Cathodoluminescence from nanocrystals in mechanically milled silicon

Mechanical milling is a technique extensively used to prepare nanocrystalline metallic materials but it has been less frequently applied to semiconductors. The preparation of nanocrystalline silicon by different methods is a subject of increasing interest due to the luminescent properties of this material and its possible application in optoelectronic devices. In this work high-energy ball milling has been used to prepare nanocrystals from single crystalline silicon wafers. The structure of the milled samples has been assessed by X-ray diffraction, transmission electron microscopy (TEM) and Raman spectroscopy, while their luminescence has been investigated by cathodoluminescence (CL) in the scanning electron microscope (SEM). The samples consist of a powder of particles with sizes of hundreds of nanometers aggregated to form bigger particles of several microns. TEM reveals that the particles consist of nanocrystals with a wide range of sizes including crystallites with dimension of few nanometers. CL spectra of the milled samples show a band at 1.61 eV, attributed to the presence of nanocrystals through a quantum confinement effect. It is suggested that a milling induced infrared emission is related to a high density of extended defects present in the milled samples