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Spring constant calibration in air - temperature

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Sjoerd posted on Thu, Aug 18 2016 2:13 AM

Hi all,

I recently optimized my approach for calibrating colloidal cantilevers. Before, I glued a bead on the cantilever, and measured the deflection sensitivity and performed the thermal tune both in liquid. The liquid and presence of the bead (10um) makes fitting an accurate curve in the thermal tune window a bit arbitrary because the peak falls off the spectrum and is assymetric. I found useful help here: http://nanoscaleworld.bruker-axs.com/nanoscaleworld/forums/p/1274/3436.aspx . I now measure the deflection sensitivity and spring constant in air, before glueing the bead on the cantilever. It is more reproducible and the fit looks very good, however I have one question regarding the temperature:

The actual experiment I want to do is in liquid at 37 degrees C. My spring constant is measured at ambient temperature since I can not heat up the air to 37 degrees. I measured the air temperature and took it into account in when calculating the spring constant (by entering the temp in the thermal tune window in Nanoscope). My question is whether I can use this spring constant for my measurements which will be performed at 37 degrees?

Thanks in advance,

Sjoerd 

 

System: Bioscope Catalyst

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Verified by Sjoerd

Hi Sjoerd,

It is generally assumed that the spring constant is constant with temperature.  That is probably not precisely true (modulus and dimensions of materials like Si change a bit with temperature), but the variation should be small compared to the uncertainty in the measurement.  If you want to investigate this further, you could try thermal tuning a different lever with a higher resonant frequency in liquid at different temperatures.  

Please note that the resonant frequency should be much higher than 1kHz so that the tail of the peak is not cut off.  Otherwise there will be a significant error associated with the integration.

--Bede

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Top 10 Contributor
280 Posts
Points 6,221
Bruker Employee
Verified by Sjoerd

Hi Sjoerd,

It is generally assumed that the spring constant is constant with temperature.  That is probably not precisely true (modulus and dimensions of materials like Si change a bit with temperature), but the variation should be small compared to the uncertainty in the measurement.  If you want to investigate this further, you could try thermal tuning a different lever with a higher resonant frequency in liquid at different temperatures.  

Please note that the resonant frequency should be much higher than 1kHz so that the tail of the peak is not cut off.  Otherwise there will be a significant error associated with the integration.

--Bede

Top 200 Contributor
6 Posts
Points 70
Sjoerd replied on Wed, Sep 28 2016 6:25 AM

Thank you Bede for your reply!

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