I was under the impression that work function should be measured in eV or meV but I have read literature stating ‘work function resolution of 1-3 eV. Is it right?
In physics, for charged particles (such as electrons) the formula E= eV applies where E is energy, 'e' is the charge on an electron and V is volts (or millivolts).
The work function is the energy required to remove an electron from the surface of a conductor such as a metal. It is an energy and the units are typically 'eV' or alternatively 'meV'.
The Kelvin probe actually measures a change in voltage either in volts or millivolts; sometimes this is called a surface potential change. So the difference between work function changes (measured in eV) and surface potential changes (measured in volts) is simply the charge on the electron 'e'. Most scientists and engineers recognise this and use the two terms independently.
You could take the following view: The Kelvin probe reports surface potential changes in mV, calibrating the tip work function and converting the measured voltage value to a sample work function allows you to quote in eV.
In summary, whilst technically correct, the work function resolution should be stated as 1-3 meV.
In addition the work function resolution is a function of the tip size. So for a larger tip (1-2 cm diameter) we will have 0.1 meV resolution. As our new Kelvin probe tip holder (which is an option) allows us to use any tip diameter then in our new literature we are quoting a work function resolution from 0.1 meV, or indeed 100 µeV.