Magnetite $({\mathrm{Fe}}_{3}{\mathrm{O}}_{4})$ doped with earth-abundant metals has become a promising catalyst material. In particular, Ni-doped magnetite $(\mathrm{Ni}/{\mathrm{Fe}}_{3}{\mathrm{O}}_{4})$ has been demonstrated as a cheap, robust, and catalytically active material in photocatalytic and electrochemical water oxidation. Recently, the incorporation of Ni atoms in ${\mathrm{Fe}}_{3}{\mathrm{O}}_{4}$ single crystalline surfaces was studied extensively with scanning tunneling microscopy and density-functional theory calculations. However, because of its importance for catalytic activity, this incorporation process and the determination of the lattice sites occupied by the Ni atoms require further experimental study. In this work, we investigated the surface structure of as-grown and annealed $\mathrm{Ni}/{\mathrm{Fe}}_{3}{\mathrm{O}}_{4}$(001) as a function of Ni coverage under ultra-high vacuum conditions with temperature-dependent x-ray and ultraviolet photoelectron spectroscopy, x-ray photoelectron diffraction, and low-energy electron diffraction. We observe that octahedrally coordinated subsurface cation vacancy sites are already occupied upon Ni deposition at room temperature and that Ni atoms start to diffuse further into the octahedral subsurface sites with increasing temperature.

The main data analysis was done with Wavemetrics Igor Pro 7.08 using user-defined macros. General Remarks The calibration factor for our electron analyzer in the laboratory source XPS measurements was determined based on the peak positions of Au 4f7/2 Ag 3d5/2, and Cu 2p3/2 acquired from freshly prepared metallic Au, Ag, and Cu samples. For a pass energy of 50 eV: CKE=(MKE-0.58267)/0.99913 where CKE and MKE represent calibrated and measured kinetic energies, respectively. The XPD and FSM patterns throughout this dataset are presented in a file structure: tab-separated YXZT. To obtain the patterns as they were represented in the manuscript, first plot Y vs. X in marker mode. Assign Z and T as marker size and color, respectively. %%% Figure 1 %%% Figure 1.a and Figure 1.b The high symmetry points: |ΓL|= √3π/a |ΓX|= 2π/a |ΓW|= √5π/a |ΓK|= √3π/2a |ΓU|= √3π/2a Figure 1.c The SBZ boundaries for the bulk and reconstructed cell: |ΓX|bulk= √2π/a |ΓX|rec= π/a Figure 1.d File: "Fig1d.tiff" LEED Image (Energy=20 eV) Figure 1.e File: "Fig1e.txt" File structure(Left-to-right): Tab separated YXZT The Fermi surface of a pristine Fe3O4(001), excitation: He Ia (21.22 eV) Figure 1.f File: "Fig1f.txt" File structure(Left-to-right): Tab separated YXZT The Fermi surface of a pristine Fe3O4(001), excitation: He IIa (40.80 eV) %%% Figure 2 %%% Angular distribution maps of photoelectrons excited from their fixed initial-state energy Ei (EF, 0.22 eV, 0.43 eV, 1.29 eV, 1.49 eV and 1.70 eV) mapped versus parallel momentum. Figure 2.a Files: "Fig2a_EF.txt, Fig2a_0p22eV.txt, Fig2a_0p43eV.txt, Fig2a_1p29eV.txt, Fig2a_1p49eV.txt, Fig2a_1p70eV.txt" File structure(Left-to-right): Tab separated YXZT The measurements were acquired with a He Ia excitation. Figure 2.b Files: "Fig2b_EF.txt, Fig2b_0p22eV.txt, Fig2b_0p43eV.txt, Fig2b_1p29eV.txt, Fig2b_1p49eV.txt, Fig2b_1p70eV.txt" File structure(Left-to-right): Tab separated YXZT The simulations, which were obtained with the RSMS code, were acquired to mimic He Ia excitation. Figure 2.c Files: "Fig2c_EF.txt, Fig2c_0p22eV.txt, Fig2c_0p43eV.txt, Fig2c_1p29eV.txt, Fig2c_1p49eV.txt, Fig2c_1p70eV.txt" File structure(Left-to-right): Tab separated YXZT The measurements were acquired with a He IIa excitation. Figure 2.d Files: "Fig2d_EF.txt, Fig2b_0p22eV.txt, Fig2d_0p43eV.txt, Fig2d_1p29eV.txt, Fig2d_1p49eV.txt, Fig2d_1p70eV.txt" File structure(Left-to-right): Tab separated YXZT The simulations, which were obtained with the RSMS code, were acquired to mimic He IIa excitation. %%% Figure 3 %%% Figure 3.a File: "Fig3a.txt" "File structure: Tab-separated YYYX, where the first three columns (from left to right) represent spectra taken from the pristine, as-grown, and post-annealed samples, respectively. Column X (Ni 2p) denotes the binding energy. Figure 3.b File: "Fig3b.txt" "File structure: Tab-separated YYYX, where the first three columns (from left to right) represent spectra taken from the pristine, as-grown, and post-annealed samples, respectively. Column X (Fe 2p) denotes the binding energy. Figure 3.c-e File: "Fig3c.txt, Fig3d.txt, Fig3e.txt " File structure(Left-to-right): Tab separated YXZT %%% Figure 4 %%% Figure 4.a File: "Fig4a_010.txt, Fig4a_110.txt, Fig4ac_kpar.txt" File structure (Left-to-right): YY….YY (Fig4a_010.txt, Fig4a_110.txt) vs. X (Fig4ac_kpar.txt) Parallel momentum range from k=0 Å-1 to k=1.83 Å-1. Energy range Ebin= 0 eV to Ebin= 2.6 eV. Plot type: MDC, Sample: Pristine Fe3O4(001), Crystal directions: [010] and [110] Note that the data presented in the manuscript were given with a Y-offset. Figure 4.b File: "Fig4b_010.txt, Fig4b_110.txt, Fig4bd_en.txt" File structure (Left-to-right): YY….YY (Fig4b_010.txt, Fig4b_110.txt) vs. X (Fig4bd_en.txt) Parallel momentum range from k=0 Å-1 to k=1.83 Å-1. Energy range Ebin= 0 eV to Ebin= 2.6 eV. Plot type: EDC, Sample: Pristine Fe3O4(001), Crystal directions: [010] and [110] Note that the data presented in the manuscript were given with a Y-offset. Figure 4.c File: "Fig4c_010.txt, Fig4c_110.txt, Fig4ac_kpar.txt " File structure (Left-to-right): YY….YY (Fig4e_010.txt, Fig4e_110.txt) vs. X (Fig4ac_kpar.txt) Parallel momentum range from k=0 Å-1 to k=1.83 Å-1. Energy range Ebin= 0 eV to Ebin= 2.6 eV. Plot type: MDC, Sample: Post-annealed 26-ML Ni/Fe3O4(001), Crystal directions: [010] and [110] Note that the data presented in the manuscript were given with a Y-offset. Figure 4.d File: "Fig4d_010.txt, Fig4d_110.txt , Fig4bd_en.txt" File structure (Left-to-right): YY….YY (Fig4d_010.txt, Fig4d_110.txt) vs. X (Fig4bd_en.txt) Parallel momentum range from k=0 Å-1 to k=1.83 Å-1. Energy range Ebin= 0 eV to Ebin= 2.6 eV. Plot type: EDC, Sample: Post-annealed 26-ML Ni/Fe3O4(001), Crystal directions: [010] and [110] Note that the data presented in the manuscript were given with a Y-offset. %%% Figure 5 %%% Figure 5.a File: "Fig5a.txt" File structure: Tab-separated YYX(Mg Ka) YYX(He Ia), where Y represents spectra taken from the pristine and post-annealed samples from left to right, respectively, and X denotes the binding energies. Figure 5.b File: "Fig5b.txt" File structure : Tab separated YX-YYYX-YX YX(Measurement) Left-to-right (Y: The spectrum from the pristine sample, X: Binding energy) YYYX(TDOS) Left-to-right (Y: Spin up, Y: Spin down, Y: Spin Tot, X: Energy(X-offset: 4.943 eV) for NixFe3-xO4 (x=0)) YX(Gaussian-broadened TDOS) Broadening:0.5 eV Left-to-right (Y: Spin Tot, X: Energy) Figure 5.c File: "Fig5c.txt" File structure: Tab separated YX-YYYX-YX YX(Measurement) Left-to-right (Y: The spectrum from the post-annealed sample, X: Binding energy) YYYX(TDOS) Left-to-right (Y: Spin up, Y: Spin down, Y: Spin Tot, X: Energy(X-offset: 5.343 eV) for NixFe3-xO4 (x=1)) YX(Gaussian-broadened TDOS) Broadening:0.5 eV Left-to-right (Y: Spin Tot, X: Energy) Figure 5.d File: "Fig5d.txt" File structure: Tab separated YX-YYYX-YX YX(Measurement) Left-to-right (Y: XP spectrum from the post-annealed sample, X: Binding Energy) YYYX(TDOS) Left-to-right (Y: Spin up, Y: Spin down, Y: Spin Tot, X: Energy(X-offset: 5.593 eV) for NixFe3-xO4 (x=2)) YX(Gaussian-broadened TDOS) Broadening:0.5 eV Left-to-right (Y: Spin Tot, X: Energy) Figure 5.e File: "Fig5e.txt" File structure: Tab separated Y-YY-YY-X Left-to-right (Y:Fe Total PDOS, Y: Fetet PDOS spin up, Y: Fetet PDOS spin down , Y: Feoct PDOS spin up, Y: Feoct PDOS spin down, X: Energy for for NixFe3-xO4 (x=0)) Gaussian Broadening: 0.2 eV Figure 5.f File: "Fig5f.txt" File structure: Tab separated Y-YY-YY-YY-X Left-to-right (Y: Ni and Fe Total PDOS, Y: Nioct PDOS spin up, Y: Nioct PDOS spin down , Y: Fetet PDOS spin up, Y: Fetet PDOS spin down, Y: Feoct PDOS spin up, Y: Feoct PDOS spin down, X: Energy(X-offset: 1.93 eV) for NixFe3-xO4 (x=1)) Gaussian Broadening: 0.2 eV Figure 5.g File: "Fig5g.txt" File structure: Tab separated Y-YY-YY-X Left-to-right (Y: Ni and Fe Total PDOS, Y: Nioct PDOS spin up, Y: Nioct PDOS spin down, Y: Fetet PDOS spin up, Y: Fetet PDOS spin down, X: Energy(X-offset: 2.12 eV) for NixFe3-xO4 (x=2)) Gaussian Broadening: 0.2 eV %%% Figure 6 %%% Figure 6.a File: "Fig6a.txt" File structure(Left-to-right): Tab separated Y-Y-Y-X (Y: 120 ML, Y:50 ML, Y: 10 ML, X: Energy) (X-offset: 2 eV) Figure 6.b File: "Fig6b.txt" File structure(Left-to-right): Tab separated Y-Y-Y-Y-X (Y: 120 ML, Y:50 ML, Y: 10 ML, Y:Pristine, X: Ni 2p Energy) %%% Figure 7 %%% Figure 7.a File: "Fig7a.txt" File structure(Left-to-right): Tab separated Y-Y-Y-Y-X (Y: 120 ML, Y:50 ML, Y: 10 ML, Y:Pristine, X: Energy) (X-offset: 2.8 eV) Figure 7.b File: "Fig7b.txt" File structure(Left-to-right): Tab separated Y-Y-Y-Y-X (Y: 120 ML, Y:50 ML, Y: 10 ML, Y:Pristine, X: Fe 2p Energy) %%% Figure 8 %%% Figure 8.a File: "Fig8a.txt" File structure(Left-to-right): Tab separated Y-Y-Y-Y-X (Y: 120 ML, Y:50 ML, Y: 10 ML, Y:Pristine, X: Energy) (X-offset: 1.1 eV) Figure 8.b File: "Fig8b.txt" File structure(Left-to-right): Tab separated Y-Y-Y-X (Y: (120 ML-Pristine), Y: (50 ML-Pristine), Y: (10 ML-Pristine), X: Energy) %%% SUPLLEMENTARY INFORMATION %%% %%% Figure SI3 %%% File: "FigSI3_pristine.txt, FigSI3_26ML_AG.txt, FigSI3_26ML_PA.txt" File structure (Left-to-right): XY1-XY2-XY3… XY9-XY10-XY11-XY12 (AG: As-grown, PA: Post-annealed) XY1 – XY9 (Y: Fit Peak, X: Energy) XY10 (Y: Cumulative Fit Peak, X: Energy) XY11 (Y: Residue, X: Energy) XY12 (Y: Shirley BG Subtracted XPS Measurement, X: Energy) %%% Figure SI4 %%% Figure SI4.a File: "FigSI4_oct.txt" File structure(Left-to-right): YYYYYY1-YYYYYY2-YYYYYY3… YYYYYY4-X YYYYYY1 (Y: PDOS eg down, PDOS Tot down, PDOS t2g down, PDOS eg up, PDOS Tot up, PDOS t2g up) Layer: S YYYYYY2 (Y: PDOS eg down, PDOS Tot down, PDOS t2g down, PDOS eg up, PDOS Tot up, PDOS t2g up) Layer: S-2 YYYYYY3 (Y: PDOS eg down, PDOS Tot down, PDOS t2g down, PDOS eg up, PDOS Tot up, PDOS t2g up) Layer: S-6 YYYYYY4 (Y: PDOS eg down, PDOS Tot down, PDOS t2g down, PDOS eg up, PDOS Tot up, PDOS t2g up) Layer: S-8 X: Energy Figure SI4.b File: "FigSI4_tet.txt" File structure(Left-to-right): YYYYYY1-YYYYYY2-YYYYYY3… YYYYYY4-X YYYYYY1 (Y: PDOS eg down, PDOS Tot down, PDOS t2g down, PDOS eg up, PDOS Tot up, PDOS t2g up) Layer: S-1 YYYYYY2 (Y: PDOS eg down, PDOS Tot down, PDOS t2g down, PDOS eg up, PDOS Tot up, PDOS t2g up) Layer: Interstitial Tet YYYYYY3 (Y: PDOS eg down, PDOS Tot down, PDOS t2g down, PDOS eg up, PDOS Tot up, PDOS t2g up) Layer: S-3 YYYYYY4 (Y: PDOS eg down, PDOS Tot down, PDOS t2g down, PDOS eg up, PDOS Tot up, PDOS t2g up) Layer: S-7 X: Energy Channeltron positions: 0.00 eV, 0.22 eV, 0.43 eV, 1.29 eV, 1.49 eV and 1.70 eV %%% Figure SI5 %%% Figure SI5.a File: "FigSI5a_EF.txt, FigSI5a_0p22eV.txt, FigSI5a_0p43eV.txt, FigSI5a_1p29eV.txt, FigSI5a_1p49eV.txt, FigSI5a_1p70eV.txt " File structure(Left-to-right): Tab separated YXZT Figure SI5.b File: "FigSI5b_EF.txt, FigSI5b_0p22eV.txt, FigSI5b_0p43eV.txt, FigSI5b_1p29eV.txt, FigSI5b_1p49eV.txt, FigSI5b_1p70eV.txt " File structure(Left-to-right): Tab separated YXZT Figure SI5.c File: "FigSI5c_EF.txt, FigSI5c_0p22eV.txt, FigSI5c_0p43eV.txt, FigSI5c_1p29eV.txt, FigSI5c_1p49eV.txt, FigSI5c_1p70eV.txt " File structure(Left-to-right): Tab separated YXZT %%% Figure SI6 %%% Figure SI6.a File: "FigSI6a_EF.txt, FigSI6a_0p22eV.txt, FigSI6a_0p43eV.txt, FigSI6a_1p29eV.txt, FigSI6a_1p49eV.txt, FigSI6a_1p70eV.txt " File structure(Left-to-right): Tab separated YXZT Figure SI6.b File: "FigSI6b_EF.txt, FigSI6b_0p22eV.txt, FigSI6b_0p43eV.txt, FigSI6b_1p29eV.txt, FigSI6b_1p49eV.txt, FigSI6b_1p70eV.txt " File structure(Left-to-right): Tab separated YXZT Figure SI6.c File: "FigSI6c_EF.txt, FigSI6c_0p22eV.txt, FigSI6c_0p43eV.txt, FigSI6c_1p29eV.txt, FigSI6c_1p49eV.txt, FigSI6c_1p70eV.txt " File structure(Left-to-right): Tab separated YXZT %%% Figure SI7 %%% Figure SI7.a File: "FigSI7a.tif" LEED Image (Energy=20 eV), Sample: Pristine Fe3O4(001) Figure SI7.b File: "FigSI7b.tif" LEED Image (Energy=20 eV), Sample: As-grown 26 ML Ni/Fe3O4(001) Figure SI7.c File: "FigSI7c.tif" LEED Image (Energy=20 eV), Sample: Post-annealed 26 ML Ni/Fe3O4(001) %%% Figure SI8 %%% File: "FigSI8_XPS_and_UPS.txt, FigSI8_Fe3O4_DOS.txt, FigSI8_NiFe2O4_DOS.txt, FigSI8_Ni2FeO4_DOS.txt" Experiment: FigSI8_XPS_and_UPS.txt File structure(Left-to-right): Tab separated YYX(Mg Ka) YYX(He Ia), where Y are the spectra taken from the pristine and post-annealed sample left to right, respectively, and X donate the binding energies. DOS (Fe3O4): FigSI8_Fe3O4_DOS.txt File structure: YYYX(TDOS) - YX(Gaussian-broadened TDOS) Broadening:0.5 eV (Y: Spin Tot, Y: Spin up, Y: Spin down, X: Energy) (X-offset: 4.943 eV) (Y: Spin Tot, X: Energy) DOS (NiFe2O4): FigSI8_NiFe2O4_DOS.txt File structure: YYYX(TDOS) - YX(Gaussian-broadened TDOS) Broadening:0.5 eV (Y: Spin Tot, Y: Spin up, Y: Spin down, X: Energy) (X-offset: 5.343 eV) (Y: Spin Tot, X: Energy) DOS (NiFe2O4): FigSI8_Ni2FeO4_DOS.txt File structure: YYYX(TDOS) - YX(Gaussian-broadened TDOS) Broadening:0.5 eV (Y: Spin Tot, Y: Spin up, Y: Spin down, X: Energy) (X-offset: 5.593 eV) (Y: Spin Tot, X: Energy) %%% Figure SI9 %%% Figure SI9.a File: "Fig9a.txt" File structure: YYYYYY1-YYYYYY2-X YYYYYY1 (Y: PDOS eg down, PDOS Tot down, PDOS t2g down, PDOS eg up, PDOS Tot up, PDOS t2g up) Coordination: Fe_oct YYYYYY2 (Y: PDOS eg down, PDOS Tot down, PDOS t2g down, PDOS eg up, PDOS Tot up, PDOS t2g up) Coordination: Fe_tet X: Energy Figure SI9.b File: "Fig9b.txt" File structure: YYYYYY1-YYYYYY2-YYYYYY3-X YYYYYY1 (Y: PDOS eg down, PDOS Tot down, PDOS t2g down, PDOS eg up, PDOS Tot up, PDOS t2g up) Coordination: Fe_oct YYYYYY2 (Y: PDOS eg down, PDOS Tot down, PDOS t2g down, PDOS eg up, PDOS Tot up, PDOS t2g up) Coordination: Fe_tet YYYYYY3 (Y: PDOS eg down, PDOS Tot down, PDOS t2g down, PDOS eg up, PDOS Tot up, PDOS t2g up) Coordination: Ni_oct X: Energy Figure SI9.c File: "Fig9c.txt" File structure(Left-to-right): YYYYYY1-YYYYYY2-X YYYYYY1 (Y: PDOS eg down, PDOS Tot down, PDOS t2g down, PDOS eg up, PDOS Tot up, PDOS t2g up) Coordination: Fe_tet YYYYYY2 (Y: PDOS eg down, PDOS Tot down, PDOS t2g down, PDOS eg up, PDOS Tot up, PDOS t2g up) Coordination: Ni_oct X: Energy %%% Figure SI10 %%% File: "FigSI10_010.txt, FigSI10_110.txt, FigSI10_Energy.txt" File structure(Left-to-right): YY….YY (FigSI10_010.txt, FigSI10_110.txt) vs. X (FigSI10_Energy.txt) Parallel momentum range from k=0 Å-1 to k=1.83 Å-1. Plot type: EDC, Sample: Pristine Fe3O4(001), Crystal directions: [010] and [110] Note that the data presented in the manuscript were given with a Y-offset. %%% Figure SI11 %%% Figure SI11.a File: "Fig SI11a.txt" File structure(Left-to-right): Tab separated Y-Y-Y-X (Y: 120 ML, Y:50 ML, Y: 10 ML, X: Energy) (X-offset: 2 eV) Figure SI11.b File: "Fig SI11b.txt" File structure(Left-to-right): Tab separated Y-Y-Y-Y-X (Y: 120 ML, Y:50 ML, Y: 10 ML, Y:Pristine, X: Ni 2p Energy) Figure SI11.c File: "FigSI11c.txt" File structure(Left-to-right): Tab separated Y-Y-Y-Y-X (Y: 120 ML, Y:50 ML, Y: 10 ML, Y: Pristine, X: Energy) (X-offset: 2.8 eV) Figure SI11.d File: "FigSI11d.txt" File structure(Left-to-right): Tab separated Y-Y-Y-Y-X (Y: 120 ML, Y:50 ML, Y: 10 ML, Y:Pristine, X: Fe 2p Energy) Figure SI11.e File: "FigSI11e.txt" File structure(Left-to-right): Tab separated Y-Y-Y-Y-X (Y: 120 ML, Y:50 ML, Y: 10 ML, Y: Pristine, X: Energy) (X-offset: 1.1 eV) Figure SI11.f File: "FigSI11f.txt" File structure(Left-to-right): Tab separated Y-Y-Y-Y-X (Y: 120 ML, Y:50 ML, Y: 10 ML, Y:Pristine, X: O 1s Energy)

The on-surface synthesis of nano-graphenes has led the charge in prototyping structures with perspectives beyond silicon-based technology. Following reports of open-shell systems in graphene-nanoribbons (GNRs), a flurry of research activity was directed at investigating their magnetic properties with a keen eye for spintronic applications. Although the synthesis of nano-graphenes is usually carried out on Au(111), the substrate is difficult to use for electronic decoupling and spin-polarized measurements. Using a binary alloy Cu3Au(111), we show possibilities for gold-like on-surface synthesis compatible with spin polarization and electronic decoupling known from copper. We prepare copper oxide layers, demonstrate the synthesis of GNRs, and grow thermally stable magnetic Co islands. We functionalize the tip of a scanning tunneling microscope with carbon-monoxide, nickelocene, or attach Co clusters for high-resolution imaging, magnetic sensing, or spin-polarized measurements. This versatile platform will be a valuable tool in the advanced study of magnetic nano-graphenes.

Magnetite (Fe3O4) doped with earth-abundant metals has become a promising catalyst material. In particular, Ni-doped magnetite (Ni/Fe3O4) has been demonstrated as a cheap, robust, and catalytically active material in photocatalytic and electrochemical water oxidation. Recently, the incorporation of Ni atoms in Fe3O4 single crystalline surfaces was studied extensively with scanning tunneling microscopy and density-functional theory calculations. However, because of its importance for catalytic activity, this incorporation process and the determination of the lattice sites occupied by the Ni atoms require further experimental study. In this work, we investigated the surface structure of as-grown and annealed Ni/Fe3O4(001) as a function of Ni coverage under ultra-high vacuum conditions with temperature-dependent x-ray and ultraviolet photoelectron spectroscopy, x-ray photoelectron diffraction, and low-energy electron diffraction. We observe that octahedrally coordinated subsurface cation vacancy sites are already occupied upon Ni deposition at room temperature and that Ni atoms start to diffuse further into the octahedral subsurface sites with increasing temperature.

The strategy of anchoring molecular catalysts on electrode surfaces combines the high selectivity and activity of molecular systems with the practicality of heterogeneous systems. The stability of molecular catalysts is, however, far less than that of traditional heterogeneous electrocatalysts, and therefore a method to easily replace anchored molecular catalysts that have degraded could make such electrosynthetic systems more attractive. Here, we apply a non-covalent “click” chemistry approach to reversibly bind molecular electrocatalysts to electrode surfaces via host-guest complexation with surface-anchored cyclodextrins. The host-guest interaction is remarkably strong and allows the flow of electrons between the electrode and the guest catalyst. Electrosynthesis in both organic and aqueous media was demonstrated on metal oxide electrodes, with stability on the order of hours. The catalytic surfaces can be recycled by controlled release of the guest from the host cavities and readsorption of fresh guest. This strategy represents a new approach to practical molecular-based catalytic systems.