| Research Abstract |
To develop compact and efficient positive ion sources for salts such as alkali halides (MX), two types of 〔A〕 molecular beam incidence upon a heated metal filament surce (S【similar or equal】0.005cmィイD12ィエD1) and 〔B〕 sample solution coating on a base metal plate (S【similar or equal】0.03cmィイD12ィエD1) were designed and manufactured, and also the current (IィイD1+ィエD1) of ion (MィイD1+ィエD1) due to surface ionization (thermal emission) was measured a function of surface temperature (T), residual gas pressure (P), etc. Thoretical analysis of the data thus achieved yields the following resuits and conclusions.
〔A〕Sample beam incidence type
(1)Among the seven metals (Nb, Mo, Ta, W, Re, Ir, Pt) studied in this work, Re is the best as a positive ion emitter. (2)When Re is kept at T【similar or equal】1100-1300K at P 【similar or equal】1μTorr, the ionization efficiency (βィイD1+ィエD1) of MX becomes 〜100% because its work function (φィイD1+ィエD1) is increased up to 〜7.5 eV mainly by residual gas adsorption. (3)βィ
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イD1+ィエD1【similar or equal】 100% holds with those thirty elements whose ionozation enegy is less than 6.5eV. (4)The current density (IィイD1+ィエD1/S=eNβィイD1+ィエD1) attains 10ィイD1-5ィエD1A/cmィイD12ィエD1 when the beam intensity (N) is 10ィイD114ィエD1molecules/cmィイD12ィエD1 sec.
〔B〕Sample solution coating type
(1)When the sample layers (θ【similar or equal】0.1〜10ィイD13ィエD1 molecular layers) of MX is heated up to 〜1300K, neutral molecular evapolation occurs mainly below melting point ? Of MX. (2)Above Tm, however, emission of MィイD1+ィエD1 becomes stronger. (3)MィイD1+ィエD1 is emitled from those active spots on the layers or the base metal (Pt). (4)Work function (φィイD1+ィエD1) of the spots is as high as 〜6-8 eV. (5)Usually, the ionization efficiency (βィイD1+ィエD1) is 10ィイD1-3ィエD1-10ィイD1-4ィエD1, but it increases up to 〜10ィイD1-2ィエD1 as θ decreases to less than unity. (6)When a thin layer (θ【less than or similar】10 molecular layers) is heated around Tm, IィイD1+ィエD1/S becomes 10ィイD1-7ィエD1-10ィイD1-9ィエD1 A/cmィイD12ィエD1.(7)This type is applicable even to such a trace amount as 10ィイD1-11ィエD1 mole of MX.
These results have already been published in international journals. Less
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