Ultrathin alumina membranes for the fabrication of blackberry-like gold nanostructure arrays

Highly ordered nanostructure arrays are currently attracting wide attention because of the broad range of potential applications of such periodic structural arrangements. However, achieving highly ordered nanostructure arrays with gaps between two neighbouring nanostructures smaller than 20 nm by a technique involving transferring ultrathin alumina membranes (UTAMs) onto substrates is difficult without introducing organic impurities as supporting layers. Here, through a unique method of transferring UTAMs and fabricating nanostructure arrays, blackberry-like Au nanostructure arrays with small gaps (10 nm) between two neighbouring nanostructures are fabricated on substrates without introducing organic impurities during the transfer process. The most important aspect of our method is the use of ridges on the topside of the UTAM as a mask during the sputter-coating process. Because the small gaps between two neighbouring blackberry-like nanostructures cause an electromagnetic field enhancement, the blackberry-like Au nanostructure itself possesses numerous hotspots. These hotspots are the major contributor to the electromagnetic field enhancement in the arrays; therefore, the blackberry-like Au nanostructure arrays have prospective applications in plasmonic nanodevices such as surface-enhanced Raman scattering substrates.