Seeded growth of asymmetric binary nanocrystals made of a semiconductor TiO2 rodlike section and a magnetic gamma-Fe2O3 spherical domain

Asymmetric binary nanocrystals (BNCs), comprising one c-axis elongated anatase TiO2 section and one gamma-Fe2O3 spherical domain attached together, are synthesized by heterogeneous nucleation of iron oxide onto the longitudinal facets of TiO2 nanorods in a ternary surfactant mixture. The topologically controlled composition of the BNCs is ascertained by a combination of powder X-ray diffraction, Raman and M?ssbauer spectroscopy, high-angle annular dark-field imaging, and high-resolution transmission electron microscopy lattice fringe mapping, while their size-dependent magnetic behavior is demonstrated by ac susceptibility measurements. The heteroepitaxial growth proceeds through a mechanism never observed before for colloidal nanoheterostructures: the two domains share a restricted and locally curved junction region, which accommodates efficiently the interfacial strain and retards the formation of misfit dislocations. It is believed that these BNCs, which combine the properties of two technologically relevant oxide materials, can pave the way to reinforced applications in several fields of nanoscience, such as in photocatalysis, in malignant cell treatments, and in nanocrystal assembly.     

Hybrid junctions of zinc(II) and magnesium(II) phthalocyanine with wide-band-gap semiconductor nano-oxides: spectroscopic and photoelectrochemical characterization

The optical properties of zinc phthalocyanine (ZnIIPc) and magnesium phthalocyanine (MgIIPc) in DMSO and DMF solutions have been extensively investigated, and the photoelectrochemical behaviors of layer-by-layer hybrid junctions formed of the two metallo(II) phthalocyanines (MIIPcs) and wide-band-gap colloidal semiconductors, namely, ZnO and TiO2 nanocrystals (NCs), have been probed. Different experimental conditions, such as the Pc center metal ion, dye concentration, and solvent identity, were investigated in order to elucidate their effects on the photoelectrochemical performances of the prepared heterojunctions. Finally, thermal treatment of either dye and NC films and control of the NC shape and surface chemistry were also studied and, interestingly, were found to be critical in affecting the performance of photochemical sensitization processes, occurring at the dye/oxide and oxide/solution interfaces.     

Efficient charge storage in photoexcited TiO2 nanorod-noble metal nanoparticle composite systems

Following UV-illumination, TiO2 nanorod-stabilized noble metal (Ag, Au) nanoparticles dispersed in deaerated organic mixtures can sustain a higher degree of conduction band electron accumulation than that achievable with pristine titania.     

A novel analytical method for the BER evaluation in optical systemsaffected by parametric gain

A novel analytical method to evaluate the bit-error rate in optical links where the amplified spontaneous emission (ASE) noise at the receiver is a nonwhite random process is presented. The technique is used to estimate the impact of the nonlinear phenomenon called parametric gain on the performance of a wavelength-division-multiplexed (WDM) system. It is also compared with the Q-factor approximation, showing how this method may lead to significant errors     

UV‐Light‐Driven Immobilization of Surface‐Functionalized Oxide Nanocrystals onto Silicon

TiO₂ nanorods (NRs) and γ‐Fe₂O₃ nanocrystals (NCs) passivated with unsaturated long‐chain carboxylic acids, namely 10‐undecylenic acid (10UDA) and oleic acid (OLEA), are covalently anchored to Si(100) at room temperature by UV‐light‐driven reaction of hydrogenated silicon with the carbon–carbon double bond (–C?C–) moieties of the capping surfactants. The high reactivity of vinyl groups towards Si provides a general tool for attaching particles of both materials via Si–C bonds. Interestingly, TiO₂ NRs were efficiently attached to silicon even when capped by OLEA. This latter finding has been explained by a photocatalytic mechanism involving the primary role of hydroxyl radicals that can be generated upon bandgap TiO₂ photoexcitation with UV light. The increased oxide coverage achievable on Si opens access to further surface manipulation, as demonstrated by the possibility of depositing an additional film of Au nanoparticles onto TiO₂ via TiO₂‐catalyzed visible‐light‐driven reduction of aqueous AuCl₄^– ions. Extensive morphological and chemical characterization of the obtained NC‐functionalized Si substrates is provided to support the effectiveness of proposed photochemical approaches.     

The identification by Raman microscopy and X-ray diffraction of iron-oxide pigments and of the red pigments found on Italian pottery fragments

The technique of Raman microscopy has been used to identify and characterise the pigments used in red shards of medieval and earlier items of pottery which have been found in various archaeological sites in the South of Italy. The research has led to the identification, on the basis of their characteristic Raman/resonance Raman spectra, of the red pigments as iron(III) oxide (e.g. Indian Red, Red Ochre or Venetian Red) and the yellow pigments as hydrated iron(III) oxyhydroxide (e.g. Yellow Ochre and Mars Yellow). X-ray powder diffraction experiments confirm the conclusions drawn above.     

High-Efficiency FRET Processes in BODIPY-Functionalized Quantum Dot Architectures

Efficient FRET systems are developed combining colloidal CdSe quantum dots (QDs) donors and BODIPY acceptors. To promote effective energy transfer in FRET architectures, the distance between the organic fluorophore and the QDs needs to be optimized by a careful system engineering. In this context, BODIPY dyes bearing amino-terminated functionalities are used in virtue of the high affinity of amine groups in coordinating the QD surface. A preliminary QD surface treatment with a short amine ligand is performed to favor the interaction with the organic fluorophores in solution. The successful coordination of the dye to the QD surface, accomplishing a short donor–acceptor distance, provides effective energy transfer already in solution, with efficiency of 76 %. The efficiency further increases in the solid state where the QDs and the dye are deposited as single coordinated units from solution, with a distance between the fluorophores down to 2.2 nm, demonstrating the effectiveness of the coupling strategy.     

Performance Analysis of Coherent 222-Gb/s NRZ PM-16QAM WDM Systems Over Long-Haul Links

We studied by simulation the nonlinear propagation of 222-Gb/s (27.75 GBaud) wavelength-division-multiplexing coherent nonreturn-to-zero polarization-multiplexed 16 quadrature amplitude modulation systems over long-haul links, considering both standard single-mode fiber (SSMF) and nonzero dispersion-shifted fiber. Many different dispersion maps, including precompensation, were explored to try and mitigate the impact of propagation impairments. Full electronic dispersion compensation without in-line dispersion-compensating units (DCUs) granted best performance with a system reach on SSMF fiber of ten spans with a span loss 23 dB. The presence of DCUs, as in lines designed for legacy 10-Gb/s intensity-modulated direct-detection systems, enhances nonlinear propagation penalties and the use of precompensation does not grant a significant advantage. A practical reach of 500–800 km can be estimated, when system margins are factored in .      

Suppression of spurious tones induced by the split-step method infiber systems simulation

Numerical approximations involved in solving the nonlinear Schrodinger equation using the split-step method may cause the generation of spurious spectral peaks which can be seen as fictitious four-wave mixing. In this letter, we present a new method for reducing and controlling such simulation artifacts by properly choosing the spatial step size     

Cover Picture: An Epoxy Photoresist Modified by Luminescent Nanocrystals for the Fabrication of 3D High‐Aspect‐Ratio Microstructures (Adv. Funct. Mater. 13/2007)

M. Lucia Curri and co‐workers report on p. 2009 an epoxy‐based negative tone photoresist that can be functionalized with red emitting CdSe@ZnS core/shell type nanocrystals and patterned by UV lithography. The 3D high aspect ratio of the microfabricated structures proves that lithographic properties of the functional nanocomposite are retained and the nanocrystals properties conveyed into the resist. The emitting nanocomposite represents a convenient model for material functionalization expandable to nanocrystals with different properties. An epoxy‐based negative‐tone photoresist, which is known as a suitable material for high‐aspect‐ratio surface micromachining, is functionalized with red‐light‐emitting CdSe@ZnS nanocrystals (NCs). The proper selection of a common solvent for the NCs and the resist is found to be critical for the efficient incorporation of the NCs in the epoxy matrix. The NC‐modified resist can be patterned by standard UV lithography down to micrometer‐scale resolution, and high‐aspect‐ratio structures have been successfully fabricated on a 100 mm scaled wafer. The “as‐fabricated”, 3D, epoxy‐based surface microstructures show the characteristic luminescent properties of the embedded NCs, as verified by fluorescence microscopy. This issue demonstrates that the NC emission properties can be conveniently conveyed into the polymer matrix without deteriorating the lithographic performance of the latter. The dimensions, the resolution, and the surface morphology of the NC‐modified‐epoxy microstructures exhibit only minor deviations with respect to that of the unmodified reference material, as examined by means of microscopic and metrologic investigations. The proposed approach of the incorporation of emitting and non‐bleachable NCs into a photoresist opens novel routes for surface patterning of integrated microsystems with inherent photonic functionality at the micro‐ and nanometer‐scale for light sensing and emitting applications.