Near-field laser heating of solid samples for nano ablation modeling and experimental study
Résumé
In surface microanalysis with sampling by laser ablation (LIBS, LA-ICP-OES or LA-ICP-MS methods), spatial resolution is determined by laser beam diffraction limits (of the order of a laser wavelength) and thermal diffusion of a deposited heating energy during laser pulse duration (proportional to the square root of the pulse duration and matter diffusivity). Being limited by these features of a laser beam and heating energy, the best LIBS spatial resolution (the crater diameter) of 1 µm was obtained by ablation with the laser pulses of 266 nm wavelength and 4 ns duration [1-2].
One of the ways to improve spatial resolution of microanalysis may be suggested as the use of laser pulses of a lower wavelength ( 266 nm) and shorter pulse durations (ps and fs). Other ways to improve spatial resolution of surface analysis is laser ablation with a highly localized electromagnetic field produced by a tip near-field enhancement. In our studies, a tip of an atomic force microscope (AFM) was illuminated by the laser pulses of 266 nm wavelength and 4 ns duration, thus producing the craters of 100 nm diameters and of some nanometers of depth with Si-, Au- and Ta-samples [3].
The experiments were followed by extensive multi-parametric theoretical studies to analyze the effect of both matter properties (absorption, thermal conductivity and capacity) and electromagnetic field parameters (spatial distribution and pulse duration) on the resulted temperature field distribution T(r, t). The simulations were made with a home-developed “3D+t” heating model [4]. The simulation results [5] with particular features of solid sample heating by highly spatially localized laser field (10-100 nm) will be presented and discussed.