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  • 1
    Electronic Resource
    Electronic Resource
    Collisional versus electronic sputtering of SiO2 (1994)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 75 (1994), S. 8109-8113 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The SiO2 sputtering yield was determined for 170–300 keV He+ ion bombardment. The low sputtering efficiency and blistering at high ion doses make high-energy He+ ion sputtering yields difficult to determine, but by modifying a measurement method previously used for heavy ions, the sputtering yield could be quite accurately determined after sputtering only 20 A(ring) of SiO2. The sputtering yield was found not to be proportional to the energy deposited by the ion in elastic collisions at the surface of SiO2. Comparison with SiO2 sputtering yields found in literature shows that the sputtering yield increases with increasing energy deposited in electronic excitations for similar energy deposited in elastic collisions, indicating that electronic effects probably have to be included in the description of the sputtering process. Since the electronic effects do not seem to be independent of the sputtering by elastic collisions, it is suggested that SiO2 sputtering be controlled by a mixed collisional-electronic mechanism. Sputtering yield measurements were also performed for varying angles of ion incidence and, here also, good agreement could be achieved with predictions based on a mixed sputtering mechanism.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.356555
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  • 2
    Electronic Resource
    Electronic Resource
    Ion beam induced oxidation of silicon (1988)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 53 (1988), S. 1838-1840 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: A new physical phenomenon causing oxidation of silicon has been observed. The phenomenon is controlled by the impact of an energetic ion beam on a clean silicon target exposed to low-pressure oxygen. An oxide layer of 50–100 A(ring) can be formed at room temperature by properly choosing the oxidation conditions. The growth was studied in situ by measuring the ion-induced secondary electron yield. A strong dependence on oxygen pressure and target temperature was observed. By studying the oxide with x-ray photoelectron spectroscopy, it was concluded that the film formed is stoichiometric SiO2 . A discussion on possible growth mechanisms is carried out in terms of ion energy deposition.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.100370
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  • 3
    Electronic Resource
    Electronic Resource
    The dependence of Si and SiO2 electron emission on the angle of ion incidence (1993)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 74 (1993), S. 6397-6400 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The electron emission from Si and SiO2 was measured as a function of the angle of ion incidence for 200–300 keV H+, N+, Ar+ and Xe+ ions. For Si, the angular variation of the electron emission was found to approximately follow the angular variation of the electronic energy deposition, provided that recoil ionization was taken into account. For SiO2, the electron emission increased much more slowly with the angle of the ion incidence than expected, but the data are reasonably well represented by a single function of the expected electronic energy deposition to the power of 0.73. It is suggested that the holes left behind by the electron cascades of individual ions in SiO2 may attract the liberated electrons and cause the probability of escape to decrease with increasing electronic energy deposition. Measurements of the dependence of the electron emission on the angle of ion incidence were found to be a powerful tool in sorting out various mechanisms that could possibly influence electron emission.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.355165
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  • 4
    Electronic Resource
    Electronic Resource
    The influence of oxygen on SiO2 sputtering (1990)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 68 (1990), S. 2962-2965 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Argon-ion sputtering of thin silicon dioxide films has been studied both in ultrahigh vacuum and in a low pressure oxygen ambient. The variation in ion-induced secondary electron yield with decreasing oxide thickness was used to determine the sputtering yield. The method was found to be a simple and accurate way of in situ measurement of thin-film sputtering. A 30% decrease in sputtering yield was observed for 200-keV Ar ion bombardment when the oxygen pressure was increased from 1×10−8 to 1×10−6 mbar. Secondary electron yield variations were found to give information also on the surface modification process. A mechanism is proposed in which oxygen is incorporated into the oxide due to the ion bombardment. Comparison with ion beam induced oxidation is also made.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.346431
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  • 5
    Electronic Resource
    Electronic Resource
    Structural improvement in sublimation epitaxy of 4H–SiC (2000)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 88 (2000), S. 1407-1411 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The sublimation epitaxy growth process has been studied. The structural quality of the grown layers improves compared with the substrate mainly due to a diminished domain structure misorientation. Optical microscopy shows that the as-grown surfaces are free of typical defects appearing in silicon carbice (SiC) epitaxy, whereas atomic force microcopy measurements show macrosteps. As a possible technique to produce high-quality 4H–SiC, sublimation epitaxy was performed on substrates containing a layer grown by liquid phase epitaxy which is a growth process for closing micropipes in the initial substrate. In spite of the initial surface roughness of the liquid phase epitaxy layer, the surface morphology of the sublimation grown epilayers remained smooth and the structural quality improvement was maintained. This does not occur if the initial surfaces are too rough. A suggestion for roughness reduction is presented. The growth conditions (growth rate ramp up, growth temperature, temperature gradient, source to substrate distance, and substrate surface orientation) leading to the results are presented. A model for the mechanism for structural improvement is outlined and supporting experimental observations are given. © 2000 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.373831
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  • 6
    Electronic Resource
    Electronic Resource
    Heteroepitaxial properties of Si1−x−yGexCy on Si(100) grown by combined ion- and molecular-beam deposition (1997)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 81 (1997), S. 3081-3091 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The heteroepitaxial growth of the new ternary, group-IV, semiconductor material, Si1−x−yGexCy on Si(100), has been investigated. The epitaxial quality of Si1−x−yGexCy is found to be inferior to that of Si1−xGex with similar Si/Ge concentration ratio, grown under identical conditions, and the quality deteriorates with increasing C fraction. Also, the surface roughness, as studied by tapping mode atomic force microscopy, increases with increasing C fraction as well as with increasing Ge fraction, suggesting a transition from Frank–van der Merwe to Stranski–Krastanov type growth. We suggest that the very large mismatch between the average bond length in the Si1−x−yGexCy material, as determined by Vegard's law, and the equilibrium Si(Single Bond)C bond length, weakens the Si(Single Bond)C bonds and reduces the elastic range of the material, thus lowering the barrier for dislocation and stacking fault formation. The change in elasticity may also be responsible for the change in growth morphology, either directly by a lowered barrier for island formation or indirectly through the formation of defects. A decrease in Ge incorporation in the Si1−x−yGexCy films with increasing C incorporation suggests a repulsive Ge–C interaction. Moreover, we observe a C-rich, Ge-deficient precursor phase to SiC precipitates at a growth temperature of 560 °C, whereas at 450 °C no such phase can be observed. The temperature dependence of the precursor formation is consistent with C bulk diffusion. Infrared absorption measurements cannot be used to detect the precursor phase. Finally, the onset of epitaxial breakdown is discussed and an accurate and independent determination of the C fraction and its substitutionality is emphasized. © 1997 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.364352
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  • 7
    Electronic Resource
    Electronic Resource
    Comparative study on dry oxidation of heteroepitaxial Si1−xGex and Si1−x−yGexCy on Si(100)+ (1996)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 80 (1996), S. 1857-1866 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The goal of this study is to investigate the effect of carbon incorporation upon thermal oxidation of Si1−xGex alloys and its role on strain compensation in Si1−xGex alloys. Si1−xGex and Si1−x−yGexCy alloys on Si(100) are grown by combined ion and molecular beam deposition and are then oxidized at 1000 °C in a dry oxygen ambient for two h. The thickness and the composition of all samples before and after oxidation are measured by Rutherford backscattering spectrometry (RBS) combined with ion channeling at 2.0 MeV and carbon nuclear resonance analysis at 4.3 MeV using 4He++ ions. In agreement with previously reported results of dry oxidation on Si1−xGex thin films, 2.0 MeV RBS analysis shows that a layer of SiO2 is formed on the top surface of both Si1−xGex and Si1−x−yGexCy thin films, while Ge segregates towards the top surface and at the SiO2/Si1−xGex and SiO2/Si1−x−yGexCy interfaces. However, it is observed for the first time that dry oxidation rates of Si1−xGex thin films decrease with increasing Ge fraction x for x(approximately-greater-than)0.20 and with increasing minimum yield. Ion channeling analysis and strain measurements indicate that the incorporation of C rather than the amount of C itself affects the dry oxidation mechanism because of its strong influence on film strain and crystalline quality. These results are discussed in conjunction with observations by secondary ion mass spectrometry, high resolution transmission electron microscopy, Fourier transform infrared spectrometry, and tapping mode atomic force microscopy. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.362998
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  • 8
    Electronic Resource
    Electronic Resource
    The onset of secondary phase precipitation during synthesis of heteroepitaxial Si1−x−yGexCy on Si(100) (1996)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 68 (1996), S. 782-784 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: An upper temperature limit of 450 °C has been established for growth of heteroepitaxial Si1−x−yGexCy solid solutions with substitutional C on Si(100) by combined ion and molecular beam deposition (CIMD). At 450 °C infrared absorption spectroscopy shows that C is on substitutional sites and no SiC precipitates are detected, whereas at 560 °C the substitutional C signal is much smaller but SiC precipitates are still not detected. High resolution transmission electron microscopy shows that Si1−x−yGexCy films deposited at 560 °C exhibit Ge deficient, coherent, secondary phase clusters in the cubic diamond matrix, which are not seen in films deposited at 450 °C. These observations suggest that the clusters are C-rich, Ge-deficient precursors to SiC, with a lattice which is distorted but free of extended defects. Ion channeling results indicate that the Si1−x−yGexCy films might have a distribution of different bond lengths. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.116531
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  • 9
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    Neutron tomography of axially symmetric objects using 14 MeV neutrons from a portable neutron generator (2014)
    American Institute of Physics (AIP)
    Details
    Publication Date: 2014-08-09
    Description: In nuclear boiling water reactor cores, the distribution of water and steam (void) is essential for both safety and efficiency reasons. In order to enhance predictive capabilities, void distribution assessment is performed in two-phase test-loops under reactor-relevant conditions. This article proposes the novel technique of fast-neutron tomography using a portable deuterium-tritium neutron generator to determine the time-averaged void distribution in these loops. Fast neutrons have the advantage of high transmission through the metallic structures and pipes typically concealing a thermal-hydraulic test loop, while still being fairly sensitive to the water/void content. However, commercially available fast-neutron generators also have the disadvantage of a relatively low yield and fast-neutron detection also suffers from relatively low detection efficiency. Fortunately, some loops are axially symmetric, a property which can be exploited to reduce the amount of data needed for tomographic measurement, thus limiting the interrogation time needed. In this article, three axially symmetric test objects depicting a thermal-hydraulic test loop have been examined; steel pipes with outer diameter 24 mm, thickness 1.5 mm, and with three different distributions of the plastic material POM inside the pipes. Data recorded with the FANTOM fast-neutron tomography instrument have been used to perform tomographic reconstructions to assess their radial material distribution. Here, a dedicated tomographic algorithm that exploits the symmetry of these objects has been applied, which is described in the paper. Results are demonstrated in 20 rixel (radial pixel) reconstructions of the interior constitution and 2D visualization of the pipe interior is demonstrated. The local POM attenuation coefficients in the rixels were measured with errors (RMS) of 0.025, 0.020, and 0.022 cm −1 , solid POM attenuation coefficient. The accuracy and precision is high enough to provide a useful indication on the flow mode, and a visualization of the radial material distribution can be obtained. A benefit of this system is its potential to be mounted at any axial height of a two-phase test section without requirements for pre-fabricated entrances or windows. This could mean a significant increase in flexibility of the void distribution assessment capability at many existing two-phase test loops.
    Print ISSN: 0034-6748
    Electronic ISSN: 1089-7623
    Topics: Electrical Engineering, Measurement and Control Technology , Physics
    Published by American Institute of Physics (AIP)
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