New, reliable sources of atomic oxygen (AO) are of interest for potential applications in catalytic converters, hydrogen reformation and solid oxygen fuel cells. Scientists at the Materials and Structures Laboratory of the Tokyo Institute of Technology and ERATO-SORST in Yokohama, Japan1, were hoping that oxygen anions would be produced when they applied an electric field to a metal oxide. However, they actually demonstrated, for the first time, that AO is the dominant emission from a solid oxide electrolyte.

Fig. 1: Schematic illustration of a device for generating atomic oxygen.

The researchers heated an oxide-containing solid electrolyte (tetragonal zirconia polycrystal, 3% Y2O3-doped ZrO2) to temperatures of 1400–1800 °C under an oxygen atmosphere at reduced pressure, and recorded the emissions using a quadrupole mass spectrometer (Fig. 1). The scientists detected O+, which indicated that AO was produced from the electrolyte. The intensity of detected AO decreased as the detector was moved away from the emitter, and reached virtually zero when a shutter was placed between the emitter and the detector. These experiments confirmed that the heated electrolyte produced AO rather than diatomic oxygen. Atomic oxygen was not produced exclusively, however. “Although we observed oxygen anions along with the AO, the emission intensity of oxygen anions was at least five orders of magnitude less than that of the atomic oxygen,” says Hayashi. Diatomic oxygen was detected at a constant concentration, showing that it came from the oxygen supplied to the chamber rather than from the electrolyte.

This discovery is interesting from the point of view of depositing an ultrathin layer of oxide onto a surface. AO is used in wafer processing to make the silicon semiconductor-based microchips used in electrical appliances. The team is collaborating with a private company to perfect this process. “We are currently testing the performance of a prototype AO generator and plan to attach it to a high-vacuum physical vapor deposition chamber,” says Hayashi. This method of AO production has a wider operating pressure range than the conventional method of plasma discharge, making Hayashi's process particularly attractive. Other potential applications include the production of novel layered oxide materials and the cleaning or modification of surfaces.