Characterization of He Bubbles in Irradiated Aluminium with High Resolution Transmission Electron Microscopy and Electron Energy Loss Spectroscopy David Rondón Brito 1 , Esteban A. Sánchez 2 and Alfredo Tolley 2* 1. Institutlo Balseiro, Comisión Nacional de Energía Atómica (CNEA) and Universidad Nacional de Cuyo, San Carlos de Bariloche, Argentina (presently at Centro Atómico Ezeiza, CNEA, Ezeiza, Argentina). 2. Centro Atómico Bariloche CNEA-CONICET, San Carlos de Bariloche, Argentina. (12pt) * Corresponding author: tolley@cab.cnea.gov.ar Irradiation effects in metallic alloys has been an active area of research since a few decades ago, and is actually stimulated by the demand of developing materials that should withstand mechanical integrity at higher temperatures and higher irradiation doses for structural components of Generation IV fission reactors and for first wall components in fusion reactors [1]. This work reports results of 20 keV He + irradiations on high purity aluminium at room temperature. The aim of the experiments was to study the formation of nanometer sized bubbles that cause swelling and embrittlement, and the effects of blistering that results from coalescence of bubbles and leads to surface erosion by exfoliation. The irradiation experiments were carried out in a 120 kV ion accelerator at Centro Atómico Bariloche. A Tecnai F20 transmission electron microscope equipped with a Quantum ER system was used for post-irradiation characterization, combining High Resolution Imaging (HRTEM) and Electron Energy Loss Spectroscopy (EELS). Figure 1a shows faceted He bubbles in the aluminium matrix, imaged with HRTEM, produced by an irradiation fluence of 5.2 x 10 16 ions/cm 2 , equivalent to an irradiation dose of 3 displacements per atom (dpa). Figure 1b corresponds to a specimen irradiated to a fluence of 2.6 x 10 17 ions/cm 2 that corresponds to 15 dpa, where faceting is more marked. The mean equivalent diameter at 15 dpa (that of a spherical bubble with the same volume as the faceted bubble) was (2.4 ± 0.1) nm, and the width of the size distribution was 0.6 nm (figure 1c). Figure 1d shows three EELS spectra for comparison obtained in i) an unirradiated pure Al specimen; ii) an irradiated Al specimen to a dose of 3 dpa and iii) an irradiated Al specimen to a dose of 15 dpa. In all spectra, typical Al volume plasmon peaks at energy losses of about 15 eV and 30 eV are clearly observed. In between these plasmon peaks, in the irradiated Al specimens a small peak can be observed. The inset in figure 1d shows a detail of the energy loss region between the plasmon peaks for the three specimens mentioned. The curves have been displaced for clarity. The small peak in the irradiated specimens corresponds to the excitation of the K shell of He. The energy of the small K shell He peak was found to vary between 21.5 eV and 24 eV. Such a variation in the energy of the K shell He peak in He bubbles formed by ion implantation has been previously reported by Jaegger and co-workers [2], and was attributed to differences in the gas pressure inside the bubbles. Summarizing the present results, He in irradiated Al has been detected by means of EELS. Further studies involving quantification of the He content as a function of the irradiation parameters are in progress. Microsc. Microanal. 26 (Suppl 1), 2020 © Microscopy Society of America 2020 doi:10.1017/S1431927620000367 25 https://doi.org/10.1017/S1431927620000367 Downloaded from https://www.cambridge.org/core. IP address: 3.235.180.21, on 22 Feb 2021 at 06:55:02, subject to the Cambridge Core terms of use, available at https://www.cambridge.org/core/terms.