For biologic studies, atomic force microscopy (AFM) has been prevailing over scanning tunneling microscopy (STM) because it has the capability of imaging non-conducting biologic specimens. However, STM generally gives better resolution than AFM, and we're talking about resolution on the atomic scale. In a recent article, Franz Giessibl (Atomic resolution of the silicon (111)- (7X7) surface by atomic force microscopy, Science 267:68-71, 1995) has demonstrated that atoms can be imaged by AFM.

Looking at samples in a scanning electron microscope often involves some type of sample preparation. The most common form of sample prep is coating the sample, usually with a heavy metal. The most common metal used for sample coating is gold. The need for coating samples is taken as a given by many people, but is it always necessary? To answer this question let us take a look at the reasons for coating a sample.

Although the secondary electron (SE) signal is still the most commonly used signal in scanning electron microscopes (SEMs), the backscattered electron (BSE) signal is now in wide use. Imaging both atomic number and surface topography have been the major applications of BSE detectors, with some applications in channelling, magnetic contrast and similar specialized applications. Over the last few years, low voltage BSE imaging has been used for imaging surface features to a depth of a few nm. But the BSE signal contains much more information and new techniques are being developed to take advantage of its versatility.

When doing replication, it is very important that all traces of the sample be removed from the replica. Adhering sample material introduces artifacts into the image and may, in extreme cases, make the replica so thick that the TEM beam cannot “see” through it. This may be a problem for both “ordinary” Pt/C replicas and freeze fracture situations. For organic samples, including both biological materials and polymers. For example, polymer latex particle fragments have a particular tendency to stick to the replica in freeze fracture preparations. Some freeze fracture samples will “wet” the replica surface if the replica is stripped by melting the substrate.

The editor of Microscopy Today has asked me to write an article which describes the Placement Office of the Microscopy Society of America and I have accepted this opportunity to bring the history and operation of the Office to the attention of ms readers in what follows the word “Candidate” refers to a member of MSA who is in good standing and who has registered appropriately with the Placement Office as actively seeking a position or a change, and “Employer” refers to institutions or companies who have registered with the Office as having a position open.

During the past two decades, the scanning electron microscope (SEM) has become an indispensable tool for morphological observation in materials and biological sciences. With energy dispersive x-ray spectroscopy (EDS) and wavelength dispersive spectroscopy (WDS), rapid chemical characterization of microscopic features has also become commonplace. As developments in manufacturing methods allow fabrication of ever smaller devices and quality control has achieved higher priority, demand for microscopic characterization by SEM has continuously increased.

Many applications where SEM/EDS evaluation could be useful involve samples that are not electrically conductive. Nonconductive samples are subject to a buildup of electrons on the examined surface. This buildup of electrons, or “charging” eventually causes scattering of the incoming electron beam, which interferes with imaging and analysis. Nonconductive samples have traditionally required pretreatment, by coating with a conductive film, before SEM examination.

Methods and results reported to our scientific, technical or law enforcement clients and/or presented in a court of law demand the assurance that all work can be duplicated precisely in every detail. The preparation of technical reports that meet high standards for accuracy and completeness are an ethical responsibility and professional obligation for managers of analytical laboratories.

As the extent or complexity of work increases, more methods and techniques may be employed, producing an array of results. The preparation of reports which accurately describe what was done, how it was done, and what was produced can become a significant challenge. The collection, handling, and analysis of physical evidence can seriously impact the search for the truth, as the O.J. Simpson trial has clearly illustrated.

There has been a tremendous expansion in the use of video in microscopy in recent years. This is probably not due to the most obvious advantage of video, that of real-time imaging of moving events, but to its use in image analysis systems. The cheapness of PCs and the associated hardware and software to store and manipulate images, coupled with the availability of lowcost CCD cameras has made the analysis of microscope images commonplace. In the article the equipment used and the sorts of analysis which can be performed will be briefly outlined. The standard text on video is that of Inoue; a more recent review is by Weiss et al. while the major video equipment manufacturers will also provide literature and advice on the more up-todate equipment.

During the early 1970's there was often heated debate over the quality of analytical performance attainable with Energy Dispersive (ED) systems using solid state detectors. Many scientists, particularly the more practical ones, were convinced that only WDX was reliable; while those with perhaps more imagination were convinced EDX was the future in microanaiysis. At that time, both groups were right.

EDX has seen remarkable improvement since those early days. At that time ED spectrometers were limited to analysis of elements above atomic number 10, and state-of-the-art resolution was improving to about 155 eV at Mn. Overlaps were handled strictly in quantitative analysis routines and even then only by use of simple overlap factors. Wavelength Dispersive (WD) spectrometers, although slow and difficult to operate, were required for light element analysis, to perform analyses when overlaps were present or suspected, and to detect trace elements.

We think that adhesion molecules hold cells together. This is the "glue" that holds us, and every other multicellular life form on this planet, together. Intriguingly, the atomic force microscope has recently been used to directly measure the binding force of one of these adhesion molecules. We now have direct evidence that adhesion molecules have the physical properties required to hold cells together. This essential new information shows that these molecules can perform the function that have been assigned to them. You'll be delighted to know that this molecule is more than strong enough to do its job!

Microscopy training has always been labor intensive. As the need grew for electron microscopists so did the need for methods of training to maintain quality while increasing the quantity of people trained. Various trends in scientific research needs, development of various types of microscopies, environmental concerns and increasing computer sophistication brought about significant changes in microscopy training and service facilities.

In the 1960's TEM research flourished. Many single user facilities appeared with scopes provided by grant funds, especially in biology. There was a great need for people trained in EM. In the mid 1960's, commercial SEMs became available, and SEM research flourished.

The fact that about half of our readers are not biologists does not mean that they are disinterested in the fascinating current developments in the field of biology any more than the biologist are disinterested in the equally fascinating progress of materials science or physics. Popular press and even trade journals often over simplify or at best give small pieces of information. It is nice when a refereed journal gives a state of the art review. Science Magazine recently gave such a review under the title "Development Frontiers in Biology". As is customary with Science, this issue also contains editorial summaries of many of the contributions in less technically obscure language.

Microscopy remains the primary tool for the analysis and quantification of asbestos in occupational and environmental studies. The American Society for Testing and Materials (ASTM) has recently approved two new Standard Methods for the analysis of asbestos in settled dust. Both methods require the use of a transmission electron microscope (TEM) equipped with an energy dispersive x-ray analysis system. Other methods curently in use require the use of a polarized light microscope {PLM) or phase contrast microscope (PCM).

Wouldn't it be nice to have some kind of laboratory hood in which gravity is greatly reduced so we could grow more perfect crystals or do biological experiments without having to go into orbit. There was a report in Science last year which hinted that gravity cancellation or modification just might be possible some day, but I doubt that any of our readers noticed it. The title was “Inertia: Does Empty Space Put Up the Resistance?”. One has to read this news report carefully to find that physicists have long pondered the connection between the inertial property of mass and the gravitational attraction between masses and that the work quoted here, suggests that once inertia is understood it might be controlled, even canceled. Upon inquiry the editor, Robert Matthews found other physicists believed that the ability to modify inertia could soon be tested experimentally but remarked that “it is a bit too early to be talking about inertia free star ships.”

Years ago electron microscopes usually had an hour meter as a standard part of the instrument Unfortunately hour meters have been eliminated from many modern scapes and are not even readily available as an option from most microscope manufacturers.

An hour meter is a very useful device. Every microscope I've owned or supervised has had an hour meter that was factory installed, added by helpful field service persons, or that I installed myself. Few of us would enthusiastically buy a car without an odometer, why should we want an electron microscope without an hour meter?

If supplying an hour meter on an electron microscope costs too much in production time or money, certainly it would take only minimal effort at the design stage to plan a connection point or plug to operate a clock as an ancillary part of an appropriate circuit.

The use of x-ray spectrometry in electron microscopy has been a powerful market driver not only for electron microscopes but also for x-ray spectrometers. More x-ray spectrometers are sold with electron microscopes than in any other configuration. A general name for the combination is AEM, or analytical electron microscope, though in modern times AEM can include other instrumentation such as electron energy loss spectroscopy and visible light spectroscopy. In previous articies I have discussed energy dispersive spectrometers (EDS). These use semiconductor crystals to detect the x-rays and measure the energy deposited in the crystal. A second type of x-ray spectrometer measures the wavelength of the x-rays, and so is called "wavelength dispersive spectrometry" (WDS).