The increased Si content results in a considerable enhancement in the coarsening of the Ge nanocrystallites, as observed when increasing the thickness of buffer Si3N4 from 8 to 15 nm (Figure 2a,b), and also serves to achieve complete coalescence of the nanocrystallites to form a single Ge QD when the buffer Si3N4 is thick enough (22 nm) (Figure 2c).
Attendant to the migration process are changes that occur to the crystallographic morphology, crystallinity, and sizes of the Ge nanocrystallites. Thus, the Ge nanocrystallites are undergoing an Ostwald ripening process  which also, in addition to the migration, appears to be facilitated by the Si interstitials. Further evidence of the Si interstitial-mediated Ostwald ripening process was provided by the sample with the Si3N4 capping IAP inhibitor layer (Figure 3) subjected to thermal annealing at 900°C for 90 min in an H2O ambient. In this case, the Ge nanocrystallite clusters PI3K Inhibitor Library within the pillars experience lateral Si interstitial fluxes in all azimuthal directions because of the surrounding Si3N4. Therefore, the in-plane symmetry of the radial Si interstitial fluxes prevents the Ge nanocrystallite clusters from adopting any one, particular direction for preferential migration as was seen in the previous case (Figure 2). However,
the Ostwald ripening proceeds unhindered and results in significant coarsening of the Ge nanocrystallites by as much as 3 to 4 × ! With the profound understanding 4EGI-1 supplier gained by the above two cases, we can now examine the case of the nanopillar sample itself, without either the underlying Si3N4 layer or the Si3N4 capping layer but also subjected to the same thermal annealing at 900°C for various times within an H2O ambient. In this case, it
is observed that the Ostwald ripening process occurs at a much slower rate with a slight change in the average size of the Ge nanocrystallites within the cluster. Gemcitabine manufacturer Starting from an original average size of 5.8 ± 1.2 nm for the as-formed Ge nanocrystallites, Figure 4a shows the time evolution of the Ge nanocrystallite clusters formed after thermal annealing at 900°C under an H2O ambient of 120-nm-diameter pillars of previously oxidized Si0.85Ge0.15 for annealing times of 10, 40, 70, and 100 min, respectively. The average nanocrystallite size changes from approximately 7 nm at 10 min of annealing to 8.7 ± 0.9 nm at 40 min, 10.5 ± 1.8 nm at 70 min, and 11.2 ± 2.5 nm at 100 min of annealing (Figure 4b). Based on the above evidence, we believe that the slight coarsening of the Ge nanocrystallites that is observed with increased annealing times is mediated by the small, residual concentration of Si interstitials left behind after thermal oxidation of the SiGe layer.