2p3d RIXS Studies of Band Gap Engineering in Transition Metal Compounds

2p3d RIXS Studies of Band Gap Engineering in Transition Metal Compounds Robert Green Aug. 14, 2013

Outline Impurity model approach to 2p3d RIXS d-d and charge transfer Transition metal monoxides vs. carbodiimides M2+O2- vs. M2+(NCN)2- Fluorescence yield XAS of aqueous Fe IPFY + PFY 2 of 19

d-d and Charge Transfer Excitations (2p3d) L3 RIXS example • d-d excitations • ≈ 0 – 5 eV • Final state 3dn* dd Charge Transfer • CT excitations • ≈ 4 – 15 eV • Final state 3dn+1*L 3 of 19

Cluster model in core level spectroscopy c 3dN+2 L c 3dN+1 L Δ + U - Q c 3dN Δ - Q c 3dN+1 3dN+1 L 3dN+1* L Δ Δ 3dN* 3dN XAS Final XPS Final Initial RIXS Intermediate RIXS Final 4 of 19

Impurity Model c 3dN+2 L Δ + U - Q c 3dN+1 3dN+1 L 3dN+1* L W Δ Δ 3dN 3dN* XAS Final RIXS Intermediate Initial RIXS Final 5 of 19

Increasing complexity… 6 of 19 [1] Ghiringhelli et al., JP:CM, 17, 5397 (2005)

Example: NiO Incident energy dependence of d-d and CT Ab initio parameters [1] 7 of 19 [1] Haverkortet al., PRB, 85, 165113 (2012)

Example: NiO Calculation Experiment [1] [1] 8 of 19 [1] Ghiringhelli et al., JP:CM, 17, 5397 (2005)

Application:Transition-metal Carbodiimides • (Mn,Fe,Co,Ni,Cu)NCN series • Comparable to the monoxides • O2-→(NCN)2- • AFM insulators • Octahedral metal site • Rocksalt→ layered • Difficult to synthesize • Powders, air/moisture sensitive • How are charge transfer, band gap affected? J. Phys. Chem. A, 115:4547-4552, (2011) 9 of 19

Nickel Carbodiimide (NiNCN) • Similar features to NiO • Oh, multiplets • Reduction of multiplet splitting • increased covalency • Similar to effects in Ni halides [1] [1] G. van der Laan, J. Zaanen, et al., Phys. Rev. B, 33, 4253 (1986) 10 of 19

NiNCN - RIXS • Similar d-d (within resolution limits) • Differences in charge transfer region. • Can impurity model provide insight? 11 of 19

XAS with Impurity Model 12 of 19

RIXS with Impurity Model 13 of 19

MnO and MnNCN 14 of 19 T. Boyko, R. Green, et al., JPC C, 117, 12754 (2013)

Fluorescence Yield vs. X-ray Absorption 15 of 19

Fluorescence Yield • Fe[(H2O)6]2+ • Measured in liquid flow cell • Silicon drift detector • 100 eV resolution • Simultaneous IPFY+PFY IPFY: A. Achkaret al., PRB, 83, 081106R (2011). 16 of 19

Fluorescence Yield • Fe[(H2O)6]2+ • Vary concentration to test for saturation and self absorption • PFY • Weaker at onset • Stronger after L3 T. Z. Regier, R. J. Green et al. (under review) 17 of 19

Fluorescence Yield T. Z. Regier, R. J. Green et al. (under review) 18 of 19

Acknowledgments • Alex Moewes • Carbodiimides • Richard Dronskowski • Teak Boyko • Calculation insights • MauritsHaverkort • Frank de Groot • George Sawatzky • Aqueous Fe • Tom Regier, Derek Peak, John Tse • David Hawthorn, Andrew Achkar 19 of 19

2p3d RIXS Studies of Band Gap Engineering in Transition Metal Compounds

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