Characterization Update Slade J. Jokela

XPS Status The hemispherical analyzer contains a 16 channel anode underneath a commercial MCP chevron pair. –One channel (#9, near center) is completely dead This channel was initially experiencing a very low count rate, but completely died after I removed the MCP module to examine it and after I checked the external amplifier, discriminator, counter circuits. Other channels increased after the above examination and subsequent bake out of chamber and hemispherical analyzer.

Troubleshooting Amplifier Circuits –Three options: Tie all 16 anodes together and run them back through all 16 amplifier circuits to see if they all give close to the same count rate Set up a pulser to test each amplifier circuit –A little more difficult than it sounds as I need to protect the electronics from overvoltage (voltage divider or proper capacitor in series). Ship the electronics back to the UK for testing at seller’s facility (PSP Vacuum).

Troubleshooting MCP Module –These MCPs were originally installed in They could stand to be replaced, but it’s not common for them to suddenly drop in count rate simply due to ageing. –Disassembly of MCP module risks shattering these MCPs, so I can’t check out the 2 nd MCP or the anodes. –Resistance across each MCP is roughly 12 MOhm when tested in air. (didn’t check under vacuum yet). –Testing the electronics should be sufficient. If the problem isn’t there, then it’s here.

SEY Progress Identified reason for difficulty controlling beam current 21 eV period To understand where this comes from, I need to discuss my system setup

Controlling Electron Beam Current Added recently for increased voltage resolution

LV1 Addition It was thought that the ripple was a result of poor voltage resolution on the Emission Grid (HV2) voltage source. –Partially true. I won’t be able to obtain very low beam current without a high resolution, high voltage source(es) Real problem is the +/- 10V PCI reference card

PCI Reference Card Test Each arrow is 0.21V apart (21eV when applied to the HV1 source)

Solution Convert set voltage to nearest binary value –(-10 to +10 V range using 16 bits) Measure voltage at each point –More accurate I’ll do whichever one doesn’t require a complete rewrite of the Labview program, leaning towards a more accurate measurement.

Some Recent(ish) Results