The document discusses approaches for synthesizing nanomaterials. It describes top-down approaches which involve breaking down bulk materials into nanostructures using techniques like ball milling. Ball milling works by impact and attrition using grinding balls. The document also describes bottom-up approaches which build materials up atom by atom using chemical vapor deposition or electric arc deposition. Chemical vapor deposition involves exposing a substrate to volatile precursors that react and deposit a compound. Electric arc deposition strikes an arc between electrodes in an inert gas to evaporate material and synthesize fullerenes or carbon nanotubes.

1. SYNTHESIS OF
NANOMATERIAL
Yogesh M 22ECR244

2. Contents of this presentation
 Introduction
 Flow chart
 Top down approach
Ball milling techniques
Principle
Types
 Bottom up approach
Chemical vapour deposition
Electric arc deposition

3. Introduction:
✓ Nanotechnology is an emerging area of research which has a potential in
replacement of conventional micron technologies and gives size dependent
properties of the functional materials.
✓ The interest in nanoscience (science of low dimensional systems) is a realization of
a famous statement by Feynman that "There's a Plenty of Room at the Bottom".
✓ Based on Feynman’s idea, K. E. Drexler advanced the idea of “molecular
nanotechnology” in 1986 in the book Engines of Creation, where he postulated the
concept of using nanoscale molecular structures to act in a machine like manner
to guide and activate the synthesis of larger molecules.
✓ When the dimension of a material is reduced from a large size, the properties
remain the same at first, then small changes occur, until finally, when the size
drops below 100 nm, dramatic changes in properties can occur

5. TOP-DOWN AND BOTTOM-UP
APPROACHES FOR SYNTHESIS
OF NANOMATERIALS
Synthesis of nanomaterials and nanostructures are the important aspect of
nanoscience and nanotechnology. New physical properties and applications
of nanomaterials are only possible when nanostructured materials are made
available with desired size, shape, morphology, crystal structure and chemical
composition. These notes provide a clear and concise understanding on Top-
down and Bottom-up approaches for synthesis of nanomaterials.

6. Top-down approach
 Top-down approach involves the breaking down of the bulk material into
nanosized structures or particles. Top-down synthesis techniques are
extension of those that have been used for producing micron sized
particles.
 Top-down approaches are inherently simpler and depend either on removal
or division of bulk material or on miniaturization of bulk fabrication
processes to produce the desired structure with appropriate properties.
 The biggest problem with the top-down approach is the imperfection of
surface structure. For example, nanowires made by lithography are not
smooth and may contain a lot of impurities and structural defects on its
surface.
 Examples of such techniques are high-energy wet ball milling, electron
beam lithography, atomic force manipulation, gas-phase condensation,
aerosol spray, etc.

7. BALL MILLING TECHNIQUES
A ball mill is a device used to grind and blend materials for use in mineral
dressing processes, paints, pyrotechnics, ceramics and selective laser
sintering. It is a physical method of synthesis of nanoparticles and is an
example of top down approach of producing nanomaterials. The ball mill
consists of a hollow cylindrical shell which rotates about its axis. The axis of
the shell may be either horizontal or inclined at a small angle to the
horizontal. It is partially filled with the balls which may be made of chrome
steel, stainless steel, ceramic or rubber. These balls form the grinding media
of the ball mill. The inner surface of the cylindrical shell is generally lined (i.e,
coated) with an abrasion resistant material e.g., rubber or mangenese steel.
Rubber is preferred for this purpose due to less wear in mills lined with
rubber. The length and diameter of the ball mill are nearly equal.

8. Principle: A ball mill works on the
principle of impact and attrition

9. Types of Ball Mill
There are two kinds of ball mill
(i) grate type, and (ii) overfall type, according to different ways of discharging material. Large to
medium sized ball mills are mechanically rotated on their axis, but small ones normally consists of a
cylindrical capped container that sits on two drive shafts. Some of the common ball mills are as
follows:
1. Vibrating ball mill
2. High energy ball mill
3. Low energy tumbling ball mill Besides common ball mills as discussed above, there is also
a planetary ball mill. A planetary ball mill is smaller than a common ball mill and is generally used in
laboratories for research purpose. It consists of at least one grinding jar which is arranged eccentrically
on a sun wheel. The sun wheel moves in a direction opposite to that of the grinding jars. The grinding
balls in the grinding jars are subjected to superimposed rotational movements. The difference in
speeds between the balls and grinding jars produces an interaction between fractional and impact
forces due to which high energies are released. The interplay between frictional or impact forces
results in very effective size reduction of the particles of the material to be ground in a planetary ball
mill.

10. Bottom-up approach
✓ The alternative approach, which has the potential of creating less waste
and hence the more economical, is the ‘bottom- up’.
✓ Bottom-up approach refers to the build up of a material from the bottom:
atom-by-atom, molecule-by-molecule, or cluster-by cluster.
✓ Many of these techniques are still under development or are just
beginning to be used for commercial production of nanopowders.
✓ Oraganometallic chemical route, revere-micelle route, sol-gel synthesis,
colloidal precipitation, hydrothermal synthesis, template assisted sol-gel,
electrodeposition etc, are some of the well- known bottom–uptechniques
reported for the preparation of luminescent nanoparticals.

11. Chemical Vapour Deposition Method
To avoid undesired chemical reactions, the substrate surface
temperature, deposition time, pressure and type of surface is
carefully selected.
• Bottom up Approach
• Substrate is exposed to
one or more volatile
precursors (chemicals)
which react decompose
and/or the on substrate
surface to produce
compound.
• desired By-products are
removed by carrier gas
flow through the reaction
chamber

12. • There are various processes such as reduction of gas, chemical reaction
between different source gases, oxidation or some disproportionate
reaction by which CVD can proceed.
• However, it is preferable that the reaction occurs at the substrate rather
than in the gas phase. Usually temperature ~ 300 to 1200 C is used at the
substrate. There are two ways viz., hot wall and cold wall by which
substrates are heated
• . In hot wall set up the depositioncan take place even on reactor walls.
This is avoidedin cold wall design.Besides this, the reaction can take
place in gas phase with hot wall design,whichis suppressed in cold wall
set up.

13. • Further, coupling of plasma with chemical reaction in cold wall set up is
feasible.
• Usually gas pressures in the range of 0.1 torr to 1.0 torr are used. Growth
rate and film quality depend upon the gas pressure and the substrate
temperature.
• When the growth takes place at low temperature, it is limited by the
kinetics of surface tension.CVD is widely used in industry because of
relatively simple instrumentation, ease of processing,possibilityof
depositingdifferent types of materials and economic viability

14. • Electric Arc Deposition:
• This is one of the simplest and useful methods, which leads to mass
scale production of fullerenes and carbon nanotubes.
• It requires water cooled vacuum chamber and electrodes to strike an
arc between them. The positive electrode itself acts as the source of
material.
• If some catalyst are to be used, there can be some additionalthermal
source of evaporation.
• Inert gas or reactive gas introductionis necessary.Usually the gap
between the electrodes is ~1mm and high current ~50 to 100 amperes is
passedfrom a low voltage power supply (~12-15 volts).
• Inert gas pressureis maintainedin the vacuum system. When an arc is
set up, anode material evaporates.

15. • This is possible as along as the discharge can be maintained. By striking
the arc between the two graphite electrodes, it is possible to get
fullerenes in large quantity.In case of fullerenes, the formation occurs at
low helium pressure as compared to that used for nanotube formation.
• Also, fullerenes are obtained by purification of soot collected from inner
walls of vacuum chamber, whereas nanotubes are found to be formed
only at high He gas pressureand in the central portion of the cathode.
• No carbon nanotubes are found on the chamber walls

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