Nanostructuring induced enhancement of radiation hardness in GaN epilayers

The radiation hardness of as-grown and electrochemically nanostructured GaN epilayers against heavy ion irradiation was studied by means of photoluminescence(PL) and resonant Raman scattering (RRS) spectroscopy. A nanostructuring induced enhancement of the GaN radiation hardness by more than one order of magnitude was derived from the PL and RRS analyses. These findings show that electrochemical nanostructuring of GaN layers is a potentially attractive technology for the development of radiation hard devices

The influence of helium-induced defects on the migration of strontium implanted into SiC above critical amorphization temperature

The presence of radiation-induced defects and the high temperature of implantation are breeding grounds for helium (He) to accumulate and form He-induced defects (bubbles, blisters, craters, and cavities) in silicon carbide (SiC). In this work, the influence of He-induced defects on the migration of strontium (Sr) implanted into SiC was investigated. Sr-ions of 360 keV were implanted into polycrystalline SiC to a fluence of 2 × 1016 Sr-ions/cm2 at 600°C (Sr-SiC). Some of the Sr-SiC samples were then co-implanted with He-ions of 21.5 keV to a fluence of 1 × 1017 He-ions/cm2 at 350°C (Sr + He-SiC). The Sr-SiC and Sr + He-SiC samples were annealed for 5 h at 1,000°C. The as-implanted and annealed samples were characterized by Raman spectroscopy, scanning electron microscopy (SEM), atomic force microscopy (AFM), transmission electron microscopy (TEM), and Rutherford backscattered spectrometry (RBS). Implantation of Sr retained some defects in SiC, while co-implantation of He resulted in the formation of He-bubbles, blisters, and craters (exfoliated blisters). Blisters close to the critical height and size were the first to exfoliate after annealing. He-bubbles grew larger after annealing owing to the capture of more vacancies. In the co-implanted samples, Sr was located in three regions: the crystalline region (near the surface), the bubble region (where the projected range of Sr was located), and the damage region toward the bulk. Annealing the Sr + He-SiC caused the migration of Sr towards the bulk, while no migration was observed in the Sr-SiC samples. The migration was governed by “vacancy migration driven by strain fileds.

MICROSTRUCTURE AND PHASE TRANSFORMATIONS IN THE ODS ALLOYS IRRADIATED BY SWIFT HEAVY IONS

Microstructure of KP4 ODS alloy irradiated with 700 MeV bismuth ions at 300K has been studied using high resolution transmission electron microscopy. No latent tracks have been observed in Y4Al2O9 particles in KP4 irradiated with Bi ions. Small oxides (~ 5 nm) in KP4 alloy remain crystalline at Bi ion fluence 1.5×1013 cm-2, while subsurface regions in large (~ 20 nm) particles faced to the beam entrance became amorphous

A New Nanoporous Material Based on Amorphous Silicon Dioxide

Processes for making nanoporous SiO2 layers on Si via the irradiation of thermally oxidized silicon wafers with fast ions followed by chemical treatment in a solution or vapor of hydrofluoric acid are presented. It is shown that the density, shape, diameter, and length to diameter ratio of channels etched in silicon dioxide can be controlled by varying the regimes of fast ion irradiation or chemical treatment of SiO2/Si structures. Track parameters calculated using the thermal spike model are compared with the chemical etching data

Investigation of the microstructure of the fine-grained YPO4_4:Gd ceramics with xenotime structure after Xe irradiation

The paper reports on the preparation of xenotime-structured ceramics by the Spark Plasma Sintering (SPS) method. Phosphates Y$_{0.95}$Gd$_{0.05}$PO$_4$ (YPO$_4$:Gd) were obtained by the sol-gel method. The synthesized nanopowders are collected in large agglomerates 10-50 mkm in size. Ceramics has a fine-grained microstructure and a high relative density (98.67%). The total time of the SPS process was approximately 18 min. High-density sintered ceramics YPO$_4$:Gd with a xenotime structure were irradiated with Xe$^{+26}$ ions (E = 167 MeV) to fluences of $1\times10^{12}$-$3\times 10^{13}$ cm$^{-2}$. Complete amorphization at maximum fluence was not achieved. As the fluence increases, an insignificant increase in the depth of the amorphous layer is observed. According to the results of grazing incidence XRD (GIXRD), with an increase in fluence from $1\times10^{12}$-$3\times 10^{13}$ cm$^{-2}$, an increase in the volume fraction of the amorphous structure from 20 to 70% is observed. The intensity of XRD peak 200 YPO$_4$:Gd after recovery annealing (700$^\circ$C, 18 h) reached a value of ~80% of the initial intensity I0.Comment: 16 pages, 10 figure

On the defect pattern evolution in sapphire irradiated by swift ions in a broad fluence range

Sapphire samples, irradiated with swift Kr (245 MeV) ions at room temperature in a broad fluence range, were investigated using a continuous and a pulsed positron beam to study the defect structure created by the passage of the ions in depths of a few micrometers. At small doses, monovacancies were identified as dominant defects and positron trapping centres. These monovacancies are assumed to be highly concentrated inside a cylindrical volume around the ion path with an estimated radius of ~1.5 nm. For higher doses a second type of trapping centre emerges. This second class of structural imperfection was associated with the overlap of the individual ion tracks leading to the formation of larger vacancy clusters or voids.http://www.sciencedirect.com/science/article/B6THY-4SHF49N-1S/1/3eb43650299e0466e76cbbbfdaca9fa

Raman Study of Polycrystalline Si3N4 Irradiated with Swift Heavy Ions

A depth-resolved Raman spectroscopy technique was used to study the residual stress profiles in polycrystalline silicon nitride that was irradiated with Xe (167 MeV, 1 × 1011 cm−2 ÷ 4.87 × 1013 cm−2 ) and Bi (710 MeV, 1 × 1011 cm−2 ÷ 1 × 1013 cm−2 ) ions. It was shown that both the compressive and tensile stress fields were formed in the irradiated specimen, separated by a buffer zone that was located at a depth that coincided with the thickness of layer, amorphized due to multiple overlapping track regions. The compressive stresses were registered in a subsurface region, while at a greater depth, the tensile stresses were recorded and their levels reached the maximum value at the end of ion range. The size of the amorphous layer was evaluated from the dose dependence of the full width at half maximum (FWHM) (FWHM of the dominant 204 cm−1 line in the Raman spectra and scanning electron microscopy. © 2021 by the authors. Licensee MDPI, Basel, Switzerland

Latent tracks of swift Bi ions in Si3N4

Parameters such as track diameter and microstruture of latent tracks in polycrystalline Si3N4 induced by 710 MeV Bi ions were studied using TEM and XRD techniques, and MD simulation. Experimental results are considered in terms of the framework of a 'core-shell' inelastic thermal spike (i-TS) model. The average track radius determined by means of electron microscopy coincides with that deduced from computer modelling and is similar to the track core size predicted by the i-TS model using a boiling criterion. Indirect (XRD) techniques give a larger average latent track radius which is consistent with the integral nature of the signal collected from the probed volume of irradiated material. © 2020 The Author(s). Published by IOP Publishing Ltd

Surface chemistry and structural properties of proton-beam irradiated graphene oxide paper

Graphene oxide (GO) is a promising material for the futuregraphene-based electronics where the surface chemistry and structural properties of GO may play an important role. One of the unique methods with great potentialfor controllable modification of materials’ properties is the ion beam irradiation. In the present study, GO paper was irradiated with 15 keV proton- beam to a fluences from 5×10 16 to 2×1017 ionscm-2 , while Fourier-transform infrared spectroscopy (ATR-FTIR), X-ray photoelectronspectroscopy (XPS) and Raman spectroscopy (RS)were used for the examination of surface chemistry and structural properties of the irradiated material. It was shown that proton beam irradiation leads to a partial reduction of GOwith the preferential removal of the alkoxy and epoxy groups. With the increasing fluence, the oxygen content from the XPS method and the intensity ratioof D and G Raman bandsboth showed decreasing trends. When oxygen content was compared to relative areas of specific functional groups and parameters of Raman peaks an interesting correlation was found that suggest optimal fluences for tuning the surface chemistry and structural properties of GO. The observed effects on surface chemistry and structural propertiescan be ascribed to physical and chemical effectsof ion beam irradiation. The interaction of functional groups with H-atom was investigated using DFT andsemi-empirical (SE) approach. SE calculations revealed that the reduction of the epoxy group appears at H-atom energies below 1.5 eV. This work identifies ion beam irradiation as a preferable technique for selective removal of surface oxygen groups and structural modification of GO where the applied fluence can be used for tuning the degree of change.IX Serbian Ceramic Society Conference - Advanced Ceramics and Application : new frontiers in multifunctional material science and processing : program and the book of abstracts; September 20-21, 2021; Belgrad