PeakForce KPFM-AM Imaging

PeakForce-KPFM-AM is a is a two-pass procedure where the surface topography and nanomechanical properties are obtained using Bruker's proprietary Peak Force Tapping Mode in the first pass and the surface potential or work function in the second pass using the Lift Mode Surface Potential Imaging (AM-KPFM) mode:

1. The cantilever measures surface topography and nanomechanical properties on the first (main) scan (trace and retrace).
2. The cantilever ascends to the Lift Scan Height.
3. The cantilever then follows the stored surface topography at the lift height above the sample while an oscillating voltage V_ACsin(ωt) is applied directly to the probe tip. If there is a DC voltage difference between the tip and sample, then there will be an oscillating electric force on the cantilever at the frequency ω. This causes the cantilever to vibrate, and an amplitude can be detected on the second (interleave) scan.

PeakForce KPFM-AM leverages the advantages of PeakForce Tapping:

• Direct force control, eliminating artifacts that result from tip and sample damage
• Self-optimization using ScanAsyst
• Dramatically improved ease of use through the ScanAsyst™ imaging mode
• Spatially correlated nanomechanical information with PeakForce QNM

PeakForce KPFM-AM Probe Requirements

Bruker recommends PFQNE-AL probes for PeakForce KPFM measurements.

Sample Preparation

Prepare the sample as described in Electrical Sample Preparation.

PeakForce KPFM-AM Procedure

	Mount a sample onto the sample holder. Mount an appropriate probe into the standard probe holder (see Prepare and Load the Cantilever Holder for details).
	Click the Select Experiment icon to open the Select Experiment window, shown in Figure 1.

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Figure 1: The PeakForce-KPFM Select Experiment window

	Select the following: Experiment Category: Electrical & Magnetic Experiment Group: Electrical & Magnetic Lift Modes Select Experiment: PeakForce KPFM-AM
	Click Load Experiment.
	Click the Setup icon to open the Setup window.
	Align the laser on the cantilever and place the crosshair there. See Figure 2.

Figure 2: Align the laser on the cantilever and place the crosshair there.

Figure 3: The HSDC window, indicating that a cantilever tune operation is underway.

	Engage the probe onto the sample
	Scan the sample.
	Set the Lift Scan Height as low as possible without hitting the sample, typically 75 - 100 nm. Entering a value in the Potential Offset field adds that value to the measured value in the Potential channel. This can be particularly useful when measuring work functions as this function measures the difference in potential between the probe and the sample - entering the value of the work function of the probe will then provide a direct measurement of work function of the sample. NOTE: The stored data is unaffected by the Potential Offset. I.e. offline measurements do not see this input. Refer to the PeakForce QNM Operation sections for details regarding PeakForce mode imaging.

Advanced PeakForce KPFM-AM Operation

Automatic frequency selection is the default for PeakForce KPFM imaging. You may wish, however, to manually select an operating frequency. To do this:

	Enter the Expanded mode.
	Set Freq. Control in the Potential (Interleave), shown in Figure 4, panel to User-defined.

Figure 4: Selecting User-defined Frequency Control

Figure 5: The PeakForce KPFM Generic Lock-In window

	Select Tapping Piezo in the Drive Routing panel of Lock-In1.
	Click Sweep to open the Generic Sweep window, shown in Figure 6.

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Figure 6: The Generic Sweep window

Figure 7: Set the Drive Routing to Internal

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