Callister - An introduction - 8th edition

754 • Chapter 18 / Electrical Properties
Figure 18.27 Top: Scanning
electron micrograph of an
integrated circuit.
Center: A silicon dot map for the
integrated circuit above, showing
regions where silicon atoms are
concentrated. Doped silicon is the
semiconducting material from
which integrated circuit elements
are made.
Bottom: An aluminum dot map.
Metallic aluminum is an electrical
conductor and, as such, wires the
circuit elements together.
Approximately 200.
Note: the discussion of Section
4.10 mentioned that an image is
generated on a scanning electron
micrograph as a beam of electrons
scans the surface of the specimen
being examined. The electrons in
this beam cause some of the
specimen surface atoms to emit x-
rays; the energy of an x-ray
photon depends on the particular
atom from which it radiates. It is
possible to selectively filter out all
but the x-rays emitted from one
kind of atom. When projected on
a cathode ray tube, small white
dots are produced that indicate
the locations of the particular
atom type; thus, a dot map of the
image is generated.
100 m
integrated circuits are shown in Figure 18.27 and in the (a) chapter-opening photographs
for this chapter.
Electrical Conduction
in Ionic Ceramics and in Polymers
Most polymers and ionic ceramics are insulating materials at room temperature
and, therefore, have electron energy band structures similar to that represented
in Figure 18.4c; a filled valence band is separated from an empty conduction band
by a relatively large band gap, usually greater than 2 eV. Thus, at normal temperatures
only very few electrons may be excited across the band gap by the
available thermal energy, which accounts for the very small values of conductivity;
Table 18.4 gives the room-temperature electrical conductivities of several