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Moungi G. Bawendi

Bio: Moungi G. Bawendi is an academic researcher from Massachusetts Institute of Technology. The author has contributed to research in topics: Quantum dot & Nanocrystal. The author has an hindex of 165, co-authored 626 publications receiving 118108 citations. Previous affiliations of Moungi G. Bawendi include United States Department of the Navy & United States Naval Research Laboratory.


Papers
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Journal ArticleDOI
TL;DR: In this paper, the molecular mechanism of colloidal quantum dot (QD) synthesis was examined and it was shown that colloidal QD growth is due exclusively to non-molecular ripening.
Abstract: This paper examines the molecular mechanism of InP colloidal quantum dot (QD) syntheses. Unlike methods for monodisperse PbSe and CdSe we found that existing InP syntheses result in total depletion of molecular phosphorous species following nucleation, so QD growth is due exclusively to non-molecular ripening. We find that amines inhibit precursor depletion via solvation, and these findings may lead to better synthetic methodology for InP QDs.

157 citations

Journal ArticleDOI
TL;DR: In this paper, a segmentation of the reacting phase with an immiscible phase can overcome such limitations by narrowing the residence-time distribution (RTD) and improving reactant mixing.
Abstract: Colloidal semiconductor quantum dots (QDs) have been used in biological imaging, electroluminescent devices, and lasers due to their size-tunable optical properties and chemical stability. Most of these applications require highly crystalline samples with narrow size distributions, which are often difficult to achieve in a single-step batch process with its often poor control of reaction conditions. Synthesis of QDs in microfluidic devices offers several advantages over conventional macroscale chemical processes, including enhancement of mass and heat transfer, reproducibility, potential for sensor integration for in situ reaction monitoring, rapid screening of parameters, and low reagent consumption during optimization. Previous studies have realized the continuous synthesis of CdSe QDs at atmospheric pressure using single-phase laminar flow microreactor designs. One difficulty of these synthetic procedures is the requirement for solvents that can both dissolve the precursors at ambient conditions and also remain liquid over the entire operatingtemperature range (25 8C to 350 8C), significantly limiting the set of solvents, ligands, and precursors that are compatible with continuous flow systems. Furthermore, the solvents that are available are typically very viscous (500mPa s< h< 1500mPa s), leading to slow mixing, broad residence-time distributions (RTD), and as a consequence, broad QD-size distributions (typically >10%). Segmentation of the reacting phase with an immiscible phase can overcome such limitations by narrowing the RTD and improving reactant mixing. Application of segmented flow for continuous synthesis of narrowly distributed CdSe QDs has been previously demonstrated for liquid–gas, and liquid–liquid segmented flows. However, even with flow segmentation, limitations on the number of compatible chemistries and the limited number of available high-boiling-point solvents have been major obsta-

153 citations

Journal ArticleDOI
TL;DR: These findings corroborate the experimental observation that incorporation of the nonbulky phosphinic acid-type ligands with high affinity and high selectivity for both the (1120) and (0001) surfaces strongly enhances unidirectional growth on the (001) surface, while incorporation of either bulky ligands or ligand with moderate affinity does not.
Abstract: To gain a better understanding of the influence of ligand−surface interactions on nanocrystalline growth, periodic density functional theory calculations were employed in the study of the binding of organic ligands on the relaxed nonpolar (1120) and polar Se terminated (0001) surfaces and the relaxed and vacancy and adatom reconstructed Cd terminated (0001) surface. We examined chemisorption properties of phosphine, amine, phosphine oxide, carboxylic acid, and phosphinic acid model ligands, including preferred binding sites and geometries, vibrational frequencies, and binding energetics, and compared findings to intrinsic growth via addition of CdSe molecules or Cd and Se atoms. Our results indicate that binding of the ligands is preferred in the electron-poor 1-fold sites on all surfaces, with secondary coordination of the acidic ligands through the hydroxyl hydrogen to the electron-rich surface sites. In general ligand adsorption directly obstructs binding sites for growth species on the (1120) surfa...

153 citations

Journal ArticleDOI
21 Jul 2013
TL;DR: In this paper, the femto-photography technique was proposed to capture and visualize the propagation of light. But, at such fast resolution, the notion of time-unwarping between the camera's and the world's space-time coordinate systems to take into account effects associated with the finite speed of light was not considered.
Abstract: We present femto-photography, a novel imaging technique to capture and visualize the propagation of light. With an effective exposure time of 1.85 picoseconds (ps) per frame, we reconstruct movies of ultrafast events at an equivalent resolution of about one half trillion frames per second. Because cameras with this shutter speed do not exist, we re-purpose modern imaging hardware to record an ensemble average of repeatable events that are synchronized to a streak sensor, in which the time of arrival of light from the scene is coded in one of the sensor's spatial dimensions. We introduce reconstruction methods that allow us to visualize the propagation of femtosecond light pulses through macroscopic scenes; at such fast resolution, we must consider the notion of time-unwarping between the camera's and the world's space-time coordinate systems to take into account effects associated with the finite speed of light. We apply our femto-photography technique to visualizations of very different scenes, which allow us to observe the rich dynamics of time-resolved light transport effects, including scattering, specular reflections, diffuse interreflections, diffraction, caustics, and subsurface scattering. Our work has potential applications in artistic, educational, and scientific visualizations; industrial imaging to analyze material properties; and medical imaging to reconstruct subsurface elements. In addition, our time-resolved technique may motivate new forms of computational photography.

152 citations

Journal ArticleDOI
TL;DR: In this article, the transport properties of artificial solids composed of colloidal CdSe nanocrystals (NCs) are studied from 6 K to 250 K, before and after annealing.
Abstract: Transport properties of artificial solids composed of colloidal CdSe nanocrystals (NCs) are studied from 6 K to 250 K, before and after annealing. Annealing results in greatly enhanced dark and photocurrent in NC solids, while transmission electron microscopy (TEM) micrographs show that the inter-dot separation decreases. The increased current can be attributed to the enhancement of inter-dot tunneling caused by the decreased separation between NCs and by chemical changes in their organic cap. In addition, the absorption spectra of annealed solids are slightly red-shifted and broadened. These red-shifts may result from the change of the dielectric environment around the NCs. Our measurements also indicate that Coulomb interactions between charges on neighboring NCs play an important role in the tunneling current.

151 citations


Cited by
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28 Jul 2005
TL;DR: PfPMP1)与感染红细胞、树突状组胞以及胎盘的单个或多个受体作用,在黏附及免疫逃避中起关键的作�ly.
Abstract: 抗原变异可使得多种致病微生物易于逃避宿主免疫应答。表达在感染红细胞表面的恶性疟原虫红细胞表面蛋白1(PfPMP1)与感染红细胞、内皮细胞、树突状细胞以及胎盘的单个或多个受体作用,在黏附及免疫逃避中起关键的作用。每个单倍体基因组var基因家族编码约60种成员,通过启动转录不同的var基因变异体为抗原变异提供了分子基础。

18,940 citations

Journal ArticleDOI
TL;DR: A review of gold nanoparticles can be found in this article, where the most stable metal nanoparticles, called gold colloids (AuNPs), have been used for catalysis and biology applications.
Abstract: Although gold is the subject of one of the most ancient themes of investigation in science, its renaissance now leads to an exponentially increasing number of publications, especially in the context of emerging nanoscience and nanotechnology with nanoparticles and self-assembled monolayers (SAMs). We will limit the present review to gold nanoparticles (AuNPs), also called gold colloids. AuNPs are the most stable metal nanoparticles, and they present fascinating aspects such as their assembly of multiple types involving materials science, the behavior of the individual particles, size-related electronic, magnetic and optical properties (quantum size effect), and their applications to catalysis and biology. Their promises are in these fields as well as in the bottom-up approach of nanotechnology, and they will be key materials and building block in the 21st century. Whereas the extraction of gold started in the 5th millennium B.C. near Varna (Bulgaria) and reached 10 tons per year in Egypt around 1200-1300 B.C. when the marvelous statue of Touthankamon was constructed, it is probable that “soluble” gold appeared around the 5th or 4th century B.C. in Egypt and China. In antiquity, materials were used in an ecological sense for both aesthetic and curative purposes. Colloidal gold was used to make ruby glass 293 Chem. Rev. 2004, 104, 293−346

11,752 citations

Journal ArticleDOI
16 Feb 1996-Science
TL;DR: In this article, the authors focus on the properties of quantum dots and their ability to join the dots into complex assemblies creates many opportunities for scientific discovery, such as the ability of joining the dots to complex assemblies.
Abstract: Current research into semiconductor clusters is focused on the properties of quantum dots-fragments of semiconductor consisting of hundreds to many thousands of atoms-with the bulk bonding geometry and with surface states eliminated by enclosure in a material that has a larger band gap. Quantum dots exhibit strongly size-dependent optical and electrical properties. The ability to join the dots into complex assemblies creates many opportunities for scientific discovery.

10,737 citations

Journal ArticleDOI
01 Apr 1988-Nature
TL;DR: In this paper, a sedimentological core and petrographic characterisation of samples from eleven boreholes from the Lower Carboniferous of Bowland Basin (Northwest England) is presented.
Abstract: Deposits of clastic carbonate-dominated (calciclastic) sedimentary slope systems in the rock record have been identified mostly as linearly-consistent carbonate apron deposits, even though most ancient clastic carbonate slope deposits fit the submarine fan systems better. Calciclastic submarine fans are consequently rarely described and are poorly understood. Subsequently, very little is known especially in mud-dominated calciclastic submarine fan systems. Presented in this study are a sedimentological core and petrographic characterisation of samples from eleven boreholes from the Lower Carboniferous of Bowland Basin (Northwest England) that reveals a >250 m thick calciturbidite complex deposited in a calciclastic submarine fan setting. Seven facies are recognised from core and thin section characterisation and are grouped into three carbonate turbidite sequences. They include: 1) Calciturbidites, comprising mostly of highto low-density, wavy-laminated bioclast-rich facies; 2) low-density densite mudstones which are characterised by planar laminated and unlaminated muddominated facies; and 3) Calcidebrites which are muddy or hyper-concentrated debrisflow deposits occurring as poorly-sorted, chaotic, mud-supported floatstones. These

9,929 citations

Journal ArticleDOI
21 Feb 1997-Science
TL;DR: In this article, surface-enhanced Raman scattering was used to detect single molecules and single nanoparticles at room temperature with the use of surface enhanced Raman, and the intrinsic Raman enhancement factors were on the order of 10 14 to 10 15, much larger than the ensemble-averaged values derived from conventional measurements.
Abstract: Optical detection and spectroscopy of single molecules and single nanoparticles have been achieved at room temperature with the use of surface-enhanced Raman scattering. Individual silver colloidal nanoparticles were screened from a large heterogeneous population for special size-dependent properties and were then used to amplify the spectroscopic signatures of adsorbed molecules. For single rhodamine 6G molecules adsorbed on the selected nanoparticles, the intrinsic Raman enhancement factors were on the order of 10 14 to 10 15 , much larger than the ensemble-averaged values derived from conventional measurements. This enormous enhancement leads to vibrational Raman signals that are more intense and more stable than single-molecule fluorescence.

9,609 citations