bluuebunny/crossref_metadata_2025 huggingface dataset:
High-Resolution Bright-Field and Dark-Field Hollow Cone Illumination
Authors: Herring R.A. , Twigg M.E.
Published: June 2020

Hollow cone illumination using a large C2 blocked-aperture (bl apt) in the conventional TEM (CTEM) can remove the beams within the zero-order Laue zone (ZOLZ) thereby making lattice images more simply interpretable. Dark-field (DF) hollow cone illumination has the added advantage of enhancing the Z-contrast within the lattice image, since the electrons contributing to the image must be scattered over a large angle (approximately 10 mrad). Both of these imaging methods have been explored, using a 600 um C2 bl apt and objective aperture sizes of 70, 20 and 10 um, and are reported in this paper.

Much interest has been generated by the report of Pennycook [1] on STEM Z-contrast imaging using annular dark-field. In earlier work ,it was noted that CTEM hollow cone imaging and STEM annular dark-field imaging are related via reciprocity [2] (Fig. 1). In addition, Zernike has shown the advantages of hollow cone illumination in optical phase-contrast microscopy [3]. The electron-optical analogues to these optical techniques are now possible because of the low Cs values achieved in modern TEMs.
Crystal Structure of K6Nb44O113 from HREM
Authors: Li F.H. , Teng C.M. , Hu J.J. , Nagata F. , Tsuruta C.
Published: June 2020

Different results about the crystal structure of K6Nb44O113 (KNO) were obtained by X-ray diffraction analysis[1,2]. This might be due to the small crystal size and the impurity of crystalline powders. Such sample are suitable for HREM investigation. Teng et al. studied the crystal by electron diffraction and HREM[3]. They compared the image of KNO with the structure model of Rb3Nb54O146(RNO) proposed by Gatehouse et al.[4]. The latter’s structure which is formed by Nb-O octahedra belongs to the tetragonal system and contains tunnels of different shapes along the four-fold axis(Fig.1). An image of KNO given by Teng et al. shows four-leaf and three-leaf shaped bright dots whose arrangement is in agreement with that of heptagonal and hexagonal tunnels in the structure of RNO respectively. Although Teng et al. proposed that the crystal structure of KNO might also be formed by Nb-O octahedra and contains various tunnels as RNO, they concluded that the symmetry of KNO should be lower than that of RNO. In this abstract it is reported that the crystal structure of KNO is isomorphic to that of RNO as well as that of CsxNb54(O,F)146[5].
Structural Transformation of a Germanium Σ=13 (510) [001] Tilt Grain Boundary under the Electron Beam
Authors: Rouvière Jean-Luc , Bourret Alain
Published: June 2020

The possible structural transformations during the sample preparations and the sample observations are important issues in electron microscopy. Several publications of High Resolution Electron Microscopy (HREM) have reported that structural transformations and evaporation of the thin parts of a specimen could happen in the microscope. Diffusion and preferential etchings could also occur during the sample preparation.

Here we report a structural transformation of a germanium Σ=13 (510) [001] tilt grain boundary that occurred in a medium-voltage electron microscopy (JEOL 400KV).

Among the different (001) tilt grain boundaries whose atomic structures were entirely determined by High Resolution Electron Microscopy (Σ = 5(310), Σ = 13 (320), Σ = 13 (510), Σ = 65 (1130), Σ = 25 (710) and Σ = 41 (910), the Σ = 13 (510) interface is the most interesting. It exhibits two kinds of structures. One of them, the M-structure, has tetracoordinated covalent bonds and is periodic (fig. 1). The other, the U-structure, is also tetracoordinated but is not strictly periodic (fig. 2). It is composed of a periodically repeated constant part that separates variable cores where some atoms can have several stable positions. The M-structure has a mirror glide symmetry. At Scherzer defocus, its HREM images have characteristic groups of three big white dots that are distributed on alternatively facing right and left arcs (fig. 1). The (001) projection of the U-structure has an apparent mirror symmetry, the portions of good coincidence zones (“perfect crystal structure”) regularly separate the variable cores regions (fig. 2).
The Contribution of Phonon-Scattered Electrons to High-Resolution Electron Micrographs of Crystals
Authors: Kohl H.
Published: June 2020

High-Resolution Electron Microscopy is able to determine structures of crystals and interfaces with a spatial resolution of somewhat less than 2 Å. As the image is strongly dependent on instrumental parameters, notably the defocus and the spherical aberration, the interpretation of micrographs necessitates a comparison with calculated images. Whereas one has often been content with a qualitative comparison of theory with experiment in the past, one is currently striving for quantitative procedures to extract information from the images [1,2]. For the calculations one starts by assuming a static potential, thus neglecting inelastic scattering processes.

We shall confine the discussion to periodic specimens. All electrons, which have only been elastically scattered, are confined to very few directions, the Bragg spots. In-elastically scattered electrons, however, can be found in any direction. Therefore the influence of inelastic processes on the elastically (= Bragg) scattered electrons can be described as an attenuation [3]. For the calculation of high-resolution images this procedure would be correct only if we had an imaging energy filter capable of removing all phonon-scattered electrons. This is not realizable in practice. We are therefore forced to include the contribution of the phonon-scattered electrons.
High-Resolution Image Simulation of a Tilted Crystal
Authors: Hetherington C. J. D.
Published: June 2020

Most high resolution images are not directly interpretable but must be compared with simulations based on model atomic structures and appropriate imaging conditions. Typically, the only parameters that are adjusted, in addition to the structure models, are crystal thickness and microscope defocus. Small tilts of the crystal away from the exact zone axis have only rarely been considered. It is shown here that, in the analysis of an image of a silicon twin intersection, the crystal tilt could be accurately estimated and satisfactorily included in the simulations.

The micrograph shown in figure 1 was taken as part of an HREM study of indentation-induced hexagonal silicon. In this instance, the intersection of two twins on different habit planes has driven the silicon into hexagonal stacking. However, in order to confirm this observation, and in order to investigate other defects in the region, it has been necessary to simulate the image taking into account the very apparent crystal tilt. The inability to orientate the specimen at the exact [110] zone was influenced by i) the buckling of the specimen caused by strains at twin intersections, ii) the absence of Kikuchi lines or a clearly visible Laue circle in the diffraction pattern of the thin specimen and iii) the avoidance of radiation damage (which had marked effects on images taken a few minutes later following attempts to realign the crystal.) The direction of the crystal tilt was estimated by observing which of the {111} planes remained close to edge-on to the beam and hence strongly imaged. Further refinement of the direction and magnitude of the tilt was done by comparing simulated images to experimental images in a through-focal series. The presence of three different orientations of the silicon lattice aided the unambiguous determination of the tilt. The final estimate of a 0.8° tilt in the 200Å thick specimen gives atomic columns a projected width of about 3Å.
Application of a Superconducting Cryo-Electron Microscope to the Physics and Material Science of Ceramics
Authors: Sugiyama Masaaki , Kubo Hiroshi , Fukushima Kurio
Published: June 2020

Superconducting cryo-electron microscope (SCM) has been mainly applied to the biological field, due to the advantages such as reduction of radiation damage and the possibility of a perfectly contamination-free environment. From the material science view point, microstructural characterization at liquid helium temperature is an attractive technique. In this presentation, some topics concerning the low temperature physics of ceramics will be discussed on the basis of the data obtained using high resolution SCM.

The principle of the superconducting lens (SCL) was first described by the Dietrich Group of Siemens AG, West Germany in 1966, following this by fitting a SCL as the objective lens of a 200kV electron microscope, a new type of electron microscope, the JEM-2000SCM, was developed by JEOL LTD, Japan. A detailed cross-sectional diagram of the SCL is shown in Fig.1. A spherical aberration coefficient of 1.2mm was obtained.
Spot Scan Imaging and the Future of High Resolution
Authors: Downing K.H.
Published: June 2020

Electron crystallographers who have been working on determination of protein structure have set a goal of obtaining image information to a resolution of about 3.5 Å, from specimens tilted up to 60 degrees. This information would allow the construction of a three-dimensional density map within which the path of the peptide chain could be followed and locations of side chains defined. The recent determination of an atomic model of the membrane protein bacteriorhodopsin (bR) from EM data (1) which was not as complete as we would like, used a good deal of other biochemical and biophysical data to constrain the model. In cases where this type of information is not as extensive as with bR, isotropic high-resolution data would be required. Significant advances in several different areas have brought us tantalizingly close to reaching our goal, but there are still improvements to be made.

The essential limitations in obtaining high resolution data from proteins arise from the radiation sensitivity of the specimen, which severely limits the electron exposure that can be used in recording an image and thus limits the signal-to-noise ratio (SNR). Increasing both the electron dose, which is possible with cold specimens, and the area processed, which required implementation of significant computer software, have each given about a factor of three improvement in SNR. Still, with conventional imaging, a study by Henderson and Glaeser (2) revealed that the best images contained only a small fraction of the signal that would be present in a perfect image. Factors such as the envelope of the contrast transfer function and the modulation transfer function of the photographic film account for some loss of contrast, but the factor causing the most loss was found to be beam-induced specimen motion. This motion results from the stress which is produced by changes in bond structure during the course of radiation damage.
An Illuminating System of a 100-kV Analytical Electron Microscope with a Field-Emission Electron Gun
Authors: Delong A. , Chmelík J. , Kolařík V.
Published: June 2020

Our aim was to design a microscope for application in both the classical transmission electron microscopy (CTEM) and in the analytical electron microscopy having in the scanning modes (SEM, STEM) a resolving power approaching that in the CTEM. The problem can be optimally solved by using the field emission source of electrons. The illuminating system and the objective lens have the following parameters:

a) The resolving power of the objective lens in the transmission mode is as high as 3.5 Å.

b) The optical aberrations of the pre—field of the objective lens and of the set of condenser lenses allow a resolution of approx. 5 Å to be achieved in the scanning mode.

c) The illuminated area of the specimen observed in the transmission mode is large enough to allow operation with the objective lens switched on at a magnification 1000 x.
Libraries of Locations for Different Specimens: An Application of Remote Specimen-Stage Control on the CM Microscope
Authors: Busing Wim M. , Coppoolse Harald P.
Published: June 2020

A session on the Transmission Electron Microscope normally starts at low magnification with an overview of the specimen to find the region(s) of interest. This region is then centered with the specimen drives and further investigation at higher magnification can start. However, the operator is often in doubt whether the region centered is actually the best, but is also reluctant to move elsewhere for fear of not being able to retrieve the present area. Thus in many cases time and photographic material are wasted on sub-optimal regions of the specimen.

The CM-series transmission electron microscopes have a goniometer stage with mechanical read-out of the position of the specimen on the micrometer drives, thereby making it possible to record specimen locations but only by hand. Optionally, the microscope can be equipped with the Specimen Relocation System which provides a digital read-out of specimen position as well as the capability to store specimen locations for later retrieval. A number of potentially interesting locations can thus be stored and, by recalling each location with the Relocation System's motordrives, these locations can be screened quickly at higher magnifications to select the best one for further work.
Development of the H-7100 Tem and its Computer System
Authors: Kobayashi H. , Tomita M. , Ukiana M. , Mizuno H. , Ueki Y. , Yotsuji T. , Konopka J.F.
Published: June 2020

Built-in TV-systems for TEM image processing and storage are becoming popular in the recent TEM instrumentation. We have completed the development of the H-7100 which has greater expanding capability than the conventional instruments. The H-7100 has been designed around the computer controlled electronics of the H-7000. The new H-7100 electronics is accessible from an external computer including the specimen stage control. When it is coupled with an EDX spectrometer, an automated microanalysis is performed.

Fig.l is a system diagram of the specimen stage. The rotation of the DC motor is converted to linear movement by transmission gears and a linear actuator. The linear motion is used to drive the specimen stage. The stage traverse is detected and regulated by numbers of pulse generated by a rotary encoder which is connected to the DC motor. The smallest traverse step of 1nm is available. The pulse signal of the rotary encoder is processed by a computer together with the working magnification to determine the optimum stage traverse. This design allows operator to perform both the low and high magnification work with maximum convenience and comfort. Further, specimen position memory, automatic tracking of the stage traverse and automatic return to a zero position have been incorporated.
The CM-CRYO: A Microscope Dedicated to Cryo-Electron Microscopy in Life Science Applications
Authors: Busing Wim. M. , de Jong Marc J.C.
Published: June 2020

Low-temperature (cryo) electron microscopy has been established as a promising approach for alleviating technical problems encountered in electron microscopy of life science materials. Cryofixation freezes in the native situation of biological material, with the rapid freezing process preventing redistribution of water-soluble elements in cellular and non-cellular compartments. Thus it becomes possible to correlate tissue morphology with chemical and physical properties.

The use of cryo techniques puts stringent demands on the electron microscope technology: an ultra-high vacuum, including special measures to tackle the water vapour released by the specimen; stable, low-drift cryo-temperature specimen holders; special functions providing low-dose imaging conditions; electron dose indicators; and a TV system for observation under low-level illumination. The new CM-CRYO combines these features with the ease of use of the CM microscope concept and the quality of the TWIN objective lens system.
Vibration Isolator System for Electron Microscope
Authors: Ohi K. , Mizuno M. , Kasai T. , Ohkura Y. , Mizuno K. , Murakami K. , Miyazaki T.
Published: June 2020

In recent years, with electron microscopes coming into wider use, their installation environments do not necessarily give their performance full play. Their environmental conditions include air-conditioners, magnetic fields, and vibrations. We report a jointly developed entirely new vibration isolator which is effective against the vibrations transmitted from the floor.

Conventionally, large-sized vibration isolators which need the digging of a pit have been used. These vibration isolators, however, are large present problems of installation and maintenance because of their large-size.

Thus, we intended to make a vibration isolator which

1) eliminates the need for changing the installation room

2) eliminates the need of maintenance and

3) are compact in size and easily installable.
Oil-Free Forepumps for Electron Microscopes
Authors: Farrant J.L. , Bez E.
Published: June 2020

Even the best present day ultrahigh resolution electron microscopes embody a paradox. They are equipped with the most modern ion pumps, cryopumps or turbomolecular pumps, but the forepumps are oil-sealed rotary pumps invented by Gaede in 1905. Consequently efficient protective systems are necessary to prevent oil-derived vapour from contaminating the specimen, the objective lens aperture diaphragm, the field emission or lanthanum boride electron sources and other sensitive areas. Continuously operable, reciprocating, dry fore-vacuum pumps, based on our designs, have been made and sold by Varian for over three years and have proved reliable in a wide range of equipment. Electron microscopes too, should be provided with oil-free forepumps.

The need for oil-free forepumps occurred to one of us in 1949 when it was shown that pump oil was the major source of the carbonaceous contamination of microscope specimens and objective lens diaphragms. Materials available at that time seemed unsuitable for the construction of oil-free forepumps but during 1968 we learnt that highly wear resistant, low-friction composites of polytetrafluoroethylene (PTFE) filled with finely divided bronze, graphite, etc. were being marketed. In 1970 we began to devise a practical oil-free pump. Rotary designs were rejected because all practicable shaft seals require oil lubrication to transfer heat from the seal to the shaft to prevent the seal material from reaching temperatures at which it would soften and wear rapidly. Each lubricated shaft seal would expose, at least, a narrow annulus of oil to the vacuum in the working chamber and seal wear would lead to substantial leakage of oil.
The Added Value of Graphical Input and Display for Electron Lens Design
Authors: Lencova B. , Wisselink G.
Published: June 2020

Recent progress in computer technology enables the calculation of lens fields and focal properties on commonly available computers such as IBM ATs. If we add to this the use of graphics, we greatly increase the applicability of design programs for electron lenses. Most programs for field computation are based on the finite element method (FEM). They are written in Fortran 77, so that they are easily transferred from PCs to larger machines.

The design process has recently been made significantly more user friendly by adding input programs written in Turbo Pascal, which allows a flexible implementation of computer graphics. The input programs have not only menu driven input and modification of numerical data, but also graphics editing of the data. The input programs create files which are subsequently read by the Fortran programs. From the main menu of our magnetic lens design program, further options are chosen by using function keys or numbers. Some options (lens initialization and setting, fine mesh, current densities, etc.) open other menus where computation parameters can be set or numerical data can be entered with the help of a simple line editor. The "draw lens" option enables graphical editing of the mesh - see fig. I. The geometry of the electron lens is specified in terms of coordinates and indices of a coarse quadrilateral mesh. In this mesh, the fine mesh with smoothly changing step size is calculated by an automeshing procedure. The options shown in fig. 1 allow modification of the number of coarse mesh lines, change of coordinates of mesh points or lines, and specification of lens parts. Interactive and graphical modification of the fine mesh can be called from the fine mesh menu. Finally, the lens computation can be called. Our FEM program allows up to 8000 mesh points on an AT computer. Another menu allows the display of computed results stored in output files and graphical display of axial flux density, flux density in magnetic parts, and the flux lines in magnetic lenses - see fig. 2. A series of several lens excitations with user specified or default magnetization curves can be calculated and displayed in one session.
Aberrations of Accelerating Tube for High-Voltage Electron Microscope
Authors: Ohye Toshimi , Uchikawa Yoshiki , Morita Chiaki , Shimoyama Hiroshi
Published: June 2020

The accelerating tube (AT) which accelerates electrons up to a desired energy also functions as an electrostatic lens, In the present paper, numerical calculations were conducted on the electron optical characteristics including the spherical aberration of the AT for the high voltage electron microscope. Several electron optical problems arising from a combination of the AT with a thermionic electron gun (TEG) or a field emission gun (FEG) were studied.

 The AT consists of 34 electrodes with the inner diameter of 3.3 cm and has the overall length of 142.3 cm (Fig.l). The voltage Va is applied between the cathode and the final electrode of the AT. The initial energy of the electron incident to the AT is eVo, where Vo is the anode voltage of the electron gun mounted on the AT. The electric field inside the AT was calculated using the surface charge method. The ray tracing was carried out on the basis of the relativistic paraxial ray equation, and the cardinal elements of the AT lens were obtained.
High-Brightness Gaseous Field ION Source for Light ION Species
Authors: Siegel Benjamin. M. , Mioduszewski John
Published: June 2020

We have reported on the very high brightness gaseous field ion source that has been developed at Cornell to produce high angular current density H2+ ion beams with low energy widths. Axially oriented H2+ ion beams from single emission sites with angular currents dl/dΩ= 10-20 μa/sr are obtained routinely. The energy width (FWHM) has been measured to be Δe=1.0 ev. H2+ beams with angular currents as high as 70 μa/sr. have been observed, but these higher current beams have a tail spread on their energy distribution curve.We have now extented this source to produce ion species of He+ with angular current densities, dl/dΩ, in the 10-15 μa/sr range and ions beams of Ne+, A+, N2+ and O+ ions with angular currents dl/dΩ of 3-7 μa/sr.

Ion beams with these characteristics have have been achieved by operating the gaseous field ion source under the following conditions:

1. In an ultrahigh vacuum system at cryogenic temperatures cooled with LHe and heated to obtain an optimum balance of gas concentration at the emitter tip with physisorption on the tip at temperatures that allow good surface transport from a large area near the apex of the tip to the emission site.
Three-Dimensional Structure of Rotavirus-Fab Complex
Authors: Prasad B.V.V. , Marietta E. , Burns J.W. , Estes M.K. , Chiu W.
Published: June 2020

Rotaviruses are spherical, double-shelled particles. They have been identified as a major cause of infantile gastroenteritis worldwide. In our earlier studies we determined the three-dimensional structures of double-and single-shelled simian rotavirus embedded in vitreous ice using electron cryomicroscopy and image processing techniques to a resolution of 40Å. A distinctive feature of the rotavirus structure is the presence of 132 large channels spanning across both the shells at all 5- and 6-coordinated positions of a T=13ℓ icosahedral lattice. The outer shell has 60 spikes emanating from its relatively smooth surface. The inner shell, in contrast, exhibits a bristly surface made of 260 morphological units at all local and strict 3-fold axes (Fig.l).

The outer shell of rotavirus is made up of two proteins, VP4 and VP7. VP7, a glycoprotein and a neutralization antigen, is the major component. VP4 has been implicated in several important functions such as cell penetration, hemagglutination, neutralization and virulence. From our earlier studies we had proposed that the spikes correspond to VP4 and the rest of the surface is composed of VP7. Our recent structural studies, using the same techniques, with monoclonal antibodies specific to VP4 have established that surface spikes are made up of VP4.
Electron Microscopic Comparison of Frozen-Hydrated with Negatively Stained and Rotary-Shadowed Creatine Kinase Single Molecules
Authors: Winkler H. , Schnyder T. , Lücken U.
Published: June 2020

The mitochondrial isoform of creatine kinase isolated from chicken cardiac muscle consists predominantly of an octameric protein species with an Mrof 364000 and a small fraction of a dimeric species (Mr=86000). Electron micrographs of negatively stained creatine kinase show the square-shaped octameric molecules (Fig. 3) and the banana-shaped dimers. Mass measurements of individual molecules by scanning transmission electron microscopy yield about 340 kDa for the octamer, and 89 kDa for the dimer. After freeze-drying and high-resolution shadowing the surface of the octameric molecules shows a distinct cross-like division into four units (Fig. 4). The image analysis with circular harmonic averaging reveals a pronounced four-fold symmetry of both the rotary-shadowed and negatively stained octamers.

Unstained creatine kinase molecules are investigated with cryo-electron microscopy. The samples were diluted with buffer solution to about 1 mg/ml. Drops of the suspension were applied to glow-discharged holey carbon films, blotted to remove excess liquid, immediately plunged into partially solidified liquid ethane, and stored under liquid nitrogen until insertion into the microscope. The specimens were examined in the DEEKO 250 electron microscope, operated at 100 kV. Micrographs were recorded by minimum-dose methods at a magnification of 60000 and an underfocus of about 1000 nm (Fig. 1).
Imaging with the Tunneling and Force Microscopes
Authors: Quate C. F.
Published: June 2020

THE SCANNING TUNNELING MICROSCOPE

The STM is an instrument that is used for measuring surface structure. The new instrument was introduced when Rohrer, together with Binnig, discovered that a single atom at the end of a sharp tungsten needle could probe the electronic structure of smooth conducting surfaces. Their atomic probe was placed in close proximity to the surface and mechanically scanned over the image. The resolution is sufficient to define the spatial positions of the atomic sites with extraordinary precision. This instrument is ideal for characterizing small structures.

The instrument operates over a wide range of temperatures - from liquid helium at 4K to room temperature and beyond. It works in a variety of atmospheres; vacuum, gases and liquids. Piezoelectric scanners are used to move the probe over the surface with the precision necessary to determine the atomic positions. The most favored scanner consists of a single piezotube with electrodes configured to provide motion in three dimensions.

The scanning tip is the STM component, more than any other, that determines the resolving power. The tip is usually formed with electrochemical etching similar to that used in making tips for the field emission microscopes. However, more elaborate systems can be used. Fink has shown that it is feasible to fabricate, in a controlled way, a tip that consists of a single atom. He uses single crystal (111) tungsten and evaporates ions from the tip with a combination of heat and high field. This procedure reduces the apex of the tungsten rod to a single atom.
High-Resolution UHV Electron Microscopy of Reconstructed and Adsorbed Surfaces
Authors: Takayanagi Kunio
Published: June 2020

High-resolution electron microscopy (HREM) has been applied for structure analyses of reconstructed and adsorbed surfaces at atomic resolution in transmission (TEM) and reflection (REM) mode by using an UHV electron microscope (modified 2000 FXV). In the last ICEM conference, we reported instrumental design of the new UHV electron microscopet[1] with a review on atomic structure study by UHV -EM[2]. In this review we show dynamic structural studies of surfaces which have been revealed by using a TV camera-and-video recording system. Details of each topic shown here are given in original papers[3-8].

The UHV electron microscope of 200 keV has the theoretical point-to-point resolution of 0.21 nm. The microscope has two exchange system for evaporators and a gas-inlet system. Surface structural changes recorded on a video tape are resolved at time resolution of 1/30 sec. Figures shown are reproduced from the video frames.

High-Resolution REM

In REM mode, we obtain lattice fringes of the surface superlattices by interference of reflections so that the position of the fringes vary with the excitation condition similarly to lattice fringes in TEM. In a certain reflection condition the lattice fringes can be regarded as the structure image. In case of Si(111)7×7 surface, positions of dark lattice fringes (0.23 nm spacing) of the 7×7 coincide almost with the steps[9,10].
Scanning Low-Energy Electron Diffraction Microscopy Combined with Scanning Tunnling Microscopy
Authors: Ichinokawa Takeo
Published: June 2020

A ultra-high vacuum scanning electron microscope (UHV-SEM) with a field emission gun (FEG) has been operated in an energy range of from 100 eV to 3 keV. A new technique of scanning low energy electron diffraction (LEED) microscopy has been added to the other techniques: scanning Auger microscopy (SAM), secondary electron microscopy, electron energy loss microscopy and the others available for the UHV-SEM. In addition to scanning LEED microscopy, a scanning tunneling microscope (STM) has been installed in the UHV-SEM-.The combination of STM with SEM covers a wide magnification range from 105 to 107 and is very effective for observation of surface structures with a high resolution of about 1 Å.

A UHV-FEG-SEM is equipped in a chamber in which the vacuum is better than 2×10-10 Torr. A movable cylindrical mirror analyzer (CMA), a two dimensional detector of diffracted LEED beams, an ion gun and a deposition source are installed in this chamber. The concept of the scanning LEED microscope is comprised of two steps: (1) the formation of a selected area LEED pattern and (2) the generation of raster images with information contained in the diffraction pattern. In the present experiment, the LEED detector assembly shown in Fig.l has been used; it consists of two hemisherical grids, a two-stage channel-plate amplifier and a position-sensitive detector. The selection of one (or more) diffracted beam is performed electronically by a window using the two-dimensional analogue comparators. The intensity of a particular beam selected by the window modulates the brightness of the scanning image and a dark field image sensitive to the surface structure is formed. The experimental spatial resolutions of 150 Å and 500 Å have been attained at the primary electron energy 1 keV and 250 eV, respectively.
High-Speed Reflection Electron Microscopy of Laser-Induced Surface Transitions
Authors: Heinricht F.
Published: June 2020

Micropatterning of bulk material by pulsed laser radiation is a promising technique for many applications, e.g. drilling and data storage. Due to the fact that laser radiation can be applied very localized, high power densities in a small volume of the treated specimen can be realized. As a result of rapid heat-up and cool-down processes, unusual phases and microstructures can be generated.

Time-resolving methods, especially imaging with short exposures times are quite useful in order to understand the physics standing behind. As a diagnostic tool electrons are superior to other probes, e.g. light optics, due to their sensitivity to topography, material composition and structure. Unfortunately , the SEM - one of the most common microscopes for surface analysis - cannot be used for investigations in the the nanoseconds time domain due to its far to slow scan time. On the other hand, the reflection electron microscope (REM) is one of the very few instruments, which is capable to image all points of the treated surface simultanously.

In order to achieve electron optical images of laser pulse induced processes on surfaces with exposures times of a few nanoseconds, a high-speed REM was developed. This new instrument is based on a conventional TEM, additionally equipped with the following units:

- a laser pulsed thermal electron gun, which delivers high-brightness electron pulses with duration of 20ns.
Applications of Scanning Tunneling Microscopy in the Materials Characterization Laboratory
Authors: Liu J.B , Clark Boyd , Fisher R.M.
Published: June 2020

Scanning tunneling microscopy, first developed by G.Binnig, H.Rohrer, Ch.Gerber, and E.Weibel [1] in 1982 as a method of directly observing atom sites at the surface of graphite and other crystalline materials, is now being used in an ever increasing variety of applications as a result of steady and rapid advances in instrumentation, interpretation, and specimen handling techniques [2]. As a result the STM is widely recognized as a powerful method of observing surface structure on an atomic scale and is fast becoming an accessory tool in materials characterization laboratories that are devoted to solving industrial problems. Some examples representative materials characterization studies are described in mis paper.

The first STM studies employed its high resolution capabilities for fundamental studies of the topography of atoms at surfaces [2]. More recently the value of the STM to observe both surface topography and electronic structure has been utilized. Figure 1 is a STM image of a charge density wave (CDW) from a TaS3 sample at 143K[3]. In this work the advantage of STM, due to sensitivity to both surface topography and electron structure, is apparent.

The development of long scan STMs with scan capabilities of several micrometers or more has opened up a whole new class of materials where the magnifications required are comparable to that of a conventional SEM. The 3-dimensional structure of a processed optical recording disk, as revealed by the STM, is illustrated in Figure 2. The ability of the STM to observe both the course and ultrafine structure of such a sample makes it a powerful tool for relating processing conditions to surface structure defects and hence to the quality and reliability of the optical storage disk itself.
Secondary Electron Imaging of Crystal Surface Steps
Authors: Liu J. , Crazier P. A. , Cowley J. M.
Published: June 2020

High resolution secondary electron (SE) images can be obtained in a scanning transmission electron microscope (STEM) by collecting the type I secondary electrons generated directly by the incident electron beam. The high resolution SE signal is, in general, localized to about 1 nm in the generation process. The escape depth of the secondary electrons, however, varies from about 1 nm for most metals to about 10 nm for some insulating materials. Surface steps can be imaged by collecting high resolution secondary electrons Among other possible contrast mechanisms for SE imaging of surface steps, topographic contrast plays an important role. The topographic contrast of surface steps depends on: (1) the incident electron probe size; (2) step height to SE escape depth ratio; (3) localization of the generated SE signals and (4) the incident beam angle relative to the specimen surface.

In our UHV STEM (MIDAS) instrument, both the entrance and exit surfaces of the sample can be imaged by collecting secondary electrons. For thin samples, the resolution is < lnm for SE images of entrance and exit surfaces but for thicker samples the resolution of the SE image obtained from the exit surface will be degraded by the beam broadening effects. For studying steps on thick or bulk crystal surfaces, secondary electrons emitted from the entrance surfaces are, in general, collected to form images with high contrast and high resolution. In this report, all the SE images are obtained, in MIDAS, by collecting secondary electrons emitted from the entrance surfaces of the samples. Figure 1 is a SE image of a MgO smoke crystal revealing the surface growth steps with high contrast. The parallel straight steps, along <100> directions, constitute the edges of unfinished atomic planes on the MgO {100} crystal surfaces. This image indicates that the {100} surfaces of MgO smoke crystals are flat surfaces. Figure 2 shows a SE image of a MoO3 crystal with surface growth steps spiraling from an end-on screw dislocation (the black dots in the SE image represent electron beam induced reduction products). The dark lines (indicated by D) represent up-steps and the bright lines (indicated by B) represent down-steps. It is interesting to note that the two-dimensional crystal growth around the dislocation is anisotropic, forming terraces with long edges parallel to [010] direction.
Variations in Secondary Electron Emission from MgO Characterized by Secondary Electron Spectroscopy
Authors: Liu J. , Crozier P. A. , Hembree G. G. , Luo F. C. H. , Cowley J. M. , Venables J. A.
Published: June 2020

The recent developments of the in-lens field emission scanning electron microscopes make it possible to image specimen surfaces with subnanometer resolution by collecting high resolution type I secondary electron (SE) signals. SE images with a resolutiori better than 1 nm have also been obtained in scanning transmission electron microscope (STEM) instruments. A problem related to the correct interpretation of these high resolution images is the lack of knowledge on the energies of the collected electrons contributing to the images. On the other hand secondary electron spectroscopy (SES) on clean surfaces has been developed for several years and biased SE imaging of several deposits on metallic and semiconductor crystal surfaces has been demonstrated. The combination of ultra-high resolution SE imaging with SES and Auger electron spectroscopy (AES) can be realized in pur UHV STEM instrument (MIDAS). The description of the performance of the MIDAS is reported elsewhere. We report here some recent results on SE imaging of MgO smoke crystals, in the MIDAS, with energy analysis of the collected secondary electrons.

Strong variations of SE signals from different MgO crystals have been observed and the intensity of the collected secondary electrons from some MgO cubes increases under electron beam irradiation. Figure 1 shows a SE image of several MgO cubes, revealing that some of the crystals (indicated by A) have much higher intensity than others (indicated by B) and bright diffuse patches on the dark crystal can be seen (indicated by D). We have used SES to study the variations in SE emission under electron irradiation. The fact that the velocity distribution of the emitted secondary electrons may depend strongly on the surface morphology of the samples studied makes the interpretation of these SE spectra complicated. In order to avoid this problem and other possible complications arising from the detector geometry we acquired SE spectra from a fixed flat area of a single crystal MgO shown in figure 2. The sample was biased at -30 V and the resolution of the SE spectrum is about 1 eV. Figure 3a shows the SE spectra, taken from the exit surface of the crystal. Spectrum 1 was obtained from a poorly emitting MgO cube as that shown in figure 2 (all the spectra were obtained from the circled area). Spectra 2, 3 and 4 were obtained after about 10, 20 and 40 minutes electron irradiation respectively. In order to study spectral shape variations the spectra were normalized so that they all had the same peak intensity. The normalized data were shown in figure 3b.
Experiments on REM and SREM using a Tem/Stem Microscope with a Configurable Angle-Resolving Detector
Authors: Banzhof H. , Daberkow I.
Published: June 2020

A Philips EM 420 electron microscope equipped with a field emission gun and an external STEM unit was used to compare images of single crystal surfaces taken by conventional reflection electron microscopy (REM) and scanning reflection electron microscopy (SREM). In addition an angle-resolving detector system developed by Daberkow and Herrmann was used to record SREM images with the detector shape adjusted to different details of the convergent beam reflection high energy electron diffraction (CBRHEED) pattern.

Platinum single crystal spheres with smooth facets, prepared by melting a thin Pt wire in an oxyhydrogen flame, served as objects. Fig. 1 gives a conventional REM image of a (111)Pt single crystal surface, while Fig. 2 shows a SREM record of the same area. Both images were taken with the (555) reflection near the azimuth. A comparison shows that the contrast effects of atomic steps are similar for both techniques, although the depth of focus of the SREM image is reduced as a result of the large illuminating aperture. But differences are observed at the lengthened images of small depressions and protrusions formed by atomic steps, which give a symmetrical contrast profile in the REM image, while an asymmetric black-white contrast is observed in the SREM micrograph. Furthermore the irregular structures which may be seen in the middle of Fig. 2 are not visible in the REM image, although it was taken after the SREM record.
HREM Observations of Deformation Recovery on and Near Surfaces of Eu2O3
Authors: Ning X.G. , Ye H.Q.
Published: June 2020

Profile imaging technigue has been achieved very much in the field of surface science since it was first proposed. This work will show the deformation recovery on and near the surfaces of Eu2O3 under electron irradiation. The experiment was carried out in a JEOL-200CX high-resolution electron microscope. The Eu2O3 phase has a complex cubic structure with a=1.087 nm. A projected unit cell has been marked in Fig. la. It has been indicated that only Eu3+ ions , which are located in f.c.c. sublattice, appeared in HR images under certain defocus and in the thin areas of specimen. The structural character of Eu2O3 shown by HR images may be analyzed based upon comparing with that of simple f.c.c. structure.

It can be seen from Fig. la that the surfaces of Eu2O3 are clean and Eu3+ ions on the (111) surfaces S1 and S2 moved /12 towards to the right (it is actually surface stacking fault). In Fig.lb the stacking fault on S2 was removed under electron irradiation but remained on S1. The stacking fault energy of Eu2O3 is high in the bulk. From Fig.l it can be known that the stacking fault energy may become lower on the (111) surface due to less constrained factors there. This kind of surface stacking fault is related to surface partial dislocations, and both of them may act as the main forms of surface deformation under electron irradiation.
LVSEM: Past Present and Future
Authors: Pawley James B.
Published: June 2020

Past: In 1960 Thornley published the first description of SEM studies carried out at low beam voltage (LVSEM, 1-5 kV). The aim was to reduce charging on insulators but increased contrast and difficulties with low beam current and frozen biological specimens were also noted. These disadvantages prevented widespread use of LVSEM except by a few enthusiasts such as Boyde. An exception was its use in connection with studies in which biological specimens were dissected in the SEM as this process destroyed the conducting films and produced charging unless LVSEM was used.

In the 1980’s field emission (FE) SEM’s came into more common use. The high brightness and smaller energy spread characteristic of the FE-SEM’s greatly reduced the practical resolution penalty associated with LVSEM and the number of investigators taking advantage of the technique rapidly expanded; led by those studying semiconductors. In semiconductor research, the SEM is used to measure the line-width of the deposited metal conductors and of the features of the photo-resist used to form them. In addition, the SEM is used to measure the surface potentials of operating circuits with sub-micrometer resolution and on pico-second time scales. Because high beam voltages destroy semiconductors by injecting fixed charges into silicon oxide insulators, these studies must be performed using LVSEM where the beam does not penetrate so far.
Real Color Cathodoluminescence (CL) in the SEM: Physics, Color Display and Applications
Authors: Saparin G.V. , Obyden S.K.
Published: June 2020

This paper is concerned with a novel technique of investigating the CL of solids in SEM by means of spectral topographical analysis (use of real color contrast determined by the local CL spectrum).

The present-day black-and-white visualizing systems allow images with the number of brightness gradations more than 100. The observer is capable of distinguishing no more than 16 levels of monochrome color (grey levels) at a time. The situation differs when color contrast is used. In the color image, the elements of the same brightness can be discriminated by color contrast. Generally, color image elements can be discriminated both by brightness contrast and by color contrast. For example, only three primary colors (red, green and blue) are employed in commercial television, and the total number of hues approaches 16. If white is used as the reference color, the number of hues amounts to 12000, of which only one third can be displayed by the standard color monitor. The knowledge of color discrimination thresholds allows one to determine the number of colors discernable by eye, this number being about 1300. Thus, color contrast in SEM increases the information content of the image by about two orders, as compared with its black-and-white counterpart. This method of information representation does not practically allow any loss of information in forming the CL image in the visible region. SEM allows the formation of the image in real colors determined by the local CL spectra of the object. The color of the point is determined by the total power of all the detected spectral bands and lines. Thus, the color CL image represents spectral topographical information about the object surface. The signal forming this image for one color channel can be presented as.
Approaches to Quantitative Electron Detection in the Scanning Electron Microscope for Topographic Studies
Authors: Hejna Jan
Published: June 2020

An electron signal in the scanning electron microscope (SEM) usually consists of contributions caused by different contrast mechanisms. The most common in practice are material and topographic contrasts. Quantification of material contrast is rather a simple matter. A backscattered electron detector placed over a specimen gives mainly material contrast which can be quantified by the use of a multichannel analyser like in the energy-dispersive x-ray spectrometry.In case of topographic contrast two problems arise. One of them is dimensional metrology, especially linewidth measurements in microelectronics, the second is reconstruction of a surface relief. The first problem needs detection conditions at which the results of SEM measurements correspond exactly with real dimensions, the second needs a signal which is related with a known formula to a local surface inclination and a procedure for converting the signal into the surface relief.

Experiments in the SEM and Monte-Carlo calculations have shown that results of dimensional measurements depend on an energy of a primary beam, on a type of detected electrons (secondary electrons (SE) or backscattered electrons (BSE)) and on a type of a detector.The use of low primary beam voltages and BSE is advisable, The problem of a poor efficiency of BSE detectors at low primary beam voltages can be overcome by accelerating BSE, after they have passed through a grid rejecting SE, by high voltage applied to a scintillator in a BSE detector.