8.1 SyntheSiS of nanoScale
MaterialS and StructureS
There are many ways of making nanoscale materials and structures.
Figure 8.1 orders them in the same matrix as that of Chapter 6. It
gives an overview, showing where each fits. We start our discussion
at the upper left: processes to make discrete, nanoscale clusters.
Methods for Making 0-d nanomaterials
Nanoclusters are made by either gas-phase or liquid-phase processes. We start with those using the gas phase, the commonest of
which are inert-gas condensation and inert-gas expansion. Liquid
phase processes use surface forces to create nanoscale particles and
structures. There are broad types of these processes: ultrasonic dispersion, sol-gel methods, and methods relying on self-assembly.
inert-gas condensation
In inert-gas condensation, an inorganic material is vaporized inside a
vacuum chamber into which an inert gas (typically argon or helium)
is periodically admitted (see Figure 8.2). The source of vapor can be
an evaporation boat, a sputtering target, or a laser-ablation target.
Once the atoms boil off, they quickly lose their energy by colliding
with the inert gas. The vapor cools rapidly and supersaturates to
form nanoparticles with sizes in the range 2–100 nm that collect
on a finger cooled by liquid nitrogen. The particles are harvested by
scraping them off the finger and are collected, still protected by the
inert gas, for further processing. Alloy particles are made using dual
sources, as shown in Figure 8.2. The main problem with this method
is that as the particles form, they tend to cluster and increase their
257
Nanomaterials: Synthesis and
Characterization
c hapter 8
Nanomaterials, Nanotechnologies and Design
Copyright 2009 Elsevier Ltd. All rights of reproduction in any form reserved.
MaterialS and StructureS
There are many ways of making nanoscale materials and structures.
Figure 8.1 orders them in the same matrix as that of Chapter 6. It
gives an overview, showing where each fits. We start our discussion
at the upper left: processes to make discrete, nanoscale clusters.
Methods for Making 0-d nanomaterials
Nanoclusters are made by either gas-phase or liquid-phase processes. We start with those using the gas phase, the commonest of
which are inert-gas condensation and inert-gas expansion. Liquid
phase processes use surface forces to create nanoscale particles and
structures. There are broad types of these processes: ultrasonic dispersion, sol-gel methods, and methods relying on self-assembly.
inert-gas condensation
In inert-gas condensation, an inorganic material is vaporized inside a
vacuum chamber into which an inert gas (typically argon or helium)
is periodically admitted (see Figure 8.2). The source of vapor can be
an evaporation boat, a sputtering target, or a laser-ablation target.
Once the atoms boil off, they quickly lose their energy by colliding
with the inert gas. The vapor cools rapidly and supersaturates to
form nanoparticles with sizes in the range 2–100 nm that collect
on a finger cooled by liquid nitrogen. The particles are harvested by
scraping them off the finger and are collected, still protected by the
inert gas, for further processing. Alloy particles are made using dual
sources, as shown in Figure 8.2. The main problem with this method
is that as the particles form, they tend to cluster and increase their
257
Nanomaterials: Synthesis and
Characterization
c hapter 8
Nanomaterials, Nanotechnologies and Design
Copyright 2009 Elsevier Ltd. All rights of reproduction in any form reserved.