New Science with Next Generation Light Sources F. J. Himpsel BESAC, February 26, 2009

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) Charge 3 from BESAC to the New Era Committee

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. Charge to the Participants of the Photon Workshop

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)

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 (collected in Section 4, the largest section)

Findings Five Cross-Cutting Challenges 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

The Sweet Spot: Stage B The active Fe 6 Mo center of nitrogenase, Nature’s efficient way of fixing nitrogen: Resolve the chemical reaction steps in time. What are the resulting structural changes ? Determine the charge flow by spectroscopy.

Comparison with the NSF Study Two new scientific frontiers, similar to our two bullets (except for reverse order, technique instead of scientific challenge) Developed independently The Science Case:

The Berkeley Workshop Report “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.” Scientific areas addressed by new light sources: (1)Chemical Physics (2)Atomic, Molecular, and Optical Physics (3)Magnetization and Spin Dynamics (4)Correlated Materials (5)Exploration of Nanoscale Dynamics and Complexity

The White Paper from the DOE Light Sources Scientific drivers:

Consider the Traditional Split between “UV” and X-ray Light Sources Gratings Crystals Electronic StructureAtomic Structure Lithography, Nanostructures Photon Energy Wave- length 10eV100eV1keV 10keV 10nm100nm1nm1Å Valence Electrons Core Electrons Sharp Deep Protein Crystallo- graphy Proteomics

Magnetism Environment Chemical Information from X-ray Absorption Spectroscopy Core to Valence Transitions : 1s  2p (  *,  *), 2p  3d, … Sharp levels (<1keV) for bond orbitals Deep levels (>1keV) for dilute species Bio Catalysts

Examples for New Possibilities

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.

What Happens during a Photochemical Reaction ? X-ray absorption spectra of a solvated organic Fe complex for the low-spin ground state (blue) and an excited high-spin state (red). 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.

Spatially Resolved Catalytic Reactions Want this chemically resolved Chemically resolved, but insufficient spatial resolution Fischer-Tropsch process for con- verting coal to liquid fuel.

Fast Switching of Spins Surprisingly-fast switching of spins in the femtosecond range. How did the angular momentum get absorbed ? Low-power electronics: Switching of spins requires little energy, but can it be fast? The limit is given by the uncertainty relation.

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.

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.

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.

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.

Backup Slides

Cross-Cutting Challenges: Stage A 1.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.)

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 3.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 Cross-Cutting Challenges: Stage B

4.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 5.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 Cross-Cutting Challenges: Stage C

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

Coherent Imaging Coherent diffraction from a yeast cell Reconstruction 3D Chemical image, phase image, optimum use of photons (min. damage) Beyond protein crystallography towards larger objects, proteomics

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.

Speckle pattern of Co:Pt film at = 1.6 nm Combine Coherent Diffraction with Time Resolution Reveal Simple Statistical Laws of Complex Systems

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

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