A5049218019- High-pressure geophysics and materials
- Geological and Geochemical Analysis
- Advanced Chemical Physics Studies
- Inorganic Fluorides and Related Compounds
- Nuclear Materials and Properties
- Rare-earth and actinide compounds
- Ion-surface interactions and analysis
- Geomagnetism and Paleomagnetism Studies
- Diamond and Carbon-based Materials Research
- Phase Equilibria and Thermodynamics
- Astro and Planetary Science
- Quantum, superfluid, helium dynamics
- X-ray Diffraction in Crystallography
- Earthquake Detection and Analysis
- Microstructure and mechanical properties
- Energetic Materials and Combustion
- X-ray Spectroscopy and Fluorescence Analysis
- Perovskite Materials and Applications
- Crystallography and molecular interactions
- Crystal Structures and Properties
- Glass properties and applications
- Electronic and Structural Properties of Oxides
- Nanocluster Synthesis and Applications
- Advanced Optical Sensing Technologies
- Multiferroics and related materials
Carnegie Institution for Science
2014-2022
University of Chicago
2017-2021
Geophysical Laboratory
2014-2020
Howard University
2014-2019
Washington University in St. Louis
2011-2015
Formation of uranium polyhydrides UH 5–9 is predicted using the evolutionary algorithm USPEX and proved by high-pressure synthesis.
Earth core is composed of iron (Fe) alloyed with light elements, e.g., silicon (Si). Its thermal conductivity critically affects structure, evolution, and dynamics, as it controls the magnitude compositional sources required to sustain a geodynamo over history. Here we directly measured conductivities solid Fe Fe-Si alloys up 144 GPa 3300 K. 15 at% Si in substantially reduces its by about 2 folds at 132 3000 An outer would have 20 W m-1 K-1, lower than pure similar pressure-temperature...
Electron attachment to closed-shell molecules is a gateway various important processes in the gas and condensed phases. The properties of an electron-attached state, such as its energy lifetime well character molecular orbital which electron attached, determine fate anion. In this experimental theoretical study copper silver fluoride anions, we introduce new type metastable anionic state. Abrupt changes photoelectron angular distributions point existence autodetaching states....
Excimers, a portmanteau of "excited dimer", are transient species that formed from the electronic interaction fluorophore in excited state with neighbor ground state, which have found extensive use as laser gain media. Although common molecular fluorophores, this work presents evidence for formation excimers new class materials: atomically precise two-dimensional semiconductor nanoplatelets. Colloidal nanoplatelets CdSe display two-color photoluminescence resolved at low temperatures one...
Raman and optical spectroscopy are versatile tools for nondestructive characterization of a wide range properties novel materials minerals in situ at extreme ambient conditions. These techniques genuinely complementary to X-ray (diffraction spectroscopy) the probe energy, momentum transfer, time scale, making concomitant probes available advanced sample analysis. We have built state-of-the-art, user-friendly integrated system Sector 13 (GeoSoilEnviroCARS, University Chicago, IL) Advanced...
Optical and synchrotron x-ray diffraction diamond anvil cell experiments have been combined with first-principles theoretical structure predictions to investigate mixtures of N2 H2 up 55 GPa. Our show the formation structurally complex van der Waals compounds [see also D. K. Spaulding et al., Nat. Commun. 5, 5739 (2014)] above 10 However, we found that these NxH (0.5 < x 1.5) transform abruptly new oligomeric materials through barochemistry 47 GPa photochemistry at pressures as low These can...
Abstract Rocky planets are thought to comprise compounds of Mg and O as these among the most abundant elements, but knowledge their stable phases may be incomplete. MgO is known remarkably very high pressure chemically inert under reduced condition Earth’s lower mantle. However, in exoplanets oxygen a more constituent. Here, using synchrotron x-ray diffraction laser-heated diamond anvil cells, we show that react at pressures above 96 GPa T = 2150 K with formation I4/mcm 2 . Raman...
This paper studies zirconium subjected to high pressure conditions. Using x-ray diffraction, the authors observe onset of melting at short times after shocking, and refreeze shortly thereafter. The latent heat crystallization is found provide energy for recrystallization process
Abstract Diatomic nitrogen is an archetypal molecular system known for its exceptional stability and complex behavior at high pressures temperatures, including rich solid polymorphism, formation of energetic states, insulator-to-metal transformation coupled to a change in chemical bonding. However, the thermobaric conditions fluid molecular–polymer phase boundary associated metallization have not been experimentally established. Here, by applying dynamic laser heating compressed using fast...
The insulator-to-metal transition in dense fluid hydrogen is an essential phenomenon the study of gas giant planetary interiors and physical chemical behavior highly compressed condensed matter. Using direct fast laser spectroscopy techniques to probe deuterium precompressed a diamond anvil cell heated on microsecond timescales, onset metal-like reflectance observed visible spectral range at
The Earth has been releasing vast amounts of heat from deep Earth's interior to the surface since its formation, which primarily drives mantle convection and a number tectonic activities. In this transport process core-mantle boundary where hot molten core is in direct contact with solid-state minerals played an essential role transfer thermal energies overlying mantle. Although dominant mechanisms at lowermost believed be both conduction radiation primary mineral, bridgmanite, radiative...
The high-pressure melting curves of metals provide simple and useful tests for theories melting, as well important constraints the modeling planetary interiors. Here, we present an experimental technique that reveals latent heat fusion a metal sample compressed inside diamond anvil cell. combines microsecond-timescale pulsed electrical heating with internally heated Further, use to measure curve platinum highest pressure measured date. Melting temperature increases from...
The response of rapidly compressed highly oriented pyrolytic graphite (HOPG) normal to its basal plane was investigated at a pressure ∼80 GPa. Ultrafast x-ray diffraction using ∼100 fs pulses the Materials Under Extreme Conditions sector Linac Coherent Light Source used probe changes in crystal structure resulting from picosecond timescale compression laser drive energies ranging 2.5 250 mJ. A phase transformation HOPG textured hexagonal diamond is observed highest energy, followed by...
Photoelectron imaging results are presented for I−·X cluster anions (X = CO2, C4H5N [pyrrole], (CH3)2CO, CH3NO2). The available detachment channels labeled according to the neutral iodine atom states produced (channel I ≡ 2P3/2 and channel II 2P1/2). At photon energies in vicinity of threshold these data compared previously reported CH3CN, CH3Cl, CH3Br, H2O). In particular, show a strong connection between dipole moment solvent molecule behavior photoelectron angular distributions this...
For decades, numerous attempts have been made to produce polar oxynitride perovskites, where some of the oxygen is replaced by nitrogen, but a ordered has never demonstrated. Caracas and Cohen [Appl. Phys. Lett. 91, 092902 (2007)] studied possible oxynitrides within density-functional theory (DFT) found few candidates that were predicted be insulating at least metastable. $\mathrm{YSi}{\mathrm{O}}_{2}\mathrm{N}$ stood out with huge polarization nonlinear optic coefficients. In this study, we...
Synthesis of high nitrogen containing materials has been the subject research interest for use as alternative clean sources fuel and explosives. Here we present experimental evidence photochemical synthesis new energetic from sodium azide (NaN3) at 4.8–8.1 GPa. We show that excitation into conduction band generates color centers within compressed α-NaN3 phase lattice with minimal or no molecular N2 evolution. Photochemical changes to sample were monitored by X-ray diffraction (XRD), infrared...
A photodissociative study of CuO2(-) is presented using a combination energy and time domain photoelectron spectroscopy. Ion source conditions are used that solely produce linear OCuO(-). Photodissociation this isomer to Cu(-) + O2 conclusively demonstrated at wavelengths between 765 340 nm. Nanosecond pulsed photoexcitation shorter than nm produces single photon detachment transitions from the first excited state CuO2(-). At longer narrow fragment observed as result sequential two process....
Cl−·CH3I cluster anion photoelectron images are recorded over a range of detachment wavelengths in the immediate post threshold region. The spectral features fall into two categories. A number weak, photon energy dependent transitions observed and attributed to atomic fragmentation products. Several more intense, higher electron binding result from single detachment. Comparison with I−·CH3I suggests that process is complicated for Cl−·CH3I. transition spacing consistent CH3I ν3 mode...