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Diffraction Studies of Nanocrystals: Theory and Experiment

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Palosz B., Grzanka E., Gierlotka S., Stel'makh S., Pielaszek R., Bismayer U., Neuefeind J., Weber H., Palosz W.

Acta Physica Polonica A

2002

vol. 102

issue 1

57-82

Based on theoretical calculations of powder diffraction data it is shown that the assumption of the infinite crystal lattice for small particles is not justified, leads to significant changes of the diffraction patterns, and may lead to erroneous interpretation of the experimental results. An alternate evaluation of diffraction data of nanoparticles, based on the so-called "apparent lattice parameter", alp, is proposed.

Generation and Relaxation of Microstrains in GaN Nanocrystals under Extreme Pressures

100%

Grzanka E., Palosz B., Gierlotka S., Pielaszek R., Bismayer U., Janik J., Wells J., Palosz F., Porsch F.

Acta Physica Polonica A

2002

vol. 102

issue 2

167-174

Nanocrystalline powders of GaN with grain sizes ranging from 2 to 30 nm were examined under high external pressures by in situ diffraction techniques in a diamond anvil cell at DESY (HASYLAB, Station F3). The experiments on densification of pure powders under high pressure were performed without a pressure medium. The mechanism of generation and relaxation of internal strains and their distribution in nanoparticles was deduced from the Bragg reflections recorded in situ under high pressures at room temperature. The microstrain was calculated from the full-width at half-maximum (FWHM) values of the Bragg lines. It was found that microstrains in GaN crystallites are generated and subsequently relaxed by two mechanisms: generation of stacking faults and change of the size and shape of the grains occurring under external stress.

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2 Acta Physica Polonica A

2 2002

2 Bismayer U.

2 Gierlotka S.

2 Grzanka E.

2 Palosz B.

2 Pielaszek R.

1 Janik J.

1 Neuefeind J.

1 Palosz F.

1 Palosz W.

1 Porsch F.

1 Stel'makh S.

1 Weber H.

1 Wells J.

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Diffraction Studies of Nanocrystals: Theory and Experiment

Generation and Relaxation of Microstrains in GaN Nanocrystals under Extreme Pressures