Bottom-up fabrication techniques

What has inspired initial research in microfluidics is similarly driving the research into optofluidics today. The goal is to make smaller features going from micro- to nanoscales in order to fill the gap between top-down and the bottom-up fabrication techniques [7]. Because most devices consist of multiple planar layers, there is motivation to develop 3-D fabrication or assembly methods for both optical and electrical components. The ultimate goal is an easy and simple technique which works well with a variety of materials and on different scales. The most successful devices up to date rely on fundamental principles of both optics and fluidics in order to avoid as many of components as possible, leaving those devices only with essentials to carry out their fimctions. 

The construction of characteristic nanoarchitectures from organic molecules using the self-assembly technique has been the subject of considerable levels of interest [1, 2]. The use of self-assembly as a key technique for the bottom-up fabrication of nanoscale functional structures in particular has received a great deal of attention ever since the concept of self assembly was estabUshed for supramolec-ular chemistry [1]. The two-dimensional (2-D) self-assembly of single-molecule... 

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 bottom-up techniques described herein are based on the use of nanosize building blocks to fabricate precisely organized solids at various scales. The final architecture of the solid, and the way these blocks combine with each other, can be conveniently adjusted by the synthesis conditions, the selection and modification of these nanoblocks, and their chemical functionality. The spontaneous arrangement of individual nanoblocks is generally obtained via self-assembly through weak interactions. The control over the organization of these components allows for the incorporation of nanoparticles, biomolecules, or chemical functionalities inside the solid structure in highly precise locations. 

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. 

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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