If in KP020 the tip is 2 mm, does that mean that the lateral resolution is also 2 mm? Or is it the length of the tip and why is this important?
We estimate that a 2 mm tip provides sufficient spatial resolution for most of our users to get started. However we also offer a 50 micron tip and in this case the scan size is typical 500 - 3000 microns per side. Please view the attached Probe Resolution PDF with some examples of large and small scans.
The Kelvin method is a capacitive method and thus the probe averages the work function underneath the tip. The spatial resolution is essentially the probe diameter. Newton’s fringing field terms do apply (to broaden the effective area) however in general this is not an issue with macroscopic tips. Professor Baikie has achieved 2 micron resolution and on binary systems (2 work function involved) has applied 2D deconvolution to determine the precise location of an interface with 1/20th of the tip diameter. Though he does not claim to be able to do both at once!
Higher spatial resolution is feasible however as we are approaching the limits of the measurement environment and operator capabilities, we have elected to supply 2 mm tips as standard and 50 micron tips for anyone who wants higher resolution. We also offer an in-line tip holder that allows the client to screw in any diameter tip they require. We use this system form our larger SPV tips: 5, 10 and 20 mm diameter (semi-transparent).
In summary the tip diameter is the lateral spatial resolution, the length of the tip is not so important, obviously if it is too long then the tip may oscillate in the lateral direction and this would degrade resolution.