High-resolution Electron Microscopy Analysis Research Articles

A 2100 year BP record of the Pacific Decadal Oscillation, El Niño Southern Oscillation and Quasi-Biennial Oscillation in marine production and fluvial input from Saanich Inlet, British Columbia

Exceptional varved sediments of 2100 years BP recovered from Saanich Inlet have been analysed using high-resolution scanning electron microscopy and spectral analysis techniques. Each varve may contain up to 22 well defined individual laminae which can be attributed to seasonal-scale processes. Sediment flux comprises alternating diatom ooze/diatomaceous mud deposited during spring through autumn and a silty-clay deposited during winter. The latter may be sporadically punctuated by clay-rich laminae. Identification of some 2000 individual consecutive laminae, based on fabric and diatom assemblage, has allowed the construction of time series data for spectral analysis. Laminae types analysed include: early spring Thalassiosira spp., late spring/early summer Skeletonema costatum, multiple summer/autumn Chaetoceros spp. diatom oozes and sporadically present clay-rich winter flood deposits. Sub-decadal periods have been identified and linked to the Quasi-Biennial Oscillation (QBO) and El Niño Southern Oscillation (ENSO), and decadal periods to the Pacific Decadal Oscillation (PDO). Comparison of spectral analysis results with modern analogues suggests associations may exist between: early spring Thalassiosira spp. laminae and stronger La Niña events; late spring/early summer S. costatum laminae and El Niño events; summer/autumn Chaetoceros spp. multiple laminae and negative Pacific Northwest Index (PNI) regimes; and sporadically present winter clay-rich laminae and PNI-regimes. The average period for an ENSO cycle was 3.6 years, QBO 2.5 years and PDO 14.8 years. Spectral analysis of the more recent PNI record shows similar significant periods of 13.2, 3.7 and 2.6 years. Multi-decadal periods recorded include: 42.2 and 31.3 years, which might suggest multiples of PDO.

Nonohmic behavior of SnO2-MnO polycrystalline ceramics. I. Correlations between microstructural morphology and nonohmic features

This report discusses important microstructural features of SnO2.MnO-based polycrystalline ceramics. The influence of the sintering time and the concentration of donor Nb2O5 on the microstructure of these ceramics are investigated, and the correlation between the microstructural features and nonohmic behavior are also discussed. High resolution analytical electron microscopy was used for a detailed characterization of the microstructure and grain boundary chemistry of the compositions, revealing that SnO2-MnO dense ceramics consist of two phases, SnO2 grains and Mn2SnO4, precipitated mainly at triple grain points. In addition, two types of SnO2-SnO2 grain boundary were identified: type I, Mn-rich and thin, and type II, Mn-poor and thick. Changes in Mn concentrations at the grain boundaries are ascribed to both grain misorientation and Mn diffusivity along the grain boundary. The identification of two kinds of junctions in SnO2-MnO has significant implications in the material’s nonohmic behavior, as will be discussed in detail here and in Part II, and is important in understanding the sintering mechanism and microstructural formation of SnO2 ceramics.

The characteristics of low-temperature-synthesized ZnS and ZnO nanoparticles

An easy and economic method is proposed to synthesize zinc sulfide (ZnS) nanocrystals. Zinc sulfide nanoparticles with different particle sizes were prepared by solid-state reaction of zinc acetate and thioacetamide at low temperature. After annealing at 600°C in air, zinc oxide (ZnO) nanoparticles were obtained. The ZnS and ZnO nanoparticles were characterized by X-ray diffraction (XRD), photoluminescence (PL) spectroscopy, differential thermal analysis and high-resolution analytical electron microscopy. The smallest crystallite size of ZnS nanoparticles obtained was 3.6 nm in diameter and the temperature for synthesizing was 100°C. The room temperature PL spectrum of ZnS sample de-convoluted by using a Lorentzian fit showed four peaks and the mechanism of emission was explained. A 26-fold increase in photoluminescence intensity has been observed in comparison with conventionally made ZnS particles. The particle size of ZnO samples calculated from XRD consistent with the TEM image was 37 nm and showed hexagonal structure. In the PL spectrum of ZnO nanoparticles, an emission peak at 501 nm was observed which was assumed to be due to the energy level of oxygen vacancies in ZnO energy band gap. By means of this method, it is easy to prepare ZnS and ZnO nanocrystals without wasting much time.

Study of wall‐painting pigments from Feng Hui Tomb by Raman spectroscopy and high‐resolution electron microscopy

AbstractThe structures and components of different pigments from the Feng Hui tomb situated in Bin County, Shaanxi Province, dated in the Five Dynasties (907–960 AD), were analyzed by Raman spectroscopy and high‐resolution electron microscopy (HREM). It is shown that the red, yellow and black samples are cinnabar, PbSO4–PbO and carbon black, respectively, and well preserved, which provide scientific data for later conservation. Moreover, the results indicate that HREM and Raman analysis are very effective for identifying ancient inorganic pigments at low concentrations. Copyright © 2004 John Wiley & Sons, Ltd.

Strategy for Applying Microanalytical Techniques

A combination of microanalysis techniques is used to reveal with great precision the composition and microstructure of typical features in engineering materials. In this paper small particles, very thin films, interfaces and their contiguous region are considered. Small silicon nitride particles in an iron matrix produced by nitriding are characterized quantitatively with High Resolution Electron Microscopy (HREM) and Electron Probe Micro Analysis (EPMA) using Wavelength Dispersive X-ray Spectrometry (WDS). Thin aluminium-oxide films grown on aluminium substrates by thermal oxidation at low pressure are investigated with HREM and X-ray Photoelectron Spectroscopy (XPS). Their thickness, composition and degree of crystallinity are established as a function of oxidation temperature and time. At and near the oxide-layer/MCrAlY-coating (M=Ni and/or Co) interface the aluminium and chromium depletion behaviour of the coating material due to high-temperature oxidation is studied with high-resolution Scanning Electron Microscopy (SEM), EPMA and Auger electron spectroscopy (AES). The composition-depth profiles obtained for the coating material are used to determine the composition dependent diffusion coefficients. These properties are crucial for the prediction through computational modelling of the coating material oxidation behaviour and enable the development of new coating materials.

Comparison of interfaces for (Ba,Sr)TiO3 films deposited on Si and SiO2/Si substrates

( Ba,Sr ) TiO 3 ( BST ) thin films were deposited by ion sputtering on both bare and oxidized Si. Spectroscopic ellipsometry results have shown that a SiO2 underlayer of nearly the same thickness (2.6 nm in average) is found at the Si interface for BST sputter depositions onto nominally bare Si, 1 nm SiO2 on Si or 3.5 nm SiO2 on Si. This result was confirmed by high-resolution electron microscopy analysis of the films, and it is believed to be due to simultaneous subcutaneous oxidation of Si and reaction of the BST layer with SiO2. Using the conductance method, capacitance–voltage measurements show a decrease in the interface trap density Dit of an order of magnitude for oxidized Si substrates with a thicker SiO2 underlayer. Further reduction of Dit was achieved for the capacitors grown on oxidized Si and annealed in forming gas after metallization.

Effect of nano oxide layer on exchange bias and GMR in Mn–Ir–Pt based spin valve

Abstract We have investigated the effect of nano oxide layers (NOLs), which were fabricated by a plasma oxidation of CoFe layer on the magnetic properties and magneto-resistance (MR) in a Mn–Ir–Pt based spin valve. The adjusted NOL could result in the high MR and the strong exchange coupling field ( H ex ). From a high resolution electron microscopy analysis the oxide was about 1 nm. The strong reflectivity at the interface of a free and oxide capping layer should lead to the decrease of an interlayer coupling field, which could possibly improve the H ex .

Effect of GeO2 and NdO1.5 Co-doping on High-temperature Ductility in TZP

Superplastic flow behavior in 1 mol% of GeO2 and 1 mol% of NdO1:5 co-doped ZrO2-3 mol%Y2O3 (3Y-TZP) was examined at 1400 � C under an initial strain rate of 1 � 10� 4 s� 1. 1 mol% of GeO2 or NdO1:5-doping slightly enhances high-temperature ductility in 3Y-TZP, but 1 mol% of GeO2 and 1 mol% of NdO1:5 co-doped TZP exhibits large elongation to failure of more than 600% at 1400 � C. The large ductility in TZP due to Ge 4þ and Nd 3þ co-doping can be explained from reduction in the flow stress. High-resolution electron microscopy (HREM) and energy-dispersive X-ray spectrometer (EDS) analysis revealed that Y 3þ ,G e 4þ and Nd 3þ cations segregate in the vicinity of grain boundaries in the present materials. The segregation width of the dopant cation across the grain boundaries in GeO2 and NdO1:5 co-doped TZP is larger than that in GeO2 or NdO1:5 singly doped TZP. The reduction in the flow stress due to GeO2 and NdO1:5 co-doping is probably related to the increment in the segregation width. (Received March 2, 2004; Accepted June 2, 2004)

Deformation structures developing on fine scales

Quantitative measurement and analysis of structural parameters has shown for a variety of metals and processes that the microstructural evolution follows a universal path of grain subdivision down to the nanoscale. This behaviour has allowed an analysis of the formation and evolution of graded nanoscale structures produced by sliding. Transmission electron microscopy studies and scaling analyses of such structures show the dominating role of dislocations in the development deformation microstructures on multiple length scales. The crucial role of dislocations has been documented by high-resolution electron microscopy analysis, which has revealed the presence of a large number of glide dislocations in layers between geometrically necessary boundaries with individual spacing as fine as 5 nm.

Novel composite anode materials for lithium ion batteries with low sensitivity towards humidity

Graphitic anode materials for lithium ion batteries processed under high humidity conditions show severe performance losses. The sensitivity of these materials towards humidity can be significantly reduced by adsorbing metal ions like silver or copper ions, with subsequent heat treatment of these composites. Results of X-ray photoelectron spectroscopy, high-resolution electron microscopy, thermogravimetry, and differential thermal analysis indicate that the deposited metals exist in metallic and carbide, M x C (M=Cu or Ag), forms. They remove or cover (i.e. deactivate) active hydrophilic sites at the surface of the graphite. These composites absorb less water during processing. The electrochemical performance, including reversible capacity, coulombic efficiency in the first cycle, and cycling behavior, is markedly improved. This approach provides a potentially powerful method to manufacture lithium ion batteries under less demanding conditions.

Structural order and disorder in Co-based layered cuprates CoSr 2(Y,Ce) sCu 2O 5+2 s ( s=1–3)

Crystal structures of a homologous series of Co-based layered cuprates, CoSr 2(Y,Ce) s Cu 2O 5+2 s ( s=1–3), have been investigated by high-resolution electron microscopy (HREM) and electron diffraction (ED) techniques. For all the three phases ED patterns showed double periodicity along a direction parallel to the CoO layers, indicating a regular alternation of two types of CoO 4-tetrahedra chains within the layers. Also seen was ordering of the chains along the layer-stacking direction for the s=1 phase (Co-1212); ED patterns simulated based on the proposed superstructure model well reproduced the observed patterns. For the s=2 (Co-1222) and s=3 (Co-1232) phases in which an additional fluorite-type layer-block is inserted between two CuO 2 planes, HREM and ED analysis revealed complete disorder of the CoO 4 chains along the layer-stacking direction. This implies that the interlayer ordering is mainly controlled by the distance between the neighboring CoO layers.

Critical Evaluation of Hot Forging Experiments: Case Study in Alumina

A new loading dilatometer was successfully developed and applied for hot forging experiments, assisted by two high‐resolution laser beams and providing accurate determination of radial and axial strains. The application of various uniaxial loads linearly increased both radial and axial strain rates of cylindrical specimens if compared at constant density. Microstructural evolution during hot forging was followed with high‐resolution scanning electron microscopy and quantitative analysis of pore size and orientation. Uniaxial loads led to elongated pores oriented in the direction of the applied load. This anisotropic microstructure exhibited an increased densification rate perpendicular to the loading axis, if free sintering was characterized after load removal. The imprinted anisotropy faded out during free sintering.

Viral assembly of oriented quantum dot nanowires.

The highly organized structure of M13 bacteriophage was used as an evolved biological template for the nucleation and orientation of semiconductor nanowires. To create this organized template, peptides were selected by using a pIII phage display library for their ability to nucleate ZnS or CdS nanocrystals. The successful peptides were expressed as pVIII fusion proteins into the crystalline capsid of the virus. The engineered viruses were exposed to semiconductor precursor solutions, and the resultant nanocrystals that were templated along the viruses to form nanowires were extensively characterized by using high-resolution analytical electron microscopy and photoluminescence. ZnS nanocrystals were well crystallized on the viral capsid in a hexagonal wurtzite or a cubic zinc blende structure, depending on the peptide expressed on the viral capsid. Electron diffraction patterns showed single-crystal type behavior from a polynanocrystalline area of the nanowire formed, suggesting that the nanocrystals on the virus were preferentially oriented with their [001] perpendicular to the viral surface. Peptides that specifically directed CdS nanocrystal growth were also engineered into the viral capsid to create wurtzite CdS virus-based nanowires. Lastly, heterostructured nucleation was achieved with a dual-peptide virus engineered to express two distinct peptides within the same viral capsid. This work represents a genetically controlled biological synthesis route to a semiconductor nanoscale heterostructure.

Measurement of the displacement field of dislocations to 0.03 A by electron microscopy.

Defects and their associated long-range strain fields are of considerable importance in many areas of materials science. For example, a major challenge facing the semiconductor industry is to understand the influence of defects on device operation, a task made difficult by the fact that their interactions with charge carriers can occur far from defect cores, where the influence of the defect is subtle and difficult to quantify. The accurate measurement of strain around defects would therefore allow more detailed understanding of how strain fields affect small structures-in particular their electronic, mechanical and chemical properties--and how such fields are modified when confined to nanometre-sized volumes. Here we report the measurement of displacements around an edge dislocation in silicon using a combination of high-resolution electron microscopy and image analysis inherited from optical interferometry. The agreement of our observations with anisotropic elastic theory calculations is better than 0.03 A. Indeed, the results can be considered as an experimental verification of anisotropic theory at the near-atomic scale. With the development of nanostructured materials and devices, we expect the use of electron microscopy as a metrological tool for strain analysis to become of increasing importance.

Microstructure of Cu2O/Si Interfaces, Made by Epitaxial Electrodeposition

Abstract Cu2O can be electrodeposited epitaxially onto Si (001) single-crystal substrates with an orientation relationship that can be described as a 45° rotation around the 〈001〉 direction that both crystals have in common along the growth direction. We show that this orientation relationship corresponds to maximum ‘reciprocal-space overlap’. In apparent contradiction to the unique orientation relationship, conventional, high-resolution, and high-resolution analytical transmission electron microscopy has revealed that an amorphous interlayer, which has a thickness of about 4 nm and mainly consists of SiO2, separates the Cu2O layer and the Si substrate. Potential micromechanisms for the evolution of this structure during early stages of growth are discussed.

Observation of heavy-ion tracks in polyimide by means of high-resolution scanning electron microscopy

The etching diameter of seven-year old latent tracks created in polyimide by 7.5 MeV/A 238U ions has been derived through high-resolution scanning electron microscopy observations and analysis according to an etching model presented herein. The diameter extracted, 6.9±1.4 nm, matches the mean width of few-weeks old latent tracks as determined recently by transmission electron microscopy. Three conclusions emerge. First, the track region that manifests itself in a highly-elevated chemical reactivity coincides with the primary structurally-altered region of the track. Second, chemical reactivity is enhanced not only by reactive alteration products but also by free volume resulted from ion-initiated processes. Third, there is no evidence of any significant healing of ion-damaged sites.

Taking close-ups of a rafting trip

![Graphic][1] Different microdomains contain K-ras and H-ras.By combining high-resolution electron microscopy and sophisticated statistical analysis, Prior et al. ( [page 165][2]) have developed a powerful new technique for studying lipid microdomains, and used it to examine the

High-Resolution Analytical Electron Microscopy Investigation of Metastable Tetragonal Phase Stabilization in Undoped, Sol-Gel Derived Zirconia Nanoceramics

ABSTRACTThe mechanisms underlying stabilization of the metastable tetragonal (t)-phase in sol-gel derived, nanocrystalline ZrO2 were studied by high-resolution analytical electron microscopy, utilizing parallel electron-energy loss (PEEL) and energy-dispersive X-ray spectroscopies. The powders were synthesized by hydrolysis of Zr (IV) n-propoxide at ratios of molar concentration of water to Zr n-propoxide, R=5 and 60, respectively, followed by calcination at 400°C. Dense particles of the as-precipitated ZrO2 (R=5) revealed 4–11 nm-sized nanocrystals embedded in the amorphous matrix that may serve as nuclei for the t-phase during calcination. The calcined particles consist of 10–100 nm–sized t-crystals. For as-precipitated ZrO2 (R=60), week aggregates (50–100 nm) of largely amorphous 4–20 nm-sized particles after calcination yield a mixture of t-and monoclinic (m-) nanocrystals. PEELS fingerprints of the band structure with the intensity threshold matching the expected position of a direct bandgap at 4–5 eV allow to differentiate between the amorphous and nanocrystalline ZrO2. Stabilization of t-phase (R=5) with sizes up to 16 times larger than reported earlier is likely due to strain-induced confinement from surrounding growing grains, which suppress the volume expansion associated with the martensitic t-m transformation. For R=60, loose nanoparticle agglomerates cannot suppress the transformation. In this case, the t-phase may be partially stabilized due to a crystal size effect and /or to the presence of m-phase.

MBE growth of (1 1 0) refractory metals on a -plane sapphire

The initial stages of growth of epitaxial (1 1 0) niobium, tantalum, and molybdenum films on (1 1 2 0) sapphire by molecular beam epitaxy, MBE, are analyzed in situ by reflection high-energy electron diffraction (RHEED), and ex situ by high-resolution electron microscopy (HREM) and X-ray diffraction (XRD) techniques. The RHEED analysis shows that both Nb and Ta initially deposit (for approximately the first two monolayers in the case of Nb and the first four monolayers for Ta) with an hexagonal surface symmetry that is not consistent with the normal bcc structure of these metals, in agreement with the previous result of Oderno et al. [1] for Nb on sapphire. On further deposition, the films are observed to relax into the normal bcc (1 1 0) structure. Intensity oscillations of the RHEED specular beam are observed during both stages of growth. The RHEED oscillations are damped out after approximately 20 monolayers of Nb (≈30 monolayers of Ta) as a steady-state surface roughness is reached. HREM analysis reveals that the initial hexagonal structure has transformed completely to the normal bcc structure in the thicker films. The epitaxial relationships at each stage of growth are identified and a model is suggested for the development of the initial hexagonal structure based on Nb–O bonding at the interface. As the thickness of the bcc film increases, strain relief is observed by the formation of misfit dislocations. The growth mode of Mo is found to be different from that of Nb and Ta. The initial deposit grows in a three-dimensional mode with poor atomic order; the RHEED patterns are not sufficiently distinct to identify whether the hexagonal structure is formed. However, the surface becomes progressively smoother as growth proceeds and thicker films of Mo are comparable in crystalline quality, as measured by X-ray rocking curves, to Nb and Ta. The different growth mode of Mo is attributed to greater mismatch with the sapphire substrate and possibly different M–O ionic bonding at the substrate interface.

Microstructure and mechanical properties of Cu doped TiN superhard nanocomposite coatings

Ti–Cu–N nanocomposite films with various copper contents were deposited by simultaneous co-deposition of titanium nitride and copper using a reactive arc ion plating and magnetron sputtering hybrid system. The structure and mechanical properties of these films were found to be dependent on the copper concentration. X-ray diffraction analysis and high resolution and conventional transmission electron microscopy analysis showed that the grain size in films decreases with increasing the copper content while no sign of copper phase was observed. Ti–Cu–N films containing 1.5 at.% of copper exhibited maximum hardness of 45 GPa and relatively low friction coefficient of 0.3. The further increase of copper content in the film resulted in sharp decrease of hardness. The obtained results are discussed with the model of film growth in the presence of impurities as related to the concept for the design of superhard nanocomposite materials. The role of soft metallic phase in two-phase composite materials containing one hard and one soft phase is also discussed.