Patrick Looney

Pressure and Vacuum Group

National Institute of Standards and Technology

100 Bureau Drive Stop 8364

Gaithersburg, MD 20899-8364

In current vacuum science, equipment for pressure measurement in the regime above about 10^-9 Pa is commercially available and widely applied. The most ubiquitous gauge for pressure measurement in this regime is undeniably the Bayard-Alpert (BA) ionization gauge. However, as pressures are reduced below 10^-8 Pa several critical processes in BA gauges, both physical and chemical in origin, limit pressure measurement. These processes can be broadly grouped into two categories: residual current (i.e. the current measured by an instrument at zero pressure) and effects due gauge operation. These factors conspire to limit the ability to measure very low pressures. Therefore, pressure measurement below this range, in the extreme high vacuum ("XHV") regime, is more of an art form than routine practice. There are few reports of pressure generation and measurement at or below 10^-10 Pa and there is little doubt limitations in vacuum gauges have contributed to this barrier.

In this talk, I will present a review of the current state-of-the-art in vacuum gauging and gauge designs for pressure measurement in the XHV regime, with a focus on the limiting mechanisms and proposed strategies to overcome them. I will also discuss some of the attempts to date to develop pressure generators for calibration and characterization of gauge performance in this extraordinarily difficult regime.