adsorption of Atomic Hydrogen and Molecular Nitric Oxide

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Spin Polarization Enhancement of an FeO(100) Surface by CoAdsorption of Atomic Hydrogen and Molecular Nitric Oxide Xia Sun, Muhammad Jibran, Andrew Pratt, Bing Wang, and Yasushi Yamauchi J. Phys. Chem. C, Just Accepted Manuscript • DOI: 10.1021/acs.jpcc.9b01790 • Publication Date (Web): 29 Apr 2019 Downloaded from http://pubs.acs.org on April 30, 2019

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The Journal of Physical Chemistry

Spin Polarization Enhancement of an Fe3O4(100) Surface by Coadsorption of Atomic Hydrogen and Molecular Nitric Oxide Xia Sun1,2*, Muhammad Jibran1, Andrew Pratt,2,3 Bing Wang1, Yasushi Yamauchi2 1.

Hefei National Laboratory for Physical Sciences at the Microscale, Key Laboratory of StronglyCoupled Quantum Matter Physics (CAS), and Department of Physics, University of Science and Technology of China, 96 Jinzhai Road, Hefei, Anhui 230026, China

2. National Institute for Materials Science, 1-2-1 Sengen, Tsukuba, Ibaraki 305-0047,Japan 3. Department of Physics, University of York, Heslington, York YO10 5DD, UK

ABSTRACT The geometric structure, electronic states and surface spin polarization of a (H, NO)co-adsorbed Fe3O4(100) surface have been studied using density functional theory (DFT) calculations. H atoms saturate the surface dangling bonds through bonding with the O atom (O1) without a tetrahedral Fe neighbor (Fe(A)), inducing a deeper level shift of the spin-up surface state bands (SSB) and a widening of the spin-up band gap between the Fermi level (EF) and the valence band maximum (VBM). NO molecules are adsorbed on surface octahedral Fe atoms (Fe(B)). The adsorbate-substrate and molecule-molecule interactions cause considerable filling and broadening of the spindown 2* states of the adsorbed NO molecule. A -100% spin polarization is obtained over the energy range of -0.8 eV to EF for the (H, NO)-co-adsorbed Fe3O4(100) surface meaning that this system has greater potential for application in spintronic devices than either the solely H-adsorbed or NO-adsorbed surfaces. Furthermore, the adsorbed NO molecule can provide a considerable density of -100% spin-polarized states. Both of 1

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these findings are significant for the application and design of spintronic devices. I.

INTRODUCTION Many of tunneling magnetoresistance (TMR) junctions were fabricated using half

metals with relatively narrow half-metallic band width and resulted in poor performances in spin sensitivity.1 One approach to overcome this situation is to utilize the spin filter effect of low tolerance conduction channel by introducing narrow band layers in junctions. This leads to low conductance of junctions. Another approach is to attain larger tolerance of spin sensitive conduction channel namely to tailor the junction interface being wider half-metallic band. Interface engineering is an effective means to enhancing the efficiency of spin injection in spintronic and organic spintronic devices.2 Beyond this, recent developments have shown that the interfacial unit itself can be considered as a separate spintronic element that opens up possibilities for active control of ‘spinterface’ properties.3 Hence, modifying the properties of native ferromagnetic surfaces is essential for next-generation spintronic device development. Motivated by this goal, we have studied the enhancement of the Fermi-level spin polarization, PEF, at the surface of Fe3O4(001) through the adsorption of atomic hydrogen4-6 or group IV elements such as C and B.7,8 Our results have shown that removing surface states through chemical modification is necessary to overcome the severe depletion of PEF from its bulk half-metallic value of -100%, which occurs in the presence of oxygen dangling bonds that are otherwise saturated in the bulk. Experimental measurements using spin-polarized metastable helium atoms,4 in addition to density functional theory calculations,6,9 indicate that the adsorption of atomic hydrogen to quench surface 2


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dangling bonds reopens the band gap in the majority spin channel so that halfmetallicity is recovered. Despite the remarkable effect of hydrogen adsorption on PEF, this system has obvious shortcomings for spintronic devices as only the metallic octahedral Fe(B) atoms have a -100% spin polarization with other surface atoms (O and H) contributing a positive spin density.6 C- and B-adsorbed Fe3O4(001) show a more global enhancement of PEF but deposition of these atomic species requires very high temperatures.7,8 We also showed recently that molecular adsorption of NO also leads to a -100% spin polarization at the Fermi level with NO molecules found to bond to surface Fe(B) atoms.10 However, the half-metallic band width of NO-adsorbed Fe3O4(001) is much narrower than that of the H-adsorbed system due to the unsaturated surface dangling bonds. Again though, positive spin polarization exists at surface oxygen atoms which somewhat negates the benefits of the NO-adsorbed system. In this work, we investigate the co-adsorbed system of H atoms and NO molecules by considering the fact that H atoms and NO molecules adsorb at different sites on the Fe3O4(001) surface. We predict that H atoms saturate the dangling bonds of surface O atoms and greatly widen the spin-up band gap between the Fermi level and the valence band maximum (VBM) (EF-VBM). At the same time, NO molecules bond with Fe(B) atoms, resulting in a considerable filling and widening of its 2* states. The cumulative effect benefitting from the co-adsorption manifests a significant global enhancement of the surface spin polarization that surpasses the effect from the surfaces with monoadsorption of H or NO. 3



II. COMPUTATION METHODS Computation methods are similar to those in our previous investigations of the adsorption of H, C and B.6-8 All calculations were completed via the Vienna ab initio simulation package (VASP) 11,12 with the generalized gradient approximation (GGA)13 and the projector-augment wave method

14,15

as well as the Monkhorst-Pack k-point

grid (441).16 An effective Hubbard parameter (U=3.8 eV) is adopted to include the strong correlated effect from Fe 3d electrons.17 The value of U is chosen according to the comparison of the calculated band gap of bulk Fe3O4 with the experimental one. GGA is not recommended for such strongly correlated systems, since it predicts not only a narrow band-gap but also a magnetic quench of the adsorbed NO molecules and the NO-attached Fe(B) atoms.10 We use a reconstructed unit cell of ( 2 × 2 )R 45o , which has been conclusively proven by kinds of measurements and calculations. 18-21 The Fe3O4(100) surface is represented by a 13-layer slab terminated by Fe(B) atoms with large vacuum region (17.5 Å). 22,23 III. RESULTS AND DISCUSSION To distinguish different oxygen atoms at topmost layer, the O atom without a tetrahedral Fe(A) neighbor is labeled by O1 and that with an Fe(A) neighbor by O2, respectively. Atomic H is known to prefer the O1 site with a large adsorption energy (3.154 eV as calculated using GGA+U).6 In contrast, a NO molecule prefers the Fe(B) site via its N-terminal with an adsorption energy of -0.823 eV.10 The bonding of NO molecules with metallic atoms has also been observed for CuFe2O4(100), ZnGaAlO4(100) and NiO(100) substrates.24-26 The geometric structure of (H, NO) co4


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adsorption can be obtained through either the adsorption of a NO molecule on the Hadsorbed Fe3O4(100) surface or of a H atom on the NO-adsorbed Fe3O4(100) surface. The H atom and NO molecule bond with surface O1 and Fe(B) atoms, respectively (Fig. 1). Interestingly, the adsorption energy of a NO molecule on the H-adsorbed Fe3O4(100) surface (-0.929 eV) is even larger than that on a clean Fe3O4(100) surface (-0.823 eV). In accordance with the larger adsorption energy, the bond length of N-Fe(B) (1.855 Å) for the (H, NO)-co-adsorbed surface is smaller than that for the NO-adsorbed surface (2.081 Å), indicating that the co-adsorption causes a stronger interaction between the Fe(B) atom and the NO molecule. Compared with the NO-adsorbed Fe3O4(100) surface, the co-adsorption of H and NO also induces an elongation of the Fe(B)-O1 bond by about 0.07-0.10 Å and the N-O bond by 0.01 Å. Figure 2 compares the spin-resolved band structure of clean, H-adsorbed, NOadsorbed and (H, NO)-co-adsorbed Fe3O4(100) surfaces. For the clean surface, several topmost spin-up valence bands (blue lines in left panel of Fig. 2a) originate from surface atoms via Fe(B)-dx2−y2 and O-p orbitals. (Supplementary Material). Induced by these spin-up surface state bands (SSB), the spin polarization and spin asymmetry at the surface are observed to be greatly decreased.4,5 Due to H adsorption, electrons are donated from H to the surface O1 atoms, resulting in a saturation of oxygen dangling bonds. Half of the spin-up SSB evolve to the O1-H bonding bands and locate at an energy level of approximately -9.0 eV. The remaining SSB shift to deeper levels and locate very close to the bulk-like valence band.6 Compared with the clean surface, H adsorption induces an enlargement of the EF-VBM by about 0.78 eV (Fig. 2b). This 5



causes a significant enhancement of the surface spin polarization, as has been proven by our SPMDS measurement.4,5 In contrast, for the NO-adsorbed Fe3O4(100) surface, all spin-up SSB locate above the bulk-like valence band although their energy levels are slightly shifted to deeper levels (blue lines in Fig. 2c). This is due to adsorbed NO molecules bonding with Fe(B) atoms with oxygen dangling bonds remaining unsaturated. For (H, NO)-co-adsorbed Fe3O4(100), the spin-up band structure close to the Fermi level is very similar to that of the H-adsorbed Fe3O4(100) surface due to common location of H adsorption on the O1 site (Fig. 2d). The EF-VBM is widened to 0.81 eV. The band-decomposed charge density indicates that the electron density of the band with the highest energy level below EF for the (H, NO)-co-adsorbed Fe3O4(100) is much less than that of H-adsorbed Fe3O4(100) due to electron redistribution (Supplemental Material). For the spin-down band structure, the most obvious variation by (H, NO) co-adsorption is the increment of the band number at the energy range of 1.0 eV to EF, which will greatly increase the density of states (DOS) of surface atoms and therefore improve the efficiency of spin injection. Figure 3 compares the DOS of adsorbates and surface atoms before and after (H, NO) co-adsorption. As indicated in the left-top panel of Fig.3a, the sharp peaks below the Fermi level correspond to 4, 1 and 5 orbitals of a free NO molecule. After adsorption, these molecular orbitals are apparently broadened. The strong N-Fe(B) bond induces new peaks at about -12 eV (by 4 orbital of NO) as well as enhanced peaks at around -8 to -5 eV (by 1/5 orbital of NO) in the DOS of surface Fe(B) atoms. Usually, a magnetic substrate may induce a slight spin polarization at the Fermi level 6


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in the adsorbed molecules by the process of electron back-donation. Different with most nonmagnetic molecules, the NO molecule has an unpaired electron, its 2* orbital locates at around the Fermi level. After adsorption, the original 2* orbital is obviously filled and broadened (-1.0 eV~ EF, 2nd and 3rd panels of Fig.3a). The prominent spindown peaks close to the Fermi level are also observed at the DOS of the surface Fe(B) and O2 atoms of the (H, NO)-co-adsorbed surface and should be very helpful to spin injection into nonmagnetic materials. For the DOS of the O1 atom (2nd panel of Fig. 3b), two noticeable phenomena are induced by co-adsorption. As well as new peaks appearing at approximately -9.0 eV due to the O1-H bonding, the sharp peaks between -1.0 eV and EF caused by spin-up SSB (3rd panel of Fig. 3b) disappear, resulting in a negligible DOS close to EF. Figure 4 shows the differential charge densities (∆n) which help visualize how the charge flows. ∆n is obtained by subtracting the electron densities of the clean substrate (nFe3O4) and the isolated adsorbate (nNO and nH) from that of the adsorbate/substrate system (n(H,NO)-Fe3O4) for the energy range of -14 eV to EF:

n  n(H, NO )  Fe3O 4  nFe3O 4  nH  nNO The geometries of the latter three systems are as same as the adsorbed one. The adsorbed H and surface O1 atoms are surrounded by yellow (electron gain) and blue (electron loss) color (Fig.4), respectively, indicating an obvious electron donation process induced by strong O1-H bonding. Due to this saturation of oxygen dangling bonds, the Fe(B)-O1 bond is weakened with an elongated bond length and the Fe(B)-N bond is strengthened with a shortened bond length, compared with those in the solely 7



NO-adsorbed surface. In contrast, the adsorbed NO molecules mainly gain electrons, as indicated by the dominance of yellow in Fig. 4. In other words, more electrons are back-donated from Fe(B) to the 2* orbital of NO than are donated from the 4, 1 and 5 orbitals of NO to Fe(B). Correspondingly, the magnetic moment of the O atom in NO molecule increases from -0.25 B to -0.41 B. Considerable electron redistribution can be observed at the surface Fe(B) atoms whilst electron density decreases (blue color) along the dx2-y2 orbital and increases (yellow color) along the dz2, dxz and dyz orbitals. The increased density is predominantly due to spin-down electrons close to the Fermi level, resulting in a reduction of the magnetic moment of Fe(B) atom from 4.15 B to 3.73 B. Electron redistribution also leads a slight increase of density at O2 atoms. The value of PEF at surface or interface is crucial for spintronic devices. Figure 5 compares the spin density ( n  n  n ) of the clean, H-adsorbed, NO-adsorbed and (H, NO)-co-adsorbed Fe3O4(100) surfaces over a wide energy (-0.8 eV to EF). For clean Fe3O4(100) surface (Fig. 5a), due to spin-up SSB states, all atoms at the topmost surface including Fe(B), O1 and O2 are surrounded by yellow color, indicating a considerable positive spin density.4,5,18 For the H-adsorbed surface (Fig. 5b), metallic Fe(B) atoms are surrounded by blue color, representing a large negative spin density along its dx2-y2 orbital. The density at other atoms (O1, O2 and the adsorbed H) is very sparse, which is a big disadvantage for spintronic materials since these atoms could not provide spin density to any contacted nonmagnetic materials. For the NO-adsorbed surface (Fig. 5c), the adsorbed NO molecules have significant negative spin density and protrude toward the vacuum. The spin density at Fe(B) atoms is also negative but shielded by adsorbates. 8


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Conversely, at this energy range, the O1 and O2 atoms have considerable positive spin density due to the unsaturated oxygen dangling bonds and therefore the spin-up SSB. For the (H, NO)-co-adsorbed surface (Fig. 5d), negative spin density appears not only at the adsorbed NO molecules but also at the surface O2 atoms. The density at O1 and the adsorbed H atoms is negligible due to the O1-H bonding. Compared to the solely NO-adsorbed surface, the (H, NO)-co-adsorbed surface has a higher surface spin polarization. Additionally, compared to the solely H-adsorbed surface, the (H, NO)-coadsorbed surface has a much larger density of -100% spin-polarized electronic states close to the Fermi level. Furthermore, due to the protrusion of NO molecules, the negative spin density of the (H, NO)-co-adsorbed surface would be easier to inject into nonmagnetic materials than the H-adsorbed surface. Therefore, among these four surfaces, the (H, NO)-co-adsorbed Fe3O4(100) appears to be the best candidate for the design of spintronic devices. Above prediction appeals for further experimental confirmation. IV. CONCLUSION The co-adsorption of H atoms and NO molecules on an Fe3O4(100) surface has been investigated using the GGA+U method. H atoms bond with surface O1 atoms, saturating its dangling bond and resulting in a widening of the EF-VBM. NO bonds with surface Fe(B) atoms, coordinated via its N atom. Adsorption induces an obvious electron back-donation to the spin-down 2* orbital of the NO molecule and an apparent broadening of this orbital. The co-adsorbed surface has a higher surface spin polarization than that of the solely NO-adsorbed surface and a significant increase in 9



the number of -100% spin-polarized electronic states over the solely H-adsorbed surface for the energy range of -0.8 eV to EF. Therefore, (H, NO)-co-adsorption is expected to greatly improve the spin injection efficiency of the Fe3O4(100) surface. Such co-adsorbed systems could open up new avenues in engineering surfaces and interfaces critical to spintronic and organic spintronic device operation, for example, by anchoring large -conjugated molecules to Fe(B) atoms whilst saturating O dangling bonds with atomic H to enhance surface spin polarization.

AUTHOR INFORMATION Corresponding Author *E-mail: [email protected]

SUPPORTING INFORMATION Top view of the band-decomposed charge density maps of the topmost valence band for spin-up electronic states of clean, H-adsorbed, NO-adsorbed and (H, NO)-coadsorbed Fe3O4(100) surfaces.

ACKNOWLEDGMENT This work was supported by the National Natural Science Foundation of China under Grant Nos. 11674297, U1632273 and Anhui Initiative in Quantum Information Technologies (AHY090300).

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REFERENCES (1) Bainsla, L.; Suresh, K. G. Equiatomic Quaternary Heusler Alloys: A Material Perspective for Spintronic Applications. Appl. Phys. Rev. 2016, 3, 031101. (2) Shi, S.; Sun, Z.; Bedoya-Pinto, A.; Graziosi, P.; Li, X.; Liu, X.; Hueso, L.; Dediu, V. A.; Luo, Y.; Fahlman, M. Hybrid Interface States and Spin Polarization at Ferromagnetic Metal–organic Heterojunctions: Interface Engineering for Efficient Spin Injection in Organic Spintronics. Adv. Funct. Mater. 2014, 24, 4812. (3) Cinchetti, M.; Dediu, V. A.; Hueso, L. E. Activating the Molecular Spinterface. Nature Mater. 2017, 16, 507. (4) Kurahashi, M.; Sun, X.; Yamauchi, Y. Recovery of the Half-metallicity of an Fe3O4(100) Surface by Atomic Hydrogen Adsorption. Phys. Rev. B: Condens. Matter Mater. Phys., 2010, 81, 193402. (5) Pratt, A.; Kurahashi, M.; Sun, X.; Yamauchi, Y. Adsorbate-induced Spinpolarization Enhancement of Fe3O4(0 0 1). J. Phys. D: Appl. Phys. 2011, 44, 064010. (6) Sun, Y.; Kurahashi, M.; Pratt, A.; Yamauchi, Y. First-principles Study of Atomic Hydrogen Adsorption on Fe3O4(100). Surf. Sci. 2011, 605, 1067. (7) Sun, X.; Li, S. D.; Wang, B.; Kurahashi, M.; Pratt, A.; Yamauchi, Y. Significant Variation of Surface Spin Polarization through Group IV Atom (C, Si, Ge, Sn) Adsorption on Fe3O4(100). Phys. Chem. Chem. Phys. 2014, 16, 95. (8) Sun, X.; Pratt, A.; Yamauchi, Y. Half-metallicity Induced by Boron Adsorption on an Fe3O4(100) Surface. Phys. Chem. Chem. Phys. 2015, 17, 15386. (9) Parkinson, G. S.; Mulakaluri, N.; Losovyj, Y.; Jacobson, P.; Pentcheva, R.; Diebold, 11



U. Semiconductor–Half Metal Transition at the Fe3O4(001) Surface upon Hydrogen Adsorption. Phys. Rev. B: Condens. Matter. Mater. Phys. 2010, 82, 125413. (10) Li, Z. Y.; Jibran, M.; Sun, X.; Pratt, A.; Wang, B.; Yamauchi, Y.; Ding, Z. J. Enhancement of the Spin Polarization of an Fe3O4(100) Surface by Nitric Oxide Adsorption. Phys. Chem. Chem. Phys. 2018, 20, 15871. (11) Kresse, G.; Furthmüller, J. Efficient Iterative Schemes for ab initio Total-energy Calculations using a Plane-wave Basis Set. Phys. Rev. B: Condens. Matter Mater. Phys., 1996, 54, 11169. (12) Kresse, G.; Furthmüller, J. Efficiency of Ab-initio Total Energy Calculations for Metals and Semiconductors using a Plane-wave Basis Set. Comput. Mater. Sci. 1996, 6, 15. (13) Perdew, J. P.; Burke, K.; Ernzerhof, M. Generalized Gradient Approximation Made Simple. Phys. Rev. Lett. 1996, 77, 3865. (14) Kresse, G.; Joubert, D. From Ultrasoft Pseudopotentials to the Projector Augmented-wave Method. Phys. Rev. B: Condens. Matter Mater. Phys., 1999, 59, 1758. (15) Blöchl, P. E. Projector Augmented-wave Method. Phys. Rev. B: Condens. Matter Mater. Phys., 1994, 50, 17953. (16) Monkhorst, H. J.; Pack, J. D. Special Points for Brillouin-zone Integrations. Phys. Rev. B, 1976, 13, 5188. (17) Anisimov, V. I.; Zaanen, J.; Andersen, O. K. Band Theory and Mott Insulators: Hubbard U Instead of Stoner I. Phys. Rev. B, 1991, 44, 943. 12


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(18) Fonin, M.; Pentcheva, R.; Dedkov, Y. S.; Sperlich, M.; Vyalikh, D. V.; Scheffler, M.; Rüdiger, U.; Güntherodt, G. Surface Electronic Structure of the Fe3O4(100): Evidence of a Half-metal to Metal Transition. Phys. Rev. B 2005, 72, 104436. (19) Pentcheva, R.; Moritz, W.; Rundgren, J.; Frank, S.; Schrupp, D.; Scheffler, M. A Combined

DFT/LEED-approach

for

Complex

Oxide

Surface

Structure

Determination: Fe3O4(001). Surf. Sci. 2008, 602, 1299. (20) Shvets, I. V.; Mariotto, G.; Jordan, K.; Berdunov, N.; Kantor, R.; Murphy, S. Long-range Charge Order on the Fe3O4(001) Surface. Phys. Rev. B: Condens. Matter Mater. Phys., 2004, 70, 155406. (21) Lodziana, Z. Surface Verwey Transition in Magnetite. Phys. Rev. Lett. 2007, 99, 206402. (22) Pentcheva, R.; Wendler, F.; Meyerheim, H. L.; Moritz, W.; Jedrecy, N.; Scheffler, M. Jahn-Teller Stabilization of a “Polar” Metal Oxide Surface: Fe3O4(001). Phys. Rev. Lett. 2005, 94, 126101. (23) Cheng, C. Structure and Magnetic Properties of the Fe3O4(001) Surface: Ab Initio Studies. Phys. Rev. B. 2005, 71, 052401. (24) Jiang, Z.; Zhang, W.; Shangguan, W.; Wu, X; Teraoka, Y. Adsorption of NO Molecule on Spinel-type CuFe2O4 Surface: A First-principles Study. J. Phys. Chem. C, 2011, 115, 13035. (25) Xiang, C.; Tan, H.; Lu, J.; Yu, L.; Song, P.; Zeng, C.; Zhang, D.; Tao, S. Firstprinciples Calculations of NO and NO2 Adsorption on a Spinel ZnGaAlO4(100) Surface. Phys. Scr. 2014, 89, 075401. 13



(26) Rohrbach, A. Hafner, J. Molecular Adsorption of NO on NiO(100): DFT and DFT+U Calculations. Phys, Rev. B, 2005, 71, 045405.

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Figure 1 The (H, NO)-co-adsorbed Fe3O4(100) surface showing (a) top view and (b) side view. Only atoms at the topmost two layers are shown. The blue, green, red, purple and pink spheres represent Fe(A), Fe(B), O, N and H atoms, respectively.

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Figure 2 The spin resolved band structure of (a) clean Fe3O4(100), (b) H-adsorbed Fe3O4(100), (c) NO-adsorbed Fe3O4(100) and (d) (H, NO)-co-adsorbed Fe3O4(100) surfaces. The black and red lines represent spin-up and spin-down electronics states, respectively. The spin-up surface state bands are specified with blue lines in the left panels of (a) and (b).

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Figure 3 (a) DOS of a free NO molecule, the O and N atoms of NO after co-adsorption of H and NO, and the surface Fe(B) atom before and after co-adsorption. (b) DOS of H after co-adsorption, and of the surface O1 and O2 atoms before and after co-adsorption of H and NO. The black and red lines represent the spin-up and spin-down DOS, respectively.

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Figure 4 Differential charge density of the (H, NO)-co-adsorbed Fe3O4(100) surface for the energy range of -14 eV to EF. The yellow or blue color indicates the gain or loss of electrons respectively. The isosurface is plotted with 0.01 eV/Å3. Only the adsorbates and atoms at the topmost surface are shown.

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Figure 5 The spin density of (a) clean Fe3O4(100), (b) H-adsorbed Fe3O4(100), (c) NOadsorbed Fe3O4(100) and (d) (H, NO)-co-adsorbed Fe3O4(100) for an energy range of -0.8 to EF. The yellow or blue color indicates positive and negative spin density. The isosurface is plotted with 0.006 eV/Å3.

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adsorption of Atomic Hydrogen and Molecular Nitric Oxide

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