Facile Organization of Colloidal Particles into Large, Perfect One- and Two-Dimensional Arrays by Dry Manual Assembly on Patterned Substrates (original) (raw)
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Self-assembly of functionalized spherical nanoparticles on chemically patterned microstructures
Nanotechnology, 2005
The production of hierarchical nanopatterns (using a top-down microfabrication approach combined with a subsequent bottom-up self-assembly process) will be an important tool in many research areas. We report the fabrication of silica nanoparticle arrays on lithographically pre-patterned substrates suitable for applications in the field of nanobiotechnology. Two different approaches to reach this goal are presented and discussed: in the first approach, we use capillary forces to self-assemble silica nanoparticles on a wettability contrast pattern by controlled drying and evaporation. This allows the efficient patterning of a variety of nanoparticle systems and-under certain conditions-leads to the formation of novel branched structures of colloidal lines, that might help to elucidate the formation process of these nanoparticle arrays. The second approach uses a recently developed chemical patterning method that allows for the selective immobilization of functionalized sub-100 nm particles at distinct locations on the surface. In addition, it is shown how these nanocolloidal micro-arrays offer the potential to increase the sensitivity of existing biosensing devices. The well-defined surface chemistry (of particle and substrate) and the increased surface area at the microspots, where the nanoparticles self-assemble, make this patterning method an interesting candidate for micro-array biosensing.
Size Selective Assembly of Colloidal Particles on a Template by Directed Self-Assembly Technique
Langmuir, 2006
We report a simple and effective approach to organize micron-and submicron-sized particles in a size selective manner. This approach utilizes the template assisted directed self-assembly technique. A topographically patterned photoresist surface is fabricated and used to create an ordered array of colloidal particles from their aqueous suspensions. Assembly of particles on this template is then achieved by using a conventional spin coating technique. Feasibility of this technique to form a large area of patterned particle assemblies has been investigated. To arrange the particles on the template, the physical confinement offered by the surface topography must overcome a joint effect of centrifugal force and the hydrophobic nature of the photoresist surface. This concept has been extended to the size selective sorting of colloidal particles. The capability of this technique for sorting and organizing colloidal particles of a particular diameter from a mixture of microspheres is demonstrated.
Formation of Two-Dimensional Colloidal Sphere Arrays on Micro-Patterns
A hydrophobic substrate patterned with hydrophilic squares is used as a template for the selective deposition of two-dimensional micron and submicron polystyrene sphere arrays. In experiment, a monodisperse colloidal solution is applied to a patterned substrate. When the colloid is drawn off the substrate, two-dimensional arrays of colloidal spheres are selectively formed in the center of the hydrophilic squares. Optical microscopy coupled with highspeed photography allows the observation of this process for 1µm and 290nm polystyrene spheres. The observations reveal that as the body of colloid recedes off the substrate, the three-phase contact line becomes pinned at the pattern edges. This pinning causes the colloid to stretch across the hydrophilic areas, forming liquid films that neck and break off from the main body of colloid. The film is sufficiently thin to force the colloidal particles into a single layer. Capillary forces from the remaining liquid centers and packs the twodimensional arrays in the hydrophilic patterns. 1 nbernots@ee.washington.edu 2
Chemistry of Materials, 2008
We report a simple approach to the fabrication of hierarchical nanoparticle arrays and film patterns using a novel combination of colloidal lithography (CL), two-step self-assembly, and reactive-ion etching (RIE). In this approach, a uniform nanoparticle film (∼15-50 nm particle diameter) is first deposited on a substrate. Then, larger (several hundred to thousands of nanometers diameter) microparticles with a different composition are self-assembled into well-ordered patterns atop the nanoparticle film. Next, reactive-ion etching is used to remove parts of the initial nanoparticle film using the upper layer of large particles as a mask. After selective removal of the remaining upper layer of large particles, hierarchical nanoparticle patterns are obtained on flat surfaces. Hexagonal patterns of small nanoparticle film arrays were easily fabricated with a monolayer of large spheres using this approach. Moreover, the shape and diameter of nanoparticle film disks depend on the etching duration while the periodicity of the selfassembled upper layer is preserved during the etching process. The profiles of the nanoparticle film patterns (pitch, thickness of film, etc.) are adjustable with the size of the large particles, thickness of nanoparticle film, and nanoparticle size. Furthermore, additional nanoparticle film patterns are possible with the use of additional layers of large particles. We have demonstrated the feasibility of this approach with both polystyrene (PS) spheres on silica nanoparticles and silica spheres on PS nanoparticles. This bottom-up approach offers a novel lithography-free method for the fabrication of patterned nanoparticle films that will be useful for material growth, biosensing, and catalysis as well as serving as a unit operation for further fabrication.
Self-assembly Patterning of Nano/micro-particles
KONA Powder and Particle Journal, 2007
We developed a self-assembly process of SiO2 particles to fabricate desired patterns of colloidal crystals having high feature edge acuity and high regularity. A micropattern of colloidal methanol prepared on a self-assembled monolayer in hexane was used as a mold for particle patterning, and slow dissolution of methanol into hexane caused shrinkage of molds to form micropatterns of close-packed SiO2 particle assemblies. We further developed spherical particle assemblies and micropatterns of them. Hydrophilic regions of a patterned self-assembled monolayer were covered with methanol solution containing SiO2 particles and immersed in decalin. Particles were assembled to form spherical shapes and consequently, micropatterns of spherical particle assemblies were successfully fabricated through self-assembly. This result is a step toward the realization of nano/micro periodic structures for next-generation photonic devices by a self-assembly process.
Size-Dependent Self-Organization of Colloidal Particles on Chemically Patterned Surfaces
Langmuir, 2006
A study of the self-organization of colloidal particles during the evaporation of particle solutions on chemically patterned surfaces is presented. On a surface with hydrophilic and hydrophobic regions, colloidal particles form compact structures on the hydrophilic sites. When a colloidal solution containing a mixture of particles with a variation in size is used, the number density of each type of particle deposited on the hydrophilic islands after evaporation decreases with increasing particle size. This makes it possible to produce a concentration gradient of the particles on islands of different sizes. It is shown that this technique could allow for particle separation.
Advanced Materials, 2004
The fabrication of nanoparticle ensembles with both shortand long-range order across a hierarchy of spatial scales remains a major challenge for nanoscience. Patterned nanoparticles on different substrates have been the focus of many investigations due to their unique potential for many applications including: nanoelectronics, nanophotonics, magnetoelectronics, and biochemical sensing. [1±5] Colloidal crystallization using silica and polystyrene particles can lead to optical-wavelength photonic crystals. [6±8] Generally, conventional lithographic approaches are nearing fundamental limits and it seems clear that directed self-assemblyÐan integration of lithography and self-assemblyÐis destined to play an important role across a wide range of nanotechnology applications. This will require a sophisticated understanding of the chemical and physical interactions between lithographically defined patterns and nanoparticles. This paper is a step towards that understanding.
Synthesis and assembly of structured colloidal particles
Journal of Materials Chemistry, 2008
Synthesis and self-assembly of structured colloids is a nascent field. Recent advances in this area include the development of a variety of practical routes to produce robust photonic band-gap materials, colloidal lithography for nanopatterns, and hierarchically structured porous materials with high surface-to-volume ratios for catalyst supports. To improve their properties, non-conventional suprastructures have been proposed, which could be built up using binary or bimodal mixtures of spherical particles and particles with internal or surface nanostructures. This Feature Article will describe the state-of-the-art in colloidal particles and their assemblies. The paper consists of three main sections categorized by the type of colloid, namely shape-anisotropic particles, chemically patterned particles and internally structured particles. In each section, we will discuss not only synthetic routes to uniform colloids with a range of structures, features and shapes, but also self-organization of these colloids into macrocrystalline structures with varying nanoscopic features and functionalities. Finally, we will outline future perspectives for these colloidal suprastructures.