Electron Energy Loss Spectrometer Research Articles

The interfacial reaction and microstructure in a ZK60-based hybrid composite

The oxidation behavior of B4C particles was investigated by measuring the weight changes during isothermal heating at 650 to 800°C. The interfacial microstructure and fractography of the B4Cp and SiCw reinforced ZK60 magnesium hybrid composite was studied using a scanning electron microscope (SEM), a transmission electron microscope (TEM) and an electron energy loss spectrometer (EELS). It was found that the oxidation of B4C particles in air at the temperatures investigated produced an amorphous B2O3 surface layer. The oxidation kinetics was limited by the diffusion rate of oxygen through the liquid B2O3 layer. The oxidation layer was found to dominate the interfacial reaction, the microstructure and the mechanical properties of the hybrid composite. The rod-like MgB2 and the granular MgO were produced due to the reaction between the B2O3 and the magnesium matrix. The intimate bonding between the MgB2 and both the reinforcements and the matrix is believed to be the main reason for the improvement of the mechanical properties of the composite.

Construction of an ELS-LEED: an electron energy-loss spectrometer with electrostatic two-dimensional angular scanning

A new version of an energy-loss spectrometer with low-energy electron diffraction (ELS–LEED, Henzler type EELS) has been constructed. Different from the prototype spectrometer, which is equipped with a single-pass 127° cylindrical deflector analyser, the present spectrometer consists of an Ibach-type double-pass monochromator, an enlarged single-pass analyser and some magnetic lenses in acceleration and deceleration lenses and in the electrostatic deflection unit for high-resolution LEED. As a preliminary result, with the Si(111)−7 × 7 surface, the present spectrometer showed an energy width (full with at half-maximum) of 18 meV at the quasi-elastic peak and a transfer width of 960 Å at the (00) diffraction spot. Copyright © 2000 John Wiley & Sons, Ltd.

The Apex Structure of Co-Produced Helical Boron Nitride and Carbon Cones

Abstract Conical whiskers of layered compounds such as graphite and hexagonal boron nitride (h-BN)2 are interesting materials because their conical morphology results from the introduction of a local topological defect at the cone apex. In the honeycomb array characteristic of graphite and h-BN basal planes, this topological defect is thought to be a non-hexagonal ring (e.g. a pentagon or a square). These defects are known to form the basis of curved nanostructures like fullerenes and buckytubes. Therefore a comparison of their occurrence in two systems known to harbour nanostructures is worthy of study. The defect structure at the apex of co-produced carbon and boron nitride whiskers was investigated by analytical transmission electron microscopy (TEM). The instrument used was a field-emission JEM3000F high-resolution electron microscope, equipped with a parallel electron energy loss spectrometer (EELS).

Ultraviolet/high resolution electron energy loss spectroscopy of CO on Pt(110) and benzene on Pt(110)

Recently there has been some controversy about how CO and benzene adsorb on platinum. With CO, there is disagreement over whether there is back donation of electrons from the metal to the CO 2π* orbital. With benzene, there is disagreement, over whether benzene adsorbs in a distorted state. In this article we use a standard high resolution electron energy loss (HREELS) spectrometer with modified electronics to measure the equivalent of a ultraviolet (UV) spectrum for two different systems: CO on Pt(110) and benzene on Pt(110) and benzene on Pt(110). In the case of CO, the UV spectrum shows peaks at 5.6 and 8.2 eV that may shift slightly with coverage. By comparison, gas-phase CO shows peaks at 6.2 and 8.3 eV. The difference between the gas-phase peak positions and those on the surface are indicative of the antibonding orbitals being stabilized, as one would expect from the Blyholder model. With benzene we observe two different spectra: a first monolayer spectrum with a broad peak centered at 4.9 eV, and a multilayer spectrum with peaks at 0.75, 3.82, 4.71, 6.20, and 6.84 eV. The multilayer spectrum matches the spectrum of condensed benzene, while the first monolayer spectrum is quite different and resembles that of a diene. Together, these results show that UV/HREELS spectroscopy provides useful information about adsorbates on surfaces.

Electron states of YAG probed by energy-loss near-edge spectrometry and ab initio calculations

Abstract Al K, Al L2,3, O K, Y L2,3, and Y M2,3 energy-loss near-edge structures (ELNESs) of Y3Al5O12 (YAG) were measured using a dedicated scanning transmission electron microscope equipped with a parallel electron energy-loss spectrometer system. An attempt was made to interpret the experimental edges with the help of calculated near-edge structures. An ab initio orthogonalized linear combination of atomic orbitals method, within the local density approximation (LDA), was used to calculate the electronic structure of YAG. Site-decomposed and symmetry projected local densities of states (LDOS) and photo-absorption cross-sections (PACS) were compared to experimental ELNES spectra. There is reasonable agreement between the five different, measured spectra and calculated near-edge structures. PACS calculations correlated better than LDOS with the experimental edges in terms of relative intensities of the peaks. Through a comparison with site-decomposed LDOS calculations, several features of the experimental...

High spatial resolution PEELS characterization of FeAl nanograins prepared by mechanical alloying

We investigate the nanograin “chemical” structure in a nanostructured material of possible industrial application (Fe–Al system) prepared by conventional mechanical alloying via ball milling in argon atmosphere. We restrict ourselves to the structural and nanochemical behaviour of ball-milled nanocrystalline Fe–Al powders with atomic composition Fe 3Al, corresponding to a well-known intermetallic compound of the Fe–Al system. Scanning transmission electron microscopy (STEM) equipped with a parallel detection electron energy loss spectrometer (PEELS) has provided an insight on the “chemical” structure of both nanograins and their surface at a spatial resolution of better than 1 nm. The energy loss near edge structure of the Al L loss reveals that the Al coordination is similar to a B2 compound and the oxidation of the powder during processing may play a significant role in the stabilization of the intermetallic phases. Conventional transmission electron microscopy (TEM) was used for the structural characterization of the material after the ball milling; powder X-ray diffraction (XRD) aided the investigation.

Calibration Specimens for Determining Energy-Dispersive X-ray k-Factors of Boron, Nitrogen, Oxygen, and Fluorine.

: We have fabricated amorphous thin-film specimens containing light elements (B, C, N, O, F, and Mg) in addition to silicon, and have measured their composition using electron energy-loss spectroscopy (EELS). The films appear to be stable during storage in air and during irradiation by an electron beam, for doses below 10(5) C/cm2. Used with a transmission electron microscope fitted with an energy-dispersive X-ray (EDX) detector, they provide a convenient means of determining light-element k-factors for X-ray microanalysis. For a TEM equipped with an electron energy-loss spectrometer, the specimens can also be used to check the EELS instrumentation and elemental-quantification procedures.

Improvements in the treatment of elastic electron diffraction profiles for local order determination in polycristalline samples

In this paper we describe how to record on-line filtered diffraction patterns rapidly with a serial electron energy loss spectrometer. A numerical treatment then yields the RDF for structural identification. Differents treatments ways of improving the accuracy of the results are proposed and examined in detail.

High-Resolution Electron Energy Loss Spectroscopy of Cs Vibration on the Ru (0001) Surface

By using a newly implemented high-resolution electron energy loss spectrometer with better resolution, a new loss at a energy near to double energy of the Cs-Ru stretching vibration, and its dependence on Cs coverage for Cs overlayer on Ru (0001) were observed. Since the energy is slightly smaller than the double energy of the Cs-Ru vibration (intrinsic loss), overtone excitation must be responsible for this new loss observed, but two-phonon process is not excluded.

Development of a TEM to study in situ structural and chemical changes at an atomic level during gas-solid interactions at elevated temperatures.

A Philips (Eindhoven, The Netherlands) 430 (300 keV) high resolution transmission electron microscope has been modified for in situ study of gas-solid interactions at elevated temperatures. This microscope can be best described as a synthesis, processing, and characterization laboratory for nano-size materials. A differentially pumped environmental cell (E-cell), capable of handling up to 20 torr of gas pressure, is fitted in the objective lens pole-piece gap. Single-tilt or double-tilt heating holders can be used to heat the samples up to 1,300 degrees C and 850 degrees C, respectively. The system can handle any non-corrosive gases such as H2, O2, N2, NH3, CO, water vapor. Electron diffraction patterns are used to elucidate the reaction path and to identify stable and/or metastable phases formed. Time, temperature, and pressure resolved electron diffraction patterns can also be used to estimate the thermodynamical conditions for the onset of a reaction and the stability range of different phases observed during the process can also be determined. The high resolution imaging capabilities enable elucidation of the basic structural mechanisms involved at near atomic level. The TV rate camera/video recording system is used to measure the reaction rates (kinetics of the reaction). A post projector energy filter (Gatan Imaging Filter, GIF) is attached at the bottom of the microscope in order to filter the inelastic scattering from the gases/thick samples as well as to obtain energy filtered images (chemical maps). The GIF can also be used as a parallel electron energy loss spectrometer (PEELS) to obtain changes in the sample composition during the reactions. The changes in the near-edge structures of PEELS spectrum is used to monitor changes in bonding and/or chemical environment elements during reaction. The chemical maps obtained can also be used to identify preferred regions of gas reactions, e.g., grain boundaries or surfaces, etc. Various modifications of the microscope are described in detail, with suitable examples showing the performance.

RDF Analysis of Radiation-Amorphized SiC using a field Emission Scanning Electron Microscope

Abstract Abstract Fast electrons are a particularly useful chemical and structural probe for the small sample volumes associated with ion- or fast electron-irradiation-induced amorphization, because of their much stronger interaction with matter than for X-rays or neutrons, and also because they can be readily focused to small probes. Three derivative signals are particularly rich in information: the angular distribution of scattered electrons (which is utilized in both diffraction and imaging studies); the energy loss spectrum of scattered electrons (electron energy loss spectroscopy, or EELS); and the emission spectrum of characteristic X-rays resulting from ionization energy losses (energy dispersive X-ray spectroscopy, or EDXS). We have applied the first two to the study of three amorphized compounds (AIPO4, SiO2, SiC) using MIT's Vacuum Generators HB603 field-emission (FEG) scanning transmission electron microscope (STEM), operating at 250 kV and equipped with a Gatan digital parallel-detection electron energy-loss spectrometer (digiPEELS).

An accurate approach for high partial-wave phase shifts in electron elastic scattering from closed-subshell atoms

An approach to calculate elastic differential cross sections of atoms and ions at small angles is shown. The key point of this approach is selecting a suitable slope before integrating the Dirac radial equations. The slope is extracted from the normalization coefficient of continuum state solutions in an effective Coulomb field. The approach is utilized to investigate the influence of high partial-wave phase shifts on the cross sections at small angles. As is known, these phase shifts are mainly produced by long-range forces such as the polarization interaction or the Coulomb interaction or both. Calculations using mercury as an example show the effect of high partial waves and different cut-offs on the small-angle differential cross sections in the first Born approximation at 25 eV. These calculations, at 1500 eV, are compared with the recent measurement with the angle-resolved electron energy-loss spectrometer in Xu's group. Furthermore, calculation results are given at the intermediate energies of 50, 100, 300 and 500 eV where the experimental data are available. Comparisons between the theory and experiment over 9-1500 eV show that further studies at the incident energy of about 100 eV are needed.

Surface state transitions on the reconstructed diamond C(100) surface

The diamond C(100) surface was investigated with a high-resolution electron energy loss spectrometer (HREELS) in both the electronic excitation and surface vibrational excitation regimes. The 0–15 eV electronic excitation spectra on the bare C(100) surface revealed three dominant loss features at 3.5, 4.7 and 5.9 eV. These peaks have been attributed to two mid-gap surface states. These states were absent on the H-terminated surface, indicating that they were localized at the surface and were due either to π-bonded dimers or dangling bonds on the surface. The separation between the states, and their possible positions relative to the valence band maximum, were compared to recent surface band structure calculations, and provide evidence for symmetric dimers on the C(100) surface.

Electron-impact study for the and ( n = 3 - 6) excitations in helium

Differential cross sections and generalized oscillator strengths for the and = 3 - 6) excitations overlapping neighbour non-dipole excitations in helium have been measured by an angle-resolved electron energy loss spectrometer at an impact energy of 1500 eV in a scattering angular range of . These data are first reported at such a high impact energy. Integral cross sections for the above (n = 3 - 6) excitations were also determined. Meanwhile, the absolute optical oscillator strength density spectrum in the valence region of helium was established at the same impact energy in a mean scattering angle of , and the absolute optical oscillator strengths for these discrete transitions corresponding to the valence region of helium are reported. All these experimental results are compared with previous appropriate published data.

Dissociative resonance activation of cyclopropane monolayers on copper: Evidence for CH and CC bond scission

Energy selective electron beam modification of cyclopropane on Cu(110) and Cu(111) single crystal surfaces was performed using the electron beam intrinsic to a high resolution electron energy loss (HREELS) spectrometer. Vibrational spectra of the resulting adsorbed dissociation fragments were recorded using the same HREELS spectrometer. Electron irradiation in the range 10–18 eV of weakly adsorbed cyclopropane was found to lead to the formation of chemisorbed dissociation fragments. HREELS and complementary thermal desorption data were used to identify the chemisorbed products as metallacyclobutane and cyclopropyl groups. The formation of these two surface species implies the existence of two dissociation channels involving CC and CH bond scission, respectively. Variations in the cross section for electron induced modification indicates the presence of a dissociative attachment resonance centered at approximately 10 eV. Cyclopropyl formation and ring opening of cyclopropane at 10 eV are attributed to competition between two decay channels of a core-excited resonance. The cross section for metallacyclobutane formation, at 10 eV, was evaluated to be roughly 0.8×10−17 cm2. The ratio of cyclopropyl to metallacyclobutane surface species, formed at 10 eV, was found to be 4:1.

Ultrahigh-Vacuum Field-Emission Electron Microscope as Applied to Observation and Analysis of Crystal Surface

Abstract UHV(ultrahigh-vacuum) TEM has long been used as a powerful tool for studying crystal surfaces, particularly for both the direct imaging of the surface structure and for in-situ observation of surface reaction processes with atomic resolution. This paper reports a newly developed 200kV UHV TEM equipped with a field emission gun(FEG). The instrument is designed to obtain information about elemental or bonding states of surfaces in addition to observation of surface atomic structure with high contrast. Basic performances of the UHV FE-TEM includes a specimen vacuum of 2.0X10-8Pa, probe size less than 1.0nm Ø with 0.5nA probe current, point-to-point resolution of 0.21 nm, and a lattice resolution of 0.10nm. A UHV Energy Dispersive X-ray Spectrometer (EDS) originally developed by JEOL Ltd. and a Parallel Electron Energy Loss Spectrometer (PEELS) are attached to the UHV FE-TEM, which combined with a fine focused probe of 1.Onm Ø allows atomic scale spectroscopy of surfaces.

PEELS and EXELFS characterization of diamond films grown by the HF-CVD technique on non-scratched Si substrates

We present a detailed energy loss characterization of natural diamond and diamond films grown on non-scratched Si substrates by the hot-filament chemical vapor deposition technique (with the help of a SiC buffer layer). The energy loss experiments were performed in a transmission electron microscope (TEM) with a GATAN-666 parallel electron energy loss spectrometer (PEELS) attachment. Diamond particles are in the 0.5–1 μm size range as observed by TEM. PEELS spectra show that the plasmon and carbon K-edge main features are very similar (in position and shapes) in both natural and our diamond film. The radial distribution function around the carbon atoms was obtained through the Fourier transform of the extended fine structure located in a 300 eV range beyond the carbon K-edge in the energy loss spectra. The values obtained for the C-C distances are very close (within 0.003 nm) to those of natural cubic diamond structure. These results confirm the good quality of the diamond films produced by our experimental technique.

Phosphatidylethanolamine production and iron homeostasis in Pseudomonas fluorescens

Pseudomonas fluorescens was found to grow in a minimal mineral medium containing citrate, the sole carbon source, complexed to 5 mM iron(III). As the tricarboxylic acid was utilized, dialysis and ultracentrifigation analysis of the spent fluid revealed that iron (III) was associated with phosphatidylethanolamine (PE). Atomic absorption studies revealed that the iron concentration in the soluble cellular fraction was maximal at 35 h of incubation and accounted for 1.3% of the total iron. However, at stationary phase of growth, most of the iron was deposited as a PE containing residue. A transmission electron microscope, equipped with an electron energy loss spectrometer (EELS), allowed the visualization of iron bodies within the bacterial cells. However, such metal inclusions were absent in cells isolated at stationary phase of growth.

RDF Analysis of Ion-Amorphized SiO2 and SiC from Electron Diffraction using Post-Specimen Scanning in the Field-Emission Scanning Transmission Electron Microscope

ABSTRACTRadial density functions (RDFs) provide important information about short- and ntermediaterange structure of topologically-disordered materials such as glasses and irradiation-amorphized materials. We have determined RDFs for irradiation-amorphized SiO2, AIPO4 and SiC by energy-filtered electron diffraction methods in a field-emission scanning transmission electron microscope (FEG-STEM) equipped with a digital parallel-detection electron energy-loss spectrometer. Post-specimen rocking was used to minimize the effects of spherical aberration in the objective lens, which interfere with the acquisition of data collected by pre-specimen rocking. Useful energy-filtered data has been collected beyond an angular range defined by q = 2 sin(Θ/2)/λ = 25 nm−1

Investigation of elemental distributions in TiAlNZrN multi-layers using analytical transmission electron microscopy

This microstructural characterisation is described of PVD multilayer coatings. Coatings of TiAlNZrN, approximately 3 μm in thickness were grown on to stainless steel substrates using a combined steered cathodic arc evaporation and unbalanced magnetron sputtering technique. The crystallography and the multilayer periodicities were investigated using X-ray diffraction. Electron-transparent cross-section samples were examined using a conventional transmission electron microscope interfaced with an imaging filter, and with a field emission gun scanning transmission microscope interfaced with an energy dispersive X-ray analyser and a parallel electron energy-loss spectrometer. Quantitative measurements of composition were acquired across individual layers of nominal 13.2 nm spacing using X-ray analysis, but not from layers with periodicity 2.6 nm. However, qualitative elemental distributions from layers of periodicity 2.6 nm were easily resolved using energy-filtered images. The energy-loss spectroscopy also revealed differences in the near-edge fine structure of the nitrogen edge between the two TiAlN and ZrN. It was not possible to clarify the extent of intermixing of the metallic elements between layers.