Li et al. Nanoscale Research Letters 2011, 6:601 http://www.nanoscalereslett.com/content/6/1/601 Page 3 of 4 Figure 2 SEM image and histogram of grains size distribution of InSb films: (a) SEM image of the InSb NCs film. Inset shows the cross- sectional TEM image of InSb NCs film. (b) Histogram of the InSb NCs grains size distribution. optical bandgap of the film is determined by applying the Tauc model [15] in the high absorbance region, αhν = D(hν − Eg)n (2) where hν is the photon energy, Eg is the optical band- gap, and D is a constant; it can be found that n = 2 cor- responds to the indirect transition-type semiconductor and n = 1/2 leads to the direct transition type one [16]. Inset shows (ahν)2 versus hν plots for the film. Follow- ing the conventional method of extrapolating the linear part of the Tauc plot, the optical bandgap energy for direct transition for the InSb NCs film was obtained, which is about 0.263 eV and agrees well with the value obtained directly from the absorption spectrum. Current-voltage characteristics of the XOI structure were measured and the results are presented in Figure 4. Figure 3 FTIR image of the InSb NCs film. Inset shows (ahν)2 versus hν plots for the film. Figure 4 I-V characteristics: (a) I-V characteristics of the InSb NCs/SiO2/p-Si heterojunction, inset shows the schematic diagram of the InSb NCs/SiO2/p-Si heterojunction, (b) the sqrt(I) plot of I-V.