bluuebunny/crossref_metadata_2025 huggingface dataset:
A Super-High-Resolution HVEM (H-1500) Newly Installed in NIRIM
Authors: Horiuchi S. , Matsui Y.
Published: June 2020

A new high-voltage electron microscope (H-1500) specially aiming at super-high-resolution (1.0 Å point-to-point resolution) is now installed in National Institute for Research in Inorganic Materials ( NIRIM ), in collaboration with Hitachi Ltd. The national budget of about 1 billion yen including that for a new building has been spent for the construction in the last two years (1988-1989). Here we introduce some essential characteristics of the microscope.

(1) According to the analysis on the magnetic field in an electron lens, based on the finite-element-method, the spherical as well as chromatic aberration coefficients ( Cs and Cc ). which enables us to reach the resolving power of 1.0Å. have been estimated as a function of the accelerating As a result of the calculaton. it was noted that more than 1250 kV is needed even when we apply the highest level of the technology and materials available at present. On the other hand, we must consider the protection against the leakage of X-ray. We have then decided to set the conventional accelerating voltage at 1300 kV. However. the maximum accessible voltage is 1500 kV, which is practically important to realize higher voltage stabillity. At 1300 kV it is expected that Cs= 1.7 mm and Cc=3.4 mm with the attachment of the specimen holder, which tilts bi-axially in an angle of 35° ( Fig.1 ). In order to minimize the value of Cc a small tank is additionally placed inside the generator tank, which must serve to seal the magnetic field around the acceleration tube. An electron gun with LaB6 tip is used.
Computer Image and Spectrum Acquisition on an HB501A STEM
Authors: Kirkland Earl J.
Published: June 2020

A DEC VAXstation 3200 color graphics computer workstation has been interfaced to a Vacuum Generators HB501A Scanning Transmission Electron Microscope (STEM) for on-line image and spectrum acquisition. Electron Energy Loss Spectra (EELS) or Auger spectra may be recorded (serially) using pulse or analog modes (using the voltage to frequency converters supplied by VG). High resolution bright field (BF) / annular dark field (ADF) image pairs may be recorded simultaneously as well as simultaneous pairs of Auger / secondary images. A resolution of 2Å (or better) has been achieved with an experimental pole piece (Cs = 1.2mm. and 0.7mm.). The image quality obtained with this system is greatly improved over the Polaroid system supplied with the microscope.

A schematic of the overall system is shown in FIG 1. To avoid possible ground loop noise the entire computer system has been optically isolated from the STEM. There are four 16 bit digital to analog converters (DAC) for controlling the x,y position, the EELS energy and the Auger energy. The output of four detectors is connected back to the computer for pulse counting using a Qbus board manufactured by Codar Technologies. This board has three AMD 9513 counter IC's (with five 16 bit counters each) to count the electron or VFC pulses. The EELS spectra are acquired using two 32 bit counters (16 bit counters concatenated) and may function in a constant dwell time or constant count (constant signal to noise ratio) mode. The Auger and BF/ADF image counters work in a constant dwell time 16 bit mode. The average CPU overhead has been measured at 50 microsec per point in polled mode (images) and 500 microsec in interrupt driven mode (spectra).
Recent Progress and Plans in Computer-Controlled High Resolution Electron Microscopy
Authors: de Ruijter W.J. , Rez Peter , Smith David J.
Published: June 2020

Digital computers are becoming widely recognized as standard accessories for electron microscopy. Due to instrumental innovations the emphasis in digital processing is shifting from off-line manipulation of electron micrographs to on-line image acquisition, analysis and microscope control. An on-line computer leads to better utilization of the instrument and, moreover, the flexibility of software control creates the possibility of a wide range of novel experiments, for example, based on temporal and spatially resolved acquisition of images or microdiffraction patterns. The instrumental resolution in electron microscopy is often restricted by a combination of specimen movement, radiation damage and improper microscope adjustment (where the settings of focus, objective lens stigmatism and especially beam alignment are most critical). We are investigating the possibility of proper microscope alignment based on computer induced tilt of the electron beam. Image details corresponding to specimen spacings larger than ∼20Å are produced mainly through amplitude contrast; an analysis based on geometric optics indicates that beam tilt causes a simple image displacement. Higher resolution detail is characterized by wave propagation through the optical system of the microscope and we find that beam tilt results in a dispersive image displacement, i.e. the displacement varies with spacing. This approach is valid for weak phase objects (such as amorphous thin films), where transfer is simply described by a linear filter (phase contrast transfer function) and for crystalline materials, where imaging is described in terms of dynamical scattering and non-linear imaging theory. In both cases beam tilt introduces image artefacts.
Improvement of Stem Images by Means of Elimination of Influence of Statistical Fluctuation in Incident Electrons
Authors: Michio Hibino , Suzuki Takahiro , Hanai Takaaki , Maruse Susumu
Published: June 2020

The noise, due to statistical fluctuation of signal electrons, determines the ultimate resolution limit of imaging and analysis. The signal electrons (N) for each pixel are formed through two stages of statistical processes; Poisson distribution for the number of incident electrons (No) and polynomial distribution for forming signal electrons. The signal electrons therefore obey the Poisson distribution of average nOp (no:average of incident electrons, p:probability of forming signal electrons) and of standard deviation . In order to improve the resolution limit set by the statistical noise of signal electrons, a new method of normalization is proposed for STEM.

In STEM imaging of thin specimens, the total transmitted electrons correspond to the incident electrons. It is therefore possible to know the incident electrons by summing up all the transmitted electrons and to normalize the signal electrons by incident electrons, for eliminating the influence of fluctuations of incident electrons. The average E and the standard deviation σ of normalized signal electrons are expressed by p and , respectively, for no> > 1 , indicating that E/σ value is improved by a factor of .
Sensitive High-Vacuum Monitoring for Philips Electron Microscopes Which Employ ION Getter Pumping
Authors: Greene Alexander. E.
Published: June 2020

A very sensitive vacuum monitor may be easily and inexpensively added to any Philips CM or 400 series electron microscope. This digital, auto-ranging volt meter will also operate as an excellent leak detector.

The newer Philips computerized transmission electron microscopes have no separate high vacuum gauge and sense high vacuum the same way as it is done on the 400 series instruments. The high vacuum monitoring technique for these microscopes is accomplished by relating the electrical current required by the Ion Getter Pump to the quality of the vacuum (i.e. the better the vacuum, the lower the current). The system for vacuum monitoring measures the voltage across a low value resistor which is placed in series with the Getter Pump and the pump power supply and is usually located near ground or earth potential. The power supply delivers about 7000 V.D.C. to the pump and the voltage across the low value resistor is proportional to the current being drawn by the pump. This voltage is measured, amplified and then compressed by a logarithmic amplifier so one meter scale or a simple digital-to-analog converter can provide a reading equivalent to the high vacuum value. Because of the logarithmic amplifier, small changes cannot be seen; only the general vacuum quality can be monitored.
Point-Cathode Electron Gun Using Electron-Beam Bombardment for Cathode Tip Heating
Authors: Iiyoshi Ryo , Maruse Susumu , Takematsu Hideo
Published: June 2020

Point cathode electron gun with high brightness and long cathode life has been developed. In this gun, a straightened tungsten wire is used as the point cathode, and the tip is locally heated to higher temperatures by electron beam bombardment. The high brightness operation and some findings on the local heating are presented.

Gun construction is shown in Fig.l. Small heater assembly (annular electron gun: 5 keV, 1 mA) is set inside the Wehnelt electrode. The heater provides a disk-shaped bombarding electron beam focusing onto the cathode tip. The cathode is the tungsten wire of 0.1 mm in diameter. The tip temperature is raised to the melting point (3,650 K) at the beam power of 5 W, without any serious problem of secondary electrons for the gun operation. Figure 2 shows the cathode after a long time operation at high temperatures, or high brightnesses. Evaporation occurs at the tip, and the tip part retains a conical shape. The cathode can be used for a long period of time. The tip apex keeps the radius of curvature of 0.4 μm at 3,000 K and 0.3 μm at 3,200 K. The gun provides the stable beam up to the brightness of 6.4×106 A/cm2sr (3,150 K) at the accelerating voltage of 50 kV. At 3.4×l06 A/cm2sr (3,040 K), the tip recedes at a slow rate (26 μm/h), so that the effect can be offset by adjusting the Wehnelt bias voltage. The tip temperature is decreased as the tip moves out from the original position, but it can be kept at constant by increasing the bombarding beam power. This way of operation is possible for 10 h. A stepwise movement of the cathode is enough for the subsequent operation. Higher brightness operations with the rapid receding rates of the tip may be improved by a continuous movement of the wire cathode during the operations. Figure 3 shows the relation between the beam brightness, the tip receding rate by evaporation (αis the half-angle of the tip cone), and the cathode life per unit length, as a function of the cathode temperature. The working life of the point cathode is greatly improved by the local heating.
Toward The Simultaneous Correction of Spherical and Chromatic Aberration in Electron Optics by Means of an Electrostatic Electron Mirror
Authors: Rempfer Gertrude. F.
Published: June 2020

Optimum performance in electron and ion imaging instruments, such as electron microscopes and probe-forming instruments, in most cases depends on a compromise either between imaging errors due to spherical and chromatic aberrations and the diffraction error or between the imaging errors and the current in the image. These compromises result in the use of very small angular apertures. Reducing the spherical and chromatic aberration coefficients would permit the use of larger apertures with resulting improved performance, granted that other problems such as incorrect operation of the instrument or spurious disturbances do not interfere. One approach to correcting aberrations which has been investigated extensively is through the use of multipole electric and magnetic fields. Another approach involves the use of foil windows. However, a practical system for correcting spherical and chromatic aberration is not yet available.

Our approach to correction of spherical and chromatic aberration makes use of an electrostatic electron mirror. Early studies of the properties of electron mirrors were done by Recknagel. More recently my colleagues and I have studied the properties of the hyperbolic electron mirror as a function of the ratio of accelerating voltage to mirror voltage. The spherical and chromatic aberration coefficients of the mirror are of opposite sign (overcorrected) from those of electron lenses (undercorrected). This important property invites one to find a way to incorporate a correcting mirror in an electron microscope. Unfortunately, the parts of the beam heading toward and away from the mirror must be separated. A transverse magnetic field can separate the beams, but in general the deflection aberrations degrade the image. The key to avoiding the detrimental effects of deflection aberrations is to have deflections take place at image planes. Our separating system is shown in Fig. 1. Deflections take place at the separating magnet and also at two additional magnetic deflectors. The uncorrected magnified image formed by the objective lens is focused in the first deflector, and relay lenses transfer the image to the separating magnet. The interface lens and the hyperbolic mirror acting in zoom fashion return the corrected image to the separating magnet, and the second set of relay lenses transfers the image to the final deflector, where the beam is deflected onto the projection axis.
Observation of Single Magnetic-Flux Quanta Using Electron Holography
Authors: Matsuda T. , Hasegawa S. , Endo J. , Osakabe N. , Tonomura A. , Aoki R.
Published: June 2020

A Magnetic flux quantum (fluxon) penetrating a superconductor plays an important role in both fundamental and practical applications of superconductivity. However, the fluxon has evaded direct observation, because it is shaped like an extremely thin filament in addition to its small flux value, h/2e (=2x10−15Wb). Several methods have already been developed to indirectly observe each filament of flux. One method is Bitter's [1], in which magnetic powder is sprinkled on the superconductor surface. The powder accumulates at the fluxons, and the image is observed by electron microscopy.

We have observed the magnetic field of a single fluxon using holographic electron interferometry [2], in which the phase distribution of an electron beam can be measured to a precision of 2Π/50. The schematic diagram of the experiment is shown in Fig. 1. A weak magnetic field is applied perpendicularly to a superconducting lead film. Fiuxons penetrating the film are observed as phase contour fringes through the electron holography process. The sample is prepared by evaporating lead on one side of a thin tungsten wire, which is shown in Fig. 2.
Advances in Photoelectron Imaging
Authors: Griffith O. Hayes , Birrell G. Bruce , Habliston Douglas H. , Hedberg Karen K.
Published: June 2020

There are many possible strategies of photoelectron imaging. The common theme is to form the image with electrons that have been photoejected from a surface by UV light (i.e. the photoelectric effect). Currently the highest resolution method is photoelectron microscopy (PEM), which is also called photoemission electron microscopy (PEEM). This approach has its roots in the early developments in electron microscopy in Germany. However, modern ultra high vacuum technology and image enhancement techniques have made possible significant advances in the capabilities of photoelectron imaging.

Photoelectron microscopy is the electron optical analog of fluorescence microscopy. Light is focused on a specimen and the emitted electrons are accelerated, and the image magnified by means of an electron optical system. The main advantage of photoelectron microscopy is the source of contrast. Small differences in the bonding of outermost electrons can cause significant contrast between molecules that would be otherwise difficult to detect. Biological systems are rich in macromolecules that differ in molecular ionization potentials and this source of information remains largely unexplored.
Development of A 350-KV Holography Electron Microscope and its Applications
Authors: Kawasaki Takeshi , Endo Junji , Matsuda Tsuyoshi , Tonomura Akira
Published: June 2020

The 350 kV field-emission electron microscope shown in Fig.1 has been developed to widen the applications of electron holography. A field emission beam is used because it is very bright at first and monochromatic. However, its brightness deteriorates while passing through accelerating electrodes and condenser lenses because of their spherical and chromatic aberrations. A magnetic lens is installed just below a (310)-oriented tungsten tip. A magnetic lens is used so that the electron source image can be located at the most favorable position between the accelerating tube and the first condenser lens to minimize the aberrations and to increase brightness. The measured brightness (probe current) ranges from 1.4x109A/cm2/sr (0.37 nA) to 6.7x108A/cm2/sr (2.2 nA) with 10 μA total emission current at 300 kV.

These increased brightness and narrow energy spread of the electron beam enable observing fine spacing lattice fringes in a gold thin film. Lattice fringes of 0.065 nm spacing were actually observed in the electron micrograph shown in Fig. 2. The incident electron beam was along the [001] axis, and the (400) andreflected beams were used to form the fringes. A 0.055 nm spacing lattice image is shown in Fig. 3. These fringes resulted from the interference of the electron beam, with an incident axis from the [111] direction into the gold thin film, by theanddiffracted beams. This spacing is the shortest observed to date.
Visualisation and Quantitative Evaluation of Small Thickness and Phase Steps from Electron Holograms by Digital Image Processing
Authors: Lauer Rolf , George Ade
Published: June 2020

Digital image processing proved to be highly suited for the quantitative decoding of the phase information stored in off-axis electron holograms [1]. We want to show here that digital processing is superiour to light optical reconstruction work because of its flexibility and extended possibilities; i.e. phases and amplitudes can be displayed directly, in contrast to modulated intensity patterns in the light optical case. When a hologram is stored digitally, no further optical or photographical processing is necessary. The reconstruction can be done interactively within seconds by means of an image processor with Fast Fourier Transform hardware [2]. We give here some examples:

(1) A flat MgO crystal which has been thinned by electron bombardment [3]. Fig.1a is a micrograph, copied on hard paper, where a quadratic deepening becomes just visible. Fig.1b is an off-axis hologram of this area. By light-optical interferometric reconstruction using the second diffraction order of the hologram, the contour map of Fig.1c has been obtained. Figs.1d,e are digital reconstructions where eight lines of equal phase correspond to a phase shift of 2π. This has been achieved with the method described by Ade and Lauer (these Proceedings). The shift d of the fringes corresponds to a height difference of 2.2nm. Fig.If is a superposition of Figs.1d,e giving a topographic view which reveals even smaller thickness variations.
Digital Phase Amplification in Electron off-Axis Holography
Authors: Ade George , Lauer Rolf
Published: June 2020

An off-axis hologram is obtained by recording the interference pattern resulting from the superposition of the object wave and a slightly tilted reference wave. The phase distribution of the object wave is a function of several parameters such as the electromagnetic potentials, the accelerating voltage of the electrons, and the object thickness. Therefore, the electromagnetic fields and the thickness of the object can be directly deduced from the phase distribution stored in the hologram.

This distribution is usually determined by light optical interferometric reconstruction of the hologram using one or two diffracted beams. If the two first order beams are utilized, a two-times phase-amplified interference image is obtained. The sensitivity of phase detection can generally be enhanced if higher diffraction orders are used. Two methods have been successfully applied for this purpose. In the first method [1], the high order beams are obtained by making a hard photographic copy of the original hologram. In the second technique [2-4], a new hologram is formed from the original one by emloying the two first order diffracted beams. The new hologram is photographically recorded on a film, and the film is bleached in order to enhance the diffraction efficiency. When this procedure is repeated n times, an amplification rate of 2n is achieved.
Three-dimensional Image Analysis of Tubular Crystals of Membrane Proteins in Ice
Authors: Toyoshima Chikashi
Published: June 2020

Frozen-hydrated electron microscopy is a powerful method that allows us to preserve biological macromolecules in physiological ionic conditions and obtain the density (Coulomb potential) maps directly. Changes in quarternary structure in different conditions have been demonstrated using this technique for the gap junction (1) and the nicotinic acetylcholine receptor (2). Since the image contrast originates from the difference in density between the specimen and ice, the method has a considerable advantage over conventional methods in resolving structure inside the lipid bilayer, especially when molecules are arranged in a helical array to form tubular crystals. The molecules in a helical array present many different views to the incident electron beam, hence the electron micrograph actually contains a large amount of three-dimensional information. By using helical image analysis, it is possible to obtain a three-dimensional image from a single micrograph in many instances. Furthermore, the data is complete: There is no "missing cone" problem arising from a limited angle of tilt; the resolution in the reconstructed image is isotropic. The mean (radial) density distribution is available from equatorial data; thus the value in the map is an absolute measure of the density.

We have been analysing tubular crystals of the nicotinic acetylcholine receptor from electric ray and the calcium ATPase from rabbit sarcoplasmic reticulum. Helical image analysis at 17 Å resolution of the narrow tubes embedded in ice has allowed two leaflets of the lipid bilayer to be resolved clearly (2). The lipid bilayer was not resolved in previous tilt reconstructions using flattened tubes at a similar (in plane) resolution and up to 60 degrees tilt (3).
Imaging Molecules and Cells with the Atomic Force Microscope
Authors: Prater C.B. , Weisenhorn A.L. , Northern B. Dixon , Peterson C.M. , Gould S.A.C. , Hansma P.K.
Published: June 2020

The atomic force microscope (AFM) gives topographic images by scanning a sharp stylus over a surface. The stylus is attached to a spring lever which is deflected when the stylus interacts with the surface. The AFM images a surface by measuring deflection as a function of position over the surface. The AFM has given atomic resolution images of both conductors and nonconductors. The AFM has also given images of amino acid polymers with subnanometer resolution. The AFM has imaged samples covered with a liquid and biological processes like blood clotting have been imaged. In this report we present several images that demonstrate the variety of samples that can be imaged with the AFM.

The AFM has imaged adsorbed molecules at subnanometer resolution. Figure 1A is an image of the bare (010) surface of the natural zeolite, clinoptilolite. Molecules of t-butanol were then adsorbed onto the surface from the liquid and the sample was imaged again (Fig. IB).

Figure 2 is an image of double stranded DNA dried onto mica. The resolution is sufficient to reveal corrugation due to the major groove of the double helix. We are currently working to gain resolution sufficient to sequence single-stranded DNA.
Three-Dimensional Reconstruction of Two Forms of the Chaperonin GRO EL
Authors: Carrascosa J.L. , Abella G. , Marco S. , Muyal M. , Carazo J.M.
Published: June 2020

Chaperonins are a class of proteins characterized by their role as morphogenetic factors. They trantsiently interact with the structural components of certain biological aggregates (viruses, enzymes etc), promoting their correct folding, assembly and, eventually transport. The groEL factor from E. coli is a conspicuous member of the chaperonins, as it promotes the assembly and morphogenesis of bacterial oligomers and/viral structures.

We have studied groEL-like factors from two different bacteria:E. coli and B.subtilis. These factors share common morphological features , showing two different views: one is 6-fold, while the other shows 7 morphological units. There is also a correlation between the presence of a dominant 6-fold view and the fact of both bacteria been grown at low temperature (32°C), while the 7-fold is the main view at higher temperatures (42°C). As the two-dimensional projections of groEL were difficult to interprete, we studied their three-dimensional reconstruction by the random conical tilt series method from negatively stained particles.
3D Reconstruction of Proteasomes Using Random Conical Tilting
Authors: Hegerl R. , Pfeifer G. , Dahlmann B. , Baumeister W.
Published: June 2020

Proteasomes isolated from the archaebacterium Thermoplasma acidophilum and negatively stained with ammonium molybdate appear in two preferred orientations on electron micrographs. Describing the particle roughly as cylinder-shaped, the orientations "end-on" and "side-on" are defined by the cylinder axis being normal and parallel to the specimen support, respectively. Two-dimensional averages are available from both views. The complexity of the particle, however, prevents an intuitive deduction of a three-dimensional model from these two views. Due to the occurence of two preferred orientations, the object is, in principle, well suited for a 3D reconstruction based on random conical tilting. The side-on view was used for 3D reconstruction for two reasons: First, two-dimensional averages led us to suppose that the particles do not suffer from rotations around their cylinder axis, and second, parallelism of the long cylinder axis and the specimen support promises to give a stable object inclination.

The proteasomes were isolated and prepared for electron microscopy as described previously. Many pairs of micrographs were taken in a Philips EM 420 at a magnification of 36000 and an electron dose of about 2000 e/nm2. The first exposure of each pair shows the specimen with a tilt angle of about 60 deg, the second one is untilted (Fig. 1). Several image pairs were selected for computer processing using a favourable distribution of particles and acceptable focus conditions as selection criteria. After digitizing corresponding areas (2048 by 2048 pixels, pixel size 15 μm = 0.42 nm at object level) in each pair using an Eikonix 1412 camera, small images of single particles were extracted from the untilted image and aligned with respect to translation and rotation. Knowing the tilt angle and tilt axis azimuth, position and rotation parameters of the particles could be transferred to the tilted image thus enabling the extraction of a set 227 of projections ready for a three-dimensional back projection (Fig. 2). All computation was done with the EM-system.
Conducting Polymer Films as EM Substrates
Authors: Simon M. N. , Lin B. Y. , Lee H. S. , Skotheim T. A. , Wall J. S.
Published: June 2020

The developing field of electroactive polymers, when the polymers are manipulated into thin film forms, offers potentially ideal materials for EM substrates. Mechanically, they are strong, flat, thin, and stable in the electron beam. For biological specimens, they are hydrophilic and their chemistry can be adapted to the particular specimen so the attachment can be gentle with no denaturation. They have the excellent electron optical properties of low Z, little grain, good electrical conductivity, and no observable radiation damage in the electron beam. Such films can be made fresh just prior to use to avoid contamination.

Up to now, thin C films have been the best EM substrates for direct deposition of biological materials. With high vacuum evaporation of C, 20A thick films with >90% coverage of 4u windows in a holey film can be obtained. However, these films rapidly become hydrophobic by absorbing contaminants from the air and so need something like the wet-film technique or glow discharge to keep them hydrophilic. Even so, there are often hot spots of irreversible attachment of biological molecules causing distortion and even denaturation. Also, C films show a significant phase grain, presumably from C60 microcrystals.
Surface Morphology Studies by Low-Energy Electron Microscopy (LEEM)
Authors: Bauer Ernst , Mundschau Michael , Swiech Waclaw , Telieps Wolfgang
Published: June 2020

The morphology of a surface determines to a large extent its physical and chemical properties. In order to understand these properties it is frequently sufficient to image the surface with a resolution in the 10 nm range, provided that the relevant surface features show sufficient contrast, as is the case in LEEM. The talk discusses the morphology information which can be obtained with LEEM and illustrates it with various examples.

Point defects, e.g. emergence points of screw dislocations, or point-like defects such as small impurity clusters cannot be resolved in LEEM but nevertheless imaged by decorating them (screw dislocations) or by their influence on surface processes (pinning centers in sublimation). Line defects, e.g. sublimation steps, growth steps or glide lines, may be imaged directly down to atomic height by geometric phase contrast or indirectly by decoration. If a step separates regions with different structures (e.g. domain orientations), then ordinary diffraction contrast will reveal the shape and location of the step. Planar defects can also be imaged by diffraction contrast but three-dimensional defects such as large sublimation hillocks frequently cause also topographic contrast.
Rem Study of Current Effect on the Structure of Clean Si(111) Surface
Authors: Yamanaka A. , Ohse H. , Yagi K.
Published: June 2020

Recently current effects on clean and metal adsorbate surfaces have attracted much attention not only because of interesting phenomena but also because of practically importance in treatingclean and metal adsorbate surfaces [1-6]. In the former case, metals deposited migrate on the deposit depending on the current direction and a patch of the deposit expands on the clean surface [1]. The migration is closely related to the adsorbate structures and substrate structures including their anisotropy [2,7]. In the latter case, configurations of surface atomic steps depends on the current direction. In the case of Si(001) surface equally spaced array of monatom high steps along the [110] direction produces the 2x1 and 1x2 terraces. However, a relative terrace width of the two domain depends on the current direction; a step-up current widen terraces on which dimers are parallel to the current, while a step-down current widen the other terraces [3]. On (111) surface, a step-down current produces step bunching at temperatures between 1250-1350°C, while a step-up current produces step bunching at temperatures between 1050-1250°C [5].

In the present paper, our REM observations on a current induced step bunching, started independently, are described.

Our results are summarized as follows.

(1) Above around 1000°C a step-up current induces step bunching. The phenomenon reverses around 1200 C; a step-down current induces step bunching. The observations agree with the previous reports [5].
High-Resolution Backscattered Electron Imaging of GaAs/Ga1-xAlxAs Superlattice Structures with a Scanning Electron Microscope
Authors: Franchi S. , Merli P.G. , Migliori A. , Ogura K. , Ono A.
Published: June 2020

It has been shown that using a Scanning Electron Microscope (SEM), equipped with a Field Emission Gun (FEG) and in-lens specimen position (ultrahigh resolution SEM), operating in the backscattered electron (BSE) mode, it is possible to obtain correct characterization of a superlattice with an image contrast related to the atomic number variation (1).

In order to check the performance of a JEOL JSM 890 SEM in the BSE imaging mode, a GaAs/ Ga1-xAlxAs superlattice structure, whose cross section is reported in Fig. 1, has been characterized. On the top there are layers with a fixed value of the mole fraction of Al (x =0.3) and thickness variable between 1 and 20 nm. Below, all the layers are 5 nm thick and the Al mole fraction varies in the range 0.05<x<0.40. Observations at different accelerating voltages show that the image contrast decreases by increasing the electron energy, whereas the resolution is improved. According to our experiments, in these specimen, the best compromise between resolution and contrast is in the energy range 10 - 15 kV. Fig. 2 shows the BSE image, taken at 13 kV, of the top superlattice structure; the GaAs layers appear bright and those of Ga0.7Al0.3As are dark. The resolution obtained on this structure, where the mean atomic number varies by ΔZ=2.7 from layer to layer (corresponding to a contrast C= 4.4% ), is 2 nm. A better evidence of this resolution is given by Fig. 3, which shows a superstructure of 2 nm AlAs / 2nm GaAs, ( ΔZ = 9, C=16%). The image of fig. 4 refers to the superlattice on the bottom of Fig. 1 and allows to specify the minimum detectable ΔZ for a fixed resolution of 5nm. The fringe contrast drops linearly, as well known, with the mean atomic number variation between the layers. As the number of visible fringes is 7, we deduce that the minimum detectable mean atomic number variation is 0.8, (C = 1.3 %).
Development of an Ultra - High - Resolution Low Voltage(LV) SEM with an Optimized “in-lens” Design
Authors: Nagatani Takashi , Sato Mitsugu , OSUMI Masako
Published: June 2020

An “in-lens” type FESEM, Hitachi S-900, developed as an ultra high resolution SEM having 0.7nm resolution at 30kV(Nagatani et al 1986), was modified for better performance at low beam energy(about 5kV or below) with small aberrations of ths objective lens and dual specimen position design. This is in responce to the recent upsurge of interest in using the LVSEM, which enables us hopefully to observe the surface topography of uncoated samples directly with maximum fidelity(Pawley 1987).

The actual visibility of the minute topographical details depends upon not anly the spot size of the scanning beam but also physics of interaction between impinging electrons and solid sample(Joy 1989). However, the resolution can never be better than the spot size. Then, it would seem logical to specify the spot size first when designing a high resolution SEM. As discussed earlier(Crewe 1985; Nagatani et al 1987), the spot size of the beam is mainly limited by spherical aberration of the objective lens and diffraction at high voltage(about 10 kV and above). On the other hand, chromatic aberration and diffraction are the dominant factors at low voltages(about 5kV or below). Source size of a cold field emission is so small that we could neglect it for simplicity.

In general, chromatic aberration can be smaller at higher excitation of a narrow gap objective pole-piece, which also made the working distance short. Therefore, some compromise is necessary among minimized aberrations, required specimen size, stage traverse and tilting angle etc. In practice, tolerable distortion of the image at low magnification and collection efficiency of the secondary electrons are another factors to be considered in designing the instrument. By taking these factors in simulation, an optimized objective lens was designed as shown in Table 1.
Secondary Electron Counting Images in SEM
Authors: Yamada S. , Ito T. , Gouhara K. , Uchikawa Y.
Published: June 2020

The conventional method of image recording in scanning electron microscopy is photographic recording of the images displayed on a monitor screen of CRT installed with the SEM. An increasing number of works related to the development of computerized systems for digital recording and processing of the image data have been reported But a serious problem exists that the digiatal image data are acquired by discretizing the analogue output of the conventional detector system. In actuality, proportionality between the analogue output and the number of detected electrons is not ensured because of various kinds of noises and nonlinearity which are parasitic with the electronic circuitry. As a solution, we proposed a detection system to measure directly the number of signal electrons. In this paper, we describe electron counting for secondary electron detection in SEM, and show that the electron counting can provide a far better image quality than the analogue output.

I. Images by Counting Method and by Analogue Method

The signal obtained by the counting method is the electron number reaching the detector. This means that the method can eliminate the thermal noise and the fluctuation of the amplification which are parasitically generated during amplification of any type of secondary electron detectors including Everhart-Thornley detector and semiconductor detectors. In addition, noises caused by electronic circuits connected to the detector can be reduced. As shown in Fig.1, even when a primary electron current is lowered to the level less than 1 pA, we could obtain clear images by the counting method as compared with those by the analogue method. It is clear that the electron counting possesses remarkable advantages, as the secondary electron signal becomes weak.
Observation of GaAs/AlAs Superlattice Structures in both Secondary and Backscattcred Electron Imaging Modes with an Ultrahigh Resolution Scanning Electron Microscope
Authors: Ogura K. , Ono A. , Franchi S. , Merli P.G. , Migliori A.
Published: June 2020

In the last few years the development of Scanning Electron Microscopes (SEM), equipped with a Field Emission Gun (FEG) and using in-lens specimen position, has allowed a significant improvement of the instrumental resolution . This is a result of the fine and bright probe provided by the FEG and by the reduced aberration coefficients of the strongly excited objective lens. The smaller specimen size required by in-lens instruments (about 1 cm, in comparison to 15 or 20 cm of a conventional SEM) doesn’t represent a serious limitation in the evaluation of semiconductor process techniques, where the demand of high resolution is continuosly increasing. In this field one of the more interesting applications, already described (1), is the observation of superlattice structures.

In this note we report a comparison between secondary electron (SE) and backscattered electron (BSE) images of a GaAs / AlAs superlattice structure, whose cross section is reported in fig. 1. The structure consist of a 3 nm GaAs layer and 10 pairs of 7 nm GaAs / 15 nm AlAs layers grown on GaAs substrate. Fig. 2, 3 and 4 are SE images of this structure made with a JEOL JSM 890 SEM operating at an accelerating voltage of 3, 15 and 25 kV respectively. Fig. 5 is a 25 kV BSE image of the same specimen. It can be noticed that the 3nm layer is always visible and that the 3 kV SE image, in spite of the poorer resolution, shows the same contrast of the BSE image. In the SE mode, an increase of the accelerating voltage produces a contrast inversion. On the contrary, when observed with BSE, the layers of GaAs are always brighter than the AlAs ones , independently of the beam energy.
A metal- coating Chamber for High-Resolution Cryo-SEM
Authors: Sheehan John G.
Published: June 2020

Improvements in particulate coatings for printable paper require understanding mechanisms of colloidal interactions in paper coating suspensions. One way to deduce colloidal interactions is to mage particle spacings and orientations at high resolution with cryo-SEM. Recent improvements in cryo-SEM technique have increased resolution enough to image particles in coating paints,vhich are sometimes smaller than 100 nm. In this report, a metal-coating chamber is described for preparation of colloidal suspensions for cryo-SEM at resolution down to 20 nm. It was found that etching is not necessary to achieve this resolution.

A 120 K cryo-SEM sample will remain in an SEM for hours without noticeable condensation of imorphous ice. This is due to the high vapor pressure of vapor-condensed amorphous ice, measured by Kouchi. However, clean vacuum is required to coat samples with the thinnest possible continuous metal films which are required for high magnification SEM. Vapor contaminants, especially hrydrocarbons, are known to interfere with thin-film nucleation and growth so that more metal is needed to form continuous films, and resolution is decreased. That is why the metal-coating chamber in fig. 1 is designed for the cleanest possible vacuum. Feedthroughs for the manipulator md the shutter, which are operated during metal coating, are sealed with leak-proof stainless-steel Dellows. The transfer rod slides through a baseplate feedthrough that is double o-ring sealed.
Molecular Views of Ice-Embedded Lumbricus Terrestris Erythrocruorin Obtained By Invariant Classification
Authors: schatz Michael , Jäger Joachim , Heel Marin van
Published: June 2020

Lumbricus terrestris erythrocruorin is a giant oxygen-transporting macromolecule in the blood of the common earth worm (worm "hemoglobin"). In our current study, we use specimens (kindly provided by Drs W.E. Royer and W.A. Hendrickson) embedded in vitreous ice (1) to avoid artefacts encountered with the negative stain preparation technigue used in previous studies (2-4).

Although the molecular structure is well preserved in vitreous ice, the low contrast and high noise level in the micrographs represent a serious problem in image interpretation. Moreover, the molecules can exhibit many different orientations relative to the object plane of the microscope in this type of preparation. Existing techniques of analysis requiring alignment of the molecular views relative to one or more reference images often thus yield unsatisfactory results.

We use a new method in which first rotation-, translation- and mirror invariant functions (5) are derived from the large set of input images, which functions are subsequently classified automatically using multivariate statistical techniques (6). The different molecular views in the data set can therewith be found unbiasedly (5). Within each class, all images are aligned relative to that member of the class which contributes least to the classes′ internal variance (6). This reference image is thus the most typical member of the class. Finally the aligned images from each class are averaged resulting in molecular views with enhanced statistical resolution.
Correction of Spherical Aberration using Defocus Modulation Technique
Authors: Taniguchi Yoshifumi , Shimizu Ryuichi , Chaya Michio , Ikuta Takashi
Published: June 2020

In the electron optical system of transmission electron microscopes, there essentially exists a spherical aberration in the objective lens. A novel method to correct the spherical aberration based on the defocus modulation technique by the image integration with bipolar weighting functions have been proposed by one of the authors (T. I.). Because a coherent optical system is assumed in this method, this technique can be extended to the transmission electron microscopy.

This paper presents the experimental confirmation of the usefulness of this method for the electron microscopy by off-line image integration of the series of though-focus images recorded on a video tape.

A thermal field emission type electron microscope (JEM-100CFEG) was used in this experiment. The accelerating voltage was 80 kV and the spherical aberration coefficient of the objective lens was 6.1 mm. The sample was amorphous carbon film of 2 nm thick. Small particles of gold were evaporated onto the film in a Bell-jar. The image filing consists of 125 images as a through-focus series by step of 13.64 nm. Because of the residual asymmetry of the objective pole piece, it was unable to coincide the current center with the voltage center which is true optical axis of the electron microscope. The misalignment of the current center was corrected by shifting the image data itself in a computer after making the image data filing of the through-focus series. The image integration to reconstruct the aberration free images was performed with the corrected image data under appropriate bipolar weighting functions for real and imaginary terms.
Ordered Arrays of Type B Botulinum Toxin On Phospholipid Vesicles
Authors: Schmid F. , DasGupta B. R. , Robinson J. P.
Published: June 2020

Botulinum neurotoxins comprise a family of potent toxins produced by the bacterium Clostridium botulinum. There are seven serologically distinct types of botulinum neurotoxins and they act near the neuromuscular junction, producing a flaccid paralysis. These neurotoxins are synthesized as single polypeptide chains which may be cleaved artificially or by endogenous proteases to more active dichain forms which are covalently held by disulfide linkage. The carboxy terminal 2/3 of the molecule is designated the heavy (H) chain, the rest is referred to as the light (L) chain. The neurotoxins have a molecular weight of approximately 150kD (for general review, Simpson, 1986)

Simpson (1986) has proposed, by analogy to other bacterial toxins and viral infection models that the mode of action of these toxins proceed in three stages: binding to the surface of a cell, internalization and an enzymatic action. These functions can be separated biochemically; for example, the chains bind to the the cell surface and internalize. The enzymatic activity probably involves the L chain. This enzymatic poisoning step in neural cells is not known.
Recent Progress In High-Resolution Shadowing For Biological Transmission Electron Microscopy
Authors: Gross Heinz , Krusche Katarina , Tittmann Peter
Published: June 2020

Freeze-drying followed by heavy metal shadowing is a long established and straight forward approach to routinely study the structure of dehydrated macromolecules. Very thin specimens such as isolated membranes or single macromolecules are directly adsorbed on C-coated grids. After rapid freezing the grids are transferred into a suitable vacuum equipment for freeze-drying and heavy metal shadowing.

To improve the resolution power of shadowing films we introduced shadowing at very low specimen temperature (−250°C). To routinely do that without the danger of contamination we developed in collaboration with Balzers an UHV (p≤10-9 mbar) machine (BAF500K, Fig.2). It should be mentioned here that at −250°C the specimen surface acts as effective cryopump for practically all impinging residual gas molecules from the residual gas atmosphere.

Common high resolution shadowing films (Pt/C, Ta/W) have to be protected from alterations due to air contact by a relatively thick C-backing layer, when transferred via atmospheric conditions into the TEM. Such an additional C-coat contributes disturbingly to the contrast at high resolution.