SR Spectroscopieson Solids, Surfaces, and Interfaces

Giancarlo Panaccione

Lesson V:Beamlines and Experiments

Fundamentals of Electron Spectroscopies

1) Handbook on Synchrotron Radiation, ed., E.-E. Koch, North-Holland Publishing Company; (North Holland, Amsterdam, 1983)

2) www.lightsource.org

3) F. Sette in New Directions in research with Third Generation Soft X-ray Synchrotron Radiation Sources, Ed. S. Schlachter and f.j. Wuilleumier, NATO ASI series, Applied Sciences Vol. 254, 1993, pp.251

4) A.Zangwill, “Physics at Surfaces”, Cambridge University Press, Cambridge 1988

5) D.P.Woodruff, T.A.Delchar, “Modern Techniques of Surface Science”, Cambridge UniversityPress, Cambridge 1986

6)http://www-bl7.lbl.gov/BL7/who/eli/SRSchoolER.pdf (Eli Rotenberg)

7) N.W.Ashcroft, N.D.Mermin, “Solid State Physics”

Useful References

SX700: astigmatic correction

ellipsoidal mirror

exit slit

source

plane grating

αβ

Fixed virtual source

Entrance slit25.2=fC

r

r ּי

r 2.252=ּי r

Historical Soft X-ray beamlines: SX-700 SuperESCA at Elettra, (r~4500 mm, r 22800~ּי mm)

Courtesy , D. Cocco, ELETTRA, Trieste

Plane mirrorrotation axis

70mm70mm

Plane gratingsrotation axis

Grating 1, 100mm x 20mm

Grating 2, 100mm x 20mm

ML mirror, 100mm x 10mm

Gold coating

Cr/C ML coating

200-1000eV ∆E/E>5000

900-4000eV ∆E ≈ 100eV

400-4000eV ∆E/E>3000

Source

M2, Plane mirror

Plane gratings18m from source

Pin hole22m from source

Collimated light SX700 (Twin-Mic, ELETTRA)Zone plate nano imaging

Courtesy , D. Cocco, ELETTRA, Trieste

Features:a) separate horizontal and vertical focusing mirrors, b) a movable exit slit to provide both high flux and high resolution. c) BL11 has 6 spherical gratings (energy range 10 eV - 1700 eV)

Historical Soft X-ray beamlines: Dragon BeamlineBL11A Taiwan

C. T. Chen, Nucl. Instrum. Methods Phys. Res. Sect. A 256, 595. (1987).C. T. Chen and F. Sette, Rev. Sci. Instrum., 60, 1616. (1989)

This beamline is the world's first Dragon beamlineoriginally designed by Dr. C. T. Chen in 1985. The beamline was transferred from NSLS to Taiwanand re-constructed in 1998.

Optical Parameters

550 ~ 1700

400 ~ 1200

200 ~ 600

100 ~ 300

Scanning Range (eV)

17001200600300Ruling Density (ℓ/mm)

Gratings

10000Resolving Power

S1 - G = 200 cm, G - S2 = 400 ~ 470 (cm)Arm Length

1.20 mm (Diameter)Beam Size at Focus Position (slit = 10 µm)

Spherical HFM, VFM and toroidal RFMMirrors

6m-SGMMonochromator

12 mradHorizontal Acceptance Angle

1.5 GeV Bending MagnetLight Source

Undulator based

Two circular polarized beam on the same spot

Dr. N. Brookes,ESRF

T.Hara et al., Nucl. Instr. and Meth. A 498 (2003) 496. "Helicity switching of circularly polarized undulator radiation by local orbit bumps",

Soft X-ray beamlines: Twin Helical Undulator BeamlineBL25 Spring8

1.30

1.20

64.0664.0464.0264.0063.98

Photon Energy (eV)

5meV

n=11

n=18

Helium 1P0 Rydberg Serie

Beamline energy resolution:Record and routine!!S.I. Fedoseenko, NIM A 505, 715 (2003)

APENoble gases Rydberg series s-1 → nl

E/∆E~13000 at 64 eV

E/∆E~16000 at 48 eV

for all polarizations

Energy resolution and Resolving Power:

Pre-focusing MirrorSpherical Gratings: different for HE and LE

Same principle

Exit Slit

Re-focusing MirrorToroidal

Sample

Photon Source(Undulator)

Mirror

Plane Grating Monochromator (PGM) +Spherical Mirrors

APE beamline: Layouthttp://www.elettra.trieste.it/experiments/beamlines/

No entrance SlitsNo pinhole!

APPLE-II quasi-periodic undulator 125 mm period, 17 periods- Energy range:10-120 eV- Monochromator – variable line spacing PGM; ( gratings: 900 lines/mm, 1200 lines/mm, 1600 lines/mm), double track- Spot size ~100x50 µm2

- Open to users on 75% base1600 lines/mm1200 lines/mm, track 21200 lines/mm, track 1

APE – Low Energy Beamline – 10 -120 eV

APPLE-II periodic undulator 60 mm period- Energy range – 150-1800 eV- Monochromator – variable line spacing PGM; ( gratings: 900 lines/mm, 1400 lines/mm, 1800 lines/mm) double track

- Spot size ~150x30 µm2

APE – High Energy Beamline – 150 -1800 eV

900 lines/mm, track 1 900 lines/mm, track 1

20x10-9

15

10

5

corre

cted

dio

de c

urre

nt

18001600140012001000800600400Photon Energy (eV)

gap:60 gap:59 gap:58 gap:57 gap:56 gap:55 gap:54 gap:53 gap:52 gap:51 gap:50 gap:49 gap:48 gap:47 gap:46 gap:45 gap:44 gap:43 gap:42 gap:41 gap:40 gap:39 gap:38 gap:37 gap:36 gap:35 gap:34 gap:33 gap:32 gap:31 gap:30

horiz pol lightgrating: 900Smirror: B2GeV; 50 slits

APE – High Energy Beamline – 150 -1800 eV

Users’ docking ports

Load-lock

Sample preparation

Sample growth and prep.

STM

APE-LEFe(100) Fermi surface

S segregation on Fe(100)

Distribution center

Phot

oem

issio

n In

tens

ity (A

rb. U

nits)

440420400380

Kinetic Energy (eV)

APE-HE

XPS vs. thickness in wedge sample

Variable polarizationphotons 8-120 eV

Variable polarizationphotons 150-1200 eV

Electron Spectroscopy with SR =CONTROL

SAMPLE

Optimized exchange of samples

Creation of common protocols

Tune transitions(electronic, magnetic, structural)

MEASURE

Chemical, elemental selectivity

Cross section (intensity, tunability)

Lateral + Temporal Resolution

ParametersM = M (H and T), Low T, doping, spin

2D (and < 2D) ScienceAnalysis of Electronic and Magnetic Properties

Credit for figure: Argonne National Laboratory

Characteristics of Synchrotron Radiation

• Tunable Energy(Element Selective)

• High Intensity

• Time Structure

• Polarization

• Coherence

• Focalisation

Why Synchrotron Radiation? 3

SR – Spectroscopy – Photon and Electron

SR – Spectroscopy – Photon and Electron

Synchrotron Radiation – Chemical Selectivity

Electronic Structure of Solids: - Core-levels: deep lying levels, little influence of environment- Valence, conduction levels: Determine most properties of solids

(chemical, magnetic, conduction, optical)

Atom Molecule Solid

Fermi energy

EF

Electronic Structure

Free ion wavefunctions: eigenfunctions of Hamiltonian operator:

H = - (h2/8π2m)∇2 - Zeff e2/r Hψ⟩ = Eψ⟩

Orbitals (s, p, d, ..) as linear combinations of hydrogen-like wave functions

ψn,l,ml = Rn,lYlml

n = principal quantum number (n ≥ 1)

l = orbital quantum number (0 ≤ l < n)

ml = projection of l on z-direction (-l ≤ ml ≤ l)

Rn,l = Radial part of wavefunction

Ylml = Angular part of wavefunction

l = 0: s-orbital, ml = 0, 2 electrons (spin up and spin down)l = 1: p-orbital, ml = -1, 0, 1 6 electronsl = 2: d-orbital, ml = -2, -1, 0, 1, 2 10 electronsl = 3: f-orbital, ml = -3, -2, -1, 0, 1, 2, 3 14 electrons

Wave functions

From (www.coe.berkeley.edu/AST/smrs)

SR Tunability = Chemical Selectivity - Copper

EACH ELEMENT=

SPECIFIC BINDING ENERGIES

Core levels: no direct influence on chemical and physical properties of material

BUT

interaction with conduction/valence levels

electrostatic interactions: chemical shifts

magnetic interactions: exchange splitting

Advantage: element selectivity due to characteristic energies of core-levels →chemical characterization, local properties.

- X-ray Photoemission Spectroscopy (XPS)

- Auger Electron Spectroscopy (AES)

- X-ray Emission Spectroscopy (XES)

- X-ray Absorption Spectroscopy (XAS)

Core Level Spectroscopies

OUR SUBJECTS

A) X-ray Photoemission Spectroscopy (XPS)Final State: one hole in core level

B) X-ray Absorption Spectroscopy (XAS)One hole in c.l., one more e- in VB

C) X-ray Emission Spectroscopy (XES)One hole in (shallow) c.l.

D) Auger Electron Spectroscopy (AES)Two holes in (shallow) c.l.

Resonant Spectroscopies: A, C and D around

absorption edge

Electron Spectroscopies

Courtesy of J. Vogel, CNRS, Grenoble, France

vale

nce

band EF

core

leve

ls

2p

2s

EF

2p

2s

Ek=hν-EB

XAS and XPS Spectroscopies

Courtesy of J. Vogel, CNRS, Grenoble, France

Cross-section:

(Fermi’s golden rule)

Final stateInitial state

Final state energy Initial state energy

Photon energy

Dipole approximation:

Dipole selection rules:

∆s = 0

∆l = ± 1 (s → p, p → s, d)

∆ J = (J′- J) = -1, 0, +1

Interaction Radiation-Matter (XPS and XAS)

Hint = H1 +H2

H1 ∝ E • r (dipole)

H2 ∝ quad.el. + mag. dip.H2/ H1 ∝ hν/mc2αZeff

H2/ H1 ∝ hν/mc2αZeffATOM K Edge (1s) L edge (2p3/2)C6 2 x 10-4

285 eV

Si14 1 x 10-3 5 x 10-6

1839 eV 100 eV

Ge32 9 x 10-3 1 x 10-4

11105 eV 1215 eV

Pb82 8 x 10-2 1.5 x 10-3

85530 eV 12285 eV

Dipolar vs Higher Order Transitions

E(eV)

Cou

nts

θ1θ2θ3θ4θ5θ6θ7

hν

e-

E(eV)

k(Å-1)

1) High Energy Resolution

1 – 10 meV @ Kinetic Energy < 50 eV

~ 100 meV @ Kinetic Energy > 500 eV

2 ) E = E(k)

Photoemission Spectroscopy: PES(Regimes of Photoemission, UPS, XPS…)

Fundamental of PES and ARPES: Lecture by A. Damascelli

http://www-bl7.lbl.gov/BL7/who/eli/SRSchoolER.pdf

X-ray Photoemission Spectroscopy: XPS

Energy Conservation: E(A) + hν = E(A+) + E(e-)

Electron's energy is kinetic energy : KE = hν - (E(A+) -E(A))

KE = hν – BE + φ

(BE = Binding energy)

(φ = work function , energy needed to extract the electron from the solid)

X-ray Photoemission Spectroscopy: XPS

X-ray Photoemission Spectroscopy: XPS

X-ray Photoemission Spectrum

of Pd metal, Mg Kα radiation

X-ray sources:Lab: Mg Kα (1253.6 eV)

Al Kα (1486.6 eV)

Synchrotron RadiationTunable

Cross sections