Parallel Electron Energy Loss Spectroscopy Research Articles

EELS Studies of Cerium Electrolyte Reveal Substantial Solute Concentration Effects in Graphene Liquid Cells.

Graphene liquid cell transmission electron microscopy is a powerful technique to visualize nanoscale dynamics and transformations at atomic resolution. However, the solution in liquid cells is known to be affected by radiolysis, and the stochastic formation of graphene liquid cells raises questions about the solution chemistry in individual pockets. In this study, electron energy loss spectroscopy (EELS) was used to evaluate a model encapsulated solution, aqueous CeCl3. First, the ratio between the O K-edge and Ce M-edge was used to approximate the concentration of cerium salt in the graphene liquid cell. It was determined that the ratio between oxygen and cerium was orders of magnitude lower than what is expected for a dilute solution, indicating that the encapsulated solution is highly concentrated. To probe how this affects the chemistry within graphene liquid cells, the oxidation of Ce3+ was measured using time-resolved parallel EELS. It was determined that Ce3+ oxidizes faster under high electron fluxes, but reaches the same steady-state Ce4+ concentration regardless of flux. The time-resolved concentration profiles enabled direct comparison to radiolysis models, which indicate rate constants and g-values of certain molecular species are substantially different in the highly concentrated environment. Finally, electron flux-dependent gold nanocrystal etching trajectories showed that gold nanocrystals etch faster at higher electron fluxes, correlating well with the Ce3+ oxidation kinetics. Understanding the effects of the highly concentrated solution in graphene liquid cells will provide new insight on previous studies and may open up opportunities to systematically study systems in highly concentrated solutions at high resolution.

Electron energy loss spectroscopy database synthesis and automation of core-loss edge recognition by deep-learning neural networks

The ionization edges encoded in the electron energy loss spectroscopy (EELS) spectra enable advanced material analysis including composition analyses and elemental quantifications. The development of the parallel EELS instrument and fast, sensitive detectors have greatly improved the acquisition speed of EELS spectra. However, the traditional way of core-loss edge recognition is experience based and human labor dependent, which limits the processing speed. So far, the low signal–noise ratio and the low jump ratio of the core-loss edges on the raw EELS spectra have been challenging for the automation of edge recognition. In this work, a convolutional-bidirectional long short-term memory neural network (CNN-BiLSTM) is proposed to automate the detection and elemental identification of core-loss edges from raw spectra. An EELS spectral database is synthesized by using our forward model to assist in the training and validation of the neural network. To make the synthesized spectra resemble the real spectra, we collected a large library of experimentally acquired EELS core edges. In synthesize the training library, the edges are modeled by fitting the multi-Gaussian model to the real edges from experiments, and the noise and instrumental imperfectness are simulated and added. The well-trained CNN-BiLSTM network is tested against both the simulated spectra and real spectra collected from experiments. The high accuracy of the network, 94.9%, proves that, without complicated preprocessing of the raw spectra, the proposed CNN-BiLSTM network achieves the automation of core-loss edge recognition for EELS spectra with high accuracy.

Low-dose electron energy-loss spectroscopy using electron counting direct detectors.

Since the development of parallel electron energy loss spectroscopy (EELS), charge-coupled devices (CCDs) have been the default detectors for EELS. With the recent development of electron-counting direct-detection cameras, micrographs can be acquired under very low electron doses at significantly improved signal-to-noise ratio. In spectroscopy, in particular in combination with a monochromator, the signal can be extremely weak and the detection limit is principally defined by noise introduced by the detector. Here we report the use of an electron-counting direct-detection camera for EEL spectroscopy. We studied the oxygen K edge of amorphous ice and obtained a signal noise ratio up to 10 times higher than with a conventional CCD.We report the application of electron counting to record time-resolved EEL spectra of a biological protein embedded in amorphous ice, revealing chemical changes observed in situ while exposed by the electron beam. A change in the fine structure of nitrogen K and the carbon K edges were recorded during irradiation. A concentration of 3 at% nitrogen was detected with a total electron dose of only 1.7 e-/Å2, extending the boundaries of EELS signal detection at low electron doses.

From a physicist's toy to an indispensable analytical tool in many fields of science: A personal view of the leading contribution of Ondrej Krivanek to the spectacular successes of EELS spectroscopy in the electron microscope

This contribution aims at reporting, from the subjective point of view of a witness based in Orsay, the fundamental role of Ondrej Krivanek in the spectacular emergence of EELS (Electron Energy-Loss Spectroscopy) as a key tool in analytical electron microscopy. In this regard, he has successively designed and built while he was at Gatan, serial EELS spectrometers, parallel EELS spectrometers and post-column energy filters which have been fitted to many different (S)TEM columns installed around the world. More recently the implementation of monochromators on the NION dedicated STEM together with the realization and performance of aberration correctors (which lie out of the scope of the present review), have placed the most advanced instrumental tool in the hands of continuously increasing populations of users in many domains of materials science and in life sciences. Furthermore, the impact of Ondrej Krivanek has spread widely beyond his technical achievements into that of a highly respected organizer of workshops, bringing together at regular intervals, all the experts from around the world and building up a real community of scientists.

Cyanoethylation of the glucans dextran and pullulan: Substitution pattern and formation of nanostructures and entrapment of magnetic nanoparticles.

Cyanoethylglucans with a degree of substitution in the range of 0.74 to 2.40 for dextran and 0.84 to 2.42 for pullulan were obtained by Michael addition of acrylonitrile to the glucans under various conditions. Products were thoroughly characterized, comprising elementary analysis, NMR and ATR–IR spectroscopy, and analysis of the substituent distribution in the glucosyl units by GC–FID and GC–MS of the constituting monosaccharide derivatives. Nanostructuring of the highly substituted cyanoethylpolysaccharides was performed by dialysis against a non-solvent. In the presence of ferromagnetic iron-oxide nanoparticles, multicore cyanoethylglucan-coated ferromagnetic nanoparticles were formed by selective entrapment. The specific interaction between cyano groups and iron could be proven. The size distribution and morphology of the nanoparticles were analyzed by dynamic light scattering (DLS), scanning electron microscopy (SEM) and energy-filtered transmission electron microscopy (EF–TEM) with parallel electron energy loss spectroscopy (PEELS).

Investigation of inter-diffusion in bilayer GeTe/SnSe phase change memory films

A metal-chalcogenide layer, SnSe, is inserted between the memory layer GeTe and the top electrode to form a phase change memory cell. The GeTe layer exhibits ovonic threshold switching at a threshold field of ~110V/μm. For subsequent implementation into applications and reliability, material inter-diffusion and sublimation are examined in bilayer phase change films of GeTe/SnSe. Transmission electron microscopy and parallel electron energy loss spectroscopy analyses reveal Sn migration to the GeTe layer, which is responsible for lowering the rhombohedral to cubic structural transformation temperature in GeTe. Incongruent sublimation of SnSe and GeTe is observed at temperatures higher than 500°C. Severe volatilization of Se results in the separation of a metallic Sn phase. The use of Al2O3 as a capping layer has been found to mitigate these effects.

A Study of Dual Phase Steel Damage Evolution with Microstructure

A detailed analysis of the evolution of industrial Dual Phase (DP) steel microstructures is carried out as a function of various annealing and tempering conditions. Advanced characterization techniques such as Parallel Electron Energy Loss Spectroscopy (PEELS) in the TEM and high spatial resolution Secondary Ion Mass Spectrometry (NanoSIMS) are employed in order to provide qualitative and quantitative measurements of local carbon concentration in the martensite. For certain annealing and tempering conditions, it is observed that local variations in carbon levels have occurred inside the individual martensite islands. These carbon variations strongly influence the damage behaviour of the steel. During tensile tests, a clear dependence of the damage mode on the local martensite carbon content is observed. Better knowledge of the relationship between the microstructure evolution at the sub-grain level and the damage behaviour can facilitate the design of DP steels with improved damage resistance.

Microstructure and intergranular diffusion in exchange-coupled Sm–Co/Fe nanocomposites

We demonstrate homogenous distribution of bcc FeCo soft phase with grain size of 20–30 nm in the annealed Sm–Co/Fe bulk samples by energy filtered transmission electron microscopy (EFTEM). Quantitative Co/Fe interdiffusion measured using both energy dispersive spectroscopy (EDS) and parallel electron energy loss spectroscopy (PEELS) shows Fe60±5%Co40±5% for the magnetically soft bcc phase and Sm2(Co0.82Fe0.18)7 and Sm(Co0.80Fe0.20)5 respectively for the magnetically hard phases in these two alloy systems after optimal annealing. The graded interface develops in both samples due to the Co/Fe interchange between the hard and soft phases and the bcc soft phase was determined.

Crystallization and grain growth behavior of CoFeB and MgO layers in multilayer magnetic tunnel junctions

The relationship between crystallization, grain growth behavior, and the diffusion of B out of CoFeB has been investigated in annealed film stacks of sputtered CoFeB∣MgO using a combination of two dimensional x-ray diffraction, transmission electron microscopy, and parallel electron energy loss spectroscopy (PEELS). The analysis shows grain growth in MgO layers. It shows crystallization at approximately 350°C, and subsequent grain growth in CoFeB layers with annealing. The orientations of the grains of MgO and CoFe are definitively shown to be (002) in the out-of-plane direction. The MgO lattice is seen to have an in-plane tensile stress, while CoFe lattice is shown to have an in-plane compressive stress. CoFe grains are observed to be smaller than MgO grains, rather than being of equal size as previously understood. The physical process of B diffusion into MgO has also been investigated using PEELS and is determined that the diffusion of B through MgO is mediated through vacancies and defect states by the formation of BOx complexes.

Study of boron diffusion in MgO in CoFeB∣MgO film stacks using parallel electron energy loss spectroscopy

Boron diffusion in MgO has been investigated in annealed film stacks of sputtered CoFeB∣MgO using transmission electron microscopy and parallel electron energy loss spectroscopy. The analyses show significant B movement when the films are annealed, with the formation of BOx complexes. Characteristic diffusion lengths have been estimated in films annealed at the commonly employed temperature range of 300–400°C for the fabrication of magnetic tunnel junctions. An activation energy of 1.3eV (±0.4eV) has been extracted from these data that represent B diffusion in MgO through vacancies and defect states mediated by the formation of BOx complexes.

Metal-organic vapor phase epitaxy of crystallographically oriented MnP magnetic nanoclusters embedded in GaP(001)

Hybrid ferromagnetic-semiconductor GaP:MnP thin films were grown at 650 °C by metal-organic vapor phase epitaxy on GaP(001) using trimethylgallium, tertiarybutylphosphine, and methyl cyclopentadienyl manganese tricarbonyl (MCTMn). Overall Mn concentrations in the hybrid films, determined by Rutherford backscattering spectrometry, were found to be nearly proportional to the MCTMn precursor gas flow rate and ranged from 2 to 3.5 at. %. Cross-sectional transmission electron microscopy (TEM) analyses revealed the presence of a homogeneous distribution of 15–30 nm wide nanoclusters in a dislocation-free GaP matrix that is fully coherent with the substrate. The nanocluster facets are predominantly aligned along the (220) planes of the GaP matrix and selected-area electron diffraction patterns in TEM indicate that the nanoclusters are coherent (or semicoherent) with the single-crystal GaP matrix. The Mn:P composition ratio in the nanoclusters was determined to be 1.00±0.05 from parallel electron energy loss spectroscopy analyses. Increasing the MCTMn flow rate during film growth resulted in an increased concentration of MnP nanoclusters in the epilayer while their dimensions remained virtually unchanged. Magnetometric characterization indicates a ferromagnetic order, with a Curie temperature of about 294 K, originating from the MnP clusters.

Determination of local carbon content in austenite during intercritical annealing of dual phase steels by PEELS analysis

Parallel electron energy loss spectroscopy has allowed to analyse and quantify local variations in the carbon concentration of austenite islands transformed during the intercritical annealing treatment of commercial dual-phase steels. These changes in the carbon content of different austenite regions are responsible for the different volume fractions of tempered martensite, martensite and retained austenite obtained after intercritical annealing and overaging treatment. This technique reveals how carbon distribution in austenite evolves as the transformation process advances.

HRTEM and EELS Studies on Structural Defects in the Superconductor Sr2CuO2+δCl2−y Newly Synthesized Under High Pressure

Structural defects in the newly high-pressure synthesized superconductor Sr2CuO2+δCl2−y have been studied by means of high-resolution transmission electron microscopy and parallel electron energy-loss spectroscopy. Two types of grain boundaries were found in the material. One is the amorphous boundaries usually lying in the ab-planes. The other is the structurally intact grain boundaries, and most of them are large-angle boundaries. One of the large angles frequently observed is the 90°〈110〉 asymmetrical tilt boundary. In some domains, periodicity lengths were changed due to the lattice distortion usually associated with atom deficiency. These domains can be regarded as “second-phase particles” embedded in the perfect grains. O-K electron energy-loss spectroscopy results suggest that those defect domains are in the hole-poor states. Quantitative composition analysis from energy dispersive of X-ray suggests the hole-poorness is caused by oxygen deficiency. Dislocations, such as the \({\textstyle{1 \over 2}}\)a[110] and \({\textstyle{1 \over 2}}\)c[001] edge dislocations, were also observed in the material. In most cases, those dislocations are very complex and exhibit stacking faults.

Cell‐cell adhesion in fresh sugar‐beet root parenchyma requires both pectin esters and calcium cross‐links

Multicellular plants depend for their integrity on effective adhesion between their component cells. This adhesion depends upon various cross‐links; ionic, covalent or weak interactions between the macromolecules of the adjacent cell walls. In sugar‐beet (Beta vulgarisL. Aztec) root parenchyma, cell‐cell adhesion is disrupted by successive extractions with a calcium‐chelating agent (imidazole) and a de‐esterifying agent (sodium carbonate) but not by the calcium‐chelating agent or the de‐esterifying agent alone. Cell‐cell adhesion in sugar‐beet parenchyma thus depends upon both ester and Ca2+cross‐linked polymers. Pectic polysaccharides are removed by these treatments. Both parallel‐electron energy‐loss spectroscopy (PEELS) and Image‐EELS show that calcium‐binding sites are removed from the wall by imidazole. Using a monoclonal antibody that recognizes a relatively unesterified epitope of homogalacturonan, JIM 5, we show that a subset of JIM 5‐reactive antigens remain in the middle lamella after Ca2+chelation and that this subset is removed by cold (4° C) Na2CO3‐induced breakage of ester bonds. Fourier transform infrared, nuclear magnetic resonance, and spectrophotometric assays show that methyl and feruloyl esters are removed from the wall by Na2CO3but acetyl esters remain. Sodium carbonate extraction at 20° C removes cell wall autofluorescence and most of the feruloylated moieties from the wall. We propose that the chelator‐resistant subset of ester‐linked JIM 5‐reactive pectins are important for cell‐cell adhesion.

"Electron Tweezers" as a Tool for In-situ Manipulation and Processing of Individual Metal Nanoparticles in a Two-Phase Partially Molten Alloy

Vladimir P. Oleshko and James M. Howe University of Virginia, Department of Materials Science & Engineering, Charlottesville, VA 22904 Understanding physical principles for controlling the dynamic behavior of nanoparticles in inhomogeneous gas (liquid) – solid systems is becoming increasingly important for nanoscience and technology. Nondestructive trapping of micron- and nano-sized dielectric and metal particles in a liquid using a laser beam, which is refracted by the particle and transfers momentum to it, is known as a single-beam gradient force optical trap, or optical tweezers [1]. Recent experiments utilizing partially molten submicron-sized Al-Si alloy spheres and a focused electron beams in a medium-voltage TEM [2] and theoretical calculations of linear and angular momentum transfer from an electron beam to small particles [3] indicate that optical trapping of particles using electron beams may occur. Such thermally assisted “electron tweezers” potentially can be utilized for manipulation and processing of individual nanoobjects and fabrication of assembled nanodevices with up to atomic level sensitivity and lateral resolution provided by modern electron optical systems. In this work, we demonstrate electron-beam trapping of solid nanoparticles inside opaque submicron-sized Al-Si alloy spheres using energy filtering TEM (EFTEM) and parallel electron energy-loss spectroscopy (PEELS). Thermally assisted motion of crystalline Al nanospheres confined within the partially molten Al-Si particles was initiated by the electron beam, which was used to control and to observe the trapping in real-time by plasmon spectroscopic imaging (Fig. 1). Such approaches enable

Synthesis of magnetic nanocomposites and alloys from platinum–iron oxide core–shellnanoparticles

This paper presents a systematic study on the generation of ironplatinum-containing magnetic nanocomposites and alloys fromPt@Fe2O3 core–shell nanoparticle precursors. These core–shell nanoparticles weremade using a sequential synthetic approach. They could form FePt alloysand alloy-containing nanocomposites through a solid-state reaction at>400 °C. The chemical compositions of FePt alloys were controllable by usingPt@Fe2O3 core–shell nanoparticles that had the designed Pt core diameter and iron oxide shell thickness.We show that face-centred tetragonal (fct) FePt@Fe core–shell nanoparticles could be made fromPt@Fe2O3 core–shell nanoparticles with 5% hydrogen in argon(v/v). Furthermore, various FePt alloys and alloy-containing nanocomposites includingmetastable intermediate phases could be obtained. The materials were characterized byhigh resolution scanning transmission electron microscopy (HR-STEM), energy dispersivex-ray (EDX) spectroscopy, powder x-ray diffraction (PXRD), parallel electron energy lossspectroscopy (PEELS), and superconducting quantum interference device (SQUID)magnetometry. These materials could have potential applications as permanent hardmagnets and data storage media.

Direct Measurement and Interpretation of Electrostatic Potentials at 24° [001] Tilt Boundaries in Undoped and Niobium-Doped Strontium Titanate Bicrystals

Phase contrast techniques in the transmission electron microscope are used to measure electrostatic potentials at 24° [001] tilt boundaries in nominally undoped and Nb-doped SrTiO3 bicrystals. All of the boundaries are found to have lower scattering potentials than the surrounding bulk crystal. Origins for the measured changes in potential are investigated through the application of high-resolution transmission electron microscopy, diffuse dark-field imaging, energy dispersive X-ray spectroscopy, and parallel electron energy loss spectroscopy. Significantly, we show that space charge is not the dominant contribution to the potential because the magnitudes of the potentials seen cannot be explained on the basis of ionic space charge theory alone.

Mineralogical characterization and genesis of hydrothermal Mn oxides from the flank of the Juan the Fuca Ridge

Several sites of active hydrothermal flow have been found on the eastern flank of the Juan de Fuca Ridge. These sites are typically located along the edge of basaltic outcrops where sediment is thin. We present data on Mn-oxides formed on such outcrops (Zona Bare and Grinin Bare). These oxides are either black-layered crust or soft micro-concretions found in partially altered sediments. X-ray diffraction (XRD) and scanning electron microscopy (SEM) analyses of Mn crusts indicate the presence of well-crystallized todorokite and birnessite encrusting detrital minerals and replacing siliceous fossil. Transmission electron microscopy (TEM) and energy dispersive X-ray spectroscopy (EDX) analyses were used to identify amorphous and poorly crystallized Mn-rich phases in partially altered sediments and crusts. TEM of impregnated samples showed textural evidence suggesting that amorphous Mn oxides are incrusting cellular structures that could be bacteria. The valence state of Mn in these oxides was determined by parallel electron energy loss spectroscopy (PEELS). Results indicate that todorokite and birnessite have an average valence state of about 3.7 whereas the poorly crystallized Mn-rich phases have a lower valence state. These data suggest that the formation of hydrothermal Mn concretions occurs in several steps. The initial step is the adsorption or precipitation of Mn, Fe, and Si around cell-wall bacteria, extracellular polymers, and siliceous fossil remains. These mineralizations are poorly crystallized phyllomanganates, which progressively increase in size and crystallinity to give the final birnessite and todorokite products. All of these Mn-rich phases are the result of interactions between hydrothermal fluid and sediments and formed in areas where hydrothermal fluids discharge through the sediment.

Multi-dot floating-gates for nonvolatile semiconductor memories: Their ion beam synthesis and morphology

Scalability and performance of current flash memories can be improved substantially by replacing the floating polycrystalline-silicon gate by a layer of Si dots. Here, we present both experimental and theoretical studies on ion beam synthesis of multi-dot layers consisting of Si nanocrystals (NCs) embedded in the gate oxide. Former studies have suffered from the weak Z contrast between Si and SiO2 in transmission electron microscopy (TEM). This letter maps Si plasmon losses with a scanning TEM equipped with a parallel electron energy loss spectroscopy system. Kinetic Monte Carlo simulations of Si phase separation have been performed and compared with Si plasmon maps. Predicted and measured Si morphologies agree remarkably well, both change with increasing ion fluence from isolated NCs to spinodal pattern. However, the predicted fluences are lower than the experimental ones. We identify as the main reason of this discrepancy the partial oxidation of implanted Si by atmospheric humidity, which penetrates into the as-implanted SiO2.

Evolution of precipitates, in particular cruciform and cuboid particles, during simulated direct charging of thin slab cast vanadium microalloyed steels

A study has been undertaken of four vanadium based steels which have been processed by a simulated direct charging route with processing parameters typical of thin slab casting, where the cast product has a thickness of 50 to 80 mm (in this study 50 mm) and is fed directly to a furnace to equalise the microstructure prior to rolling. In the direct charging process, cooling rates are faster, equalisation times shorter, and the amount of deformation introduced during rolling less than in conventional practice. Samples in this study were quenched after casting, after equalisation, after the fourth rolling pass, and after coiling, to follow the evolution of microstructure. The mechanical and toughness properties and the microstructural features might be expected to differ from equivalent steels which have undergone conventional processing. The four low carbon steels (~0.06 wt-%) which were studied contained 0.1 wt-%V (V – N), 0.1 wt-%V and 0.010 wt-%Ti (V – Ti), 0.1 wt-%V and 0.03 wt-%Nb (V – Nb), and 0.1 wt-%V, 0.03 wt-%Nb and 0.007 wt-%Ti (V – Nb – Ti). steels V – N and V – Ti contained around 0.02 wt-% N, while the other two contained about 0.01 wt-%N. The as cast steels were heated at three equalising temperatures of 1050°C, 1100°C, or 1200°C and held for 30 – 60 min before rolling. Optical microscopy and analytical electron microscopy, including parallel electron energy loss spectroscopy (PEELS), were used to characterise the precipitates. In the as cast condition, dendrites and plates were found. Cuboid particles were seen at this stage in steel V – Ti, but they appeared only in the other steels after equalisation. In addition, in the final product of all the steels, fine particles were seen, but it was only in the two titanium steels that cruciform precipitates were present. PEELS analysis showed that the dendrites, plates, cuboids, cruciforms, and fine precipitates were essentially nitrides. The two Ti steels had better toughness than the other steels but inferior lower yield stress values. This was thought to be, in part, due to the formation of cruciform precipitates in austenite, thereby removing nitrogen and the microalloying elements, which would have been expected to precipitate in ferrite as dispersion hardening particles.