| Summary: | 博士 === 國立成功大學 === 材料科學及工程學系碩博士班 === 100 === The rapid and effective pattern transfer method would be empolyed by the solvent-assisted imprinting lithography. Polymethylmethacrylate (PMMA) and ethyl alcohol (EtOH) are chosen for demonstrating a solvent-assisted imprint process working at room temperature and low pressure (0.001~0.01 MPa) with a soft mold. The poor solvents (such as EtOH, acetone and THF) cause a physical swelling reaction for both the PDMS mold and polymer resist (such as PMMA, PS and PC). The swollen PMMA gel has excellent filling capability for applying in imprinting lithography. During imprinting process, the PDMS mold absorbs the poor solvent from the resist, which deswells the polymer gel and helps pattern setting. This method can be applied extensively for micro-nanolithography and plastics industry to prepare micron-nanometer scale structures. Besides, by controlling the imprinting conditions, the residual-layer-free pattern through the polymer dewetting effect could be obtained.
The solvent vapor-assisted imprinting lithography (SVAIL) using the flexible PDMS membrane mold (0.5-1 mm thickness) as a solvent transport medium in a vapor environment has also been demonstrated. By adjusting the solvent vapor pressure and temperature, the transport mechanism provides the sufficient solvent to soften the thin polystyrene resist (〈100 nm) and avoids the unexpected deformation of imprinted nanopatterns. The idea shows the potential of SVAIL for large-area pattern (5x5 cm2) without any external loading. The residual-layer-free pattern can be obtained through the SAVIL because of the ultra thin coated polymer films. The multiple imprinting has been performed to obtain 2D hierarchical structures using simple 1D stripe patterned stamps. To combine this method with wet etching process and metal electrodeposition, the Si grating and Ni pattern can be fabricated.
A controlled dewetting process for fabricating an ordered nanostructure on a polymer thin film is demonstrated. Uniform PS pattern can be fabricated at room temperature and low pressure (0.01MPa) by a solvent-assisted method. The imprinted PS microlens have marked change in morphology from dome to sphere because spinodal dewetting effects after acetone treatment. By adjusting thickness of the residual layer between imprinted domes, the self-organization PS sphere arrays with multiple sizes can be fabricated. Furthermore, the sub-micrometer PS pre-pattern can be turned into photonic crystal arrays with 555 nm pitch by dewetting process.
A simple and cost-effective method for creating patterned nanoindentations on Al surface via a mold-assisted chemical etching process has been carried out. This study shows a reaction-diffusion method which formed nanoscale shallow etch pits (25 nm deep) by the absorption/liberation behavior of etchant in PDMS stamp. After anodization, we can get the ordered nanopore arrays with 277 nm pitch that are guided by the prepatterned etch pits. The proposed method can also find applications in other metals and semiconductors for preparing ordered nanopore or nanochannel arrays through pretexturing.
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