Detection of trace substances adhered to a metal surface by laser-induced breakdown spectroscopy

Laser-induced breakdown spectroscopy (LIBS) was applied to inspect trace substances on aluminum alloy surfaces. Silicone oil, which is often used as a release agent, was employed as the adhered substance. Nanosecond laser pulses at UV wavelengths (KrF laser, lambda = 248 nm) were employed for the LIBS measurements. Although the absorption of silicone oil at 248 nm was negligible, the Si emission of surface-adhered silicone oil was detected. The intensity ratio of the Si emission at 288 nm to the Al emission at 309 nm increased with increasing surface concentrations in the range 1-35 mu g cm(-2), and a linear dependence on the silicone oil surface concentration was observed at low surface concentrations (<5.0 mu g cm(-2)). The limit of detection was evaluated to be 1.18 mu g cm(-2).