Autoprobe Questions

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Thomas Mueller replied on Wed, Jan 5 2011 6:05 PM

rated by 0 users

Hi Crimsonhen,

It is a question of working on the right side of the peak (for noncontact) vs the left side of the peak (for tapping).

To be more precise, in what is sometimes referred to as non-contact mode in ambient conditions, the drive frequency is set on the right side of the peak at a location where the amplitude has decreased by some fraction compared to the peak amplitude, typically a half width or a bit less from the top of the peak. The rationale being that a longer range attractive ("non-contact") interaction is present in addition to the shorter range repulse ("contact") force. The attractive interaction effectively lowers the resonance as if the spring constant was lowered. So then the expectation is that when entering the attractive regime, a stable feedback point is reached where the response on the high frequency side is lowered. In practice though, ambient conditions often lead to ill defined and varying shielding of long range forces, reducing the robustness of this approach irrespective of any instrumental factors. The result is often either loss of tracking (thus losing resolution) or a transition to hard tapping, that is, to a strong repulsive interaction, that may lead to premature tip damage. One of these may be happening if you are observing loss of resolution over time. This is why on our recently introduced new platforms, like the Innova that has replaced the Autoprobe, we tend to recommend the light tapping condition (and it is the default SW setting), where the resonance is set slightly to the left of the peak (typically at a position where the amplitude has dropped just 3-10%), which in most cases leads to more stable operation at minimal tip and sample wear.

Hope this explanation helps. Let us know if you have any additional questions.

Best,

Thomas