Synthesis of nanomaterials Top down Approach

1. Synthesis of Nanomaterials
Top-down Bottom-up
R.Gandhimathi

2. ▪ Nanomaterial-A single unit, sized between 1-100nm
▪ E.g., metal nanoparticles, quantum dots (QDs), carbon
nanotubes (CNTs), graphene, and their composites
▪ It possess unique physiochemical properties like
ultrasmall size, large surface area, and the ability to
target specific actions which arise from their nanoscale
dimensions
▪ Nanomaterials can occur naturally, be created as the
by-products of combustion reactions, or be produced
purposefully through engineering to perform a
specialized function
https://www.nature.com/ar
ticles/s41392-019-0068-3
Nano materials

3. ▪ Nanomaterials/nanoparticles are prepared through diverse range of synthesis
approaches like lithographic techniques, ball milling, etching, and sputtering
▪ Synthesis/Fabrication of nanomaterials with tailored properties involve the control of
size, shape, structure, composition and purity of their constituents
▪ Hence the nanomaterial properties can be tuned as desired via precisely controlling the
size, shape, synthesis conditions, and appropriate functionalization.
Synthesis of Nanomaterials

4. Top-down approaches
Slicing of a bulk material to get nano sized particles
Bottom-up approaches
Build up materials atom by atom
(in which nanoparticles are grown from simpler molecules)
Fabrication of nanomaterials include nanostructured surface, nanoparticles
and nanoporous materials
Nanoparticles are typically synthesized from
a top-down or bottom-up approach
Approaches for the synthesis of nanomaterials

6. TOP-DOWN APPROACH

7. Mechanical milling
▪ A grinding method that grinds nanotubes into
extremely fine powders
▪ During the ball milling process, the collision
between the tiny rigid balls in a concealed
container will generate localized high pressure.
▪ Usually, ceramic, flint pebbles and stainless steel
are used
▪ Produces uniform fine powder of 2-20nm in size
▪ Size depends upon the speed of the rotation of the
balls
▪ Possibility of combining it with chemical
treatments, allows obtaining the desired products
with minimal effort.
▪ Ball-milled carbon nanomaterials are considered a
novel class of nanomaterial, providing the
opportunity to satisfy environmental remediation,
energy storage, and energy conversion demands
https://pubs.rsc.org/en/content/articlehtml/2019/na/c8na00238j
• Cost-effective method
• Ideal method for producing blends of
different phases
• Helpful in the production of
nanocomposites
• Used to produce oxide- and carbide-
strengthened aluminum alloys, wear-
resistant spray coatings,
aluminum/nickel/magnesium/copper-
based nanoalloys, and many other
nanocomposite materials.

8. Electrospinning
▪ simplest top-down method
▪ used to produce nanofibers from a wide variety of materials, typically polymers.
▪ Lengths of these ultrathin nanomaterials can be extended to several centimeters.
▪ Core–shell and hollow polymer, inorganic, organic, and hybrid materials
An electrostatic potential is
applied between a
spinneret and a collector
https://www.sciencedirect.com/scie
nce/article/pii/S136970210671389X

9. Lithography
A useful tool for developing nanoarchitectures using a
focused beam of light or electrons
Mask less lithography
▪ In mask less lithography,
arbitrary nanopattern writing is
carried out without the
involvement of a mask
▪ 3D freeform micro-nano-
fabrication can be
achieved via ion implantation
with a focused ion beam in
combination with wet chemical
etching
▪ Includes scanning probe
lithography, focused ion beam
lithography, and electron beam
lithography
https://link.springer.com/referenceworkentry/10.1007%2F978-0-387-92897-5_1051
Masked lithography
In masked
nanolithography, nano-
patterns are transferred
over a large surface area
using a specific mask or
template.
Includes photolithography,
nano-imprint lithography &
soft lithography

10. Sputtering
▪ An effective method for producing thin films of nanomaterials
▪ Bombarding solid surfaces with high-energy particles such as plasma or gas, it
produces nanomaterials
Steps involved
▪ Ions are generated via plasma and directed towards target which sputter target atoms
▪ Ejected atoms are transported to the substrate, there it condenses and form a thin film
▪ Performed in an evacuated chamber
Different sputtering methods
• Magnetron
• Radio-frequency diode
• DC diode sputtering
Advantages
▪ Sputtered nanomaterial composition
remains the same as the target
material with fewer impurities
▪ Cost-effective compared with
electron-beam lithography

11. Laser ablation
▪ Involves nanoparticle generation using a
powerful laser beam that hits the target
material
▪ Source material or precursor vaporizes
due to the high energy of the laser
irradiation, resulting in nanoparticle
formation
▪ E.g., metal nanoparticles, carbon
nanomaterials, oxide composites, and
ceramics
▪ Utilizing laser ablation for the
generation of noble metal nanoparticles
can be considered as a green technique,
as there is no need for stabilizing agents
or other chemicals
https://www.researchgate.net/figure/Schematic-of-
experiment-setup-for-silver-nanoparticle-production-
with-laser-ablation_fig1_293637284

12. Bottom-up approaches
To be continued………

13. Thank you
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