Tapping mode oscillation amplitudes - how to determine the physical amplitude from the RMS values/ setpoint. (Also imaging liquid surfaces, in liquids!!!)

karamathj posted on Thu, May 23 2013 12:46 PM

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Dear experienced users!,

This is probably embarrassingly simple, but here goes... I want to know what amplitude, in nanometers, I am tapping with. I set my tune target to 1 V or thereabouts, the system seems to decide what setpt to use (I try to set it as close to 0.9 V or so to minimize forces, but it always seems to engage lower than that). In contact mode I know that for force curves one needs the V <-> nm conversion of the optical lever system. Is there a conversion factor I need in tapping mode to know the amplitude in nm???

I'm doing this because I'm trying to image oil drop surfaces. I've been very successful at this in air, but I always have to change my DRIVE AMPLITUDE after engage - increase it often by 5 or 6 times. This is to avoid a very jaggy image (the surface is followed but in a sawtooth way otherwise). The RMS increases only very slightly (although after retracting it shoots up). Does massively increasing the drive not mean I am massively increasing the amplitude of oscillation??? I'm caught between thinking I should use a large amplitude to get the RTESP tip the "energy" to escape the surface forces vs using tiny oscillations because, erm, I don't know, but large oscillations just seem wrong. Actually, I'm trying also to get images of the surfaces in water (in a liquid cell) too, with much more limited success. The trace and retrace really don't follow each other well. Ah - that's why I thought to use much smaller oscillations - I wanted to avoid moving the ambient water in the hope that this would improve the imaging.

Summary - (1) how can I find out the tapping mode oscillation amplitude in nanometers

(2) any tips on liquid surface imaging, especially in liquids and especially with reference to what amplitudes I should be using. I haven't found an article on this yet - if anyone knows of any, that would be great too!!!

Many many thanks in advance,

James Karamath