Using evaporators

Knudsen-cell evaporators

We have two simple home-made Knudsen-cell evaporators. They have no shutters and no water cooling. They can be used only in the preparation chamber - bottom.



The cell consists of a crucible made of alumina ceramic tube with a tantalum heating spiral wound around it. The backside of the ceramic tube is closed with a piece of aluminum foil into which the K-type thermocouple for temperature reading is inserted. Temperatures up to 400 °C can be reached.

For the operation we use the dedicated controller containing Delta Elektronika ES015-10 power supply and Eurotherm EPC3016 temperature regulator. The regulation loop is active when the switch is in the KEEP TEMPERATURE position. For the most typical temperatures up to 200 °C (set by up/down arrows)  the CURRENT LIMIT should be set to 2.0-2.5 A.

Alternatively, PS2342-06B DC power supply and thermocouple voltage reading on multimeter can be used (recalculate voltage to temperature using  a table).

The deposition is timed by rotating and/or translating the sample holder attached to the transfer rod. The evaporator is to be preheated sufficiently in advance, in order to provide constant deposition rate. The rate can be checked by quartz crystal microbalance and adjusted by the heating current while observing the crucible temperature.

After use the crucibles should be properly cleaned (in supersonic bath, solvents, furnace...) and degassed by annealing in vacuum in order to avoid cross-contamination of the following material to be evaporated.