(a) 30-, (b) 60-, and (c) 180-s etch durations. The top surfaces of the nanostructures remain smooth after the process due to a good degree
of protection offered by the NIL masking layer. This contrasts with the rougher sidewalls. Slight narrowing in the lateral dimensions of the Si nanostructures from approximately 180 nm to approximately 160 nm occurs when the etching duration is increased from 30 to 180 s. The fine lines or streaks observed SGC-CBP30 manufacturer in (b) and to a greater degree in (c) between the Si nanostructures are attributable to non-uniform gold coating of low-relief surfaces between higher structures prior to FESEM to reduce charging effects. While maintaining relatively low doping levels in the Si wafers (resistivity 10 to 20 Ω.cm) may play a contributory role in slowing the progress of porosity attack, the preservation of the smooth top surface is more likely linked to the use of the NIL mask. The latter is formed by the UV polymerization of a proprietary
silicon-containing acrylate resist, the adhesion of which is strongly enhanced by the use of the planarization/primer layer. This is shown to be highly resistant to chemical attack by both acids and bases, with complete removal being effected by immersion in boiling piranha solution only. The NIL mask caps remain after MCEE and are shown in Figure 5b,c. The observations show that under our conditions of etching, the mask offers good EPZ5676 protection to the Si surface Saracatinib datasheet against chemical attack by the HF/H2O2 etching solution. The integrity of the Si nanostructure is further shown in the high-resolution transmission electron microscopy (HR-TEM) images of Figure 7. A smooth morphology of the top surfaces (Figure 7a,b) is observed in contrast to the rougher sidewalls (Figure 7c,d). The preservation of the top surface can have potential device applications which are currently being explored.
Figure 7 HR-TEM images of metal-catalyzed electrolessly etched Si nanostructure (after a 60-s etch Teicoplanin and removal of NIL mask). (a) Top left corner. (b) Top surface. The well-defined and flat top interface is a consequence of the resistance of the NIL mask against chemical attack. (c) Left sidewall near the top surface. The etched sidewall shows a higher extent of surface roughness of about 3 nm due to attack by the HF/H2O solution. (d) Left sidewall towards base of nanostructure. Surface roughness is smaller due to shorter exposure to etching solution. (e) TEM image of the entire MCEE Si nanostructure. Red-outlined boxes show the locations of where the magnified HR-TEM images were taken. The etching proceeds preferentially along the <100 > direction. (f) The single crystal quality of the Si is evident from the SAED pattern.