Introduction

The self-assembly (SA) of nanoparticles in an organized array has become increasingly important. The current methods used for the design of ultra-thin films include: spin-coating and solution-casting, thermal deposition, polyion layer-by-layer assembly, chemical self-assembly, the Langmuir-Blodgett technique, and free-standing films. The optimal combination of molecular order and stability of films determines the practical usefulness of these technologies [1-6].

The most ordered macromolecular films are free-standing liquid crystalline films, but they are very unstable. The Langmuir-Blodgett method allows to construct lipid multilayers with a thickness from 5 to 500 nm, but only flat substrates can be covered by this film and it has intrinsic defects at the lipid grain borders. Another method that can be applied to surface modification is a monolayer self-assembly, based on thiol or silane compounds [1]. By this method, one can achieve self-assembly of 2-5 nm thick organic layers on silicon or gold surfaces, but there is no simple means for thicker film construction. Other widely used methods for the industrial manufacture of thin films are spin-coating and thermal deposition of macromolecules onto a substrate. Unfortunately, unlike the methods considered above, these methods do not allow one to control a film composition in the direction perpendicular to the surface.

Finally, there is a newer method for film self-assembly that makes use of the alternate adsorption of oppositely charged components (polymers, nanoparticles, and proteins) [2-9]. The assembly of alternating layers of oppositely charged linear or branched polyions and nanoparticles is simple and provides the means to form 5-500-nm thick films with monolayers of various substances growing in a preset sequence on any substrate at a growth step of about 1 nm. Mallouk [4] has called this technique "molecular beaker epitaxy," meaning that with simple instruments (exploiting the materials' self-assembly tendency), one can produce molecularly organized films similar to the ones obtained with sophisticated and expensive molecular beam epitaxy technology.

One can assemble on a standard silicon wafer, multilayers containing different nanoparticles and polymers and then apply lithography to manufacture microdevices with nano-structured elements. Such a combination of nano-assembly with traditional micromanufacturing is the topic of this review.

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