Figure 2b shows the SEM image of the Au mesh film obtained after depositing the Au film on the patterned silicon (100) surface by ion sputtering (corresponding to Figure 1e). Due to the closure effect [13], the average apertures of the Au mesh decrease with increased thickness of the Au film. After depositing a 45-nm-thick Au film, the average hole diameter decreases to 65 nm ± 15%, as shown in Figure 2d. selleck Figure 2 SEM image and diameter distribution of the patterned silicon surface and the Au mesh. (a) SEM image and (c) diameter distribution of the patterned silicon

surface after the removal of the AAO mask and SiO2 layer. (b) SEM image and (d) diameter distribution of the Au mesh after the deposition of the Au film on the patterned silicon surface. The bars in (c) and (d) represent the see more measured statistical data, and the line is a Gaussian fitting. The sputtering

process resulted in a uniform deposition of the Au on the top surface of the patterned silicon, partially coating on the upper side walls, but not on the bottom of the holes, as shown selleck screening library in Figure 3, which can be primarily attributed to the large depth-width ratio of the holes (approximately 5.6), considering the poor step coverage and the undemanding deposition conditions of ion sputtering. Figure 3 Cross-sectional SEM image of the patterned Si substrate covered with Au film. Structure of the SiNW arrays The resulting large-area, vertically aligned SiNW array is shown in Figure 4a. Upon close examination, Au can be clearly observed at the interfacial region between the SiNWs and the substrates, while no Au particle is found on the top of each SiNW. This result is consistent with the observation that Au is not deposited at the bottom of the holes (see Figure 3). Figure 4b shows that the SiNW exhibits a uniform diameter along the height direction, indicating that Au is inert against oxidative dissolution in the etching solution and is superior to the Ag catalyst which resulted in the tapered morphologies Epothilone B (EPO906, Patupilone) of the SiNWs with larger diameters at the bottom part due to the dissolution-induced gradual increase of the hole sizes of the Ag mesh during etching [12, 13]. Figure 4 Plan-view (a)

and cross-sectional (b) SEM images of the large-area, vertically aligned SiNW arrays. For the SEM observation, the sample was tilted by 15°. Effect of Au mesh thickness on the etching rate The Au films with thicknesses of 15, 30, and 45 nm were deposited on the same patterned Si substrate and then subjected to metal-assisted chemical etching for 10 min at 22°C. Interestingly, the height of the SiNWs catalyzed using a thick Au mesh was much larger compared with that catalyzed using a thin one (see Figure 5). The average heights of the resulting SiNWs are 220, 458, and 1,076 nm, respectively. Clearly, the disparity in the height of the SiNWs can be attributed to the different etching rates of the Si catalyzed using the Au meshes with different thicknesses.