The Dynamic Nature of Hydridosilsesquioxane Clusters on Gold Surfaces

The chemisorption of the hydridosilsesquioxane clusters H<INF>8</INF>Si<INF>8</INF>O<INF>12</INF> and H<INF>10</INF>Si<INF>10</INF>O<INF>15</INF> onto a freshly evaporated gold surface has been observed by X-ray photoemission and reflection−absorption infrared spectroscopies. On the basis of these analytical techniques and supporting nonlocal density functional calculations, a single Si−Au bond at a cluster vertex is created through a surprising gold-mediated Si−H bond activation. The chemisorbed clusters are stable in a vacuum and when exposed to oxygen or water. Coverage-dependent peak frequency and infrared intensity shifts, characteristic of a chemically dynamic interface, are detected as a function of cluster overpressure. An equilibrium between the clusters and the gold surface is proposed, evidenced by a fairly constant rate of adsorption to gold for several coverage regimes.