bluuebunny/crossref_metadata_2025 huggingface dataset:
Modulated structures in (Bi,Pb)-Sr-Ca-Cu-O films
Authors: Ikeda Shozo , Hayakawa Hirotoshi , Dietderich Daniel R.
Published: June 2020

Pb addition makes easier to form the high Tc phase in the BSCCO system. However, Pb easily vaporized at high temperature. A controlled Pb potential method has been applied to grow the high Tc phase in films. Initially, films are deposited on cleaved MgO substrates using an rf magnetron sputtering system. These amorphous as-deposited films are heat treated in a sealed gold capsule along with a large pellet of Pb-added BSCCO. Details of the process and characterization of the films have been reported elsewhere (1). Films trated for 0.5h at 850° C contain mainly the low Tc phase with a small amount of the high Tc phase. Hawever, films treated for 3h at 850°C consist mainly of the high Tc phase. This film is superconductive with a Tc(zero) of 106K. The Pb/Bi ratio of the films, analysed by SEM- EDS, are 0.12 and 0.18 for heat tratment times of 0.5 and 3h, respectively. The present study investigates the modulated structures of these films using HREM.
Stacking variations in bulk Y2Ba4Cu8O16 materials
Authors: Alexander K. B. , Williams R. K. , Pennycook S. J.
Published: June 2020

The structure and properties of the Y2Ba4Cu6+nO14+n (n = 0,1,2) series of high temperature superconducting materials have recently been examined. The structural difference between these materials is the number of planes containing Cu-O chains that exist between the Ba-O layers. In YBa2Cu3O7−x (123), a single plane of Cu-O is observed, whereas in Y2Ba4Cu8O16 (124) two planes of Cu-O are present and result in a double square planar chain along the b-axis (Fig. 1). In the Y2Ba4Cu7O15 (247) structure, alternate single and double planes of Cu-O chains are observed. The advantages of the 124 materials are that the tetragonal-to-orthorhombic transformation observed in 123 materials does not occur and the difference between the a and b lattice parameters is one-half that of the 123 materials. It has also been reported that the oxygen stoichiometry is stable, probably due to the fact that the oxygen atoms in the double chains are bonded to three rather than two copper atoms. High oxygen pressures must be used to fabricate 124 in bulk form. Superconducting temperatures (Tc) up to approximately 90K have been observed in 124 materials with calcium additions.
On the 2√2 a × 2√2 a supestructure phase
Authors: Reyes-Gasga J.
Published: June 2020

Recently Reyes-Gasga et. al. have studied the superstructures phases produced by the ordering of vacancies (or oxygen) in the YBa2Cu3Ox, supercondutor compound. In these papers they also discussed briefly a posible interpretation of the diffraction pattern based on a square unit cell with edges 2√2 a × 2√2 a, where a=0.38nm (fig. 1e), and suggested that this pattern might not be due to a pure vacancy ordered structure but should presumably be attributed to a deformation modulated superstructure of a highly oxygen deficient perovskite phase. This diffraction pattern was studied previously in detail and it has been attributed to a number of oxygen vacancy ordered orthorhombic structures with different oxygen content. In this report I shall inform about some experiments concerning with the formation conditions and temperature behavior of the phase that produces this pattern.

Heating the YBa2Cu3O7, superconductor compound in situ in the TEM is possible to obtain not only diffuse streaks and superstructure spots unless also new arrays of superstructure spots. Therefore the experimental procedure consists in the in situ heating of this compound in the JEDL 200C TEM using a heating holder. It is well known that the exact temperature value in this kind of experiments is hard to specify and here only an average temperature range is reported.
Structural studies of small amorphous volumes by electron diffraction
Authors: Moine Pierre
Published: June 2020

Qualitatively, amorphous structures can be easily revealed and differentiated from crystalline phases by their Transmission Electron Microscopy (TEM) images and their diffraction patterns (fig.1 and 2) but, for quantitative structural information, electron diffraction pattern intensity analyses are necessary. The parameters describing the structure of an amorphous specimen have been introduced in the context of scattering experiments which have been, so far, the most used techniques to obtain structural information in the form of statistical averages. When only small amorphous volumes (< 1/μm in size or thickness) are available, the much higher scattering of electrons (compared to neutrons or x rays) makes, despite its drawbacks, electron diffraction extremely valuable and often the only feasible technique.

In a diffraction experiment, the intensity IN (Q) of a radiation, elastically scattered by N atoms of a sample, is measured and related to the atomic structure, using the fundamental relation (Born approximation) : IN(Q) = |FT[U(r)]|.
Multislice calculations for quasi-periodic and non-periodic objects
Authors: Herrera R. , Gómez A.
Published: June 2020

Computer simulations of electron diffraction patterns and images are an essential step in the process of structure and/or defect elucidation. So far most programs are designed to deal specifically with crystals, requiring frequently the space group as imput parameter. In such programs the deviations from perfect periodicity are dealt with by means of “periodic continuation”.

However, for many applications involving amorphous materials, quasiperiodic materials or simply crystals with defects (including finite shape effects) it is convenient to have an algorithm capable of handling non-periodicity. Our program “HeGo” is an implementation of the well known multislice equations in which no periodicity assumption is made whatsoever. The salient features of our implementation are: 1) We made Gaussian fits to the atomic scattering factors for electrons covering the whole periodic table and the ranges [0-2]Å−1 and [2-6]Å−1.
Crystallisation kinetics and microstructural evolution of Ni24Zr76 amorphous alloy
Authors: Ghosh G. , Chen F.R.
Published: June 2020

Apart from technological applications, scientifically amorphous —> crystal transformation is very important in understanding the atomic processes involved. For in-depth understanding of the crystallisation process, it is necessary to employ a combination of a number of experimental techniques. In this investigation, the details of the crystallisation of Ni24Zr76 amorphous alloy has been studied by differential scanning calorimtry (DSC), transmission electron microscopy (TEM) and high-resolution electron microscopy (HREM). This amorphous alloy undergoes eutectic crystallisation i.e., it transforms to (α-Zr) + NiZr2 crystals. It is our interest to study the kinetics of the crystallisation as well as the different steps involved in the evolution of equilibrium microstructure.

Ribbons of 2-3 mm wide and 25-30 μm thick were produced by melt-spinning technique. Dynamic as well as isothermal crystallisation were studied in a Du-pont DSC 910 cell coupled with computer controlled thermal analyser (TA9900) having system control and data acquisition capabilities.
Long-period modulated superstructures in Pd-12.5 at.%Ce and Pd-15 at.%Ce alloys
Authors: Kuwano Noriyuki , Itakura Masaru , Oki Kensuke
Published: June 2020

Pd-Ce alloys exhibit various anomalies in physical properties due to mixed valences of Ce, and the anomalies are thought to be strongly related with the crystal structures. Since Pd and Ce are both heavy elements, relative magnitudes of (fcc-fpd) are so small compared with  that superlattice reflections, even if any, sometimes cannot be detected in conventional x-ray powder patterns, where fee and fpd are atomic scattering factors of Ce and Pd, and  the mean value in the crystal. However, superlattices in Pd-Ce alloys can be analyzed by electron microscopy, thanks to the high detectability of electron diffraction. In this work, we investigated modulated superstructures in alloys with 12.5 and 15.0 at.%Ce.

Ingots of Pd-Ce alloys were prepared in an arc furnace under atmosphere of ultra high purity argon. The disc specimens cut out from the ingots were heat-treated in vacuum and electrothinned to electron transparency by a jet method.
Observation of discommensuration arrays in transition metal substituted TaTe4
Authors: Bennett J.C. , Boswell F.W. , Corbett J.M. , Prodan A. , Kohara S.
Published: June 2020

TaTe4 is a quasi-one-dimensional crystal in which chains of Ta atoms along the c-axis are centered within extended cages of Te atoms in square antiprismatic coordination. The subcell structure is tetragonal with axes (axaxc). At room temperature, the crystal is modulated by a commensurate charge-density wave (CDW) which gives rise to a supercell with axes (2ax2ax3c). Transition metal doping of TaTe4 causes the modulation to become incommensurate.

A series of mixed crystals (Ta1−xMx)Te with M = Nb, Ti or Zr have been examined using electron diffraction and electron microscopy. In each case, the modulation periodicity (as measured from the positions of the satellites in electron diffraction patterns) remains commensurate until a threshold concentration ( x ∼ .3 for Nb, ∼ .1 for Ti and Zr) is reached and then jumps discontinuously to an incommensurate value. Upon further substitution by Nb, the modulation periodicity varies with x, approaching that of NbTe as x approaches 1.0.
Toughening ceramics and Electron Microscopy
Authors: Hannink Richard H.J.
Published: June 2020

In the last one and a half decades great progress has been made in the development and understanding of tough ceramics. The principal advance has been in the micro- structural tailoring of ceramic systems and in this area electron microscopy has played a major role.

Increased toughness in ceramics is most readily achieved by mechanisms which reduce the effective driving force on a crack. Microstructural mechanisms which promote such reductions are said to impart “crack tip shielding” and ultimately R-curve behaviour. These mechanisms can generally be divided into two broad classes: process zone shielding and bridging or contact zone shielding. Phenomena which contribute to process zone shielding include transformation and micro-crack toughening while bridging or contact zone shielding includes fibre and whisker reinforcement. In reality however, a number of mechanisms will be operating within the same material.

This presentation will describe the development and microstructural aspects of, predominantly, process zone shielding mechanisms. The salient microstructural features for the successful application of fibre reinforced ceramics will also be described.
Study of surface plasmon excitation of nanometer size metallic particles in the STEM
Authors: Ouyang F. , Batson P. E. , Isaacson M.
Published: June 2020

The study of small particles or microclusters has been very active in recent years. When the particle size becomes smaller, its electronic properties deviate from those of bulk material and become size dependent. This phenomenon is referred to as the quantum size effect. In order to study the electronic states of small particles, the excitation energies of the surface plasmon (SP) have been measured by optical absorption spectroscopy and by broad beam angular resolved electron energy loss spectroscopy (EELS). Changes in the SP excitation energy were observed when the particle diameters were smaller than 40 Å.

With the high spatial resolution of the scanning transmission electron microscope (STEM), we hope to overcome the difficulties associated with effects of particle size distribution encountered in previous broad beam measurements. For particles with diameters ranging from 100 Å to 200 Å, the SP energy was found decreasing with decrease of the particle size.
AEM-investigations disclose the structure of metal-graphite reagents
Authors: Fürstner A. , Hofer F. , Weidmann H.
Published: June 2020

Compared to the great utility due to the high reactivity of metal-graphite compounds, found to be useful catalysts as well as most favourable reducing agents little was hitherto known of their structural features. The conflicting reports, viewing these reagents as products of intercalation on the one hand or merely as graphite supported finely dispersed metals on the other were seemingly resulting from factors such as the mode of preparation, work-up procedure, and last not least the limited reliability of a single analytical technique.

With the reduction of metal halides by potassium-graphite laminate (C8K) in THF a generally applicable method was at hand which readily and reproducibly allowed the formation of various kinds of metal-graphite combinations suitable for a comprehensive study by analytical electron microscopy in combination with X-ray diffraction (XRD) and photoelectron spectroscopy (XPS).
Atomic structure of internal interfaces in metals and alloys by HREM
Authors: Penisson J.M.
Published: June 2020

Internal interfaces (grain boundaries and interphase interfaces) are nearly always present in the real materials and their physical properties depend strongly on the structure of these interfaces. Solving this structure is then an important point in the understanding of the properties. For more than a decade High Resolution Electron Microscopy (HREM) has been employed in the study of interfaces and many examples can be found in the litterature (a review can be found in Ref. 1). Nowadays, many microscopes working at accelerating voltages from 200kV to 1MeV have a resolution power and stabilities which make the atomic imaging of internal interfaces in metals and alloys rather easy. This evolution leads to a much more precise determination of the atomic positions and their accurate comparison to calculated models mainly in the grain boundary field. Some models can then be discarded because they are really different from the experimental images. In some cases, the different models are so close that it is not possible to eliminate one or the other. In other cases,different structural units have clearly distinguished. The detection limit is now between 0.1 and 0.2Å. The same limitation is present when the translation of one crystal relative to the other one is measured even if sophisticated computer analysis is employed.
High Resolution Electron Microscopy of internal interfaces in layered materials
Authors: Ishida Yoichi , Ichinose Hideki , Takahashi Yutaka , Wang Jin-yeh
Published: June 2020

Layered materials draw attention in recent years in response to the world-wide drive to discover new functional materials. High-Tc superconducting oxide is one example. Internal interfaces in such layered materials differ significantly from those of cubic metals. They are often parallel to the layer of the neighboring crystals in sintered samples(layer plane boundary), while periodically ordered interfaces with the two neighboring crystals in mirror symmetry to each other are relatively rare. Consequently, the atomistic features of the interface differ significantly from those of cubic metals. In this paper grain boundaries in sintered high-Tc superconducting oxides, joined interfaces between engineering ceramics with metals, and polytype interfaces in vapor-deposited bicrystal are examined to collect atomic information of the interfaces in layered materials. The analysis proved that they are not neccessarily more complicated than that of simple grain boundaries in cubic metals. The interfaces are majorly layer plane type which is parallel to the compound layer. Secondly, chemical information is often available, which helps the interpretation of the interface atomic structure.
TEM-nanometer-area electron diffraction of interfaces in semiconductor superlattices
Authors: Tanaka Nobuo , Mihama Kazuhiro , Kakibayashi Hiroshi , Ito Kazuhiro
Published: June 2020

Recent progress of transmission electron microscope(TEM) enables us to perform electron diffraction from nm-sized areas(nano-diffraction) with a good correspondence with HREM. Nano-diffraction is useful for obtaining local structural information. One of the present authors (NT) applied the method to interfaces of GaAs/AlGaAs superlattices for detection of compositional variation of aluminum(Al) and to nm-sized γ-iron crystallites in MgO for analysis of the strain. Although nano-diffraction has been performed successfully in STEM instruments by Cowley and others, the method in TEM has an advantage in a good compatibility with the structure-imaging method and the established bright and dark-field(BF & DF) imaging methods. In the present paper we report for the first time the detection of lattice strain around interfaces of InP/InGaP strained superlattices as well as results of GaAs/InGaAs, GaAs/AlGaAs and Ge/Si superlattices by using the TEM nano-diffraction method.

The nano-diffraction was performed with 200 kV transmission electron microscopes of Cs = 1.2 mm(JEM-2000FX) and Cs = 0.5mm(JEM-2010L Before focusing an election probe, HREM and DF images of the interfaces were taken in the [100] zone axis at 100-400 k in direct magnification.
Misfit accommodation in epitaxial Ge films on Si
Authors: Chisholm M. F. , Pennycook S. J.
Published: June 2020

Electron microscopy is well suited for the study of the initial stages of misfit dislocation nucleation and of dislocation reactions. High-resolution Z-contrast imaging has the added advantages of producing intuitively interpretable images with chemical sensitivity. This technique has been used to study film formation and misfit accommodation in epitaxial Ge films grown on Si. The epitaxial Ge films studied herein were produced by steam oxidation of Ge-implanted (001) Si. The implanted Ge is rejected by the growing SiO2 layer and has no time to diffuse into the Si. The partitioned Ge forms a distinct strained epitaxial layer on Si. With this growth process the Ge films are constrained to grow layer-by-layer instead of the normally observed island mode. The growth morphology in turn governs the interfacial misfit dislocation nucleation, location, and character.

Figure 1 shows a cross-section view of a dislocation-free 5-nm thick Ge film on (001)Si produced by the oxidation of a Ge (2×l016 ions/cm2) implanted Si wafer. This is three to six times thicker than the observed critical thickness for Ge films grown on Si by more conventional growth processes. Ge normally grows as islands on Si and, after the equivalent of six monolayers of Ge is deposited, dislocations are introduced at the island parameters to relieve the misfit strains.
Growth of hematite on (0001) and {1102} sapphire substrates
Authors: Tietz Lisa A. , Summerfelt Scott R. , Barry Carter C.
Published: June 2020

Defects in thin films are often introduced at the substrate-film interface during the early stages of growth. The interface structures of semiconductor heterojunctions have been extensively studied because of the electrical activity of defects in these materials. Much less attention has been paid to the structure of oxide-oxide heterojunctions. In this study, the structures of the interfaces formed between hematite (α-Fe2O3) and two orientations of sapphire (α-Al2O3) are examined in relationship to the defects introduced into the hematite film. In such heterojunctions, the oxygen sublattice is expected to have a strong influence on the epitaxy; however, defects which involve only the cation sublattice may be introduced at the interface with little increase in interface energy.

Oxide heterojunctions were produced by depositing small quantities of hematite directly onto electrontransparent sapphire substrates using low-pressure chemical vapor deposition. Prior to deposition, the ionthinned substrates were chemically cleaned and annealed at 1400°C to give “clean”, crystalline surfaces. Hematite was formed by the reaction of FeCl3 vapor with water vapor at 1150°C and 1-2 Torr. The growth of the hematite and the interface structures formed on (0001) and {102} substrates have been studied by bright-field, strong- and weak-beam dark-field imaging techniques.
A survey of new electron-optical materials characterisation techniques
Authors: Spence J.C.H.
Published: June 2020

It is rare that the detection of a new signal from a solid-state system does not in time prove useful for materials characterisation. At the same time, the increasing number of detectors fitted to modem electron microscopes, their improved probe-forming capabilities and vacuum performance and the trend toward full digital control and data aquisition, together with the use of more self-explanatory human interfaces in software has greatly increased the number of useful signals and their combinations, making the modem electron microscope an extraordinarily powerful and versatile instrument for materials characterisation. We list below some of the more promising new ways in which the signals available from modem TEM/STEM and SEM instruments may be used in materials science.

1. Backscattered channelling imaging. By detecting elastically back-scattered electrons using an energy filter, striking diffraction contrast images of line and planar defects may be obtained from bulk samples. A field-emission SEM instrument is required for this work, operating at about 50 kV.The spatial resolution achieved is about 10 nm, the images come from a depth of less than about 100 nm, and atomically clean surfaces are not required.
TEM Z-contrast imaging with wide-angle hollow-cone illumination
Authors: Bentley J. , Alexander K. B. , Wang Z. L.
Published: June 2020

High resolution scanning transmission electron microscopy (STEM) images with contrast sensitive to atomic number (Z-contrast) have been obtained with the use of a high-angle annular detector. The equivalent conventional transmission electron microscopy (TEM) dark-field mode reciprocally related to Z-contrast STEM is wide-angle hollow-cone illumination with an on-axis objective aperture. There are two ways to obtain hollow cone illumination; with an annular condenser aperture or by conically scanning the beam tilt coils. As in the case of STEM Z-contrast imaging, resolution with hollow-cone illumination should theoretically be higher than for phase contrast imaging in the same instrument.

Philips CM30/STEM, CM12/STEM, and EM400T/FEG/STEM instruments have been used to investigate this imaging technique. The conical illumination dark-field mode is standard on the CM series and was implemented with a hybrid diffraction unit on the EM400. Commercial (SPI Supplies #1780) copper annular apertures with inner and outer diameters of 600 and 900 μm, respectively, spot welded to suitable supports for use as condenser apertures, resulted in cone angles too small to give good Z-contrast in the microprobe mode, because there is still a large diffraction contrast contribution.
A new approach to study diffuse scattering
Authors: Zhu Yimei , Suenaga M. , Sabatini R.L.
Published: June 2020

A new approach combining high resolution electron microscopy with computer imaging techniques is used to study streaking of electron diffuse scattering. It was found that this newly developed technique has many merits for studying modulated structures. It can form images directly from the weak diffuse scattering intensity representing a small area on the order of several nm and with less double diffraction effect as compared with the selected area diffraction (SAD). The diffractogram produced has no artifacts from a hard aperture and can show much more detail as compared with the optical diffraction technique.

This technique is based on analyzing a HREM image intensity. Fig. 1 is an example of study involving tweed structure, which exhibits a roughly periodic cross-hatched contrast in morphology associated with streaks in diffraction in Fe doped YBa2Cu3O7 [see inset of Fig. 1(a)]. Since the streak is short and its intensity is weak, it is not possible to form a dark-field image from the streak in an electron microscope. Nevertheless, with this new technique, we can form an image by Fourier transforming the streak. Shown in Fig. 1(a) is a digitized image from a HREM micrograph negative using an Eikomix camera and the SEMPER program. The digitized image was then Fourier-transformed to form a diffractogram. By placing small windows around all fundamental spots including all streaks, a subsequent inverse transformation strongly suppressed the non-periodic noise in the image.
Imaging with plasmon energy loss electrons
Authors: Xiaofeng Duan , Anyan Du , Chu Y. M.
Published: June 2020

Collision of electron with the specimen in electron microscope are either elastic or inelastic. There are mainly two types of characteristic energy loss: the plasmon energy loss and the inner shell ionization loss. In metals and semiconductors the plasmon energy loss Ep is proportional to , where Nf is the number of free electrons in unit volume. Normally Ep is 10 - 20 eV and the plasmon peak in EELS is well defined. In insulators, the plasmon peak usually has a broad maximum in the range 20-30eV. If the separation of plasmon peaks of species in a multi-phase sample is large enough, they can be distinguished by means of energy filtered imaging technique. In this paper we report two examples to illustrate the ability of this method in material science. The machine used is a TEM Opton CEM 902 at 80 kV.

The first example is a-Si:H/C:H superlattice sample. Fig. 1a shows the CTEM image. Fig. 1b and 1c show the inelastic images. The energy window are set at about the plasmon energy loss of Si( E = 16 eV) and a-carbon( E=26 eV respectively. In Fig.1b the bright strips are a-Si layers.
Diffraction contrast of dislocations in icosahedral quasicrystals
Authors: Urban K. , Zhang Z. , Wollgarten M. , Gratias D.
Published: June 2020

Recently dislocations have been observed by electron microscopy in the icosahedral quasicrystalline (IQ) phase of Al65Cu20Fe15. These dislocations exhibit diffraction contrast similar to that known for dislocations in conventional crystals. The contrast becomes extinct for certain diffraction vectors g. In the following the basis of electron diffraction contrast of dislocations in the IQ phase is described. Taking account of the six-dimensional nature of the Burgers vector a “strong” and a “weak” extinction condition are found.

Dislocations in quasicrystals canot be described on the basis of simple shear or insertion of a lattice plane only. In order to achieve a complete characterization of these dislocations it is advantageous to make use of the one to one correspondence of the lattice geometry in our three-dimensional space (R3) and that in the six-dimensional reference space (R6) where full periodicity is recovered . Therefore the contrast extinction condition has to be written as gpbp + gobo = 0 (1). The diffraction vector g and the Burgers vector b decompose into two vectors gp, bp and go, bo in, respectively, the physical and the orthogonal three-dimensional sub-spaces of R6.
Characterization of the inverted tetrahedral twin particles in the heteroepitaxial KNbO3 thin films
Authors: Rou Shang H. , Hren John J. , Hren Philip D. , Graettingcr Thomas M. , Ameen Michael S. , Aucicllo Orlando , Kingon Angus I.
Published: June 2020

Perovskite potassium niobate (KNbO3) possesses good electrooptic properties for modulated channel waveguide applications, Epitaxial KNbO3 thin films were deposited onto (100) MgO substrates using an ion beam sputtering technique equipped with a novel computer-controlled rotating target holder , Conventional transmission electron microscopy (TEM) and high resolution transmission electron microscopy (HRTEM) were employed to perform defect structure and microstructure analysis. Special TEM sample preparation procedures have been developed, which will be reported elsewhere, Tetrahedral twin particles (TTP's) were observed in the epitaxial KNbO3 thin films. Since, the orientation difference between the TTP's and the matrix may affect the polarization switching properties, it is essential to understand their origin and eliminate them if possible.

A selected area diffraction pattern of a KNbO3 thin film taken along the substrate (012) (figure 1) reveals twin and double diffraction spots. The mirror planes are determined to be of the {211} family. Figure 2(a) shows the electron diffraction pattern taken along the substrate (100). Twin spots coincide with some of the matrix spots indicating that the twin also maintains an epitaxial relationship with the MgO substrate. The orientation relationship between the twins and the matrix is [221]twin//[100]matrix.
A study on sink strength of dislocations through analyses of loop formation process under defect concentration gradient
Authors: Nakai Kiyomichi , Kinoshita Chiken
Published: June 2020

The behavior of point defects around sinks has been greatly investigated for evaluating their bias effects on void formation and swelling. It is, however, laborious to estimate sink strength connected with the bias, because it depends greatly on the sink character. In the present paper the sink strength for interstitials is confirmed through analyses of nucleation and growth process of dislocation loops around characterized dislocations under electron irradiation.

A Nb-40.0wt.%Zr alloy having the interface between bcc structures of βNb and βZr phases was irradiated with 1MeV electrons in the JEM-1000 high-voltage electron microscope at the HVEM Laboratory, Kyushu University.

The orientation relationship between βNb and βZr phases follows the cube/cube, and the interfaces are. The interface dislocations run parallel to [111] and at a regular interval and respectively have Burgers vectors of b = 1/2 and 1/2[111]. Misfit between the phases as well as distance between interface dislocations are also confirmed by dark-field microscopy, trace analysis and electron diffraction.
On the interpretation of dislocation-loop growth during in-situ high-voltage Electron Microscopy
Authors: Holzäpfel E. , Phillipp F. , Wilkens M.
Published: June 2020

During in-situ radiation damage experiments aiming on the investigation of vacancy-migration properties interstitial-type dislocation loops are used as probes monitoring the development of the point defect concentrations. The temperature dependence of the loop-growth rate v is analyzed in terms of reaction-rate theory yielding information on the vacancy migration enthalpy. The relation between v and the point-defect production rate P provides a critical test of such a treatment since it is sensitive to the defect reactions which are dominant. If mutual recombination of vacancies and interstitials is the dominant reaction, vαP0.5 holds. If, however, annihilation of the defects at unsaturable sinks determines the concentrations, a linear relationship vαP is expected.

Detailed studies in pure bcc-metals yielded vαPx with 0.7≾×≾1.0 showing that besides recombination of vacancies and interstitials annihilation at sinks plays an important role in the concentration development which has properly to be incorporated into the rate equations.
Effects of krypton ion irradiation on the structure and morphology of germanium — An in situ TEM study
Authors: Wang L.M. , Birtcher R.C.
Published: June 2020

Although it was initially thought that irradiation could not further damage an amorphous material, an anomalous ion-induced morphological instability on the surface of amorphous Ge has been reported previously by several authors. In this study, the structural and morphological changes of Ge were monitored during 1.5 MeV Kr ion irradiation by in situ TEM to obtain insight into the damage evolution in ion-irradiated Ge.

The in situ study was performed on the HVEM-Tandem Accelerator Facility at Argonne National Laboratory. The facility consists of a modified Kratos/AEI EM7 high voltage electron microscope (HVEM) and a 2 MV tandem ion accelerator. The samples were jet-polished polycrystalline Ge (99.99999 at. % pure) TEM discs with grain size > 5 μm in dimension. The Kr ion irradiation was carried out at room temperature, and the electron energy of the HVEM was 300 kV. According to a TRIM computer simulation, over 99% of the Kr ions penetrate through the electron transparent areas of the Ge sample, and a dose of 1×1015 Kr/cm2 created an average of ∽4 displacements per atom and an average Kr concentration of ∽12 appm in the observation region of the sample.
Dynamic observation of dislocation generation in rapidly solidified titanium - 4 wt% cerium
Authors: Wittig J.E.
Published: June 2020

Dynamic observation of dislocation generation and/or motion in the transmission electron microscope is possible for a variety of experimental conditions. In situ straining and heating experiments are traditional methods for observing dislocation interactions caused by deformation, phase transformations, and large differences in thermal expansion coefficients (e.g. metal matrix composites). In addition to external stimuli, the electron beam can also influence defect formation and movement. High voltage electron irradiation has become a standard technique to simulate radiation damage, and for the special case of CdTe, electron beam induced heating has been used to record movement of partial dislocations at lattice resolution.

In the current study, the interaction of 200 kV electrons with Ce rich precipitates has been observed to induce dislocation generation and movement in Ti-4wt%Ce alloys. The microstructural condition required for this observation has only been achieved by rapid solidification of an undercooled liquid.
An environmental cell Transmission Electron Microscope
Authors: Dewald D.K. , Lee T.C. , Eades J.A. , Robertson I.M. , Bimbaum H.K.
Published: June 2020

The ability to observe directly and at high spatial resolution the interactions between environments and materials affords the material scientist new and unique opportunities. This capability is realized in the Environmental Cell Transmission Electron Microscope Facility which has been installed as part of the Center for Microanalysis of Materials at the Materials Research Laboratory of the University of Illinois at Urbana-Champaign.

The Facility is based on a JEOL 4000EX equipped with a specially designed pole piece. An aperture limited, differentially pumped, environmental cell has been installed in this pole piece. The system is shown schematically in Figures 1 and 2. Figure 1 is a plan view of a section through the objective lens pole-piece, with the microscope axis perpendicular to the plane of the paper, showing the cell enclosing the sample rod, the gas handling system and the location of the magnetically levitated Turbo-Molecular pumps. Figure 2 shows a cross-sectional view of the environmental cell and the gas handling system. As shown in Figure 2 the electron beam passes through a series of five apertures which allow the column vacuum to be maintained while the cell pressure is increased. The actual cell apertures are located at the apex of cones to minimize the gas path length, allow maximum tilt and still permit high- angle diffraction data to be obtained. Differential pumping of the cell is achieved by the four turbo- molecular pumps, the location of which can be seen in the Figures. With this arrangement the environmental cell is capable of supporting 400 torr of N2 gas which has no noticeable effect on the microscope operation. This allows the microscope to be operated with a LaB6 filament. The gas handling system was designed to handle a variety of environments including corrosive ones.
Surface nucleated half-loops in strained epilayers
Authors: Kvam Eric P.
Published: June 2020

Mismatched epilayers, grown beyond some critical thickness, have commonly been observed to have arrays of misfit-relieving dislocations at the heterointerface. In diamond or sphalerite structures, these arrays are orthogonal <110> networks of long 60° type dislocations, which are glissile and have inclined Burgers vectors. Up to the point at which growth becomes three-dimensional (about 2% mismatch in the (In,Ga)As/GaAs system), internal defects act as the sources for the misfit dislocations. Examples of such sources include pre-existing threading dislocations, internal loops, precipitates, and mechanical damage.

In higher mismatch two-dimensional growth, such as can be produced in the GeSi/Si(001) system, the density of epithreading dislocations suddenly increases as the length of interfacial misfit dislocations falls. Almost simultaneously, the misfit dislocation type changes from 60° to edge. While in-situ hot stage experiments have shown that 60° type dislocations become mobile at about the growth temperature of the epilayer, and have observable velocities from this temperature on up, our observations of edge dislocations in the same system have shown that velocities for edge dislocations are essentially nil (measurable limit <lnm/s) even at 750°C, some 200°C above the growth temperature.
Anisotropy of interfacial defects in the initial stage of MOVPE GaAs growth On Si
Authors: Vannuffel C. , Schiller C. , Chevalier J. P.
Published: June 2020

Recently, interest has focused on the epitaxy of GaAs on Si as a promising material for electronic applications, potentially for integration of optoelectronic devices on silicon wafers. The essential problem concerns the 4% misfit between the two materials, and this must be accommodated by a network of interfacial dislocations with the lowest number of threading dislocations. It is thus important to understand the detailed mechanism of the formation of this network, in order to eventually reduce the dislocation density at the top of the layers.

MOVPE growth is carried out on slightly misoriented, (3.5°) from (001) towards , Si substrates. Here we report on the effect of this misorientation on the interfacial defects, at a very early stage of growth. Only the first stage, of the well-known two step growth process, is thus considered. Previously, we showed that full substrate coverage occured for GaAs thicknesses of 5 nm in contrast to MBE growth, where substantially greater thicknesses are required.
Scanning-DLTS and TEM-investigations in Lec-GaAs: New arguments on the EL2-generation mechanism
Authors: Breitenstein O. , Fornari R. , Frigeri C. , Gleichmann R. , Heydenreich J.
Published: June 2020

Scanning-DLTS (SDLTS) uses the focused electron beam of a SEM to locally excite deep levels in semiconductor space charge structures (Schottky-diodes or pn-junctions). This results in rf-capacitance changes of the sample, which are detected as a function of temperature by a specialized high-sensitive DLTS-spectrometer leading to a measure of the local concentration of energetically well-defined deep level defects. The detection limit of this technique, hitherto being around 1013cm-3 for a spatial resolution of a few microns, exceeds that of most of the other microanalytical tools by several orders of magnitude.

LEC-GaAs crystals have been grown from melts with a Ga/As-fTaction from varying e.g. from 1.05 at the top to 1.35 at the bottom of the crystals. Thus, the decisive position-dependent parameter of the material was the melt-stoichiometry. TEM-investigations revealed the grown-in dislocations and of perfect (interstitial-type) discolation loops, both being decorated with As-rich precipitates(Fig. 1).
Electron beam induced current study of thin silicon layers on insulator substrate
Authors: Buczkowski A. , Radzimski Z. J. , Russ J. C. , Rozgonyi G. A.
Published: June 2020

If a thickness of a semiconductor is smaller than the penetration depth of the electron beam, e.g. in silicon on insulator (SOI) structures, only a small portion of incident electrons energy , which is lost in a superficial silicon layer separated by the oxide from the substrate, contributes to the electron beam induced current (EBIC). Because the energy loss distribution of primary beam is not uniform and varies with beam energy, it is not straightforward to predict the optimum conditions for using this technique. Moreover, the energy losses in an ohmic or Schottky contact complicate this prediction. None of the existing theories, which are based on an assumption of a point-like region of electron beam generation, can be used satisfactorily on SOI structures. We have used a Monte Carlo technique which provide a simulation of the electron beam interactions with thin multilayer structures. The EBIC current was calculated using a simple one dimensional geometry, i.e. depletion layer separating electron- hole pairs spreads out to infinity in x- and y-direction. A point-type generation function with location being an actual location of an incident electron energy loss event has been assumed. A collection efficiency of electron-hole pairs was assumed to be 100% for carriers generated within the depletion layer, and inversely proportional to the exponential function of depth with the effective diffusion length as a parameter outside this layer. A series of simulations were performed for various thicknesses of superficial silicon layer. The geometries used for simulations were chosen to match the "real" samples used in the experimental part of this work. The theoretical data presented in Fig. 1 show how significandy the gain decreases with a decrease in superficial layer thickness in comparison with bulk material. Moreover, there is an optimum beam energy at which the gain reaches its maximum value for particular silicon thickness.
Cross-sectional observation of LSI by high resolution TEM
Authors: Song Minghui , Hashimoto Hatsujiro , Yokota Yasuhiro , Matsukawa Takayuki , Ajika Natsuo , Ogo Ikuo
Published: June 2020

A high density A mega bits DRAM (dynamic random access memory) which was named as FASIC (folded bit line adaptive side wall isolated capacitor cell) was made and reported in 1986. The cell has been fabricated on P-type Si single crystal substrate as four layers (one poly-Si, two poly-silicides and one Al layer) and has a size of 2.6μm × 4.2μm (one million cells in 2.6mm × 4.2mm).

Figure 1 shows a light micrograph of a part of FASIC DRAM 6-inch wafer. The unit chip of the circuit in the wafer which is a square of 15mm × 15mm are shown by a circle A. The region indicated by B is the circuit for testing the memory cells and the ones indicated by C and D have 2M and AM memories in 7.5mm × 5mm and 15mm x 5mm respectively. AA' and BB' show two directions rectangular each other. Figure 2 shows schematically the cross-section along AA' direction, which parallel to bit line (BL). The cross sections of word line (WL), A1 line contact and trench (capacitor) are shown. The word line is vertical to bit line and parallel to BB' direction shown in Figure 1.
Electron Microscopy investigations of buried Si3N4 isolation layers
Authors: Maksimov S.K. , Kukin V.N.
Published: June 2020

Formation of buried Si3N4 layers obtained by using repeated cycles of implantation and annealing has been investigated. Structure investigations were made with the use of a CM30 Twin electron microscope (whose diaphragm is 0.18 nm-1 ). In HREM studies, axial micrographs in Si reflections of the 000, 111 and 220 types were employed. Two types of samples were used: "plane view" samples and those of a "cross section". Si3N4 precipitates were identified by application of the EELS method on the LN and Lsiedges.

N+ - ions were implanted into silicon wafers (of p-type, (001), 10 Ω cm) at a room temperature- The dose pf ions implanted in each cycle was 5.1010 cm-2 . The total dose was 5.1017 cm-2 , The energy of ions - 150 keV, the current density of the ion beam 25 μA/cm-2 . Annealing in the atmosphere of nitrogen was made at 1100° C which lasted 2 hours after the first cycle of implantation; in the other cycles it lasted 0.5 hours at 850° C. After the operation of ion beam synthesis was completed a silicon epitaxial layer 0.8-1 μm thick was grown.
Study on microstructures of As+ implanted Ti-Si bilayers with micro-micro beam technique
Authors: Shao Beiling , Liu Ansheng , Yuan Jianming , Ding Furong
Published: June 2020

A basic understanding of structures of Ti silicide—Si bilayers formed by ion implantation is of considerable interest because of the increasing application of MOS in VLSI. The aim of the present investigation is to explore the effect of ion implanting conditions on structures in Ti-Si bilayers. Rubloff et al. and Holloway et al. have studied Ti—Si interfaces and suggested that two processes may occur at Ti-Si interfaces, a reaction process other than silicide formation and a grain boundary diffusion process leading to localized silicide formation in the grain boundaries. The reaction processes in Ti—Si bilayers implanted by As+ ions were investigated in this work. An analytical electron microscope (JEOL 2000FX - LINK SYSTEM) with micro—micro beam (MMB) technique was employed.

66nm Ti films were deposited onto P type <100> orientated Si substrates with a sputtering system at room temperature and the Ti-Si bilayers were implanted with 250 and 300 KeV and 1016 As+/cm2 respectively.
CBED study of strain in InGaAs/GaAs strained layer superlattices
Authors: Xie Q.H. , Fung K.K.
Published: June 2020

In this paper, we have studied the strain in InGaAs/GaAs superlattices by using CBED. Some authors have started similar reseach in SLSs and epi-layers. Our samples are grown by MOVCVD on exact [001] GaAs substrates with alternate InGaAs layers and GaAs layers. Plan-viewed specimens are prepared by ion-milling from the back side. All our experiments are carried out in regions without dislocations, which can be considered as free superlattices. Phillips EM 430 is used to take the CBED ZAP at 100kV.

Using CBED technique, we obtain distribution of intensity of sidebands in two kinds of SLSs InGaAs(100Å)/GaAs(200Å) (Sample A) and InGaAs(150Å)/GaAs(150Å)(Sample B) all with 6% In content. Intensity of HOLZ lines can be got by kinetic calculation because of large extinction distance of these reflections. ϕg is expressed as folows:
TEM investigation of lattice-matched In0.53Ga0.47 as layers grown on InP by low-pressure metalorganic vapor-phase epitaxy
Authors: Sung C.M. , Ostreicher KJ. , Abdalla M. , Kenneson D.G. , Powazinik W. , Hefter J.
Published: June 2020

High-quality defect-free In0.53Ga0.47 As thin film layers lattice matched to InP are important materials for the efficient operation of many optoelectronic devices used in long wavelength communication systems. The presence of defects in these devices is known to have a marked effect on their performance and long-term reliability. The In0.53Ga0.47 As layers reported here were grown by a low-pressure metalorganic vapor phase epitaxy method using tertiarybutylarsine as the As precursor; the layers were found to have high mobility and low background carrier concentrations. The aim of the present work is to investigate the microstructure, ordering, and degree of lattice misfit between the epitaxial In0.53Ga0.47 As layer and the InP using cross-sectional TEM (XTEM) and convergent beam electron diffraction (CBED) methods.

A bright-field TEM image (Philips EM400T, 120 keV) taken in the cross-sectional view shows the In0.53Ga0.47As layer, a thin InP buffer layer (≈0.05μm), and the InP (Fe-doped) substrate (Figure 1). The dark cluster-like regions in the InP substrate are Fe-rich (confirmed by EDX).
TEM studies of fine low dimensional modulated fringes (FLDMF) in GaAs/Ga1-xAlx As multilayer heterojunction structure grown by MBE
Authors: Fan Rongtuan
Published: June 2020

The characteristics of GaAs/Ga1-x Alx As superstructure grown by MBE are always noticed. Recently, as well known, cross-sectional trasmission electron microscopy (XTEM) has been used and many workers have observed the superstructure(multilayer heterojunction structure) of GaAs/Ga1-x Alx, As hetero-multilayer. They usually observed a wide fringes with several nanometers or even more in GaAs/GaAlAs multilayer structure.In this work, we have studied a phenomenon which was named"Fine Low Dimensional Modulated Fringes" of GaAs/GaAlAs heteromutilayer structure grown by MBE, using XTEM technique. It is found that the FLDMFs are an equal width and very narrow, the order of Å’s.

The GaAs/GaAls layers that are examined were grown on (001) GaAs substrate by MBE. Cross-section TEM specimens with a wafer cleaved along (110) plane were prepared, and thinned by argon ion.

A typical structure is given in Fig.l, the image is of superlattice(SL) and Fine Low Dimensional Modulated Fringes area of MBE grown GaAs/GaAlAs heteromutilayer.