bluuebunny/crossref_metadata_2025 huggingface dataset:
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.
Observation of reconstruction on (111) Surfaces of MgO
Authors: Crozier P. A. , Gajdardziska-Josifovska M. , Cowley J. M.
Published: June 2020

The physical properties of the (111) surfaces of ionically bonded crystals with a rocksalt structures have not been well characterised. In the (111) direction, this crystal structure consists of alternating rows of cations and anions and the bulk terminated surface will therefore be a polar surface and possess a net dipole moment perpendicular to the surface. Theoretical calculations show that polar surfaces have an infinite surface energy (or very large surface energy for finite crystals) and are therefore highly unstable. These electrostatic arguments indicate that the (111) surface of ionically bonded rocksalt crystals can only exist if substantial reconstruction or adsorption of charged species occurs at the surface. We have used reflection high energy electron diffraction (RHEED) and reflection electron microscopy (REM) to study the (111) surface of MgO. MgO is an ionically bonded insulating oxide with a rocksalt structure and consists of alternating planes of Mg2+ and O2− in the (111) direction. It is therefore expected that there will be a substantial re-arrangement of atoms on the (111) surface.
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.
STEM characterization of supported catalyst clusters
Authors: Liu J. , Spinnler G. E. , Pan M. , Cowley J. M.
Published: June 2020

Scanning transmission electron microscopy (STEM) offers a powerful extension to the conventional transmission electron microscopy (TEM) by combining high resolution microanalysis with a variety of imaging and diffraction modes. Bright-field (BF) and dark-field STEM imaging (with or without energy filtering) can be used to obtain structural images or to locate small particles and other inhomogeneous sample areas for microanalysis. The microdiffraction technique can provide crystallographic information on nanometer-scale small particles. Secondary electron (SE) images with a resolution approaching the probe size (0.5 nm) can be obtained in STEM instruments, providing topographic information on the samples studied. High-angle annular dark field (HAADF) imaging is also available in dedicated STEM instruments. The intensity of high-angle scattered electrons depends strongly on the atomic number (Z). This unique property makes the HAADF imaging a powerful microscopic technique in characterizing supported catalyst systems which often comprize high atomic number particles supported on low atomic number substrates.
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.
CBED analysis of extended defects in melt-grown GaSe single crystals
Authors: De Blasi C. , Manno D.
Published: June 2020

The study of dislocations and stacking faults in melt grown GaSe single crystals has been carried out by the Convergent Beam Electron Diffraction (CBED) technique.

The presence of stacking faults induces distortions in the Kikuchi lines observed in the CBED transmitted disk. According to the kinematical condition of the stacking fault visibility, such lines show modifications when g·R is not integer, The displacement vector R has been determined by the analysis of the visibility and invisibility conditions in the transmitted disk, recorded according to the Tanaka method, The Burgers vector b of dislocations has been determined by the analysis of the modifications induced both in Kikuchi lines and in the First Order Laue Zone (FOLZ) reflections, observed in low camera length CBED patterns. Splitting and unsplitting of the reflections correspond to the visibility and invisibility of the dislocations in the kinematical approximation of diffraction contrast, The condition g·b = 0 is not strictly a sufficient condition for the vanishing of the modifications induced by the dislocation, neverthless it is generally very useful as a criterion for determining the direction of b, Moreover, some reflections g give g·b = ⅓ in the case of partial dislocations. This condition does not produce enough contrast to be detected, so that it is one more for the defect invisibility. The Thompson construction has been used in order to calculate the amplitude of b and to discriminate perfect or partial dislocations.
In situ straining experiments in the Transmission Electron Microscope
Authors: Messerschmidt Ulrich
Published: June 2020

Recently a number of in situ straining experiments have been carried out at temperatures between about 80 K and 1200 K. A new HVEM straining stage was constructed for temperatures above 1300 K. Its design features are: top entry double tilting stage, thermal expansion drive of high stiffness, heating by electron bombardment, and water cooling to quickly reach a steady state.

The following deformation phenomena have successfully been treated by in situ experiments:

Determination of the effective stress from the curvature of bowed-out dislocation segments: As shown by in situ experiments on MgO crystals, the line tension of dislocations may differ from its theoretical value. Nevertheless, the anomalous temperature dependence of the effective stress in ordered alloys as well as for prismatic slip in Be has been determined in accordance with macroscopic experiments. Measurement of velocities and kinematic behaviour of dislocations: In situ experiments allow the coordination of the motion of individual dislocation segments with their geometrical configuration.
Experimental module concept for in situ high-voltage electron microscopy
Authors: Allen C. W. , Ockers S. T. , Ryan E. A. , Zaluzec N. J.
Published: June 2020

Historically specimens for TEM have been introduced into TEMs either in a small cup into a top entry stage or as a part of a specimen rod in side entry, the various translations and tilt/rotations of the specimen being controlled by a stage mechanism which is essentially permanently installed in the TEM. Generally this technology, when applied to high voltage instruments, has simply been scaled up with the increased objective pole piece gap associated with such emersion lens instruments. While this has allowed somewhat improved access for incorporation of various in situ capabilities, only a very small part of the available space within the objective lens region of an HVEM has ever actually been utilized, typically 5 percent or even less. The concept of an "experimental module" for HVEM in situ studies combines the specimen holder and stage into a single, significantly larger system which can retain most of the convenience of a side entry holder, yet utilize 80 or 90 percent of the available space rather than 5 percent, This allows development and inclusion of a much more diverse array of experimental components, services and analytical capabilities, along with the possibility of improved vacuum or of other environments. The concept of "experimental module" is well established in the synchrotron community, for example, where a given experiment is assembled into a system, the "module", which is interfaced finally to the photon source at the time of the experiment. In the electron microscopy community, however, commonly specimen holders have been designed to be accommodated by the instrument as supplied by the manufacturer, with little resultant design flexibility. With the emergence of contemporary HVEMs having significantly improved specifications for image resolution and analytical capability, it is now time to rethink this, especially for the case of microscopes to be employed for observations of dynamic phenomena.
TEM study of buried yttrium silicide formed by ion implantation
Authors: Alford T.L. , Theodore N.D. , Barbour J.C. , Carter C.B. , Mayer J.W.
Published: June 2020

Metal silicides are now used extensively in very-large-scale-integrated (VLSI) electronics due to their low resistivity, good thermal stability, and ability to form on Si. Of these silicides, yttrium silicide, YSi2-x has essentially 0% lattice mismatch with (111)Si, a low Schottky barrier height on n-type Si, and a unit cell based on the AlB2-type structure, but with 15-20% vacancies on the Si sublattice. Recent investigations of high-temperature ion implantation of yttrium ions into Si have emphasized the formation of buried-silicide layers. This study is focussed on the microstructure and defects in the vicinity of buried YSi2-x layers formed by Y-ion implantation into Si.

Yttrium-silicide buried layers were formed by implanting 330 or 660 keV Y ions into (11l)Si substrates held at 450°C followed by a 1000°C, 1-hour vacuum anneal. The implant fluences varied from 1 to 3.6×l017 Y/cm2. Cross-section transmission electron microscopy (XTEM) analysis was carried out using a JEOL 4000EX electron microscope operating at 400 kV.
Characterization of defects in Si films on SiO2 layer
Authors: Liu Ansheng , Shao Beiling , Yuan Jianming
Published: June 2020

SOI (Silicon-on-lnsulator) offers many advantages for integrated circuits including faster switching speed, high packing density, radiation resistance, and latch-up free. It can also be used in the integration of high voltage devices and/ or sensors. Defect-free Si films with a small interior stress are required for the application mentioned above. Therefore a heat-sink and a valley entrainment structure (Fig. 1) were made in order to confine defects to predetermined locations and to leave the other areas of the recrystallized silicon film defect-free.

Using a cross—section specimen electron microscopy we have observed some kinds of defects in unseeded rapid zone-melting-recrystallized (RZMR) Si films which were prepared with a RF-induced graphite strip heater system. The scanning speed of the graphite strip heater is 11 mm / sec. Fig.2 shows a cross-section image of a valley structure specimen. Not any defect has been found in region A, which means that about 10μm wide defect-free Si film can be obtained by the process. Region C is an unpatterned normal area with a uniform thickness.The subgrain boundaries (SGBs) with an interval less than 6μm were observed in the region C.
Electron microscope study of differential ion implantation damage in AlAs/GaAs epitaxial layers
Authors: Cullis A G , Jacobson D C , Poate J M , Smith P W
Published: June 2020

Ion implantation processing applied to superlattice structures can produce controlled intermixing of the different strata and a range of studies have focused with special interest upon the GaAs-GaAlAs and InP-InGaAs systems. However, there can be marked differences in the susceptibilities of the superlattice materials to ion damage build-up which, thus, complicates interpretation. The present work has applied transmission electron microscopy (TEM) to the study of differential ion damage in the GaAs-AlAs system, together with an examination of thermal annealing behaviour.

Single ˜90nm heteroepitaxial layers of AlAs were produced within a GaAs matrix grown by molecular beam epitaxy upon (001) GaAs substrates. Ion damage was introduced (77K) using Si+ ions with overlaid doses of 3.5×l014 ions/cm2 at 150keV and 7×1014 ions/cm2 at 200keV. Some samples were then subjected to rapid thermal annealing for 10s at 600°C or 800°C. The structure of the material after the various treatments was studied in cross-sectional samples by both conventional and high resolution TEM using a JEM 4000EX instrument operated at 400kV.
TEM identification of secondary phases in non-stoichiometric polycrystalline CuInSe2 thin films
Authors: Goral J.P. , Al-Jassim M.M. , Albin D. , Tuttle J.R. , Noufi R.
Published: June 2020

Polycrystalline thin films of CuInSe2 and CuGaSe2 are currently being developed as low-cost photovoltaic devices. These films are vacuum-deposited onto molybdenum metallized alumina substrates. The film composition may be varied by manipulation of the deposition parameters. For photovoltaic applications, the desired phase has a stoichiometry close to CuInSe2. This compound is a zincblende variant, the cations and anions occupying separate fcc sublattices. Under certain growth conditions, the Cu and In atoms adopt an ordered configuration within the cationic sublattice resulting in the tetragonal chalcopyrite structure. Even when the deposition parameters are manipulated to produce nominally stoichiometric films, powder x-ray traces often exhibit anomalous peaks indicative of the presence of impurity phases. The identification of these minority phases by x-ray diffraction alone is not possible in this materials system due to low peak intensity and overlap considerations. The formation of the secondary phases has a detrimental effect on the electrical and optical properties of the thin film device.
HREM study of ferroelectric materials
Authors: Bursill L.A. , JuLin Peng
Published: June 2020

High-resolution imaging of ferroelectric materials poses unusual problems, since specimens tend to be mechanically unstable in the electron beam due to electrostatic interactions. It is often difficult to correct specimen induced astigmatism. Despite this situation significant new information has been obtained concerning the atomic structure and configurations of lattice defects, domain walls and commensurate/incommensurate as well as normal crystallographic structural phase transitions. Our studies have concerned a wide range of ferroelectric materials, such as the perovskite-type structures of KNbO3 BaTiO3 lithium niobate type LiTaO3 (Li1-x, Ag)TaO3 , proton-exchanged and doped lithium niobate (LiNbO3 : Fe,Ti,H) , the hexagonal bronze potassium niobium tungstate PNT, the essentially tetragonal tungsten bronze framework structures of Ba2NaNb5O15 (BNN) and (Sr1-x, Ba x) Nb2O6 (SBN) and the microstructure of lead zirconium titanate (PZT). Some interesting results concerning direct determination of surface polarity of ruby, sapphire and haematite will also be reviewed. The deliberate use of incident beam tilting techniques, in conjunction with dark-field imaging, proved most beneficial for revealing weak symmetry elements in superlattice structures.
Silicon-induced disordering in GaAs-AlAs superlattices
Authors: Baba-Ali N. , Harrison I. , Tuck B. , Ho H.P.
Published: June 2020

Compositional disordering of quantum well structures by impurity diffusion has attracted increasing interest since it was first discovered by Laidig et al in 1981. This phenomenon not only provides a simple way of fabricating new integrated optical devices but also enables fundamental studies of impurity diffusion and self-diffusion. Silicon has been found to induce intermixing in AlGaAs based multiquantum wells. Various techniques have been used to incorporate Si, these are diffusion from the surface, implantation followed by annealing and diffusion from a grown-in source.

In the present work, diffusion in Molecular Beam Epitaxy (MBE) grown samples has been carried out from a grown-in source. The TEM characterization of the as-received specimen has revealed that the structure consisted in a 0.4 um thick Si-doped Al0.33Ga0.66As layer which was sandwiched between two superlattice areas each of which consisted of 17 periods of alternating GaAs(400A)-AlAs(200A) layers (Figure 1) .The samples were annealed in sealed Silica ampoules under various Arsenic pressures at 815°C and 915°C. Secondary Ion Mass Spectroscopy (Figures 4 and 5) demonstrates that the change in the Ga and Al profiles is the consequence of Si diffusion through the Superlattice layers. The TEM investigation of the samples (Figures 2 and 3) confirmed that intermixing had been induced during the diffusion. It also revealed the formation of intrinsic dislocation loops in the annealed specimens. The contrast analysis of the loops indicates that these are of the interstitial type. Finally,increasing the Arsenic overpressure has been found to cause preferential diffusion of Si towards the surface (Figures 6,7 and 8).
Amorphous structure of semiconducting CdAs2 doped with Ge
Authors: Hong K.S. , Berta Y. , Speyer R.F.
Published: June 2020

In crystalline CdAs2, Cd and As atoms are arranged spirally, to form comparatively large (A- site) and small (B-site) vacant sites, bordered by As atoms. This crystalline structure is shown in Fig. 1. The structure of amorphous CdAs2 has been taken to closely resemble that of the crystalline form; doping the compound with Ge atoms would initially cause Ge occupation of the large A-sites with minimal local lattice distortion. Larger amounts of the dopant, in excess of the solubility limit, would cause the rejection of Ge atoms from the lattice, since occupation of the comparatively smaller B-site occupation would otherwise cause severe lattice distortion. With germanium additions in excess of CdGe0.6As2, the amorphous CdAs2 structure transforms to the CdGeAs2 structure, wherin the cation-sites are equally occupied by Cd and Ge at alternate sites.

Samples with appropriate compositions were fabricated by water-quenching the molten compound,vacuum sealed in carbon coated (by pyrolysis) fused silica tubes. The samples were mechanically thinned and ion-milled using a liquid nitrogen cold stage, for examination in the TEM and for EDS.
The formation and structure of Pd2InP on InP
Authors: Ivey Douglas G. , Zhang Lin , Jian Ping
Published: June 2020

Palladium appears to be an important component in contact metallizations to p-type III-V semiconductors. Several successful ohmic contacts containing Pd have been fabricated to p-type GaAs; e.g. Au/Pd/Zn/Pd to GaAs. Palladium is easily deposited on and reacts readily with GaAs, at relatively low temperatures, to form binary and ternary compounds. The formation of these compounds helps generate Ga vacancies in GaAs, necessary for dopant incorporation. Palladium also aids in the wetting of metals, such as Zn to GaAs, improving their adherance to the semiconductor surface. For the same reasons expressed above, Pd may also prove to be a valuable component in contact metallizations to p- type InP. Very little work has been done on the interaction between Pd and InP, however. Krishnan et al have reported on the formation of a Pd InP ternary phase, which is predominantly amorphous with some signs of crystallinity. The interaction between Pd and InP, under annealing conditions usually encountered in contact fabrication, is discussed in this paper. Particular emphasis is put on one ternary phase that forms during annealing, i.e Pd2InP.
Microstructural evaluation of reactive ion etched - regrown GaAs
Authors: Cole M.W. , Dutta M. , Rossabi J. , Lehman J.L.
Published: June 2020

Reactive ion etching (RIE) is a preferred dry process step for fabrication of submicron III-V semiconductor device structures. This kinetically assisted chemical dry etch process offers several important advantages over other etching methods, namely etch anisotropy, etch rate control, selectively, accuracy, uniformity across the wafer and reproducibility. As a result of these desirable characteristics, a number of semiconductor device designs involve REE in their device fabrication process. Some of the more novel designs involve lateral quantum well arrays, whereby fabrication requires molecular beam epitaxial (MBE) regrowth on RIE semiconductors.

A major drawback of RIE is the potential lattice damage introduced by energetic ion bombardment and contamination. This material damage may lead to deterioration of device performance. It is important to identify and understand this RIE induced damage in order to develop and refine the RIE process, i.e. minimize crystal damage and thus optimize device performance. This study identifies and analyzes the damage associated with various RIE parameters used for quantum well fabrication. Microstructural characterization via TEM is used to identify the nature of lattice defects, their distribution, and density. Optical methods, Photoluminescence and Raman spectroscopy are used to evaluate the crystal damage and serve as a reliable comparators for the TEM results.
Post-Ion milling chemical polishing, and enhancement of interface view by transverse polishing during dimpling
Authors: Mardinly AJ.
Published: June 2020

A widely used specimen preparation technique applied in the study of electronic materials uses mechanical dimpling and polishing, followed by final thinning by ion milling at a grazing angle. Usually, artifacts induced by this process are inconsequential. However, the milling does lead to the formation of a layer of amorphous material that can interfere with high-resolution imaging. This problem is most severe in milling of compound semiconductors. The surface of III-V compound semiconductors can become mottled by droplets of the lower melting temperature metal formed by disproportionation of the compound, in addition to the amorphous layer. Cooling the specimen to liquid nitrogen temperatures and milling at reduced accelerating voltage and current can only reduce, not eliminate these problems. Beam heating of the thinnest areas also appears to induce diffusion at interfaces in GaAs-lnGaAs superlattices. Reactive ion milling using iodine ions at low voltage and current and at liquid nitrogen temperatures has been shown to be an effective solution to the problems of artifacts. However, conversion of ion-mills to iodine use is complex, and introduces its own unique problems.
Observation of magnetic domain in magnetic disk
Authors: Nagata F. , Shimotsu T. , Tsuruta C. , Kubozoe M.
Published: June 2020

A technological key to successful development of high-density magnetic disk lies in how to prevent mutual interference between adjacent bits i.e. how to provide narrower and simpler configulation of magnetic domain. Development of observation technique of finer magnetic domain, therefore, has been strongly required. Lorentz microscopy is one of the most promising method. Some studies have been made to observe recorded magnetic thin films.

The purpose of the present investigation is to develop high resolution Lorentz microscopy(out of focus method) for investigation of recorded magnetic disk.

High resolution and high voltage electron microscope (H-9000UHR) is used operating at 300kV. Objective lens is excited to realize smaller aberration. In order to protect specimens from magnetic field of objective lens, a special specimen holder is developed. Figure 1 shows a sectional view of objective lens and specimen holder.
The effect of sputtering pressure on microstructure and recording performance of high-density magnetic recording media
Authors: Nguyen Thao A. , Yogi Tadashi , Lambert Steven E.
Published: June 2020

Understanding the magnetic properties of thin films applicable to high density recording requires detailed knowledge of the microstructure and microchemistry of the film. Interactions such as exchange and magnetostatic as well as anisotropies have been shown theoretically to influence the magnetic properties and recording characteristics of the media. These magnetic interactions and anisotropies are very sensitive to microstructure. This study reports the efTcct of sputtering pressure on the microstructurc and magnetic properties of thin CoPtCr films. The relation between the microstructural features and the magnetic interactions will be discussed.

The film structure, C/Co77Pt6Cr17/Cr, was sequentially sputtered onto Si and NiP/AlMg substrates precleaned by an rf plasma. The thicknesses were 25/25-60/100 nm respectively. Sputtering pressures ranging from 3 to 24 mtorr were investigated. The magnetic properties of the films (coercive field, Hc, coercive squareness, S*, remanent and saturation moments, Mrand Ms) were determined by vibrating sample magnetometry. The magnetic recording measurements were made with thin film inductive write heads and experimental shielded magnetoresistive read head with a track width of about 10μm. The head-media spacing was 5 μin. Noise voltages for transition densities up to 3000 fc/mm were determined in the usual fashion. The microstructures were studied using the JEOL JEM 2000 FX and 4000 EX transmission electron microscopes.
Effects of electron irradiation on alkaline earth fluorides
Authors: Diehl P. , McCartney M.R. , Smith David J.
Published: June 2020

Alkaline earth fluorides are important materials in the electronics industry because of their use in the epitaxial growth of semiconductor-on-insulator (SOI) devices. Their main advantages are their close lattice match with the common semiconductors, and the fact that they evaporate as molecular units upon heating which implies good control of film stoichiometry in Molecular Beam Epitaxy. More recently, further interest has developed relating to their use in nanolithography because they are materials which can be suitably patterned with an electron beam in device processing.Moreover, some inorganic fluorides potentially offer inherently higher resolution than resists so far used.

Various studies have been made on the effects of irradiation on these Group IIA fluorides. It has also been noted during electron microscope characterization of the SOI structures that these fluorides are very easily damaged. Since image detail is lost, it has been suggested that the fluorides are becoming amorphous.
Response of intermetallic compounds to electron irradiation
Authors: Luzzi D.E.
Published: June 2020

Intermetallic alloys exhibit a wide spectrum of responses to electron irradiation at energies above the threshold energy for ballistic damage. All chemically ordered compounds will chemically disorder at low temperatures whereas disordered compounds will order at temperatures above approximately room temperature. Volume expansion of the material can be associated with the irradiation as well as mechanical softening. At low temperatures, an amorphous solid solution phase is often the end result of the irradiation process whereas at temperatures above room temperature (and below the crystallization temperature) irradiation leads to the crystallization of an amorphous phase. It has also been shown that the structural response to irradiation in these compounds may be anisotropic. The response to irradiation has been shown to be strongly influenced by several material properties and experimental conditions some of which are listed below.