Molecular Scale Imaging with a Smooth Optical Superlens

We utilize a unique approach to grow ultrasmooth silver films characterized by much smaller root mean square (RMS) surface roughness. An intermediate ultrathin Ge layer ( ~1nm) is introduced before depositing Ag. Utilizing Ag–Ge surface interactions, smooth superlens down to 15 nm Ag thickness was fabricated. Roughness measurements of thin silver films (15 nm) deposited with and without Ge layer (1 nm) were performed using atomic force microscopy (AFM) and x-ray reflectivity techniques. These measurements indicate drastic improvement in Ag surface morphology with roughness below 0.8 nm with introduction of Ge layer. It is postulated that Ge acts as a wetting layer for Ag and helps a layer by layer growth. A detailed study of the growth of Ag on Ge has been described elsewhere.9 Some earlier works have indicated that thin and smooth Ag films can also be prepared epitaxially with metal oxides such as magnesium oxide and nickel oxide. The configuration of the smooth silver superlens can be illustrated. An array of chrome (Cr) gratings 40 nm thick with 30 nm half-pitch, which serve as the object, was patterned using a nanoimprint process developed by Hewlett-Packard Laboratory.