Energy Loss Spectroscopy Spectra Research Articles

UHV AFM based colloidal probe studies of adhesive properties of VAlN hard coatings

Abstract The adhesion of polystyrene (PS) on V0.27Al0.29N0.44 and the related influence of the oxidation states of both surfaces was investigated using X-Ray Photoelectron Spectroscopy (XPS) and Colloidal Force Spectroscopy (CFS) in Ultra-High Vacuum (UHV). Complementary, the intimate relation between the adhesion force, the chemical structure and surface polarizability was investigated by XPS valence band spectroscopy and the calculation of non-retarded Hamaker coefficients using Lifshitz theory based on optical data as derived from Reflection Electron Energy Loss Spectroscopy (REELS) spectra. The combined electron and force spectroscopic analysis of the interaction forces disclosed quantitatively the separation of the adhesion force in van der Waals and Lewis acid-base contributions. Further, the surface polarizability of VAlN was shown to be unaffected by oxygen incorporation due to the formation of an only gradually oxidized surface comprising a range of vanadium oxidation states. In contrast, the adhesion force analysis revealed additional Lewis acid-base interactions between the oxidized and non-oxidized VAlN surfaces and carboxyl groups present in the surface of PS after an oxidative oxygen beam treatment.

General theory of intraband relaxation processes in heavily doped graphene

The frequency and wave-vector-dependent memory function in the longitudinal conductivity tensor of weakly interacting electronic systems is calculated by using an approach based on quantum transport equations. In this paper, we show that there is a close relation between the single-electron self-energy, the electron-hole pair self-energy, and the memory function. It is also shown in which way singular long-range Coulomb interactions, together with other $\mathbf{q}\ensuremath{\approx}\mathbf{0}$ scattering processes, drop out of both the memory function and the related transport equations. The theory is illustrated on heavily doped graphene, which is the prototype of weakly interacting single-band electron-phonon systems. A steplike increase of the width of the quasiparticle peak in angle-resolved photoemission spectra at frequencies of the order of the frequency of in-plane optical phonons is shown to be consistent with the behavior of an intraband plasmon peak in the energy loss spectroscopy spectra. Both anomalies can be understood as a direct consequence of weak electron scattering from in-plane optical phonons.

Quantification of absolute iron content in mineral cores of cytosolic ferritin molecules in human liver

The authors present aberration corrected scanning transmission electron microscopy (SuperSTEM) and electron energy loss spectroscopy (EELS) spectrum imaging data for the iron hydroxide mineral cores of cytosolic ferritin molecules in situ within human liver sections measured at a controlled electron dose. The authors have quantified the absolute iron content in individual cores using EELS and have checked the results against similar data obtained from synthetic maghemite nanoparticles of known composition and dimensions. Using these results the authors have then determined the quantitative relationship between the STEM high angle annular dark field (HAADF) image intensity of a ferritin core normalised to the background matrix intensity and the absolute iron content of the core as determined by EELS. This procedure then allows us to perform a rapid assessment of the iron content of any core within a tissue section based on the STEM HAADF image intensity.

EELS Spectrum Imaging and Tomography Studies of Simulated Nuclear Waste Glasses

AbstractElectron energy loss spectroscopy (EELS) has been widely used in analysis of ceramic, minerals and semiconductors. It can provide the unique advantage of sensitivity to composition, coordination and valency, while providing nano-scale spatial resolution. Due to the electron irradiation sensitivity, EELS studies on glass are quite rare. However, using special care in glass-composition selection and by recording time series of EELS-spectra to monitor any structural changes, EELS then becomes a very useful technique to study glass-chemistry and glass structure with the highest spatial resolution of all chemically sensitive techniques. Alkali borosilicate glasses (ABS) doped with Cr2O3 (2 mol%), CeO2 (4 mol%) and ZrO4 (4 mol%) were melted, cooled and annealed in the context of simulating radionuclide immobilisation glasses. Precipitates with diameter in the range of ∼20 nm to ∼200 nm were found homogeneously distributed in the glass. In preliminary studies we measured the oxidation state in the glass and in precipitates via evaluation of the Ce-M-edge double white line ratio, confirming the crystals as Ce(IV) oxide. We also found Boron K-edge ELNES spectra as a sensitive signal to boron coordination (N4 = BO4/(BO3+BO4)), which is found at N4 ratios of around 35-45%.In the present study we have extended this work to the acquisition of dense line scans (spectrum imaging) across an area of interest on our composite glass with emphasis on three questions:(i) Change of cerium valence upon transition from the glass to the precipitates?(ii) Possible oscillation of boron N4-ratio in the glass within a line scan as a consequence of random medium-order related glass fluctations when scanning the <5nm probe across a seemingly homogeneous area?(iii) N4-changes in the immediate glass layer surrounding the precipitates?Our ongoing research has produced results which prove a systematic change of the Ce oxidation state from precipitates (+IV) to glass (mixed +III/+IV). It is found that boron coordination is constant within the sensitivity given by signal-to-noise in the glass matrix. A change of the Boron K-edge fine structure upon crossing a nanoparticle during one particular linescan has been observed, which could hint to a coordination change of the glass layer surrounding the particle. Other linescan measurements have not shown any change and acquisition of an enlarged better statistic is work in progress.The ABS-glass with distributed nanoparticles provides an ideal example of a 3D nanocomposite. The only proven technique for the three-dimensional reconstruction of such materials on the nanoscale is electron tomography. We present the first results of a 3D reconstructed nuclear waste glass by using a tilt series of ADF STEM images covering a glass fragment of 2000nm field of view containing several tens of nanoparticles distributed around its volume.

An evaluation of the differential inelastic mean free path from REELS spectrum using Monte Carlo simulation: application to TiC

In previous work, we showed that reflection electron energy loss spectroscopy (REELS) spectra for primary 1 keV electrons reflected from a gold surface were affected significantly by both multiple inelastic scattering and multiple elastic scattering. This work aims at developing analytical and experimental REELS techniques in order to obtain the differential inelastic mean free path (DIMFP) for real samples. From Monte Carlo simulation, we point out that there are specific experimental conditions under which DIMFP analysis avoids the complicated effect of the differential elastic scattering cross-section. An application of this approach to TiC reveals that surface excitation is the essential contribution to DIMFP for TiC.

Grain boundary bonding state and fracture energy in small amount of oxide-doped fine-grained Al2O3

Grain boundary structure and chemical bonding state were characterized in high-purity Al2O3, 0.1 wt% MgO, 0.1 wt% Y2O3 or 0.1 wt% ZrO2-doped Al2O3. High resolution electron microscopy (HREM) and energy dispersive X-ray spectroscopy (EDS) revealed that all samples examined have single phase structure, and that doped cations segregate along grain boundaries. Electron energy loss spectroscopy (EELS) spectra taken from grain boundaries in doped Al2O3 shows slight chemical shift in comparison with those from grain interior. This result suggests that the chemical bonding state in grain boundaries changes by the segregated ions. The change in chemical bonding state seems to affect the grain boundary fracture energy of Al2O3.

The growth mode of aluminium on silver (111)

The geometric and electronic structures occuring during the growth of Al on a single crystal Ag(111) surface have been studied using a combination of low energy electron diffraction (LEED), Auger electron spectroscopy (AES), energy loss spectroscopy (ELS) and work function measurements. The Auger signal versus deposition time plots, which were used to monitor the growth mode, are shown to behave in an identical fashion to that expected for layer-by-layer (Frank-van der Merwe) growth. LEED was used to determine the lateral periodicity of thin Al films and shows that Al forms, at very small coverages, 2D islands which have the same structure as the Ag(111) substrate and which grow together to form the first monolayer. At substrate temperatures of 150 K a well defined (1 × 1) structure with the same orientation as the underlying Ag(111) can be seen up to at least 12 ML. After completion of the third monolayer the ELS spectrum approached that observed for bulk aluminium. At a coverage of 3 ML the work function decreases by 0.4 eV from the clean silver value.

Characterization of epitaxial (111) MgO thin films

(111)-oriented MgO thin films were epitaxially grown on ultrahigh-vacuum-cleaved mica. The MgO films were characterized in situ by Auger electron spectroscopy (AES), energy loss spectroscopy (ELS), and electron energy loss fine structure (EELFS). AES and ELS spectra are characteristic of bulk MgO, but Auger peak intensities indicate a magnesium enrichment of the MgO film surface. EELFS measurements on clean MgO and on MgO films covered with epitaxially deposited Pd clusters suggest that the (111) MgO polar surface is terminated by magnesium atoms.

Lifetimes of molecular negative ion resonances on surfaces

Publisher Summary This chapter discusses the lifetimes of molecular negative ion resonances on surfaces. The lifetime of the resonance of molecular O 2 physisorbed on graphite is qualitatively probed via the ratio of overtone to fundamental vibrational intensities in the resonant energy loss spectroscopy (EELS) spectrum as a function of surface coverage. Resonant vibrational excitation occurs because of nuclear motion in the potential of the temporary negative ion formed by electron capture. The impact energy is set near the observed peak in the cross-section for vibrational excitation, close to the peak assigned by gas phase workers to the ion state. The frequencies of the observed modes correspond to the fundamental and overtone excitations of gas phase O 2 . Future work is planned to focus on the coverage dependence of the resonance lifetime and also of shifts in the resonance energy.

The oxidation of polycrystalline boron: The interpretation of AES and ELS results

The room temperature oxidation of polycrystalline boron has been studied by Energy Loss Spectroscopy (ELS) and Auger Electron Spectroscopy (AES). Features of the ELS spectra from oxidized boron are interpreted as transitions from valence levels to excitonic and conduction band states as well as plasmon losses from elemental boron. The energy dependence of these features is consistent with the surface being partially oxidized with domains of both elemental and oxidized boron. Background-subtracted, deconvoluted B(KVV) Auger spectra from oxidized boron are found to consist of a superposition of clean and oxidized features consistent with this model. We observed some electron beam induced reduction of the oxide surface. The oxide lineshape is interpreted in a manner analogous to recent work on SiO 2 and found to be B 2O 3-like. The AES lineshape of elemental boron is compared with those obtained from other second row elements.