Determination of Contact Potential Difference by the Kelvin Probe (Part I) I. Basic Principles of Measurements

Abstract

Determination of electric potential difference using the Kelvin probe, i.e. vibrating capacitor technique, is one of the most sensitive measuring procedures in surface physics. Periodic modulation of distance between electrodes leads to changes in capacitance, thereby causing current to flow through the external circuit. The procedure of contactless, non-destructive determination of contact potential difference between an electrically conductive vibrating reference electrode and an electrically conductive sample is based on precise control measurement of Kelvin current flowing through a capacitor. The present research is devoted to creation of a new low-cost miniaturised measurement system to determine potential difference in real time and at high measurement resolution. Furthermore, using the electrode of a reference probe, the Kelvin method leads to both the indirect measurement of an electronic work function, or a contact potential of sample, and of a surface potential for insulator type samples. In the article, the first part of the research, i.e., the basic principles and prerequisites for establishment of such a measurement system are considered.

Determination of Contact Potential Difference by the Kelvin Probe (Part II) 2. Measurement System by Involving the Composite Bucking Voltage

“…At the same time, we have obtained high resolution in comparison with setups described above [8], i.e., 1-2 mV, besides, the proposed system provides continuous CPD measuring mode. That way the series of disadvantages mentioned above [1], [6] for such systems are eliminated, which creates preconditions of their wider dissemination and use.…”

“…Accordingly, as a result of the above-mentioned and fixed [1], [6] interaction between the main linearly rising component of bucking voltage and its second -the triangular component, the variablie voltage with average value V B (V B1 or types V B2 , see Fig. 1b) is generated.…”

“…This is a continuation (Part II) of article [1], which presents description of the corona discharge physics. Determination of the surface electric potential difference by the Kelvin probe, i.e., vibrating capacitor technique, is one of the most sensitive measuring procedures in surface physics for contact potential difference (CPD) measurement.…”

“…This contactless non-destructive method is based on using the traditional Kelvin probe placed plane-parallel to the sample electrode (see Fig. 1a) at a distance d 0 in stationary state, shaping the simple two-plate capacitor C. Based on the previous part of the paper [1], it can be assumed that prior ohmically contacting to the back side of either the electrically conductive or the semiconductor sample electrode to the metallic probe electrode the capacitor electrodes are electrically neutral, no macroscopic electric field arises, and the solids of electrodes share the same local vacuum level.…”

“…This charge transfers results, in accordance with the law of Volta's serial contacts, as an electric field at the gap between two plates of Kelvin condenser and a drop of a local vacuum level across this gap. Thus, the capacitor at a stationary electrode distance d 0 capacity C is charged by charge Q, and in this case the corresponding potential difference V CPD (Volta potential difference) in a gap between two electrodes is determined by difference of work functions of each electrode substance V CPD =DY, see more details [1]. Thereby, CPD must be measured in an open circuit, i.e., using the dielectric such as vacuum or air between the surfaces of inner plates.…”