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.

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: SAES datasheet

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°C, so the source will be glowing:

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!

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: