Effect of the chemical state of the surface on the relaxation of the surface shell atoms in SiC and GaN nanocrystals (original) (raw)
2002, Acta Crystallographica Section A Foundations of Crystallography
The effect of the chemical state of the surface of nanoparticles on the relaxation in the near-surface layer was examined using the concept of the apparent lattice parameter (alp) determined for different diffraction vectors Q. At low diffraction vectors the peak positions are affected mainly by the structure of the near-surface layer, while at high Qvalues only the interior of the grain contributes to the diffraction pattern. Theoretical alp-Q relations were obtained from diffraction patterns calculated for models of nanocrystals with a strained surface. We studied nanocrystalline SiC and GaN with average crystallite size from 5 to 30 nm. Following the measurements of as synthesized powders we investigated powders annealed at 400°C under vacuum, and same powders wetted with water. A strong dependence of the experimental alp-Q plots on the grain size and purity was found. Evaluation of the strain at the surface shell was made by comparison of experimental alp-Q plots with those computed for the core-shell model. We estimated the thickness of the shell in SiC nanocrystals to be 4-6 Å, with the tensile strain of about 10%. In GaN, the shell thickness is approximately 7Å with the compressive strain in the range 10-15%. Annealing the powders at 400°C under vacuum, as well as wetting them with water leads to a strong change of the measured alp values, Fig.1. We interpret this effect as a reconstruction of the atomic structure of the surface with simultaneous decrease of the surface strain.
Sign up for access to the world's latest research.
checkGet notified about relevant papers
checkSave papers to use in your research
checkJoin the discussion with peers
checkTrack your impact
Loading Preview
Sorry, preview is currently unavailable. You can download the paper by clicking the button above.