Figure 3b,c corresponds to respective images using SF6/O2 and SF6/CHF3 gas mixtures. From the images, it is obvious that the etch rate with the SF6 gas is higher than the etch rate with the two other gases, and as expected, the etching is isotropic, thus resulting in almost full release of the PAA thin film after RIE of the samples for 20 s. Thus,

the nanopatterned Si surface after PAA removal shows quite shallow features. When adding O2 to SF6, the etching process is slowed down and is more anisotropic. Dibutyryl-cAMP solubility dmso As a result, the 20-s etch time does not lead to PAA mask release, but instead, a nanopatterned surface with features well separated by pore walls are formed (Figure 3b image 1). When replacing O2 by CHF3, the RIE process is even slower and more anisotropic, thus resulting in shallower etched features at each pore bottom and thicker pore walls, as clearly depicted in Figure 3c. Figure 3 SEM micrographs of the Si surface of sample 1 after RIE through PAA film and alumina dissolution. Three different gas LY2874455 concentration mixtures were used for etching, which are indicated on top of the images. The etching duration was 20 s. Micrographs 1 of (a), (b), and (c) are cross-sectional images of the PAA layer/Si stack, while micrographs 2 and 3 are plane view SEM images (slightly tilted in images

2 of (a), (b), and (c); at vertical e-beam incidence in images 3). By increasing the etching Angiogenesis inhibitor time, the depth of the etched holes at each pore bottom increases, but gradually, the lateral etching results in almost full etching of the inter-hole walls, starting from their top, and finally PAA membrane release. This happens earlier with SF6 (isotropic etching) than with the other two gas mixtures. Figure 4 depicts the SEM images of sample 1 after etching in SF6/O2 (Figure 4a) and in SF6/CHF3 (Figure 4b) for 40 s (images 1 and 2 of Figure 4a, and images 1 and 2 of Figure 4b) and 60 s (images 3 of Figure 4a,b). Already for 40-s etching time, the Epothilone B (EPO906, Patupilone) PAA film is fully released when

using SF6/O2 gas mixture, and the Si inter-hole walls are reduced in height. With SF6/CHF3 gas mixture, well-separated nanofeatures on Si are formed, with the inter-pore Si walls intact at their top surface. Finally, for the 60-s etching time, the PAA layer was fully released in both gas mixtures. Figure 4 SEM micrographs of sample 1 after RIE in two different gas mixtures. Micrographs 1 of (a) and (b) are cross-sectional images, while images 2 and 3 of (a) and (b) are plane view images. Etching was performed in SF6/O2 (images 1 to 3 of (a)) and in SF6/CHF3 (images 1 to 3 of (b)). The etching duration was 40 s in images 1 and 2, and 60 s in images 3. In the cross-sectional images, the PAA mask is present; in the plane view images, it is removed, revealing the nanopatterned Si surface.