Spectroscopy of Stochastic Signals (3S) has been used to study conduction behavior in electrochemically deposited conductive polymers (CP) using as example polyaniline and poly(3-methyl thiophene). Within the 3S approach, the conduction process is considered as a stochastic process in heterogeneous disordered system rather than as some classical conduction mechanisms like Schottky or Poole-Frenkel emission.
We have been able to distinguish several modes of the conduction process in conducting polymers using the 3S methodology. Particularly, we have established that the transport of charge carriers in highly doped CPs is much less correlated than in non-doped ones, that is, at low doping levels elementary processes involved in the conduction are more correlated than in highly doped polymer. By increasing applied electric field we also achieve lower correlation in a sequence of elementary events contributing to the conductivity of CP.
Apparently, the change in the correlation length corresponds to changing mechanism of the electrical conduction. The lower correlation in highly doped sample can be attributed to various factors including change in CP conformation, enhancement in inter-chain charge transfer and generation of polaron lattice.
The obtained results show the high informative potential of the 3S method in studying conduction mechanism in conducting polymers.
The paper analyses the nature of chaotic and well-ordered oscillations of the anodic potential and open circuit potential of silicon immersed in aqueous electrolytes. These oscillations are observed when experimental conditions are fine tuned in what corresponds to the current flowing through the system, composition of electrolyte, its viscosity, etc. It is assumed that the oscillations are due to the accumulation of mechanical stress in the thin (50-80 nm) oxide film formed at the surface of silicon as a result of electrochemical anodic reaction. The stress is released by local etching of the oxide and its lifting-on from the Si surface. The process repeats again and again yielding long-lasting oscillations of the anodic potential value (amplitude around 1-15 V, period 20-150 s) or of the open circuit potential (several hundreds milli-volts). Along with temporal ordering of the process (oscillations of potential) there occurs a spatial ordering in the system - the surface of corroding Si sample is covered with hexagonally ordered semi-spherical cells (diameter about 700 nm). The effect is well-fit by the general phenomenology of chaos-order transitions in che4mical systems (bifurcations), strange attractors are the intrinsic features of these oscillations) and its kinetics is very similar to that of the Belousov-Zabotinsky reaction. However, oscillatory processes on the corroding Si surface are caused by quite specific physical and chemical mechanisms, which are not well understood presently. We present the microscopic model for the oscillatory behavior which involves, generation of local mechanical stress at the Si/electrolyte interface, non-linear electrochemical etching of Si, localization of the electric field at the etched surface, etc.
Conference Committee Involvement (1)
Noise and Information in Nanoelectronics, Sensors, and Standards II
26 May 2004 | Maspalomas, Gran Canaria Island, Spain