Studies of low-energy electron attachment at surfaces
Studies of the formation of negative ions at heated metal surfaces are reported under two experimental conditions: (1) laser desorption/ablation ionization and (2) heated metal wires in the presence of fluorine gas. In condition (1), nanoclusters of boron nitride/graphite are first produced by laser...
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Published in | International journal of mass spectrometry Vol. 205; no. 1; pp. 309 - 323 |
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Main Authors | , , |
Format | Journal Article |
Language | English |
Published |
Elsevier B.V
20.02.2001
|
Subjects | |
Online Access | Get full text |
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Summary: | Studies of the formation of negative ions at heated metal surfaces are reported under two experimental conditions: (1) laser desorption/ablation ionization and (2) heated metal wires in the presence of fluorine gas. In condition (1), nanoclusters of boron nitride/graphite are first produced by laser ablation of boron nitride mixed with graphite in a heated (∼1100 °C) rare gas followed by laser desorption negative ionization to yield a wide variety of cluster anions. The negative ion mass spectra for laser ablation/desorption ionization of small cluster ions from fullerenes, graphite, or most carbon containing metals (e.g. stainless steel) show common features (C
n
− for
n = 1 to ∼10, with even > odd alternation). The laser serves to heat the surface, produce clusters, and provides free and “quasifree” electrons for attachment and to dissociate larger negative ions/neutrals to produce low-mass cluster anions. Laser desorption of C
60H
36 and C
60F
48 at high laser power results in intense H
− and F
− ion signals, respectively. In the case of C
60H
36, the H
− ion production is attributed to dissociative electron attachment, i.e.
e + C
60H
36 → C
60H
35 + H
−. For the case of C
60F
48, both dissociative attachment and photodissociation of C
60F
48
− are believed responsible for the F
− ion yield. These observations form the basis for the development of intense pulsed ion sources of H
− and F
− ions for use in energy production (fuel injection into fusion reactors), spallation neutron devices, lithography, and other applications. In condition (2), heated metal wires of Al, Au, Au/Pd, Nb, Ni/Cr, Pt, Re, Ta, Ti, V, W, and Zr are “burned” in a low pressure vapor of fluorine gas (∼10
−4 Torr) resulting in a wide variety of molecular anions (e.g. Al
2F
9
−; AuF
2,3
−; NbF
6
−; ReF
5,6
−; TaF
6
−; Ti
4,5
−; VF
4,5
−; WF
5,6
−; ZrF
5
−, and Zr
2F
9
−) of varying intensity. Also of interest are the occurrences of F
3
− and the “impurity” ion Na
2F
3
−. |
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ISSN: | 1387-3806 1873-2798 |
DOI: | 10.1016/S1387-3806(00)00276-1 |