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Hi,
I try to get (high) resolution images of intermediate filaments on mica in buffer solution. In principle it works but I have a strange reproducible problem during engage:
When I am far away from the surface the applied drive amplitude is around 500mV which results in 200-250mV amplitude at a frequency of 6-7kHz. During the approach at some point (a few microns above the surface) the measured amplitude increases heavily (20-50%). A few seconds later I get the TM Deflection delta error (deflection is higher than 5V) and the AFM false engages. At this point the tip is in hard contact with the surface and the deflection goes up about 5-9V (free deflection was 0V). Then increasing the amplitude set-point releases the tip from the surface and I have normal feedback with the deflection again at the initial 0V.
If I go down with the tip manually until the measured amplitude is maximized, set a proper set-point and engage with the step motor I have the same problem. The deflection immediately jumps up 5-9V when I go into contact and increasing the setpoint then releases somehow the tip and I have again the initial deflection. It is not dependend on the setpoint which is normally about 5mV below the free amplitude.
When I do normal force volume on the surface I do not see any huge attractive force at the used buffer conditions (max 20pN below 2nm tip-sample distance).
Setup: Multimode V with NS V controller, standard liquid-cell (MTFML). Cantilever is SNL-C (0.12N/m, 120um) in buffer (250mM monovalent salt, pH 7.4). Software is Nanoscope 7.3.
Are there any known solutions for this problem?
Thank you.
Hi Raphael,
It sounds like your sample is lifting up causing the problem. Check that i) your sample is properly glued down and ii) that your cleave of the mica is good. Another observation is that you mentioned you use the c-lever with 0.12 N/m. The c-lever should be stiffer. Please select the thin short lever.
Good luck and keep us posted,
Stefan
The sample is glued properly and the cleave is also good. I have the same problem also with glass and silicon surfaces.
Stefan, you're right, the c-lever I'm using has its k around 0.15-0.25.
I am now playing with the "tapping engage" settings which shows some effect but the problem still exists.
The only way of a "smooth" engage is to go down via the engage process of the software while monitoring the amplitude. As soon as the amplitude increases faster, I stop the engage process, go into false engage mode and finish the last steps using the step motor function of the software.
Is it normal for the short C-lever on an SNL chip that the amplitude is around 300mV with a drive amplitude of about 600-1000mV ? (Multimode V with normal liquid cell MTFML)
Cheers, Raphael