Parallel Electron Energy Loss Spectroscopy Research Articles

COMBINED HRTEM AND PEELS ANALYSIS OF NANOPOROUS AMORPHOUS CARBON

Both the mass density (1.37 kgm/m 3) and sp3/sp2+sp3 bonding fraction (0.15) were determined for an unusual nanoporous amorphous carbon consisting of curved single graphitic sheets. A combination of High-Resolution Transmission Electron Microscopy (HRTEM) and Parallel Electron Energy Loss Spectroscopy (PEELS) was used. The values of these two parameters provide important constraints for the determination of the structure of this relatively low density variety of nanoporous carbon. The results are relevant also in the search for negatively-curved Schwarzite-related carbon structures. New data are also presented for Highly-Oriented Pyrollytic Graphite (HOPG), Chemically Vapour Deposited (CVD) diamond, C60, Glassy Carbon (GC) and Evaporated Amorphous Carbon (EAC); these are compared with the results for NAC. Kramers-Kronig Analysis (KKA) of the low-loss PEELS data shows that the band gaps of both NAC and EAC are collapsed relative to that of CVD diamond.

Hydrogen-free deposition of diamond-like coatings from a graphite source

We successfully deposited diamond-like hydrogen-free carbon coatings by pulsed electron beam vapor deposition (by pseudospark discharges), which is a novel technique in this field. Transmission electron microscopy and electron diffraction demonstrate that these layers consist essentially of two components: (i) amorphous spherical particles with an average diameter of 50 nm, which form an amorphous particle network, and (ii) single crystalline diamond crystallites of up to 10 μm in diameter. The investigation of the amorphous regions by parallel electron energy loss spectroscopy permits to distinguish amorphous carbon and amorphous diamond.

Multi-imaging and multivariate statistics used for 3D characterization at surfaces

Several microanalytical imaging techniques—energy dispersive X-ray detection, parallel electron energy loss spectroscopy, secondary ion mass spectroscopy, photoelectron spectroscopy and XPS) and scanning Auger microscopy—have reached the stage where they are capable of producing images of a surface with a section of a spectrum in each pixel. The resulting image-spectrum is a complex data structure which requires the use of special methodologies if the data are to be interpreted effectively. Appropriate methods have been developed for Earth satellite image processing and are directly applicable to surface microanalysis. The use of scatter diagrams, interactive correlation partitioning, factor and target factor analysis and principal component analysis are outlined in this paper and their application to semiconducting, catalytic and magnetic structures is illustrated. This field of endeavour can be thought of as being the beginning of an area of study which may be called surface chemometrics .

Ion Gradients Across Contractile Vacuole Membranes of Amoebae Grown Under Different Osmotic Conditions

The contractile vacuole (CV) regulates internal osmolality of free-living protozoa such as amoebae. The CV membrane is known to contain a V-H+ ATPase but the other ion transporters involved in the water pumping mechanism are not yet established. Here we continue our earlier investigation by analytical electron microscopy to measure vacuolar and cytoplasmic ion concentrations inAcanthamoeba castellanii. The present aim is to determine concentrations of ions transported across the CV membrane of amoebae grown under different osmotic conditions.Subcellular ion concentrations in freeze-dried cryosections can generally be determined from x-ray microanalysis using the Hall method.4However, this approach is not suitable for measuring ion concentrations in the CV, which contains mainly inorganic salts and little, if any, organic compounds. A new method based on electron scattering measurements was therefore devised to deal with this highly aqueous compartment. This method involves: (i) measuring the volume of water in the hydrated cryosectioned vacuole with parallel electron energy loss spectroscopy (PEELS); (ii) measuring the mass of vacuolar salt in the freeze-dried cryosection by dark-field scanning transmission electron microscopy (STEM); and (iii) measuring the ratios of ions by energy-dispersive x-ray spectroscopy (EDXS).

Comparison of Techniques for EELS Mapping in Biology

Elemental mapping of biological specimens by electron energy loss spectroscopy (EELS) can be carried out both in the scanning transmission electron microscope (STEM), and in the energy-filtering transmission electron microscope (EFTEM). Choosing between these two approaches is complicated by the variety of specimens that are encountered (e.g., cells or macromolecules; cryosections, plastic sections or thin films) and by the range of elemental concentrations that occur (from a few percent down to a few parts per million). Our aim here is to consider the strengths of each technique for determining elemental distributions in these different types of specimen.On one hand, it is desirable to collect a parallel EELS spectrum at each point in the specimen using the ‘spectrum-imaging’ technique in the STEM. This minimizes the electron dose and retains as much quantitative information as possible about the inelastic scattering processes in the specimen. On the other hand, collection times in the STEM are often limited by the detector read-out and by available probe current. For example, a 256 x 256 pixel image in the STEM takes at least 30 minutes to acquire with read-out time of 25 ms. The EFTEM is able to collect parallel image data using slow-scan CCD array detectors from as many as 1024 x 1024 pixels with integration times of a few seconds. Furthermore, the EFTEM has an available beam current in the µA range compared with just a few nA in the STEM. Indeed, for some applications this can result in a factor of ~100 shorter acquisition time for the EFTEM relative to the STEM. However, the EFTEM provides much less spectral information, so that the technique of choice ultimately depends on requirements for processing the spectrum at each pixel (viz., isolated edges vs. overlapping edges, uniform thickness vs. non-uniform thickness, molar vs. millimolar concentrations).

Chemical nature of the luminescent centre in fresh and aged porous silicon layers

In this study we have used high resolution parallel electron energy loss spectroscopy (PEELS) and X-ray excited optical luminescence (XEOL) to investigate the chemical nature of the luminescence centre in fresh and aged porous silicon. We find that regardless of the non-stoichiometric oxides which were observed by PEELS in our fresh porous silicon layers, SiSi bonded material is involved in the luminescence process. However, in the case of aged porous silicon both SiSi and SiO bonded material are involved.

Mechanical properties and microstructural analysis of a diamond-like carbon coating on an alumina/glass composite

We investigate the mechanical and microstructural properties of a diamond-like carbon coating (DLC) which is deposited by plasma enhanced chemical vapor deposition (PECVD) onto an alumina/aluminosilicate glass composite used for biomedical applications. Ball-on-ring tests yield a fracture strength that is essentially influenced by the surface topology/roughness. The surface topology of the coating is investigated by atomic force microscopy (AFM). Tribology tests and nanoindentation represent the wear resistance and hardness; these are properties that are mainly influenced by the microstructural properties of the DLC coating. This microstructure is investigated by transmission electron microscopy (TEM) and analyzed by parallel electron energy loss spectroscopy (PEELS). For the general applicability of the coated composite, the interfacial adhesion of the DLC coating on the comparably rough substrate (roughness amplitudes and wavelengths are in the micrometer range) is important. Therefore, we focus on TEM investigations that show the interface to be free of gaps and pores that we, together with a characteristic microstructure adjacent to the interface, relate to the excellent adhesion. The interlayer consists of a high density of SiC grains, part of them directly bound to the substrate, and part of them bound to other SiC grains. This interlayer is followed by an essentially different region of the coating as concerns the microstructure; this region consists of nanocrystalline diamond particles embedded in an amorphous carbon matrix. It is this heterogeneous microstructure to which we attribute (i) the good adhesion based upon the interface stabilizing SiC grains, and (ii) the high hardness and wear resistance based upon the diamond nanocrystals in the coating.

An investigation of acceptor-doped grain boundaries in

Grain boundary (GB) doped exhibits interesting electroceramic phenomena including varistor and barrier layer capacitor behaviour. We present here our investigation of GB acceptor-doped using analytical electron microscopy including electron holography. Mn was diffused into sintered polycrystalline to attain GBs which are rich in Mn. The presence and spatial extent of Mn at the GBs were analysed using x-ray emission spectroscopy (XES) and parallel electron energy loss spectroscopy (PEELS). The valence state of Mn was determined using PEELS to be predominantly +2. Finally, transmission high-energy electron holography was utilized to directly image and quantify the electrostatic potential and associated space-charge across the GBs directly. The holography results reveal a negatively charged GB with positive space-charge, indicating that Mn with a valence of +2 resides as an acceptor dopant on the Ti site at the GB core. The barrier height and local charge density distribution, including the Debye length, of the double Schottky barrier at the GB are derived from these holography results. This investigation demonstrates the usefulness of electron holography as a bulk-sensitive technique to probe the statics and dynamics of electrostatic field distribution and electrical charge across interfaces in technologically useful materials, and the need to employ diverse analytical techniques for such an investigation.

The Composition of Fine-Scale Precipitates in Al-Mg-Si Alloys

The compositions of intermediate precipitates in Al-Mg-Si alloys have been examined using atom probe field ion microscopy (APFIM), energy dispersive electron spectroscopy (EDS) and parallel electron energy loss spectroscopy (PEELS). It was found that the Mg:Si ratios in small, equiaxed precipitates, β precipitates and β' precipitates were close to 1.1 (atomic). The Mg:Si ratio in a B' precipitate was approximately 0.9. The implications of these results to the understanding of the mechanical properties of Al-Mg-Si alloys are discussed.

Electron energy loss spectroscopy studies of CoCrTaPt/Cr thin films for high-density longitudinal magnetic recording media

The effects of Ta content in CoCrTaPt thin films on the near-edge structure of Co and Cr L 2.3 absorption edges have been studied using parallel electron energy loss spectroscopy (PEELS). It was found that the addition of Ta decreased the 3d band occupancy in CoCrTaPt thin films. The addition of Ta was also observed to decrease the L 3/L 2 white line intensity ratio, which showed a qualitative correlation with Curie temperature measurements. This result indicates a decrease in the ferromagnetic exchange interaction between neighboring Co atoms which may account for the low noise of CoCrTaPt thin film media.

Parallel electron energy-loss spectroscopy (PEELS) study of B in minerals; the electron energy-loss near-edge structure (ELNES) of the B K edge

The B K-edge spectra of a wide variety of minerals have been measured using the technique of parallel electron energyJoss spectroscopy (PEELS) conducted in a scanning transmission electron microscope (STEM) from sample areas of nanometer dimensions. The B K edges of the minerals exhibit electron energy-loss near-edge structure (ELNES) characteristic of B coordination. For threefold-coordinated B ft3;, the spectra are dominated by a sharp peak at ca. 194 eV because of transitions to unoccupied states of zr* character, followed by a broader peak at ca. 203 eV attributed to states of a* character. The ELNES on the B K edge (B K ELNES) of fourfold-coordinated B (tat3; consists of a sharp rise in intensity with a maximum at ca. 199 eV followed by several weaker structures. For tolB, the ELNES is interpreted as transitions to states of antibonding o* character. Minerals that possess both tstB and talB exhibit an edge shape that is composed of B K edges from the respective BO. and BOo units, and we demonstrate the feasibility of quantifrcation of relative site occupancies in minerals containing a mixture of B coordinations. The origins of the B K ELNES are discussed in terms of both molecular orbital (MO) and multiple scattering (MS) theory. We also present the B K-edge spectra of selected nonminerals and show how differences in edge shapes and energy onsets allow these nonminerals to be readily distinguished from borates and borosilicates.

Interfacial structure and strength of silicon–silicon diffusion bonds

Silicon wafers were bonded in air at various temperatures up to 1200°C. The resultant interfacial structures were analysed using transmission electron microscopy, parallel electron energy loss spectroscopy, and energy dispersive X-ray spectroscopy, and relationships between the bonding strength and bonding parameters (bonding temperature and bonding time) were determined. When the specimen was prebonded at room temperature before heat treatment, the bonding strength was higher than in those specimens without prebonding. The shear strength increased with bonding temperature, and approached the maximum of 18 and 9 MN m−2 for specimens bonded at 1000°Cfor 1·5 h with and without prebonding, respectively. In specimens bonded at 1000°C or less after prebonding, a layer of silicon dioxide existed at the interface, and the thickness of the silicon oxide layer increased with bonding temperature. When the specimen was bonded at 1200°C, no oxide layer was observed at the interface because of decomposition of the oxide layer. The relationship between the temperature dependence of the bonding strength and the chemical reaction at the interface was discussed. The formation and decomposition processes of the oxide layer were also discussed.MST/3153

Problems in quantitatively analyzing individual salt aerosol particles using electron energy loss spectroscopy

Polydisperse standard aerosols of NaCl, (NH 4) 2SO 4 and KNO 3 have been generated from their solutions by pneumatic nebulization. These aerosol particles are electron beam sensitive and therefore special precautions are necessary. A methodology is proposed for serially recording electron energy loss spectra (EELS) from sub-micrometer salt particles. The results of quantification are compared with those obtained by parallel electron energy loss spectroscopy (PEELS). Experimental conditions such as the intensity of the primary beam, time of radiation and temperature are responsible for large deviations from the theoretical values. These deviations arise because heavy mass losses occur, especially during the serial spectrum acquisition. The more time consuming serial EELS is therefore at a disadvantage relative to the parallel method. The best results are obtained for NaCl because the halogen loss can be reduced more efficiently than nitrogen and oxygen losses. The results show that nitrogen loss occurs within the first few seconds of the experiment at normal radiation doses. Even at cryogenic temperatures, losses of volatile elements cannot be avoided.

Parallel EELS of polymers in a TEM: energy calibration of the carbon-K-edge

Electron energy loss spectroscopy (EELS) measures the loss in energy of the primary electrons caused by inelastic scatter at the electron shell. The energy loss can be detected with magnetic spectrometers operating in parallel (PEELS) and with imaging magnetic/electrostatic Castaing or magnetic omega filters. To detect EEL-spectra of radiation sensitive polymers a PEEL-spectrometer is useful, because it allows a very fast detection of the spectrum. Dynamic measurements that show the changes in the PEEL spectra during irradiation, yield additional information.An important part of recording the spectrum at high energy resolution is the energy calibration. In parallel detection, the spectrum is displayed on a diode array with a finite number of diodes (1,024). So at high energy resolution (0.05 eV/ch) it is in general only possible to observe a narrow section of about 50 eV of the total spectrum. At higher energy losses that do not allow simultaneous measurement of the elastic peak, it is only possible to give a very approximate value in terms of eV units as the primary radiation energy can drift during the measurement. It is therefore impossible to compare spectra with one another as the absolute energy scale is not known. But, as the chemical shifts of interest have an order of magnitude ranging from fractions of an eV to several eV, it is essential to know the absolute energy scale.

Quantitative analysis of interfacial chemistry in TiC/Ti composite using electron-energy-loss spectroscopy

Due to titanium carbide`s physical and elastic properties, titanium carbide particles are widely used as a reinforcement in titanium-alloy-based composites. Previous studies have shown that no obvious reaction products were detected on the interface region in TiC/Ti alloy systems; instead, a nonstoichiometric region in the TiC particle between the Ti{sub 6}Al{sub 4}V alloy and the stoichiometric TiC was found. However, the nature and the extent of the nonstoichiometric zone have not been quantitatively described. The present communication reports some results of a parallel electron-energy-loss spectroscopy (PEELS) study on a 10 vol pct TiC-particle-reinforced IMI-829 metal-matrix composite.

High-Pressure, High-Temperature Synthesis of Superhard Boron Suboxide

ABSTRACTA multianvil device was used to investigate the formation of BxO phases produced in the 2 to 10 GPa pressure range with temperatures between 1000 and 1800 °C.Amorphous and crystalline B and BP were oxidized using B2O3 and CrO3. Using powder X-ray diffraction and parallel electron energy-loss spectroscopy (PEELS), we were unable to detect graphitic or diamondstructured B2O, reported in previous studies. The refractory boride B6O, which has the α-rhombohedral boron structure, is the dominant suboxide in the P and T range of our investigation. PEELS with a transmission electron microscope was used to characterize the boron oxides.

Electron Beam Induced Crystallisation in Iron (III) Fluoride

ABSTRACTMetal fluorides are excellent candidates as high resolution inorganic resists in electron beam nanolithography. Hence it is important to study their damage characteristics under the electron beam to understand their behaviour as inorganic resists. In this paper the electron beam induced damage process in amorphous FeF3 films deposited by different techniques is investigated using selected area diffraction patterns and time resolved parallel electron energy loss spectroscopy. It is found that fluorine is lost from amorphous FeF3 during irradiation and that the material crystallises mainly to FeF2 with some crystalline FeF3. Time resolved energy loss spectroscopy studies show that the coordination polyhedra in amorphous FeF3 are randomly arranged FeF6 octahedra which arrange themselves to give a long range order in the electron beam during crystallisation to FeF2 and FeF3.

Determining the local coordination of aluminium in cement using electron energy loss near-edge structure

The local site symmetry of aluminium in Al-substituted calcium silicate hydrate phases, similar to those found in hardened Portland cement pastes, has been determined by experimental measurement and theoretical modelling of the electron energy loss near-edge structure associated with the aluminium K-edge measured using parallel electron energy loss spectroscopy in the transmission electron microscope. Changes in the local aluminium environment were observed between different regions of the microstructure which are explained in terms of aluminium substitution into both tetrahedral silicon and octahedral magnesium sites. This spatially-resolved information is in excellent agreement with27Al and29Si magic angle spinning nuclear magnetic resonance data on bulk samples as well as the predictions based upon compositional trends derived from the results of energy dispersive X-ray and electron energy loss elemental microanalysis. In a wider context we wish to stress the complementarity of both spatially-resolved and bulk spectroscopic techniques, which possess differing degrees of sensitivity, in the analysis of materials science samples.

High-resolution parallel electron energy-loss spectroscopy of Mn L2,3-edges in inorganic manganese compounds

Parallel electron energy-loss spectroscopy (PEELS) in a scanning transmission electron microscope (STEM) was used to record the Mn L2,3-edges from a range of natural and synthetic manganese containing materials, covering valences 0, II, III, IV and VII, with an energy resolution of ca. 0.5 eV. The Mn L2,3 electron-loss near-edge structure (ELNES) of these edges provided a sensitive fingerprint of its valence. The Mn2+ L2,3-edges show little sensitivity to the local site symmetry of the ligands surrounding the manganese. This is illustrated by comparing the Mn L2,3-edges from 4-, 6- and 8-fold coordinated Mn2+. In contrast, the Mn L3-edges from Mn3+ and Mn4+ containing minerals exhibited ELNES that are interpreted in terms of a crystal-field splitting of the 3d electrons, governed by the symmetry of the surrounding ligands. The Mn L3-edges for octahedrally coordinated Mn2+, Mn3+ and Mn4+ showed variations in their ELNES that were sensitive to the crystal-field strength. The crystal-field strength (10Dq) was measured from these edges and compared very well with published optically determined values. The magnitude of 10Dq measured from the Mn L3-edges and their O K-edge prepeaks of the manganese oxides were almost identical. This further confirms that the value of 10Dq measured at the Mn L3-edge is correct. Selected spectra are compared with theoretical 2p atomic multiplet spectra and the differences and similarities are explained in terms of the covalency and site symmetry of the manganese. The Mn L3-edges allow the valence of the manganese to be ascertained, even in multivalent state materials, and can also be used to determine 10Dq.

A high-sensitivity CCD system for parallel electron energy-loss spectroscopy (CCD for EELS).

A cooled frame transfer CCD camera system was developed and tested as a parallel detector in an electron energy-loss spectrometer mounted on a transmission electron microscope. The use of a shutterless camera with a frame transfer CCD collected virtually 100% of the photon signal with a reasonably fast acquisition time. The system detective quantum efficiency was over 90% under normal experimental conditions. Because of the low channel to channel gain variations in the CCD, the signal-to-noise ratio and the detection limit were substantially better than that obtained with a silicon intensified target (SIT) camera, and direct fitting to the standard data was feasible. Quantitation at the phosphorus L edge generated from a phosphoprotein, phosvitin, showed that, under identical experimental conditions, direct fitting of spectra obtained with this CCD system gave better sensitivity than that given by the SIT camera system. Because of its larger pixel charge well, the CCD system can also operate at a much higher beam current, resulting in a significant reduction in the time required for elemental mapping at a given sensitivity.