Kim and Cho Nanoscale Research Letters 2012, 7:408 http://www.nanoscalereslett.com/content/7/1/408 Page 4 of 8 Figure 3 Cross-section and plane view SEM images. Micrographs (a), (b) and (c) are cross-section views of the samples with resistivities of 5 × 10−3, 4 and 15 Ω cm, respectively. Micrographs (d), (e) and (f) are plane views of the samples with resistivities of 5 × 10−3, 4, and 15 Ω cm, respectively. with the raw data with a reliability of approximately 90 % to 95 %. The mean nanocrystallite size was deter- mined from the FWHM of the XRD peaks using the Scherrer equation [23] as follows: where D, λ and w mean the nanocrystallite size, X-ray wavelength and FWHM, respectively. The Si crystallites 0:9λ D ¼ w cosθ ; 1 ð Þ Figure 4 BET results of the PS. The change in the surface area per unit volume of the PS as a function of the resistivity of the wafers. embedded in the etched layer of sample 1 were 5.3, 16.5 and 96.0 nm, respectively. The relative volume fractions of the crystals with sizes of 5.3, 16.5 and 96.0 nm were 47 %, 40 % and 13 % respectively. Therefore, in sample 1, the crystallite size varied widely; approximately 5-nm- sized crystallites are expected to contribute mainly to the light emitting of the PS at room temperature. Figure 5b shows the XRD patterns of samples 2, 3 and 4. The main peaks at 28.4° were assigned to the (111) plane of Si. The Lorentzian function was also applied to exam- ine the nanocrystallite size of these patterns. The nano- crystallite size of these samples ranged from 3.1 to 2.0 nm; the FWHM increased with increasing the resist- ivity of the Si wafer. We carried out the grazing incidence X-ray diffraction (GIXD) analysis for samples 2, 3 and 4 [24,25]. In these samples, most nanocrystallites are located on the etched surface, and GIXD analysis is very effective to get good response from the top-etched surface. On the other hand, for sample 1, the thin film X-ray analysis was used to observe the presence of nanocrystallites. This is mainly because about 20-μm-thick etched layer was formed in sample 1, and nanocrystallites are spread all over the etched layer. Figure 6 shows the Raman spectra of PS samples 1 to 4. The best Gaussian fits of the Raman spectra are shown for each spectrum. The broad peak at 480 cm−1 indicates the presence of amorphous silicon, and the shoulder peak at 490 to 520 cm−1 was assigned to the presence of nanocrystallite silicon (nc-Si) [26]. The symmetric main peak of bulk Si is centered at 521 cm−1 [27]. The deconvoluted Gaussian fits provide