Photoelectrochemically induced periodical deposition patterns of platinum on p-InP. Part 1: experiment and observations

Abstract

Platinum was deposited photocathodically on single-crystalline p-InP from hexachloroplatinate(IV) in buffered aqueous solution (pH 2). A scanning optical microscope set up equipped with a He/Ne-laser (632.8 nm) was used for producing the deposits at different electrode potentials and under variable conditions of light exposure time and intensity. This was done in different spatially confined regions of the electrode surface, which were laser-scanned continuously each along a line. In unstirred solution spatially periodical patterns of platinum deposits (period length 13–19 µm) showing regular variations in the amount of platinum and concomitant oscillations of the deposition photocurrent were observed. The periodicity of the pattern was almost invariant with changes of potential, light intensity and scan speed of the laser spot. Scanning electron microscopy demonstrated that the pattern arises from an agglomerate of platinum grains (diameter ca. 0.3 µm) having a periodically varying number per unit area. The tendency of pattern formation was diminished in stirred solution. The observations are discussed qualitatively.