Research Of Microstructures Fabricated By Self-Assembly And Transfer Printing Based On PDMS

With the development of science and technology, miniaturization has become major concern in many fields. As a conventional technique for fabricating microstructures, photolithography has manufactured ultra-large scale integrated circuits from the micro- to nanoscale with high precision, which has been widely used in industrial production and scientific research. But common photolithophography needs expensive optical exposure equipments and its maintenance, rigid circumstances, complex processes, and only used to fabricate semiconductor, metal, and several photosensitive resist. Microstructures fabricated by non-conventional lithography with low cost, high efficiency and simple process based on non-semiconductor are urgently required in some emerging fields such as microfluidics, biologic chips, chip on a lab, micro total analysis system and organic electronics, as well as in conventional field such as analytical chemistry, life science and physics. Therefore, study on microfabricaiton based on non-semiconductor is of great significance to the above mentioned fields whatever in theory or in application.Because of their length scale, well-defined architecture, controlled synthesis, ease of processing and wide range of chemical functionality that can be incorporated, polymers are widely used in many areas, especially fabricating patterns in micro- and nanoscale. At present numerous non-lithographic technologies based on polymers are under development to fabricate patterns in micro- and nanoscale, for example, nanoimprint lithography, soft lithography, and self-assembly. As we know, the most effective approach is integration with these developed technologies to fully utilize each advantage to fabricate functional pattern based on polymers. In this thesis, polydimethylsiloxane (PDMS) was investigated in quality. And the techniques based on self assembly and transfer printing were developed to fabricate microstructures based on PDMS, which provided a reliable and economical route to pattern in micro- and nanoscale. The detailed contents of this thesis contain:Chemical construction, synthetic reaction and main characteristic of PDMS were investigated to study its potential application. Nanoindentation was used to measure elastic modulus and hardness of PDMS with different mixing ratio. Experimental result indicated that PDMS with mixing ratio of 6:1 had maximal elastic modulus and hardness from 10:1 to 1:1. Nanopatterns made by nanoindentation and machanical scratch based on AFM diamond tip were replicated to PDMS surface. By replication of 2D and 3D microstructures with complex morphology, resolution and quality factor of replica molding were investigated to ganrantee the performance of PDMS as a mold material.Due to the large thermal expansion mismatch, a thin metal film thermally deposited on a thick compliant elastomer substrate undergoes compression strain when the system is cooled. And then the metal film buckles spontaneously into complex, ordered structures with distinctive features. Theoretical analysis and experimental research about wrinkle patterns in a metal film deposited on a thick PDMS substrate were both studied to establish effective steps which could prevent, reduce or avoid wrinkle formation. The specification and evaluation criteria for typical wrinkle morphology was established, whick was based on two dimensional Fast Fourior Transfer (FFT) and gray level co-occurance matrix. The distribution, direction and order of wrinkle patterns can be exactly judged by this criterion.Depend on patterned PDMS surface replicated from hard masters fabricated by photolithography and ultra-precision machining technique, ordered wrinkle patterns were modulated. Owing to interrelation between wrinkle and substrate in characteristic size, two different modulated patterns were obtained. Herringbone wrinkles were achieved by stripe substrates which were replicated from etched Si wafers and tooth marks in Al samples manufactured by ultra-precision turning. Foramation mechanics of herringbone wrinkle was investigated.A transfer printing technique based on PDMS adhesion was established to fabricate Au/Ti/PDMS composite patterns. By nanoscratch experiements, the quantitative measurement was implemented to estimate and compare adhesion strength of coating-substrate deposited respetively by electron beam evaporation and ion sputtering. And the qualitative measurement was performed to evaluate adhesion force of PDMS with different mixing ratio. Aboved mentioned measure results provided experimental foundation for transfer printing. A Ti/Au bilayer in nanoscale was first deposited on a patterned Si wafer by electron beam evaporation, and then placed onto the PDMS relief surface replicated from tooth marks in Al samples without applied pressure. Due to strong adhesion between PDMS and Ti/Au, Au/Ti bilayer on contact regions could be transferred from the Si wafer to PDMS surface.