Studies of low-energy electron attachment at surfaces

Studies of the formation of negative ions at heated metal surfaces are repo rted under two experimental conditions: (1) laser desorption/ablation ioniz ation and (2) heated metal wires in the presence of fluorine gas. In condit ion (1), nanoclusters of boron nitride/graphite are first produced by laser ablation of boron nitride mixed with graphite in a heated (similar to 1100 degreesC) rare gas followed by laser desorption negative ionization to yie ld a wide variety of cluster anions. The negative ion mass spectra for lase r ablation/desorption ionization of small cluster ions from fullerenes, gra phite, or most carbon containing metals (e.g. stainless steel) show common features (C-n(-) for n = 1 to similar to 10, with even > odd alternation). The laser selves to heat the surface, produce clusters, and provides free a nd "quasifree" electrons for attachment and to dissociate larger negative i ons/neutrals to produce low-mass cluster anions. Laser desorption of C60H36 and C60F48 at high laser power results in intense H- and F- ion signals, r espectively. In the case of C60H36, the H- ion production is attributed to dissociative electron attachment, i.e. e + C60H36 --> C60H35 + H-. For the case of C60F48, both dissociative attachment and photodissociation of C60F4 8- are believed responsible for the F- ion yield. These observations form t he basis for the development of intense pulsed ion sources of H- and F- ion s for use in energy production (fuel injection into fusion reactors), spall ation 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, an d Zr are "burned" in a low pressure vapor of fluorine gas (similar to 10(-4 ) Torr) resulting in a wide variety of molecular anions (e.g. Al2F9-; AuF2. 3-; NbF6-; ReF5.6-; TaF6-; Ti-4.5(-); VF4.5-; WF5.6-; ZrF5- and Zr2F9-) of varying intensity. Also of interest are the occurrences of F-3(-) and the " impurity" ion Na2F3-. (Int J Mass Spectrom 205 (2001) 309-323) (C) 2001 Els evier Science B.V.