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  • 1
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 73 (1993), S. 4836-4840 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The depth profiles of 10B and 11B implanted into amorphous silicon have been analyzed by secondary ion mass spectrometry. Implantation energies between 0.4 and 5.0 MeV were used, and each sample was sequentially implanted with both 10B and 11B without changing the acceleration voltage but only the field in the mass analyzing magnet. A shift between the two profiles is clearly resolved and has been carefully studied as a function of ion energy. A maximum shift of 3.5% in mean projected range (Rp) is revealed at 0.6–0.8 MeV [Rp(11B)≥Rp(10B)], and for higher energies the ratio Rp(11B)/Rp(10B) decreases slowly to a value of ∼1.006 at 5.0 MeV. This reverse shift (heavier isotope penetrates deeper) is attributed to a larger electronic stopping cross section (Se) for 10B than for 11B at a given energy E where Se∼Ep and p≥0. The experimental data for Rp(11B)/Rp(10B) and Rp(11B) are compared with calculations, and it is demonstrated that the variation of Rp(11B)/Rp(10B) with ion energy hinges strongly on the Se vs E dependence. A close velocity proportional dependence (p=0.50±0.03) is found to be valid up to ∼300 keV, and then p decreases gradually with a maximum in Se (p=0) at ∼2.0 to 2.5 MeV. A semiempirical expression is presented for Se and shown to yield excellent agreement with both the relative isotope shift and the absolute range values; the deviations are less than 0.2% and 3.0%, respectively.
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 71 (1992), S. 1215-1218 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The transient enhanced diffusion of implanted boron has been examined by secondary ion mass spectrometry in crystalline silicon, in germanium preamorphized silicon, and in germanium amorphized and epitaxially regrown material. The total germanium dose used for amorphization of the silicon crystal was 1.2×1015 ions/cm2. The transient enhanced diffusion in regrown material was merely one-third of the diffusion in original crystalline silicon while the enhanced diffusion in preamorphized silicon had been retarded to 70% of the crystalline silicon value. This shows that a medium germanium implantation dose is sufficient to reduce the depth of the boron doping profile during furnace high-temperature annealing.
    Type of Medium: Electronic Resource
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  • 3
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 70 (1991), S. 3025-3030 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The production of stable vacancy-related point defects in silicon irradiated with 1.3 MeV protons has been studied as a function of ion flux (protons s−1 cm−2), while keeping the total fluence constant. Since the total fluence was very low (5 × 109 protons cm−2), no interference between neighboring ion tracks was expected. The defect concentrations have been measured by deep-level transient spectroscopy, and a decrease in the resulting defect density is found for increasing flux. This effect was unexpected and shows that there is an overlap between ion tracks, in spite of the low fluence. The behavior is attributed to the rapidly diffusing silicon interstitials, which overlap the vacancy distributions produced in adjacent ion tracks. When the ion flux is low, the distribution of vacancies from one ion becomes diluted and recombination with interstitials from ions impacting at a later time is rare. As the flux is increased the vacancy distribution from one ion will still be confined to a small volume when it is overlapped by interstitials from a later ion, leading to an increased recombination of vacancies and interstitials. Thus, within this low-fluence regime, the total concentration of stable vacancy-related defects decreases for a high flux. This result is supported by computer simulations of the defect generation kinetics.
    Type of Medium: Electronic Resource
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  • 4
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 73 (1993), S. 691-698 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Studies of the diffusion of Ge, Sn, As, and Sb in Si at high donor concentrations provided by phosphorous doping have been performed. It is found that for donor concentrations, CD below ∼2×1020 cm−3, the diffusivity depends linearly on CD; for doping concentrations above ∼2×1020 cm−3, however, the diffusivity increases dramatically with increasing donor concentrations. This behavior has been successfully modeled within the vacancy–percolation model, and it is concluded that collective phenomena play a significant role at high donor concentrations.
    Type of Medium: Electronic Resource
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  • 5
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 71 (1992), S. 4212-4216 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Schottky barrier structures have been formed by the deposition of Cu and Pt on n-type Si(100) at room temperature. The structures were irradiated by 300 keV protons or 1.3 MeV alpha particles to doses between 109 and 1010 cm−2. Deep level transient spectroscopy measurements performed in the temperature range 80–290 K revealed a new level ∼0.31 eV below the conduction band edge in the proton-bombarded Cu/Si(100) samples. The level exhibits metastable properties, and reversible cycling of its strength can be accomplished by a procedure where thermal annealing, forward biasing (hole injection), and white light excitation are undertaken. Evidence is presented showing that the level is associated with both Cu and H. Furthermore, the production rate of electrically active defects, e.g., divacancy and vacancy oxygen centers, is found to be substantially lower in the Cu/Si(100) samples compared with Pt/Si(100) samples irradiated under identical conditions. This is attributed to passivation of the irradiation-induced acceptor centers by fast diffusing interstitial Cu+, and in particular, the effect is more pronounced at shallow depths close to the Cu/Si interface than in the deep tail beyond the implantation peak.
    Type of Medium: Electronic Resource
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  • 6
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 68 (1990), S. 73-77 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The range distributions of 10B+ and 11B+ ions implanted into silicon have been studied by secondary ion mass spectrometry. Implantation energies in the range of 50 to 250 keV were used. An isotope effect on the boron profiles is clearly resolved for the energies above ∼100 keV. Projected range and parallel straggling values extracted from the measured profiles are compared with calculated values obtained from Monte Carlo simulations and from numerical computations applying Boltzmann's transport equation. A good agreement is found, and also the computed values reveal a clear isotope dependence. This effect is attributed to a larger electronic stopping cross section Se for the 10B+ ions than for the 11B+ ions at a given energy in the range where Se is roughly proportional to the ion velocity. 5
    Type of Medium: Electronic Resource
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  • 7
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 89 (2001), S. 5400-5405 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Two kinds of silicon samples have been used in this work: one containing a sequence of boron spikes and one with a sequence of alternating boron and antimony spikes, both grown by molecular beam epitaxy. These samples were irradiated with 2.5 MeV protons at an elevated temperature ranging from 500 to 830 °C and characterized by secondary-ion-mass spectrometry. The energy of the proton beam was chosen such that the generation rate of point defects can be considered as uniform throughout the delta-doped Si samples. The influence of the sample surface and of the boron concentration (ranging from 5×1015 to 3.2×1018 B/cm3 in the different samples) on the diffusion of boron have been studied in detail. The effect of antimony on boron diffusion has also been analyzed. For each sample, the B diffusion coefficient is increased under irradiation as compared to the B diffusion coefficient in unirradiated areas. This enhancement is dependent on the irradiation temperature, on the position of the boron spike and on the boron concentration. Further, the presence of antimony enhances the boron diffusion during low-temperature proton irradiation. © 2001 American Institute of Physics.
    Type of Medium: Electronic Resource
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  • 8
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 85 (1999), S. 3556-3560 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Platinum has been diffused at 300–800 °C for 30 min into n-type epitaxial silicon samples during 2 MeV electron irradiation using a dose of 1×1017 e− cm−2. Thereafter the samples were characterized by capacitance–voltage measurements and deep level transient spectroscopy. The samples with irradiation temperatures of 500, 600, and 700 °C could be analyzed, while the compensation in the others was too high. Most of the observed deep levels were characterized using the Arrhenius method. Their possible identities are discussed. The deep level of substitutional platinum first appears in the sample irradiated at 600 °C and is the dominant defect level at even higher temperatures. We observe that at a chosen distance from the sample surface (17 μm), the concentration of electrically active platinum after an irradiation at 700 °C is a factor of 1000 higher than in an ordinarily diffused sample. Taking into account experiments where platinum was diffused into pre-irradiated samples, the observed behavior is attributed to a reduced correlated recombination of interstitials and vacancies. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
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  • 9
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 87 (2000), S. 4629-4631 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The effect of strain and composition on deep electronic levels in the energy band gap of epitaxial Si0.87Ge0.13 layers grown by chemical vapor deposition has been investigated by deep level transient spectroscopy. Two major levels attributed to a vacancy–phosphorus (VP) pair and a singly negative divacancy [V2(−/0)] have been observed. It has been found that VP and V2(−/0) demonstrate opposite behavior on the Ge composition: the activation enthalpy of VP increases with respect to pure Si while that of V2(−/0) decreases. The apparent intensity of the VP level has been observed to decrease in the Si0.87Ge0.13 layers with respect to that in Si while the formation of V2 is enhanced during annealing above ∼100 °C. © 2000 American Institute of Physics.
    Type of Medium: Electronic Resource
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  • 10
    ISSN: 1471-4159
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Medicine
    Notes: Abstract: Okadaic acid (OA) is a frequently used phosphatase inhibitor that by inhibiting dephosphorylation increases the net phosphorylation level in various systems. In the present study OA was used to assess the role of balanced phosphorylation-dephosphorylation reactions for successful regeneration of peripheral nerves. To achieve this, the effects of OA on phosphorylation levels, neurite outgrowth, injury-induced support cell proliferation, and neurofilament stability, respectively, were investigated in the in vitro regenerating, adult frog sciatic sensory nerve. OA at a moderate concentration (20 nM) increased phosphorylation levels and almost completely inhibited the in vitro regeneration in a reversible way. The effect on regeneration was not due to induced neurofilament instability and was only seen when the drug was applied in the outgrowth region. The latter and the absence of effects on support cell proliferation indicate that OA acts locally at the level of newly formed axons. However, the inhibition of regeneration was not a consequence of reduced delivery of proteins by axonal transport, because this process in fact was increased by OA. Altogether, the study suggests that properly balanced phosphorylating-dephosphorylating reactions are critical for regeneration of peripheral nerves.
    Type of Medium: Electronic Resource
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