Experimental observation of two-dimensional charge polarization in unisized platinum cluster disk bonded to silicon(1 1 1) surface

Geometry control of size selected Pt clusters bound to Si substrate surface by cluster impact deposition

Geometry of platinum clusters, Pt_N (N = 30-71), supported on a silicon substrate was investigated, aiming to control the geometry. The supported clusters were prepared by the impact of size-selected Pt_N ⁺ onto the substrate at a given collision energy (cluster-impact deposition), and their geometry was observed by means of a scanning-tunneling microscope. Even at the collision energy of 1 eV per Pt atom, sufficiently strong Pt-Si interaction between Pt_N (N = 30 and 45) and the Si substrate allows them to be supported as close-packed monatomic-layered Pt disks, while at N = 60, multilayered shapes exist besides the monatomic-layered shape, the fraction of which increases at N = 71. When the collision energy is increased, Si atoms located at the interface between the cluster and Si substrate dissolve into the cluster, and with further increase in the collision energy, the Pt-Si cluster is partially implanted into the substrate. The transition in the shape of the supported clusters with the collision energy and the cluster size was explained according to the deformation of the clusters and the substrate surface by the cluster impact. It is proposed that the momentum of Pt_N ⁺ per its cross section is a good index to control the geometry in the case of strong cluster-support interaction such as Pt and Si.

Steady-state reaction kinetics of CO oxidation catalyzed by uni-sized Pt30 clusters directly bound to Si surface

Catalytic CO oxidation driven by uni-sized Pt₃₀ bound to a Si substrate, at the interface of which electrons are accumulated. The low-temperature and anti-CO-poisoning performance has been evidenced with continuous and simultaneous supply of CO and O₂.

Systematic study on novel catalytic activity of CO oxidation driven by strong electronic interaction between the monatomic-layered Pt30 cluster disk and the Si substrate

Catalytic activity of thermal CO oxidation was studied for monatomic-layered platinum cluster disks, Pt30, bonded to the (111) surface of a silicon substrate. Temperature-programmed desorption (TPD) measurements were repeated for a given cluster sample with a systematic change in the reactant amounts supplied, and the peaks observed in the TPD spectra were deconvoluted so as to obtain probabilities of individual reactions. It was concluded that this system possesses an ability of low-temperature reductive activation of oxygen molecules, which is one of the critical steps in the CO oxidation. This high performance is explained in terms of negative charges accumulated at a sub-nano interface between the cluster disk and the silicon substrate surface as a result of their strong electronic interaction.