While the LPL, as in the monolayer case, PCI-32765 ic50 transforms into spherical voids with lower surface area and facets, the HPL becomes almost 100% porous, with a few silicon “pillars” connecting the LPL to the Si bulk (see SEM images of Figure 7). The gradual disappearance of these pillars by increasing the annealing time

can be expected to result in a relaxation of the whole stack and a decrease in strain, since the disappearance of connections between the LPL and the bulk releases the two mismatched lattices at the origin of strain. To provide support for this hypothesis of the role of the HPL’s pillars in releasing the strain of the entire stack, samples were prepared with the same LPL but different HPL porosities, as detailed in Table 1 (column “Pillars evolution”). Samples with lower (HPL-1), standard (STDHPL), and higher (HPL-2) porosity HPL were prepared. The etching time during the HPL formation was adjusted to ensure that all samples keep the same thickness of

300 nm. The annealing temperature was kept constant while the annealing time was varied (10, 30, and 120 min.). Figure 9 shows the out-of-plane compressive strain for the annealed double layer of PSi at different HPL porosities. The strain of the whole PSi stack tends to decrease with annealing time, as previously observed, except for the HPL-2 annealed for longer 120 min. That sample however, because of its very low pillar density, showed a tendency for flaking when handled, which made the measurement difficult. Besides, it is possible that the foil Akt inhibitor may have locally collapsed on the bulk parent wafer, that behavior being frequent for such unstable stacks. Finally, for a given annealing time, the strain decreases with increasing the porosity of the HPL, e.g., with lowering the density and/or the number of the pillars in the HPL. The cross-sectional SEM monographs in Figure 10 depict the disappearance of the pillars in the HPL-2, compared to STDHPL and HPL-1.One

notice is to be added IMP dehydrogenase on the discrepancy between the strain values of the two samples with a LPL 750-nm thick annealed for 10 min in Figures 8 and 9. We believe this difference could be attributed to the different reorganization rate, which is dependent on the ageing of the tube of the Epi-reactor (as mentioned in the “Methods”), since the two samples were loaded inside the tube at different moments in time. In fact, this reorganization rate affects the evolution of the pore shape and of the pillar “inter-connections” between the Si-substrate and the seed layer and, hence, the strain values. The sample in Figure 8 has a strain value lower than its counterpart in Figure 9. This is seemingly a result of the slower rate of reorganization, which is indicated by the slightly larger number of pillars in the SEM images. Figure 9 The out-of-plane compressive strain values of the annealed double layer of PSi with different HPL porosities.