5
structures should not be affected by quantum effects. In terms of
Brownian motion, we should consider the nanocomponents as harmonic oscillators. In this context, molecular collisions are as likely
to absorb energy as to release it, and thus no net effect is expected.
Finally, in regard to friction and wear effects at the nanoscale, the
repulsive fields between the molecules should provide the necessary
lubrication. Products such as oil should be avoided because they
cause contamination. For example, a molecular bearing of 2 nm
rotating at 1 MHz dissipates about 10
−6 picowatts due to friction,
whereas a micron-size mechanical component dissipates 1–1000
picowatts (R. Freitas, Nanomedicine). In general, the skeptical
questions we’ve posed can be disqualified because so far, nanotechnology does not seem to violate any physical law.
What are the possible approaches to making nanomaterials and
nanotechnologies? There are basically two routes: a top-down
approach and a bottom-up approach. The idea behind the topdown approach is the following: An operator first designs and controls a macroscale machine shop to produce an exact copy of itself,
but smaller in size. Subsequently, this downscaled machine shop
will make a replica of itself, but also a few times smaller in size. This
process of reducing the scale of the machine shop continues until a
nanosize machine shop is produced and is capable of manipulating
nanostructures. One of the emerging fields based on this top-down
approach is the field of nano- and micro-electromechanical systems
(NEMS and MEMS, respectively). MEMS research has already produced various micromechanical devices, smaller than 1 mm
2
,
which are able to incorporate microsensors, cantilevers, microvalves, and micropumps. An interesting example is the microcar fabricated by Nippondenso Co. (see Figure 1.3). The car is 4800 µm
long, 1800 µm wide, and 1800 µm high. Each tire is 690 µm diameter and 170 µm wide, whereas the license plate is 10 µm thick. The
car has 24 components, including tires, wheels, axles, bumpers, all
parts assembled by a micromechanical manipulator.
Which technologies can be used to produce nanostructures using a
top-down approach? At the moment, the most used is photolithography. It has been used for a while to manufacture computer chips
and produce structures smaller than 100 nm. This process is discussed extensively in Chapter 8. Typically, an oxidized silicon (Si)
wafer is coated with a 1µm thick photoresist layer. After exposure to
ultraviolet (UV) light, the photoresist undergoes a photochemical
reaction, which breaks down the polymer by rupturing the polymer
chains. Subsequently, when the wafer is rinsed in a developing
solution, the exposed areas are removed. In this fashion, a pattern
Figure 1.3
Microcar produced by Nippondenso Co. The latest
model has a micromotor 1 mm in diameter. With
power supplied by a 25 micron copper wire, the
car runs smoothly at a speed of about 1 cm/s
with 3 V voltage and 20 mA current. (Courtesy of
Nippondenso.)
Why Nanomaterials?
structures should not be affected by quantum effects. In terms of
Brownian motion, we should consider the nanocomponents as harmonic oscillators. In this context, molecular collisions are as likely
to absorb energy as to release it, and thus no net effect is expected.
Finally, in regard to friction and wear effects at the nanoscale, the
repulsive fields between the molecules should provide the necessary
lubrication. Products such as oil should be avoided because they
cause contamination. For example, a molecular bearing of 2 nm
rotating at 1 MHz dissipates about 10
−6 picowatts due to friction,
whereas a micron-size mechanical component dissipates 1–1000
picowatts (R. Freitas, Nanomedicine). In general, the skeptical
questions we’ve posed can be disqualified because so far, nanotechnology does not seem to violate any physical law.
What are the possible approaches to making nanomaterials and
nanotechnologies? There are basically two routes: a top-down
approach and a bottom-up approach. The idea behind the topdown approach is the following: An operator first designs and controls a macroscale machine shop to produce an exact copy of itself,
but smaller in size. Subsequently, this downscaled machine shop
will make a replica of itself, but also a few times smaller in size. This
process of reducing the scale of the machine shop continues until a
nanosize machine shop is produced and is capable of manipulating
nanostructures. One of the emerging fields based on this top-down
approach is the field of nano- and micro-electromechanical systems
(NEMS and MEMS, respectively). MEMS research has already produced various micromechanical devices, smaller than 1 mm
2
,
which are able to incorporate microsensors, cantilevers, microvalves, and micropumps. An interesting example is the microcar fabricated by Nippondenso Co. (see Figure 1.3). The car is 4800 µm
long, 1800 µm wide, and 1800 µm high. Each tire is 690 µm diameter and 170 µm wide, whereas the license plate is 10 µm thick. The
car has 24 components, including tires, wheels, axles, bumpers, all
parts assembled by a micromechanical manipulator.
Which technologies can be used to produce nanostructures using a
top-down approach? At the moment, the most used is photolithography. It has been used for a while to manufacture computer chips
and produce structures smaller than 100 nm. This process is discussed extensively in Chapter 8. Typically, an oxidized silicon (Si)
wafer is coated with a 1µm thick photoresist layer. After exposure to
ultraviolet (UV) light, the photoresist undergoes a photochemical
reaction, which breaks down the polymer by rupturing the polymer
chains. Subsequently, when the wafer is rinsed in a developing
solution, the exposed areas are removed. In this fashion, a pattern
Figure 1.3
Microcar produced by Nippondenso Co. The latest
model has a micromotor 1 mm in diameter. With
power supplied by a 25 micron copper wire, the
car runs smoothly at a speed of about 1 cm/s
with 3 V voltage and 20 mA current. (Courtesy of
Nippondenso.)
Why Nanomaterials?