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Accelerating electrons to achieve chemical and biological effects is a well-established competence of Fraunhofer FEP. Today, there is a large variety of low-energy electron beam applications with a broad range of absorbed doses, e.g. modification of plastics, plasma-chemical syntheses, pollutant removal in wastewaters and exhaust gases, sterilization of medical products, disinfection of seeds, biocompatible functionalization of implants and stimulation of biotechnological processes. This calls for reliable, sensitive, and flexible methods for dosimetry. Radiochromic films are suitable tools to measure electron dose distributions for the characterization and quality control of Fraunhofer FEP’s irradiation facilities. Risø B3 radiochromic film from DTU Health Tech, the dosimeter of choice at FEP, reliably detects doses in the range of 10–100 kGy. However, with new upcoming applications, doses in the single-digit kGy range and even lower come to the fore. Hence, the palette of dosimeters at FEP must be extended. Gafchromic’s HD-V2 film is a welcome complement and widens the accessible dose range down to 10 Gy. Using a UV-VIS spectrophotometer for read-out of the films and custom analysis algorithms further increase the sensitivity of the dosimetric setup. Additionally, dosimeters based on the optically stimulated luminescence (OSL) of beryllium oxide offer a wide dose range and high sensitivity. They were used to measure doses induced by secondary X-ray components to gain more information about a specific radiation field. The work gives an overview of the dosimetric toolbox at Fraunhofer FEP and the efforts to implement new methods of detection for low-dose applications and X-ray dosimetry.

In recent years, the use of low-energy electrons in various ecological and biotechnological applications has become increasingly relevant. One important application is the treatment of wastewater, wherein highly reactive species produced by water irradiation are used to oxidize pollutants. Low-energy electron irradiation has several advantages, such as minimal demands on radiation protection and electron beam (EB) source dimensions. However, to play into the main advantages of this technology and keep it economically viable, it is necessary to keep the absorbed dose as low as possible. This calls for a liquid dosimeter with sensitivity in the single digit kGy range. An extract from natural Hibiscus sabdariffa (Roselle) has been reported to show a radiochromic effect in this dose range. In the present work, Roselle dosimeter solutions were closely investigated and optimized to characterize a new module for EB wastewater treatment. Upon EB irradiation, the dosimeter solution demonstrated a dose-dependent fading in color, making it useful in the 0.3–7.5 kGy dose range.

Proceeding from the Boltzmann kinetic equation for electrons, the system of multigroup equations for the zero and first moments of the distribution function of low-energy electrons is derived within the Lorentz approximation. The system includes the balance equations for concentration and flux density of electrons and is intended for numerical simulation of the transport and kinetics of electrons in the energy range from zero to several tens of electron volt where the angular distribution of electrons is weakly anisotropic. Results of the numerical calculations of electron transport in helium in homogeneous and inhomogeneous electric fields according to the developed multigroup model are compared with results obtained by the Monte Carlo method. [ABSTRACT FROM AUTHOR]

The lowest single and doubly excited autoionizing states of neon have been studied using a non-monochromatic electron beam and a high-resolution electrostatic analyzer at incident electron energies from 43.37 to 202 (±0.4) eV at three ejection angles, 40°, 90° and 130°. The 2s2p63s(3,1S) and 2s2p63p(3,1P) as well as the 2p43s3p doubly excited states have been observed and their energy determined. The influence of the PCI effect in the energy region of the 2s2p63s(3,1S) states has been investigated. New features in the ejected electron spectra in the low kinetic energy region 3–20 eV at 202 eV incident energy have been observed and assigned. [ABSTRACT FROM AUTHOR]

Motivated by the potential of focused-electron-beam-induced deposition (FEBID) in the fabrication of functional gold nanostructures for application in plasmonic and detector technology, we conducted a comprehensive study on [Au(CH3)2Cl]2 as a potential precursor for such depositions. Fundamental electron-induced dissociation processes were studied under single collision conditions, and the composition and morphology of FEBID deposits fabricated in an ultrahigh-vacuum (UHV) chamber were explored on different surfaces and at varied beam currents. In the gas phase, dissociative ionization was found to lead to significant carbon loss from this precursor, and about 50% of the chlorine was on average removed per dissociative ionization incident. On the other hand, in dissociative electron attachment, no chlorine was removed from the parent molecule. Contrary to these observations, FEBID in the UHV setup was found to yield a quantitative loss and desorption of the chlorine from the deposits, an effect that we attribute to electron-induced secondary and tertiary reactions in the deposition process. We find this precursor to be stable at ambient conditions and to have sufficient vapor pressure to be suitable for use in HV instruments. More importantly, in the UHV setup, FEBID with [Au(CH3)2Cl]2 yielded deposits with high gold content, ranging from 45 to 61 atom % depending on the beam current and on the cleanliness of the substrates surface.

Technological advancement has produced a variety of instruments and methods to generate electron beams that have greatly assisted in the extensive theoretical and experimental efforts devoted to investigating the effect of secondary electrons with energies approximately less than 100 eV, which are referred as low-energy electrons (LEEs). In the past two decades, LEE studies have focused on biomolecular systems, which mainly consist of DNA and proteins and their constituents as primary cellular targets of ionizing radiation. These studies have revealed that compared to other reactive species produced by high-energy radiation, LEEs have distinctive pathways and considerable efficiency in inducing lethal DNA lesions. The present work aims to briefly discuss the current state of LEE production technology and to motivate further studies and improvements of LEE generation techniques in relation to biological electron-driven processes associated with such medical applications as radiation therapy and cancer treatment.

The estimate of the total electron yield is fundamental for our understanding of the test-mass charging associated with cosmic rays in the Laser Interferometer Space Antenna (LISA) Pathfinder mission and in the forthcoming gravitational wave observatory LISA. To unveil the role of low energy electrons in this process owing to galactic and solar energetic particle events, in this work we study the interaction of keV and sub-keV electrons with a gold slab using a mixed Monte Carlo (MC) and ab-initio framework. We determine the energy spectrum of the electrons emerging from such a gold slab hit by a primary electron beam by considering the relevant energy loss mechanisms as well as the elastic scattering events. We also show that our results are consistent with experimental data and MC simulations carried out with the GEANT4-DNA toolkit. [ABSTRACT FROM AUTHOR]

The lowest single and doubly excited autoionizing states of neon have been studied using a non-monochromatic electron beam and a high-resolution electrostatic analyzer at incident electron energies from 43.37 to 202 (±0.4) eV at three ejection angles, 40°, 90° and 130°. The 2s2p63s(3,1S) and 2s2p63p(3,1P) as well as the 2p43s3p doubly excited states have been observed and their energy determined. The influence of the PCI effect in the energy region of the 2s2p63s(3,1S) states has been investigated. New features in the ejected electron spectra in the low kinetic energy region 3–20 eV at 202 eV incident energy have been observed and assigned.

Metal nanoparticles are considered as highly promising radiosensitizers in cancer radiotherapy. Understanding their radiosensitization mechanisms is critical for future clinical applications. This review is focused on the initial energy deposition by short-range Auger electrons; when high energy radiation is absorbed by gold nanoparticles (GNPs) located near vital biomolecules; such as DNA. Auger electrons and the subsequent production of secondary low energy electrons (LEEs) are responsible for most the ensuing chemical damage near such molecules. We highlight recent progress on DNA damage induced by the LEEs produced abundantly within about 100 nanometers from irradiated GNPs; and by those emitted by high energy electrons and X-rays incident on metal surfaces under differing atmospheric environments. LEEs strongly react within cells; mainly via bound breaking processes due to transient anion formation and dissociative electron attachment. The enhancement of damages induced in plasmid DNA by LEEs; with or without the binding of chemotherapeutic drugs; are explained by the fundamental mechanisms of LEE interactions with simple molecules and specific sites on nucleotides. We address the major challenge of metal nanoparticle and GNP radiosensitization; i.e., to deliver the maximum local dose of radiation to the most sensitive target of cancer cells (i.e., DNA). To achieve this goal the emitted electrons from the absorbed high energy radiation must be short range, and produce a large local density of LEEs, and the initial radiation must have the highest possible absorption coefficient compared to that of soft tissue (e.g., 20–80 keV X-rays). [ABSTRACT FROM AUTHOR]

Technological advancement has produced a variety of instruments and methods to generate electron beams that have greatly assisted in the extensive theoretical and experimental efforts devoted to investigating the effect of secondary electrons with energies approximately less than 100 eV, which are referred as low-energy electrons (LEEs). In the past two decades, LEE studies have focused on biomolecular systems, which mainly consist of DNA and proteins and their constituents as primary cellular targets of ionizing radiation. These studies have revealed that compared to other reactive species produced by high-energy radiation, LEEs have distinctive pathways and considerable efficiency in inducing lethal DNA lesions. The present work aims to briefly discuss the current state of LEE production technology and to motivate further studies and improvements of LEE generation techniques in relation to biological electron-driven processes associated with such medical applications as radiation therapy and cancer treatment. [ABSTRACT FROM AUTHOR]

Focused-electron-beam-induced deposition (FEBID) is a powerful nanopatterning technique where electrons trigger the local dissociation of precursor molecules, leaving a deposit of non-volatile dissociation products. The fabrication of high-purity gold deposits via FEBID has significant potential to expand the scope of this method. For this, gold precursors that are stable under ambient conditions but fragment selectively under electron exposure are essential. Here, we investigated the potential gold precursor (CH3)AuP(CH3)3 using FEBID under ultra-high vacuum (UHV) and spectroscopic characterization of the corresponding metal-containing deposits. For a detailed insight into electron-induced fragmentation, the deposit's composition was compared with the fragmentation pathways of this compound through dissociative ionization (DI) under single-collision conditions using quantum chemical calculations to aid the interpretation of these data. Further comparison was made with a previous high-vacuum (HV) FEBID study of this precursor. The average loss of about 2 carbon and 0.8 phosphor per incident was found in DI, which agreed well with the carbon content of the UHV FEBID deposits. However, the UHV deposits were found to be as good as free of phosphor, indicating that the trimethyl phosphate is a good leaving group. Differently, the HV FEBID experiments showed significant phosphor content in the deposits. [ABSTRACT FROM AUTHOR]

Five monolayer plasmid DNA films were irradiated by low-energy electrons (LEEs) (1~20 eV) in ultra-high vacuum. Crosslinks, single-strand breaks, double-strand breaks and the loss of the supercoiled configuration were analyzed via agarose gel electrophoresis. Base damages were revealed by Escherichia coli base excision and repair endonucleases (Nth and Fpg). The electron energy dependence for the effective yields of various DNA damages showed that no clustered damage within 20 base pairs could be caused by electrons

Due to the increase in the survival probability for patients treated with modern radiotherapy techniques to live enough for experimenting the late radiation effect, low dose outside the treatment volume becomes a concern. However, besides the absorbed dose, the beam quality outside the field edge should be taken into account. This work aimed at investigating the photon and electron fluence spectra outside the field edges for several small radiotherapy fields for determining the quality of the beams in order to better evaluate the secondary effect after modern radiotherapy treatments. Phase-space files of a 6 MV X-ray beam produced by a Varian iX linac for eight small fields of 0.7 × 0.7 cm2, 0.9 × 0.9 cm2, 1.8 × 1.8 cm2, 2.2 × 2.2 cm2, 2.7 × 2.7 cm2, 3.1 × 3.1 cm2, 3.6 × 3.6 cm2, and 4.5 × 4.5 cm2 and for the reference 10 × 10 cm2 field at SSD = 100 cm were generated using the BEAMnrc code. The photon and electron fluences in each field were calculated at 0.15, 1.35, and 9.85 cm water depth and several off-axis distances using FLURZnrc. The number of low-energy electrons between 1 and 10 keV at 2 cm outside the field edge increases by 60% compared to the central axis. Due to the relatively high linear energy transfer (LET) of these electrons, the results of this work should help to better evaluate the possible late effect of secondary radiation on healthy organs close to the tumor volume after radiotherapy treatment. We also observed high-energy electrons outside the field edge that are attributed to the leakage of the primary electron beam from the head of the linac. From a standpoint of radiological protection, these electrons should be taken into account when evaluating the dose delivered to the patient’s skin.

• Stopping power for low-energy electrons is calculated. • The Full Penn Algorithm has been followed. • Band gap and exciton states have been considered. • Good agreement is obtained in the limit where the Bethe Approximation is valid. Stopping powers (SP) for electrons with energies greater than 10 keV are well described through the Bethe approximation. However, for energies below, such an approach is inadequate. SP in LiF, CaF 2 and Al 2 O 3 as the luminescent materials commonly used for dosimetry study and liquid-water are scarce at energies below 10 keV. This work investigated SP and CSDA-range of electrons in in these compounds from the energy gap up to 433 keV using the full Penn algorithm. In particular, the influence of the exciton states was evaluated. The experimental optical data were selected after a rigorous evaluation process. The results indicate that the exciton states affect the SP mainly at energies below 100 eV by up to 48%, 39%, 32% and 15% for liquid-water, LiF, CaF 2 and Al 2 O 3 , respectively. Furthermore, we observed a certain relationship between the minimum excitation-energy (exciton state) and the energy at which the SP is maximum. [ABSTRACT FROM AUTHOR]

Although reactive oxygen species (ROS)‐mediated tumor treatments are predominant in clinical applications, ROS‐induced protective autophagy promotes cell survival, especially in hypoxic tumors. Herein, X‐ray triggered nitrite (NO2−) is used for hypoxic prostate cancer therapy by inhibiting autophagy and inducing nitrosative stress based on an electrophilic zeolitic imidazole framework (ZIF‐82‐PVP). After internalization of pH‐responsive ZIF‐82‐PVP nanoparticles, electrophilic ligands and Zn2+ are delivered into cancer cells. Electrophilic ligands can not only consume GSH under hypoxia but also capture low‐energy electrons derived from X‐rays to generate NO2−, which inhibits autophagy and further elevates lethal nitrosative stress levels. In addition, dissociated Zn2+ specifically limits the migration and invasion of prostate cancer cells through ion interference. In vitro and in vivo results indicate that ZIF‐82‐PVP nanoparticles under X‐ray irradiation can effectively promote the apoptosis of hypoxic prostate cancer cells. Overall, this nitrosative stress‐mediated tumor therapy strategy provides a novel approach targeting hypoxic tumors. [ABSTRACT FROM AUTHOR]

Background: Focused electron beam induced deposition (FEBID) allows for the deposition of free standing material within nanometre sizes. The improvement of the technique needs a combination of new precursors and optimized irradiation strategies to achieve a controlled fragmentation of the precursor for leaving deposited material of desired composition. Here a new class of copper precursors is studied following an approach that probes some surface processes involved in the fragmentation of precursors. We use complexes of copper(II) with amines and perfluorinated carboxylate ligands that are solid and stable under ambient conditions. They are directly deposited on the surface for studying the fragmentation with surface science tools.Results: Infrared spectroscopy and high-resolution electron energy loss spectroscopy (HREELS) are combined to show that the precursor is able to spontaneously lose amine ligands under vacuum. This loss can be enhanced by mild heating. The combination of mass spectrometry and low-energy electron irradiation (0–15 eV) shows that full amine ligands can be released upon irradiation, and that fragmentation of the perfluorinated ligands is induced by electrons of energy as low as 1.5 eV. Finally, the cross section for this process is estimated from the temporal evolution in the experiments on electron-stimulated desorption (ESD).Conclusion: The release of full ligands under high vacuum and by electron irradiation, and the cross section measured here for ligands fragmentation allow one to envisage the use of the two precursors for FEBID studies.

Monte Carlo simulations can classify DNA damage into different types and predict the amount of energy deposited. Geant4-DNA was used to predict simple and complex DNA damage induced by irradiation of low-energy electrons at 0.1–50 keV. The number of molecules generated at different energy levels of radiation was analyzed after observing the gradual changes in the level of water radiolysis. A DNA model was used to categorize direct damage according to the location of strand breaks at the atomic level. The parameters of energy threshold (minimum amount of energy needed to break DNA strands) and 10 base pairs (maximum distance that separates two strand breaks) were set. All instances of water radiolysis including the main OH radical occurred most frequently at 1 keV followed by at 1.5 and 0.5 keV. Direct strand breaks most commonly occurred at 0.5 keV followed by at 0.3 keV. Finally, most of strand breaks occurred more frequently at 0.5 keV than at 0.3 keV. The computational measurement results for indirect and direct effects of irradiation depend on the type of simulation code and the DNA model used. Values used in Geant4 (physics list, chemical interaction time and energy threshold) may also influence the results. [ABSTRACT FROM AUTHOR]

This paper describe a new kind of electron transmission window (ETW) with periodic arrays micro-pattern and one-dimensional nanostructure, which is fabricated by microfabrication and chemical etching from a 500 ± $10~\mu \text{m}$ -thick n-type Si wafer. The arrays field emission electrode (AFEE) is produced to emit well focused electrons, which is powered by nanosecond-pulse voltage (the absolute value ≤8.5KV). The ETW shows the transmission ability for low-energy electrons verified by transmission performance analysis and visualization diagnosis. [ABSTRACT FROM AUTHOR]

Monte Carlo simulations of low-energy (< 50 keV) electron transport in matter are essential for a broad range of application fields. Several Monte Carlo codes have developed specialized treatments for this case, but a comprehensive validation of low-energy electron transport for general-purpose simulations remains lacking in the literature. One approach to accomplish this validation is calculation of stopping power using low-energy electron transport physics, as stopping power is a fundamental radiation transport quantity which must be simulated accurately for nearly any application. In this work, we use the Monte Carlo N-Particle (MCNP) radiation transport code with the single-event method for electron transport to calculate stopping powers of low-energy electrons (50 eV to 30 keV) in 41 elemental solids, 14 compound solids, and five rare gas solids, comparing simulation results to published semi-empirical stopping power calculations from optical measurements. In general, the simulations give good agreement (typically within ± 10%) with semi-empirical stopping power values at higher energies: 300 eV and above for most elemental solids, 1 keV and above for compound solids, and 400 eV and above for rare gas solids. Agreement between MCNP and semi-empirical values is worse below these energies. The most significant source of error is the EPRDATA14 cross section data, which does not account for changes in electronic structure due to solid-state bonding, particularly in compound materials. The simplistic model of atomic excitation used to generate the EPRDATA14 cross sections is another key source of error. Additionally, the breakdown of the continuous slowing-down approximation introduces significant uncertainty at low energies, although this is a limitation of the calculation method and not of the simulation procedure. Accounting for these and other uncertainty sources, the single event method in MCNP is robust and able to give good accuracy for a variety of low-energy electron transport problems through diverse kinds of materials. • General validation of low-energy electron transport by the single-event method. • Strong agreement with semi-empirical stopping powers for electrons above 300 eV. • Divergence for electrons below 300 eV due to uncertainty in cross section data. • Performance for compound materials is weaker due bonding effects on cross section. [ABSTRACT FROM AUTHOR]

We present first experiments on electron beam induced deposition of silacyclohexane (SCH) and dichlorosilacyclohexane (DCSCH) under a focused high-energy electron beam (FEBID). We compare the deposition dynamics observed when growing pillars of high aspect ratio from these compounds and we compare the proximity effect observed for these compounds. The two precursors show similar behaviour with regards to fragmentation through dissociative ionization in the gas phase under single-collision conditions. However, while DCSCH shows appreciable cross sections with regards to dissociative electron attachment, SCH is inert with respect to this process. We discuss our deposition experiments in context of the efficiency of these different electron-induced fragmentation processes. With regards to the deposition dynamics, we observe a substantially faster growth from DCSCH and a higher saturation diameter when growing pillars with high aspect ratio. However, both compounds show similar behaviour with regards to the proximity effect. With regards to the composition of the deposits, we observe that the C/Si ratio is similar for both compounds and in both cases close to the initial molecular stoichiometry. The oxygen content in the DCSCH deposits is about double that of the SCH deposits. Only marginal chlorine is observed in the deposits of from DCSCH. We discuss these observations in context of potential approaches for Si deposition.

At geosynchronous Earth orbit, the radiation belt/ring current electron fluxes with energies up to several hundred kiloelectron volts can vary widely in magnetic local time (MLT). This study aims to develop Nonlinear AutoRegressive eXogenous models using system science techniques, which account for the spatial variation in MLT. This is difficult for system science techniques, since there is sparse data availability of the electron fluxes at different MLT. To solve this problem, the data are binned from Geostationary Operational Environmental Satellites (GOES) 13, 14, and 15 by MLT, and a separate Nonlinear AutoRegressive eXogenous model is deduced for each bin using solar wind variables as the inputs to the model. These models are then conjugated into one spatiotemporal forecast. The model performance statistics for each model varies in MLT with a prediction efficiency between 47% and 75% and a correlation coefficient between 51.3% and 78.9% for the period from 1 March 2013 to 31 December 2017. Key Points: This study develops Nonlinear AutoRegressive eXogenous models that account for the spatial variation in MLT of GEO 30‐ to 500‐keV electron fluxesThe model performance varies with MLT having a prediction efficiency between 47% and 75% and a correlation coefficient between 51% and 79%The resulting models show that the IMF has the largest control over the variations in the GEO 30‐ to 50‐keV electron fluxes [ABSTRACT FROM AUTHOR]

The measurement of clustered damages in Pt‐chemotherapeutic‐drugs‐DNA complexes induced by low‐energy (0‐30 eV) electrons (LEEs) may provide further understanding of the synergy mechanism in cancer treatment with concomitant chemoradiation therapy (CRT). Five‐monolayer films of Pt‐DNA complexes, containing cisplatin, carboplatin and oxaliplatin with ratio 5:1 were irradiated with mono‐energetic electrons of 10 eV, the most prominent energy for bond dissociation by LEE impact. Damages to plasmid DNA including crosslinks, SSBs, DSBs and the loss of the supercoiled configuration were analyzed by the electrophoresis. Base damages (BDs) occurring within two turns of DNA helix were detected by the treatment of E. coli base excision repair endonuclease (Nth and Fpg). The total DNA damages to Pt‐DNA complexes was found to be 350 ± 42, 296 ± 45 and 434 ± 46 ×10−15 electron−1molecule−1, respectively, while the percentages of BDs in this total were 56%, 54% and 60%, respectively. Compared to unmodified DNA, binding of Pt‐drugs to DNA increased BDs by factors of 1.9, 1.6 and 2.6, respectively, which partly resulted in significant enhancements of potentially lethal lesions (i. e. crosslinks, double strand breaks (DSBs) and non‐DSB cluster damages). These results reveal the significant role that LEEs play in the formation of clustered DNA damages related to BDs, which are expected to contribute to the higher efficacy of cancer treatment by CRT with the Pt‐drugs investigated. Binding of Pt‐drugs to DNA with electron irradiation at 10 eV significantly lead to enhancements of potentially lethal lesions, including crosslinks, double strand breaks (DSBs) and non‐DSB cluster damages. Base damages contributes the important perspective in the LEEs‐induced clustered DNA damages mechanism, which are expected to benefit the higher efficacy of cancer treatment by CRT with the Pt‐drugs. [ABSTRACT FROM AUTHOR]

Motivated by the potential of focused-electron-beam-induced deposition (FEBID) in the fabrication of functional gold nanostructures for application in plasmonic and detector technology, we conducted a comprehensive study on [Au(CH 3 ) 2 Cl] 2 as a potential precursor for such depositions. Fundamental electron-induced dissociation processes were studied under single collision conditions, and the composition and morphology of FEBID deposits fabricated in an ultrahigh-vacuum (UHV) chamber were explored on different surfaces and at varied beam currents. In the gas phase, dissociative ionization was found to lead to significant carbon loss from this precursor, and about 50% of the chlorine was on average removed per dissociative ionization incident. On the other hand, in dissociative electron attachment, no chlorine was removed from the parent molecule. Contrary to these observations, FEBID in the UHV setup was found to yield a quantitative loss and desorption of the chlorine from the deposits, an effect that we attribute to electron-induced secondary and tertiary reactions in the deposition process. We find this precursor to be stable at ambient conditions and to have sufficient vapor pressure to be suitable for use in HV instruments. More importantly, in the UHV setup, FEBID with [Au(CH 3 ) 2 Cl] 2 yielded deposits with high gold content, ranging from 45 to 61 atom % depending on the beam current and on the cleanliness of the substrates surface., Competing Interests: The authors declare no conflict of interest., (Copyright © 2023, Bilgilisoy et al.)

Highlights • Electron scattering in Si x Ge 1 − x and GaAs x N 1 − x targets. • Modeling of penetration range of electrons impinging on Si x Ge 1 − x and GaAs x N 1 − x targets. • Modeling of transport cross-sections of electrons in Si x Ge 1 − x and GaAs x N 1 − x targets. • Backscattering coefficient of electrons penetration in Si x Ge 1 − x and GaAs x N 1 − x targets. • Composition dependence of electron range and backscattering coefficient in Si x Ge 1 − x and GaAs x N 1 − x targets. Abstract The alloy composition dependence of penetration range and backscattering coefficient of electrons normally impinging on Si x Ge 1 − x and GaAs x N 1 − x semiconductor alloys targets for beam energies in the range 0.5–3.5 keV has been investigated. The electron penetration range is calculated using the Ashley's model. The electron backscattering coefficient is determined using both the Vicanek and Urbassek theory where the transport cross-sections are obtained more accurately via an improved approximation and Monte Carlo method in which the inelastic scattering processes are treated via Ashley's optical model. Our results regarding the electron backscattering coefficient for Si and Ge targets are found to be much higher than those of experiment when using the Vicanek and Urbassek theory. However, the use of Ashley's model via Monte Carlo method gives results that are in reasonably good accord with the experimental data reported in the literature in the low energy regime being considered here. [ABSTRACT FROM AUTHOR]

Abstract: High‐energy radiation is used in combination with radiosensitizing therapeutics to treat cancer. The most common radiosensitizers are halogenated nucleosides and cisplatin derivatives, and recently also metal nanoparticles have been suggested as potential radiosensitizing agents. The radiosensitizing action of these compounds can at least partly be ascribed to an enhanced reactivity towards secondary low‐energy electrons generated along the radiation track of the high‐energy primary radiation, or to an additional emission of secondary reactive electrons close to the tumor tissue. This is referred to as physico‐chemical radiosensitization. In this Concept article we present current experimental methods used to study fundamental processes of physico‐chemical radiosensitization and discuss the most relevant classes of radiosensitizers. Open questions in the current discussions are identified and future directions outlined, which can lead to optimized treatment protocols or even novel therapeutic concepts. [ABSTRACT FROM AUTHOR]

Abstract: In a recent study, Liang et al. (2017, https://doi.org/10.1002/2017JA024127) repeatedly identified strong electron temperature (Te) enhancements when Swarm satellites traversed pulsating auroral patches. In this study, we use joint optical and Poker Flat Incoherent Scatter Radar (PFISR) observations to further investigate the F region plasma signatures related to pulsating auroras. On 19 March 2015 night, which contained multiple intervals of pulsating auroral activities, we identify a statistical trend, albeit not a one‐to‐one correspondence, of strong Te enhancements (~500–1000 K) in the upper F region ionosphere during the passages of pulsating auroras over PFISR. On the other hand, there is no discernible and repeatable density enhancement in the upper F region during pulsating auroral intervals. Collocated optical and NOAA satellite observations suggest that the pulsating auroras are composed of energetic electron precipitation with characteristic energy >10 keV, which is inefficient in electron heating in the upper F region. Based upon PFISR observations and simulations from Liang et al. (2017) model, we propose that thermal conduction from the topside ionosphere, which is heated by precipitating low‐energy electrons, offers the most likely explanation for the observed electron heating in the upper F region associated with pulsating auroras. Such a heating mechanism is similar to that underlying the “stable auroral red arcs” in the subauroral ionosphere. Our proposal conforms to the notion on the coexistence of an enhanced cold plasma population and the energetic electron precipitation, in magnetospheric flux tubes threading the pulsating auroral patch. In addition, we find a trend of enhanced ion upflows during pulsating auroral intervals. [ABSTRACT FROM AUTHOR]

Electron–molecule interactions have been studied for a long time. Most of these studies have in the past been limited to the gas phase. In the condensed-phase processes that have recently attracted attention from academia as well as industry, a theoretical understanding is mostly based on electron–molecule interaction data from these gas phase experiments. When transferring this knowledge to condensed-phase problems, where number densities are much higher and multi-body interactions are common, care must be taken to critically interpret data, in the light of this chemical environment. The paper presented here highlights three typical challenges, namely the shift of ionization energies, the difference in absolute cross-sections and branching ratios, and the occurrence of multi-body processes that can stabilize otherwise unstable intermediates. Examples from recent research in astrochemistry, where radiation driven chemistry is imminently important are used to illustrate these challenges.

In this work, we present our study of suspended graphene with low-energy electrons based on a point projection microscopic/diffractive imaging technique. Both exfoliated and chemical vapor deposition (CVD) graphene samples were studied in an ultra-high vacuum chamber. This method allows imaging of individual adsorbates at the nanometer scale and characterizing graphene layers, graphene lattice orientations, ripples on graphene membranes, etc. We found that long-duration exposure to low-energy electron beams induced aggregation of adsorbates on graphene when the electron dose rate was above a certain level. We also discuss the potential of this technique to conduct coherent diffractive imaging for determining the atomic structures of biological molecules adsorbed on suspended graphene. [ABSTRACT FROM AUTHOR]

While imaging individual atoms can routinely be achieved in high resolution transmission electron microscopy, visualizing the potential distribution of individually charged adsorbates leading to a phase shift of the probing electron wave is still a challenging task. Low-energy electrons (30 – 250 eV) are sensitive to localized potential gradients. We employed low-energy electron holography to acquire in-line holograms of individual charged impurities on free-standing graphene. By applying an iterative phase retrieval reconstruction routine we recover the potential distribution of the localized charged impurities present on free-standing graphene. [ABSTRACT FROM AUTHOR]

Purpose: To investigate the molecular aspects of the synergy between ionizing radiation and platinum (Pt) chemotherapeutic agents in cancer treatment with chemoradiation therapy (CRT) by measuring damages induced by low-energy electrons (LEE) to DNA bound to cisplatin. LEE are produced abundantly by any type of ionizing radiation and cisplatin represents a typical Pt-chemotherapeutic agents. Materials and methods: Our strategy involves two parallel administrations of cisplatin and irradiation with a 4.6 and 9.6 eV electron fluence of 1.1 × 1012: (1) LEE bombardment of supercoiled DNA and its subsequent reaction with cisplatin; (2) the reaction of DNA with cisplatin followed by LEE irradiation. The damage yields for the loss of supercoiled (LS), single-strand breaks (SSB) and double-strand breaks (DSB) were obtained from gel electrophoresis analysis. Base modifications were revealed by treating the samples with Escherichia coli base excision repair endonuclease (Nth and Fpg). Results: The yields were deduced from the respective time–response for the reaction of DNA with cisplatin. The results show that binding cisplatin to DNA followed by LEE irradiation, consistently yields more DNA damages than the reverse order. In comparison to non-treated DNA, administration (2) results in an increase of LS and SSB of 1.4–3.3 folds and of DSB by more than an order of magnitude. Furthermore, after enzyme treatment, the yields of DSB rise by factors of 5.3–15.4, indicating a large increase of clustered damages, which should at least partially translate into an increase of lethal damages in cancer cells during the CRT. Conclusions: Our results demonstrate that a strong synergy between radiation and cisplatin can only be achieved at the molecular level, if the drug is present at the time of irradiation. Furthermore, this work confirms the LEE mechanism previously proposed to explain the synergy between radiation and Pt drugs in CRT. It involves chemical sensitization of DNA prior to irradiation, to facilitate strand breaks and clustered damages induced by the highly reactive LEE. [ABSTRACT FROM AUTHOR]

Low-energy electrons effectively decompose the isomers 2-nitroimidazole and 4(5)-nitroimidazole by dissociative electron attachment (DEA) into a variety of fragment anions and radicals. The present study shows that a distinct selectivity for the two isomers occurs in the DEA reactions. Several new decay channels are observed for 2-nitroimidazole, including a dominant one leading to the loss of molecular H2O by attachment of a low-energy electron. In contrast, the loss of a single hydrogen atom is a much more efficient reaction in DEA to 4(5)-nitroimidazole. Quantum chemical calculations were carried out to explain the pronounced isomer effect found in the DEA experiment. Although the free energies of the reactions are similar for the different isomers, the very different natures of the dipole-bound states and valence-bound anions lead to preference for or hindrance of a particular dissociation channel. Nitroimidazolic compounds are considered as radiosensitizing compounds in tumor radiation therapy. The enhanced formation of fragments, including the highly reactive hydroxyl radical, in DEA to 2-nitroimidazole suggests that it may be a more efficient radiosensitizing agent than 4(5)-nitroimidazoles. [ABSTRACT FROM AUTHOR]

The electron transport at low and very low energy (10 eV–2 keV) is investigated with a Monte Carlo (MC) code in silicon and aluminum. The elastic scattering with nuclei is described by Mott’s model of partial waves, whereas the inelastic collisions with electrons are described by the complex dielectric function theory. Comparisons of MC simulations with electron emission yields (EEY) and energy loss spectra experimentally measured in ultrahigh vacuum on Ar-etched samples are given. The practical ranges and the ionizing dose calculations are presented down to 10 eV for electrons in silicon and aluminum. The simulation results show a correlation between the EEY and the ionizing doses. At low energy, while the electrons stay in the first ~10 nm from the surface due to the elastic scattering, the EEY increases and the ratio of the ionizing dose over the incident energy decreases. Above 200 eV, when the electrons go deeper into the solid due to the inelastic scattering, the EEY decreases and the ionizing dose ratio increases. [ABSTRACT FROM PUBLISHER]

Electron-beam-induced deposition of various materials from suitable precursors has represented an established branch of nanotechnology for more than a decade. A specific alternative is carbon deposition on the basis of hydrocarbons as precursors that has been applied to grow various nanostructures including masks for subsequent technological steps. Our area of study was unintentional electron-beam-induced carbon deposition from spontaneously adsorbed hydrocarbon molecules. This process traditionally constitutes a challenge for scanning electron microscopy practice preventing one from performing any true surface studies outside an ultrahigh vacuum and without in-situ cleaning of samples, and also jeopardising other electron-optical devices such as electron beam lithographs. Here we show that when reducing the energy of irradiating electrons sufficiently, the e-beam-induced deposition can be converted to e-beam-induced release causing desorption of hydrocarbons and ultimate cleaning of surfaces in both an ultrahigh and a standard high vacuum. Using series of experiments with graphene samples, we demonstrate fundamental features of e-beam-induced desorption and present results of checks for possible radiation damage using Raman spectroscopy that led to optimisation of the electron energy for damage-free cleaning. The method of preventing carbon contamination described here paves the way for greatly enhanced surface sensitivity of imaging and substantially reduced demands on vacuum systems for nanotechnological applications. [ABSTRACT FROM AUTHOR]

When low-energy electrons, such as Auger electrons, interact with liquid water, they induce highly localized ionizing energy depositions over ranges comparable to cell diameters. Monte Carlo track structure (MCTS) codes are suitable tools for performing dosimetry at this level. One of the main MCTS codes, Geant4-DNA, is equipped with only two sets of cross section models for low-energy electron interactions in liquid water (“option 2” and its improved version, “option 4”). To provide Geant4-DNA users with new alternative physics models, a set of cross sections, extracted from CPA100 MCTS code, have been added to Geant4-DNA. This new version is hereafter referred to as “Geant4-DNA-CPA100”. In this study, “Geant4-DNA-CPA100” was used to calculate low-energy electron dose-point kernels (DPKs) between 1 keV and 200 keV. Such kernels represent the radial energy deposited by an isotropic point source, a parameter that is useful for dosimetry calculations in nuclear medicine. In order to assess the influence of different physics models on DPK calculations, DPKs were calculated using the existing Geant4-DNA models (“option 2” and “option 4”), newly integrated CPA100 models, and the PENELOPE Monte Carlo code used in step-by-step mode for monoenergetic electrons. Additionally, a comparison was performed of two sets of DPKs that were simulated with “Geant4-DNA-CPA100” – the first set using Geant4′s default settings, and the second using CPA100′s original code default settings. A maximum difference of 9.4% was found between the Geant4-DNA-CPA100 and PENELOPE DPKs. Between the two Geant4-DNA existing models, slight differences, between 1 keV and 10 keV were observed. It was highlighted that the DPKs simulated with the two Geant4-DNA’s existing models were always broader than those generated with “Geant4-DNA-CPA100”. The discrepancies observed between the DPKs generated using Geant4-DNA’s existing models and “Geant4-DNA-CPA100” were caused solely by their different cross sections. The different scoring and interpolation methods used in CPA100 and Geant4 to calculate DPKs showed differences close to 3.0% near the source. [ABSTRACT FROM AUTHOR]

Using a recent extension of the Low-Energy Particle Track Simulation (LEPTS) Monte Carlo code, we model the slowing-down of heavy charged particles propagating in water, combined with an explicit molecular-level description of radiation effects due to the formation of secondary electrons, their propagation through the medium, and electron-induced molecular dissociations. As a case study, we consider the transport of protons with the initial energy of 1 MeV until their thermalization, so that we cover the energy range that contributes mainly to the energy deposition in the Bragg peak region. In order to include protons into the simulation procedure, a comprehensive dataset of integral and differential cross sections of elastic and inelastic scattering of intermediate- and low-energy protons from water molecules is created. Experimental and theoretical cross sections available in the literature are carefully examined, compared and verified. The ionization cross section by protons includes recent experimental measurements of the production of different charged fragments. [ABSTRACT FROM AUTHOR]

We report the first observation of the coupling of strong optical near fields to wavepackets of free, 100 eV electrons with <50 fs temporal resolution in an ultrafast point-projection microscope. Optical near fields are created by excitation of a thin, nanometer-sized Yagi-Uda antenna, with 20 fs near-infrared laser pulses. Phase matching between electrons and near fields is achieved due to strong spatial confinement of the antenna near field. Energy-resolved projection images of the antenna are recorded in an optical pump-electron probe scheme. We show that the phase modulation of the electron by transverse-field components results in a transient electron deflection while longitudinal near-field components broaden the kinetic energy distribution. This low-energy electron near-field coupling is used here to characterize the chirp of the ultrafast electron wavepackets, acquired upon propagation from the electron emitter to the sample. Our results bring direct mapping of different vectorial components of highly localized optical near fields into reach.

UV photon-driven condensed phase cosmic ice reactions have been the main focus in understanding the extraterrestrial synthesis of complex organic molecules. Low-energy (≤ 20 eV) electron-induced reactions, on the other hand, have been largely ignored. In this article, we review studies employing surface science techniques to study low-energy electron-induced condensed phase reactions relevant to astrochemistry. In particular, we show that low-energy electron irradiation of methanol ices leads to the synthesis of many of the same complex molecules formed through UV irradiation. Moreover, our results are qualitatively consistent with the hypothesis that high-energy condensed phase radiolysis is mediated by low-energy electron-induced reactions. In addition, due to the numbers of available low-energy secondary electrons resulting from the interaction of high-energy radiation with matter as well as differences between electron- and photon-induced processes, low-energy electron-induced reactions are perhaps as, or even more, effective than photon-induced reactions in initiating condensed-phase chemical reactions in the interstellar medium. Consequently, we illustrate a need for astrochemical models to include the details of electron-induced reactions in addition to those driven by UV photons. Finally, we show that low-energy electron-induced reactions may lead to the production of unique molecular species that could serve as tracer molecules for electron-induced condensed phase reactions in the interstellar medium. [ABSTRACT FROM AUTHOR]

Visualizing individual charges confined to molecules and observing their dynamics with high spatial resolution is a challenge for advancing various fields in science, ranging from mesoscopic physics to electron transfer events in biological molecules. We show here that the high sensitivity of low-energy electrons to local electric fields can be employed to directly visualize individual charged adsorbates and to study their behavior in a quantitative way. This makes electron holography a unique probing tool for directly visualizing charge distributions with a sensitivity of a fraction of an elementary charge. Moreover, spatial resolution in the nanometer range and fast data acquisition inherent to lens-less low-energy electron holography allows for direct visual inspection of charge transfer processes. [ABSTRACT FROM AUTHOR]

Methylammonium lead iodide perovskite (MAPbI3), a prototype material for potentially high-efficient and low-cost organic-inorganic hybrid perovskite solar cells, has been investigated intensively in recent years. A study of low-energy electron-induced transformations in MAPbI3 is presented, performed by combining controlled electron-impact irradiation with X-ray photoelectron spectroscopy and scanning electron microscopy. Changes were observed in both the elemental composition and the morphology of irradiated MAPbI3 thin films as a function of the electron fluence for incident energies from 4.5 to 60 eV. The results show that low-energy electrons can affect structural and chemical properties of MAPbI3. It is proposed that the transformations are triggered by the interactions with the organic part of the material (methylammonium), resulting in the MAPbI3 decomposition and aggregation of the hydrocarbon layer. [ABSTRACT FROM AUTHOR]

We have designed, fabricated and tested a micron-sized electron column with an overall length of about 700 microns comprising two electron lenses; a micro-lens with a minimal bore of 1 micron followed by a second lens with a bore of up to 50 microns in diameter to shape a coherent low-energy electron wave front. The design criteria follow the notion of scaling down source size, lens-dimensions and kinetic electron energy for minimizing spherical aberrations to ensure a parallel coherent electron wave front. All lens apertures have been milled employing a focused ion beam and could thus be precisely aligned within a tolerance of about 300 nm from the optical axis. Experimentally, the final column shapes a quasi-planar wave front with a minimal full divergence angle of 4 mrad and electron energies as low as 100 eV. [ABSTRACT FROM AUTHOR]

We present here theoretical investigations of electronic states and electron scattering cross-sections of the thiazole molecule. Spectroscopic calculations are performed on ground and excited states of thiazole using density functional theory (DFT) and time dependent DFT, while the electron impact scattering calculations are carried out using ab initio R-Matrix method. The optimized geometrical parameters and computed vibrational frequencies of neutral and cationic thiazole molecule are in good agreement with earlier work. Detailed comparison of the present computed vertical excitation energies with earlier experimental studies helps to confirm several of the earlier assigned Rydberg transitions while leading to revised assignments for some of the earlier observed peaks. Extensive electron scattering cross-sectional data; Elastic cross-sections include symmetry decomposition, differential and momentum transfer cross-sections while inelastic cross-sectional data comprises of discrete electronic excitations and ionization cross-sections along with their rate-coefficients. According to literature survey, this is the first report of cross-section data and rate coefficients for inelastic processes. A comparison of the total cross-sectional (TCS) data of thiazole with the TCS data of the isoelectronic thiophene molecule reveals the overall TCS values being higher in thiazole, as expected due to its higher dipole moment. Further, resonant peaks in the TCS are observed to be shifted to lower energies in thiazole as compared to thiophene, which is attributed to the higher electronegativity of the N atom as compared to the CH group in thiophene. For the first time, a comprehensive spectroscopic and electron scattering study of thiazole is summarized in this paper. • Comprehensive spectroscopy and electron scattering study on thiazole. • The geometrical parameters and IR frequencies agree well with earlier work. • Comparison with earlier data; confirm/revised assignments of Rydberg states. • Low energy electron scattering data for Thiazole from 0.1 eV to 20 eV. • This data help to understand various electron induced biochemical processes. [ABSTRACT FROM AUTHOR]

The current state of the art in structural biology is led by NMR, X-ray crystallography and TEM investigations. These powerful tools however all rely on averaging over a large ensemble of molecules. Here, we present an alternative concept aiming at structural analysis at the single molecule level. We show that by combining electron holography and coherent diffraction imaging estimations concerning the phase of the scattered wave become needless as the phase information is extracted from the data directly and unambiguously. Performed with low-energy electrons the resolution of this lens-less microscope is just limited by the De Broglie wavelength of the electron wave and the numerical aperture, given by detector geometry. In imaging freestanding graphene, a resolution of 2 Å has been achieved revealing the 660.000 unit cells of the graphene sheet from a single data set. Once applied to individual biomolecules the method shall ultimately allow for non-destructive imaging and imports the potential to distinguish between different conformations of proteins with atomic resolution. [ABSTRACT FROM AUTHOR]

Core-inner-valence ionization of high-Z nanoparticle atomic clusters can de-excite electrons through various interatomic de-excitation processes, thereby leading to the ionization of both directly exposed atoms and adjacent neutral atoms within the nanoparticles, and to an enhancement in photon-electron emission, which is termed the nanoradiator effect. To investigate the nanoradiator-mediated dose enhancement in the radio-sensitizing of high-Z nanoparticles, the production of reactive oxygen species (ROS) was measured in a gadolinium oxide nanoparticle (Gd-oxide NP) solution under core-inner-valence excitation of Gd with either 50 keV monochromatic synchrotron X-rays or 45 MeV protons. This measurement was compared with either a radiation-only control or a gadolinium-chelate magnetic resonance imaging contrast agent solution containing equal amounts of gadolinium as the separate atomic species in which Gd-Gd interatomic de-excitations are absent. Ionization excitations followed by ROS measurements were performed on nanoparticle-loaded cells or aqueous solutions. Both photoexcitation and proton impact produced a dose-dependent enhancement in the production of ROS by a range of factors from 1.6 to 1.94 compared with the radiation-only control. Enhanced production of ROS, by a factor of 1.83, was observed from Gd-oxide NP atomic clusters compared with the Gd-chelate molecule, with a Gd concentration of 48 μg/mL in the core-level photon excitation, or by a factor of 1.82 under a Gd concentration of 12 μg/mL for the proton impact at 10 Gy ( p < 0.02). The enhanced production of ROS in the irradiated nanoparticles suggests the potential for additional therapeutic dose enhancements in radiation treatment via the potent Gd-Gd interatomic de-excitation-driven nanoradiator effect. [ABSTRACT FROM AUTHOR]

Comparative experiments on sintering zirconia ceramics are performed using colliding beams of low-energy electrons and under conditions of thermal heating. The density and microhardness of ceramic materials manufactured via different processes are determined. The use of a regime of bilateral heating by high-intensity,low-energy electron beams is shown to intensify the sintering process and yield material specimens with improved characteristics compared to those formed by thermal sintering. [ABSTRACT FROM AUTHOR]