Single-crystal clean surface

The chemisorption of species occurs at specific sites on the electrode, for example on top of certain atoms, or in the bridge position between two atoms. Therefore, most adsorption studies are performed on well-defined surfaces, which means either on the surface of a liquid electrode or on a particular surface plane of a single crystal. Only fairly recently have electrochemists learned to prepare clean single crystal electrode surfaces, and much of the older work was done on mercury or on amalgams. 

Comparisons with the vibrational spectroscopic studies of the adsorption and dehydrogenation of ethene on single-crystal Pt surfaces (Section X.B.l) show that the di-cr-C2H4 to ethylidyne conversion occurs on (111) facets of the Pt crystallites of the catalysts. It is considered that the di-cr -C2H4 species occur on metal sites on which this conversion is not allowed, perhaps on (100), (110), or (210) facets. It is not clear whether the labile it-C2H4 species is formed on amorphous areas of the clean Pt particles or whether it occurs on sites which are affected by proximity of the metal oxide support (408) we favor the former possibility. 

The techniques and difficulties involved in the preparation and characterization of single crystal metal surfaces have been considered here in detail because the evaluation of chemical activity in terms of surface structure, particularly of the crystallographic surface structure, is one of the most promising applications of the vacuum microbalance. The preparation of flat, clean, undistorted single crystal samples suitable for surface studies is a difficult and tedious assignment. 

The tip is usually prepared by electropolishing, using one of the established recipes, a short length of the specimen material in the form of a thin rod or wire. Because of its small size, the resulting tip is usually a single crystal, the surface of which has to be cleaned in ultra-high vacuum within the microscope. Cleaning is usually accomplished either by low-temperature field evaporation or by thermal desorption. Field... 

Even a clean, single crystal emitter surface is not made up of a single plane alone for such a surface the work function, determined from the Fowler-Nordheim plot, is an average quantity. The total emission from a point is the sum of currents from the microscopic regions of uniform characteristics, which will be denoted by the subscript i. In the high applied fields, each contributes independently, and... 

This weakening ofNi-Ni surface bonds by adsorbed sulfur might lead one to expect that the corrosion rate should increase in this case. In fact, an increased anodic dissolution rate was observed for Ni Fe (100) in 0.05 M H2SO4 [9]. Figure A3.10.4 shows the anodic polarization curves for clean and S-covered single-crystal alloy surfaces. While both surfaces show the expected current increase with potential increase, the sulfur-covered surface clearly has an increased rate of dissolution. In addition, the sulfur coverage (measured using... 

Manufacturing of metal OTEs has been desaibed in detail by Bauhofer [362], Apart from the demands of the optical and electrical performance and the purity of the materials, the OTE-substrate system must meet the mechanical and chemical stability requirements (including the adhesion of the film to the substrate). To obtain a well-ordered, clean single-crystal metal surface (Pt, Ir Au,) the sample can be sputtered with Ar" ions, oxidized in 10 mbar of oxygen at 1000 K to remove surface carbon, and annealed at 1400 K [661, 662],... 

When atoms, molecules, or molecular fragments adsorb onto a single-crystal surface, they often arrange themselves into an ordered pattern. Generally, the size of the adsorbate-induced two-dimensional surface unit cell is larger than that of the clean surface. The same nomenclature is used to describe the surface unit cell of an adsorbate system as is used to describe a reconstructed surface, i.e. the synmietry is given with respect to the bulk tenninated (unreconstructed) two-dimensional surface unit cell. 

The Clean Single-Crystal-Surface Approach to Surface Reactions N. E. Farnsworth... 

Figure 2.8. STM image (unfiltered) of a Pt( 111) surface of a Pt single crystal interfaced with P"-A1203, a Na+ conductor showing different domains of Na coverage. The Pt(l 11 )-(2x2)-0 surface was initially covered by the Pt(ll l)-(2x2)-Na adlattice (domain A) and was intentionally only partly electrochemically cleaned (via positive UWR=1V potential application and Na+ removal into the P"-A1203 lattice) leading to the formation of clean domains (domain B) and of higher Na coverage domains (domain C) corresponding to a (V3 x V3 )-Na adlattice.

D.G. Kelly, M. Salmeron, and G.A. Somorjai, The adsorption and reactions of hydrocarbons on molybdenum single crystal surfaces when clean and in presence of coadsorbed sulfur or carbon, Surf. Sci. 175,465 (1986). 

Kinetics over the Mo(lOO) Crystal Surface. We have studied the hydrodesulfurization of thiophene over the initially clean Mo(lOO) single crystal surface in the temperature range 520K - 690K and at reactant pressures of 100 Torr < P(H ) 800 Torr and 0.1 Torr P(Th) < 10 Torr. Under these conditions the reaction is catalyzed at a constant rate for a period of approximately one hour after which the rate begins to decrease with time. The rates reported here are all initial rates of reaction calculated from data collected in the period over which they remain constant. 

Kinetics of Structure Insensitive Reactions Over Clean Single Crystal Surfaces... 

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