bluuebunny/crossref_metadata_2025 huggingface dataset:
Experimental and theoretical X-Ray distribution function, δ(ρz), for microanalysis of thin
Authors: Zreiba N. A. , Pico C. A. , Kelly T. F.
Published: June 2020

Absorption and fluorescence corrections used in the quantitative microanalysis of thin specimens usually require prior knowledge of the variation of the generated x-ray intensity, ϕ(ρz), with mass depth, ρz. In the analysis of electron-transparent thin foils, ϕ(ρz) is generally assumed to be independent of mass thickness. This assumption may not apply when absorption and/or fluorescence corrections are necessary. As shown by Stenton et al, the x-ray distribution, ϕ(ρz) in thin foils can be determined experimentally by using the Tracer technique. ϕ(ρz)s for thin specimens have also been calculated theoretically by using the Monte Carlo technique.

In our laboratory submicron spheres of pure or stoichiometric compound materials have been produced by a process called electrohydrodynamic (EHD) atomization for the purpose of determining the detector efficiency function of electron microscope x-ray detectors. Because the assumption of constant ϕ(ρz) may not apply for compounds that require absorption and/or fluorescence corrections, it was necessary to determine ϕ(ρz) for thin spheres.
AEM analysis of condensed-phase xenon in UO2 spent fuel
Authors: Thomas L. E. , Guenther R. J.
Published: June 2020

Release of the abundant fission gases xenon and krypton in UO2 reactor fuels is a limiting factor in normal performance of fuel rods and a concern in possible accidents involving transient overheating of the fuel. Consequently, a knowledge of the fission gas behavior in fuel is of great interest. Although fission gases in fuel are widely believed to exist as gas bubbles or atoms in solution in the UO2, we have obtained evidence by analytical electron microscopy that the xenon and krypton can also exist as a condensed phase, i.e. as a liquid or solid at high internal pressures in the UO2. This finding is likely to be important in modeling fission gas release.

In a typical light-water power reactor (LWR), operating temperatures vary from about 650K at the edge of a fuel pellet to about 1400K at peak-power axial regions. Samples prepared from different radial locations in peak-power sections of low gas-release LWR fuels ATM-101 and ATM-103 were examined in a 200 KV AEM to determine how the gas and solid fission products varied with local fuel operating temperature.
Elemental microanalysis of the human lens
Authors: Shuting Ma , Shilling Zhang , Shoujing Fu
Published: June 2020

Some chemical elementals, such as K, P, Na, Ca and Cl are widely implicated in a variety of lens cel1-functions. For an exact assessment of their role one needs to know the quantitative distribution of these elements in and around the lens cells. The EDXA of bulk specimens possibly permits such measurement to be made in a reliable and nondestructive way. The paper on the distribution of the elements in human normal lens, which was finished with the technique of electron prob x-ray microanalysis has not been published. The purpose of the present study is to explore the intracellular K/Na ratios and the elemental distribution between human normal and cataractous lens.

In this study, only human lenses were used and the fresh tissues were obtained at cataractous and traumatic surgery. All the samples were rapidly frozen on a metal disc maintained at liquid nitrogen temperatures. The frozen samples were fractured, lyophilized and coated.
Symmetry — breaking in convergent-beam electron diffraction
Authors: Eaglesham D.J.
Published: June 2020

Symmetry determination remains the major application of CBED in materials science. Its power lies not only in the small-probe capability, but in the sensitivity to small deviations from symmetry, and the ability to distinguish centro- and non-centrosymmetric structures. However, there are a large number of artefacts which can lead to lowering of the observed symmetry, so that procedures for CBED point and space-group determinations generally stipulate that, where two different symmetries are observed, the higher-symmetry pattern should be regarded as representative of the perfect crystal (eg.l). This has lead to the occasional controversy (notably in the recent case of the 1-2-3 superconducting ceramics) as to whether symmetry-lowering is “genuine” or not. The purpose of the present paper is to review the possible sources of symmetry-breaking in CBED patterns and to attempt to establish a basis on which to distinguish “genuine” symmetry-breaking from artefacts. The various sources of symmetry-breaking will be addressed in turn.
Digital x-ray mapping of nanometer-size supported bimetallic catalysts
Authors: Germinario L. T.
Published: June 2020

Understanding the role of metal cluster composition in determining catalytic selectivity and activity is of major interest in heterogeneous catalysis. The electron microscope is well established as a powerful tool for ultrastructural and compositional characterization of support and catalyst. Because the spatial resolution of x-ray microanalysis is defined by the smallest beam diameter into which the required number of electrons can be focused, the dedicated STEM with FEG is the instrument of choice. The main sources of errors in energy dispersive x-ray analysis (EDS) are: (1) beam-induced changes in specimen composition, (2) specimen drift, (3) instrumental factors which produce background radiation, and (4) basic statistical limitations which result in the detection of a finite number of x-ray photons. Digital beam techniques have been described for supported single-element metal clusters with spatial resolutions of about 10 nm. However, the detection of spurious characteristic x-rays away from catalyst particles produced images requiring several image processing steps.
Formation of eta-phase in CVD-coated cemented carbides
Authors: Skogsmo J. , Norden H.
Published: June 2020

Chemical vapour deposition (CVD) is commonly used to produce wear resistant coatings on cemented carbide cutting tools. These coatings may consist of several layers but the innermost layer is usually TiC. The adherence and mechanical properties of the coated tool are mainly determined by the composition of the transition region substrate-coating. The high process temperature and the presence of reactive gases can result in a decarburizing of the substrate surface layer. If the cobalt binder phase is decarburized, its solubility of W will increase and this may eventually lead to the formation of a new phase, the eta-phase commonly of the type Co6W6C, which is very brittle and can have detrimental effect on the coating.

In this study two types of specimens were used, very sharp (apex radius 50 nm) needles and flat cutting tool inserts. The coating process was performed with CH4 at 1000 °C and 50 torr, using very short (30s-3min) deposition times to obtain sufficiently thin layers. The needles have the advantage that they can be examined directly by STEM-EDS without any further specimen preparation, Fig.1.
A TEM investigation of a hyper-eutectic lead-tin alloy
Authors: Sutliff John A.
Published: June 2020

Near-eutectic Pb-Sn alloys are important solders used by the electronics industry. In these solders, the eutectic mixture, which solidifies last, is the important microstructural consituent. The orientation relation (OR) between the eutectic phases has previously been determined for directionally solidified (DS) eutectic alloys using x-ray diffraction or electron chanelling techniques. In the present investigation the microstructure of a conventionally cast, hyper-eutectic Pb-Sn alloy was examined by transmission electron microscopy (TEM) and the OR between the eutectic phases was determined by electron diffraction. Precipitates of Sn in Pb were also observed and the OR determined. The same OR was found in both the eutectic and precipitation reacted materials. While the precipitation of Sn in Pb was previously shown to occur by a discontinuous precipitation reaction,3 the present work confirms a recent finding that volume diffusion controlled precipitation can also occur.

Samples that are representative of the solder's cast microstructure are difficult to prepare for TEM because the alloy is multiphase and the phases are soft.
The hierarchy of grain boundary structures in SiC bicrystals
Authors: Ishida Y. , Ichinose H. , Inomata Y.
Published: June 2020

The standard geometrical theory having been developed to describe periodically ordered grain boundaries in metals, ie coincidence-site lattice theory faces a new frontier to be expanded in terms of hierarchy of atomic structures in low energy grain boundaries of polytype SiC bicrystals. The unit translation lattice of the polytype crystal is large and elongated in the direction perpendicular to the basal plane. With the elongated translation lattice, the coincidence-site lattice is generally very large. Often too large to be physically significant, although the predictive role of the coincidence-site lattice theory in specifying the orientation of periodically ordered interface was still preserved. Such periodically ordered boundaries were indeed found to occur in the present SiC bicrystals as is predicted by the geometrical theory. A dual description of the grain boundary structure in terms of hierarchy of atomic structures is shown useful in characterizing the bicrystal boundaries.

High purity SiC bicrystals were produced by sublimation-deposition method by cooling the encapseled SiC slowly from 2800K.
Lattice imaging of antiphase boundaries in GaAs grown on Si
Authors: Liliental-Weber Zuzanna , O'Keefe Michael A. , Washburn Jack
Published: June 2020

The growth of GaAs on Si has been recognized as a highly desirable technology goal for a number of years. However, the large lattice misfit between GaAs and Si and the problem of growing a polar crystal on a nonpolar substrate can result in a high density of lattice defects, including antiphase disorder. At an antiphase boundary (APB) the Ga-As bonds are replaced by As-As and Ga-Ga bonds. It is expected that APBs can be highly charged, and they might collect charged impurities unless alternating As-As and Ga-Ga bonds are so close that they can neutralize each other. APBs can result from the coalescence of GaAs domains independently nucleated on the Si substrate. This can occur due to a single step or an odd number of (a/4) Si surface steps, or when the coalescing domains have grown so that one domain starts with a Ga layer and the other domain starts with an As layer.
Crystallizing Y2Si2O7 at the grain boundaries of a Si3N4 ceramic
Authors: Hiltnas G. E. , Lee W. E.
Published: June 2020

Improving the high temperature properties of Si3N4 containing glass at the grain boundaries may be possible by crystallizing the glass to a refractory phase as first suggested by Tsuge et al. AEM has recently been used to examine the morphology of cordierite (Mg2Al4Si5O18) and garnet (Y3Al5O12) crystallized at the grain boundaries of SiAlON ceramics. We present here results of an AEM investigation of the morphology of Y2Si2O7 crystallized from a 6 weight % Y2O3-Si3N4 ceramic.

Bars were isostatically pressed and then sintered at 2140°C for 2 hours in 50 atm N2. Crystallization was at 1500°C in 50 atm N2 for various times up to 20 hours. Microscopy samples were prepared using conventional techniques and examined in a JEOL 200CX AEM.

The microstructure of an as-sintered specimen is shown in Figure 1. A few of the hexagonal β-Si3N4 grains contain dislocations (arrowed). These are most likely simple growth defects from the a →β-Si3N4 solution-reprecipitation sintering process.
Role of boundaries in the crystallization of amorphous films
Authors: Smith D. A.
Published: June 2020

The nucleation and growth processes which lead to the formation of a thin film are particularly amenable to investigation by transmission electron microscopy either in situ or subsequent to deposition. In situ studies have enabled the observation of island nucleation and growth, together with addition of atoms to surface steps. This paper is concerned with post-deposition crystallization of amorphous alloys. It will be argued that the processes occurring during low temperature deposition of one component systems are related but the evidence is mainly indirect. Amorphous films result when the deposition conditions such as low temperature or the presence of impurities (intentional or unintentional) preclude the atomic mobility necessary for crystallization. Representative examples of this behavior are CVD silicon grown below about 670°C, metalloids, such as antimony deposited at room temperature, binary alloys or compounds such as Cu-Ag or Cr O2, respectively. Elemental metals are not stable in the amorphous state.
Minimum-dose electron energy-loss spectroscopy
Authors: Kundmann Michael K. , Krivanek Ondrej L. , Martin J.M.
Published: June 2020

Parallel-detection electron energy-loss spectrometers have greatly reduced the irradiation doses needed to acquire electron energy-loss spectroscopy (EELS) data. This raises the possibility that changes in chemical bonding due to radiation damage, which usually precede changes incomposition, may be studied by examining alterations in low-loss and core-edge fine structure with increasing dose.

The quality of data attainable with low-doses in parallel-detection EELS is illustrated by Fig. 1, which shows the K-edge region for a thin amorphous carbon film. This spectrum was collected in 2sec with a 1pm-diameter probe at 100kV in (microscope) diffraction mode. A 20cm camera length ensured that virtually all scattered electrons passed through the 3mm entrance aperture of the spectrometer. Spectrum dispersion is 3eV/channel and the energy resolution is ∼1eV/channel as the π* peak is clearly resolved. The total incident current, as determined in image mode (no objective aperture) from the viewing-screen meter, was only 40pA. The total dose for this K-edge spectrum was consequently only 6.4e-/Å2.
A CCD parallel detection system for electron diffraction and imaging with large dynamic range
Authors: Zuo J.M. , Spence J.C.H. , Hoier R. , Wheatley J.
Published: June 2020

The quantitative recording of convergent-beam electron diffraction patterns (CBED), spot patterns. RHEED patterns and high resolution images requires a parallel detection system with large dynamic range. Systems based on YAG detectors and television tubes are ideal for recording rapidly changing events, however the integration of many such images provides a limited improvement in dynamic range since the read-out process itself introduces noise. Charge-coupled devices (CCDs) have been shown to provide a promising alternative for recording diffraction patterns. Our system is intended for recording the weak reflections from reconstructed surfaces in transmission on the U.H.V. Philips-Gatan EM430. and for structure-factor refinement by quantitative CBED (see these proceedings). Our CCD system, fitted to a Philips EM400, is based on the Photometries CC210 camera (see figure 1). A YAG single-crystal screen is bonded to fibre-optics, which transfers the image out of the vacuum and onto a Thomson-CSF TH7882CDA 576x384x14 bit CCD cooled by liquid nitrogen.
Transfer optics for high spatial resolution electron spectroscopy
Authors: Hembree G. G. , Hong Luo Chuan , Bennett P.A. , Venables J.A.
Published: June 2020

A new field emission scanning transmission electron microscope has been constructed for the NSF HREM facility at Arizona State University. The microscope is to be used for studies of surfaces, and incorporates several surface-related features, including provision for analysis of secondary and Auger electrons; these electrons are collected through the objective lens from either side of the sample, using the parallelizing action of the magnetic field. This collimates all the low energy electrons, which spiral in the high magnetic field. Given an initial field Bi∼1T, and a final (parallelizing) field Bf∼0.01T, all electrons emerge into a cone of semi-angle θf≤6°. The main practical problem in the way of using this well collimated beam of low energy (0-2keV) electrons is that it is travelling along the path of the (100keV) probing electron beam. To collect and analyze them, they must be deflected off the beam path with minimal effect on the probe position.
Design of a high-performance auger spectrometer in the STEM
Authors: Ouyang Feng
Published: June 2020

In high resolution electron beam instruments, Auger analysis is usually performed by keeping the sample in a field free region and employing a standard energy analyzer such as hemispherical sector (HSA) or a cylindrical mirror (CMA). In spite of its simplicity, this arrangement results in long focal length operation and consequently a relatively large spot size. In addition, the collection efficiencies of the energy analyzer coupled with such STEM/SEM/SAM systems tend to be small. If however we perform Auger analysis with the sample immersed in the objective lens field, not only would we have the capability of producing a subnanometer diameter probe, but we can also use the post- or pre-specimen field to parallelize the emitted electrons to yield higher collection efficiency.

One approach is to use an electrostatic optics extraction system. In this paper magnetic optics extraction will be considered.
A comparison of two windowless x-ray detector designs on VG HB501 STEMs
Authors: Nicholls A. W.
Published: June 2020

Windowless X-ray detectors are routinely used on VG HB501 STEMs allowing detection of all elements from B upwards (fig 1). The original design for the HB501 built by Link Analytical had a theoretical solid angle of 0.077sr but recently a new design has appeared with a solid angle of 0.181sr. In order to compare these two designs it would be useful to develop a test that could be carried out on the microscope column that would accurately characterise the performance of the detector in the low energy range (<1keV) as well as at higher energies. Recently there has been much interest in characterising X-ray detector microscope systems using the peak to background (P' B) ratio from specially prepared evaporated Cr films. As an extension to this method this type of specimen has-been used to look at the ratio of effective detector solid angles and also the low energy area by comparing CrK to CrL intensities in order to fully characterise the detectors on VG HB501 STEMs.
Quantitative evaluation of materials by scanning electron microscopy
Authors: Pignolet-Brandom S. , Reid K. J.
Published: June 2020

QEM*SEM, or quantitative evaluation of materials by scanning electron microscopy, is a fully automated scanning electron microscope system that was designed and engineered by CSIRO in Australia for applications to the minerals industry. It is an integrated system in which the computer and its associated hardware and software control SEM operations. Minerals can be identified in point, linear or area scans. Depending on the type of scan, information is extracted from the data files and summarized in tables and graphs covering mineral abudances, associations, sizes, free surface area and the degree of liberation. In addition, area scans can be replayed on a graphics monitor to produce QEM*SEM mineral species maps.

The QEM*SEM system consists of an International Scientific Instruments SX-40 scanning electron microscope with a specially designed sample chamber that permits 100 mm movement of the stage. The EDS units were designed for rapid collection of x-ray spectra and consist of four lithium drifted silicon detectors each with a separate preamplifier.
REM and RHEED investigation of the epitaxy of evaporated gold film on a CaAs (110) surface
Authors: Yao N. , Cowley J. M.
Published: June 2020

Detailed understanding of the epitaxial grown gold thin film is highly desirable, both for fundamental physical reasons and due to increasingly sophisticated applications. In this paper, we present the utilization of the significant advantages of both REM and RHEED in a commercial Philip-400T instrument to investigate the crystalline quality and topography of epitaxical gold layers on GaAs(110) surfaces.

The specimen preparation was carried out in a commercial FC-12E UHV system containing a quartz crystal sensor for thickness control. The experimental arrangement inside the UHV chamber is shown in Fig. 1, where the evaporating source is set in a position equally distance from the crystal sensor and the specimen substrate. The bulk shield next to the specimen is to block a part of the gold flux, thus the growing film with a certain variation of thickness can be formed on the GaAs (110) plane which faces the shield.
Surface resonance channelling in scanning reflection electron microscopy
Authors: Cowley J.M. , Crozier P.A.
Published: June 2020

The phenomena of the channelling of electrons along planes or rows of atoms in the surface layers of crystals has been investigated recently in relation to microdiffraction and RHEED, REM, (reflection electron microscopy) and REELS (reflection electron energy loss spectroscopy) by using a conventional TEM in the reflection mode.

The renewed interest in this phenomenon, known for many years, is the evidence from calculations of dynamical diffraction effect at surfaces that the electrons may be channelled along the topmost layers of atoms on a crystal surface and that the RHEED, REM and REELS signals may thus be sensitive to the structure and composition of the surface layer. These techniques may therefore provide a powerful new approach to the study of surfaces in which surface microanalysis and diffraction studies may be combined with nanometer-resolution imaging.

An investigation has now been made of the analogous techniques which may be applied to the study of surfaces by use of a scanning transmission electron microscope.
What catalysis needs from the electron microscopist
Authors: Bell Alexis T.
Published: June 2020

Heterogeneous catalysts, used in industry for the production of fuels and chemicals, are microporous solids characterized by a high internal surface area. The catalyticly active sites may occur at the surface of the bulk solid or of small crystallites deposited on a porous support. An example of the former case would be a zeolite, and of the latter, a supported metal catalyst. Since the activity and selectivity of a catalyst are known to be a function of surface composition and structure, it is highly desirable to characterize catalyst surfaces with atomic scale resolution. Where the active phase is dispersed on a support, it is also important to know the dispersion of the deposited phase, as well as its structural and compositional uniformity, the latter characteristics being particularly important in the case of multicomponent catalysts. Knowledge of the pore size and shape is also important, since these can influence the transport of reactants and products through a catalyst and the dynamics of catalyst deactivation.
Microdiffraction studies of small crystallites
Authors: Bradley S. A. , Robota H. J.
Published: June 2020

Identification of nano-crystallites (<5 nm) on a high surface area support such as a catalyst is critical in the development of improved catalysts. Bright field imaging of small particles can be obscured by the phase contrast of the support. A common approach is to utilize annular dark field microscopy; however, wide angle scattering from the high surface area support can easily appear in the annular dark field image. Often one utilizes the energy dispersive detector to identify conclusively the nanosized metal crystallite, but this approach is troublesome when crystallites are very thin since counting times for imaging can become excessive. One technique for avoiding some of these difficulties is to utilize microdiffraction to identify the crystallite and then to image the crystallite by axial dark field microscopy.

In the work reported here, the imaging was performed with a dedicated VG HB-5 scanning transmission electron microscope.
Intermetallic phases in Pt-Sn model catalyst
Authors: Behal S. K. , Disko M. M. , Ayer R. , Scanlon J. , Meitzner G. , Fung S.C. , Sinfelt J.H. , Via G.H.
Published: June 2020

Bimetallic reforming catalysts play an important role in the production of automotive fuels. In the past twenty years, detailed studies with techniques that include EXAFS of the Pt-Ir system have shown evidence of highly dispersed bimetallic clusters which produce catalysts that have high stability and activity. Supported platinum-tin catalysts are another important system. The structure and composition of the metallic clusters in this type of catalyst are known to vary with the method of preparation. We have combined x-ray diffraction (XRD), extended x-ray absorption fine structure (EXAFS), energy dispersive x-ray (EDX), microdiffraction and high resolution imaging in order to characterize the structure of two Pt-Sn samples supported on silica (Cab-o-sil HS-5). The first sample (R) had a high metal loading (5 wt. % Pt - 3 wt. % Sn) and the metal impregnated silica was dried in air at 380 K and then reduced under hydrogen at 775 K.
Void nucleation by interface decohesion in whisker-reinforced composites
Authors: Nutt S.R.
Published: June 2020

Metal-matrix and ceramic-matrix composites reinforced with whiskers or short fibers exhibit improvements in certain mechanical properties. In the case of metal-matrix composites, improvements in yield strength and modulus are commonly achieved, but often at the expense of ductility and fracture toughness. Interestingly, ceramics reinforced with whiskers frequently show improvements in fracture toughness, while there is little effect on fracture strength compared with the unreinforced material. Also, both classes of materials are generally more resistant to creep deformation. Mechanisms of damage leading to composite failure can be directly observed in the TEM by examination of specimens from tests interrupted at specific stages prior to failure. One damage mechanism common to both types of composites is the nucleation of voids at fiber interfaces. This process can be simulated in model-based calculations, yielding quantitative information about interface properties.

Creep tests were conducted on 2124 Al-SiC and Al2O3-SiC composites in which the whisker reinforcement loadings were 13 and 33 v/o respectively.
HREM interface studies in SiC-whisker-reinforced Al2O3and Si3N4ceramics
Authors: Braue W. , Carpenter R.W. , Smith D.J.
Published: June 2020

Whisker and fiber reinforcement has been established as an effective toughening concept for monolithic structural ceramics to overcome limited fracture toughness and brittleness. SiC whiskers in particular combine both high strength and elastic moduli with good thermal stability and are compatible with most oxide and nonoxide matrices. As the major toughening mechanisms - crack branching, deflection and bridging - in SiC whiskenreinforced Al2O3and Si3N41are critically dependent on interface properties, a detailed TEM investigation was conducted on whisker/matrix interfaces in these all-ceramic- composites.

In this study we present HREM images obtained at 400 kV from β-SiC/α-Al2O3and β-SiC/β-Si3N4interfaces, as well as preliminary analytical data. The Al2O3- base composite was hotpressed at 1830 °C/60 MPa in vacuum and the Si3N4-base material at 1725 °C/30 MPa in argon atmosphere, respectively, adding a total of 6 vt.% (Y2O3+ Al2O3) to the latter to promote densification.
Image analysis and SEM characterization of SiC whiskers and ceramic composites
Authors: Chen R. T. , Jamieson M. G.
Published: June 2020

Recently, attention has been focused on whisker reinforced ceramic composites Ipecause of their potential in high temperature structural applications. Aspect ratios of whiskers and particle size distributions of the matrix ceramic powders are critical parameters which can effect processing and microstructure/properties of the final composite materials. In this paper, quantification of these parameters using SEM and automated image analysis, as well as their significance in the development of whisker reinforced ceramic composites will be discussed.

The present study involved the evaluation of microstructures of SiC reinforced alumina ceramic composites. In the evaluation of SiC whiskers, good whisker dispersal is a prerequisite for automated image analysis. A dispersion technique was used to break up the agglomerated SiC whiskers. Whiskers were dispersed on glass slides and aspect ratios were measured using a Quantimet-970 image analyzer interfaced to an optical microscope. Because of the submicron nature of the starting alumina powders, SEM was needed to provide images. For grain size evaluation, both fracture surfaces and polished/etched surfaces were examined in a JEOL JXA-840 SEM.
TEM study of the T2 phase in Al-Li-Cu alloys at elevated temperatures
Authors: Reed J. R. , Michel D. J.
Published: June 2020

The discovery of an alloy phase exhibiting five-fold symmetry in rapidly quenched Al-Mn alloys has led to reports of similar phases in other alloys systems. Other studies have suggested that the T2 phase in Al-Li-Cu alloys exhibits five-fold symmetry and forms as a stable phase by solidification directly from the bulk alloy. Although considerable effort has been expended to investigate the icosahedral phases, including the T2 phase in the Al-Li-Cu system, the thermal stability of this phase remains unknown. The purpose of this paper is to report results from an investigation of the thermal response of the T2 phase in Al-Li-Cu alloys during an in-situ elevated temperature transmission electron microscope study.

The 3-mm diameter specimens used for the transmission electron study were prepared from a specially melted Al-2.5 Li-2.5 Cu alloy produced by conventional procedures. The TEM disc specimens were solutioned 1 h at 550°C and aged 50 h at 190°C in air to develop the microstructure.
Electron microscopy of modulated and ordered alloys
Authors: Bentley J.
Published: June 2020

Modulated and ordered alloys are of interest not only from a basic standpoint but also because they often possess interesting properties or form the basis of commercial materials. Transmission electron microscopy (TEM) provides much unique and valuable information in the study of phase transformations in such alloys but, as this overview of the applicable methods will try to illustrate, the experimental work is often challenging and data interpretation is rarely straightforward.

In alloys with a modulated structure, spinodal decomposition is the transformation process of most interest. In cubic crystals, elastic anisotropy usually leads to triaxially modulated structures with composition modulations along <100>, whereas in isotropic systems, randomly oriented, highly interconnected structures are formed. TEM has most commonly been used to image the spinodal microstructure and to measure wavelength and waveshape. The observations are often only qualitative because of the complex nature of the image, but quantitative measurements of coarsening behavior have been attempted.
A Transmission Electron Microscopy study of the B2-DO3 ordering phase transformations in Fe-6.3wt% Si after rapid quenching and annealing
Authors: Wittig J. E.
Published: June 2020

Iron-silicon alloys are extensively used in transformer cores owing to exceptional soft magnetic behavior that is optimized at about 6.5 wt% Si. Unfortunately this equilibrium microstructure is completely brittle at room temperature. The brittle behavior coincides with the onset of an ordering reaction of the disordered A2 into the B2 and DO3 superlattices at approximately 5 wt% Si. Rapid solidification methods have been shown to improve the ductility of Fe- 6.3 to 6.5 wt% Si. In this investigation, rapidly quenched and annealed samples of Fe-6.3wt% Si were examined in the transmission electron microscope (TEM) to study the ordering phase transformations of this alloy and its effect on the mechanical behavior.

Samples of Fe-6.3wt% Si were rapidly solidified by melt spinning into ribbons (t=20-80 microns) as well as by splatting using an opposing piston double anvil method. Rapidly quenched samples were subsequently heat treated in evacuated quartz tubes at 500, 600, and 700 C for 24 h.
Disordering and phase decomposition of a nickel-aluminum intermetallic under lowtemperature electron irradiation
Authors: Kenik E. A. , Nastasi M.
Published: June 2020

In situ electron irradiations at 300 and 1000 kV have been performed at 100 and 300 K on Ni2Al3 for comparison with its response under ion irradiation. In addition, the behavior of Ni2Al3 will be compared to that of NiAl3 reported previously. Thin multilayered films of alternating nickel and aluminum were electron beam deposited onto a NaCl substrate. The substrate was dissolved in deionized water and the Ni/Al film was mounted on 3 mm diam grids. The films were vacuum annealed for 1—2 h at 623 K to allow interdiffusion between the layers. Electron diffraction indicated that the films were fine-grained (∼20 nm diam) Ni2Al3, which is the prototype for the hexagonal D513 structure. No appreciable amount of other phases was detected.

The specimens were irradiated with 1000 kV electrons in a Hitachi HU-1000B or with 200—300 kV electrons in Philips EM430 and CM30 microscopes. All three microscopes are equipped for nominal room temperature or low temperature (∼100 K) irradiations.
Microstructure of rapidly solidified Fe-Ni-Al-C Alloys
Authors: Myers S.A.
Published: June 2020

Studies on the quench rate-structure relationship in Fe-Al-C base alloys have yielded controversial results. Inoue et al reported a non-equilibrium Cu3AU (LI2) type structure in the Fe-Al-C and the Fe(Ni,Mn)-Al-C systems based on electron diffraction analysis from melt spun samples of thickness 70-200 μm. Han and Choo, in an x ray diffraction study, observed a disordered fcc phase accompanied by phase decomposition for 30-48 μm thick ribbons of the same composition. Chen, Myers and Koch using an arc hammer apparatus, studied the effect of quench rate and composition on the structure of the (Fe,Ni)3Al-C system. Three widely different cooling rates were studied by varying the thickness of the samples. The ordered L12 was not found by x ray diffraction in the composition range of 7-55 w/o Ni, 3-9 w/o Al and 0.8-2.4 w/o C. However, a very thick sample of Fe-20Ni-8Al-1.8C, 75-100 μm thick, analyzed by electron diffraction, exhibited the ordered fcc structure and cuboidal ordered domains similar to the observations of Inoue et al.
A combined TEM/APFIM approach to the study of phase transformations: Phase identification in the Fe-Be system
Authors: Burke M.G. , Miller M.K.
Published: June 2020

Phase transformation investigations rely on the identification and characterization of the microstructure in order to understand the formation, development, and relative stability of the constituent phases. Although transmission and associated analytical electron microscopy techniques have made substantial contributions by providing structural and chemical data necessary for the detailed microstructural analysis, the direct atomic structure and chemistry are not readily discernable. By combining TEM techniques with atom probe field-ion microscopy (APFIM), it is possible to obtain a complete structural and chemical analysis of the constituent phases. In this paper, the microstructural development which occurs during ageing in an Fe-25 at. % Be alloy is presented to illustrate the complementary nature of the techniques and demonstrate the applicability of the combined TEM/APFIM approach in the study of phase transformations.

An Fe-25 at. % Be alloy was solution annealed at 1100°C for 0.5 h and water-quenched prior to isothermal ageing at 650°C for 4 h. Thin foil specimens were examined in a Philips EM430T operated at 300 kV and in a JEOL 200CX operated at 200 kV. FIM needle specimens were electropolished and analyzed in the ORNL energy-compensated APFIM.
Rapidly solidified and thermally treated microstructures of beryllium-1wt.% Yttrium alloy
Authors: Jacobson L. A. , Martin P.L. , Mitchell T. E.
Published: June 2020

Renewed interest in the possible use of beryllium at elevated temperatures has led to the examination of several dilute beryllium alloys with elements that form high melting point beryllide intermetallic compounds. One such alloying element is yttrium, which forms a beryllide, YBe13, with a melting point of over 1900° C. This system has been reported to have a eutectic between Be and YBe13at a composition under 1 wt% Y. 13 Dilute alloys in this system have been investigated as to their superplastic behavior.

Samples were prepared by arc melting l0g buttons of Be-1wt% Y alloy, melting at least three times to promote homogeneity. Very small pieces of a button were then arc melted on a water cooled copper hearth and splat-quenched by means of a spring loaded hammer. Pieces of splat material were heat treated for 2h at 1000°C, and 3mm disks were punched out for subsequent twin jet electrolytic thinning and examination by transmission electron microscopy.
Observation by HVEM of the martensite transformation and the superconducting transition in Nb3Sn
Authors: Kirk M. A. , Baker M. C. , Kestel B. J. , Weber H. W.
Published: June 2020

It is well known that a number of compound superconductors with the A15 structure undergo a martensite transformation when cooled to the superconducting state. Nb3Sn is one of those compounds that transforms, at least partially, from a cubic to tetragonal structure near 43 K. To our knowledge this transformation in Nb3Sn has not been studied by TEM. In fact, the only low temperature TEM study of an A15 material, V3Si, was performed by Goringe and Valdre over 20 years ago. They found the martensite structure in some foil areas at temperatures between 11 and 29 K, accompanied by faults that consisted of coherent twin boundaries on {110} planes. In pursuing our studies of irradiation defects in superconductors, we are the first to observe by TEM a similar martensite structure in Nb3Sn.

Samples of Nb3Sn suitable for TEM studies have been produced by both a liquid solute diffusion reaction and by sputter deposition of thin films.
XTEM study of phase transition in MeV ion-implanted InP
Authors: Xiong Fulin
Published: June 2020

MeV ion implantation into III-V compound semiconductors has attracted great attention in recent years because of its high potential for 3-dimensional device fabrication technology. However, a thorough understanding of associated physical processes involved is crucial before it can be universally applied. Our study on this subject with InP using cross sectional and high resolution transmission electron microscopy (XTEM, HRTEM) reveals clearly the structural changes occurring during MeV-ion-implantation and subsequent thermal annealing. It has lead to a better understanding of the mechanism of phase transition in InP under MeV ion irradiation.

Samples of n-type InP(lOO) single crystalline wafers were implanted with 5 MeV-N-ions in room temperature with doses ranging from 1014 to 1016/cm2. Post-implantation annealing was carried out in a graphite strip heater at 500 C with ambient H2 flow.

Fig. 1 shows a typical XTEM view of an implanted sample at a dose of 1 x 1016/cm2. A wide implanted layer is buried at a maximum depth of 4μm with a slightly damaged top surface. The buried layer appears as a highly disordered crystalline structure when the sample was annealed, whereas it is amorphous in an as-implanted sample.
Reaction couples of ceramic thin films prepared by CVD
Authors: Susnitzky D.W. , Summerfelt S.R. , Carter C.B.
Published: June 2020

Solid-state reactions have traditionally been studied in the form of diffusion couples. This ‘bulk’ approach has been modified, for the specific case of the reaction between NiO and Al2O3, by growing NiAl2O4 (spinel) from electron-transparent Al2O3 TEM foils which had been exposed to NiO vapor at 1415°C. This latter ‘thin-film’ approach has been used to characterize the initial stage of spinel formation and to produce clean phase boundaries since further TEM preparation is not required after the reaction is completed. The present study demonstrates that chemical-vapor deposition (CVD) can be used to deposit NiO particles, with controlled size and spatial distributions, onto Al2O3 TEM specimens. Chemical reactions do not occur during the deposition process, since CVD is a relatively low-temperature technique, and thus the NiO-Al2O3 interface can be characterized. Moreover, a series of annealing treatments can be performed on the same sample which allows both Ni0-NiAl2O4 and NiAl2O4-Al2O3 interfaces to be characterized and which therefore makes this technique amenable to kinetics studies of thin-film reactions.
Growth of hematite by surface oxidation of olivine
Authors: McKernan S. , Carter C. B.
Published: June 2020

The oxidation of natural olivine has previously been performed on bulk samples and the reactions followed by preparation of TEM specimens from the annealed material. These results show that below ∼1000°C hematite and amorphous silica are formed, particularly around dislocations. At higher temperatures magnetite and some enstatite-like phase are formed. In both cases the olivine is left almost totally Fe depleted. By performing the oxidation on characterized thin TEM specimens it is possible to obtain more information on the nucleation and growth of the second phases formed. The conditions in a thin foil, however, are very different from those in the bulk especially with regard to surface effects. The nucleation of precipitates in particular may be expected to occur differently in these thin foils than in the bulk.

TEM specimens of natural olivine (approximate composition Mg+Fe+Si2o4) which had been annealed at 1000°C for 1 hr were prepared by mechanical polishing and dimpling, followed by Ar ion milling to perforation. The specimens were characterized in the electron microscope and then heated in air in alumina boats to 900°C for between 30 and 180 minutes.
An overview of North American user facilities for electron microscopy in the physical sciences
Authors: Gronsky R.
Published: June 2020

Physical scientists working in North America have access to five major User Facilities for advanced applications of electron microscopy. These Facilities are distributed geographically as shown in Figure 1, and provide a wide range of sophisticated instrumentation not normally found in the conventional electron microscope laboratory. Born of the need to maintain state-of- the-art equipment for research in the physical sciences and created because of the increasing cost and sophistication of such instrumentation, they operate on a “shareable” basis, having been funded by the government agencies to serve as regional and national resources, not for exclusive parochial access.

The five facilities described here are: [1] the National Center for Electron Microscopy at the Lawrence Berkeley Laboratory, funded by the Department of Energy; [2] the Facility for High Resolution Electron Microscopy at Arizona State University, funded by the National Science Foundation; [3] the Center for Microanalysis of Materials at the University of Illinois, Urbana-Champaign, funded by both the Department of Energy and the National Science Foundation;
The National Facility for High Resolution Electron Microscopy at Arizona State University
Authors: Barry J. C.
Published: June 2020

The National Facility for High Resolution Electron Microscopy, within the Center for Solid State Science at Arizona State University, was established in 1979 by the National Science Foundation. The Facility was established for the purposes of advancing knowledge in the field of high resolution electron microscopy, and promoting the application of new research methods to problems of current scientific and technological importance. The current Director of the Facility is Dr. John M. Cowley.

The major equipment at the Facility is as follows.

JEM 4000EX 400keV ultra-high resolution electron microscope (installed 1984). Structure resolution limit of 1.7 Å, and information limit of 1.6 Å. The 4000EX can be placed under computer control (using a system developed at ASU) for the purposes of alignment; that is, the computer automatically corrects the focus, stigmation and beam tilt. At 1.7 Å resolution, direct structure images of virtually all crystalline materials can be obtained, and individual atomic columns may be resolved in many samples. The 4000EX has been applied to characterization of defects, interfaces and surfaces of ceramics, metals and semiconductors.
The National Center for Electron Microscopy at Berkeley: An Update
Authors: Westmacott K. H. , Dahmen U.
Published: June 2020

Since its establishment in 1984 the National Center for Electron Microscopy (NCEM) has provided a wide variety of users with advanced electron microscopy facilities for microstructural characterization. It has, in addition continued to develop and improve its resources to expand the range of features available to users.

A major effort has been expended in building up a comprehensive computing facility to assist microscopists in optimizing instrument performance and extracting the maximum information from experimental data. The best currently available hardware has been assembled and a long menu of user-friendly software programs have been developed for general use. Sophisticated image simulation and image enhancement programs provide users of the Atomic Resolution Microscope all the necessary information for the correct interpretation of high resolution images. Direct links to both the ARM and the 1.5 MeV Kratos HVEM allow Fast Fourier Transforms to be performed, producing on-line diffractograms and greatly facilitating the effective and efficient use of the microscopes.
On the accuracy of structure-factor measurements in GaAs by CBED
Authors: Zuo J.M. , O'Keeffe M. , Spence J.C.H.
Published: June 2020

By comparing the experimental intensity in convergent-beam electron diffraction (CBED) patterns along the [h,0,0], [h,h,0] and [h,h,h] systematics directions with three-dimensional Bloch-wave calculations, we have refined the low-order structure factor amplitudes of GaAs. (For Si, see) The experimental data were collected using a Philips EM400 electron microscope and a Gatan model 607 electron energy loss spectrometer (EELS) tuned to the elastic peak. By placing the scan coils of the microscope under the control of a PDP11 computer, the CBED patterns could be scanned over the EELS entrance slit. Data were collected at 120kV and -183°C to reduce phonon scattering and contamination. The angular resolution was 0.6% of the (200) Bragg angle. The refinement parameters in the calculations were high voltage (obtained from HOLZ lines), thickness (obtained from outer CBED fringes), absorption potentials (from the asymmetry of the (000) disk) and the low-order structure factors Vg(from inner peaks).
A very rapid in situ Kikuchi technique to determine relative crystal misorientation
Authors: Bennetch J. I.
Published: June 2020

In a recent study of the superplastic forming (SPF) behavior of certain Al-Li-X alloys, the relative misorientation between adjacent (sub)grains proved to be an important parameter. It is well established that the most accurate way to determine misorientation across boundaries is by Kikuchi line analysis. However, the SPF study required the characterization of a large number of (sub)grains in each sample to be statistically meaningful, a very time-consuming task even for comparatively rapid Kikuchi analytical techniques.

In order to circumvent this problem, an alternate, even more rapid in-situ Kikuchi technique was devised, eliminating the need for the developing of negatives and any subsequent measurements on photographic plates. All that is required is a double tilt low backlash goniometer capable of tilting ± 45° in one axis and ± 30° in the other axis. The procedure is as follows. While viewing the microscope screen, one merely tilts the specimen until a standard recognizable reference Kikuchi pattern is centered, making sure, at the same time, that the focused electron beam remains on the (sub)grain in question.