The stress dependence of the subgrain size in aluminium

Etch-pit (EP) technique and transmission electron microscopy (TEM) have been used to investigate the subgrain size, , as a function of applied shear stress, , during high-temperature creep of aluminium. Examination of thin foils, prepared from deformed specimens, in the electron microscope shows the presence of very large equiaxed sub-grains that approximate those observed in etch-pit photographs. By measuring the average subgrain size from transmission micrographs of representative areas of the foils, two observations are made. First, the average subgrain size is smaller than that determined from etch-pit procedure, but exhibits the same stress dependence: /b (/G)^– where b is the Burgers vector and G is the shear modulus. Second, the TEM subgrain size data of aluminium and those of other metals and alloys, when plotted in the normalized form of /Gb against /Gb on a logarithmic scale, where is the stacking-fault energy of the material, fall within a narrow, horizontal band, confirming earlier reports that the subgrain size is insensitive to stacking-fault energy.     

Instability origin of subgrain formation in plastically deformed materials

The review is focused on two methods of formulation and solution of the subgrain formation problem: an energetic approach and a model of incremental deformations. Both methods are based on a reduced single slip version of crystal plasticity. The mathematical analysis of the energetic approach is done for a single slip model only; in the incremental approach the deformation are assumed small, hence, multi slip can be treated as a sum of single slips. The energetic approach has been employed in analysis of the crystal plasticity model of shear and kink bands. The incremental higher strain gradient model provides an insight into an initial stage of the subgrain formation and the mechanism controlling the subgrain size.     

Al particles size effect on the microstructure of the co-deposited Ni-Al composite coatings

Micrometer and nanometer Al particles were codeposited with nickel by electrodeposition from a nickel sulfate bath containng a similar content of Al particles. The effect of Al particles size on the microstructure of the electrodeposited Ni-Al composite coatings was analyzed. The results indicated that at a given Al particles content the incorporation of Al nanoparticles instead of the microscale countparts significantly increased the particle number per unit volume in the composite, led to a more homogeneous distribution of particles, and finer Ni grains due to nucleation of smaller Ni grains on the surface of Al nanoparticles, which changed the direction of the local Ni growth and caused the formation of a fine equiaxed grain structure.     

Oxidative control of surface plasmon resonance of bismuth nanometal in bismuth glass nanocomposites

We demonstrate here a novel oxidative process to control the metallic bismuth (Bi°) nanoparticles (NPs) formation in bismuth glass nanocomposites by using KClO₄ and KNO₃ as oxidant instead of usual reducing technique. The formation of Bi° NPs has been monitored by its distinctive surface plasmon resonance (SPR) band at 460 nm in the UV–vis absorption spectra. It is further confirmed by the TEM images of Bi° NPs using KNO₃ and KClO₄ which show the formation of spherical Bi° NPs of 2–15 nm sizes and the SAED pattern reveals their crystalline rhombohedral phase. Using this technique it is possible to control the SPR band of nanobismuth (Bi°) in bismuth glasses.     

Langmuir-Blodgett films of Cu(II)-tetrakis (3,3-dimethylbutoxycarbonyl) phthalocyanine: a spectrophotometric and TEM analysis of their structure and morphology

Langmuir-Blodgett (LB) films of copper(II)-tetrakis (3,3-dimethylbutoxycarbonyl) phthalocyanine [Cu(dmbc)Pc] have been prepared from toluene solutions; multilayers (up to 80 layers) were deposited onto hydrophobic quartz substrates. The refractive index n and extinction coefficient κ at normal incidence have been determined from both transmission and reflection measurements carried out in the 400–800 nm spectral range. The optical absorption spectrum as a function of the incident photon energy was also registered in order to determine the optical transition type in Cu(dmbc)Pc LB films by using a band model approach. Linearly polarised light absorbance measurements were performed at room temperature in the same spectral range. The average orientation of the phthalocyanine molecular rings in the LB film, with respect to the normal to the substrate and the dipping direction, has been evaluated. We have found that such orientation differs from that determined for LB films deposited from ethyl acetate solutions.

Structural and morphological analysis were also carried out by transmission electron microscopy techniques. Small ordered domains in a low range order matrix were observed by high resolution images. The structure of the material in the substrate plane has been determined by electron diffraction performed on single ordered domains.     

Quantitative characterization of clay dispersion in polypropylene-clay nanocomposites by combined transmission electron microscopy and optical microscopy

This paper presents a novel method to describe the microstructure of polymer/clay nanocomposites quantitatively. Based on the image analyses of transmission electron microscopy (TEM) and optical microscopy micrographs, two parameters, degree of dispersion (χ) and mean interparticle distance per unit volume of clay (λ_V) are proposed to describe the level of clay dispersion. The degree of dispersion gives the percentage of exfoliation, and λ_V is a measure of spatial separation between particles relative to clay loading. A polypropylene/clay system was chosen as an example to show the effects of processing conditions and biaxial stretching on clay dispersion using the proposed quantifiers. It provides insights into the ‘real’ clay dispersion using a combination of both microscopical and macroscopical aspects.     

Substrate temperature dependence of electrical and structural properties of Ru films

Microstructures and resistivities of sputtered Ru films were investigated as a function of substrate temperature to obtain a single-layered Ru barrier without a Ta/TaN under layer. High resistivity Ru films with a high density of crevices, which enhances Cu diffusion along the crevices, were formed by the conventional sputtering process, i.e., sputtering at room temperature and annealing at 400 °C-700 °C for 30 min in Ar + 3%H₂. But, crevice-free and smooth Ru films with low resistivity, the same as that for the bulk phase, were formed when substrate temperature add sputtering was raised to 700 °C. Ru films formed by this process had (002) preferred orientation and then Cu (111) was formed by plating. This result corresponded to the tendency predicted by ab initio calculations.     

The simultaneous improvements of strength and ductility in additive manufactured Ni-based superalloy via controlling cellular subgrain microstructure

Fine cellular subgrain structure was formed in the Selective Laser Melting(SLM) manu factured IN718 alloy via optimizing the processing parameters.During the subsequent homogenization heat treatment process,the Laves phase dispersed at the subgrain boundaries can be eliminated while the cellular subgrain structure is reserved in the printed samples after holding at 1080℃ for 50 min.With the prolongation of the holding time,the subgrain boundaries undergo low angle rotation via the motion ofdislocation,which leads to the annihilation of the cellular subgrain structure.Moreover,during the subsequent double aging heat treatment process,the reserved cellular subgrain structure in the homogenized samples promotes the precipitation of γ" second phase nanoparticles,and these precipitated γ" phase nanoparticles prefer to distribute at subgrain boundaries.It was found that these unique subgrain boundaries with γ" phase precipitates can hinder but not fully terminate the motion of dislocation during the plastic deformation process,which contributes to increasing the strength as well as holding the stable plastic flow.Hence,the strength and ductility of final prepared IN718 alloy with cellular subgrain microstructure were improved simultaneously compared to the prepared alloy without cellular subgrain structure,which even exceed the mechanical properties standards(AMS 5662) of wrought IN718 alloy.These results in our work suggest that controlling the subgrain structure is a promising effective strategy to improve the mechanical properties of SLM manu factured nickel-based superalloy.     

有关电子显微技术的几个实验和建议

本文涉及两个和电子显微技术有关的问题：豆．透射电子显微镜试样薄片表面沉淀相颗粒存在状况的实验观察．２．扫描电子显微镜背反射电子象用作定量金相测定的建议。     

Titanium aluminide (Ti-48Al) powder synthesis,size refinement and sintering

Titanium aluminide based alloys have shown significant potential in high temperature applications, but the high production cost of TiAl considerably limits its utilisation. Although the use of powder metallurgy processes can reduce the cost by minimising post-machining, an economical powder production route is still required. Therefore, in the present study a pre-alloyed Ti-48Al powder is developed using an elemental Ti and Al powder blend prepared using a simple vacuum heat treatment. A formation model of the intermetallic phases (i.e. TiAl, Ti₃Al, TiAl₂, TiAl₃) during powder synthesis is proposed. In order to improve the sinterability, various milling methods (i.e. ball, attrition and shatterbox milling) are examined to reduce the particle size. The sintered microstructures, particularly the two-phased (α₂-Ti₃Al γ-TiAl) lamellar structures are also investigated. Improved densification is achieved at 1300 °C, held for 2 h, using the manufactured powder, compared to the elemental powder blend (～55%). With higher sintering temperatures or longer hold periods, increased density TiAl components are possible.     

The effect of carbon content on the microstructure of hydrogen-free physical vapour deposited titanium carbide films

Titanium carbide (TiC) coatings for tribological applications were deposited on high speed steel. Several coatings with different titanium to carbon ratio were deposited by means of physical vapour deposition in which titanium was evaporated and carbon was sputtered. The coatings were characterised using analytical electron microscopy. It was observed that the change in titanium to carbon ratio significantly changed the microstructure of the coatings. The low carbon containing coatings consisted of columnar grains exhibiting a preferred crystallographic orientation whereas the coating with highest carbon content consisted of randomly ordered TiC grains in an amorphous carbon matrix. Energy filtered transmission electron microscopy revealed a change in Ti/C ratio as the distance from the substrate increased. The titanium to carbon ratio was observed to increase with distance from the substrate until a stable level was reached. This is due to a variation in the titanium evaporation during the early stages of film growth. This change of the titanium to carbon ratio affected the columnar growth in the initial stage of coating growth for the coatings with low carbon content.     

Grain size and strain in thin sputter-deposited Ni0.8Fe0.2 and Cu films

The average grain size and strain in the direction parallel to the surface of thin Ni_0.8Fe_0.2 and Cu films, sandwiched between Ta layers, have been determined as a function of layer thickness by grazing incidence X-ray diffraction. The in-plane grain size and grain size distribution were also assessed by plan-view transmission electron microscopy. Standard θ-2θ X-ray powder diffraction was used to determine the uniform strain in the direction perpendicular to the surface. Both for Ni_0.8Fe_0.2 and Cu, an elongation of the lattice parameter perpendicular to the surface and a compression of the lattice parameter in the plane of the film is observed, which decreases with increasing film thickness. Additionally, for Ni_0.8Fe_0.2 a non-uniform elongation of the perpendicular interactomic distance at the Ta interfaces is deduced by fitting a kinematical model to the θ-2θ diffraction spectrum. This study illustrates the strength and the complementary character of standard powder X-ray diffraction, grazing incidence X-ray diffraction and transmission electron microscopy for the structural analysis of thin metal films.     

载体炭与Pt催化剂之间的相互作用及其引起的尺寸效应(英文)

通过乙二醇还原,在VulcanXC-72炭黑上负载了三种具有不同平均粒径(1.7nm,3.0nm和5.0nm)的Pt催化剂。利用透射电子显微镜,研究了载体炭黑表面的微孔与Pt催化剂之间的几何相互作用。结果表明:尺寸较小的Pt颗粒(平均粒径为1.7nm)通常被包含在载体表面的微孔中,表现为被一薄碳层所覆盖并嵌入炭黑基体。而尺寸较大的Pt颗粒(平均粒径为3.0nm和5.0nm)则不存在这种现象,往往显示出裸露的清洁表面。这种与载体表面微孔的不同相互作用引起了Pt颗粒在电化学活性比表面上的反常尺寸效应,进而影响了其催化甲醇氧化的质量比活性。     

Microstructure Characterization of Single-crystal ZnO Nanorods Synthesized by Solvothermal at Low Temperature

Single-crystalline ZnO nanorods have been synthesized by a simple solvothermal process at low temperature. Transmission electron microscopy （TEM） observations have confirmed that the as-synthesized products have rod-like morphologies with diameters ranging from several nanometers to 30 nm and lengths from 100 nm to 2 μm. Such hexagonal ZnO nanorods are structurally uniform and the growth direction is identified to be [0001]. Growth mechanism of the ZnO nanorods was proposed.     

Structural and optical properties of sol gel derived Cu2ZnSnS4 nanoparticles

The spherical Cu₂ZnSnS₄ nanoparticles with the average diameters (～8–10 nm) have been synthesized by sol gel method. The effects of solvents and reaction temperatures on the properties of the as-synthesized nanoparticles were investigated. The X-ray diffraction shows as grown Cu₂ZnSnS₄ nanoparticles exhibit kesterite crystal structure along preferential orientation (1 1 2) plane. The crystalline nature of nanoparticles was improved in ethylene glycol solvent with the increase in reaction temperature. Rietveld refinement study was performed and structural parameters were determined for the Cu₂ZnSnS₄ nanoparticles. The Raman spectra show the main characteristic peak of A₁ vibrational mode which confirmed the formation of Cu₂ZnSnS₄ phase in all the samples. Scanning electron micrographs depict the irregular aggregate formation of nanoparticles in methanol solvent and uniformly distributed aggregates of nanoparticles with ethylene glycol solvent. Transmission electron microscopy results show the synthesis of polycrystalline porous nanostructures and uniform spherical nanoparticles in methanol and ethylene glycol solvents respectively at the temperature of 250 °C. UV–vis absorption spectra indicated the broad absorption in visible range and the band gap of the nanoparticles was found to 1.38 and 1.45 eV which is suitable for absorbing the solar radiation. The obtained results revealed ethylene glycol as a suitable solvent and 250 °C as the favorable synthesis temperature.     

New Developments in Transmission Electron Microscopy for Nanotechnology

High‐resolution transmission electron microscopy (HRTEM) is one of the most powerful tools used for characterizing nanomaterials, and it is indispensable for nanotechnology. This paper reviews some of the most recent developments in electron microscopy techniques for characterizing nanomaterials. The review covers the following areas: in‐situ microscopy for studying dynamic shape transformation of nanocrystals; in‐situ nanoscale property measurements on the mechanical, electrical and field emission properties of nanotubes/nanowires; environmental microscopy for direct observation of surface reactions; aberration‐free angstrom‐resolution imaging of light elements (such as oxygen and lithium); high‐angle annular‐dark‐field scanning transmission electron microscopy (STEM); imaging of atom clusters with atomic resolution chemical information; electron holography of magnetic materials; and high‐spatial resolution electron energy‐loss spectroscopy (EELS) for nanoscale electronic and chemical analysis. It is demonstrated that the picometer‐scale science provided by HRTEM is the foundation of nanometer‐scale technology.     

Vertical dislocations in Ge films selectively grown in submicron Si windows of patterned substrates

The structural properties of straight screw dislocations extended in the [001] direction formed in squared- and line shaped- Ge(001) films selectively grown on submicron regions of Si(001) substrates were investigated by transmission electron microscopy. The screw dislocations propagating as a result of spiral surface growth were redirected toward the SiO₂ sidewalls. This redirection is linked to the formation of facets such as {111} facets in the growing Ge films. In the process of strain relaxation upon annealing, the screw dislocations were dissociated into dislocations with Burgers vectors of the a/2<110> type, which glided on the {111} surfaces and disappeared.     

Characterisation of dislocations, nanopipes and inversion domains in GaN by transmission electron microscopy

Transmission electron microscopy is used to analyse a range of defects observed in hexagonal GaN films grown on sapphire and GaN substrates by metalorganic chemical vapour deposition. Large angle convergent beam electron diffraction is used to analyse the Burgers vectors of dislocations and to show that hollow tubes, or nanopipes, are associated with screw dislocations having Burgers vectors±c. Weak-beam electron microscopy shows that dislocations are dissociated into partials in the (0001) basal plane, but that threading segments are generally undissociated. The presence of high densities of inversion domains in GaN/sapphire films is confirmed using convergent beam electron diffraction and the atomic structure of the {

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} inversion domain boundary is determined by an analysis of displacement fringes seen in inclined domains.     

Study of the growth of rhodium particles on different substrates

We have investigated the growth of small supported rhodium particles on different substrates (mica, Al₂O₃, NaCl). The particles were deposited in a vacuum from a special source permitting a low evaporation rate. The particle size, density and crystallographic structure dependencies on mean deposit thickness, deposition rate and substrate temperature during the deposition were studied by transmission electron microscopy and diffraction (TEM and TED). The results showed that it is possible to prepare a model Rh catalyst with a well-defined particle population by vacuum vapour deposition. These catalysts form relatively stable systems with respect to the thermal treatment. It was observed that the particle density, the mean size and the size dispersion of Rh particles are controlled by either atom diffusion or by particle migration on the substrate. The diffusion of atoms and clusters increases with the substrate temperature and the growth takes place also by particle coalescence.     

TEM study of the indentation behaviour of thin Au film on GaAs

Au films of 8.9 nm thickness have been sputter deposited onto a (001) GaAs substrate at room temperature. An average grain size of 10 nm and no texture were obtained. Subsequent, nanoindentation tests were performed on the coated specimens and the mechanical response was compared to that of a bulk GaAs sample with the same crystallographic orientation. Furthermore, the loading–unloading curves were analysed in view of transmission electron microscopy plan-view images obtained on the deformed substrate–film specimens and compared to results previously reported in the literature for bulk sample. Constrained plasticity of the films was observed to occur for residual depth to thickness ratio below 0.67. Further, plastic deformation of the substrate happened on coated specimens at loads less than those required to plastically deform bare substrate.