bluuebunny/crossref_metadata_2025 huggingface dataset:
Structure of superconducting fibers prepared by laser-heated pedestal growth method
Authors: Cai L.Y. , Huo Y.J. , Mao S.N. , Liu M.L. , Li F.H.
Published: June 2020

Superconducting fibers have drawn great attention because of the latent prospect for applications. Fibers of superior quality were obtained by means of the laser-heated pedestal growth (LHPG) method. For LHPG method a fine laser beam is focused at the “source rod” made of raw material so that a small molten zone is formed on its upper end. Then a seed crystal is introduced into the melt and drawn from it to grow crystalline fibers. In this paper the structure of bismuth based Bi-Sr-Ca-Cu-O and Bi-Pb-Sr-Ca-Cu-O superconducting fibers prepared by LHPG is reported. The values of Tc for the two kinds of fibers are 85k and 108k respectively. The critical current density Jc can reach 5150A/cm2. The diameters of fibers are ranged from 35μm-200μm. The thin fibers are flexible.

Fig.1 shows the transition region between the source rod (R) and the LHPG fiber (G). It indicates that the source crystal first melts and then recrystallizes along a certain cry stenographic direction.
Microstructures of Cu- and Y-rich YBa2Cu3O7−x thin films
Authors: Marshall A.F.
Published: June 2020

The defect microstructure of Cu- and Y-rich thin films of the high Tc superconductor YBa2Cu3O7−x (123) is of interest for several reasons. The highest Tc' reported for well-ordered stoichiometric films are typically 90-91 K. Post-annealed Cu- and Y-rich films may exhibit Tc's of 95-96 K. X-ray diffraction showed these non-stoichiometric films to be a highly faulted mixture of the 123 and 248 (Y2Ba4Cu8O16,Tc=80 K) phases. In situ films made by sputtering or electron beam evaporation typically show sharp but depressed Tc's (75-85 K); for our films these values approach 90 K when the films are Cu- and Y-rich. Both post annealed and in situ films exhibit high critical currents on and off stoichiometry; the pinning characteristics, which may be highly influenced by the defect microstructure, are superior for the in situ techniques.

Transmission electron microscopy analysis shows that excess Cu and Y can be incorporated both as stacking fault (SF) defects and as second phase precipitates.
Texture formation in YBa2Cu3O7−x tapes without a substrate
Authors: Choi Jae-Sung , Javadpour Jafar , Han Chan , Thiel Bradley L. , Sarikaya Mehmet , Aksay Ilhan A.
Published: June 2020

Texture formation in thin films of YBa2Cu3O7−x has been attributed to epitaxy due to the substrate. However, even in substrates with randomly oriented grains, or substrates which do not provide epitaxy, there is a high degree of c-axis grain alignment in the direction perpendicular to the surface in thin films. In the present study, this texture formation is observed even in tapes which do not have a substrate, We present a model which explains the texture formation in YBa2Cu3O7−x prepared in constrained geometries.

The tapes used in this study were prepared by first dispersing the YBa2Cu3O7−x superconducting powder in a medium consisting of methylethylketone, ethylalcohol, menhaden fish oil, and polyvinyl butynal. The stable suspension was then cast onto a mylar surface. The green tapes were heated in air at the rate of 1° C/min to 950° C. After soaking at this temperature for 1 h, the samples were cooled to room temperature at a rate of 1° C/min.
An electron diffraction study of superconducting oxides Ba1−xPbxBiO3 and Ba1−yPbyBiO3
Authors: Koyama Yasumasa , Ishimaru Manabu
Published: June 2020

Before the discovery of superconductivity in La-Ba-Cu-O by Bednorz and Müller, it has been known that BaPb1−xBixO3 (BPB) exhibits superconductivity below about 13 K. In particular, because Ba1−yKyBiO3 (BKB) was found to be a superconductor with Tc of about 30 K, the Ba-oxides become more important in order to understand the mechanism of superconductivity of the oxide superconductors. Characteristic features for the Ba-Oxides are that their crystal structure is basically the cubic perovskite structure and there is not a Cu-O layer which is responsible for the superconductivity in the oxide superconductors having the Cu-O layer, such as Y-Ba-Cu-O and Bi-Sr-Ca-Cu-O. That is, the O(2p)-[Pb(6s), Bi(6s)] hybridized orbitals would play an important role in the case of the Ba-oxides. In the present work, in order to understand features of the crystal structure of the Ba-oxides, including a structural disorder, the details of the structure have been examined by means of electron diffraction.
Electron diffraction studies of amorphous and polycrystalline thin films
Authors: Cockayne D J H , McKenzie D R
Published: June 2020

The study of amorphous and polycrystalline materials by obtaining radial density functions G(r) from X-ray or neutron diffraction patterns is a well-developed technique. We have developed a method for carrying out the same technique using electron diffraction in a standard TEM. It has the advantage that studies can be made of thin films, and on regions of specimen too small for X-ray and neutron studies. As well, it can be used to obtain nearest neighbour distances and coordination numbers from the same region of specimen from which HREM, EDS and EELS data is obtained.

The reduction of the scattered intensity I(s) (s = 2sinθ/λ ) to the radial density function, G(r), assumes single and elastic scattering. For good resolution in r, data must be collected to high s. Previous work in this field includes pioneering experiments by Grigson and by Graczyk and Moss. In our work, the electron diffraction pattern from an amorphous or polycrystalline thin film is scanned across the entrance aperture to a PEELS fitted to a conventional TEM, using a ramp applied to the post specimen scan coils. The elastically scattered intensity I(s) is obtained by selecting the elastically scattered electrons with the PEELS, and collecting directly into the MCA. Figure 1 shows examples of I(s) collected from two thin ZrN films, one polycrystalline and one amorphous, prepared by evaporation while under nitrogen ion bombardment.
HREM study of amorphization of CuTi irradiated by 1 MeV electron
Authors: Xu Genbao , Chiou W.A. , Meshii M. , Okamoto P. R.
Published: June 2020

Electron irradiation-induced amorphization of CuTi was studied by high resolution electron microscopy (HREM). Special attention was directed to correlate the spacial distribution of structural change from the perfect crystalline state to the complete amorphous state with the electron density distribution of the focussed beam which was used to amorphize the specimens.

An alloy button of Cu-54 at % Ti was prepared by arc-melting and subsequently annealed at 1173K for three days. HREM samples were spark-cut and thinned by jet polishing. The samples were first examined in a Hitachi H 9000 HREM and selected for irradiation at 10K in a 1.2 MeV Kratos-AEl EM 7 high voltage electron microscope. The irradiation was carried out by a fully focused beam for which the electron density distribution was pre-determined. Finally, the irradiated samples were reexamined across the crystal/amorphous (C/A) boundary in the H 9000. The electron dose at the point of examination was estimated by carefully comparing the positions in HREM images with the interrupted position of bend contour in low magnification and utilizing the electron density distribution.
Structure of pure metallic and semiconductor glasses
Authors: Holzman Louis M. , Kim Yeon-Wook , Kelly Thomas F.
Published: June 2020

There has been a great deal of interest in amorphous materials as the advance of technology has enabled a greater variety of alloys and elements to be quenched into the amorphous state and as new uses for amorphous materials have been developed. Because the analysis of the structure of amorphous alloys is quite complicated, it is highly desirable to have specimens available of pure elements in the amorphous state in order to more easily study amorphous structure and for comparison with theory. However, very few pure elements have been quenched into the amorphous state and most of those that have been are only stable at temperatures close to absolute zero. This has limited the methods available for the study of their structure. We have produced room-temperature-stable amorphous samples of pure elements (V,Nb,Ta,Mo,W,Fe,Co,Ni,Si,Ge) from the melt using electrohydrodynamic (EHD) atomization. Diffraction patterns of these samples were obtained using a Vacuum Generators HB501 STEM and these patterns were analyzed to obtain the radial distribution function for the pure element specimens.
Structure of long-period tetragonal lattice formed by solid-state alloying in Bi-Mn double-layer thin films
Authors: Yoshida Kentaroh , Yamada Takashi
Published: June 2020

It has been a well known fact that BI and Mn are, by melting, immiscible with each other and only a ferromagnetic phase, MnBi, forms by a peritectic reaction at 446°C between solid Mn and the melt. However, the authors succeeded in mixing these two atomic elements by simultaneous vacuum deposition and found that a new metastable phase, Mn3Bi, appears as a crystallization product of the as-deposited amorphous films at 180°C, when their composition is in a range 85 to 65 at% Mn. They derived its atomic arrangement only by means of high resolution electron microscopy. In the present investigation, double layer thin films, consisting of Bi layer (300 Å) and of Mn layer (200°Å), were prepared by successive deposition and were heated at 265°C, just below the melting point of Bi (271°C), for 150 to 200 hr. By this heat treatment, solid-state alloying reaction takes place at the interface between the two layers and as many as four kinds of new alloy phases were found to appear.
Electron microscopy of the commensurate-incommensurate phase transition with the discommensuration network in 1T-TaS2
Authors: Ishiguro Takashi , Sato Hiroshi
Published: June 2020

Phase transitions of lT-TaS2 both on cooling from the incommensurate (IC) phase and on heating from the commensurate (C) phase are investigated by high resolution (HR) transmission electron microscopy because phase transitions are strongly hysteretic. The phases which had been identified were Normal(T>543K,no modurated wave, the Cdl2 type of structure, ao=0.336nm co=0.590nm), IC(354K< T< 543K), NC(non-commensurate or nearly commensurate, 185K<T<353K) and C(T<K). On heating from the C phase, the new phase called the T phase (nearly commensurate triclinic ) appears between 200K and 280K, and that has the discommensuration (DC) network. The HR observations at low temperature reveal both the three dimentional structure of the C phase and the DC network structure of the T phase.

On cooling from the IC phase, the structure of the NC phase is essentially incommensurate in the basal plane and a continuous rotation of the moduration direction towards the C phase occurs.
In situ studies on grain boundary migration in ceria-stabilized TZP
Authors: Schmid Herbert K
Published: June 2020

Tetragonal zirconia polycrystals (TZP) have become of interest due to their exceptionally good combination of mechanical properties. In a previous study the microstructure/microchemistry of grain boundaries (GBs) in CeO2 stabilized ZrO2 (Ce-TZP) was investigated and evidence was found on the existence of vitreous ana crystalline intergranular phases in these ceramics. Recently, the observation of wavy GBs in ceria-zirconia was reported. This phenomenon was attributed to diffusion-induced grain boundary migration (DIGM). In the present work, the in-situ TEM observation of GB migration in Ce-TZP, nominally at room temperature, is reported.

Thin foils for TEM observations were prepared from a Ce-TZP ceramic nominally composed of 90 mol% ZrO2 plus 10 mol% CeO2 and were examined in a Philips EM 420 analytical STEM, operated at 120 kV. Grain boundaries were observed to migrate in specimen areas exposed to extensive electron irradiation during TEM experiments. The micrograph in Fig. 1 shows a BF image of a triple grain junction (TJ) area in the as-prepared state.
The value of Electron Microscope studies of imperfect natural diamonds
Authors: Walmsley J C , Lang A R
Published: June 2020

Interest in the defects and impurities in natural diamond, which are found in even the most perfect stone, is driven by the fact that diamond growth occurs at a depth of over 120Km. They display characteristics associated with their origin and their journey through the mantle to the surface of the Earth. An optical classification scheme for diamond exists based largely on the presence and segregation of nitrogen. For example type Ia, which includes 98% of all natural diamonds, contain nitrogen aggregated into small non-paramagnetic clusters and usually contain sub-micrometre platelet defects on {100} planes. Numerous transmission electron microscope (TEM) studies of these platelets and associated features have been made e.g. . Some diamonds, however, contain imperfections and impurities that place them outside this main classification scheme. Two such types are described.

First, coated-diamonds which possess gem quality cores enclosed by a rind that is rich in submicrometre sized mineral inclusions. The transition from core to coat is quite sharp indicating a sudden change in growth conditions, Figure 1. As part of a TEM study of the inclusions apatite has been identified as a major constituent of the impurity present in many inclusion cavities, Figure 2.
Electron Microscopy of hydrothermally treated gamma-alumina
Authors: Mansour S.A. , Halabl M. , Scholz R.
Published: June 2020

Transmission electron microscopy (TEM) was utilized to study the microstructural changes that take place as a result of treating gamma-alumina extrudates at various temperatures for different treatment times. The value of the study comes from the numerous uses of gamma-alumina, the most important being as a support for catalysts, and from its ability to obtain valuable submicron-level information related to pore structure by TEM. The pore characteristics of the extrudates were controlled through controlling the treatment process. Extrudates were heated in an autoclave at temperatures of 150, 200 and 300°C for treatment times of 1,2,4 and 8h.

A JEOL JEM-1200EX transmission electron microscope (TEM) operating at 120 kV was used. The TEM specimens were prepared by crushing the extrudates in a mortar and ultrasonically suspending the fine gamma-alumina powder in alcohol. The suspended particles were deposited on a perforated carbon film supported on a copper grid.
High-resolution studies of small metallic particles in supported catalysts
Authors: José-Yacamán M.
Published: June 2020

One of the key issues in the study of catalytic activity of small particles is the identification of surface sites in which reactions are promoted. This requires the characterization of the surface roughness. Profile HREM images has been used to characterize the surface of smal1 particles. This method has yield interesting information about surface reconstruction. In the study of supported catalysts, one has to deal with the contribution to the image from the (usually amorphous) substrate. A typical catalyst of Pt supported in γ-Al2O3 is shown in Fig. 1. The active part of the catalyst is the metallic particle. The thickness of the support is not known. Noise from the substrate makes surface profiling somewhat difficult. An alternative technique to study surface roughness is presented in this work. The method takes advantage of the fact that images of atomic columns are shifted as a function of the thickness. Fig. 2 shows a superposition of a calculated image for a cubo-octahedral at-300Å defocuss and the projected potential. The image clearly shows a shift on the images, which is mainly related to thickness changes (at a given defocuss). combining calculations with image processing of the High resolution photographs it is possible to obtain a very accurate information about surface topography.
Observation of catalytic Cu in methanol synthesis catalysts by atomic-resolution TEM
Authors: Schabes-Retchkiman P.S. , Rendon L.
Published: June 2020

Much effort has been done for the characterization of catalysts in which CuO is found together with ZnO and ZnO/alumina, since these combinations constitute catalysts for the synthesis of methanol by the hydrogenation of carbon monoxide. Active catalysts are obtained after reduction in hydrogen at pressures between 50-100 atm and 225° to 275° C. The activity of the catalyst is largely due to the strong interaction between the CuO and ZnO phases. It is clear however that it is copper in various valence states, that is responsible for the catalytic activity, with the ZnO probably acting as both a structural and chemical promoter. However there is still controversy regarding the active sites for catalysis. Several hypotesis have been put forward: 1) The reaction occurs at isolated Cu(I) cations dissolved in the ZnO lattice. 2) The reaction occurs primarily on the metallic Cu component of the catalysts.
High-Resolution Electron Microscopy of interfaces in TiAl alloys
Authors: Singh S.R. , Howe J. M.
Published: June 2020

Alloys based on TiAl are being considered as potential candidate materials for advanced aerospace applications. The interphase interfaces and twin interfaces in these alloys play important roles during deformation and can vary with ternary additions. Various HREM studies of interphase interfaces have been made in metallic systems during the last few years. When combined with image simulations, HREM has the capability of revealing local structural and compositional information. This investigation discusses HREM analyses of the crystallography of γ/α2 interfaces, twin interfaces and stacking faults in γ-TiAl with ternary additions of Mn and Ta.

The γ-TiAl alloys were solutionized at 1200°C for 2 hrs, isothermally aged for 24 hrs at 900°C in the α2+γ phase field and quenched. Thin foil specimens were polished in a 5% sulphuric acid/methanol electrolyte at -40°C and 20V. The samples were examined in Philips EM420T and JEOL 4000EX microscopes at 120 and 400 kV, respectively. Image simulations were perfomed with the TEMPAS multislice programs, using typical operating conditions for a JEOL 4000EX.
Direct imaging of segregation layers in Bi-doped Cu grain boundaries
Authors: Luzzi D.E.
Published: June 2020

Upon aging of a quenched-in super-saturated alloy at lower temperatures, the Bi segregates to the grain boundaries and ebritt1ement and faceting occur. Recent data suggest that the distribution of facet orientations for Σ = 3 misorientation grains evolves with aging at 600 C with a preference for the eventual formation of (-111)|(1-11) facets. Whereas the concentration of Bi on the facets and the macroscopic orientation of the facets has been established, little is known about the structure of these facets on the atomistic scale. In this abstract, the summarized results from a detailed analysis of the internal structure of a Σ = 3 (-111)|(1-11) grain boundary facet is presented and contrasted with the structure of a Σ = 3 (111) twin.
An EELS study of oxygen distribution in SiC(w)/Si3N4interfaces
Authors: Das Chowdhury K. , Carpenter R. W. , Weiss J. K. , Braue W.
Published: June 2020

The interfacial structure and composition of SiC(w)/Si3N4interfaces in ceramic composite are expected to influence the mechanical properties and may depend on processing variables. Whisker/matrix interfaces and matrix grain boundaries are beginning to be intensively investigated in these composites mainly, by HREM to determine the existence of glassy phase that may result from sintering aid reactions. We have shown that the glassy phase volume fraction appears to depend on the sintering aid added for full densification,and that oxygen could not be detected at fully crystalline interfaces by serial EELS (1). Other HREM observations led to emphasis on the continuous character of glassy thin films at all SiC/Si3N4interfaces (2). SiC(w) and SiC powders synthesized by different processes also contain different amounts of oxygen that may contribute to amorphous phase formation (3). Thus there are at least two important variables that can contribute to the amount and distribution of glassy phase in composites. Fully crystalline interfaces in these materials often exhibit a superimposed diffuse background intensity that may result from a very thin amorphous layer that cannot be fully resolved; this problem is further complicated by the requirement that the interfacial plane be atomically flat and tilted to contain the beam. In this paper we report first results of a high spatial resolution parallel EELS study of oxygen in these interfaces, and correlate the EELS results with HREM observations.
Investigation of Si/CoSi2/Si(001) interfaces formed by high-dose Co implantation using HREM and image simulations
Authors: Bulle-Lieuwma C.W.T. , de Jong A.F. , Vandenhoudt D.E.W.
Published: June 2020

Cobaltdisilicide has been the subject of much study, because of the good lattice matching with Si, its low resistivity, and the formation of atomically abrupt interfaces. Hetero-epitaxial Si/ CoSi2/Si structures are of interest due to their potential application as metal and permeable base transistors. We have synthesized mesotaxial CoSi2 films of aligned orientation by high-dose implantation of Co+ ions into Si (001) substrates followed by a high-temperature treatment of 30 minutes at 1000 °C. The Si wafers were implanted with 170 keV Co+ ions, with doses of 1 to 2 × 1017 Co+/cm2 , at an ion current density of 11 μA/cm2. The atomic structure of the CoSi2/ Si (001) interface has been investigated by high-resolution microscopy (HREM) combined with image simulations. The electronic properties of the CoSi2 films, such as the Schottky barrier height between the metal and the semiconductor, may be influenced by the atomic structure of the interface. Moreover, detailed knowledge of the atomic interface structure can give insight into mechanisms of silicide growth. Recently, Loretto et al. have shown that the structure of a CoSi2 /Si (001) interface grown by molecular beam epitaxy (MBE) is a 2×1 reconstruction of silicon dimers with bond length 0.23 nm, similar to the Si (001) 2×1 surface. This model (see fig. 1a) differs from that of Cherns et al. concerning NiSi2/Si (001), by the presence of an extra row of atoms at the interface. The additional Si atoms can form dimer chains, reducing the number of dangling bonds. This interface model projected along [110], is shown in Fig. 1a (see lower interface). The upper interface can be considered as a projection of the same structure along [10] .
Weak-beam electron microscopy of Σ =3 incoherent twin boundary in SUS316 austenitic stainless steel
Authors: Tanaka Koji , Mori Minoru , Ishida Yoichi
Published: June 2020

Weak beam (α-fringe) electron microscopy allows one to determine the Burgers vector of a grain boundary dislocation unambiguously. The rigid body translation or excess volume atomic displacements at the boundary between two ajacent crystals may be measured 3 — dimentionally by this method.

The specimen was commercial austenitic stainless steel SUS316, which was cold rolled to sheet specimen of about 0.2mm in thickness, annealed at 950°C for 2hr, and was furnance cooled to introduce annealing twins. The annealed specimen was polished electrically in 90% acetic acid and 10% perchloric acid solution at ice water temperature. The polished specimens were observed in a JEM-1250 high voltage electron microscope at 1000keV. The weak beam α-fringe changes only monotonously with displacement at weak beam common diffraction conditions. The translation term R is measured directly from the relative displacement of the extinction contour Δn at the interface. By the standard dynamical theory, the following equation can be derived:
High-resolution imaging of the (111) Ag/Ni interface
Authors: Gao Y. , Merkle K. L.
Published: June 2020

Computer simulations of Ag/Ni interfaces using embedded atom potentials have predicted that the interfacial energy of the (111) Ag/Ni interface is lowest. However, the semi-coherent interface configuration implied by these calculations has not been confirmed by experimental observation. It is well known that in heterophase systems with small misfit, the misfit is accommodated by misfit dislocations at the interface, forming a semi-coherent interface. However, it is not clear whether or not and to what degree misfit localization will occur at the interfaces with as large a misfit as 14% (Ag/Ni interface). The purpose of this investigation was to examine the atomic structure of the (111) Ag/Ni interface by high-resolution electron microscopy (HREM) and to compare the result to calculated images based on relaxed and rigid models.

Metal-metal composite thin films of Ni particles in a Ag matrix were produced by epitaxial growth on (110) NaCl substrates using a special technique described in detail elsewhere. HREM observations were performed using H-9000 at a Northwestern University operated at 300 kV. The images were obtained near optimum defocus without objective aperture. All image simulations were carried out using the multislice method with EMS program package.
Thermal vibrations in simulated ADF STEM
Authors: Loane R. F. , Silcox J.
Published: June 2020

Thermal vibrations reduce Bragg scattering, create a thermal diffuse background, and disrupt channeling, all of which may affect the ADF STEM signal. There are claims that thermal vibrations can change the relative contrast of different elements in the ADF STEM image, which is different from the simple Z- contrast interpretation. Evaluating the effects of thermal vibrations may be necessary for correct interpretation of experimental results. We present an investigation of ADF STEM imaging including thermal vibrations based on the frozen phonon model.

Thermal vibrations can be included in the multislice calculation with a Monte Carlo technique. Since, the interaction time for 100 keV electrons is ≤ 10-4 atomic vibration periods, the atoms may be considered stationary. The time between successive electrons in the STEM is ≥ 102 vibration periods, so the atomic positions seen by different electrons are uncorrelated. The technique is to offset every atom in the specimen (many slices) by a small random amount perpendicular to the beam before performing a standard multislice calculation. A set of random offsets freezes one phonon configuration into the specimen. The calculation is then repeated and averaged over an ensemble of different configurations.
Strain measurements using electron backscattering diffraction patterns
Authors: Dingley D J , Wilkinson A J , Burns G P
Published: June 2020

The Electron Backscatter Diffraction (EBSP) technique, first applied to the Scanning Electron Microscope by Venables and Harland and later by Dingley et al., is now widely used, particularly for crystal orientation determination , and for the determination of crystal symmetry,. Methods have also been sought to apply it for measurement of internal strain and this paper reviews and reports the findings. Plastic strain measurements from diffraction patterns obtained using the related selected area channelling technique have been widley reported and are reviewed in reference.

Elastic and plastic strain in crystals causes a shift in the diffraction line positions, line broadening, and a decrease in diffracted intensity. Measurement of these changes in EBSP is hindered by several problems peculiar to the method. As the patterns are formed by Bragg scattering of initially ine1 astica11y scattered electrons, there is a natural line broadening arising from an energy spread in the diffracted electrons amounting to 1% of the incident beam energy. This is compounded by the fact that the Bragg angle for diffraction is generally less than 2° and that dynamical diffraction effects result in the diffraction profiles being highly assymetric with long tails. Consequently there is considerable overlapp of profiles. Other problems arise from the gnomonic projection of the pattern producing a distortion which increase towards the edges of the pattern and from the need to tilt the specimen towards the recording film which produces further asymmetry in the line profile. Finally, surface contamination is observed to degrade the diffraction pattern reducing line intensity in much the same way as plastic strain.
Simulating the fine structure in HRTEM images of defects
Authors: Mills M. J.
Published: June 2020

The macroscopic properties of materials are often determined by the atomic structure of crystalline defects. High resolution transmission electron microscopy (HRTEM) enables the study of internal defects on the atomic scale. Image simulations represent an essential step in these studies since it is generally not possible to deduce the atomic positions near defects directly from the image intensities. Fortunately, image simulations which employ the multislice method and incorporate image formation theory for partially coherent illumination offer an accurate means of simulating images. With the availability of faster computers with larger memory capacity, the routine calulation of images of aperiodic defects is now feasible. This discussion will focus on the use of image simulations to extract structural information at defects, and to account for the artifacts which are frequently encountered in these studies.
HRTEM study of valleriite, a hydroxide-bearing copper sulfide
Authors: Wang S. , Buseck P. R.
Published: June 2020

Valleriite is an unusual mineral, consisting of intergrowths of sulfide layers (corresponding in structure to the mineral smythite - Fe9S11) and hydroxide layers (corresponding to brucite - Mg(OH2)). It has a composition of approximately 1.526[Mg.68Al.32(OH)2].[Fe1.07Cu.93S2] and consists of two interpenetrating lattices, each of which retains its individual structural and diffraction characteristics parallel to the layering. The valleriite structure is related to that of tochilinite, an unusual iron-rich mineral that is of considerable interest for the origin of certain carbonaceous chondrite meteorites and to those of franckeite and cylindrite, two minerals that are of interest because of their unique morphological and crystallographic properties, e.g., the distinctive curved form of cylindrite and the perfect mica-like cleavage with unusual striations and the long-period wavy structure of franckeite.

Our selected-area electron diffraction (SAED) patterns and high-resolution transmission electron microscope (HRTEM) images of valleriite provide new structural data. A basic structure and a new superstructure have been observed.
TEM study on dislocation structures of Al66Fe9Ti24 intermetallic alloy deformed at room temperature
Authors: Shipu Chen , Xiaohua Wu , Gengxiang Hu
Published: June 2020

The ordered intermetallic AL3Ti has potential for high temperature structural purpose, but is very brittle at ambient temperature. Recently much attention has been paid to the alloying of Al3Ti so as to change its tetragonal DO22 structure to cubic L12. The latter may have sufficient number of slip systems, and ductility improvement looks promising. Our investigation on the L12-type Al66Fe9Ti24 alloy has shown appreciable compressive ductility at room temperature. TEM study was undertaken to explore its deformation mechanism. The deformation mode was found to be the slip of dislocations instead of twinning in AL3Ti. Fig.1a shows a row of a[10
] superdislocations slipping in (111) glide plane and each of them dissociated into two partials. Contrast analysis delineated that the superpartials are of a/<211>-type. bounding a superlattice intrinsic stacking fault(SISF) with Rf=a/[111]. i.e. a[10
] → a/3[11
] + SISF + a/3[2
], The contrast effects of the partials and faults are typically given in Fig.1b and 1c.
Surface relaxation effect on diffraction contrast at Ni4W composite particles
Authors: Zhao H. , Weatherly G.C. , Aust K.T.
Published: June 2020

In TEM studies, difficulties may arise in understanding the image contrast of a defect if surface relaxation effects are not considered. It is desirable to calculate the displacement function which includes the effect from both the defect itself and surface relaxation in a thin foil whenever possible. A TEM study of the Ni4W phase in a Ni-37%wtW alloy has revealed the multivariant domain (MVD) structures of the Ni4W bet phase as the low energy configuration. Ni4W plates were composed of laths of perpendicular twins aligned along the <110>m direction with perpendicular twin boundaries (PTBs) parallel to the {110}m plane of the (Ni) fee matrix. At the MVD/matrix interface, anomalous diffraction contrast was observed under various two beam conditions when the sample was viewed along the <011>m direction with the MVD/matrix interface parallel to the beam direction. A typical example is shown in Fig. 1. This phenomenon can be attributed to a surface relaxation effect which is related to the alternating shear strain fields resulting from the formation of the MVDs.
Observation of small vacancy detect clusters produced by high- energy collision recoils
Authors: Proennecke Stephan , Victoria Max , Gotthardt Rolf , Horsewell Andy
Published: June 2020

The observation and analysis of small defect clusters produced by energetic particle irradiation is of importance in understanding the basic mechanisms of radiation damage. Renewed interest in fundamental studies stems from the need to understand very high energy recoil damage typical both of 14 MeV fusion neutrons and spallation neutrons produced around targets in high energy particle accelerators.

The defect clusters may be of vacancy or interstitial type. Vacancy clusters occur -as vacancy loops, stacking fault tetrahedra, or three dimensional void embryos. Interstitial clusters occur as interstitial loops or three dimensional clusters. For irradiations carried out at temperatures below that which vacancies are predominantly immobile, analysis of the vacancy component of the total defect cluster population may be used to document the cascade collision processes produced by high energy recoils. The information required is defect cluster type, defect size distribution, and defect density. Since the defects of interest are generally in the size range 0.5 - 5 nm, electron microscopy imaging and analysis techniques are currently being re-assessed.
Defects in ErSi2/Si(111) epitaxial films
Authors: Meneau D'Anterroches C.
Published: June 2020

Silicides are studied in electronic engineering for their good metallic properties. Among them the group of rare earth silicides shows particular properties. Indeed, some of them, including ErSi2, crystallize in the AIB2 structure although they do not have the exact stoechiometry, their composition being about 1.7. Thus the physical properties and the influence of vacancies on the structure are studied.

The film studied in this work was obtained by in-situ annealing, in ultra high vacuum, of a Si-Er film codeposited on a clean Si (111) substrate. Details are given by F. Arnaud d'Avitaya et al. The epitaxial relationship is (111 )Si//(001 )ErSi2 and (112)Si//(100)ErSi2. According to this orientation the lattice mismatch at the interface is - 1.3 %. The films were analysed using high resolution transmission electron microscopy : they are continuous when annealed at 900°C, and show some extra-spots in their diffraction patterns depending on the zone axis. Extra spots were observed along the {111} (3) and {112} zone axes, but not along {110} (4), We will focus in this paper on the {112}Si or {120}ErSi2 zone axis, the corresponding electron diffraction pattern being in Fig. 1.
TEM study of buried cobalt disilicide layers formed by ion implantation: Identification of cobalt monosilicide inclusions
Authors: De Veirman A. , Van Landuyt J. , Reeson K.J. , Gwilliam R. , Jeynes C. , Sealy B.J.
Published: June 2020

In analogy to the formation of SIMOX (Separation by IMplanted OXygen) material which is presently the most promising silicon-on-insulator technology, high-dose ion implantation of cobalt in silicon is used to synthesise buried CoSi2 layers. So far, for high-dose ion implantation of Co in Si, only formation of CoSi2 is reported. In this paper it will be shown that CoSi inclusions occur when the stoichiometric Co concentration is exceeded at the peak of the Co distribution. 350 keV Co+ ions are implanted into (001) Si wafers to doses of 2, 4 and 7×l017 per cm2. During the implantation the wafer is kept at ≈ 550°C, using beam heating. The subsequent annealing treatment was performed in a conventional nitrogen flow furnace at 1000°C for 5 to 30 minutes (FA) or in a dual graphite strip annealer where isochronal 5s anneals at temperatures between 800°C and 1200°C (RTA) were performed. The implanted samples have been studied by means of Rutherford Backscattering Spectroscopy (RBS) and cross-section Transmission Electron Microscopy (XTEM).
An Electron Microscopy study of the BaxLa1-xFeO3-x/2 (1/2≤x≤2/3) system
Authors: Parras M. , González-Calbet J.M. , Vallet-Regí M. , Grenier J.C.
Published: June 2020

In a previous paper we have shown that compositional variations in BaxLa1-xFeO3-y materials prepared in air. are accommodated in a different way than in other perovskite-related ferrites probably due to the bigger size of barium.

When oxidated BaxLa1-xFe3+,4+O3-y samples in the 1/2 ≤ x ≤ 2/3 range, are reduced by annealing at 1100°C for 24h. in flowing Ar-5%H2, all iron,as deduced from chemical analysis data, is found in the III state oxidation. Powder X-ray diffraction data in this range (La1/2Ba1/2FeO2.75-La1/3Ba2/3FeO2.67) can be indexed on the basis of a single cubic perovskite unit cell (ac ≃ 3.95Å)

In order to elucidate the way in which anionic vacancies are accommodated in these solids an electron diffraction (ED) and microscopy study was performed, similar results being obtained in both La1/2Ba1/2 FeO2.75 and La1/3Ba2/3FeO2.67samples.
Profiling semiconductor multilayer structures by CBED and CBIM techniques
Authors: Cherns D
Published: June 2020

Strain and composition profiles are of great importance in understanding properties of semiconductor multilayers, increasingly so as layer dimensions decrease. Recent advances in measuring these profiles have been achieved using convergent beam electron diffraction (CBED) and convergent beam imaging (CBIM) techniques. In both methods a converging incident beam allows us to map rocking curve information approximately parallel to the incident beam direction as the Ewald sphere is scanned through a given reflection. CBIM may be usefully compared with the large angle technique of CBED (LACBED). Both methods essentially utilise the same illumination condition with the incident probe brought to a focus in a plane appreciably removed from the specimen (fig 1). In CBIM an in-focus image of the specimen is recorded. In LACBED the object plane is that of the minimum probe and the diffraction pattern is recorded; this means that the illuminated area is mapped onto each diffraction disc. In both methods the smallest probe is important, defining the area of angular uncertainty (effectively angular resolution) in CBIM, and the spatial resolution in LACBED.
TEM cathodoluminescence of chemical vapor deposited diamond
Authors: Graham R.J. , Disko Mark M. , Moustakas T.D.
Published: June 2020

Diamond films grown by chemical vapor deposition (CVD) are curently of great interest with potential applications in semiconductors and as wear resistant coatings. In order to understand and optimize the growth and properties of these films, it is necessary to characterize their microstructure. While such techniques as TEM and cathodoluminescence (CL) (in a SEM) can be used independently to provide microstructural and optical/electronic information respectively, the direct correlation of these two pieces of information is highly desirable. This is possible using the TEM CL technique (CL in a TEM) because the electron transparent specimen allows a direct comparison of CL with microstructure. The preliminary results obtained for CVD diamond films by this technique are presented here.

The films examined were grown on a silicon (100) substrate by filament assisted CVD from a mixture of methane (2% vol.) and hydrogen at a pressure of 30 torr, using a tungsten filament operated at 1800°C.
The surface structure of GaAs(100) studied by RHEED and REM
Authors: Hsu Tung , Petrich G.S. , Cohen P. I.
Published: June 2020

Three GaAs( 100) samples, each grown on a differently misoriented GaAs( 100) substrate, were prepared using molecular beam epitaxy (MBE) and characterized by in situ reflection high energy electron diffraction (RHEED) and ex situ RHEED and reflection electron microscopy (REM): A: the substrate is 2° off the (100) toward [011] (A misorientation),

B: the substrate is 2° off the (100) toward (B misorientation), and

C: the substrate is within 0.1° of (100) (Fig. 1).

The goals were to compare the effects of MBE growth and oxidation on the different types of steps formed on these surfaces. Understanding the processes involved in promoting ordering of terrace lengths, and reduction of meandering and step bunching is crucial to current attempts to fabricate quantum wire structures.

Samples were prepared by chemically etching the substrates and then growing 0.2μm of GaAs at 600°C, at a rate of 0.4μm/h, and using a 3:1 As:Ga flux ratio. Shapes of the in situ RHEED spots were used to measure the step configuration while the oscillation of RHEED intensities was used to determine the thickness of the grown film.
Diffusion of TEM grid material into amorphous silicon films
Authors: Kritzinger S. , Lombaard J.C. , Bedeker C.J.
Published: June 2020

While investigating the silicide formation reaction between thin bilayers of amorphous Si (a-Si) and Cr, an unintended interaction occurred between the specimens and the supporting TEM grids. In an attempt to understand this phenomenon, the interaction between a single film of a-Si and TEM grids made of Cu, Ni, Au and Mo were investigated by in situannealing in a Siemens Elmiskop 101. The 60 nm films, prepared by e-beam evaporation of pure Si onto glass substrates, covered with an acetone-soluble release agent, were amorphous.

In Fig. 1 the interaction between the a-Si film and a Cu TEM grid is shown. Areas I, II, III and IV in (a) show different stages of the interaction, area IV being closest to the Cu grid bar, and area I being pure a-Si. The reaction started at about 600°C by crystallisation of the a-Si film at different spots in contact with the grid bars, and fanned out from these nucleation sites (area II).
TEM and DSL photoetching investigations of Si-implanted LEC GaAs substrates
Authors: Frigeri C. , Weyher J. L. , De Potter M.
Published: June 2020

Combined use of TEM and DSL photoetching (Diluted Sirtl-like etchant with Light) has been employed to investigate the origin of DSL etch features in ion implanted GaAs. The undoped, semi-insulating (001) LEC GaAs wafers were implanted with 29Si with fluences varying between 1.5-1012 and 3.0-1014 at/cm2. After implantation, rapid thermal annealing (RTA) was carried out at 900 °C for 10 s.

The implantation damage was revealed by DSL in the form of microroughness in both as-implanted and annealed samples. The degree of microroughness varied according to the implantation dose and to whether the sample was as-implanted or annealed. A calibration by TEM was, thus, carried out in order to establish the nature of the underlying defects and the threshold implantation dose for their formation. To avoid the influence of the as-grown dislocations on the formation of the DSL etch features due to ion implantation, a shallow DSL photoetching was used as a preliminary step in the thin foil preparation procedure for TEM to clearly mark the dislocation cell structure. TEM observations were then performed inside the dislocation cells only.
Transmission Electron Microscopy characterization of epitaxial III-V semiconductor thin films grown on Si(100) by ion-assisted deposition
Authors: Hultman L. , Choi C.-H. , Kaspi R. , Ai R. , Barnett S.A.
Published: June 2020

III-V semiconductor films nucleate by the Stranski-Krastanov (SK) mechanism on Si substrates. Many of the extended defects present in the films are believed to result from the island formation and coalescence stage of SK growth. We have recently shown that low (-30 eV) energy, high flux (4 ions per deposited atom), Ar ion irradiation during nucleation of III-V semiconductors on Si substrates prolongs the 1ayer-by-layer stage of SK nucleation, leading to a decrease in extended defect densities. Furthermore, the epitaxial temperature was reduced by >100°C due to ion irradiation. The effect of ion bombardment on the nucleation mechanism was explained as being due to ion-induced dissociation of three-dimensional islands and ion-enhanced surface diffusion.

For the case of InAs grown at 380°C on Si(100) (11% lattice mismatch), where island formation is expected after ≤ 1 monolayer (ML) during molecular beam epitaxy (MBE), in-situ reflection high-energy electron diffraction (RHEED) showed that 28 eV Ar ion irradiation prolonged the layer-by-layer stage of SK nucleation up to 10 ML. Otherion energies maintained layer-by-layer growth to lesser thicknesses. The ion-induced change in nucleation mechanism resulted in smoother surfaces and improved the crystalline perfection of thicker films as shown by transmission electron microscopy and X-ray rocking curve studies.
Investigation of single crystals and epitaxial layers (EL) Of SiC by means of real color SEM technique
Authors: Mokhov E.N. , Chukichev M.V. , Roenkov A.D. , Saparin G.V. , Obyden S.K. , Ivanov A.I.
Published: June 2020

Investigations were undertaken with SiC, a large-bandgap semiconductor material, that is rather promising for designing different optoelectronic devices. The characteristic feature of SiC is the availability of a large number of modifications, i.e. polytypes, strongly differing in the band-gap. The important problems that stand in the way of mastering SiC are the detectable doping of single crystals and epitaxial structures, the transformation of polytypes, and the structure of the intermediate layer. Crystals of SiC and its EL of 3C, 15R, 6H, 4H polytypes doped with N, Al, Ga and B were investigated. Single crystals were grown by the Leli method at T = 2600-2700°C as plates with basis planes {0001} . Epitaxial layers were grown by the sublimation "sandwich method" at T = 1700-2400°C in a vacuum or in an argon atmosphere.

An analysis of the luminescence micrographs in the SEM and of the CL spectra shows that the distribution of impurities and polytype inclusions in single crystals considerably differs from that in EL. In the first case there occurs a striated inhomogeneity of CL across the whole width of the crystal which is obviously connected with an inhomogeneous distribution of dopes. Such a distribution of impurities was not observed in EL.
Characterization of zinc diffusion induced disordering in GaAs/AlGaAs multiquantum well structures by Transmission Electron Microscopy
Authors: Bourqui B. , Buffat P. A. , Ganière J.D. , Reinhart F. K.
Published: June 2020

Diffusion of impurities, such as zinc or silicon, enhances the intermixing of Ga-Al atoms at GaAs/AlGaAs interfaces. This process is useful to modify the bandedge properties of multilayered structures such as (AlxGa1-xAs/GaAs). Important technological applications are due to this effect. Information about electronic states of the disordered structure is directly obtained by photoluminescence. The impurity induced disordering depth is, usually, estimated either by scanning electron microscopy (SEM) or by secondary ion mass spectroscopy (SIMS). We used transmission electron microscopy on wedge shaped specimen (WTEM) is used to obtain local information on the disordering depth and to check the chemical homogeneities of the diffused samples.

The multiquantum well structures (MQW) were grown by molecular beam epitaxy (MBE) on n doped [001] substrate at surface temperature of 600 °C. A specimen structure is given in Figure 1. Zinc diffusions were performed by using the sealed quartz tube method at 575°C. The ZnAs2 source provide sufficient partial pressure of arsine to maintain the surface at equilibrium.