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High Pressure Spectroscopies at HPCAT

High Pressure Spectroscopies at HPCAT. Yuming Xiao. Outline. Introduction X-ray Emission Spectroscopy (R/XES) Nuclear Resonant Scattering (NRIXS/NFS) Inelastic X-ray Scattering (IXS/XRS) Future Developments. Synchrotron Spectroscopies under High Pressure. Challenges:

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High Pressure Spectroscopies at HPCAT

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  1. High Pressure Spectroscopies at HPCAT Yuming Xiao

  2. Outline • Introduction • X-ray Emission Spectroscopy (R/XES) • Nuclear Resonant Scattering (NRIXS/NFS) • Inelastic X-ray Scattering (IXS/XRS) • Future Developments

  3. Synchrotron Spectroscopies under High Pressure • Challenges: • small samples (~a few tens µm in diameter and thickness) • background scattering from other DAC components Spectroscopic methods already applied to HP studies: XFS XAS(XANES, EXAFS) XMCD R/XES HERIX MERIX IXSXRS SAXS NRS (NRIXS, NFS) XPCS DAC (Diamond Anvil Cell) • Strategies at 16 ID-D: • variable focused sizes depending on experimental requirements (large 1-meter long KB mirrors to maximize flux at sample position or portable 200mm long KB mirrors to minimize beam size) • increase solid angle collection (mini-XES, polycap-XES, 17-element system for XRS) • post-sample collimation (tweezers slit, polycapillary lens for IXS)

  4. 16 ID-D of HPCAT

  5. A dedicated XES/RXES setup coupled to the main 2.7 m spectrometer X-ray Emission Spectroscopy One 4-inch analyzer Amptek Si SSD Low temperature (down to ~10k) online ruby membrane control Rueff & Shukla, Rev.Modern. Phys., 2011

  6. XES of Ce across the γ-αVollume Collapse Transition • satellite structure of cerium : the exchange interaction of the 4f with the 4d level • comparison with the very weak structure of CeO2 at ambient conditions shows that cerium’s moment reduces by approximately 30 % across the volume collapse. • the data lend further support to the Kondo volume collapse model • a general experimental methodology to study relevant strongly correlated f-electron systems Lipp et al. Phys. Rev. Lett., 109, 195705 (2012)

  7. HP Evolution of Fe2O3 Electronic Structure Revealed by PFY-XAS • High-spin insulator to low-spin metal transition was reflected in the pre-edge of XAS spectra. • Crystal-field splitting energy was found to increase monotonically with pressure up to 48GPa • Ligand hybridization significantly reduces the critical high-spin/low-spin transition pressure Wang et al. Phys. Rev. B 82, 144428 (2010)

  8. SWD XES and Polycapillary XES Pacoldet al. J. Syn.Rad.,19,245-251 (2012) Bradley et al. Phys. Rev. B., 85, 100102 (2012) Mortensen et al. unpublished

  9. Nuclear Resonant Scattering NRIXS density of states (DOS):vibrational kinetic energy, vibrational entropy, Debye temperature, and Debye sound velocity NFS hyperfine interactions parameters: valence, spin state and magnetic ordering

  10. Pressure-Induced Invar Behavior in Pd3Fe • The NFS revealed a collapse of the 57Fe magnetic moment between 8.9 and 12.3 GPa at 300 K, coinciding with a transition in bulk modulus found by XRD • Heating the sample at 7GPa showed negligible thermal expansion from 300 to 523K Winterrose et al. PRB 83, 134304 (2011) Winterrose et al. PRL 102, 237202 (2009)

  11. FeSe under High Pressure tetragonal P4/nmm hexagonal P63/mmc LT orthorhombic Cmma HP orthorhombic Pbnm Kumar et al. APL, 2011 Kumar et al. J.Phys.Chem. B, 2010

  12. Inelastic X-ray Scattering Back scattering energy 9.886keV 17 2-inch Si ( 5 5 5) analyzers Amptek Si SSD Energy resolution 1eV XRS light element (C, B, N, etc.) K –edge XAS under high pressure IXS electronic band structure, excitons, plasmons and their dispersion under high pressure

  13. Amorphous Diamond: A High Pressure Superhard Carbon Allotrope • observed a new carbon allotrope with a fully sp3-bonded amorphous structure and diamond-like strength by compressing glassy carbon above 40 GPa • XRS revealed a continuous pressure induced sp2-to-sp3 bonding change • XRD confirmed the perseverance of non-crystallinity • transition was reversible upon releasing pressure Lin et al. Phys. Rev. Lett. 107, 175504 (2011)

  14. Electronic Structure of Crystalline 4He under HP • rich electron excitation spectrum • a sharp excitation peak showing linear volume dependence • determined electronic dispersion along h00 direction and provided a quantitative picture of helium exciton beyond the simplified Wannier-Frenkel description Mao et al. Phys. Rev. Lett. 105, 186404 (2010)

  15. Polycapillary Collimation for IXS • focus length ~3.5mm • focus size ~20µm • exit focus size ~150µm • exit cone ~2.5° secondary focus source to IXS analyzer

  16. Future Developments • Better beam focus • 5x5µm regularly, special case for 1 (V) x 5 (H)µm or even 1x1µm • ~100meV IXS • multi-analyzer XES • in-line HRM • Integration

  17. Acknowledgements • HPCAT • Paul Chow • Genevieve Boman • Eric Rod • Curtis Kenny-Benson • Arun Bommannavar • Guoyin Shen HPCAT 16 ID-D Users HPCAT is supported by CIW, CDAC, UNLV and LLNL through funding from DOE-NNSA, DOE-BES and NSF. APS is supported by DOE-BES, under Contract No. DE-AC02-06CH11357.

  18. Thank you!

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