Bottom-up technique

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. 

An excellent example that shows the potential of combining various bottom-up techniques is the joint work by Whitesides and Stucky [4]. Hierarchical metallic oxides were produced by combining (i) sol-gel self-assembly of neutral surfactants, (ii) spherical polystyrene templates, and (iii) molds with micrometric cavities (micromolding). Figure 3.12 shows how the described materials are hierarchically organized at several scales ranging from a few nanometers to hundreds of micrometers. 

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. 

The bottom-up approach represents the concept of constructing a nanomaterial from basic building elements, that is, atoms or molecules. This approach illustrates the possibility of creating materials of SEs with exactly the properties desired. The second approach, the top-down method, involves restructuring a bulk material in order to create a nanostructure. Inert gas condensation, considered a bottom-up technique, was the first method used to intentionally construct a nanostructured material, and has become a widespread means of producing nanostructured metals, alloys, intermetallics, ceramic oxides, and composites... 

Hierarchical clustering procedures iteratively partition the item set into disjointed subsets. There are top-down and bottom-up techniques. The top-down techniques partition can be into two or more subsets, and the number of subsets can be fixed or variable. The aim is to maximize the similarity of the items within the subset or to maximize the difference of the items between subsets. The bottom-up techniques work the other way around and build a hierarchy by assembling iteratively larger clusters from smaller clusters until the whole item set is contained in a single cluster. A popular hierarchical technique is nearest-neighbor clustering, a technique that works bottom up by iteratively joining two most similar clusters to a new cluster. 

Here we start with a process in that stoichiometry is involved either with considerations related to top-down and bottom-up techniques. The particular task is relevant in steel industries How to make iron from iron oxide For simplicity, we are engaged with FeO. Thus... 

Equations (13.26) and (13.27) correspond to a bottom-up technique of finding a viable process for the reduction of iron oxide. However, there is a difference in Eq. (13.25), as we have introduced carbon to get a viable process. Moreover, the final product is no longer oxygen. 

The bottom-up technique refers to synthesis based on atom-by-atom or molecule-by-molecule arrangement in a controlled manner, which is regulated by thermodynamic means (Keck et al. 2008). The process takes place through controlled chemical reactions, either gas or liquid phase, resulting in nucleatiOT and growth of nanoparticles. Bottom-up techniques (like supercritical fluid antisolvent techniques, precipitation methods etc.) create heavily clustered masses of particles that do not break up on reconstitution (Shrivastava 2008 Mishra et al. 2010). 

The overall handling of nanoparticles in terms of safety becomes also more and more an important issue. Thus, the preparation of safe and easy to handle dispersions is of great technical importance. Those particles being synthesized in I Ls may be used direcdy, being inherently safe [13]. On the other hand, nanoparticles that are manufactured by other chemical bottom-up-techniques or via top-down techniques can be dispersed by using specific ILs, also because of their generally versatile surface active properties [14]. 

Co-axial electrospinning has also been used to develop hollow nanofibers or nanotubes from ceramic and ceramic-polymer composites that are otherwise commonly prepared using tedious processes, such as self-assembly and template synthesis. The latter are known as bottom-up techniques in nanotechnology,as they require atoms and molecules to be manipulated and assembled in desirable structures that are at least an order of magnitude larger than the molecules themselves. The procedure for making hollow fibers at nano level is, in fact, opposite to that illustrated in Fig. 2.33. In the current case (Fig. 2.34), the core, instead of the sheath, is selectively removed. 

Functional nanomaterials are a powerful tool for bottom-up techniques in addition to the simphcity of large-scale preparation and the low manufacturing cost. Within a short time span, nanomaterials will be used in multiple examples of electronic, sensor, optical, and other devices. One of the great benefits of self-organized systems is that they can easily traverse different scales and be integrated with microscale devices. From that point of view, the chitosan-based functional nanomaterials will find more opportunities and success. 

CTA is a bottom-up technique used broadly to analyse the relationships between system hazards (identified by the System Hazard Assessment in Figure 7) and operational tasks and the HMI design. The analysis works in a bottom-up fashion from operational tasks, related to base events, to identified service-level hazards. 

Note that there are currently very few techniques to make wholly microporous silicon (see handbook chapter Microporous Silicon ) where the average pore diameter is under 2 nm. For virtually all top-down techniques, the porous silicon created is poly crystalline. For some bottom-up techniques such as sputtering/dealloying (Fukatani et al. 2005), electrodeposition (Krishnamurthy et al. 2011), or sodiothermic reduction (Wang et al. 2013), it is reported to be amorphous. Choice of fabrication technique for both mesoporous and macroporous silicon is very much dictated by application area, which in turn has differing requirements on porosity levels, pore morphology, skeleton purity, physical form, cost, and volume. 

We can peer into the future with reasonable confidence. We can be confident that we will witness many breakthroughs based on bottom-up approaches in the next decades, leading to nanostructured materials with novel and unique material properties and functionalities, and to increasingly sophisticated nanodevices. While cnrrent indications are that bottom-up nanofabrication methods will not completely replace top-down nanofabrication techniques, in the decades to come we will see more applications originating either from bottom-up techniques alone or from hybrid approaches combining the strengths of bottom-up and top-down methods. 

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