Analysis of strain fields in silicon nanocrystals

Strain has a crucial effect on the optical and electronic properties of nanostructures. We calculate the atomistic strain distribution in silicon nanocrystals up to a diameter of 3.2 nm embedded in an amorphous silicon dioxide matrix. A seemingly conflicting picture arises when the strain field is expressed in terms of bond lengths versus volumetric strain. The strain profile in either case shows uniform behavior in the core, however, it becomes nonuniform within 2-3 A distance to the nanocrystal surface: tensile for bond lengths whereas compressive for volumetric strain. We reconcile their coexistence by an atomistic strain analysis.