Use of LiftMode with TappingMode

Additional considerations when using LiftMode with TappingMode AFM are discussed below.

Main Drive Amplitude and Frequency selection

As usual, these parameters are set when you tune the cantilever prior to engaging. It is helpful to keep in mind the measurements to be done in LiftMode when setting these values. For example, if Amplitude data will be monitored during the Lift scan for Magnetic Force Microscopy (MFM), the Drive Frequency should be set to the side of the resonance (however, certain parameters can be set independently for the interleave scan; see below.)

Setpoint Selection

When the main and interleave Drive AmplitudeAmplitude of the signal used to oscillate a tip in TappingMode. and Drive FrequencyFrequency of the signal used to oscillate a tip in TappingMode. are set to the same value (i.e., when these parameters in the Interleave panel are grayed out), the cantilever oscillation amplitude increases to the free oscillation amplitude when the tip is lifted off the surface in LiftMode. If a small setpointOperator-selected threshold used as the target of the feedback control loop. value forces a large decrease in oscillation amplitude while the feedback is running, the amplitude can grow considerably when the tip is lifted free of the sample surface. The change can also be large if the main Drive Amplitude was increased or the main Drive Frequency altered after the tip was engaged. The vibration amplitude remains at the setpoint during the main scan even if these parameters are changed. This could result in the tip hitting the surface in the lift scan for small Lift Scan Heights.

Interleave Drive Amplitude and Frequency Selection

The cantilever Drive Amplitude for the Lift scan can be set independently of the main Drive Amplitude. Click on the parameter in the Interleave panel to enable it (turns green) and adjust the value. This allows the tuning of a measurement in the Lift scan lines without disturbing the topography data acquired during the Main scan lines. The Interleave Drive Amplitude must be set low enough that the tip does not strike the surface during the Lift pass.

The Interleave Drive Frequency can also be adjusted, which may be useful if acquiring amplitude data in LiftMode.

Amplitude Data Interpretation

When monitoring amplitude data in LiftMode, brighter regions correspond to larger amplitude, and darker regions to smaller amplitude.

Cantilever Oscillation Amplitude

The selection of the oscillation amplitude in LiftMode depends on the quantity to be measured. For force gradients that are small in magnitude but occur over relatively large distances (sometimes hundreds of nanometers, as with magnetic or electric forces), the oscillation amplitude can be large, which for some applications may be beneficial. The Lift Scan Height must be correspondingly large so that the tip does not strike the surface. However, the lateral resolution of far field (MFM or EFM) measurements decreases with distance from the surface. Typically, the resolution is limited to a value (in nm) roughly equal to the Lift scan height.

Small amplitudes must be used to sense force gradients, such as Van der Waals forces, which occur over short distances (typically a few nm). As much of the cantilever travel as possible should be within the range of the force gradient.

Related Topics

Open topic with navigation