Top-down and Bottom-Up Techniques

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 

Actually, we can write down a complete equation thinking of using carbon for the reduction 

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. 

In order to illustrate a top-down process of finding a solution, we rewrite and split Eq. (13.25) into 

The last equation in the set of Eq. (13.29) we had to add. Actually, the set of Eq. (13.29) adds up to Eq. (13.25), and we have invented the electrochemical cleavage of iron oxide into iron and oxygen. Clearly, the sulfuric acid that we have introduced acts in a catalytic way, unlike the introduction of carbon in the previous processes. 

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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. 

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. 

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. 

As a probe of lattice vibrations, Raman spectroscopy is very sensitive to intrinsic crystal properties and extrinsic stimuli, especially in semiconductors. It may be employed to study crystal structure and quality, crystal orientation, optical interactions, chemical composition, phases, dopant concentration, surface and interface chemistry, and local temperatme or strain. As an optical technique, important sample information may be obtained rapidly and nondestructively with minimal sample preparation. Submicron lateral resolution is possible with the use of confo-cal lenses. These features have made it a vital tool for research labs studying semiconductor-based technologies. They also are increasingly important for the study of semiconductor NWs fabricated by both top-down and bottom-up approaches since many of the common characterization methods used with bulk crystals or thin films cannot be applied to NWs in a direct manner. 

The basic difference between conventional processing and nanofabrication is the dimension of the structures to be fabricated. There are basically two possible approaches top-down and bottom-up approaches. In the top-down approach, micro and nanostructures are achieved by controlled removal of extra amount of material by applying an external source of energy such as mechanical, thermal, chemical, and electrochemical energy. The top-down approach of micro and nanofabrication is schematically shown in Fig. 1.2. This approach is difficult to apply at nanoscale however at microscale, it has been utilized successfully by various means. In the bottom-up approach, positions of atoms or molecules are manipulated to build up the nanodevices or nanostmctures, as illustrated in Fig. 1.3. Various techniques of this approach are under development at the laboratory level and need further improvements. 

Madou MJ (2002) Comparison of miniaturization techniques top-down and bottom-up manufacturing. In Fundamentals of microfabrication the science of miniaturization. CRC, Boca Raton, Florida, USA, pp. 402-411... 

Typically, two iterations of each analysis should be undertaken to cover human requirements specification and realisation phases and, as the analyses become more focused, the results fiom each one will inform and focus the other. In addition, diese HF activities are entirely complementary as CTA and HEA are bottom-up and top-down analysis techniques respectively (from a hazard to human event perspective).This combination of top-down and bottom-up analyses significantly increases the probability of identifying inconsistencies in the individual techniques and thus enhances safety assurance. 

Currently, both top-down and bottom-up methods are used to analyze mi-erobial proteins by MS. In top-down approach, proteins are analyzed to determine molecular masses of intact proteins and to characterize them by using gas-phase fiagmenlation techniques. The bottom-up characterization of proteins uses prote-... 

Combining Top-Down and Bottom-Up Patterning Techniques to Enhance Long-Range Order... 

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