Thermogalvanic Behavior of Acidic Cu2+/Cu System Induced by Laser Irradiation

Abstract

The mechanism responsible for the electroless copper deposition on a copper electrode in an acidic copper sulfate solution upon laser irradiation was investigated. The system served as a thermogalvanic cell and a highly selective copper deposit was formed at the laser‐irradiated center without any chemical reductant added. The deposit's thickness reached 510 μm after an hour's irradiation with the incident laser power density being controlled at . The deposition rates, however, decayed as the incident laser power was further raised. Finally an etched hole instead of a deposit was found as the incident laser power density exceeded . The rather peculiar decay of the copper deposition rate at high incident laser power densities can be interpreted to be owing to three competitive processes involved in the electroless copper deposition: (i) a thermogalvanic deposition process, which is the predominant one at the lower incident laser power densities condition, (ii) a copper dissolution process due to the corrosion reaction, , which is predominant at high incident laser power densities, (iii) incomplete consecutive discharge reduction process due to the loss of cuprous ions by violent microstirring under high laser power density irradiation condition. A net etching effect instead of an electroless deposition can be obtained under the extreme case.