Photoluminescence from mechanically milled Si and SiO 2 powders
Contributors: T.D. Shen, I. Shmagin, C.C. Koch, R.M. Kolbas, Y. Fahmy, L. Bergman, Robert J. Nemanich, M.T. McClure, Z. Sitar, and M.X. Quan
ABSTRACT
The photoluminescence (PL) in as-received and milled Si andSiO
2
powder is reported. The Si and
SiO
2
powder is characterized by chemical analysis, Raman scattering, x-ray photoelectron spectra, infrared absorption, x-ray diffraction, and differential thermal analysis. The results indicate that the Si powder has amorphous Si oxide and suboxide surface layers. The milling of Si powder results in the formation of nanocrystalline/amorphous Si components. An amorphous
SiO
2
component is formed by milling crystalline
SiO
2
. The PL spectra for as-received Si, milled Si, and
SiO
2
powder exhibit similar peak shapes, peak maxima, and full width at half maximum values. For both the as-received and the milled Si powder, experimental results appear to exclude mechanisms for PL related to an amorphous Si component or Si-H or Si-OH bonds, or the quantum confinement effect. Similarly, for milled
SiO
2
powder mechanisms for PL do not appear related to Si-H or Si-OH bonds. Instead the greatly increased intensity of PL for milled
SiO
2
can be related to both the increased volume fraction of the amorphous
SiO
2
component and the increased density of defects introduced in the amorphous
SiO
2
upon milling. It is suggested that the PL for as-received Si, milling-induced nanocrystalline/amorphous Si, and milled
SiO
2
results from defects, such as the nonbridging oxygen hole center, in the amorphous Si suboxide and/or
SiO
2
components existing in these powder samples. The PL measurement for milled
SiO
2
is dependent on air pressure whereas that for as-received
SiO
2
is not, suggesting that new emitting centers are formed by milling.