Chapter
1 Introduction
1.1 Overview
The EBE-1 uses electron bombardment to produce intense localised heating. Rods
and/or small crucibles may be heated in this way. They are placed inside a ring filament
at ground potential. Electrons from the incandescent filament are attracted towards
the rod or crucible, which is held at high positive potential and must be electrically con-
ducting. By accelerating the electrons to 2 kV and allowing the emission of up to 200
mA of electron current, a total heating power of up to 400 W may be delivered into a
very small area creating extremely high power densities and allowing temperatures in
excess of 3500
o
C to be reached. Material evaporated in rod form may be fed continu-
ously into the e-beam heating zone as it evaporates away. Lengths of up to 50 mm may
be evaporated.
1.2 Rods and Crucibles
Materials which are electrically conducting and develop a useful vapour pressure before
melting may be evaporated directly from their rod form. Perfect examples of such ma-
terials are chromium and carbon which both sublime as the temperature is increased, as
well as many refractory metals such as molybdenum and tungsten which develop use-
fully high vapour pressures before melting.
Materials which melt before reaching high enough evaporation temperatures will ball-
up on the end of the rod before eventually dripping off the rod. This balling effect can
be controlled in some borderline materials such as silicon where use of a 4 mm or 5 mm
EBE-1 1
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