THE STRUCTURE AND PROPERTY CHARACTERISTICS OF AMORPHOUS NANOCRYSTALLINE SILICON PRODUCED BY BALL-MILLING

The structural transformation of polycrystalline Si induced by high en ergy ball milling has been studied. The structure and property charact eristics of the milled powder have been investigated by x-ray diffract ion, scanning electron microscopy, high-resolution electron microscopy , differential scanning calorimetry, Raman scattering, and infrared ab sorption spectroscopy. Two phase amorphous and nanocrystalline compone nts contain some defects such as dislocations, twins, and stacking fau lts which are typical of defects existing in conventional coarse-grain ed polycrystalline materials. The volume fraction of amorphous Si is a bout 15% while the average size of nanocrystalline grains is about 8 n m. Amorphous elemental Si without combined oxygen can be obtained by b all milling. The distribution of amorphous Si and the size of nanocrys talline Si crystallites is not homogeneous in the milled powder. The a morphous Si formed is concentrated near the surface of milled particle s while the grain size of nanocrystalline Si ranges from 3 to 20 nm. S tructurally, the amorphous silicon component prepared by ball milling is similar to that obtained by ion implantation or chemical vapor depo sition. The amorphous Si formed exhibits a crystallization temperature of about 660-degrees-C at a heating rate of 40 K/min and crystallizat ion activation energy of about 268 kJ/mol. Two possible amorphization mechanisms, i.e., pressure-induced amorphization and crystallite-refin ement-induced amorphization, are proposed for the amorphization of Si induced by ball milling.