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Hi, All,
Could anyone check if my imagination of tip movement during ramp in contact mode in liquid is correct or not? Could you correct any mistakes?
1. Once engaged, the tip is on the surface with a deflection that corresponds to the setpoint in the feedback panel.
2. Once shift to ramp mode from scan mode, the tip is still on the surface and maintained on the surface by the feedback system. The deflection is still the value defined by the setpoint.
3. When a ramp is initiated, the z piezo is retracted, and the tip moves up from the surface. The moving up stops when the distance between tip and surface equals to the ramp size. The above process from 1 to 3 is not shown in the force curve.
4. The z piezo extends and the tip moves toward the surface. When the deflection reaches the value set by the trigger threshold, the moving downward stops. This is the approaching portion of the force curve.
5. The z piezo retracts and the tip moves away from the surface. The moving stops at a distance defined by the ramp size. This is the withdrawing portion of the force curve.
6. The tip will not rest at this position. Instead, it will move down to the surface until the deflection reaches the value defined by the setpoint in the feedback panel if it is a single ramp. If it is a continuous ramp, this is skipped. This process is not shown in the force curve.
Additional information: Dimension Icon, 8.10 SW, relative trigger mode
Thanks a lot,
Shiyue
Hi Shiyue,
For ramping in contact mode there are some differences from what you have written:
Once you have switched into ramp mode, the scan feedback is turned off and the probe is immediately retracted to a position such that the distance between the probe and the surface is equal to the specified ramp size in the ramp parameters. This happens before any ramp is initiated - so you do not see this movement. When a ramp is initiated the probe moves towards the surface until the deflection reaches the value set by the trigger threshold (this is the approach portion of the force curve). Once the trigger threshold has been reached the piezo then turns around and the probe is moved away from the surface - thus starting the retract portion of the force curve. The probe continues to retract from the surface until it reaches a distance from the surface that, again, is equivalent to the ramp size. The probe then stops and stays at this position until another force curve is initiated.
Best,
Andrea
I want to add to Andrea's explanation, that after some operations in the Ramp mode the tip is moved towards the surface until the deflection setpoint (not the trigger point) is reached and then retracted.
At least it looks like that when watching the deflection signal during operations in the ramp mode.
This doesn't happen during ramping, but I think after X/Y offset and possibly other operations, and maybe before the ramping starts for the first time... is this correct?
Cheers,
Janne
Thanks a lot, Andrea and Janne.
In the ramp mode, when I lowered the feedback setpoint to below 0.2 V (to minimize any potential force between tip and surface), and tried to ramp again, the ramp size is automatically changed to 0 nm. And the value cannot be changed back or any other number until the feedback setpoint is increased. I thought that in the ramp mode, the feedback is off since the tip off surface. When it hits the surface during ramp, the force is controlled by the trigger threshold. So, I was confused. Janne's addition might explain. Therefore, after a ramp, the tip is off the surface. However, it will occasionally "feel" the surface and the feedback will occasionally be turned on in the ramp mode when ramp is not executed. And this keeps the relative positions of tip and surface.
Is my understanding correct? Does anyone know exactly how often or under what circumstances the tip will "feel" the surface?
Knowing exactly how the tip moves is important for the project I am doing.
Thanks again,