NST 13th Lecture (Unit 3).pptx

Nanoparticles synthesis
Unit 3_Lecture 13

Contents
 Top down and bottom-up approach
 Colloids
 Emulsions
 Micelles
 Polymers
 Mechanical attrition
 High energy ball milling

Low Temperature Methods are
basically Bottom Up Approaches
 Low Temperature Routes also known as “Chimie Douce”
 Its meaning in French is Soft Chemistry

Low Temperature Routes
 Sol-Gel (Citrate-Gel) methods (Depending on Citric Acid)
 Polyhydroxy acids for the formation of the Sol
 Micro emulsion method

Sol-Gel
 It is a general term for many of the processes

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

Sol-
Gel
Powders:
Nanocrystalline,
microcrystalline,
amorphous
Monoliths,
Coatings, Films,
Fibers
Glasses, Ceramics,
Hybrid materials
Aerogels

Steps involved
Hydrolysis
Condensation
Gelation
Ageing
Drying
Densification

 One is a 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.

Top-down approach
 The most 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.

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.

NST 13th Lecture (Unit 3).pptx

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NST 13th Lecture (Unit 3).pptx