bluuebunny/crossref_metadata_2025 huggingface dataset:
Study of Tip-Surface Interactions in Scanning Tunneling Microscopy (STM) by Reflection Electron Microscopy (REM)
Authors: Lo W. , Spence J.C.H. , Kuwabara M.
Published: June 2020

Work on the integration of STM with REM has demonstrated the usefulness of this combination. The STM has been designed to replace the side entry holder of a commercial Philips 400T TEM. It allows simultaneous REM imaging of the tip/sample region of the STM (see fig. 1). The REM technique offers nigh sensitivity to strain (<10−4) through diffraction contrast and high resolution (<lnm) along the unforeshortened direction. It is an ideal technique to use for studying tip/surface interactions in STM.

The elastic strain associated with tunnelling was first imaged on cleaved, highly doped (S doped, 5 × 1018cm-3) InP(110). The tip and surface damage observed provided strong evidence that the strain was caused by tip/surface contact, most likely through an insulating adsorbate layer. This is consistent with the picture that tunnelling in air, liquid or ordinary vacuum (such as in a TEM) occurs through a layer of contamination. The tip, under servo control, must compress the insulating contamination layer in order to get close enough to the sample to tunnel. The contaminant thereby transmits the stress to the sample. Elastic strain while tunnelling from graphite has been detected by others, but never directly imaged before. Recent results using the STM/REM combination has yielded the first direct evidence of strain while tunnelling from graphite. Figure 2 shows a graphite surface elastically strained by the STM tip while tunnelling (It=3nA, Vtip=−20mV). Video images of other graphite surfaces show a reversible strain feature following the tip as it is scanned. The elastic strain field is sometimes seen to extend hundreds of nanometers from the tip. Also commonly observed while tunnelling from graphite is an increase in the RHEED intensity of the scanned region (see fig.3). Debris is seen on the tip and along the left edges of the brightened scan region of figure 4, suggesting that tip abrasion of the surface has occurred. High resolution TEM images of other tips show what appear to be attached graphite flakes. The removal of contamination, possibly along with the top few layers of graphite, seems a likely explanation for the observed increase in RHEED reflectivity. These results are not inconsistent with the “sliding planes” model of tunnelling on graphite“. Here, it was proposed that the force due to the tunnelling probe acts over a large area, causing shear of the graphite planes when the tip is scanned. The tunneling current is then modulated as the planes of graphite slide in and out of registry. The possiblity of true vacuum tunnelling from the cleaned graphite surface has not been ruled out. STM work function measurements are needed to test this.
Characterization of Surface Resonance Conditions for Surface Imaging
Authors: Yao Nan , Cowley John M.
Published: June 2020

In order to increase intensity and contrast in the image of a surface, the surface resonance conditions have been widely used to enhance the Bragg reflection for image formation in REM (Reflection Electron Microscopy). However, detailed studies of how the resonance conditions relate to the imaging contrast have not been reported. This paper will concentrate on the general properties of the different resonance conditions, as well as the resulting image contrast.

Figure 1 shows a series of RHEED (Reflection High Energy Electron Diffraction) patterns and REM images from the same region of a Pt(l11) surface with the incident electron beam in a direction close to the [112] zone axis at 200 KeV, with a glancing incident angle of about 24 mrad which corresponds to the (555) Bragg reflection condition inside the crystal. For the purpose of convenience in discussion, the four different diffraction conditions shown in figures l(al)-(dl) have been named as D1-D4. With Dl, the specular reflected spot falls in an intersection of a parallel Kikuchi line with a parabola; with D2, the specular reflected spot coincides with an intersection of the Kikuchi lines running parallel to and inclined to the crystal surface; with D3, the specular reflected spot crosses only the parallel Kikuchi line; and with D4, the specular reflected spot intersects only with a parabola. It was found that the diffraction conditions Dl and D2 can not be considered as identical, although the specular reflected spots for both cases are commonly regarded as (555) Bragg reflection in the RHEED pattern. Detailed inspection indicates that for Dl, both the Bragg reflection and the electron surface channelling wave are excited, and for D2, the excitement of simultaneous Bragg reflection occurs closely associated with the properties of three-dimensional dynamical diffraction for a bulk crystal.
Surface Structure Study by High Resolution Electron Holography: Contrast Simulation
Authors: Tanji Takayoshi , Yada Keiji
Published: June 2020

The potential advantage of an electron holography in researching the atomic structure at crystal surfaces with high spatial resolution has been reveald by using the computer simulation for the 7×7 super structure rearranged on a Si(111) clean surface. In order to realize the holography of the surface, problems still remain unsolved in addition to instrumentation of a high resolutional TEM equipped with a highly coherent electron source and a high vacuum specimen chamber. The most essential one among such problems is the determination of imaging conditions necessary for restoring the image blured by the aberration of an objective lens. Especially, the amount of out-of-focus is difficult to know directly from the hologram recorded as the interference pattern of the specimen transmitted wave with the reference wave passing in a vacuum area.

Restricting to the case of a weak phase object, Franke et al. suggested the possibility of restoring the image without the knowledge of focussing condition. Electron scattering at a surface is very weak and may be considered approximately kinematical. Therefore the applicability of the Franke's method to surface structures of Si(lll) thin films was examined. As the atomic positions of the 7×7 structure, DAS model was adopted, and the electron diffraction was treated dynamically with the multi-slice method. Reconstructing a wave front from a hologram, we obtain the wave function in the reciprocal space as,
The Possibilities for Analytical Methods in Photoemission and Low-Energy Electron Microscopy
Authors: Bauer Ernst
Published: June 2020

One of the major shortcomings of conventional PEEM and of LEEM is the lack of chemical information about the surface. Although the imaging of the LEED pattern in the back focal plane of the objective lens of a LEEM instrument allows chemical characterization via the crystalline structure derived from the LEED pattern, this method fails in the absence of a characteristic LEED pattern. Direct information about the atomic composition of the surface is then needed which can be best obtained from inner shell electrons either directly by x-ray-induced photoemission (XPEEM) or by x-ray- or electron-induced Auger electron emission (AEEM). These modes of excitation and imaging can be combined with conventional PEEM and LEEM in one instrument which is presently being developed. Thus a complete structural and chemical characterization becomes possible in one instrument, with parallel detection and high resolution.

In contrast to LEEM, in which up to more than 50% of the incident intensity is available for image formation, the intensity of the emitted electrons is much lower in XPEEM and AEEM and the signal is much lower than the background in AEEM. Therefore, intensity I and resolution d have to be optimized simultaneously which is best done by maximizing Q = I/d2 with respect to maximum emission angle α and relative energy distribution ε = ΔVo/V accepted by the instrument. For a well-designed magnetic lens section of the cathode lens its aberrations are determined by the accelerating field F in front of the specimen. For a homogeneous accelerating field F and a cosine emission distribution one obtains for the optimum α and ε values αo,εo a radius of the minimum disc of confusion of
Low-Energy Electron Microscope of Novel Design
Authors: Liebl Helmut , Senftinger Berthold
Published: June 2020

The pioneering work of Bauer and Telieps stimulated us to construct a low-energy electron microscope intended mainly for imaging solid surfaces with reflected and diffracted electrons in the 10 to 100 eV range, as well as with photoelectrons. Several novel design features were incorporated.

Figure 1 shows the layout of the instrument. The primary-beam column consists essentially of the electron gun, the primary-beam lens, the energy-focusing deflector and the magnet. al lenses are electrostatic. The electron gun comprises the cathode and two acceleration electrodes, the first of which is shaped semi-spherical about the cathode tip and is connected to a variable voltage supply, and the second is the tubular vacuum housing. This constitutes an immersion lens with variable focal length. The cathode is operated in the diode mode. Its virtual diameter is assumed to be dv = dtip √2.7 kT/eVa because in thermionic emission the energy distribution drops to half the peak value at 2.7 kT. The final acceleration voltage is Va = 15 KV. The variable immersion lens together with the primary-beam lens provides a magnification range of about 1 to about 70 without a crossover from the cathode to the backfocal plane of the emission lens. For example, a pointed W cathode with a tip diameter of 1μm imaged with 15× magnification yields a lμm diameter image.
Scanning vs Direct Imaging Emission Microscopy
Authors: Veneklasen Lee H.
Published: June 2020

With the addition of an imaging energy analyzer to a low energy emission microscope (LEKM) (1), it becomes possible to use inelastic scattering (secondaries, Auger and x-ray emissions) to form high resolution images. One can then obtain complimentary diffraction, structural, topological (2) and chemical information in the same instrumental environment. The favorable noise/bandwidth associated with the parallel imaging of many pixels may allow dynamic surface processes to be observed. The goal of this paper is to compare hypothetical scanning (SEM/SAM) with direct imaging (SPEC-LEEM) instruments in terms of resolution and signal/noise ratio vs integration time (visibility). By comparison, one may extrapolate experience with the more common scanning instrument (3), in order to predict the advantages and disadvantages of the newer analytic imaging technology.

The complete analysis will be published in “Ultramicroscopy”.Briefly, the signal to noise ratio within an image element is expressed in terms of incident flux density, net collection efficiency, integration time and quantum yields for spectral lines upon a diffuse background. While ultimate resolution is determined by lens aberrations, practical resolution is defined by a minimum tolerable signal/noise criteria. Aperture angles, energy window, lens field strength, and electron gun configuration are considered (within technical limits) to be free variables that can be optimized for a given resolution requirement, emission spectrum, and surface standoff field strength. The optimization techniques are developed in a form applicable to both instruments, and comparative predictions are made for a specific numerical example.
Comparison of Beam Damage of Hydrated Biological Specimens in High-Pressure Scanning Electron Microscopy and Low-Temperature Scanning Electron Microscopy
Authors: Farley A.N. , Beckett A. , Shah J.S.
Published: June 2020

High Pressure Scanning Electron Microscopy (HPSEM) is a technique in which biological materials are viewed close to their natural state in a saturated water vapour environment and at ambient temperatures. The absence of chemical or cryogenic fixation in this technique can offer considerable advantages in the reduction of preparative artifacts in labile specimens but it is also necessary to consider the effects of the electron beam interaction with the specimen. A comparative study has been undertaken with low temperature scanning electron microscopy (LTSEM) to evaluate the relative damage rates in the labile specimen Narcissus sp. . The results are compared with those expected from theoretical models of the beam-specimen interaction developed by other workers. Full details of the theory and practice of HPSEM have been presented elsewhere.

Fresh, untreated perianth segments of Narcissus sp. were excised and examined in HPSEM at a saturated water vapour pressure of 1716 Pa, with a beam voltage of 10 kV and beam current of approximately 100 pA. The beam dose rate was therefore approximately 15 MJ.Kg−1s−1 over the scanned area. Fully frozen hydrated specimens were prepared for LTSEM and examined in an uncoated condition at a beam voltage of 3kV to reduce charging artifacts. No metal films were applied to the LTSEM specimens since this would artificially increase the thermal conductivity of the surface.
Monte Carlo Modelling of Secondary Electron Yield from Rough Surfaces
Authors: Russ John C.
Published: June 2020

Monte-Carlo programs are well recognized for their ability to model electron beam interactions with samples, and to incorporate boundary conditions such as compositional or surface variations which are difficult to handle analytically. This success has been especially powerful for modelling X-ray emission and the backscattering of high energy electrons. Secondary electron emission has proven to be somewhat more difficult, since the diffusion of the generated secondaries to the surface is strongly geometry dependent, and requires analytical calculations as well as material parameters. Modelling of secondary electron yield within a Monte-Carlo framework has been done using multiple scattering programs, but is not readily adapted to the moderately complex geometries associated with samples such as microelectronic devices, etc.

This paper reports results using a different approach in which simplifying assumptions are made to permit direct and easy estimation of the secondary electron signal from samples of arbitrary complexity. The single-scattering program which performs the basic Monte-Carlo simulation (and is also used for backscattered electron and EBIC simulation) allows multiple regions to be defined within the sample, each with boundaries formed by a polygon of any number of sides. Each region may be given any elemental composition in atomic percent. In addition to the regions comprising the primary structure of the sample, a series of thin regions are defined along the surface(s) in which the total energy loss of the primary electrons is summed. This energy loss is assumed to be proportional to the generated secondary electron signal which would be emitted from the sample. The only adjustable variable is the thickness of the region, which plays the same role as the mean free path of the secondary electrons in an analytical calculation. This is treated as an empirical factor, similar in many respects to the λ and ε parameters in the Joy model.
Analytical Self-Consistent Theory of Three Dimensional Image Reconstruction from Projections
Authors: Ximen Jiye
Published: June 2020

Image reconstruction techniques have been widely applied to electron microscopy and computerized tomography. The classic algebraic reconstruction problem is to reconstruct the three dimensional (3D) objects from experimentally measured two dimensional (2D) projections. In literature, only approximate algorithm and iterative procedure have been investigated. Recently, an analytical self-consistent reconstruction method has been proposed by the author. A discrete/continuous object is given:

whlie 2D projections are
Prospect for HEW Applications of Multivariate Statistical Analysis in Microscopy and Spectroscopy
Authors: Bonnet N. , Simova E. , Lebonvallet S.
Published: June 2020

Multivariate Statistical Analysis has been developed in order to process large data sets and to extract from them the significant information.

It has been introduced in electron microscopy in order to process image series of macromolecules and to classify individual images into several subsets of the series. This kind of series can be considered as a spatial series.

In fact, electron microscopy and spectroscopy are using more and more image sequences in order to be able to access more precisely the content of the object studied. Among the different types of sequences which are already used and which will be used more extensively in the near future, one can mention :

—spatial series (several slightly different objects, whose images are to be classified and combined ; or several microanalytical spectra recorded at different places of the object).

—time series : in order to study changes induced in the object, one has to record successive images or spectra.

—series in energy : one possibility to study the behavior of a specimen is to vary the accelerating voltage, to record several images or spectra and process the whole data set. Another exemple of series in energy is given by energy loss elemental mapping (or Auger elemental mapping) where several energy filtered images must be recorded (below and above the edge of interest) in order to get a “true” elemental map.

—more “exotic” series can also be obtained, for instance series obtained by varying the spot size in MEB, series obtained with different configured detectors in STEM...
Electron Microscopy of Selfassembling Lipids With Carbohydrate Headgroups and Their Stereochemical Interactions
Authors: Boettcher Christoph
Published: June 2020

The spontaneous aggregation of amphiphilic molecules into ordered structures plays an important role in many biological and chemical systems. The stereochemistry of headgroups and their interaction in the mixed systems strongly influence the size and shape of the formed membranous aggregates .

Upon cooling of the aqueous solution, containing D-Glu-8, micellar fibers of at least bimolecular diameter (4 nm) are formed and then converted within seconds into complex helical ropes of uniform screw sense. The preliminary structure, identified as a double stranded helix, could be detected by EM (a) after stabilisation in the presence of 2% phosphotungstic acid (Fig.1) and (b) using frozen hydrated specimens (Fig.2), which were prepared under controlled environment conditions at 60°C before plunging into liquid ethane. Small differences in the size and shape of the fibers, which were confirmed by image analysis, were traced back to adsorption effects on the carbon film and can be neglected, if frozen hydrated specimens are used.

In an equimolar mixture of gluconamides, differentiated in the chain length, the formation of fibers is retarded and intermediate structures, such as micellar clusters are detectable (Fig.3). Racemic mixtures of hexonamides usually produce bilayer platelets (“Chiral Bilayer Effect”); if the enantiomers are again differentiated in the chain length, a spontaneous racemate resolution is observed (Fig.4, left-(M) and right-(P)handed helices!) and the formation of platelets (Fig.5) is retarded.
On the Use of POCS for Restoring the “Missing Wedge” in Electron Tomography
Authors: Zhang Neng-Yu , McEwen Bruce F. , Frank Joachim
Published: June 2020

Reconstructions of asymmetric objects computed by electron tomography are distorted due to the absence of information, usually in an angular range from 60 to 90°, which produces a “missing wedge” in Fourier space. These distortions often interfere with the interpretation of results and thus limit biological ultrastructural information which can be obtained. We have attempted to use the Method of Projections Onto Convex Sets (POCS) for restoring the missing information. In POCS, use is made of the fact that known constraints such as positivity, spatial boundedness or an upper energy bound define convex sets in function space. Enforcement of such constraints takes place by iterating a sequence of function-space projections, starting from the original reconstruction, onto the convex sets, until a function in the intersection of all sets is found. First applications of this technique in the field of electron microscopy have been promising.

To test POCS on experimental data, we have artificially reduced the range of an existing projection set of a selectively stained Golgi apparatus from ±60° to ±50°, and computed the reconstruction from the reduced set (51 projections). The specimen was prepared from a bull frog spinal ganglion as described by Lindsey and Ellisman and imaged in the high-voltage electron microscope.
Computer-Controlled Hrem Alignment Using Automated Diffractogram Analysis
Authors: Fan G.Y. , Krivanek O.L.
Published: June 2020

Full alignment of a high resolution electron microscope (HREM) requires five parameters to be optimized: the illumination angle (beam tilt) x and y, defocus, and astigmatism magnitude and orientation. Because neither voltage nor current centering lead to the correct illumination angle, all the adjustments must be done on the basis of observing contrast changes in a recorded image. The full alignment can be carried out by a computer which is connected to a suitable image pick-up device and is able to control the microscope, sometimes with greater precision and speed than even a skilled operator can achieve. Two approaches to computer-controlled (automatic) alignment have been investigated. The first is based on measuring the dependence of the overall contrast in the image of a thin amorphous specimen on the relevant parameters, the other on measuring the image shift. Here we report on our progress in developing a new method, which makes use of the full information contained in a computed diffractogram.
A UHV-Compatible Photobmission Microscope for Applications in Surface Science
Authors: Engel W. , Rotermund H.H. , Kordesch M. , Kubala S. , Oertzen A.v. , Jakubith S.
Published: June 2020

The intention was to develop a low-cost reliable photoemission microscope (Fig.l) which gives only modest lateral resolution but allows full advantage to be taken of its ability to reveal small variations of the sample‘s work function with high contrast. Another important point was its applicability in the field of heterogeneous catalysis, i.e. the possibility of observing catalyst surfaces during catalitic reactions.

The microscope can be attached to any vacuum chamber which has been provided with a port for a standard LEED system. It is mounted on an 8-inch OD CF flange, and the flange-to-sample distance has the standard length of 10 inches. The sample is at ground potential whereas the microscope column is at +20 kV. The microscope is connected to an auxiliary pump, and a fixed aperture (diameter 300 μn) in the back focal plane of the objective lens permits differential pumping. Pressures in the sample area even approaching 10−3 Torr do not effect the operation of the microscope and its channel-plate image intensifier.
Methods and Applications of UV Photoelectron Microscopy in Surface Science
Authors: Mundschau M. , Bauer E. , ᔒwięch W.
Published: June 2020

Photoelectron microscopy is sensitive to single atomic or molecular layers on surfaces at submonolayer coverages. A significant advance for fundamental studies in surface science has been the construction of ultra-high vacuum versions of classical photoelectron microscopes and the combination with other techniques of surface analysis - most notably low-energy electron diffraction and microscopy. This is essential for the proper interpretation of the micrographs. The technique is well suited for in situ studies of large flat samples such as silicon wafers, single crystals and polished metallurgical samples.

One of the most promising fields for application of the photoelectron microscope is in the area of epitaxial growth.In epitaxy a crystalline substance grows as an oriented overgrowth atop a substrate. It has widespread use in the semiconductor industry and in the field of quantum electronics, in which epitaxially grown structures have the dimensions of the same order of magnitude as the wavelengths of the conducting electrons.
Design for a New Low Energy and Photo-Emission Electron Microscope for Surface Science Studies
Authors: Tromp Ruud M.
Published: June 2020

A new LEEM/PEEM apparatus has been designed for the study of surfaces and surface processes in Ultra High Vacuum (UHV). The design follows the general layout of the microscope operated succesfully by Prof. Bauer and coworkers, but differs significantly in a number of details. We designed a magnetic/electrostatic cathode lens with a resolution limit close to that of the uniform electrostatic accelerating field between sample and lens. The projection system consists of transfer lens, intermediate lens and projector lens. Total magnification is between 1,000x and 10,000x, with a field of view between 4 and 40 micrometer. The illuminating system features a continuously adjustable range of illumination, such that the loss of image intensity at high magnification can be balanced by a reduction of the illumiated area, without significant loss of electron beam intensity. Both bright field and dark field imaging are possible. The location of the diffraction aperture in the projection column allows for more flexible operation of the microscope in dark field mode. Care has been taken in the design of the microscope to integrate the stringent vacuum requirements with the geometric constraints of the electron optical components. A sample stage, featuring two orthogonal translations and two (eucentric) tilts, sample heating, as well as in situ sample exchange capability has been constructed. All motions are driven by remote control, UHV compatible piezoelectric actuators, eliminating the need for mechanical feedthroughs, and ensuring a short mechanical path between sample and cathode lens. In situ deposition, using e-beam evaporators and/or Knudsen cells will be possible. A sample preparation chamber contains standard surface cleaning and analytical equipment. We will report on the progress in the construction of this machine.
Images and Applications of Ion Explosion Spike Pits
Authors: Fraundorf P. , Tentschert J.
Published: June 2020

Since the discovery of their etchability in the early 1960‘s, nuclear particle tracks in insulators have had a diverse and exciting history of application to problems ranging from the selective filtration of cancer cells from blood to the detection of244Pu in the early solar system. Their usefulness stems from the fact that they are comprised of a very thin (e.g. 20-40Å) damage core which etches more rapidly than does the bulk material. In fact, because in many insulators tracks are subject to radiolysis damage (beam annealing) in the transmission electron microscope, the body of knowledge concerning etched tracks far outweighs that associated with latent (unetched) tracks in the transmission electron microscope.

With the development of scanned probe microscopies with lateral resolutions on the near atomic scale, a closer look at the structure of unetched nuclear particle tracks, particularly at their point of interface with solid surfaces, is now warranted and we think possible. The ion explosion spike model of track formation, described loosely, suggests that a burst of ionization along the path of a charged particle in an insulator creates an electrostatically unstable array of adjacent ions which eject one another by Coulomb repulsion from substitutional into interstitial sites. Regardless of the mechanism, the ejection process which acts to displace atoms along the track core seems likely to operate at track entry and exit surfaces, with the added feature of mass loss at those surfaces as well. In other words, we predict pits whose size is comparable to the track core width.
Molecular imaging of Organo-Calcium salts by High Resolution Electron Microscopy and Image Processing
Authors: Miller G. , Fryer J.R. , Kunath W. , Weiss K.
Published: June 2020

Unfortunatly Wolfgang Kunath died January 1990

High resolution electron microscopy and image processing are being used to determine the molecular packing within the crystal unit cell of the, organic-azo calcium salt. Due to the beam sensitive nature of the organic moiety which contains both aromatic and and aliphatic components, low dose techniques were used. This concisted of, searching the sample in the diffraction mode to find single crystals exibiting point like reflection to at least .2nm resolution, (fig. 1). Focusing and astigmatism correction was performed by moving the beam of the crystal (off axis). The beam was then moved on axis and a series of four, 10 e/A images taken, (fig. 2). Images were primarily recorded using an on line T.V. recording device. These images were then available for processing using the Semper image processing system. Two crystal orientations were found. Type 1 consisted of thin plate like crystals up to 5um diameter and generally 10nm to 20nm thick. Type 2 were thicker crystals with a 3.2nm lattice spacing. The power specrta of the first low dose images were calculated to asses the quality of the of the structural information present. For the type 1 crystal the power spectrum had to show at least second order reflections in two directions ( fig. 3 ). Type 2 crystals showed the 3.2nm reflection often down to the fith order. These crystals also showed parallel side bands corresponding to a d-spacing of about .8nm. With these results the unit cell was found to be tetragonal with a= .78nm b= 3.2nm c= .78nm. In accordance with the diffraction patterns exibited.
Accuracy of Stereoscopic Technique in S.E.M.
Authors: Wang D. , Feng Y. , Lu H.
Published: June 2020

The principle of 3-D reconstrution for SEM image is not so conplex, ie. the SEM image of polar project is treated with a rectangular coordinate, however, it accuracy is an attractatble topic. The accuracy of a stereopair is effected by following factors:

(1) Sample’s position:

Image’s field depth of SEM is determined by

where, F4: the depth of field

D0: resolution of image

β : condence angle of E-beam (about 1 × 10−3 rad.)

when the magnificaton is 1000 times, ie. Do = 0.1μm, then Ff = 100μm. To get an accurate stereopair, one should keep the interested points on the specimen in the same field depth before and after tilting operation. During the operation, a point displacement is sketched in Fig.1, where 0 is tilting axis. Ao is the original position of A, A, is tilted one, α is tilted angle and β is the angle betweem 0Ao and Z axis. After the tilt, the perpendicular displacement of A point is

and the horizontal one is

Generally, the magnification is 1000X, ie. Ff=100μm, α≈10°, if β<=30° then, 0Ao<=700μm is the condition for that ZA < = 100 m.
Development of Field Emission Gun for High Voltage Electron Microscope
Authors: Shimoyama H. , Morita C. , Arai S. , Yokoi N. , Miyauchi K. , Onai T. , Matsui I. , Katsuta T. , Enomoto Y.
Published: June 2020

For the last few years we have been developing a field emission (FE) gun system for our high voltage electron microscope (HVEM) H-1250 ST (maximum accelerating voltage of 1.25 MV) at Nagoya University, in order to attain much higher level of performance of the instrument and to exploit further extended field of application. In the first stage of the project during the period from 1986 to 1987, the FE gun system had been mounted on the top of the accelerating tube, and successfully been operated at the accelerating voltage of 1 MV for the first time pin the world. The operation was very stable and high resolution images for both scanning transmission electron microscopy (STEM) and conventional transmission electron microscopy (CTEM) modes were possible at this stage. At the same time, however, several practical problems related to incorporating the FE gun into the HVEM were made clear. Since then several important modifications on instrumentation and electronics have been made and the project is now at the second stage. In this paper a brief outline of the FE gun system developed for our HVEM is described especially from the view point of instrumentation and electronics.
The Analysis of Composition Variations in LED's Using CBED
Authors: Liliental Z. , Ishizuka K.
Published: June 2020

The investigation of the degradation process in the light emitted diodes (LED's) requires a method for distinguishing the particular layers in order to observe where dark line defects responsible for that process are created. Such diodes are formed on GaAs substrate, but particular layers with different functions are epi-layers of Ga1-XAlXAS (for active layer x=10%, for window and confinement layers x=30%)(Fig. 1). To distinguish the particular layers with the aid of an electron microscope we mostly employ a dark field image using the (200) reflection because the difference structure factor for this reflection is the most sensitive to composition variations in the zinc blende structure. It was interesting to see how the structure factor changed if 30% of Ga atoms were substituted by Al. To observe these changes a CBED pattern was obtained for the systematic row (200) close to {001} zone axis.
Evaluation of human resources needed and comparison with human resources available to implement emergency vaccination in case of foot and mouth disease outbreaks in Tunisia
Authors: Marsot Maud , Durand Benoit , Ben Hammouda Wafa , Hadj Ammar Heni , Zrelli Malek , Khorchani Roukaya
Published: June 2020

Foot and mouth disease (FMD) is a highly contagious viral disease that affects domestic and wild artiodactyl animals and causes considerable economic losses related to outbreak management, production losses and trade impacts. In Tunisia, the last FMD outbreak took place in 2018–2019. The effectiveness of control measures implemented to control FMD depends, in particular, on the human resources used to implement them. Tunisia has the ultimate objective of obtaining OIE status as ‘FMD-free with vaccination’. The aim of this study was to determine and compare the necessary and available human resources to control FMD outbreaks in Tunisia using emergency vaccination and to assess the gaps that would play a role in the implementation of the strategy. We developed a resources-requirement grid of necessary human resources for the management of the emergency vaccination campaign launched after the identification of a FMD-infected premises in Tunisia. Field surveys, conducted in the 24 governorates of Tunisia, allowed quantifying the available human resources for several categories of skills considered in the resources-requirement grid. For each governorate, we then compared available and necessary human resources to implement vaccination according to eight scenarios mixing generalised or cattle-targeted vaccination and different levels of human resources. The resources-requirement grid included 11 tasks in three groups: management of FMD-infected premises, organisational tasks and vaccination implementation. The available human resources for vaccination-related tasks included veterinarians and technicians from the public sector and appointed private veterinarians. The comparison of available and necessary human resources showed vaccination-related tasks to be the most time-consuming in terms of managing a FMD outbreak. Increasing the available human resources using appointed private veterinarians allowed performing the emergency vaccination of animals in the governorate in due time, especially if vaccination was targeted on cattle. The overall approach was validated by comparing the predicted and observed durations of a vaccination campaign conducted under the same conditions as during the 2014 Tunisian outbreak. This study could provide support to the Tunisian Veterinary Services or to other countries to optimise the management of a FMD outbreak.
Integration – Care Work – Diversity Management
Authors: Berchem Davis Johannes
Published: June 2020

Zusammenfassung. Die Integration von Geflüchteten sowie der Umgang mit Diversity stellt für den Pflege- und Gesundheitssektor in Deutschland ein wichtiges Kernanliegen dar. Der Beitrag beleuchtet ein Praxisprojekt im St. Augustinus Memory Zentrum in Neuss, das durch die Hochschule für Gesundheit in Bochum wissenschaftlich begleitet wurde.
Tree‐Branching‐Based Enhancement of Kinetic Energy Models for Reproducing Channelization Processes of Pyroclastic Density Currents
Authors: Aravena A. , Cioni R. , Bevilacqua A. , de' Michieli Vitturi M. , Esposti Ongaro T. , Neri A.
Published: June 2020

Kinetic energy models, also called kinetic models, are simple tools able to provide a fast estimate of the inundation area of pyroclastic density currents (PDCs). They are based on the calculation of the PDC front kinetic energy as a function of the distance from a source point. On a three‐dimensional topography, the PDC runout distance is estimated by comparing the flow kinetic energy with the potential energy associated with the topographic obstacles encountered by the PDC. Since kinetic models do not consider the occurrence of channelization processes, the modeled inundation areas can be significantly different from those observed in real deposits. To address this point, we present a new strategy that allows improving kinetic models by considering flow channelization processes, and consists in the inclusion of secondary source points in the expected channelization zones, adopting a tree branch‐like structure. This strategy is based on the redistribution of a key physical variable, such as the flow energy or mass depending on the considered kinetic model, and requires the adoption of appropriate equations for setting the characteristics of the secondary sources. Two models were modified by applying this strategy: the energy cone and the box model. We tested these branching models by comparing their results with those derived from their traditional formulations and from a two‐dimensional depth‐averaged model, considering two specific volcanoes (Chaitén and Citlaltépetl). Thereby, we show the capability of this strategy of improving the accuracy of kinetic models and considering flow channelization processes without including additional, unconstrained input parameters.
Relative Dispersion of Surface Drifters in the North Sea: The Effect of Tides on Mesoscale Diffusivity
Authors: Meyerjürgens Jens , Ricker Marcel , Schakau Vanessa , Badewien Thomas H. , Stanev Emil V.
Published: June 2020

We examine the relative dispersion and the contribution of tides on the relative diffusivities of surface drifters in the North Sea. The drifters are released in two clusters, yielding 43 pairs, in the vicinity of a tidal mixing front in the German Bight, which is located in the southeastern area of the North Sea. Both clusters indicate decreasing dispersion when crossing the tidal mixing front, followed by exponentially increasing dispersion with e‐folding times of 0.5 days for Cluster 1 and 0.3 days for Cluster 2. A transition of the dispersion regimes is observed at scales of the order of the Rossby radius of deformation (10 km). After that, the relative dispersion grows with a power‐law dependency with a short period of ballistic dispersion (quadratic growth), followed by a Richardson regime (cubic growth) in the final phase. Scale‐dependent metrics such as the relative diffusivities are consistent with these findings, while the analysis of the finite‐scale Lyapunov exponents (FSLEs) shows contradictory results for the submesoscales. In summary, the analysis of various statistical Lagrangian metrics suggests that tracer stirring at the submesoscales is nonlocal and becomes local at separation scales larger than 10 km. The analysis of meridional and zonal dispersion components indicates anisotropic dispersion at the submesoscales, which changes into isotropic dispersion on the mesoscales. Spectral analysis of the relative diffusivity gives evidence that semidiurnal and shallow‐water tides influence relative diffusivity at the mesoscales, especially for drifter separations above 50 km.
Atmospheric Lifetimes of Halogenated Hydrocarbons: Improved Estimations From an Analysis of Modeling Results
Authors: Orkin Vladimir L. , Kurylo Michael J. , Fleming Eric L.
Published: June 2020

Detailed results of computer modeling of halocarbon removal rates from the atmosphere are analyzed to find simple correlations useful for improving estimations of the atmospheric lifetimes of industrial chemicals based on the rate constants for their reactions with OH and O(1D) and their UV absorption spectra. This analysis is limited to relatively long‐lived chemicals that are well mixed in the troposphere.
Teaching Machines to Detect Climate Extremes
Authors: Barbuzano Javier
Published: June 2020

Artificial intelligence can be used to analyze massive amounts of data from climate simulations, but more training data are needed.
Quantifying the Human Health Benefits of Using Satellite Information to Detect Cyanobacterial Harmful Algal Blooms and Manage Recreational Advisories in U.S. Lakes
Authors: Stroming Signe , Robertson Molly , Mabee Bethany , Kuwayama Yusuke , Schaeffer Blake
Published: June 2020

Significant recent advances in satellite remote sensing allow environmental managers to detect and monitor cyanobacterial harmful algal blooms (cyanoHAB), and these capabilities are being used more frequently in water quality management. A quantitative estimate of the socioeconomic benefits generated from these new capabilities, known as an impact assessment, was missing from the growing literature on cyanoHABs and remote sensing. In this paper, we present an impact assessment framework to characterize the socioeconomic benefits of satellite remote sensing for detecting cyanoHABs and managing recreational advisories at freshwater lakes. We then apply this framework to estimate the socioeconomic benefits of satellite data that were used to manage a 2017 cyanoHAB event in Utah Lake. CyanoHAB events on Utah Lake can pose health risks to people who interact with the blooms through recreation. We find that the availability of satellite data yielded socioeconomic benefits by improving human health outcomes valued at approximately $370,000, though a sensitivity analysis reveals that this central estimate can vary significantly ($55,000–$1,057,000 in benefits) as a result of different assumptions regarding the time delay in posting a recreational advisory, the number of people exposed to the cyanoHAB, the number of people who experience gastrointestinal symptoms, and the cost per case of illness.
Linking Magma Storage and Ascent to Eruption Volume and Composition at an Arc Caldera
Authors: Miller David , Bennington Ninfa , Haney Matthew , Bedrosian Paul , Key Kerry , Thurber Clifford , Hart Laney , Ohlendorf Summer
Published: June 2020

Conceptual models of magma storage and transport under calderas favor a connected system of sills and dikes. These features are individually below the resolution of standard seismic tomography, but radial seismic anisotropy can reveal where they exist in aggregate. We model radial anisotropy at Okmok caldera, Alaska, to demonstrate the presence of a caldera‐centered stacked sill complex and surrounding dike system. We show that ascending magma, inferred from seismicity, either intersects the sill complex, resulting in a larger volume eruption of evolved magma, or bypasses the overlying sill complex via dikes, resulting in a low‐volume mafic eruption. Our results exemplify how the locations of magma storage and paths of transport impact eruption size and composition. As this type of crustal storage is likely common to many calderas, this analysis offers a potential new framework for volcano observatories to forecast the size of impending eruptions.
A Shortening of the Life Cycle of Major Tropical Cyclones
Authors: Wang S. , Rashid T. , Throp H. , Toumi R.
Published: June 2020

In this study a comprehensive picture of the changing intensity life cycle of major (Category 3 and higher) tropical cyclones (TCs) is presented. Over the past decades, the lifetime maximum intensity has increased, but there has also been a significant decrease in duration of time spent at intensities greater than Category 1. These compensating effects have maintained a stable global mean‐accumulated cyclone energy of individual major TCs. The global mean duration of major TCs has shortened by about 1 day from 1982 to 2018. There has been both faster intensification (Categories 1 to 3) and weakening (Categories 3 to 1) by about 40%. The probabilities of rapid intensification and rapid weakening have both risen in the period 2000–2018 compared to 1982–1999. A statistically significant anticorrelation is found between the lifetime maximum intensity and the following duration of the final weakening. This suggests an element of self‐regulation of TC life cycles.
Synonymous GATA2 mutations result in selective loss of mutated RNA and are common in patients with GATA2 deficiency
Authors: Kozyra Emilia J. , Pastor Victor B. , Lefkopoulos Stylianos , Sahoo Sushree S. , Busch Hauke , Voss Rebecca K. , Erlacher Miriam , Lebrecht Dirk , Szvetnik Enikoe A. , Hirabayashi Shinsuke , Pasaulienė Ramunė , Pedace Lucia , Tartaglia Marco , Klemann Christian , Metzger Patrick , Boerries Melanie , Catala Albert , Hasle Henrik , de Haas Valerie , Kállay Krisztián , Masetti Riccardo , De Moerloose Barbara , Dworzak Michael , Schmugge Markus , Smith Owen , Starý Jan , Mejstrikova Ester , Ussowicz Marek , Morris Emma , Singh Preeti , Collin Matthew , Derecka Marta , Göhring Gudrun , Flotho Christian , Strahm Brigitte , Locatelli Franco , Niemeyer Charlotte M. , Trompouki Eirini , Wlodarski Marcin W. ,   European Working Group of MDS in Childhood (EWOG-MDS)
Published: June 2020

Deficiency of the transcription factor GATA2 is a highly penetrant genetic disorder predisposing to myelodysplastic syndromes (MDS) and immunodeficiency. It has been recognized as the most common cause underlying primary MDS in children. Triggered by the discovery of a recurrent synonymous GATA2 variant, we systematically investigated 911 patients with phenotype of pediatric MDS or cellular deficiencies for the presence of synonymous alterations in GATA2. In total, we identified nine individuals with five heterozygous synonymous mutations: c.351C>G, p.T117T (N = 4); c.649C>T, p.L217L; c.981G>A, p.G327G; c.1023C>T, p.A341A; and c.1416G>A, p.P472P (N = 2). They accounted for 8.2% (9/110) of cases with GATA2 deficiency in our cohort and resulted in selective loss of mutant RNA. While for the hotspot mutation (c.351C>G) a splicing error leading to RNA and protein reduction was identified, severe, likely late stage RNA loss without splicing disruption was found for other mutations. Finally, the synonymous mutations did not alter protein function or stability. In summary, synonymous GATA2 substitutions are a new common cause of GATA2 deficiency. These findings have broad implications for genetic counseling and pathogenic variant discovery in Mendelian disorders.