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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
13 May 1999-Nature
TL;DR: In this article, it was shown that far-field polarization microscopy can yield the 3D orientation of certain highly symmetric single chromophores (CdSe nanocrystal quantum dots in the present case).
Abstract: A complete understanding of any complex molecular system generally requires a knowledge of the three-dimensional (3D) orientation of its components relative both to each other, and to directional perturbations such as interfaces and electromagnetic fields. Far-field polarization microscopy is a convenient and widespread technique for detecting and measuring the orientation of single chromophores. But because the polarized electromagnetic field that is used to probe the system lacks a significant longitudinal component, it was thought that, in general, only 2D orientation information could be obtained1,2,3. Here we demonstrate that far-field polarization microscopy can yield the 3D orientation of certain highly symmetric single chromophores (CdSe nanocrystal quantum dots in the present case). The key requirement is that the chromophores must have a degenerate transition dipole oriented isotropically in two dimensions, which gives rise to a perpendicular ‘dark axis’ that does not couple to the light field. By measuring the fluorescence intensity from the dipole as a function of polarization angle, it is possible to calculate both the tilt angle between the dark axis and the sample plane, as well as the in-plane orientation, and hence obtain the 3D orientation of the chromophore

276 citations

Journal ArticleDOI
TL;DR: Although efficient green-emitting core–shell semiconductor NCs that emit at l= 525 nm have been synthesized, they have not been successfully incorporated into a QD-LED suitable for display applications, and herein, the synthesis of a (CdSe)ZnS core-shell material is reported.
Abstract: Semiconductor nanocrystals (NCs) or quantum dots (QDs) show great promise for use in QD-LED (quantum dot lightemitting device) displays, owing to their unique optical properties and the continual development of new core and core–shell structures to meet specific color needs. This in combination with the recent development of more efficient and saturated QD-LEDs as well as new QD-LED fabrication techniques, suggests that QD-LEDs have the potential to become an alternative flat-panel display technology. The ideal red, green, and blue emission spectrum of an LED for a display application should have a narrow bandwidth and a wavelength such that its color coordinates on the Commission Internationale de l+Eclairage (CIE) chromaticity diagram lie outside the current National Television System Committee (NTSC) standard color triangle (see Figure 2). For a Gaussian emission spectrum with a full width at half maximum (FWHM) of 30 nm and a maximized perceived power, the optimal peak wavelength for display applications is l= 610– 620 nm for red, l= 525–530 nm for green, and l= 460– 470 nm for blue. For the red pixels, wavelengths longer than l= 620 nm become difficult for the human eye to perceive, while those shorter than l= 610 nm have coordinates that lie inside the standard NTSC color triangle. Optimization of wavelength for the blue pixels follows the same arguments as for the red pixel, but at the other extreme of the visible spectrum. For green pixels, l= 525–530 nm provides a color triangle with the largest area on the CIE chromaticity diagram (and therefore the largest number of colors accessible by a display). Wavelengths longer than l= 530 nm make some of the blue/green area of the triangle inaccessible. Wavelengths shorter than l= 525 nm compromise the yellow display emissions. To date, efficient red-emitting QD-LEDs with a peak emission wavelength optimized for display applications have been realized using (CdSe)ZnS core–shell NCs, while blue QD-LEDs with a peak wavelength of emission optimized for display applications have been realized with a (CdS)ZnS core–shell material. To date, although efficient green-emitting core–shell semiconductor NCs that emit at l= 525 nm have been synthesized, they have not been successfully incorporated into a QD-LED suitable for display applications. Previous work using (CdSe)ZnS core–shell NCs gave QD-LEDs that emit at wavelengths no shorter than l= 540–560 nm. 14] Using (CdSe)ZnS core–shell NCs to achieve l= 525 nm emission requires making small CdSe cores ( 2.5 nm in diameter). 16] Such small CdSe semiconductor NCs can be difficult to synthesize with narrow size distributions and high quantum efficiencies, and are also more difficult to process and overcoat with a higher-band-gap inorganic semiconductor, which is necessary for incorporation into solid-state structures. A core–shell composite, rather than an organically passivated NC, is desirable in a solid-state QD-LED device owing to the enhanced photoluminescence and electroluminescence (EL) quantum efficiencies of core– shell NCs and their greater tolerance to the processing conditions necessary for device fabrication. Larger NCs are also more desirable for use in QD-LEDs because the absorption cross section of NCs scales with size. Larger NCs with larger absorption cross sections lead to an increase in the efficiency of F?rster energy transfer from electroluminescing organic molecules to NCs in a working QD-LED, which in turn leads to more efficient devices. Herein, we report the synthesis of a CdxZn1 xSe alloy core on which we then grew a CdyZn1 yS shell to create a core– shell NC material with the ideal spectral characteristics for green emission in a QD-LED display and with a size large enough for fabricating a working QD-LED. Our CdxZn1 xSe core synthesis was based on work recently published, in which Cd and Se precursors were slowly introduced into a growth solution of ZnSe NCs. A three-step synthetic route was employed to prepare the (CdxZn1 xSe)CdyZn1 yS core–shell NCs. In the first step, ZnSe NCs were prepared by rapidly injecting 0.7 mmol of diethylzinc (Strem) and 1 mL of tri-noctylphosphine selenide (TOPSe; 1m) dispersed in 5 mL of tri-n-octylphosphine (TOP; 97% Strem) into a round-bottom flask containing 7 grams of degassed hexadecylamine (distilled from 90% Sigma–Aldrich) at 310 8C and by then growing the NCs at 270 8C for 90 min. The second step consisted of transferring 8 mL of the above ZnSe NC growth solution, at 160 8C, into a degassed solution of 16 grams of trin-octylphosphine oxide (TOPO; distilled from 90% Sigma– Aldrich) and 4 mmol of hexylphosphonic acid (HPA; Alfa Aesar), also at 160 8C. A solution of 1.1 mmol of dimethylcadmium (Strem) and 1.2 mL of TOPSe (1m) dispersed in 8 mL of TOP (97% Strem) was then introduced dropwise [*] Dr. J. S. Steckel, Dr. P. Snee, Dr. J. P. Zimmer, J. E. Halpert, Prof. M. G. Bawendi Massachusetts Institute of Technology Department of Chemistry Center for Materials Science and Engineering and The Institute for Soldier Nanotechnologies 77 Massachusetts Avenue, Room 6-221 Cambridge, MA 02139 (USA) Fax: (+1)617-253-7030 E-mail: mgb@mit.edu Dr. S. Coe-Sullivan, P. Anikeeva, L.-A. Kim, Prof. V. Bulovic Massachusetts Institute of Technology Laboratory of Organic Optics and Electronics Department of Electrical Engineering and Computer Science Cambridge, MA 02139 (USA) [] These authors contributed equally to this work.

271 citations

Journal ArticleDOI
TL;DR: In this paper, the effects of thermal fluctuations, stacking faults, surface reconstructions, and bond compressions on powder patterns of CdSe clusters using the Debye formula were analyzed.
Abstract: X‐ray powder patterns obtained from three different types of 35–40 A CdSe nanoclusters are analyzed. We simulate the effects of thermal fluctuations, stacking faults, surface reconstructions, and bond compressions on powder patterns of CdSe clusters using the Debye formula. We find that the spectra of capped and annealed CdSe particles grown in inverse micelles are best fit by a mixture of crystalline structures intermediate between zinc‐blende and wurtzite. We describe a new preparation for CdSe clusters, the structure of which appears to be well‐defined wurtzite with, on average, less than one stacking fault per cluster. Thermal effects are found to be important and to mask the subtle effects of likely surface and core reconstructions.

269 citations

Journal ArticleDOI
TL;DR: A highly sensitive rapid technique for SLN mapping of the lung that permits precise real-time imaging and therefore overcomes many limitations of currently available techniques is reported.

266 citations

Journal ArticleDOI
TL;DR: The NIR fluorescence-guided SLN mapping technology is likely to eliminate the need for radioactive and colored tracers, permits real-time image guidance throughout the procedure, and assists the pathologist in tissue analysis.
Abstract: Background Invisible near-infrared (NIR) fluorescent light permits high sensitivity, real-time image-guidance during oncologic surgery without changing the look of the surgical field. In this study, we complete pre-clinical development of the technology for sentinel lymph node (SLN) mapping using a large animal model of spontaneous melanoma.

265 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