Publications

2019
Guohua Jia, Yingping Pang, Jiajia Ning, Uri Banin, and Botao Ji. 2019. “Heavy‐Metal‐Free Colloidal Semiconductor Nanorods: Recent Advances and Future Perspectives.” Advanced Materials, 31, 25, Pp. 1900781. Publisher's Version Abstract

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"Quasi‐1D colloidal semiconductor nanorods (NRs) are at the forefront of nanoparticle (NP) research owing to their intriguing size‐dependent and shape‐dependent optical and electronic properties. The past decade has witnessed significant advances in both fundamental understanding of the growth mechanisms and applications of these stimulating materials. Herein, the state‐of‐the‐art of colloidal semiconductor NRs is reviewed, with special emphasis on heavy‐metal‐free materials. The main growth mechanisms of heavy‐metal‐free colloidal semiconductor NRs are first elaborated, including anisotropic‐controlled growth, oriented attachment, solution–liquid–solid method, and cation exchange. Then, structural engineering and properties of semiconductor NRs are discussed, with a comprehensive overview of core/shell structures, alloying, and doping, as well as semiconductor–metal hybrid nanostructures, followed by highlighted practical applications in terms of photocatalysis, photodetectors, solar cells, and biomedicine. Finally, challenges and future opportunities in this fascinating research area are proposed."

Gil Aizik, Nir Waiskopf, Majd Agbaria, Meital Ben-David-Naim, Yael Levi-Kalisman, Amit Shahar, Uri Banin, and Gershon Golomb. 2019. “Liposomes of Quantum Dots Configured for Passive and Active Delivery to Tumor Tissue.” Nano letters, 19, 9, Pp. 5844-5852. Publisher's Version Abstract

"The majority of developed and approved anticancer nanomedicines have been designed to exploit the dogma of the enhanced permeability and retention (EPR) effect, which is based on the leakiness of the tumor’s blood vessels accompanied by impeded lymphatic drainage. However, the EPR effect has been under scrutiny recently because of its variable manifestation across tumor types and animal species and its poor translation to human cancer therapy. To facilitate the EPR effect, systemically injected NPs should overcome the obstacle of rapid recognition and elimination by the mononuclear phagocyte system (MPS). We hypothesized that circulating monocytes, major cells of the MPS that infiltrate the tumor, may serve as an alternative method for achieving increased tumor accumulation of NPs, independent of the EPR effect. We describe here the accumulation of liposomal quantum dots (LipQDs) designed for active delivery via monocytes, in comparison to LipQDs designed for passive delivery (via the EPR effect), following IV administration in a mammary carcinoma model. Hydrophilic QDs were synthesized and entrapped in functionalized liposomes, conferring passive (“stealth” NPs; PEGylated, neutral charge) and active (monocyte-mediated delivery; positively charged) properties by differing in their lipid composition, membrane PEGylation, and charge (positively, negatively, and neutrally charged). The various physicochemical parameters affecting the entrapment yield and optical stability were examined in vitro and in vivo. Biodistribution in the blood, various organs, and in the tumor was determined by the fluorescence intensity and Cd analyses. Following the treatment of animals (intact and mammary-carcinoma-bearing mice) with disparate formulations of LipQDs (differing by their lipid composition, neutrally and positively charged surfaces, and hydrophilic membrane), we demonstrate comparable tumor uptake of QDs delivered by the passive and the active routes (mainly by Ly-6Chi monocytes). Our findings suggest that entrapping QDs in nanosized liposomal formulations, prepared by a new facile method, imparts superior structural and optical stability and a suitable biodistribution profile leading to increased tumor uptake of fluorescently stable QDs."

Jin He, Botao Ji, Somnath Koley, Uri Banin, and David Avnir. 2019. “Metallic Conductive Luminescent Film.” ACS nano, 13, 9, Pp. 10826-10834. Publisher's Version Abstract

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"We report a solution for the challenge of having luminescence and metal conductivity from the same material. The fabrication of a hybrid metal–conductive luminescent film that manifests this dual property is described: the conductivity arising from a continuous gold thin film structure and luminescence originating from the embedded fluorescent emitters (nanoparticles of silica-coated CdSe/CdS quantum dots (QD/SiO2 NPs)). The embedding of the QD/SiO2 NPs is performed via a self-templating gold electroless process. The presence of the insulating silica layer on the QDs avoids quenching and enables luminescence, while still allowing plasmonic coupling of the QDs, as observed by luminescence lifetime analysis and by surface-enhanced Raman scattering. The potential applications of this special dual functionality are demonstrated by its used as a temperature probe: Passing current (heating the gold thin film) affects the emission intensity and induces a spectral red-shift of the QD/SiO2 NPs. All properties of this metal–conductive luminescent film required the special embedding architecture and are not observed with simple adsorption of QD/SiO2 NPs on a continuous Au film."

Danielle Perry, Nir Waiskopf, Lior Verbitsky, Sergei Remennik, and Uri Banin. 2019. “Shell stabilization of photocatalytic ZnSe nanorods.” ChemCatChem, 11, 24, Pp. 6208-6212. Publisher's Version Abstract

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"Zinc chalcogenides nanostructures are promising newly‐studied materials for photocatalytic reactions such as water reduction for hydrogen generation and photoinitiation of radical polymerization processes. Herein, we introduced a straightforward synthesis of thin ZnS shell on ZnSe nanorods and characterized the resulting core/shell ZnSe/ZnS nanorods by electron microscopy techniques and X‐ray photoelectron spectroscopy. Then, the photocatalytic activities of the nanorods were studied by gas chromatography for hydrogen generation and by Fourier transform infrared spectroscopy for the photoinitiation capability. While such core/shell systems may limit charge transfer to the solution due to the type‐I band alignment, we find that the photochemical stability and photocatalytic activity of this system is significantly enhanced over pristine ZnSe nanorods. ZnSe/ZnS nanorods with Ni(NO3)2 co‐catalyst are used for hydrogen generation and the effects of the nanorods’ surface coating, pH conditions and type of hole scavenger are examined. The best performances were observed for nanorods after ligand stripping with Meerwein′s reagent using ascorbic acid as a hole acceptor at pH 4.5. All three parameters were found to affect the photocatalytic activity. Yet, the surface coating and pH dependence differ from previous reports on cadmium chalcogenides photocatalysts. The origin of their differences is discussed and attributed to the band alignment of the systems and the nature of the co‐catalyst. The stable heavy‐metal free ZnSe/ZnS nanorods system presented here holds promise for various photocatalytic applications."

Guy Lazovski, Galit Bar, Botao Ji, Nurit Atar, Uri Banin, and Raz Gvishi. 2019. “A simple method for preparation of silica aerogels doped with monodispersed nanoparticles in homogeneous concentration.” The Journal of Supercritical Fluids. Publisher's Version Abstract

"Silica aerogel is a solid matrix, capable of preserving the unique properties of nanoparticles incorporated in it; forming a macroscopic structure that benefits from nano-metric properties.

We developed a simple method for preparation of doped silica aerogels. Dopants are implemented as silica coated nanoparticles suspended in alcohol or alcohol:water mixture. This suspension replaces a portion of the pure solvent in the one-step base catalyzed silica aerogel recipe.

Aerogels doped with, Au nano-spheres, Ag nano-platelets, and CdSe/CdS core/shell quantum dots, were prepared. These aerogels exhibit homogeneous mono-dispersion of the nanoparticles, and possess the nanoparticles' unique optical properties. Additionally, doping does not affect the gelation process or the silica matrix.

We envision that using this methodology, many other silica coated nanoparticles can be implemented as dopants. Furthermore, complex systems of several co-dopants can be obtained in a reproducible manner. Such aerogels can be tailor made for a vast range of applications."

 

Botao Ji, Yossef E Panfil, Nir Waiskopf, Sergei Remennik, Inna Popov, and Uri Banin. 2019. “Strain-controlled shell morphology on quantum rods.” Nature communications, 10, 1, Pp. 1-9. Publisher's Version Abstract

figure1"Semiconductor heterostructure nanocrystals, especially with core/shell architectures, are important for numerous applications.  Here we show that by decreasing the shell growth rate the morphology of ZnS shells on ZnSe quantum rods can be tuned from flat to islands-like, which decreases the interfacial strain energy. Further reduced growth speed, approaching the thermodynamic limit, leads to coherent shell growth forming unique helical-shell morphology.  This reveals a template-free mechanism for induced chirality at the nanoscale. The helical morphology minimizes the sum of the strain and surface energy and maintains band gap emission due to its coherent core/shell interface without traps, unlike the other morphologies. Reaching the thermodynamic controlled growth regime for colloidal semiconductor core/shell nanocrystals thus offers morphologies with clear impact on their applicative potential."

Durgesh C Tripathi, Lior Asor, Gil Zaharoni, Uri Banin, and Nir Tessler. 2019. “Surface Versus Impurity-Doping Contributions in InAs Nanocrystal Field Effect Transistor Performance.” The Journal of Physical Chemistry C, 123, 30, Pp. 18717-18725. Publisher's Version Abstract

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"The Electrical Functionality of an Array of Semiconductor Nanocrystals (NCs) depends critically on the free carriers that may arise from impurity or surface doping. Herein, we used InAs NC thin films as a model system to address the relative contributions of these doping mechanisms by comparative analysis of as-synthesized and Cu-doped NC-based field effect transistor (FET) characteristics. By applying FET simulation methods used in conventional semiconductor FETs, we elucidate surface and impurity-doping contributions to the overall performance of InAs NC-based FETs. As-synthesized InAs NC-based FETs show n-type characteristics assigned to the contribution of the surface electron accumulation layer that can be considered as an actual electron-donating doping level with specific doping density and is energetically located just below the conduction band. The Cu-doped InAs NC FETs show enhanced n-type conduction as expected from the Cu impurity location as an interstitial n-dopant in InAs NCs. The simulated curves reveal the additional contribution from electrons within an impurity sub-band close to the conduction band onset of the InAs NCs. The work therefore demonstrates the utility of the bulk FET simulation methodology also to NC-based FETs. It provides guidelines for control of doping of NC arrays separately from surface contributions and impurity doping in colloidal semiconductor NCs toward their future utilization as building blocks in bottom-up prepared optoelectronic devices."

2018
Yuval Ben-Shahar, John P Philbin, Francesco Scotognella, Lucia Ganzer, Giulio Cerullo, Eran Rabani, and Uri Banin. 2018. “Charge Carrier Dynamics in Photocatalytic Hybrid Semiconductor–Metal Nanorods: Crossover from Auger Recombination to Charge Transfer.” Nano letters, 18, 8, Pp. 5211-5216. Publisher's Version Abstract

"Hybrid semiconductor–metal nanoparticles (HNPs) manifest unique, synergistic electronic and optical properties as a result of combining semiconductor and metal physics via a controlled interface. These structures can exhibit spatial charge separation across the semiconductor–metal junction upon light absorption, enabling their use as photocatalysts. The combination of the photocatalytic activity of the metal domain with the ability to generate and accommodate multiple excitons in the semiconducting domain can lead to improved photocatalytic performance because injecting multiple charge carriers into the active catalytic sites can increase the quantum yield. Herein, we show a significant metal domain size dependence of the charge carrier dynamics as well as the photocatalytic hydrogen generation efficiencies under nonlinear excitation conditions. An understanding of this size dependence allows one to control the charge carrier dynamics following the absorption of light. Using a model hybrid semiconductor–metal CdS–Au nanorod system and combining transient absorption and hydrogen evolution kinetics, we reveal faster and more efficient charge separation and transfer under multiexciton excitation conditions for large metal domains compared to small ones. Theoretical modeling uncovers a competition between the kinetics of Auger recombination and charge separation. A crossover in the dominant process from Auger recombination to charge separation as the metal domain size increases allows for effective multiexciton dissociation and harvesting in large metal domain HNPs. This was also found to lead to relative improvement of their photocatalytic activity under nonlinear excitation conditions."

Yossef E Panfil, Meirav Oded, and Uri Banin. 2018. “Colloidal quantum nanostructures: emerging materials for display applications.” Angewandte Chemie International Edition, 57, 16, Pp. 4274-4295. Publisher's Version Abstract

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"Colloidal semiconductor nanocrystals (SCNCs) or, more broadly, colloidal quantum nanostructures constitute outstanding model systems for investigating size and dimensionality effects. Their nanoscale dimensions lead to quantum confinement effects that enable tuning of their optical and electronic properties. Thus, emission color control with narrow photoluminescence spectra, wide absorbance spectra, and outstanding photostability, combined with their chemical processability through control of their surface chemistry leads to the emergence of SCNCs as outstanding materials for present and next‐generation displays. In this Review, we present the fundamental chemical and physical properties of SCNCs, followed by a description of the advantages of different colloidal quantum nanostructures for display applications. The open challenges with respect to their optical activity are addressed. Both photoluminescent and electroluminescent display scenarios utilizing SCNCs are described."

Jiajia Ning, Jing Liu, Yael Levi-Kalisman, Anatoly I Frenkel, and Uri Banin. 2018. “Controlling anisotropic growth of colloidal ZnSe nanostructures.” Journal of the American Chemical Society, 140, 44, Pp. 14627-14637. Publisher's Version Abstract

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"Semiconductor nanocrystals serve as outstanding model systems for studying quantum confined size and shape effects. Shape control is an important knob for controlling their properties but so far it has been well developed mainly for heavy-metal containing semiconductor nanocrystals, limiting their further widespread utilization. Herein, we report a synthesis of heavy-metal free ZnSe nanocrystals with shape and size control through utilization of well-defined molecular clusters. In this approach, ZnSe nanowires are synthesized and their length and shape control is achieved by introduction of controlled amounts of molecular clusters. As a result of [Zn4(SPh)10](Me4N)2 clusters (Zn4 clusters) addition, short ZnSe nanorods or ZnSe nanodots can be obtained through tuning the ratio of Zn4 clusters to ZnSe. A study using transmission electron microscopy revealed the formation of a hybrid inorganic–organic nanowire, whereby the ligands form a template for self-assembly of ZnSe magic size clusters. The hybrid nanowire template becomes shorter and eventually disappears upon increasing amount of Zn4 clusters in the reaction. The generality of the method is demonstrated by using isostructural [Cu4(SPh)6](Me4N)2 clusters, which presented a new approach to Cu doped ZnSe nanocrystals and provided also a unique opportunity to employ X-ray absorption fine structure spectroscopy for deciphering the changes in the local atomic-scale environment of the clusters and explaining their role in the process of the nanorods formation. Overall, the introduction of molecular clusters presented here opens a path for growth of colloidal semiconductor nanorods, expanding the palette of materials selection with obvious implications for optoelectronic and biomedical applications."

Uri Banin and Yuval Ben-Shahar. 2018. “A hybrid solution.” Nature Energy, 3, 10, Pp. 824-825. Publisher's Version Abstract

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Photocatalytic water splitting is a route to clean H2, but approaches based on hybrid semiconductor–metal nanoparticles often rely on sacrificial reagents to complete the oxidation half of the overall reaction. New research uses CdS nanocrystals modified with metallic and molecular co-catalysts to simultaneously produce H2 and O2 from water using visible light.

Douglas R Nevers, Curtis B Williamson, Benjamin H Savitzky, Ido Hadar, Uri Banin, Lena F Kourkoutis, Tobias Hanrath, and Richard D Robinson. 2018. “Mesophase formation stabilizes high-purity magic-sized clusters.” Journal of the American Chemical Society, 140, 10, Pp. 3652-3662. Publisher's Version Abstract

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"Magic-sized clusters (MSCs) are renowned for their identical size and closed-shell stability that inhibit conventional nanoparticle (NP) growth processes. Though MSCs have been of increasing interest, understanding the reaction pathways toward their nucleation and stabilization is an outstanding issue. In this work, we demonstrate that high concentration synthesis (1000 mM) promotes a well-defined reaction pathway to form high-purity MSCs (>99.9%). The MSCs are resistant to typical growth and dissolution processes. On the basis of insights from in situ X-ray scattering analysis, we attribute this stability to the accompanying production of a large (>100 nm grain size), hexagonal organic–inorganic mesophase that arrests growth of the MSCs and prevents NP growth. At intermediate concentrations (500 mM), the MSC mesophase forms, but is unstable, resulting in NP growth at the expense of the assemblies. These results provide an alternate explanation for the high stability of MSCs. Whereas the conventional mantra has been that the stability of MSCs derives from the precise arrangement of the inorganic structures (i.e., closed-shell atomic packing), we demonstrate that anisotropic clusters can also be stabilized by self-forming fibrous mesophase assemblies. At lower concentration (<200 mM or >16 acid-to-metal), MSCs are further destabilized and NPs formation dominates that of MSCs. Overall, the high concentration approach intensifies and showcases inherent concentration-dependent surfactant phase behavior that is not accessible in conventional (i.e., dilute) conditions. This work provides not only a robust method to synthesize, stabilize, and study identical MSC products but also uncovers an underappreciated stabilizing interaction between surfactants and clusters."

David Stone, Yuval Ben‐Shahar, Nir Waiskopf, and Uri Banin. 2018. “The Metal Type Governs Photocatalytic Reactive Oxygen Species Formation by Semiconductor‐Metal Hybrid Nanoparticles.” ChemCatChem, 10, 22, Pp. 5119-5123. Publisher's Version Abstract

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Semiconductor‐metal hybrid nanoparticles (HNPs) are promising photocatalysts for redox reactions, including water reduction for hydrogen generation and reactive oxygen species (ROS) formation. Herein we study the effect of the metal co‐catalyst type on the light‐induced ROS formation using a combination of spectrophotometric and fluorescence assays, as well as electron paramagnetic resonance spectroscopy. We find that although Pt tips are more efficient for H2 generation, hydrogen peroxide and hydroxyl radicals are formed more effectively by Au tipped HNPs. These variations are attributed to the different surface reactivity and selectivity related to the metal tip composition. The obtained understanding contributes to the optimal design of these hybrid nanosystems as photocatalysts in various ROS‐driven applications such as photopolymerization, and environmental and biomedical scenarios.

Nir Waiskopf, Yuval Ben‐Shahar, and Uri Banin. 2018. “Photocatalytic hybrid semiconductor–metal nanoparticles; from synergistic properties to emerging applications.” Advanced Materials, 30, 41, Pp. 1706697. Publisher's Version Abstract

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Hybrid semiconductor–metal nanoparticles (HNPs) manifest unique combined and often synergetic properties stemming from the materials combination. These structures exhibit spatial charge separation across the semiconductor–metal junction upon light absorption, enabling their use as photocatalysts. So far, the main impetus of photocatalysis research in HNPs addresses their functionality in solar fuel generation. Recently, it was discovered that HNPs are functional in efficient photocatalytic generation of reactive oxygen species (ROS). This has opened the path for their implementation in diverse biomedical and industrial applications where high spatially temporally resolved ROS formation is essential. Here, the latest studies on the synergistic characteristics of HNPs are summarized, including their optical, electrical, and chemical properties and their photocatalytic function in the field of solar fuel generation is briefly discussed. Recent studies are then focused concerning photocatalytic ROS formation with HNPs under aerobic conditions. The emergent applications of this capacity are then highlighted, including light‐induced modulation of enzymatic activity, photodynamic therapy, antifouling, wound healing, and as novel photoinitiators for 3D‐printing. The superb photophysical and photocatalytic properties of HNPs offer already clear advantages for their utility in scenarios requiring on‐demand light‐induced radical formation and the full potential of HNPs in this context is yet to be revealed.

2017
Jugun Prakash Chinta, Nir Waiskopf, Gur Lubin, David Rand, Yael Hanein, Uri Banin, and Shlomo Yitzchaik. 2017. “Carbon nanotube and semiconductor nanorods hybrids: preparation, characterization, and evaluation of photocurrent generation.” Langmuir, 33, 22, Pp. 5519-5526. Publisher's Version Abstract

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Carbon nanotubes (CNTs) and semiconductor nanocrystals (SCNCs) are known to be interesting donor–acceptor partners due to their unique optical and electronic properties. These exciting features have led to the development of novel composites based on these two nanomaterials and to their characterization for use in various applications, such as components in sensors, transistors, solar cells and biomedical devices. Two approaches based on covalent and noncovalent methods have been suggested for coupling the SCNCs to CNTs. Most covalent conjugation methods used so far were found to disrupt the electronic structure of the CNTs or interfere with charge transfer in the CNT–SCNC interface. Moreover, it offers random and poorly organized nanoparticle coatings. Therefore, noncovalent methods are considered to be ideal for better electronic coupling. However, a key common drawback of noncovalent methods is the lack of stability which hampers their applicability. In this article, a method has been developed to couple semiconductor seeded nanorods onto CNTs through π–π interactions. The CNTs and pyrene conjugated SCNC hybrid materials were characterized by both microscopic and spectroscopic techniques. Fluorescence and photocurrent measurements suggest the proposed pi-stacking approach results in a strong electronic coupling between the CNTs and the SCNCs leading to better photocurrent efficiency than that of a covalent conjugation method reported using similar SCNC material. Overall, the CNT–SCNC films reported in the present study open the scope for the fabrication of optoelectronic devices for various applications.

Gil Aizik, Nir Waiskopf, Majd Agbaria, Yael Levi-Kalisman, Uri Banin, and Gershon Golomb. 2017. “Delivery of liposomal quantum dots via monocytes for imaging of inflamed tissue.” ACS nano, 11, 3, Pp. 3038-3051. Publisher's Version Abstract

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Quantum dots (QDs), semiconductor nanocrystals, are fluorescent nanoparticles of growing interest as an imaging tool of a diseased tissue. However, a major concern is their biocompatibility, cytotoxicity, and fluorescence instability in biological milieu, impeding their use in biomedical applications, in general, and for inflammation imaging, in particular. In addition, for an efficient fluorescent signal at the desired tissue, and avoiding systemic biodistribution and possible toxicity, targeting is desired. We hypothesized that phagocytic cells of the innate immunity system (mainly circulating monocytes) can be exploited as transporters of specially designed liposomes containing QDs to the inflamed tissue. We developed a liposomal delivery system of QDs (LipQDs) characterized with high encapsulation yield, enhanced optical properties including far-red emission wavelength and fluorescent stability, high quantum yield, and protracted fluorescent decay lifetime. Treatment with LipQDs, rather than free QDs, exhibited high accumulation and retention following intravenous administration in carotid-injured rats (an inflammatory model). QD–monocyte colocalization was detected in the inflamed arterial segment only following treatment with LipQDs. No cytotoxicity was observed following LipQD treatment in cell cultures, and changes in liver enzymes and gross histopathological changes were not detected in mice and rats, respectively. Our results suggest that the LipQD formulation could be a promising strategy for imaging inflammation.

Botao Ji, Yossef E Panfil, and Uri Banin. 2017. “Heavy-metal-free fluorescent ZnTe/ZnSe nanodumbbells.” ACS nano, 11, 7, Pp. 7312-7320. Publisher's Version Abstract

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For visible range emitting particles, which are relevant for display and additional applications, Cd-chalcogenide nanocrystals have reached the highest degree of control and performance. Considering potential toxicity and regulatory limitations, there is a challenge to successfully develop Cd-free emitting nanocrystals and, in particular, heterostructures with desirable properties. Herein, we report a colloidal synthesis of fluorescent heavy-metal-free Zn-chalcogenide semiconductor nanodumbbells (NDBs), in which ZnSe tips were selectively grown on the apexes of ZnTe rods, as evidenced by a variety of methods. The fluorescence of the NDBs can be tuned between ∼500 and 585 nm by changing the ZnSe tip size. The emission quantum yield can be greatly increased through chloride surface treatment and reaches more than 30%. Simulations within an effective-mass-based model show that the hole wave function is spread over the ZnTe nanorods, while the electron wave function is localized on the ZnSe tips. Quantitative agreement for the red-shifted emission wavelength is obtained between the simulations and the experiments. Additionally, the changes in radiative lifetimes correlate well with the calculated decrease in electron–hole overlap upon growth of larger ZnSe tips. The heavy-metal-free ZnTe/ZnSe NDBs may be relevant for optoelectronic applications such as displays or light-emitting diodes.

Adam Faust, Yorai Amit, and Uri Banin. 2017. “Phonon–Plasmon Coupling and Active Cu Dopants in Indium Arsenide Nanocrystals Studied by Resonance Raman Spectroscopy.” The journal of physical chemistry letters, 8, 11, Pp. 2519-2525. Publisher's Version Abstract

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Doping of semiconductor nanocrystals is an emerging tool to control their properties and has recently received increased interest as the means to characterize the impurities and their effect on the electronic characteristics of the nanocrystal evolve. We present a temperature-dependent Raman scattering study of Cu-doped InAs nanocrystals observing changes in the relative scattering intensities of the different modes upon increased dopant concentrations. First, the longitudinal optical (LO) phonon overtone mode is suppressed, indicating weakening of the coupling strength related to the effect of screening by the free electrons. Second, the transverse optical (TO) mode is relatively enhanced compared to the LO mode, which is attributed to the appearance of a coupled phonon–plasmon mode analogous to observations for n-type doped bulk InAs. These signatures indicate that the Cu impurities serve as active dopants and occupy an impurity-related pseudo sub-band akin to the heavy doping limit.

Yuval Ben-Shahar, Kathy Vinokurov, Héloïse de Paz-Simon, Yosef Gofer, Matan Leiter, Uri Banin, and Yaron S Cohen. 2017. “Photoelectrochemistry of colloidal Cu 2 O nanocrystal layers: the role of interfacial chemistry.” Journal of Materials Chemistry A, 5, 42, Pp. 22255-22264. Publisher's Version Abstract

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Colloidal Cu2O nanocrystal layers on Au substrates are studied as photocathodes in the context of solar electrochemical water-splitting applications. The photoelectrochemical response of the nanocrystal layers in aqueous solutions under simulated solar light conditions depends strongly on the interfacial chemistry and its impact on the transport of the charge carriers across the Au/nanocrystals/liquid interfaces. The Cu2O nanocrystals are originally stabilized with octadecylamine ligands. While octadecylamine is an efficient capping ligand for the colloidal synthesis of highly uniform nanocrystals, its low conductivity impedes the charge transport across the Au/nanocrystals/liquid interfaces. The photoresponse of the nanocrystals can be enhanced by the replacement of the octadecylamine ligands with more conductive and hydrophilic molecules, such as 1,2-ethanedithiol and benzene-1,4-dithiol. The conductivity and hydrophilicity of the ligands were investigated and found to be important for the photo-induced charge separation and transport across the Au/nanocrystals/liquid interfaces and transfer to the liquid. Furthermore, the interfacial energetics of the Au/nanocrystals/liquid junction and the resulting photoresponse of the Cu2O nanocrystal photocathode can be optimized by rational design of the exchanging ligands with desired functionalities and dipoles at the specific interfaces. A comparison of the photoresponse of Cu2O nanocrystal layers to that of electrodeposited Cu2O layers shows that the former is, yet, lower, due to the apparent low conductivity of the ligands. However, the nanocrystal organic ligands impart high hydrophobicity, which prevents the contact of the aqueous solution with the nanocrystals and improves their stability against photocorrosion and reduction to Cu0, as confirmed by X-ray diffraction measurements.

Amol Ashok Pawar, Shira Halivni, Nir Waiskopf, Yuval Ben-Shahar, Michal Soreni-Harari, Sarah Bergbreiter, Uri Banin, and Shlomo Magdassi. 2017. “Rapid three-dimensional printing in water using semiconductor–metal hybrid nanoparticles as photoinitiators.” Nano letters, 17, 7, Pp. 4497-4501. Publisher's Version Abstract

Additive manufacturing processes enable fabrication of complex and functional three-dimensional (3D) objects ranging from engine parts to artificial organs. Photopolymerization, which is the most versatile technology enabling such processes through 3D printing, utilizes photoinitiators that break into radicals upon light absorption. We report on a new family of photoinitiators for 3D printing based on hybrid semiconductor–metal nanoparticles. Unlike conventional photoinitiators that are consumed upon irradiation, these particles form radicals through a photocatalytic process. Light absorption by the semiconductor nanorod is followed by charge separation and electron transfer to the metal tip, enabling redox reactions to form radicals in aerobic conditions. In particular, we demonstrate their use in 3D printing in water, where they simultaneously form hydroxyl radicals for the polymerization and consume dissolved oxygen that is a known inhibitor. We also demonstrate their potential for two-photon polymerization due to their giant two-photon absorption cross section.