Weeks SEM Users Meeting November 29 2010 TopicsFollowups
Weeks SEM Users Meeting November 29, 2010
Topics/Followups -- Drivers Test -- Filament failure mystery solved -- Quantify SEM beam current measure -- Effect of beam current intensity on epoxy -- Ca/Si EDS measurement compared to WDS -- Carbon coater leak repaired -- Questions/comments -- Guest speaker: Dr. Patrick Camus of Thermo. Fisher Scientific on our EDS system’s features
Immediately after our last meeting, Don Gramer and John F spent 2 hours troubleshooting Took out Wehnalt that was in operation only a few weeks as there was discoloration around the hole EDS did not clarify…. but imaging the Wehnalt did…
Wenhalt aperture (~ 1 mm diameter) rim
… Tungsten oxide … vacuum leak Wenhalt aperture
• To check vacuum, we found out for first time that there is NO high vacuum gauge in the Hitachi SEM • A couple days later, Don brought a high vacuum meter (we needed a special fitting otherwise we could have used Wisc. SIMS Lab’s spare meter) • We hooked it up and found…
• The specs say the maximum vacuum should be 1. 5 X 10 -5 torr • We first checked the VP mode which we expected to be lower, and it was 1. 1 x 10 -4 torr …. ok • Then we switched to high Vac mode and found 1 x 10 -3 torr! We had a huge vacuum leak -- which would explain all out, filament premature failure, PLUS the welding of the Wehnalt to Al filament base.
• We then started poking and pulling on the detectors attached to the chamber, and found no change in vacuum • We opened the chamber door and after a minute or two, and with the help of a flashlight…
We found something in the chamber door’s o-ring …a little hair caused all our problems
Poor vacuum filaments “died” ~last summer
Sample current measurement with Faraday Cup
Faraday Cup current measurement Acc. Voltage=15 KV, Fil. Sat. =89, Gun bias=0 Probe Current Faraday cup (n. A) 50 1. 5 60 4 70 8 80 17. 5 90 37. 4 100 75 Sample Current (n. A) 80 70 60 50 40 30 20 10 0 0 20 40 60 Probe Current 80 100
The good: Probe current=60 Hard to tell square on epoxy The bad: Probe ~4 n. A ~8 n. A current=65 Faint square can be seen on epoxy The ugly: Probe current=70 Distinctive square can be noticed on epoxy ~6 n. A
BSE imaging “mystery”
Why such high contrast? Charging? ?
EDS vs. WDS: quantitative analysis
Ca/Si ratios EDS quantitative analysis (SD ranges from 0. 007 -0. 028) 3 Ca/Si ratio 2, 5 2 1, 5 EDS WDS 1 0, 5 0 An Aug Dio Wo Ak Standard Ge
Carbon coater leak found and repaired We Peter Sobol’s help, a small persistent and worsening leak was found. This was likely causing the ‘cycling’ as well as poor vacuum over past month. We are now keeping much more detailed records on all carbon coater usage. If you use it, fill out the log.
- Slides: 20