1
State of the art of electron spectrometers at the ALS
Alexei Fedorov $$
/November 13 2001, ALS monthly meeting/
$$ Supported by:
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Plan:
OrientationPhotoelectron Spectroscopy
InstrumentationGammadata-Scienta spectrometers
Examples of the research
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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: [email protected] | 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: [email protected] | 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: [email protected] | 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)
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