A5082137937- High-pressure geophysics and materials
- Rare-earth and actinide compounds
- Iron-based superconductors research
- Crystallography and Radiation Phenomena
- Hemoglobin structure and function
- Nuclear Materials and Properties
- Thermodynamic and Structural Properties of Metals and Alloys
- Porphyrin and Phthalocyanine Chemistry
- Physics of Superconductivity and Magnetism
- Enzyme Structure and Function
- Spectroscopy and Quantum Chemical Studies
- Porphyrin Metabolism and Disorders
- Advanced Condensed Matter Physics
- Superconductivity in MgB2 and Alloys
- Quantum, superfluid, helium dynamics
- Ferroelectric and Piezoelectric Materials
- Magnetic and transport properties of perovskites and related materials
- Advanced Electron Microscopy Techniques and Applications
- X-ray Spectroscopy and Fluorescence Analysis
- X-ray Diffraction in Crystallography
- Transition Metal Oxide Nanomaterials
- Material Dynamics and Properties
- Electronic and Structural Properties of Oxides
- Nuclear materials and radiation effects
- Electron Spin Resonance Studies
Argonne National Laboratory
2011-2021
Miami University
2018-2021
Transelectrica (Romania)
2021
United States Department of Energy
2013
Beijing Research Institute of Uranium Geology
2012
Dioxide Materials (United States)
2012
Northeastern University
2005-2011
University of Notre Dame
2004-2005
Steacie Institute for Molecular Sciences
2004
National Academies of Sciences, Engineering, and Medicine
2004
We use quantitative experimental and theoretical approaches to characterize the vibrational dynamics of Fe atom in porphyrins designed model heme protein active sites. Nuclear resonance spectroscopy (NRVS) yields frequencies, amplitudes, directions for 57Fe vibrations a series ferrous nitrosyl porphyrins, which provide benchmark evaluation quantum chemical calculations. Detailed normal mode predictions result from DFT calculations on tetraphenylporphyrin Fe(TPP)(NO), its cation...
Inelastic x-ray scattering is used to investigate charge-density wave (CDW) formation and the low-energy lattice dynamics of underdoped high-temperature superconductor ortho-II YBa${}_{2}$Cu${}_{3}$O${}_{6.54}$. We find that, for a temperature $\ensuremath{\sim}1/3$ CDW onset ($\ensuremath{\approx}$155 K), order static within resolution experiment, that inverse lifetime less than 0.3 meV. In same region, phonons near ordering vector show large increases in their linewidths. This contrasts...
Joint inelastic neutron and x-ray scattering measurements have been performed on heavy water across the melting point. The spectra bear clear evidence of low- high-frequency shoulders related to transverse longitudinal modes, respectively. Upon increasing momentum transfer, spectral shape evolves from a viscoelastic regime, where low-frequency mode is clearly over-damped, toward an elastic one its propagation becomes instead allowed. crossover between two regimes occurs whenever both...
We present an investigation of the lattice dynamics charge density wave (CDW) compound 2$H$-NbSe${}_{2}$. analyze precise nature vector-dependent electron-phonon coupling (EPC) and derive bare dispersion CDW soft phonon mode using inelastic x-ray scattering combined with ab initio calculations. Experimentally, modes along \ensuremath{\Gamma}\ensuremath{-}$M$ line, i.e., q $=$ ($h$,0,0), 0 \ensuremath{\le} $h$ 0.5 same longitudinal symmetry (${\ensuremath{\Sigma}}_{1}$) as mode, were...
We experimentally investigate the symmetry in Hidden Order (HO) phase of intermetallic URu2Si2 by mapping lattice and magnetic excitations via inelastic neutron x-ray scattering measurements HO high-temperature paramagnetic phases. At all temperatures respect zone edges body-centered tetragonal phase, showing no signs reduced spatial symmetry, even phase. The originate from transitions between hybridized bands track Fermi surface, whose feature are corroborated phonon measurements. Due to a...
We use nuclear resonance vibrational spectroscopy (NRVS) to identify the Fe−NO stretching frequency in NO adduct of myoglobin (MbNO) and related six-coordinate porphyrin Fe(TPP)(1-MeIm)(NO). Frequency shifts observed MbNO Raman spectra upon isotopic substitution Fe or nitrosyl nitrogen confirm extend NRVS results. In contrast with previous assignments, these complexes lies 70−100 cm-1 lower than analogous five-coordinate complexes, indicating a significant weakening bond presence trans...
Abstract Magnetite exhibits unique electronic, magnetic and structural properties in extreme conditions that are of great research interest. Previous studies have suggested a number transitional models, although the nature magnetite at high pressure remains elusive. We studied highly stoichiometric using inelastic X-ray scattering, diffraction emission Raman spectroscopies diamond anvil cells up to ~20 GPa, while complementary electrical conductivity measurements were conducted cubic cell...
Inelastic x-ray and neutron scattering were used to measure two matching lattice excitations on the $[01\ensuremath{\zeta}]$ zone boundary in $\ensuremath{\alpha}$-uranium. The have same polarization reciprocal-space structure, but one has energy consistent with thermal activation of other, indicating that it creates mode. implied mechanism, where a mode is created by an amplitude fluctuation mirrors itself, intrinsically localized (ILM), this supported thermodynamic data. however, indicates...
Abstract The juxtaposition of a liquid iron‐dominant alloy against mixture silicate and oxide minerals at Earth's core‐mantle boundary is associated with wide range complex seismological features. One category observed structures ultralow‐velocity zones, which are thought to correspond either aggregates partially molten material or solid, iron‐enriched assemblages. We measured the phonon dispersion relations (Mg,Fe) O magnesiowüstite containing 76 mol % FeO, candidate zone phase, high...
Inelastic X-ray scattering is a powerful and versatile technique for studying lattice dynamics in materials of scientific technological importance. In this article, the design capabilities momentum-resolved high-energy-resolution inelastic spectrometer (HERIX) at beamline 30-ID Advanced Photon Source are reported. The instrument operates 23.724 keV has an energy resolution 1.3-1.7 meV. It can accommodate momentum transfers up to 72 nm-1, typical flux 4.5 × 109 photons s-1 meV-1 sample. A...
In the iron pnictides, strong sensitivity of magnetic moment to arsenic position suggests a significant relationship between phonons and magnetism. We measured phonon dispersion several branches in high-temperature tetragonal phase ${\text{CaFe}}_{2}{\text{As}}_{2}$ using inelastic x-ray scattering on single-crystal samples. These measurements were compared ab initio calculations phonons. Spin-polarized imposing antiferromagnetic order present low-temperature orthorhombic dramatically...
Nuclear resonance vibrational spectroscopy (NRVS) and Raman on 54Fe- 57Fe-enriched cytochrome c (cyt c) identify multiple bands involving vibrations of the heme Fe. Comparison with predictions from Fe isotope shifts reveals that 70% NRVS signal in 300−450 cm−1 frequency range corresponds to resolved Soret-enhanced spectra. This dominates "stiffness", an effective force constant determined by density states (VDOS), which measures strength nearest-neighbor interactions The stiffness low-spin...
Using inelastic x-ray scattering, we determine the phonon density of states PuO${}_{2}$ (+2$%$ Ga) and compare results with recent predictions made using functional theory (DFT), DFT plus Hubbard U (DFT+U), dynamical mean-field theory. The prediction underestimates measured energies most features. DFT+U accurately reflects low-energy features but incorrectly splits off an isolated high-energy oxygen mode. Ramifications for thermodynamic transport properties this nuclear fuel material are discussed.
Compressibility characterizes three interconnecting properties of a protein: dynamics, structure, and function. The compressibility values for the electron-carrying protein cytochrome c other proteins, as well, available in literature vary considerably. Here, we apply two synchrotron-based techniques––nuclear resonance vibrational spectroscopy inelastic x-ray scattering––to measure adiabatic this protein. This is first report any material measured with method. Unlike methods previously used,...
Phonons, the quantum mechanical representation of lattice vibrations, and their coupling to electronic degrees freedom are important for understanding thermal electric properties materials. For first time, phonons have been measured using resonant inelastic x-ray scattering (RIXS) across Cu K-edge in cupric oxide (CuO). Analyzing these spectra an ultra-short core-hole lifetime approximation exact diagonalization techniques, we can explain essential features. The relative spectral intensities...
The low-energy phonons of two different graphite intercalation compounds (GICs) have been measured as a function temperature using inelastic x-ray scattering (IXS). In the case non-superconductor BaC${}_{6}$, observed are significantly higher (up to 20%) in energy than those predicted by theory, contrast reasonable agreement found superconducting CaC${}_{6}$. Additional IXS intensity is below 15 meV both BaC${}_{6}$ and It has previously suggested that this additional may arise from defect...
Reducing the size of a superconductor below its characteristic length scales can either enhance or suppress critical temperature (${T}_{c}$). Depending on bulk value electron-phonon coupling strength, electronic and phonon confinement effects will play different roles in modification ${T}_{c}$. Experimentally disentangling each contribution has remained challenge. We have measured both density states ${T}_{c}$ Sn nanowires with diameters 18, 35, 100 nm order to quantify superconductivity....
We studied the collective excitations in an aqueous solution of lithium chloride over temperature range 270–205 K using neutron and x-ray Brillouin scattering. Both experiments revealed presence low- high-frequency excitations, similar to pure water. These two were detectable through entire experiment, at all probed values scattering momentum transfer (0.2 Å − 1 < Q 1.8 1). A wider was investigated elastic intensity scans. Clear evidence crossover dynamics water molecules observed...
We report a study of the pressure-induced antiferrodistortive cubic-to-tetragonal phase transition in strontium titanate (SrTiO3) at ambient temperature. High-resolution inelastic x-ray scattering measurements reveal softening phonon mode zone boundary; static distortion sets critical pressure 9.5 GPa, which corresponds to volume reduction 5.3%. Prior studies have shown that similar and ensuing lattice can be induced under by lowering sample temperature through 105 K. The relationship...
The control of phonon propagation in nanoparticle arrays is one the frontiers nanotechnology, potentially enabling discovery materials with unknown functionalities for potential innovative applications. exploration terahertz window appears quite promising as phonons this range are leading carriers heat transport insulators and their key to implement devices flow management. Unfortunately, scientific field still its infancy, even a basic topic such influence floating nanoparticles on...