![]() ![]() Our approach is based on a two-step process ( Fig. Such stepwise approach is inherently slow and requires sophisticated feedback control systems.ĭroplet-assisted laser processing (DALP) addresses the challenges encountered in current micro and nanopatterning techniques. In addition, to generate nanopatterns over an extended surface one needs to mechanically translate the SIL along different positions of the sample. Promising methods such as photopolymerization 22 or chemical etching 21 can produce high-quality micro-SILs, but the fabrication process remains cumbersome. ![]() Small lenses are desirable since they suffer from less aberrations and they can be easily positioned at local uniform parts of an overall uneven surface. In fact, conventional grinding techniques are time consuming and are limited to SILs with diameters larger than 1 mm 21. This is particularly problematic due to the challenges involved in the fabrication of SILs. For instance, the relative high laser energies usually required for processing a surface, especially in the case where laser ablation is to be performed, can irreversibly damage SILs. However, the use of SILs for surface nanopatterning presents a series of problems that prevent this approach to be widely implemented. Successful implementations of SILs include microscopy 14, 15, 16, spectroscopy 17, photolithography 18 and optical recording 19, with reported feature sizes as small as 100 nm 20. A SIL effectively increases the numerical aperture of a focusing optical system, producing an enhancement in lateral resolution only limited by the refractive index of the SIL material. Since these methods are based on the particular photophysics of the material to be patterned 13, resolution enhancement is material-dependent and optimal results are typically constraint to a narrow range of available photoresists.Īn interesting alternative for sub-wavelength optical patterning consists of using a dielectric hemispherical lens, known as a solid immersion lens (SIL), placed in contact with the surface. In contrast, sub-wavelength feature sizes can also be fabricated by exploiting non-linarites in the interaction of light with a particular material, as in multiphoton absorption 8, 9, 10 or photopolymerization inspired by reversible saturable optical fluorescence transition (RESOLFT) microscopy 11, 12. Self-positioning systems 6 offer an interesting solution, although they tend to be time consuming and/or require complex setups 7. In this way, feature sizes below 100 nm can be produced, but maintaining the spacing between probe and substrate is extremely critical and difficult to perform in practice. By focusing light through the tip of an atomic force microscope 1, a microsphere 2, 3, 4, or a plasmonic lens 5, evanescent waves can be coupled to the material enabling deep sub-wavelength patterning. The primary strategy to overcome diffraction has been the use of near-field effects. However, the far-field diffraction barrier limits the minimum feature size in optical systems to about half the processing wavelength, imposing a serious restriction for nanopatterning at visible or infrared wavelengths. Optical methods are unrivaled as patterning tools thanks to the possibility to operate in ambient conditions, integration in direct-writing systems and ease of use.
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