6.6.
CARBON STABILIZATION OF NAKED SECTIONS
205
required which the investigator will have to learn by experience. However, the porcelain should be decidedly darkened as in Fig. 23(e).
There is some evidence (Renshaw and Schneidmiller, 1958) that the
strongest carbon films are those produced most rapidly at temperatures
substantially above the minimum required to evaporate carbon. One can
design a holder for carbon rods in such a way that a controlled amount
of carbon is evaporated at high temperature, and then the machine automatically shuts itself off. This is done most simply by planning to evaporate a given length of narrow carbon shaft. Tips are made essentially
as in Fig. 23(b). A stiff spring drives one carriage into the other, and an
adjustable stop is added which can be set to limit the movement of this
carriage so that a known short length of the tip can be evaporated, and
then the advance is stopped. A predetermined amperage can be applied
suddenly by throwing a switch. The carbon tips are heated in the most
rapid way possible, and the full complement of carbon is vaporized almost explosively with sparks flying. A disadvantage of the method is that
the shower of incandescent carbon chips can damage the film as it is being
made.
6.6. Carbon Stabilization of Naked Sections
Carbon can be evaporated directly on naked sections after these have
been picked up on screens. The carbon film so formed will stabilize methacrylate and give it necessary support. A very thin film of carbon suffices,
one which barely begins to darken the porcelain indicator [Fig. 23(d)].
No other method is capable of producing a more electron-transparent
support. There are limitations and inconveniences to the method, however, so that more elegantly prepared supporting films are desirable in
many instances.
It is possible that evaporating carbon directly upon methacrylate sections sometimes produces a fine order damage which destroys their usefulness for high resolution work. The damage, when it occurs, probably
is from heat coming from the intense bombardment of the methacrylate
by the infrared radiation inevitably present as the carbon is evaporated
at over 3500°C. This damage is not likely to be detectable at moderate
magnifications so the method is quite applicable to survey work and its
CARBON STABILIZATION OF NAKED SECTIONS
205
required which the investigator will have to learn by experience. However, the porcelain should be decidedly darkened as in Fig. 23(e).
There is some evidence (Renshaw and Schneidmiller, 1958) that the
strongest carbon films are those produced most rapidly at temperatures
substantially above the minimum required to evaporate carbon. One can
design a holder for carbon rods in such a way that a controlled amount
of carbon is evaporated at high temperature, and then the machine automatically shuts itself off. This is done most simply by planning to evaporate a given length of narrow carbon shaft. Tips are made essentially
as in Fig. 23(b). A stiff spring drives one carriage into the other, and an
adjustable stop is added which can be set to limit the movement of this
carriage so that a known short length of the tip can be evaporated, and
then the advance is stopped. A predetermined amperage can be applied
suddenly by throwing a switch. The carbon tips are heated in the most
rapid way possible, and the full complement of carbon is vaporized almost explosively with sparks flying. A disadvantage of the method is that
the shower of incandescent carbon chips can damage the film as it is being
made.
6.6. Carbon Stabilization of Naked Sections
Carbon can be evaporated directly on naked sections after these have
been picked up on screens. The carbon film so formed will stabilize methacrylate and give it necessary support. A very thin film of carbon suffices,
one which barely begins to darken the porcelain indicator [Fig. 23(d)].
No other method is capable of producing a more electron-transparent
support. There are limitations and inconveniences to the method, however, so that more elegantly prepared supporting films are desirable in
many instances.
It is possible that evaporating carbon directly upon methacrylate sections sometimes produces a fine order damage which destroys their usefulness for high resolution work. The damage, when it occurs, probably
is from heat coming from the intense bombardment of the methacrylate
by the infrared radiation inevitably present as the carbon is evaporated
at over 3500°C. This damage is not likely to be detectable at moderate
magnifications so the method is quite applicable to survey work and its