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.

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.

I manage a university service electron microscope facility which provides transmission, scanning transmission, and scanning electron microscopy, each with X-ray energy spectrometry, as well as feature analysis, specimen preparation, and training services. Clients of the facility do basic and applied research in:

• human, animal, and plant health, pharmacy, and bioengineering;

• air, water, and soil ecology, pollution, and resource development and conservation;

• forest pathology, productivity, and development and performance of wood products;

• foods and nutrition:

• engineering, advanced metallic, ceramic, glass, and polymeric materials development, failure analysis, and tribology:

• botany, entomology, microbiology, zoology, chemistry, geology, and physics.

Frequently, the need arises for the measurement of the beam current in an electron microscope. For good quantitative analysis with either energy dispersive or wavelength dispersive spectrometers, the beam current is essential. The value of the beam current is used in quantitative microanalysis programs to equilibrate the production of X-ray generation between an unknown sample and a known calibration sample, i.e., a standard. Measurement of the beam current over time can also be quite helpful in determining problems with instrument stability. The following is a description of two very inexpensive methods for making a Faraday cup for measuring beam current in an SEM. It assumes that the microscope has a specimen current meter.

A new class of SEM has evolved over the past few years which provides some startling capabilities never before available to electron microscopists. These instruments, typically referred to as environmental SEMs or variable pressure SEMs. have opened up a host of new applications that are difficult or impossible with a standard SEM. Many of the constraints of sample preparation and handling that exist with a conventional SEM do not apply to environmental SEMs.

An environmental SEM functions like a conventional SEM except that you can introduce air or any other gas into the chamber and raise the chamber pressure above the normal high vacuum range of 10-5 or 10-6 Torr. Inmost instruments the vacuum can be raised to as much as 1 Torr. This represents a 6 order of magnitude increase in chamber pressure. Environmental SEMs can achieve this high chamber pressure without damage to the electron source by using differential pumping apertures in the column.

Numerous scanned probe microscopes (SPM) have been developed over the past decade. Most are based on the precise positioning of sample and probe using piezoelectric transducers, and some have the capability of imaging flat surfaces with atomic resolution. The first atomic resolution SPM applied to biological samples was the scanning tunneling microscope (STM). The atomic force microscope (AFM) was subsequently developed and over the past few years has become the instrument of choice for biological applications.