|
Poly(ethylene teraphthalate) (PET) is a thermoplastic polymer with uncommon physical and chemical characteristics. Its properties include high transparency and flexibility, impact-resistant, light weight, as well as non-permeability to oxygen and carbon dioxide. It has optimal physico-chemical characteristics for many applications like in biomedical devices thanks to its bio-compatibility or, due to its flexilibiliy and transparency, in flexible displays.
The use of such promising material needs specific, high-resolution processing techniques which allow sub-micron patterning while maintaining unchanged the physical characteristics of the polymer. Unfortunately, PET reacts with many organic solvents and developers used in standard nano-fabrication and, furthermore, it can not be heat up to typical resist baking temperature without loosing its nominal characteristics. In fact, depending on its processing and thermal history, PET can exist both as amorphous (transparent) and as semi-crystalline (opaque and white) material. This last state can happen due polymer heating above its glass transition temperature and leads to evident degradation of the transparency.
Here we present low-damage nano-topographic modification of PET. High-resolution nanopatterning over macroscopic areas was performed by "low-temperature" thermal nanoimprint lithography (NIL). While for standard NIL the temperature is raised up to tens of degrees above the polymer Tg, we were able to obtain optimal results at a temperature nominally equal to PET Tg. We shall show nanogratings and nano-bar-codes transferred on PET commercial sheets, demonstrating reliable sub-100-nm resolution while maintaining original substrate properties (i.e biocompatibility, transparency and flexibility). This result constitutes a relevant advance in plastic processing, opening the way to the engineering of new marked containers for efficient tracking and classification. Furthermore, PET is a good candidate for artificial tissues and original nano-patterned substrates are essential investigation tools for advanced bio-engineering experiments.
|