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Silicon nanowires: synthesis, optical properties and biosensing applications.
Semiconductor nanowires (NW) are currently attracting the interest of a wide scientific community for cutting-edge applications in photonics, sensing and photovoltaics. Using percolative Au layers that exhibit a fractal arrangement as the catalyst of a metal-assisted wet etching process, we achieved a 2D random fractal array of vertically aligned Si NW, realized without any lithographic process. By designing different fractal textures through the optimization of NW size and spatial arrangement, we were able to control and tune the optical properties of the system. Strong in-plane multiple scattering and efficient light trapping related to the fractal structure were observed. NW achieved by this technique exhibited a very bright room temperature PL, tunable with NW size in agreement with the occurrence of quantum confinement effects. Light emitting devices based on Si NW, showing an efficient room temperature EL at low voltage, were also reported. By exploiting the impressive aspect ratio of the NW array, we realized an innovative Si NW-based optical biosensor, which exploits the PL properties for the detection of proteins in a wide range of concentrations, down to the femtomolar limit, attesting also the great potentiality of this material for biosensing.