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C. Balasubramanian
3.3 Advantages of Plasma Process for Nanomaterial
Synthesis
The major advantages of the plasma process for synthesis of nanomaterials are that
(i) the process is easily scalable;
(ii) faster time scales of synthesis and
(iii) single step process with significant control over impurities.
For commercial/industrial-scale production of nanomaterials, these three points
are a game changer. Apart from the above, other advantages are:
(iv) The plasma process operates under atmospheric pressure and hence, unlike
CVD process, does not require the cumbersome and time-consuming vacuum
creation and so on.
(v) The high temperature of the plasma zone can evaporate all materials and hence
nanostructures of most materials can be prepared using the same apparatus and
setup.
(vi) The high temperature of plasma also promotes high rates of chemical reactivity
and the products are generally highly crystalline. Additionally, it is also possible to produce metastable crystalline phases which are not normally formed
in a low temperature process.
(vii) Plasma process also yields a range of morphological features with minor
changes in the operational parameters.
Plasma process can also be used to prepare varied types of nanomaterials—metals, metal oxides, metal nitrides, metal carbides and so on. The gas ambient in the
synthesis chamber dictates the product formation. If the anode material is evaporated
in an inert ambient (argon or helium gas), then metal nanoparticles can be obtained.
If the ambient is air or oxygen, one can obtain metal oxide nanoparticles. For nitrides,
a high concentration of nitrogen ambient is sufficient to get the desired results. For
carbides one can mix graphite/carbon powder along with the anode material in an
inert atmosphere.
The sole disadvantage of the plasma process of nanomaterial synthesis is the wide
size distribution of the nanostructures formed. Though this is unavoidable, it can be
minimised. The reason for the large size distribution is: The steep temperature gradient (thousands of degree centigrade per centimetre) combined with high velocities
(thousands of metres per second) of the evaporated material leads to very fast time
scales of nucleation and growth of the nanostructures. Depending on the flight path
of the evaporated atom/molecule clusters, the thermal history and condensation rates
vary and hence the size of the nanoclusters also varies.
In the following sections, details of the different types of nanomaterials that
have been synthesised as well as the morphological and other variations that can
be obtained by varying certain plasma parameters will be provided.
C. Balasubramanian
3.3 Advantages of Plasma Process for Nanomaterial
Synthesis
The major advantages of the plasma process for synthesis of nanomaterials are that
(i) the process is easily scalable;
(ii) faster time scales of synthesis and
(iii) single step process with significant control over impurities.
For commercial/industrial-scale production of nanomaterials, these three points
are a game changer. Apart from the above, other advantages are:
(iv) The plasma process operates under atmospheric pressure and hence, unlike
CVD process, does not require the cumbersome and time-consuming vacuum
creation and so on.
(v) The high temperature of the plasma zone can evaporate all materials and hence
nanostructures of most materials can be prepared using the same apparatus and
setup.
(vi) The high temperature of plasma also promotes high rates of chemical reactivity
and the products are generally highly crystalline. Additionally, it is also possible to produce metastable crystalline phases which are not normally formed
in a low temperature process.
(vii) Plasma process also yields a range of morphological features with minor
changes in the operational parameters.
Plasma process can also be used to prepare varied types of nanomaterials—metals, metal oxides, metal nitrides, metal carbides and so on. The gas ambient in the
synthesis chamber dictates the product formation. If the anode material is evaporated
in an inert ambient (argon or helium gas), then metal nanoparticles can be obtained.
If the ambient is air or oxygen, one can obtain metal oxide nanoparticles. For nitrides,
a high concentration of nitrogen ambient is sufficient to get the desired results. For
carbides one can mix graphite/carbon powder along with the anode material in an
inert atmosphere.
The sole disadvantage of the plasma process of nanomaterial synthesis is the wide
size distribution of the nanostructures formed. Though this is unavoidable, it can be
minimised. The reason for the large size distribution is: The steep temperature gradient (thousands of degree centigrade per centimetre) combined with high velocities
(thousands of metres per second) of the evaporated material leads to very fast time
scales of nucleation and growth of the nanostructures. Depending on the flight path
of the evaporated atom/molecule clusters, the thermal history and condensation rates
vary and hence the size of the nanoclusters also varies.
In the following sections, details of the different types of nanomaterials that
have been synthesised as well as the morphological and other variations that can
be obtained by varying certain plasma parameters will be provided.