The Gopher, although as industrious as the Beaver and the skilled architect of complex subterranean mazes which should inspire as much awe as the dams and lodges built by beavers, is rarely revered as the mascot of Institutes of Higher Education. In real life many, my wife and I included, relentlessly pursue the garden variety gopher who dares to intrude and destroy prized plants, or for that matter even plants we do not care about. It is my job to deal with them and I do it like a Daemon that's BinHex-ed. However there is a highly prized and very beneficial, if virtual, species of GOPHERS. These creatures, created at the U. of Minnesota (home of the Golden Gophers), put their tunneling ability to good use, digging out otherwise hard to find information and so performing great services on the latter day wonder of electronic communication, the Information Superhighway, the Internet.

The electron source is the most important component of the Scanning Electron Microscope (SEM) since it is this which will determine the overall performance of the machine. The gun performance can be described in terms of quantities such as its brightness, its source size, its energy spread, and its stability and, depending on the chosen application, any of these factors may be the most significant one. The task of the electron gun in a SEM is, in fact, particularly difficult because of the very wide range of operational parameters that may be required, e.g. a variation in probe size of from a few angstroms to a few microns, and a probe current which may go from less than a pico-amp. to more than a microamp. This wide range of operating parameters makes the choice of the optimum source for scanning microscopy a difficult decision.

Having been brought up on monocular microscopes I find the omnipresent binocular systems a luxury. To support this viewpoint I'd like to suggest some benefits you may not have considered.

Because I'm used to monocular viewing I sometimes use two different oculars, say 10X and 25X, in order to scan quickly to find an area of interest and then to examine the detail with higher magnification. Occasionally I use both oculars simultaneously and “concentrate” on either image to the exclusion of the other. A better way is to set the interocular distance at the extreme setting most different from your own interocular distance. By moving your head about a centimeter either way you can use either ocular.

A variation of this theme is very helpful when you are trying to find good crystals showing useful interference figures.

Cross-sectioning of microelectronic devices for the purpose of construction or failure analysis by SEM and/or TEM has always been considered a major challenge. The ever increasing complexity and shrinking dimensions of these devices have pushed the art and science of the related specimen preparation beyond their conventional limits. The need for SEM failure analysis of sub-micron elements of a failed device requires the capability of cross-sectioning the sample with a high spatial-resolution within a specific transverse piane. An image of the device structure obtained at sufficiently high magnification from the above specimen generally reveals the defect(s) responsible for the failure. If the imaging resolution and contrast offered by an SEM prove to be inadequate for the above purpose, device structure will be inspected via TEM. Analysis of such device by TEM imposes the additional requirement of back-thinning the above specimen to electron transparency at the site of failure.

In microscopy, there is an increasing need for images to be recorded electronically and stored digitally on disk or tape. This image data can be shared by mailing these magnetic media or by electronic transmission along telephone lines (e.g. modem transfer) or special networks, such as Bitnet or Internet. In each case, the format in which the image is stored or transmitted must be known to the recipient in order to correctly recover all the information. Because there are many image formats to choose from, it would undoubtedly save misunderstanding and frustration if a group of individuals with similar interests and needs could agree upon a common format. The Microscopy Society of America Standards Committee has surveyed several formats which could be of particular interest to microscopist, with a view to making a recommendation to our community.

The preparation of electron micrographs for 2″ x 2″ slide presentations is usually done by photographing EM prints with a 35 mm camera. However, for some of our better electron micrographs, many of us have enjoyed printing the negatives directly on 2″ x 2″ Kodak Projector Slide Plates (#s 140 6875 & 140 6867), which can yield projected images of particularly pleasing tonal quality.

A previous issue of Microscopy Today (issue 94-2, March 1994} contained a brief article my me describing a method for making 2″ x 2″ EM slides with Projector Slide Plates. Unfortunately, it now appears that Kodak has raised the price of these plates to a level that is well beyond what most of us can afford. My first inkling of this came after the article was in the hands of the editor. I telephoned Kodak and confirmed that the price was now about $560 per box of 36 plates, roughly 10 times the former price. However, it still seemed possible that this had been an oversight on the part of Kodak, and that it could be rectified.

It was suggsted by a few that since the film is outgassing it is OK to backfill a TEM with lab air which has a high moisture content because the film in the camera chamber has a significant outgassing rate. My general comment is that you want to keep as much water and oxygen out of a vacuum system as possible. There is no need to add more to what may already be there.

In a vacuum system without any leaks or severe outgassing problems and with properly cleaned surfaces, the major factor which limits the ultimate pressure and pumpdown time is the water adsorbed on the exposed surfaces of the system. Depending on the type of surface, water molecules car either adsorb or chemisorb onto the surface. A chemisorbed species is characterized by having an exchange of electrons with the atoms on the surface and will have a higher energy associated with the desorption of the molecule from the surface.

One of the major difficulties with the older DEC PDP-11 based EDS systems is that they were designed as standalone units. Their manufacturers believed that the systems were capable of performing all the spectral processing that the users would ever need, and therefore did not allow for transfer of data to other computer systems. While some of the vendors have attempted to offer file transfer capabilities as upgrades, typically these upgrades are based on a serial connection using a file transfer program like Kermit. Although such solutions are acceptable for the transfer of small numbers of spectra, they cannot seriously handle hundreds of spectra or digital images data without tying up the EDS computer for extended periods of time. In multi-user environments, it is often desirable to move the data taken in one users microscope session immediately, to avoid filling to capacity the disk space on the acquisition system and rendering the system unusable for the next user.

Having been brought up on monocular microscopes I find the omnipresent binocular systems a luxury. To support this viewpoint I'd like to suggest some benefits you may not have considered.

Because I'm used to monocular viewing I sometimes use two different oculars, say 10X and 25X, in order to scan quickly to find an area of interest and then to examine the detail with higher magnification. Occasionally I use both oculars simultaneously and “concentrate” on either image to the exclusion of the other. A better way is to set the interocular distance at the extreme setting most different from your own interocular distance. By moving your head about a centimeter either way you can use either ocular.

Spiderman carefully slid the sample of mud into the microscope. As he increased the magnification he caught sight of a tiny spherical crystal. Zooming in on it, he said “Let's see what it's made of”. He reached over and flipped on the x-ray detector. As the spectrum formed on the screen a gasp went through the small group of researchers. “Kryptonite…the intruder is from another comic strip!”

The primary function of a microscope is to get a closer look at a sample. Many times a closer look is enough. Other times you need as much information as possible to solve a problem. In the above example, a reading of the chemical elements contained in the sample gave important clues about the sample's origin. X-ray analysis in electron microscopy combines elemental analysis with high resolution imaging. Of all the analytical techniques available to microscopists, it is the most highly developed and easiest to use.

One of the major advancements applied to scanning electron microscopy (SEM) during the past 10 years has been the development and application of digital imaging technology. Advancements in technology, notably the availability of less expensive, high-density memory chips and the development of high speed analog-to-digital converters, mass storage and high performance central processing units have fostered this revolution. Today, most modern SEM instruments have digital electronics as a standard feature. These instruments, generally have 8 bit or 256 gray levels with, at least, 512 X 512 pixel density operating at TV rate. In addition, current slow-scan commercial frame-grabber cards, directly applicable to the SEM, can have upwards of 12-14 bit lateral resolution permitting image acquisition at 4096 X 4096 resolution or greater.

Successful immunolabeling in electron microscopy of animal and plant tissues requires a combination of excellent antigen preservation while maintaining the original structure of the tissue. One important element is tissue embedding which accomplishes two goals for the immunohistochemist, the preservation of tissue specimen structure and maintenance of biological antigenicity. Tissue embedding in plastic resins is a common method in which several important elements must be considered.

1. 1. Fine tissue structure must not be damaged by the polymerization.

2. 2. The plastic must be stable to the electron beam.

3. 3. Light scattering properties of the plastic should be minimal.

4. 4. The plastic should cut easily.

5. 5. The plastic must be of sufficiently low viscosity to infiltrate the tissue.