NST 13th Lecture (Unit 3).pptx

NST 13th Lecture (Unit 3).pptx

• 1.
  Nanoparticles synthesis Unit 3_Lecture13
• 2.
  Contents  Top downand bottom-up approach  Colloids  Emulsions  Micelles  Polymers  Mechanical attrition  High energy ball milling
• 3.
  Low Temperature Methodsare basically Bottom Up Approaches  Low Temperature Routes also known as “Chimie Douce”  Its meaning in French is Soft Chemistry
• 4.
  Low Temperature Routes Sol-Gel (Citrate-Gel) methods (Depending on Citric Acid)  Polyhydroxy acids for the formation of the Sol  Micro emulsion method
• 5.
  Sol-Gel  It isa general term for many of the processes
• 6.
  What is Sol-Gel? Solid particles dispersed in the liquid (a sol)  Agglomerate together to form a continuous 3 dimensional network extending throughout a liquid (a gel)  It involves hydrolysis and poly-condensation
• 8.
  Sol- Gel Powders: Nanocrystalline, microcrystalline, amorphous Monoliths, Coatings, Films, Fibers Glasses, Ceramics, Hybridmaterials Aerogels
• 9.
  Why Sol-Gel?
• 10.
  Steps involved Hydrolysis Condensation Gelation Ageing Drying Densification
• 11.
   One isa top-down strategy of miniaturizing current technologies, while the other is a bottom-up strategy of building ever-more-complex molecular devices atom by atom. Top-down approaches are good for producing structures with long-range order and for making macroscopic connections, while bottom-up approaches are best suited for assembly and establishing short-range order at nanoscale dimensions. The iintegration of top-down and bottom-up techniques is expected to eventually provide the best combination of tools for nanofabrication. Nanotechnology requires new tools for fabrication and measurement.
• 13.
  Top-down approach  Themost common top-down approach to fabrication involves lithographic patterning techniques using short-wavelength optical sources.  A key advantage of the top-down approach—as developed in the fabrication of integrated circuits is that the parts are both patterned and built in place, so that no assembly step is needed.  Optical lithography is a relatively mature field because of the high degree of refinement in microelectronic chip manufacturing , with current short- wavelength optical lithography techniques reaching dimensions just below 100 nanometres (the traditional threshold definition of the nanoscale).  Shorter-wavelength sources, such as extreme ultraviolet and X-ray, are being developed to allow lithographic printing techniques to reach dimensions from 10 to 100 nanometres.  Scanning beam techniques such as electron-beam lithography provide patterns down to about 20 nanometres.  Here the pattern is written by sweeping a finely focused electron beam across the surface.  Focused ion beams are also used for direct processing and patterning of wafers, although with somewhat less resolution than in electron-beam lithography.  Still-smaller features are obtained by using scanning probes to deposit or remove thin layers.
• 14.
  Bottom-up approach  Bottom-up,or self-assembly, approaches to nanofabrication use chemical or physical forces operating at the nanoscale to assemble basic units into larger structures.  As component size decreases in nanofabrication, bottom-up approaches provide an increasingly important complement to top-down techniques.  Inspiration for bottom-up approaches comes from biological systems, where nature has harnessed chemical forces to create essentially all the structures needed by life  Researchers hope to replicate nature’s ability to produce small clusters of specific atoms, which can then self-assemble into more-elaborate structures.