In the past few years the field of near-field scanning optical microscopy (NSOM) has developed rapidly with applications spanning all the physical sciences. A key goal of this form of microscopy is to obtain resolution at levels well beyond those possible with the usual far-field optics. In contrast to far-field optics, which is bounded by the well known limits imposed by diffraction, near-field optics has no “in principle” fundamental lower limit in lateral size, at least down to atomic dimensions, although in practice, signal-to-noise considerations may restrict the application of NSOM to a few nanometers.

It must have seemed rather fantastic back in the fifties, when Russell Steere froze chunks of plant viruses (tobacco mosaic virus, tobacco nngspot virus, and squash mosaic virus) in drops of water, planed them freehand with a scalpel blade, made a replica of the surface, and examined the replica in a transmission electron microscope. But that was the birth of freeze-fracture and freeze-etch methodology that yielded enormous amounts of information about the morphology of membranes.

For sample preparation, e.g. cross-sectioning and thinning, SEM and TEM microscopists routinely use mechanical techniques (e.g., cleaving, slicing, lapping, polishing, and microtoming) and chemical or broad beam ion thinning. Two problems they run into are (1) locating the site of and crosssectioning or thinning at the site of extremely small features at specific locations (site specific samples) and (2) dealing with materials and material systems that are altered or destroyed by mechanical sample preparation (material-specific samples). These material systems may contain multiple components with dramatically different characteristics, such as hardness or chemical reactivity.

Many of these limitations can be overcome by using focused ion beam (FIB) micromachining, often referred to as “FIB microsurgery.” This technique can locate micron and submicron features and use precisely placed cuts to cross section and thin samples.

I attend a local entrepreneur's luncheon once a month. Since the small town 1 live is the home of Word Perfect Corporation, and Novell, inc. is just down the road, you can imagine that mamy members are doing exciting things with software. When I tell them that MOXTEK makes windows (or X-ray detectors they really light up, until I tell them that! mean real windows.

X-ray detectors are used in electron microscopy to add chemical element analysis to the imaging capability of the microscope. A typical energy dispersive spectrometer uses a silicon crystal about the si2e of a shirt button to detect and measure the energy of incoming X-rays.

The combination of electron microscope and x-ray spectrometer is a very powerful tool. Not only can one see a sample in great detail, but one can determine, and even map, the chemical elements, in Part 1, I discussed some of the basics of energy dispersive x-ray spectroscopy (EDS, EDX). In Part 2,1 went into detail about the construction of the detector, and discussed counting statistics. In this installment I will discuss the interaction between the x-ray and the detecting crystal, things that can go wrong in the process, and the phenomena which can make false peaks in a spectrum.

The first man-made optical instruments were the looking glass, the magnifying glass and the burning glass. These were known by the fifth century BC. The next advance was eighteen centuries later when similar positive lenses were used to correct presbyopia. As lens making technology advanced to fulfill this demand, negative lenses were invented and used to improve the vision of near sighted people. Soon there were spectacle shops dotting Europe, and it was inevitable that people would start to play with combinations of lenses. This all came together at the end of the sixteenth century when the microscope and the telescope were invented in several places independently.

In transmission electron microscopy (TEM), it is often desirable to focus our attention on certain cells or structures that are sparsely distributed throughout a large tissue block. One method that is often used is to serially section through a large tissue block and then scan each thin section on the TEM for the cell or structure of interest. A much simpler and far less tedious method is to cut thick sections of the resin block, screen the sections using light microscopy for the cells or structures of interest and then somehow reembed only those sections with the cell or structure of interest so that they can be thin sectioned for TEM.