Advanced Electron Microscopy Techniques Research Articles

STEM HAADF Tomography of Molybdenum Disulfide with Mesoporous Structure

AbstractA highly ordered mesoporous molybdenum disulfide has been developed for catalysis in heavy oil refining. The morphology, structure, and composition of the material have been systematically characterized with advanced electron microscopy techniques. Scanning transmission electron microscopy with high‐angle annular dark field tomography has been used to investigate the porous structure to give spatial information on the nanometre scale, and offer a direct view of individual porous particles in three‐dimensions. The pore‐size distribution, connectivity of the pores, and the mesoporous surface area have also been analyzed and offer useful information towards catalyst design.

Screen-Printable Silver Pastes with Metallic Nano-Zinc and Nano-Zinc Alloys for Crystalline Silicon Photovoltaic Cells

Silver metallization pastes for crystalline silicon PV cells containing nanosized metallic zinc were found to be superior to commercial pastes containing micrometer-sized metallic zinc and micrometer sized zinc oxide in terms of efficiency and firing window. Efficiency performance decreases as the size of the particles increases: nano-Zn > 3.6 μm Zn > 4.4 μm Zn. Advanced electron microscopy techniques were used to investigate the interfacial microstructure between the front-side contact and the Si emitter of nanosized zinc additive based cells fired at temperatures from below to above optimal. These microstructural observations confirmed the possibility of a tunneling mechanism of current flow (a "nano-Ag colloid assisted tunneling" model) in the absence of Ag crystallites. Contact resistance maps were used to guide sampling, leading to a better understanding of the relationship between microstructure and contact resistance. Low contact resistance and higher cell efficiency, especially at under- and overfiring temperature conditions, are due to more uniform silicon nitride etching obtained through the use of nanosized metallic zinc additives.

Synthesis and Characterization of Branched Gold Nanoparticles

In this work we present the synthesis of branched gold nanoparticles based on the seed mediated growth technique. The materials have been characterized by advanced electron microscopy techniques in order to elucidate morphology, size and internal structure.

Transmission Electron Microscopy Study on Microstructure of Ag-Based Conductive Adhesives

We used advanced electron microscopy techniques to study the microstructure of Ag-based conductive adhesives, which are promising alternatives to Pb-free solders. Systematic microscopy observations revealed the development of connections between Ag agglomerates, when the weight density of Ag (Ag content) was increased up to 92 mass%. However, in a sample containing 94 mass% Ag, disconnection between well-defined Ag agglomerates and/or formation of voids between Ag-filler particles were observed. These results appeared to be consistent with the plot of resistivity versus Ag content: the resistivity decreased to a minimum value at 92 mass% Ag. We also demonstrated the formation of very small Ag particles in a thin-foil specimen subjected to electrical breakdown. This microscopic observation may be useful for understanding the process of electric breakdown in thin-foil specimens.

Analysis of fouling within microporous membranes in biopharmaceutical applications using latex microsphere suspensions

A better understanding of how biological fluids foul membrane filters will allow membranes to be better designed and more appropriately chosen for the filtration of biopharmaceutical products. For this study, a model fluid has been developed to facilitate the study of membrane loading capacity and particle retention using normal flow, polymeric microporous membranes for liquid-phase sterile filtration. The model fluid approximates process fluids that have high loads of submicron particles (such as cell debris and agglomerated proteins), as found in cell culture harvests. Using this model fluid, foulants can be visualized within the membrane structure by advanced electron microscopy techniques, giving insight to where and in some cases how fouling occurs. While the model fluid was not a perfect mimic of the biological fluids to which we compared it, fouling did occur within the same region of the membrane, indicating that the model fluid could be used to understand fouling trends. By using the right model fluid, the relative performance of the membrane tested was the same as in relevant biological fluids, so that while absolute capacities could not be reproduced with the model fluids, the fouling trends that impact capacity for biological fluids could be approximated.

Magnetic Nanocrystals in Organisms

Research Article| August 01, 2009 Magnetic Nanocrystals in Organisms Mihály Pósfai; Mihály Pósfai 1Department of Earth and Environmental Sciences University of Pannonia, H-8200 Veszprém, Hungary E-mail: mihaly.posfai@gmail.com Search for other works by this author on: GSW Google Scholar Rafal E. Dunin-Borkowski Rafal E. Dunin-Borkowski 2Center for Electron Nanoscopy, Technical University of Denmark DK-2800 Kongens Lyngby, Denmark E-mail: rafaldb@gmail.com Search for other works by this author on: GSW Google Scholar Elements (2009) 5 (4): 235–240. https://doi.org/10.2113/gselements.5.4.235 Article history first online: 09 Mar 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn MailTo Tools Icon Tools Get Permissions Search Site Citation Mihály Pósfai, Rafal E. Dunin-Borkowski; Magnetic Nanocrystals in Organisms. Elements 2009;; 5 (4): 235–240. doi: https://doi.org/10.2113/gselements.5.4.235 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyElements Search Advanced Search Abstract Ferrimagnetic nanocrystals are present in virtually every organism. they are used by bacteria, algae, mollusks, insects, and vertebrates either for navigating in the geomagnetic field or for hardening their tissues. advanced transmission electron microscopy techniques, including electron holography, reveal the complex interplay between the physical and magnetic properties and biological functions of ferrimagnetic nanocrystals in bacteria. although some information is now available about magnetic sensory systems in more complex organisms, much further research is required to understand fully the origin and function of biomagnetism. You do not have access to this content, please speak to your institutional administrator if you feel you should have access.

Experimental Evidence of Self-Limited Growth of Nanocrystals in Glass

Growth of nanocrystals precipitated in glasses with specific compositions can be effectively limited by diffusion barriers forming around crystallites. For the first time, we do experimentally prove this concept of self-limited growth on the nanoscale for a SiO(2)/Al(2)O(3)/Na(2)O/K(2)O/BaF(2) glass in which BaF(2) nanocrystals are formed. As shown by advanced analytical transmission electron microscopy techniques, the growth of these BaF(2) crystals, having great potential for photonic applications, is inherently limited by the formation of a ca. 1 nm wide SiO(2) shell.

Groundwater Nanoparticles in the Far-Field at the Nevada Test Site: Mechanism for Radionuclide Transport

Colloid-like nanoparticles in groundwater have been shown to facilitate migration of several radionuclides: (239,240)Pu, 137Cs, (152,154, 155)Eu, and 60Co. However, the exact type of nanoparticle and the speciation of the associated radionuclides has remained unknown. We have investigated nanoparticles sampled from the far-field at the Nevada Test Site, Nevada, utilizing advanced electron microscopytechniques, including high-angle annular dark-field scanning TEM (HAADF-STEM). Fissiogenic elements: Cs, rare earth elements (REE), activation elements: Co; and actinides: U and Th, were detected. Cesium is associated with U-forming cesium uranate with a Cs/U atomic ratio of approximately 0.12. Light REEs and Th are associated with phosphates, silicates, or apatite. Cobalt occurs as a metallic aggregate, associated with Cr, Fe, Ni, and +/-Mo. Uranyl minerals; Na-boltwoodite and oxide hydrates are also present as colloids. Because of these chemical associations with nanoscale particles, in the size range <100 nm, these particles may facilitate transport, and a variety of trace nanoscale phases may be responsible for the migration of fissiogenic and actinide elements in groundwater. To accurately model the transport of these contaminants, predictive transport models should include consideration of nanoparticle-facilitated transport.

Scanning Transmission Electron Microscopy Studies of Interface Stability and Point Defects in Gate Stacks with High-k Dielectrics

Advanced gate dielectric stacks are comprised of multiple layers of different materials, including high-k gate dielectrics, metal gate electrodes and interfacial layers with sub-nanometer thickness. The composition, point defect chemistry, interface atomic structure and interaction between the layers determine the properties of these gate stacks. This paper reviews recent applications of advanced scanning transmission electron microscopy techniques to determine the atomic structure and defects in advanced gate stacks.

Correlation of superconducting properties and microstructure of MgB 2 wires and tapes

Within the “Hipermag” project, MgB 2 wires and tapes were prepared by the powder in tube method using different precursor powders and processing technologies. Either pre-reacted MgB 2 (ex-situ), mixture of MgH 2 + 2B (in-situ) or mechanically alloyed (MA) MgB 2 is used. In this work superconducting properties of a long length 14-filament tape with standard ex-situ powder, MA tapes, and hydrostatically extruded wires with in-situ MgB 2 powder with SiC nanoinclusions, are correlated with their microstructure investigated using advanced electron microscopy techniques. Apart from the conventional diffraction imaging, EDX elemental maps in SEM and TEM and electron spectroscopic imaging (ESI) in TEM have been used to study the MgB 2 phase formation and granularity. The critical current densities of the wires and tapes were measured at 4.2 and 20 K for different magnetic fields. Wires and tapes prepared by different technologies show large differences by orders of magnitude in their critical current densities. MgB 2 colony formation is found as a universal phenomenon with several grains forming a dense colony. Such colonies are embedded in a matrix of reduced density introducing granularity in MgB 2 wires and tapes. Wires and tapes that do not show colony formation contain a large fraction of B-rich phases and their critical current density is limited by the MgB 2 phase formation.

Electron microscopy and physical studies of a new tungsten doped indium oxide transparent conductor

Advanced electron microscopy techniques – HREM and EFTEM – were used to study a new transparent conductive material: Indium Tungsten Oxide (IWO, in this work), which was synthesized from an aerosol. Indium oxide thin films doped with tungsten were deposited by spray pyrolysis for several %W concentration using (NH 4)10W 12O 41 and InCl 3 dissolved in ethanol as starting compounds. The W 6+ ions fulfill the electronic and structural requirements to work like a donor impurity in In 2O 3 materials. The solution was sprayed onto silicon and glass substrates kept at 525 °C. Structural analysis was carried out from X-ray diffraction and selected area electron diffraction results reveal the structure of In 2O 3 with very small variations in crystallographic parameters. From electron microscopy observations, the nanostructured nature of the IWO compound was derived and from EFTEM micrographs the distribution of W reveals an increasing concentration in grain boundaries. Also scanning electron and atomic force microscopy techniques were used in order to determine the morphological and topological characteristics of the films. Also the number of carrier increases when W grows up to 5% weight and remains constant close to η e = 28 × 10 19 cm − 3 . The mobility grows up 2% W weight and the decreases monotonically. The optical transmittance of the IWO was close to 78% for all the cases. From XPS studies, low intensity signals form W orbitals were detected. The identified signals correspond to W-4d 5/2 and to W-4f 7/2 which were found very close to 250 and 37 eV respectively. These signals correspond to W atoms surrounded by O atoms in a similar configuration to the one reported for WO 3.

Phase Analysis of Multilayered, Nanostructured Titanium-Base Alloys by Analytical Electron Microscopy

Microstructure, chemical and phase composition of the hard layer formed on the Ti-6Al-4V alloy after duplex surface treatment were investigated by light microscopy (LM), X-ray diffraction (XRD) and analytical scanning, transmission and scanning transmission electron microscopy (SEM, TEM, STEM), electron diffraction and focused ion beam (FIB). Advanced electron microscopy techniques used for unambiguous identification of phases present in the surface multilayer are critically discussed. The relationship between multilayer micro/nanostructure containing several phases from the Ni-Ti-P-Al system and improved mechanical and tribological properties is established.

Advanced Electron Beam Techniques

After 100 years from the time of discovery of electron, we now have many applications of electron beam in science and technology. In this report, we review two important applications of electron beam: electron microscopy and pulsed-electron beam. Advanced electron microscopy techniques to investigate atomic and electronic structures, and pulsed-electron beam for investigating time-resolved structural change are described.

Identifying Contributing Degradation Phenomena in PEM Fuel Cell Membrane Electride Assemblies Via Electron Microscopy

Advanced electron microscopy and ultramicrotomy specimen preparation techniques have been used to characterize the microstructural changes within PEM fuel cell membrane electrode assemblies (MEAs) that contribute to performance loss. Atomic- level structural and compositional analyses have been conducted on intact 3-layer MEAs before and after life-testing to identify the microstructural degradation of individual constituents comprising the MEA, i.e., carbon support, electrocatalyst, polymer membrane, and recast ionomer. Analyses conducted in this way are required to correlate observed microstructural changes with durability and fuel cell performance.

Understanding the shapes of bacteria just got more complicated

The paper by Briegel et al. in this issue of Molecular Microbiology uses advanced cryo-transmission electron microscopy (cryoTEM) techniques to reveal four separate locations of cytoplasmic filament bundles in Caulobacter crescentus. Intuitively, these filaments should be rather rigid protein structures and composed of previously identified shape-forming proteins, such as crescentin or MreB. Yet, deletion mutants lacking these proteins still possessed filaments and still possessed wild-type morphology. These results suggest that a complex combination of protein structures, including those of crescentin, MreB and these newly identified bundles, in combination with the cell envelope help maintain the complicated shape of C. crescentus. Other bacteria might have similar architectural proteins to assist in maintaining the cell contours during growth and division.

Nanoscale magnetic properties of iron minerals in bacteria

We have used a combination of advanced transmission electron microscopy techniques to study the physical and chemical properties of intracellular ferrimagnetic magnetite (Fe3O4) and greigite (Fe3S4) nanocrystals insidemagnetotactic bacteria that were collected from lakes and streams. The relative orientations and themorphologies of magnetic nanocrystals in magnetosome chains were identified using electron diffraction, highresolution electron microscopy and high-angle annular dark field electron tomography. Whereas magnetite chains were found to be analogous to beads on a string, in which biological control set the [111] magnetocrystalline easy axes of the crystals parallel to each chain axis, greigite crystals had more random orientations. Within each bacterial strain, magnetite magnetosomes were observed to have distinct and well-controlled morphologies. In contrast, greigite crystals appeared to have more irregular shapes. We used off-axis electron holography to record magnetic induction maps from the magnetosome chains. The magnetic signal was dominated by inter-particle interactions and by the shapes of the individual crystals. Magnetite nanocrystals were found to be uniformly magnetized, parallel to the magnetosome chain axes. In contrast, the disordered three-dimensional arrangement of multiple chains of greigite crystals resulted in the magnetic field following a meandering path between adjacent crystals. Over a three-year period, with the sample stored in air, each greigite crystal developed an amorphous iron oxide shell and its magnetic moment decreased. Our results are useful for obtaining an insight into biomineralization processes, and for studying the fundamental effects that influence the magnetic properties of closely-spaced nanoscale magnets. m12.o02

Biomineralization and self-assembled nanostructures – structure determination and material properties

We have used a combination of advanced transmission electron microscopy techniques to study the physical and chemical properties of intracellular ferrimagnetic magnetite (Fe3O4) and greigite (Fe3S4) nanocrystals insidemagnetotactic bacteria that were collected from lakes and streams. The relative orientations and themorphologies of magnetic nanocrystals in magnetosome chains were identified using electron diffraction, highresolution electron microscopy and high-angle annular dark field electron tomography. Whereas magnetite chains were found to be analogous to beads on a string, in which biological control set the [111] magnetocrystalline easy axes of the crystals parallel to each chain axis, greigite crystals had more random orientations. Within each bacterial strain, magnetite magnetosomes were observed to have distinct and well-controlled morphologies. In contrast, greigite crystals appeared to have more irregular shapes. We used off-axis electron holography to record magnetic induction maps from the magnetosome chains. The magnetic signal was dominated by inter-particle interactions and by the shapes of the individual crystals. Magnetite nanocrystals were found to be uniformly magnetized, parallel to the magnetosome chain axes. In contrast, the disordered three-dimensional arrangement of multiple chains of greigite crystals resulted in the magnetic field following a meandering path between adjacent crystals. Over a three-year period, with the sample stored in air, each greigite crystal developed an amorphous iron oxide shell and its magnetic moment decreased. Our results are useful for obtaining an insight into biomineralization processes, and for studying the fundamental effects that influence the magnetic properties of closely-spaced nanoscale magnets. m12.o02

Demonstration of lanthanum in liver cells by energy‐dispersive X‐ray spectroscopy, electron energy loss spectroscopy and high‐resolution transmission electron microscopy

The appearance of lanthanum in liver cells as a result of the injection of lanthanum chloride into rats is investigated by advanced transmission electron microscopy techniques, including electron energy loss spectroscopy and high-resolution transmission electron microscopy. It is demonstrated that the lysosomes contain large amounts of lanthanum appearing in a granular form with particle dimensions between 5 and 25 nm, whereas no lanthanum could be detected in other surrounding cellular components.

Bonding at copper–alumina interfaces established by different surface treatments: a critical review

The present study summarizes the effects of processing conditions and substrate cleaning procedures on the structure, chemistry and bonding of Cu/(0001)Al2O3 interfaces as determined by advanced transmission electron microscopy techniques. The Cu/(0001)Al2O3 samples were prepared by molecular beam epitaxy (MBE) and solid-state diffusion bonding. Investigations of the MBE samples showed that the Al2O3 cleaning procedure alters the interfacial bonding. Metallic bonds occurred for an Ar+ ion sputtering and subsequent ultra-high vacuum (UHV) annealing treatment. Strongly ionic–covalent bonds were found for a wet chemical cleaning process followed by UHV annealing. The interfacial electronic structure did not reveal any significant changes compared to the bulk electronic structure for samples where the substrate surface was annealed in an oxygen-containing atmosphere after Ar+ ion pre-sputtering and UHV annealing. The results obtained at the solid-state diffusion-bonded Cu/Al2O3 samples indicated that the processing parameters such as temperature and load do not change the bonding behavior. Post-annealing of the solid-state diffusion-bonded Cu/Al2O3 samples in a well-defined oxygen partial pressure led to the formation of CuAlO2 at the interface between Cu and Al2O3, which improved the adhesion.

Electron-beam radial distribution analysis of irradiation-induced amorphous SiC

Advanced electron microscopy techniques have been employed to examine atomistic structures of ion-beam-induced amorphous silicon carbide (SiC). Single crystals of 4H-SiC were irradiated at a cryogenic temperature (120K) with 300keV Xe ions to a fluence of 1015cm−2. A continuous amorphous layer formed on the topmost layer of the SiC substrate was characterized by energy-filtering transmission electron microscopy in combination with imaging plate techniques. Atomic pair-distribution functions obtained by a quantitative analysis of energy-filtered electron diffraction patterns revealed that amorphous SiC networks contain heteronuclear Si–C bonds, as well as homonuclear Si–Si and C–C bonds, within the first coordination shell. The effects of inelastically-scattered electrons on atomic pair-distribution functions were discussed.