High-energy Electron Irradiation Research Articles

Short-Range Atomic Ordering Accelerated by Severe Plastic Deformation in FCC Invar Fe–Ni Alloys

The deformation-enhanced atomic redistribution, i.e., accelerated ordering upon warm (573 K) and disordering upon cold (298 K) high pressure torsion, has been investigated using Mossbauer spectroscopy in the binary invar Fe100 –xNix (x = 34.2–35.5 at %) alloys. Results of deformation-induced ordering and high-energy electron irradiation have been compared.

Degradation and regeneration of radiation-induced defects in silicon: A study of vacancy-hydrogen interactions

Silicon lattice vacancies exist in all silicon wafers, will increase in concentration due to high temperature processing, can form recombination active defects and have been proposed as a possible candidate for LeTID. Despite this, there have been relatively few studies in the solar field dedicated to investigating vacancies, their recombination properties or their interaction with hydrogen. In this work, we use high energy electron radiation to create large numbers of vacancies in silicon and study the lifetime response to subsequent thermal processes in the presence or absence of bulk hydrogen. The radiation results in the formation of radiation-induced defects which we interpret as being related to the creation of vacancies in the silicon bulk. Modelling of injection dependent minority carrier lifetime finds that the defects formed via this radiation process have different Shockley-Read-Hall properties to LeTID and are as such, unlikely to be related. Furthermore, this defect can be removed during low temperature annealing but only if hydrogen is present in the bulk of the silicon wafers. This is in contrast to samples with no bulk hydrogen which do not recover during low temperature annealing. The study thus finds no evidence for any link between LeTID and vacancies in silicon, but it does demonstrate the ability of hydrogen to repair radiation damage.

Optically Coherent Nitrogen-Vacancy Centers in Micrometer-Thin Etched Diamond Membranes

Diamond membrane devices containing optically coherent nitrogen-vacancy (NV) centers are key to enable novel cryogenic experiments such as optical ground-state cooling of hybrid spin-mechanical systems and efficient entanglement distribution in quantum networks. Here, we report on the fabrication of a (3.4 ± 0.2) μm thin, smooth (surface roughness rq < 0.4 nm over an area of 20 μm by 30 μm) diamond membrane containing individually resolvable, narrow linewidth (< 100 MHz) NV centers. We fabricate this sample via a combination of high-energy electron irradiation, high-temperature annealing, and an optimized etching sequence found via a systematic study of the diamond surface evolution on the microscopic level in different etch chemistries. Although our particular device dimensions are optimized for cavity-enhanced entanglement generation between distant NV centers in open, tunable microcavities, our results have implications for a broad range of quantum experiments that require the combination of narrow optical transitions and micrometer-scale device geometry.

Computational identification of Ga-vacancy related electron paramagnetic resonance centers in β-Ga2O3

A combined experimental/theoretical study of the electron paramagnetic resonance (EPR) centers in irradiated β-Ga2O3 is presented. Four EPR spectra, two S = 1/2 and two S = 1, are observed after high-energy proton or electron irradiation. Three of them have been reported before in neutron irradiated samples. One of the S = 1/2 spectra (EPR1) can be observed at room temperature and below and is characterized by the spin Hamiltonian parameters gb = 2.0313, gc = 2.0079, and ga* = 2.0025 and a quasi-isotropic hyperfine interaction with two equivalent Ga neighbors of ∼14 G on 69Ga and correspondingly ∼18 G on 71Ga in their natural abundances. The second (EPR2) is observed after photoexcitation (with a threshold of 2.8 eV) at low temperature and is characterized by gb = 2.0064, gc = 2.0464, and ga* = 2.0024 and a quasi-isotropic hyperfine interaction with two equivalent Ga neighbors of 10 G (for 69Ga). A spin S = 1 spectrum with a similar g-tensor and a 50% reduced hyperfine splitting accompanies each of these, which is indicative of a defect of two weakly coupled S = 1/2 centers. Density functional theory calculations of the magnetic resonance fingerprint (g-tensor and hyperfine interaction) of a wide variety of native defect models and their complexes are carried out to identify these EPR centers in terms of specific defect configurations. The EPR1 center is proposed to correspond to a complex of two tetrahedral VGa1 with an interstitial Ga in between them and oriented in a specific direction in the crystal. This model was previously shown to have lower energy than the simple tetrahedral Ga vacancy and has a 2−/3− transition level higher than other VGa related models, which would explain why the other ones are already in their diamagnetic 3− state and are thus not observed if the Fermi level is pinned approximately at this level. The EPR2 spectra (S = 1/2 as well as the related S = 1) are proposed to correspond to the octahedral VGa2 in which the spin is located on an oxygen off the defect’s mirror plane and has a tilted spin density. Models based on self-trapped holes and oxygen interstitials are ruled out because they would have hyperfine interaction with more than two Ga nuclei and because they cannot support a corresponding S = 1 center.

Reflection high energy electron diffraction (RHEED) study of ice nucleation and growth on Ni(111): influences of adspecies and electron irradiation.

How interfacial molecular interactions influence nucleation and growth processes of water ice is explored using pristine, oxygenated, and CO-adsorbed Ni(111) substrates based on RHEED, together with the effects of high-energy electron irradiation on the crystallization kinetics. A monolayer of amorphous solid water deposited onto the pristine Ni(111) substrate crystallizes into ice Ic at ca. 150 K, whereas ice Ih (Ic) is formed preferentially during water vapor deposition at 135 K (125 K). The ice nucleation tends to be hampered on the oxygenated Ni(111) surface because of the hydrogen bond formation with chemisorbed oxygen, leading to the growth of randomly-oriented ice Ic crystallites via spontaneous nucleation. The amorphization and recrystallization of initially crystalline ices are observed during prolonged RHEED measurements at 20 and 70 K, respectively, signifying that high-energy electron irradiation has both thermal and non-thermal effects on the water phase transition. The epitaxial growth (non-epitaxial growth) of ice occurs during electron irradiation of amorphous solid water formed on the pristine and oxygenated Ni(111) substrates (CO-adsorbed Ni(111) substrate) even at 100 K (120 K) because nucleation and growth are initiated at the substrate interface (in the ASW film interior).

Влияние облучения электронами высокой энергии на характеристики ударных токов высоковольтных интегрированных 4H-SiC p-n-диодов Шоттки

The effect of high energy (0.9 MeV) electron irradiation on surge currents of high-voltage 4H-SiC JBS was investigated in the microsecond range of the forward current pulses duration. With irradiation dose  growth, the threshold of hole injection monotonically increases, and the base modulation level by minority carriers (holes) decreases. At = 1.5×1016 cm-2, the hole injection is not observed up to forward voltage values of ~ 30 V and forward current density j  9000 A/cm2.

10. Commissioning and Operation of External High-energy Electron Radiation Therapy

10. Commissioning and Operation of External High-energy Electron Radiation Therapy

DEFORMATION DEPENDENCE OF POLYMER MATERIALS ON THE DOSE OF ELECTRONIC RADIATION

In this paper we consider the effect of high-energy electron irradiation, load and temperature on the mechanical properties of Mylar films. The simplest physical model is developed. Studies have shown that with an increase in the dose of electron irradiation to 104 Gy, there is a slow decrease in deformation for Mylar, and a further increase to 106 Gy leads to a sharp decrease in it. At the same time, with increasing temperature, the relative elongation increases by more than 50 %, associated with the growth of destructive processes in the material. The dependences of strain and stress on the dose of electron irradiation are described by exponential functions and are in satisfactory agreement with experimental data.

The role of chemical disorder and structural freedom in radiation-induced amorphization of silicon carbide deduced from electron spectroscopy and ab initio simulations

Chemical disorder has previously been proposed as an explanation for the anomalously facile amorphization of silicon carbide (SiC), on the basis of topological connectivity arguments alone. In this exploratory study, “amorphous” (formally, aperiodic) SiC structures produced in ab initio molecular dynamics simulations were assessed for their connectivity topology and used to compute synthetic electron energy-loss spectra (EELS) using the ab initio real-space multiple scattering code FEFF. The synthesized spectra were compared to experimental EELS spectra collected from an ion-amorphized SiC specimen. A threshold level of chemical disorder χ (expressed as the ratio of the number of carbon-carbon bonds to the number of carbon-silicon bonds) was found to be χ ≈ 0.38, above which structural relaxation resulted in formally aperiodic structures. Different disordering methodologies resulted in identifiably different aperiodic structures, as assessed by local-cluster analysis and confirmed by collecting near-edge electron energy-loss spectra (ELNES). Such structural differences are predicted to arise for SiC crystals amorphized by irradiations involving different damage mechanisms—and therefore differing disordering mechanisms—for example, when contrasting the respective amorphized products of ion irradiation, neutron irradiation, and high-energy electron irradiation. Evidence for sp2-hybridized carbon bonding is observed, both experimentally in the irradiated sample and in simulations, and related to connectivity topology-based models for the amorphization of silicon carbide. New information about the probable intermediate-range structures present in amorphized silicon carbide is deduced from enumeration of primitive rings and evolution of local cluster configurations during the ab initio-modelled amorphization sequences.

Bismuth oxide-based nanocomposite for high-energy electron radiation shielding

A novel polymer-based nanocomposite was fabricated to investigate its shielding properties against high-energy electron radiation for potential applications in space industry. Bismuth oxide (Bi2O3) nanoparticles and multi-walled carbon nanotubes (MWCNT) were added to poly (methyl methacrylate) (PMMA) to fabricate the nanocomposite. Radiation shielding efficiency of different samples, pure PMMA, PMMA/MWCNT, and PMMA/MWCNT/Bi2O3, was characterized and compared with aluminum (Al). The electron-beam attenuation characteristics show that PMMA/MWCNT/Bi2O3 nanocomposite was 37% lighter in comparison with Al at the same radiation shielding effectiveness in electron energy range of 9–20 MeV. Furthermore, mechanical and thermal properties indicate that PMMA/MWCNT/Bi2O3 can achieve significantly improved tensile strength, initial decomposition temperature, and glass transition temperature over pure PMMA. The stabled thermal properties, chemical structures, and morphology of all materials before and after electron irradiation lead to excellent radiation resistance of PMMA and nanocomposite. In conclusion, the proposed nanocomposite is a promising material for high-energy, electron-beam shielding applications.

Effect of environment on charge transport properties of polyimide films damaged by high-energy electron radiation

Ground based measurements are critical to understanding the space environment-induced modifications of spacecraft materials and predictive spacecraft modeling. The interaction of high-energy electrons with spacecraft materials, such as polyimide (PI, Kapton-H®), is known to modify the material's chemical and consequently physical properties. Highly stable in its pristine state, radiation-damaged PI becomes chemically reactive due to the formation of species containing unpaired electrons (radicals). As a result, the reaction of residual gases, even at low partial pressures, changes the damaged PI's properties and obscures the understanding of the radiation damage mechanisms. In the presented paper, the authors demonstrated that even very limited air exposure will have a dramatic effect on the charge transport properties of radiation-damaged PI. Further, they also evaluated the effects of several major constituents of the Earth's atmosphere (Ar, N2, O2, and H2O) on the charge transport properties of PI damaged by exposure to 90 keV electrons.

Effects of High-Energy Electron Irradiation on Quantum Emitters in Hexagonal Boron Nitride.

Hexagonal boron nitride (hBN) mono and multilayers are promising hosts for room-temperature single photon emitters (SPEs). In this work we explore high-energy (∼MeV) electron irradiation as a means to generate stable SPEs in hBN. We investigate four types of exfoliated hBN flakes-namely, high-purity multilayers, isotopically pure hBN, carbon-rich hBN multilayers and monolayered material-and find that electron irradiation increases emitter concentrations dramatically in all samples. Furthermore, the engineered emitters are located throughout hBN flakes (not only at flake edges or grain boundaries) and do not require activation by high-temperature annealing of the host material after electron exposure. Our results provide important insights into controlled formation of hBN SPEs and may aid in identification of their crystallographic origin.

Effect of High Energy Electron Irradiation on Electrical and Noise Properties of 4H-SiC Schottky Diodes

Electron irradiation of high voltage Ni/4H-SiC Schottky diodes with the dose Φ=(0.2-7)×1016cm-2 led to increase in the base resistance, appearance of slow relaxation processes at extremely small currents, and increase of the low frequency noise. On exponential part of the current-voltage characteristics and on linear part of current-voltage characteristics in non-irradiated samples, low frequency noise always has the form of the 1/f noise. On linear part of the current-voltage characteristics in irradiated diodes the generation recombination (GR) noise predominates. Temperature dependences of the base resistivity and character of GR noise indicate that mainly Z1/2 center contributes to the change in the parameters of irradiated samples. Capture cross section of this level, obtained from noise measurements, is within the range (8×10-16-2×10-15) cm2 and only weakly depends on temperature.

Magnetic Field Sensing with 4H SiC Diodes: N vs P Implantation

We explore the magnetic sensing capabilities of two 4H-SiC n+p diodes fabricated by NASA Glenn which only differ in the implanted ion species, nitrogen and phosphorus, and the implant activation annealing time. We use low-and high-field electrically detected magnetic resonance (EDMR) to investigate the defect structure used to sense magnetic fields as well as to evaluate the sensitivity. In addition, we expose these devices to high energy electron radiation to evaluate the defect sensing capability in a harsh radiation environment. The results from this work will allow us to tailor our processing methods to design a more optimal 4H-SiC pn diode for magnetic field sensing in harsh environments.

Using electron irradiation to probe iron-based superconductors

High-energy electron irradiation at low temperatures is an efficient and controlled way to create vacancy–interstitial Frenkel pairs in a crystal lattice, thereby inducing nonmagnetic point-like scattering centers. In combination with London penetration depth and resistivity measurements, the electron irradiation was used as a phase-sensitive probe to study the superconducting order parameter in iron-based superconductors (FeSCs), lending strong support to sign-changing s± pairing. Here, we review the key results of the effect of electron irradiation in FeSCs.

Regulating Dielectric and Ferroelectric Properties of Poly(vinylidene fluoride-trifluoroethylene) with Inner CH=CH Bonds.

Poly(vinylidene fluoride) (PVDF) based ferroelectric polymers have attracted considerable attention both academically and industrially due to their tunable ferroelectric properties. By pinning the conformation of the polymer chain and the ferroelectric phase physically or chemically, the ferroelectric behaviors of PVDF based polymers could be finely turned from normal ferroelectric into relaxor ferroelectric, anti-ferroelectric like, and even linear dielectric. Besides high energy electron irradiation and chemical copolymerization with the bulky monomers, in this work, an alternative strategy is presented to regulate the dielectric and ferroelectric performances of PVDF based ferroelectric polymer for the first time. CH=CH bonds with the desired content are inserted by a controlled dehydrofluorination reaction into a poly(vinylidene fluoride-trifluoroethylene) (P(VDF-TrFE)) copolymer (TrFE refers to trifluoroethylene) synthesized from the hydrogenation of P(VDF-CTFE) (CTFE refers to chlorothrifluoroethylene). The influence of the CH=CH bonds along with the fabrication conditions on the crystallization and ferroelectric relaxation of the resultant copolymers (referred to P(VDF-TrFE-DB)) was carefully characterized and discussed. The nonrotatable CH=CH bonds result in depressed dielectric and ferroelectric performances in the as-cast films by confining the orientation of ferroelectric grains in P(VDF-TrFE). The normal ferroelectric performance of P(VDF-TrFE) is turned into anti-ferroelectric like behavior in the resultant P(VDF-TrFE-DB). The cleavage of CH=CH bonds is responsible for the recovery of the ferroelectric behavior in the annealed samples. Uniaxial stretching favors the alignment of the polymer chain and ferroelectric domains, which may address the further regulated ferroelectric characters in the stretched samples.

Effect of electron irradiation on the optical properties of SrTiO3: An experimental and theoretical investigations

Diffuse reflectance spectroscopy (DRS) measurement has been carried out on pure and electron irradiated single crystal samples of SrTiO3. Interestingly, it has been observed that electron-irradiated sample have new absorption peak in optical absorption spectra. In order to understand the origin of a new absorption peak in electron irradiated sample, first principle calculation for optical spectra considering defects at Sr, Ti and O site using GGA + U approximation have been carried out. It has been observed that the features present in the experimental optical absorption spectra match with that of simulated one having oxygen vacancy. Present investigation suggests that high energy electron irradiation produces oxygen defects in SrTiO3 and DRS is found to be a useful technique to probe the signature of such defects experimentally.

High energy electron irradiation effects on Ga-doped ZnO thin films for optoelectronic space applications

Gallium-doped ZnO (GZO) thin films of thickness 394 nm were prepared by a simple, cost-effective sol–gel spin coating method. The effect of 8 MeV electron beam irradiation with different irradiation doses ranging from 0 to 10 kGy on the structural, optical and electrical properties was investigated. Electron irradiation influences the changes in the structural properties and surface morphology of GZO thin films. X-ray diffraction analysis showed that the polycrystalline nature of the GZO films is unaffected by the high energy electron irradiation. The grain size and the surface roughness were found maximum for the GZO film irradiated with 10 kGy electron dosage. The average transmittance of GZO thin films decreased after electron irradiation. The optical band gap of Ga-doped ZnO films was decreased with the increase in the electron dosage. The electrical resistivity of GZO films decreased from 4.83 × 10−3 to 8.725 × 10−4 Ω cm, when the electron dosage was increased from 0 to 10 kGy. The variation in the optical and electrical properties in the Ga-doped ZnO thin films due to electron beam irradiation in the present study is useful in deciding their compatibility in optoelectronic device applications in electron radiation environment.

CIGS Solar Cells for Space Applications: Numerical Simulation of the Effect of Traps Created by High-Energy Electron and Proton Irradiation on the Performance of Solar Cells

Numerical simulation is carried out using the Silvaco ATLAS software to predict the effect of 1-MeV electron and 4-MeV proton irradiation on the performance of a Cu(In, Ga)Se2 (CIGS) solar cell that operates under the air mass zero spectrum (AM0). As a consequence of irradiation, two types of traps are induced including the donor- and acceptor-type traps. Only one of them (the donor-type trap) is found responsible for the degradation of the open-circuit voltage (VOC), fill factor (FF) and efficiency (η), while the short circuit current (JSC) remains essentially unaffected. The modelling simulation validity is verified by comparison with the experimental data. This article shows that CIGS solar cells are suited for space applications.

Nanoporous gold synthesized by plasma-assisted inert gas condensation: room temperature sintering, nanoscale mechanical properties and stability against high energy electron irradiation

With a plasma assisted gas condensation system it is possible to achieve high-purity nanoporous Au (np-Au) structures with minimal contaminations and impurities. The structures consist of single Au-nanoparticles, which partially sintered together due to their high surface to volume ratio. Through electron microscopy investigations a porosity >50% with ligament sizes between 20–30 nm was revealed. The elastic modulus of the np-Au was determined via peak force quantitative nanomechanical mapping and resulted in values of 7.5 ± 1.5 GPa. The presented structures partially sintered at room temperature, but proved to be stable to electron irradiation with energies of 7 MeV up to doses of 100 MGy. The electron irradiation stability opens the venue for electron assisted functionalization with biomolecules.