Low-energy Electron Irradiation Research Articles

Formation of oxygen protective layer on monolayer MoS2 via low energy electron irradiation.

Monolayer molybdenum disulfide (MoS2) semiconductors are the new generation of two-dimensional materials that possess several advantages compared to graphene due to their tunable bandgap and high electron mobility. Several approaches have been used to modify their physical properties for optical device applications. Here, we report a facile and non-destructive surface modification method for monolayer MoS2 via electron irradiation at a low, 5 kV accelerating voltage. After electron irradiation, the results of Raman and photoluminescence spectroscopy confirmed that the structure remains unchanged. However, when the modified surface was illuminated with a 532 nm laser for a prolonged period, the PL intensity was quenched as a result of oxygen desorption. Interestingly, the PL intensity can be recovered when left in ambient conditions for 10 h. The analysis of the PL spectrum revealed a decrease of trion, which is consistent with the readsorbed O2 molecules on the surface that deplete electrons and lead to PL recovery. We attribute this effect to the enhancement of the n-type character of monolayer MoS2 after electron irradiation. The sensitive nature of the modified surface to oxygen suggests that this approach may be used as a tool for the fabrication of MoS2 oxygen sensors.

Novel liquid dosimeters for low-energy electron beam irradiation in low and medium dose ranges

Low-energy electron beam irradiation, which refers to the treatment of matter with accelerated electrons at energies below 300 keV, is gaining attention for many applications in life sciences. In the scope of vaccine production, low-energy electron irradiation is an efficient and chemical free technology to inactivate viruses. Low-energy electron beam irradiation has also been proposed to be a powerful technique for its use in biotechnological processes. As biotechnological applications operate in an aqueous environment, there is an urgent need for accurate dose quantification in liquids, especially for low (< 500 Gy) and medium doses (500–5000 Gy). This study investigated dye solutions of xylenol orange tetrasodium, 1,9-dimethylmethylene blue, resazurin sodium, and tartrazine for their suitability as radiochromic liquid dosimeters. The solutions were evaluated regarding their dose–response characteristics and storage stability prior to irradiation over a range of pH values and concentrations. The radiochromic dosimeters were irradiated with electrons with maximal energies of 200 keV and dose rates of 6.5 Gy/s to 45 Gy/s. Then, the absorbance was measured and response curves were plotted. The dye solutions of 1,9-dimethylmethylene blue and resazurin sodium covered a low to medium dose range from 100–1500 Gy and 100–1000 Gy, respectively. Tartrazine at pH 4 was suitable for quantification of doses from 100 Gy to 3500 Gy, which covers a wide dose range of biotechnological applications.

World experience in the application of low-energy electron irradiation in agriculture

According to the long-term observations of the FAO, losses of plant-based agricultural products are estimated to be between 10 and 30 %. The main causes of these losses are plant pathogens, spoilage microorganisms, and insect pests. The study discusses the problems of ensuring phytosanitary safety of agricultural products and proposes the use of radiation technology instead of chemical treatment. Radiation technology has a long history of research and application, spanning over 75 years. The most extensive and detailed data on the application of this technology have been obtained for gamma installations, which use natural radioactive isotopes. Lowenergy (less than 300 keV) electron accelerators were invented relatively recently, so the question of their use in agriculture is relevant. Treatment with low-energy electron radiation combines all the advantages of radiation treatment of food and agricultural products with gamma radiation, and at the same time, significantly reduces the risk of damage to biological structures inside the irradiated object due to the low penetrating power of the radiation. This study notes that low-energy electron accelerators can be successfully used to combat plant infectious diseases, reducing the amount of plant pathogens on seeds, without affecting their growth parameters. The use of low-energy electron irradiation to prevent microbiological spoilage is also discussed. The nutritional qualities of irradiated products are not significantly altered. The method of radiation disinfestation (control of insect pests) using low-energy electron radiation has also proven to be effective. However, it should be noted that additional research is necessary to determine the optimal doses of low-energy radiation for each type of product and to ensure safety for human health and the environment. Generally, the use of radiation technology in agriculture has great potential and can become an effective means of improving productivity and food safety. This method of food processing has been recognized as safe for human health by several authoritative international organizations, including the UN (FAO), WHO, IAEA, and others.

Electron-stimulated desorption kinetics of ultra-thin LiCl films on graphene

Ultra-thin alkali halide films are an important substrate for studying single quantum objects at the atomic scale, as they serve as decoupling scaffolds. However, their stability upon exposure to electrons and photons, the most common probes used to study nanomaterials, is not fully understood. Here we present a study of the evolution of the structure of ultra-thin LiCl films, grown on graphene, upon low-energy electron irradiation by means of microspot-low-energy electron diffraction and microscopy. We find that the intensity of the LiCl diffraction spots irradiated at various electron energies follows a bi-exponential decay function, which can be rationalized by two different desorption regimes. In addition, we detect a change in the work function caused by the electron irradiation, confirming desorption of the LiCl film from the graphene layer. We understand the underlying mechanisms for the electron-induced desorption of the salt film in terms of the evolution of the elementary quasiparticles involved in the process: holes, excitons and F and H center pairs. Moreover, a direct comparison of the electron-induced and the soft X-ray photon-induced processes reveal that, in addition to LiCl desorption, the intercalation of lithium into graphene reported for X-ray induced desorption does not take place in electron-stimulated desorption.

DNA irradiating system with 35-keV electron beam

This work aims to design the experimental system for investigating the effect of low energy electron irradiation on DNA by means of particle tracking and mechanical strength simulations. The electron beam produced with a DC accelerator having uniform kinetic energy of 35keV and the current of 10nA is used as a source of primary electrons. Two situations of DNA irradiation, in vacuo and in ambient, are studied. For both cases, the main objective is to choose appropriate materials to serve as the windows for the in vacuo sample cell and the vacuum window for ambient electron beam extraction. Silicon nitride with varied thickness has been proposed to be used as the electron exposing window for the sample cell and has been examined in Geant4 particle tracking simulation and SolidWorks mechanical strength test while titanium (Ti), beryllium (Be), and high-density polyethylene (HDPE) are considered to be used as the vacuum window and the properties are studied with the same method. The optimal materials are used to construct the system where electron beam is irradiated on a DNA sample. The interaction of electrons with the DNA and its damages is performed with the Geant4-DNA simulation. Based on our limiting conditions, it is found that the DNA double strand breaks can only be observed when the DNA sample is irradiated inside the vacuum part of the accelerator unit.

Apicomplexan parasites are attenuated by low-energy electron irradiation in an automated microfluidic system and protect against infection with Toxoplasma gondii

Radiation-attenuated intracellular parasites are promising immunization strategies. The irradiated parasites are able to invade host cells but fail to fully replicate, which allows for the generation of an efficient immune response. Available radiation technologies such as gamma rays require complex shielding constructions and are difficult to be integrated into pharmaceutical production processes. In this study, we evaluated for the first time low-energy electron irradiation (LEEI) as a method to generate replication-deficient Toxoplasma gondii and Cryptosporidium parvum. Similar to other radiation technologies, LEEI mainly damages nucleic acids; however, it is applicable in standard laboratories. By using a novel, continuous, and microfluidic-based LEEI process, tachyzoites of T. gondii and oocysts of C. parvum were irradiated and subsequently analyzed in vitro. The LEEI-treated parasites invaded host cells but were arrested in intracellular replication. Antibody-based analysis of surface proteins revealed no significant structural damage due to LEEI. Similarly, excystation rates of sporozoites from irradiated C. parvum oocysts were similar to those from untreated controls. Upon immunization of mice, LEEI-attenuated T. gondii tachyzoites induced high levels of antibodies and protected the animals from acute infection. These results suggest that LEEI is a useful technology for the generation of attenuated Apicomplexan parasites and has potential for the development of anti-parasitic vaccines.

Low-energy electron microdosimetry assessment based on the two-dimensional monolayer human normal mesh-type cell population model

In radiobiology, in vitro irradiation experiments on cells are often conducted to investigate the relationship between radiation dose and biological effects, where the phenotypic indicators of cells in culture are generally measured with macroscopic dosimetric indicators of the absorbed dose. The intracellular transport behavior of low-energy electrons are of particular importance. Considering the states of cells in culture, two-dimensional monolayer mesh-type cell population models were constructed in this work based on two human mesh-type cell models to evaluate the microdosimetric distribution of monoenergetic electrons with two energy levels in the cell population. Two-dimensional monolayer mesh-type and equivalent-volume concentric sphere cell population models of two cell lines, i.e., BEAS-2B and FHs74Int, with different cell numbers and shapes were constructed. Monte Carlo toolkit, GATE, was used as the simulation platform. The impacts of different deposition doses from the 100 keV and 200 keV monoenergetic electron beams on the average specific energy z‾ of the nucleus and cytoplasm, the specific energy frequency function f(z,D), and their relative standard deviation σz/z‾ were assessed. Under the same irradiation conditions, the mesh-type and equivalent-volume sphere cell population models showed small differences in f(z,D), whereas the z‾ of the nucleus and cytoplasm differed significantly. As the cumulative absorbed dose reached the mGy level under the irradiation of the monoenergetic electron beam with an initial energy of 100 keV, the nucleus z‾ of the FHs74Int circular mesh-type population model with 848 cells was 19.88 mGy, whereas the nucleus z‾ of the concentric sphere cell population model was 23.96 mGy. The lower dose (∼mGy level) under the same geometry resulted in a more pronounced uncertainty in the absorbed dose value. Specifically, take the FHs74Int quadrate mesh-type population model with 484 cells as an example, the σz/z‾ were 3.61% and 23.35%, respectively, at the ∼Gy and ∼mGy levels under electrons with the initial energy of 200 keV. In addition, the volume and shape of the cell population impact the specific energy distribution. Through the constructed two-dimensional monolayer mesh-type cell population model, this work quantitatively demonstrates that the dose distribution within subcellular regions under low-energy electron irradiation for low-dose level is significantly affected by the cell volume and shape. This study provides a viable means of simulating and quantifying the energy deposition distribution of radiation within the culture dish based on radiobiological cell irradiation scenarios, which can provide method and data support to build biophysical models.

Electron Beam Characterization of REBCO-Coated Conductors at Cryogenic Conditions

Particle accelerators with superconducting magnets operating at cryogenic temperatures use a beam screen (BS) liner that extracts heat generated by the circulating bunched charge particle beam before it can reach the magnets. The BS surface, commonly made of high–conductivity copper, provides a low impedance for beam stability reasons, low secondary electron yield (SEY) to mitigate the electron–cloud (EC) effect, and low electron–stimulated desorption yield (ESD) to limit the dynamic pressure rise due to EC. Rare–earth barium copper oxide (REBCO) high–temperature superconductors (HTSs) recently reached technical maturity, are produced as coated conductor tapes (REBCO–CCs), and will be considered for application in future colliders to decrease the BS impedance and enable operation at around 50 K, consequently relaxing the cryogenic requirements. Aside from HTS properties, industry–grade REBCO–CCs also need qualification for EC and dynamic vacuum compatibility under accelerator–like conditions. Hence, we report the SEY and ESD measured at cryogenic temperatures of 12 K under low–energy electron irradiation of 0–1.4 keV. We also verify the sample compositions and morphologies using the XPS, SEM, and EDS methods. The energy and dose dependencies of ESD are comparable to those of technical–grade metals and one sample reached SEYMAX = 1.2 after electron conditioning.

Engineering Multicolor Radiative Centers in hBN Flakes by Varying the Electron Beam Irradiation Parameters.

Recently, hBN has become an interesting platform for quantum optics due to the peculiar defect-related luminescence properties. In this work, multicolor radiative emissions are engineered and tailored by position-controlled low-energy electron irradiation. Varying the irradiation parameters, such as the electron beam energy and/or area dose, we are able to induce light emissions at different wavelengths in the green-red range. In particular, the 10 keV and 20 keV irradiation levels induce the appearance of broad emission in the orange-red range (600-660 nm), while 15 keV gives rise to a sharp emission in the green range (535 nm). The cumulative dose density increase demonstrates the presence of a threshold value. The overcoming of the threshold, which is different for each electron beam energy level, causes the generation of non-radiative recombination pathways.

Hemocompatibility tuning of an innovative glutaraldehyde-free preparation strategy using riboflavin/UV crosslinking and electron irradiation of bovine pericardium for cardiac substitutes

Hemocompatibility tuning was adopted to explore and refine an innovative, GA-free preparation strategy combining decellularization, riboflavin/UV crosslinking, and low-energy electron irradiation (SULEEI) procedure. A SULEEI-protocol was established to avoid GA-dependent deterioration that results in insufficient long-term aortic valve bioprosthesis durability. Final SULEEI-pericardium, intermediate steps and GA-fixed reference pericardium were exposed in vitro to fresh human whole blood to elucidate effects of preparation parameters on coagulation and inflammation activation and tissue histology. The riboflavin/UV crosslinking step showed to be less efficient in inactivating extracellular matrix (ECM) protein activity than the GA fixation, leading to tissue-factor mediated blood clotting. Intensifying the riboflavin/UV crosslinking with elevated riboflavin concentration and dextran caused an enhanced activation of the complement system. Yet activation processes induced by the previous protocol steps were quenched with the final electron beam treatment step. An optimized SULEEI protocol was developed using an intense and extended, trypsin-containing decellularization step to inactivate tissue factor and a dextran-free, low riboflavin, high UV crosslinking step. The innovative and improved GA-free SULEEI-preparation protocol results in low coagulant and low inflammatory bovine pericardium for surgical application.

Study of irregular electron beam correcting permanent-magnet-quadrupole doublet lens for irradiation accelerator.

In this paper, a permanent-magnet-quadrupole doublet lens with strong-focusing is designed and manufactured. Such an instrument could solve the problem of irregular beam spots produced by the weak focusing of conventional solenoid-focusing systems in low-energy electron irradiation accelerators. It could provide a better and more appropriate initial beam spot before the beam enters the subsequent magnetic spreading system or magnetic scanning system, thus, improving the irradiation uniformity. The association of the parameters of the rectangular permanent magnet with the quadrupole magnetic field is investigated. Focusing results, obtained using irregular beam spots with different profiles and different energies, and magnetic field measurement results, both from the instrument, verify the engineering feasibility of this permanent-magnet-quadrupole doublet lens.

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.

Role of surface chemistry in conditioning of materials in particle accelerators

For the vacuum scientists and the accelerator community, finding solutions to mitigate pressure rises induced by electron, photon and ion desorption, and also beam instabilities induced by ion and electron clouds is a major issue. Along the time, changes in the surface chemistry of vacuum chambers are observed during beam operations, leading to modifications of: outgassing rates, stimulated desorption processes and secondary emission yields (SEY). To understand the role of the surface chemistry of air exposed materials in the electron conditioning process, typical air exposed materials used in particle accelerators : thin film coatings (NEG, i.e a Ti-Zr-V alloy, and carbon), copper (and its oxides Cu2O and CuO) and niobium were conditioned by low energy electron irradiation for a better understanding of electron-cloud effect. First, SEY was measured to understand the changes of surface conditioning upon particle irradiation; then, surface chemistry evolution after electron irradiation was investigated by both XPS and TOF-SIMS analyses using the ANDROMEDE facility at IJCLab. Finally, the relationship between the surface chemistry and the conditioning phenomenon will be discussed.

Anionic clusters produced in low-energy electron irradiation of methanol liquid

In the low-energy electron impacts with a liquid beam of methanol, we detect the anionic yields using a linear time-of-flight mass spectrometer. With help of quantum chemistry calculations, we further identify these anionic products as the hydrogenbonding clusters, i.e., CH3OH·CH3O− and CH3OH·CH3OH·CH3O−, and their singly occupied molecular orbitals show the valence-bound feature. In contrast, CH3OH·CH3OH− and CH3OH−CH3OH·CH3OH− are unfavored in energetics with respect to the dehydrogenated ones, although they also correspond to the minima on the potential energy surfaces. Furthermore, the singly occupied molecular orbitals of CH3OH·CH3OH− and CH3OH·CH3OH·CH3OH− indicate the typical feature of aqueous-solvated electron.

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.

Periodic Structural Defects in Graphene Sheets Engineered via Electron Irradiation.

Artificially-induced defects in the lattice of graphene are a powerful tool for engineering the properties of the crystal, especially if organized in highly-ordered structures such as periodic arrays. A method to deterministically induce defects in graphene is to irradiate the crystal with low-energy (<20 keV) electrons delivered by a scanning electron microscope. However, the nanometric precision granted by the focused beam can be hindered by the pattern irradiation itself due to the small lateral separation among the elements, which can prevent the generation of sharp features. An accurate analysis of the achievable resolution is thus essential for practical applications. To this end, we investigated patterns generated by low-energy electron irradiation combining atomic force microscopy and micro-Raman spectroscopy measurements. We proved that it is possible to create well-defined periodic patterns with precision of a few tens of nanometers. We found that the defected lines are influenced by electrons back-scattered by the substrate, which limit the achievable resolution. We provided a model that takes into account such substrate effects. The findings of our study allow the design and easily accessible fabrication of graphene devices featuring complex defect engineering, with a remarkable impact on technologies exploiting the increased surface reactivity.

The O-doped layer under electron irradiation induced high sensitivity simultaneous electrochemical determination of colorants in the graphene intercalated carbon film

In this work, we studied the high electrochemical activity induced by the O-doped layer on the graphene intercalated carbon (GIC) film under low energy electron irradiation. The GIC film was prepared by using the electron cyclotron resonance (ECR) plasma sputtering system and the top layer was deposited with 5 % oxygen doped under electron irradiation with different energy. Based on the nanostructure characterization, the electron irradiation played the key role to activate the bonding with oxygen and carbon atoms. In our experiments, doping 5 % oxygen under electron irradiation with energy of 50 V promoted more graphene edges and functional groups formed. The GIC film with O-doped top layer under electron irradiation of 50 V exhibits high electrochemical activity in Fe(CN)64−/3− and Fe3+/2+ redox systems, and realized the simultaneous detecting of sunset yellow (SY) and tartrazine (TT). The mechanism could be that the graphene edge and functional group formed by the activated oxygen atoms provide more active sites to accelerate the electron transfer.

Distinguishing the EH1 and S1 defects in n-type 4H-SiC by Laplace DLTS

We report on the low-energy electron and fast neutron irradiated 4H-SiC studied by deep-level transient spectroscopy (DLTS) and Laplace DLTS. Irradiations introduced two defects, E c −0.4 eV and E c −0.7 eV. They were previously assigned to carbon interstitial (Ci) labeled as EH1/3 and silicon-vacancy (V Si) labeled as S1/2, for the low-energy electron and fast neutron irradiation, respectively. This work demonstrates how Laplace DLTS can be used as a useful tool for distinguishing the EH1 and S1 defects. We show that EH1 consists of a single emission line arising from the Ci(h), while S1 has two emission lines arising from the V Si(h) and V Si(k) lattice sites.

Stability, Evolution and Diffusion of Intrinsic Point Defects in 4H-SiC

Silicon carbide (SiC) is a wide band-gap semiconductor of great technological importance, showing promise for application areas ranging from quantum computing and communication to power devices. Vital in both the contexts of power devices and quantum technology is the understanding of intrinsic defects that are introduced during various device processing steps, both immediately after their formation and over the course of defect evolution with temperature. Here we monitor the formation and evolution of intrinsic point defects in n-type 4H-SiC after proton irradiation at room temperature and subsequent annealing in the temperature range 300-1000 °C, and discuss the nature and origin of the EH4 and EH5 deep level defects observed by deep level transient spectroscopy around 400-500 K. In particular, the controversy on the nature of the EH5 trap in particular is addressed, where we propose the presence of two overlapping defect peaks: one metastable level that appears after low energy electron irradiation below the silicon displacement limit, and one more stable level that gradually decreases in concentration until an annealing temperature of 1000°C. We argue that the former is likely related to carbon interstitials, while the latter was recently tentatively attributed to the carbon antisite-vacancy pair.

Investigations Into the Suitability of Bacterial Suspensions as Biological Indicators for Low-Energy Electron Irradiation.

Low-energy electron irradiation is an emerging alternative technology for attenuated or complete pathogen inactivation with respect to medical, biotechnological, and pharmaceutical applications. Pathogen inactivation by ionizing radiation depends mainly on the absorbed electron dose. In low-energy electron irradiation processes, determination of the absorbed electron dose is challenging due to the limited, material-dependent penetration depth of the accelerated electrons into the matter. In general, there are established dosimetry systems to evaluate the absorbed dose under dry irradiation conditions. However, there is no system for precise dose monitoring of low-energy irradiation processes in liquids or suspensions so far. Therefore, in this study three different bacterial species were investigated as biological dose indicators, especially in the range of low doses (< 6.5 kGy) in aqueous solutions or suspensions. Escherichia coli, Bacillus subtilis, and Staphylococcus warneri were comparatively evaluated for their suitability as biological dose indicators. Thin homogeneous films of the respective bacterial suspensions were irradiated with increasing doses of low-energy accelerated electrons. The average absorbed dose was determined using a colorimetric dosimeter based on a tetrazolium salt solution. The maximum and minimum absorbed doses were measured with a referenced film dosimeter. Subsequently, the inactivation kinetics was determined in terms of inactivation curves and D10 values. Thus, the minimum inactivation dose of bacterial growth was assessed for E. coli and S. warneri. The effect of irradiation with low-energy accelerated electrons on the growth behavior and activity of the bacteria was studied in more detail using impedance spectroscopy. With increasing irradiation doses growth was delayed.