2010, Articolo in rivista, ENG
Pisanello F., Martiradonna L., Lemenager G., Spinicelli P., Fiore A., Manna L., Hermier J.P., Cingolani R., Giacobino E., De Vittorio M. and Bramati A.
We propose colloidal CdSe/CdS dots in rods as nonclassical sources for quantum information technology. Such nanoemitters show specific properties such as strongly polarized emission of on-demand single photons at room temperature, dipolelike behavior and mono-exponential recombination rates, making us envision their suitability as sources of single photons with well defined quantum states in quantum cryptography based devices.
2008, Articolo in rivista
Zanella, M; Falqui, A; Kudera, S; Manna, L; Casula, MF; Parak, WJ
Colloidal hybrid nanoparticles with blebs of II-VI and IV-VI particles on top of FePt particles were successfully grown. Whereas in the case of XE = CdS, ZnS, PbS and CdSe, FePt-XE dimer structures were successfully obtained, the growth failed for XE = ZnSe, PbSe. Structural, magnetic, and optical analysis of the structures revealed a moderate influence of the semiconductor domain on the magnetic properties of the FePt core particle, which can be ascribed to the effect of annealing conditions, atom diffusion and compositional variations during heterostructure formation. On the other hand, we report a significant fluorescence quenching of the semiconductor bleb due to the underlying FePt particle.
2008, Articolo in rivista
de Paiva, R; Di Felice, R
By means of plane-wave pseudopotential periodic-supercell density functional theory calculations with a gradient-corrected exchange-correlation functional, we investigated the formation and the electronic structure of thin Au overlayers on CdSe(0001) and CdSe(000 (1) over bar) surfaces. We explored several possible Au/CdSe interfaces, including nonstoichiometric cases in which the very interface layer is mixed, namely, contains atoms of both the metal and the semiconductor. The relative formation energies of the computed model structures indicate that the formation of a very thin Au layer on CdSe surfaces can be epitaxial in the very early deposition stages but only in rather Au-rich conditions. The analysis of the band structures, densities of states, and wave functions for the low-energy interfaces reveals that hybridization occurs between the metal and the semiconductor electron states. This hybridization is confined at the very interface and is not expected to have significant consequences on the plasmonic and excitonic excitations that are appealing for nanotechnology applications of metal-semiconductor nanoparticles.
2008, Articolo in rivista, ENG
Creti, A; Lomascolo, M; Leo, G; Manna, L; Anni, M
We quantitatively investigated, by time-resolved photoluminescence (PL) spectroscopy, the shell thickness dependence of exciton trapping and its effects on the PL quantum yield (QY) in colloidal CdSe/CdS/ZnS core/shell quantum rods. The defects passivation, due to a thin shell (0.6 monolayer), leads to a 2 times reduction of the trapping from both emitting and high-energy excited states, thus explaining the observed 4.3 times increase of the PL QY. Moreover, the QY decrease in the thick shell (1.3 monolayers) sample is fully explained in terms of increased trapping from the emitting states, which is ascribed to new defects caused by the strain relaxation at the core-shell interface. (C) 2007 Elsevier B.V. All rights reserved.
2007, Articolo in rivista
Kudera, S; Carbone, L; Carlino, E; Cingolani, R; Cozzoli, PD; Manna, L
The interest in research on inorganic colloidal nanoparticles has moved to more complex structures, such as anisotropically shaped particles and branched objects. Recently, schemes for the synthesis of heterostructures have also been presented. In this article we discuss the synthesis conditions for spherical and branched nanoparticles. The influence of parameters as temperature and composition of the mixture of surfactants on the shape of the growing particles is discussed. Also, an overview on different approaches for the formation of heterostructures is presented briefly. (C) 2006 Elsevier B.V. All rights reserved.
2006, Articolo in rivista, ENG
Carbone, Luigi; Kudera, Stefan; Giannini, Cinzia; MANNA, LIBERATO; CINGOLANI, ROBERTO; Cozzoli, Pantaleo Davide; Ciccarella, Giuseppe
A strategy to access several types of Au- tipped dumbbell- like nanocrystal heterostructures is presented, which involves the selective oxidation of either PbSe or CdTe sacrificial domains, initially grown on CdSe and CdS nanorods, with a Au( III) : surfactant complex. The formation of gold patches is supported by TEM, XRD and elemental analysis. This approach has allowed us to grow Au domains onto specific locations of anisotropically shaped nanocrystals for which direct metal deposition is unfeasible, as for the case of CdS nanorods. We believe that this strategy may be of general utility to create other types of complex colloidal nanoheterostructures, provided that a suitable sacrificial material can be grown on top of the starting nanocrystal seeds.
2006, Articolo in rivista
Carbone, L; Kudera, S; Carlino, E; Parak, WJ; Giannini, C; Cingolani, R; Manna, L
Branching in semiconductor nanocrystals, which leads to tetrapods and to more complex architectures, is the subject of intensive investigation. Here we support the model according to which branching in CdTe nanocrystals is driven by the formation of multiple wurtzite twins. This is in contrast to previous models for this material. We found that twinning, as well as anisotropic growth, can be triggered by the presence of suitable molecules, such as for instance methylphosphonic acid. In the case of CdTe nanocrystals, we designed a robust growth scheme in which the variation of a single parameter (the concentration of methylphosphonic acid in solution) leads to the controlled formation of nanocrystals with shapes ranging from spheres to anisotropic structures with varying level of branching, as both twinning and anisotropic growth are progressively favored. We believe that these concepts can be extended to other nanocrystal systems.
2006, Articolo in rivista
Cademartiri, L; Bertolotti, J; Sapienza, R; Wiersma, DS; von Freymann, G; Ozin, GA
High-quality PbS nanocrystals were produced in multigram-scale quantities through a solventless, heterogeneous, and relatively green route. The heterogeneous nature of this reaction allows one to limit the diffusion in the system, allowing for unprecedented monodispersity and quality of the product demonstrated by a full-width at half-maximum of the photoluminescence peak (PL fwhm) as low as 52 meV, a Stokes shift as low as 10 meV, and a quantum yield (QY) of 40%. The growth of the nanocrystals is interpreted in the framework of a diffusion-control led Ostwald growth in conditions of strong supersaturation.
2006, Articolo in rivista
Malkmus, S; Kudera, S; Manna, L; Parak, WJ; Braun, M
We present transient absorption studies with femtosecond time resolution on the electron-hole dynamics in CdTe tetrapod nanostructures. Electron-hole pairs are generated by optical excitation in the visible spectral range, and an immediate bleach and induced absorption signal are observed. The relaxation dynamics to the lowest excitonic state is completed in about 6 ps. Experiments with polarized excitation pulses give information about the localization of the excited-state wave functions. The influence of the nanocrystal shape on the optical properties of CdTe nanoparticles is discussed.
2006, Articolo in rivista
Kudera, S; Carbone, L; Zanella, M; Cingolani, R; Parak, WJ; Manna, L
Research on inorganic colloidal nanocrystals has moved from the synthesis of simple structures, such as spherical nanoparticles, to more elaborate particles with shapes such as rods, stars, discs, and branched nanocrystals, and recently to nanoparticles that are composed out of sections of different materials. Nanocrystal heterostructures represent a convenient approach to the development of nanoscale building blocks, as they merge sections with different functionality in the same particle, without the need of inorganic cross-linkers. The present article gives an overview of synthesis strategies to complex nanocrystals and will highlight their structural properties, as well as discuss some envisaged applications.
2006, Articolo in rivista, ENG
Carbone, L; Kudera, S; Giannini, C; Ciccarella, G; Cingolani, R; Cozzoli, PD; Manna, L
A strategy to access several types of Au- tipped dumbbell- like nanocrystal heterostructures is presented, which involves the selective oxidation of either PbSe or CdTe sacrificial domains, initially grown on CdSe and CdS nanorods, with a Au( III) : surfactant complex. The formation of gold patches is supported by TEM, XRD and elemental analysis. This approach has allowed us to grow Au domains onto specific locations of anisotropically shaped nanocrystals for which direct metal deposition is unfeasible, as for the case of CdS nanorods. We believe that this strategy may be of general utility to create other types of complex colloidal nanoheterostructures, provided that a suitable sacrificial material can be grown on top of the starting nanocrystal seeds.
2003, Articolo in rivista, ENG
Iadonisi, G and Cantele, G and Ramaglia, VM and Ninno, D
The single particle spectrum of a charged particle in a nanometric ellipsoidal quantum dot is calculated taking also into account the surface polarization effects. Furthermore the optical properties of the absorption coefficient also depending on the light polarisation are discussed and compared with the experimental data.
2001, Articolo in rivista, ENG
Cantele, G and Ninno, D and Iadonisi, G
The ground state of two conduction-band electrons confined in ellipsoidally shaped quantum dots has been calculated within the effective-mass approximation, using both a perturbative scheme and a variational approach. The problem is studied using prolate spheroidal coordinates, which allows us to exactly solve the single-particle problem and therefore to make a suitable ansatz for the two-electron variational wave function. The different contributions arising from the Coulomb repulsion and dielectric effects are calculated and discussed. The dot anisotropy is shown to strongly influence the electron-electron correlation.