In this work, the capability of gas phase synthesis for
crystal
shape engineering of silicon nanoparticles (SiNPs) in a hot wall reactor
is demonstrated. Therefore, the necessary boundary conditions for
the formation of monodisperse spherical SiNPs as well as octahedral-shaped
particles from silane pyrolysis are systematically deduced. The different
shapes of the SiNPs are ascribed to different growth regimes (reaction
limitation, diffusion limitation) depending on the global process
parameters. Single crystalline, defect-free, spherical particles with
a mean diameter of 30 nm (geometric standard deviation below 1.1)
and octahedra with a mean edge length of about 100 nm could be obtained
solely by process parameter adjustment. Particle size and shape as
well as crystallinity were characterized by scanning electron microscopy
and X-ray diffraction. The inner structure and faceting of the particles
were analyzed in detail by high resolution transmission electron microscopy.
A model that elucidates the orientation relation between the inner
silicon structure and the particle shape is derived for the octahedra.