Plasmons in Atomically Thin Crystalline Silver Nanostructures Grown on Patterned Silicon

We demonstrate the fabrication of ultrathin, crystalline Ag nanostructures on pre-patterned Si substrates and characterize their novel plasmonic properties. Nanostructures are first produced by etching the Si(111) substrate by electron beam lithography. This is followed by wet chemical etching to remove resist and native Si-oxide from the surface, which is then coated with ultrathin (less than 5 nm), crystalline Ag by molecular beam epitaxy. The preparation steps are monitored by electron spectroscopy and microscopy methods. High quality mid-infrared plasmonic resonances of the resulting nanostructured Ag are characterized by Fourier transform infrared spectroscopy. Multiple higher-order modes are found in various types of nanostructures (e.g. triangles, bowties, disks). Our process results in Ag nanostructures covered with only a thin passivating layer, which is advantageous for interfacing and chemical sensing applications.