Photoelectron diffraction structure determination of Cu(1 0 0)c(2×2)-N (original) (raw)
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Photoelectron diffraction determination of the local adsorption geometry of CO on Cu(2 1 0)
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Using C 1s and O 1s scanned-energy mode photoelectron diraction, the local adsorption site and orientation of CO adsorbed on Cu(2 1 0) has been determined. The results show that the molecule adsorbs in an essential on-top site through the C atom with C±Cu and C±O bondlengths generally consistent with previous studies on low index Cu surfaces. The molecule has a signi®cant tilt 18 AE 6° of the C±O axis away from the surface normal, with components both perpendicular and parallel to the [0 0 1] steps on this surface.
Adsorption geometry of CN on Cu(111) and Cu(111)/O
Surface Science, 2004
The adsorption geometry of CN on Cu(1 1 1), both with and without predosing with oxygen, has been investigated using N K-edge near-edge X-ray absorption fine structure (NEXAFS) and C 1s and N 1s scanned-energy mode photoelectron diffraction (PhD). The NEXAFS shows clearly that adsorbed onto clean Cu(1 1 1) the C-N axis is closely parallel to the surface, but in the presence of coadsorbed oxygen the average orientation has the axis tilted by 25°away from the surface; this confirms a much earlier report of an oxygen-induced reorientation of CN on this surface based on vibrational spectroscopy. The PhD data show very weak modulations which are rather insensitive to the emission geometry, clearly implying a high degree of disorder or a local adsorption site well-removed from any position of high point group symmetry. The best-fit structure corresponds to the CN lying slightly displaced from the threefold coordinated hollow sites but with the C and N atoms having single Cu atom nearest neighbours at distances of 1.98 ± 0.05 and 2.00 ± 0.05 A respectively.
Angle-scanned photoelectron diffraction chemisorption study of c( 2 × 2)-O on Ni( 1 ML)/Cu( 100)
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A new method for the determination of chemisorption site geometries using an angle-scanned forward scattering approach is proposed. The idea is based on the use of a heteroepitaxial monolayer deposited on a suitable single-crystal substrate as the source of the primary photoelectron wave. Preliminary single scattering clusier simulations performed on model systems show that the method might be successful with well-ordered adsorbates at high surface coverage, while it is of little use for low-coverage and/or disordered molecular overlayers.
A leed crystallographic analysis for the Cu(100)c(2×2)-N surface structure
Surface Science, 1987
An intensity analysis with low-energy electron diffraction is reported for the c(2 • 2) surface structure obtained on the (100) surface of copper by the adsorption at room temperature of nitrogen activated by an ion gun. The surface was annealed at around 270 ~ before sets of intensity-versus-energy curves were measured with a video LEED analyser. The curves measured for ten independent diffracted beams were compared with those calculated by full multiple scattering methods. The structural conclusions differ markedly from those in two earlier reports in the literature. We find this surface structure involves N atoms incorporated deeply into the expected hollow sites to become closely coplanar with the topmost copper layer. Each N atom becomes essentially 5-fold coordinated with bonding to the atom directly below in the second copper layer, and the topmost Cu-Cu interlayer spacing is indicated to be expanded by about 8% from the bulk value. Further second-order relaxations are possible, but these basic structural features fit a model for the surface derived from the structure of bulk Cu3N.
Surface Science, 2003
Using the chemical shift in the N 1s photoemission peak from the two inequivalent N atoms of N 2 adsorbed on Ni(1 0 0) we have performed a scanned-energy mode photoelectron diffraction (PhD) structure determination of the Ni(1 0 0)c(2 • 2)-N 2 weak chemisorption system. The N 2 is found to adsorb atop surface Ni atoms with the N-N axis perpendicular to the surface at a Ni-N nearest-neighbour distance of 1.81 ± 0.02 A A. This is very significantly shorter than the value (2.25 A A) found in an earlier published study. An independent density-functional theory slab calculation yields a value of 1.79 A A, in excellent agreement with the results of the current experiment. Analysis of the PhD modulations of the N 1s photoemission satellite peak show that these are consistent with this comprising separable components localised at the two N atoms as has previously been assumed in an earlier investigation based on (anglescan) X-ray photoelectron diffraction. Both experiment and theory indicate a small extension of the N-N distance due to the adsorption (0.03 ± 0.03 A A and 0.02 A A respectively).
The Cu(1 0 0)-c(2×2) N structure studied by combined nc-AFM/STM
Applied Surface Science, 2003
The Cu(1 0 0)-c(2 Â 2) N reconstructed surface has been studied by combined non-contact force and tunneling microscopy. Frequent tip changes produced all kinds of contrast in the interaction between the tip and differently reconstructed areas on the surface. Atomic resolution has been obtained using the tunneling current as feedback.
Photoelectron diffraction determination of the structure of the Cu(100)c - Mn surface phase
Journal of Physics: Condensed Matter, 1996
The structure of the Cu(100)c(2 × 2)-Mn surface phase has been determined using scanned-energy mode photoelectron diffraction (PhD) from the Mn 2p 3/2 core level. The results confirm the earlier finding of a quantitative LEED study, namely that the surface layer comprises an ordered, strongly corrugated two-dimensional alloy in which the Mn atoms occupy substitutional sites. By using near-grazing as well as near-normal emission directions, the PhD data are found to be sensitive to the locations of both the alloy (approximately coplanar) and the underlying substrate Cu atoms relative to the Mn emitter. This can be seen both in direct 'projection method' data inversion maps of the emitter environment and in full multiple-scattering simulations. The PhD data indicate a large outward relaxation of the Mn atoms relative to the surrounding alloy-layer Cu atoms (0.39 ± 0.08Å), but this is consistent with the previous LEED study within the quoted precisions. There are, however, statistically significant differences between the LEED and PhD conclusions regarding some of the structural parameter values, most notably the layer spacing of the Mn atoms to the underlying pure Cu substrate layer.
Structure of N2 adlayers on the highly corrugated Cu(110)–(2×1)O surface
Surface Science, 1999
The adsorption and structure of molecular nitrogen on the reconstructed Cu(110)-(2×1)O surface has been studied by He-diffraction and temperature programmed desorption. Owing to the ''added row'' reconstruction, the Cu(110)-(2×1)0 surface exhibits a large corrugation along the [11 :0] direction, i.e. perpendicular to the Cu-O rows. This has a marked influence on the adsorption properties and structure compared with the bare Cu(110) surface. The N 2 molecules initially adsorb in a lattice gas phase which is stable up to rather high density. In this phase the desorption proceeds via first-order desorption kinetics. With increasing coverage the lattice gas eventually condenses into a (4×3) commensurate phase where the molecules are much more weakly bound. Potential calculations corroborate the existence of a low density phase in which the N 2 molecules adsorb along the troughs between Cu-O added rows with only negligible lateral interactions. The (4×3) phase is found to contain up to eight N 2 molecules per unit cell, half of which occupy sites on top of the Cu-O added rows. A possible novel desorption channel involving a metastable bi-molecular precursor is proposed that could provide a consistent explanation of the N 2 desorption data. (faces) of the same substrate material.
Chemical Physics Letters, 1997
We have determined the atomic spatial structure of c(2 X 2) N,/Ni(IOO) with angle-resolved photoemission extended fine structure using the nitrogen 1s core level. The chemically shifted N 1s peak intensities were summed to obtain ARPEFS curves for both nitrogen atoms in the molecule. We used a new, highly optimized program based on the Rehr-Albers scattering matrix formalism to find the adsorption site and to determine the bond lengths quantitatively. The nitrogen molecule stands upright at an atop site, with a N-Ni bond length of 2.25(l) A, a N-N bond length of 1.10 .&, and a first layer Ni-Ni spacing of 1.76(4) A. The shake-up peak shows an identical ARPEFS diffraction pattern, confiiing its intrinsic nature and supporting a previous use of this feature to decompose the peak into contributions from the chemically inequivalent nitrogen atoms. Comparison to a previously published theoretical treatment of N-N-Ni and experimental structures of analogous adsorbate systems demonstrates the importance of adsorbate-adsorbate interactions in weakly chemisorbed systems.