Improved Ambient Pressure Pyroelectric Ion Source

The detection of volatile vapors of unknown species in a complex field environment is required in many different applications. Mass spectroscopic techniques require subsystems including an ionization unit and sample transport mechanism. All of these subsystems must have low mass, small volume, low power, and be rugged. A volatile molecular detector, an ambient pressure pyroelectric ion source (APPIS) that met these requirements, was recently reported by Caltech researchers to be used in in situ environments.APPIS creates ions through temperature changes of the crystal. A change in temperature of the pyroelectric crystal creates a potential difference between the +z and –z surface. With a sufficient voltage buildup, electrical discharge occurs at the surface of the crystal and either positive or negative ions are produced depending on the crystal face. This discharge ionizes compounds on and near the surface of the crystal. If thermal cycling is applied to the pyroelectric crystal (i.e., heated and cooled repeatedly), one can obtain negative and positive ions through a thermal cycle. This process, however, creates ions at random times throughout operations and makes the source difficult to use with several detection techniques.