A detailed study was made of strain in free-standing Ge nanocrystals by using X-ray diffraction line-profile analysis, supported by high-resolution transmission microscopy imaging. Free-standing Ge nanocrystals, down to ~7nm in size, were synthesized by using the ball-milling technique, and investigated with regard to the nature of the strain. A detailed analysis of size and lattice strain in the nanocrystals revealed that the strain was anisotropic in the nanocrystals. Nanocrystal sizes and strain anisotropy factors were calculated by taking into consideration a dislocation contrast factor. The analysis suggested that screw-type dislocations were the main contributors to the strain anisotropy and that the dislocation density and corresponding strain varied with crystallite size. The maximum of both quantities was produced by 20h of milling. Direct evidence of strain caused by dislocations in individual nanocrystals was provided by HRTEM imaging. Relaxation of the strain was studied by means of differential scanning calorimetry.

Strain Analysis on Freestanding Germanium Nanocrystals. P.K.Giri: Journal of Physics D, 2009, 42[24], 245402