Sub-diffractional nanopatterning and nanocharacterization of silk fibroin using tip-enhanced near-field optics




Lee, Woonsoo

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Mid-IR scattering-type scanning near-field optical microscope (s-SNOM) has extended spatial resolution of vibrational microscopy and spectroscopy to ~10 nm, over two orders of magnitude better than one-half-wavelength diffraction limit. Concentrated near-field light can also be used for creating features with nanoscopic precision. This dissertation documents the development of a novel nanopatterning approach based on s-SNOM that can be used to pattern sub-diffractional, dual-tone, and grayscale nanostructures onto ultra-thin silk fibroin film. This approach is named tip-enhanced near-field infrared nanolithography (TNINL). TNINL was conceived with the aim of combining nano-characterization capabilities of s-SNOM with the lithography potential of tip-enhanced near-field optics. This dissertation examines the potential of s-SNOM as a basic tool for closed-loop lithography, a versatile nanopatterning platform with inherent feedback to optimize the writing process. In this context, the use of silk is advantageous because silk interface well with both biotic and abiotic interfaces. In addition, its strength, robustness, cytocompatibility, biocompatibility, biodegradability, and tunable water-solubility make silk favorable functional substrate for various nanofabricated devices. In the development of TNINL, various approaches for patterning silk with s-SNOM were conceived and tested. Nanoscale features were patterned and characterized in-situ, revealing both topographical and conformational modifications. System input parameters were empirically and analytically studied, and a thermomechanical patterning mechanism was proposed. A versatile patterning capability is demonstrated, and potential applications are investigated


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