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A graphite insert for a varian electron gun evaporator
NUCLEAR
INSTRUMENTS
AND
METHODS
99
0972) 3 7 9 ; ©
NORTH-HOLLAND
PUBLISHING
CO.
A G R A P H I T E I N S E R T F O R A VARIAN E L E C T R O N G U N E V A P O R A T O R * J. P. S O K O L
Department of Physics, University of Notre Dame, Notre Dame, Indiana 46556, U.S.A. Received 8 October 1971 A graphite insert has been f o u n d effective w h e n evaporating small samples in a Varian electron gun.
We have encountered some problems in using the Varian electron gun (Model-908-0001) to evaporate small amounts of isotopic carbon and boron powder. These materials are evaporated to form thin film targets for nuclear reaction studies. The Varian electron gun is basically a production device intended for a sample of several grams, whereas a typical sample we use would be several milligrams of material. Our solution has been to use a graphite insert formed from a 1- diameter rod, ½ to ~3 t! tall, with a depression to hold the material made with a ~" drill. The figure shows a cross section of the insert in the crucible. The use of the graphite insert accomplishes several things. Firstly, the gun appears designed for a sample which fills the crucible because the focus is at a point iV' above the top of the electron gun crucible. A better focussed beam means a higher temperature at the point of evaporation with lower filament currents. High filament currents have been found to have an adverse '~ W o r k s u p p o r t e d in part by the N a t i o n a l Science F o u n d a t i o n .
379
effect on the substrate by causing too much radiant heating. Secondly, it is observed that powdered materials show less tendency to jump out of the insert than they do when placed in the crucible of the electron gun itself. Thirdly, the electrons are in the magnetic field a shorter time and thus strike the material vertically rather than tunneling in at an angle as happens without the insert. This means more of the material evaporated is directed upwards towards the substrate. This technique has been useful in producing 10-20/~g/cm 2 boron and carbon foils.
evaporant I I graphite powder
,
] I
~"diameter graphite insert E-gun crucible
Fig. 1. Cross-section of crucible o f Varian electron gun evaporator showing graphite insert.
INSTRUMENTS
AND
METHODS
99
0972) 3 7 9 ; ©
NORTH-HOLLAND
PUBLISHING
CO.
A G R A P H I T E I N S E R T F O R A VARIAN E L E C T R O N G U N E V A P O R A T O R * J. P. S O K O L
Department of Physics, University of Notre Dame, Notre Dame, Indiana 46556, U.S.A. Received 8 October 1971 A graphite insert has been f o u n d effective w h e n evaporating small samples in a Varian electron gun.
We have encountered some problems in using the Varian electron gun (Model-908-0001) to evaporate small amounts of isotopic carbon and boron powder. These materials are evaporated to form thin film targets for nuclear reaction studies. The Varian electron gun is basically a production device intended for a sample of several grams, whereas a typical sample we use would be several milligrams of material. Our solution has been to use a graphite insert formed from a 1- diameter rod, ½ to ~3 t! tall, with a depression to hold the material made with a ~" drill. The figure shows a cross section of the insert in the crucible. The use of the graphite insert accomplishes several things. Firstly, the gun appears designed for a sample which fills the crucible because the focus is at a point iV' above the top of the electron gun crucible. A better focussed beam means a higher temperature at the point of evaporation with lower filament currents. High filament currents have been found to have an adverse '~ W o r k s u p p o r t e d in part by the N a t i o n a l Science F o u n d a t i o n .
379
effect on the substrate by causing too much radiant heating. Secondly, it is observed that powdered materials show less tendency to jump out of the insert than they do when placed in the crucible of the electron gun itself. Thirdly, the electrons are in the magnetic field a shorter time and thus strike the material vertically rather than tunneling in at an angle as happens without the insert. This means more of the material evaporated is directed upwards towards the substrate. This technique has been useful in producing 10-20/~g/cm 2 boron and carbon foils.
evaporant I I graphite powder
,
] I
~"diameter graphite insert E-gun crucible
Fig. 1. Cross-section of crucible o f Varian electron gun evaporator showing graphite insert.