Investigation of tribo-chemistry by means of stable isotopic tracers: Mechanism for durability of monomolecular boundary film

A monomolecular film of octadecanoic acid on a Si(1 0 0) surface was prepared using a computer-controlled Langmuir trough. The tribological properties were acquired by a ball-on-flat type tribo-tester under reciprocating motion. Considerable effects of ball material on lifetime for low friction were observed; a glass ball was excellent while a steel ball was poor. The rubbed surfaces on ball and flat were studied by time-of-flight secondary ion mass spectroscopy. Transfer of the carboxylic acid and silicon onto the ball surface from the flat specimen was found. The role of the transferred acid that prolongs the lifetime of low friction was proposed. It should be emphasized that deuterium-labeled carboxylic acid makes the target of TOF-SIMS analysis clear.