Chemisorption of CO on Ir(100) studied by photoemission☆
Abstract
Chemisorption of cabon monoxide on a reconstructed Ir(100) surface has been studied by means of LEED and photoemission. In the photoemission spectrum, apart from a low lying peak due to the 4σ-orbital of CO, there is also a broad bump divided by a clear dip. The upper part of this double peak is assigned to the 5σ orbital and the lower part to the 1 π orbital of CO.
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Cited by (58)
Effective Work Functions of the Elements: Database, Most probable value, Previously recommended value, Polycrystalline thermionic contrast, Change at critical temperature, Anisotropic dependence sequence, Particle size dependence
2022, Progress in Surface ScienceAs a much-enriched supplement to the previous review paper entitled the “Effective work functions for ionic and electronic emissions from mono- and polycrystalline surfaces” [Prog. Surf. Sci. 83 (2008) 1–165], the present monograph summarizes a comprehensive and up-to-date database in Table 1, which includes more than ten thousands of experimental and theoretical data accumulated mainly during the last half century on the work functions (, and ) effective for positive-ionic, electronic and negative-ionic emissions from mono- and polycrystalline surfaces of 88 kinds of chemical elements (1H–99Es), and also which includes the main experimental condition and method employed for each sample specimen (bulk or film) together with 490 footnotes. From the above database originating from 4461 references published to date in the fields of both physics and chemistry, the most probable values of , and for substantially clean surfaces are statistically estimated for about 600 surface species of mono- and polycrystals. The values recommended for together with and in Table 2 are much more abundant in both surface species and data amount, and also they may be more reliable and convenient than those in popular handbooks and reviews consulted widely still today by great many workers, because the latter is based on less-plentiful data on published generally before 1980 and also because it covers no value recommended for and . Consequently, Table 1 may be more advantageous as the latest and most abundant database on work functions (especially ) for quickly referring to a variety of data obtained under specified conditions. Comparison of the most probable values of recommended for each surface species between this article and other literatures listed in Tables 2 and 3 indicates that consideration of the recent work function data accumulated particularly during the last 40 years is very important for correct analysis of these surface phenomena or processes concerned with either work function or its changes. On the basis of our simple model about the work function of polycrystal consisting of a number of patchy faces (1–i) having each a fractional area (F) and a local work function (), its values of both and are theoretically calculated and also critically compared with a plenty of experimental data. In addition, the “polycrystalline thermionic work function contrast” () well-known as the thermionic peculiarity inherent in every polycrystal is carefully analyzed as a function of the degree of monocrystallization () corresponding to the largest (F) among F’s (Tables 4–6 and Fig. 1), thereby yielding the conclusions as follows: (1) const (>0) holds for the generally called “polycrystalline” surfaces (usually < 50%), (2) ranges from 0.3 eV (Pt) to 0.7 eV (Nb) depending upon the polycrystalline surface species, (3) in the case of the “submonocrystal” (50 < < 100%) tentatively named here, decreases parabolically down to zero as increases from 50% up to 100% (monocrystal), (4) applies to a clean and smooth monocrystalline surface ( 100%) alone, (5) regarding negative ion emission, on the other hand, our theoretical prediction of is experimentally verified to hold for any surface species under any surface conditions (Table 7), (6) every polycrystal (usually, < 50%) may be concluded in general to have a unique value of characteristic of its species with little dependence upon , (7) this conclusion affords us first a sound basis for supporting theoretically the experimental fact (Table 2) that every species of polycrystal has a nearly constant value of as well as (usually within the uncertainty of 0.1 eV) depending little upon the difference in the surface components (F and ) among specimens so long as < 50%, (8) on the contrary to polycrystal ( < 50%), any submonocrystal (50 < < 100%) has such an anomaly that it does not possess the unique value of work function characteristic of the surface species itself, because its as well as changes considerably depending upon , (9) consequently, submonocrystal must be taken as another type (category) different from both poly- and monocrystals, (10) in this way, acts as the key factor mainly governing the work functions in the different mode between poly- and submonocrystals with lower and higher than the “critical point” of 50%, respectively, (11) on the contrary to , belonging to has a differential effect on both and , but their values remain nearly constant so long as < 50% and, thus interestingly, (12) the complicate governance of and by both and and also the anomaly of submonocrystal (cf. (8) above) observed first by our theoretical analysis may be considered as a new contribution to the work function studies developed to date. Together with brief comments and experimental conditions, typical data on and/or are summarized from the various aspects of (1) examination of the work function dependence upon the surface atom density of low-Miller-index monocrystals of typical metals such as Al, Ni, W and Re (Table 8), (2) demonstration of the above dependence usually called the “anisotropic work function dependence sequences” of both (110) > (100) > (111) and (110) > (100) > (111) for various bcc-metals (e.g., Nb, Mo, Ta and W) exactly obeying the Smoluchowski rule (Table 9), (3) substantiation of both (111) > (100) > (110) for a variety of fcc-metals (except Al and Pb) and (111) > (100) > (110) for Ni strictly following the above rule (Table 10), (4) verification of the quantitative relations between work function and surface energy and also melting point of the three low index planes of several metals (typically, Ni), (5) examination of the work function change () due to allotropic transformation from to or to phase (Table 11) together with a concise outline of the Burgers orientation relationship, (6) evaluation of due to liquefying (Table 12), (7) estimation of due to transformation from ferro- to paramagnetic state (Table 13) in addition to a brief description of the Curie point dependence upon metastable metal film thickness above one monolayer, (8) estimation of due to transition from normal to superconducting state (Table 14), (9) study of the work function dependence on the Wigner–Seitz radius and also comparison between its theoretical values (by Kohn) and experimental data (Fig. 2), (10) inspection of the annealing effect on work function for layers or films, (11) verification of the coincidence of work function values among different experimental methods, and (12) inquisition of the work function dependence upon the size of fine particles (20–100 Å in radius) studied by theory and experiment.
Adsorption of CO on the unreconstructed and reconstructed Ir(100) surface
1991, Surface ScienceThe adsorption of CO on both the (1 × 1) and the (5 × 1) reconstructed Ir(100) surface at room temperature has been investigated using electron energy loss spectroscopy (EELS) and LEED. CO is adsorbed on both surfaces at all coverages in on-top sites. All four vibrational modes of the adsorbate have been detected. Upon adsorption of CO on the (5 × 1) surface the reconstruction is locally lifted giving rise to a (1 × 1) LEED pattern. Adsorption of CO on the (1 × 1) surface leads to a c(2 × 2) structure. The vibrational frequencies of the CO-molecules on both surfaces differ only slightly. At saturation the iridium-CO and the C-O stretching frequencies are 485 and 2075 cm−1 on the (5 × 1) and 497 and 2068 cm−1 on the (1 × 1) surface, respectively. The frequency of the rotational mode of the CO molecule is found to be 425 cm−1 and the frustrated translation at 53 cm−1, both showing no dispersion along ḡGM̄ direction. The C-O stretching vibration shows dispersion due to dipole-dipole interaction, also when the overlayer is not ordered.
Chemisorption of Probe Molecules
1990, Studies in Surface Science and CatalysisThis chapter discusses chemisorption of probe molecules. Standard methods for catalytic surface area determinations formally exist for several supported-metal catalysts. However, there is not general acceptance of such methods for supported-metal oxides (or sulfides). There are inherent difficulties in selecting any method as a standard for surface area measurements, because catalyst manufacturers throughout the world prepare their materials from different precursors and in different ways. These differences can cause marked variations in the procedure required to measure accurately the surface area of metal oxides. The chemisorption of suitable probe molecules is the method of choice for such purposes. It is also of great interest to combine the chemisorption measurements with appropriate surface spectroscopic techniques, in order to determine precisely the stoichiometry between the probe and the surface area of the supported active component and the number of sites responsible for a given reaction. One may not select a catalyst on the basis of a “standard test.” High surface area is, however, of such basic importance to any catalytic process that it should always be measured as a necessary, but not sufficient, characteristic of the system.
Chapter 1 Chemisorption of Probe Molecules
1990, Studies in Surface Science and CatalysisThis chapter discusses chemisorption of probe molecules. Standard methods for catalytic surface area determinations formally exist for several supported-metal catalysts. However, there is not general acceptance of such methods for supported-metal oxides (or sulfides). There are inherent difficulties in selecting any method as a standard for surface area measurements, because catalyst manufacturers throughout the world prepare their materials from different precursors and in different ways. These differences can cause marked variations in the procedure required to measure accurately the surface area of metal oxides. The chemisorption of suitable probe molecules is the method of choice for such purposes. It is also of great interest to combine the chemisorption measurements with appropriate surface spectroscopic techniques, in order to determine precisely the stoichiometry between the probe and the surface area of the supported active component and the number of sites responsible for a given reaction. One may not select a catalyst on the basis of a “standard test.” High surface area is, however, of such basic importance to any catalytic process that it should always be measured as a necessary, but not sufficient, characteristic of the system.
A tabulation and classification of the structures of clean solid surfaces and of adsorbed atomic and molecular monolayers as determined from low energy electron diffraction patterns
1986, Progress in Surface ScienceA tabulation is presented of the ordering characteristics of clean and adsorbate-covered single crystal surfaces based on diffraction patterns observed with LEED (Low Energy Electron Diffraction). Over 3000 structures are classified by rotational symmetry of the substrate surfaces, and by important sub-classes which reflect recent directions of LEED studies. These include metallic monolayers, alloy surfaces, organic overlayers, coadsorbed overlayers, physisorbed overlayers, and high-Miller-index (stepped) surfaces. We review the important characteristics of each sub-class, and propose future directions of LEED investigations.
Preparation of atomically clean surfaces of selected elements: A review
1982, Applications of Surface ScienceSurface cleaning procedures for seventy four of the elements having vapor pressures below 1.3 × 10−7 Pa at room temperature have been reviewed and evaluated. The emphasis was on in-situ procedures used to produce a clean surface on a macroscopic bulk sample in an ultra-high vacuum environment. In this review an atomically clean surface was defined to be an annealed surface (except where noted) at ambient temperature with a total surface contamination level of less than a few percent of a monolater. Wherever possible only cleaning methods documented by element- specific, surface-analytical techniques were reviewed and subsequently incorporated into the table of recommended procedures. For some elements a variety of procedures was deemed acceptable. Any differences in methods for polycrystalline and single-crystalline surfaces of the same element have been detailed. References to the reviewed literature are grouped by element.
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Supported by NSF grant DMR 71-01769-A02 and by ARPA, through the Cornell Materials Science Center.