The high temperature adsorption of oxygen and the room temperature adsorption of CO on the Pt3Sn(111) and Pt3Sn(110) surfaces have been investigated by scanning tunneling microscopy (STM), low-energy electron diffraction (LEED), and Auger electron spectroscopy (AES). Beforehand the structure of the clean surfaces has been reviewed. After exposure to several 1000 L O2 at sample temperatures of about 750 K on both Pt3Sn(111) and (110) an ultra-thin Sn-O surface layer is formed. For the (111) X-ray photoelectron spectroscopy (XPS) indicates that this layer does not yet exhibit oxide properties. STM topographs of the Sn-O phase show on both surfaces meshes of highly corrugated protrusions commensurate with the substrate. In the case of the (111), after additional thermal annealing with STM and LEED a (4 × 4) reconstruction is observed, that is due to a (2 × 2) supermesh of depressions in the p(2 × 2) mesh of protrusions. This structure is similar to findings reported for the oxidation of Sn/Pt(111) surface alloys. X-ray photoelectron diffraction (XPD) measurements in comparison with simulations yield a tentative model for the (111) Sn-O layer. On the Pt3Sn(110) surface after oxygen exposure a c(2 × 2) hexagonal grid of protrusions with regard to the (2 × 1) substrate is observed with STM and LEED. STM reveals the existence of domains due to two equivalent positions of the Sn-O layer relative to the substrate. The domain boundaries zigzag around the [1-10] direction. The Sn-O layer can on both surfaces be removed by thermal annealing to more than 1050 K. After CO adsorption at room temperature on both Pt3Sn(111) and (110) adsorbate structures are observable with the STM. On the (111) two different types of structures are found: ordered patches of protrusions and unordered clusters. These structures are seen only on (√3 × √3)R30° substrate regions, not on p(2 × 2) regions. Surprisingly on the (110) the CO molecules mostly arrange in dimers. For both (111) and (110) saturation coverage is already reached at about 30% of a closed monolayer. The CO can be desorbed by slightly heating the samples to about 400 K. STM topographs show that on both surfaces CO adsorbes in Pt sites, not on Sn. It was possible to observe the CO adsorption on the (110) directly live with the STM. The observed adsorption processes hint to a dimer formation mechanism where a preadsorbed monomer and a CO molecule form the gas phase or a precursor phase stick together. When on partially Sn-O phase covered Pt3Sn(111) and (110) surfaces CO is adsorbed at room temperature, the respective structures coexist. Neither is CO observed on the Sn-O phase nor does a reaction between CO and O occur.

Dynamic behavior of impacting water drops on superhydrophobic solid surfaces provides important details on the stability/durability of such solid surfaces. Multi-scale surface roughness combined with a layer of low energy chemical is an essential surface modification process followed to create superhydrophobic capabilities on solid surfaces. The present work aims at studying the effect of low energy surface coating on droplet impact dynamics by carrying out experiments of water drop impacts on rough solid surfaces with and without chemical modification. A group of six aluminium alloy (Al6061) surfaces (three pairs) are prepared. Roughness, characterized in terms mean surface roughness, Ra, is introduced to these metallic surfaces using sand-paper polishing, electric discharge machining (EDM), and chemical based surface etching process. Low energy surface layer is laid on the rough surfaces by coating NeverWet hydrophobic solution, octadecyl-trichloro-silane (OTS), and perfluorodecyltricholorosilane (FAS-17). The impact dynamics of water drops is analyzed by capturing high speed videos for a range of drop Weber number from 1 to 570 and the salient features of drop impact process on the coated rough surfaces are compared with the corresponding uncoated rough surfaces. A one-to-one comparison on the spreading, fingering, receding, and final equilibrium of impacting drops on the coated and uncoated target surfaces is presented. Upon coating NeverWet, the original surface features of the base aluminium surface are completely covered by the hydrophobic coating material resulting in a fresh top surface layer. The outcomes as well as the bounce-off characteristics of impacting water drops on the coated surface are comparable to those observed on lotus leaf. The surface morphology features of rough aluminium surfaces coated with OTS and FAS-17 are comparable to those of the corresponding uncoated surfaces. The quantitative measurements on primary spreading and maximum spread factor of impacting drops are largely unaffected by the presence of low energy chemical coating. The dominant effect of surface coating is seen on the receding of impacting drops and hence the final drop configuration. This behavior is more prominently seen on EDM fabricated rough surface (larger Ra) combined with OTS coating than that on etching based rough surface (smaller Ra) combined with FAS-17 coating highlighting the dependence of coating effect with roughness features.