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The existence of a massive dark component to the matter distribution of galaxies (the ‘missing mass’) is inferred from the now overwhelming evidence for flat rotation curves in galaxies. However observational data on the linear extent of such a dark component and its total mass contribution is usually restricted by the limited radial distance to which rotation curves of individual galaxies can be measured (typically < 100 kpc). The magnitude of the mass contained within a larger radius around a galaxy can in principal be inferred by studying the kinematics of small groups of galaxies and making assumptions about their dynamical stability (see Faber and Gallagher, 1979, for review). However, one of the major difficulties in such studies is the question of group membership. The inclusion of disrelated foreground or background galaxies into a dynamical calculation of mass obtained for example via the Virial Theorem, can lead to spurious results. The effects of varying membership criteria on the dynamical properties of groups is well illustrated by the work of Huchra and Geller (1982).
We present early results from the analysis of HST imaging observations for several pairs of interacting galaxies. We include two cases that were specifically chosen to represent a strong early (young) encounter and a weak late (old) encounter. The goals of the project include a determination of the timing, frequency, strength, and characteristics of the young star clusters formed in these two limiting cases of tidal encounters.
EMU is a wide-field radio continuum survey planned for the new Australian Square Kilometre Array Pathfinder (ASKAP) telescope. The primary goal of EMU is to make a deep (rms ∼ 10 μJy/beam) radio continuum survey of the entire Southern sky at 1.3 GHz, extending as far North as +30° declination, with a resolution of 10 arcsec. EMU is expected to detect and catalogue about 70 million galaxies, including typical star-forming galaxies up to z ∼ 1, powerful starbursts to even greater redshifts, and active galactic nuclei to the edge of the visible Universe. It will undoubtedly discover new classes of object. This paper defines the science goals and parameters of the survey, and describes the development of techniques necessary to maximise the science return from EMU.
The University of Florida (UF) have recently collaborated with Raith Inc. to modify Raith’s ion beam lithography, nanofabrication and engineering (ionLiNE) station that utilizes only Ga ions, into a multi-ion beam system (MionLiNE) by adding the capabilities to use liquid metal alloy sources (LMAIS) to access a variety of ions and an EXB filter for mass separation. The MionLiNE modifications discussed below provide a wide range of spatial and temporal precision that can be used to investigate ion solid interactions under extended boundary conditions, as well as for ion lithography and nanofabrication. Here we demonstrate the ion beam lithographic capabilities of the MionLiNE for fabricating patterned arrays of Au and Si nanocrystals, with nanoscale dimensions, in SiO2 substrates, by direct implantation; and show that the same directwrite/maskless-implantation features can be used for in situ fabrication of nanoelectronic devices. Additionally, the spatial and temporal capabilities of the MionLiNE are used to explore the effects of dose rate on the long-standing surface morphological transformation that occurs in ion bombarded Ge.
Pulsed laser annealing and ion beam mixing have been used as surface modification techniques to enhance the physical properties of polycrystalline α-SiC. Thin Ni overlayers (20 nm - 100 nm) were evaporated onto the SiC surface. The specimens were subsequently irradiated with pulses of a ruby or krypton fluoride (KrF) excimer laser or bombarded with high energy Xe+ or Si+ ions. Both processes are non-equilibrium methods and each has been shown to induce unique microstructural changes at the SiC surface which are not attainable by conventional thermal treatments. Under particular (and optimum) processing conditions, these changes considerably increased the mechanical properties of the SiC; following laser irradiation, the fracture strength of the SiC was increased by as much as 50%, but after ion beam mixing, no strength increase was observed.
High resolution cross-section transmission electron microscopy (X-TEM), scanning electron microscopy (SEM), and Rutherford backscattering techniques were used to characterize the extent of mixing between the Ni and the SiC as a result of the surface modification.
Cooper and platinum films were deposited by evaporation and sputtering techniques onto prepared substrates of alumina, sapphire (cut along an a or c axis) and yttria stabilized zirconia. The films are then bombarded with ions of H, He, Ne and Kr at energies within and outside the ion beam mixing regime. Ion beam induced modification in adhesion and its thermal stability were measured by three techniques - a scratch test, a pull test and a peel test. Adhesive energies of these solid-solid systems were determined by contact angle measurements using scanning electron microscopy. The resistance of the films to chemical attack is modified by ion bombardment and will be shown to correlate with adhesion alterations.
Progress in applying rapid thermal annealing for activating implants is surveyed. Advantages to be gained through curtailing substrate semiinsulating loss, enhancing heavy n-type activation, and in reducing the diffusive redistribution of p-type implants are discussed in detail. Consideration is given to encapsulation requirements and the role of stoichiometry in activation. While the emphasis is on GaAs, work on InP and InGaAs has also been included.
We report on an investigation of ‘buried’ oxygen implants formed by 0+ implantation at 400 KeV and 3.5 MeV into p-type CZ (100) wafers with a dopant density NA 1015 cm−3. Peak concentrations of 1 × 1019 cm−3 to 2 × 1020 cm−3. were investigated. Test devices were fabricated on implanted and annealed wafers using conventional wafer processing. For the 400 keV implants, a 4 µm epitaxial buffer layer was grown subsequent to the 0+ implant. For a dose of 3 × 1015 cm−2 the lifetime reduction ratio for the effective generation lifetime τg at the implant peak is greater than 103 relative to an unimplanted region where τg = 150 µS. C-V and SRP profiles show evidence for oxygen donor compensation. TEM analysis reveals a well defined layer at 1 µm with respect to the original implant surface containing a relatively high density of small precipitates and dislocation loops. DLTS measurements on diodes reveal 2 electron traps designated as E1 and E2. The trap energy ∆E and capture cross section σ are (EC-ET)1 = 0.41 ± 0.020 eV and (EC-ET)2 = 0.22 ± 0.030 eV with σ 1019 cm-3. The estimated trap density NT for the dominant trap is 8.2 × 1013 cm−3 for a calculated peak 0+ implant concentration of 6.8 × 1019 cm−3. The values of ∆E are in good agreement with values for unimplanted CZ wafers subjected to 2-step precipitation anneals. The experimental results provide direct evidence that ion implantation provides an effective method of introducing atomic oxygen in silicon at concentration exceeding its solid solubility during processing to produce a buried low lifetime region.
LiNbO3 is the best substrate for modulators and switches for integrated optics. Efficient low loss waveguides for light in LiNbO3 are formed by introducing Ti-ions into its lattice, thus increasing locally the ordinary and the extraordinary indices of refraction. We are the first to use the very versatile technique of ion-implantation to administer Ti into LiNbO3. This implantation process offers the possibility to introduce significantly more Ti into a well-defined volume than conventional diffusion techniques. During this process first an amorphous non-equilibrium phase is generated, which has to be kept at low temperatures in order to prevent segregation. Subsequent thermal treatment leads to solid phase epitaxy and restores the desired stable crystalline state. We have used this technique to fabricate excellent planar waveguides, channel waveguides and Mach-Zehnder modulators.
Outgassing of HUNT HPR 204 photoresist during ion implantation has been characterized by means of quadrupole mass analysis. The influence of the various parameters (implantation eneray, beam current, ion species) has been studied in order to point out the evolutions, in terms of time or implanted dose, of the target chamber pressure and the peaks at masses 26 and 28, characteristic of the photoresist outqassing. The pressure integral in the target chamber which is easily related to the integrated outgassing flux, has been found essentially dependent on the total energy deposited in the photoresist layer and on the ion penetration depth.
The rate of ion induced mixing of 700 Å Au layers vapor deposited on amorphous and single crystalline Si substrates held at room temperature was measured as a function of dose using 300 key Si, 350 keV Ar, and 525 keV Kr ion beams.Mixing profiles were measured at various fluences by Rutherford backscattering techniques and were found to be consistent with mixed layers whose thicknesses increased with ion dose. Mixing compositions, which were stoichiometric over the entire mixed region at Au-28.5 at.% Si, were found to be independent of ion species or implant fluence. For all ion species the dose dependence of mixing was closer to linear than the square root power law reported previously . In addition, the mixing rate for Au on single crystalline substrates was significantly higher than Au n substrates amorphised by Si (self-ion) implantation at liquid nitrogen temperature. No difference was found between the mixing rates when the amorphous substrates were prepared by room temperature implantation. Preliminary results indicate similar behavior for the Au/Ge couple.
Irradiation with high energy heavy ion beams has been investigated as a technique for improving the quality of highly reflecting metallic surfaces to be used as laser mirrors. Properties such as reflectivity, corrosion resistance, film bonding, and threshold to laser surface damage have been examined. Modifications of composition and microstructure of the material associated with the heavy ion irradiation have been measured with RBS, TEM, SEM, Auger, and ESCA. Reflectivity and extinction coefficient measurements were made using ellipsometry techniques. Observations indicate that keV heavy ion irradiations in the fluence range of 1015 to 1016 cm−2 produce significant surface smoothing. Additionally, MeV implants of heavy ions into films of Cu, Ag, Au and Al deposited on molybdenum substrates resulted in improvements to both tarnish resistance and structural bonding integrity.
The Boltzmann transport equation has been used to calculate range anddamage distributions in multilayer targets of general interest for semiconductor fabrication. A comprehensive review of the calculations will be presented, with particular emphasis on how large angle scattering events and channeling phenomena may be included. Examples of the quality of fit between the theory and experiment show that difficult phenomena (such as residual channeling) can be reasonable modelled.
Various models for predicting high fluence ion collection profiles are reviewed. Recent calculations based on the diffusion approximation are described. The solute and defect probability distributions are calculated by a MONTECARLO code, TRIM. The method takes into account the effects of sputtering, including preferential sputtering of one of the components, and lattice dilation. In addition, the effects of radiation enhanced diffusion and radiation induced segregation are also considered. The calculations include the coupling of solute and defect fluxes. The described formalism can account for observed maximum attainable concentrations and distributions in high fluence implantation conditions of practical interest.