Photoemission from diamond and fullerene films for advanced accelerator applications

Abstract

The photoemission properties of thin diamond and fullerene films were investigated for advanced accelerator applications, using subpicosecond laser pulses at three different wavelengths (650, 325, and 217 nm). The quantum efficiency (QE) obtained at 217 nm with a boron-doped, p-type, (111) polycrystalline diamond film (2.6/spl middot/10/sup -4/) was only five times smaller than the QE obtained with a mirror polished copper sample (1.3/spl middot/10/sup -3/) but more than nine times larger than the QE obtained with a pure diamond film or with natural diamond monocrystals. Similar results were obtained for the two-photon electron yields at 325 mm. The electron yields obtained with pure fullerene films were small and comparable to the ones observed with the pure diamond samples. With 650 mn pulses, the damage threshold of the [110] Type IIa natural diamond monocrystal (9.38/spl middot/10/sup 4/ /spl mu/J cm/sup -2/), defined here as the fluence leading to an onset of ion emission, was 25 times larger than the damage threshold for a copper sample (3.75/spl middot/10/sup 3/ /spl mu/J cm/sup -2/). The damage threshold of the boron-doped sample at the same wavelength was two times larger than that of copper. Damage thresholds with 325 nm pulses were lower, and with 217 mn pulses ion emission was observed at all fluences probably attributed to ablation of surface hydrocarbon contaminants. Results show that high-quality high-boron concentration diamond films could be a good candidate for high-RF electron guns.