Magnification Range Research Articles

The application of scanning electron microscopy for the characterization of powders

The examination of powder surfaces is limited in optical microscopy due to its short depth of focus, and in transmission electron microscopy due to sample preparation requirements. A relatively new and fast developing technique-scanning electron microscopy—offers many features most attractive in the study of powders in metallic and nonmetallic systems. The unique advantages of the scanning electron microscope include direct examination, a very large depth of focus, a wide range of magnifications, minimal or no sample preparation, a low specimen current, and sufficient resolution for most work involving direct examination of powder surface. The principle of operation of SEM is briefly discussed. The results of examination of 12 metal and alloy powders by the SEM and optical microscope are presented and compared. The SEM should be very useful in the field of powder studies in providing information pertaining to size, shape, surface topography and texture, porosity and pore shape, surface contamination, oxides and absorbed layer on surfaces, microstructure and agglomeration tendencies.

Preliminary examination of bull, ram and rabbit spermatozoa with the stereoscan electron microscope.

The stereoscan electron microscope (Cambridge Instrument Co.) enables the surface of objects to be examined over a wide range of magnifications, but the object must be carefully washed to remove substances which might obscure its outlines, and when the object is biological the substances washed away may be an important part of the surface. With this limitation in mind, samples of ejaculated bull and rabbit, and testicular ram spermatozoa were prepared in the following way: (1) Seminal plasma (or testicular fluid) was removed from semen by centrifuging at 20,000 g for 20 min. (2) Spermatozoa were resuspended in 40·0 ml phosphate-buffered saline (0·125 m-NaCl, 0·02 m-phosphate buffer, pH 7·4) and centrifuged at 1000 g for 10 min; the supernatant was removed. This was repeated four times. (3) The spermatozoa were fixed by adding 0·1 ml of sperm suspension to 0·9 ml 2·5% glutaraldehyde at pH 7·0 and keeping at 4·0° C for 1 hr. (4) The fixative was removed by centrifuging at 1000 g for 10 min. The spermatozoa were resuspended in distilled water. This process was repeated twice. (5) A drop containing fixed spermatozoa in distilled water was allowed to evaporate on a glass cover slip and examined in vacuo with the stereoscan microscope.

Zoom lenses for gaussian beams

In some applications of gas lasers it is desirable to keep the beam waist at a fixed longitudinal position while varying its width. The paper gives the relevant theory and shows that this can be done with acceptable precision over a useful magnification range by using the simplest possible zoom lens system.

The lattice spacing of crystalline catalase as an internal standard of length in electron microscopy

The preparation of crystals of bovine liver catalase, and their use as an internal standard of length in electron microscopy, are described. Absolute sizes in the magnification range x 10,000 to x 150,000 may be determined simply and routinely with an accuracy of ± 2.5 %, and relative sizes with an accuracy of 1.5 %. Measurement of the lattice spacings of crystalline catalase by low-angle electron diffraction is described. Results of other techniques are discussed in relation to this measurement. A critical appraisal of all available data suggests a figure of 172±4 A for the principal catalase lattice spacing. Lattice lines separated by half this distance are used in actual size determinations.

Development of Electron Mirror Microscope

Our electron mirror microscope has been improved by adopting magnetic lenses, which enable a wide range of magnification to be obtained. This improved version, known as the JEM-M1 (35kV acceleration) uses the straight design and shadow projection method.The construction of the newly designed instrument is illustrated in Fig. 1 and Fig. 2 shows a sectional view of its electron optical column. The electron gun assembly is located under the console table. Incident beam alignment is carried out by means of the deflection coil knob, the electron gun horizontal movement knob and the condenser lens knob located on the table. The zircaloy crystal located above the screen and on the optical axis enables the alignment procedure to be carried out easily and simply because it radiates light when impinged by the electron beam. The projector lens, having a short focal length, combined with the condenser lens, forms a small source for the shadow projection image on its back focal plane. The intermediate lens, acting on the reflected beam, produces image magnification by changing the excitation current. Magnification in the range x200 – x1500 is possible without any appreciable distortion.

Comparison of Transmission Electron Microscopy and Scanning Electron Microscopy of Fracture Surfaces

Based on the above considerations, the scanning electron microscope has unique capabilities for the study of fracture surfaces and should extensively replace the replication fractography currently used with the TEM. The most attractive advantages of the SEM are (a) direct examination, (b) no sample preparation, (c) accommodation of large size samples, (d) satisfactory resolution, (e) range of magnification from 20X to 100,000X, (f) very large depth of focus, and (g) capability to examine a specimen in a number of orientations. Despite the absence of diffraction in the SEM (which appears to be the only disadvantage of this process, at present), it is obvious that, for fractography purposes, scanning electron microscopy has an equally important or a greater role to play than TEM fractography in the coming years.

Plaque titration of herpes simplex with antibody-free liquid overlay.

SummaryTwo reliable methods for plaque titration of herpes simplex in antibody-free liquid culture medium have been described. Some advantages over plaque titrations with solid or antibody-containing overlays are elimination of inhibitory effects of agar and antiserum, greater choice in type of culture vessel which allows for saving of culture materials, technician's time, and incubator space, optional elimination of carbon dioxide incubators, greater range of magnification, and more flexibility in manipulation of cultures.

Investigation of the sintering of cermet materials by means of capacitive dilatometers

1. A method for the application of A. V.Panov's high-sensitivity capacitive dilatometer in investigating of cermet materials has been developed. The advantages of this dilatometer over other systems are the following: a wide range of magnifications, the possibility of using specimens with a simple shape that can readily be prepared by means of processes ordinarily used in the cermet industry, automatic recording of all variables (the temperature, the time and the strain), and the possibility of using a controlled sintering atmosphere. 2. The dependence of shrinkage on the temperature and the sintering time obtained in our experiments lead to the conclusion that the recovery and recrystallization processes are retarded if aluminum oxide is introduced in copper. 3. In sintering copper, the intermediate exposure for the removal of residual oxides must take place at a temperature of 600°. 4. The sintering of copper-aluminum oxide materials can be pertormed without such exposure.

Aquilapollenites: Fossil Pollen as Seen Under the Scanning Electron Microscope

Photographs of a Late Cretaceous species of Aquilapollenites illustrate the usefulness of the scanning electron microscope (SEM) for the study of fossil pollen. The SEM has the advantages of great depth of focus and wide range of magnification; using present techniques, its use for the study of unsectioned specimens is limited to the observation of surface detail.

The Scanning Electron Microscope, a Major Break-through for Micropaleontology

Significant new vistas are opened up in micropaleontology by the advent of the scanning electron microscope. This instrument accepts whole microfossils and images them with extreme depth of field over a range of magnifications from 15 x to over 50,000 x. The greatly increased potential for observation of detail of specimen surface topography will significantly affect our understanding of morphology, as well as phylogenetic, biostratigraphic, and paleoecological interpretations based on morphological data. Furthermore, the vexing problem of scientific illustration is at last provided with an elegant means of solution. The scanning electron microscope, a major break-through for micropaleontology WILLIAM W. HAY AND PHILIP A. SANDBERG University of Illinois Urbana, Illinois

The Use of the Scanning Electron Microscope for the Examination of Sectioned Tissue

In previous studies from this laboratory the scanning electron microscope has been used to examine biological materials in the cathodo-luminescense and secondary electron modes. In these studies intact cells or even entire insects have been examined, some in the living state. Epithelial surfaces have been exposed and examined. Prior to the work to be described, no reports of the examination of tissue sections in the scanning electron microscope have been found, although sufaces of solid one millimeter cubes of tissue have been examined.In the present work blocks of solid tissue fixed in buffered aldehyde have been dehydrated in graded alcohols, embedded in paraffin, section at 4μ and examined successfully in the scanning electron microscope. These sections have been over 1 cm square and have been stained for subsequent comparative examination with the light microscope. With the scanning electron microscope in the secondary electron mode, magnifications of X5,000 have been found useful. In addition to the increased resolution as compared to the light microscope, a three dimensional image is obtained. An advantage over the conventional electron microscope is that tissue areas 1,000 times greater may be examined in the large sections without any obscuring grid bars, again with the three dimensional image. With the cathode ray display tube used, magnifications range from X30 to over X20,000

Uniformity of Magnification from Different Electron Microscopes

The method demonstrated is an adaptation of a proven procedure for accurately determining the magnification of light photomicrographs. Because of the stability of modern electrical lenses, the method is shown to be directly applicable for providing precise reproducibility of magnification in various models of electron microscopes.A readily recognizable area of a carbon replica of a crossed-line diffraction grating is used as a standard. The same area of the standard was photographed in Phillips EM 200, Hitachi HU-11B2, and RCA EMU 3F electron microscopes at taps representative of the range of magnification of each. Negatives from one microscope were selected as guides and printed at convenient magnifications; then negatives from each of the other microscopes were projected to register with these prints. By deferring measurement to the print rather than comparing negatives, correspondence of magnification of the specimen in the three microscopes could be brought to within 2%.

A 1 mev Electron Microscope Facility

The resolution and transmissive power of the transmission electron microscope improve markedly with increasing accelerating voltage. In order to realize the advantages of high voltage microscopy in U. S. Steel's metallurgical research program, the Board of Directors, in December 1965, approved the construction of a 1 mev electron microscope at the Fundamental Research Laboratory. All three phases of the microscope facility, i.e. 1 mev accelerator, electron optical column and special building, have progressed rapidly since that time and the present projection is that the instrument will go into operation in early summer of 1967.The microscospe uses an open Cockcroft-Walton accelerator manufactured by Haefely Ltd. as the electron source and scaled-up conventional magnetic lenses in the optics. The column, manufactured by RCA, has a number of unique features including a 6th lens used as a projector to enlarge a selected area diffraction pattern and to give a wider range of magnifications at the highest voltages.

Use of scanning electron microscope for the examination of actinomycetes.

SUMMARY: Organisms belonging to several genera of the order Actinomycetales were examined using the ‘Stereoscan’ electron microscope of the Cambridge Instrument Company. Unlike the transmission electron microscope, this instrument provides surface views of fine structures without the need for preparation of replicas. Using a simple preparation procedure, surface views of intact sporing structures of several actinomycetes were observed over a range of magnifications. The potential value of using scanning electron microscopes for the examination of actinomycetes was assessed.

An Improvised Table-Type Microprojector

Good line drawings are often superior to photomicrographs in scientific illustration, but to make a faithful freehand drawing of something seen through a microscope is usually difficult. Because scientific workers are often unskilled in artistic reproduction, numerous devices have been used for projecting accurate microscopic-slide images to obtain precise drawings. Commercially made microprojectors are the most sophisticated instruments for this purpose, but they are expensive. The camera lucida, perhaps the best-known device for microprojection, has the disadvantage of a restricted range of magnifications; also, a delicate light balance is needed to see an image.

New Thermionic Emission Microscope

A new thermionic emission microscope has been designed and constructed. It is a two lens microscope having a combination electrostatic-electromagnetic objective lens and an electromagnetic projector lens. The microscope has a magnification range of 78 to 5600× and a resolution of about 500 Å which is independent of magnification. It is capable of operating at a vacuum of 10−8 Torr at 1600°C. A specimen temperature and control system has been incorporated which operates with an accuracy better than ±5°C. The microscope stage is so constructed that the specimen can be independently moved in the x, y, and z directions. The electron-optical axis is horizontal to facilitate the recording of data.

The correction of distortion in the electron microscope

Methods commonly used for reducing or for eliminating image distortion in the electron microscope image frequently cause inconvenience to the operator or are effective only over a limited range of magnification. In the present investigation previous calculations of Liebmann and Haine are extended in order to evaluate the distortion at the final screen of a multi-stage electron microscope. The results of the calculation are expressed in terms of the principal dimensions of the instrument and the electron-optical constants of the lenses. It is shown theoretically and experimentally that for microscopes with two or more projection lenses distortion may be substantially eliminated by following a simple operating procedure of universal application. The elimination of image distortion at low magnification confers no benefits unless an adequate field of view is maintained. This aspect of the problem is also considered quantitatively.

The examination of surfaces.

SYNOPSISAttention is drawn to the inadequacy of the standard methods of qualitative assessment of surfaces, particularly for translucent specimens in the magnification range intermediate between the light and electron microscopes. The advantages of certain unconventional methods, namely metal shadowing for light microscopy, reflection electron microscopy, and scanning electron microscopy are discussed.

Precision microphotometer for use with a Vickers projection microscope

A microphotometer has been designed to measure photographic density and density gradients in autoradiographs. The equipment is designed to be used with a Vickers projection microscope, being particularly useful in the quantitative study of autoradiographs from metallurgical specimens. Results can be obtained over a magnification range of 18.6 to 400 times. The photographic density is measured by balancing the output of two photomultipliers, one in the incident beam and one in the transmitted beam. Densities measured on this instrument were compared with the quoted values on a standardized density wedge and gave a standard deviation of 0.006.

A new camera for medical stereophotography with special reference to the eye.

DESPITE its obvious advantages, three-dimensional photography of the eye has been infrequently employed.* A special camera for this purpose was described by me several years ago. 6 Subsequent models utilizing the same basic principles have now been used in the Howe Laboratory of Ophthalmology for five years, but the modifications have been sufficiently extensive to warrant designating the present model as a new camera. The advantages of the present camera, leading to simpler operation, are these: (1) a new device for more accurate focusing; (2) a single film holder; (3) a more compact construction; (4) a wider range of magnification with a single focal length lens, and (5) a reflex mirror system. It retains the advantages of parallax correction without distortion (by translation), variable interlens distance, and the use of electronic flash (Strobe light). Although this camera was primarily designed for use in photography of the anterior segment and lens