Subsequent Electron Irradiation Research Articles

Elucidating slipping behaviors between carbon nanotubes: Using nitrogen doping and electron irradiation to suppress slippage

The slipping phenomenon of carbon nanotubes (CNTs) and nitrogen-doped CNTs (NCNTs) compromises their mechanical strength and potential applications. Elucidation of this microscopic phenomenon is essential for applying CNTs as high-strength materials. This study investigates the slip mechanisms in CNTs and NCNTs, with the aim of enhancing their mechanical properties. By combining various analytical techniques, we elucidated the adhesion and slipping behaviors of CNT bundles under various conditions. van der Waals forces were found to dominate the stick–slip phenomenon in stable CNT stacks. The introduction of amorphous carbon and subsequent electron irradiation led to the formation of stronger covalent bonds between the tubes, enhancing the mechanical resilience. Notably, NCNTs exhibited a higher frequency of covalent bond excitation by electron irradiation than CNTs. These findings indicate the crucial role of electron irradiation in strengthening the covalent bonds within CNT and NCNT bundles, marking a significant contribution to the mechanical applications of nanotechnology.

Влияние комбинированного ионного и электронного облучения на полосу люминесценции 2 eV в гексагональном нитриде бора

Point defects in wide-bandgap semiconductors, in particular in hexagonal boron nitride, are promising candidates for single-photon emitters, used in quantum informatics. We investigated cathodoluminescence of ion beam induced defects in hexagonal boron nitride, as well as the effect of prolonged electron irradiation on the intensity of the luminescence. It has been shown that the intensity of both band-to-band emission and defect related emission decreased after ion irradiation, and during subsequent electron irradiation the intensity of 2 eV luminescence band increased, whereas the intensity of other bands remained unchanged.

Sequential ion-electron irradiation of zirconium carbide ceramics: Microstructural analysis

Zirconium Carbide (ZrCx) was irradiated with 10 MeV Au3+ ions to a dose of 10 displacements per atoms (dpa) and subsequently with 100 and 300 keV electrons in a transmission electron microscope (TEM). After ion irradiation, dislocation loops were observed in the microstructure and an increase in the number of carbon vacancies was revealed by Raman spectroscopy. Grazing incidence X-ray diffraction (GIXRD) analysis showed that neither amorphization nor oxidation occurred during ion irradiation of the specimen. Subsequent electron irradiation of the pre-implanted ZrCx foil led to formation of nanosized tetragonal ZrO2 precipitates (5−10 nm diameter) on the surface of the TEM lamella. The formation of the new oxide phase was not related to the electron beam-induced heating of the specimen, but to electron stimulated oxidation caused by the residual oxygen inside the transmission electron microscope. Changes in size and density of ZrO2 crystallites were observed between the pristine and ion irradiated ZrCx regions following electron irradiation, suggesting that the initial microstructure of the ZrCx substrate played a key role in the nucleation and growth of the oxide islands. The obtained results provide insights into the microstructural response of ZrCx to different types of radiation and the inadvertent effects of the electron beam during TEM analysis of in-situ and ex-situ ion irradiated ZrCx. Additionally, the findings of this work suggest a method to prepare local ZrO2 nanoprecipitates within ZrCx grains by selective electron beam irradiation.

Effects of Helium Implantation and Subsequent Electron Irradiation on Microstructures of Fe-11 wt.% Cr Model Alloy**Supported by the National Natural Science Foundation of China under Grant Nos U1832133, 11475229 and 91426301.

Helium effects on dislocation and cavity formation of Fe-11 wt.% Cr model alloy are investigated. Single-beam (electron) and dual-beam (He+/e−) irradiations are performed at 350°C and 400°C using an ultra-high voltage electron microscope combined with ion accelerators. In-situ observation shows that the growth rate of dislocation loops is reduced in the helium pre-injected specimen. The mean size of cavities decreased in the helium pre-injected specimen. The possible mechanisms are discussed.

Some new insights into the impact of annealing on single stacking faults in 4H-SiC

The impact of annealing in the 350–500 °C temperature range on the stacking faults, generated by electron beam irradiation of 4H-SiC crystals, have been studied. We have demonstrated that the partial dislocations driving the stacking faults expansion are also mobile under annealing and lead to shrinking of stacking faults. Gliding of 90° partial dislocations with both C- and Si-core is detected after annealing. It is observed that SSFs introduced from indentation by annealing have not pronounced crystallographic orientation that can prevent their expansion under subsequent electron irradiation. An anomalous excess carriers transport along the stacking faults at distances of 10 and 50 μm in highly- and low-doped 4H-SiC is detected.

Investigation of a combined platinum and electron lifetime control treatment for silicon

In silicon, the effect of Combined Lifetime Treatment (CLT) involving platinum diffusion and subsequent electron irradiation is different from the separate treatments of platinum diffusion and electron irradiation, even the treatment of electron irradiation followed by platinum diffusion. In this paper, we investigated the experimental behavior of different kinds of lifetime treated samples. We found that the reverse leakage current (Irr) increases with the increasing platinum diffusion temperature or electron irradiation dose in the separate treatments. Conversely, Irr of the CLT samples decreased with rising platinum diffusion temperature at the same dose of subsequent electron irradiation. By deep-level transient spectroscopy (DLTS), a new energy level E7 (Ec −0.376eV) was found in our CLT samples. The new level E7 suppresses the dominance of the deeper level E8 (Ec −0.476eV), which is caused by electron irradiation directly and results in Irr’s increase. The formation of the level E7 comes from the complex defect-combined effect between platinum atoms and silicon vacancies, and it affects device’s characteristics finally. These research will be helpful to the development of platinum-diffused devices used in intense electron irradiation environments.

Temperature effects on luminescence centers in natural type IIb diamonds

Blue diamonds are among the rarest and most valuable of naturally occurring gemstones. In this study, 12 rough naturally-sourced type IIb diamonds were subjected to HPHT annealing, three different irradiation energies, and then all were stepwise annealed from 200°C to 1100°C and the optical defects were documented by changes in phosphorescence and photoluminescence spectroscopy. Several optical features that are removed from natural type IIb diamonds by HPHT processing, such as 3H, 648.2nm peak, 776.4nm peak, and 660nm band (red) phosphorescence, can be reintroduced into these diamonds with subsequent electron irradiation and annealing at low-to-moderate temperatures. The thermal stability of these centers along with their spatial distribution provided additional insights into their configuration and distinguished them from nitrogen-bearing diamonds.

Deuterium ion irradiation induced precipitation in Fe–Cr alloy: Characterization and effects on irradiation behavior

A new phase was found to precipitate in a Fe–Cr model alloy after 58keV deuterium ion irradiation at 773K. The nanoscale radiation-induced precipitate was studied systematically using high resolution transmission electron microscopy (HRTEM), image simulation and in-situ ultrahigh voltage transmission electron microscopy (HVEM). B2 structure is proposed for the new Cr-rich phase, which adopts a cube-on-cube orientation relationship with regard to the Fe matrix. Geometric phase analysis (GPA) was employed to measure the strain fields around the precipitate and this was used to explain its characteristic 1-dimensional elongation along the 〈100〉 Fe direction. The precipitate was stable under subsequent electron irradiation at different temperatures. We suggest that the precipitate with a high interface-to-volume ratio enhances the radiation resistance of the material. The reason for this is the presence of a large number of interfaces between the precipitate and the matrix, which may greatly reduce the concentration of point defects around the dislocation loops. This leads to a significant decrease in the growth rate.

Microstructure evolution during electron and ion irradiation in commercial purity magnesium

Microstructure evolution during in situ electron irradiation at room temperature within the transmission electron microscope has been studied on commercial purity magnesium. Magnesium foils of purity 99.8% were examined for comparative studies of defect structure formed by 200 keV electrons and 1 MeV krypton ions. Transmission electron microscopy has been used to quantify the type and nature of the microstructural changes taking place during irradiation. Hexagonal-shaped faulted c-component dislocation loops with Burgers vector of are formed by electron irradiation. Formation of inner un-faulted loops also takes place inside the faulted loops. Analysis shows that all the faulted c-component dislocation loops are interstitial in nature and growth rate of these loops is proportional to the irradiation time. Dislocation loops with Burgers vector also form but most of these loops shrink and disappear during subsequent electron irradiation. In some of the foils, only the pre-existing dislocations in the microstructure were observed to transform into vacancy type loops and helical configurations and no other irradiation damage appeared. Ion irradiation for a dose up to 0.1 dpa produced dislocation loops with Burgers vector of and these loops were mixed vacancy and interstitial in character.

Dislocation loop formation under various irradiations of laser and/or electron beams

A high-voltage electron microscope (HVEM) equipped with a laser head (laser-HVEM) was developed at Hokkaido University and is used to investigate the surface modification of semiconductors and the behaviour of lattice point defects in metals under various irradiations of laser (photon) and/or electron beams. In the present study, the annealing effect of pulsed laser irradiation on a face-centred-cubic metal was experimentally investigated and theoretically calculated. The systematic assessment of dislocation loop evolution under laser-electron sequential irradiation and laser-electron dual-beam irradiation was performed. Our results show that the rapid heating and quenching that occurred during pulsed laser irradiation caused vacancies to be introduced at the surface of the specimen and to diffuse to the interior, which led to the formation and growth of vacancy-type (V-type) dislocation loops. These loops gradually shrank and finally disappeared during the subsequent electron irradiation of the sample. During laser-electron simultaneous dual-beam irradiation, the type of loop formed, interstitial-type (I-type) or V-type loops, is determined by the relative intensities of the laser beam and electron beam, which indicates that the loop type can be controlled by changing the relative intensities of the beams. Accordingly, models of dislocation loop formation during various irradiations were proposed. The newly developed laser-HVEM instrument is expected to be employed in the exploration of mechanisms in material science, as well as in other scientific fields.

The Irradiation Effect of a Simultaneous Laser and Electron Dual-beam on Void Formation

Randomly distributed lattice point defects such as supersaturated vacancies (SVs) and Frenkel-pairs (FPs, an interstitial and a vacancy) can be simultaneously introduced into the crystal by energetic beam irradiation in outer space and/or nuclear reactors, but their behavior has not been fully understood. Using a high-voltage electron microscope equipped with a laser (laser-HVEM), we show the striking effects of simultaneous laser-electron (photon-electron) dual-beam irradiation on void formation. Our results reveal that during laser-electron sequential irradiation, pre-laser irradiation enhanced void nucleation and subsequent electron irradiation enhanced void growth. However, the laser-electron dual-beam irradiation was analyzed to depress void swelling remarkably because the recombination of SVs and interstitials was enhanced. The results provide insight into the mechanism underlying the dual-beam radiation-induced depression of void swelling in solids.

Effects of deuterium implantation and subsequent electron irradiation on the microstructure of Fe–10Cr model alloy

The interactions between deuterium atoms and irradiation defects in materials are important for designing materials in fusion reactors due to the fact that deuterium widely exists in nuclear reactions, and that the interactions provide a means to study the dynamic behavior of the isotopes of hydrogen in the material based on the isotope effects. In the current paper, the effects of deuterium implantation and the subsequent electron irradiation on the microstructure of Fe–10wt%Cr model alloy have been investigated using ultra-high voltage transmission electron microscopy (TEM). The in situ observation showed that the size of dislocation loops increases with increasing electron irradiation dose and irradiation temperature. No distinct voids were observed at irradiation temperature up to 823K. The migration energy (Em) of deuterium–vacancy complex was calculated from the growth speed of dislocation loops at 623–773K. A high-resolution TEM image of dislocation loops because of deuterium ion implantation was also achieved.

Fabrication of nano-/micro-patterns on iron phosphate glass surfaces by focused energetic beams

Both focused electron and ion beams (FEB and FIB) were used for fabricating patterned nano-/micro-structures on the surfaces of an iron phosphate glass (FePO). Periodically arranged, nano-sized holes/tubes/rings with their walls being made of Fe nanoparticles were fabricated by FEB direct writing. The diameters of the holes/tubes can be controlled by the beam size and dwell time, as well as by subsequent electron irradiation. Micro- and nano-sized patterns, also with Fe-nanoparticles sitting on the surfaces, were fabricated by FIB sputtering. These result in the possible exploitation of new applications of the glass, particularly in biomaterials, optical circuits, high-density data storage, and controlling the growth of some nanowires/tubes.

Fabrication by electron beam induced deposition and transmission electron microscopic characterization of sub-10-nm freestanding Pt nanowires

We present a method to reduce the size and improve the crystal quality of freestanding nanowires grown by electron beam induced deposition from a platinum metal organic precursor in a dual beam system. By freestanding horizontal growth and subsequent electron irradiation in a transmission electron microscope, sub-10-nm polycrystalline platinum nanowires have been obtained. A combined transmission electron microscopy–electron energy loss analysis has shown that the amorphous carbon, mixed to nanocrystalline platinum in the as-deposited material, is removed from the wires during irradiation. The same treatment progressively transforms nanocrystals dispersed in the amorphous matrix in a continuous polycrystalline platinum wire.

Evidence of electron-stimulated self-diffusion in GaN crystals

In situ transmission electron microscopy (TEM) experiments revealed that dimples formed in hexagonal GaN thin crystals by irradiation of a focused TEM electron beam recovers to flatten the surface under a subsequent electron irradiation with a moderately defocused beam. The electron-stimulated recovery can be attributed neither to knock-on damage nor beam heating effects but to electronically enhanced self-diffusion in the GaN crystals.

A new approach to modelling radiation noise in CCDs

The energy depositions reported by Monte Carlo electron-photon radiation transport codes are subject to a random error due to the finite number of particle histories used to generate the results. These statistical variations, normally a nuisance, may also be identified with the real radiation noise effects experienced by CCD pixels in persistent radiation environments. This paper explores the practicability of such radiation noise modelling by applying the ACCEPT code from the ITS suite to the case of a shielded CCD exposed to an electron flux. The results are compared with those obtained in a subsequent electron irradiation of the CCD by a Van de Graaff accelerator.

Formation of vacancy clustered defects from cascade collisions during heavy-ion irradiation and their annihilation by freely-migrating interstitial atoms

Heavy-ion irradiation of several fcc metals and their ordered alloys was performed. The behavior of ion-irradiation induced point defect clusters during subsequent electron irradiation indicates that about 90% of the clusters are of vacancy type and 10% of interstitials. For any given ion and energy, a wide variation of the collision cascade zone size was found. In general, the larger zones were associated with a larger number of point-defect clusters. A collision zone of a given size was associated with the same average number of clusters even when they were produced by ions of different energy. The dependence of cluster formation on ion energy, target material, and angle of incidence of the ion beam can be correlated with a unique parameter, the depth in the foil of defect cluster formation. The defect yield increases linearly with irradiation dose for shallow depth distributions but then increases with a square-root relationship for deeper distributions. These results are analyzed in terms of a variation in the role of freely-migrating interstitials for the two cases.

Stability of Cascades Under ion and Electron Irradiation in Germanium

AbstractConcurrent irradiation with ions and electrons has been done in a high voltage electron microscope interfaced with an ion accelerator. The objective is to clarify the stability of cascades in Ge in terms of the elementary processes associated with the concurrent irradiation. Amorphous-like cascade contrast is observed under ion irradiation and increases in number eventually leading to saturation. The cascade contrast is produced within cascade regions through sequential overlaps of cascades and heavier ions form more stable cascade regions. The concurrent or subsequent electron irradiation recrystallizes cascade regions through shrinkage of the cascade contrast. Point defects and their diffusion induced by electrons contribute to the recrystallization of cascade regions.

Formation of interstitial loops on transmutation products in aluminum

Effects of the transmutation products on the nucleation of interstitial loops in aluminum have been investigated by electron microscopy. Zone refined aluminum was pre-irradiated with neutrons, helium, and hydrogen ions at elevated temperature and further irradiated with 200 keV electrons at temperatures between 100–323 K to investigate the formation of the interstitial loops. The loop density showed remarkable enhancement by pre-irradiation and dependence on the electron-irradiation temperature. It was suggested that isolated silicon atoms, helium-vacancy complexes, a hydrogen-vacancy complexes act as nucleation sites for the interstitial loops during the subsequent electron irradiation.

Effect of hydrogen on the formation of interstitial loops in hydrogen-irradiated aluminum

The role of hydrogen atoms in the formation of interstitial type dislocation loops in aluminum irradiated with 15 keV hydrogen ions was investigated by electron microscopy. It was found that the loop density satisfied and Arrhenius relation with the pre-irradiation temperature, yielding an apparent activation energy of about 0.3 eV. Experimental results are interpreted in terms of the mechanism that small hydrogen-vacancy complexes formed by the pre-irradiation of hydrogen ions act as nucleation sites of dislocation loops in the subsequent electron irradiation. A basically identical mechanism seems to be acting in the irradiation with hydrogen ions at room temperature.