In this work, AAMs with three segments with different channel diameters are fabricated by controlling etching and anodization time. Additional file 1: Screening Library chemical structure Figure S4 illustrates the schematic process. In brief, a substrate has undergone the second anodization for time t A1 and etched for t E1 to broaden the pores and form the large-diameter segment of the membrane. Then, the third anodization step was performed for another time t A2 followed by chemical etch for time t E2 BGB324 to form the medium-diameter segment. In the end, the fourth anodization step was carried out for time t A3 ending with time t E3 wet etching to form the small-diameter

segment. Note that in this scenario the first segment (Figure  3d) was etched for time t E1  + t E2  + t E3, and the third segment was etched only for t E3 to broaden the pore size. In a generalized case, if there are n segments in total, the total etching time for the mth segment will be . Therefore, the diameter of the mth segment can be determined by the etching calibration curve and the fitted function (Additional file 1: Figure S1a,b) . In addition, the total depth of the AAM substrate is with the mth segment’s depth of H m  = G(t Am ) which can be determined by the plots shown in Additional file 1: Figure S1c,d. Figure  3d demonstrates the cross section of a 1-μm-pitch tri-diameter AAM fabricated by a

four-step anodization process. Such a structure CHIR98014 chemical structure has been used to template PC nanotowers, as shown in Figure  3e,f, by the aforementioned thermal press process (Additional file 1: Figure S2b). Note that as the length of each diameter segment is controllable, a smooth oxyclozanide internal slope on the side wall can be achieved by properly shortening each segment. Therefore, a nanocone structure can be obtained, as shown in Figure  3f. It is worth noting that the above nanostructure

templating process can be extended to other materials. In practice, we have also fabricated PI nanopillar arrays (Additional file 1: Figure S3) with spin-coating method. Besides using thermal press method to template nanostructures, material deposition method was also used to fabricate well designed nanostructures with AAM. Particularly, a-Si nanocone arrays have been fabricated with plasma-enhanced chemical vapor deposition (PECVD), as shown in Figure  4a with the inset showing the AAM template. The nanocones are formed by a-Si thin-film deposition. Additional file 1: Figure S5 shows the cross section of the a-Si nanocones embedded in the AAM. In order to characterize the nanocones, they are transferred to a supporting substrate followed by etching away the AAM template in HF solution. Figure 4 SEM image, optical reflectance, and photo/schematic of a-Si and cross-sectional | E | distribution of the electromagnetic (EM) wave. (a) The 60°-tilted-angle-view SEM image of amorphous Si (a-Si) nanocone arrays fabricated with plasma-enhanced chemical vapor deposition (PECVD), with the AAM template shown in the inset.