Chuck Fadley X-ray Photoelectron Spectroscopy and Diffraction in ...

X-ray Photoelectron Spectroscopy and Diffraction 

in the Hard X-Ray Regime: An Overview 

Chuck Fadley 

Department of Physics 

University of California Davis 

and 

Materials Sciences Division 

Lawrence Berkeley National Laboratory 

Basic considerations: probing depth, cross sections, 

source, analyzer, detector, surface vs. bulk sensitivity 

X-ray optics, spectral background, and standing waves 

Core- and valence- level spectroscopy 

Valence bands, the XPS limit, photon wave vector, phonons, etc. 

Photoelectron diffraction and Kikuchi bands 

Summary and future prospects 

Plus see: Nucl. Inst. and Meth. A, Volume 547, Issue 1, Pages 1-238 (2005) 

2 nd Int’l Workshop-2006, Program/Abstrasts 

http://haxpes2006.spring8.or.jp/ 

Special thanks to: C. Dallera, T. Hattori, K. Kobayashi, T. L. Lee, R. 

Moberg, G. Panaccione, O. Schaff, S. Suga, Y. Takata, J. Zegenhagen 

Japanese Physical Society Meeting, Chiba, Sept., 2006

And 101 years later: 

Photoemission/photoelectron spectroscopy: 

UPS, XPS, ARPES 

Photoelectron diffraction: 

PD, XPD, PhD 

Typical photon energies: 5------------1500 eV 

laser, VUV soft x-ray 

ΔE: ≤1 meV ∼50 meV 

Hard x-ray photoemission: 

HAXPES, HXPS, HIKE,… 

Photon energies from ∼5-15 keV? 

ΔE ∼50-75 meV→10 meV 

Why? To probe more bulklike properties, deeper into multilayer structures, 

new physics, new applications… 

To date: 

• HAXPES2004 Workshop-ESRF (J. Zegenhagen) 

Nucl. Inst. and Meth. A, Volume 547, Issue 1, Pages 1-238 (2005) 

• HAXPES2006 Workshop-SPring8 (S. Suga, K. Kobayashi) 

Program/Abstracts @ http://haxpes2006.spring8.or.jp/ 

• 20 published papers on “hard x-ray photoemission”, most from Japan 

• Talks by Tjeng, Suga, Sekiyama this morning,….

A first experiment 

SPEAR 

hν = 8,000 eV 

CMA, single-channel det. 

25 cts./sec 

Siegbahn et al., late 1950s, then Pianetta, Lindau, Nature 250, 214 (1974)

Outline 



X-ray optics, spectral background 

Standing waves 

Core and valence spectroscopy 



Summary and future prospects

Electron inelastic mean free paths in solids—the “universal curve” 

Seah & Dench, Surf. Int. Anal. 1, 2 (1979)

Electron inelastic mean free paths in solids—the “universal curve” 

Graphite 

Germanium 

Tanuma, Powell, Penn, Surf. Interface Analysis, 17, 911-926 (1991); 

36, 1 (2004) and refs. therein

How much deeper do we 

probe at 5-10 keV? 

(nm) 

8 

7 

Typical elements: 

50-200 A 

• 6.93 nm 

Au 

Inelastic attenuation length 

TPP-2M formula 

of Tanuma, Powell, Penn 

6 

5 

∝ (E kin ) 0.75 

• 4.72 nm 

• 5.86 nm 

• 3.48 nm 

4-5x deeper 

than normal 

XPS 

• 2.07 nm 

15-20x deeper 

than normal 

ARPES 

| | | | | 

4000 6000 8000 10,000 

http://www.ss.teen.setsunan.ac.jp/e-imfp.html

Detection of SiO 2 /Si Interface Through Thick Overlayer 

Si 1s 

Photoelectrons 

Hard X-ray 

NiGe 

SiO 2 

Si sub. 

Θ 

7∼15 nm 

12 nm 

Intensity (arb. units) 

Si 1s 

Θ = 80º 

NiGe Layer 

Thickness 

7 nm 

12 nm 

15 nm 

hν = 7935 eV 

SiO 2 

Si 

1850 1846 1842 1838 1834 

Binding energy (eV) 

H. Kondo et al. (Nagoya Univ.) unpublished.

High-k Dielectric Layers-post-deposition thermal annealing (PDA) 

temperature dependence of LaOx(4 nm)/Si(100) interfaces (room temp 

deposition, 10min annealing in N 2 ambient at 300 C, 400 C,and 500 C) 

La silicate formation by annealing 

Formation of interface transition layers 

La Silicate (Si-O-La) is already formed by room 

temperature deposition. Amount of the silicate 

rapidly increases by annealing. 

Electronegativities χ Si (1.8) > χ La (1.2) 

H. Nohira, et al., ECS Transactions, Vol. 1 (2005) pp. 87-95.

E kin ≈ 500-1000 eV 

Inner potential 

f(θ scat ) 

Varying surface sensitivity for lower 

electron takeoff angles 

• 

Simplest interpretation: 

Average emission depth = Λ inelastic sinθ takeoff 

How valid? 

E.g.: A. Jablonski and C. J. Powell, 

J. Vac. Sci. Tech. A 21, 274 (2003): 

→ Mean Emission Depth (MED) 

more relevant than Λ inelastic 

θ takeoff 

>20-30° 

E kin ≈ 10,000 eV 

PD modulations 

weaker 

f(θ scat ) 

• 

θ takeoff 

down 

to 5-10° 

Simpler analysis 

Cleaner bulk & surface distinction 

C. J. Powell, W. Werner et al., priv. comm.; 

C.S.F., Nucl. Inst. & Meth. A 547, 24 (2005)

Variable takeoff-angle Si 1s photoelectron spectra 

from NiGe(12-nm)/SiO 2 (12-nm)/Si(100) 

Si 1s 

Si 1s 

8 keV 

hν = 7935 eV 

Si-O 

Si-Si 

Hard X-ray 

NiGe 

SiO 2 

Si sub. 

Θ 

7∼15 nm 

12 nm 

Intensity [a. u .] 

More bulk 

sensitive 

More interface sensitive 

θ = 80º 

35º 

12º 

1848 

1844 

1840 

1836 

Binding energy [eV] 

T. Hattori et al., Int. J. High Speed Electronics 16 (2006) 353.

Photoelectron intensities from a semi-infinite substrate-- 

atom Q with subshell nlj (e.g. Au4f 7/2 ) 

I(Qnlj) = (incident flux) × (area of illuminated sample seen by analyzer) 

(Qnlj differential cross section) × (solid angle accepted by analyzer) × 

(density of atoms Q) × (photoelectron inelastic attenuation length) × 

(overall detection efficiency) 

I(Qnlj) = I 0 (hν) × (dσ Qnlj (hν→E kin )/dΩ) ×ρ Q ×Λ e (E kin ≈ hν) × A 0 /sinθ inc × Ω 0 × D 0 

Sample brightness = B 0 

Energy-dep. analyzer prop. 

Given atom @ high energy--lower l subshells favored (n- l -1 radial nodes) : 

dσ Qnlj (hν)/dΩ ∝1/(hν) N ≈1/(E kin ) N → For Au: 1/(E kin ) ∼2.0 for s subshells 

1/(E kin ) ∼2.5 for p subshells 

1/(E kin ) ∼3.0-3.5 for d subshells 

1/(E kin ) ∼4.0-4.5 for f subshell 

and Λ e (hν→E kin ) ∝ (E kin ) 0.75 

So intensity per incident photon falls off as 1/(E kin ) ∼1.25-3.75 ! 

What can you do with the source, the analyzer+detector 

S.T. Manson 

10 11 -10 12 /s into A 0 /sinθ inc 

a small spot 

C.J. Powell

Photon energy dependence of cross sections for gold 

Subshell Cross Section (Barns) 

1000000 

100000 

10000 

1000 

100 

10 

5p 3/2 

5d 

4f 

Au cross sections--Scofield 

5s,5p 1/2 

6s 

5s,p 

5d 

4f 

4s 1/2 

4p 1/2 

4p 3/2 

4d 3/2 

4d 5/2 

4f 5/2 

4f 7/2 

5s 1/2 

5p 1/2 

5p 3/2 

5d 3/2 

5d 5/2 

6s 1/2 

1 

0 2000 4000 6000 8000 10000 12000 14000 16000 

Photon Energy (eV)

Changes in relative cross 

section with photon energy 

Kunz et al., Nucl. Inst. & Meth. A 547, 73 (2005)


















S.T. Manson 


a small spot 

C.J. Powell

One experimental setup: SPring-8 8 BL29XU 

Y. Takata et al., Nuclear Instrum. and Methods A547, 50 (2005). 

T. Ishikawa et al., Nuclear Instrum. and Methods A547, 42 (2005). 

★ Excitation energy: 5.95 or 7.94keV, Δ(hν): 40-60meV 

★ Photon flux: 10 11 photons/sec @ 55(Hor.)x 50(Vert.) μm 2 

★ Analyzer: R4000-10kV (Gammadata-Scienta) 

Other mfrs.: MBS and Specs; Another project: Suga et al., ∼6x more flux

High Energy Resolution & High Throughput 

Au VB @ hν=5.95 keV 

ΔE=75 

meV 

at 5.95keV 

(E/ΔE=79000) 

ΔE=90meV 

at 7.94keV 

(E/ΔE=88000) 

E pass 

= 200eV 

220sec 

ΔE=208 meV 

E pass 

= 200eV 

30sec 

E pass 

=50eV 

335 meV 

Lorentzian 

Y. Takata et al., Nuclear Instrum. and Methods. A547, 50 (2005)

HAXPES/HXPS in the World 

• • 

• 

• 

• 

ESRF—Castro et al. 

Panaccione et al. 

Zegenhagen et al. 

Hasylab—Drube et al. 

BESSY---Bressler,Svensson et al. 

Felser, Fecher et al. 

SPring8—Kobayashi et al. 

Takata et al. 

Suga et al. 

???


















S.T. Manson 


a small spot 

C.J. Powell

Measurement of inelastic 

attenuation lengths 

º 

∝ 

º 

º 

∝ E 

0.75 # 

kin 

º 

∝ 0.75E 

0.50 


# 

More accurate 

Dallara et al. NIMA 547, 113 (2005)


















S.T. Manson 


a small spot 

C.J. Powell

Quantitative analysis of peak intensities using theoretical cross sections: 

La 0.7 

Sr 0.3 

MnO 3 

, hν = 7700 eV 

La4s 

Sr3s 

La4p: classis many-e - effect 

4p 5 4d n + configs. 4p 6 4d n-1 E 

1 

F 

Intensity (arb.units) 

5000 

Sr3p 1/2 

Sr3p 3/2 

La 4d 

La5s 

Sr4s 

Sr3d 

O2s,Sr4p,La5p 

Mn3s 

0 

Mn3p 

VB 

400 200 0 

Binding Energy (eV) 

Pardini, Offi, 

Panaccione, CF, TBP

Quantitative analysis of peak intensities using theoretical cross 

sections (Scofield): La 0.7 Sr 0.3 MnO 3 , hν = 7700 eV 

Concentration-weighted subshell cross sestion (Mb) 

1200 

1000 

800 

600 

400 

200 

0 

450 

400 

350 

300 

250 

200 

Mn3p 

150 

La5s 

Mn3s 

La4d 

Sr3s 

100 

50 

Sr4s Sr3d 

0 

0 5000 10000 15000 20000 25000 

La4p 

Core-level cross sections work very well→ 

More accurate “bulk” quantitative analysis 

0 10000 20000 30000 40000 50000 60000 70000 

Core peak intensity (a.u.) 


Panaccione, CF, TBP

Other considerations as energy increases: 

--Atom recoil in core-level emission (ala Mőssbauer): 

• 

M 

1/2 

2 2 

⎛me 

⎞ 

⎡E ⎛ 


2E ⎞ 


hν 

⎤ h ke 

-4 ⎡ E 

kin(eV) 

⎤ 

E 

recoil 

(eV ) = hν 

⎜ 5.5 x 10 

2 2 

M 

⎟ ⎢ + ⎜ ⎟ + ⎥ ≈ ≈ 

hν 

mc 

e 

2mc 

e 

2M 

⎢ 

M(amu) 

⎥ 

⎝ ⎠⎢ ⎣ ⎝ ⎠ 

⎥⎦ 

⎣ ⎦ 

Fraction of transitions recoil free = f RF 

= exp(-3E recoil 

/2k B 

Θ D 

) at T = 0 

At 10 keV: 

= exp[-1.7x10 4 E recoil 

(eV)/Θ D 

(K)] 

Atom H C Ni Au 

E recoil 

6.0 eV 0.5 eV 0.1eV 0.03 eV 

Θ D 

(K) --- 2230 450 225 

f RF 

--- 0.02 0.02 0.10 

An extra energy shift/broadening? Yes-Takata et al., graphite! 

Source for electronic excitations? 

--Smearing of coherent emission from valence bands: 

Fraction of transitions that are “direct” with no phonon momentum k r phonon 

involved: 1 st estimate ≈ Debye-Waller Factor = W(T) ≈ exp(-k 

2 

e 

) 

= exp(-CE kin 

) (more later)

Experimental observation 

of atomic recoil in graphite: 

Theory using Debye model 

Takata et al., 

arXiv:cond-mat/0609241 (11 Sep 2006)

Other considerations as energy increases: 

--Atom recoil in core-level emission (ala Mőssbauer): 

• 

M 

1/2 

2 2 

⎛me 

⎞ 

⎡E ⎛ 


2E ⎞ 


hν 

⎤ h ke 

-4 ⎡ E 

kin(eV) 

⎤ 

E 

recoil 

(eV ) = hν 

⎜ 5.5 x 10 

2 2 

M 

⎟ ⎢ + ⎜ ⎟ + ⎥ ≈ ≈ 

hν 

mc 

e 

2mc 

e 

2M 

⎢ 

M(amu) 

⎥ 

⎝ ⎠⎢ ⎣ ⎝ ⎠ 

⎥⎦ 

⎣ ⎦ 

Fraction of transitions recoil free = f RF 

= exp(-3E recoil 

/2k B 

Θ D 

) at T = 0 

At 10 keV: 

= exp[-1.7x10 4 E recoil 

(eV)/Θ D 

(K)] 

Atom H C Ni Au 

E recoil 

6.0 eV 0.5 eV 0.1eV 0.03 eV 

Θ D 

(K) --- 2230 450 225 

f RF 

--- 0.02 0.02 0.10 

An extra energy shift/broadening? Yes-Takata et al., graphite! 

Source for electronic excitations? 

--Smearing of coherent emission from valence bands: 

Fraction of transitions that are “direct” with no phonon momentum k r phonon 

involved: 1 st estimate ≈ Debye-Waller Factor = W(T) ≈ exp(-k 

2 

e 

) 

= exp(-C 1 

E kin 

) exp(-C 2 


T) (more later) 

⎯⎯⎯→

Other considerations as energy increases (cont’d) : 

Dipole 

--Non-dipole effects in matrix elements: 

r r r 

r r r 

r 

Int. ∝ Ψ | exp( ik • ) eˆ •∇| Ψ ≈ Ψ | (1 + ik • + ...) eˆ •∇| Ψ ≈ Ψ | eˆ 

•∇| 

Ψ 

f 

2 2 2 

hv i 

f hv 

i 

f 

• Photon momentum k r hv cannot always be neglected, e.g. in 

r r r r r r r 2 

valence-band studies: Int. ∝ u ˆ 

f 

exp( ikf • ) | exp( ikhv 

• r ) e • ∇ | uiexp( iki 

• 

) 

r r r r 

→ k + k + g = k 

• Additional non-dipole matrix elements: E2, M1,… 

i 

hv 

f 

i 

• And differential cross section more complex: 

φ 

θ p 

e - ê 

= 

light polarization 

dσ σ ⎡ β 

2 2 

⎤ 

= 1 (3cos θ 

p 

1) ( δ γ cos θp )sinθpcosφ 

dΩ 

4π 

⎢ 

+ − + + 

⎣ 2 

⎥ 

⎦ 

Dipole 

Non-Dipole 

≈ 1.0 at 4 keV electron energy 

Woodruff, Nucl. Inst. and Meth. A 547, 187 (2005) 

ˆk 

h ν










Au 4f intensity (counts/sec)→ 

X-ray Optical Effects 

in Photoemission: 

The Beginning 

B.L. Henke, Phys. Rev. A 6, 94 (1972) 

•Enhanced x-ray penetration depth as 

critical angle approached 

•Effects on average depth and intensity 

in photoemission 

•Determination of optical constants 

from data 

θ c 

inc 

θ inc 

e - 

Incidence angle (degrees)→ 

X-ray attenuation length (Å)→ 

Au 4f intensity (normalized)→ 

1487 eV 183 eV 109 eV 

Incid. angle (mrad)→ 

Critical angle (mrad)→ 

θ crit 

X-ray optical theory 

Experiment 

Incidence angle (mrad)→

Problem: inelastic 

backgrounds in core 

spectra with multi-keV 

excitation- 

Solution: reduction via 

total reflection 

Kawai et al., Spectrochim. 

Acta B 47, 983 (‘92) 

Chester & Jach, Phys. Rev. 

B 4817262 (’93) 

Jach & Landree, Surf. & Int. 

Anal. 31, 768 (‘01) 

The JEOL JPS-9010MC 

e - 

lens

Surface Insensitivity & High Throughput 

inc 

Photoelectron Intensity 

SiO 2 

-0.8nm/Si(100) 

hν=7.94 keV 

θ=1 deg. 

30 sec!! 

Si 2p 

SiO 2 

Si 

7830 7835 7840 

Kinetic Energy (eV) 

Takata et al., SPring8










Standing wave formation in reflection from a surface, 

or single-crystal Bragg planes + , or a multilayer mirror 

Incident 

Reflected 

1 

e - hν 

λ SW (|E 2 |) = 

λ x /2sinθ inc 

R 

• Rocking curve: 

I(θ ) ∝ 1 + R(θ ) + 2 R(θ ) f cos[φ(θ ) − 

2πP] 

inc inc inc inc 

• Energy scan: 

I(hν ) ∝ 1 + R( hν ) + 2 R( hν ) f cos[φ( hν ) − 

2πP] 

with: f = coherent fraction, P = phase of atomic position 

% modulation ≈ 

100 x 4√R 

∴ R = 5% → 90% mod. 

• Phase scan with wedge-shaped sample (“Swedge” method): 

+ 

Standing waves via Bragg reflection of hard x-rays: Batterman, Phys. Rev A 133, 759 (1964)

Standing waves in Bragg reflection from TiO 2 : 

Scanning energy within Bragg rocking curve--hν = 3 keV 

Standing 

wave on Ti 

Standing 

wave on O 

Woicik, NIMA 547, 227 (2005) 

and earlier papers

0.009400 

0.008080 

0.006760 

0.005440 

0.004120 

0.002800 

Site-specific valence electronic structure of SrTiO3 

S. Thieß, T.-L. Lee, F. Bottin, B. Cowie and J. Zegenhagen 

Relative photon energy ΔE (eV) 

normalised Intensities 

Intensity [a.u.] 

0.6 

0.4 

0.2 

0.0 


10 9 8 7 6 5 4 3 

E = 2.75 keV 

Ti 

Sr 

SrTiO 3 

valence band 

O 3 

ΔE 

+ 

+ 

10 9 8 7 6 5 4 3 


Valence band XSW 

_- 

- 

Ti 

2p 

+ 0.5 

Sr 

O 

Ti 

(111) 

Reflectivity 

0.8 0.6 0.4 0.2 0.0 

SrTiO 3 

(111) 

O 

Sr 

1s 

3p 

2.0 1.5 1.0 0.5 0.0 

normalised Intensity 

Core-level XSW 

0.6 

0.4 

0.2 

0.0 

Relative photon energy ΔE (eV) 

(112)

Probing Buried Interfaces 

with Soft X-ray Standing 

Wave/Wedge (“Swedge”) 

Method: core spectra 

and depth distributions 

X-ray 

900 eV 

Photoelectron 

Al 2 O 3 /Co 65 Pt 35 /Ru cap: 

Tunnel junction system 

(see Kaiser et al., PRL 

94, 247203 (2005) 

12Å Ru cap with Oxide surface 

15Å CoPt(65/35) 

30 sec oxidation 

Al 2 O 3 wedge 

θ Bragg 

Scanned standing wave 

∼0.1 mm 

spot 

M Co 

Multilayer 

Mirror 

B 4 C 

W 

B 4 C 

W 

Sell, Yang, Watanabe, 

Mun, Parkin et al., TBP 

SiO 2 

Si-wafer 

Scanned sample 

∼6.0 mm

Representative spectra: 

4100000 

4000000 

3900000 

3800000 

3700000 

3600000 

3500000 

3400000 

Co 2p 

Co 

500000 

450000 

400000 

350000 

300000 

Co 2+ 

250000 

200000 

150000 

Pt 4f 

2200000 

2000000 

Ru 3d 

1800000 

1600000 

1400000 

1200000 

1000000 

800000 

600000 

400000 

200000 

0 

300 295 290 285 280 275 270 265 


784 782 780 778 776 774 772 770 


100000 

50000 

84 82 80 78 76 74 72 70 68 66 64 62 60 

Intensity (arb. unit) 

O 1s 

Adsorbed 

O 

RuO x 


B.C. Sell et al. 

40000 

35000 

30000 

25000 

20000 

15000 

10000 

VB 

5000 

536 534 532 530 528 526 524 522 


0 

12 10 8 6 4 2 0 -2 -4 -6 

Binding Energy (eV)

Co 2p spectrum during a standing wave scan 

2.4 eV 

7.0 eV 

Klingenberg et al., Surf. 

Sci. 283, 13 (1997)

Standing waves from multilayers in the hard x-ray regime 

Electric Field Strength (|E| 2 ) 

Reflectivity 

0.0 0.5 1.0 

(a) 

(c) 

R = 0.28 

hν = 1.0 keV 

0.0 5.0 10.0 15.0 

Incidence angle (°) 

2.5 Vac. B 4 

C/W Multilayer 

2.0 

1.5 

1.0 

0.5 

0.0 

-100 0 100 200 300 400 500 

Depth, z (Å) 

1.0 keV 

θ Bragg 

= 9.3 o 

Reflectivity 

0.0 0.5 1.0 

(b) 

(d) 

Electric Field Strength (|E| 2 ) 

R = 0.80 

hν = 10.0 keV 

0.0 1.0 2.0 3.0 

Incidence angle (°) 

4.0 Vac. B 4 

C/W Multilayer 

3.5 

3.0 

2.5 

2.0 

1.5 

1.0 

0.5 

10.0 keV 

θ Bragg 

= 0.93 o 

0.0 

-100 0 100 200 300 400 500 

Depth, z (Å) 

S.H. Yang










LaMnO 3 thin film--2p core levels 

with varying degrees of surface sensitivity 

“Surface” 

“Near-Surface” 

“Bulk” 

Bulkassociated 

screening 

feature 

Horiba et al., PRL 93, 236401 (2004)

Electronic Structure of Strained Manganite Thin Films with Room Temperature 

Ferromagnetism Investigated by Hard X-ray Photoemission Spectroscopy: 

La 0.85 

Ba 0.15 

MnO 3 

5.95 keV 

Strain/Mag 

netismassociated 


feature 

Tanaka et al., Spring8, PRB, in press

Fractured “cubic” La 0.7 

Sr 0.3 

MnO 3 

T = 150K 

Manella et al., TBP 

Pardini, Offi, Panaccione, CF, TBP

Electronic Structure of Bulk Manganite Crystals with No Room Temperature 

Remanent FM Investigated by Hard X-ray Photoemission Spectroscopy: 

“Cubic” La 0.7 

Sr 0.3 

MnO 3 

—fractured in situ 

Intensity (arb.units) 

30000 

25000 

hν = 7700 eV 

∼ 0.5 eV 

Opposite 

Direction 

∼ No shift 

T 

150 

300 

423 

T C 

Structural 

and/or 

SRMOassociated 


feature? 

20000 

665 660 655 650 645 640 635 


Pardini, Offi, Panaccione, CF, TBP

Temperature- 

Dependent 

Soft X-Ray 

Photoemission : 

La 0.7 

Sr 0.3 

MnO 3 

(a) 

O more positive 

Mn higher spin, 

more negative 

Mannella et al., 

Phys. Rev. Lett. 92, 

166401 (2004) 

Photoelectron Intensity (a.u.) 

(c) 

BE Displacement (meV) 

1000 

800 

600 

400 

200 

LSMO, x = 0.3, T dependence of Mn 3s 

T = 135 K 

T max = 500 K 

T C = 370 K 

T = 110 K 

0 

96 

94 

92 

90 

ΔE 3s 

88 

86 

84 

82 


Mn 3s 

hv = 212 eV 

Longer 

times 

Mn 3s 

hv = 212 eV 

80 

-200 

100 150 200 250 300 350 400 450 500 550 

Temperature (K) 

T 

I 

M 

E 

78 

T dependence of Mn 3s binding energies 

(b) 

Photoelectron Intensity (a.u.) 

T c 

T sat Change in ΔE 3s 

Average 3s BE 

TIME→ 

T sat 

(d) 

LSMO, x = 0.3, T dependence of O 1s 

T = 135 K 

T max = 500 K 

T C = 370 K 

T = 110 K 

533 532 531 

BE Displacement (meV) 

400 

300 

200 

100 

0 

“Bulk” 

“Surface” 

530 529 528 


O 1s-”bulk” 

hv = 652 eV 

O1s 

T c 

O 1s 

hv = 652 eV 

T 

I 

M 

E 

527 526 525 

T dependence of O 1s binding energy 

TIME→ 

-100 

100 150 200 250 300 350 400 450 500 550 

Temperature (K) 

T sat

e 

Strain/Mag 

netismassociated 


feature 


Panaccione, CF, TBP 

T = 110 K (start) 

T = 500 K (T max 

) 

T = 110 K (start) 

T = 500 K 

Mannella et al., 

Phys. Rev. Lett. 92, 

166401 (2004) 

Qualitat. the 

same, but 

still some 

surface 

influence?

More dramatic screening effects in strongly correlated materials— 

high T C Nd 2-x 

Ce x 

CuO 4 

(5.9keV) 

(1.5keV) 

M. Taguchi et al., Phys. Rev. Lett. 95, 17702 (2005).

(6.0 keV) 

(1.5 keV) 

Evidence for a suppressed core-hole 

screening on the surface of hightemperature 

superconductors 

La 2-x 

Sr x 

CuO 4 

and Nd 2-x 

Ce x 

CuO 4 

Intense screened/shakedown peak in e- 

doped cuprates 

Zhang-Rice singlet in LCO not in NCCO 

Screening due to delocalized coherent 

state at E F 

Screening within the first 15 Å of the 

surface is different from the bulk! 

M. Taguchi et al., 

PRL 95, 177002 (2005)

V 2 O 3 --2p core level--transfer of spectral weight across 

the metal-insulator transition 

Photoemission Intensity (Arb. Units) 

V 2p core level--hν = 5934 eV 

300 K (PM phase) 

140 K (AFI phase) 

Difference 

Photoemission Intensity (Arb. Units) 

T= 190 K 

T= 180 K 

T= 170 K 

T= 155 K 

T= 145 K 

hν = 5934 eV 

V 2p 3/2 

525 520 515 510 


518 516 514 512 


G. Panaccioned et al., VOLPE @ ESRF

Core and valence effects in V 2 O 3 

Photoemission Intensity (Arb. units) 

QP peak 

V 3d 

Sample 1 (flat) 

Sample 2 (rough) 

Polished 

Screening/ 

Shakedown 

V 2p 3/2 

G. Panaccione et al., VOLPE ESRF 

2.5 2.0 1.5 1.0 0.5 0.0 


514 513 512 


See also: M. Taguchi et al. PRB 71, 155102 (2005)

Valence effects in the metal-to-insulator transition of VO 2 

Photoemission intensity (arb. units) 

a 

12 8 4 0 

b 

O 2p 

valence 

band 

3 2 1 0 -1 

c 

1 


Metal 

Insulator 

V 3d 

350 K 

PES data 

PES/FD 

0 

O 2p valence band : clear change 

I: two peaks at 7.3 and 5.2 eV. 

7.3 eV peak shifts toward E F 

by 

0.6 eV. The high E B 

tail is 

enhanced around 9 eV. 

⇐increased hybridization in the 

M phase. The threshold of the 

non bonding peak between 5 and 

2.7 eV shifts by 0.3 eV toward E F 

. 

3d peak is at 0.9 eV in I phase. 

Minimum gap is 0.28 eV. (π band is 

expected ∼0.5 eV above E F 

. 

(Interband gap can be 0.78 eV.) 

M phase: FD cut off. QP DOS 

increases beyond E F 

. Higher 

energy tail of 3d spectra is due to 

the incoherent state. 0.9 eV peak 

in I phase is a coherent QP. 

Crystal distortion⇒band changes 

⇒trigger MIT (renorm. Peierls Ins.) 

Suga et al.










Valence-Band Photoemission at High Energy-- 

What & Where is the “XPS Limit”?: 

Additional effects at higher energies: 

• non-dipole--the photon momentum 

• angular acceptance→B.Z. averaging 

• lattice recoil, phonon creation→more 

k hν @ 

1,253 eV 

k hν @ 

10,000 eV 

B.Z. averaging, ∼Debye-Waller factor = W(T) ≈ exp[-(k f ) 2 ] 

….the “XPS limit” of full B.Z. averaging and 

D.O.S. sensitivity 

Hussain et al., Phys. 

Rev. B 22, 3750 (‘80)

XPS and HXPS in k space: 

hν = 1254 eV 

r r r r 

f 

ki 

+ g = k −kh 

ν 

hν = 10,000 eV 

r 

g = 26(2 π / a)yˆ 

f 

k r 

k f = 25.80 (2π/a), k hν 

= 2.54(2π/a) 

g r 

ACCEPTANCE 

CONE OF ±0.5° 

−k r 

h ν 

Angular resolutions 

of 0.02º with an acceptance 

±2º may be possible! 

B. Wannberg, P. Balzer

Gold Valence Spectrum 

In the XPS Limit 

Intensity (a.u.) 

XPS 

Broadened 

Theo. DOS 

10 8 6 4 2 0 


E F 

15 

10 

Gold Valence Spectrum 

300 (b) K 

D.W. 

factor 

≈ 6x10 -6 ! 

Siegbahn XPS @ 1.487 keV 

Silver Valence Spectrum 

5 

0 

Fixed mode 

Measurement Time 3:40 x1 

5938 

5940 

5942 

5944 

5946 

5948 

5950 

Intensity (a.u.) 

XPS 

Broadened 

Theo. DOS 

E F 

eV 

Measurement time: 3 min 40 s 

Total resolution: ca. 80 meV 

Takata et al., SPring8 @ 5.495 keV 

10 8 6 4 2 0 

Binding energy (eV)

In the XPS 

Limit— 

Comparison to 

theoretical 

DOSs 

15 

10 

Total DOS 

Expt. 

(b) 


SPring8 @ 

5.495 keV 

5 

High energy 

suggests analysis as: 

Band / MO 

dσ 

dσ 

∝ |P | 

AO 

j 2 Aλ 

∑ Aλj 

dΩ Atom A dΩ 

Orbital λ 

with P 

Aλj 

= 

0 

5938 

projected density of states 

or MO population analysis 

Fixed mode 

Measurement Time 3:40 x1 

5940 

5942 

5944 

5946 

eV 

5948 

5950 

Cross sec. 

6s x 5 1.00 

6p x 5 ----- 

5d total 3.88 

5d e g 

5d t 2g 

Z. Yin 

W.E. Pickett 

E F

Normalized Intensity 

In the XPS Limit 

SiO 2 -0.58nm/Si(100) 

@0.85keV 

(Exp.) 

SiO 2 

@7.94keV 

(Exp.) 

a 

20 15 10 5 0 

b 

c 


XPS— 

850 eV 

HXPS— 

7940 eV 

300 sec!! 

Theory: 

Si DOS 

s 

p 

a b c 

σ Si3s 

(8 keV) = 14.9 Barns 

∼1/27 

σ Si3p 

(8 keV) = 0.54 Barns 


Appl.Phys.Lett. 

84, 4310 (2004) 

Papaconstantopoulos

W at room temp.—not 

quite the XPS limit: Effect 

of photon momentum on k 

conservation: W(110) at 

1253.6 eV and room temp. 

W(001) 

300 K 

hν 

hν 

hν 

Symmetry-related 

spectra shifted by 

6.0° for best match. 

Calculated 4.8° 

due to k hν 

Hussain et al., 

Phys. Rev. 22, 

3750 (1980)

Suppression 

of direct-transition 

effects with 

temperature: 

W(110) at 1253.6 eV 

Hussain et al., 

Phys. Rev. 22, 

3750 (1980)

Aluminum soft x-ray valence spectra: Direct transitions to >710 eV 

Surface 

state 

300 K 

W = 0.19 

Surface— 

less affected? 

Hofmann et al., PRB 66, 245422 (2002)

T = 300K, T/Θ Debye 

= 0.75 


12 10 8 6 4 2 0 -2 


12 10 8 6 4 2 0 -2 

90 95 100 105 

Emission angle (deg) 

470K, 1.18 607K, 1.52 780K, 1.95 

90 95 100 105 


90 95 100 105 


90 95 100 105 


780K 

607K 

470K 

300K 

12 10 8 6 4 2 0 2 

780K 780K, .22 

607K, .31 

470K 470K, .40 

300K, D.W. = 0.55 

W(110) 

T-Dep. Soft X-Ray 

ARPES 

hν = 260 eV 

90º = normal 

800 angle channels 

Θ Debye 

= 400K 

L. Plucinski 

B.C. Sell 

Absolute photocurrent-20 channels (a.u.) 



12 10 8 6 4 2 0 -2 


12 10 8 6 4 2 0 -2

The W Band 

Structure 

(Christensen & 

Feuerbacher; 

Bylander & 

Kleinman) 

“Gap”

W(110) 

Soft X-Ray ARPES 

Compared to simple DT theory 

hν = 260 eV 

90º = normal 

T = 300K 

Free-e - DT 

Theory 

“Gap” 

| 

Γ 

| 

N 

[110] 


Free-e - DT 

Theory 

+ Secondary cones?

T = 300K, T/Θ 300K Debye 

= 0.75 470K, 1.18 607K, 1.52 780K, 780K 1.95 

“Gap” 

| 

N 

| 

Γ 


D.O.S. 

14 12 10 8 6 4 2 0 

780K, .22 

607K, .31 

470K, .40 

300K, D.W. = .55 

W(110) 

Not-So-Soft X-Ray ARPES 

hν = 870 eV 

90º = normal 

800 angle channels 

Θ Debye 

= 400K 

L. Plucinski

W(110) X-Ray ARPES 

Not-So-Soft X-Ray ARPES 

Compared to simple DT theory 

hν = 870 eV & 900 eV 

90º = normal 

T = 300K 


| 

N 

870 eV 

| 

Γ 

870 eV 900 eV

Now take it up to 10 keV: 

hν = 870 eV 

T = 780K 

W ≈ 0.21 

hν = 10,000 eV 

r 

g = 26(2 π / a)yˆ 

f 

k r 

k f = 25.80 (2π/a), k hν 

= 2.54(2π/a) 

g r 

ACCEPTANCE 

CONE OF ±0.5° 

−k r 

h ν 

Θ Debye = 310K, (10 -20 cm 2 ) = 5.34 + 0.0583T 0.0583T 

Debye-Waller Factor = W(T) ≈ exp(-k e 

2 

) 

High T 

⎯⎯⎯→ 

High T 

⎯⎯⎯→ 

= exp(-C 1 


) exp(-C 2 


T) 

W at 4K: W ≈ 0.21, ≈ 21% direct 

at 77K: W ≈ 0.16, ≈ 16% direct 

at 300K: W ≈ 0.01, ≈ 1% direct 

Correlated vibrations and a better theory (e.g. Phys. Rev. B 35, 1147 

(‘87) and 53, 7524 (’96) + 54, 14703 (‘96)) may suggest higher DT 

percentages, but needs further E&T study

Quantitative systematics—Tungsten : 

Debye-Waller Factor = 

sensitive 

More than 

50% band










Photoelectron 

diffraction→ 

holography: 

Elementspecific 

short-range 

atomic 

structure 

FORWARD SCATT. = “O TH ORDER” 

θ scat 

HIGHER ORDERS 

Bond & Low-Index 

Directions 

Bond Lengths 

& 

Atomic 

Positions 

→Holographic 

fringes

Photoelectron diffraction: Fine structure at ∼1 keV energy 

φ = 0° 

[001] 

hν 

θ inc 

[011] 

φ 

W(011) 

e - 

θ 

AZIMUTHAL ANGLE φ

XPD @ 1 keV 

B 1s from hex-BN 

monolayer on 

Ni(111) 

N on-top on Ni(111) 

B fcc on Ni(111), 0.1 Å below N 

Expt.-Osterwalder et al 

Theory-Osterwalder et al. 

Program by Kaduwela

X-ray Photoelectron Diffraction 

from Diamond Lattice (111) Surfaces 

Fwd. 

scatt. 

Lattice 

Constants 

3.57Å 

Kikuchi 


C 1s (964eV) from diamond(111) 

Widths of Kikuchi bands 

scale inversely with 

interplanar spacing 

And will scale directly with 

photoelectron wavelength, 

e.g at 10 keV 

Fwd. 

scatt. 

5.43Å 

Kikuchi 


Si 2p (1154eV) from Si(111) 

J. Osterwalder, R. Fasel, A. 

Stuck, P. Aebi, L. Schlapbach, 

JESRP 68, 1 (1994)

Small-cluster simulations of photoelectron diffraction 

W(100) 

Expt.— 

Effects of 

∼50% seen 

in TiS 2 

(Takata et al.) 

Theory: 

Emitter 


= 1500 eV E kin 

= 6000 eV E kin 

= 10,000 eV 

J. Garcia de Abajo, EDAC online program for PD: 

http://csic.sw.ehu.es/jga/software/edac/index.html

Statistics: Growth of HAXPES User 

Beamtime at SPring8 

No.o f A c c e pte d P ro po sals 

HX-PES User Beam time Shifts 

30 

25 

20 

15 

180 

160 

140 

120 

100 

80 

TotalS h ifts 

User Shifts 

In te rn al R & D 

Shifts 

10 

60 

5 

40 

20 

0 

2004A 2004B 2005A 2005B 2006A 

0 

2004A 2004B 2005A 2005B 2006A 

Main Beamline BL47XU. Partly we use Bl29XU, BL39XU, and BL22XU. 

K. Kobayashi










SUMMARY AND FUTURE PROSPECTS 

Basic intensity/resolution considerations: 

Source, analyzer, detector—several working systems 

Much more a bulk probe, ∼ 50 meV→10 meV resolution, recoil limit? 

Quantitative analysis simpler 

Spectral background, surface vs. bulk: grazing incidence, variable takeoff 

Probing multilayer nanostructures/devices: many applied systems 

X-ray optics and standing waves (SWs): 

Probing site-specific DOSs via Bragg-reflection SWs 

Probing buried layers and interfaces via multilayer SWs 

Core and valence level spectroscopy 

High resolution core spectra: ∼ 50 meV 

Observation of new screened peaks in TM 2p and valence spectra of oxides, SC 

materials: surface vs. bulk electron screening 

MCD and spin-resolved PS--future 

Valence bands, the XPS limit, photon wave vector, phonons 

Expect DOS-like spectra often, but with cryocooling and high angular resolution ≤ 

0.1º, band mapping possible up to at least 1 keV, 

maybe higher—but 10 keV likely smeared out 

High resolution VB DOS spectra—partial DOS determinations 

Photoelectron diffraction (short-range)←→Kikuchi bands (long-range) 

In both core and valence emission, 

Sensitive probe of local structure in bulk, e.g. dopants 

---------------------------------- 

Plus see: Nucl. Inst. and Meth. A, Volume 547, Issue 1, Pages 1-238 (2005) 

2nd Int’l Workshop-2006, Program/Abstracts http://haxpes2006.spring8.or.jp/

Chuck Fadley X-ray Photoelectron Spectroscopy and Diffraction in ...

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