Conventional Transmission Electron Microscopy Imaging Research Articles

Diffraction contrast imaging using virtual apertures

Two methods on how to obtain the full diffraction information from a sample region and the associated reconstruction of images or diffraction patterns using virtual apertures are demonstrated. In a STEM-based approach, diffraction patterns are recorded for each beam position using a small probe convergence angle. Similarly, a tilt series of TEM dark-field images is acquired. The resulting datasets allow the reconstruction of either electron diffraction patterns, or bright-, dark- or annular dark-field images using virtual apertures. The experimental procedures of both methods are presented in the paper and are applied to a precipitation strengthened and creep deformed ferritic alloy with a complex microstructure. The reconstructed virtual images are compared with conventional TEM images. The major advantage is that arbitrarily shaped virtual apertures generated with image processing software can be designed without facing any physical limitations. In addition, any virtual detector that is specifically designed according to the underlying crystal structure can be created to optimize image contrast.

Conventional transmission electron microscopy imaging beyond the diffraction and information limits.

There are mainly two complementary imaging modes in transmission electron microscopy (TEM): Conventional TEM (CTEM) and scanning TEM (STEM). In the CTEM mode the specimen is illuminated with a plane electron wave, and the direct image formed by the objective lens is recorded in the image plane. STEM is based on scanning the specimen surface with a focused electron beam and collecting scattered electrons with an extended disk or ring-shaped detector. Here we show that combination of CTEM imaging with STEM illumination generally allows extending the point resolution of CTEM imaging beyond the diffraction limit. This new imaging mode improves imaging characteristics, is more robust against chromatic aberration, exhibits direct structural imaging with superior precision, visualizes light elements with excellent contrast, and even allows us to overcome the conventional information limit of a microscope.

Bright field and dark field STEM‐IN‐SEM imaging of polymer systems

ABSTRACTThe microstructural analysis of polymer systems (e.g., polymers and their composites) has largely been conducted by transmission electron microscopy (TEM). However, hard materials (e.g., metals and ceramics) are better suited for TEM imaging because such materials can withstand the high energy electron beam generated in TEM instruments. Recently, scanning TEM in scanning electron microscopy (STEM‐IN‐SEM) has emerged as a viable alternative to TEM imaging of polymer systems. STEM‐IN‐SEM uses a versatile and user‐friendly SEM instrument for examining the microstructure of polymer systems. In this study, we outline our method for STEM‐IN‐SEM imaging and apply it to the imaging of various commercial and model polymer systems. Imaging results are evaluated on the basis of measured signal intensity, which compare favorably to microstructural analysis using more costly TEM and STEM instruments. Furthermore, these comparable signal intensities are achieved through STEM‐IN‐SEM imaging with specimens that are three times thicker than those required for conventional TEM imaging. In this respect, as compared to TEM, STEM‐IN‐SEM offers faster specimen preparation times coupled with easier usability and lower maintenance costs, which are all attractive attributes for efficient quality control measures in industry. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014, 131, 40851.

An Analytical Technique to Extract Surface Information of Negatively Stained or Heavy-Metal Shadowed Organic Materials within the TEM

Using a series of uranyl acetate stained or platinum-palladium shadowed organic samples, an empirical analytical method to extract surface information from energy-filtered transmission electron microscopy (EFTEM) images is described. The distribution of uranium or platinum-palladium atoms, which replicate the sample surface topography, have been mathematically extracted by dividing the image acquired in the valence bulk plasmon energy region (between 20 and 30 eV) by the image acquired at the carbon K ionization edge (between 284 and 300 eV). The resulting plasmon-to-carbon ratio (PCR) image may be interpreted as a precise metal replica of the sample surface. In contrast to conventional EFTEM elemental mapping, including an absolute quantification approach, this technique can be applied to 200-600 nm thick organic samples. A combination of conventional TEM and PCR imaging allows one to detect complementary transmission and topographical information with nanometer precision of the same area of carbon-based samples. The advantages and limitations of PCR imaging are highlighted.

Oxidation of Gold Nanoparticles by Au(III) Complexes in Toluene

The rapid, stoichiometric oxidation of gold nanoparticles by tetraalkylammonium and tetraalkylphosphonium Au(III) complexes in toluene is reported here. Nanoparticle oxidation proceeds via a comproportionation mechanism and generates stable Au(I) complexes of the ammonium and phosphonium cations used. These reactions are studied for several organo-soluble nanoparticle systems, employing different cations and halides in the Au(III) oxidant complex, and a mechanism for the comproportionation reaction is proposed. It is demonstrated that Au nanorods stabilized in toluene can be progressively “sculpted” by Au(III) complexes. Measurement artifacts caused by the reduction of Au(I) and Au(III) species during conventional TEM imaging are also demonstrated and discussed. The results presented here provide insight into a host of issues in the chemistry of Au nanoparticles: nanoparticle oxidation, reduction of Au(III) species to Au(0) nanoparticles, galvanic replacement reactions using Au(III), and sample changes in...

Identifying Hexagonal Boron Nitride Monolayers by Transmission Electron Microscopy

Multislice simulations in the transmission electron microscope (TEM) were used to examine changes in annular-dark-field scanning TEM (ADF-STEM) images, conventional bright-field TEM (BF-CTEM) images, and selected-area electron diffraction (SAED) patterns as atomically thin hexagonal boron nitride (h-BN) samples are tilted up to 500 mrad off of the [0001] zone axis. For monolayer h-BN the contrast of ADF-STEM images and SAED patterns does not change with tilt in this range, while the contrast of BF-CTEM images does change; h-BN multilayer contrast varies strongly with tilt for ADF-STEM imaging, BF-CTEM imaging, and SAED. These results indicate that tilt series analysis in ADF-STEM image mode or SAED mode should permit identification of h-BN monolayers from raw TEM data as well as from quantitative post-processing.

Hidden defects in silicon nanowires

Recent publications have reported the presence of hexagonal phases in Si nanowires. Mostof these reports were based on ‘odd’ diffraction patterns and HRTEM images—‘odd’ meansthat these images and diffraction patterns could not be obtained on perfect silicon crystalsin the classical diamond cubic structure. We analyze the origin of these ‘odd’ patterns andimages by studying the case of various Si nanowires grown using either Ni or Au ascatalysts in combination with P or Al doping. Two models could explain theexperimental results: (i) the presence of a hexagonal phase or (ii) the presence ofdefects that we call ‘hidden’ defects because they cannot be directly observed inmost images. We show that in many cases one direction of observation is notsufficient to distinguish between the two models. Several directions of observationshave to be used. Secondly, conventional TEM images, i.e. bright-field two-beamand dark-field images, are of great value in the identification of ‘hidden’ defects.In addition, slices of nanowires perpendicular to the growth axis can be veryuseful. In the studied nanowires no hexagonal phase with long range order is foundand the ‘odd’ images and diffraction patterns are mostly due to planar defectscausing superposition of different crystal grains. Finally, we show that in Ramanexperiments the defect-rich NWs can give rise to a Raman peak shifted to 504–511 cm − 1 with respect to theSi bulk peak at 520 cm − 1, indicating that Raman cannot be used to identify a hexagonal phase.

Systematic row and zone axis STEM defect image simulations

Transmission electron microscopy (TEM) has been instrumental in advancing the field of crystalline defect analysis. Conventional TEM imaging techniques, such as bright field (BF), dark field (DF), and weak beam dark field (WBDF or g–3g) imaging, have been well-documented in the scientific literature, with simulation methods readily available for each. The present contribution highlights the use of a field-emission TEM, operated in scanning transmission electron microscopy mode, as a viable tool for defect analysis. Common techniques such as two-beam diffraction contrast and zone axis imaging are applied to defect analysis; both experimental and computational results are presented. Effects of experimental parameters such as camera length, beam divergence angle, and diffraction aperture placement are also discussed and illustrated by both experimental and computed micrographs of stacking faults.

Transmission electron microscopy with a liquid flow cell

The imaging of microscopic structures at nanometre-scale spatial resolution in a liquid environment is of interest for a wide range of studies. Recently, a liquid flow transmission electron microscopy (TEM) holder equipped with a microfluidic cell has been developed and shown to exhibit flow of nanoparticles through an electron transparent viewing window. Here we demonstrate the application of the flow cell system for both scanning and conventional transmission electron microscopy imaging of immobilized nanoparticles with a resolution of a few nanometres in liquid water of micrometre thickness. The spatial resolution of conventional TEM bright field imaging is shown to be limited by chromatic aberration due to multiple inelastic scattering in the water, and we demonstrate that the liquid in the cell can be displaced by a gas phase that forms under intense electron irradiation. Our data suggest that under appropriate conditions, TEM imaging with a liquid flow cell is a promising method for understanding the in situ behaviour of nanoscale structures in a prescribed and dynamically changing chemical environment.

Advantages of HAADF vs. Conventional TEM Imaging for Study of PSS-PMB Diblock Copolymer Systems

Extended abstract of a paper presented at Microscopy and Microanalysis 2010 in Portland, Oregon, USA, August 1 – August 5, 2010.

Plant cell biology on DVD

For readers of a certain age their initiation into the art of botanical electron microscopy was probably aided by Gunning and Steer's (1975) collection of TEM images. I well remember the hours I spent poring over its beautiful illustrations, which acted as sirens tempting me into the hidden world of plant cell ultrastructure. Now those days can not only be revisited in a suitably modern electronic way with Brian Gunning's Plant cell biology on DVD (hereafter referred to as PCB), but a new generation can be inspired by the joys of cells. PCB certainly delivers what it promises – the whole of plant cell biology on one DVD. But, although there will be few surprises with its contents – e.g. survey of cell types, plastids, ER, Golgi, cytoskeleton, mitochondria (plant cell contents are, after all, reasonably well catalogued) – this DVD is much more than just a digital version of Gunning and Steer's (1975) black-and-white image collection (although PCB boasts approx. 2000 of those!). One of the great strengths of PCB is its wealth of >240 moving images that bring alive the dynamic nature of plant cells in a way that no static image can. Another strength is the impressive number of colourful fluorescence studies, which really impress upon the viewer the truly wonderful world of plant cell structure and ultrastructure that is still to be fully explored. In browsing PCB you run out of superlatives to describe the wonders within; whilst many of the images will be familiar to users of Gunning & Steer's hard copy publication, many more are new and often provided by some of the world's leading exponents of plant cell biology. The large number in colour serves to dramatically update Gunning & Steer's largely conventional TEM images of 1975 with the intervening >30 years of developments in molecular biology, particularly its use of fluorescent reporter genes. Although PCB is firmly rooted in the TEM world, almost all of the movie sequences are at the LM level, which latter serve both to bridge the structural and ultrastructural levels and dramatically demonstrate structure-and-function aspects of plant cell biology. Probably unusual for a cerebral, academic publication, PCB truly is a labour of love. However, lest we be too readily seduced by the beauty of the images into accepting that seeing is believing, PCB provides an excellent opportunity to present information on the techniques used to generate the images, particularly comparing various TEM preparation procedures. Although this has been done to some extent in the Golgi ‘chapter’ where CTEM, freeze-etching, HP freezing and tomography are ‘compared’, I feel a separate section devoted to this could have been very instructive (perhaps something for a future revised edition?). A most useful feature that is present is the 11-image sequence of the same cell showing different degrees of information revealed by different optical/staining techniques in LM. Computer skills are needed to use the DVD, but not of a very high order; most people should be able to make use of PCB with little trouble. Consequently, whilst a period of practice with the disk and its various functions is advisable to get the fullest benefit, it can be used immediately with just the basic screen copy function. Although the built-in facility to make your own customized recordings of selected images is useful, I suspect many users – like me – will simply want to liberate the beautiful images and use their own favourite presentation programs for teaching purposes. Competition for PCB? I'm not aware of anything that comes close! Although Donaldson and Bond's (2005) DVD is a super collection of images and techniques, it concentrates specifically on the fluorescence microscopy of wood anatomy and can't compete with the sheer range of PCB. The publisher tell us that PCB has been written (strange emphasis for such a visual feast) for a wide audience, including lecturers, researchers and students in plant cell biology, but also with school-teachers in mind. This latter group can be very influential in opening the eyes of the young to the wonders of plants, and if showing off PCB's movies to that audience can help to dispel the myth that plants ‘don't do anything’ that would be great. And if that inspires a new generation to become botanists, that would be an added bonus! So, Plant cell biology on DVD, what's not to like? Professor Gunning is to be congratulated on making this amazing collection of images – and movies – available to a wide audience. And at approx. £0·025 per image/movie, PCB is also excellent value. Unlike many rental DVDs, this is definitely one to buy, and watch time and again!

Characterization of a FinFET 6T-SRAM cell by tomography

A 0.186μm2 6T-SRAM cell composed of FinFETs is analysed by high-angle annular dark field scanning transmission electron microscopy (HAADF-STEM) tomography. It allows to reveal features that are not observed in the conventional (S)TEM images due to the overlap of different materials over the thickness of the TEM specimen. The influence of the specimen thickness on the quality of the obtained tomograms is studied.

Phase Characterization of Two-Phase BiSn Alloy Nanoparticles Using Conventional TEM and EFTEM Spectral Imaging Techniques

Extended abstract of a paper presented at Microscopy and Microanalysis 2009 in Richmond, Virginia, USA, July 26 – July 30, 2009

Defect characterization and analysis of III‐V nanowires grown by Ni‐promoted MBE

AbstractWe report on transmission electron microscopy (TEM) and scanning transmission electron microscopy (STEM) analysis of GaN and Al0.2Ga0.8N nanowires (NWs) grown by radio frequency plasma assisted Molecular Beam Epitaxy (PAMBE) on c‐sapphire substrates. Conventional TEM images of single nanowires removed from the substrate exhibit a high density of basal stacking faults. Further analyses were performed using the aberration‐corrected SuperSTEM facility. Geometric phase analysis (GPA) was applied to this data revealing the characteristic lattice displacement introduced by intrinsic basal stacking faults. The nickel‐based “seeds”, which were employed to promote the NW‐type growth, are found to be situated at the tip of each nanowire. Different types of analyses were applied to lattice images of these seeds including GPA, projection method analysis and Fast Fourier transform of the HREM images. All three approaches yielded lattice constants and displacements with good agreement. The measured lattice values in the GaN nanowire body were in good agreement with the lattice constants of relaxed bulk GaN. For the seed particles the resulting lattice spacing was attributable, within the experimental error, to either nickel oxide, Ni3Ga, or an intermediate alloy phase. The defect density was measured in the AlGaN nanowires and was found to be in the order of 106 cm–1. The results are critically discussed in relation to the possible growth mechanisms of the NWs. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Reaction-induced phase decomposition of thermoset/thermoplastic blends investigated by energy filtering transmission electron microscopy

Energy-filtering transmission electron microscopy (EFTEM) was employed to investigate the morphology developments of thermoset/thermoplastic blends of poly(2,6-dimethyl-1,4-phenylene ether)/bis(vinylphenyl) ethane, PPE/BVPE. Neither conventional TEM images nor energy-filtered images at any energy loss levels showed any evidences for the phase separation of the blends, while those could be shown and characterized by the oxygen maps representing the differences in the oxygen concentrations between the two phases, which could be characterized as the PPE-rich phase (oxygen-rich phase) and the BVPE-rich phase (oxygen-poor phase). The blends undergo phase decomposition into the two phases through the crosslinking reaction of BVPE. The effect of the composition and the curing time on the phase decomposition behaviors was investigated by quantitative analysis of EELS spectra acquired from the two phases. Reactive functional moiety was introduced onto PPE and the effect of the reaction between the two components on the phase decomposition behaviors was also investigated. We show the possibility of EFTEM for the investigation of the mechanism of reaction-induced phase separations.

Correlation between microstructure and degradation in conductivity for cubic Y 2O 3-doped ZrO 2

The application of Yttria-stabilized Zirconia (YSZ) as solid electrolyte in high-temperature solid oxide fuel cells (SOFC) is well established. However, the strong decrease of the ionic conductivity in 8.5 mol% Y 2O 3-doped ZrO 2 at high temperature has not yet been clarified completely. To contribute to the understanding of the degradation process, transmission electron microscopy (TEM) was applied to analyze the microstructure in YSZ electrolyte substrates in as-sintered and aged material. Selected area electron diffraction and conventional TEM imaging were performed to investigate the evolution of different phases and phase transitions in YSZ. Grain boundary charging and the possible formation of a glassy phase at grain boundaries after aging were investigated using transmission electron holography and high-resolution TEM. The ionic conductivity was characterized by dc-conductivity measurements and impedance spectroscopy.

Z-contrast imaging of the arrangement of Cu in precipitates in 6XXX-series aluminium alloys

High-resolution annular dark field imaging has been used to study small precipitates in the Al matrix of 6XXX-series aluminium alloys. Cu-containing columns in precipitates were imaged by atomic number contrast along a ⟨100⟩ matrix direction. At an under-aged condition, large, lath-shaped particles of the Cu-containing Q′-phase were observed at grain boundaries. At over-aged conditions, Q′ was the main matrix phase. In both cases the laths showed an Al {150} habit plane. A precursor phase was found, with different arrangement of Cu-rich columns from that of the Q′-phase and sharing Al {100} habit planes. Precipitates containing elements of both the Q′-phase and the precursor were found to be common. Annular dark field imaging can differentiate directly between phases. The method complements and aids interpretation of conventional high-resolution TEM images and nano beam diffraction observations. The results obtained contribute to an improved understanding of the crystallography of the precursor and details of the structural transformation taking place during the precipitation process.

High Resolution Imaging with an Aberration Corrected JEOL 2200FS-AC STEM/TEM

A new JEOL 2200FS 200kV field emission STEM/TEM with a hexapole Cs-corrector (CEOS GmbH) for the probe-forming lens and an in-column Omega-type energy filter has recently been installed at the Advanced Microscopy Laboratory (AML) at Oak Ridge National Laboratory (ORNL). The microscope is intended primarily for high-resolution imaging of catalyst systems that are of interest to the U.S. Department of Energy for increased energy efficiency and energy security. In this paper we report on the high-resolution imaging characteristics of our microscope for both conventional high-resolution TEM and STEM imaging. The TEM Scherzer point resolution for our objective lens polepiece (C{sub s} = 0.5 mm) is 0.19 nm, but more significantly the information limit has been demonstrated to be better than 0.09 nm, as shown in Fig. 1. This figure shows a Young's fringe experiment carried out on an amorphous Ge specimen which was estimated to be 10 nm thick. The thickness of the sample damps out the Thon rings to some extent, but the information transfer to sub 0.1 nm resolution is clearly evident. The electron wave at the specimen exit surface with resolution out to the information limit of a microscope may be reconstructed via computational processing of amore » focal or tilt series of images. The extension of the TEM information limit to the sub-0.1 nm range in our microscope can be attributed primarily to the improved objective lens and high tension power supply stabilities provided by JEOL Co. to satisfy our instrument specifications. A contrast transfer function (CTF) calculated using the parameters for our microscope is shown in Fig. 2, computed at the alpha-null defocus condition used for FSR processing. The CTF closely matches the demonstrated Young's fringe pattern, indicating the ability of the microscope to achieve ultimate performance in TEM mode. Characterization of catalyst systems will be a primary focus of the aberration-corrected JEOL 2200FS and therefore high-resolution STEM high-angle annular dark field (HA-ADF) imaging will be applied to understand the atomic-scale arrangement of supported catalyst clusters. By correcting for the primary resolution-limiting aberration of a round electromagnetic lens - the third-order spherical aberration - smaller electron probes with greater probe current can be formed, with resulting improvements in both the point-to-point resolution for HA-ADF imaging and the signal-to-noise ratio. Both benefits are important for the study of the atomic arrangement of catalyst clusters. Figure 3 shows initial HA-ADF imaging images of very small Pt clusters on a 1.1 nm thick amorphous carbon film. Individual Pt atoms are clearly visible with a high signal-to-noise, as is shown in Fig. 4.« less

FIB Lift-Out and Milling of Cylindrical Specimens for Electron Tomography (or Atom Probe Field Ion Microscopy)

Abstract Electron tomography using transmission electron microscopy (TEM) and related techniques (e.g., scanning transmission electron microscopy (STEM) or energy filtered TEM (EFTEM)) allow for 3-D microstructural and elemental mapping of specimens, and has been used successfully in the biological sciences where mass-thickness contrast dominates these mostly amorphous materials. Z-contrast STEM imaging via high angle annular dark field (HAADF) tomography has also been used successfully in the physical sciences. STEM, EFTEM, and holography tomography are more useful techniques for crystalline materials, since diffraction contrast in conventional TEM images can hinder image reconstruction. Typical tomography routines utilize conventional electron transparent foils, whereby the dimensions of the specimen perpendicular to the electron beam may be orders of magnitude greater than the specimen thickness parallel to the electron beam. Using this conventional specimen geometry, the effective specimen thickness increases as the specimen is tilted through the ± 70 degrees necessary for the tomographic acquisition process.

Complex Observation in Electron Microscopy: IV. Reconstruction of Complex Object Wave from Conventional and Half Plane Phase Plate Image Pair

An extension of the Complex Observation series based on a novel imaging mode of the transmission electron microscope (TEM) is presented. A half plane phase plate is used to produce images that exhibit topographic-like appearances and have spectral modulation similar to the modulation of Zernike phase contrast TEM (ZPC-TEM) images. The Differential Interference Contrast (DIC) technique in light microscopy produces a similar contrast. The main difference between the two techniques is the asymmetry in one direction of the spectral modulation of the half plane phase plate images, which causes the topographic-like appearance of these images. The complex form of the object wave can be numerically rebuilt using a properly demodulated half plane phase plate image and a conventional TEM image. Experimental results demonstrating the success of the complex reconstruction scheme are presented.