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I am using a BioScope Catalyst AFM and I am having a hard time with my E-Box. When I am using the EasyAlign to align the laser on the back of the cantilever i can maximize the Sum signal and then I adjust the knobs until the vertical and horizontal deflection are 0.00 or there about. However, immediately the vertical deflection begins to drift, either up or down and usually quite rapidly. The sum signal will also usually change, which I imagine would be expected. I am a relatively new AFM user and perhaps this is user error. Does anyone have any suggestions or thoughts? Is this a common problem? Any help would be greatly appreciated.
Thanks in advance!
Joshua Price
Wheaton College
Joshua,
In addition to the possible causes that Alexandre mentions, temperature changes are also a very common source of deflection drift. Many cantilevers have a metal coating, so as the temperature changes the metal coating expands at a different rate than the silicon nitride or silicon cantilever and so the cantilever bends in response to that stress (i.e. a "bimetal effect"). Once the temperature stabilizes the drift should too.
This sort of drift is especially common when you are working in liquid because liquids conduct heat much more readily to the cantilever than air. Also the liquid may be considerably warmer or cooler than room temperature. It's best to let your solutions equilibrate to room temperature before adding them to your sample on the AFM. Even then there will be some drift, but it will slow down and become more stable in 5-15 minutes or so.
I recently measured deflection drift on a Catalyst using a TESP probe (very stiff silicon cantilever with no metal coating) in air. During a 6 hour period where the temperature was stable within about 0.2°C the deflection didn't drift more than 0.1V. But when the room temperature changed by ~2°C overnight the deflection drifted by about 0.8V. Drift will be greater with soft silicon nitride cantilevers, metal coated cantilevers, and when measured in liquid instead of air. But this should give you a well-controlled baseline test to compare against.
Air bubbles can also cause large deflection drift if they are on or close to the cantilever or adjacent cantilevers. Sometimes they will be visible on the EasyAlign. If not, you should be able to see them for sure (if they are present) once you put the head on the microscope. Usually you can get rid of them by raising and lowering the probe through the air-water interface. Sometimes you need to dry the probe (wick away the fluid carefully with a Kimwipe at the edge of the probe substrate) and try putting it back in the fluid.
As Alexandre said, please be sure to contact us again if these suggestions don't solve your problem.
Best Regards,
-Ben
Dear Joshua,
Aligning the laser directly on the stage can be tricky but normally the Easy Align is supposed to make it easier. What can happen is that it can be sometimes hard to maximize the SUM signal. The reasons can be that the chip is not properly inserted (tilt) or when you switch from liquid to air environment (or vice versa) you might have to move a lot the detector to bring it back to the field of detection, but it doesn’t seem to be the case since you can get a good SUM. So I see several potential reasons:
1) If the drift is very progressive, it can be due to a loss of coating. If you tell me which probes you are using, I can tell you more. I guess you align in liquid. Which buffer are you using? Any solvent?
2) If all signals (SUM and horizontal and vertical positions) brutally drop down to zero, this can be just a whacky display of the ebox. Then you have to control the SUM on the real time window or your working session. This can be fixed by unplugging and re-plugging the power cable. Don’t touch any other cable!!!
3) It can also happen if you gently touch the protection glass window with the probe but normally this should not happen. Even at the lowest position of the head, you should be way off.
If you can’t fix it, please contact me directly:
alexandre.berquand@bruker-nano.com
tel: +49 (0) 174 333 94 62
Don’t let this spoil your experiment...
Alex.
Thanks for your help Alex,
At this point I'm using MSNL-10 probes but I've experienced this issue with ScanAsyst Fluid and Air probes as well. I am aligning in liquid but at this point its just pure reagent grade water. Eventually I'll be using Alsevers solution, but for now I'm just using water. As far as all the signals dropping to zero, that doesn't seem to be the issue. Often the horizontal signal remains relatively constant and the sum signal fluctuates with the vertical drift, but not nearly as much as the vertical signal. I dont think the probe is low enough to touch the window...I'm imaging a pretty tall object so it tends to be raised fairly high. I'll pay attention as I image today and see if I can observe any of these things and let you know if I see anything different.
Thank you for your help
Thank you both so much for the help. I think Ben was right on the money which the liquids. Today I am imaging in air and am having no problems as the room has been very closely controlled. Its amazing how many little things I dont think of at this point. Thanks again for your help!