HVEM-Tandem Facility Research Articles

Ion beam-induced amorphisation of freudenbergite

Using the HVEM-tandem facility at Argonne National Laboratory, the critical dose of 1.5 MeV Kr + ions for amorphisation of freudenbergite ( D c (freudenbergite)) at room temperature was found to be 1.6±0.3×10 18 ions m −2. D c (freudenbergite) is lower than D c (zirconolite) and D c (perovskite) (3.5–5.5 and 3.9–9.2 × 10 18 ion m −2, respectively). Freudenbergite can occur in Synroc-C, a titanate wasteform designed for immobilising high level radioactive waste (HLW). In Synroc-C, zirconolite and perovskite will contain the majority of the actinides in HLW. Freudenbergite will contain less than 0.2 wt% actinides but will experience displacement damage due to the alpha decay of actinides in surrounding phases. In agreement with the experimental findings of previous authors, our calculations show that in Synroc-C, freudenbergite will remain crystalline after zirconolite and perovskite have become amorphous. Neither of the two current parameters (structural freedom, f or susceptibility to amorphisation, S) for estimating the relative radiation resistance of different phases is capable of predicting the relative radiation resistance of freudenbergite, zirconolite and perovskite. The low D c of freudenbergite may result from Na + ions having significantly lower E d values compared to the other elements in freudenbergite, zirconolite and perovskite, in the electric fields induced by heavy ion irradiation of TEM specimens. If this hypothesis is true, it challenges the assumption that heavy ion irradiation can be used to compare the relative radiation resistance of different phases and will have serious implications for the predictive parameters of radiation resistance.

Observation of an Elementary Cuboctahedron Of Xe Nanocrystal in an Al Matrix

When a noble gas element such as Xe is implanted in an fee metal matrix such as Al at room temperature, a fine dispersion of precipitates forms. The precipitates are elementary fee crystals up to diameters of several nanometers (for Xe in Al, 8-10 nm), above which they are non-crystalline. The precipitates exhibit a cube-on-cube orientation relation with the matrices and have lattice parameters which are much larger than those of the matrices (axe ≃ 1-5aAl). Thus the interphase interfaces are incommemsurate though the lattices are isotactic. The precipitates assume the shape of matrix cavities; for an Al matrix, at equilibrium this is a cuboctahedron, a {111} octahedron truncated at the corners on {100}. Fig. 1 is a sketch of a dispersion of such cuboctahedra, viewed approximately along a <110>.For this study specimens were prepared in the HVEM-Tandem Facility at Argonne National Laboratory by implanting 35 keV Xe to a dose of 4x1019 m−2 into well-annealed 5N Al discs which had been thinned by jet electropolishing.

Temperature dependence of Kr ion-induced amorphization of mica minerals

Four different mica compositions, i.e., muscovite [KAl 2(AlSi 3O 10)(OH,F) 2], phlogopite [KMg 3(AlSi 3O 10)(OH,F) 2], biotite [K(Mg,Fe) 3(AlSi 3O 10)(OH,F) 2] and lepidolite [K(Li,Al) 3(Al,Si) 4O 10(OH,F) 2], were irradiated with 1.5 MeV Kr + ions in the temperature range between 20 and 1023 K using the HVEM-Tandem Facility at Argonne National Laboratory. The irradiation effects were characterized by in situ and high resolution transmission electron microscopy (TEM). All four micas are susceptible to irradiation-induced amorphization with relatively low critical amorphization doses ( D c) (1–2 × 10 14 ions/cm 2, fractions of a dpa) below or at room temperature. D c increased with irradiation temperature for all phases above 400 K. The predicted critical temperatures ( T c), above which amorphization will not occur, for the four micas are all at or above 1000 K. Lepidolite is the most easily amorphized among the four micas at all irradiated temperatures with a predicted T c of 1300 K. Large gas bubbles (1–2 μm in diameter) were observed in a 800 keV Kr 2+ irradiated biotite after 1 × 10 15 ions/cm 2.

Cross-Section TEM Study On Kr+ Irradiation-Induced Amorphization in Quartz

Abstract Radiation damage in quartz has been of interest to the semiconductor industry, optical fiber industry, and nuclear industry. Cross-section transmission electron microscopy (TEM) is a powerful tool for investigating the irradiation effects since it provides a direct measurement of the ion and the damage distributions, and can also provide detailed microstructural information such as the presence of amorphous regions and the size, density and chemical nature of defect aggregates. The results reported below are from a systematic cross-section TEM study on 1.5 MeV Kr+ ion irradiated quartz. 3-mm discs of quartz (along 010 face) were prepared with 100 μm in thickness. One side for each discs was well polished using a 0.05 μm diamond paste. The well-polished side was irradiated at room temperature with 1.5 MeV Kr ions in the HVEM-Tandem Facility at Argonne National Laboratory. Following irradiation, cross-section TEM specimens were prepared using the so-called T-tool technique, a modified tripot technique

Ion-beam-induced amorphization of LaPO 4 and ScPO 4

LaPO 4 and ScPO 4 were irradiated by a 1.5 MeV Kr + ion beam using the HVEM-tandem Facility at Argonne National Laboratory. The ion-beam-induced amorphization was investigated over a temperature range of 20 to 570 K and the degree of amorphization was determined in-situ by monitoring the gradual loss of electron diffraction maxima. Subsequent high-resolution TEM analysis revealed the development of an amorphous phase. LaPO 4 and ScPO 4 were found to have activation energies for irradiation-enhanced annealing of 0.02 and 0.11 eV, attributed to diffusion-driven epitaxial recrystallization. The critical temperatures of amorphization were found to be 365 and 540 K, respectively. Both materials recrystallized under electron irradiation. These results suggest that the phosphates are generally less sensitive to ion-beam irradiation over a wide temperature range than are their silicate structure analogues and that the zircon structure-type has a higher energy barrier to recrystallization than the related monazite structure-type.

Amorphization of Al 2SiO 5 polymorphs under ion beam irradiation

The three polymorphs of Al 2SiO 5 (kyanite, andalusite and sillimanite) were irradiated with 1.5 MeV Xe + using the HVEM-Tandem Facility at Argonne National Laboratory. Irradiations were completed over a temperature range of 300 to 973 K. In situ TEM, followed by HREM, was used to characterize the effects of the ion beam damage. All three Al 2SiO 5 polymorphs became amorphous after doses of 0.3 dpa at room temperature. However, the high temperature behavior of the three phases was different. The thermodynamic stabilities of the three phases were found not to have a direct relation to susceptibility to amorphization. Irradiation-induced amorphization is discussed in terms of a cascade quenching model.

HREM study of phase transformation induced by ion irradiation in Al-Cu-Co-Ge single decagonal quasicrystal

Irradiation-induced phase transformation in crystals has been an interesting research field for the past twenty years. Since the discovery of quasicrystals in Al-based alloys, there have been some reports on irradiation-induced phase transformation in quasicrystals by in situ TEM observations. However, detailed study on phase transformation in quasicrystals under ion irradiation at atomic level using HREM is necessary for the fundamental understanding of the process. In this paper, we report the results from a systematic HREM study on phase transformation induced by ion irradiation in Al-Cu-Co-Ge single decagonal quasicrystal (31.4 wt.% Cu, 21.8 wt.% Co and 5.4 wt.% Ge).The TEM specimens of single decagonal quasicrystal were prepared perpendicular to the tenfold axis. The transformation in single quasicrystal was studied by in situ TEM during 1.5 MeV Xe+ ion irradiation at room temperature using the HVEM-Tandem Facility at Argon National Laboratory and examined in detail by HREM using a JEM2010 microscope at the University of New Mexico after the irradiation.

The irradiation-induced crystalline-to-amorphous phase transition in α-SiC

The ion-beam-induced crystalline-to-amorphous phase transition in single crystal α-SiC has been studied as a function of irradiation temperature. The evolution of the amorphous state has been followed in situ in specimens irradiated with 1.5 MeV Xe + ions over the temperature range from 20 to 475 K using the HVEM-tandem facility at Argonne National Laboratory. Specimens also have been irradiated at 170 and 370 K with 360 keV Ar + ions, and the damage accumulation process followed in situ by Rutherford backscattering spectroscopy in channeling geometry using dual-beam facilities at Los Alamos National Laboratory. The displacement dose for complete amorphization in α-SiC at 20 K is 0.25 dpa and increases with temperature in two stages. The simultaneous recovery process associated with the high-temperature stage (above 100 K) has an activation energy of 0.12±0.02 eV. The critical temperature above which amorphization does not occur is 485 K under these irradiation conditions. Dechanneling results are consistent with disordering occurring by the local accumulation of defects and show a decrease in disordering rate with increasing temperature.

In Situ Ion Beam Research In Argonne's Intermediate Voltage Electron Microscope

AbstractSince Fall 1995, a state-of-the-art intermediate voltage electron microscope (IVEM) has been operational in the HVEM-Tandem Facility with in situ ion irradiation capabilities similar to those of the HVEM of the Facility. A 300 kV Hitachi H-9000NAR is interfaced to the two ion accelerators of the Facility, with a demonstrated point-topoint spatial resolution for imaging of 0.25 nm with the ion beamline attached to the microscope. The IVEM incorporates a Faraday cup system for ion dosimetry with measurement aperture 6.5 cm from the TEM specimen, which was described in Symposium A of the 1995 MRS Fall Meeting. The IVEM is now employed for a variety of in situ ion beam studies ranging from low dose ion damage experiments with GaAs, in which damage zones individual displacement cascades are observed, to implantation studies in metals, in which irradiation-induced noble gas precipitate mobility is studied in real time. In this presentation, the new instrumentation and its specifications will be described briefly, several basic concepts relating to in situ experiments in transmission electron microscopes will be summarized and examples of in situ experiments will be presented which exploit the experimental capabilities of this new user facility instrumentation.

Amorphization of Ceramic Materials by Ion-Beam-Irradiation: Parallels to Glass Formation

AbstractIon-beam-induced amorphization of a wide variety of ceramic materials has been investigated using in situ TEM at the HVEM-Tandem Facility at Argonne National Laboratory with 1.5 MeV Kr+ or Xe+ ions at temperatures between 20 to 1000 K. The critical amorphization temperatures and the activation energies associated with the expitaxial recovery of displacement cascades during irradiation have been determined from the temperature dependence of the critical amorphization dose. The results for phases in the A12 O3-MgO-SiO2 system suggested a parallel in the kinetics between ion-beam-induced amorphization and glass formation. Based on a cascade quenching model, a semiempirical parameter, S, which can easily be calculated from both structural and chemical parameters of a material, has been developed to predict the susceptibility of ceramics to amorphization. The critical amorphization temperature, above which irradiationinduced amorphization cannot be completed, is closely related to the glass transition temperature. The ratio between glass transition and melting temperatures can also be used to predict the susceptibility of a ceramic material to amorphization, equivalent to the Debye temperature criterion.

On the Determination of Loop Nature in the Tem

AbstractWe have carried out systematic experiments to explore the range of applicability of the two direct methods which are available for the determination of the nature of small clusters. Experiments in heavy-ion irradiated silver and copper, including direct comparisons with the results of Black-White contrast analysis (B-W), forced us to the conclusion that use of the 21/2D technique for the analysis of faulted loops is effectively impossible because of reciprocal-lattice spike and other effects. We used B-W analysis to investigate the nature of the clusters produced by room-temperature heavy-ion irradiation of copper. In-situ irradiations were performed in the Argonne HVEM-Tandem Facility using 40keV and 80keV Kr+ ions. Nearly all of the analysable first-layer loops were found to be vacancy in nature. Some deeper clusters were also certainly vacancy. There is no unequivocal evidence for interstitial loops under these conditions. The near impossibility of establishing that interstitial loops are not present is shown by the fact that a large fraction of loops - over 50% - could not be analysed either because they did not display clear B-W contrast under any condition or sufficiently consistent B-W contrast under several different operating conditions.

The temperature dependence of ion-beam-induced amorphization in β-SiC

The ion-beam-induced crystalline-to-amorphous transition in monolithic β-SiC has been studied as a function of irradiation temperature using the HVEM-Tandem Facility at Argonne National Laboratory. Specimens were irradiated with 1.5 MeV Xe + ions over the temperature range from 40 to 550 K, and the evolution of the amorphous state was followed in situ using the HVEM. At 40 K, the displacement dose for complete amorphization in β-SiC is 0.34 dpa and increases with temperature in two stages. The simultaneous recovery process associated with the high-temperature stage (above 200 K) has an activation energy of 0.097 ± 0.019 eV. The critical temperature above which amorphization does not occur is 498 K under these irradiation conditions.

Crystallization of nano-size thallous oxide during ion irradiation of Tl-Ba-Ca-Cu-O high-temperature superconductors

The Tl-Ba-Ca-Cu-O class of type-II high temperature superconductors (HTS) have Tc's as high as 125K. Although they have good critical current values, when a field is applied the weak pinning and consequent flow of magnetic vortices are a major impediment to the usefulness of these materials. Ion irradiation has been shown to enhance the pinning. High quality single crystals, as determined with x-ray precession and HRTEM, with sharp HTS Meissner signals, were irradiated with 1.5 MeV Kr+ and Xe+ ions using the HVEM-Tandem facility at Argonne National Laboratory. Ion beam microstructural modification was studied in-situ using electron diffraction and after irradiation using HRTEM and nano-beam EDS on Tl-1212 and Tl-2212 (numbers designate the stoichiometry Tl-Ba- Ca-Cu-O) single-crystal HTS. After irradiation, microstructure was studied using the JEOL 2010 in the Earth and Planetary Science Department at the University of New Mexico in order to characterize the resulting irradiation-induced nano-size precipitates.

New Instrumentation in Argonne's Hvem-Tandem Facility: Expanded Capability for in Situ Ion Beam Studies+

AbstractDuring 1995, a state-of-the-art intermediate voltage electron microscope (IVEM) has been installed in the HVEM-Tandem Facility with in situ ion irradiation capabilities similar to those of the HVEM. A 300 kV Hitachi H-9000NAR has been interfaced to the two ion accelerators of the Facility, with a spatial resolution for imaging which is nearly an order of magnitude better than that for the 1.2 MV HVEM which dates from the early 1970s. The HVEM remains heavily utilized for electron- and ion irradiation-related materials studies, nevertheless, especially those for which less demanding microscopy is adequate. The capabilities and limitations of this IVEM and HVEM are compared. Both the HVEM and IVEM are part of the DOE funded User Facility and therefore are available to the scientific community for materials studies, free of charge for non-proprietary research.

In Situ Study of the Temperature Dependence of Irradiation-Induced Amorphization in A-Sic

ABSTRACTIon-beam-induced amorphization in single crystal α-SiC has been studied as a function of temperature. Specimens have been irradiated with 1.5 MeV Xe+ ions over the temperature range from 20 to 475 K using the HVEM-Tandem Facility (ANL), and the evolution of the amorphous state has been followed in situ in the HVEM. Specimens also have been irradiated at 170, 300, and 370 K with 360 keV Ar+ ions, and the damage accumulation process followed in situ by Rutherford backscattering spectroscopy/channeling using the dual beam facilities at the Ion Beam Materials Laboratory (LANL). At 20 K, the displacement dose for complete amorphization is 0.25 dpa and increases with temperature in two stages. The activation energy associated with the simultaneous recovery processes above 100 K is 0.12 ± 0.02 eV. The critical temperature above which amorphization does not occur is 485 K under the 1.5 MeV Xe+ irradiation conditions. Ion channeling results suggest that the rate of simultaneous recovery increases with temperature only above a critical damage level. Raman spectroscopy indicates that rapid chemical disordering occurs during irradiation.

Effect of concurrent irradiation with electrons on ion-induced amorphization in silicon

The effect of concurrent irradiation with electrons on ion-induced amorphization has been investigated under irradiation with high energy ions and fast electrons in the HVEM-TANDEM Facility at Argonne National Laboratory. The simultaneous irradiation with a focused electron beam prevents or retards the ion-induced amorphization, forming a distinct interface between crystalline and amorphous regions. The position of the interface has been converted to the critical electron flux, which increases with increasing energy deposition density and flux of ions and energy of electrons. It is concluded that amorphous embryos are essentially formed through overlap of subcascades, and that the prevention of ion-induced amorphization is mainly caused by athermal migration of point defects.

Ion-Beam and Electron-Beam Induced Amorphization of Berlinite (AIPO4)

AbstractBerlinite (AIPO4) is isostructural with α-quartz. Like α-quartz, berlinite undergoes a pressure-induced amorphization at 15 ±3 GPa; however, upon release of the pressure, unlike α-quartz which remains amorphous, berlinite returns to the original crystalline structure of the single crystal. Berlinite was irradiated with 1.5 MeV Kr+ at temperatures ranging from 20 to 600K. The onset of amorphization was examined by monitoring the electron diffraction pattern by in situ transmission electron microscopy (TEM) at the HVEM-Tandem Facility at Argonne National Laboratory. The berlinite was easily amorphized at 20K at a relatively low dose of 4x1013 ions/cm2 or 0.05 dpa (displacements per atom). The critical amorphization dose increases with the sample temperature. These experiments also showed that the focused electron beam can locally amorphize the berlinite. After these irradiations, berlinite remained amorphous. At 500 °C, berlinite began to recrystallize: small areas of crystalline material appear in the aperiodic matrix. These results suggest that pressure-induced amorphization and ion-beam induced amorphization, in the case of berlinite, are different processes that result in two different aperiodic structural states.

Temperature Dependence of Amorphization for Zirconolite and Perovskite Irradiated with 1 Mev Krypton Ions

AbstractA transmission electron microscope investigation was made of zirconolites and perovskites irradiated to amorphization with 1 MeV krypton ions using the HVEM-Tandem Facility at Argonne National Laboratory. Three specimens were examined - a prototype zirconolite CaZrTi2O7, a gadolinium doped zirconolite Ca0.75Gd0.50Zr0.75Ti2O7and a uranium doped zirconolite Ca0.75U0.50Zr0.75Ti2O7. The critical amorphization dose Dc was determined at several temperatures between 20K to 675K. Dc was inversely proportional with temperature. For example, pure zirconolite requiring 10x the dose for amorphization at 475K compared with gadolinium zirconolite. Using an Arrhenius plot, the activation energy Ea for annealing in these compounds was found to be 0.129 eV and 0.067 eV respectively. The greater ease of amorphization for the gadolinium sample is probably a reflection of this element’s large cross section for interaction with heavy ions. Uranium zirconolite was very susceptible to damage and amorphised under 4 keV argon ions during the preparation of microscope specimens. In each sample, zirconolite coexisted with minor perovskite, reduced rutile (Magneli phases) and zirconia. These phases were more resistant to ion irradiation than zirconolite. Even for high gadolinium loadings, perovskite (Ca0.8Gd0.2TiO3) was 3-4 times more stable to ion irradiation than the surrounding zirconolite crystals.

Characterization of Collision Cascade Damage in Ca2La8(SiO4)6O2 by Hrtem

AbstractCa2La8(SiO4)6O2 thin crystals become amorphous under ion beam irradiation. The ion dose required for complete amorphization of the thin crystal (critical amorphization dose, Dc) increased with the increasing irradiation temperature and decreased with ion mass at elevated temperatures. Samples irradiated with 1-1.5 MeV Ar+, Kr+ and Xe+ ions to doses much lower than Dc, in the temperature range from 20 to 498 K were used for a detailed HRTEM investigation to study the amorphization process. The residual collision cascade damage after irradiation appeared as nanometer scale amorphous domains. The images of these domains are extremely sensitive to the sample thickness. Small domains of cascade size were found only at the very thin edge of the sample. In thicker regions, amorphous domains appear after higher doses as the result of cascade overlap in projection. At higher temperatures, the observed amorphous domains are smaller indicating thermal recovery at the amorphous/crystalline interface. The amorphous domains are also larger in size after irradiation with ions of higher mass at a fixed ion dose. These results are consistent with the Dc-temperature curves determined by in situ TEM with the HVEM-Tandem Facility at Argonne National Laboratory. The width of the amorphous rim along the edge of the specimen grew with increasing ion dose suggesting that amorphization also proceeds from the sample surface. Images of the collision cascade damage were compared to the cascade sizes calculated with the TRIM code. Some digitally acquired HRTEM images of the cascade damage were processed to reveal more detailed information.

HRTEM study of heavy ion irradiation damage in Ca2La8(SiO4)6O2

Radiation effects in complex ceramic materials, including the crystalline phases with the apatite structure are of interest to the materials science, geoscience and biomedical communities. It has been shown by in situ TEM experiments that these materials can easily be rendered amorphous under heavy ion irradiations. Detailed study at atomic level using HRTEM on this crystalline to aperiodic transition is necessary for the fundamental understanding of the process. The results reported below are from a systematic HRTEM study on 1.5 MeV Kr ion irradiated synthetic Ca2La8(SiO4)6O2.The TEM samples were prepared from (0001) thin foils by Ar ion-milling which was finished at 3.5 kV and 13°. As shown in fig. 1, the width of the amorphous rim at the sample edge after ion milling is less than 2 nanometers. The pre-thinned TEM samples were irradiated at room temperature with 1.5 MeV Kr ions in the HVEM-Tandem Facility at Argonne National Laboratory.