382
16.
VACUUM TECHNIQUE
gure 16—17, is supported in a bell jar at a distance of 7 cm. from
the face of a 10 cm. platinum disc cathode C, and the air pressure
is reduced to 0.004 mm. of mercury, a 10,000 volt transformer
maintaining a potential difference of 5000 volts across the discharge
sends a current of 10 milliamperes betWeen the electrodes. This
‘
'would be expected to deposit an opaque platinum mirror upon
_
the glass in the course of two hours. However, there are so many
variable factors entering into the phenomenon that accurate predictions are difcult to make.
Other conditions remaining the
same, the mass in grams deposited uniformly over unit area each
second (the rate of sputtering) is directly proportional to the rst
power of the current and inversely proportional to the rst power
of the distance from the cathode C to the plate G.
,
'
'
Two kinds of particles leave the cathode. One kind consists of '
.
,.
uncharged molecules or atoms of the cathode metal which diffuse
'
in all directions so that the plate, and to some extent the jar, become coated with a thin lm of the metal.
The other particles are
electrons Which leave the cathode at right angles and travel with
high velocity, causing considerable heating of the plate and jar.
These electrons may be deected by a small magnetic eld (10 to
25 oersteds) so as to prevent overheating the plate. The sputtering
is thought to be due to evaporation of the metal from small spots
on
the cathode surface which have been struck by ions falling
.
through the large potential drop in the cathode dark space.
The
'
ions come from the 'gas in the jar. Metals Which sputter With
_
diiculty in the residual air can be made to do so if certain gases,
such as argon, are used.
Gold, platinum, copper, iron, tungsten,
_
silver and nickel maybe deposited with comparative ease.in the
residual air, while aluminum and silicon are difcult to sputter.
Ï
-»
If the cathodedark space touches the plate where the deposit18
formed, the cross gradient of potential sets up large currents
.
the
blistering it.
_
…
Ï
16—24 -Eyap0ratîon Process.9—_—_It is possible to deposit a
onïthe surface of a body With the apparatus
…—
Sh0wnmgurelô—18 In ‘ilthiS
apparatus
5
Volatil.iZèdtmtheheatmgœ(C)
Partmïesof themater1a1 tie—vel 0üff fromC mstra1ght 1mesand
dpwtnthe1wersurfaceofthe plt
16.
VACUUM TECHNIQUE
gure 16—17, is supported in a bell jar at a distance of 7 cm. from
the face of a 10 cm. platinum disc cathode C, and the air pressure
is reduced to 0.004 mm. of mercury, a 10,000 volt transformer
maintaining a potential difference of 5000 volts across the discharge
sends a current of 10 milliamperes betWeen the electrodes. This
‘
'would be expected to deposit an opaque platinum mirror upon
_
the glass in the course of two hours. However, there are so many
variable factors entering into the phenomenon that accurate predictions are difcult to make.
Other conditions remaining the
same, the mass in grams deposited uniformly over unit area each
second (the rate of sputtering) is directly proportional to the rst
power of the current and inversely proportional to the rst power
of the distance from the cathode C to the plate G.
,
'
'
Two kinds of particles leave the cathode. One kind consists of '
.
,.
uncharged molecules or atoms of the cathode metal which diffuse
'
in all directions so that the plate, and to some extent the jar, become coated with a thin lm of the metal.
The other particles are
electrons Which leave the cathode at right angles and travel with
high velocity, causing considerable heating of the plate and jar.
These electrons may be deected by a small magnetic eld (10 to
25 oersteds) so as to prevent overheating the plate. The sputtering
is thought to be due to evaporation of the metal from small spots
on
the cathode surface which have been struck by ions falling
.
through the large potential drop in the cathode dark space.
The
'
ions come from the 'gas in the jar. Metals Which sputter With
_
diiculty in the residual air can be made to do so if certain gases,
such as argon, are used.
Gold, platinum, copper, iron, tungsten,
_
silver and nickel maybe deposited with comparative ease.in the
residual air, while aluminum and silicon are difcult to sputter.
Ï
-»
If the cathodedark space touches the plate where the deposit18
formed, the cross gradient of potential sets up large currents
.
the
blistering it.
_
…
Ï
16—24 -Eyap0ratîon Process.9—_—_It is possible to deposit a
onïthe surface of a body With the apparatus
…—
Sh0wnmgurelô—18 In ‘ilthiS
apparatus
5
Volatil.iZèdtmtheheatmgœ(C)
Partmïesof themater1a1 tie—vel 0üff fromC mstra1ght 1mesand
dpwtnthe1wersurfaceofthe plt