3. Results and discussion
The shape of the profiles is as usual although, under the experimental
conditions used here, there are no indications about grain boundary
diffusion as one could expect for polycrystalline samples. At higher
depths, the signal levels-off close to the natural abundance of the 18O2.
Some scatter is most probably caused by non-linearity of the electron
multiplier between very high 16O and very low 18O signal. Another
source of a slightly increased 18O/16O ratio can be some hydrogen
in the recipient or in the resin in which the samples were embedded.
Background correction of the line scan profiles with a zinc oxide single
crystal has confirmed that no grain boundary diffusion occurs under
the experimental conditions chosen.
The surface fraction of 18Owas in all samples more than one order of
magnitude greater than the natural background abundance (Fig. 3),
thus confirming that the reliable values of D* and k* can be obtained
from the same experiment according to [55,56].
The parameters for oxygen diffusion obtained by fitting measured
diffusion profiles i.e. the self-diffusion coefficient D* and surface
exchange coefficient k*, for the ATLS samples as determined by SIMS
analysis of the diffusion profiles are given in Tables 3 and 4 respectively.
3. Results and discussionThe shape of the profiles is as usual although, under the experimentalconditions used here, there are no indications about grain boundarydiffusion as one could expect for polycrystalline samples. At higherdepths, the signal levels-off close to the natural abundance of the 18O2.Some scatter is most probably caused by non-linearity of the electronmultiplier between very high 16O and very low 18O signal. Anothersource of a slightly increased 18O/16O ratio can be some hydrogenin the recipient or in the resin in which the samples were embedded.Background correction of the line scan profiles with a zinc oxide singlecrystal has confirmed that no grain boundary diffusion occurs underthe experimental conditions chosen.The surface fraction of 18Owas in all samples more than one order ofmagnitude greater than the natural background abundance (Fig. 3),thus confirming that the reliable values of D* and k* can be obtainedfrom the same experiment according to [55,56].The parameters for oxygen diffusion obtained by fitting measureddiffusion profiles i.e. the self-diffusion coefficient D* and surfaceexchange coefficient k*, for the ATLS samples as determined by SIMSanalysis of the diffusion profiles are given in Tables 3 and 4 respectively.
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