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Theses

Diamond photonic crystals for new bio-sensors

Abstract : Over the last years, the research on the label-free biosensor topic has experienced a very rapid growth because of the need to develop high-performing methods to detect and measure low concentrations of specific molecules in various fields. Among all the methods proposed, photonic crystals (PhC) structures offers a good alternative due to their sensitivity. Moreover, the use of diamond as material make the proposed device more attractive due to its optical properties, high chemical stability and efficiency of surface functionalization. In this context, this PhD thesis propose a new design of optical bio-sensor based on diamond two-dimensional photonic crystals, working at the wavelength near 800 nm.An original geometry of circular air holes arranged in squared lattice was chosen in order to maximize the sensitivity of such photonic structures to refractive index changes on their surface. It was analytically proven that modes with low group velocity are more sensitive to these variations. Numerical methods gave the necessary information to determine the optimal geometrical parameters of the PhC. The proposed design is based on measuring the shift of the angular reflectivity of a low group velocity guided mode resonance (GMR) PhC when probed with a single frequency light.Polycrystalline diamond films were grown on two different substrates, with thicknesses ranging from a few hundreds of nanometers to several micrometers. The technological processes required for the realization of PhC on polycrustalline diamond were developed or optimized, such as surface planarization by inductively coupled plasma (ICP) dry etching, diamond film transfer onto new substrate by wafer bonding process, diamond films thinning and surface patterning with PhC using Electronic Beam Lithography (EBL) and ICP methods.The samples realized in clean-room facilities were optically measured and the theoretical assumptions were validated. A GMR with a c/100 group velocity at a wavelength of 800 nm was measured and its sensitivity is estimated to be in the order of 500 degrees/ refractive index unit (°/RIU), a value that is one order of magnitude higher than the typical values encountered for sensors based on 2D PhC. These results represents a first step towards a highly sensitive bio-sensor, including a diamond surface functionalization for specific target recognition.
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Petru Borta. Diamond photonic crystals for new bio-sensors. Optics [physics.optics]. Université Paris Saclay (COmUE), 2019. English. ⟨NNT : 2019SACLS006⟩. ⟨tel-02014478⟩

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