Molecular Scale Imaging With a Mutlilayer Superlens

Recent theory [1] suggested a thin negative index film should function as a “superlens”, providing image detail with resolution beyond the diffraction limit—a limitation to which all positive index optics are subject. The superlens allows the recovery of evanescent waves in the image via the excitation of surface plasmons. It has been demonstrated experimentally [2] that a silver superlens allows to resolve features well below the working wavelength. Resolution as high as 60 nanometer (λ/6) half-pitch has been achieved. This unique class of superlens will enable parallel imaging and nanofabrication in a single snapshot, a feat that are not yet available with other nanoscale imaging techniques such as atomic force microscope or scanning electron microscope. In this paper, we explore the possibility of further refining the image resolution using a multilayer superlens [3]. Using a stable transfer matrix scheme, our numerical calculations show an ultimate imaging resolution of λ/24. This is made possible using alternating stacks of alumina (Al₂O₃) and silver (Ag) layers to enhance a broad spectrum of evanescent waves via surface plasmon modes. Furthermore, we present the effect of alterations in number of layers and thickness to the image transfer function. With optimized design of multilayer superlens (working wavelength of 387.5nm), our study indicates the feasibility of resolving features of 16nm and below. Moreover, our tolerance analysis indicates that a 380 nm commercial light source would degrade slightly the imaging resolution to about 20nm. Preliminary experiments are ongoing to demonstrate the molecular scale imaging resolution. The development of potential low-loss and high resolution superlens opens the door to exciting applications in nanoscale optical metrology and nanomanufacturing.