We report results from a first-principles total-energy study of primitive (1 x 1) O chemisorbed on magnetic Fe(OOl). The adsorption-induced relaxation is found to be a factor of 3 larger than was inferred earlier from an analysis of LEED intensity data, reflecting strong covalent O-Fe bonding. The resulting arrangement of surface Fe and O atoms already closely resembles a rocksalt FeO monolayer which is comparatively weakly bound to the substrate. The surface bands are compared with angle-resolved photoemission data of Panzner, Mueller, and Rhodin. PACS numbers: 71.45.Nt, 68.55.Jk, 73.20.Dx Though gaseous chemisorption on metallic surfaces is known to induce outward surface relaxations, very little is understood about the origin and nature of this effect and its impact on electronic and magnetic structure. In the case of oxygen chemisorbed on Fe(OOl), which may be an important precursor of the oxidation of Fe surfaces, not only is surprisingly little known about the associated adsorption-induced relaxation of the Fe surface [Fe/(5)1 layer, only limited information is available about this particular adsorption.Disagreement has existed within the last five years concerning even such a fundamental question as whether or not specific ordered O/Fe chemisorption phases occur. 1 " 4 For the one phase which has been consistently observed, primitive lxl lp(\x\)]O on Fe/(001), nonspin-polarized, angle-resolved, ultraviolet photoemission experiments by Panzner, Mueller, and Rhodin 5 provide the only measurements of the adsorbate-induced, surface-state spectrum. Huang and Hermanson 6 have performed the only ab initio calculation of the electronic and magnetic structure of p(\ x 1) O/Fe(00l), but these authors did not attempt to determine the associated relaxation or adsorbate height. In the handful of firstprinciples studies of gaseous chemisorption in which some attempt has been made to determine the adsorbate-surface geometry 7,8 from the minimum of the total energy, none has incorporated the possibility of surface relaxation.In this Letter we report the first first-principles determination of an adsorption-induced surface relaxation, which includes the determination of the positions of both the surface and adsorbate from the minimum of the local-density total energy. The results indicate that for p(\ x 1) O/Fe(001), the outward relaxation of the FeCS) layer is a factor of 3 larger than the value which was inferred earlier by Legg, Jona, Jepsen, and Marcus 3 (henceforth, LJJM) from the analysis of LEED intensity data. However, LJJM only considered a small range of Fe relaxations. We also find evidence for considerable covalence, including an adsorption-induced enhancement of the magnetism in the Fe(S) layer as well as a 0.2^6 moment on the oxygen atom. This is also reflected in a surprising sensitivity of the adsorption-induced change in work function A(p with respect to variation of the adsorbate and surface positions. The agreement of our calculated value for A0 with experiment is considerably better when the relaxa...

Abstract. In this paper we investigate the underlying dynamics associated with a strong, line-shaped submesoscale feature that was observed in radar imagery at the boundary between Gulf Stream (GS) and shelf water near Cape Hatteras during the first Naval Research Laboratory High-Resolution Remote Sensing Experiment (HIRES 1). The lineshaped feature, which appears as a pronounced (---10 dB) increase in radar cross section, extends several kilometers in the east-west direction. In situ current measurements have shown that this feature coincides with the boundary of a sharp current convergence front. These measurements also indicate that the frontal dynamics is associated with the subduction of denser GS water under lighter shelf water. Using the observation that the convergence can be attributed to a hydrodynamic instability at the water interface, we have modeled the resulting subsurface hydrodynamics on the basis of a rigid-lid, twodimensional solution of the Navier Stokes equation. The calculations of subsurface current flow were used as input to a spectral (wave action) model of wave-current interaction to obtain the surface wave field, which in turn was used to provide input for modeling of radar backscatter. The resulting description also includes the effects of surfactant-induced wave damping on electromagnetic backscatter. Our predictions are compared with real aperture radar imagery and in situ measurements from the HIRES 1 experiment. IntroductionThe ability to infer the underlying current and depth structure from microwave frequency radar imagery of the ocean surface is a long-standing problem of considerable interest. Efforts to infer subsurface structure are inherently limited since radar signals at best penetrate the subsurface at the level of tens of centimeters or less. As a consequence, in the absence of ground truth, it is possible to understand subsurface structure in this manner only on the basis of some understanding and modeling of the underlying dynamics. On the other hand, interpretation of features apparent in ocean imagery is possible only if the link between radar modulation and variations in the small-scale surface roughness due to currents, depth, wind, and the associated momentum fluxes is correctly described. Further complicating the problem, especially at low wind speed, is the effect of wave damping from surfactants. A complete analysis of this problem is manifold, involving subsurface and surface hydrodynamics and electromagnetic backscatter. shown that this signature occurs along the boundary of a sharp current convergence front. These measurements also indicate that the frontal dynamics is associated with the subduction of denser Gulf Stream (GS) water under lighter shelf water. The goal of this paper is to marry subsurface current flow, surface wave-current interaction, and radar imaging, on the basis of a full-spectral representation, to obtain an understanding of this high radar backscatter feature, which will be referred to as a current "rip." As shown in Plate 1, the resul...

No abstract

No abstract

The adsorption of cesium on the (100) faces of W, Mo, and Ta for coverages between 0 and 1 monolayer is studied by angle-resolved ultraviolet photoemission spectroscopy with use of synchrotron radiation, by electron-energy-loss spectroscopy, and by low-energy electron diffraction. Withincreasing cesiation, the W(100) surface state at I located 0.3 eV below the Fermi level is shifted by up to 1.0 eV to larger binding energies while remaining sharp and intense. A similar behavior is observed on Ta(100), whereas ori Mo(100) the shift of 0.9 eV of this surface state is accompanied by a pronounced attenuation of its intensity. These experimental shifts are shown to be in excellent agreement with all-electron local-density-functional results obtained with the full-potential linearized augmented-plane-wave method for Cs monolayers on the W(100) and Mo (100) surfaces. Based on these ab initio results, the electronic origin of the shifts is understood by the formation of strongly polarized covalent bonds between the d-like surface states and the Cs 6sderived valence states.It is argued that even at high Cs coverages, the main electron-energy-loss peaks, which are observed between 1 and 2 eV, could be interpreted as Cs 6s~6plike interband transitions rather than as surface-plasmon peaks.