one of the most exciting fields of condensed matter science

1. Promising emulsion-detection technology for ultrafast time-resolved study of structural phase transitions Katsumi Tanimura, Condensed Matter Science Division The Institute of Scientific and Industrial Research, Osaka University ultrafast crystallography by MeV-electron diffraction one of the most exciting fields of condensed matter science

2. photons electron-photon interaction lattice system (phonons) electronic system electron-phonon interaction a system of charged particles with high velocities v <<c solids (many-body system in complete dark) example: structures of Si

3. Solid State Physics (traditional) physical understanding of several properties of given solids (crystals) structural, electronic , magnetic, optical, etc targets: solids, given by nature, or fabricated thermodynamically limited functions for device performance (for human life) Nanotechnology (current Condensed Matter Science) artificial fabrication of solid structures from atomic levels in order to generate desired functions one needs “fight” against nature (equilibrium, adiabatic processes) how ?

4. Photons in Action !! controlling bonding orders in solids photoinduced new surface-phase creation photoinduced structural phase transitions

5. phase transition: one of the most typical phenomena of solids solids: quantum many-body system several modes of interactions electronic structural （phase, electronic, magnetic, structural, etc） structural phase transition： dramatic changes in symmetry, structures, and electronic properties 　（multi-stability of condensed phase） an example: graphite diamond traditional studies： 1）structures and electronic properties of thermodynamically stable (metastable) phases 2）transition dynamics on quasi-static processes thermodynamicl transitions：simultaneous excitation of all degrees of freedom! impossible to detect, elucidate, and control a given fundamental process involved no way to control modes of condensation !!

6. Energy photoexcitation metastable photoinduced Graphite-to-Diamond transition thermal excitation stable Photoinduced Phase transitions light transitions in non-equilibrated systems by external stimulation initial changes only in the electronic systems: selective excitation lattice electrons real-time detection of a given fundamental process triggered (10-13 s) (10-15 s) significance 1) microscopic study (atomic, temporal) of macroscopic transitions revealing the crucial process that governs the modes of condensation 2) ”hidden phases” unable to be reached by thermodynamical processes！ new structures (phases) creation

7. graphite STM tip 798nm ( 1.57eV ) 80 fs 100~1kHz a direct probe of atomic structures of solids: Scanning Tunneling Microscope (STM) (hexagonal graphite) surface atomic arrangement of InP(110) spatial resolution (<10-8cm） atomic resolution!

8. lex=800 nm w=80 fs p-polarized STM-image structures changes in a large-scale area (d~20nm) including ~104 C atoms photoinduced phase transition depressed periodically ! STM observation of photoinduced phase transition on Graphite surface after irradiation prior to irradiation completely absent prior to irradiation

9. “ Diaphite ” back bonding via sp2 sp3 bond-order change a new phase of diamond (?) photoinduced structural transformation on graphite surface not conventional Diamond formed thermodynamically! a new phase of C specific to photoexcitation ! mode of atomic displacements

10. issues to be solved STM observation of new phases signature of ultrafast transformation processes probed by optical technique (reflection changes) DR/R fs-laser pulse dynamics of phase transition Diaphite direct structural information in fs-temporal domain

11. faulted half unfaulted half adatom rest atom structural determination by electron diffraction: typical examples Our goal: • transmission electron diffraction (TED) • detecting bulk properties • 2) single-shot detection • for studying irreversible processes • 3) time resolution less than 100 fs (10-13s) • for ultrafast dynamics K. Takayanagi et al. J. Vac. Sci Technol A3 (1985) 1502 Si(111)-(7x7): a typical example of surface reconstruction 1) a new type of photocathode RF gun to generate MeV e- beams 2) highly sensitive detection of MeV electrons

12. Femtosecond time-resolved electron diffraction studies: a trend examples of the research efforts

13. advantages and issues in the femtosecond time-resolved electron diffraction ultrafast and direct structural determination！ advantages over X-ray diffraction 1）time resolution better than 100fs: possible 2）elastic scattering cross-section: larger than X rays by a factor of 1000 highly sensitive detection and significant reduction of any inelastic effects 3）high precision in beam control (great progress in electron microscope technology) challenges: B. J. Siwick et al (2004) space-charge induced broadening effects ! generation of electron pulses with width less than 100 fs: easy propagation dynamics of short electron pulses: destroying temporal and energy characteristics

14. Science, 318, 788 (2007) (CALTECH) issues to be overcome • reflection mode • only surface regions • 2) high repetition rate (1 kHz) • only for reversible processes

15. Ultrafast Transmission Electron Diffraction system under construction beam characteristics for UTED • temporal width ＜100 fs • DE/E<0.05% • emittance <0.1 mm-mrad • Energy：1~4MeV • 5) number of electrons per pulse：as many as possible

16. summary of particle simulation femtosecond laser RF l=262, 266nm 2856MHz、~MW＠4ms photocathode RF cavity ~100MV/m solenoid magnet temporal width：< 100 fs emittance： 0.02mm-mrad DE/E：<2x10-4 beam energy (E): ~2 MeV beam size: r=0.2 cm number of e-：<106/pulse (~0.1pC/pulse )

17. answer (promising!!) emulsion detection; sensitivity of one-electron detection! 3D-automatic imaging technique (Niwa’s group; Ngoya Univ.) This is our hope! final message (love call) to nuclear emulsion technology! ultrafast (<10-13s) single-shot structural analysis: Dt<10-13 s challenge highly sensitive detection of MeV electrons !