A UHV guarded Kelvin probe

A probe for use in measurements of contact potential differences (CPD) has been designed and constructed. The probe has the following unique features: (i) it is guarded against capacitive coupling between the probe and surfaces other than the sample; (ii) it can be heated so that adsorbed gases can be flashed off; (iii) it is excellent for use in UHV systems; (iv) it can be made small enough for nonuniformities in the work function of the sample material to be examined; (v) it is simple to construct. The effectiveness of such a probe to measure true CPD value was tested and the data presented here. Specifically the author is interested in: (i) the contact potential difference against the measured distances between probe and sample; (ii) resolution of the probe (the size of sample area contributing to the observed CPD); (iii) contact potential differences against amplitude of vibration of the probe and against the tilt of the probe about the axis perpendicular to the sample.