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A simple method for analyzing the causes of a change in effective work function for thermal positive ionization

1985; Elsevier BV; Volume: 66; Issue: 2 Linguagem: Inglês

10.1016/0168-1176(85)83001-9

1873-2801

Hiroyuki Kawano, Tsutomu Kenpō,

Advanced Chemical Physics Studies

The effective work function (φ+) for producing a positive ion on a polycrystalline rhenium filament heated at a residual gas pressure of 2×10−7 torr was previously found to increase by up to ≈1.5 eV at surface temperatures of ≈1000–2200 K. In order to analyze the causes of this increase, the emission current of Li+ produced from LiI was measured as a function of both the elapsed time after flashing the filament with the sample beam shutter closed and the delay time before opening the shutter. When the sample beam flux (N) was as low as 6.6×1012 molecules cm−2 s−1, the increase was caused by adsorption of residual gas molecules (RGM). When N was increased ten times at as low a temperature as 1160 K, on the other hand, the increase due to the adsorption was suppressed by incidence of LiI, and hence θ+ was a complex function of coadsorption of RGM and LiI.