Telescopes and Microscopes
Tools like the telescope and microscope have led the recent explosion
of knowledge of our universe. Today telescopes allow us to see
galaxies 13 billion light-years away (1025 m) and
microscopes allow us to see even single atoms (about 10-10
m)! Discoveries made with telescopes have shaped current theories
about the nature and origin of the universe. Discoveries made
with microscopes have shed light on the nature and origin of
the matter that makes up the universe and on the nature and
origin of life.
Space has often been called the "final frontier" but the micro/nano
universe is an equally unknown frontier that exists all around
us right here on earth. In exploring outer space we probe the
secrets of galaxies, stars and planets with telescopes. In exploring
micro/nano space we probe the secrets of cells, molecules and
atoms with microscopes. Often times, discoveries made in micro/nano
space can teach us about outer space and vice-versa.
Scale of our material world, from galaxies to atoms
Many people are fascinated with outer space. The discovery of
distant galaxies and planets that might sustain extra-terrestrial
life stir the imagination. It is largely because of this fascination
that Galileo's discoveries with the telescope are among the
most well known in history. Although the names of those who
made discoveries with the microscope may be less well known,
the discoveries they made about terrestrial life and matter
are just as worthy of recognition. As telescopes were developed
and we saw greater and greater distances, we learned more and
more about the universe. As microscopes developed and we saw
smaller and smaller distances, we learned more and more about
the micro/nano universe.
The development of three major types of microscopes over time
is outlined in the graph above. To learn more about some of the
events along the way, click on the different parts of the map.
Figure 2: A brief overview
of history of microscopes. Roll your mouse over various areas
of the graph to read more about it.
The optical microscope is aptly named since it is often used
to resolve objects in the micrometer (10-6m) range.
Meanwhile, electron microscopes (EM) and scanning probe microscopes
(SPM) are often used to resolve objects a thousand times smaller
than the micrometer. These tools can resolve objects in the
nanometer (10-9m) range. Although we still call EM
and SPM "microscopes," it might be more appropriate to label
them "nanoscopes." As we continue to use and develop these micro
and nanoscopes we continue to learn more about the new micro/nano
frontier, the home of the building blocks of life and matter.
The first microscopes were optical microscopes. These early visualization
tools used glass lenses to focus and magnify light. Major scientific
discoveries began about 60 years after the invention of the microscope.
As optical microscopes improved, smaller and smaller objects could
be seen and more and more discoveries were made.
|Figure 3: A modern
|Figure 4: Images taken
with an Optical microscope
Optical microscopes are by far the most common types of microscopes
and are still important in the exploration of the micro/nano
universe today. A good optical microscope can generally distinguish
objects as small as 200nm (2 X 10-7
m). 200nm are about the diameter of a large virus or very small
bacterium, such as mycoplasm.
|Figure 5: A Trans-
The limit of resolution for optical microscopes, about 200nm,
is a physical limit imposed by the wavelength of light. While
this is very small, it is still more than 1000 times larger than
the diameter of a carbon atom. Since optical resolution is limited
by light, visualization of objects smaller than 200nm had to come
from a microscope that does not use light. Electron microscopes
use accelerated electrons instead of light, and magnetic coils
instead of glass lenses to make an image.
|Figure 6: Images
a Scanning Electron Microscope
The electrons have an associated wavelength that is 10 to 100
thousand times smaller than the wavelength of light. Because
of this, electron microscopes are not limited by wavelength
and are able to resolve objects 1000 times smaller than the
smallest resolvable object in a light microscope. The electron
microscope has extended our vision into the realm of sub-cellular
organelles, viruses, proteins, DNA, molecules and even atoms.
It has radically changed all science and engineering.
|Figure 7: An Atomic
Electron microscopes are invaluable tools for the exploration
of the micro/nano universe, but have many limitations. In general,
samples must be examined under a vacuum and require careful preparation.
However, the newest family of microscopes, called scanning probe
microscopes (SPM) can achieve electron microscope resolution in
plain air or even liquid. Also, SPM samples require much less
preparation than electron microscope samples. This has enabled
imaging of many more types of samples, including living cells.
|Figure 8: An ant's
taken with an AFM. The head of
an ant is too large for an AFM.
Scanning probe microscopes can visualize a sample surface in three
dimensions and make micro/nano images of sample properties that
other microscopes cannot see. These include thermal properties,
friction, hardness, magnetic properties and chemical binding.
Instead of using light or focussed electrons, scanning probe microscopes
use a tiny needle like probe attached to a cantilever that is
scanned back and forth across a surface. The interactions between
the probe and the atoms composing the sample can be recorded and
processed to form an image. These images are changing the way
we see the micro/nano universe.