Fabricating Ordered Microstructures On The Basis Of Self-assembled Colloidal Crystals

In the past two decades, ordered microstructures with special functions have attracted more and more interests. And they have been widely used in fields of micro-reactor, biosensors, microelectronics, optical devices and micromechanics. So far, many approaches for surface patterning have been established, including traditional photolithography, e-beam lithography, X-ray lithography, scanning probe lithography, micro-contact printing and soft lithography, etc. Each of these techniques shows their own advantages and shortages in surface patterning according to the precision, repetition, productivity and cost. As a kind of mesoscopic ordered microstructures, self-assembly colloidal crystals show special optical properties, which are important for their potential applications in photonic crystals, high-density storage, and bio- & chemical sensors. Meanwhile, colloidal crystals have provided low-cost templates for preparing various microstructures in nano- and micro-meter scale. Combining with selective deposition, etching, polymerization and photolithography techniques, colloidal crystals have been used as templates for constructing two and three dimensional microstructures. These patterned microstructures will promote the micromachining techniques, physics, chemistry, biology, medicine and hasten the crosslink of different subjects. In this paper, we prepared colloidal crystals of different structures. Using these special colloidal crystals as templates, many different ordered microstructures have been prepared, widening the applications of colloidal-crystal-template strategy.In chapter 2, high quality stable colloidal crystal chips have been prepared by two-substrate vertical deposition method. The microstructure and optical property of colloidal crystals in these chips have been studied, as well as the influence of experimental conditions on the lattice of colloidal crystals. It is well known that colloidal crystals are not stable under the infiltration of solvents (water or other solvents). However, the confinement in between two close substrates would make colloidal crystal chips more stable against the filling medium and help to control and protect them better in the ensuing procedures. Due to their excellent stability, these colloidal crystal chips can be used as elements in some optical devices directly, and their optical properties can be adjusted by simply filling solutions containing functional materials and some available precursors into them. Moreover, based on the rheology of polymer microspheres, we prepared nonspherical colloidal crystals constructed from polyhedrons by thermal-pressing the polymer colloidal crystal chips. Our strategy provided a new routine for preparation of nonspherical colloidal crystals. At the temperature slightly lower than Tg of polymer colloids, high pressure were applied to make the colloidal spheres transform into polyhedrons. As the working temperature lower than Tg effectively prevented the colloidal crystals from fusing into films, the spherical colloidal crystals had been transformed greatly. Characterized by SEM and AFM, it has proved that the nonspherical colloidal crystals we prepared were constructed from particles of dodecahedron. By controlling the thermal-pressing conditions, we can adjust the deformation of the colloidal spheres. And colloidal crystals of different lattice orientations will lead to nonspherical colloidal crystals of different symmetry. Constructing spherical and nonspherical colloidal crystals from microspheres of different sizes, we studied the optical property change during the thermal-pressing process. It has been proved that the diffraction peak of the colloidal crystals would blue-shift in the thermal-pressing process. And the extent of blue-shift depends on the size of the microspheres, which can be explained by Bragg equation.In chapter 3, we prepared two kinds of TiO₂ macroporous materials based on the nonspherical colloidal crystals. One kind of macroporous materials were prepared by using polymer nonspherical colloidal crystals as templates. Infiltrating titanium precursor into colloidal crystals by sol-gel process and removing the template by calcining, macroporous TiO₂ structures with super-high porosity have been prepared. This kind of microstructures is constructed from nanosticks, and their porosity is not less then 90%. The skeleton-like structures can be destroyed by ultrasonication, leaving two dimensional TiO₂ nano-networks on the substrates. The other kind of macroporous materials was prepared based on PS@TiO₂ core-shell colloidal crystals. Firstly, we prepared well ordered PS@TiO₂ core-shell colloidal crystals. Then thermal-pressing process was applied to transform them into nonspherical ones. Using this kind of special colloidal crystals as templates, macroporous materials with ordered close polyhedron cavities have been prepared, which possess lower porosity than macroporous material prepared by other colloidal-crystal-template methods.In chapter 4, we developed colloidal crystal-assisted lithography (CCAL), utilizing 3D colloidal crystals to produce surfaces with 2D patterned arrays. On one hand, imprinting the polymer films with 3D silica colloidal crystals, polymer microstructure arrays of different morphology have been achieved. By varying the polymer film thickness and other experimental conditions in the imprinting process, we can intentionally control the morphology of the resulting polymer microstructures. On the other, Ag microstructures have been chemically deposited on Au substrates covered by 3D polymer colloidal crystals. The morphologies of the Ag structures formed on Au substrates can be controlled by adjusting the chemical deposition time and template nanosphere size. The resultant Ag-coated Au substrates thus prepared can be used as surface-enhanced Raman scattering (SERS) substrates, and can provide ideal models for researching the mechanism of SERS effect. Compared with other methods, CCAL method has at least three advantages in preparing 2D patterned arrays: (1) as 3D colloidal crystals are accessible in a large area, CCAL is an efficient and facile way of preparing patterned arrays in a large area; (2) both the periodicity and morphology of the patterns can be intentionally adjusted by varying the template nanosphere size and other parameters; (3) a mass of functional materials from molecules to polymers, oxides and metals can be applied in CCAL.In chapter 5, we put up a convenient and universal strategy for preparing nanoring arrays of different compositions, based on combining CCAL method with physical and chemical etching techniques. Large area arrays of PS, magnetite, Au, Si, magnetite nanoparticle/PS and Au/PS double-layer composite nanorings have been prepared. The specific dimensions of the nanoring arrays could be controlled by intentionally altering the experimental conditions, which is important for adjusting the properties and applications of nanoring structures. Many kinds of the nanoring structures, including Fe₃O₄ nanoparticle/PS and Au/PS double-layer nanorings, can be released from the substrates, resulting in free-standing composite nanorings, which might be used as self-assembly building blocks and ultra-sensitive bio- and chemical sensors.