Parallel Electron Energy Loss Spectrometer Research Articles

Effects of Cu and Ag additions on age-hardening behavior during multi-step aging in AlMgSi alloys

Low Cu and Ag additions (≤0.10at%) were found to strongly affect the age-hardening behavior in AlMgSi alloys with Mg+Si>1.5at%. The hardness increased during aging at 170°C and the formation of β″ precipitates was kinetically accelerated. The activation energy of the formation of the β″ phase was calculated to 127, 105, 108 and 99KJmol−1 in the base, Cu-added, Ag-added and CuAg-added alloys, respectively using the Kissinger method. The negative effect of two-step aging caused by the formation of Cluster (1) during natural aging was not overcome by the addition of microalloying elements. However, it was suppressed by the formation of Cluster (2) through a pre-aging at 100°C. Quantitative analysis of the precipitate microstructure was performed using a transmission electron microscope equipped with a parallel electron energy loss spectrometer for the determination of specimen thickness. The formation of Cluster (2) was found to increase the number density of β″ precipitates, whereas the formation of Cluster (1) decreased the number density and increased the needle length. The effects of low Cu and Ag additions in combination with multi-step aging are discussed based on microstructure observations and hardness and resistivity measurements.

Nuclei for heterogeneous formation of graphite spheroids in ductile cast iron

The crystal structure and composition of nuclei for graphite spheroids in a ductile cast iron containing small amounts of magnesium and traces of aluminium have been studied in a transmission electron microscope equipped with EDX and parallel electron energy loss spectrometer and in an electron microprobe analyser. The particles were identified as Al–Mg–Si nitrides, having a trigonal superlattice crystal structure derived from a hexagonal AlN type fundamental cell. The superlattice can be indexed according to a hexagonal Bravais lattice, with parameters a=0.544 nm and c=0.482 nm. The parameters of the fundamental cell are af=0.314 nm and cf=0.482 nm, deviating only 1–3% from the parameters of hexagonal AlN. Based on the compositional analysis, the chemical formula of the nitride particles is suggested to be AlMg2.5Si2.5N6.

Quantitative Measurement of Compositional Enrichment in Strained Alloy Quantum Dots

High spatial resolution information on the structure and composition of semiconductor quantum dots is necessary to relate microstructure to macroscopic electron-optical properties [1]. Scanning transmission electron microscopy (STEM) combined with electron energy-loss spectroscopy (EELS) can be used to determine the elemental composition of nanometer-sized particles. Applying these techniques to quantum dots is challenging because the dot nucleates on a very thin wetting layer of similar composition and is embedded in a matrix. Here we present a strategy to extract absolute compositional information on InGaAs dots. The method relies on modeling both the dot shape and the electron probe profile.Samples were prepared by depositing four monolayers of In0.5Ga0.5As onto a GaAs substrate giving a nominal wetting layer thickness of 1.2 nm [2]. STEM was performed on a Vacuum Generator's HB501 equipped with a GATAN parallel electron energy-loss spectrometer. An ES Vision system was used to acquire spatially resolved electron energy-loss spectra from the wetting layer and the quantum dots.

Microscopic Analysis of Twin Grain Boundaries in Alumina

Extended structural defects in α-Al2O3 (alumina), a technologically important, complex ceramic material were quantitatively analyzed with respect to grain boundary segregation, atomic and electronic structures using spatially resolved electron energy-loss spectroscopy (EELS), energy dispersive X-ray spectroscopy (EDS) and first-principles local-density-functional (LDFT) calculations. in this study the results of analytical investigations will be compared with the outcome of LDFT calculations.The analytical measurements were performed with a dedicated scanning transmission electron microscope (TEM) VG HB501UX, operating at 100 kV and with a typical beam diameter of lnm. For the spatially resolved EELS a parallel electron energy-loss spectrometer (Gatan model 666) with an energy resolution of better than 0.8 eV was used. For the chemical analysis an EDS system (Noran-Gresham with a Si(Li) detector and a Norvar window) was applied. The detection limit of the EDX system for measuring interface excess is in the range of 0.3 atoms/nm2.

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).

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...

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.

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.

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.

Localization of Calcium in Porcine Epidermis Using Electron Energy Loss Spectroscopy (EELS)

The properties of biological systems are often governed by variations in the distribution of trace (0.01-0.1%) constituents. The importance of calcium ions for differentiation and proliferation of keratinocytes in vitro is well known. The situation in vivo warrants study. A major contribution to that study involves the determination of calcium ion distribution in the stratified layers of the epidermis. We describe here the first study to localize and verify calcium distribution in chemically fixed porcine skin using EELS.Freshly dissected porcine skin is processed according to Menon and Elias. Briefly, tissue fixed in a buffer containing 90 mM potassium oxalate and formaldehyde/glutaraldehyde is post fixed in 1% osmium tetroxide containing 2% potassium pyroantimonate. Control specimens are prepared without pyroantimonate treatment. Tissue dried in a graded series of acetone is embedded in Spurr resin and 30-40 nm sections are cut. Stained and unstained sections are examined using a Philips CM 20 FEG TEM equipped with parallel electron energy loss spectrometer (Gatan EELS) and a spectrum imaging system (EMiSpec). The microscope is used in STEM mode for the EELS work and second difference spectra are acquired.

Momentum-resolved low-loss EELS in oxide superconductor

Valence band EELS spectra can be analyzed in terms of dielectric theory by Kramers-Kronig analysis. While dielectric function can also be obtained by optical techniques with higher energy resolution, EELS offers several advantages over the optical techniques: (i) transmission EELS is a bulk sensitive techniques and can provide dielectric function in a wide energy range (from infrared to soft x-ray); (ii) a large momentum (q) transfer in EELS, under favorable condition, can give rise to optical forbidden transitions; (iii) such q-resolved EELS spectra can be used to determine the localized (or otherwise) nature of excitations. In addition to that, a cold field emission gun (cFEG) electron microscopy (TEM) equipped with a parallel electron energy loss spectrometer provides a reasonable energy resolution (~0.5 eV), a small beam probe and a high counting rate, which eases conditions of sample preparation and makes certain EELS measurements more feasible to do, such as crystal orientation dependent dielectric function and dispersion of excitations in solids without acquiring a large size single crystal.

Application of High Spatial Resolution Electron Diffraction Techniques to the Study of Local Properties of Crystalline Solids

ABSTRACTThe addition of a Gatan imaging parallel electron-energy loss spectrometer (IPEELS) to a Hitachi HF 2000 cold field emission TEM has allowed us to produce high quality energy-filtered coherent electron diffraction patterns and electron holograms from a wide variety of materials. In this paper we review the recent achievements and make an assessment of the use of coherent electron diffraction in solving problems at high spatial resolution in materials science.

Commercial spectrometer modifications for energy filtering of electron diffraction patterns and images

A commercial parallel electron energy loss spectrometer (PEELS) system has been modified to allow it to record, line by line, two-dimensional energy-filtered electron diffraction patterns or images. The results given for convergent beam electron diffraction patterns in silicon show that the performance of the system is intermediate between that of an imaging energy filter (such as an omega filter) and a serial scanned readout Grigson system.

The experimental conditions for Compton scattering in the electron microscope

Electron Compton scattering from solids (ECOSS) is a technique for obtaining the momentum density distributions of charge carriers in a solid on a scale of mu m or less. The authors discuss the possibilities and the problems of this experimental technique, which uses a conventional transmission electron microscope (CTEM) equipped with a parallel electron energy-loss spectrometer (PEELS). Favourable experimental conditions are proposed, including a scattering geometry that minimizes contributions from Bragg scattering. The procedures leading from raw spectra to Compton profiles that can be compared with theoretical predictions are described, with emphasis on background handling and deconvolution. It is shown that experiments agree well with theory. An ultimate momentum resolution of 0.05 atomic units appears feasible.

In-Situ Electron Energy Loss Spectroscopy of Silicon Carbide Crystals During Electron Irradiation After Hydrogen Ion Implantation

Observations of damage structure and analysis of compositional changes are important to elucidate the fundamental process of radiation damage in ion-irradiated ceramics. We have developed an in-situ observation system consisting of a 100 keV transmission electron microscope linked with both an ion accelerator and a parallel electron energy loss spectrometer (P-EELS), as shown in Fig.1[1,2]. Using this system, the plasmon loss peaks of SiC crystals were found to shift to the lower energy side during hydrogen ion irradiation at room temperature (RT)[3].The present paper reports the results of in-situ observation and analysis by P-EELS of SiC crystals during hydrogen ion irradiation and the effects of 100keV electron irradiation after hydrogen ion implantation.Specimens used in the present work were SiC sintered crystals supplied from Hitachi Research Lab., Hitachi LTD. Thin films suitable for electron microscopy were made by 2-4 keV Ar+ions etching after mechanical polishing and then irradiated with 10keV H2+ions by use of ion accelerator combined with EM at RT and 800 °C, respectively.

Iron L 3,2 near-edge fine structure studies

L 2,3 near-edge fine structures of iron in different oxidation states and coordination numbers, measured with a parallel electron energy-loss spectrometer operating at 1.0–1.3 V resolution, show distinct splittings of the white lines. The splittings have been interpreted in terms of a simple atomic approach involving ligand field splitting of the d orbitals. It is shown that Fe(III) fine structure is particularly sensitive to its coordination.

Electron-beam damage of oxides at high current densities

It is well-known that electron-beam irradiation within the electron microscope can induce a variety of surface reactions. In the particular case of maximally-valent transition-metal oxides (TMO), which are susceptible to electron-stimulated desorption (ESD) of oxygen, it is apparent that the final reduced product depends, amongst other things, upon the ionicity of the original oxide, the energy and current density of the incident electrons, and the residual microscope vacuum. For example, when TMO are irradiated in a high-resolution electron microscope (HREM) at current densities of 5-50 A/cm2, epitaxial layers of the monoxide phase are found. In contrast, when these oxides are exposed to the extreme current density probe of an EM equipped with a field emission gun (FEG), the irradiated area has been reported to develop either holes or regions almost completely depleted of oxygen. ’ In this paper, we describe the responses of three TMO (WO3, V2O5 and TiO2) when irradiated by the focussed probe of a Philips 400ST FEG TEM, also equipped with a Gatan 666 Parallel Electron Energy Loss Spectrometer (P-EELS). The multi-channel analyzer of the spectrometer was modified to take advantage of the extremely rapid acquisition capabilities of the P-EELS to obtain time-resolved spectra of the oxides during the irradiation period. After irradiation, the specimens were immediately removed to a JEM-4000EX HREM for imaging of the damaged regions.