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I am new to force measurements and I am having trouble with the thermal tune method to calibrate the cantilever's spring constant. I would appreciate any help.
I am using TESP probes with a D3100 system and Nanoscope software v7.30.
I start by calibrating the deflection sensitivity on a silicon wafer, typically getting values around 37 nm/V. (from TM deflection vs. Z plots)
1. Is a deflection sensitivity of 37 nm/V seem correct for a TESP tip? Are there any rules of thumb for what to expect for this type of probe or others?
Then I withdraw the tip and open the thermal tune window.
The deflection sensitivity that I just updated through the software does not seem to be automatically updated in the thermal tune parameter list.
2. Is it normal for the just-updated deflection sensitivity to not be automatically entered in the thermal tune parameter list? If so, I should update it manually, then, right?
3. Should the thermal tune frequency range be selected based on the resonant frequency of the probe (e.g. TESP is nominally 320 kHz, so use the 5-2000 kHz range)?
I've tried both ranges and I think I see something that may be a peak around the resonant frequency of the TESP tip, but it is hard to tell for sure:
All the manuals I've seen about thermal tune seem to show a nice big obvious curve with a flat baseline, but that is not really what I am getting.
4. Does the above data look normal?
5. Is there a way to zoom in on the data in the plot, specifically the horizontal axis?
I think it would help if I could zoom in on the data, but I can't figure out how. One manual I saw had a magnifying glass button in the thermal tune window, but I don't seem to have that in this version.
I've tried dragging the cursor lines to either side of what I think is the peak, but the calculated spring constant varies widely based on just exactly where the cursor lines are placed.
One time I managed to get a not unreasonable spring constant value of ~69 N/m (TESP is nominally 42, but ranges from 20-80 N/m according to spec). Other times I get huge values or negative values.
6. Any other advice or suggestions? Is there something else I should be doing?
Thanks a lot in advance!
Zoom in by holding Ctrl and dragging a box with the mouse around the area that you want to enlarge. Zoom out by double-clicking on the graph or clicking on the magnifying glass which will appear after zooming.
Cheers,
Janne
Thank you, Janne. Zooming in on the region of interest did help.Calculating the spring constant is still pretty sensitive to the position of the cursor bars, but now I can see if the fit looks any good.After testing different cursor positions I got what seemed to me to be a pretty good fit and the calculated spring constant is somewhat reasonable: I measured ~58 N/m for a TESP tip, which is nominally 42, with a range of 20-80 N/m:
The data and the fit still do not look nearly as nice as what is pictured in the Nanoscope manuals about thermal tune:
I read somewhere that higher spring constant probes will give a weaker signal. Is that why my PSD peak is much weaker and the baseline is much noisier? Or is there something I can do to improve the data and results?
Thanks a lot!
The example shown in the manual taken with the range set to 1-100kHz, and yours is 5-2000kHz, data density is different. if you would like to have a smoother curve, you can trying changing bin width and median filter width.
Ang Li