9.5.3 Nanowire synthesis
Two general concepts exist for nanowire synthesis, each with their own
unique synthetic strategies. The “top-down” approach is one such
concept. In this approach, nanowires are synthesized starting from a bulk
substrate from which material is removed until only a field of nanowires
remain. Nanolithography and electrophoresis are examples of the topdown techniques employed to make nanowires. However, it is difficult
using current instruments to synthesize ideal one-dimensional nanowires
via top-down methods. The instruments and techniques are currently
limited by the length and width of the nanowires they can synthesize as
well as the general accuracy they exhibit when working on a substrate. For
these reasons, the top-down approach is presently less commonly
employed than its alternative.
The “bottom-up” approach synthesizes nanowires by continuously
extending a thread of bound molecules. Various techniques have developed using the bottom-up approach including suspension-based techniques, where a nanowire is elongated in a vacuum using chemical
etching or ion-bombardment techniques, and vapor–liquid–solid (VLS)
techniques, where a nanowire is synthesized via a catalyst converting a
vapor into a solid below the catalyst, continuously elongating the chain of
solid molecules (Crossland et al., 2007). Solution-based bottom-up
techniques hold particular promise since they allow scientists to synthesize nanowires in much larger numbers than alternative methods. One
particularly intriguing solution-based technique uses copolymers to form
templates inside which nanowires can be synthesized (Figure 9.22).
Certain copolymers are ideal for template formation because, at the
correct temperature and electric field strength, they form evenly spaced
hexagonal pores. Once the substrate is added, these pores serve as the
locations for nanowire synthesis. Mild reagents can then be used to
degrade the template and isolate the nanowires.
9.5.4 Summary
Nanowires have great potential. As the field grows, we will begin to see
new synthetic techniques capable of producing highly elongated
nanowires in large quantities. These techniques will be exceedingly
precise, allowing for wire shape and function to be maintained during the
entirety of the nanowire synthesis. As the study of nanowires continues to
progress, new imaging devices will be forced to develop in parallel to
NANOWIRES 369
Two general concepts exist for nanowire synthesis, each with their own
unique synthetic strategies. The “top-down” approach is one such
concept. In this approach, nanowires are synthesized starting from a bulk
substrate from which material is removed until only a field of nanowires
remain. Nanolithography and electrophoresis are examples of the topdown techniques employed to make nanowires. However, it is difficult
using current instruments to synthesize ideal one-dimensional nanowires
via top-down methods. The instruments and techniques are currently
limited by the length and width of the nanowires they can synthesize as
well as the general accuracy they exhibit when working on a substrate. For
these reasons, the top-down approach is presently less commonly
employed than its alternative.
The “bottom-up” approach synthesizes nanowires by continuously
extending a thread of bound molecules. Various techniques have developed using the bottom-up approach including suspension-based techniques, where a nanowire is elongated in a vacuum using chemical
etching or ion-bombardment techniques, and vapor–liquid–solid (VLS)
techniques, where a nanowire is synthesized via a catalyst converting a
vapor into a solid below the catalyst, continuously elongating the chain of
solid molecules (Crossland et al., 2007). Solution-based bottom-up
techniques hold particular promise since they allow scientists to synthesize nanowires in much larger numbers than alternative methods. One
particularly intriguing solution-based technique uses copolymers to form
templates inside which nanowires can be synthesized (Figure 9.22).
Certain copolymers are ideal for template formation because, at the
correct temperature and electric field strength, they form evenly spaced
hexagonal pores. Once the substrate is added, these pores serve as the
locations for nanowire synthesis. Mild reagents can then be used to
degrade the template and isolate the nanowires.
9.5.4 Summary
Nanowires have great potential. As the field grows, we will begin to see
new synthetic techniques capable of producing highly elongated
nanowires in large quantities. These techniques will be exceedingly
precise, allowing for wire shape and function to be maintained during the
entirety of the nanowire synthesis. As the study of nanowires continues to
progress, new imaging devices will be forced to develop in parallel to
NANOWIRES 369