Quantum size effect does not yield photoluminescence in nanometer silicon crystals

Silicon particles with sizes ranging from micrometer to nanometer were prepared by milling, oxidization and etching. The Raman peak is almost unshifted for the oxidized nanocrystals with respect to its bulk value owing to the compensation of phonon confinement affected by the confined volume and strained lattice, but shifts by similar to 6 cm(-1) as the strains are relieved by chemical etching. No photoluminescence (PL) was observed even when the particle size was reduced to smaller than 4 nm, implying that the PL of porous silicon is not evoked from the quantum size effect. (C) 1997 Elsevier Science S.A.