From the web:
This amazing little device known as the Zerostat Antistatic Gun is an antistatic "generator" which has numerous applications in any microscopy laboratory. Just squeeze the "trigger" of the Zerostat and a steady stream of ions is released. The "magic" comes from two powerful piezoelectric crystals and a patented compression trigger. Originally developed for removing dust from "vinyl" and before that, normal "phonograph records". In later years the Zerostat antistatic gun was discovered to have great applicability for use in a photographic darkroom to remove dust from film and negatives. After that, a wider range of applications came into being when people running SEM labs found out that it was also ideal for eliminating dust from critical samples or other critical surfaces when the dust attraction was being caused by electrostatic charge. Others have reported that certain insulating specimens, when treated this way, can actually be viewed (admittedly briefly) by SEM without the need to apply further coating.
Each Zerostat unit has a "two cycle" type of operation. When the trigger is squeezed, positive ions are generated and when the trigger is relaxed, negative ions flow. This means that it is possible to induce a charge on a neutral surface using the Zerostat. If the trigger is squeezed, and the Zerostat is removed from the surface before allowing the trigger to return to its original position, a positive charge will be induced. Similarly, pointing the Zerostat at the surface only for the release of the trigger will induce a negative charge