PeakForce KPFM-HV Imaging

The PeakForce Kelvin Probe Force Microscopy-HV mode maps the electrostatic potential at the sample surface by applying an AC voltage to the probe and measuring harmonics of that voltage. This AC technique extends the measurement range of AM-KPFM (see Lift Mode Surface Potential Imaging (AM-KPFM)) up to approximately ±200 V.

PeakForce KPFM-HV also 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 HV Theory

 

The electrostatic force on the cantilever is the derivative of the potential:

Equation 1:

where the voltage difference is:

Equation 2:

Combining Equation 1 with Equation 2 we get:

Equation 3:

For V_DC = 0 we have

Equation 4:

and

Equation 5:

Measuring the amplitudes at ω and 2ω, we use Equation 4 to measure the surface potential φ. Equation 5 provides an additional property channel, ∂C/∂z.

PeakForce KPFM HV Operation

PeakForce KPFM HV requires a PF KPFM-HV Application Module, shown in Figure 6.

Figure 6: The PF KPFM-HV Application Module (Dimension SPMs only)

The PF-KPFM HV Application Module requires an Applications Module Probe Holder. Either the Dimension SCM Probe Holder or the Dimension SSRM, TUNA and C-AFM Probe Holder will work.

PF KPFM-HV Probe Requirements

Bruker recommends PFQNE-AL probes for PeakForce KPFM-HV measurements.

Sample Preparation

Prepare the sample as described in Electrical Sample Preparation.

PF KPFM-HV 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.

(Hover over the image to view larger)

Figure 7: The PF KPFM-HV Select Experiment window

	Select the following: Experiment Category: Electrical & Magnetic Experiment Group: Electrical & Magnetic Lift Modes Select Experiment: PeakForce KPFM-HV
	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 8.

Figure 8: Align the laser on the cantilever and place the crosshair there.

	Engage the probe onto the sample
	Scan the sample
	Set the Lift Scan Height as low as possible without hitting the sample. Increase the Lift Scan Height if the probe touches the sample - symptoms will be a very noisy potential scan. Refer to the PeakForce QNM Operation sections for details regarding PeakForce mode imaging.

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