Publications

2015
Chunfan Yang, Itay Gdor, Yorai Amit, Adam Faust, Uri Banin, and Sanford Ruhman. 2015. “Exciton dynamics in Cu-doped InAs colloidal quantum dots.” In Ultrafast Phenomena XIX, Pp. 267-270. Springer.
Reut Timor, Hana Weitman, Nir Waiskopf, Uri Banin, and Benjamin Ehrenberg. 2015. “PEG-phospholipids coated quantum rods as amplifiers of the photosensitization process by FRET.” ACS applied materials & interfaces, 7, 38, Pp. 21107-21114. Publisher's Version Abstract

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Singlet oxygen (1O2) generated upon photostimulation of photosensitizer molecules is a highly reactive specie which is utilized in photodynamic therapy. Recent studies have shown that semiconductor nanoparticles can be used as donors in fluorescence resonance energy transfer (FRET) process to excite attached photosensitizer molecules. In these studies, their unique properties, such as low nanoscale size, long-term photostability, wide broad absorbance band, large absorption cross section, and narrow and tunable emission bands were used to provide advantages over the traditional methods to produce singlet oxygen. Previous studies that achieved this goal, however, showed some limitations, such as low FRET efficiency, poor colloidal stability, nonspecific interactions, and/or complex preparation procedure. In this work, we developed and characterized a novel system of semiconductor quantum rods (QRs) and the photosensitizer meso-tetra(hydroxyphenyl) chlorin (mTHPC), as a model system that produces singlet oxygen without these limitations. A simple two-step preparation method is shown; Hydrophobic CdSe/CdS QRs are solubilized in aqueous solutions by encapsulation with lecithin and PEGylated phospholipid (PEG–PL) of two lipid lengths: PEG350 or PEG2000. Then, the hydrophobic photosensitizer mTHPC, was intercalated into the new amphiphilic PEG–PL coating of the QR, providing a strong attachment to the nanoparticle without covalent linkage. These PEGylated QR (eQR)–mTHPC nanocomposites show efficient FRET processes upon light stimulation of the QR component which results in efficient production of singlet oxygen. The results demonstrate the potential for future use of this concept in photodynamic therapy schemes.

 

Ido Hadar, Tsafrir Abir, Shira Halivni, Adam Faust, and Uri Banin. 2015. “Size‐Dependent Ligand Layer Dynamics in Semiconductor Nanocrystals Probed by Anisotropy Measurements.” Angewandte Chemie, 127, 42, Pp. 12640-12644.
Uri Banin and JIA Guohua. 2015. “Colloidal semiconductor metal chalcogenide nanostructures.” United States of America.
Yuval Ben‐Shahar, Francesco Scotognella, Nir Waiskopf, Ilka Kriegel, Stefano Dal Conte, Giulio Cerullo, and Uri Banin. 2015. “Effect of surface coating on the photocatalytic function of hybrid CdS–Au nanorods.” Small, 11, 4, Pp. 462-471. Publisher's Version Abstract

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Hybrid semiconductor–metal nanoparticles are interesting materials for use as photocatalysts due to their tunable properties and chemical processibility. Their function in the evolution of hydrogen in photocatalytic water splitting is the subject of intense current investigation. Here, the effects of the surface coatings on the photocatalytic function are studied, with Au‐tipped CdS nanorods as a model hybrid nanoparticle system. Kinetic measurements of the hydrogen evolution rate following photocatalytic water reduction are performed on similar nanoparticles but with different surface coatings, including various types of thiolated alkyl ligands and different polymer coatings. The apparent hydrogen evolution quantum yields are found to strongly depend on the surface coating. The lowest yields are observed for thiolated alkyl ligands. Intermediate values are obtained with L‐glutathione and poly(styrene‐co ‐maleic anhydride) polymer coatings. The highest efficiency is obtained for polyethylenimine (PEI) polymer coating. These pronounced differences in the photocatalytic efficiencies are correlated with ultrafast transient absorption spectroscopy measurements, which show a faster bleach recovery for the PEI‐coated hybrid nanoparticles, consistent with faster and more efficient charge separation. These differences are primarily attributed to the effects of surface passivation by the different coatings affecting the surface trapping of charge carriers that compete with effective charge separation required for the photocatalysis. Further support of this assignment is provided from steady‐state emission and time‐resolved spectral measurements, performed on related strongly fluorescing CdSe/CdS nanorods. The control and understanding of the effect of the surface coating of the hybrid nanosystems on the photocatalytic processes is of importance for the potential application of hybrid nanoparticles as photocatalysts.

Yorai Amit, Yuanyuan Li, Anatoly I Frenkel, and Uri Banin. 2015. “From Impurity Doping to Metallic Growth in Diffusion Doping: Properties and Structure of Silver-Doped InAs Nanocrystals.” ACS nano, 9, 11, Pp. 10790-10800. Publisher's Version Abstract

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Tuning of the electronic properties of presynthesized colloidal semiconductor nanocrystals (NCs) by doping plays a key role in the prospect of implementing them in printed electronics devices such as transistors and photodetectors. While such impurity doping reactions have already been introduced, the understanding of the doping process, the nature of interaction between the impurity and host atoms, and the conditions affecting the solubility limit of impurities in nanocrystals are still unclear. Here, we used a postsynthesis diffusion-based doping reaction to introduce Ag impurities into InAs NCs. Optical absorption spectroscopy and analytical inductively coupled plasma mass spectroscopy (ICP-MS) were used to present a two-stage doping model consisting of a “doping region” and a “growth region”, depending on the impurity to NC ratio in the reaction vessel. X-ray absorption fine-structure (XAFS) spectroscopy was employed to determine the impurity location and correlate between the structural and electronic properties for different sizes of InAs NCs and dopant concentrations. The resulting structural model describes a heterogeneous system where the impurities initially dope the NC, by substituting for In atoms near the surface of the NC, until the “solubility limit” is reached, after which the rapid growth and formation of metallic structures are identified.

 

Shira Halivni, Shay Shemesh, Nir Waiskopf, Yelena Vinetsky, Shlomo Magdassi, and Uri Banin. 2015. “Inkjet printed fluorescent nanorod layers exhibit superior optical performance over quantum dots.” Nanoscale, 7, 45, Pp. 19193-19200. Publisher's Version Abstract

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Semiconductor nanocrystals exhibit unique fluorescence properties which are tunable in size, shape and composition. The high quantum yield and enhanced stability have led to their use in biomedical imaging and flat panel displays. Here, semiconductor nanorod based inkjet inks are presented, overcoming limitations of the commonly reported quantum dots in printing applications. Fluorescent seeded nanorods were found to be outstanding candidates for fluorescent inks, due to their low particle–particle interactions and negligible self-absorption. This is manifested by insignificant emission shifts upon printing, even in highly concentrated printed layers and by maintenance of a high fluorescence quantum yield, unlike quantum dots which exhibit fluorescence wavelength shifts and quenching effects. This behavior results from the reduced absorption/emission overlap, accompanied by low energy transfer efficiencies between the nanorods as supported by steady state and time resolved fluorescence measurements. The new seeded nanorod inks enable patterning of thin fluorescent layers, for demanding light emission applications such as signage and displays.

Hagai Arbell and Uri Banin. 2015. “Lighting devices with prescribed colour emission.” United States of America.
2014
Amit Halevi, Shira Halivni, Meirav Oded, Axel HE Müller, Uri Banin, and Roy Shenhar. 2014. “Co-assembly of A–B diblock copolymers with B′-type nanoparticles in thin films: effect of copolymer composition and nanoparticle shape.” Macromolecules, 47, 9, Pp. 3022-3032. Publisher's Version Abstract

 

41. co-assembly of B'-type nanorods in A-B block copolymers

The coassembly of A B diblock copolymers with B'-type nanoparticles (i.e., nanoparticles that are slightly incompatible with the B domain) leads to hierarchical structures, where the block copolymer phase separates first and the nanoparticles create close-packed arrays within the B domains due to a slower, secondary phase separation process. Here we report the results of a comprehensive study, which focused on two aspects: the influence of the nanoparticle shape (spherical vs rod-like) and the effect of the volume composition of the blocks. Three polystyrene-block-poly(methyl methacrylate) (PS-b-PMMA) copolymers featuring similar molecular weights but differing in PS volume fraction were mixed with spherical and rod-shaped poly(ethylene oxide)- (PEO-) capped CdS nanoparticles at different filling fractions and cast as thin films. Our results highlight the mutual influence between the block copolymer and the nanoparticles on the resulting morphology, demonstrating the ability to control the film morphology by the filling fraction of the nanoparticles and their tendency to localize at the film surface, and by confinement-induced nanoparticle aggregation. Most importantly, the results reveal the influence of the nanoparticle shape on the structure of the film.

Guohua Jia and Uri Banin. 2014. “A general strategy for synthesizing colloidal semiconductor zinc chalcogenide quantum rods.” Journal of the American Chemical Society, 136, 31, Pp. 11121-11127. Publisher's Version Abstract

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Quasi-one-dimensional (1D) semiconductor nanocrystals manifest linearly polarized emission, reduced lasing threshold, and improved charge transport compared with their counterparts such as spherical quantum dots. Present investigations of colloidal semiconductor quantum rods are mainly based on cadmium chalcogenide systems because of their facile synthetic accessibility. However, it is still a big challenge to fabricate quasi-1D zinc chalcogenide nanocrystals with controlled aspect ratios. Here we report a general strategy for synthesizing zinc chalcogenide quantum rods via a colloidal chemical synthetic approach. Unlike the most common growth mechanisms of quasi-1D colloidal nanocrystals such as monomer attachment and particle coalescence, the synthesis of zinc chalcogenide quantum rods is performed by a ripening process starting from their respective ultrathin nanowires through thermodynamically driven material diffusion. We anticipate that this strategy is general and could be applied to other systems to construct quasi-1D nanostructures. Moreover, the presence of cadmium-free (or “green”) zinc chalcogenide quantum rods synthesized through this strategy provides a desirable platform for eco-friendly photocatalysis, optoelectronic devices, biolabeling, and other applications.

Uri Banin, Yuval Ben-Shahar, and Kathy Vinokurov. 2014. “Hybrid semiconductor–metal nanoparticles: from architecture to function.” Chemistry of Materials, 26, 1, Pp. 97-110.
Shlomit Kraus‐Ophir, Yuval Ben‐Shahar, Uri Banin, and Daniel Mandler. 2014. “Perpendicular Orientation of Anisotropic Au‐Tipped CdS Nanorods at the Air/Water Interface.” Advanced Materials Interfaces, 1, 1, Pp. 1300030.
Kathy Vinokurov, Yehonadav Bekenstein, Vitaly Gutkin, Inna Popov, Oded Millo, and Uri Banin. 2014. “Rhodium growth on Cu 2 S nanocrystals yielding hybrid nanoscale inorganic cages and their synergistic properties.” CrystEngComm, 16, 40, Pp. 9506-9512.
Roy Shenhar, Uri Banin, Elina Ploshnik, and Asaf Salant. 2014. “Assemblies comprising block co-polymer films and nanorods.” United States of America.
Guohua Jia, Amit Sitt, Gal B Hitin, Ido Hadar, Yehonadav Bekenstein, Yorai Amit, Inna Popov, and Uri Banin. 2014. “Couples of colloidal semiconductor nanorods formed by self-limited assembly.” Nature materials, 13, 3, Pp. 301. Publisher's Version Abstract

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Colloidal nanocrystal synthesis provides a powerful approach for creating unique nanostructures of relevance for applications. Here, we report that wurtzite ZnSe nanorod couples connected by twinning structures can be synthesized by means of a self-limited assembly process. Unlike for individual nanorods, the band-edge states calculated for the nanorod couples are predominantly confined to the short edges of the structure and this leads to low photoluminescence polarization anisotropy, as confirmed by single-particle fluorescence. Through a cation-exchange approach, the composition of nanorod couples can be readily expanded to additional materials, such as CdSe and PbSe. We anticipate that this family of nanorod-couple structures with distinct compositions and controlled properties will constitute an ideal system for the investigation of electronic coupling effects between individual nanorod components on the nanoscale, with relevance to applications in optics, photocatalysis and optoelectronic devices.

Uri Banin, Shlomo Yitzchaik, Ori Cheshnovsky, Yael Hanein, and Evelyne Sernagor. 2014. “Photoelectrical devices for stimulating neurons.” United States of America.
Lilach Bareket, Nir Waiskopf, David Rand, Gur Lubin, Moshe David-Pur, Jacob Ben-Dov, Soumyendu Roy, Cyril Eleftheriou, Evelyne Sernagor, and Ori Cheshnovsky. 2014. “Semiconductor nanorod–carbon nanotube biomimetic films for wire-free photostimulation of blind retinas.” Nano letters, 14, 11, Pp. 6685-6692. Publisher's Version Abstract

We report the development of a semiconductor nanorod-carbon nanotube based platform for wire-free, light induced retina stimulation. A plasma polymerized acrylic acid midlayer was used to achieve covalent conjugation of semiconductor nanorods directly onto neuro-adhesive, threedimensional carbon nanotube surfaces. Photocurrent, photovoltage, and fluorescence lifetime measurements validate efficient charge transfer between the nanorods and the carbon nanotube films. Successful stimulation of a light-insensitive chick retina suggests the potential use of this novel platform in future artificial retina application

2013
Amit Sitt, Na’ama Even-Dar, Shira Halivni, Adam Faust, Lior Yedidya, and Uri Banin. 2013. “Analysis of shape and dimensionality effects on fluorescence resonance energy transfer from nanocrystals to multiple acceptors.” The Journal of Physical Chemistry C, 117, 43, Pp. 22186-22197. Publisher's Version Abstract

The dynamic process of energy transfer from semiconductor nanocrystals acting as donors to multiple acceptors attached to their surface emerges as an important tool for probing the nanoparticle environment in the nanometric scale. Understanding the underlying principles which govern the dynamics of the energy transfer process, and in particular the role of the shape and dimensions of the nanocrystal in determining it, is crucial for utilizing it for a range of applications including sensing, biolabeling, and energy funneling. We describe and theoretically analyze the temporal behavior of energy transfer from core/shell spherical dot, dot in a rod, and dot in a pod nanocrystals to multiple acceptors linked to their surface. Using a modified restricted geometries model, we evaluate the different parameters which affect the energy transfer and demonstrate the role of the nanocrystal geometry and dimensions in determining the dynamics of the energy transfer process. The modeled dynamics show good agreement to experimental data measured for spherical and dot in a rod nanocrystals. The results obtained from the model indicate that energy transfer may be used for extracting the dimensions and dimensionalities of nanocrystals and for probing real-time processes in the ensemble level, which are relevant for characterization and sensing applications.

Amit Sitt, Ido Hadar, and Uri Banin. 2013. “Band-gap engineering, optoelectronic properties and applications of colloidal heterostructured semiconductor nanorods.” Nano Today, 8, 5, Pp. 494-513.
Yorai Amit, Adam Fasut, Oded Milo, Eran Rabani, Anatoly Frenkel, and Uri Banin. 2013. “How to Dope a Semiconductor Nanocrystal.” ECS Transactions, 58, 7, Pp. 127.