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Hello,
I am using Veeco dimension icon.
I want to measure DMT modulus of hydrogel in the water. How to calibrate the deflection sensitivity, spring constant and tip radius? Should I do the calibration ScanAsyst fluid tip in the water or in the air? If in the water, how to do?
When I scan some PDMS samples, the line of DMT modules is flat or pixel. And I couldn't get a nice image of DMT modules. What should I do to fix this problem?
Thanks for your help!
Fangfang
Hi, you can calibrate deflection sens and spring constant in water on a flat and hard surface, for soft cantilever like scanasyst fluid, a glass sample should be ok for this calibration. tip radius can be done after exp in air. I would suggest you run single point force ramp to measure the modulus of hydrogel amd the new analysis software is quite convenient to analyze the force curves.
I guess you have overestimated your deflection sensitivity and thus it appears lines or pixels in DMT channel, you can try lowering your deflection sens value to see whether the problem can be solved.
Ang Li
Hi Fangfang,
I would recommend precalibrating the spring constant in air since the thermal tune method does not work as well in fluid. After doing this, you MUST do the deflection sensitivity calibration in fluid since it will be significantly different from the deflection sensitivity in air.
If the deflection sensitivity is not the problem (as Ang Li suggests), you may want to try changing the DMT modulus limit in case your modulus values are either out of range (>DMTModulus Limit/2), or at the bit noise level (<DMTModulus Limit/65536) of the measurement.
--Bede
Hello Ang and Bede,
Thanks for the suggestions. I will try to do some experiments in the fluid.
Regarding the DMT modulus, I calibrated the deflection sensitivity for ScanAsyst Air is about 67nm/V. It works good on the PDMS soft-1 reference sample. But if I scan to my own sample, it didn't work. I reduced the deflection sensitivity as Ang suggested to about 11 nm/V. The image of DMT modulus was back to normal. Should I trust the value from DMT modulus since I have changed the deflection sensitivity a lot.
Thanks!
I have one more question.
I was scanning some samples by ScanAsyst in air. When scanning, the z piezo voltage was not stable. The peak force was ok. At the start point, it was about -55 V. After 10 mins scanning, it changed to +80 V, and it kept increase until it turned to red. Why? and How to fix?
That usually means that something is wrong with the setup. For example, the sample may not be fixed well to the sample chuck or there is a problem with the tip or holder, or there has been a very large temperature change.
To debug, I would go back to your calibration standard and install a new probe. If that works, the problem most likely lies with the sample...
If the deflection sensitivity measured on a hard sample (Si, SiOx, etc.) is around 67nm/V, you should not have to reduce the defl sens so much (and you shouldn't believe numbers taken with such a low defl sens). Try adjusting the limits...
Hello Bede,
I tried to adjust the DMT modulus limit. It doesn't help. The line of DMT modulus was a flat line. I don't know where to adjust the bit noise level. Would you please tell me where it is?
fangfang