Stress in the film causes the substrate to bend, which the researchers measure by bouncing laser beams off the sample. When the dots form and change shape, the stress changes and so does the amount of bend in the substrate. Therefore, mapping the substrate as it bends reveals when dots first form and how their shapes evolve. As more film layers are deposited, the dots grow closer and closer and, because they repel each other, they are forced to become more uniform in size, line up in orderly fashion, and change their shape. The researchers used clusters of dots, called islands, as they are easier to examine.
Islands are thousands, rather than hundreds, of angstroms in size and are made of silicon germanium.
The larger semiconductor entities in groups interact the same way as smaller semiconductor entities. Floro said the researchers directly measure the kinetics of nucleation, coarsening, self-organization, and phase transformations within growing island arrays. As more layers were deposited, the film broke up into tiny pyramid-shaped islands. The researchers, not content with one novel tool to examine dots, realized they had another. Because light direction and intensity varies depending on the size, shape, and spacing of the islands, the results offer information in real time to determine what is happening to the tiny islands as temperatures, material compositions, and stresses change.