Inelastic Peaks Research Articles

Neutron scattering study of magnetic ordering and excitations in the ternary rare-earth diborocarbideCe11B2C2

Neutron scattering experiments have been performed on the ternary rare-earth diborocarbide ${\mathrm{Ce}}^{11}{\mathrm{B}}_{2}{\mathrm{C}}_{2}$. The powder-diffraction experiment confirms formation of a long-range magnetic order at ${T}_{\mathrm{N}}=7.3\phantom{\rule{0.3em}{0ex}}\mathrm{K}$, where a sinusoidally modulated structure is realized with the modulation vector $\mathbit{q}=[0.167(3),0.167(3),0.114(3)]$. Inelastic excitation spectra in the paramagnetic phase comprise significantly broad quasielastic and inelastic peaks centered at $\ensuremath{\hbar}\ensuremath{\omega}\ensuremath{\approx}0$, 8, and $65\phantom{\rule{0.3em}{0ex}}\mathrm{meV}$. Crystalline-electric-field (CEF) analysis satisfactorily reproduces the observed spectra, confirming their CEF origin. The broadness of the quasielastic peak indicates strong spin fluctuations due to coupling between localized $4f$ spins and conduction electrons in the paramagnetic phase. A prominent feature is suppression of the quasielastic fluctuations, and concomitant growth of a sharp inelastic peak in a low-energy region below ${T}_{\mathrm{N}}$. This suggests dissociation of the conduction and localized $4f$ electrons on ordering, and contrasts the presently observed incommensurate phase with spin-density-wave order frequently seen in heavy fermion compounds, such as ${\mathrm{Ce}}_{x}{\mathrm{La}}_{1\ensuremath{-}x}{\mathrm{Ru}}_{2}{\mathrm{Si}}_{2}$.

Concentration−Temperature Dependencies of Structural Relaxation Time in Trehalose−Water Solutions by Brillouin Inelastic UV Scattering

A Brillouin scattering investigation has been carried out on trehalose-water solutions in a wide range of concentrations (0<phi<0.74) in the ultraviolet regime. A complete set of data as a function of temperature (-10 degrees C<or=T<or=100 degrees C) has been obtained for each concentration. The T-phi evolution of the system has been analyzed in terms of energy position and line width of inelastic peaks. These results have been used to derive the structural relaxation time, tau, of the system. This was found to be in the tens of picoseconds time scale, and its T dependence can be described with an activation (Arrhenius) law. Most importantly, a significant slowing down of the relaxation dynamics has been observed as trehalose concentration was increased. At low phi, the activation energy of the relaxation has been found to be consistent with literature data for pure water and comparable with intermolecular hydrogen bond (HB) energy. This evidence strongly supports the hypothesis that the main microscopic mechanism responsible for the relaxation process in trehalose solutions lies in the continuous rearrangement of the HB network. Finally, the results are discussed in terms of the evolution of the system upon increasing trehalose concentration, in order to provide a complete description of the viscoelastic stiffening in real biological conditions.

Crystal field excitations in the cubic compound Ce 3Rh 4Sn 13

The recent heat capacity measurements of Ce 3Rh 4Sn 13 have revealed a broad peak at 1 K with an entropy of 3R ln(2) per f.u., but no clear sign of any magnetic ordering down to 100 mK. In order to understand this anomalous heat capacity behaviour of Ce 3Rh 4Sn 13, we have carried out low- and high-energy inelastic neutron scattering measurements. Our high-energy studies reveal two well-resolved crystal field (CF) excitations at ∼9 meV and 38 meV. The observation of two CF excitations in the cubic structure of Ce 3Rh 4Sn 13 could be explained on the basis of tetragonal point symmetry of the Ce ions. Interestingly, the low-energy measurements apparently show, or are best described by, a quasi-elastic peak and an inelastic peak at ∼0.2 meV at 1.5 K, both of Lorentzian shape. We attribute the low-energy peak to Zeeman splitting of the ground state doublet, in the presence of short range magnetic ordering. Further, the low-energy peak explains the observed anomaly in the heat capacity.

Crystal field excitations in the filled skutterudite [formula omitted

We have performed inelastic neutron scattering experiment on a powder sample of the ferromagnetic filled skutterudite compound NdOs 4 Sb 12 in order to clarify the crystal-field (CF) states of 4f electrons in this system. At lowest temperature 15 K, two inelastic peaks have been observed at energy transfers 23.0 and 30.2 meV. The intensity of these two peaks decreases with increasing temperature, as expected for excitations from the CF ground state. This observation of CF excitations evidences the localized character of 4f electrons in NdOs 4 Sb 12 . From this result and the bulk magnetic susceptibility of NdOs 4 Sb 12 , possible CF level schemes are discussed.

Inelastic neutron scattering study of the spin-gap cuprateβ−AgCuPO4

We studied magnetism of $\ensuremath{\beta}\text{\ensuremath{-}}\mathrm{Ag}\mathrm{Cu}\mathrm{P}{\mathrm{O}}_{4}$ using inelastic neutron scattering and magnetic susceptibility measurements on powder samples. A well-defined asymmetric broad inelastic peak was observed at $6.2\phantom{\rule{0.3em}{0ex}}\mathrm{meV}$ in constant-$Q$ (scattering vector) scan spectra, indicating spin-gap excitation. From results of these measurements, we have obtained that the strongest exchange interaction exists in a Cu-O-P-O-Cu path in spite of the existence of Cu-O-Cu paths and that the antiferromagnetic alternating chain model with two exchange interaction values of 80 and $14\phantom{\rule{0.3em}{0ex}}\mathrm{K}$ can explain the experimental results quantitatively. Our results are consistent with the prediction of Yahia et al. [Inorg. Chem. 45, 5501 (2006)].

Energy and intensity distributions of 0.279 MeV multiply Compton-scattered photons in soldering material

An inverse response matrix converts the observed pulse-height distribution of a NaI(Tl) scintillation detector to a photon spectrum. This also results in extraction of intensity distribution of multiply scattered events originating from interactions of 0.279 MeV photons with thick targets of soldering material. The observed pulse-height distributions are a composite of singly and multiply scattered events in addition to bremmstrahlung-and Rayleigh-scattered events. To evaluate the contribution of multiply scattered events, the spectrum of singly scattered events contributing to inelastic Compton peak is reconstructed analytically. The optimum thickness (saturation depth), at which the number of multiply scattered events saturates, has been measured. Monte Carlo calculations also support the present results.

First nucleation steps during deposition of SiO 2 thin films by plasma enhanced chemical vapour deposition

The initial nucleation stages during deposition of SiO 2 by remote plasma enhanced chemical vapour deposition (PECVD) have been monitored by XPS inelastic peak shape analysis. Experiments have been carried out on two substrates, a flat ZrO 2 thin film and a silicon wafer with a native silicon oxide layer on its surface. For the two substrates it is found that PECVD SiO 2 grows in the form of islands. When the SiO 2 particles reach heights close to 10 nm they coalesce and cover completely the substrate surface. The particle formation mechanism has been confirmed by TEM observation of the particles grown on silicon substrates. The kinetic Monte Carlo simulation of the nucleation and growth of the SiO 2 particles has shown that formation of islands is favoured under PECVD conditions because the plasma species may reach the substrate surface according to off-perpendicular directions. The average energy of these species is the main parameter used to describe their angular distribution function, while the reactivity of the surface is another key parameter used in the simulations.

Influence of angle of incidence on seismic demands for inelastic single-storey structures subjected to bi-directional ground motions

This study examines the influence that the angle of incidence of the ground motion has on several engineering demand parameters (EDPs) for a single-storey structure subjected to bi-directional ground motions. The models in this work had various degrees of inelasticity, were subjected to a set of 39 ground motion pairs for which nonlinear time histories were conducted, and had fundamental periods that ranged from 0.2 to 2.0 s for both symmetrical and asymmetrical structures. It is demonstrated that applying bi-directional ground motions only along the principal axes of an inelastic building underestimates the inelastic peak deformation demands when compared to those obtained at other angles of incidence. Although an optimal building orientation that minimizes demands for all the EDPs considered for a given model cannot be determined explicitly, for a given degree of inelasticity, the average ratio of peak deformation responses based on all angles of incidence to the peak deformation response when the ground motions are applied at principal building orientations shows stable trends. Generally, these ratios increase with the fundamental period of vibration. These average ratios typically vary between 1.1 and 1.6; however, ratios for individual ground motions can be as high as 5 for the EDPs examined. Maximum responses for individual ground motions were found to occur for virtually any angle of incidence and varied with the degree of inelasticity, which implies that inaccurate estimates of structural performance and damage may result if based on ground motions applied at principal orientations alone.

Many-body effect in the coincidence L 3 and M 3 photoelectron spectroscopy spectra of Cu metal

The coincidence L 3 and M 3 photoelectron spectroscopy (PES) main lines of Cu metal are calculated by a many-body theory. There is no peak-energy shift between the singles PES main line and the coincidence one. The asymmetric narrowing of the coincidence PES main line on the low kinetic energy (KE) side is very small. This is in accord with recent experimental findings. In Cu metal, the shakeup satellite intensity is small and the main-line satellite separation energy is much larger than the core–hole lifetime width. The interference via the final-state interaction is negligible. In the PES main line, the imaginary part of the self-energy by shakeup excitations, which is very small compared to the core–hole lifetime width, decreases very slowly in linear with photoelectron KE. The branching ratio of Auger decay of a single hole state then increases very slowly in linear with photoelectron KE so that the deviation of the coincidence PES main line from the singles one is very small. The 939 eV structure seen only in the coincidence L 3 PES spectrum of Cu metal is attributed to the enhancement of the inelastic peak of a smaller energy loss due to electrons of a smaller average emission depth measured in coincidence with the elastic Auger peak. The structure will not be enhanced in the singles PES spectrum. The background subtraction in the coincidence spectrum cannot be the same as that in the singles one. Such consideration is necessary before we can conclude about the asymmetric narrowing on the low KE side. A unique capability of APECS by which one can determine the photoelectron KE dependent part of the imaginary part of the self-energy is pointed out.

Inelastic energy losses of He+ ions singly scattered from polycrystalline chromium

The inelastic energy losses of He+ ions singly scattered from polycrystalline chromium (Cr) surface in the 0.7–2.0keV energy range were experimentally investigated in this work. The energy spectra of ions scattered to 90° were measured. The peak corresponding to singly scattered ions is resolved into two Gaussians. The one at higher energies (elastic peak) corresponds to the He+ ions that were not neutralized along the trajectory, while that at lower energy (inelastic peak) is attributed to the He+ ions that were neutralized while approaching the surface and then reionized during the violent collision with Cr surface atoms. The difference between the positions of these Gaussians is a measure of the inelastic energy losses caused by the projectile reionization. These discrete inelastic losses are interpreted using the model of Tsuneyuki and Tsukada. It was observed that the energy difference between the elastic and inelastic peak increases with the incident ion energy. The elastic and inelastic peak intensities depend on the incoming angle and the character of this dependence abruptly changes for the incident ion energies in the range 1350–1400eV, which cannot be explained by the existing theoretical models.

Magnetic excitations in the crystalline and quasicrystalline Zn–Mg–Ho phases

A comparative study has been carried out on magnetic excitations in the primitive- (p-) and face-centred- (f-) icosahedral quasicrystalline phases, as well as crystalline phase, in the Zn–Mg–Ho system. The magnetic excitation spectrum in both the quasicrystalline phases has only a broad quasielastic peak centred at the elastic position; the signal for the positive energy-transfer (ℏω) side is found to be almost temperature independent in a wide temperature range 1.5 <T <200K. The magnetic excitation spectrum in the crystalline Zn65.2Mg27.9Ho6.9 phase is quite similar to that of the quasicrystalline phases at high temperatures; however, well-defined inelastic peaks due to crystalline-electric-field (CEF) splitting levels appear as the temperature is decreased. The appearance of the sharp CEF peaks confirms well-defined site symmetry around the rare-earth sites in the hexagonal phase, whereas the temperature-independent quasielastic signal suggests anomalous spin fluctuations in the quasicrystalline phases.

Effect of light Sr doping on the spin–state transition in [formula omitted

We present an inelastic neutron scattering study of the low energy crystal-field excitations in the lightly doped cobalt perovskite La 0.998 Sr 0.002 CoO 3 . In contrast to the parent compound LaCoO 3 an inelastic peak at energy transfer ∼ 0.75 meV was found at temperatures below 30 K. This excitation apparently corresponds to a transition between a ground state orbital singlet and a higher excited orbital doublet, originating from a high-spin triplet split by a small trigonal crystal field. Another inelastic peak at an energy transfer ∼ 0.6 meV was found at intermediate temperatures starting from T > 30 K . This confirms the presence of a thermally induced spin–state transition from the low-spin Co 3 + to a magnetic high-spin state in the non-disturbed LaCoO 3 matrix. We suggest that hole doping of LaCoO 3 leads to the creation of a magnetic polaron and hence to the low-to-high spin state transition on the relevant Co sites.

Study of the first nucleation steps of thin films by XPS inelastic peak shape analysis

AbstractThe initial steps in the formation of thin films have been investigated by analysis of the peak shape (both inelastic background and elastic contributions) of X‐ray photoelectron spectra. Surface coverage and averaged height of the deposited particles have been estimated for several overlayers (nanometre range) after successive deposition cycles. This study has permitted the assessment of the type of nucleation and growth mechanisms of the films. The experiments have been carried out in situ in the preparation chamber of an XPS spectrometer. To check the performance of the method, several materials (i.e. cerium oxide, vanadium oxide and cadmium sulfide) have been deposited on different substrates using a variety of preparation procedures (i.e. thermal evaporation, ion beam assisted deposition and plasma enhanced chemical vapour deposition). It is shown that the first deposited nuclei of the films are usually formed by three‐dimensional particles whose heights and degree of surface coverage depend on the chemical characteristics of the growing thin film and substrate materials, as well as the deposition procedure. It is concluded that XPS peak shape analysis can be satisfactorily used as a general method to characterize morphologically the first nanometric moieties that nucleate a thin film. Copyright © 2006 John Wiley &amp; Sons, Ltd.

Spin gaps in pseudo-one-dimensional RMn 4Al 8 compounds (R=Y, Ce and La)

LaMn 4Al 8 displays large amplitude spin fluctuations arising from linear chains of Mn atoms. Inelastic neutron scattering data for LaMn 4Al 8 shows that the dynamical magnetic response has two components: a quasielastic component and a broad inelastic peak centred near 30 meV.YMn 4Al 8 and CeMn 4Al 8 display maxima in their susceptibilities near 500 and 300 K, respectively. This has been taken as evidence for the presence of a magnetic pseudogap in YMn 4Al 8, possibly arising from one-dimensional AF correlations. We report inelastic neutron scattering data for the weak magnetic response of both YMn 4Al 8 and CeMn 4Al 8. In YMn 4Al 8 a clear spin gap of order 27 meV is evident for a limited range of wavevectors. In CeMn 4Al 8 the gap formation is less obvious, being partly masked by the intermediate-valence response of the cerium.

Low-energy magnetic fluctuations in [formula omitted

Inelastic neutron scattering experiments were performed on U ( Ru 1 - x Rh x ) 2 Si 2 with x = 0 and 0.02 in order to investigate the variations of the antiferromagnetic (AF) fluctuations with doping Rh. We have found that the energy of the magnetic excitation observed at Q = ( 1 , 0 , 0 ) in the hidden order (HO) phase markedly decreases from ∼ 2.6 meV ( x = 0 ) to ∼ 0 ( x = 0.02 ) with increasing x . In addition, the staggered susceptibility χ Q estimated from the inelastic peak develops in the HO phase at x = 0.02 , while it is suppressed at x = 0 . These results indicate that the AF fluctuation in the HO phase is significantly enhanced with doping Rh.

Magnetic excitation of TmTe in the anomalous metallic state under high pressure

The magnetic excitation spectrum of TmTe before and after the insulator-to-metal transition under high pressure has been studied by inelastic neutron scattering. Below the critical pressure of about 2 GPa, there seems to be no qualitative difference in comparison with the spectrum at P = 0 . In contrast, in the ferromagnetic anomalous metallic state above the critical pressure, an inelastic peak appears at 9 meV as in TmSe at P = 0 . The 9 meV excitation is considered to be a characteristic of the valence fluctuating ground state in Tm monochalcogenides, where both valence states are magnetic.

Fingerprints of the Magnetic Polaron in Nonequilibrium Electron Transport through a Quantum Wire Coupled to a Ferromagnetic Spin Chain

We study nonequilibrium quantum transport through a mesoscopic wire coupled via local exchange to a ferromagnetic spin chain. Using the Keldysh formalism in the self-consistent Born approximation, we identify fingerprints of the magnetic polaron state formed by hybridization of electronic and magnon states. Because of its low decoherence rate, we find coherent transport signals. Both elastic and inelastic peaks of the differential conductance are discussed as a function of external magnetic fields, the polarization of the leads, and the electronic level spacing of the wire.

Rotational transitions and diffraction in D2 scattering from the LiF(001) surface: Theory and experiment

High probabilities of energy transfer from translation to molecular rotations are observed in the scattering of n-D(2) from LiF(001) at an incident beam energy of 85.3 meV. For the 100 incidence direction, close-coupling calculations yield ratios of the rotationally inelastic (j=0-->2) and (j=1-->3) peaks to the rotationally elastic specular peaks (G=0) that are in reasonable agreement with experiment, as are the ratios of the rotationally elastic diffraction peak intensities to the specular peak intensities. The agreement between theory and experiment is also quite good for the rotationally inelastic diffractive (-1-1) transitions for (j=1-->3), but rather poor for (j=0-->2). The calculations show that the interaction between the electrostatic field of the surface ions and the quadrupole moment of the D(2) molecule efficiently promotes the (j=0-->2) and (j=1-->3) transitions. If this electrostatic interaction is excluded from the potential model, the ratios of the (j=0-->2) and (j=1-->3) rotationally inelastic peaks to the corresponding specular peaks show a large discrepancy with experiment, underlining the importance of this interaction. The close-coupling calculations show a somewhat worse agreement with experiment for the 110 incidence direction. In particular, the sharp peaks observed experimentally in the ratios of the peak intensities of the rotationally inelastic G=0 (j=0-->2) and (j=1-->3) to the rotationally elastic G=0 transitions as a function of incident angle are not reproduced by the calculations. The theoretical ratios of the peak intensities of the rotationally elastic diffraction to G=0 transitions are shifted to lower incidence angles with respect to experiment. The rotationally inelastic diffractive (-10) transitions present an interesting resonance phenomenon for the (j=0-->2) rotational transition. This resonance is predicted by both theory and experiment, although at rather different incident angles.

First stages of growth of cerium oxide deposited on alumina and reduced titania surfaces

AbstractWe have studied the first nucleation steps and the chemical interactions of small amounts of cerium oxide deposited on two surfaces with different chemical nature, alumina and a partially reduced titania. Cerium oxide was deposited by electron bombardment of CeO2 pellets in ultra‐high vacuum conditions. All experiments were done in situ in order to avoid contamination related to exposure to air. The relative amounts of Ce3+ and Ce4+ species present at the successive deposition steps have been quantified. It is found that for initial steps of deposition, high amounts of Ce3+ are stabilised at the CeOx/TiOx interface, while an approximately even mixture of Ce3+ and Ce4+ species appear at the CeOx/Al2O3 interface. Thicker deposits are characterised by the presence of only Ce4+ species independently of the substrate. It is found that cerium oxide grows in the form of islands on both substrates. These islands are taller in the case of deposition on reduced titania than on alumina. This result is confirmed by both angle resolved X‐ray photoelectron spectroscopy (XPS) and inelastic XPS peak shape analysis. The correlation between the growing microstructure and the chemical interaction at the interfaces is discussed. Copyright © 2006 John Wiley &amp; Sons, Ltd.

Inelastic scattering of light by a cold trapped atom: Effects of the quantum center-of-mass motion

The light scattered by a cold trapped ion, which is in the stationary state of laser cooling, presents features due to the mechanical effects of atom-photon interaction. These features appear as additional peaks (sidebands) in the spectrum of resonance fluorescence. Among these sidebands the literature has discussed the Stokes and anti-Stokes components, namely the sidebands of the elastic peak. In this manuscript we show that the motion also gives rise to sidebands of the inelastic peaks. These are not always visible, but, as we show, can be measured in parameter regimes which are experimentally accessible.