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Relativistic multireference many-body perturbation theory calculations on F-, Ne-, Na-, Mg-, Al-, Si-, and P-like xenon ions

Description: Many-Body Perturbation Theory (MBPT) has been employed to calculate with high wavelength accuracy the extreme ultraviolet (EUV) spectra of F-like to P-like Xe ions. They discuss the reliability of the new calculations using the example of EUV beam-foil spectra of Xe, in which n = 3, {Delta}n = 0 transitions of Na-, Mg-, Al-like, and Si-like ions have been found to dominate. A further comparison is made with spectra from an electron beam ion trap, that is, from a device with a very different (low density) excitation balance.
Date: December 22, 2005
Creator: Vilkas, M J; Ishikawa, Y & Trabert, E
Partner: UNT Libraries Government Documents Department

The interactions of high-energy, highly-charged ions with fullerenes

Description: In 1985, Robert Curl and Richard Smalley discovered a new form of carbon, the fullerene, C{sub 60}, which consists of 60 carbon atoms in a closed cage resembling a soccer ball. In 1990, Kritschmer et al. were able to make macroscopic quantities of fullerenes. This has generated intense activity to study the properties of fullerenes. One area of research involves collisions between fullerenes and atoms, ions or electrons. In this paper we describe experiments involving interactions between fullerenes and highly charged ions in which the center-of-mass energies exceed those used in other work by several orders of magnitude. The high values of projectile velocity and charge state result in excitation and decay processes differing significantly from those seen in studies 3 at lower energies. Our results are discussed in terms of theoretical models analogous to those used in nuclear physics and this provides an interesting demonstration of the unity of physics.
Date: March 1, 1996
Creator: Ali, R.; Berry, H.G. & Cheng, S.
Partner: UNT Libraries Government Documents Department

The effect of displacement cascades on small helium bubbles in aluminum and gold

Description: The evolution of individual helium bubbles in thin foils of gold and aluminum irradiated with 400 keV Ar+ and 200 keV Xe+ has been followed with in-situ transmission electron microscopy for a comparison between the effects of dilute (Al) and dense (Au) collision cascades. Bubble shrinkage in Al has been attributed to direct displacement of the gas out of the bubbles. Effects in Au, include the disappearance and Brownian motion of bubbles under irradiation, and are consistent with thermal spike processes seen in molecular dynamics simulations.
Date: December 1, 1994
Creator: Donnelly, S.E.; Valizadeh, R.; Vishnyakov, V.; Birtcher, R.C. & Templier, C.
Partner: UNT Libraries Government Documents Department

In situ beam analysis of radiation damage kinetics in MgTiO{sub 3} single crystals at 170-470 K

Description: Radiation damage kinetics in synthetic MgTiO{sub 3} (geikielite) single crystals have been studied using the in situ ion beam facility at Los Alamos National Laboratory. The geikielite samples were irradiated at temperatures of 170, 300, and 470 K with 400 keV xenon ions and the radiation damage was sequentially measured with Rutherford backscattering using a 2 MeV He ion beam along a channeling direction. Threshold doses of I and 5x l0{sup 15} Xe/cm{sup 2} were determined for the crystalline-to-amorphous transformation induced by Xe ion irradiation at 170 and 300 K, respectively. However, geikielite retained its crystallinity up to a dose of 2.5xl0{sup 16}Xe/cm{sup 2} at the irradiation temperature of 470 K. This study has shown that MgTiO{sub 3}, which has a corundum derivative structure, is another radiation resistant material that has the potential for use in radiation environments.
Date: December 31, 1995
Creator: Yu, Ning; Mitchell, J.N.; Sickafus, K.E. & Nastasi, M.
Partner: UNT Libraries Government Documents Department

HRTEM analysis of solid precipitates in Xe-implanted aluminum

Description: High-resolution TEM was carried out to determine shape and atomic arrangement of solid Xe precipitates in Al. Polycrystalline Al TEM specimens were implanted with 30 keV Xe{sup +} at RT to a dose of 3x10{sup 20} ions/m{sup 2} and then annealed at 523 K. Below a size 4 nm dia, the Xe precipitates are solid with an fcc crystal structure mesotacticly aligned with the Al lattice. In HRTEM along [011] projection, the difference in the lattice parameters of solid Xe and Al produces a precipitate image dominated by a 2-D Moire pattern that repeats in both the <001> and <111> directions every 3 Al (or 2 Xe) lattice spacings. Multi-slice image simulations, using a 3-D atomic model, demonstrates that the precipitates are tetradecahedra with faces parallel to the dense {l_brace}111{r_brace} planes and the {l_brace}100{r_brace} planes. Off-Bragg illumination of the precipitates minimizes Al lattice fringes and generates precipitate images which are in good agreement with the model.
Date: September 1, 1996
Creator: Allen, C.W.; Birtcher, R.; Ishikawa, N.; Furuya, K. & Awaji, M.
Partner: UNT Libraries Government Documents Department

Threshold irradiation dose for amorphization of silicon carbide

Description: The amorphization of silicon carbide due to ion and electron irradiation is reviewed with emphasis on the temperature-dependent critical dose for amorphization. The effect of ion mass and energy on the threshold dose for amorphization is summarized, showing only a weak dependence near room temperature. Results are presented for 0.56 MeV silicon ions implanted into single crystal 6H-SiC as a function of temperature and ion dose. From this, the critical dose for amorphization is found as a function of temperature at depths well separated from the implanted ion region. Results are compared with published data generated using electrons and xenon ions as the irradiating species. High resolution TEM analysis is presented for the Si ion series showing the evolution of elongated amorphous islands oriented such that their major axis is parallel to the free surface. This suggests that surface or strain effects may be influencing the apparent amorphization threshold. Finally, a model for the temperature threshold for amorphization is described using the Si ion irradiation flux and the fitted interstitial migration energy which was found to be {approximately}0.56eV. This model successfully explains the difference in the temperature dependent amorphization behavior of SiC irradiated with 0.56 MeV Si{sup +} at 1 x 10{sup -3} dpa/s and with fission neutrons irradiated at 1 x 10{sup -6} dpa/s irradiated to 15 dpa in the temperature range of {approximately}340{+-}10K.
Date: March 1, 1997
Creator: Snead, L.L. & Zinkle, S.J.
Partner: UNT Libraries Government Documents Department

Modeling of ion implantation and diffusion in Si

Description: Classical molecular dynamics simulations are used to study damage produced during implantation of semiconductors with different ion masses and energies between 1-25 keV. The time scale for these simulations is only on the order of ns, and therefore problems like transient enhanced diffusion of dopants or formation of extended defects can not be studied with these models. Monte Carlo simulations, including as input the results obtained from molecular dynamics calculations, are used to extend the simulation time, and in particular, to study processes like ion implantation and defects diffusion in semiconductors. As an example, we show results for diffusion of the damage produced by implantation of Si with 5 keV Xe ions at low doses. Results of the simulations are compared with experiments in order to validate the model.
Date: September 1, 1996
Creator: Caturla, M-J; Diaz de la Rubia, T. & Bedrossian, P.J.
Partner: UNT Libraries Government Documents Department

Measurements of cross sections and resonance structures following electron-impact excitation/ionization of Na-like Kr and Xe

Description: We report high-resolution measurements of electron impact excitation and ionization cross sections for the Na-like ions Kr{sup 25+} and Xe{sup 43+}. Ions with ionization states centered on the Na-like configurations were produced in an electron beam ion trap (EBIT) using electrons with energies below the L shell ionization thresholds. The Na-like ions were exposed to an electron beam with an energy between 3 and 7 keV. The Na- and Ne-like ions were then extracted and their intensities measured as a function of the electron beam energy. Theoretical ionization cross sections were calculated using relativistic distorted wave methods. Complex resonance structures that appear in the computed cross sections are observed in the experimental results. These results are the first experimental observation of resonant-excitation-double-autoionization (REDA) in highly charged high-Z ions.
Date: September 28, 1994
Creator: Schneider, D.; Dewitt, D.; Knapp, D.A.; Reed, K.J. & Chen, M.H.
Partner: UNT Libraries Government Documents Department

Experimental methods in RIB target/ion source development and characterization

Description: We have developed off-line experimental techniques and apparatuses that permit direct measurement of effusive-flow delay-times and ionization efficiencies for nearly any chemically reactive element in high-temperature target/ion sources (TISs) commonly used for on-line radioactive ion beam (RIB) generation. The apparatuses include a hot Ta valve for effusive-flow delay-time measurements, a cooled molecular-injection system for determination of ionization efficiencies and a gas-flow measurement/control system for introducing very low, well-defined molecular flows into the TIS. Measurements are performed on a test-stand using molecular feed compounds containing stable complements of the radioactive nuclei of interest delivered to the TIS at flow-rates commensurate with on-line RIB generation. In this report, the general techniques are described and effusive-flow delay-times and ionization efficiency measurements are reported for fluorine in an electron-beam-plasma target/ion source (EBPTIS) developed for RIB generation and operated in both positive and negative ion extraction modes.
Date: November 1, 1997
Creator: Welton, R.F.; Alton, G.D.; Murray, S.N. & Cui, B.
Partner: UNT Libraries Government Documents Department

Plastic flow in fcc metals induced by single-ion impacts

Description: Irradiation of Au and Pb foils with Xe ions at temperatures between 30 and 450 K has been monitored using in-situ transmission electron microscopy. Single ion impacts give rise to surface craters on the irradiated surface with sizes as large as 12 nm. Approximately 2--5% of impinging ions produce craters on Au while only about 0.6% produce craters on Pb. Larger craters on Au frequently have expelled material associated with them. Temporal details of crater formation and annihilation has been recorded on video with a time resolution of 33 milliseconds. Craters annihilate in discrete steps due to subsequent ion impacts or anneal in a continuous manner due to surface diffusion. Craters production (those persisting for one or more video frames) as a function of temperature indicates that the surface diffusion process responsible for thermal annealing of craters has an activation energy of 0.76 eV in Au. Crater creation results from plastic flow associated with near surface cascades. Crater annihilation in discrete steps results from plastic flow induced by subsequent ion impacts, including those that do not themselves produce a crater.
Date: September 1997
Creator: Birtcher, R. C. & Donnelly, S. E.
Partner: UNT Libraries Government Documents Department

Sealing behaviour and hall conductivity of mixed-state hall effect in heavy-ion irradiated YBa{sub 2}Cu{sub 3}O{sub 7} crystals

Description: The Hall effect ({rho}{sub xy}) and longitudinal resistivity ({rho}{sub xx}) measured in YBa{sub 2}Cu{sub 3}O{sub 7} crystals before and after the irradiation of Sn and Xe ions. We found a clear evidence that the strong pinning induced by the columnar defects not only modifies the scaling behavior between the Hall resistivity {rho}{sub xy} and longitudinal resistivity {rho}{sub xx} but also affects the temperature dependence of the Hall conductivity. For the irradiated crystals with columnar defects, the scaling exponent {beta} of {rho}{sub xy} = A{rho}{sub xx}{sup {beta}} was found to be {beta} = 1.55 {+-} 0.1, whereas {beta} of the unirradiated one was larger than 1.8. In case of the Hall conductivity, the pinning strength dependence was also observed. The Hall conductivity after irradiation exhibited a clear deviation from that of the unirradiated crystal at low temperatures. These results are in a good agreement with the work by Wang et al. in which pinning plays an important role.
Date: December 31, 1995
Creator: Kim, D.H.; Shim, S.Y. & Kang, W.N.
Partner: UNT Libraries Government Documents Department

Formation of a metastable crystalline phase during ion irradiation of spinel

Description: We have examined the radiation resistance of magnesio-aluminate spinel by irradiating single crystals of MgAl{sub 2}O{sub 4} with 400 keV Xe++ions at 100 K. At low irradiation doses, the material transformed into a metastable crystalline phase with half the lattice spacing of the original crystal. Electron diffraction analysis revealed that this structural change can be explained in terms of the redistribution of cations among octahedral, tetrahedral, and three- fold coordinated interstitial sites of the close-packed anion lattice. Corresponding to this transformation, the hardness and elastic modulus increased with dose to values about 10% greater than those of unirradiated spinel. We believe that the formation of this metastable phase plays an important role in determining the radiation resistance of spinel.
Date: December 31, 1995
Creator: Devanathan, R.; Yu, Ning; Sickafus, K. & Nastasi, M.
Partner: UNT Libraries Government Documents Department

Craters produced on metals by single ion impacts.

Description: Single ion impacts have been observed using in-situ transmission electron microscopy during irradiation. In addition to internal defects, single-ion impacts create surface craters as large as 12 nm on In, Ag, Pb and Au. Crater formation rates have been determined from video recordings with a time-resolution of 33 milliseconds. The cratering rate for Xe ions increases linearly with increasing target mass density above a threshold density of approximately 7 gm/cm{sup 3}. The cratering rate increases as the ion mass is increased. These results suggest that cratering requires a high energy-density, near-surface displacement cascade. TRIM calculations have been made in an effort to establish a near-surface energy-density criterion for cratering.
Date: December 23, 1998
Creator: Birtcher, R. C.
Partner: UNT Libraries Government Documents Department

Sputter roughening instability on the Ge(001) surface: Energy and flux dependence

Description: We have measured surface roughening kinetics during low energy Xe ion sputtering of Ge (001) surfaces. Results are interpreted in terms of an instability theory developed by Bradley and Harper. Although the calculated magnitude of the roughening rate does not agree with the measured value, the variation of the rate with ion flux and energy is on agreement with the theory.
Date: December 31, 1995
Creator: Chason, E.; Mayer, T.M. & Kellerman, B.K.
Partner: UNT Libraries Government Documents Department

Plastic flow in FCC metals induced by single-ion impacts.

Description: Irradiation of Au and Pb foils with Xe ions at temperatures between 30 and 450 K has been monitored using in-situ transmission electron microscopy. Single ion impacts give rise to surface craters on the irradiated surface with sizes as large as 12 nm. Approximately 2--5% of impinging ions produce craters on Au while only about 0.6% produce craters on Pb. Larger craters on Au frequently have expelled material associated with them. Temporal details of crater formation and annihilation has been recorded on video with a time-resolution of 33 milliseconds. Craters annihilate in discrete steps due to subsequent ion impacts or anneal in a continuous manner due to surface diffusion. Craters production (those persisting for one or more video-frames) as a function of temperature indicates that the surface diffusion process responsible for thermal annealing of craters has an activation energy of 0.76 eV in Au. Crater creation results from plastic flow associated with near surface cascades. Crater annihilation in discrete steps results from plastic flow induced by subsequent ion impacts, including those that do not themselves produce a crater.
Date: October 30, 1997
Creator: Birtcher, R. C. & Donnelly, S. E.
Partner: UNT Libraries Government Documents Department

Damage growth in MgAl{sub 2}O{sub 4} crystals by Xe ion irradiations

Description: We have studied damage kinetics in single crystal MgAl{sub 2}O{sub 4} (spinel) with (l00) orientation under 370 keV Xe ion irradiations at temperatures of {minus}100 and 400C. In-situ Rutherford Backscattering Spectrometry (RBS) and ion channeling have been used to monitor the damage accumulation in spinel following sequential Xe ion irradiations. A significant temperature effect on the irradiation damage has been found. Channeling data show that at {minus}100C, the irradiated spinel layer reaches the same level as in a random spectrum at a dose of 8 {times} 10{sup 15} Xe/cm{sup 2} (20 DPA for peak damage), while at 400C, the near surface region (50 nm) remains single-crystalline up to 2 {times} l0{sup l6} Xe/cm{sup 2}.
Date: December 31, 1993
Creator: Yu, Ning; Nastasi, M.; Hollander, M. G.; Evans, C. R.; Maggiore, C. J.; Sickafus, K. E. et al.
Partner: UNT Libraries Government Documents Department

Fragmentation of biomolecules using slow highly charged ions

Description: We present first results of biomolecular fragmentation studies with slow highly charged ions (HCI). A layer of the tripeptide RVA was deposited on gold targets and irradiated with slow (few 100 keV) ions, e.g. Xe{sup 50+} and Xe{sup 15+}, extracted from the LLNL EBIT (electron beam ion trap). The secondary ions released upon ion impact were mass analyzed via Time-Of-Flight Secondary-Ion-Mass-Spectrometry (TOF-SIMS). The results show a strong dependence of the positive and negative ion yields on the charge state of the incident ion. We also found that incident ions with high charge states cause the ejection of fragments with a wide mass range as well as the intact molecule (345 amu). The underlying mechanisms are not yet understood but electron depletion of the target due to the high incident charge is likely to cause a variety of fragmentation processes. 6 refs., 2 figs.
Date: November 1, 1996
Creator: Ruehlicke, C.; Schneider, D.; Balhorn, R. & DuBois, R.
Partner: UNT Libraries Government Documents Department

Ion beam modification of Tl-Ba-Ca-Cu-O type high temperature superconductors during irradiation

Description: Microstructural modification of high temperature superconductor (HTS) single-crystal plates of Tl-1212 and Tl-2212 (numbers designate the Tl/Ba/Ca/Cu cation ratio) was studied during 1.5 MeV Kr{sup +} and Xe{sup +} ion irradiation with in-situ electron diffraction and after ion irradiation with high resolution TEM (HRTEM). Similar in-situ temperature dependence effects are seen for both phases. During irradiations from 22K to 673K, an amorphous halo develops after very low ion dose or fluence (1.7 {times} 10{sup 12} ions/cm{sup 2}). During irradiation at 100 and 300K, complete amorphization is obtained, while at 22 and {ge}533K, the halo fades slightly and a polycrystalline ring pattern develops, indicating ion irradiation induced crystallization occurred. After a low ion dose (8.5 {times} 10{sup 12} ions/cm{sup 2}) at 100 and 300K, HRTEM reveals amorphous regions 5-20 nm in size which are not columnar and do not all penetrate the entire sample thickness. At 22 and {ge}533K, Moire fringes and misoriented crystallites of cascade size are observed. The 4-6nm crystallites are thallium-rich.
Date: December 31, 1994
Creator: Newcomer, P.P.; Morosin, B. & Wang, L.M.
Partner: UNT Libraries Government Documents Department

Plastic flow induced by single ion impacts on gold

Description: In situ TEM was used to follow RT irradiation of thinned bulk and 62nm thick gold films with Xe ions at 50-400 keV. Energy spikes from single ion impacts give rise to surface craters and holes which exist until annihilated by subsequent ion impacts. Video recording provided details with a time resolution of 33 ms. Craters were produced on the irradiated surface at all ion energies and on the opposite surface when the ions had enough energy to traverse the specimen. Crater sizes were as large as 12nm for the higher energy irradiations. On average, about 6% of impinging ions result in craters. A single 200 keV Xe ion may produce a hole in thin gold foils. Hole formation involves the movement by plastic flow of massive amounts of material, on the order of tens of thousand Au atoms per ion impact. Individual ion impacts also result in a filling of both holes and craters as well as a thickening of the gold foil. Change in morphology during irradiation is attributed to a localized, thermal-spike induced melting, coupled with plastic flow under the influence of surface forces.
Date: December 1996
Creator: Birtcher, R. C. & Donnelly, S. E.
Partner: UNT Libraries Government Documents Department

Progress on an EBIS for RHIC

Description: Work is continuing on the development of an Electron Beam Ion source (EBIS) which could be used as part of a new heavy ion injector for RHIC. On a test EBIS, the authors have operated with an electron beam current of up to 1.14A, and have extracted ions such as Tl{sup 41+}, Xe{sup 26+}, Ar{sup 14+}, N{sup 7+}, and Na{sup 7+}. Recent experimental results are reported. In addition, they discuss plans for a new electron beam test stand that is now being built. This will allow operation with electron currents of 10 A, as well as testing of a warm-bore superconducting magnet system, methods for fast extraction of ions, and possible off-axis collection of the electron beam.
Date: July 1, 1997
Creator: Alessi, J.; Beebe, E.; Hershcovitch, A.; Kponou, A.; Lockey, R.; Pikin, A. et al.
Partner: UNT Libraries Government Documents Department

AFM studies of a new type of radiation defect on mica surfaces caused by highly charged ion impact

Description: Radiation induced defects on mica caused by the impact of slow very highly charged ions (SVHCI) have been investigated with an atomic force microscope (AFM). Freshly cleaved surfaces of different types of muscovite were irradiated with SVHCI extracted from the LLNL electron beam ion trap (EBIT) at velocities of ca. 2 keV/amu. Atomic force microscopy of the surface reveals the formation of blisterlike defects associated with single ion impact. The determined defect volume which appears to increase linearly with the incident charge state and exhibits a threshold incident charge state has been determined using the AFM. These results indicate that target atoms are subjected to mutual electrostatic repulsion due to ionization through potential electron emission upon approach of the ion. If the repulsion leads to permanent atomic displacement, surface defects are formed.
Date: September 28, 1994
Creator: Ruehlicke, C.; Briere, M.A. & Schneider, D.
Partner: UNT Libraries Government Documents Department

Sputtering of Au induced by single Xe ion impacts

Description: Sputtering of Au thin films has been determined for Xe ions with energies between 50 and 600 keV. In-situ transmission electron microscopy was used to observe sputtered Au during deposition on a carbon foil near the specimen. Total reflection and transmission sputtering yields for a 62 nm thick Au thin film were determined by ex-situ measurement of the total amount of Au on the carbon foils. In situ observations show that individual Xe ions eject Au nanoparticles as large as 7 nm in diameter with an average diameter of approximately 3 nm. Particle emission correlates with crater formation due to single ion impacts. Nanoparticle emission contributes significantly to the total sputtering yield for Xe ions in this energy range in either reflection or transmission geometry.
Date: December 6, 1999
Creator: Birtcher, R. C. & Donnelly, S. E.
Partner: UNT Libraries Government Documents Department

Irradiation-induced phase transformations. Final report, July 1, 1995--June 30, 1997

Description: During the course of this two year program, the authors attention focused largely on the synthesis, structure and properties of group IV semiconductor nanocrystals. They also drew to a close the investigations of defects in amorphous silicon. Work on control of nucleation in amorphous silicon and germanium is ongoing, and has taken important new directions at the interface between basic and applied research under DOE Office of Energy Efficiency support via a subcontract from the National Renewable Energy Laboratory and the BES Center for Synthesis and Processing of Advanced Materials` project on High Efficiency Thin Film Photovoltaics. During the course of this project, scientific and scholarly output included: (1) 10 invited talks related to work on Si and Ge nanocrystals; (2) 5 Applied Physics Letters published on Si and Ge nanocrystals; (3) 3 Caltech Ph.D. Theses on Si and Ge Nanocrystal work; and (4) New directions on control of crystallization in thin semiconductor films.
Date: August 1, 1998
Creator: Atwater, H.A.
Partner: UNT Libraries Government Documents Department

Electronic sputtering of solids by slow, highly charged ions: fundamentals and applications

Description: Electronic sputtering in the interaction of slow (v&lt;v{sub Bohr}), highly charged ions (SHCI) with solid surfaces have been subject of controversial discussions for almost 20 years. We review results from recent studies of total sputtering yields and discuss distinct microscopic mechanisms (such as defect mediated desorption, Coulomb explosions and effects of intense electronic excitation) in the response of insulators and semiconductors to the impact of SHCI. We then describe an application of ions like Xe{sup 44+} and Au{sup 69+} as projectiles in time-of-flight secondary ion mass spectrometry for surface characterization of semiconductors.
Date: July 20, 1999
Creator: Banks, J C; Barnes, A V; Doyle, B L; Hamza, A V; Machioane, G A; McDonald, J W et al.
Partner: UNT Libraries Government Documents Department