2p3d RIXS Studies of Band Gap Engineering in Transition Metal

Report
Outline
Impurity model
approach to 2p3d RIXS
Transition metal
monoxides vs.
carbodiimides
Fluorescence yield XAS
of aqueous Fe
d-d and Charge Transfer
Excitations (2p3d)
d-d excitations
• ≈ 0 – 5 eV
• Final state 3dn*
CT excitations
• ≈ 4 – 15 eV
• Final state 3dn+1*L
Cluster model in core level
spectroscopy
c
c 3dN+2 L
3dN+1 L
c 3dN
c 3dN+1
Δ-Q
3dN+1 L
3dN+1* L
Δ
3dN*
3dN
XPS Final
Initial
Δ+U-Q
XAS Final
RIXS Intermediate
RIXS Final
Δ
Impurity Model
c 3dN+2 L
c 3dN+1
3dN+1 L
Δ+U-Q
3dN+1* L
W
Δ
Δ
3dN
Initial
XAS Final
RIXS Intermediate
3dN*
RIXS Final
XES Intensity (arb. units)
Increasing
complexity…
NiO
Oxygen
K XES
520
525
530
Emission Energy (eV)
[1] Ghiringhelli et al., JP:CM, 17, 5397 (2005)
Example: NiO
Incident energy
dependence of d-d
and CT
Ab initio
parameters [1]
[1] Haverkort et al., PRB, 85, 165113 (2012)
Example: NiO
Calculation
Experiment [1]
[1]
[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)
• Similar features to NiO
• Oh, multiplets
• Reduction of multiplet
splitting
• increased covalency
• Similar to effects in
Ni halides [1]
XAS Intensity (arb. units)
Nickel Carbodiimide
(NiNCN)
L2,3 XAS
NiO
NiNCN
850
855
860
865
870
Excitation Energy (eV)
[1] G. van der Laan, J. Zaanen, et al.,
Phys. Rev. B, 33, 4253 (1986)
875
NiNCN - RIXS
• Differences in charge
transfer region.
• Can impurity model
provide insight?
Intensity (arb. units)
• Similar d-d (within
resolution limits)
Ni L3 RIXS
NiO
NiNCN
-10
-5
0
Relative Emission Energy (eV)
Emission Energy (eV)
XAS with Impurity Model
385
390
395
Intensity (arb. units)
1.8
Ni L2,3 XAS
1.6
1.4
Exp.
Theory
1.2
1.0
0.8
NiNCN
0.6
XES Intensity (arb. units)
NiNCN
Nitrogen
K XES
NiO
0.4
0.2
Oxygen
K XES
NiO
0.0
850 855 860 865 870 875
Excitation Energy (eV)
520
525
530
Emission Energy (eV)
RIXS with
Impurity Model
Ni L3 RIXS
Exp.
Theory
NiO
NiNCN
Δeff (eV)
3.8
3.0
% 3d8
82.3
74.2
% 3d9 L
17.2
25.0
% 3d10 L2
0.4
0.7
Intensity (arb. units)
1.2
0.8
NiNCN
0.4
NiO
0.0
-10
-5
0
Relative Emission Energy (eV)
MnO and MnNCN
T. Boyko, R. Green, et al., JPC C, 117, 12754 (2013)
MnO
MnNCN
Δeff (eV)
3.8
3.2
% 3d5
90.4
88.6
% 3d6 L
9.6
11.4
Fluorescence Yield vs. X-ray Absorption
Fluorescence Yield
Fe[(H2O)6]2+
• Measured in liquid
flow cell
• Silicon drift detector
• 100 eV resolution
• Simultaneous IPFY+PFY
IPFY: A. Achkar et al., PRB, 83, 081106R (2011).
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)
Fluorescence Yield
  =
T. Z. Regier, R. J. Green et al. (under review)
 , ′ ′
Acknowledgments
• Alex Moewes
Carbodiimides
• Richard Dronskowski
• Teak Boyko
Aqueous Fe
• Tom Regier, Derek Peak, John Tse
• David Hawthorn, Andrew Achkar
Calculation insights
• Maurits Haverkort
• Frank de Groot
• George Sawatzky

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