I am using triangular MLCT probes purchased from Bruker. I would like to measure the spring constant of cantilever using thermal noise method. I have measured time series of cantilever deflection at 200kHz and calculated power spectral density.
1. Is it the area under the whole curve that gives the spring constant or fitting to some equation is required?
2. Is the procedure same in for data acquired in both air and water because the resonant frequencies would be different? Are there any correction factors involved?
3. And what can we infer from the Quality factor of cantilever and how do we measure it? Does it affect the resolution of force measurements?
1. To calculate the spring constant, the measured PSD curve is fitted to the following equation:
k = kBT/ z2= kBT/ P
where k is the spring constant, kB boltzman constant, T temperation, and P the power.
For more info, please check the documents:
(1) NanoScope V Controller Manual NanoScope Software v 8 page 86
(2) Calibration of Atomic-Force Microscope Tips, by Jeffrey L. Hutter and John Bechhoefer, in Review of Scientific Instruments, 64(7), July 1993, page 1868
2. The protocols for air and liquid are the inherently the same. The bruker operation software provide Lorentzian and simple harmonic oscillator models for air and liquid conditions, respectively. The quality factor is considered in the simple harmonic oscillator (liquid) model.
3. The quality factor Q can be calculated using the measured PSD curve, directly through the built-in function (compute Q) in the operation software. Q affects the resonant measurement very much, especially in liquid condition.
Hope the above info helps you.
Best,
Zhipeng
Take a look at this paper. It should help you to perform the thermal calibration and also give you fundamental physical insights. I think that it is a "mandatory" reading to this topic.
Best regards,
Sérgio
Hi Sumanth,
Which AFM system are you using? Most systems have thermal tuning incorporated into their software, which facilitates calculations. Each system has the instructions for this on their operating manuals.
Best wishes,
Sebastian
Take a look at this paper also, let me know if it helps to you.
Hi Kumar, it is important to perform the calibration in air or water depending on the environment the experiments will be done in.
- Badges
- Science topic
- Similar topics
- Physical Sciences
- Waves