In this third and final installment on x-ray analysis in the environmental and low vacuum SEM, I will present experimental methods for measuring beam scatter. In my previous two articles I discussed how operating conditions detemine beam scatter. It was shown that the type of gas used, the gas pressure in the chamber, the working distance or beam gas path length, and the accelerating voltage all have an effect on how much the electron beam scatters. I also discussed how the beam scatter influences x-ray results by producing x-rays beyond the area of the primary beam. Furthermore, I showed how software models could be used to determine the amount of beam scatter based on different combinations of the four variables (pressure, gas, working distance, and kV).

Electron probe microanalysis (EPMA) is not only an excellent technique for measuring the chemical composition of a wide variety of materials, but also provides an effective means to quantitatively evaluate the chemical homogeneity of the material, In this contribution I present an easy approach for determining the chemical homogeneity of specimens in a statistically meaningful way.

The decree of chemical heterogeneity may be determined by a variety of methods varying both in ease snd rigor. One might apply a simple test for the sake of classifying the material as homogeneous or heterogeneous.

Vibration in microscopes may seem a bit baffling, but we have found that solutions to vibration problems are usually quite simple. Vibration is the result of an object being moved until it collides with another object and bounces back. Yes, it can be as simple as shaking, but the normal definition involves collisions. Some source must continuously supply energy to the moving part(s). As long as energy is supplied to the moving part(s) and the part(s) collide, bouncing can occur at a constant frequency. If the parts can be moved so they do not collide or if the energy can be absorbed, the frequency of the bouncing can be changed or stopped.

Reagents available for laboratory, research, and clinical use are often acquired with a specified expiration date. Yet, many are not, depending on the manufacturer and reagent type. What a manufacturer does is frequency determined by how they label the product.

The U.S. Ricd and Drug Administration [FDA] has defined categories by which reagents can he labeled based on their “intended use”. individual reagents (e.g., antibodies) intended for clinical diagnostic laboratory use will be labeled as an in Vitro Diagnostic [IVD] or Analyte Specific Reagent [ASR]. Under these categories, specified expiration dates must be supported by stability testing which establishes the product shelf life.

Pioloform F (Wacker Chemie Co., Munich, Germany) is an excellent plastic for use as a support film for electron microscopy. The advantages of Pioloform F are high mechanical and thermal stability, and low material bulk (Stockem, 1970). Because of these properties, thinner films than Formvar or collodion may be used and remain stable under the electron beam without subsequent stabilization by carton coating. Thin support films of gray interference color are prepared by dissolving 0.5 grams of Pioloform F powder in 100 milliliters of anhydrous chloroform (Stockem, 1970), using the dip method described by Reimer (1967).

Negative staining is a simple yet extremely useful procedure for examining nanometer-sized specimens such as intact microorganisms (viruses and some bacteria), subcellular components, and even nonbidogical particulates. It is a well established procedure, with extensive literature in many disciplines (Hayat and Miller, 1990). Although numerous variations exist, the basic procedure involves placing the specimen and stain onto a grid containing a substrate - usually plastic with or without a carbon backing. The stains consist of salts of heavy metals such as tungsten, uranium, or molybdenum which surround and often penetrate the specimen. Afier drying into an amorphous, glass-like background, the stains provide contrast based upon differential thickness.

When CD-ROM was introduced in 1983, it started a revolution in data storage that is still going on. But it was not until 1992, when the first desktop CD Recorders were shipped, that the real power of compact disc reached consumers. The ability to make on ones own desktop as few as one disc with up to 650 Megabyte of data in a formal that was readable en any computer with a CD-ROM drive, made massive data storage and file interchange a reality. That revolution is continuing with the advent of DVD-Recordable in 1998, allowing up to 3.9 Gigabytes on a single disc. In the next year or so, storing the full 4.7 Gigabytes specified in the DVD standards will be possible.