Vibrational Spectroscopy on Laser-Heated High Density Fluids in Diamond Anvil Cell

1. Vibrational Spectroscopy on Laser-Heated High Density Fluids in Diamond Anvil Cell Presented at Laser Heating Workshop at the APS, March 20, 2004 Choong-Shik Yoo Lawrence Livermore National Laboratory Livermore, California 94583 (yoo1@llnl.gov; (925) 422 - 5848) Collaborators Bruce Baer, Magnus Lipp, Alex Goncharov

2. N2 CO2 C H2O 10-50 GPa 1000-5000 K Giant planets 10-700 GPa 8000 K H2, He H2O, CH4, NH3 Laser-heated DAC creates the P,T conditions of energetic detonation and Giant planetary interiors Structures and stabilities of simple molecules are not known at high P,T

3. Strong disparity in bonding results in a huge kinetic barrier (metastability) T (K) Dissociation Ionization 3000 T- ionization Liquid Kinetic line Solid Atomic metal Molecular metal Molecular Associated Extended 0 100 P(GPa) P- electron delocalization Extreme materials research with laser-heated DAC for synthesis New opportunities for synthesis of exotic materials !!! Laser-heated DAC is capable of exploring a delicate balance between mechanical (PDV) and thermal (TDS) energies

4. Strong, coherently emitted CARS (Coherent Anti-stokes Raman Spectroscopy) probes molecular vibration in-situ at high P,T

5. Optical setup for CARS applied to laser-heated DAC

6. SPEC/CCD Q/CW-YLF DAC ML,QS- Nd:Yag Narrow band Dye laser Broad band Dye laser LLNL- CARS setup ready for studies of high density fluids

7. Before heating d-N2 300 K at 13 GPa W-toroid N2 100 mm Fluid-N2 2300 K at 13 GPa During heating CARS of laser-heated N2 at high pressures

8. DAC Fast spectrograph Raman Raman laser 476 nm (Ar ion) Probe Dispersive beamsplitter Hot plate Diamond cell Spatial filter Sample Laser Heating Gasket Tunable notch filters Laser heating 1053 nm (YLF) 50 W Fast spectrograph radiometry CCD camera Spontaneous Raman spectroscopy on laser-heated materials at high pressures

9. Ar-Ion laser (Spec-Phys) TEM00 -YLF (Antares) HeNe HeNe Iris PBS TEM01* YLF (Quantronix) HRLM dual coated 4xBE WP PM Lasers with different mode structures enable to heat selected areas in various configurations Heating targets can be tailored into various shapes such as flat foils, toroids, micro-furnaces, steps, etc.

10. N2 Spatial filter ~ 100 m Laser Hot donut (W) N2 at 20GPa &1700K Diamond Raman Ruby Laser Raman intensity N2 vibron Discrimination of thermal radiation using both spatial and spectral filters Planck-fit to thermal emission 39 GPa 1861 K • Spatial filtering to eliminate thermal radiation from hot donut • Raman notch spectral filter to minimize straight laser light • Use “blue” excitation to reduce thermal radiation

11. 1500 - 2000 K 2 31 GPa 12 26 GPa 1 20 GPa Spontaneous Raman spectroscopy on laser-heated N2 at high pressures The presence of n12 is evident for high temperature, yet that of n1 indicates a large temperature gradient near diamond surface

12. Laser Heating 27 GPa 39 GPa Probe ~ 1700K ~ 1820K Gasket Sample Al2O3 matrix Hot donut RT RT Thermal insulation of hot plate by Al2O3

13. Challenges in vibrational spectroscopy on laser-heated materials • Sample preparation: • Micro-fabrication of heat absorber • Thermal insulation of hot plate and sample from diamond • Highly reactive high density fluids • Laser-heating: • Uniform heating of hot plate and sample • In-situ pressure measurements • Spontaneous Raman: • Weak signal • Limited to low emissivity materials and relatively low T <2000K • Alternative routes: deep “blue”, pulse Raman, coherent Raman • CARS: • Optical transparency of sample • Diamond damage • Materials application: • Complex chemistry with multiple path ways • Difficulties in characterization: structure, order, (meta-)stability, etc

14. What are the most important experiments? • Melting and phase diagram studies above 100GPa: • Melting vs. recrystallization, amorphorization vs. phase transitions vs. diffusive motions • Melt probes: speckle pattern, reflectivity, laser power, etc. • Structural studies: • Ordered systems: polycrystals, single crystals, mixtures and alloys • Disordered systems: liquid, amorphous, glass • Novel materials applications: - Superhard, HEDM, optical, high-Tc, etc. • Mechanical properties: • Materials strength, elastic properties, plastic deformation, • Microstructures, textures, preferred orientation

15. What are the most important experiments? • X-ray spectroscopy: elastic and inelastic • Interatomic potentials, molecular configuration, electronic structure • X-ray induced chemistry: ionization, excite state fluorescence, • Real-time structural studies: • Thermodynamic(stability) vs. kinetic(metastability) • Reology and dynamics • Transport properties: thermal diffusion, viscosity, • Associated technology developments: • In-situ diagnostics for intrinsic material properties: X-ray, Raman, CARS, reflectivity • In-situ P,T probes: pyrometer, calibrated thermocouple, X-ray induced fluorescence • Internal P,T standard materials • New DAC cells: Membrane-DAC, Large volume DAC, Dynamic DAC, etc. • Laser-heating: CO2 heating, short pulse heating, • Sample fabrication: Micro-furnace, insulation,

16. What should the guiding philosophy be? • Time constraints: • Simple and easy in operation: • Optimized alignment and calibration procedures • Compatibility: • DAC in different types • Software: x-ray and laser-heating operation • Hardware: not too many computers, remote & manual controller, visual aids, fibers • Balanced approach: • Dx=10mm at 50GPa: DP~2-5%, DV~1~2%, DT~2-5% • Unknown melt diagnostic, yet DT < 10-20o (?) • Practicality: • Experimental geometry: axial and radial x-ray experiments • Integrated experiments: laser-heating with ADXD, Raman, IXS, etc. • Operational principles: • It is an x-ray experiment, not laser-heating • 24-hr operation: minimize downtime for laser alignment and sample preparation • Mentor/Buddy system: any first-time user should team up with an expert