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Sample records for metal nanocrystals simple

  1. Shape-Controlled Synthesis of Metal Nanocrystals: Simple Chemistry Meets Complex Physics?

    PubMed Central

    Xia, Younan; Xiong, Yujie; Lim, Byungkwon; Skrabalak, Sara E.

    2009-01-01

    Nanocrystals are fundamental to modern science and technology. Mastery over the shape of a nanocrystal enables control of its properties and enhancement of its usefulness for a given application. The aim of this article is to present a comprehensive review of current research activities that center on the shape-controlled synthesis of metal nanocrystals. We begin with a brief introduction to nucleation and growth within the context of metal nanocrystal synthesis, followed by a discussion of the possible shapes that a metal nanocrystal might take under different conditions. We then focus on a variety of experimental parameters that have been explored to manipulate the nucleation and growth of metal nanocrystals in solution-phase syntheses in an effort to generate specific shapes. We then elaborate on these approaches by selecting examples in which there is already reasonable understanding for the observed shape control or at least the protocols have proven to be reproducible and controllable. Toward the end of this article, we highlight a number of applications that have been enabled and/or enhanced by the shape-controlled synthesis of metal nanocrystals. We conclude this article with personal perspectives on the directions toward which future research in this field might take. PMID:19053095

  2. Shape-controlled synthesis of metal nanocrystals: simple chemistry meets complex physics?

    PubMed

    Xia, Younan; Xiong, Yujie; Lim, Byungkwon; Skrabalak, Sara E

    2009-01-01

    Nanocrystals are fundamental to modern science and technology. Mastery over the shape of a nanocrystal enables control of its properties and enhancement of its usefulness for a given application. Our aim is to present a comprehensive review of current research activities that center on the shape-controlled synthesis of metal nanocrystals. We begin with a brief introduction to nucleation and growth within the context of metal nanocrystal synthesis, followed by a discussion of the possible shapes that a metal nanocrystal might take under different conditions. We then focus on a variety of experimental parameters that have been explored to manipulate the nucleation and growth of metal nanocrystals in solution-phase syntheses in an effort to generate specific shapes. We then elaborate on these approaches by selecting examples in which there is already reasonable understanding for the observed shape control or at least the protocols have proven to be reproducible and controllable. Finally, we highlight a number of applications that have been enabled and/or enhanced by the shape-controlled synthesis of metal nanocrystals. We conclude this article with personal perspectives on the directions toward which future research in this field might take.

  3. A simple dissolved metals mixing method to produce high-purity MgTiO{sub 3} nanocrystals

    SciTech Connect

    Pratapa, Suminar E-mail: suminar-pratapa@physics.its.ac.id; Baqiya, Malik A. E-mail: suminar-pratapa@physics.its.ac.id; Istianah, E-mail: suminar-pratapa@physics.its.ac.id; Lestari, Rina E-mail: suminar-pratapa@physics.its.ac.id; Angela, Riyan E-mail: suminar-pratapa@physics.its.ac.id

    2014-02-24

    A simple dissolved metals mixing method has been effectively used to produce high-purity MgTiO{sub 3} (MT) nanocrystals. The method involves the mixing of independently dissolved magnesium and titanium metal powders in hydrochloric acid followed by calcination. The phase purity and nanocrystallinity were determined by making use of laboratory x-ray diffraction data, to which Rietveld-based analyses were performed. Results showed that the method yielded only one type magnesium titanate powders, i.e. MgTiO{sub 3}, with no Mg{sub 2}TiO{sub 4} or MgTi{sub 2}O{sub 5} phases. The presence of residual rutile or periclase was controlled by adding excessive Mg up to 5% (mol) in the stoichiometric mixing. The method also resulted in MT nanocrystals with estimated average crystallite size of 76±2 nm after calcination at 600°C and 150±4 nm (at 800°C). A transmission electron micrograph confirmed the formation of the nanocrystallites.

  4. Evaporating metal nanocrystal arrays

    NASA Astrophysics Data System (ADS)

    Zhang, Xue; Joy, James C.; Zhao, Chenwei; Kim, Jin Ho; Fernandes, Gustavo; Xu, J. M.; Valles, James M., Jr.

    2017-03-01

    Anodic aluminum oxide (AAO) substrates with a self-ordered triangular array of nanopores provide the means to fabricate multiple forms of nano materials, such as nanowires and nanoparticles. This study focuses on nanostructures that emerge in thin films of metals thermally evaporated onto the surface of AAO. Previous work showed that films of different evaporated metals assume dramatically different structures, e.g. an ordered triangular array of nearly monodisperse nanoparticles forms for lead (Pb) while a polycrystalline nanohoneycomb structure forms for silver (Ag). Here, we present investigations of the effects of substrate temperature and deposition angle that reveal the processes controlling the nano particle array formation. Our findings indicate that arrays form provided the grain nucleation density exceeds the pore density and the atomic mobility is high enough to promote grain coalescence. They introduce a method for producing films with anisotropic grain array structure. The results provide insight into the influence of substrate nano-morphology on thin film growth energetics and kinetics that can be harnessed for creating films with other novel nano-structures.

  5. Evaporating metal nanocrystal arrays.

    PubMed

    Zhang, Xue; Joy, James C; Zhao, Chenwei; Kim, Jin Ho; Fernandes, Gustavo; Xu, J M; Valles, James M

    2017-03-10

    Anodic aluminum oxide (AAO) substrates with a self-ordered triangular array of nanopores provide the means to fabricate multiple forms of nano materials, such as nanowires and nanoparticles. This study focuses on nanostructures that emerge in thin films of metals thermally evaporated onto the surface of AAO. Previous work showed that films of different evaporated metals assume dramatically different structures, e.g. an ordered triangular array of nearly monodisperse nanoparticles forms for lead (Pb) while a polycrystalline nanohoneycomb structure forms for silver (Ag). Here, we present investigations of the effects of substrate temperature and deposition angle that reveal the processes controlling the nano particle array formation. Our findings indicate that arrays form provided the grain nucleation density exceeds the pore density and the atomic mobility is high enough to promote grain coalescence. They introduce a method for producing films with anisotropic grain array structure. The results provide insight into the influence of substrate nano-morphology on thin film growth energetics and kinetics that can be harnessed for creating films with other novel nano-structures.

  6. The Surface Chemistry of Metal Chalcogenide Nanocrystals

    NASA Astrophysics Data System (ADS)

    Anderson, Nicholas Charles

    The surface chemistry of metal chalcogenide nanocrystals is explored through several interrelated analytical investigations. After a brief discussion of the nanocrystal history and applications, molecular orbital theory is used to describe the electronic properties of semiconductors, and how these materials behave on the nanoscale. Quantum confinement plays a major role in dictating the optical properties of metal chalcogenide nanocrystals, however surface states also have an equally significant contribution to the electronic properties of nanocrystals due to the high surface area to volume ratio of nanoscale semiconductors. Controlling surface chemistry is essential to functionalizing these materials for biological imaging and photovoltaic device applications. To better understand the surface chemistry of semiconducting nanocrystals, three competing surface chemistry models are presented: 1.) The TOPO model, 2.) the Non-stoichiometric model, and 3.) the Neutral Fragment model. Both the non-stoichiometric and neutral fragment models accurately describe the behavior of metal chalcogenide nanocrystals. These models rely on the covalent bond classification system, which divides ligands into three classes: 1.) X-type, 1-electron donating ligands that balance charge with excess metal at the nanocrystal surface, 2.) L-type, 2-electron donors that bind metal sites, and 3.) Z-type, 2-electron acceptors that bind chalcogenide sites. Each of these ligand classes is explored in detail to better understand the surface chemistry of metal chalcogenide nanocrystals. First, chloride-terminated, tri-n-butylphosphine (Bu 3P) bound CdSe nanocrystals were prepared by cleaving carboxylate ligands from CdSe nanocrystals with chlorotrimethylsilane in Bu3P solution. 1H and 31P{1H} nuclear magnetic resonance spectra of the isolated nanocrystals allowed assignment of distinct signals from several free and bound species, including surface-bound Bu3P and [Bu3P-H]+[Cl]- ligands as well as a Bu

  7. Shaping metal nanocrystals through epitaxial seeded growth

    SciTech Connect

    Habas, Susan E.; Lee, Hyunjoo; Radmilovic, Velimir; Somorjai,Gabor A.; Yang, Peidong

    2008-02-17

    Morphological control of nanocrystals has becomeincreasingly important, as many of their physical and chemical propertiesare highly shape-dependent. Nanocrystal shape control for both single andmultiple material systems, however, remains fairly empirical andchallenging. New methods need to be explored for the rational syntheticdesign of heterostructures with controlled morphology. Overgrowth of adifferent material on well-faceted seeds, for example, allows for the useof the defined seed morphology to control nucleation and growth of thesecondary structure. Here, we have used highly faceted cubic Pt seeds todirect the epitaxial overgrowth of a secondary metal. We demonstrate thisconcept with lattice matched Pd to produce conformal shape-controlledcore-shell particles, and then extend it to lattice mismatched Au to giveanisotropic growth. Seeding with faceted nanocrystals may havesignificant potential towards the development of shape-controlledheterostructures with defined interfaces.

  8. Simple citric acid-catalyzed surface esterification of cellulose nanocrystals.

    PubMed

    Ávila Ramírez, Jhon Alejandro; Fortunati, Elena; Kenny, José María; Torre, Luigi; Foresti, María Laura

    2017-02-10

    A simple straightforward route for the surface esterification of cellulose nanocrystals (CNC) is herein proposed. CNC obtained from microcrystalline cellulose were acetylated using as catalyst citric acid, a α-hydroxy acid present in citrus fruits and industrially produced by certain molds in sucrose or glucose-containing medium. No additional solvent was added to the system; instead, the acylant (acetic anhydride) was used in sufficient excess to allow CNC dispersion and proper suspension agitation. By tuning the catalyst load, CNC with two different degree of substitution (i.e. DS=0.18 and 0.34) were obtained. Acetylated cellulose nanocrystals were characterized in terms of chemical structure, crystallinity, morphology, thermal decomposition and dispersion in a non-polar solvent. Results illustrated for the first time the suitability of the protocol proposed for the simple surface acetylation of cellulose nanocrystals.

  9. Metal halide solid-state surface treatment for nanocrystal materials

    DOEpatents

    Luther, Joseph M.; Crisp, Ryan; Beard, Matthew C.

    2016-04-26

    Methods of treating nanocrystal and/or quantum dot devices are described. The methods include contacting the nanocrystals and/or quantum dots with a solution including metal ions and halogen ions, such that the solution displaces native ligands present on the surface of the nanocrystals and/or quantum dots via ligand exchange.

  10. Biomimetic synthesis of noble metal nanocrystals

    NASA Astrophysics Data System (ADS)

    Chiu, Chin-Yi

    At the nanometer scale, the physical and chemical properties of materials heavily depend on their sizes and shapes. This fact has triggered considerable efforts in developing controllable nanomaterial synthesis. The controlled growth of colloidal nanocrystal is a kinetic process, in which high-energy facets grow faster and then vanish, leading to a nanocrystal enclosed by low-energy facets. Identifying a surfactant that can selectively bind to a particular crystal facet and thus lower its surface energy, is critical and challenging in shape controlled synthesis of nanocrystals. Biomolecules exhibiting exquisite molecular recognition properties can be exploited to precisely engineer nanostructured materials. In the first part of my thesis, we employed the phage display technique to select a specific multifunctional peptide sequence which can bind on Pd surface and mediate Pd crystal nucleation and growth, achieving size controlled synthesis of Pd nanocrystals in aqueous solution. We further demonstrated a rational biomimetic approach to the predictable synthesis of nanocrystals enclosed by a particular facet in the case of Pt. Specifically, Pt {100} and Pt {111} facet-specific peptides were identified and used to synthesize Pt nanocubes and Pt nano-tetrahedrons, respectively. The mechanistic studies of Pt {111} facet-specific peptide had led us to study the facet-selective adsorption of aromatic molecules on noble metal surfaces. The discoveries had achieved the development of design strategies to select facet-selective molecules which can synthesize nanocrystals with expected shapes in both Pt and Pd system. At last, we exploited Pt facet-specific peptides and controlled the molecular interaction to produce one- and three- dimensional nanostructures composed of anisotropic nanoparticles in synthetic conditions without supramolecular pre-organization, demonstrating the full potential of biomolecules in mediating material formation process. My research on biomimetic

  11. Metal nanocrystal/metal-organic framework core/shell nanostructure from selective self-assembly induced by localization of metal ion precursors on nanocrystal surface.

    PubMed

    Ohhashi, Takashi; Tsuruoka, Takaaki; Matsuyama, Tetsuhiro; Takashima, Yohei; Nawafune, Hidemi; Minami, Hideto; Akamatsu, Kensuke

    2015-08-01

    Metal nanocrystal/metal-organic framework core/shell nanostructures have been constructed using metal ion-trapped nanocrystals as scaffolds through a selective self-assembly of framework components on the nanocrystal surfaces. The resulting nanostructures exhibit unique catalytic activity toward nitrophenol analogs.

  12. Galvanic displacement of metals on semiconductor nanocrystals

    NASA Astrophysics Data System (ADS)

    Johnson, Melanie; Kelly, Joel A.; Henderson, Eric J.; Veinot, Jonathan G. C.

    2009-11-01

    We report the galvanic displacement (GD) of germanium from germanium nanocrystals (Ge-NCs) with silver. The Ge-NCs are synthesized by reductive thermal processing of germanium suboxide sol-gel prepolymers. Thermal processing yields size-controlled oxide-embedded Ge-NCs, which are liberated by dissolution of the germanium oxide matrix in water. Subsequent exposure of the freestanding Ge-NCs to aqueous solutions of AgNO3 leads to deposition of silver nanostructures by GD. The resulting metal structures were analyzed by XRD, XPS, TEM and EDX, confirming deposition of elemental silver in a variety of shapes and sizes.

  13. Silicon nanocrystal-noble metal hybrid nanoparticles

    NASA Astrophysics Data System (ADS)

    Sugimoto, H.; Fujii, M.; Imakita, K.

    2016-05-01

    We report a novel and facile self-limiting synthesis route of silicon nanocrystal (Si NC)-based colloidally stable semiconductor-metal (gold, silver and platinum) hybrid nanoparticles (NPs). For the formation of hybrid NPs, we employ ligand-free colloidal Si NCs with heavily boron (B) and phosphorus (P) doped shells. By simply mixing B and P codoped colloidal Si NCs with metal salts, hybrid NPs consisting of metal cores and Si NC shells are spontaneously formed. We demonstrate the synthesis of highly uniform and size controllable hybrid NPs. It is shown that codoped Si NCs act as a reducing agent for metal salts and also as a protecting layer to stop metal NP growth. The process is thus self-limiting. The development of a variety of Si NC-based hybrid NPs is a promising first step for the design of biocompatible multifunctional NPs with broad material choices for biosensing, bioimaging and solar energy conversion.We report a novel and facile self-limiting synthesis route of silicon nanocrystal (Si NC)-based colloidally stable semiconductor-metal (gold, silver and platinum) hybrid nanoparticles (NPs). For the formation of hybrid NPs, we employ ligand-free colloidal Si NCs with heavily boron (B) and phosphorus (P) doped shells. By simply mixing B and P codoped colloidal Si NCs with metal salts, hybrid NPs consisting of metal cores and Si NC shells are spontaneously formed. We demonstrate the synthesis of highly uniform and size controllable hybrid NPs. It is shown that codoped Si NCs act as a reducing agent for metal salts and also as a protecting layer to stop metal NP growth. The process is thus self-limiting. The development of a variety of Si NC-based hybrid NPs is a promising first step for the design of biocompatible multifunctional NPs with broad material choices for biosensing, bioimaging and solar energy conversion. Electronic supplementary information (ESI) available: Additional TEM images and extinction spectra of Si-metal hybrid NPs are shown in Fig. S1

  14. Generalized and facile synthesis of semiconducting metal sulfide nanocrystals.

    PubMed

    Joo, Jin; Na, Hyon Bin; Yu, Taekyung; Yu, Jung Ho; Kim, Young Woon; Wu, Fanxin; Zhang, Jin Z; Hyeon, Taeghwan

    2003-09-10

    We report on the synthesis of semiconductor nanocrystals of PbS, ZnS, CdS, and MnS through a facile and inexpensive synthetic process. Metal-oleylamine complexes, which were obtained from the reaction of metal chloride and oleylamine, were mixed with sulfur. The reaction mixture was heated under appropriate experimental conditions to produce metal sulfide nanocrystals. Uniform cube-shaped PbS nanocrystals with particle sizes of 6, 8, 9, and 13 nm were synthesized. The particle size was controlled by changing the relative amount of PbCl(2) and sulfur. Uniform 11 nm sized spherical ZnS nanocrystals were synthesized from the reaction of zinc chloride and sulfur, followed by one cycle of size-selective precipitation. CdS nanocrystals that consist of rods, bipods, and tripods were synthesized from a reaction mixture containing a 1:6 molar ratio of cadmium to sulfur. Spherical CdS nanocrystals (5.1 nm sized) were obtained from a reaction mixture with a cadmium to sulfur molar ratio of 2:1. MnS nanocrystals with various sizes and shapes were synthesized from the reaction of MnCl(2) and sulfur in oleylamine. Rod-shaped MnS nanocrystals with an average size of 20 nm (thickness) x 37 nm (length) were synthesized from a 1:1 molar ratio of MnCl(2) and sulfur at 240 degrees C. Novel bullet-shaped MnS nanocrystals with an average size of 17 nm (thickness) x 44 nm (length) were synthesized from the reaction of 4 mmol of MnCl(2) and 2 mmol of sulfur at 280 degrees C for 2 h. Shorter bullet-shaped MnS nanocrystals were synthesized from a 3:1 molar ratio of MnCl(2) and sulfur. Hexagon-shaped MnS nanocrystals were also obtained. All of the synthesized nanocrystals were highly crystalline.

  15. Charge transport in metal oxide nanocrystal-based materials

    NASA Astrophysics Data System (ADS)

    Runnerstrom, Evan Lars

    There is probably no class of materials more varied, more widely used, or more ubiquitous than metal oxides. Depending on their composition, metal oxides can exhibit almost any number of properties. Of particular interest are the ways in which charge is transported in metal oxides: devices such as displays, touch screens, and smart windows rely on the ability of certain metal oxides to conduct electricity while maintaining visible transparency. Smart windows, fuel cells, and other electrochemical devices additionally rely on efficient transport of ionic charge in and around metal oxides. Colloidal synthesis has enabled metal oxide nanocrystals to emerge as a relatively new but highly tunable class of materials. Certain metal oxide nanocrystals, particularly highly doped metal oxides, have been enjoying rapid development in the last decade. As in myriad other materials systems, structure dictates the properties of metal oxide nanocrystals, but a full understanding of how nanocrystal synthesis, the processing of nanocrystal-based materials, and the structure of nanocrystals relate to the resulting properties of nanocrystal-based materials is still nascent. Gaining a fundamental understanding of and control over these structure-property relationships is crucial to developing a holistic understanding of metal oxide nanocrystals. The unique ability to tune metal oxide nanocrystals by changing composition through the introduction of dopants or by changing size and shape affords a way to study the interplay between structure, processing, and properties. This overall goal of this work is to chemically synthesize colloidal metal oxide nanocrystals, process them into useful materials, characterize charge transport in materials based on colloidal metal oxide nanocrystals, and develop ways to manipulate charge transport. In particular, this dissertation characterizes how the charge transport properties of metal oxide nanocrystal-based materials depend on their processing and

  16. Shape-Controlled Metal Nanocrystals for Heterogeneous Catalysis.

    PubMed

    Ruditskiy, Aleksey; Peng, Hsin-Chieh; Xia, Younan

    2016-06-07

    The ability to control the shape of metal nanocrystals allows us to not only maneuver their physicochemical properties but also optimize their activity in a variety of applications. Heterogeneous catalysis, in particular, would benefit tremendously from the availability of metal nanocrystals with controlled shapes and well-defined facets or surface structures. The immediate benefits may include significant enhancements in catalytic activity and/or selectivity along with reductions in the materials cost. We provide a brief account of recent progress in the development of metal nanocrystals with controlled shapes and thereby enhanced catalytic performance for several reactions, including formic acid oxidation, oxygen reduction, and hydrogenation. In addition to monometallic nanocrystals, we also cover a bimetallic system, in which the two metals are formulated as alloyed, core-shell, or core-frame structures. We hope this article will provide further impetus for the development of next-generation heterogeneous catalysts essential to a broad range of applications.

  17. A Novel Thermal Electrochemical Synthesis Method for Production of Stable Colloids of "Naked" Metal (Ag) Nanocrystals

    SciTech Connect

    Hu, Michael Z.; Easterly, Clay E

    2009-01-01

    Solution synthesis of nanocrystal silver is reviewed. This paper reports a novel thermal electrochemical synthesis (TECS) for producing metal Ag nanocrystals as small as a few nanometers. The TECS method requires mild conditions (25-100oC), low voltage (1-50 V DC) on Ag electrodes, and simple water or aqueous solutions as reaction medium. Furthermore, a tubular dialysis membrane surround electrodes proves favorable to produce nanosized (<10 nm) Ag nanocrystals. Different from those nanocrystals reported in literature, our nanocrystals have several unique features: (1) small nanometer size, (2) nakedness , i.e., surfaces of metal nanocrystals are free of organic ligands or capping molecules and no need of dispersant in synthesis solutions, and (3) colloidally stable in water solutions. It was discovered that Ag nanoparticles with initially large size distribution can be homogenized into near-monodispersed system by a low power (< 15 mW) He-Ne laser exposure treatment. The combination of the TECS technique and the laser treatment could lead to a new technology that produces metal nanoparticles that are naked, stable, and uniform sized. In the presence of stabilizing agent (also as supporting electrolyte) such as polyvinyl alcohol (PVA), large yield of silver nanoparticles (<100nm) in the form of thick milky sols are produced.

  18. Template Synthesis of Noble Metal Nanocrystals with Unusual Crystal Structures and Their Catalytic Applications.

    PubMed

    Fan, Zhanxi; Zhang, Hua

    2016-12-20

    Noble metal nanocrystals own high chemical stability, unique plasmonic and distinctive catalytic properties, making them outstanding in many applications. However, their practical applications are limited by their high cost and scarcity on the earth. One promising strategy to solve these problems is to boost their catalytic performance in order to reduce their usage amount. To realize this target, great research efforts have been devoted to the size-, composition-, shape- and/or architecture-controlled syntheses of noble metal nanocrystals during the past two decades. Impressively, recent experimental studies have revealed that the crystal structure of noble metal nanocrystals can also significantly affect their physicochemical properties, such as optical, magnetic, catalytic, mechanical, electrical and electronic properties. Therefore, besides the well-established size, composition, shape, and architecture control, the rise of crystal structure-controlled synthesis of noble metal nanocrystals will open up new opportunities to further improve their functional properties, and thus promote their potential applications in energy conversion, catalysis, biosensing, information storage, surface enhanced Raman scattering, waveguide, near-infrared photothermal therapy, controlled release, bioimaging, biomedicine, and so on. In this Account, we review the recent research progress on the crystal structure control of noble metal nanocrystals with a template synthetic approach and their crystal structure-dependent catalytic properties. We first describe the template synthetic methods, such as epitaxial growth and galvanic replacement reaction methods, in which a presynthesized noble metal nanocrystal with either new or common crystal structure is used as the template to direct the growth of unusual crystal structures of other noble metals. Significantly, the template synthetic strategy described here provides an efficient, simple and straightforward way to synthesize unusual

  19. Tracking Energy Relaxation Within Plasmonic Metal Oxide Nanocrystals

    DTIC Science & Technology

    2016-11-30

    AFRL-AFOSR-VA-TR-2016-0378 Tracking Energy Relaxation Within Plasmonic Metal Oxide Nanocrystals Sean Roberts UNIVERSITY OF TEXAS AT AUSTIN 101 EAST...DATES COVERED (From - To) 9/1/2015-8/31/2016 4. TITLE AND SUBTITLE Tracking Energy Relaxation Within Plasmonic Metal Oxide Nanocrystals 5a. CONTRACT...picosecond timescale that later cool by releasing their energy to lattice phonons. Both of these processes alter the center frequency and linewidth of

  20. Metal-insulator transition in films of doped semiconductor nanocrystals.

    PubMed

    Chen, Ting; Reich, K V; Kramer, Nicolaas J; Fu, Han; Kortshagen, Uwe R; Shklovskii, B I

    2016-03-01

    To fully deploy the potential of semiconductor nanocrystal films as low-cost electronic materials, a better understanding of the amount of dopants required to make their conductivity metallic is needed. In bulk semiconductors, the critical concentration of electrons at the metal-insulator transition is described by the Mott criterion. Here, we theoretically derive the critical concentration nc for films of heavily doped nanocrystals devoid of ligands at their surface and in direct contact with each other. In the accompanying experiments, we investigate the conduction mechanism in films of phosphorus-doped, ligand-free silicon nanocrystals. At the largest electron concentration achieved in our samples, which is half the predicted nc, we find that the localization length of hopping electrons is close to three times the nanocrystals diameter, indicating that the film approaches the metal-insulator transition.

  1. Defect Chemistry and Plasmon Physics of Colloidal Metal Oxide Nanocrystals.

    PubMed

    Lounis, Sebastien D; Runnerstrom, Evan L; Llordés, Anna; Milliron, Delia J

    2014-05-01

    Plasmonic nanocrystals of highly doped metal oxides have seen rapid development in the past decade and represent a class of materials with unique optoelectronic properties. In this Perspective, we discuss doping mechanisms in metal oxides and the accompanying physics of free carrier scattering, both of which have implications in determining the properties of localized surface plasmon resonances (LSPRs) in these nanocrystals. The balance between activation and compensation of dopants limits the free carrier concentration of the most common metal oxides, placing a ceiling on the LSPR frequency. Furthermore, because of ionized impurity scattering of the oscillating plasma by dopant ions, scattering must be treated in a fundamentally different way in semiconductor metal oxide materials when compared with conventional metals. Though these effects are well-understood in bulk metal oxides, further study is needed to understand their manifestation in nanocrystals and corresponding impact on plasmonic properties, and to develop materials that surpass current limitations in free carrier concentration.

  2. Ion irradiation effects on metallic nanocrystals

    SciTech Connect

    Kluth, P.; Johannessen, B.; Giulian, R.; Schnohr, C.S.; Foran, G.J.; Cookson, D.J.; Byrne, A.P.; Ridgway, M.C.

    2008-04-02

    We have investigated structural and morphological properties of metallic nanocrystals (NCs) exposed to ion irradiation. NCs were characterized by transmission electron microscopy in combination with advanced synchrotron-based analytical techniques, in particular X-ray absorption spectroscopy and small-angle X-ray scattering. A number of different effects were observed depending on the irradiation conditions. At energies where nuclear stopping is predominant, structural disorder/amorphization followed by inverse Ostwald ripening/dissolution due to ion beam mixing was observed for Au and Cu NCs embedded in SiO{sub 2}. The ion-irradiation-induced crystalline to amorphous transition in the NCs, which cannot be achieved in the corresponding bulk metals, was attributed to their initially higher structural energy as compared to bulk material and possibly preferential nucleation of the amorphous phase at the NC/SiO{sub 2} interface. At very high irradiation energies (swift heavy ion irradiation), where the energy loss is nearly entirely due to electronic stopping, a size-dependent shape transformation of the NCs from spheres to rod like shapes was apparent in Au NCs. Our preliminary results are in good agreement with considerations on melting of the NCs in the ion track as one mechanism involved in the shape transformation.

  3. Solution based synthesis of simple fcc Si nano-crystals under ambient conditions.

    PubMed

    Balcı, Mustafa H; Sæterli, Ragnhild; Maria, Jerome; Lindgren, Mikael; Holmestad, Randi; Grande, Tor; Einarsrud, Mari-Ann

    2013-02-28

    We demonstrate for the first time that simple face-centered cubic (fcc) silicon nano-crystals can be produced by a solution based bottom-up synthesis route under ambient conditions. Simple fcc Si nano-crystals (2-7 nm) were prepared at room temperature by using sodium cyclopentadienide as a reducing agent for silicon tetrachloride. Photoluminescence emission at 550 nm was observed for the fcc silicon nano-crystals upon excitation at 340 nm, indicating that fcc Si nano-crystals were exhibiting direct bandgap like semiconductor properties with very fast radiative recombination rates. The new synthesis route makes possible the production and study of simple fcc polymorphs of Si nano-crystals with an easy alteration of surface termination groups.

  4. Formation of noble metal nanocrystals in the presence of biomolecules

    NASA Astrophysics Data System (ADS)

    Burt, Justin Lockheart

    One of the most promising, yet least studied routes for producing biocompatible nanostructures involves synthesis in the presence of biomolecules. I hypothesized that globular proteins could provide a suitable framework to regulate the formation of noble metal nanocrystals. As proof of concept, I designed two novel synthesis protocols utilizing bovine serum albumin (BSA) protein to regulate the formation of gold nanocrystals. In the first case, the standard protocol for polyol reduction was modified by replacing ethylene glycol with glycerin, replacing synthetic polymers with BSA as protecting agent, and decreasing the reaction temperature. In the second case, the Brust-Schiffrin two-phase reduction was modified by replacing alkylthiols with BSA as protecting agent, which facilitated a strictly aqueous phase synthesis. Due to superior product yield and rapid reduction at room temperature, the aqueous protocol became the foundation for subsequent studies. I extended this approach to produce well-dispersed ˜2nm silver, gold, and platinum nanocrystals. Having demonstrated the feasibility of BSA-functionalized nanocrystals, some potential uses were explored. BSA-functionalized silver nanocrystals were employed in a broader study on the interaction of silver nanocrystals with HIV. BSA-functionalized gold nanocrystals were utilized for in vivo dosage of a contrast enhancing agent to bacteria. BSA-functionalized platinum nanocrystals were studied as hydrogenation catalysts. Since many intriguing uses for protein-functionalized nanocrystals involve incorporation into biosystems, I sought to enhance biocompatibility by using ascorbic acid as reducing agent. Initial experiments revealed elongated and branched nanocrystals. Such structures were not observed in previous synthesis protocols with BSA, so I hypothesized ascorbic acid was driving their formation. To test my assertion, I reduced ionic gold in an aqueous solution of ascorbic acid, thereby discovering a new method

  5. Highly Emissive Transition Metal Ion Doped Semiconducting Nanocrystals

    NASA Astrophysics Data System (ADS)

    Jana, Santanu; Srivastava, Bhupendra B.; Sarma, D. D.; Pradhan, Narayan

    2011-07-01

    Doped semiconductor nanocrystals (d-dots), specifically ones not containing heavy metal ions, have the potential to become a class of mainstream emissive materials. Mn- and Cu-doped ZnSe or ZnS d-dots can cover an emission window similar to that of the current workhorse of intrinsic quantum dot (q-dots) emitters, CdSe nanocrystals. We synthesized high quality stable Cu doped ZnSe in nonpolar as well as polar solvent. The emission intensity of these doped nanocrystals is found stable for months under UV irradiation, after different multifunctional ligand which is important for any biological detection. We have also synthesized the stable Mn doped ZnS in nonpolar solvent more than 50% QY.. The doped nanocrystals are characterized by TEM, XRD, EPR and ICP analysis.

  6. Hybrid semiconductor quantum dot-metal nanocrystal structures prepared by molecular beam epitaxy

    NASA Astrophysics Data System (ADS)

    Urbańczyk, A.; Hamhuis, G. J.; Nötzel, R.

    2011-05-01

    We report the formation of In nanocrystals and their alignment near dilute InAs quantum dots (QDs) on GaAs (0 0 1) by molecular beam epitaxy. The In nanocrystals exhibit surface plasmon resonances in the near-infrared range, which can be matched with the emission wavelength of In(Ga)As QDs. The alignment of the In nanocrystals near the InAs QDs is due to the strain-driven migration yielding single isolated QD-metal nanocrystal pairs and isolated QD-metal nanocrystal dimer structures, representing the basic hybrid QD-metal nanocrystal plasmonic nanostructures.

  7. Architectural design of heterogeneous metallic nanocrystals--principles and processes.

    PubMed

    Yu, Yue; Zhang, Qingbo; Yao, Qiaofeng; Xie, Jianping; Lee, Jim Yang

    2014-12-16

    CONSPECTUS: Heterogeneous metal nanocrystals (HMNCs) are a natural extension of simple metal nanocrystals (NCs), but as a research topic, they have been much less explored until recently. HMNCs are formed by integrating metal NCs of different compositions into a common entity, similar to the way atoms are bonded to form molecules. HMNCs can be built to exhibit an unprecedented architectural diversity and complexity by programming the arrangement of the NC building blocks ("unit NCs"). The architectural engineering of HMNCs involves the design and fabrication of the architecture-determining elements (ADEs), i.e., unit NCs with precise control of shape and size, and their relative positions in the design. Similar to molecular engineering, where structural diversity is used to create more property variations for application explorations, the architectural engineering of HMNCs can similarly increase the utility of metal NCs by offering a suite of properties to support multifunctionality in applications. The architectural engineering of HMNCs calls for processes and operations that can execute the design. Some enabling technologies already exist in the form of classical micro- and macroscale fabrication techniques, such as masking and etching. These processes, when used singly or in combination, are fully capable of fabricating nanoscopic objects. What is needed is a detailed understanding of the engineering control of ADEs and the translation of these principles into actual processes. For simplicity of execution, these processes should be integrated into a common reaction system and yet retain independence of control. The key to architectural diversity is therefore the independent controllability of each ADE in the design blueprint. The right chemical tools must be applied under the right circumstances in order to achieve the desired outcome. In this Account, after a short illustration of the infinite possibility of combining different ADEs to create HMNC design

  8. Simple approach to reinforce hydrogels with cellulose nanocrystals

    NASA Astrophysics Data System (ADS)

    Yang, Jun; Han, Chun-Rui; Xu, Feng; Sun, Run-Cang

    2014-05-01

    The physical crosslinking of colloidal nanoparticles via dynamic and directional non-covalent interactions has led to significant advances in composite hydrogels. In this paper, we report a simple approach to fabricate tough, stretchable and hysteretic isotropic nanocomposite hydrogels, where rod-like cellulose nanocrystals (CNCs) are encapsulated by flexible polymer chains of poly(N,N-dimethylacrylamide) (PDMA). The CNC-PDMA colloidal clusters build a homogeneously cross-linked network and lead to significant reinforcing effect of the composites. Hierarchically structured CNC-PDMA clusters, from isolated particles to an interpenetrated network, are observed by transmission electron microscopy measurements. Dynamic shear oscillation measurements are applied to demystify the differences in network rheological behaviors, which were compared with network behaviors of chemically cross-linked PDMA counterparts. Tensile tests indicate that the hybrid hydrogels possess higher mechanical properties and a more efficient energy dissipation mechanism. In particular, with only 0.8 wt% of CNC loading, a 4.8-fold increase in Young's modulus, 9.2-fold increase in tensile strength, and 5.8-fold increase in fracture strain are achieved, which is ascribed to a combination of CNC reinforcement in the soft matrix and CNC-PDMA colloidal cluster conformational rearrangement under stretching. Physical interactions within networks serve as reversible sacrificial bonds that dissociate upon deformation, exhibiting large hysteresis as an energy dissipation mechanism via cluster mobility. This result contrasts with the case of chemically cross-linked PDMA counterparts where the stress relaxation is slow due to the permanent cross-links and low resistance against crack propagation within the covalent network.The physical crosslinking of colloidal nanoparticles via dynamic and directional non-covalent interactions has led to significant advances in composite hydrogels. In this paper, we report

  9. Highly efficient one-step synthesis of carbon encapsulated nanocrystals by the oxidation of metal π-complexes.

    PubMed

    Liu, Boyang; Shao, Yingfeng; Xiang, Xin; Zhang, Fuhua; Yan, Shengchang; Li, Wenge

    2017-08-11

    Various carbon encapsulated nanocrystals, including MnS and MnO, Cr2O3, MoO2, Fe7S8 and Fe3O4, and ZrO2, are prepared in one step and in situ by a simple and highly efficient synthesis approach. The nanocrystals have an equiaxed morphology and a median size smaller than 30 nm. Tens and hundreds of these nanocrystals are entirely encapsulated by a wormlike amorphous carbon shell. The formation of a core-shell structure depends on the strongly exothermic reaction of metal π-complexes with ammonium persulfate in an autoclave at below 200 °C. During the oxidation process, the generated significant amounts of heat will destroy the molecular structure of the metal π-complex and cleave the ligands into small carbon fragments, which further transform into an amorphous carbon shell. The central metal atoms are oxidized to metal oxide/sulfide nanocrystals. The formation of a core-shell structure is independent of the numbers of ligands and carbon atoms as well as the metal types, implying that any metal π-complex can serve as a precursor and that various carbon encapsulated nanocrystals can be synthesized by this method.

  10. Highly efficient one-step synthesis of carbon encapsulated nanocrystals by the oxidation of metal π-complexes

    NASA Astrophysics Data System (ADS)

    Liu, Boyang; Shao, Yingfeng; Xiang, Xin; Zhang, Fuhua; Yan, Shengchang; Li, Wenge

    2017-08-01

    Various carbon encapsulated nanocrystals, including MnS and MnO, Cr2O3, MoO2, Fe7S8 and Fe3O4, and ZrO2, are prepared in one step and in situ by a simple and highly efficient synthesis approach. The nanocrystals have an equiaxed morphology and a median size smaller than 30 nm. Tens and hundreds of these nanocrystals are entirely encapsulated by a wormlike amorphous carbon shell. The formation of a core-shell structure depends on the strongly exothermic reaction of metal π-complexes with ammonium persulfate in an autoclave at below 200 °C. During the oxidation process, the generated significant amounts of heat will destroy the molecular structure of the metal π-complex and cleave the ligands into small carbon fragments, which further transform into an amorphous carbon shell. The central metal atoms are oxidized to metal oxide/sulfide nanocrystals. The formation of a core-shell structure is independent of the numbers of ligands and carbon atoms as well as the metal types, implying that any metal π-complex can serve as a precursor and that various carbon encapsulated nanocrystals can be synthesized by this method.

  11. Engineering the architectural diversity of heterogeneous metallic nanocrystals.

    PubMed

    Yu, Yue; Zhang, Qingbo; Xie, Jianping; Lee, Jim Yang

    2013-01-01

    Similar to molecular engineering where structural diversity is used to create more property variations for application explorations, the architectural engineering of heterogeneous metallic nanocrystals (HMNCs) can likewise increase the versatility of metallic nanocrystals (NCs). Here we present a synthesis strategy capable of engineering the architectural diversity of HMNCs through rational and independent programming of every architecture-determining element, that is, the shape and size of the component NCs and their spatial arrangement. The strategy is based on the galvanic replacement reaction of a self-sustaining layer formed by underpotential deposition on a polyhedral NC. The selective deposition of satellite NCs on specific site of the central NC is realized by creating a geometry-dependent heterogeneous electron distribution. This site-selective deposition approach is applicable to central NCs in various polyhedral shapes and sizes. The satellite NCs can further develop their own shape and size through crystal growth kinetics control.

  12. Tunable and responsive plasmonic properties of metal oxide nanocrystals

    NASA Astrophysics Data System (ADS)

    Milliron, Delia

    2015-03-01

    Degenerately doped metal oxide semiconductors, like ITO, exhibit plasmonic resonance at near and mid-infrared wavelengths tunable by varying their composition. Nanocrystals of many such materials have now been synthesized and applications are emerging that leverage the responsiveness of their localized surface plasmon resonance (LSPR) to electronic charging and discharging. For example, electrochromic glass that can dynamically control heat loads in buildings is under development. In biological systems, plasmonic oxide nanocrystals can act as remote sensors, where changes in their optical absorption indicates biochemical redox has occurred. Nonetheless, significant fundamental questions remain open regarding the nature of the infrared optical response in these doped oxides. Dopant impurities influence the optoelectronic properties beyond simply donating free carriers. For example, the distribution of Sn in ITO was found to dramatically influence the line shape of the LSPR and the effective electron mobility. In addition, by post-synthetically modifying carrier concentrations (through photodoping or electrochemical doping), we have observed that aliovalent doping and electronic doping each modify LSPR spectra, providing access to a broad range of tunable optical properties. Heterogeneous broadening, uncovered by single nanocrystal spectroscopy, also contributes to ensemble line shapes, complicating direct interpretation of LSPR spectra. Finally, the possibility of electric field enhancement by metal oxide LSPRs is critically examined to suggest what future applications might be on the horizon.

  13. A feasible strategy to balance the crystallinity and specific surface area of metal oxide nanocrystals.

    PubMed

    Zhang, Q P; Xu, X N; Liu, Y T; Xu, M; Deng, S H; Chen, Y; Yuan, H; Yu, F; Huang, Y; Zhao, K; Xu, S; Xiong, G

    2017-04-24

    Practical, efficient synthesis of metal oxide nanocrystals with good crystallinity and high specific surface area by a modified polymer-network gel method is demonstrated, taking ZnO nanocrystals as an example. A novel stepwise heat treatment yields significant improvement in crystal quality. Such nanophase materials can effectively degrade common organic dyes under solar radiation and can perform very well in photo-assisted detection of NO2 gas. Other typical metal oxide nanocrystals with good crystallinity and high specific surface area were also synthesized successfully under similar conditions. This work provides a general strategy for the synthesis of metal oxide nanocrystals, balancing the crystallinity and specific surface area.

  14. Generalized chemical route to develop fatty acid capped highly dispersed semiconducting metal sulphide nanocrystals

    SciTech Connect

    Patel, Jayesh D.; Mighri, Frej; Ajji, Abdellah

    2012-08-15

    Highlights: ► Chemical route for the synthesis of OA-capped CdS, ZnS and PbS at low temperature. ► Synthesized nanocrystals via thermolysis of their metal–oleate complexes. ► Size quantized nanocrystals were highly dispersed and stable at room temperature. -- Abstract: This work deals with the synthesis of highly dispersed semiconducting nanocrystals (NCs) of cadmium sulphide (CdS), zinc sulphide (ZnS) and lead sulphide (PbS) through a simple and generalized process using oleic acid (OA) as surfactant. To synthesize these NCs, metal–oleate (M–O) complexes were obtained from the reaction at 140 °C between metal acetates and OA in hexanes media. Subsequently, M–O complexes were sulphurized using thioacetamide at the same temperature. Transmission electron microscopy (TEM) and X-ray diffraction (XRD) characterizations show that the synthesized products are of nanoscale-size with highly crystalline cubic phase. The optical absorption of OA-capped metal sulphide NCs confirms that their size quantization induced a large shift towards visible region. Photoluminescence (PL) spectrum of CdS NCs shows a broad band-edge emission with shallow and deep-trap emissions, while PL spectrum of ZnS NCs reveals a broad emission due to defects states on the surface. The thermogravimetric analysis (TGA) and Fourier transform infrared (FTIR) spectroscopy indicate that fatty acid monolayers were bound strongly on the nanocrystal surface as a carboxylate and the two oxygen atoms of the carboxylate were coordinated symmetrically to the surface of the NCs. The strong binding between the fatty acid and the NCs surface enhances the stability of NCs colloids. In general, this generalized route has a great potential in developing nanoscale metal sulphides for opto-electronic devices.

  15. Metallic Carbon Nanotubes and Ag Nanocrystals

    SciTech Connect

    Brus, Louis E

    2014-03-04

    The goal of this DOE solar energy research was to understand how visible light interacts with matter, and how to make electric excitations evolve into separated electrons and holes in photovoltaic cells, especially in nanoparticles and nanowires. Our specific experiments focused on A) understanding plasmon enhanced spectroscopy and charge-transfer (metal-to-molecule) photochemistry on the surface of metallic particles and B) the spectroscopy and photochemistry of carbon nanotubes and graphene. I also worked closely with R. Friesner on theoretical studies of photo-excited electrons near surfaces of titanium dioxide nanoparticles; this process is relevant to the Gratzel photovoltaic cell.

  16. Facile synthesis of magnetic metal (Mn, Fe, Co, and Ni) oxides nanocrystals via a cation-exchange reaction.

    PubMed

    Ning, Jiajia; Xiao, Guanjun; Wang, Li; Zou, Bo; Liu, Bingbing; Zou, Guangtian

    2011-02-01

    Magnetic metal (Mn, Fe, Co, and Ni) oxides nanocrystals with small size and uniform size distribution are synthesized via a cation-exchange reaction. Two experimental stages are included in the synthesis of metal oxides nanocrystals. Firstly, Cu(OH)2 decomposes to CuO nanocrystals, induced by free metal cations. Compared to CuO nanocrystals produced without any free metal cation, the free metal cation has an important influence on the shape and size of CuO. Secondly, free metal cations exchange with the Cu2+ cation in the CuO nanocrystals to get Mn3O4, Fe2O3, CoO and NiO nanocrystals by cation-exchange reactions. The magnetic properties of these metal oxides nanocrystals have been investigated, all the nanocrystals are superparamagnetic at room temperature.

  17. Water-soluble semiconductor nanocrystals cap exchanged with metalated ligands.

    PubMed

    Liu, Di; Snee, Preston T

    2011-01-25

    We report a novel method for cap exchange of emissive semiconductor nanocrystals (NCs) using thiol functional ligands metalated with zinc. Utilizing this method, the NCs can be several times brighter and much more resistant to precipitation compared to control samples. This method has been applied using a variety of caps such as dihydrolipoic acid and cysteine. Our data suggest that the improved properties of the metalated cap exchanged NCs are due to a ligand metathesis process occurring at the NC surface where the zinc complex reacts with NC surface bound ligands, gently removing them and replacing them with another cap. Overall, the use of metalated ligands helps resolve many long-standing issues concerning the application of small cap exchanged NCs for biological imaging.

  18. A general procedure to synthesize highly crystalline metal oxide and mixed oxide nanocrystals in aqueous medium and photocatalytic activity of metal/oxide nanohybrids.

    PubMed

    Nguyen, Thanh-Dinh; Dinh, Cao-Thang; Do, Trong-On

    2011-04-01

    A conventional and general route has been exploited to the high yield synthesis of many kinds of highly crystalline metal oxide and mixed oxide nanocrystals with different morphologies including belt, rod, truncated-octahedron, cubic, sphere, sheet via the hydrothermal reaction of inorganic precursors in aqueous solution in the presence of bifunctional 6-aminohexanoic acid (AHA) molecules as a capping agent. This method is a simple, reproducible and general route for the preparation of a variety of high-crystalline inorganic nanocrystals in scale-up. The shape of inorganic nanocrystals such as CoWO(4), La(2)(MoO(4))(3) can be controlled by simply adjusting the synthesis conditions including pH solution and reaction temperature. Further, by tuning precursor monomer concentration, the mesocrystal hierarchical aggregated microspheres (e.g., MnWO(4), La(2)(MoO(4))(3)) can be achieved, due to the spontaneous assembly of individual AHA-capped nanoparticles. These obtained AHA-capped nanocrystals are excellent supports for the synthesis of a variety of hybrid metal/oxide nanocrystals in which noble metal particles are uniformly deposited on the surface of each individual nanosupport. The photocatalytic activity of Ag/TiO(2) nanobelts as a typical hybrid photocatalyst sample for Methylene Blue degradation was also studied.

  19. Nonthermal plasma synthesis of metal sulfide nanocrystals from metalorganic vapor and elemental sulfur

    NASA Astrophysics Data System (ADS)

    Thimsen, Elijah; Kortshagen, Uwe R.; Aydil, Eray S.

    2015-08-01

    Nanocrystal synthesis in nonthermal plasmas has been focused on elemental group IV semiconductors such as Si and Ge. In contrast, very little is known about plasma synthesis of compound nanocrystals and the time is ripe to extend this synthesis approach to nanocrystals comprised of two or more elements such as metal sulfides, oxides and nitrides. Towards this end, we studied, in an argon-sulfur plasma, the synthesis of ZnS, Cu2S and SnS nanocrystals from metalorganic precursors diethyl Zn(II), hexafluoroacetylacetonate Cu(I) vinyltrimethylsilane, and tetrakis(dimethylamido) Sn(IV), respectively. In situ optical emission spectroscopy was used to observe changes in relative concentrations of various plasma species during synthesis, while ex situ material characterization was used to examine the crystal structure, elemental composition and optical absorption of these nanocrystals. For a constant metalorganic vapor feed rate, the elemental composition of the nanocrystals was found to be independent of the sulfur flow rate into the plasma, above a small threshold value. At constant sulfur flow rate, the nanocrystal composition depended on the metalorganic vapor feed rate. Specifically, the ensemble metal atomic fraction in the nanocrystals was found to increase with increasing metalorganic vapor flow rates, resulting in more metal-rich crystal phases. The metalorganic feed rate can be used to control the composition and crystal phase of the metal-sulfide nanocrystals synthesized using this plasma process.

  20. Nanocrystal structures

    DOEpatents

    Eisler, Hans J.; Sundar, Vikram C.; Walsh, Michael E.; Klimov, Victor I.; Bawendi, Moungi G.; Smith, Henry I.

    2006-12-19

    A structure including a grating and a semiconductor nanocrystal layer on the grating, can be a laser. The semiconductor nanocrystal layer can include a plurality of semiconductor nanocrystals including a Group II–VI compound, the nanocrystals being distributed in a metal oxide matrix. The grating can have a periodicity from 200 nm to 500 nm.

  1. Nanocrystal structures

    DOEpatents

    Eisler, Hans J [Stoneham, MA; Sundar, Vikram C [Stoneham, MA; Walsh, Michael E [Everett, MA; Klimov, Victor I [Los Alamos, NM; Bawendi, Moungi G [Cambridge, MA; Smith, Henry I [Sudbury, MA

    2008-12-30

    A structure including a grating and a semiconductor nanocrystal layer on the grating, can be a laser. The semiconductor nanocrystal layer can include a plurality of semiconductor nanocrystals including a Group II-VI compound, the nanocrystals being distributed in a metal oxide matrix. The grating can have a periodicity from 200 nm to 500 nm.

  2. Remote electronic control of DNA hybridization through inductive coupling to an attached metal nanocrystal antenna

    NASA Astrophysics Data System (ADS)

    Hamad-Schifferli, Kimberly; Schwartz, John J.; Santos, Aaron T.; Zhang, Shuguang; Jacobson, Joseph M.

    2002-01-01

    Increasingly detailed structural and dynamic studies are highlighting the precision with which biomolecules execute often complex tasks at the molecular scale. The efficiency and versatility of these processes have inspired many attempts to mimic or harness them. To date, biomolecules have been used to perform computational operations and actuation, to construct artificial transcriptional loops that behave like simple circuit elements and to direct the assembly of nanocrystals. Further development of these approaches requires new tools for the physical and chemical manipulation of biological systems. Biomolecular activity has been triggered optically through the use of chromophores, but direct electronic control over biomolecular `machinery' in a specific and fully reversible manner has not yet been achieved. Here we demonstrate remote electronic control over the hybridization behaviour of DNA molecules, by inductive coupling of a radio-frequency magnetic field to a metal nanocrystal covalently linked to DNA. Inductive coupling to the nanocrystal increases the local temperature of the bound DNA, thereby inducing denaturation while leaving surrounding molecules relatively unaffected. Moreover, because dissolved biomolecules dissipate heat in less than 50picoseconds (ref. 16), the switching is fully reversible. Inductive heating of macroscopic samples is widely used, but the present approach should allow extension of this concept to the control of hybridization and thus of a broad range of biological functions on the molecular scale.

  3. Galvanic Exchange in Colloidal Metal/Metal-Oxide Core/Shell Nanocrystals

    PubMed Central

    2016-01-01

    While galvanic exchange is commonly applied to metallic nanoparticles, recently its applicability was expanded to metal-oxides. Here the galvanic exchange is studied in metal/metal-oxide core/shell nanocrystals. In particular Sn/SnO2 is treated by Ag+, Pt2+, Pt4+, and Pd2+. The conversion dynamics is monitored by in situ synchrotron X-ray diffraction. The Ag+ treatment converts the Sn cores to the intermetallic AgxSn (x ∼ 4) phase, by changing the core’s crystal structure. For the analogous treatment by Pt2+, Pt4+, and Pd2+, such a galvanic exchange is not observed. This different behavior is caused by the semipermeability of the naturally formed SnO2 shell, which allows diffusion of Ag+ but protects the nanocrystal cores from oxidation by Pt and Pd ions. PMID:27635186

  4. Electrochemical electron beam lithography: Write, read, and erase metallic nanocrystals on demand.

    PubMed

    Park, Jeung Hun; Steingart, Daniel A; Kodambaka, Suneel; Ross, Frances M

    2017-07-01

    We develop a solution-based nanoscale patterning technique for site-specific deposition and dissolution of metallic nanocrystals. Nanocrystals are grown at desired locations by electron beam-induced reduction of metal ions in solution, with the ions supplied by dissolution of a nearby electrode via an applied potential. The nanocrystals can be "erased" by choice of beam conditions and regrown repeatably. We demonstrate these processes via in situ transmission electron microscopy using Au as the model material and extend to other metals. We anticipate that this approach can be used to deposit multicomponent alloys and core-shell nanostructures with nanoscale spatial and compositional resolutions for a variety of possible applications.

  5. Contact Radius and the Insulator-Metal Transition in Films Comprised of Touching Semiconductor Nanocrystals.

    PubMed

    Lanigan, Deanna; Thimsen, Elijah

    2016-07-26

    Nanocrystal assemblies are being explored for a number of optoelectronic applications such as transparent conductors, photovoltaic solar cells, and electrochromic windows. Majority carrier transport is important for these applications, yet it remains relatively poorly understood in films comprised of touching nanocrystals. Specifically, the underlying structural parameters expected to determine the transport mechanism have not been fully elucidated. In this report, we demonstrate experimentally that the contact radius, between touching heavily doped ZnO nanocrystals, controls the electron transport mechanism. Spherical nanocrystals are considered, which are connected by a circular area. The radius of this circular area is the contact radius. For nanocrystals that have local majority carrier concentration above the Mott transition, there is a critical contact radius. If the contact radius between nanocrystals is less than the critical value, then the transport mechanism is variable range hopping. If the contact radius is greater than the critical value, the films display behavior consistent with metallic electron transport.

  6. Biomimetic Synthesis of Noble Metal Nanocrystals and the Mechanism Studies

    NASA Astrophysics Data System (ADS)

    Ruan, Lingyan

    Nanostructured materials with dimensions reaching the nanoscale possess novel properties different from their bulk counterparts. Engineering nanomaterials to exploit their improved functions show important applications in catalysis, electrocatalysis, electronics, optoelectronics, and energy devices. One of the challenges to date is to develop methods for producing nanomaterials in a controllable and predictable fashion. We seek to develop novel biomimetic synthetic protocols for programmable nanomaterial synthesis, i.e., using biomolecules with specific material recognition properties to manipulate nanomaterial morphologies and structures. Starting with three Pt binding peptides with distinct recognition properties, i.e., a Pt material specific peptide BP7A and two Pt facet specific peptides T7 (Pt {100} facet specific) and S7 (Pt {111} facet specific), we demonstrate a rational creation of Pt bipyramids, a new type of shape for Pt nanocrystals. The BP7A peptide is found to be able to introduce twinning during Pt nanocrystal growth. We use it to generate single twinned seeds for Pt nanocrystals. Together with targeted facet stabilization using T7/S7 peptides, Pt {100} bipyramid and {111} bipyramid are successfully synthesized for the first time. We further utilize the twin introducing property of the BP7A peptide to generate ultrathin Pt nanowire with high twin densities. We show that the Pt nanowire possesses higher electrocatalytic activity and durability in oxygen reduction and methanol oxidation reactions due to its one-dimensional nanostructure and the presence of dense twin defects, demonstrating the concept of defect engineering in nanocrystals as a strategy in the design of novel electrocatalyst. The organic-inorganic interface is a key issue in many fields including colloidal syntheses and biomimetics, the understanding of which can enable the design of new material synthetic strategies. We aim to understand how the Pt binding peptides modulate the

  7. 1/f noise in semiconductor and metal nanocrystal solids

    SciTech Connect

    Liu, Heng Lhuillier, Emmanuel Guyot-Sionnest, Philippe

    2014-04-21

    Electrical 1/f noise is measured in thin films of CdSe, CdSe/CdS, ZnO, HgTe quantum dots and Au nanocrystals. The 1/f noise, normalized per nanoparticle, shows no systematic dependence on the nanoparticle material and the coupling material. However, over 10 orders of magnitude, it correlates well with the nearest neighbor conductance suggesting some universal magnitude of the 1/f noise in these granular conductors. In the hopping regime, the main mechanism of 1/f noise is determined to be mobility fluctuated. In the metallic regime obtained with gold nanoparticle films, the noise drops to a similar level as bulk gold films and with a similar temperature dependence.

  8. Effective optical Faraday rotations of semiconductor EuS nanocrystals with paramagnetic transition-metal ions.

    PubMed

    Hasegawa, Yasuchika; Maeda, Masashi; Nakanishi, Takayuki; Doi, Yoshihiro; Hinatsu, Yukio; Fujita, Koji; Tanaka, Katsuhisa; Koizumi, Hitoshi; Fushimi, Koji

    2013-02-20

    Novel EuS nanocrystals containing paramagnetic Mn(II), Co(II), or Fe(II) ions have been reported as advanced semiconductor materials with effective optical rotation under a magnetic field, Faraday rotation. EuS nanocrystals with transition-metal ions, EuS:M nanocrystals, were prepared by the reduction of the Eu(III) dithiocarbamate complex tetraphenylphosphonium tetrakis(diethyldithiocarbamate)europium(III) with transition-metal complexes at 300 °C. The EuS:M nanocrystals thus prepared were characterized using X-ray diffraction (XRD), transmission electron microscopy (TEM), inductively coupled plasma atomic emission spectroanalysis (ICP-AES), and a superconducting quantum interference device (SQUID) magnetometer. Enhanced Faraday rotations of the EuS:M nanocrystals were observed around 550 nm, and their enhanced spin polarization was estimated using electron paramagnetic resonance (EPR) measurements. In this report, the magneto-optical relationship between the Faraday rotation efficiency and spin polarization is discussed.

  9. A simple method to tailor spherical nanocrystal hydroxyapatite at low temperature

    NASA Astrophysics Data System (ADS)

    Zhang, Yanjie; Lu, Jinjun

    2007-08-01

    A simple method, chemical precipitation at low temperature from Ca(NO3)2·4H2O and (NH4)2HPO4 to tailor single phase, highly crystalline nanocrystal hydroxyapatite (HAp) powders was introduced in this paper. HAp powders with controlled morphologies (spherical and rod-like) and different grain sizes have been obtained by varying the reaction temperature, reaction mode, and heat treatment accordingly. X-ray diffraction (XRD) results combined with the Fourier transform-infrared spectroscopy (FT-IR) indicates that the single phase, nanocrystal HAp powder could be obtained in one-step without further heat treatment. At 40 °C with a quick mixing mode, ultra-fine complete spherical HAp particles with diameter range size of 20-50 nm could be obtained.

  10. Dense simple plasmas as high-temperature liquid simple metals

    NASA Technical Reports Server (NTRS)

    Perrot, F.

    1990-01-01

    The thermodynamic properties of dense plasmas considered as high-temperature liquid metals are studied. An attempt is made to show that the neutral pseudoatom picture of liquid simple metals may be extended for describing plasmas in ranges of densities and temperatures where their electronic structure remains 'simple'. The primary features of the model when applied to plasmas include the temperature-dependent self-consistent calculation of the electron charge density and the determination of a density and temperature-dependent ionization state.

  11. Equation of State of Simple Metals.

    DTIC Science & Technology

    1982-05-10

    This is the final report of A. L. Ruoff and N. W. Ashcroft on Equation of State of Simple Metals. It includes experimental equation of state results for potassium and theoretical calculations of its equation of state . (Author)

  12. Synthesis of colloidal metal nanocrystals in droplet reactors: the pros and cons of interfacial adsorption.

    PubMed

    Zhang, Lei; Wang, Yi; Tong, Limin; Xia, Younan

    2014-07-09

    Droplet reactors have received considerable attention in recent years as an alternative route to the synthesis and potentially high-volume production of colloidal metal nanocrystals. Interfacial adsorption will immediately become an important issue to address when one seeks to translate a nanocrystal synthesis from batch reactors to droplet reactors due to the involvement of higher surface-to-volume ratios for the droplets and the fact that nanocrystals tend to be concentrated at the water-oil interface. Here we report a systematic study to compare the pros and cons of interfacial adsorption of metal nanocrystals during their synthesis in droplet reactors. On the one hand, interfacial adsorption can be used to generate nanocrystals with asymmetric shapes or structures, including one-sixth-truncated Ag octahedra and Au-Ag nanocups. On the other hand, interfacial adsorption has to be mitigated to obtain nanocrystals with uniform sizes and controlled shapes. We confirmed that Triton X-100, a nonionic surfactant, could effectively alleviate interfacial adsorption while imposing no impact on the capping agent typically needed for a shape-controlled synthesis. With the introduction of a proper surfactant, droplet reactors offer an attractive platform for the continuous production of colloidal metal nanocrystals.

  13. Hydrogen storage in Pd nanocrystals covered with a metal-organic framework

    NASA Astrophysics Data System (ADS)

    Li, Guangqin; Kobayashi, Hirokazu; Taylor, Jared M.; Ikeda, Ryuichi; Kubota, Yoshiki; Kato, Kenichi; Takata, Masaki; Yamamoto, Tomokazu; Toh, Shoichi; Matsumura, Syo; Kitagawa, Hiroshi

    2014-08-01

    Hydrogen is an essential component in many industrial processes. As a result of the recent increase in the development of shale gas, steam reforming of shale gas has received considerable attention as a major source of H2, and the more efficient use of hydrogen is strongly demanded. Palladium is well known as a hydrogen-storage metal and an effective catalyst for reactions related to hydrogen in a variety of industrial processes. Here, we present remarkably enhanced capacity and speed of hydrogen storage in Pd nanocrystals covered with the metal-organic framework (MOF) HKUST-1 (copper(II) 1,3,5-benzenetricarboxylate). The Pd nanocrystals covered with the MOF have twice the storage capacity of the bare Pd nanocrystals. The significantly enhanced hydrogen storage capacity was confirmed by hydrogen pressure-composition isotherms and solid-state deuterium nuclear magnetic resonance measurements. The speed of hydrogen absorption in the Pd nanocrystals is also enhanced by the MOF coating.

  14. Direct observation of narrow mid-infrared plasmon linewidths of single metal oxide nanocrystals

    NASA Astrophysics Data System (ADS)

    Johns, Robert W.; Bechtel, Hans A.; Runnerstrom, Evan L.; Agrawal, Ankit; Lounis, Sebastien D.; Milliron, Delia J.

    2016-05-01

    Infrared-responsive doped metal oxide nanocrystals are an emerging class of plasmonic materials whose localized surface plasmon resonances (LSPR) can be resonant with molecular vibrations. This presents a distinctive opportunity to manipulate light-matter interactions to redirect chemical or spectroscopic outcomes through the strong local electric fields they generate. Here we report a technique for measuring single nanocrystal absorption spectra of doped metal oxide nanocrystals, revealing significant spectral inhomogeneity in their mid-infrared LSPRs. Our analysis suggests dopant incorporation is heterogeneous beyond expectation based on a statistical distribution of dopants. The broad ensemble linewidths typically observed in these materials result primarily from sample heterogeneity and not from strong electronic damping associated with lossy plasmonic materials. In fact, single nanocrystal spectra reveal linewidths as narrow as 600 cm-1 in aluminium-doped zinc oxide, a value less than half the ensemble linewidth and markedly less than homogeneous linewidths of gold nanospheres.

  15. Hydrogen storage in Pd nanocrystals covered with a metal-organic framework.

    PubMed

    Li, Guangqin; Kobayashi, Hirokazu; Taylor, Jared M; Ikeda, Ryuichi; Kubota, Yoshiki; Kato, Kenichi; Takata, Masaki; Yamamoto, Tomokazu; Toh, Shoichi; Matsumura, Syo; Kitagawa, Hiroshi

    2014-08-01

    Hydrogen is an essential component in many industrial processes. As a result of the recent increase in the development of shale gas, steam reforming of shale gas has received considerable attention as a major source of H2, and the more efficient use of hydrogen is strongly demanded. Palladium is well known as a hydrogen-storage metal and an effective catalyst for reactions related to hydrogen in a variety of industrial processes. Here, we present remarkably enhanced capacity and speed of hydrogen storage in Pd nanocrystals covered with the metal-organic framework (MOF) HKUST-1 (copper(II) 1,3,5-benzenetricarboxylate). The Pd nanocrystals covered with the MOF have twice the storage capacity of the bare Pd nanocrystals. The significantly enhanced hydrogen storage capacity was confirmed by hydrogen pressure-composition isotherms and solid-state deuterium nuclear magnetic resonance measurements. The speed of hydrogen absorption in the Pd nanocrystals is also enhanced by the MOF coating.

  16. Direct observation of narrow mid-infrared plasmon linewidths of single metal oxide nanocrystals

    PubMed Central

    Johns, Robert W.; Bechtel, Hans A.; Runnerstrom, Evan L.; Agrawal, Ankit; Lounis, Sebastien D.; Milliron, Delia J.

    2016-01-01

    Infrared-responsive doped metal oxide nanocrystals are an emerging class of plasmonic materials whose localized surface plasmon resonances (LSPR) can be resonant with molecular vibrations. This presents a distinctive opportunity to manipulate light–matter interactions to redirect chemical or spectroscopic outcomes through the strong local electric fields they generate. Here we report a technique for measuring single nanocrystal absorption spectra of doped metal oxide nanocrystals, revealing significant spectral inhomogeneity in their mid-infrared LSPRs. Our analysis suggests dopant incorporation is heterogeneous beyond expectation based on a statistical distribution of dopants. The broad ensemble linewidths typically observed in these materials result primarily from sample heterogeneity and not from strong electronic damping associated with lossy plasmonic materials. In fact, single nanocrystal spectra reveal linewidths as narrow as 600 cm−1 in aluminium-doped zinc oxide, a value less than half the ensemble linewidth and markedly less than homogeneous linewidths of gold nanospheres. PMID:27174681

  17. Direct observation of narrow mid-infrared plasmon linewidths of single metal oxide nanocrystals

    DOE PAGES

    Johns, Robert W.; Bechtel, Hans A.; Runnerstrom, Evan L.; ...

    2016-05-13

    Infrared-responsive doped metal oxide nanocrystals are an emerging class of plasmonic materials whose localized surface plasmon resonances (LSPR) can be resonant with molecular vibrations. This presents a distinctive opportunity to manipulate light-matter interactions to redirect chemical or spectroscopic outcomes through the strong local electric fields they generate. Here we report a technique for measuring single nanocrystal absorption spectra of doped metal oxide nanocrystals, revealing significant spectral inhomogeneity in their mid-infrared LSPRs. Our analysis suggests dopant incorporation is heterogeneous beyond expectation based on a statistical distribution of dopants. The broad ensemble linewidths typically observed in these materials result primarily from sammore » ple heterogeneity and not from strong electronic damping associated with lossy plasmonic materials. In fact, single nanocrystal spectra reveal linewidths as narrow as 600 cm -1 in aluminium-doped zinc oxide, a value less than half the ensemble linewidth and markedly less than homogeneous linewidths of gold nanospheres.« less

  18. Direct observation of narrow mid-infrared plasmon linewidths of single metal oxide nanocrystals

    SciTech Connect

    Johns, Robert W.; Bechtel, Hans A.; Runnerstrom, Evan L.; Agrawal, Ankit; Lounis, Sebastien D.; Milliron, Delia J.

    2016-05-13

    Infrared-responsive doped metal oxide nanocrystals are an emerging class of plasmonic materials whose localized surface plasmon resonances (LSPR) can be resonant with molecular vibrations. This presents a distinctive opportunity to manipulate light-matter interactions to redirect chemical or spectroscopic outcomes through the strong local electric fields they generate. Here we report a technique for measuring single nanocrystal absorption spectra of doped metal oxide nanocrystals, revealing significant spectral inhomogeneity in their mid-infrared LSPRs. Our analysis suggests dopant incorporation is heterogeneous beyond expectation based on a statistical distribution of dopants. The broad ensemble linewidths typically observed in these materials result primarily from sam ple heterogeneity and not from strong electronic damping associated with lossy plasmonic materials. In fact, single nanocrystal spectra reveal linewidths as narrow as 600 cm -1 in aluminium-doped zinc oxide, a value less than half the ensemble linewidth and markedly less than homogeneous linewidths of gold nanospheres.

  19. Control of metal nanocrystal size reveals metal-support interface role for ceria catalysts.

    PubMed

    Cargnello, Matteo; Doan-Nguyen, Vicky V T; Gordon, Thomas R; Diaz, Rosa E; Stach, Eric A; Gorte, Raymond J; Fornasiero, Paolo; Murray, Christopher B

    2013-08-16

    Interactions between ceria (CeO2) and supported metals greatly enhance rates for a number of important reactions. However, direct relationships between structure and function in these catalysts have been difficult to extract because the samples studied either were heterogeneous or were model systems dissimilar to working catalysts. We report rate measurements on samples in which the length of the ceria-metal interface was tailored by the use of monodisperse nickel, palladium, and platinum nanocrystals. We found that carbon monoxide oxidation in ceria-based catalysts is greatly enhanced at the ceria-metal interface sites for a range of group VIII metal catalysts, clarifying the pivotal role played by the support.

  20. Control of Metal Nanocrystal Size Reveals Metal-Support Interface Role for Ceria Catalysts

    SciTech Connect

    Cargnello, M; Doan-Nguyen, VVT; Gordon, TR; Diaz, RE; Stach, EA; Gorte, RJ; Fornasiero, P; Murray, CB

    2013-08-15

    Interactions between ceria (CeO2) and supported metals greatly enhance rates for a number of important reactions. However, direct relationships between structure and function in these catalysts have been difficult to extract because the samples studied either were heterogeneous or were model systems dissimilar to working catalysts. We report rate measurements on samples in which the length of the ceria-metal interface was tailored by the use of monodisperse nickel, palladium, and platinum nanocrystals. We found that carbon monoxide oxidation in ceria-based catalysts is greatly enhanced at the ceria-metal interface sites for a range of group VIII metal catalysts, clarifying the pivotal role played by the support.

  1. Synthesis and characterization of transition-metal-doped zinc oxide nanocrystals for spintronics

    NASA Astrophysics Data System (ADS)

    Wang, Xuefeng

    Spintronics (spin transport electr onics), in which both spin and charge of carriers are utilized for information processing, is believed to challenge the current microelectronics and to become the next-generation electronics. Nanostructured spintronic materials and their synthetic methodologies are of paramount importance for manufacturing future nanoscale spintronic devices. This thesis aims at studying synthesis, characterization, and magnetism of transition-metal-doped zinc oxide (ZnO) nanocrystals---a diluted magnetic semiconductor (DMS)---for potential applications in future nano-spintronics. A simple bottom-up-based synthetic strategy named a solvothermal technique is introduced as the primary synthetic approach and its crystal growth mechanism is scrutinized. N-type cobalt-doped ZnO-based DMS nanocrystals are employed as a model system, and characterized by a broad spectrum of advanced microscopic and spectroscopic techniques. It is found that the self-orientation growth mechanism, imperfect oriented attachment, is intimately correlated with the high-temperature ferromagnetism via defects. The influence of processing on the magnetic properties, such as compositional variations, reaction conditions, and post-growth treatment, is also studied. In this way, an in-depth understanding of processing-structure-property interrelationships and origins of magnetism in DMS nanocrystals are obtained in light of the theoretical framework of a spin-split impurity band model. In addition, a nanoscale spinodal decomposition phase model is also briefly discussed. Following the similar synthetic route, copper- and manganese-doped ZnO nanocrystals have been synthesized and characterized. They both show high-temperature ferromagnetism in line with the aforementioned theoretical model(s). Moreover, they display interesting exchange biasing phenomena at low temperatures, revealing the complexity of magnetic phases therein. The crystal growth strategy demonstrated in this work

  2. Scalable strategies for the synthesis of well-defined copper metal and oxide nanocrystals.

    PubMed

    Lignier, Pascal; Bellabarba, Ronan; Tooze, Robert P

    2012-03-07

    This tutorial review highlights the most promising methods for the preparation of well-defined copper metal and oxide nanocrystals. These methodologies could be applied to other metals. We present the main synthetic strategies and associated mechanisms to control monodispersity, size, morphology and structure of metal and oxide nanomaterials which can adopt spherical, polyhedral, cubic, rod, wire, plate shapes and possibly hollow structures. We also consider the scale-up of the production of these nanocrystals, which is crucial for a wide range of potential applications such as catalysis, photovoltaics, electronics, optics and electrocatalysis. This journal is © The Royal Society of Chemistry 2012

  3. A simple route to alloyed quaternary nanocrystals Ag-In-Zn-S with shape and size control.

    PubMed

    Gabka, Grzegorz; Bujak, Piotr; Giedyk, Kamila; Ostrowski, Andrzej; Malinowska, Karolina; Herbich, Jerzy; Golec, Barbara; Wielgus, Ireneusz; Pron, Adam

    2014-05-19

    A convenient method of the preparation of alloyed quaternary Ag-In-Zn-S nanocrystals is elaborated, in which a multicomponent mixture of simple and commercially available precursors, namely, silver nitrate, indium(III) chloride, zinc stearate, 1-dodecanethiol, and sulfur, is used with 1-octadecene as a solvent. The formation of quaternary nanocrystals necessitates the use of an auxiliary sulfur precursor, namely, elemental sulfur dissolved in oleylamine, in addition to 1-dodecanethiol. Without this additional precursor binary ZnS nanocrystals are formed. The optimum reaction temperature of 180 °C was also established. In these conditions shape, size, and composition of the resulting nanocrystals can be adjusted in a controlled manner by changing the molar ratio of the precursors in the reaction mixture. For low zinc stearate contents anisotropic rodlike (ca.3 nm x 10 nm) and In-rich nanocrystals are obtained. This is caused by a significantly higher reactivity of the indium precursor as compared to the zinc one. With increasing zinc precursor content the reactivities of both precursors become more balanced, and the resulting nanocrystals are smaller (1.5-4.0 nm) and become Zn-rich as evidenced by transmission electron microscopy, X-ray diffraction, and energy-dispersive spectrometry investigations. Simultaneous increases in the zinc and sulfur precursor content result in an enlargement of nanocrystals (2.5 to 5.0 nm) and further increase in the molar ZnS content (up to 0.76). The prepared nanoparticles show stable photoluminescence with the quantum yield up to 37% for In and Zn-rich nanocrystals. Their hydrodynamic diameter in toluene dispersion, determined by dynamic light scattering, is roughly twice larger than the diameter of their inorganic core.

  4. Unravelling the surface chemistry of metal oxide nanocrystals, the role of acids and bases.

    PubMed

    De Roo, Jonathan; Van den Broeck, Freya; De Keukeleere, Katrien; Martins, José C; Van Driessche, Isabel; Hens, Zeger

    2014-07-09

    We synthesized HfO2 nanocrystals from HfCl4 using a surfactant-free solvothermal process in benzyl alcohol and found that the resulting nanocrystals could be transferred to nonpolar media using a mixture of carboxylic acids and amines. Using solution (1)H NMR, FTIR, and elemental analysis, we studied the details of the transfer reaction and the surface chemistry of the resulting sterically stabilized nanocrystals. As-synthesized nanocrystals are charge-stabilized by protons, with chloride acting as the counterion. Treatment with only carboxylic acids does not lead to any binding of ligands to the HfO2 surface. On the other hand, we find that the addition of amines provides the basic environment in which carboxylic acids can dissociate and replace chloride. This results in stable, aggregate-free dispersions of HfO2 nanocrystals, sterically stabilized by carboxylate ligands. Moreover, titrations with deuterated carboxylic acid show that the charge on the carboxylate ligands is balanced by coadsorbed protons. Hence, opposite from the X-type/nonstoichiometric nanocrystals picture prevailing in literature, one should look at HfO2/carboxylate nanocrystals as systems where carboxylic acids are dissociatively adsorbed to bind to the nanocrystals. Similar results were obtained with ZrO2 NCs. Since proton accommodation on the surface is most likely due to the high Brønsted basicity of oxygen, our model could be a more general picture for the surface chemistry of metal oxide nanocrystals with important consequences on the chemistry of ligand exchange reactions.

  5. Electrochemical electron beam lithography: Write, read, and erase metallic nanocrystals on demand

    PubMed Central

    Park, Jeung Hun; Steingart, Daniel A.; Kodambaka, Suneel; Ross, Frances M.

    2017-01-01

    We develop a solution-based nanoscale patterning technique for site-specific deposition and dissolution of metallic nanocrystals. Nanocrystals are grown at desired locations by electron beam–induced reduction of metal ions in solution, with the ions supplied by dissolution of a nearby electrode via an applied potential. The nanocrystals can be “erased” by choice of beam conditions and regrown repeatably. We demonstrate these processes via in situ transmission electron microscopy using Au as the model material and extend to other metals. We anticipate that this approach can be used to deposit multicomponent alloys and core-shell nanostructures with nanoscale spatial and compositional resolutions for a variety of possible applications. PMID:28706992

  6. Emergence of intrinsic half-metallicity in MoS2 nano-crystals : A first principles study

    NASA Astrophysics Data System (ADS)

    Mandal, S. C.; Chatterjee, S.; Taraphder, A.

    2017-05-01

    Using first principles density functional theory we investigate the electronic structure of MoS2 nano-crystals of diameter 1nm. Our calculations suggest that MoS2 nano-crystals are inherently half-metallic, the half-metallicity being robust with respect to the constitution as well as the morphology of the surface and also with respect to the length of the nano-crystal. Thus, MoS2 nano-crystals, may turn out to be very important for application in spintronics based solid state devices.

  7. Template-directed assembly of metal-chalcogenide nanocrystals into ordered mesoporous networks.

    SciTech Connect

    Vamvasakis, Ioannis; Subrahmanyam, Kota S.; Kanatzidis, Mercouri G.; Armatas, Gerasimos S.

    2015-04-01

    Although great progress in the synthesis of porous networks of metal and metal oxide nanoparticles with highly accessible pore surface and ordered mesoscale pores has been achieved, synthesis of assembled 3D mesostructures of metal-chalcogenide nanocrystals is still challenging. In this work we demonstrate that ordered mesoporous networks, which comprise well-defined interconnected metal sulfide nanocrystals, can be prepared through a polymer-templated oxidative polymerization process. The resulting self-assembled mesostructures that were obtained after solvent extraction of the polymer template impart the unique combination of light-emitting metal chalcogenide nanocrystals, three-dimensional open-pore structure, high surface area, and uniform pores. We show that the pore surface of these materials is active and accessible to incoming molecules, exhibiting high photocatalytic activity and stability, for instance, in oxidation of 1-phenylethanol into acetophenone. We demonstrate through appropriate selection of the synthetic components that this method is general to prepare ordered mesoporous materials from metal chalcogenide nanocrystals with various sizes and compositions.

  8. Colloidal metal oxide nanocrystal catalysis by sustained chemically driven ligand displacement.

    PubMed

    De Roo, Jonathan; Van Driessche, Isabel; Martins, José C; Hens, Zeger

    2016-05-01

    Surface chemistry is a key enabler for colloidal nanocrystal applications. In this respect, metal oxide nanocrystals (NCs) stand out from other NCs as carboxylic acid ligands adsorb on their surface by dissociation to carboxylates and protons, the latter proving essential in electron transfer reactions. Here, we show that this binding motif sets the stage for chemically driven ligand displacement where the binding of amines or alcohols to HfO2 NCs is promoted by the conversion of a bound carboxylic acid into a non-coordinating amide or ester. Furthermore, the sustained ligand displacement, following the addition of excess carboxylic acid, provides a catalytic pathway for ester formation, whereas the addition of esters leads to NC-catalysed transesterification. Because sustained, chemically driven ligand displacement leaves the NCs-including their surface composition-unchanged and preserves colloidal stability, metal oxide nanocrystals are thus turned into effective nanocatalysts that bypass the tradeoff between colloidal stability and catalytic activity.

  9. Colloidal metal oxide nanocrystal catalysis by sustained chemically driven ligand displacement

    NASA Astrophysics Data System (ADS)

    de Roo, Jonathan; van Driessche, Isabel; Martins, José C.; Hens, Zeger

    2016-05-01

    Surface chemistry is a key enabler for colloidal nanocrystal applications. In this respect, metal oxide nanocrystals (NCs) stand out from other NCs as carboxylic acid ligands adsorb on their surface by dissociation to carboxylates and protons, the latter proving essential in electron transfer reactions. Here, we show that this binding motif sets the stage for chemically driven ligand displacement where the binding of amines or alcohols to HfO2 NCs is promoted by the conversion of a bound carboxylic acid into a non-coordinating amide or ester. Furthermore, the sustained ligand displacement, following the addition of excess carboxylic acid, provides a catalytic pathway for ester formation, whereas the addition of esters leads to NC-catalysed transesterification. Because sustained, chemically driven ligand displacement leaves the NCs--including their surface composition--unchanged and preserves colloidal stability, metal oxide nanocrystals are thus turned into effective nanocatalysts that bypass the tradeoff between colloidal stability and catalytic activity.

  10. Floating gate memory-based monolayer MoS2 transistor with metal nanocrystals embedded in the gate dielectrics.

    PubMed

    Wang, Jingli; Zou, Xuming; Xiao, Xiangheng; Xu, Lei; Wang, Chunlan; Jiang, Changzhong; Ho, Johnny C; Wang, Ti; Li, Jinchai; Liao, Lei

    2015-01-14

    Charge trapping layers are formed from different metallic nanocrystals in MoS2 -based nanocrystal floating gate memory cells in a process compatible with existing fabrication technologies. The memory cells with Au nanocrystals exhibit impressive performance with a large memory window of 10 V, a high program/erase ratio of approximately 10(5) and a long retention time of 10 years. © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  11. Thermal stability increase in metallic nanoparticles-loaded cellulose nanocrystal nanocomposites.

    PubMed

    Goikuria, U; Larrañaga, A; Vilas, J L; Lizundia, E

    2017-09-01

    Due to the potential of CNC-based flexible materials for novel industrial applications, the aim of this work is to improve the thermal stability of cellulose nanocrystals (CNC) films through a straightforward and scalable method. Based of nanocomposite approach, five different metallic nanoparticles (ZnO, SiO2, TiO2, Al2O3 and Fe2O3) have been co-assembled in water with CNCs to obtain free-standing nanocomposite films. Thermogravimetric analysis (TGA) reveals an increased thermal stability upon nanoparticle. This increase in the thermal stability reaches a maximum of 75°C for the nanocomposites having 10wt% of Fe2O3 and ZnO. The activation energies of thermodegradation process (Ea) determined according to Kissinger and Ozawa-Flynn-Wall methods further confirm the delayed degradation of CNC nanocomposites upon heating. Finally, the changes induced in the crystalline structure during thermodegradation were followed by wide angle X-ray diffraction (WAXD). It is also observed that thermal degradation proceeds at higher temperatures for nanocomposites having metallic nanoparticles. Overall, experimental findings here showed make nanocomposite approach a simple low-cost environmentally-friendly strategy to overcome the relatively poor thermal stability of CNCs when extracted via sulfuric acid assisted hydrolysis of cellulose. Copyright © 2017 Elsevier Ltd. All rights reserved.

  12. Impact of the Metallic Crystalline Structure on the Properties of Nanocrystals and Their Mesoscopic Assemblies.

    PubMed

    Pileni, Marie-Paule

    2017-08-15

    positions. These vibrational properties show a full analogy with atomic crystals: In supracrystals, atoms are replaced by (uncompressible) nanocrystals and atomic bonds by coating agents (carbon chains), which act like mechanical springs holding together the nanocrystals. Electronic properties of very thick (more than a few micrometers) supracrystals reveal homogeneous conductance with the fingerprint of the isolated nanocrystal. Triangular single crystals formed by heat-induced (50 °C) coalescence of thin supracrystals deposited on a substrate as epitaxial growth of metal particles on a substrate with specific orientation produced by ultrahigh vacuum (UHV). Here we demonstrate that marked changes can occur in the chemical and physical properties of nanocrystals differing by their nanocrystallinity, that is, their crystalline structure. Furthermore, the properties (mechanical, growth processes) of supracrystals also change with the nanocrystallinity of the nanoparticles used as building blocks.

  13. Metal-Particle-Decorated ZnO Nanocrystals: Photocatalysis and Charge Dynamics.

    PubMed

    Lin, Wei-Hao; Chiu, Yi-Hsuan; Shao, Pao-Wen; Hsu, Yung-Jung

    2016-12-07

    Understanding of charge transfer processes is determinant to the performance optimization for semiconductor photocatalysts. As a representative model of composite photocatalysts, metal-particle-decorated ZnO has been widely employed for a great deal of photocatalytic applications; however, the dependence of charge carrier dynamics on the metal content and metal composition and their correlation with the photocatalytic properties have seldom been reported. Here, the interfacial charge dynamics for metal-decorated ZnO nanocrystals were investigated and their correspondence with the photocatalytic properties was evaluated. The samples were prepared with a delicate antisolvent approach, in which ZnO nanocrystals were grown along with metal particle decoration in a deep eutectic solvent. By modulating the experimental conditions, the metal content (from 0.6 to 2.3 at%) and metal composition (including Ag, Au, and Pd) in the resulting metal-decorated ZnO could be readily controlled. Time-resolved photoluminescence spectra showed that an optimal Au content of 1.3 at% could effectuate the largest electron transfer rate constant for Au-decorated ZnO nanocrystals, in conformity with the highest photocatalytic efficiency observed. The relevance of charge carrier dynamics to the metal composition was also inspected and realized in terms of the energy level difference between ZnO and metal. Among the three metal-decorated ZnO samples tested, ZnO-Pd displayed the highest photocatalytic activity, fundamentally according with the largest electron transfer rate constant deduced in carrier dynamics measurements. The current work was the first study to present the correlations among charge carrier dynamics, metal content, metal composition, and the resultant photocatalytic properties for semiconductor/metal heterostructures. The findings not only helped to resolve the standing issues regarding the mechanistic foundation of photocatalysis but also shed light on the intelligent design

  14. A simple route to Bi2Se3 and Bi2Te3 nanocrystals

    NASA Astrophysics Data System (ADS)

    Mntungwa, Nhlakanipho; Rajasekhar, Pullabhotla V. S. R.; Ramasamy, Karthik; Revaprasadu, Neerish

    2014-05-01

    Monodisperse nanocrystals of Bi2Se3 and Bi2Te3 capped with alkylamines have been synthesized via facile solution based method. The method involves reduction of selenium or tellurium using sodium borohydride, followed by thermolysis in an alkylamine at high temperature. Spherical shaped Bi2Se3 nanocrystals were obtained at 190 °C, whereas the reaction at 270 °C, yielded faceted nanocrystals. Similarly, spherical Bi2Te3 nanocrystals were obtained at all temperatures with hexadecylamine and oleylamine capping agents.

  15. Supersaturation-dependent surface structure evolution: from ionic, molecular to metallic micro/nanocrystals.

    PubMed

    Lin, Hai-xin; Lei, Zhi-chao; Jiang, Zhi-yuan; Hou, Chang-ping; Liu, De-yu; Xu, Min-min; Tian, Zhong-qun; Xie, Zhao-xiong

    2013-06-26

    Deduced from thermodynamics and the Thomson-Gibbs equation that the surface energy of crystal face is in proportion to the supersaturation of crystal growth units during the crystal growth, we propose that the exposed crystal faces can be simply tuned by controlling the supersaturation, and higher supersaturation will result in the formation of crystallites with higher surface-energy faces. We have successfully applied it for the growth of ionic (NaCl), molecular (TBPe), and metallic (Au, Pd) micro/nanocrystals with high-surface-energy faces. The above proposed strategy can be rationally designed to synthesize micro/nanocrystals with specific crystal faces and functionality toward specific applications.

  16. Radial Dopant Placement for Tuning Plasmonic Properties in Metal Oxide Nanocrystals.

    PubMed

    Crockett, Brandon M; Jansons, Adam W; Koskela, Kristopher M; Johnson, Darren W; Hutchison, James E

    2017-08-22

    Doped metal oxide nanocrystals that exhibit tunable localized surface plasmon resonances (LSPRs) represent an intriguing class of nanomaterials that show promise for a variety of applications from spectroscopy to sensing. LSPRs arise in these materials through the introduction of aliovalent dopants and lattice oxygen vacancies. Tuning the LSPR shape and energy is generally accomplished through controlling the concentration or identity of dopants in a nanocrystal, but the lack of finer synthetic control leaves several fundamental questions unanswered regarding the effects of radial dopant placement, size, and nanocrystalline architecture on the LSPR energy and damping. Here, we present a layer-by-layer synthetic method for core/shell nanocrystals that permits exquisite and independent control over radial dopant placement, absolute dopant concentration, and nanocrystal size. Using Sn-doped In2O3 (ITO) as a model LSPR system, we synthesized ITO/In2O3 core/shell as well as In2O3/ITO core/shell nanocrystals with varying shell thickness, and investigated the resulting optical properties. We observed profound influence of radial dopant placement on the energy and linewidth of the LSPR response, noting (among other findings) that core-localized dopants produce the highest values for LSPR energies per dopant concentration, and display the lowest damping in comparison to nanocrystals with shell-localized or homogeneously distributed dopants. Inactive Sn dopants present on ITO nanocrystal surfaces are activated upon the addition of a subnanometer thick undoped In2O3 shell. We show how LSPR energy can be tuned fully independent of dopant concentration, relying solely on core/shell architecture. Finally, the impacts of radial dopant placement on damping, independent of LSPR energy, are explored.

  17. Slip-activated surface creep with room-temperature super-elongation in metallic nanocrystals

    NASA Astrophysics Data System (ADS)

    Zhong, Li; Sansoz, Frederic; He, Yang; Wang, Chongmin; Zhang, Ze; Mao, Scott X.

    2017-04-01

    Nanoscale metallic crystals have been shown to follow a `smaller is stronger’ trend. However, they usually suffer from low ductility due to premature plastic instability by source-limited crystal slip. Here, by performing in situ atomic-scale transmission electron microscopy, we report unusual room-temperature super-elongation without softening in face-centred-cubic silver nanocrystals, where crystal slip serves as a stimulus to surface diffusional creep. This interplay mechanism is shown experimentally and theoretically to govern the plastic deformation of nanocrystals over a material-dependent sample diameter range between the lower and upper limits for nanocrystal stability by surface diffusional creep and dislocation plasticity, respectively, which extends far beyond the maximum size for pure diffusion-mediated deformation (for example, Coble-type creep). This work provides insight into the atomic-scale coupled diffusive-displacive deformation mechanisms, maximizing ductility and strength simultaneously in nanoscale materials.

  18. Synthesis and characterization of metal chalcogenide semiconductor nanocrystals using dialkyl dichalcogenide precursors

    NASA Astrophysics Data System (ADS)

    Norako, Michelle E.

    Metastable semiconductor nanocrystals have been shown to possess new and interesting properties that are highly reliant upon their synthetic reaction parameters. A versatile method for a relatively low temperature synthesis of metastable metal chalcogenide nanocrystals using dialkyl dichalcogenides as the chalcogen source has been developed. These precursors decompose in solution to promote the growth of kinetically controlled nanoscale products. Monodisperse metastable copper indium sulfide (CuInS2) nanocrystal were synthesized using di­tert­butyl disulfide as the sulfur source at 180 °C. In a similar fashion, metastable wurtzite copper indium selenide (CuInSe2) and metastable wurtzite copper tin selenide (CTSe) were synthesized and characterized for the first time. This method was further expanded to synthesize Cu2GeSe 3, Cu2SnS3, Ni0.95Se, CuSbS2, and PbS also using dialkyl dichalcogenide precursors. To further study these products, the nanocrystal growth mechanism was explored for the dichalcogenide­mediated synthesis of wz­CuInS2 and the potential applicability of the wurtzite CTSe nanocrystals as a photovoltaic material was assessed.

  19. Lead Halide Perovskites and Other Metal Halide Complexes As Inorganic Capping Ligands for Colloidal Nanocrystals

    PubMed Central

    2014-01-01

    Lead halide perovskites (CH3NH3PbX3, where X = I, Br) and other metal halide complexes (MXn, where M = Pb, Cd, In, Zn, Fe, Bi, Sb) have been studied as inorganic capping ligands for colloidal nanocrystals. We present the methodology for the surface functionalization via ligand-exchange reactions and the effect on the optical properties of IV–VI, II–VI, and III–V semiconductor nanocrystals. In particular, we show that the Lewis acid–base properties of the solvents, in addition to the solvent dielectric constant, must be properly adjusted for successful ligand exchange and colloidal stability. High luminescence quantum efficiencies of 20–30% for near-infrared emitting CH3NH3PbI3-functionalized PbS nanocrystals and 50–65% for red-emitting CH3NH3CdBr3- and (NH4)2ZnCl4-capped CdSe/CdS nanocrystals point to highly efficient electronic passivation of the nanocrystal surface. PMID:24746226

  20. The colloidal chemistry synthesis and electron microscopy characterization of shape-controlled metal and semiconductor nanocrystals

    NASA Astrophysics Data System (ADS)

    Biacchi, Adam J.

    Solution methods of materials synthesis have found application in a variety of fields due to the diversity of products accessible, facility of process scalability, and the ease of tuning their properties through prudent selection of reaction conditions. Control of experimental variables during the formation of colloidally stable nanoscale solids within a liquid matrix allows for tailoring of the particles' characteristics, including shape, size, composition, and surface chemistry. In this dissertation, I will discuss how the manipulation of reaction chemistries can be used to synthesize shape-controlled metal and semiconductor colloidal nanocrystals. Further, I will elaborate on the mechanisms by which these particles form from molecular precursors and describe how their properties can differ from their bulk analogues through extensive characterization, especially using transmission electron microscopy. These studies contribute to the continued development of chemical routes to nanocrystals and their application as functional materials. First, I will review recent advances in the synthesis and characterization of shape-controlled nanocrystals, as well as highlight their promising applicability in a number of emerging technologies. These principles will then be leveraged to the specific case of catalytically-active rhodium nanocrystals, which can be synthesized with morphological and dimensional control using a polyol solution-mediated strategy. I describe an innovative shape-controlled synthesis to monodisperse colloidal rhodium icosahedra, cubes, triangular plates, and octahedra using this route. Additionally, new insights into the important role of the polyol reducing solvent on the synthesis of these nanocrystals are revealed, and how these might be exploited to engender superior reaction control and novel products. Next, I will describe how a crystallization mechanism was established for the synthesis of numerous morphologies of noble metal nanocrystals. I

  1. Quasi-epitaxial Metal-Halide Perovskite Ligand Shells on PbS Nanocrystals.

    PubMed

    Sytnyk, Mykhailo; Yakunin, Sergii; Schöfberger, Wolfgang; Lechner, Rainer T; Burian, Max; Ludescher, Lukas; Killilea, Niall A; YousefiAmin, AmirAbbas; Kriegner, Dominik; Stangl, Julian; Groiss, Heiko; Heiss, Wolfgang

    2017-02-28

    Epitaxial growth techniques enable nearly defect free heterostructures with coherent interfaces, which are of utmost importance for high performance electronic devices. While high-vacuum technology-based growth techniques are state-of-the art, here we pursue a purely solution processed approach to obtain nanocrystals with eptaxially coherent and quasi-lattice matched inorganic ligand shells. Octahedral metal-halide clusters, respectively 0-dimensional perovskites, were employed as ligands to match the coordination geometry of the PbS cubic rock-salt lattice. Different clusters (CH3NH3(+))(6-x)[M((x+))Hal6]((6-x)-) (M(x+) = Pb(II), Bi(III), Mn(II), In(III), Hal = Cl, I) were attached to the nanocrystal surfaces via a scalable phase transfer procedure. The ligand attachment and coherence of the formed PbS/ligand core/shell interface was confirmed by combining the results from transmission electron microscopy, small-angle X-ray scattering, nuclear magnetic resonance spectroscopy and powder X-ray diffraction. The lattice mismatch between ligand shell and nanocrystal core plays a key role in performance. In photoconducting devices the best performance (detectivity of 2 × 10(11) cm Hz (1/2)/W with > 110 kHz bandwidth) was obtained with (CH3NH3)3BiI6 ligands, providing the smallest relative lattice mismatch of ca. -1%. PbS nanocrystals with such ligands exhibited in millimeter sized bulk samples in the form of pressed pellets a relatively high carrier mobility for nanocrystal solids of ∼1.3 cm(2)/(V s), a carrier lifetime of ∼70 μs, and a low residual carrier concentration of 2.6 × 10(13) cm(-3). Thus, by selection of ligands with appropriate geometry and bond lengths optimized quasi-epitaxial ligand shells were formed on nanocrystals, which are beneficial for applications in optoelectronics.

  2. Process for making surfactant capped metal oxide nanocrystals, and products produced by the process

    DOEpatents

    Alivisatos, A. Paul; Rockenberger, Joerg

    2006-01-10

    Disclosed is a process for making surfactant capped nanocrystals of metal oxides which are dispersable in organic solvents. The process comprises decomposing a metal cupferron complex of the formula MXCupX, wherein M is a metal, and Cup is a N-substituted N-Nitroso hydroxylamine, in the presence of a coordinating surfactant, the reaction being conducted at a temperature ranging from about 150 to about 400.degree. C., for a period of time sufficient to complete the reaction. Also disclosed are compounds made by the process.

  3. Ground-state energies of simple metals

    NASA Technical Reports Server (NTRS)

    Hammerberg, J.; Ashcroft, N. W.

    1974-01-01

    A structural expansion for the static ground-state energy of a simple metal is derived. Two methods are presented, one an approach based on single-particle band structure which treats the electron gas as a nonlinear dielectric, the other a more general many-particle analysis using finite-temperature perturbation theory. The two methods are compared, and it is shown in detail how band-structure effects, Fermi-surface distortions, and chemical-potential shifts affect the total energy. These are of special interest in corrections to the total energy beyond third order in the electron-ion interaction and hence to systems where differences in energies for various crystal structures are exceptionally small. Preliminary calculations using these methods for the zero-temperature thermodynamic functions of atomic hydrogen are reported.

  4. Highly directional emission and photon beaming from nanocrystal quantum dots embedded in metallic nanoslit arrays.

    PubMed

    Livneh, Nitzan; Strauss, Ayelet; Schwarz, Ilai; Rosenberg, Itamar; Zimran, Adiel; Yochelis, Shira; Chen, Gang; Banin, Uri; Paltiel, Yossi; Rapaport, Ronen

    2011-04-13

    We demonstrate a directional beaming of photons emitted from nanocrystal quantum dots that are embedded in a subwavelength metallic nanoslit array with a divergence angle of less than 4°. We show that the eigenmodes of the structure result in localized electromagnetic field enhancements at the Bragg cavity resonances, which could be controlled and engineered in both real and momentum space. The photon beaming is achieved using the enhanced resonant coupling of the quantum dots to these Bragg cavity modes, which dominates the emission properties of the quantum dots. We show that the emission probability of a quantum dot into the narrow angular mode is 20 times larger than the emission probability to all other modes. Engineering nanocrystal quantum dots with subwavelength metallic nanostructures is a promising way for a range of new types of active optical devices, where spatial control of the optical properties of nanoemitters is essential, on both the single and many photons level.

  5. Exploiting differential electrochemical stripping behaviors of Fe3O4 nanocrystals toward heavy metal ions by crystal cutting.

    PubMed

    Yao, Xian-Zhi; Guo, Zheng; Yuan, Qing-Hong; Liu, Zhong-Gang; Liu, Jin-Huai; Huang, Xing-Jiu

    2014-08-13

    This study attempts to understand the intrinsic impact of different morphologies of nanocrystals on their electrochemical stripping behaviors toward heavy metal ions. Two differently shaped Fe3O4 nanocrystals, i.e., (100)-bound cubic and (111)-bound octahedral, have been synthesized for the experiments. Electrochemical results indicate that Fe3O4 nanocrystals with different shapes show different stripping behaviors toward heavy metal ions. Octahedral Fe3O4 nanocrystals show better electrochemical sensing performances toward the investigated heavy metal ions such as Zn(II), Cd(II), Pb(II), Cu(II), and Hg(II), in comparison with cubic ones. Specifically, Pb(II) is found to have the best stripping performance on both the (100) and (111) facets. To clarify these phenomena, adsorption abilities of as-prepared Fe3O4 nanocrystals have been investigated toward heavy metal ions. Most importantly, combined with theoretical calculations, their different electrochemical stripping behaviors in view of facet effects have been further studied and enclosed at the level of molecular/atom. Finally, as a trial to find a disposable platform completely free from noble metals, the potential application of the Fe3O4 nanocrystals for electrochemical detection of As(III) in drinking water is demonstrated.

  6. Planar Heterojunction Perovskite Solar Cells Incorporating Metal-Organic Framework Nanocrystals.

    PubMed

    Chang, Ting-Hsiang; Kung, Chung-Wei; Chen, Hsin-Wei; Huang, Tzu-Yen; Kao, Sheng-Yuan; Lu, Hsin-Che; Lee, Min-Han; Boopathi, Karunakara Moorthy; Chu, Chih-Wei; Ho, Kuo-Chuan

    2015-11-25

    Zr-based porphyrin metal-organic framework (MOF-525) nanocrystals with a crystal size of about 140 nm are synthesized and incorporated into perovskite solar cells. The morphology and crystallinity of the perovskite thin film are enhanced since the micropores of MOF-525 allow the crystallization of perovskite to occur inside; this observation results in a higher cell efficiency of the obtained MOF/perovskite solar cell.

  7. Light-Induced In Situ Transformation of Metal Clusters to Metal Nanocrystals for Photocatalysis.

    PubMed

    Xiao, Fang-Xing; Zeng, Zhiping; Hsu, Shao-Hui; Hung, Sung-Fu; Chen, Hao Ming; Liu, Bin

    2015-12-30

    In situ transformation of glutathione-capped gold (Aux) clusters to gold (Au) nanocrystals under simulated solar light irradiation was achieved and utilized as a facile synthetic approach to rationally fabricate Aux/Au/TiO2 ternary and Au/TiO2 binary heterostructures. Synergistic interaction of Aux clusters and Au nanocrystals contributes to enhanced visible-light-driven photocatalysis.

  8. Novel and Simple Solution-processed MIS Ultraviolet (UV) Detector Based on Core-Shell Si/SiO2 Nanocrystals

    NASA Astrophysics Data System (ADS)

    SayyedFattahi, S. J.; Rostami, A.; Pouladian, M.; Dolatyari, M.; Rashidi, M.; Rostami, G.

    2014-04-01

    In the present study, we report a simple and solution-processed visible blind metal-insulator-semiconductor (MIS) ultraviolet (UV) detector based on core-shell Si/SiO2 nanocrystals that are fabricated on interdigitated electrodes. The fabricated photo detector shows high photosensitivity in the UV-B and UV-C wavelength ranges. The absorption spectra of the nano-structured materials used in this work is simulated by the density functional theory (DFT) method and analyzed based on the electronic structure. It is then compared with the experimental results. The synthesized nano materials show very low density of structural defects based on the measured photoluminescence spectra, which results in a fast response time for the fabricated photodetector. Compared to the previously reported similar Si/SiO2-based photo-detectors, the fabricated detector shows very good photo responsivity.

  9. Methodology for robust superhydrophobic fabrics and sponges from in situ growth of transition metal/metal oxide nanocrystals with thiol modification and their applications in oil/water separation.

    PubMed

    Wang, Ben; Li, Jing; Wang, Guiyuan; Liang, Weixin; Zhang, Yabin; Shi, Lei; Guo, Zhiguang; Liu, Weimin

    2013-03-13

    Solid surfaces possessing both superhydrophobic and superoleophilic properties have attracted significant interest in fundamental investigations and potential applications in the fields of self-cleaning surfaces, oil/water separation, and microfluidic channels. In this paper, a general methodology for robust superhydrophobic fabrics and sponges was proposed via the in situ growth of both transition-metal oxides and metallic nanocrystals, including the simple neutralization reaction and oxidation-reduction reaction. The porous surfaces coated with Group VIII and IB nanocrystals (such as Fe, Co, Ni, Cu, and Ag) can not only present multiscale surface roughness, but also readily coordinate with thiols, leading to special wettability. In our previous work, it has been confirmed that the interaction between the nanocrystals and thiols plays a significant role in the introduction of hydrophobic ingredients. In this work, it has been demonstrated that the efficient control of the nucleation and growth of Group VIII and IB nanocrystals on the porous surfaces becomes the key factor in the formation of multiscale surface roughness, resulting in the achievement of controllable special wettability. In addition, these as-prepared superhydrophobic and superoleophilic fabrics and sponges were successfully used for application in oil/water separation.

  10. Rare-earth-doped bifunctional alkaline-earth metal fluoride nanocrystals via a facile microwave-assisted process.

    PubMed

    Pang, Min; Liu, Dapeng; Lei, Yongqian; Song, Shuyan; Feng, Jing; Fan, Weiqiang; Zhang, Hongjie

    2011-06-20

    Rare-earth-doped magnetic-optic bifunctional alkaline-earth metal fluoride nanocrystals have been successfully synthesized via a facile microwave-assisted process. The as-prepared nanocrystals were monodisperse and could form stable colloidal solutions in polar solvents, such as water and ethanol. They show bright-green fluorescence emisson. Furthermore, Gd(3+)-doped ones exhibit paramagnetic behavior at room temperature and superparamagnetic behavior at 2 K.

  11. The effectiveness of metal oxide nanocrystal-enhanced polymers as hardmasks for photolithography

    NASA Astrophysics Data System (ADS)

    Hockey, Mary Ann; Lin, Qin; Calderas, Eric

    2012-09-01

    Utilizing thin photoresist imaging layers for successful pattern transfer has gained acceptance as a lithography process of record, primarily due to the incorporation of silicon-containing hardmask (HM) layers for added etching resistance. Our work includes understanding the impact of incorporating metal oxide (HfO2, ZrO2, ZnO, and TiZrO2) nanocrystal additives supplied by Pixelligent Technologies into polymer-based spin-on HM coatings. The goal was to quantify etch selectivity and analyze lithography process latitudes with the addition of nanocrystals into polymers. Results indicate such additions provide substantial process window advantages with improvements in the depth of focus (DOF) and overall pattern collapse margins.

  12. Design of a multi-coordinating polymer as a platform for functionalizing metal, metal oxide and semiconductor nanocrystals

    NASA Astrophysics Data System (ADS)

    Wang, Wentao; Ji, Xin; Kapur, Anshika; Mattoussi, Hedi

    2016-03-01

    We introduce a new set of amphiphilic polymers as multifunctional, metal-coordinating ligands adapted to surfacefunctionalize quantum dots (QDs), iron oxide nanoparticles (IONPs) and gold nanoparticles/nanorods (AuNPs/AuNRs). The ligand design relies on the introduction of several anchoring groups, hydrophilic moieties and reactive functionalities into a polymer chain, via one-step nucleophilic addition reaction. Such synthetic scheme also allows the insertion of target biomolecules during the ligand synthesis. This functionalization strategy yields nanocrystals that exhibit long-term colloidal stability over a broad range of biological conditions, such as pH changes and when mixed with growth media. When zwitterion groups are used as hydrophilic motifs, this provides compact nanocrystals that are compatible with conjugation to proteins via metal-polyhistidine self-assembly. In addition, we show that QDs ligated with these polymers can engage in energy or charge transfer interactions. Furthermore, nanocrystals coated with folic acid-modified polymers could promote the delivery of nanoparticle-conjugates into cancer cells via folate receptormediated endocytosis.

  13. Electrocatalysis using transition metal carbide and oxide nanocrystals

    NASA Astrophysics Data System (ADS)

    Regmi, Yagya N.

    Carbides are one of the several families of transition metal compounds that are considered economic alternatives to catalysts based on noble metals and their compounds. Phase pure transition metal carbides of group 4-6 metals, in the first three periods, were synthesized using a common eutectic salt flux synthesis method, and their electrocatalytic activities compared under uniform electrochemical conditions. Mo2C showed highest hydrogen evolution reaction (HER) and oxygen reduction reaction (ORR) activities among the nine metal carbides investigated, but all other metal carbides also showed substantial activities. All the metal carbides showed remarkable enhancement in catalytic activities as supports, when compared to traditional graphitic carbon as platinum support. Mo2C, the most active transition metal carbide electrocatalyst, was prepared using four different synthesis routes, and the synthesis route dependent activities compared. Bifunctional Mo 2C that is HER as well as oxygen evolution reaction (OER) active, was achieved when the carbide was templated on a multiwalled carbon nanotube using carbothermic reduction method. Bimetallic carbides of Fe, Co, and Ni with Mo or W were prepared using a common carbothermic reduction method. Two different stoichiometries of bimetallic carbides were obtained for each system within a 60 °C temperature window. While the bimetallic carbides showed relatively lower electrocatalytic activities towards HER and ORR in comparison to Mo2C and WC, they revealed remarkably higher OER activities than IrO2 and RuO2, the state-of-the-art OER catalysts. Bimetallic oxides of Fe, Co, and Ni with Mo and W were also prepared using a hydrothermal synthesis method and they also revealed OER activities that are much higher than RuO2 and IrO2. Additionally, the OER activities were dependent on the degree and nature of hydration in the bimetallic oxide crystal lattice, with the completely hydrated, as synthesized, cobalt molybdate and nickel

  14. In situ capping for size control of monochalcogenides (ZnS, CdS, and SnS) nanocrystals produced by anaerobic metal-reducing bacteria

    SciTech Connect

    Jang, Gyoung Gug; Jacobs, Christopher B.; Ivanov, Ilia N.; Joshi, Pooran C.; Meyer, III, Harry M.; Kidder, Michelle; Armstrong, Beth L.; Datskos, Panos G.; Graham, David E.; Moon, Ji -Won

    2015-07-24

    Metal monochalcogenide quantum dot nanocrystals of ZnS, CdS and SnS were prepared by anaerobic, metal-reducing bacteria using in situ capping by oleic acid or oleylamine. Furthermore, the capping agent preferentially adsorbs on the surface of the nanocrystal, suppressing the growth process in the early stages, thus leading to production of nanocrystals with a diameter of less than 5 nm.

  15. In situ capping for size control of monochalcogenides (ZnS, CdS, and SnS) nanocrystals produced by anaerobic metal-reducing bacteria

    DOE PAGES

    Jang, Gyoung Gug; Jacobs, Christopher B.; Ivanov, Ilia N.; ...

    2015-07-24

    Metal monochalcogenide quantum dot nanocrystals of ZnS, CdS and SnS were prepared by anaerobic, metal-reducing bacteria using in situ capping by oleic acid or oleylamine. Furthermore, the capping agent preferentially adsorbs on the surface of the nanocrystal, suppressing the growth process in the early stages, thus leading to production of nanocrystals with a diameter of less than 5 nm.

  16. Colloidal metal oxide nanocrystals as charge transporting layers for solution-processed light-emitting diodes and solar cells.

    PubMed

    Liang, Xiaoyong; Bai, Sai; Wang, Xin; Dai, Xingliang; Gao, Feng; Sun, Baoquan; Ning, Zhijun; Ye, Zhizhen; Jin, Yizheng

    2017-02-28

    Colloidal metal oxide nanocrystals offer a unique combination of excellent low-temperature solution processability, rich and tuneable optoelectronic properties and intrinsic stability, which makes them an ideal class of materials as charge transporting layers in solution-processed light-emitting diodes and solar cells. Developing new material chemistry and custom-tailoring processing and properties of charge transporting layers based on oxide nanocrystals hold the key to boosting the efficiency and lifetime of all-solution-processed light-emitting diodes and solar cells, and thereby realizing an unprecedented generation of high-performance, low-cost, large-area and flexible optoelectronic devices. This review aims to bridge two research fields, chemistry of colloidal oxide nanocrystals and interfacial engineering of optoelectronic devices, focusing on the relationship between chemistry of colloidal oxide nanocrystals, processing and properties of charge transporting layers and device performance. Synthetic chemistry of colloidal oxide nanocrystals, ligand chemistry that may be applied to colloidal oxide nanocrystals and chemistry associated with post-deposition treatments are discussed to highlight the ability of optimizing processing and optoelectronic properties of charge transporting layers. Selected examples of solution-processed solar cells and light-emitting diodes with oxide-nanocrystal charge transporting layers are examined. The emphasis is placed on the correlation between the properties of oxide-nanocrystal charge transporting layers and device performance. Finally, three major challenges that need to be addressed in the future are outlined. We anticipate that this review will spur new material design and simulate new chemistry for colloidal oxide nanocrystals, leading to charge transporting layers and solution-processed optoelectronic devices beyond the state-of-the-art.

  17. Integration of colloidal silicon nanocrystals on metal electrodes in single-electron transistor

    NASA Astrophysics Data System (ADS)

    Higashikawa, Yasuhiro; Azuma, Yasuo; Majima, Yutaka; Kano, Shinya; Fujii, Minoru

    2016-11-01

    We develop a facile process to integrate colloidal silicon nanocrystals (Si NCs) with metal electrodes in a single-electron transistor by self-assembly. Gold (Au) surface is modified by an amine-terminated self-assembled monolayer to have a positive potential. All-inorganic boron (B) and phosphorus (P) codoped Si NCs, with a negative surface potential and size-controllability, are selectively adsorbed on an amine-terminated Au surface by electrostatic attraction. We demonstrate the fabrication of SETs consisting of electroless-plated Au nanogap electrodes and codoped Si NCs using this process and observation of clear Coulomb diamonds at 9 K.

  18. High performance pseudocapacitor based on 2D layered metal chalcogenide nanocrystals.

    PubMed

    Muller, Guillaume A; Cook, John B; Kim, Hyung-Seok; Tolbert, Sarah H; Dunn, Bruce

    2015-03-11

    Single-layer and few-layer transition metal dichalcogenides have been extensively studied for their electronic properties, but their energy-storage potential has not been well explored. This paper describes the structural and electrochemical properties of few-layer TiS2 nanocrystals. The two-dimensional morphology leads to very different behavior, compared to corresponding bulk materials. Only small structural changes occur during lithiation/delithiation and charge storage characteristics are consistent with intercalation pseudocapacitance, leading to materials that exhibit both high energy and power density.

  19. Beyond metallo-carbohedrenes. Growth and decomposition of metal-carbon nanocrystals

    SciTech Connect

    Pilgrim, J.S.; Duncan, M.A. )

    1993-10-20

    The recently discovered family of metal-carbon clusters, designated metallo-carbohedrenes or [open quotes]met-cars[close quotes] by Castleman and co-workers, are reinvestigated with a focus on titanium and vanadium systems. In addition to the stable M[sub 8]C[sub 12][sup +] clusters reported previously, a family of larger metal-carbon systems are observed. Mass spectroscopy and mass-selected laser photodissociation measurements are used to investigate the structures and stabilities of these systems, which contain up to 60 atoms in the cluster framework. The larger metal-carbon species exhibit 1/1 M/C stoichiometries characteristics of cubic lattice structures and are therefore designated as [open quotes]nanocrystals[close quotes]. The species Ti[sub 14]C[sub 13][sup +] and V[sub 14]C[sub 13][sup +], which are proposed to have the 3 X 3 X 3 cubic structure, are especially abundant and are believed to have stabilities comparable to those of the M[sub 8]C[sub 12] species. Photodissociation of larger nanocrystals produces both the 8/12 and 14/13 stoichiometries as abundant photofragments. Evidence is also presented for the formation of endohedral met-car clusters containing a central carbon atom, which are formed as photodissociation products from larger systems. 37 refs., 5 figs., 1 tab.

  20. A Simple MO Treatment of Metal Clusters.

    ERIC Educational Resources Information Center

    Sahyun, M. R. V.

    1980-01-01

    Illustrates how a qualitative description of the geometry and electronic characteristics of homogeneous metal clusters can be obtained using semiempirical MO (molecular orbital theory) methods. Computer applications of MO methods to inorganic systems are also described. (CS)

  1. Resonant Coupling between Molecular Vibrations and Localized Surface Plasmon Resonance of Faceted Metal Oxide Nanocrystals.

    PubMed

    Agrawal, Ankit; Singh, Ajay; Yazdi, Sadegh; Singh, Amita; Ong, Gary K; Bustillo, Karen; Johns, Robert W; Ringe, Emilie; Milliron, Delia J

    2017-04-12

    Doped metal oxides are plasmonic materials that boast both synthetic and postsynthetic spectral tunability. They have already enabled promising smart window and optoelectronic technologies and have been proposed for use in surface enhanced infrared absorption spectroscopy (SEIRA) and sensing applications. Herein, we report the first step toward realization of the former utilizing cubic F and Sn codoped In2O3 nanocrystals (NCs) to couple to the C-H vibration of surface-bound oleate ligands. Electron energy loss spectroscopy is used to map the strong near-field enhancement around these NCs that enables localized surface plasmon resonance (LSPR) coupling between adjacent nanocrystals and LSPR-molecular vibration coupling. Fourier transform infrared spectroscopy measurements and finite element simulations are applied to observe and explain the nature of the coupling phenomena, specifically addressing coupling in mesoscale assembled films. The Fano line shape signatures of LSPR-coupled molecular vibrations are rationalized with two-port temporal coupled mode theory. With this combined theoretical and experimental approach, we describe the influence of coupling strength and relative detuning between the molecular vibration and LSPR on the enhancement factor and further explain the basis of the observed Fano line shape by deconvoluting the combined response of the LSPR and molecular vibration in transmission, absorption and reflection. This study therefore illustrates various factors involved in determining the LSPR-LSPR and LSPR-molecular vibration coupling for metal oxide materials and provides a fundamental basis for the design of sensing or SEIRA substrates.

  2. Seeded growth of metal-doped plasmonic oxide heterodimer nanocrystals and their chemical transformation.

    PubMed

    Ye, Xingchen; Reifsnyder Hickey, Danielle; Fei, Jiayang; Diroll, Benjamin T; Paik, Taejong; Chen, Jun; Murray, Christopher B

    2014-04-02

    We have developed a generalized seeded-growth methodology for the synthesis of monodisperse metal-doped plasmonic oxide heterodimer nanocrystals (NCs) with a near-unity morphological yield. Using indium-doped cadmium oxide (ICO) as an example, we show that a wide variety of preformed metal NCs (Au, Pt, Pd, FePt, etc.) can serve as the seeds for the tailored synthesis of metal-ICO heterodimers with exquisite size, shape, and composition control, facilitated by the delayed nucleation mechanism of the CdO phase. The metal-ICO heterodimers exhibit broadly tunable near-infrared localized surface plasmon resonances, and dual plasmonic bands are observed for Au-ICO heterodimers. We further demonstrate that the oxide domain of the Au-ICO heterodimers can be selectively and controllably transformed into a series of partially and completely hollow cadmium chalcogenide nanoarchitectures with unprecedented structural complexity, leaving the metal domain intact. Our work not only represents an exciting addition to the rapidly expanding library of chemical reactions that produce colloidal hybrid NCs, but it also provides a general route for the bottom-up chemical design of multicomponent metal-oxide-semiconductor NCs in a rational and sequential manner.

  3. A simple method to obtain Fe-doped CeO2 nanocrystals at room temperature

    NASA Astrophysics Data System (ADS)

    Almeida, J. M. A.; Santos, P. E. C.; Cardoso, L. P.; Meneses, C. T.

    2013-02-01

    Ce1-xFexO2 nanocrystals (0

  4. Pattern-based sensing with simple metal-dye complexes.

    PubMed

    Severin, Kay

    2010-12-01

    Different strategies for the creation of optical sensors with metal-dye complexes are discussed. The focus is on sensors, which are used in conjunction with pattern recognition protocols. It is shown that remarkably powerful sensors can be obtained by combining commercially available dyes with simple transition metal complexes. Copyright © 2010 Elsevier Ltd. All rights reserved.

  5. Simple transition metal oxides (Conference Presentation)

    NASA Astrophysics Data System (ADS)

    Schuller, Ivan K.; Basaran, Ali C.; de la Venta, Jose; Ramirez, Juan Gabriel; Saerbeck, Thomas; Valmianski, Ilya; Wang, Siming

    2016-10-01

    Hybrid materials allow the engineering of new material properties by creative uses of proximity effects. When two dissimilar materials are in close physical proximity the properties of each one may be radically modified or occasionally a completely new material emerges. In the area of magnetism, controlling the magnetic properties of ferromagnetic thin films without magnetic fields is an on- going challenge with multiple technological implications for low- energy consumption memory and logic devices. Interesting possibilities include ferromagnets in proximity to dissimilar materials such as antiferromagnets or oxides that undergo metal-insulator transitions. The proximity of ferromagnets to antiferromagnets has given rise to the extensively studied Exchange Bias[1]. Our recent investigations in this field have addressed crucial issues regarding the importance of the antiferromagnetic [2-3] and ferromagnetic [4] bulk for the Exchange Bias and the unusual short time dynamics [5]. In a series of recent studies, we have investigated the magnetic properties of different hybrids of ferromagnets (Ni, Co and Fe) and oxides, which undergo metal-insulator and structural phase transitions. Both the static as well as dynamical properties of the ferromagnets are drastically affected. Static properties such as the coercivity, anisotropy and magnetization [6-8] and dynamical properties such as the microwave response are clearly modified by the proximity effect and give raise to interesting perhaps useful properties. Work supported by US-AFOSR and US-DOE

  6. Thermally induced growth of ZnO nanocrystals on mixed metal oxide surfaces.

    PubMed

    Inayat, Alexandra; Makky, Ayman; Giraldo, Jose; Kuhnt, Andreas; Busse, Corinna; Schwieger, Wilhelm

    2014-06-23

    An in situ method for the growth of ZnO nanocrystals on Zn/Al mixed metal oxide (MMO) surfaces is presented. The key to this method is the thermal treatment of Zn/Al layered double hydroxides (Zn/Al LDHs) in the presence of nitrate anions, which results in partial demixing of the LDH/MMO structure and the subsequent crystallization of ZnO crystals on the surface of the forming MMO layers. In a first experimental series, thermal treatment of Zn/Al LDHs with different fractions of nitrate and carbonate in the interlayer space was examined by thermogravimetry coupled with mass spectrometry (TG-MS) and in situ XRD. In a second experimental series, Zn/Al LDHs with only carbonate in the interlayer space were thermally treated in the presence of different amounts of an external nitrate source (NH4NO3). All obtained Zn/Al MMO samples were analysed by electron microscopy, nitrogen physisorption and powder X-ray diffraction. The gas phase formed during nitrate decomposition turned out to be responsible for the formation of crystalline ZnO nanoparticles. Accordingly, both interlayer nitrate and the presence of ammonium nitrate led to the formation of supported ZnO nanocrystals with mean diameters between 100 and 400 nm, and both methods offer the possibility to tailor the amount and size of the ZnO crystals by means of the amount of nitrate.

  7. Metal-organic framework ZIF-8 nanocrystals as pseudostationary phase for capillary electrokinetic chromatography.

    PubMed

    Li, Li-Man; Wang, He-Fang; Yan, Xiu-Ping

    2012-09-01

    The outstanding properties such as large surface area, diverse structure, and accessible tunnels and cages make metal organic frameworks (MOFs) attractive as novel separation media in separation sciences. However, the utilization of MOFs in EKC has not been reported before. Here we show the exploration of zeolitic imidazolate framework-8 (ZIF-8), one of famous MOFs, as the pseudostationary phase (PSP) in EKC. ZIF-8 nanocrystals were used as the PSP through dispersing in the running buffer (20 mM phosphate solution containing a 1% v/v methanol (pH 9.2)) to enhance the separation of the phenolic isomers (p-benzenediol, m-benzenediol, o-benzenediol, m-nitrophenol, p-nitrophenol, and o-nitrophenol). ZIF-8 nanocrystals in the running buffer were negatively charged, and interacted with the phenolic hydroxyl groups of the analytes, and thus greatly improved the separation of the phenolic isomers. Inclusion of 200 mg L-(1) ZIF-8 in the running buffer as the background electrolyte gave a baseline separation of the phenolic isomers within 4 min. The relative standard deviations for five replicate separations of the phenolic isomers were 0.2-1.1% for migration time and 4.5-9.7% for peak area. The limits of detection varied from 0.44 to 2.0 mg L-(1) . The results show that nanosized MOFs are promising for application in EKC.

  8. From Metal Thiobenzoates to Metal Sulfide Nanocrystals: An Experimental and Theoretical Investigation

    PubMed Central

    Zhang, Zhihua; Lim, Wen Pei; Wong, Chiong Teck; Xu, Hairuo; Yin, Fenfang; Chin, Wee Shong

    2012-01-01

    A simple preparation of metal sulfide nanoparticles via the decomposition of thiobenzoate precursors at room temperature is presented and discussed. Long chain alkylamines were found to mediate the breakdown of metal thiobenzoates, such as those containing Ag, Cu, In and Cd, to produce uniform Ag2S, Cu2−xS, In2S3 and CdS nanoparticles respectively. The long chain amines are assumed to play dual roles as the nucleophilic reagent and the capping agent. It was found that sizes of the nanoparticles can be controlled by changing the type of amine used, as well as the molar ratio between amine and the precursor. We performed DFT calculations on a proposed mechanism involving an initial nucleophilic addition of amine molecule onto the thiocarboxylates. The proposed reaction was also confirmed through the analysis of by-products via infrared spectroscopy. On the basis of this understanding, we propose to manipulate the stability of the precursors by coordination with suitable stabilizing groups, such that the reaction kinetics can be modified to generate different nanostructures of interest.

  9. Slip-activated surface creep with room-temperature super-elongation in metallic nanocrystals.

    PubMed

    Zhong, Li; Sansoz, Frederic; He, Yang; Wang, Chongmin; Zhang, Ze; Mao, Scott X

    2017-04-01

    Nanoscale metallic crystals have been shown to follow a 'smaller is stronger' trend. However, they usually suffer from low ductility due to premature plastic instability by source-limited crystal slip. Here, by performing in situ atomic-scale transmission electron microscopy, we report unusual room-temperature super-elongation without softening in face-centred-cubic silver nanocrystals, where crystal slip serves as a stimulus to surface diffusional creep. This interplay mechanism is shown experimentally and theoretically to govern the plastic deformation of nanocrystals over a material-dependent sample diameter range between the lower and upper limits for nanocrystal stability by surface diffusional creep and dislocation plasticity, respectively, which extends far beyond the maximum size for pure diffusion-mediated deformation (for example, Coble-type creep). This work provides insight into the atomic-scale coupled diffusive-displacive deformation mechanisms, maximizing ductility and strength simultaneously in nanoscale materials.

  10. Enhanced ethylene separation and plasticization resistance in polymer membranes incorporating metal-organic framework nanocrystals

    NASA Astrophysics Data System (ADS)

    Bachman, Jonathan E.; Smith, Zachary P.; Li, Tao; Xu, Ting; Long, Jeffrey R.

    2016-08-01

    The implementation of membrane-based separations in the petrochemical industry has the potential to reduce energy consumption significantly relative to conventional separation processes. Achieving this goal, however, requires the development of new membrane materials with greater selectivity, permeability and stability than available at present. Here, we report composite materials consisting of nanocrystals of metal-organic frameworks dispersed within a high-performance polyimide, which can exhibit enhanced selectivity for ethylene over ethane, greater ethylene permeability and improved membrane stability. Our results suggest that framework-polymer interactions reduce chain mobility of the polymer while simultaneously boosting membrane separation performance. The increased stability, or plasticization resistance, is expected to improve membrane utility under real process conditions for petrochemical separations and natural gas purification. Furthermore, this approach can be broadly applied to numerous polymers that encounter aggressive environments, potentially making gas separations possible that were previously inaccessible to membranes.

  11. Enhanced ethylene separation and plasticization resistance in polymer membranes incorporating metal-organic framework nanocrystals.

    PubMed

    Bachman, Jonathan E; Smith, Zachary P; Li, Tao; Xu, Ting; Long, Jeffrey R

    2016-08-01

    The implementation of membrane-based separations in the petrochemical industry has the potential to reduce energy consumption significantly relative to conventional separation processes. Achieving this goal, however, requires the development of new membrane materials with greater selectivity, permeability and stability than available at present. Here, we report composite materials consisting of nanocrystals of metal-organic frameworks dispersed within a high-performance polyimide, which can exhibit enhanced selectivity for ethylene over ethane, greater ethylene permeability and improved membrane stability. Our results suggest that framework-polymer interactions reduce chain mobility of the polymer while simultaneously boosting membrane separation performance. The increased stability, or plasticization resistance, is expected to improve membrane utility under real process conditions for petrochemical separations and natural gas purification. Furthermore, this approach can be broadly applied to numerous polymers that encounter aggressive environments, potentially making gas separations possible that were previously inaccessible to membranes.

  12. Shock wave compression and metallization of simple molecules

    SciTech Connect

    Ross, M.; Radousky, H.B.

    1988-03-01

    In this paper we combine shock wave studies and metallization of simple molecules in a single overview. The unifying features are provided by the high shock temperatures which lead to a metallic-like state in the rare gases and to dissociation of diatomic molecules. In the case of the rare gases, electronic excitation into the conduction band leads to a metallic-like inert gas state at lower than metallic densities and provides information regarding the closing of the band gap. Diatomic dissociation caused by thermal excitation also leads to a final metallic-like or monatomic state. Ina ddition, shock wave data can provide information concerning the short range intermolecular force of the insulator that can be useful for calculating the metallic phase transition as for example in the case of hydrogen. 69 refs., 36 figs., 2 tabs.

  13. Mesoscopic constructs of ordered and oriented metal-organic frameworks on plasmonic silver nanocrystals.

    PubMed

    Zhao, Yingbo; Kornienko, Nikolay; Liu, Zheng; Zhu, Chenhui; Asahina, Shunsuke; Kuo, Tsung-Rong; Bao, Wei; Xie, Chenlu; Hexemer, Alexander; Terasaki, Osamu; Yang, Peidong; Yaghi, Omar M

    2015-02-18

    We enclose octahedral silver nanocrystals (Ag NCs) in metal-organic frameworks (MOFs) to make mesoscopic constructs O(h)-nano-Ag⊂MOF in which the interface between the Ag and the MOF is pristine and the MOF is ordered (crystalline) and oriented on the Ag NCs. This is achieved by atomic layer deposition of aluminum oxide on Ag NCs and addition of a tetra-topic porphyrin-based linker, 4,4',4″,4‴-(porphyrin-5,10,15,20-tetrayl)tetrabenzoic acid (H4TCPP), to react with alumina and make MOF [Al2(OH)2TCPP] enclosures around Ag NCs. Alumina thickness is precisely controlled from 0.1 to 3 nm, thus allowing control of the MOF thickness from 10 to 50 nm. Electron microscopy and grazing angle X-ray diffraction confirm the order and orientation of the MOF by virtue of the porphyrin units being perpendicular to the planes of the Ag. We use surface-enhanced Raman spectroscopy to directly track the metalation process on the porphyrin and map the distribution of the metalated and unmetalated linkers on a single-nanoparticle level.

  14. Structural, Optical and Electrical Properties of PbSe Nanocrystal Solids Treated Thermally or with Simple Amines

    SciTech Connect

    Law, M.; Luther, J. M.; Song, Q.; Hughes, B. K.; Perkins, C. L.; Nozik, A. J.

    2008-01-01

    We describe the structural, optical, and electrical properties of films of spin-cast, oleate-capped PbSe nanocrystals that are treated thermally or chemically in solutions of hydrazine, methylamine, or pyridine to produce electronically coupled nanocrystal solids. Postdeposition heat treatments trigger nanocrystal sintering at {approx}200 C, before a substantial fraction of the oleate capping group evaporates or pyrolyzes. The sintered nanocrystal films have a large hole density and are highly conductive. Most of the amine treatments preserve the size of the nanocrystals and remove much of the oleate, decreasing the separation between nanocrystals and yielding conductive films. X-ray scattering, X-ray photoelectron and optical spectroscopy, electron microscopy, and field-effect transistor electrical measurements are used to compare the impact of these chemical treatments. We find that the concentration of amines adsorbed to the NC films is very low in all cases. Treatments in hydrazine in acetonitrile remove only 2-7% of the oleate yet result in high-mobility n-type transistors. In contrast, ethanol-based hydrazine treatments remove 85-90% of the original oleate load. Treatments in pure ethanol strip 20% of the oleate and create conductive p-type transistors. Methylamine- and pyridine-treated films are also p-type. These chemically treated films oxidize rapidly in air to yield, after short air exposures, highly conductive p-type nanocrystal solids. Our results aid in the rational development of solar cells based on colloidal nanocrystal films.

  15. Controllable synthesis of metal selenide heterostructures mediated by Ag2Se nanocrystals acting as catalysts.

    PubMed

    Zhou, Jiangcong; Huang, Feng; Xu, Ju; Wang, Yuansheng

    2013-10-21

    Ag2Se nanocrystals were demonstrated to be novel semiconductor mediators, or in other word catalysts, for the growth of semiconductor heterostructures in solution. This is a result of the unique feature of Ag2Se as a fast ion conductor, allowing foreign cations to dissolve and then to heterogrow the second phase. Using Ag2Se nanocrystals as catalysts, dimeric metal selenide heterostructures such as Ag2Se-CdSe and Ag2Se-ZnSe, and even multi-segment heterostructures such as Ag2Se-CdSe-ZnSe and Ag2Se-ZnSe-CdSe, were successfully synthesized. Several interesting features were found in the Ag2Se based heterogrowth. At the initial stage of heterogrowth, a layer of the second phase forms on the surface of an Ag2Se nanosphere, with a curved junction interface between the two phases. With further growth of the second phase, the Ag2Se nanosphere tends to flatten the junction surface by modifying its shape from sphere to hemisphere in order to minimize the conjunct area and thus the interfacial energy. Notably, the crystallographic relationship of the two phases in the heterostructure varies with the lattice parameters of the second phase, in order to reduce the lattice mismatch at the interface. Furthermore, a small lattice mismatch at the interface results in a straight rod-like second phase, while a large lattice mismatch would induce a tortuous product. The reported results may provide a new route for developing novel selenide semiconductor heterostructures which are potentially applicable in optoelectronic, biomedical, photovoltaic and catalytic fields.

  16. Fabrication of hollow metal oxide nanocrystals by etching cuprous oxide with metal(ii) ions: approach to the essential driving force

    NASA Astrophysics Data System (ADS)

    Sohn, Jong Hwa; Cha, Hyun Gil; Kim, Chang Woo; Kim, Do Kyoung; Kang, Young Soo

    2013-10-01

    Hollow metal oxide nanocrystals were prepared by etching cuprous oxide with metal ions and were applied as photoelectrodes. As a hard template, polyvinylpyrrolidone stabilized cuprous oxide (PVP-Cu2O) and non-stabilized cuprous oxide (nPVP-Cu2O) were synthesized by a precipitation method. Hollow iron oxide and cobalt oxide nanocrystals with a truncated octahedral morphology were fabricated by an etching reaction with transition metal(ii) ions (Fe2+ or Co2+). In the etching reaction process, a cationic exchange reaction occurs between the divalent metal ion and Cu+ due to the higher Lewis acidity. Facet selective etching of cuprous oxide has been observed during the ionic exchange reaction of Cu+ and O2- ions in PVP-Cu2O complexes with transition metal(ii) ions (Fe2+ or Co2+) at the surface of a (110) facet. Amorphous states of hollow metal oxide products were annealed to form α-Fe2O3 (hematite) and Co3O4 and their crystal structure was examined with X-ray diffraction and HR-TEM. The optical absorption behavior of semiconductor nanocrystals was measured with UV-vis spectroscopy to define band gap energy. The hollow hematite structure has a 2.08 eV band gap and Co3O4 (Co(ii,iii) oxide) has a 1.80 eV indirect band gap. Using these hollow nanocrystals, a metal oxide monolayer film was fabricated with a secondary growth approach and was studied for its photocatalytic properties.Hollow metal oxide nanocrystals were prepared by etching cuprous oxide with metal ions and were applied as photoelectrodes. As a hard template, polyvinylpyrrolidone stabilized cuprous oxide (PVP-Cu2O) and non-stabilized cuprous oxide (nPVP-Cu2O) were synthesized by a precipitation method. Hollow iron oxide and cobalt oxide nanocrystals with a truncated octahedral morphology were fabricated by an etching reaction with transition metal(ii) ions (Fe2+ or Co2+). In the etching reaction process, a cationic exchange reaction occurs between the divalent metal ion and Cu+ due to the higher Lewis acidity

  17. X-Ray Absorption Studies of Vanadium-Containing Metal Oxide Nanocrystals

    SciTech Connect

    Hohn, Keith, L.

    2006-01-09

    Metal oxide nanocrystals offer significant potential for use as catalysts or catalyst supports due to their high surface areas and unique chemical properties that result from the high number of exposed corners and edges. However, little is known about the catalytic activity of these materials, especially as oxidation catalysts. This research focused on the preparation, characterization and use of vanadium-containing nanocrystals as selective oxidation catalysts. Three vanadium-containing nanocrystals were prepared using a modified sol-gel procedure: V/MgO, V/SiO2, and vanadium phosphate (VPO). These represent active oxidation catalysts for a number of industrially relevant reactions. The catalysts were characterized by x-ray diffraction and Raman, UV-VIS, infrared and x-ray absorption spectroscopies with the goal of determining the primary structural and chemical differences between nanocrystals and microcrystals. The catalytic activity of these catalysts was also studied in oxidative dehydrogenation of butane and methanol oxidation to formaldehyde. V/MgO nanocrystals were investigated for activity in oxidative dehydrogenation of butane and compared to conventional V/MgO catalysts. Characterization of V/MgO catalysts using Raman spectroscopy and x-ray absorption spectroscopy showed that both types of catalysts contained magnesium orthovanadate at vanadium loadings below 15 weight%, but above that loading, magnesium pyrovanadate may have been present. In general, MgO nanocrystals had roughly half the crystal size and double the surface area of the conventional MgO. In oxidative dehydrogenation of butane, nanocrystalline V/MgO gave higher selectivity to butene than conventional V/MgO at the same conversion. This difference was attributed to differences in vanadium domain size resulting from the higher surface areas of the nanocrystalline support, since characterization suggested that similar vanadium phases were present on both types of catalysts. Experiments in

  18. Nanoscale Transformations in Covellite (CuS) Nanocrystals in the Presence of Divalent Metal Cations in a Mild Reducing Environment

    PubMed Central

    2015-01-01

    We studied the structural and compositional transformations of colloidal covellite (CuS) nanocrystals (and of djurleite (Cu1.94S) nanocrystals as a control) when exposed to divalent cations, as Cd2+ and Hg2+, at room temperature in organic solvents. All the experiments were run in the absence of phosphines, which are a necessary ingredient for cation exchange reactions involving copper chalcogenides, as they strongly bind to the expelled Cu+ ions. Under these experimental conditions, no remarkable reactivity was indeed seen for both CuS and Cu1.94S nanocrystals. On the other hand, in the covellite structure 2/3 of sulfur atoms form covalent S–S bonds. This peculiarity suggests that the combined presence of electron donors and of foreign metal cations can trigger the entry of both electrons and cations in the covellite lattice, causing reorganization of the anion framework due to the rupture of the S–S bonds. In Cu1.94S, which lacks S–S bonds, this mechanism should not be accessible. This hypothesis was proven by the experimental evidence that adding ascorbic acid increased the fraction of metal ions incorporated in the covellite nanocrystals, while it had no noticeable effect on the Cu1.94S ones. Once inside the covellite particles, Cd2+ and Hg2+ cations engaged in exchange reactions, pushing the expelled Cu+ ions toward the not-yet exchanged regions in the same particles, or out to the solution, from where they could be recaptured by other covellite nanoparticles/domains. Because no good solvating agent for Cu ions was present in solution, they essentially remained in the nanocrystals. PMID:26617434

  19. CADDIS Volume 2. Sources, Stressors and Responses: Metals - Simple Conceptual Model Diagram

    EPA Pesticide Factsheets

    Introduction to the metals module, when to list metals as a candidate cause, ways to measure metals, simple and detailed conceptual diagrams for metals, metals module references and literature reviews.

  20. On the role of surface diffusion in determining the shape or morphology of noble-metal nanocrystals

    PubMed Central

    Xia, Xiaohu; Xie, Shuifen; Liu, Maochang; Peng, Hsin-Chieh; Lu, Ning; Wang, Jinguo; Kim, Moon J.; Xia, Younan

    2013-01-01

    Controlling the shape or morphology of metal nanocrystals is central to the realization of their many applications in catalysis, plasmonics, and electronics. In one of the approaches, the metal nanocrystals are grown from seeds of certain crystallinity through the addition of atomic species. In this case, manipulating the rates at which the atomic species are added onto different crystallographic planes of a seed has been actively explored to control the growth pattern of a seed and thereby the shape or morphology taken by the final product. Upon deposition, however, the adsorbed atoms (adatoms) may not stay at the same sites where the depositions occur. Instead, they can migrate to other sites on the seed owing to the involvement of surface diffusion, and this could lead to unexpected deviations from a desired growth pathway. Herein, we demonstrated that the growth pathway of a seed is indeed determined by the ratio between the rates for atom deposition and surface diffusion. Our result suggests that surface diffusion needs to be taken into account when controlling the shape or morphology of metal nanocrystals. PMID:23569268

  1. Metal oxide nanostructures by a simple hot water treatment.

    PubMed

    Saadi, Nawzat S; Hassan, Laylan B; Karabacak, Tansel

    2017-08-02

    Surfaces with metal oxide nanostructures have gained considerable interest in applications such as sensors, detectors, energy harvesting cells, and batteries. However, conventional fabrication techniques suffer from challenges that hinder wide and effective applications of such surfaces. Most of the metal oxide nanostructure synthesis methods are costly, complicated, non-scalable, environmentally hazardous, or applicable to only certain few materials. Therefore, it is crucial to develop a simple metal oxide nanostructure fabrication method that can overcome all these limitations and pave the way to the industrial application of such surfaces. Here, we demonstrate that a wide variety of metals can form metal oxide nanostructures on their surfaces after simply interacting with hot water. This method, what we call hot water treatment, offers the ability to grow metal oxide nanostructures on most of the metals in the periodic table, their compounds, or alloys by a one-step, scalable, low-cost, and eco-friendly process. In addition, our findings reveal that a "plugging" mechanism along with surface diffusion is critical in the formation of such nanostructures. This work is believed to be of importance especially for researchers working on the growth of metal oxide nanostructures and their application in functional devices.

  2. Simple Preparation of Novel Metal-Containing Mesoporous Starches †

    PubMed Central

    Ojeda, Manuel; Budarin, Vitaliy; Shuttleworth, Peter S.; Clark, James H.; Pineda, Antonio; Balu, Alina M.; Romero, Antonio A.; Luque, Rafael

    2013-01-01

    Metal-containing mesoporous starches have been synthesized using a simple and efficient microwave-assisted methodology followed by metal impregnation in the porous gel network. Final materials exhibited surface areas >60 m2 g−1, being essentially mesoporous with pore sizes in the 10–15 nm range with some developed inter-particular mesoporosity. These materials characterized by several techniques including XRD, SEM, TG/DTA and DRIFTs may find promising catalytic applications due to the presence of (hydr)oxides in their composition. PMID:28809249

  3. Simple Preparation of Novel Metal-Containing Mesoporous Starches.

    PubMed

    Ojeda, Manuel; Budarin, Vitaliy; Shuttleworth, Peter S; Clark, James H; Pineda, Antonio; Balu, Alina M; Romero, Antonio A; Luque, Rafael

    2013-05-10

    Metal-containing mesoporous starches have been synthesized using a simple and efficient microwave-assisted methodology followed by metal impregnation in the porous gel network. Final materials exhibited surface areas >60 m² g(-1), being essentially mesoporous with pore sizes in the 10-15 nm range with some developed inter-particular mesoporosity. These materials characterized by several techniques including XRD, SEM, TG/DTA and DRIFTs may find promising catalytic applications due to the presence of (hydr)oxides in their composition.

  4. Metallic-like bonding in plasma-born silicon nanocrystals for nanoscale bandgap engineering.

    PubMed

    Vach, Holger; Ivanova, Lena V; Timerghazin, Qadir K; Jardali, Fatme; Le, Ha-Linh Thi

    2016-10-27

    Based on ab initio molecular dynamics simulations, we show that small nanoclusters of about 1 nm size spontaneously generated in a low-temperature silane plasma do not possess tetrahedral structures, but are ultrastable. Apparently small differences in the cluster structure result in substantial modifications in their electric, magnetic, and optical properties, without the need for any dopants. Their non-tetrahedral geometries notably lead to electron deficient bonds that introduce efficient electron delocalization that strongly resembles the one of a homogeneous electron gas leading to metallic-like bonding within a semiconductor nanocrystal. As a result, pure hydrogenated silicon clusters that form by self-assembly in a plasma reactor possess optical gaps covering most of the solar spectrum from 1.0 eV to 5.2 eV depending simply on their structure and, in turn, on their degree of electron delocalization. This feature makes them ideal candidates for future bandgap engineering not only for photovoltaics, but also for many nano-electronic devices employing nothing else but silicon and hydrogen atoms.

  5. Graphene oxide/metal nanocrystal multilaminates as the atomic limit for safe and selective hydrogen storage

    PubMed Central

    Cho, Eun Seon; Ruminski, Anne M.; Aloni, Shaul; Liu, Yi-Sheng; Guo, Jinghua; Urban, Jeffrey J.

    2016-01-01

    Interest in hydrogen fuel is growing for automotive applications; however, safe, dense, solid-state hydrogen storage remains a formidable scientific challenge. Metal hydrides offer ample storage capacity and do not require cryogens or exceedingly high pressures for operation. However, hydrides have largely been abandoned because of oxidative instability and sluggish kinetics. We report a new, environmentally stable hydrogen storage material constructed of Mg nanocrystals encapsulated by atomically thin and gas-selective reduced graphene oxide (rGO) sheets. This material, protected from oxygen and moisture by the rGO layers, exhibits exceptionally dense hydrogen storage (6.5 wt% and 0.105 kg H2 per litre in the total composite). As rGO is atomically thin, this approach minimizes inactive mass in the composite, while also providing a kinetic enhancement to hydrogen sorption performance. These multilaminates of rGO-Mg are able to deliver exceptionally dense hydrogen storage and provide a material platform for harnessing the attributes of sensitive nanomaterials in demanding environments. PMID:26902901

  6. Graphene oxide/metal nanocrystal multilaminates as the atomic limit for safe and selective hydrogen storage

    NASA Astrophysics Data System (ADS)

    Cho, Eun Seon; Ruminski, Anne M.; Aloni, Shaul; Liu, Yi-Sheng; Guo, Jinghua; Urban, Jeffrey J.

    2016-02-01

    Interest in hydrogen fuel is growing for automotive applications; however, safe, dense, solid-state hydrogen storage remains a formidable scientific challenge. Metal hydrides offer ample storage capacity and do not require cryogens or exceedingly high pressures for operation. However, hydrides have largely been abandoned because of oxidative instability and sluggish kinetics. We report a new, environmentally stable hydrogen storage material constructed of Mg nanocrystals encapsulated by atomically thin and gas-selective reduced graphene oxide (rGO) sheets. This material, protected from oxygen and moisture by the rGO layers, exhibits exceptionally dense hydrogen storage (6.5 wt% and 0.105 kg H2 per litre in the total composite). As rGO is atomically thin, this approach minimizes inactive mass in the composite, while also providing a kinetic enhancement to hydrogen sorption performance. These multilaminates of rGO-Mg are able to deliver exceptionally dense hydrogen storage and provide a material platform for harnessing the attributes of sensitive nanomaterials in demanding environments.

  7. Adsorption of heavy metal ions from aqueous solution by carboxylated cellulose nanocrystals.

    PubMed

    Yu, Xiaolin; Tong, Shengrui; Ge, Maofa; Wu, Lingyan; Zuo, Junchao; Cao, Changyan; Song, Weiguo

    2013-05-01

    A novel nanoadsorbent for the removal of heavy metal ions is reported. Cotton was first hydrolyzed to obtain cellulose nanocrystals (CNCs). CNCs were then chemically modified with succinic anhydride to obtain SCNCs. The sodic nanoadsorbent (NaSCNCs) was further prepared by treatment of SCNCs with saturated NaHCO3 aqueous solution. Batch experiments were carried out with SCNCs and NaSCNCs for the removal of Pb2+ and Cd2+. The effects of contact time, pH, initial adsorption concentration, coexisting ions and the regeneration performance were investigated. Kinetic studies showed that the adsorption equilibrium time of Pb2+ and Cd2+ was reached within 150 min on SCNCs and 5 min on NaSCNCs. The adsorption capacities of Pb2+ and Cd2+ on SCNCs and NaSCNCs increased with increasing pH. The adsorption isotherm was well fitted by the Langmuir model. The maximum adsorption capacities of SCNCs and NaSCNCs for Pb2+ and Cd2+ were 367.6 mg/g, 259.7 mg/g and 465.1 mg/g, 344.8 mg/g, respectively. SCNCs and NaSCNCs showed high selectivity and interference resistance from coexisting ions for the adsorption of Pb2+. NaSCNCs could be efficiently regenerated with a mild saturated NaCl solution with no loss of capacity after two recycles. The adsorption mechanisms of SCNCs and NaSCNCs were discussed.

  8. Immobilization of Metal-Organic Framework Nanocrystals for Advanced Design of Supported Nanocatalysts.

    PubMed

    Li, Ping; Zeng, Hua Chun

    2016-11-02

    In recent years, metal-organic frameworks (MOFs) have been employed as heterogeneous catalysts or precursors for synthesis of catalytic materials. However, conventional MOFs and their derivatives usually exhibit limited mass transfer and modest catalytic activities owing to a lengthy diffusion path and less exposed active sites. In contrast, it has been generally conceived that nanoscale MOFs are beneficial to materials utilization and mass transport, but their instability poses a serious issue to practical application. To tackle above challenges, herein we develop a novel and facile approach to the design and synthesis of nanocomposites through in situ growth and directed immobilization of nanoscale MOFs onto layered double hydroxides (LDH). The resulting supported nano-MOFs inherit advantages of pristine MOF nanocrystals and meanwhile gain enhanced stability and workability under reactive environments. A series of uniform nanometer-sized MOFs, including monometallic (ZIF-8, ZIF-67, and Cu-BTC) and bimetallic (CoZn-ZIF), can be readily synthesized onto hierarchically structured flowerlike MgAl-LDH supports with high dispersion and precision. Additionally, the resultant MgAl-LDH/MOFs can serve as a generic platform to prepare integrated nanocatalysts via controlled thermolysis. Knoevenagel condensation and reduction of 4-nitrophenol (4-NP) are used as model reactions for demonstrating the technological merits of these nanocatalysts. Therefore, this work elucidates that the synthetic immobilization of nanoscale MOFs onto conventional catalyst supports is a viable route to develop integrated nanocatalysts with high controllability over structural architecture and chemical composition.

  9. Graphene oxide/metal nanocrystal multilaminates as the atomic limit for safe and selective hydrogen storage

    DOE PAGES

    Cho, Eun Seon; Ruminski, Anne M.; Aloni, Shaul; ...

    2016-02-23

    Interest in hydrogen fuel is growing for automotive applications; however, safe, dense, solid-state hydrogen storage remains a formidable scientific challenge. Metal hydrides offer ample storage capacity and do not require cryogens or exceedingly high pressures for operation. However, hydrides have largely been abandoned because of oxidative instability and sluggish kinetics. We report a new, environmentally stable hydrogen storage material constructed of Mg nanocrystals encapsulated by atomically thin and gas-selective reduced graphene oxide (rGO) sheets. This material, protected from oxygen and moisture by the rGO layers, exhibits exceptionally dense hydrogen storage (6.5 wt% and 0.105 kg H2 per litre in themore » total composite). As rGO is atomically thin, this approach minimizes inactive mass in the composite, while also providing a kinetic enhancement to hydrogen sorption performance. In conclusion, these multilaminates of rGO-Mg are able to deliver exceptionally dense hydrogen storage and provide a material platform for harnessing the attributes of sensitive nanomaterials in demanding environments.« less

  10. Surface passivation of lead sulfide nanocrystals with low electron affinity metals: photoluminescence and photovoltaic performance.

    PubMed

    Tavakoli, Mohammad Mahdi; Mirfasih, Mohammad Hassan; Hasanzadeh, Soheil; Aashuri, Hossein; Simchi, Abdolreza

    2016-04-28

    During the last decade, solution-processed colloidal quantum dots (CQDs) have attracted significant attention for low-cost fabrication of optoelectronic devices. In this study, lead sulfide (PbS) CQDs were synthesized via the hot injection method and the effect of doping elements with low electron affinity, including cadmium, calcium and zinc, on the passivation of trap states was investigated. A red-shift in the luminescence emission was observed by doping through passivation of lead dangling bonds. Time-resolved photoluminescence measurements showed that the lifetime of charged carriers was significantly enhanced by cadmium doping (∼80%) which is quite noticeable compared with calcium- and zinc-doped nanocrystals. External quantum efficiency measurements on thin solid films (∼300 nm) prepared by spin coating supported improved lifetime of carriers through passivation of mid-gap trap states. In order to show the potential application of the doping process, bulk heterojunction CQD solar cells were fabricated. It was found that the power conversion efficiency (PCE) was improved up to ∼40%; the highest improvement was observed with the Cd treatment. Finally, density functional theory (DFT) and electrochemical impedance spectroscopy (EIS) were employed to study the effect of doping on the density of states. The results showed that doping with low electron affinity metals effectively reduced the deep trap states of PbS QDs.

  11. Graphene oxide/metal nanocrystal multilaminates as the atomic limit for safe and selective hydrogen storage.

    PubMed

    Cho, Eun Seon; Ruminski, Anne M; Aloni, Shaul; Liu, Yi-Sheng; Guo, Jinghua; Urban, Jeffrey J

    2016-02-23

    Interest in hydrogen fuel is growing for automotive applications; however, safe, dense, solid-state hydrogen storage remains a formidable scientific challenge. Metal hydrides offer ample storage capacity and do not require cryogens or exceedingly high pressures for operation. However, hydrides have largely been abandoned because of oxidative instability and sluggish kinetics. We report a new, environmentally stable hydrogen storage material constructed of Mg nanocrystals encapsulated by atomically thin and gas-selective reduced graphene oxide (rGO) sheets. This material, protected from oxygen and moisture by the rGO layers, exhibits exceptionally dense hydrogen storage (6.5 wt% and 0.105 kg H2 per litre in the total composite). As rGO is atomically thin, this approach minimizes inactive mass in the composite, while also providing a kinetic enhancement to hydrogen sorption performance. These multilaminates of rGO-Mg are able to deliver exceptionally dense hydrogen storage and provide a material platform for harnessing the attributes of sensitive nanomaterials in demanding environments.

  12. Graphene oxide/metal nanocrystal multilaminates as the atomic limit for safe and selective hydrogen storage

    SciTech Connect

    Cho, Eun Seon; Ruminski, Anne M.; Aloni, Shaul; Liu, Yi-Sheng; Guo, Jinghua; Urban, Jeffrey J.

    2016-02-23

    Interest in hydrogen fuel is growing for automotive applications; however, safe, dense, solid-state hydrogen storage remains a formidable scientific challenge. Metal hydrides offer ample storage capacity and do not require cryogens or exceedingly high pressures for operation. However, hydrides have largely been abandoned because of oxidative instability and sluggish kinetics. We report a new, environmentally stable hydrogen storage material constructed of Mg nanocrystals encapsulated by atomically thin and gas-selective reduced graphene oxide (rGO) sheets. This material, protected from oxygen and moisture by the rGO layers, exhibits exceptionally dense hydrogen storage (6.5 wt% and 0.105 kg H2 per litre in the total composite). As rGO is atomically thin, this approach minimizes inactive mass in the composite, while also providing a kinetic enhancement to hydrogen sorption performance. In conclusion, these multilaminates of rGO-Mg are able to deliver exceptionally dense hydrogen storage and provide a material platform for harnessing the attributes of sensitive nanomaterials in demanding environments.

  13. III-V nanocrystals capped with molecular metal chalcogenide ligands: high electron mobility and ambipolar photoresponse.

    PubMed

    Liu, Wenyong; Lee, Jong-Soo; Talapin, Dmitri V

    2013-01-30

    In this work, we synthesized InP and InAs nanocrystals (NCs) capped with different inorganic ligands, including various molecular metal chalcogenide complexes (MCCs) and chalcogenide ions. We found that MCCs and chalcogenide ions can quantitatively displace organic ligands from the surface of III-V NCs and serve as the inorganic capping groups for III-V NC surfaces. These inorganic ligands stabilize colloidal solutions of InP and InAs NCs in polar solvents and greatly facilitate charge transport between individual NCs. Charge transport studies revealed high electron mobility in the films of MCC-capped InP and InAs NCs. For example, we found that bridging InAs NCs with Cu(7)S(4)(-) MCC ligands can lead to very high electron mobility exceeding 15 cm(2)/(V s). In addition, we observed unprecedented ambipolar (positive/negative) photoresponse of MCC-capped InAs NC solids that changed sign depending on the ligand chemistry, illumination wavelength, and doping of the NC solid. For example, the sign of photoconductance of InAs NCs capped with Cu(7)S(4)(-) or Sn(2)S(6)(4-) ions converted from positive at 0.80 and 0.95 eV to negative at 1.27 and 1.91 eV. We propose an explanation of this unusually complex photoconductivity of InAs NC solids.

  14. First-order metal-insulator transition and infrared identification of shape-controlled magnetite nanocrystals

    NASA Astrophysics Data System (ADS)

    Zheng, Lei; Su, Wei; Qi, Zeming; Xu, Yang; Zhou, Min; Xie, Yi

    2011-12-01

    The first-order metal-insulator transition (MIT) in magnetite has been known for a long time but is still controversial in its nature. In this study, well-defined magnetite nanocrystals (NCs) with controllable size, shape and terminated surface are first employed to elucidate this important issue, and new discoveries such as a highly suppressed phase transition temperature are identified by monitoring the variable-temperature electric resistance and infrared spectroscopy. Significantly, by carefully comparing the infrared vibrational bands of the as-prepared magnetite NCs with octahedral and cubic shapes, respectively, we found that these two forms of magnetite NCs exhibited different transmittance changes and frequency shifts of the infrared characteristics, presumably due to the differences in the lattice distortions on the corresponding {001} and {111} terminal surfaces. This result produced evidence in support of the charge ordering of Fe atoms along the low dimensionality at octahedral B sites undergoing the MIT. Taken together, infrared identification was proposed to be an available characterization strategy for MIT, which can reflect more information on the elusive lattice distortion of crystallographic structure or exposed surfaces.

  15. Preparation of glibenclamide nanocrystals by a simple laboratory scale ultra cryo-milling

    NASA Astrophysics Data System (ADS)

    Martena, Valentina; Censi, Roberta; Hoti, Ela; Malaj, Ledjan; Di Martino, Piera

    2013-06-01

    The objective of this study is to evaluate the ability to reduce the particle size of glibenclamide (GBC) to the nanometric scale through a very simple and well-known laboratory scale method, the laboratory scale ultra cryo-milling. The effect of milling on GBC crystalline properties and dissolution behaviour was deliberately evaluated in the absence of any surfactants as stabilizers. The milling procedure consisted in adding particles to liquid nitrogen and milling them by hand in a mortar with a pestle for different time intervals (15, 30, 40 min). For comparison, the same milling procedure was also applied without liquid nitrogen. The particle size reduction was evaluated for the coarsest samples (>3 μm) by measuring the particle Ferret's diameter through scanning electron microscopy, while for the smallest one (<3 μm) by dynamic light scattering. A time grinding of 40 min in the presence of liquid nitrogen was revealed highly efficacious to obtain particles of nanodimensions, with a geometric mean particle size of 0.55 ± 0.23 μm and more than the 80 % of particles lower than 1,000 nm. Interestingly, non-agglomerated particles were obtained. Differential scanning calorimetry and X-ray powder diffractometry allowed to assess that under mechanical treatment no polymorphic transitions were observed, while a decrease in crystallinity degree occurred depending on the milling procedure (presence or absence of liquid nitrogen) and the milling time (crystallinity decreases at increasing milling time from 15 to 40 min). A comparison of the intrinsic dissolution rate and the dissolution from particles revealed an interesting improvement of particle dissolution particularly for particles milled in the presence of liquid nitrogen due to an increase in particle surface area and concentration gradient, according to the Noyes-Whitney equation.

  16. In Situ Preparation of Metal Halide Perovskite Nanocrystal Thin Films for Improved Light-Emitting Devices.

    PubMed

    Zhao, Lianfeng; Yeh, Yao-Wen; Tran, Nhu L; Wu, Fan; Xiao, Zhengguo; Kerner, Ross A; Lin, YunHui L; Scholes, Gregory D; Yao, Nan; Rand, Barry P

    2017-04-25

    Hybrid organic-inorganic halide perovskite semiconductors are attractive candidates for optoelectronic applications, such as photovoltaics, light-emitting diodes, and lasers. Perovskite nanocrystals are of particular interest, where electrons and holes can be confined spatially, promoting radiative recombination. However, nanocrystalline films based on traditional colloidal nanocrystal synthesis strategies suffer from the use of long insulating ligands, low colloidal nanocrystal concentration, and significant aggregation during film formation. Here, we demonstrate a facile method for preparing perovskite nanocrystal films in situ and that the electroluminescence of light-emitting devices can be enhanced up to 40-fold through this nanocrystal film formation strategy. Briefly, the method involves the use of bulky organoammonium halides as additives to confine crystal growth of perovskites during film formation, achieving CH3NH3PbI3 and CH3NH3PbBr3 perovskite nanocrystals with an average crystal size of 5.4 ± 0.8 nm and 6.4 ± 1.3 nm, respectively, as confirmed through transmission electron microscopy measurements. Additive-confined perovskite nanocrystals show significantly improved photoluminescence quantum yield and decay lifetime. Finally, we demonstrate highly efficient CH3NH3PbI3 red/near-infrared LEDs and CH3NH3PbBr3 green LEDs based on this strategy, achieving an external quantum efficiency of 7.9% and 7.0%, respectively, which represent a 40-fold and 23-fold improvement over control devices fabricated without the additives.

  17. Tuning the magnetic properties of metal oxide nanocrystal heterostructures by cation exchange.

    PubMed

    Sytnyk, Mykhailo; Kirchschlager, Raimund; Bodnarchuk, Maryna I; Primetzhofer, Daniel; Kriegner, Dominik; Enser, Herbert; Stangl, Julian; Bauer, Peter; Voith, Michael; Hassel, Achim Walter; Krumeich, Frank; Ludwig, Frank; Meingast, Arno; Kothleitner, Gerald; Kovalenko, Maksym V; Heiss, Wolfgang

    2013-02-13

    For three types of colloidal magnetic nanocrystals, we demonstrate that postsynthetic cation exchange enables tuning of the nanocrystal's magnetic properties and achieving characteristics not obtainable by conventional synthetic routes. While the cation exchange procedure, performed in solution phase approach, was restricted so far to chalcogenide based semiconductor nanocrystals, here ferrite-based nanocrystals were subjected to a Fe(2+) to Co(2+) cation exchange procedure. This allows tracing of the compositional modifications by systematic and detailed magnetic characterization. In homogeneous magnetite nanocrystals and in gold/magnetite core shell nanocrystals the cation exchange increases the coercivity field, the remanence magnetization, as well as the superparamagnetic blocking temperature. For core/shell nanoheterostructures a selective doping of either the shell or predominantly of the core with Co(2+) is demonstrated. By applying the cation exchange to FeO/CoFe(2)O(4) core/shell nanocrystals the Neél temperature of the core material is increased and exchange-bias effects are enhanced so that vertical shifts of the hysteresis loops are obtained which are superior to those in any other system.

  18. Highly Efficient Light-Emitting Diodes of Colloidal Metal-Halide Perovskite Nanocrystals beyond Quantum Size.

    PubMed

    Kim, Young-Hoon; Wolf, Christoph; Kim, Young-Tae; Cho, Himchan; Kwon, Woosung; Do, Sungan; Sadhanala, Aditya; Park, Chan Gyung; Rhee, Shi-Woo; Im, Sang Hyuk; Friend, Richard H; Lee, Tae-Woo

    2017-07-25

    Colloidal metal-halide perovskite quantum dots (QDs) with a dimension less than the exciton Bohr diameter DB (quantum size regime) emerged as promising light emitters due to their spectrally narrow light, facile color tuning, and high photoluminescence quantum efficiency (PLQE). However, their size-sensitive emission wavelength and color purity and low electroluminescence efficiency are still challenging aspects. Here, we demonstrate highly efficient light-emitting diodes (LEDs) based on the colloidal perovskite nanocrystals (NCs) in a dimension > DB (regime beyond quantum size) by using a multifunctional buffer hole injection layer (Buf-HIL). The perovskite NCs with a dimension greater than DB show a size-irrespective high color purity and PLQE by managing the recombination of excitons occurring at surface traps and inside the NCs. The Buf-HIL composed of poly(3,4-ethylenedioxythiophene)/poly(styrenesulfonate) (PEDOT:PSS) and perfluorinated ionomer induces uniform perovskite particle films with complete film coverage and prevents exciton quenching at the PEDOT:PSS/perovskite particle film interface. With these strategies, we achieved a very high PLQE (∼60.5%) in compact perovskite particle films without any complex post-treatments and multilayers and a high current efficiency of 15.5 cd/A in the LEDs of colloidal perovskite NCs, even in a simplified structure, which is the highest efficiency to date in green LEDs that use colloidal organic-inorganic metal-halide perovskite nanoparticles including perovskite QDs and NCs. These results can help to guide development of various light-emitting optoelectronic applications based on perovskite NCs.

  19. Simple methods for characterization of metals in historical textile threads.

    PubMed

    Rezić, Iva; Curković, Lidija; Ujević, Magdalena

    2010-06-30

    Characterization of metal threads on historical textile materials is important for preservation of valuable cultural heritage. Obtained results dictate decisions on cleaning, conservation and restoration steps. The most important part of characterization is chemical analysis of originally applied materials, since this enables understanding the nature of chemical and physical degradation and determines the cleaning methods. Methods applied should be non-destructive and sensitive enough to detect trace elements in small sample amounts. The goal of this research was to describe the most useful procedures for fast and simple determination of specific metals of interest. Therefore we propose application of scanning electron microscopy equipped with EDS detector (SEM-EDS) for sample surface analysis and inductively coupled plasma-optical emission spectroscopy (ICP-OES) for chemical analysis of metals threads. For quality insurance reasons, a comparative method applied for chemical analysis was atomic absorption spectrometry (AAS). This combination of methods has proven to be very useful in analysis of historical samples, since SEM-EDS was a simple and non-destructive method which provided information on chemical composition of sample surfaces, while ICP-OES and AAS enabled the full insight into the average chemical composition of samples. Nevertheless, both ICP-OES and AAS were destructive methods which demanded dissolving of samples prior to the analysis. In this work nine different metal fibers collected from historical textile materials were characterized. Proposed methods enabled obtaining information on sample constitution, morphology, topology and chemical composition. Copyright 2010 Elsevier B.V. All rights reserved.

  20. Effect of embedded metal nanocrystals on the resistive switching characteristics in NiN-based resistive random access memory cells

    SciTech Connect

    Yun, Min Ju; Kim, Hee-Dong; Man Hong, Seok; Hyun Park, Ju; Su Jeon, Dong; Geun Kim, Tae

    2014-03-07

    The metal nanocrystals (NCs) embedded-NiN-based resistive random access memory cells are demonstrated using several metal NCs (i.e., Pt, Ni, and Ti) with different physical parameters in order to investigate the metal NC's dependence on resistive switching (RS) characteristics. First, depending on the electronegativity of metal, the size of metal NCs is determined and this affects the operating current of memory cells. If metal NCs with high electronegativity are incorporated, the size of the NCs is reduced; hence, the operating current is reduced owing to the reduced density of the electric field around the metal NCs. Second, the potential wells are formed by the difference of work function between the metal NCs and active layer, and the barrier height of the potential wells affects the level of operating voltage as well as the conduction mechanism of metal NCs embedded memory cells. Therefore, by understanding these correlations between the active layer and embedded metal NCs, we can optimize the RS properties of metal NCs embedded memory cells as well as predict their conduction mechanisms.

  1. Unravelling a simple method for the low temperature synthesis of silicon nanocrystals and monolithic nanocrystalline thin films

    NASA Astrophysics Data System (ADS)

    Kim, Ka-Hyun; Johnson, Erik V.; Kazanskii, Andrey G.; Khenkin, Mark V.; Roca I Cabarrocas, Pere

    2017-01-01

    In this work, we present new results on the plasma processing and structure of hydrogenated polymorphous silicon (pm-Si:H) thin films. pm-Si:H thin films consist of a low volume fraction of silicon nanocrystals embedded in a silicon matrix with medium range order, and they possess this morphology as a significant contribution to their growth comes from the impact on the substrate of silicon clusters and nanocrystals synthesized in the plasma. Quadrupole mass spectrometry, ion flux measurements, and material characterization by transmission electron microscopy (TEM) and atomic force microscopy all provide insight on the contribution to the growth by silicon nanocrystals during PECVD deposition. In particular, cross-section TEM measurements show for the first time that the silicon nanocrystals are uniformly distributed across the thickness of the pm-Si:H film. Moreover, parametric studies indicate that the best pm-Si:H material is obtained at the conditions after the transition between a pristine plasma and one containing nanocrystals, namely a total gas pressure around 2 Torr and a silane to hydrogen ratio between 0.05 to 0.1. From a practical point of view these conditions also correspond to the highest deposition rate achievable for a given RF power and silane flow rate.

  2. Unravelling a simple method for the low temperature synthesis of silicon nanocrystals and monolithic nanocrystalline thin films

    PubMed Central

    Kim, Ka-Hyun; Johnson, Erik V.; Kazanskii, Andrey G.; Khenkin, Mark V.; Roca i Cabarrocas, Pere

    2017-01-01

    In this work, we present new results on the plasma processing and structure of hydrogenated polymorphous silicon (pm-Si:H) thin films. pm-Si:H thin films consist of a low volume fraction of silicon nanocrystals embedded in a silicon matrix with medium range order, and they possess this morphology as a significant contribution to their growth comes from the impact on the substrate of silicon clusters and nanocrystals synthesized in the plasma. Quadrupole mass spectrometry, ion flux measurements, and material characterization by transmission electron microscopy (TEM) and atomic force microscopy all provide insight on the contribution to the growth by silicon nanocrystals during PECVD deposition. In particular, cross-section TEM measurements show for the first time that the silicon nanocrystals are uniformly distributed across the thickness of the pm-Si:H film. Moreover, parametric studies indicate that the best pm-Si:H material is obtained at the conditions after the transition between a pristine plasma and one containing nanocrystals, namely a total gas pressure around 2 Torr and a silane to hydrogen ratio between 0.05 to 0.1. From a practical point of view these conditions also correspond to the highest deposition rate achievable for a given RF power and silane flow rate. PMID:28091562

  3. Seed-induced growth of flower-like Au-Ni-ZnO metal-semiconductor hybrid nanocrystals for photocatalytic applications.

    PubMed

    Chen, Yuanzhi; Zeng, Deqian; Cortie, Michael B; Dowd, Annette; Guo, Huizhang; Wang, Junbao; Peng, Dong-Liang

    2015-03-25

    The combination of metal and semiconductor components in nanoscale to form a hybrid nanocrystal provides an important approach for achieving advanced functional materials with special optical, magnetic and photocatalytic functionalities. Here, a facile solution method is reported for the synthesis of Au-Ni-ZnO metal-semiconductor hybrid nanocrystals with a flower-like morphology and multifunctional properties. This synthetic strategy uses noble and magnetic metal Au@Ni nanocrystal seeds formed in situ to induce the heteroepitaxial growth of semiconducting ZnO nanopyramids onto the surface of metal cores. Evidence of epitaxial growth of ZnO{0001} facets on Ni {111} facets is observed on the heterojunction, even though there is a large lattice mismatch between the semiconducting and magnetic components. Adjustment of the amount of Au and Ni precursors can control the size and composition of the metal core, and consequently modify the surface plasmon resonance (SPR) and magnetic properties. Room-temperature superparamagnetic properties can be achieved by tuning the size of Ni core. The as-prepared Au-Ni-ZnO nanocrystals are strongly photocatalytic and can be separated and re-cycled by virtue of their magnetic properties. The simultaneous combination of plasmonic, semiconducting and magnetic components within a single hybrid nanocrystal furnishes it multifunctionalities that may find wide potential applications.

  4. General synthetic approach to heterostructured nanocrystals based on noble metals and I-VI, II-VI, and I-III-VI metal chalcogenides.

    PubMed

    Liu, Minghui; Zeng, Hua Chun

    2014-08-19

    Solid metal precursors (alloys or monometals) can serve both as a starting template and as a source material for chemical transformation to metal chalcogenides. Herein, we develop a simple solution-based strategy to obtain highly monodisperse noble-metal-based heterostructured nanocrystals from such precursor seeds. By utilizing chemical and structural inhomogeneity of these metal seeds, in this work, we have synthesized a total of five I-VI (Ag2S, Ag2Se, Ag3AuS2, Ag3AuSe2, and Cu9S5), three II-VI (CdS, CdSe, and CuSe), and four I-III-VI (AgInS2, AgInSe2, CuInS2, and CuInSe2) chalcogenides, together with their fifteen associated heterodimers (Au-Ag2S, Au-Ag2Se, Au-Ag3AuS2, Au-Ag3AuSe2, Au-AgInS2, Au-AgInSe2, Au-CdS, Au-CdSe, Ag-Ag2S, Ag-AgInS2, Au-Cu9S5, Au-CuInS2, Au-CuSe, Au-CuInSe2, and Pt-AgInS2) to affirm the process generality. Briefly, by adding elemental sulfur or selenium to AuAg alloy seeds and tuning the reaction conditions, we can readily obtain phase-pure Au-Ag2S, Au-Ag2Se, Au-Ag3AuS2, and Au-Ag3AuSe2 heterostructures. Similarly, we can also fabricate Au-AgInS2 and Au-AgInSe2 heterostructures from the AuAg seeds by adding sulfur/selenium and indium precursors. Furthermore, by partial or full conversion of Ag seeds, we can prepare both single-phase Ag chalcogenide nanocrystals and Ag-based heterostructures. To demonstrate wide applicability of this strategy, we have also synthesized Au-based binary and ternary Cu chalcogenide (Au-Cu9S5, Au-CuSe, Au-CuInS2, and Au-CuInSe2) heterostructures from alloy seeds of AuCu and Pt chalcogenides (e.g., Pt-AgInS2) from alloy seeds of PtAg. The structure and composition of the above products have been confirmed with X-ray diffraction, high-resolution transmission electron microscopy, X-ray photoelectron spectroscopy, and energy-dispersive X-ray spectroscopy methods. A kinetic investigation of the formation mechanism of these heterostructures is brought forward using Au-AgInS2 and Ag-CuInS2 as model examples.

  5. Tuning the Magnetic Properties of Metal Oxide Nanocrystal Heterostructures by Cation Exchange

    PubMed Central

    2013-01-01

    For three types of colloidal magnetic nanocrystals, we demonstrate that postsynthetic cation exchange enables tuning of the nanocrystal’s magnetic properties and achieving characteristics not obtainable by conventional synthetic routes. While the cation exchange procedure, performed in solution phase approach, was restricted so far to chalcogenide based semiconductor nanocrystals, here ferrite-based nanocrystals were subjected to a Fe2+ to Co2+ cation exchange procedure. This allows tracing of the compositional modifications by systematic and detailed magnetic characterization. In homogeneous magnetite nanocrystals and in gold/magnetite core shell nanocrystals the cation exchange increases the coercivity field, the remanence magnetization, as well as the superparamagnetic blocking temperature. For core/shell nanoheterostructures a selective doping of either the shell or predominantly of the core with Co2+ is demonstrated. By applying the cation exchange to FeO/CoFe2O4 core/shell nanocrystals the Neél temperature of the core material is increased and exchange-bias effects are enhanced so that vertical shifts of the hysteresis loops are obtained which are superior to those in any other system. PMID:23362940

  6. Rescaling of metal oxide nanocrystals for energy storage having high capacitance and energy density with robust cycle life.

    PubMed

    Jeong, Hyung Mo; Choi, Kyung Min; Cheng, Tao; Lee, Dong Ki; Zhou, Renjia; Ock, Il Woo; Milliron, Delia J; Goddard, William A; Kang, Jeung Ku

    2015-06-30

    Nanocrystals are promising structures, but they are too large for achieving maximum energy storage performance. We show that rescaling 3-nm particles through lithiation followed by delithiation leads to high-performance energy storage by realizing high capacitance close to the theoretical capacitance available via ion-to-atom redox reactions. Reactive force-field (ReaxFF) molecular dynamics simulations support the conclusion that Li atoms react with nickel oxide nanocrystals (NiO-n) to form lithiated core-shell structures (Ni:Li2O), whereas subsequent delithiation causes Ni:Li2O to form atomic clusters of NiO-a. This is consistent with in situ X-ray photoelectron and optical spectroscopy results showing that Ni(2+) of the nanocrystal changes during lithiation-delithiation through Ni(0) and back to Ni(2+). These processes are also demonstrated to provide a generic route to rescale another metal oxide. Furthermore, assembling NiO-a into the positive electrode of an asymmetric device enables extraction of full capacitance for a counter negative electrode, giving high energy density in addition to robust capacitance retention over 100,000 cycles.

  7. Rescaling of metal oxide nanocrystals for energy storage having high capacitance and energy density with robust cycle life

    PubMed Central

    Jeong, Hyung Mo; Choi, Kyung Min; Cheng, Tao; Lee, Dong Ki; Zhou, Renjia; Ock, Il Woo; Milliron, Delia J.; Goddard, William A.; Kang, Jeung Ku

    2015-01-01

    Nanocrystals are promising structures, but they are too large for achieving maximum energy storage performance. We show that rescaling 3-nm particles through lithiation followed by delithiation leads to high-performance energy storage by realizing high capacitance close to the theoretical capacitance available via ion-to-atom redox reactions. Reactive force-field (ReaxFF) molecular dynamics simulations support the conclusion that Li atoms react with nickel oxide nanocrystals (NiO-n) to form lithiated core–shell structures (Ni:Li2O), whereas subsequent delithiation causes Ni:Li2O to form atomic clusters of NiO-a. This is consistent with in situ X-ray photoelectron and optical spectroscopy results showing that Ni2+ of the nanocrystal changes during lithiation–delithiation through Ni0 and back to Ni2+. These processes are also demonstrated to provide a generic route to rescale another metal oxide. Furthermore, assembling NiO-a into the positive electrode of an asymmetric device enables extraction of full capacitance for a counter negative electrode, giving high energy density in addition to robust capacitance retention over 100,000 cycles. PMID:26080421

  8. Assembling metal oxide nanocrystals into dense, hollow, porous nanoparticles for lithium-ion and lithium-oxygen battery application

    NASA Astrophysics Data System (ADS)

    Ming, Jun; Wu, Yingqiang; Park, Jin-Bum; Lee, Joong Kee; Zhao, Fengyu; Sun, Yang-Kook

    2013-10-01

    New dense hollow porous (DHP) metal oxide nanoparticles that are smaller than 100 nm and composed of Co3O4, FeOx, NiO and MnOx were prepared by densely assembling metal oxide nanocrystals based on the hard-template method using a carbon colloid as a sacrificial core. These nanoparticles are quite different from the traditional particles as their hollow interior originates from the stacking of nanocrystals rather than a spherical shell. The DHP nanoparticles preserve the intriguing properties of nanocrystals and possess desirable surface area and pore volume that enhance the active surface, which ultimately benefits applications such as lithium-ion batteries. The DHP Co3O4 nanoparticles demonstrated an enhanced capacity of 1168 mA h g-1 at 100 mA g-1vs. 590 mA h g-1 of powders and stable cycling performance greater than 250 cycles when used as an anode material. Most importantly, the electrochemical performance of DHP Co3O4 nanoparticles in a lithium-O2 battery was also investigated for the first time. A low charge potential of ~4.0 V, a high discharge voltage near 2.74 V and a long cycle ability greater than 100 cycles at a delivered capacity of 2000 mA h g-1 (current density, 200 mA g-1) were observed. The performances were considerably improved compared to recent results of mesoporous Co3O4, Co3O4 nanoparticles and a composite of Co3O4/RGO and Co3O4/Pd. Therefore, it would be promising to investigate such properties of DHP nanoparticles or other hollow metal (oxide) particles for the popular lithium-air battery.New dense hollow porous (DHP) metal oxide nanoparticles that are smaller than 100 nm and composed of Co3O4, FeOx, NiO and MnOx were prepared by densely assembling metal oxide nanocrystals based on the hard-template method using a carbon colloid as a sacrificial core. These nanoparticles are quite different from the traditional particles as their hollow interior originates from the stacking of nanocrystals rather than a spherical shell. The DHP

  9. Assembling metal oxide nanocrystals into dense, hollow, porous nanoparticles for lithium-ion and lithium-oxygen battery application.

    PubMed

    Ming, Jun; Wu, Yingqiang; Park, Jin-Bum; Lee, Joong Kee; Zhao, Fengyu; Sun, Yang-Kook

    2013-11-07

    New dense hollow porous (DHP) metal oxide nanoparticles that are smaller than 100 nm and composed of Co3O4, FeOx, NiO and MnOx were prepared by densely assembling metal oxide nanocrystals based on the hard-template method using a carbon colloid as a sacrificial core. These nanoparticles are quite different from the traditional particles as their hollow interior originates from the stacking of nanocrystals rather than a spherical shell. The DHP nanoparticles preserve the intriguing properties of nanocrystals and possess desirable surface area and pore volume that enhance the active surface, which ultimately benefits applications such as lithium-ion batteries. The DHP Co3O4 nanoparticles demonstrated an enhanced capacity of 1168 mA h g(-1) at 100 mA g(-1)vs. 590 mA h g(-1) of powders and stable cycling performance greater than 250 cycles when used as an anode material. Most importantly, the electrochemical performance of DHP Co3O4 nanoparticles in a lithium-O2 battery was also investigated for the first time. A low charge potential of ∼4.0 V, a high discharge voltage near 2.74 V and a long cycle ability greater than 100 cycles at a delivered capacity of 2000 mA h g(-1) (current density, 200 mA g(-1)) were observed. The performances were considerably improved compared to recent results of mesoporous Co3O4, Co3O4 nanoparticles and a composite of Co3O4/RGO and Co3O4/Pd. Therefore, it would be promising to investigate such properties of DHP nanoparticles or other hollow metal (oxide) particles for the popular lithium-air battery.

  10. Magnesium nanocrystals embedded in a metal-organic framework: hybrid hydrogen storage with synergistic effect on physi- and chemisorption.

    PubMed

    Lim, Dae-Woon; Yoon, Ji Woong; Ryu, Keun Yong; Suh, Myunghyun Paik

    2012-09-24

    Hexagonal-disk-shaped magnesium nanocrystals (MgNCs) are fabricated within a porous metal-organic framework (MOF, see picture). The MgNCs@MOF stores hydrogen by both physi- and chemisorptions, exhibiting synergistic effects to decrease the isosteric heat of H(2) physisorption compared with that of pristine MOF, and decrease the H(2) chemisorption/desorption temperatures by 200 K compared with those of bare Mg powder. Copyright © 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  11. Tuning electronic properties of novel metal oxide nanocrystals using interface interactions: MoO3 monolayers on Au(111)

    SciTech Connect

    Quek, S; Biener, M M; Biener, J; Friend, C M; Kaxiras, E

    2004-04-20

    Metal oxide nanocrystals deposited on metal surfaces have novel electronic properties due to interface and nanoscale effects. Crystals and nanoscale ribbons of MoO{sub 3} are highly effective catalysts and field emitters. This renders MoO{sub 3} an interesting prototype. Whilst MoO{sub 3} exists as bilayers in the bulk crystal5, in this work, monolayer MoO{sub 3} nanocrystals were grown epitaxially on Au(111). Ab initio calculations reveal that Au stabilizes the MoO{sub 3} monolayer through electronic charge redistribution at the interface. The Mo-O bonds are able to rotate about one another, allowing the MoO{sub 3} monolayer to adjust to the Au lattice. As a result, the monolayer is semimetallic, unlike bulk MoO{sub 3} which is semiconducting. This remarkable flexibility of the oxide lattice suggests the possibility of tuning electronic properties of transition metal oxides via interface interactions. The overall surface pattern obtained is affected by an interplay between the Au(111) surface reconstruction and the edges of the deposited MoO{sub 3} islands.

  12. The Interaction of Hydrogen with Simple and Noble Metals Surfaces

    NASA Astrophysics Data System (ADS)

    Sprunger, Phillip T.

    The basic concepts of adsorption are illustrated by the investigation of a simple adsorbate (hydrogen) with the "simplest" metals (simple and noble metals). Theoretically tractable, these systems serve as an excellent test of our basic understanding of chemisorption. The interaction of atomic and molecular hydrogen with the surfaces of Mg(0001), Mg(1120), Li(110), K(110), Ag(110), and Ag(111) have been studied with a variety of experimental probes. In all cases, no evidence for H_2 associative or dissociative adsorption is observed at the substrate temperature investigated (>=q90 K). In the case of the simple metals below 150 K, atomic hydrogen is bound to the surfaces in a strongly chemisorbed state (hydride). For Mg and Li, the hydride is localized to the surface wherein the substrate electron density is lower than the bulk. Because of the low electron density, hydrogen is absorbed into the bulk of K at low temperatures and forms a bulk-hydride phase. However, these low-temperature phases are metastable. In the case of Mg, hydrogen moves into lower energy configuration bonding sites which are closer to or below the surface plane. However, the hydride characteristics are absent; the H atom is effectively screened because of the higher jellium density. In contrast, upon annealing, hydrogen is absorbed into the bulk of Li and K and phase separation occurs forming regions of clean metal and bulk hydride areas. The results are compared to theoretical studies; the propensity for absorption over adsorption is understood in terms of jellium-based models. In the case of silver, at 100 K, atomic hydrogen bonds in trigonal sites on both the (110) and (111) surfaces. As a function of H concentration, a sequence of lattice gas superstructures is observed; these phases are accompanied by small H-induced displacements of the substrate surface atoms. In the case of Ag(110), the low-temperature phase is metastable; upon annealing, hydrogen desorption from low energy states is

  13. Thermal Stability of Metal Nanocrystals: An Investigation of the Surface and Bulk Reconstructions of Pd Concave Icosahedra [On the Thermal Stability of Metal Nanocrystals: An Investigation of the Surface and Bulk Reconstructions of Pd Concave Icosahedra

    DOE PAGES

    Gilroy, Kyle D.; Elnabawy, Ahmed O.; Yang, Tung -Han; ...

    2017-04-27

    Despite the remarkable success in controlling the synthesis of metal nanocrystals, it still remains a grand challenge to stabilize and preserve the shapes or internal structures of metastable kinetic products. In this work, we address this issue by systematically investigating the surface and bulk reconstructions experienced by a Pd concave icosahedron when subjected to heating up to 600 °C in vacuum. We used in situ high-resolution transmission electron microscopy to identify the equilibration pathways of this far-from-equilibrium structure. We were able to capture key structural transformations occurring during the thermal annealing process, which were mechanistically rationalized by implementing self-consistent plane-wavemore » density functional theory (DFT) calculations. Specifically, the concave icosahedron was found to evolve into a regular icosahedron via surface reconstruction in the range of 200–400 °C, and then transform into a pseudospherical crystalline structure through bulk reconstruction when further heated to 600 °C. As a result, the mechanistic understanding may lead to the development of strategies for enhancing the thermal stability of metal nanocrystals.« less

  14. Simple charge-transfer model for metallic complexes.

    PubMed

    Ramírez-Ramírez, José-Zeferino; Vargas, Rubicelia; Garza, Jorge; Gázquez, José L

    2010-08-05

    In the chemistry of metallic complexes, two important concepts have been used to rationalize the recognition and selectivity of a host by a guest: preorganization and complementarity. Both of these concepts stem from geometrical features. Less explored in the literature has been the interactional complementarity, where mainly the electronic factors in the intermolecular forces are involved. Because the charge transfer between a species rich in electrons (ligand) and another deficient in them (cation) is one of the main intermolecular factors that control the binding energies in metallic complexes, for such systems, we propose a simple model based on density functional theory. We define an interactional energy in which the geometrical energy changes are subtracted from the binding energies and just the electronic factors are taken into account. The model is tested for the complexation between bidentate and cyclic ligands and Ca, Pb, and Hg metal dications. The charge-transfer energy described by our model fits nicely with the interactional energy. Thus, when the geometrical changes do not contribute in a significant way to the complexation energy, the interactional energy is dominated by charge-transfer effects.

  15. Pair potentials for simple metallic systems: Beyond linear response

    NASA Astrophysics Data System (ADS)

    Porter, J. A.; Ashcroft, N. W.; Chester, G. V.

    2010-06-01

    The formalism of electron response theory is extended to second order in a perturbing pseudopotential, and the consequences for effective ionic pair potentials of simple metals under standard conditions are then examined. Inclusion of second-order response terms in the pair potentials leads to the potential minima for sodium, magnesium, aluminum, and metallic silicon being located quite close to the experimental nearest-neighbor distances in the respective crystalline solids. Second-order effects are found to become increasingly important with higher valence. As a test case, it is also found that, for an assumed metallic form of hydrogen, inclusion of second-order response terms is insufficient to reproduce the experimental intramolecular distance under standard conditions: higher-order response terms are necessary to obtain the correct (Heitler-London-type) result. For any element treatable by response methods, the results further show that neglect of even one of the second-order response terms may significantly impact the determination of the pair potential.

  16. Thermal Stability of Metal Nanocrystals: An Investigation of the Surface and Bulk Reconstructions of Pd Concave Icosahedra

    DOE PAGES

    Gilroy, Kyle D.; Elnabawy, Ahmed O.; Yang, Tung-Han; ...

    2017-05-02

    Despite the remarkable success in controlling the synthesis of metal nanocrystals, it still remains a grand challenge to stabilize and preserve the shapes or internal structures of metastable kinetic products. In this work, we address this issue by systematically investigating the surface and bulk reconstructions experienced by a Pd concave icosahedron when subjected to heating up to 600 °C in vacuum. We used in situ high-resolution transmission electron microscopy to identify the equilibration pathways of this far-from-equilibrium structure. We were able to capture key structural transformations occurring during the thermal annealing process, which were mechanistically rationalized by implementing self-consistent plane-wavemore » density functional theory (DFT) calculations. Specifically, the concave icosahedron was found to evolve into a regular icosahedron via surface reconstruction in the range of 200–400 °C, and then transform into a pseudospherical crystalline structure through bulk reconstruction when further heated to 600 °C. The mechanistic understanding may lead to the development of strategies for enhancing the thermal stability of metal nanocrystals.« less

  17. Ultrafine Metal Phosphide Nanocrystals in Situ Decorated on Highly Porous Heteroatom-Doped Carbons for Active Electrocatalytic Hydrogen Evolution.

    PubMed

    Zhu, Yun-Pei; Xu, Xueyan; Su, Huan; Liu, Yu-Ping; Chen, Tiehong; Yuan, Zhong-Yong

    2015-12-30

    In spite of being technologically feasible, electrochemical water reduction to facilitate hydrogen production is confronted with issues mainly due to the lack of affordable and efficient catalysts for the water reduction half reaction. Reported herein is the fabrication of metal phosphides nanocrystals uniformly loaded on highly porous heteroatom-modified carbons through one-step carbonization-phosphization methodology. Remarkably, the well-structured porosity and the increased electrochemically accessible active sites ensure the high catalytic efficiency for electrochemical hydrogen evolution in acidic medium in terms of small onset potentials (33 mV) and large cathodic current density (0.481 mA cm(-2)), even comparable to the state-of-the-art Pt/C benchmark. The easily prepared composite catalysts of structural and textural peculiarities may serve as promising non-noble metal catalysts for realistic hydrogen evolution.

  18. Study of simple CFRP-metal joint failure

    NASA Astrophysics Data System (ADS)

    Cheng, Jingquan; Rodriguez, Antonio; Emerson, Nicolas; Symmes, Arthur

    2008-07-01

    In millimeter wavelength telescope design and construction, there have been a number of mysterious failures of simple CFRF-metal joints. Telescope designers have not had satisfactory interpretations of these failures. In this paper, factors which may influence the failure of joints are discussed. These include stress concentration, material creep, joint fatigue, reasons related to chemical process and manufacture process. Extrapolation formulas for material creep, joint fatigue, and differential thermal stresses are derived in this paper. Detailed chemical and manufacturing factors are also discussed. All these issues are the causes of a number of early failures under a loading which is significantly lower than the strength of adhesives used. For ensuring reliability of a precision instrument structure joint, the designer should have a thorough understanding of all these factors.

  19. Promotion of the halide effect in the formation of shaped metal nanocrystals via a hybrid cationic, polymeric stabilizer: Octahedra, cubes, and anisotropic growth

    NASA Astrophysics Data System (ADS)

    Sneed, Brian T.; Golden, Matthew C.; Liu, Yejing; Lee, Hiang K.; Andoni, Ilektra; Young, Allison P.; McMahon, Greg; Erdman, Natasha; Shibata, Masateru; Ling, Xing Yi; Tsung, Chia-Kuang

    2016-06-01

    To promote the effect of halide ions (Cl-, Br-, and I-) in facet-selective growth of {111} and {100} of shaped metal nanocrystals, we utilize PDADMAC, a hybrid cationic, polymeric stabilizer. SERS and synthesis experiments provide evidence supporting that the higher amount of PDADMA+ at surfaces promotes the local adsorption of halides, allowing the creation of Pd cubes, octahedra, and cuboctopods.

  20. Binding of an adatom to a simple metal surface

    NASA Technical Reports Server (NTRS)

    Huntington, H. B.; Turk, L. A.; White, W. W., III

    1975-01-01

    The density functional formalism of Hohenberg and Kohn is used to investigate the energies, charge densities and forces which hold an adatom on the surface of a simple metal. The valence wavefunction of the adatom is fitted to the Herman-Skillman solutions at large distance and is simplified somewhat in the core region. The field of the ion is represented by the Ashcroft pseudopotential. For the metal the jellium model is used. Detailed calculations are carried out for a sodium adatom on a sodium surface. Simply juxtaposing adatom and surface gives a binding energy of about 1/3 eV. This value is approximately twice the surface energy per atom in the close-packed plane. Charge redistributions as determined variationally increase the binding energy by about 10%. The equilibrium distance for the adatom turns out to be 1.66 A from the surface, as compared with 1.52 A, the observed value for one-half the distance between the close-packed planes.

  1. Binding of an adatom to a simple metal surface

    NASA Technical Reports Server (NTRS)

    Huntington, H. B.; Turk, L. A.; White, W. W., III

    1975-01-01

    The density functional formalism of Hohenberg and Kohn is used to investigate the energies, charge densities and forces which hold an adatom on the surface of a simple metal. The valence wavefunction of the adatom is fitted to the Herman-Skillman solutions at large distance and is simplified somewhat in the core region. The field of the ion is represented by the Ashcroft pseudopotential. For the metal the jellium model is used. Detailed calculations are carried out for a sodium adatom on a sodium surface. Simply juxtaposing adatom and surface gives a binding energy of about 1/3 eV. This value is approximately twice the surface energy per atom in the close-packed plane. Charge redistributions as determined variationally increase the binding energy by about 10%. The equilibrium distance for the adatom turns out to be 1.66 A from the surface, as compared with 1.52 A, the observed value for one-half the distance between the close-packed planes.

  2. Simple Electrical Logging Technique for Base Metal Exploration

    NASA Astrophysics Data System (ADS)

    Pant, P. R.; Gupta, D.

    It is well known that electrical logs of boreholes can play a signi|fi|cant role in base metal exploration in identifying mineralised zones, especially when there is core loss or the borehole diameter is small or if drilling is by percussion. However, electrical logging is not widely utilised because of the additional burden on finances and time.A simple electrical logging technique, based on a pole-pole (hole-to-surface) configuration with one borehole electrode and nearly akin to the single point method, for S.P., resistivity and I.P. parameters, is presented. It is shown that it has the resolution of the single point method and the penetration of a very long normal sonde which is helpful for detection. Besides these features, the main advantage of this technique is that it can be easily carried out using ground I.P. (time domain) equipment.The electrical logs obtained in different base metal belts in Rajasthan, India, employing this technique and using ground I.P. equipment in connection with mise-à-la-masse surveys, illustrate the above features. A comparison with logs recorded by means of multi-electrode drill hole I.P. equipment of Scintrex, Canada, substantiates the same.

  3. Chemical design of nanocrystal solids.

    PubMed

    Kovalenko, Maksym V

    2013-01-01

    This account highlights our recent and present activities dedicated to chemical synthesis and applications of inorganic nanostructures. In particular, we discuss the potential of metal amides as precursors in the synthesis of metallic and semiconductor nanocrystals. We show the importance of surface chemical functionalization for the emergence of collective electronic properties in nanocrystal solids. We also demonstrate a new kind of long-range ordered, crystalline matter comprising colloidal nanocrystals and atomically defined inorganic clusters. Finally, we point the reader's attention to the high potential benefits of size- and shape-tunability of nanocrystals for achieving higher performance of rechargeable Li-ion battery electrodes.

  4. Synthesis and characterization of different metal oxide nanostructures by simple electrolysis based oxidation of metals.

    PubMed

    Singh, Dinesh Pratap; Srivastava, Onkar Nath

    2009-09-01

    We report the Synthesis of different metal oxide (Cu2O, SnO2, Fe3O4 and PbO2) nanostructures by simple electrolysis based oxidation of metals (Cu, Sn, Fe and Pb). We have utilized the two electrode set up for the electrolysis and used different metal electrodes as anode and platinum as cathode. The synthesized nanomaterials were delaminated in the electrolyte. The microstructural characterization of synthesized materials in electrolytes after electrolysis at different electrode potentials revealed that the nanostructures strongly depend on the applied voltage between the electrodes. Various nanostructures (nanothreads, nanowires, nanocubes, nanotetrapods and hexagons-like) of metal oxides have been synthesized by this method. In case of copper electrode we have found nanothreads and nanowires of cuprous oxide. Tin electrode resulted nanothreads, nanotetrapod and nanocube like structures of tin oxide. Iron electrode resulted, nanowire like structures of iron oxide and lead sheet transformed into hexagon like and six petals like structures of lead oxide.

  5. Simple and sensitive detection method for Cobalt(II) in water using CePO4:Tb3+ nanocrystals as fluorescent probes.

    PubMed

    Chen, Hongqi; Yuan, Fei; Xu, Juan; Zhang, Yiyang; Wu, Yong; Wang, Lun

    2013-04-15

    A simple and sensitive method for detecting cobalt by synchronous fluorescence spectrometry technique with a novel fluorescence probe CePO4:Tb(3+) has been developed. CePO4:Tb(3+) nanocrystals were synthesized in aqueous solutions and characterized by transmission electron microscopy, electron diffraction pattern spectroscopy and spectrofluorometry. When Δλ=210 nm, the selected synchronous fluorescence is produced at 284 nm. CePO4:Tb(3+) nanocrystals were negatively charged under weakly basic conditions (pH=8.2), which can interact with Co(2+) via electrostatic interaction. Moreover, there is the spectrum overlap between the emission wavelength of CePO4:Tb(3+) NCs and the absorbance of Co(2+). So the energy transfer would occur, leading to the quenching phenomenon. The quenching equation of the system was agreed with the Stern-Volmer equation. The linear range and detection limit of Co(2+) were 5-1.8 μM and 3.5 nM, respectively. The method is successfully applied to the quantification of Co(2+) in water samples.

  6. Nanocrystal dispersed amorphous alloys

    NASA Technical Reports Server (NTRS)

    Perepezko, John H. (Inventor); Allen, Donald R. (Inventor); Foley, James C. (Inventor)

    2001-01-01

    Compositions and methods for obtaining nanocrystal dispersed amorphous alloys are described. A composition includes an amorphous matrix forming element (e.g., Al or Fe); at least one transition metal element; and at least one crystallizing agent that is insoluble in the resulting amorphous matrix. During devitrification, the crystallizing agent causes the formation of a high density nanocrystal dispersion. The compositions and methods provide advantages in that materials with superior properties are provided.

  7. Nanocrystal-Powered Nanomotor

    SciTech Connect

    Regan, B.C.; Aloni, S.; Jensen, K.; Ritchie, R.O.; Zettl, A.

    2005-07-05

    We have constructed and operated a nanoscale linear motorpowered by a single metal nanocrystal ram sandwiched between mechanicallever arms. Low-level electrical voltages applied to the carbon nanotubelever arms cause the nanocrystal to grow or shrink in a controlledmanner. The length of the ram is adjustable from 0 to more than 150 nm,with extension speeds exceeding 1900 nm/s. The thermodynamic principlesgoverning motor operation resemble those driving frost heave, a naturalsolid-state linear motor.

  8. Simple one-pot synthesis of solid-core@porous-shell alloyed PtAg nanocrystals for the superior catalytic activity toward hydrogen evolution and glycerol oxidation.

    PubMed

    Weng, Xuexiang; Liu, Qing; Wang, Ai-Jun; Yuan, Junhua; Feng, Jiu-Ju

    2017-05-15

    In this work, solid-core@porous-shell alloyed PtAg nanocrystals (PtAg NCs) were fabricated via a simple one-pot co-reduction wet-chemical method on a large scale. Diprophylline (DPP) was employed as the stabilizing agent and shape-directing agent, without any surfactant, polymer, seed or template. The products were mainly analyzed by a series of characterization technique. The hierarchical architectures had enhanced stability and improved electrocatalytic activity for hydrogen evolution reaction (HER) and glycerol oxidation reaction (GOR) in contrast with commercial available Pt/C and Pt black catalysts. For the prepared PtAg NCs catalyst, the Tafel slope is 40mVdec(-1) toward HER in 0.5M H2SO4, coupled with the specific activity and mass activity of 77.91mAcm(-2) and 1303mAmg(-1)Pt toward GOR, respectively.

  9. Metal-organic framework nanocrystals as sacrificial templates for hollow and exceptionally porous titania and composite materials.

    PubMed

    Yang, Hui; Kruger, Paul E; Telfer, Shane G

    2015-10-05

    We report a strategy that employs metal-organic framework (MOF) crystals in two roles for the fabrication of hollow nanomaterials. In the first role the MOF crystals provide a template on which a shell of material can be deposited. Etching of the MOF produces a hollow structure with a predetermined size and morphology. In combination with this strategy, the MOF crystals, including guest molecules in their pores, can provide the components of a secondary material that is deposited inside the initially formed shell. We used this approach to develop a straightforward and reproducible method for constructing well-defined, nonspherical hollow and exceptionally porous titania and titania-based composite nanomaterials. Uniform hollow nanostructures of amorphous titania, which assume the cubic or polyhedral shape of the original template, are delivered using nano- and microsized ZIF-8 and ZIF-67 crystal templates. These materials exhibit outstanding textural properties including hierarchical pore structures and BET surface areas of up to 800 m(2)/g. As a proof of principle, we further demonstrate that metal nanoparticles such as Pt nanoparticles, can be encapsulated into the TiO2 shell during the digestion process and used for subsequent heterogeneous catalysis. In addition, we show that the core components of the ZIF nanocrystals, along with their adsorbed guests, can be used as precursors for the formation of secondary materials, following their thermal decomposition, to produce hollow and porous metal sulfide/titania or metal oxide/titania composite nanostructures.

  10. Selective degradation of chemical bonds: from single-source molecular precursors to metallic Ag and semiconducting Ag2S nanocrystals via instant thermal activation.

    PubMed

    Tang, Qun; Yoon, Seok Min; Yang, Hyun Jin; Lee, Yoonmi; Song, Hyun Jae; Byon, Hye Ryung; Choi, Hee Cheul

    2006-03-14

    Selective formation of metallic Ag and semiconducting Ag(2)S nanocrystals has been achieved via a modified hot-injection process from a single-source precursor molecule, Ag(SCOPh), which can potentially generate both [Ag] and [AgS] fragments simultaneously. When the precursor molecules are injected into a preheated reaction system at 160 degrees C, spherical Ag(2)S nanocrystals are directly obtained even without a molecular activator, such as alkylamines. Mixtures of Ag and Ag(2)S or pure metallic Ag nanocrystals are obtained if the precursor molecules are injected at lower than 160 degrees C or room temperature. These results are attributed to the direct transfer of thermal energies to precursor molecules, which are enough to dissociate S-C as well as Ag-S bonds simultaneously. Detailed characterizations about the produced nanocrystals have been performed using powder X-ray diffraction (XRD), transmission electron microscopy (TEM), as well as energy-dispersive X-ray (EDX) spectrum.

  11. Functionalization of Cellulose Nanocrystals with PEG-Metal-Chelating Diblock Copolymers via Controlled Conjugation in Aqueous Medium

    NASA Astrophysics Data System (ADS)

    Guo, Melinda

    The surface of cellulose nanocrystals (CNCs) was successfully functionalized with metal chelating diblock copolymers via HyNic-4FB conjugation. Two types of PEG-metal-chelating block polymers with hydrazinonicotinate acetone hydrazine (HyNic) end groups were synthesized: mPEG-PGlu(DTPA) 18-HyNic and mPEG-PGlu(DTPA)25-HyNic. These two polymers both had a methoxy PEG (M ˜ 2000 Da) block that differed in the mean degree of polymerization of the metal-chelating block. They were characterized by 1H NMR spectroscopy and gel-permeation chromatography (GPC). 4-Formylbenzamide (4FB) groups were introduced onto the surface of CNCs and quantified through their reaction with 2-hydrazinopyridine. The polymers were grafted onto the surface of CNCs via bis-aryl hydrazone bond formation, and the kinetics of this reaction was explored by UV/Vis spectroscopy. The CNCs were also labeled with rhodamine and Alexa FluorRTM 488 dyes. Students in our collaborator's group in Pharmacy are examining applications of these materials as radiotherapeutic agents for cancer treatment.

  12. Probing the interface between semiconducting nanocrystals and molecular metal chalcogenide surface ligands: insights from first principles

    NASA Astrophysics Data System (ADS)

    Scalise, Emilio; Wippermann, Stefan; Galli, Giulia; Talapin, Dmitri

    Colloidal nanocrystals (NCs) are emerging as cost-effective materials offering exciting prospects for solar energy conversion, light emission and electronic applications. Recent experimental advances demonstrate the synthesis of fully inorganic nanocrystal solids from chemical solution processing. The properties of the NC-solids are heavily determined by the NCs surface and their interactions with the host matrix. However, information on the atomistic structure of such composites is hard to obtain, due to the complexity of the synthesis conditions and the unavailability of robust experimental techniques to probe nanointerfaces at the microscopic level. Here we present a systematic theoretical study of the interaction between InAs and InP NCs with Sn2S64- ligands. Employing a grand canonical ab initio thermodynamic approach we investigate the relative stability of a multitude of configurations possibly realized at the NC-ligand interface. Our study highlights the importance of different structural details and their strong impact on the resulting composite's properties. We show that to obtain a detailed understanding of experimental data it is necessary to take into account complex interfacial structures beyond simplified NC-ligand model interfaces. S. W. acknowledges BMBF NanoMatFutur Grant No. 13N12972. G.G. acknowledges DOE-BES for funding part of this work.

  13. Origin of Transitions between Metallic and Insulating States in Simple Metals

    SciTech Connect

    Naumov, Ivan I.; Hemley, Russell J.

    2015-04-17

    Unifying principles that underlie recently discovered transitions between metallic and insulating states in elemental solids under pressure are developed. Using group theory arguments and first principles calculations, we show that the electronic properties of the phases involved in these transitions are controlled by symmetry principles not previously recognized. The valence bands in these systems are described by simple and composite band representations constructed from localized Wannier functions centered on points unoccupied by atoms, and which are not necessarily all symmetrical. The character of the Wannier functions is closely related to the degree of s-p(-d) hybridization and reflects multi-center chemical bonding in these insulating states. The conditions under which an insulating state is allowed for structures having an integer number of atoms per primitive unit cell as well as re-entrant (i.e., metal-insulator-metal) transition sequences are detailed, resulting in predictions of novel behavior such as phases having three-dimensional Dirac-like points. The general principles developed are tested and applied to the alkali and alkaline earth metals, including elements where high-pressure insulating phases have been identified or reported (e.g., Li, Na, and Ca).

  14. Origin of Transitions between Metallic and Insulating States in Simple Metals

    DOE PAGES

    Naumov, Ivan I.; Hemley, Russell J.

    2015-04-17

    Unifying principles that underlie recently discovered transitions between metallic and insulating states in elemental solids under pressure are developed. Using group theory arguments and first principles calculations, we show that the electronic properties of the phases involved in these transitions are controlled by symmetry principles not previously recognized. The valence bands in these systems are described by simple and composite band representations constructed from localized Wannier functions centered on points unoccupied by atoms, and which are not necessarily all symmetrical. The character of the Wannier functions is closely related to the degree of s-p(-d) hybridization and reflects multi-center chemical bondingmore » in these insulating states. The conditions under which an insulating state is allowed for structures having an integer number of atoms per primitive unit cell as well as re-entrant (i.e., metal-insulator-metal) transition sequences are detailed, resulting in predictions of novel behavior such as phases having three-dimensional Dirac-like points. The general principles developed are tested and applied to the alkali and alkaline earth metals, including elements where high-pressure insulating phases have been identified or reported (e.g., Li, Na, and Ca).« less

  15. Origin of Transitions between Metallic and Insulating States in Simple Metals.

    PubMed

    Naumov, Ivan I; Hemley, Russell J

    2015-04-17

    Unifying principles that underlie recently discovered transitions between metallic and insulating states in elemental solids under pressure are developed. Using group theory arguments and first-principles calculations, we show that the electronic properties of the phases involved in these transitions are controlled by symmetry principles. The valence bands in these systems are described by simple and composite band representations constructed from localized Wannier functions centered on points unoccupied by atoms, and which are not necessarily all symmetrical. The character of the Wannier functions is closely related to the degree of s-p(-d) hybridization and reflects multicenter chemical bonding in these insulating states. The conditions under which an insulating state is allowed for structures having an integer number of atoms per primitive unit cell as well as reentrant (i.e., metal-insulator-metal) transition sequences are detailed, resulting in predictions of behavior such as phases having band-contact lines. The general principles developed are tested and applied to the alkali and alkaline earth metals, including elements where high-pressure insulating phases have been reported (e.g., Li, Na, and Ca).

  16. Simple synthesis of PbSe nanocrystals and their self-assembly into 2D ‘flakes’ and 1D ‘ribbons’ structures

    SciTech Connect

    Díaz-Torres, E.; Ortega-López, M.; Matsumoto, Y.; Santoyo-Salazar, J.

    2016-08-15

    Highlights: • PbSe is obtained in a simple way by the co-precipitation method at low-temperature. • The structural, morphological and optical properties of PbSe were studied. • Adding NH{sub 4}OH to the precursor solutions influences on the morphology. • 2D- and 1D-PbSe structures assemble by oriented attachment. • PbSe can be a potential candidate for thermoelectric applications. - Abstract: This work presents a simple and low-temperature method to prepare a variety of Lead selenide (PbSe) nanostructures, using aqueous solutions of Pb(NO{sub 3}){sub 2} and NaHSe. Nanostructures with different morphology were obtained by varying the Pb:Se molar ratio, as well as the mixing sequence of NH{sub 4}OH with either Pb(NO{sub 3}){sub 2} or NaHSe. Nanoparticles with different shapes (spherical and octahedral), and self-assembled structures (flakes and ribbons) were observed by Transmission Electron Microscopy. X-ray results confirmed that the PbSe rock-salt crystalline structure was obtained for all of the prepared samples. The crystal size is in the order of 7.3 to 8.9 nm for single nanocrystals. The absorption spectra of the samples show exciton absorption bands at 1395 nm and 1660 nm. This material could be used to develop more advanced structures for thermoelectric generators.

  17. Chelating ligands for nanocrystals' surface functionalization.

    PubMed

    Querner, Claudia; Reiss, Peter; Bleuse, Joël; Pron, Adam

    2004-09-22

    A new family of ligands for the surface functionalization of CdSe nanocrystals is proposed, namely alkyl or aryl derivatives of carbodithioic acids (R-C(S)SH). The main advantages of these new ligands are as follows: they nearly quantitatively exchange the initial surface ligands (TOPO) in very mild conditions; they significantly improve the resistance of nanocrystals against photooxidation because of their ability of strong chelate-type binding to metal atoms; their relatively simple preparation via Grignard intermediates facilitates the development of new bifunctional ligands containing, in addition to the anchoring carbodithioate group, a second function, which enables the grafting of molecules or macromolecules of interest on the nanocrystal surface. To give an example of this approach, we report, for the first time, the grafting of an electroactive oligomer from the polyaniline family-aniline tetramer-on CdSe nanocrystals after their functionalization with 4-formyldithiobenzoic acid. The grafting proceeds via a condensation reaction between the aldehyde group of the ligand and the terminal primary amine group of the tetramer. The resulting organic/inorganic hybrid exhibits complete extinction of the fluorescence of its constituents, indicating efficient charge or energy transfer between the organic and the inorganic semiconductors.

  18. Probing atomic ordering and multiple twinning in metal nanocrystals through their vibrations

    PubMed Central

    Portales, H.; Goubet, N.; Saviot, L.; Adichtchev, S.; Murray, D. B.; Mermet, A.; Duval, E.; Pileni, M.-P.

    2008-01-01

    Control of nanocrystal (NC) crystallinity currently raises great interest because of its potential benefits in both physics modeling and technological applications. Advances in methods for synthesizing perfect single-crystalline NCs are recent, so that the effect of crystallinity on NC properties has received only limited study and still needs to be properly investigated. Here, we report that crystallinity of gold NCs dramatically modifies their vibrations. Using low-frequency Raman scattering, we clearly demonstrate that single-domain NCs vibrate differently than their multiply twinned counterparts, through the splitting of the quadrupolar vibrations, which is only observed for the former. Using the resonant ultrasound approach, we calculate the vibrational frequencies of a gold sphere and show that elastic anisotropy induces a lift of degeneracy of the quadrupolar mode in good agreement with our experimental measurements. These findings open up challenging perspectives on using Raman spectroscopy to characterize nanocrystallinity. PMID:18818308

  19. Experimental investigation of the vibrational density of states and electronic excitations in metallic nanocrystals

    NASA Astrophysics Data System (ADS)

    Bayle, M.; Benzo, P.; Combe, N.; Gatel, C.; Bonafos, C.; Benassayag, G.; Carles, R.

    2014-05-01

    An investigation of the vibrational density of states (VDOS) in silver nanocrystals is performed using Raman scattering. A specific sample architecture, setup configuration, and original elaboration process are used in order to take simultaneously advantage of spectrally and spatially localized surface plasmon resonance, optical amplification, and dark-field spectroscopy. Disentangling the contributions of atom vibrations and electron-hole excitations (i.e., the so-called "background" in surface-enhanced Raman scattering) is performed. The extracted VDOS is successfully compared with theoretical ones obtained by atomic scale simulations. The effects of size, strain, and disorder on the VDOS are analyzed; in particular, the strain effect is investigated experimentally using the geometrical phase analysis coupled with high-resolution transmission electron microscopy. This work offers an opportunity to examine thermodynamic properties, like specific heat, at the nanoscale.

  20. Oxygen Vacancy Engineering of Co3 O4 Nanocrystals through Coupling with Metal Support for Water Oxidation.

    PubMed

    Zhang, Jun-Jun; Wang, Hong-Hui; Zhao, Tian-Jian; Zhang, Ke-Xin; Wei, Xiao; Jiang, Zhi-Dong; Hirano, Shin-Ichi; Li, Xin-Hao; Chen, Jie-Sheng

    2017-07-21

    Oxygen vacancies can help to capture oxygen-containing species and act as active centers for oxygen evolution reaction (OER). Unfortunately, effective methods for generating a high amount of oxygen vacancies on the surface of various nanocatalysts are rather limited. Here, we described an effective way to generate oxygen-vacancy-rich surface of transition metal oxides, exemplified with Co3 O4 , simply by constructing highly coupled interface of ultrafine Co3 O4 nanocrystals and metallic Ti. Impressively, the amounts of oxygen vacancy on the surface of Co3 O4 /Ti surpassed the reported values of the Co3 O4 modified even under highly critical conditions. The Co3 O4 /Ti electrode could provide a current density of 23 mA cm(-2) at an OER overpotential of 570 mV, low Tafel slope, and excellent durability in neutral medium. Because of the formation of a large amount of oxygen vacancies as the active centers for OER on the surface, the TOF value of the Co3 O4 @Ti electrode was optimized to be 3238 h(-1) at an OER overpotential of 570 mV, which is 380 times that of the state-of-the-art non-noble nanocatalysts in the literature. © 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

  1. A Simple Model for Fine Structure Transitions in Alkali-Metal Noble-Gas Collisions

    DTIC Science & Technology

    2015-03-01

    A SIMPLE MODEL FOR FINE STRUCTURE TRANSITIONS IN ALKALI - METAL NOBLE-GAS COLLISIONS THESIS Joseph A. Cardoza, Captain, USAF AFIT-ENP-MS-15-M-079... ALKALI - METAL NOBLE-GAS COLLISIONS THESIS Presented to the Faculty Department of Engineering Physics Graduate School of Engineering and Management Air...AFIT-ENP-MS-15-M-079 A SIMPLE MODEL FOR FINE STRUCTURE TRANSITIONS IN ALKALI - METAL NOBLE-GAS COLLISIONS Joseph A. Cardoza, BS Captain, USAF Committee

  2. A Simple Method for Drawing Chiral Mononuclear Octahedral Metal Complexes

    ERIC Educational Resources Information Center

    Mohamadou, Aminou; Haudrechy, Arnaud

    2008-01-01

    Octahedral transition-metal complexes are involved in a number of reactions and octahedral coordination geometry, frequently observed for metallic centers, includes important topographical stereochemistry. Depending on the number and nature of different ligands, octahedral coordination units with at least two different monodentate ligands give…

  3. A Simple Method for Drawing Chiral Mononuclear Octahedral Metal Complexes

    ERIC Educational Resources Information Center

    Mohamadou, Aminou; Haudrechy, Arnaud

    2008-01-01

    Octahedral transition-metal complexes are involved in a number of reactions and octahedral coordination geometry, frequently observed for metallic centers, includes important topographical stereochemistry. Depending on the number and nature of different ligands, octahedral coordination units with at least two different monodentate ligands give…

  4. Exploiting the colloidal nanocrystal library to construct electronic devices

    NASA Astrophysics Data System (ADS)

    Choi, Ji-Hyuk; Wang, Han; Oh, Soong Ju; Paik, Taejong; Sung, Pil; Sung, Jinwoo; Ye, Xingchen; Zhao, Tianshuo; Diroll, Benjamin T.; Murray, Christopher B.; Kagan, Cherie R.

    2016-04-01

    Synthetic methods produce libraries of colloidal nanocrystals with tunable physical properties by tailoring the nanocrystal size, shape, and composition. Here, we exploit colloidal nanocrystal diversity and design the materials, interfaces, and processes to construct all-nanocrystal electronic devices using solution-based processes. Metallic silver and semiconducting cadmium selenide nanocrystals are deposited to form high-conductivity and high-mobility thin-film electrodes and channel layers of field-effect transistors. Insulating aluminum oxide nanocrystals are assembled layer by layer with polyelectrolytes to form high-dielectric constant gate insulator layers for low-voltage device operation. Metallic indium nanocrystals are codispersed with silver nanocrystals to integrate an indium supply in the deposited electrodes that serves to passivate and dope the cadmium selenide nanocrystal channel layer. We fabricate all-nanocrystal field-effect transistors on flexible plastics with electron mobilities of 21.7 square centimeters per volt-second.

  5. On the Evolution from Non-Plasmonic Metal Nanoclusters to Plasmonic Nanocrystals

    DTIC Science & Technology

    2014-09-24

    discrete electronic energy levels, as opposed to the continuous band of conduction electrons in the metallic state. Conventional gold nanoparticles ...with size above 5 nm are well known to exhibit the surface plasmon resonance (SPR)⎯which is a distinct feature of the metallic-state nanoparticles . In...HOMO-LUMO gap) becomes distinct, in other words, ultrasmall metal nanoparticles become semiconducting. The properties of nanoclusters become very

  6. Highly luminescent and biocompatible, L-citrulline-capped ZnS:Mn nanocrystals for rapid screening of metal accumulating Lysinibacillus fusiformis bacteria.

    PubMed

    Sajimol, Augustine M; Roselin, Alex; Sreevalsa, V G; Deepa, G D; Bhat Sarita, G; Jayalekshmi, S

    2013-01-01

    Biocompatible and highly luminescent manganese doped zinc sulfide (ZnS:Mn) nanocrystals of average particle size 10 nm have been synthesized by capping with a novel amino acid ligand, L-citrulline. Though there are many reports on the bioimaging applications of nanostructured semiconductors, the present study focused on the detection of a special type of metal accumulating bacteria, Lysinibacillus fusiformis. This bacterium has significant applications in the disposal of metal components from industrial effluents. In this context, the detection of this bacterium is quite important and the present work demonstrates a novel technique for this bacterial detection. The synthesized nanocrystals were attached to Lysinibacillus fusiformis and characteristics of the bioconjugated system were studied. The blue shift observed in the ultraviolet-visible absorption and photoluminescence spectra of the bioconjugated system, confirms conjugation of the Lysinibacillus fusiformis with L-citrulline-capped ZnS:Mn. When the bioconjugated system (capped ZnS:Mn + bacteria) was observed using a fluorescent microscope under excitation wavelengths 365.4 nm (ultraviolet), 435.8 nm (blue) and 546.1 nm (green), fluorescence emissions were obtained in yellow, green and red regions respectively. The study of relative growth of Lysinibacillus fusiformis in the presence of L-citrulline-capped ZnS:Mn proves biocompatible property of these nanocrystals and their tunable color properties under different excitation wavelengths make them ideal for biolabeling applications.

  7. Localized surface plasmons modulated nonlinear optical processes in metal film-coupled and upconversion nanocrystals-coated nanoparticles (Conference Presentation)

    NASA Astrophysics Data System (ADS)

    Lei, Dangyuan

    2016-09-01

    In the first part of this talk, I will show our experimental investigation on the linear and nonlinear optical properties of metal film-coupled nanosphere monomers and dimers both with nanometric gaps. We have developed a new methodology - polarization resolved spectral decomposition and color decoding to "visualizing" unambiguously the spectral and radiation properties of the complex plasmonic gap modes in these hybrid nanostructures. Single-particle spectroscopic measurements indicate that these hybrid nanostructures can simultaneously enhance several nonlinear optical processes, such as second harmonic generation, two-photon absorption induced luminescence, and hyper-Raman scattering. In the second part, I will show how the polarization state of the emissions from sub-10 nm upconversion nanocrystals (UCNCs) can be modulated when they form a hybrid complex with a gold nanorod (GNR). Our single-particle scattering experiments expose how an interplay between excitation polarization and GNR orientation gives rise to an extraordinary polarized nature of the upconversion emissions from an individual hybrid nanostructure. We support our results by numerical simulations and, using Förster resonance energy transfer theory, we uncover how an overlap between the UCNC emission and GNR extinction bands as well as the mutual orientation between emission and plasmonic dipoles jointly determine the polarization state of the UC emissions.

  8. Simple theory of elastically deformed metals: Surface energy, stress, and work function

    NASA Astrophysics Data System (ADS)

    Kiejna, Adam; Pogosov, Valentin V.

    2000-10-01

    The effect of uniaxial strain on surface properties of simple metals is considered within the stabilized jellium model. The modified equations for the stabilization energy of the deformed Wigner-Seitz cells are derived as a function of the bulk electron density and the given deformation. The model requires as input the density parameter rs, the Poisson ratio, and Young's modulus of the metal. The results for surface energy, surface stress, and work function of simple metals calculated within the self-consistent Kohn-Sham method are also presented and discussed. A consistent explanation of the independent experiments on stress-induced contact potential difference at metal surfaces is given.

  9. A simple approach to metal hydride alloy optimization

    NASA Technical Reports Server (NTRS)

    Lawson, D. D.; Miller, C. G.; Landel, R. F.

    1976-01-01

    Hildebrand-Scott (1950) solubility parameters can be obtained for metals and alloys by calculating the cohesive energy density (CED), equal to the square of the solubility parameter, and a function of the heat of sublimation and the atomic volume. It is suggested that the solubility parameter permits estimation of the hydrogen storage capacity of an alloy and that alloys with a solubility parameter approximately equal to the parameter for hydrogen will have greater hydrogen storage capacity than other alloys. Equilibrium pressure - temperature relationships for some metal hydrides are presented in conjunction with the calculated solubility parameter and correlated with characteristics which would be useful in hydrogen-powered vehicles. Alloy properties which increase the amount of nonstoichiometric reversible hydrogen absorption are discussed.

  10. A simple approach to metal hydride alloy optimization

    NASA Technical Reports Server (NTRS)

    Lawson, D. D.; Miller, C.; Landel, R. F.

    1976-01-01

    Certain metals and related alloys can combine with hydrogen in a reversible fashion, so that on being heated, they release a portion of the gas. Such materials may find application in the large scale storage of hydrogen. Metal and alloys which show high dissociation pressure at low temperatures, and low endothermic heat of dissociation, and are therefore desirable for hydrogen storage, give values of the Hildebrand-Scott solubility parameter that lie between 100-118 Hildebrands, (Ref. 1), close to that of dissociated hydrogen. All of the less practical storage systems give much lower values of the solubility parameter. By using the Hildebrand solubility parameter as a criterion, and applying the mixing rule to combinations of known alloys and solid solutions, correlations are made to optimize alloy compositions and maximize hydrogen storage capacity.

  11. A simple approach to metal hydride alloy optimization

    NASA Technical Reports Server (NTRS)

    Lawson, D. D.; Miller, C.; Landel, R. F.

    1976-01-01

    Certain metals and related alloys can combine with hydrogen in a reversible fashion, so that on being heated, they release a portion of the gas. Such materials may find application in the large scale storage of hydrogen. Metal and alloys which show high dissociation pressure at low temperatures, and low endothermic heat of dissociation, and are therefore desirable for hydrogen storage, give values of the Hildebrand-Scott solubility parameter that lie between 100-118 Hildebrands, (Ref. 1), close to that of dissociated hydrogen. All of the less practical storage systems give much lower values of the solubility parameter. By using the Hildebrand solubility parameter as a criterion, and applying the mixing rule to combinations of known alloys and solid solutions, correlations are made to optimize alloy compositions and maximize hydrogen storage capacity.

  12. A simple approach to metal hydride alloy optimization

    NASA Technical Reports Server (NTRS)

    Lawson, D. D.; Miller, C. G.; Landel, R. F.

    1976-01-01

    Hildebrand-Scott (1950) solubility parameters can be obtained for metals and alloys by calculating the cohesive energy density (CED), equal to the square of the solubility parameter, and a function of the heat of sublimation and the atomic volume. It is suggested that the solubility parameter permits estimation of the hydrogen storage capacity of an alloy and that alloys with a solubility parameter approximately equal to the parameter for hydrogen will have greater hydrogen storage capacity than other alloys. Equilibrium pressure - temperature relationships for some metal hydrides are presented in conjunction with the calculated solubility parameter and correlated with characteristics which would be useful in hydrogen-powered vehicles. Alloy properties which increase the amount of nonstoichiometric reversible hydrogen absorption are discussed.

  13. A simple, general route to 2-pyridylidene transition metal complexes.

    PubMed

    Roselló-Merino, Marta; Díez, Josefina; Conejero, Salvador

    2010-12-28

    Pyridinium 2-carboxylates decompose thermally in the presence of a variety of late transition metal precursors to yield the corresponding 2-pyridylidene-like complexes. The mild reaction conditions and structural diversity that can be generated in the heterocyclic ring make this method an attractive alternative for the synthesis of 2-pyridylidene complexes. IR spectra of the Ir(i) carbonyl compounds [IrCl(NHC)(CO)(2)] indicate that these N-heterocyclic carbene ligands are among the strongest σ-electron donors.

  14. Heterogeneous Catalytic Oxidation of Simple Alcohols by Transition Metals

    PubMed Central

    2017-01-01

    The “exploding” flask demonstration presents a well-known illustration of heterogeneous catalyzed methanol oxidation. We find that for the same vapor pressure, the demonstration also works for all primary and secondary alcohols up to butanol but not for a tertiary alcohol. Also, we show that the demonstration works for a large range of transition metal catalysts. Hence, this demonstration, which is often applied for the repetitive explosions when methanol is used, may also be used to argue the requirement of initial dehydrogenation of the alcohol to an aldehyde in the catalytic reaction mechanism to support the general insensitivity to reactant molecules in heterogeneous catalysis in contrast to biological catalysis and to provide proof for activity trends as often depicted by volcano plots. PMID:28919644

  15. Heterogeneous Catalytic Oxidation of Simple Alcohols by Transition Metals.

    PubMed

    Jacobse, Leon; Vink, Sebastiaan O; Wijngaarden, Sven; Juurlink, Ludo B F

    2017-09-12

    The "exploding" flask demonstration presents a well-known illustration of heterogeneous catalyzed methanol oxidation. We find that for the same vapor pressure, the demonstration also works for all primary and secondary alcohols up to butanol but not for a tertiary alcohol. Also, we show that the demonstration works for a large range of transition metal catalysts. Hence, this demonstration, which is often applied for the repetitive explosions when methanol is used, may also be used to argue the requirement of initial dehydrogenation of the alcohol to an aldehyde in the catalytic reaction mechanism to support the general insensitivity to reactant molecules in heterogeneous catalysis in contrast to biological catalysis and to provide proof for activity trends as often depicted by volcano plots.

  16. Simple Molecular Reactive Force Field for Metal-Organic Synthesis.

    PubMed

    Andrejevic, Jovana; Stevenson, James; Clancy, Paulette

    2016-02-09

    For colloidal quantum dots to transition from research laboratories to deployment as optical and electronic products, there will be a need to scale-up their production to large-scale manufacturing processes. This demand increases the need to understand their formation via a molecular representation of the nucleation of lead sulfide (PbS) quantum dot systems passivated by lead oleate complexes. We demonstrate the effectiveness of a new type of reactive potential, custom-made for this system, that is drawn from simple Morse, Lennard-Jones, and Coulombic components, which can reproduce reactions across a broad range of PbS quantum dot sizes with good accuracy. We validate the capability of this model to capture reactive systems by comparison to ab initio calculations for a reaction between two dots.

  17. Electronic transport in arrays of gold nanocrystals

    NASA Astrophysics Data System (ADS)

    Parthasarathy, Raghuveer

    We examine electronic transport through two-dimensional arrays of gold nanocrystals. Recently developed techniques of particle synthesis and array self-assembly provide ordered (and disordered) monolayers of six-nanometer diameter gold nanocrystals on substrates with in-plane electrodes. These well-characterized superlattices allow investigation of basic questions about electronic conduction in metal quantum dot assemblies, answers to which have previously remained elusive. We first address the relation between current and voltage. Central to transport is the Coulomb blockade, the energetic cost of adding a single electron to a nanocrystal. Theoretical studies suggest power-law scaling of current beyond a threshold voltage in Coulomb blockade dominated systems. In ordered arrays, our data follow a power-law form, but with a scaling exponent significantly higher than the theoretical prediction. In disordered arrays, power-law scaling is violated; we explain that disorder disturbs the branching of current-carrying paths responsible for power-law conduction. Second, we examine the effect of temperature on transport. We find a large low-temperature regime (up to about 100 K) in which thermal energy acts only to linearly suppress the threshold voltage, leaving the current scale unaffected. We provide a simple, analytic model of thermally assisted tunneling which quantitatively describes the data. Third, we develop a simple and novel technique to tune the interparticle electronic couplings of the arrays---deposition of small amounts of germanium on the monolayers. The germanium dopant lowers the voltage threshold, and also increases conductivity. It also increases the temperature dependence of transport, suggesting the introduction of trapped states between the gold nanocrystal cores.

  18. Composite materials with metal oxide attached to lead chalcogenide nanocrystal quantum dots with linkers

    DOEpatents

    Fuke, Nobuhiro; Koposov, Alexey Y; Sykora, Milan; Hoch, Laura

    2014-12-16

    Composite materials useful for devices such as photoelectrochemical solar cells include a substrate, a metal oxide film on the substrate, nanocrystalline quantum dots (NQDs) of lead sulfide, lead selenide, and lead telluride, and linkers that attach the NQDs to the metal oxide film. Suitable linkers preserve the 1s absorption peak of the NQDs. A suitable linker has a general structure A-B-C where A is a chemical group adapted for binding to a MO.sub.x and C is a chemical group adapted for binding to a NQD and B is a divalent, rigid, or semi-rigid organic spacer moiety. Other linkers that preserve the 1s absorption peak may also be used.

  19. Facet-dependent electrochemical properties of Co3O4 nanocrystals toward heavy metal ions

    PubMed Central

    Yu, Xin-Yao; Meng, Qiang-Qiang; Luo, Tao; Jia, Yong; Sun, Bai; Li, Qun-Xiang; Liu, Jin-Huai; Huang, Xing-Jiu

    2013-01-01

    We revealed an interesting facet-dependent electrochemical behavior toward heavy metal ions (HMIs) based on their adsorption behaviors. The (111) facet of Co3O4 nanoplates has better electrochemical sensing performance than that of the (001) facet of Co3O4 nanocubes. Adsorption measurements and density-functional theory (DFT) calculations reveals that adsorption of HMIs is responsible for the difference of electrochemical properties. Our combined experimental and theoretical studies provide a solid hint to explain the mechanism of electrochemical detection of HMIs using nanoscale metal oxides. Furthermore, this study not only suggests a promising new strategy for designing high performance electrochemical sensing interface through the selective synthesis of nanoscale materials exposed with different well-defined facets, but also provides a deep understanding for a more sensitive and selective electroanalysis at nanomaterials modified electrodes. PMID:24097175

  20. Selectively catalytic micro- and nanocrystals of metal-organic framework [Co(4-bpdh)(HIA)]∝

    NASA Astrophysics Data System (ADS)

    Ye, Jing; Gou, Yongxia; Xu, Zhen-Liang; Xu, Haitao

    2015-03-01

    Metal-organic framework micro-crystals [Co(4-bpdh)(HIA)]∝ (1Co), crystallized in the monoclinic system (space group P12/n1, a=10.0009(16) Å, b=15.472(3) Å, c=18.563(3) Å, β=91.81(0)°, and Z=4), were controllably synthesized through the adjustment of the solvent system. The Co2+ ion center located in a six-coordinated environment combined with 5-hydroxyisophthalic acid (HIA) to produce ladder-like structures, which again linked with 2,5-bis(4-pyridyl)-3,4-diaza-2,4-hxadiene (4-bpdh) to yield a double-layer network. Micro-crystals 1Co exhibited selectively oxidation-catalytic properties for the degradation of methyl orange (conversion 90%) owing to ligand to metal charge transfer. Our work determined that the synthesized catalyst is not only highly selective for degradation of organic dyes, but also very efficient.

  1. Growth of copper oxide nanocrystals in metallic nanotubes for high performance battery anodes.

    PubMed

    Zhao, Yuxin; Mu, Shanjun; Sun, Wanfu; Liu, Quanzhen; Li, Yanpeng; Yan, Zifeng; Huo, Ziyang; Liang, Wenjie

    2016-12-08

    A rational integration of 1D metallic nanotubes and oxide nanoparticles has been demonstrated as a viable strategy for the production of both highly stable and efficient anodes for lithium ion batteries. We encapsulated copper oxide (CuO) nanoparticles in ultra-long metallic copper nanotubes with engineered interspaces, and explored their electrochemical properties. Such a hierarchical architecture provides three important features: (i) a continuous nanoscale metallic Cu shell to minimize electronic/ionic transmitting impedance; (ii) a unique quasi-one-dimensional structure with a large aspect ratio to reduce self-aggregation; (iii) free space for volume expansion of CuO nanoparticles and stable solid-electrolyte interphase (SEI) formation. The anode materials with such hierarchical structures have high specific capacity (around 600 mA h g(-1) at a current density of 0.1 A g(-1)), excellent cycling stability (over 94% capacity retention after 200 cycles) and superb reversible capacity of 175 mA h g(-1) at a high charging rate of 15 A g(-1).

  2. Metal-semiconductor phase transition of order arrays of VO2 nanocrystals

    NASA Astrophysics Data System (ADS)

    Lopez, Rene; Suh, Jae; Feldman, Leonard; Haglund, Richard

    2004-03-01

    The study of solid-state phase transitions at nanometer length scales provides new insights into the effects of material size on the mechanisms of structural transformations. Such research also opens the door to new applications, either because materials properties are modified as a function of particle size, or because the nanoparticles interact with a surrounding matrix material, or with each other. In this paper, we describe the formation of vanadium dioxide nanoparticles in silicon substrates by pulsed laser deposition of ion beam lithographically selected sites and thermal processing. We observe the collective behavior of 50 nm diameter VO2 oblate nanoparticles, 10 nm high, and ordered in square arrays with arbitrary lattice constant. The metal-semiconductor-transition of the VO2 precipitates shows different features in each lattice spacing substrate. The materials are characterized by electron microscopy, x-ray diffraction, Rutherford backscattering. The features of the phase transition are studied via infrared optical spectroscopy. Of particular interest are the enhanced scattering and the surface plasmon resonance when the particles reach the metallic state. This resonance amplifies the optical contrast in the range of near-infrared optical communication wavelengths and it is altered by the particle-particle coupling as in the case of noble metals. In addition the VO2 nanoparticles exhibit sharp transitions with up to 50 K of hysteresis, one of the largest values ever reported for this transition. The optical properties of the VO2 nanoarrays are correlated with the size of the precipitates and their inter-particle distance. Nonlinear and ultra fast optical measurements have shown that the transition is the fastest known solid-solid transformation. The VO2 nanoparticles show the same bulk property, transforming in times shorter than 150 fs. This makes them remarkable candidates for ultrafast optical and electronic switching applications.

  3. Nanomanipulation and controlled self-assembly of metal nanoparticles and nanocrystals for plasmonics.

    PubMed

    Gwo, Shangjr; Chen, Hung-Ying; Lin, Meng-Hsien; Sun, Liuyang; Li, Xiaoqin

    2016-10-21

    Localized surface plasmon resonances (LSPRs) associated with metallic nanostructures offer unique possibilities for light concentration beyond the diffraction limit, which can lead to strong field confinement and enhancement in deep subwavelength regions. In recent years, many transformative plasmonic applications have emerged, taking advantage of the spectral and spatial tunability of LSPRs enabled by near-field coupling between constituent metallic nanostructures in a variety of plasmonic metastructures (dimers, metamolecules, metasurfaces, metamaterials, etc.). For example, the "hot spot" formed at the interstitial site (gap) between two coupled metallic nanostructures in a plasmonic dimer can be spectrally tuned via the gap size. Capitalizing on these capabilities, there have been significant advances in plasmon enhanced or enabled applications in light-based science and technology, including ultrahigh-sensitivity spectroscopies, light energy harvesting, photocatalysis, biomedical imaging and theranostics, optical sensing, nonlinear optics, ultrahigh-density data storage, as well as plasmonic metamaterials and metasurfaces exhibiting unusual linear and nonlinear optical properties. In this review, we present two complementary approaches for fabricating plasmonic metastructures. We discuss how meta-atoms can be assembled into unique plasmonic metastructures using a variety of nanomanipulation methods based on single- or multiple-probes in an atomic force microscope (AFM) or a scanning electron microscope (SEM), optical tweezers, and focused electron-beam nanomanipulation. We also provide a few examples of nanoparticle metamolecules with designed properties realized in such well-controlled plasmonic metastructures. For the spatial controllability on the mesoscopic and macroscopic scales, we show that controlled self-assembly is the method of choice to realize scalable two-dimensional, and three-dimensional plasmonic metastructures. In the section of applications

  4. "Quantized" Doping of Individual Colloidal Nanocrystals Using Size-Focused Metal Quantum Clusters.

    PubMed

    Santiago-González, Beatriz; Monguzzi, Angelo; Pinchetti, Valerio; Casu, Alberto; Prato, Mirko; Lorenzi, Roberto; Campione, Marcello; Chiodini, Norberto; Santambrogio, Carlo; Meinardi, Francesco; Manna, Liberato; Brovelli, Sergio

    2017-06-27

    The insertion of intentional impurities, commonly referred to as doping, into colloidal semiconductor quantum dots (QDs) is a powerful paradigm for tailoring their electronic, optical, and magnetic behaviors beyond what is obtained with size-control and heterostructuring motifs. Advancements in colloidal chemistry have led to nearly atomic precision of the doping level in both lightly and heavily doped QDs. The doping strategies currently available, however, operate at the ensemble level, resulting in a Poisson distribution of impurities across the QD population. To date, the synthesis of monodisperse ensembles of QDs individually doped with an identical number of impurity atoms is still an open challenge, and its achievement would enable the realization of advanced QD devices, such as optically/electrically controlled magnetic memories and intragap state transistors and solar cells, that rely on the precise tuning of the impurity states (i.e., number of unpaired spins, energy and width of impurity levels) within the QD host. The only approach reported to date relies on QD seeding with organometallic precursors that are intrinsically unstable and strongly affected by chemical or environmental degradation, which prevents the concept from reaching its full potential and makes the method unsuitable for aqueous synthesis routes. Here, we overcome these issues by demonstrating a doping strategy that bridges two traditionally orthogonal nanostructured material systems, namely, QDs and metal quantum clusters composed of a "magic number" of atoms held together by stable metal-to-metal bonds. Specifically, we use clusters composed of four copper atoms (Cu4) capped with d-penicillamine to seed the growth of CdS QDs in water at room temperature. The elemental analysis, performed by electrospray ionization mass spectrometry, X-ray fluorescence, and inductively coupled plasma mass spectrometry, side by side with optical spectroscopy and transmission electron microscopy

  5. Nanocrystal assembly for tandem catalysis

    DOEpatents

    Yang, Peidong; Somorjai, Gabor; Yamada, Yusuke; Tsung, Chia-Kuang; Huang, Wenyu

    2014-10-14

    The present invention provides a nanocrystal tandem catalyst comprising at least two metal-metal oxide interfaces for the catalysis of sequential reactions. One embodiment utilizes a nanocrystal bilayer structure formed by assembling sub-10 nm platinum and cerium oxide nanocube monolayers on a silica substrate. The two distinct metal-metal oxide interfaces, CeO.sub.2--Pt and Pt--SiO.sub.2, can be used to catalyze two distinct sequential reactions. The CeO.sub.2--Pt interface catalyzed methanol decomposition to produce CO and H.sub.2, which were then subsequently used for ethylene hydroformylation catalyzed by the nearby Pt--SiO.sub.2 interface. Consequently, propanal was selectively produced on this nanocrystal bilayer tandem catalyst.

  6. Nanocrystal synthesis

    SciTech Connect

    Tisdale, William; Prins, Ferry; Weidman, Mark; Beck, Megan

    2016-11-01

    A method of preparing monodisperse MX semiconductor nanocrystals can include contacting an M-containing precursor with an X donor to form a mixture, where the molar ratio between the M containing precursor and the X donor is large. Alternatively, if additional X donor is added during the reaction, a smaller ratio between the M containing precursor and the X donor can be used to prepare monodisperse MX semiconductor nanocrystals.

  7. Effects of Thickness on the Metal-Insulator Transition in Free-Standing Vanadium Dioxide Nanocrystals.

    PubMed

    Fadlelmula, Mustafa M; Sürmeli, Engin C; Ramezani, Mehdi; Kasırga, T Serkan

    2017-03-08

    Controlling solid state phase transitions via external stimuli offers rich physics along with possibilities of unparalleled applications in electronics and optics. The well-known metal-insulator transition (MIT) in vanadium dioxide (VO2) is one instance of such phase transitions emerging from strong electronic correlations. Inducing the MIT using electric field has been investigated extensively for the applications in electrical and ultrafast optical switching. However, as the Thomas-Fermi screening length is very short, for considerable alteration in the material's properties with electric field induced MIT, crystals below 10 nm are needed. So far, the only way to achieve thin crystals of VO2 has been via epitaxial growth techniques. Yet, stress due to lattice mismatch as well as interdiffusion with the substrate complicate the studies. Here, we show that free-standing vapor-phase grown crystals of VO2 can be milled down to the desired thickness using argon ion-beam milling without compromising their electronic and structural properties. Among our results, we show that even below 4 nm thickness the MIT persists and the transition temperature is lowered in two-terminal devices as the crystal gets thinner. The findings in this Letter can be applied to similar strongly correlated materials to study quantum confinement effects.

  8. Removal of zinc by live, dead, and dried biomass of Fusarium spp. isolated from the abandoned-metal mine in South Korea and its perspective of producing nanocrystals.

    PubMed

    Velmurugan, Palanivel; Shim, Jaehong; You, Youngnam; Choi, Songho; Kamala-Kannan, Seralathan; Lee, Kui-Jae; Kim, Hee Joung; Oh, Byung-Taek

    2010-10-15

    Bioremediation is an innovative and alternative technology to remove heavy metal pollutants from aqueous solution using biomass from various microorganisms like algae, fungi and bacteria. In this study biosorption of zinc onto live, dead and dried biomass of Fusarium spp. was investigated as a function of initial zinc(II) concentration, pH, temperature, agitation and inoculum volume. It was observed that dried, dead and live biomass efficiently removed zinc at 60 min at an initial pH of 6.0+/-0.3. Temperature of 40 degrees C was optimum at agitation speed of 150 or 200 rpm. The initial metal concentration (10-320 mg L(-1)) significantly influenced the biosorption of the fungi. Overall, biosorption was high with 30-60% by dried, live and dead biomass. In addition to this, the potential of Fusarium spp. to produce zinc nanocrystals was determined by transmission electron microscopy, energy-dispersive spectroscopy, X-ray diffraction and fourier transform infrared spectroscopy, which showed that dead biomass was not significantly involved in production of zinc nanocrystals. 2010 Elsevier B.V. All rights reserved.

  9. A general and robust strategy for the synthesis of nearly monodisperse colloidal nanocrystals

    NASA Astrophysics Data System (ADS)

    Pang, Xinchang; Zhao, Lei; Han, Wei; Xin, Xukai; Lin, Zhiqun

    2013-06-01

    Colloidal nanocrystals exhibit a wide range of size- and shape-dependent properties and have found application in myriad fields, incuding optics, electronics, mechanics, drug delivery and catalysis, to name but a few. Synthetic protocols that enable the simple and convenient production of colloidal nanocrystals with controlled size, shape and composition are therefore of key general importance. Current strategies include organic solution-phase synthesis, thermolysis of organometallic precursors, sol-gel processes, hydrothermal reactions and biomimetic and dendrimer templating. Often, however, these procedures require stringent experimental conditions, are difficult to generalize, or necessitate tedious multistep reactions and purification. Recently, linear amphiphilic block co-polymer micelles have been used as templates to synthesize functional nanocrystals, but the thermodynamic instability of these micelles limits the scope of this approach. Here, we report a general strategy for crafting a large variety of functional nanocrystals with precisely controlled dimensions, compositions and architectures by using star-like block co-polymers as nanoreactors. This new class of co-polymers forms unimolecular micelles that are structurally stable, therefore overcoming the intrinsic instability of linear block co-polymer micelles. Our approach enables the facile synthesis of organic solvent- and water-soluble nearly monodisperse nanocrystals with desired composition and architecture, including core-shell and hollow nanostructures. We demonstrate the generality of our approach by describing, as examples, the synthesis of various sizes and architectures of metallic, ferroelectric, magnetic, semiconductor and luminescent colloidal nanocrystals.

  10. A general and robust strategy for the synthesis of nearly monodisperse colloidal nanocrystals.

    PubMed

    Pang, Xinchang; Zhao, Lei; Han, Wei; Xin, Xukai; Lin, Zhiqun

    2013-06-01

    Colloidal nanocrystals exhibit a wide range of size- and shape-dependent properties and have found application in myriad fields, incuding optics, electronics, mechanics, drug delivery and catalysis, to name but a few. Synthetic protocols that enable the simple and convenient production of colloidal nanocrystals with controlled size, shape and composition are therefore of key general importance. Current strategies include organic solution-phase synthesis, thermolysis of organometallic precursors, sol-gel processes, hydrothermal reactions and biomimetic and dendrimer templating. Often, however, these procedures require stringent experimental conditions, are difficult to generalize, or necessitate tedious multistep reactions and purification. Recently, linear amphiphilic block co-polymer micelles have been used as templates to synthesize functional nanocrystals, but the thermodynamic instability of these micelles limits the scope of this approach. Here, we report a general strategy for crafting a large variety of functional nanocrystals with precisely controlled dimensions, compositions and architectures by using star-like block co-polymers as nanoreactors. This new class of co-polymers forms unimolecular micelles that are structurally stable, therefore overcoming the intrinsic instability of linear block co-polymer micelles. Our approach enables the facile synthesis of organic solvent- and water-soluble nearly monodisperse nanocrystals with desired composition and architecture, including core-shell and hollow nanostructures. We demonstrate the generality of our approach by describing, as examples, the synthesis of various sizes and architectures of metallic, ferroelectric, magnetic, semiconductor and luminescent colloidal nanocrystals.

  11. Hollow nanocrystals and method of making

    DOEpatents

    Alivisatos, A Paul [Oakland, CA; Yin, Yadong [Moreno Valley, CA; Erdonmez, Can Kerem [Berkeley, CA

    2011-07-05

    Described herein are hollow nanocrystals having various shapes that can be produced by a simple chemical process. The hollow nanocrystals described herein may have a shell as thin as 0.5 nm and outside diameters that can be controlled by the process of making.

  12. Structure Map for Embedded Binary Alloy Nanocrystals

    SciTech Connect

    Yuan, C.W.; Shin, S.J.; Liao, C.Y.; Guzman, J.; Stone, P.R.; Watanabe, M.; Ager III, J.W.; Haller, E.E.; Chrzan, D.C.

    2008-09-20

    The equilibrium structure of embedded nanocrystals formed from strongly segregating binary-alloys is considered within a simple thermodynamic model. The model identifies two dimensionlessinterface energies that dictate the structure, and allows prediction of the stable structure for anychoice of these parameters. The resulting structure map includes three distinct nanocrystal mor-phologies: core/shell, lobe/lobe, and completely separated spheres.

  13. "Nanocrystal bilayer for tandem catalysis"

    SciTech Connect

    Yamada, Yusuke; Tsung, Chia Kuang; Huang, Wenyu; Huo, Ziyang; E.Habas, Susan E; Soejima, Tetsuro; Aliaga, Cesar E; Samorjai, Gabor A; Yang, Peidong

    2011-01-24

    Supported catalysts are widely used in industry and can be optimized by tuning the composition and interface of the metal nanoparticles and oxide supports. Rational design of metal-metal oxide interfaces in nanostructured catalysts is critical to achieve better reaction activities and selectivities. We introduce here a new class of nanocrystal tandem catalysts that have multiple metal-metal oxide interfaces for the catalysis of sequential reactions. We utilized a nanocrystal bilayer structure formed by assembling platinum and cerium oxide nanocube monolayers of less than 10 nm on a silica substrate. The two distinct metal-metal oxide interfaces, CeO2-Pt and Pt-SiO2, can be used to catalyse two distinct sequential reactions. The CeO2-Pt interface catalysed methanol decomposition to produce CO and H2, which were subsequently used for ethylene hydroformylation catalysed by the nearby Pt-SiO2 interface. Consequently, propanal was produced selectively from methanol and ethylene on the nanocrystal bilayer tandem catalyst. This new concept of nanocrystal tandem catalysis represents a powerful approach towards designing high-performance, multifunctional nanostructured catalysts

  14. Intermetallic Nanocrystals: Syntheses and Catalytic Applications.

    PubMed

    Yan, Yucong; Du, Jingshan S; Gilroy, Kyle D; Yang, Deren; Xia, Younan; Zhang, Hui

    2017-02-24

    At the forefront of nanochemistry, there exists a research endeavor centered around intermetallic nanocrystals, which are unique in terms of long-range atomic ordering, well-defined stoichiometry, and controlled crystal structure. In contrast to alloy nanocrystals with no elemental ordering, it is challenging to synthesize intermetallic nanocrystals with a tight control over their size and shape. Here, recent progress in the synthesis of intermetallic nanocrystals with controllable sizes and well-defined shapes is highlighted. A simple analysis and some insights key to the selection of experimental conditions for generating intermetallic nanocrystals are presented, followed by examples to highlight the viable use of intermetallic nanocrystals as electrocatalysts or catalysts for various reactions, with a focus on the enhanced performance relative to their alloy counterparts that lack elemental ordering. Within the conclusion, perspectives on future developments in the context of synthetic control, structure-property relationships, and applications are discussed.

  15. Optoperforation of Intact Plant Cells, Spectral Characterization of Alloy Disorder in InAsP Alloys, and Bimetallic Concentric Surfaces for Metal-Enhanced Fluorescence in Upconverting Nanocrystals

    NASA Astrophysics Data System (ADS)

    Merritt, Travis R.

    The techniques of optoperforation, spectral characterization of alloy disorder, and metal-enhanced uorescence were applied to previously unconsidered or disregarded systems in order to demonstrate that such applications are both feasible and consequential. These applications were the subject of three disparate works and, as such, are independently discussed. Despite being ostensibly restricted to mammalian cells, optoperforation was demonstrated in intact plant cells by means of successful femtosecond-laser-mediated infiltration of a membrane impermeable dextran-conjugated dye into cells of vital Arabidopsis seedling stems. By monitoring the rate of dye uptake, and the reaction of both CFP-expressing vacuoles and nanocellulose substrates, the intensity and exposure time of the perforating laser were adjusted to values that both preserved cell vitality and permitted the laser-assisted uptake of the uorophore. By using these calibrated laser parameters, dye was injected and later observed in targeted cells after 72 hours, all without deleteriously affecting the vital functions of those cells. In the context of alloy disorder, photoluminescence of excitonic transitions in two InAsxP1--x alloys were studied through temperature and magnetic field strength dependencies, as well as compositionally-dependent time-resolved behavior. The spectral shape, behavior of the linewidths at high magnetic fields, and the divergence of the peak positions from band gap behavior at low temperatures indicated that alloy disorder exists in the x=0.40 composition while showing no considerable presence in the x=0.13 composition. The time-resolved photoluminescence spectrum for both compositions feature a fast and slow decay, with the slow decay lifetime in x=0.40 being longer than that of x=0.13, which may be due to carrier migration between localized exciton states in x=0.40. In order to achieve broadband metal-enhanced uorescence in upconverting NaYF4:Yb,Er nanocrystals, two nanocomposite

  16. Binding in pair potentials of liquid simple metals from nonlocality in electronic kinetic energy

    NASA Technical Reports Server (NTRS)

    Perrot, F.; March, N. H.

    1990-01-01

    The paper presents an explicit expression for the pair potential in liquid simple metals from low-order density-gradient theory when the superposition of single-center displaced charges is employed. Numerical results are presented for the gradient expansion pair interaction in liquid Na and Be. The low-order density-gradient equation for the pair potential is presented.

  17. Binding in pair potentials of liquid simple metals from nonlocality in electronic kinetic energy

    NASA Technical Reports Server (NTRS)

    Perrot, F.; March, N. H.

    1990-01-01

    The paper presents an explicit expression for the pair potential in liquid simple metals from low-order density-gradient theory when the superposition of single-center displaced charges is employed. Numerical results are presented for the gradient expansion pair interaction in liquid Na and Be. The low-order density-gradient equation for the pair potential is presented.

  18. Nanocrystal conversion chemistry: A unified and materials-general strategy for the template-based synthesis of nanocrystalline solids

    SciTech Connect

    Vasquez, Yolanda; Henkes, Amanda E.; Chris Bauer, J.; Schaak, Raymond E.

    2008-07-15

    The concept of nanocrystal conversion chemistry, which involves the use of pre-formed nanoparticles as templates for chemical transformation into derivative solids, has emerged as a powerful approach for designing the synthesis of complex nanocrystalline solids. The general strategy exploits established synthetic capabilities in simple nanocrystal systems and uses these nanocrystals as templates that help to define the composition, crystal structure, and morphology of product nanocrystals. This article highlights key examples of 'conversion chemistry' approaches to the synthesis of nanocrystalline solids using a variety of techniques, including galvanic replacement, diffusion, oxidation, and ion exchange. The discussion is organized according to classes of solids, highlighting the diverse target systems that are accessible using similar chemical concepts: metals, oxides, chalcogenides, phosphides, alloys, intermetallic compounds, sulfides, and nitrides. - Graphical abstract: Nanocrystal conversion chemistry uses pre-formed nanoparticles as templates for chemical transformation into derivative solids, helping to define the composition, crystal structure, and morphology of product nanocrystals that have more complex features than their precursor templates. This article highlights the application of this concept to diverse classes of solids, including metals, oxides, chalcogenides, phosphides, alloys, intermetallics, sulfides, and nitrides.

  19. Microwave irradiation assisted, one pot synthesis of simple and complex metal oxide nanoparticles: a general approach

    NASA Astrophysics Data System (ADS)

    Brahma, Sanjaya; Liu, Chuan-Pu; Shivashankar, S. A.

    2017-10-01

    We demonstrate a standard approach for the growth of binary/ternary metal oxide nanostructures within 5 min at a low temperature (<100 °C) by using metal acetylacetonates as the starting precursor material and microwave as the source of energy in the presence/absence of a surfactant. Nanoparticles of some functionally advanced binary/ternary metal oxides (MnO2, Fe2O3, NiO, CdO, Ga2O3, Gd2O3, ZnFe2O4, ZnMn2O4) are synthesized and the structure/microstructure is analyzed to ensure the phase and crystallinity. This synthesis procedure can be extended to the large scale production of many other simple and complex metal oxides.

  20. Thermophysical properties of simple liquid metals: A brief review of theory

    NASA Technical Reports Server (NTRS)

    Stroud, David

    1993-01-01

    In this paper, we review the current theory of the thermophysical properties of simple liquid metals. The emphasis is on thermodynamic properties, but we also briefly discuss the nonequilibrium properties of liquid metals. We begin by defining a 'simple liquid metal' as one in which the valence electrons interact only weakly with the ionic cores, so that the interaction can be treated by perturbation theory. We then write down the equilibrium Hamiltonian of a liquid metal as a sum of five terms: the bare ion-ion interaction, the electron-electron interaction, the bare electron-ion interaction, and the kinetic energies of electrons and ions. Since the electron-ion interaction can be treated by perturbation, the electronic part contributes in two ways to the Helmholtz free energy: it gives a density-dependent term which is independent of the arrangement of ions, and it acts to screen the ion-ion interaction, giving rise to effective ion-ion pair potentials which are density-dependent, in general. After sketching the form of a typical pair potential, we briefly enumerate some methods for calculating the ionic distribution function and hence the Helmholtz free energy of the liquid: monte Carlo simulations, molecular dynamics simulations, and thermodynamic perturbation theory. The final result is a general expression for the Helmholtz free energy of the liquid metal. It can be used to calculate a wide range of thermodynamic properties of simple metal liquids, which we enumerate. They include not only a range of thermodynamic coefficients of both metals and alloys, but also many aspects of the phase diagram, including freezing curves of pure elements and phase diagrams of liquid alloys (including liquidus and solidus curves). We briefly mention some key discoveries resulting from previous applications of this method, and point out that the same methods work for other materials not normally considered to be liquid metals (such as colloidal suspensions, in which the

  1. Oxide Nanocrystal Model Catalysts.

    PubMed

    Huang, Weixin

    2016-03-15

    as the active sites, respectively, to produce acrolein, propylene oxide, and CO2. Ceria rods enclosed with the {110} and {100} crystal planes, ceria cubes enclosed with the {100} crystal planes, and ceria octahedra enclosed with the {111} crystal planes exhibit distinct morphology-dependent oxygen vacancy concentrations and structures that can be well correlated with the surface compositions and structures of exposed crystal planes. Consequently, the metal-ceria interactions, structures, and catalytic performances of ceria-supported catalysts depend on the CeO2 morphology. Our results comprehensively reveal the morphology-dependent surface chemistry and catalysis of oxide nanocrystals that not only greatly deepen the fundamental understanding of oxide catalysis but also demonstrate a morphology-engineering strategy to optimize the catalytic performance of oxide catalysts. These results adequately exemplify the concept of oxide nanocrystal model catalysts for the fundamental investigations of oxide catalysis without the "materials gap" and "pressure gap". With the structure-catalytic property relationships learned from oxide nanocrystal model catalyst studies and the advancement of controlled-synthesis methods, it is promising to realize the structural design and controlled synthesis of novel efficient oxide catalysts in the future.

  2. METALLICITY GRADIENTS THROUGH DISK INSTABILITY: A SIMPLE MODEL FOR THE MILKY WAY'S BOXY BULGE

    SciTech Connect

    Martinez-Valpuesta, Inma; Gerhard, Ortwin E-mail: gerhard@mpe.mpg.de

    2013-03-20

    Observations show a clear vertical metallicity gradient in the Galactic bulge, which is often taken as a signature of dissipative processes in the formation of a classical bulge. Various evidence shows, however, that the Milky Way is a barred galaxy with a boxy bulge representing the inner three-dimensional part of the bar. Here we show with a secular evolution N-body model that a boxy bulge formed through bar and buckling instabilities can show vertical metallicity gradients similar to the observed gradient if the initial axisymmetric disk had a comparable radial metallicity gradient. In this framework, the range of metallicities in bulge fields constrains the chemical structure of the Galactic disk at early times before bar formation. Our secular evolution model was previously shown to reproduce inner Galaxy star counts and we show here that it also has cylindrical rotation. We use it to predict a full mean metallicity map across the Galactic bulge from a simple metallicity model for the initial disk. This map shows a general outward gradient on the sky as well as longitudinal perspective asymmetries. We also briefly comment on interpreting metallicity gradient observations in external boxy bulges.

  3. A simple urea-based route to ternary metal oxynitride nanoparticles

    SciTech Connect

    Gomathi, A.; Reshma, S.; Rao, C.N.R.

    2009-01-15

    Ternary metal oxynitrides are generally prepared by heating the corresponding metal oxides with ammonia for long durations at high temperatures. In order to find a simple route that avoids use of gaseous ammonia, we have employed urea as the nitriding agent. In this method, ternary metal oxynitrides are obtained by heating the corresponding metal carbonates and transition metal oxides with excess urea. By this route, ternary metal oxynitrides of the formulae MTaO{sub 2}N (M=Ca, Sr or Ba), MNbO{sub 2}N (M=Sr or Ba), LaTiO{sub 2}N and SrMoO{sub 3-x}N{sub x} have been prepared successfully. The oxynitrides so obtained were generally in the form of nanoparticles, and were characterized by various physical techniques. - Graphical abstract: Nanoparticles of ternary metal oxynitrides can be synthesized by means of urea route. Given is the TEM image of the nanoparticles of CaTaO{sub 2}N so obtained and the insets show the SAED pattern and HREM image of the nanoparticles.

  4. Protonation of transition-metal hydrides: a not so simple process.

    PubMed

    Besora, Maria; Lledós, Agustí; Maseras, Feliu

    2009-04-01

    The protonation of a transition-metal hydride is a formally simple process between a proton donor and a proton acceptor with several potential basic centres. The detailed mechanism is however quite subtle, with multistep reactions and involvement of different intermediates. The process is furthermore very sensitive to the nature of both the proton donor and the transition-metal complex, as well as to the solvent and to the presence and identity of eventual counteranions. This tutorial review summarizes the recent progress in the understanding of the reaction, obtained through the joint application of a number of computational and experimental techniques.

  5. Simple model explaining and predicting coverage-dependent atomic adsorption energies on transition metal surfaces

    NASA Astrophysics Data System (ADS)

    Inoǧlu, Nilay; Kitchin, John R.

    2010-07-01

    The adsorption energies of simple atomic adsorbates are coverage dependent. We use density-functional theory to show that the coverage dependence is due to an adsorbate-induced modification of the surface d -band structure. We developed a simple model for predicting the d -band widths of clean and adsorbate-covered metallic surfaces using a tight-binding formalism. The new model can be used in conjunction with the d -band adsorption model to estimate adsorption energies as a function of coverage.

  6. Spectroscopic analysis on metal-oxide-semiconductor light-emitting diodes with buried Si nanocrystals and nano-pyramids in SiO(x) film.

    PubMed

    Lin, Gong-Ru

    2008-03-01

    The difference between the white and near-infrared electroluminescence of metal-oxide-semiconductor light-emitting diodes fabricated on 1,100 degrees C-annealed Si-rich SiO(x)/p-Si substrate with interfacial pyramidal Si dots (Si nano-pyramids) was characterized. By changing the substrate temperature and induced coupled plasma power during the plasma enhanced chemical vapor deposition of Si-rich SiO(x) films, the effects of the growth conditions on the defect- and Si nano-pyramid-related carrier transport and Si nanocrystal-related electroluminescence spectroscopy were also investigated. The annealed Si-rich SiO(x)/p-Si films grown at higher synthesized substrate temperate (350 degrees C) show the larger Si nano-pyramids precipitating near the Si/SiO2 interface. The indium tin oxide/Si-rich SiO(x)/p-Si/Al metal-oxide-semiconductor light-emitting diodes with Si-rich SiO(x) films exhibit different white-light electroluminescence spectra at wavelengths from 400 to 650 nm. The Si nanocrystal-related electroluminescence spectra at 650-850 nm are confirmed, whereas the electroluminescence spectra are shorter wavelengths is attributed to oxygen related defects. These defects become an electron-preferred transporting path within the Si-rich SiO(x) film, whose densities are decreased by increasing the substrate temperature or reducing the induced coupled plasma power. Defect-related white-light electroluminescence emits power for a relatively short lifetime. The lifetime can be lengthened and the electroluminescence power can be raised simultaneously by increasing deposition temperature to 350 degrees C and adjusting the induced coupled plasma power to a threshold of 30 W, which effectively increases the densities of Si nanocrystals and nano-pyramids in the Si-rich SiO(x) film with Si concentration of up to 40 at%. A nearly defect-free Si-rich SiO(x) sample can be grown under such conditions, which contributes to the most stable and largest near-infrared electroluminescence

  7. Hybrid solar cells of conjugated polymers metal-oxide nanocrystals blends; state of the art and future research challenges in Indonesia

    NASA Astrophysics Data System (ADS)

    Bahtiar, Ayi

    2013-09-01

    Ever-increasing world energy demand, depleting non-renewable energy resources and disruptive climate change due to greenhouse gases has aroused much interest in alternative renewable energy sources. Solar energy is one of the best available alternatives, for it is both abundant and clean. Solar cell is an effective device for converting solar energy into electricity. Indonesia is located on the equator where the sunlight is always available in abundance throughout the year; therefore solar cell would become the main source of electrical energy in Indonesia. However, the high cost of inorganic solar cells in spite of their high power conversion efficiency (PCE) has been a major constrain for their mass utilization in Indonesia. The only way to reduce the cost of production and installation is to find other materials which offer low-cost and easy processing into solar cells. Polymer solar cells have been intensively investigated for high performance and low-cost solar cells. Today, 9-11% power conversion efficiency (PCE) of small area polymer solar cells and 2-4% PCE of large area or module solar cells are already achieved. However, for practical application and mass production, 10% or higher PCE of module solar cells is highly required. The main strategic issue for improving the PCE is to use blend of conjugated polymer-metal oxide nanocrystals as active materials for hybrid solar cells, due to the good combination of the versatile solution processability of conjugated polymers and high charge carrier mobility of metal-oxide nanocrystals. In this paper, current development of hybrid solar cells worldwide and future research challenges in Indonesia will be discussed.

  8. A simple evolutional model of Habitable Zone around host stars with various mass and low metallicity

    NASA Astrophysics Data System (ADS)

    Oishi, Midori; Kamaya, Hideyuki

    2016-02-01

    Habitable Zone (HZ) is defined as a life existence area, where water at the surface of the terrestrial planet is in liquid phase. This is caused by the balance of flux from the host star and effective radiative cooling with greenhouse effect of the planet. However, the flux varies according to evolutional phase of the host star. So, a simple but newest HZ model considering stellar mass range from 0.08 to 4.00 M⊙ has been proposed. It studies both at zero-age main sequence (ZAMS) and terminal-age main sequence (TMS) phases to examine persistence of HZ. By the way, it discusses the case of the metallicity like the Sun. Actually, it is interesting to study a HZ model considering host stars with low metallicity. So, we examine the effect of metallicity, following the precedent simple model. In our analysis, metallicity affects little for HZ orbital range at ZAMS, while it affects clearly in case of TMS. Since the inner and outer HZ boundaries at TMS are shifted outward especially in the mass range from 1.5 to 2.0 M⊙, we find persistent HZ is allowed above about 1.8 M⊙. The age of the universe is 13.8 Gyr, which is comparable to main sequence life time of about 0.8 M⊙ for the low metallicity case. Then, the effect of metallicity to estimate HZ of low metallicity host stars is important for the mass range from 0.8 to 1.8 M⊙.

  9. Synthesis and Doping of Silicon Nanocrystals for Versatile Nanocrystal Inks

    NASA Astrophysics Data System (ADS)

    Kramer, Nicolaas Johannes

    The impact of nanotechnology on our society is getting larger every year. Electronics are becoming smaller and more powerful, the "Internet of Things" is all around us, and data generation is increasing exponentially. None of this would have been possible without the developments in nanotechnology. Crystalline semiconductor nanoparticles (nanocrystals) are one of the latest developments in the field of nanotechnology. This thesis addresses three important challenges for the transition of silicon nanocrystals from the lab bench to the marketplace: A better understanding of the nanocrystal synthesis was obtained, the electronic properties of the nanocrystals were characterized and tuned, and novel silicon nanocrystal inks were formed and applied using simple coating technologies. Plasma synthesis of nanocrystals has numerous advantages over traditional solution-based synthesis methods. While the formation of nanoparticles in low pressure nonthermal plasmas is well known, the heating mechanism leading to their crystallization is poorly understood. A combination of comprehensive plasma characterization with a nanoparticle heating model presented here reveals the underlying plasma physics leading to crystallization. The model predicts that the nanoparticles reach temperatures as high as 900 K in the plasma as a result of heating reactions on the nanoparticle surface. These temperatures are well above the gas temperature and sufficient for complete nanoparticle crystallization. Moving the field of plasma nanoparticle synthesis to atmospheric pressures is important for lowering its cost and making the process attractive for industrial applications. The heating and charging model for silicon nanoparticles was adapted in Chapter 3 to study plasmas maintained over a wide range of pressures (10 -- 105 Pa). The model considers three collisionality regimes and determines the dominant contribution of each regime under various plasma conditions. Strong nanoparticle cooling at

  10. Synthesis of new nanocrystal materials

    NASA Astrophysics Data System (ADS)

    Hassan, Yasser Hassan Abd El-Fattah

    Colloidal semiconductor nanocrystals (NCs) have sparked great excitement in the scientific community in last two decades. NCs are useful for both fundamental research and technical applications in various fields owing to their size and shape-dependent properties and their potentially inexpensive and excellent chemical processability. These NCs are versatile fluorescence probes with unique optical properties, including tunable luminescence, high extinction coefficient, broad absorption with narrow photoluminescence, and photobleaching resistance. In the past few years, a lot of attention has been given to nanotechnology based on using these materials as building blocks to design light harvesting assemblies. For instant, the pioneering applications of NCs are light-emitting diodes, lasers, and photovoltaic devices. Synthesis of the colloidal stable semiconductor NCs using the wet method of the pyrolysis of organometallic and chalcogenide precursors, known as hot-injection approach, is the chart-topping preparation method in term of high quality and monodisperse sized NCs. The advancement in the synthesis of these artificial materials is the core step toward their applications in a broad range of technologies. This dissertation focuses on exploring various innovative and novel synthetic methods of different types of colloidal nanocrystals, both inorganic semiconductors NCs, also known as quantum dots (QDs), and organic-inorganic metal halide-perovskite materials, known as perovskites. The work presented in this thesis focuses on pursuing fundamental understanding of the synthesis, material properties, photophysics, and spectroscopy of these nanostructured semiconductor materials. This thesis contains 6 chapters and conclusions. Chapters 1?3 focus on introducing theories and background of the materials being synthesized in the thesis. Chapter 4 demonstrates our synthesis of colloidal linker--free TiO2/CdSe NRs heterostructures with CdSe QDs grown in the presence of Ti

  11. Prediction of heavy metal behavior in soil by means of simple field tests

    SciTech Connect

    Blume, H.P.; Bruemmer, G. )

    1991-10-01

    Binding and retention against uptake by plants, and groundwater pollution of the metal ions Cd, Mn, Ni, Co, Zn, Cu, Cr(III), Pb, Hg, Fe(III), and Al by soils in relation to pH, redox potential, texture, organic matter, and iron oxide contents can be diagnosed in the form of rough relative values with simple field methods. A comparison with the results of some pot and field trials showed the practicability of this method.

  12. Efficient hydrogen evolution in transition metal dichalcogenides via a simple one-step hydrazine reaction.

    PubMed

    Cummins, Dustin R; Martinez, Ulises; Sherehiy, Andriy; Kappera, Rajesh; Martinez-Garcia, Alejandro; Schulze, Roland K; Jasinski, Jacek; Zhang, Jing; Gupta, Ram K; Lou, Jun; Chhowalla, Manish; Sumanasekera, Gamini; Mohite, Aditya D; Sunkara, Mahendra K; Gupta, Gautam

    2016-06-10

    Hydrogen evolution reaction is catalysed efficiently with precious metals, such as platinum; however, transition metal dichalcogenides have recently emerged as a promising class of materials for electrocatalysis, but these materials still have low activity and durability when compared with precious metals. Here we report a simple one-step scalable approach, where MoOx/MoS2 core-shell nanowires and molybdenum disulfide sheets are exposed to dilute aqueous hydrazine at room temperature, which results in marked improvement in electrocatalytic performance. The nanowires exhibit ∼100 mV improvement in overpotential following exposure to dilute hydrazine, while also showing a 10-fold increase in current density and a significant change in Tafel slope. In situ electrical, gate-dependent measurements and spectroscopic investigations reveal that hydrazine acts as an electron dopant in molybdenum disulfide, increasing its conductivity, while also reducing the MoOx core in the core-shell nanowires, which leads to improved electrocatalytic performance.

  13. Efficient hydrogen evolution in transition metal dichalcogenides via a simple one-step hydrazine reaction

    NASA Astrophysics Data System (ADS)

    Cummins, Dustin R.; Martinez, Ulises; Sherehiy, Andriy; Kappera, Rajesh; Martinez-Garcia, Alejandro; Schulze, Roland K.; Jasinski, Jacek; Zhang, Jing; Gupta, Ram K.; Lou, Jun; Chhowalla, Manish; Sumanasekera, Gamini; Mohite, Aditya D.; Sunkara, Mahendra K.; Gupta, Gautam

    2016-06-01

    Hydrogen evolution reaction is catalysed efficiently with precious metals, such as platinum; however, transition metal dichalcogenides have recently emerged as a promising class of materials for electrocatalysis, but these materials still have low activity and durability when compared with precious metals. Here we report a simple one-step scalable approach, where MoOx/MoS2 core-shell nanowires and molybdenum disulfide sheets are exposed to dilute aqueous hydrazine at room temperature, which results in marked improvement in electrocatalytic performance. The nanowires exhibit ~100 mV improvement in overpotential following exposure to dilute hydrazine, while also showing a 10-fold increase in current density and a significant change in Tafel slope. In situ electrical, gate-dependent measurements and spectroscopic investigations reveal that hydrazine acts as an electron dopant in molybdenum disulfide, increasing its conductivity, while also reducing the MoOx core in the core-shell nanowires, which leads to improved electrocatalytic performance.

  14. Efficient hydrogen evolution in transition metal dichalcogenides via a simple one-step hydrazine reaction

    PubMed Central

    Cummins, Dustin R.; Martinez, Ulises; Sherehiy, Andriy; Kappera, Rajesh; Martinez-Garcia, Alejandro; Schulze, Roland K.; Jasinski, Jacek; Zhang, Jing; Gupta, Ram K.; Lou, Jun; Chhowalla, Manish; Sumanasekera, Gamini; Mohite, Aditya D.; Sunkara, Mahendra K.; Gupta, Gautam

    2016-01-01

    Hydrogen evolution reaction is catalysed efficiently with precious metals, such as platinum; however, transition metal dichalcogenides have recently emerged as a promising class of materials for electrocatalysis, but these materials still have low activity and durability when compared with precious metals. Here we report a simple one-step scalable approach, where MoOx/MoS2 core-shell nanowires and molybdenum disulfide sheets are exposed to dilute aqueous hydrazine at room temperature, which results in marked improvement in electrocatalytic performance. The nanowires exhibit ∼100 mV improvement in overpotential following exposure to dilute hydrazine, while also showing a 10-fold increase in current density and a significant change in Tafel slope. In situ electrical, gate-dependent measurements and spectroscopic investigations reveal that hydrazine acts as an electron dopant in molybdenum disulfide, increasing its conductivity, while also reducing the MoOx core in the core-shell nanowires, which leads to improved electrocatalytic performance. PMID:27282871

  15. Electric relaxation processes in chemodynamics of aqueous metal complexes: from simple ligands to soft nanoparticulate complexants.

    PubMed

    van Leeuwen, Herman P; Buffle, Jacques; Town, Raewyn M

    2012-01-10

    The chemodynamics of metal complexes with nanoparticulate complexants can differ significantly from that for simple ligands. The spatial confinement of charged sites and binding sites to the nanoparticulate body impacts on the time scales of various steps in the overall complex formation process. The greater the charge carried by the nanoparticle, the longer it takes to set up the counterion distribution equilibrium with the medium. A z+ metal ion (z > 1) in a 1:1 background electrolyte will accumulate in the counterionic atmosphere around negatively charged simple ions, as well as within/around the body of a soft nanoparticle with negative structural charge. The rate of accumulation is often governed by diffusion and proceeds until Boltzmann partition equilibrium between the charged entity and the ions in the medium is attained. The electrostatic accumulation proceeds simultaneously with outer-sphere and inner-sphere complex formation. The rate of the eventual inner-sphere complex formation is generally controlled by the rate constant of dehydration of the metal ion, k(w). For common transition metal ions with moderate to fast dehydration rates, e.g., Cu(2+), Pb(2+), and Cd(2+), it is shown that the ionic equilibration with the medium may be the slower step and thus rate-limiting in their overall complexation with nanoparticles.

  16. New metal phthalocyanines/metal simple hydroxide multilayers: experimental evidence of dipolar field-driven magnetic behavior.

    PubMed

    Bourzami, Riadh; Eyele-Mezui, Séraphin; Delahaye, Emilie; Drillon, Marc; Rabu, Pierre; Parizel, Nathalie; Choua, Sylvie; Turek, Philippe; Rogez, Guillaume

    2014-01-21

    A series of new hybrid multilayers has been synthesized by insertion-grafting of transition metal (Cu(II), Co(II), Ni(II), and Zn(II)) tetrasulfonato phthalocyanines between layers of Cu(II) and Co(II) simple hydroxides. The structural and spectroscopic investigations confirm the formation of new layered hybrid materials in which the phthalocyanines act as pillars between the inorganic layers. The magnetic investigations show that all copper hydroxide-based compounds behave similarly, presenting an overall antiferromagnetic behavior with no ordering down to 1.8 K. On the contrary, the cobalt hydroxide-based compounds present a ferrimagnetic ordering around 6 K, regardless of the nature of the metal phthalocyanine between the inorganic layers. The latter observation points to strictly dipolar interactions between the inorganic layers. The amplitude of the dipolar field has been evaluated from X-band and Q-band EPR spectroscopy investigation (Bdipolar ≈ 30 mT).

  17. Simple relationship between oxidation state and electron affinity in gas-phase metal-oxo complexes.

    PubMed

    Waller, Sarah E; Ray, Manisha; Yoder, Bruce L; Jarrold, Caroline Chick

    2013-12-19

    The photoelectron spectra of WO3H(-) and WO2F(-) are presented and analyzed in the context of a series of previous similar measurements on MO(y)(-) (M = Mo, W; y = 0-3), MO4H(-) and AlMOy(-) (y ≤ 4) complexes. The electronic structures of the WO3H and WO2F anion and neutral complexes were investigated using the B3LYP hybrid density functional method. The spectra of WO3H(-), WO2F(-), and previously measured AlWO3(-) photoelectron spectra show that the corresponding neutrals, in which the transition metal centers are all in a +5 oxidation state, have comparable electron affinities. In addition, the electron affinities fit the general trend of monotonically increasing electron affinity with oxidation state, in spite of the WO3H(-), WO2F(-), and AlWO3(-) having closed shell ground states, suggesting that the oxidation state of the metal atom has more influence than shell closing on the electron affinity of these transition metal-oxo complexes. Results of DFT calculations suggest that the neutrals are pyramidal and the anions are planar. However, the barriers for inversion on the neutral surface are low, and attempts to generate simple Franck-Condon simulations based on simple normal coordinate displacement, ignoring the effects of inversion, are inadequate.

  18. Slip-activated surface creep with room-temperature super-elongation in metallic nanocrystals

    SciTech Connect

    Zhong, Li; Sansoz, Frederic; He, Yang; Wang, Chongmin; Zhang, Ze; Mao, Scott X.

    2016-11-28

    Atom diffusion assisted by surfaces or interfaces (e.g. Coble creep) has been known to be the origin of large creep rates and superplastic softening in nanosized crystals at low temperature. By contrast, source-limited crystal slip in defect-free nanostructures engenders important strengths, but also premature plastic instability and low ductility. Here, using in-situ transmission electron microscopy, we report a slip-activated surface creep mechanism that suppresses the tendency towards plastic instability without compromising the strength, resulting in ultra-large room-temperature plasticity in face-centered-cubic silver nanocrystals. This phenomenon is shown experimentally and theoretically to prevail over a material-dependent range of diameters where surface dislocation nucleation becomes a stimulus to diffusional creep. This work provides new fundamental insight into coupled diffusive-displacive deformation mechanisms maximizing ductility and strength simultaneously in nanoscale materials.

  19. Enhanced photophysical properties of plasmonic magnetic metal-alloyed semiconductor heterostructure nanocrystals: a case study for the Ag@Ni/Zn1-xMgxO system.

    PubMed

    Paul, Sumana; Ghosh, Sirshendu; Saha, Manas; De, S K

    2016-05-14

    Understanding the effect of homovalent cation alloying in wide band gap ZnO and the formation of metal-semiconductor heterostructures is very important for maximisation of the photophysical properties of ZnO. Nearly monodisperse ZnO nanopyramid and Mg alloyed ZnO nanostructures have been successfully synthesized by one pot decomposition of metal stearate by using oleylamine both as activating and capping agent. The solid solubility of Mg(ii) ions in ZnO is limited to ∼30% without phase segregation. An interesting morphology change is found on increasing Mg alloying: from nanopyramids to self-assembled nanoflowers. The morphology change is explained by the oriented attachment process. The introduction of Mg into the ZnO matrix increases the band gap of the materials and also generates new zinc interstitial (Zni) and oxygen vacancy related defects. Plasmonic magnetic Ag@Ni core-shell (Ag as core and Ni as shell) nanocrystals are used as a seed material to synthesize Ag@Ni/Zn1-xMgxO complex heterostructures. Epitaxial growth is established between Ag(111) and ZnO(110) planes in the heterostructure. An epitaxial metal-semiconductor interface is very crucial for complete electron-hole (e-h) separation and enhancement of the exciton lifetime. The alloyed semiconductor-metal heterostructure is observed to be highly photocatalytically active for dye degradation as well as photodetection. Incorporation of magnetic Ni(0) makes the photocatalyst superparamagnetic at room temperature which is found to be helpful for catalyst regeneration.

  20. Simple metal under tensile stress: layer-dependent herringbone reconstruction of thin potassium films on graphite

    PubMed Central

    Yin, Feng; Kulju, Sampo; Koskinen, Pekka; Akola, Jaakko; Palmer, Richard E.

    2015-01-01

    While understanding the properties of materials under stress is fundamentally important, designing experiments to probe the effects of large tensile stress is difficult. Here tensile stress is created in thin films of potassium (up to 4 atomic layers) by epitaxial growth on a rigid support, graphite. We find that this “simple” metal shows a long-range, periodic “herringbone” reconstruction, observed in 2- and 3- (but not 1- and 4-) layer films by low-temperature scanning tunneling microscopy (STM). Such a pattern has never been observed in a simple metal. Density functional theory (DFT)simulations indicate that the reconstruction consists of self-aligned stripes of enhanced atom density formed to relieve the tensile strain. At the same time marked layer-dependent charging effects lead to substantial variation in the apparent STM layer heights. PMID:25959681

  1. A simple formulation for magnetoresistance in metal-insulator granular films with increased current

    NASA Astrophysics Data System (ADS)

    Boff, M. A. S.; Canto, B.; Baibich, M. N.; Pereira, L. G.

    2013-02-01

    We studied the tunnel magnetoresistance in metal/insulator granular films when the applied current is varied. The tunnel magnetoresistance shows a strong modification related to a non-Ohmic behaviour of theses materials. It was verified that spin-dependent tunnelling is the main mechanism for magnetoresistance at low applied current. However, when the current is high, another mechanism gets to be important: it is independent of the magnetization and is associated to variable range hopping between metallic grains. In this work, we propose a simple modification of Inoue and Maekawa's model for tunnelling magnetoresistance in granulars, rewriting the expression for resistance as a function of magnetic field and temperature, also taking into account the two different contributions.

  2. From fullerenes to nanocrystals and nanocrystal arrays: Novel preparation and characterization methods

    NASA Astrophysics Data System (ADS)

    Vezmar, Igor

    1998-09-01

    The success of cluster physics and chemistry and the macroscopic isolation of fullerenes motivated the research of nanometer-size from assemblies based on other elements. In this work an alternative fullerene generation method, utilizing the annealing of an all-carbon precursor formed in the reaction of halocarbons with alkali metals, has been demonstrated. Furthermore, a novel method of nanocrystal processing has been achieved via a compact, well-controlled, multi-stage inert gas flow system operating at near atmospheric pressure. The versatility and adaptability of the nanocrystal flow processor allows for the preparation of various nanostructured materials. Nanocrystal processing in the context of this work means the controlled growth of nanocrystals in a vapor phase environment, their annealing to obtain preferred morphologies, and subsequent full surface stabilization to facilitate collection and handling. The nanocrystal flow processor is coupled in-line to a time-of-flight mass spectrometer for real-time nanocrystal size and composition determination. Continuous sampling and mass analyzing of nanocrystals in the nanometer-diameter size range (up to one million Daltons) at part per billion concentrations has been achieved. Sampling of helium flows bearing benzene, fullerenes, as well as sodium, magnesium, silver, and cesium-iodide nanocrystals has been demonstrated. Using the nanocrystal processing approach, stable silver and gold nanocrystals of uniform size and shape distribution, passivated by self-assembled monolayers of long-chain thiol molecules were successfully prepared. The post-analysis of noble metal nanocrystals included optical spectroscopy, electron microscopy imaging and diffraction, x-ray diffraction and mass spectrometry. Stable and intense cluster beams from gold and silver nanocrystals were produced by laser desorption of molecular films. The mass onset of the desorbed entities corresponds directly to the dimensions of the nanocrystal core

  3. Quantum theory of electroabsorption in semiconductor nanocrystals.

    PubMed

    Tepliakov, Nikita V; Leonov, Mikhail Yu; Baranov, Alexander V; Fedorov, Anatoly V; Rukhlenko, Ivan D

    2016-01-25

    We develop a simple quantum-mechanical theory of interband absorption by semiconductor nanocrystals exposed to a dc electric field. The theory is based on the model of noninteracting electrons and holes in an infinitely deep quantum well and describes all the major features of electroabsorption, including the Stark effect, the Franz-Keldysh effect, and the field-induced spectral broadening. It is applicable to nanocrystals of different shapes and dimensions (quantum dots, nanorods, and nanoplatelets), and will prove useful in modeling and design of electrooptical devices based on ensembles of semiconductor nanocrystals.

  4. Patterning nanocrystals using DNA

    SciTech Connect

    Williams, Shara Carol

    2003-01-01

    One of the goals of nanotechnology is to enable programmed self-assembly of patterns made of various materials with nanometer-sized control. This dissertation describes the results of experiments templating arrangements of gold and semiconductor nanocrystals using 2'-deoxyribonucleic acid (DNA). Previously, simple DNA-templated linear arrangements of two and three nanocrystals structures have been made.[1] Here, we have sought to assemble larger and more complex nanostructures. Gold-DNA conjugates with 50 to 100 bases self-assembled into planned arrangements using strands of DNA containing complementary base sequences. We used two methods to increase the complexity of the arrangements: using branched synthetic doublers within the DNA covalent backbone to create discrete nanocrystal groupings, and incorporating the nanocrystals into a previously developed DNA lattice structure [2][3] that self-assembles from tiles made of DNA double-crossover molecules to create ordered nanoparticle arrays. In the first project, the introduction of a covalently-branched synthetic doubler reagent into the backbone of DNA strands created a branched DNA ''trimer.'' This DNA trimer templated various structures that contained groupings of three and four gold nanoparticles, giving promising, but inconclusive transmission electron microscopy (TEM) results. Due to the presence of a variety of possible structures in the reaction mixtures, and due to the difficulty of isolating the desired structures, the TEM and gel electrophoresis results for larger structures having four particles, and for structures containing both 5 and 10 nm gold nanoparticles were inconclusive. Better results may come from using optical detection methods, or from improved sample preparation. In the second project, we worked toward making two-dimensional ordered arrays of nanocrystals. We replicated and improved upon previous results for making DNA lattices, increasing the size of the lattices to a length greater than

  5. Toxicity and Bio-Safety Evaluation of Magnetic Nanocrystals Designed for Nano-Medical Sensors

    DTIC Science & Technology

    2006-09-15

    synthesized various types of magnetic nanocrystals including inverse spinel metal ferrites (e.g. Fe3O4, MnFe2O4, CoFe2O4, & NiFe2O4), cobalt nanocrystals...cytotoxicity of inverse spinel metal ferrite nanocrystals with four different magnetic compositions (i.e. Fe3O4, MnFe2O4, CoFe2O4, NiFe2O4) on...magnetic nanocrystals under both in vitro and in vivo conditions. In specific, cytotoxicity of inverse spinel metal ferrite nanocrystals with four

  6. Synthesis and characterization of embedded germanium nanocrystals

    NASA Astrophysics Data System (ADS)

    Xu, Qing

    induce nucleation of amorphous Ge clusters in the irradiated area, and therefore can be used for masked patterning. In situ heating and cooling experiments inside a TEM have been performed on embedded Ge and Au nanocrystals. A very large thermal hysteresis of about 470K centered on the bulk melting temperature of Ge, 1211K, is observed for Ge nanocrystals embedded in silica. This phenomenon can be explained by a simple kinetic theory, which attributes the superheating and supercooling to the energy barrier a nucleus encounters when it grows. In contrast, Ge nanocrystals embedded in sapphire exhibit no hysteresis and has a melting point close to that of bulk Ge. This is attributed to the large size of the nanocrystals in sapphire.

  7. Silver(I)-directed growth of metal-organic complex nanocrystals with bidentate ligands of hydroquinine anthraquinone-1,4-diyl diethers as linkers at the water-chloroform interface

    NASA Astrophysics Data System (ADS)

    Tang, Ying; Wang, Hui-Ting; Chen, Meng; Qian, Dong-Jin; Zhang, Li; Liu, Minghua

    2014-09-01

    Immiscible liquid-liquid interfaces provide unique double phase regions for the design and construction of nanoscale materials. Here, we reported Ag(I)-directed growth of metal-organic complex nanocrystals by using AgNO3 as a connector in the aqueous solution and bidentate ligand of 1,4-bis(9-O-dihydroquininyl)anthraquinone [(DHQ)2AQN] and its enantiomer of (DHQD)2AQN in the chloroform solutions as linkers. The Ag-(DHQ)2AQN and Ag-(DHQD)2AQN complex nanocrystals were formed at the liquid-liquid interfaces and characterized by using UV-vis absorption and fluorescence spectroscopy and X-ray photoelectron spectroscopy, as well as by using scanning electron microscopy. Screw-like nanocrystals were formed at the initial 30 min after the interfacial coordination reaction started, then they grew into nanorods after several days, and finally became cubic microcrystals after 2 weeks. The pure ligand showed two emission bands centered at about 363 and 522 nm in the methanol solution, the second one of which was quenched and shifted to about 470 nm in the Ag-complex nanocrystals. Two couples of reversible redox waves were recorded for the Ag-complex nanocrystals; one centered at about -0.25 V (vs. Ag/AgCl) was designated to one electron transfer process of Ag - (DHQ)2AQN and Ag - (DHQ)2AQN+, and the other one centered at about 0.2 V was designated to one electron transfer process of Ag - (DHQ)2AQN and Ag+ - (DHQ)2AQN.

  8. Silver(I)-directed growth of metal-organic complex nanocrystals with bidentate ligands of hydroquinine anthraquinone-1,4-diyl diethers as linkers at the water-chloroform interface

    PubMed Central

    2014-01-01

    Immiscible liquid-liquid interfaces provide unique double phase regions for the design and construction of nanoscale materials. Here, we reported Ag(I)-directed growth of metal-organic complex nanocrystals by using AgNO3 as a connector in the aqueous solution and bidentate ligand of 1,4-bis(9-O-dihydroquininyl)anthraquinone [(DHQ)2AQN] and its enantiomer of (DHQD)2AQN in the chloroform solutions as linkers. The Ag-(DHQ)2AQN and Ag-(DHQD)2AQN complex nanocrystals were formed at the liquid-liquid interfaces and characterized by using UV-vis absorption and fluorescence spectroscopy and X-ray photoelectron spectroscopy, as well as by using scanning electron microscopy. Screw-like nanocrystals were formed at the initial 30 min after the interfacial coordination reaction started, then they grew into nanorods after several days, and finally became cubic microcrystals after 2 weeks. The pure ligand showed two emission bands centered at about 363 and 522 nm in the methanol solution, the second one of which was quenched and shifted to about 470 nm in the Ag-complex nanocrystals. Two couples of reversible redox waves were recorded for the Ag-complex nanocrystals; one centered at about -0.25 V (vs. Ag/AgCl) was designated to one electron transfer process of Ag - (DHQ)2AQN and Ag - (DHQ)2AQN+, and the other one centered at about 0.2 V was designated to one electron transfer process of Ag - (DHQ)2AQN and Ag+ - (DHQ)2AQN. PMID:25246874

  9. A simple practical protocol for care of metal-skin interface of external fixation.

    PubMed

    Saw, A; Chan, C K; Penafort, R; Sengupta, S

    2006-02-01

    Patients treated with external fixation for limb reconsturciton or fracture stabilization equire regular and prolongedperiod of pin-tract care involving frequent visits to clinic and dressing traditionally carried out by trained nurses or medical assistants. A simple method of do-it-yourself dressing was introduced in our institution and this study was undertaken to evaluate the effectiveness of the protocol. Sixty patients (40 trauma-related problems and 20 congenital or developmental disorders) were enrolled into the study. Following application of external fixation, the patients and/or their caretakers were taught on how to do pin-site dressing using normal saline or drinking water as cleansing solution on daily basis. Patients were discharged on the second or third post-operative day and were followed-up every two weeks for an average 182 days (range 66 to 379 days) with special attention on identifying pin-tract infection. A simple grading system for pin-tract infections was proposed. Of 40 patients with trauma-related problems. 65% were post-traumatic infections. There were 788 metal-skin interfaces (239 half-pin fixations and 549 tensioned wire fixations. A total 143 metal-skin interface infections (18.1%) involving half-pin sites (41.3%) and tensioned wire sites (58.7%) was noted. Majority were grade I infections (79.7%), 18.8% grade II and only 1.4% grade III. Most infections (81%)were caused by Staphylococcus aureus. Grade I infections were successfully treated with frequent dressing, grade II by adjunctive oral antibiotic but grade III infections required removal of fixator. All eventually healed. Do yourself non-sterile dressing of metal-skin interfaces is a cost-effective method of pin-site care with a low infection rate. The infections were sucessfully treated using guidelines according to the proposed classification of pin-tract infections.

  10. Efficient hydrogen evolution in transition metal dichalcogenides via a simple one-step hydrazine reaction

    SciTech Connect

    Cummins, Dustin R.; Martinez, Ulises; Sherehiy, Andriy; Kappera, Rajesh; Martinez-Garcia, Alejandro; Schulze, Roland K.; Jasinski, Jacek; Zhang, Jing; Gupta, Ram K.; Lou, Jun; Chhowalla, Manish; Sumanasekera, Gamini; Mohite, Aditya D.; Sunkara, Mahendra K.; Gupta, Gautam

    2016-06-10

    In this study, hydrogen evolution reaction is catalyzed efficiently with precious metals, such as platinum; however, transition metal dichalcogenides have recently emerged as a promising class of materials for electrocatalysis, but these materials still have low activity and durability when compared with precious metals. Here we report a simple one-step scalable approach, where MoOx/MoS2 core-shell nanowires and molybdenum disulfide sheets are exposed to dilute aqueous hydrazine at room temperature, which results in marked improvement in electrocatalytic performance. The nanowires exhibit ~100 mV improvement in over potential following exposure to dilute hydrazine, while also showing a 10-fold increase in current density and a significant change in Tafel slope. In situ electrical, gate-dependent measurements and spectroscopic investigations reveal that hydrazine acts as an electron dopant in molybdenum disulfide, increasing its conductivity, while also reducing the MoOx core in the core-shell nanowires, which leads to improved electrocatalytic performance.

  11. Efficient hydrogen evolution in transition metal dichalcogenides via a simple one-step hydrazine reaction

    DOE PAGES

    Cummins, Dustin R.; Martinez, Ulises; Sherehiy, Andriy; ...

    2016-06-10

    In this study, hydrogen evolution reaction is catalyzed efficiently with precious metals, such as platinum; however, transition metal dichalcogenides have recently emerged as a promising class of materials for electrocatalysis, but these materials still have low activity and durability when compared with precious metals. Here we report a simple one-step scalable approach, where MoOx/MoS2 core-shell nanowires and molybdenum disulfide sheets are exposed to dilute aqueous hydrazine at room temperature, which results in marked improvement in electrocatalytic performance. The nanowires exhibit ~100 mV improvement in over potential following exposure to dilute hydrazine, while also showing a 10-fold increase in current densitymore » and a significant change in Tafel slope. In situ electrical, gate-dependent measurements and spectroscopic investigations reveal that hydrazine acts as an electron dopant in molybdenum disulfide, increasing its conductivity, while also reducing the MoOx core in the core-shell nanowires, which leads to improved electrocatalytic performance.« less

  12. General synthesis of noble metal (Au, Ag, Pd, Pt) nanocrystal modified MoS2 nanosheets and the enhanced catalytic activity of Pd-MoS2 for methanol oxidation

    NASA Astrophysics Data System (ADS)

    Yuwen, Lihui; Xu, Fei; Xue, Bing; Luo, Zhimin; Zhang, Qi; Bao, Biqing; Su, Shao; Weng, Lixing; Huang, Wei; Wang, Lianhui

    2014-05-01

    A general and facile method for water-dispersed noble metal (Au, Ag, Pd, Pt) nanocrystal modified MoS2 nanosheets (NM-MoS2 NSs) has been developed. By using sodium carboxymethyl cellulose as a stabilizer, well-dispersed NM-MoS2 NSs with homogeneously deposited noble metal nanocrystals (NM NCs) can be synthesized in aqueous solutions. Due to the transition from the semiconducting 2H phase to the metallic 1T phase, the chemically exfoliated MoS2 (ce-MoS2) NSs have improved electrochemical activity. The partially metallic nature of the ce-MoS2 NSs and the catalytic activity of the NM NCs synergistically make NM-MoS2 NSs a potential electrochemical catalyst. For the first time, Pd-MoS2 NSs were used as an electrocatalyst for methanol oxidation in alkaline media. The results showed that Pd-MoS2 NSs have enhanced catalytic activity with 2.8-fold anodic peak current mass density compared to a commercial Pd/C catalyst, suggesting potential for application in direct methanol fuel cells (DMFCs).A general and facile method for water-dispersed noble metal (Au, Ag, Pd, Pt) nanocrystal modified MoS2 nanosheets (NM-MoS2 NSs) has been developed. By using sodium carboxymethyl cellulose as a stabilizer, well-dispersed NM-MoS2 NSs with homogeneously deposited noble metal nanocrystals (NM NCs) can be synthesized in aqueous solutions. Due to the transition from the semiconducting 2H phase to the metallic 1T phase, the chemically exfoliated MoS2 (ce-MoS2) NSs have improved electrochemical activity. The partially metallic nature of the ce-MoS2 NSs and the catalytic activity of the NM NCs synergistically make NM-MoS2 NSs a potential electrochemical catalyst. For the first time, Pd-MoS2 NSs were used as an electrocatalyst for methanol oxidation in alkaline media. The results showed that Pd-MoS2 NSs have enhanced catalytic activity with 2.8-fold anodic peak current mass density compared to a commercial Pd/C catalyst, suggesting potential for application in direct methanol fuel cells (DMFCs

  13. Building robust architectures of carbon and metal oxide nanocrystals toward high-performance anodes for lithium-ion batteries.

    PubMed

    Jia, Xilai; Chen, Zheng; Cui, Xia; Peng, Yiting; Wang, Xiaolei; Wang, Ge; Wei, Fei; Lu, Yunfeng

    2012-11-27

    Design and fabrication of effective electrode structure is essential but is still a challenge for current lithium-ion battery technology. Herein we report the design and fabrication of a class of high-performance robust nanocomposites based on iron oxide spheres and carbon nanotubes (CNTs). An efficient aerosol spray process combined with vacuum filtration was used to synthesize such composite architecture, where oxide nanocrystals were assembled into a continuous carbon skeleton and entangled in porous CNT networks. This material architecture offers many critical features that are required for high-performance anodes, including efficient ion transport, high conductivity, and structure durability, therefore enabling an electrode with outstanding lithium storage performance. For example, such an electrode with a thickness of ∼35 μm could deliver a specific capacity of 994 mA h g(-1) (based on total electrode weight) and high recharging rates. This effective strategy can be extended to construct many other composite electrodes for high-performance lithium-ion batteries.

  14. Cu nanocrystal growth on peptide nanotubes by biomineralization: Size control of Cu nanocrystals by tuning peptide conformation

    NASA Astrophysics Data System (ADS)

    Banerjee, Ipsita A.; Yu, Lingtao; Matsui, Hiroshi

    2003-12-01

    With recent interest in seeking new biologically inspired device-fabrication methods in nanotechnology, a new biological approach was examined to fabricate Cu nanotubes by using sequenced histidine-rich peptide nanotubes as templates. The sequenced histidine-rich peptide molecules were assembled as nanotubes, and the biological recognition of the specific sequence toward Cu lead to efficient Cu coating on the nanotubes. Cu nanocrystals were uniformly coated on the histidine-incorporated nanotubes with high packing density. In addition, the diameter of Cu nanocrystal was controlled between 10 and 30 nm on the nanotube by controlling the conformation of histidine-rich peptide by means of pH changes. Those nanotubes showed significant change in electronic structure by varying the nanocrystal diameter; therefore, this system may be developed to a conductivity-tunable building block for microelectronics and biological sensors. This simple biomineralization method can be applied to fabricate various metallic and semiconductor nanotubes with peptides whose sequences are known to mineralize specific ions.

  15. Growth and characterization of well-aligned densely-packed rutile TiO2 nanocrystals on sapphire substrates via metal organic chemical vapor deposition

    NASA Astrophysics Data System (ADS)

    Chen, C. A.; Chen, Y. M.; Korotcov, A.; Huang, Y. S.; Tsai, D. S.; Tiong, K. K.

    2008-02-01

    Well-aligned densely-packed rutile TiO2 nanocrystals (NCs) have been grown on sapphire (SA) (100) and (012) substrates via metal-organic chemical vapor deposition (MOCVD), using titanium-tetraisopropoxide (TTIP, Ti(OC3H7)4) as a source reagent. The surface morphology as well as structural and spectroscopic properties of the as-deposited NCs were characterized using field-emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM), selected-area electron diffractometry (SAED), x-ray diffraction (XRD) and micro-Raman spectroscopy. FESEM micrographs reveal that vertically aligned NCs were grown on SA(100), whereas the NCs on the SA(012) were grown with a tilt angle of ~33° from the normal to substrates. TEM and SAED measurements showed that the TiO2 NCs on SA(100) with square cross section have their long axis directed along the [001] direction. The XRD results reveal TiO2 NCs with either (002) orientation on SA(100) substrate or (101) orientation on SA(012) substrate. A strong substrate effect on the alignment of the growth of TiO2 NCs has been demonstrated and the probable mechanism for the formation of these NCs has been discussed.

  16. Controllable growth of nanoscale conductive filaments in solid-electrolyte-based ReRAM by using a metal nanocrystal covered bottom electrode.

    PubMed

    Liu, Qi; Long, Shibing; Lv, Hangbing; Wang, Wei; Niu, Jiebin; Huo, Zongliang; Chen, Junning; Liu, Ming

    2010-10-26

    Resistive memory (ReRAM) based on a solid-electrolyte insulator is a promising nanoscale device and has great potentials in nonvolatile memory, analog circuits, and neuromorphic applications. The underlying resistive switching (RS) mechanism of ReRAM is suggested to be the formation and rupture of nanoscale conductive filament (CF) inside the solid-electrolyte layer. However, the random nature of the nucleation and growth of the CF makes their formation difficult to control, which is a major obstacle for ReRAM performance improvement. Here, we report a novel approach to resolve this challenge by adopting a metal nanocrystal (NC) covered bottom electrode (BE) to replace the conventional ReRAM BE. As a demonstration vehicle, a Ag/ZrO(2)/Cu NC/Pt structure is prepared and the Cu NC covered Pt BE can control CF nucleation and growth to provide superior uniformity of RS properties. The controllable growth of nanoscale CF bridges between Cu NC and Ag top electrode has been vividly observed by transmission electron microscopy (TEM). On the basis of energy-dispersive X-ray spectroscopy (EDS) and elemental mapping analyses, we further confirm that the chemical contents of the CF are mainly Ag atoms. These testing/metrology results are consistent with the simulation results of electric-field distribution, showing that the electric field will enhance and concentrate on the NC sites and control location and orientation of Ag CFs.

  17. ZnO Nanocrystal Networks Near the Insulator-Metal Transition: Tuning Contact Radius and Electron Density with Intense Pulsed Light.

    PubMed

    Greenberg, Benjamin L; Robinson, Zachary L; Reich, K V; Gorynski, Claudia; Voigt, Bryan N; Francis, Lorraine F; Shklovskii, B I; Aydil, Eray S; Kortshagen, Uwe R

    2017-08-09

    Networks of ligand-free semiconductor nanocrystals (NCs) offer a valuable combination of high carrier mobility and optoelectronic properties tunable via quantum confinement. In principle, maximizing carrier mobility entails crossing the insulator-metal transition (IMT), where carriers become delocalized. A recent theoretical study predicted that this transition occurs at nρ(3) ≈ 0.3, where n is the carrier density and ρ is the interparticle contact radius. In this work, we satisfy this criterion in networks of plasma-synthesized ZnO NCs by using intense pulsed light (IPL) annealing to tune n and ρ independently. IPL applied to as-deposited NCs increases ρ by inducing sintering, and IPL applied after the NCs are coated with Al2O3 by atomic layer deposition increases n by removing electron-trapping surface hydroxyls. This procedure does not substantially alter NC size or composition and is potentially applicable to a wide variety of nanomaterials. As we increase nρ(3) to at least twice the predicted critical value, we observe conductivity scaling consistent with arrival at the critical region of a continuous quantum phase transition. This allows us to determine the critical behavior of the dielectric constant and electron localization length at the IMT. However, our samples remain on the insulating side of the critical region, which suggests that the critical value of nρ(3) may in fact be significantly higher than 0.3.

  18. Growth and characterization of well-aligned densely-packed rutile TiO(2) nanocrystals on sapphire substrates via metal-organic chemical vapor deposition.

    PubMed

    Chen, C A; Chen, Y M; Korotcov, A; Huang, Y S; Tsai, D S; Tiong, K K

    2008-02-20

    Well-aligned densely-packed rutile TiO(2) nanocrystals (NCs) have been grown on sapphire (SA) (100) and (012) substrates via metal-organic chemical vapor deposition (MOCVD), using titanium-tetraisopropoxide (TTIP, Ti(OC(3)H(7))(4)) as a source reagent. The surface morphology as well as structural and spectroscopic properties of the as-deposited NCs were characterized using field-emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM), selected-area electron diffractometry (SAED), x-ray diffraction (XRD) and micro-Raman spectroscopy. FESEM micrographs reveal that vertically aligned NCs were grown on SA(100), whereas the NCs on the SA(012) were grown with a tilt angle of ∼33° from the normal to substrates. TEM and SAED measurements showed that the TiO(2) NCs on SA(100) with square cross section have their long axis directed along the [001] direction. The XRD results reveal TiO(2) NCs with either (002) orientation on SA(100) substrate or (101) orientation on SA(012) substrate. A strong substrate effect on the alignment of the growth of TiO(2) NCs has been demonstrated and the probable mechanism for the formation of these NCs has been discussed.

  19. Determination of active doping in highly resistive boron doped silicon nanocrystals embedded in SiO2 by capacitance voltage measurement on inverted metal oxide semiconductor structure

    NASA Astrophysics Data System (ADS)

    Zhang, Tian; Puthen-Veettil, Binesh; Wu, Lingfeng; Jia, Xuguang; Lin, Ziyun; Yang, Terry Chien-Jen; Conibeer, Gavin; Perez-Wurfl, Ivan

    2015-10-01

    We investigate the Capacitance-Voltage (CV) measurement to study the electrically active boron doping in Si nanocrystals (ncSi) embedded in SiO2. The ncSi thin films with high resistivity (200-400 Ω cm) can be measured by using an inverted metal oxide semiconductor (MOS) structure (Al/ncSi (B)/SiO2/Si). This device structure eliminates the complications from the effects of lateral current flow and the high sheet resistance in standard lateral MOS structures. The characteristic MOS CV curves observed are consistent with the effective p-type doping. The CV modeling method is presented and used to evaluate the electrically active doping concentration. We find that the highly boron doped ncSi films have electrically active doping of 1018-1019 cm-3 despite their high resistivity. The saturation of doping at about 1.4 × 1019 cm-3 and the low doping efficiency less than 5% are observed and discussed. The calculated effective mobility is in the order of 10-3 cm2/V s, indicating strong impurity/defect scattering effect that hinders carriers transport.

  20. Determination of active doping in highly resistive boron doped silicon nanocrystals embedded in SiO{sub 2} by capacitance voltage measurement on inverted metal oxide semiconductor structure

    SciTech Connect

    Zhang, Tian Puthen-Veettil, Binesh; Wu, Lingfeng; Jia, Xuguang; Lin, Ziyun; Yang, Terry Chien-Jen; Conibeer, Gavin; Perez-Wurfl, Ivan

    2015-10-21

    We investigate the Capacitance-Voltage (CV) measurement to study the electrically active boron doping in Si nanocrystals (ncSi) embedded in SiO{sub 2}. The ncSi thin films with high resistivity (200–400 Ω cm) can be measured by using an inverted metal oxide semiconductor (MOS) structure (Al/ncSi (B)/SiO{sub 2}/Si). This device structure eliminates the complications from the effects of lateral current flow and the high sheet resistance in standard lateral MOS structures. The characteristic MOS CV curves observed are consistent with the effective p-type doping. The CV modeling method is presented and used to evaluate the electrically active doping concentration. We find that the highly boron doped ncSi films have electrically active doping of 10{sup 18}–10{sup 19 }cm{sup −3} despite their high resistivity. The saturation of doping at about 1.4 × 10{sup 19 }cm{sup −3} and the low doping efficiency less than 5% are observed and discussed. The calculated effective mobility is in the order of 10{sup −3} cm{sup 2}/V s, indicating strong impurity/defect scattering effect that hinders carriers transport.

  1. Ultra-large-scale syntheses of monodisperse nanocrystals

    NASA Astrophysics Data System (ADS)

    Park, Jongnam; An, Kwangjin; Hwang, Yosun; Park, Je-Geun; Noh, Han-Jin; Kim, Jae-Young; Park, Jae-Hoon; Hwang, Nong-Moon; Hyeon, Taeghwan

    2004-12-01

    The development of nanocrystals has been intensively pursued, not only for their fundamental scientific interest, but also for many technological applications. The synthesis of monodisperse nanocrystals (size variation <5%) is of key importance, because the properties of these nanocrystals depend strongly on their dimensions. For example, the colour sharpness of semiconductor nanocrystal-based optical devices is strongly dependent on the uniformity of the nanocrystals, and monodisperse magnetic nanocrystals are critical for the next-generation multi-terabit magnetic storage media. For these monodisperse nanocrystals to be used, an economical mass-production method needs to be developed. Unfortunately, however, in most syntheses reported so far, only sub-gram quantities of monodisperse nanocrystals were produced. Uniform-sized nanocrystals of CdSe (refs 10,11) and Au (refs 12,13) have been produced using colloidal chemical synthetic procedures. In addition, monodisperse magnetic nanocrystals such as Fe (refs 14,15), Co (refs 16-18), γ-Fe2O3 (refs 19,20), and Fe3O4 (refs 21,22) have been synthesized by using various synthetic methods. Here, we report on the ultra-large-scale synthesis of monodisperse nanocrystals using inexpensive and non-toxic metal salts as reactants. We were able to synthesize as much as 40 g of monodisperse nanocrystals in a single reaction, without a size-sorting process. Moreover, the particle size could be controlled simply by varying the experimental conditions. The current synthetic procedure is very general and nanocrystals of many transition metal oxides were successfully synthesized using a very similar procedure.

  2. Structural expansions for the ground state energy of a simple metal

    NASA Technical Reports Server (NTRS)

    Hammerberg, J.; Ashcroft, N. W.

    1973-01-01

    A structural expansion for the static ground state energy of a simple metal is derived. An approach based on single particle band structure which treats the electron gas as a non-linear dielectric is presented, along with a more general many particle analysis using finite temperature perturbation theory. The two methods are compared, and it is shown in detail how band-structure effects, Fermi surface distortions, and chemical potential shifts affect the total energy. These are of special interest in corrections to the total energy beyond third order in the electron ion interaction, and hence to systems where differences in energies for various crystal structures are exceptionally small. Preliminary calculations using these methods for the zero temperature thermodynamic functions of atomic hydrogen are reported.

  3. Ag/ZnO heterostructure nanocrystals: synthesis, characterization, and photocatalysis.

    PubMed

    Zheng, Yuanhui; Zheng, Lirong; Zhan, Yingying; Lin, Xingyi; Zheng, Qi; Wei, Kemei

    2007-08-20

    A high yield of the dimer-type heterostructure of Ag/ZnO nanocrystals with different Ag contents is successfully prepared through a simple solvothermal method in the absence of surfactants. The samples are characterized by X-ray diffraction, transmission electron microscopy, X-ray photoelectron spectroscopy, UV-vis spectroscopy, and IR spectroscopy. The results show that all samples are composed of metallic Ag and ZnO; Ag nanoparticles locate on the surface of ZnO nanorods; the binding energy of Ag 3d(5/2) for the Ag/ZnO sample with a Ag content of 5.0 atom % shifts remarkably to the lower binding energy compared with the corresponding value of pure metallic Ag because of the interaction between Ag and ZnO nanocrystals; the concentration of oxygen vacancy for the as-synthesized samples varies with the increasing Ag content, and the Ag/ZnO sample with a Ag content of 5.0 atom % has the largest density of oxygen vacancy. In addition, the relationship between their structure and photocatalytic property is investigated in detail. It is found that the photocatalytic property is closely related to its structure, such as heterostructure, oxygen defect, and crystallinity. The presence of metallic Ag nanoparticles and oxygen vacancy on the surface of ZnO nanorods promotes the separation of photogenerated electron-hole pairs and thus enhances the photocatalytic activity.

  4. Hydrogenation of 4-nitrophenol to 4-aminophenol at room temperature: Boosting palladium nanocrystals efficiency by coupling with copper via liquid phase pulsed laser ablation

    NASA Astrophysics Data System (ADS)

    Park, Hanbit; Reddy, D. Amaranatha; Kim, Yujin; Lee, Seunghee; Ma, Rory; Lim, Manho; Kim, Tae Kyu

    2017-04-01

    Ultra-dispersed bimetallic nanomaterials have attracted much attention in the hydrogenation of highly toxic aromatic nitro compounds to aromatic amines owing to their high stability, superior activity, reusability, and unique optical and electronic properties, as compared to monometalic nanocrystals. However, the lack of facile and economically controllable strategies of producing highly pure ultra-dispersed bimetallic nanocatalysts limits their practical industrial applications. Considering the above obstacles, we present a simple and effective strategy for the formation of bimetallic (PdCu) nanocrystals by liquid phase pulsed laser ablation using a bulk Pd metal plate submerged in CuCl2 solutions with different concentrations, in contrast to the complex and costly experimental methods used previously. The microstructural and optical properties of the synthesized nanocrystals indicate that the obtained bimetallic nanostructures are highly pure and monodispersed. Moreover, bimetallic PdCu nanostructures show a higher catalytic activity than monometallic Pd nanocrystals for the hydrogenation of 4-nitrophenol to 4-aminophenol at room temperature, also exhibiting high stability for up to four recycles. The mechanism of the enhanced catalytic activity and stability of bimetallic nanocrystals is discussed in detail. Finally, we believe that the presented design strategy and utilization of bimetallic nanocrystals for catalytic applications enables the development of novel bimetallic nanostructures by liquid phase pulsed laser ablation and their catalytic application for environmental remediation.

  5. A simple laser ablation ICPMS method for the determination of trace metals in a resin gel.

    PubMed

    Gao, Yue; Lehto, Niklas

    2012-04-15

    Trace metal analysis of DGT gels using laser ablation inductively coupled plasma (LA-ICP-MS) has traditionally been carried out by ablating single spots along a line to provide high resolution data on trace metal distributions on a resin gel. This work compares the performance of two different LA-ICPMS systems, one at Lancaster University, UK and another at VUB, Belgium, in terms of instrument sensitivity and limit of detection in the analysis of trace metals (Co, Ni, Cu, Zn, Cd, and Pb) bound by a DGT resin gel using SPR-IDA resin. No defocusing of the laser beam was necessary to prevent burning through the resin gel and the internal standardization became very simple by using (13)C, naturally present in the resin-gel, instead of impregnating a back-up layer with (115)In. Furthermore, this work also explores the option of analysing the spatial distribution of resin bound trace metals by means of ablating a continuous line between two points and considers the advantages of using this approach. The work found that the LODs assessed on blank samples for Cu and Pb are similar for both LA-ICPMS systems, while for Co, Ni and Zn they are lower for the one at VUB and for Cd for the other one at Lancaster. The work found that the laser ablation systems at the two laboratories allowed more precise control over laser power and spot size than previously reported. For the line scan, the optimum scan parameters were determined as: scan speed of 50 μm s(-1), output energy of 40% and repetition rate of 30 Hz. An acquisition time of 25 ms, resulted in a much lower resolution (10 μm) compared to the spot ablation (a crater size of 100 μm and also some space between craters) and a better sensitivity. The LODs using the line scan were found to be lower than those obtained by the spot ablation. However, for some of the metals the difference is rather small. This work suggests that the time and gas consumption achieved by using the line scan is about 30% lower than for the

  6. A simple scheme to determine potential aquatic metal toxicity from mining wastes

    USGS Publications Warehouse

    Wildeman, T.R.; Smith, K.S.; Ranville, J.F.

    2007-01-01

    A decision tree (mining waste decision tree) that uses simple physical and chemical tests has been developed to determine whether effluent from mine waste material poses a potential toxicity threat to the aquatic environment. For the chemical portion of the tree, leaching tests developed by the United States Geological Survey, the Colorado Division of Minerals and Geology (Denver, CO), and a modified 1311 toxicity characteristic leaching procedure (TCLP) test of the United States Environmental Protection Agency have been extensively used as a surrogate for readily available metals that can be released into the environment from mining wastes. To assist in the assessment, element concentration pattern graphs (ECPG) are produced that compare concentrations of selected groups of elements from the three leachates and any water associated with the mining waste. The MWDT makes a distinction between leachates or waters with pH less than or greater than 5. Generally, when the pH values are below 5, the ECPG of the solutions are quite similar, and potential aquatic toxicity from cationic metals, such as Pb, Cu, Zn, Cd, and Al, is assumed. Below pH 5, these metals are mostly dissolved, generally are not complexed with organic or inorganic ligands, and hence are more bioavailable. Furthermore, there is virtually no carbonate alkalinity at pH less than 5. All of these factors promote metal toxicity to aquatic organisms. On the other hand, when the pH value of the water or the leachates is above 5, the ECPG from the solutions are variable, and inferred aquatic toxicity depends on factors in addition to the metals released from the leaching tests. Hence, leachates and waters with pH above 5 warrant further examination of their chemical composition. Physical ranking criteria provide additional information, particularly in areas where waste piles exhibit similar chemical rankings. Rankings from physical and chemical criteria generally are not correlated. Examples of how this

  7. Simple preparation of aminothiourea-modified chitosan as corrosion inhibitor and heavy metal ion adsorbent.

    PubMed

    Li, Manlin; Xu, Juan; Li, Ronghua; Wang, Dongen; Li, Tianbao; Yuan, Maosen; Wang, Jinyi

    2014-03-01

    By a simple and convenient method of using formaldehyde as linkages, two new chitosan (CS) derivatives modified respectively with thiosemicarbazide (TSFCS) and thiocarbohydrazide (TCFCS) were synthesized. The new compounds were characterized and studied by Fourier transform infrared spectroscopy, elemental analysis, thermal gravity analysis and differential scanning calorimetry, and their surface morphologies were determined via scanning electron microscopy. These CS derivatives could form pH dependent gels. The behavior of 304 steel in 2% acetic acid containing different inhibitors or different concentrations of inhibitor had been studied by potentiodynamic polarization test. The preliminary results show that the new compound TCFCS can act as a mixed-type metal anticorrosion inhibitor in some extent; its inhibition efficiency is 92% when the concentration was 60 mg/L. The adsorption studies on a metal ion mixture aqueous solution show that two samples TSFCS and TCFCS can absorb As (V), Ni (II), Cu (II), Cd (II) and Pb (II) efficiently at pH 9 and 4.

  8. Development of simple high-resolution embedded printing for transparent metal grid conductors

    NASA Astrophysics Data System (ADS)

    Hokari, Ryohei; Kurihara, Kazuma; Takada, Naoki; Hiroshima, Hiroshi

    2017-08-01

    We developed a simple embedded printing method that is capable of forming high-resolution patterns for transparent metal grid conductors. The simple printing method involves embedding conductive ink in a groove structure formed by nanoimprinting. Since this printing utilizes capillary force, conductive ink easily fills groove structures with small widths of several microns to the submicron scale. An embedded pattern with a line width of 300 nm was printed. In addition, a high aspect ratio of 3.1 was achieved with a 1.6 μm embedded pattern. A prototype transparent conductive film was developed with excellent optical and electrical performances: a high transmittance of 82.7% and a low sheet resistance of 5.1 Ω/sq at a grid width of 3.0 μm and a grid pitch of 150 μm. The grid parameters can easily be changed by mold design during the nanoimprint process. The transparent conductive film (TCF) showed excellent bending resistance compared with indium tin oxide.

  9. Tunable mid IR plasmon in GZO nanocrystals.

    PubMed

    Hamza, M K; Bluet, J-M; Masenelli-Varlot, K; Canut, B; Boisron, O; Melinon, P; Masenelli, B

    2015-07-28

    Degenerate metal oxide nanoparticles are promising systems to expand the significant achievements of plasmonics into the infrared (IR) range. Among the possible candidates, Ga-doped ZnO nanocrystals are particularly suited for mid IR, considering their wide range of possible doping levels and thus of plasmon tuning. In the present work, we report on the tunable mid IR plasmon induced in degenerate Ga-doped ZnO nanocrystals. The nanocrystals are produced by a plasma expansion and exhibit unprotected surfaces. Tuning the Ga concentration allows tuning the localized surface plasmon resonance. Moreover, the plasmon resonance is characterized by a large damping. By comparing the plasmon of nanocrystal assemblies to that of nanoparticles dispersed in an alumina matrix, we investigate the possible origins of such damping. We demonstrate that it partially results from the self-organization of the naked particles and also from intrinsic inhomogeneity of dopants.

  10. Self-assembly of lead chalcogenide nanocrystals.

    PubMed

    Quan, Zewei; Valentin-Bromberg, Loriana; Loc, Welley Siu; Fang, Jiye

    2011-05-02

    This review focuses on recent developments in the self-assembly of lead chalcogenide nanocrystals into two- and three-dimensional superstructures. Self-assembly is categorized by the shapes of building blocks, including nanospheres, nanocubes, nano-octahedra, and nanostars. In the section on nanospheres, rapid assemblies of lead chalcogenide-based multicomponent nanocrystals with additional components, such as semiconductors, noble metals, and magnetic nanocrystals, are further highlighted. In situ self-assembly of lead chalcogenide nanocrystals into one-dimensional nanostructures at elevated temperatures is also covered. Each section of this paper highlights examples extracted from recent publications. Finally, relatively novel properties and applications arising from lead chalcogenide superlattices as typical examples are also discussed.

  11. Thermodynamic and Electronic Properties of Liquid Binary Alloys of Simple Metals: Charge-Transfer Effects.

    NASA Astrophysics Data System (ADS)

    Lai, San-Kiong

    It is demonstrated that low order pseudopotential perturbation theory is inadequate to determine the equilibrium atomic volumes even for simple liquid metals and their alloys in variational thermodynamic calculations. A high order perturbative correction is suggested and has subsequently been applied in the spirit of the model pseudopotential theory. A theoretical method is proposed to determine a model potential parameter (denoted by (mu)) using the calculated unmodified ((mu) = 0) Helmholtz free energy. Results of the applications to the (i) excess entropy and (ii) isothermal compressibility indicate that the parameter (mu) is insignificant for the liquid alkali metals, Zn and Mg but becomes more important for such heavy elements as In. Based on this conclusion the calculations for the liquid alkali binary alloys are carried out by setting (mu) = 0. We apply our obtained hard sphere diameters to calculate the concentration dependences of (i) the isothermal compressibility, (ii) the excess entropy of mixing and (iii) the enthalpy and free energy of mixing within the framework of the hard sphere theory. Then, the anomalies of the thermodynamic mixing properties for these alloys, as experimentally reported, are interpreted by considering valence-electron charge transfer effects. The alloy formfactors have also been applied to study the electronic properties. Before embarking on the calculation, we first check the high-order effects on the electronic density of states. They are found to be unimportant for those liquid metals for which (mu)(, )<(, )0.1. Then, we set (mu) = 0 and study the concentration dependences of the (i) electron density of states, (ii) electrical resistivity and thermopower and (iii) temperature coefficient of the resistivity for the alkali, Li-Na and Li-Mg alloys. It also emerges from these applications that charge transfer effects, which give rise to the partial localisation of the valence electrons on the electronegative ions, are

  12. Bright White Light Emission from Ultrasmall Cadmium Selenide Nanocrystals

    SciTech Connect

    Rosson, Teresa; Claiborne, Sarah; McBride, James; Stratton, Benjamin S; Rosenthal, Sandra

    2012-01-01

    A simple treatment method using formic acid has been found to increase the fluorescence quantum yield of ultrasmall white light-emitting CdSe nanocrystals from 8% to 45%. Brighter white-light emission occurs with other carboxylic acids as well, and the magnitude of the quantum yield enhancement is shown to be dependent on the alkyl chain length. Additionally, the nanocrystal luminescence remains enhanced relative to the untreated nanocrystals over several days. This brightened emission opens the possibility for even further quantum yield improvement and potential for use of these white-light nanocrystals in solid-state lighting applications.

  13. Bright white light emission from ultrasmall cadmium selenide nanocrystals.

    PubMed

    Rosson, Teresa E; Claiborne, Sarah M; McBride, James R; Stratton, Benjamin S; Rosenthal, Sandra J

    2012-05-16

    A simple treatment method using formic acid has been found to increase the fluorescence quantum yield of ultrasmall white light-emitting CdSe nanocrystals from 8% to 45%. Brighter white-light emission occurs with other carboxylic acids as well, and the magnitude of the quantum yield enhancement is shown to be dependent on the alkyl chain length. Additionally, the nanocrystal luminescence remains enhanced relative to the untreated nanocrystals over several days. This brightened emission opens the possibility for even further quantum yield improvement and potential for use of these white-light nanocrystals in solid-state lighting applications.

  14. Growth of platinum nanocrystals

    SciTech Connect

    2009-01-01

    Movie showing the growth of platinum nanocrystals in a liquid cell observed in situ using the JEOL 3010 TEM at the National Center for Electron Microscopy. This is the first ever-real time movie showing nucleation and growth by monomer attachment or by smaller nanocrystals coalescing to form larger nanocrystals. All the nanocrystals end up being roughly the same shape and size. http://newscenter.lbl.gov/feature-stories/2009/08/04/growth-spurts/

  15. Molecular mechanism of monodisperse colloidal tin-doped indium oxide nanocrystals by a hot-injection approach

    PubMed Central

    2013-01-01

    Molecular mechanisms and precursor conversion pathways associated with the reactions that generate colloidal nanocrystals are crucial for the development of rational synthetic protocols. In this study, Fourier transform infrared spectroscopy technique was employed to explore the molecular mechanism associated with the formation of tin-doped indium oxide (ITO) nanocrystals. We found that the reaction pathways of the indium precursor were not consistent with simple ligand replacements proposed in the literature. The resulting understanding inspired us to design a hot-injection approach to separate the ligand replacements of indium acetate and the aminolysis processes, generating quality ITO nanocrystals with decent size distributions. The hot-injection approach was readily applied to the synthesis of ITO nanocrystals with a broad range of tin doping. Structural, chemical, and optical analyses revealed effective doping of Sn4+ ions into the host lattices, leading to characteristic and tunable near-infrared surface plasmon resonance peaks. The size control of ITO nanocrystals by multiple hot-injections of metal precursors was also demonstrated. PMID:23547801

  16. Infrared colloidal lead chalcogenide nanocrystals: synthesis, properties, and photovoltaic applications.

    PubMed

    Fu, Huiying; Tsang, Sai-Wing

    2012-04-07

    Simple solution phase, catalyst-free synthetic approaches that offer monodispersed, well passivated, and non-aggregated colloidal semiconductor nanocrystals have presented many research opportunities not only for fundamental science but also for technological applications. The ability to tune the electrical and optical properties of semiconductor nanocrystals by manipulating the size and shape of the crystals during the colloidal synthesis provides potential benefits to a variety of applications including photovoltaic devices, light-emitting diodes, field effect transistors, biological imaging/labeling, and more. Recent advances in the synthesis and characterization of colloidal lead chalcogenide nanocrystals and the achievements in colloidal PbS or PbSe nanocrystals solar cells have demonstrated the promising application of infrared-emitting colloidal lead chalcogenide nanocrystals in photovoltaic devices. Here, we review recent progress in the synthesis and optical properties of colloidal lead chalcogenide nanocrystals. We focus in particular upon the size- and shape-controlled synthesis of PbS, PbSe, and PbTe nanocrystals by using different precursors and various stabilizing surfactants for the growth of the colloidal nanocrystals. We also summarize recent advancements in the field of colloidal nanocrystals solar cells based on colloidal PbS and PbSe nanocrystals. This journal is © The Royal Society of Chemistry 2012

  17. Shape control from thermodynamic growth conditions: the case of hcp ruthenium hourglass nanocrystals.

    PubMed

    Watt, John; Yu, Chenlong; Chang, Shery L Y; Cheong, Soshan; Tilley, Richard D

    2013-01-16

    Recent successes in forming different shaped face centered cubic (fcc) metal nanostructures has enabled a greater understanding of nanocrystal growth mechanisms. Here we extend this understanding to the synthesis of hexagonally close packed (hcp) metal nanostructures, to form uniquely faceted ruthenium nanocrystals with a well-defined hourglass shape. The hourglass nanocrystals are formed in a three-step thermodynamic growth process with dodecylamine as the organic stabilizer. The hourglass nanocrystals are then shown to readily self-assemble to form a new type of nanocrystal superlattice.

  18. General synthesis of noble metal (Au, Ag, Pd, Pt) nanocrystal modified MoS2 nanosheets and the enhanced catalytic activity of Pd-MoS2 for methanol oxidation.

    PubMed

    Yuwen, Lihui; Xu, Fei; Xue, Bing; Luo, Zhimin; Zhang, Qi; Bao, Biqing; Su, Shao; Weng, Lixing; Huang, Wei; Wang, Lianhui

    2014-06-07

    A general and facile method for water-dispersed noble metal (Au, Ag, Pd, Pt) nanocrystal modified MoS2 nanosheets (NM-MoS2 NSs) has been developed. By using sodium carboxymethyl cellulose as a stabilizer, well-dispersed NM-MoS2 NSs with homogeneously deposited noble metal nanocrystals (NM NCs) can be synthesized in aqueous solutions. Due to the transition from the semiconducting 2H phase to the metallic 1T phase, the chemically exfoliated MoS2 (ce-MoS2) NSs have improved electrochemical activity. The partially metallic nature of the ce-MoS2 NSs and the catalytic activity of the NM NCs synergistically make NM-MoS2 NSs a potential electrochemical catalyst. For the first time, Pd-MoS2 NSs were used as an electrocatalyst for methanol oxidation in alkaline media. The results showed that Pd-MoS2 NSs have enhanced catalytic activity with 2.8-fold anodic peak current mass density compared to a commercial Pd/C catalyst, suggesting potential for application in direct methanol fuel cells (DMFCs).

  19. Influence of Nano-Crystal Metals on Texture and Biological Properties of Water Soluble Polysaccharides of Medicinal Plants

    NASA Astrophysics Data System (ADS)

    Churilov, G.; Ivanycheva, J.; Kiryshin, V.

    2015-11-01

    When treating the plants seeds with nano-materials there are some quality and quantity changes of polysaccharides, the molecular mass increase and monosaccharides change that leads to the increase of physiological and pharmacological activity of carbohydrates got from medicinal plants. We have got water soluble polysaccharides and nano-metals combinations containing 0.000165-0.000017 mg/dm3 of the metal. In a case of induced anemia the blood composition has practically restored on the 10th day of the treatment with nanocomposites. The use of pectin polysaccharides (that are attributed to modifiers of biological respond) to get nano-structured materials seems to be actual relative to their physiological activity (radio nuclides persorption, heavy metals ions, bacteria cells and their toxins; lipids metabolism normalization; bowels secreting and motor functions activation and modulation of the endocrine system.

  20. All-Inorganic Germanium Nanocrystal Films by Cationic Ligand Exchange.

    PubMed

    Wheeler, Lance M; Nichols, Asa W; Chernomordik, Boris D; Anderson, Nicholas C; Beard, Matthew C; Neale, Nathan R

    2016-03-09

    We introduce a new paradigm for group IV nanocrystal surface chemistry based on room temperature surface activation that enables ionic ligand exchange. Germanium nanocrystals synthesized in a gas-phase plasma reactor are functionalized with labile, cationic alkylammonium ligands rather than with traditional covalently bound groups. We employ Fourier transform infrared and (1)H nuclear magnetic resonance spectroscopies to demonstrate the alkylammonium ligands are freely exchanged on the germanium nanocrystal surface with a variety of cationic ligands, including short inorganic ligands such as ammonium and alkali metal cations. This ionic ligand exchange chemistry is used to demonstrate enhanced transport in germanium nanocrystal films following ligand exchange as well as the first photovoltaic device based on an all-inorganic germanium nanocrystal absorber layer cast from solution. This new ligand chemistry should accelerate progress in utilizing germanium and other group IV nanocrystals for optoelectronic applications.

  1. All-inorganic Germanium nanocrystal films by cationic ligand exchange

    DOE PAGES

    Wheeler, Lance M.; Nichols, Asa W.; Chernomordik, Boris D.; ...

    2016-01-21

    In this study, we introduce a new paradigm for group IV nanocrystal surface chemistry based on room temperature surface activation that enables ionic ligand exchange. Germanium nanocrystals synthesized in a gas-phase plasma reactor are functionalized with labile, cationic alkylammonium ligands rather than with traditional covalently bound groups. We employ Fourier transform infrared and 1H nuclear magnetic resonance spectroscopies to demonstrate the alkylammonium ligands are freely exchanged on the germanium nanocrystal surface with a variety of cationic ligands, including short inorganic ligands such as ammonium and alkali metal cations. This ionic ligand exchange chemistry is used to demonstrate enhanced transport inmore » germanium nanocrystal films following ligand exchange as well as the first photovoltaic device based on an all-inorganic germanium nanocrystal absorber layer cast from solution. This new ligand chemistry should accelerate progress in utilizing germanium and other group IV nanocrystals for optoelectronic applications.« less

  2. Pyrite Nanocrystal Solar Cells: Promising, or Fool's Gold?

    PubMed

    Steinhagen, Chet; Harvey, Taylor B; Stolle, C Jackson; Harris, Justin; Korgel, Brian A

    2012-09-06

    Pyrite-phase iron sulfide (FeS2) nanocrystals were synthesized to form solvent-based dispersions, or "solar paint," to fabricate photovoltaic devices (PVs). Nanocrystals were sprayed onto substrates as absorber layers in devices with several different architectures, including Schottky barrier, heterojunction, and organic/inorganic hybrid architectures, to explore their viability as a PV material. None of the devices exhibited PV response. XRD and Raman spectroscopy confirmed the pyrite composition and phase purity of the nanocrystals. The electrical conductivity of the nanocrystal films was about 4 to 5 S/cm, more typical of metal nanocrystal films than semiconductor nanocrystal films, and the lack of PV response appears to derive from the highly conductive surface-related defects in pyrite that have been proposed.

  3. All-inorganic Germanium nanocrystal films by cationic ligand exchange

    SciTech Connect

    Wheeler, Lance M.; Nichols, Asa W.; Chernomordik, Boris D.; Anderson, Nicholas C.; Beard, Matthew C.; Neale, Nathan R.

    2016-01-21

    In this study, we introduce a new paradigm for group IV nanocrystal surface chemistry based on room temperature surface activation that enables ionic ligand exchange. Germanium nanocrystals synthesized in a gas-phase plasma reactor are functionalized with labile, cationic alkylammonium ligands rather than with traditional covalently bound groups. We employ Fourier transform infrared and 1H nuclear magnetic resonance spectroscopies to demonstrate the alkylammonium ligands are freely exchanged on the germanium nanocrystal surface with a variety of cationic ligands, including short inorganic ligands such as ammonium and alkali metal cations. This ionic ligand exchange chemistry is used to demonstrate enhanced transport in germanium nanocrystal films following ligand exchange as well as the first photovoltaic device based on an all-inorganic germanium nanocrystal absorber layer cast from solution. This new ligand chemistry should accelerate progress in utilizing germanium and other group IV nanocrystals for optoelectronic applications.

  4. 3D assembly of semiconductor and metal nanocrystals: hybrid CdTe/Au structures with controlled content.

    PubMed

    Lesnyak, Vladimir; Wolf, André; Dubavik, Aliaksei; Borchardt, Lars; Voitekhovich, Sergei V; Gaponik, Nikolai; Kaskel, Stefan; Eychmüller, Alexander

    2011-08-31

    A 3D metal ion assisted assembly of nanoparticles has been developed. The approach relies on the efficient complexation of cadmium ions and 5-mercaptomethyltetrazole employed as the stabilizer of both colloidal CdTe and Au nanoparticles. It enables in a facile way the formation of hybrid metal-semiconductor 3D structures with controllable and tunable composition in aqueous media. By means of critical point drying, these assemblies form highly porous aerogels. The hybrid architectures obtained are characterized by electron microscopy, nitrogen adsorption, and optical spectroscopy methods.

  5. Spectral and photometric evolution of simple stellar populations at various metallicities

    NASA Astrophysics Data System (ADS)

    Schulz, J.; Fritze-v. Alvensleben, U.; Möller, C. S.; Fricke, K. J.

    2002-09-01

    A new set of evolutionary synthesis spectra are presented for Simple Stellar Populations (SSPs) covering ranges in metallicity from 0.02 <= Z/Zsun <= 2.5 and ages from 4x 106 yr <= t <= 16 Gyr. They are based on the most recent isochrones from the Padova group that extend earlier models by the inclusion of the thermal pulsing AGB phase for stars in the mass range 2 Msun <= m <= 7 Msun in accordance with the fuel consumption theorem. We show that with respect to earlier models, inclusion of the TP-AGB phase leads to significant changes in the (V-I) and (V-K) colors of SSPs in the age range from 108 to 109 yr. Using model atmosphere spectra from Lejeune et al. (\\cite{lej2}, \\cite{lej}), we calculate the spectral evolution of single burst populations of various metallicities covering the wavelength range from 90 Å through 160 mu m. Isochrone spectra are convolved with filter response functions to describe the time evolution of luminosities and colors in Johnson, Thuan & Gunn, Koo, HST, Washington and Strömgren filters. The models and their results are not only intended for use in the interpretation of star clusters but also for combination with any kind of dynamical galaxy formation and/or evolution model that contains a star formation criterion. Moreover, the evolution of these single burst single metallicity stellar populations is readily folded with any kind of star formation - and eventually chemical enrichment - history to describe the evolutionary spectral synthesis of composite stellar populations like galaxies of any type with continuous or discontinuous star formation. For these latter purposes we also present the time evolution of ejection rates for gas and metals for two different Initial Mass Functions (IMFs) as well as cosmological and evolutionary corrections for all the filters as a function of redshift for 0 <= z <= 5 and two different cosmologies. Extensive data files are provided in the electronic version, at CDS, and at our above www-address.

  6. Numerical model of a single nanocrystal devoted to the study of disordered nanocrystal floating gates of new flash memories

    NASA Astrophysics Data System (ADS)

    Leroy, Yann; Armeanu, Dumitru; Cordan, Anne-Sophie

    2011-05-01

    The improvement of our model concerning a single nanocrystal that belongs to a nanocrystal floating gate of a flash memory is presented. In order to extend the gate voltage range applicability of the model, the 3D continuum of states of either metallic or semiconducting electrodes is discretized into 2D subbands. Such an approach gives precise information about the mechanisms behind the charging or release processes of the nanocrystal. Then, the self-energy and screening effects of an electron within the nanocrystal are evaluated and introduced in the model. This enables a better determination of the operating point of the nanocrystal memory. The impact of those improvements on the charging or release time of the nanocrystal is discussed.

  7. One-pot synthesis of CuInS2 nanocrystals using different anions to engineer their morphology and crystal phase.

    PubMed

    Tang, Aiwei; Hu, Zunlan; Yin, Zhe; Ye, Haihang; Yang, Chunhe; Teng, Feng

    2015-05-21

    A simple one-pot colloidal method has been described to engineer ternary CuInS2 nanocrystals with different crystal phases and morphologies, in which dodecanethiol is chosen as the sulfur source and the capping ligands. By a careful choice of the anions in the metal precursors and manipulation of the reaction conditions including the reactant molar ratios and the reaction temperature, CuInS2 nanocrystals with chalcopyrite, zincblende and wurtzite phases have been successfully synthesized. The type of anion in the metal precursors has been found to be essential for determining the crystal phase and morphology of the as-obtained CuInS2 nanocrystals. In particular, the presence of Cl(-) ions plays an important role in the formation of CuInS2 nanoplates with a wurtzite-zincblende polytypism structure. In addition, the molar ratios of Cu to In precursors have a significant effect on the crystal phase and morphology, and the intermediate Cu2S-CuInS2 heteronanostructures are formed which are critical for the anisotropic growth of CuInS2 nanocrystals. Furthermore, the optical absorption results of the as-obtained CuInS2 nanocrystals exhibit a strong dependence on the crystal phase and size.

  8. Surface chemical modification of nanocrystals

    DOEpatents

    Helms, Brett Anthony; Milliron, Delia Jane; Rosen, Evelyn Louise; Buonsanti, Raffaella; Llordes, Anna

    2017-03-14

    Nanocrystals comprising organic ligands at surfaces of the plurality of nanocrystals are provided. The organic ligands are removed from the surfaces of the nanocrystals using a solution comprising a trialkyloxonium salt in a polar aprotic solvent. The removal of the organic ligands causes the nanocrystals to become naked nanocrystals with cationic surfaces.

  9. Simple hand-held metal detectors are an effective means of detecting cardiac pacemakers in the deceased prior to cremation.

    PubMed

    Stone, Jason Lyle; Williams, John; Fearn, Lesley

    2010-05-01

    The hazard of undetected cardiac pacemakers exploding in crematoria is well described. This short report describes the use of an affordable hand-held metal detector to detect cardiac pacemakers. Over the course of a year, the metal detector located 100% of cardiac pacemakers in a district general hospital mortuary. A simple model using pigskin and fat is also used to demonstrate the effectiveness in vitro. Commercially purchased hand-held metal detectors should be used in all mortuaries responsible for detection and removal of cardiac pacemakers prior to cremation.

  10. Green and scalable production of colloidal perovskite nanocrystals and transparent sols by a controlled self-collection process.

    PubMed

    Liu, Shuangyi; Huang, Limin; Li, Wanlu; Liu, Xiaohua; Jing, Shui; Li, Jackie; O'Brien, Stephen

    2015-07-21

    Colloidal perovskite oxide nanocrystals have attracted a great deal of interest owing to the ability to tune physical properties by virtue of the nanoscale, and generate thin film structures under mild chemical conditions, relying on self-assembly or heterogeneous mixing. This is particularly true for ferroelectric/dielectric perovskite oxide materials, for which device applications cover piezoelectrics, MEMs, memory, gate dielectrics and energy storage. The synthesis of complex oxide nanocrystals, however, continues to present issues pertaining to quality, yield, % crystallinity, purity and may also suffer from tedious separation and purification processes, which are disadvantageous to scaling production. We report a simple, green and scalable "self-collection" growth method that produces uniform and aggregate-free colloidal perovskite oxide nanocrystals including BaTiO3 (BT), Ba(x)Sr(1-x)TiO3 (BST) and quaternary oxide BaSrTiHfO3 (BSTH) in high crystallinity and high purity. The synthesis approach is solution processed, based on the sol-gel transformation of metal alkoxides in alcohol solvents with controlled or stoichiometric amounts of water and in the stark absence of surfactants and stabilizers, providing pure colloidal nanocrystals in a remarkably low temperature range (15 °C-55 °C). Under a static condition, the nanoscale hydrolysis of the metal alkoxides accomplishes a complete transformation to fully crystallized single domain perovskite nanocrystals with a passivated surface layer of hydroxyl/alkyl groups, such that the as-synthesized nanocrystals can exist in the form of super-stable and transparent sol, or self-accumulate to form a highly crystalline solid gel monolith of nearly 100% yield for easy separation/purification. The process produces high purity ligand-free nanocrystals excellent dispersibility in polar solvents, with no impurity remaining in the mother solution other than trace alcohol byproducts (such as isopropanol). The afforded stable

  11. Process for making surfactant capped nanocrystals

    DOEpatents

    Alivisatos, A Paul; Rockenberger, Joerg

    2002-01-01

    Disclosed is a process for making surfactant capped nanocrystals of transition metal oxides. The process comprises reacting a metal cupferron complex of the formula M Cup, wherein M is a transition metal, and Cup is a cupferron, with a coordinating surfactant, the reaction being conducted at a temperature ranging from about 250 to about 300 C., for a period of time sufficient to complete the reaction.

  12. One-step facile synthesis of noble metal nanocrystals with tunable morphology in a nematic liquid crystalline medium

    SciTech Connect

    Dan, Kaustabh; Satpati, Biswarup; Datta, Alokmay

    2016-05-23

    The present study describes in-situ synthesis of noble metal nano structures (MNCs) (Au and Ag) within a nematic liquid crystalline medium MBBA [N-(4-methoxybenzylidene)-4-butylaniline] without using any seed mediated growth protocol or without using any external stabilizing or reducing agent. Detailed Transmission Electron Microscopy (TEM) study indicates that apart from Kinetic based mechanism, the thermodynamical parameters also influence greatly the morphological evolution of these MNCs. The MNCs are of diverse shapes including nano prisms, hexagons, urchins, cubes, and rods which depend on the time of reaction and the choice of nanoparticle precursor.

  13. One-step facile synthesis of noble metal nanocrystals with tunable morphology in a nematic liquid crystalline medium

    NASA Astrophysics Data System (ADS)

    Dan, Kaustabh; Satpati, Biswarup; Datta, Alokmay

    2016-05-01

    The present study describes in-situ synthesis of noble metal nano structures (MNCs) (Au and Ag) within a nematic liquid crystalline medium MBBA [N-(4-methoxybenzylidene)-4-butylaniline] without using any seed mediated growth protocol or without using any external stabilizing or reducing agent. Detailed Transmission Electron Microscopy (TEM) study indicates that apart from Kinetic based mechanism, the thermodynamical parameters also influence greatly the morphological evolution of these MNCs. The MNCs are of diverse shapes including nano prisms, hexagons, urchins, cubes, and rods which depend on the time of reaction and the choice of nanoparticle precursor.

  14. Formation of a new archetypal Metal-Organic Framework from a simple monatomic liquid

    SciTech Connect

    Metere, Alfredo Oleynikov, Peter; Dzugutov, Mikhail; O’Keeffe, Michael

    2014-12-21

    We report a molecular-dynamics simulation of a single-component system of particles interacting via a spherically symmetric potential that is found to form, upon cooling from a liquid state, a low-density porous crystalline phase. Its structure analysis demonstrates that the crystal can be described by a net with a topology that belongs to the class of topologies characteristic of the Metal-Organic Frameworks (MOFs). The observed net is new, and it is now included in the Reticular Chemistry Structure Resource database. The observation that a net topology characteristic of MOF crystals, which are known to be formed by a coordination-driven self-assembly process, can be reproduced by a thermodynamically stable configuration of a simple single-component system of particles opens a possibility of using these models in studies of MOF nets. It also indicates that structures with MOF topology, as well as other low-density porous crystalline structures can possibly be produced in colloidal systems of spherical particles, with an appropriate tuning of interparticle interaction.

  15. Application of metal hydride paper to simple pressure generator for use in soft actuator systems.

    PubMed

    Ino, Shuichi; Sakaki, Kouji; Hosono, Minako; Doi, Kouki; Shimada, Shigenobu; Chikai, Manabu

    2015-01-01

    Metal hydride (MH) actuators have a simple structure and a number of features that make them attractive for use in rehabilitation engineering and assistive technology. The MH actuator provides a high power-to-weight ratio, high-strain actuation, human-compatible softness, and noiseless operation, while being environmentally benign. On the other hand, there remain technical challenges to be overcome to improve the MH actuator regarding its speed of operation and energy efficiency, given the low heat conductivity of the MH powder that is used as the pressure generator for soft actuation. To overcome the issues of low heat conductivity and the handling of MH powder, we developed an MH paper, which is a special paper incorporating MH powder and carbon fiber, for use as a new pressure-generating element for a soft MH actuator system. In addition, the basic properties and structure of the proposed MH paper were investigated through scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDX), and several thermodynamic experiments. The results of these experiments showed that the hydrogen absorption and desorption rates of the MH paper were significantly higher than those of the MH powder around room temperature.

  16. Formation of a new archetypal Metal-Organic Framework from a simple monatomic liquid.

    PubMed

    Metere, Alfredo; Oleynikov, Peter; Dzugutov, Mikhail; O'Keeffe, Michael

    2014-12-21

    We report a molecular-dynamics simulation of a single-component system of particles interacting via a spherically symmetric potential that is found to form, upon cooling from a liquid state, a low-density porous crystalline phase. Its structure analysis demonstrates that the crystal can be described by a net with a topology that belongs to the class of topologies characteristic of the Metal-Organic Frameworks (MOFs). The observed net is new, and it is now included in the Reticular Chemistry Structure Resource database. The observation that a net topology characteristic of MOF crystals, which are known to be formed by a coordination-driven self-assembly process, can be reproduced by a thermodynamically stable configuration of a simple single-component system of particles opens a possibility of using these models in studies of MOF nets. It also indicates that structures with MOF topology, as well as other low-density porous crystalline structures can possibly be produced in colloidal systems of spherical particles, with an appropriate tuning of interparticle interaction.

  17. Formation of a new archetypal Metal-Organic Framework from a simple monatomic liquid

    NASA Astrophysics Data System (ADS)

    Metere, Alfredo; Oleynikov, Peter; Dzugutov, Mikhail; O'Keeffe, Michael

    2014-12-01

    We report a molecular-dynamics simulation of a single-component system of particles interacting via a spherically symmetric potential that is found to form, upon cooling from a liquid state, a low-density porous crystalline phase. Its structure analysis demonstrates that the crystal can be described by a net with a topology that belongs to the class of topologies characteristic of the Metal-Organic Frameworks (MOFs). The observed net is new, and it is now included in the Reticular Chemistry Structure Resource database. The observation that a net topology characteristic of MOF crystals, which are known to be formed by a coordination-driven self-assembly process, can be reproduced by a thermodynamically stable configuration of a simple single-component system of particles opens a possibility of using these models in studies of MOF nets. It also indicates that structures with MOF topology, as well as other low-density porous crystalline structures can possibly be produced in colloidal systems of spherical particles, with an appropriate tuning of interparticle interaction.

  18. Quantitative tunneling spectroscopy of nanocrystals

    SciTech Connect

    First, Phillip N; Whetten, Robert L; Schaaff, T Gregory

    2007-05-25

    The proposed goals of this collaborative work were to systematically characterize the electronic structure and dynamics of 3-dimensional metal and semiconducting nanocrystals using scanning tunneling microscopy/spectroscopy (STM/STS) and ballistic electron emission spectroscopy (BEES). This report describes progress in the spectroscopic work and in the development of methods for creating and characterizing gold nanocrystals. During the grant period, substantial effort also was devoted to the development of epitaxial graphene (EG), a very promising materials system with outstanding potential for nanometer-scale ballistic and coherent devices ("graphene" refers to one atomic layer of graphitic, sp2 -bonded carbon atoms [or more loosely, few layers]). Funding from this DOE grant was critical for the initial development of epitaxial graphene for nanoelectronics

  19. Colloidal inorganic nanocrystals: Nucleation, growth and biological applications

    NASA Astrophysics Data System (ADS)

    Lynch, Jared James

    Colloidal inorganic nanocrystals are a class of material whose size ranges from a few nanometers to a hundred nanometers in dimension. These nanocrystals have size dependent properties that differ significantly from the bulk material counterparts. Due to their unique physical properties colloidal inorganic nanocrystals have several promising applications in a diverse range of areas, such as biomedical diagnosis, catalysis, plasmonics, high-density data storage and solar energy conversion. This dissertation presents the study of the formation of iron oxide nanocrystals under the influence of solvent and Ar gas bubbles, the phase transfer of metal oxide nanocrystals into water using inorganic ions, and the doping of semiconductor CdS/ZnS core/shell nanocrystals with copper and silver ions. First, the formation of iron oxide nanocrystals is investigated in the presence of boiling solvent or Ar bubbles. Using a non-injection based synthesis method, the thermal decomposition of iron oleate was studied under various reaction conditions, and the role of the bubbles on the nucleation and growth of iron oxide nanocrystals was determined. Kinetics studies were used to elucidate how latent heat transfer from the bubbles allows for "active monomers" to form preferentially from exothermic reactions taking place during nucleation. General insights into colloidal inorganic nanocrystal formation are discussed. Second, a non-injection based synthesis for CdS/ZnS core/shell nanocrystals is used to make high quality semiconductor particles which are intentionally doped with Cu or Ag ions. The Ag ions effect on the optical properties of the CdS/ZnS nanocrystals is investigated. The absorption and fluorescence of the samples is measured as a function of time and temperature. Proposed mechanisms for the observations are given and thoroughly discussed. Comparisons between previous results for Cu doped CdS/ZnS nanocrystals are also made to further understand how doping of semiconductor

  20. Simple and fast fabrication of superhydrophobic metal wire mesh for efficiently gravity-driven oil/water separation.

    PubMed

    Song, Botao

    2016-12-15

    Superhydrophobic metal wire mesh (SMWM) has frequently been applied for the selective and efficient separation of oil/water mixture due to its porous structure and special wettability. However, current methods for the modification of metal wire mesh to be superhydrophobic suffered from problems with respect to complex experimental procedures or time-consuming process. In this study, a very simple, time-saving and single-step electrospray method was proposed to fabricate SMWM and the whole procedure required about only 2min. The morphology, surface composition and wettability of the SMWM were all evaluated, and the oil/water separation ability was further investigated. In addition, a commercial available sponge covered with SMWM was fabricated as an oil adsorbent for the purpose of oil recovery. This study demonstrated a convenient and fast method to modify the metal wire mesh to be superhydrophobic and such simple method might find practical applications in the large-scale removal of oils.

  1. Plasma-produced nanocrystals enable new insights in semiconductor physics

    NASA Astrophysics Data System (ADS)

    Greenberg, Benjamin; Robinson, Zachary; Gorynski, Claudia; Voigt, Bryan; Francis, Lorraine; Aydil, Eray; Kortshagen, Uwe

    2016-09-01

    The transition from semiconducting (insulating) to metallic behavior is a central problem of semiconductor physics. In bulk semiconductors, this insulator-to-metal transition is described by the well-known Mott criterion. However, in films of semiconductor nanocrystals the Mott criterion fails completely. Recent progress in the nonthermal plasma synthesis of films of highly doped silicon nanocrystals has contributed to the development of a new theory that presents a consistent analog to the Mott criterion for nanocrystal materials. Here, we study films of nonthermal plasma produced zinc oxide (ZnO) nanocrystals to in detail investigate the insulator-to-metal transition. We produce high-purity monodisperse ZnO nanocrystals in a nonthermal plasma and form dense films via supersonic impact deposition. We then modulate the free carrier density, n, and nanocrystal contact facet radius, ρ, via xenon-flashlamp intense pulsed light annealing, which induces necking between the clean surfaces of adjacent nanocrystals. Preliminary electrical measurements indicate that the electron mobility can be finely tuned and that the films cross the insulator-to-metal transition for sufficiently high n and ρ. This work was supported by the MRSEC program of the U.S. National Science Foundation under grant DMR-1420013.

  2. Fabrication and electronic transport studies of single nanocrystal systems

    SciTech Connect

    Klein, David Louis

    1997-05-01

    Semiconductor and metallic nanocrystals exhibit interesting electronic transport behavior as a result of electrostatic and quantum mechanical confinement effects. These effects can be studied to learn about the nature of electronic states in these systems. This thesis describes several techniques for the electronic study of nanocrystals. The primary focus is the development of novel methods to attach leads to prefabricated nanocrystals. This is because, while nanocrystals can be readily synthesized from a variety of materials with excellent size control, means to make electrical contact to these nanocrystals are limited. The first approach that will be described uses scanning probe microscopy to first image and then electrically probe surfaces. It is found that electronic investigations of nanocrystals by this technique are complicated by tip-sample interactions and environmental factors such as salvation and capillary forces. Next, an atomic force microscope technique for the catalytic patterning of the surface of a self assembled monolayer is described. In principle, this nano-fabrication technique can be used to create electronic devices which are based upon complex arrangements of nanocrystals. Finally, the fabrication and electrical characterization of a nanocrystal-based single electron transistor is presented. This device is fabricated using a hybrid scheme which combines electron beam lithography and wet chemistry to bind single nanocrystals in tunneling contact between closely spaced metallic leads. In these devices, both Au and CdSe nanocrystals show Coulomb blockade effects with characteristic energies of several tens of meV. Additional structure is seen the transport behavior of CdSe nanocrystals as a result of its electronic structure.

  3. Germanium nanocrystals: Synthesis, characterization, and applications

    NASA Astrophysics Data System (ADS)

    Gerung, Henry

    The aim of this work was to demonstrate a simple synthesis route of Ge nanostructures (nanoparticles and nanowires), to characterize the physical and optical properties of Ge nanocrystal, and to demonstrate their biological and optoelectronics applications. The appropriate organometallic Ge 2+ precursors for the synthesis of Ge nanocrystals were identified. These precursors were used to develop a simple route that produced high quality Ge nanocrystals in high yield under mild conditions without using potentially contaminating catalysts and forming byproducts. The particle size was varied from 1 to 10 nm, depending on the reaction parameters. The relatively low-temperature, low-pressure nanocrystal synthesis condition allowed the use of organic solvents and surfactants. We also demonstrated morphological control over Ge nanocrystals via Ge2+ precursor reactivity modification. During synthesis, the surfactants passivate the nanocrystal surface and minimize surface oxidation. This synthesis method allowed optical characterization of Ge nanocrystals decoupled from contamination and oxidation. When excited with photons, Ge nanoparticles exhibit quantum confinement effect in both infrared and ultraviolet regions, as well as optical nonlinearity by the presence of two-photon absorption. These free-standing Ge nanocrystals could be further become integral elements in various optoelectronic devices. Herein, the production of water-soluble Ge nanoparticles was demonstrated as a proof of the effectiveness of our synthesis method. Addition of secondary layer surfactants such as cationic cetyltrimethylammonium bromide (CTAB) or functionalized polyethylene glycol (PEG), transforms the Ge nanoparticles to become water-soluble. The biocompatible, functionalized, water-soluble Ge nanoparticles were bound to extracellular receptors and also incorporated into the cells as a proof-of-concept demonstration for potential biomarker applications. In expectation of forming a 3-D

  4. A simple route utilizing surfactant-assisted templating sol-gel process for synthesis of mesoporous Dy2O3 nanocrystal.

    PubMed

    Sreethawong, Thammanoon; Chavadej, Sumaeth; Ngamsinlapasathian, Supachai; Yoshikawa, Susumu

    2006-08-01

    A simple route of combined sol-gel process with surfactant-assisted templating technique was successfully employed for the first time to synthesize nanocrystalline mesoporous Dy(2)O(3) with narrow monomodal pore size distribution under mild conditions. The nanocrystalline Dy(2)O(3) with monomodal mesoporous characteristic was ultimately achieved by controlling the hydrolysis and condensation steps of dysprosium n-butoxide modified with acetylacetone in the presence of laurylamine hydrochloride surfactant aqueous solution. The synthesized material was methodically characterized by thermogravimetry and differential thermal analysis (TG-DTA), X-ray diffraction (XRD), scanning electron microscopy (SEM), high resolution transmission electron microscopy (HRTEM), selected-area electron diffraction (SAED), N(2) adsorption-desorption, Brunauer-Emmett-Teller (BET) surface area analysis, and Barrett-Joyner-Halenda (BJH) pore size distribution analysis. The particle size of the synthesized Dy(2)O(3) in nanosized range obtained from the SEM and HRTEM micrographs was in good accordance with the crystallite size estimated from the XRD result. The N(2) adsorption-desorption result exhibited hysteresis pattern with single loop, indicating the existence of monomodal mesopore. The extremely narrow pore size distribution with mean pore diameter in the mesopore region of the synthesized Dy(2)O(3) was also confirmed by the BJH result.

  5. Interactions and Assemblies of Polymeric Materials and Colloidal Nanocrystals

    NASA Astrophysics Data System (ADS)

    Williams, Teresa Elaine

    Our need to reduce global energy use is well known and without question, not just from an economic standpoint but also to decrease human impact on climate change. Emerging advances in this area result from the ability to tailor-make materials and energy-saving devices using solution-phase chemistry and deposition techniques. Colloidally synthesized nanocrystals, with their tunable size, shape, and composition, and unusual optical and electronic properties, are leading candidates in these efforts. Because of recent advances in colloidal chemistries, the inventory of monodisperse nanocrystals has expanded to now include metals, semiconductors, magnetic materials, and dielectric materials. For a variety of applications, an active layer composed of a thin film of randomly close-packed nanocrystals is not ideal for optimized device performance; here, the ability to arrange these nano building units into mesoporous (2 nm < d < 50 nm) architectures is highly desirable. Given this, the goal of the work in this dissertation is to determine and understand the design rules that govern the interactions between ligand-stripped nanocrystals and polymeric materials, leading to their hierarchical assembly into colloidal nanocrystal frameworks. I also include the development of quantitative, and novel, characterization techniques, and the application of such frameworks in energy efficiency devices such as electrochromic windows. Understanding the local environment of nanocrystal surfaces and their interaction with surrounding media is vital to their controlled assembly into higher-order structures. Though work has continued in this field for over a decade, researchers have yet to provide a simple and straightforward procedure to scale across nanoscale material systems and applications allowing for synthetic and structural tunability and quantitative characterization. In this dissertation, I have synthesized a new class of amphiphilic block copolymer architecture-directing agents

  6. Encapsulation of redox polysulphides via chemical interaction with nitrogen atoms in the organic linkers of metal-organic framework nanocrystals

    PubMed Central

    Park, Jung Hyo; Choi, Kyung Min; Lee, Dong Ki; Moon, Byeong Cheul; Shin, Sang Rim; Song, Min-Kyu; Kang, Jeung Ku

    2016-01-01

    Lithium polysulphides generated during discharge in the cathode of a lithium-sulphur redox cell are important, but their dissolution into the electrolyte from the cathode during each redox cycle leads to a shortened cycle life. Herein, we use in situ spectroelectrochemical measurements to demonstrate that sp2 nitrogen atoms in the organic linkers of nanocrystalline metal-organic framework-867 (nMOF-867) are able to encapsulate lithium polysulphides inside the microcages of nMOF-867, thus helping to prevent their dissolution into the electrolyte during discharge/charge cycles. This encapsulation mechanism of lithiated/delithiated polysulphides was further confirmed by observations of shifted FTIR spectra for the C = N and C-N bonds, the XPS spectra for the Li-N bonds from nMOF-867, and a visualization method, demonstrating that nMOF-867 prevents lithium polysulphides from being dissolved in the electrolyte. Indeed, a cathode fabricated using nMOF-867 exhibited excellent capacity retention over a long cycle life of 500 discharge/charge cycles, with a capacity loss of approximately 0.027% per cycle from a discharge capacity of 788 mAh/g at a high current rate of 835 mA/g. PMID:27149405

  7. Linearized self-consistent quasiparticle GW method: Application to semiconductors and simple metals

    NASA Astrophysics Data System (ADS)

    Kutepov, A. L.; Oudovenko, V. S.; Kotliar, G.

    2017-10-01

    We present a code implementing the linearized quasiparticle self-consistent GW method (LQSGW) in the LAPW basis. Our approach is based on the linearization of the self-energy around zero frequency which differs it from the existing implementations of the QSGW method. The linearization allows us to use Matsubara frequencies instead of working on the real axis. This results in efficiency gains by switching to the imaginary time representation in the same way as in the space time method. The all electron LAPW basis set eliminates the need for pseudopotentials. We discuss the advantages of our approach, such as its N3 scaling with the system size N, as well as its shortcomings. We apply our approach to study the electronic properties of selected semiconductors, insulators, and simple metals and show that our code produces the results very close to the previously published QSGW data. Our implementation is a good platform for further many body diagrammatic resummations such as the vertex-corrected GW approach and the GW+DMFT method. Program Files doi:http://dx.doi.org/10.17632/cpchkfty4w.1 Licensing provisions: GNU General Public License Programming language: Fortran 90 External routines/libraries: BLAS, LAPACK, MPI (optional) Nature of problem: Direct implementation of the GW method scales as N4 with the system size, which quickly becomes prohibitively time consuming even in the modern computers. Solution method: We implemented the GW approach using a method that switches between real space and momentum space representations. Some operations are faster in real space, whereas others are more computationally efficient in the reciprocal space. This makes our approach scale as N3. Restrictions: The limiting factor is usually the memory available in a computer. Using 10 GB/core of memory allows us to study the systems up to 15 atoms per unit cell.

  8. Nanocrystal doped matrixes

    DOEpatents

    Parce, J. Wallace; Bernatis, Paul; Dubrow, Robert; Freeman, William P.; Gamoras, Joel; Kan, Shihai; Meisel, Andreas; Qian, Baixin; Whiteford, Jeffery A.; Ziebarth, Jonathan

    2010-01-12

    Matrixes doped with semiconductor nanocrystals are provided. In certain embodiments, the semiconductor nanocrystals have a size and composition such that they absorb or emit light at particular wavelengths. The nanocrystals can comprise ligands that allow for mixing with various matrix materials, including polymers, such that a minimal portion of light is scattered by the matrixes. The matrixes of the present invention can also be utilized in refractive index matching applications. In other embodiments, semiconductor nanocrystals are embedded within matrixes to form a nanocrystal density gradient, thereby creating an effective refractive index gradient. The matrixes of the present invention can also be used as filters and antireflective coatings on optical devices and as down-converting layers. Processes for producing matrixes comprising semiconductor nanocrystals are also provided. Nanostructures having high quantum efficiency, small size, and/or a narrow size distribution are also described, as are methods of producing indium phosphide nanostructures and core-shell nanostructures with Group II-VI shells.

  9. Ultrasonic cavitation induced water in vegetable oil emulsion droplets--a simple and easy technique to synthesize manganese zinc ferrite nanocrystals with improved magnetization.

    PubMed

    Sivakumar, Manickam; Towata, Atsuya; Yasui, Kyuichi; Tuziuti, Toru; Kozuka, Teruyuki; Iida, Yasuo; Maiorov, Michail M; Blums, Elmars; Bhattacharya, Dipten; Sivakumar, Neelagesi; Ashok, M

    2012-05-01

    In the present investigation, synthesis of manganese zinc ferrite (Mn(0.5)Zn(0.5)Fe(2)O(4)) nanoparticles with narrow size distribution have been prepared using ultrasound assisted emulsion (consisting of rapeseed oil as an oil phase and aqueous solution of Mn(2+), Zn(2+) and Fe(2+) acetates) and evaporation processes. The as-prepared ferrite was nanocrystalline. In order to remove the small amount of oil present on the surface of the ferrite, it was subjected to heat treatment at 300 °C for 3h. Both the as-prepared and heat treated ferrites have been characterized by X-ray diffraction (XRD), infrared spectroscopy (IR), TGA/DTA, transmission electron microscopy (TEM) and energy dispersion X-ray spectroscopy (EDS) techniques. As-prepared ferrite is of 20 nm, whereas the heat treated ferrite shows the size of 33 nm. In addition, magnetic properties of the as-prepared as well as the heat treated ferrites have also been carried out and the results of which show that the spontaneous magnetization (σ(s)) of the heat treated sample (24.1 emu/g) is significantly higher than that of the as-synthesized sample (1.81 emu/g). The key features of this method are avoiding (a) the cumbersome conditions that exist in the conventional methods; (b) usage of necessary additive components (stabilizers or surfactants, precipitants) and (c) calcination requirements. In addition, rapeseed oil as an oil phase has been used for the first time, replacing the toxic and troublesome organic nonpolar solvents. As a whole, this simple straightforward sonochemical approach results in more phase pure system with improved magnetization.

  10. Simple but Efficient Method for Inhibiting Sintering and Aggregation of Catalytic Pt Nanoclusters on Metal-Oxide Supports.

    PubMed

    Koizumi, Kenichi; Nobusada, Katsuyuki; Boero, Mauro

    2017-01-31

    A simple and efficient method to inhibit aggregation of Pt clusters supported on metal oxide was developed, preserving the accessible clusters surface where catalytically active sites are located even at relatively high temperatures up to 700 K. The key idea was the inclusion of transition metal atoms such as Ni into the Pt clusters, thus anchoring the clusters through formation of strong chemical bonds with oxygen atoms of the metal-oxide support. To elucidate the efficiency of the method, first-principles molecular dynamics enhanced with free-energy sampling methods were used. These virtual experiments showed how doped Ni atoms, having a stronger affinity to O than Pt, anchor the Pt clusters tightly to the metal-oxide supports and inhibit their tendency to aggregate on the support. © 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

  11. Fabrication of Infrared Photodetectors Utilizing Lead Selenide Nanocrystals

    NASA Astrophysics Data System (ADS)

    Horst, Matthew Jared

    Colloidal lead selenide and lead selenide / lead sulfide core/shell nanocrystals were grown using a wet chemical synthesis procedure. Absorbance and photoluminescence measurements were made to verify the quality of the produced nanocrystals. Absorbance spectra were measured at room temperature, while photoluminescence spectra were measured at 77 K. Organic ligands were exchanged for shorter ligands in order to increase the conductivity of the nanocrystals. Absorption and PL spectra for both core and core/shell nanocrystals were compared. Interdigital photodetector devices with varying channel widths were fabricated by depositing gold onto a glass substrate. Lead selenide nanocrystals were deposited onto these metallic structures using drop casting. Current-voltage characterization was performed on these devices and showed approximately one order of magnitude enhancement in the photocurrent. The detectivity and responsivity were extracted from the current-voltage characterization.

  12. Intermediate-range order in simple metal-phosphate glasses: The effect of metal cations on the phosphate anion distribution

    SciTech Connect

    Sales, B.C.; Boatner, L.A.; Ramey, J.O.

    1997-06-01

    The technique of high-performance liquid chromatography (HPLC) has been used to probe the phosphate anion distribution in a variety of metal phosphate glasses including glasses made with trivalent metal cations (Al, In, Ga, La). The composition of each glass was chosen so that the average phosphate chain length was between 2 and 4 PO{sub 4} tetrahedra. The widths of the resulting phosphate anion distributions were determined directly from an analysis of the HPLC chromatograms. Literature values for the free energy of formation of the crystalline metal-orthophosphate compounds with respect to P{sub 2}O{sub 5} and the metal oxide, were compared to the chromatogram widths. It was found that the smaller the energy of formation, the wider the distribution of phosphate chains, and the greater the ease of glass formation.

  13. Nanocrystal Bioassembly: Asymmetry, Proximity, and Enzymatic Manipulation

    SciTech Connect

    Claridge, Shelley A.

    2008-05-01

    Research at the interface between biomolecules and inorganic nanocrystals has resulted in a great number of new discoveries. In part this arises from the synergistic duality of the system: biomolecules may act as self-assembly agents for organizing inorganic nanocrystals into functional materials; alternatively, nanocrystals may act as microscopic or spectroscopic labels for elucidating the behavior of complex biomolecular systems. However, success in either of these functions relies heavily uponthe ability to control the conjugation and assembly processes.In the work presented here, we first design a branched DNA scaffold which allows hybridization of DNA-nanocrystal monoconjugates to form discrete assemblies. Importantly, the asymmetry of the branched scaffold allows the formation of asymmetric2assemblies of nanocrystals. In the context of a self-assembled device, this can be considered a step toward the ability to engineer functionally distinct inputs and outputs.Next we develop an anion-exchange high performance liquid chromatography purification method which allows large gold nanocrystals attached to single strands of very short DNA to be purified. When two such complementary conjugates are hybridized, the large nanocrystals are brought into close proximity, allowing their plasmon resonances to couple. Such plasmon-coupled constructs are of interest both as optical interconnects for nanoscale devices and as `plasmon ruler? biomolecular probes.We then present an enzymatic ligation strategy for creating multi-nanoparticle building blocks for self-assembly. In constructing a nanoscale device, such a strategy would allow pre-assembly and purification of components; these constructs can also act as multi-label probes of single-stranded DNA conformational dynamics. Finally we demonstrate a simple proof-of-concept of a nanoparticle analog of the polymerase chain reaction.

  14. Simple isolation method for the bulk isolation of wear particles from metal on metal bearing surfaces generated in a hip simulator test.

    PubMed

    Lu, Fang; Royle, Matt; Lali, Ferdinand V; Hart, Alister J; Collins, Simon; Housden, Jonathan; Shelton, Julia C

    2012-04-01

    Isolation and characterization of metal-on-metal (MoM) wear particles from simulator lubricants is essential to understand wear behaviour, ion release and associated corrosive activity related to the wear particles. Substantial challenges remain to establish a simple, precise and repeatable protocol for the isolation and analysis of wear particles due to their extremely small size, their tendency to agglomerate and degrade. In this paper, we describe a simple and efficient method for the bulk isolation and characterisation of wear particles from MoM bearings. Freeze drying was used to remove the large volume of water from the serum lubricant, enzymes used to digest the proteins and ultracentrifugation to finally isolate and purify the particles. The present study involved a total of eight steps for the isolation process and a wear particle extraction efficiency of 45% was achieved.

  15. Gold nanocrystals with DNA-directed morphologies

    PubMed Central

    Ma, Xingyi; Huh, June; Park, Wounjhang; Lee, Luke P.; Kwon, Young Jik; Sim, Sang Jun

    2016-01-01

    Precise control over the structure of metal nanomaterials is important for developing advanced nanobiotechnology. Assembly methods of nanoparticles into structured blocks have been widely demonstrated recently. However, synthesis of nanocrystals with controlled, three-dimensional structures remains challenging. Here we show a directed crystallization of gold by a single DNA molecular regulator in a sequence-independent manner and its applications in three-dimensional topological controls of crystalline nanostructures. We anchor DNA onto gold nanoseed with various alignments to form gold nanocrystals with defined topologies. Some topologies are asymmetric including pushpin-, star- and biconcave disk-like structures, as well as more complex jellyfish- and flower-like structures. The approach of employing DNA enables the solution-based synthesis of nanocrystals with controlled, three-dimensional structures in a desired direction, and expands the current tools available for designing and synthesizing feature-rich nanomaterials for future translational biotechnology. PMID:27633935

  16. Gold nanocrystals with DNA-directed morphologies

    NASA Astrophysics Data System (ADS)

    Ma, Xingyi; Huh, June; Park, Wounjhang; Lee, Luke P.; Kwon, Young Jik; Sim, Sang Jun

    2016-09-01

    Precise control over the structure of metal nanomaterials is important for developing advanced nanobiotechnology. Assembly methods of nanoparticles into structured blocks have been widely demonstrated recently. However, synthesis of nanocrystals with controlled, three-dimensional structures remains challenging. Here we show a directed crystallization of gold by a single DNA molecular regulator in a sequence-independent manner and its applications in three-dimensional topological controls of crystalline nanostructures. We anchor DNA onto gold nanoseed with various alignments to form gold nanocrystals with defined topologies. Some topologies are asymmetric including pushpin-, star- and biconcave disk-like structures, as well as more complex jellyfish- and flower-like structures. The approach of employing DNA enables the solution-based synthesis of nanocrystals with controlled, three-dimensional structures in a desired direction, and expands the current tools available for designing and synthesizing feature-rich nanomaterials for future translational biotechnology.

  17. Self-Organized Ultrathin Oxide Nanocrystals

    SciTech Connect

    Huo, Ziyang; Tsung, Chia-kuang; Huang, Wenyu; Fardy, Melissa; Yan, Ruoxue; Li, Yadong; Yang, Piedong; Zhang, Xiaofeng

    2009-01-08

    Sub-2-nm (down to one-unit cell) uniform oxide nanocrystals and highly ordered superstructures were obtained in one step using oleylamine and oleic acid as capping and structure directing agents. The cooperative nature of the nanocrystal growth and assembly resulted in mesoscopic one-dimensional ribbon-like superstructures made of these ultrathin nanocrystals. The process reported here is general and can be readily extended to the production of many other transition metal (TiO2, ZnO, Nb2O5) and rare earth oxide (Eu2O3, Sm2O3, Er2O3, Y2O3, Tb2O3, and Yb2O3) systems.

  18. Simple Methods for Production of Nanoscale Metal Oxide Films from Household Sources

    ERIC Educational Resources Information Center

    Campbell, Dean J.; Baliss, Michelle S.; Hinman, Jordan J.; Ziegenhorn, John W.; Andrews, Mark J.; Stevenson, Keith J.

    2013-01-01

    Production of thin metal oxide films was recently explored as part of an outreach program with a goal of producing nanoscale structures with household items. Household items coated with various metals or titanium compounds can be heated to produce colorful films with nanoscale thicknesses. As part of a materials chemistry laboratory experiment…

  19. Simple Methods for Production of Nanoscale Metal Oxide Films from Household Sources

    ERIC Educational Resources Information Center

    Campbell, Dean J.; Baliss, Michelle S.; Hinman, Jordan J.; Ziegenhorn, John W.; Andrews, Mark J.; Stevenson, Keith J.

    2013-01-01

    Production of thin metal oxide films was recently explored as part of an outreach program with a goal of producing nanoscale structures with household items. Household items coated with various metals or titanium compounds can be heated to produce colorful films with nanoscale thicknesses. As part of a materials chemistry laboratory experiment…

  20. A flexible method for depositing dense nanocrystal thin films: impaction of germanium nanocrystals

    SciTech Connect

    Holman, Zachary C.; Kortshagen, Uwe R.

    2010-07-27

    Nanomaterials are exciting candidates for use in new optical and electronic devices ranging from solar cells to gas sensors. However, to reach their full potential, nanomaterials must be deposited as dense thin films on flexible substrates using inexpensive processing technologies such as roll-to-roll printing. We report a new, flexible technique for depositing aerosolized nanocrystals that lends itself to roll-to-roll processes. Germanium nanocrystals produced in a plasma are accelerated through a slit orifice by a supersonic gas jet and are impacted onto a translated substrate. A uniform nanocrystal film is quickly deposited over large areas, and features as small as 2 µm can then be patterned using conventional lift-off photolithography. The density of a deposited film depends on the pressures upstream and downstream of the orifice, their ratio, and the distance between the orifice and the substrate. Nanocrystal film densities exceeding 50% of the density of bulk germanium are routinely achieved with several sizes of nanocrystals, approaching the theoretical limit for randomly packed spheres. A simple model is presented that shows that the calculated nanocrystal velocity upon impaction is strongly correlated with the resulting film density.

  1. Biomineralization: Nanocrystals by design

    NASA Astrophysics Data System (ADS)

    Shang, Li; Nienhaus, Gerd Ulrich

    2015-10-01

    Nanocrystals with precisely defined structures offer promise as components of advanced materials yet they are challenging to create. Now, a nanocrystal made up of seven cadmium and twelve chloride ions has been synthesized via a biotemplating approach that uses a de novo designed protein.

  2. Universal Quake Statistics: From Compressed Nanocrystals to Earthquakes.

    PubMed

    Uhl, Jonathan T; Pathak, Shivesh; Schorlemmer, Danijel; Liu, Xin; Swindeman, Ryan; Brinkman, Braden A W; LeBlanc, Michael; Tsekenis, Georgios; Friedman, Nir; Behringer, Robert; Denisov, Dmitry; Schall, Peter; Gu, Xiaojun; Wright, Wendelin J; Hufnagel, Todd; Jennings, Andrew; Greer, Julia R; Liaw, P K; Becker, Thorsten; Dresen, Georg; Dahmen, Karin A

    2015-11-17

    Slowly-compressed single crystals, bulk metallic glasses (BMGs), rocks, granular materials, and the earth all deform via intermittent slips or "quakes". We find that although these systems span 12 decades in length scale, they all show the same scaling behavior for their slip size distributions and other statistical properties. Remarkably, the size distributions follow the same power law multiplied with the same exponential cutoff. The cutoff grows with applied force for materials spanning length scales from nanometers to kilometers. The tuneability of the cutoff with stress reflects "tuned critical" behavior, rather than self-organized criticality (SOC), which would imply stress-independence. A simple mean field model for avalanches of slipping weak spots explains the agreement across scales. It predicts the observed slip-size distributions and the observed stress-dependent cutoff function. The results enable extrapolations from one scale to another, and from one force to another, across different materials and structures, from nanocrystals to earthquakes.

  3. Silicon Nanocrystal Laser

    SciTech Connect

    Yu, J

    2005-03-09

    The purpose of this feasibility study project was to attempt to demonstrate the silicon-nanocrystal-based laser. Such a silicon laser (made using conventional silicon-manufacturing technologies) would provide the crucial missing link that would enable a completely-silicon-based photonic system. We prepared thin layers of silicon nanocrystal material by ion-implanting Si in fused silica substrates, followed by a high temperature anneal process. These Si nanocrystals produced intense photoluminescence when optically pumped with ultraviolet light. Laser structures based on Fabry-Perot cavity and distributed feedback (DFB) designs were fabricated using the Si nanocrystals as the ''lasing'' medium. We optically pumped the samples with CW lasers at 413nm wavelength to quickly assess the feasibility of making lasers out of the Nanocrystal Si material and to verify the gain coefficients reported by other research groups.

  4. Perfect absorbers based on metal-insulator-metal structures in the visible region: a simple approach for practical applications

    NASA Astrophysics Data System (ADS)

    Kenanakis, G.; Mavidis, Ch. P.; Vasilaki, E.; Katsarakis, N.; Kafesaki, M.; Economou, E. N.; Soukoulis, C. M.

    2017-01-01

    Perfect absorbers based on metal-insulator-metal (MIM) structures are proposed and demonstrated, both theoretically and experimentally, in the visible region. The proposed structures may possess either sharp or broadband absorption peaks, by simply choosing a single layer of the proposed MIM structure or building several layers of them, while no nanofabrication steps or structure patterning are required, and thus can be easily made to cover a large area. The highly efficient absorption of the MIM structures is maintained for both TE and TM incident polarization, and for angles of incidence up to 75°, indicating that the proposed perfect absorbers can be potentially deployed for solar cells applications and optics.

  5. One-step electrochemical synthesis of preferentially oriented (111) Pd nanocrystals supported on graphene nanoplatelets for formic acid electrooxidation

    NASA Astrophysics Data System (ADS)

    Chen, Qing-Song; Xu, Zhong-Ning; Peng, Si-Yan; Chen, Yu-Min; Lv, Dong-Mei; Wang, Zhi-Qiao; Sun, Jing; Guo, Guo-Cong

    2015-05-01

    Pd nanocrystals supported on graphene nanoplatelets (Pd/GNP) have been successfully synthesized by simultaneously electrochemical milling of Pd wire and graphite rod. It should be stressed that without the assistance of graphite rod, the Pd nanocrystals are unable to be obtained individually from Pd wire under the same conditions. Investigations of SEM and TEM demonstrate that Pd/GNP are preferentially decorated with (111) faceted nanocrystals. XPS studies confirm the strong metal-support interaction in Pd/GNP and reveal the surface is almost composed of Pd(0) species. Electrochemical measurements show that the prepared Pd based catalyst exhibits superior electrocatalytic activity towards formic acid oxidation, which may be attributed to the combined effects involving the preferentially oriented (111) surface structure, specific electronic structure and high dispersion of Pd nanocrystals as well as the support effects of graphene nanoplatelets. The synthesis method is simple and effective to prepare excellent new carbon-supported electrocatalysts, which is of great significance for direct organic molecule fuel cell.

  6. Green and scalable production of colloidal perovskite nanocrystals and transparent sols by a controlled self-collection process

    NASA Astrophysics Data System (ADS)

    Liu, Shuangyi; Huang, Limin; Li, Wanlu; Liu, Xiaohua; Jing, Shui; Li, Jackie; O'Brien, Stephen

    2015-07-01

    Colloidal perovskite oxide nanocrystals have attracted a great deal of interest owing to the ability to tune physical properties by virtue of the nanoscale, and generate thin film structures under mild chemical conditions, relying on self-assembly or heterogeneous mixing. This is particularly true for ferroelectric/dielectric perovskite oxide materials, for which device applications cover piezoelectrics, MEMs, memory, gate dielectrics and energy storage. The synthesis of complex oxide nanocrystals, however, continues to present issues pertaining to quality, yield, % crystallinity, purity and may also suffer from tedious separation and purification processes, which are disadvantageous to scaling production. We report a simple, green and scalable ``self-collection'' growth method that produces uniform and aggregate-free colloidal perovskite oxide nanocrystals including BaTiO3 (BT), BaxSr1-xTiO3 (BST) and quaternary oxide BaSrTiHfO3 (BSTH) in high crystallinity and high purity. The synthesis approach is solution processed, based on the sol-gel transformation of metal alkoxides in alcohol solvents with controlled or stoichiometric amounts of water and in the stark absence of surfactants and stabilizers, providing pure colloidal nanocrystals in a remarkably low temperature range (15 °C-55 °C). Under a static condition, the nanoscale hydrolysis of the metal alkoxides accomplishes a complete transformation to fully crystallized single domain perovskite nanocrystals with a passivated surface layer of hydroxyl/alkyl groups, such that the as-synthesized nanocrystals can exist in the form of super-stable and transparent sol, or self-accumulate to form a highly crystalline solid gel monolith of nearly 100% yield for easy separation/purification. The process produces high purity ligand-free nanocrystals excellent dispersibility in polar solvents, with no impurity remaining in the mother solution other than trace alcohol byproducts (such as isopropanol). The afforded stable

  7. Coupling of Surface Plasmons and Semiconductor Nanocrystals for Nanophotonics Applications

    NASA Astrophysics Data System (ADS)

    Jayanti, Sriharsha V.

    The goal of this thesis is to engineer the interaction between surface plasmons and semiconductor nanocrystals for nanophotonic applications. Plasmonic metals support surface plasmon polaritons, hybrid photon and electron waves that propagate along a metal-dielectric interface. Unlike photons, surface plasmons can be confined in sub-diffraction geometries. This has two important consequences: 1) optical devices can be designed at the nanoscale, and 2) the high density of electromagnetic fields allows study of enhanced light-matter interactions. Surface plasmons have been exploited to demonstrate components of optoelectronic circuits, optical antennas, surface enhanced spectroscopy, enhanced fluorescence from fluorophores, and nanolasers. Despite the advances, surface plasmon losses limit their propagation lengths to tens of micrometers in the visible wavelengths, hindering many applications. Recently, the template-stripping approach was shown to fabricate metal films that exhibit larger grains and smoother surface, reducing the grain boundary and roughness scattering. To further improve the plasmonic properties, we investigate the importance of deposition conditions in the template-stripping approach. We provide insight and recipes to enhance the plasmonic performance of the most commonly used metals in the ultraviolet, visible, and near-infrared. We also explore the potential of low temperatures to improve the performance of metal films, where the electron-electron and electron-phonon scattering should be reduced. This sets a limit on the minimum loss metals can exhibit. Using this knowledge, we study the optical properties of quantum-confined semiconductor nanocrystals near metal structures. Semiconductor nanocrystals have many attractive characteristics that make them suitable for solid-state lighting and solar cells among others. Specifically, CdSe nanocrystals have been heavily studied for their large absorption and emission cross-sections, size dependent

  8. Simple methods for polymer nanostructuring by plasma modification, metal sputtering, and annealing

    NASA Astrophysics Data System (ADS)

    Jurik, Petr; Slepicka, Petr; Svorcik, Vaclav

    2016-09-01

    Self-organization offer cost-efficient and easily scalable way to nanopattern polymer surfaces for various applications ranging from medical use to sensing applications. For example poly-L-lactic acid can be modified either by metal sputtering and/or plasma discharge to form ripple-like structures after annealing with size and regularity highly dependent on processing variables. Such samples have enhanced biocompatibility and as such they are promising substrates for use as various implants. Another example is annealing of polyethersulfone film modified by metal sputtering that causes coalescence of metal layer into separated metal nanoclusters. This structure exhibit localized surface Plasmon resonance, which can be used for example in Surface enhanced Raman spectroscopy.

  9. a Simple Interpretation of the Rice Spectral Indices Space for Assessment of Heavy Metal Stress

    NASA Astrophysics Data System (ADS)

    Wang, P.; Huang, F.; Liu, X. N.

    2016-06-01

    Heavy metal stress will induce the change of the bio-parameters like chlorophyll, nitrogen and water content of rice. In this paper, we analyzed the traditional spectral index which has strong relationship in general with the three bio-parameters using hyperspectral data acquired by ASD. It is found that some indies do not work well when the heavy metal stress exists, however, some indies still has ability to estimate the above three bio-parameters. A new interpretation is proposed to classify the stress level based on both the physical mechanism analysis and the statistic model after we describe and discuss studies on the expression of spectral indices of rice under heavy metal stress. The 3-axes spectral indices spaces, which are constructed of 3 spectral indices sensitive to rice's chlorophyll concentration, nitrogen concentration and water concentration respectively, are used to visualize the linkage between heavy metal stress and spectrum of rice canopy.

  10. Simple and robust resistive dual-axis accelerometer using a liquid metal droplet

    NASA Astrophysics Data System (ADS)

    Huh, Myoung; Won, Dong-Joon; Kim, Joong Gil; Kim, Joonwon

    2017-12-01

    This paper presents a novel dual-axis accelerometer that consists of a liquid metal droplet in a cone-shaped channel and an electrode layer with four Nichrome electrodes. The sensor uses the advantages of the liquid metal droplet (i.e., high surface tension, electrical conductivity, high density, and deformability). The cone-shaped channel imposes a restoring force on the liquid metal droplet. We conducted simulation tests to determine the appropriate design specifications of the cone-shaped channel. Surface modifications to the channel enhanced the nonwetting performance of the liquid metal droplet. The performances of the sensor were analyzed by a tilting test. When the acceleration was applied along the axial direction, the device showed 6 kΩ/g of sensitivity and negligible crosstalk between the X- and Y-axes. In a diagonal direction test, the device showed 4 kΩ/g of sensitivity.

  11. Formation of hollow nanocrystals through the nanoscale kirkendall effect

    SciTech Connect

    Yin, Yadong; Rioux, Robert M.; Erdonmez, Can K.; Hughes, Steven; Somorjai, Gabor A.; Alivisatos, A. Paul

    2004-03-11

    We demonstrate that hollow nanocrystals can be synthesized through a mechanism analogous to the Kirkendall Effect, in which pores form due to the difference in diffusion rates between two components in a diffusion couple. Cobalt nanocrystals are chosen as a primary example to show that their reaction in solution with oxygen, sulfur or selenium leads to the formation of hollow nanocrystals of the resulting oxide and chalcogenides. This process provides a general route to the synthesis of hollow nanostructures of large numbers of compounds. A simple extension of this process yields platinum-cobalt oxide yolk-shell nanostructures which may serve as nanoscale reactors in catalytic applications.

  12. Steroid Nanocrystals Prepared Using the Nano Spray Dryer B-90

    PubMed Central

    Baba, Koichi; Nishida, Kohji

    2013-01-01

    The Nano Spray Dryer B-90 offers a new, simple, and alternative approach for the production of drug nanocrystals. In this study, the preparation of steroid nanocrystals using the Nano Spray Dryer B-90 was demonstrated. The particle size was controlled by selecting the mesh aperture size. Submicrometer steroid particles in powder form were successfully obtained. These nanoparticles were confirmed to have a crystal structure using powder X-ray diffraction pattern analysis. Since drug nanocrystals have recently been considered as a novel type of drug formulation for drug delivery systems, this study will be useful for nano-medical applications. PMID:24300400

  13. Diorganyl dichalcogenides as useful synthons for colloidal semiconductor nanocrystals.

    PubMed

    Brutchey, Richard L

    2015-11-17

    The ability to synthesize colloidal semiconductor nanocrystals in a well-controlled manner (i.e., with fine control over size, shape, size dispersion, and composition) has been mastered over the past 15 years. Much of this success stems from careful studies of precursor conversion and nanocrystal growth with respect to phosphine chalcogenide precursors for the synthesis of metal chalcogenide nanocrystals. Despite the high level of success that has been achieved with phosphine chalcogenides, there has been a longstanding interest in exploring alternate chalcogenide precursors because of issues associated with phosphine chalcogenide cost, purity, toxicity, etc. This has resulted in a large body of literature on the use of sulfur and selenium dissolved in octadecene or amines, thio- and selenoureas, and silyl chalcogenides as alternate chalcogenide precursors for metal chalcogenide nanocrystal synthesis. In this Account, emerging work on the use of diorganyl dichalcogenides (R-E-E-R, where E = S, Se, or Te and R = alkyl, allyl, benzyl, or aryl) as alternate chalcogenide precursors for the synthesis of metal chalcogenide nanocrystals is summarized. Among the benefits of these dichalcogenide synthons are the following: (i) they represent the first and only common precursor type that can function as chalcogen transfer reagents for each of the group VI elements (i.e., to make metal oxide, metal sulfide, metal selenide, and metal telluride nanocrystals); (ii) they possess relatively weak E-E bonds that can be readily cleaved under mild thermolytic or photolytic conditions; and (iii) the organic substituents can be tuned to affect the reactivity. These combined attributes have allowed dichalcogenide precursors to be employed for a wide range of metal chalcogenide nanocrystal syntheses, including those for In2S3, SnxGe1-xSe, SnTe, Cu2-xSySe1-y, ZnSe, CdS, CdSe, MoSe2, WSe2, BiSe, and CuFeS2. Interestingly, a number of metastable phases of compositionally complex

  14. Nanocrystal powered nanomotor

    DOEpatents

    Regan, Brian C [Los Angeles, CA; Zettl, Alexander K [Kensington, CA; Aloni, Shaul [Albany, CA

    2011-01-04

    A nanoscale nanocrystal which may be used as a reciprocating motor is provided, comprising a substrate having an energy differential across it, e.g. an electrical connection to a voltage source at a proximal end; an atom reservoir on the substrate distal to the electrical connection; a nanoparticle ram on the substrate distal to the atom reservoir; a nanolever contacting the nanoparticle ram and having an electrical connection to a voltage source, whereby a voltage applied between the electrical connections on the substrate and the nanolever causes movement of atoms between the reservoir and the ram. Movement of the ram causes movement of the nanolever relative to the substrate. The substrate and nanolever preferably comprise multiwalled carbon nanotubes (MWNTs) and the atom reservoir and nanoparticle ram are preferably metal (e.g. indium) deposited as small particles on the MWNTs. The substrate may comprise a silicon chip that has been fabricated to provide the necessary electrodes and other electromechanical structures, and further supports an atomic track, which may comprise an MWNT.

  15. Jingle-bell-shaped ferrite hollow sphere with a noble metal core: Simple synthesis and their magnetic and antibacterial properties

    SciTech Connect

    Li Siheng; Wang Enbo Tian Chungui; Mao Baodong; Kang Zhenhui; Li Qiuyu; Sun Guoying

    2008-07-15

    In this paper, a simple strategy is developed for rational fabrication of a class of jingle-bell-shaped hollow structured nanomaterials marked as Ag(MFe{sub 2}O{sub 4}) (M=Ni, Co, Mg, Zn), consisting of ferrite hollow shells and metal nanoparticle cores, using highly uniform colloidal Ag(C) microspheres as template. The final composites were obtained by direct adsorption of metal cations Fe{sup 3+} and M{sup 2+} on the surface of the Ag(C) spheres followed by calcination process to remove the middle carbon shell and transform the metal ions into pure phase ferrites. The as-prepared composites were characterized by X-ray photoelectron spectroscopy (XPS), energy-dispersive X-ray analysis (EDX), X-ray powder diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), UV-vis spectroscopy and SQUID magnetometer. The results showed that the composites possess the magnetic property of the ferrite shell and the optical together with antibacterial property of the Ag core. - Graphical abstract: MFe{sub 2}O{sub 4} (M=Ni, Co, Mg, Zn) hollow spheres with a noble metal nanoparticle core were successfully prepared by using colloidal metal(C) core-shell spheres as templates with no need of surface modification. The shell thickness and magnetic properties of the ferrite hollow spheres could be controlled by varying the synthetic parameters.

  16. Tiny grains give huge gains: nanocrystal-based signal amplification for biomolecule detection.

    PubMed

    Tong, Sheng; Ren, Binbin; Zheng, Zhilan; Shen, Han; Bao, Gang

    2013-06-25

    Nanocrystals, despite their tiny sizes, contain thousands to millions of atoms. Here we show that the large number of atoms packed in each metallic nanocrystal can provide a huge gain in signal amplification for biomolecule detection. We have devised a highly sensitive, linear amplification scheme by integrating the dissolution of bound nanocrystals and metal-induced stoichiometric chromogenesis, and demonstrated that signal amplification is fully defined by the size and atom density of nanocrystals, which can be optimized through well-controlled nanocrystal synthesis. Further, the rich library of chromogenic reactions allows implementation of this scheme in various assay formats, as demonstrated by the iron oxide nanoparticle linked immunosorbent assay (ILISA) and blotting assay developed in this study. Our results indicate that, owing to the inherent simplicity, high sensitivity and repeatability, the nanocrystal based amplification scheme can significantly improve biomolecule quantification in both laboratory research and clinical diagnostics. This novel method adds a new dimension to current nanoparticle-based bioassays.

  17. Nanocrystal diffusion doping.

    PubMed

    Vlaskin, Vladimir A; Barrows, Charles J; Erickson, Christian S; Gamelin, Daniel R

    2013-09-25

    A diffusion-based synthesis of doped colloidal semiconductor nanocrystals is demonstrated. This approach involves thermodynamically controlled addition of both impurity cations and host anions to preformed seed nanocrystals under equilibrium conditions, rather than kinetically controlled doping during growth. This chemistry allows thermodynamic crystal compositions to be prepared without sacrificing other kinetically trapped properties such as shape, size, or crystallographic phase. This doping chemistry thus shares some similarities with cation-exchange reactions, but proceeds without the loss of host cations and excels at the introduction of relatively unreactive impurity ions that have not been previously accessible using cation exchange. Specifically, we demonstrate the preparation of Cd(1-x)Mn(x)Se (0 ≤ x ≤ ∼0.2) nanocrystals with narrow size distribution, unprecedentedly high Mn(2+) content, and very large magneto-optical effects by diffusion of Mn(2+) into seed CdSe nanocrystals grown by hot injection. Controlling the solution and lattice chemical potentials of Cd(2+) and Mn(2+) allows Mn(2+) diffusion into the internal volumes of the CdSe nanocrystals with negligible Ostwald ripening, while retaining the crystallographic phase (wurtzite or zinc blende), shape anisotropy, and ensemble size uniformity of the seed nanocrystals. Experimental results for diffusion doping of other nanocrystals with other cations are also presented that indicate this method may be generalized, providing access to a variety of new doped semiconductor nanostructures not previously attainable by kinetic routes or cation exchange.

  18. Synthesis of Ultra-Small Palladium Nanoparticles Deposited on CdS Nanorods by Pulsed Laser Ablation in Liquid: Role of Metal Nanocrystal Size in the Photocatalytic Hydrogen Production.

    PubMed

    Park, Hanbit; Reddy, D Amaranatha; Kim, Yujin; Lee, Seunghee; Ma, Rory; Kim, Tae Kyu

    2017-09-21

    It is imperative to suppress the rate of recombination of photogenerated carriers to improve the semiconductor-catalyzed solar-driven production of hydrogen. To this end, photocatalysts comprising active sunlight-harvesting photo-absorbers and stable metal co-catalysts have attracted significant attention. However, the size, clean surface, and highly dispersed nature of the metal co-catalysts are crucial factors affecting catalyst performance and reaction rate. Nevertheless, most of the available metal nanocrystals have been synthesized by complex procedures using harmful organic templates and stabilizers, affording high-purity compounds with difficulty and high cost. To overcome these problems, in this study, the pulsed laser ablation in liquid approach was utilized to generate palladium and bimetallic palladium-platinum nanoparticles with an average size and distribution by adjusting the laser wavelength and fluence. A high rate of evolution of hydrogen of 130.33 mmol g(-1)  h(-1) was obtained by using the optimized CdS-PdPt catalyst under simulated sunlight irradiation. This value is 51.31 times greater than that observed for bare CdS nanostructures. Furthermore, the amount of hydrogen evolved was significantly better than that obtained by using several other noble-metal co-catalysts deposited on CdS. This proposed strategy is thought to open new avenues for the design of advanced photocatalytic materials for efficient solar-driven production of hydrogen. © 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

  19. Ternary Silver Halide Nanocrystals.

    PubMed

    Abeyweera, Sasitha C; Rasamani, Kowsalya D; Sun, Yugang

    2017-07-18

    Nanocrystalline silver halides (AgX) such as AgCl, AgBr, and AgI, a class of semiconductor materials with characteristics of both direct and indirect band gaps, represent the most crucial components in traditional photographic processing. The nanocrystal surfaces provide sensitivity specks that can turn into metallic silver, forming an invisible latent image, upon exposure to light. The photographic processing implies that the AgX nanoparticles possess unique properties. First, pristine AgX nanoparticles absorb light only at low efficiency to convert surface AgX into tiny clusters of silver atoms. Second, AgX nanoparticles represent an excellent class of materials to capture electrons efficiently. Third, small metallic silver clusters can catalyze the reduction of AgX nanoparticles to Ag nanoparticles in the presence of mild reducing reagents, known as self-catalytic reduction. These properties indicate that AgX nanoparticles can be partially converted to metallic silver with high precision, leading to the formation of hybrid AgX/Ag nanoparticles. The nanosized metallic Ag usually exhibit intense absorption bands in the visible spectral region due to their strong surface plasmon resonances, which make the AgX/Ag nanoparticles a class of promising visible-light-driven photocatalysts for environmental remediation and CO2 reduction. Despite the less attention paid to their ability of capturing electrons, AgX nanoparticles might be a class of ideal electron shuttle materials to bridge light absorbers and catalysts on which electrons can drive chemical transformations. In this Account, we focus on ternary silver halide alloy (TSHA) nanoparticles, containing two types of halide ions, which increase the composition complexity of the silver halide nanoparticles. Interdiffusion of halide ions between two types of AgX at elevated temperatures has been developed for fabricating ternary silver halide alloy crystals, such as silver chlorobromide optical fibers for infrared

  20. A simple method for the prediction of the detonation performances of metal-containing explosives.

    PubMed

    Wang, Yuan; Zhang, Jichuan; Su, Hui; Li, Shenghua; Zhang, Shaowen; Pang, Siping

    2014-06-26

    Accurate prediction to the detonation performances of different kinds of energetic materials has attracted significant attention in the area of high energy density materials (HEDMs). A common approach for the estimation of CHNO explosives is the Kamlet-Jacobs (K-J) equation. However, with the development of energetic materials, the components of explosives are no longer restricted to CHNO elements. In this study, we have extended the K-J equation to the calculation of certain metal-containing explosives. A new empirical method, in which metal elements are assumed to form metallic oxides, has been developed on the basis of the largest exothermic principle. In this method, metal oxides can be deemed as inert solids that release heat other than gases. To evaluate the prediction accuracy of new method, a commercial program EXPLO5 has been employed for the calculation. The difference involved in the ways of treating products has been taken into account, and the detonation parameters from two methods were subject to close comparison. The results suggest that the mean absolute values (MAVs) of relative deviation for detonation velocity (D) and detonation pressure (P) are less than 5%. Overall, this new method has exhibited excellent accuracy and simplicity, affording an efficient way to estimate the performance of explosives without relying on sophisticated computer programs. Therefore, it will be helpful in designing and synthesizing new metallic energetic compounds.

  1. A simple model for large-scale simulations of fcc metals with explicit treatment of electrons

    NASA Astrophysics Data System (ADS)

    Mason, D. R.; Foulkes, W. M. C.; Sutton, A. P.

    2010-01-01

    The continuing advance in computational power is beginning to make accurate electronic structure calculations routine. Yet, where physics emerges through the dynamics of tens of thousands of atoms in metals, simplifications must be made to the electronic Hamiltonian. We present the simplest extension to a single s-band model [A.P. Sutton, T.N. Todorov, M.J. Cawkwell and J. Hoekstra, Phil. Mag. A 81 (2001) p.1833.] of metallic bonding, namely, the addition of a second s-band. We show that this addition yields a reasonable description of the density of states at the Fermi level, the cohesive energy, formation energies of point defects and elastic constants of some face-centred cubic (fcc) metals.

  2. On Ultrasmall Nanocrystals

    PubMed Central

    McBride, James R.; Dukes, Albert D.; Schreuder, Michael A.; Rosenthal, Sandra J.

    2010-01-01

    Ultrasmall nanocrystals are a growing sub-class of traditional nanocrystals that exhibit new properties at diameters typically below 2 nm. In this review, we define what constitutes an ultrasmall nanoparticle while distinguishing between ultrasmall and magic-size nanoparticles. After a brief overview of ultrasmall nanoparticles, including ultrasmall gold clusters, our recent work is presented covering the optical properties, structure, and application of ultrasmall CdSe nanocrystals. This unique material has potential application in solid state lighting due to its balanced white emission. This section is followed by a discussion on the blurring boundary between what can be considered a nanoparticle and a molecule. PMID:21132106

  3. Simple magneto-optic transition metal models for time-domain simulations.

    PubMed

    Wolff, Christian; Rodríguez-Oliveros, Rogelio; Busch, Kurt

    2013-05-20

    Efficient modelling of the magneto-optic effects of transition metals such as nickel, cobalt and iron is a topic of growing interest within the nano-optics community. In this paper, we present a general discussion of appropriate material models for the linear dielectric properties for such metals, provide parameter fits and formulate the anisotropic response in terms of auxiliary differential equations suitable for time-domain simulations. We validate both our material models and their implementation by comparing numerical results obtained with the Discontinuous Galerkin time-domain (DGTD) method to analytical results and previously published experimental data.

  4. Nickel nanocrystal formation on HfO2 dielectric for nonvolatile memory device applications

    NASA Astrophysics Data System (ADS)

    Lee, Jong Jin; Harada, Yoshinao; Pyun, Jung Woo; Kwong, Dim-Lee

    2005-03-01

    This letter presents the formation of nickel nanocrystal on HfO2 high-k dielectric and its application to the nonvolatile memory devices. The effects of the initial nickel layer thickness and annealing temperature on nickel nanocrystal formation are investigated. The n-metal-oxide-semiconductor field-effect transistor with nickel nanocrystals and HfO2 tunneling dielectrics is fabricated and its programming, data retention, and endurance properties are characterized to demonstrate its advantages for nonvolatile memory device applications.

  5. Hcp cobalt nanocrystals with high magnetic anisotropy prepared by easy one-pot synthesis.

    PubMed

    Meziane, L; Salzemann, C; Aubert, C; Gérard, H; Petit, C; Petit, M

    2016-11-10

    Herein we describe the first synthesis of pure mono-disperse spherical hcp-nanocrystals ferromagnetic at room temperature. Our strategy, based on the simple combination of oleylamine and ClCo(PPh3)3, allows the one-pot synthesis of size-controlled hcp-nanocrystals. The size and shape of the nanocrystals can be tuned by varying the reaction time or the concentration.

  6. A Simple Classroom Simulation of Heat Energy Diffusing through a Metal Bar

    ERIC Educational Resources Information Center

    Kinsler, Mark; Kinzel, Evelyn

    2007-01-01

    We present an iterative procedure that does not rely on calculus to model heat flow through a uniform bar of metal and thus avoids the use of the partial differential equation typically needed to describe heat diffusion. The procedure is based on first principles and can be done with students at the blackboard. It results in a plot that…

  7. A Simple Classroom Simulation of Heat Energy Diffusing through a Metal Bar

    ERIC Educational Resources Information Center

    Kinsler, Mark; Kinzel, Evelyn

    2007-01-01

    We present an iterative procedure that does not rely on calculus to model heat flow through a uniform bar of metal and thus avoids the use of the partial differential equation typically needed to describe heat diffusion. The procedure is based on first principles and can be done with students at the blackboard. It results in a plot that…

  8. Simple metal binary phases based on the body centered cubic structure: Electronic origin of distortions and superlattices

    NASA Astrophysics Data System (ADS)

    Degtyareva, Valentina F.; Afonikova, Nataliya S.

    2013-01-01

    Binary alloy phases of the noble metals with the main group elements are analyzed in relation to the body centered cubic structure with distortions, vacancies and superlattices. The stability of these distorted phases is studied in terms of the Fermi sphere-Brillouin-Jones zone interaction within the nearly free-electron model in order to understand the importance of the band structure energy contribution to the overall crystal energy. Examination of Brillouin-Jones zone configurations with respect to the Fermi sphere for several representative phases has shown how significant the electron energy contribution is in forming the distorted structures with superlattices and ordered vacancies. This approach may be useful for understanding the complex structures recently found in compressed simple alkali metals.

  9. Comparison of Residual Stresses in Inconel 718 Simple Parts Made by Electron Beam Melting and Direct Laser Metal Sintering

    NASA Astrophysics Data System (ADS)

    Sochalski-Kolbus, L. M.; Payzant, E. A.; Cornwell, P. A.; Watkins, T. R.; Babu, S. S.; Dehoff, R. R.; Lorenz, M.; Ovchinnikova, O.; Duty, C.

    2015-03-01

    Residual stress profiles were mapped using neutron diffraction in two simple prism builds of Inconel 718: one fabricated with electron beam melting (EBM) and the other with direct laser metal sintering. Spatially indexed stress-free cubes were obtained by electrical discharge machining (EDM) equivalent prisms of similar shape. The (311) interplanar spacings from the EDM sectioned sample were compared to the interplanar spacings calculated to fulfill stress and moment balance. We have shown that applying stress and moment balance is a necessary supplement to the measurements for the stress-free cubes with respect to accurate stress calculations in additively manufactured components. In addition, our work has shown that residual stresses in electron beam melted parts are much smaller than that of direct laser metal sintered parts most likely due to the powder preheating step in the EBM process.

  10. Nanocrystals for electronics.

    PubMed

    Panthani, Matthew G; Korgel, Brian A

    2012-01-01

    Semiconductor nanocrystals are promising materials for low-cost large-area electronic device fabrication. They can be synthesized with a wide variety of chemical compositions and size-tunable optical and electronic properties as well as dispersed in solvents for room-temperature deposition using various types of printing processes. This review addresses research progress in large-area electronic device applications using nanocrystal-based electrically active thin films, including thin-film transistors, light-emitting diodes, photovoltaics, and thermoelectrics.

  11. A simple method of interface-state reduction in metal-nitride-oxide-semiconductor structures

    NASA Astrophysics Data System (ADS)

    Sheu, Yea-Dean

    1991-04-01

    A method for reducing the interface-state density in polysilicon gate metal-nitride-oxide-semiconductor (MNOS) capacitors is reported. The method involves deposition of a sacrificial blanket aluminum layer on top of a chemical-vapor-deposition (CVD) oxide over MNOS capacitors. The entire stack was then annealed at 450 °C in nitrogen and then the metal and CVD oxide were stripped away. The interface state density was reduced from 1011 to 1010 cm-2 eV-1 after this anneal. It is believed that Al reacts with trace water in the CVD oxide and generates active hydrogen. The hydrogen diffuses to the Si/SiO2 interface and passivates the interface states.

  12. A Simple Classroom Simulation of Heat Energy Diffusing Through a Metal Bar

    NASA Astrophysics Data System (ADS)

    Kinsler, Mark; Kinzel, Evelyn

    2007-09-01

    We present an iterative procedure that does not rely on calculus to model heat flow through a uniform bar of metal and thus avoids the use of the partial differential equation typically needed to describe heat diffusion. The procedure is based on first principles and can be done with students at the blackboard. It results in a plot that illustrates several principles of thermodynamics and can be easily implemented with a spreadsheet program on the computer.

  13. Catalytic Addition of Simple Alkenes to Carbonyl Compounds Using Group 10 Metals

    PubMed Central

    Schleicher, Kristin D.

    2011-01-01

    Recent advances using nickel complexes in the activation of unactivated monosubstituted olefins for catalytic intermolecular carbon–carbon bond-forming reactions with carbonyl compounds, such as simple aldehydes, isocyanates, and conjugated aldehydes and ketones, are discussed. In these reactions, the olefins function as vinyl- and allylmetal equivalents, providing a new strategy for organic synthesis. Current limitations and the outlook for this new strategy are also discussed. PMID:21904421

  14. Mn-Doped Multinary CIZS and AIZS Nanocrystals.

    PubMed

    Manna, Goutam; Jana, Santanu; Bose, Riya; Pradhan, Narayan

    2012-09-20

    Multinary nanocrystals (CuInS2, CIS, and AgInS2, AIS) are widely known for their strong defect state emission. On alloying with Zn (CIZS and AIZS), stable and intense emission tunable in visible and NIR windows has already been achieved. In these nanocrystals, the photogenerated hole efficiently moves to the defect-induced state and recombines with the electron in the conduction band. As a result, the defect state emission is predominantly observed without any band edge excitonic emission. Herein, we report the doping of the transition-metal ion Mn in these nanocrystals, which in certain compositions of the host nanocrystals quenches this strong defect state emission and predominantly shows the spin-flip Mn emission. Though several Mn-doped semiconductor nanocrystals are reported in the literature, these nanocrystals are of its first kind that can be excited in the visible window, do not contain the toxic element Cd, and provide efficient emission. Hence, when Mn emission is required, these multinary nanocrystals can be the ideal versatile materials for widespread technological applications.

  15. Photoemission Investigations of the Bonding and Interactions of Simple Molecules on Metal Surfaces.

    NASA Astrophysics Data System (ADS)

    Heskett, David Robert

    Various experimental techniques, particularly angle-resolved photoemission, have been used to probe the bonding of CO and N(,2) to metal surfaces, the intermolecular interactions within an adsorbate overlayer, and the effects of coadsorbing CO or N(,2) with an alkali metal. The two-dimensional band-like dispersion of the CO and N(,2) 4(sigma) and 5(sigma) valence levels of the systems CO/Co(0001), CO/Ru(001), CO/Cu(111), and N(,2)/Ru(001) have been measured. In almost all cases of CO adsorbed on a transition metal surface, the bandwidth of the 4(sigma) level is directly related to the CO spacing and geometry in the overlayer. This dispersion results from the direct overlap of the 4(sigma) orbitals of neighboring molecules, with the substrate not playing a significant role. The 5(sigma) bandwidths, on the other hand, are not consistently related to the CO spacing. We attribute this to the greater 5(sigma)-substrate interaction vs. the 4(sigma) level. In cases of weak chemisorption, one or both of the (sigma) bandwidths is anomalously small compared with the strongly chemisorbed cases above. We show that this is a many-body effect related to the presence of intense multielectron excitations, or shake-up peaks, in the valence regions of these latter systems. Many chemisorption properties of CO adsorbed to copper vs. transition metal surfaces are compared. A number of qualitative and quantitative differences are found. This suggests that there is a fundamentally different bonding mechanism on these two types of surfaces, which we propose is related to the degree of CO 2(pi) occupancy in these systems. We have performed detailed UPS investigations of the systems CO + K/Cu(100) and CO + K/Ru(001). Our results are quite similar in these two systems and to previous investigations. In both cases, we have observed a strong hybridization and splitting of the CO 5(sigma) and 1(pi) levels in the presence of K and significant changes in the line shape of the K 3p core level when

  16. Photocatalytic Solar Fuel Generation on Semiconductor Nanocrystals

    NASA Astrophysics Data System (ADS)

    Feldmann, Jochen

    2015-03-01

    I will review our scientific work on photocatalytic solar fuel generation utilizing colloidal semiconductor nanocrystals decorated with catalytic metal clusters. In particular, nanocrystals made of CdS, TiO2 and organo-metal halide perovskites will be discussed. Key issues are the role of hole scavangers (M. Berr et al., Appl. Phys. Lett. 100, 223903 (2012)), the size and density of catalytic clusters (M. Berr et al.: Appl. Phys. Lett. 97, 093108 (2010) and Nano Letters 12, 5903 (2012) , and dependencies on external parameters such as pH (T. Simon et al., Nature Mat. 13, 1013 (2014)). Financially supported by the Bavarian Research Cluster ``Solar Technologies Go Hybrid: SolTech''.

  17. Technical Advances in Intracellular Detection Using Immuno-Gold Particles: Simple Cryofixation with Metal Contact Quick Freezing.

    PubMed

    Song, Chihong; Lee, Ju Huck; Jun, Sangmi; Chung, Jeong Min; Hyun, Jaekyung; Jung, Hyun Suk

    2016-05-01

    The preparation of biological specimens using cryofixation techniques ensures excellent visibility of intracellular structures and preserves the antigenic sites of subcellular molecules. Hence, cryofixation is an effective method of preparing samples for analyses using antibodies conjugated to gold nanoparticles that are designed to detect the localization of specific target molecules within cells. However, cryofixation cannot be utilized easily because it requires expensive equipment and skilled technologists, resulting in a high level of expense for researchers. Here, we describe a simple technical approach to cryofixation that uses metal contact quick freezing followed by a modified freeze substitution technique and immuno-gold labeling electron microscopy. Micrograph images of cells prepared using this modified cryofixation method demonstrated its superiority over chemical fixation for high contrast visualization of the morphologies of cellular components and preservation of antigenicity for immuno-gold labeling. This report provides valuable technical information related to the advancement of metal contact quick freezing techniques, which can be used to visualize biomedical events of interest in an easy, simple, and rapid manner.

  18. A simple approach to obtain hybrid Au-loaded polymeric nanoparticles with a tunable metal load

    NASA Astrophysics Data System (ADS)

    Luque-Michel, Edurne; Larrea, Ane; Lahuerta, Celia; Sebastian, Víctor; Imbuluzqueta, Edurne; Arruebo, Manuel; Blanco-Prieto, María J.; Santamaría, Jesús

    2016-03-01

    A new strategy to nanoengineer multi-functional polymer-metal hybrid nanostructures is reported. By using this protocol the hurdles of most of the current developments concerning covalent and non-covalent attachment of polymers to preformed inorganic nanoparticles (NPs) are overcome. The strategy is based on the in situ reduction of metal precursors using the polymeric nanoparticle as a nanoreactor. Gold nanoparticles and poly(dl-lactic-co-glycolic acid), PLGA, are located in the core and shell, respectively. This novel technique enables the production of PLGA NPs smaller than 200 nm that bear either a single encapsulated Au NP or several smaller NPs with tunable sizes and a 100% loading efficiency. In situ reduction of Au ions inside the polymeric NPs was achieved on demand by using heat to activate the reductive effect of citrate ions. In addition, we show that the loading of the resulting Au NPs inside the PLGA NPs is highly dependent on the surfactant used. Electron microscopy, laser irradiation, UV-Vis and fluorescence spectroscopy characterization techniques confirm the location of Au nanoparticles. These promising results indicate that these hybrid nanomaterials could be used in theranostic applications or as contrast agents in dark-field imaging and computed tomography.A new strategy to nanoengineer multi-functional polymer-metal hybrid nanostructures is reported. By using this protocol the hurdles of most of the current developments concerning covalent and non-covalent attachment of polymers to preformed inorganic nanoparticles (NPs) are overcome. The strategy is based on the in situ reduction of metal precursors using the polymeric nanoparticle as a nanoreactor. Gold nanoparticles and poly(dl-lactic-co-glycolic acid), PLGA, are located in the core and shell, respectively. This novel technique enables the production of PLGA NPs smaller than 200 nm that bear either a single encapsulated Au NP or several smaller NPs with tunable sizes and a 100% loading

  19. Colloidal Nanocrystals Fluoresced by Surface Coordination Complexes

    PubMed Central

    Wang, Guan; Ji, Jianwei; Zhang, Xinwen; Zhang, Yan; Wang, Qiangbin; You, Xiaozeng; Xu, Xiangxing

    2014-01-01

    Colloidal Nanocrystals (NCs) with fluorescence originating from surface complexes are successfully prepared. The components of these NCs range from insulator, semiconductor to metal, with either pure phase, doped or core/shell structures. The photoluminescence of these NCs can be reversibly tuned across the visible to infrared spectrum, and even allow multi-color emission. A light emitting device is fabricated and a new in vivo cell imaging method is performed to demonstrate the power of this technology for emerging applications. PMID:24970242

  20. Inhibition of palm oil oxidation by zeolite nanocrystals.

    PubMed

    Tan, Kok-Hou; Awala, Hussein; Mukti, Rino R; Wong, Ka-Lun; Rigaud, Baptiste; Ling, Tau Chuan; Aleksandrov, Hristiyan A; Koleva, Iskra Z; Vayssilov, Georgi N; Mintova, Svetlana; Ng, Eng-Poh

    2015-05-13

    The efficiency of zeolite X nanocrystals (FAU-type framework structure) containing different extra-framework cations (Li(+), Na(+), K(+), and Ca(2+)) in slowing the thermal oxidation of palm oil is reported. The oxidation study of palm oil is conducted in the presence of zeolite nanocrystals (0.5 wt %) at 150 °C. Several characterization techniques such as visual analysis, colorimetry, rheometry, total acid number (TAN), FT-IR spectroscopy, (1)H NMR spectroscopy, and Karl Fischer analyses are applied to follow the oxidative evolution of the oil. It was found that zeolite nanocrystals decelerate the oxidation of palm oil through stabilization of hydroperoxides, which are the primary oxidation product, and concurrently via adsorption of the secondary oxidation products (alcohols, aldehydes, ketones, carboxylic acids, and esters). In addition to the experimental results, periodic density functional theory (DFT) calculations are performed to elucidate further the oxidation process of the palm oil in the presence of zeolite nanocrystals. The DFT calculations show that the metal complexes formed with peroxides are more stable than the complexes with alkenes with the same ions. The peroxides captured in the zeolite X nanocrystals consequently decelerate further oxidation toward formation of acids. Unlike the monovalent alkali metal cations in the zeolite X nanocrystals (K(+), Na(+), and Li(+)), Ca(2+) reduced the acidity of the oil by neutralizing the acidic carboxylate compounds to COO(-)(Ca(2+))1/2 species.

  1. A simple approach to obtain hybrid Au-loaded polymeric nanoparticles with a tunable metal load.

    PubMed

    Luque-Michel, Edurne; Larrea, Ane; Lahuerta, Celia; Sebastian, Víctor; Imbuluzqueta, Edurne; Arruebo, Manuel; Blanco-Prieto, María J; Santamaría, Jesús

    2016-03-28

    A new strategy to nanoengineer multi-functional polymer-metal hybrid nanostructures is reported. By using this protocol the hurdles of most of the current developments concerning covalent and non-covalent attachment of polymers to preformed inorganic nanoparticles (NPs) are overcome. The strategy is based on the in situ reduction of metal precursors using the polymeric nanoparticle as a nanoreactor. Gold nanoparticles and poly(DL-lactic-co-glycolic acid), PLGA, are located in the core and shell, respectively. This novel technique enables the production of PLGA NPs smaller than 200 nm that bear either a single encapsulated Au NP or several smaller NPs with tunable sizes and a 100% loading efficiency. In situ reduction of Au ions inside the polymeric NPs was achieved on demand by using heat to activate the reductive effect of citrate ions. In addition, we show that the loading of the resulting Au NPs inside the PLGA NPs is highly dependent on the surfactant used. Electron microscopy, laser irradiation, UV-Vis and fluorescence spectroscopy characterization techniques confirm the location of Au nanoparticles. These promising results indicate that these hybrid nanomaterials could be used in theranostic applications or as contrast agents in dark-field imaging and computed tomography.

  2. Size control and quantum confinement in Cu2ZnSnS4 nanocrystals.

    PubMed

    Khare, Ankur; Wills, Andrew W; Ammerman, Lauren M; Norris, David J; Aydil, Eray S

    2011-11-14

    Starting with metal dithiocarbamate complexes, we synthesize colloidal Cu(2)ZnSnS(4) (CZTS) nanocrystals with diameters ranging from 2 to 7 nm. Structural and Raman scattering data confirm that CZTS is obtained rather than other possible material phases. The optical absorption spectra of nanocrystals with diameters less than 3 nm show a shift to higher energy due to quantum confinement.

  3. Plasmonic engineering of spontaneous emission from silicon nanocrystals

    PubMed Central

    Goffard, Julie; Gérard, Davy; Miska, Patrice; Baudrion, Anne-Laure; Deturche, Régis; Plain, Jérôme

    2013-01-01

    Silicon nanocrystals offer huge advantages compared to other semi-conductor quantum dots as they are made from an abundant, non-toxic material and are compatible with silicon devices. Besides, among a wealth of extraordinary properties ranging from catalysis to nanomedicine, metal nanoparticles are known to increase the radiative emission rate of semiconductor quantum dots. Here, we use gold nanoparticles to accelerate the emission of silicon nanocrystals. The resulting integrated hybrid emitter is 5-fold brighter than bare silicon nanocrystals. We also propose an in-depth analysis highlighting the role of the different physical parameters in the photoluminescence enhancement phenomenon. This result has important implications for the practical use of silicon nanocrystals in optoelectronic devices, for instance for the design of efficient down-shifting devices that could be integrated within future silicon solar cells. PMID:24037020

  4. Charge-tunable quantum plasmons in colloidal semiconductor nanocrystals.

    PubMed

    Schimpf, Alina M; Thakkar, Niket; Gunthardt, Carolyn E; Masiello, David J; Gamelin, Daniel R

    2014-01-28

    Nanomaterials exhibiting plasmonic optical responses are impacting sensing, information processing, catalysis, solar, and photonics technologies. Recent advances have expanded the portfolio of plasmonic nanostructures into doped semiconductor nanocrystals, which allow dynamic manipulation of carrier densities. Once interpreted as intraband single-electron transitions, the infrared absorption of doped semiconductor nanocrystals is now commonly attributed to localized surface plasmon resonances and analyzed using the classical Drude model to determine carrier densities. Here, we show that the experimental plasmon resonance energies of photodoped ZnO nanocrystals with controlled sizes and carrier densities diverge from classical Drude model predictions at small sizes, revealing quantum plasmons in these nanocrystals. A Lorentz oscillator model more adequately describes the data and illustrates a closer link between plasmon resonances and single-electron transitions in semiconductors than in metals, highlighting a fundamental contrast between these two classes of plasmonic materials.

  5. ZnO-Ag Composite Nanocrystals from Nanoemulsion: Synthesis, Magnetic, and Optical Properties

    NASA Astrophysics Data System (ADS)

    Gim, Ji Seok; Wu, JunHua; Lee, Ji Sung; Yoon, Hayoung; Min, Ji Hyun; Ju, Jae-Seon; Kim, Young Keun

    2013-06-01

    We report a simple approach to synthesize ZnO-Ag composite nanocrystals with different ZnO/Ag ratios via a nanoemulsion process. The morphology and structure of the nanocrystals are investigated by X-ray diffraction and transmission electron microscopy, showing the high crystallinity of the nanocrystals with narrow size distributions. The corresponding optical and magnetic properties are analyzed with photoluminescence spectroscopy, ultraviolet-visible spectrometry and physical property measurement system in detail. The ensuing magnetism is interpreted in terms of nanosizing and other effects. Such ZnO-Ag nanocrystals may be further explored for biomedical applications and spintronic devices with interesting optical and magnetic properties.

  6. Electrochemically Induced Transformations of Vanadium Dioxide Nanocrystals.

    PubMed

    Dahlman, Clayton J; LeBlanc, Gabriel; Bergerud, Amy; Staller, Corey; Adair, Jacob; Milliron, Delia J

    2016-10-12

    Vanadium dioxide (VO2) undergoes significant optical, electronic, and structural changes as it transforms between the low-temperature monoclinic and high-temperature rutile phases. Recently, alternative stimuli have been utilized to trigger insulator-to-metal transformations in VO2, including electrochemical gating. Here, we prepare and electrochemically reduce mesoporous films of VO2 nanocrystals, prepared from colloidally synthesized V2O3 nanocrystals that have been oxidatively annealed, in a three-electrode electrochemical cell. We observe a reversible transition between infrared transparent insulating phases and a darkened metallic phase by in situ visible-near-infrared spectroelectrochemistry and correlate these observations with structural and electronic changes monitored by X-ray absorption spectroscopy, X-ray diffraction, Raman spectroscopy, and conductivity measurements. An unexpected reversible transition from conductive, reduced monoclinic VO2 to an infrared-transparent insulating phase upon progressive electrochemical reduction is observed. This insulator-metal-insulator transition has not been reported in previous studies of electrochemically gated epitaxial VO2 films and is attributed to improved oxygen vacancy formation kinetics and diffusion due to the mesoporous nanocrystal film structure.

  7. Fluorescence enhancement, blinking suppression, and gray states of individual semiconductor nanocrystals close to gold nanoparticles.

    PubMed

    Ma, Xuedan; Tan, Hua; Kipp, Tobias; Mews, Alf

    2010-10-13

    The optical properties of nanocrystals are drastically changed by the interaction with adjacent metal nanoparticles. By time-resolved photoluminescence spectroscopy, we investigate CdSe multishell nanocrystals coupled to self-assembled films of Au nanoparticles. The distance between emitter and metal is adjusted by coating the nanocrystals with silica shells. These NCs showed increased fluorescence intensity, a decreased fluorescence lifetime, strong blinking suppression, and fluorescence from gray states. These observations can be explained by the metal particle induced change of excitation and recombination rates.

  8. A simple method to estimate relative stabilities of polyethers cationized by alkali metal ions.

    PubMed

    Kuki, Ákos; Nagy, Lajos; Shemirani, Ghazaleh; Memboeuf, Antony; Drahos, László; Vékey, Károly; Zsuga, Miklós; Kéki, Sándor

    2012-02-15

    Dissociation of doubly cationized polyethers, namely [P + 2X](2+) into [P + X](+) and X(+), where P = polyethylene glycol (PEG), polypropylene glycol (PPG) and polytetrahydrofuran (PTHF) and X = Na, K and Cs, was studied by means of energy-dependent collision-induced dissociation tandem mass spectrometry. It was observed that the collision voltage necessary to obtain 50% fragmentation (CV(50)) determined for the doubly cationized polyethers of higher degree of polymerization varied linearly with the number of degrees of freedom (DOF) values. This observation allowed us to correlate these slopes with the corresponding relative gas-phase dissociation energies for binding of alkali ions to polyethers. The relative dissociation energies determined from the corresponding slopes were found to decrease in the order Na(+)  > K(+)  > Cs(+) for each polyether studied, and an order PPG ≈ PEG > PTHF can be established for each alkali metal ion.

  9. A simple route to diverse noble metal-decorated iron oxide nanoparticles for catalysis

    NASA Astrophysics Data System (ADS)

    Walker, Joan M.; Zaleski, Jeffrey M.

    2016-01-01

    Developing facile synthetic routes to multifunctional nanoparticles combining the magnetic properties of iron oxides with the optical and catalytic utility of noble metal particles remains an important goal in realizing the potential of hybrid nanomaterials. To this end, we have developed a single route to noble metal-decorated magnetic nanoparticles (Fe3O4@SiO2-M M = Au, Pd, Ag, and PtAg) and characterized them by HRTEM and STEM/EDX imaging to reveal their nanometer size (16 nm Fe3O4 and 1-5 nm M seeds) and uniformity. This represents one of the few examples of genuine multifunctional particles on the nanoscale. We show that these hybrid structures have excellent catalytic activity for the reduction of 4-nitrophenol (knorm = 2 × 107 s-1 mol(Pd)-1 5 × 106 s-1 mol(Au)-1 5 × 105 s-1 mol(PtAg)-1 7 × 105 s-1 mol(Ag)-1). These rates are the highest reported for nano-sized comparables, and are competitive with mesoparticles of similar composition. Due to their magnetic response, the particles are also suitable for magnetic recovery and maintain >99% conversion for at least four cycles. Using this synthetic route, Fe3O4@SiO2-M particles show great promise for further development as a precursor to complicated anisotropic materials or for applications ranging from nanocatalysis to biomedical sensing.Developing facile synthetic routes to multifunctional nanoparticles combining the magnetic properties of iron oxides with the optical and catalytic utility of noble metal particles remains an important goal in realizing the potential of hybrid nanomaterials. To this end, we have developed a single route to noble metal-decorated magnetic nanoparticles (Fe3O4@SiO2-M M = Au, Pd, Ag, and PtAg) and characterized them by HRTEM and STEM/EDX imaging to reveal their nanometer size (16 nm Fe3O4 and 1-5 nm M seeds) and uniformity. This represents one of the few examples of genuine multifunctional particles on the nanoscale. We show that these hybrid structures have excellent catalytic

  10. Unprecedented Topological Complexity in a Metal-Organic Framework Constructed from Simple Building Units.

    PubMed

    Inge, A Ken; Köppen, Milan; Su, Jie; Feyand, Mark; Xu, Hongyi; Zou, Xiaodong; O'Keeffe, Michael; Stock, Norbert

    2016-02-17

    A bismuth-based metal-organic framework (MOF), [Bi(BTC)(H2O)]·2H2O·MeOH denoted CAU-17, was synthesized and found to have an exceptionally complicated structure with helical Bi-O rods cross-linked by 1,3,5-benzenetricarboxylate (BTC(3-)) ligands. Five crystallographically independent 1D channels including two hexagonal channels, two rectangular channels, and one triangular channel have accessible diameters of 9.6, 9.6, 3.6, 3.6, and 3.4 Å, respectively. The structure is further complicated by twinning. Rod-incorporated MOF structures typically have underlying nets with only one unique node and three or four unique edges. In contrast, topological analysis of CAU-17 revealed unprecedented complexity for a MOF structure with 54 unique nodes and 135 edges. The complexity originates from the rod packing and the rods themselves, which are related to aperiodic helices.

  11. Plasmon-modulated light scattering from gold nanocrystal-decorated hollow mesoporous silica microspheres.

    PubMed

    Xiao, Manda; Chen, Huanjun; Ming, Tian; Shao, Lei; Wang, Jianfang

    2010-11-23

    Localized surface plasmon resonances of noble metal nanocrystals are powerful in enhancing a variety of linear and nonlinear optical signals and photorelated processes. Here we demonstrate the plasmonic enhancement of the light scattering from hollow mesoporous silica microspheres by attaching a dense layer of gold nanocrystals onto the outer surface of the microspheres. The attachment of gold nanocrystals induces both the shift and intensity increase in the resonant scattering peaks of the microspheres. The spectral region of the resonant scattering enhancement can be controlled by using gold nanocrystals with different plasmon resonance wavelengths. The spectral region of the enhancement is independent of the microsphere diameter. The scattering enhancement factor ranges from 20 to 130, depending on the plasmonic properties and surface coverage of the attached gold nanocrystals. The systematic evolution of the scattering spectra of the individual microspheres is also revealed by chemically etching away the attached gold nanocrystals gradually.

  12. Unconfined twist : a simple method to prepare ultrafine grained metallic materials.

    SciTech Connect

    Zhao, Y.; Liao, Xiaozhou; Zhu, Y. T.

    2004-01-01

    A new simple method - unconfined twist was employed to prepare ultrafine grained (UFG) Fe,wire. A coarse grained (CG) Fe wire with a diameter of 0.85 mm was fixed at one end, and twisted at the other end. After maximum twist before fracture, in the cross-sectional plane, concentrically deformed layers with a width of several micrometers formed surrounding the center axis of the wire. The near-surface deformed layers consist of lamella grains with a width in submicrometer range. In the longitudinal plane, deformed bands (with a width of several micrometers) formed uniformly, which were composed of lamella crystallites (with a width in submicrometer range). The tensile yield strength and ultimate strength of the twisted Fe wire are increased by about 150% and 100% compared with the values of its CG counterpart.

  13. Infrared emitting and photoconducting colloidal silver chalcogenide nanocrystal quantum dots from a silylamide-promoted synthesis.

    PubMed

    Yarema, Maksym; Pichler, Stefan; Sytnyk, Mykhailo; Seyrkammer, Robert; Lechner, Rainer T; Fritz-Popovski, Gerhard; Jarzab, Dorota; Szendrei, Krisztina; Resel, Roland; Korovyanko, Oleksandra; Loi, Maria Antonietta; Paris, Oskar; Hesser, Günter; Heiss, Wolfgang

    2011-05-24

    Here, we present a hot injection synthesis of colloidal Ag chalcogenide nanocrystals (Ag(2)Se, Ag(2)Te, and Ag(2)S) that resulted in exceptionally small nanocrystal sizes in the range between 2 and 4 nm. Ag chalcogenide nanocrystals exhibit band gap energies within the near-infrared spectral region, making these materials promising as environmentally benign alternatives to established infrared active nanocrystals containing toxic metals such as Hg, Cd, and Pb. We present Ag(2)Se nanocrystals in detail, giving size-tunable luminescence with quantum yields above 1.7%. The luminescence, with a decay time on the order of 130 ns, was shown to improve due to the growth of a monolayer thick ZnSe shell. Photoconductivity with a quantum efficiency of 27% was achieved by blending the Ag(2)Se nanocrystals with a soluble fullerene derivative. The co-injection of lithium silylamide was found to be crucial to the synthesis of Ag chalcogenide nanocrystals, which drastically increased their nucleation rate even at relatively low growth temperatures. Because the same observation was made for the nucleation of Cd chalcogenide nanocrystals, we conclude that the addition of lithium silylamide might generally promote wet-chemical synthesis of metal chalcogenide nanocrystals, including in as-yet unexplored materials.

  14. Nanocrystal Solar Cells

    SciTech Connect

    Gur, Ilan

    2006-01-01

    This dissertation presents the results of a research agenda aimed at improving integration and stability in nanocrystal-based solar cells through advances in active materials and device architectures. The introduction of 3-dimensional nanocrystals illustrates the potential for improving transport and percolation in hybrid solar cells and enables novel fabrication methods for optimizing integration in these systems. Fabricating cells by sequential deposition allows for solution-based assembly of hybrid composites with controlled and well-characterized dispersion and electrode contact. Hyperbranched nanocrystals emerge as a nearly ideal building block for hybrid cells, allowing the controlled morphologies targeted by templated approaches to be achieved in an easily fabricated solution-cast device. In addition to offering practical benefits to device processing, these approaches offer fundamental insight into the operation of hybrid solar cells, shedding light on key phenomena such as the roles of electrode-contact and percolation behavior in these cells. Finally, all-inorganic nanocrystal solar cells are presented as a wholly new cell concept, illustrating that donor-acceptor charge transfer and directed carrier diffusion can be utilized in a system with no organic components, and that nanocrystals may act as building blocks for efficient, stable, and low-cost thin-film solar cells.

  15. Analysis of simple 2-D and 3-D metal structures subjected to fragment impact

    NASA Technical Reports Server (NTRS)

    Witmer, E. A.; Stagliano, T. R.; Spilker, R. L.; Rodal, J. J. A.

    1977-01-01

    Theoretical methods were developed for predicting the large-deflection elastic-plastic transient structural responses of metal containment or deflector (C/D) structures to cope with rotor burst fragment impact attack. For two-dimensional C/D structures both, finite element and finite difference analysis methods were employed to analyze structural response produced by either prescribed transient loads or fragment impact. For the latter category, two time-wise step-by-step analysis procedures were devised to predict the structural responses resulting from a succession of fragment impacts: the collision force method (CFM) which utilizes an approximate prediction of the force applied to the attacked structure during fragment impact, and the collision imparted velocity method (CIVM) in which the impact-induced velocity increment acquired by a region of the impacted structure near the impact point is computed. The merits and limitations of these approaches are discussed. For the analysis of 3-d responses of C/D structures, only the CIVM approach was investigated.

  16. A simple method for understanding the triangular growth patterns of transition metal dichalcogenide sheets

    SciTech Connect

    Zhu, Siya; Wang, Qian

    2015-10-15

    Triangular nanoflake growth patterns have been commonly observed in synthesis of transition metal dichalcogenide sheets and their hybrid structures. Triangular nanoflakes not only show exceptional properties, but also can serve as building blocks for two or three dimensional structures. In this study, taking the MoS{sub 2} system as a test case, we propose a Matrix method to understand the mechanism of such unique growth pattern. Nanoflakes with different edge types are mathematically described with configuration matrices, and the total formation energy is calculated as the sum of the edge formation energies and the chemical potentials of sulfur and molybdenum. Based on energetics, we find that three triangular patterns with the different edge configurations are energetically more favorable in different ranges of the chemical potential of sulfur, which are in good agreement with experimental observations. Our algorithm has high efficiency and can deal with nanoflakes in microns which are beyond the ability of ab-initio method. This study not only elucidates the mechanism of triangular nanoflake growth patterns in experiment, but also provides a clue to control the geometric configurations in synthesis.

  17. Simple hydrothermal synthesis of metal oxides coupled nanocomposites: Structural, optical, magnetic and photocatalytic studies

    NASA Astrophysics Data System (ADS)

    Ganeshraja, Ayyakannu Sundaram; Clara, Antoni Samy; Rajkumar, Kanniah; Wang, Yanjie; Wang, Yu; Wang, Junhu; Anbalagan, Krishnamoorthy

    2015-10-01

    The present article is focused on recent developments toward the preparation of room temperature ferromagnetic nanocomposites using better photocatalytic performance. These nanocomposites were successfully prepared by a simple hydrothermal method and their molecular formulas were confirmed as Ti0.90Sn0.10O2 (S1), 0.2CuO-Ti0.73Sn0.06Cu0.21O2-δ (S2), and Ti0.82Sn0.09Fe0.09O2-δ (S3). The ICP, XRD, DRS, FTIR, Raman, XAFS, XPS, EPR, SEM-EDX, HRSEM, HRTEM, photoluminescence and vibrating sample magnetometric measurements were employed to characterize the phase structures, morphologies, optical and magnetic properties of the photocatalysts. The local structures of Sn4+ and Fe3+ were confirmed by 119Sn and 57Fe Mössbauer analysis. The photocatalytic activities of the samples were evaluated by the degradation of methyl orange in water under visible light irradiation. Among the samples, tin doped TiO2 (S1) showed the best photocatalytic performance and stability.

  18. Synthesis of Doped Semiconductor Nanocrystals and Conductive Coatings

    NASA Astrophysics Data System (ADS)

    Wills, Andrew Wilke

    measurements reveal that the nanocrystal Fermi level rises with increasing Al content. The third thrust is achieved by the use of primary dithiocarbamates as ligands to stabilize CdSe, and PbSe / CdSe core/shell nanoparticles. Primary dithiocarbamates bind well to metals but include a weak chemical bond that can be broken with gentle heating. This enables us to bind them to nanoparticles, process the particles into devices, then remove the ligand via gentle heating. Characterization of the ligand-particle interactions show excellent ligand binding to the particle surface and easy ligand removal with heating. After ligand removal, the inter-particle spacing shrinks. Transistor measurements reveal that this reduces the barrier to interparticle electron transport, enhancing the conductivity of the film.

  19. Comparison of residual stresses in Inconel 718 simple parts made by electron beam melting and direct laser metal sintering

    SciTech Connect

    Kolbus, Lindsay M.; Payzant, E. Andrew; Cornwell, Paris A.; Watkins, Thomas R.; Babu, Sudarsanam Suresh; Dehoff, Ryan R.; Duty, Chad E.; Lorenz, M.; Ovchinnikova, O. S.

    2015-01-10

    Residual stress profiles were mapped using neutron diffraction in two simple prism builds of Inconel 718: one fabricated with electron beam melting and the other with direct laser sintering. Spatially indexed stress-free cubes were obtained by EDM sectioning equivalent prisms of similar shape. The (311) interplanar spacing examined for the EDM sectioned sample was compared to the interplanar spacings calculated to fulfill force and moment balance. We have shown that Applying force and moment balance is a necessary supplement to the measurements for the stress-free cubes with respect to accurate stress calculations in additively manufactured components. Furthermore, our work has shown that residual stresses in electron beam melting parts are much smaller than that of direct laser metal sintering parts.

  20. Effects of macroscopic inhomogeneities on the magnetoresistivity of simple metals and critical field anisotropy in granular aluminum

    NASA Astrophysics Data System (ADS)

    Loeffler, K. M.

    The effects of macroscopic voids on the high field thermal magnetoresistivity of the simple metals, including the effects of the lattice conductivity were determined. The calculations were performed using a Green's function approach and a boundary value method. The presence of the lattice conductivity causes large deviations from the linear term evident in the electrical magnetoresistivity. The thermal magnetoresistivity, both transverse and longitudinal, saturates in sufficiently strong fields. The deviation from linearity occurs for 10 is equal to or less than omega sub c tau is equal to or less than 100 depending upon the magnitude of k sub g. The Righi-Leduc coefficient was determined and it was found that the voids caused light increase. The magnetoresistance anomalies of potassium cannot be explained by the presence of voids. Critical field and fluctuation conductivity for extreme type 2 granular aluminum films were measured and found to exhibit a strong temperature dependent anisotropy.

  1. Comparison of residual stresses in Inconel 718 simple parts made by electron beam melting and direct laser metal sintering

    DOE PAGES

    Kolbus, Lindsay M.; Payzant, E. Andrew; Cornwell, Paris A.; ...

    2015-01-10

    Residual stress profiles were mapped using neutron diffraction in two simple prism builds of Inconel 718: one fabricated with electron beam melting and the other with direct laser sintering. Spatially indexed stress-free cubes were obtained by EDM sectioning equivalent prisms of similar shape. The (311) interplanar spacing examined for the EDM sectioned sample was compared to the interplanar spacings calculated to fulfill force and moment balance. We have shown that Applying force and moment balance is a necessary supplement to the measurements for the stress-free cubes with respect to accurate stress calculations in additively manufactured components. Furthermore, our work hasmore » shown that residual stresses in electron beam melting parts are much smaller than that of direct laser metal sintering parts.« less

  2. Simple preparation of magnetic metal-organic frameworks composite as a "bait" for phosphoproteome research.

    PubMed

    Han, Guobin; Zeng, Qiaoling; Jiang, Zhongwei; Deng, Wenchan; Huang, Chengzhi; Li, Yuanfang

    2017-08-15

    Phosphospecific enrichment techniques and mass spectrometry (MS) are primary tools for comprehending the cellular phosphoproteome. In this work, a rational and extremely facile route to synthesize the magnetic metal-organic frameworks (mMOFs) was employed and the prepared composite was first utilized as a "bait" for selective enrichment of phosphopeptides. Typically, the mMOFs was synthesized via electrostatic self-assembly between the negatively charged Fe3O4 magnetic nanoparticles (MNPs) and positively charged MIL-101(Fe). The obtained Fe3O4/MIL-101(Fe) composite possessed well-defined structures, rough surface, highly specific surface area and excellent magnetic property. To demonstrate their ability for enrichment of phosphopeptides, we applied Fe3O4/MIL-101(Fe) as a "bait" to capture the phosphopeptides from standard protein digestion and practical samples. The enriched phosphopeptides were analyzed by matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS). The MS results show that the Fe3O4/MIL-101(Fe) exhibits superior enrichment performance for phosphopeptides with low detectable concentration assessed to be 8 fmol, selectivity investigated to be 1:1000 using β-casein/bovine serum albumin mixture and enrichment recovery evaluated to be 89.8%. Based on these excellent properties, the prepared composite was used to enrich the phosphopeptides from tilapia eggs biological samples for the first time. A total number of 51 phosphorylation sites were identified from the digest of tilapia eggs proteins, suggesting the excellent potential of Fe3O4/MIL-101(Fe) composite in the practical application. Copyright © 2017 Elsevier B.V. All rights reserved.

  3. A simple synthesis method to produce metal oxide loaded carbon paper using bacterial cellulose gel and characterization of its electrochemical behavior in an aqueous electrolyte

    NASA Astrophysics Data System (ADS)

    Miyajima, Naoya; Jinguji, Ken; Matsumura, Taiyu; Matsubara, Toshihiro; Sakane, Hideto; Akatsu, Takashi; Tanaike, Osamu

    2016-04-01

    A simple synthetic chemical process to produce metal oxide loaded carbon papers was developed using bacterial cellulose gel, which consisted of nanometer-sized fibrous cellulose and water. Metal ions were successfully impregnated into the gel via aqueous solution media before drying and carbonization methods resulting in metal oxide contents that were easy to control through variations in the concentration of aqueous solutions. The papers loaded by molybdenum oxides were characterized as pseudocapacitor electrodes preliminary, and the large redox capacitance of the oxides was followed by a conductive fibrous carbon substrate, suggesting that a binder and carbon black additive-free electrode consisting of metal oxides and carbon paper was formed.

  4. SIMPLE MODELS OF METAL-LINE ABSORPTION AND EMISSION FROM COOL GAS OUTFLOWS

    SciTech Connect

    Prochaska, J. Xavier; Rubin, Kate

    2011-06-10

    We analyze the absorption and emission-line profiles produced by a set of simple, cool gas wind models motivated by galactic-scale outflow observations. We implement Monte Carlo radiative transfer techniques that track the propagation of scattered and fluorescent photons to generate one-dimensional spectra and two-dimensional spectral images. We focus on the Mg II {lambda}{lambda}2796, 2803 doublet and Fe II UV1 multiplet at {lambda} {approx} 2600 A, but the results are applicable to other transitions that trace outflows (e.g., Na I, H I Ly{alpha}, Si II). By design, the resonance transitions show blueshifted absorption but one also predicts strong resonance and fine-structure line emission at roughly the systemic velocity. This line-emission 'fills in' the absorption, reducing the equivalent width by up to 50%, shifting the absorption-line centroid by tens of km s{sup -1}, and reducing the effective opacity near systemic. Analysis of cool gas outflows that ignores this line emission may incorrectly infer that the gas is partially covered, measure a significantly lower peak optical depth, and/or conclude that gas at systemic velocity is absent (e.g., an interstellar or slowly infalling component). Because the Fe II lines are connected by optically thin transitions to fine-structure levels, their profiles more closely reproduce the intrinsic opacity of the wind. Together these results naturally explain the absorption and emission-line characteristics observed for star-forming galaxies at z < 1. We also study a scenario promoted to describe the outflows of z {approx} 3 Lyman break galaxies and find profiles inconsistent with the observations due to scattered photon emission. Although line emission complicates the analysis of absorption-line profiles, the surface brightness profiles offer a unique means of assessing the morphology and size of galactic-scale winds. Furthermore, the kinematics and line ratios offer powerful diagnostics of outflows, motivating deep

  5. The surface structure of silver-coated gold nanocrystals and its influence on shape control

    SciTech Connect

    Padmos, J. Daniel; Personick, Michelle L.; Tang, Qing; Duchesne, Paul N.; Jiang, De-en; Mirkin, Chad A.; Zhang, Peng

    2015-07-08

    Understanding the surface structure of metal nanocrystals with specific facet indices is important due to its impact on controlling nanocrystal shape and functionality. However, this is particularly challenging for halide-adsorbed nanocrystals due to the difficulty in analysing interactions between metals and light halides (for example, chloride). Here we uncover the surface structures of chloride-adsorbed, silver-coated gold nanocrystals with {111}, {110}, {310} and {720} indexed facets by X-ray absorption spectroscopy and density functional theory modelling. The silver–chloride, silver–silver and silver–gold bonding structures are markedly different between the nanocrystal surfaces, and are sensitive to their formation mechanism and facet type. A unique approach of combining the density functional theory and experimental/simulated X-ray spectroscopy further verifies the surface structure models and identifies the previously indistinguishable valence state of silver atoms on the nanocrystal surfaces. Overall, this work elucidates the thus-far unknown chloride–metal nanocrystal surface structures and sheds light onto the halide-induced growth mechanism of anisotropic nanocrystals.

  6. The surface structure of silver-coated gold nanocrystals and its influence on shape control

    NASA Astrophysics Data System (ADS)

    Padmos, J. Daniel; Personick, Michelle L.; Tang, Qing; Duchesne, Paul N.; Jiang, De-En; Mirkin, Chad A.; Zhang, Peng

    2015-07-01

    Understanding the surface structure of metal nanocrystals with specific facet indices is important due to its impact on controlling nanocrystal shape and functionality. However, this is particularly challenging for halide-adsorbed nanocrystals due to the difficulty in analysing interactions between metals and light halides (for example, chloride). Here we uncover the surface structures of chloride-adsorbed, silver-coated gold nanocrystals with {111}, {110}, {310} and {720} indexed facets by X-ray absorption spectroscopy and density functional theory modelling. The silver-chloride, silver-silver and silver-gold bonding structures are markedly different between the nanocrystal surfaces, and are sensitive to their formation mechanism and facet type. A unique approach of combining the density functional theory and experimental/simulated X-ray spectroscopy further verifies the surface structure models and identifies the previously indistinguishable valence state of silver atoms on the nanocrystal surfaces. Overall, this work elucidates the thus-far unknown chloride-metal nanocrystal surface structures and sheds light onto the halide-induced growth mechanism of anisotropic nanocrystals.

  7. The surface structure of silver-coated gold nanocrystals and its influence on shape control.

    PubMed

    Padmos, J Daniel; Personick, Michelle L; Tang, Qing; Duchesne, Paul N; Jiang, De-en; Mirkin, Chad A; Zhang, Peng

    2015-07-08

    Understanding the surface structure of metal nanocrystals with specific facet indices is important due to its impact on controlling nanocrystal shape and functionality. However, this is particularly challenging for halide-adsorbed nanocrystals due to the difficulty in analysing interactions between metals and light halides (for example, chloride). Here we uncover the surface structures of chloride-adsorbed, silver-coated gold nanocrystals with {111}, {110}, {310} and {720} indexed facets by X-ray absorption spectroscopy and density functional theory modelling. The silver-chloride, silver-silver and silver-gold bonding structures are markedly different between the nanocrystal surfaces, and are sensitive to their formation mechanism and facet type. A unique approach of combining the density functional theory and experimental/simulated X-ray spectroscopy further verifies the surface structure models and identifies the previously indistinguishable valence state of silver atoms on the nanocrystal surfaces. Overall, this work elucidates the thus-far unknown chloride-metal nanocrystal surface structures and sheds light onto the halide-induced growth mechanism of anisotropic nanocrystals.

  8. The surface structure of silver-coated gold nanocrystals and its influence on shape control

    DOE PAGES

    Padmos, J. Daniel; Personick, Michelle L.; Tang, Qing; ...

    2015-07-08

    Understanding the surface structure of metal nanocrystals with specific facet indices is important due to its impact on controlling nanocrystal shape and functionality. However, this is particularly challenging for halide-adsorbed nanocrystals due to the difficulty in analysing interactions between metals and light halides (for example, chloride). Here we uncover the surface structures of chloride-adsorbed, silver-coated gold nanocrystals with {111}, {110}, {310} and {720} indexed facets by X-ray absorption spectroscopy and density functional theory modelling. The silver–chloride, silver–silver and silver–gold bonding structures are markedly different between the nanocrystal surfaces, and are sensitive to their formation mechanism and facet type. A uniquemore » approach of combining the density functional theory and experimental/simulated X-ray spectroscopy further verifies the surface structure models and identifies the previously indistinguishable valence state of silver atoms on the nanocrystal surfaces. Overall, this work elucidates the thus-far unknown chloride–metal nanocrystal surface structures and sheds light onto the halide-induced growth mechanism of anisotropic nanocrystals.« less

  9. The surface structure of silver-coated gold nanocrystals and its influence on shape control

    PubMed Central

    Padmos, J. Daniel; Personick, Michelle L.; Tang, Qing; Duchesne, Paul N.; Jiang, De-en; Mirkin, Chad A.; Zhang, Peng

    2015-01-01

    Understanding the surface structure of metal nanocrystals with specific facet indices is important due to its impact on controlling nanocrystal shape and functionality. However, this is particularly challenging for halide-adsorbed nanocrystals due to the difficulty in analysing interactions between metals and light halides (for example, chloride). Here we uncover the surface structures of chloride-adsorbed, silver-coated gold nanocrystals with {111}, {110}, {310} and {720} indexed facets by X-ray absorption spectroscopy and density functional theory modelling. The silver–chloride, silver–silver and silver–gold bonding structures are markedly different between the nanocrystal surfaces, and are sensitive to their formation mechanism and facet type. A unique approach of combining the density functional theory and experimental/simulated X-ray spectroscopy further verifies the surface structure models and identifies the previously indistinguishable valence state of silver atoms on the nanocrystal surfaces. Overall, this work elucidates the thus-far unknown chloride–metal nanocrystal surface structures and sheds light onto the halide-induced growth mechanism of anisotropic nanocrystals. PMID:26153854

  10. Electron-Phonon Coupling and Energy Flow in a Simple Metal beyond the Two-Temperature Approximation

    NASA Astrophysics Data System (ADS)

    Waldecker, Lutz; Bertoni, Roman; Ernstorfer, Ralph; Vorberger, Jan

    2016-04-01

    The electron-phonon coupling and the corresponding energy exchange are investigated experimentally and by ab initio theory in nonequilibrium states of the free-electron metal aluminium. The temporal evolution of the atomic mean-squared displacement in laser-excited thin freestanding films is monitored by femtosecond electron diffraction. The electron-phonon coupling strength is obtained for a range of electronic and lattice temperatures from density functional theory molecular dynamics simulations. The electron-phonon coupling parameter extracted from the experimental data in the framework of a two-temperature model (TTM) deviates significantly from the ab initio values. We introduce a nonthermal lattice model (NLM) for describing nonthermal phonon distributions as a sum of thermal distributions of the three phonon branches. The contributions of individual phonon branches to the electron-phonon coupling are considered independently and found to be dominated by longitudinal acoustic phonons. Using all material parameters from first-principles calculations except the phonon-phonon coupling strength, the prediction of the energy transfer from electrons to phonons by the NLM is in excellent agreement with time-resolved diffraction data. Our results suggest that the TTM is insufficient for describing the microscopic energy flow even for simple metals like aluminium and that the determination of the electron-phonon coupling constant from time-resolved experiments by means of the TTM leads to incorrect values. In contrast, the NLM describing transient phonon populations by three parameters appears to be a sufficient model for quantitatively describing electron-lattice equilibration in aluminium. We discuss the general applicability of the NLM and provide a criterion for the suitability of the two-temperature approximation for other metals.

  11. Entropy-driven formation of binary semiconductor-nanocrystal superlattices.

    PubMed

    Evers, Wiel H; De Nijs, Bart; Filion, Laura; Castillo, Sonja; Dijkstra, Marjolein; Vanmaekelbergh, Daniel

    2010-10-13

    One of the main reasons for the current interest in colloidal nanocrystals is their propensity to form superlattices, systems in which (different) nanocrystals are in close contact in a well-ordered three-dimensional (3D) geometry resulting in novel material properties. However, the principles underlying the formation of binary nanocrystal superlattices are not well understood. Here, we present a study of the driving forces for the formation of binary nanocrystal superlattices by comparing the formed structures with full free energy calculations. The nature (metallic or semiconducting) and the size-ratio of the two nanocrystals are varied systematically. With semiconductor nanocrystals, self-organization at high temperature leads to superlattices (AlB(2), NaZn(13), MgZn(2)) in accordance with the phase diagrams for binary hard-sphere mixtures; hence entropy increase is the dominant driving force. A slight change of the conditions results in structures that are energetically stabilized. This study provides rules for the rational design of 3D nanostructured binary semiconductors, materials with promises in thermoelectrics and photovoltaics and which cannot be reached by any other technology.

  12. Growth of gold nanocrystals on BSA thin films

    NASA Astrophysics Data System (ADS)

    Bhowal, Ashim Chandra; Kundu, Sarathi

    2017-05-01

    Biomacromolecules like proteins have got much attention due to their ability to synthesize nanomaterials. A very simple and one step method of growing nanocrystals on BSA protein thin films is explored by using UV-Vis and photoluminescence spectroscopy, X-ray diffraction (XRD) and atomic force microscopy (AFM). It is observed that if different interaction times are provided between BSA thin films and HAuCl4 aqueous solutions of mM concentration, then different nanocrystals form on BSA thin films, however, they are poly dispersed in nature. The formation of gold nanocrystals is confirmed by the presence of UV-Vis absorption peak at ≈ 525 nm and the corresponding plasmonic emission is also observed. XRD analysis shows the formation of gold nanocrystals having fcc structure with preferred growth in (111) crystal plane direction. Surface morphologies of the prepared thin films are investigated through AFM and it is observed that more nanocrystals are formed where more interaction time is provided between BSA and HAuCl4 aqueous solution. Langmuir-like exponential growth behavior is identified for such nanocrystals formation.

  13. Nonvolatile memory devices based on self-assembled nanocrystals

    NASA Astrophysics Data System (ADS)

    Lee, Jang-Sik

    2013-06-01

    Nonvolatile memory devices are one of the most important components in modern electronic devices. Many efforts have been made to fabricate high-density, low-cost, nonvolatile solid-state memory devices for use in portable/mobile electronic devices such as laptop computers, tablet devices, smart phones, etc. Among the many available nonvolatile memory devices, flash memory devices are of great interest to the electronics industry owing to their simple device structure, enabling high-density memory applications. Flash memory devices in which nanoparticles or nanocrystals are used as the charge-trapping elements have advantages over conventional flash memory devices because the charge-trapping layer and memory performance of the former can be readily optimized. Active research has recently been conducted to fabricate and characterize self-assembled-nanocrystal-based nonvolatile memory devices. We reviewed various strategies for fabricating nanocrystal-based nonvolatile memory devices and discussed the programmable memory properties and the device reliability characteristics of nanocrystal-based memory devices to possibly apply nanocrystal-based memory devices to those used in portable/mobile electronic devices. Finally, novel device applications such as printed/flexible/transparent electronic devices were explored based on nanocrystal-based memory devices.

  14. Reversible solvent vapor-mediated phase changes in nanocrystal superlattices.

    PubMed

    Goodfellow, Brian W; Korgel, Brian A

    2011-04-26

    Colloidal nanocrystals are being explored for use in a variety of applications, from solar cells to transistors to medical diagnostics and therapy. Ordered assemblies of nanocrystals, or superlattices, are one particularly interesting class of these materials, in which the nanocrystals serve as modular building blocks to construct nanostructures by self-assembly with spatial and temporal complexity and unique properties. From a fundamental perspective, the nanocrystals are simple molecular models that can be manipulated and studied to test statistical mechanical and thermodynamic models of crystallization and disorder. An article by Bian et al. in this issue of ACS Nano reports surprising new phase behavior in semiconductor nanocrystal superlattices: reversible transitions between non-close-packed body-centered cubic (bcc) and body-centered tetragonal (bct) structures, and close-packed face-centered cubic (fcc) structures, observed by real-time in situ grazing incidence small-angle X-ray scattering (GISAXS) measurements, upon solvent vapor exposure and increased interparticle separation. These studies offer new insight and raise new questions about superlattice structure and the forces that control self-assembly. Accompanying computer simulations show that ligand-ligand interactions are important. Furthermore, it appears that ligand-coated nanocrystals have more in common with soft microphase-separated materials, like diblock copolymers and surfactant assemblies, than previously realized.

  15. Segmented flow reactors for nanocrystal synthesis.

    PubMed

    Nightingale, Adrian M; Demello, John C

    2013-04-04

    In the past decade microreactors have emerged as a compelling technology for the highly controlled synthesis of colloidal nanocrystals, offering multiple advantages over conventional batch synthesis methods (including improved levels of control, reproducibility, and automation). Initial work in the field employed simple continuous phase reactors that manipulate miscible streams of a single reagent phase. Recently, however, there has been increasing interest in segmented flow reactors that use an immiscible fluid to divide the reagent phase into discrete slugs or droplets. Key advantages of segmented flow include the elimination of velocity dispersion (a significant cause of polydispersity) and greatly reduced susceptibility to reactor fouling. In this progress report we review the operation of segmented flow microreactors, their application to the controlled synthesis of nanocrystals, and some of the principal challenges that must be addressed before they can become a mainstream technology for the controlled production of nanomaterials. Copyright © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  16. Polyhedral Au nanocrystals exclusively bound by {110} facets: the rhombic dodecahedron.

    PubMed

    Jeong, Gyoung Hwa; Kim, Minjung; Lee, Young Wook; Choi, Wonjun; Oh, Won Taek; Park, Q-Han; Han, Sang Woo

    2009-02-11

    The rhombic dodecahedral Au nanocrystals enclosed by 12 {110} facets could be readily prepared without the use of any seeds, surfactants, or foreign metal ions but only with N,N-dimethylformamide as both reductant and solvent.

  17. Synthesis and characterization of titanium nitride, niobium nitride, and tantalum nitride nanocrystals via the RAPET (reaction under autogenic pressure at elevated temperature) technique

    NASA Astrophysics Data System (ADS)

    George, P. P.; Gedanken, A.; Makhlouf, Shirly Ben-David; Genish, I.; Marciano, A.; Abu-Mukh, Riam

    2009-05-01

    TiN, NbN, and TaN nanocrystals have been selectively prepared through a simple, solvent-free, and convenient reaction under autogenic pressure at moderate temperature (RAPET) process at 350 °C for 12 h, reacting transition metal chlorides and sodium azide. The nanostructures obtained are characterized by powder X-ray diffraction (PXRD), transmission electron microscopy (TEM), and scanning electron microscopy (SEM). A reaction mechanism is suggested based on the experimental results. These rapid reactions produce nanocrystals of TiN, NbN, and TaN with average sizes of approximately 30, 28, and 27 nm, respectively (as calculated from X-ray line broadening). An octahedral inorganic fullerene was detected among the various structures of the TiN.

  18. Synthesis and applications of heterostructured semiconductor nanocrystals

    NASA Astrophysics Data System (ADS)

    Khon, Elena

    Semiconductor nanocrystals (NCs) have been of great interest to researchers for several decades due to their unique optoelectronic properties. These nanoparticles are widely used for a variety of different applications. However, there are many unresolved issues that lower the efficiency and/or stability of devices which incorporate these NCs. Our research is dedicated to addressing these issues by identifying potential problems and resolving them, improving existing systems, generating new synthetic strategies, and/or building new devices. The general strategies for the synthesis of different nanocrystals were established in this work, one of which is the colloidal growth of gold domains onto CdS semiconductor nanocrystals. Control of shape and size was achieved simply by adjusting the temperature and the time of the reaction. Depending on the exact morphology of Au and CdS domains, fabricated nano-composites can undergo evaporation-induced self-assembly onto a substrate, which is very useful for building devices. CdS/Au heterostructures can assemble in two different ways: through end-to-end coupling of Au domains, resulting in the formation of one-dimensional chains; and via side-by-side packing of CdS nanorods, leading to the onset of two-dimensional superlattices. We investigated the nature of exciton-plasmon interactions in Au-tipped CdS nanorods using femtosecond transient absorption spectroscopy. The study demonstrated that the key optoelectronic properties of electrically coupled metal and semiconductor domains are significantly different from those observed in systems with weak inter-domain coupling. In particular, strongly-coupled nanocomposites promote mixing of electronic states at semiconductor-metal domain interfaces, which causes a significant suppression of both plasmon and exciton carrier excitations. Colloidal QDs are starting to replace organic molecules in many different applications, such as organic light emmiting diods (OLEDs), due to their

  19. Substitutional doping in nanocrystal superlattices

    NASA Astrophysics Data System (ADS)

    Cargnello, Matteo; Johnston-Peck, Aaron C.; Diroll, Benjamin T.; Wong, Eric; Datta, Bianca; Damodhar, Divij; Doan-Nguyen, Vicky V. T.; Herzing, Andrew A.; Kagan, Cherie R.; Murray, Christopher B.

    2015-08-01

    Doping is a process in which atomic impurities are intentionally added to a host material to modify its properties. It has had a revolutionary impact in altering or introducing electronic, magnetic, luminescent, and catalytic properties for several applications, for example in semiconductors. Here we explore and demonstrate the extension of the concept of substitutional atomic doping to nanometre-scale crystal doping, in which one nanocrystal is used to replace another to form doped self-assembled superlattices. Towards this goal, we show that gold nanocrystals act as substitutional dopants in superlattices of cadmium selenide or lead selenide nanocrystals when the size of the gold nanocrystal is very close to that of the host. The gold nanocrystals occupy random positions in the superlattice and their density is readily and widely controllable, analogous to the case of atomic doping, but here through nanocrystal self-assembly. We also show that the electronic properties of the superlattices are highly tunable and strongly affected by the presence and density of the gold nanocrystal dopants. The conductivity of lead selenide films, for example, can be manipulated over at least six orders of magnitude by the addition of gold nanocrystals and is explained by a percolation model. As this process relies on the self-assembly of uniform nanocrystals, it can be generally applied to assemble a wide variety of nanocrystal-doped structures for electronic, optical, magnetic, and catalytic materials.

  20. Static and Dynamical Structural Investigations of Metal-Oxide Nanocrystals by Powder X-ray Diffraction: Colloidal Tungsten Oxide as a Case Study

    SciTech Connect

    Caliandro, Rocco; Sibillano, Teresa; Belviso, B. Danilo; Scarfiello, Riccardo; Dooryhee, Eric; Manca, Michele; Cozzoli, P. Davide

    2016-02-02

    In this study, we have developed a general X-ray powder diffraction (XPD) methodology for the simultaneous structural and compositional characterization of inorganic nanomaterials. The approach is validated on colloidal tungsten oxide nanocrystals (WO3-x NCs), as a model polymorphic nanoscale material system. Rod-shaped WO3-x NCs with different crystal structure and stoichiometry are comparatively investigated under an inert atmosphere and after prolonged air exposure. An initial structural model for the as-synthesized NCs is preliminarily identified by means of Rietveld analysis against several reference crystal phases, followed by atomic pair distribution function (PDF) refinement of the best-matching candidates (static analysis). Subtle stoichiometry deviations from the corresponding bulk standards are revealed. NCs exposed to air at room temperature are monitored by XPD measurements at scheduled time intervals. The static PDF analysis is complemented with an investigation into the evolution of the WO3-x NC structure, performed by applying the modulation enhanced diffraction technique to the whole time series of XPD profiles (dynamical analysis). Prolonged contact with ambient air is found to cause an appreciable increase in the static disorder of the O atoms in the WO3-x NC lattice, rather than a variation in stoichiometry. Finally, the time behavior of such structural change is identified on the basis of multivariate analysis.

  1. Static and Dynamical Structural Investigations of Metal-Oxide Nanocrystals by Powder X-ray Diffraction: Colloidal Tungsten Oxide as a Case Study

    DOE PAGES

    Caliandro, Rocco; Sibillano, Teresa; Belviso, B. Danilo; ...

    2016-02-02

    In this study, we have developed a general X-ray powder diffraction (XPD) methodology for the simultaneous structural and compositional characterization of inorganic nanomaterials. The approach is validated on colloidal tungsten oxide nanocrystals (WO3-x NCs), as a model polymorphic nanoscale material system. Rod-shaped WO3-x NCs with different crystal structure and stoichiometry are comparatively investigated under an inert atmosphere and after prolonged air exposure. An initial structural model for the as-synthesized NCs is preliminarily identified by means of Rietveld analysis against several reference crystal phases, followed by atomic pair distribution function (PDF) refinement of the best-matching candidates (static analysis). Subtle stoichiometry deviationsmore » from the corresponding bulk standards are revealed. NCs exposed to air at room temperature are monitored by XPD measurements at scheduled time intervals. The static PDF analysis is complemented with an investigation into the evolution of the WO3-x NC structure, performed by applying the modulation enhanced diffraction technique to the whole time series of XPD profiles (dynamical analysis). Prolonged contact with ambient air is found to cause an appreciable increase in the static disorder of the O atoms in the WO3-x NC lattice, rather than a variation in stoichiometry. Finally, the time behavior of such structural change is identified on the basis of multivariate analysis.« less

  2. Static and Dynamical Structural Investigations of Metal-Oxide Nanocrystals by Powder X-ray Diffraction: Colloidal Tungsten Oxide as a Case Study.

    PubMed

    Caliandro, Rocco; Sibillano, Teresa; Belviso, B Danilo; Scarfiello, Riccardo; Hanson, Jonathan C; Dooryhee, Eric; Manca, Michele; Cozzoli, P Davide; Giannini, Cinzia

    2016-03-03

    We have developed a general X-ray powder diffraction (XPD) methodology for the simultaneous structural and compositional characterization of inorganic nanomaterials. The approach is validated on colloidal tungsten oxide nanocrystals (WO3-x NCs), as a model polymorphic nanoscale material system. Rod-shaped WO3-x NCs with different crystal structure and stoichiometry are comparatively investigated under an inert atmosphere and after prolonged air exposure. An initial structural model for the as-synthesized NCs is preliminarily identified by means of Rietveld analysis against several reference crystal phases, followed by atomic pair distribution function (PDF) refinement of the best-matching candidates (static analysis). Subtle stoichiometry deviations from the corresponding bulk standards are revealed. NCs exposed to air at room temperature are monitored by XPD measurements at scheduled time intervals. The static PDF analysis is complemented with an investigation into the evolution of the WO3-x NC structure, performed by applying the modulation enhanced diffraction technique to the whole time series of XPD profiles (dynamical analysis). Prolonged contact with ambient air is found to cause an appreciable increase in the static disorder of the O atoms in the WO3-x NC lattice, rather than a variation in stoichiometry. The time behavior of such structural change is identified on the basis of multivariate analysis.

  3. Nanocrystal superlattices: No need to wait

    NASA Astrophysics Data System (ADS)

    Liu, Kun; Kumacheva, Eugenia

    2017-09-01

    In contrast with protocols reporting self-assembly of nanocrystals after synthesis, Pd nanocrystals rapidly form 3D micrometre-size superlattices during growth. The nanocrystals keep growing after assembly, tuning the size of the lattice.

  4. Hierarchial Junction Solar Cells Based on Hyper-Branched Semiconductor Nanocrystals

    DTIC Science & Technology

    2009-06-30

    that copper (I) sulfide and iron disulfide pyrite generated a much broader impact for photovoltaic solar cell applications. First, a simple low...pure phase iron disulfide pyrite nanocrystals with high purity through a surfactant-assisted hydrothermal reaction. These nanocrystals represent new...and iron disulfide pyrite (FeS2) for photovoltaic solar cell application. First, we demonstrated a simple low temperature solution phase synthesis of

  5. Soluble precursors for CuInSe2, CuIn(1-x)Ga(x)Se2, and Cu2ZnSn(S,Se)4 based on colloidal nanocrystals and molecular metal chalcogenide surface ligands.

    PubMed

    Jiang, Chengyang; Lee, Jong-Soo; Talapin, Dmitri V

    2012-03-21

    We report a new platform for design of soluble precursors for CuInSe(2) (CIS), Cu(In(1-x)Ga(x))Se(2) (CIGS), and Cu(2)ZnSn(S,Se)(4) (CZTS) phases for thin-film potovoltaics. To form these complex phases, we used colloidal nanocrystals (NCs) with metal chalcogenide complexes (MCCs) as surface ligands. The MCC ligands both provided colloidal stability and represented essential components of target phase. To obtain soluble precursors for CuInSe(2), we used Cu(2-x)Se NCs capped with In(2)Se(4)(2-) MCC surface ligands or CuInSe(2) NCs capped with {In(2)Cu(2)Se(4)S(3)}(3-) MCCs. A mixture of Cu(2-x)Se and ZnS NCs, both capped with Sn(2)S(6)(4-) or Sn(2)Se(6)(4-) ligands was used for solution deposition of CZTS films. Upon thermal annealing, the inorganic ligands reacted with NC cores forming well-crystallized pure ternary and quaternary phases. Solution-processed CIS and CZTS films featured large grain size and high phase purity, confirming the prospects of this approach for practical applications.

  6. X-ray diffraction and Raman scattering study of thermal-induced phase transformation in vertically aligned TiO 2 nanocrystals grown on sapphire(1 0 0) via metal organic vapor deposition

    NASA Astrophysics Data System (ADS)

    Chen, C. A.; Chen, K. Y.; Huang, Y. S.; Tsai, D. S.; Tiong, K. K.; Chien, F. Z.

    2008-07-01

    We report a detailed study of thermal-induced phase transformation in TiO 2 nanocrystals (NCs) via X-ray diffraction (XRD) and Raman scattering (RS) spectroscopy. Vertically aligned anatase TiO 2(1 1 0) NCs were grown on the sapphire (SA)(1 0 0) substrate at 550 °C by metal organic chemical vapor deposition, using titanium-tetraisopropoxide (TTIP, Ti[OCH(CH 3) 2] 4), as the source reagent. The effects of thermal annealing of TiO 2 NCs in oxygen atmosphere between 600 and 1000 °C were investigated. XRD and RS spectra showed the onset of the phase transformation process from the as-grown anatase TiO 2(1 1 0) NCs into rutile TiO 2(0 0 1) at the annealing temperature of 800 °C. At annealing temperature higher than 900 °C, pure rutile phase of TiO 2(0 0 1) NCs were formed and the crystalline quality of TiO 2 NCs could be further improved upon higher annealing temperature.

  7. Fabrication of Supported AuPt Alloy Nanocrystals with Enhanced Electrocatalytic Activity for Formic Acid Oxidation through Conversion Chemistry of Layer-Deposited Pt(2+) on Au Nanocrystals.

    PubMed

    Kim, Seong Hyeon; Jeong, Hwakyeung; Kim, Jongwon; Lee, In Su

    2015-10-07

    The exploitation of nanoconfined conversion of Au- and Pt-containing binary nanocrystals for developing a controllable synthesis of surfactant-free AuPt nanocrystals with enhanced formic acid oxidation (FAO) activity is reported, which can be stably and evenly immobilized on various support materials to diversify and optimize their electrocatalytic performance. In this study, an atomic layer of Pt(2+) species is discovered to be spontaneously deposited in situ on the Au nanocrystal generated from a reverse-microemulsion solution. The resulting Au/Pt(2+) nanocrystal thermally transforms into a reduced AuPt alloy nanocrystal during the subsequent solid-state conversion process within the SiO2 nanosphere. The alloy nanocrystals can be isolated from SiO2 in a surfactant-free form and then dispersedly loaded on the carbon sphere surface, allowing for the production of a supported electrocatalyst that exhibits much higher FAO activity than commercial Pt/C catalysts. Furthermore, by involving Fe3O4 nanocrystals in the conversion process, the AuPt alloy nanocrystals can be grown on the oxide surface, improving the durability of supported metal catalysts, and then uniformly loaded on a reduced graphene oxide (RGO) layer with high electroconductivity. This produces electrocatalytic AuPt/Fe3O4/RGO nanocomposites whose catalyst-oxide-graphene triple-junction structure provides improved electrocatalytic properties in terms of both activity and durability in catalyzing FAO. © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  8. Atomically precise gold nanocrystal molecules with surface plasmon resonance.

    PubMed

    Qian, Huifeng; Zhu, Yan; Jin, Rongchao

    2012-01-17

    Since Faraday's pioneering work on gold colloids, tremendous scientific research on plasmonic gold nanoparticles has been carried out, but no atomically precise Au nanocrystals have been achieved. This work reports the first example of gold nanocrystal molecules. Mass spectrometry analysis has determined its formula to be Au(333)(SR)(79) (R = CH(2)CH(2)Ph). This magic sized nanocrystal molecule exhibits fcc-crystallinity and surface plasmon resonance at approximately 520 nm, hence, a metallic nanomolecule. Simulations have revealed that atomic shell closing largely contributes to the particular robustness of Au(333)(SR)(79), albeit the number of free electrons (i.e., 333 - 79 = 254) is also consistent with electron shell closing based on calculations using a confined free electron model. Guided by the atomic shell closing growth mode, we have also found the next larger size of extraordinarily stability to be Au(~530)(SR)(~100) after a size-focusing selection--which selects the robust size available in the starting polydisperse nanoparticles. This work clearly demonstrates that atomically precise nanocrystal molecules are achievable and that the factor of atomic shell closing contributes to their extraordinary stability compared to other sizes. Overall, this work opens up new opportunities for investigating many fundamental issues of nanocrystals, such as the formation of metallic state, and will have potential impact on condensed matter physics, nanochemistry, and catalysis as well.

  9. Stabilizing Agents for Drug Nanocrystals: Effect on Bioavailability

    PubMed Central

    Tuomela, Annika; Hirvonen, Jouni; Peltonen, Leena

    2016-01-01

    Drug nanocrystals are a versatile option for drug delivery purposes, and while the number of poorly soluble drug materials is all the time increasing, more research in this area is performed. Drug nanocrystals have a simple structure—a solid drug core is surrounded by a layer of stabilizing agent. However, despite the considerably simple structure, the selection of an appropriate stabilizer for a certain drug can be challenging. Mostly, the stabilizer selection is based purely on the requirement of physical stability, e.g., maintaining the nanosized particle size as long as possible after the formation of drug nanocrystals. However, it is also worth taking into account that stabilizer can affect the bioavailability in the final formulation via interactions with cells and cell layers. In addition, formation of nanocrystals is only one process step, and for the final formulation, more excipients are often added to the composition. The role of the stabilizers in the final formulation can be more than only stabilizing the nanocrystal particle size. A good example is the stabilizer’s role as cryoprotectant during freeze drying. In this review, the stabilizing effect, role of stabilizers in final nanocrystalline formulations, challenges in reaching in vitro–in vivo correlation with nanocrystalline products, and stabilizers’ effect on higher bioavailability are discussed. PMID:27213435

  10. 2009 Clusters, Nanocrystals & Nanostructures GRC

    SciTech Connect

    Lai-Sheng Wang

    2009-07-19

    For over thirty years, this Gordon Conference has been the premiere meeting for the field of cluster science, which studies the phenomena that arise when matter becomes small. During its history, participants have witnessed the discovery and development of many novel materials, including C60, carbon nanotubes, semiconductor and metal nanocrystals, and nanowires. In addition to addressing fundamental scientific questions related to these materials, the meeting has always included a discussion of their potential applications. Consequently, this conference has played a critical role in the birth and growth of nanoscience and engineering. The goal of the 2009 Gordon Conference is to continue the forward-looking tradition of this meeting and discuss the most recent advances in the field of clusters, nanocrystals, and nanostructures. As in past meetings, this will include new topics that broaden the field. In particular, a special emphasis will be placed on nanomaterials related to the efficient use, generation, or conversion of energy. For example, we anticipate presentations related to batteries, catalysts, photovoltaics, and thermoelectrics. In addition, we expect to address the controversy surrounding carrier multiplication with a session in which recent results addressing this phenomenon will be discussed and debated. The atmosphere of the conference, which emphasizes the presentation of unpublished results and lengthy discussion periods, ensures that attendees will enjoy a valuable and stimulating experience. Because only a limited number of participants are allowed to attend this conference, and oversubscription is anticipated, we encourage all interested researchers from academia, industry, and government institutions to apply as early as possible. An invitation is not required. We also encourage all attendees to submit their latest results for presentation at the poster sessions. We anticipate that several posters will be selected for 'hot topic' oral

  11. A one-step green route to synthesize copper nanocrystals and their applications in catalysis and surface enhanced Raman scattering

    NASA Astrophysics Data System (ADS)

    Zhang, Pinhua; Sui, Yongming; Wang, Chao; Wang, Yingnan; Cui, Guangliang; Wang, Chunzhong; Liu, Bingbing; Zou, Bo

    2014-04-01

    A nontoxic, simple, inexpensive, and reproducible strategy, which meets the standard of green chemistry, is introduced for the synthesis of copper nanocrystals (Cu NCs) with olive oil as both reducing agent and capping agent. By changing the reaction parameters, the shape, size and surface structure of the Cu NCs can be well controlled. The obtained Cu nanocubes show excellent catalytic properties for the catalytic reduction of dyes and CO oxidation. Moreover, the prepared Cu nanocubes as substrates exhibit surface enhanced Raman scattering (SERS) activity for 4-mercaptopyridine (4-Mpy). Therefore, this facile route provides a useful platform for the fabrication of Cu NCs which have the potential to replace noble metals for certain applications.A nontoxic, simple, inexpensive, and reproducible strategy, which meets the standard of green chemistry, is introduced for the synthesis of copper nanocrystals (Cu NCs) with olive oil as both reducing agent and capping agent. By changing the reaction parameters, the shape, size and surface structure of the Cu NCs can be well controlled. The obtained Cu nanocubes show excellent catalytic properties for the catalytic reduction of dyes and CO oxidation. Moreover, the prepared Cu nanocubes as substrates exhibit surface enhanced Raman scattering (SERS) activity for 4-mercaptopyridine (4-Mpy). Therefore, this facile route provides a useful platform for the fabrication of Cu NCs which have the potential to replace noble metals for certain applications. Electronic supplementary information (ESI) available. See DOI: 10.1039/c4nr00412d

  12. Sorting fluorescent nanocrystals with DNA

    SciTech Connect

    Gerion, Daniele; Parak, Wolfgang J.; Williams, Shara C.; Zanchet, Daniela; Micheel, Christine M.; Alivisatos, A. Paul

    2001-12-10

    Semiconductor nanocrystals with narrow and tunable fluorescence are covalently linked to oligonucleotides. These biocompounds retain the properties of both nanocrystals and DNA. Therefore, different sequences of DNA can be coded with nanocrystals and still preserve their ability to hybridize to their complements. We report the case where four different sequences of DNA are linked to four nanocrystal samples having different colors of emission in the range of 530-640 nm. When the DNA-nanocrystal conjugates are mixed together, it is possible to sort each type of nanoparticle using hybridization on a defined micrometer -size surface containing the complementary oligonucleotide. Detection of sorting requires only a single excitation source and an epifluorescence microscope. The possibility of directing fluorescent nanocrystals towards specific biological targets and detecting them, combined with their superior photo-stability compared to organic dyes, opens the way to improved biolabeling experiments, such as gene mapping on a nanometer scale or multicolor microarray analysis.

  13. Leaching characteristics of arsenic and heavy metals in urban roadside soils using a simple bioavailability extraction test.

    PubMed

    Wang, Xue-song; Qin, Yong; Chen, Yong-kang

    2007-06-01

    Regular ingestion of soils could pose a potential health threat due to long-term toxic element exposure. In order to estimate the human bioavailability quotients for As and heavy metals, 12 urban roadside soil samples were collected and analyzed for As, Pb, Cu, Zn, Ni, Co, and Cr using Simple Bioavailability Extraction Test (SBET). The quantities of As, Pb, Cu, Zn, Ni, Co, and Cr leached from soils within the simulated human stomach for 1 h indicated, on average, 27.3, 71.7, 40.4, 59.3, 17.7, 27.2 and 5.6% bioavailability, respectively. Significant positive correlations were observed between the amounts leached using SBET and the total amounts dissolved with HNO(3)-HCl-HF acid mixtures. Stepwise multiple regression analysis indicated that the amounts leached with SBET for As, Pb, Zn, Ni, and Co were not related to any of the physic-chemical parameters measured (i.e., soil texture, pH, total organic matter). These results may be valuable for providing input data for risk assessment at sites subject to anthropogenic soil contamination.

  14. Wide-range photoabsorption cross-sections of simple metals: large basis-set OPW calculations for sodium

    NASA Astrophysics Data System (ADS)

    Kitamura, Hikaru

    2013-02-01

    Photoabsorption cross-sections of simple metals are formulated through a solid-state band theory based on the orthogonalized-plane-wave (OPW) method in Slater’s local-exchange approximation, where interband transitions of core and conduction electrons are evaluated up to the soft x-ray regime by using large basis sets. The photoabsorption cross-sections of a sodium crystal are computed for a wide photon energy range from 3 to 1800 eV. It is found that the numerical results reproduce the existing x-ray databases fairly well for energies above the L2,3-edge (31 eV), verifying a consistency between solid-state and atomic models for inner-shell photoabsorption; additional oscillatory structures in the present spectra manifest solid-state effects. Our computed results in the vacuum ultraviolet regime (6-30 eV) are also in better agreement with experimental data compared to earlier theories, although some discrepancies remain in the range of 20-30 eV. The influence of the core eigenvalues on the absorption spectra is examined.

  15. Nanocrystal waveguide (NOW) laser

    DOEpatents

    Simpson, John T.; Simpson, Marcus L.; Withrow, Stephen P.; White, Clark W.; Jaiswal, Supriya L.

    2005-02-08

    A solid state laser includes an optical waveguide and a laser cavity including at least one subwavelength mirror disposed in or on the optical waveguide. A plurality of photoluminescent nanocrystals are disposed in the laser cavity. The reflective subwavelength mirror can be a pair of subwavelength resonant gratings (SWG), a pair of photonic crystal structures (PC), or a distributed feedback structure. In the case of a pair of mirrors, a PC which is substantially transmissive at an operating wavelength of the laser can be disposed in the laser cavity between the subwavelength mirrors to improve the mode structure, coherence and overall efficiency of the laser. A method for forming a solid state laser includes the steps of providing an optical waveguide, creating a laser cavity in the optical waveguide by disposing at least one subwavelength mirror on or in the waveguide, and positioning a plurality of photoluminescent nanocrystals in the laser cavity.

  16. High-Brightness Blue and White LEDs based on Inorganic Perovskite Nanocrystals and their Composites

    DOE PAGES

    Yao, En -Ping; Yang, Zhanlue; Meng, Lei; ...

    2017-04-10

    Inorganic metal halide perovskite nanocrystals (NCs) have been employed universally in light-emitting applications during the past two years. Here, blue-emission (≈ 470 nm) Cs-based perovskite NCs are derived by directly mixing synthesized bromide and chloride nanocrystals with a weight ratio of 2:1. High-brightness blue perovskite light-emitting diodes (PeLEDs) are obtained by controlling the grain size of the perovskite films. Moreover, a white PeLED is demonstrated for the first time by blending orange polymer materials with the blue perovskite nanocrystals as the active layer. Exciton transfer from the blue nanocrystals to the orange polymers via Forster or Dexter energy transfer ismore » analyzed through time resolved photoluminescence. In conclusion, by tuning the ratio between the perovskite nanocrystals and polymers, pure white light is achieved with the a CIE coordinate at (0.33,0.34).« less

  17. High-Brightness Blue and White LEDs based on Inorganic Perovskite Nanocrystals and their Composites.

    PubMed

    Yao, En-Ping; Yang, Zhanlue; Meng, Lei; Sun, Pengyu; Dong, Shiqi; Yang, Ye; Yang, Yang

    2017-04-10

    Inorganic metal halide perovskite nanocrystals (NCs) have been employed universally in light-emitting applications during the past two years. Here, blue-emission (≈470 nm) Cs-based perovskite NCs are derived by directly mixing synthesized bromide and chloride nanocrystals with a weight ratio of 2:1. High-brightness blue perovskite light-emitting diodes (PeLEDs) are obtained by controlling the grain size of the perovskite films. Moreover, a white PeLED is demonstrated for the first time by blending orange polymer materials with the blue perovskite nanocrystals as the active layer. Exciton transfer from the blue nanocrystals to the orange polymers via Förster or Dexter energy transfer is analyzed through time resolved photoluminescence. By tuning the ratio between the perovskite nanocrystals and polymers, pure white light is achieved with the a CIE coordinate at (0.33,0.34).

  18. Calpain inhibitor nanocrystals prepared using Nano Spray Dryer B-90

    NASA Astrophysics Data System (ADS)

    Baba, Koichi; Nishida, Kohji

    2012-08-01

    The Nano Spray Dryer B-90 offers a new, simple, and alternative approach for the production of drug nanocrystals. Among attractive drugs, calpain inhibitor that inhibits programmed cell death `apoptosis' is a candidate for curing apoptosis-mediated intractable diseases such as Alzheimer's disease and Parkinson's disease. In this study, the preparation of calpain inhibitor nanocrystals using Nano Spray Dryer B-90 was demonstrated. The particle sizes were controlled by means of selecting mesh aperture sizes. The obtained average particle sizes were in the range of around 300 nm to submicron meter.

  19. Growth of gold nanoclusters and nanocrystals induced by lysozyme protein in thin film conformation

    NASA Astrophysics Data System (ADS)

    Bhowal, Ashim Chandra; Kundu, Sarathi

    2016-08-01

    Structures and growth behavior of gold nanoclusters and nanocrystals have been explored on thin films of globular protein lysozyme by using UV-vis and photoluminescence spectroscopy, X-ray diffraction (XRD) and atomic force microscopy (AFM). A simple and one-step environment friendly method has been used to grow nanocrystals on protein surface from HAuCl4 solution. It has been found that if different interaction times are provided between lysozyme films and HAuCl4 solution, then initially formed tiny gold nanoclusters on protein surface transform into nanocrystals with the passage of time. XRD analysis shows the formation of faced-centered cubic lattice along (1 1 1) crystalline direction and AFM images confirm the presence of circular, rod-like, triangular and hexagonal crystal structures. Langmuir-like growth behavior has been identified for both the gold nanoclusters and nanocrystals formation induced by the lysozyme films, however, nanocrystal growth is relatively slower than nanocluster.

  20. Utilizing boron nitride sheets as thin supports for high resolution imaging of nanocrystals.

    PubMed

    Wu, Yimin A; Kirkland, Angus I; Schäffel, Franziska; Porfyrakis, Kyriakos; Young, Neil P; Briggs, G Andrew D; Warner, Jamie H

    2011-05-13

    We demonstrate the use of thin BN sheets as supports for imaging nanocrystals using low voltage (80 kV) aberration-corrected high resolution transmission electron microscopy. This provides an alternative to the previously utilized 2D crystal supports of graphene and graphene oxide. A simple chemical exfoliation method is applied to get few layer boron nitride (BN) sheets with micrometer-sized dimensions. This generic approach of using BN sheets as supports is shown by depositing Mn doped ZnSe nanocrystals directly onto the BN sheets and resolving the atomic structure from both the ZnSe nanocrystals and the BN support. Phase contrast images reveal moiré patterns of interference between the beams diffracted by the nanocrystals and the BN substrate that are used to determine the relative orientation of the nanocrystals with respect to the BN sheets and interference lattice planes. Double diffraction is observed and has been analyzed.

  1. Hot-injection synthesis of Ni-ZnO hybrid nanocrystals with tunable magnetic properties and enhanced photocatalytic activity

    NASA Astrophysics Data System (ADS)

    Zeng, Deqian; Qiu, Yulong; Chen, Yuanzhi; Zhang, Qinfu; Liu, Xiang; Peng, Dong-Liang

    2017-04-01

    Magnetic metal-semiconductor hybrid nanocrystals containing ferromagnetic Ni and semiconductor ZnO have been prepared via a hot-injection route. The Ni-ZnO hybrid nanocrystals have a flower-like morphology that consists of Ni inner cores and ZnO petal shells. In spite of their large lattice mismatch, ZnO nanocrystals can still grow on faceted Ni nanocrystals to form stable interfaces. The composition of Ni-ZnO hybrid nanocrystals is readily controlled, and the average size of Ni core is tunable from 25 to 50 nm. Room temperature ferromagnetic properties are observed in these hybrid nanocrystals, and tunable magnetic properties also can be achieved by varying the size of Ni core. The as-prepared Ni-ZnO hybrid nanocrystals exhibit enhanced photocatalytic performance under ultraviolet light illumination as compared to pure ZnO nanocrystals. Furthermore, the superior reusability of hybrid nanocrystals for photocatalytic application is achieved by virtue of their magnetic properties. The facile and efficient seed-mediate strategy is particularly attractive to construct hybrid magnetic-semiconducting heterostructures. The as-obtained Ni-ZnO hybrid nanocrystals offer great potential for various applications due to their combined magnetic and semiconducting properties and low-cost earth-abundant availability.

  2. Selectivity on Etching: Creation of High-Energy Facets on Copper Nanocrystals for CO2 Electrochemical Reduction.

    PubMed

    Wang, Zhenni; Yang, Guang; Zhang, Zhaorui; Jin, Mingshang; Yin, Yadong

    2016-04-26

    Creating high-energy facets on the surface of catalyst nanocrystals represents a promising method for enhancing their catalytic activity. Herein we show that crystal etching as the reverse process of crystal growth can directly endow nanocrystal surfaces with high-energy facets. The key is to avoid significant modification of the surface energies of the nanocrystal facets by capping effects from solvents, ions, and ligands. Using Cu nanocubes as the starting material, we have successfully demonstrated the creation of high-energy facets in metal nanocrystals by controlled chemical etching. The etched Cu nanocrystals with enriched high-energy {110} facets showed significantly enhanced activity toward CO2 reduction. We believe the etching-based strategy could be extended to the synthesis of nanocrystals of many other catalysts with more active high-energy facets.

  3. Co@CoO@Au Core-Multi-Shell Nanocrystals

    DTIC Science & Technology

    2010-01-01

    their tendency to agglomerate and their instability in air. These difficulties commonly arise in ferromagnetic (FM) Co nanoparticles, which oxidize to...form antiferromagnetic (AFM) face-centered-cubic CoO. When the surface of the Co oxidizes to create an AFM shell around the ferromagnetic Co, an...has not oxidized . Our findings suggest that the presence of a metal shell surrounding a transition-metal core nanocrystal following such a reduction

  4. Solution-Processed Large-Area Nanocrystal Arrays of Metal-Organic Frameworks as Wearable, Ultrasensitive, Electronic Skin for Health Monitoring.

    PubMed

    Fu, Xiaolong; Dong, Huanli; Zhen, Yonggang; Hu, Wenping

    2015-07-15

    Pressure sensors based on solution-processed metal-organic frameworks nanowire arrays are fabricated with very low cost, flexibility, high sensitivity, and ease of integration into sensor arrays. Furthermore, the pressure sensors are suitable for monitoring and diagnosing biomedical signals such as radial artery pressure waveforms in real time. © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  5. 1D nanocrystals with precisely controlled dimensions, compositions, and architectures.

    PubMed

    Pang, Xinchang; He, Yanjie; Jung, Jaehan; Lin, Zhiqun

    2016-09-16

    The ability to synthesize a diverse spectrum of one-dimensional (1D) nanocrystals presents an enticing prospect for exploring nanoscale size- and shape-dependent properties. Here we report a general strategy to craft a variety of plain nanorods, core-shell nanorods, and nanotubes with precisely controlled dimensions and compositions by capitalizing on functional bottlebrush-like block copolymers with well-defined structures and narrow molecular weight distributions as nanoreactors. These cylindrical unimolecular nanoreactors enable a high degree of control over the size, shape, architecture, surface chemistry, and properties of 1D nanocrystals. We demonstrate the synthesis of metallic, ferroelectric, upconversion, semiconducting, and thermoelectric 1D nanocrystals, among others, as well as combinations thereof.

  6. Broadband enhancement of infrared absorption in microbolometers using Ag nanocrystals

    SciTech Connect

    Hyun, Jerome K.; Ahn, Chi Won; Kim, Woo Choong; Kim, Tae Hyun; Hyun, Moon Seop; Kim, Hee Yeoun E-mail: jhpark@nnfc.re.kr; Park, Jae Hong E-mail: jhpark@nnfc.re.kr; Lee, Won-Oh

    2015-12-21

    High performance microbolometers are widely sought for thermal imaging applications. In order to increase the performance limits of microbolometers, the responsivity of the device to broadband infrared (IR) radiation needs to be improved. In this work, we report a simple, quick, and cost-effective approach to modestly enhance the broadband IR response of the device by evaporating Ag nanocrystals onto the light entrance surface of the device. When irradiated with IR light, strong fields are built up within the gaps between adjacent Ag nanocrystals. These fields resistively generate heat in the nanocrystals and underlying substrate, which is transduced into an electrical signal via a resistive sensing element in the device. Through this method, we are able to enhance the IR absorption over a broadband spectrum and improve the responsivity of the device by ∼11%.

  7. Photoemission studies of semiconductor nanocrystals

    SciTech Connect

    Hamad, K. S.; Roth, R.; Alivisatos, A. P.

    1997-04-01

    Semiconductor nanocrystals have been the focus of much attention in the last ten years due predominantly to their size dependent optical properties. Namely, the band gap of nanocrystals exhibits a shift to higher energy with decreasing size due to quantum confinement effects. Research in this field has employed primarily optical techniques to study nanocrystals, and in this respect this system has been investigated extensively. In addition, one is able to synthesize monodisperse, crystalline particles of CdS, CdSe, Si, InP, InAs, as well as CdS/HgS/CdS and CdSe/CdS composites. However, optical spectroscopies have proven ambiguous in determining the degree to which electronic excitations are interior or surface admixtures or giving a complete picture of the density of states. Photoemission is a useful technique for understanding the electronic structure of nanocrystals and the effects of quantum confinement, chemical environments of the nanocrystals, and surface coverages. Of particular interest to the authors is the surface composition and structure of these particles, for they have found that much of the behavior of nanocrystals is governed by their surface. Previously, the authors had performed x-ray photoelectron spectroscopy (XPS) on CdSe nanocrystals. XPS has proven to be a powerful tool in that it allows one to determine the composition of the nanocrystal surface.

  8. Nanocrystal/sol-gel nanocomposites

    DOEpatents

    Petruska, Melissa A [Los Alamos, NM; Klimov, Victor L [Los Alamos, NM

    2012-06-12

    The present invention is directed to solid composites including colloidal nanocrystals within a sol-gel host or matrix and to processes of forming such solid composites. The present invention is further directed to alcohol soluble colloidal nanocrystals useful in formation of sol-gel based solid composites

  9. Nanocrystal/sol-gel nanocomposites

    DOEpatents

    Petruska, Melissa A [Los Alamos, NM; Klimov, Victor L [Los Alamos, NM

    2007-06-05

    The present invention is directed to solid composites including colloidal nanocrystals within a sol-gel host or matrix and to processes of forming such solid composites. The present invention is further directed to alcohol soluble colloidal nanocrystals useful in formation of sol-gel based solid composites.

  10. Electronic spectra of semiconductor nanocrystals

    SciTech Connect

    Alivisatos, A.P.

    1993-12-31

    Semiconductor nanocrystals smaller than the bulk exciton show substantial quantum confinement effects. Recent experiments including Stark effect, resonance Raman, valence band photoemission, and near edge X-ray adsorption will be used to put together a picture of the nanocrystal electronic states.

  11. Method of synthesizing pyrite nanocrystals

    DOEpatents

    Wadia, Cyrus; Wu, Yue

    2013-04-23

    A method of synthesizing pyrite nanocrystals is disclosed which in one embodiment includes forming a solution of iron (III) diethyl dithiophosphate and tetra-alkyl-ammonium halide in water. The solution is heated under pressure. Pyrite nanocrystal particles are then recovered from the solution.

  12. Effect of location of Si or Ge nanocrystals on the memory behavior of MNOS structures

    NASA Astrophysics Data System (ADS)

    Horváth, Zs. J.; Basa, P.; Molnár, K. Z.; Molnár, Gy.; Jászi, T.; Pap, A. E.

    2013-06-01

    Charge injection and retention behaviors of metal-nitride-oxide-silicon (MNOS) memory structures with Si or Ge nanocrystals embedded at a depth of 3 nm in the nitride layer were studied. The effect of Si nanocrystals on these properties was opposite in comparison with that of Ge nanocrystals. To understand the origin of these opposite effects, the influence of the oxide thickness and of the depth, size and location of semiconductor nanocrystals has been studied on the charging behavior of MNOS non-volatile memory structures by the calculation of electron and hole tunneling probabilities, and by the simulation of memory window, memory hysteresis and retention behavior. For MNOS structures it is obtained that the presence of nanocrystals enhances the charge injection resulting in better performance, but only for structures with thin tunnel oxide layer (below 3 nm), and if the nanocrystals are located close to the oxide/nitride interface. In the case of very high tunneling probability, i.e., of high tunneling currents the system approaches equilibrium and the memory behavior collapses. There is a narrow range of oxide thickness or depth of nanocrystals, where the charging properties change very fast. Retention exhibits a very sharp dependence on the oxide thickness and on depth of nanocrystals as well. Most part of the experimental results can be explained on the basis of the results of simulations.

  13. Nanocrystals encapsulated in SiO2 particles: silanization and homogenous coating for bio applications.

    PubMed

    Yang, Ping; Li, Xiaoyu; Zhang, Ruili; Liu, Ning; Zhang, Yulan

    2013-03-01

    Sol-gel procedures have been developed to encapsulate inorganic nanocrystals including metallic Au and II-VI semiconductor materials (CdSe/Cd(1-x)Zn(x)S) in SiO2 particles by using tetraethyl orthosilicate. The key strategy was the control of a sol-gel procedure. The anisotropic deposition of SiO2 monomers occurs because well-developed crystal facets having different affinity to SiO2 monomers. SiO2 monomers were not homogeneously deposited on nonspherical Au and CdSe/Cd(1-x)Zn(x)S nanocrystals. A surface silanization process, partly hydrolyzed tetraethyl orthosilicate were attached to the nanocrystals instead of initial ligands, plays an important role for the nanocrystals coated homogeneously with a SiO2 layer. Furthermore, CdSe/Cd(1-x)Zn(x)S nanocrystals were homogeneously coated with a thin SiO2 layer by the surface silanization process and a subsequent reverse micelle route. Colloidal Au nanocrystals were homogeneously coated with a SiO2 shell by the surface silanization process and subsequent Stöber synthesis without using a silane coupling agent or bulk polymer as the surface primer to render the Au surface vitreophilic. These results indicated partly hydrolyzed tetraethyl orthosilicate has an ability to replace the ligand on nanocrystals. After surface modification, the SiO2 particles with nanocrystals were conjugated with antibody for bioapplications.

  14. Controlling the Photonic Properties of Cholesteric Cellulose Nanocrystal Films with Magnets.

    PubMed

    Frka-Petesic, Bruno; Guidetti, Giulia; Kamita, Gen; Vignolini, Silvia

    2017-08-01

    The self-assembly of cellulose nanocrystals is a powerful method for the fabrication of biosourced photonic films with a chiral optical response. While various techniques have been exploited to tune the optical properties of such systems, the presence of external fields has yet to be reported to significantly modify their optical properties. In this work, by using small commercial magnets (≈ 0.5-1.2 T) the orientation of the cholesteric domains is enabled to tune in suspension as they assemble into films. A detailed analysis of these films shows an unprecedented control of their angular response. This simple and yet powerful technique unlocks new possibilities in designing the visual appearance of such iridescent films, ranging from metallic to pixelated or matt textures, paving the way for the development of truly sustainable photonic pigments in coatings, cosmetics, and security labeling. © 2017 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  15. Fabrication of metallic electrodes with nanometer separation by electromigration

    SciTech Connect

    Park, H.; Lim, A.K.; Alivisatos, A.P.; Park, J.; McEuen, P.L.

    1999-07-01

    A simple yet highly reproducible method to fabricate metallic electrodes with nanometer separation is presented. The fabrication is achieved by passing a large electrical current through a gold nanowire defined by electron-beam lithography and shadow evaporation. The current flow causes the electromigration of gold atoms and the eventual breakage of the nanowire. The breaking process yields two stable metallic electrodes separated by {approximately}1 nm with high efficiency. These electrodes are ideally suited for electron-transport studies of chemically synthesized nanostructures, and their utility is demonstrated here by fabricating single-electron transistors based on colloidal cadmium selenide nanocrystals. {copyright} {ital 1999 American Institute of Physics.}

  16. Cobalt Nanocrystals as Starting Materials for Shape Modificationand Assembly Formation

    SciTech Connect

    Erdonmez, Can Kerem

    2005-01-01

    Surfactant-coated cobalt nanocrystals can be prepared with areasonable degree of control over particle size and shape using athermolytic route. The small crystallite size, enhanced reactivity andtunable interparticle interactions enable use of this material asstarting material for demonstration of achievement of novel structuresusing extremely simple solution-based approaches. In particular,formation of hollow cobalt sulfide nanocrystals upon chemicalmodification and emergence of long-range orientational order upondrying-mediated assembly of cobalt nanocrystals is reportedhere.Colloidal preparation of Co nanocrystals has been well-studied.Here, we emphasize general principles and crystallographic/morphologicalcharacterization of disk-shaped hcp-Co nanocrystals. Use of surfactantmolecules enables achievement of multiple morphologies in one syntheticsystem.Formation of hollow structures upon in-solution sulfidation of Conanocrystals is presented and discussed. A Kirkendall-type effect,involving dominant outward mass transport during formation of the ionicshell material explains the results naturally. It is expected that thisphenomenon will generalize extensively to formation of hollow structuresof an enormous variety of compositions. Detailed study of particlemorphology as a function of reaction conditions suggest phenomena likelyto be generally relevant to use of this approach. A short report ofcrystallographic co-alignment into vortex-like structures is alsoprovided. Our current best picture of this process involves an interplayof packing and magnetic interactions between facetedparticles.

  17. Roles of aromatic side chains and template effects of the hydrophobic cavity of a self-assembled peptide nanoarchitecture for anisotropic growth of gold nanocrystals.

    PubMed

    Tomizaki, Kin-ya; Kishioka, Kohei; Kobayashi, Hiroki; Kobayashi, Akitsugu; Yamada, Naoki; Kataoka, Shunsuke; Imai, Takahito; Kasuno, Megumi

    2015-11-15

    decreasing the mole fraction of [Ant(6)]-RU006 against the total concentration of [Ant(6)]-RU006 and [Phe(6)]-RU006: absorption spectra similar to that for RU006 were obtained. Differences in the redox properties of the anthracene and naphthalene moieties scarcely affected morphology. We propose that construction of an appropriate hydrophobic cavity is important for templating gold nanocrystal architectures by peptide self-assembly. This mechanism would be applicable for developing simple, low toxicity, mild synthetic methods for constructing metallic nanomaterials for therapeutic use.

  18. Mechanical Properties of Nanocrystal Supercrystals

    SciTech Connect

    Tam, Enrico; Podsiadlo, Paul; Shevchenko, Elena; Ogletree, D. Frank; Delplancke-Ogletree, Marie-Paule; Ashby, Paul D.

    2009-12-30

    Colloidal nanocrystals attract significant interest due to their potential applications in electronic, magnetic, and optical devices. Nanocrystal supercrystals (NCSCs) are particularly appealing for their well ordered structure and homogeneity. The interactions between organic ligands that passivate the inorganic nanocrystal cores critically influence their self-organization into supercrystals, By investigating the mechanical properties of supercrystals, we can directly characterize the particle-particle interactions in a well-defined geometry, and gain insight into both the self-assembly process and the potential applications of nanocrystal supercrystals. Here we report nanoindentation studies of well ordered lead-sulfide (Pbs) nanocrystal supercrystals. Their modulus and hardness were found to be similar to soft polymers at 1.7 GPa and 70 MPa respectively and the fractures toughness was 39 KPa/m1/2, revealing the extremely brittle nature of these materials.

  19. Nanocrystal/sol-gel nanocomposites

    DOEpatents

    Klimov, Victor L.; Petruska, Melissa A.

    2010-05-25

    The present invention is directed to a process for preparing a solid composite having colloidal nanocrystals dispersed within a sol-gel matrix, the process including admixing colloidal nanocrystals with an amphiphilic polymer including hydrophilic groups selected from the group consisting of --COOH, --OH, --SO.sub.3H, --NH.sub.2, and --PO.sub.3H.sub.2 within a solvent to form an alcohol-soluble colloidal nanocrystal-polymer complex, admixing the alcohol-soluble colloidal nanocrystal-polymer complex and a sol-gel precursor material, and, forming the solid composite from the admixture. The present invention is also directed to the resultant solid composites and to the alcohol-soluble colloidal nanocrystal-polymer complexes.

  20. Size-Controlled TiO2 nanocrystals with exposed {001} and {101} facets strongly linking to graphene oxide via p-Phenylenediamine for efficient photocatalytic degradation of fulvic acids.

    PubMed

    Yan, Wen-Yuan; Zhou, Qi; Chen, Xing; Yang, Yong; Zhang, Yong; Huang, Xing-Jiu; Wu, Yu-Cheng

    2016-08-15

    Photocatalytic degradation is one of the most promising methods for removal of fulvic acids (FA), which is a typical category of natural organic contamination in groundwater. In this paper, TiO2/graphene nanocomposites (N-RGO/TiO2) were prepared via simple chemical functionalization and one-step hydrothermal method for efficient photodegradation of FA under illumination of a xenon lamp as light source. Here, p-phenylenediamine was used as not only the linkage chemical agent between TiO2 nanocrystals and graphene, but also the nitrogen dopant for TiO2 nanocrystals and graphene. During the hydrothermal process, facets of TiO2 nanocrystals were modulated with addition of HF, and sizes of TiO2 nanocrystals were controlled by the contents of graphene oxide functionalized with p-phenylenediamine (RGO-NH2). The obtained N-RGO/TiO2 nanocomposites exhibited a much higher photocatalytic activity and stability for degradation of methyl blue (MB) and FA compared with other TiO2 samples under xenon lamp irradiation. For the third cycle, the 10wt%N-RGO/TiO2 catalyst maintains high photoactivity (87%) for the degradation of FA, which is much better than the TiO2-N/F (61%) in 3h. This approach supplies a new strategy to design and synthesize metal oxide and graphene oxide nanocomposites with highly efficient photocatalytic performance.

  1. Silicon nanocrystal inks, films, and methods

    DOEpatents

    Wheeler, Lance Michael; Kortshagen, Uwe Richard

    2015-09-01

    Silicon nanocrystal inks and films, and methods of making and using silicon nanocrystal inks and films, are disclosed herein. In certain embodiments the nanocrystal inks and films include halide-terminated (e.g., chloride-terminated) and/or halide and hydrogen-terminated nanocrystals of silicon or alloys thereof. Silicon nanocrystal inks and films can be used, for example, to prepare semiconductor devices.

  2. Universal Quake Statistics: From Compressed Nanocrystals to Earthquakes

    SciTech Connect

    Uhl, Jonathan T.; Pathak, Shivesh; Schorlemmer, Danijel; Liu, Xin; Swindeman, Ryan; Brinkman, Braden A. W.; LeBlanc, Michael; Tsekenis, Georgios; Friedman, Nir; Behringer, Robert; Denisov, Dmitry; Schall, Peter; Gu, Xiaojun; Wright, Wendelin J.; Hufnagel, Todd; Jennings, Andrew; Greer, Julia R.; Liaw, P. K.; Becker, Thorsten; Dresen, Georg; Dahmen, Karin A.

    2015-11-17

    Slowly-compressed single crystals, bulk metallic glasses (BMGs), rocks, granular materials, and the earth all deform via intermittent slips or “quakes”. We find that although these systems span 12 decades in length scale, they all show the same scaling behavior for their slip size distributions and other statistical properties. Remarkably, the size distributions follow the same power law multiplied with the same exponential cutoff. The cutoff grows with applied force for materials spanning length scales from nanometers to kilometers. The tuneability of the cutoff with stress reflects “tuned critical” behavior, rather than self-organized criticality (SOC), which would imply stress-independence. A simple mean field model for avalanches of slipping weak spots explains the agreement across scales. It predicts the observed slip-size distributions and the observed stressdependent cutoff function. In conclusion, the results enable extrapolations from one scale to another, and from one force to another, across different materials and structures, from nanocrystals to earthquakes.

  3. Universal Quake Statistics: From Compressed Nanocrystals to Earthquakes

    PubMed Central

    Uhl, Jonathan T.; Pathak, Shivesh; Schorlemmer, Danijel; Liu, Xin; Swindeman, Ryan; Brinkman, Braden A. W.; LeBlanc, Michael; Tsekenis, Georgios; Friedman, Nir; Behringer, Robert; Denisov, Dmitry; Schall, Peter; Gu, Xiaojun; Wright, Wendelin J.; Hufnagel, Todd; Jennings, Andrew; Greer, Julia R.; Liaw, P. K.; Becker, Thorsten; Dresen, Georg; Dahmen, Karin A.

    2015-01-01

    Slowly-compressed single crystals, bulk metallic glasses (BMGs), rocks, granular materials, and the earth all deform via intermittent slips or “quakes”. We find that although these systems span 12 decades in length scale, they all show the same scaling behavior for their slip size distributions and other statistical properties. Remarkably, the size distributions follow the same power law multiplied with the same exponential cutoff. The cutoff grows with applied force for materials spanning length scales from nanometers to kilometers. The tuneability of the cutoff with stress reflects “tuned critical” behavior, rather than self-organized criticality (SOC), which would imply stress-independence. A simple mean field model for avalanches of slipping weak spots explains the agreement across scales. It predicts the observed slip-size distributions and the observed stress-dependent cutoff function. The results enable extrapolations from one scale to another, and from one force to another, across different materials and structures, from nanocrystals to earthquakes. PMID:26572103

  4. A simple laminate theory using the orthotropic viscoplasticity theory based on overstress. I - In-plane stress-strain relationships for metal matrix composites

    NASA Technical Reports Server (NTRS)

    Krempl, Erhard; Hong, Bor Zen

    1989-01-01

    A macromechanics analysis is presented for the in-plane, anisotropic time-dependent behavior of metal matrix laminates. The small deformation, orthotropic viscoplasticity theory based on overstress represents lamina behavior in a modified simple laminate theory. Material functions and constants can be identified in principle from experiments with laminae. Orthotropic invariants can be repositories for tension-compression asymmetry and for linear elasticity in one direction while the other directions behave in a viscoplastic manner. Computer programs are generated and tested for either unidirectional or symmetric laminates under in-plane loading. Correlations with the experimental results on metal matrix composites are presented.

  5. A simple laminate theory using the orthotropic viscoplasticity theory based on overstress. I - In-plane stress-strain relationships for metal matrix composites

    NASA Technical Reports Server (NTRS)

    Krempl, Erhard; Hong, Bor Zen

    1989-01-01

    A macromechanics analysis is presented for the in-plane, anisotropic time-dependent behavior of metal matrix laminates. The small deformation, orthotropic viscoplasticity theory based on overstress represents lamina behavior in a modified simple laminate theory. Material functions and constants can be identified in principle from experiments with laminae. Orthotropic invariants can be repositories for tension-compression asymmetry and for linear elasticity in one direction while the other directions behave in a viscoplastic manner. Computer programs are generated and tested for either unidirectional or symmetric laminates under in-plane loading. Correlations with the experimental results on metal matrix composites are presented.

  6. Synthesis of ZnO Nanocrystals and Application in Inverted Polymer Solar Cells

    NASA Astrophysics Data System (ADS)

    Dong, Jing-Jing; Wu, Jian; Hao, Hui-Ying; Xing, Jie; Liu, Hao; Gao, Hua

    2017-09-01

    Controllable synthesis of various ZnO nanocrystals was achieved via a simple and cost-effective hydrothermal process. The morphology evolution of the ZnO nanostructures was well monitored by tuning hydrothermal growth parameters, such as solution concentration, reaction temperature, and surfactant. As-obtained ZnO nanocrystals with different morphologies, e.g., ZnO nanorods, nanotetrapods, nanoflowers, and nanocubes, were further introduced into the organic bulk heterojunction solar cells as the electron transport channel. It was found that the device performance was closely related to the morphology of the ZnO nanocrystals.

  7. Synthesis of ZnO Nanocrystals and Application in Inverted Polymer Solar Cells.

    PubMed

    Dong, Jing-Jing; Wu, Jian; Hao, Hui-Ying; Xing, Jie; Liu, Hao; Gao, Hua

    2017-09-09

    Controllable synthesis of various ZnO nanocrystals was achieved via a simple and cost-effective hydrothermal process. The morphology evolution of the ZnO nanostructures was well monitored by tuning hydrothermal growth parameters, such as solution concentration, reaction temperature, and surfactant. As-obtained ZnO nanocrystals with different morphologies, e.g., ZnO nanorods, nanotetrapods, nanoflowers, and nanocubes, were further introduced into the organic bulk heterojunction solar cells as the electron transport channel. It was found that the device performance was closely related to the morphology of the ZnO nanocrystals.

  8. Synthesis of Semiconductor Nanocrystals, Focusing on Nontoxic and Earth-Abundant Materials.

    PubMed

    Reiss, Peter; Carrière, Marie; Lincheneau, Christophe; Vaure, Louis; Tamang, Sudarsan

    2016-09-28

    We review the synthesis of semiconductor nanocrystals/colloidal quantum dots in organic solvents with special emphasis on earth-abundant and toxic heavy metal free compounds. Following the Introduction, section 2 defines the terms related to the toxicity of nanocrystals and gives a comprehensive overview on toxicity studies concerning all types of quantum dots. Section 3 aims at providing the reader with the basic concepts of nanocrystal synthesis. It starts with the concepts currently used to describe the nucleation and growth of monodisperse particles and next takes a closer look at the chemistry of the inorganic core and its interactions with surface ligands. Section 4 reviews in more detail the synthesis of different families of semiconductor nanocrystals, namely elemental group IV compounds (carbon nanodots, Si, Ge), III-V compounds (e.g., InP, InAs), and binary and multinary metal chalcogenides. Finally, the authors' view on the perspectives in this field is given.

  9. Biopolymer coated gold nanocrystals prepared using the green chemistry approach and their shape-dependent catalytic and surface-enhanced Raman scattering properties.

    PubMed

    Chou, Chih-Wei; Hsieh, Hui-Hsuan; Hseu, You-Cheng; Chen, Ko-Shao; Wang, Gou-Jen; Chang, Hsien-Chang; Pan, Yong-Li; Wei, Yi-Syuan; Chang, Ko Hsin; Harn, Yeu-Wei

    2013-07-21

    This study deals with the preparation of multi-shaped nanoscale gold crystals under synthetically simple, green, and efficient conditions using a seed-mediated growth approach in the presence of hyaluronic acid (HA). These highly biocompatible multi-shaped gold nanocrystals were examined to evaluate their catalytic and surface enhanced Raman scattering (SERS) properties. The results show that the size and shape of the nanocrystals are mainly correlated to the amount of seed, seed size, HA concentration, and reaction temperature. Gold seeds accelerate the reduction of the gold precursor to form gold nanocrystals using HA. The HA serves as a reducing agent and a growth template for the reduction of Au(III) and nanocrystal stabilization. The multi-shaped gold nanocrystals showed superior catalytic properties and higher SERS performance. The simple, green approach efficiently controls the nanocrystals and creates many opportunities for future applications.

  10. Pyramidal and Chiral Groupings of Gold Nanocrystals Assembled Using DNA Scaffolds

    PubMed Central

    Mastroianni, Alexander; Claridge, Shelley; Alivisatos, A. Paul

    2009-01-01

    Nanostructures constructed from metal and semiconductor nanocrystals conjugated to, and organized by DNA are an emerging class of material with collective optical properties. We created discrete pyramids of DNA with gold nanocrystals at the tips. By taking small angle X-ray scattering (SAXS) measurments from solutions of these pyramids we confirmed that this pyramidal geometry creates structures which are more rigid in solution than linear DNA. We then took advantage of the tetrahedral symmetry to demonstrate construction of chiral nanostructures. PMID:19331419

  11. Pyramidal and Chiral Groupings of Gold Nanocrystals Assembled Using DNA Scaffolds

    SciTech Connect

    Mastroianni, Alexander; Claridge, Shelley; Alivisatos, A. Paul

    2009-03-30

    Nanostructures constructed from metal and semiconductor nanocrystals conjugated to, and organized by DNA are an emerging class of material with collective optical properties. We created discrete pyramids of DNA with gold nanocrystals at the tips. By taking small angle X-ray scattering (SAXS) measurments from solutions of these pyramids we confirmed that this pyramidal geometry creates structures which are more rigid in solution than linear DNA. We then took advantage of the tetrahedral symmetry to demonstrate construction of chiral nanostructures.

  12. In situ growth of Au nanocrystals on graphene oxide sheets

    NASA Astrophysics Data System (ADS)

    Qin, Yong; Li, Juan; Kong, Yong; Li, Xiazhang; Tao, Yongxin; Li, Shan; Wang, Yuan

    2014-01-01

    Au nanocrystals (AuNCs) with a size of 10-20 nm decorated on graphene oxide (GO) were fabricated successfully through a hydrothermal reduction and crystallization route without any extra reductants and capping agents. The hydrophobic areas of GO benefit the formation of nanocrystals (NCs) with {111} facets totally exposed; however, the hydrophilic areas are detrimental to the crystallization. The morphology of AuNCs could be tailored by the degree of oxidation on the GO surface. The shape-controllable and reducing properties of GO are in favor of ``clean'' synthesis of noble metal NCs decorated on graphene.Au nanocrystals (AuNCs) with a size of 10-20 nm decorated on graphene oxide (GO) were fabricated successfully through a hydrothermal reduction and crystallization route without any extra reductants and capping agents. The hydrophobic areas of GO benefit the formation of nanocrystals (NCs) with {111} facets totally exposed; however, the hydrophilic areas are detrimental to the crystallization. The morphology of AuNCs could be tailored by the degree of oxidation on the GO surface. The shape-controllable and reducing properties of GO are in favor of ``clean'' synthesis of noble metal NCs decorated on graphene. Electronic supplementary information (ESI) available: Fig. S1-S4. See DOI: 10.1039/c3nr04714h

  13. Synthesis and characterizations of nanoribbons and monodispersed nanocrystals of CuBr

    SciTech Connect

    Yang Ming; Zhu Junjie . E-mail: jjzhu@nju.edu.cn

    2005-02-15

    Nanoribbons and monodispersed nanocrystals of CuBr have been prepared by a simple reaction between CuO suspension, NH{sub 2}OH.HCl and KBr in the presence of deionized gelatin at 10 deg. C. The products were characterized by X-ray powder diffraction, transmission electron microscopy and UV-vis absorption spectroscopy. The sizes of the monodispersed nanocrystals of CuBr were estimated by Debye-Scherrer formula according to XRD spectrum.

  14. Silicon nanocrystals as handy biomarkers

    NASA Astrophysics Data System (ADS)

    Fujioka, Kouki; Hoshino, Akiyoshi; Manabe, Noriyoshi; Futamura, Yasuhiro; Tilley, Richard; Yamamoto, Kenji

    2007-02-01

    Quantum dots (QDs) have brighter and longer fluorescence than organic dyes. Therefore, QDs can be applied to biotechnology, and have capability to be applied to medical technology. Currently, among the several types of QDs, CdSe with a ZnS shell is one of the most popular QDs to be used in biological experiments. However, when the CdSe QDs were applied to clinical technology, potential toxicological problems due to CdSe core should be considered. To eliminate the problem, silicon nanocrystals, which have the potential of biocompatibility, could be a candidate of alternate probes. Silicon nanocrystals have been synthesized using several techniques such as aerosol, electrochemical etching, laser pyrolysis, plasma deposition, and colloids. Recently, the silicon nanocrystals were reported to be synthesized in inverse micelles and also stabilized with 1-heptene or allylamine capping. Blue fluorescence of the nanocrystals was observed when excited with a UV light. The nanocrystals covered with 1-heptene are hydrophobic, whereas the ones covered with allylamine are hydrophilic. To test the stability in cytosol, the water-soluble nanocrystals covered with allylamine were examined with a Hela cell incorporation experiment. Bright blue fluorescence of the nanocrystals was detected in the cytosol when excited with a UV light, implying that the nanocrystals were able to be applied to biological imaging. In order to expand the application range, we synthesized and compared a series of silicon nanocrystals, which have variable surface modification, such as alkyl group, alcohol group, and odorant molecules. This study will provide a wider range of optoelectronic applications and bioimaging technology.

  15. Biomolecular Assembly of Gold Nanocrystals

    SciTech Connect

    Micheel, Christine Marya

    2005-05-20

    Over the past ten years, methods have been developed to construct discrete nanostructures using nanocrystals and biomolecules. While these frequently consist of gold nanocrystals and DNA, semiconductor nanocrystals as well as antibodies and enzymes have also been used. One example of discrete nanostructures is dimers of gold nanocrystals linked together with complementary DNA. This type of nanostructure is also known as a nanocrystal molecule. Discrete nanostructures of this kind have a number of potential applications, from highly parallel self-assembly of electronics components and rapid read-out of DNA computations to biological imaging and a variety of bioassays. My research focused in three main areas. The first area, the refinement of electrophoresis as a purification and characterization method, included application of agarose gel electrophoresis to the purification of discrete gold nanocrystal/DNA conjugates and nanocrystal molecules, as well as development of a more detailed understanding of the hydrodynamic behavior of these materials in gels. The second area, the development of methods for quantitative analysis of transmission electron microscope data, used computer programs written to find pair correlations as well as higher order correlations. With these programs, it is possible to reliably locate and measure nanocrystal molecules in TEM images. The final area of research explored the use of DNA ligase in the formation of nanocrystal molecules. Synthesis of dimers of gold particles linked with a single strand of DNA possible through the use of DNA ligase opens the possibility for amplification of nanostructures in a manner similar to polymerase chain reaction. These three areas are discussed in the context of the work in the Alivisatos group, as well as the field as a whole.

  16. A facile one-pot route to cationic cellulose nanocrystals

    NASA Astrophysics Data System (ADS)

    Jasmani, Latifah; Eyley, Samuel; Wallbridge, Rachel; Thielemans, Wim

    2013-10-01

    Pyridinium-grafted-cellulose nanocrystals were prepared by a simple one-pot reaction using 4-(1-bromoethyl/bromomethyl)benzoic acid, pyridine and cellulose nanocrystals (CNCs). The grafting consists of an esterification reaction between 4-(1-bromoethyl/bromomethyl)benzoic acid and CNCs and a nucleophilic attack on the C-Br bond of 4-(1-bromoethyl/bromomethyl)benzoic acid by pyridine. This reaction simplifies existing cationization methods, which leads to a higher grafting density while retaining the CNC crystallinity.Pyridinium-grafted-cellulose nanocrystals were prepared by a simple one-pot reaction using 4-(1-bromoethyl/bromomethyl)benzoic acid, pyridine and cellulose nanocrystals (CNCs). The grafting consists of an esterification reaction between 4-(1-bromoethyl/bromomethyl)benzoic acid and CNCs and a nucleophilic attack on the C-Br bond of 4-(1-bromoethyl/bromomethyl)benzoic acid by pyridine. This reaction simplifies existing cationization methods, which leads to a higher grafting density while retaining the CNC crystallinity. Electronic supplementary information (ESI) available: Experimental description, FTIR, XPS and XRD spectra and detailed characterisation results of all compounds. See DOI: 10.1039/c3nr03456a

  17. Tuning optoelectronic properties and understanding charge transport in nanocrystal thin films of earth abundant semiconducting materials

    NASA Astrophysics Data System (ADS)

    Riha, Shannon C.

    2011-12-01

    With the capability of producing nearly 600 TW annually, solar power is one renewable energy source with the potential to meet a large fraction of the world's burgeoning energy demand. To make solar technology cost-competitive with carbon-based fuels, cheaper devices need to be realized. Solution-processed solar cells from nanocrystal inks of earth abundant materials satisfy this requirement. Nonetheless, a major hurdle in commercializing such devices is poor charge transport through nanocrystal thin films. The efficiency of charge transport through nanocrystal thin films is strongly dependent on the quality of the nanocrystals, as well as their optoelectronic properties. Therefore, the first part of this dissertation is focused on synthesizing high quality nanocrystals of Cu2ZnSnS4, a promising earth abundant photovoltaic absorber material. The optoelectronic properties of the nanocrystals were tuned by altering the copper to zinc ratio, as well as by introducing selenium to create Cu2ZnSn(S1-xSe x)4 solid solutions. Photoelectrochemical characterization was used to test the Cu2ZnSnS4 and Cu2ZnSn(S 1-xSex)4 nanocrystal thin films. The results identify minority carrier diffusion and recombination via the redox shuttle as the major loss mechanisms hindering efficient charge transport through the nanocrystal thin films. One way to solve this issue is to sinter the nanocrystals together, creating large grains for efficient charge transport. Although this may be quick and effective, it can lead to the formation of structural defects, among other issues. To this end, using a different copper-based material, namely Cu2Se, and simple surface chemistry treatments, an alternative route to enhance charge transport through nanocrystals thin films is proposed.

  18. Cellulose nanocrystal submonolayers by spin coating.

    PubMed

    Kontturi, Eero; Johansson, Leena-Sisko; Kontturi, Katri S; Ahonen, Päivi; Thüne, Peter C; Laine, Janne

    2007-09-11

    Dilute concentrations of cellulose nanocrystal solutions were spin coated onto different substrates to investigate the effect of the substrate on the nanocrystal submonolayers. Three substrates were probed: silica, titania, and amorphous cellulose. According to atomic force microscopy (AFM) images, anionic cellulose nanocrystals formed small aggregates on the anionic silica substrate, whereas a uniform two-dimensional distribution of nanocrystals was achieved on the cationic titania substrate. The uniform distribution of cellulose nanocrystal submonolayers on titania is an important factor when dimensional analysis of the nanocrystals is desired. Furthermore, the amount of nanocrystals deposited on titania was multifold in comparison to the amounts on silica, as revealed by AFM image analysis and X-ray photoelectron spectroscopy. Amorphous cellulose, the third substrate, resulted in a somewhat homogeneous distribution of the nanocrystal submonolayers, but the amounts were as low as those on the silica substrate. These differences in the cellulose nanocrystal deposition were attributed to electrostatic effects: anionic cellulose nanocrystals are adsorbed on cationic titania in addition to the normal spin coating deposition. The anionic silica surface, on the other hand, causes aggregation of the weakly anionic cellulose nanocrystals which are forced on the repulsive substrate by spin coating. The electrostatically driven adsorption also influences the film thickness of continuous ultrathin films of cellulose nanocrystals. The thicker films of charged nanocrystals on a substrate of opposite charge means that the film thickness is not independent of the substrate when spin coating cellulose nanocrystals in the ultrathin regime (<100 nm).

  19. Occurrence of selected trace metals and their oral bioaccessibility in urban soils of kindergartens and parks in Bratislava (Slovak Republic) as evaluated by simple in vitro digestion procedure.

    PubMed

    Hiller, Edgar; Mihaljevič, Martin; Filová, Lenka; Lachká, Lucia; Jurkovič, Ľubomír; Kulikova, Tatsiana; Fajčíková, Katarína; Šimurková, Mária; Tatarková, Veronika

    2017-10-01

    A total of eighty surface soil samples were collected from public kindergartens and urban parks in the city of Bratislava, and the <150µm soil fraction was evaluated for total concentrations of five metals, Cd, Cu, Hg, Pb and Zn, their oral bioaccessibilities, non-carcinogenic and carcinogenic health risks to children, and lead isotopic composition. The mean metal concentrations in urban soils (0.29, 36.1, 0.13, 30.9 and 113mg/kg for Cd, Cu, Hg, Pb and Zn, respectively) were about two times higher compared with background soil concentrations. The order of bioaccessible metal fractions determined by Simple Bioaccessibility Extraction Test was: Pb (59.9%) > Cu (43.8%) > Cd (40.8%) > Zn (33.6%) > Hg (12.8%). Variations in the bioaccessible metal fractions were mainly related to the total metal concentrations in urban soils. A relatively wide range of lead isotopic ratios in urban soils (1.1598-1.2088 for (206)Pb/(207)Pb isotopic ratio) indicated a combination of anthropogenic and geogenic sources of metals in the soils. Lower values of (206)Pb/(207)Pb isotopic ratio in the city centre and similar spatial distribution of total metal concentrations, together with their increasing total concentrations in soils towards the city centre, showed that traffic and coal combustion in former times were likely the major sources of soil contamination. The non-carcinogenic and carcinogenic health risks to children due to exposure to metals in kindergarten and urban park soils were low, with hazard index and cancer risk values below the threshold values at all studied sites. Copyright © 2017 Elsevier Inc. All rights reserved.

  20. A simple metal staining procedure for identification and visualization of single cells by LA-ICP-MS.

    PubMed

    Herrmann, A J; Techritz, S; Jakubowski, N; Haase, A; Luch, A; Panne, U; Mueller, L

    2017-05-21

    High lateral resolution of metal detection in single cells by use of laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) demands powerful staining methods. In this work different staining procedures for the single cell analysis with LA-ICP-MS were optimized. An iridium intercalator was utilized to stain the cell nuclei whereas the whole cell was stained by the use of maleimido-mono-amide-DOTA (mDOTA) complexing lanthanide(iii) ions. The content of the artificially introduced metals per cell was quantified using a matrix matched calibration approach based on cellulose membranes onto which standards were spotted by a microarray spotter. Absolute metal stain amounts in the range of 2.34 to 9.81 femtomole per cell were determined. The metal staining procedures allow direct identification and visualization of single cells and their cell compartments by element microscopy without the use of bright field images of the sample.

  1. Early stage of nanocrystal growth

    SciTech Connect

    2012-01-01

    Berkeley Lab researchers at the Molecular Foundry have elucidated important mechanisms behind oriented attachment, the phenomenon that drives biomineralization and the growth of nanocrystals. This electron microscopy movie shows the early stage of nanocrystal growth. Nanoparticles make transient contact at many points and orientations until their lattices are perfectly matched. The particles then make a sudden jump-to-contact to form attached aggregates. (Movie courtesy of Jim DeYoreo)

  2. Effects of aqueous stable fullerene nanocrystal (nC60) on copper (trace necessary nutrient metal): Enhanced toxicity and accumulation of copper in Daphnia magna.

    PubMed

    Tao, Xianji; He, Yiliang; Fortner, John D; Chen, Yongsheng; Hughes, Joseph B

    2013-08-01

    Our focus herein is to evaluate the potential interaction between nC60 and copper, a trace necessary metal, in light of the impact on toxicity. The non-observable effects concentration (NOEC) of nC60 was confirmed as 100μgL(-1) before. When Daphnia magna was exposed to the mixture of copper solution and nC60 suspension (100μgL(-1)), LC50 of 48h was lower than that when they were exposed to copper solution alone. This result clearly showed the decrease in NOEC of copper at the presence of nC60. Cu(2+)-ATPase activity was enhanced at the presence of nC60, indicating that copper transport involved with the uptake, distribution and depuration in body was increased. We further conducted experiments on accumulation of copper in D. magna. The observed equilibrium copper concentration in D. magna in the mixture of 100μgL(-1) nC60 and 1μgL(-1) copper solution reached 131μg (kg wet weight)(-1), which was more than twice that in copper solution only: 60μg (kg wet weight)(-1). This result demonstrated that the accumulation of copper in D. magna was significantly enhanced at the presence of even low nC60 concentration. Experiments also showed that copper was quickly adsorbed onto nC60. The absorption of copper onto D. magna was statistically correlated to the absorption of nC60 onto D. magna; this might be caused by nC60 facilitating the transfer of copper into D. magna. The absorption and desorption of copper to nC60 (pH=5.0) reached equilibrium quickly, which may be involved with the co-bioaccumulation and decrease in NOEC of Cu(2+) and nC60.

  3. Ultra-small photoluminescent silicon-carbide nanocrystals by atmospheric-pressure plasmas.

    PubMed

    Askari, Sadegh; Ul Haq, Atta; Macias-Montero, Manuel; Levchenko, Igor; Yu, Fengjiao; Zhou, Wuzong; Ostrikov, Kostya Ken; Maguire, Paul; Svrcek, Vladimir; Mariotti, Davide

    2016-10-06

    Highly size-controllable synthesis of free-standing perfectly crystalline silicon carbide nanocrystals has been achieved for the first time through a plasma-based bottom-up process. This low-cost, scalable, ligand-free atmospheric pressure technique allows fabrication of ultra-small (down to 1.5 nm) nanocrystals with very low level of surface contamination, leading to fundamental insights into optical properties of the nanocrystals. This is also confirmed by their exceptional photoluminescence emission yield enhanced by more than 5 times by reducing the nanocrystals sizes in the range of 1-5 nm, which is attributed to quantum confinement in ultra-small nanocrystals. This method is potentially scalable and readily extendable to a wide range of other classes of materials. Moreover, this ligand-free process can produce colloidal nanocrystals by direct deposition into liquid, onto biological materials or onto the substrate of choice to form nanocrystal films. Our simple but efficient approach based on non-equilibrium plasma environment is a response to the need of most efficient bottom-up processes in nanosynthesis and nanotechnology.

  4. Assemblies of Cellulose Nanocrystals

    NASA Astrophysics Data System (ADS)

    Kumacheva, Eugenia

    The entropically driven coassembly of nanorods (cellulose nanocrystals, CNCs) and different types of nanoparticles (NPs), including dye-labeled latex NPs, carbon dots and plasmonic NPs was experimentally studied in aqueous suspensions and in solid films. In mixed CNC-NP suspensions, phase separation into an isotropic NP-rich and a chiral nematic CNC-rich phase took place; the latter contained a significant amount of NPs. Drying the mixed suspension resulted in CNC-NP films with planar disordered layers of NPs, which alternated with chiral nematic CNC-rich regions. In addition, NPs were embedded in the chiral nematic domains. The stratified morphology of the films, together with a random distribution of NPs in the anisotropic phase, led to the films having close-to-uniform fluorescence, birefringence, and circular dichroism properties.

  5. Simple Machines Made Simple.

    ERIC Educational Resources Information Center

    St. Andre, Ralph E.

    Simple machines have become a lost point of study in elementary schools as teachers continue to have more material to cover. This manual provides hands-on, cooperative learning activities for grades three through eight concerning the six simple machines: wheel and axle, inclined plane, screw, pulley, wedge, and lever. Most activities can be…

  6. Simple Machines Made Simple.

    ERIC Educational Resources Information Center

    St. Andre, Ralph E.

    Simple machines have become a lost point of study in elementary schools as teachers continue to have more material to cover. This manual provides hands-on, cooperative learning activities for grades three through eight concerning the six simple machines: wheel and axle, inclined plane, screw, pulley, wedge, and lever. Most activities can be…

  7. Simple way to engineer metal-semiconductor interface for enhanced performance of perovskite organic lead iodide solar cells.

    PubMed

    Xu, Yuzhuan; Shi, Jiangjian; Lv, Songtao; Zhu, Lifeng; Dong, Juan; Wu, Huijue; Xiao, Yin; Luo, Yanhong; Wang, Shirong; Li, Dongmei; Li, Xianggao; Meng, Qingbo

    2014-04-23

    A thin wide band gap organic semiconductor N,N,N',N'-tetraphenyl-benzidine layer has been introduced by spin-coating to engineer the metal-semiconductor interface in the hole-conductor-free perovskite solar cells. The average cell power conversion efficiency (PCE) has been enhanced from 5.26% to 6.26% after the modification and a highest PCE of 6.71% has been achieved. By the aid of electrochemical impedance spectroscopy and dark current analysis, it is revealed that this modification can increase interfacial resistance of CH3NH3PbI3/Au interface and retard electron recombination process in the metal-semiconductor interface.

  8. Charging behavior of silicon nitride based non-volatile memory structures with embedded semiconductor nanocrystals

    NASA Astrophysics Data System (ADS)

    Horváth, Zs. J.; Basa, P.; Jászi, T.; Molnár, K. Z.; Pap, A. E.; Molnár, Gy.

    2013-03-01

    The charging behavior of MNS (metal-nitride-silicon) and MNOS (metal-nitride-oxide-silicon) structures containing Si or Ge nanocrystals were studied by capacitance-voltage (C-V) and memory window measurements and by simulation. Both the width of hysteresis of C-V characteristics and the injected charge exhibited exponential dependence on the charging voltage at moderate voltage values, while at high voltages the width of hysteresis of C-V characteristics and the injected charge exhibited saturation. The memory window for reference MNS structure without nanocrystals was wider than that for reference MNOS structures. The presence of nanocrystals enhanced the charging behavior of MNOS structures, but in MNS structures nanocrystals exhibited the opposite effect. The main conclusion is that the presence of nanocrystals or other deep levels close to the Si surface enhances the charge injection properties due to the increased tunneling probability, but nanocrystals or other deep levels located far from the Si surface in the nitride layer do not enhance, but even can degrade the charging behavior by the capture of charge carriers.

  9. Binary superlattices from colloidal nanocrystals and giant polyoxometalate clusters.

    PubMed

    Bodnarchuk, Maryna I; Erni, Rolf; Krumeich, Frank; Kovalenko, Maksym V

    2013-04-10

    We report a new kind of long-range ordered binary superlattices comprising atomically defined inorganic clusters and colloidally synthesized nanocrystals. In a model system, we combined surfactant-encapsulated, nearly spherical giant polyoxometalate clusters containing 2.9 nm polyoxomolybdate or 2.5 nm polyoxovanadomolybdate cores with monodisperse colloidal semiconductor nanocrystals (PbS, CdSe, PbS/CdS; 4-11 nm). The results are rationalized on the basis of dense packing principles of sterically stabilized particles with predominantly hard-spherelike interparticle interactions. By varying the size-ratios and relative concentrations of constituents, we obtained known thermodynamically stable binary packings of hard-spheres such as NaCl, AlB2, and NaZn13 lattices and also CaCu5-type lattice and aperiodic quasicrystals with 12-fold symmetry. These results suggest that other kinds of cluster materials such as fullerenes and magic-sized metallic and semiconductor clusters can also be integrated into supramolecular assemblies with nanocrystals. Furthermore, synergistic effects are expected from the combination of redox and catalytic properties of polyoxometalates with excitonic and plasmonic properties of inorganic nanocrystals.

  10. Efficient thermolysis route to monodisperse Cu₂ZnSnS₄ nanocrystals with controlled shape and structure.

    PubMed

    Zhang, Xiaoyan; Guo, Guobiao; Ji, Cheng; Huang, Kai; Zha, Chenyang; Wang, Yifeng; Shen, Liming; Gupta, Arunava; Bao, Ningzhong

    2014-05-28

    Monodisperse Cu2ZnSnS4 (CZTS) nanocrystals with tunable shape, crystalline phase, and composition are synthesized by efficient thermolysis of a single source precursor of mixed metal-oleate complexes in hot organic solvents with dissolved sulfur sources. Suitable tuning of the synthetic conditions and the Cu/(Zn + Sn) ratio of the precursor has enabled precise control of the crystalline phase in the form of kesterite, or a newly observed wurtzite structure. Nanocrystals with morphology in the form of spherical, rice-like, or rod-like shapes are obtained over a wide range of compositions (0.5 ≤ Cu/(Zn + Sn) ≤ 1.2). Both the final products and intermediates for each shape exhibit consistent composition and structure, indicating homogenous nucleation and growth of single-phase nanocrystals. Thin films prepared from colloidal nanocrystal suspensions display interesting shape-dependent photoresponse behavior under white light illumination from a solar simulator.

  11. Incorporating lanthanide cations with cadmium selenide nanocrystals: a strategy to sensitize and protect Tb(III).

    PubMed

    Chengelis, Demetra A; Yingling, Adrienne M; Badger, Paul D; Shade, Chad M; Petoud, Stéphane

    2005-12-07

    The electronic structure of CdSe semiconductor nanocrystals has been used to sensitize Tb3+ in solution by incorporation of Tb3+ cations into the nanocrystals during synthesis. Doping of luminescent Tb3+ metal ions in semiconductor nanocrystals utilizes the positive attributes of both species' photophysical properties, resulting in a final product with long luminescence lifetimes, sharp emission bands, high absorptivities, and strong resistance to decomposition. This strategy also helps protect the lanthanide cations from nonradiative deactivation from C-H, N-H, and O-H oscillators of solvent molecules or traditional organic lanthanide ligands, leading to long Tb3+ luminescence lifetimes. This new type of nanomaterial synergistically combines the photophysical properties of nanocrystals and Tb3+.

  12. Dielectric properties of colloidal Gd2O3 nanocrystal films fabricated via electrophoretic deposition

    NASA Astrophysics Data System (ADS)

    Mahajan, S. V.; Dickerson, J. H.

    2010-03-01

    We investigated the dielectric characteristics of [Al/Gd2O3/Si] metal-oxide-semiconductor (MOS) capacitors, which were fabricated from films of gadolinium oxide (Gd2O3) nanocrystals used as the gate oxide layer. Electrophoretic deposition cast Gd2O3 nanocrystal films of different thicknesses by varying the concentration of the nanocrystal suspensions. Capacitance-voltage (C-V) measurements of the MOS capacitors exhibited hysteresis, which indicated potentially favorable charge-storage properties. The films' dielectric constant (κ =3.90), calculated from the C-V data, led to the packing density of nanocrystals within the film (66%), which is in the glassy regime approximated by randomly closed packed spheres.

  13. Enzyme mediated synthesis of phytochelatin-capped CdS nanocrystals

    NASA Astrophysics Data System (ADS)

    Liu, Fang; Kang, Seung Hyun; Lee, Young-In; Choa, Yong-ho; Mulchandani, Ashok; Myung, Nosang V.; Chen, Wilfred

    2010-09-01

    We reported the enzyme mediated synthesis of CdS nanocrystals by immobilized phytochelatin synthase, which converts glutathione into the metal-binding peptide phytochelatin (PC). Formation of CdS nanocrystals were observed upon the addition of CdCl2 and Na2S with PC as the capping agent. By varying the reaction times, different compositions of PCs (form PC2 to PC3) can be synthesized, resulting in the formation of highly stable nanocrystals with tunable sizes (from 2.0 to 1.6 nm diameter). This approach may be generalized to guide the in vitro self assembly of a wide range of nanocrystals with different compositions and sizes.

  14. Preparation of ternary Cd1- x Zn x S nanocrystals with tunable ultraviolet absorption by mechanical alloying

    NASA Astrophysics Data System (ADS)

    Zhang, Qi; Zhang, Huihui; Liu, Limin; Li, Shaohua; Murowchick, James B.; Wisner, Clarissa; Leventis, Nickolas; Peng, Zhonghua; Tan, Guolong

    2015-03-01

    Composition-tunable ternary Cd1- x Zn x S nanocrystals are among the most extensively studied alloyed semiconductor nanocrystals. However, they are almost exclusively prepared by wet chemical routes, which lead to surface-capped nanoparticles. Herein, we present a simple mechanical alloying process to prepare uncapped Zn1- x Cd x S nanocrystals throughout the entire composition range. The resulting nanocrystals have average sizes smaller than 9 nm, are chemically homogenous, and exhibit linear lattice parameter-composition and close-to-linear band-gap-composition relationships. Continuous lattice contraction of the Cd1- x Zn x S nanocrystals with the atomic Zn concentration results in a successional enlargement of their band gap energies expanding from the visible region to the ultraviolet (UV) region, demonstrating the ability for precise control of band gap engineering through composition tuning and mechanical alloying. [Figure not available: see fulltext.

  15. The solvothermal synthesis of magnetic iron oxide nanocrystals and the preparation of hybrid poly(L-lactide)-polyethyleneimine magnetic particles.

    PubMed

    Stojanović, Zoran; Otoničar, Mojca; Lee, Jongwook; Stevanović, Magdalena M; Hwang, Mintai P; Lee, Kwan Hyi; Choi, Jonghoon; Uskoković, Dragan

    2013-09-01

    We report a simple and green procedure for the preparation of magnetic iron oxide nanocrystals via solvothermal synthesis. The nanocrystal synthesis was carried out under mild conditions in the water-ethanol-oleic acid solvent system with the use of the oleate anion as a surface modifier of nanocrystals and glucose as a reducing agent. Specific conditions for homogenous precipitation achieved in such a reaction system lead to the formation of uniform high-quality nanocrystals down to 5 nm in diameter. The obtained hydrophobic nanocrystals can easily be converted to hydrophilic magnetic nanoparticles by being immobilized in a poly(L-lactide)-polyethyleneimine polymeric matrix. These hybrid nano-constructs may find various biomedical applications, such as magnetic separation, gene transfection and/or magnetic resonance imaging. Copyright © 2013 Elsevier B.V. All rights reserved.

  16. Tuning the formation and functionalities of ultrafine CoFe2O4 nanocrystals via interfacial coherent strain.

    PubMed

    Hsieh, Ying-Hui; Kuo, Ho-Hung; Liao, Sheng-Chieh; Liu, Heng-Jui; Chen, Ying-Jiun; Lin, Hong-Ji; Chen, Chien-Te; Lai, Chih-Huang; Zhan, Qian; Chueh, Yu-Lun; Chu, Ying-Hao

    2013-07-21

    Complex oxide nanocrystals with a spinel structure show their remarkable optical, electronic, mechanical, thermal, and magnetic properties. In this study, we present a simple yet versatile strategy to grow self-assembled epitaxial CoFe2O4 nanocrystals with well-controlled size (less than 10 nm) and single orientation. CoFe2O4 nanocrystals were fabricated via phase separation in a BiFeO3-CoF2O4 ultrathin film by pulsed laser deposition. The coherent strain at the BiFeO3-CoF2O4 interface suppressed the growth of the nanocrystals regardless of substrate temperatures. This strain also resulted in the ferromagnetic anisotropy and interesting conducting behaviors of ultrafine CFO nanocrystals.

  17. Reproducible manipulation of spin ordering in ZnCoO nanocrystals by hydrogen mediation

    SciTech Connect

    Lee, Seunghun; Cho, Yong Chan; Kim, Sung-Jin; Cho, Chae Ryong; Jeong, Se-Young; Kim, Su Jae; Kim, Jong Pil; Choi, Yong Nam; Sur, Jean Man

    2009-05-25

    Through a simple post hydrogen plasma treatment, we show the strong inducement of the room temperature ferromagnetism in Zn{sub 0.9}Co{sub 0.1}O:H nanocrystals fabricated by sol-gel process. X-ray diffraction, high resolution transmission electron microscopy, and neutron high resolution powder diffraction measurements of Zn{sub 0.9}Co{sub 0.1}O nanocrystals before and after hydrogenation process confirmed that there are no structural changes in nanocrystal and any creation of magnetic secondary phase. Nevertheless, the clear ferromagnetic hysteresis loop of the hydrogenated Zn{sub 0.9}Co{sub 0.1}O nanocrystal was observed in superconducting quantum interference device. These results indicate that the ferromagnetism can be derived from a short-range spin ordering by hydrogen mediation in Co doped ZnO.

  18. Synthesis and characterization of Sm and Pr-doped CaWO4 nano-crystals

    NASA Astrophysics Data System (ADS)

    Suneetha, P.; Rajesh, Ch; Ramana, M. V.

    2017-04-01

    In this paper, we report a simple method to dope rare-earth ions, such as samarium (Sm) and praseodymium (Pr), in calcium tungstate (CaWO4) nano-crystals. To estimate the size as well as incorporation of rare-earth ions in the host lattice, several techniques are used. The x-ray diffraction method was used to identify the phase of the nano-crystals, and scanning electron microscopy was used to calculate the size of the nano-crystals. The incorporation of rare-earth ions was confirmed using energy dispersive analysis x-ray studies. These studies reveal that nano-crystals of calcium tungstate doped with Sm3+ and Pr3+ with a size around 60 nm could be synthesized using this method.

  19. Preparation of ZnSe Nanocrystals Using Water-in-Oil Microemulsions

    NASA Astrophysics Data System (ADS)

    Hyun Soo Kim,; Jong Sung Kim,; Sang Joon Park,

    2010-06-01

    ZnSe nanocrystals were prepared using a safe and simple synthetic method by employing a sodium bis(2-ethylhexyl) sulfosuccinate (AOT)/water/oil microemulsion system with aqueous ZnSO4 and Se2- solutions, and characterized by X-ray diffraction (XRD) analysis, photoluminescence (PL) spectroscopy, and transmission electron microscopy (TEM). To control the diameter of nanocrystals in the quantum confinement region, the synthesis was performed with different oil phases (heptane and cyclohexane) and various water-to-surfactant ratios, W ([H2O]/[surfactant]). Cubic zinc blende ZnSe nanocrystals were synthesized and their size was controlled in the range from 2.5 to 17 nm. The maximum PL efficiency was 14% for the smallest ZnSe nanocrystal.

  20. Semiconductor nanocrystal-based phagokinetic tracking

    DOEpatents

    Alivisatos, A Paul; Larabell, Carolyn A; Parak, Wolfgang J; Le Gros, Mark; Boudreau, Rosanne

    2014-11-18

    Methods for determining metabolic properties of living cells through the uptake of semiconductor nanocrystals by cells. Generally the methods require a layer of neutral or hydrophilic semiconductor nanocrystals and a layer of cells seeded onto a culture surface and changes in the layer of semiconductor nanocrystals are detected. The observed changes made to the layer of semiconductor nanocrystals can be correlated to such metabolic properties as metastatic potential, cell motility or migration.

  1. Colloidal synthesis of Cu-ZnO and Cu@CuNi-ZnO hybrid nanocrystals with controlled morphologies and multifunctional properties.

    PubMed

    Zeng, Deqian; Gong, Pingyun; Chen, Yuanzhi; Zhang, Qinfu; Xie, Qingshui; Peng, Dong-Liang

    2016-06-02

    Metal-semiconductor hybrid nanocrystals have received extensive attention owing to their multiple functionalities which can find wide technological applications. The utilization of low-cost non-noble metals to construct novel metal-semiconductor hybrid nanocrystals is important and meaningful for their large-scale applications. In this study, a facile solution approach is developed for the synthesis of Cu-ZnO hybrid nanocrystals with well-controlled morphologies, including nanomultipods, core-shell nanoparticles, nanopyramids and core-shell nanowires. In the synthetic strategy, Cu nanocrystals formed in situ serve as seeds for the heterogeneous nucleation and growth of ZnO, and it eventually forms various Cu-ZnO hetero-nanostructures under different reaction conditions. These hybrid nanocrystals possess well-defined and stable heterostructure junctions. The ultraviolet-visible-near infrared spectra reveal morphology-dependent surface plasmon resonance absorption of Cu and the band gap absorption of ZnO. Furthermore, we construct a novel Cu@CuNi-ZnO ternary hetero-nanostructure by incorporating the magnetic metal Ni into the pre-synthesized colloidal Cu nanocrystals. Such hybrid nanocrystals possess a magnetic Cu-Ni intermediate layer between the ZnO shell and the Cu core, and exhibit ferromagnetic/superparamagnetic properties which expand their functionalities. Finally, enhanced photocatalytic activities are observed in the as-prepared non-noble metal-ZnO hybrid nanocrystals. This study not only provides an economical way to prepare high-quality morphology-controlled Cu-ZnO hybrid nanocrystals for potential applications in the fields of photocatalysis and photovoltaic devices, but also opens up new opportunities in designing ternary non-noble metal-semiconductor hybrid nanocrystals with multifunctionalities.

  2. Metal-free transannulation reaction of indoles with nitrostyrenes: a simple practical synthesis of 3-substituted 2-quinolones†

    PubMed Central

    Aksenov, Alexander V.; Smirnov, Alexander N.; Aksenov, Nicolai A.; Aksenova, Inna V.; Frolova, Liliya V.; Kornienko, Alexander; Magedov, Igor V.; Rubin, Michael

    2016-01-01

    3-Substituted 2-quinolones are obtained via a novel, metal-free transannulation reaction of 2-substituted indoles with 2-nitroalkenes in polyphosphoric acid. The reaction can be used in conjunction with the Fisher indole synthesis offering a practical three-component heteroannulation methodology to produce 2-quinolones from arylhydrazines, 2-nitroalkenes and acetophenone. PMID:23999797

  3. Metal-free transannulation reaction of indoles with nitrostyrenes: a simple practical synthesis of 3-substituted 2-quinolones.

    PubMed

    Aksenov, Alexander V; Smirnov, Alexander N; Aksenov, Nicolai A; Aksenova, Inna V; Frolova, Liliya V; Kornienko, Alexander; Magedov, Igor V; Rubin, Michael

    2013-10-18

    3-Substituted 2-quinolones are obtained via a novel, metal-free transannulation reaction of 2-substituted indoles with 2-nitroalkenes in polyphosphoric acid. The reaction can be used in conjunction with the Fisher indole synthesis offering a practical three-component heteroannulation methodology to produce 2-quinolones from arylhydrazines, 2-nitroalkenes and acetophenone.

  4. Separation of single-walled carbon nanotubes into metallic and semiconducting groups: a simple and large-scale method

    NASA Astrophysics Data System (ADS)

    Lu, Jing; Maeda, Y.

    2006-03-01

    Separation of a large number of single-walled carbon nanotubes (SWNTs) into groups each with specifically metallic and semiconducting properties is an extremely important task for technology application. Even though effective methods (1, 2) have been devised, they suffer from drawbacks such as either the yield is low (3) or expense is high (4). In this work, we study the problem from a theoretical approach, we notice that based on the first principles calculations the binding strengths of methylamine to the semiconducting [13, 0] SWNT are only 36˜61% of that to the metallic [7, 7] SWNT, which suggests that the amines is much more attractive toward the pure metallic than the semiconducting SWNTs. Therefore starting from as-prepared SWNTs and with the assistance of amines, we achieved SWNTs with enriched metallic properties over semiconducting in a convenient and large-scale manner. References: (1) D. Chattopadhyay, L. Galeska, F. Papadimitrakopoulos, Journal of the American Chemical Society 125, 3370 (MAR 19, 2003). (2) H. P. Li et al., Journal of the American Chemical Society 126, 1014 (FEB 4, 2004). (3) R. Krupke, F. Hennrich, H. von Lohneysen, M. Kappes, SCIENCE 301, 344 (JUL 18, 2003). (4) M. Zheng et al., Science 302, 1545 (NOV 28, 2003).

  5. Mapping the exciton diffusion in semiconductor nanocrystal solids.

    PubMed

    Kholmicheva, Natalia; Moroz, Pavel; Bastola, Ebin; Razgoniaeva, Natalia; Bocanegra, Jesus; Shaughnessy, Martin; Porach, Zack; Khon, Dmitriy; Zamkov, Mikhail

    2015-03-24

    Colloidal nanocrystal solids represent an emerging class of functional materials that hold strong promise for device applications. The macroscopic properties of these disordered assemblies are determined by complex trajectories of exciton diffusion processes, which are still poorly understood. Owing to the lack of theoretical insight, experimental strategies for probing the exciton dynamics in quantum dot solids are in great demand. Here, we develop an experimental technique for mapping the motion of excitons in semiconductor nanocrystal films with a subdiffraction spatial sensitivity and a picosecond temporal resolution. This was accomplished by doping PbS nanocrystal solids with metal nanoparticles that force the exciton dissociation at known distances from their birth. The optical signature of the exciton motion was then inferred from the changes in the emission lifetime, which was mapped to the location of exciton quenching sites. By correlating the metal-metal interparticle distance in the film with corresponding changes in the emission lifetime, we could obtain important transport characteristics, including the exciton diffusion length, the number of predissociation hops, the rate of interparticle energy transfer, and the exciton diffusivity. The benefits of this approach to device applications were demonstrated through the use of two representative film morphologies featuring weak and strong interparticle coupling.

  6. A simple in situ preconcentration method for the simultaneous determination of major and minor alkali and alkaline-earth metals in natural waters using iminodiacetate-grafted fiber.

    PubMed

    Kot, Fyodor S; Fujiwara, Kunio; Kochva, Malik

    2017-06-01

    A simple and effective procedure was developed for the simultaneous in situ preconcentration of major and minor alkali and alkaline-earth metals (Li, Na, K, Rb, Mg, Ca, Sr, and Ba) from natural waters with iminodiacetate-grafted fiber (IDA-fiber), using soil water extracts as an example. The method was verified on mixed standard solutions of the metals at concentrations and ionic strengths reported for regular soil solutions. When complemented with routine microfiltration procedures, the method could distinguish between the dissolved in hydrated ion form and bound fractions of these metals, presumably colloidal and firmly complexed. The method was tested on water extracts from heavy clayey Vertisol and light red sandy-loam soils. The results showed that most of the Rb, Mg, Ca, Sr, and Ba of the 0.45-μm filtrate were bound to unreactive water-mobile compounds, whereas K and Na were determined predominantly in dissolved/reactive forms. The preliminary charged IDA-fiber can be used to preconcentrate the metals in situ from soil water and other types of natural waters with subsequent determination in a stationary laboratory, thus avoiding the critical step of storage and transportation of the unstable water samples. Graphical abstract A bundle of preliminary charged iminodiacetate-grafted fiber placed in a water-sample during in-field preconcentration procedure.

  7. Evaluation of the bioaccessible gastric and intestinal fractions of heavy metals in contaminated soils by means of a simple bioaccessibility extraction test.

    PubMed

    Jorge Mendoza, C; Tatiana Garrido, R; Cristian Quilodrán, R; Matías Segovia, C; José Parada, A

    2017-06-01

    A study is made to evaluate the bioaccessibility of heavy metals in contaminated soils through a simple bioaccessibility extraction test (SBET), applied to the analysis of both the gastric and intestinal phases. Soils with high metal content of the Mapocho, Cachapoal, and Rancagua series were studied; they are located in suburban areas of large cities in the central valley of Chile. The bioaccessible concentrations of Cd, Cr, Cu, Ni, Pb, and Zn were related to the main physicochemical characteristics of the soils and to the chemical forms obtained by sequential extraction. The elements Cd, Cu, Ni, and Zn are distributed in the soils between the exchangeable fractions, bound to oxides, to organic matter, and in the residual fraction. On the other hand, Cr and Pb are found mainly in the fractions bound to organic matter and in the residual fraction. The three soils have a high Cu content, (640-2060 mg/kg), in the order Cachapoal > Rancagua > Mapocho. The SBET test allowed establishing a different bioaccessibility for the elements in the soil. Cu was notoriously bioaccessible in both the gastric and intestinal phases in the three soils, reaching more than 50% in the Cachapoal and Rancagua soils. The other elements, regardless of the soil, were bioaccessible only in one of the phases, more frequently in the gastric phase. The multiple correlation study indicates that the metal forms have a higher incidence than the soil's physicochemical factors on the extractability to evaluate the human oral bioaccessibility of the metals.

  8. A GREENER SYNTHESIS OF CORE (FE, CU)-SHELL (AU, PT, PD AND AG) NANOCRYSTALS USING AQUEOUS VITAMIN C

    EPA Science Inventory

    A greener method to fabricate the novel core (Fe and Cu)-shell (noble metals) metal nanocrystals using aqueous ascorbic acid (vitamin C) is described. Transition metal salts such as Cu and Fe were reduced using ascorbic acid, a benign naturally available antioxidant, and then add...

  9. A GREENER SYNTHESIS OF CORE (FE, CU)-SHELL (AU, PT, PD AND AG) NANOCRYSTALS USING AQUEOUS VITAMIN C

    EPA Science Inventory

    A greener method to fabricate the novel core (Fe and Cu)-shell (noble metals) metal nanocrystals using aqueous ascorbic acid (vitamin C) is described. Transition metal salts such as Cu and Fe were reduced using ascorbic acid, a benign naturally available antioxidant, and then add...

  10. Core/Shell semiconductor nanocrystals.

    PubMed

    Reiss, Peter; Protière, Myriam; Li, Liang

    2009-02-01

    Colloidal core/shell nanocrystals contain at least two semiconductor materials in an onionlike structure. The possibility to tune the basic optical properties of the core nanocrystals, for example, their fluorescence wavelength, quantum yield, and lifetime, by growing an epitaxial-type shell of another semiconductor has fueled significant progress on the chemical synthesis of these systems. In such core/shell nanocrystals, the shell provides a physical barrier between the optically active core and the surrounding medium, thus making the nanocrystals less sensitive to environmental changes, surface chemistry, and photo-oxidation. The shell further provides an efficient passivation of the surface trap states, giving rise to a strongly enhanced fluorescence quantum yield. This effect is a fundamental prerequisite for the use of nanocrystals in applications such as biological labeling and light-emitting devices, which rely on their emission properties. Focusing on recent advances, this Review discusses the fundamental properties and synthesis methods of core/shell and core/multiple shell structures of II-VI, IV-VI, and III-V semiconductors.

  11. Linearly arranged polytypic CZTSSe nanocrystals

    PubMed Central

    Fan, Feng-Jia; Wu, Liang; Gong, Ming; Chen, Shi You; Liu, Guang Yao; Yao, Hong-Bin; Liang, Hai-Wei; Wang, Yi-Xiu; Yu, Shu-Hong

    2012-01-01

    Even colloidal polytypic nanostructures show promising future in band-gap tuning and alignment, researches on them have been much less reported than the standard nano-heterostructures because of the difficulties involved in synthesis. Up to now, controlled synthesis of colloidal polytypic nanocrsytals has been only realized in II-VI tetrapod and octopod nanocrystals with branched configurations. Herein, we report a colloidal approach for synthesizing non-branched but linearly arranged polytypic I2-II-IV-VI4 nanocrystals, with a focus on polytypic non-stoichiometric Cu2ZnSnSxSe4−x nanocrystals. Each synthesized polytypic non-stoichiometric Cu2ZnSnSxSe4−x nanocrystal is consisted of two zinc blende-derived ends and one wurtzite-derived center part. The formation mechanism has been studied and the phase composition can be tuned through adjusting the reaction temperature, which brings a new band-gap tuning approach to Cu2ZnSnSxSe4-x nanocrystals. PMID:23233871

  12. Simple whole-cell biodetection and bioremediation of heavy metals based on an engineered lead-specific operon.

    PubMed

    Wei, Wei; Liu, Xiangzhi; Sun, Peiqing; Wang, Xin; Zhu, Hong; Hong, Mei; Mao, Zong-Wan; Zhao, Jing

    2014-03-18

    A lead-specific binding protein, PbrR, and promoter pbr from the lead resistance operon, pbr, of Cupriavidus metallidurans CH34 was incorporated into E. coli in conjunction with an engineered downstream RFP (red fluorescence protein), which allowed for highly sensitive and selective whole-cell detection of lead ions. The subsequent display of PbrR on the E. coli cell surface permitted selective adsorption of lead ions from solution containing various heavy metal ions. The surface-engineered E. coli bacteria effectively protected Arabidopsis thaliana seed germination from the toxicity of lead ions at high concentrations. Engineering the E. coli bacteria harboring these lead-specific elements from the pbr operon may potentially be a valuable general strategy for biodetection and bioremediation of toxic heavy metal ions in the environment.

  13. A Radiation-Tolerant, Low-Power Non-Volatile Memory Based on Silicon Nanocrystal Quantum Dots

    NASA Technical Reports Server (NTRS)

    Bell, L. D.; Boer, E. A.; Ostraat, M. L.; Brongersma, M. L.; Flagan, R. C.; Atwater, H. A.; deBlauwe, J.; Green, M. L.

    2001-01-01

    Nanocrystal nonvolatile floating-gate memories are a good candidate for space applications - initial results suggest they are fast, more reliable and consume less power than conventional floating gate memories. In the nanocrystal based NVM device, charge is not stored on a continuous polysilicon layer (so-called floating gate), but instead on a layer of discrete nanocrystals. Charge injection and storage in dense arrays of silicon nanocrystals in SiO2 is a critical aspect of the performance of potential nanocrystal flash memory structures. The ultimate goal for this class of devices is few- or single-electron storage in a small number of nanocrystal elements. In addition, the nanocrystal layer fabrication technique should be simple, 8-inch wafer compatible and well controlled in program/erase threshold voltage swing was seen during 100,000 program and erase cycles. Additional near-term goals for this project include extensive testing for radiation hardness and the development of artificial layered tunnel barrier heterostructures which have the potential for large speed enhancements for read/write of nanocrystal memory elements, compared with conventional flash devices. Additional information is contained in the original extended abstract.

  14. A Radiation-Tolerant, Low-Power Non-Volatile Memory Based on Silicon Nanocrystal Quantum Dots

    NASA Technical Reports Server (NTRS)

    Bell, L. D.; Boer, E. A.; Ostraat, M. L.; Brongersma, M. L.; Flagan, R. C.; Atwater, H. A.; deBlauwe, J.; Green, M. L.

    2001-01-01

    Nanocrystal nonvolatile floating-gate memories are a good candidate for space applications - initial results suggest they are fast, more reliable and consume less power than conventional floating gate memories. In the nanocrystal based NVM device, charge is not stored on a continuous polysilicon layer (so-called floating gate), but instead on a layer of discrete nanocrystals. Charge injection and storage in dense arrays of silicon nanocrystals in SiO2 is a critical aspect of the performance of potential nanocrystal flash memory structures. The ultimate goal for this class of devices is few- or single-electron storage in a small number of nanocrystal elements. In addition, the nanocrystal layer fabrication technique should be simple, 8-inch wafer compatible and well controlled in program/erase threshold voltage swing was seen during 100,000 program and erase cycles. Additional near-term goals for this project include extensive testing for radiation hardness and the development of artificial layered tunnel barrier heterostructures which have the potential for large speed enhancements for read/write of nanocrystal memory elements, compared with conventional flash devices. Additional information is contained in the original extended abstract.

  15. The role of electron-electron repulsion in the problem of epitaxial graphene on a metal: Simple estimates

    NASA Astrophysics Data System (ADS)

    Davydov, S. Yu.

    2017-08-01

    For single-layer graphene placed on a metal substrate, the influence of intra- and interatomic Coulomb repulsion of electrons ( U and G, respectively) on its phase diagram is considered in the framework of an extended Hartree-Fock theory. The general solution of the problem is presented, on the basis of which special cases allowing for analytical consideration are analyzed: free and epitaxial graphene with and without regard for the energy of the electron transition between neighboring atoms of graphene. Three regions of the phase diagram are considered: spin and charge density waves (SDW and CDW, respectively) and the semimetal (SM) state uniform in the spin and charge. The main attention is paid to undoped graphene. It is shown that the allowance for the interaction with a metal substrate expands the SM existence domain. However, in all the considered cases, the boundary between the SDW and CDW states is described by the equation U = zG, where z = 3 is the number of nearest neighbors in graphene. The widening of the SM state region also results from the doping of graphene, and the effect is independent of the sign of free carriers introduced into epitaxial graphene by the substrate. According to estimates made, the only state possible in the buffer layer is the metal-type SM state, whereas, in epitaxial graphene, the CDW state is possible. The influence of temperature on the phase diagram of epitaxial graphene is discussed.

  16. Metal flux and dynamic speciation at (bio)interfaces. Part VI: The roles of simple, fulvic and aggregate complexes on computed metal flux in freshwater ligand mixtures; comparison of Pb, Zn and Ni at planar and microspherical interfaces

    NASA Astrophysics Data System (ADS)

    Zhang, Zeshi; Buffle, Jacques

    2009-03-01

    The computations of metal flux in aquatic systems, at consuming interfaces like microorganism surfaces are of major importance in ecotoxicology and dynamic risk assessment. In this paper, the flux of Zn(II) and Ni(II), at a planar consuming interface in a typical natural freshwater, are studied. The system includes (a) simple ligands (OH -, CO32-); (b) fulvics; (c) aggregates, as complexants, i.e., those which play the major roles in controlling the metal distribution and/or metal flux in aquatic media. The above two metals are chosen because they participate, respectively, to intermediate and very slow chemical reactions with complexing sites, and are thus complementary to Pb(II) and Cu(II) (two metals with very fast reactions) studied in Parts III-V of this series. The effects of the various physico-chemical factors, in particular, the diffusion layer thickness, the stability constants and complexing site distribution of fulvics and the size distribution of aggregates, are studied in details. The contribution to the flux, of each complex type, is computed. This paper also compares the dynamic behaviour of Pb(II), Zn(II) and Ni(II) as well as the labilities and flux contributions of their various complexes at planar and microspherical interfaces. This enables to make predictions on biouptake by microorganisms.

  17. Hydrothermal Gelation of Aqueous Cellulose Nanocrystal Suspensions.

    PubMed

    Lewis, Lev; Derakhshandeh, Maziar; Hatzikiriakos, Savvas G; Hamad, Wadood Y; MacLachlan, Mark J

    2016-08-08

    We report the facile preparation of gels from the hydrothermal treatment of suspensions of cellulose nanocrystals (CNCs). The properties of the hydrogels have been investigated by rheology, electron microscopy, and spectroscopy with respect to variation in the temperature, time, and CNC concentration used in preparation. Desulfation of the CNCs at high temperature appears to be responsible for the gelation of the CNCs, giving highly porous networks. The viscosity and storage modulus of the gels was shown to increase when samples were prepared at higher treatment temperature. Considering the wide natural abundance and biocompatibility of CNCs, this simple, green approach to CNC-based hydrogels is attractive for producing materials that can be used in drug delivery, insulation, and as tissue scaffolds.

  18. Nanocrystals for luminescent solar concentrators.

    PubMed

    Bradshaw, Liam R; Knowles, Kathryn E; McDowall, Stephen; Gamelin, Daniel R

    2015-02-11

    Luminescent solar concentrators (LSCs) harvest sunlight over large areas and concentrate this energy onto photovoltaics or for other uses by transporting photons through macroscopic waveguides. Although attractive for lowering solar energy costs, LSCs remain severely limited by luminophore reabsorption losses. Here, we report a quantitative comparison of four types of nanocrystal (NC) phosphors recently proposed to minimize reabsorption in large-scale LSCs: two nanocrystal heterostructures and two doped nanocrystals. Experimental and numerical analyses both show that even the small core absorption of the leading NC heterostructures causes major reabsorption losses at relatively short transport lengths. Doped NCs outperform the heterostructures substantially in this critical property. A new LSC phosphor is introduced, nanocrystalline Cd(1-x)Cu(x)Se, that outperforms all other leading NCs by a significant margin in both small- and large-scale LSCs under full-spectrum conditions.

  19. Metal colloids and quantum dots: linear and nonlinear optical properties

    SciTech Connect

    Henderson, Don O.

    1997-05-12

    Nanophase materials have found a wide application in a variety of technological areas which include ultrafast optical switching high density information storage and retrieval, electronics, and catalysts, to mention a few. Nanocrystal science has also drawn considerable interest from the fundamental perspective engaging physicists, chemists, and material scientists into this area of rapidly expanding and challenging research. Basic questions concerning how matter evolves from atomic like behavior to molecular and onto bulk lie at the center nanocrystal research. In addition, because of the high surface to volume ratio of the nanocrystals, the interaction potential between a nanocrystal and its surrounding environment becomes an important issue in determining its properties. While significant progress has been made in nanocrystal research, there are many problems concerned with their fabrication. In particular, the difficulty of incorporating nanocrystals into a matrix that is appropriate for ultimate device development has hindered some aspects of nanocrystal research. Ion implantation is a method that is now established as a technique for fabricating metal and semiconductor nanocrystals. It is highly versatile in that one may select nearly any host material for incorporating the nanocrystals of interest. The flexibility of being able to select the host matrix is also interesting from the point of view that it opens the opportunity to investigate matrix-nanocrystal interactions. We summarize in the following sections results on metal and semiconductor nanocrystals formed by ion implantation into dielectric hosts.

  20. Geometric and electronic effects on hydrogenation of cinnamaldehyde over unsupported Pt-based nanocrystals.

    PubMed

    Oduro, William O; Cailuo, Nick; Yu, Kai Man K; Yang, Hongwei; Tsang, Shik Chi

    2011-02-21

    It is reported that catalytic hydrogenation of cinnamaldehyde to cinnamyl alcohol is a structural sensitive reaction dependent on size and type of metal doper of unsupported platinum nanocrystals used. Smaller sizes of platinum nanocrystals are found to give lower selectivity to cinnamyl alcohol, which suggests the high index Pt sites are undesirable for the terminal aldehyde hydrogenation. A plot of reaction selectivity across the first row of transition metals as dopers gives a typical volcano shape curve, the apex of which depicts that a small level of cobalt on platinum nanocrystals can greatly promote the reaction selectivity. The selectivity towards cinnamyl alcohol over the cobalt doped Pt nanocrystals can reach over 99.7%, following the optimization in reaction conditions such as temperature, pressure and substrate concentration. Detailed studies of XRD, CO chemisorption (for FTIR), TEM, SEM, AES and XPS of the nanostructure catalyst clearly reveal that the decorated cobalt atoms not only block the high index sites of Pt nanocrystals (sites for Co deposition) but also exert a strong electronic influence on reaction pathways. The d-band centre theory is invoked to explain the volcano plot of selectivity versus metal doper.