electron irradiation. This crystallization was induced by irradiation not only at room temperature but also even at 90 K. It should be emphasized that the crystallization can be realized by 75 keV irradiation at 90 K via the electronic excitation; where both knock-on damage and a possible thermal crystallization can be excluded. A resultant product of the crystallization after electronic excitation (i.e., electron irradiation), hexagonal Pd2Si, differs from that of thermal annealing (orthorhombic Pd3Si). Evidence for decomposition of a-SiOx by electronic excitation contributes essentially to the crystallization of the a-Pd-Si in the composite film has been obtained in this study. Supply of dissociated Si to the a-Pd-Si layer may cause instability of the amorphous phase, which serves as the trigger for the remarkable structural change; i.e., additional solute atom mediated crystallization.

Operability timescale of defect-engineered graphene

Defects in the lattice are of primal importance to tune graphene chemical, thermal and electronic properties. Electron-beam irradiation is an easy method to induce defects in graphene following pre-designed patterns, but no systematic study of the time evolution of the resulting defects is available. In this paper, the change over time of defected sites created in graphene with low-energy (≤20 keV) electron irradiation is studied both experimentally via micro-Raman spectroscopy for a period of 6×103 h and through molecular dynamics simulations. During the first 10 h, the structural defects are stable at the highest density value. Subsequently, the crystal partially reconstructs, eventually reaching a stable, less defected condition after more than one month. The simulations allow the rationalization of the processes at the atomic level and confirm that the irradiation induces composite clusters of defects of different nature rather than well-defined nanoholes as in the case of high-energy electrons. The presented results identify the timescale of the defects stability, thus establishing the operability timespan of engineerable defect-rich graphene devices with applications in nanoelectronics. Moreover, long-lasting chemical reactivity of the defective graphene is pointed out. This property can be exploited to functionalize graphene for sensing and energy storage applications.

Arc Formation on Solar Array Surfaces Under Energetic Electron Irradiation and Vacuum Exposure

The harsh space environment induces local discharges (arcs) on satellite solar panels, which can cause reduced optical transmission through solar array coverglasses, thus negatively affecting long-term satellite missions. This article presents the experimental results of low-energy (4–5 keV) electron irradiation of three common types of space solar array coverglass, CMX, CMG, and fused silica at various bias voltages. The dependence of the discharge rate on the bias voltage, coverglass composition, energy of the incident electrons, vacuum exposure, and surface conductivity was investigated. It is shown that the arc frequency is inversely related to the incident electron energy. Physicochemical models of the mechanisms occurring in different types of space array coverglasses under low-energy electron irradiation are proposed to explain the experimental findings.

In Situ Time-of-Flight Mass Spectrometry of Ionic Fragments Induced by Focused Electron Beam Irradiation: Investigation of Electron Driven Surface Chemistry inside an SEM under High Vacuum.

Recent developments in nanoprinting using focused electron beams have created a need to develop analysis methods for the products of electron-induced fragmentation of different metalorganic compounds. The original approach used here is termed focused-electron-beam-induced mass spectrometry (FEBiMS). FEBiMS enables the investigation of the fragmentation of electron-sensitive materials during irradiation within the typical primary electron beam energy range of a scanning electron microscope (0.5 to 30 keV) and high vacuum range. The method combines a typical scanning electron microscope with an ion-extractor-coupled mass spectrometer setup collecting the charged fragments generated by the focused electron beam when impinging on the substrate material. The FEBiMS of fragments obtained during 10 keV electron irradiation of grains of silver and copper carboxylates and shows that the carboxylate ligand dissociates into many smaller volatile fragments. Furthermore, in situ FEBiMS was performed on carbonyls of ruthenium (solid) and during electron-beam-induced deposition, using tungsten carbonyl (inserted via a gas injection system). Loss of carbonyl ligands was identified as the main channel of dissociation for electron irradiation of these carbonyl compounds. The presented results clearly indicate that FEBiMS analysis can be expanded to organic, inorganic, and metal organic materials used in resist lithography, ice (cryo-)lithography, and focused-electron-beam-induced deposition and becomes, thus, a valuable versatile analysis tool to study both fundamental and process parameters in these nanotechnology fields.

Damage effects and mechanism of electron irradiation on flexible solar cell coverglass-pseudomorphic glass

Flexibility, light weight and high reliability are the development themes of space solar cells. Pseudomorphic Glass (PMG) is considered as a novel feasible flexible encapsulation solution for solar cells. In this paper, the degeneration and damage mechanism of PMG morphology, optical and mechanical properties under 170 keV electron irradiation were studied. The change of PMG surface wrinkles structure under the fluence of 1 × 1013 cm−2 to 1 × 1016 cm−2 was observed by Scanning Electron Microscope (SEM). After electron irradiation, the defect optical absorption peak intensity of PMG was significantly lower than that of room-temperature-vulcanized silicon rubber (RTV) sheet, showing obviously excellent electron irradiation stability. The transmittance of PMG at the wavelength greater than 500 nm increased significantly while the RTV sheet remained unchanged when the fluence reached 1 × 1016 cm−2, which was mainly caused by the decrease of scattering loss at the bead-adhesive interface. Fourier transform infrared spectroscopy (FT-IR) and X-ray photoelectron spectroscopy (XPS) indicated that “organic silicon” was transformed into “inorganic silicon” and Si–OH groups were formed during electron irradiation. Furthermore, the stress-strain test showed that the elongation at break (Eb) decreased from 113% to 9% and the modulus of elasticity increased from 2.5 MPa to 9 MPa.

Beam-driven dynamics of aluminium dopants in graphene

Substituting heteroatoms into graphene can tune its properties for applications ranging from catalysis to spintronics. The further recent discovery that covalent impurities in graphene can be manipulated at atomic precision using a focused electron beam may open avenues towards sub-nanometer device architectures. However, the preparation of clean samples with a high density of dopants is still very challenging. Here, we report vacancy-mediated substitution of aluminium into laser-cleaned graphene, and without removal from our ultra-high vacuum apparatus, study their dynamics under 60 keV electron irradiation using aberration-corrected scanning transmission electron microscopy and spectroscopy. Three- and four-coordinated Al sites are identified, showing excellent agreement with ab initio predictions including binding energies and electron energy loss spectrum simulations. We show that the direct exchange of carbon and aluminium atoms predicted earlier occurs under electron irradiation, although unexpectedly it is less probable than the same process for silicon. We also observe a previously unknown nitrogen–aluminium exchange that occurs at Al–N double-dopant sites at graphene divacancies created by our plasma treatment.

Radiation stability of optical properties of Wollastonite powder with SiO2 nanoparticle addition

We studied the phase composition, diffuse reflectance spectra (ρλ), and integral absorption coefficient (аs) and their variations after a 30 keV electron irradiation of wollastonite powder with added silicon dioxide nanoparticles.It was found that after heating and nanoparticle addition, the reflectivity of wollastonite decreases in the UV and visible ranges, and increases in the near-IR range. The addition of 0.5 and 1 wt% SiO2 nanoparticles increases the radiation stability of the wollastonite powder by 255 and 233%, respectively.Such nanoparticle-micro powder systems can be used in high-performance spacecraft thermal control coatings and other applications where optical properties should be resistant to radiation.

O2 Loaded Germanosilicate Optical Fibers: Experimental In Situ Investigation and Ab Initio Simulation Study of GLPC Evolution under Irradiation

In this work we present a combined experimental and ab initio simulation investigation concerning the Germanium Lone Pair Center (GLPC), its interaction with molecular oxygen (O2), and evolution under irradiation. First, O2 loading has been applied here to Ge-doped optical fibers to reduce the concentration of GLPC point defects. Next, by means of cathodoluminescence in situ experiments, we found evidence that the 10 keV electron irradiation of the treated optical fibers induces the generation of GLPC centers, while in nonloaded optical fibers, the irradiation causes the bleaching of the pre-existing GLPC. Ab initio calculations were performed to investigate the reaction of the GLPC with molecular oxygen. Such investigations suggested the stability of the dioxagermirane (DIOG) bulk defect, and its back conversion into GLPC with a local release of O2 under irradiation. Furthermore, it is also inferred that a remarkable portion of the O2 passivated GLPC may form Ge tetrahedra connected to peroxy bridges. Such structures may have a larger resistance to the irradiation and not be back converted into GLPC.

Modelling energy deposition in polymethyl methacrylate with low-energy electron irradiation

Energy deposition in dielectric materials by electron irradiation is important in evaluating irradiation effects in various applications. Herein, we developed a novel Monte Carlo model to calculate the actual distribution of energy deposition in polymethyl methacrylate (PMMA) by simulating low-energy electron transport, including secondary electron cascades. We compared the energy deposition calculated using this model with the distribution of energy loss based on the continuous slowing down approximation (CSDA). The difference in depth distribution between energy deposition and energy loss near the surface is attributed to the secondary electron emission. The characteristics of energy deposition distributions at various incident angles and primary energy were analysed. Energy depositions based on different energy loss mechanisms were classified. Approximately half of the total energy deposition was formed in paths of the secondary cascade at keV-electron irradiation. The temporal properties of energy deposition show that the fast process of energy deposition occurs first near the surface of the dielectric material, then deep inside and 1-keV electrons deposit their energy in 10−14 s.

Mid-IR and VUV spectroscopic characterisation of thermally processed and electron irradiated CO2 astrophysical ice analogues

The astrochemistry of CO2 ice analogues has been a topic of intensive investigation due to the prevalence of CO2 throughout the interstellar medium and the Solar System, as well as the possibility of it acting as a carbon feedstock for the synthesis of larger, more complex organic molecules. In order to accurately discern the physico-chemical processes in which CO2 plays a role, it is necessary to have laboratory-generated spectra to compare against observational data acquired by ground- and space-based telescopes. A key factor which is known to influence the appearance of such spectra is temperature, especially when the spectra are acquired in the infrared and ultraviolet. In this present study, we describe the results of a systematic investigation looking into: (i) the influence of thermal annealing on the mid-IR and VUV absorption spectra of pure, unirradiated CO2 astrophysical ice analogues prepared at various temperatures, and (ii) the influence of temperature on the chemical products of electron irradiation of similar ices. Our results indicate that both mid-IR and VUV spectra of pure CO2 ices are sensitive to the structural and chemical changes induced by thermal annealing. Furthermore, using mid-IR spectroscopy, we have successfully identified the production of radiolytic daughter molecules as a result of 1 keV electron irradiation and the influence of temperature over this chemistry. Such results are directly applicable to studies on the chemistry of interstellar ices, comets, and icy lunar objects and may also be useful as reference data for forthcoming observational missions.

Efficient neutralization of core ionized species in an aqueous environment.

Core ionization dynamics of argon-water heteroclusters ArM[H2O]N are investigated using a site and process selective experimental scheme combining 3 keV electron irradiation with Auger electron-ion-ion multi-coincidence detection. The formation of Ar 2p-1 vacancies followed by non-radiative decay to intermediate one-site doubly ionized states Ar2+(3p-2)-ArM-1[H2O]N and subsequent redistribution of charge to the cluster environment are monitored. At low argon concentrations the emission of an [H2O]n'H+/[H2O]n''H+ ion pair is the dominant outcome, implying on high efficiency of charge transfer to the water network. Increasing the condensation fraction of argon in the mixed clusters and/or to pure argon clusters is reflected as a growing yield of Arm'+/Arm''+ ion pairs, providing a fingerprint of the precursor heterocluster beam composition. The coincident Auger electron spectra, resolved with better than 1 eV resolution, show only subtle differences and thereby reflect the local nature of the initial Auger decay step. The results lead to better understanding of inner shell ionization processes in heterogeneous clusters and in aqueous environments in general.

Ozone production in electron irradiated CO2:O2 ices.

The detection of ozone (O3) in the surface ices of Ganymede, Jupiter's largest moon, and of the Saturnian moons Rhea and Dione, has motivated several studies on the route of formation of this species. Previous studies have successfully quantified trends in the production of O3 as a result of the irradiation of pure molecular ices using ultraviolet photons and charged particles (i.e., ions and electrons), such as the abundances of O3 formed after irradiation at different temperatures or using different charged particles. In this study, we extend such results by quantifying the abundance of O3 as a result of the 1 keV electron irradiation of a series of 14 stoichiometrically distinct CO2:O2 astrophysical ice analogues at 20 K. By using mid-infrared spectroscopy as our primary analytical tool, we have also been able to perform a spectral analysis of the asymmetric stretching mode of solid O3 and the variation in its observed shape and profile among the investigated ice mixtures. Our results are important in the context of better understanding the surface composition and chemistry of icy outer Solar System objects, and may thus be of use to future interplanetary space missions such as the ESA Jupiter Icy Moons Explorer and the NASA Europa Clipper missions, as well as the recently launched NASA James Webb Space Telescope.

Radiation Hardness of Si Compared to 4H-SiC for Betavoltaics Assessed by Accelerated Aging Using an Electron Beam System

With the advancement of three-dimensional electronic technologies, 3D betavoltaics consisting of a mixture of a semiconductor converter and a beta emitter have been investigated to increase output power by maximizing the beta absorption in the semiconductor. Semiconductor radiation robustness has typically been evaluated by monitoring electrical properties during the beta irradiation process over a long dwell time. To quickly and safely assess semiconductor candidates for betavoltaics without incorporating high-activity beta emitters, a custom-designed electron beam system as a beta source surrogate has been used. In this work, we report the change of electrical performance of planar 4H-SiC, planar Si, and 3D Si ridge p-i-n diodes irradiated by high-flux and high-fluence electrons. The 4H-SiC diodes were found to suffer 45% degradation to output power with 100 keV electron irradiation at a fluence of 1.3 × 1018 cm−2; however, the Si diodes showed no decrease in performance at the highest fluence of 100 keV electron irradiation of 7 × 1018 cm−2. This demonstrates that Si is more radiation hard than 4H-SiC for 147Pm-based betavoltaics, with an average beta energy of 62 keV.

Athermal Solid Phase Reaction in Pt/SiO x Thin Films Induced by Electron Irradiation.

Microelectronics based on Si requires metal silicide contacts. The ability to form platinum silicide (Pt2Si) by electronic excitation instead of thermal processes would benefit the field. We studied the effects of electron irradiation on Pt2Si formation in composite films—composed of Pt and amorphous silicon oxides (a-SiOx)—by transmission electron microscopy and electron diffraction. Pt2Si formed in Pt/a-SiOx bilayer and a-SiOx/Pt/a-SiOx sandwiched films by 75 keV electron irradiation, at 298 and 90 K. The reaction is attributable to dissociation of SiOx triggered by electronic excitation. In a-SiOx/Pt/a-SiOx sandwiched films, reflections of pure Pt were not present after irradiation, i.e., Pt was completely consumed in the reaction to form Pt2Si at 298 K. However, in Pt/a-SiOx bilayer films, unreacted Pt remained under the same irradiation conditions. Thus, it can be said that the extent of the interfacial area is the predominant factor in Pt2Si formation. The morphology of Pt islands extensively changed during Pt2Si formation even at 90 K. Coalescence and growth of metallic particles (Pt and Pt–Si) are not due to thermal effects during electron irradiation but to athermal processes accompanied by silicide formation. To maintain the reaction interface between metallic particles and the dissociation product (i.e., Si atoms) by electronic excitation, a considerable concomitant morphology change occurs. Elemental analysis indicates that the decrease in Si concentration near Pt is faster than the decrease in O concentration, suggesting formation of a Si depletion zone in the amorphous silicon oxide matrix associated with formation of Pt2Si.

Phase Transformation by 100 keV Electron Irradiation in Partially Stabilized Zirconia

Partially stabilized zirconia (PSZ) is considered for use as an oxygen-sensor material in liquid lead-bismuth eutectic (LBE) alloys in the radiation environment of an acceleration-driven system (ADS). To predict its lifetime for operating in an ADS, the effects of radiation on the PSZ were clarified in this study. A tetragonal PSZ was irradiated with 100 keV electrons and analyzed by X-ray diffraction (XRD). The results indicate that the phase transition in the PSZ, from the tetragonal to the monoclinic phase, was caused after the irradiation. The deposition energy of the lattice and the deposition energy for the displacement damage of a 100 keV electron in the PSZ are estimated using the particle and heavy ion transport code system and the non-ionizing energy loss, respectively. The results suggest that conventional radiation effects, such as stopping power, are not the main mechanism behind the phase transition. The phase transition is known to be caused by the low-temperature degradation of the PSZ and is attributed to the shift of oxygen ions to oxygen sites. When the electron beam is incident to the material, the kinetic energy deposition and excitation-related processes are caused, and it is suggested to be a factor of the phase transition.

Transformation of SiO2 to amorphous silicon caused by high-energy electrons

In order to study the effect of high-energy electrons on the structure of SiO2 film for gate dielectric. A kind of complex structure SiO2 film was irradiated under 1 MeV electron irradiation with different fluences. The changes in composition, microstructure and phase distribution of the SiO2 film surface induced by the 1 MeV electrons were characterized by Raman scattering spectroscopy (Raman), transmission electron microscopy (TEM) and X-ray photoelectron spectroscopy (XPS). The Raman scattering and TEM results show that the amorphous silicon (α-Si) is formed on the surface of the SiO2 film after 1 MeV electron irradiation. However, the amorphous silicon does not appear after 90 keV electron irradiations. Based on the comparison for different energy electrons, it can be believed that the formation of amorphous silicon is attributed to the displacement of oxygen atoms as s result of 1 MeV electron irradiation. In addition, XPS analyses show that the double-oxygen ions are formed in the surface layer of the SiO2 film after the irradiation.