SAMPLE AND PLUME LUMINESCENCE IN FAST HEAVY-ION-INDUCED DESORPTION

The luminescence arising in Cf-252-fission fragment induced desorption events has been measured using the time-correlated single photon coun ting technique. Photons emitted from the sample have been guided from a plasma desorption ion source to a photodetector by an optical fibre. Spectra and decay functions have been obtained using thin layers of C oronene or POPOP as samples. The results are strongly dependent on the acceleration field applied for ion extraction. Approximately 10 photo ns per fission fragment have been produced when applying no accelerati ng voltage. The results clearly show that these photons come from radi ative electronic relaxations of molecules in the solid sample. Conside rably more photons pet fission fragment have been produced when applyi ng a positive acceleration voltage, The intensity increases almost lin early for acceleration fields below 10 kV/cm and saturates at a nearly 10-fold higher value when compared to no acceleration. The intensity is also affected by the homogeneity of the accelerating field. These a dditional photons are attributed to radiative electronic relaxations o f desorbed neutral molecules in the plume excited by inelastic collisi ons with accelerated positive ions. No additional photons have been ob served when extracting negative ions. The negative ions produced do ob viously not hit and/or excite desorbed neutral molecules, presumably d ue to their specific desorption characteristics. The experimental data have been analyzed by comparing with the cw and time-resolved sample luminescence obtained by optical excitation. The findings demonstrate that valuable information on ion-solid interactions, on specific desor ption quantities and on processes in the plume can be obtained by meas uring and analyzing the luminescence induced by the impact of high ene rgy primary ions.