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The secondary ion emission from amino acids evaporated onto clean metal surfaces under UHV conditions was investigated. Besides the well‐known quasimolecular ions (M±H)± and (M+Me)+, where Me stands for the substrate metal, a considerable (M+Me)- signal was detected additionally. For an alanine monolayer on Au the yields of (M+Au)+ and (M+Au)- were comparable while the Au-/Au+ intensity was greater than 103. Regarding Ni, the coadsorption with deuterium demonstrated that the amino acids are adsorbed intact. During glycine adsorption/desorption cycles a similar behavior of (M–H)- and (M+Ni)-, on one hand, and of (M+H)+ and (M+Ni)+, on the other, was observed. Both the (M+H)+ and the (M+Ni)+ formation required multilayer structures. In contrast to that, (M±H)± and (M+Au)± showed the same increase during glycine layer growth on Au. As many of these results cannot be explained by the models of organic ejection which are currently being discussed, it is believed that cluster dissociation processes are important in organic secondary ion formation, at least for the quasimolecular ions (M+Me)±.
Journal of Vacuum Science & Technology A: Vacuum, Surfaces, and Films (Volume:5 , Issue: 5 )
Date of Publication: Sep 1987