New Science with Next Generation Light Sources

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New Science with
Next Generation Light Sources
F. J. Himpsel BESAC, February 26, 2009
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Charge 3 from BESAC to the New Era
Committee

• Identify new science and the photon
  attributes of next generation light sources
  required to carry it out, such as
• Energy range (from vacuum UV to hard X-rays)
• Coherence
• Time resolution (femtosecond regime)
• Brilliance (average, peak)
• Polarization (circular, linear)

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Charge to the Participants of the Photon Workshop

• Identify connections between major research
  opportunities
• and the capabilities of next generation light
  sources.
• Find killer applications that could become
  scientific drivers.
• Emphasize energy-related research and life
  sciences.
• Consider the VUV to X-ray range and include
  both accelerator-
• based light sources and laser-based sources.
• Do not choose a specific light source design,
  consider only the
• photon attributes required for the most
  promising research.
• Strong coupling of theory and experiment.

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Program of the Photon Workshop ? 100
Participants, chaired by W. Eberhardt and F. J.
Himpsel

• Overview talks
• Energy (Crabtree, ANL)
• Life Sciences (Moffat, Chicago)
• Next Generation Light Sources
• Free Electron Lasers (Pellegrini, UCLA)
• Energy Recovery Linacs (Hofstaetter, Cornell)
• High Harmonic Lasers (Sandner, Germany)
• Next Generation Storage Rings (Martensson,
  Sweden)
• Breakout Groups
• Extensive discussions, write-up of highlights
  (1½ days)

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Breakout Groups
Coordinator 1. Nanoscale Electrons and
Spins Hermann Dürr (Berlin) 2. Correlated
Electrons Z. X. Shen (Stanford) 3. Catalysis
and Chemistry Robert Schlögl (Berlin) 4.
Nano-Materials for Energy Applications Rick
Osgood (Columbia) 5. Life Sciences Janos
Kirz (Berkeley) 6. Atomic and Molecular Physics
Nora Berrah (West. Michigan) 7a. Matter
under Extreme Environments Rus Hemley (Carnegie
Inst., DC) 7b. Environmental Science, Earth
Science Gordon Brown (Stanford) 8. Novel
Structural and Electronic Materials Julia
Phillips (Sandia) 9. Cross-Cutting Issues
John Hemminger (Irvine) Generated an
extensive number of scientific opportunities (coll
ected in Section 4, the largest section)

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• Findings
• Five Cross-Cutting Challenges
• Three Stages of Difficulty

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Three Stages of Difficulty

• Stage A
• Widest range of applications, largest user
  community
• Least aggressive in terms of machine requirements
  
• (but clearly beyond available light sources)
• Stage B
• Novel experiments, demanding a new kind of light
  source
• Widespread applications, many potential users
• Could become the centerpiece of next generation
  light sources
• Stage C
• Most aggressive, highest risk, but also high
  potential payoff

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The Sweet Spot Stage B

• The active Fe6Mo center of nitrogenase,
• Natures efficient way of fixing nitrogen
• Resolve the chemical reaction steps in time.
• What are the resulting structural changes ?
• Determine the charge flow by spectroscopy.

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Comparison with the NSF Study http//www.nsf.gov/a
ttachments/109807/public/LightSourcePanelFinalRepo
rt9-15-08.pdf
The Science Case

• Two new scientific frontiers, similar to our
  two bullets
• (except for reverse order, technique instead of
  scientific challenge)
• Developed independently

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The Berkeley Workshop Report https//hpcrd.lbl.gov
/sxls/Workshop_Report_Final.pdf

• Scientific areas addressed by new light sources
• Chemical Physics
• Atomic, Molecular, and Optical Physics
• Magnetization and Spin Dynamics
• Correlated Materials
• Exploration of Nanoscale Dynamics and Complexity

No light source in existence, under
construction, or on the drawing board can deliver
the beams required for the cutting edge science
described in this document.
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The White Paper from the DOE Light
Sources http//www-ssrl.slac.stanford.edu/aboutssr
l/documents/future-x-rays-09.pdf
Scientific drivers
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Core Electrons Sharp
Deep
Valence Electrons
Photon Energy Wave- length
Protein Crystallo- graphy
Lithography, Nanostructures
Proteomics
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Chemical Information from X-ray Absorption
Spectroscopy Core to Valence Transitions 1s ?
2p (?, ?) , 2p ? 3d,
Sharp levels (lt1keV) for bond orbitals Deep
levels (gt1keV) for dilute species
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Examples for New Possibilities
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Organic Molecules with a Transition Metal as
Active Center (LEDs, Solar Cells, Enzymes
Bio-Catalysts)
Detect oxidation state, spin state, ligand
field for one Fe atom.
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What Happens during a Photochemical Reaction ?
These measurements on the 100 picosecond time
scale provide information about spin excitations
and their lifetime. To learn about structural
dynamics one needs 100 femtosecond (fs) time
resolution, and for electronic excitations a
few fs . That is only possible with next
generation light sources.
X-ray absorption spectra of a solvated organic Fe
complex for the low-spin ground state (blue) and
an excited high-spin state (red).
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Spatially Resolved Catalytic Reactions
Chemically resolved, but insufficient spatial
resolution
Want this chemically resolved
Fischer-Tropsch process for con-verting coal to
liquid fuel.
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Fast Switching of Spins
Low-power electronics Switching of spins
requires little energy, but can it be fast? The
limit is given by the uncertainty relation.
Surprisingly-fast switching of spins in the
femtosecond range. How did the angular momentum
get absorbed ?
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Proteins in Action
Can observe slow recombination, but not yet the
fast initial biochemical reaction.
Time-evolution of a protein structure after
stimulating the Fe atom in the heme.
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Spectroscopy of Isolated Nanoclusters with
Well-Defined Atomic Structure
Control materials atom by atom.
The energy gap between the highest occupied and
lowest unoccupied energy level of mass-selected
atomic clusters. Need higher photon energy to
see all the other energy levels.
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Towards Spectroscopy of an Isolated Nano-Object
Reach atomic precision in nanotechnology.
Optical spectra of self-assembled quantum dots
show a broad continuum due to the size
distribution. Selecting fewer dots with smaller
apertures reveals the discrete line spectrum
expected from an isolated dot ( artificial
atom). Need higher photon energy to access all
levels, including core levels.
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Conclusions Two science drivers (killer-apps)
for new light sources are identified which
combine the deepest science impact with the
broadest user base

• Femtosecond time resolution opens completely new
  territory where atoms can be followed in real
  time and electronic excitations can be resolved
  down to their intrinsic time scale.
• Sub-nanometer spatial resolution opens the
  length scale where quantum confinement dominates
  electronic behavior and where catalytic activity
  begins. Spectroscopy of individual
  nanometer-scale objects rather than
  conglomerates will eliminate blurring of the
  energy levels induced by the size and shape
  distribution and thereby reveal active sites in
  catalysis and the traps where electrons are lost
  in photovoltaics.

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Backup Slides
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Cross-Cutting Challenges Stage A

• Designing Materials, Controlling Processes
• The Synthesis-Analysis-Prediction-Loop
• Materials Complex materials with correlated
  electrons, operating devices, batteries,
  supported catalysts, organic conductors for
  photovoltaics, lighting, quantum-engineered
  cluster assemblies
• Interfaces In-situ, buried, nano-structured,
  bio-inorganic, sequestration, grain boundaries in
  solar cells and superconductors, damage in
  nuclear reactor materials
• Catalysts For artificial photosynthesis,
  splitting water, in realistic situations
  (presence of gases, liquids)
• Static measurement (time-resolved in 2.,
  spatially-resolved in 3., both in 5.)

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Cross-Cutting Challenges Stage B

• 2. Real Time Evolution of Chemical Reactions,
  Movements of Electrons and Spin
• Photovoltaics, Photosynthesis Harvest sunlight
  efficiently and economically
• Reactions at defects Loss of (photo)electrons,
  radiation damage, in real time
• Spintronics How fast can one switch spins
• Chemical reaction mechanisms Catalysis,
  biochemistry in real time
• Individual Nano-Objects
• Atomic clusters Tailoring new forms of matter
  with atomic precision
• Nanocrystals Beating the size distribution
• New materials Find the electronic structure of
  a small crystallite
• Large protein assemblies From proteomics to
  cells

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Cross-Cutting Challenges Stage C

• Statistical Laws of Complex Systems
• Fluctuations of floppy spins and soft materials
  at the nanometer scale
• Utilize the full coherence and high degeneracy
  of a laser
• Utilize a shaped pulse to reach the minimum
  uncertainty product
• Small and Fast
• Resolve the coupled motion of electrons and
  nuclei
• Imaging of elementary chemical reactions at the
  molecular level
• Electrons travel nanometers in femtoseconds,
  challenging the limits of combined spatial
  and temporal resolution

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Measuring S(q,?) by Resonant Inelastic X-ray
Scattering (RIXS)

• Complete characterization of a solid
• Find the boson that pairs electrons in high
  temperature superconductors
• Need 10x better energy resolution and
  statistics to be relevant

RIXS data from a high temperature superconductor
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Coherent Imaging

• 3D
• Chemical image, phase image, optimum use of
  photons (min. damage)
• Beyond protein crystallography towards larger
  objects, proteomics

Coherent diffraction from a yeast cell
Reconstruction
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Imaging Wave Functions

• Obtain the wave function of electrons in
  nano-objects
• Transfer lensless imaging techniques from
  photons to electrons
• Needs strong coupling to theory to describe
  multiple electron scattering

Angle-resolved photoemission data, transformed
from reciprocal space to real space.
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Combine Coherent Diffraction with Time
ResolutionReveal Simple Statistical Laws of
Complex Systems
Speckle pattern of CoPt film at ? 1.6 nm
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Small and Fast

• Ultrafast optoelectronics via plasmonics
• Electron velocity in metals ? nm/fs
• Electron lifetime in metals ? 10 fs ?
  mean free path ? 10 nm

Light trapped in nanometer-sized Ag structures
during femtoseconds via localized plasmons
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Interference Lithography

• Large-scale nano-patterning at ? 13 nm (EUV
  lithography)
• Controlled placement of self-assembled units
  (dots, wires, biomolecules)
• Patterned high-density data storage media

Flat substrate block-copolymer
Patterned substrate Size of a molecule determines
linewidth, smoothness