Multilayer relaxation and search for ferromagnetic order at the (100) surface of bulk paramagnetic vanadium

Abstract

Low-energy-electron-diffraction ͑LEED͒ intensity measurements and multiple-scattering analysis for V͑100͒, supported by accurate characterization of surface impurity concentrations based on Auger-electron spectroscopy, are used to obtain a meaningful extrapolation of the first-layer relaxation to the clean surface value: d 12 = 1.36± 0.05 Å, corresponding to ⌬ 12 = −10% ± 3% relative to the bulk value d 0 = 1.514 Å. A highsensitivity probe for surface magnetism based on magneto-optic Kerr effect polarimetry using the cleanest surfaces achieved in the LEED experiment ͑ϳ5% C͒ yields a ͑sensitivity limited͒ null result with an estimated upper limit of 0.05 B /surface atom. These results are discussed within the framework of related experiments and in relation to the predictive accuracy of ab initio calculations that explore the surface structure and magnetism of V͑100͒ both of which are sensitive to different approximations for the exchange-correlation potential in density-functional theory.

Temperature-dependent multilayer relaxation of clean and hydrogen-dosed Nb(100)

“…These prior studies suggest that the properties associated with the hydrogen-Nb͑100͒ surface are governed by hydrogen atoms at tetrahedral lattice sites near the surface. The results also extend our study [26][27][28][29] of trends in multilayer relaxation of reactive transition metal surfaces. This experimental program was stimulated by systematic inconsistencies 30,31 between top-layer relaxation obtained from ab initio calculations and corresponding results from LEED crystallography.…”

“…1,[12][13][14]17,18 The problems are very similar to those encountered for V͑100͒. 29 Nb is a 4d metal that lies just below V ͑3d metal͒ in the Periodic Table. Both V and Nb exhibit high reactivity to and solubility of hydrogen and other elements, including carbon and oxygen. The best efforts to date have yielded only technically clean surfaces of both V͑100͒ and Nb͑100͒.…”

“…The LEED intensity-versus-voltage ͑I-V͒ spectra were measured using frame-grabbing instrumentation interfaced to a SIT camera. The instrument has been used in prior LEED [26][27][28][29] and inelastic electron scattering 17 studies, and the LEED methodology has been described in prior publications. [26][27][28][29] Clean surface preparation of Nb͑100͒ presents significant challenges as noted in prior publications.…”

“…The instrument has been used in prior LEED [26][27][28][29] and inelastic electron scattering 17 studies, and the LEED methodology has been described in prior publications. [26][27][28][29] Clean surface preparation of Nb͑100͒ presents significant challenges as noted in prior publications. 1,[12][13][14]17,18 The problems are very similar to those encountered for V͑100͒.…”

“…The best efforts to date have yielded only technically clean surfaces of both V͑100͒ and Nb͑100͒. In the case of V͑100͒, bulk carbon limits the cleanliness of a prepared surface to 4%-5% carbon; 29,32 for Nb͑100͒, the strong chemical affinity, high solubility, and high desorption temperature associated with oxygen and the Nb surface have limited the purity of technically clean Nb͑100͒ to about 8% oxygen. Fortunately, recent detailed characterization of ordered surface chemisorbed layers ͓oxygen for Nb͑100͒ ͑Ref.…”