Effective Decrease Of Photoelectric Emission Threshold From Gold Plated Surfaces

Many applications require charge neutralization of isolated test bodies, and this has been successfully done using photoelectric emission from surfaces which are electrically benign (gold) or superconducting (niobium). Gold surfaces nominally have a high work function (similar to 5.1 eV) which should require deep UV photons for photoemission. In practice, it has been found that it can be achieved with somewhat lower energy photons with indicative work functions of (4.1-4.3 eV). A detailed working understanding of the process is lacking, and this work reports on a study of the photoelectric emission properties of 4.6 x 4.6 cm(2) gold plated surfaces, representative of those used in typical satellite applications with a film thickness of 800 nm, and measured surface roughnesses between 7 and 340 nm. Various UV sources with photon energies from 4.8 to 6.2 eV and power outputs from 1 nW to 1000 nW illuminated similar to 0.3 cm(2) of the central surface region at angles of incidence from 0 degrees to 60 degrees. Final extrinsic quantum yields in the range 10 ppm-44 ppm were reliably obtained during 8 campaigns, covering a period of similar to 3 years but with intermediate long-term variations lasting several weeks and, in some cases, bake-out procedures at up to 200 degrees C. Experimental results were obtained in a vacuum system with a baseline pressure of similar to 10(-7) mbar at room temperature. A working model, designed to allow accurate simulation of any experimental configuration, is proposed.