Lattice contraction in nanosized silicon particles produced by laser pyrolysis of silane

We used laser-induced decomposition of silane for the fabrication of nanosi zed Si particles and studied in detail their structural characteristics by conventional and high resolution electron microscopy. The silane gas flow r eactor incorporated in a molecular beam apparatus was operated without size selection to achieve a broad size distribution. Deposition at low energy o n carbon substrates yielded single crystalline, spherical Si particles almo st completely free of planar lattice defects. The particles, covered by thi n amorphous oxide shells, are not agglomerated into larger aggregates. The lattice of diamond cubic type exhibits deviations from the bulk spacing whi ch vary from distinct contraction to dilatation as with decreasing particle size the oxide shell thickness is reduced. This effect is discussed in ter ms of the strong Si/oxide interfacial interaction and compressive stresses arising upon oxidation. A negative interface stress, as determined from the size dependence of the lattice spacing, limits the curvature of the interf ace, i.e., at small sizes Si oxidation must be considered as a self-limitin g process.