bluuebunny/crossref_metadata_2025 huggingface dataset:
TEM study of order, structure and defects of β and martensite in Cu-Al-Mn shape memory alloys
Authors: Guilemany J.M. , Peregrin F.
Published: June 2020

The shape memory effect (SME) shown by Cu-Al-Mn alloys stems from the thermoelastic martensitic transformation occuring between a β (L2,) metastable phase and a martensitic phase. The TEM study of both phases in single and polycrystalline Cu-Al-Mn alloys give us greater knowledge of the structure, order and defects.

The alloys were obtained by vacuum melting of Cu, Al and Mn and single crystals were obtained from polycrystalline alloys using a modified Bridgman method. Four different alloys were used with (e/a) ranging from 1.41 to 1.46 . Two different heat treatments were used and the alloys also underwent thermal cycling throughout their characteristic temperature range -Ms, Mf, As, Af-. The specimens were cut using a low speed diamond saw and discs were mechanically thinned to 100 μm and then ion milled to perforation at 4 kV. Some thin foils were also prepared by twin-jet electropolishing, using a (1:10:50:50) urea: isopropyl alcohol: orthophosphoric acid: ethanol solution at 20°C. The foils were examinated on a TEM operated at 200 kV.
Observations on the structure at the transformation interface of pearlite in steel
Authors: Khalid F. A. , Edmonds D. V.
Published: June 2020

The austenite/pearlite growth interface in a model alloy steel (Fe-1 lMn-0.8C nominal wt%) is being investigated. In this particular alloy pearlite nodules can be grown isothermally in austenite that remains stable at room temperature, thus facilitating examination of the transformation interfaces. This study presents preliminary results of thin foil TEM of the austenite/pearlite interface, as part of a programme of aimed at studying alloy carbide precipitation reactions at this interface which can result in significant strengthening of microalloyed low- and medium- carbon steels L Similar studies of interface structure, made on a partially decomposed high- Mn austenitic alloy, have been reported recently.

The experimental alloys were made as 50 g argon arc melts using high purity materials and homogenised. Samples were hot- rolled, swaged and machined to 3mm diameter rod, solution treated at 1300 °C for 1 hr and WQ. Specimens were then solutionised between 1250 °C and 1000 °C and isothermally transformed between 610 °C and 550 °C for 10-18 hr and WQ.
An Electron Microscopical study of an incoloy 800H pipe used in the petrochemical industry
Authors: Tekin Erdoğan
Published: June 2020

Alloy 800 is a family of fully austenitic Fe-Ni-Cr alloys containing minor amounts of C, Al and Ti. These alloys are used for high temperature applications as they have good creep properties.Incoloy 800H is a high carbon version (0.07%C) and is used extensively in the petrochemical industry. Most of the information on incoloy 800H concerns microstructural changes that occur below 850°C and there is hardly any study available on the microstructural effects at or above 900°C. The present study was carried out to determine the microstructural effects that are produced at service temperatures of 960-970°C.

Specimens were prepared from 2 different pipe samples: One in the as-received condition and the other had been in service for over 4 years at 960-970°C. The SEM specimens were examined in a JEOL 840A model SEM having attachments for x-ray point analysis and elemental x-ray mapping.
Micropore structure of carbon by HREM and adsorption
Authors: Fryer J.R. , Innes R.W. , Stoeckli H.F.
Published: June 2020

Investigations have been undertaken on a series of microporous carbons, using both the technique of high resolution electron microscopy(HREM) and of immersion calorimetry. The combined use of these methods in elucidating the micropore size distribution, has enabled us to measure the interaction radius of an adsorbate molecule and show that the radius is reduced on adsorption within a micropore, as was previously suggested from theoretical calculations of Everett and Powl . The data obtained in the present work, however, shows that the reduction is greater than previously thought.

A series of carbons,of differing degrees of burn-off, were prepared from a soft wood precursor, by activation in a fluidised bed reactor using carbon dioxide at 850°C. Micropore size distributions were obtained from these carbons by the technique of immersion calorimetry. This technique involves the exposure of the surface to molecules of different sizes,so that the heat evolved indicates the extent to which the molecules were capable of entering and adsorbing into micropores.
In-situ dynamic observation on cluster formation in amorphous oxide films
Authors: Iijima Sumio
Published: June 2020

Morphologies of small metal particles and arrangements of their internal atoms became unstable under electron beam irradiation. Such structural instability cannot be explained simply by temperature effect but additional effects such as charging up effect . In the study, instability of the particle-support films of amorphous carbon and SiO2 themselves, which were exposed inevitably to the electron beam, was noticed by observing intensity fluctuations in granular images of the films. Our preliminary work showed that fluctuation occurs with a frequency of several tens of Hertz and diminishes with a decrease in the electron beam intensity (below 10amp.). Migratory motion of atoms in small particles and the amorphous films was thought to be responsible for the image intensity fluctuation. Such an intensity fluctuation, therefore, is important for understanding small particle stability and crystallization. The present work deals with in-situ observation on amorphous oxide films using the TV recording technique. The observation was conducted on an ABT- 002B microscope at 200kV.
The microstructure of ultrafine carbonyl iron powder
Authors: Lin X. W. , Chen L. M. , Zhu Jing
Published: June 2020

Carbonyl iron powder has a wide application in the electrical and magnetic industry. In this paper a ultra-fine carbonyl iron powder (UFCIP) of about 20nm in size was examined by CTEM, EELS, HREM and microdiffraction on JEOL—2000FX operating at 200kv. The UFCIP was suspended in ultrasonically agitated alcohol before it was spreaded on a micromesh.

Two types of particles exist in that UFCIP as shown in Fig. 1. The larger particles ranging from 50 to 80 nm are zeta—Fe2N, that was identified by microdiffraction. The majority of the UFCIP particles ranging from 5 to 30 nm in diameter were determined to be Fe3O4 and alpha—Fe by the selected area diffraction. At higher magnification it was found that there are two kinds of fine powder in smaller particles: one has a dark core and another one has a bright core. The microdiffractions with a probe of about 6nm in diameter were performed, it indicated that the dark core is the particles of alpha—Fe enclosed in 5nm thick skin of polycrystalline Fe3O4 as shown in Fig. 2 and that the particles with a bright core are composed of polycrystalline gamma—Fe2O3. The HREM images in Fig. 3a and 3b were taken from a same particle but had two orientations with about 10 degree difference related to the incident beam, as the particle was rotated, the bright core remained visible and a round core became an elliptical core.
Coherent electron nanodiffraction from small metal particles
Authors: Pan M.
Published: June 2020

Small electron probes of 10-15 Å in diameter can be easily formed at specimens in scanning transmission electron microscopes (STEM) using field emission guns (FEG). Nanodiffraction patterns from individual small metal particles (< 50 Å) obtained with such a probe contain non-overlapping CBED disks. As a first order approximation, these patterns can be interpreted similarly to those for parallel beam illumination and then bulk crystallographic information is obtained. However there is more information contained in the nanodiffraction patterns. In the case of small metal particles, spot splitting occurs when the small electron beam is close to a particle edge, which results from the coherence of the probe. Spot splitting is a manifestation of a crystallographic surface plane of a particle being parallel to the beam since the splitting is along the direction normal to the particle edge. This phenomenon is one of the characteristic features of coherent electron nanodiffraction patterns of small metal particles. It will be shown that it is essentially a particle size effect!
HREM study of Fe—pillared smectite
Authors: Hansen P.L. , Bender Koch C. , Mørup S.
Published: June 2020

During the process of pillaring smectite, a metal oxide precursor is introduced into the interlayer space of the layered clay mineral. By subsequent heating of the precursor, a metal oxide forms, increasing the interlayer spacing 0.5—1.0 nm, as observed in XRD.

Pillaring of clays increases the active surface area, and the materials may find use as molecular sieves and catalysts.

Most of the information on the oxide pillars has been derived from indirect spectroscopic and structural methods. In the present study we have used HREM to obtain direct evidence for the pillar formation.
Scanning Electron Microscopy of a supported molten salt CuC1-KCl/SiO2catalyst
Authors: Schmitz Andrew D. , Eyman Darrell P. , Moore Kenneth C.
Published: June 2020

Carbon monoxide hydrogenation reactions catalyzed by heterogeneous catalysts are of significant industrial importance. Most methanol synthesis catalysts contain copper in synergism with ZnO and other metal oxide components. The chemical constitution and physical form of the copper phase in the working alcohol synthesis catalyst has been the subject of considerable concern. Recent NMR and x-ray, spectroscopic and microscopic investigation of alkali metal-promoted copper catalysts confirm earlier reports that the copper phase in methanol synthesis catalysts is a mixture of Cu(O) and Cu(I). Stabilization of a dispersion of Cu(I) is imperative for high activity.
TEM study on the formation and charge stabilization of nanosized colloidal particles
Authors: Liu Jun , Sarikaya Mehmet , Shih Wan Y , Shih Wei-Heng , Aksay Ilhan A.
Published: June 2020

Spherical colloidal silica particles of uniform size are formed through aggregation. This observation contradicts the well-accepted concept that aggregation must be inhibited to produce monosized colloidal particles. In an attempt to explain this dilemma, the present work was undertaken to address the following questions: (i) why do particles form aggregates first and then break into small particles in later stages, (ii) what determines the final particle size, and (iii) why do final particles have a narrow size distribution.

Colloidal gold particles, which were produced by reducing gold chloride with sodium citrate in dilute aqueous solution, were the chosen system. The particles were studied by TEM at different stages of the formation process with a Phillips EM 430T at 300 kV. The TEM samples were prepared by transferring a small amount of the solution onto a TEM copper grid covered with a carbon film and the excess water was removed immediately by filter paper. During the formation stages, the mobility of the particles was also monitored by electrophoretic light scattering.
Studies of copper selenide ultrafine particles by newly developed gas evaporation method
Authors: Kaito Chihiro , Saito Yoshio
Published: June 2020

The direct evaporation of metallic oxides or sulfides does not always given the same compounds with starting material, i.e. decomposition took place. Since the controll of the sulfur or selenium vapors was difficult, a similar production method for oxide particles could not be used for preparation of such compounds in spite of increasing interest in the fields of material science, astrophysics and mineralogy. In the present paper, copper metal was evaporated from a molybdenum silicide heater which was proposed by us to produce the ultra-fine particles in reactive gas as shown schematically in Figure 1. Typical smoke by this method in Ar gas at a pressure of 13 kPa is shown in Figure 2. Since the temperature at a location of a few mm below the heater, maintained at 1400° C , were a few hundred degrees centigrade, the selenium powder in a quartz boat was evaporated at atmospheric temperature just below the heater. The copper vapor that evaporated from the heater was mixed with the stream of selenium vapor,and selenide was formed near the boat. If then condensed by rapid cooling due to the collision with inert gas, thus forming smoke similar to that from the metallic sulfide formation. Particles were collected and studied by a Hitachi H-800 electron microscope.

Figure 3 shows typical EM images of the produced copper selenide particles. The morphology was different by the crystal structure, i.e. round shaped plate (CuSe;hexagona1 a=0.39,C=l.723 nm) ,definite shaped p1 ate(Cu5Se4;Orthorhombic;a=0.8227 , b=1.1982 , c=0.641 nm) and a tetrahedron(Cu1.8Se; cubic a=0.5739 nm). In the case of compound ultrafine particles there have been no observation for the particles of the tetrahedron shape. Since the crystal structure of Cu1.8Se is the anti-f1uorite structure, there has no polarity.
High-resolution imaging of symmetric tilt and mixed character boundaries in Al
Authors: Shamzuzzoha M. , Deymier P.A. , Smith David J.
Published: June 2020

The determination of the core structure of grain boundaries is central to a better understanding of the properties of polycrystalline materials. With the recent advent of intermediate-voltage electron microscopes (300-400kV), it is possible to obtain atomic-resolution images of grain boundaries in many metals - for example, the atomic structure of periodic grain boundaries in selected metals has been studied. Our knowledge of materials properties can be further enhanced by investigating more complex, arbitrarily misoriented grain boundaries. In this paper, we will report HREM imaging of a symmetric tilt low-angle grain boundary and a twist-and-tilt (mixed character) grain boundary in Al.

The Al bicrystals used in this study were produced by cross-rolling and annealing methods described in detail elsewhere. Thin foil specimens of 3mm diameter containing specific boundaries were obtained by spark-cutting and subsequent electropolishing in 73% methanol, 25% nitric acid and 2% hydrochloric acid. HREM was performed with a JEM-4000EX operated at 400kV, using axial illumination and without an objective aperture. High-resolution electron micrographs were recorded near the optimum defocus, typically at a magnification of 500,000 times.
Crystal structures and transformation of Cu-Se and Ag-Te in solid-solid reactions
Authors: Hirota Yoshihiro , Isshiki Toshiyuki , Shiojiri Makoto
Published: June 2020

Cu-Se and Ag-Te crystals which grew by solid-solid reactions of vacuum-deposited metal and chalcogen films were investigated with a JEM 200-CX electron microscope (Cs= 1.2 mm), with the aid of image simulation and optical diffraction.

Fig. 1 shows an image of a slender crystal observed 10 days after an amorphous Se film was mounted on a holey Cu film. The image in A matches with a calculated image shown in Fig. 2a. The calculation was carried out for a CuSe crystal (P63/mmc, a=0.394, c=1.725 nm) 20 nm thick, with the a-axis relatively tilted at 1° about the [012] axis to the incident electron beam, at an underfocus of Δf=50 nm. The optical diffractogram from the image of the area A was used for the calibration of the distance in the optical diffractograms from the other areas B∼ E. The crystal in B formed before the formation of the CuSe crystal.
A Transmission Electron Microscopy study of the B-type CoSi2/Si(111) interface
Authors: Daykin A.C. , Kiely C.J. , Pond R.C.
Published: June 2020

CoSi2 layers grown on clean Si(111) substrates can form in two distinct orientations. A-type CoSi2 has the same orientation as the Si substrate, whereas the B-type CoSi2 is rotated by 180° about the [111] surface normal. The epitaxial films studied were prepared by depositing Co on to a Si(111) surface at room temperature under UHV conditions and annealing at 650°C. This produces mixed A and B-type CoSi2 of approximately 50Å thickness. Fig.1a shows a diffraction pattern taken on tilting the bicrystal such that the beam direction is [114] in the Si and [110] in B-type CoSi2, the corresponding schematic diagram is shown in Fig.1b. Dark field microscopy can be used to image g=111 B-type CoSi2 reflections which, if at the exact Bragg condition, give rise to images such as Fig.2.The micrograph shows B-type CoSi2 with some strongly diffracting areas and at least three other different weaker contrasts. This paper is a study of the origins of the contrast effects noted in Fig.2.
Compositional observations of franckeite using high-angle annular dark-field microscopy
Authors: Wang S. , Liu J. , Buseck P. R. , Cowley J. M.
Published: June 2020

Franckeite (˜FeSn3Pb5Sb2Si14) has a complex modulated structure containing alternating layers of different composition. The complex composition and structure, lack of a well-defined unit cell, incommensurate character, and poor quality of crystals has made it difficult to study by standard X-ray and electron-diffraction methods. High-angle annular dark-field (HAADF) STEM imaging provides a way of mapping the compositional distributions directly and with atomic resolution. For thin regions of the sample, the intensity of the electrons scattered at high angles depends strongly on the atomic number of the scatterer. This unique property makes HAADF imaging powerful for studying compositional modulations on the atomic scale. By comparing the structure as viewed by high-resolution imaging to the compositional information provided by the HAADF technique, we have been able to obtain an improved understanding of crystal structures with displacive and compositional modulations, such as franckeite. We use the HAADF technique to test the assumption that in franckeite two kinds of layers (SnS2 and PbS) are stacked along the a axis with a 1.73 nm repeat, and that Sb and Fe produce structural modulations in the c direction.
Probing nucleation and growth phenomena on silicon surfaces by scanning tunneling microscopy/spectroscopy
Authors: Hamers R.J. , Kohler U.K. , Demuth J.E.
Published: June 2020

Nucleation and growth processes at surfaces are determined by a complex interplay between surface diffusion and adsorption at terraces, step edges, and defects. Localized defects strongly affect both the electronic properties of the surfaces as well as their reactivity, therby affecting nucleation and growth. Reconstruction of seminconductor surfaces further complicates the picture, by providing various types of inequivalent adsorption sites even on “perfect” surfaces. In an effort to understand these processes at the atomistic level, we have used scanning tunneling microscopy to probe the epitaxial growth of silicon on Si(001) and Si(111)-(7×7) surfaces at temperatures where the diffusion length of the impinging adatoms is smaller than the spacing between steps, so that groth occurs through the formation of islands rather than at step edges. Scanning tunneling microscopy is capable of probing both the local surface geometry and local electronic structure, permitting adsorption and chemical reactivity to be studied on an atom-by-atom basis.
Three Dimensional materials characterisation at ultrahigh resolution using a position-sensitive atom probe
Authors: Mackenzie R A D , Smith G D W , Cerezo A , Godfrey T J , Brown J.E.
Published: June 2020

The conventional atom probe field ion microscope permits very high resolution chemical information to be determined with a lateral spatial resolution of typically 2 nm. This spatial resolution is determined by the need to define the analysis area using an aperture. A recent development, the position sensitive atom probe (POSAP), has largely removed this limitation. In a conventional atom probe the ions passing through the aperture, which have come from a circular area of the order of 2 nm in diameter, travel along a long flight path where the mass to charge ratios are determined with high precision. In the position sensitive atom probe the aperture assembly, long flight tube and ion detector (a channel plate) are replaced with a position sensitive detector held at a known distance from the specimen surface. This detector consists of two parts, a channel plate component which permits the flight times (and hence mass to charge ratios) to be determined, and a wedge and strip anode which permits the position of the incoming ion to be calculated. This arrival position corresponds directly to the position on the specimen from which the ion came. The total field of view of the POSAP is a disc approximately 20 nm in diameter. With a conventional atom probe the data acquired during the evaporation sequence can be considered as a core extracted from the specimen, where the average composition as a function of depth is known. The position sensitive atom probe permits us to record data from a much wider core (20 nm rather than 2 nm in diameter), and also to retain the spatial information within the core. As the evaporation proceeds the two dimensional information yielded by the position sensitive detector builds up into a three dimensional block of data. We have, therefore, both chemical and spatial information in three dimensions at very high resolution from the sampled volume of material.
Electron channelling contrast imaging of dislocations
Authors: Czernuszka J.T. , Long N.J. , Hirsch P.B.
Published: June 2020

In the 1970s there was considerable interest in the development of the electron channelling contrast imaging (ECCI) technique for imaging near surface defects in bulk (electron opaque) specimens. The predictions of the theories were realised experimentally by Morin et al., who used a field emission gun (FEG) operating at 40-50kV and an energy filter such that only electrons which had lost no more than a few 100V were detected. This paper presents the results of a set of preliminary experiments which show that an energy filter system is unneccessary to image and characterise the Burgers vectors of dislocations in bulk specimens. The examples in the paper indicate the general versatility of the technique.

A VG HB501 STEM with a FEG was operated at l00kV. A single tilt cartridge was used in the reflection position of the microscope. A retractable back-scattered electron detector was fitted into the secondary electron port and positioned to within a few millimetres of the specimen. The image was acquired using a Synoptics Synergy framestore and digital scan generator and subsequently processed using Semper 6.
Atomic resolution Z-contrast imaging of bulk crystal surfaces in Scanning Reflection Electron Microscopy
Authors: Wang Z. L. , Bentley J.
Published: June 2020

The success of obtaining atomic-number-sensitive (Z-contrast) images in scanning transmission electron microscopy (STEM) has shown the feasibility of imaging composition changes at the atomic level. This type of image is formed by collecting the electrons scattered through large angles when a small probe scans across the specimen. The image contrast is determined by two scattering processes. One is the high angle elastic scattering from the nuclear sites,

where ϕNe is the electron probe function centered at bp = (Xp, yp) after penetrating through the crystal; F denotes a Fourier transform operation; D is the detection function of the annular-dark-field (ADF) detector in reciprocal space u. The other process is thermal diffuse scattering (TDS), which is more important than the elastic contribution for specimens thicker than about 10 nm, and thus dominates the Z-contrast image. The TDS is an average “elastic” scattering of the electrons from crystal lattices of different thermal vibrational configurations,
A search-match program for materials identification in the Transmission Electron Microscope using electron diffraction pattern analysis
Authors: Vale S.H.
Published: June 2020

A program has been written for an energy dispersive x-ray microanalysis system computer to identify a sample by combining data from an electron diffraction pattern collected in a TEM with chemical information from the sample. The combined information is compared with a large database held on the computer to find a suitable set of matching compounds.

The program was written for a Link Analytical AN10000 microanalysis system which is based on a computer with a 16 bit word length, 20 MHz CPU with 512 kbyte of memory for programs and data, 40 Mbyte hard disk and a 512 × 512 pixel colour image display with its own memory. The database used was the NBS/SANDIA/ICDD electron diffraction database adapted for the AN 10000 computer. This database contains about 70000 compound entries and occupies 9 Mbyte of disk space.
TEM study of dislocation core configurations in Ni3(Al,l%Ta) deformed at high temperatures
Authors: Baluc N.
Published: June 2020

The Ni3Al intermetallic compound of the ordered L12 structure with various alloying elements (such as Ta or Ti) reinforces most of the industrial superalloys which are designed for high temperature applications. Therefore, the understanding of its mechanical properties is of primary importance. The yield strength, measured in constant strain rate tests, exhibits an anomalous behaviour as a function of temperature: it increases up to a peak temperature above which it finally decreases. The anomalous increase has been extensively studied during the last 30 years, including weak-beam and high resolution transmission electron microscopy (TEM) observations and computer simulations. Numerous models have been proposed to explain this anomalous variation in which the structure of the dislocation core plays a fundamental role. A review of core effects on the plasticity of ordered alloys was given by Vitek (1985). In the present investigation, the Ni3(Al,l%Ta) phase was deformed at temperatures above the yield strength peak and the detailed core configurations of dislocations have been analyzed using weak-beam and high resolution TEM techniques.
Structure refinements in M7C3 (M=Cr,Fe) carbide
Authors: He A.Q. , Ye H.Q. , van Tendeloo G. , Kuo K.H.
Published: June 2020

The crystal defects in M7C3 (M=Cr,Fe) have been investigated by electron microscopy. The results show that there exist a lot of planar defects such as antiphase boundaries, and twin boundaries in it. According to Rouault et al., the structure of Cr7C3 is orthorhombic but based on a hexagnoal sublattice with a=0.701, b=1.214, c=0.452nm, i. e b/a=. For a perfect hexagonal sublattice the defects in {110} would be invisible both in electron diffraction patterns and in electron microscopic images when detected exactly along [001], So, these defects in M7C3 were observed by diffracted contrast method in which electron beam tilts a little from c axis or by HREM image with special beam direction but not [001] zone.

e have found however in our sample the strcture of the M7C3 is probably orthorhombic but b/a≠3, such that no hexagnoal sublattice. A structure based on a non-hexagnoal lattice which produces twining is no longer invisble along [001] by HREM.

Powder of M7C3 carbide was extracted by electricity chemistry from a cast-iron superalloy. The composition (wt) is: Cr-24.94%, Ni-20%, Mn-0.43%, Si-1.42%, S-0.017%, P-0.017%, C-0.41%. It was collected by carbon grid, and examined in JEOL 200CX.
High-temperature high-resolution in-situ microscopy of grain boundary migration and structure change
Authors: Ichinose Hideki , Kizuka Tokuji , Ishida Yoichi
Published: June 2020

A high resolution high temperature specimen stage of 200kV HRTEM was newly designed and produced in order to investigate the physical and mechanical nature of materials at high temperature.The atomic process of silicon grain boundary migration and the structure change was successfully observed in-situ at 1000K by the new specimen stage.

The high temperature specimen stage consists of a heating specimen holder, a high stability power supply and a high stability current controller. Heat is provided by an induction free double spiral coil heater which is made of tungsten. Excellent current stability, better than 10−6 , prevents the objective lens from the magnetic disturbance which is caused by heating current. The highest temperature of the specimen is designed to be 1100K. The accuracy of the temperature measurement is checked by the melting test of tin. In order to keep the high resolution of the microscope(JEM-200CX) at such high temperature as 1100K an objective lens is also newly designed and produced. Aberration constants of the new lens are respectively Cs=0.7mm and Cc=1.2mm. Resulted resolution at high temperature is as same level as the that of the original JEM-200CX at room temperature. Images are recorded by a video tape recorder.
Environmental cell studies of deformation and fracture
Authors: Birnbaum H. K. , Robertson I. M.
Published: June 2020

Studies of the effects of hydrogen environments on the deformation and fracture of fcc, bcc and hep metals and alloys have been carried out in a TEM environmental cell. The initial experiments were performed in the environmental cell of the HVEM facility at Argonne National Laboratory. More recently, a dedicated environmental cell facility has been constructed at the University of Illinois using a JEOL 4000EX and has been used for these studies. In the present paper we will describe the general design features of the JEOL environmental cell and some of the observations we have made on hydrogen effects on deformation and fracture.

The JEOL environmental cell is designed to operate at 400 keV and below; in part because of the available accelerating voltage of the microscope and in part because the damage threshold of most materials is below 400 keV. The gas pressure at which chromatic aberration due to electron scattering from the gas molecules becomes excessive does not increase rapidly with with accelerating voltage making 400 keV a good choice from that point of view as well. A series of apertures were placed above and below the cell to control the pressures in various parts of the column.
In-situ observations of microvoid coalescence: Stacking fault energy effects
Authors: Vecchio Kenneth S.
Published: June 2020

Although it has been well established that microvoid coalescence occurs during static or quasi-static fracture in ductile materials, the exact mechanism for microvoid formation is still unclear. It has been argued that microvoids initiate and grow from second phase particles. However this argument cannot be used to explain the existence of microvoids on the fracture surfaces of "pure" materials. An alternative mechanism for their formation in "pure" materials is that they initiate and grow along dislocation cell walls. If this premise is true; then the nature and extent of microvoid coalescence should be related to the stacking fault energy (SFE) of the material since the latter is a controlling parameter in the formation of dislocation cells. The relationship between microvoid coalescence and stacking fault energy may have some basis since absolute cell dimensions are of the same magnitude as the observed dimple sizes. The present study examines the effect of dislocation cell structures on the formation of microvoids as a function of the stacking fault energy of a given material through direct observation of the void formation and growth process within the TEM. The fundamental aspects of the work is to correlate the dislocation substructures, void initiation, growth, and coalescence to the resulting fracture surfaces.
An in situ TEM study of nucleation and growth of the Ω phase in an Al-4.0Cu-0.5Mg-0.5Ag alloy
Authors: Garg A. , Howe J. M.
Published: June 2020

Addition of small amounts of Ag to Al-Cu-Mg alloy with high Cu:Mg ratios stimulates precipitation of a new phase, designated Ω, which has an orthorhombic structure and forms as thin coherent hexagonal plates on {lll} α planes. This phase significantly increases the age hardening characteristics of the alloy, particularly at elevated temperatures. The mechanism of nucleation of Ω phase is not known but is believed to be fundamentally different from that of θ’ and S’ phases which also form in these alloys. The presence of Ag and Mg only in trace quantities makes the problem of finding the actual mechanism of nucleation of Ω phase difficult.

An in situ hot stage TEM study was conducted on an Al-4.0Cu-0.5Mg-0.5Ag(wt.%) alloy in order to understand the nucleation and growth behavior of Ω phase. Two types of initial microstructures were used: 1) homogenized, solution-treated and cold water-quenched, 2) as-quenched and aged for 1 hr. at 190°C. The as-quenched structure shown in Fig. 1(a) consists of a high density of small dislocation loops, some helical dislocations and a few straight dislocations. When this foil was heated in the microscope, observable precipitation occured at about 205°C.
Structural properties of GaAs/InGaAs/GaAs (001) and InGaAs/GaAs (001) heterostructures and correlation with electronic properties
Authors: Bonar J.M. , Hull R. , Malik R. , Ryan R. , Walker J.F.
Published: June 2020

In this study we have examined a series of strained heteropeitaxial GaAs/InGaAs/GaAs and InGaAs/GaAs structures, both on (001) GaAs substrates. These heterostructures are potentially very interesting from a device standpoint because of improved band gap properties (InAs has a much smaller band gap than GaAs so there is a large band offset at the InGaAs/GaAs interface), and because of the much higher mobility of InAs. However, there is a 7.2% lattice mismatch between InAs and GaAs, so an InxGa1-xAs layer in a GaAs structure with even relatively low x will have a large amount of strain, and misfit dislocations are expected to form above some critical thickness. We attempt here to correlate the effect of misfit dislocations on the electronic properties of this material.

The samples we examined consisted of 200Å InxGa1-xAs layered in a hetero-junction bipolar transistor (HBT) structure (InxGa1-xAs on top of a (001) GaAs buffer, followed by more GaAs, then a layer of AlGaAs and a GaAs cap), and a series consisting of a 200Å layer of InxGa1-xAs on a (001) GaAs substrate.
A study of lattice distortion in GexSi1-x, superlattice by convergent beam electron diffraction
Authors: Xiaofeng Duan , Fung K. K. , Chu Y. M.
Published: June 2020

Strained-layer superlattice GexSi1-x/Si have received much attention because of their potential applications. Convergent beam electron diffraction has been used to study strains and composition modulation in semiconductor superlattices. In this paper we report the result of a study of GeSi/Si superlattice sample with mismatch = 2% and composition and strain modulation wavelength = 30nm. The sample has been grown at temperature 470 °C on (001) Si substrate by molecular beam epitaxy (MBE), with a Si buffer layer of thickness ≈ l00nm. The sublayer thickness are tGeSi=5nm and tSi=25nm. The number of period is 20. The CBED patterns were obtained by operating Philips EM420 at 100kV.

Fig.l shows a XTEM bright field image of a GeSi superlattice specimen. The interface between the GeSi layer and the Si substrate is even and clear. Also the interfaces between the sub-layers of GeSi and Si in superlattice are good. Only a few defects are visible near the bottom of the superlattice( pointed by arrow 1). Its look like microtwins.
Microscopy of plasma anodised materials for VLSI
Authors: Ringnalda J. , Zhang J.F. , Taylor S. , Maher D.M.
Published: June 2020

Plasma anodisation is an attractive technique for growing insulating layers of SiO2 at much lower temperatures then those needed for thermal oxide growth. Defects can be generated in silicon when it is subjected to prolonged high temperature oxidation processes, which in turn lead to degradation in both yield and performance of small geometry devices. An additional disadvantage of thermal oxide growth lies in the lateral oxidation behaviour (i.e. oxidation underneath the mask or ‘bird-beaking’ effect) which limits the minimum device separation which can be achieved. Although plasma anodisation has been widely investigated (see and references therein), previous studies have highlighted the severe difficulty of producing effective masks for this process, particularly during the high power anodisation studies which are the subject of this paper. Most of the established masks against thermal oxidation appear to be consumed during the plasma anodisation process. Therefore an important issue with regard to plasma anodisation is to find material systems in which the vertical oxidation rate of the mask is low compared to silicon and the lateral oxidation of both the mask and the silicon substrate under the mask are minimal. For the present study, two materials systems have been investigated; Si3N4/SiO2 strips on Si and Al/SiO2 strips on Si.
Stereoscopic observation and determination of surface orientation of voids in stress-thermal-migrated aluminium lines of LSI with UHVEM
Authors: Ura Katsumi , Takaoka Akio , Nishino Akira , Mori Hirotaro
Published: June 2020

The ultra-high voltage electron microscope (UHVEM) HU-2000 is a powerful tool for the observation of multilayer devices such as LSI. By using the method of stereo-microscopy, we can determine the shape and orientation of each crystal under the passivation layer. We applied it to the observation of voids in the stress-thermal-migrated aluminium lines of LSI. The acceleration voltage was 2 MV.

Figure 1 shows the structure and dimension of the specimen. After the processes of these layers, the specimen was annealed at 450°C for 15 min and cooled slowly; then, the voids are generated by the stress- and thermal-induced migration. The two types of specimens for UHVEM are prepared; the passivation layer is removed by dry etching (Fig.2) and not removed (Fig.3). The voids are always observed at the grain boundary and the top side (the passivation side) of voids is wider than its bottom side. This suggests that the tension from the passivation layer is much stronger than from the substrate. The void surface is formed by some facets and its inclination angle is usually 60°∼°. The orientation of the facet is (111) in most cases as shown in Figs.2 and 3. This result agrees with the fact that the surface (111) for Al has a minimum surface energy.
Fracture analysis of soldered wire by plasma ashing and SEM
Authors: Narayan P.B.
Published: June 2020

The increasing demand for higher quality and reliability in the computer peripherals industry requires that the components function without premature materials failure. SEM has been found to be an indispensable technique for studies leading to improved materials and processes. Because of the variety of materials used, SEM specimen preparation requires continuing innovation.

Low temperature oxygen plasma-ashing was found to be a convenient technique to remove organic resins and other hydrocarbons. A gaseous plasma, consisting of neutral, energized and ionized atoms, is created by sending oxygen through a high voltage electric field. The plasma readily reacts with the hydrocarbons forming gaseous carbonaceous by-products. The addition of argon to oxygen provides sputter-etching and a more effective resin removal. The temperature of the specimen rarely goes above 50°C and so it is called low temperature gas plasma. The plasma does not alter surfaces or bulk properties of metals and ceramics.
Morphology of uranium precipitates in silicon
Authors: Kannan V. C. , Filo A. J. , Brown I. G.
Published: June 2020

Soft errors induced by incident alpha particles have been observed in dynamic Metal-Oxide- Semiconductor Random Access Memory (MOS RAMs), charge coupled devices (CCDs), static MOS RAMs and in bipolar RAMS. The focus of attention has been the occurrence of soft errors as a result of alpha particle decay of uranium present even in trace amounts, typically a few ppm (parts per million), in the silicon substrate along with the devices as well as the packaging material. A study of segregation of uranium in silicon is of special interest since a single alpha particle of approximately 40 MeV that has a track length of about 20 μ in silicon can give rise to nearly 106 electron-hole pairs if all the deposited energy is converted to the generation of excess carriers. If these excess carriers are developed in a critical volume depending upon the density of devices in a product, the effect can be large enough to limit the mean time of failure to a few days or weeks for a 64k memory cell. In order to study the diffusion and segregation characteristics of uranium in silicon, uranium was deliberately ion implemented into bare silicon to a dose of 1014/cm2 and subsequently annealed at several temperatures often encountered in device processing. In this paper, we present TEM results especially pertaining to the morphology of uranium precipitates in silicon. Conventional microstructural observations, using bright field (BF) imaging, stereographic projection analysis using electron diffraction patterns, and projected directions of the precipitate with respect to matrix reflection from silicon onto a stereogram, and moire patterns using phase contrast imaging, were used to determine the morphology of fine uranium precipitates in ion implanted and annealed samples.
Investigation of NEV Au++ implanted silicon
Authors: Alford T.L. , Theodore N.D. , Mayer J.W. , Carter C.B. , Cheung N.W.
Published: June 2020

There has recently been increasing use of MeV ion beams for materials modification. When compared to more common lower, keV-energy implantation, MeV-ion irradiation has a broader variation in the type of damage along the ion path. This is because of the more significant difference between damage and range distributions in the case of MeV implants as opposed to keV implants. Previous works showed that MeV-implanted Si-ions react differently with various types of lattice damage in silicon; interactions range from simple point-defect annihilation to the formation of extended defects. Earlier investigations of Au implanted into previously amorphized silicon have observed Au segregation as a result of its being expelled from the recrystallizing amorphous layer during ion-beam irradiation. In this study, the interaction of MeV Au++ atoms with the different types of damage produced along the MeV-ion beam path is investigated.

Silicon (100) single crystal wafers were given a HF dip and were then mounted on a copper sample stage; the stage functions as a heat-sink. The stage together with the specimen was then placed in a Tandem ion-implanter. The specimens were implanted with gold; implant-energies varied from 1.8 - 4.4 MeV and fluences ranged between 0.1 - 10×1016 Au++/cm2.
Cross-sectionnal Electron Microscopy investigation of silicon amorphisation during high temperature zinc-ion bombardment
Authors: Faure J. , Simov S. , Balossier G. , Bharadwaj L.M. , Claverie A. , Bonhomme P.
Published: June 2020

In silicon technology, the use of zinc as a dopant reveals a great interest in optoelectronic device fabrication, such as photoresistors, light amplifiers, photodiodes etc. Recently, zinc implantation has received a new attention in thermal oxidation of silicon. Oxidation kinetics are strongly correlated to zinc segregation at the oxide-silicon interface and to the nature of the ion induced damage which is stable at the implantation temperature. We used cross-sectionnal electron microscopy (XTEM) for the characterisation of the structural modifications induced in a monocrystalline silicon substrate during high temperature Zn+implantation. During irradiation, silicon wafers (111 oriented) were heated to 110°C by use of a resistively heated copper block, while the incident ion beam had an energy of 120keV and a current density less than 3μA.cm-2.

Figure 1 presents the effect of Zn+ implantation associated with a 1014 ions.cm-2 implanted dose. This 220 DF image reveals, in black, a buried noncrystalline layer lying from about 30 to 85nm from the arrowed silicon surface.
Defect morphology in thick relaxed layers of InGaAs on GaAs
Authors: Dixon R H , Kidd P , Goodhew P J
Published: June 2020

Thick relaxed InGaAs layers grown epitaxially on GaAs are potentially useful substrates for growing high indium percentage strained layers. It is important that these relaxed layers are defect free and have a good surface morphology for the subsequent growth of device structures.

3μm relaxed layers of InxGa1-xAs were grown on semi - insulating GaAs substrates by Molecular Beam Epitaxy (MBE), where the indium composition ranged from x=0.1 to 1.0. The interface, bulk and surface of the layers have been examined in planar view and cross-section by Transmission Electron Microscopy (TEM). The surface morphologies have been characterised by Scanning Electron Microscopy (SEM), and the bulk lattice perfection of the layers assessed using Double Crystal X-ray Diffraction (DCXRD).

The surface morphology has been found to correlate with the growth conditions, with the type of defects grown-in to the layer (e.g. stacking faults, microtwins), and with the nature and density of dislocations in the interface.
Cross-sectional Transmission Electron Microscopy of (AlAs)15(InAs)1 Superlattices
Authors: Ballesteros C. , Piqueras J. , Vázquez M. , Silveira J.P. , González L. , Briones F.
Published: June 2020

Multibeam and bright field transmission electron microscopy are used to determine the structure of (InAs)1/(AlAs)15 superlattices. The interest of InAs/AlAs system arises from the large gap difference. The main problem in the obtention of strained layer superlattices (SLS), with a large lattice mismach, 7% is that of controlling the growth process to obtain high quality layers with sharp interfaces.

A modification of the conventional MBE technique, Atomic Layer Molecular Beam Epitaxy (ALMBE) seems to be very appropiate for the growth of such strained layer structures. In particular, high quality layers of materials that demand different growth conditions by MBE, like InAs and AlAs can be obtained at a common low substrate temperature (350-400°) by ALMBE due to the ability to force 2D or layer by layer nucleation and growth. Present superlattices are part of a series with structure (AlAs)15/(InAs)n (n = 1, 2, 3 and 5 ml) whose study by HREM is under way in order to determine critical thickness limits.
Direct observation of strain distribution in InP/In1−xGaxP heterointerfaces by CAT method
Authors: Kakibayashi Hiroshi , Nagata Fumio , Itoh Kazuhiro
Published: June 2020

The characteristics of electronic and optical devices, which have been developed utilizing a strained superlattice composed of multilayered structure accommodating lattice mismatch, are considerably affected by the strain distribution at the heterointerfaces. It has been, however, very difficult to measure the nanometer areas due to poor spatial resolution of the usual evaluation methods such as X-ray diffraction, Raman scattering, photoluminescence.

The authors proposed a new transmission electron microscopy based on the compositional analysis by thickness-fringe (CAT) which was successfully applied for evaluating the compositional profiles in GaAs/AlxGa1−xxAs superstructures with a high spatial resolution of 0.4 nm. In this study, the CAT method is applied to evaluate the strain distribution with high spatial resolution and sensibility. The intensity distribution of the thickness fringe is affected not only by the composition but also by the Bragg conditions of electron diffraction. The lattice planes near the heterointerface bend due to the lattice distortion between two crystals with different lattice constant. The change of Bragg condition at the bent plane can be detected in the CAT image as the shift of thickness fringe.