Molecular beam epitaxial growth of III-V semiconductor ... - KOBRA

Experimental Growth and Characterization Techniques
of the specimen which is then magnied by the remaining imaging lenses and
projected onto the viewing device.
Figure 4.6: Transmission electron microscopy. (a) Electron beam prole passing
through dierent lenses and apertures. (b) Real TEM scheme with its main components
embedded in vacuum column or chamber [74].
When electrons impinge on the specimen, this can cause some of the electrons
are absorbed as a function of the thickness and composition of the specimen;
these cause what is called amplitude (or mass thickness) contrast in the image.
Other electrons are scattered over small angles, depending on the composition
and structure of the specimen; these cause what is called phase contrast in the
image. However, in crystalline specimens, the electrons are scattered in very distinct
directions that are a function of the crystal structure; these cause what is
called diraction contrast in the image. In a standard TEM, mass thickness is
the primary contrast mechanism for non-crystalline (biological) specimens, while
phase contrast and diraction contrast are the most important factors in image
formation for crystalline specimens (most non-biological materials). Therefore,
collimated high-energy electrons from a condenser lens impinge on the semiconductor
specimen and are transmitted through it. The electrons are scattered into
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