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Kapilashrami M, Wang YJ, Li X, Glans PA, Fang M, Riazanova AV, Belova LM, Rao KV, Luo Y, Barbiellini B, Lin H, Markiewicz R, Bansil A, Hussain Z, Guo J. Understanding the magnetic interaction between intrinsic defects and impurity ions in room-temperature ferromagnetic Mg1-xFexO thin films. JOURNAL OF PHYSICS. CONDENSED MATTER : AN INSTITUTE OF PHYSICS JOURNAL 2016; 28:156002. [PMID: 26987741 DOI: 10.1088/0953-8984/28/15/156002] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/05/2023]
Abstract
Understanding the nature and characteristics of the intrinsic defects and impurities in the dielectric barrier separating the ferromagnetic electrodes in a magnetic tunneling junction is of great importance for understanding the often observed 'barrier-breakdown' therein. In this connection, we present herein systematic experimental (SQUID and synchrotron-radiation-based x-ray absorption spectroscopy) and computational studies on the electronic and magnetic properties of Mg1-xFexO thin films. Our studies reveal: (i) defect aggregates comprised of basic and trimer units (Fe impurity coupled to 1 or 2 Mg vacancies) and (ii) existence of two competing magnetic orders, defect- and dopant-induced, with spin densities aligning anti-parallel if the trimer is present in the oxide matrix. These findings open up new avenues for designing tunneling barriers with high endurance and tunneling effect upon tuning the concentration/distribution of the two magnetic orders.
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Affiliation(s)
- Mukes Kapilashrami
- Advanced Light Source, Lawrence Berkeley National Laboratory, Berkeley, CA 94720, USA. Center for Engineering Concepts Development, Department of Mechanical Engineering, University of Maryland, College Park, MD 20742, USA
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Kapilashrami M, Zhang Y, Liu YS, Hagfeldt A, Guo J. Probing the Optical Property and Electronic Structure of TiO2 Nanomaterials for Renewable Energy Applications. Chem Rev 2014; 114:9662-707. [DOI: 10.1021/cr5000893] [Citation(s) in RCA: 379] [Impact Index Per Article: 37.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/20/2023]
Affiliation(s)
- Mukes Kapilashrami
- Advanced
Light Source, Lawrence Berkeley National Laboratory, Berkeley, California 94720, United States
| | - Yanfeng Zhang
- College
of Chemistry and Material Science, Hebei Normal University, Shijiazhuang, Hebei 050024, People’s Republic of China
| | - Yi-Sheng Liu
- Advanced
Light Source, Lawrence Berkeley National Laboratory, Berkeley, California 94720, United States
| | - Anders Hagfeldt
- Physical
Chemistry, Department of Chemistry−Ångström Laboratory, Uppsala University, 751 20 Uppsala, Sweden
| | - Jinghua Guo
- Advanced
Light Source, Lawrence Berkeley National Laboratory, Berkeley, California 94720, United States
- Department
of Chemistry and Biochemistry, University of California, Santa Cruz, California 95064, United States
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Augustsson A, Zhuang GV, Butorin SM, Osorio-Guillén JM, Dong CL, Ahuja R, Chang CL, Ross PN, Nordgren J, Guo JH. Electronic structure of phospho-olivines Li(x)FePO4 (x = 0, 1) from soft-x-ray-absorption and -emission spectroscopies. J Chem Phys 2007; 123:184717. [PMID: 16292931 DOI: 10.1063/1.2107387] [Citation(s) in RCA: 69] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/15/2022] Open
Abstract
The electronic structure of the phospho-olivine Li(x)FePO4 was studied using soft-x-ray-absorption (XAS) and emission spectroscopies. Characteristic changes in the valence and conduction bands are observed upon delithation of LiFePO4 into FePO4. In LiFePO4, the Fe-3d states are localized with little overlap with the O-2p states. Delithiation of LiFePO4 gives stronger hybridization between Fe-3d states and O-2p states leading to delocalization of the O-2p states. The Fe L-edge absorption spectra yield "fingerprints" of the different valence states of Fe in LiFePO4 and FePO4. Resonant soft-x-ray-emission spectroscopy at the Fe L edge shows strong contributions from resonant inelastic soft x-ray scattering (RIXS), which is described using an ionic picture of the Fe-3d states. Together the Fe L-edge XAS and RIXS study reveals a bonding character of the Fe 3d-O2p orbitals in FePO4 in contrast to a nonbonding character in LiFePO4.
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Affiliation(s)
- A Augustsson
- Advanced Light Source, Lawrence Berkeley National Laboratory, Berkeley, California 94720, USA
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Harada Y, Takeuchi T, Kino H, Fukushima A, Takakura K, Hieda K, Nakao A, Shin S, Fukuyama H. Electronic structure of DNA nucleobases and their dinucleotides explored by soft X-ray spectroscopy. J Phys Chem A 2007; 110:13227-31. [PMID: 17149838 DOI: 10.1021/jp062720j] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
The electronic structures of a series of DNA nucleobases and their dinucleotides were investigated by N 1s X-ray absorption, X-ray photoemission, and resonant X-ray emission spectroscopy. Resonant X-ray emission spectra of the guanine base and its dinucleotide indicate that it has a weak structure at the lowest binding energy; at this energy, it isolates from the main valence band and forms the HOMO state. This indicates that the HOMO state is localized in the guanine base, as claimed by valence and core photoemissions and expected from theoretical predictions. In addition, the XAS and XES profiles of the guanine dinucleotide indicate that disruption of the aromatic character of the six-membered ring results in the localization of the pi state at the imine (-N=) site of the guanine base; this may favor charge transfer among stacked guanine bases and further influence the conductivity of DNA.
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Affiliation(s)
- Yoshihisa Harada
- Riken SPring-8 Center, 1-1-1 Kouto Sayo-cho Sayo-gun Hyogo 679-5148, Japan, National Institute for Materials Science, 1-2-1 Sengen Tsukuba Ibaraki 305-0047, Japan.
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Freelon B, Augustsson A, Guo JH, Medaglia PG, Tebano A, Balestrino G. Electron correlation and charge transfer in superconducting superlattices. PHYSICAL REVIEW LETTERS 2006; 96:017003. [PMID: 16486500 DOI: 10.1103/physrevlett.96.017003] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/06/2004] [Indexed: 05/06/2023]
Abstract
We use x-ray spectroscopy to examine the electronic structure of high-temperature superconducting superlattices [(Ba0.9Nd0.10)CuO(2 + delta)]2/[CaCuO2]2. The O 2p density of states reveals the insulating character of the individual component layers and the metallic character of the superlattices. We report the first direct observation of Zhang-Rice singlets in artificial high-temperature superconducting heteroepitaxial structures. The experimental findings in the superlattices and its component layers offer evidence of charge transport from the so-called charge reservoir layer to the superconducting infinite layer. This suggests a strong link between superconductivity and both electron correlation and charge transfer within the superlattices.
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Affiliation(s)
- B Freelon
- Advanced Light Source, Lawrence Berkeley National Laboratory, Berkeley, California 94720, USA.
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Guo JH, Luo Y, Augustsson A, Rubensson JE, Såthe C, Agren H, Siegbahn H, Nordgren J. X-ray emission spectroscopy of hydrogen bonding and electronic structure of liquid water. PHYSICAL REVIEW LETTERS 2002; 89:137402. [PMID: 12225062 DOI: 10.1103/physrevlett.89.137402] [Citation(s) in RCA: 111] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/27/2002] [Indexed: 05/23/2023]
Abstract
We use x-ray emission spectroscopy to examine the influence of the intermolecular interaction on the local electronic structure of liquid water. By comparing x-ray emission spectra of the water molecule and liquid water, we find a strong involvement of the a(1)-symmetry valence-orbital in the hydrogen bonding. The local electronic structure of water molecules, where one hydrogen bond is broken at the hydrogen site, is separately determined. Our results provide an illustration of the important potential of x-ray emission spectroscopy for elucidating basic features of liquids.
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Affiliation(s)
- J-H Guo
- Department of Physics, Uppsala University, Box 530, SE-751 21 Uppsala, Sweden.
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13. Soft X-Ray Fluorescence Spectroscopy. ACTA ACUST UNITED AC 1998. [DOI: 10.1016/s0076-695x(08)60286-0] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register]
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Glans P, Gunnelin K, Skytt P, Guo J, Wassdahl N, Nordgren J, Ågren H, Gel'mukhanov FK, Warwick T, Rotenberg E. Resonant x-ray emission spectroscopy of molecular oxygen. PHYSICAL REVIEW LETTERS 1996; 76:2448-2451. [PMID: 10060702 DOI: 10.1103/physrevlett.76.2448] [Citation(s) in RCA: 40] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/23/2023]
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Butorin SM, Guo J, Wassdahl N, Skytt P, Nordgren J, Ma Y, Ström C, Johansson L, Qvarford M. Electronic structure of Bi2Sr2CaCu2O8+ delta and Tl2Ba2CaCu2O8: Near-O-1s-threshold excitation x-ray fluorescence studies. PHYSICAL REVIEW. B, CONDENSED MATTER 1995; 51:11915-11923. [PMID: 9977933 DOI: 10.1103/physrevb.51.11915] [Citation(s) in RCA: 18] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 04/12/2023]
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Ma Y. Soft X‐ray emission and resonant inelastic scattering experiments at the NSLS. ACTA ACUST UNITED AC 1995. [DOI: 10.1080/08940889508602786] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/21/2022]
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