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A late summer study of marine bacteria activities, and the interrelationships with the microbial
loop and the microbial food chain was carried out from 22 January to 10 February 2000 in a coastal area of
Terra Nova Bay (Ross Sea). The objective was to investigate the transition from the end of a phytoplanktonic
bloom to the start of winter. Intense bacterial activities, comparable to those of temperate marine
environments, were observed. The carbon potentially mobilized from proteinaceous matter was
quantitatively the most important source of carbon for the bacterioplankton. The leucine aminopeptidase
activity was higher in January samples and decreased towards 10 February whereas an opposite trend was
observed for alkaline phosphatase and ï¿½-glucosidase activities. The bacterial production was supported by
c. 0.2% of the amounts of dissolved organic carbon mobilised by hydrolytic activities and by 7% of
inorganic phosphate mobilised by alkaline phosphatase activity. A sharp reduction in the bacterial biomass,
possibly due to zooplankton grazing or viral lysis, was observed for the first time in Terra Nova Bay.
The growth of preamorphized silicon layers doped by multiple energy implants of boron, phosphorus, and boron plus phosphorus ions was investigated under irradiation with a 600 keV Kr+ + beam. The target temperature was set in the range 250–450 °C. During irradiation the growth was measured in situ by transient reflectivity. Boron and phosphorus at a concentration of 1 × 1020/cm3 enhance the rate by a factor of 3 and 2, respectively, whilst in compensated samples the rate is still more than a factor of 2 higher than in intrinsic or Ge-doped samples. This growth rate is characterized by an activation energy of 0.32 ± 0.05 eV which is, within the experimental uncertainties, independent of the dopant. The results are tentatively explained in terms of an interaction between generated point defects and impurities that increases the lifetime of defects at the crystal–amorphous interface.
Ion-assisted regrowth of chemical vapor deposited amorphous Si layers was investigated for different cleaning procedures. The process was directly monitored by transient reflectivity measurements. The c-a interface stops at the deposited layer/substrate interface for doses depending on the effectiveness of the cleaning procedure in removing the native oxide. Small concentrations of twins are found in the regrown layer. Their amount is also correlated to the cleaning procedure. In oxygen implanted bare Si samples the ion-induced growth rate is reduced to 0.3 of the normal value at a peak O concentration of 1 X 1021/cm3. The results on the ion-induced regrowth of deposited layers are explained in terms of oxygen profile broadening during irradiation and retardation of the growth for the presence of dissolved O.
Thin layers of Si were chemical vapor deposited onto as - received p-type <100> Si wafers and implanted with 80 KeV of As or Ge to a fluence of 1 × 1015 /cm2. Irradiation at 450°C with 600 KeV Kr++ ions causes the epitaxial growth of the entire deposited and amorphized Si layer. At lower irradiation temperatures the regrowth rate of the deposited layers is substantially reduced with respect that of the implanted amorphous layers. The presence of As enhances the regrowth rate of a factor 2.5. The results are explained qualitatively in terms of a dynamical bond breaking of SiO2, and of a dopant influence on the migration energy of the defects responsible for the growth.
The damage produced by high current density ∿l0µA/cm2 implants of 120 keV P+ into <111> and <100> silicon wafers, 500 °m thick, has been investigated in the fluence range 1×l01 5/cm2-l×l016 /cm2 by ion channeling and by transmission electron microscopy. For both orientations the thickness of the damage layers increases with the fluence up to 2×1015 /cm2 and then decreases. The rate of regrowth is a factor two faster for the <100> with respect to the <111> oriented Si crystals. Similar ratios have been found in pre-amorphized samples and irradiated with Kr+ ions in the temperature range 350°C-430°C. The TEM analysis reveals the presence of hexagonal silicon and of twins in small amounts for both orientations. The beam induced epitaxial growth depends also on the species present in the amorphous layer. A comparison between self-annealing and beam annealing in Si <100> preamorphized with Ar+ or P+ shows a noticeable retardation of the growth rate in the presence of Ar+.
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