# Fileset [FeSi2_TEM_Suppl_revised.pdf](https://mdr.nims.go.jp/filesets/ce6d5e69-5b0c-46ee-8f1a-e136d8cfd166/download) ## Creator [Keisuke Sagisaka](https://orcid.org/0000-0002-5089-4271), [Kazutaka Mitsuishi](https://orcid.org/0000-0002-9361-4057) ## Rights [Creative Commons BY-NC-ND Attribution-NonCommercial-NoDerivs 4.0 International](https://creativecommons.org/licenses/by-nc-nd/4.0/) ## Other metadata [Atomic and electronic structures of the β-FeSi2/Si(001) interface](https://mdr.nims.go.jp/datasets/9073ee02-4503-4116-a361-1f61eb949120) ## Fulltext Supplementary materials for ”Atomic and electronic structures ofthe β-FeSi2/Si(001) interface”Keisuke Sagisaka1, ∗ and Kazutaka Mitsuishi11Center for Basic Research on Materials,National Institute for Materials Science,1-2-1 Sengen, Tsukuba, Ibaraki 305-0047, Japan.∗ SAGISAKA.Keisuke@nims.go.jp1I. THE β-FESI2/SI(001) INTERFACE STRUCTUREIn order to determine the β-FeSi2 /Si(001) interface structure, we examined several modelsby optimizing their structures by DFT calculation and simulating STEM images. Figure S1shows selected three slab models: (a) a β-FeSi2 slab and a Si(001) slab are bonded throughSi dimers, (b) a β-FeSi2 slab is simply stacked on a Si(001) slab without modifications, (c)a β-FeSi2 slab and a Si(001) slab are bonded another configuration of Si dimers.FIG. S1. Representative slab models used for the DFT calculations of the β-FeSi2/Si(001) interface.(a) is the model that yields the best agreement with STEM observations and the most stablestructure among examined models. Each energy represented is the total energy relative to that ofthe slab in (a).2Figure S2 shows the detailed atom configurations of the β-FeSi2/Si(001) interface deter-mined in this study. Their fractional atomic coordinates are represented in Table S1.FIG. S2. Detailed structure of the β-FeSi2/Si(001) interface determined in this study.3TABLE S1. Fractional atomic coordinates (x, y, and z) of β-FeSi2/Si(001) for a unit cell size of a= 0.986 nm for β-FeSi2 and b and c = 0.731 nm for Si, calculated using the PBE functional. Theatom numbers correspond to those labeled in Fig. S2.Layer Atom Number x y zFe1 1 0.205 0.801 0.1152 0.705 0.701 0.1153 0.301 0.300 0.1154 0.801 0.201 0.015Fe2 5 0.002 0.501 0.3976 0.502 0.000 0.3977 0.502 0.500 0.3288 0.002 0.001 0.328Fe3 9 0.693 0.813 0.61210 0.193 0.689 0.61211 0.810 0.313 0.61212 0.310 0.189 0.612Si-2 13 0.014 0.245 -0.26114 0.514 0.256 -0.26115 0.000 0.756 -0.26116 0.499 0.745 -0.261Si-1 17 0.264 0.274 -0.12318 0.763 0.227 -0.12319 0.249 0.773 -0.12320 0.749 0.728 -0.123Si0 21 0.155 0.525 0.00022 0.853 0.476 0.00023 0.353 0.025 0.00024 0.655 0.976 0.000Si1 25 0.730 0.955 0.24226 0.230 0.546 0.24227 0.775 0.455 0.24128 0.276 0.046 0.24229 0.462 0.775 0.23130 0.962 0.727 0.23131 0.044 0.275 0.23132 0.544 0.226 0.231Si2 33 0.957 0.774 0.48334 0.457 0.727 0.48335 0.547 0.274 0.48336 0.047 0.227 0.48337 0.229 0.951 0.48438 0.729 0.551 0.48439 0.275 0.451 0.48540 0.775 0.051 0.4854II. STM OBSERVATION OF THE β-FESI2 SURFACEFigure S3 represents an STM image of the β-FeSi2 surface, which exhibits surface undu-lation of approximately 0.1 nm. The image clearly shows that the β-FeSi2 surface, coveredwith the p(2 × 2) superstructure, displays continuous height variation without the formationof steps.FIG. S3. STM image of the β-FeSi2 surface and a line profile along the black line in the STMimage. White dots are unknown defects. Imaging parameters: sample bias of +1.0 V, tunnelingcurrent of 50 pA, and sample temperature of 4.3 K, The image dimensions are 30 × 30 nm2.5III. BAND STRUCTURE OF THE β-FESI2/SI(001) INTERFACE.A. Pseud-hydrogen atom terminaion on the topmost surface of the slabBefore initiating band calculations, we investigated the effect of hydrogen termination onSi atoms on the topmost surface of a β-FeSi2/Si(001) slab. Since the top layer of the β-FeSi2slab terminated with Si atoms also has a metallic electronic state [1], its band diagramexhibits a complex band structure near the Fermi energy, complicating the identification ofbands originating from the β-FeSi2/Si(001) interface. To mitigate this complexity, reducingthe charges on the top Si atoms via hydrogen termination is effective. However, the precisecharge values on the Si atoms in the β-FeSi2 surface are unknown. Therefore, we examinedthe effect of termination using pseud-hydrogen atoms with different charges (q = 1.0, 1.25,1.5, 1.66, and 1.75).Figure S4 shows the projected density of states (PDOS) for atoms in varisou layers of theSlab. In the normal β-FeSi2/Si(001) slab, the Si atom in the first layer exhibits significantcharge densities around the Fermi energy, with these charges penetrating several layers deepinto the β-FeSi2 slab. The application of pseud-hydrogen termination with a charge of 1.5effectively reduces these charges. Consequently, we utilized this termination for our bandcalculations. It is important to note that pseud-hydrogen termination, regardless of thecharge value, does not impact the electronic state at the β-FeSi2/Si(001) interface.6FIG. S4. The effect of pseud-hydrogen atom termination on the β-FeSi2 surface.B. Band assignmentThe origin of the bands was examined by plotting charge densities for each eigenvalue.Figure S5 represents the charge density distributions for representative positions of thebands: the β-FeSi2/Si(001) interface, the bulk β-FeSi2, and bulk Si. The charges for theinterface states are well localized on the Fe1 atoms and extend along the interface. Thesestates are also situated within the band gaps of both the bulk β-FeSi2 and bulk Si. Thedecay depth of these states into the β-FeSi2 film is examined by plotting PDOS for Fe atomsin different layer near the interface (Fig. S6). The result shows that the states associated7with these bands decay to 46% in the Fe2 layer and further diminished to 6% in the Fe3layer. The orbital-decomposed PDOS for the Fe1 and Si0 atoms, displayed in Fig. S7,reveals that these bands originate from 3d orbitals of Fe and 2p orbitals of Si.C. Spin-polarized band calculationsThe band structure for the β-FeSi2/Si(001) interface was investigated using both non-spin-polarized and spin-polarized calculations. The bulk bands of β-FeSi2 projected ontothe (001) plane exhibit completely degeneracy between the up and down spin bands [Fig.S8]. However, according to the result of the slab calculation, this degeneracy is significantlylifted for the interface bands and slightly for the bulk β-FeSi2 bands.[1] K. Sagisaka, T. Kusawake, D. Bowler, S. Ohno, Emergence of metallic surface states and neg-ative differential conductance in thin β-FeSi2 films on Si(001), Journal of Physics: CondensedMatter 35, 135001 (2023).8FIG. S5. Non-spin polarized bands and charge density distributions of the β-FeSi2/Si(001) slab.Charge densities are visualized with the isosurface values of 0.005 e/Å3. Color scale representsheight in z direction.9FIG. S6. PDOS for various layers near the interface.FIG. S7. PDOS decomposed to electron orbitals for the Si dimer in the S0 layer and the Fe atomin the Fe1 layer.10FIG. S8. Spin polarized bands and PDOS calculated with a bulk β-FeSi2 cell. The red and bluecurves correspond to bands with up and down spin, respectively.FIG. S9. Spin polarized band structure of the β-FeSi2/Si(001) slab. The red and blue curvescorrespond to bands with up and down spin, respectively.11