Anomalous X-Ray Scattering On Self-Assembled Islands: Direct Evaluation Of Composition Profile, Strain Relaxation, And Elastic Energy

The growth of Ge on Si(001) produces a wealth of morphologies of nanocrystals. After the deposition of a two-dimensional Ge film 3.5 monolayers thick, islands are formed, and several shape transitions can be observed depending on the growth temperature, rate and deposited thickness. In this work we combine atomic force microscopy and two different types of measurements of anomalous x-ray scattering to determine this elastic energy both in pyramid and dome shaped islands. By comparing pyramids and domes data, we have observed both an increase of lattice parameter and enhancement of interdiffusion for the domes. These results show that there is a drastic decrease of the elastic energy stored per atom upon this particular shape transition.