X-Rays and Materials

A Vision of the Future

Joachim Stöhr Stanford Synchrotron Radiation Laboratory

In $$$$$'sInformation technology: 800 BillionChemical Industry: 400 BillionSemiconductors: 80 BillionMagnetic materials: 25 Billion

Pharmaceutical industry: 220 BillionBiotech Industry: 30 Billion

The big $$$ Picture: US Gross Domestic Product: $10 Trillion

Modern materials are complex – studies require sophisticated techniques

Present: Size > 0.1 m, Speed > 1 nsecFuture: Size < 0.1 m, Speed < 1 nsec Ultrafast Nanoscale Dynamics

Growth of X-Ray Brightness and Magnetic Storage Density

Why X-Rays? - Chemical Sensitivity

Core level shifts

and

Molecular orbital shifts

Stöhr et.al

Polarization Dependence

290295 300 305

NormalIncidence

C

C

C

FF

FF

FF

E

GrazingIncidence

C

C

C

FF

FF

FF

E

Nor

mal

ized

Int

ensi

ty (

a.u

.)

Photon Energy (eV)

F8 22°C

C F

C F

C O

C C

Magnetic Spectroscopy and Microscopy

Real Space Imaging

1895 1993

X-Rays have come a long way……

The Future: PEEM3

PEEM2 PEEM3 nm nm

Resolution 50 nm < 5 nm (1% transmission)

Transmission 1% 50%@ 50 nm Resolution

Relativephoton flux 1 20

RelativeFlux density 1 >1000

Source / bend EPU (arbitrary)Polarization

PEEM2 on BL 7.3.1.1

Photoemission Electron Microscopy – PEEM at ALS

4.0.3 PEEM3 Microscope

- total electron yield imaging

- no LEEM mode (as in SMART)

Resolution vs Transmission

868 870 872 874

0.00

0.05

0.10

0.15

TE

Y (

a.u.

)

Photon Energy(eV)

777 778 779

0

4

8

TE

Y (

a.u.

)

Photon Energy (eV)

m

[010]

NiOXMLD

CoXMCD

Spectromicroscopy of Ferromagnets and Antiferromagnets

AFM domainstructure at surface of NiOsubstrate

FM domainstructure inthin Co film onNiO substrate

H. Ohldag, A. Scholl et al., Phys. Rev. Lett. 86(13), 2878 (2001).

Non Resonant X-Ray Scattering

Relative Intensity: (h/ mc2)2Relative Intensity: 1

h ~ 10 keV, mc2 = 500 keV

Kortright and Kim, Phys. Rev. B 62, 12216 (2000)

Fe metal – L edge

Fe

Resonant Magnetic Soft X-ray Scattering

M

e

e’

I exp( i qrn ) fnn 2

fne' eFn(0) i (e'e)Mn Fn

(1)charge magnetic -XMCD

= f1 + i f2

Note: at resonance f1 = 0

where Fn(i) are complex

Kortright and Kim, Phys. Rev. B 62, 12216 (2000)

Small Angle ScatteringCoherence length larger than domains,but smaller than illuminated area

SpeckleCoherence lengthlarger than illuminated area

Incoherent vs. Coherent X-Ray Scattering

log (intensity)40

-20

-40

0

20

-40 -20 0 20 40

-40

-20

0

20

40

scattering vector q (m-1)

scat

teri

ng v

ecto

r q

(m

-1)

log (intensity)40

-20

-40

0

20

-40 -20 0 20 40

-40

-20

0

20

40

scattering vector q (m-1)

scat

teri

ng v

ecto

r q

(m

-1)

informationabout

domainstatistics

trueinformation

about domainstructure

Present Pump/Probe Experiments

330 ns

50 ps

X-Raypulse

Laserpulse• Pump:

Laser

• Probe: delayed photon pulse

• Vary the delay between laser and x-ray pulses

+V

Laser focus

Switch Injection device

-V

+V

Laser focus

Switch Injection device

-V

Can also produce current pulses

Storage rings

Single pass linear colliders

Development of High Energy Physics and X-Ray Sources

HEP SR

Single pass linacs

Free electron lasers (FELs)Energy recovery linacs (ERLs)

-- From storage rings to linacs --

X-Ray Brightness and Pulse Length

• X-ray brightness determined by electron beam brightness

• X-ray pulse length determined by electron beam pulse length

Storage ring Emittance and bunch length are result of an equilibriumtypical numbers: 2 nm rad, 50 psec

Linac beam can be much brighter and pulses much shorter– at cost of “jitter”

Linac Normalized emittance is determined by gun Bunch length is determined by compressiontypical numbers: 0.03 nm rad, 100 fs

• SASE gives 106 intensity gain over spontaneous emission

• FELs can produce ultrafast pulses (of order 100 fs)

LLINACINAC C COHERENTOHERENT L LIGHTIGHT S SOURCEOURCE2 Km

0 Km

3 Km

Based on single pass free electron laser (FEL)

Uses high energy linac (~15 GeV) to provide compressed electron beam to long undulator(s) (~120 m) – 200 fs or less

Based on SASE physics to produce 800-8,000eV (up to 24KeV in 3rd harmonic) radiation - 1012 photon/shot

Analogous in concept to XFEL of TESLA project at DESY

Planned operation starting in 2008

Concepts of the LCLS:

From Molecules to Solids: Ultra-fast Phenomena

Chemistry& Biology:

H2OOH + H

about 10 fs

time depends on mass and size

Condensed Matter: typical vibrational

period is 100 fsSpeed of sound is 100 fs / Å- coherent acoustic phonons

H

S

90o spin precession time 10 ps for H = 1 Tesla

Fundamental atomic and molecular reaction and dissociation processes

Fundamental motions of charge and spin on the nanoscale (atomic – 100nm size)

Note in quantum regime: 1 eV corresponds to fluctuation time of 4 fs

transversely coherent X-ray pulse from LCLS

sample

X-Ray Photon Correlation Spectroscopy Using Split Pulse

In picoseconds - nanoseconds range:Uses high peak brilliance

sum of speckle patternsfrom prompt and delayed pulses

recorded on CCD

I(Q,t)

splitter

variable delay t

t

Con

tras

t

Analyze contrastas f(delay time)

10 ps 3mm

TransmissionX-ray

Microscope

Reconstructionfrom

Speckle Intensities

5 m(different areas)

Single shot Imaging by Coherent X-Ray Diffraction

Phase problem can be solved by “oversampling” speckle image

S. Eisebitt, M. Lörgen, J. Lüning, J. Stöhr, W. Eberhardt, E. Fullerton (unpublished)

Mag

neti

zati

on

Temperature t = (T-Tc) / Tc

Tc

Spin Block Fluctuations around Critical Temperature

T < Tc T Tc T > Tc

Structural Studies on Single Particles and Biomolecules

Proposed method: diffuse x-ray scattering from single protein moleculeNeutze, Wouts, van der Spoel, Weckert, Hajdu Nature 406, 752-757 (2000)

Implementation limited by radiation damage:

In crystals limit to damage tolerance is about 200 x-ray photons/Å2 For single protein molecules need about 1010 x-ray photons/Å2 (for 2Å resolution)

LysozymeCalculated scattering pattern from lysozyme molecule

Conventional method: x-ray diffraction from crystal

X-Ray Diffraction from a Single Molecules

Just before LCLS pulse

Just after pulse

A bright idea:

Use ultra-short, intense x-ray pulse to produce scattering pattern before molecule explodes

Long after pulse

The million dollar question: Can we produce an x-ray pulse that is short enough? intense enough?

X-FELs will deliver:

unprecedented brightness and femtosecond pulses

Understanding of laser physics and technology well founded

FELs promise to be extraordinary scientific tools

Applications in many areas:

chemistry, biology, plasma physics, atomic physics,

condensed matter physics

Summary

The End