chapter 8 nanomaterials: Synthesis and characterization
258
size, defeating the original objective. To avoid this, the processing
parameters have to be carefully controlled.
inert-gas (free-jet) expansion
In inert-gas or free-jet expansion, evaporated atoms are carried by a
high-pressure helium gas stream that is expanded from a nozzle
into a low-pressure chamber at supersonic velocities (see Figure
8.3). The adiabatic expansion of the gas leads to sudden cooling,
causing the evaporated atoms to form clusters a few nanometers
in diameter. As in the case of inert-gas condensation, the agglomeration of nanoparticles is a problem, requiring careful control of
evaporation rate and inert gas flow; it is these that determine the
particle size and distribution.
Sonochemical processing
In sonochemical processing, ultrasound is used to nucleate a chemical
reaction. Ultrasound spans the frequencies in the range 15 kHz to
1 GHz. A magnetostrictive or piezoelectric transducer (or “horn”)
is used to generate ultrasonic waves with a wavelength of 1–10,000
microns in a liquid-filled reaction vessel (see Figure 8.4). These
are not molecular dimensions, so there is no direct coupling of
the acoustic field with the chemical species. The reaction comes
Figure 8.1
The matrix of processes used to make
nanomaterials.
Classes
Dimensionality
Class 1
Discrete nanoobjects
Class 2
Surface nanofeatured materials
Class 3
Bulk nanostructured materials
Lithographic methods
Electrodeposition
Physical vapor deposition (PVD)
Chemical vapor deposition (CVD)
0-D
All 3 dimensions
on nanoscale
1-D
2 dimensions
on nanoscale
2-D
1 dimension
on nanoscale
Physical or chemical
vapor deposition
(PVD or CVD)
Inert gas condensation
Evaporation
Colloidal methods
Directional growth from
catalyst dots
Templating
Beating (gold foil)
Electrodeposition
PVD, CVD
Self-assembled films
Equiangle extrusion
Cryomilling
Consolidation of
nanoparticles by sintering
Incorporation of nanotubes and
rods into polymer or
metal matrices
Rotating shutter PVD and CVD
Cyclic electrodeposition
Figure 8.2
Inert gas condensation. The nanoclusters that form
on the cold finger are harvested by the scraper
and collector and subsequently consolidated to
make products.
Scraper
Clusters
Inert gas
Vacuum
pump
Cold finger
Evaporation
sources
Collection
tray
258
size, defeating the original objective. To avoid this, the processing
parameters have to be carefully controlled.
inert-gas (free-jet) expansion
In inert-gas or free-jet expansion, evaporated atoms are carried by a
high-pressure helium gas stream that is expanded from a nozzle
into a low-pressure chamber at supersonic velocities (see Figure
8.3). The adiabatic expansion of the gas leads to sudden cooling,
causing the evaporated atoms to form clusters a few nanometers
in diameter. As in the case of inert-gas condensation, the agglomeration of nanoparticles is a problem, requiring careful control of
evaporation rate and inert gas flow; it is these that determine the
particle size and distribution.
Sonochemical processing
In sonochemical processing, ultrasound is used to nucleate a chemical
reaction. Ultrasound spans the frequencies in the range 15 kHz to
1 GHz. A magnetostrictive or piezoelectric transducer (or “horn”)
is used to generate ultrasonic waves with a wavelength of 1–10,000
microns in a liquid-filled reaction vessel (see Figure 8.4). These
are not molecular dimensions, so there is no direct coupling of
the acoustic field with the chemical species. The reaction comes
Figure 8.1
The matrix of processes used to make
nanomaterials.
Classes
Dimensionality
Class 1
Discrete nanoobjects
Class 2
Surface nanofeatured materials
Class 3
Bulk nanostructured materials
Lithographic methods
Electrodeposition
Physical vapor deposition (PVD)
Chemical vapor deposition (CVD)
0-D
All 3 dimensions
on nanoscale
1-D
2 dimensions
on nanoscale
2-D
1 dimension
on nanoscale
Physical or chemical
vapor deposition
(PVD or CVD)
Inert gas condensation
Evaporation
Colloidal methods
Directional growth from
catalyst dots
Templating
Beating (gold foil)
Electrodeposition
PVD, CVD
Self-assembled films
Equiangle extrusion
Cryomilling
Consolidation of
nanoparticles by sintering
Incorporation of nanotubes and
rods into polymer or
metal matrices
Rotating shutter PVD and CVD
Cyclic electrodeposition
Figure 8.2
Inert gas condensation. The nanoclusters that form
on the cold finger are harvested by the scraper
and collector and subsequently consolidated to
make products.
Scraper
Clusters
Inert gas
Vacuum
pump
Cold finger
Evaporation
sources
Collection
tray