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Height tracking with the SKP370 or SKP470 module – Scanning Probes – Application Note 1

Latest updated: May 6, 2020

Abstract

Local electrochemistry probe measurements and especially Scanning Kelvin Probe (SKP) are most commonly used in constant height mode.
This has two drawbacks:

1. The topography of the sample can affect the measurement, hence it is necessary to perform scans at constant distance.
2. Some samples can be non-flat or curved and cannot be measured in constant height mode because the tip would simply crash.

By using SKP as a capacitance measurement, it is possible to measure the topography of the sample surface. Topography data can then be integrated in the actual SKP scan to maintain the probe at a constant distance from the sample, also called height-tracking. The use of SKP is now extended to any non-flat samples.
The note shows how to operate M370/M470 Scanning Kelvin Probe in height tracking-mode.

 

Introduction

The signal strength of the SKP technique and thus the ability to extract sensitive data depends on numerous factors. The main influences are the work-function difference of the materials involved (sample and probe), the probe tip size, the vibration amplitude and the proximity of the vibrating probe to the sample surface. A user may expect that the ambient noise throughout the M370 or M470 systems and the surrounding environment to remain approximately the same throughout an experiment, however, the signal strength can change due to variations in the parameters mentioned above.
Any measurement relies on a good signal to noise ratio, even that based on statistical techniques. At some point the noise can exceed the signal tosuch an extent that the measurement becomes undeterminable. To avoid this situation, the SKP370 or SKP470 user will want to maximise the signal strength in all cases, and will need to consider the effects of the parameters mentioned above to obtain good measurements. One way to can enhance the signal to noise ratio is to ensure a small probe to sample distance and maintain this distance constant over the whole scan area. To do this successfully, it is necessary to have the sample’s topography information over the scan area and to relieve the probe’s position as dictated by this topography as the probe scans over the surface. There are a number of different techniques that can provide the sample’s topography information…

 

To view the entire application note please click the download button below.