Secondary ion emission from phosphatidic acid sandwich films under atomic and molecular primary ion bombardment

Secondary ion yields increase considerably when changing from atomic to mol ecular primary ions. Since secondary ion emission from deeper layers could result in a pronounced yield increase, the secondary ion emission depth of molecular fragments was investigated. A phosphatidic acid Langmuir-Blodgett (LB) sandwich system was applied. The well-defined layer structure of the applied sample allows the assignment of different depths of origin to the s elected fragment ions. At least 93% of the detected characteristic molecula r fragment ions originate from the first and second layers. This holds true for all applied atomic and molecular primary ions. (C) 2001 Published by E lsevier Science B.V.