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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).
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.
A low-energy ion beam deposition system has been developed at Oak Ridge National Laboratory and has been applied successfully to the growth of epitaxial films at low temperatures for a number of different elements. The deposition system utilizes the ion source and optics of a commercial ion implantation accelerator. The 35 keV mass- and energy-analyzed ion beam from the accelerator is decelerated in a four-element electrostatic lens assembly to energies between 10 and 500 eV for direct deposition onto a target under UHV conditions. Current densities on the order of 10 A/cm are achieved with good uniformity over a 1.4 cm diameter spot. The completed films are characterized by Rutherford backscattering, ion channeling, cross-section transmission electron microscopy, and x-ray diffraction. The effects of substrate temperature, ion energy, and substrate cleaning have been studied. Epitaxial overlayers which show good minimum yields by ion channeling (3–4%) have been produced at temperatures as low as 375°C for Si on Si(100) and 250°C for Ge on Ge(100) at growth rates that exceed the solid-phase epitaxy rates at these temperatures by more than an order of magnitude.
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.
The linearity of mixing rates of ion-beam mixing of metals on silicon has been found to depend critically upon the method by which the mixed depth is calculated. For nonstoichiometric mixing, several methods of calculating the mixed depth may be used, namely: integrated area, halfheight, moment, error function, and 10%-90%. When applied to the same data, these methods can yield divergent results, from linear to square-root dependences of the mixed depth upon the mixing dose. For stoichiometric mixing, the calculation of mixed depth is more straightforward, but different methods of calculation still yield widely differing results. Possible causes for these discrepancies are discussed.
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.
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.
N- and p-channel enhancement-mode MOSFETs have been fabricated in Si films prepared by zone-melting recrystallization of poly-Si deposited on SiO2-coated Si substrates. The transistors exhibit high surface mobilities, in the range of 560–620 cm2/V−s for electrons and 200–240 cm2/V−s for holes, and low leakage currents of the order of 0.1 pA/μm (channel width). Uniform device performance with a yield exceeding 90% has been measured in tests of more than 100 devices. The interface between the Si film and the SiO2 layer on the substrate is characterized by an oxide charge density of 1–2 × 1011 cm−2 and a high surface carrier mobility. N-channel MOSFETs fabricated inSi films recrystallized on SiO2-coated fused quartz subtrates exhibit surface electron mobilities substantially higher than those of single-crystal Si devices because the films are under a large tensile stress.
Lattice defects and precipitates induced in unimplanted and Sb-implanted <110> single crystal Al by single pulse irradiation with a Q-switched ruby laser were studied using ion beam analysis and electron microscopy. The absorbed laser energy during irradiation is directly measured in these studies to allow precise numerical modeling of the melt times and temperature profiles. For unimplanted Al, slip deformation gives rise to increased channeled yields throughout the analyzed depth and occurs for energies well below the melt threshold energy of 3.5 J/cm2. Slip deformation is also observed for irradiation energies above the melt threshold energy, and melting is accompanied by a discontinuous increase in the minimum channeling yield, X min- Implanted Sb (to ∼2 at.% peak concentrations) is found to impede epitaxial regrowth and result in polycrystalline Al formation for laser energies such that the melt front is believed not to penetrate through the Sb-containing region. For deeper melt depths, a metastable alloy is formed with up to 35% of the Sb located in substitutional sites. AlSb precipitate formation in the melt was not observed for room temperature irradiations; however, randomly oriented AlSb precipitates are observed for irradiation at substrate temperatures of 100 and 200 °C These measurements yield an estimated time for nucleation of AlSb precipitates in molten Al of 5 nsec < tnuc < 25 nsec.
We report simultaneous measurements of time resolved reflection and transmission of low intensity 1.06 μm, 35 ps pulses subsequent to excitation of 50 KeV, 1016 cm−2 boron implanted silicon by 0.53 μm 35 ps pulses of varying energy densities. The samples are examined by optical and scanning electron microscopy in conjunction with defect etching. These data are discussed from the point of view of both the thermal melting model and plasma model.
Compaan and co-workers have reported the results of time-resolved optical experiments on ion-implanted silicon which they claim prove the melting model of pulsed laser annealing cannot be correct. These results concern the rapid onset of a Raman signal after a heating laser pulse, the simultaneous occurrence of a Raman signal and the high reflectivity phase characteristic of molten silicon, and the lattice temperature measured by the Raman Stokes/anti-Stokes intensity ratio. In this paper, we show by detailed numerical calculations with the melting model that there is, in fact, excellent agreement between the results of the calculations and the experimental results reported by Compaan and co-workers.
Pulsed laser annealing of silicon implanted by Group (III, V) dopants leads to the formation of supersaturated alloys by nonequilibrium processes occurring in the interfacial region during liquid phase epitaxial regrowth. The distribution coefficient from the melt (k') and the maximum dopant substitutional solubility (CSmax) are far greater than equilibrium values and both are functions of growth velocity. Substitutional solubility is limited by lattice strain and by constitutional supercooling at the interface during regrowth. Values for CSmax obtained at different growth velocities are compared with predictions of thermodynamic limits for solute trapping.
The surface regions of (100), (110) and (111) oriented single crystals of GaAs have been investigated by the combine techniques of LEED, AES and RBS subsequent to their irradiation in UHV with the output of a Q–switched, ruby laser (0.15−0.8 J/cm2, 15 × 10−9 sec). Clean surfaces, as determined by AES, were obtained after Ar+ sputtering followed by laser irradiation. LEED observations indicate that the degree of disorder in the outermost surface layers remaining after irradiation depends on the crystal orientation. Although the relative intensities of Ga and As Auger transitions in spectra obtained from sputtered and laser annealed surfaces are similar, the differences in lineshape in these spectra of the M2,3M4,5M4,5 Ga Auger transition indicate that in the laser annealed case there are local regions which are nonstoichiometric. These observations are confirmed by RBS results, and this technique has been used to determine the stoichiometry and to characterize the damage in the subsurface region for all orientations.
The motional correlation time, τc, in liquid Se and Se-rich Se-Te alloys has been investigated between 500 and 900°C using time differential perturbed angular correlations of y-rays from dilute 111Cd impurities. In all alloys we find τc ∝ exp (E0/kT) at low T where E0 = 0.36 eV. τC deviates from this relation at high T. At low T, τCis tentatively identified as the lifetime of a Cd to host molecule bond, and at high T as the average lifetime of bonds in the host molecule.
To determine the nature and effect of defects which occur in the growth of crystalline semiconductor films on amorphous substrates, one must carry out microstructural and electrical studies on the same material regions. In previous publications we have demonstrated that by controlling optical absorption in and around delineated silicon areas, the nucleation and growth processes can be controlled. In this way we have been able to produce single crystal islands >20 μm on a side. Using a simple, novel parylene lift –off technique we can now routinely study the material crystallized on bulk glass using transmission electron microscopy. We report here preliminary results of correlated electrical and structural studies on pre – patterned silicon films crystallized under various conditions. Electrical characterization consists mainly of I – V measurements on diodes and MOSFETS fabricated in the crystallized material by conventional silicon IC processing techniques. For microstructural characterization of the same devices we rely on TEM, EBIC and spatially– resolved Raman scattering.
In this paper we report experiments on annealing of arsenic-implanted silicon using a pulsed imploding-plasma X-ray source. Silicon wafers of <100> orientation were implanted with arsenic ions at 50 keV to a dose of 3.5 ∼ 1015 cm−2 and exposed to a single 50 ns pulse of X-rays in the energy density range of 0.15 to 0.55 J/cm2 The characteristic X-ray absorptiog coeificient in silicon for these experiments was 1.6 ∼ 10 cm−1, resulting in most of the energy being absorbed in the first 100 nm of the wafer surface.
For wafers annealed in the energy density range of 0.3 to 0.4 J/cm2 backscattering and channeling measurements show recovery of the crystallinity of the damaged layer with incorporation of about 86% of the implanted arsenic onto substitutional lattice positions. Evidence of redistribution and flattening of the arsenic profile in the annealed wafer was observed in the backscattering data and confirmed by SIMS profiling. Detailed results on the electrical and structural properties of these annealed layers will be presented. High energy pulsed X-ray sources offer the unique capability of simultaneously exposing large numbers of wafers to an extremely uniform energy flux at much higher efficiencies than conventional lasers.
Incorporation of Group III, IV, V dopants in silicon occurs as a result of solute trapping during laser annealing. Distribution coefficients and substitutional solubilities are far greater than equilibrium values, and can be functions of growth velocity and crystal orientation. Mechanisms limiting dopant incorporation at high concentrations are identified and discussed.