NOVEL GEOMETRICAL EFFECTS OBSERVED IN DEBRIS WHEN POLYMERS ARE LASER SPUTTERED

When polymers are sputtered with 248 or 308 nm laser pulses there are two generically different responses. The most straightforward is where the emitted particles expand outwards away from the target surface obeying, in so doing, the laws of one-dimensional adiabatic flow. The other is where the particles expand both outwards and sideways and, because a certain fraction recondenses on the target surface, there is a prominent deposit of debris lying around the bombarded spot. For spots with other than circular shape the debris show interesting symmetry in which there is rotation with respect to the spot. We show that this rotation occurs wholly through the laws of flow and we conclude, therefore, that the debris phenomenon is a purely gas-dynamic effect. It follows that the elimination of debris can be approached in gas-dynamic terms. We also show that the numerical extent of debris formation increases with the complexity of the particles involved, a result which suggests additional methods to control debris.