Publications

Moletronics II

Photonic Luminescent Solar Concentrator Design for High Efficiency, Low Cost Multijunction Photovoltaics

Despite the extraordinary advances in solar cell efficiency in laboratory settings, the deployment of solar cells continues to be limited to low efficiency (<25%) silicon cells because of cost. In this work, we take advantage of the extraordinary optical properties afforded by nanophotonic structures to create a photonic luminescent solar concentrator for an InGaP-Si multijunction concentrator cell. Finite difference time domain (FDTD) simulations demonstrated a concentrator that could effectively capture, downconvert, and guide concentrated light to an InGaP subcell while still transmitting longer wavelengths to a Si subcell. We fabricated the photonic luminescent solar concentrator, which was comprised of CdSe/CdS quantum dots embedded within alternating layers of Si 3 N 4 and SiO 2 , and experimentally verified the optical performance, showing a 40% increase in light guiding and a significant reduction in reabsorption losses in the plane of the luminescent concentrator as compared to traditional designs. Finally, we utilized modified detailed balance calculations that accounted for cell and optical losses and showed >30% efficiencies are possible with this design, demonstrating the potential to meet the demands for high efficiency, inexpensive solar modules.

Structure determination and homogeneous optical properties of CdS/HgS quantum dots

Abstract The structural and optical properties of heterogeneous semiconductor nanoparticles consisting of CdS and HgS are investigated by High Resolution Electron Microscopy (HRTEM) and selective spectroscopy like Hole Burning (HB) and Fluorescence Line Narrowing (FLN). The HRTEM study shows that epitaxy is possible in nanocrystals, provided the crystallites have well defined faceted shapes to begin with. From the HB‐ and FLN experiments homogeneous absorption and fluorescence spectra are calculated. It could be shown that the absorption is coupled to HgS‐like phonons (250 cm −1 ) whereas the emission frequency is closer to the LO phonon frequency of CdS.

Ultrafast dephasing dynamics and multi-level electronic structure of InP nanocrystals

Semiconductor nanocrystals are a novel class of materials intermediate between the molecular and solid state forms of matter. Their homogenous linewidths and electronic structure are of considerable interest for the understanding of the physics of quantum confinement. In this work we study the electronic and vibrational dephasing dynamics in InP nanocrystals using femtosecond three pulse photon echo (3PPE) experiments 1 complemented by nanosecond transient hole-burning (HB) spectroscopy. 2 The echo decay is explained by taking into account the multi-level electronic structure as observed in the hole-burning experiment.

Shaped nanocrystal particles and methods for making the same

Shaped nanocrystal particles and methods for making shaped nanocrystal particles are disclosed. One embodiment includes a method for forming a branched, nanocrystal particle. It includes (a) forming a core having a first crystal structure in a solution, (b) forming a first arm extending from the core having a second crystal structure in the solution, and (c) forming a second arm extending from the core having the second crystal structure in the solution.

Nanothermodynamics:  A Personal Perspective by Terrell Hill

ADVERTISEMENT RETURN TO ISSUEEditorialNEXTNanothermodynamics: A Personal Perspective by Terrell HillPaul AlivisatosView Author Information EditorCite this: Nano Letters 2001, 1, 3, 109Publication Date (Web):February 17, 2001Publication History Published online17 February 2001Published inissue 1 March 2001https://pubs.acs.org/doi/10.1021/nl010012yhttps://doi.org/10.1021/nl010012yeditorialACS PublicationsCopyright © 2001 American Chemical Society. This publication is available under these Terms of Use. Request reuse permissions This publication is free to access through this site. Learn MoreArticle Views1263Altmetric-Citations5LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InRedditEmail PDF (7 KB) Get e-AlertscloseSUBJECTS:Nanoscale,Nanoscience,Thermodynamics Get e-Alerts

Combinatorial approaches toward patterning nanocrystals

A scheme for generating complex, spatially separated patterns of multiple types of semiconducting and/or metallic nanocrystals is presented. The process is based on lithographic patterning of organic monolayers that contain a photolabile protection group and are covalently bound to SiO2 surfaces. The process results in spatially and chemically distinct interaction sites on a single substrate. Nanocrystal assembly occurs with a high selectivity on just one type of site. We report on the production of binary, tertiary, and quatemary patterns of nanocrystals. We highlight and discuss the differences between nanocrystal/substrate assembly and molecule/substrate assembly. Finally, we investigate the assembled structures using photoluminescence and absorption spectroscopy.

Controlling electron beam-induced structure modifications and cation exchange in cadmium sulfide–copper sulfide heterostructured nanorods

Reaction Chemistry and Ligand Exchange at Cadmium−Selenide Nanocrystal Surfaces

The surface chemistry of cadmium selenide nanocrystals, prepared from tri-n-octylphosphine selenide and cadmium octadecylphosphonate in tri-n-octylphosphine oxide, was studied with 1H and {1H}31P NMR spectroscopy as well as ESI-MS and XPS. The identity of the surface ligands was inferred from reaction of nanocrystals with Me3Si-X (X = -S-SiMe3, -Se-SiMe3, -Cl and -S-(CH2CH2O)4OCH3)) and unambiguous assignment of the organic byproducts, O,O'-bis(trimethylsilyl)octadecylphosphonic acid ester and O,O'-bis(trimethylsilyl)ocatdecylphosphonic acid anhydride ester. Nanocrystals isolated from these reactions have undergone exchange of the octadecylphosphonate ligands for -X as was shown by 1H NMR (X = -S-(CH2CH2O)4OCH3) and XPS (X = -Cl). Addition of free thiols to as prepared nanocrystals results in binding of the thiol to the particle surface and quenching of the nanocrystal fluorescence. Isolation of the thiol-ligated nanocrystals shows this chemisorption proceeds without displacement of the octadecylphosphonate ligands, suggesting the presence of unoccupied Lewis-acidic sites on the particle surface. In the presence of added triethylamine, however, the octadecylphosphonate ligands are readily displaced from the particle surface as was shown with 1H and {1H}31P NMR. These results, in conjunction with previous literature reports, indicate that as-prepared nanocrystal surfaces are terminated by X-type binding of octadecylphosphonate moieties to a layer of excess cadmium ions.

Shape control of CdSe nanocrystals

Elucidating the Weakly Reversible Cs–Pb–Br Perovskite Nanocrystal Reaction Network with High-Throughput Maps and Transformations

Advances in automation and data analytics can aid exploration of the complex chemistry of nanoparticles. Lead halide perovskite colloidal nanocrystals provide an interesting proving ground: there are reports of many different phases and transformations, which has made it hard to form a coherent conceptual framework for their controlled formation through traditional methods. In this work, we systematically explore the portion of Cs-Pb-Br synthesis space in which many optically distinguishable species are formed using high-throughput robotic synthesis to understand their formation reactions. We deploy an automated method that allows us to determine the relative amount of absorbance that can be attributed to each species in order to create maps of the synthetic space. These in turn facilitate improved understanding of the interplay between kinetic and thermodynamic factors that underlie which combination of species are likely to be prevalent under a given set of conditions. Based on these maps, we test potential transformation routes between perovskite nanocrystals of different shapes and phases. We find that shape is determined kinetically, but many reactions between different phases show equilibrium behavior. We demonstrate a dynamic equilibrium between complexes, monolayers, and nanocrystals of lead bromide, with substantial impact on the reaction outcomes. This allows us to construct a chemical reaction network that qualitatively explains our results as well as previous reports and can serve as a guide for those seeking to prepare a particular composition and shape.

Thermodynamic Investigation of Increased Luminescence in Indium Phosphide Quantum Dots by Treatment with Metal Halide Salts

Increasing the quantum yields of InP quantum dots is important for their applications, particularly for use in consumer displays. While several methods exist to improve quantum yield, the addition of inorganic metal halide salts has proven promising. To further investigate this phenomenon, InP quantum dots dispersed in tetrahydrofuran were titrated with ZnCl₂, ZnBr₂, and InCl₃. The optical properties were observed, and the reactions were studied by using quantitative ¹H NMR and thermodynamic measurements from isothermal titration calorimetry. These measurements contradict the previously hypothesized reaction mechanism in which metal halide salts, acting as Z-type ligands, passivate undercoordinated anions on the surface of the quantum dots. This work provides evidence for a newly proposed mechanism wherein the metal halide salts undergo a ligand exchange with indium myristate. Thermodynamic measurements prove key to supporting this new mechanism, particularly in describing the organic ligand interactions on the surface. An Ising model was used to simulate the quantum dot surface and was fit by using thermodynamic and ¹H NMR data. Together, these data and the proposed exchange mechanism provide greater insight into the surface chemistry of quantum dots.

Germanium quantum dots: Optical properties and synthesis

Three different size distributions of Ge quantum dots (≳200, 110, and 60 Å) have been synthesized via the ultrasonic mediated reduction of mixtures of chlorogermanes and organochlorogermanes (or organochlorosilanes) by a colloidal sodium/potassium alloy in heptane, followed by annealing in a sealed pressure vessel at 270 °C. The quantum dots are characterized by transmission electron microscopy, x-ray powder diffraction, x-ray photoemission, infrared spectroscopy, and Raman spectroscopy. Colloidal suspensions of these quantum dots were prepared and their extinction spectra are measured with ultraviolet/visible (UV/Vis) and near infrared (IR) spectroscopy, in the regime from 0.6 to 5 eV. The optical spectra are correlated with a Mie theory extinction calculation utilizing bulk optical constants. This leads to an assignment of three optical features to the E(1), E(0′), and E(2) direct band gap transitions. The E(0′) transitions exhibit a strong size dependence. The near IR spectra of the largest dots is dominated by E(0) direct gap absorptions. For the smallest dots the near IR spectrum is dominated by the Γ25→L indirect transitions.

Process for forming shaped group II-VI semiconductor nanocrystals, and product formed using process

A process for the formation of shaped Group II-VI semiconductor nanocrystals comprises contacting the semiconductor nanocrystal precursors with a liquid media comprising a binary mixture of phosphorus-containing organic surfactants capable of promoting the growth of either spherical semiconductor nanocrystals or rod-like semiconductor nanocrystals, whereby the shape of the semiconductor nanocrystals formed in said binary mixture of surfactants is controlled by adjusting the ratio of the surfactants in the binary mixture.

Electrophoretic and Structural Studies of DNA-Directed Au Nanoparticle Groupings

Discrete Au nanoparticle/DNA conjugates have been isolated by electrophoresis and used to form small groupings of particles, such as dimers and trimers. The use of purified conjugates leads to a higher yield of the target structure, and it has allowed us better control and understanding of the system. Newly accessible questions, such as the electrophoretic mobility of nanoparticle/DNA hybrids and the critical role of particle surface charge on mobility, have been studied. Detailed characterization by transmission electron microscopy (TEM) has now been done because of the higher quality of the samples. A computer program to generate pair distribution functions from TEM images was developed, pointing out the dependence of interparticle distance with DNA length on dimers of particles.

Studying Diffusion of Colloidal Nanoparticles in Solution Using Liquid Phase TEM and Machine Learning

Journal Article Studying Diffusion of Colloidal Nanoparticles in Solution Using Liquid Phase TEM and Machine Learning Get access Vida Jamali, Vida Jamali Department of Chemistry, University of California – Berkeley, Berkeley, CA, United States Corresponding author: vidaj@berkeley.edu, paul.alivisatos@berkeley.edu Search for other works by this author on: Oxford Academic Google Scholar A Paul Alivisatos A Paul Alivisatos Department of Chemistry, University of California – Berkeley, Berkeley, CA, United States Corresponding author: vidaj@berkeley.edu, paul.alivisatos@berkeley.edu Search for other works by this author on: Oxford Academic Google Scholar Microscopy and Microanalysis, Volume 28, Issue S1, 1 August 2022, Pages 142–143, https://doi.org/10.1017/S1431927622001465 Published: 01 August 2022

Dataset of automatically extracted sizes and morphologies of AuNPs from literature-mined SEM/TEM images

This is a dataset of automatically extracted sizes and morphologies of Gold nanoparticles, which have been obtained from the analysis of 4365 literature-mined SEM/TEM images. The dataset contains 4365 records, each of which contains extracted size/morphology information and metadata corresponding to a single microscopy image.

Isolation of Discrete Nanoparticle−DNA Conjugates for Plasmonic Applications

Discrete DNA−gold nanoparticle conjugates with DNA lengths as short as 15 bases for both 5 and 20 nm gold particles have been purified by anion-exchange HPLC. Conjugates comprising short DNA (<40 bases) and large gold particles (≥20 nm) are difficult to purify by other means and are potential substrates for plasmon coupling experiments. Conjugate purity is demonstrated by hybridizing complementary conjugates to form discrete structures, which are visualized by TEM.