INFRARED SYNCHROTRON RADIATION: SPECTROSCOPY AND … · Outline n Electromagnetic Spectrum; n...

INFRARED SYNCHROTRON RADIATION: SPECTROSCOPY AND MICROSCOPY

Stefano Lupi

Department of Physics University of Rome La Sapienza,

CNR-INFM COHERENTIA and SISSI@Elettra (EU-Italy)

Outlinen Electromagnetic Spectrum;n Infrared Synchrotron Radiation;n Experimental Apparatus: Michelson Interferometry+Infrared Microscopyn Solid-State Applications:a Superconduting Transition (THz and Far-IR Spectroscopy) Flux Gain1. Gap determination2. Spectral-Weight and penetration depthb Metal-to-Insulator Transitions (from THz to visible)

Brilliance Gain1. Mott-Hubbard Physics2. Peierls and e-ph Physicsn Geological Applications:1. Microscopic fluid inclusions Brilliance Gainn Chemistry:1. Adbsorption at solid surfaces Brilliance Gain§ Biology:1. Cellular absoption Brilliance Gainn Cultural Heritage

FIR MIR NIR

Phonons; Drude absorption;Gaps in superconductors;Molecular Rotations;

Molecular Vibrations Fingerpr ints forChemistry, Biology, And Geology

Molecular Overtones and Combinations bands;Excitons;Gaps in semiconductors

The “THzgap” , Collective Excitations in Macromolecules and exotic electronic materials

Electromagnetic Spectrum

IR Units: 200 cm-1=300 K= 25 meV = 50 µµµµm = 7 THz

Infrared History

1976 Meyer&Lagarde (LURE, Orsay) publish the first paper on IRSR

1981 Duncan and Yarwood observe at Daresbury the first IRSRemission

1985 The first IRSR spectrum (on N2O) is collected at Bessy(Berlin)

1986 The first beamline becomes operating at UVSOR (Japan)

1987 Beamline at Brookhaven (USA)

1992-94 Beamlines at Orsay (France), Lund (Sweden), Daresbury(GB)

1995 First international workshop on IRSR, Rome (Italy)

IRSR Chronology

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sono necessari per visualizzare quest'immagine.

IRSR Beamlines in the World

Advantages of IRSR

ADVANTAGES:ADVANTAGES:

Diffraction Limited Spatial ResolutionDiffraction Limited Spatial Resolution

Better SignalBetter Signal--toto--NoiseNoise

Faster Data CollectionFaster Data Collection MICROSCOPY

BRILLIANCE

SPECTROSCOPY

BROADBAND SOURCE

LINEAR & CIRCULAR POLARIZATION

FAR-IR SOURCE PULSED EMISSION

Source

A Michelson Interferometer is

based on the interference effect among the two emwaves at the beam-

splitter site

Detector Measure of the figure of interferenceInterferogram

Mobile mirror M2

Fixed mirror M1

Beamsplitterx=0

Instrumentation I:Michelson Interferometer

Spectral Resolution∆ν∆ν∆ν∆ν~1/d (cm-1) ~ 0.001 cm-1 ~ 1µµµµeV

d

Interferogram

Spectrum

Interferogram

Spectrum

Interferogram

Spectrum

Mon

ocro

mat

icP

olic

rom

atic

IR S

ourc

e

Fourier Transform

x

x

x

ν

ν

ν

ν0

ν1 νn

Synchrotronbeam

Interferometer

IR detector

White light

X-Y microstages

SchwarzschildObjectives

Sample visualisation

Adjustable aperture

Adjustable aperture

Instrumentation IIInfrared Microscopy

Infrared Microscope---->Beam CondenserVisualize and measure small and/or no-homogenous sample (size<100 µm)

with a high spatial resolution

Bruker-Hyperion

λλδ ≈=NA

61.0

In the IR spatial Resolution is determined by diffraction

For example with a 36x objective with NA=0.5, one obtains:

λλλλ

λλλλ

Production of IRSR



Standard Bending radiation (emitted during the circular trajectory in the bending due to the constant B field)



P (λλλλ) = 4.4 1014 x I x ΘΘΘΘH x bw x (ρ/ρ/ρ/ρ/λλλλ)1/3 photons s-1

I is the current in amperes,ΘΘΘΘH (rads) the horizontal collection angle,

bw the bandwidth in per cent, λλλλ the wavelength, and ρρρρ the radius of the bending

ΦΦΦΦV-NAT(mrad) = 1.66(1000 x λ (µm)/ ρ(m))1/3

at ALS for λ= 100 µm ΦΦΦΦV-NAT= 50 mrads

Very large emission angles SISSI: H=70 mrads; V=25 mrads

In the Far-Field approximation:

P = α α α α x I x γγγγ4ΘΘΘΘ2222/(1+ γ/(1+ γ/(1+ γ/(1+ γ2ΘΘΘΘ2222))))2222 photons s-1

I is the current in amperes,Θ(rads) the emission angle

(concentrated in ΘΘΘΘmax ~ 1/γγγγ ~10 mrads)

Edge Emission(emitted at the entrance (exit) of a bending magnet due to the rapid variation of the B field)





IRSR FLUX

The IRSR flux and Brilliance depend only on:

-beam current-source size/emittance-extraction aperture-transmission optics

Instead scarcely depend on the machine energy

ElettraI= 300 mA

~(λλλλc/λλλλ)1/3

Increasing the Far-IR Flux:Coherent vs Incoherent Synchrotron Radiation

Flux:

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are needed to see this picture.

Far-IR X-rays

SR

CSR

incohvcohincoh IfNfNIII ))1(( 2ν+−=+=

2)cos()(= dzeznf zi

vθπ Bunch form factor

Diffraction due to chamber size

Production of Coherent Synchrotron RadiationTwo main methods

SISSI@Elettra: E. Karanzoulis, A. Perucchi and S.L.,2007

Low-αααα mode Needed to change the magnetic optics:

Only dedicated runs

Momentum compaction factor αααα : ∆∆∆∆p/p=αααα=σσσσ/LWhere σ is the bunch length and L is the length of the ideal trajectory inside the machine

IRIS@Bessy-II: U. Schade et al, PRL 2003

Low-e beam energyInjected the machine at low-E:Reducing life-time and stability

3/2E≈σ

IRSR BrillianceThe most important figure of merit for IRSR is the Brilliance

BSR

=d 2F

dθdϕASA

(photons/0.1%bw/cm2/str)

Where the Actual Source Area is an estimation of the dimension of the source at the exit port (Hulbert and Weber,92; A. Nucara, 1998)

Limiting NoiseSN

= 100A1/ 2D*

B(ν )∆νεt1 / 2ξWhere: A detector area, D* detectivity, B brilliance, ∆νbandwidth, ε etendue, t measuring time, ξ optical efficiency %N =

Brilliance gain at SISSI

S. Lupi et al, 2007





Brilliance gain at SISSI

Experimental Techniques III

ωω

ω

Via Kramers-KronigTransformation

real and immaginary part of the optical response

functions εσcan be

obtained

Incident Radiation I0Incident Radiation I0

Reflection IR

Sample

Emission

Scattering

Transmittance ITAbsorbanceAbsorbance

Reflectivity, Transmittance, and Absorption R+T+A=1

Reflectivity experiments

Single crystals may be very small:

Reference:gold evaporated in

situReflectivity:

R = IRcrys/ IRgold

Kramers-Kronig transf.

optical conductivity

σ(ω)

Sample

Cryostat

Remotelycontrolled mirrors

Interferometer

Detector

Solid-State Applications ISuperconductivity

(FLUX GAIN)

Superconductivity today:

1. Looking for new materials• 1986: High-Tc cuprates• 1990: C60 fullerene• 2000: MgB2• 2003: NaxCoO2·3H2O• 2004: B-doped diamond

2. Understanding new materials

Infrared spectroscopy plays a role...

... because

Superconductivity is ruled by low-energy electrodynamics:

• Superconducting gap : THz-range• Spectral weight of condensate and penetration depth:THz-range

• Mediators of pairing (phonons, etc.): Far-infrared• Free-carrier conductivity above Tc: Infrared

Basic optics of Superconductors

[σ1(ω, T>Tc) - σ1(ω, T<Tc)] dω = ω2ps/8 = nse2/m*--> λ=c/ωps

Ferrel-Glover-Tinkham Rule

Superconducting gap observed if:•sample in the dirty-limit (2∆ < Γ) •Cooper pairs in s-wave symmetry

40x103

30

20

10

0

σ1(

ω) (

Ω−1

cm-1)

200150100500

ω (cm-1)

Normal State T = 0.9 Tc T = 0.6 Tc T = 0

Superconducting Gap

σ1sup(ω ) = ω 2

ps

8δ (ω ) + σ1

reg(ω )

1.000

0.995

0.990

0.985

0.980

Ref

lect

ance

100806040200

ω (cm-1)

Normal State T = 0.9 Tc T = 0.6 Tc T = 0

2∆ Drude absorption

Drude reflectance Γ

2∆

Minimum excitation energy:Cooper-pair breaking 2∆

Diamond: the “silicon” of the future?

Oppenheimer Diamond 254.7 carats

Takenouchi-Kawarada-Takano Diamond film : 0.7 carats

A diamond-based electronics?

nChemical Vapor Deposition films: less expensive and suitable for devices

nMechanically stable

nLarge-gap insulator (5.5 eV)nExcellent thermal conductivity (2 to 4 times that of Cu)

nStrong hole-doping already obtained

(nh >1022eh/cm3)

nElectron-doping comingn…and superconducting!(E.A. Ekimov et al., Nature 428, 542

(2004)).

THz Reflectivity of Superconducting Diamond

s-wave Dirty-Limit Regime; 2∆∆∆∆(2.6 K)=12±1 cm-1 2∆∆∆∆/kBTC=3.2 ± 0.5

1.05

1.00

3020100

1.00.80.60.40.20.0

T=2.6 K 3.4 K 4.6 K 7.2 K 15 K

8

6

4

2

01.00.50.0

∆ ∆ ∆ ∆ (c

m-1

)

T / TC

ω ω ω ω (THz)

Rs(

T)

/ Rn(

15K

)

ω ω ω ω (cm-1)

Mattis-Bardeen Model

ω Γ (T) : Rn (ω) = 1 - [8ωΓ(T)/ ωp2]1/2 ω 2∆(T) : Rs(ω) = 1

Peak at 2∆ in Rs/Rn

M. Ortolani, S. L. et al, PRL 2006

1.00

0.95

0.90

0.85

Ref

lect

ance

604020ω(cm-1)

T=2.6K 3.4 4.6 7.2 15

Tc=6.2 K

Absolute reflectivity and conductivity ofSuperconducting Diamond

2∆(0) = 12.5 cm-1 = 3 kBTc [BCS: 3.53]

Missing area

Penetration depth λ

λ(Τ) BCS-likeλ(0) = 1 µm(dirty limit)

M. Ortolani, S. L. et al, PRL 2007)

Which interaction is responsible for pairing?Electron-phonon coupling

The only optical phonons in diamond (~1300 cm-1=160 meV) is not IR-active, but Raman-activeThe peak in a2F(ω) indicates hole-phonon interaction.

Holes interact with a broad phonon branch centered around 140 meV:

A phonon branch appears at 70 meV with B-doping, which also interacts with the charges

α 2F(ω) ∝ W(ω ) = 12π

d 2

dω 2 [ωΓ(ω )]

α2F(ω) from theory

M. Ortolani, S. L. et al, PRL 2007

Anomalous-Drude model:

Superconducting CCa6

c-axis oriented policrystals Tc=11.4 K (G. Loupias et al, 2005)1.10

1.05

1.00

0.95

0.90

R(2

.6K

)/R

(15K

)

6 7 8 910

2 3 4 5 6 7 8 9100

ω (cm-1)

CaC6

Tc= 11.6 K

Graphite Incoherent RadiationCoherent Radiation

DiamondR(2.6 K)/R(10K)

Clean-limit regime Ca-Doped Graphite ------> No Optical Information (Gap, Penetration depth, …) about Superconducting State

M. Ortolani, S.L. et al, unpublished

CaAlSi (anisotropic superconductor)polarized gap measurements

exagonal plane c-axis

s-wave Dirty-Limit Regime both along the exagonal plane and along the c-axis:

2∆∆∆∆ab(0 K)=19±1 cm-1 2∆∆∆∆ab/kBTC=3.9 ± 0.22∆∆∆∆c(0 K)=23±1 cm-1 2∆∆∆∆c/kBTC=4.5 ± 0.2 S. Lupi et al, PRL 2007

Josephson Plasma Resonance along the c-axis of a High-Tc SC: La-Ba-Sr-Cu-O

JPR Edge at 14 cm-1 = 0.4 THz

M. Ortolani et al., Phys. Rev. B 2006

in-plane SC

in-plane SC

JPR

Tc = 36 K

Tc = 10 K

Solid-State Applications IIMetal-to-Insulator Transition

(BRILLIANCE GAIN)

Metal-to-Insulator Transition (MIT)

Theory of Metal to Insulator Transitions

High-Pressure IRSR Spectroscopy

Electron-Electron interaction and insulator-to-metal transition (MIT)

Electronic correlation: failure of band modelHubbard model

><↓↑

+ ++−=σ

σσij i

iiji nnUchcctH .).(

Pressure may increase t and therefore the t/U ratio inducing a MIT

t : hopping integral (strongly dependent on atomic distances)U : coulomb repulsion

U prevents double on-site occupancy. the opening of a gap in the

spectra of excitations is induced

Electron-Lattice interactionPeierls MIT

[from Gruner (88)]

A charge density wave (CDW) ground state develops in low-dimensional metals as a consequence of electron-phonon interaction.

Electron density, lattice distortion and single particle band in (a) the metallic state for T >TCDW and (b) in the CDW state at T = 0.The figure is for a one-dimensional, half-filled system. In this case a gap (D) opens in the single-particle spectra of excitations.

[3] G. Grüner, Density Waves in Solids, Addison Wesley (New York, 1994)

Pressure may increase t and reduce lattice distorsion inducing a MIT

IRSR Microscopy at high pressures

Force

Diamond

Gasket

Sample size<300µm

T=IT / I0

Op.D. = -ln(T) = αd

Rdiam/sam=IR / I0

Small optical troughput

Vanadium di-oxide VO2

T-dependent MIT (TMIT= 340 K) concomitant with a lattice modification from a low-T monoclinic (M1) to a high-T rutile (R) phase.

MIT Hubbard or Peierls mechanism?

Pressure dependent measurements may provide useful information

!"#$#

%&'(

)

Infrared measurements on VO2

Simultaneous measurements of reflected and transmitted intensity on a slab of VO2, 5

microns thick.

Iteratively from T and R the optical conductivity of VO2 has been obtained

A sudden increase is visible in the optical conductivity (especially in the MIR region)

above 10 GPa. A delocalized electronic state is therefore achieved in the monoclinic Peierls

state.

Spectral Weight (SW), obtained at low and high frequency shows a different behavior

below and above this pressure. E. Arcangeletti, et al PRL 2007

La0.96 Ca0.04MnO3-δδδδ

La0.8 Ca0.20MnO3

La0.75 Ca0.25MnO3

MIT transition of a manganite in the FIR

Pressure-induced MIT at 300 K

FAR-IR

A. Sacchetti et al., Phys. Rev. Lett. 2006 (sinbad@frascati)

In manganite high pressure measurements have shown that the MIT and the Curie transition are intrisically coupled

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Geological Applications: liquid inclusion in mineralsBrilliance gain

Liquid Inclusion in quarzite

Water Distribution

CO2 Distribution

3 µm

A. Perucchi, S.L. et al, 2006

Liquid Inclusion in quarzite

Infrared Spectra

Optical Image

3µm

Mapping with 3µµµµm x 3µµµµm (diffraction limited)

Chemistry

CO adsorbed molecules on Cu metallic surface

Hindered rotation

Vibration

G. Williams et al, PRL 1998



Noise less than 0.01%



How look the IR spectrum of a cell?

Medical and Biological Application of IR MicroscopyBrilliance gain

Lipids

Proteins

DNA,RNA

Vibration Frequencies correspond to finger-print for the molecule

IRSR spectrum of a single cell during mitosis


sono necessari per visualizzare quest'immagine.QuickTime™ e un

decompressore TIFF (LZW)sono necessari per visualizzare quest'immagine.

P. Dumas et al, 2004



Studying hair by IRSR microscopy



P. Dumas et al, 2004

Collective (conformational) modes of macromolecules

Absorption coefficient

Organic macro-molecules must be in an acqueus environment to function, i.e. to undergo their conformational switching at THz frequencies

needed for high power THz intensity

Frequency (THz) Frequency (THz)

THz Single Strand and double strands DNA spectra

The coupling with sugar skeleton and with the complementary base induce a splitting of the conformational modes and the appearing of low-frequency (<1.5 THz) collective vibrations.

Possibility to detect conformational changing

A. Perucchi, S.L. et al, 2005

Application to Cultural HeritageStudy of the aging of an ancient paper

Intensity of the carbonyl group along a 10 µm fiber

Aging propagates along the fiber

Perspectives

1. Mid-IR and Far-IR imaging coupled with x-ray imaging for biomedical applications;

2. THz Imaging and spectroscopy at III° Generation machines;

3. Circular polarization and dichroism in the Far-IR coupled with High-Magnetic fields

4. fs pulsed THz radiation from IV° generation machine for no-linear time-resolved spectroscopy [email protected]

* %+,- .

P. Calvani and A. Nucara, L. Baldassarre

IRS Group, University of Rome “La Sapienza”

& CNR-INFM CoherentiaM. Ortolani and U. SchadeSynchrotron BESSY II Berlin

P. PostorinoHP Group, University of Rome “La

Sapienza”& CNR-INFM Coherentia

L. De GiorgiETH ZurichL. Malavasi

Dipartimento di Chimica, University of Pavia

M. MarsiCNRS-LPSU, France

V.A. SidorovInstitute for High Pressure Physics

Troitsk, Moscow Region RussiaP. Roy&P. Dumas

Synchrotron Soleil Paris (France)G.Williams

Jefferson Laboratory (USA)

and many others…….

The SISSI-ELETTRA group: A. Perucchi, R. Sopracase

D. Eichert, L. Vaccari, F. Morgera,

M. Kiskinova

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