This contains some of the techniques for the formation of nanoparticles by bottom up approach.

1. BOTTOM-UP APPROACHES FOR
SYNTHESIS OF NANOMATERIALS
Kusum
Msc Biotechnology
Semester 3rd
Session 2020-2022
Central University of Haryana

2. Top-down approach
Top-down approach involves the breaking down
of the bulk material into nanosized structures or
particles.
The biggest problem with the top-down
approach is the imperfection of surface
structure.
Among the top-down and bottom-up
approaches, the bottom-up approach is more
accepted in synthesis of nanoparticles due to
many merits as fewer defects, more
homogenous chemical composition and better
ordering.
https://ccsuniversity.ac.in/bridge-library/pdf/L-
3%20Synthesis%20of%20Nanostructured%20M
aterials%20Prof%20BPS.pdf
Disadvantages
-Control over deposition
parameters
is difficult to achieve
-Impurities: stresses, defects
and
imperfections get introduced
• Expensive technique

3. Bottom up Approach
Bottom-up (“Molecular nanotechnology”)
applies to building organic and inorganic
structures atom-by-atom and molecule-by-
molecule.
All the Bottom-up techniques,the starting
material is either gaseous state or
liquid state of matter .
The properties of nanoparticles depend on their size
and morphology. https://image.slidesharecdn.com/muntaseerfinal-
161208121452/95/nanoparticle-synthesis-10-
638.jpg?cb=1481199352

4. Bottom-Up Synthesis
Synthesis of nanoparticles is a
combination of two stage
process, nucleation and growth.
Nucleation is the process
whereby nuclei (seeds) act as
templates for crystal growth.The
process that determines how long
we have to wait before the new
phase or self-organised structure,
appears.
.
Phase classification
I. Gas (Vapor) Phase
Fabrication:
PVD:
- Inert Gas Condensation,
Evaporation (Thermal , e-
beam)
Plasma Arcing,
Laser ablation,
- Sputtering
CVD: (PECVD and
Microwave-PECVD)
II. Liquid Phase
Fabrication:
- Wet chemical
synthesis,
- Sol-gel,
- Self assembled
Monolayer(SAM)
- Microemulsion
method
- Spray Pyrolysis

5. Physical methods(With starting phase as gas phase)
Physical vapor deposition(PVD)
Involves generation and condensation of vapor phase species via thermal
evaporation,sputtering or laser ablation
Inert-gas condensation(IGC)
Nanoparticles are formed via the evaporation of a metallic source in an inert gas.
Widely used in the synthesis
of ultrafine metal
particles
The size, morphology,
and yield of the NPs
should be controlled

6. A metal is evaporated inside an ultra-
high vacuum (UHV) chamber filled with inert gas (He).
The vaporized species collide with Helium molecules
thus losing kinetic energy.
As collisions limit the mean free path, supersaturation can be
achieved above the vapors source.
At high supersaturation, the vapors rapidly form no. of clusters
that grow via coalescence and agglomeration.
These clusters get condensed on liquid nitrogen cooled
surfaces to form nanoparticles.
http://www.lscollege.ac.in/sites/default/files/e-
content/Bottom%20up%20Synthesis%20of%20Nanomaterials.pdf

7. Advantages of Inert Gas Condensation Method
An extensive range of materials such as intermetallic compounds, ceramics metals, alloys, semiconductors and composites
can be synthesized via inert gas condensation technique.
Specifically, it is possible to generate nanoscale particles from just about any material that can be vaporized.
Very flexible one in terms of cluster sizes to be made, controlling the size and the size distribution of the particles over a
broad range through the process and parameter alteration such as temperature and pressure.
Particle surface cleanliness and ultrafine sizes of the particles make it possible to overcome the conventional restrictions of
kinetics and phase equilibria through the combination of high driving forces, diffusion distances and more importantly,
uncontaminated surfaces.
https://nanografi.com/blog/inert-gas-condensation-for-nanoparticle-
synthesis/#:~:text=The%20inert%20gas%20condensation%20method%20is%20a%20simple%20technique%20that,parts%20
of%20the%20operation%20chamber.

8. Thermal evaporation
Thermal deposition inside a vacuum
chamber where the
material, usually in a boat is heated
typically to its melting point and the
substrate to be deposited on is
positioned facing the source. A high
current flowing through the boat
heats it up and causes evaporation.
A crystal monitor is mounted close
to the substrate, which provides an
estimate of how much and how fast
the material is being deposited.
Limitations-
• High temperature process ( 500-1200oC)
• Ultra high vacuum(10-6 torr)
• High cost
Image source -
ibec_corefacilities_thermal.pdf

9. Evaporation technique

10. Electron beam evaporation
This technique is based in the heat produced by high energy electron beam bombardment on the material to be
deposited. A high dc voltage is applied to a tungsten filament that causes electrons to be emitted out. These
emitted electrons are accelerated to excites the target solid and produces vapors, which travels to the substrate.
As they reach the surface, they condense and form a thin film coating.•
Used for depositing materials with high melting point
(W, Ta, C, etc.)
• As electrons can be focalized, it is possible to obtain a
very localized heating on the material to evaporate,
with a high density of evaporation power (several kW)

11. Sputtering
Sputter deposition are methods of depositing thin films
by sputtering. They involve ejecting material from a
“target” that is a source onto a “substrate” such as a
silicon wafer.
Atoms of Target (source) materials are ejected or
sputtered by high energy ionbombardment of high-
energy noble gas atoms, commonly Argon,
produced by a high voltage DC discharge. These
ejected sputtered atoms (due to momentum
transfer) form a thin film coating after condensing
on substrate kept as anode plate
Some of the bombarding ions are reflected back and
are neutralized( still sufficiently energetic to reach
the substrate were the film is being deposited).This
can be a source of substrate bombardment (back
scattering) which can effect the resulting properties
of the film... The ejected atoms will have random
directions but, the sputtering process can induce
texture in the resulting films due to the sputtering
conditions
.Secondary electrons which are emitted either join
the oscillating plasma gas, which cause the
continuous ionization of the gas to sustain the
incident ions needed for sputtering, or they liberate
their energy in the form of heat on colliding with the
substrate or other parts of the chamber. The
sputtered target atoms which are deposited at the
substrate form the resulting thin film. .

12. The mobility of the incident atoms arriving at the substrate is highly dependent upon the sputtering
parameters (pressure and power), the temperature of the substrate, the distance between target and
substrate, and the surface.
http://www.lscollege.ac.in/sites/default/files/e-
content/Bottom%20up%20Synthesis%20of%20Nanomaterials.pdf

13. Schematic of thin-film growth based on DC sputtering technique. The processes include (a) migration of single atoms on substrate,
(b) aggregation of single atoms, (c) nucleation to form nanoparticles, (d) growth of nanoparticles, (e) coalescence of nanoparticles,
and (f) formation of continuous film
http://www.lscollege.ac.in/sites/default/files/e-
content/Bottom%20up%20Synthesis%20of%20Nanomaterials.pdf

14. By separating the content & applying a DC arc discharge b/w 2 pure carbon rods ,
the evaporation of the anode carbon realized the mass production of fullerene.
This arc evaporation of carbon electrodes produced a deposit on the cathode
which included multiwalled carbon nanotubes(MWCN).
By a method similar to that for MWNT production, but using graphite rods
including catalytic metals, single-walled carbon nanotubes (SWNTs) were
discovered in chamber soot (not in cathode deposit).
https://www.researchgate.net/publication/267972345_Synthesis_of_Carbon_Nanotubes_by_Arc-
Discharge_Method/link/5498c8d20cf2c5a7e342c63c/download
Arc discharge technique

15. Two graphite electrodes are installed
vertically, and the distance between the
two rod tips is maintained in the range of 1-
2 mm.
After the evacuation of the chamber by a
diffusion pump, rarefied ambient gas is
introduced.
When a dc arc discharge is applied
between the two graphite rods, the anode
is consumed, and fullerene is formed in the
chamber soot. Then, part of the
evaporated anode carbon is deposited on
the top of the cathode; this is called the
'cathode deposit'. Schematic diagram of apparatus for preparing CNTs.
https://www.researchgate.net/publication/267972345_Synthesis_of_Carbon_Nanotubes_by_Arc-

16. Optical image of section of cathode deposit grown by dc arc discharge method in He (1.33x104 Pa)
after 8-min evaporation.(4) Region A is the tip of the cathode. Region B has a columnar texture and
contains MWNTs. Region C is the top of the cathode deposit facing the anode. Region D shows
hard graphite layers. d is the thickness of the deposit
https://www.researchgate.net/publication/267972345_Synthesis_of_Carbon_Nanotubes_b
y_Arc-Discharge_Method/link/5498c8d20cf2c5a7e342c63c/download

17. Laser ablation
Utilizes laser as an energy source for
ablating solid target materials.
Extremely high energy is concentrated at
specific point on solid surface to evaporate
light absorbing material.
In this method, a solid metal rod is ablated using a Nd:YAG
laser (high Power) in a chamber containing Ar gas. In the
plasma that results from the laser ablation, metal atoms are
evaporated and condensed on water cooled substrate. Later
the substrate is heated to remove the impurities. NPs of Iron,
gold, palladium, and compounds of sulphide are pepared by
this method.
Advantage: • capable of High deposition rate of 2-3 g/min
Disadvantage: • High temperature method • low quality of
material deposited
https://www.jstage.jst.go.jp/article/ko
na/advpub/0/advpub_2017009/_pdf/-
char/en
Particle generation procedure in
laser ablation

18. Chemical method-Microemulsion method
Microemulsions are
thermodynamically stable
systems composed of two
inmiscible liquids (usually,
water and oil) and a surfactant.
Droplets of water-in-oil (W/O)
or oil-in-water (O/W) are
stabilized by surfactants when
small amounts of water or oil
are used, respectively.
These nanodroplets can be
used as nanoreactors to carry
out chemical reactions.
http://www.lscollege.ac.in/sites/default/files/e-content/Bottom%20up%20Synthesis%20of%20Nanomaterials.pdf
Aqueous solvent Organic liquid
Dispersion
medium

19. MNPs synthesized by microemulsion method using the anionic surfactant
Prepared two microemulsions, one them solubilizing FeCl3 aqueous solution in AOT/cyclohexane and the
other aqueous NH3 in AOT/cyclohexane; both were mixed join
To obtain the formation of Fe3O4 in the micelle, authors added a FeCl2 solution to the mixture of two
microemulsions.
A diluted solution of the colloid obtained was characterized by TEM to
determine the crystal structure and size distribution by electron micrography.
Once the particles are formed, the surfactant particles act as surface agents,
limiting the future growth of the particles.
The sizes of the microemulsion droplets can be tuned between 5 and 50 nm by changing the relation of the
components of the microemulsion (e.g., W = [H2O]/[AOT]) or varying the microemulsion itself.
The results for Fe particles obtained in an AOT microemulsion system (W = 22.2; [AOT] = 0.05 M; reactant A: [FeCl2]
= 1.9 × 10−4 M; reactant B: [NaBH4] = 8.8 × 10−4 M) were discriminated using XRD.
. Nucleation process was confirmed by enhancing the number of scattering centers and hence the scattering intensity.
Conversely, growth of the particles is associated with a decrease on the scattering intensity because of the
“disappearing” of the smaller particles during their growth.
https://www.intechopen.com/chapters/63347

20. Spray pyrolysis
Involves spraying a metal salt solution onto a
heated substrate. Droplets impact on the
substrate surface, spread into a disk shaped
structure, and undergo thermal
decomposition. The shape and size of the
disk depends on the momentum and volume
of the droplet, as well as the substrate
temperature Film is usually composed of
overlapping disks of metal salt being
converted into oxides on the heated
substrate.
https://www.slideshare.net/MUHAMMADAADIL16/thin-film-deposition-using-spray-pyrolysis-87996557
http://www.lscollege.ac.in/sites/default/files/e-content/Bottom%20up%20Synthesis%20of%20Nanomaterials.pdf

21. Flame spray pyrolysis
In flame spray pyrolysis an aqueous
metal salt solution is sprayed as a fine
mist, through a capillary and into a
flame.
Then, small droplets are formed while
the solvent burns inside the flame.
The conversion of the salt into the
metal oxide occurs upon the pyrolysis
reaction and the metal oxide atoms
aggregate into nanoparticles, which
are then collected on a substrate .
https://www.sciencedirect.com/topics/engineering/flame-spray-pyrolysis

22. Reference
https://www.sciencedirect.com/topics/engineering/flame-spray-pyrolysis
https://www.intechopen.com/chapters/63347
https://www.researchgate.net/publication/267972345_Synthesis_of_Carbon_Nanotubes_by_Arc-
Discharge_Method/link/5498c8d20cf2c5a7e342c63c/download
http://www.lscollege.ac.in/sites/default/files/e-content/Bottom%20up%20Synthesis%20of%20Nanomaterials.pdf
https://www.slideshare.net/MUHAMMADAADIL16/thin-film-deposition-using-spray-pyrolysis-87996557
https://nanografi.com/blog/inert-gas-condensation-for-nanoparticle-
synthesis/#:~:text=The%20inert%20gas%20condensation%20method%20is%20a%20simple%20technique%20th
at,parts%20of%20the%20operation%20chamber
https://ccsuniversity.ac.in/bridge-library/pdf/L-
3%20Synthesis%20of%20Nanostructured%20Materials%20Prof%20BPS.pdf