Adsorption of oxygen onPt3Sn(110)studied by STM and LEED

Abstract

The adsorption of oxygen on the Pt 3 Sn͑110͒ alloy surface was studied by means of scanning tunneling microscopy ͑STM͒ and low-energy electron diffraction ͑LEED͒. After exposure to 2300 L O 2 at 750 K LEED shows additional c͑2 ϫ 2͒ spots with regard to the substrate p͑2 ϫ 1͒ pattern. This agrees straightforward with STM topographies revealing a thin layer of large protrusions, arranged in a pseudohexagonal lattice. This layer is split into domains separated by distinctive zigzagging boundaries. Post-annealing allowed to partially uncover substrate regions. That way it could be shown that the protrusions are located above Sn locations. Further post-annealing restored the original substrate completely. A model of the adlayer structure consistent with all STM and LEED findings is given. These features observed after high temperature oxygen exposure of the Pt 3 Sn͑110͒ surface resemble to a large extent structures obtained on the Pt 3 Sn͑111͒ surface under similar conditions. The observed structures can be understood in terms of Sn-O entities interacting with each other. However, results from the oxidation of Pt 3 Sn͑111͒ indicate the formation of a Sn layer with chemisorbed oxygen on top, but not of separated SnO x entities. The protrusion patterns observed with STM on both surfaces are a topographic signature of such Sn-O layers on Pt 3 Sn.

Promoter Effect of Early Stage Grown Surface Oxides: A Near-Ambient-Pressure XPS Study of CO Oxidation on PtSn Bimetallics

“…The question of the nature of the active phase is usually addressed on monometallic catalysts; however, such a question is even more relevant for bimetallic systems where the presence of the second metal adds a further interesting complexity. Among the most promising materials, PtSn systems have already given rise to exciting experimental and theoretical studies, − mainly as Pt 3 Sn, either bulk or surface alloy. Compared with pure Pt generally used as anode material in fuel cells, this alloy is expected to decrease the CO poisoning effect.…”

Structure of an Ultrathin Oxide on Pt3Sn(111) Solved by Machine Learning Enhanced Global Optimization**

“…Attempts at structure determination for this phase have been made using several techniques, including scanning tunneling microscopy (STM), low energy electron diffraction (LEED), X-ray photoelectron spectroscopy and diffraction (XPS/XPD) and low energy ion scattering (LEIS), [10,11] and further attempts have been made to characterize very similar tin oxide phases formed by deposition and oxidation of Sn on Pt(111). [7,9] Though it has been established that the structure is terminated by tin and oxygen, [11] the tin in the structure shows an XPS binding energy very close to that of tin in the alloy, hindering characterization of tin in the oxide and leading to the suggestion that most of the tin in the structure is in fact still alloyed with platinum, in a so-called "quasimetallic" state. [9] The dominance of only three protruding atoms-of unknown type-per unit cell in scanning probe micrographs and the absence of other features that would guide the construction of atomic models has further hindered structure determination by direct deduction.…”

“…Though the materials are of importance for a variety of catalytic processes, [1–6] the structures of oxides formed on their surfaces and the details of metal‐oxide interfaces involved remain poorly understood at the atomic level. This is despite several attempts, using a variety of techniques, to characterize experimentally the well‐defined oxide layers formed on single crystal surfaces [7–12] . A promising solution is to couple experiments closely with atomic structure prediction based on theory‐driven global optimization.…”

“…This is despite several attempts, using a variety of techniques, to characterize experimentally the well-defined oxide layers formed on single crystal surfaces. [7][8][9][10][11][12] A promising solution is to couple experiments closely with atomic structure prediction based on theorydriven global optimization. Density functional theory (DFT) based global optimization strategies have played an increasing role in structure prediction efforts for more than a decade, partly replacing labor intensive, intuition guided strategies.…”

Coexistence of type-II Dirac point and weak topological phase in Pt3Sn

“…2a. Experimentally, Pt 3 Sn has been studied regarding the electronic structure 31 , the atomic structure 29 , the surface structure [32][33][34][35][36] , the oxygen adsorption 37,38 , the catalytic properties 39 , etc. However, the topological features of the electronic structure have not been noticed.…”