Self-Assembly of Two- and Three-Dimensional Nanostructures for Electronic Applications
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The need for increasing miniaturization of circuitry, as described by Moore's law, requires the reduction of feature size for electronic components, decreasing by an order of magnitude every 10 years. With contemporary minimum feature sizes of ∼ 0.1 µm, circuits with dimensions on the atomic length scale will need to be achieved within the next 30 years for this progress to continue.
There are two possible routes to smaller feature sizes: 1) the traditional “top–down” approach, where feature size is simply reduced by scaling of presently used devices; and 2) the more recent “bottom–up” approach based on enlargement, where the self-assembly of macromolecular and colloidal building blocks is used to create larger, functional devices. “Top–down” fabrication processes presently experience a bottleneck because most common lithographic techniques used for the creation of small features are limited to a spatial resolution in the upper nanometer range. Feature sizes down to 10 nm have been realized by special techniques, but the small-area and low-throughput properties of these processes are economically challenging. Thus new avenues toward smaller-scale and more densely packed structures need to be explored, and new fabrication methods using the bottom–up approach need to be developed. Two-dimensional and three-dimensional structures can be self-assembled using nanometer-sized objects with the control of feature size in the nanometers to hundreds of nanometer range, bridging the gap between atomic manipulation and modern lithography. The simplicity and low processing costs connected with it make methods based on self-assembly economically interesting. Nanoparticles present ideal building blocks for self-assembly because: 1) they can be synthesized with narrow size distributions (σ ≤ 5%) from a variety of materials; 2) they come in many different shapes; and 3) their small dimensions lead to a wide functional diversity with respect to their electronic, optical, and catalytic properties, which is usually very different from bulk materials.
This entry reviews recent accomplishments in the fabrication of two-dimensional and three-dimensional nanoparticle structures using self-assembly, which may be used in electronic applications. Synthetic approaches to monodisperse metallic, semiconducting, insulating, and core–shell structured nanoparticles are briefly reviewed. The basic principles behind two-dimensional and three-dimensional nanoparticle assembly from solutions, by templating and by networking with organic and biological molecules, are presented. Some interesting properties of various nanoparticle arrays and their possible applications in optical and electronic devices are discussed. Finally, recent developments in the self-assembly of nanobuilding blocks other than nanoparticles are briefly mentioned.