Nano architecture: self assembly and template methods.NANO-FABRICATION ,UNIT FABRICATION,SILICA ,POLYDIMETHYSILOXANE

1. THE INSTITUE OF SCIENCE,MUMBAI.
Topic : Nano architecture: self
assembly and template methods.
Semister –III.
Paper-III.
-SANA SHAIKH.
M.Sc-PART TWO
SEM-3.

2. Self Assembly
• Self Assembly is defined as the spontaneous
association of numerous individual units of
material into well organized, well defined
structures without external instruction.

3. Self - assembly can 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 is the 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 mainstream approaches.
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 in nanofabrication.
• 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.
• Fabrication for 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 unit fabrications.
• coating.
• symmetry breaking.
• Templating.
• Masking.
• hybridization.
• Alignment.
• stacking.
• crossing.
• curving.
• reconstruction.
• deposition.

11. Templating
• Templating and masking 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 of materials 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 to use 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 .
• If we 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 are made 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 process of 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 three typical liquid crystals structures of
surfactant .hexagonal,cubical,lamellar.

20. Polydimethysiloxane.
• The main differencebetween 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-ASSEMBLY AND 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. Thank you.