Electrochemical Noise A Powerful General Tool

The minimum value of the noise generated by a system is the thermal or Johnson noise resulting from the random motion of electrons or ions within the system when it is in thermal equilibrium with its surroundings. An expression for the Johnson noise in terms of a fluctuating voltage was first derived by Nyquist [2] in 1928 and takes the form 

Developments in Electrochemistry Science Inspired by Martin Fleischmann, First Edition. Edited by Derek Fletcher, Zhong-Qun Xian and David E. Williams. 

T is the absolute temperature, Re[Z] is the real part of the impedance of the system, and A/ the frequency bandwidth within which the noise is measured. Clearly, any noise that is to be studied must be detectable above the Johnson noise of the system. 

When the system under investigation is far from equilibrium - that is, when the current in one direction can be neglected in comparison with the current for the process being studied - the electrical noise may be presented as a random sequence of noncorrelated current pulses. Each of these pulses transfers an electric charge of value ye in the external circuit (shot noise), where e is the elementary electronic charge. The current noise of such a system is described by Schottky s theorem [3]  

During the late 1970s, instrumentation was improved by the availability of operational amplifiers of increasingly better quality (high open loop gain, wide frequency bandwidth. 

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