Potential-dependent water orientation on Pt(111) stepped surfaces from laser-pulsed experiments

Coulostatic potential transients induced by nanosecond pulsed laser irradiation on Pt(1 1 1) stepped surfaces in perchloric acid solutions are analyzed here. The results provide unique information on the effect of the structure of the metal surface on the potential-dependent water reorientation at the electrified interphase. The most significant information is obtained from the sign and shape of the laser-induced transients. The existence of two potentials where the transient is zero can be related to the local properties of the surface, i.e. the existence of two local potentials of zero free charge, corresponding to the step and terrace sites. The dependency of these quantities with the step density is studied in detail. In addition, it is found that the presence of steps significantly slows down the coulostatic response at potentials in the double-layer region, which has been interpreted as a decrease in the velocity of water reorganization. The corresponding relaxation time is estimated and its dependency with the step density is also analyzed. (c) 2008 Elsevier Ltd. All rights reserved.