Characterization of the μ and P phase precipitates in the CMSX‐4 single crystal superalloy

A combination of scanning electron microscopy (SEM), transmission electron microscopy (TEM) and scanning‐transmission electron microscopy (STEM) using high‐angle annular‐dark‐field (HAADF) imaging, focussed ion beam‐ scanning electron microscopy (FIB‐SEM) tomography, selected area electron diffraction with beam precession (PED), as well as spatially resolved energy‐dispersive X‐ray spectroscopy (EDS) and electron energy loss spectroscopy (EELS), was used to investigate topologically close‐packed (TCP) phases, occurring in the CMSX‐4 superalloy subjected to high temperature annealing and creep deformation. Structural and chemical analyses were performed to identify the TCP phases and provide information concerning the compositional partitioning of elements between them. The results of SEM and FIB‐SEM tomography revealed the presence of merged TCP particles, which were identified by TEM and PED analysis as coprecipitates of the μ and P phases. Inside the TCP particles that were several micrometres in size, platelets of alternating μ and P phases of nanometric width were found. The combination of STEM‐HAADF imaging with spatially resolved EDS and EELS microanalysis allowed determination of the significant partitioning of the constituent elements between the μ and P phases.     

Electron energy-loss spectroscopy study of thin film hafnium aluminates for novel gate dielectrics

We have used conventional high‐resolution transmission electron microscopy and electron energy‐loss spectroscopy (EELS) in scanning transmission electron microscopy to investigate the microstructure and electronic structure of hafnia‐based thin films doped with small amounts (6.8 at.%) of Al grown on (001) Si. The as‐deposited film is amorphous with a very thin (～0.5 nm) interfacial SiO_x layer. The film partially crystallizes after annealing at 700 °C and the interfacial SiO₂‐like layer increases in thickness by oxygen diffusion through the Hf‐aluminate layer and oxidation of the silicon substrate. Oxygen K‐edge EELS fine‐structures are analysed for both films and interpreted in the context of the films’ microstructure. We also discuss valence electron energy‐loss spectra of these ultrathin films.     

On the estimation variance for the specific Euler–Poincaré characteristic of random networks

The factors that determine the local magnetic properties of FeCo/SiO₂ nanocomposite powders and films have been analysed by electron energy‐loss spectroscopy (EELS) and transmission electron microscopy (TEM). Attention has been given to the chemical composition, the local electronic structure and the atomic arrangement. The results show that the nanoparticles from sol‐gel prepared powders are generally Fe‐rich, whereas they are Co‐rich in sol‐gel prepared films. In addition, a subnanometre oxide layer at the surface of the FeCo nanoparticles has been clearly observed in the powder sample. It is found that the magnetic moment should be partly governed by alloying effects. Numerical values of the near‐surface magnetic moment have been obtained using the ab‐initio layer‐KKR method. These values should be helpful in understanding the layer‐by‐layer changes of the white line ratio close to the surface of the nanoparticles.     

Energy dispersive spectroscopy analysis of aluminium segregation in silicon carbide grain boundaries

The aluminium distribution in polycrystalline SiC hot‐pressed with aluminium, boron and carbon additives was studied using X‐ray energy‐dispersive spectroscopy (EDS) and transmission electron microscopy (TEM). The Al excess in homophase SiC grain boundary films was determined, taking into account dissolved Al in the SiC lattice. In the spot‐EDS analysis, an electron beam probe with a calibrated diameter was formed, and the total beam–specimen interaction volume was defined, taking the beam spreading through crystalline TEM foil into consideration. EDS spectra were collected from regions containing intergranular films and adjacent matrix grains, respectively. A theoretical treatment was presented and experimental errors were estimated, with a further discussion about the effects of foil thickness. Experimental examples are given, followed by statistical EDS analyses for grain boundary films in SiC samples hot‐pressed with increased amounts of Al additions. The results demonstrated a substantial Al segregation in the nanometer‐wide intergranular films in all samples. Al additions higher than 3 wt% saturated the Al concentrations in SiC grains and in grain boundary films. The effect of foil thickness, and the parameters for determining the optimum incident beam diameter in the EDS analysis are discussed.     

Combining Ar ion milling with FIB lift-out techniques to prepare high quality site-specific TEM samples

Focused ion beam (FIB) techniques can prepare site‐specific transmission electron microscopy (TEM) cross‐section samples very quickly but they suffer from beam damage by the high energy Ga⁺ ion beam. An amorphous layer about 20–30 nm thick on each side of the TEM lamella and the supporting carbon film makes FIB‐prepared samples inferior to the traditional Ar⁺ thinned samples for some investigations such as high resolution transmission electron microscopy (HRTEM) and electron energy loss spectroscopy (EELS). We have developed techniques to combine broad argon ion milling with focused ion beam lift‐out methods to prepare high‐quality site‐specific TEM cross‐section samples. Site‐specific TEM cross‐sections were prepared by FIB and lifted out using a Narishige micromanipulator onto a half copper‐grid coated with carbon film. Pt deposition by FIB was used to bond the lamellae to the Cu grid, then the coating carbon film was removed and the sample on the bare Cu grid was polished by the usual broad beam Ar⁺ milling. By doing so, the thickness of the surface amorphous layers is reduced substantially and the sample quality for TEM observation is as good as the traditional Ar⁺ milled samples.     

Microstructural characterization of nitrided Timetal 834

The microstructure of Timetal 834, in as‐received condition and after nitriding under glow discharge has been examined by light microscopy and analytical transmission electorn microscopy (TEM) methods (SAED, EDS, EELS and EFTEM). The microstructure of the as‐received alloy consists of the α phase and a small amount of the β phase. Silicide precipitates (Zr₅Si₄) are present both inside the grains and at the grain boundaries. TEM investigations of cross‐sectional thin foils allow for detailed analysis of the nitrided layer microstructure. It was found that the nitrided layer exhibits a graded character with continuously varying nitrogen content. The outermost sublayer consists of nanocrystals of δ‐TiN. The following sublayers consist mainly of δ′‐Ti₂N and ?‐Ti₂N grains. The last sublayer, closest to the substrate, is identified as a nitrogen‐rich α(N) solid solution containing up to 14 at% of nitrogen.     

A system for acquiring simultaneous electron energy-loss and X-ray spectrum-images

A compositional imaging system based on simultaneous scanning electron energy‐loss spectroscopy (EELS) and energy‐dispersive X‐ray spectroscopy (EDS) was developed. This system utilizes the combined power of EELS and EDS for quantitative compositional imaging at nanometre resolution. The system is particularly suitable for, but not limited to, biological research, as it simultaneously provides sensitive maps of an element such as Ca or P from EELS and of many other elements from EDS. Degradation of resolution by specimen drift is prevented by correcting for drift during data acquisition, using image cross‐correlation. Several advanced features are implemented for real‐time and/or off‐line quantitative analysis, and the performance of the system is illustrated with practical applications to compositional imaging of cardiac muscle.     

Detecting single atoms of calcium and iron in biological structures by electron energy-loss spectrum-imaging

As techniques for electron energy‐loss spectroscopy (EELS) reach a higher degree of optimization, experimental detection limits for analysing biological structures are approaching values predicted by the physics of the electron scattering. Theory indicates that it should be possible to detect a single atom of certain elements like calcium and iron contained in a macromolecular assembly using a finely focused probe in the scanning transmission electron microscope (STEM). To test this prediction, EELS elemental maps have been recorded with the spectrum‐imaging technique in a VG Microscopes HB501 STEM coupled to a Gatan Enfina spectrometer, which is equipped with an efficient charge‐coupled device (CCD) array detector. By recording spectrum‐images of haemoglobin adsorbed onto a thin carbon film, it is shown that the four heme groups in a single molecule can be detected with a signal‐to‐noise ratio of ～10 : 1. Other measurements demonstrate that calcium adsorbed onto a thin carbon film can be imaged at single atom sensitivity with a signal‐to‐noise ratio of ～5 : 1. Despite radiation damage due to the necessarily high electron dose, it is anticipated that mapping single atoms of metals and other bound elements will find useful applications in characterizing large protein assemblies.     

Combining FIB milling and conventional Argon ion milling techniques to prepare high‐quality site‐specific TEM samples for quantitative EELS analysis of oxygen in molten iron

This paper reports a procedure to combine the focused ion beam micro‐sampling method with conventional Ar‐milling to prepare high‐quality site‐specific transmission electron microscopy cross‐section samples. The advantage is to enable chemical and structural evaluations of oxygen dissolved in a molten iron sample to be made after quenching and recovery from high‐pressure experiments in a laser‐heated diamond anvil cell. The evaluations were performed by using electron energy‐loss spectroscopy and high‐resolution transmission electron microscopy. The high signal to noise ratios of electron energy‐loss spectroscopy core‐loss spectra from the transmission electron microscopy thin foil, re‐thinned down to 40 nm in thickness by conventional Argon ion milling, provided us with oxygen quantitative analyses of the quenched molten iron phase. In addition, we could obtain lattice‐fringe images using high‐resolution transmission electron microscopy. The electron energy‐loss spectroscopy analysis of oxygen in Fe_0.94O has been carried out with a relative accuracy of 2%, using an analytical procedure proposed for foils thinner than 80 nm. Oxygen K‐edge energy‐loss near‐edge structure also allows us to identify the specific phase that results from quenching and its electronic structure by the technique of fingerprinting of the spectrum with reference spectra in the Fe‐O system.     

Electron-beam-induced reduction of Fe in iron phosphate dihydrate,ferrihydrite, haemosiderin and ferritin as revealed by electron energy-loss spectroscopy

The effect of high-energy electron irradiation on ferritin/haemosiderin cores (in an iron-overloaded human liver biopsy), its mineral analogue; six-line ferrihydrite (6LFh), and iron phosphate dihydrate (which has similar octahedral ferric iron to oxygen coordination to that in ferrihydrite and ferritin/haemosiderin cores) has been investigated using electron energy-loss spectroscopy (EELS). Fe L_2,3-ionisation edges were recorded on two types of electron microscope: a 200 keV transmission electron microscope (TEM) and a 100 keV scanning transmission electron microscope (STEM), in order to investigate the damage mechanisms in operation and to establish a methodology for minimum specimen alteration during analytical electron microscopic characterisation. A specimen damage mechanism dominated by radiolysis that results in the preferential loss of iron co-ordinating ligands (O, OH and H₂O) is discussed. The net result of irradiation is structural re-organisation and reduction of iron within the iron hydroxides. At sufficiently low electron fluence and particularly in the lower incident energy, finer probe diameter STEM, the alteration is shown to be minimal. All the materials examined exhibit damage which as a function of cumulative fluence is best fitted by an inverse power-law, implying that several chemical and structural changes occur in response to the electron beam and we suggest that these are governed by secondary processes arising from the primary ionisation event. This work affirms that electron fluence and current density should be considered when measuring mixed valence ratios with EELS.     

Successful application of spatial difference technique to electron energy-loss spectroscopy studies of Mo/SrTiO3 interfaces

The electron energy‐loss near‐edge structure (ELNES) of Mo/SrTiO₃ interfaces has been studied using high spatial resolution electron energy‐loss spectroscopy (EELS) in a dedicated scanning transmission electron microscope. Thin films of Mo with a thickness of 50 nm were grown on (001)‐orientated SrTiO₃ surfaces by molecular beam epitaxy at 600 °C. High‐resolution transmission electron microscopy revealed that the interfaces were atomically abrupt with the (110)_Mo plane parallel to the substrate surface. Ti‐L_2,3 (～460 eV), O‐K (～530 eV), Sr‐L_2,3 (～1950 eV) and Mo‐L_2,3 (～2500 eV) absorption edges were acquired by using the Gatan Enfina parallel EELS system with a CCD detector. The interface‐specific components of the ELNES were extracted by employing the spatial difference method. The interfacial Ti‐L_2,3 edge shifted to lower energy values and the splitting due to crystal field became less pronounced compared to bulk SrTiO₃, which indicated that the Ti atoms at the interface were in a reduced oxidation state and that the symmetry of the TiO₆ octahedra was disturbed. No interfacial Sr‐L_2,3 edge was observed, which may demonstrate that Sr atoms do not participate in the interfacial bonding. An evident interface‐specific O‐K edge was found, which differs from that of the bulk in both position (0.8 ± 0.2 eV positive shift) and shape. In addition, a positive shift (0.9 ± 0.3 eV) occurred for the interfacial Mo‐L_2,3, revealing an oxidized state of Mo at the interface. Our results indicated that at the interface SrTiO₃ was terminated with TiO₂. The validity of the spatial difference technique is discussed and examined by introducing subchannel drift intentionally.     

Electron spectroscopy imaging to study ELNES at a nanoscale

Series of energy‐filtered TEM images have been acquired with very narrow energy slit using a post‐column energy filter. This allowed us to reconstruct spectra with an energy resolution estimated to 2 eV, and a spatial resolution in the order of 0.5 nm. In that way, fine structures of the N‐K edge in AlN/GaN heterostructures have been investigated and compared to EELS spectra. The fine structure in the two nitrides is very sensitive to the local environment. Very good agreement between ESI and EELS spectra was found. Moreover, this technique allowed analysis of the AlN/GaN interface at a nanoscale. The second example is an application of the technique to construct bonding maps. In this case, maps differentiating AlN nanoprecipitates with either the cubic or the hexagonal phase were created.     

Structural analyses of Nd-doped CeO2 thin films deposited by pulsed laser deposition

CeO₂ thin films doped with neodymium oxides for application to gas sensors have been elaborated by the pulsed laser deposition technique. The films were deposited on orientated Si (100) substrates with variable deposition times (t = 90, 180 and 360 s) and molar fractions of Nd₂O₃ (0, 6.5, 15, 21.5 and 27 at.%). The resulting Nd–CeO₂ thin films were characterized by means of X‐ray diffraction analysis, scanning electron microscopy and transmission electron microscopy equipped with EDS (Energy Dispersive Spectrometer) microanalysis. From X‐ray diffraction analyses, it is clearly established that the texture is modified by Nd additions. The preferred (111) orientations of the CeO₂ crystals change into the (200) orientation. The morphology of the CeO₂ grains changes from triangles, for pure CeO₂ thin films, to spherical grains for Nd‐doped films. In addition, cell parameter analyses from X‐ray diffraction data show that a partial chemical substitution of Ce by Nd should occur in the face‐centred cubic lattice of ceria: this should give rise to Ce_1‐xNd_xO_2?z phases with oxygen non‐stoichiometry.     

Electronic property investigations of single-walled carbon nanotube bundles in situ within a transmission electron microscope: an evaluation

We have evaluated a combined transmission electron microscopy (TEM)–scanning tunnelling microscopy (STM) (hence TEM-STM) sample holder for the investigation of the mechanical and electrical properties of individual bundles of single-walled carbon nanotubes (SWCNTs) together with their simultaneous observation, analysis and mechanical modification in the TEM. Current-voltage (I–V) measurements from bundles of SWCNTs were observed to change as the bundles were deformed both reversibly and irreversibly, although the observed behaviour was somewhat complex. Electron energy loss spectroscopy (EELS) analysis revealed measurable changes in the bonding of the carbon atoms within the graphene layers upon bundle deformation, with measurable changes in the π*/(π*+σ*) peak ratios observed at the carbon K-edge. Reversible deformation of the bundles was consistent with the sensitivity of σ bonding to deviations from nonplanarity, whereas irreversible deformation was consistent with the introduction of nonhexagonal defects into the graphene sheets.     

Analytical electron microscopy and focused ion beam: complementary tool for the imaging of copper sorption onto iron oxide aggregates

Nanometre‐scale electron spectroscopic imaging has been applied to characterize the operation of a copper filtration plant in environmental science. Copper washed off from roofs and roads is considered to be a major contributor to diffuse copper pollution of urban environments. A special adsorber system has been suggested to control the diffusion of copper fluxes by retaining Cu with a granulated iron hydroxide. The adsorber was tested over an 18‐month period on facade runoff. The concentrations range of Cu in the runoff water was measured between 10 and 1000 p.p.m. and could be reduced by between 96% and 99% in the adsorption ditch. Before the analysis of the adsorber, the suspended material from the inflow was ultracentrifuged onto TEM grids and analysed by energy‐filtered transmission electron microscopy (EFTEM). Copper was found either as small precipitates 5–20 nm in size or adsorbed onto organic and inorganic particles. This Cu represents approximately 30% of the total dissolved Cu, measured by atomic emission spectrometry. To locate where the copper sorption takes place within the adsorber, the granulated iron oxide was analysed by analytical electron microscopy after exposure to the roof run‐off water. A section of the granulated iron hydroxide was prepared by focused ion beam milling. The thickness of the lamina was reduced to 100 nm and analysed by EFTEM. The combination of these two techniques allowed us to observe the diffusion of Cu into the aggregate of Fe. Elemental maps of Fe and Cu revealed that copper was not only present at the surface of the granules but was also sorbed onto the fine particles inside the adsorber.     

Energy-filtering TEM and electron energy-loss spectroscopy of double structure tabular microcrystals of silver halide emulsions

Composite Ag(Br,I) tabular microcrystals of photographic emulsions were studied by the combination of energy-filtering electron microscopy (EFTEM) and electron energy-loss spectroscopy (EELS) in conjunction with energy-dispersive X-ray (EDX) microanalysis. The contrast tuning under the energy-filtering in the low-loss region was used to observe more clearly edge and random dislocations, {11⁻1} stacking faults in the grain shells parallel to {11⁻2} edges and bend and edge contours. Electron spectroscopic diffraction patterns revealed numerous extra reflections at commensurate positions in between the Bragg reflections and diffuse honeycomb contours; these were assigned to the number of defects in the shell region parallel to the grain edges and polyhedral clusters of interstitial silver cations, respectively. Inner-shell excitation bands of silver halide were detected and confirmed by EDX analyses, i.e. the Ag N_2,3 edge at 62 eV (probably overlapped with the weak I N_4,5 edge at 52 eV and the Br M_4,5 edge at 70 eV), the I M_4,5 edge at about 620 eV, and the Br L_2,3 edge at about 1550 eV energy losses. Energy-loss near-edge structure of the Ag M_4,5 edge at about 367 eV energy losses and low-loss fine structure arisen as a result of interband transitions and excitons, possibly superimposed with many electron effects, have been revealed. The crystal thickness was determined by a modified EELS log-ratio technique in satisfactory agreement with measurements on grain replicas.     

SEM-EDS technique employed in evaluating the aggregation behaviors of amphiphilic ABC-type triblock copolymers in mixed solvents with tuned polarities

In this paper, a scanning electron microscopy‐energy dispersive spectroscopy (SEM‐EDS) technique has been developed for evaluating the aggregation structure of amphiphilic fluorinated ABC‐type triblock copolymers MeOPEO₁₆‐PSt₂₂₀‐PFHEA₂₂ in mixed solvents with different polarities. The polarities of mixed solvents can be tuned by changing volume ratios of toluene, anhydrous ethanol, and distilled water, which leads to the changes in morphology and size of self‐assembled colloidal particles of the copolymers in the system. The aggregation behaviors of the copolymers are revealed by SEM, transmission electron microscopy (TEM), and corresponding SEM‐EDS techniques. The variations in concentrations of O and F elements over the thickness of copolymers particles give direct evidence for a better understanding of the arrangement of each block segment of copolymers in solution. And the technique can also help to explain the aggregation structure of micro‐ or nanomaterial with shell‐core structure. Microsc. Res. Tech., 2011. © 2011 Wiley Periodicals, Inc.     

A proposal for dichroic experiments in the electron microscope

Building upon the similarities between inelastic electron scattering and X-ray absorption we show that dichroism can be observed in electron energy loss spectrometry (EELS) in the transmission electron microscope (TEM). Natural or magnetic linear dichroism can be studied in electron scattering experiment with definite wave vector transfer in the interaction.The detection of circular dichroism in the TEM relies on interferometric EELS in a particular scattering geometry that allows extraction of the mixed dynamic form factor from energy loss spectra. Similarities between dichroic signals in energy loss near edge structures and X-ray absorption near edge structures are discussed, and a new experimental setup for dichroic measurements in the TEM is proposed.     

The influence of lens chromatic aberration on electron energy-loss spectroscopy quantitative measurements.

An investigation has been made into the effect of chromatic aberrations of a pre-spectrometer lens system on quantitative elemental analysis by electron energy loss spectroscopy (EELS). In transmission electron microscopy (TEM) diffraction mode, the measured effects are typically 150-330 times larger than if only objective-lens chromatic aberration were important. We discuss several methods of avoiding errors arising from chromatic aberration, including selection of a suitable optical mode (dependent on the desired spatial resolution), adjustment of the TEM imaging system so as to focus the system for a chosen energy loss, and analysis of a large area of a uniform specimen.