Uri Banin - Profile on Academia.edu (original) (raw)

Papers by Uri Banin

Nature Communications, May 27, 2023

Proceedings of the nanoGe Spring Meeting 2022, Feb 7, 2022

Coupling of atoms is the basis of chemistry, yielding the beauty and richness of molecules. We ut... more 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 wavefunction hybridization are manifested by a red shift 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 nanocrystals 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.

Research Square (Research Square), Dec 14, 2022

Electron transfer is an important and fundamental process in chemistry, biology and physics, and ... more Electron transfer is an important and fundamental process in chemistry, biology and physics, and has received significant attention in recent years. Perhaps one of the most intriguing questions concerns with the realization of the transitions between nonadiabatic and adiabatic regimes of electron transfer, as the coupling (hybridization) energy, J, between the donor and acceptor is varied. Here, using colloidal quantum dot molecules, a new class of coupled quantum dot dimers, we computationally demonstrate how the hybridization energy between the donor and acceptor quantum dots can be tuned by simply changing the neck dimensions and/or the quantum dot size. This provides a handle to tune the electron transfer from the nonadiabatic over-damped Marcus regime to the coherent adiabatic regime in a single system, without changing the reorganization energy, λ, or the typical phonon frequency, ωc. We develop an atomistic model to account for several donor and acceptor states and how they couple to the lattice vibrations, and utilize the Ehrenfest mean-field mixed quantum-classical method to describe the charge transfer dynamics as the nonadiabatic parameter, γ, is varied. We find that charge transfer rates increase by several orders of magnitude as the system is driven to the coherent, adiabatic limit, even at elevated temperatures, and delineate the inter-dot and torsional acoustic modes that couple most strongly to the charge transfer reaction coordinate.

Lawrence Berkeley National Laboratory, Mar 30, 2006

Nano Letters, Jul 9, 2018

Hybrid semiconductor-metal nanoparticles (HNPs) manifest unique, synergistic electronic and optic... more 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.

SSRN Electronic Journal

Fused homodimer Colloidal Quantum Dot Molecules (CQDMs), analogous to homonuclear diatomic molecu... more Fused homodimer Colloidal Quantum Dot Molecules (CQDMs), analogous to homonuclear diatomic molecules, exhibit hybridization of the confined electronic states controlled by the neck girth at the fusion interface. Their constituent "artificial atom" CQDs manifest tunable optoelectronic properties relevant for numerous applications, including in future quantum technologies. Thus, the concept of "nanocrystal chemistry" underlying the CQDMs, greatly enriches the selection of such artificial constructs. Numerous new bright multiexcitonic configurations may form in the CQDM, unlike the multiexcitons in CQDs which are dimmed by strong non-radiative Auger recombination processes. The handle of the neck girth is found to dictate the many-body interplay in CQDMs and determines the photon purity, where in narrow neck girth (weak coupling), the CQDM acts as a multiphoton emitter, while neck filled CQDMs (strong coupling) regain single photon emission characteristics typical of the monomers. The unique attributes of the CQDMs manifesting excellent absorbing and bright tunable excitonic and multiexcitonic states highlights their relevance for potential light emitting applications. In this manuscript, we investigate the charge re-distribution upon optical excitation of various necked homodimer CQDMs using single particle emission spectroscopy. By tuning the hybridization of the electron wavefunction at a fixed center-to-center distance through controlling the neck girth, we reveal two coupling limits. On one hand a "connected-but-confined" situation where neighbouring CQDs are weakly fused to each other manifesting a weak coupling regime, and on the other hand, a "connected-and-delocalized" situation, where the neck is filled beyond the facet size leading to a rod-like architecture manifesting strong-coupling. Either coupling regimes entrust distinct optical signatures clearly resolved at room temperature in terms of photoluminescence quantum yield, intensity time traces, lifetimes, and spectra of the neutral-exciton, charged-exciton, and biexciton states. The interplay between the radiative and non-radiative Auger decays of these states, turns emitted photons from the CQDMs in the "weak-coupling" regime highly bunched unlike CQD monomers, while the antibunching is regained at the "strong-coupling' regime. This behavior correlates with the hybridization energy being smaller than the thermal energy (kT ~25meV) at the "weak-coupling" limit (∆E~5-10meV), leading to exciton localization suppressing Auger decay. In the neck-filled architectures, the larger hybridization energy (∆E~20-30meV) leads to exciton delocalization while activating the fast charged and multi-exciton Auger decay processes. This work sets an analogy for the artificial molecule CQDMs with regular molecules, where the two distinct regimes of weak-and strong-coupling correspond to ionic-or covalent-type bonding, respectively.

Nano Letters, 2021

Recently, it was demonstrated that charge separation in hybrid metal-semiconductor nanoparticles ... more 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 backtransfer 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.

Science, 2019

Cluster isomerization Structural rearrangements at the atomic scale can range from isomerization ... more Cluster isomerization Structural rearrangements at the atomic scale can range from isomerization of small molecules to solid-solid phase transformations of crystals. Williamson et al. show that magic-size cadmium sulfide (CdS) crystalline clusters, which are about 2 nanometers in diameter and expose a large fraction of surface atoms capped by bidentate oleate ligands, undergo a reversible isomerization. The initial α-Cd 37 S 20 phase, which has a wurtzite-like crystal structure, isomerizes to β-Cd 37 S 20 , which has a zinc blende–like structure upon exposure to methanol, and then transforms back under vacuum. This transition is driven by distortion of the ligand shell and shifts the excitonic energy gap of the clusters. Science , this issue p. 731

Kolloidale Quantennanostrukturen: neue Materialien für Displayanwendungen

Angewandte Chemie, 2018

Kolloidale Halbleiternanokristalle (“semiconductor nanocrystals”, SCNC), oder weiter gefasst koll... more Kolloidale Halbleiternanokristalle (“semiconductor nanocrystals”, SCNC), oder weiter gefasst kolloidale Quantennanostrukturen, stellen außergewöhnliche Modellsysteme zur Untersuchung von Größen‐ und Dimensionalitätseffekten dar. Aufgrund ihrer nanoskaligen Abmessungen kommt es zu Quantelungseffekten, die eine Abstimmung optischer und elektronischer Eigenschaften ermöglichen. Die Steuerung der Emissionsfarbe bei engen Photolumineszenzspektren, breite Absorptionsspektren sowie eine außergewöhnliche Photostabilität und eine gute chemische Verarbeitbarkeit durch Steuerung der Oberflächenchemie machen SCNS zu herausragenden Materialien für Displays der aktuellen und der nächsten Generation. In diesem Aufsatz beschreiben wir die chemischen und physikalischen Eigenschaften der SCNC und stellen die Vorteile verschiedener kolloidaler Quantennanostrukturen für Displayanwendungen vor, und wir betrachten mögliche Photolumineszenz‐ und Elektrolumineszenzdisplays unter Verwendung von SCNC.

Nano Letters, 2018

Physical Review B, 1997

The electronic level structure and dephasing dynamics of InP nanocrystals in the strong quantumco... more The electronic level structure and dephasing dynamics of InP nanocrystals in the strong quantumconfinement regime are studied by two complementary techniques: nanosecond hole burning and the femtosecond three-pulse photon echo. Hole burning yields the homogeneous electronic level structure while the photon echo allows the extraction of the linewidth of the band-gap transition. The congestion of electronic levels observed close to the band-edge transition in the hole-burning experiments gives rise to a pulse-widthlimited initial decay in the photon-echo signal. The level structure is calculated and assigned using a model which includes valence-band mixing. The homogeneous linewidth of the band-edge transition is approximately 5 meV at 20 K and is broadened considerably at higher temperatures. The temperature dependence of the linewidth is consistent with an intrinsic dephasing mechanism of coupling to low-frequency acoustic modes mediated by the deformation potential. Quantum-confinement effects in III-V semiconductor InP are compared to those of the prototypical CdSe II-VI semiconductor nanocrystal system. ͓S0163-1829͑97͒02111-5͔

Zeitschrift für Physikalische Chemie, 2015

Quantum confinement effects are observed in transport measurements of Cu2S nanocrystal based devi... more Quantum confinement effects are observed in transport measurements of Cu2S nanocrystal based devices. Two nanocrystals sizes are studied, 3 nm being in the quantum-confinement regime, and 14 nm, lacking confinement. The effect of ligand length on the charge transport mechanism is studied via conductance temperature dependence measurements. While in the 14 nm nanocrystal based devices unique non-monotonic temperature dependence is observed, the 3 nm based devices show only thermally activated transport for all ligands. The difference is attributed to a cross-over from inter-particle hopping to intra-particle dominated transport as the ligand length increases. In the 3 nm devices the effect of ligand length on the charge-hopping activation energy is also discussed.

ACS chemical neuroscience, Jan 16, 2011

Butyrylcholinesterase (BChE) is the major acetylcholine hydrolyzing enzyme in peripheral mammalia... more Butyrylcholinesterase (BChE) is the major acetylcholine hydrolyzing enzyme in peripheral mammalian systems. It can either reside in the circulation or adhere to cells and tissues and protect them from anticholinesterases, including insecticides and poisonous nerve gases. In humans, impaired cholinesterase functioning is causally involved in many pathologies, including Alzheimer's and Parkinson's diseases, trait anxiety, and post stroke conditions. Recombinant cholinesterases have been developed for therapeutic use; therefore, it is important to follow their in vivo path, location, and interactions. Traditional labeling methods, such as fluorescent dyes and proteins, generally suffer from sensitivity to environmental conditions, from proximity to different molecules or special enzymes which can alter them, and from relatively fast photobleaching. In contrast, emerging development in synthesis and surface engineering of semiconductor nanocrystals enable their use to detect and...

Physical Review B, 1999

Localization of carrier wave functions to the quantum-well portion of the CdS/HgS quantum-dot qua... more Localization of carrier wave functions to the quantum-well portion of the CdS/HgS quantum-dot quantum well ͑QDQW͒ is investigated. Nanosecond hole-burning ͑HB͒ spectra measure the photoinduced exciton coupling to a 250-cm Ϫ1 HgS phonon mode indicative of localization. Femtosecond pump-probe spectroscopy of these QDQW, however, show the photoinduced exciton couples to coherent 300-cm Ϫ1 CdS longitudinal optical-phonon modes, which is indicative of delocalization throughout the QDQW. Femtosecond HB and three pulse pump-dump experiments reveal these results are dependent on the time scale of the experiment. These experiments indicate that the initially photoexcited electron and hole wave functions are weakly confined to the HgS monolayer. Only after long times ͑ϳ400 fs͒ will the exciton localize to the HgS well. These results indicate that the primary optical interaction excites electrons from a delocalized QDQW ground state and not from a localized HgS well state. ͓S0163-1829͑99͒10307-2͔

ChemInform, 2010

Synthesis of Size-Selected, Surface-Passivated InP Nanocrystals. -Highly crystalline, monodispers... more Synthesis of Size-Selected, Surface-Passivated InP Nanocrystals. -Highly crystalline, monodisperse quantum-confined InP nanocrystals of 20-50 Å particle diameter are prepared by reaction of InCl3 and P( SiMe3)3 in trioctylphosphine oxide (TOPO) at 265 • C. The nanocrystals which are soluble in various nonpolar organic solvents, can be surface-modified with a variety of ligands resulting in different passivation behavior. By size-selective reprecipitation the narrowest size distributions for a III-V semiconductor is achieved. Characterization by powder XRD, TEM, Raman spectroscopy, and XPS shows a 30-100% TOPO surface coverage of the InP nanocrystals before oxidation and complete passivation after exposure to air. Photoluminescence is highly sensitive to surface passivation with surface oxidation being necessary for emission. -(GUZELIAN, A. A.

Nano Letters, 2014

We report the development of a semiconductor nanorod-carbon nanotube based platform for wire-free... more 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 applications.

Physical Review B, 2012

We report a bi-polar multiple periodic negative differential conductance (NDC) effect on a single... more We report a bi-polar multiple periodic negative differential conductance (NDC) effect on a single cage-shaped Ru nanoparticle measured using scanning tunneling spectroscopy. This phenomenon is assigned to the unique multiply-connected cage architecture providing two (or more) defined routes for charge flow through the cage. This, in turn, promotes a selfgating effect, where electron charging of one route affects charge transport along a neighboring channel, yielding a series of periodic NDC peaks. This picture is established and analyzed here by a theoretical model.

ECS Transactions, 2013

The doping of colloidal semiconductor nanocrystals (NCs) presents an additional knob beyond size ... more The doping of colloidal semiconductor nanocrystals (NCs) presents an additional knob beyond size and shape for controlling the electronic properties. An important problem for impurity doping is associated with resolving the location and structural surrounding of the dopant within the small NCs, in light of tendency for driving of the impurity atom to the surface of the NC. A post-synthesis diffusion-based doping approach for introducing metal impurities into InAs NCs is described and characterized. This enables accurate correlation between the emerged electronic properties and the doping process. Optical absorption spectroscopy and scanning tunneling spectroscopy (STS) measurements revealed the n-type and p-type behavior of the doped NCs, depending on the identity of selected impurities. X-ray absorption fine structure (XAFS) spectroscopy measurements demonstrated the interstitial location of Cu within the InAs NCs, acting as an n-type dopant, which was found to occupy a single uniq...

The Journal of Physical Chemistry B, 2004

Two-photon polarization fluorescence microscopy is used to study the nature of the emission and n... more Two-photon polarization fluorescence microscopy is used to study the nature of the emission and nonlinear absorption dipole of single CdSe/ZnS quantum rods. Rods showed strongly polarized nonlinear excitation with sharp angular dependence, following a cos 4 (φ) functional form, in agreement with the predicted twophoton absorption process. The two-photon absorption is parallel to the emission polarization and allows high orientation selectivity in excitation to be achieved. This further demonstrates the role of single molecule measurements in unraveling basic principles of light-matter interactions otherwise masked by ensemble averaging.

The Journal of Physical Chemistry B, 2006

The photo-induced enhancement of second harmonic generation, and the effect of nanocrystal shape ... more The photo-induced enhancement of second harmonic generation, and the effect of nanocrystal shape and pump intensity on confined acoustic phonons in semiconductor nanocrystals, has been investigated with time-resolved scattering and absorption measurements. The second harmonic signal showed a sublinear increase of the second order susceptibility with respect to the pump pulse energy, indicating a reduction of the effective one-electron second-order nonlinearity with increasing electron-hole density in the nanocrystals. The coherent acoustic phonons in spherical and rod-shaped semiconductor nanocrystals were detected in a time-resolved absorption measurement. Both nanocrystal morphologies exhibited oscillatory modulation of the absorption cross section, the frequency of which corresponded to their coherent radial breathing modes. The amplitude of the oscillation also increased with the level of photoexcitation, suggesting an increase in the amplitude of the lattice displacement as well.