Vibrating capacitor methods

Fig. 4-28. Schematic layout of Kelvin s vibrating capacitor method to measure relative electrode potential of (a) electrode immersed in aqueous solution and of (b) electrode emersed from solution KP = Kelvin s probe 4 s = outer potential of aqueous solution 4>kp = outer potential of Kelvin s probe V and = applied voltages to cancel out a difference in the outer potential.

There are various experimental methods that can lead us to the value of Vs Physico-chemists consider the vibrating capacitor method to be one of the most efficient because it allows us to work under gas and at different temperatirre. 

The vibrating capacitor method known as the Kelvin-Zisman method was developed by Zisman based on the previous method. Instead of simply distancing the electrodes from each other, Zisman periodically vibrates an electrode, thus creating an alternating current that is easier to detect. 

Figure 6.34 presents the working principle of the vibrating capacitor method U is an opposite electromotive force that is inserted in the measurement circuit, Vdpc is the change in contact potential between the solid that forms the electrodes of capacitor C (previously denoted by Vrs), and R is an electrical resistance. 

The vibrating capacitor method is a zero-determining method, where measuring the contact potential difference Vdpc amoimts to measuring the opposite voltage U that leads to a zero current. Compared to other methods, this one has some interesting characteristics which we will develop throughout this study. 

The vibrating capacitor method, or Kelvin-Zisman method, is a non-destructive method that does not disturb the surface using photon or electron beams. It can be used for a large number of materials, and in a wide temperatnre and pressure range. It is therefore highly appropriate for the stndy of snrface properties of polyciystalline metal oxides. 

The vibrating capacitor method does not require high vacuums it measures work function values over a wide range of pressures and in varions atmosphere types. 

The following tables summarize the results of experimental work function data. Tjub is the substrate temperature in K during deposition. RT denotes room temperature. The methods of work function measurement are VC Vibrating capacitor method RP Retarding potential method SEC(E) and SEC(P) Electron- and photon-induced secondary electron method respectively FE Field emission method. A( )min is the work function change at the minimum, A( )ML is the work function change at one saturated monolayer, fig is the initial dipole moment. Where appears in the table, a minimum was not observed. The tables are adapted and updated from [89A1],... 

Experimental studies of interaction have been made on well-defined Pt (100) and (1010) surfaces [64, 65]. The experiments were performed in a standard UHV system equipped with facilities for LEED, AES work function measurement () with a Quadruple Mass Spectrometer and self-compensation vibration capacitor method. 

The vibrating capacitor method is based on the work of Lord Kelvin [1898K] and of Zisman [32Z]. A condensor is formed of the surface to be studied and a reference electrode in front of it which are connected by a ammeter and a variable voltage source. If the capacitance between the plates (sample and reference electrode) is changed, e.g., by changing their distance, a current will flow. By compensating the... 

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