Monolayer particle arrays

Monolayer Particle Arrays Formed by Vapor Deposition... 

Imaging Technology based on Monolayer Particle Array... 

The production of fatty acid-capped silver nanoparticles by a heating method has been reported [115]. Heating of the silver salts of fatty acids (tetradecanoic, stearic, and oleic) under a nitrogen atmosphere at 250°C resulted in the formation of 5-20-nm-diameter silver particles. Monolayers of the capped particles were spread from toluene and transferred onto TEM grids. An ordered two-dimensional array of particles was observed. The oleic acid-capped particle arrays had some void regions not present for the other two fatty acids. 

The creation of 2D crystals of both micron sized and nanometre sized particles remains a somewhat empirical process due to the ill-defined role of the substrate or surface on which nucleation takes place. Perrin first observed diffusion and ordering of micron sized gamboge 2D crystals in 1909 under an optical microscope [32]. Several techniques have been proposed for the formation of 2D arrays at either solid-liquid surfaces or at the air-water interface. Pieranski [33], Murray and van Winkle [34] and later Micheletto et al. [14] have simply evaporated latex dispersions. Dimitrov and coworkers used a dip-coating procedure, which can produce continuous 2D arrays [35,36]. The method involves the adsorption of particles from the bulk solution at the tricontact phase line. Evaporation of the thin water film leads to an attractive surface capillary force which aids condensation into an ordered structure. By withdrawing the film at the same rate as deposition is occurring, a continuous film of monolayered particles is created. Since the rate of deposition is measured with a CCD camera, it is not possible to use nanometer sized particles with this method, unless a nonoptical monitor for the deposition process can be found. 

Figure 13. FESEM images of (a) ordered alumina through-pore array induced by solution-dipping on PS (1000 nm in diameter) colloidal monolayer using 0.2 M A1(N03>3 and (b)Au particle array by deposition (for 20 min at 1 mA/cm ) on the template shown in (a). Inset of (b) water droplet on the surface after modification with 1-hexadecanethiol. (c) Magnified image of a local area in (b). Scale bars are 1000 nm for (a) and (b) and 200 nm for (c). (d) Photograph of a water droplet on the Au particle array on ITO.

FIGURE 17. Preparation of iron particles arrays from a Langmuir monolayer of ferritin. Polymer, lipid, protein, etc. 

In 1997, a Chinese research group [78] used the colloidal solution of 70-nm-sized carboxylated latex particles as a subphase and spread mixtures of cationic and other surfactants at the air-solution interface. If the pH was sufficiently low (1.5-3.0), the electrostatic interaction between the polar headgroups of the monolayer and the surface groups of the latex particles was strong enough to attract the latex to the surface. A fairly densely packed array of particles could be obtained if a 2 1 mixture of octadecylamine and stearic acid was spread at the interface. The particle films could be transferred onto solid substrates using the LB technique. The structure was studied using transmission electron microscopy. 

To further extend the utility of CPMV virions as tools in nanobiotechnology, it was shown that CPMV particles can be utilized as building blocks for the construction of monolayer, bilayer, and multilayer arrays on surfaces in a controlled manner [109]. CPMV virions were labeled with two different ligands fluorescent dyes that enabled differential detection, and biotin molecules that allowed the... 

Andres and coworkers demonstrated the iCP of densely packed alkanethiolate-functionalized Au nanoparticle arrays in monolayer and multilayer structures.81,82 Dense and hexagonally packed monolayers of nanoparticles were first assembled on a water surface. By using the Langmuir-Schafer technique, the Au nanoparticle monolayer was transferred to a PDMS stamp, and printed onto a substrate. Multilayers were prepared by repeating the printing process in an LbL scheme, in which subsequent particle layers may be made up of the same or different types of particles. Similarly, the assembly of irregular, densely packed monolayers of polystyrene nanoparticles on iCP substrates via carbodiimide coupling was reported.83 The conformal contact of the carbodiimide-functionalized polystyrene particles resulted in the covalent attachment of the nanoparticles at a carboxylate-functionalized surface. 

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