bluuebunny/crossref_metadata_2025 huggingface dataset:
Special grain boundaries in YBa2Cu3O7-x
Authors: Tietz L.A. , Carter C.B. , Lathrop D.K. , Russek S.E. , Buhrman R.A.
Published: June 2020

Much attention has recently been paid to the characterization of twin boundaries in YBa2Cu3O7-x (YBCO). However, in polycrystalline samples other high-angle grain boundaries may have a much more significant effect on, not only the superconducting behavior, but also the chemical and mechanical stability of the material. In the present study, attention has therefore also been focussed on several types of low-angle and high-angle grain boundaries. Such boundaries are frequently found in thin films of this material which are grown on {001}-oriented, single-crystal yttria-stabilized zirconia (YSZ) or magnesium oxide by electron beam co-evaporation of the metals in an oxygen atmosphere. The fact that over most of the substrate these films are oriented epitactically with respect to the zirconia substrate means that these high-angle grain boundaries can be characterized in a relatively routine manner using selected-area diffraction. The high-angle boundaries observed in this study include those produced by 23.5°, 29°, and 45° rotations about [001] and 90° rotations about [100] or [010]. These boundaries are compared to special high-angle grain boundaries in cubic materials.
Modulated structure of superconducting Bi2CaSr2Cu2O8+δ
Authors: Gronsky R. , Fendorf M. , Fortunati K. , Hor P. , Meng R.-L. , Chu C.W.
Published: June 2020

In the continuing search for new oxide superconductors, attention has recently been drawn to the Bi-Sr-Cu-O system by Michel et al who achieved a resistance drop onset at 22K for an ultrapure compound with composition Bi2Sr2Cu2O7+δ. Independent pursuits by the groups in Japan and Houston led to their simultaneous announcements of a new material with consistently high transition temperatures in the 100K range. This new compound is believed to have nominal composition Bi2Sr2Cu2O8+δ and orthorhombic unit cell dimensions of a = 5.44Å, b = 27.2Å, and c = 30.78Å. Subsequent electron microscopy investigations of the material identified both an incommensurate structure, and a two phase mixture, related structurally to the original Bi2CaSr2Cu2O8+δ phase. This investigation seeks further understanding of the microstructure of the new compound by a transmission electron microscopy study of single crystals (Tc = 85K) grown at the University of Houston.

Specimens were prepared by crushing to a fine powder in an agate mortar, dispersing the powder in 200 proof ethanol, and suspending the particles on a holey carbon grid.
TEM analysis of TiSi2 on Si and polysilicon
Authors: Lewis Nathan , Shenai Krishna , Hall Ernest L.
Published: June 2020

TiSi2, when deposited on poly-Si and Si, exhibits very low sheet resistance ana can be easily integrated into existing device and IC fabrication environments. However, the high temperature process stability of TiSi2 is rather limited. The silicide must be able to withstand processing temperatures in the 800°C-1000°C range for the fabrication of many high voltage devices and integrated circuits. In the present investigation the high temperature stability of the TiSi2 structures were examined using TEH on both planar and cross-sectional specimens.

The starting materials in this study were <100> Si substrates doped with 1x1016 cm-3 boron. The gate SiO2 was grown and then the poly-Si deposited on the substrate followed by TiSi2 formation on the poly-Si, creating an actual MOS structure used for device fabrication. The TiSi2 was formed by rf sputtering of Ti followed by either a two-step thermal or rapid thermal anneal (RTA) to form the silicide.
Characterization of GaAs films grown on Si substrates by molecular beam epitaxy
Authors: Posthill J.B. , Tarn J. , Humphreys T.P. , Das K. , Wortman J.J. , Parikh N.R.
Published: June 2020

Because of several potential applications and advantages afforded by the heteroepitaxial GaAs-on-Silicon material system, several groups world-wide are attempting to grow device-quality GaAs on Si substrates.eg.1 Both metalorganic chemical vapor deposition (MOCVD) and molecular beam epitaxy (MBE) growth techniques have been widely utilized to achieve heteroepitaxial growth. However, certain fundamental materials and growth problems have thus far prevented any group from achieving heteroepitaxial GaAs of a quality similar to that obtainable from bulk GaAs crystals. A high density of threading dislocations, microtwins/stacking faults, antiphase domain boundaries (APBs) and microfissures can form under non-ideal conditions. These defects result, in part, from stresses generated due to the ∼4% lattice mismatch and the different coefficients of thermal expansion between GaAs and Si.2 Ex-situ characterization of this materials system is essential to assess the material quality and to provide direction for future growth experiments. This contribution describes the TEM characterization methodology that we employ to analyze our GaAs grown on Si substrates by MBE.
Observation of double ribbons in GaAs
Authors: McKernan S. , Carter C. B.
Published: June 2020

The characterization of GaAs on Si is usually performed using cross-section TEM specimens which have been prepared so that the heterojunction is perpendicular to the plane of the foil. In this configuration, however, dislocations present in the GaAs (which lie in the {111} glide planes) are all inclined to the foil. Only a short segment of the dislocation will thus be visible in the thin foil, and even this short segment will be affected over most of its length by the presence of the surface so that it may not be representative of dislocations in the ‘bulk’ epilayer. By preparing TEM cross-section specimens such that the foil normal is close to <111>, long dislocation segments may be observed lying in their glide plane. Observations on specimens prepared in this manner reveal the presence of significant numbers of stacking-fault double-ribbons. This defect appears as a group of three partial dislocations, having the same Burgers vector, bounding two stacking-fault ribbons.
Phase morphology studies of polyarylate/copolyester blends by transmission electron microscopy (TEM) and x-ray diffraction (XRD)
Authors: Plummer H. K. , Peters C. , Golovoy A.
Published: June 2020

Injection molded blends of polyarylate (PAR) (ARDEL D-100,AMOCO) and a copolyester (PCTG) (PCTG-5445, EASTMAN CHEMICALS) were found to be single phase and transparent. Upon annealing, above the glass transition temperature, but below the melt temperature of each blend, a single glass transition temperature remained but blends up to 50% PAR become opaque due to crystallization of the PCTG. These morphological changes with annealing have necessitated this study.

Cross sections of blends containing 85%, 70%, 50% and 30% PCTG, annealed at l60°C-1h, l60°C-4h, l85°C-4h and l85°C-16h respectively, were prepared for TEM using an LKB Ultramicrotome III with diamond knife. Thin, approx. 50 nm sections, supported on carbon film substrates on TEM grids were examined, as sectioned, by bright field TEM (BF TEM), in a JEOL 2000FX TEM operated at 200 keV. Additional thin sections of each blend were examined by BF TEM and selected area electron diffraction (SAED) after they were treated with a solvent mixture (methylene chloride(MeCl)/dioxane(Diox)) to remove the amorphous fraction and reveal the crystalline portion of the PCTG.
From tar sands to synthetic crude: Applications of microscopy
Authors: Mikula R.J. , Munoz V.A.
Published: June 2020

The production of synthetic crude oil from tar sands is a complex process involving initial separation of the bitumen from the sand via the hot water process, separation of the bitumen from the water and finally coking of the residual bitumen to maximize the yield of crude oil. Many of the processing concerns center around decreasing the amount of water and clay which is carried with the bitumen product and decreasing the amount of bitumen which is carried with the water, sand and clay tailings. The crude oil yield in the final coking step is then dependent upon the efficiency of these preliminary steps as well as the coking conditions.

Both electron and optical microscopy have important applications in understanding these systems. Direct observation of frozen hydrated samples in the electron microscope has been utilized for evaluation of both the size distribution of the dispersed phase and the chemical composition.
An HREM study of crystal imperfections in epitaxial lanthanide phthalocyanine films
Authors: Zhang W. P. , Kuo K. H.
Published: June 2020

Because of their interesting electrochromic and gas-sensitive properties, lanthanide phthalocyanine (LnPc2H) films have received much attention recently. It is important to know the local structures of these films for understanding their chemical and physical behavior. LnPc2H is a sandwich-type complex (Fig. 1 (a)), with an ion at the center between two parallel phthalocyanine ligands which are rotated respectively by an angle of about 37°. As shown in Fig. 1 (c), two geometric isomers appear resulting from the different sense of rotation of two ligands. With the strong n-electron interaction between the molecular planes, these molecules tend to form molecular columns (Fig. 1 (b)) during crystal growth so that molecular images can be obtained along the column axis.

Thin films of LnPc2H (Ln = Nd, Tb, Er, Tm, Yb and Lu) were epitaxially prepared on KC1 and NaCl substrates. The KC1 and NaCl crystals were cleaved along (100) in air and immediately placed into a vacuum evaporator.
Preparation and characterisation of vanadium pentoxide supported rhodium catalyst
Authors: Legrouri A.
Published: June 2020

The industrial importance of metal catalysts supported on reducible oxides has stimulated considerable interest during the last few years. This presentation reports on the study of the physicochemical properties of metallic rhodium supported on vanadium pentoxide (Rh/V2O5). Electron optical methods, in conjunction with other techniques, were used to characterise the catalyst before its use in the hydrogenolysis of butane; a reaction for which Rh metal is known to be among the most active catalysts.

V2O5 powder was prepared by thermal decomposition of high purity ammonium metavanadate in air at 400 °C for 2 hours. Previous studies of the microstructure of this compound, by HREM, SEM and gas adsorption, showed it to be non— porous with a very low surface area of 6m2/g3. The metal loading of the catalyst used was lwt%Rh on V2Q5. It was prepared by wet impregnating the support with an aqueous solution of RhCI3.3H2O.
Bevelled plan-view TEM specimen preparation and an artifact due to dimpling
Authors: Lee D.M. , Posthill J.B. , Rozgonyi G.A.
Published: June 2020

The microstructure and metallic impurity gettering efficiency of misfit dislocation (MD) networks generated in Si/Si-2%Ge epitaxial films has been examined using TEM. Metallic elements were evaporated onto the top surface where alternating open windows and oxide masks were defined. The subsequent annealing permitted metal (i.e., gold in the present discussion) to diffuse through open windows into the wafer. The details of the sample structure and results can be found elsewhere in this proceedings. It is desirable to make microscopic observations in both cross-section and in plan-view. This contribution briefly outlines our procedure for making bevelled plan-view TEM specimens and describes a novel specimen preparation artifact.

The top surface was treated with aqua regia (75% HCI, 25% HNO3) for a few seconds in order to remove the gold after the diffusion anneal. 2 mm square sections were cut from a gold diffused wafer and half of the top surface was polished at 2° angle with 6 μm and 1 μm diamond paste followed by final polishing with cyton using a vibrating lapping machine
High resolution scanned tip microscopies
Authors: Wickramasinghe H.K.
Published: June 2020

The invention of Scanning Tunneling Microscopy (STM) which won the 1986 Nobel Prize in Physics has allowed one to image atoms on the surface of a metal or semiconductor by scanning a fine tip (whose diameter is 1000 Å in a controlled fashion very close (2Å) to the sample surface.

In the STM, the tip to sample distance is controlled by measuring the tunneling current -i.e. the current that flows between the tip and sample when a voltage is applied between them- (which changes very rapidly with this distance) and using piezoelectric transducers to precisely position the tip in 3-dimensional space to lÅ accuracy. The STM responds to variations in the electron density of states of the sample surface.

In this paper, we show how one can use the same piezoelectric positioning and control concepts demonstrated with the STM but rely on other physical interactions than the tunneling current to control the tip-sample spacing.
Grain boundaries in high-Tc superconductors
Authors: Chisholm M.F.
Published: June 2020

One crucial property for most superconductor applications is the materials critical current density. Measurements on single crystals of YBa2Cu3O7, show critical currents to be in excess of 105 A/cm2 at 77K. However, polycrystalline samples show values of 103 A/cm2 or less at 77K. The critical current, unlike other superconductivity properties, is not a property of a specific composition but of a specific sample. Defects, introduced during the material processing, exert a pinning force which makes it possible for Type-II superconductors to carry current without losses. At the same time these defects represent an interruption in the structural and chemical order which has been shown to be necessary for superconductivity in the YBa2Cu3Ox phase, and so they may also act as a weak link in the conduction path. The most direct measurements of the role of individual grain boundaries on the critical current density are those of Chaudhari et al. who examined patterned YBa2Cu3O7 films grown on SrTiO3 substrates.
Some HREM observations on silicon small particles
Authors: Iijima Sumio
Published: June 2020

In recent years, small particles have attracted the attentions of by some researchers for their physical and chemical anomaly as well as technological application to ceramics and catalyst industries. For these studies, morphological investigations on small particles seem to be important. HREM methods are the most direct approach to obtain particle crystal structures at atomic level resolution. This talk reviews some of the works on small particle research that have been done as a part of the fine particle research project by Japanese Research development Corporation (fully government-supported project). Among the many TEM observations on small particles that have been done, some specific problems using Si particles are presented.

Small particle production Small particles of Si were prepared by a gasevaporation method which utilizes the evaporation and condensation of Si vapors in an Ar gas at 300Torr. The Si vapors were obtained by heating Si rods by an arc discharge1.
A high resolution experimental electron microscope for observations at liquid helium temperatures
Authors: Siegel Benj. M. , Shimoyama H. , Van Der Leeden E.
Published: June 2020

We have developed a special experimental electron microscope for the study of radiation sensitive materials at high resolution. The most important features are related to the specimen environment which keeps the specimen under UHV conditions and at liquid He temperatures to minimize contamination and hopefully radiation damage. This instrument has been in operation for the past few years and a number of important modifications have been made that we wish to report on. The instrument is currently being set up to make systematic studies on radiation damage on materials at liquid He temperatures.

The instrument is shown in the photograph in Fig. 1. The entire column is evacuated with three separate ion pumps, each pumping on a section of the microscope column; the illuminating system, the cryostat and the viewing chamber. Each section of the microscope can be closed off from the others by all metal gate valves. The illuminating and viewing chamber sections can be baked over 300°C to obtain an UHV.
Field emission scanning electron microscope
Authors: Aihara R. , Saito S. , Kohinata II. , Ogura K. , Otsuji H.
Published: June 2020

A compact type field emission scanning electron microscope (JSM-F15) has recently been developed (Fig. 1). Moreover, due to the simplicity of the electron optical column and the automatically controlled ultra high vacuum system, a good quality and high resolution image can easily be obtained.

The electron optical column, which is shown in Fig. 2, comprises a field emission gun, an electromagnetic lens, scanning coils, etc. The gun, which is composed of a field emitter, a wehnelt and an anode, is pre-aligned. The accelerating voltage is 15 kV and the emitter tip, made of tungsten single crystal, has a [310] orientation in the electron optical axis. The wehnelt is biased through a feedback circuit so as to maintain the emission current constant without varying the accelerating voltage.

The electron probe current at the specimen surface is about 3 × 10-11 amp and the probe diameter is about 30Å at the working distance of 15 mm.
Magnetic einzel lens satisfying anastigmatic and achromatic conditions
Authors: Baba Norio , Nagashima Keiji , Kanaya Koichi
Published: June 2020

Starting from the rigorous treatment on a magnetic einzel lens given by the field distribution along the optical axis z; H(z)= Ho (z/a)m-1/ [1+(z/a)2m], where m is the parameter depending on the double gap pole- piece geometry and the magnetic flux concentration, the lens model is the simple einzel lens whose solution of paraxial ray paths can be obtained in the hypergeometric function. For m=2, it corresponds to the permanent einzel lens introduced by Lenz(1956).

Based on this solution, the important optical quantities and third order aberrations for the practical lens representing the true field distribution which is classified by m=3, as shown in Fig.1, are analytically formulated.

Anastigmatic and achromatic lenses satisfying the anastigmatic and achromatic conditions are presented at the view-point of lens design.

1] Field distribution and paraxial ray paths The paraxial differential equation for a magnetic field of rotational symmetry is, u"+K2u=0; K=Kof(z/a), and Ko2=(e/m)Ho2/(8)Φ (1), where Ho is the maximum value of the field,(e/m) the specific charge of the electron, Φ the accelerating potential and f(z/a) expresses the function of the field distribution along the axis z/a.
An objective lens for an electron microscope with compensated axial chromatic aberration
Authors: Koops H. , Bernhard W.
Published: June 2020

The resolving power of transmission microscopes is limited by diffraction and by spherical and chromatic aberrations of the objective lens.

To compensate the axial chromatic aberration, electric quadrupole fields may be used (1,2). We therefore combined a condenser-objective lens of 2 mm focal length with an electron-optical aplanator (3). Earlier experiments showed that the axial chromatic aberration of the aplanator can be compensated by counteracting electric and magnetic quadrupole fields (4,5). High values of these correcting fields yield a negative chromatic error of the aplanator. It compensates the positive chromatic aberration coefficient of 1.5 mm of the objective lens.

The specimen is situated near the middle plane of the condenser-objective lens. This lens produces a 60-fold magnified virtual image in a plane 122 mm above the specimen. The aplanator transfers this image 1:1 into the object plane of the intermediate lens and compensates the aberrations (6).

Figure 1 shows a micrograph of a resolution test specimen.
Characteristics of the foil lens for the correction of the spherical aberration and its application to STEM
Authors: Hibino M. , Kuzuya M. , Hanai T. , Maruse S.
Published: June 2020

There have been a number of methods proposed and investigated for the correction of the spherical aberration, since this aberration is one of the most important factors which limit the performance of various kinds of electron beam instruments. A foil lens has been investigated preliminarily and the possibility of correcting the spherical aberration of a conventional magnetic lens with reasonable ease has been shown for the first time.The foil lens studied consists of an aperture diaphragm and a thin conducting foil fundamentally as is shown in Fig. 1, and is simple enough in design and adjustment. When the voltage is applied between the diaphragm and the foil, the curved potential distribution is produced around the aperture and the foil lens acts as a concave or negative lens. This concave lens produces the negative spherical aberration and can be utilized to correct the positive spherical aberration of the conventional magnetic lens.
On-line electron-optical correlation computing in the CTEM
Authors: Guckenberger R. , Hoppe W.
Published: June 2020

Light diffractograms of electron micrographs are frequently used to study the transfer function of the microscope. In order to utilize diffractograms for control operations in the microscope, several attempts have been undertaken to obtain on-line diffractograms /1 - 3/. Alternatively correlation functions (CF) may be used /4-8/. In this paper we describe an electron-optical device for the computation of such CF and its on-line operation in a microscope.

The auto-correlation function (ACF) is the inverse Fourier transform of the squared modulus of the Fourier transform (diffractogram) of an image. Therefore it also contains the transfer function. It is its zero peak (main peak) which is of particular interest. In noisy images the main ACF-peak of the noise contributes in an unwanted way to the main ACF-peak of the image. This can be avoided if the ACF will be computed of two images which are identical except for noise /9/ (noise-reduced ACF= NRACF).
A digital storage and processing system which permits aposteriqri image accumulation
Authors: Rust H.-P. , Krahl D. , Herrmann K.-H.
Published: June 2020

The investigation of radiation-sensitive specimens at minimum exposure conditions requires an image-recording system of high DQE which allows immediate observation and processing of the image even at small electron doses. The TV image intensifier, connected to a digital storage unit which counts single electron events, has proved suitable [1]. Since the compromise between signal-to-noise ratio and radiation damage cannot be anticipated due to the statistic character of the damage, it is advisable to store a sequence of very slightly exposed single images in order to carry out subsequent accumulations which can be repeated and optimized. For this purpose a video recorder has been applied [2,3] which records a sequence of single frames. In the following, a system is presented which is not only optimal for the above mentioned purpose but which can also be used for the registration of other dynamic processes.

The single electron video signals which are supplied by the intensifier chain are digitized and normalized -- with regard to spatial and temporal multiple counting -- by a signal processor (Fig. 1).
A direct electron beam photographic recording system for large area scanning electron microscopy readout
Authors: Rao V.R.M. , Nixon W.C.
Published: June 2020

The conventional techniques employed for the recording of images given by SEMs and STEMs on to film, using sealed off cathode ray tubes, are limited in their resolution capability by the electron to light to emulsion energy conversion. This imposes restrictions on the amount by which the negative may be enlarged or the positive may be projected in order to observe fine detail and yet retain a large field of view. These restrictions have been overcome by eliminating the phosphor and the glass optics and instead employing an electron beam that is synchronously scanned with that in the microscope and which is modulated with the video signal produced to expose directly a high resolution photographic emulsion within a single vacuum system. The post lens single deflection coils that are being employed at present can resolve 5000 lines over an area of 4.5 cm x 4.5 cm with a working distance of 10 cm and an angular aperture of 2 mr.
FIM and microanalysis of aluminium alloys
Authors: Boyes E.D.
Published: June 2020

It was originally thought that FIM was restricted to the more refractory metals by mechanical stability considerations, whilst for the surface to be intrinsically stable it is clearly necessary for the ionisation field Fi of the imaging gas to be lower than that (Fe) required to field evaporate the specimen. However, the extent to which both these parameters are variables has been realised only relatively recently. The range of materials was increased substantially when UHV (< 5xl0-11torr) FIMs were equipped with microchannel-plate image intensifiers which facilitated the use of lower ionisation potential, and hence image gases, especially argon (Fi = 1.9v/Å). The argon-ion microscopy of aluminium and some of its alloys is well established, but some improvements have now been made to reduce the influence of the image gas during field evaporation by using 10ns EHT pulses. From the desorption microscopy it was found that the presence of argon reduced the evaporation field FE to about 75% of the vacuum lefels there is also a small pressure dependence and its presence precludes the practical use of lower (<50K) specimen temperatures to improve the stability of the specimen surface or to enhance the image resolution.
A high-performance oil-free backing pump for electron microscopes
Authors: Balkau G.K.W. , Bez E. , Farrant J.L.
Published: June 2020

The earliest account of the contamination of electron microscope specimens by the deposition of carbonaceous material during electron irradiation was published in 1947 by Watson who was then working in Canada. It was soon established that this carbonaceous material is formed from organic vapours, and it is now recognized that the principal source is the oil-sealed rotary pumps which provide the backing vacuum. It has been shown that the organic vapours consist of low molecular weight fragments of oil molecules which have been degraded at hot spots produced by friction between the vanes and the surfaces on which they slide. As satisfactory oil-free pumps are unavailable, it is standard electron microscope practice to reduce the partial pressure of organic vapours in the microscope in the vicinity of the specimen by using liquid-nitrogen cooled anti-contamination devices. Traps of this type are sufficient to reduce the contamination rate to about 0.1 Å per min, which is tolerable for many investigations.
Simplified vacuum system for routine transmission electron microscopes
Authors: Egle W. , Guetter E.
Published: June 2020

The outstanding features of the new ZEISS transmission electron microscope are a vacuum system (ion getter pump with rotary pump) which is not standard in a high-performance, middle-class instrument, and its compatibility with a new external photographic system. The external photography facility which is described in a separate paper, is superior to the normal documentation systems in that it does not load the vacuum system. The evacuated interior of the instrument does not come into contact with gassing photographic material.

These characteristics of external photography, intended primarily for routine work with high photographic workload, make the concept of a simplified vacuum system for electron microscopes, with a fore-vacuum pump only, most attractive. The results of investigations dealing with such a simplified, low-cost vacuum system are described below.

Fig. 1 shows the examined version of the vacuum system mounted on the new TEM. It consists of a two-stage, 8 m3/h rotary pump with baking adsorption trap, vacuum measuring point and two electromagnetic valves.
Topographical measurements at grazing incidence on the SEM
Authors: Reisner J. H. , Johnston L. B.
Published: June 2020

The SEM used at grazing incidence for topographical measurement of small surface detail has been the quantitative basis for studies of signal depth and wave shape in the development of the RCA SelectaVision VideoDisc. Signal amplitudes as small as 150 Å are encountered and measured with a probable error of 50 Å (Figures 3, 4).

The method is described by R. A. Hoover [1]. It exploits a Y/X scan length ratio considerably less than unity to increase the magnification and resolution in the Y (vertical) direction without sacrificing field in the X (horizontal) direction. It further establishes a direction along which the surface contour is to be measured by using the X scan of the electron beam to deposit a line of contamination on the specimen surface.
New STEM spectroscopic techniques for simultaneous electronic analysis and observation of defects in semiconductor materials and devices
Authors: Petroff P.M. , Lang D.V. , Strudel J.L. , Savage A.
Published: June 2020

The main interest in the study of defects in semiconductor materials lies in their electronic properties and their effects on the device characteristics. Conventional transmission electron microscopy (CTEM) and scanning transmission electron microscopy (STEM) provide the tools for analyzing the crystallographic nature of defects in these materials. However, until now, there have been no techniques which allow for the simultaneous observation of a defect along with an analysis of its electronic properties, e.g., energy level, radiative and nonradiative behavior. We have developed on a STEM unit several techniques which permit displaying and analyzing the spatial distribution of nonradiative and/or radiative recombination centers in a thin semiconductor sample which may be simultaneously analyzed by STEM and CTEM.

The first technique uses the electron beam induced current (EBIC) in the thin sample which contains a p-n junction or a Schottky barrier. The surface recombination effects have been minimized to allow for high contrast EBIC images of the recombination centers in the material.
Misfit dislocations in heteroepitaxial systems with low dislocation density
Authors: Hagen W. , Strunk H.
Published: June 2020

The growth of heteroepitaxial layers causes stress across the interface which in a certain range of layer thickness may he relaxed by the formation of misfit dislocations at the interface. Systematic investigations of such misfit structures by transmission electron microscopy (TEM) have previously heen conducted only on systems with a relatively large misfit parameter f, i.e. with a high dislocation density. However, this case presents difficulties in the analysis because of the complexity of the dense structures.

Interfaces containing a low density of misfit dislocations, e.g. heteroepitaxial systems with low misfit, should consequently be investigated. High voltage electron microscopy (HVEM) enables us to study specimens of several μm in thickness and offers decisive advantages over 100 kV TEM: i) generally, specimens can he prepared by thinning the substrate only, ii) thick foils are mechanically stable, which allows the preparation of specimens with an electron transparent area of several mm2.

We report here new results on the initial formation of misfit dislocation structures in the heteroepitaxial system Ge on GaAs (f = 0.074%).
Study of ferroelectric domains on G.A.S.H. single crystals by the scanning electron microscope
Authors: Le Bihan R. , Jouet G.
Published: June 2020

The ferroelectric properties of guanidine aluminium sulphate hexahydrate (G.A.S.H.) were discovered in 1955 (1). The polar axis was found to be perpendicular to the natural cleavage plane. The domain structure of G.A.S.H. have been observed by Pearson and Feldman (2) by pulver technique, Yuri at al. (3) by electroluminescence and B. Hilczer at al. (4-5) by electron microscope decoration technique

We study domain structure in G.A.S.H. single crystals whithout metallization with a scanning electron microscope (S.E.M.). Figure 1 shows the observations obtained on a no etched crystal observed with a scanning electron microscope in the secondary electron emission mode; we see a domain. When the accelerating voltage Vacc of the incident beam pass from 2.3 KV. to 5 KV. the contrast between domains is inversed. At 3.5 KV. the contrast is the same that at 5 KV. but the domain wall is more precise. The inversion of contrast is obtained between 3.3 KV. and 3.4 KV. ; and in this inversion zone we have not any contrast due to the domain or to its boundary.
Emission microscopical investigation of the proximity effect in electron beam lithography
Authors: Hasselbach F. , Rieke U.
Published: June 2020

In electron beam lithography the thin film of electron resist - usually polymethyl methacrylate (PMMA) - is not only exposed to the incident primary electron beam but also to electrons backscattered in the substrate. In contrast to the well focused primaries the backscattered electrons leave, for instance, a silicon substrate as far as 4 μm from the impinging point of the primary beam and therefore contribute to the exposure of the electron resist several microns away. As a consequence the optimum exposure of an array of closely spaced lines or dots is different from that for single isolated structures /1/. We have investigated this proximity effect in two ways: First, we measured the line width as a function of the linear charge density used for exposure. PMMA-films about 150 nm in thickness on a silicon substrate were exposed along parallel lines by a 23 keV electron beam with a halfwidth of about 500 nm.
Temperature dependence of ECP contrast: independent or dependent Bloch wave model?
Authors: Kohl H.-J.
Published: June 2020

The temperature dependence of the ECP contrast of thick Si, Cu, Ag, Au crystals has been investigated with the rocking crystal method /1,2,3/. The ECP is written into a storage unit. The contrast measurements could be performed by writing linescans of the ECP signal on an x-y recorder at a specimen temperature of 500 K and at room temperature. The results obtained with silicon and silver (fig. 2) show a decrease of contrast c with increasing value g of the reciprocal lattice vector belonging to the investigated band edge (c=(IBmax-IBmin)/(IBmax+IBmin), IB: intensity of the backscattered electrons).

With the two beam case of the dynamical theory the temperature dependence of the ECP contrast could be calculated. The contrast is produced by a modulation of the Bloch wave field in the crystal. If absorption is ignored the modulation does not change with depth in the independent Bloch wave model, but in the dependent Bloch wave model it is developing with depth due to the interference between the Bloch waves.
The energy dependence of diffusion model for an electron probe into solid targets
Authors: Kanaya Koichi , Ono Susumu
Published: June 2020

The penetration and energy loss characteristics of an electron probe with energies 1 and 103 KeV in solid targets are obtained by using the potential function as V(r)=(Ze2/a)(r/a)(l/n)-2exp(-r/a) with the screening radius a=0.77aHZ-1/6 [Å], where e is the electronic charge, Z the atomic number, aH the Bohr radius of hydrogen, and n indicates the degree of screening ( n goes 1 ∼ ∞ as the incident energy E∘ decreases and is determined based on the empirical basis1)).

Then, combining the diffusion effect due to multiple collision) and the energy retardation in accordance with E/E∘=(1-y)n/(l+n), with the scattering cross section σ in the Lenard absorption law of ηT=exp(-Nσx), consistent expressions are obtained for the transmission ηT, backscattering fraction ηB with the reduced depth y=x/R and the maximum energy loss depth yE, normalized by the penetration range R as a function of the parameter γ which is derived as functions of the incident energy E∘ and the atomic number Z.
Application of the monte carlo method to high energy electron scattering (0.3-1.5 MeV)
Authors: Soum G. , Arnal F. , Balladore J.L. , Jouffrey B. , Verdier P.
Published: June 2020

Techniques for using the Monte-Carlo method for studying electron scattering in solids have been developed by several authors (1). The method is used to determine the angular distribution of electrons emerging from amorphous or polycrystalline specimens ; the total transmission and backscattering coefficients can also be obtained.

- Method of calculation -Let Iθ be the intensity scattered in the direction making an angle θ with the incident electrons ; thus Iθ represents the number of electrons scattered in this direction within a solid angle Δw = πα2, where α is the semi-angle of the collector as seen from the specimen. For a specimen of thickness x, the angular distribution function may be written:

I∘ denotes the intensity of the incident monoenergetic electron beam, Tα the transmission coefficient along the direction of incidence for a semi-angular aperture α and TθN the normalized transmission coefficient in the direction θ
Thickness determination of thin films by electron backscattering: principles, problems, and applications
Authors: Niedrig H.
Published: June 2020

For thin films with thicknesses D ≪ R/2 (R: range of primary electrons within the film material) the total electron backscattering ratio η = Ir/IO proved to be proportional to λ4NAZ2D for mean and high atomic numbers Z (λ: electron wavelength, NA: atomic number density), from which a thickness determination method has been developed.

The observed high values of the backscattering ratio can only be explained by assuming multiple scattering starting very rapidly at thicknesses of about 10 nm even at low atomic numbers thus increasing the backscattered intensity from single scattering events (fig. 1) and by using the Mott scattering cross-section for high atomic numbers (fig. 2). For very thin films of low atomic numbers single Rutherford scattering seems to be applicable.

By focusing the electron beam into the film plane and scanning the beam across the film the thickness distribution of self-supporting crystalline films can be determined.
A new image processing software system for structural analysis and contrast enhancement
Authors: Frank Joachim , Shimkin Brian
Published: June 2020

We report on the development of a new image processing software system SPIDER (System for Processing of Image Data in Electron Microscopy and Related Fields). The need for a user-oriented software system for electron image processing has been previously recognized /1-4/. These systems have in common that they allow users with a minimum amount of computer experience to define complex operations on images.

The present system runs under the PDP 11/45 RSX-11D (Digital Equipment Corp.) executive in a multi-user, multi-task environment. Image enhancement of large images (e.g., box convolution and point mapping operations) as well as structural electron microscopy (Fourier operations, 3-d reconstruction) had to be accommodated. Characteristic for the electron microscope application is the need to process series of images closely related to each other (defocus, tilting, and averaging series).

In SPIDER, the images are read and transferred by magnetic tape from the microdensitometer to PDP 11 disk files.
Comparison of molecuie images simulated by use of point models and kinematical structure amplitudes
Authors: Neumann W. , Hillebrand R.
Published: June 2020

In electron microscopic practice for high-resolution imaging both the criterion of linearity of the optical transfer and the conditions for the small angle approximation are fulfilled. The intensity distribution of the image does not only depend on the properties of the objects but also on the illumination conditions, the lens aberrations, the aperture and the focus situation. Because of the relatively large depth of focus most of the electron optical specimens can be considered as two dimensional objects. From the above mentioned conditions it follows that the imaging process can be represented by an appropriate sequence of mathematical operations, i.e. the convolution with a propagation function or the multiplication with a transmission function. Using the Fresnel approximation of the diffraction theory the imaging process of an electron microscopic objective lens taking into consideration the defocusing value Δ is completely described by eq. 1 (the reduction to one dimension is possible without any loss of generality):
Molecular images of phthalocyanines and hydrocarbons
Authors: Fryer J.R.
Published: June 2020

Reported efforts to obtain molecular images have hitherto been confined to chlorinated copper phthalocyanine that is atypical in having a high thermal and radiation stability. The radiation limited resolution of molecules has been described by the minimum resolvable object size

C being object contrast

f electron utilisation factor

Ncrcritical exposure for specimen destruction

The normal value used for C is approximately 0.1 but since this is the parameter most ameanable to improvement, efforts to increase C were made These efforts included the use of a high resolution objective lens of Cs = 0.67mm so that the constant phase contrast transfer envelope extended down to 3Å at the Scherzer defocus, and a 20μm condenser aperture Minimal exposure techniques were used with Ilford X-ray film to overcome the difficulties of low beam intensity and mechanical vibration of the specimen.

Our previous studies on α' copper phthalocyanine(2) had required the specimen to be tilted for molecular superimposition on the unit cell b axis, A survey of a variety of hydrocarbons revealed that structures of planar molecules where the molecular plane makes an angle of greater than 40° to the b axis, tend to grow on KC1 with the b axis normal to substrate - i,e. no tilting is required to image a column of superimposed molecules.
Transmission electron microscopy analyses of complex ceramics
Authors: Shaw T.
Published: June 2020

Many potentially useful ceramic materials have complex structures which are difficult to determine using x-ray analysis alone. By the use of contemporary transmission electron microscopy-techniques such as lattice fringe imaging and contrast experiments much information can be obtained about such structures greatly simplifying structure determination. It has already been demonstrated that images of “open” structures bearing a one to one correspondence with the projected structure can be obtained. However, in many commercially important ceramics atoms or atom concentrations are two closely spaced to be resolved directly by current microscopes. In this presentation examples are shown of the type of structural information that is obtainable from such “close packed” structures using transmission electron microscopy, two examples being given below.

In Fig. 1(a) a two dimensional fringe image of a region of a 15 R polytype from the Be-Si-N system is shown on the left. It can be seen from this image that the structure is made up of three identical blocks of five close packed planes each related by a translation of 1/3[100] giving a repeat stacking in the close packed [001] direction of fifteen close packed layers.
Theoretical investigation of superlattice-fringe images of ordered alloys
Authors: Allen Samuel M.
Published: June 2020

A computer simulation of lattice-fringe imaging of ordered Fe-Al and Cu-Au alloys has been carried out, using multiple-beam dynamical diffraction theory. This study corrects and extends results presented earlier for an Fe-Al alloy and provides additional results to those of Sinclair et al. for Cu3Au.

Systematic-row calculations were carried out in which eight or nine beams were excited, depending on whether two or three beams, respectively, were allowed to contribute to the image. The computed parameters of the dynamical theory (Bloch wave amplitudes and vectors) were used to compute superlattice-fringe images, taking into account the effects of lens aberrations as described by Sinclair et al. (4). Four different diffraction geometries (imaging modes) were employed in the study, as indicated in Figure 1 (Only the beams allowed to contribute to the image are shown.).
7-beam lattice images of (110) oriented Ge
Authors: Parsons J.R. , Hoelke C.W.
Published: June 2020

The direct imaging of a crystal lattice has intrigued electron microscopists for many years. What is of interest, of course, is the way in which defects perturb their atomic regularity. There are problems, however, when one wishes to relate aperiodic image features to structural aspects of crystalline defects. If the defect is inclined to the foil plane and if, as is the case with present 100 kV transmission electron microscopes, the objective lens is not perfect, then terminating fringes and fringe bending seen in the image cannot be related in a simple way to lattice plane geometry in the specimen (1).

The purpose of the present work was to devise an experimental test which could be used to confirm, or not, the existence of a one-to-one correspondence between lattice image and specimen structure over the desired range of specimen spacings. Through a study of computed images the following test emerged.
The study of defects in Sb2S3 by method of direct lattice resolution
Authors: Kosevich V.M. , Sokol A.A. , Bagmut A.G.
Published: June 2020

1.Sb2S3 has the orthorombic lattice with a=11,23;b=11,31; c=3,84 Å. Its crystal structure is constructed of the double ribbons of antimony and sulphur atoms,parallel to [00l].Vacuum deposited films of Sb2S3 re amorphous{they were crystallyzed in spherolite mode by the electronbeam heating.

The study of defect structure of the Sb2S3 spherolite crystals by method of direct lattice resolution was the aim of present work.The images of (100),(200),(010),(020),(110) and (110) planes were obtained.

2.Several types of the ribbons stacking faults were obserwed in Sb2S3 crystals with (001) parallel to the substrate plane (Fig.1).The stac-kingfault planes and their displacement vectors R are the following: a) (010),(110),R=1/2 [010];b) (100),R=1/2 [210],R=1/4[210].

3.There were obtained the images of partial dislocations with b=1/2 [010] and small-andle boundaries,consisted of the dissociated partial dislocation pairs,in Sb2s3 crystals with (100) and (010) planes parallel to the substrate.Small-angle boundaries appeared on initial stage of the spherolite growth,when splitting of spherolite single-crystal nucleus was taking place (Fig.2).
Point defect generation during the oxidation of silicon
Authors: Lambert J.A. , Dobson P.S.
Published: June 2020

The interstitial defects created during ion-implantation in silicon condense out during annealing to form extrinsically faulted Frank loops and perfect dislocation loops. The annealing behaviour of these defects has been investigated by annealing electron microscope thin foils. It was found that the loops shrink and eventually disappear after annealing in the temperature range 900-1020° C in vacuum. Figure 1a shows faulted and perfect loops after implanting with 10 15 boron ions cm-2 at 40kV and bulk annealing for 50 minutes in nitrogen at 950° C. The thin foil was then annealed for 30 minutes at 1000° C in vacuum and figure 1b shows that the loops have shrunk during this treatment.

The loop shrinkage is caused by the diffusion of interstitial point defects from the loop to the surface and the driving force for this process is provided by the self energy of the loops. The rate of shrinkage is given by

where A is a geometrical factor, Ds is the coefficient of self diffusion and ΔF is
the change in the free energy of the loop per emitted interstitial.