Inelastic X-ray Scattering Spectroscopy Research Articles

Time-Resolved X-ray Emission Spectroscopy and Resonant Inelastic X-ray Scattering Spectroscopy of Laser Irradiated Carbon.

The existence of liquid carbon as an intermediate phase preceding the formation of novel carbon materials has been a point of contention for several decades. Experimental observation of such a liquid state requires nonthermal melting of solid carbon materials at various laser fluences and pulse properties. Reflectivity experiments performed in the mid-1980s reached opposing conclusions regarding the metallic or insulating properties of the purported liquid state. Time-resolved X-ray absorption studies showed shortening of C-C bonds and increasing diffraction densities, thought to evidence a liquid or glassy carbon state, respectively. Nevertheless, none of these experiments provided information on the electronic structure of the proposed liquid state. Herein, we report the results of time-resolved resonant inelastic X-ray scattering (RIXS) and time-resolved X-ray emission spectroscopy (XES) studies on amorphous carbon (a-C) and ultrananocrystalline diamond (UNCD) as a function of delay time between the irradiating pulse and X-ray probe. For both a-C and UNCD, we attribute decreases in RIXS or XES signals to transition blocking, relaxation, and finally, ablation. Increased signal at 20 ps following the irradiation of the UNCD is attributed to the probable formation of nanoscale structures in the ablation plume. Differences in the amount of signal observed between a-C and UNCD are explained by the difference in sample thickness and, specifically, incomplete melting of the UNCD film. Comparisons to spectral simulations based on MD trajectories at extreme conditions indicate that the carbon state in our experiments is crystalline. Normal mode analysis confirmed that symmetrical bending or stretching of the C-C bonds in the diamond lattice results in XES spectra with small intensity differences. Overall, we observed no evidence of melting to a liquid state, as determined by the lack of changes in the spectral properties for up to 100 ps delays following the melting pulses.

Pressure-Driven Changes in the Electronic Bonding Environment of GeO2 Glass above Megabar Pressures.

Noncrystalline oxides under pressure undergo gradual structural modifications, highlighted by the formation of a dense noncrystalline network topology. The nature of the densified networks and their electronic structures at high pressures may account for the mechanical hardening and the anomalous changes in electromagnetic properties. Despite its importance, direct probing of the electronic structures in amorphous oxides under compression above the Mbar pressure (>100 GPa) is currently lacking. Here, we report the observation of pressure-driven changes in electronic configurations and their delocalization around oxygen in glasses using inelastic X-ray scattering spectroscopy (IXS). In particular, the first O K-edge IXS spectra for compressed GeO2 glass up to 148 GPa, the highest pressure ever reached in an experimental study of GeO2 glass, reveal that the glass densification results from a progressive increase of oxygen proximity. While the triply coordinated oxygen [3]O is dominant below ∼50 GPa, the IXS spectra resolve multiple edge features that are unique to topologically disordered [4]O upon densification above 55 GPa. Topological compaction in GeO2 glass above 100 GPa results in pronounced electronic delocalization, revealing the contribution from Ge d-orbitals to oxide densification. Strong correlations between the glass density and the electronic configurations beyond the Mbar conditions highlight the electronic origins of densification of heavy-metal-bearing oxide glasses. Current experimental breakthroughs shed light on the direct probing of the electronic density of states in high-Z oxides above 1 Mbar, offering prospects for studies on the pressure-driven changes in magnetism, superconductivity, and electronic transport properties in heavy-metal-bearing oxides under compression.

Phonon Lifetime Observation in Epitaxial ScN Film with Inelastic X-Ray Scattering Spectroscopy.

Phonon-phonon scattering dominates the thermal properties in nonmetallic materials, and it directly influences device performance in applications. The understanding of the scattering has been progressing using computational approaches, and the direct and systematic observation of phonon modes that include momentum dependences is desirable. We report experimental data on the phonon dispersion curves and lifetimes in an epitaxially grown ScN film using inelastic x-ray scattering measurements. The momentum dependence of the optical phonon lifetimes is estimated from the spectral width, and the highest-energy phonon mode around the zone center is found to possess a short lifetime of 0.21ps. A comparison with first-principles calculations shows that our observed phonon lifetimes are quantitatively explained by three-body phonon-phonon interactions.

Resonant Inelastic X-ray Scattering Spectroscopy at MERLIN Beamline at the Advanced Light Source

Strong correlations between charge, spin, orbital, and lattice degrees of freedom in complex materials can often lead to the emergence of exotic properties, such as high temperature superconductivity (HTSC), colossal magnetoresistance (CMR), multiferroicity, insulator-to-metal transition (IMT), electron fractionalization, and many more [1–12]. These properties not only show great promise for the technological breakthroughs that can transform our way of life, but also provide ideal test grounds for exploring the fundamental physics of electronic correlations on various energy, length, and time scales.

Electronic excitations investigated by inelastic x-ray scatteringspectroscopy

It is shown how non-resonant and resonant inelastic x-ray scatteringspectroscopy (IXSS) offer valuable information about electronic excitations insolids. After a presentation of the basic relations, applications of IXSS on alarge variety of systems and electronic excitations are discussed, where inmost cases synchrotron radiation is utilized

Fano-like coupling of collective and particle-hole excitations in Li metal

The dynamic structure factor of Li with [110] and 0.88 a.u. <q< 1.03 a.u., as measured with 1 eV resolution by means of synchrotron radiation based inelastic X-ray scattering spectroscopy (IXSS), exhibits, in the energy loss range between 3 and 12 eV, a fine structure, which appears as a resonance around 4 eV and an antiresonance around 8 eV, when the difference between the experimental -spectra with [110] and [111] is considered. In order to find out the origin of this fine structure we have interpreted recent TLDA (time dependent local density approximation) calculations of the Li- [#!ref12!#], which were based on the inversion of the full dielectric matrix, by utilizing a simple two-plasmon-band model. In this way the fine structure can be traced back to a Fano-like coupling of the discrete collective excitations (both the regular plasmon and the so-called zone-boundary collective states (ZBCS's)) and the particle-hole excitation continuum, mediated by the off-diagonal elements of the dielectric matrix, , where (1,1,0).

Multiple scattering in inelastic X-ray scattering spectroscopy: A Monte-Carlo study

A Monte-Carlo code is presented with the aim of investigating the influence of multiple scattering on the experimental data of the dynamic structure factor as measured by means of inelastic X-ray scattering spectroscopy (IXSS). It is shown that the contribution of double scattering to the valence electron part of the dynamic structure factor does not exceed 4% for typical cases, investigated so far. It is demonstrated that, in agreement with recent measurements (Schülke et al., Phys. Rev. B 40 (1989) 12215), the double-scattered part does not introduce additional structure into the spectra, so that multiple scattering cannot account for the so-called double-peak structure of the dynamic structure factor of simple metals.

Bethe Surface of Liquid Water Determined by Inelastic X-Ray Scattering Spectroscopy and Electron Correlation Effects

Abstract By means of inelastic X-ray scattering spectroscopy, the generalized oscillator strength (GOS) of liquid water has been experimentally determined over a range 0.69 ≤ q ≤ 3.59 a.u., where q is the momentum transfer. The Bethe surface was constructed from the GOS, and the loss function, the dielectric response function, and the static structure factor were deduced. It was found that the GOS of liquid water is dominated by individual molecular properties over the q range studied, and that the static structure factor agrees quite well with a calculation including electron-electron correlation effects.

Experimental station for inelastic scattering spectroscopy of electronic excitations

An experimental station for inelastic x-ray scattering spectroscopy (IXSS) of phonons and electronic excitation is being built on the undulator beamline of Sector 3 at the Advanced Photon Source. The subject of the present article is a description of the instrumentation for the spectroscopy of electronic excitations. The goal of this program is to provide users with the possibility to study IXSS in low- and middle-Z materials with an energy resolution from 1 eV (with a beam coming directly from the high-heat-load monochromator to the specimen) to 100 meV (with a second channel-cut monochromator) in the energy transfer range of 200 eV. The optical scheme of the station is described, and status of the station is reported.

Performance of a versatile instrumentation for inelastic X-ray scattering spectroscopy (IXSS) with synchrotron radiation

The performance and test of an instrument for inelastic X-ray scattering spectroscopy (IXSS) using synchrotron radiation from the HARWI wiggler at DESY/HASYLAB, Hamburg, are described. The instrument can be used both for Compton profile measurements with 0.13 a.u. momentum space resolution using 32 keV X-rays and for measurements of the electronic dynamic structure factor S( q, ω), with 1.6 eV resolution using 13.7 keV X-rays. The fixed-exit monochromator consists of a plane water-cooled Si (511) crystal acting together in a nondispersive setup with a cylindrically bent sagittally focusing second Si (511) crystal. The energy analysis for Compton profile measurement is performed by means of a Cauchois-type cylindrically bent Si crystal and a 1D position sensitive 200-strip Ge detector. The energy analysis for S( q, ω)-measurements is done by using a spherically bent nearly back-reflecting Si crystal in full Rowland geometry, where the advantages of dispersion compensation are fully exploited. Test measurements on Si (Compton profiles) and graphite ( S( q, ω)) are presented.

Plasmon-Fano resonance inside the particle-hole excitation spectrum of simple metals and semiconductors.

It is shown that local-field effects in simple metals and semiconductors couple the plasmon into the large-wave-vector q particle-hole excitation spectrum, leading to a plasmon antiresonance (plasmon-Fano resonance). The resulting structure is observed in inelastic x-ray scattering spectroscopy (IXSS) of single-crystal Si for scattering vectors q along the 〈111〉 direction. The inclusion of exchange and correlation effects is important to obtain good agreement between theory and experiment. Previously unexplained structures in the IXSS of single-crystal Li for q along the 〈110〉 direction and of single-crystal Be for q along 〈100〉 and 〈001〉 are also identified as plasmon-Fano resonances.

Interlayer states of LiC 6 investigated by inelastic X-ray scattering spectroscopy (IXSS) using Li-core excitation

Li-core excitation spectra of stage-1 Li intercalated graphite (LiC 6), obtained by means of inelastic X-ray scattering spectroscopy (IXSS) for momentum transfer q parallel and perpendicular to the c-axis, are presented and discussed together with the Li-core excitation spectra of Li-metal. The main features of the LiC 6 spectra can be assigned to the symmetry projected DOS of the so-called interlayer states (IS's), where the q-orientation dependence of the spectra enables us to separate the σ-type from the π-type IS's. This interpretation of the Li-core excitation spectra is guided by band structure calculations of Holzwarth et al. ( Phys. Rev. B28, 1013 (1983)), which are near the Fermi level in good agreement with experimental results.

Information about the band structure of LiC 6 from inelastic synchrotron X-ray scattering

Inelastic X-ray scattering spectroscopy (IXSS) is a useful tool for getting information about the band structure. Here IXSS-measurements of LiC 6 and HOPG are presented. A nearly rigid-band behavior of the unoccupied energy levels is observed, except for the σ-type interlayer state, which shifts down in energy by 2 eV upon intercalation. By estimating the number of unoccupied π-states from the integral intensity of the core excitation spectra for LiC 6 and HOPG the amount of charge transfer to the graphite π-bands could be established.