Tool bar and button bar Many SEM functions
Tool bar and button bar (Many SEM functions are mouse-controlled)
To insert your sample • Check that high voltage (HV) is off (no yellow background) • Click on Vent • Insert sample. Wear gloves or use tools. • Check sample height with “elephant nose”. Bottom of nose is where highest point on sample should be. • Click on quadrant showing CCD image (typically lower right) • Make sure image is live, not paused! (No double green bars in upper right corner. ) • Slowly close door while watching monitor to assure that sample/holder is clear of pole piece and detector • Click on “Pump” with left hand while holding door shut with right hand. Check that door is shut! • Push top of door against chamber.
Before pumpdown: get oriented • With the door open – Move the stage to be under the beam: • X=0, y=0 • “Control zero” is also supposed to work • Enter positive and negative values for x and y • Observe and record the direction the stage moves • Perform a similar operation after you get an image to correlate directions on screen to directions on the sample
Magnetic hazards • Ferromagnetic particles are potentially the most dangerous thing you can image • If they get sucked into the column, the rebuild will cost $60 -100 k! • Trying to image loose ferromagnetic particles in immersion mode will be fatal!!! • They can be imaged in EDX mode • They can be imaged in immersion mode if firmly embedded in plastic. Do not use tape!!
Secondary Electron Detector Backscattered Electron Detector Fractured Aluminum
Getting started toward an image • When adequate vacuum has been reached, chamber icon becomes green and HV button changes from grey to black. • Click on HV!
Get an image! • Black screen: – Check that H(igh) V(oltage) is on: yellow background? • HV automatically shuts off when switching between High Vac and Low Vac! – Turn on waveform feature • Increase contrast and brightness so waveform fills region between lines – Go to minimum magnification • Can you see the aperture? • If not, you are in big trouble. Check HV! • Try spot size = 4, 15 k. V
Link • Initially your stage should be about 13 mm down if you have not raised it to the 10 mm mark. . but could be anywhere: it has no way of knowing where you mounted the top of your sample! • Focus • Increase magnification • Focus • Link • Z-coordinate is now correct • Less crucial if using only samples of minimal thickness • Absolutely crucial for samples of widely varying thickness • Extremely crucial if sample is taller than elephant nose!
Image optimization • With Everhart-Thornley or Low Vac Detector, raise stage to about 5 mm – Typically during pump-down with roller ball – With cursor low on screen, press roller ball and roll mouse up – Watch active (not paused!) image of sample mount on CCD – Translation speed is proportional to distance cursor is from starting point
• • • Increase magnification Re-adjust focus Repeat process At about 5 k. X, link Raise sample to 5 mm Switch to TLD (Through Lens Detector) Re-focus Go to immersion mode Optimize image
More stuff on the Nova. Nano • The generic working distance is 5 mm. (It was 10 mm on the Quanta) – ETD – TLD (SE and BSE, “field-free” and “immersion” modes) – LVD – Also the eucentric working distance – Focus to about 5000 X, then Link. Do this early in the process. Do it repeatedly…especially if using the Helix detector
Furthermore • If you are using the 2 -sample holder, the pins are 16 mm apart • If you are using the 8 -sample holder, the pins are 19 mm apart. – Always make a drawing of the locations of your samples on the holder – Be extremely careful of orientation: get the sides of the holder on the translation axes – Remember that the CCD camera is mounted in the rear of the chamber
Further still more • You can move the stage in the x- and ydirections by typing coordinates into the boxes in the “Navigation” page • You can also move the stage from the image (not CCD) by holding down the roller ball and moving the mouse – The arrow points in the direction you want to look – The arrow points in the direction opposite to the one in which the stage moves
Still further more yet • If you move the stage by typing a value into the box on the “Navigation” page – Activate by clicking the Go. To button – “Go. To” will immediately change to “Stop” – Watch the rising stage on the CCD monitor – If the stage is in danger of hitting the detector or pole piece, immediately click “Stop” – “Escape” is an alternative “Panic button”
• “"When I Use a Word, It Means Precisely What I Want It To Mean. . “ Humpty Dumpty • In the lexicon of Leo, “Beam current” is the current leaving the filament and “Probe current” is an approximation to the current incident on the sample, usually high by about a factor of two. • From FEI, “Beam current” is an excellent approximation to the current actually striking the sample.
Low vacuum • Why?
Polystyrene balls High vacuum, 16 k. X
Polystyrene balls High vacuum, 100 k. X
Polystyrene balls Low vacuum, 16 k. X
Polystyrene balls Low vacuum, 100 k. X LVD. Helix detector in immersion mode will improve image by approximately one order of magnitude!
Low vacuum • Why? – For non-conducting samples – To avoid rapid deposition of crud on your sample. • ETD does not work • New detector must be installed…while wearing gloves – LVD is relatively cheap and adequate for images up to about 50 k. X – Helix is very expensive but gives killer images on nonconducting samples to 500 k. X or more! • PLA must be installed sufficiently tightly that it does not leak and kill the column • “WD” must be redefined if a PLA has been installed!
Low vacuum cont’d • You get to low vac faster if you start by going through high vac • Start with the minimum water pressure • Increase water pressure by clicking on the right arrow – Observe image on screen – Image will get brighter; reduce brightness! – When image brightness no longer increases with water pressure, experiment with small changes
Adjusting water pressure Range: 0. 08 – 1. 5 Torr 10 – 200 Pa Image brightness will increase with water pressure. Increase water pressure until image stops getting brighter!
Pressure limiting Aperture (PLA)
- Slides: 24