The Fabrication Of Ordered Colloidal Crystal Microstructures

Colloidal crystals made of sub-micrometer monodisperse inorganic or polymer microspheres packed in ordered arrays represent a new class of advanced materials that have many potential applications in fields such as photonics, optics, and sensing. Due to the importance of their applications in many areas, colloidal crystals have attracted extensive interest for a long time. Various self-assembly techniques based on exploiting gravity sedimentation, electrostatic interaction, and capillary force have been developed to form colloidal crystals on a solid substrate. Although some of these techniques are capable of producing large, single-crystalline domains, for the practical device applications it is usually necessary to fabricate colloidal crystal films onto substrates with specific microstructures. As the continuously developing surface patterning techniques are gradually accessible to common labs, researchers can use a variety of patterned surfaces as templates to direct the self-assembly of microspheres for creating colloidal crystals with defined crystalline orientations, shapes, and sizes. Although some of these methods are efficient in controlling the size, structure, and crystalline orientation of colloidal crystals, challenges in this field still exist. At the same time, the realization of practical application of colloidal crystals in industries still relies on the development of surface patterning techniques for colloidal crystals.In Chapter 2, we developed a lift-up soft lithography technique to pattern the obtained colloidal crystals by using a combination of soft lithography and self-assembly technique. Because this non-template method is based on the selective transfer of a single layer of close-packed microspheres from the colloidal crystal film to the PDMS stamp surface, it is possible to realize fine control over the microstructures of colloidal crystal film using a layer-by-layer lift-up process. This method also offers an effective route for creating a 2D colloidal crystal film on the PDMS stamp. We suggest that this lift-up soft lithography technique has provided a complementary strategy to other existing patterning methods and will open new ways to design and fabricate colloidal crystal-based devices.In Chapter 3, based on the use of polymer thin film as glue to provide an efficient interaction between the microsphere "ink" and substrate, we have developed a simple modified μcp technique to directly pattern 2D colloidal crystals on solid substrates. Taking advantage of the flexibility of μcp, this method is versatile for patterning colloidal crystals on the non-planar surface and creating ordered heterogeneous colloidal crystal structures. We suggest that this method has demonstrated a new interaction between "ink" and substrates for the transfer of materials and will extend the use of μcp for the fabrication of colloidal crystal-based devices.