STh4K.3.pdf CLEO:2016 © OSA 2016 Self-assembling of Gold Nanoparticles on Si-based Laser Nanotextured 1D Surface for Plasmonic Application I. Gnilitskyi 1 , M. Dusheyko 2 , T. Borodinova 3 , S. Mamykin 4 , N. Maksimchuk ², A. Ivaschuk 2 , Yu.Yakymenko 2 and L. Orazi 1 1 - University of Modena and Reggio Emilia, Reggio Emilia, Italy 2 - National Technical University of Ukraine “Kiev Polytechnic Institute”, Kyiv, Ukraine 3 - Institute of Biocolloid Chemistry, National Academy of Sciences of Ukraine, Kyiv, Ukraine 4 - V. E. Lashkaryov Institute of Semiconductor Physics, National Academy of Sciences of Ukraine, Kyiv, Ukraine iaroslav.gnilitskyi@unimore.it Abstract: Excitation of surface plasmon resonances has been observed on laser-induced highly- regular 1D periodic Si surface covered with Au nanoparticles. The nanostructured surfaces open new perspectives for production of photonic and plasmonic sensor elements. OCIS codes: (240.6680) Surface plasmons; (220.4241) Nanostructure fabrication; (240.5420) Plasmonics; 1. Introduction Nanoscale metal structures (e.g., dots and nanowires) assembled into one-dimensional (1D) or two-dimensional (2D) periodic arrangements similar to diffraction gratings exhibit anomalous optical extinction for visible light. This property is associated with the unique ability of regular periodic configurations to support specific surface waves [1,2]. Au nanoparticles organized into periodic 1D array support two types of fundamental electromagnetic modes: surface plasmon-polaritons (SPP) characteristic of a periodic system of nanoparticles; and surface plasmon (SP) excitation attributed to individual nanoparticles. Due to strong resonant properties of those waves, sensors based on SP and SPP are widely used to detect small changes in refractive indices of the environment in bio- and chemical sensor systems [3]. Fabrication of diffraction-grating type substrates for deposition of nanoparticles is still a quite complicated and expensive stage of sensor production. A few methods are used to improve manufacturing technology for this stage and reduce its cost, e. g., microcontact printing and selective etching of semiconductor substrate by imprinting a pattern created by interface of laser beams. We propose to use highly-regular laser-induced periodic surface structures (HR- LIPSS) produced by direct ablation of semiconductor substrate by femtosecond laser. HR-LIPSS result from local superheating followed by ablation and provide low-cost single-step technique which allows to cover a large area surface of virtually any material by highly periodic nanostructures. 2. Proposed method, experiment details, and results Here we report the creation of photonic structure on Si substrates by HR-LIPSS. Key features of this approach such as superior uniformity and ability to process non-flat surfaces directly result from interference between incident laser beam and surface electromagnetic waves (SEW). Applications of LIPSS nanostructures have been reported for various fields including electronics, optoelectronics, and mechanics [4,5] although the problems of material and process control and optimization of output have not been completely resolved. Treatment of virtually indefinitely large areas at unprecedented high speed and quality is feasible by usage of both galvoscanner and motorized stage. This approach to the technology of LIPSS generation is highly suitable for transfer to industrial applications. The structures presented below were manufactured in 3 steps and combined a p-n junction, HR-LIPSS, and gold nanoparticles deposited on peaks of LIPSS. First, a shallow p-n junction was formed in p-type Si (111) wafer by diffusion of phosphorus followed by removal of oxide layer from the polished side of the wafer. The depth of p-n junction was about 100 nm and sheet resistivity was 90 Ω/sq. Second, HR-LIPSS were etched by femtosecond pulses on the silicon substrate to the depth small enough to avoid destruction of the p-n junction. Third, gold nanoparticles were deposited on the Si substrate covered with LIPSS by 3 methods. Each of the methods delivered nanoparticles of specific shape varying from spheres to triangular and/or hexagonal nanoprisms and nanowires. Shape and dimensions of the nanoparticles were controlled by composition of reducing chemical agent of ions of gold and the stabilizer of gold nanoparticles, temperature and time synthesis of nanoparticles. Optical properties of Si-nanotextured samples covered with gold nanoparticles were experimentally characterized by spectral and angular dependence of polarized-light reflection in the wavelength range 0.4÷1.1 µm and angles of incidence varied from 10° to 70°. Those measurements allowed building dispersion curves of excited optical modes and to identifying their type. Using expressions (1) & (2), the dispersion curves of SPPs excited at metal-air or metal-substrate interfaces are