Narrow Results

This presentation is a short review of some scientific insights on the possibilities of photonic applications of nanostructured silicon (NS–Si), porous Si(p-Si) and Si nanocrystals (NC–Si), one of the most interesting problems in nano-crystallite physics. The emission mechanism of a very bright photo-luminescence (PL) band and relatively weak electro-luminescence (EL) are presently the main issue. The basic question lies in whether the emission is an extrinsic or intrinsic property of nanocrystals. It is important from a fundamental physics viewpoint because of the potential application of Si wires and quantum dots in optoelectronic devices and information technology. Nanostructuring silicon is an effective way to turn silicon into a photonic material. It is observed that low-dimensional (one and two dimensions) silicon shows light amplification, photon confinement, photon trapping as well as non-linear optical effects. There is strong evidence of light localization and gas sensing properties of such nanostructures. Future nano-technology would replace electrical with optical interconnects, which has appealing potential for higher-speed performance and immunity to signal cross talk.

The classic Grangier et al. (1996) experiment is revisited to suggest an alternative model of a single photon. Photon-counting experiments using spontaneous parametric down conversion (SPDC) show that not every single-photon incident on a detector triggers it, and that coincident triggering of detectors can occur during a single gate. The latter is usually interpreted as being caused by spurious photons entering the gate from different SPDC events. However, a pseudo-classical-type model is suggested which dispenses with these intruder photons. Here, a single-photon manifests as a transversely-iterated front of non-rotating screw threads. Each advancing thread has the potential to trigger a detector, and each allows the transfer of spin angular momentum (SAM). On exiting a beam splitter, a single-photon front can produce multiple triggering of detectors on different parts of the front with a probability of at most $5.02\times {10}^{-5}-3.54\times {10}^{-4}$ for the experiments presented.

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The tremendous potential for the manifold applications of porphyrins, porphyrazines, and phthalocyanines derives from their photophysical and electrochemical properties, their remarkable stability, and their predictable and rigid structure. These applications include nonlinear optics, catalysts, sensors, actuators, molecular sieves, and therapeutics. All of these properties are modulated by appending various chemical moieties onto the macrocycles, by choice of metallo derivative, and by the choice of environment. In multichromophoric systems, furthermore, the relative orientation of the chromophores, the nature of the linker, and the size of the system also dictate the properties. The synthesis of multichromophoric systems – both via covalent and noncovalent linkers – is driven by the desire to make new materials and to understand biological processes such as the various aspects of photosynthesis. Though electron and energy transfer processes continue to drive the synthesis of ever more complex systems, more recent focus has shifted toward other applications and functionalities of these structures. The focus of this perspective is on four recent developments in formation and characterization of functional, porphyrinic materials and devices: (1) self-assembly and self-organization of porphyrin arrays and aggregates into phototransistors and photonic devices; (2) self-assembled porphyrin squares for sensors, sieves, and catalysts; (3) covalently bound arrays of different chromophores as photonic materials; and (4) spatially separated arrays of metalloporphyrins as cross-reactive sensors.