Surface Modification of Silicon at the Nanometer Scale

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In order to improve the efficiency and applicability of laser micro- and nano-strucutring of silicon, the interaction of silicon with single- and multi-pulsed radiation is comprehensively investigated by time-resolved metrology and theoretical simulations. We develop a hybrid atomistic-continuum multiscale model that combines several numerical techniques in a single mesoscopic computational approach. The model includes at least five physical phenomena: First, the MD part for describing the laser-induced transient states of matter at the atomic level. Second, the effect of laser-generated free carriers (the electron-hole pairs) accounted in continuum. Third, non-thermal phase transitions due to newly developed interatomic potential. Fourth, the effect of SPP excitation on the laser-energy deposition. And finally, the CGMD method for modeling of large volumes of matter under low excitation and smooth laser-induced phase transitions under local equilibrium conditions. Moreover, the obtained laser-induced structures constituting the final periodic patterns can be separately studied in ab-initio calculations subjects to their new optical properties. The theoretical simulations are supported by spectroscopic imaging pump-probe ellipsometry measurements, which enable the comprehensive determination of the complex refractive index upon irradiation. Therefore, the investigation of the Si surface restructuring processes and its transient optical properties can be seen as a successful implementation and interconnection of the following theoretical and experimental objectives: Theoretical objectives:1) Development of the theoretical description of the ultrashort laser-pulse interaction with semiconductors on the example with Si.2) Verification of the model predictions with the experimental measurements.3) Investigation of the role of non-thermal processes involved into the laser-induced phase transitions in Si.4) Development of the methodology of designing the experiment for functionalization of Si surface with demanded optical properties in IT-technologies.Experimental objectives:1) extend spectral range of pump probe setup into the UV.2) comprehensive investigation of transient complex refractive index n ̃(t,H,λ).3) develop optical gradient index model by complementary consideration of experiment and simulation.4) determine transient complex refractive index n ̃(t,H,λ) for multipulse irradiation for LIPSS formation.The project studies the transient state of Si as a representative of a large group of semiconductors. A number of results obtained in this project, therefore, can be extended to In, As, Ge, and other materials, highly demanded in microelectronics and nanotechnologies. The deep understanding of the laser-induced processes can result in ability of manipulation with the transient optical properties of Si and development of new generation of electronic devices at the nanoscale.