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Kuchibhatla, Satyanarayana, V. N. T.; Adusumilli, P.; Prosa, T. J.; Ulfig, R. M.; Shutthanandan, V.; Arey, B. W.; Thevuthasan, S. |
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Influence of embedded Au-nanoclusters on the Atom Probe Tomography of Bulk MgO |
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2010 |
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Advances in Optical and Electron Microscopy, Vol. 2, R. Barer and V. E. Cosslett, eds., Academic Press, London (1968) 343analysis |
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The advent of laser-pulsing in atom probe tomography (APT) has significantly expanded the scope
of this high spatial resolution, three-dimensional analysis technique to study insulating materials
such as oxides. Recent first-of-their-kind studies on bulk insulating magnesium oxide single crystal
substrates, with and without embedded gold nanoparticles, have revealed some very interesting
information. This presentation will include some of these results describing the influence of laser
energy on the field evaporation characteristics of pure and Au clusters imbedded MgO specimens
during laser-assisted APT. The Au clusters imbedded specimens were prepared by implanting 2.0
MeV 2x1017 Au+/cm2 in bulk MgO crystals at various temperatures and subsequently annealing the
specimens at 1000oC for 10 hours in air. Samples for APT were prepared using a dual-beam focused
ion beam microscope using the lift-out technique. Significant variations have been observed in the
mass resolution and the TOF-mass spectrum as a function of the presence of nanoclusters in the
oxide matrix. While the average dimensions of the gold nanoparticles in the matrix agree with the
TEM and STEM measurements, APT data indicates that the Au-clusters may not be pure as reported
by researchers in the past. Furthermore, using atom-probe reconstructions, (see Figures 1 and 2
below), the presentation will shed light on the different evaporation characteristics observed at high
and low laser energies. Additionally, the influence of laser energy and Au nanoparticle presence on
the bulk composition will also be discussed here.
While it is too early to make conclusive propositions on the Au-MgO system, these results are highly
encouraging to pursue the analysis of bulk insulators and dielectric materials using laser assisted
atom probe tomography. It is being hypothesized that the selective absorption of the laser by the Au
nanoparticles might result in localized heating and there by result in magnesium oxide clustering in
the vicinity of Au clusters. MgO clustering effects appear to depend on the laser energy and the
results clearly demonstrate that complex MgO clustering can be avoided by utilizing low laser
energies as shown in Fig. 1. |
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