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How can a Dimension Nanoman user measure the Cantilever Amplitude in Nanometers?
Is more info needed to address this question?
Thanks,
Sergio
Hi Sergio,
Yes, you can measure the cantilever amplitude in nanometers on the Dimension Nanoman system (and other systems as well).
The most common way to do this is to take a force curve while in TappingMode which produces an amplitude vs Z curve. This will show the amplitude change from a constant amplitude to a relatively linear decreases once the probe starts tapping on the sample. You will the part of th curve where the probe is tapping on the sample to determine the "amplitude sensitivity", which calibrates the voltage signal on the PSD into nanometers (nm/V). In version 7 (or later ) software you can also conduct a standard force curve in contact mode where you determine deflection sensitivity, and the system use this for the amplitude sensitivity determination as well. Once you have conducted this calibration, the Amplitude value on the force curve will appear in nm instead of volts. To get the full peak-to-peak ampitude of the cantilever oscillation, you will need to multiply this number by 2. This needs to be conducted on a relatively stiff material, and care needs to be taken to prevent moving the tip into the sample to the point that the tip is not longer oscillating in the amplitude vs Z curve, which may dull the probe. This can be done by using the Trigger settings, or with careful use of the Z scan start and Ramp parameters.
You can also determine the nanometers of oscillation by collecting an image of the change in osciallation. This can be done by collecting an image with a Scan Size of 0nm, Data Type of Height (or Z Sensor), and Offline Planefit to Offset (or None). Collect a scan while changing the Amplitude Setpoint in the middle of the scan by some incremental value and save the image. You can then measure the size of your step in the saved image using Section, and then multiply by 2 to get the peak-to-peak oscillation of that incremental change in the setpoint. From them you can determine the full oscillation value.
I hope this helps,
John
I fine point to bear in mind is the fact that the angle of cantilever inclination at the laser spot location, as is effectively measured by the split photodiode, is different for a freely oscillating cantilever and an end-loaded cantilever. (See papers from mid 1990's; as I recall Hans-Jurgen Butt was one to point this out.) That is, for a given amount of Z vertical displacement of the tip, the change of photodiode signal is different when the tip is freely oscillating compared to when it is end loaded (i.e., in contact with the sample in a force curve). As I recall this results in a ~10% lesser change of signal for the case of free oscillation.
This is not an immediate solution for Nanoman but I would like to mention that the our NANOS AFM head (an essential part of our NEOS AFM-based inspection microscope) uses fiberoptical interferometry for measuring the cantilever deflection. The interferometer signal (==> amplitude) is calibrated in nanometers.
Frank