Nano is an abbreviation of nanometer (nm) which
is a unit of length. It is one billionth of a meter, a very
small length indeed. The diameter of human's hair is about
sixty thousand to eighty thousand nanometers. If we could
put hydrogen atoms together, one nanometer would approximately
equal to the length of ten hydrogen atoms that put together
in a line. A material is called the nano-material if the size
of the material is below 100 nm. You may wonder why 100 nm
but not 1000 nm or 10 nm? This is because many physical and
chemical properties of the material change significantly when
its size is below 100 nm. For instance, the surface effect
will play a major role for nano-material. Suppose we have
a cube with side a, the surface area is 6 aa.
If we divide it into eight (222)
smaller cubes each with side a/2, then the total surface area
is 86(a/2)(a/2)=12aa.
In general, we can divide it into NNN
smaller cubes each with side a/N, the total surface area is
N6aa.
We conclude that the smaller the cubes, the larger the total
surface area to volume ratio. Therefore if we have a gram
of gold grains whose size is below 100 nm the surface of the
grain will become very important. We know that the atoms on
the material surface are highly unstable and very active in
the chemical reaction. As a result, the increasing of the
surface area will greatly enhance the chemical reaction, the
ability of surface absorption, and the catalytic ability of
the material. In addition, the ability of heat conduction,
mechanical strength, as well as optical property of the nano-materials
are also very different from that of bulk system. For example,
the melting point of metal gold is about 1000
whereas for the nano sized gold grains with typical size of
2 nm, the melting point is down to 330 .
The absorption of ultra violet of some nano materials can
be enhanced significantly. Furthermore, new effects start
to manifest when the size is below 100 nm. Hence a class of
new materials emerges at nano scale.
Can we make nano-sized material? Can we create new materials
using clusters of molecules or atoms as building blocks? The
answer is yes. Such nano-technology exist now and due to its
advance the nano-science becomes possible. To move atoms individually
has been the dream of scientists for a long time. The Nobel
laureate Richard Feynman said in 1959 "The problems of
chemistry and biology can be greatly helped if our ability
to see what we are doing, and to do things on an atomic level,
is ultimately developed --- a development which I think cannot
be avoided." Indeed, one can manipulate atoms now using
Scanning tunneling microscope (STM). A STM is a device for
imaging surfaces of materials with very high magnification,
down to atomic scale. Using STM one can create various exciting
atomic structures (see Fig.1: Xenon on Nickel). The invention
of STM is really revolutionary and essential for the study
of nano science. Because of this it won the Nobel Prize in
physics in 1986.
(Figure 1- This photo was downloaded
from STM Image Gallery website http://www.almaden.ibm.com/vis/stm/atomo.html)
Besides the interest from the fundamental science,
another driving force of nano science is of course the potential
device applications. We know that many of our daily electrical
appliances consist of transistors as basic components. The
first transistor is made in 1941 whose size is about one cubic
cm. The scientist who invented the transistor later won the
Nobel Prize in physics in 1956. Due to the advance of modern
technology, the size of transistor that one can make becomes
smaller and smaller. Consequently, the number of transistors
that can be put in a computer chip doubles in every 18 months.
This is so called Moore's law. In 1991, a computer chip of
size one cubic cm contains about three million transistors.
According to Moore's law, the dimension of the transistor
in the computer chip will reach 130 nm in the near future.
In such a small length scale, previous traditional technology
of fabricating transistor can no longer be used. New nano
technology has to be developed. More importantly, new physical
laws will emerge in such a small dimension.
Why nano science: it offers one of the most
exciting prospects for new phenomena, new materials, and new
science. Some people believe that it will lead to a new industrial
revolution. Roughly speaking, the nano technology has been
applied to the four disciplines: (1). nano electronics: new
electronic devices with novel functions and the advantage
of high speed and at the same time consuming less energy power.
(2). nano material science: new materials with novel properties,
which grow perfectly without any impurities and defects, ideal
for nano devices. (3). nano biology including mapping the
genetic information in DNA and RNA molecules. (4). nano medicine:
discover, design, and deliver new drugs on nano level.
Currently the nano science and technology has
been a "hot" project in many countries who invest
tremendous amount of money. For instance, in early 2000 United
States former president Clinton announced the "national
nano technology initiative" and put in 225 million US
dollars for this plan. In 2001, the amount of research funding
doubles. In Japan, the nano science and technology is one
of the four key areas of future development with total research
grant over 380 million US dollars. In Europe, the five-year
plan for nano science and technology (99-03) in ongoing. In
China, huge amount of research grants are available for nano
science.
The application of nano science and technology
has a huge market worldwide with market value over 50 billion
US dollars in 2000, most of it is in the application of nano
materials. Germany predicted that the market value in the
year 2010 will be over 1 trillion US dollars. People believe
that the application of nano biology and nano medicine will
have a breakthrough in the near future. However, for the full
application of nano electronics, which is the most important
area in nano science and technology, we probably have to wait
for some 20 years.
One of the examples of nano-materials is the
Carbon nanotube: a man-made nano-material which can not be
found in nature. It has many interesting physical and chemical
properties and many of them have great potential device application.
There are four kinds of structure made of Carbon: (1). diamond
structure. (2). graphite (honeycomb) structure: pencil lead.
(3). Carbon 60: Buckyball (its discovery won 1996 Nobel Prize
in chemistry). (4). Carbon nanotube (CNT): by rolling up a
graphite sheet (see Fig.2) as a cylinder like a straw. Different
ways of rolling the graphite sheet give different kinds of
CNT: armchair nanotube, zigzag nanotube, and chiral nanotube.
For instance, connecting the coordinates (0,0) and (5,5) gives
an armchair structure denoted as (5,5); connecting (0,0) and
(9,0) gives a zigzag structure (9,0); connecting (0,0) and
(6,2) gives chiral structure (6,2). The first CNT was discovered
by a Japanese scientist Iijima in 1991. The smallest CNT in
the world has been made in 2001 at The Hong Kong University
of Science and Technology by a group of physicists. The diameter
is around 0.4 nm. Depending on different ways of rolling,
CNT could be good or poor conductor. It has very good mechanical
properties as well. For instance, it is about 100 time stronger
than steel with only one sixth of the weight. They can sustain
large force without breaking up. The scientists are exploring
ways to blend CNTs with plastics and ceramics to produce new
composites with unprecedented strength to weight ratios and
high conductivity. For example, it is found that by adding
one to five percent of CNT into epoxy resin, the hardness
will be increased by three-fold.
(Figure 2a )
(Figure 2b)
(1). A new ceramics (or porcelain) material.
As is well known that the traditional ceramics is very brittle
with poor tenacity and strength. The ceramics made of nano
sized material has high hardness and good tenacity. One can
even make a spring from the new ceramics material. Hard to
believe, isn't it?
(2). A new way of cancer treatment. In 2002,
a hospital in Germany developed a new way of cancer therapy
using nano technology. Traditional method is to expose part
of human body with cancer tumor in the electromagnetic radiation
so that the temperature of the tumor is raised to 40
in order to kill the cancer cells. However, large portion
of the normal around the cancer cells are also damaged. The
new method is to inject nano sized particle  into
the cancer tumor. In the time varying magnetic field, the
temperature of the nano sized
will rise to 45
which will kill the cancer cell and leaving the normal cell
intact.
(3). The nano sized  and
 have
strong absorption to the ultra violet. We all know that the
ultra violet in the sun light is very harmful to the human
being. If these nano sized materials such as
are used to make Sun-block lotion or Sun-screen make-ups.
The damage of the ultra violet radiation to human can be greatly
reduced.
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