Structural analysis of Fe/Ni(001) films by photoelectron diffraction

Abstract

The structure of Fe films, epitaxially grown on Ni͑001͒, has been studied in the 0-14 ML coverage range by means of photoelectron diffraction ͑PD͒ in the forward scattering regime. Quantitative analysis by a multiple scattering approach has been performed on Fe films at a coverage of 3 and 7 ML. Analysis of the 3-ML data showed that growth was not layer-by-layer but rather occurred through islands nucleation and that transition from the pseudomorphic fcc to the bcc phase was located in this early stage of growth. In fact, best fit was obtained by calculations on a 2 ML bcc͑110͒/3 ML fcc͑001͒ Fe film with the bcc͗111͘ʈfcc͗110͘ in-plane orientation. Interlayer spacings of 2.05Ϯ0.06 Å, 2.01Ϯ0.03 Å, and 1.85Ϯ0.03 Å were found in the bcc region, between bcc and fcc layers and in the fcc region, respectively. Best-fit in-plane nearest-neighbors ͑n-n͒ distance was 2.49Ϯ0.02 Å, in registry with that of the Ni substrate. To analyze the 7-ML data a 4 ML bcc͑110͒/3 ML fcc͑001͒ film was employed, varying the fitting parameters in the bcc region only. Best fit was obtained for an interlayer spacing of 2.04Ϯ0.04 Å and in plane n-n distance of 2.47Ϯ0.01 Å. At 14 ML the PD pattern collected over a 94°azimuthal range displayed symmetry around the ͓110͔ substrate direction, which was explained by the equipopulation of the 4 bcc͑110͒ domains satisfying the bcc͗111͘ʈfcc͗110͘ alignment.

Ab initiocalculation of phase boundaries in iron along the bcc-fcc transformation path and magnetism of iron overlayers

“…However, the experimental point 30 is distinctly in the AFMD region, and our theoretical prediction lies again within the experimental limits. In reality, however, magnetic polarization due to FM Ni substrate may induce FM order in the film.…”

Thin-film nanostructures: Substructural aspects

“…At the same time, a match between the fcc lattices (a Ni = 0.352 nm) requires a compression as small as 2%. The formation of a pseudomorphous fcc Fe phase on (001) Ni and the subsequent transition to the bcc structure were also observed in later studies [43,44]. At a small mismatch between dissimilar lattices, e.g., in the Fe/Au(001) and Fe/Ir(001) systems [45], the body-centered pseudomorphous phase persists.…”

Investigation of FIB irradiation damage in La0.7Sr0.3MnO3 thin films

“…Finally, at doses above 1 Â 10 17 ions/cm 2 , the milling process results in the usual trench-like profiles, with the rim remaining as a fingerprint of the swelling effect, similar to what is reported in Refs. [9,16]. We notice that for a dose of 1 Â 10 17 ions/cm 2 an erosion depth corresponding to the film thickness is reached, therefore the morphology observed at the highest dose belongs to the SrTiO 3 substrate.…”

“…FIB patterning was performed in a dual beam system (FEI DB235M ) described elsewhere [9], with a Ga ion beam of 30 keV energy, 10 pA current (corresponding to 10 nm spotsize), 10 ms pixel dwell time, and normal incidence angle. Ion doses ranged from 5 Â 10 12 to 3 Â 10 17 ions/cm 2 .…”

“…A noteworthy potential in this field is related to the recent improvements in nanopatterning techniques, applied to manganites, such as electron beam lithography [3,4], local anodisation by atomic force microscopy (AFM) [5], focused ion beam (FIB) [6][7][8] direct lithography. In particular, FIB patterning is usually performed with two different approaches: one is to remove material by ion milling [9], the other is to change locally the magnetic properties by ion-induced damage at low-dose irradiation, without material erosion. The latter approach has been used to drive a local ferromagnetic to paramagnetic transition in ferromagnetic films [10] and in manganites [11], and to induce easy nucleation regions for magnetisation reversal [12].…”