XRD spectrum of the as-milled and the chemically etched Si showing broadening of the peak with increasing milling time and with oxidation. The different planes of Si are indexed according to Ref. 40.
(a) Topographic and (b) phase contrast AFM images of the chemically and thermally treated ball-milled silicon (75 h milled) and the corresponding line profile analyses. The size of the particle indicated in (a) is estimated to be 10.5 nm; (b) shows the presence of core-shell structures with the darker region representing a core surrounded by a brighter zone of silicon oxide. Particles with varying core and shell sizes are decipherable. Line profile analysis of the marked particle reveals a core diameter of 6.9 nm with a shell thickness of about 90 nm. The histograms show a variation in core sizes from 4 to 10 nm and shell sizes between 55 and 170 nm for the particles captured in the AFM image.
HRTEM images of chemically oxidized, ball-milled Si. (a) Bright field image of the sample powder dispersed in a copper grid. The inset shows the corresponding SAD pattern. (b) Near surface image showing presence of nc-Si with dimensions , embedded in amorphous background. (c) nc-Si islands consisting of all the three planes identified by XRD shown in Fig. 1. (d) Near surface image showing random orientation of neighboring crystallites. The inset is the corresponding FFT image.
PL spectra of the chemically and thermally oxidized nc-Si dispersed in ethanol under external excitation with 2.71 (—◻—), 2.60 (—○—), 2.54 (—×—), and 2.41 (—△—) eV monochromatic energies of an argon ion laser. The inset shows the variation in PL band peak energy with excitation energy. The emission-excitation data for excitation by 3.49 eV, which gave a peak at 2.47 eV, were obtained by exciting the sample with the 355 nm line of a neodymium doped yttrium aluminum garnet laser for recording the time resolved PL of the sample that has been reported in Ref. 11.
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