We present a detailed study of an electric-field-induced phase transition of a single layer of Fe on a Ni(111) substrate. Scanning tunneling microscopy at 4 K substrate temperature is used to provide the necessary electric field and to follow the transition from face-centered cubic to hexagonal close-packed stacking with atomic resolution.
DOI:https://doi.org/10.1103/PhysRevB.91.184107
©2015 American Physical Society
(a), (d) topography of similar amounts of Fe deposited at about 30 . (a) Standard preparation leading to a highly contaminated surface and irregular islands with a superstructure induced by adsorbates on an Fe island (enclosed in red) and on the Ni surface (b). (c) Atomically resolved STM topography of the bare Ni(111) single crystal surface, . (d) Fe film prepared with optimized preparation with reduced surface contamination. Tunneling parameters: (a) , (b) , (c) , (d) .
Reuse & PermissionsFe/Ni(111): (a) STM topography of a 1 ML Fe film (light gray) at a Ni step edge (black) with domain boundaries appearing in white. (b) In a map at [see inset, position indicated by red rectangle in (a)], two different intensities divide the 1 ML Fe terrace into domains. spectra outside the domain on the Fe terrace (solid orange) and inside the domain (dashed blue) show different spectra for the two phases. (c) Atomic resolution scanning tunneling micrograph showing a coexistence of hcp and fcc lattices with light domain walls. The overlaid hexagonal grid is adjusted to the fcc lattice and colored orange on the fcc area and blue on the hcp area. (d) Same area as in (c) after an electric-field-induced change of the lattice. About 20 atoms change their stacking from hcp to fcc thus shifting the domain boundary to the left by about . Tunneling parameters: (a) ; (c) and (d) .
Reuse & PermissionsReproducible switching of the crystallographic structure of 1 ML Fe/Ni(111) imaged on map). (a) The initial hcp domain is indicated by a blue line, the fcc domain by an orange line, and domain boundaries appear dark. An electric field pulse is applied on the position marked with the red cross after the acquisition of the image. The new configuration with a smaller hcp domain is imaged in (b) with the initial position of the domains indicated by dashed lines. A second pulse brings the system back to the initial state (c). Critical parameters for the transition were identified as follows: (d) The same line across a hcp domain (blue frame) is repeatedly scanned while the voltage is ramped. Above a certain critical voltage (here , the structure partially changes from hcp to fcc and the domain boundary (dark) is shifted to the right. Repetition of this measurement at different tip-sample separations gives the critical electric field shown in (e). The measurement described in (d) corresponds to one data point (black cross). The linear relation between the critical voltage and the tip-sample separation corresponds to a critical electric field of about 10 . Tunneling parameters: (a)–(c) , (d) .
Reuse & Permissions(a) Switching the domain boundary left and right when scanning across an hcp domain at a constant field of 7.6 map). b) Switching left by field pulses of 1.4 and right by scanning at 1.0 across an hcp domain (blue) map). (c) In a histogram of the differential conductance, only two stable states are found. (d) Exponential decay of the fcc state with a lifetime of . Tunneling parameters: (a) , (b) .
Reuse & Permissions(a) A map of Fe/Ni(111) films thicker than 1 ML shows a stripe pattern perpendicular to the closed-packed directions. The lattice directions given in (c) also hold for (a). (b) Three different intensities of the stripes are found. (c) STM image on the bare Ni surface, Fe and Fe with atomic resolution. (d) Atomic model of 2 ML Fe/Ni(111) for the observed stripe pattern. The relative atomic distances of the top layer (gray circles) are taken from the measurement in (c). The expansion of the top layer by 7.5% in the direction leads to a periodicity of 13 interatomic distances . The bcc lattice (green rectangle) is characterized by a twofold bridge-stacking while the two possible threefold hollow sites correspond to fcc (orange triangle) and hcp domains (blue triangle). Tunneling parameters: (a) and (b) , (c) .
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