bluuebunny/crossref_metadata_2025 huggingface dataset:
High-resolution imaging of Σ=5 tilt boundaries in gold
Authors: Cosandey F. , Chan S.-W. , Stadelmann P.
Published: June 2020

Until recently most of the information concerning the atomic structure of grain boundaries in metals has been obtained using molecular static and molecular dynamic computational techniques. With the recent developments of intermediate voltage microscope (300-400KV) this situation has changed and grain boundary atomic resolution is now possible for most metals. The purpose of this research is to examine the atomic structure of Σ=5 tilt boundaries in Au by high resolution microscopy and to compare the results to computational models.

Thin film Au bicrystals containing Σ=5 (θ=36.5°±0.5) tilt grain boundaries were produced by epitaxial growth on NaCl bicrystalline substrates using a technique described in detail elsewhere. All high resolution images were obtained with a Philips 430 ST microscope using axial illumination and without objective aperture. All image simulations were obtained using the multislice formalism with EMS programs. All four {200} reflections from each crystal were used for the simulations with the following instrumental parameters; accelerating voltage V=300KV, spherical aberration constant Cs=1.1mm, defocus spread Δ=8nm and semi-angle beam divergence α=8mrad.
Clustering of coincident site lattice boundaries in polycrystals
Authors: fendle Valerie , Ralph Brian
Published: June 2020

The distribution of coincident site lattice (CSL) and other geometrically special boundaries have been analysed in the form of “grain misorientation texture” (GMT) plots for several systems (pure nickel, a number of austenitic stainless steels and a complex superalloy, 1-5). Several heat treatment conditions have been investigated for each system. Principally, electron back scattering (EBS) in a scanning electron microscope has been used to collect the “microtexture” (i.e. grain specific) data which combines the considerable advantages of bulk specimen texture analysis, grain environment specification with semi-automatic operation. These data are currently being supplemented with thin foil transmission electron microscope (TEM) analyses which permit more detailed investigation of the grain boundary parameters (especially grain boundary planes).

Conventional texture measurement shave akey role in assessing the overall changes which occur during thermomechanical processing. However, the very detailed orientation measurements give only a statistical picture and this means that neither the geometry of individual boundaries (the GMT) nor ary tendency for clustering of particular texture types or boundary types may be detected.
New imaging modes in STEM
Authors: Jones A.V.
Published: June 2020

The most often quoted advantage of STEM over conventional TEM is the ability to produce multiple simultaneous images by the use of multiple detector systems. In practice, this postulated advantage has seldom been fully utilised, mainly because of the practical difficulties in designing such detector systems.

Most STEMs to date have been constructed as two-channel instruments combining annular dark-field imaging with either filtered bright-freld or inelastic imaging. More complex forms of bright-field detector have been employed1, as have parallel-readout systems for energy-loss spectra but the ability of the spectrometer to produce multiple simultaneous images has not been fully utilised.

The basis of the problem lies in the fact that the objective lens and the detector system(s) have in most cases been designed by the manufacturers as separate entities in order to simplify the later addition of user-specific detectors. Since the acceptance angle of even the best spectrometers is relatively small, additional post-specimen lenses [with their attendant aberrations] had to be added in order to make full use of the spectrometer.
Instrumentation for a corrected STEM
Authors: Crewe Albert V.
Published: June 2020

In accepting an invitation to speak in this symposium all the speakers today are exposing themselves to great hazards, and none more so than me. The capabilities of computers, their variety, the associated instrumentation, are all expanding so rapidly and changes are taking place with such a frequency that we are all inevitably out of date. The mere fact of having to prepare an abstract in March for a meeting in August presents hazards. Who knows what revolution in the state of the art will be announced in the meantime?

My own project was started four or five years ago so that we may be considerably behind the times. As time went along we were able to take advantage of some of the new developments in technology but in many cases we were simply too far along to make adjustments. As a result, if one were to ask whether our project should serve as a model or whether we would do it the same way again, the answer would have to be “no.” On the other hand, some of the features are good and may serve as examples for future projects. The reader will have to decide.
EELS parallel detection using 2-dimensional CCD array
Authors: Zaluzec N.J. , Strauss M. G.
Published: June 2020

Conventional parallel detectors for Electron Energy Loss Spectroscopy (EELS) have been mainly based upon systems using linear photodiode arrays in a conjugate image plane of an electron spectrometer. We have developed a unique two dimensional charge coupled device (CCD) camera system which can be used as a detector for EEL spectroscopy and imaging, utilizing high sensitivity, high resolution CCD's, which are typically used in medial or astronomic imaging.

The present detector system is based upon a Tektronics TK512M 512 x 512 pixel CCD array, (figure 1) which is optically coupled to a YAG:Ce single crystal scintillator. This CCD imaging system views an electron energy loss spectrum which is magnified by a quadrupole doublet lens attached to a Gatan 607 electron spectrometer on a Philips EM420 TEM as is illustrated in figure 2. The CCD controller, detector head electronics and electron optics were developed at Argonne specifically for high speed data acquisition and allow the recording of complete spectra in as short a time as 10 μsec or approximately 103times faster than the typical 1024 pixel photodiode arrays’ thus allowing the potential for time resolved spectroscopy.
Recent developments in EDS for TEM/STEM
Authors: McCarthy J.J.
Published: June 2020

The development of TEM and STEM in the 100 keV to 400 keV range has prompted the increased use of energy dispersive spectrometers (EDS) for analytical studies on these instruments. The TEM/STEM environment is a harsh one for the EDS in comparison to the SEM. In response to this special environment, spectrometers specifically for TEM/STEM have been developed. This paper will provide a general review of these developments and indicate future directions.

Space near the specimen holder is at a premium in most TEMs. This reduces the solid angle subtended by the Si(Li) detector. Increased cooperation between EM and EDS manufacturers, and the use of new materials for shielding, collimation, and internal detector parts have improved this situation. The use of graded material collimators, removable ultra thin windows (UTW), and compact gate valve arrangements can reduce detector size. The routine use of computer aided design (CAD) systems and computer controlled machining allow extremely close tolerances to be incorporated in the latest designs.
Surface roughness and stability of very thin gold films
Authors: Krakow William
Published: June 2020

The surface roughness of thin Au (111) films observed in the transmission electron microscope has revealed apparent atomic step heights by imaging forbidden reflections. It has also been demonstrated that in medium voltage microscopes (400kV) considerable sputtering takes place at the lower film surface in Au by electron beam irradiation. These studies have relied upon diffraction contrast to observe the surface structures and etch pits produced down to a dimension of perhaps 10 to 20Å which does not allow the surface topographic features to be revealed at an atomic level. At the atomic resolution level, the type of image features observed for surfaces in very thin (111) Au films has been achieved in a high resolution microscope at 200 kV incident beam energy. These results show the type image features depend on both the number of excess layers and the concentration of vacancies from partially filled layers of the bulk lattice from both the top and bottom Au film surfaces.
Characterization of double contours and twin images in REM
Authors: Yao N. , Cowley J. M.
Published: June 2020

The REM technique may be used to reveal detail on the surfaces of large crystals. The single-atom-height steps on certain single crystal surfaces can be seen with high contrast. The observations of double contours of atomic steps on single crystal surfaces have been reported recently. The doubling has been interpreted as Fresnel diffraction contrast or as effects caused by the distortion field around the surface steps. However, due to the foreshortening and other effects, the resolution in the observation direction is limited and details of the surface structure can be obscured by imaging and diffraction artefacts.

The InP(110) surface was obtained by cleavage of a (100) wafer in air. In order to reduce the contamination effects, a nitrogen cooling holder was employed during the observation. The Pt (111) surface was prepared and observed under the conditions described by Hsu and Cowley.
Analysis of Surface species in a Co/La/alumina catalyst
Authors: Lyman C. E.
Published: June 2020

Lanthanum oxide is sometimes used as a promoter for Co-based CO hydrogenation catalysts. However, there is evidence that a high La content decreases catalyst activity and shifts catalyst selectivity. Analysis of such a catalyst by x-ray photoelectron spectroscopy(XPS), Raman spectroscopy, and powder x-ray diffraction suggested the formation of a surface Co-La interaction species. Unfortunately, interpretation of XPS data alone can be difficult if the surface is covered with several compounds of different composition and size. In the present case, there was a need to determine the composition of the surface Co-La interaction species without interference from other compounds containing Co and/or La. Analytical electron microscopy (AEM) is a technique that can provide information about the composition of the catalyst in specific regions of the catalyst surface between the other phases that may be present. Digital x-ray mapping was used here to locate the catalyst areas,free of interfering Co-La compounds,where analysis of the Co-La surface species can be made.
HREM studies on interfaces in internally oxidized alloys
Authors: Mader W.
Published: June 2020

Precipitation of metal oxides by internal oxidation of metal alloys has been widely used for dispersion strengthening of materials in electrical contact applications. Like in other precipitate systems, the oxide precipitates have the freedom to form with any shape and relative orientation with respect to the metal matrix. It is expected that natural, low energy interfaces which are perfectly flat at an atomic scale can be produced by this technique. For these reasons, such interfaces are ideal objects for HREM studies. Interfaces between Nb and Al2O3 and between Ag and CdO, produced using internal oxidation were investigated by HREM techniques in order to extract structural and chemical information at the atomic level.

Specimens of Nb containing 3.5 at% A1 were oxidized at 1500°C in a controlled atmosphere with a low oxygen pressure in order to avoid external oxidation. Small plate-like Al2O3 precipitates 15-30 nm thick and 200-800 nm wide were observed.
Fractographic study of an Al2O3/Al composite
Authors: Flinn B. D.
Published: June 2020

Ceramics have limited engineering applications due mainly to inherent brittleness and catastrophic failure. However the fracture toughness of ceramics has been increased significantly by incorporating ductile second phases into the ceramic matrix. The exact toughening mechanism(s) have not been clearly determined, although several likely models have been proposed. In particular, the ductile phase is thought to contribute to the toughness of the composite if intact particles remain in the crack wake. The intact particles deform plastically and exert tractions on the crack surfaces which inhibit crack opening and hence increase toughness. In order to further enhance understanding of ductile dispersion toughened ceramics, the fracture behavior of an innovative composite composed of co-continuous Al2O3 and A1 (20 vol. %) phases is described.

The fracture behavior was investigated by examining indentation induced cracks and mode I fracture surfaces with a JEOL 840A SEM.
The coprecipitation of Cr3P and Cr in Cu
Authors: Witcomb M.J. , Dahmen U. , Westmacott K.H.
Published: June 2020

Cu-Cr age-hardening alloys are of interest as a model system for the investigation of fcc/bcc interface structures. Several past studies have investigated the morphology and interface structure of Cr precipitates in a Cu matrix (1-3) and good success has been achieved in understanding the crystallography and strain contrast of small needle-shaped precipitates. The present study investigates the effect of small amounts of phosphorous on the precipitation behavior of Cu-Cr alloys.

The same Cu-0.3% Cr alloy as was used in earlier work was rolled to a thickness of 150 μm, solution treated in vacuum at 1050°C for 1h followed by quenching and annealing for various times at 820 and 863°C.

Two laths and their corresponding diffraction patterns in an alloy aged 2h at 820°C are shown in correct relative orientation in Fig. 1. To within the limit of accuracy of the diffraction patterns the orientation relationship was that of Kurdjumov-Sachs (KS), i.e. parallel close-packed planes and directions.
An in situ HVEM study of the migration of bcc/glass interfaces in TiCr2 induced by 1 MeV krypton irradiation at 80-180 K
Authors: Allen C. W. , Rehn L. E.
Published: June 2020

The Laves phase TiCr2 is readily amorphized by 1 MeV Kr irradiation at temperatures below about 250 K. After an ion dose of order 1019 m-2, however, the amorphous phase (a-TiCr2) gradually transforms to the metastable bcc structure without measureable change of composition. This reaction proceeds by a nucleation and growth mechanism and by growth of any bcc material in the initial microstructure. An in situ study of the temperature dependence of the interface velocity in the temperature range 80-180 K has been conducted in the HVEM-Tandem User Facility at Argonne, which allows simultaneous ion irradiation and TEM observation. A single tilt liquid helium stage was employed with a sample of Cr+30 at. pct. Ti, prepared for TEM by mechanical dimpling and ion milling. The sample initially was composed of two phases, the Laves phase TiCr2 and the Cr-rich bcc phase β. During the experiment the temperature was measured and controlled by a platinum resistance thermometer attached to the stage cold block.
Identification of Cr and Cr2Nb precipitates in as-melt-spun Cu-Cr-Nb ribbons
Authors: Ellis D. L. , Michal G. M.
Published: June 2020

A material with high thermal conductivity and mechanical strength at elevated temperatures is required for certain aerospace applications. Copper based alloys precipitation hardened with near zero solubility phases are candidate materials. Utilizing rapid solidification technology, elements such as Cr and Nb can be dissolved into liquid copper and fully precipitated out in the solid state. However, such elemental precipitates readily coarsen at elevated temperatures. The aim of this work was to create a more stable refractory metal intermetallic phase, C2Nb, in an essentially pure copper matrix via melt spinning.

Ribbon was produced by induction melting a master alloy in an alumina crucible with a hole diameter of 1 mm (0.040-inch) using a graphite susceptor under an argon atmosphere. The alloy was heated to 1593°C (2900°F)and ejected onto a Cu wheel with a surface velocity of 20 m/s using a pressure of 0.07 MPa (10 psi). The resulting composition of the ribbon was 1.95 a/o Cr and 0.48 a/o Nb as determined by bulk spectrographic analysis.
Multislice calculations: “Slicing” and those upper Laue layer interactions
Authors: Kilaas Roar
Published: June 2020

Scattering involving reflections outside the zero'th order Laue zone has generally been ignored in multislice calculation. It can be argued that in most cases the contribution from higher zones are negligible and can safely be ignored, but a more accurate description of the problem of including ULL effects is given by the following two statements:

i) the multislice program in question lacks the facility to include ULL layer interactions

ii) the calculation takes too long to be practical

Given the fact that computers are becoming cheaper and faster, ii) will at one point no longer be valid and we are left with i). With few exceptions, multislice programs were not written with ULL interactions in mind. To understand why this is the case, it is necessary to understand why certain scattering angles are included in the calculation and why others are not. As one will see below, the “inclusion” of ULL interactions are directly related to the slice thickness used in multislice calculation and the method of determining a “projected” potential for that slice.
Thickness dependence of the intensities of the 200 forbidden reflections in the TiBe2 diamond type structure
Authors: Liu Dang-Rong , Williams D. B.
Published: June 2020

It is interesting to note that for the diamond type structure of Si, Ge and diamond, the forbidden {200} reflections in the exact <100> orientation diffraction pattern cannot be seen. In contrast, we also note a standing controversy over the structure of the MgAl2O4, spinel. Its structure was determined long ago by x-ray powder method as Fd3m (the diamond type). However, its electron diffraction pattern taken in the <100> orientation shows weak {200} reflections, which are taken as evidence that the spinel should have the space group F43m (the blende type), rather than Fd3m. Others speculate that these {200} reflections result from the high order Laue zone (HOLZ) reflections, and the spinel should be Fd3m. Nevertheless, still others think that these analyses are not conclusive. We have carefully studied the space group of TiBe2 using the convergent beam electron diffraction technique, and unambiguously demonstrated that its space group must be Fd3m.
Revealing depth information by processing EBIC images
Authors: Radzimski Z. , Humphreys T. , Russ J.
Published: June 2020

The conventional use and interpretation of electron beam induced current (EBIC) images in the SEM suffer from several inherent problems. One such problem is the superposition of topographic details, e.g., scratches, dust, contact damage, on the subsurface EBIC signal. Moreover, the use of an accelerating voltage to select depth may not distinguish information from regions close in depth. This exists in depth dependent defect imaging in multi-layer heteroepitaxial structures where two or more defect layers may overlap in the EBIC image.

To alleviate these problems, techniques of image processing may be employed. By digitizing and storing several images, for example in the first problem EBIC and secondary electron image and in the second problem EBIC images obtained at different accelerating voltages, it is possible to use image differencing to extract a more selective image that reveals the desired information. In principle, image differencing requires simple subtraction (or division) of the brightness of each pixel in one image from that in the second.
Electron microscopy of superconducting and related oxides
Authors: Morrissey K. J. , Subramanian M. A. , Torardi C. C. , McCarron E. M. , Calabrese J. C. , Gopalakrishnan J. , Horowitz H. S. , Michel J. B. , Askew T. R. , Flippen R.B. , Chowdhry U. , Sleight A. W.
Published: June 2020

It is important to combine characterization techniques such as electron microscopy with novel materials synthesis in the study of high Tc superconducting phases. Results from electron microscopy studies have been correlated with structure determinations made using x-ray and neutron diffraction (1.2,3.4). Superconducting phases studied to date include YBa2Cu3O7-x, La1.25Ba1.75Cu3O7, Bi2Sr2CuO6, Bi2Sr2CaCu2O8, Tl2Ba2CuO6 Tl2Ba2CaCu2O8, and Tl2Ba2Ca2Cu3O8. A comparison between structures and defect populations suggests that structural defects, which modify the Cu-O arrangement (sheets or chains) intergrowths and grain boundaries, will affect superconductivity. Techniques used in this investigation include HREM, CBED, AEM, SAD and conventional imaging techniques.

Samples characterized in this study were prepared in our laboratory, using both conventional and novel synthesis routes. Powder samples in the Tl-Ba-Cu-O system were prepared by heating mixtures of high purity BaO2, Tl2O2 and CuO to 850-900°C in sealed gold tubes for 1-6 hours (3,4). Similar procedures were followed in the Bi2Sr2CaCu2O8 system using Bi2O3, CaCO3, SrO2/Sr(NO3)2 and CuO. heating the mixtures in air at 700-900°C for 12-36 hours (2.4).
High resolution electron microscopy of bismuth and thallium superconductors
Authors: Zhang J. P. , Li D. J. , Shibahara H. , Marks L. D.
Published: June 2020

A new frontier has opened up in the field of superconductivity with the very recent discovery of compounds of bismuth and thallium which appear to superconduct above 100 K. Both of these compounds appear to be perovskite derivatives with intergrowth of the basic perovskite with bismuth double-layers and perhaps thallium double layers. The structure of these compounds, however, is not as yet completely established, particularly the thallium material which to date has only been produced in very small quantities due to the toxic nature of thallium.

We have very recently been studying both the bismuth and thallium superconductors by high resolution electron microscopy. The bismuth material appears to be an intergrowth of a five layer perovskite with a buckling of the structure along the b axis (see Figure 1) which preliminary image simulations suggest is in the form of a shear wave of amplitude in the region of 0.25 Angstroms.
Microstructure of the superconducting phase (85K) in the Bi-Sr-Ca-Cu-O System
Authors: Sung C. M. , Harmer M. P. , Smyth D. M. , Williams D. B.
Published: June 2020

The discovery of high temperature superconductivity by Bednorz and Muller in a cuprate-based system generated an extensive search for new superconducting oxide phases. Superconductivity at 90K was observed by Wu et al. in the Y-Ba-Cu-O system and this temperature, until recently, had not been exceeded reproducibly. Superconductivity at 20K was reported in another cuprate system containing bismuth instead of yttrium, and recently superconductivity at 85K and 110K was reported by Maeda et al. in a Bi-Sr-Ca-Cu-O system. A Bi2Sr2CaCu2O8.2 phase has been found to be the origin of the 85K superconducting transition, and its crystal structure was determined by x-ray diffraction. In this paper, we comment on the microstructure and chemistry of the new superconducting phase using selected-area electron diffraction (SAED), convergent beam electron diffraction (CBED), and x-ray energy dispersive spectroscopy (EDS) experiments.

The superconducting Bi2Sr2CaCu2O8+x samples investigated were synthesized in air by standard solid-state reaction techniques from appropriate amounts of Bi2O3, CuO, SrCO3, and CaCO3.
Planar defects in ordered (Ga,In)P
Authors: McKernan S. , Carter C. B. , Bour D. , Shealy J. R.
Published: June 2020

The growth of ternary III-V semiconductors by organo-metallic vapor phase epitaxy (OMVPE) is widely practiced. It has been generally assumed that the resulting structure is the same as that of the corresponding binary semiconductors, but with the two different cation or anion species randomly distributed on their appropriate sublattice sites. Recently several different ternary semiconductors including AlxGa1-xAs, Gaxln-1-xAs and Gaxln1-xP1-6 have been observed in ordered states. A common feature of these ordered compounds is that they contain a relatively high density of defects. This is evident in electron diffraction patterns from these materials where streaks, which are typically parallel to the growth direction, are associated with the extra reflections arising from the ordering. However, where the (Ga,ln)P epilayer is reasonably well ordered the streaking is extremely faint, and the intensity of the ordered spot at 1/2(111) is much greater than that at 1/2(111). In these cases it is possible to image relatively clearly many of the defects found in the ordered structure.
Spectraplot: A PC-based spectrum translation and display program
Authors: Colijn H. O.
Published: June 2020

Many labs today wish to transfer data between their EDS systems and their existing PCs and minicomputers. Our lab has implemented SpectraPlot, a low- cost PC-based system to allow offline examination and plotting of spectra. We adopted this system in order to make more efficient use of our microscopes and EDS consoles, to provide hardcopy output for an older EDS system, and to allow students to access their data after leaving the university.

As shown in Fig. 1, we have three EDS systems (one of which is located in another building) which can store data on 8 inch RT-11 floppy disks. We transfer data from these systems to a DEC MINC computer using “SneakerNet”, which consists of putting on a pair of sneakers and running down the hall. We then use the Hermit file transfer program to download the data files with error checking from the MINC to the PC.
Microstructure of a Y2Ba2Cu3O7-Σ superconductor pellet prepared by shock consolidation
Authors: Antrim R. F. , Marti J. , Iqbal Z.
Published: June 2020

R&D in high Tc superconductors encompasses two broad areas, namely, 1) synthesis and characterization of high Tc superconducting powders and 2) consolidation of the powders into useful parts. In the latter area, techniques such as thin film deposition, high temperature sintering of the powders and continuous casting are being pursued by various groups. Another technique which could prove useful in the fabrication of larger pieces is that of shock compaction. In this approach, explosives are used to propel a piston, resulting in a shock wave which leads to high pressure- high temperature consolidation of the powder. In this report we examine the microstructure that results when a superconducting powder was consolidated into a pellet using the shock-loading technique.

The nominal composition of the starting powder was Y1Ba2Cu3O7δ (“123”). Explosives were used to create a shock-wave with an estimated peak pressure of 60 GPa and temperatures of about 800°C.
Transmission electron microscope characterization of dislocation structure in BiSrCaCu superconducting oxide
Authors: Liang J.M. , Chang L. , Chen Y.C. , Tang S.F. , Chiao Y.S. , Wu P.T. , Chen L.J.
Published: June 2020

The recently discovered new class of BiSrCaCu superconducting oxide with Tc as high as 120 K has generated a new wave of intense research on the high Tc superconducting systems. in this presentation, we report the results of a transmission electron microscope (TEM) study of dislocation structure in a superconducting BiSrCaCuO compound.

The superconducting oxide with nominal composition of Bi2Sr2CaCu2Oy was prepared by quenching or slow cooling the solid-state-reaction sintered specimens which had been calcined from mixed Bi2O3, CaCo3, CuO, and SrCO3 powders. Thin foils for TEM examinations were generally prepared by grinding in a pestle and mortar. A JEOL-2000FX transmission electron microscope operating at 200 keV was used.

The quencehed specimens exhibited Tc-onset at 120 K and Tc-zero at 90 K, whereas the slowly cooled specimens showed Tc-onset at 104 K and Tc-zero at 75 K. X-ray diffraction and TEM/EDS data showed that the sintered samples were mainly of a phase with nominal composition Bi2Sr2CaCu2Oy, XRD, SAD and CBED identified that the crystal structure is orthorhombic with a=0.541 nm, b=2.69 nm, and c=3.07 nm.
The relative effects of the Debye Waller factor and inelastic scattering on high resolution imaging of [100] and [010] orientations of YBa2CuO7-8
Authors: Hytch M. J. , Stobbs W. M.
Published: June 2020

Even though it is now well recognised that the grain boundary stucture can be the dominant factor in limiting the critical current of the high Tc oxide YBa2Cu3O7-δ, it remains interesting to determine the degree of ordering of the [010] O-Cu-O chains in the basal planes, between the Ba atoms. This is because, although chain ordering is not apparently essential for other high Tc oxides2, it is clear that the degree of ordering and the value of Tc are closely linked for YBa2Cu3O7-δ. In this context, Ourmazd and Spence have suggested that the [100] and [010] orientations can at least be distinguished through details of high resolution contrast. At the same time, Huxford et al amongst others, have argued that the thermal vibrations of the O atoms in the O-Cu-O chains should reduce these contrast differences - making the degree of ordering hard to quantify.
Field emission SEM with wide operating voltage range
Authors: Norioka S. , Miyokawa T. , Goto S. , Niikura T. , Sakurai S.
Published: June 2020

A newly developed conical anode field emission electron gun (FE-GUN)has been installed on the JSM-840F Scanning Electron Microscope (SEM). The cross sectional view of the column is shown in Fig. 1. The gun is usable at a wide accelerating voltage range from 0.5 kV to 40 kV, and is suitable for general purpose SEMs. The gun can be used within the virtual source range even at an extract voltage as high as 7 kV and an accelerating voltage as low as 0.5 kV. The extract voltage can be raised up to 7 kV even when the emitter tip radius becomes larger after repeated flashing for smoothing the emitter tip surface. This allows elongation of the emitter life.

With the FE-GUN, since the electron source (virtual source) moves with accelerating voltage change, an image may disappear due to the deviation of the electron probe from the optical axis when the accelerating voltage is changed.
Sample preparation of sub-micron precipitates in rapidly solidified Mg-20Nd
Authors: Omlor Ralph E. , Robertson Lt Erica , Lloyd Pamela F.
Published: June 2020

The Mg-20Nd melt spun ribbonsare being examined in depth because of their potentiodynamic polarization response as compared to that of 7075-T73 aluminum. The Mg-20Nd ribbon exhibited pseudopassivation behavior at a current density approximately one order of magnitude less than the aluminum alloy. In previous work, this was found to be due to the presence of a tessellatal precipitated network which formed in the ribbons during melt spinning. EDS results on TEM foils gave similar compositional values on both matrix and precipitates. These results were not trusted due to the small size and large volume fraction of the precipitates.

The Mg-20Nd ribbon was swabbed with a dilute solution of sulfuric acid to loosen the particles in the matrix. A heavy oxide film was also formed on the surface at this time. Plastic replication solution was then applied to this surface and stripped away when dry. The particle side of the plastic film was then carbon coated. This film was placed on 3mm grids and the plastic dissolved away leaving the carbon film and the oxide precipitate mixture.
Correlated and combined confocal and conventional modes (and color coding) in tandem scanning reflected light microscopy
Authors: Boyde A.
Published: June 2020

It has been proposed that an overriding advantage of the “black-box” configuration of confocal scanning laser microscope (CSLM) is that it enables the use of all the familiar and conventional light microscope (LM) modes to discover a location of interest in a prepared, contrived, biological sample and then to switch to the confocal mode when desired. By implication, it has been assumed that this would not be possible in the Tandem Scanning Reflected Light Microscope (TSM). It is shown here that such suppositions are incorrect, and that correlations with different LM modes are very easily achieved in standard TSMs. In fact, because of the slow scanning speed of existing commercial CSLMs, it is not just an advantage to have other modes of image formation available, but a pure necessity, since finding the area of interest would otherwise be too difficult.
X-ray microtomography
Authors: Deckman H.W. , Flannery B.F. , Dunsmuir J.H. , Amico K.D'
Published: June 2020

We have developed a new X-ray microscope which produces complete three dimensional images of samples. The microscope operates by performing X-ray tomography with unprecedented resolution. Tomography is a non-invasive imaging technique that creates maps of the internal structure of samples from measurement of the attenuation of penetrating radiation. As conventionally practiced in medical Computed Tomography (CT), radiologists produce maps of bone and tissue structure in several planar sections that reveal features with 1mm resolution and 1% contrast. Microtomography extends the capability of CT in several ways. First, the resolution which approaches one micron, is one thousand times higher than that of the medical CT. Second, our approach acquires and analyses the data in a panoramic imaging format that directly produces three-dimensional maps in a series of contiguous stacked planes. Typical maps available today consist of three hundred planar sections each containing 512x512 pixels. Finally, and perhaps of most import scientifically, microtomography using a synchrotron X-ray source, allows us to generate maps of individual element.
An integral field emission “microSEM” for UHV surface analysis
Authors: Veneklasen Lee H. , Todd George , Poppa Helmut
Published: June 2020

It has been recognized for some time that the application of high sensitivity surface analytical techniques at high spacial resolution is highly desirable. For surface characterization, concentration distribution and topography are superior to average concentration, and sensitivity is increased by localizing the analysis to regions of higher concentration. In the field of Auger electron spectroscopy, this trend is reflected by the increasing popularity of scanning AES (SAM) instrumentation.

Due to the low yield of characteristic secondary particles (e.g. Auger electrons or X-rays), the central technological challenge is the delivery of relatively large beam currents into sufficiently small probes (often <30nm). However, electron optical design must also provide for optimum detector collection efficiency, for in many cases beam induced alterations and specimen damage rather than electron optics may limit the useable beam current in small probes.

Two basic instrumental configurations are in use; the off-axis approach that treats beam generation and signal detection systems as isolated entities, and the coaxial approach in which the electron gun is an integral part of the detector (e.g. cylindrical mirror analyzer).
Outline of an imaging magnetic energy filter free of second-order aberrations
Authors: Pejas W. , Rose H.
Published: June 2020

An imaging magnetic energy filter free of second-order aberrations is proposed for a high-resolution fixed-beam transmission electron microscope. The filter consists of four homogeneous bending magnets symmetrically arranged about the central plane of the filter (see Fig. 1). A distorted stigmatic image of the object plane is located at the midplane (see Fig. 2). Due to the required midplane symmetry of the fields and the Gaussian rays, the dispersion of first degree, the second-order aperture aberration, and the second-order distortion vanish in the image plane. The remaining second-order aberrations in this plane, the inclination of image field, and the field astigmatism consist of three linearly independent components. These aberrations decisively limit the field of view.

Energy selection is performed at the diffraction image D2 on the far side of the filter. The field aberrations cause the selected energy to depend on the off-axial position of the object points [1]. To guarantee a large field of view with equally well-resolved image points, all second-order aberrations must be cancelled or sufficiently reduced.
Theoretical investigations on rotationally symmetric guns with field-emission source
Authors: Kern D.
Published: June 2020

The principal procedure in computing the properties of an electron-optical system consists of two steps, first the calculation of the electric or magnetic field, and then the calculation of trajectories, from which the properties may be obtained.

In regions free from current and charge, the electric or magnetic field follows as the gradient of a solution of Laplace's equation for a scalar potential. Analytic solutions are known only for a few specific cases. They are essentially based upon the separation of Laplace's equation in curvilinear orthogonal coordinates; the difficulties arise from boundaries which cannot be represented as coordinate surfaces.

With a numerical solution of this problem, using either the finite-element or the finite-difference-method, difficulties arise when dividing the region considered into triangles or meshes, since the dimensions of the electrodes and of the tip in a field emission gun differ by several orders of magnitude. Combining an analytical with a numerical solution, these difficulties can be avoided.
A comparative study on the cold type and thermal type field emission guns used in the same electron microscope
Authors: Iwatsuki M. , Kokubo Y. , Harada Y.
Published: June 2020

On accout of its high brightness, small optical source size, and minimal energy spread, the field emission gun (FEG) has the advantage that it provides the conventional transmission electron microscope (TEM) with a highly coherent illumination system and directly improves the resolving power and signal-to-noise ratio of the scanning electron microscope (SEM). The FEG is generally classified into two types; the cold field emission (C-FEG) and thermal field emission gun (T-FEG). The former, in which a field emitter is used at the room temperature, was successfully developed as an electron source for the SEM. The latter, in which the emitter is heated to the temperature range of 1000-1800°K, was also proved to be very suited as an electron source for the TEM, as well as for the SEM. Some characteristics of the two types of the FEG have been studied and reported by many authors. However, the results of the respective types have been obtained separately under different experimental conditions.
New type electron gun with electrostatic and electromagnetic lenses
Authors: Ichinokawa T. , Maeda H.
Published: June 2020

I. Introduction

Thermionic electron gun with the Wehnelt grid is popularly used in the electron microscopy and electron beam micro-fabrication. It is well known that this gun could get the ideal brightness caluculated from the Lengumier and Richardson equations under the optimum condition. However, the design and ajustment to the optimum condition is not so easy. The gun has following properties with respect to the Wehnelt bias; (1) The maximum brightness is got only in the optimum bias. (2) In the larger bias than the optimum, the brightness decreases with increasing the bias voltage on account of the space charge effect. (3) In the smaller bias than the optimum, the brightness decreases with bias voltage on account of spreading of the cross over spot due to the aberrations of the electrostatic immersion lens.

In the present experiment, a new type electron gun with the electrostatic and electromagnetic lens is designed, and its properties are examined experimentally.
In-situ cleaning of crystal surfaces in electron microscope by means of ion sputtering
Authors: Yagi K. , Morita E. , Takayanagi K. , Kobayashi K. , Honjo G.
Published: June 2020

In-situ observation of epitaxial thin film growth in an electron microscope requires a versatile UHV electron microscope (10-8-10-10Torr) [1] and clean surface preparation techniques for thin substrate crystals. Present authors have developed following clean substrate preparation methods. (a) Flash cleaning by heating an air cleaved layer structure thin crystal at 800°C at the UHV specimen position (MoS2, graphite)[2].(b) In-situ sublimation cleaning at specimen position (PbS) [3]. (c) In-situ vacuum cleavage at specimen position by means of electron beam flashing (MgO)[4]. (d) In-situ epitaxial deposition of substrate crystal on thin crystals prepared by the methods (a) and (c) (Ag, Au, Pd, Pb Se, SnTe,..)[5]. Thus the wide range of substrate-deposit combinations has been studied and various growth modes have been observed in detail.

In the present paper, in-situ ion sputter cleaning technique and its applications to MgO, Au and Si are described. Since the technique can clean surfaces of thin crystals which are prepared by chemical or elect-rolitical etching of bulk crystals, it allows us wider selection of substrate crystals.
A theory of contamination in electron microscopes by surface diffusion
Authors: Fourie J.T.
Published: June 2020

Contamination in electron microscopes can be a serious problem in STEM or in situations where a number of high resolution micrographs are required of the same area in TEM. In modern instruments the environment around the specimen can be made free of the hydrocarbon molecules, which are responsible for contamination, by means of either ultra-high vacuum or cryo-pumping techniques. However, these techniques are not effective against hydrocarbon molecules adsorbed on the specimen surface before or during its introduction into the microscope. The present paper is concerned with a theory of how certain physical parameters can influence the surface diffusion of these adsorbed molecules into the electron beam where they are deposited in the form of long chain carbon compounds by interaction with the primary electrons.
Electron microscopy on etched thin foils. A comparative SEM, STEM and TEM analysis
Authors: Österlund R. , Vingsbo O.
Published: June 2020

During the last decade, much effort has been devoted to relations between structure and mechanical properties, particularly in metals. The need for sophisticated structure studies has increased accordingly. Combinations of different types of microscope methods have been tried, for example by performing optical and scanning electron microscopy (SEM) on etched metallographic sections.

Particularly in the case of more intricate phase analyses, it is often necessary to add information about the internal structure by means of transmission electron microscopy (TEM). The scope of the present work has been to combine the advantages of the “classical” methods of studying etched surfaces with those of transmission studies of the same field of observation. For that purpose, the scanning transmission electron microscope (STEM) technique is ideal, and has been applied on thin foils, which, after ordinary electro-polishing, were etched (nital, 10 sec.) and thereby given a structure-related surface topography. The microscope used was a JEOL 200B TEM with scanning attachment, operated at 200 kV in emissive SEM, STEM and conventional TEM mode.
Gold-germanium contacts on gallium arsenide
Authors: Rackham G.M. , Steeds J.W.
Published: June 2020

Introduction One common method of preparing Ohmic contacts to GaAs uses evaporated Au-3%wt Ge-l%wt In fired at about 450°C. We have previously described a new phase AuGeAs [l] seen in such contacts and determined its lattice constants and space group from zero layer detail in convergent beam electron diffraction patterns. The specimens then available were too buckled to yield results showing higher order Laue zone (HOLZ) lines which may enable a more positive identification of the crystal symmetry or a more accurate measure of lattice parameter. Samples were prepared with a much larger proportion of Ge than is usual with such contacts using 5wt% Ge, 12 wt % Ge (eutectic with Au) and 20 wt % Ge on a (100) substrate. The Au was removed after firing by the use of mercury, and the interface was examined by scanning microscopy. Transmission specimens were prepared by a Cl2 /methanol polish from the back face of mercury treated substrates. Figures 1-4 show the general details of the three samples.
A non-cyanide method of electropolishing silver
Authors: Lyles R. L. , Rothman S. J. , Jäger W.
Published: June 2020

Standard techniques of electropolishing silver and silver alloys for electron microscopy in most instances have relied on various CN recipes. These methods have been characteristically unsatisfactory due to difficulties in obtaining large electron transparent areas, reproducible results, adequate solution lifetimes, and contamination free sample surfaces. In addition, there are the inherent health hazards associated with the use of CN solutions. Various attempts to develop noncyanic methods of electropolishing specimens for electron microscopy have not been successful in that the specimen quality problems encountered with the CN solutions have also existed in the previously proposed non-cyanic methods.

The technique we describe allows us to jet polish high quality silver and silver alloy microscope specimens with consistant reproducibility and without the use of CN salts.

The solution is similar to that suggested by Myschoyaev et al. It consists, in order of mixing, 115ml glacial actic acid (CH3CO2H, specific wt 1.04 g/ml), 43ml sulphuric acid (H2SO4, specific wt. g/ml), 350 ml anhydrous methyl alcohol, and 77 g thiourea (NH2CSNH2).
Orientation control of vacuum deposited epitaxial metal films by applying external stress
Authors: Maruyama S. , Yamamoto K.
Published: June 2020

The orientation of vacuum deposited, epitaxial metal films was controlled, by applying external stress, on copper gold ordered alloy, and on gold manganese ordered alloy.

Ordered tetragonal or quasi-tetragonal epitaxial films such as CuAuI and gold manganese α″ have the mixed orientation of the shorter axis normal and parallel to the film plane,in the usual deposition in vacuum, i.e., (i)when the copper was deposited immediately after the gold was deposited, on cleaved surface of rock salt and homogenized, as is shown in Fig.la., or (ii)when it is formed by flash method (the two constituent atoms are deposited simultaneously), as shown in Fig.2a. This is very troublesome for the analysis or interpretation of the ordered structure of alloys. The author controlled the orientation so that the shorter axis is overall normal to the film plane in both CuAuI and gold manganese α″ by the following way. An epitaxial gold film held at room temperature for one night was rapidly heated to 350°C (at the rate of 15°C per minute), then copper or manganese was deposited onto it at that temperature, and homogenized
Growth and morphology of crystals in vacuum-deposited tellurium films
Authors: Shiojiri M. , Saito Y. , Sato M.
Published: June 2020

Crystals of Te prepared by vacuum-deposition on cleaved NaCl surfaces at temperatures ranging from 20 to 140°C have been studied by SEM and TEM observations. The deposition was done at a deposition rate of 0.3 nm/s, monitored with quartz crystal oscillating microbalance. After the deposited films were backed by carbon films, they were wet-stripped from the substrates and mounted on standard electron microscope grids.

Figure 1 shows electron micrographs of the films in different thicknesses which were prepared at different substrate temperatures. At the initial stage of deposition, spherical or polyhedral crystallites with the hexagonal structure grew with random orientations on the substrates. On the substrate at room temperature, the crystallites became large keeping the same shape and the number of the crystallites increased, as the film thickness increased. On the substrates above 80°C, they grew into slender crystals elongating along the c-axes, with increasing film thickness. The number of crystals did not increased so much.