DESORPTION YIELDS USING keV POLYATOMIC PROJECTILES (original) (raw)

1989, Le Journal de Physique Colloques

RBsund. : Nous avons etudiO leemission d'ions negatifs . 4 partir d e cibles solides organiques bombardees par d e s ions moleculaires et d e s agregats atomiques. Nous presentons ici les resultats obtenus avec u n e cible d e phenylalanine. Nous avons utilise les projectiles organiques d e masse 73 + CSi (CH )+I , 147CSi (CH3 1 30Si (CH3)+ I, 309 tion moleculaire d u coronene +3 + CZ4Hi2 , 598 Cle dimsre d u coronene 2 ( M -H ) I, et les ions atomiquffi et + + + polyatomiques d e masse 133 CCsl , 393 CCsZIl, 653 CCs3IZ1 . C e s ions primaires ont etO produits e n bombardant u n e cible d e c o r o n h e e t d e CsI par d e s produits d e fission d u 252~f. Ensuite ces ions ont Bt12 accelerls et focalises sur l'&chantillon A etudier, D e s mesures d e temps d e vol sophistiqubes d e s ions primaires et secondaires ont &te execut&es avec u n systGme d'acquisition d e donnees speciales. TOUS les temps d e vol ont et12 enregistrfis simul tanement . L e rendement d e s ions mol@culaires d e phenylalanine a etrS etudie en fonction d e 1'Bnergie e t d e la masse d e s projectiles. U n e grande augmentation d u rendement est observee avec l'energie et la masse. Abstract : We have studied the negative secondary ion emission from solid organic targets bombarded by molecular ions and cluster ions. A s an example w e present here t h e results obtained with the compound phenylalanine-W e h a v e + used organic projectiles of mass 7 3 CSi (CH 1 1 , 147CSi (CH31JOSi (CH3)Zl+l 300 + Cmolecular ion of coronene C H 3 + , 598 C:oronene dimer 2(M-HI I , and atomic 24 iZ + + + and polyatomic ions of mass 133 CCsl, 393 CCsZIl , 653 CCs31Z3 . These primary ions h a v e been produced in t h e bombardment of targets of coronene and CsI by fission fragment from a 2 5 Z~f source. They were accelerated and focussed on the sample target. Sophisticated time of flight measurements of the primary and secondary ions have been performed with a special data acquisition system. All the time o f flight mass spectra were recorded at one. T h e secondary molecular ion yield of t h e phenilalanine (M-HI-= 164 h a s been studied a s a function o f t h e energy o f impact and of t h e mass o f t h e projectile. A large enhancement of the yield with the mass and the energy is observed. Article published online by EDP Sciences and available at http://dx.JOURNAL DE PHYSIQUE I NTKODUCTI ON Recently there has been much interest in the secondary ion emission from materials induced by cluster ion bombardment / I / . The incident cluster ions have velocities in three different regimes : greater than the Bohr velocity, v = 0.22 cm/nsec (fast), approximately equal to vo, and much less than 0 + phenylalanine desorbed by C 5 I is clearly seen. This new method o f time o f flight measurement allows t o extract several spectra from one single spectrum. The experimental conditions a r e kept the s a m e during the experiment (same target, s a m e detection...). t h e secondary ion yields d u e to the bombardment of the target by different kinds of projectiles can b e extracted from o n e experiment, The emission yield for a n ion of mass M is given by : NM i s t h e number o f counts in the peak of mass M in t h e TOF spectrum in coincidence with the primary ions. R e f e r e n c e s / 1 / See for example : J.P.Thomas, P.E.Filpus-Luyckx, M-Fallavier and E-A-Schweikert, Phsy. Rev. Lett. 5 5 ( 1 9 8 5 ) 103 ; M.'Salehpour, D-L-Fishel, J.E.Hunt, Int. J. M a s s