As the year ends there is a bumper crop of announcements of advances that I find absolutely amazing. First of course is the continued clever use of light as a veritable tool in manipulating everything from atoms (entrapping them in “atomic molasses”) to having tugs of war with biological motors (using “light tweezers”). But these developments will be for discussion another time. What I want to talk about in this installment are advances in Near Field Scanning Optical Microscopy (NSOM), which has now been used by Chichester and Betzig to visualize single molecules.

In classical (far field) optics, resolution is limited by diffraction to about 1/2 the wavelength of the radiation used for imaging. Near field optics overcome this limitation by use of scanning techniques similar to those employed in Scanning Tunneling or Scanning Force Microscopy.

The microscope has always played an important part in the field of environmental science. Initially it was involved mostly with those who analyzed for biological indicators of pollution or those who examined air pollution particles, but more recently it is being used by a large number of analysts of particulate samples following the concern over asbestos in schools. With the Asbestos Hazard Emergency Response Act (AHERA) of 1987, transmission electron microscopy (TEM) formally joined polarized light microscopy (PLM) and phase contrast microscopy (PCM) as a recognized regulation-required standard procedure for the analysis of asbestos. While asbestos remains a considerable activity in environmental microscopy, other areas including analysis of nan-asbestos fibers such as ceramic fibers, lead particle source determination, respirable silica measurement, and indoor air qualify particle examination have seen some interesting developments.

Pressure scales can be extremely confusing to new operators. This is not surprising. To my mind, there are three primary areas of confusion.

Firstly, the pressure of gas inside an instrument changes over many orders of magnitude during pumpdown. The change is about 9 orders of magnitude for a traditional Scanning Electron Microscope and about 13 orders of magnitude for an ultra-high vacuum instrument such as a Scanning Auger Microprobe.

To give an idea about the scale of change involved in vacuum, consider that the change in going from ambient pressure to that inside a typical ultra high vacuum system is like comparing one meter with the mean radius of the planet Pluto's orbit. The fact is that we don't often get to play with things on that scale. As a consequence, many of us have to keep reminding ourselves that 1 X 10-3 is one thousand times the value of 1 X 10-6 - not twice the value.

An interesting sidelight of building our own 3″ diffusion pumps is that as we built ever larger vacuum equipment, larger pumps were required. Motivated by our success with the 3″ pump, we gradually built a series of larger pumps going up one size at a time to 10″ diameter.

Critical point drying was invented by Tom Anderson and described in his fine paper in 1952. He was a bit ahead of his time as the widespread use of the technique was not until the arrival of the SEM in about 1970.

I became involved in critical point drying when Dr. Gennaro of New York University asked if I could make him a unit.. He sent me a copy of Tom's original paper and we visited Tom's lab for a demonstration.

With Tom's dryer, the chamber opening and closing involved a high pressure threaded seal. Fortunately, he had working with him a man big enough to be a NHL defensive end who manhandled a three foot wrench to seal and unseal the chamber.