The surface and materials science of tin oxide

Supported Catalysts Weiting Yu,† Marc D. Porosoff,† and Jingguang G. Chen*,†,‡,§ †Catalysis Center for Energy Innovation, Department of Chemical and Bimolecular Engineering, University of Delaware, Newark, Delaware 19716, United States ‡Department of Chemical Engineering, Columbia University, New York, New York 10027, United States Chemistry Department, Brookhaven National Laboratory, Upton, New York 11973, United States

Review of Pt-based bimetallic catalysis: from model surfaces to supported catalysts.

Nanostructured oxides in chemistry: characterization and properties.

Germanene, a 2D honeycomb lattice analogous to graphene, is fabricated on a Pt(111) surface. It exhibits a buckled configuration with a (3 x 3) superlattice coinciding with the substrate's (root 19 x root 19) superstructure. Covalent bonds exist throughout the germanene layer. The resulting high-quality germanene enables researchers to explore the fundamentals of germanene and its potential applications.

Buckled Germanene Formation on Pt(111)

A graphene monolayer has been prepared on an Ir(111) single crystal via pyrolytic cleavage of ethylene (C2H4). The resulting superstructure has been examined with scanning tunneling microscopy (STM) and low energy electron diffraction. It has been identified as a well aligned, incommensurate (9.32?9.32) pattern, which is described as a moir?. This pattern shows three distinct regions resulting from different local configurations of the carbon adlayer with respect to the Ir-substrate. These regions are imaged differently by STM and differ strongly in their ability to bind metal deposits.

https://iopscience.iop.org/article/10.1088/1367-2630/10/4/043033/pdf

Structure of epitaxial graphene on Ir(111)

Tin-oxide films were grown on Pt(111) substrates by oxidation of Sn/Pt surface alloys using ${\mathrm{NO}}_{2}$ exposures or by deposition of Sn in an ${\mathrm{NO}}_{2}$ ambient gas. Structural aspects of monolayer tin-oxide films were reported previously [Phys. Rev. B 64, 245402/1 (2001)]. At elevated substrate temperatures, growth of tin-oxide multilayers proceeds in a Stranski-Krastanov mode, i.e., the Pt substrate is covered with a monolayer thick tin-oxide wetting-layer before Sn-oxide crystallites form. The crystallites were tens to hundreds of nanometers in lateral size and were identified by scanning tunneling microscopy to be rutile ${\mathrm{SnO}}_{2}.$ These had a height of a few monolayers exposing the (011) crystal plane parallel to the Pt substrate. The low misfit of this crystal face with respect to the Pt(111) lattice apparently stabilizes this plane which is otherwise relatively energetically unfavorable. These studies demonstrate the importance of metal substrates in imposing structure and crystallographic orientation on oxide films. X-ray photoelectron spectroscopy studies of the tin-oxide films confirmed the existence of three Sn states that have been labeled previously as metallic, ``quasimetallic,'' and oxidic Sn. We conclude that the ``quasimetallic'' state results from oxidized Sn that is still alloyed within the Pt surface layer. Ultraviolet photoelectron spectroscopy of the valance band and electron energy loss spectroscopy confirmed a ${\mathrm{SnO}}_{2}$ stoichiometry for multilayer tin-oxide films. High-resolution electron energy loss spectroscopy was used to identify characteristic vibrational modes for the different monolayer films. The ${\mathrm{SnO}}_{2}$ crystallites, although only a few monolayers high and tens of nanometers in width, exhibit bulklike vibrational and electronic properties.

Epitaxial growth of tin oxide on Pt(111): Structure and properties of wetting layers and SnO 2 crystallites

Electronic contrast in scanning tunneling microscopy of Sn–Pt(111) surface alloys

Submonolayer Sn deposits on Pt(111) and Sn incorporated in a $(\sqrt{3}\ifmmode\times\else\texttimes\fi{}\sqrt{3})R30\ifmmode^\circ\else\textdegree\fi{}$ Sn/Pt(111) surface alloy were oxidized by ${\mathrm{NO}}_{2}$ under ultrahigh-vacuum conditions. The oxide films formed were characterized by Auger-electron spectroscopy, low-energy electron diffraction (LEED), and scanning tunneling microscopy (STM). Four different surface morphologies were identified, depending on the preparation conditions, each of them exhibiting a distinct LEED pattern. STM revealed two ordered epitaxial overlayers. One is interpreted as the adsorption of SnO pseudomolecules at preferential sites to form a $(4\ifmmode\times\else\texttimes\fi{}4)$ coincidence lattice with the substrate. The other structure forms an incommensurate tin oxide overlayer, exhibiting a long-range Moir\'e pattern. The remaining LEED patterns are associated with the formation of a regular stress-relief pattern that can transform into an ordered array of tin oxide islands upon repeated oxidation. This ordered island array exhibited a $(5\ifmmode\times\else\texttimes\fi{}5)$ superlattice with respect to the Pt(111) substrate. The variety of ${\mathrm{SnO}}_{x}$ overlayer morphologies is attributed to subtle differences in the oxide stoichiometry and alterations in the oxide/metal interface, in particular Pt-Sn alloying.

Structure of monolayer tin oxide films on Pt(111) formed using NO 2 as an efficient oxidant

TPD, HREELS and UPS study of the adsorption and reaction of methyl nitrite (CH3ONO) on Pt(111)

Ordered (2×2) and (√3×√3)R30° Pt–Sn(111) surface alloys were oxidized by NO2 exposure at 400 K under ultrahigh vacuum conditions. The evolution of the surface morphology with annealing temperature was characterized by using low energy electron diffraction (LEED), scanning tunneling microscopy, Auger electron spectroscopy, and x-ray photoelectron spectroscopy. Both oxidized surface alloys form a SnOx overlayer that wets the substrate. However, the SnOx film does not completely cover the surface for the oxidized (2×2) surface alloy. For the oxidized (√3×√3)R30° surface alloy, an ordered (4×4) LEED pattern is formed upon flash annealing above 900 K. The formation of this ordered SnOx adlayer coincides with Sn segregation from the bulk to the interface region. A model for the (4×4) structure is discussed. The SnOx overlayer formed by oxidation of the (2×2) surface alloy is significantly less thermally stable than the oxidized (√3×√3)R30° surface alloy. Exothermic alloying of Sn with Pt may facilitate the decomposition of the oxide overlayers. Differences in the amount of subsurface tin and its segregation to the surface is proposed to explain the thermal stabilities of the oxide layers. The incompleteness of the SnOx overlayer and less subsurface tin for the oxidized (2×2) surface alloy is proposed to explain its significant lower thermal stability.Ordered (2×2) and (√3×√3)R30° Pt–Sn(111) surface alloys were oxidized by NO2 exposure at 400 K under ultrahigh vacuum conditions. The evolution of the surface morphology with annealing temperature was characterized by using low energy electron diffraction (LEED), scanning tunneling microscopy, Auger electron spectroscopy, and x-ray photoelectron spectroscopy. Both oxidized surface alloys form a SnOx overlayer that wets the substrate. However, the SnOx film does not completely cover the surface for the oxidized (2×2) surface alloy. For the oxidized (√3×√3)R30° surface alloy, an ordered (4×4) LEED pattern is formed upon flash annealing above 900 K. The formation of this ordered SnOx adlayer coincides with Sn segregation from the bulk to the interface region. A model for the (4×4) structure is discussed. The SnOx overlayer formed by oxidation of the (2×2) surface alloy is significantly less thermally stable than the oxidized (√3×√3)R30° surface alloy. Exothermic alloying of Sn with Pt may facilitate the deco...

Tin-oxide overlayer formation by oxidation of Pt–Sn(111) surface alloys

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