High-resolution Electron Microscopy Analysis Research Articles

Nano-scale structural analysis of (La,Fe)TiO 3 prepared by Fe/Li ion-exchange

Nano-scale structural analysis of (La,Fe)TiO 3 prepared by Fe/Li ion-exchange has been performed by high resolution transmission electron microscopy and analytical electron microscopy. An ion-exchange reaction has been microscopically confirmed. On the other hand, the nano-crystalline bcc-Fe phase segregates as a secondary phase at grain boundaries. Interfaces between grain boundaries and matrix grains of (La,Fe)TiO 3 maintain the coherency. The bcc-Fe phase at the grain boundaries may be the origin of the ferromagnetic behavior in (La,Fe)TiO 3.

Electrothermal characterization of tungsten-coated carbon microcoils for micropropulsion systems

Laser-induced chemical vapor deposition is used to deposit tungsten-coated carbon microcoils from the gas phase. Because the microcoils are used as heating elements in cold/hot gas microthrusters in nanosatellites, it is important to characterize their electrothermal behavior so that the performance of the thruster may be predicted. The coils are deposited using an argon-ion laser (wavelength 514.5nm) at 360mW and 930mbar of C2H4. Bent arms are then deposited at the ends of the 1mm long coils using 600mW of laser power and 700mbar of C2H4. The arms serve as electrical contacts and as mechanical supports to hold the coils in the thruster by a locking mechanism. A layer of tungsten is then applied to the carbon coils by the hydrogen-reduction of WF6 using a 20:1 (H2:WF6) pressure ratio at a total pressure of 105mbar and 400mW of laser power. High-resolution scanning electron microscopy analysis showed the tungsten coating to be 1.5–3.5μm thick on the body of the coil and less than 2μm on the contact arms. The tungsten coating reduced the resistance of the carbon coils by an order of magnitude and reached higher temperatures at lower voltages. In vacuum, the tungsten coating is the dominant current carrier below 1300–1700°C; above this range carbon dominates. Peak temperatures for the tungsten-coated coils are 2050°C in vacuum and 1940°C in N2 – several hundred degrees higher than the non-coated coils.

Effect of a high axial magnetic field on the microstructure in a directionally solidified Al–Al 2Cu eutectic alloy

The effect of a high axial magnetic field (up to 12 T) on the microstructure in a directionally solidified Al–Al 2Cu eutectic alloy has been investigated experimentally. The results show that a high magnetic field decreases the eutectic spacing and degenerates the lamellar structure into a wavy one at a low growth speed. X-ray diffraction, selected-area electron diffraction and high-resolution electron microscopy analyses indicate that the field changes the preferred orientation. The Al 2Cu crystal is oriented with the 〈0 0 1〉-crystal direction along the solidification direction (i.e., the magnetic field direction). At a pulling velocity of 0.5 μm/s, the magnetic field ( B ⩾ 4T) is responsible for the segregation; which consists of Al striations on the longitudinal section and Al-rich zones on the transverse section. The effects of the field may be attributed to the orientation of the Al 2Cu and the Al crystals and the decrease of the diffusion coefficient caused by the magnetic field.

Stress and strain around grain-boundary dislocations measured by high-resolution electron microscopy

Stresses and strains around a dislocation at a grain boundary in germanium are measured by a combination of high-resolution electron microscopy and geometric phase analysis. The method is established by first measuring the strains around a matrix dislocation in silicon. Stresses are determined using linear elastic theory and bulk elastic constants. Strain measurements are shown to agree with theoretical calculations based on linear anisotropic elastic theory to 0.2% at a spatial resolution of 2–3 nm. A dislocation constricted at a coherent twin boundary in germanium is subsequently analyzed. The method is adapted to cope with the problem that the reference lattice is not identical for the whole field of view, due to the grain boundary. Strains are compared with theoretical calculations of a matrix dislocation in germanium. Whereas strains in the grains on either side of the twin boundary agree closely with the isolated dislocation case, significant additional strains are localized at the boundary plane. By comparing the stresses and strains across the boundary plane, values for the elastic modulus of the twin boundary are proposed. The significant reduction in elastic modulus for the boundary, when compared to bulk elastic constants, is interpreted in terms of the non-equilibrium configuration of the boundary. An extension of the method is proposed to measure more generally the elastic properties of grain boundaries and interfaces.

Single InGaAs nanowhiskers characterized by analytical transmission electron microscopy

Single crystal In x Ga1−x As nanowhisker were grown by metal-organic vapour-phase epitaxy on (111)B GaAs substrates using the vapour–liquid–solid growth mode. Present study is aimed to the direct evaluation of the lattice parameter, the phase, and the composition of nanowhiskers with high spatial resolution by high-resolution transmission electron microscopy and analytical transmission electron microscopy including energy-dispersive X-ray spectroscopy in nano probe mode. The goal is the direct identification of the quantified concentrations and the local element distributions at characteristic whisker areas. In particular, chemical measurements provide insights into the segregation of the gallium and arsenic out of the gold seed particle and the presence of indium remaining in the Au particle of the as-prepared whiskers. For comparison, InGaAs nanowhiskers are characterized by high-resolution X-ray diffractometry providing the mean whisker composition information indirectly by substituting the X-ray data into the formula of the law of Vegard.

State of disperse alloy particles catalyzing hydrocarbon decomposition by the carbide cycle mechanism: TEM and EDX studies of the Cu-Ni/Al2O3 and Cu-Co/Al2O3 catalysts

The state of disperse bimetallic alloy particles in the Cu-Ni/Al2O3 and Cu-Co/Al2O3 catalysts during their carbonization in butadiene-1,3 is studied by high-resolution electron microscopy and energy-dispersive X-ray analysis. During the formation of carbon nanofilaments by the carbide cycle mechanism, the catalyst is in a dissipative state such that the bimetallic particles vary in composition and have an anomalous component distribution in their bulk. The extrapolation of this state provides insight into the processes occurring in the dissipative system.

Atomic structures of iron-based single-crystalline nanowires crystallized inside multi-walled carbon nanotubes as revealed by analytical electron microscopy

Atomic structures of single-crystalline iron-based nanowires crystallized inside multi-walled carbon nanotubes during pyrolysis on silicon substrates with ferrocene as a precursor were analyzed using high-resolution analytical transmission electron microscopy and electron diffraction. Standard crystal lattices, namely body-centered cubic (bcc) α-Fe, face-centered cubic (fcc) γ-Fe and orthorhombic cementite Fe 3C, were all found to form inside the nanotubes. A fraction of α-Fe nanowires, thermodynamically favorable at room temperature, was found to be dominant. Both bcc and fcc nanowires display a wide variety of lattice planes being parallel to the nanotube walls, with none of the orientations being preferable. The minor fraction of the nanowires had unidentified long-period crystal lattices with doubled or tripled periodicities as compared to those found in the standard cubic iron phases. The crystal matching of these unusual structures to stable orthorhombic Fe 3C or less stable iron carbides, e.g., Fe 5C 2, Fe 7C 3, failed. The non-conventional phases were tentatively assigned to rarely seen silicon-doped octahedral iron carbides. Both long-period and standard cementite nanowires exhibited well-defined transient zones in the vicinity of nanowire–tube shell interfaces, where perfectly ordered carbide lattice fringes disappeared. The results suggest the non-existence of metastable equilibrium in the nanoscale Fe–C system between carbide and graphite phases during iron crystallization inside graphitic tubular channels.

Structure and magnetic properties of nanocrystalline SrFe 12O 19 alloy produced by high-energy ball milling and annealing

The structure of SrFe 12O 19 powders, subjected to mechanochemical treatment in a high-energy ball mill and subsequent annealing, were studied by X-ray diffraction technique, high-resolution scanning electron microscopy and sedimentation analysis. The magnetic properties were measured in a vibrating sample magnetometer. As a result of the milling under Ar or air atmosphere an amorphous phase was formed in the powder and its amount rised with increase of the milling time. In addition, the milling resulted in a reduction of powder particles and SrFe 12O 19 crystallite size as well as in increase of microstrain in the SrFe 12O 19 lattice. The milling caused a deterioration of the magnetic properties. The annealing led to a sharp improvement of the magnetic properties due to crystallization and formation of the SrFe 12O 19 phase with fine crystallites. The best properties ( μ 0 H ci≈0.42 T, B r≈0.24 T and ( BH) max≈9.6 kJ/m 3) were reached after the milling and annealing of the powder at 950–1000 °C for 1 hr. In this case, the average particles size was about 1 μm and the average crystallite size was 100–200 nm. The high magnetic properties of the annealed powder may be explained by the formation of SrFe 12O 19 nanocrystallites with a size smaller than the critical dimension of the single-domain particles.

Determination of Optical Isomers for Left-Handed or Right-Handed Chiral Double-Wall Carbon Nanotubes

The handedness relationship between adjacent layers in nested double-wall carbon nanotubes (DWNTs) has been investigated for the first time. Our high-resolution electron microscopy analysis on a series of specimen tilts can successfully tell the handedness of each constituent nanotube in a DWNT, and therefore the chiral indices (n, m) including their optical isomers [(n, m) or (m, n)] of inner and outer nanotubes can be uniquely determined. It is shown that right-handed and left-handed nanotubes are equally distributed for both the inner and outer nanotubes in the examined specimens and a preferable handedness relationship between the adjacent layers in DWNT may exist.

Configuration of twins in glass‐embedded silver nanoparticles of various origin

AbstractStructural characterization using high resolution electron microscopy and diffractogram analysis of silver nanoparticles embedded in glass by various routes of fabrication was aimed at revealing the characteristic features of twin faults occuring in such particles. Nearly spherical silver nanoparticles well below 10 nm size embedded in commercial soda‐lime silicate float glass have been fabricated either by silver/sodium ion exchange or by Ag+ ion implantation. Twinned nanoparticles, besides single crystalline species, have frequently been observed for both fabrication routes, mainly at sizes above 5 nm, but also at smaller sizes, even around 1 nm. The variety of particle forms comprises single crystalline particles of nearly cuboctahedron shape, particles containing single twin faults, and multiply twinned particles containing parallel twin lamellae, or cyclic twinned segments arranged around axes of fivefold symmetry. Parallel twinning is distinctly favoured by ion implantation whereas cyclic twinning preferably occurs upon ion exchange processing. Regardless of single or repeated twinning, parallel or cyclic twin arrangement, one may classify simple twin faults of regular atomic configuration and compound twin faults whose irregular configuration consists of additional planar defects like associated stacking faults or secondary twin faults. Besides, a particular superstructure composed of parallel twin lamellae of only three atomic layers thickness is observed. (© 2005 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Strain mapping around dislocations in diamond and cBN

AbstractStrain fields around dislocations in diamond and cBN have been quantitatively characterized at a sub nanometer scale. The combination of experimental high resolution electron microscopy (HREM) and image analysis using the geometric phase method provides an accurate determination of the local deformations and strain. The results of the strain analysis of the 60° perfect dislocation in diamond and cBN are discussed. (© 2005 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

High-Resolution Analytical TEM and Energy-Filtered Imaging of CoPt-Oxide Perpendicular Magnetic Recording Media

Perpendicular magnetic media are expected to replace longitudinal hard-disk media in the near future, and to provide continued increases in areal density beyond the current maximum capacity of longitudinal media. High-resolution analytical electron microscopy is required for the study of these novel thin films because they comprise nanoscale grains and grain boundaries (often {approx}8 nm and {approx} 1 nm, respectively), and because the importance of examining the elemental distribution at near atomic level is paramount to understanding the magnetic performance. While perpendicular media offer many advantages, quantum-mechanical exchange coupling between grains is still problematic and requires the separation of grains similar to that required in longitudinal media. Energy-filtered TEM (EFTEM) imaging, which was used to examine compositional grain separation in longitudinal media, is capable of generating maps of the elemental distribution within the grains and the boundaries thereby depicting the extent of compositional separation. Combining EFTEM with other microanalytical techniques, such as high resolution TEM with energy-dispersive X-ray spectrometry, allows for both corroboration and easy quantification of individual grain and grain boundary areas. For this analytical TEM study, grain separation was attempted by generating non-magnetic oxygen-rich boundaries, either by flowing O{sub 2} gas during deposition or by sputtering a stablemore » oxide into the magnetic film. These CoPt-O and CoPt-oxide films were DC-magnetron sputtered at room temperature with increasing reactive O{sub 2} or oxide content. Magnetic properties were measured using a magneto-optical polar Kerr magnetometer. Both reactive O{sub 2} and oxide deposition methods, individually, increase grain separation and reduce intergranular exchange coupling, as shown by the hysteresis loop trends in Figures 1a and 2a. The difference between coercivity (Hc) and nucleation field (Hn) is a measure of the extent of exchange decoupling. The large increase in this loop shearing parameter as O{sub 2} or oxide content is increased is clear evidence of a corresponding decrease in exchange coupling.« less

Nucleation mechanism of the seed of tetrapod ZnO nanostructures

Tetrapod zinc oxide (T-ZnO) nanorods have been synthesized by evaporation and recondensation of metallic Zn under ambient conditions. The total sizes of the T-ZnO nanostructures range from 300nmto15μm with leg diameters of about 30to650nm, depending on the deposition temperature. A detailed high-resolution electron microscopy analysis showed that the center core of T-ZnO nanorods consists of four hexagonal grains with a twinlike relation. The nucleation and growth mechanism has been generated on the basis of energy considerations during a phase transition from a fullerenelike ZnO cluster to a nanometer-sized tetrahedron, which is directly visible in our high-resolution transmission electron microscopy investigations.

Photonic crystals of titanium dioxide fabricated by swift heavy ions

We have developed a method of fabricating nano-micro-structures in a rutile TiO 2 single crystal using swift heavy-ion irradiation that takes advantage of the good etching selectivity induced by ion irradiation. The areas into which ions heavier than Cl and accelerated with MeV-order high energy had been irradiated were readily etched by 20% hydrofluoric acid. By comparison, etching was not observed in pristine TiO 2 single crystals. We discovered that the irradiated area could be etched to a depth at which the electronic stopping power of the ion decayed to a value of 6.2 keV/nm. In other words, etching was not observed in TiO 2 single crystals possessing electron stopping power below a threshold value of 6.2 keV/nm. We also found that the value of the electronic stopping power first increased, and then decreased with depth in TiO 2 single crystals when irradiated with, for example, 84.5 MeV Ca ion. Using this type of beam, the inside of the TiO 2 single crystal was selectively etched with 20% hydrofluoric acid, while the top surface of the TiO 2 single crystal subjected to irradiation was not etched. It initially appeared that an air gap was created in the region 4– 8 μ m from the top surface subjected to irradiation by 84.5 MeV Ca ion at an accumulated dosage of 3 × 10 14 cm - 2 followed by etching. The roughness of the new surface created in the single crystal was within 7 nm as measured by atomic force microscopy. X-ray diffraction and high-resolution electron microscope analyses indicated that the irradiated area was composed of amorphous and stressed rutile phases. Both phases were highly soluble in 20% hydrofluoric acid.

Surface Diffusion and Coalescence of Mobile Metal Nanoparticles

The diffusion and coalescence of metal nanoparticles play important roles in many phenomena. Here, we offer a new integrated overview of the main factors that control the nanoparticle coalescence process. Three factors are considered in our description of the coalescence process: nanoparticle diffusion across the surface, their physical and thermodynamic properties, and the mechanism of coalescence. We demonstrate that the liquid-like properties of the surface layers of the nanoparticles play an essential role in this process. We present experimental evidence for our opinion, based on the high-resolution electron microscopic analysis of several different types of nanoparticles.

Short, thin asbestos fibers contribute to the development of human malignant mesothelioma: pathological evidence

Based on animal studies, long and thin asbestos fibers (⩾8 μm in length and ⩽0.25 μm in width) have been postulated to be strongly carcinogenic inducing pleural malignant mesothelioma, while shorter, thicker fibers have been postulated to pose a lesser risk (Stanton hypothesis). The objective of this study is to test the validity of the Stanton hypothesis through direct pathologic analysis of human mesothelioma tissue. Digested bulk tissue samples, or ashed 25 μm thick sections, or both, were prepared from lung and mesothelial tissues taken from 168 cases of human malignant mesothelioma. In these tissues, 10,575 asbestos fibers (4820 in the lung and 5755 in mesothelial tissues (1259 in fibrotic serosa and 4496 in mesotheliomatous tissue)) were identified by high-resolution analytical electron microscopy. Dimensions of these asbestos fibers were measured in printed electron micrographs. Results were as follows: (1) long, thin asbestos fibers c onsistent with the Stanton hypothesis comprised only 2.3% of total fibers (247/10,575) in these tissues; (2) the majority (89.4%) of the fibers in the tissues examined were shorter than or equal to 5 μm in length (9454 of 10,575), and generally (92.7%) smaller than or equal to 0.25 μm in width (9808 of 10,575). (3) Among asbestos types detected in the lung and mesothelial tissues, chrysotile was the most common asbestos type to be categorized as short, thin asbestos fibers. (4) Compared with digestion technique of the bulk tissue, ashing technique of the tissue section was more effective to detect short, thin fibers. We conclude that contrary to the Stanton hypothesis, short, thin, asbestos fibers appear to contribute to the causation of human malignant mesothelioma. Such fibers were the predominant fiber type detected in lung and mesothelial tissues from human mesothelioma patients. These findings suggest that it is not prudent to take the position that short asbestos fibers convey little risk of disease.

5 nm ruthenium thin film as a directly plateable copper diffusion barrier

Interfacial stability of electroplated copper on a 5nm ruthenium film supported by silicon, Cu∕(5nmRu)∕Si, was investigated using Rutherford backscattering and high-resolution analytical electron microscopy. Transmission electron microscopy (TEM) imaging shows that a 5nm Ru film is amorphous in contrast to the columnar microstructures of thicker films (20nm). Direct Cu plating on a 5nm Ru film yielded a homogeneous Cu film with over 90% plating efficiency. It is demonstrated that 5nm Ru can function as a directly plateable Cu diffusion barrier up to at least 300°C vacuum anneal. TEM reveals an interlayer between Ru∕Si, which expands at the expense of Ru upon annealing. Electron energy loss spectroscopy analyses show no oxygen (O) across the Cu∕(5nmRu)∕Si interfaces, thereby indicating that the interlayer is ruthenium silicide (RuxSiy). This silicidation is mainly attributed to the failure of the ultrathin Ru barrier at the higher annealing temperature.

Low-temperature, solvent-free solid-state synthesis of single-crystalline titanium nitride nanorods with different aspect ratios

Titanium nitride nanorods have been successfully synthesized by low temperature solid-state metathesis of titanium (III) chloride and sodium azide without using any organic solvent. The conditions required for the synthesis of these nanorods have been optimized. It was found that the temperature and time of reaction had a significant effect on the product morphology. Thermal treatment at 360 °C, for 3 days gave the nanorods of the aspect ratio ∼10 (i.e. diameter ∼50 nm and length ∼ 500 nm), whereas the thermal treatment at 400 °C for 3 days gave the nanorods of the aspect ratio ∼50 (i.e. diameter ∼50 nm and length ∼2–3 μm). Scanning and transmission electron microscopies clearly showed the rod-type morphology. Further evidence for the phase purity and crystallinity of titanium nitride nanorods was given by X-ray diffraction, field emission high-resolution electron microscopy and X-ray photoelectron spectroscopy analyses.

High-resolution electron-microscopy analysis of splitting patterns in Ni alloys

The late stages of coarsening of coherent solid particles is strongly influenced by the reduction of elastic strain energy. This produces migration and alignment of particles as well as some other effects. In this investigation, the origin of the so-called splitting pattern arrangement of γ′ precipitate particles, an arrangement which has often been interpreted as being due to splitting of a larger particle into smaller ones, has been studied. The two-particle relationship as to whether they are in-phase or out-of-phase is examined by means of a translation order domain analysis of high-resolution electron-microscopy images along a zone axis parallel to [001]. Ni alloys have been used for the investigation including a binary Ni–Al alloy (producing different volume fractions) and two commercial multicomponent alloys with high volume fraction. About 72% of two-particle pairs forming the splitting configuration are in the out-of-phase relationship, indicating that adjacent pairs are randomly formed and that they are not formed by the splitting of a large particle. In addition, an elasticity analysis shows that the elastic interaction energy of two γ′ particles exhibits a minimum at a certain separation distance along ⟨ 100⟩.

Intergrowth of graphite within phlogopite from Finero ultramafic complex (Italian Western Alps): implications for mantle crystallization of primary-texture mica

High Resolution Transmission and Analytical Electron Microscopy (HRTEM-AEM) of phlogopite crystals from the Finero lherzolite (Italian Western Alps) revealed nanometric intergrowths of graphite-like layers. The intergrowths consist of 4 to 6 graphite-like layers (c ≈ 3.3 A) with the basal plane parallel to (001) of the phlogopite host. The phlogopite crystals contain between 0.024 and 0.048 wt % of carbon. The carbon isotope composition varies from δ 13 C graphite = −16.1 %° to −10.4 %° (VPDB). These values are compatible with carbon phases found in other mantle-derived ultramafic rocks. A Raman analysis confirms the presence of a graphite-like phase intergrown within phlogopite. Geochemical and microtextural data point to a primary origin of the phlogopite-graphite intergrowths and suggest simultaneous crystallization of both phases from a trapped partial melt.