Electric Techniques

The two most common electric techniques used with the MultiMode 8 microscope are Electric Force Microscopy (EFM) and Surface Potential Detection. Both modes make use of Interleave and LiftMode procedures. Ensure you are familiar with Operation of Interleave Scanning and LiftMode before attempting electric measurements.

Electric techniques are similar to Magnetic Force Microscopy (MFM). The two-pass LiftMode measurement allows the imaging of relatively weak but long-range electrostatic interactions while minimizing the influence of topography. In the case of MFM, the system is measuring long-range magnetic fields. LiftMode records measurements in two passes, each consisting of one trace and one retrace, across each scan line. First, LiftMode records topographical data in TappingMode on one trace and retrace. Then, the tip raises to the Lift Scan Height, and performs a second trace and retrace while maintaining a constant separation between the tip and local surface topography.

Electric Force Microscopy Overview

Electric Force Microscopy (EFM) measures variations in the electric field gradient above a sample. The sample may be conducting, nonconducting, or mixed. Because the surface topography shapes the electric field gradient, large differences in topography make it difficult to distinguish electric field variations due to topography or due to a true variation in the field source. The best samples for EFM are samples with fairly smooth surface topography. The field source could be trapped charges, applied voltage, and so on. Samples with insulating layers (passivation) on top of conducting regions are also good candidates for EFM.

Surface Potential Imaging Overview

Surface Potential Detection measures the effective surface voltage of the sample by adjusting the voltage on the tip so that it feels a minimum electric force from the sample. (In this state, the voltage on the tip and sample is the same.) Samples for surface potential measurements should have an equivalent surface voltage of less than ±10 V, and operation is easiest for voltage ranges of ±5 V. The noise level of this technique is typically 10 mV. Samples may consist of conducting and nonconducting regions, but the conducting regions should not be passivated. Samples with regions of different materials will also show contrast due to contact potential differences. Quantitative voltage measurements can be made of the relative voltages within a single image.

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