2. INTRODUCTION
• Materials scientists are conducting research to
develop novel materials with better
properties, more functionality and lower cost
than the existing one.
• Several physical, chemical methods have been
developed to enhance the performance of
nanomaterials displaying improved properties
with the aim to have a better control over the
particle size, distribution
3. Methods to Synthesis of
Nanomaterials
• In general, top-down and bottom-up are the
two main approaches for nanomaterials
synthesis.
• a. Top-down: size reduction from bulk
materials.
• b. Bottom-up: material synthesis from atomic
level.
4. TOP-DOWN
• Top-down routes are included in the typical
solid –state processing of the materials.
• This route is based with the bulk material and
makes it smaller, thus breaking up larger
particles by the use of physical processes like
crushing, milling or grinding.
5. Cont..
• Usually this route is not suitable for preparing
uniformly shaped materials, and it is very difficult
to realize very small particles even with high
energy consumption.
• The biggest problem with top-down approach is
the imperfection of the surface structure.
• Such imperfection would have a significant
impact on physical properties and surface
chemistry of nanostructures and nanomaterials.
6. Top-Down: lithography
• At the moment, the most used top-down
approach is photolithography.
• It has been used for a while to manufacture
computer chips and produce structures
smaller than 100 nm.
• Typically, an oxidized silicon (Si) wafer is
coated with a 1µm thick photoresist layer.
7. Cont..
• After exposure to ultraviolet (UV) light, the
photoresist undergoes a photochemical
reaction, which breaks down the polymer by
rupturing the polymer chains.
• Subsequently, when the wafer is rinsed in a
developing solution, the exposed areas are
removed.
8.
9. NANOLITHOGRAPHY
• Nanolithography is the branch of nanotechnology
concerned with the study and application of
fabricating nanometer-scale structures, meaning
patterns with at least one lateral dimension
between 1 and 100 nm
• It comes from the Greek word “nanos” meaning
dwarf and “graphene” meaning to write.
• It is a very active area of research in academia
and in industry.
10. WORKING
• It used for further fabrications of nanometer
materials and molecules.
• Two of most important instruments used in
the nanolithography processing are
• Scanning Probe Microscope (SPM)
• Atomic Force Microscope (ATM)
12. OPTICAL NANOLITHOGRAPHY
• Traditional method of lithography
• It is a technique for patterning the various
surfaces and have the capability for producing
sub patterns up-to to 100 nm with minor wave
lengths.
• Optical nanolithography requires the use of
liquid immersion and resolution host.
• Most cost effective method of lithography
13. X RAY NANOLITHOGRAPHY
• It is quite different from traditional X-ray
lithography.
• It has the ability to improve and extend optical
resolution of 15 nm by using the short
wavelengths of 1 nm for the illumination.
• This is performed by printing approach and is
used for batch processing.
• It consists of 3 elements-A mask consisting of a
pattern made with an X ray absorbing material on
a thin x ray transparent membrane, an X ray
source, an X ray sensitive resist material
14.
15. Cont..
• It is the most famous nanolithography
method which makes use of electron beam to
draw a pattern.
• It is mostly used in the polymers to obtain
different patterns of polymeric structures
16. Electron Beam Lithography (EBL)
• Electron Beam Lithography (EBL) uses a tightly
focussed beam of electrons scanned over the
surface of a substrate to etch a pattern of
nano sized features.
• EBL can produce features as small as 20nm
but is very expensive and time consuming.
• For example a lithographic process that would
take 5 minutes using photolithography would
take approximately 5 hours using EBL.
17. Nanoimprint lithography
• Nanoimprint lithography is a simple process that uses a
mould to emboss the resist with the required pattern.
• After embossing the resist, compressed resist material
is removed using anisotropic etching and the substrate
exposed.
• Nanoimprint lithography can give resolutions lower
than 10nm with high throughput and low cost.
• The current barrier to production at these resolutions
is the development of the mould itself.
• Nanomanufacturing using self assembly may hold the
solution to this hurdle.
18. Scanning Probe Microscope
Lithography (SPM)
• Scanning Probe Microscope Lithography (SPM)
uses the electric field at the tip of a scanning
probe microscope to oxidise material in a
specific pattern.
• The oxidised material can then be removed
by preferential etching
19. Chemical Vapor Deposition (CVD)
• This process is often used in the semiconductor
industry to produce high-purity, high-
performance thin films.
• In a typical CVD process, the substrate is exposed
to volatile precursors, which react and/or
decompose on the substrate surface to produce
the desired film.
• Frequently, volatile by products that are
produced are removed by gas flow through the
reaction chamber.
20. Cont.
• The quality of the deposited materials strongly
depends on the reaction temperature, the
reaction rate, and the concentration of the
precursors.
• Cao et al. prepared Sn4+-doped TiO2
nanoparticles films by the CVD method and
found that more surface defects were present
on the surface due to doping with Sn .
21. Cont..
• Gracia et al.synthesized M (Cr, V, Fe, Co)-
doped TiO2 by CVD and found that TiO2
crystallized into the anatase or rutile
structures depending on the type and amount
of cation present in the synthesis process
• Moreover, upon annealing, partial segregation
of the cations in the form of M2On was
observed.
22. Cont..
• The advantages of this method include the
uniform coating of the nanoparticles or nano
film.
• However, this process has limitations including
the higher temperatures required, and it is
difficult to scaleup .
23. 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.
• This route is more often used for preparing
most of the nano-scale materials with the
ability to generate a uniform size, shape and
distribution.
24. Cont.
• It effectively covers chemical synthesis and
precisely controlled the reaction to inhibit
further particle growth.
• Although the bottom-up approach is nothing
new, it plays an important role in the
fabrication and processing of nanostructures
an nanomaterials.
25. Cont..
• Synthesis of nanoparticles to have a better
control over particles size distribution,
morphology, purity, quantity and quality, by
employing environment friendly economical
processes has always been a challenge for the
researchers
26. SOL-GEL METHOD
• Two types of materials or components- “sol”
and “gel”
• M. Ebelman synthesized them in 1845
• Low temperature process- less energy
consumption and less pollution Generates
highly pure, well controlled ceramics
• Economical route, provided precursors are not
expensive Possible to synthesize
nanoparticles, nanorods, nanotubes etc.,
27. Cont..
• Sols are solid particles in a liquid- subclass of
colloids
• Gels – polymers containing liquid
• The process involves formation of ‘sols’ in a
liquid and then connecting the sol particles to
form a network
• Liquid is dried- powders, thin films or even
monolithic solid Particularly useful to
synthesize ceramics or metal oxides
28.
29. Cont..
• The precursors for synthesizing these colloids
consist : -
• metal alkoxides e.g: tetramethoxysilane
(TMOS) and tetraethoxysilane (TEOS)
• Metal chlorides
• They readily react with water.
• Three reactions are generally used to describe
the sol-gel process: - hydrolysis –
condensation-polycondensation
30. Cont..
• For ex: in SiO₄, Si is at the centre and 4 oxygen
atoms at the apexes of tetrahedron
• Very ideal for forming sols
• By polycondensation process sols are
nucleated and sol-gel is formed
31.
32.
33. Application of Sol-Gel
• Protective Coatings
• Thin film and fibers
• Nanoscales powder
• Opto-mechanical
34. Advantages
• Cheap and low temperature operation
• Very thin of metals oxide can be obtained
• Better alternative approach to conventional
production of glasses
• Sol gel material can be obtained as bulks, thin
films (nano) powders
35. CHEMICAL METHODS OF SYNTHESIS
• Advantages
• Simple techniques
• Inexpensive instrumentation
• Low temperature (<350ºC) synthesis
• Doping of foreign atoms (ions) is possible during
synthesis
• Large quantities of material can be obtained
Variety of sizes and shapes are possible
• Self assembly or patterning is possible
36. COLLOIDS AND COLLOIDS IN
SOLUTION
• Nanoparticles synthesized by chemical methods
form “colloids”
• Two or more phases (solid, liquid or gas) of same
or different materials co-exist with the
dimensions of at least one of the phases less than
a micrometre
• May be particles, plates or fibres
• Nanomaterials are a subclass of colloids, in which
the dimensions of colloids is in the nanometre
range
37.
38. SYNTHESIS OF METAL NANOPARTICLES
BY COLLOIDAL ROUTE
• Reduction of some metal salt or acid
• Highly stable gold particles can be obtained
by reducing chloroauric acid
• Metal gold nanoparticles exhibit intense red,
magenta etc., colours depending upon the
particle size
39.
40. Cont..
• Gold nanoparticles can be stabilised by
repulsive Coloumbic interactions
• Also stabilised by thiol or some other capping
molecules
• In a similar manner, silver, palladium, copper
and few other metal nanoparticles can be
synthesized.
