bluuebunny/crossref_metadata_2025_split huggingface dataset:
Analysis of metastable structures in quenched Cr-Ti alloys
Authors: Sinkler Wharton , Luzzi David E. 
Published: June 2020

Metastable water-quenched bcc Cr40Ti60 is reported to undergo solid state amorphization during sub-eutectoid temperature anneals. Electron diffraction of the metastable bcc phase reveals complex patterns of diffuse scattering indicating the presence of deviation, topological, chemical or both, from the ideally random solid solution. The hypothesis that the microstructure causing the diffuse scattering plays a role in the amorphization process is supported by studies in which an electron- irradiated bcc-based Cu-Ti alloy shows similar diffuse scattering just prior to irradiation-induced amorphization.Diffuse scattering is observed in all major zone axes of the as-quenched alloy except for (111). Analysis of the spatial frequencies of diffuse scattering maxima indicates that in spite of a clear directional relationship between the bcc matrix scattering and the diffuse scattering, at least some diffuse intensity maxima have spatial frequencies which are incommensurate with the bcc matrix. For instance, the streaked diffuse form along <11> in the (110) zone axis pattern (Fig. 1, arrow), which has been determined to be due to kinematical scattering, does not correspond to any possible bcc superlattice spacing along the [11] direction. This suggests that the microstructure of the as-quenched phase includes regions in which static displacements from the bcc equilibrium sites are encountered.
Quasicrystals in a rapidly solidified AlMnCrSi alloy
Authors: Guo Y.X. , Andersen S. , Høier R. 
Published: June 2020

Since the icosahedral quasicrystal (IQ) was first reported and described, transmission electron microscopy (TEM) has played an important role in structural studies of the material. Several types of IQ structural models have been reported, but the detailed structure is still not solved. In addition the quasicrystals are frequently strained and dislocation models have been suggested. The present investigation is focused on these latter aspects through TEM-studies of interface boundaries and defects in a rapidly solidified Al-Mn-Cr-Si alloy.The bright field image in Fig. 1 shows IQ precipitates in an Al-matrix. The particles have two different orientation relationships with the matrix. These relationships have been found through detailed determination of the reciprocal lattice for several particle/matrix combinations. The diffraction pattern in Fig. 2a shows a <100> Al zone. Here three orthogonal 2-fold axes in the quasicrystal are along the three 4-fold aluminium axes. In Fig. 2b one of the three orthogonal 2- fold axes is along a cube direction and the two others along two orthogonal <110> axes in the facecentered Al matrix. The first relationship corresponds to the one observed previously for much smaller icosahedral particles.
Dislocation density and oxidation behavior in mineral and coal pyrites
Authors: Pollack S. S. , Martello D. V. , Tamilia J. P. , Booher H. B. , Souza R. A. 
Published: June 2020

Unstable iron pyrites known as ‘rotten’ pyrite, have been a problem for mineral collectors since these pyrites spontaneously react to form iron sulfates with subsequent fracturing of the specimens when they are stored under ambient conditions. Much of the pyrite found in coal is also highly reactive, and produces acid mine drainage, with associated environmental problems. Other iron pyrites are chemically stable under identical weathering conditions. The authors propose that the increased pyrite oxidation behavior of the coal and ‘rotten’ pyrites may be explained by differences in the crystal defect concentration.In the present study, stable and ‘rotten’ mineral pyrites, and coal pyrite crystals have been examined using light microscopy and scanning electron microscopy. Etch pits observed on the pyrite crystal faces are presumed to result from the intersection of dislocations with the free surface and hence provide a measure of crystal line defect density.
Imaging single platinum atoms on zeolites in the STEM
Authors: Rice Stephen B. , Treacy Michael M. J. , Disko Mark M. 
Published: June 2020

High angle annular dark-field (HAAD) imaging in the scanning transmission electron microscope has been shown in recent years to be a very effective tool in characterizing materials in which there are large differences in atomic number. Supported metal catalysts, in particular, have been explored extremely successfully using this Z-contrast technique. HAAD has very good sensitivity to high atomic number clusters on low atomic number supports, due to the approximately Z2 relationship. Furthermore, since the image contrast is due primarily to amplitude contrast, the resulting images are maps of mass thickness. Owing to the linear proportionality between intensity and the number of atoms probed, the intensity values integrated over metal clusters can be used as a measure of the cluster size.High resolution bright-field imaging is better suited for resolving structure in periodic specimens, and can be used to obtain structure images of zeolites. However, even with contrast enhancements such as Fourier filtering available from image processing, bright-field images are ineffective for detecting clusters containing fewer than about 20 Pt atoms in supports thicker than about 100Å. In comparison, we have demonstrated that the HAAD technique can be used successfully to detect single atoms of platinum on a 200Å thick zeolite support.
Investigation of cluster layers of small netal particles by TEM, SEM, EELS and by photoacoustic spectroscopy
Authors: Seiler H. , Haas U. , Körtje K.H. 
Published: June 2020

The physical properties of small metal particles reveal an intermediate position between atomic and bulk material. Especially Ag has shown pronounced size effects. We compared silver layers evaporated in high vacuum with cluster layers of small silver particles, evaporated in N2 at a pressure of about 102 Pa. The investigations were performed by electron optical methods (TEM, SEM, EELS) and by Photoacoustic (PA) Spectroscopy (gas-microphone detection).The observation of cluster layers with TEM and high resolution SEM show small silver particles with diameters of about 50 nm (Fig. 1 and Figure 2, respectively). The electron diffraction patterns of homogeneous Ag layers and of cluster layers are similar, whereas the low loss EELS spectra due to plasmon excitation are quite different. Fig. 3 and Figure 4 show first results of EELS spectra of a cluster layer of small silver particles on carbon foil and of a homogeneous Ag layer, respectively.
High Resolution Electron Microscopy on zeolites
Authors: Zandbergen H. W. , Dyck D. van 
Published: June 2020

Zeolites are very suitable for high-resolution electron microscopical investigation since their pore structure often allows an unambiguous interpretation of the images, especially when taken with the electron beam parallel to one of the pore channel direction. HREM can give very useful information on a number of subjects of major importance in zeolite synthesis
a.Nucleation;b.Defect characterization;c.Characterization of growth mechanisms of denser phases;d.Structure determination;e.Identification of small metal particles inside the zeolite matrix.f.Structural changes due to (catalytic) reactions.
The surface structure of platinum catalyst particles
Authors: Harris Peter J.F. 
Published: June 2020

For many metal-catalysed reactions, activity and selectivity depend strongly on the structure of the metal surface. However, surprisingly little is known about the surface structures of supported ultrafine metal particles of the type used in practical catalysts. Transmission electron microscopy can play an important role in this area, and is beginning to produce results which could have a major impact on our understanding of processes such as catalyst poisoning and promotion.In this study, which builds on previous work, the effect of various heat-treatments on the shapes and surface structures of alumina-supported platinum particles has been investigated using both conventional bright field TEM and high-resolution imaging. It has been found, for example, that heating in hydrogen tends to produce almost spherical particles with little faceting, as shown in Figure 1. Heating in sulphur-containing atmospheres, on the other hand, produces sharp (100) faceting so that the particles often display square or rectangular profiles, as shown in Figure 2. It is well known that sulphur poisoning can produce changes in catalytic selectivity without deactivating the catalyst completely.
Genesis of Pd-Fe particles by Fe carbonyl surface reaction on Pd/Al2O3: Influence of the precursor activation
Authors: Szymanski R. , Sarrazin P. , Ruterana P. , Merlen E. , Boitiaux J.P. 
Published: June 2020

Bimetallic Pd-Fe catalysts supported on a transition alumina have been synthetised by reacting Fe carbonyl with the metal surface of a Pd/Al2O3 precursor under mild conditions. The genesis of bimetallic particles was characterized by STEM (VG HB5) and HREM (Jeol 120 CX and Philips EM 430).The monometallic Pd/Al2O3 was prepared by impregnation with nitrate precursor, drying, calcination at 773 K in air and reduction at 723 K in H2. A solution of Fe (CO)5 in toluene was then reacted with the reduced precursor at 298 K under flowing hydrogen (procedure 1). An alternative consisted in reacting the carbonyl directly with the calcined precursor (Procedure 2). Alloy formation was achieved in both cases by a subsequent reduction at 723 K.The general Pd-Fe particle morphology is close to that of the reduced Pd precursor. An amorphous layer at the periphery of a number of particles indicates a surface segregation which has probably occured during the transfer to the microscope of the sample kept in air, due to the high reactivity of Fe towards oxygen (Figure 1).
Atomic structure of stair rod misfit dislocations at the GaAs on Si(100) interface
Authors: Gerthsen D. 
Published: June 2020

The prospect of technical applications has induced a lot of interest in the atomic structure of the GaAs on Si(100) interface and the defects in its vicinity which are often studied by high resolution transmission electron microscopy. The interface structure is determined by the 4.1% lattice constant mismatch between GaAs and Si, the large difference between the thermal expansion coefficients and the polar/nonpolar nature of the GaAs on Si interface. The lattice constant mismatch is compensated by misfit dislocations which are characterized by a/2<110> Burgers vectors b which are oriented parallel or inclined on {111} planes with respect to the interface. Stacking faults are also frequently observed. They are terminated by partial dislocations with b = a/6<112> on {111} planes. In this report, the atomic structure of stair rod misfit dislocations is analysed which are located at the intersection line of two stacking faults at the interface.A very thin, discontinous film of GaAs has been grown by MBE on a Si(100) substrate. Fig.1.a. shows an interface section of a 27 nm wide GaAs island along [110] containing a stair rod dislocation. The image has been taken with a JEOL 2000EX with a spherical aberration constant Cs = 1 mm, a spread of focus Δz = 10 nm and an angle of beam convergence ϑ of 2 mrad.
Diffusion in multilayers, studied by quantitative chemical mapping at the atomic level
Authors: Kim Y. , Ourmazd A. 
Published: June 2020

Using chemical lattice imaging in combination with vector pattern recognition, we study diffusion and interdiffusion at single interfaces in mulilayered semiconductors quantitatively with atomic plane resolution. 20 periods of 50Å C-doped GaAs/50Å undoped GaAs/50Å Al0.4Ga0.6As grown by Molecular Beam Epitaxy(MBE) at 600C was examined to study interdiffusiuori across single GaAs/AlGaAs interfaces as a function of temperature (650C to 750C), depth of interface beneath the surface, and doping . After annealing in bulk form, cross-sectional TEM samples were prepared chemically. Chemical lattice images in the <100> zone axis obtained at an accelerating voltage of 400KV with a JEOL 4000-EX high resolution transmission electron microscope were analyzed by a digital pattern recognition method to obtain composition profiles at each interface before and after annealing.Figure 1 is a chemical lattice image of a C:GaAs/AlGaAs interface. The compositional information in the sample is contained in the local patterns that make up such images. The analysis of such chemical images by the pattern recognition yields quantitative composition profiles across single interfaces. The composition profiles shown in Figure 2 refer to a single interface at a depth of 300Å, before and after annealing at 700C for one hr.
The determination of the rigid-body translation across anti-phase boundaries in GaAs
Authors: McKernan Stuart , René Rasmussen D. , Barry Carter C. 
Published: June 2020

The growth of a polar material on a non-polar substrate leads to the possibility of anti-phase boundary (APB) formation. Across the boundary there will be bonding between like atoms. The stoichiometry of the material may, or may not, be affected, depending on the relative proportion of A-A and B-B bonds in the boundary. This will depend on the crystallographic orientation of the boundary plane. Because of the different nature of the bonding at an APB, it has been assumed that the physical properties, particularly the electrical characteristics, of the polar layer will be adversely affected by the presence of APBs. Much effort has therefore gone into the development of growth conditions which minimize the likelihood of APB formation, particularly in the GaAs on Si system.Little work, however, has been done on the fine-structure of the APB itself. In this paper the results of a quantitative comparison of the α fringes produced in 2-beam images of APBs, with calculated images will be presented. The theoretical images were calculated using the COMIS program, which uses a manybeam formalism based on the Howie-Whelan equation. The samples were prepared from GaAs epilayers deposited on a (100) Ge substrate. The Ge substrate was removed by mechanical polishing prior to ion milling of the epilayer in a liquid nitrogen cooled specimen stage. The epilayer was examined at a number of low index zone axes, using a number of different 2-beam conditions. A representative selection is shown in figure 1. Images A, B, and C, were obtained close to the [001] zone axis, image D was obtained near the [101] zone axis and shows the horizontal APB nearly flat-on, but out of contrast. Near the [101] zone axis this APB appears as a line defect, and therefore must lie on the (101) plane.
Interfaces in a slowly cooled Al-SiC composite
Authors: Bardal Asgeir , Høier Ragnvald 
Published: June 2020

In various metal-based composites ceramical powders are added for increased mechanical properties. Commercial materials are made through different production routes and in all cases the physical properties are determined by the production determined microstructure, i.e. by the grain and particle size, the dislocation density and the local structure near and at the interface between the matrix and the ceramical powder. In the present studies it has been focused on the two latter aspects.The matrix of the material investigated is the commercial Al alloy AA6061, with Mg and Si as the major alloying elements, and the powder added is SiC. The material has been subject to various heat-treatments and is being studied by use of TEM, EELS and EDS. In this work we will focus on material produced via a powder route, and specimens which have been heat treated at 400°C for 8 hours, extruded, slowly cooled (l°C/min) down to 180°C and then quenched to room temperature. This gives a material with good ductility, strength a little lower than the unreinforced alloy and a stiffness which is about 50% higher.
Observation of the structural phase transition in SrFio3 by diffuse electron scattering
Authors: Zuo J.M. , Rez Peter 
Published: June 2020

Thermal streaks were first observed in electron diffraction patterns by Honjo et al and were attributed to low frequency acoustic waves. Recently Hua et al have also used electron diffraction to invetsigate phonons in NiAs and KCP.Strontium titanate (SrTiO3) has a perovskite structure, and is of interest because it undergoes a second order displacive structural phase transition at above 110K. Below the transition temperature, the structure changes to tetragonal with a unit cell (a, a, 2 c) , the c-axis being slightly elongated with c/a=1.0006. This structural phase transition is believed to be due to the softening of the phonon at the (111) Brillouin zone boundary, i.e. q=(lll)/2. The detailed phonon dispersion has been measured by neutron workers (for example, see 5), and is shown in Fig. 1. The phonon dispersion shows a characteristic dip at q=( 111 )/2, which is further lowered (softening) as the temperature decreases till the transition temperature is reached.
Electron Microscopy for the determination of preferred crystal orientations: A concise review
Authors: Schwarzer Robert A. , Weiland Hasso 
Published: June 2020

The distribution of grain orientations (“crystal texture”, “preferred orientations”) is a distinctive feature of microstructure, since important material properties are anisotropic, and changes of crystal texture may be found in workpieces which are typical for fabrication processes and use. Two complementary computerized techniques /1/ are available for the study of preferred crystal orientations on a microscale using electron microscopy:the measurement of individual grain orientations (TEM, SEM)polefigure measurements (TEM).The standard methods of orientation determination grain by grain using a TEM are the interpretation of SAD spot and of microbeam diffraction Kikuchi patterns. Thin samples, however, are required which are transparent for high-energy electrons.
Fine-scale structural defects in dislocation cores
Authors: Hirth John P. 
Published: June 2020

We are now entering what one might consider the third phase of study of dislocations by transmission electron microscopy (TEM). The first phase, in the 1950’s and 1960’s led to classifications of dislocation behavior, concepts of low angle boundaries, equilibrium nodes, and dislocation extension, for example. The second, with the advent of the weak-beam technique, produced improved estimates of stacking fault energy on the basis of dislocation extension, revealed more types of extended dislocation configurations, particularly in ordered intermetallic compounds and inorganic compounds, and revealed finer scale partial dislocations such as misfit dislocations and grain boundary dislocations. With improved resolution for both imaging and direct lattice resolution, we can now be thought to be entering a third phase where information on even finer scale core structure of dislocations might be revealed.The improvement in direct core structure resolution is exciting to those working on the physics of dislocation configurations or on dislocation motion and mechanical properties because of the possibility of direct confirmation of mechanisms and models that have heretofore only been tested by indirect correlations.
Shearing mechanisms of γ' precipitates by dissociated single-matrix dislocations in nickel-based superalloys
Authors: Décamps Brigitte , Morton Allan J. 
Published: June 2020

Superlattice stacking faults play an important part in the deformation processes of γ/γ' Ni-based superalloys. However, recent studies using the weak-beam technigue have brought into question the previously accepted mechanism for shearing of the γ'precipitates. A new shearing mechanism involving a single a/2<110> matrix dislocation and the nucleation of a Shockley partial has been proposed. In the present study, TEM weak-beam and bright field image matching techniques have been used to study the elementary shearing configurations of γ'precipitates in [001] single crystals of superalloys after creep (intermediate temp.) and dynamical (high temp.) tests in compression and tension.The observations show a change of configurations between compression and tension: in dynamical compression, precipitates are mainly sheared by leading S-ESF (Fig. 1); and in tension creep by leading S-ISF (Fig. 2). Both dynamical tension and compression creep give a mixture of S-ISF and S-ESF.
Interface and twins in GaAs/Si grown by both MBE And MOCVD
Authors: Fan Rongtuan 
Published: June 2020

Recently, A number of the scientists have studied GaAs/si In this work, we intend to investigateo the interface and the twins in GaAs/Si which was grown by both MBE and MOCVD. TEM studies were performed on (011) crosssections of the GaAs/Si using TEM and HREM. TEM specimens were produced by sandwiching, dimpling, and atom- milling with ˜5KV Ar ions at liquid nitrogen temperatures.It showed the cross-sectional images in GaAs/Si in Fig.la, there were a lot of defects in the interface of GaAs/Si. Fig.lb obtained using the weak beam tecnique have showed the distribution of the twins and the defects to same interface of Fig.la. As well known,in the process of growth, deformation and phase transformation for crystals, it is not only often to produce the twins, but also the twins will be continuously produced in the twins, called secondary twins. If the phenomenon which continued to produce twins in the twins would be sustained by many times, then called trine, quaternary and multiple twins boundary will emerge from the interface. In the deformation, the twins on two difference twins plane intersect with each other in move, so that, the secondary twins may be produced in the crossing section, see Fig.1b and 2. It is interesting to compare epilayers grown by MOCVD and MBE, that reveals a systematic difference between the twinning produced by the two processes.MBE growth results in very large numbers of microtwins ˜50 Å -100 Å in width in the first 1000Å or so of the layer. MOCVD tends to generate much smaller numbers of large twins (up to 1.5μ) which can penetrate right through a thick (>10μm) epilayer, Fig.1. But, by way of exception, in our research in this year, the dislocations in GaAs/Si were observed only, there was nothing for twins, Fig.3.These twins grow up in {111} , i . e . , {111} is twinning plane, section direction <112>. microtwins with 3 times that of a lattice period(Fig.4).
Direct imaging of order-disorder and antiphase domain structures in Ti3Al intermetallic compound
Authors: Ye H. Q. , Xie T.S. , Li D. 
Published: June 2020

The Ti3Al intermetallic compound has long been recognized as potentially useful structural materials. It offers attractive strength to weight and elastic modulus to weight ratios. Recent work has established that the addition of Nb to Ti3Al ductilized this compound. In this work the fundamental problem of this alloy, i.e. order-disorder and antiphase domain structures was investigated at the atomic scale.The Ti3Al+10at%Nb alloys used in this study were treated at 1060°C and then aged at 700°C for 2 hours. The specimens suitable for TEM were prepared by standard jet electrolytic-polishing technique. A JEM-200CX electron microscope with an interpretable resolution of about 0.25 nm was used for HREM.The [100] and [001] projections of the α2 phase were shown in Fig.l.The alloy obtained consist of at least two phases-α2(Ti3Al) and β0 structures. Moreover, a disorder α phase with small volume fraction was also observed. Fig.2 gives [100] and [001] diffraction patterns of the α2 phase. Since lattice parameters of the ordered α2 (a=0.579, c=0.466 nm) and disorder α phase (a0=0.294≈a/2, c0=0.468 nm) are almost the same, their diffraction patterns are difficult to be distinguished when they are overlapped with epitaxial orientation relationships.