Engineering Magnetic Hybridization at Organic–Ferromagnetic

May 1, 2015 - Large magnetoresistance has been reported for C60-based vertical spin valves. But for the underlying organic–ferromagnetic interfacial...
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Engineering Magnetic Hybridization at Organic−Ferromagnetic Interfaces by C60-Adsorption-Induced Fe(001) Surface Reconstruction Zhen-Hua Yang,†,‡ Rui Pang,† and Xing-Qiang Shi*,† †

Department of Physics, South University of Science and Technology of China, Shenzhen 518055, China School of Materials Science and Engineering, Key Laboratory of Materials Design and Preparation Technology of Hunan Province, Xiangtan University, Xiangtan 411105, China

‡

S Supporting Information *

ABSTRACT: Large magnetoresistance has been reported for C60-based vertical spin valves. But for the underlying organic−ferromagnetic interfacial atomistic structures, both experimental and theoretical works have assumed unreconstructed atomic structures for the magnetic surfaces, although organic molecule (e.g., fullerene and thiolate) adsorption frequently induces nonmagnetic surfaces reconstruction. Here we report that C60 adsorption can induce a prototype ferromagnetic surface, Fe(001), reconstruction, via thorough structural search from first-principles calculations. We propose that Fe(001) surface reconstruction should already occur under the reported annealing temperature in literature. Reconstruction solidifies C60/Fe interface bonding and enhances C60 spin-polarization. More importantly, only our reconstructed structure can explain the experimental observation of an inversion of C60 spin-polarization around Fermi-level relative to that of Fe substrate, which is attributed to the C60 lowest unoccupied molecular orbitals LUMO-derived states are shifted to Fermi level by charge transfer and to the strong coupling in the reconstructed structure. One could expect that surface reconstruction occur not only at the C60/Fe(001) interface, but also at interfaces of other moleculemagnetic metals. Hence our work offers a new pathway to interface engineering, that is, via surface reconstruction to manipulate spintronic properties and promote the field of interface-assisted spintronics.

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INTRODUCTION The tunneling of spin-polarized electrons through organic semiconductors has attracted broad attentions in recent years in the area of organic spintronics.1−6 Organic materials have the advantages of high flexibilities in functional modification and long spin-relaxation time.7 The development in the area of spinterface science offers the possibility of inventing novel organic spintronic devices based upon interface engineering: it has been demonstrated that the atomic-contact details at the molecule-electrode interfaces determinate the transport properties in many cases.8,9 For example, after adsorption on magnetic electrode surfaces, a nonmagnetic molecule may show opposite spin-polarization relative to that of the electrode because of the spin-split hybridization of electronic states at these interfaces.10,11 Molecule adsorption can have significant influence on the electrode surface atomic-structure. Especially, surface reconstruction has been observed to occur frequently with the adsorption of fullerene, thiolate and graphene on various electrode surfaces.12−16 These reconstructions change the molecule-electrode interfacial contact, which have decisive influence on their behavior as molecular devices.17 Fullerene C60 and its derivatives are building blocks of potential high performance organic electronic devices.18,19 C60 can offer distinctly strong interaction to the substrate so that enhanced © 2015 American Chemical Society

state hybridizations can be expected, which are quite important for organic spintronics.20 For instance, some recent reports show large magnetoresistance in C60-based vertical spin valves.21−23 On the other hand, many works have reported that the strong interaction by C60 can induce metal surface reconstruction, such as the reconstruction of Ag, Cu, and Al surfaces24−26 with C60 adsorption. However, all these above investigations have focused only on nonmagnetic metal surface reconstruction. It is still unclear whether C60 can induce surface reconstruction on magnetic metal surfaces. And, if reconstructed, what are the effects of reconstruction on the organic− ferromagnetic interface spin-polarization? It is essential to clarify these questions for the development of interface-assisted spintronics.27 The present work reports C60 adsorption can induce reconstruction of a prototype ferromagnetic metal surface Fe(100)28,29 based on density functional theory simulations. The stability of unreconstructed and various reconstructed structures are thoroughly examined. We find that a 4-atom-hole reconstructed structure (Figure 2e) is the most stable compared to all other structures. Surface reconstruction solidifies the C60−Fe interface bonding. More importantly, Received: April 24, 2015 Published: May 1, 2015 10532

DOI: 10.1021/acs.jpcc.5b03954 J. Phys. Chem. C 2015, 119, 10532−10537

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The Journal of Physical Chemistry C reconstruction inverses and enhances C60 spin-polarization around Fermi-level compared to that in the unconstructed structure. Our findings offer a new method, that is, via surface reconstruction to manipulate spintronic properties at organic− metal interfaces and promote the field of interface-assisted spintronics.27

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COMPUTATIONAL DETAILS Calculations are performed using the plane-wave-basis-set Vienna ab initio simulation package (VASP).30 Projector augmented wave potentials31 are employed with a kinetic energy cutoff of 400 eV. Test calculations with 500 eV cutoff give essentially the same results (see Supporting Information). The Fe semicore p states are included as valence electrons. For the exchange and correlation functional, the Perdew−Burke− Ernzerhof generalized gradient approximation32 is utilized. The bcc-Fe(001) substrate is modeled by a seven-layer-slab with a 4 × 4 surface unit cell, and the corresponding K-points sampling is 4 × 4. The molecule−surface supercell thus contains 112 Fe atoms and 60 C atoms in the unreconstructed structure. The bottom four Fe layers are fixed at their bulk-like positions with a calculated lattice constant of 2.83 Å, and all other atoms are allowed to relax until the remaining force on each atom falls below the convergence criterion of 0.02 eV/Å. The calculated magnetic moment is 2.23 μB for bulk Fe, which is very close to the experimental value of 2.22 μB.33 To search for the magnetic ground state, different initial magnetic configurations are tried: includes C and Fe atoms in parallel/antiparallel initial magnetic configurations, and C with zero initial magnetic moment. The largest initial magnetic moments tried for Fe and C are five and one μB per atom, respectively. After search with different initial magnetic configurations, we find the final “antiparallel” magnetic configuration between Fe and C is most favored, in which configuration C has a much smaller magnetic moment than that of Fe.

Figure 1. Adsorption of C60 on unreconstructed Fe(001). (a) Highsymmetry adsorption sites on bcc-Fe(001) surface with 2- and 4-fold rotational symmetry; (b−d) high-symmetry sites of the C60 adsorbate with 2-, 3-, and 5-fold rotational symmetry, respectively. (e) Top and side views of the most stable unreconstructed (unrec) adsorption structure of Fe(001)-(4 × 4)-C60; only C atoms in the lower-half of C60 and Fe atoms in the top two layers are shown to display the interfacial structure clearer.

From the above symmetry analysis, the highest symmetry of the C60/Fe composite system can be obtained when a 2-fold site of C60 (Figure 1b, that is, the 6:6 double bond shared by two hexagons) adsorbed on Fe(001). And our total energy structure relaxations show that the C60 molecule binds most strongly with the 6:6 double bond parallel to the surface and the C60 just sits on top of a Fe atom (Figure 1e, top and side views). The Fe atom just below C60 is inward relaxed so that four more surrounding Fe atoms can also bond strongly with C atoms in the bottom two hexagons. The total energies comparison of different trial structures is provided in Supporting Information. Note that no symmetry constraints are imposed in our structure relaxations, so that the relaxed structure could be a lower-symmetric structure if it is more stable. Figure 1e shows that five Fe atoms bonds strongly to C60 (only show C−Fe bonds with bond lengths less than 2.1 Å) for the most stable unreconstructed structure. The adsorption energy of this structure is −3.06 eV, which is more stable by 0.16 eV than the best structure found in a recent work.29 The difference between our structure and the structure in literature is a small rotation of C60 around its bottom 6:6 double bond along the surface ⟨110⟩ direction (see Figure 1b in ref 29). The discovery of our new lowest energy structure for the unreconstructed case manifests the importance of our thorough structural search. Reconstructed Adsorption. Now let us move to the reconstructed adsorption: after deposition of C60s on Fe(001), in addition to the above-discussed C60s’ movement and rotation in three dimensions, C60s may also reconstruct the surface under increasing annealing temperature, repelling one34 or several35 atoms below it and form nanopits on surfaces. For C60 on Ag(100), 1-, 4-, and 5-atom hole reconstructions are studied.36 Based on similar considerations as on Ag(100), we also investigate 1-, 4-, and 5-atom hole reconstructions for C60 on the Fe(001), as shown in Figure 2b−d. Note that whether the reconstructed structure is favored or not depends on the competition between the energy gain from forming more C-metal bonds in the reconstructed structure and

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RESULTS AND DISCUSSION Unreconstructed Adsorption. Following, we discuss the unreconstructed adsorption first, and then for the reconstructed case. To find the most stable unreconstructed structure of C60 on Fe(001), we consider all high-symmetry adsorption structures based upon symmetry-matching analysis between the C60 adsorbate and the Fe(001) surface, namely match their high-symmetry sites (Figure 1a−1d, also see the Supporting Information). The basic idea behind symmetry-matching analysis is in experiment preparation, after deposition of the highly symmetric buckyball C60 molecules on bcc-Fe(001), under thermal activation, C60 values move to find the optimum adsorption site on the surface (Figure 1a), and C60 values rotate in three dimensions to find the best orientation (Figure 1b−d and plus rotation around the surface normal at each adsorption site in structural relaxation to simulate the three-dimensional rotation). Since both the C60 molecule and the bcc-Fe(001) surface are highly symmetric, for the final adsorption structure some of the common symmetry between the two subsystems should remain in the C60/Fe(001) composite system, such as sharing one or two common mirror planes. It is highly probable that the final structure has (part of) the common symmetry of the subsystems. We have tried all the possible adsorption structures with common symmetry of the two subsystems. 10533

DOI: 10.1021/acs.jpcc.5b03954 J. Phys. Chem. C 2015, 119, 10532−10537

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Fe(001) surface reconstruction should already occur in those works compared to the surface reconstruction annealing temperatures of about 340−570 K for other closed-packed fcc(111) surfaces with C60 adsorption.16,24,39,40 In the unreconstructed case C60 molecule sits with a 6:6 double bond above a surface Fe atom and six C−Fe bonds are formed (Figure 1e). However, in reconstructed case, C60 pentagon sinks-in a surface 4-atom hole and 13 C−Fe bonds are formed (Figure 2e): both the top layer eight surrounding Fe atoms and one second layer Fe atom just below C60 pentagon bond strongly to C60 in the reconstructed structure. Thus, with reconstruction the coupling between C60 molecule and Fe(001) surface is much stronger than without reconstruction. The adsorption structure is highly ordered on Fe(001)38 but aperiodic on Ag(100),36 although the two surfaces with similar two-dimensional lattice, presumably because of the stronger interaction between C60/Fe than C60/Ag since Ag d-band is completely filled; and the stronger C60−Fe bonding fixes C60 on Fe surface lattice sites,38 while for the weaker C60−Ag interaction the inter-C60 interaction cannot be neglected, making the aperiodic structure because of lattice-mismatch between C60 and Ag(100). More discussion can be found in the Supporting Information, about why a C60 pentagon face-down onto Fe(100) but not a 6:6 double bond face-down as on Ag(100). Electronic and Magnetic Properties. Above are about structural properties with and without reconstruction, we now turn to the effect of surface reconstruction on the C60 electronic and magnetic properties because of changes in interfacial bonding. The spin-resolved density of states projected (PDOS) onto the C atoms of C60 on unreconstructed and reconstructed Fe(001) surface are shown in Figure 3a. The PDOS of an isolated C60 molecule was also given as a reference. Only the PDOS of C-2p orbitals are given since they are dominant in the energy range of the plot. Adsorption significantly broadens and shifts-down the C60 molecular orbitals due to hybridization with the Fe d-electrons and the accompany charge transfer. The PDOS of C60 is sensitive to the interaction between C60 and Fe(001) substrate. The energy level broadening and shiftsdown is larger in the reconstructed case. From Bader charge analysis,41 the number of transferred electrons to C60 with reconstruction is 3.36, compared to 1.81 for the unreconstructed case. Hence the broadened highest-occupied molecular orbitals (HOMO) and lowest-unoccupied molecular orbitals (LUMO) in the reconstructed case moves to even lower energies than that in the unreconstructed case. These above differences in electronic properties of course arise from the different interfacial bonding between C60 and Fe(001) (Figure 1e versus 2e). More important case is the magnetic properties. Reconstruction of Fe(001) results in an enhanced and inversed spinpolarization on C 60 around Fermi compared to the unreconstructed case (Figure 3b). In order to quantify the effect of reconstruction on the spin-polarization of C60, we calculate the spin-polarization-ratio (SPR), which is defined as SPR = (N↑ − N↓)/(N↑ + N↓), where N↑ and N↓ are the PDOS for the spin-up and spin-down electrons, respectively. The SPRs as a function of energy are shown in Figure 3b for the unreconstructed and reconstructed structures, and for a bulklike Fe atom in the slab model. At Fermi-level, for the unreconstructed structure the SPR is 0.08, while it is −0.16 for the reconstructed structure, which indicates that reconstruction can enhance C60 spin-polarization around Fermi. More

Figure 2. Adsorption of C60 on reconstructed Fe(001). (a−d) Different types of reconstruction: perfect surface without reconstruction and 1-, 4-, and 5-atom hole reconstructions. (e) Top and side views of the most stable reconstructed adsorption structure with C60 pentagon sinks-in a 4-atom hole (4 hole rec); only C atoms in the lower-half of C60 and Fe atoms in the top two layers are shown to display the interfacial structure clearer.

the energy cost due to the forming of a several-atom-hole. Reconstructed structure with a larger hole needs larger vacancy formation energy. The size of a four atom hole in the top layer is suitable to contain one C60 molecule, and larger hole is not needed. So we only need consider structures with 1-, 2,- 3,- and 4-atom hole for the top layer. Note that 2- and 3-atom hole reconstructions can be excluded from symmetry- and sizematching between C60 and the hole: the size of 2- and 3-atom holes cannot allow a C60 molecule to sinks-in the hole to form more C-metal bonds, and the lower symmetry of the 3-atom hole structure cannot maximize the number of C-metal bonds. In addition to consider atoms missing in the top layer, based on the 4-atom-hole structure, we also considered a 5-atom-hole structure with an additional second layer Fe atom missing. Similar to the previous symmetry discussion in unreconstructed adsorption, we consider three types of C60 orientations (Figure 1b−d) on the reconstructed Fe(001) surface with 1-, 4-, and 5-atom holes (Figure 2b−d), and in each case the C60 rotation around surface normal are further considered (details see Supporting Information). We need compare the relative stability between unreconstructed adsorption and three types of reconstructed adsorption structures with 1, 4, and 5 surface atoms missing, namely compare systems with different number of missing atoms, so we need consider the vacancy formation energy Evac. We adopt the kinked-edge model37 to calculate Evac, which model follows the more probable fate of the missing atoms on surfaces and put the missing atoms at the surface kinked-edge sites (also see Supporting Information for the model structures and for the calculated Evac). The adsorption energies corrected by vacancy formation energies Evac can then be expressed as Eads = Etotal − EC60 − Esurf + Evac, where Etotal, EC60, and Esurf are total energies of C60/Fe(001), isolated C60, and Fe(001), respectively. After structural search, the most stable reconstructed geometry turns out to be a structure with a C60 pentagon sinks-in a surface 4-atom hole (Figure 2e). The corresponding adsorption energy (after correction for Evac) is −3.92 eV, which is much more stable than the best unreconstructed structure of −3.06 eV. Actually, under the literature reported annealing temperature of 553 K28,38 for C60 adsorbing on Fe(001), the 10534

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Fermi. This is another evidence that the Fe(001) surface is reconstructed in the experiment28 in addition to the evidence from annealing temperature as discussed previously. We focus on the energy range around Fermi-level for the SPR discussion because C60 LUMO is partially filled and shifted-down to around Fermi. From literature11 one knows that that for strong coupling, the inversion of spin-polarization in the molecule is expected to occur when the molecular orbital is shifted very close to Fermi, due to the level broadening for each spin component is in proportion to the metal spin-polarized density of states.20 For the reconstructed case, the C60 LUMO is half-filled because about three electrons are transferred to the C60 triply degenerate LUMO and hence the center of LUMO is very close to Fermi. While in the unreconstructed case, the LUMO peak is way above Fermi since only less than two electrons are transferred. Figure 4 shows the magnetic moments at the C60/Fe(001) reconstructed interface. As can be seen from Figure 4a and 4c the inversion of magnetic moments is mainly localized on the bottom C atoms that form C−Fe bonds. Besides, the magnetic moments of Fe atoms decrease with C60 adsorption (see Figure 4b). Note that for Fe(001) surface without C60, the average magnetic moment of first and second layer Fe atoms are 2.98 μB and 2.37 μB, respectively. In particular, the magnetic moment of the Fe atom just below the C60 is dramatically reduced to 1.75 μB. The total magnetic moment of adsorbed C60 is −0.33 μB with reconstruction, compared to −0.24 μB in the unreconstructed case, which shows an enhancement of magnetic moment with reconstruction. More electronic property analysis can be found in the Supporting Information.

Figure 3. (a) Spin-resolved projected density of states (DOS) of C-2p orbitals of gas phase C60 (divided by 2), of C60 in the unreconstructed (unrec, Figure 1e), and reconstructed (4 hole rec, Figure 2e) structures; insert a magnified view from −1 to +1 eV. (b) Sinpolarization-ratio (SPR) as a function of energy for C60 in the unreconstructed (unrec) and reconstructed (4 hole rec) cases, and for that of bulk-like Fe. The Fermi-level is set to zero.

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SUMMARY

The stable adsorption structures of C60 on unreconstructed and reconstructed Fe(001) surfaces have been thoroughly searched based on symmetry-matching analysis; and the effect of reconstruction on C60 electronic and magnetic properties are probed. For the unreconstructed case, we find a more stable structure than the one reported in literature.29 We first report that C60 adsorption can reconstruct the Fe(100) surface, and show that the surface reconstruction should already occur under the reported annealing temperature in literature.28,38 Reconstruction solidifies the C60−Fe interfacial bonding, enhances the C60 spin-polarization around Fermi-level, and enhances the C60 magnetic moment. More importantly, only

importantly, there’s an inversion of spin-polarization around Fermi for C60 in the reconstructed structure compared to that of the Fe substrate. The inversion of SPR is important due to a recent X-ray magnetic circular dichroism experiment observed the inversion of spin-polarization of C60 LUMO relative to Fe substrate.28 Figure 3b shows taht only the reconstructed structure shows the inversion of spin-polarization around Fermi energy relative to that of Fe, while the unreconstructed structure show the same sign of polarization with Fe around

Figure 4. (a) Spin-density plot of the reconstructed structure as shown in Figure 2e, yellow (blue) corresponds to majority (minority) spins. (b, c) Magnetic moments at the interface (in μB): for Fe(001) top two layers (b) and for C60 bottom part (c). 10535

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(5) Requist, R.; Modesti, S.; Baruselli, P. P.; Smogunov, A.; Fabrizio, M.; Tosatti, E. Kondo conductance across the smallest spin 1/2 radical molecule. Proc. Natl. Acad. Sci. U.S.A. 2014, 111, 69−74. (6) Kim, W. Y.; Kim, K. S. Tuning Molecular Orbitals in Molecular Electronics and Spintronics. Acc. Chem. Res. 2010, 43, 111−120. (7) Sanvito, S. Molecular spintronics. Chem. Soc. Rev. 2011, 40, 3336−3355. (8) Sanvito, S. Molecular spintronics: The rise of spinterface science. Nat. Phys. 2010, 6, 562−564. (9) Caffrey, N. M.; Ferriani, P.; Marocchi, S.; Heinze, S. Atomic-scale inversion of spin polarization at an organic-antiferromagnetic interface. Phys. Rev. B 2013, 88, No. 155403. (10) Atodiresei, N.; Caciuc, V.; Lazic, P.; Bluegel, S. Engineering the magnetic properties of hybrid organic−ferromagnetic interfaces by molecular chemical functionalization. Phys. Rev. B 2011, 84, No. 172402. (11) Barraud, C.; Seneor, P.; Mattana, R.; Fusil, S.; Bouzehouane, K.; Deranlot, C.; Graziosi, P.; Hueso, L.; Bergenti, I.; Dediu, V.; Petroff, F.; Fert, A. Unravelling the role of the interface for spin injection into organic semiconductors. Nat. Phys. 2010, 6, 615−620. (12) Maksymovych, P.; Sorescu, D. C.; Voznyy, O.; Yates, J. T., Jr Hybridization of phenylthiolate-and methylthiolate-adatom species at low coverage on the Au (111) surface. J. Am. Chem. Soc. 2013, 135, 4922−4925. (13) Torrelles, X.; Pedio, M.; Cepek, C.; Felici, R. (2√3× 2√3) R 30° induced self-assembly ordering by C60 on a Au (111) surface: Xray diffraction structure analysis. Phys. Rev. B 2012, 86, No. 075461. (14) Liu, C.; Qin, Z.; Chen, J.; Guo, Q.; Yu, Y.; Cao, G. Molecular orientations and interfacial structure of C60 on Pt (111). J. Chem. Phys. 2011, 134, No. 044707. (15) Otero, G.; Gonzalez, C.; Pinardi, A. L.; Merino, P.; Gardonio, S.; Lizzit, S.; Blanco-Rey, M.; Van de Ruit, K.; Flipse, C.; Méndez, J. Ordered vacancy network induced by the growth of epitaxial graphene on Pt (111). Phys. Rev. Lett. 2010, 105, No. 216102. (16) Shi, X.; Pang, A.; Man, K.; Zhang, R.; Minot, C.; Altman, M.; Van Hove, M. A. C60 on the Pt (111) surface: Structural tuning of electronic properties. Phys. Rev. B 2011, 84, No. 235406. (17) French, W. R.; Iacovella, C. R.; Rungger, I.; Souza, A. M.; Sanvito, S.; Cummings, P. T. Structural Origins of Conductance Fluctuations in Gold−Thiolate Molecular Transport Junctions. J. Phys. Chem. Lett. 2013, 4, 887−891. (18) Maeyoshi, Y.; Saeki, A.; Suwa, S.; Omichi, M.; Marui, H.; Asano, A.; Tsukuda, S.; Sugimoto, M.; Kishimura, A.; Kataoka, K.; Seki, S. Fullerene nanowires as a versatile platform for organic electronics. Sci. Rep. 2012, 2, 600. (19) Guldi, D. M.; Illescas, B. M.; Ma Atienza, C.; Wielopolskia, M.; Martin, N. Fullerene for organic electronics. Chem. Soc. Rev. 2009, 38, 1587−1597. (20) Galbiati, M.; Tatay, S.; Barraud, C.; Dediu, A. V.; Petroff, F.; Mattana, R.; Seneor, P. Spinterface: Crafting spintronics at the molecular scale. MRS Bull. 2014, 39, 602−607. (21) Gobbi, M.; Golmar, F.; Llopis, R.; Casanova, F.; Hueso, L. E. Room-Temperature Spin Transport in C60-Based Spin Valves. Adv. Mater. 2011, 23, 1609−1613. (22) Tran, T.; Le, T. Q.; Sanderink, J. G.; van der Wiel, W. G.; de Jong, M. P. The multistep tunneling analogue of conductivity mismatch in organic spin valves. Adv. Funct. Mater. 2012, 22, 1180− 1189. (23) Gobbi, M.; Pascual, A.; Golmar, F.; Llopis, R.; Vavassori, P.; Casanova, F.; Hueso, L. E. C-60/NiFe combination as a promising platform for molecular spintronics. Org. Electron. 2012, 13, 366−372. (24) Pai, W. W.; Hsu, C. L.; Lin, M. C.; Lin, K. C.; Tang, T. B. Structural relaxation of adlayers in the presence of adsorbate-induced reconstruction: C-60/Cu(111). Phys. Rev. B 2004, 69, No. 125405. (25) Hinterstein, M.; Torrelles, X.; Felici, R.; Rius, J.; Huang, M.; Fabris, S.; Fuess, H.; Pedio, M. Looking underneath fullerenes on Au (110): Formation of dimples in the substrate. Phys. Rev. B 2008, 77, No. 153412.

the reconstructed structure shows an inversion of spinpolarization relative to that of the Fe substrate, which explains a recent experiment observation,28 while the unreconstructed structure cannot explain the experiment, which is due to only in the reconstructed case the charge transfer is strong enough to shift LUMO adequately close to Fermi level and because of the C60−Fe strong coupling. One could expect that surface reconstruction occur not only at the C60/Fe(001) interface, but also interfaces at other organic molecule-magnetic metals. Surface reconstruction or not can be tuned by changing annealing temperatures in experiment. The coexistence of structures with and without reconstruction can also be obtained.35 In addition, different types of reconstruction can be expected for different magnetic metal surfaces. Hence our work offers a new method for engineering the organic-magnetic interfaces, that is, via surface reconstruction, to manipulate spintronic properties and promote the field of interface-assisted spintronics. Other magnetic surface reconstructions induced by C60/C70 adsorption are under investigation.

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ASSOCIATED CONTENT

S Supporting Information *

Details of calculations including high-symmetry adsorption configurations and adsorption energies, vacancy formation energies, comparison with Ag(100), electronic structure analysis. The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/ acs.jpcc.5b03954.

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AUTHOR INFORMATION

Corresponding Author

*E-mail: [email protected]. Author Contributions

Z.Y. and R.P. have equal contributions. Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS This work is financially supported by National Natural Science Foundation of China (Grants 11474145 and 11334003). Project supported by Hunan Provincial Natural Science Foundation of China (Grant 12JJ6041) and Start-up funds for doctor supported by Xiangtan University (Grant 12QDZ02) and National Supercomputing Center in Shenzhen.

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REFERENCES

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DOI: 10.1021/acs.jpcc.5b03954 J. Phys. Chem. C 2015, 119, 10532−10537

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DOI: 10.1021/acs.jpcc.5b03954 J. Phys. Chem. C 2015, 119, 10532−10537