Somnath Koley, Jiabin Cui, Yossef E Panfil, and Uri Banin. 2021. “Coupled Colloidal Quantum Dot Molecules.” Accounts of Chemical Research, 54, 5, Pp. 1178-1188. Publisher's Version Abstract

"Electronic coupling and hence hybridization of atoms  serves as the bas is for the rich properties for the endless library of naturally occurring molecules. Colloidal quantum dots (CQDs) manifesting quantum strong confinement possess atomic-like characteristics with s and p electronic levels, which popularized the notion of CQDs as artificial atoms. Continuing this analogyACR_2021, when two atoms are close enough to form a molecule so that their orbitals start overlapping, the orbitals energies start to split into bonding and antibonding states made out of hybridized orbitals. The same concept is also applicable for two fused core–shell nanocrystals in close proximity. Their band edge states, which dictate the emitted photon energy, start to hybridize, changing their electronic and optical properties. Thus, an exciting direction of “artificial molecules” emerges, leading to a multitude of possibilities for creating a library of new hybrid nanostructures with novel optoelectronic properties with relevance toward diverse applications including quantum technologies.

The controlled separation and the barrier height between two adjacent quantum dots are key variables for dictating the magnitude of the coupling energy of the confined wave functions. In the past, coupled double quantum dot architectures prepared by molecular beam epitaxy revealed a coupling energy of few millielectron volts, which limits the applications to mostly cryogenic operation. The realization of artificial quantum molecules with sufficient coupling energy detectable at room temperature calls for the use of colloidal semiconductor nanocrystal building blocks. Moreover, the tunable surface chemistry widely opens the predesigned attachment strategies as well as the solution processing ability of the prepared artificial molecules, making the colloidal nanocrystals as an ideal candidate for this purpose. Despite several approaches that demonstrated enabling of the coupled structures, a general and reproducible method applicable to a broad range of colloidal quantum materials is needed for systematic tailoring of the coupling strength based on a dictated barrier.

This Account addresses the development of nanocrystal chemistry to create coupled colloidal quantum dot molecules and to study the controlled electronic coupling and their emergent properties. The simplest nanocrystal molecule, a homodimer formed from two core/shell nanocrystal monomers, in analogy to homonuclear diatomic molecules, serves as a model system. The shell material of the two CQDs is structurally fused, resulting in a continuous crystal. This lowers the potential energy barrier, enabling the hybridization of the electronic wave functions. The direct manifestation of the hybridization reflects on the band edge transition shifting toward lower energy and is clearly resolved at room temperature. The hybridization energy within the single homodimer molecule is strongly correlated with the extent of structural continuity, the delocalization of the exciton wave function, and the barrier thickness as calculated numerically. The hybridization impacts the emitted photon statistics manifesting faster radiative decay rate, photon bunching effect, and modified Auger recombination pathway compared to the monomer artificial atoms. Future perspectives for the nanocrystals chemistry paradigm are also highlighted."


Yoav Ninio, Nir Waiskopf, Idan Meirzada, Yoav Romach, Galya Haim, Shira Yochelis, Uri Banin, and Nir Bar-Gill. 2021. “High-Sensitivity, High-Resolution Detection of Reactive Oxygen Species Concentration Using NV Centers.” ACS Photonics, 8, 7, Pp. 1917–1921. Publisher's Version Abstract

ACSPhoto_2021Nitrogen-vacancy (NV) color centers in diamond have been demonstrated as useful magnetic sensors, in particular for measuring spin fluctuations and achieving high sensitivity and spatial resolution. These abilities can be used to explore various biological and chemical processes, catalyzed by reactive oxygen species (ROS). Here we demonstrate a novel approach to measure and quantify hydroxyl radicals with high spatial resolution, using the fluorescence difference between NV charged states. According to the results, the achieved NV sensitivity is , realized in situ without spin labels and localized to a volume of ∼10 picoliters.

Alex Pinkas, Nir Waiskopf, Shira Gigi, Tom Naor, Almog Layani, and Uri Banin. 2021. “Morphology Effect on Zinc Oxide Quantum Photoinitiators for Radical Polymerization.” Nanoscale, 13, Pp. 7152-7160. Publisher's Version Abstract
 d1nr00896j-f1.tifSemiconductor nanocrystal based photoinitiators, quantum PIs, are a viable alternative to organic photoinitiators demonstrating unique advantages, including a broad and tunable excitation window, limited migration, and more. Aiming towards efficient quantum PIs with tunable properties, a deeper understanding of the relationships between the nanoparticle properties and their efficiency is required. Herein, we studied the morphological effect on ZnO nanocrystals functioning as photoinitiators in both water-based and solvent-free formulations by comparing rod and pyramidal shaped particles of similar volumes and nearly identical surface area.  Superior polymerization performances are measured for the nanorods. Photocatalytic characterization including oxygen consumption and reactive oxygen species formation as well as dyes reduction and oxidation, also showed enhanced activities for the nanorods. The different performances were attributed to the anisotropic nanorod morphology which is beneficial for charge separation as well as to the presence of a reactive [0001] facet in the nanorods, which is known to increase the adsorption of molecular oxygen and anionic molecules, thus affecting the catalytic activity. These observations, along with the higher photoinitiation efficiency of the ZnO nanorods, bring them closer to functionality as photoinitiators in numerous photopolymerization applications.


Jiabin Cui, Somnath Koley, Yossef E Panfil, Adar Levi, Nir Waiskopf, Sergei Remennik, Meirav Oded, and Uri Banin. 2021. “Semiconductor Bowtie Nanoantenna from Coupled Colloidal Quantum Dot Molecules.” Angewandte Chemie International Edition, 60, Pp. 2-8. Publisher's Version Abstract
TOC_angewTop-down fabricated nanoantenna architectures of both metallic and dielectric materials show powerful functionalities for Raman and fluorescence enhancement with relevance to single molecule sensing while inducing directionality of chromophore emission with implications for single photon sources. We synthesize the smallest bow-tie nanoantenna by selective tip-to-tip fusion of two tetrahedral colloidal quantum dots (CQDs) forming a dimer. While the tetrahedral monomers emit non-polarized light, the bow-tie architecture manifests nanoantenna functionality of enhanced emission polarization along the bow-tie axis, as predicted theoretically and revealed by single-particle spectroscopy.  Theory also predicts the formation of an electric-field hotspot at the bow-tie epicenter. This is utilized for selective light-induced photocatalytic metal growth at that location, unlike growth on the free tips in dark conditions, thus demonstrating bow-tie dimer functionality as a photochemical reaction center.


Franco VA Camargo, Yuval Ben-Shahar, Tetsuhiko Nagahara, Yossef E Panfil, Mattia Russo, Uri Banin, and Giulio Cerullo. 2021. “Visualizing Ultrafast Electron Transfer Processes in Semiconductor–Metal Hybrid Nanoparticles: Toward Excitonic–Plasmonic Light Harvesting.” Nano Letters, 21, 3, Pp. 1461–1468. Publisher's Version Abstract
nl2021"Recently, it was demonstrated that charge separation in hybrid metal–semiconductor nanoparticles (HNPs) can be obtained following photoexcitation of either the semiconductor or of the localized surface plasmon resonance (LSPR) of the metal. This suggests the intriguing possibility of photocatalytic systems benefiting from both plasmon and exciton excitation, the main challenge being to outcompete other ultrafast relaxation processes. Here we study CdSe-Au HNPs using ultrafast spectroscopy with high temporal resolution. We describe the complete pathways of electron transfer for both semiconductor and LSPR excitation. In the former, we distinguish hot and band gap electron transfer processes in the first few hundred fs. Excitation of the LSPR reveals an ultrafast (<30 fs) electron transfer to CdSe, followed by back-transfer from the semiconductor to the metal within 210 fs. This study establishes the requirements for utilization of the combined excitonic–plasmonic contribution in HNPs for diverse photocatalytic applications."


Botao Ji, Eran Rabani, Alexander L Efros, Roman Vaxenburg, Or Ashkenazi, Doron Azulay, Uri Banin, and Oded Millo. 2020. “Dielectric Confinement and Excitonic Effects in Two-Dimensional Nanoplatelets.” ACS nano. Publisher's Version Abstract

"Quasi-two-dimensional (2D) Semiconductor Nanoplatelets manifest strong quantum confinement with exceptional optical characteristics of narrow photoluminescence peaks with energies tunable by thickness with monolayer precision.  We employed scanning tunneling spectroscopy (STS) in conjunction with optical measurements to probe the thickness-dependent band gap and density of excited states in a series of CdSe nanoplatelets.botao_acsnano_2020 The tunneling spectra, measured in the double-barrier tunnel junction configuration, reveal the effect of quantum confinement on the band gap taking place mainly through a blue-shift of the conduction band edge, along with a signature of 2D electronic structure intermixed with finite lateral-size and/or defects effects. The STS fundamental band gaps are larger than the optical gaps as expected from the contributions of exciton binding in the absorption, as confirmed by theoretical calculations. The calculations also point to strong valence band mixing between the light- and split-off hole levels. Strikingly, the energy difference between the heavy-hole and light-hole levels in the tunneling spectra are significantly larger than the corresponding values extracted from the absorption spectra. Possible explanations for this, including an interplay of nanoplatelet charging, dielectric confinement, and difference in exciton binding energy for light and heavy holes, are analyzed and discussed."

Lior Asor, Jing Liu, Yonatan Ossia, Durgesh C. Tripathi, Nir Tessler, Anatoly. I. Frenkel, and Uri Banin. 2020. “InAs Nanocrystals with Robust p-Type Doping.” Adv. Funct. Mater., 31, Pp. 2007456 (1-12). Publisher's Version Abstract
lior_AFM_2020"Robust Control Over the Carrier Type is fundamental for the fabrication of nanocrystal-based optoelectronic devices, such as the p–n homojunction, but effective incorporation of impurities in semiconductor nanocrystals and its characterization is highly challenging due to their small size. Herein, InAs nanocrystals, post-synthetically doped with Cd, serve as a model system for successful p-type doping of originally n-type InAs nanocrystals, as demonstrated in field effect transistors (FETs).   Advanced structural analysis, using atomic resolution electron microscopy and synchrotron X-ray absorption fine structure spectroscopy reveal that Cd impurities reside near and on the nanocrystal surface acting as substitutional p-dopants replacing Indium. Commensurately, Cd-doped InAs FETs exhibit remarkable stability of their hole conduction, mobility, and hysteretic behavior over time when exposed to air, while intrinsic InAs NCs FETs are easily oxidized and their performance quickly declined. Therefore, Cd plays a dual role acting as a p-type dopant, and also protects the nanocrystals from oxidation, as evidenced directly by X-ray photoelectron spectroscopy measurements of air exposed samples of intrinsic and Cd-doped InAs NCs films. This study demonstrates robust p-type doping of InAs nanocrystals, setting the stage for implementation of such doped nanocrystal systems in printed electronic devices."


Yossef E. Panfil, Meirav Oded, Nir Waiskopf, and Uri Banin. 2020. “Material Challenges for Colloidal Quantum Nanostructures in Next Generation Displays.” AsiaChem, 1, 1, Pp. 26-35. Publisher's Version Abstract
"The Recent Technological Advancements have greatly improved the quality and resolution of displays. Yet, issues like full color gamut representation and long lasting durability of the color emitters require further progression. Colloidal quantum dots manifest an inherent narrow spectral emission with optical stability, combined with various chemical processability options which will allow for their integration in display applications. Apart from their numerous advantages, they also present unique opportunities for the next technological leaps in the field."


U Banin, N Waiskopf, L Hammarström, G Boschloo, M Freitag, EMJ Johansson, J Sá, H Tian, MB Johnston, and LM Herz. 2020. “Nanotechnology for catalysis and solar energy conversion.” Nanotechnology, 32, 4, Pp. 042003. Publisher's Version Abstract
nanotech2020"This Roadmap on Nanotechnology for Catalysis and Solar Energy Conversion focuses on the application of nanotechnology in addressing the current challenges of energy conversion: 'high efficiency, stability, safety, and the potential for low-cost/scalable manufacturing' to quote from the contributed article by Nathan Lewis. This roadmap focuses on solar-to-fuel conversion, solar water splitting, solar photovoltaics and bio-catalysis.  It includes dye-sensitized solar cells (DSSCs), perovskite solar cells, and organic photovoltaics. Smart engineering of colloidal quantum materials and nanostructured electrodes will improve solar-to-fuel conversion efficiency, as described in the articles by Waiskopf and Banin and Meyer. Semiconductor nanoparticles will also improve solar energy conversion efficiency, as discussed by Boschloo et al in their article on DSSCs. Perovskite solar cells have advanced rapidly in recent years, including new ideas on 2D and 3D hybrid halide perovskites, as described by Spanopoulos et al 'Next generation' solar cells using multiple exciton generation (MEG) from hot carriers, described in the article by Nozik and Beard, could lead to remarkable improvement in photovoltaic efficiency by using quantization effects in semiconductor nanostructures (quantum dots, wires or wells). These challenges will not be met without simultaneous improvement in nanoscale characterization methods. Terahertz spectroscopy, discussed in the article by Milot et al is one example of a method that is overcoming the difficulties associated with nanoscale materials characterization by avoiding electrical contacts to nanoparticles, allowing characterization during device operation, and enabling characterization of a single nanoparticle. Besides experimental advances, computational science is also meeting the challenges of nanomaterials synthesis. The article by Kohlstedt and Schatz discusses the computational frameworks being used to predict structure–property relationships in materials and devices, including machine learning methods, with an emphasis on organic photovoltaics. The contribution by Megarity and Armstrong presents the 'electrochemical leaf' for improvements in electrochemistry and beyond. In addition, biohybrid approaches can take advantage of efficient and specific enzyme catalysts. These articles present the nanoscience and technology at the forefront of renewable energy development that will have significant benefits to society."


Nir Waiskopf, Shlomo Magdassi, and Uri Banin. 2020. “Quantum Photoinitiators: Toward Emerging Photocuring Applications.” Journal of the American Chemical Society, 143, 2, Pp. 577-587. Abstract
JACS_2020"Semiconductor Nanocrystals are Promising Photocatalysts for a wide range of applications, ranging from alternative fuel generation to biomedical and environmental applications. This stems from their diverse properties, including flexible spectral tunability, stability, and photocatalytic efficiencies. Their functionality depends on the complex influence of multiple parameters, including their composition, dimensions, architecture, surface coating, and environmental conditions. A particularly promising direction for rapid adoption of these nanoparticles as photocatalysts is their ability to act as photoinitiators (PIs) for radical polymerization. Previous studies served to demonstrate the proof of concept for the use of quantum confined semiconductor nanocrystals as photoinitiators, coining the term Quantum PIs, and provided insights for their photocatalytic mechanism of action. However, these early reports suffered from low efficiencies while requiring purging with inert gases, use of additives, and irradiation by high light intensities with very long excitation durations, which limited their potential for real-life applications. The progress in nanocrystal syntheses and surface engineering has opened the way to the introduction of the next generation of Quantum PIs. Herein, we introduce the research area of nanocrystal photocatalysts, review their studies as Quantum PIs for radical polymerization, from suspension polymerization to novel printing, as well as in a new family of polymerization techniques, of reversible deactivation radical polymerization, and provide a forward-looking view for the challenges and prospects of this field."


Guy Lazovski, Galit Bar, Botao Ji, Nurit Atar, Uri Banin, and Raz Gvishi. 2020. “A simple method for preparation of silica aerogels doped with monodispersed nanoparticles in homogeneous concentration.” The Journal of Supercritical Fluids, 159, Pp. 104496. Publisher's Version Abstract
j_sup_fluid_2020"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."


Orian Elimelech, Omer Aviv, Meirav Oded, and Uri Banin. 2020. “A Tale of Tails–Thermodynamics of CdSe Nanocrystal Surface Ligand Exchange.” Nano Letters, 20, 9, Pp. 6396–6403. Publisher's Version Abstract
Orian_NL_2020"The Surface Ligands of Semiconductor Nanocrystals (NCs) are central for determining their properties and for their flexible implementation in diverse applications. Thus far, the thermodynamic characteristics of ligand exchange reactions were attained by indirect methods. Isothermal titration calorimetry is utilized to directly and independently measure both the equilibrium constant and the reaction enthalpy of a model ligand exchange reaction from oleate-capped CdSe NCs  to a series of alkylthiols. Increased reaction exothermicity for longer chains, accompanied by a decrease in reaction entropy with an overall enthalpy–entropy compensation behavior is observed, explained by the length-dependent interchain interactions and the organization of the bound ligands on the NCs’ surface. An increase in the spontaneity of the reaction with decreasing NC size is also revealed, due to their enhanced surface reactivity. This work provides a fundamental understanding of the physicochemical properties of the NC surface with implications for NC surface ligand design."


Gil Aizik, Nir Waiskopf, Majd Agbaria, Meital Ben-David-Naim, Mirjam M Nordling-David, Doaa Jbara-Agbaria, Uri Banin, and Gershon Golomb. 2020. “Targeting and imaging of monocyte-derived macrophages in rat's injured artery following local delivery of liposomal quantum dots.” Journal of Controlled Release, 318, Pp. 145-157. Publisher's Version Abstract

"Quantum Dots Offer Superior Optical Features and hold a great potential as an imaging tool in comparison to ‘conventional’ fluorescent dyes. However, in vivo application in inflammatory-associated disorders is limited due to potential toxicity following systemic administration. Vascular inflammation contributes to cardiovascular diseases such as restenosis (re-narrowing of the artery following angioplasty), and poor Unlabelled Image prognosis is associated with the increased number of monocytes-derived macrophages (MDMs) in the arterial wall.  Local administration of a suitable delivery system targeting MDMs could provide effective fluorescent imaging while minimizing systemic exposure and toxicity. We report here on the physicochemical characteristics and the structural stability of MDMs-targeted liposomal QDs (LipQDs), cellular uptake and cytotoxicity, the systemic biodistribution of LipQDs following local intra-luminal administration of LipQDs in carotid-injured rats vs. systemic administration, and imaging of QDs in the arterial tissue. The local treatment with LipQDs was found to be a suitable approach for targeting QDs to MDMs in the injured artery. In contrast to free QDs, the LipQDs formulation exhibited unique properties including structural and fluorescent stability, increased accumulation and retention for up to 24 h, and targeting properties enabling imaging of MDMs. MDMs imaging by targeted nanoparticles (NPs) could potentially serve for the detection of MDMs density in the injured artery for diagnostic purposes."


Botao Ji, Somnath Koley, Ilya Slobodkin, Sergei Remennik, and Uri Banin. 2020. “ZnSe/ZnS Core/Shell Quantum Dots with Superior Optical Properties through Thermodynamic Shell Growth.” Nano Letters, 20, Pp. 2387-2395. Publisher's Version Abstract
Abstract Image"Epitaxial Growth of a Protective Semiconductor Shell on a colloidal quantum dot (QD) core is the key strategy for achieving high fluorescence quantum efficiency and essential stability for optoelectronic applications and biotagging with emissive QDs. Herein we investigate the effect of shell growth rate on the structure and optical properties in blue-emitting ZnSe/ZnS QDs with narrow emission line width. Tuning the precursor reactivity modifies the growth mode of ZnS shells on ZnSe cores  transforming from kinetic (fast) to thermodynamic (slow) growth regimes. In the thermodynamic growth regime, enhanced fluorescence quantum yields and reduced on–off blinking are achieved.  This high performance is ascribed to the effective avoidance of traps at the interface between the core and the shell, which are detrimental to the emission properties. Our study points to a general strategy to obtain high-quality core/shell QDs with enhanced optical properties through controlled reactivity yielding shell growth in the thermodynamic limit.Epitaxial growth of a protective semiconductor shell on a colloidal quantum dot (QD) core is the key strategy for achieving high fluorescence quantum efficiency and essential stability for optoelectronic applications and biotagging with emissive QDs. Herein we investigate the effect of shell growth rate on the structure and optical properties in blue-emitting ZnSe/ZnS QDs with narrow emission line width. Tuning the precursor reactivity modifies the growth mode of ZnS shells on ZnSe cores transforming from kinetic (fast) to thermodynamic (slow) growth regimes. In the thermodynamic growth regime, enhanced fluorescence quantum yields and reduced on–off blinking are achieved. This high performance is ascribed to the effective avoidance of traps at the interface between the core and the shell, which are detrimental to the emission properties. Our study points to a general strategy to obtain high-quality core/shell QDs with enhanced optical properties through controlled reactivity yielding shell growth in the thermodynamic limit."


Curtis B Williamson, Douglas R Nevers, Andrew Nelson, Ido Hadar, Uri Banin, Tobias Hanrath, and Richard D Robinson. 2019. “Chemically reversible isomerization of inorganic clusters.” Science, 363, 6428, Pp. 731-735. Publisher's Version Abstract

"Structural transformations in molecules and solids have generally been studied in isolation, whereas intermediate systems have eluded characterization. We show that a pair of cadmium sulfide (CdS) cluster isomers provides an advantageous experimental platform to study isomerization in well-defined, atomically precise systems. The clusters coherently interconvert over an ~1–electron volt energy barrier with a 140–milli–electron volt shift in their excitonic energy gaps. There is a diffusionless, displacive reconfiguration of the inorganic core (solid-solid transformation) with first order (isomerization-like) transformation kinetics. Driven by a distortion of the ligand-binding motifs, the presence of hydroxyl species changes the surface energy via physisorption, which determines “phase” stability in this system. This reaction possesses essential characteristics of both solid-solid transformations and molecular isomerizations and bridges these disparate length scales."

Lior Verbitsky, Nir Waiskopf, Shlomo Magdassi, and Uri Banin. 2019. “A clear solution: semiconductor nanocrystals as photoinitiators in solvent free polymerization.” Nanoscale, 11, 23, Pp. 11209-11216. Publisher's Version Abstract

nanoscale2019"Semiconductor nanocrystals have been shown to have unique advantages over traditional organic photoinitiators for polymerization in solution. However, efficient photoinitiation with such nanoparticles in solvent-free and additive-free formulations so far has not been achieved. Herein, the ability to use semiconductor nanocrystals for efficient bulk polymerization as sole initiators is reported, operating under modern UV-blue-LED light sources found in 3D printers and other photocuring applications. Hybrid semiconductor–metal nanorods exhibit superior photoinitiation capability to their pristine semiconductor counterparts, attributed to the enhanced charge separation and oxygen consumption in such systems. Moreover, photoinitiation by semiconductor nanocrystals overcoated by inorganic ligands is reported, thus increasing the scope of possible applications and shedding light on the photoinitiation mechanism; in light of the results, two possible pathways are discussed – ligand-mediated and cation-coordinated oxidation. A demonstration of the unique attributes of the quantum photoinitiators is reported in their use for high-resolution two-photon printing of optically fluorescing microstructures, demonstrating a multi-functionality capability. The bulk polymerization demonstrated here can be advantageous over solvent based methods as it alleviates the need of post-polymerization drying and reduces waste and exposure to toxic solvents, as well as broadens the possible use of quantum photoinitiators for industrial and research uses."

Jiabin Cui, Yossef E Panfil, Somnath Koley, Doaa Shamalia, Nir Waiskopf, Sergei Remennik, Inna Popov, Meirav Oded, and Uri Banin. 2019. “Colloidal quantum dot molecules manifesting quantum coupling at room temperature.” Nature Communications, 10, 1, Pp. 1-10. Publisher's Version Abstract


"Coupling of atoms is the basis of chemistry, yielding the beauty and richness of molecules. We utilize semiconductor nanocrystals as artificial atoms to form nanocrystal molecules that are structurally and electronically coupled. CdSe/CdS core/shell nanocrystals are linked to form dimers which are then fused via constrained oriented attachment. The possible nanocrystal facets in which such fusion takes place are analyzed with atomic resolution revealing the distribution of possible crystal fusion scenarios. Coherent coupling and wave-function hybridization are manifested by a redshift of the band gap, in agreement with quantum mechanical simulations. Single nanoparticle spectroscopy unravels the attributes of coupled nanocrystal dimers related to the unique combination of quantum mechanical tunneling and energy transfer mechanisms. This sets the stage for nanocrystal chemistry to yield a diverse selection of coupled nanocrystal molecules constructed from controlled core/shell nanocrystal building blocks. These are of direct relevance for numerous applications in displays, sensing, biological tagging and emerging quantum technologies."

Richard Weichelt, Jingjing Ye, Uri Banin, Alexander Eychmüller, and Ralf Seidel. 2019. “DNA‐Mediated Self‐Assembly and Metallization of Semiconductor Nanorods for the Fabrication of Nanoelectronic Interfaces.” Chemistry–A European Journal, 25, 38, Pp. 9012-9016. Publisher's Version Abstract


"DNA nanostructures provide a powerful platform for the programmable assembly of nanomaterials. Here, this approach is extended to semiconductor nanorods that possess interesting electrical properties and could be utilized for the bottom‐up fabrication of nanoelectronic building blocks. The assembly scheme is based on an efficient DNA functionalization of the nanorods. A complete coverage of the rod surface with DNA ensures a high colloidal stability while maintaining the rod size and shape. It furthermore supports the assembly of the nanorods at defined docking positions of a DNA origami platform with binding efficiencies of up to 90 % as well as the formation of nanorod dimers with defined relative orientations. By incorporating orthogonal binding sites for gold nanoparticles, defined metal‐semiconductor heterostructures can be fabricated. Subsequent application of a seeded growth procedure onto the gold nanoparticles (AuNPs) allows for to establish a direct metal‐semiconductor interface as a crucial basis for the integration of semiconductors in self‐assembled nanoelectronic devices."

Moussa Biaye, Yorai Amit, Kamil Gradkowski, Natalia Turek, Sylvie Godey, Younes Makoudi, Dominique Deresmes, Athmane Tadjine, Christophe Delerue, and Uri Banin. 2019. “Doped Colloidal InAs Nanocrystals in the Single Ionized Dopant Limit.” The Journal of Physical Chemistry C, 123, 23, Pp. 14803-14812. Publisher's Version Abstract

We investigate the electronic properties of individual n-type (Cu) doped and p-type (Ag) doped InAs colloidal nanocrystals (NCs) in the 2–8 nm size range from their charge transfers toward a highly oriented pyrolytic graphite (HOPG) substrate, using ultrahigh vacuum Kelvin probe force microscopy (KPFM) with elementary charge sensitivity at 300 K. The NC active dopant concentration is measured as ND = 8 × 1020 cm–3 and NA > 5 × 1020 cm–3 for n- and p-type doping, respectively. The electrostatic equilibrium between the NC and the HOPG reference substrate is investigated and reveals an enhancement of the Fermi-level mismatch between the NCs and the HOPG substrate at reduced NC sizes, both for n- and p-type doping. It also shows, for n-type doped NCs with smallest sizes (∼2 nm), the existence of a full depletion regime, in which smallest NCs containAbstract Image single ionized dopants. Results are compared with self-consistent tight-binding calculations of the electronic structure of InAs NCs, including hydrogenoid impurities and the presence of a host substrate, in the case of n-type doped NCs. The observed enhancement of the NC–HOPG Fermi-level mismatch can be understood by considering a size-dependent electrostatic contribution attributed to dipolar effects at the NC–ligand interface. The estimated surface dipole density equals a few Debye/nm2 and is increased at smallest NC sizes, which follows the enhancement of ligand densities at small NC sizes previously reported for metallic or semiconducting NCs. The results put forward the role played by the NC–ligand interface electrostatics for electronic applications.

Yossef E Panfil, Doaa Shamalia, Jiabin Cui, Somnath Koley, and Uri Banin. 2019. “Electronic coupling in colloidal quantum dot molecules; the case of CdSe/CdS core/shell homodimers.” The Journal of Chemical Physics, 151, 22, Pp. 224501. Publisher's Version Abstract


"Coupled colloidal quantum dot molecules composed of two fused CdSe/CdS core/shell sphere monomers were recently presented. Upon fusion, the potential energy landscape changes into two quantum dots separated by a pretuned potential barrier with energetics dictated by the conduction and valence band offsets of the core/shell semiconductors and the width controlled by the shell thickness and the fusion reaction conditions. In close proximity of the two nanocrystals, orbital hybridization occurs, forming bonding and antibonding states in analogy to the hydrogen molecule. In this study, we examine theoretically the electronic and optical signatures of such a quantum dot dimer compared to its monomer core/shell building-blocks. We examine the effects of different core sizes, barrier widths, different band offsets, and neck sizes at the interface of the fused facets on the system wave-functions and energetics. Due to the higher effective mass of the hole and the large valence band offset, the hole still essentially resides in either of the cores, breaking the symmetry of the potential for the electron as well. We found that the dimer signature is well expressed in a red shift of the band gap both in absorption and emission, in slower radiative lifetimes and in an absorption cross section which is significantly enhanced relative to the monomers at energies above the shell absorption onset, while remains essentially at the same level near the band-edge. This study provides essential guidance to predesign of coupled quantum dot molecules with specific attributes which can be utilized for various new opto-electronic applications."