High-resolution Electron Image Research Articles

Electron tomography and STEM investigations of the structure of multilayer amorphous and nanocrystalline alloys of CoP-CoNiP, CoW-CoNiW systems under external action

The structure of amorphous and nanocrystalline alloys of the CoP-CoNiP and CoW-CoNiW systems under the external action is investigated by means of high-resolution transmission electron microscopy and electron tomography. It is revealed that the crystalline phase is predominantly nucleated in the regions with the maximum density gradient. Algorithms for image filtering and reconstruction for a graphical processor unit are implemented.

Refinement procedure for the image alignment in high-resolution electron tomography

High-resolution electron tomography from a tilt series of transmission electron microscopy images requires an accurate image alignment procedure in order to maximise the resolution of the tomogram. This is the case in particular for ultra-high resolution where even very small misalignments between individual images can dramatically reduce the fidelity of the resultant reconstruction. A tomographic-reconstruction based and marker-free method is proposed, which uses an iterative optimisation of the tomogram resolution. The method utilises a search algorithm that maximises the contrast in tomogram sub-volumes. Unlike conventional cross-correlation analysis it provides the required correlation over a large tilt angle separation and guarantees a consistent alignment of images for the full range of object tilt angles. An assessment based on experimental reconstructions shows that the marker-free procedure is competitive to the reference of marker-based procedures at lower resolution and yields sub-pixel accuracy even for simulated high-resolution data.

ChemInform Abstract: Photodissociation and Photoelectron Imaging of Molecular Ions: Probing Multisurface and Multichannel Dynamics.

AbstractReview: 66 refs.

Characterization of Platelet Alpha-Granule Dynamics

AbstractAbstract 327 Background:Platelets, anucleated cells that play a critical role in blood clotting, store proteins and small molecules in alpha-granules and dense granules, respectively, for secretion. Alpha-granules contain several proteins including von Willebrand factor and fibrinogen and dense granules contain serotonin. Rab4, a marker for the early endosomes has been implicated in regulating alpha granule secretions (Sirakawa et al, 2010). Previous fluorescence microscopy mapping of alpha-granule protein distributions suggested that there are either two different alpha-granule types or subdomains within a single granule population (Storrie and Seghal, 2007; Italiano et al, 2008). More recent work based on electron tomography (Kamykowski et al, manuscript in preparation) indicates that human platelets are comprised of one alpha granule population. We hypothesized that there was a single population of alpha-granules in which all fibrinogen is similarly compartmentalized. Hence, fibrinogen endocytocized by guinea pig megakaryocytes and platelets in vivo at 4 h (short label) and 24 h (long label) would map to the same location. Aims:We carried out several experiments to form a basis for future high-resolution (5 nm) electron tomography to establish packaging of HRP-conjugated fibrinogen or nanogold conjugated fibrinogen into platelet alpha-granules. (a) Using PD-10 columns, we prepared Cy3 conjugated fibrinogen. Using an in vivo guinea pig model to test the ability of guinea pig platelets to take up fluorescently labeled fibrinogen, we injected 10 mg/ml of Cy3 conjugated fibrinogen (short label, 4 h) and 10 mg/ml of commercially purchased AlexaFluor 488 conjugated fibrinogen (long label, 28 h) into guinea pigs. Platelets were then fixed, purified and confocal microscopy performed. (b) Using triple immunofluorescence, serotonin antibody was applied to fixed and purified resting state human and guinea pig platelets and immunofluorescence microscopy was performed to provide whole platelet information on the staining pattern of the dense granules in comparison to the alpha-granules and early endosomes. (c) Preliminary Electron Microscopy fixation conditions were also tested on guinea pig platelets. Results:For the uptake experiment, spinning-disk confocal microscopy was used to collect full platelet volume image stacks which were then deconvolved, pixel shift corrected for red and green channels and analyzed. Overlap of green and red fibrinogen conjugates was observed where the fluorescently tagged fibrinogens were taken up by structures presumed to be alpha-granules. For the triple labeling experiments, the distribution of serotonin, Rab4 and von Willebrand factor was observed in resting state platelets. Using spinning-disk confocal microscopy, full platelet volume image stacks were collected, deconvolved, pixel shift corrected for red, far red and green channels and analyzed. Serotonin antibody gave an abundant punctate staining pattern in both the triple-labeled human and guinea pig platelets. In both the human platelets and the guinea pig platelets, the serotonin positive punctate granules, presumed to be dense granules, had a more similar pattern to the von Willebrand factor positive punctate alpha granules, than to the Rab4 positive punctate granules, presumed to be the early endosomes. The triple label results were unexpected because previous electron microscopy studies have indicated that the dense granules in human platelets are fewer in number than the alpha-granules and fewer than the corresponding dense granules in guinea pig platelets. Results of the electron microscopy preparations are pending. Conclusions:Our results indicate that the guinea pig model, while its platelets are a much smaller size than human platelets, is a good system for loading alpha-granules with labeled proteins for electron tomography. The serotonin distribution results together with previous electron tomography also raise the question as to whether dense granules could be a specialized form of the alpha-granules. A summary of this research will be presented at the Promoting Minorities in Hematology event during the 2010 ASH meeting. Disclosures:No relevant conflicts of interest to declare.

Preparation of hydroxyapatite–carbon nanotube composite nanopowders

Here we report a simple preparation of composite nanopowders made of hydroxyapatite (HA) and carbon nanotube (CNT). In particular, CNTs were ionically modified to dissolve homogeneously in a series of organic solvents, including tetrahydrofuran and ethanol. The addition of HA nanopowders within the CNTs solution resulted in rapid precipitation of the composite HA–CNTs nanopowders. High resolution electron image revealed individual CNTs were evenly distributed within the cluster of HA nanoparticulates. A maximal concentration of CNTs to be organized within the HA nanopowder was highly dependent on the physicochemical characteristics of HA powders. A pilot biological assessment of the composite powders demonstrated favorable adhesion and growth of tissue cells. The developed HA–CNTs composite nanopowders may be potentially useful as an initial powder source for HA-CNT nanocomposites or coatings in biomedical applications.

Magnetic, Multilayered Nanotubes of Low Aspect Ratios for Liquid Suspensions

This work presents a synthesis route for low-aspect-ratio nanotubes consisting of a layer of magnetite (Fe3O4) sandwiched between SiO2 layers. In this template-based strategy, self-ordered porous alumina membranes are combined with the atomic layer deposition of SiO2 and Fe2O3. An optimized electrochemical setup yields nanoporous Al2O3 membranes on 4-inch Al substrates, which serve as templates for the large-scale fabrication of nanotubes. A selective chemical etching step releases the magnetic tubes for suspension in a carrier fluid and permits recycling of the underlying aluminum foils for the fabrication of subsequent nanotube batches. The nanotubes consisting of an iron oxide layer protected by a silica shell are magnetically characterized in suspensions as well as in dried form on a substrate. High-resolution transmission electron imaging reveals a polycrystalline, magnetite spinel structure of iron oxide, with the proper stoichiometry proven by the presence of the Verwey transition. Furthermore, field-dependent viscosity measurements show an enhancement of the magnetoviscosity, thus demonstrating the technological potential of nanotube suspensions as a new class of ferrofluidic solutions. Owing to the tubular shape being closed at one end, these nanoparticles might additionally function as magnetic containers for targeted drug-delivery or as chemical nanoreactors.

High-Resolution Secondary Electron Imaging of a FIB Prepared Si Sample with an Aberration Corrected Electron Microscope

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

Photodissociation and photoelectron imaging of molecular ions: probing multisurface and multichannel dynamics

High-resolution ion and electron imaging techniques have been used to explore a series of problems in the reaction dynamics of gas phase ions. These have applications ranging from fundamental dynamical studies to atmospheric chemistry and astrochemistry. In this minireview we illustrate these approaches with several examples from our recent work. We examine the conformationally- and vibrationally-mediated photodissociation dynamics of propanal and ethylene cations, and show how these can reveal reaction dynamics across multiple electronic potential surfaces of these molecules. Recent results for methylamine cation photodissociation provide insight into the rich chemistry of the ionosphere of Saturn's great moon, Titan. The combination of high-resolution ion and photoelectron imaging, REMPI spectroscopy and state-of-the-art ab initio calculations yields a powerful multifaceted approach to studying photoionization and photofragmentation dynamics in ions.

When atoms move around

The degree of atomic ordering in magnetic nanoparticles decreases strongly with the particles' size. The origin of such a phenomenon has been determined by high-resolution transmission electron microscopy and tomography, which shows how correct heat treatment can lead to atomic order also in very small nanoparticles.

Principles and prospects of direct high resolution electron image acquisition with CMOSdetectors at low energies

Two types of direct electron detectors, potentially useful in low energy electronmicroscopy and photoemission electron microscopy (LEEM/PEEM) experiments, arereviewed in this paper. Hybrid pixel detectors, using a silicon sensor and based onMedipix2 offer a high detective quantum efficiency, due to an essentially noiselessreadout, but are technically challenging. Backthinned monolithic active pixel sensors(MAPS) are not noise-free but have other advantages as discussed in this review.

Fundamental Investigation of Oxygen Reduction Reaction on Rhodium Sulfide-Based Chalcogenides

Synchrotron-based X-ray absorption spectroscopy (XAS), including the surface-specific ΔXANES technique, is used to investigate the active reaction site for water activation and the oxygen reduction reaction (ORR) on the novel, mixed-phase chalcogenide electrocatalyst RhxSy/C (De Nora). The specific adsorption of water, OH, and O as a function of overpotential is reported. This study builds on a prior communication based solely on interpreting the XAS spectra of RhxSy with respect to the metallic Rh3S4 phase. Here, a more extensive overview of the electrocatalysis is provided on RhxSy/C, the thermally grown Rh2S3/C and Rh3S4/C preferential phases and a standard 30 wt % Rh/C electrocatalyst, including results obtained by X-ray diffraction (XRD), XAS, high-resolution transmission electron imaging, microanalysis, and electrochemical investigations. Heating of the RhxSy catalysts to prepare the two preferential phases causes Rh segregation and the formation of Rh metal particles, and immersion in TFMSA causes S dissolution and the formation of a Rh skin on the RhxSy samples. It is shown that some Rh−Rh interactions are needed to carry out the ORR. This is present on the Rh6 moieties in both the Rh3S4 and RhxSy catalysts, but a partial Rh skin (present from acid dissolution) is also contributing to the ORR observed on RhxSy. This to our knowledge is the first time a reaction site in a multiphase inorganic framework structure has been investigated in terms of electrocatalytic pathway for oxygen reduction.

Statolith sedimentation kinetics and force transduction to the cortical endoplasmic reticulum in gravity-sensing Arabidopsis columella cells.

The starch statolith hypothesis of gravity sensing in plants postulates that the sedimentation of statoliths in specialized statocytes (columella cells) provides the means for converting the gravitational potential energy into a biochemical signal. We have analyzed the sedimentation kinetics of statoliths in the central S2 columella cells of Arabidopsis thaliana. The statoliths can form compact aggregates with gap sizes between statoliths approaching <30 nm. Significant intra-aggregate sliding motions of individual statoliths suggest a contribution of hydrodynamic forces to the motion of statoliths. The reorientation of the columella cells accelerates the statoliths toward the central cytoplasm within <1 s of reorientation. During the subsequent sedimentation phase, the statoliths tend to move at a distance to the cortical endoplasmic reticulum (ER) boundary and interact only transiently with the ER. Statoliths moved by laser tweezers against the ER boundary experience an elastic lift force upon release from the optical trap. High-resolution electron tomography analysis of statolith-to-ER contact sites indicate that the weight of statoliths is sufficient to locally deform the ER membranes that can potentially activate mechanosensitive ion channels. We suggest that in root columella cells, the transduction of the kinetic energy of sedimenting statoliths into a biochemical signal involves a combination of statolith-driven motion of the cytosol, statolith-induced deformation of the ER membranes, and a rapid release of kinetic energy from the ER during reorientation to activate mechanosensitive sites within the central columella cells.

Amphiboles between the sheets: observations of interesting morphologies by TEM and FESEM

We observed interesting amphibole morphologies by transmission electron microscopy (TEM) in air samples collected by the United States Environmental Protection Agency (USEPA) in Libby, Montana. Individual amphibole particles were identified and photographed on approximately 200 randomly selected air samples. Transfer of the TEM grids and relocation of these amphiboles in the field emission scanning electron microscope (FESEM) produced high-resolution secondary electron images that allowed a closer examination of these particles. Some of the amphiboles were perfect euhedral single crystals (several micrometers long and 200–500 nanometers wide) showing the classic {110} forms, while other single crystals appeared to be attached to sheet silicates and yet others appeared to have “wings” or “fins,” often less than one micrometer in width, attached to their edges. Energy Dispersive X-Ray Spectroscopy (EDS) and selected area electron diffraction (SAED) from the TEM confirmed that these particles were intergrown amphiboles and sheet silicates. Soil samples collected by the USEPA in Libby, Montana were also analyzed. FESEM investigation revealed that the soil samples contained amphiboles with the same morphologies as observed in the air samples, and were also intergrown with sheet silicates. Thus, these amphiboles occur as single crystals between the layers of vermiculite and hydrobiotite.

High-resolution electron imaging of amorphous layers with aberration-corrected probes

Extended abstract of a paper presented at Microscopy and Microanalysis 2008 in Albuquerque, New Mexico, USA, August 3 – August 7, 2008

Excimer laser processing as a tool for photocatalytic design of sol–gel TiO 2 thin films

Nanostructured sol–gel TiO 2 thin films spin coated on silicate glass plates are subjected to excimer (KrF *) pulsed laser irradiation in order to tailor their structure and photocatalytic properties. The surface morphology of virgin and laser-processed films are followed applying electron optical imaging and atomic force microscopy. The evolution of the surface roughness and pore formation are shown to be accompanied by optical absorption edge shift to infrared wavelength range. Conventional X-ray diffraction analysis and high-resolution transmission electron imaging are applied in order to obtain information on the phase composition. Co-existence of amorphous and anatase TiO 2 phases in nonirradiated sol–gel films is found. It is established that after laser processing the most intense XRD anatase peak is shifted to lower 2 θ range. The analysis of high-resolution transmission electron images of film profiles evidences for the laser induced phase transitions. Formation of rutile and brookite TiO 2 accompanied by evolution of oxygen deficient Ti n O 2 n−1 phases are identified in the subsurface region. The contribution of laser processing for increasing the photocatalytic efficiency of laser-modified films toward the oxidation of methylene blue water solution is demonstrated. The results obtained reveal a novel-processing route for designing sol–gel titania films with improved photocatalytical activity.

TEM characterization of Ge precipitates in an Al–1.6 at% Ge alloy

The growth mechanism and morphology of Ge precipitates in an Al–Ge alloy was characterized by a combination of in-situ transmission electron microscopy, high-resolution transmission electron microscopy and three-dimensional electron tomography. Anisotropic growth of rod-shaped Ge precipitates was observed by in-situ transmission electron microscopy over different time periods, and faceting of the precipitates was clearly seen using high-resolution transmission electron microscopy and three-dimensional electron tomography. This anisotropic growth of rod-shaped Ge precipitates was enhanced by vacancy concentration as proposed previously, but also by surface diffusion as observed during the in-situ experiment. Furthermore, a variety of precipitate morphologies was identified by three-dimensional electron tomography.

Imaging Si nanoparticles embedded in SiO 2 layers by (S)TEM-EELS

Fabrication of systems in which Si nanoparticles are embedded in a thin silica layer is today mature for non-volatile memory and opto-electronics applications. The control of the different parameters (position, size and density) of the nanoparticles population is a key point to optimize the properties of such systems. A review of dedicated transmission electron microscopy (TEM) methods, which can be used to measure these parameters, is presented with an emphasis on those relying on electron energy-loss spectroscopy (EELS). Defocused bright-field imaging can be used in order to determine topographic information of a whole assembly of nanoparticles, but it is not efficient for looking at individual nanoparticles. High-resolution electron imaging or dark-field imaging can be of help in the case of crystalline particles but they always provide underestimated values of the nanocrystals population. EELS imaging in the low-energy-loss domain around the Si plasmon peak, which gives rise to strong signals, is the only way to visualize all Si nanoparticles within a silica film and to perform reliable size and density measurements. Two complementary types of experiments are investigated and discussed more extensively: direct imaging with a transmission electron microscope equipped with an imaging filter (EFTEM) and indirect imaging from spectrum-imaging data acquired with a scanning transmission electron microscope equipped with a spectrometer (STEM-PEELS). The direct image (EFTEM) and indirect set of spectra (STEM-PEELS) are processed in order to deliver images where the contribution of the silica matrix is minimized. The contrast of the resulting images can be enhanced with adapted numerical filters for further morphometric analysis. The two methods give equivalent results, with an easier access for EFTEM and the possibility of a more detailed study of the EELS signatures in the case of STEM-PEELS. Irradiation damage in such systems is also discussed.

A high-resolution transmission electron microscopy study of defects in γ-Al2O3 nanorods

Surface and planar defect structures of γ-Al2O3 nanorods synthesized by the arc-discharge method were studied by means of high-resolution transmission electron microscopy and image simulation. Our investigation showed that there was a high number density of twins in the nanorods. We suggested a possible configuration of {111} twins in γ-Al2O3, and this model fit our experimental result well. In some nanorods, the ordering of nanotwins gave rise to a local hexagonal-like structure. The twinned nanorods were usually enclosed by {100} and {111} facets, and their growth direction was changed from 〈110〉 into 〈111〉. The surface structures of the nanorods confirmed that the {111}-type surface should be more stable.

A modular model of the crystal structure of the pyrochlore-murataite polysomatic series

This paper reports on the results of a structural investigation of an important group of synthetic compounds with derivative structures of the mineral murataite, a potential matrix for immobilization of radioactive wastes. A model describing the structure of the entire group of compounds is proposed on the basis of analyzing the results obtained using chemical (electron microprobe) analysis methods, high-resolution transmission electron microscopy (high-resolution electron images and microdiffraction patterns), and X-ray diffractometry of a large array of artificial murataite ceramics. In essence, the proposed structural model is as follows: in the structure, layers of two (pyrochlore and murataite) packing types alternate along the [111] direction of the cubic supercell, so that the resulting structures can undergo substitutional and displacive modulations. Experiments on irradiation of different murataite modifications with heavy ions demonstrate that these modifications have close values of the radiation resistance, which is higher than that of the pyrochlore coexisting with them.

Application of electron tomography to fungal ultrastructure studies

Access to structural information at the nanoscale enables fundamental insights into many complex biological systems. The development of the transmission electron microscope (TEM) has vastly increased our understanding of multiple biological systems. However, when attempting to visualize and understand the organizational and functional complexities that are typical of cells and tissues, the standard 2-D analyses that TEM affords often fall short. In recent years, high-resolution electron tomography methods, coupled with advances in specimen preparation and instrumentation and computational speed, have resulted in a revolution in the biological sciences. Electron tomography is analogous to medical computerized axial tomography (CAT-scan imaging) except at a far finer scale. It utilizes the TEM to assemble multiple projections of an object which are then combined for 3-D analyses. For biological specimens, tomography enables the highest 3-D resolution (5 nm spatial resolution) of internal structures in relatively thick slices of material (0.2-0.4 microm) without requiring the collection and alignment of large numbers of thin serial sections. Thus accurate and revealing 3-D reconstructions of complex cytoplasmic entities and architecture can be obtained. Electron tomography is now being applied to a variety of biological questions with great success. This review gives a brief introduction into cryopreservation and electron tomography relative to aspects of cytoplasmic organization in the hyphal tip of Aspergillus nidulans.