Silicon nanowires (NWs) are attracting the interest of the scientific community as building blocks for a wide range of future nanoscaled devices for sensing, photovoltaic and photonic applications.
We demonstrate the synthesis of NWs by a cheap, fast and maskless approach compatible with Si technology, using metal-assisted chemical etching of Si substrates catalyzed by thin metallic layers.
NWs realized by this technique exhibit a very bright room temperature photoluminescence whose emission wavelength can be tuned with the NW diameter in agreement with the occurrence of quantum confinement effects.
Light emitting devices based on Si NWs showing an efficient room temperature electroluminescence at low voltage were also reported, opening the route towards low-cost, Si-based photonics.
Moreover, we fabricated low-cost multiwavelength light sources working at room temperature, achieved by combining Si NWs and carbon nanotubes (CNT). The NW/CNT hybrid systems exhibit a tunable emission both in the visible range, due to Si NWs, and in the IR range from CNTs.
We demonstrate the realization of 2D random fractal arrays of vertically aligned Si NWs by engineering the deposition of percolative Au layers that exhibit a fractal arrangement without the use of any lithographic processes by means of a low cost approach compatible with Si technology.
The Au fractal layers act as catalysts during the etching and transfer their complimentary fractal arrangement onto the Si NW arrays.
We were able to control and tune the optical properties of the system by realizing different fractal geometries through the optimization of the NW spatial arrangement .
Strong in-plane multiple scattering and efficient light trapping overall the visible range were observed due to the fractal structure, remarking thepromising potential of Si NWs for both photovoltaic and photonic applications.
We report the first experimental observation of coherent backscattering of Raman light from strongly diffusing Si nanowires. The Raman Coherent Backscattering (RCBS) arises from the constructive interference of inelastically scattered Raman radiation that undergoes to multiple scattering within the random network of Si NW arrays. The RCBS results are interpreted with a theoretical model of mixed Rayleigh-Raman random walks, exploiting the role of phase coherence in multiple scattering phenomena.
An innovative class of Si NW-based optical biosensors was realized by exploiting the detection of proteins over a wide range of concentrations as a function of the PL of NWs. We achieved tailored selectivity and ultra-high sensitivity down to the femtomolar limit, demonstrating the great potentialities of this material for biosensing.
1. Light: Science & Applications 5 (4), e16062, 2016
2. Nature Photonics, 11, pp 170–176, 2017