Directed self-assembly of silica nanoparticles: two-dimensional patterns and three-dimensional structures with applications to nanofluidics

The fabrication of patterned arrays of nanoparticles is an essential step towards the creation of novel nanoscale materials and devices. These micro/nanoscale colloidal arrays may find application in photonics, biochemical sensors and micro-/nano-fluidics. Most previous work has focused on template-directed self-assembly of micro- and nanoparticles (>100-nm) into micrometer or larger periodic patterns. Achieving 1D/2D patterned arrays and 3D structures with 10- to 100-nm diameter nanoparticles in controlled morphologies remains an important nanofabrication challenge.; Both hard-template (e.g., SiO2) and soft-template (photoresist) directed self-assembly of silica nanoparticles into 1D and 2D nanoscale patterns using a combination of interferometric lithography (IL) and spin coating were reported here. Single linear silica particle chain patterns and isolated 2D particle patterns were easily formed on patterned surfaces while silica particle rows, interconnected networks, and isolated posts with controllable thickness were formed on flat surfaces.; An improved approach for fabricating lithographically-defined mesoscopic colloidal nanoparticle patterns over large areas by spin coating a uniform layer of nanoparticles and then patterning using IL and reactive-ion etching is introduced. Both 1D and 2D patterns are produced with sub-micrometer periodicity, high quality, and excellent uniformity over large areas.; An approach to the fabrication of enclosed nanoscale 3D structures composed of silica nanoparticles using IL, spin-coating, and high-temperature calcinations was developed. Enclosed nanoscale 3D structures include channels, isolated cavities, continuous networks and multiple-layer structures. The formation processing and stability of the resultant structures were investigated in detail with Thermogravimetric analysis, high resolution scanning electron microscope and conventional stability test. The resultant 3D structures has the heterogeneous spatial scales of 100-nm channels with ∼10nm porosity controllable by combination of lithography and particle sizes. This process opens a new route to fabricating 3D enclosed nanostructures with complex porosities for potential uses in photonics, molecular/biological sensors, biological separation and catalysis.; Finally, a new nanofluidic phenomenon of oscillatory drying/filling was observed in these porous silica nanoparticle channels. Evaporation-induced transport of fluids was proposed to explain this phenomenon.