Laser Light and Electrodes: Interaction Mechanisms and Electroanalytical Applications

摘要

The effect of 355 nm, 10 ns laser pulses of 3-11 MW cm~(-2) intensity on gold macrodisk electrodes has been investigated. Repetitive pulsing increases the standard heterogeneous +electron transfer rate constant, k°, for Fe(CN)_6~(3-/4-) from (9.2 ± 0.3) * 10~(-5) to (2.4 ± 0.1) * 10~(-3) cm s~(-1). The k°value becomes larger with increasing laser pulse intensity, and the enhancement is removed by conventional mechanical polishing. The effect of laser irradiation on the electrode surface has been investigated using scanning electron microscopy and by measuring the capacitance as well as the open circuit potential. These results suggest that the primary activation mechanism involves thermally driven desorption of adventitious surface impurities. The dependence of the laser-induced current-time transients on the applied potential has also been investigated. These transients do not exhibit the single exponential decay behavior expected if the laser pulse caused a simple change in the interfacial potential, e.g., through changes in the interfacial ion distribution. Rather, they are interpreted in terms of double layer charging at short times in response to a laser-induced change in the interfacial potential followed by a thermal diffusion process that depends on the applied potential. While the resistance is independent of the applied potential, the double layer capacitance of this interface that has been heated by the laser pulse to approximately 500 K shows a minimum at +0.100 V that is consistent with the potential of zero charge. The thermal conductivity and heat capacity depend strongly on the applied potential reaching maximum values at approximately +0.100 V of 3.19 J cm~(-1)K~(-1) and 0.13 J g~(-1)K~(-1), respectively. The lower values observed at more extreme potentials are consistent with laser-induced heating of the interface and provide a powerful new insight into the potential dependence of heat conduction in metals.