1,721,533 research outputs found
Projecting the nanoworld: concepts, results and perspectives of molecular electronics
No full textA bottom-up approach is a promising alternative to build nanodevices and/or nanomachines starting from molecular building blocks. The idea of molecular electronics comes from a farsighted paper by Aviram and Ratner, predicting that single molecules with a donor-spacer-acceptor structure would have rectifying properties when placed between two electrodes. Today, molecular electronics is emerging as an alternative to Si-nanoelectronics for building integrated devices. This review aims to give an overview of this emerging field, analysing the concepts, the key results and the perspectives
Modal selective tuning in a photonic crystal cavity
No full textWe present a way to selectively tune the properties of the degenerated modes confined in a single point defect two-dimensional photonic crystal cavity based on a triangular lattice of air holes. We investigate the dependence of the modal properties of the resonator on the position of the first neighbor holes, showing that it is possible to finely tune the resonant frequency of only one of these two modes and to increase the quality factor of the mode that has no frequency shift. This is achieved by controlling the wavevector components inside the cavity. This approach is a viable strategy for the development and the optimization of several innovative devices based on bi-modal cavity arrays, such as arrays of integrated optical filters and optical read-out sections for biosensing applications
Bragg reflector by means of the form birefringence effect in dielectric rings
No full textIn this work, form birefringence physics and the mechanisms of Si/SiO2 dielectric concentric optical rings are investigated. The optical rings are modeled by means of a Bragg reflector. Similarly to a negative uniaxial crystal, the dielectric concentric pattern admits two preferred propagation directions defined by an extraordinary and an ordinary refractive index representing two field polarizations. The circular grating profile splits the electromagnetic field into a radial (extraordinary field) and a tangential (ordinary field) component which represent two modes of the periodic structure. These two modes are characterized by the refractive index ellipse obtained by the Huygens principle. The model is developed through the wave front propagation inside the anisotropic structure. The Bragg theory and conservation of momentum vectors provide the Bragg angles of the ordinary and extraordinary rays for different optical wavelengths. The Bragg theoretical model is validated by the finite difference time domain (FDTD) approach for a wavelength of λ = 0.98 μ m
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