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Robust activation method for negative electron affinity photocathodes

United States Patent

September 13, 2011
View the Complete Patent at the US Patent & Trademark Office
A method by which photocathodes(201), single crystal, amorphous, or otherwise ordered, can be surface modified to a robust state of lowered and in best cases negative, electron affinity has been discovered. Conventional methods employ the use of Cs(203) and an oxidizing agent(207), typically carried by diatomic oxygen or by more complex molecules, for example nitrogen trifluoride, to achieve a lowered electron affinity(404). In the improved activation method, a second alkali, other than Cs(205), is introduced onto the surface during the activation process, either by co-deposition, yo-yo, or sporadic or intermittent application. Best effect for GaAs photocathodes has been found through the use of Li(402) as the second alkali, though nearly the same effect can be found by employing Na(406). Suitable photocathodes are those which are grown, cut from boules, implanted, rolled, deposited or otherwise fabricated in a fashion and shape desired for test or manufacture independently supported or atop a support structure or within a framework or otherwise affixed or suspended in the place and position required for use.
Mulhollan; Gregory A. (Dripping Springs, TX), Bierman; John C. (Austin, TX)
12/ 321,805
January 26, 2009
FEDERALLY SPONSORED RESEARCH This work was supported by the Department of Energy SBIR under Grant No. DE-FG02-07ER84832.