Alkali deposition
=================================

The analyzer chamber has a permanently mounted cluster alkali source (SAES type), enabling deposition of K, Cs and Rb on the measurement manipulator. This is done at the upper transfer level of the chamber - it's not possible to deposit while measuring.

.. image:: /_static/alkali/clustersource.jpg
  :width: 500
  :align: center
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=====================   ========================   ========================  ================================
Source                  SAES product code          Evaporation starts        Suggested core level to monitor
=====================   ========================   ========================  ================================
Rb                      RB/NF/4.8/17 FT10+10       5.3 A                     Rb 3d at 111.5eV
K                       K/NF/3.1/17 FT10+10        5.3 A                     K 3p at ~18.5eV 
Cs                      CS/NF/5.5/17 FT10+10       4.7 A                     Cs 4d at 77eV
=====================   ========================   ========================  ================================

See also: :download:`SAES datasheet <_static/alkali/datasheet.pdf>`

All sources can be degassed up to 3.3A without anything happening.  You will likely need to perform multiple depositions to get the coverage you want. A recommended starting current is 5.6A for 60s, then scale the time or current up or down depending on how that goes. This corresponds to around 700\ |deg|\ C, so the source will be glowing:

.. image:: /_static/alkali/glowing.jpg
  :width: 500
  :align: center
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However note that the evaporation you will achieve is a non-linear function of current and of time.

The sticking coefficient is also highly dependent on the sample surface and temperature. Some samples require evaporation cycles of only a few seconds where others might need minutes. As a general rule, alkali evaporation will not work above 200K due to rapid re-evaporation or intercalation.

To operate the source, connect a DC power supply with the custom cable set. Please be very gentle with the feedthrough pins!

.. image:: /_static/alkali/powersupply.png
  :align: center
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Below are two example measurements taken on SiC graphene while testing the Rb source. At hv=180eV there is already a small Rb core level present after 30s / 5.5A, and the doping had not saturated after 5 deposition cycles of escalating time and current:


.. image:: /_static/alkali/shortDose.png
  :align: center
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.. image:: /_static/alkali/longDose.png
  :align: center
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.. |deg|    unicode:: U+00B0