High-resolution Electron Microscopy Observations Research Articles

AlN Nanorods synthesized by a Mechanothermal Process

ABSTRACTWell-crystallized AlN nanorods have been produced by mechanical milling and subsequent annealing treatment of the milling powders (mechanothermal process). High purity AlN powders were used as the starting material. Mechanical milling was carried out in a vibratory SPEX mill for 30 h, using vials and balls of silicon nitride. The annealing treatment was carried out at 1200 ºC for 10 min. The characterization of the samples was performed by X-ray diffractometry and transmission electron microscopy (TEM). TEM observations indicated that the synthesized nanorods consisted of 30 nm in diameter and 100 nm in length. High resolution electron microscopy observations have been used in the structural characterization. AlN nanorods exhibit a well-crystallized structure. The growing direction of the nanorods is close to the [001] direction. The structural configurations have been explored through comparisons between experimental HREM images and theoretically simulated images obtained with the multislice method of the dynamical theory of electron diffraction.

Interface Structure of Gold Particles on TiO<SUB>2</SUB> Anatase

Gold particles supported on titanium dioxide (TiO2) are known to activate many catalytic reactions. In this study, interface structure of gold on anatase was examined in the case on an anatase {101} surface, since the surface is the most important for several photocatalytic reactions. Anatase TiO2 nanorods having clear washboard-like {101} outer surfaces were synthesized by using a double surfactants system. From high resolution electron microscopy observation for gold particle on the {101} surface, the (113) plane of gold was found to be parallel to the (101) surface of TiO2. Such an epitaxy is corresponding to be the axial and planar orientations of [03\\bar1] (200)Au || [\\bar31\\bar1] (113)TiO2, being originated from the smallest lattice mismatching, instead of the previous cases of [01\\bar1] (111)Au || [02\\bar1] (112)TiO2 on the {110} and {112} surfaces of anatase TiO2.

Neutron-irradiation-induced crystalline defects in β-silicon nitride and their thermal stability

A hot-pressed Si3N4 was neutron-irradiated in the JOYO experimental fast reactor. The ranges of irradiation fluence and temperature were (0.4–3.7)×1026n/m2 (E>0.1MeV) and (377–727)°C, respectively. Based on high-resolution electron microscope observation, several kinds of tiny interstitial dislocation loops on the {101¯0} or {112¯0} planes were identified. It was clarified that area density and average size of each planar defect was greater after irradiation to higher doses at higher temperatures. The density of planar defects on {101¯0} was higher than that of on {112¯0}, regardless of irradiation conditions. After annealing, size distribution of the defects on the {101¯0} planes was not changed up to 1350°C in the case of the specimen irradiated at the lowest temperature (0.5×1026n/m2 at 377°C). On the other hand, the number of dislocations with diameter smaller than 4nm decreased at over 900°C and the loop size distribution shifted larger size after annealing at temperatures higher than 1350°C in the case of higher irradiation temperature specimen (0.4×1026n/m2 at 542°C).

Preparation and Characterization on Self-Catalytic of SnO<sub>2</sub> Nanowire Junctions

Multiple branched SnO2 nanowire junctions have been synthesized by thermal evaporation of SnO powder. Their nanostructures were studied by transmission electron microscopy and field emission scanning electron microcopy. It was observed that Sn nanoparticles generated from decomposition of the SnO powder acted as self-catalysts to control the SnO2 nanojunction growth. Orthorhombic SnO2 was found as a dominate phase in nanojunction growth instead of rutile structure; The branches and stems of nanojunctions were found to be an epitaxial growth by electron diffraction analysis and high-resolution electron microscopy observation. The growth directions of the branched SnO2 nanojunctions went along the orthorhombic [110] and [1—,10]. A self-catalytic vapor–liquid–solid growth mechanism is proposed to describe the growth process of the branched SnO2 nanowire junctions. Introduction

HREM Observation of Age-Precipitated Particles in Practical Cu-bearing Ultra-Low Carbon Steels

Morphology, distribution and crystal structures of age-precipitated particles in practical Cu-bearing steels with ultra-low carbon were studied by high resolution electron microscopy (HREM). The age-precipitation behavior was explored when poly-microalloying elements Cu, Nb, Cr, Mo and Ni were used and ɛ-Cu particles coexisted with carbides (carbonitrides) in steels. The fine dispersed ɛ-Cu particles and carbides of microalloying element Nb, Cr, Mo being about 10 nm only in size were observed in peak aging specimens and over-aging specimens. The twin structures and stacking faults in the particles and the transient structures formed in the early stage of the particle precipitation were also observed. The crystal structure of three types of age-precipitation particles was firstly identified by lattice streaks in HREM images of the single particles. The experimental method identifying crystal structure of fine and dispersed particles using HREM images of single particle was proposed.

Medium range ordering and some magnetic properties of amorphous Fe 90Zr 7B 3 alloy

High-resolution electron microscopy (HREM) reveals in the as-quenched Fe 90Zr 7B 3 alloy the existence of medium range ordered (MRO) regions 1–2 nm in size. Transmission Mössbauer spectroscopy confirms that these regions are α-Fe MRO ones. Above the Curie point of the amorphous phase ( T C =(257±2)K) they behave like non-interacting superparamagnetic particles with the magnetization decreasing linearly with the temperature. For these particles the average magnetic moment of 390μ B and the average size of 1.7 nm, in excellent agreement with HREM observations, were estimated. The maximum of the isothermal magnetic entropy change at the maximum magnetizing field induction of 2 T occurs at the Curie temperature of the amorphous phase and equals to 1.05 Jkg −1 K −1. The magnetic entropy changes exhibit the linear dependence on the maximum magnetizing field induction in the range 0.5–2 T below, near and above T C . Such correlations are attributed to superparamagnetic behavior of α-Fe MRO regions.

Heterogeneous nucleation and epitaxial crystal growth of magmatic minerals

Electron backscatter diffraction analysis of dendritic clinopyroxene (cpx) forming in rapidly cooled basalt reveals two features that are unexpected for phases growing from a liquid: (1) helical growth about {010} cpx , the crystallographic b-axis, with incremental rotation (up to 0.4° μm −1 ) within branch segments and large rotational jumps (10°–46°) between closely spaced branch segments, and (2) strong crystallographic preferred orientation (CPO) between cpx and titanomagnetite (timt) decorating branch tips, such that {010} cpx aligns with one of the six symmetrically equivalent {110} timt face poles. More than 80% of timt crystals occur within 5° of the CPO with cpx substrate, as do 22% of timt crystals in contact with euhedral cpx in natural Etna basalt. The probability distribution of distances between an arbitrary unit vector and the nearest {110} timt normal unit vector was found by numerical simulation and indicates that the observed alignment to within 5° occurs with frequency 0.024; thus the CPO occurs 9–33 times more commonly than expected from randomly distributed crystals. The CPO matches previous observations of epitaxial relationship between spinel and host pyroxene during subsolidus exsolution, but has not previously been reported among magmatic cpx and timt. Conspicuous contiguity among phenocryst phases is inferred to result from heterogeneous nucleation facilitated by epitaxy associated with CPO, an inference supported by high-resolution electron microscopy observations of 150 nm timt crystals adhering preferentially to silicate substrates. Epitaxial relationships among phases nucleating from a melt may contribute to fabrics in magnetic properties, dictate the textures of igneous rocks by promoting development of crystal clusters, and even influence magma transport and eruption styles through a control over magma rheology.

TEM studies of plasma nitrided austenitic stainless steel

Cross-sectional transmission electron microscopy and X-ray phase analysis were used to study the structure of a layer formed during nitriding the AISI 316L stainless steel at temperature 440 degrees C. It was found that the applied treatment led to the formation of 6-microm-thick layer of the S-phase. There is no evidence of CrN precipitation. The X-ray diffraction experiments proved that the occurred austenite lattice expansion - due to nitrogen atoms - depended on the crystallographic direction. The cross-sectional transmission electron microscopy studies showed that the layer consisted of a single cubic phase that contained a lot of defects such as dislocations, stacking faults, slip bands and twins. The high-resolution electron microscopy observations were applied to study the defect formation due to the nitriding process. It was shown that the presence of great number of stacking faults leads to formation of nanotwins. Weak, forbidden {100} reflections were still another characteristic feature of the S-phase. These were not detected in the X-ray spectra of the phase. Basing on the high-resolution electron microscopy studies it can be suggested that the short-range ordering of the nitrogen atoms in the octahedral sites inside the f.c.c. matrix lattice takes place and gives rise to appearance of these spots. It is suggested that the cubic lattice undergoes not only expansion but also slight rombohedral distortion that explains differences in the lattice expansion for different crystallographic directions.

Nano‐TiC obtained through a reaction of MWCNTs with Zr(Y,Ti)O2

The zirconia nanopowder stabilized with 2.5 mol% Y(2)O(3) and doped with 18 mol% TiO(2) (Zr(Y,Ti)O(2)) was homogenized with 5.2 wt% multiwall carbon nanotubes (MWCNT) through colloidal processing. The resultant mixture was heat-treated for 2 h at 1200 degrees C in vacuum under a pressure of 5 x 10(-4) mbar. The microstructure characterization was performed using the TECNAI FEG (200 kV) SuperTWIN transmission electron microscope, equipped with the integrated EDAX detector. The TEM observations of the as-received samples showed single strands of the carbon nanotubes uniformly dispersed among zirconia crystallites. Heat treatment of the Zr(Y,Ti)O(2)-MWCNT mixture caused the transformation of carbon nanotubes into polycrystalline TiC nanofibres and nanorods as confirmed by both the energy dispersive X-ray spectroscopy microanalysis and the high-resolution electron microscopy (HREM) observations. Relying on the above, a mechanism of the TiC in situ crystallization controlled by carbon diffusion through the newly formed TiC phase was discussed.

Electrochemical growth behavior, surface properties, and enhanced in vivo bone response of TiO2 nanotubes on microstructured surfaces of blasted, screw-shaped titanium implants

TiO(2) nanotubes are fabricated on TiO(2) grit-blasted, screw-shaped rough titanium (ASTM grade 4) implants (3.75 x 7 mm) using potentiostatic anodization at 20 V in 1 M H(3)PO(4) + 0.4 wt.% HF. The growth behavior and surface properties of the nanotubes are investigated as a function of the reaction time. The results show that vertically aligned nanotubes of approximately 700 nm in length, with highly ordered structures of approximately 40 nm spacing and approximately 15 nm wall thickness may be grown independent of reaction time. The geometrical properties of nanotubes increase with reaction time (mean pore size, pore size distribution [PSD], and porosity approximately 90 nm, approximately 40-127 nm and 45%, respectively for 30 minutes; approximately 107 nm, approximately 63-140 nm and 56% for one hour; approximately 108 nm, approximately 58-150 nm and 60% for three hours). It is found that the fluorinated chemistry of the nanotubes of F-TiO(2), TiOF(2), and F-Ti-O with F ion incorporation of approximately 5 at.%, and their amorphous structure is the same regardless of the reaction time, while the average roughness (Sa) gradually decreases and the developed surface area (Sdr) slightly increases with reaction time. The results of studies on animals show that, despite their low roughness values, after six weeks the fluorinated TiO(2) nanotube implants in rabbit femurs demonstrate significantly increased osseointegration strengths (41 vs 29 Ncm; P = 0.008) and new bone formation (57.5% vs 65.5%; P = 0.008) (n = 8), and reveal more frequently direct bone/cell contact at the bone-implant interface by high-resolution scanning electron microscope observations as compared with the blasted, moderately rough implants that have hitherto been widely used for clinically favorable performance. The results of the animal studies constitute significant evidence that the presence of the nanotubes and the resulting fluorinated surface chemistry determine the nature of the bone responses to the implants. The present in vivo results point to potential applications of the TiO(2) nanotubes in the field of bone implants and bone tissue engineering.

Synthesis of molybdenum disulfide (MoS 2) for lithium ion battery applications

This paper reports the use of a rheological phase reaction method for preparing MoS 2 nanoflakes. The characterization by powder X-ray diffraction indicated that MoS 2 had been formed. High resolution electron microscopy observation revealed that the as-prepared MoS 2 nanoflakes had started to curve and partly form MoS 2 nanotubes. The lithium intercalation/de-intercalation behavior of as-prepared MoS 2 nanoflake electrode was also investigated. It was found that the MoS 2 nanoflake electrode exhibited higher specific capacity, with very high cycling stability, compared to MoS 2 nanoparticle electrode. The possible reasons for the high electrochemical performance of the nanoflakes electrodes are also discussed. The outstanding electrochemical properties of MoS 2 nanoflakes obtained by this method make it possible for MoS 2 to be used as a promising anode material.

Creep cavitation can establish a dynamic granular fluid pump in ductile shear zones

The feedback between fluid migration and rock deformation in mid-crustal shear zones is acknowledged as being critical for earthquake nucleation, the initiation of subduction zones and the formation of mineral deposits. The importance of this poorly understood feedback is further highlighted by evidence for shear-zone-controlled advective flow of fluids in the ductile lower crust and the recognition that deformation-induced grain-scale porosity is a key to large-scale geodynamics. Fluid migration in the middle crust cannot be explained in terms of classical concepts. The environment is considered too hot for a dynamic fracture-sustained permeability as in the upper crust, and fluid pathways are generally too deformed to be controlled by equilibrium wetting angles that apply to hotter, deeper environments. Here we present evidence that mechanical and chemical potentials control a syndeformational porosity generation in mid-crustal shear zones. High-resolution synchrotron X-ray tomography and scanning electron microscopy observations allow us to formulate a model for fluid migration in shear zones where a permeable porosity is dynamically created by viscous grain-boundary sliding, creep cavitation, dissolution and precipitation. We propose that syndeformational fluid migration in our 'granular fluid pump' model is a self-sustained process controlled by the explicit role of the rate of entropy production of the underlying irreversible mechanical and chemical microprocesses. The model explains fluid transfer through the middle crust, where strain localization in the creep regime is required for plate tectonics, the formation of giant ore deposits, mantle degassing and earthquake nucleation. Our findings provide a key component for the understanding of creep instabilities in the middle crust.

High-resolution electron microscopy observations of continuous precipitates with Pitsch-Schrader orientation relationship in an Mg–Al based alloy and interpretation with the O-lattice theory

High-resolution electron microscopy was applied to analyze the continuous precipitated particles of the γ-Mg 17Al 12 phase with Pitsch-Schrader OR in the heat-treated AZ91 alloy at 473 K for 8 h. The existence of a continuous precipitated particle with the Pitsch-Schrader OR including the selection of the habit plane and the growth direction in Mg–Al system is rationalized by the constrained coincidence site lattice/constrained complete pattern shift lattice (CCSL/CDSCL) model and the O-lattice theory.

Synthesis of ZnO2 Nanocrystals Produced by Hydrothermal Process

ABSTRACTZinc peroxide (ZnO2) nanocrystals were directly produced by hydrothermal process. The nanocrystals were synthesized using zinc acetate as precursor and hydrogen peroxide as oxidant agent. The ZnO2 powders were characterized by X-ray powder diffraction and transmission electron microscopy. The results of transmission electron microscopy indicated that the ZnO2powders consisted of nanocrystals with diameters below to 20 nm and a faceted morphology. High resolution electron microscopy observations have been used in order to the structural characterization. ZnO2 nanocrystals exhibit a well-crystallized structure.

Structural defects in Al–Ni–Rh and Al–Pd–Fe crystalline approximant phases

Abstract Structural defects of high density have been observed to exist in the as-cast crystalline approximants Al–Ni–Rh ξ and Al–Pd–Fe ε 16 which contain columnar atom clusters as the most fundamental building blocks. By means of high-resolution electron microscopy (HREM), the structural and distributional features of these defects have been revealed. It is clearly shown that, accommodating structural defects of high density in the Al–Ni–Rh ξ-phase can lead to the formation of a unique mixed structure in which nearly regular arrangement of structural defects can be established. On the basis of HREM observations, long-range structural features of the defective ξ- and ε 16-structures have been discussed in terms of the characteristic arrays of columnar atom clusters.

Structure, morphology, thermal stability and carbonization mechanism studies of electrospun PA6/Fe-OMT nanocomposite fibers

In the present work, Fe-montmorillonite (Fe-MMT) was synthesized by hydrothermal method, and then was modified by cetyltrimethyl ammonium bromide (CTAB). The polyamide 6 (PA6)/organic-modified Fe-montmorillonite (Fe-OMT) nanocomposite fibers were prepared by a facile compounding and electrospinning. The catalyzing carbonization studies of the Fe-OMT based on PA6 nanocomposite fibers were performed. It was found from High-resolution electron microscopic (HREM) observations that the silicate clay layers were well dispersed within the nanocomposite fibers and was oriented along the fiber axis. The Scanning electron microscopic (SEM) images indicated that the nanofibers were randomly distributed to form the fibrous web and the Fe-OMT additives decreased the diameters of nanocomposite fibers. The Thermogravimetric analyses (TGA) revealed that the loading of the Fe-OMT led to the crosslinking of the PA6, promoted the charred residue yield and catalytic graphitization effect. The structure and morphology of the purified charred residue, characterized by XRD, HREM, Selected area electron diffraction (SAED) and Laser Raman spectroscopic (LR), approved further the presence of graphite sheets. The possible catalyzing carbonization mechanisms included: (1) catalyzing effect of the Fe 3+, which promoted the crosslinking of polymer, (2) Hofmann degradation of the Fe-OMT, whose degraded products had also positive role in promoting crosslinking reactions, (3) gas barrier properties of the nano-dispersed silicate clay layers stopped or reduced the releases of the pyrolytic products, which was dehydrogenated and aromatized to form graphite.

Simulations of high-resolution electron microscopy images of icosahedral quasicrystals

We apply the scattering matrix formulation for calculating the images of high-resolution electron microscopy (HREM) images of quasiperiodic crystals and discuss their basic properties. The main feature in the image formation comes from the truncation effects of the q-basis, especially the perpendicular components which must be numerous enough for properly reproducing quasiperiodicity. A comparison between two types of atomic structural model is presented that illustrates the difficulties of differentiating the models from the HREM observations.

Synthesis of spherical porous vanadium pentoxide and its electrochemical properties

Spherical porous vanadium pentoxide (V 2O 5) phase is synthesized by a spray-pyrolysis method followed by heat-treatment, as confirmed by powder X-ray diffraction. Under high-resolution electron microscope observation, the as-prepared particles are spherical and porous, with uniform particle size. On investigation of the electrochemical properties of V 2O 5 synthesized by this method, it is found that the initial specific capacity of the V 2O 5 is 399 mAh g −1, and it exhibits good cycleability during the discharge and charge processes. The experimental results suggest that V 2O 5 synthesized by this method could be a promising electrode material for lithium-ion batteries.

Characterization of Highly Porous Polymeric Materials with Pore Diameters Larger than 100 nm by Mercury Porosimetry and X-ray Scattering Methods

Highly porous polymeric materials with pore sizes ranging from 100 nm to 1 microm are a very challenging class of materials not only to prepare synthetically (due to the high capillary pressures generated upon solvent removal) but also to characterize structurally. Through the examples of three different types of porous compounds synthesized in our laboratory (i) high-density melamine-based "MF-hd" with monomodal pore diameters around 500-900 nm, (ii) low-density melamine-based "MF-ld" with bimodal pore size distribution and average diameters around 2.3 microm and 350 nm, (iii) highly porous polyurethane "PU" with monomodal pore sizes around 150 nm, we confirm the limitations of mercury porosimetry as a means to investigate the architecture of materials with very high porosity (>80 vol %) and low compressive strength. Instead, a combination of high-resolution scanning electron microscopy and small-angle and ultrasmall-angle X-ray scattering (SAXS and USAXS, respectively) studies of these three types of materials helps in determining both the network and the pore structures. This work elucidates the need and applicability of the SAXS/USAXS techniques in characterizing such porous materials. For instance, the polyurethane specimens can only be quantitatively characterized by scattering techniques, the results of which are corroborated by high-resolution scanning electron microscopy observations.

Defect Structures in Al-Ni-Rh Crystalline Approximants Studied by HREM and HAADF Techniques

By means of a combination of high-resolution electron microscopy (HREM) and high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM) techniques, we have directly revealed that periodic arrangements in different manners for flattened hexagons constructed with atom columnar clusters can form two Al-Ni-Rh crystalline approximant phases. In contrast to periodic arrangements of flattened hexagons, configurations and distributions of various defects in these structurally-complicated alloy phases have been examined and their structural characteristics discussed. HREM observations clearly show that structural defects in Al-Ni-Rh crystalline approximants are of phason type and they are correlated with incorrect arrangements of atom columnar clusters. The distribution of high density planar defects can destroy the long-range periodicity in at least one direction in the pseudo decagonal symmetry plane. By means of the HAADF-STEM imaging technique, the existence of ill-formed atom columnar clusters in the core area of a linear defect, which is usually not visible in HREM observations, has been clearly revealed.