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Hi, I'm a masters student writing my thesis and I had a question regarding the Bioscope AFM.
I just wanted to know if there was more information or literature available on the autotune function, as well as the spring constant tuning function.
I know that the numbers given on the AFM probe information sheets are only nominal, thus requiring individual confirmation. I also know that there is a thermal method for the determination of spring constant, but am not sure if that is what the AFM system uses.
However, now that I'm writing my thesis, I wanted more information on the background of these functions, and specifically had the question about whether these functions would still work appropriately in liquid.
If there was any further information on this, I'd greatly appreciate it.
Thanks,
Charles Ang
Hi Charles,
If you are using a BioScope II or Catalyst system, it does have the ability to use the thermal tune method for calibration of spring constant. If I recall correctly the BioScope SZ system may also have thermal tune capabilities with the Nanoscope IV controller - although the thermal tune would not be able to go to as high frequencies as the Nanoscope V controller (which is not really an issue for most probes used in fluid).
Autotune is not recommended for fluid imaging. Due to fluid coupling and mechanical resonances, there are often multiple peaks within the recommended frequency range for a specific probe. This makes it difficult for the system to identify which peak is the resonant peak. Rule of thumb for fluid operation is that the resonance frequency of a probe drops 1/2 to 2/3 of the resonance frequency in air. The nomimal frequencies on the probes information sheet typically correspond to the values for operation in air. The probes database - available in our recent software versions - does provide nominal frequency values for fluid, which is nice.
You should use the manual tune for fluid imaging. Doing a thermal tune beforehand or a fast thermal tune which overlays on the cantilever tuning curve (if your system has this), can help you identify which peak is the resonant peak in the manual tuning curve. You may have to manually adjust the drive amplitude as well to get sufficient free amplitude (which you do not have to do for auto tune).
Here is a link to one of our application notes which provide some nice background on the thermal tune and spring constant calibration methods:
http://nanoscaleworld.bruker-axs.com/nanoscaleworld/media/p/143.aspx
Best of luck with your thesis!
Andrea