Publications

2005
Eli Rothenberg, Miri Kazes, Ehud Shaviv, and Uri Banin. 2005. “Electric field induced switching of the fluorescence of single semiconductor quantum rods.” Nano letters, 5, 8, Pp. 1581-1586. Publisher's Version Abstract

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The exceptional fluorescence properties of single CdSe quantum rods (QRs) arising from internal and external electric fields are studied. Reversible external field induced switching of the emission in single QRs is reported for the first time. This effect was correlated with local field induced emission intensity reduction and newly observed darkening mechanism. Bimodal spectral jumps under a zero field were also observed and assigned to charged exciton emission, a phenomenon that was likewise directly controlled through an external field. These phenomena point to the use of single QRs as spectrally tunable charge sensitive fluorophores with polarized emission in fluorescence tagging and optical switching applications.

Taleb Mokari, Claudia G Sztrum, Asaf Salant, Eran Rabani, and Uri Banin. 2005. “Formation of asymmetric one-sided metal-tipped semiconductor nanocrystal dots and rods.” Nature Materials, 4, 11, Pp. 855-863. Publisher's Version Abstract

Multicomponent nanoparticles represent a new approach for creating smart materials, requiring the development of the growth of different material types on one particle. Here, we report the synthesis of asymmetric metal–semiconductor heterostructures where gold is grown on one side of CdSe nanocrystal quantum rods and dots, creating nanostructures offering intrinsic asymmetry for diverse device functionalities such as diode elements, along with one-sided chemical accessibility through the gold tips. Surprisingly, one-sided growth is preceded by two-sided growth and is generally observed in different particle shapes. Theoretical modelling in a lattice-gas model and experimental analysis show that a ripening process drives gold from one end to the other, transforming two-sided growth to one-sided growth. Ripening is therefore occurring on the nanostructure itself, leading to a phase-segregated structure. This thereby extends the realm of ripening phenomena and their significance in nanostructure synthesis, in particular for nanocrystals composed of different materials.

Dan T Fuchs, Ronen Rapaport, Gang Chen, Ylva K Olsson, Vikram C Sundar, L Lucas, S Vilan, Assaf Aharoni, Uri Banin, and Jonathan S Steckel. 2005. “Making waveguides containing nanocrystalline quantum dots”. Publisher's Version Abstract

A new material platform is described that enables inclusion of nanocrystalline quantum dots into a polymer. This technology is compatible with semiconductor processing and may enable integration of active materials into current waveguide technologies. We describe the steps preformed to fabricate a waveguide chip that contains IR-emitting quantum dots. Optical tests demonstrate guiding and preservation of the quantum dots optical properties through the processing steps. Time resolved optical measurements indicate presence of gain in the InAs quantum dot impregnated polymer.

Gang Chen, Ronen Rapaport, Dan T Fuchs, Leah Lucas, Andrew J Lovinger, Sahar Vilan, Assaf Aharoni, and Uri Banin. 2005. “Optical gain from InAs nanocrystal quantum dots in a polymer matrix.” Applied Physics Letters, 87, 25, Pp. 251108. Publisher's Version Abstract

We report on the observation of optical gain from InAs nanocrystal quantum dots which emit at 1.55microns1.55microns and are imbedded in a novel polymer platform. The measurements are based on a three-beam time resolved pump-probe technique, which enables extracting the intrinsic gain cross section, lifetime, and recovery time. These experiments are another step toward the realization of active optical devices based on InAs nanocrystals.

Olga Solomeshch, Ariel Kigel, Aldona Saschiuk, Vlad Medvedev, Assaf Aharoni, Alexey Razin, Yoav Eichen, Uri Banin, Efrat Lifshitz, and Nir Tessler. 2005. “Optoelectronic properties of polymer-nanocrystal composites active at near-infrared wavelengths.” Journal of Applied Physics, 98, 7, Pp. 074310. Publisher's Version Abstract

We report a systematic study of the optoelectronic processes occurring in composites made of near-infrared (IR) emitting nanocrystals and conjugated polymers. We focus on PbSe and InAs/ZnSe blended with polyphenylenevinylene-type polymers. We find that the process responsible for quenching the visible luminescence of the polymer by the nanocrystal varies depending on the nanocrystal composite. Moreover, the high (66%) energy-transfer efficiency from the polymer to the PbSe nanocrystal does result in significant emission at the near IR. Our measurements suggest that the host may be doping the PbSe nanocrystal, thus making the nonradiative Auger process favorable. For InAs we find the energy levels well aligned inside the polymer band gap, making it an efficient charge trap which acts as a luminescence center. Through two-dimensional numerical modeling of the charge transport in such composite films we highlight the importance of morphology (nanocrystal distribution) control.

Ron Gill, Itamar Willner, Itzhak Shweky, and Uri Banin. 2005. “Fluorescence resonance energy transfer in CdSe/ZnS− DNA conjugates: probing hybridization and DNA cleavage.” The Journal of Physical Chemistry B, 109, 49, Pp. 23715-23719. Publisher's Version Abstract

Nucleic-acid-functionalized CdSe/ZnS quantum dots (QDs) were hybridized with the complementary Texas-Red-functionalized nucleic acid. The hybridization was monitored by following the fluorescence resonance energy transfer from the QDs to the dye units. Treatment of the QD/dye DNA duplex structure with DNase I resulted in the cleavage of the DNA and the recovery of the fluorescence properties of the CdSe/ZnS QDs. The luminescence properties of the QDs were, however, only partially recovered due to the nonspecific adsorption of the dye onto the QDs. Similarly, nucleic-acid-functionalized Au nanoparticles (Au NPs) were hybridized with the complementary Texas-Red-labeled nucleic acid. The hybridization was followed by the fluorescence quenching of the dye by the Au NPs. Treatment of the Au NP/dye DNA duplex with DNase I resulted in the cleavage of the DNA and the partial recovery of the dye fluorescence. The incomplete recovery of the dye fluorescence originated from the nonspecific binding of the dye units to the Au NPs. The nonspecific binding of the dye to the CdSe/ZnS QDs and the Au NPs is attributed to nonprotected surface vacancies in the two systems.

Taleb Mokari, Claudia G Sztrum, Asaf Salant, Eran Rabani, and Uri Banin. 2005. “Formation of asymmetric one-sided metal-tipped semiconductor nanocrystal dots and rods.” Nature Materials, 4, 11, Pp. 855. Publisher's Version Abstract

figure2

Multicomponent nanoparticles represent a new approach for creating smart materials, requiring the development of the growth of different material types on one particle. Here, we report the synthesis of asymmetric metal–semiconductor heterostructures where gold is grown on one side of CdSe nanocrystal quantum rods and dots, creating nanostructures offering intrinsic asymmetry for diverse device functionalities such as diode elements, along with one-sided chemical accessibility through the gold tips. Surprisingly, one-sided growth is preceded by two-sided growth and is generally observed in different particle shapes. Theoretical modelling in a lattice-gas model and experimental analysis show that a ripening process drives gold from one end to the other, transforming two-sided growth to one-sided growth. Ripening is therefore occurring on the nanostructure itself, leading to a phase-segregated structure. This thereby extends the realm of ripening phenomena and their significance in nanostructure synthesis, in particular for nanocrystals composed of different materials.

Oded Millo, Dov Steiner, David Katz, Assaf Aharoni, ShiHai Kan, Taleb Mokari, and Uri Banin. 2005. “Transition from zero-dimensional to one-dimensional behavior in InAs and CdSe nanorods.” Physica E: Low-dimensional Systems and Nanostructures, 26, 1-4, Pp. 1-8. Publisher's Version Abstract

Tunneling and optical spectroscopy performed on InAs nanorods 7–25 nm long, reveal a clear dependence of the band gap on length. This (zero-dimension like) behavior is different from that of CdSe rods, where the band gap is nearly independent of length, a signature of quasi-one-dimensionality. The transition between these two regimes is governed by the ratio between the Bohr radius and the nanorods length. The gaps measured by tunneling spectroscopy are larger than the optical gaps by a factor that depends on the tunneling configuration. This is attributed to a combination of the Coulomb interaction and the voltage division between the two tunnel junctions in the STM experiment. However, the tunneling gaps were found to reduce in dense aggregates of rods.