Life Sciences Commons^™

X-Ray Microanalysis Of Hollow Heart Potatoes, W. P. Mohr, A. R. Spurr, P. Fenn, H. Timm

Food Structure

Electron microprobe and X-ray fluorescence techniques were used to study elemental gradients associated with the physiological disorder hollow heart i n potato tubers. Gradients were found along the length and across the width of mature tubers. These were not rela ted to the disorder, however . Tubers with advanced symptoms of the disorder had elemental levels and gradients similar to those in healthy, control tubers. The results suggest that if the disorder is initially caused by an elemental deficiency, as has sometimes been proposed , the deficiency is temporary and no longer exists in mature tubers with advanced hollow heart. …

The Effect Of Salt And Pyrophosphate On The Structure Of Meat, C. A. Voyle, P. D. Jolley, G. W. Offer

Food Structure

Our obective was to determine whether or not salt and pyrophosphate have the same effect on the structure of pieces of meat as they have on isolated myofibrils. Blocks of pig M. longissimus dorsi were incubated in solutions of sodium chloride at pH 5.5 or sodium chloride plus sodium pyrophosphate at pH 5.5 or 8.0. The blocks were obtained from fresh (24h post- mortem) or aged (72h post-mor tem) muscle and incubated for 5 or 24h with minimal agitation. There was considerable uptake of water by the tissue especially at the higher pH and longer times.

Electron microscopy of the …

Morphological Development In Sorghum Grain, C. W. Glennie, N.V.D. W. Liedenberg, H. J. Van Tonder

Food Structure

Immature sorghum grain was harvested at various stages of maturity and its development followed by transmission and scanning electron microscopy . This was done to study the developmental morphology of the sorghum grain. The period immediately following fertilization is a time of rapid development in the sorghum caryopsis. The endosperm expands crush i ng the nucellus and in the nonbirdres i stant sorghums the inner integument is also crushed during this expansion. The cells of the ovary wal 1 expand and elongate to form the peri carp . By the soft dough stage the endosperm has gained most of its …

Light And Scanning Electron Microscopy Of Wheat And Rye-Bread Crumb. Interpretation Of Specimens Prepared By Various Methods, Y. Pomeranz, D. Meyer

Food Structure

The crumb of bread baked from wheat flour, rye flour, and rye meal was examined by light( LM ) and scanning electron-microscopy {SEM) . Whereas in the wheat bread the crumb is held together by a matrix of denatured protein, in the rye bread crumb highly expanded starch granules fulfill that r ole . Fractur i ng freeze-dried crumb ~rovided different information than sectioning !Jrior to freeze-drying . In the first case, little damage was caused to components of outer surfaces of vacuoles. In the second case , the protein matrix and starch granules were broken. At the same time, …

Effect Of Environment On The Physical Structure Of The Peanut (Arachis Hypogaea L.), Clyde T. Young, William E. Schadel

Food Structure

Peanuts produced under the drought conditions of 1980 were marred by off-flavors when processed. Several phys ical characteri stics of these peanuts were noted to be related to these flavor problems. This paper deals with the investigation of these physical peculiarities using scanning electron microscopy. Major findings include previously unreported physical abnormalities such as: (1) tissue damage which appears as spotting on the outer surface of the cotyledon which is a result of cracking and fissuring; (2) tissue damage which appears as a narrow band along the inner face of the outer rounded surface and the flattened edge of the …

Magnetic Electron Lenses, Wolfgang Dieter Riecke

Scanning Electron Microscopy

The electron optical properties of magnetic lenses are determined by the ratio S/D of gap width S to bore diameter D, by the actual size of the gap and by the lens strength NJ√U*. Objective lenses of particularly small aberrations are obtained if the specimen is positioned close to the center of the gap and if the width of the gap is made as small as possible. For projector lenses the best performance results if the lens is employed at its minimum focal length. Another aspect important for high resolution lenses is that a stigmator is available for the correction …

Magnetic Electron Lenses Ii, T. Mulvey

Scanning Electron Microscopy

Conventional magnetic electron lenses have evolved to their present highly developed state under the pressure of meeting the exacting requirements of high resolution electron microscopy. More recently, however, the desire to extract quantitative analytical information from the specimen has led to significant changes in the design of electron optical systems. The introduction of efficient lanthanum hexaboride cathodes and high beam current field-emission sources has strengthened this tendency. In addition, more complex lens systems than previously envisaged are now possible since microprocessors can be employed to assist in the rapid and reliable readjustment of the lens system, including the extensive alignment …

Various Attempts To Reduce The Dimensions Of Magnetic Electron Lenses Used For High Voltage Microscopes, J. L. Balladore, R. Murillo, J. Trinquier

Scanning Electron Microscopy

Magnetic fields are used in electron microscopy for a variety of purposes: image formation, energy analysis and correction of astigmatism, for example.

We are interested in the problems of designing short focal length lenses to be used for focusing high energy electrons in the energy range 1-3 MeV.

These lenses are generally very large and we have tried to reduce their dimensions to simplify their construction and use. From this point of view, it is necessary to diminish the magnetic coil and the magnetic circuit iron.

Several solutions have been proposed in the case of the coil. We have obtained …

Electrostatic And Magnetic Imaging Without Image Rotation, Zhou Li-Wei, Ni Guo-Qiang, Fang Er-Lun

Scanning Electron Microscopy

A method is discussed for designing electrostatic and magnetic imaging systems without image rotation. Tsukkerman's condition for an imaging system free of rotation does not appear to be applicable to practical designs. We have modified his theory to obtain two other conditions for the normalized axial electric potential V(z), the normalized axial magnetic induction G(z), and a lens strength parameter 𝞴 which can be interpreted as an eigen-value. Some analytical examples and numerical results are given.

The Application Of The Alternating Procedure Of H.A. Schwarz For Computing Three-Dimensional Electrostatic Fields In Electron-Optical Systems, Christoph H. Schaefer

Scanning Electron Microscopy

The numerical solution of three-dimensional electrostatic field problems in electron-optical devices with complicated boundaries requires the use of very large and fast computers. A numerical counterpart of the Alternating Procedure by H. A. Schwarz (SAP) makes efficient use of both storage space and time available on the computer and therefore represents a useful new method in this context. In this method. the domain of solution is decomposed into independent subdomains where the appropriate individual methods of solution may be chosen. Correspondingly. the original boundary value problem is decomposed into a sequence of boundary value problems in these subdomains. SAP requires …

Constrained Optimization Design Of An Electron Optical System, Chang-Xin Gu, Li-Ying Shan

Scanning Electron Microscopy

An electron optical system can be optimized using the "simplex method" or "complex method". By these methods, the final structure of an electron optical system, for example, an extended field lens (EFL), can be searched with a criterion of minimum objective parameter (in the present case, the coefficient of spherical aberration). Because there is no constraint in the simplex method, the constrained optimization method (the complex method) described in this paper is better than the simplex method in the design of electron optical systems. In the simplex method as well as the complex method, it is not necessary to know …

Progress In The Theory Of Electron-Beam Deflection, E. F. Ritz Jr.

Scanning Electron Microscopy

Analysis, simulation, and design of electron-beam-deflection systems are reviewed in light of the current state of theoretical understanding. A brief review of the physical principles is followed by a detailed discussion of electrostatic, magnetostatic, mixed-field, traveling-wave, and scan-expansion systems. Each methodology is examined from a triple perspective: calculation of electromagnetic fields, calculation of electron trajectories, and calculation of the ensemble of trajectories forming the beam. Applications discussed include deflectors for television displays, lithography, scanning microscopes, and CRT oscillography. Developments of the last ten years are stressed, thereby supplementing and updating the author's previous review on this subject.

In field calculation, …

Field Emission Source Optics, L. W. Swanson

Scanning Electron Microscopy

The use of field emission processes as a means of generating high brightness sources of both electrons and ions is becoming of increasing practical use in electron/ion optical systems. A review is given of the source optics and emission characteristics of a zirconium oxide coated, <100> oriented, tungsten (Zr0/W(l00)), thermal field emitter electron (TFE) source and a liquid metal ion source (LMIS). The primary interest at present is the use of these high field sources in microprobe focusing columns where beam sizes of < 0.5 µm and target current densities of ~ 1 to 10 A/cm² (in the case of a LMIS) and 10² to 10⁴ A/cm² (in the case …

Thermionic Emission Studies Of Micro-Flat Single Crystal Lanthanum Hexaboride Cathodes, P. B. Sewell, A. Delâge

Scanning Electron Microscopy

A new type of high brightness thermionic cathode has been developed. The cathode utilises emission from a small flat surface (generally less than 50 μm diameter) prepared parallel to a specific crystal plane on a single crystal of Lanthanum Hexaboride. Emission from the rest of the single crystal is suppressed by the use of a high work function coating of pyrolytic graphite. When used in a conventional triode gun, the maximum total electron emission is controlled by the area of the micro-flat, the work function and the temperature of the emitter. The Wehnelt potential serves a minor role in controlling …

Determination Of Optical Properties Of A Field Emission Gun Coupled With A Linear Accelerator For High Voltage Microscopy, M. Denizart, S. Roques, F. Sonier, B. Jouffrey

Scanning Electron Microscopy

The electron optical properties of a field emission gun plus a twenty-stage linear accelerator system have been determined in the case where the entrance pupil of the system is defined by one of the electrode apertures.

The first part of the calculation concerns the electrical and geometrical parameters of triode and tetrode field emission guns which can give a fixed location of the source and a small spherical aberration coefficient.

The second part is related to the possibility of placing a tetrode field emission gun at the top of the linear accelerator of the scanning high voltage electron microscope which …

Electron Detectors Used For Imaging In The Scanning Electron Microscope, V. N. E. Robinson

Scanning Electron Microscopy

Electron detectors used for imaging in the scanning electron microscope include those which detect secondary electrons, various portions of the backscattered electron signal, and the residual specimen current. The use of a different detector will often produce a different image of the same specimen. The information contained in these images depends upon the signal detected and the properties of the detector used. The choice of detector to be used depends upon the information desired.

Microchannel Plates As Specialized Scanning Electron Microscopy Detectors, P. E. Russell

Scanning Electron Microscopy

The need for a specialized detector for low beam voltage and low beam current applications has led to the investigation of a microchannel plate detector for SEM. The application requirements are described in detail, with the case of integrated circuit metrology used as an example. The microchannel plate (MCP) detector has proven to meet almost all of the design objectives of a low voltage metrology SEM detector. The symmetry of the detector and the ability to mount it directly to the final pole piece are among the most important features.

Study Of Space Charge Limitation Of Thermionic Cathodes In Triode Guns, A. Delâge, P. B. Sewell

Scanning Electron Microscopy

A computer program has been developed to compute the emission of cathodes from the fully space charge limited diode equation. The emission of four different gun arrangements with thermionic cathodes of the type used in electron microscopes is investigated. Microflat cathodes with a small (≤50𝜇m in diameter) fixed emitting area show several advantages for high brightness possibilities whereas other types of cathodes for which the emitting area increases with the brightness are usually limited by too great a total emission.

The Influence Of Sample And Detector Angles Upon Auger Electron Signal, Robert L. Gerlach

Scanning Electron Microscopy

The effects of the sample to incident electron beam angle and of the detector. angle on the Auger electron signal are important for quantitative Auger analysis, particularly for Auger mapping and line scans. A first approximation, single scattering, mean free path model is employed to simulate the Auger signal resulting from a range of sample and detector angles. The model is single scattering in the sense that the excitation path is taken to be a straight line into the solid. A second model approximates multiple scattering by a normal distribution of ionizing flux angles about the incident beam direction.

Since …

Electron Image Simulation: A Complementary Processing Technique, Michael A. O'Keefe

Scanning Electron Microscopy

At present it is difficult to use direct image processing techniques to determine the specimen structure from electron micrographs obtained under non-linear imaging conditions, and impossible when the effects of dynamical scattering are strong (as in the case of thicker specimens). However, computing techniques are available to simulate high-resolution transmission electron microscope (HRTEM) images of postulated model structures. With these techniques it is possible to confirm the validity of interpretation of recorded micrographs, to help analyze crystal defects, to characterize microscope parameters, and to determine the ranges of validity of commonly used interpretive approximations. Because processed micrographs can lead to …

Displays: Market And Technologies, Steve Blazo

Scanning Electron Microscopy

Displays provide the essential human interface to virtually all electronics instrumentation. The market is large with new applications appearing every year; sometimes with profound impact. Digital watches with liquid crystal displays appeared in the early 1970s and have virtually wiped out the mechanical timepiece industry. Personal computers with cathode ray tube (CRT) displays are proliferating with diverse applications in the industry and in the home. Work stations with high-resolution color displays are changing the way architects, draftsmen, and IC designers perform their job. The CRT is the dominant technology in today's market, and will, no doubt, continue to be for …

A Computer Controlled Scanning Transmission Electron Microscope Equipped With An Energy Analyzer For Special Investigations On Electron Diffraction- And Channeling Patterns, W. Hylla, H.-J. Kohl, H. Niedrig, D. Wendtland

Scanning Electron Microscopy

A scanning electron microscope was equipped with a double tilting stage, driven by stepping motors, to investigate electron channeling patterns (ECPs) and large angle convergent beam patterns (LACBPs) of single crystals. Transmitted electrons may be energy-selected by a magnetic sector-field energy analyzer. The recording of experimental data and the experimental arrangement are controlled by a microprocessor system, including a picture storage unit of 512 x 512 pixels of 16 bit. Recorded patterns can be stored on 1 Megabyte floppies.

A set of useful programs allows one to perform calculations with stored patter ns, e.g., contrast enhancement or -inversion, noise reduction, …

Energy Selecting Electron Microscopy, F. P. Ottensmeyer

Scanning Electron Microscopy

One of the major improvements in transmission electron microscopy over the last years is the addition of the capability of producing images with electrons that have specific narrow energy bands out of the total spectrum of energies they possess after having passed through the specimen. Though the idea is not new, the power of this application is only beginning to be recognized. Most simply, selection of elastically scattered electrons permits increased contrast in high resolution i mages in bright field, dark field, and diffraction. The use of combined elastic and inelastic signals adds entirely new contrast mechanisms, partially independent of …

Optimization Of Stroboscopic Electron Deflection Systems, H. Rose, J. Zach

Scanning Electron Microscopy

Highly corrected electron-beam blanking systems (EBBS) are required for analyzing fast periodic processes at submicron spatial resolutions by stroboscopic methods. The deleterious degradation of the probe during the blanking operation can be avoided by a new straight-vision deflection system. Chopping of the beam is performed within this system by deflecting it across a knife edge. Calculations demonstrate that this system should be able to generate almost rectangular beam pulses with rise times of a few picoseconds and spot sizes smaller than 0.5 µm. The proposed EBBS consists of two wedge-shaped plate capacitors located symmetrically about the midplane of a rotationally …