Cold ablation driven by localized forces: a femtosecond electron diffraction study

Transcription

1 Cold ablation driven by localized forces: a femtosecond electron diffraction study Masaki Hada*, R. J. Dwayne Miller Atomically Resolved Dynamics Division, Max Planck Institute for the Structure and Dynamics of Matter *Present address: Tokyo Institute of Technology, JST-PRESTO

2 Acknowledgements Hamburg (MPSD) R. J. Dwayne Miller German Sciaini Kostyantyn Pichugin Stuart Hayes Alexander Marx Stephanie Manz Regis Gengler Shin-ichiro Ideta Gaston Cothey Günther Kassier Julian Hirscht Dongfang Zhang Sercan Keskin Albert Casandruc Univesity of Toronto Gustavo Moriena Hubert Jean-Ruel Ray Gao Lai Chung Liu Tokyo institute of Technology Tadahiko Ishikawa Shin-ya Koshihara RIKEN Mitsushiro Nomura Reizo Kato Kyoto University Jiro Matsuo Toshio Seki Edinburg University Michał Kochman Derek Wann Carole Morrison

3 Outline Electron diffraction setup Motivation DC gun, RF gun, Relativistic gun Pulse characterization Science with electron diffraction Single-shot experiment KI Cold ablation driven by localised forces Multiple-shot experiment Pt(dmit) 2 Coherent phonon in large lattice material

4 Femtosecond electron diffraction Optical pump Electron probe method Optical pump Electron diffraction pattern X-ray diffraction pattern (line) Pulsed electron (X-ray) probe Crystal sample How a molecular moves at the femtosecond time scale? Optical delay Δτ 30 um = 100 fs F. Schotte, et. al., Science 300, (2003)

5 Electron diffraction studies from Toronto Al, Au, Bi, Si melting TaS 2 CDW M. Eichberger et al, Nature 468, 799 (2010). G. Sciaini et al, Nature 458, 56 (2009). (EDO-TTF) 2 PF 6 Diarylethene Phase transition M. Gao et al, Nature 496, 343 (2013).

6 Electron vs X-ray Electrons (100 kev) X-ray (10 kev) Wavelength [Å] Mechanism of radiation damage Ratio (inelastic/elastic) scattering events Energy deposited relative electron per elastic event Secondary electron emission Photoelectric >1000 Elastic mean free path Coherence length 1 10 nm >1 µm

7 XFEL and Electron gun LCLA/ Stanford SACLA/ Spring8 European XFEL/ DESY ~100 kev DC electron gun/ Hamburg

8 DC Femtosecond electron diffraction anode Magnetic lens Sample on TEM mesh Optical pulses 800 nm, 400 nm Optical pulse (266 nm) Photo cathode -100 kv Pulsed electron Accel voltage : kv Pulse duration : fs Electron density: electrons/pulse Electron diffraction pattern

9 Femtosecond Electron diffraction + RF Buncher Machine 100 kev 10 Hz e/pulse IRF 400 fs (FWHM) M. Gao, H. Jean-Ruel et al., Opt. Express 20, (2012). REGAE 3 5 MeV 12.5 Hz e/pulse IRF <50 fs (FWHM)

10 Pulse characterization Ponderomotive -500 fs -250 fs 0 fs 250 fs 500 fs

11 Streak camera Günther Kassier Pulsed electron Photo switch CCD camera Without streak Streak plate With streak 0.05 HV pulser 0.04 Signal [arb. u.] /- 40 fs Delay time [ps] G. Kassier et al., Appl. Phys. B 109, 249 (2012)

12 Outline Electron diffraction setup Motivation DC gun, RF gun, Relativistic gun Pulse characterization Science with electron diffraction Single-shot experiment KI Cold ablation driven by localized forces Multiple-shot experiment Pt(dmit) 2 Coherent phonon in large lattice material

13 Single-shot experiment Melting, Ablation and irreversible reactions Single or highly-oriented crystal sample Homogenous and large area sample Julian Hirscht Dongfang Zhang

14 Si nonthermal melting Nonthermal melting in Si! P. Stampfli et al. Phys. Rev. B 49, 7299 (1994)

15 Strong localized force in alkali halides anion cation Potential energy [ev] Na + Cl - Pauli repulsion well Na* Cl hν Na-Cl distance [nm] Self-trapped exciton, color center formation

16 Sample preparation KI thin crystals 3000 Self standing SiN (30 nm) mesh by chemical etching process Pre-annealed (400 degrees) Thermal deposition of KI (50 nm) Coating with Carbon (4 5 nm) Intensity [cps] KI (200) KI (400) C (4 5 nm) KI (50 nm) SiN (30 nm) Si substrate Intensity [cps] KI(200) Gauss fitting

17 Optical studies R/R R/R mj/cm 2 35 mj/cm mj/cm mj/cm mj/cm mj/cm Si CsI Time delay [ps] 70 mj/cm mj/cm mj/cm mj/cm mj/cm mj/cm J/cm KI mj/cm NaCl 120 mj/cm mj/cm mj/cm Time delay [ps]

18 Sample surface after irradiation depth [nm] KI X axis [ m] 180 mj/cm2 depth [nm] mj/cm Si mj/cm2 Depth [nm] Y axis [ m] 0 CsI 140 mj/cm2 200 Y axis [ m] mj/cm 60 mj/cm Distance ( m) X axis [ m] Micron deep crater formation in alkali halides with low laser fluence 2 200

19 Micron deep crater in alkali halides F Depth (Si) F Depth (NaCl) 350 mj/cm 2 26 nm 420 mj/cm nm 210 mj/cm 2 16 nm 350 mj/cm nm 70 mj/cm 2 9 nm F Depth (KI) F Depth (CsI) 180 mj/cm 2 >2500 nm 280 mj/cm nm 120 mj/cm nm 140 mj/cm nm 60 mj/cm nm 105 mj/cm nm

20 Electron diffraction (020) (022) F = 140 mj/cm 2 Absorption = ~2% Film thickness: 50 nm 2-photon absorption Norm. intensity [arb. u.] ps +30 ps +1.8 ns (020) (022) s [Å -1 ] Temperature raise ~780 K (melting point 954 K) Excited halide center ~4%

21 Thermal? Plasma? 1.2 Norm. intensity % 55% (020) plane 140 mj/cm 2 (022) plane 140 mj/cm 2 (020) plane ~1 J/cm 2 89% 82% E9 Time delay [ps] 1200~1800 K I F D M K G K f K D K exp 2 ik r j F K exp 2 j 1 j j 8 U sin j K B exp 8 exp j K U j 2 j 725 ±110 K Plasma generation

22 Localized force in alkali halides R/R (a) Recrystallization Thermalization 4% KI excitation (halogen centers) Inhomogeneous Local photoexciation lattice disorder stress (stress) These defects and disordered regions introduce strong electronic stress that leads to the expulsion of material. R/R (b) Frequency [GHz] Magnitude /- 1.9 GHz delay time [ps]

23 Multiple shot experiments Photoinduced repetitive reactions Single crystal Large structural modification Find a proper material

24 Me 4 P(Pt(dmit) 2 ) 2 HT phase (>215 K) Å Paramagnetic metal 37 Å 29 Å LT phase (>215 K) 0-2 Stuart Hayes Tadahiko Ishikawa Collaboration work Miller Group, Max Planck Institute Koshihara Group, Tokyo Institute of Technology Kato Group, RIKEN Charge-ordered state Non magnetic insulator

25 Sample preparation Microtome the sample down to 150 nm Sercan Keskin

26 Coherent phonon oscillation Crystal with large lattice parameters We can go for protein crystals!? We observed the coherent phonon oscillation We have not put the index yet

27 Thank you for your attention!