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Nano architecture: self assembly and template methods.
The document discusses nano architecture with a focus on self-assembly and template methods for nano-fabrication. It describes the classification of self-assembly processes and compares top-down and bottom-up approaches for creating nanostructured systems. The content emphasizes the mechanisms of templating and masking in the fabrication of silica and outlines various unit fabrication processes.
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Nano architecture: self assembly and template methods.
- 1. THE INSTITUE OFSCIENCE,MUMBAI. Topic : Nano architecture: self assembly and template methods. Semister –III. Paper-III. -SANA SHAIKH. M.Sc-PART TWO SEM-3.
- 2. Self Assembly • SelfAssembly is defined as the spontaneous association of numerous individual units of material into well organized, well defined structures without external instruction.
- 3. Self - assemblycan be classified: 1. By the size/nature of building unit: atomic, molecular, and colloidal. 2. By the system where it occurs: biological and interfacial The classification of self - assembly can be further expanded by the nature of its process: thermodynamic or kinetic. The former includes atomic, molecular, bio- logical, and interfacial self - assemblies, while the latter has colloidal and some interfacial self - assemblies. Some of the self - assembly processes are random , while others are directional to some degree.
- 5. Self Assembly isthe Key to Inexpensive Nano-Fabrication . • It is low in cost. • Reduced fuel costs. • Depend on chemical and physical forces to combine materials not petroleum. • Can have high reproducibility. • In nature, materials self assemble with little variation. • Is able to use a variety of materials for creation. • All the building blocks of biology and chemistry.
- 6. The two mainstreamapproaches. The top-down approch. • The top - down approach adapts the concept that the construction of nano structured systems that eventually consist of the length scale of atoms or molecule should begin with bulk materials • By removing the exces portion of bulk materials by physical, chemical, and mechanical means, the desired nanostructured systems can be constructed. • Hard lithography using optical laser -light, electron - beam, or x - ray are typical examples. The bottom –up approch. • The bottom - up approach, on the other hand, starts with the individual building units that are the objects ofthe nanometer scale, such as atoms, molecules, polymers, and colloids. • By assembling these building units with the needed controllability, the desired nanostructured systems can be obtained.
- 8. Self –assembly innanofabrication. • Nanofabrication can be defined as “ a process that is necessary to fabricate nano structured objects. ” • This is a top - down approach but face problem of resolution dilemma. • A new bottom –up approach has been adapted to overcome this the bottom- up approach based on self –assembly is used . • Instead of carving out the nanoscale features from the bulk, the fabricated system is designed to be assembled through the force interactions between its building units.
- 9. Unit fabrication. • Fabricationfor nanofabricated systems and nanodevices can be tricky and complicated. It might be acquired with just one step of the process. It also might take a series of multisteps. • majority of those fabrication processes can be broken into a small number of fundamental processes that commonly appear throughout different nanofabrication processes.These will be designated as unit fabrications
- 10. Types of unitfabrications. • coating. • symmetry breaking. • Templating. • Masking. • hybridization. • Alignment. • stacking. • crossing. • curving. • reconstruction. • deposition.
- 11. Templating • Templating andmasking are done to create structures or patterns that are copied or determined by the already - existing and prefabricated nanostructures . • Templating always begins with nanostructures that can serve as nanoscale “ molds ” for the intended nanofabricated systems.
- 12. A variety ofmaterials can be used as templates as long as they are not damaged by the interaction with precursors. This includes amphiphilic micelles, liquid crystals, colloidal crystals,surface structures, and biological entities. The precursors interact with the surfaces of the templates and react into the hard structure. Removal of the template leaves the copies of the nanostructures originated from the template. The most typical example of this unit fabrication is the formation of the mesostructured materials.
- 13. Masking means touse a mask (or shield) to create mainly surface patterns. This mask is not destroyed during the process. Rather, it sometimes becomes apart of the nanofabricated systems ( soft masking ) . Using photomasks for photolithography and using prefabricated colloidal crystals for other lithographic patterning are good examples of hard masking . The most abundant example of soft masking is found in the fabrication of patterned self - assembled monolayers. Templating and masking are suitable for mass - patterning of solid surfaces, mass - fabricating of highly regular structures, and even for mass - synthesizing of hybrid materials.
- 15. Silica . • Ifwe were to create a piece of silica whith periodically arranged pores of 2-3 nm in diameter as a chemist we might go for bottom-up method by growing silica filled with pores which natuarally lead to the comcept of templating • Templets can be cylindrical . • It should be removable from silica ,such templets are called micelles .
- 16. • Micelles aremade up of two connected parts one is hydrophilic (polar) and other is hydrophobic(long alkyl chain of methylenes). • They are formed from amphiphilic molecules. • They are spontaneously formed from assemblies with defined shapes and sizes in order to maximize the contact of water with hydrophilic head and minimize with hydrophobic tail. • Mesostructures of silicas are formed only above CMC.
- 18. • The processof co-assembly of micelles with si has allowed the formation of material called as periodic mesophorus silicas (PMSs). • PMS are type of silica with regularly arranged pores in the size range 2-5 nm they hace very high surface areas
- 19. There are threetypical liquid crystals structures of surfactant .hexagonal,cubical,lamellar.
- 20. Polydimethysiloxane. • The maindifferencebetween PDMS and si surface is extremly low silanoldensity on the PDMS surface and the presence of organic methyl (-CH3) group • Both factors imply a larger hydrophobicity and lower surface energy. • Surface energy is also responsible for the adhesion between two surface .
- 23. Reference Books • SELF-ASSEMBLYAND NANOTECHNOLOGY A Force Balance Approach, A JOHN WILEY & SONS, INC., PUBLICATION • Ludovico Cademartiri and Geoffrey A. Ozin, Concepts of Nanochemistry, Wiley – • VCH Verlag GmbH &co, 2009
- 24.