By: Handijaya Soedradjat
Nanowires: Changing Technology, Changing Lives
Abstract
Nanowires are unlike any other materials because they can act as conductors, insulators
or semiconductors. Even though big companies such as IBM and Intel are currently
experimenting with using nanowires in their chips, these materials still belong in
laboratories. Currently, methods for growing nanowires are inefficient and researchers
have not been able to find the ideal method to mass produce the right amount of
nanowires for commercial use. However, nanowires are the future of nanotechnology
because they have been proven to increase the efficiency of the solar panels, can act as a
“free” source of energy and can also convert lower grade energy to higher grade. It is
just a matter of time before nanowires can be used intensively and change the way we
live.
Introduction
Do you remember the evolution of phone sizes: from bulky phones to the sleekest designs
and sizes? Over the years, researchers have been exploring the use of nanotechnology to
create smaller yet more powerful devices. These devices come mainly in the form of
supercomputers that change how we do work in the 21st century. But the fundamentals
that make up these devices, such as the transistors and nanowires (nano sized chemical
bonds shaped like wires), are equally as important as the device.
The key to making processors faster is to speed up the transmission of electric signals by
adding as many transistors as possible in a given space. Since researchers are trying to
make devices smaller but faster, they have to rely on nanotechnology to create nanotransistors that come in the form of nanowires.
Nanowires (Fig. 1) are chemical structures grown in a chamber that look like slender
wires. They are about one billionth the size of an average ant and can only be seen using
certain microscopes. With the development of nanowires, it is now possible to
continuously manufacture and create smaller products that are more efficient. Upon
further study, researchers also discovered that nanowires could be used in a variety of
fields including solar panels, implantable devices, super computers and renewable “free”
sources of energy to increase efficiency.
http://www.iet.ntnu.no/files/images/NW_SEM_0.img_assist_custom-300x252.png
Figure 1: Vertical growth of nanowires
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By: Handijaya Soedradjat
Background of nanotechnology
The idea of creating micro-scale devices only began to surface in the late 1950s [1].
However, due to the lack of technological advancement at that time, the manufacturing
processes were only designed to produce materials in bulk. Thirty years later, a
breakthrough occurred when researchers discovered how to build micro-scale devices
such as micro-transistors and then invented the Atomic Force Microscopy (AFM),
microscopes that could image nanoscale particles [1]. Subsequently, the government
allocated significant funds to research projects that took advantage of the imaging
capability of AFM and focused on exploiting the potential of nanotechnology.
Researchers started to see the interactions between molecules and realized that these
molecules could be used as building blocks for other materials such as carbon
composites.
Nanowires specifically began to be developed and researched in the beginning of the 21st
century. Wagner and Ellis first discovered the method of growing nanowires while
working at Bell Labs [2]. Since then, researchers have discovered that nanowires are
unlike any other material. They can be designed to have various properties that include
conducting, insulating, and semiconducting [3], all depending on the user’s end goal.
This would be similar to having a multipurpose ball that could be used as a tennis ball, a
baseball or a ping-pong ball. These findings were crucial, as they connected all three
properties that contribute to the major improvements of supercomputers.
From those findings, researchers began to experiment using different materials to study
the effect of mechanical stress on nanowires. Upon further inspection, researchers found
that a handful of materials, such as zinc oxide nanowires were able to convert mechanical
energy into electrical signals upon application of pressure. In other words, these
nanowires could potentially become a power source. But the most important aspect of the
discovery was the biocompatibility of zinc oxide [4], which meant that electronic waste
could be recycled and reduced significantly. This might be the answer for the growing
crisis of electronic consumer waste we face today.
Growing method of nanowires
Even though some computer chips today have nanowire components, these materials
mostly still belong in laboratories. Scientists use a bottom up process to grow nanowires
on a substrate (pot) (Fig. 2) [5]. In other words, nanowires act like a plant: scientists use a
catalyst such as gold nanoparticles (functioning as seeds) to attract the formation of
nanowires on the substrate (functioning as a pot). Next, the substrate is put inside a
chamber filled with appropriate gases to create bonds which forms long wires or chains
of nanowires (analogous to the synthesis reaction with the sun, which causes the seeds to
eventually grow into plants). Nonetheless, this method is prone to failure because
researchers have not been able to successfully scale it up. The current method of
producing nanowires is inefficient as one “seed” only produces one “plant” [5]. However,
under commercial manufacturing conditions, nanowires would be needed in mass
quantities. For any given application, scientist would have to produce an array, with the
right amount of nanowires. However, if the array of nanowires were too dense and
compact, electrical signals sent between the nanowires would be distorted and might even
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cause an electrical failure [5]. This could be compared to a forest of trees that grew too
close to each other and are fighting for sunlight to survive. Therefore, the right spacing to
ensure nanowire growth is also essential. Currently, the method of growing nanowires is
not efficient and is just a matter of time before it is readily available for commercial use.
Figure 2 [5]: Illustration of the growth of Nanowires
Current uses of nanowires
Despite the impracticality of using nanowires in commercial applications, large processor
chip companies such as Intel and IBM have been using nanowires in their transistors for
semiconducting purposes (Fig. 3) [6]. The nanowires not only allow the companies to
reduce the size of the microchip, but they also make data transfer faster and more
effective. Since the chips are made of nanowires, which are smaller than the conventional
silicon material used, engineers are able to fit more transistors into a single chip. As a
result, this increases the efficiency and transfer speed of the electric signal, making the
processor faster. In addition, nanowires are being used in solar panels. Researchers found
that nanowires were able to concentrate and converge the intensity of sunlight while also
trapping heat; this is similar to a greenhouse effect. As a result, solar cell efficiencies
increased by fifteen times compared to those of conventional solar cells [7]. Nanowires
are also used in sensors. Since nanowires can achieve a large surface area to volume ratio
[8], the nanowires can increase the sensitivity and lifespan of the sensors dramatically
[9]. Even though the current uses of nanowires are still limited, they show great potential
for future applications.
http-//www.intechopen.com/source/html/16378/media/image13.png
Figure 3: Nanowires used as bridge in transistors
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Future developments and uses of nanowires
In a matter of years, nanotechnology will be the foundation of our lives. Researchers have
discovered that zinc oxide (ZnO) nanowires could generate “free” sources of electrical
energy (Fig. 4). This method of creating “free” energy follows the principle of the
piezoelectric effect, a phenomenon that produces electricity as a result of the mechanical
stress or pressure applied on the material [10]. Imagine hiking in a jungle, with no power
outlets nearby, when suddenly your handheld device runs out of battery power. With this
relatively new nanotechnology, you would not need to worry. It would be possible to
charge handheld devices on the go, without even needing to stop and to find a power
outlet. These nanowires could either be built inside the handheld device or be worn as a
belt. Imagine the future without needing to find power outlets or-the best part of itwithout needing to pay for electricity.
http://images.gizmag.com/hero/nanowire-nanogenerator
Figure 4: Nanogenerators made up of nanowires that are used to power a device
In addition, research conducted in South Korea has shown that piezoelectric nanowires
have the ability to become an electricity generator (Fig. 5). Researchers have shown that
nanowires could successfully convert sound of approximately one hundred decibels into
approximately fifty millivolts of alternating current [11]. This opens the possibility of
exploring the use of nanowires for handheld devices. As an example, these nanowires can
convert voices during calls into electric current that can act as a charging port for mobile
phones. This amazing discovery could be a stepping stone for greater engineering
efficiency and thus, our phones will never run out of battery power.
http://spectrum.ieee.org/image/1701849
Figure 5: Sound waves, creating pressure on strings of Zinc Oxide (ZnO) nanowires,
converting it into electrical signals.
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By: Handijaya Soedradjat
Nanowires are also known as one of the few materials that could effectively convert
lower-grade energy such as thermal energy into a higher-grade energy such as electrical
and mechanical energy; thermal energy is regarded as waste and low-grade energy
because it cannot be converted efficiently into other forms of useful energy. With this
discovery, thermal waste could be reused and cars would become more efficient; only
about 25-35% of fuel in a car is converted into useful energy, and the remaining is
converted into thermal waste. Therefore, with the advancement of nanowires, global
warming could potentially be reduced and efficiency could be increased.
Besides using nanowires in electronics and energy applications, they could also be used
in next-generation implantable devices. These devices are thought to be the future of
biomedical engineering and the extensive use of nanowires within them are extremely
important. Since nanowires are flexible and biocompatible, these devices could be placed
inside the human body safely, without the fear of chemical hazards or of breaking apart,
due to body movements [12]. In addition, since piezoelectric nanowires have the ability
to become a source of energy, they can be implanted for a long time without needing to
replace the batteries [13]. Imagine the future without needing to remember any medical
records. Just by scanning the implantable device, healthcare providers would be able to
retrieve all the medical records instantly.
Conclusion
Nanowires show great potential for many applications because they can function as
conductors, insulators or semiconductors, depending on the needs of the user. Nanowires
not only make our electronic devices relatively smaller, but they also increase the
effectiveness of transferring data and the efficiency of converting thermal energy into
higher-grade and more useful form of energy. Even though piezoelectric nanowires have
not been used commercially, studies have indicated that these materials will be of great
use in the future. A future is envisioned in which nanowires will allow us to charge our
handheld devices on the go, thus enhancing our communications. Nanowires will also be
used in implantable devices that would change the way we live. The next-generation
implantable devices will be more compatible with the human body because it is less
hazardous and flexible. The implantable devices will not need to be maintained regularly,
which means they can be placed in the human body for a long time. As the time goes by,
nanowires will make a huge difference in the way we live our lives. They will shape the
future and be a stepping stone toward greater innovations to come.
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