Abstract
This thesis is focused on the influence of properties of substrate on formability of direct nanoimprint technique. Using silicon or glass material as the substrate for the direct metal imprint, it is found that higher imprinting force and fracture of mold may occur. Consequently, the formation of hard film/soft substrate system like Al/PMMA in replace of the soft film/hard substrate system is studied herein. The mechanical properties of aluminum thin film on different substrates are characterized by nanoindentation experiments. Subsequently, formation height will be applied to analyze the formation qualities in the nanoimprint process. It can be compared with results of nanoindentation, the relationship between mechanical properties of aluminum thin films on different substrate effects and formation height will be comprehended. In addition, formation mechanism will be understood via observing the cross-section of the microstructures of thin films after imprint process by using FIB and SEM. Based on the indentation results, the following phenomena can be observed. In the case of Al on silicon, the plastic deformation is contained within the film and this system exhibits strain gradient effects and pile-up phenomenon occurs. On the other hand, in the case of Al on PMMA, the hardness decreases with increase of the depth of indentation because that PMMA substrate starts yielding. Al/PMMA system exhibits sink-in phenomenon. Analyzing the imprint results, the formation height on Al/PMMA system is better than Al/Si system and formation ratio can be used to estimate the surface topology of deformed thin films. Surface topology of deformed Al/PMMA is single peak and the case of Al/Si is dual peak, this result conformed that deformed thin films should be single peak when the formation quality is good. Subsequently, formation mechanism of Al/PMMA system was led by plastic deformation of PMMA substrate, this result can be used to explain that Al thin film was bent, fractured and stretched by the behavior of PMMA filling into cavity of mold. This bi-layer structure still possesses potential optical properties even though the nanostructure is different from original design. According to the EDS results, there is neither aluminum composition nor PMMA being found on the silicon molds and the adhesion behavior between molds and thin films could be negligible.