Energy-filtered Transmission Electron Microscopy Images Research Articles

Achromatic Elemental Mapping Beyond the Nanoscale in the Transmission Electron Microscope

Newly developed achromatic electron optics allows the use of wide energy windows and makes feasible energy-filtered transmission electron microscopy (EFTEM) at atomic resolution. In this Letter we present EFTEM images formed using electrons that have undergone a silicon L(2,3) core-shell energy loss, exhibiting a resolution in EFTEM of 1.35 Å. This permits elemental mapping beyond the nanoscale provided that quantum mechanical calculations from first principles are done in tandem with the experiment to understand the physical information encoded in the images.

Study on Gallium Nitride-Based Metal–Oxide–Semiconductor Capacitors With RF Magnetron Sputtered $\hbox{Y}_{2}\hbox{O}_{3}$ Gate

Effects of postdeposition annealing (PDA) temperatures (200°C-1000°C) in argon ambient on radio-frequency magnetron sputtered Y <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> film on n-type GaN substrate were studied. As-deposited Y <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> film was amorphous as no Y <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> phase was detected by X-ray diffraction. A transformation of the amorphous to polycrystalline phase happened when PDA (≥ 200°C) was carried out. The detection of β-Ga <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> phase for samples annealed beyond 400°C denoted the formation of interfacial layer (IL) consisting of an Y <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> and β-Ga <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> mixture. The formation of IL was revealed by cross-sectional energy-filtered transmission electron microscopy images. Metal-oxide-semiconductor characteristics of Y <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> /GaN structure annealed at different temperatures were correlated with structural and surface morphology analysis. The 400-°C-annealed sample demonstrated the highest electric breakdown field (~ 10.7 MV/cm) due to the attainment of the lowest effective oxide charge, semiconductor-oxide interface-trap density, and total interface-trap density.

Direct functionalization of pristine single-walled carbon nanotubes by diazonium-based method with various five-membered S- or N- heteroaromatic amines

Reactivity of five-membered, variously substituted, heteroaromatic diazonium salts was studied toward pristine single-walled carbon nanotubes (SWCNTs), prepared by high-pressure CO conversion (HiPCO) method. Average size range of individual HiPCO SWCNTs was 0.8–1.2 nm (diameter) and 100–1,000 nm (length). Functionalizations were performed by a one-pot diazotization–dediazotization method with methyl-2-aminothiophene-3-carboxylate, 2-aminothiophene-3-carbonitrile, 2-aminoimidazole sulfate, or 3-aminopyrazole in acetic acid using sodium nitrite at room temperature or by heating. According to Raman and Fourier transform infrared spectroscopy, all used heterocyclic diazonium salts formed a covalent bond with SWCNTs and yielded new kinds of five-membered heterocycle-functionalized SWCNTs. Methyl-2-thiophenyl-3-carboxylate-functionalized SWCNTs formed a highly soluble, stable dispersion in tetrahydrofuran (THF), 3-pyrazoyl-functionalized SWCNTs in ethanol, and 2-imidazoyl- or 2-thiophenyl-3-carbonitrile-functionalized SWCNTs in ethanol and THF. The thermogravimetric analysis as well as energy-filtered transmission electron microscopy imaging of the products confirmed the successful functionalization of SWCNTs.

3D Analysis of the Morphology and Spatial Distribution of Nitrogen in Nitrogen-Doped Carbon Nanotubes by Energy-Filtered Transmission Electron Microscopy Tomography

We present here the application of the energy-filtered transmission electron microscopy (EFTEM) in the tomographic mode to determine the precise 3D distribution of nitrogen within nitrogen-doped carbon nanotubes (N-CNTs). Several tilt series of energy-filtered images were acquired on the K ionization edges of carbon and nitrogen on a multiwalled N-CNT containing a high amount of nitrogen. Two tilt series of carbon and nitrogen 2D maps were then calculated from the corresponding energy-filtered images by using a proper extraction procedure of the chemical signals. Applying iterative reconstruction algorithms provided two spatially correlated C and N elemental-selective volumes, which were then simultaneously analyzed with the shape-sensitive reconstruction deduced from Zero-Loss recordings. With respect to the previous findings, crucial information obtained by analyzing the 3D chemical maps was that, among the two different kind of arches formed in these nanotubes (transversal or rounded ones depending on their morphology), the transversal arches contain more nitrogen than do the round ones. In addition, a detailed analysis of the shape-sensitive volume allowed the observation of an unexpected change in morphology along the tube axis: close to the round arches (with less N), the tube is roughly cylindrical, whereas near the transversal ones (with more N), its shape changes to a prism. This relatively new technique is very powerful in the material science because it combines the ability of the classical electron tomography to solve 3D structures and the chemical selectivity of the EFTEM imaging.

Microstructural changes induced by the pyrolysis step on epitaxial La2Zr2O7 thin films grown by metalorganic decomposition

La2Zr2O7 (LZO) thin films are used as buffer layers in second generation high Tc superconductor tapes. The microstructure of LZO films grown by metalorganic decomposition is characterized by the presence of nanovoids throughout the whole thickness of the films. We introduced an out-gassing plateau under vacuum during the pyrolysis process to decrease the size of voids. The temperature of this plateau was determined by Fourier transformed infrared spectroscopy, electron back scattering diffraction and X-Ray diffraction characterizations. The dwelling time was also varied. Transmission Electron Microscopy (TEM) studies revealed that a high heating ramp in combination with a less than an hour pyrolysis plateau decreased pore size. The deposition rate during dip-coating was also decreased to enhance out-gassing at the plateau. Successive LZO layers were deposited and energy filtered TEM images at C K-edge were performed to identify the role of carbon in the nucleation mechanisms.

Polymer Crystallization of Partially Miscible Polythiophene/Fullerene Mixtures Controls Morphology

Mixtures of polythiophene and fullerene are intensely studied for organic photovoltaic applications. Control of nanoscale morphology of these materials is critical for device performance, but characterization and understanding of this morphology and how it arises is lacking. We use energy-filtered transmission electron microscopy (EFTEM) to obtain high-contrast images of P3HT nanocrystals in organic semiconductor mixtures. Grazing-incidence small-angle X-ray scattering correlates well with the length scales obtained from EFTEM images; we combine the two techniques to follow the morphology evolution under different material processing histories. EFTEM also measures local P3HT concentration in PCBM-rich regions, proving that these components are partially miscible. We determine the P3HT-PCBM χ parameter and Flory–Huggins phase diagram, which predicts miscibility for P3HT volume fractions above 0.42. This miscibility suppresses fullerene crystallization. The nanoscale morphology in these materials, critical for solar cell performance, is driven by P3HT crystallization from a partially miscible blend.

Synthesis and electron microscopic analysis of the self‐assembly of polymer and ferritin core‐shell structures

Self-assembly of poly(4-vinylpyridine) (P4VP) and ferritin produced a spherical core-shell structure, which was analyzed by scanning electron microscopy (SEM) and transmission electron microscopy (TEM). In particular, for better understanding, the organization of such core-shell nanostructures, an optimal protocol for preparation of TEM thin sectioning of ferritin-P4VP composites, was developed. It entails fixing the ferritin-P4VP complex with 2.5% glutaraldehyde and infiltrating it with a mixture of acetone/resin while omitting the OsO(4) postfixation and ethanol dehydration steps of the conventional protocol. Using this method, a round-shaped thin section structure with unevenly distributed dark and white components was observed. The dark component from the thin section structure was determined to contain ferritin by energy-filtered TEM imaging and iron element mapping, whereas the white part was identified as P4VP by its energy dispersive X-ray spectroscopy (EDS) spectrum.

Automated identification and characterisation of secondary and tertiary γ′ precipitates in nickel-based superalloys

The use of different electron loss edges in energy-filtered transmission electron microscopy (EFTEM) has allowed researchers to capture images of the morphology and size of precipitates in nickel-based superalloys. In this work, the authors discuss a computational methodology for automated detection of secondary and tertiary γ′ precipitates in EFTEM images. The optimum parameters for the automated region growing technique were identified using a combination of visual inspection and intensity information from the EFTEM images. The microstructural statistics obtained from the segmented γ′ precipitates agreed with those of the manually segmented precipitates. Then, automated segmented precipitates are used to extract microstructural information about the distributions of equivalent diameters of 656 tertiary precipitates along with the distances to the nearest secondary precipitates. The significance of this technique is its ability to automate segmentation of precipitates in a reproducible manner for acquiring microstructural statistics that relate to both processing and properties.

Study of structures at the boundary and defects in organic thin films of perchlorocoronene by high-resolution and analytical transmission electron microscopy

Both the periodic and non-periodic structures of perchlorocoronene (C 24Cl 12) crystals were characterized by high-resolution transmission electron microscopy (HRTEM), electron diffraction (ED), electron energy-loss spectroscopy (EELS), and energy-filtered transmission electron microscopy (EFTEM). The HRTEM images at the boundary of the C 24Cl 12 crystals exhibit the flexibility of defect structures, where molecules align to compensate for the discontinuity between two different domains. Emphasized by the filtered images, it was found that the non-periodic regions are created everywhere with a small electron beam irradiation (∼10 6 electrons nm −2) and then spread over the entire regions to completely destroy the periodic structures after a higher electron dose (∼2×10 6 electrons nm −2). The effect of the electron beam irradiation was monitored by ED, EELS, and EFTEM, where periodic structures and content elements are well preserved up to 10 6 electrons nm −2, but chlorine atoms decreased with a much higher electron dose. This is explained by the breakage of the C–Cl bond to detach chlorine atoms, confirmed by energy-loss near the edge structures (ELNES) of carbon π⁎ peaks and chlorine loss at the edge of the specimen, as well as by theoretical simulation. The detachment of chlorine is localized at the peripheral edge around a hole confirmed by core-loss EFTEM imaging.

Interface Structures of La0.67Sr0.33MnO3/SrTiO3 Superlattices Studied by TEM and EELS

The layered structures of La 0.67 Sr 0.33 MnO 3 /SrTiO 3 superlattices have been investigated by energy filtered transmission electron microscopy (EFTEM) and spatially resolved electron energy loss spectroscopy (EELS). A general picture of the elemental distribution of the chemically modulated layers was given by the EFTEM images. Chemical shift in both Ti-L 2,3 and Mn-L 2,3 edges, together with an appearance of distinctive shoulders in both Mn-L 3 and Mn-L 2 edges at the interfacial region were observed. These electronic structure changes suggest a stronger crystal field and/or a partial loss of oxygen at the interfaces, accounting for the observed oscillatory exchange coupling and enhanced magnetoresistance in such superlattices.

Optimization of EFTEM image acquisition by using elastically filtered images for drift correction

Because of its high spatial resolution, energy-filtering transmission electron microscopy (EFTEM) has become widely used for the analysis of the chemical composition of nanostructures. To obtain the best spatial resolution, the precise correction of instrumental influences and the optimization of the data acquisition procedure are very important. In this publication, we discuss a modified image acquisition procedure that optimizes the acquisition process of the EFTEM images, especially for long exposure times and measurements that are affected by large spatial drift. To alleviate the blurring of the image caused by the spatial drift, we propose to take several EFTEM images with a shorter exposure time (sub-images) and merge these sub-images afterwards. To correct for the drift between these sub-images, elastically filtered images are acquired between two subsequent sub-images. These elastically filtered images are highly suitable for spatial drift correction based on the cross-correlation method. The use of the drift information between two elastically filtered images permits to merge the drift-corrected sub-images automatically and with high accuracy, resulting in sharper edges and an improved signal intensity in the final EFTEM image. Artefacts that are caused by prominent noise-peaks in the dark reference image have been suppressed by calculating the dark reference image from three images. Furthermore, using the information given by the elastically filtered images, it is possible to drift-correct a set of EFTEM images already during the acquisition. This simplifies the post-processing for elemental mapping and offers the possibility for active drift correction using the image shift function of the microscope, leading to an increased field of view.

Transmission electron microscopy (TEM) of Earth and planetary materials: A review

AbstractUsing high intensity beams of fast electrons, the transmission electron microscope (TEM) and scanning transmission electron microscope (STEM) enable comprehensive characterization of rocks and minerals at micrometre to sub-nanometre scales. This review outlines the ways in which samples of Earth and planetary materials can be rendered sufficiently thin for TEM and STEM work, and highlights the significant advances in site-specific preparation enabled by the focused ion beam (FIB) technique. Descriptions of the various modes of TEM and STEM imaging, electron diffraction and X-ray and electron spectroscopy are outlined, with an emphasis on new technologies that are of particular relevance to geoscientists. These include atomic-resolution Z-contrast imaging by high-angle annular dark-field STEM, electron crystallography by precession electron diffraction, spectrum mapping using X-rays and electrons, chemical imaging by energy-filtered TEM and true atomic-resolution imaging with the new generation of aberration-corrected microscopes. Despite the sophistication of modern instruments, the spatial resolution of imaging, diffraction and X-ray and electron spectroscopy work on many natural materials is likely to remain limited by structural and chemical damage to the thin samples during TEM and STEM.

Molecular Mapping by Low-Energy-Loss Energy-Filtered Transmission Electron Microscopy Imaging

Structure-function relationships in supramolecular systems depend on the spatial distribution of molecules, ions, and particles within complex arrays. Imaging the spatial distribution of molecular components within nanostructured solids is the objective of many recent techniques, and a powerful tool is electron spectroscopy imaging in the transmission electron microscope (ESI-TEM) in the low-energy-loss range, 0-80 eV. This technique was applied to particulate and thin film samples of dielectric polymers and inorganic compounds, providing excellent distinction between areas occupied by various macromolecules and particles. Domains differentiated by small changes in molecular composition and minor differences in elemental contents are clearly shown. Slight changes in the molecules produce intensity variations in molecular spectra that are in turn expressed in sets of low-energy-loss images, using the standard energy-filtered transmission electron microscopy (EFTEM) procedures. The molecular map resolution is in the nanometer range and very close to the bright-field resolution achieved for the same sample, in the same instrument. Moreover, contrast is excellent, even though sample exposure to the electron beam is minimal.

Image simulation of high resolution energy filtered TEM images

Inelastic image simulation software is presented, implementing the double channeling approximation which takes into account the combination of multiple elastic and single inelastic scattering in a crystal. The approach is described with a density matrix formalism. Two applications in high resolution energy filtered (EFTEM) transmission electron microscopy (TEM) images are presented: thickness-defocus maps for SrTiO 3 and exit plane intensities for an ( LaAlO 3 ) 3 ( SrTiO 3 ) 3 multilayer system. Both systems show a severe breakdown in direct interpretability which becomes worse for higher acceleration voltages, thicker samples and lower excitation edge energies. Since this effect already occurs in the exit plane intensity, it is a fundamental limit and image simulations in EFTEM are indispensable just as they are indispensable for elastic high resolution TEM images.

Quantitative comparison of energy-filtering transmission electron microscopy and atom probe tomography

Whereas transmission electron microscopy (TEM) is a well established method for the analysis of thin film structures down to the sub-nanometer scale, atom probe tomography (APT) is less known in the microscopy community. In the present work, local chemical analysis of sputtered Fe/Cr multilayer structures was performed with energy-filtering transmission electron microscopy (EFTEM) and APT. The single-layer thickness was varied from 1 to 6 nm in order to quantify spatial resolution and chemical sensitivity. While both the methods are able to resolve the layer structure, even at 2 nm thickness, it is demonstrated that the spatial resolution of the APT is about a factor of two, higher in comparison with the unprocessed EFTEM data. By calculating the influence of the instrumental parameters on EFTEM images of model structures, remaining interface roughness is indicated to be the most important factor that limits the practical resolution of analytical TEM.

Self-assembly of nanostructured polymetallaynes

Organometallic conjugated polymers containing transition metal centers in the main chain (polymetallynes), with general formula –[M–(PBu3)2–CC–X–CC–]n– with M=Pt(II) and Pd(II), X=organic conjugated spacer, namely poly[1,1′-bis(ethynyl)-4,4′-biphenyl-(bis-tributylphosphine)Pd(II)] (Pd-DEBP), poly[1,1′-bis(ethynyl)-4,4′-biphenyl-(bis-tributylphosphine)Pt(II)] (Pt-DEBP) and poly-[1,4-bis(ethynyl)-2,5-dihexadecyloxybenzene-bis(triphenylphosphine)platinum(II)] (Pt-BOB) were synthesized and fully characterized. The polymeric compounds were cast deposited onto glass substrates and their morphologies studied by means of SEM (Scanning Electron Microscopy) and EF-TEM (Energy Filtered-Transmission Electron Microscopy). The formation of nanostructured fibrils with diameters in the range 100–300nm was revealed by SEM. EF-TEM images showed that the fibers are made of hollow nanotubes, randomly oriented, with external diameter of about 6–7nm.

Transmission electron microscopy and X-ray diffraction study of microstructural evolution in magnetoresistive Cu–Fe–Ni ribbons

The evolution of the microstructure of a granular Cu80Fe10Ni10 (at%) melt-spun ribbon is studied by transmission electron microscopy (TEM), energy-filtered transmission electron microscopy (EFTEM) and X-ray diffraction. This system is interesting as large giant magnetoresistance (GMR) values have been measured for this composition. We have shown the presence of two face-centred cubic phases, an (Fe,Ni)-rich phase and a Cu-rich phase. The lattice parameters of these two phases are close and no diffraction or elastic contrast is involved in displaying the two phases in TEM bright-field mode. With EFTEM imaging, we have shown the presence of a fine-scale (Fe,Ni)-rich precipitation inside the Cu-rich fcc matrix. The precipitates are 2–4 nm in the as-spun state and 4–6 nm after annealing for 2 h at 400°C. The lattice parameter of the Cu-rich phase in the as-spun sample is 0.3608 nm and 0.3610 nm for the (Fe,Ni)-rich phase. After a 24-h annealing treatment at 600°C, the mean diameter of the particle is 20 nm and the lattice parameter of the (Fe,Ni)-rich phase has decreased to 0.3600 nm, while that of the Cu-rich phase has increased to 0.3613 nm, which is consistent with a segregation of Fe and Ni in the precipitates. The composition and volume fraction of the two phases measured for this annealed sample are in good agreement with the Thermocalc® predictions.

Energy-filtered electron microscopy for imaging core–shell nanostructures

CuAg core–shell nanoparticles are synthesized by ultra-high vacuum thermal evaporation. We show on this system how the Energy-Filtered Transmission Electron Microscopy (EFTEM) technique allows one to improve the characterization by precisely pointing out the formation of core–shell arrangements in bimetallic nanoparticle assemblies. A criterion to measure the shell thickness from EFTEM images on unique core–shell nanoparticles is defined, that can be used for core–shell nanoparticles of any sizes, with shell thicknesses over 1 nm. It is based on the intensity variation along a line drawn across a core–shell nanoparticle on a EFTEM image. This criterion has been validated by a close comparison of the shell thickness measurements performed in this work and the ones obtained by acoustic micro-Raman spectroscopy. Using this criterion, we report a strong correlation between the size of the Cu cores and the formation of the core–shell arrangements in the nanoparticle assembly studied in this work. The influence of the Cu core shape is also evidenced. The characterisation of such systems using High Resolution TEM (HRTEM) is also discussed.

Chemical and structural variations at augite (100) deformation twin boundaries

It is commonly found that deformation twinning response to plastic deformation results in structural variations at a twin boundary (TB). Chemical heterogeneity at a TB, compared to the host, however, has rarely been reported. An augite sample with a high density of deformation twinning lamellae from Lofoten, Norway was examined using high-resolution transmission electron microscopy (HRTEM) and energy-filtered TEM (EFTEM) techniques to characterize both structural and chemical variations at a TB. HRTEM experimental results combined with high-resolution image simulation unambiguously resolve the augite deformation TB structure as a half unit cell of orthopyroxene. EFTEM images at TB demonstrate that Ca is depleted, whereas Fe is enriched at this sub-nanometer scale (0.9 nm) interface. In addition, distance-least-squares (DLS) program was applied to verify that the TB structure is geometrically stabilized by substitution of Fe for Ca.

Microstructural and chemical transformation of thin Ti/Pd and TiD y /Pd bilayer films induced by vacuum annealing

Using a combination of scanning electron microscopy, transmission electron microscopy (TEM), X-ray diffraction and X-ray photoelectron spectroscopy (XPS), we made a comparative study of the high-temperature annealing impact on thin titanium deuteride (TiD(y)) films covered by an ultrathin Pd layer, and on Ti/Pd bilayer films. The bilayer films were prepared under ultrahigh vacuum conditions and were in situ annealed using the same annealing procedure. It was found that the surface and the bulk morphology of both films undergo different annealing-induced transformations, leading to an extensive intermixing between the Ti and Pd layers and the formation of a new PdTi(2) bimetallic phase. Energy-filtered TEM imaging and energy-dispersive X-ray spectrometry analysis, as well as XPS depth profiling all provided evidence of a different distribution of Pd and Ti in the annealed TiD(y)/Pd film compared with the annealed Ti/Pd film. Our results show that thermal decomposition of TiD(y), as a consequence of annealing the TiD(y)/Pd film, modifies the intermixing process, thereby promoting Ti diffusion into the Pd-rich top layer of the TiD(y) film and thus providing a more likely path for the formation of the PdTi(2) phase than in an annealed Ti/Pd film.