High energy heavy ion irradiation effects in α-Al2O3

doi:10.1016/0168-583X(93)90748-U

Nuclear Instruments and Methods in Physics Research Section B: Beam Interactions with Materials and Atoms

Volumes 80–81, Part 2, 1993, Pages 1114-1118

https://doi.org/10.1016/0168-583X(93)90748-U Get rights and content

Abstract

Single crystals of Al₂O₃ have been irradiated at GANIL with 3.5 MeV/amu Pb ions, at a temperature of ≌ 8 K. The fluence range extended from 4×10¹¹ to 1.2×10¹² ions cm⁻². The effects of high electronic excitation induced in the samples have been characterized by Rutherford backscattering on channeling (RBS) in conjunction with optical absorption measurements. Moreover, some samples preliminary implanted with 10¹⁶⁵⁷Fe⁺ ions cm⁻² at 110 keV and annealed at 1673 K during one hour were studied using conversion electron Mössbauer specroscopy (CEMS) in order to obtain complementary informations. Preliminary RBS results (77 K irradiations) indicate a damage cross section of ∼ 10⁻¹³ cm², consistent with a track radius of about 1.8 nm. The defect efficiency has been also investigated as a function of the electronic stropping power (dE/Dx)_c.

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We report the modifications of lattice structure, optical and electrical properties of α-Al₂O₃ by 100 MeV Ag⁹⁺ ion beam irradiation with fluences in the range of 1 × 10¹¹ -1 × 10¹³ ions/cm². X-ray diffraction patterns have confirmed the polycrystalline form of rhombohedral structure (space group R-3c) for both pristine and irradiated samples. The Raman active phonon-modes of the pristine sample gradually disappeared with the increase of fluence. The Field Emission Scanning Electron Microscopic images indicated a transformation of the surface morphology from a distinct and layered-type grain structure in pristine sample to a soft layered-type grain structure in the irradiated sample of highest infuence. The Energy Dispersive X-Ray Analysis confirmed elemental composition of the irradiated samples close to nominal value of pristine sample. The X-ray Photoelectron spectroscopy confirmed chemical state modification at the surface of irradiated samples, where a fraction of the Al–O bonds has reduced into metallic Al state. The electrical conductivity in irradiated samples has been enhanced and showed thermal irreversibility where the conductivity in the cooling mode is smaller than that in the warming mode. The optical band gap and activation energy for the electronic transition from valence band to conduction band of α-Al₂O₃ have been affected by Ag⁹⁺ ion beam irradiation.
In-situ kinetics of modifications induced by swift heavy ions in Al<inf>2</inf>O<inf>3</inf>: Colour centre formation, structural modification and amorphization
2017, Acta Materialia
This paper details in-situ studies of modifications induced by swift heavy ion irradiation in α-Al2O3. This complex behaviour is intermediary between the behaviour of amorphizable and non-amorphizable materials, respectively. A unique combination of irradiation experiments was performed at the IRRSUD beam line of the GANIL facility, with three different characterisation techniques: in-situ UV–Vis absorption, in-situ grazing incidence X-Ray diffraction and ex-situ transmission electron microscopy. This allows a complete study of point defects, and by depth profile of structural and microstructural modifications created on the trajectory of the incident ion. The α-Al2O3 crystals have been irradiated by 92 MeV Xenon and 74 MeV Krypton ions, the irradiation conditions have been chosen rather similar with an energy range where the ratio between electronic and nuclear stopping power changes dramatically as function of depth penetration. The main contribution of electronic excitation, above the threshold for track formation, is present beneath the surface to finally get almost only elastic collisions at the end of the projected range. Amorphization kinetics by the overlapping of multiple ion tracks is observed. In the crystalline matrix, long range strains, unit-cell swelling, local microstrain, domain size decrease, disordering of oxygen sublattice as well as colour centre formation are found. This study highlights the relationship between ion energy losses into a material and its response. While amorphization requires electronic stopping values above a certain threshold, point defects are predominantly induced by elastic collisions, while some structural modifications of the crystalline matrix, such as unit-cell swelling, are due to contribution of both electronic and nuclear processes.
On the threshold of damage formation in aluminum oxide via electronic excitations
2014, Nuclear Instruments and Methods in Physics Research, Section B: Beam Interactions with Materials and Atoms
This work is aimed to determine the threshold of dense ionization induced damage formation and their morphology in sapphire single crystals irradiated with 1.2 MeV/amu Xe ions. Cross-sectional TEM examination of r-oriented Al₂O₃ specimens irradiated to fluences of 2 × 10¹² and 2 × 10¹³ cm⁻² has revealed discontinuous ion tracks visible from the irradiated surface up to a depth of 7.6 ± 0.1 μm. According to the SRIM code calculation, the threshold electronic stopping power for track formation in Al₂O₃ is within the range 9.8 ÷ 10.5 keV/nm. This value agrees with those predicted by both inelastic and analytical thermal spike models.
Damage creation threshold of Al <inf>2</inf>O <inf>3</inf> under swift heavy ion irradiation
2012, Nuclear Instruments and Methods in Physics Research, Section B: Beam Interactions with Materials and Atoms
Citation Excerpt :
Based on the results obtained by different physical characterization techniques such as scanning force microscopy, profilometry, and channelling Rutherford backscattering, the mean electronic energy loss threshold value for damage creation in Al2O3 is deduced to be 9.5 ± 1.5 keV/nm. This value is significant smaller than values reported earlier [3–5], although the experimental damage data are quite in agreement. For a correct data analysis it has to be taken into account that the damage saturation level is below unity and depends on the electronic energy loss.
Among insulators, sapphire (Al₂O₃) is less sensitive than any amorphizable oxides regarding the irradiation with heavy ions in the electronic energy loss regime. Earlier experimental results indicated a critical energy loss for damage creation of around of 20 keV/nm, while calculations based on the inelastic thermal spike model predict a value of ∼10 keV/nm. In order to clarify this discrepancy, additional irradiation experiments were performed with different ions between Ni and U covering electronic energy losses between 10 and 43 keV/nm and kinetic energies in the range from 1 to 11 MeV/u. Irradiation effects were characterized by atomic force microscopy (hillock formation), profilometry (swelling), and channeling Rutherford backscattering (near-surface disorder). Combining the results from these measurements, an electronic energy loss threshold of 9.5 ± 1.5 keV/nm is extracted, indicating that the earlier threshold was overestimated and confirming the predictive power of the inelastic thermal spike model. Threshold predictions based on thermal spike model calculations are given for lower and higher beam energies.
Nanometric transformation of the matter by short and intense electronic excitation: Experimental data versus inelastic thermal spike model
2012, Nuclear Instruments and Methods in Physics Research, Section B: Beam Interactions with Materials and Atoms
Citation Excerpt :
It should be point out that Al2O3 is a material which is difficult to amorphize [96]. regarding its iconicity value (∼0.6 [53]) It presents a threshold of damage creation [97–99] which is quite large as compared to any other insulators [27,59] as suggested [100]. Furthermore it presents also a two step processes in order to reach complete disorder by channeling Rutherford backscattering: first a non-amorphized disorder is observed which is followed by an amorphization coming from the surface that appears only after incubation fluence [101,102].
Experimental investigations of ion tracks and sputtering phenomena with energetic heavy projectiles in the electronic energy loss regime are re-examined in metallic and insulating materials. An overview of track data such as the velocity dependence of the track size and the critical electronic energy loss for track formation is presented. Different physical characterizations of the material transformation are listed in order to deduce a track size which is independent of the observations. It will point out the differences of damage creation by electronic energy loss compared to nuclear energy loss. In the second part, we present a theoretical description of track formation based on the inelastic thermal spike model. This thermodynamic approach combines the initial size of the energy deposition with the subsequent diffusion process in the electronic and lattice subsystems of the target. The track size, resulting from the quench of a molten phase, is determined by the energy density deposited on the atoms around the ion path governed by the electron–phonon strength. Finally, we discuss the general validity of this model in metallic materials and its suitability to describe track formation in amorphizable and non-amorphizable insulators.
Structural disorder in sapphire induced by 90.3 MeV xenon ions
2010, Nuclear Instruments and Methods in Physics Research, Section B: Beam Interactions with Materials and Atoms
In our previous work [15], we have evidenced, using RBS-C, two effects in the aluminium sublattice of sapphire irradiated with 90.3 MeV xenon ions: a partial disorder creation that saturates at ∼40% followed above a threshold fluence by a highly disordered layer appearing behind the surface. In this work, by RBS-C analysis of the oxygen sublattice, we have observed only one regime of partial disorder creation that saturates at ∼60% in tracks of cross-section double of that found for the aluminium sublattice. Complementary analysis by X-ray diffraction shows that the lattice strain increases with the fluence until a maximum is reached about 7.5 × 10¹² ions/cm². For higher fluences, strain decreases first indicating a little stress relaxation in the material and tends afterwards, to remain constant. This stress relaxation is found to be related to the aluminium sublattice high disorder.

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^☆: Experiments performed at GANIL (Caen).

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High energy heavy ion irradiation effects in α-Al2O3☆

Abstract

Nucl. Instr. and Meth.

Nucl. Instr. and Meth.

Nucl. Instr. and Meth.

Appl. Phys. Lett.

Point Defects in Materials

Nuclear Tracks in Solids

GSI Darmstadt Scientific Report

Phys. Rev. Lett.

High energy heavy ion irradiation effects in α-Al₂O₃☆