emerging photoemission techniques for probing buried

Slide 1Emerging Photoemission Techniques
HAXPES, HARPES and SWARPES
Currently at SLAC National Accelerator Laboratory
Funded by the U.S. Department of Energy, U.S. Army Research Office, and the Humboldt Foundation
The Advanced
Light Source
The Advanced
Light Source
A. X. Gray1,2
Institutions 1UC Davis, 2LBNL, 3University of Erlangen, 4University of Mainz, 5University of Dortmund, 6ALS, 7SPring-8, 8SLS, PSI, 9TASC, Elettra, 10University of Twente, 11UC Berkeley, 12UCSB, 13Ludwig-
Maximilians-Universität München, 14Research Center Jülich, 15MPI Halle, 16IBM Almaden, 17Utrecht
University
Measurements
The Advanced
Light Source
The Advanced
Light Source
Funded by the U.S. Department of Energy, U.S. Army Research Office, and the Humboldt Foundation
Outline
• W, GaAs, and Ga0.97Mn0.03As
• Standing-Wave Excited ARPES (SWARPES)
11/20/2011 Materials Science Division. Fadley Group. 3
S. Tanuma, C. J. Powell, and D. R. Penn, Surf. Interface Anal. 43, 689 (2010).
Inelastic Mean-Free Path VS Ekin
4-5× deeper than
soft x-ray XPS
Traditional soft X-ray
BULK electronic structure
With multi-keV excitation
Hard X-ray Photoemission (HAXPES) How much Deeper does Photoemission Probe with Hard X-Rays?
Energy resolutions down to 50
meV (10 meV in future)
Angular resolutions to 0.2

???

at the ALS: Based largely on existing
beamline and end station-in progress
(5-10x faster than BL X24A at NSLS-1-the only HXPS show in the US)
ARPES at 3-6 keV: A.X. Gray et al., Nature Materials 10, 759 (2011); D.L.
Feng, News and Views, ibid., 10, 729 (2011)
4th International HAXPES Workshop, DESY, Hamburg, Sept. 2011
http://haxpes2011.desy.de,
https://indico.desy.de/materialDisplay.py?materialId=slides&confId=3713
Fadley, JESRP 178–179 2–32 (2010
e
c
T = 30 K (Raw data), W = 0.45, hv = 5956 eV
B in
d in
g En
e rg
y (e
T = 300 K (Raw data), W = 0.09, hv = 5956 eV
B in
d in
g En
e rg
y (e
One-Step Theory
[100]
[110]
Conductivity (J. Son, S. Stemmer)
J. Son et al., APL 96, 062114 (2010)
Mott Materials
theory predicts metallic behavior.
transition can be controlled.
transition.
optical and magnetic.
condensed matter physics.
Application of HAXPES Mott Behavior in LaNiO3 Epitaxial Thin Films
Substrate
2.8 nm LNO 4.2 nm LNO 11.1 nm LNO 17.6 nm LNO
hv=5950.3 eV
LNO Thin Film
Sample Set 1: LAO Substrate
Sample Set 2: LSAT Substrate
Conductivity (J. Son, S. Stemmer)
LNO/LSAT
Epitaxial layers with TEM thickness det’n.
(J. Son, J. LeBeau, S. Stemmer)
LNO/LAO
J. Son et al., APL 96, 062114 (2010)
Application of HAXPES Mott Behavior in LaNiO3 Epitaxial Thin Films
Hard X-ray Photoemission at hv=5.95 keV
4400 4600 4800 5000 5200
0.0
La3p3/2
Ni2s
Ni2p1/2
Ni2p3/2
La3d3/2
La3d5/2
Substrate
hv=5950.3 eV
LNO Thin Film
Probing ~70 Å into the sample Experiment with S. Ueda, K. Kobayashi
Hard X-ray Photoemission at hv=5.95 keV
Substrate
hv=5950.3 eV
LNO Thin Film
Probing ~70 Å into the sample
5300 5400 5500 5600 5700 5800 5900
0.0
Substrate Core-Peak Photoemission Spectra
365 360 355 35028 27 26 25 24
122 120 118 116 114 75 70 65
1562 1560 1558 1556
P h
o to
e m
is s
io n
I n
te n
s it
y ( a
rb . u
n it
Al 2p
Ni 3p
Ta 4p3/2 Ta 4f Sr 3s
Core peaks originating from the substrate lose intensity as the overlayer
thickness becomes larger: ILSAT e[tLNO/EAL,LNO]
Substrate
hv=5950.3 eV
LNO Thin Film
Calculating Effective Attenuation Lengths
0 5 10 15 20
2 4 6 8 10 12 2 4 6 8 10 12
0 5 10 15 0 5 10 15 0 5 10 15
Al 1s Al 2s Al 2p
Ta 4p3/2 Ta 4f Sr 3s
Ekin= 5593.3 eV
Ekin= 5832.3 eV
Ekin= 4390.8 eV Ekin= 5877.8 eV
L o
g 1
0 o
f In
te g
ra te
d P
E P
e a
k I
n te
n s
it y (
a rb
s )
LNO Film Thickness (nm) LNO Film Thickness (nm) LNO Film Thickness (nm)
EAL = 4.26 nm EAL = 5.68 nm EAL = 5.43 nm
EAL = 5.02 nm EAL = 5.24 nm EAL = 5.15 nm
Effective attenuation lengths for the photoelectrons can be calculated by
analyzing core peak intensities according to:
/ EALt
4500 5000 5500 6000
Al1s
LNO EALs within 20% of the much-used semi-empirical TPP-2M formula, if
corrected for elastic scattering
Remaining expt./theory discrepancy may be due to lack of resonant absorption
edges in theory: an effect not considered previously
S. Tanuma, C. J. Powell, and D. R. Penn,
Surf. Interface Anal. 43, 689 (2011).
A. Jablonski and C. J. Powell, J. Vac. Sci.
Technol. A 27, 253 (2009).
Valence-Band Decomposition
10 5 0 10 5 0 10 5 0
10 5 0 10 5 0 10 5 0
LSAT DOS
LNO DOS
P h
o to
e m
is s
io n
I n
te n
s it
s )
Valence band spectra can now be decomposed into the film and substrate DOS
components using the EALs and EAL EALt / t /( 0 )
t LNO,t LAO( LSAT ),tI [1 e ]I e I
Thickness and Substrate Dependence of LNO DOS
10 5 0
ll ) LAO Theory
Binding Energy (eV) Binding Energy (eV) Binding Energy (eV) Binding Energy (eV)
LNO (on LAO)
P h
o to
e m
transition is observed for the thinnest (2.7 nm)
LaNiO3 film on an LSAT substrate. Gray et al., PRB 84, 075104 (2011)
Outline
• Standing-Wave Excited Photoemission (SWARPES)
S. Tanuma, C. J. Powell, and D. R. Penn, Surf. Interface Anal. 43, 689 (2010).
Inelastic Mean-Free Path VS Ekin
5-20× deeper than
Traditional ARPES
BULK electronic structure
With multi-keV excitation
VUV
Angle-Resolved Photoemission at High Energies What and Where is the “XPS Limit”?
kh @
Phys. Rev. B 22, 3750 (1980)
• Magnitude of the wavevector associated with the final photoelectron
momentum increases. Brillouin zone averaging
• The magnitude of the photon momentum cannot be ignored anymore.
Must consider shifts due to photon-electron interactions
• The effects of phonon creation and annihilation must be considered
• Low photoelectric cross sections d- and f- states are suppressed
• Recoil can shift energies and broaden features, esp. lighter atoms
The Debye-Waller Factor Estimate of the Fraction of Direct Transitions
D ebye-W
aller Factor =
D ebye-W
aller Factor =
30
W(110) First Experimental Data (hv=5.95keV)
Detector Angle ( ) -4 -2 0 2 4 6
(Ef) 0
B in
d in
g En
e rg
y (e
B in
d in
g En
e rg
y (e
5948
5946
5944
5942
5940
5938
5936
700600500400300
DW = 0.09
DW = 0.45
Gray et al., Nature Mat. 10, 759 (2011)
Detector Angle ( ) -4 -2 0 2 4 6
(Ef) 0
B in
d in
g En
e rg
y (e
B in
d in
g En
e rg
y (e
5948
5946
5944
5942
5940
5938
5936
700600500400300
DW = 0.09
DW = 0.45
- Minar
The Debye-Waller Factor Estimate of the Fraction of Direct Transitions: GaAs
L. Plucinski, et al. PRB 78, 035108 (2008)
Mix of
T = 300 K (Raw Data), W = 0.01, hv = 3238 eV
Detector Angle ( )
HARPES of GaAs (hv = 3.24 keV, IMFP = 57Å)
D O
T = 20 K (Raw Data), W = 0.31, hv = 3238 eV
B in
d in
g En
e rg
y (e
14
12
10
8
6
4
2
0
700600500400
10
12
14
T = 300 K (Raw Data), W = 0.01, hv = 3238 eV
Detector Angle ( )
D O
T = 20 K (Raw Data), W = 0.31, hv = 3238 eV
B in
d in
g En
e rg
y (e
10
12
14
2
8
4
14
12
10
8
6
4
2
0
700600500400
10
12
14
T = 300 K (Raw Data), W = 0.01, hv = 3238 eV
Detector Angle ( )
D O
T = 20 K (Raw Data), W = 0.31, hv = 3238 eV
B in
d in
g En
e rg
y (e
10
12
14
2
8
4
+5 -5
1
14
12
10
8
6
4
2
0
700600500400
10
12
14
T = 300 K (Raw Data), W = 0.01, hv = 3238 eV
Detector Angle ( )
D O
T = 20 K (Raw Data), W = 0.31, hv = 3238 eV
B in
d in
g En
e rg
y (e
10
12
14
2
8
4
Free-electron theory
0
-4
0
-4
12 10 8 6 4 2 0
P h
o to
e m
is s
io n
I n
te n
s it
P
P h
o to
e m
is s
io n
I n
te n
s it
P h
o to
e m
is s
io n
I n
te n
s it
P h
o to
e m
is s
io n
I n
te n
s it
a)
b)
Total
P h
o to
e m
is s
io n
I n
te n
s it
P h
o to
e m
is s
io n
I n
te n
s it
P h
o to
e m
is s
io n
I n
te n
s it
P h
o to
e m
is s
io n
I n
te n
s it
P h
o to
e m
is s
io n
I n
te n
s it
HARPES of (Ga,Mn)As (hv = 3.24 keV)
S. Ohya et al., Nature Physics 7, 342 (2011)
Outline
• Standing-Wave Excited Photoemission (SWARPES)
SrTiO3
La0.7Sr0.3MnO3
SrTiO3
La0.7Sr0.3MnO3
SrTiO3
La0.7Sr0.3MnO3
SrTiO3
La0.7Sr0.3MnO3
11/20/2011 32 Materials Science Division. Fadley Group.
Standing-Wave Excited Photoemission
PRB 82, 205116 (2010).
.)
hν = 833.2 eV hν = 5956.4 eV hν = 833.2 eV hν = 5956.4 eV
Incidence Angle (°) Incidence Angle (°) Incidence Angle (°) Incidence Angle (°)
Experimental Results
1.80 1.85 1.90 1.95 0.97
0.98
0.99
1.00
0.92
0.96
1.00
0.94
0.96
0.98
1.00
0.8
1.0
0.6
0.8
1.0
0.6
0.8
1.0
0.6
0.8
0.90
0.95
0.92
0.96
1.00
.)
hν = 833.2 eV hν = 5956.4 eV hν = 833.2 eV hν = 5956.4 eV
Incidence Angle (°) Incidence Angle (°) Incidence Angle (°) Incidence Angle (°)
1.80 1.85 1.90 1.95 0.97
0.98
0.99
1.00
0.92
0.96
1.00
0.94
0.96
0.98
1.00
0.8
1.0
0.6
0.8
1.0
0.6
0.8
1.0
0.6
0.8
0.90
0.95
0.92
0.96
1.00
Exp.
S. H. Yang, A. X. Gray et al., JESRP (submitted).
The Advanced
Light Source
The Advanced
Light Source
The Advanced
Light Source
The Advanced
Light Source
Resulting Structure for the
La0.7Sr0.3MnO3/SrTiO3 Interface and Multilayer
top to bottom
× 4 8
L S
M O
4 U
× 4
8
× 4
8
Probing
Interface
LSMO
SrTiO3
La0.7Sr0.3MnO3
SrTiO3
La0.7Sr0.3MnO3
SrTiO3
La0.7Sr0.3MnO3
SrTiO3
La0.7Sr0.3MnO3
SrTiO3 SubstrateSrTiO3 Substrate
0.7
0.8
0.9
0.7
0.8
0.9
1.0
(in preparation)

h = 833.2 eV (still)
Depth-Resolved ARPES: Bulk LSMO
11/20/2011 Materials Science Division. Fadley Group. 38 200 400 600 800
Detector Ch. / Angle θ
N o
rm . P
E I
n t.
3 2 = Mn3d t2g
T il
t A
n g
le ( β
Mn3p
XPD
100%
20%
60%
80%
40%
40
30
20
10
0
800700600500400300200
pixel
40
30
20
10
0
800700600500400300200
pixel
hv = 833.2 eV
T = 20 K
N o
rm . P
E I
n t.
3 2 = Mn3d t2g
T il
t A
n g
le ( β
Mn3p
XPD
100%
20%
60%
80%
40%
Detector Ch. / Angle θ 200 400 600 800
pixel
pixel
E
1
2
4
5
3
N o
rm . P
E I
n t.
3
4 5 200 400 600 800 Detector Ch. / Angle θ
2 = Mn3d t2g 1 = Mn3d eg 100%
20%
60%
80%
40%
200 400 600 800 Detector Ch. / Angle θ
T il
t A
n g
le ( β
pixel
pixel
C
1
2
4
5
3
N o
rm . P
E I
n t.
3
20%
60%
80%
40%
T il
t A
n g
le ( β
pixel
pixel
E
1
2
4
5
3
N o
rm . P
E I
n t.
C
3
0%
3.0%
1.5%
T il
t A
n g
le ( β
pixel
pixel
Enhanced
N o
rm . P
E I
n t.
C
5
3
4
0%
3.0%
1.5%
54
k y (Å
k y (Å
t2g: Bulk LSMO Interface LSMO
Bulk – Interface- 8%
0 2 4 6 8 0 2 4 6 8
4
2
0
-2
-4
-1)
Experiment:
Bulk LSMO Interface LSMO Normal Emission
V e
rt ic
a l
P o
la ri
[SrTiO3/La0.7Sr0.3MnO3]120 Variable-Polarization SWARPES
9.0 9.5 10.0 10.5
V e
rt ic
a l
P o
la ri
Polarization-Dependent Standing-Wave ARPES of
La0.7Sr0.3MnO3/SrTiO3 Magnetic Tunnel Junction
7 8 9 10 11 12 13 0.4
0.6
0.8
1.0
1.2
0.6
0.8
1.0
1.2
0.6
0.8
1.0
1.2
0.6
0.8
1.0
1.2
0.6
0.8
1.0
1.2
0.6
0.8
1.0
1.2
0.6
0.8
1.0
1.2
0.4
0.6
0.8
1.0
1.2
Core-Level Rocking Curves: Interface Profile Standing-Wave ARPES of the Valence Bands
Mn3d t2g
V e rt
ic a l
BiFeO3 BiFeO3
Summary
• Characterization of buried layers and interfaces
• Hard X-ray Angle-Resolved Photoemission (HARPES)
• Band mapping in keV regime
• True bulk electronic band structure
• No need for surface cleaning, in-situ cleaving, etc.
• Standing-Wave Excited ARPES (SWARPES)
• Chemical and electronic structure profiling
• Interface-specific changes in the electronic structure
• Soon to come – HAXPES and HARPES at ALS (9.3.1)

emerging photoemission techniques for probing buried

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