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If you wish to look inside an arbitrary piece of material and you own a light microscope (LM) or scanning electron microscope (SEM), there are probably three ways that you may accomplish your aim: (a) embed the material in epoxy, then grind and polish it flat; (b) embed the material and use a microtome to obtain cross sections; or (c) CRACK IT. In this short article, it is the last option that will be discussed. The last method is the simplest and quickest of the textbook sample preparation methods for SEM .
It was in October of 1964 when I first used a TEM, it was at the Siemens training school run by their agent Aeon Laboratories. A service engineer (we didn't call them technicians in those days), Robin Willis ran the course, five days for just alignment and cleaning! Robin, by the way, moved to University College London, Anatomy department and became the first person to publish on the tilting of biological samples. He actually invented tomography without knowing it! He used a fish tank within which he hung the negatives of his +60 to -60 tilt series. This procedure created a three dimensional image of the thin section, again I would guess, for the first time.
Abstract In order to understand the focusing action of a TEM objective lens, a simple imaging system (figure 1) is best considered. This system consists of an objective lens and a single projector. In operation, the projector is adjusted as required within the total imaging system to achieve a magnification, M2, on the screen. This results in a focal length of F1, with the lens seeking to find an image in the position M1. If the objective lens does not place the image at M1 the result on the screen is an out of focus condition. The objective lens may have produced an image short of M1, overfocus, or beyond M1, underfocus.
Abstract Does quality exist in the electron microscope laboratory? What is quality? Quality is when a product or service meets all of the customers' requirements, is delivered in the correct quantity at the required time, to the right place and at a price the customer is prepared to pay. In an open competitive environment all of the above would apply. In an electron microscope laboratory are we totally satisfied that we have given consideration to our product? We also provide a service, are we happy that the service we provide is of a sufficiently high standard, a standard that we would expect if we were the customers in a hotel or a garage? If we follow the example of world trends in industry, then simple product and service quality, in isolation, fs no longer sufficient, and focus must be given to a total quality approach.
Many words have been written about filament saturation and filament life, not all with years of experience behind them] Sometimes when visiting laboratories one has the feeling that the life of the filament is far more important than the quality of the results, so let us try to demystify filament life? The life of a tungsten hairpin filament very much depends upon its use and the applications present in a particular laboratory. Medturn to low magnification applications in the transmission electron microscope (TEM) may only require low emission currents (10 to 15 micro amps) with a long filament life resulting. High resolution studies require higher operating currents (20 to 45 micro amps) but, by demanding more emission current the life of the filament will suffer. Whilst a long filament life is good for the laboratory, it is not worthy of boasting, for those who have a short filament life may well be using the instrument near to the limit of its performance, a far more relevant boast!
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It is most important that any test specimens used to audit an instrument are from a traceable source and are certified by a recognised body. Traditional methods for the evaluation of resolution in the scanning electron microscope rely upon a high-density particle upon a low-density substrate, the most popular method being evaporated gold on a carbon substrate. Although most manufacturers use this method, it is subject to abuse as there is no inbuilt magnification standard and therefore the evaluation of the image may only be made through measurement. To simply judge the specimen by appearance as most scientists do, could lead to a misleading result. An ideal specimen for the evaluation of scanning electron microscope performance is dried polystyrene latex sputter coated with gold, or gold palladium for the evaluation of higher performance (e.g., field emission instruments) (Figure1). The specimen requires very pure polystyrene latex that is allowed to settle and dry down over a period of time sufficient for it to form a solid block. The block is fixed to a specimen stub with silver Dag and the adhesive allowed to dry.
Recently, there was a thread on the microscopy listserver about focusing TEMs, in particular whether to focus at crossover, or at the illumination level used for recording images. When setting the image focus there are a number of problems that may complicate matters.
During a recent one week "Intensive SEM" course that took place in Johannesburg, South Africa, the students came up with a superb cleaning technique that they wished to report upon. The results are, or should be, interesting to everyone who has to clean a cathode assembly! This note was originally posted on MSA's microscopy listserver and generated several replies. I have included more information below in response to these replies. Often the most time consuming operation during the routine use of a SEM or TEM is the cleaning of a cathode assembly. The procedure, outlined as follows, requires little operator intervention, is free from possible cathode contamination by the cleaning media, and takes comparatively very iittle time
The world of scanning electron microscopy seems to spin in such a way that every four years there is a dramatic step forward. Field emission sources (FEG), developed in the late 1960's, started life as a commercial disaster. In spite of the problems, certain manufacturers persisted with the first really user friendly FEG SEM reaching the market in the early 1980s. The FEG has been developed through the 1990's to be, without doubt, the source for SEU. But other advances in SEM performance have added to the instrument's performance, the most recent dramatic step being the introduction of semi-inlens imaging, a technique based upon 1980's dual detector imaging systems.
Abstract Microscopes in an electron microscope laboratory are built to be within specific tolerances in relation to resolution and magnification. The final specification from the manufacturer should include detail of magnification accuracy, drift rate, contamination rate and resolution, On delivery, the onus is on the installation engineer to confirm that the microscope meets specification. However, the final responsibility for microscope acceptance to specifications is the responsibility of the lab management.. Energy dispersive instrumentation is also specified as to specific resolution; and should also be confirmed on installation. In some cases, those with final responsibility for equipment performance might not resolve with the manufacturer's representee, at installation, that the instrumentation meets all specifications.
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