Polymer underlayer assisted dewetting of a top metal nanofilm

We demonstrated polymethylmethacrylate (PMMA) polymer underlayer assisted, focused-ion-beam (FIB)-induced dewetting of a top Au nanofilm where we found that the underlayer played a prominent and, in some cases, a useful role in the dewetting of the top layer. For an Au nanofilm deposited on a thick uniform PMMA underlayer, where the underlayer is stable and therefore does not dewet, irregularly spaced Au nanoparticles (AuNPs) were formed as expected by raster-scanning of a focused Ga-ion beam. On the other hand, topographically pre-patterned thin PMMA film provided heterogeneous nucleation sites for both the Au top layer and the PMMA underlayer to initiate dewetting at and guidance for forming regularly spaced AuNPs with much narrower size distribution at significantly lower ion dose levels when compared to the thick, uniform underlayer case. We also found that the underlayer assisted dewetting in this case relaxes the restriction on pre-pattern periodicity to obtain a single NP per pattern period, which is a noteworthy departure from the pre-patterned solid substrate case. FIB-induced AuNP areas can have sharp boundaries and can be positioned on a selected area of a substrate with high positional accuracy, which is important for the implementation of devices in sensing, nano-optics/photonics, and optoelectronic applications.