Angle -Scanned X-ray Photoelectron Diffraction (XPD)

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Angle -Scanned X-ray Photoelectron Diffraction
(XPD)
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Energy -Scanned X-ray Photoelectron
Diffraction Angle Resolved Photoemission Fine
Structure (ARPEFS)
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The Physical Origin of Intensity Modulations
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The Shape of the Primary Wave
dipole selection rules Dl1
s initial state Dl1
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The Amplitude of Scattered Waves Scattering
Factors and their Energy Dependence
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FS vs BS
FS dominates for KE500 eV - direct information
about interatomic directions with no
need of theoretical simulations
- if simulations are needed, Single
Scattering is often OK.
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Simulations
-cluster based (from a few to several hundred
atoms)

• real space (long range order not explicitly
  needed)

• electron waves (plane or curved) scattered off
  muffin-tin atomic potentials

- calculations of I(k) repeated as a function of
(q, f) or k.
-SSC-SW
-MSC-SW (MSCD by Chen and van Hove TXPD by
Fadley and coworkers)
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A Note on Short-Range Order
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Experimental - Home Lab
XPD
LEED
XPS
e-beam evaporator
Gas line
ARXPS
e-beam heater
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Experimental - ELETTRA SRS
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Chemisorption Formate on Cu (100)
M. Sambi, G. Granozzi, M. Casarin, G. A. Rizzi,
A. Vittadini, L. S. Caputi and G. Chiarello
Surf. Sci., 315 (1994) 309.

1. Cross Bridge (CB)
2. Diagonal Atop (DA)
3. Short Bridge (SB)

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Quantitative determination SSC-SW simulations
d(Cu-O) 1.950.05 Å lt(OCO) 1295
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• pseudomorphic growth

• Kikuchi bands developed medium-to-long range
  order

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Polar PD
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zV-O(expt.)0.720.07 Å zV-O(DFT)0.723 Å
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Soft phonon mode involving in-plane
displacements of O scatterers with respect to V
emitters?
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w4025 cm-1
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O 1s and Zn 3s, KE300 eV
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Why does it work?
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Near Node Photoelectron Holography
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• problems due to the strong anisotropy of
  electron-atom scattering
• both in amplitude and in phase

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Near Node Photoelectron Holography - the
Experiment
J. Wider, F. Baumberger, M. Sambi, R. Gotter, A.
Verdini, F. Bruno, D. Cvetko, A. Morgante, T.
Greber and J. Osterwalder,Phys. Rev. Lett. 86
(2001) 2337.
J. Spence, Nature 410 (2001) 1037.
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BESSY II
The role of the Si-suboxide structure at the
interface an angle scanned photoelectron
diffraction study
C. Westphal, S. Dreiner, M. Schürman, F. Senf, H.
Zacharias, Thin Solid Films 400 (2001) 101.
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ALS
Surface core level shift PD clean W (110), (1x1)
Fe/W(110) and (7x14) Gd/W(110)
C.S. Fadley M. Van Hove Group, Berkeley
Surf. Sci. 441 (1999) 301.
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PRL 79 (1997) 2085.
Z12 2.0760.05 Å Z23 2.2860.05 Å.
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Epitaxial growth - Vanadium and Vanadium
Oxides on TiO2 (110)
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Bridging oxygen relaxation
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ASTRID
1 ML V on TiO2 (110) annealing at 473 K in O2
CHEMICAL SHIFT PD