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Hi,
I am trying to do nanoindentation on flat metal tapes with a Dimension Edge AFM using Point Spectroscopy. The main purpose of doing this is to measure the hardness of oxide films deposited on the metal tape. I have a PDNISP-HS probe. I understand that I first have to calibrate the sensitivity, and then do a thermal tune to calculate the spring constant to get force vs. displacement curves when doing point spectroscopy. But, since I am new to this I have a few questions:1. What ramp rates should I start with? The help menu in the AFM suggests to use +/- 5 um (+999 to -999) as Z end and start respectively, which automatically adjusts the ramp rates to about 2 um/sec.2. Is adjusting the trigger voltage same as adjusting the load? What is the different between changing the trigger voltage and changing the setpoint to vary the load?3. Is it recommended to use tapping mode point spectroscopy over contact mode, since my samples are metal tapes?4. What is the effect of adjusting the cycle hold time?5. After doing point spectroscopy, can the same probe (PDNISP-HS) be used to image the sample?
I appreciate any feedback provided!
Thank you.
Hi Aarthi,
Let me take a stab at this:
Before performing force curves make sure that i) You select "relative movements" and turn the "linearizer, closed loop z" on. Realtive movements will relate all distances you type into the SW to the actual z-position at setpoint, i.e. the z-position at setpoint is set as "zero" and negative numbers are away from the surface.
1. Ramp rate. I would start with a ramp- rate of 1um/s before gradually increasing if desired. You want a ramp rate that is faster then the response of your closed loop z you will see hysteresis.
2. The trigger defines a maximum deflection value. Upon reaching that value the f/s curve is aborted. You can look at this as a safety and, yes, as the deflection is basically your load it adjusts your maximum load. If you select, however, not to push far enough to actually reach the trigger the value of the trigger is meaningless for any load calculations.
3. No. Actually in tapping mode you can turn the tapping oscillation off to measure a static load curve.
4. The probe waits before performing another cycle. If you want to let your sample relax for a certain time before perfoming another cycle, this a way of doing it.
5. The PDNISP-HS probes are very stiff and not recommended for imaging. I recommend a TESPA or RTESPA instead if using Tapping Mode operation.
6. You are correct that the EDGE currently restricts the thermal tune to 50kHz probes. So your choices are to eiterh use the data from the supplied spec sheet, calculate by dimensional parameters, or use another published method for experimentally determining spring constants.
Best regards,
Stefan
Another question
6. I am using a PDNISP-HS probe. The calibration sheet that came with it said it has a frequency of 73 KHz and sensitivity of 198 nm/V. In order to check it with the Edge, I did a point spectroscopy on a <111> Si wafer to get the sensitivity (~128 nm/V). To calculate the spring constant, I used thermal tune, but looks like the AFM has a limit of 50 KHz. So when I do a curve fit, it gives me a Q factor of 700.
How do I calculate the spring constant? I know it can be calculated using the physical parameters of the cantilever, or could I just use the value in the calibration sheet?
Thank you for the response Stefan.
Initially, since I did not know whether the same probe could be used for imaging, I always swtiched to an OTESPA probe, to be safe. But the problem with switching the probe was finding the exact same spot for imaging. Since the cantilever lengths are different, I have to scan around to find the spot. I will measure the cantilever lengths and input the difference in length and try to image the sample. Hope it works!
Thank you again!
Aarthi
I have been trying to make a few measurements but I am not getting the right force curves. The samples that I indented are alloy tapes (50 um thick). I used the following settings:
Z linearizer onZ-relative onClosed loop ZOscialltion offRamp rate: 0.5 um/sec, 1 um/secZ start: 0 umZ end: 5 umTrigger voltage: 5 V, 2VCould you please tell me what I am doing wrong?
I am not sure what exactly you mean by not getting "the right force curves". You are pushing from your feedback point into the sample and then go only back to feedback with a quite stiff cantilever. Maybe you can try the experiment with a slightly softer cantilever and compare the slope of the force curve. Let me know and I can have a few sample cantilevers send out to you.
Regards,
Stefan,
If you see the voltage vs. z curves that I obtained, there seems to be some hysterisis (it forms a loop at the top). I have tried decreasing the trigger voltage down to 0.5 V and it still gives me a similar curve but not a good indentation. I would really appreciate it if you could send me the softer cantilevers. Could I please have your email address so that I can send the details?
Sure here it is:
stefan.kaemmer at bruker-nano dot com