An experimental technique for characterising distortions in scanning Kelvin probe microscope images

What is it about?

In optical microscopy, a common technique for characterising the resolution of a microscope involves measuring a point spread function, which describes the image that would be generated by a tiny point of light much smaller than the microscope's resolution. In this work, we wanted to show how a similar approach could be applied to scanning Kelvin probe microscopy (a non-optical technique for imaging the electrical properties of surfaces). We found that the measured point spread functions are not simply related to the geometry of the microscope but also vary significantly with measurement parameters such as scan speed or feedback settings.

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Photo by Laura Ockel on Unsplash

Photo by Laura Ockel on Unsplash

Why is it important?

In a typical scanning Kelvin probe microscopy image, the measured signal is distorted by long-range interactions between the scanning probe and distant parts of the samples. These distortions can be made worse by using high scanning speeds or an improperly tuned feedback system. In order to achieve the best possible resolution, without compromising scan speed, it is necessary to understand and correct for these distortions. Previous approaches focused on using known information about the system geometry to account for long-range electrostatic interactions between the probe and sample; however, these approaches can fail to reveal or correct for measurement specific effects such as scan speed or an improperly tuned feedback system. Our approach involves measuring a suitable calibration target using measurement settings which match those used to measure the sample in order to characterise and correct for the effect of these long range interactions.

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