Analytical and Experimental Investigation of Laser-Microsphere Interaction for Nanoscale Surface Modification

An analytical and experimental investigation on the features created on silicon by the irradiation of microspheres on the substrate surface with a pulsed laser is presented. Silica microspheres of $1.76μm$ diameter are deposited on the silicon substrate and are irradiated with a pulsed Nd:YAG laser of wavelength $532nm$⁠. An analytical model based on Mie theory is developed, which includes all evanescent terms and does not rely on either far-field or size-parameter approximations. The predicted intensity distributions on the substrate indicate a strong near-field enhancement confined to a very small area (nanometer scale). A multidimensional, numerical model was built to simulate the heat transfer through the silicon. An explicit scheme of the enthalpy method was employed to track the solid∕liquid phase boundary. The experiment was performed for various laser energies used in the modeling, and the features obtained are characterized using a scanning electron microscope. The experimental results correlate well with the predicted results.