High-resolution Electron Microscopy Observations Research Articles

Low dielectric constant porous diamond films formed by diamond nanoparticles

The reduction of the dielectric constant of interlayer insulating films in ultra large scale integrated circuits is an important factor in improving resistance-capacitance delay. A “porous diamond” film, composed of nanoscale diamond particles, is proposed as a material with a low dielectric constant, and is prepared by spin coating a 5% diamond colloidal solution mixed by 4 nm diamond nanoparticles in purified water. High-resolution scanning electron microscope observations show that the film contains nanoscale pores. The mechanical strength and adhesion of the porous diamond films were improved by forming the chemical bonds between diamond nanoparticles and also between the nanoparticles and the substrate. The chemical bonds were created by introducing a bi-functional silane coupler such as hexachlorodisiloxan molecules followed by annealing at 300 °C. A low dielectric constant of 1.63, estimated from the refractive index, was obtained by using high purity diamond nanoparticles after the reinforcing process by hexachlorodisiloxan. The porous diamond films are expected to have a higher thermal stability and a superior mechanical strength compared with other porous low dielectric constant materials.

Direct evidence of correlation between {2 0 1̄} B19 ′ and {1 1 4} B2 deformation twins in Ti–Ni shape memory alloy

The correlation between {2 0 1 ̄ } B19 ′ twinning in the deformed martensite and {1 1 4} B2 twinning in the reverse transformed parent phase in the Ti–Ni shape memory alloy is directly demonstrated by in situ heating conventional transmission electron microscopy (CTEM) and high resolution electron microscopy (HREM) observations.

Transmission Electron Microscopy Study of Polymorphism in Barium Gallate BaGa2O4

Polymorphism in barium gallate BaGa2O4 was studied using electron diffraction and high resolution electron microscopy. Three modifications of BaGa2O4 with structures closely related to the high-temperature α-form were observed. The phase transitions from γ-BaGa2O4 (a γ = 18.6143(2) Å = 2<formula><radical><radicand>3</radicand></radical></formula>a α, c γ = 8.6544(1) Å = c α, S.G. P63) to β-BaGa2O4 (a β = 2a α, c β = c α S.G. P63) and to the new δ-polymorph having a monoclinic structure (a δ = c α, b δ = 2a α + b α, c δ = 2b α and β ≈ 92°, S.G. P21/c) were induced by electron beam irradiation. High resolution electron microscopy (HREM) observations allow to establish the close similarity between the structures of δ-BaGa2O4 and β-SrGa2O4. The γ→β and β→δ transitions involve a rearrangement of oxygen atoms in the BaO layers together with a tilting distortion of the tetrahedral framework. The microstructure of the δ-phase is characterised by the presence of numerous translation and orientation domains.

Connection structures between type-I and type-II defects in neutron irradiated beta-Si3N4.

High-resolution electron microscopy (HREM) observation clarified that various types of interstitial dislocations were induced into beta-Si3N4 by high-dose neutron irradiation, and two of them have been analysed and reported in our previous papers. These two defective structures are called type-I and type-II. They are interstitial dislocation loops introduced into [100] and [110] planes, respectively. In this study, it was found that some of these dislocation loops connected with each other. The connections of type-I-L2-type-II-B and type-I-R2-type-II-A dislocations were observed by HREM. Tetrahedral arrangements of the connected parts are proposed, based on the simplified crystal structure model of beta-Si3N4. In addition, a new type of defect, type-III, was found. Type-III is an interstitial dislocation loop introduced into [100] planes. It was also found that type-I-A and type-III dislocations connected with each other.

Fabrication of monodispersive FePt nanoparticle films stabilized on rigid substrates

Monodispersive FePt nanoparticle films can be stabilized firmly on rigid Si substrates using amino-functional silane, such as [3-(2-aminoethlyamino) propyl]trimethoxysilane, as a coupling layer. The Si substrate/SiO2/APTS/FePt nanoparticles heterostructure was confirmed using high-resolution electron microscopy (HREM). The HREM result agreed well with the x-ray reflectivity measurement upon the individual layer thickness. The as-made superparamagnetic FePt nanoparticle film transformed from chemically disordered fcc structure to chemically ordered L10 phase upon annealing at 800 °C for 30 min under a vacuum of 10−8 Torr. Plan-view high-resolution scanning electron microscopy (HRSEM) observation indicated that under high-vacuum annealing, coalescence of the monodispersive nanoparticle film was not significant. The HRSEM result was consistent with the in-plane x-ray diffractometry measurement, in which sharpening of the diffraction peaks occurred only very slightly for the annealed films.

Studies of nanocluster coalescence at high temperature

Molecular Dynamics simulations and high resolution electron microscope observations were used to determine the mechanism of nanocluster coalescence in detail. In the simulations, the tight-binding second momentum approximation potential was used to describe the interatomic interactions. The calculations not only reproduced the experimentally observed translation and reorientation during the coalescing process, but also made it possible to determine the time scale of each step in the process and to observe details of the process that could not be obtained from the experiment. For high temperature coalescence, a new mechanism differing from classical theory is proposed.

The dislocation microstructure of a nickel-base single-crystal superalloy after tensile fracture

The dislocation microstructure after tensile deformation for a Ni-base single-crystal superalloy has been studied by transmission electron microscopy. The samples were strained to fracture at temperatures from room temperature to 1273 K. It was found that for deformation at intermediate temperatures, the dislocation microstructure was inhomogeneous due to the formation of dislocation concentrations with high-density tangling. These dislocation concentrations lie mainly along 〈1 0 0〉 or 〈1 1 0〉 directions, and extend over a length of a few micrometers. In addition, the structure of dislocation networks at the γ/γ′ interfaces formed at high temperature was also studied. Although previous studies have proposed basic configurations for these dislocation networks, the nature of a dislocation segment along the 〈0 1 0〉 direction was unresolved (Phil. Mag. A vol. 74 (1996) 229). In this work, high-resolution electron microscopy observation was used to study these dislocation networks. It was found that most of these segments are actually composed of two pairs of a/2〈1 1 0〉 dislocations with an average spacing of 8.5 nm, while only few of them are composed of single-line a〈1 0 0〉 dislocations.

The microstructure of melt spun Ti–Ni–Cu–Zr shape memory alloys

NiTi base shape memory melt spun ribbons with a high substitution of Ni by Cu and Ti by Zr have been analysed. Depending of the chemical composition of the alloy, the ribbons are crystalline or amorphous. Transmission electron microscopy (TEM) studies in the as-cast state and after crystallization indicated that in the as-cast state the Ti40Ni25Cu25Zr10 ribbons are constituted of two phases (Ti2Ni+amorphous phase) whereas the Ti40Ni35Cu15Zr10 ribbons are fully amorphous and are single phase after crystallisation with a B2 structure. High resolution electron microscopy (HREM) observations have shown that the crystalline/amorphous phase interface is highly wavy even at the nanometric scale and that the B2 particles are single ordered domains.

SEM and HRTEM study of zirconium-based glass forming alloys cast at various cooling rates

The microstructure of Zr–Ti–Ni–Cu–X (X=Ag,Al) ingots or melt-spun ribbons was investigated. The ingots were analyzed using a scanning electron microscope with an X-ray energy-dispersive spectroscopy system, and the alloy composition was modified to increase the amount of eutectic on expense of primary crystals. High-resolution electron microscopy observation of thin foils from ribbons of a composition near the eutectic show only extremely small ordered aggregates, while ribbons from alloys near the NiTiCu compound contain nanocrystallites. The addition of silver into Zr–Ti–Ni–Cu alloys results in precipitation of spherical silver crystallites in slowly cooled and melt-spun ribbons. However, their presence has no effect on the alloy’s glass forming ability, as they do not serve as nucleation sites for other phases.

Shock-induced localized amorphization in boron carbide.

High-resolution electron microscope observations of shock-loaded boron carbide have revealed the formation of nanoscale intragranular amorphous bands that occur parallel to specific crystallographic planes and contiguously with apparent cleaved fracture surfaces. This damage mechanism explains the measured, but not previously understood, decrease in the ballistic performance of boron carbide at high impact rates and pressures. The formation of these amorphous bands is also an example of how shock loading can result in the synthesis of novel structures and materials with substantially altered properties.

Population statistics of gold nanoparticle morphologies: direct determination by HREM observations

Population distributions of gold nanoparticle morphologies were able to be derived as a function of size by collecting a great number of high-resolution electron microscopy (HREM) images. We observed more than 4000 individual gold nanoparticles (3–18 nm) which were generated from an inert gas aggregation source using helium and deposited on amorphous carbon films. To obtain structural features three-dimensionally and not to miss high-contrast images, 20 photos were taken for each particle by changing tilting angle of a specimen holder in combination with the through-focus procedure. In order to perform reliable structural determinations, HREM images and their tilting sequences were directly compared with multislice-simulation results for icosahedral, decahedral and face-centered cubic morphologies, and finally the population distribution of each morphology was obtained as a function of size. In the present sample, icosahedral particles were dominantly populated over the observed size range and decahedral particles with non-spherical truncated bi-pyramid shape were secondly dominant. Even though a large number of sampling has been done, few crystalline particles were observed. The present experimental statistical results on morphologies provide important information on cluster growth phenomena.

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.

Potassium titanate nanowires: Structure, growth, and optical properties

A simple one step hydrothermal reaction among ${\mathrm{TiO}}_{2}$ nanoparticles and KOH solution was found to result in potassium titanate nanowires. The diameters of these nanowires are about 10 nm and the lengths range from 500 nm to $2\ensuremath{\mu}\mathrm{m}.$ The nanowires were analyzed by a range of methods including powder x-ray diffraction (XRD), high resolution electron microscopy (HREM), selected area electron diffraction, electron energy loss spectroscopy, XRD and HREM image simulations. The structure of the nanowires is determined to be of the type of ${\mathrm{K}}_{2}{\mathrm{Ti}}_{6}{\mathrm{O}}_{13}.$ Based on HREM observations of the growth process of the nanowires, we propose that the growth of the namowire was initiated by the formation of the ${\mathrm{K}}_{2}{\mathrm{Ti}}_{6}{\mathrm{O}}_{13}$ nuclei inside the anatase matrix following the crystallographic relation ${(200)}_{\mathrm{nanowire}}{//(101)}_{\mathrm{anatase}}.$ These nuclei subsequently grew to form one-dimensional nanowires via preferential growth along the [010] direction. Absorption experiments show that the potassium titanate nanowires are wide-band semiconductors with a band width ${E}_{g}\ensuremath{\sim}3.45\mathrm{eV}.$

Coating of Y 2O 3 additive on Al 2O 3 powder and its effect on the wetting behaviour in the system Al 2O 3p/Al

Al 2O 3 powder was coated with Y 2O 3 percursor generated by in situ precipitation of Y(NO 3) 3·6H 2O in aqueous solution. After calcining at high temperature, the precursor was completely transformed into a crystalline Y 2O 3, and Y 2O 3-coated Al 2O 3 powder was obtained. Transmission electron microscope (TEM), high resolution electron microscope (HREM) observation and elemental analysis clearly showed that the Y 2O 3 was successfully coated on the surface of the Al 2O 3 particles. The coated powders were also characterized by energy dispersive spectrum (EDAX) and X-ray diffractometry (XRD). The wetting behaviour of molten aluminum on the coated Al 2O 3 powders was investigated by the sessile drop method. Due to the introduction of Y 2O 3, the wettability of the coated-Al 2O 3 powders by liquid aluminum was dramatically improved in comparison with that of the as-received powders.

A bending angle of 180° of single walled carbon nanotubes: novel high resolution electron microscopy observations

Direct high resolution transmission electron microscopy images (HREM) showed the high flexibility of single walled carbon nanotubes (SWCNT) without load. Bending angle of approximately 180° was shown, in which no visible nanotube distortion was revealed. “Unbent” SWCNT persisted in HREM image. Bending SWCNT in 180° indicated an interesting network at the bottom of the bent region. The new morphology image showing bent and unbent SWCNT bundles may provide interesting mechanical and electronic properties and structural characteristics.

Large Co Cluster Deposition on Naturally and Artificially Patterned Substrates

Monodispersed Co clusters with mean cluster diameter d=13 nm have been deposited on a stepped graphite surface and a lithography-patterned Si wafer using a plasma-gas-condensation cluster beam deposition apparatus. High-resolution scanning electron microscope observation indicates that 1) cluster aggregation is much more limited at the steps than on the flat terrace regions of the graphite surface, and 2) cluster density is much higher in the grooves than on the flat top of the lithography-patterned Si wafers. These results suggest the possibility of the regular arrangement of monodispersed Co clusters if the pattern size (the width of grooves and tops) is comparable with the cluster size.

Effect of bottom electrodes on microstructures and electrical properties of sol–gel derived Pb(Zr 0.53 Ti 0.47)O 3 thin films

Lead zirconate titanate (PZT) thin films were fabricated by adding 15 mol.% excess of Pb to the starting solution and spin coating onto Pt/Ti/SiO 2/Si and Ir/IrO 2/SiO 2/Si substrates. The effect of bottom electrodes on the microstructures, crystalline phases and electrical properties of the PZT thin films was investigated. It was found that the films deposited on Pt/Ti bottom electrode consisted of perovskite phase without pyrochlore phase, whereas the films deposited on the Ir/IrO 2 bottom electrode consisted of mainly perovskite phase with a small amount of pyrochlore phase. Bottom electrodes were also found to influence the preferred orientation and microstructure as well as the surface morphology of the PZT films. The Pt/Ti bottom electrode favored a (100) orientation and fine-grained structure as well as a smooth surface, whereas the Ir/IrO 2 bottom electrode favored a random orientation, non-uniform structure and rough surface. High-resolution electron microscopy observation reveals that there is an intermediate layer of IrO 2 at the PZT/Ir interface. This indicates that the intermediate layer of IrO 2 influenced the orientation and microstructure of the PZT films on the Ir/IrO 2 bottom electrode. Ferroelectricity was investigated by observing the polarization hysteresis loops. The remanent polarization and saturation polarization of the PZT films on the Ir/IrO 2 bottom electrode were smaller than those of the PZT films on the Pt/Ti bottom electrode. The difference between the dielectric and the ferroelectric properties in these PZT films was correlated to their crystalline phases and microstructure.

Optimization of Soft Magnetic Properties in Fe-B and Fe-B-Si Amorphous Alloys Obtained by Melt Spinning Method

In the present paper the process of optimization of soft magnetic properties have been studied by applying different experimental techniques (magnetic measurements, electric measurements, X-ray analysis, and high-resolution electron microscopy observations). It has been shown that an increase in magnetic permeability after optimization annealing can be mainly attributed to annealing out of microvoids.

Pt Doping of SnO2 Thin Films: A Transmission Electron Microscopy Analysis of the Porosity Evolution

In Pt-doped thin films prepared by using a submicroscopic aerosol pyrolysis method where the metal elements are codeposited, the best CO sensitivity is obtained from low concentration Pt precursor solutions. Transmission electron microscopy (TEM) observations of thin films doped by small amounts of platinum have been performed to analyze in detail the structural properties as a function of Pt doping concentration. Strong evidence of porous structure has been found in the TEM images and an assessment of the porous volume fraction could be done. Although this approach clearly underestimates the assessed porous fraction, results for undoped films nevertheless indicate that the film density is close to half of the bulk value. It increases with the film doping concentration, as films become thinner. For doping concentrations higher than 2%, no significant number of pores could be detected and the thickness reaches a plateau likely corresponding to the maximum density that can be obtained using our synthesis conditions. The usually observed maximum in the film sensitivity at solution concentrations close to 0.6% film doping, i.e., 3% in terms of solution concentration, coincides with a maximum in the product of the porous volume and the density of small Pt aggregates. Additionally, high-resolution electron microscopy observations of selected film samples have been performed to examine grain arrangements and microstructural effects of Pt and nanocrystallites. © 2002 The Electrochemical Society. All rights reserved.

TEM studies of an incommensurate charge ordering modulation in La 0.5Ca 0.5MnO 3

Electron energy-loss spectroscopy in the transmission electron microscope has been used to determine the valence state of manganese in La 0.5Ca 0.5MnO 3 at room temperature and at 93 K. An incommensurate charge ordering modulation in La 0.5Ca 0.5MnO 3 was detected by transmission electron microscopy. A structural model, based on the selected area electron diffraction and high-resolution electron microscopy observation, is proposed for the incommensurate modulation.