SOL-GEL Method:

Sols are solid particles in a liquid. They are sub class of

colloids. Gels are nothing but a continuous network of
particles with pores filled with liquid or polymer containing
liquid.
Synthesis of sol-gel in general involves hydrolysis of
precursors, condensation followed by poly-condensation to
form particles.
Alkoxides or metal salts can be used. Alkoxides have
generalformula M(ROH)n
 Thin Film Deposition Using Thermal Evaporation

Thermal evaporation is one of the commonly used

Physical Vapor Deposition (PVD) techniques.
This is a type of thin film deposition, a vacuum-based
technique for coating various
materials’ surfaces with pure materials. The coatings, also
known as films, can be made of a
single material or a combination of materials arranged in
layers. Their typical thickness ranges
from angstroms to microns. Thermal evaporation
techniques can be used to apply compounds
like oxides and nitrides as well as pure atomic elements,
including both metals and non-metals.
In the Figure 1, The material is typically found in the bottom
of the chamber, frequently in the form of an upright crucible,
because it is liquid and heated to its melting point in most
thermal Evaporation procedures. Following this bottom
source, the vapour rises, holding the substrates inverted in the
proper fixtures at the chamber’s top. Thus, in order to obtain
their coating, the surfaces intended for coating are directed
downward toward the hot source material. To ensure film
adhesion and regulate different film properties as needed,
actions may need to be taken.
To give process engineers the opportunity to obtain desired
outcomes for factors like thickness, homogeneity, adhesion
strength, stress, grain structure, optical or electrical
properties, etc., thermal evaporation system design and
processes fortunately allow adjustability of a variety of
parameters.
For thickness measurement for thin film, on the left side
there is movable shield, from which we can control the
deposition thickness. Roughing valve joins chamber to
rotary pump and backing valve joins chamber to diffusion
pump which help to create the vacuum.
 Experimental parameters
• Input voltage : 110 V
• Current: 40-70 A
• Deposition time: 10 – 20 s
Analysis of the thickness of the film
• After taking out (carefully) the covered glass slides
from the chamber, weigh them (i.e.W1, W2).
• Account for the thickness of the film by evaluating
the weights difference with surface area.
Advantages of thermal evaporator
• No substrate heating.
• Films can be deposited at high rates (e.g., 0.5m/min)
• Low energy atoms ( 0.1 ev) leave little surface damage.
• Little residual gas and impurity incorporation due to high
vacuum conditions.
• Usually consists of multiple samples (cu, Au, Ni etc)

Disdvantages of thermal evaporator

• Limited to the low melting point metals.
• Small filament size limit the deposition thickness.
• Cr coated substrate is required for gold thin film
deposition.
Pulsed Laser Deposition
 Characteristics of PLD growth
* A vapour pulse causes the nucleation of a high density of small
subcritical clusters, i.e. clusters that are much smaller that those
that would be stable for a lower instantaneous deposition rate. The
subcritical clusters are expected to be unstable once the vapour
pulse has decayed after approximately 1 ms.
* The subcritical clusters will tend to dissociate into mobile
species.
* The mobile species will nucleate new clusters on a different
scale during the time of no vapour arrival - typically 100 ms (laser
repetition rate of 10 Hz).
* The next pulse will initiate the same sequence with some of the
mobile atoms being added to the clusters formed following the
first pulse.
ADVANTAGES OF PLD PLD:
1. Stoichiometric transfer of the target material to
the substrate.
2. Highly energetic species during deposition
demands lower substrate temperature.
3. Utilization of multi-targets ease out the
multilayers deposition without breaking vacuum.
4. Target fabrication is easy.
• DISADVANTAGES OF PLD :
1. Uniform deposition over small area with high
risk of substrate surface damage.
2. Unsuitable for mass production.
3. Ablation of material highly depends on the
incident laser energy
Ball Milling method
 ELECTRIC ARC METHOD

• In this method, a potential of 20–25 V is applied

across the pure graphite electrodes separated by
1 mm distance and maintained at 500 torr
pressure of flowing helium gas filled inside the
quartz chamber.
• Under these conditions it produces an electric arc. The energy
produced in the arc is transferred to the anode which ionizes the
carbon atoms of pure graphite anode and produces C+ ions and
forms plasma (Plasma is atoms or molecules in vapor state at high
temperature). These positively charged carbon ions moves
towards cathode, gets reduced and deposited and grow as CNTs
on the cathode. As the CNTs grow, the length of the anode
decreases, but the electrodes are adjusted and always maintain a
gap of 1 mm between the two electrodes. If proper cooling of
electrodes are achieved uniform deposition of CNTs are formed
on the cathode which is achieved by inert gas maintained at
proper pressure .
• By this method multi-walled carbon nanotubes are synthesized
and to synthesize single-walled carbon nanotubes catalyst
nanoparticles of Fe, Co, and Ni are incorporated in the central
portion of the positive electrode. The obtained CNTs are further
purified to get the pure form of CNTs.
 NANOPARTICLES BY COLLOIDAL ROUTE

• Colloids are phase separated sub-micrometer particles in the form of

spherical particles. They are the particles suspended in some host
matrix. Metal, alloy, semiconductor and insulator particles of
different shapes and sizes can be synthesized in aqueous or non-
aqueous media. Nanomaterials are a special class of colloidal
particles, which are few hundred of nanometer or smaller in size.
Metal nanoparticles by colloidal route
NANOPARTICLES BY MICROEMULSIONS
NANOPARTICLES BY MICROEMULSIONS
 Epitaxial growth
• During the growth of thin films deposited material tend to
assume some atomic arrangements depending on various factors
such as crystallographic structures of deposited material and of
the substrate.
• An ordered arrangement of a deposit on a single crystal
substrate is called “epitaxy” to imply an oriented overgrowth of
a crystalline material over another as observed in many
naturally occurring single crystal minerals.
• The term ‘epi’ means upon and ‘taxy’ means an orderly
arrangement.
• There are two types of epitaxy…
• (i) Homotaxy: where the deposit or overgrowth and the substrate
are of the same species.
• (ii) Heterotaxy: where the deposit or overgrowth and the
substrate are of different species.
• Epitaxy implies that both the deposit and the substrate must be
single crystal.
• If one of them is not single crystal then growth is not epitaxial.
• Thus if a single crystal grows on an amorphous substrate like
glass or plastic or even polycrystalline material, the growth is
not epitaxial.
 Molecular Beam Epitaxy
• Molecular beam epitaxy (MBE) is an epitaxial growth
technique used to deposit thin-film of single crystals. MBE is
performed in high or ultra high vacuum (10−8 to 10−12 Torr)
conditions. It is extensively used in manufacturing of
semiconductor devices.
• Molecular beam epitaxy (MBE) involves taking a base
material, called substrate, onto which the film will be
deposited.
• The substrate is heated upto a suitable temperature.
• The precursor material is heated to high temperatures such
that it is present in gas state.
• The gaseous precursor is then bombarded onto the substrate
in the form of focused beam of atoms or molecules. The
source from where the beam is incident on the substrate is
called gun or the effusion cell.
• For firing different type of atoms/molecules on the
substrate, different gun is needed, i.e., same gun is not
used for different materials.
• The atoms or molecules, on reaching the surface of the
substrate condense and gradually grow into ultra-thin
layers. Thus, the crystal usually grows one atomic or
molecular layer at a time.
• This gives precise control over the thickness of the
deposited films and it makes MBE an excellent
technique to deposit high quality and uniform thickness
thin films over a wide array of substrates.
• The advantages:
• It can be used to prepare high quality, defect-free, and
highly uniform semiconductor crystals of a wide array of
compounds.
• Precise control over film thickness is possible.
• The disadvantages:
• The disadvantages of MBE include very slow deposition
rates which result in very long residence times.
Additionally, it is a laborious technique. Thus, this
technique is more suitable for scientific research
purposes, and commercial production using this
technique is expensive. The equipment is very complex
and expensive which originates from the requirements of
extremely clean and ultra-high vacuum conditions.
Thin film by photolithography
• Photolithography is the process of using optical
projection to transfer a pattern from a mask or
template onto a substrate. The main advantage
of photolithography is its capacity to produce
accurate and timely complicated and fine-
grained designs.
• Thin film deposition is a type of coating process
used on the surface of a substrate. This process
can be used to create protective layers and can
also be used to make reflective devices like
mirrors.
Advantages of Thin Film Deposition:
• It provides a high degree of control over the surface
topography, allowing for the production of micro-
structures.
• It helps in forming specific interfaces between
different layers in the device.
• It can be used to form barriers to electrical or
chemical diffusion.
• It can be used to produce highly conductive metal
layers as well as other insulators and
semiconductors.
• It allows for tight control of the thickness of the
layers deposited onto the substrate, resulting in a
homogeneous layer.
ELECTROCHEMICAL ETCHING