Complete Report - University of New South Wales

4.5.3.1.3 Grazing Incidence X-Ray Diffraction (GIXRD)
During 2005 X-ray diffraction (XRD) analysis has been developed for the Si nanostructure
samples. This gives information on crystallinity, nanocrystal size and crystal fraction and
potentially on nanocrystal size distribution, shape and any preferred orientation. The
technique is complementary to TEM analysis and has the advantage that very little sample
preparation is required.
Two approaches have been used: analysis using X-ray tube diffractometers in the School of
Materials Science at UNSW and analysis using synchrotron XRD at the Australian Nuclear
Beamline Facility, Tsukuba, Japan.
In both cases the experiments aimed to measure XRD from the thin-fi lms at grazing
Incidence (GIXRD). Figure 4.5.8 shows a result using X-ray tube for a sample with 62 bilayers
of alternating 4.5nm SRO/SiO 2 layers (sample DK24) [SRO refers to silicon rich oxide]. It
confi rms that (at least for this sample):
• The lattice constant given by the {111} peak does not vary from the bulk silicon value
by more than 0.2%.
• The average Si nanocrystal size is 4.5nm - thus for this sample, the SRO layer
thickness controlled the size of the nanocrystals.
• There was no measurable microstrain present in the nanocrystals (i.e. no small
variations of lattice constant from dot to dot).
• The crystal orientations of the dots were perfectly random.
Figure 4.5.8: X-ray tube
XRD of a 62 bi-layer,
4.2nm, SRO/SiO2
sample.
An important aspect of the analysis is comparison of X-ray tube with synchrotron XRD data
and comparison of both with information from TEM. Figure 4.5.9 shows two-theta plots of
the same Si QD in nitride sample for which the TEM is shown in Figure 4.5.7. The sample has
20 bilayers of 10nm Si rich nitride layers. It shows that:
• The average Si nanocrystal size is 4.3nm – thus for this sample the SRO layer
thickness was too thick to control the nanocrystal size.
• Lattice parameter has less than 0.1% deviation from bulk value.
• Deviation of intensities from random orientation are less than 10%.
The presence of crystalline Si is clear from these plots. In terms of quantitative analysis, the
viability of both techniques for extracting average size, strain and lattice parameters of the
nanocrystals is being examined.
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