Dual-mode mini e-beam evaporator
The Oxford Scientific OS-Vap is acombined mini e-beam evaporator and e-beam heated effusion cell and is capable of evaporating small quantities of almost any material.
The material either in rod form, or in a crucible, is heated by electron bombardment from the surrounding filament.
The capacity for electrons to be directed to deliver up their energy in a confined area, leads to extremely high power densities and local heating, allowing temperatures in excess of 3000K to be reached.
Dual mode
e-beam heated effusion
cell
The OS-Vap
is designed so that an optional thermocouple may be fitted to measure the
temperature near the rod or crucible. The temperature can therefore be used,
as in conventional effusion cells, to control the power supply via a PID controller.
The result is an e-beam evaporator with the operational characteristics, in
terms of stability and repeatability, of conventional effusion cells, with
which many users will already be familiar.
e-beam evaporator
In "standard" mode the evaporator is controlled either manually
or with the flux monitor option (see below). The power is adjusted to give
the desired evaporation rates.
Triple control
(1) "Standardl" operation is by manually controlled evaporation from rod or crucible. In combination with a quartz crystal monitor this is the most common use of the instrument and is ideal for depositing a few mono-layers of material.
(2) The thermocouple option allows temperature measurement near the crucible to be fed back to a PID controller which in turn regulates the power supply, providing classic temperature stable evaporation associated with effusion cells. The fixed thermocouple design of this instrument allows this mode to be used whether evaporating from rod or crucibles.
(3) Closed loop control may also be obtained using the integrated flux monitor option to measure the ion current in a portion of the partially ionized evaporant beam. The monitor signal is amplified and fed back to a PID controller to regulate the supply. This method provides a direct qualitative measurement of the flux actually leaving the evaporator but is more susceptible to rod position/crucible fill levels and insulating materials, than the thermocouple technique.
(i) The unique design, incorporating both the high voltage and thermocouple feedthroughs (optional) on an exclusively designed 2" linear motion thimble, means that (1) there are no flexing leads in vacuum which can lead to fatigue and shorting problems and (2) the thermocouple can be used at all times whether operating from rod or crucible and can be more securely and robustly mounted.
(ii) The fixed thermocouple allows the instrument to be used as a true e-beam heated effusion cell.
(iii) The evaporation zone is completely enclosed in a water-cooled copper shroud. The water sees only stainless steel and welded joints for long term corrosion resistance, with the stainless steel cooling pipes permanently bonded through the copper for complete and reliable thermal contact.
(v) The filament assembly is constructed as an easily replaced unit and yet still allows the user to replace just the filament using standard tungsten wire. Spare filament assemblies can be purchased or prepared in advance and can be quickly and easily replaced without disassembling the evaporator head.
(vi) The filament encircles the rod or crucible providing much more even heat distribution than one-sided filaments. Higher temperatures are therefore possible without local damage to crucibles.
(vii) A long filament also provides more surface area for electron emission than shorter varieties allowing operation at lower temperatures with a consequent improvement in filament lifetime.
(viii) Fine control of the electron emission current for improved operation at very low rates and 50mm rod feed are provided as standard.
(ix) The simple, rugged
and modular power supply design can generate enough power to evaporate the thickest
rods (6mm) and yet is also robust enough to survive misuse without the dire
consequences seen in more complex failure-prone electronics.
Schematic Drawing and Electrical Diagrams for beam flux monitor, thermocouple and shutter
Download
your Dual Mode Mini E-Beam Evaporator Brochure 
(PDF)
Specifications
Options
Mounting
flange:
2.75"
(NW35CF)
In
vacuum length:
200mm
(7.9")
In
vacuum diameter:
34mm
(1.34") max
Bakeout
temperature:
200oC
Rod
feed:
50mm
(2") as standard
Rod
diameters:
2,3,4,5
or 6mm (2mm supplied as standard. Also accepts crucibles. Larger diameter
rod holders optional)
Crucible
volume:
0.25cc
Crucible
materials:
W,
Ta, Mo, Pyrolytic Graphite
Deposition
Rate:
Measured
at 100mm:
Refractory materials e.g.
W, Ta: ~2nm/min
Higher vapour pressure materials e.g.
Ag, Cu: up to 1nm/second.
Deposition rates controllable down to
<0.01A/s = 0.2 monolayer/min.
Beam
Divergence:
~15o
half angle ( ~10o with flux monitor fitted)
Size:
19"
rack mount. 3U height. 230VAC, 50Hz (115V, 60Hz optional)
E-beam
Power:
0-300W
1
Thermocouple:
Permits
measurement of the temperature near the rod or crucible. Includes the
thermocouple (Type C) and feedthrough
2
PID
controller:
For
PID control of the power supply. Requires option (1) above
3
Shutter:
For
shutting off the beam. Can be operated within the ID of a 2 ¾” port
4
Shutter
motorisation:
Solenoid
drive. Requires option (3) above.
5
Flux
monitor:
A
small electrode is used to intercept the edge of the beam and collects
the ions present in the partially ionised evaporant. Includes electrode,
feedthrough and display unit with bias control.
6
Flux
controller:
As
at (5) above but with PID controller for closed loop control.
7
Crucibles:
Mini-crucibles
with 0.25cc capacity in a variety of materials including, W, Ta, Mo, PG
(pyrolytic graphite). Matching lids also available.
8
Crucible
liners:
For
reactive materials e.g. aluminium, an inert crucible liner is recommended.
These are available in BN and pyrolytic graphite.
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