Hard X-ray Photoelectron Spectroscopy
(HAXPES)
Of Correlated Materials
A. Chainani,1,2 Y. Takata,1* M. Oura,2
M. Taguchi,3 M. Matsunami,3 R. Eguchi,3 S. Shin,3
1 Coherent X-ray Optics Lab
2 Advanced Photon Technology Division
3 Soft X-ray Spectroscopy Lab
RIKEN Harima Institute @ SPring-8
*deceased
4/7/2015
1
4/7/2015
2
Acknowledgements
For the development of HAXPES @ BL29XU
Coherent X-ray Optics Lab. @ RIKEN SPring8 Center
M. Yabashi, K. Tamasaku, Y. Nishino, D. Miwa, T. Ishikawa
JASRI/SPring-8
E. Ikenaga (BL47XU), K. Kobayashi（BL15XU, NIMS)
HiSOR, Hiroshima Univ.
M. Arita, K. Shimada, H. Namatame, M. Taniguchi
Musashi Inst. Technology
H. Nohira, T. Hattori (Tohoku Univ.)
VG SCIENTA
4/7/2015
3
Acknowledgements
For Collaborations
Titanates
Vanadates
Manganites
Cobaltates
Cuprates
Ruthenates
Ce compounds
Yb compounds
Nitrides
4/7/2015
H. Hwang, H. Takagi
H. Hwang, K Motoya, Z Hiroi
M. Oshima, Y. Tokura
E. Takayama-Muromachi
T. Mochiku, K Hirata
A. Yamamoto
H. Sugawara
N. Tsujii, A. Ochiai, S Nakatsuji
K. Takenaka
4
Outline
1) Introduction
2) Experimental Setup, Performance &
Characteristics
3) Applications : Strongly correlated electron systems
4) Future directions
5) Summary
4/7/2015
5
Main Characteristic of HAXPES
Large probing depth!
Inelastic Mean Free Path (IMFP) of Electron
(From NIST Database)
Inelastic Mean Path (A)
250
140Å
(SiO2)
200
210Å
（SiO2) NaCl
SiO2
150
30Å
（SiO2)
100
Al Ka
Si
GaAs
Au
50
0
0
4/7/2015
2000
4000
6000
8000
Electron Kinetic Energy (eV)
IMFPs
1-4nm @ 1 keV
7-20nm @ 8 keV
10000
Bulk sensitive
Free from surface prep.
Functional thin films
Chemical depth analysis
Embedded interfaces
(non destructive)
6
Early HAXPES with Cu Ka@8keV
S. Hagstrom, C. Nordlimg,
K. Siegbahn, Phys. Lett. 9, 235 (1964)
4/7/2015
Chuck Fadley, S. Hagstrom, J. Hollander,
M. Klein, D. A. Shirley, Science 157, 1571 (1967)
7
The first HAXPES with SR
I. Lindau, P. Pianetta, S. Doniach & W E Spicer, Nature 250, 214 (1974)
Au 4f
4/7/2015
core level: possible
valence band: impossible
8
Obstacle to development of HAXPES
(Mb/atom) at 1.04 KeV
1E-3
abs
Small10photoionization Cross Sections
1s
1E-8
1
0.1
0.01
1E-4
1E-5
1E-6
1keV
1E-7
0
10
20
30
40
50
60
70
80
90
2s
2p
3s
3p
4s
3d
4p
5s
4d
5p
6s
5d
4f
6p
abs
(Mb/atom) at 8.05 KeV
Atomic Number
Rapid decrease!
~ 1/100
1s
10
1
0.1
8keV
0.01
1E-3
1E-4
1E-5
1E-6
1E-7
1E-8
0
10
20
30
40
50
60
70
80
90
2s
2p
3s
3p
4s
3d
4p
5s
4d
5p
6s
5d
4f
6p
Atomic Number
4/7/2015
9
High-energy Ce-3d photoemission: Bulk properties of CeM2 (M=Fe,Co,Ni) and Ce7Ni3
L. Braicovich, N. B. Brookes, C. Dallera, M. Salvietti, and G. L. Olcese
Phys. Rev. B 56, 15047 (1997) @ESRF
High-energy resonant photoemission and resonant Auger spectroscopy in Ce-Rh compounds @ESRF
P. Le Fèvre, H. Magnan, D. Chandesris, J. Vogel, V. Formoso, and F. Comin
Phys. Rev. B 58, 1080 (1998)
Hybridization and Bond-Orbital Components in Site-Specific X-Ray Photoelectron Spectra of Rutile TiO2 @NSLS
J. C. Woicik, E. J. Nelson, Leeor Kronik, Manish Jain, James R. Chelikowsky, D. Heskett, L. E. Berman, and G. S.
Herman, Phys. Rev. Lett. 89, 077401 (2002)
Quadrupolar Transitions Evidenced by Resonant Auger Spectroscopy @HASYLAB
J. Danger, P. Le Fèvre, H. Magnan, D. Chandesris, S. Bourgeois, J. Jupille, T. Eickhoff, and W. Drube, Phys. Rev.
Lett. 88, 243001 (2002)
Looking 100 Å deep into spatially inhomogeneous dilute systems with hard x-ray photoemission @ESRF
C Dallera, L. Duò, L. Braicovich, G. Panaccione, G. Paolicelli, B. Cowie, and J. Zegenhagen Appl. Phys. Lett. 85,
4532 (2004)
High resolution-high energy x-ray photoelectron spectroscopy using third-generation synchrotron radiation source,
and its application to Si-high k insulator systems @SPring8
K. Kobayashi et al.
Appl. Phys. Lett. 83, 1005 (2003)
A probe of intrinsic valence band electronic structure: Hard x-ray photoemission @SPring8
Y. Takata et al.
Appl. Phys. Lett. 84, 4310 (2004)
HAXPES for Valence Bands with
hn = 6 – 8 KeV.
4/7/2015
10
Experimental Setup
4/7/2015
11
Pol.
How to gain in stability, resoluton, photoelectron intensity
1. High brilliance SR at SPring-8
55mm(V) 1deg.
35mm(H)
2. High performance analyzer
3. Top-up injection
4. Matching the detection angle to the polarization of SR
5. Grazing incidence of X-rays
6. Well-focused X-ray beam
7. Low emittance operation
90
3
2
120
b value
magic
angle
attenuation
length
-1
10mm range
-0.5
60
IMFP
150
10nm
range e-
30
X-ray
1
0
0
0.5
1
1.5
2
180
0
1 deg.
330
electric
vector
1
2
3
210
240
300
270
angular
For linearly polarized light,
intensity distribution of
photoemitted electrons depends on the asymmetry parameter b
b>0 at energies of several keV, for almost all subshells
J.Yeh & I.Lindau At. Data.Nucl Data Tables 32, 1(1985)
Their intensities have a maximum in a direction
parallel to the electric polarization vector
Experimental setup at BL29XU in SPring-8
Y. Takata et al., Nuclear Instrum. and Methods A547, 50 (2005).
T. Ishikawa et al., Nuclear Instrum. and Methods A547, 42 (2005).
He flow cryostat to reduce sample vibration
★ excitation energy: 5.95 or 7.94keV, DE (hn): 55 meV
★ photon flux: ~5x1011 photons/sec @ 55(V)x 35(H) mm2
★ analyzer:R4000-10kV (VG Scienta)
4/7/2015
13
Optics Layout for the HAXPES experiments
4/7/2015
14
High Energy Resolution & High Throughput
(at 7.94 keV)
VOLPE @ESRF
DE=55±5 meV (Ep=50 eV)
E/DE=140000!
5 sec
15min
30 sec
P. Torelli et al.,
Rev. Sci. Instrum. 76, 023909 (2005)
4/7/2015
15
VOLPE
@ ESRF
4/7/2015
P. Torelli et al.,
Rev. Sci. Instrum. 76, 023909 (2005)
16
KMC-1@ BESSY-II
F. Schafers et al.,
Rev. Sci. Instrum. 78, 123102 (2007)
4/7/2015
17
Au 4f core levels @ BESSY-II
4/7/2015
18
Surface Insensitivity
SiO2/Si(100) @ 7.94keV
SiO2-0.8nm/Si(100)
@0.85keV
(Exp.)
Si 1s
BE:1840eV
Intensity
Normalized Intensity
SiO2
Si
x 10
SiO2-0.8nm/Si(100)
10sec
SiO2
Intensity
SiO2-0.58nm/Si(100)
Si
Si 2p
BE:100eV
x 10
30sec
SiO2
0
6090
@7.94keV
(Exp.)
15
7830
7835
Kinetic Energy (eV)
7840
Si : SiO2=42 : 1
SiO2 contribution < 3%
10
5
Binding Energy (eV)
Y. Takata et al.
Appl. Phys. Lett.
84, 4310 (2004)
4/7/2015
6100
Kinetic Energy (eV)
300sec
20
6095
0
Contribution of surface SiO2 is negligible!
IMFP: Si=12nm, SiO2=16nm @ 8keV
Si=1.8nm, SiO2=3nm @ 0.85keV
19
Effect of Grazing Incidence of X-rays
see also V Strocov, condmat/2013
4/7/2015
20
High Sensitivity
(Buried Layer and Interface)
H. Wadati, A. Fujimori, H. Y. Hwang et al., PRB77, 045122 (2008)
LaAlO3:3ML
LaVO3:3ML
LaAlO3:30ML
abs
(Mb/atom) at 8.05 KeV
SrTiO3
10
1
0.1
0.01
1E-3
1E-4
1E-5
1E-6
5x10-7 Mb
1E-7
1E-8
0
10
20
30
40
50
60
70
80
90
1s
2s
2p
3s
3p
4s
3d
4p
5s
4d
5p
6s
5d
4f
6p
Photoelectron Intensity
hn=7.94 keV
V 1s (BE:5467eV)
2465
2470
2475
Kinetic Energy (eV)
Atomic Number
4/7/2015
21
Large Probing Depth
e-
eLa0.85Ba0.15MnO3 (20nm)
SrTiO3
Normalized Intensity
Sr 2p3/2 (BE=1940eV)
x65
4015
4010
Kinetic Energy (eV)
4005
H. Tanaka et al.,
Phys. Rev. B
73, 094403
(2006)
4/7/2015
22
Applications
4/7/2015
23
La1-xSrxMnO3 M-I transition with Colossal magnetoresistance
A.Urushibara et al.,
Phys. Rev. B 51, 14103 (1995)
H. Fujishiro et al.,
J. Phys. Soc. Jpn. 67, 1799 (1998)
Feature absent in earlier
soft-ray PES
A.Chainani et al. Phys. Rev. B
47, 15397 (1993)
T.Saitoh et al., Phys. Rev. B 56
8836 (1997)
MO6 Cluster model calculations
Ground state：linear combination of 6 configurations
3d6C2
UH
D
3d5C
3d4
3d6LC
3d5L
LH
3d6L2
１．Intra-atomic multiplets
２．Crystal Field
D*
EF
U
O
2p
band
4．Hybridization between
coherent states at EF and
Ru 3d orbitals : metallicity
３．Hybridization between
O 2p and Ru 3d orbital : Covalency
M. Taguchi
G. Van der Laan et al PRB 23,
4369(1981)
J. Imer & E. Wuilloud. Z Phys. B
21
66, 153 (1987)
Comparison with cluster calculations
Good agreement!
AFM
V* = 0.28V
Δ* = 3.6 eV
FM
V* = 0.39V
Δ* = 4.0 eV
FM
V* = 0.425V
Δ* = 4.0 eV
AFI
4/7/2015
V* = 0.25V
Δ* = 3.0 eV
low BE feature
CT from coherent states
2p53d5C
K. Horiba et al.
Phys. Rev. Lett 93,
236401 (2004)
29
V1.98Cr0.02O3 (experiments)
Insulator
Metal
(hn : 5950 eV)
(hn = Al Ka :1486.7 eV)
M. Taguchi et al.
PRB 71,155102(2005)
K. Smith et al.
PRB 50, 1382 (1994)
V2O3 VB Photoemission (Coherent Peak)
Coherent part
DMFT cal.
U
Mo et al. PRL 90, 186403 (2003)
Zhang et al. PRL 70, 1666 (1993)
Incoherent part
Calculation vs. Experiment
|g>
2p53d2
|D-Udc|
2p53dL
3d3L
D
3d3C
|f >
D*
|D*- Udc|
2p53d3C
3d2
M. Taguchi et al.
PRB 71,155102(2005)
Hole- and Electron-Doped High-Tc Cuprates
* M. van Veenendaal et al.
PRB 49, 1407 (1994)
* Ino et al., PRL 79, 2101 (1997)
* Harima et al., PRB 64, 220507(R) (2001)
* Steeneken et al. PRL 90, 247005 (2003)
La2CuO4
Nd2CuO4
Background（doping induced chemical potential shift)
Mid-gap pinning scenario
formation of new states within
the band gap on doping
Crossing the gap scenario
M. van Veenendaal et al. PRB 49, 1407 (1994)
m moves to the top of the valence band by hole-doping
and bottom of the conduction band on electron-doping
Calculation vs. Experiment
|g >
2p53d9
|D-Udc|
2p53d10L
3d10L
D
3d10C
3d9
|f >
D*
|D*- Udc|
2p53d10C
M. Taguchi et al.
Phys. Rev. Lett. 95,
17702 (2005).
Cu 2p XPS (Estimated Parameters)
NCCO
D
UH
B
D*
LSCO
EF
D
UHB
D*
O 2p band
O 2p band
EF
CT type system: Nd1.85Ce0.15CuO4 (NCCO)
M. Taguchi et al., Phys. Rev. Lett. 95, 17702 (2005).
Charge-Transfer type
5.9keV
1.5keV
UH
D
D*
EF
O 2p band
U
LH
See also
G. Panaccione et al. PRB 77, 125133 (2008)
4/7/2015
37
Valence Transition of YbInCu4
5950eV
800eV
43eV
H. Sato et al., Phys. Rev. Lett., 93,
246404 (2004)
4/7/2015
See also Suga et al., J. Phys. Soc. Jpn, 78, 074704 (2009)
38
Combining HAXPES with optical spectroscopy
Evidence for purely Yb2+ bulk state, Yb3+ surface state,
and energy-loss satellite due to interband transitions
YbS: Ionic crystal Yb2+S2-, hence typical Yb2+ system
However, the Yb valence estimated by L-edge RIXS & XAS:
K. Syassen, Physica B+C 139-140 (1986) 277.
E. Annese et al., Phys. Rev. B 70 (2004) 075117.
e- 
Intensity (arb. units)
Yb 3d
hn = 7.94 keV
hn
YbS
YbS
T = 300 K
 = 80°
 = 0°
YbCu2Si2
T = 20 K
 = 0°
Yb
1600
4/7/2015
3+
Yb
Binding Energy (eV)
1550 1540 1530 1520
Intensity (arb. units)
~2.08
~2.35
2+
Yb
1580
1560
1540
Binding
Energy (eV)
M. Matsunami
3+
Yb
2+
1520
et al., Phys.
78, 185118(2008)
Yb 3d5/2
 = 0°
 = 80°
×3
Loss Function
[Im(1/)]
optical
reflectivity
0
10
20
Rev. Relative
B, Energy (eV)
30
-10
39
Remote hole-doping at an interface
M. Takizawa et al., PRL. 102, 236401(2009)
V3+(bulk)
For LaAlO3/SrTiO3,
see M. Sing et al. PRL 102,
176805 (2009)
4/7/2015
40
• Electronic structure of the room temperature
ferromagnet Co:TiO2 anatase
Science, 291, 854 (2001)
4/7/2015
41
Nature Materials
4,173(2005)
Carriers : hydrogenic type
4/7/2015
42
Core level spectra
4/7/2015
T. Ohtsuki et al
PRL 106,
047602(2011)
Al Ka XPS
J W Quilty et al
PRL 96, 027202(2006)
43
Valence band spectra
CoO/Co metal
J W Quilty et al
PRL 96, 027202(2006)
4/7/2015
44
J. Woicik et al Phys. Rev. Lett. 89, 077401(2002)
4/7/2015
45
Co 2p-3d XAS
4/7/2015
46
Co 2p-3d Resonant PES
4/7/2015
47
Ti 2p-3d Resonant PES
Coherent
+
Incoherent
feature
T. Ohtsuki et al
PRL 106,
047602(2011)
4/7/2015
48
4/7/2015
49
charge neutrality condition :
Co2+ + VO 2− + 2Ti 4+  Co 2+ + 2Ti 3+
(VO is oxygen vacancy)
Surface Science,
601, 5034(2007)
4/7/2015
50
correspondence between the well-screened feature and coherent states
S. Biermann et al, PRL, 94, 026404,
2005 ; J. M. Tomczak & S. Biermann, J. Phys.:
Cond. Matter, 19, 365206, 2007.
J. M. 4/7/2015
Tomczak, F. Aryasetiawan & Silke Biermann,
PRB, 78,115103, 2008.
See also T. Koethe et al PRL 97,
166402(2006) ; S. Suga et al, New J. Physics
11, 103015 (2009).
51
Hg2Ru2O7 and Tl2Ru2O7 exhibit
first order metal-insulator transitions(MIT)
•
•
•
•
•
•
•
•
Hg2Ru2O7
Tc = 108 K
meff ~3.7mB
Ru 5+
Tl2Ru2O7
Tc = 125 K
meff ~ 2.8mB
Ru 4+
A Yamamoto et al JPSJ(Letters) 4, 043703 (2007)
W. Klein et al J. Mat. Chemistry 17, 1356 (2007)
S. Lee et al Nature Materials 5, 471 (20
2
Clear
temperature
dependence
across the
MIT
Covalency and metallicity of TMCs
and some standard bonding energies
.
Compound
Tl2Ru(IV)2O7
Hg2Ru(V)2O7
Ti4O7
VO2
V2O3
CrN
La0.8Sr0.2MnO3
La0.85Ba0.15MnO3
La1.85Sr0.15CuO4
Nd1.85Ce0.15CuO4
Standard bond
C-H bond
C-C bond
C-N bond
Hydrogen bonding
Van der Waals
Metallic
bonding
energy
(kcal/mol)
12.60
21.68
20.06
11.07
17.29
17.53
9.80
9.22
28.83
41.51
energies
in water
bonding
Covalent
bonding
energy
(kcal/mol)
50.73
46.12
66.88
55.34
66.88
62.26
67.80
67.80
86.48
80.71
99
83
73
~5
~1
Reference No.
present work
present work
44
45
22
46
30
47
24
24
1
1
1
1
1
A. Chainani et al. PRB 87, 045108 (2013)
HAXPES results from our group :
Zhang-Rice doublet state in NiO PRL 100 206401(2008)
Changes across successive first-order transitions in the
Magneli compound Ti4O7
PRL 104,106401(2010)
Paramagentic insulator to Anti-ferromagnetic metal transition
in CrN
PRL 104,236404(2010)
Mixed Valency in a quantum critical f-electron system YbAlB4
PRL 104,247401(2010)
Recoil effects of core and valence photoelectron in solids
Y. Takata, et al., PRL101, 137601(2008)
Recoil effects in PES:
C 1s core level spectra of graphite
Y. Takata et al., PRB 75, 233404 (2007)
Pnotoelectron Intensity
KE dependence at normal emission
hn=870eV
(DE=100meV)
hn=5950eV
(DE=120meV)
hn=7940eV
(DE=120meV)
285.5
285.0
284.5
Binding Energy (eV)
284.0
★ not observed in Au
★ not due to semimetallic
character
★ not due to bulk vs
surface but due to recoil
effect !
Recoil effects in core level spectra of
other light elements, such as
(Be, B, Al)
Recoil effects in valence band (Fermi-edge) of Al
@ 7.94keV
Y. Takata, Y. Kayanuma et al.,Phys. Rev. Lett.101, 137601(2008)
Intensity (arb. units)
M(Au): 197
(m/M)xE: 22meV
1.0
M(Al): 27.0
(m/M)xE: 160meV
dE=119meV
2p:115meV
hn = 7.94 keV
DE = 120 meV
T = 20 K
Al
Au
0.5
0.0
-0.5
Binding Energy (eV)
-1.0
Gaussian width
Au:124meV
Al: 160meV
Theory by Y. Kayanuma, S. Tanaka and S. Oshima
Y. Takata, Y. Kayanuma et al.,Phys. Rev. Lett.101, 137601(2008)
isotropic Debye model
4/7/2015
61
4/7/2015
62
Bulk electronic structure of Ga1-xMnxAs
4/7/2015
A X Gray et al, Nature Materials,
11, 957(2012)
63
Bulk electronic structure of Ga1-xMnxAs
4/7/2015
A X Gray et al, Nature Materials,
11, 957(2012)
64
Future Prospects
★ Improvement of energy resolution to ~10 meV
★ Angle resolved measurements
VB mapping
Gray et al
Photoelectron diffraction
★ Polarization dependence
Ueda et al
★ Atoms and molecules
Simon et al
Castro et al
non-dipole effects
★ Dynamics using time resolved HAXPES
★Application to high vapor pressure systems
Liquids/Wet samples/Gels
4/7/2015
65
Y Takashima et al
Nature Commun. Dec 2012
DOI:10.1038/ncomms2280
4/7/2015
66
Irene Chen et al.,
Advanced
Functional
Materials
22, 2535(2012)
4/7/2015
67
HAXPES has become a valuable tool !
SPring-8 (6 beamlines, not dedicated)
ESRF
BNL
BESSY II
SOLEIL
PETRA III
ERL ?
…..
4/7/2015
68
International WS to Conferences on HAXPES
1st in 2003 @ ESRF by Zegenhagen
2nd in 2006@ SPring-8 by Kobayashi and Suga
3rd in 2009 @ NSLS by Woicik and Fadley
4th in 2011 @ HASYLAB by Drube
5th in 2013 @ Uppsala by Svensson and Martensson
4/7/2015
69
Thank you very much
for your attention
4/7/2015
70