Picosecond needs for phonon dynamics in nanoscience / energy science

1. Picosecond needs for phonon dynamics in nanoscience / energy science Yuelin Li, X-ray Science Division, Argonne National Laboratory

2. Thermoelectricity and energy future • 90% of US power is from heat engines with efficiency at 30-40%, thus about 15 TW of heat is lost to the environment • Thermoelectric devices can potential convert part of these into electricity. At 1% level, this is equivalent to the total power of 100 1 GW nuclear power plants. • Solar thermoelectricity • However: efficiency/economics are the key • Figure of merit ZT=S2sT/k K: heat conductivity

3. Thermal electricity and nanoscience: Engineering in thermal electric systems • Link the function and structure at nanoscale • Use nanostructure to manipulate energy carrier • Allow electrons to flow, block phonons • Figure of merit ZT=S2sT/k Nanoscience research for energy needs: Report of the national naothechnology initiative grad challenge workshop, http://www.sc.doe.gov/BES/reports/files/NREN_rpt.pdf

4. Bottom upAcoustic oscillation in a nanoparticles/structures • Phonon = Lattice vibration • Lattice vibration of nanoparticles: optical methods • Oscillation period T: D (particle size)/ v (sound velocity) • For gold nano particles, eg., D=10 nm gives T=3 ps (v=3240 m/s ) • Perner et al., ‘,’PRL 85, 792 (2000). • Vn Dijk et al., PRL 95, 267406 (2005). • Jerebtsov et al., PRB 76, 184301 (2007). • Courty, et al., Vibrational coherence of self-organized silver nanocrystals in f.c.c. supra-crystals. Nature Mater. 4, 395–398 (2005). • Vibration of nano super lattice • Layer structure, ps time scale • Trigo et al., ‘Probing Unfolded Acoustic Phonons with X-rays’, PRL. 101, 025505 (2008) • Bargheet et al., ‘Coherent Atomic Motions in a Nanostructure Studied by Femtosecond X-ray Diffraction,’ Science 306, 1771 (2004). Self organized silver nanoparticle and vibration GaAs/AlGaAs superlattice

5. Bottom upapproachCoupling of phonon oscillation between particle via plasmon oscillation: • SPR/lattice vibration is dependent on the particle separation Huang, et al., ‘The Effect of Plasmon Field on the Coherent Lattice Phonon Oscillation in Electron-Beam Fabricated Gold Nanoparticle Pairs,’ Nano Letters20077 (10), 3227-3234

6. Top-down approachMaterials with promising Macroscopic-property (heat conductivity) • Nano scale structures for low thermal conductivity (0.05 W m-1K-1), and ZT~2.4 • Chiritescu et al., Ultralow Thermal Conductivity in Disordered, Layered WSe2 Crystals, SCIENCE 315, 351 (2007) • Hochbaum et al., ‘Enhanced thermoelectric performance of rough silicon nanowires’, Nature 451, 163 (2008) • Boukai et al., ‘Silicon nanowires as efficient thermoelectric materials,’ Nature 451, 168 (2008) • A. Majumdar, Thermoelectricity in semiconductor nanostructures, Science 303,777 (2004). • Venkatasubramanian, et al., Thin-film thermoelectric devices with high roomtemperature figures of merit, Nature 413, 597 (2001). • Harmon et al., Quantum dot superlattice thermoelectric materials and devices, Science 297, 2229 (2002). • Challenges • Phonon dynamics unknown • Very challenging to model (for all nano sctructures!) Disordered WSe2 layers Silicon naowires

7. Time resolved x-ray measurement:Bridge the macro to nano scales: phonon/propagation • Heat = Phonon = Lattice vibration • Excite phonons: Laser pump • See phonons and propagation: x-ray probe with XRD, GISAX, …… • Requires ps resolution • Ultrafast lasers: Yes  • ps x-ray pulses: No  • ps detector: Y&N (streak camera at Sector. 7) • Theory and simulation • We already have other resources: • CNM, MSD, APS, U-Chicago, North-Western, and other • With the ps x-ray source, we can • better understand nanostructure for all purposes • design better thermoelectric material for future sustainable energy source • help others time resolved activities

8. We need the ps source!

9. Taking LCLS into account • APS Short pulse/detector vs. LCLS • Pro: • Existing infrastructure and collaboration • Stability, availability • Higher average photon flux • Better sample survivability • Con • Low peak photon flux • Mentally less dazzling • LCLS pro and con • Pro • Shorter pulse with high photon flux • Mentally more dashing • Con • Availability and beam time allocation • Sample survivability • unwilling travel for users