  Synthesis of rationally designed nanostructured materials with optimized
mechanical properties, e.g., high strength with considerable ductility,
requires rigorous control of diverse microstructural parameters including the
mean size, size dispersion and spatial distribution of grains. However,
currently available synthesis techniques can seldom satisfy these requirements.
Here, we report a new methodology to synthesize thin films with unprecedented
microstructural control via systematic, in-situ seeding of nanocrystals into
amorphous precursor films. When the amorphous films are subsequently
crystallized by thermal annealing, the nanocrystals serve as preferential grain
nucleation sites and control their microstructure. We demonstrate the
capability of this approach by precisely tailoring the size, geometry and
spatial distribution of nanostructured grains in structural (TiAl) as well as
functional (TiNi) thin films. The approach, which is applicable to a broad
class of metallic alloys and ceramics, enables explicit microstructural control
of thin film materials for a wide spectrum of applications.
