Electron Energy Loss Spectrometer Research Articles

The synthesis, structure and cathodoluminescence of ellipsoid-shapedZnGa2O4 nanorods

We fabricated ellipsoid-shaped ZnGa2O4 nanorods using a newly-designed chemical vapor deposition (CVD) process, different fromthe conventional methods. The optical properties of nanorods were studied usingcathodoluminescence (CL) measurements. The nanorods displayed three distinct emissionscentered at 360, 450 and 550 nm. The luminescence mechanism is thoroughly discussed andexplained based on a detailed structural and compositional study with a transmissionelectron microscope (TEM) equipped with an electron energy loss spectrometer (EELS).

Chemical and photoluminescence analyses of new carbon-based boron oxynitride phosphors

Analyses of newly developed carbon-based boron oxynitride phosphors using an electron energy-loss spectrometer and a spectroflurophotometer were carried out. The results showed that the prepared phosphor powder has covalently bonded boron, nitrogen, and oxygen atoms with a soft carbon framework. Photoluminescence characterization revealed that the resultant phosphor has a direct bandgap transition with defect broadened band edges, resulting in a high quantum efficiency, because the atomic distances of the phosphor are smaller than those of conventional carbon-based boron nitride compounds, which have an indirect bandgap transition and a low quantum efficiency. The atomic distances of the phosphor are smaller owing to the presence of oxygen atoms, which have a higher electron affinity and a smaller covalent bond radius compared with boron, carbon and nitrogen.

Complementary techniques for the characterization of thin film Ti/Nb multilayers

An aberration corrector on the probe-forming lens of a scanning TEM (STEM) equipped with an electron energy-loss spectrometer (EELS) and X-ray energy-dispersive spectrometer (XEDS) has been employed to investigate the compositional variations as a function of length scale in nanoscale Ti/Nb metallic multilayers. The composition profiles of EELS and XEDS were compared with the profiles obtained from the complementary technique of 3D atom probe tomography. At large layer widths ( h≥7 nm, where h is the layer width) of Ti and Nb, XEDS composition profiles of Ti/Nb metallic multilayers are in good agreement with the EELS results. However, at reduced layer widths ( h≈2 nm), profiles of EELS and atom probe exhibited similar compositional variations, whereas XEDS results have shown a marked difference. This difference in the composition profiling of the layers has been addressed with reference to the effects of beam broadening and the origin of the signals collected in these techniques. The advantage of using EELS over XEDS for these nanoscaled multilayered materials is demonstrated.

TEM analysis of Cr–Mo–W–B phase in a DS nickel based superalloy

Rene 80 is a precipitation hardened nickel-based superalloy, which is widely used to manufacture components of gas turbine engines for aerospace and power generation applications. It is designed to withstand service temperatures of up to 980 C [1] and possesses remarkable hot corrosion resistance, long-term microstructural stability, and hightemperature strength produced primarily by precipitation hardening by ordered intermetallic Ni3(Al,Ti) c0 precipitates. Directional solidification (DS) processing of the alloy results in further improvement of its elevated temperature properties and permits the use of a higher service temperature, which improves the thermal efficiency of gas turbines [2–5]. It has been reported that in DS Rene 80, the tensile strength is increased by about 10–15% and the creep rupture life is extended by 2–4 times relative to conventionally cast material [5]. Boron is an essential minor elemental addition to these heat resistant materials primarily to improve their creep rupture properties [3, 4]. Nevertheless, it has been recognized that the mode in which boron exists on grain boundary regions, either in austenitic solid solution form or selectively partitioned into second phase particles, can significantly influence the creep properties of superalloys [6, 7]. Experimental study is crucial in establishing the presence and nature of intergranular borides in multi-component superalloys due to the influence of interfacial elemental segregation that is not generally considered during thermodynamic equilibrium calculations of theoretical models [8]. The objective of this investigation was to perform transmission electron microscopy (TEM) study of heat-treated DS Rene 80 superalloy to understand the nature of boron rich second phase particles present along its grain boundary regions. The composition of the DS Rene 80 material used in this study was (wt%) 0.2C, 14.1Cr, 9.52Co, 4.0W, 3.98Mo, 0.02Nb, 0.18Fe, 2.9Al, 4.98Ti, 0.028Zr, 0.013B balance nickel. The alloy was subjected to standard solution heat treatment for 2 h at 1200 C and was subsequently aged at 1025 C for 16 h. Thin foils from the aged material for TEM study were prepared by mechanical polishing and dimpling to a thickness of less than 10 lm followed by ion milling in a Gatan precision ion polishing system (PIPS). TEM microchemical and crystal-structure analyses were performed in a field emission gun JEOL 2100F scanning transmission electron microscope equipped with Oxford energy dispersive spectrometer (EDS), Gatan imaging filter (GIF) system, and electron energy-loss spectrometer (EELS). High-resolution TEM micrographs were filtered using an inverse fourier fast transform (FFT) program in Gatan Digital Micrography software. A TEM boron post-edge electron energy loss image of the heat-treated alloy consisting of c0 precipitates and particles of a different phase along the grain boundary and inside the grain identified with arrows is shown in Fig. 1a. Microchemical analysis by X-ray energy dispersive spectroscopy indicated that the particles are rich in Cr, Mo, W, and B (Fig. 1b), and have much different composition from the adjoining regions (Fig. 1c). The presence of boron in the particles was further confirmed by EELS analysis (Fig. 1d) and EELS-based energy filtered transmission electron microscopy (EFTEM) elemental mapping (Fig. 1e). TEM Electron diffraction pattern (EDP) analysis was performed by systematic titling of particle of this phase along certain crystallographic directions to determine its crystal structure. Figure 2a is a [001] zone-axis EDP showing a fourfold symmetry of the phase. Figure 2b and c were obtained by H. R. Zhang O. A. Ojo (&) Department of Mechanical and Manufacturing Engineering, University of Manitoba, Winnipeg, MB, Canada R3T 5V6 e-mail: ojo@cc.umanitoba.ca

An energy stabilized post-column electron energy-loss spectrometer for transmission electron microscopy

An energy stabilizing system for electron energy loss spectrometers in a transmission electron microscope (TEM) is described. A wire-based fast response detector is used to position the zero-loss peak. A digital-based real-time processor is used to stabilize the energy-dispersed electron spectrum and simultaneously to acquire a drift corrected electron energy loss spectrum. The performance of the stabilizing system is evaluated.

An energy stabilizing system for electron energy-loss spectrometers in transmission electron microscopy

An energy stabilizing system for electron energy loss spectrometers in a transmission electron microscope (TEM) is described. The key element is a wire sensor based fast electron detector that can sample the 'zero-loss' component of the transmitted electrons at a high refreshing rate. A digital based real-time processor is used to determine the relative shift in the zero-loss component beam and to produce a closed feedback loop to stabilize the energy dispersed electron distribution at the back focal plane of the post-column spectrometer. The system had the distinctive advantage of simultaneously acquiring a drift corrected electron energy loss spectrum over the energy range where the beam is sensed while stabilizing the whole energy loss distribution for more efficient acquisition by a separate (parallel) detector. A TEM version of the alignment figure is described to aid the alignment and operation of the system for an energy stabilized post-column spectrometer in a conventional transmission electron microscope. The effect of aberration on the accuracy of the energy stabilization is discussed. © 2008 Elsevier B.V. All rights reserved.

Studying Atomic Structures by Aberration-Corrected Transmission Electron Microscopy

Seventy-five years after its invention, transmission electron microscopy has taken a great step forward with the introduction of aberration-corrected electron optics. An entirely new generation of instruments enables studies in condensed-matter physics and materials science to be performed at atomic-scale resolution. These new possibilities are meeting the growing demand of nanosciences and nanotechnology for the atomic-scale characterization of materials, nanosynthesized products and devices, and the validation of expected functions. Equipped with electron-energy filters and electron-energy-loss spectrometers, the new instruments allow studies not only of structure but also of elemental composition and chemical bonding. The energy resolution is about 100 milli-electron volts, and the accuracy of spatial measurements has reached a few picometers. However, understanding the results is generally not straightforward and only possible with extensive quantum-mechanical computer calculations.

EELS analysis of internal metal – oxide interfaces

Abstract The heterophase boundaries between precipitates such as spherical amorphous SiO particles inside a copper matrix as well as crystalline CuO precipitates inside a silver matrix and the surrounding metal matrix are examined with high spatial resolution using a scanning transmission electron microscope equipped with an electron energy loss spectrometer. Typical features of the electron energy loss near – edge fine structure of the oxygen O-K and of characteristic metal ionization edges allow determination of the bonding state of oxygen and thus detection of fine interlayers at the phase boundary. The results obtained are interpreted in a tentative way, supporting basic ideas of Kirchheim's structural vacancy model of oxygen segregation to metal – oxide interfaces. The model predicts that no interfacial accumulation of excess oxygen should occur to the phase boundary of amorphous precipitates. In Ag – Cu alloys there is the additional degree of freedom for the oxidation value of copper and we present indications that structural vacancies change the oxidation value at the phase boundary.

Ultra-thin and high-aspect-ratio TiN nanosheets

Ultra-thin and high-aspect-ratio titanium nitride (TiN) nanosheets were successfully synthesized by a chemical vapor deposition method using TiCl 4 and N 2 as source materials without catalyst assistance. Nanosheet thickness was around 3.2 nm determined from atomic force microscopy (AFM) and electron energy-loss spectrometer (EELS) measurements. According to FESEM images, length of nanosheet ranged from 5 to 20 μm, indicating that the nanosheets had the high aspect ratio in the range between 1500 and 5500. Because of the extremely thin thickness, translucent TiN nanosheets were capable of exhibiting bending, folding, as well as rolling. The 1 3 {2 2 0} and 1 3 {4 2 2} forbidden reflections were observed in SAED patterns, confirmed by the observation of the threefold {4 2 2} lattice fringes in high-resolution transmission electron microscopy (HRTEM) image. The observed and possible minor phases such as TiSi 2, Si 3N 4 and titanium oxynitride probably resulted from the complex reactions involving TiCl 4, TiN and Si substrates.

Photoluminescence enhancement of ZnS:Mn nanoparticles by SiO 2 coating

ZnS:Mn nanoparticles (∼3.1 nm) of a cubic structure were prepared by a coprecipitation method and then dispersed with various weights (0.5–8 g) into a solution containing ammonium hydroxide, ethanol and tetraethyl orthosilicate (TEOS) for surface coating. X-ray diffraction (XRD) analysis of these coated ZnS:Mn powders revealed the presence of amorphous materials after the coating process. Characterization of the coated powders using a transmission electron microscope (TEM) and an electron energy loss spectrometer (EELS) showed that ZnS:Mn nanoparticles were randomly embedded in the larger particles of amorphous SiO 2 (50–100 nm). The optical properties of photoluminescence (PL) and diffuse reflection of the SiO 2-coated ZnS:Mn powders were found to depend on the quantity of ZnS:Mn nanoparticles in the coating solution. The increased PL intensity of ZnS:Mn at 590 nm after SiO 2 coating was proposed to result from the inhibition of excitation energy transfer to quenching centers or surface states based on the observation of the reduced absorption in the region of 370–450 nm.

Cross sections for low-energy electron scattering from adenine in the condensed phase

Measurements of the vibrational and electronic excitation of a sub-monolayer up to a monolayer film of adenine were performed with a high resolution electron energy-loss (HREEL) spectrometer. The integral cross sections (over the half-space angle) for excitation of the normal vibrational modes of the ground electronic state and electronically excited states are calculated from the measured reflectivity EEL spectra. Most cross sections for vibrational excitation are of the order of 10(-17) cm(2), the largest being the out-of-plane wagging of the amino-group and the six-member ring deformations. A wide resonance feature appears in the incident energy dependence of the vibrational cross sections at 3-5 eV, while a weak shoulder is present in this dependence for combined ring deformations and bending of hydrogen atoms. For the five excited electronic states, at 4.7, 5.0, 5.5, 6.1 and 6.6 eV, the cross sections are of the order of 10(-18) cm(2), except in the case of the state at the energy of 6.1 eV, for which it is two to three times higher.

High resolution electron energy loss spectrometer for the study of vapor phase samples

An electron energy loss spectrometer for measuring vapor phase and gaseous samples is described. Electron energy losses of krypton and xenon due to excitations of valence electrons are presented. The energies of the loss peaks are assigned and compared with existing data. Relative intensities of transitions in different scattering angles are presented. Using the data obtained from these results the performance of the spectrometer is evaluated. Future plans, modifications and improvements are discussed.

Iron filled singlewalled carbon nanotubes – synthesis and characteristic properties

AbstractAn efficient and simple wet chemistry methodology to synthesize iron filled singlewalled carbon nanotubes (Fe‐SWCNT) is presented. The route leads to the formation of long continuous iron cables within the tubes. Partial filling is also observed. The morphology, high filling aspect and the chemical profile of the produced sample is studied by high resolution transmission electron microscopy and its X‐ray energy dispersive spectroscopy (EDX) mode. The bulk scale chemical composition is confirmed with a bulk sensitive electron energy‐loss spectrometer (EELS). The resulting material exhibits ferromagnetic properties at room temperature and 3 K. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

High‐Pressure Synthesis of a Gallium Oxonitride with a Spinel‐Type Structure.

AbstractFor Abstract see ChemInform Abstract in Full Text.

Advances in Gallium Oxonitride Ceramics: A New Class of Materials in the System Ga‐O‐N

AbstractThis research news highlights the history, synthesis and new developments of gallium oxonitride phases. Many practical applications are expected of this class of materials because of its analogy to aluminium oxonitride phases. A new approach to gallium oxonitride ceramics is a synthesis pathway starting from a precursor that provides gallium simultaneously bonded to nitrogen and oxygen on a molecular level. One suitable precursor is the dimethylamine adduct of gallium tris‐(t‐butoxide), Ga(OtBu)3·HNMe2. The optimization of the pyrolysis process was controlled by analyzing the nitrogen to oxygen content and the reduction of carbon content in the ceramic. The samples were investigated using FTIR spectroscopy and elemental analysis. The degree of crystallinity was determined by transmission electron microscopy in combination with an electron energy loss spectrometer. The precursor‐derived gallium oxonitride ceramic remains nanocrystalline up to 600 °C and reacts to GaN with the wurtzite type structure by loss of all oxygen in an ammonia atmosphere at temperatures above 600 °C.

High-Pressure Synthesis of a Gallium Oxonitride with a Spinel-Type Structure

The new compound Ga2.81O3.57N0.43 was crystallized under high-pressure / high-temperature conditions in a spinel-type structure from a prestructured gallium oxonitride ceramic, which was obtained from the single-source molecular precursor [Ga(OtBu)2NMe2]2 by thermal treatment in an ammonia atmosphere. The optimized precursor-derived gallium oxonitride ceramic remains nanocrystalline up to 600 °C and can be transformed at 7 GPa and 1100 °C into the crystalline phase Ga2.81O3.57N0.43. The structure, homogeneity, and nitrogen to oxygen ratio were determined using TEM coupled with an electron energy loss spectrometer (EELS) and an energy dispersive X-ray (EDX) spectrometer. For phase analysis and structure confirmation, X-ray powder diffraction data were measured.

An Environmental Transmission Electron Microscope for in situ Synthesis and Characterization of Nanomaterials

The world of nanomaterials has become the real world for most applications in the area of nanotechnology. As postsynthesis handling of materials at the nanoscale level is impractical, nanomaterials must be synthesized directly as part of a device or circuit. The demands of nanotechnology have led to modifications in the design of transmission electron microscopes (TEMs) that enable in situ synthesis and characterization simultaneously. The environmental TEM (ETEM) is one such modified instrument that has often been used to follow gas–solid and/or liquid–solid interactions at elevated temperatures. Although the history and development of the ETEM, also called the controlled atmosphere or environmental cell TEM, is as old as transmission electron microscopy itself, developments in the design of medium-voltage TEMs have succeeded in bringing resolutions down to the subnanometer level. A modern ETEM equipped with a field-emission gun, energy filter or electron energy-loss spectrometer, scanning transmission electron microscopy coils, and bright-field and dark-field detectors can be a versatile tool for understanding chemical processes at the nanometer level. This article reviews the design and operations of a dedicated ETEM. Its applications range from the in situ characterization of reaction steps, such as oxidation-reduction and hydroxylation, to the in situ synthesis of nanomaterials, such as quantum dots and carbon nanotubes. Some examples of the current and the future applications for the synthesis and characterization of nanomaterials are also discussed.

Extended defect related energy loss in CVD diamond revealed by spectrum imaging in a dedicated STEM

This article aims at investigations of the low EEL region in the wide band gap system diamond. The advent of the UHV Enfina electron energy loss spectrometer combined with Digital Micrograph acquisition and processing software has made reliable detection of absorption losses below 10 eV possible. Incorporated into a dedicated STEM this instrumentation allows the acquisition of spectral information via spectrum maps (spectrum imaging) of sample areas hundreds of nanometers across, with nanometers pixel sizes, adequate spectrum statistics and 0.3 eV energy resolution, in direct correlation with microstructural features in the mapping area. We aim at discerning defect related losses at band gap energies, and discuss different routes to simultaneously process and analyse the spectra in a map. This involves extracting the zero loss peak from each spectrum and constructing ratio maps from the intensities in two energy windows, one defect related and one at a higher, crystal bandstructure dominated energy. This was applied to the residual spectrum maps and their first derivatives. Secondly, guided by theoretical EEL spectra calculations, the low loss spectra were fitted by a series of gaussian distributions. Pixel maps were constructed from amplitude ratios of gaussians, situated in the defect and the unaffected energy regime. The results demonstrate the existence of sp 2-bonded carbon in the vicinity of stacking faults and partial dislocations in CVD diamond as well as additional states below conduction band, tailing deep into the band gap, at a node in a perfect dislocation. Calculated EEL spectra of shuffle dislocations give similar absorption features at 5–8 eV, and it is thought that this common feature is due to sp 2-type bonding.

Focus on Laboratory Equipment

Focus on Laboratory Equipment

A multichannel electron energy loss spectrometer for low-temperature condensed films

We describe a wide-gap multichannel cylindrical deflection electron energy analyzer suitable for measuring the weak signals characteristic of electronically inelastic electron energy loss spectra. The analyzer has nearly ideal fringing field termination, and its resolution and energy dispersion were characterized as a function of energy by solving numerically the equation of motion of electrons in an ideal cylindrical electric field. The numerical results for the radial location of the electrons at the detector as a function of the entrance location, angle, and energy are closely approximated by a second order polynomial, and match closely with those observed. The detection efficiency of the analyzer is 100-150 times better than that of an equivalent single-channel instrument, but limited energy transmission of the zoom lens system used in our case reduced it by a factor of about 2. The performance of the new instrument was demonstrated by measuring the (3)E(1u) electronic spectrum of benzene in only 2 min and the spectrum of endo-benzotricyclo[4.2.1.0(2.5)]nonane.