First-principles determination of giant adsorption-induced surface relaxation in p(11) O/Fe(001)

Abstract

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...

Effect of oxygen on the magnetic coupling of a Mn thin film on Fe(001) substrate

“…20% higher than its value in the clean Mn/Fe(0 0 1) case. Such effect has already been reported for O adsorbed directly on Fe(1 0 0) substrate [47] where the enhancement has been found to occur not only at the surface but also at the second Fe layers.…”

“…In the case of the pure Fe(0 0 1) surface large outward relaxations of the first Fe-Fe layer spacing were found both in theory [47] and experiment [50,51]. LEED measurements [50] give 7.5% expansion of the first Fe-Fe interlayer spacing with respect to its value in the bulk, while Auger electron spectroscopy and ion scattering experiment [51] measured a value of 11% due to the surface oxidation of Fe(0 0 1).…”

Self-organized chromium oxide monolayers on Fe(001)

“…Oxygen chemisorption on the Fe(001) surface followed by annealing resulted in the oxygen-saturated and well-ordered Fe(001)-p(1 × 1)O superstructure, characterized by one oxygen atom per surface unit cell, lying in the fourfold hollow site of the Fe surface. 33,45 Cr films were grown onto Fe(001)-p(1 × 1)O substrates by MBE under UHV conditions, with a typical growth rate of about 1 equivalent monolayer 46 (ML) per minute, as measured by a quartz microbalance. In the set of measurements discussed in this paper the substrate was held at 400 • C during Cr deposition, as measured by a thermocouple attached in close proximity to the sample position.…”

Adsorbate-Induced Restructuring of the Fe(100) Surface: Model Cluster Studies

“…Previous more precise data obtained from LEED intensity analysis, as well as theoretical consideration confirm the locations of oxygen [15][16][17][18] and nitrogen [14][15][16][17][18][19][20][21][22][23][24][25][26][27][28][29][30] atoms. The EHT calculations performed in this study show full accordance in the case of oxygen adsorption.…”