4 1.4 73 1.4 73 1.4 50 73 97 Porosity [%] 30 ± 5 30 ± 5 55 ± 5 30 ± 5 55 ± 5 30 ± 5 ND 55 ± 5 ND Etching time [s]/thickness [nm] 150/350 30% ± 5% 6/300 (I) 300/750 6/300 300/750 8/300 6/300 4/300 300/750 50/150 600/1300 150/350 900/1700 300/750 450/900 (II) 600/1300 6/300 600/1300 900/1700 1200/2000 Figure 2 Schematic view of the temperature profile. The solid line represents the typical profile of the annealing and the dotted
selleck line represents the additional time for the epitaxial growth. Results and discussions Effect of PSi layer thickness on strain and surface roughness The case of PSi monolayers To investigate the effect of the thickness of the PSi stack (monolayer and double layers), on the strain and surface
roughness, several PSi layers were prepared with different thicknesses and porosities as summarized in Table 1 (column “Impact of thickness”). Figure 3 shows the XRD profiles of the as-etched and the annealed, 1,300-nm-thick, low-porosity monolayer of PSi of about 30% ± 5% of porosity. click here That XRD profile (plotted on a semi-logarithmic scale) is typical for a PSi layer attached to a Si Cobimetinib supplier substrate showing two characteristic peaks (see Figure 3). The higher intensity peak corresponds to the monocrystalline silicon substrate while the lower intensity peak is due to the PSi layer. Upon annealing, the PSi peak shifts from lower to higher angle relative to the Si-peak, indicating a change in the type of the out-of-plane strain (i.e., tensile to compressive). A broad hump (D), which is reported also by Bensaid et al. , is observed below the two narrow peaks. This is due to the diffuse scattering caused by the presence nanometric structure of silicon crystallites. The relative expansion or contraction Δa/a in the PSi lattice structure with respect to the silicon substrate along the (001) direction perpendicular to the sample Fossariinae surface is directly proportional to the angular splitting Δθ B between the two XRD spectrum peaks : Δa/a = −Δθ B cot θ B where θ B is the
Bragg’s angle. Figure 3 XRD profiles of the as-etched and the annealed, 1,300-nm-thick, low-porosity monolayer of PSi. XRD profiles combined with the cross-sectional SEM image of the as-etched ( a ) and annealed ( b ) monolayer of PSi, 1300-nm-thick, displaying two clear peaks corresponding to the Si substrate and the PSi layer, on top of a broad hump (D). Upon annealing, the PSi peak shifts from lower to higher angle relative to the Si-peak, indicating a change in the out-of-plane strain from tensile to compressive. The PSi peak is at a lower angle relative to the Si reference peak. This is the case for all the as-etched samples but with different angular splitting Δθ B between the two peaks.