208
6.
SECTION MOUNTING
6.9. Stripping Pure Carbon Films
Carbon films evaporated on glass surfaces ordinarily cannot be stripped;
this has prevented the exploitation of this potential method. As will be
seen later, however, specially prepared glass surfaces can be used. However, freshly split mica is a good substrate, and carbon films can be floated
from this easily.
Pieces of mica, approximately an inch square, are split just before use.
A clean razor blade can be used for this purpose, but be sure not to contaminate the fresh mica surface with oil or grease films that may coat
new blades. Enough carbon is evaporated to discolor decidedly the porcelain marker as in Fig. 23(e). Then the film is floated off on a clean
water surface by dipping the mica under the water at a low angle. Breathing on the film to "frost" it with condensed moisture droplets seems to
help, but ordinarily there will not be difficulty in stripping the film. As
one corner of the mica is submerged, the operator should pause and be
sure the film is separating. It can, of course, be seen by reflected light. If
separation will not start in one place, it probably will in another. Spencer (1959) indicates his belief that 10% acetone, which can be expected
to reduce surface tension, is less hazardous than pure water. But films are
not apt to lift when stronger solutions are used.
Carbon films that are stripped from mica surfaces do not look particularly smooth to the naked eye as they float upon the water surface. However, on the small scale they are beautifully smooth and uniform.
To mount the carbon films, individual grids are submerged below the
water surface while being held by fine pointed forceps. They are slowly
lifted out of the water through the floating carbon film and transferred to
filter paper for drying.
Unfortunately, carbon films do not adhere well to copper grids. However, it is possible to precoat the grid wires with an adhesive that helps.
This author has, from time to time, used an extremely dilute solution of
rubber cement in carbon tetrachloride. Or, the adhesive on a short length
(about 4 in.) of cellophane tape can be dissolved in an ounce of chloroform. The grids should be dipped in this and quickly dried on filter paper. The adhesive must be so dilute that there is no tendency for it to
form films or strands across the grid openings.
Evaporated carbon films apparently do not adhere strongly to a truly
6.
SECTION MOUNTING
6.9. Stripping Pure Carbon Films
Carbon films evaporated on glass surfaces ordinarily cannot be stripped;
this has prevented the exploitation of this potential method. As will be
seen later, however, specially prepared glass surfaces can be used. However, freshly split mica is a good substrate, and carbon films can be floated
from this easily.
Pieces of mica, approximately an inch square, are split just before use.
A clean razor blade can be used for this purpose, but be sure not to contaminate the fresh mica surface with oil or grease films that may coat
new blades. Enough carbon is evaporated to discolor decidedly the porcelain marker as in Fig. 23(e). Then the film is floated off on a clean
water surface by dipping the mica under the water at a low angle. Breathing on the film to "frost" it with condensed moisture droplets seems to
help, but ordinarily there will not be difficulty in stripping the film. As
one corner of the mica is submerged, the operator should pause and be
sure the film is separating. It can, of course, be seen by reflected light. If
separation will not start in one place, it probably will in another. Spencer (1959) indicates his belief that 10% acetone, which can be expected
to reduce surface tension, is less hazardous than pure water. But films are
not apt to lift when stronger solutions are used.
Carbon films that are stripped from mica surfaces do not look particularly smooth to the naked eye as they float upon the water surface. However, on the small scale they are beautifully smooth and uniform.
To mount the carbon films, individual grids are submerged below the
water surface while being held by fine pointed forceps. They are slowly
lifted out of the water through the floating carbon film and transferred to
filter paper for drying.
Unfortunately, carbon films do not adhere well to copper grids. However, it is possible to precoat the grid wires with an adhesive that helps.
This author has, from time to time, used an extremely dilute solution of
rubber cement in carbon tetrachloride. Or, the adhesive on a short length
(about 4 in.) of cellophane tape can be dissolved in an ounce of chloroform. The grids should be dipped in this and quickly dried on filter paper. The adhesive must be so dilute that there is no tendency for it to
form films or strands across the grid openings.
Evaporated carbon films apparently do not adhere strongly to a truly