Structure of nano-crystals: a key to understanding the unique properties of nano-materials

Bogdan F. Palosz 

Polish Academy of Sciences, Institute of High Pressure Physics (UNIPRESS), Sokolowska 29/37, Warszawa 01-142, Poland

Abstract

A key problem of "nanoscience" is understanding what is the origin of the difference in the properties between nano- and single crystals. In contrast to single- for nano-crystals one cannot disregard the fact that there is a large number of atoms located at the surface and, consequently, one has to accept that the crystallographic structure of a very small size particle may deviate from that in the bulk crystals. In a tentative model, a nanocrystal might be presented as a two-phase system formed by the grain core and the surface shell, both having characteristic dimensions.

There are no standard procedures established for performance of structural analysis of a nanocrystal. The problem is that its complex structure cannot be well represented by a unit cell. Only for this reason the methods which are used for elaboration of powder diffraction data based on Bragg equation should not be applied for examination of nanocrystalline materials. The values of lattice parameters calculated from individual Bragg reflection differ between each other, and because they vary with the diffraction vector Q, they are rather "apparent lattice parameters", alp's. Although Bragg equation is not fulfilled for very small crystals, it might be practical to base analysis of real structure of nanocrystals referring to Bragg type scattering and concentrate on interpretation of the deviations of diffraction images of nanocrystals from those corresponding to a perfect crystal lattice.

Examples of examination of distribution of strains among nano-grain core and surface shell has been examined at ambient conditions, but also under high pressures and high temperatures are given based on X-ray and neutron scattering experimental data. Advantages of the analysis referring to reciprocal and real spaces of nano-structures are discussed.

Related papers
  1. Analysis of density waves in CdSe, SiC, and diamond nanocrystals by application of NanoPDF software package to experimental Pair Distribution Functions.
  2. Looking at the real structure of nanocrystals with powder diffraction: the apparent lattice parameter approach
  3. Looking beyond limitations of diffraction methods of structural analysis of nanocrystalline materials
  4. Dyfraktometryczna analiza mikro- i makro-naprężeń w spiekach i kompozytach otrzymanych pod wysokim ciśnieniem i wysoką temperaturą.
  5. Badania własności termicznych nanokryształów metodami dyfraktometrycznymi
  6. Nanocrystalline SiC compacts obtained by sintering of laser synthesized nanopowders under extreme pressures
  7. Synthesis and properties of GaAs nano-composites
  8. MD simulation of atomic structure of nanocrystals
  9. SiC-Zn nanocomposites obtained using high-pressure infiltration technique
  10. Structural and luminescence properties of yttrium-aluminum garnet (YAG) nanoceramics
  11. X-ray diffraction studies of thermal properties of bulk- and surface-atoms of nanocrystalline SiC
  12. Characterization of nanostructured hydroxyapatite ceramics densified at high-pressure and temperature
  13. Powder precursors for nanoceramics: cleaning and compaction
  14. Examination of the atomic Pair Distribution Function (PDF) of SiC nanocrystals by in-situ high pressure diffraction
  15. Investigation of the microstructure of SiC-Zn nanocomposites by microscopic methods: SEM, AFM and TEM
  16. Sythesis of metal-ceramic nanocomposites by high-pressure infiltration
  17. X-Ray Characterization of Nanostructured Materials
  18. Generetion and Relaxation of Strain in SiC and GaN under Extreme Pressure
  19. Surface Diffraction Effects from Nanopowders under Pressure
  20. Influence of high pressure on the polytype structure of nanocrystalline GaN
  21. Transformation of fractal microstructure of nanocrystalline SiC and diamond in high pressures - Small Angle Scattering Study

Presentation: invited oral at E-MRS Fall Meeting 2005, Symposium I, by Bogdan F. Palosz
See On-line Journal of E-MRS Fall Meeting 2005

Submitted: 2005-07-20 11:21
Revised:   2009-06-07 00:44
Google
 
Web science24.com
© 1998-2018 pielaszek research, all rights reserved Powered by the Conference Engine