Senior Secondary Science Programme
Probing into nano scale
Teachers' Notes
Subject
Physics
Level
S4-S6
Duration:
17 minutes
Key Points
1. Physical properties of materials in nano scale.
2. Seeing at nano scale
3. The basic working principle of transmission electron microscope
The programme consists four segments:
1.
What is nano?
Nano is the unit of length. One nano equals one billionth of a metre. One tenth of a metre
roughly equals the size of the palm of a child; the size of one hundredth of a metre is the skin
surface; one thousandth of a metre can see the smaller parts of the skin surface; one ten
thousandth of a metre gives us the view of the cells of the body; one hundred thousandth of a
metre shows us the chromosome; one millionth of a metre reveals the fabric of chromosome;
one ten millionth of a metre, that is 100 nanometres, displays the structures of the fabric of
chromosome; one hundred millionth of a metre, that is 10 nanometres, exhibits the double
helix of DNA; one billionth of a metre, that is 1 nanometre, can see the molecular structure of
DNA.
2.
Transmission Electron Microscope
A transmission electron microscope consists of two parts: an electron gun and the magnetic
lens system. When the cathode is heated, it emits electrons. The electrons are accelerated by
the high electric potential of the anode. The electrons are then focused by the magnetic
condenser lens so that a unidirectional electron beam is formed.
The electron beam is
directed onto the object being observed and the transmitted electrons record the details of the
object. The transmitted beam is further deflected by the objective lens and projection lens to
magnify the image.
3. Different Forms of Nano Material
Nano materials refer to materials with dimension of size between 1 to 100 nm. Nano materials
can exist in different forms and each form has different shapes and structures. Examples are
nano wire, nano tube and nano particle. Scientists can engineer heaps of exotic new materials,
such as transparent materials that can conduct electricity and glue with high thermal
conductivity. When an object is subdivided into smaller and smaller pieces, the ratio of total
surface area to volume will increase. The increase in surface area will increases the rate of
chemical reaction, the ability of absorption and the catalytic action. Since the ratio of surface
area to volume of nano materials is enormous, structures which usually not stable under normal
condition can be stable at nano scale. It was known that carbon only includes “graphite in which
carbon atoms layered in flat surface” and “diamond in which carbon atoms in tetrahedral
structure” until the discovery of C60 in the 80s of the last century. C60 is a closed structure
composed of 60 carbon atoms arranged in the form of a hollow ball, usually called buckyball.
Its structure is exactly the same as a football, a combination of 20 hexagons and 12 pentagons.
Apart from C60, C70, C76, C78, C82 have subsequently been discovered.
These spherical
shells of carbon are called fullerene.
4. Carbon Nanotube
Beside arranging in spherical shape, carbon atoms can be arranged in many other ways to
produce other forms of carbon. Carbon nanotubes are hollow tubes made of carbon.
single-walled carbon looks like a seamless steel cylinder.
A
It is rolled from a single atomic
layer of graphite sheet, with a diameter ranging from one tenth of a nanometre to few ten
nonometres. Multi-walled carbon nanotubes are rolled from a few layers of graphite sheets,
forming a concentric cylinder. Nanotubes are not only special in their shapes; their physical
properties are also very interesting. Carbon nanotubes have variable conductivity. Depending on
the rolling direction of the graphite sheet and the diameter of the formed tube, it is interesting to
find that a single-walled carbon nanotube can be a conductor or a semiconductor. Carbon
nanotube is the thinnest material that can be found till today. Through it is very thin, its
mechanical strength is 50 to 100 times stronger but its weight is just one sixth of steel. Because
of their light, stiff composition, the tubes have also begun turning up in high-end sporting
equipment such as bike handlebars and golf-club shafts. The application of nanotubes on screen
display is one of the key researches in recent years.
Suggested Learning Activities
Preparation before viewing the programme
1.
Teacher may discuss with students how they know about nano.
Activities after viewing the programme
1.
2.
Student may, under the guidance of teacher, review the physical concepts presented in the
programme.
The teacher may discuss with students why nano is so important to modern technology.