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Instruments / Technical Area	Publication Details	Published
I09-Surface and Interface Structural Analysis	Distinct behavior of localized and delocalized carriers in anatase TiO2 (001) during reaction with O2 Chiara Bigi , Zhenkun Tang , Gian Marco Pierantozzi , Pasquale Orgiani , Pranab Kumar Das , Jun Fujii , Ivana Vobornik , Tommaso Pincelli , Alessandro Troglia , Tien-lin Lee , Regina Ciancio , Goran Drazic , Alberto Verdini , Anna Regoutz , Phil D. C. King , Deepnarayan Biswas , Giorgio Rossi , Giancarlo Panaccione , Annabella Selloni Physical Review Materials 4 DOI: 10.1103/PhysRevMaterials.4.025801 Diamond Proposal Number(s): [16041] Show Abstract ▼ Abstract: Two-dimensional (2D) metallic states induced by oxygen vacancies ( V O s ) at oxide surfaces and interfaces provide opportunities for the development of advanced applications, but the ability to control the behavior of these states is still limited. We used angle resolved photoelectron spectroscopy combined with density-functional theory (DFT) to study the reactivity of V O -induced states at the (001) surface of anatase TiO 2 , where both 2D metallic and deeper lying in-gap states (IGs) are observed. The 2D and IG states exhibit remarkably different evolutions when the surface is exposed to molecular O 2 : while IGs are almost completely quenched, the metallic states are only weakly affected. DFT calculations indeed show that the IGs originate from surface V O s and remain localized at the surface, where they can promptly react with O 2 . In contrast, the metallic states originate from subsurface vacancies whose migration to the surface for recombination with O 2 is kinetically hindered on anatase TiO 2 (001), thus making them much less sensitive to oxygen dosing.	Feb 2020
I09-Surface and Interface Structural Analysis	Proximity-induced ferromagnetism and chemical reactivity in few-layer VSe 2 heterostructures G. Vinai , C. Bigi , A. Rajan , M. D. Watson , T.-l. Lee , F. Mazzola , S. Modesti , S. Barua , M. Ciomaga Hatnean , G. Balakrishnan , P. D. C. King , P. Torelli , G. Rossi , G. Panaccione Physical Review B 101 DOI: 10.1103/PhysRevB.101.035404 Diamond Proposal Number(s): [21429] Show Abstract ▼ Abstract: Among transition-metal dichalcogenides, mono and few-layers thick VSe 2 has gained much recent attention following claims of intrinsic room-temperature ferromagnetism in this system, which have nonetheless proved controversial. Here, we address the magnetic and chemical properties of Fe / VSe 2 heterostructure by combining element sensitive x-ray absorption spectroscopy and photoemission spectroscopy. Our x-ray magnetic circular dichroism results confirm recent findings that both native mono/few-layer and bulk VSe 2 do not show intrinsic ferromagnetic ordering. Nonetheless, we find that ferromagnetism can be induced, even at room temperature, after coupling with a Fe thin film layer, with antiparallel alignment of the moment on the V with respect to Fe. We further consider the chemical reactivity at the Fe / VSe 2 interface and its relation with interfacial magnetic coupling.	Jan 2020
I09-Surface and Interface Structural Analysis	Insights into the electronic structure of OsO 2 using soft and hard x-ray photoelectron spectroscopy in combination with density functional theory Anna Regoutz , Alex M. Ganose , Lars Blumenthal , Christoph Schlueter , Tien-lin Lee , Gregor Kieslich , Anthony K. Cheetham , Gwilherm Kerherve , Ying-sheng Huang , Ruei-san Chen , Giovanni Vinai , Tommaso Pincelli , Giancarlo Panaccione , Kelvin H. L. Zhang , Russell G. Egdell , Johannes Lischner , David O. Scanlon , David J. Payne Physical Review Materials 3 DOI: 10.1103/PhysRevMaterials.3.025001 Diamond Proposal Number(s): [12673] Show Abstract ▼ Abstract: Theory and experiment are combined to gain an understanding of the electronic properties of OsO2, a poorly studied metallic oxide that crystallizes in the rutile structure. Hard and soft valence-band x-ray photoemission spectra of OsO2 single crystals are in broad agreement with the results of density-functional-theory calculations, aside from a feature shifted to high binding energy of the conduction band. The energy shift corresponds to the conduction electron plasmon energy measured by reflection electron energy loss spectroscopy. The plasmon satellite is reproduced by many-body perturbation theory.	Feb 2019
	Role of spin-orbit coupling in the electronic structure of Ir O 2 Pranab Kumar Das , Jagoda Sławińska , Ivana Vobornik , Jun Fujii , Anna Regoutz , Juhan M. Kahk , David O. Scanlon , Benjamin J. Morgan , Cormac Mcguinness , Evgeny Plekhanov , Domenico Di Sante , Ying-sheng Huang , Ruei-san Chen , Giorgio Rossi , Silvia Picozzi , William R. Branford , Giancarlo Panaccione , David J. Payne Physical Review Materials 2 DOI: 10.1103/PhysRevMaterials.2.065001 Show Abstract ▼ Abstract: The delicate interplay of electronic charge, spin, and orbital degrees of freedom is in the heart of many novel phenomena across the transition metal oxide family. Here, by combining high-resolution angle-resolved photoemission spectroscopy and first principles calculations (with and without spin-orbit coupling), the electronic structure of the rutile binary iridate, IrO2, is investigated. The detailed study of electronic bands measured on a high-quality single crystalline sample and use of a wide range of photon energy provide a huge improvement over the previous studies. The excellent agreement between theory and experimental results shows that the single-particle DFT description of IrO2 band structure is adequate, without the need of invoking any treatment of correlation effects. Although many observed features point to a 3D nature of the electronic structure, clear surface effects are revealed. The discussion of the orbital character of the relevant bands crossing the Fermi level sheds light on spin-orbit-coupling-driven phenomena in this material, unveiling a spin-orbit-induced avoided crossing, a property likely to play a key role in its large spin Hall effect.	Jun 2018
I09-Surface and Interface Structural Analysis	Quantifying the critical thickness of electron hybridization in spintronics materials T. Pincelli , V. Lollobrigida , F. Borgatti , A. Regoutz , B. Gobaut , C. Schlueter , T.-l. Lee , D. J. Payne , M. Oura , K. Tamasaku , A. Y. Petrov , P. Graziosi , F. Miletto Granozio , M. Cavallini , G. Vinai , R. Ciprian , C. Back , G. Rossi , M. Taguchi , H. Daimon , G. Van Der Laan , G. Panaccione Nature Communications 8 DOI: 10.1038/ncomms16051 Diamond Proposal Number(s): [11322] Show Abstract ▼ Abstract: In the rapidly growing ﬁeld of spintronics, simultaneous control of electronic and magneticproperties is essential, and the perspective of building novel phases is directly linked to the control of tuning parameters, for example, thickness and doping. Looking at the relevanteffects in interface-driven spintronics, the reduced symmetry at a surface and interface corresponds to a severe modiﬁcation of the overlap of electron orbitals, that is, to a change of electron hybridization. Here we report a chemically and magnetically sensitive depth-dependent analysis of two paradigmatic systems, namely La1xSrxMnO3 and (Ga,Mn)As. Supported by cluster calculations, we ﬁnd a crossover between surface and bulk in the electron hybridization/correlation and we identify a spectroscopic ﬁngerprint of bulk metallic character and ferromagnetism versus depth. The critical thickness and the gradient of hybridization are measured, setting an intrinsic limit of 3 and 10 unit cells from the surface,respectively, for (Ga,Mn)As and La1xSrxMnO3, for fully restoring bulk properties.	Jul 2017
I10-Beamline for Advanced Dichroism	Electronic structure of (Ga,Mn)As as seen by synchrotron radiation Kevin Edmonds , Gerrit Van Der Laan , Giancarlo Panaccione Semiconductor Science And Technology 30 (4) DOI: 10.1088/0268-1242/30/4/043001 Diamond Proposal Number(s): [8571] Show Abstract ▼ Abstract: Diluted magnetic semiconductors, and particularly (Ga,Mn)As, have been the subject of considerable debate regarding the nature of the interplay between their electronic and magnetic properties. Here, we review the recent insights and advances offered by synchrotron-based x-ray spectroscopies studies of these materials, with a particular focus on x-ray magnetic circular dichroism and hard x-ray photoelectron spectroscopy. Such measurements offer a combined probe of the element-specific magnetic order and the local densities of states, revealing detailed information about the hybridization of diluted magnetic ions and the host crystal.	Apr 2015
	Observation of Distinct Bulk and Surface Chemical Environments in a Topological Insulator under Magnetic Doping Ivana Vobornik , Giancarlo Panaccione , Jun Fujii , Zhi-huai Zhu , Francesco Offi , Benjamin R. Salles , Francesco Borgatti , Piero Torelli , Jean Pascal Rueff , Denis Ceolin , Alberto Artioli , Manju Unnikrishnan , Giorgio Levy , Massimiliano Marangolo , Mamhoud Eddrief , Damjan Krizmancic , Huiwen Ji , Andrea Damascelli , Gerrit Van Der Laan , Russell George Egdell The Journal Of Physical Chemistry C 118 (23), 12333 - 12339 DOI: 10.1021/jp502729u Show Abstract ▼ Abstract: The influence of magnetic dopants on the electronic and chemical environments in topological insulators (TIs) is a key factor when considering possible spintronic applications based on topological surface state properties. Here we provide spectroscopic evidence for the presence of distinct chemical and electronic behavior for surface and bulk magnetic doping of Bi2Te3. The inclusion of Mn in the bulk of Bi2Te3 induces a genuine dilute ferromagnetic state, with reduction of the bulk band gap as the Mn content is increased. Deposition of Fe on the Bi2Te3 surface, on the other hand, favors the formation of iron telluride already at coverages as low as 0.07 monolayer, as a consequence of the reactivity of the Te-rich surface. Our results identify the factors that need to be controlled in the realization of magnetic nanosystems and interfaces based on TIs.	Jun 2014
	Understanding the Electronic Structure of IrO 2 Using Hard-X-ray Photoelectron Spectroscopy and Density-Functional Theory J. M. Kahk , C. G. Poll , F. E. Oropeza , J. M. Ablett , D. Céolin , J. P. Rueff , S. Agrestini , Y. Utsumi , K. D. Tsuei , Y. F. Liao , F. Borgatti , G. Panaccione , A. Regoutz , R. G. Egdell , B. J. Morgan , D. O. Scanlon , D. J. Payne Physical Review Letters 112 DOI: 10.1103/PhysRevLett.112.117601 PMID: 24702416 Show Abstract ▼ Abstract: The electronic structure of IrO 2 has been investigated using hard x-ray photoelectron spectroscopy and density-functional theory. Excellent agreement is observed between theory and experiment. We show that the electronic structure of IrO 2 involves crystal field splitting of the iridium 5d orbitals in a distorted octahedral field. The behavior of IrO 2 closely follows the theoretical predictions of Goodenough for conductive rutile-structured oxides [J. B. Goodenough, J. Solid State Chem. 3, 490 (1971)]. Strong satellites associated with the core lines are ascribed to final state screening effects. A simple plasmon model for the satellites applicable to many other metallic oxides appears to be not valid for IrO 2 .	Mar 2014
	Identifying the Electronic Character and Role of the Mn States in the Valence Band of (Ga,Mn)As J. Fujii , B. R. Salles , M. Sperl , S. Ueda , M. Kobata , K. Kobayashi , Y. Yamashita , P. Torelli , M. Utz , C. S. Fadley , A. X. Gray , J. Braun , H. Ebert , I. Di Marco , O. Eriksson , P. Thunström , G. H. Fecher , H. Stryhanyuk , E. Ikenaga , G. Van Der Laan , G. Panaccione , J. Minar , C. H. Back Physical Review Letters 111 (9) DOI: 10.1103/PhysRevLett.111.097201 PMID: 24033065 Show Abstract ▼ Abstract: We report high-resolution hard x-ray photoemission spectroscopy results on (Ga,Mn)As films as a function of Mn doping. Supported by theoretical calculations we identify, for both low (1%) and high (13%) Mn doping values, the electronic character of the states near the top of the valence band. Magnetization and temperature-dependent core-level photoemission spectra reveal how the delocalized character of the Mn states enables the bulk ferromagnetic properties of (Ga,Mn)As.	Aug 2013

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