材料期刊网

Photoluminescence and Raman scattering spectra were used to study three types of free-standing porous Si: as-grown samples with various porosities referred to as APS samples, these samples oxidized in air at 200 degreesC fur 200 h as OPS samples, and these samples aged further in air at room temperature for 20 months as AOPS samples. The PL peak energies of OPS and AOPS samples have shifted in small energy ranges centered at about 1.61 and 1.59 eV, respectively. Each Raman spectrum was fitted with an amorphous and a crystalline component. The crystalline component was used to determine the sizes of nanometer Si particles (NSPs), which were in ranges of 2.5-2.2 and 3.3-2.3 nm in OPS and AOPS samples, respectively. The reason why OPS or AOPS samples with different NSP sizes have almost the same FL peak wavelength is discussed with a novel multiple mechanism model.