Effect Of Low-energy Electron Irradiation Research Articles

О возможности внедрения в агропромышленный комплекс низкоэнергетических (до 300 кэВ) электронных ускорителей (обзор)

An important place in the system of measures to ensure the phytosanitary safety of agricultural produce is traditionally given to chemicals. However, due to negative effects of the chemicals on the environment, new more effective and safe technologies were needed. Feasibility of the use of radiation technologies to improve food safety and agricultural quality has been studied for more than 75 years. Recently radiation-based technologies have become increasingly important in agricultural produce processing to preserve food spoilage during storage. Currently the use of electron beams with energy below 300 keV generated by electron accelerators is increasingly grown in agriculture. The key feature of electron beams is their ability to produce disinfectant ef-fect on irradiated object due to low electrons permeability. It prevents the characteristic radiation-chemical reactions and damage to the structure in the internal volume of the biological specie Such objects are seeds of agricultural plants susceptible to infectious diseases caused by phyto-pathogens. The study aims at the evaluation of the possibility to use low-energy (below 300 keV) electron accelerators in the agro-industrial complex. The paper describes the device and the principle of operation of the state-of-the-art low-energy electron accelerators, as well as their ap-plication in the agricultural sector. The paper considers the effects of low-energy electron irradia-tion of agricultural products on seed phytopathogens and pests. From the analysis of feasibility of use of the low-energy electron accelerators for radiation-induced disinfection and disinsection it becomes evident that irradiation of the crop with low-energy electrons is effective approach to minimize adverse effects of phytopathogens and to prevent destruction of irradiated biological objects. Electron-beam irradiation minimally effects on the nutritional quality of food products.

Effect of low-energy electron irradiation on voltage-capacity curves of Al/SiO2/Si structure

Charging of dielectric targets by electron irradiation is a well-known phenomenon which should be taken into account in characterization of dielectric materials and coatings with electron microscopy, in electron beam lithography, in development of dielectric coatings for spacecrafts and other fields of science and engineering. Charging kinetics is strongly affected by spatial distribution of electrons and holes formed by irradiation. At the experimental electron beam energy electron penetration depth is smaller than dielectric thickness and this allows identifying the contribution of excess carrier transport to trap formation at the SiO2/Si interface. Low-energy electron beams have been shown to substantially affect C–V curve slope, i.e., to form traps at the interface. We have studied the effect of bias applied to the test structure before and after electron beam irradiation. The experiment has shown that bias of either polarity applied to the test MOS structure before low-energy electron beam irradiation practically does not affect the C–V curves of the test structure. Positive bias applied to the metallization layer during low-energy electron beam irradiation has a strong effect on the C–V curve pattern while negative bias affects the C–V curves but slightly. Study of the stability of the changes caused by electron beam irradiation has shown that the C–V curves of the test structure restore slowly even at room temperature. Application of negative bias decelerated charge relaxation.

Effect of Low-Energy Electron Irradiation on DNA Damage by Cu2+ Ion

Effect of Low-Energy Electron Irradiation on DNA Damage by Cu2+ Ion

Effect of low-energy electron irradiation on the optical properties of structures containing multiple InGaN/GaN quantum well

Data on the temperature dependence of the cathodoluminescence intensity in multiple InGaN/GaN quantum-well structures in the temperature range 80–300 K are reported. Unirradiated structures and structures irradiated with electrons with subthreshold energy are studied. It is shown that, upon irradiation, the temperature dependence becomes weaker. From analysis of the results obtained in this study and previously, it can be suggested that electron irradiation initiates the relaxation of strains produced in quantum wells due to the InGaN-GaN lattice mismatch.

Effect of Low-Energy Electron Irradiation on DNA Damage by Fe3+Ion

We investigated the combined effects of low-energy electron irradiation and Fe(3+) ion on DNA damage. We used lyophilized pBR322 plasmid DNA films with various concentrations (0 ~ 7 mM) of Fe(3+) ions and irradiation with monochromatic, low-energy 3 or 5 eV electrons for these studies. DNA-Fe(3+) films were recovered and analyzed by agarose gel electrophoresis to identify and compare the effects of Fe(3+) ions and/or low-energy electrons alone or in combination on DNA damage. In nonirradiated DNA-Fe(3+) films, there was little DNA damage observed (less than 10% of the total DNA loaded on the gel appeared damaged) for Fe(3+) ion up to 7 mM concentration. In irradiated DNA films without Fe(3+) ions, there was also very little DNA damage observed (less than 3% of the total DNA loaded on the gel appeared damaged). However, when DNA-Fe(3+) films, were irradiated with low-energy electrons, DNA damage was significantly increased compared to the sum of the damage caused both by either Fe(3+) ion or low-energy electrons irradiation alone. We proposed that both DEA and/or electron transfer processes might play a role in the enhanced DNA damage when DNA-Fe(3+) films were irradiated by low-energy electrons.

Effects of low-energy electron irradiation on formation of nitrogen–vacancy centers in single-crystal diamond

Exposure to beams of low-energy electrons (2–30 keV) in a scanning electron microscope locally induces formation of NV-centers without thermal annealing in diamonds that have been implanted with nitrogen ions. We find that non-thermal, electron-beam-induced NV-formation is about four times less efficient than thermal annealing. But NV-center formation in a consecutive thermal annealing step (800 °C) following exposure to low-energy electrons increases by a factor of up to 1.8 compared to thermal annealing alone. These observations point to reconstruction of nitrogen–vacancy complexes induced by electronic excitations from low-energy electrons as an NV-center formation mechanism and identify local electronic excitations as a means for spatially controlled room-temperature NV-center formation.

Effect of low-energy electron irradiation on the cathodoluminescence of multiple quantum well (MQW) InGaN/GaN structures

The effect of low-energy electron-beam (e-beam) irradiation on the InGaN-related cathodoluminescence in multiple quantum well (MQW) InGaN/GaN light-emitting diode (LED) structures has been studied. It is shown that the e-beam exposure leads to an increase of emission intensity and to a formation of new blue-shifted emission bands. The changes observed were explained by the enhancement of In diffusion stimulated by excess carrier recombination.

Modification of surface properties of thin polysaccharide films by low-energy electron exposure

The effect of low-energy electron irradiation on thin layers of two different polysaccharide materials, namely amylose and chitosan, has been investigated. Modification of the samples occurs at electron energies as low as 5 eV. In the case of amylose, a change in the wetting properties is observed upon exposure. Loss of oxygen from the hydroxyl groups and consequent formation of a hydrocarbon material is responsible for this effect as revealed by analysing the samples before and after electron exposure by means of reflection absorption infrared spectroscopy (RAIRS) and X-ray photoelectron spectroscopy (XPS). It is shown that the amide side groups in chitosan are more reactive than the hydroxyl groups and consequently dominate the modifications in this case. Additional experiments by high-resolution electron energy loss spectroscopy (HREELS) on thin condensed films of the model compound α- d-glucose show that facile oxidation of the saccharide occurs in the presence of O 2. Traces of O 2 as a residual gas can therefore be held responsible for the formation of carboxyl groups that are observed by RAIRS in samples of amylose after electron exposure.

Effect of low-energy electron irradiation on (Bi, Pb)-2212 superconductors

The effect of low-energy electron irradiation on the properties of the Bi-based superconductors is studied. Two sets of polycrystalline (Bi, Pb)-2212 samples were synthesized by heating the appropriate mixtures of powders at 840 °C for 100 h, then quenched or furnace cooled to room temperature. The samples were irradiated by low-energy (1–10 keV), pulsed (20 ns) electron beam up to a dose of 6.2×10 15 cm −2. X-ray diffraction patterns, resistance-temperature behaviours, critical currents, and micrographs of the samples were examined before and after the irradiation. For the quenched samples, the normal state resistance increases and the T c drastically decreases with electron irradiation. For the furnace-cooled samples, T c first improves by about 15 °C up to a dose of 1.7×10 15 cm −2, then drops down with further irradiation. At high levels of doses, the super conducting parameters degrade or vanish due to the increased resistance of the samples. We propose that the electron irradiation causes ionizations that may alter the oxygen and hole concentrations as well as the pining centers and the links between the grains leading the changes reported here.

Electron Irradiation of Poly(3-hexylthiophene) Films

The effects of low-energy electron irradiation on spin-coated films of regioregular poly(3-hexylthiophene) have been studied with fluorescence, mass spectrometry, and a variety of electron spectroscopies, including photoemission. Electron impact by 180 eV electrons causes a decrease in photoluminescence intensity, broadening of the thiophene ring valence electronic state features, and diminution in intensity of the peaks due to π electrons delocalized along the backbone. Electron bombardment also results in a decrease in the X-ray photoelectron spectroscopy sulfur-to-carbon ratio, but only minor shifts in the binding energies of the C 1s and S 2p peaks occur. Quadrupole mass spectrometry has been used to detect electron-stimulated desorption from the polymer films. Ionic desorption includes S-, SH-, S+, and CxHy+ species. Auger electron spectroscopy confirms removal of sulfur from the near-surface region by a 5 keV electron dose of 1.8 × 1018 electrons/cm2, and electron energy loss spectroscopy suggests formation of a graphitic surface.

Low-energy electron-beam effects on poly(methyl methacrylate) resist films

The effects of low-energy electron irradiation (10–50 eV, up to ∼2×1017 e cm−2) on thin films of poly(methyl methacrylate) (PMMA), deposited on air-exposed Al, have been studied in situ as a function of temperature (∼200–300 K) using polarization-modulated infrared reflection absorption spectroscopy. Near 300 K damage is seen in the form of a loss of material, as shown by a decrease in the intensity of the entire PMMA spectrum. At low temperature, in addition to damage, evidence is seen for a radiation-induced change in chain configuration leading to an increased interaction between ester groups and the Al surface. This configuration is unstable and is removed by annealing to ∼300 K.

Effects of low-energy electron irradiation on submonolayer ammonia adsorbed on Pt(111)

The effects of electron impact on ammonia-covered Pt(111) have been studied using temperature-programmed desorption (TPD) and electron-stimulated desorption (ESD). For coverages below one monolayer, ammonia adsorbs on the surface in two distinct TPD states: the α-state is broad and desorbs over the temperature range 150–350 K, and the β-state appears as a sharper peak at 150 K. The β-state was seen to be damaged by electron-beam impact much more readily than the α-state, resulting in the formation of atomically adsorbed N on the surface. The mass 28 recombinative nitrogen desorption TPD peak appearing at 550 K exhibited second-order desorption kinetics, further confirming the presence of atomically adsorbed nitrogen. The ESD kinetic energy distributions (KEDs) were obtained for m/e=1 amu, which exhibited broad peaks generally. The H+ KEDs were analyzed using empirical curve fits, with the resulting conclusion that the H+ KEDs contain contributions from at least three different hydrogen-containing surface species. We believe that these three H+ KED peaks are due to ESD from adsorbed NH3, NH2 and H. The ESD cross-section for NH3 removal was measured in three different ways, all of which were found to be in general agreement, and which gave an averaged cross-section value of Qtot=4×10−17 cm2. © 1998 John Wiley & Sons, Ltd.

Electron Beam Induced Degradation of 2Deg in AlGaAs/GaAs Heterostructure

AbstractThe effects of low-energy electron irradiation on the two-dimensional electron gases (2DEG's) in AlGaAs/GaAs heterostructures have been investigated. Not only the electron mobility of the 2DEG's but also the two-dimensional (2D) carriers are found to be reduced by the electron irradiation with the incident energies between 3.5 k and 8 keV and the electron dose of 1×1016 and 1×1017 /cm2. The degraded mobility and the removed carriers by the low-energy electron irradiation are shown to recover by isochronal annealing to some extent, but not completely below 400°C. It is also found that considerable amount of scatterers which are created by an electron irradiation at room temperature are also created by an irradiation at 90 K. Comparing the experimental results with the Monte Carlo simulation, we speculate that the mobility degradation and the 2D carrier compensation are partly caused by the formation of complex defects in the GaAs buffer layer which are due to the excitations of core electrons of As, and that the mobility is further degraded by the formation of short-range scatterers in the heterointerface.

Radiation Effects on Silicon Schottky Barriers

Because of a variety of important new applications, it is desirable to determine the effects of radiation on silicon Schottky barrier diodes. In the present study, both neutron and low-energy electron irradiation were employed and a variety of Schottky diode structures were investigated. These included the p-n junction guard ring structure and a gate-controlled structure which was used to separate surface from bulk effects. The two main effects of low-energy electron irradiation are: increase of surface recombination velocity and buildup of a positive space charge in the oxide. These results are consistent with previous studies of p-n junction diodes. For Schottky diodes without gate electrodes, the breakdown voltage is decreased and some excess current is present at low forward bias after irradiation. The effects of nuclear irradiation are (in addition to the surface effects mentioned above): decrease of bulk lifetime and carrier removal, again consistent with previous studies on p-n junction devices. Recombination-generation current increases manyfold due to the decrease in lifetime after irradiation. This component of current is important for Pt Schottky diodes which have a high barrier (0.85 eV). However, for Al diodes, since the barrier is relatively low (0.69 eV) and the thermionic emission current relatively high, recombination-generation current is not important until very high neutron dosage.