Femtosecond laser ablation (fs-LA) XPS - A novel XPS depth profiling technique for thin films, coatings and multi-layered structures

Sputter depth profiling has been employed for XPS/AES depth profiling since the late 1960s. However, for many materials, ion beam induced damage distorts the chemical state information and chemical composition, limiting the value of the analysis. A novel methodology is presented in which XPS depth profiles are generated using a 160 fs pulse length, 1030 nm peak wavelength femtosecond laser in place of the traditional ion gun. Femtosecond laser ablation (fs-LA) XPS depth profiles are compared with argon monatomic and cluster ion beam depth profiles for different classes of materials, including ceramics, semiconductors, polymers and metals. In all cases, the XPS spectra recorded following femtosecond laser ablation are fully representative of the original chemical composition and chemical state, with no ablation induced damage. The technique is also shown to be very versatile with ablation rates of <20 nm per pulse being achieved for thin films but profiles to depths of >30 mu m are also realisable in practical time scales. fs-LA XPS depth profiling promises to be a very exciting new methodology for the XPS community, complementing sputter depth profiling but avoiding the chemical damage induced by ion beams and offering valuable new depth profiling capabilities.