Due to unique properties such as low vapor pressure and high ionic conductivity, room-temperature ionic liquids (RTILs) are very attractive not only for the chemical industry, but also for nano- and microstructures fabrication. The fabrication process conventionally involves usage of radiation sensitive polymer-based solutions (resists). We propose to replace those resists with eco-friendly solvent-free RTILs, which are polymerized by electron beam or UV light. Ionic liquids are also promising material for passive and active photonics components fabrication since their properties can be tuned in many ways by introducing special functionalities to the chemical structure of ions. In the present study, it is shown that different ionic liquids (with allyl or vinylbenzyl substituent) can be solidified on solid substrates (e.g. silicon or glass) by standard patterning lithography methods such as electron beam lithography in vacuum chamber and optical lithography with UV lamp. The thickness of the layer can be modified with ionic liquids mixture or by modified spin coating technique. By using patterning techniques, microstructures of different geometrical shapes are obtained from polymerizable RTILs containing fluorescein dianions. The shapes of obtained polymerized microstructures are also related to properties of the material including viscosities of selected ionic liquids. Various properties of polymerizable ionic liquids, such as thermal stability, viscosity, refractive index and light absorption can be adapted depending on the final application. Due to good optical properties, the fabricated microstructures can be used as photonic components, such as optical microresonators and waveguides.
In this work, results of measurements of surface tension of KOH and TMAH solutions containing alcohol additives were
used to assess the behavior of the alcohols during silicon anisotropic etching. Surface tension of KOH and TMAH
solutions containing additives of alcohols with one or more hydroxyl groups as well as etching rates and surface
roughness of Si(100) and Si(110) surfaces etched in these solutions were analyzed. An improvement in roughness of
both the planes was observed after addition of the alcohols to the KOH and TMAH solutions, however reduction of
etching rates of Si(110) planes occurred only in KOH solutions. Based on surface tension measurements, it was stated
that reduction of etching rates results from selective adsorption of the surface active compound on Si surfaces, which is
possible due to adsorption layer formed on the solution surface of KOH etchant. The adsorption layer does not appear in
TMAH + alcohols solutions, which accounts for a different behavior of TMAH-based etchants.
Anisotropic etching process of Si (100) and (110) planes in low concentrated potassium hydroxide (KOH) solutions
containing Triton X-100 surfactant is studied in this paper. Addition of a little amount of the surfactant to the etchant
considerably reduces etch rates of both the planes, though the etch rate ratio R(100)/R(110) > 1 is obtained. The (110)
surface roughness is significantly decreased when Triton is added to the solution, too. Therefore, the {110} sidewall
planes could be used as micromirrors inclined at 45° towards the (100) substrate. The {110} surface roughness is low in
a wide range of Triton concentration, which gives some flexibility in the choice of surfactant concentration for
fabrication of smooth micromirrors. Better understanding of etching processes with surfactants could help select a
composition of the etching solution which yields little rough {110} planes. For that reason, the adsorption of Triton
molecules on Si surface is investigated using contact angle measurements. The results show that the (110) surface is
more hydrophilic as well as better wetted by the surfactant solution than the (100) one, though both the planes are rather
hydrophobic. This suggests that a little more hydrophilic surface should be more advantageous to the surfactant
adsorption. The explanation, based on literature reports and theoretical considerations, is proposed and associated with
the etching results.
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