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I'm currently trying to image a polymer blend and have had some issues with the data on the DMT Modulus channel. If you look at the trace and retrace, you see normal peaks and valleys. However, the peaks themselves are cut off. I've already gone through deflection sensitivity calibration on sapphire, did thermal tune etc. and have changed the modulus limits. However, nothing seems to remedy the problem. I've tried using different probes such as ScanAsyst Air and TAP150A, but those appear to be too soft.
Unfortunately the computer and instrument are not on the network so I can't set up remote access to a Bruker-Nano expert.
Any ideas on why the modulus data looks like it is going off scale with flat peaks instead of normal ones? I can arrange to send image files or screenshots via email...
The first thing to check is the DMTModulus Limit. Increase it and see if that helps.
If that does not solve the problem, it is likely that there is something wrong with your sensitivity calibration -- I would suggest entering a low value (maybe 10 nm/V) for the deflection sensitivity and see if that helps. If so, put in a hard, clean sample and redo the deflection sensitivity (in ramp mode).
--Bede
Hi bede,
thanks for the quick response.
I tried increasing the DMT Modulus limit but it doesn't seem to do anything. I've redone the deflection sensitivity calibration on sapphire a couple of times with different probes with the same result - bad DMT Modulus data. For the ScanAsyst Air I am getting deflection sensitivities around 35 nm/V and spring constasnts that are between 0.4 and 0.6 N/m. For RTESP I get deflection sensitivities around 70-80 nm/V and spring constants around 20 to 40 N/m.
I haven't tried entering a very low value for deflection sensitivity but will try that. If it means anything, the problems started last week right after a window popped up on my screen and asked me if I wanted to update the deflection sensitivity. It said the current value was around 1100 nm/V !! That sounded completely absurd so I clicked "no". Ever since then I've been having sporadic issues. One minute I get a decent image, the next time I don't...
Update:
I Just tried your suggestion to set the deflection sensitivity to 10 nm/V to see if that helped. At first it seemed that it did, however another strange problem started around the same time. After the system engagesand makes its initial adjustments it zooms out to a 10 micron scan as I originally set it at. Then all of a sudden a window pops up that says something like "warning: tip protection engaged. withdraw trip and realign the laser". I didn't think there was a problem with the laser alignment, but I went ahead and checked anyway. I did it twice but still get the same error message. Another strange problem is that the system will periodically go from a 10x10 micron scan to something much larger. It almost looks as if it's going out to the full 150x150 micron scan range. It seems to do this at random, but usually in conjunction with the "tip protection" warning.
I don't think I'm doing anything different than usual and I've been able to obtain plenty of good PeakForce QNM data in the past, so all these things are a complete mystery.
any other ideas? I've even tried shutting everything down, rebooting the computer, turning the controller back on, but no luck.
Usually the tip protection occurs when the sum drops to a value that is too small. This might happen due to poor laser alignment or if the cantilever has a poor coating. Does it happen with every probe or just that one?
I've never seen the system automatically increase the scan size like that (except when I meant to type 150nm and I typed 150um instead), but scanning a huge scan size at a high rate can cause problems since the tip might be in contact with the surface long enough to build up lateral force at very large tip velocities. I believe there is a warning message associated with that. Maybe that is what you saw?
Even I have seen crappy results with PFQNM on Bioscope Catalyst. I don't understand why one should manipulate the value of deflection sensitivity (DS) values just to get good results. Once, the DS and spring constant has been calibrated, the only parameter that can be tweaked is the modulus limit and tip radius. The problem mainly appears because of the huge stiffness of substrates like Mica & Silicon.
Actually, I really don't believe in accuracy of PFQNM data even though there are some papers in very good journals that have reported PFQNM data. Even if all calibration has been done perfectly, you can still observe negative value of elastic modulus, which is absolutely absurd.
Hi Krishnashish,
I'm sorry to hear about your troubles with the Catalyst. I agree that you should not have to manipulate the value of the deflection sens. In the previous post I recommended to try reducing the value as a troubleshooting method. If that helps, you should go back to the hard sample and try to figure out why the deflection sens came out too high previously.
As you note, there are some great papers out there where people have sucessfully used PFQNM. Using Catalyst in liquid has some unique challenges, but it works well if you are careful with calibration and you do not operate at high frequencies and large amplitudes.
It is actually not possible for the system to give a negative value for modulus -- as you say that would be absurd so the software looks for that case and will repeat the previous value if a negative slope is found. The only way that the modulus could be negative is if a planefit or flatten has been applied to the data. If you can provide some screenshots or raw data files, I will help you debug this issue (and we can investigate the possibility of a bug).
Thanks Bede for your reply.
How am I supposed to work with the modulus channel (or any channel) without flattening it?
How do I upload a nanoscope file here?
But even without any flattening, negative value is observed in Stiffness and Log DMT modulus channels. Another issue is that, it barely showed any difference between proteins and Mica substrate.
You can control the scale of the images without flattening or plane fitting. In Nanoscope analysis, right-click on the scale bar and choose 'Color Scale'.
I believe that you can upload anything with a .jpg extension. If you rename the file, I can rename it back...
As I said, the software should not allow any negative values in modulus. How are you measuring the value? If you use roughness, what is the mean?
I would also like to highlight that the PFQNM experiments I did on Bioscope catalyst was 2 yrs ago, when I was in India. Since then I have not used any system with PFQNM. Probably, it was a bug that has already been fixed.
By the way, your website is definitely not user-friendly. I can't even upload a simple .jpg file from my computer. Strangely, I can't even edit my sentences once I have posted. You should definitely report this to the site administrator.
Did you try going to the 'options' tab when you are writing your post and upload there? I'll try it myself on this post. Let me know if you still can't upload.
I will report the editing issue...
It says: "Enter the URL where an existing file resides."
So I just copied the physical address in my computer. Hope it works.
You don't have a button 'choose file' like this? I'm using Chrome...