Template-assisted Self-assembly Research Articles

Highly ordered defect arrays of 8CB (4′-n-octyl-4-cyano-biphenyl) liquid crystal via template-assisted self-assembly

A synthetic rod-like smectic liquid crystal containing a rigid aromatic group and semi-fluorinated chains generates well-ordered toroidal structures called toric focal conic domains (TFCDs) as self-assembling building blocks when confined within rectangular micro-channels. However, in the case of common smectic liquid crystals with alkyl-terminated chains, the ordered arrangement of TFCDs is challenging work because of their high mobility and low elasticity. Here, we present a simple method to fabricate highly mono-dispersed periodic patterns using the most commonly used smectic liquid crystal, 8CB (4′-n-octyl-4-cyano-biphenyl), by changing the geometry of confined microchannel with a controlled surface polarity. This is attributed to the combining effects between antagonistic surface anchoring conditions and precisely directed molecular orientation onto inclined side walls of a trapezoidal channel. Furthermore, size and ordering of arrays of 8CB can be simply controlled by varying the feature dimension of bottom width (l) and depth (h) in the trapezoid-shaped channel. The use of 8CB will generalize fabrication of the spatial arrangement of TFCD arrays for future nanotechnology and liquid crystal research.

Template-assisted self-assembly: a versatile approach to complex micro- and nanostructures

Template-assisted self-assembly (TASA) is a process in which colloidal aggregates with well-controlled sizes, shapes, and structures are fabricated by dewetting aqueous dispersions of building blocks across surfaces patterned with two-dimensional arrays of templates. Since our first demonstration in 2001, the capability and feasibility of this approach has been illustrated with the organization of polymer latex spheres or silica beads into homo-aggregates, including circular rings; polygonal and polyhedral clusters; and linear, zigzag, and spiral chains. It has been demonstrated to produce hetero-aggregates in the configuration of HF and H2O molecules that contained colloidal spheres of different sizes, compositions, densities, optical properties, or a combination of these features. More recently, TASA has also been successfully extended to colloidal building blocks with sizes well below 100 nm, expanding this technique to the nanoscale where it is expected to impact on a broad range of applications such as surface-enhanced Raman scattering (SERS) detection.

Template-assisted self-assembly of colloidal crystals

We present the self-assembly of polystyrene particles to colloidal crystals via the dipping method on a topologically structured template. On this system we demonstrate the potential of grazing incidence small angle X-ray scattering as an analytical tool to monitor properties of colloidal crystals. Moreover, energy dispersive X-ray reflectometry has been used to investigate the dynamics of the self-assembly in situ.

Plasma within Templates: Molding Flexible Nanocrystal Solids into Multifunctional Architectures

Recently, there has been a great deal of progress in the synthesis of colloidal nanocrystals with tailored physical and chemical properties through control of size and shape, chemical composition, and surface functionalization (Alivisatos, A. P. Science 1996, 271 (5251), 933−937; Burda, C.; Chen, X. B.; Narayanan, R.; El-Sayed, M. A. Chem. Rev. 2005, 105 (4), 1025−1102). Nanocrystals are thus ideal building blocks for hierarchical self-assembly of topologically complex, multifunctional architectures with properties tuneable at each level of the hierarchy. Here, we present a method, which combines template-assisted self-assembly of nanocrystals with plasma polymerization (Cademartiri, L.; von Freymann, G.; Arsenault, A. C.; Bertolotti, J.; Wiersma, D. S.; Kitaev, V.; Ozin, G. A. Small 2005, 1 (12), 1184−1187) to realize hierarchical architectures that both retain the properties of the nanocrystals and offer multifunctionality. As examples, we describe CoFe2O4−PbS mixed nanocrystal nanorods, which photolumi...

Versatile Method of Submicroparticle Pattern Formation Using Self-Assembly and Two-Step Transfer

We propose a method of submicroparticle pattern formation with high productivity, flexibility, and accuracy. The proposed process is composed of template-assisted self-assembly for particle self-assembly and a subsequent two-step transfer of the assembled particles. Optimization of the process parameters was performed by carrying out experiments to evaluate the effects of the parameters on the yields of each process. Polystyrene particles that are 500 nm in diameter were used, and a silicon wafer was used as a target substrate in the experiments that are described in this paper. In the self-assembly process, 70% of the pattern was successfully self-assembled on a silicon template substrate. In the first transfer step, a transfer yield of 79% was obtained with a self-assembled-monolayer-coated polydimethylsiloxane carrier substrate. In the second transfer step, a transfer temperature of 115 provided the maximum transfer yield of 85%. The overall process yield of 48% was achieved by the optimized process parameters, and it was successfully demonstrated that the proposed method can fabricate any submicroparticle pattern.

Template controlled self-assembly of bidentate phosphine complexes with hemilabile coordination behaviour

Template-assisted self-assembly of ditopic catechol phosphines creates complexes containing a chelating diphosphine ligand, which display hemilabile coordination properties with prospects for applications in catalysis.

Template-assisted crystallization and colloidal self-assembly with use of the polymer micrometrically scaled honeycomb template

Droplets of NaCl water solution were deposited on a micrometrically scaled polymer honeycomb relief and evaporated. Template-assisted crystallization was observed. Crystals of NaCl with a characteristic dimension of 500–1000 nm filled the relief cells. Small nanometrically scaled crystals were observed as well. Wetting properties of the surface are discussed. The process of crystallization depended on the evaporation rate. The same honeycomb relief was used for template-assisted self-assembly of nanometric colloidal particles of polyvinylidene fluoride. Both template-assisted crystallization of NaCl and the TASA process supplied valuable information about the topography of honeycomb relief.

Optical properties of tetragonal photonic crystal synthesized via template-assisted self-assembly

A (001) oriented three-dimensionally periodic photonic crystal, free of cracks, has been fabricated via a modified template-assisted colloidal self-assembly method with polystyrene spheres. Analysis of the opal-type crystals has revealed the structure to be noncubic. This is a face-centered tetragonal (fct), (001) oriented photonic crystal. The optical properties of the crystals have been characterized at near-normal incidence by reflectance spectroscopy. It is found that the photonic stop band shifts to shorter wavelengths compared with an identical cubic structure oriented along the (001) direction. We have also simulated the stop band behavior of such fct crystals and their inverse silicon analogs, revealing that the polymer opal could provide an inverse template for the formation of photonic crystals with a complete band gap.

Chemically synthesized L1/sub 0/-type FePt nanoparticles and nanoparticle arrays via template-assisted self-assembly

Chemically ordered L1/sub 0/-type FePt nanoparticle agglomerates were synthesized directly by the co-reduction of Fe(III) and Pt(II) acetylacetonates in tetraethylene glycol at 300/spl deg/C in the absence of surfactants. These nanoparticles could be dispersed in n-hexane by coating with oleic acid and oleylamine. However, the dispersed particles exhibited only chemically disordered fcc phase and superparamagnetic behavior. The FePt nanoparticle film composed of dispersed particles and stabilized using amino-silane began to structurally transform to ordered L1/sub 0/ phase at 600/spl deg/C, which is lower compared to that prepared by the hot soap method. Rotational hysteresis loss measurement suggested that the ordering was incomplete at 600/spl deg/C and the nanoparticle film had the distribution of magnetocrystalline anisotropy field values. The FePt nanoparticle array was fabricated using the template-assisted self-assembly technique. To produce periodic dots on a substrate, positive-biased pulse voltage was applied to the substrate coated with octadecyltrichlorosilane monolayer by using a conducting cantilever used in a scanning probe microscope. This process induced electrochemical modification of -CH/sub 3/ groups into polar ones. The resulting template had well-aligned sub-100-nm dot arrays with sub-100-nm periodicity. The FePt nanoparticles were fixed on the patterned areas selectively.

Template-assisted self-assembly: a practical route to complex aggregates of monodispersed colloids with well-defined sizes, shapes, and structures.

This paper describes a strategy that combines physical templating and capillary forces to assemble monodispersed spherical colloids into uniform aggregates with well-controlled sizes, shapes, and structures. When an aqueous dispersion of colloidal particles was allowed to dewet from a solid surface that had been patterned with appropriate relief structures, the particles were trapped by the recessed regions and assembled into aggregates whose structures were determined by the geometric confinement provided by the templates. We have demonstrated the capability and feasibility of this approach by assembling polystyrene beads and silica colloids (> or =150 nm in diameter) into complex aggregates that include polygonal or polyhedral clusters, linear or zigzag chains, and circular rings. We have also been able to generate hybrid aggregates in the shape of HF or H2O molecules that are composed of polymer beads having different diameters, polymer beads labeled with different organic dyes, and a combination of polymeric and inorganic beads. These colloidal aggregates can serve as a useful model system to investigate the hydrodynamic and optical scattering properties of colloidal particles having nonspherical morphologies. They should also find use as the building blocks to generate hierarchically self-assembled systems that may exhibit interesting properties highly valuable to areas ranging from photonics to condensed matter physics.

Template-assisted Self-assembly and Cobalt Doping of Ordered Mesoporous Titania Nanostructures

Template-assisted Self-assembly and Cobalt Doping of Ordered Mesoporous Titania Nanostructures

Template-assisted Self-assembly and Cobalt Doping of Ordered Mesoporous Titania Nanostructures

Template-assisted Self-assembly and Cobalt Doping of Ordered Mesoporous Titania Nanostructures