Energy Loss Data Research Articles

Strong phonon-plasmon coupled modes in the graphene/silicon carbide heterosystem

We report on strong coupling of the charge carrier plasmon $\omega_{PL}$ in graphene with the surface optical phonon $\omega_{SO}$ of the underlying SiC(0001) substrate with low electron concentration ($n=1.2\times 10^{15}$ $cm^{-3}$) in the long wavelength limit ($q_\parallel \rightarrow 0$). Energy dependent energy-loss spectra give for the first time clear evidence of two coupled phonon-plasmon modes $\omega_\pm$ separated by a gap between $\omega_{SO}$ ($q_\parallel \rightarrow 0$) and $\omega_{TO}$ ($q_\parallel >> 0$), the transverse optical phonon mode, with a Fano-type shape, in particular for higher primary electron energies ($E_0 \ge 20eV$). A simplified model based on dielectric theory is able to simulate our energy - loss spectra as well as the dispersion of the two coupled phonon-plasmon modes $\omega_\pm$. In contrast, Liu and Willis [1] postulate in their recent publication no gap and a discontinuous dispersion curve with a one-peak structure from their energy-loss data.

Low energy electron induced characteristic losses in the Fe 73.6Cu 1Nb 2.4Si 15.8B 7.2 (FINEMET) alloy surface

Electron Energy Loss Spectroscopy has been employed for investigation of the electronic states of amorphous and crystalline Fe 73.6Cu 1Nb 2.4Si 15.8B 7.2 (FINEMET) alloy surface and alloy components. Electron energy losses have been measured for primary electron beam energies E 0 from 150 to 650 eV. The characteristic energy loss spectra were composed of main peaks which we have interpreted due to surface and bulk plasmons, a combination of surface and bulk losses, high harmonics of plasma losses, inter-band transitions and ionization of core levels. The measured energies for the plasmon excitations were found not to agree with calculated values according to the classical theory for the collective oscillations in solids. Changes in the intensity lines of the surface and bulk plasmons were observed for all specimens depending on primary electron energy E 0. The present results are compared with characteristic energy loss data reported in the literature.

Combined Effects of Pipe Diameter, Reynolds Number and Wall Heat Flux and on Flow, Heat Transfer and Second-Law Characteristics of Laminar-Transitional Micro-Pipe Flows

Fluid flow, heat transfer and entropy generation characteristics of micro-pipes are investigated computationally by considering the simultaneous effects of pipe diameter, wall heat flux and Reynolds number in detail. Variable fluid property continuity, Navier-Stokes and energy equations are numerically handled for wide ranges of pipe diameter (d = 0.50–1.00 mm), wall heat flux (q''= 1000–2000 W/m2) and Reynolds number (Re = 1 – 2000), where the relative roughness is kept constant at e/d = 0.001 in the complete set of the scenarios considered. Computations indicated slight shifts in velocity profiles from the laminar character at Re = 500 with the corresponding shape factor (H) and intermittency values (γ) of H = 3.293→3.275 and γ = 0.041→0.051 (d = 1.00→0.50 mm). Moreover, the onset of transition was determined to move down to Retra = 1,656, 1,607, 1,491, 1,341 and 1,272 at d = 1.00, 0.90, 0.75, 0.60 and 0.50 mm, respectively. The impacts of pipe diameter on friction mechanism and heat transfer rates are evaluated to become more significant at high Reynolds numbers, resulting in the rise of energy loss data at the identical conditions as well. In cases with low pipe diameter and high Reynolds number, wall heat flux is determined to promote the magnitude of local thermal entropy generation rates. Local Bejan numbers are inspected to rise with wall heat flux at high Reynolds numbers, indicating that the elevating role of wall heat flux on local thermal entropy generation is dominant to the suppressing function of Reynolds number on local thermal entropy generation. Cross-sectional total entropy generation is computed to be most influenced by pipe diameter at high wall heat flux and low Reynolds numbers.

Generation of warm dense matter and strongly coupled plasmas using the High Radiation on Materials facility at the CERN Super Proton Synchrotron

A dedicated facility named High Radiation on Materials (HiRadMat) is being constructed at CERN to study the interaction of the 450 GeV protons generated by the Super Proton Synchrotron (SPS) with fixed solid targets of different materials. The main purpose of these future experiments is to study the generation and propagation of thermal shock waves in the target in order to assess the damage caused to the equipment, including collimators and absorbers, in case of an accident involving an uncontrolled release of the entire beam at a given point. Detailed numerical simulations of the beam-target interaction of several cases of interest have been carried out. In this paper we present simulations of the thermodynamic and the hydrodynamic response of a solid tungsten cylindrical target that is facially irradiated with the SPS beam with nominal parameters. These calculations have been carried out in two steps. First, the energy loss of the protons is calculated in the solid target using the FLUKA code [Fasso et al., “FLUKA: A multi-particle transport code,” Report Nos. CERN-2005-10, INFN/TC-05/11, and SLAC-R-773, 2005; Fasso et al., Conference on Computing in High Energy and Nuclear Physics, La Jolla, CA, 24–28 March 2003] and this energy loss data is used as input to a sophisticated two-dimensional hydrodynamic code, BIG2 [Fortov et al., Nucl. Sci. Eng. 123, 169 (1996)], which is based on a Godunov-type numerical scheme. The transverse intensity distribution in the beam focal spot is Gaussian. We consider three different sizes of the focal spot that are characterized by standard deviations, σ=0.088, 0.28, and 0.88 mm, respectively. This study has shown that the target is severely damaged in all the three cases and the material in the beam-heated region is transformed into warm dense matter including a strongly coupled plasma state. This new experimental facility can therefore also be used for dedicated experiments to study high energy density matter.

Electron excitations in grazing diffraction of fast He on a Ag(1 1 0) surface. A tribute to Hannspeter Winter

Grazing incidence diffraction of fast atoms (GIFAD) on surfaces has first been discovered on ionic insulators where electronic excitations are strongly reduced due to the large band gap. At variance no threshold exists for electronic excitations close to the Fermi edge of a metal surface. New results of energy resolved diffraction of keV helium atoms on a Ag(110) surface are presented which considerably extend the application range of GIFAD. The combined analysis of the energy loss and diffraction data could help providing a detailed description of the collision of helium with the surface electrons.

Synthesis and Characterization of Single-Crystal Strontium Hexaboride Nanowires

Catalyst-assisted growth of single-crystal strontium hexaboride (SrB6) nanowires was achieved by pyrolysis of diborane (B2H6) over SrO powders at 760-800 degrees C and 400 mTorr in a quartz tube furnace. Raman spectra demonstrate that the nanowires are SrB6, and transmission electron microscopy along with selected area diffraction indicate that the nanowires consist of single crystals with a preferred [001] growth direction. Electron energy loss data combined with the TEM images indicate that the nanowires consist of crystalline SrB 6 cores with a thin (1 to 2 nm) amorphous oxide shell. The nanowires have diameters of 10-50 nm and lengths of 1-10 microm.

Functional analysis of Fontan energy dissipation

We formalize the hydrodynamic energy dissipation in the total cavopulmonary connection (TCPC) using dimensional analysis and examine the effect of governing flow variables; namely, cardiac output, flow split, body surface area, Reynolds number, and certain geometric characteristics. A simplistic and clinically useful mathematical model of the dependence of energy dissipation on the governing variables is developed. In vitro energy loss data corresponding to six patients’ anatomies validated the predicted dependency of each variable and was used to develop a predictive, semi-empirical energy dissipation model of the TCPC. It is shown that energy dissipation is a cubic function of pulmonary flow split in the physiological range. Furthermore, non-dimensional energy dissipation, which is a measure of resistance of the connection, is dependent on Reynolds number and geometrical factors alone. Non-dimensional energy dissipation decreases with Reynolds number as Re −0.25 ( R 2>0.95). In addition, for high Reynolds numbers, within physiological exercise limits, dissipation strongly correlates to minimum PA area as a power law decay with an exponent of −5/4 ( R 2>0.88). This study presents a simple analytical form of energy dissipation rate in complex patient-specific TCPCs that accurately captures the effect of cardiac output, flow split, body surface area, Reynolds number, and pulmonary artery size within physiological limits. Further studies with larger sample sizes are necessary for incorporating finer geometrical parameters such as vessel curvatures and offsets.

Differential ionisation measurements for positron impact

An overview of methods being used at the University of Missouri-Rolla to measure differential ionisation for positron impact is presented. Examples of triply differential electron emission and doubly differential positron scattering and energy loss data are given and contributions to each due to binary and recoil events are discussed. In addition, angular distribution data for electron emission due to double and triple ionisation are presented.

Observations on the resonant inelastic x-ray scattering cross section in copper oxide compounds

We report properties of the resonant inelastic x-ray scattering (RIXS) cross section in a number of cuprates. We find that the observed spectra have the periodicity of the underlying crystal lattice, that is, the excitations are a function of reduced momentum $\mathbf{q}$ and not the total momentum $\mathbf{Q}=\mathbf{G}+\mathbf{q}$, where $\mathbf{G}$ is a reciprocal lattice vector. Measurements with two different incident photon polarizations show that the line shape and momentum dependence of the observed spectra are independent of the particular state the $4p$ photoelectron resides in the intermediate state. These latter results support theoretical approaches in which the $4p$ is taken to be a spectator in the RIXS process. In addition, a discussion is presented of what might be expected to be generic features of the RIXS cross section with the aid of some crude models, and a comparison is made between RIXS and electron energy loss data for a number of cuprates both at $\mathbf{q}=0$ and at finite $\mathbf{q}$. Taken together, there is a suggestion in the data that RIXS measures an $S(\mathbf{q},\ensuremath{\omega})$-like response.

Application of high-resolution EFTEM SI in an AEM

In this work we show how energy-filtered imaging can be used to obtain spectrum images of electron energy-loss spectrometric data. Focus is placed on improved energy resolution within these data sets. Using two multilayer samples (GaN/AlN and InP/InAs), we demonstrate the advantages of spectrum-imaging and its extended mapping capabilities. Plasmon-ratio maps are used to quickly create high-contrast material maps with high signal-to-noise ratio, ratio-contrast plots are used to gain optimum settings for the ratio maps, and plasmon-position maps are used to map small shifts of the energy position of bulk plasmon peaks.

Surface excitation parameter for electrons crossing the AlN surface

Fast electrons crossing a solid surface induce surface excitations. The total probability of such excitations for electrons moving outside the solid, i.e. in vacuum, is characterized by the surface excitation parameter (SEP). In the present work, the SEP was calculated for either incident or escaping electrons with normal or glancing crossing angles over the surface of aluminum nitride (AlN), a wide-band-gap semiconductor. These calculations were performed based on the dielectric response theory using the sum-rule-constrained extended Drude dielectric function with parameters obtained from a fit of this function to experimental optical data and electron energy-loss data. Dependences of the SEP on electron energy and crossing angle were analyzed. A simple formula was proposed for the fitting of SEP as a function of electron energy and crossing angle.

Local structure modulation of the low La-doped layered strontium manganite Sr4Mn3O10 studied by transmission electron microscopy and electron energy-loss spectroscopy

Transmission electron microscopy (TEM) and electron energy-loss spectroscopy (EELS) have been used to characterize the structure and microstructure of the low La-doped layered manganite LaxSr4−xMn3O10 (x ≤ 0.15). The structure of the perfect phase has been identified as an n = 3 layered structure of the hexagonal series by electron diffraction (ED), high-resolution electron microscopy (HRTEM) together with numerical image simulations. The presence of local superstructure modulation associated with La ordering in the compounds was revealed by electron diffraction and high-resolution electron microscopy. Electron diffraction data indicate that this superstructure modulation is two-dimensional, and the modulation plane lies in the ac plane. The two primary modulation vectors are \( q_{1} = (1/4)a^{*} \) and \( q_{2} = (1/2)c^{*} . \) In addition, another type of modulated structure associated with periodic lattice distortion was occasionally visible in the La0.15Sr3.85Mn3O10 phase. Energy-loss spectroscopy data indicate that the periodic lattice distortion is led by ordered oxygen deficiency.

Energy loss of Cl q+ (52 MeV) through dilute H2 target: Evidence of non-linear term and non-Coulombian potential contribution

This report states about correlated charge and energy loss measurements in the collisional system Cl ions (1.5 Mev/ u) in H 2. A windowless gaseous target with different thicknesses was used to measure simultaneously the charge state distributions (CSD) and the energy losses by the main populated outgoing charge states ( q=12–15). The Markov chain of the charge-changing process was deduced from a Monte-Carlo computation of the CSD evolution. The stopping cross-sections for individual charge states were finally deduced from energy loss data. Comparison of the experimental results with detailed calculations gives a clear evidence of relative importance of the individual contribution of non-linear correction terms and of the electron cloud bound to the projectiles. These two effects may be important for HI-ICF scenarios where a non-equilibrium charge state behavior is likely to occur.

Application of Aberration-Corrected TEM and Image Simulation to Nanoelectronics and Nanotechnology

The image quality in electron microscopy often suffers from lens aberration. As a result of lens aberrations, critical information appears distorted at the atomic scale in high-resolution transmission electron microscopy (HRTEM). In scanning TEM (STEM), the spatial resolution of images and the quality of spectroscopic data are greatly reduced. With the recent introduction of aberration-corrected lenses and monochromators, new and exciting images with sub-0.1-nm spatial resolution are now recorded routinely, and electron energy loss data has been used to determine the location of a single atom in an atomic column. As a result of the decreased focal depth of an aberration-corrected lens used in STEM, the dream of three-dimensional (3-D) atomic resolution is one step closer and for HRTEM it was shown that 3-D imaging with atomic resolution is feasible. However, understanding imaging and spectroscopy in HRTEM and STEM still requires refined modeling of the underlying electron scattering processes by multislice image simulation. Since research into the physics and technology of nanoelectronic devices has already moved into sub-10-nm transistor gate lengths, the need for well-understood imaging and spectroscopy at nanoscale dimensions is already upon us. Fortunately, nanowires and other nanotechnology materials serve as useful test samples as well as being potential materials for future nanoelectronics. This enables early development of microscopy methods that will be used to investigate future generations of integrated circuits

A simple and accurate approach for calculating the vibration spectra of molecules on surfaces: Comparisons to high resolution electron energy loss data for ethylene on silicon

Peak assignment is a complex but important task for analyzing the vibration spectra of surface-bound molecules. Here we describe a simple approach for calculating infrared and Raman spectra for surface-bound molecules using a cluster model approach with quantum capping potentials (QCPs). The utility of the approach is demonstrated by comparisons to the measured high resolution electron energy loss spectra for ethylene on clean silicon. By capping the silicon cluster with QCPs we computed spectra that agree very well with the HREEL spectrum, allowing us to easily assign the experimental peaks. QCPs are similar to effective core potentials, can be used with any ab initio technique and most computational chemistry packages, and their use requires no special expertise.

Quantitative x-ray photoelectron spectroscopy: Quadrupole effects, shake-up, Shirley background, and relative sensitivity factors from a database of true x-ray photoelectron spectra

An analysis is provided of the x-ray photoelectron spectroscopy (XPS) intensities measured in the National Physical Laboratory (NPL) XPS database for 46 solid elements. This present analysis does not change our previous conclusions concerning the excellent correlation between experimental intensities, following deconvolving the spectra with angle-averaged reflection electron energy loss data, and the theoretical intensities involving the dipole approximation using Scofield's cross sections. Here, more recent calculations for cross sections by Trzhaskovskaya et al. involving quadrupole terms are evaluated and it is shown that their cross sections diverge from the experimental database results by up to a factor of 5. The quadrupole angular terms lead to small corrections that are close to our measurement limit but do appear to be supported in the present analysis. Measurements of the extent of shake-up for the 46 elements broadly agree with the calculations of Yarzhemsky et al. but not in detail. The predicted constancy in the shake-up contribution by Yarzhemsky et al. implies that the use of the Shirley background will lead to a peak area that is a constant fraction of the true peak area including the shake-up intensities. However, the measured variability of the shake-up contribution makes the Shirley background invalid for quantification except for situations where the sensitivity factors are from reference samples similar to those being analyzed.

Actual energy loss due to entropy generation in low-and high-temperature machines and plants

An attempt has been made to interrelate two data sources of decisive importance for analysis of refrigerating, cryogenic, and thermal power plants: data obtained by entropic method of analysis of energy loss and experimental statistical data accumulated over a long period of practical work on thermodynamic efficiency (degree of thermodynamic perfection) of real low-and high-temperature machines and plants. An entropostatistical version of the analysis is proposed.

Electron emission induced by fast heavy ions in a thin silicon crystal

We report observations of backward and forward electron emission by a thin silicon crystal target traversed by $29\phantom{\rule{0.3em}{0ex}}\text{MeV}∕\mathrm{u}$ ${\mathrm{Pb}}^{56+}$ incident ions. For each incident ion we have performed measurements of backward and forward electron emission, of the energy loss and of the charge state of the transmitted ion. The crystal target was traversed by incident ions either in random incidence or in axial alignment conditions. In both cases these correlated measurements bring original information on electron emission. In random conditions, using an incident ion species with a charge quite far from equilibrium, we observe correlations between backward and forward electron emission, that we understand when analyzing the associated charge exchange and energy-loss data. In channeling conditions, we added electron emission measurements to simultaneous energy-loss and charge state measurements (that are known to characterize quite precisely the type of trajectory of a projectile transmitted through a thin crystal). This allowed us to observe the reduced electron emission due to hyperchanneled ions, that interact mainly with target valence electrons, and also the enhanced electron emission due to projectiles entering the crystal very close to atomic strings.

A TEM study of nanoparticles in lustre glazes

Transmission electron microscopy (TEM) has been used to investigate the nanoscale morphology of some contemporary lustre glazes. High-resolution TEM, electron energy-loss spectroscopy and energy-dispersive X-ray analysis data imply that two kinds of nanoparticles are present in the lustre layer, namely metallic Ag and metallic Cu particles. Moreover, these particles appear separated in the material. The dense top layer consists of Ag particles and the particles occurring below this upper layer are metallic Cu. A depth profile of the sizes of the nanoparticles with respect to their penetration depths has been drawn. The particle sizes are mainly situated in the range of 5 nm to 15 nm, though smaller and larger particles occur frequently.

Surface Phonons of D:C(001)−(2×1)

We report the surface phonon spectrum of the deuterium-terminated D:C(001)-(2×1) surface calculated using a semiempirical total energy approach. The surface exhibits a number of salient normal modes whose vibrational nature is analyzed. The calculated mode energies are found to be in gratifying agreement with recent electron energy loss data and allow us to identify the physical origin of the measured features.