In earlier reports, microscopic images of the surfaces of metallic electrodes used in high-pressure gas-filled 805 MHz RF cavity experiments were used to investigate the mechanism of RF breakdown of tungsten, molybdenum, and beryllium electrode surfaces. Plots of remnants were consistent with the breakdown events being due to field emission, due to the quantum mechanical tunnelling of electrons through a barrier as described by Fowler and Nordheim. In the work described here, these studies have been extended to include tin, aluminium, and copper. Contamination of the surfaces, discovered after the experiments concluded, have cast some doubt on the proper qualities to assign to the metallic surfaces. However, two significant results are noted. First, the maximum stable RF gradient of contaminated copper electrodes is higher than for a clean surface. Second, the addition of as little as 0.01% of SF6 to the hydrogen gas increased the maximum stable gradient, which implies that models of RF breakdown in hydrogen gas will be important to the study of metallic breakdown
