bluuebunny/crossref_metadata_2025 huggingface dataset:
Scanning tunneling microscopy of planar biomembranes
Authors: Fisher K. A. , Whitfield S. , Thomson R. E. , Yanagimoto K. , Gustafsson M. , Clarke J.
Published: June 2020

The scanning tunneling microscope (STM) is capable of imaging conductive surfaces at atomic resolution. When STMs are used to image biological samples, however, STM resolution is limited to nanometer levels whether samples are hydrated, air-dried, or metal-coated. Lateral resolution is poor due to the nature of biological macromolecules (large Image aspect ratios) as well as to STM tip effects (shape, multiple tips, and tip/sample Interactions). If samples are adsorbed to highly-oriented pyrolytic graphite (HOPG) surfaces and scanned in the topographic (constant current) mode, vertical resolution is also uncertain due to contamination-mediated surface deformation artifacts. Nevertheless, because the STM is capable of detecting sub-Ångstrom displacements in z (e.g. to 0.02 Å in UHV), we have examined the feasibility of using the STM to determine the thickness of planar membranes attached to glass and mica surfaces. Planar membrane monolayers also uniquely provide the opportunity to correlate biochemical and TEM information with STM topographic images.
Design and application of a scanning tunneling microscope for the observation of large machined surfaces
Authors: Grigg D.A. , Dow T. A. , Russell P. E.
Published: June 2020

The scanning tunneling microscope is an instrument which can be used to image conductive surfaces with angstrom resolution. This makes the STM an ideal instrument for microscopic studies on machined metals and semiconductors. Several papers have been published showing the effectiveness of the scanning tunneling microscope (STM) to image single point diamond turned metal surfaces such as gold and aluminum.

A large sample STM has been constructed specifically to handle machined samples as large as 76 mm in diameter (Fig. 1). A tube scanner has been implimented which allows scan lengths of up to 10 μm. The STM has been designed for quick and easy sample/tip exchange.

STM studies have been made on single point diamond turned metals and semiconductor materials. Two forms of copper were diamond turned and studied using the large sample STM;
Probing nucleation and growth phenomena on silicon surfaces by scanning tunneling microscopy/spectroscopy
Authors: Hamers R.J. , Kohler U.K. , Markert K. , Demuth J.E.
Published: June 2020

Nucleation and growth processes have long been studied using diffraction technique On semiconductor surfaces, localized defects strongly affect both the electron properties of the surfaces as well as their reactivity, therby affecting nucleat and growth. In order to identify the role of local electronic structure, and surface irregularities such as steps and defects, a real-space probe of electronic structure is needed. Scanning tunneling microscopy is capable of probing both the local surface geometry and local electronic structure, permitting adsorption and chemical reactivity to be studied on an atom-by-atom basis.
Observation of elastic strain by REM while tunneling from a contaminated surface
Authors: Kuwabara M. , Lo W. , Spence J. C. H.
Published: June 2020

To explain anomalously low work functions observed by Scanning Tunneling Spectroscopy (STS) a anomalously large corrugation heights observed by Scanning Tunneling Microscopy (STM) it has be suggested that the STM tip and an insulating adsorbate layer on the sample surface may be contact. STM contrast mechanisms for atomic resolution imaging of graphite and other layer compounds and for imaging uncoated DNA in a buffer solution have also been suggested based on t possibility that the tip and sample are in contact. Whether or not tip-sample contact occurs whitunneling is, clearly, an important question which has not been satisfactorily answered by STM/STS.
Accuracy and precision in data analysis
Authors: Trebbia P.
Published: June 2020

Every time an experiment is carried out within an Analytical Electron Microscope (AEM) or any other instrument, the measurement contains information related not only to the object under study, but also to the instrument itself.

Let O be an object (a precipitate in an alloy or a protein in a membrane). This object is usually supported by a background B1 (the alloy prepared as a thin specimen, the embedding material in biological sections). The specimen (O + B1) is then sampled by an interacting probe (visible light in optical microscopy, electrons in AEM) which gives an image I1 of the specimen, defined by : I1 = f(O + B1). The function f, called the transfer function of the instrument, is probably not linear over all the spatial frequencies exhibited by the specimen and does not transmit all the information contained in O. For example, in AEM, the image obtained on a screen does not contain in a direct form the information about the phase. Moreover, the instrument adds its own background B2 (parallel detectors such as photographic plates,
Computers and diffraction analysis
Authors: Eades J. A.
Published: June 2020

For well over two decades computers have played an important role in electron microscopy; they now pervade the whole field - as indeed they do in so many other aspects of our lives. The initial use of computers was mainly for large (as it seemed then) off-line calculations for image simulations; for example, of dislocation images.

Image simulation has continued to be one of the most notable uses of computers particularly since it is essential to the correct interpretation of high resolution images. In microanalysis, too, the computer has had a rather high profile. In this case because it has been a necessary part of the equipment delivered by manufacturers. By contrast the use of computers for electron diffraction analysis has been slow to prominence. This is not to say that there has been no activity, quite the contrary; however it has not had such a great impact on the field.
Recent developments in automated Transmission Electron MI
Authors: de Ruijter W.J. , Rez P. , Smith David J.
Published: June 2020

There is growing interest in the on-line use of computers in high-resolution electron n which should reduce the demands on highly skilled operators and thereby extend the r of the technique. An on-line computer could obviously perform routine procedures hand, or else facilitate automation of various restoration, reconstruction and enhan These techniques are slow and cumbersome at present because of the need for cai micrographs and off-line processing. In low resolution microscopy (most biologic; primary incentive for automation and computer image analysis is to create a instrument, with standard programmed procedures. In HREM (materials researc computer image analysis should lead to better utilization of the microscope. Instru (improved lens design and higher accelerating voltages) have improved the interpretab the level of atomic dimensions (approximately 1.6 Å) and instrumental resolutior should become feasible in the near future.
Ultra-high resolution secondary electron imaging
Authors: Liu J.
Published: June 2020

The recent developments of the in-lens field emission scanning electron microscopes (FESEM) make it possible to image specimen surfaces with subnanometer resolution by collecting type I secondary electrons, with an incident electron probe size of about 0.5 nm in diameter. A resolution of the same order of magnitude has also been obtained in a STEM instrument with secondary electron signals. Both in-lens FESEM and STEM utilize field emission gun as electron beam source (high intensity and small probe size) and high excitation objective lenses to reduce abberations. The examined samples have to be positioned inside the objective pole-pieces. Thus the emitted secondary electrons will experience a strong magnetic field and spiral around the magnetic field lines (cyclotron orbit) before they are collected by the secondary electron detector. The radius and the pitch height of the cyclotron orbit depend on the secondary electron energy and the emission angle with respect to the magnetic field axis.
Low-voltage high-resolution SEM of biological samples
Authors: Pawley James B.
Published: June 2020

There are three reasons for the recent upsurge of interest in using the SEM at a beam voltage (Vo) around 1 kV (LVSEM). The most common one arises from applications in the semiconductor industry and emphasizes the reduction in charging artifacts and in subsurface beam damage obtainable at low Vo

The second reason derives from the belief that, given instrumentation capable of producing a sufficiently small probe, the increased contrast in the topographic component of the secondary electron signal will permit an important improvement in real topographic spatial resolution.

The third reason is that recent developments in instrumentation have shown that by coupling a cold field-emission source with a short focal length lens, it is indeed possible to obtain small probe diameters at low voltage. Although they are considerably larger than probes obtained at higher voltage, they are nonetheless smaller than the smallest topographical feature yet imaged in the secondary electron (SE) mode. (Fig 1)
High resolution at low voltage: A new approach
Authors: Jones Arthur V.
Published: June 2020

With the introduction of field-emission sources and “immersion-type” objective lenses, the resolution obtainable with modern scanning electron microscopes is approaching that obtainable in STEM and TEM-but only with specific types of specimens. Bulk specimens still suffer from the restrictions imposed by internal scattering and the need to be conducting. Advances in coating techniques have largely overcome these problems but for a sizeable body of specimens, the restrictions imposed by coating are unacceptable.

For such specimens, low voltage operation, with its low beam penetration and freedom from charging artifacts, is the method of choice.

Unfortunately the technical dificulties in producing an electron beam sufficiently small and of sufficient intensity are considerably greater at low beam energies — so much so that a radical reevaluation of convential design concepts is needed.

The probe diameter is usually given by
Development of imaging plate system for a TEM
Authors: Oikawa T. , Mori N. , Ichikawa R. , Ohnishi M. , Kawasaki M.
Published: June 2020

The superior characteristics of the “Imaging Plate” (IP) for electrons have already been ascertained, and its fundamental characteristics and application data reported. Conventionally, however, the IP, which was developed for X-ray radiography was applied to TEM image recording. So, its superior characteristics had not been given full play and it had been necessary to optimally redesign the IP for TEM. This report introduces our newly developed Imaging Plate System for TEM (TEM-IP System), which includes processes of taking, reading, processing and printing images.

Fig.l shows the block diagram of the TEM- IP system. The newly developed devices are as follows:

1.

IP for TEM

2.

Camera chamber of TEM

3.

Image reader (including eraser)

4.

Image processor

5.

Printer.

 The IP exposed in the camera chamber, can be loaded in the image reader together with its magazine, Lo carry out image reading. After completion of image reading and erasing in the image reader, the IP can be reloaded in the camera chamber, for repeated exposure.
Confocal laser scanned microscopy: Analog preprocessing
Authors: Turner JN , Barnard DP , Szarowski DH , Swann JW , Smith K
Published: June 2020

Confocal laser scanned images often have such a large dynamic range that interpretation is hampered. We employed analog preprocessing to overcome this limitation, using a homomorphic filter and a differentiator. Individual neurons in thick brain slices were injected with a fluorescent dye, and imaged as test objects. The dye density varied for different subcellular regions, and the specimen acted as an attenuater as a function of depth. Thus, each “optical section” had a large signal range that was extreme when the sections were stack to form projections or stereo pairs. Images of either the fine processes (low signal) with a saturated cell body, or a cell body (high signal) with loss of the fine processes resulted from standard methods, but the homomorphic filter and differentiator produced high quality images of both in the same field.
Structural imaging of polytypoids in high Tc oxide superconductors
Authors: Ramesh R. , Wang E. , Tarascon J.M. , Thomas G.
Published: June 2020

The structure of the superconducting polytypoid in the newly discovered high Tc super conducting system, Pb2Sr2Cu2Oy has been examined by high resolution electron microscopy, electron diffraction and xray microanalysis. High resolution imaging has shown the presence of the Pb2Sr2Cu2Oy at the grain boundaries. In analogy to the Bi-Ca-Sr-Cu-O(BCSCO)system, it is suggested that this polytypoid could have a lower transition temperature compared to the matrix. This may explain the steps in the resistivity plot. It is also shown that complex cationic ordering, such as replacement of Sr by Ca and/or Y, could lead to extra reflections in the diffraction patterns.

Pb-Sr-(Ca-RE)-Cu-O sintered samples were prepared by standard solid state processing techniques. Samples were prepared under 1% flowing oxygen. Samples for electron microscopy were prepared by argon ion milling at liquid nitrogen temperature at 6kV. High resolution electron microscopy was carried out in the Berkeley Atomic Resolution Microscope at 800kV.
Scanning probe parallel EELS analysis of interfaces in ceramics and ceramic composites
Authors: Weiss J. K. , Carpenter R. W. , Braue W. , Higgs A. A.
Published: June 2020

Much recent work has centered on the structure of interfaces in polycrystalline sintered ceramic and ceramic composite materials. The suggestion that most interfaces are wetted by a thin (1-10 nm) amorphous layer has been tested by the use of high resolution imaging, along with some work being done using microanalytical techniques. This study utilizes a system developed to acquire numerous electron energy loss spectra with a parallel detector while scanning a small electron probe across the various interfaces.

The work was performed on a Philips EM400ST equipped with a high-intensity field emission gun capable of producing a probe with a “diameter” of 2±.5 nm and a current of up to 5 nA . The parallel EELS spectrometer was a Galan 666 equipped with a 1024-channel photodiode array coupled to a YAG scintillator, capable of full spectrum acquisition in as little as 25 msec with an energy resolution of < 1 eV. The PEELS was controlled byan MCA microcomputer designed at ASU, which also controls the probe scan sychronously with the multiple spectrum acquisition by an external voltage added to the beam deflection circuit from a set of DACs.
EDS analysis of .04% Zn in GaAs using x-ray filters
Authors: Christenson K. K. , Eades J. A. , Whitehead M. E.
Published: June 2020

The x-ray Mass Absorption Coefficient (MAC) of an element varies with the energy of the x-ray. Absorption is strong for low energy x-rays and drops with increasing energy until the x-ray has sufficient energy to excite an inner shell electron. At this point there is a large jump in absorption referred to as an “absorption edge” followed by another steady decline with increasing energy (Fig. 1). This variation in transmission can be used either to eliminate x-rays from a low z matrix (a “high pass” filter) or, by utilizing the absorption edge, to eliminate x-rays with an energy above the desired signal (“band pass” filtering).

While the use of such filters in XRF analysis is an established practice, their use in EDS analysis has only been suggested recently. In this experiment a Cu foil placed over the outer face of the x-ray collimator was used as a band pass filter to suppress the Ga and As matrix signals which allowed the quantification of .04% Zn in GaAs. This work was carried out at 120 keV in a Philips EM420 with an EDAX 9900 x-ray detector system (standard detector with a 15 mm WD and 30 mm2 area).
Composition and microstructure of a nickel-base superalloy, UDIMET 720
Authors: More k.L. , Miller M.K.
Published: June 2020

A wide range of nickel-base superalloys are currently used for land- and marine-based turbines. Small amounts of carbon and boron are added to improve the high temperature mechanical properties of these alloys. During a standard heat treatment, large carbides evolve at the grain and twin boundaries and small, intragranular precipitates of the γ′phase form. It has been proposed that the carbides improve the high temperature strength by inhibiting grain boundary sliding. The role of boron is, however, not fully understood. Decker suggests that boron stabilizes the γ′ precipitates and prevents the formation of denuded zones at the grain boundaries thus inhibiting microcrack formation at transverse grain boundaries. The purpose of this study was twofold; to characterize the microstructure of Udimet 720 using atom probe field-ion microscopy (APFIM), analytical electron microscopy (AEM), and secondary ion mass spectroscopy (SIMS) and to determine if boron and carbon segregate to boundaries and γ/γ′interfaces. This is a continuation of work started by Burke et al.
The microstructure change of low-carbon electrical steels by residual aluminum
Authors: Hou C.K. , Hu C.T. , Lee Sanboh
Published: June 2020

The fully processed low-carbon electrical steels are generally fabricated through vacuum degassing to reduce the carbon level and to avoid the need for any further decarburization annealing treatment. This investigation was conducted on eighteen heats of such steels with aluminum content ranging from 0.001% to 0.011% which was believed to come from the addition of ferroalloys.

The sizes of all the observed grains are less than 24 μm, and gradually decrease as the content of aluminum is increased from 0.001% to 0.007%. For steels with residual aluminum greater than 0. 007%, the average grain size becomes constant and is about 8.8 μm as shown in Fig. 1. When the aluminum is increased, the observed grains are changed from the uniformly coarse and equiaxial shape to the fine size in the region near surfaces and the elongated shape in the central region. SEM and EDAX analysis of large spherical inclusions in the matrix indicate that silicate is the majority compound when the aluminum propotion is less than 0.003%, then the content of aluminum in compound inclusion increases with that in steel.
Solidification of alternative phases in submicron spheres of pure nickel
Authors: Lin Hong-Ming , Kelly Thomas F.
Published: June 2020

Alternative phases which are other than the most stable crystalline phase can be formed from highly supercooled liquids. Phase selection occurs during nucleation which is strongly affected by the extent of supercooling. A large supercooling in the liquid is generally needed in order to nucleate alternative phases. Supercooling will increase with suppression of heterogeneous nucleation and with increasing cooling rate. Thus, high cooling rate and isolation of the heterogeneous catalytic sites should be simultaneously reaLized in order to achieve large supercooling. From a practical point of view, production of very small liquid droplets in high vacuum using electrohydrodynamic (EHD) atomization is a very effective way to achieve large liquid supercoolings.

Seventeen pure elements have been studied previously by using the electrohydrodynamic (EHD) process. The results show that pure nickel forms an amorphous phase in the smallest (< 10 nm diameter) submicron spheres.
Microstructures of Ni3Al alloys as a function of Cr and Al levels
Authors: Horton J.A. , Liu C.T.
Published: June 2020

Several alloys based on boron-doped Ni3Al are undergoing alloy development for a wide range of potential uses. The microstructures of several of these alloys were characterized by transmission electron microscopy as a function of the chromium and aluminum levels. The series included alloys with 0 to 10 at. % Cr and with 15.6 to 21% Al, see Table I.

In Ni-AI alloys with low aluminum content and in most Ni-Al alloys with chromium additions, a twophase γ’ plus γ structure resulted. The major phase (and matrix) was ordered γ’ and the minor phase disordered γ· Both phases appeared interconnected and were completely epitactic. The ordered phase was aluminum-enriched while the disordered phase was chromium-enriched. Within the disordered phase a reprecipitation of γ’ often occurred, depending on heat treatment, and gave an appearance of a “disordered web”. Typical x-ray energy dispersive spectroscopic (EDS) analyses are listed in Table II.
Dislocations in B2 ordered alloys
Authors: Baker I.
Published: June 2020

Intermetallic compounds are currently the subject of considerable research effort because of their possible structural applications, particularly at high temperature. The B2 structure, sometimes called L20, ordered body-centered cubic or CsCl-type, is the simplest ordered structure an AB-type compound can adopt. Nevertheless, three different dislocation Burgers’ vectors are found, namely <100>, <110> and <111>, depending on the compound and the temperature of deformation. Only <100> and <111> are normally observed at lower temperatures. For example, figure 1 shows <100> slip in PdIn and <111> slip in FeAl. An important practical difference between <111> and <100> slip is that the latter provides only three independent slip systems and, thus, can lead to only limited general plastic flow in a polycrystal.

At low temperature, why <100> or <111> slip occurs is not wholly clear, although there have been several attempts at rationalizing the experimentally observed slip vectors. Rachinger and Cottrell made the first attempts at rationalization when they used a nearest-neighbor model to estimate a critical ordering energy above which <100> slip would operate and below which <111> slip was presumed to occur.
Sectorized crystallization of higher n-alkanes: A high resolution search for oblique chain packing
Authors: Dorset D. L. , Wittmann J. C. , Lotz B. , McConnell C. H. , Fryer J. R. , Zemlin F.
Published: June 2020

Although it was once thought that a major distinction between paraffin and polyethylene lozenge crystals was the sectorization of the latter due to polarization of chain fold surfaces, a recent study has shown that n-paraffins longer than C44H90, but with unfolded chains, also crystallize as sectorized lozenges (Fig. 1) with bright field fringes running along <130> compared to the <130> direction in polyethylene. High resolution electron microscopy and microdiffraction of corrugated polyethylene lozenges, furthermore, have shown that, for the infinite chain folded polymer, these fringes correspond to local oblique chain packings. Although shadowing with C-Pt indicates that the sectorized paraffin lozenges are not corrugated like polyethylene, it was thought that chain obliquity, nevertheless, should also be the cause of the Bragg fringe contrast in Fig. 1.

An attempt was made to visualize the detail directly using the SULEIKA cryomicroscope at the Fritz Haber Institute in Berlin, given our previous success in obtaining 2.5Å resolution images of the C44H90 chain packing.
A remarkable property of the angular distribution of plural inelastic scattering, with benign consequences for the deconvolution of electron energy-loss spectra
Authors: Egerton R.F. , Liou S.-H.
Published: June 2020

Electrons which have been inelastically scattered two or more times during passage through a thin specimen are known to be distributed more broadly in angle than those which are scattered only once. However, the literature contains no simple guide or analytical formula for the plural-scattering angular distribution. We decided to calculate this distribution by two-dimensional self-convolution of the single-scattering angular distribution, taking the latter to be a Lorentzian function: with characteristic angle ΘE and with an abrupt cut-off of the intensity at scattering angle Θ = Θc.

The results are given in Fig. 1 in integral form: Fn(β) is the fraction of the electrons (which have been scattered n times) collected by an on-axis aperture of semi-angle β. Also shown in Fig. 1 are dashed curves representing the square and cube of F1. The close correspondence between the calculated points (F2 and F3) and the dashed curves is noteworthy. Similar agreement was obtained for cut-off angles in the range 50ΘE to 200ΘE, typical of most materials.
TEM observation of cylindrite
Authors: Wang Su
Published: June 2020

Cylindrite, approximately FePb3Sn4Sb2S14, contains two different types of layers, pseudo-tetragonal(t-lattice) with PbS structure and pseudo-hexagonal (h-lattice) with SnS2 structure. The two kinds of layers are superimposed in the order of htht.., and the repeat periodicity is a. In the past only the composite SAED pattern corresponding to the b*c* plane of the two lattices was obtained as shown in Fig. 1a. Now we have succeeded, by careful tilting, in taking separate SAED patterns and HREM images of these two lattices(Figs. 2 and 3). The CBED pattern containing two [100] zone axes indicates: , as shown in Fig. lb.

In the SAED patterns shown in Figs. 2, 3 and 4, each main reflection is accompanied by a row of satellite spots caused by the common structural modulation of the two lattices shown by the dark bands inthe HREM images. The rows of satellites, defined by q, in general donot parallel to any axes defined by the main reflections. In the q direction, the additional long-range periodicity corresponding to the satellites and the basic periodicity of both lattices are incommensurate.
A Transmission Electron Microscopic study of the densification of 10:90 colloidal silica: Alkali silicate sol-gels
Authors: Kerch H. M. , Gerhardt R. A. , Grazul J. L.
Published: June 2020

The sintering behavior of a low density 10:90 wt% colloidal silica: potassium silicate sol-gel is being investigated. This material is of technological interest because of its ease of processing, high purity and relatively low sintering temperature. Porous structures are most frequently characterized by mercury penetration porosimetry and B.E.T. sorption technique. The underlying theory of both these procedures assume a priori knowledge of the pore geometry. Conversely, microscopic analysis allows direct observation of the pore network provided sample preparation does not alter the structure. To this end, the techniques of ultramicrotomy and Pt/C replication were adopted.

Specimen preparation for ultramicrotomy is described elsewhere. All thin-sectioning was performed with a D.D.K. diamond knife using a distilled water media. The replicas were produced by a Balzers 301 freeze etch apparatus at a vacuum of 1 X 10-7 Torr. Platinum was evaporated at a thickness of 2.5 nm at 45° followed by a 15 nm layer of carbon deposited at 90°. The replicas were retrieved by immersing the gel in HF with a distilled water rinse. Both ultramicrotomed sections and replicas were collected onto carbon coated 400 mesh grids. All micrographs were taken on a JEOL 100CX in bright field mode.
Transmission Electron Microscopy of Epitaxial silicides grown by ultra high vacuum deposition
Authors: Loretto D. , Gibson J. M. , Yalisove S. M.
Published: June 2020

The silicides CoSi2 and NiSi2 are both metallic with the fee flourite structure and lattice constants which are close to silicon (1.2% and 0.6% smaller at room temperature respectively) Consequently epitaxial cobalt and nickel disilicide can be grown on silicon. If these layers are formed by ultra high vacuum (UHV) deposition (also known as molecular beam epitaxy or MBE) their thickness can be controlled to within a few monolayers. Such ultrathin metal/silicon systems have many potential applications: for example electronic devices based on ballistic transport. They also provide a model system to study the properties of heterointerfaces. In this work we will discuss results obtained using in situ and ex situ transmission electron microscopy (TEM).

In situ TEM is suited to the study of MBE growth for several reasons. It offers high spatial resolution and the ability to penetrate many monolayers of material. This is in contrast to the techniques which are usually employed for in situ measurements in MBE, for example low energy electron diffraction (LEED) and reflection high energy electron diffraction (RHEED), which are both sensitive to only a few monolayers at the surface.
Structure factor determination from critical voltages in electron diffraction
Authors: Gjønnes J. , Matsuhata H. , Taftø J.
Published: June 2020

The principle of the critical voltage method in electron diffraction is an attractive one: a relation between structure factors can be determined with high precision from measurement of the condition for vanishing contrast of a contrast detail in the Kikuchi pattern or in the CBED pattern. In practice the method meets with some apparent and real limitations. The original, second order critical voltage in the systematic case (Watanabe, Uyeda and Fukuhara) depends on high accelerating voltage and can be applied mainly to strong low order structure factors from simple substances. Accurate additional information about other structure factors and temperature factors must be obtained from other methods. In order to increase the utility of the method a wider selection of configurations suitable for measurement has to be found. Several investigators have focussed on non-systematic cases: Gjønnes and Høier, Steeds.
A generalized Kambe approximation for transmission electron diffraction
Authors: Zuo J. M.
Published: June 2020

The methods used by Kambe to treat nonsystematic three-beam interaction have been extended to a more general case, in which there are two groups of reflections, gi (i = 1..n) and hi (i = 1..m). Each reflection has strong interactions with reflections in its own group and weak interactions with reflections in another group. Thus

Practical cases of interest are (i) parallel rows of reflections in the ZOLZ and (ii) HOLZ and ZOLZ groups. In the following we will develop an approximate intensity expression for reflections, hi, with weak coupling to the incident beam. We assign g1 = 0 as the incident beam. This intensity expression can be used to describe the intensity distribution in CBED disks of nonsystematic reflections for cases (i) and (ii) above.

Many-beam dynamical electron diffraction in RHEED with reflections gi and hi is described by
Reflection Electron Microscopy (REM) observation of () planes of α-Al2O3 single crystals
Authors: Kim Yootaek , Hsu Tung
Published: June 2020

The surfaces of α-Al2O3(R-Surfaces) which are used as substrates for the growth of SOS (Silicon on Sapphire) were investigated with the REM technique. Most of the studies using TEM and SEM have been centered on SOS interfaces but only limited studies have been conducted on surfaces of sapphire before the growth of Si. The purpose of this paper is to show that surfaces have different distributions of steps and facets as compared to the (0001) and surfaces which are characterized by large atomically flat areas separated by steps that are several atomis high.

Specimens were obtained from Sapphikon Inc., NH. Polished and cleaned faces were observed before and after annealing at 1400°C for 24 hrs in air. All observations were carried out using a JEOL-JEM 200CX microscope at 100kV.
Phase identification and defect structures in II-IV-V2 heteroepitaxial semiconductor thin films grown on III-V substrates
Authors: Posthill J.B. , Xing G.C. , Solomon G.S. , Bachmann K.J. , Timmons M.L.
Published: June 2020

The ternary chalcopyrite-structure compound semiconductors (space group , Fig. 1) offer several promising materials properties that may be useful in electronic and optoelectronic devices. These compounds have a wide range of direct and pseudodirect band gaps, and they generally lattice match well to available substrates for heteroepitaxial growth. However, before the properties of this class of materials can be fully exploited, specific issues pertaining to the crystal growth (both bulk and epitaxial) must be understood and optimized. This contribution briefly describes some of our microstructural studies of heteroepitaxial ZnGeAs2-on-GaAs(100) and ZnGeP2-on-GaP(100) grown by organometallic chemical vapor deposition (OMCVD).

The details of OMCVD growth of these materials are described in detail elsewhere. Cross-section [110] samples for transmission electron microscopy (TEM) were held at reduced temperature using a liquid nitrogen cooled stage to minimize the deleterious effects of Ar+ ion bombardment during final thinning. Diffraction contrast and phase contrast (HRTEM) imaging was accomplished at 200 kV.
HREM at orthogonal projections of GaAs islands on silicon
Authors: Ponce F. A. , Hetherington C. J. D.
Published: June 2020

HREM studies typically examine only one projection of a structure and information in the electron beam direction is lost. In most cases, the structure in this direction is uniform and already known, but in others a second projection needs to be observed. This could involve preparing a second specimen sectioned at right angles to the first, or as described here, tilting a specimen through ±45° and observing the same volume in orthogonal projections. The specimen used here was of GaAs islands on <001> silicon, examined in the Atomic Resolution Microscope at LBL.

In the effort to grow defect-free GaAs films on silicon substrates, understanding of the early stages of growth is required. For this experiment we chose a specimen of ultra-thin GaAs grown on silicon substrate by metal-organic chemical vapor deposition (MOCVD). The GaAs was grown at 550°C for a nominal thickness of20nm from trimethyl gallium and arsine sources.The growth conditions lead to three-dimensional growth of islands bound by {111}A planes, terminated on Ga layers.
A computer-control program for TEM in situ fatigue experiments
Authors: Vecchio Kenneth S. , Hunt John A.
Published: June 2020

In-situ experiments conducted within a transmission electron microscope provide the operator a unique opportunity to directly observe microstructural phenomena, such as phase transformations and dislocation-precipitate interactions, “as they happen”. However, in-situ experiments usually require a tremendous amount of experimental preparation beforehand, as well as, during the actual experiment. In most cases the researcher must operate and control several pieces of equipment simultaneously. For example, in in-situ deformation experiments, the researcher may have to not only operate the TEM, but also control the straining holder and possibly some recording system such as a video tape machine. When it comes to in-situ fatigue deformation, the experiments became even more complicated with having to control numerous loading cycles while following the slow crack growth. In this paper we will describe a new method for conducting in-situ fatigue experiments using a camputer-controlled tensile straining holder.

The tensile straining holder used with computer-control system was manufactured by Philips for the Philips 300 series microscopes. It was necessary to modify the specimen stage area of this holder to work in the Philips 400 series microscopes because the distance between the optic axis and holder airlock is different than in the Philips 300 series microscopes. However, the program and interfacing can easily be modified to work with any goniometer type straining holder which uses a penrmanent magnet motor.
Studies of phase transformation of Fe1-xS by in Situ TEM
Authors: Nguyen Thao A. , Hobbs Linn W.
Published: June 2020

The transformation from Fe1-xS (IC) phase to a mixture of FeS (2C) and iron poor Fe1-xS (IC) phases has been investigated by a series of in-situ heating experiments. The purpose of this study is to resolve the controversy over the mechanism of phase transformation (spinodal decomposition versus nucleation and growth) and to explain the different microstructures observed in the two phase mixture of FeS and Fe1-xS (Figure 1).

In-situ heating experiments were carried out using a JEOL JEM EM-SHTH double tilt heating holder. Synthetic “single” Fe0.97S crystals were cut into 3 mm disks, mechanically and ion thinned to electron transparency. In all cooling experiments, the sample was first held at 390 K, a temperature above the transition temperature in order to generate an initial single phase material; then, the temperature was quickly reduced to the temperature of interest.

Figure 2a shows the development of a lamellar type microstructure after the sample's temperature was reduced from 390 K to 363 K and then held at this temperature for ten minutes. At 363 K, the undercooling is 27 K. The troilite FeS (2C) phase heterogeneously nucleates and grows along the edge of the sample. Diffraction analysis shows that the FeS (2C) phase is embedded in the iron-poor Fe1-x,S matrix with a rod-like structure.
Radiation-induced amorphization of intermetallic compounds
Authors: Okamoto P. R.
Published: June 2020

Many ordered intermetallic compounds become amorphous when irradiated at low temperatures with energetic particles. There is still no fundamental understanding of why some compounds but not others are susceptible to amorphization. However, recent studies indicate that a progressive loss of chemical long-range order (LRO) is a necessary, though not a sufficient condition for the crystal-to-glass transformation. To shed further light on the role of chemical disordering, our work has focused on correlating the structural effects of chemical disorder on the shear modulus of a number of LI2, B2, and A-15 type intermetallic compounds under irradiation conditions where some become amorphous and others remain crystalline.

The Brillouin scattering technique was used to measure the change in the velocity of sound (Vs) relative to that of the unirradiated state (Vos) in Zr3Al, FeAl, FeTi, NiAl, and Nb3Ir during irradiation at 298 K with 1-MeV Kr+ ions. The corresponding changes in the Bragg-Williams LRO parameter (S/So), and lattice expansion (Δa/ao) were measured by means of electron diffracting during in-situ irradiation with 1-MeV Kr in the ANL high voltage electron microscope.
Utilization of a high-speed x-ray analysis system with a SEM
Authors: Sandborg A. O. , Anderhalt R. W.
Published: June 2020

A high speed x-ray analysis system has been developed using a scanning electron microscope(SEM) with an energy dispersive spectrometer(EDS). In this system digital beam control is combined with other microscope control from the EDS system. The EDS system has specially designed software to allow a full quantitative analysis to be performed in fractions of a second. This allows several novel forms of analysis, such as fully quantitative x-ray maps and analysis of non-homogeneous specimens. Due to the high speed of the software, conventional intensity x-ray maps are made into quantitative maps, during the process of acquiring them. Non-homogeneous samples are analysed by randomly positioning the beam on the sample, doing a full analysis, then moving the beam to a new point. When this procedure is repeated many times, the specimen is sampled in a way to produce a true average analysis.

Background and peak overlap corrections must be applied to obtain net elemental intensities from the EDS spectrum. It is impractical to store a full spectrum at each analysis location of the map, so the corrections must be made “on the fly”. Normally it requires tens of seconds to obtain net elemental intensities and to convert these to concentrations with a ZAF technique. In this work these times have been reduced to 100 milliseconds by the use of optimized programming of the various correction procedures.
Direct measurement of electron-diffraction-pattern intensities using an energy loss spectrometer
Authors: Jackson A. G. , Rowe M.
Published: June 2020

Diffraction intensities from intermetallic compounds are, in the kinematic approximation, proportional to the scattering amplitude from the element doing the scattering. More detailed calculations have shown that site symmetry and occupation by various atom species also affects the intensity in a diffracted beam. [1] Hence, by measuring the intensities of beams, or their ratios, the occupancy can be estimated. Measurement of the intensity values also allows structure calculations to be made to determine the spatial distribution of the potentials doing the scattering. Thermal effects are also present as a background contribution. Inelastic effects such as loss or absorption/excitation complicate the intensity behavior, and dynamical theory is required to estimate the intensity value.

The dynamic range of currents in diffracted beams can be 104or 105:1. Hence, detection of such information requires a means for collecting the intensity over a signal-to-noise range beyond that obtainable with a single film plate, which has a S/N of about 103:1. Although such a collection system is not available currently, a simple system consisting of instrumentation on an existing STEM can be used as a proof of concept which has a S/N of about 255:1, limited by the 8 bit pixel attributes used in the electronics. Use of 24 bit pixel attributes would easily allowthe desired noise range to be attained in the processing instrumentation. The S/N of the scintillator used by the photoelectron sensor is about 106 to 1, well beyond the S/N goal. The trade-off that must be made is the time for acquiring the signal, since the pattern can be obtained in seconds using film plates, compared to 10 to 20 minutes for a pattern to be acquired using the digital scan. Parallel acquisition would, of course, speed up this process immensely.
Detection of crystalline phase in cross-section multilayer thin film by High-Resolution Transmission Electron Microscopy
Authors: Nguyen Tai D. , Gronsky Ronald , Kortright Jeffrey B.
Published: June 2020

High-resolution transmission electron microscopy has proven to be very useful in direct detection of crystalline phases that exist over extremely small volumes, yielding information about structure, orientation, and, under appropriate circumstances, composition. In this paper, we report the detection of a crystalline phase in the tungsten-rich layer of an annealed 7 nm-period tungsten-carbon multilayer produced at the Center for X-Ray Optics at the Lawrence Berkeley Laboratory.

The multilayers were prepared by dc magnetron sputtering at floating temperature. The argon sputter gas pressure was 0.0020 torr. Different techniques were employed to produce cross-section and plan-view samples for TEM. For cross-section samples, 70 bilayers of W and C were sputtered on semiconductor-grade Si (111) wafers. For plan-view samples, the substrates on which the multilayer was grown consisted of 3 mm-diameter 300-mesh copper microscope grids, mounted on glass slide with Crystalbond® vacuum adhesive. After a deposition of 4 bilayers of W-C, keeping the same sputtering parameters as those of the Si substrates to guarantee the same layer thicknesses, the glass slide was soaked in acetone to disolve the Crystalbond®, leaving the multilayer spanning the holes of the copper grids. Both the Si-substrate and copper-grid samples were annealed at 500°C for 4 hours under vacuum of 10−6 torr. The annealed Si-substrate sample was then prepared for cross-section by mechanical grinding, and ion milling in a cold stage at 5kV. The cross-section sample was studied in a JEOL JEM 200CX with ultrahigh resolution goniometer, with the eletron beam parallel to the [112] of the Si substrate. The plan-view sample was studied in a Philips 301 operating at 100kV.
Use of ion milling to expose and highlight defects on cross-sectioned integrated circuits
Authors: Martinek K.H. , Benedict J.P. , Klepeis S.J. , Joseph T. , Vandygrift G.
Published: June 2020

Polishing and cross-sectioning of integrated circuits is standard practice in failure analysis. With most integrated circuit defects, all that is usually needed is mechanical polishing to the cross-sectioned plane of interest. The sample is then ready for examination in the scanning electron microscope (SEM). However, some defects are too small or too subtle to be seen without delineating them in some way. Chemical etching is useful in many situations but sometimes does not highlight the defect and may introduce artifacts. In this experiment, cross-sectioned chips were ion milled for a short period to highlight or uncover defects.

After locating failing transistors, samples were cross-sectioned on diamond paper using the open block method (i.e., not encapsulated in epoxy). A special ion mill sample holder was designed to accommodate the polishing fixture. This holder is inserted into the ion mill. (This eliminates the need to transfer the chip from one fixture to another, avoiding damage or contamination.) Samples were milled in a Gatan ion mill for an initial period of two minutes at a 20 degree tilt. A current of ˙5 mA and voltage of 5 kV were used. Samples were positioned so that maximum milling occurred in the area of the failing transistors.
Intracellular structures of rapid frozen biological samples observed by high-resolution low-temperature Scanning Electron Microscopy
Authors: Inoué T. , Koike H.
Published: June 2020

Low temperature scanning electron microscopy (LTSEM) is useful to avoid artifacts such as deformation and extraction, because specimens are not subjected to chemical fixation, dehydration and critical-point drying. Since Echlin et al developed a LTSEM, many techniques and instruments have been reported for observing frozen materials. However, intracellular structures such as mitochondria and endoplasmic reticulum have been unobservable by the method because of the low resolving power and inadequate specimen preparation methods. Recently, we developed a low temperature SEM that attained high resolutions. In this study, we introduce highly magnified images obtained by the newly developed LTSEM, especially intracellular structures which have been rapidly frozen without chemical fixation.

[Specimen preparations] Mouse pancreas and brown adipose tissues (BAT) were used as materials. After the tissues were removed and cut into small pieces, the specimen was placed on a cryo-tip and rapidly frozen in liquid propane using a rapid freezing apparatus (Eiko Engineering Co. Ltd., Japan). After the tips were mounted on the specimen stage of a precooled cryo-holder, the surface of the specimen was manually fractured by a razor blade in liquid nitrogen. The cryo-holder was then inserted into the specimen chamber of the SEM (ISI DS-130), and specimens were observed at the accelerating voltages of 5-8 kV. At first the surface was slightly covered with frost, but intracellular structures were gradually revealed as the frost began to sublimate. Gold was then coated on the specimen surface while tilting the holder at 45-90°. The holder was connected to a liquid nitrogen reservoir by means of a copper braid to maintain low temperature.
Seasonal variation in Golgi dictyosomes in mesophyll cells of Taxus SP.
Authors: Rivera E.R.
Published: June 2020

In plants, the Golgi dictyosomes are active in cell wall synthesis. During cell growth and division the dictyosomes are very numerous; many of them are components of the phragmoplast. After the cells mature, the dictyosome population decreases. Mesophyll cells of Taxus canadensis and Taxus cuspidata were observed over a two year period to determine dictyosome population variations in cells that survive for more than one growing season.

Leaves of Taxus canadensis and Taxus cuspidata were collected every two weeks starting in May when new buds expanded. Collections were continued over two years in three experiments. The final specimens had gone through two full seasonal cycles. All specimens were fixed with 5% glutaraldehyde in 0.075M PIPES buffer pH 8. They were post fixed in 2% osmium tetroxide and embedded in Spurr's resin. Determination of oxidizable sugar residues was done by the periodic acid-thiosemicarbozide-silver protein method. For this study observations were limited to the mesophyll palisade cells on the upper half of the leaf. Random searches were done in the viewing screen as well as on micrographs.