High-throughput realization of an infrared selective absorber/emitter by DUV microsphere projection lithography.

In this paper, we present a low-cost and high-throughput nanofabrication method to realize metasurfaces that have selective absorption/emission in the mid-infrared region of the electromagnetic spectrum. We have developed DUV projection lithography to produce arbitrary patterns with sub-80 nm feature sizes. As examples of practical applications, we experimentally demonstrate structures with single and double spectral absorption/emission features, and in close agreement with numerical simulation. The fundamental mechanism of perfect absorption is discussed as well. Selective infrared absorbers/emitters are critical elements in realizing efficient thermophotovoltaic cells and high-performance biosensors.

Deep-UV microsphere projection lithography.

In this Letter, we present a single-exposure deep-UV projection lithography at 254-nm wavelength that produces nanopatterns in a scalable area with a feature size of 80 nm. In this method, a macroscopic lens projects a pixelated optical mask on a monolayer of hexagonally arranged microspheres that reside on the Fourier plane and image the mask's pattern into a photoresist film. Our macroscopic lens shrinks the size of the mask by providing an imaging magnification of ∼1.86×10(4), while enhancing the exposure power. On the other hand, microsphere lens produces a sub-diffraction limit focal point-a so-called photonic nanojet-based on the near-surface focusing effect, which ensures an excellent patterning accuracy against the presence of surface roughness. Ray-optics simulation is utilized to design the bulk optics part of the lithography system, while a wave-optics simulation is implemented to simulate the optical properties of the exposed regions beneath the microspheres. We characterize the lithography performance in terms of the proximity effect, lens aberration, and interference effect due to refractive index mismatch between photoresist and substrate.