Top-down fabrication techniques

In this review, we describe the recent developments of chemically directed self-assembly of nanoparticle structures on surfaces. The first part focuses on the chemical interactions used to direct the assembly of nanoparticles on surfaces. The second part highlights a few major top-down patterning techniques employed in combination with chemical nanoparticle assembly in manufacturing two- or three-dimensional nanoparticle structures. The combination of top-down and bottom-up techniques is essential in the fabrication of nanoparticle structures of various kinds to accommodate the need for device applications. 

In device fabrication, the location of functional materials is as important as their properties. The integration of solid particles into devices usually requires placing them in specific positions. Hence, the combination of top-down patterning techniques and bottom-up self-assembly is crucial in obtaining (submicron) patterned functional nanostructures on surfaces. 

While nanotechnology is predominantly focussed on top-down lithographic type techniques for fabricating nanoscale objects and devices, chemistry has a major part to play in bottom-up nanotechnology, often inspired by natural molecular machinery found in biology. 

The limits of the top down and bottom up approaches, illustrated in Fig. 1.5, leave a majority of the nanoworld hard to access. Although constant improvements in technology and chemical synthesis mean that these limits are always shrinking, materials and objects that span the gap between 10 and 100 nm remain hard to fabricate to the level of accuracy and reproducibility expected of most manufacturing techniques. Until recently there was only one way to work on this scale leave it to Nature. 

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