SECONDARY MOLECULAR ION EMISSION FROM ALIPHATIC POLYMERS BOMBARDED WITH LOW-ENERGY IONS - EFFECTS OF THE MOLECULAR-STRUCTURE AND THE ION-BEAM-INDUCED SURFACE DEGRADATION

The influence of the molecular structure on the secondary ion producti on is studied for three saturated aliphatic polymers (low-density poly ethylene, polypropylene and polyisobutylene) bombarded with low energy ions. These polymers differ only by the presence and nature of the pe ndant group. The intensities of the most characteristic secondary mole cular ions are followed as a function of the primary ion dose in the ( 10(12) ions/cm(2)-10(14) ions/cm(2)) range for two primary ion bombard ment conditions (4 keV Xe+ and 15 keV Ga+). The results show that ther e is a direct relationship between the polymer degradation and the emi ssion of molecular fragments. No truly ''static'' conditions are found , rather, the polymer surface undergoes a continuous transformation un der ion beam bombardment. The most spectacular effect is its dehydroge nation. By rationalizing the competition between the two related proce sses, surface degradation and molecular ion production, a kinetic mode l is proposed in order to explain the behavior of molecular fragments belonging to the C8 cluster.