the bessy hike project - brookhaven national laboratory · mihaela gorgoi 20.05.2009 photoemission...

Mihaela Gorgoi 20.05.2009

The BESSY HIKE Project The BESSY HIKE Project

Mihaela Gorgoi


IR to x-Ray (11 x-Ray Beamlines)29 ID-Beamlines25 DIP-Beamlines

4 lin. Undulators6 ell. Undulators

1.7 GeV 300 mA16 straight sections

3 7T-WLS1 7T-Wiggler

VUVXUV:

x-Ray:

BESSY II


Photoemission Photoemission SpectroscopySpectroscopy

monochromatic photon beam ionises electrons from sample

the kinetic energy (Ekin ) of photoelectrons in vacuum outside sample is measured

Ekin = hν

- BEbinding energy of electrons in the sample

• core levels strongly localized, thus BE's give elemental identification• chemical shifts give information on: chemical environment of emitter atoms

oxidation / valence / bonding state


Why high kinetic energy ? Why high kinetic energy ?

Large Sampling Depth

(Bulk sensitive)

Less Surface Sensitive

Non-destructive

Advantages

Disadvantage

Low photoionization cross sections

Bulk structures, multilayers, buried nano layers and interfaces

Typical samples:

10 100 1000 100000,1

1

10

100

0,1

1

10

100

2

Total yieldin transitionmetals and rare earths

"classic" range for photoelectron spectroscopy

HIKE - range

extrapolated:Electron escape depths - experimental:

Inel

astic

mea

n fr

ee p

ath

(nm

)

Electron kinetic energy (eV)


KMCKMC--1 Beamline 1 Beamline Double-crystal monochromator:

angular range 5° - 82°Si (111) 1997 - 12000 eVSi (422) 5639 - 12000 eVSi (311) 4000 - 12000 eV

F. Schäfers, M. Mertin, M. Gorgoi, Rev. Sci. Instrum. 78 (2007) 123102

toroidalmirror

11540 11800

6 mrad

apertureBe-foil

12978 28098 35273distance to source (mm)

top view

aperture wall focus

0

InSbSi 111Si 311Si 422

distance between elements (mm)15120 717512978

3 mrad

source

179.2 °

328

side view

crystal 1

crystal 2

<0.5 mrad

<0.2 mrad


2 4 6 8 10

0.1

1

10

Si (444)Si (333)

InSb (111)

Si (111)

Si (311)

Si (422)

Res

olut

ion

(eV

)

Energy (keV)2 4 6 8 10 12 14

108

109

1010

1011

1012

Energy (keV)

Si (422)

In LIII,II,I

Pt LIII

Sb LIII,II,I

Pt LII

Phot

on F

lux

/ 100

mA

InSb (111)

Si (111)

Pt LI

The resolution becomes very high at certain photon energies

KMCKMC--1 Beamline 1 Beamline


The HIKE SetThe HIKE Set--upupMotorized

5-axis samplemanipulator:

Electronspectrometer:Scienta R4000 optimized for high kinetic

energies up to 10 KeV

Load-lockfor sample

introduction & storage

Motorized chamber

stand

KMC-1

M. Gorgoi et al. Nucl. Instrum. and Meth. A 601 (2009) 48


Typical Experiment Typical Experiment

FermiFermi levellevel of Au(111)of Au(111)

Inte

nsity

[arb

itrar

y un

its]

2006.02005.62005.22004.8Kinetic Energy [eV]

0.27 eV width @ RT

Excitation energy:2010 eV

Gaussian contribution = Gaussian contribution = beamline resolution:beamline resolution:~ ~ 0.22 0.22 eVeV

M. Gorgoi et al. Eur. Phys. J. Special Topics 169, 221–225 (2009)

AnalyzerAnalyzer::PE 200 / 0.3 mm PE 200 / 0.3 mm slitslit150 150 meVmeV

resolutionresolution

TheThe

HIKE HIKE station at BESSY IIstation at BESSY II

Chamber stand positioning

accuracy within 2 μm !


HIKE on Au: Depth Profiling with HIKE on Au: Depth Profiling with Fixed Monochromator SettingFixed Monochromator Setting

Si (444)Si (444)2 hours2 hours

Si (111)Si (111)4 min.4 min.

ΔΔE=E=0.210.21±±0.01 0.01 eVeV

Si (333)Si (333)40 min.40 min.

ΔΔE=E=0.0500.050±±0.02 0.02 eVeV ΔΔE=E=0.0730.073±±0.02 0.02 eVeV

Inte

nsity

(arb

. un.

)

19161914191219101908Kinetic Energy / eV

Au 4f Si(111)2002 eV

Inte

nsity

(arb

. un.

)


Si(333)6006 eV

Au 4f

Inte

nsity

(arb

. un.

)


Au 4f Si(444)8008 eV

F. Schäfers, M. Mertin, M. Gorgoi, BESSY Annual Report 2006, 211


Selected ResultsSelected Results

•• Metal multilayers Metal multilayers –– interdiffusioninterdiffusion

•• OrganicOrganic and inorganic solarand inorganic solar cellscells

•• XX--ray standing wavesray standing waves

•• Ni 1s and satellitesNi 1s and satellites


Addressing interfacial quality in Addressing interfacial quality in CuNi multilayersCuNi multilayers

Grown by UHV-based dc magnetron sputtering

Bilayers: 5ML Cu / 5ML Ni5ML Cu / 5ML Ni

Heating to a preset temperature2010 eV excitation energy 0.26 eV overall resolution

E. Holmström, W. Olovsson, I.A. Abrikosov, A.M.N. Niklasson, B. Johansson, M. Gorgoi, O. Karis, S. Svensson, F. Schäfers, W. Braun, G. Öhrwall, G. Andersson, M. Marcellini, W. Eberhardt, Phys. Rev. Let. 97

(2006)

266106


Imperfect interfacesImperfect interfaces

✦

What we observe as ”one”

core photoelectron line is in reality an envelope originating from a distribution of many chemically shifted core levels.

✦

A calculation of the chemical shift therefore originates from many calculations (using DFT and other tricks)

Use a GAUSSIAN distribution of chemically inequivalent atoms around the interface, where the imperfection is described by the distribution width Γ


Example: Example: x

= 5 ML

Interface Interface TheoreticalTheoretical

ModelModel

••

ΓΓ

describes the quality of the describes the quality of the interfaceinterface

Ni NiCu

Results SummaryResults Summary

E. Holmström, W. Olovsson, I.A. Abrikosov, A.M.N. Niklasson, B. Johansson, M. Gorgoi, O. Karis, S. Svensson, F. Schäfers, W. Braun, G. Öhrwall, G. Andersson, M. Marcellini, W. Eberhardt, Phys. Rev. Let. 97

(2006)

266106

the experimentally determined shifts converge towards the theoretically predicted value of dilute alloy state.


Results: Cu 2p3/2 spectra of NiResults: Cu 2p3/2 spectra of Ni55CuCu55

2nd experiment –

new samples with the same composition


Results: Binding energies ofResults: Binding energies of 22--peakpeak--fit components in Nifit components in Ni55CuCu55


The intensities of Cu 2p, Ni 2p core-levels relative to the intensity of Pt 4f core level from the cap.

Intensity variations in surveysIntensity variations in surveys


Repeated heating results in alloying of the cap into the

multilayer!


Cu 2p3/2 coreCu 2p3/2 core--level spectra of level spectra of NiNi55CuCu55

wwithout Pt capithout Pt cap


Cu 2pCu 2p3/23/2

corecore--level spectra of level spectra of NiNi55CuCu55

without Pt capwithout Pt cap

Similar to previous data for low -

intermediate

temperature anneal

Core level shift almost vanish for high temperatures?!


Cu enrichment of surface during repeated anneals at high temperatures

Intensity ratiosIntensity ratios

of Niof Ni55CuCu55 without Pt capwithout Pt cap


We recover the picture from the first published results.

At 6 keV

excitation energy the contribution from the outermost layers is further suppressed.

Cu 2pCu 2p3/23/2

corecore--level spectra of level spectra of NiNi55CuCu55

without Pt cap without Pt cap --

6 6 keVkeV


HIKE on HIKE on OrganicOrganic ThinThin Film Solar Film Solar CellsCells

F8DTBT PCBM

Sample: polymer blend (1:1)

• At 2keV none of the shake-up features characteristic to the C60 cage are present. no surface presence of PCBM.

• The presence of the shake-ups at 6keV indicates the segregation of PCBM to the inner layers of the film.

M.P.Felicissimo, D.M.Jarzab, M.Gorgoi, M.A.Loi, M.Foster, U.Scherf, M.Scharber, S.Mattila, P.Rudolf, S. Svensson, BESSY annual

report

2007, 241 & J. Mat. Chem. accepted

C60 cage

PCBMF8DTBT+PCBM F8DTBT+PCBM


MetalMetal--LigandLigand

Interaction in the Valence Interaction in the Valence Electronic Structure of Ruthenium ComplexesElectronic Structure of Ruthenium Complexes

Binding Energy [eV]

4

3

2

0

14 12 10 8 6 4 2

CN2 Cl2 N719 BD

Inte

nsity

[a.u

.]

NN

NN

Ru NCS

NCSCOOH

COO TBA

COOH

COO TBA

- +

- +

Dye 2 (N719)

NN

RuN

NCS

NCS

NCS

Dye 1 (BD)

-+

COOH

COO

-+COO

TBA +

TBA

TBA

NN

NN

Ru CN

CNCOOH

COOH

COOH

COOH

Dye 3(CN2)

NN

NN

Ru Cl

ClCOOH

COOH

COOH

COOH

Dye 4 (Cl2)

• HOMO is determined as a function of ligands•

The splitting of the Ru 4d level into two peaks

depends on the ligands.

E.M.J. Johansson, M. Odelius, M. Gorgoi, O. Karis, R. Ovsyannikov, F. Schäfers, S. Svensson, H. Siegbahn, H. Rensmo, Chem. Phys. Let. 464 (2008) 192


HIKE on HIKE on InorganicInorganic

ThinThin

Film Solar Film Solar CellsCells

Cu(In,Ga)Se2 (CIGS)Zn(O,S) -

15 nm buffer

layer

Glass + Mo

Inte

nsity

/ a.

u.

2500eV 2000 1500 1000Binding Energy / eV

Se2p

Ga2p

Cu2p

9000eV 8000eV 7000eV 6500eV 6000eV 5500eV 5000eV 4000eV 3000eV

Inte

nsity

/ a.

u.

1500eV 1480 1460 1440 1420Binding Energy / eV

Se2p

Inte

nsity

/ a.

u.

960eV940920Binding Energy / eV

Cu2p

Above approximately 5 keV excitation energy the absorber becomes visible!

Depth profiling of Depth profiling of the devicethe device is is

possible!possible!

E.M.J. Johansson et al, BESSY annual

report

2006, 508 F. Schäfers,

M. Mertin, M. Gorgoi,

Rev. Sci. Intrum. 78 123102 (2007)

S 1s

Zn 2s 2p

Se 2p

Cu 2p

Se 2p

Ga 2p

Cu 2p


Cu-Diffusion into In2 S3 -Cover Layer

Cu 2p3/2

Cu(In,Ga)Se2

20 nm In2 S3Excitation energy: 4000 eVHeating rate: 2˚

C/min

Kinetic Energy [eV]Temperature [°C]

Countrate[kcts/s]

P.Pistor, N.Allsop, W.Braun, R.Caballero, C.Camus, Ch-H.Fischer, M.Gorgoi, A.Grimm, B.Johnson, T.Kropp, I.Lauermann, S.Lehmann, H.Mönig, S.Schorr, A.Weber, R.Klenk, Physica Status Solidi A 206 (2009) 1059


X-ray Standing Waves

Standing wave formation in reflection from a surface,Standing wave formation in reflection from a surface,or singleor single--crystal Bragg planes, or a multilayer mirrorcrystal Bragg planes, or a multilayer mirror

Incident Reflected

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

ee--hν

RI

courtesy Chuck Fadley


X-ray Standing Waves - SWEDGE

Scanned sampleSi-wafer

WSiO2

W

Cr wedge

B4C

Fe

B4CMultilayer

Mirror

∼6.0 mm

Scanned standing wave

MFe

dML

1st order Bragg:λx =2dML sinθBragg

λSW (|E2|) =λx /2sinθinc

≈

dML

BuriedInterface

X-ray

Photo-Electron

Or SoftX-ray

∼0.1 mmspot

θBragg

Fixed phase

Probing Buried Interfaces:

The Standing Wave- Wedge Method

courtesy Chuck Fadley


Al 1s

O 1sAlOx

O 1sMgO Mg 1s

Fe 2p

20 m

m

80 x 39.8 Å

Si/Mobilayers

SiO

2

Fe-0

-200

ÅM

gO-2

0 Å

AlO

x-2

0 Å

Dee

per

39.8 Å

F. Schonbohm, U.Berges, S.Döring, M. Gorgoi,C. Westphal, D. Buergler, C. Schneider, C. Papp, B. Balke, C.Fadley...

Mo

Si

Mihaela Gorgoi 20.05.2009 O. Karis, S. Svensson, J. Rusz, P. M. Oppeneer, M. Gorgoi, F. Schäfers, W. Braun, W. Eberhardt, N. Martensson, Phys. Rev. B 78, 233105 (2008)

HIKE on Ni Core Levels (6 eV satellite)

• DFT calculation: 3d shake up • Difference in core hole screening

and localisation of 1s and 2p states

• Famous, „classical“

problem

in condensed-matter

physics: • Enormous

attention

for

several

decades

-

many

publications

(sampling

surface

or

bulk?)• Correlation

effects

giving

rise

to the

satellites

in the

Ni PES: surface

plasmon

vs. excitonic

states

• Satellites are located at different energyw.r.t. the main 1s (2p) core level line

• Ni 1s measured for the first time !

6 keV

Ni 2p

12.6 keV

Ni 1s


Summary Summary

0

10

20

30

HIKE Users 2004 - 2009 and beyond

Prop

osal

s

2004 2006 2008 20100

10

20

30

21

20

max.

Jan-June

30

2

9

14

114

14

24

Year

KM

C-1

Bea

mtim

e w

eeks

06.10.2008 FS

Bending magnet Bending magnet beamlinesbeamlines atatthird generation facilities providethird generation facilities provideattractive opportunities for HIKEattractive opportunities for HIKE

‘‘highhigh’’ flux flux continuumcontinuum from soft tofrom soft tohard (2hard (2--12 12 keVkeV))

sometimes sometimes crystal limited resolutioncrystal limited resolution(~100 (~100 meVmeV))

resolution always < 1 resolution always < 1 eVeV

HIKE allows depth profiling of realdevices, especially electronicproperties of buried interfaces

HIKE allows determination of corelevel energy shifts


Acknowledgements

HZB, BESSY II, Berlin:

Franz SchäfersMarcel MertinWalter Braun Wolfgang Eberhardt

Uppsala Universitet:

Svante SvenssonHans SieghbanHakan RensmoErik Johannson

University of Groningen:

Marcella P. FelicissimoPetra Rudolf

IFW, BESSYJörg Fink

TIFRKalo Maiti

University of AmsterdamMark GoldenSanne de Jong

WMIAndreas Erb

Sari GranrothOlof KarisRonny Knut

MPI-FKS'Abt. Keimer'

University of Dortmund:

Sven DöringFrank SchonbohmUlf BergesCarsten Westphal

University of California

Chris Papp, Benny BalkeChuck Fadley

the bessy hike project - brookhaven national laboratory · mihaela gorgoi 20.05.2009 photoemission...

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