74
C. Balasubramanian
change in properties of a material just by reducing its size has generated a large interest among the scientific community, not only to understand the basic phenomenon
but also to explore the potential applications it holds. These applications are wide
ranging right from biomedical (Salata 2004) to optoelectronics to day-to-day consumer products. In fact, it would not be an exaggeration if it is suggested that the
far-reaching potential applications are actually driving the research and development
of varied nanomaterials. Already nanomaterials, like zinc oxide, titanium dioxide,
iron oxide and so on, have found industrial uses, and industrial houses are looking
at ways to produce them in bulk quantities.
A range of methods are available for synthesis of various nanomaterials. Sol–
gel and chemical vapour deposition (CVD) are the most commonly used techniques,
especially at laboratory scale. A review of various liquid-phase syntheses of inorganic
nanoparticles is discussed by Cushing et al. (2004). Apart from this liquid-phase
synthesis, a range of gas-phase synthesis techniques are also available, like laser
ablation, inert gas phase condensation and so on. When talking in terms of large
industrial-scale production, both the commonly used techniques of sol–gel and CVD
have certain limitations, like difficulty in scaling up; multistep processes; long time
scales and so on, that restrict its production capacity.
Nanomaterials can also be produced by plasma, which is a high-temperature
physical process. This process, though not so common, has distinct advantages for
commercial-scale generation of various nanostructures. The various advantages of
this process are given in Sect. 4.3. This chapter elucidates on the various aspects of
the plasma process, methodologies, control parameters, advantages, disadvantages
and so on. It also describes in detail the various nanomaterials that have been prepared
using this process. Prior to this, it would be helpful to understand what is “Plasma”.
2 Plasma
Plasma is the fourth state of matter. The other three states—solid, liquid and gas—
are well-known and well-studied even in the school curricula. Almost all the natural
terrestrial matters come under one of these states of solid or liquid or gas. However,
terrestrial natural plasma state is not so common other than in lightening and ionosphere—this, probably, is the reason for plasma state not being taught in schools.
However, more than 97% of the universe exists in plasma state!
So what exactly is plasma state? It is a state in which matter exists in ionised
form—where the constituents are either negatively charged or positively charged.
The properties of a plasma state, as expected, differ widely with respect to the other
states of matter. Unlike gaseous state which is electrically neutral, plasma state, in
which the constituents are charged particles, is the best conductor of electricity. It
also responds to magnetic fields. The energy content of plasma state is much higher
than that of the gaseous state. The most common example that is used to explain the
four states of matter is the transformation of ice (solid state) to water (liquid state)
and then to water vapour (gaseous state). Stretching it further, the water vapour with
C. Balasubramanian
change in properties of a material just by reducing its size has generated a large interest among the scientific community, not only to understand the basic phenomenon
but also to explore the potential applications it holds. These applications are wide
ranging right from biomedical (Salata 2004) to optoelectronics to day-to-day consumer products. In fact, it would not be an exaggeration if it is suggested that the
far-reaching potential applications are actually driving the research and development
of varied nanomaterials. Already nanomaterials, like zinc oxide, titanium dioxide,
iron oxide and so on, have found industrial uses, and industrial houses are looking
at ways to produce them in bulk quantities.
A range of methods are available for synthesis of various nanomaterials. Sol–
gel and chemical vapour deposition (CVD) are the most commonly used techniques,
especially at laboratory scale. A review of various liquid-phase syntheses of inorganic
nanoparticles is discussed by Cushing et al. (2004). Apart from this liquid-phase
synthesis, a range of gas-phase synthesis techniques are also available, like laser
ablation, inert gas phase condensation and so on. When talking in terms of large
industrial-scale production, both the commonly used techniques of sol–gel and CVD
have certain limitations, like difficulty in scaling up; multistep processes; long time
scales and so on, that restrict its production capacity.
Nanomaterials can also be produced by plasma, which is a high-temperature
physical process. This process, though not so common, has distinct advantages for
commercial-scale generation of various nanostructures. The various advantages of
this process are given in Sect. 4.3. This chapter elucidates on the various aspects of
the plasma process, methodologies, control parameters, advantages, disadvantages
and so on. It also describes in detail the various nanomaterials that have been prepared
using this process. Prior to this, it would be helpful to understand what is “Plasma”.
2 Plasma
Plasma is the fourth state of matter. The other three states—solid, liquid and gas—
are well-known and well-studied even in the school curricula. Almost all the natural
terrestrial matters come under one of these states of solid or liquid or gas. However,
terrestrial natural plasma state is not so common other than in lightening and ionosphere—this, probably, is the reason for plasma state not being taught in schools.
However, more than 97% of the universe exists in plasma state!
So what exactly is plasma state? It is a state in which matter exists in ionised
form—where the constituents are either negatively charged or positively charged.
The properties of a plasma state, as expected, differ widely with respect to the other
states of matter. Unlike gaseous state which is electrically neutral, plasma state, in
which the constituents are charged particles, is the best conductor of electricity. It
also responds to magnetic fields. The energy content of plasma state is much higher
than that of the gaseous state. The most common example that is used to explain the
four states of matter is the transformation of ice (solid state) to water (liquid state)
and then to water vapour (gaseous state). Stretching it further, the water vapour with