For low work function materials try AgO:Cs, NaSb, KSb, CsSb. best regards mark Mark W. Lund, PhD Director >> Soft X-ray Web page http://www.moxtek.com<< MOXTEK, Inc. 452 West 1260 North Orem UT 84057 801-225-0930 FAX 801-221-1121 lundm@xray.byu.edu "367 billion dollars of coal clearly has 367,000 times the value of a million dollar view."