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substrate
picture
electron
optics
electron gun
Fig. 1.8 Scheme of the scanning electron microscope
should be the wavelength of electrons, and this necessitates an increase of their
energy. In its turn, higher energy of the electrons incident on the specimen results in
a weakened interaction with matter, primarily with light atoms. Therefore, the
image loses contrast. Various techniques have been developed to improve the
image obtained by high-energy electrons. One possibility is to spray a thin layer
of heavy atoms, such as tungsten, on the studied object. However, this generally
causes the distortion of the information received. To a major degree, the way out of
this situation was the creation of the scanning electron microscope (Fig.
1.8
).
In it the electron beam is reflected from the surface of the investigated specimen,
and the resulting image is recorded with the electron-optical system. Scanning
electron microscope allows to obtain contrasting images of objects. Several typical
examples shown in Fig.
1.9
include:
• The head of mosquito with magnification of 200 (A) and 1000 (B) times
• Bird blood
• Crystalline silver dendrites
However the resolution power of scanning electron microscopes is much lower
compared to transmission microscopes. The minimum size of structural features
that can be registered amounts to merely a few nanometers.
In the 1970s-1980s of the last century, different versions of electron micro-
scopes were refined to become convenient commercially available tools. Neverthe-
less, they could not meet the needs of nanotechnological research. A dramatic
turning point occurred in the early 1980s, when the scanning tunneling microscope
was created.
In 1981 Gerd Binnig and Heinrich Rohrer at the IBM research laboratories in
Zurich created the first scanning tunneling microscope. The significance of this
work is apparent from the fact that just 5 years later, in 1986, they won the Nobel
