Showing papers on "Transmission electron microscopy published in 2004"
TL;DR: Direct images from an aberration-corrected scanning TEM are presented that resolve a lattice in which the atomic columns are sepa-rated by less than 0.1 nanometer.
Abstract: Despite the use of electrons with wavelengths of just a few picometers, spatial resolution in a transmission electron microscope (TEM) has been limited by spherical aberration to typically around 0.15 nanometer. Individual atomic columns in a crystalline lattice can therefore only be imaged for a few low-order orientations, limiting the range of defects that can be imaged at atomic resolution. The recent development of spherical aberration correctors for transmission electron microscopy allows this limit to be overcome. We present direct images from an aberration-corrected scanning TEM that resolve a lattice in which the atomic columns are separated by less than 0.1 nanometer.
486 citations
TL;DR: In this article, the effect of impurity doping on the photoactivity of TiO2 rutile single crystals was subjected to a combined surface-science and bulk-analysis study.
Abstract: The effect of impurity doping on the photoactivity of TiO2 rutile single crystals was subjected to a combined surface-science and bulk-analysis study. The incorporation of nitrogen ions, N-, into TiO2 single crystals was achieved by sputtering with N2+/Ar+ mixtures and subsequent annealing to 900 K under ultrahigh vacuum conditions. This procedure leads to a 90 A thick structurally modified near-surface region, which, by the use of cross sectional transmission electron microscopy, can be described as rutile grains imbedded within a monocrystalline strained rutile matrix. The presence of N- ions distributed in the first 200 A below the surface was revealed by X-ray photoelectron spectroscopy, in agreement with sputter depth profiles obtained by secondary ion mass spectroscopy. The concentration of N- doping is about 1020 cm-3 in the first 200 A of the near-surface region. The photodesorption of O2 was employed to study the changes in the photochemical properties of nitrogen-implanted crystals. The action c...
371 citations
TL;DR: Porous magnesium hydroxide nanoplates were obtained directly from commercial bulk magnesium oxide crystals by a simple hydrothermal treatment as discussed by the authors, and the obtained materials exhibit bimodal pore size distributions in the mesoporous domain.
Abstract: Porous magnesium hydroxide nanoplates were prepared directly from commercial bulk magnesium oxide crystals by a simple hydrothermal treatment. These thin plates would aggregate into large spherical particles. The platelike morphology was retained after calcination, and porous magnesium oxide nanoplates were obtained. These plates have a wormhole-like porous structure with high surface area. The obtained materials exhibit bimodal pore size distributions in the mesoporous domain. The aggregation of the nanoplates gives rise to large mesopores with a size of about 36 nm. In addition, each plate has small wormhole mesopores with a size of about 3.7 nm. The growth of magnesium hydroxide nanoplates occurred through a dissolution−recrystallization process. X-ray diffraction and electron diffraction, transmission electron microscopy, scanning electron microscopy, and nitrogen sorption have been employed to characterize these nanoplates. Such porous nanoplates with high surface area and high crystallinity have man...
318 citations
TL;DR: In this paper, the photoluminescence properties of SiO2 nanoclusters were investigated by thermal annealing of SiOx films prepared by plasma enhanced chemical vapor deposition.
Abstract: Si nanoclusters embedded in SiO2 have been produced by thermal annealing of SiOx films prepared by plasma enhanced chemical vapor deposition. The structural properties of the system have been investigated by energy filtered transmission electron microscopy (EFTEM). EFTEM has evidenced the presence of a relevant contribution of amorphous nanostructures, not detectable by using the more conventional dark field transmission electron microscopy technique. By also taking into account this contribution, an accurate quantitative description of the evolution of the samples upon thermal annealing has been accomplished. In particular, the temperatures at which the nucleation of amorphous and crystalline Si nanoclusters starts have been determined. Furthermore, the nanocluster mean radius and density have been determined as a function of the annealing temperature. Finally, the optical and the structural properties of the system have been compared, to demonstrate that the photoluminescence properties of the system depend on both the amorphous and crystalline clusters.
314 citations
TL;DR: In this article, structural, optical, and magnetic measurements on epitaxial Zn0.9Co0.1O films grown on c-plane sapphire single crystal, at various temperatures (500 −650°C), using pulsed-laser deposition were performed.
Abstract: Here we report a systematic study of structural, optical, and magnetic measurements on epitaxial Zn0.9Co0.1O films grown on c-plane sapphire single crystal, at various temperatures (500–650°C), using pulsed-laser deposition. The main emphasis in this work has been on the correlation of microstructure with properties, specifically with magnetic properties and the fate of cobalt ions into substitutional sites versus precipitates. The reasons for room-temperature ferromagnetism are explored, and convincingly proved to be one of the inherent properties of the material. Most importantly, the presence of nanoclusters of any magnetic phase was ruled out. This was determined by high-resolution transmission electron microscopy, coupled with electron energy loss spectroscopy and STEM-Z (scanning transmission electron microscopy-atomic number) contrast studies.
297 citations
TL;DR: The modified Ti2O9 group unit thus formed reduces the grain boundary energy and provides a way of accommodating oxygen vacancies occurring in oxygen-deficient material by the formation of a nanotwin lamellae structure.
Abstract: Using high-resolution imaging at negative spherical aberration of the objective lens in an aberration-corrected transmission electron microscope, we measure the concentration of oxygen in Σ3{111} twin boundaries in BaTiO 3 thin films at atomic resolution. On average, 68% of the boundary oxygen sites are occupied, and the others are left vacant. The modified Ti 2 O 9 group unit thus formed reduces the grain boundary energy and provides a way of accommodating oxygen vacancies occurring in oxygen-deficient material by the formation of a nanotwin lamellae structure. The atomically resolved measurement technique offers the potential for studies on oxide materials in which the electronic properties sensitively depend on the local oxygen content.
285 citations
TL;DR: Fluorescence emission, electron paramagnetic resonance, and X-ray absorption spectroscopy provide evidence for the presence of Mn in the interior as well as on the surface of the nanocrystals of Mn-doped ZnO.
Abstract: We report the synthesis and characterization of several sizes of Mn-doped ZnO nanocrystals, both in the free-standing and the capped particle forms. The sizes of these nanocrystals could be controlled by capping them with polyvinylpyrollidone under different synthesis conditions and were estimated by X-ray diffraction and transmission electron microscopy. The absorption properties of PVP-capped Mn-doped ZnO exhibit an interesting variation of the band gap with the concentration of Mn. Fluorescence emission, electron paramagnetic resonance, and X-ray absorption spectroscopy provide evidence for the presence of Mn in the interior as well as on the surface of the nanocrystals.
282 citations
TL;DR: In this paper, an array of well-aligned single-crystal zinc oxide (ZnO) nanowires of uniform diameter and length have been synthesized on a (100) silicon substrate via a simple horizontal double-tube system using chemical vapor transport and condensation method.
Abstract: Arrays of well-aligned single-crystal zinc oxide (ZnO) nanowires of uniform diameter and length have been synthesized on a (100) silicon substrate via a simple horizontal double-tube system using chemical vapor transport and condensation method. X-ray diffraction and transmission electron microscopy (TEM) characterizations showed that the as-grown nanowires had the single-crystal hexagonal wurtzite structure with detectable defects and a growth direction. Raman spectra revealed phonon confinement effect when compared with those of ZnO bulk powder, nanoribbons, and nanoparticles. Photoluminescence exhibited strong ultraviolet emission at 3.29 eV under 355 nm excitation and green emission at 2.21 eV under 514.5 nm excitation. No catalyst particles were found at the tip of the nanowires, suggesting that the growth mechanism followed a self-catalyzed and saturated vapor–liquid–solid (VLS) model. Self-alignment of nanowires was attributed to the local balance and steady state of vapor flow at the substrate. The growth technique would be of particular interest for direct integration in the current silicon-technology-based optoelectronic devices.
275 citations
TL;DR: Anatase TiO2 nanoparticles with average particle size ranging between 12 and 23 nm were synthesized by metalorganic chemical vapor deposition and the structure and particle size were determined by x-ray diffraction and transmission electron microscopy as mentioned in this paper.
Abstract: Anatase TiO2 nanoparticles with average particle size ranging between 12 and 23 nm were synthesized by metalorganic chemical vapor deposition. The structure and particle size were determined by x-ray diffraction and transmission electron microscopy. The specific surface areas were measured by Brunauer-Emmett-Teller and ranged from 65 to 125m2∕g. The size effects on the stability of TiO2 in the air were studied by x-ray diffraction and transmission electron diffraction for isochronally annealed samples in the temperature range of 700–800 °C. Only anatase to rutile phase transformation occurred. With the decrease of initial particle size the onset transition temperature was decreased. An increased lattice compression of anatase with the raising of temperature was observed by the x-ray peak shifts. Larger distortions existed in samples with smaller particle size. The calculated activation energy for phase transformation decreased from 299 to 180 kJ∕mol with the decrease of initial anatase particle size from ...
261 citations
TL;DR: In this article, single-walled nitrogen doped nanotubes were prepared using two novel approaches in an arc discharge process, in which a nitrogen-rich precursor was introduced into the anode rods together with graphite and the catalysts.
233 citations
TL;DR: Monte Carlo modelling of the damage formed indicates that recoil silicon atoms contribute significantly to the damaged formed in the specimen, indicating that redeposition of milled material, enriched in gallium, can occur depending on the geometry of the mill employed.
Abstract: The damage created in silicon transmission electron microscope specimens prepared using a focused ion beam miller is assessed using cross-sections of trenches milled under different beam conditions. Side-wall damage consists of an amorphous layer formed by direct interaction with the energetic gallium ion beam; a small amount of implanted gallium is also detected. By contrast, bottom-wall damage layers are more complex and contain both amorphous films and crystalline regions that are richer in implanted gallium. More complex milling sequences show that redeposition of milled material, enriched in gallium, can occur depending on the geometry of the mill employed. The thickness of the damage layers depends strongly on beam energy, but is independent of beam current. Monte Carlo modelling of the damage formed indicates that recoil silicon atoms contribute significantly to the damaged formed in the specimen.
TL;DR: The alloy La275Zr275Al25Cu10Ni10 was found to phase separate during quenching from the melt into (La-Cu)-rich and (ZrNi)-rich glassy phases with compositions close to those of Zr-Ni-Al and La-Cu-Al bulk metallic glasses as discussed by the authors.
TL;DR: In this article, a spray pyrolysis method using citric acid as a polymeric agent was used to synthesize layered Li[Ni1/3Co 1/3Mn1/ 3]O2 powders by means of X-ray diffraction, charge/discharge cycling, cyclic voltammetry, and high-resolution transmission electron microscopy.
TL;DR: In this paper, the formation of the initial gel to the complete transformation into a zeolite-type material was studied at the nanometer scale using transmission electron microscopy (TEM) and in situ synchrotron XRD analysis.
Abstract: FAU-type zeolite was synthesized at room temperature to study the mechanism of its formation. The sluggish crystal growth kinetics at ambient conditions permitted us to track down the entire sequence of crystallization events from the formation of the initial gel to the complete transformation into a zeolite-type material. The processes taking place at the nanometer scale were studied by transmission electron microscopy (TEM). The crystalline character of the particles observed during the induction period was determined by in situ synchrotron XRD analysis. The study was completed by ex situ X-ray diffraction (XRD), infrared (IR), dynamic light scattering (DLS), N2 adsorption measurements and chemical analyses. The combined TEM/synchrotron XRD analysis of the initial crystallization stage revealed that zeolite nuclei were formed during the homogenization (1.5 h) of the initial reactants. Nevertheless, a relatively long induction period (10 days) was observed. During this period, extensive exchange between ...
TL;DR: In this article, the influence of synthesis parameters on the morphological characteristics and sizes of magnesium hydroxide nanoparticles precipitated in an aqueous medium was investigated, such as types of surfactants or water soluble polymeric dispersants, reaction temperature and concentration, addition method and rate, and hydrothermal treatment of reactants.
TL;DR: Different morphologies of copper and copper oxide nanocrystallites, including radially arrayed whiskers, cubic particles and sphere particles, have been successfully synthesized by a microwave-induced method under ambient conditions as discussed by the authors.
Abstract: Different morphologies of copper and copper oxide nanocrystallites, including radially arrayed whiskers, cubic particles and sphere particles, have been successfully synthesized by a microwave-induced method under ambient conditions. In aqueous solution containing different ethylene glycol concentrations, copper acetate hydrate produces different reduction products. The as-prepared copper and copper oxide crystallites were characterized by various techniques, including X-ray powder diffraction, transmission electron microscopy, selected-area electron diffraction and UV/Vis absorption spectroscopy. It was found that microwave irradiation plays a critical role in the formation of the products; temperature was also found to be important in the reaction. The irradiation time and copper acetate concentration also affect the morphology of the products. The possible formation mechanism is also discussed. ((c) Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004)
TL;DR: In this paper, a low-temperature hydrothermal reaction is provided to generate crystalline perovskite nanotubes such as barium titanate (BaTiO3) and strontium titanite (SrTiOO3), which have an outer diameter from about 1 nm to about 500 nm and a length from about 10nm to about 10 micron.
TL;DR: In this article, the results indicated that the protonated single crystals can be exfoliated to MnO2 nanosheets by the intercalation of TMA+ ions followed by water-washing.
Abstract: We report in this paper the studies on protonation, exfoliation, and self-assembly of birnessite-type manganese oxide single crystals. The protonation was carried out by extracting K+ ions from the potassium manganese oxide single crystals in a (NH4)2S2O8 aqueous solution heated at 60 °C, exfoliation to nanosheets by the intercalation of TMA+ ions followed by water-washing, and the self-assembly of MnO2 nanosheets in a dilute NaCl solution. The structures of the samples at these stages were systematically investigated using X-ray diffraction, scanning electron microscopy, transmission electron microscopy, atomic force microscopy, X-ray photoelectron spectroscopy, Fourier transform infrared, thermogravimetric analysis-differential thermal analysis, and chemical compositional analysis. Electron density distribution in the protonated single crystal was visualized by whole-pattern fitting based on the maximum entropy method. The results indicated that the protonated single crystals can be exfoliated to MnO2 u...
TL;DR: Titania nanotubes synthesized by a soft chemical process are described, having diameters of 8 nm to 10 nm and lengths ranging from approximately 0.1 μm to 1 μm as mentioned in this paper.
Abstract: Titania nanotubes synthesized by a soft chemical process are described, having diameters of 8 nm to 10 nm and lengths ranging from approximately 0.1 μm to 1 μm. X-ray diffraction studies show the structure of the as-prepared nanotubes is the same as that of the starting anatase TiO2 nanoparticles. Energy-dispersive x-ray analysis and electron energy loss spectroscopy studies further indicate that the as-prepared nanotubes are composed of titania. Studies using transmission electron microscopy verified that the nanotubes are formed during alkali treatment, with subsequent acidic treatments having no effect on nanotube structure and shape.
TL;DR: The microwave-assisted polyol reduction method was applied to the synthesis of core-shell gold/palladium bimetallic nanoparticles by the simultaneous reduction of the AuIII and PdII ions.
Abstract: The microwave-assisted polyol reduction method was applied to the synthesis of core−shell gold/palladium bimetallic nanoparticles by the simultaneous reduction of the AuIII and PdII ions. The thickness of the palladium shell was calculated to be ∼3 nm, and the gold core diameter is 9 nm. The structure and composition of the bimetallic particles were characterized by high-resolution transmission electron microscopy equipped with a nanoarea energy-dispersive X-ray spectroscopy attachment, transmission electron microscopy, X-ray diffraction, and X-ray photoelectron spectroscopy.
TL;DR: In this article, the authors report on InP nanowires grown by metalorganic vapor phase epitaxy directly on (001)InP substrates, which have nearly square cross sections and a perfect zinc-blende crystalline structure free of stacking faults.
Abstract: We report on [001]InP nanowires grown by metalorganic vapor phase epitaxy directly on (001)InP substrates. Characterization by scanning electron microscopy and transmission electron microscopy reveals wires with nearly square cross sections and a perfect zinc-blende crystalline structure that is free of stacking faults. Photoluminescence measurements of single [001] nanowires exhibit a narrow and intense emission peak at approximately 1.4eV, whereas ⟨111⟩B grown reference wires show additional broad luminescence peaks at lower energy. The origin of this uncommon wire growth direction [001] is discussed as a means of controlled formation of [00l]-oriented nanowires on (001) substrates.
TL;DR: In this article, the authors studied the crystallization of amorphous Ge2Sb2Te5 films (10, 40, and 70 nm) by in situ heating in a transmission electron microscope (TEM).
Abstract: Crystallization of amorphous Ge2Sb2Te5 films (10, 40, and 70 nm thick) was studied by in situ heating in a transmission electron microscope (TEM). Electron irradiation-induced crystallization is possible at room temperature using a 400 kV electron beam where the reciprocal of the incubation time for crystallization scales linearly with the current density during electron irradiation. Without electron-beam exposure, crystallization starts at 130 °C. Using a 200 kV beam, crystallization also occurred in the temperature interval between 70 and 130 °C. In principle, electron irradiation always affects the crystallization kinetics, strongly promoting nucleation and probably not hampering growth. At 130 °C without electron-beam exposure, 400 nm diameter colonies of 10–20 nm grains develop in the 40 and 70 nm thick films showing clear symmetric bending contour contrast. These spherulites prefer to have in their center the 〈111〉 zone axis of the Fm3m structure perpendicular to the surface of the film and show a ...
TL;DR: ZnO tetrapod nanostructures were prepared by evaporating Zn metal under humid argon flow, and diffusion doping was performed at two different temperatures (600 and 800 °C) as mentioned in this paper.
Abstract: ZnO tetrapod nanostructures were prepared by evaporating Zn metal under humid argon flow. After the fabrication, Mn diffusion doping was performed at two different temperatures (600 and 800 °C). The samples were characterized by scanning electron microscopy, transmission electron microscopy, x-ray fluorescence, x-ray diffraction (XRD), superconducting quantum interference device magnetometer, and photoluminescence. Diffusion doping resulted in the increase of the size of tetrapods, but no new peaks were found in XRD spectrum. Mn doped ZnO tetrapod structures were found to be ferromagnetic with Curie temperature ∼50 K, and showed large coercive field (∼3500 Oe for 800 °C sample, ∼5500 Oe for 600 °C sample).
TL;DR: In this article, the microstructure and compositions of the constituent phases in a sintered Sm(Co0.72Fe0.20Cu0.055Zr0.025)7 permanent magnet with different cooling processes have been investigated by transmission electron microscopy and the 3DAP technique.
TL;DR: Stable CoFe(2)O(4) nanoparticles have been obtained by co-precipitation using a microwave heating system and AC magnetization data indicate the presence of magnetic interactions between the nanoparticles.
TL;DR: In this paper, the shape and phase-controlled synthesis of ZnS nanocrystals (nanorods and nanodots) was realized by the selection of ligand molecules with a simple method of thermolysing single-source precursor Zn(exan)2 with octylamine (OA) or trioctylphosphine (TOP) as precursor solvent.
Abstract: The shape- and phase-controlled synthesis of ZnS nanocrystals (nanorods and nanodots) was realized by the selection of ligand molecules with a simple method of thermolysing single-source precursorzinc ethylxanthate (Zn(exan)2) with octylamine (OA) or trioctylphosphine (TOP) as precursor solvent. The as-prepared nanocrystals were characterized by transmission electron microscopy (TEM), high-resolution transmission electron microscopy (HRTEM), selected area electron diffraction (SAED), and X-ray diffraction (XRD). In hexadecylamine (HDA) + OA system, diameter- and aspect-ratio-tunable hexagonal wurtzite ZnS nanorods were attained in the temperature range of 150−250 °C, and the nanorods self-assembled into two-dimensional (2-D) aligned arrays. While in the HDA + TOP system, a shape change from rod to spherical particle and a phase transition from wurtzite to sphalerite simultaneously occurred with the increase of TOP content in the solution, and sphalerite nanodots were prepared in high TOP content or in TOP...
TL;DR: In this paper, large-scale cupric oxide (CuO) nanowires have been synthesized by thermal evaporating copper foils in O2 ambient at the temperatures from 300°C to 900°C.
TL;DR: The application of a novel imaging mode based on the adjustment of a negative value of the spherical aberration CS of the objective lens of a transmission electron microscope equipped with a multipole aberration corrector system to the imaging of oxygen in SrTiO3 and YBa2Cu3O7 demonstrates the benefit to materials science investigations.
Abstract: A novel imaging mode for high-resolution transmission electron microscopy is described. It is based on the adjustment of a negative value of the spherical aberration C S of the objective lens of a transmission electron microscope equipped with a multipole aberration corrector system. Negative spherical aberration applied together with an overfocus yields high-resolution images with bright-atom contrast. Compared to all kinds of images taken in conventional transmission electron microscopes, where the then unavoidable positive spherical aberration is combined with an underfocus, the contrast is dramatically increased. This effect can only be understood on the basis of a full nonlinear imaging theory. Calculations show that the nonlinear contrast contributions diminish the image contrast relative to the linear image for a positive-C S setting whereas they reinforce the image contrast relative to the linear image for a negative-C S setting. The application of the new mode to the imaging of oxygen in SrTiO3 and YBa2Cu3O7 demonstrates the benefit to materials science investigations. It allows us to image directly, without further image processing, strongly scattering heavy-atom columns together with weakly scattering light-atom columns.
TL;DR: In this paper, a single crystalline indium oxide pyramid and column structures were synthesized by a simple physical evaporation technique without any catalytic action while the column structure was produced using gold as the catalyst.
Abstract: Single crystalline indium oxide pyramid and column structures were synthesized by a simple physical evaporation technique. The pyramid structure was obtained without any catalytic action while the column structure was produced using gold as the catalyst. The nanostructures were characterized by x-ray diffraction, scanning electron microscopy and transmission electron microscopy. A blue-green photoluminescence band in the visible region was observed in the In2O3 structures which could be ascribed to the existence of a large amount of singly ionized oxygen vacancies, confirmed by electron paramagnetic resonance.
TL;DR: In this article, secondary ion mass spectroscopy (SIMS) and transmission electron microscopy (TEM) were used for diffusion studies on physical vapor deposited Cu/Ru(∼20 nm)/Si samples.
Abstract: Diffusion studies were carried out on physical vapor deposited Cu/Ru(∼20 nm)/Si samples using secondary ion mass spectroscopy (SIMS) and transmission electron microscopy (TEM). Back side SIMS depth profiling revealed well-defined interfaces and showed that Cu interdiffusion was impeded by Ru thin film up to 450°C vacuum annealing. TEM showed a 20-22 nm Ru barrier layer with a columnar microstructure oriented vertically with respect to Si substrate. TEM results corroborate with SIMS data to indicate stability of the Ru film barrier for annealing temperatures up to 450°C. Direct Cu electroplating on ultrathin Ru barrier layers (<20 nm) was investigated in sulfuric acid. The electroplated Cu film is shiny, smooth, and without agglomeration under scanning electron microscopy. Excellent adhesion between interfacial layers was confirmed by the scribe-peel test. The interfacial characterization results indicate that Ru thin film is a promising candidate as a directly plateable Cu diffusion barrier.