1

State of the art of electron spectrometers at the ALS

Alexei Fedorov $$

/November 13 2001, ALS monthly meeting/

$$ Supported by:

2

Plan:

OrientationPhotoelectron Spectroscopy

InstrumentationGammadata-Scienta spectrometers

Examples of the research

3

The SES 50is a very high resolutionanalyzer complete with electronicsand software. The 50 mm full hemi-spherical analyzer is Herzog-plate ter-minated and is equipped with resolu-tion optimization electrodes.

The multi-element lens system is com-pletely customized to suit (almost) anymeasurement situation. For in-stancethe lens can be optimized for variableangular dispersion over its kineticenergy scan range. Other possibil-ities are different lens magnificationsor optimization for maximum trans-mission from a specified sample area.

The detector system consists of aMCP detector and a 2-D resistiveanode encoder which offers a reso-lution of 256 by 256 pixels. The dataacquisition system enables parallelrecording of up to 128 spectral ‘slices’, which can represent slightlydifferent sample positions or take-offangles. An analog output from thedetector enables real-time optimiza-tion of the experiment set-up.

The high voltage system is built up ofmodules of highly stable and linearpower supplies. All electrode volt-ages have ripple and noice levels

<< 1 mV even in environments withstrong electromagnetic interferencThe analyser is completely controlled from the PC via an optic bus using menu controlled softwarThe analyzer is designed to be mouned inside an existing vacuum chamber. It can be fixed to a goniomeinternal frame etc. via 4 mountholes on the back side of the ouhemisphere. All electrical connectto the spectro-meter can be made vone single CF35 flange.

Gammadata Scienta AB

P.O. Box 15 120 | S-750 15 Uppsala | Sweden

Phone: +46 18 480 58 00 | Fax: +46 18 555 888 | E-mail: info@gammadata.se | Internet: www.

Features:

< 3 meV energy resolution

Angle multiplexing recording

from small area samples

Extremely low noise, high

stability power supplies

Customized lens design

Multi-channel resistive anode

detector

Main application:

High resolution electron

spectroscopy

High resolution

photo-electron diffractionion

High resolution angular

resolved spectroscopy

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SCIENTA SES 50

ELECTRON SPECTROMET

Scienta spectrometers at ALS

The SES 2002is a full hemisphericalanalyzer specially designed for veryhigh resolution spectroscopy. Theanalyzer is Herzog-plate terminatedand is equipped with an accelerat-ing/retarding multi-element electro-static lens system.

The analyzer is equipped with anadjustment facility to achieve optimumfocussing, ensuring close to theoreti-cal energy resolution down to thelowest pass energies. Double µ-metalshielding ensures optimum perform-ance even in the presence of strongmagnetic fields.

The lens can be utilized in severalmodes of operation in order to giveoptimum performance in differenttypes of experiments. Switching be-tween different modes is done fromthe software.

In the unique angular mode a diffrac-tion plane is made to coincide withthe entrance slit plane facilitatingparallel multi angle recordings. Sinceno acceptance angle reducing aper-ture is used the highest angular res-olution is achieved with minimal lossof intensity.

The detector system consists oa chevron mounted micro-channel plate detector with a phosphor scrand CCD-camera. The 2-D read-outof the detector enables real-tioptimization of the experiment set

The high voltage system is built umodules of highly stable and linpower supplies. The high voltage stem is galvanically decoupled from control computer via a fiber optic

Gammadata Scienta AB

P.O. Box 15 120 | S-750 15 Uppsala | Sweden

Phone: +46 18 480 58 00 | Fax: +46 18 555 888 | E-mail: info@gammadata.se | Internet: www

Features:

< 2 meV energy resolution

Angle multiplexing recording

from large area samples

Extremely low noise, high

stability power supplies

Double µ-metal shielding

2-D CCD multi-channel

detection system, > 400

energy channels

Light weight design

Main application:

High resolution electron

spectroscopy

High resolution photoelectron

diffraction

High resolution angular

resolved spectroscopy

High resolution

spectromicroscopy

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SCIENTA SES 200

ELECTRON SPECTROMET

The SES 100is a new, high perform-ance electron analyzer. It is based onthe same technology as the SES2002 but is smaller in size andsomewhat simplified. It is speciallydesigned to have high energy resolu-tion combined with high flexibility inthe unique angular resolved mode. Itis small in size to facilitate transpor-tation between different beam linesand rotation around the incoming lightbeam.

The unique angular mode allows theuser to work with a variable angulardispersion, thereby optimizing theangular resolution for each type ofexperiment. Since the angular modeworks without any acceptance anglereducing aperture, but multiplexes theangular data acquisition, the highest

angular resolution can be achievedwith minimal loss of count rate.

The angular mode is extremely versa-tile, as an example it is possible toobtain an angular resolution of betterthan 5 mrad. within an angular inter-val of ± 100 mrad. or an even betterangular resolution, < 1 mrad. withinan interval of ± 30 mrad., for sourcesizes up to Ø 1 mm.

The SES 100 has double µ-metal shielding and utilizes the highly stableand linear power supplies needed toachieve the ultra high performance ofthe Gammadata Scienta SES-analyz-ers.

The software is built on a dynamic-linklibrary (DLLs) where the spectrom-

eter interface is available to thIt enables the user to write theisoftware to control the data acqution of the analyzer together with equipment in a large experiment sup.

The SES 100analyzer has a workingdistance of 45 mm to allow folarge samples and space for 3-Dmovements of the sample. The distance from the mounting flange(NW100CF) to the sample is 400 mmto make it possible to mount the SES100 analyzer on large sample analysis chambers.

Gammadata Scienta AB

P.O. Box 15 120 | S-750 15 Uppsala | Sweden

Phone: +46 18 480 58 00 | Fax: +46 18 555 888 | E-mail: info@gammadata.se | Internet: www

Features

< 3 meV energy resolution

Angle multiplexing recording

with variable angular

dispersion and resolution

Extremely low noise, high

stability power supplies

Double µ-metal shielding

2-D multi-channel detection

system, > 400 energy channels

Main application:

High resolution electron

spectroscopy

High resolution photoelectron

diffraction

High resolution angular

resolved spectroscopy

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•

SCIENTA SES 10

ELECTRON SPECTROMET

BL-10.0.1 (2)BL-12.0.1 (1)

BL-7.0.1BL-12.0.1BL-9.3.2BL-8.0.1

NONE

4

5

Other facilities also have it:

NSLS, Brookhaven: SES-200 (1)

SSRL, Stanford: SES-200 (1+)

SRC, Stoughton: SES-200 (1+), SES-50

CAMD, Baton Rouge: SES-200 (1)

6

Photoemission /inverse photoemission/

Experiment Data

Important parameters:Energy resolution (~20 meV)Angular resolution (~2º )

Excitation Radiation• photon energy• polarization• angle of incidence

Photoelectrons• kinetic energy• emission angle• polarization

sp hν

e

Θφ

n

samplehole

Energy Distribution Curves (photocurrent vs. kinetic energy) measured at certain emission angle

Electron momentum (Å-1)

hν

e

e

Core levels

Delocalized states

Aim: learn Electronic structure or Chemical compositionApproach: fitting Data using appropriate models

7A.V. Fedorov et al., PRL 73, 601 (1994)

Surface core level shifts in 4-f metals

A.V. Fedorov et al., PRL 70, 1719 (1992)

R CF AUS E

BULK

8

A.V. Fedorov et al., PRB 50, 2739 (1994)

A.V. Fedorov et al., PRL 82, 2179 (1999)

Electronic structure ofHigh Temperature SuperconductorAnd Ferromagnetic Gd

9

What is an electron spectrometer?

e

Intensity, Energy,and Emission angle

Θ

Plus:Excellent resolution

Multiplexing

Good apparatus

10

Hyperbolic field analyzer/M. Jacka et al., RSI 70, 2282 (1999)/

11

Display Analyzer/single energy, all angles/

12

13

Double toroidal analyzer/C.Miron et al., RSI 68, 3728 (1997)/

Energy window: ∆E~15% PEResolving power: EP/δE ~100

FIG. 8. ~a!The image on the PSD of the 1s(NC ,NT) photoelectrons of N2O molecule excited with hn5 470 eV photons, recorded with the DTA. ~b!Thecorresponding I(r) spectrum.

14

V.D. Belov and M.I. Yavor, RSI 71, 1651 (2000)

B. Wannberg, U. Gelius, and K. Sieghban, J. Phys. E, Sci. Instrum. 7, 149 (1974)

R.C.G. Leckey, J. Electron Spectr. Relat. Phenom. 43, 183 (1987)

Suggested reading:

15

Sample

Excitationradiation

hνPhotoelectrons

New Instrumentation from Gammadata-Scienta

Magnifyinghigh-transmissionimaging Electron Lens

Energy

Ang

le

Wide-band Energy Analyzer

2-Dimensional (Energy and Angle)high-resolution electron detector

EP/δE ~1400EP= 2eV, <2meVδΘ~10 mradδS~9 µm

16

2-dimensional detector/Micro-channel plates coupled to the phosphor screen/

Is it:FastUniformLinearStable

?

17

24

68

10 16.016.5

17.017.5

18.0

PE 2 eVAngular mode 1Swept mode

Kinetic Energy (eV)

Angle (some units)

Solving detector mysteries

18

Engineering expertiseis essential for makingour analyzers to work

Magnetic screens /µ-metal/ go inside the chamber

19

Charge Density WavesR.E. Peirls, Quantum Theory of Solids (Clarendon, Oxford, 1955); H. Fröhlich, Proc. R. Soc. Lond. A 223, 296 (1954);

A.W. Overhauser, Phys. Rev. 167, 691 (1968); S.-K. Chan and V. Heine, J. Phys. F 3, 795 (1973)

G. Grüner, Density Waves in Solids (Addison-Wesley, Reading, 1994)

1. Lets take one-dimensional electron gas...

aε F Fk

m=η2 2

2k N

aF =0

2π

qdeqrq

rqi ρρρ ρρ

∫= )()( φφ

2. Consider response of an electron gasto a time independent potential:

3. Rearrangement of the charge density:

4. χ(q)–Lindhard response function:

χ(q) diverges at q=2kF

⇓One-dimensional gas is unstable

with respect to the formation of aperiodically varying electron charge density

ρ χ φind q q q( ) ( ) ( )ρ ρ ρ=

qkk

qkkd

ffkdq+

+

−

−= ∫ εεπ

χ)2(

)(ρ

ρ

χπ

( ) lnq ev

q kq kF

F

F

=− +

−

2 22η

In one dimension:

( ) mkk 222η=ε

20

= 352. k TB CDWMF

Consequences of charge modulation/and electron-phonon coupling/

Periodic lattice modulationand Pierls transition /opening of a gap at kF/

Modification of phonon spectrum/Kohn anomaly or phonon softening at 2kF/

q2kF

ωq

1D

2D3D

CDW in a real system: K0.3MoO4

Quasi-one-dimensional crystal structure

X-ray scattering Resistivity ARPES spectra at kF

EF400

150 K

200 K

21

Electronic structure of K0.3MoO3/tight-binding calculations/

M.-H. Whangbo and L.F. Schneemeyer, Inor. Chem. 25,2424 (1986)

22

Temperature (K)

Structural studies of CDW in K0.3MoO3/incommensurate to commensurate transition/

Temperature dependent neutron scatteringM.Sato, H. Fujishita and S.Hoshito,

J. Phys. C: Solid State phys., 16, L877 (1983)

q CDW

Diffuse X-ray scatteringJ.-P. Pouget et al.

23

Electron Momentum along ΓΧ (Å-1)0.2 0.3 0.4

EF

0.1

0.2

Bind

ing

Ene

rgy

(eV

)

hν = 21.4 eV

Direct monitoring electron bands in K0.3MoO3/3-D maps of photocurrent/

Experimental details:

Samples cleaved in situ

Liquid He cryostat providestemperatures from ~20 K to ~450 K

Temperature monitored with OMEGA CY7 sensor

24

Inte

nsity

at t

he F

erm

i lev

el

Electron Momentum along ΓΧ (Å-1)

kF1

kF2

0.2 0.3 0.4

Momentum Distribution Curves at EF

T=300 K

200 K

180 K

150 K

120 K

100 K

80 K

62 K

40 K

25

Present work

Neutron scatteringR.M. Flemming, L.F. Schneemeyer and D.E. Moncton, PRB 31,899 (1985)

Temperature (K)50 150 250

Incommensurate to commensurate CDW transition in K0.3MoO3

/viewed by photoemission/

1-[k

F1+

k F2] a

nd 1

-qCD

W(b

×un

its)

0.255

0.250

0.260

0.265

26

Γ

Χ

ΥΥ

t//

t⊥

coupling alongchains

coupling betweenchains in a unit cell

t interchaincoupling

t reduced by 10%

kF1

kF2

Fermi surface is given by:

µ = -2cos(k//) ± (t⊥ + 2t⊥ t cos(k⊥ )+t)1/2

Fermi surface of an array of coupled chains/tight binding calculation/

A.V. Fedorov et al., Journal of Physics: Condensed Matter (Letters to the Editor) 12, L191 (2000)

27Binding Energy (eV)

EF0.10.20.3

∆Θ = ± 0.1°

∆Θ = ± 1°

k = kF

Suppression of spectral weight in photoemissionfrom low-dimensional conductors:influence of momentum resolution

28

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79%

1. Doping and Temperature Dependence of the MassEnhancement Observed in the Cuprate Bi[sub 2]Sr[sub 2]CaCu[sub 2]O[sub 8 + delta ] PDF (251 kB) GZipped PS Order

P D Johnson, T Valla, A V Fedorov

Phys. Rev. Lett. 87, 177007 (2001)

79%

2. Many-Body Effects in Angle-Resolved Photoemission:Quasiparticle Energy and Lifetime of a Mo(110) SurfaceState PDF (735 kB) GZipped PS Order

T Valla, A V Fedorov, P D Johnson

Phys. Rev. Lett. 83, 2085 (1999)

79%3. Temperature Dependent Photoemission Studies ofOptimally Doped Bi[sub 2]Sr[sub 2]CaCu[sub 2]O[sub 8] PDF (125 kB) GZipped PS Order

A V Fedorov, T Valla, P D Johnson

Phys. Rev. Lett. 82, 2179 (1999)

77%

4. Evidence of Electron Fractionalization fromPhotoemission Spectra in the High TemperatureSuperconductors PDF (134 kB) GZipped PS Order

D Orgad, S A Kivelson, E W Carlson

Phys. Rev. Lett. 86, 4362 (2001)

77%5. Charge-Density-Wave-Induced Modifications to theQuasiparticle Self-Energy in 2H-TaSe[sub 2] PDF (187 kB) GZipped PS Order

T Valla, A V Fedorov, P D Johnson

Phys. Rev. Lett. 85, 4759 (2000)

77% 6. Reply: Smith et al. PDF (36 kB) GZipped PS Order

Kevin E Smith, Jinyu Xue, L-C Duda

Phys. Rev. Lett. 85, 3986 (2000)

77%

7. Temperature Dependent Scattering Rates at the FermiSurface of Optimally Doped Bi[sub 2]Sr[sub 2]CaCu[sub 2]O[sub 8 + delta] PDF (224 kB) GZipped PS Order

T Valla, A V Fedorov, P D Johnson

Phys. Rev. Lett. 85, 828 (2000)

77%8. Electronic Structure near the Fermi Surface in the Quasi-One-Dimensional Conductor Li[sub 0.9]Mo[sub 6]O[sub 17] PDF (561 kB) GZipped PS Order

Jinyu Xue, L-C Duda, Kevin E Smith

Phys. Rev. Lett. 83, 1235 (1999)

77%9. Magnetic Properties at Surface Boundary of a Half-Metallic Ferromagnet La[sub 0.7]Sr[sub 0.3]MnO[sub 3] PDF (211 kB) GZipped PS Order

J-H Park, E Vescovo, H-J Kim

Phys. Rev. Lett. 81, 1953 (1998)

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79%1. Anomalous Electronic Structure and Pseudogap Effects inNd[sub 1.85]Ce[sub 0.15]CuO[sub 4] PDF (361 kB) GZipped PS Order

N P Armitage, D H Lu, C Kim

Phys. Rev. Lett. 87, 147003 (2001)

79%2. Bilayer Splitting in the Electronic Structure of HeavilyOverdoped Bi[sub 2]Sr[sub 2]CaCu[sub 2]O[sub 8 + delta ] PDF (457 kB) GZipped PS Order

D L Feng, N P Armitage, D H Lu

Phys. Rev. Lett. 86, 5550 (2001)

79%3. Superconducting Gap and Strong In-Plane Anisotropy inUntwinned YBa[sub 2]Cu[sub 3]O[sub 7 - delta ] PDF (1886 kB) GZipped PS Order

D H Lu, D L Feng, N P Armitage

Phys. Rev. Lett. 86, 4370 (2001)

79%4. Superconducting Gap Anisotropy in Nd[sub 1.85]Ce[sub0.15]CuO[sub 4]: Results from Photoemission PDF (188 kB) GZipped PS Order

N P Armitage, D H Lu, D L Feng

Phys. Rev. Lett. 86, 1126 (2001)

79%5. Fermi Surface, Surface States, and Surface Reconstructionin Sr[sub 2]RuO[sub 4] PDF (257 kB) GZipped PS Order

A Damascelli, D H Lu, K M Shen

Phys. Rev. Lett. 85, 5194 (2000)

77%

6. Dual Nature of the Electronic Structure of (La[sub 2 - x - y]Nd[sub y]Sr[sub x])CuO[sub 4] and La[sub 1.85]Sr[sub 0.15]CuO[sub 4] PDF (204 kB) GZipped PS Order

X J Zhou, T Yoshida, S A Kellar

Phys. Rev. Lett. 86, 5578 (2001)

77%7. Evidence of Electron Fractionalization from PhotoemissionSpectra in the High Temperature Superconductors PDF (134 kB) GZipped PS Order

D Orgad, S A Kivelson, E W Carlson

Phys. Rev. Lett. 86, 4362 (2001)

77%

8. Angle-Resolved Photoemission Study of Insulating andMetallic Cu-O Chains in PrBa[sub 2]Cu[sub 3]O[sub 7] andPrBa[sub 2]Cu[sub 4]O[sub 8] PDF (163 kB) GZipped PS Order

T Mizokawa, C Kim, Z-X Shen

Phys. Rev. Lett. 85, 4779 (2000)

77%9. Evidence for an Energy Scale for Quasiparticle Dispersionin Bi[sub 2]Sr[sub 2]CaCu[sub 2]O[sub 8] PDF (175 kB) GZipped PS Order

P V Bogdanov, A Lanzara, S A Kellar

Phys. Rev. Lett. 85, 2581 (2000)