Sample records for nanocrystal bioassembly asymmetry

  1. Automated 3D bioassembly of micro-tissues for biofabrication of hybrid tissue engineered constructs.

    PubMed

    Mekhileri, N V; Lim, K S; Brown, G C J; Mutreja, I; Schon, B S; Hooper, G J; Woodfield, T B F

    2018-01-12

    Bottom-up biofabrication approaches combining micro-tissue fabrication techniques with extrusion-based 3D printing of thermoplastic polymer scaffolds are emerging strategies in tissue engineering. These biofabrication strategies support native self-assembly mechanisms observed in developmental stages of tissue or organoid growth as well as promoting cell-cell interactions and cell differentiation capacity. Few technologies have been developed to automate the precise assembly of micro-tissues or tissue modules into structural scaffolds. We describe an automated 3D bioassembly platform capable of fabricating simple hybrid constructs via a two-step bottom-up bioassembly strategy, as well as complex hybrid hierarchical constructs via a multistep bottom-up bioassembly strategy. The bioassembly system consisted of a fluidic-based singularisation and injection module incorporated into a commercial 3D bioprinter. The singularisation module delivers individual micro-tissues to an injection module, for insertion into precise locations within a 3D plotted scaffold. To demonstrate applicability for cartilage tissue engineering, human chondrocytes were isolated and micro-tissues of 1 mm diameter were generated utilising a high throughput 96-well plate format. Micro-tissues were singularised with an efficiency of 96.0 ± 5.1%. There was no significant difference in size, shape or viability of micro-tissues before and after automated singularisation and injection. A layer-by-layer approach or aforementioned bottom-up bioassembly strategy was employed to fabricate a bilayered construct by alternatively 3D plotting a thermoplastic (PEGT/PBT) polymer scaffold and inserting pre-differentiated chondrogenic micro-tissues or cell-laden gelatin-based (GelMA) hydrogel micro-spheres, both formed via high-throughput fabrication techniques. No significant difference in viability between the construct assembled utilising the automated bioassembly system and manually assembled construct was

  2. Bio-assembled, piezoelectric prawn shell made self-powered wearable sensor for non-invasive physiological signal monitoring

    NASA Astrophysics Data System (ADS)

    Ghosh, Sujoy Kumar; Mandal, Dipankar

    2017-03-01

    A human interactive self-powered wearable sensor is designed using waste by-product prawn shells. The structural origin of intrinsic piezoelectric characteristics of bio-assembled chitin nanofibers has been investigated. It allows the prawn shell to make a tactile sensor that performs also as a highly durable mechanical energy harvester/nanogenerator. The feasibility and fundamental physics of self-powered consumer electronics even from human perception is highlighted by prawn shells made nanogenerator (PSNG). High fidelity and non-invasive monitoring of vital signs, such as radial artery pulse wave and coughing actions, may lead to the potential use of PSNG for early intervention. It is presumed that PSNG has enormous future aspects in real-time as well as remote health care assessment.

  3. Capping Ligand Vortices as "Atomic Orbitals" in Nanocrystal Self-Assembly.

    PubMed

    Waltmann, Curt; Horst, Nathan; Travesset, Alex

    2017-11-28

    We present a detailed analysis of the interaction between two nanocrystals capped with ligands consisting of hydrocarbon chains by united atom molecular dynamics simulations. We show that the bonding of two nanocrystals is characterized by ligand textures in the form of vortices. These results are generalized to nanocrystals of different types (differing core and ligand sizes) where the structure of the vortices depends on the softness asymmetry. We provide rigorous calculations for the binding free energy, show that these energies are independent of the chemical composition of the cores, and derive analytical formulas for the equilibrium separation. We discuss the implications of our results for the self-assembly of single-component and binary nanoparticle superlattices. Overall, our results show that the structure of the ligands completely determines the bonding of nanocrystals, fully supporting the predictions of the recently proposed Orbifold topological model.

  4. Inorganic Nanocrystals Functionalized Mesoporous Silica Nanoparticles: Fabrication and Enhanced Bio-applications

    NASA Astrophysics Data System (ADS)

    Zhao, Tiancong; Nguyen, Nam-Trung; Xie, Yang; Sun, Xiaofei; Li, Qin; Li, Xiaomin

    2017-12-01

    Mesoporous SiO2 nanoparticles (MSNs) are one of the most promising materials for bio-related applications due to advantages such as good biocompatibility, tunable mesopores and large pore volume. However, unlike the inorganic nanocrystals with abundant physical properties, MSNs alone lack functional features. Thus, they are not sufficiently suitable for bio-applications that require special functions. Consequently, MSNs are often functionalized by incorporating inorganic nanocrystals, which provide a wide range of intriguing properties. This review focuses on inorganic nanocrystals functionalized MSNs, both their fabrication and bio-applications. Some of the most utilized methods for coating mesoporous silica (mSiO2) on nanoparticles were summarized. Magnetic, fluorescence and photothermal inorganic nanocrystals functionalized MSNs were taken as examples to demonstrate the bio-applications. Furthermore, asymmetry of MSNs and their effects on functions were also highlighted.

  5. Capping Ligand Vortices as “Atomic Orbitals” in Nanocrystal Self-Assembly

    DOE PAGES

    Waltmann, Curt; Horst, Nathan; Travesset, Alex

    2017-10-27

    In this work, we present a detailed analysis of the interaction between two nanocrystals capped with ligands consisting of hydrocarbon chains by united atom molecular dynamics simulations. We show that the bonding of two nanocrystals is characterized by ligand textures in the form of vortices. These results are generalized to nanocrystals of different types (differing core and ligand sizes) where the structure of the vortices depends on the softness asymmetry. We provide rigorous calculations for the binding free energy, show that these energies are independent of the chemical composition of the cores, and derive analytical formulas for the equilibrium separation.more » We discuss the implications of our results for the self-assembly of single-component and binary nanoparticle superlattices. Overall, our results show that the structure of the ligands completely determines the bonding of nanocrystals, fully supporting the predictions of the recently proposed Orbifold topological model.« less

  6. 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.

  7. 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.

  8. 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

  9. 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.

  10. Surface chemical modification of nanocrystals

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Helms, Brett Anthony; Milliron, Delia Jane; Rosen, Evelyn Louise

    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.

  11. Living Nanocrystals: Synthesis of Precisely Defined Metal Oxide Nanocrystals Through a Continuous Growth Process

    NASA Astrophysics Data System (ADS)

    Jansons, Adam Wayne

    Colloidal nanocrystals offer new and improved performance in applications as well as less environmental impact when compared to traditional device fabrication methods. The important properties that enable improved applications are a direct result of nanocrystal structure. While there have been many great advances in the production of colloidal nanocrystals over the past three decades, precise, atomic-level control of the size, composition, and structure of the inorganic core remains challenging. Rather than dictate these material aspects through traditional synthetic routes, this dissertation details the development and exploitation of a colloidal nanocrystal synthetic method inspired by polymerization reactions. Living polymerization reactions offer precise control of polymer size and structure and have tremendously advanced polymer science, allowing the intuitive production of polymers and block co-polymers of well-defined molecular weights. Similarly, living nanocrystal synthetic methods allow an enhanced level of structural control, granting the synthesis of binary, doped, and core/shell nanocrystals of well-defined size, composition, and structure. This improved control in turn grants enhanced nanocrystal property performance and deepens our understanding of structure/property relationships. This dissertation defines living nanocrystal growth and demonstrates the potential of the living methods in the colloidal production of oxide nanocrystals. After a brief introduction, living growth is defined and discussed in the context of synthetic prerequisites, attributes, and outcomes. Living growth is also compared to more traditional colloidal nanocrystal synthetic methods. The following chapters then demonstrate the precise control living approaches offer in three separate studies; the first highlights sub-nanometer control of nanocrystal size from 2-22+ nm in diameter. Next the improvement in nanocrystal composition is illustrated using several transition metal

  12. 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.

  13. Nanocrystals Technology for Pharmaceutical Science.

    PubMed

    Cheng, Zhongyao; Lian, Yumei; Kamal, Zul; Ma, Xin; Chen, Jianjun; Zhou, Xinbo; Su, Jing; Qiu, Mingfeng

    2018-05-17

    Nanocrystals technology is a promising method for improving the dissolution rate and enhancing the bioavailability of poorly soluble drugs. In recent years, it has been developing rapidly and applied to drug research and engineering. Nanocrystal drugs can be formulated into various dosage forms. This review mainly focused on the nanocrystals technology and its application in pharmaceutical science. Firstly, different preparation methods of nanocrystal technology and the characterization of nanocrystal drugs are briefly described. Secondly, the application of nanocrystals technology in pharmaceutical science is mainly discussed followed by the introduction of sustained release formulations. Then, the scaling up process, marketed nanocrystal drug products and regulatory aspects about nanodrugs are summarized. Finally, the specific challenges and opportunities of nanocrystals technology for pharmaceutical science are summarized and discussed. This review will provide a comprehensive guide for scientists and engineers in the field of pharmaceutical science and biochemical engineering. Copyright© Bentham Science Publishers; For any queries, please email at epub@benthamscience.org.

  14. Fabrication of all-inorganic nanocrystal solids through matrix encapsulation of nanocrystal arrays.

    PubMed

    Kinder, Erich; Moroz, Pavel; Diederich, Geoffrey; Johnson, Alexa; Kirsanova, Maria; Nemchinov, Alexander; O'Connor, Timothy; Roth, Dan; Zamkov, Mikhail

    2011-12-21

    A general strategy for low-temperature processing of colloidal nanocrystals into all-inorganic films is reported. The present methodology goes beyond the traditional ligand-interlinking scheme and relies on encapsulation of morphologically defined nanocrystal arrays into a matrix of a wide-band gap semiconductor, which preserves optoelectronic properties of individual nanoparticles while rendering the nanocrystal film photoconductive. Fabricated solids exhibit excellent thermal stability, which is attributed to the heteroepitaxial structure of nanocrystal-matrix interfaces, and show compelling light-harvesting performance in prototype solar cells. © 2011 American Chemical Society

  15. 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.

  16. 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.

  17. 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.

  18. Switchable Ni–Mn–Ga Heusler nanocrystals

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Zayak, Alexey T.; Beckman, Scott P.; Tiago, Murilo L.

    2008-10-02

    Here, we examined bulk-like Heusler nanocrystals using real-space pseudopotentials constructed within density functional theory. The nanocrystals were made of various compositions of Ni-Mn-Ga in the size range from 15 up to 169 atoms. Among these compositions, the closest to the stoichiometric Ni 2MnGa were found to be the most stable. The Ni-based nanocrystals retained a tendency for tetragonal distortion, which is inherited from the bulk properties. Surface effects suppress the tetragonal structure in the smaller Ni-based nanocrystals, while bigger nanocrystals develop a bulk-like tetragonal distortion. We suggest the possibility of switchable Ni-Mn-Ga nanocrystals, which could be utilized for magnetic nano-shape-memorymore » applications.« less

  19. Charge Transport in Semiconductor Nanocrystal Solids

    NASA Astrophysics Data System (ADS)

    Talapin, Dmitri; Shevchenko, Elena; Lee, Jong Soo; Urban, Jeffrey; Mitzi, David; Murray, Christopher

    2007-03-01

    Self-assembly of chemically-synthesized nanocrystals can yield complex long-range ordered structures which can be used as model systems for studying transport phenomena in low-dimensional materials [1]. Treatment of close-packed PbSe nanocrystal arrays with hydrazine enhanced exchange coupling between the nanocrystals and improved conductance by more than ten orders of magnitude compared to native nanocrystal films [2]. The conductivity of PbSe nanocrystal solids can be switched between n- and p-type transports by controlling the saturation of electronic states at nanocrystal surfaces. Nanocrystal arrays form the n- and p-channels of field-effect transistors with electron and hole mobilities of 2.5 cm^2V-1s-1 and 0.3 cm^2V-1s-1, respectively, and current modulation Ion/Ioff˜10^3-10^4. The field-effect mobility in PbSe nanocrystal arrays is higher than the mobility of organic transistors while the easy switch between n- and p-transport allows realization of complimentary circuits and p-n junctions for nanocrystal-based solar cells and thermoelectric devices. [1] E. V. Shevchenko, D. V. Talapin, N. A. Kotov, S. O'Brien, C. B. Murray. Nature 439, 55 (2006). [2] D. V. Talapin, C. B. Murray. Science 310, 86 (2005).

  20. Nanocrystal synthesis

    DOEpatents

    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.

  1. Biomolecular Assembly of Gold Nanocrystals

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    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 inmore » 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.« less

  2. Electron transfer between colloidal ZnO nanocrystals.

    PubMed

    Hayoun, Rebecca; Whitaker, Kelly M; Gamelin, Daniel R; Mayer, James M

    2011-03-30

    Colloidal ZnO nanocrystals capped with dodecylamine and dissolved in toluene can be charged photochemically to give stable solutions in which electrons are present in the conduction bands of the nanocrystals. These conduction-band electrons are readily monitored by EPR spectroscopy, with g* values that correlate with the nanocrystal sizes. Mixing a solution of charged small nanocrystals (e(-)(CB):ZnO-S) with a solution of uncharged large nanocrystals (ZnO-L) caused changes in the EPR spectrum indicative of quantitative electron transfer from small to large nanocrystals. EPR spectra of the reverse reaction, e(-)(CB):ZnO-L + ZnO-S, showed that electrons do not transfer from large to small nanocrystals. Stopped-flow kinetics studies monitoring the change in the UV band-edge absorption showed that reactions of 50 μM nanocrystals were complete within the 5 ms mixing time of the instrument. Similar results were obtained for the reaction of charged nanocrystals with methyl viologen (MV(2+)). These and related results indicate that the electron-transfer reactions of these colloidal nanocrystals are quantitative and very rapid, despite the presence of ~1.5 nm long dodecylamine capping ligands. These soluble ZnO nanocrystals are thus well-defined redox reagents suitable for studies of electron transfer involving semiconductor nanostructures.

  3. A novel approach for the fabrication of all-inorganic nanocrystal solids: Semiconductor matrix encapsulated nanocrystal arrays

    NASA Astrophysics Data System (ADS)

    Moroz, Pavel

    Growing fossil fuels consumption compels researchers to find new alternative pathways to produce energy. Along with new materials for the conversion of different types of energy into electricity innovative methods for efficient processing of energy sources are also introduced. The main criteria for the success of such materials and methods are the low cost and compelling performance. Among different types of materials semiconductor nanocrystals are considered as promising candidates for the role of the efficient and cheap absorbers for solar energy applications. In addition to the anticipated cost reduction, the integration of nanocrystals (NC) into device architectures is inspired by the possibility of tuning the energy of electrical charges in NCs via nanoparticle size. However, the stability of nanocrystals in photovoltaic devices is limited by the stability of organic ligands which passivate the surface of semiconductors to preserve quantum confinement. The present work introduces a new strategy for low-temperature processing of colloidal nanocrystals into all-inorganic films: semiconductor matrix encapsulated nanocrystal arrays (SMENA). This methodology goes beyond the traditional ligand-interlinking scheme and relies on the encapsulation of morphologically-defined nanocrystal arrays into a matrix of a wide-band gap semiconductor, which preserves optoelectronic properties of individual nanoparticles. Fabricated solids exhibit excellent thermal stability, which is attributed to the heteroepitaxial structure of nanocrystal-matrix interfaces. The main characteristics and properties of these solids were investigated and compared with ones of traditionally fabricated nanocrystal films using standard spectroscopic, optoelectronic and electronic techniques. As a proof of concept, we. We also characterized electron transport phenomena in different types of nanocrystal films using all-optical approach. By measuring excited carrier lifetimes in either ligand-linked or

  4. 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

  5. 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.

  6. Connecting the Particles in the Box - Controlled Fusion of Hexamer Nanocrystal Clusters within an AB6 Binary Nanocrystal Superlattice

    PubMed Central

    Treml, Benjamin E.; Lukose, Binit; Clancy, Paulette; Smilgies, Detlef-M; Hanrath, Tobias

    2014-01-01

    Binary nanocrystal superlattices present unique opportunities to create novel interconnected nanostructures by partial fusion of specific components of the superlattice. Here, we demonstrate the binary AB6 superlattice of PbSe and Fe2O3 nanocrystals as a model system to transform the central hexamer of PbSe nanocrystals into a single fused particle. We present detailed structural analysis of the superlattices by combining high-resolution X-ray scattering and electron microscopy. Molecular dynamics simulations show optimum separation of nanocrystals in agreement with the experiment and provide insights into the molecular configuration of surface ligands. We describe the concept of nanocrystal superlattices as a versatile ‘nanoreactor' to create and study novel materials based on precisely defined size, composition and structure of nanocrystals into a mesostructured cluster. We demonstrate ‘controlled fusion' of nanocrystals in the clusters in reactions initiated by thermal treatment and pulsed laser annealing. PMID:25339169

  7. 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

  8. Composite material including nanocrystals and methods of making

    DOEpatents

    Bawendi, Moungi G.; Sundar, Vikram C.

    2010-04-06

    Temperature-sensing compositions can include an inorganic material, such as a semiconductor nanocrystal. The nanocrystal can be a dependable and accurate indicator of temperature. The intensity of emission of the nanocrystal varies with temperature and can be highly sensitive to surface temperature. The nanocrystals can be processed with a binder to form a matrix, which can be varied by altering the chemical nature of the surface of the nanocrystal. A nanocrystal with a compatibilizing outer layer can be incorporated into a coating formulation and retain its temperature sensitive emissive properties.

  9. Composite material including nanocrystals and methods of making

    DOEpatents

    Bawendi, Moungi G [Boston, MA; Sundar, Vikram C [New York, NY

    2008-02-05

    Temperature-sensing compositions can include an inorganic material, such as a semiconductor nanocrystal. The nanocrystal can be a dependable and accurate indicator of temperature. The intensity of emission of the nanocrystal varies with temperature and can be highly sensitive to surface temperature. The nanocrystals can be processed with a binder to form a matrix, which can be varied by altering the chemical nature of the surface of the nanocrystal. A nanocrystal with a compatibilizing outer layer can be incorporated into a coating formulation and retain its temperature sensitive emissive properties

  10. Quantum confinement of nanocrystals within amorphous matrices

    NASA Astrophysics Data System (ADS)

    Lusk, Mark T.; Collins, Reuben T.; Nourbakhsh, Zahra; Akbarzadeh, Hadi

    2014-02-01

    Nanocrystals encapsulated within an amorphous matrix are computationally analyzed to quantify the degree to which the matrix modifies the nature of their quantum-confinement power—i.e., the relationship between nanocrystal size and the gap between valence- and conduction-band edges. A special geometry allows exactly the same amorphous matrix to be applied to nanocrystals of increasing size to precisely quantify changes in confinement without the noise typically associated with encapsulating structures that are different for each nanocrystal. The results both explain and quantify the degree to which amorphous matrices redshift the character of quantum confinement. The character of this confinement depends on both the type of encapsulating material and the separation distance between the nanocrystals within it. Surprisingly, the analysis also identifies a critical nanocrystal threshold below which quantum confinement is not possible—a feature unique to amorphous encapsulation. Although applied to silicon nanocrystals within an amorphous silicon matrix, the methodology can be used to accurately analyze the confinement softening of other amorphous systems as well.

  11. Synthesis of ligand-stabilized metal oxide nanocrystals and epitaxial core/shell nanocrystals via a lower-temperature esterification process.

    PubMed

    Ito, Daisuke; Yokoyama, Shun; Zaikova, Tatiana; Masuko, Keiichiro; Hutchison, James E

    2014-01-28

    The properties of metal oxide nanocrystals can be tuned by incorporating mixtures of matrix metal elements, adding metal ion dopants, or constructing core/shell structures. However, high-temperature conditions required to synthesize these nanocrystals make it difficult to achieve the desired compositions, doping levels, and structural control. We present a lower temperature synthesis of ligand-stabilized metal oxide nanocrystals that produces crystalline, monodisperse nanocrystals at temperatures well below the thermal decomposition point of the precursors. Slow injection (0.2 mL/min) of an oleic acid solution of the metal oleate complex into an oleyl alcohol solvent at 230 °C results in a rapid esterification reaction and the production of metal oxide nanocrystals. The approach produces high yields of crystalline, monodisperse metal oxide nanoparticles containing manganese, iron, cobalt, zinc, and indium within 20 min. Synthesis of tin-doped indium oxide (ITO) can be accomplished with good control of the tin doping levels. Finally, the method makes it possible to perform epitaxial growth of shells onto nanocrystal cores to produce core/shell nanocrystals.

  12. 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.

  13. 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

  14. Barium titanate nanocrystals and nanocrystal thin films: Synthesis, ferroelectricity, and dielectric properties

    NASA Astrophysics Data System (ADS)

    Huang, Limin; Chen, Zhuoying; Wilson, James D.; Banerjee, Sarbajit; Robinson, Richard D.; Herman, Irving P.; Laibowitz, Robert; O'Brien, Stephen

    2006-08-01

    Advanced applications for high k dielectric and ferroelectric materials in the electronics industry continues to demand an understanding of the underlying physics in decreasing dimensions into the nanoscale. We report the synthesis, processing, and electrical characterization of thin (<100nm thick) nanostructured thin films of barium titanate (BaTiO3) built from uniform nanoparticles (<20nm in diameter). We introduce a form of processing as a step toward the ability to prepare textured films based on assembly of nanoparticles. Essential to this approach is an understanding of the nanoparticle as a building block, combined with an ability to integrate them into thin films that have uniform and characteristic electrical properties. Our method offers a versatile means of preparing BaTiO3 nanocrystals, which can be used as a basis for micropatterned or continuous BaTiO3 nanocrystal thin films. We observe the BaTiO3 nanocrystals crystallize with evidence of tetragonality. We investigated the preparation of well-isolated BaTiO3 nanocrystals smaller than 10nm with control over aggregation and crystal densities on various substrates such as Si, Si /SiO2, Si3N4/Si, and Pt-coated Si substrates. BaTiO3 nanocrystal thin films were then prepared, resulting in films with a uniform nanocrystalline grain texture. Electric field dependent polarization measurements show spontaneous polarization and hysteresis, indicating ferroelectric behavior for the BaTiO3 nanocrystalline films with grain sizes in the range of 10-30nm. Dielectric measurements of the films show dielectic constants in the range of 85-90 over the 1KHz -100KHz, with low loss. We present nanocrystals as initial building blocks for the preparation of thin films which exhibit highly uniform nanostructured texture and grain sizes.

  15. 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

  16. Self-assembly of water-soluble nanocrystals

    DOEpatents

    Fan, Hongyou [Albuquerque, NM; Brinker, C Jeffrey [Albuquerque, NM; Lopez, Gabriel P [Albuquerque, NM

    2012-01-10

    A method for forming an ordered array of nanocrystals where a hydrophobic precursor solution with a hydrophobic core material in an organic solvent is added to a solution of a surfactant in water, followed by removal of a least a portion of the organic solvent to form a micellar solution of nanocrystals. A precursor co-assembling material, generally water-soluble, that can co-assemble with individual micelles formed in the micellar solution of nanocrystals can be added to this micellar solution under specified reaction conditions (for example, pH conditions) to form an ordered-array mesophase material. For example, basic conditions are used to precipitate an ordered nanocrystal/silica array material in bulk form and acidic conditions are used to form an ordered nanocrystal/silica array material as a thin film.

  17. Nanocrystal thin film fabrication methods and apparatus

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Kagan, Cherie R.; Kim, David K.; Choi, Ji-Hyuk

    Nanocrystal thin film devices and methods for fabricating nanocrystal thin film devices are disclosed. The nanocrystal thin films are diffused with a dopant such as Indium, Potassium, Tin, etc. to reduce surface states. The thin film devices may be exposed to air during a portion of the fabrication. This enables fabrication of nanocrystal-based devices using a wider range of techniques such as photolithography and photolithographic patterning in an air environment.

  18. 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.

  19. Electronic displays using optically pumped luminescent semiconductor nanocrystals

    DOEpatents

    Weiss, Shimon; Schlamp, Michael C.; Alivisatos, A. Paul

    2010-04-13

    A multicolor electronic display is based on an array of luminescent semiconductor nanocrystals. Nanocrystals which emit light of different colors are grouped into pixels. The nanocrystals are optically pumped to produce a multicolor display. Different sized nanocrystals are used to produce the different colors. A variety of pixel addressing systems can be used.

  20. Electronic displays using optically pumped luminescent semiconductor nanocrystals

    DOEpatents

    Weiss, Shimon; Schlamp, Michael C.; Alivisatos, A. Paul

    2005-03-08

    A multicolor electronic display is based on an array of luminescent semiconductor nanocrystals. Nanocrystals which emit light of different colors are grouped into pixels. The nanocrystals are optically pumped to produce a multicolor display. Different sized nanocrystals are used to produce the different colors. A variety of pixel addressing systems can be used.

  1. Electronic displays using optically pumped luminescent semiconductor nanocrystals

    DOEpatents

    Weiss, Shimon; Schlamp, Michael C.; Alivisatos, A. Paul

    2015-06-23

    A multicolor electronic display is based on an array of luminescent semiconductor nanocrystals. Nanocrystals which emit light of different colors are grouped into pixels. The nanocrystals are optically pumped to produce a multicolor display. Different sized nanocrystals are used to produce the different colors. A variety of pixel addressing systems can be used.

  2. Electronic displays using optically pumped luminescent semiconductor nanocrystals

    DOEpatents

    Weiss, Shimon; Schlamp, Michael C; Alivisatos, A. Paul

    2014-02-11

    A multicolor electronic display is based on an array of luminescent semiconductor nanocrystals. Nanocrystals which emit light of different colors are grouped into pixels. The nanocrystals are optically pumped to produce a multicolor display. Different sized nanocrystals are used to produce the different colors. A variety of pixel addressing systems can be used.

  3. Electronic displays using optically pumped luminescent semiconductor nanocrystals

    DOEpatents

    Weiss, Shimon; Schlamp, Michael C.; Alivisatos, Paul A.

    2015-11-10

    A multicolor electronic display is based on an array of luminescent semiconductor nanocrystals. Nanocrystals which emit tight of different colors are grouped into pixels. The nanocrystals are optically pumped to produce a multicolor display. Different sized nanocrystals are used to produce the different colors. A variety of pixel addressing systems can be used.

  4. Electronic displays using optically pumped luminescent semiconductor nanocrystals

    DOEpatents

    Weiss, Shimon [Pinole, CA; Schlamp, Michael C [Plainsboro, NJ; Alivisatos, A Paul [Oakland, CA

    2011-09-27

    A multicolor electronic display is based on an array of luminescent semiconductor nanocrystals. Nanocrystals which emit light of different colors are grouped into pixels. The nanocrystals are optically pumped to produce a multicolor display. Different sized nanocrystals are used to produce the different colors. A variety of pixel addressing systems can be used.

  5. Electronic displays using optically pumped luminescent semiconductor nanocrystals

    DOEpatents

    Weiss, Shimon; Schlam, Michael C; Alivisatos, A. Paul

    2014-03-25

    A multicolor electronic display is based on an array of luminescent semiconductor nanocrystals. Nanocrystals which emit tight of different colors are grouped into pixels. The nanocrystals are optically pumped to produce a multicolor display. Different sized nanocrystals are used to produce the different colors. A variety of pixel addressing systems can be used.

  6. Electronic displays using optically pumped luminescent semiconductor nanocrystals

    DOEpatents

    Weiss, Shimon; Schlamp, Michael C.; Alivisatos, A. Paul

    2017-06-06

    A multicolor electronic display is based on an array of luminescent semiconductor nanocrystals. Nanocrystals which emit tight of different colors are grouped into pixels. The nanocrystals are optically pumped to produce a multicolor display. Different sized nanocrystals are used to produce the different colors. A variety of pixel addressing systems can be used.

  7. 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

  8. Copper Selenide Nanocrystals for Photothermal Therapy

    PubMed Central

    Hessel, Colin M.; Pattani, Varun; Rasch, Michael; Panthani, Matthew G.; Koo, Bonil; Tunnell, James W.; Korgel, Brian A.

    2011-01-01

    Ligand-stabilized copper selenide (Cu2−xSe) nanocrystals, approximately 16 nm in diameter, were synthesized by a colloidal hot injection method and coated with amphiphilic polymer. The nanocrystals readily disperse in water and exhibit strong near infrared (NIR) optical absorption with a high molar extinction coefficient of 7.7 × 107 cm−1 M−1 at 980 nm. When excited with 800 nm light, the Cu2−xSe nanocrystals produce significant photothermal heating with a photothermal transduction efficiency of 22%, comparable to nanorods and nanoshells of gold (Au). In vitro photothermal heating of Cu2−xSe nanocrystals in the presence of human colorectal cancer cell (HCT-116) led to cell destruction after 5 minutes of laser irradiation at 33 W/cm2, demonstrating the viabilitiy of Cu2−xSe nanocrystals for photothermal therapy applications. PMID:21553924

  9. Development Considerations for Nanocrystal Drug Products.

    PubMed

    Chen, Mei-Ling; John, Mathew; Lee, Sau L; Tyner, Katherine M

    2017-05-01

    Nanocrystal technology has emerged as a valuable tool for facilitating the delivery of poorly water-soluble active pharmaceutical ingredients (APIs) and enhancing API bioavailability. To date, the US Food and Drug Administration (FDA) has received over 80 applications for drug products containing nanocrystals. These products can be delivered by different routes of administration and are used in a variety of therapeutic areas. To aid in identifying key developmental considerations for these products, a retrospective analysis was performed on the submissions received by the FDA to date. Over 60% of the submissions were for the oral route of administration. Based on the Biopharmaceutics Classification System (BCS), most nanocrystal drugs submitted to the FDA are class II compounds that possess low aqueous solubility and high intestinal permeability. Impact of food on drug bioavailability was reduced for most nanocrystal formulations as compared with their micronized counterparts. For all routes of administration, dose proportionality was observed for some, but not all, nanocrystal products. Particular emphasis in the development of nanocrystal products was placed on the in-process tests and controls at critical manufacturing steps (such as milling process), mitigation and control of process-related impurities, and the stability of APIs or polymorphic form (s) during manufacturing and upon storage. This emphasis resulted in identifying challenges to the development of these products including accurate determination of particle size (distribution) of drug substance and/or nanocrystal colloidal dispersion, identification of polymorphic form (s), and establishment of drug substance/product specifications.

  10. Cellulose nanocrystals: synthesis, functional properties, and applications

    PubMed Central

    George, Johnsy; Sabapathi, SN

    2015-01-01

    Cellulose nanocrystals are unique nanomaterials derived from the most abundant and almost inexhaustible natural polymer, cellulose. These nanomaterials have received significant interest due to their mechanical, optical, chemical, and rheological properties. Cellulose nanocrystals primarily obtained from naturally occurring cellulose fibers are biodegradable and renewable in nature and hence they serve as a sustainable and environmentally friendly material for most applications. These nanocrystals are basically hydrophilic in nature; however, they can be surface functionalized to meet various challenging requirements, such as the development of high-performance nanocomposites, using hydrophobic polymer matrices. Considering the ever-increasing interdisciplinary research being carried out on cellulose nanocrystals, this review aims to collate the knowledge available about the sources, chemical structure, and physical and chemical isolation procedures, as well as describes the mechanical, optical, and rheological properties, of cellulose nanocrystals. Innovative applications in diverse fields such as biomedical engineering, material sciences, electronics, catalysis, etc, wherein these cellulose nanocrystals can be used, are highlighted. PMID:26604715

  11. Hydrothermal synthesis of tungsten doped tin dioxide nanocrystals

    NASA Astrophysics Data System (ADS)

    Zhou, Cailong; Li, Yufeng; Chen, Yiwen; Lin, Jing

    2018-01-01

    Tungsten doped tin dioxide (WTO) nanocrystals were synthesized through a one-step hydrothermal method. The structure, composition and morphology of WTO nanocrystals were characterized by x-ray diffraction, x-ray photoelectron spectroscopy, energy dispersive x-ray spectroscopy, UV-vis diffuse reflectance spectra, zeta potential analysis and high-resolution transmission electron microscopy. Results show that the as-prepared WTO nanocrystals were rutile-type structure with the size near 13 nm. Compared with the undoped tin dioxide nanocrystals, the WTO nanocrystals possessed better dispersity in ethanol phase and formed transparent sol.

  12. Optical determination of crystal phase in semiconductor nanocrystals

    PubMed Central

    Lim, Sung Jun; Schleife, André; Smith, Andrew M.

    2017-01-01

    Optical, electronic and structural properties of nanocrystals fundamentally derive from crystal phase. This is especially important for polymorphic II–VI, III–V and I-III-VI2 semiconductor materials such as cadmium selenide, which exist as two stable phases, cubic and hexagonal, each with distinct properties. However, standard crystallographic characterization through diffraction yields ambiguous phase signatures when nanocrystals are small or polytypic. Moreover, diffraction methods are low-throughput, incompatible with solution samples and require large sample quantities. Here we report the identification of unambiguous optical signatures of cubic and hexagonal phases in II–VI nanocrystals using absorption spectroscopy and first-principles electronic-structure theory. High-energy spectral features allow rapid identification of phase, even in small nanocrystals (∼2 nm), and may help predict polytypic nanocrystals from differential phase contributions. These theoretical and experimental insights provide simple and accurate optical crystallographic analysis for liquid-dispersed nanomaterials, to improve the precision of nanocrystal engineering and improve our understanding of nanocrystal reactions. PMID:28513577

  13. 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.

  14. Ultrasonication of Bismuth Telluride Nanocrystals Fabricated by Solvothermal Method

    NASA Technical Reports Server (NTRS)

    Chu, Sang-Hyon; Choi, Sang H.; Kim, Jae-Woo; King, Glen C.; Elliott, James R.

    2006-01-01

    The objective of this study is to evaluate the effect of ultrasonication on bismuth telluride nanocrystals prepared by solvothermal method. In this study, a low dimensional nanocrystal of bismuth telluride (Bi2Te3) was synthesized by a solvothermal process in an autoclave at 180 C and 200 psi. During the solvothermal reaction, organic surfactants effectively prevented unwanted aggregation of nanocrystals in a selected solvent while controlling the shape of the nanocrystal. The atomic ratio of bismuth and tellurium was determined by energy dispersive spectroscopy (EDS). The cavitational energy created by the ultrasonic probe was varied by the ultrasonication process time, while power amplitude remained constant. The nanocrystal size and its size distribution were measured by field emission scanning electron microscopy (FESEM) and a dynamic light scattering system. When the ultrasonication time increased, the average size of bismuth telluride nanocrystal gradually increased due to the direct collision of nanocrystals. The polydispersity of the nanocrystals showed a minimum when the ultrasonication was applied for 5 min. Keywords: bismuth telluride, nanocrystal, low-dimensional, ultrasonication, solvothermal

  15. Plasmonic light-sensitive skins of nanocrystal monolayers

    NASA Astrophysics Data System (ADS)

    Akhavan, Shahab; Gungor, Kivanc; Mutlugun, Evren; Demir, Hilmi Volkan

    2013-04-01

    We report plasmonically coupled light-sensitive skins of nanocrystal monolayers that exhibit sensitivity enhancement and spectral range extension with plasmonic nanostructures embedded in their photosensitive nanocrystal platforms. The deposited plasmonic silver nanoparticles of the device increase the optical absorption of a CdTe nanocrystal monolayer incorporated in the device. Controlled separation of these metallic nanoparticles in the vicinity of semiconductor nanocrystals enables optimization of the photovoltage buildup in the proposed nanostructure platform. The enhancement factor was found to depend on the excitation wavelength. We observed broadband sensitivity improvement (across 400-650 nm), with a 2.6-fold enhancement factor around the localized plasmon resonance peak. The simulation results were found to agree well with the experimental data. Such plasmonically enhanced nanocrystal skins hold great promise for large-area UV/visible sensing applications.

  16. Optical properties of silicon nanocrystals synthesized in supercritical fluids

    NASA Astrophysics Data System (ADS)

    Pell, Lindsay; Korgel, Brian A.

    2002-11-01

    We developed a supercritical solution phase synthesis of silicon nanocrystals. High temperature and pressure (500°C, >140 bar) conditions allow a wet chemical approach to this challenging synthesis. Diphenylsilane was used as a silicon precursor and long chain thiols and alcohols were used to sterically stabilize the luminescent nanocrystals. Moderate size separation was achieved via size exclusion chromatography using crosslinked styrene divinylbenzene beads. Size separated fractions of silicon nanocrystals exhibit quantum efficiencies of 12% while polydisperse samples have quantum efficiencies of 5%. Nanocrystal size distributions have been determined with transmission electron microscopy and further characterized with atomic force microscopy (AFM). These silicon nanocrystals have size tunable photoluminescence as indicated by their ensemble spectroscopy and further verified through AFM and single nanocrystal photoluminescence spectroscopy. Fluorescence intermittency (characteristic of single CdSe nanocrystals) is present in our isolated silicon nanocrystals and is one of the criteria used to distinguish single crystals from clusters of particles.

  17. High-temperature crystallization of nanocrystals into three-dimensional superlattices

    DOE PAGES

    Wu, Liheng; Willis, Joshua J.; McKay, Ian Salmon; ...

    2017-07-31

    Crystallization of colloidal nanocrystals into superlattices represents a practical bottom-up process with which to create ordered metamaterials with emergent functionalities. With precise control over the size, shape and composition of individual nanocrystals, various single-and multi-component nanocrystal superlattices have been produced, the lattice structures and chemical compositions of which can be accurately engineered. Nanocrystal superlattices are typically prepared by carefully controlling the assembly process through solvent evaporation or destabilization or through DNA-guided crystallization. Slow solvent evaporation or cooling of nanocrystal solutions (over hours or days) is the key element for successful crystallization processes. Here we report the rapid growth (seconds) ofmore » micrometre-sized, face-centred-cubic, three-dimensional nanocrystal superlattices during colloidal synthesis at high temperatures (more than 230 degrees Celsius). Using in situ small-angle X-ray scattering, we observe continuous growth of individual nanocrystals within the lattices, which results in simultaneous lattice expansion and fine nanocrystal size control due to the superlattice templates. Thermodynamic models demonstrate that balanced attractive and repulsive interparticle interactions dictated by the ligand coverage on nanocrystal surfaces and nanocrystal core size are responsible for the crystallization process. The interparticle interactions can also be controlled to form different superlattice structures, such as hexagonal close-packed lattices. In conclusion, the rational assembly of various nanocrystal systems into novel materials is thus facilitated for both fundamental research and for practical applications in the fields of magnetics, electronics and catalysis.« less

  18. High-temperature crystallization of nanocrystals into three-dimensional superlattices.

    PubMed

    Wu, Liheng; Willis, Joshua J; McKay, Ian Salmon; Diroll, Benjamin T; Qin, Jian; Cargnello, Matteo; Tassone, Christopher J

    2017-08-10

    Crystallization of colloidal nanocrystals into superlattices represents a practical bottom-up process with which to create ordered metamaterials with emergent functionalities. With precise control over the size, shape and composition of individual nanocrystals, various single- and multi-component nanocrystal superlattices have been produced, the lattice structures and chemical compositions of which can be accurately engineered. Nanocrystal superlattices are typically prepared by carefully controlling the assembly process through solvent evaporation or destabilization or through DNA-guided crystallization. Slow solvent evaporation or cooling of nanocrystal solutions (over hours or days) is the key element for successful crystallization processes. Here we report the rapid growth (seconds) of micrometre-sized, face-centred-cubic, three-dimensional nanocrystal superlattices during colloidal synthesis at high temperatures (more than 230 degrees Celsius). Using in situ small-angle X-ray scattering, we observe continuous growth of individual nanocrystals within the lattices, which results in simultaneous lattice expansion and fine nanocrystal size control due to the superlattice templates. Thermodynamic models demonstrate that balanced attractive and repulsive interparticle interactions dictated by the ligand coverage on nanocrystal surfaces and nanocrystal core size are responsible for the crystallization process. The interparticle interactions can also be controlled to form different superlattice structures, such as hexagonal close-packed lattices. The rational assembly of various nanocrystal systems into novel materials is thus facilitated for both fundamental research and for practical applications in the fields of magnetics, electronics and catalysis.

  19. High-temperature crystallization of nanocrystals into three-dimensional superlattices

    NASA Astrophysics Data System (ADS)

    Wu, Liheng; Willis, Joshua J.; McKay, Ian Salmon; Diroll, Benjamin T.; Qin, Jian; Cargnello, Matteo; Tassone, Christopher J.

    2017-08-01

    Crystallization of colloidal nanocrystals into superlattices represents a practical bottom-up process with which to create ordered metamaterials with emergent functionalities. With precise control over the size, shape and composition of individual nanocrystals, various single- and multi-component nanocrystal superlattices have been produced, the lattice structures and chemical compositions of which can be accurately engineered. Nanocrystal superlattices are typically prepared by carefully controlling the assembly process through solvent evaporation or destabilization or through DNA-guided crystallization. Slow solvent evaporation or cooling of nanocrystal solutions (over hours or days) is the key element for successful crystallization processes. Here we report the rapid growth (seconds) of micrometre-sized, face-centred-cubic, three-dimensional nanocrystal superlattices during colloidal synthesis at high temperatures (more than 230 degrees Celsius). Using in situ small-angle X-ray scattering, we observe continuous growth of individual nanocrystals within the lattices, which results in simultaneous lattice expansion and fine nanocrystal size control due to the superlattice templates. Thermodynamic models demonstrate that balanced attractive and repulsive interparticle interactions dictated by the ligand coverage on nanocrystal surfaces and nanocrystal core size are responsible for the crystallization process. The interparticle interactions can also be controlled to form different superlattice structures, such as hexagonal close-packed lattices. The rational assembly of various nanocrystal systems into novel materials is thus facilitated for both fundamental research and for practical applications in the fields of magnetics, electronics and catalysis.

  20. Transition-Metal Decorated Aluminum Nanocrystals.

    PubMed

    Swearer, Dayne F; Leary, Rowan K; Newell, Ryan; Yazdi, Sadegh; Robatjazi, Hossein; Zhang, Yue; Renard, David; Nordlander, Peter; Midgley, Paul A; Halas, Naomi J; Ringe, Emilie

    2017-10-24

    Recently, aluminum has been established as an earth-abundant alternative to gold and silver for plasmonic applications. Particularly, aluminum nanocrystals have shown to be promising plasmonic photocatalysts, especially when coupled with catalytic metals or oxides into "antenna-reactor" heterostructures. Here, a simple polyol synthesis is presented as a flexible route to produce aluminum nanocrystals decorated with eight varieties of size-tunable transition-metal nanoparticle islands, many of which have precedence as heterogeneous catalysts. High-resolution and three-dimensional structural analysis using scanning transmission electron microscopy and electron tomography shows that abundant nanoparticle island decoration in the catalytically relevant few-nanometer size range can be achieved, with many islands spaced closely to their neighbors. When coupled with the Al nanocrystal plasmonic antenna, these small decorating islands will experience increased light absorption and strong hot-spot generation. This combination makes transition-metal decorated aluminum nanocrystals a promising material platform to develop plasmonic photocatalysis, surface-enhanced spectroscopies, and quantum plasmonics.

  1. Engineering Plasmonic Nanocrystal Coupling through Template-Assisted Self-Assembly

    NASA Astrophysics Data System (ADS)

    Greybush, Nicholas J.

    The construction of materials from nanocrystal building blocks represents a powerful new paradigm for materials design. Just as nature's materials orchestrate intricate combinations of atoms from the library of the periodic table, nanocrystal "metamaterials" integrate individual nanocrystals into larger architectures with emergent collective properties. The individual nanocrystal "meta-atoms" that make up these materials are themselves each a nanoscale atomic system with tailorable size, shape, and elemental composition, enabling the creation of hierarchical materials with predesigned structure at multiple length scales. However, an improved fundamental understanding of the interactions among individual nanocrystals is needed in order to translate this structural control into enhanced functionality. The ability to form precise arrangements of nanocrystals and measure their collective properties is therefore essential for the continued development of nanocrystal metamaterials. In this dissertation, we utilize template-assisted self-assembly and spatially-resolved spectroscopy to form and characterize individual nanocrystal oligomers. At the intersection of "top-down" and "bottom-up" nanoscale patterning schemes, template-assisted self-assembly combines the design freedom of lithography with the chemical control of colloidal synthesis to achieve unique nanocrystal configurations. Here, we employ shape-selective templates to assemble new plasmonic structures, including heterodimers of Au nanorods and upconversion phosphors, a series of hexagonally-packed Au nanocrystal oligomers, and triangular formations of Au nanorods. Through experimental analysis and numerical simulation, we elucidate the means through which inter-nanocrystal coupling imparts collective optical properties to the plasmonic assemblies. Our self-assembly and measurement strategy offers a versatile platform for exploring optical interactions in a wide range of material systems and application areas.

  2. Nanocrystal Targeting In Vivo

    DTIC Science & Technology

    2002-08-01

    Shearwater Polymers , Huntsville, AL) was thiolated with iminothiolane. Thiolated PEG was directly added to a solution of mercaptoacetic acid- coated qdots...Nanocrystal targeting in vivo Maria E. Åkerman*†‡, Warren C. W. Chan†‡, Pirjo Laakkonen*, Sangeeta N. Bhatia†, and Erkki Ruoslahti*§ *Cancer Research...set out to explore the feasibility of in vivo targeting by using semiconductor quantum dots (qdots). Qdots are small (᝺ nm) inorganic nanocrystals

  3. Colloidal nanocrystals and method of making

    DOEpatents

    Kahen, Keith

    2015-10-06

    A tight confinement nanocrystal comprises a homogeneous center region having a first composition and a smoothly varying region having a second composition wherein a confining potential barrier monotonically increases and then monotonically decreases as the smoothly varying region extends from the surface of the homogeneous center region to an outer surface of the nanocrystal. A method of producing the nanocrystal comprises forming a first solution by combining a solvent and at most two nanocrystal precursors; heating the first solution to a nucleation temperature; adding to the first solution, a second solution having a solvent, at least one additional and different precursor to form the homogeneous center region and at most an initial portion of the smoothly varying region; and lowering the solution temperature to a growth temperature to complete growth of the smoothly varying region.

  4. Measuring the Valence of Nanocrystal Surfaces

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Owen, Jonathan Scharle

    2016-11-30

    The goal of this project is to understand and control the interplay between nanocrystal stoichiometry, surface ligand binding and exchange, and the optoelectronic properties of semiconductor nanocrystals in solution and in thin solid films. We pursued three research directions with this goal in mind: 1) We characterized nanocrystal stoichiometry and its influence on the binding of L-type and X-type ligands, including the thermodynamics of binding and the kinetics of ligand exchange. 2) We developed a quantitative understanding of the relationship between surface ligand passivation and photoluminescence quantum yield. 3) We developed methods to replace the organic ligands on the nanocrystalmore » with halide ligands and controllably deposit these nanocrystals into thin films, where electrical measurements were used to investigate the electrical transport and internanocrystal electronic coupling.« less

  5. Optical Properties of CdSe/ZnS Nanocrystals

    PubMed Central

    Gaigalas, Adolfas K; DeRose, Paul; Wang, Lili; Zhang, Yu-Zhong

    2014-01-01

    Measurements are presented of the absorbance, fluorescence emission, fluorescence quantum yield, and fluorescence lifetime of CdSe/ZnS nanocrystals, also known as quantum dots (QDs). The study included three groups of nanocrystals whose surfaces were either passivated with organic molecules, modified further with carboxyl groups, or conjugated with CD14 mouse anti-human antibodies. The surface modifications had observable effects on the optical properties of the nanocrystals. The oscillator strength (OS) of the band edge transition was about 1.0 for the nanocrystals emitting at 565 nm, 605 nm, and 655 nm. The OS could not be determined for QDs with emission at 700 nm and 800 nm. The fluorescence lifetimes varied from 26 ns for nanocrystals emitting near 600 nm to 150 ns for nanocrystals emitting near 800 nm. The quantum yield ranged between 0.4 and 0.9 for the nanocrystals in this study. A brightness index (BI) was used to evaluate the suitability of the nanocrystal labels for flow cytometer measurements. Most QD labels are at least as bright as fluorescein for applications in flow cytometer assays with 488 nm excitation. For optimal brightness the QDs should be excited with 405 nm light. We observed a strong dependence of the QD absorbance at 250 nm on the surface modification of the QD. PMID:26601047

  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. Lean Mass Asymmetry Influences Force and Power Asymmetry During Jumping in Collegiate Athletes

    PubMed Central

    Bell, David R.; Sanfilippo, Jennifer L.; Binkley, Neil; Heiderscheit, Bryan C.

    2015-01-01

    The purpose of this investigation was to: (1) examine how asymmetry in lower extremity lean mass influenced force and power asymmetry during jumping, (2) determine how power and force asymmetry affected jump height, and (3) report normative values in collegiate athletes. Force and power were assessed from each limb using bilateral force plates during a countermovement jump in 167 Division 1 athletes (mass=85.7±20.3kg, age=20.0±1.2years, 103M/64F). Lean mass of the pelvis, thigh, and shank was assessed via dual-energy X-ray absorptiometry. Percent asymmetry was calculated for lean mass at each region (pelvis, thigh, and shank) as well as force and power. Forward stepwise regressions were performed to determine the influence of lean mass asymmetry on force and power asymmetry. Thigh and shank lean mass asymmetry explained 20% of the variance in force asymmetry (R2=0.20, P<0.001), while lean mass asymmetry of the pelvis, thigh and shank explained 25% of the variance in power asymmetry (R2=0.25, P<0.001). Jump height was compared across level of force and power asymmetry (P>0.05) and greater than 10% asymmetry in power tended to decrease performance (effect size>1.0). Ninety-five percent of this population (2.5th to 97.5th percentile) displayed force asymmetry between −11.8 to 16.8% and a power asymmetry between −9.9 to 11.5%. A small percentage (<4%) of these athletes displayed more than 15% asymmetry between limbs. These results demonstrate that lean mass asymmetry in the lower extremity is at least partially responsible for asymmetries in force and power. However, a large percentage remains unexplained by lean mass asymmetry. PMID:24402449

  8. Lean mass asymmetry influences force and power asymmetry during jumping in collegiate athletes.

    PubMed

    Bell, David R; Sanfilippo, Jennifer L; Binkley, Neil; Heiderscheit, Bryan C

    2014-04-01

    The purpose of this investigation was to (a) examine how asymmetry in lower extremity lean mass influenced force and power asymmetry during jumping, (b) determine how power and force asymmetry affected jump height, and (c) report normative values in collegiate athletes. Force and power were assessed from each limb using bilateral force plates during a countermovement jump in 167 division 1 athletes (mass = 85.7 ± 20.3 kg, age = 20.0 ± 1.2 years; 103 men and 64 women). Lean mass of the pelvis, thigh, and shank was assessed using dual-energy x-ray absorptiometry. Percent asymmetry was calculated for lean mass at each region (pelvis, thigh, and shank) as well as force and power. Forward stepwise regressions were performed to determine the influence of lean mass asymmetry on force and power asymmetry. Thigh and shank lean mass asymmetry explained 20% of the variance in force asymmetry (R = 0.20, p < 0.001), whereas lean mass asymmetry of the pelvis, thigh, and shank explained 25% of the variance in power asymmetry (R = 0.25, p < 0.001). Jump height was compared across level of force and power asymmetry (p > 0.05) and greater than 10% asymmetry in power tended to decrease the performance (effect size >1.0). Ninety-five percent of this population (2.5th to 97.5th percentile) displayed force asymmetry between -11.8 and 16.8% and a power asymmetry between -9.9 and 11.5%. A small percentage (<4%) of these athletes displayed more than 15% asymmetry between limbs. These results demonstrate that lean mass asymmetry in the lower extremity is at least partially responsible for asymmetries in force and power. However, a large percentage remains unexplained by lean mass asymmetry.

  9. Nasopupillary asymmetry.

    PubMed

    Arenas, Eduardo; Muñoz, Diana; Matheus, Evelyn; Morales, Diana

    2014-01-01

    To establish the prevalence of nasopupillary asymmetry (difference in nasopupillary distances) in the population and its relation with the interpupillary distance. A retrospective descriptive study was conducted by reviewing of 1262 medical records. The values of nasopupillary asymmetry and the interpupillary distance were obtained. A statistical analysis was made and the correlation between these variables was established. Seventy-nine percent of the population presented some degree of nasopupillary asymmetry. The interpupillary distance had a very low correlation with the nasopupillary asymmetry (r = 0.074, P = 0.0). It is advisable to use the nasopupillary distance of each eye as a standard measurement.

  10. Enhanced oral bioavailability of glycyrrhetinic acid via nanocrystal formulation.

    PubMed

    Lei, Yaya; Kong, Yindi; Sui, Hong; Feng, Jun; Zhu, Rongyue; Wang, Wenping

    2016-10-01

    The purpose of this study was to prepare solid nanocrystals of glycyrrhetinic acid (GA) for improved oral bioavailability. The anti-solvent precipitation-ultrasonication method followed by freeze-drying was adopted for the preparation of GA nanocrystals. The physicochemical properties, drug dissolution and pharmacokinetic of the obtained nanocrystals were investigated. GA nanocrystals showed a mean particle size of 220 nm and shaped like short rods. The analysis results from differential scanning calorimetry and X-ray powder diffraction indicated that GA remained in crystalline state despite a huge size reduction. The equilibrium solubility and dissolution rate of GA nanocrystal were significantly improved in comparison with those of the coarse GA or the physical mixture. The bioavailability of GA nanocrystals in rats was 4.3-fold higher than that of the coarse GA after oral administration. With its rapid dissolution and absorption performance, the solid nanocrystal might be a more preferable formulation for oral administration of poorly soluble GA.

  11. 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.

  12. Isolating and moving single atoms using silicon nanocrystals

    DOEpatents

    Carroll, Malcolm S.

    2010-09-07

    A method is disclosed for isolating single atoms of an atomic species of interest by locating the atoms within silicon nanocrystals. This can be done by implanting, on the average, a single atom of the atomic species of interest into each nanocrystal, and then measuring an electrical charge distribution on the nanocrystals with scanning capacitance microscopy (SCM) or electrostatic force microscopy (EFM) to identify and select those nanocrystals having exactly one atom of the atomic species of interest therein. The nanocrystals with the single atom of the atomic species of interest therein can be sorted and moved using an atomic force microscope (AFM) tip. The method is useful for forming nanoscale electronic and optical devices including quantum computers and single-photon light sources.

  13. Interfacial interactions between calcined hydroxyapatite nanocrystals and substrates.

    PubMed

    Okada, Masahiro; Furukawa, Keiko; Serizawa, Takeshi; Yanagisawa, Yoshihiko; Tanaka, Hidekazu; Kawai, Tomoji; Furuzono, Tsutomu

    2009-06-02

    Interfacial interactions between calcined hydroxyapatite (HAp) nanocrystals and surface-modified substrates were investigated by measuring adsorption behavior and adhesion strength with a quartz crystal microbalance (QCM) and a contact-mode atomic force microscope (AFM), respectively. The goal was to develop better control of HAp-nanocrystal coatings on biomedical materials. HAp nanocrystals with rodlike or spherical morphology were prepared by a wet chemical process followed by calcination at 800 degrees C with an antisintering agent to prevent the formation of sintered polycrystals. The substrate surface was modified by chemical reaction with a low-molecular-weight compound, or graft polymerization with a functional monomer. QCM measurement showed that the rodlike HAp nanocrystals adsorbed preferentially onto anionic COOH-modified substrates compared to cationic NH2- or hydrophobic CH3-modified substrates. On the other hand, the spherical nanocrystals adsorbed onto NH2- and COOH-modified substrates, which indicates that the surface properties of the HAp nanocrystals determined their adsorption behavior. The adhesion strength, which was estimated from the force required to move the nanocrystal in contact-mode AFM, on a COOH-grafted substrate prepared by graft polymerization was almost 9 times larger than that on a COOH-modified substrate prepared by chemical reaction with a low-molecular-weight compound, indicating that the long-chain polymer grafted on the substrate mitigated the surface roughness mismatch between the nanocrystal and the substrate. The adhesion strength of the nanocrystal bonded covalently by the coupling reaction to a Si(OCH3)-grafted substrate prepared by graft polymerization was approximately 1.5 times larger than that when adsorbed on the COOH-grafted substrate.

  14. Iron Oxide Nanocrystals for Magnetic Hyperthermia Applications

    PubMed Central

    Armijo, Leisha M.; Brandt, Yekaterina I.; Mathew, Dimple; Yadav, Surabhi; Maestas, Salomon; Rivera, Antonio C.; Cook, Nathaniel C.; Withers, Nathan J.; Smolyakov, Gennady A.; Adolphi, Natalie; Monson, Todd C.; Huber, Dale L.; Smyth, Hugh D. C.; Osiński, Marek

    2012-01-01

    Magnetic nanocrystals have been investigated extensively in the past several years for several potential applications, such as information technology, MRI contrast agents, and for drug conjugation and delivery. A specific property of interest in biomedicine is magnetic hyperthermia—an increase in temperature resulting from the thermal energy released by magnetic nanocrystals in an external alternating magnetic field. Iron oxide nanocrystals of various sizes and morphologies were synthesized and tested for specific losses (heating power) using frequencies of 111.1 kHz and 629.2 kHz, and corresponding magnetic field strengths of 9 and 25 mT. Polymorphous nanocrystals as well as spherical nanocrystals and nanowires in paramagnetic to ferromagnetic size range exhibited good heating power. A remarkable 30 °C temperature increase was observed in a nanowire sample at 111 kHz and magnetic field of 25 mT (19.6 kA/m), which is very close to the typical values of 100 kHz and 20 mT used in medical treatments. PMID:28348300

  15. Application of precipitation methods for the production of water-insoluble drug nanocrystals: production techniques and stability of nanocrystals.

    PubMed

    Xia, Dengning; Gan, Yong; Cui, Fude

    2014-01-01

    This review focuses on using precipitation (bottom-up) method to produce water-insoluble drug nanocrystals, and the stability issues of nanocrystals. The precipitation techniques for production of ultra-fine particles have been widely researched for last few decades. In these techniques, precipitation of solute is achieved by addition of a non-solvent for solute called anti-solvent to decrease the solvent power for the solute dissolved in a solution. The anti-solvent can be water, organic solvents or supercritical fluids. In this paper, efforts have been made to review the precipitation techniques involving the anti-solvent precipitation by simple mixing, impinging jet mixing, multi-inlet vortex mixing, the using of high-gravity, ultrasonic waves and supercritical fluids. The key to the success of yielding stable nanocrystals in these techniques is to control the nucleation kinetics and particle growth through mixing during precipitation based on crystallization theories. The stability issues of the nanocrystals, such as sedimentation, Ostwald ripening, agglomeration and cementing of crystals, change of crystalline state, and the approaches to stabilizing nanocrystals are also discussed in detail.

  16. Enhanced luminescence of Cu-In-S nanocrystals by surface modification.

    PubMed

    Kim, Young-Kuk; Cho, Young-Sang; Chung, Kookchae; Choi, Chul-Jin; Shin, Pyung-Woo

    2012-04-01

    We have synthesized highly luminescent Cu-In-S nanocrystals by heating the mixture of metal carboxylates and alkylthiol under inert atmosphere. We modified the surface of CIS nanocrystals with zinc carboxylate and subsequent injection of alkylthiol. As a result of the surface modification, highly luminescent CIS@ZnS core/shell nanocrystals were synthesized. The luminescence quantum yield (QY) of best CIS@ZnS nanocrystals was above 50%, which is more than 10 times higher than the initial QY of CIS nanocrystals before surface modification (QY = 3%). Detailed study on the luminescence mechanism implies that etching of the surface of nanocrystals by dissociated carboxylate group (CH3COO-) and formation of epitaxial shell by Zn with sulfur from alkylthiol efficiently removed the surface defects which are major non-radiative recombination sites in semiconductor nanocrystals. In this study, we developed a novel surface modification route for monodispersed highly luminescent Cu-In-S nanocrystals with less toxic and highly stable precursors.

  17. 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.

  18. 2-Hydroxypropyltrimethylammonium xylan adsorption onto rod-like cellulose nanocrystal.

    PubMed

    Sim, Jae Hyun; Dong, Shuping; Röemhild, Katrin; Kaya, Abdulaziz; Sohn, Daewon; Tanaka, Keiji; Roman, Maren; Heinze, Thomas; Esker, Alan R

    2015-02-15

    Chemical incompatibility and relatively weak interaction between lignocellulosic fibers and synthetic polymers have made studies of wood fiber-thermoplastic composite more challenging. In this study, adsorption of 2-hydroxypropyltrimethylammonium xylans onto rod-like cellulose nanocrystals are investigated by zeta-potential measurements, and polarized and depolarized dynamic light scattering as a factor for better understanding of lignocellulosic fibers and cellulose nanocrystals. Zeta-potential measurements show xylan derivative adsorption onto cellulose nanocrystals. Decay time distributions of the ternary system and binary system from dynamic light scattering show that aggregates exist in the binary system and they disappear in the ternary system. At low 2-hydroxypropyltrimethylammonium xylan concentrations relative to that of cellulose nanocrystal, xylan derivatives adsorbed onto some of the cellulose nanocrystal. Hence, more xylan derivatives adsorbed onto cellulose nanocrystal increased with increasing xylan derivative concentration. Also, the concentration dependence of the ratio of the rotational diffusion coefficient to the translational diffusion coefficient revealed a strong adsorptive interaction between xylan derivatives and the cellulose nanocrystals. Copyright © 2014 Elsevier Inc. All rights reserved.

  19. Controlling upconversion nanocrystals for emerging applications

    NASA Astrophysics Data System (ADS)

    Zhou, Bo; Shi, Bingyang; Jin, Dayong; Liu, Xiaogang

    2015-11-01

    Lanthanide-doped upconversion nanocrystals enable anti-Stokes emission with pump intensities several orders of magnitude lower than required by conventional nonlinear optical techniques. Their exceptional properties, namely large anti-Stokes shifts, sharp emission spectra and long excited-state lifetimes, have led to a diversity of applications. Here, we review upconversion nanocrystals from the perspective of fundamental concepts and examine the technical challenges in relation to emission colour tuning and luminescence enhancement. In particular, we highlight the advances in functionalization strategies that enable the broad utility of upconversion nanocrystals for multimodal imaging, cancer therapy, volumetric displays and photonics.

  20. Zirconia nanocrystals as submicron level biological label

    NASA Astrophysics Data System (ADS)

    Smits, K.; Liepins, J.; Gavare, M.; Patmalnieks, A.; Gruduls, A.; Jankovica, D.

    2012-08-01

    Inorganic nanocrystals are of increasing interest for their usage in biology and pharmacology research. Our interest was to justify ZrO2 nanocrystal usage as submicron level biological label in baker's yeast Saccharomyces cerevisia culture. For the first time (to our knowledge) images with sub micro up-conversion luminescent particles in biologic media were made. A set of undoped as well as Er and Yb doped ZrO2 samples at different concentrations were prepared by sol-gel method. The up-conversion luminescence for free standing and for nanocrystals with baker's yeast cells was studied and the differences in up-conversion luminescence spectra were analyzed. In vivo toxic effects of ZrO2 nanocrystals were tested by co-cultivation with baker's yeast.

  1. Doping effect in Si nanocrystals

    NASA Astrophysics Data System (ADS)

    Li, Dongke; Xu, Jun; Zhang, Pei; Jiang, Yicheng; Chen, Kunji

    2018-06-01

    Intentional doping in semiconductors is a fundamental issue since it can control the conduction type and ability as well as modify the optical and electronic properties. To realize effective doping is the basis for developing semiconductor devices. However, by reducing the size of a semiconductor, like Si, to the nanometer scale, the doping effects become complicated due to the coupling between the quantum confinement effect and the surfaces and/or interfaces effect. In particular, by introducing phosphorus or boron impurities as dopants into material containing Si nanocrystals with a dot size of less than 10 nm, it exhibits different behaviors and influences on the physical properties from its bulk counterpart. Understanding the doping effects in Si nanocrystals is currently a challenge in order to further improve the performance of the next generation of nano-electronic and photonic devices. In this review, we present an overview of the latest theoretical studies and experimental results on dopant distributions and their effects on the electronic and optical properties of Si nanocrystals. In particular, the advanced characterization techniques on dopant distribution, the carrier transport process as well as the linear and nonlinear optical properties of doped Si nanocrystals, are systematically summarized.

  2. From symmetry to asymmetry: Phylogenetic patterns of asymmetry variation in animals and their evolutionary significance

    PubMed Central

    Palmer, A. Richard

    1996-01-01

    Phylogenetic analyses of asymmetry variation offer a powerful tool for exploring the interplay between ontogeny and evolution because (i) conspicuous asymmetries exist in many higher metazoans with widely varying modes of development, (ii) patterns of bilateral variation within species may identify genetically and environmentally triggered asymmetries, and (iii) asymmetries arising at different times during development may be more sensitive to internal cytoplasmic inhomogeneities compared to external environmental stimuli. Using four broadly comparable asymmetry states (symmetry, antisymmetry, dextral, and sinistral), and two stages at which asymmetry appears developmentally (larval and postlarval), I evaluated relations between ontogenetic and phylogenetic patterns of asymmetry variation. Among 140 inferred phylogenetic transitions between asymmetry states, recorded from 11 classes in five phyla, directional asymmetry (dextral or sinistral) evolved directly from symmetrical ancestors proportionally more frequently among larval asymmetries. In contrast, antisymmetry, either as an end state or as a transitional stage preceding directional asymmetry, was confined primarily to postlarval asymmetries. The ontogenetic origin of asymmetry thus significantly influences its subsequent evolution. Furthermore, because antisymmetry typically signals an environmentally triggered asymmetry, the phylogenetic transition from antisymmetry to directional asymmetry suggests that many cases of laterally fixed asymmetries evolved via genetic assimilation. PMID:8962039

  3. Structural white matter asymmetries in relation to functional asymmetries during speech perception and production.

    PubMed

    Ocklenburg, Sebastian; Hugdahl, Kenneth; Westerhausen, René

    2013-12-01

    Functional hemispheric asymmetries of speech production and perception are a key feature of the human language system, but their neurophysiological basis is still poorly understood. Using a combined fMRI and tract-based spatial statistics approach, we investigated the relation of microstructural asymmetries in language-relevant white matter pathways and functional activation asymmetries during silent verb generation and passive listening to spoken words. Tract-based spatial statistics revealed several leftward asymmetric clusters in the arcuate fasciculus and uncinate fasciculus that were differentially related to activation asymmetries in the two functional tasks. Frontal and temporal activation asymmetries during silent verb generation were positively related to the strength of specific microstructural white matter asymmetries in the arcuate fasciculus. In contrast, microstructural uncinate fasciculus asymmetries were related to temporal activation asymmetries during passive listening. These findings suggest that white matter asymmetries may indeed be one of the factors underlying functional hemispheric asymmetries. Moreover, they also show that specific localized white matter asymmetries might be of greater relevance for functional activation asymmetries than microstructural features of whole pathways. © 2013.

  4. Single-exciton optical gain in semiconductor nanocrystals.

    PubMed

    Klimov, Victor I; Ivanov, Sergei A; Nanda, Jagjit; Achermann, Marc; Bezel, Ilya; McGuire, John A; Piryatinski, Andrei

    2007-05-24

    Nanocrystal quantum dots have favourable light-emitting properties. They show photoluminescence with high quantum yields, and their emission colours depend on the nanocrystal size--owing to the quantum-confinement effect--and are therefore tunable. However, nanocrystals are difficult to use in optical amplification and lasing. Because of an almost exact balance between absorption and stimulated emission in nanoparticles excited with single electron-hole pairs (excitons), optical gain can only occur in nanocrystals that contain at least two excitons. A complication associated with this multiexcitonic nature of light amplification is fast optical-gain decay induced by non-radiative Auger recombination, a process in which one exciton recombines by transferring its energy to another. Here we demonstrate a practical approach for obtaining optical gain in the single-exciton regime that eliminates the problem of Auger decay. Specifically, we develop core/shell hetero-nanocrystals engineered in such a way as to spatially separate electrons and holes between the core and the shell (type-II heterostructures). The resulting imbalance between negative and positive charges produces a strong local electric field, which induces a giant ( approximately 100 meV or greater) transient Stark shift of the absorption spectrum with respect to the luminescence line of singly excited nanocrystals. This effect breaks the exact balance between absorption and stimulated emission, and allows us to demonstrate optical amplification due to single excitons.

  5. 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

  6. Structure and transformation of tactoids in cellulose nanocrystal suspensions

    NASA Astrophysics Data System (ADS)

    Wang, Pei-Xi; Hamad, Wadood Y.; MacLachlan, Mark J.

    2016-05-01

    Cellulose nanocrystals obtained from natural sources are of great interest for many applications. In water, cellulose nanocrystals form a liquid crystalline phase whose hierarchical structure is retained in solid films after drying. Although tactoids, one of the most primitive components of liquid crystals, are thought to have a significant role in the evolution of this phase, they have evaded structural study of their internal organization. Here we report the capture of cellulose nanocrystal tactoids in a polymer matrix. This method allows us to visualize, for the first time, the arrangement of cellulose nanocrystals within individual tactoids by electron microscopy. Furthermore, we can follow the structural evolution of the liquid crystalline phase from tactoids to iridescent-layered films. Our insights into the early nucleation events of cellulose nanocrystals give important information about the growth of cholesteric liquid crystalline phases, especially for cellulose nanocrystals, and are crucial for preparing photonics-quality films.

  7. One-step DNA-programmed growth of luminescent and biofunctionalized nanocrystals

    NASA Astrophysics Data System (ADS)

    Ma, Nan; Sargent, Edward H.; Kelley, Shana O.

    2009-02-01

    Colloidal semiconductor nanocrystals are widely used as lumiphores in biological imaging because their luminescence is both strong and stable, and because they can be biofunctionalized. During synthesis, nanocrystals are typically passivated with hydrophobic organic ligands, so it is then necessary either to replace these ligands or encapsulate the nanocrystals with hydrophilic moieties to make the lumiphores soluble in water. Finally, biological labels must be added to allow the detection of nucleic acids, proteins and specific cell types. This multistep process is time- and labour-intensive and thus out of reach of many researchers who want to use luminescent nanocrystals as customized lumiphores. Here, we show that a single designer ligand-a chimeric DNA molecule-can controllably program both the growth and the biofunctionalization of the nanocrystals. One part of the DNA sequence controls the nanocrystal passivation and serves as a ligand, while another part controls the biorecognition. The synthetic protocol reported here is straightforward and produces a homogeneous dispersion of nanocrystal lumiphores functionalized with a single biomolecular receptor. The nanocrystals exhibit strong optical emission in the visible region, minimal toxicity and have hydrodynamic diameters of ~6 nm, which makes them suitable for bioimaging. We show that the nanocrystals can specifically bind DNA, proteins or cells that have unique surface recognition markers.

  8. Plasmonic Properties of Silicon Nanocrystals Doped with Boron and Phosphorus.

    PubMed

    Kramer, Nicolaas J; Schramke, Katelyn S; Kortshagen, Uwe R

    2015-08-12

    Degenerately doped silicon nanocrystals are appealing plasmonic materials due to silicon's low cost and low toxicity. While surface plasmonic resonances of boron-doped and phosphorus-doped silicon nanocrystals were recently observed, there currently is poor understanding of the effect of surface conditions on their plasmonic behavior. Here, we demonstrate that phosphorus-doped silicon nanocrystals exhibit a plasmon resonance immediately after their synthesis but may lose their plasmonic response with oxidation. In contrast, boron-doped nanocrystals initially do not exhibit plasmonic response but become plasmonically active through postsynthesis oxidation or annealing. We interpret these results in terms of substitutional doping being the dominant doping mechanism for phosphorus-doped silicon nanocrystals, with oxidation-induced defects trapping free electrons. The behavior of boron-doped silicon nanocrystals is more consistent with a strong contribution of surface doping. Importantly, boron-doped silicon nanocrystals exhibit air-stable plasmonic behavior over periods of more than a year.

  9. Si nanocrystals-based multilayers for luminescent and photovoltaic device applications

    NASA Astrophysics Data System (ADS)

    Lu, Peng; Li, Dongke; Cao, Yunqing; Xu, Jun; Chen, Kunji

    2018-06-01

    Low dimensional Si materials have attracted much attention because they can be developed in many kinds of new-generation nano-electronic and optoelectronic devices, among which Si nanocrystals-based multilayered material is one of the most promising candidates and has been extensively studied. By using multilayered structures, the size and distribution of nanocrystals as well as the barrier thickness between two adjacent Si nanocrystal layers can be well controlled, which is beneficial to the device applications. This paper presents an overview of the fabrication and device applications of Si nanocrystals, especially in luminescent and photovoltaic devices. We first introduce the fabrication methods of Si nanocrystals-based multilayers. Then, we systematically review the utilization of Si nanocrystals in luminescent and photovoltaic devices. Finally, some expectations for further development of the Si nanocrystals-based photonic and photovoltaic devices are proposed. Project supported by the National Natural Science Foundation of China (Nos. 11774155, 11274155).

  10. Extraordinary Interfacial Stitching between Single All-Inorganic Perovskite Nanocrystals

    PubMed Central

    2018-01-01

    All-inorganic cesium lead halide perovskite nanocrystals are extensively studied because of their outstanding optoelectronic properties. Being of a cubic shape and typically featuring a narrow size distribution, CsPbX3 (X = Cl, Br, and I) nanocrystals are the ideal starting material for the development of homogeneous thin films as required for photovoltaic and optoelectronic applications. Recent experiments reveal spontaneous merging of drop-casted CsPbBr3 nanocrystals, which is promoted by humidity and mild-temperature treatments and arrested by electron beam irradiation. Here, we make use of atom-resolved annular dark-field imaging microscopy and valence electron energy loss spectroscopy in a state-of-the-art low-voltage monochromatic scanning transmission electron microscope to investigate the aggregation between individual nanocrystals at the atomic level. We show that the merging process preserves the elemental composition and electronic structure of CsPbBr3 and takes place between nanocrystals of different sizes and orientations. In particular, we reveal seamless stitching for aligned nanocrystals, similar to that reported in the past for graphene flakes. Because the crystallographic alignment occurs naturally in drop-casted layers of CsPbX3 nanocrystals, our findings constitute the essential first step toward the development of large-area nanosheets with band gap energies predesigned by the nanocrystal choice—the gateway to large-scale photovoltaic applications of inorganic perovskites. PMID:29355301

  11. Extraordinary Interfacial Stitching between Single All-Inorganic Perovskite Nanocrystals.

    PubMed

    Gomez, Leyre; Lin, Junhao; de Weerd, Chris; Poirier, Lucas; Boehme, Simon C; von Hauff, Elizabeth; Fujiwara, Yasufumi; Suenaga, Kazutomo; Gregorkiewicz, Tom

    2018-02-14

    All-inorganic cesium lead halide perovskite nanocrystals are extensively studied because of their outstanding optoelectronic properties. Being of a cubic shape and typically featuring a narrow size distribution, CsPbX 3 (X = Cl, Br, and I) nanocrystals are the ideal starting material for the development of homogeneous thin films as required for photovoltaic and optoelectronic applications. Recent experiments reveal spontaneous merging of drop-casted CsPbBr 3 nanocrystals, which is promoted by humidity and mild-temperature treatments and arrested by electron beam irradiation. Here, we make use of atom-resolved annular dark-field imaging microscopy and valence electron energy loss spectroscopy in a state-of-the-art low-voltage monochromatic scanning transmission electron microscope to investigate the aggregation between individual nanocrystals at the atomic level. We show that the merging process preserves the elemental composition and electronic structure of CsPbBr 3 and takes place between nanocrystals of different sizes and orientations. In particular, we reveal seamless stitching for aligned nanocrystals, similar to that reported in the past for graphene flakes. Because the crystallographic alignment occurs naturally in drop-casted layers of CsPbX 3 nanocrystals, our findings constitute the essential first step toward the development of large-area nanosheets with band gap energies predesigned by the nanocrystal choice-the gateway to large-scale photovoltaic applications of inorganic perovskites.

  12. Nimodipine nanocrystals for oral bioavailability improvement: preparation, characterization and pharmacokinetic studies.

    PubMed

    Fu, Qiang; Sun, Jin; Zhang, Dong; Li, Mo; Wang, Yongjun; Ling, Guixia; Liu, Xiaohong; Sun, Yinghua; Sui, Xiaofan; Luo, Cong; Sun, Le; Han, Xiaopeng; Lian, He; Zhu, Meng; Wang, Siling; He, Zhonggui

    2013-09-01

    This study intended to develop nimodipine (NMD) nanocrystals with different sizes for oral administration and to investigate the relationship between dissolution and pharmacokinetics for NMD nanocrystals and Nimotop(®). NMD nanocrystals were prepared by combination of microprecipitation and high pressure homogenization and were further lyophilized. The particle size, morphology and aqueous solubility of the NMD nanocrystals were determined. With Nimotop(®) as the control, the dissolution rate was evaluated and the pharmacokinetic study was undertaken in beagle dogs. NMD nanocrystals with mean diameters of about 159.0, 503.0 and 833.3 nm were prepared, respectively. The lyophilization didn't affect the particle sizes of the redispersed nanocrystals. The aqueous solubility was significantly improved and displayed a size-dependent manner. The nanocrystals exhibited lower dissolution patterns than Nimotop(®) under non-sink condition, but bioavailability of the two nanocrystals (159.0 and 833.3 nm) was equivalent, about 2.6-fold higher than Nimotop(®). In conclusion, oral nanocrystal drug delivery system was a promising strategy in improving the oral bioavailability of poorly soluble or insoluble drugs. But we could not establish a favorable in vitro in vivo correlation for NMD nanocrystals and Nimotop(®) and thus the oral absorption mechanism of the NMD nanocrystals required further study. Copyright © 2013 Elsevier B.V. All rights reserved.

  13. Colloidal Nanocrystals with Near-infrared Optical Properties: Synthesis, Characterization, and Applications

    NASA Astrophysics Data System (ADS)

    Panthani, Matthew George

    2011-07-01

    Colloidal nanocrystals with optical properties in the near-infrared (NIR) are of interest for many applications such as photovoltaic (PV) energy conversion, bioimaging, and therapeutics. For PVs and other electronic devices, challenges in using colloidal nanomaterials often deal with the surfaces. Because of the high surface-to-volume ratio of small nanocrystals, surfaces and interfaces play an enhanced role in the properties of nanocrystal films and devices. Organic ligand-capped CuInSe2 (CIS) and Cu(InXGa 1-X)Se2 (CIGS) nanocrystals were synthesized and used as the absorber layer in prototype solar cells. By fabricating devices from spray-coated CuInSe nanocrystals under ambient conditions, solar-to-electric power conversion efficiencies as high as 3.1% were achieved. Many treatments of the nanocrystal films were explored. Although some treatments increased the conductivity of the nanocrystal films, the best devices were from untreated CIS films. By modifying the reaction chemistry, quantum-confined CuInSe XS2-X (CISS) nanocrystals were produced. The potential of the CISS nanocrystals for targeted bioimaging was demonstrated via oral delivery to mice and imaging of nanocrystal fluorescence. The size-dependent photoluminescence of Si nanocrystals was measured. Si nanocrystals supported on graphene were characterized by conventional transmission electron microscopy and spherical aberration (Cs)-corrected scanning transmission electron microscopy (STEM). Enhanced imaging contrast and resolution was achieved by using Cs-corrected STEM with a graphene support. In addition, clear imaging of defects and the organic-inorganic interface was enabled by utilizing this technique.

  14. Inorganic Chemistry Solutions to Semiconductor Nanocrystal Problems

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Alvarado, Samuel R.; Guo, Yijun; Ruberu, T. Purnima A.

    2014-03-15

    The optoelectronic and chemical properties of semiconductor nanocrystals heavily depend on their composition, size, shape and internal structure, surface functionality, etc. Available strategies to alter these properties through traditional colloidal syntheses and ligand exchange methods place a premium on specific reaction conditions and surfactant combinations. In this invited review, we apply a molecular-level understanding of chemical precursor reactivity to reliably control the morphology, composition and intimate architecture (core/shell vs. alloyed) of semiconductor nanocrystals. We also describe our work aimed at achieving highly selective, low-temperature photochemical methods for the synthesis of semiconductor–metal and semiconductor–metal oxide photocatalytic nanocomposites. In addition, we describemore » our work on surface modification of semiconductor nanocrystal quantum dots using new approaches and methods that bypass ligand exchange, retaining the nanocrystal's native ligands and original optical properties, as well as on spectroscopic methods of characterization useful in determining surface ligand organization and chemistry. Using recent examples from our group and collaborators, we demonstrate how these efforts have lead to faster, wider and more systematic application of semiconductor nanocrystal-based materials to biological imaging and tracking, and to photocatalysis of unconventional substrates. We believe techniques and methods borrowed from inorganic chemistry (including coordination, organometallic and solid state chemistry) have much to offer in reaching a better understanding of the synthesis, functionalization and real-life application of such exciting materials as semiconductor nanocrystals (quantum dots, rods, tetrapods, etc.).« less

  15. 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

  16. Size-Dependent Melting Behavior of Colloidal In, Sn, and Bi Nanocrystals

    PubMed Central

    Liu, Minglu; Wang, Robert Y.

    2015-01-01

    Colloidal nanocrystals are a technologically important class of nanostructures whose phase change properties have been largely unexplored. Here we report on the melting behavior of In, Sn, and Bi nanocrystals dispersed in a polymer matrix. This polymer matrix prevents the nanocrystals from coalescing with one another and enables previously unaccessed observations on the melting behavior of colloidal nanocrystals. We measure the melting temperature, melting enthalpy, and melting entropy of colloidal nanocrystals with diameters of approximately 10 to 20 nm. All of these properties decrease as nanocrystal size decreases, although the depression rate for melting temperature is comparatively slower than that of melting enthalpy and melting entropy. We also observe an elevated melting temperature during the initial melt-freeze cycle that we attribute to surface stabilization from the organic ligands on the nanocrystal surface. Broad endothermic melting valleys and very large supercoolings in our calorimetry data suggest that colloidal nanocrystals exhibit a significant amount of surface pre-melting and low heterogeneous nucleation probabilities during freezing. PMID:26573146

  17. 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.

  18. Cellulose nanocrystals with tunable surface charge for nanomedicine

    NASA Astrophysics Data System (ADS)

    Hosseinidoust, Zeinab; Alam, Md Nur; Sim, Goeun; Tufenkji, Nathalie; van de Ven, Theo G. M.

    2015-10-01

    Crystalline nanoparticles of cellulose exhibit attractive properties as nanoscale carriers for bioactive molecules in nanobiotechnology and nanomedicine. For applications in imaging and drug delivery, surface charge is one of the most important factors affecting the performance of nanocarriers. However, current methods of preparation offer little flexibility for controlling the surface charge of cellulose nanocrystals, leading to compromised colloidal stability under physiological conditions. We report a synthesis method that results in nanocrystals with remarkably high carboxyl content (6.6 mmol g-1) and offers continuous control over surface charge without any adjustment to the reaction conditions. Six fractions of nanocrystals with various surface carboxyl contents were synthesized from a single sample of softwood pulp with carboxyl contents varying from 6.6 to 1.7 mmol g-1 and were fully characterized. The proposed method resulted in highly stable colloidal nanocrystals that did not aggregate when exposed to high salt concentrations or serum-containing media. Interactions of these fractions with four different tissue cell lines were investigated over a wide range of concentrations (50-300 μg mL-1). Darkfield hyperspectral imaging and confocal microscopy confirmed the uptake of nanocrystals by selected cell lines without any evidence of membrane damage or change in cell density; however a charge-dependent decrease in mitochondrial activity was observed for charge contents higher than 3.9 mmol g-1. A high surface carboxyl content allowed for facile conjugation of fluorophores to the nanocrystals without compromising colloidal stability. The cellular uptake of fluoresceinamine-conjugated nanocrystals exhibited a time-dose dependent relationship and increased significantly with doubling of the surface charge.Crystalline nanoparticles of cellulose exhibit attractive properties as nanoscale carriers for bioactive molecules in nanobiotechnology and nanomedicine. For

  19. Microscopic theory of cation exchange in CdSe nanocrystals.

    PubMed

    Ott, Florian D; Spiegel, Leo L; Norris, David J; Erwin, Steven C

    2014-10-10

    Although poorly understood, cation-exchange reactions are increasingly used to dope or transform colloidal semiconductor nanocrystals (quantum dots). We use density-functional theory and kinetic Monte Carlo simulations to develop a microscopic theory that explains structural, optical, and electronic changes observed experimentally in Ag-cation-exchanged CdSe nanocrystals. We find that Coulomb interactions, both between ionized impurities and with the polarized nanocrystal surface, play a key role in cation exchange. Our theory also resolves several experimental puzzles related to photoluminescence and electrical behavior in CdSe nanocrystals doped with Ag.

  20. Conjugated polymer/nanocrystal nanocomposites for renewable energy applications in photovoltaics and photocatalysis.

    PubMed

    Su, Yu-Wei; Lin, Wei-Hao; Hsu, Yung-Jung; Wei, Kung-Hwa

    2014-11-01

    Conjugated polymer/nanocrystal composites have attracted much attention for use in renewable energy applications because of their versatile and synergistic optical and electronic properties. Upon absorbing photons, charge separation occurs in the nanocrystals, generating electrons and holes for photocurrent flow or reduction/oxidation (redox) reactions under proper conditions. Incorporating these nanocrystals into conjugated polymers can complement the visible light absorption range of the polymers for photovoltaics applications or allow the polymers to sensitize or immobilize the nanocrystals for photocatalysis. Here, the current developments of conjugated polymer/nanocrystal nanocomposites for bulk heterojunction-type photovoltaics incorporating Cd- and Pb-based nanocrystals or quantum dots are reviewed. The effects of manipulating the organic ligands and the concentration of the nanocrystal precursor, critical factors that affect the shape and aggregation of the nanocrystals, are also discussed. In the conclusion, the mechanisms through which conjugated polymers can sensitize semiconductor nanocrystals (TiO2 , ZnO) to ensure efficient charge separation, as well as how they can support immobilized nanocrystals for use in photocatalysis, are addressed. © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  1. Cation Exchange Reactions for Improved Quality and Diversity of Semiconductor Nanocrystals

    NASA Astrophysics Data System (ADS)

    Beberwyck, Brandon James

    Observing the size and shape dependent physical properties of semiconductor nanocrystals requires synthetic methods capable of not only composition and crystalline phase control but also molecular scale uniformity for a particle consisting of tens to hundreds of thousands of atoms. The desire for synthetic methods that produce uniform nanocrystals of complex morphologies continues to increase as nanocrystals find roles in commercial applications, such as biolabeling and display technologies, that are simultaneously restricting material compositions. With these constraints, new synthetic strategies that decouple the nanocrystal's chemical composition from its morphology are necessary. This dissertation explores the cation exchange reaction of colloidal semiconductor nanocrystals, a template-based chemical transformation that enables the interconversion of nanocrystals between a variety of compositions while maintaining their size dispersity and morphology. Chapter 1 provides an introduction to the versatility of this replacement reaction as a synthetic method for semiconductor nanocrystals. An overview of the fundamentals of the cation exchange reaction and the diversity of products that are achievable is presented. Chapter 2 examines the optical properties of nanocrystal heterostructures produced through cation exchange reactions. The deleterious impact of exchange on the photoluminescence is correlated to residual impurities and a simple annealing protocol is demonstrated to achieve photoluminescence yields comparable to samples produced by conventional methods. Chapter 3 investigates the extension of the cation exchange reaction beyond ionic nanocrystals. Covalent III-V nanocrystal of high crystallinity and low size dispersity are synthesized by the cation exchange of cadmium pnictide nanocrystals with group 13 ions. Lastly, Chapter 4 highlights future studies to probe cation exchange reactions in colloidal semiconductor nanocrystals and progress that needs to be

  2. 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

  3. Size- and shape-dependent surface thermodynamic properties of nanocrystals

    NASA Astrophysics Data System (ADS)

    Fu, Qingshan; Xue, Yongqiang; Cui, Zixiang

    2018-05-01

    As the fundamental properties, the surface thermodynamic properties of nanocrystals play a key role in the physical and chemical changes. However, it remains ambiguous about the quantitative influence regularities of size and shape on the surface thermodynamic properties of nanocrystals. Thus by introducing interface variables into the Gibbs energy and combining Young-Laplace equation, relations between the surface thermodynamic properties (surface Gibbs energy, surface enthalpy, surface entropy, surface energy and surface heat capacity), respectively, and size of nanocrystals with different shapes were derived. Theoretical estimations of the orders of the surface thermodynamic properties of nanocrystals agree with available experimental values. Calculated results of the surface thermodynamic properties of Au, Bi and Al nanocrystals suggest that when r > 10 nm, the surface thermodynamic properties linearly vary with the reciprocal of particle size, and when r < 10 nm, the effect of particle size on the surface thermodynamic properties becomes greater and deviates from linear variation. For nanocrystals with identical equivalent diameter, the more the shape deviates from sphere, the larger the surface thermodynamic properties (absolute value) are.

  4. 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.

  5. Osteoblasts Growth Behaviour on Bio-Based Calcium Carbonate Aragonite Nanocrystal

    PubMed Central

    Zakaria, Zuki Abu Bakar

    2014-01-01

    Calcium carbonate (CaCO3) nanocrystals derived from cockle shells emerge to present a good concert in bone tissue engineering because of their potential to mimic the composition, structure, and properties of native bone. The aim of this study was to evaluate the biological response of CaCO3 nanocrystals on hFOB 1.19 and MC3T3 E-1 osteoblast cells in vitro. Cell viability and proliferation were assessed by MTT and BrdU assays, and LDH was measured to determine the effect of CaCO3 nanocrystals on cell membrane integrity. Cellular morphology was examined by SEM and fluorescence microscopy. The results showed that CaCO3 nanocrystals had no toxic effects to some extent. Cell proliferation, alkaline phosphatase activity, and protein synthesis were enhanced by the nanocrystals when compared to the control. Cellular interactions were improved, as indicated by SEM and fluorescent microscopy. The production of VEGF and TGF-1 was also affected by the CaCO3 nanocrystals. Therefore, bio-based CaCO3 nanocrystals were shown to stimulate osteoblast differentiation and improve the osteointegration process. PMID:24734228

  6. 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.

  7. Cerebellar asymmetry and its relation to cerebral asymmetry estimated by intrinsic functional connectivity

    PubMed Central

    Wang, Danhong; Buckner, Randy L.

    2013-01-01

    Asymmetry of the human cerebellum was investigated using intrinsic functional connectivity. Regions of functional asymmetry within the cerebellum were identified during resting-state functional MRI (n = 500 subjects) and replicated in an independent cohort (n = 500 subjects). The most strongly right lateralized cerebellar regions fell within the posterior lobe, including crus I and crus II, in regions estimated to link to the cerebral association cortex. The most strongly left lateralized cerebellar regions were located in lobules VI and VIII in regions linked to distinct cerebral association networks. Comparison of cerebellar asymmetry with independently estimated cerebral asymmetry revealed that the lateralized regions of the cerebellum belong to the same networks that are strongly lateralized in the cerebrum. The degree of functional asymmetry of the cerebellum across individuals was significantly correlated with cerebral asymmetry and varied with handedness. In addition, cerebellar asymmetry estimated at rest predicted cerebral lateralization during an active language task. These results demonstrate that functional lateralization is likely a unitary feature of large-scale cerebrocerebellar networks, consistent with the hypothesis that the cerebellum possesses a roughly homotopic map of the cerebral cortex including the prominent asymmetries of the association cortex. PMID:23076113

  8. Near-infrared light emitting device using semiconductor nanocrystals

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Supran, Geoffrey J.S.; Song, Katherine W.; Hwang, Gyuweon

    A near-infrared light emitting device can include semiconductor nanocrystals that emit at wavelengths beyond 1 .mu.m. The semiconductor nanocrystals can include a core and an overcoating on a surface of the core.

  9. Plasmonic engineering of spontaneous emission from silicon nanocrystals.

    PubMed

    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.

  10. One-Step Synthesis of Monodisperse In-Doped ZnO Nanocrystals

    NASA Astrophysics Data System (ADS)

    Wang, Qing Ling; Yang, Ye Feng; He, Hai Ping; Chen, Dong Dong; Ye, Zhi Zhen; Jin, Yi Zheng

    2010-05-01

    A method for the synthesis of high quality indium-doped zinc oxide (In-doped ZnO) nanocrystals was developed using a one-step ester elimination reaction based on alcoholysis of metal carboxylate salts. The resulting nearly monodisperse nanocrystals are well-crystallized with typically crystal structure identical to that of wurtzite type of ZnO. Structural, optical, and elemental analyses on the products indicate the incorporation of indium into the host ZnO lattices. The individual nanocrystals with cubic structures were observed in the 5% In-ZnO reaction, due to the relatively high reactivity of indium precursors. Our study would provide further insights for the growth of doped oxide nanocrystals, and deepen the understanding of doping process in colloidal nanocrystal syntheses.

  11. Flexible and low-voltage integrated circuits constructed from high-performance nanocrystal transistors.

    PubMed

    Kim, David K; Lai, Yuming; Diroll, Benjamin T; Murray, Christopher B; Kagan, Cherie R

    2012-01-01

    Colloidal semiconductor nanocrystals are emerging as a new class of solution-processable materials for low-cost, flexible, thin-film electronics. Although these colloidal inks have been shown to form single, thin-film field-effect transistors with impressive characteristics, the use of multiple high-performance nanocrystal field-effect transistors in large-area integrated circuits has not been shown. This is needed to understand and demonstrate the applicability of these discrete nanocrystal field-effect transistors for advanced electronic technologies. Here we report solution-deposited nanocrystal integrated circuits, showing nanocrystal integrated circuit inverters, amplifiers and ring oscillators, constructed from high-performance, low-voltage, low-hysteresis CdSe nanocrystal field-effect transistors with electron mobilities of up to 22 cm(2) V(-1) s(-1), current modulation >10(6) and subthreshold swing of 0.28 V dec(-1). We fabricated the nanocrystal field-effect transistors and nanocrystal integrated circuits from colloidal inks on flexible plastic substrates and scaled the devices to operate at low voltages. We demonstrate that colloidal nanocrystal field-effect transistors can be used as building blocks to construct complex integrated circuits, promising a viable material for low-cost, flexible, large-area electronics.

  12. Octacosanol educes physico-chemical attributes, release and bioavailability as modified nanocrystals.

    PubMed

    Sen Gupta, Surashree; Ghosh, Mahua

    2017-10-01

    Octacosanol is a lesser known nutraceutical with the potential for treatment of several inflammatory diseases, high cholesterol, Parkinson's symptoms and tumour growth along with the capacity to improve athletic performance. But its lipophilicity and large structure inhibits extended solubility in water resulting in poor absorption and a low bioavailability. In the present work, sodium salt of octacosyl sulfate was synthesized. It displayed improved water solubility. Its nanocrystals, synthesized by means of nanoprecipitation technique, enhanced diffusion velocity, antioxidant capacity, shelf-life, penetrability and bioavailability. Particle size of the nanocrystals ranged between 197 and 220nm. Both modified octacosanol and its nanocrystals displayed maximum lipid peroxidation activities at a concentration 1000ppm, but nanocrystals demonstrated higher prevention. From freeze-thaw cycles it was evident that normal octacosanol crystals were far more prone to temperature variations than the nanocrystals. A pronounced increase in release/diffusion rate and bioavailability was observed for the nanocrystals of the modified octacosanol. In vitro release kinetics, bioavailability and bioequivalence were studied. Relative bioavailability for gastric passage and pancreatic passage of nanocrystals was 2.58 times and 1.81 times that of normal crystals respectively. Furthermore the nanocrystals displayed a superior in vitro release rate, while following a non-Fickian mode. Copyright © 2017 Elsevier B.V. All rights reserved.

  13. Uncovering the intrinsic size dependence of hydriding phase transformations in nanocrystals.

    PubMed

    Bardhan, Rizia; Hedges, Lester O; Pint, Cary L; Javey, Ali; Whitelam, Stephen; Urban, Jeffrey J

    2013-10-01

    A quantitative understanding of nanocrystal phase transformations would enable more efficient energy conversion and catalysis, but has been hindered by difficulties in directly monitoring well-characterized nanoscale systems in reactive environments. We present a new in situ luminescence-based probe enabling direct quantification of nanocrystal phase transformations, applied here to the hydriding transformation of palladium nanocrystals. Our approach reveals the intrinsic kinetics and thermodynamics of nanocrystal phase transformations, eliminating complications of substrate strain, ligand effects and external signal transducers. Clear size-dependent trends emerge in nanocrystals long accepted to be bulk-like in behaviour. Statistical mechanical simulations show these trends to be a consequence of nanoconfinement of a thermally driven, first-order phase transition: near the phase boundary, critical nuclei of the new phase are comparable in size to the nanocrystal itself. Transformation rates are then unavoidably governed by nanocrystal dimensions. Our results provide a general framework for understanding how nanoconfinement fundamentally impacts broad classes of thermally driven solid-state phase transformations relevant to hydrogen storage, catalysis, batteries and fuel cells.

  14. Multicolour synthesis in lanthanide-doped nanocrystals through cation exchange in water

    NASA Astrophysics Data System (ADS)

    Han, Sanyang; Qin, Xian; An, Zhongfu; Zhu, Yihan; Liang, Liangliang; Han, Yu; Huang, Wei; Liu, Xiaogang

    2016-10-01

    Meeting the high demand for lanthanide-doped luminescent nanocrystals across a broad range of fields hinges upon the development of a robust synthetic protocol that provides rapid, just-in-time nanocrystal preparation. However, to date, almost all lanthanide-doped luminescent nanomaterials have relied on direct synthesis requiring stringent controls over crystal nucleation and growth at elevated temperatures. Here we demonstrate the use of a cation exchange strategy for expeditiously accessing large classes of such nanocrystals. By combining the process of cation exchange with energy migration, the luminescence properties of the nanocrystals can be easily tuned while preserving the size, morphology and crystal phase of the initial nanocrystal template. This post-synthesis strategy enables us to achieve upconversion luminescence in Ce3+ and Mn2+-activated hexagonal-phased nanocrystals, opening a gateway towards applications ranging from chemical sensing to anti-counterfeiting.

  15. Organization of 'nanocrystal molecules' using DNA

    NASA Astrophysics Data System (ADS)

    Alivisatos, A. Paul; Johnsson, Kai P.; Peng, Xiaogang; Wilson, Troy E.; Loweth, Colin J.; Bruchez, Marcel P.; Schultz, Peter G.

    1996-08-01

    PATTERNING matter on the nanometre scale is an important objective of current materials chemistry and physics. It is driven by both the need to further miniaturize electronic components and the fact that at the nanometre scale, materials properties are strongly size-dependent and thus can be tuned sensitively1. In nanoscale crystals, quantum size effects and the large number of surface atoms influence the, chemical, electronic, magnetic and optical behaviour2-4. 'Top-down' (for example, lithographic) methods for nanoscale manipulation reach only to the upper end of the nanometre regime5; but whereas 'bottom-up' wet chemical techniques allow for the preparation of mono-disperse, defect-free crystallites just 1-10 nm in size6-10, ways to control the structure of nanocrystal assemblies are scarce. Here we describe a strategy for the synthesis of'nanocrystal molecules', in which discrete numbers of gold nanocrystals are organized into spatially defined structures based on Watson-Crick base-pairing interactions. We attach single-stranded DNA oligonucleotides of defined length and sequence to individual nanocrystals, and these assemble into dimers and trimers on addition of a complementary single-stranded DNA template. We anticipate that this approach should allow the construction of more complex two-and three-dimensional assemblies.

  16. Shaped nanocrystal particles and methods for making the same

    DOEpatents

    Alivisatos, A Paul [Oakland, CA; Scher, Erik C [Menlo Park, CA; Manna, Liberato [Berkeley, CA

    2011-11-22

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

  17. Shaped nanocrystal particles and methods for making the same

    DOEpatents

    Alivisatos, A. Paul; Scher, Erik C; Manna, Liberato

    2013-12-17

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

  18. Shaped nanocrystal particles and methods for working the same

    DOEpatents

    Alivisatos, A. Paul; Sher, Eric C.; Manna, Liberato

    2007-12-25

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

  19. Gold nanocrystals with DNA-directed morphologies.

    PubMed

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

    2016-09-16

    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.

  20. Engineering of Organic Nanocrystals by Electrocrystallization

    NASA Astrophysics Data System (ADS)

    Kilani, Mohamed

    This work discusses the experimental and theoretical methods used to control the morphology of nanocrystals. The hypothesis of the thermodynamic/kinetic control of the morphology was verified. We applied the electrocrystallization to make K(def)TCP nanocrystals and we tuned the electrochemical parameters to determine their influence on the nanocrystals morphologies. The characterization was mainly performed with AFM and FE-SEM. We presented in this work the possibility to control the morphology of K(def)TCP using the electrochemical parameters. The obtained shapes ranged from nanorods to rhombohedral shape, which is reported for the first time. The observed growth behavior was modeled and simulated with a method based on Monte-Carlo techniques. The simulation results show a qualitative match with the experimental findings. This work contributes to the understanding of the crystal growth behavior and the thermodynamic/kinetic morphology transition using electrocrystallization.

  1. 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.

  2. Photophysical properties of wavelength-tunable methylammonium lead halide perovskite nanocrystals

    DOE PAGES

    Freppon, Daniel J.; Men, Long; Burkhow, Sadie J.; ...

    2016-11-25

    Here we present the time-correlated luminescence of isolated nanocrystals of five methylammonium lead mixed-halide perovskite compositions (CH 3NH 3PbBr 3$-$xI x) that were synthesized with varying iodide and bromide anion loading. All analyzed nanocrystals had a spherical morphology with diameters in the range of 2 to 32 nm. The luminescence maxima of CH 3NH 3PbBr 3$-$xI x nanocrystals were tuned to wavelengths ranging between 498 and 740 nm by varying the halide loading. Both CH 3NH 3PbI 3 and CH 3NH 3PbBr 3 nanocrystals exhibited no luminescence intermittency for more than 90% of the 250 s analysis time, as definedmore » by a luminescence intensity three standard deviations above the background. The mixed halide CH 3NH 3PbBr 0.75I 0.25, CH 3NH 3PbBr 0.50I 0.50, and CH 3NH 3PbBr 0.25I 0.75 nanocrystals exhibited luminescence intermittency in 18%, 4% and 26% of the nanocrystals, respectively. Irrespective of luminescence intermittency, luminescence intensities were classified for each nanocrystal as: (a) constant, (b) multimodal, (c) photobrightening, and (d) photobleaching. Finally, based on their photophysics, the CH 3NH 3PbBr 3$-$xI x nanocrystals can be expected to be useful in a wide-range of applications where low and non-intermittent luminescence is desirable, for example as imaging probes and in films for energy conversion devices.« less

  3. Photophysical properties of wavelength-tunable methylammonium lead halide perovskite nanocrystals

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Freppon, Daniel J.; Men, Long; Burkhow, Sadie J.

    Here we present the time-correlated luminescence of isolated nanocrystals of five methylammonium lead mixed-halide perovskite compositions (CH 3NH 3PbBr 3$-$xI x) that were synthesized with varying iodide and bromide anion loading. All analyzed nanocrystals had a spherical morphology with diameters in the range of 2 to 32 nm. The luminescence maxima of CH 3NH 3PbBr 3$-$xI x nanocrystals were tuned to wavelengths ranging between 498 and 740 nm by varying the halide loading. Both CH 3NH 3PbI 3 and CH 3NH 3PbBr 3 nanocrystals exhibited no luminescence intermittency for more than 90% of the 250 s analysis time, as definedmore » by a luminescence intensity three standard deviations above the background. The mixed halide CH 3NH 3PbBr 0.75I 0.25, CH 3NH 3PbBr 0.50I 0.50, and CH 3NH 3PbBr 0.25I 0.75 nanocrystals exhibited luminescence intermittency in 18%, 4% and 26% of the nanocrystals, respectively. Irrespective of luminescence intermittency, luminescence intensities were classified for each nanocrystal as: (a) constant, (b) multimodal, (c) photobrightening, and (d) photobleaching. Finally, based on their photophysics, the CH 3NH 3PbBr 3$-$xI x nanocrystals can be expected to be useful in a wide-range of applications where low and non-intermittent luminescence is desirable, for example as imaging probes and in films for energy conversion devices.« less

  4. The Use of Cellulose Nanocrystals for Potential Application in Topical Delivery of Hydroquinone.

    PubMed

    Taheri, Azade; Mohammadi, Mina

    2015-07-01

    Nanotechnology-based drug delivery systems can enhance drug permeation through the skin and improve the drug stability. The biodegradability and biocompatibility of cellulose nanocrystals have made these nanoparticles good candidates to use in biomedical applications. The hyperpigmentation is a common skin disorder that could be caused by number of reasons such as sun exposure and pregnancy. Hydroquinone could inhibit the production of melanin and eliminate the discolorations of skin. This study is aimed at introducing cellulose nanocrystals as suitable carriers for drug delivery to skin. Prepared cellulose nanocrystals were characterized by dynamic light scattering and atomic force microscopy. The size of cellulose nanocrystals determined using dynamic light scattering was 301 ± 10 nm. Hydroquinone-cellulose nanocrystal complex was prepared by incubating of hydroquinone solution in cellulose nanocrystals suspension. The size of hydroquinone-cellulose nanocrystal complex determined using dynamic light scattering was 310 ± 10 nm. The hydroquinone content of the hydroquinone-cellulose complex was determined using UV/vis spectroscopy. Hydroquinone was bound to cellulose nanocrystals representing 79.3 ± 2% maximum binding efficiency when 1.1 mg hydroquinone was added to 1 mL of cellulose nanocrystals suspension (2 mg cellulose nanocrystal). The hydroquinone-cellulose nanocrystal complex showed an approximately sustained release profile of hydroquinone. Approximately, 80% of bound hydroquinone released in 4 h. © 2014 John Wiley & Sons A/S.

  5. State of the art of nanocrystals technology for delivery of poorly soluble drugs

    NASA Astrophysics Data System (ADS)

    Zhou, Yuqi; Du, Juan; Wang, Lulu; Wang, Yancai

    2016-09-01

    Formulation of nanocrystals is a distinctive approach which can effectively improve the delivery of poorly water-soluble drugs, thus enticing the development of the nanocrystals technology. The characteristics of nanocrystals resulted in an exceptional drug delivery conductance, including saturation solubility, dissolution velocity, adhesiveness, and affinity. Nanocrystals were treated as versatile pharmaceuticals that could be delivered through almost all routes of administration. In the current review, oral, pulmonary, and intravenous routes of administration were presented. Also, the targeting of drug nanocrystals, as well as issues of efficacy and safety, were also discussed. Several methods were applied for nanocrystals production including top-down production strategy (media milling, high-pressure homogenization), bottom-up production strategy (antisolvent precipitation, supercritical fluid process, and precipitation by removal of solvent), and the combination approaches. Moreover, this review also described the evaluation and characterization of the drug nanocrystals and summarized the current commercial pharmaceutical products utilizing nanocrystals technology.

  6. Creating ligand-free silicon germanium alloy nanocrystal inks.

    PubMed

    Erogbogbo, Folarin; Liu, Tianhang; Ramadurai, Nithin; Tuccarione, Phillip; Lai, Larry; Swihart, Mark T; Prasad, Paras N

    2011-10-25

    Particle size is widely used to tune the electronic, optical, and catalytic properties of semiconductor nanocrystals. This contrasts with bulk semiconductors, where properties are tuned based on composition, either through doping or through band gap engineering of alloys. Ideally, one would like to control both size and composition of semiconductor nanocrystals. Here, we demonstrate production of silicon-germanium alloy nanoparticles by laser pyrolysis of silane and germane. We have used FTIR, TEM, XRD, EDX, SEM, and TOF-SIMS to conclusively determine their structure and composition. Moreover, we show that upon extended sonication in selected solvents, these bare nanocrystals can be stably dispersed without ligands, thereby providing the possibility of using them as an ink to make patterned films, free of organic surfactants, for device fabrication. The engineering of these SiGe alloy inks is an important step toward the low-cost fabrication of group IV nanocrystal optoelectronic, thermoelectric, and photovoltaic devices.

  7. Level Anticrossing of Impurity States in Semiconductor Nanocrystals

    PubMed Central

    Baimuratov, Anvar S.; Rukhlenko, Ivan D.; Turkov, Vadim K.; Ponomareva, Irina O.; Leonov, Mikhail Yu.; Perova, Tatiana S.; Berwick, Kevin; Baranov, Alexander V.; Fedorov, Anatoly V.

    2014-01-01

    The size dependence of the quantized energies of elementary excitations is an essential feature of quantum nanostructures, underlying most of their applications in science and technology. Here we report on a fundamental property of impurity states in semiconductor nanocrystals that appears to have been overlooked—the anticrossing of energy levels exhibiting different size dependencies. We show that this property is inherent to the energy spectra of charge carriers whose spatial motion is simultaneously affected by the Coulomb potential of the impurity ion and the confining potential of the nanocrystal. The coupling of impurity states, which leads to the anticrossing, can be induced by interactions with elementary excitations residing inside the nanocrystal or an external electromagnetic field. We formulate physical conditions that allow a straightforward interpretation of level anticrossings in the nanocrystal energy spectrum and an accurate estimation of the states' coupling strength. PMID:25369911

  8. Anomalous Suppression of Valley Splittings in Lead Salt Nanocrystals

    NASA Astrophysics Data System (ADS)

    Poddubny, Alexander; Nestoklon, Mikhail; Goupalov, Serguei

    2012-02-01

    Atomistic sp^3d^5s^* tight-binding theory of PbSe and PbS nanocrystals is developed. It is demonstrated, that the valley splittings of confined electrons and holes strongly and peculiarly depend on the geometry of a nanocrystal. When the nanocrystal lacks a microscopic center of inversion and has Td symmetry, the splittings are strongly suppressed as compared to the more symmetric nanocrystals with Oh symmetry, having an inversion center. This effect is quite unusual because typically a higher symmetry of a physical system implies a higher degeneracy of its energy levels, while in our case the suppression of the splittings occurs in NCs having lower symmetry. Nevertheless, we were able to explain this puzzling behavior using mathematical apparatus of the group theory.

  9. Colloidal synthesis of biocompatible iron disulphide nanocrystals.

    PubMed

    Santos-Cruz, J; Nuñez-Anita, R E; Mayén-Hernández, S A; Martínez-Alvarez, O; Acosta-Torres, L S; de la Fuente-Hernández, J; Campos-González, E; Vega-González, M; Arenas-Arrocena, M C

    2018-08-01

    The aim of this research was to synthesis biocompatible iron disulphide nanocrystals at different reaction temperatures using the colloidal synthesis methodology. Synthesis was conducted at the 220-240 °C range of reaction temperatures at intervals of 5 °C in an inert argon atmosphere. The toxicity of iron disulphide nanocrystals was evaluated in vitro using mouse fibroblast cell line. Two complementary assays were conducted: the first to evaluate cell viability of the fibroblast via an MTT assay and the second to determine the preservation of fibroblast nuclei integrity through DAPI staining, which labels nuclear DNA in fluorescence microscopes. Through TEM and HRTEM, we observed a cubic morphology of pyrite iron disulphide nanocrystals ranging in sizes 25-50 nm (225 °C), 50-70 nm (230 °C) and >70 nm (235 °C). Through X-ray diffraction, we observed a mixture of pyrite and pyrrohotite in the samples synthesized at 225 °C and 240 °C, showing the best photocatalytic activity at 80% and 65%, respectively, for the degradation of methylene blue after 120 minutes. In all experimental groups, iron disulphide nanocrystals were biocompatible, i.e. no statistically significant differences were observed between experimental groups as shown in a one-way ANOVA and Tukey's test. Based on all of these results, we recommend non-cytotoxic semiconductor iron sulphide nanocrystals for biomedical applications.

  10. 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.

  11. Nanocrystal sensitized photovoltaics and photodetectors with performance enhanced using ligand engineering

    NASA Astrophysics Data System (ADS)

    Schut, David M.; Williams, George M., Jr.; Arteaga, Stefan; Allen, Thomas L.; Novet, Thomas

    2011-06-01

    Nanocrystal quantum dot photovoltaics and photodetectors with performance optimized by engineering the nanocrystals size and the optoelectronic properties of the nanocrystal's chemical coating are reported. Due to the large surface-to-volume ratio inherent to nanocrystals, the surface effects of ligands used to chemically coat and passivate nanocrystals play a significant role in device performance. However, the optoelectronic properties of ligands are difficult to ascertain, as the band structure of the ligand-capped nanoparticle system is complex and difficult to model. Using density-of-states measurements, we demonstrate that modeling of electropositive and electronegative substituents and use of the Hammett equation, are useful tools in optimizing nanocrystal detector performance. A new particle, the Janus-II nanoparticles, developed using 'charge-donating' and 'charge-withdrawing' ligands distributed over opposite surfaces of the nanocrystal, is described. The polarizing ligands of the Janus-II nanoparticle form a degeneracy-splitting dipole, which reduces the overlap integral between excitonic states, and thus reduces the probability of carrier recombination, allowing carrier extraction to take place more efficiently. This is shown to allow increased photodetection efficiencies and to allow the capture of multiple exciton events in working photodetectors.

  12. Formic acid-assisted synthesis of palladium nanocrystals and their electrocatalytic properties.

    PubMed

    Wang, Qinchao; Wang, Yiqian; Guo, Peizhi; Li, Qun; Ding, Ruixue; Wang, Baoyan; Li, Hongliang; Liu, Jingquan; Zhao, X S

    2014-01-14

    Palladium (Pd) nanocrystals have been synthesized by using formic acid as the reducing agent at room temperature. When the concentration of formic acid was increased continuously, the size of Pd nanocrystals first decreased to a minimum and then increased slightly again. The products have been investigated by a series of techniques, including X-ray diffraction, high-resolution transmission electron microscopy (HRTEM), UV-vis absorption, and electrochemical measurements. The formation of Pd nanocrystals is proposed to be closely related to the dynamical imbalance of the growth and dissolution rate of Pd nanocrystals associated with the adsorption of formate ions onto the surface of the intermediates. It is found that small Pd nanocrystals showed blue-shifted adsorption peaks compared with large ones. Pd nanocrystals with the smallest size display the highest electrocatalytic activity for the electrooxidation of formic acid and ethanol on the basis of cyclic voltammetry and chronoamperometric data. It is suggested that both the electrochemical active surface area and the small size effect are the key roles in determining the electrocatalytic performances of Pd nanocrystals. A "dissolution-deposition-aggregation" process is proposed to explain the variation of the electrocatalytic activity during the electrocatalysis according to the HRTEM characterization.

  13. Nuclear magnetic relaxation studies of semiconductor nanocrystals and solids

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Sachleben, Joseph Robert

    1993-09-01

    Semiconductor nanocrystals, small biomolecules, and 13C enriched solids were studied through the relaxation in NMR spectra. Surface structure of semiconductor nanocrystals (CdS) was deduced from high resolution 1H and 13C liquid state spectra of thiophenol ligands on the nanocrystal surfaces. The surface coverage by thiophenol was found to be low, being 5.6 and 26% for nanocrystal radii of 11.8 and 19.2 Å. Internal motion is estimated to be slow with a correlation time > 10 -8 s -1. The surface thiophenol ligands react to form a dithiophenol when the nanocrystals were subjected to O 2 and ultraviolet. A method formore » measuring 14N- 1H J-couplings is demonstrated on pyridine and the peptide oxytocin; selective 2D T 1 and T 2 experiments are presented for measuring relaxation times in crowded spectra with overlapping peaks in 1D, but relaxation effects interfere. Possibility of carbon-carbon cross relaxation in 13C enriched solids is demonstrated by experiments on zinc acetate and L-alanine.« less

  14. Nuclear magnetic relaxation studies of semiconductor nanocrystals and solids

    NASA Astrophysics Data System (ADS)

    Sachleben, J. R.

    1993-09-01

    Semiconductor nanocrystals, small biomolecules, and C-13 enriched solids were studied through the relaxation in NMR spectra. Surface structure of semiconductor nanocrystals (CdS) was deduced from high resolution H-1 and C-13 liquid state spectra of thiophenol ligands on the nanocrystal surfaces. The surface coverage by thiophenol was found to be low, being 5.6 and 26% for nanocrystal radii of 11.8 and 19.2 angstrom. Internal motion is estimated to be slow with a correlation time greater than 10(exp -8) s(exp -1). The surface thiophenol ligands react to form a dithiophenol when the nanocrystals were subjected to O2 and ultraviolet. A method for measuring (N-14)-(H-1) J-couplings is demonstrated on pyridine and the peptide oxytocin; selective 2D T(sub 1) and T(sub 2) experiments are presented for measuring relaxation times in crowded spectra with overlapping peaks in 1D, but relaxation effects interfere. Possibility of carbon-carbon cross relaxation in C-13 enriched solids is demonstrated by experiments on zinc acetate and L-alanine.

  15. Potentiometric Titrations for Measuring the Capacitance of Colloidal Photodoped ZnO Nanocrystals.

    PubMed

    Brozek, Carl K; Hartstein, Kimberly H; Gamelin, Daniel R

    2016-08-24

    Colloidal semiconductor nanocrystals offer a unique opportunity to bridge molecular and bulk semiconductor redox phenomena. Here, potentiometric titration is demonstrated as a method for quantifying the Fermi levels and charging potentials of free-standing colloidal n-type ZnO nanocrystals possessing between 0 and 20 conduction-band electrons per nanocrystal, corresponding to carrier densities between 0 and 1.2 × 10(20) cm(-3). Potentiometric titration of colloidal semiconductor nanocrystals has not been described previously, and little precedent exists for analogous potentiometric titration of any soluble reductants involving so many electrons. Linear changes in Fermi level vs charge-carrier density are observed for each ensemble of nanocrystals, with slopes that depend on the nanocrystal size. Analysis indicates that the ensemble nanocrystal capacitance is governed by classical surface electrical double layers, showing no evidence of quantum contributions. Systematic shifts in the Fermi level are also observed with specific changes in the identity of the charge-compensating countercation. As a simple and contactless alternative to more common thin-film-based voltammetric techniques, potentiometric titration offers a powerful new approach for quantifying the redox properties of colloidal semiconductor nanocrystals.

  16. Nanocrystal for ocular drug delivery: hope or hype.

    PubMed

    Sharma, Om Prakash; Patel, Viral; Mehta, Tejal

    2016-08-01

    The complexity of the structure and nature of the eye emanates a challenge for drug delivery to formulation scientists. Lower bioavailability concern of conventional ocular formulation provokes the interest of researchers in the development of novel drug delivery system. Nanotechnology-based formulations have been extensively investigated and found propitious in improving bioavailability of drugs by overcoming ocular barriers prevailing in the eye. The advent of nanocrystals helped in combating the problem of poorly soluble drugs specifically for oral and parenteral drug delivery and led to development of various marketed products. Nanocrystal-based formulations explored for ocular drug delivery have been found successful in achieving increase in retention time, bioavailability, and permeability of drugs across the corneal and conjunctival epithelium. In this review, we have highlighted the ocular physiology and barriers in drug delivery. A comparative analysis of various nanotechnology-based ocular formulations is done with their pros and cons. Consideration is also given to various methods of preparation of nanocrystals with their patented technology. This article highlights the success achieved in conquering various challenges of ocular delivery by the use of nanocrystals while emphasizing on its advantages and application for ocular formulation. The perspectives of nanocrystals as an emerging flipside to explore the frontiers of ocular drug delivery are discussed.

  17. Colloidal infrared reflective and transparent conductive aluminum-doped zinc oxide nanocrystals

    DOEpatents

    Buonsanti, Raffaella; Milliron, Delia J

    2015-02-24

    The present invention provides a method of preparing aluminum-doped zinc oxide (AZO) nanocrystals. In an exemplary embodiment, the method includes (1) injecting a precursor mixture of a zinc precursor, an aluminum precursor, an amine, and a fatty acid in a solution of a vicinal diol in a non-coordinating solvent, thereby resulting in a reaction mixture, (2) precipitating the nanocrystals from the reaction mixture, thereby resulting in a final precipitate, and (3) dissolving the final precipitate in an apolar solvent. The present invention also provides a dispersion. In an exemplary embodiment, the dispersion includes (1) nanocrystals that are well separated from each other, where the nanocrystals are coated with surfactants and (2) an apolar solvent where the nanocrystals are suspended in the apolar solvent. The present invention also provides a film. In an exemplary embodiment, the film includes (1) a substrate and (2) nanocrystals that are evenly distributed on the substrate.

  18. Nanocrystal Additives for Advanced Lubricants

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Cooper, Gregory; Lohuis, James; Demas, Nicholaos

    The innovations in engine and drivetrain lubricants are mainly driven by ever more stringent regulations, which demand better fuel economy, lower carbon emission, and less pollution. Many technologies are being developed for the next generations of vehicles to achieve these goals. Even if these technologies can be adopted, there still is a significant need for a “drop-in” lubricant solution for the existing ground vehicle fleet to reap immediate fuel savings at the same time reduce the pollution. Dramatic improvements were observed when Pixelligent’s proprietary, mono-dispersed, and highly scalable metal oxide nanocrystals were added to the base oils. The dispersions inmore » base and formulated oils are clear and without any change of appearance and viscosity. However, the benefits provided by the nanocrystals were limited to the base oils due to the interference of exiting additives in the fully formulated oils. Developing a prototype formulation including the nanocrystals that can demonstrate the same improvements observed in the base oils is a critical step toward the commercialization of these advanced nano-additives. A ‘bottom-up’ approach was adopted to develop a prototype lubricant formulation to avoid the complicated interactions with the multitude of additives, only minimal numbers of most essential additives are added, step by step, into the formulation, to ensure that they are compatible with the nanocrystals and do not compromise their tribological performance. Tribological performance are characterized to come up with the best formulations that can demonstrate the commercial potential of the nano-additives.« less

  19. Optical properties of Si and Ge nanocrystals: Parameter-free calculations

    NASA Astrophysics Data System (ADS)

    Ramos, L. E.; Weissker, H.-Ch.; Furthmüller, J.; Bechstedt, F.

    2005-12-01

    The cover picture of the current issue refers to the Edi-tor's Choice article of Ramos et al. [1]. The paper gives an overview of the electronic and optical properties of silicon and germanium nanocrystals determined by state-of-the-art ab initio methods. Nanocrystals have promising applications in opto-electronic devices, since they can be used to confine electrons and holes and facilitate radiative recombination. Since meas-urements for single nanoparticles are difficult to make, ab initio theoretical investigations become important to understand the mechanisms of luminescence.The cover picture shows nanocrystals of four sizes with tetrahedral coordination whose dangling bonds at the surface are passivated with hydrogen. As often observed in experiments, the nanocrystals are not perfectly spherical, but contain facets. Apart from the size of the nanocrystals, which determines the quantum confinement, the way their dangling bonds are passivated is relevant for their electronic and optical properties. For instance, the passivation with hydroxyls reduces the quantum confine-ment. On the other hand, the oxidation of the silicon nanocrys-tals increases the quantum confinement and reduces the effect of single surface terminations on the gap. Due to the oscillator strengths of the lowest-energy optical transitions, Ge nanocrys-tals are in principle more suitable for opto-electronic applica-tions than Si nanocrystals.The first author, Luis E. Ramos, is a postdoc at the Institute of Solid-State Physics and Optics (IFTO), Friedrich-Schiller University Jena, Germany. He investigates electronic and optical properties of semiconductor nanocrystallites and is a member of the European Network of Excellence NANO-QUANTA and of the European Theoretical Spectroscopy Facility (ETSF).

  20. Optical Properties of Nanocrystal Interfaces in Compressed MgO Nanopowders

    PubMed Central

    2011-01-01

    The optical properties and charge trapping phenomena observed on oxide nanocrystal ensembles can be strongly influenced by the presence of nanocrystal interfaces. MgO powders represent a convenient system to study these effects due to the well-defined shape and controllable size distributions of MgO nanocrystals. The spectroscopic properties of nanocrystal interfaces are investigated by monitoring the dependence of absorption characteristics on the concentration of the interfaces in the nanopowders. The presence of interfaces is found to affect the absorption spectra of nanopowders more significantly than changing the size of the constituent nanocrystals and, thus, leading to the variation of the relative abundance of light-absorbing surface structures. We find a strong absorption band in the 4.0−5.5 eV energy range, which was previously attributed to surface features of individual nanocrystals, such as corners and edges. These findings are supported by complementary first-principles calculations. The possibility to directly address such interfaces by tuning the energy of excitation may provide new means for functionalization and chemical activation of nanostructures and can help improve performance and reliability for many nanopowder applications. PMID:21443262

  1. Increased electronic coupling in silicon nanocrystal networks doped with F4-TCNQ.

    PubMed

    Carvalho, Alexandra; Oberg, Sven; Rayson, Mark J; Briddon, Patrick R

    2013-02-01

    The modification of the electronic structure of silicon nanocrystals using an organic dopant, 2,3,5,6-tetrafluoro-7,7,8,8-tetracyanoquinodimethane (F4-TCNQ), is investigated using first-principles calculations. It is shown that physisorbed F4-TCNQ molecules have the effect of oxidizing the nanocrystal, attracting the charge density towards the F4-TCNQ-nanocrystal interface, and decreasing the excitation energy of the system. In periodic F4-TCNQ/nanocrystal superlattices, F4-TCNQ is suggested to enhance exciton separation, and in the presence of free holes, to serve as a bridge for electron/hole transfer between adjacent nanocrystals.

  2. Synthesis of icosahedral gold nanocrystals: a thermal process strategy.

    PubMed

    Zhou, Min; Chen, Shenhao; Zhao, Shiyong

    2006-03-16

    We demonstrate a one-step thermal process route to the synthesis of icosahedral gold nanocrystals. By regulating the concentrations of poly(vinyl pyrrolidone) (PVP) and HAuCl4 or changing the temperature, we can readily access the shapes of icosahedral nanocrystals with good uniformity. These gold nanostructures, with unique geometrical shapes, might find use in areas that include photonics, optoelectronics, and optical sensing. We also observed that these gold nanocrystals have a strong tendency to be immobilized spontaneously on the glass substrate.

  3. Lifetime of excitons localized in Si nanocrystals in amorphous silicon

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Gusev, O. B.; Belolipetskiy, A. V., E-mail: alexey.belolipetskiy@mail.ioffe.ru; Yassievich, I. N.

    2016-05-15

    The introduction of nanocrystals plays an important role in improving the stability of the amorphous silicon films and increasing the carrier mobility. Here we report results of the study on the photoluminescence and its dynamics in the films of amorphous hydrogenated silicon containing less than 10% of silicon nanocrystals. The comparing of the obtained experimental results with the calculated probability of the resonant tunneling of the excitons localized in silicon nanocrystals is presented. Thus, it has been estimated that the short lifetime of excitons localized in Si nanocrystal is controlled by the resonant tunneling to the nearest tail state ofmore » the amorphous matrix.« less

  4. Recent Progress in Photocatalysis Mediated by Colloidal II-VI Nanocrystals

    PubMed Central

    Wilker, Molly B; Schnitzenbaumer, Kyle J; Dukovic, Gordana

    2012-01-01

    The use of photoexcited electrons and holes in semiconductor nanocrystals as reduction and oxidation reagents is an intriguing way of harvesting photon energy to drive chemical reactions. This review focuses on recent research efforts to understand and control the photocatalytic processes mediated by colloidal II-VI nanocrystalline materials, such as cadmium and zinc chalcogenides. First, we highlight how nanocrystal properties govern the rates and efficiencies of charge-transfer processes relevant to photocatalysis. We then describe the use of nanocrystal catalyst heterostructures for fuel-forming reactions, most commonly H2 generation. Finally, we review the use of nanocrystal photocatalysis as a synthetic tool for metal–semiconductor nano-heterostructures. PMID:24115781

  5. Ligand Exchange Governs the Crystal Structures in Binary Nanocrystal Superlattices.

    PubMed

    Wei, Jingjing; Schaeffer, Nicolas; Pileni, Marie-Paule

    2015-11-25

    The surface chemistry in colloidal nanocrystals on the final crystalline structure of binary superlattices produced by self-assembly of two sets of nanocrystals is hereby demonstrated. By mixing nanocrystals having two different sizes and the same coating agent, oleylamine (OAM), the binary nanocrystal superlattices that are produced, such as NaCl, AlB2, NaZn13, and MgZn2, are well in agreement with the crystalline structures predicted by the hard-sphere model, their formation being purely driven by entropic forces. By opposition, when large and small nanocrystals are coated with two different ligands [OAM and dodecanethiol (DDT), respectively] while keeping all other experimental conditions unchanged, the final binary structures markedly change and various structures with lower packing densities, such as Cu3Au, CaB6, and quasicrystals, are observed. This effect of the nanocrystals' coating agents could also be extended to other binary systems, such as Ag-Au and CoFe2O4-Ag supracrystalline binary lattices. In order to understand this effect, a mechanism based on ligand exchange process is proposed. Ligand exchange mechanism is believed to affect the thermodynamics in the formation of binary systems composed of two sets of nanocrystals with different sizes and bearing two different coating agents. Hence, the formation of binary superlattices with lower packing densities may be favored kinetically because the required energetic penalty is smaller than that of a denser structure.

  6. Atomic force microscopy nanomanipulation of silicon nanocrystals for nanodevice fabrication

    NASA Astrophysics Data System (ADS)

    Decossas, Sébastien; Mazen, Frédéric; Baron, Thierry; Brémond, Georges; Souifi, Abdelkader

    2003-12-01

    An atomic force microscopy (AFM) tip has been used to manipulate silicon nanocrystals deposited by low-pressure chemical vapour deposition on thermally oxidized p-type Si wafer. Three nanomanipulation methods are presented. The first one catches a nanocrystal with the AFM tip and deposits it elsewhere: the tip is used as an electrostatic 'nano-crane'. The second one simultaneously manipulates a set of nanocrystals in order to draw well-defined unidimensional lines: the tip is used as a 'nano-broom'. The third one manipulates individual nanocrystals with a precision of about 10 nm using both oscillating and contact AFM modes. Switching from strong interaction forces (chemical) to weak ones (van der Waals, electrostatic or capillarity) is the basis of these manipulation methods. We have applied the second method to connect two electrodes drawn by e-beam and lift-off with a 70 nm long silicon nanocrystal chain. Current versus voltage characterization of the nanofabricated device shows that the increase in nanocrystal density gives rise to conduction between the connected electrodes. Resonant tunnelling effects resulting from Si nanocrystal (nc-Si) multiple tunnel junctions have been observed at 300 K. We also show that offset charges directly influence the position of the resonant tunnelling peaks. Finally, the possibility of manipulating nc-Si with a diameter of around 5 nm is shown to be a promising way to fabricate single electron devices operating at room temperature and fully compatible with silicon technology.

  7. Band gap and composition engineering on a nanocrystal (BCEN) in solution.

    PubMed

    Peng, Xiaogang

    2010-11-16

    Colloidal nanocrystals with "artificial" composition and electron band structure promise to expand the fields of nanomaterials and inorganic chemistry. Despite their promise as functional materials, the fundamental science associated with the synthesis, characterization, and properties of colloidal nanocrystals is still in its infancy and deserves systematic study. Furthermore, such studies are important for our basic understanding of crystallization, surface science, and solid state chemistry. "Band gap and composition engineering on a nanocrystal" (BCEN) refers to the synthesis of a colloidal nanocrystal with composition and/or electron energy band structure that are not found in natural bulk crystals. The BCEN nanostructure shown in the Figure includes a magnetic domain for the separation and recycling of the complex nanostructure, a photoactivated catalytic center, and an additional chemical catalytic center. A thin but porous film (such as a silicate) might be coated onto the nanocrystal, both to provide chemical stability and to isolate the reaction processes from the bulk solution. This example is a catalytic complex analogous to an enzyme that facilitates two sequential reactions in a microenvironment different from bulk solution. The synthesis of colloidal nanocrystals has advanced by a quantum leap in the past two decades. The field now seems ready to extend colloidal nanocrystal synthesis into the BCEN regime. Although BCEN is a very new branch of synthetic chemistry, this Account describes advances in related synthetic and characterization techniques that can serve as a useful starting point for this new area of investigation. To put these ideas into context, this Account compares this new field with organic synthesis, the most developed branch in synthetic chemistry. The structural and functional diversity of organic compounds results from extending design and synthesis beyond the construction of natural organic compounds. If this idea also holds true

  8. Systems and methods of detecting force and stress using tetrapod nanocrystal

    DOEpatents

    Choi, Charina L.; Koski, Kristie J.; Sivasankar, Sanjeevi; Alivisatos, A. Paul

    2013-08-20

    Systems and methods of detecting force on the nanoscale including methods for detecting force using a tetrapod nanocrystal by exposing the tetrapod nanocrystal to light, which produces a luminescent response by the tetrapod nanocrystal. The method continues with detecting a difference in the luminescent response by the tetrapod nanocrystal relative to a base luminescent response that indicates a force between a first and second medium or stresses or strains experienced within a material. Such systems and methods find use with biological systems to measure forces in biological events or interactions.

  9. 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

  10. Metal Sulfide Nanocrystals inside Ferritin with Photovoltaic Applications

    NASA Astrophysics Data System (ADS)

    Hansen, Kameron; Peterson, J. Ryan; Olsen, Cameron; Hogg, Heather; Colton, John; Watt, Richard; Colton Team

    Ferritin is a spherical protein shell used universally by organisms to store iron. Due to a number of ferritin's properties (a conductive shell, ability to be arranged in ordered arrays, and high stability), recent theoretical work has proposed that non-native semiconductor nanocrystals inside ferritin can be used for high-efficiency solar energy conversion. We present research on the synthesis of a variety of these nanocrystals (PbS, CuS, Mo2S, ZnS, and PbSe) inside ferritin's hollow interior and band gap energies of the resulting ferritin-nanocrystal constructs. We also report preliminary solar cell results for dye sensitized solar cells with PbS-ferritin as the dye.

  11. Surface treatment of nanocrystal quantum dots after film deposition

    DOEpatents

    Sykora, Milan; Koposov, Alexey; Fuke, Nobuhiro

    2015-02-03

    Provided are methods of surface treatment of nanocrystal quantum dots after film deposition so as to exchange the native ligands of the quantum dots for exchange ligands that result in improvement in charge extraction from the nanocrystals.

  12. Hierarchial Junction Solar Cells Based on Hyper-Branched Semiconductor Nanocrystals

    DTIC Science & Technology

    2009-06-30

    Hyper-Branched Semiconductor Nanocrystals 4 2. Cu2S- CdS all-inorganic nanocrystal solar cells. We demonstrated the rational synthesis of... Hydrothermal Synthesis of Single Phase Pyrite FeS2 Nanocrystals. We demonstrated a single-source molecular precursor that can be used for the synthesis ... CdS Semiconductor Nanostructures,” Advanced Materials, (2008), 20(22), 4306. Y. Wu, C. Wadia, W. Ma, B. Sadtler, A. P. Alivisatos, “ Synthesis of

  13. Synthesis, characterization and design of a nanocrystal based photovoltaic device

    NASA Astrophysics Data System (ADS)

    Erwin, Mary Margaret

    Nanocomposites have shown promise as the active layer for photovoltaic energy conversion. Devices consisting of CdSe nanocrystals and semiconducting polymer, and devices consisting of C60 and semiconducting polymer have been recently investigated. This work will present the rational design, synthesis, fabrication and characterization of a nanocomposite photovoltaic device-containing Poly 3-hexylthiophene (P3HT), Cadmium Selenium (CdSe) nanocrystals, and C60. The use of these three components allows for a dedicated light harvester, CdSe nanocrystals, a dedicated hole transporter, P3HT, and a dedicated electron transporter, C60. Two primary premises were investigated in this work; first what effect the size of the nanocrystal would have on the efficiency of the devices and second would the addition of C 60 to a CdSe nanocrystal/semiconducting polymer device increase the efficiency of the devices. Three sizes of CdSe nanocrystals (30A, 45A, and 72A) were used in the photoactive layer. Five different composites were used for the photoactive layer ranging from 20% CdSe or C60 to 80% CdSe or C60 of each size of CdSe nanocrystal, while the percentage of P3HT was held constant at 20%. All of the composites were tested at 514 nm at 5 W/m2 and at the industry standard of AM 1.5 at 1000 W/m2 (1 sun). After all the results were analyzed, it was seen that with the addition of C60 only a small percentage of CdSe nanocrystals would be required to make an efficient device, thus making this device cost effective and with more research a viable new source of photovoltaic energy.

  14. Synthesis and spectroscopic properties of silica-dye-semiconductor nanocrystal hybrid particles.

    PubMed

    Ren, Ting; Erker, Wolfgang; Basché, Thomas; Schärtl, Wolfgang

    2010-12-07

    We prepared silica-dye-nanocrystal hybrid particles and studied the energy transfer from semiconductor nanocrystals (= donor) to organic dye molecules (= acceptor). Multishell CdSe/CdS/ZnS semiconductor nanocrystals were adsorbed onto monodisperse Stöber silica particles with an outer silica shell of thickness 2-23 nm containing organic dye molecules (Texas Red). The thickness of this dye layer has a strong effect on the energy transfer efficiency, which is explained by the increase in the number of dye molecules homogeneously distributed within the silica shell, in combination with an enhanced surface adsorption of nanocrystals with increasing dye amount. Our conclusions were underlined by comparison of the experimental results with numerically calculated FRET efficiencies and by control experiments confirming attractive interaction between the nanocrystals and Texas Red freely dissolved in solution.

  15. Emission efficiency limit of Si nanocrystals

    PubMed Central

    Limpens, Rens; Luxembourg, Stefan L.; Weeber, Arthur W.; Gregorkiewicz, Tom

    2016-01-01

    One of the important obstacles on the way to application of Si nanocrystals for development of practical devices is their typically low emissivity. In this study we explore the limits of external quantum yield of photoluminescence of solid-state dispersions of Si nanocrystals in SiO2. By making use of a low-temperature hydrogen passivation treatment we demonstrate a maximum emission quantum efficiency of approximately 35%. This is the highest value ever reported for this type of material. By cross-correlating PL lifetime with EQE values, we obtain a comprehensive understanding of the efficiency limiting processes induced by Pb-defects. We establish that the observed record efficiency corresponds to an interface density of Pb-centers of 1.3 × 1012 cm12, which is 2 orders of magnitude higher than for the best Si/SiO2 interface. This result implies that Si nanocrystals with up to 100% emission efficiency are feasible. PMID:26786062

  16. Deep level transient spectroscopy (DLTS) on colloidal-synthesized nanocrystal solids.

    PubMed

    Bozyigit, Deniz; Jakob, Michael; Yarema, Olesya; Wood, Vanessa

    2013-04-24

    We demonstrate current-based, deep level transient spectroscopy (DLTS) on semiconductor nanocrystal solids to obtain quantitative information on deep-lying trap states, which play an important role in the electronic transport properties of these novel solids and impact optoelectronic device performance. Here, we apply this purely electrical measurement to an ethanedithiol-treated, PbS nanocrystal solid and find a deep trap with an activation energy of 0.40 eV and a density of NT = 1.7 × 10(17) cm(-3). We use these findings to draw and interpret band structure models to gain insight into charge transport in PbS nanocrystal solids and the operation of PbS nanocrystal-based solar cells.

  17. Protein unfolding versus β-sheet separation in spider silk nanocrystals

    NASA Astrophysics Data System (ADS)

    Alam, Parvez

    2014-03-01

    In this communication a mechanism for spider silk strain hardening is proposed. Shear failure of β-sheet nanocrystals is the first failure mode that gives rise to the creation of smaller nanocrystals, which are of higher strength and stiffness. β-sheet unfolding requires more energy than nanocrystal separation in a shear mode of failure. As a result, unfolding occurs after the nanocrystals separate in shear. β-sheet unfolding yields a secondary strain hardening effect once the β-sheet conformation is geometrically stable and acts like a unidirectional fibre in a fibre reinforced composite. The mechanism suggested herein is based on molecular dynamics calculations of residual inter-β-sheet separation strengths against residual intra-β-sheet unfolding strengths.

  18. Nanocrystal assembly for bottom-up plasmonic materials

    NASA Astrophysics Data System (ADS)

    Tao, Andrea Rae

    2007-12-01

    Plasmonic materials are emerging as key platforms for applications that rely on the manipulation of light at small length scales. Materials that possess sub-wavelength metallic features support either localized or propagating surface plasmons that can induce huge local electromagnetic fields at the metal surface, facilitating a host of extraordinary optical phenomena. For many of the breakthrough photonic, spectroscopic, and optoelectronic applications of plasmonics, the bottom-up fabrication of these materials from low-dimensional structures has yet to be explored. Because colloidal metal nanostructures can be readily synthesized with controlled shapes and sizes, and because these structures also generate plasmon-mediated evanescent fields near their surfaces when irradiated with light, Ag nanocrystals and nanowires are ideal building blocks for rationally designed plasmonic materials. This dissertation addresses three major challenges: (1) the synthesis of Ag polyhedral nanocrystals and nanowires, (2) the bottom-up organization of these nanostructures into one-, two-, and three-dimensional assemblies, and (3) the application of these assemblies as spectroscopic sensing platforms. Faceted Ag colloids were synthesized in high yield and with remarkable monodispersity using the polyol process, where Ag+ is reduced in the presence of a polymer capping agent that serves to regulate nucleation and crystallographic growth direction. The resulting nanocrystals and nanowires are bound exclusively by {100} and {111} crystal planes, where nanowires possess pentagonal cross-sections and nanocrystals possess octahedral symmetry. Because allowed plasmon modes are explicitly dictated by geometric considerations, each shape exhibits a unique scattering spectrum in the optical wavelengths. These shaped colloidal building blocks were assembled into ordered groupings and superlattices to achieve controlled electromagnetic coupling between individual nanostructures. Of particular

  19. General method for the synthesis of hierarchical nanocrystal-based mesoporous materials.

    PubMed

    Rauda, Iris E; Buonsanti, Raffaella; Saldarriaga-Lopez, Laura C; Benjauthrit, Kanokraj; Schelhas, Laura T; Stefik, Morgan; Augustyn, Veronica; Ko, Jesse; Dunn, Bruce; Wiesner, Ulrich; Milliron, Delia J; Tolbert, Sarah H

    2012-07-24

    Block copolymer templating of inorganic materials is a robust method for the production of nanoporous materials. The method is limited, however, by the fact that the molecular inorganic precursors commonly used generally form amorphous porous materials that often cannot be crystallized with retention of porosity. To overcome this issue, here we present a general method for the production of templated mesoporous materials from preformed nanocrystal building blocks. The work takes advantage of recent synthetic advances that allow organic ligands to be stripped off of the surface of nanocrystals to produce soluble, charge-stabilized colloids. Nanocrystals then undergo evaporation-induced co-assembly with amphiphilic diblock copolymers to form a nanostructured inorganic/organic composite. Thermal degradation of the polymer template results in nanocrystal-based mesoporous materials. Here, we show that this method can be applied to nanocrystals with a broad range of compositions and sizes, and that assembly of nanocrystals can be carried out using a broad family of polymer templates. The resultant materials show disordered but homogeneous mesoporosity that can be tuned through the choice of template. The materials also show significant microporosity, formed by the agglomerated nanocrystals, and this porosity can be tuned by the nanocrystal size. We demonstrate through careful selection of the synthetic components that specifically designed nanostructured materials can be constructed. Because of the combination of open and interconnected porosity, high surface area, and compositional tunability, these materials are likely to find uses in a broad range of applications. For example, enhanced charge storage kinetics in nanoporous Mn(3)O(4) is demonstrated here.

  20. The aggregation and characteristics of radiation-induced defects in lithium fluoride nanocrystals

    NASA Astrophysics Data System (ADS)

    Voitovich, A. P.; Kalinov, V. S.; Korzhik, M. V.; Martynovich, E. F.; Runets, L. P.; Stupak, A. P.

    2013-02-01

    It has been established that diffusion activation energies for anion vacancies and centres ? in lithium fluoride nanocrystals are higher than those in bulk crystals. In nanocrystals, ? centres migrating in the range of the temperature close to room temperature is not observed and these centres remain stable. The ratio of centres ? and F 2 concentrations in nanocrystals is higher than in bulk crystals. A new type of colour centres, which is absent in bulk crystals, is discovered in nanocrystals.

  1. Animal left-right asymmetry.

    PubMed

    Blum, Martin; Ott, Tim

    2018-04-02

    Symmetry is appealing, be it in architecture, art or facial expression, where symmetry is a key feature to finding someone attractive or not. Yet, asymmetries are widespread in nature, not as an erroneous deviation from the norm but as a way to adapt to the prevailing environmental conditions at a time. Asymmetries in many cases are actively selected for: they might well have increased the evolutionary fitness of a species. Even many single-celled organisms are built asymmetrically, such as the pear-shaped ciliate Paramecium, which may depend on its asymmetry to navigate towards the oxygen-richer surface of turbid waters, at least based on modeling. Everybody knows the lobster with its asymmetric pair of claws, the large crusher usually on the left and the smaller cutter on the right. Snail shells coil asymmetrically, as do the organs they house. Organ asymmetries are found throughout the animal kingdom, referring to asymmetric positioning, asymmetric morphology or both, with the vertebrate heart being an example for the latter. Functional asymmetries, such as that of the human brain with its localization of the language center in one hemisphere, add to the complexity of organ asymmetries and presumably played a decisive role for sociocultural evolution. The evolutionary origin of organ asymmetries may have been a longer than body length gut, which allows efficient retrieval of nutrients, and the need to stow a long gut in the body cavity in an orderly manner that ensures optimal functioning. Vertebrate organ asymmetries (situs solitus) are quite sophisticated: in humans, the apex of the asymmetrically built heart points to the left; the lung in turn, due to space restrictions, has fewer lobes on the left than on the right side (two versus three in humans), stomach and spleen are found on the left, the liver on the right, and small and large intestine coil in a chiral manner (Figure 1A). In very rare cases (1:10,000), the organ situs is inverted (situs inversus

  2. Process for forming shaped group III-V semiconductor nanocrystals, and product formed using process

    DOEpatents

    Alivisatos, A. Paul; Peng, Xiaogang; Manna, Liberato

    2001-01-01

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

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

    DOEpatents

    Alivisatos, A. Paul; Peng, Xiaogang; Manna, Liberato

    2001-01-01

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

  4. Syntheses and applications of manganese-doped II-VI semiconductor nanocrystals

    NASA Astrophysics Data System (ADS)

    Yang, Heesun

    Syntheses, characterizations, and applications of two different Mn-doped semiconductor nanocrystals, ZnS:Mn and CdS:Mn/ZnS core/shell, were investigated. ZnS:Mn nanocrystals with sizes between 3 and 4 nm were synthesized via a competitive reaction chemistry. A direct current (dc) electroluminescent (EL) device having a hybrid organic/inorganic multilayer structure of an indium tin oxide (ITO) transparent conducting electrode, a (poly(3,4-ethylenedioxythiophene)/poly(styrenesulfonate) (PEDOT-PSS) and a poly(N-vinylcarbazole) (PVK) bilayer hole transport film, a ZnS:Mn nanocrystal layer, and Al dot contacts was demonstrated to emit blue (˜445 and ˜495 nm) from PVK and yellow (˜600 nm) light from Mn activator in ZnS. The EL emission spectrum was dependent upon both the voltage and Mn concentration, showing a decreasing nanocrystal to PVK emission ratio from 10 at 20 V to 4 at 28 V, and an increasing ratio from 1.3 at 0.40 mol % to 4.3 at 2.14 mol %. Mn-doped CdS core nanocrystals were produced ranging from 1.5 to 2.3 nm in diameter with a ZnS shell via a reverse micelle process. In contrast to CdS:Mn nanocrystals passivated by n-dodecanethiol, ZnS-passivated CdS:Mn (CdS:Mn/ZnS core/shell) nanocrystals were efficient and photostable. CdS:Mn/ZnS core/shell nanocrystals exhibited a quantum yield of ˜18%, and the photoluminescence (PL) intensity increased by 40% after 400 nm UV irradiation in air. X-ray photoelectron spectroscopy (XPS) data showed that UV irradiation of CdS:Mn/ZnS nanocrystals induces the photooxidation of the ZnS shell surface to ZnSO4. This photooxidation product is presumably responsible for the increased PL emission by serving as a passivating surface layer. Luminescent lifetime data from the core/shell nanocrystals could be fit with two exponential functions, with a time constant of ˜170 nsec for the defect-related centers and of ˜1 msec for the Mn centers. The CdS:Mn/ZnS nanocrystals with a core crystal diameter of 2.3 nm and a 0.4 nm thick Zn

  5. CO2 controlled flocculation of microalgae using pH responsive cellulose nanocrystals

    NASA Astrophysics Data System (ADS)

    Eyley, Samuel; Vandamme, Dries; Lama, Sanjaya; van den Mooter, Guy; Muylaert, Koenraad; Thielemans, Wim

    2015-08-01

    Cellulose nanocrystals were grafted with imidazole functionalities up to DS 0.06 using a one-pot functionalization strategy. The resulting nanocrystals were shown to have a pH responsive surface charge which was found to be positive below pH 6 and negative above pH 7. These imidazolyl cellulose nanocrystals were tested for flocculation of Chlorella vulgaris using CO2 to induce flocculation. Up to 90% flocculation efficiency was achieved with 200 mg L-1 dose. Furthermore, the modified cellulose nanocrystals showed good compatibility with the microalgae during cultivation, giving potential for the production of reversible flocculation systems.Cellulose nanocrystals were grafted with imidazole functionalities up to DS 0.06 using a one-pot functionalization strategy. The resulting nanocrystals were shown to have a pH responsive surface charge which was found to be positive below pH 6 and negative above pH 7. These imidazolyl cellulose nanocrystals were tested for flocculation of Chlorella vulgaris using CO2 to induce flocculation. Up to 90% flocculation efficiency was achieved with 200 mg L-1 dose. Furthermore, the modified cellulose nanocrystals showed good compatibility with the microalgae during cultivation, giving potential for the production of reversible flocculation systems. Electronic supplementary information (ESI) available: Spectra for all products. See DOI: 10.1039/C5NR03853G

  6. Quantifying asymmetry: ratios and alternatives.

    PubMed

    Franks, Erin M; Cabo, Luis L

    2014-08-01

    Traditionally, the study of metric skeletal asymmetry has relied largely on univariate analyses, utilizing ratio transformations when the goal is comparing asymmetries in skeletal elements or populations of dissimilar dimensions. Under this approach, raw asymmetries are divided by a size marker, such as a bilateral average, in an attempt to produce size-free asymmetry indices. Henceforth, this will be referred to as "controlling for size" (see Smith: Curr Anthropol 46 (2005) 249-273). Ratios obtained in this manner often require further transformations to interpret the meaning and sources of asymmetry. This model frequently ignores the fundamental assumption of ratios: the relationship between the variables entered in the ratio must be isometric. Violations of this assumption can obscure existing asymmetries and render spurious results. In this study, we examined the performance of the classic indices in detecting and portraying the asymmetry patterns in four human appendicular bones and explored potential methodological alternatives. Examination of the ratio model revealed that it does not fulfill its intended goals in the bones examined, as the numerator and denominator are independent in all cases. The ratios also introduced strong biases in the comparisons between different elements and variables, generating spurious asymmetry patterns. Multivariate analyses strongly suggest that any transformation to control for overall size or variable range must be conducted before, rather than after, calculating the asymmetries. A combination of exploratory multivariate techniques, such as Principal Components Analysis, and confirmatory linear methods, such as regression and analysis of covariance, appear as a promising and powerful alternative to the use of ratios. © 2014 Wiley Periodicals, Inc.

  7. Alkyl Passivation and Amphiphilic Polymer Coating of Silicon Nanocrystals for Diagnostic Imaging

    PubMed Central

    Hessel, Colin M.; Rasch, Michael R.; Hueso, Jose L.; Goodfellow, Brian W.; Akhavan, Vahid A.; Puvanakrishnan, Priyaveena; Tunnell, James W.

    2011-01-01

    We show a method to produce biocompatible polymer-coated silicon (Si) nanocrystals for medical imaging. Silica-embedded Si nanocrystals are formed by HSQ thermolysis. The nanocrystals are then liberated from the oxide and terminated with Si-H bonds by HF etching, followed by alkyl monolayer passivation by thermal hydrosilylation. The Si nanocrystals have an average diameter of 2.1 ± 0.6 nm and photoluminesce (PL) with a peak emission wavelength of 650 nm, which lies within the transmission window of 650–900 nm that is useful for biological imaging. The hydrophobic Si nanocrystals are then coated with an amphiphilic polymer for dispersion in aqueous media with pH ranging between 7 and 10 and ionic strength between 30 mM and 2 M, while maintaining a bright and stable PL and a hydrodynamic radius of only 20 nm. Fluorescence imaging of polymer-coated Si nanocrystals in a biological tissue host is demonstrated, showing the potential for in vivo imaging. PMID:20818646

  8. Spindly cobalt ferrite nanocrystals: preparation, characterization and magnetic properties.

    PubMed

    Cao, Xuebo; Gu, Li

    2005-02-01

    In this paper we describe the preparation of homogeneously needle-shaped cobalt ferrite (CoFe(2)O(4)) nanocrystals on a large scale through the smooth decomposition of urea and the resulting co-precipitation of Co(2+) and Fe(3+) in oleic acid micelles. Furthermore, we found that other ferrite nanocrystals with a needle-like shape, such as zinc ferrite (ZnFe(2)O(4)) and nickel ferrite (NiFe(2)O(4)), can be prepared by the same process. Needle-shaped CoFe(2)O(4) nanocrystals dispersed in an aqueous solution containing oleic acid exhibit excellent stability and the formed colloid does not produce any precipitations after two months, which is of prime importance if these materials are applied in magnetic fluids. X-ray diffraction (XRD) measurements were used to characterize the phase and component of the co-precipitation products, and demonstrate that they are spinel ferrite with a cubic symmetry. Transmission electron microscopy (TEM) observation showed that all the nanocrystals present a needle-like shape with a 22 nm short axis and an aspect ratio of around 6. Varying the concentration of oleic acid did not bring about any obvious influence on the size distribution and shapes of CoFe(2)O(4). The magnetic properties of the needle-shaped CoFe(2)O(4) nanocrystals were evaluated by using a vibrating sample magnetometer (VSM), electron paramagnetic resonance (EPR), and a Mössbauer spectrometer, and the results all demonstrated that CoFe(2)O(4) nanocrystals were superparamagnetic at room temperature.

  9. High-purity Cu nanocrystal synthesis by a dynamic decomposition method.

    PubMed

    Jian, Xian; Cao, Yu; Chen, Guozhang; Wang, Chao; Tang, Hui; Yin, Liangjun; Luan, Chunhong; Liang, Yinglin; Jiang, Jing; Wu, Sixin; Zeng, Qing; Wang, Fei; Zhang, Chengui

    2014-12-01

    Cu nanocrystals are applied extensively in several fields, particularly in the microelectron, sensor, and catalysis. The catalytic behavior of Cu nanocrystals depends mainly on the structure and particle size. In this work, formation of high-purity Cu nanocrystals is studied using a common chemical vapor deposition precursor of cupric tartrate. This process is investigated through a combined experimental and computational approach. The decomposition kinetics is researched via differential scanning calorimetry and thermogravimetric analysis using Flynn-Wall-Ozawa, Kissinger, and Starink methods. The growth was found to be influenced by the factors of reaction temperature, protective gas, and time. And microstructural and thermal characterizations were performed by X-ray diffraction, scanning electron microscopy, transmission electron microscopy, and differential scanning calorimetry. Decomposition of cupric tartrate at different temperatures was simulated by density functional theory calculations under the generalized gradient approximation. High crystalline Cu nanocrystals without floccules were obtained from thermal decomposition of cupric tartrate at 271°C for 8 h under Ar. This general approach paves a way to controllable synthesis of Cu nanocrystals with high purity.

  10. High-purity Cu nanocrystal synthesis by a dynamic decomposition method

    NASA Astrophysics Data System (ADS)

    Jian, Xian; Cao, Yu; Chen, Guozhang; Wang, Chao; Tang, Hui; Yin, Liangjun; Luan, Chunhong; Liang, Yinglin; Jiang, Jing; Wu, Sixin; Zeng, Qing; Wang, Fei; Zhang, Chengui

    2014-12-01

    Cu nanocrystals are applied extensively in several fields, particularly in the microelectron, sensor, and catalysis. The catalytic behavior of Cu nanocrystals depends mainly on the structure and particle size. In this work, formation of high-purity Cu nanocrystals is studied using a common chemical vapor deposition precursor of cupric tartrate. This process is investigated through a combined experimental and computational approach. The decomposition kinetics is researched via differential scanning calorimetry and thermogravimetric analysis using Flynn-Wall-Ozawa, Kissinger, and Starink methods. The growth was found to be influenced by the factors of reaction temperature, protective gas, and time. And microstructural and thermal characterizations were performed by X-ray diffraction, scanning electron microscopy, transmission electron microscopy, and differential scanning calorimetry. Decomposition of cupric tartrate at different temperatures was simulated by density functional theory calculations under the generalized gradient approximation. High crystalline Cu nanocrystals without floccules were obtained from thermal decomposition of cupric tartrate at 271°C for 8 h under Ar. This general approach paves a way to controllable synthesis of Cu nanocrystals with high purity.

  11. Asymmetry in the epithalamus of vertebrates

    PubMed Central

    L. CONCHA, MIGUEL; W. WILSON, STEPHEN

    2001-01-01

    The epithalamus is a major subdivision of the diencephalon constituted by the habenular nuclei and pineal complex. Structural asymmetries in this region are widespread amongst vertebrates and involve differences in size, neuronal organisation, neurochemistry and connectivity. In species that possess a photoreceptive parapineal organ, this structure projects asymmetrically to the left habenula, and in teleosts it is also situated on the left side of the brain. Asymmetries in size between the left and right sides of the habenula are often associated with asymmetries in neuronal organisation, although these two types of asymmetry follow different evolutionary courses. While the former is more conspicuous in fishes (with the exception of teleosts), asymmetries in neuronal organisation are more robust in amphibia and reptiles. Connectivity of the parapineal organ with the left habenula is not always coupled with asymmetries in habenular size and/or neuronal organisation suggesting that, at least in some species, assignment of parapineal and habenular asymmetries may be independent events. The evolutionary origins of epithalamic structures are uncertain but asymmetry in this region is likely to have existed at the origin of the vertebrate, perhaps even the chordate, lineage. In at least some extant vertebrate species, epithalamic asymmetries are established early in development, suggesting a genetic regulation of asymmetry. In some cases, epigenetic factors such as hormones also influence the development of sexually dimorphic habenular asymmetries. Although the genetic and developmental mechanisms by which neuroanatomical asymmetries are established remain obscure, some clues regarding the mechanisms underlying laterality decisions have recently come from studies in zebrafish. The Nodal signalling pathway regulates laterality by biasing an otherwise stochastic laterality decision to the left side of the epithalamus. This genetic mechanism ensures a consistency of

  12. Exciton-Delocalizing Ligands Can Speed Up Energy Migration in Nanocrystal Solids.

    PubMed

    Azzaro, Michael S; Dodin, Amro; Zhang, Diana Y; Willard, Adam P; Roberts, Sean T

    2018-05-09

    Researchers have long sought to use surface ligands to enhance energy migration in nanocrystal solids by decreasing the physical separation between nanocrystals and strengthening their electronic coupling. Exciton-delocalizing ligands, which possess frontier molecular orbitals that strongly mix with nanocrystal band-edge states, are well-suited for this role because they can facilitate carrier-wave function extension beyond the nanocrystal core, reducing barriers for energy transfer. This report details the use of the exciton-delocalizing ligand phenyldithiocarbamate (PDTC) to tune the transport rate and diffusion length of excitons in CdSe nanocrystal solids. A film composed of oleate-terminated CdSe nanocrystals is subjected to a solid-state ligand exchange to replace oleate with PDTC. Exciton migration in the films is subsequently investigated by femtosecond transient absorption. Our experiments indicate that the treatment of nanocrystal films with PDTC leads to rapid (∼400 fs) downhill energy migration (∼80 meV), while no such migration occurs in oleate-capped films. Kinetic Monte Carlo simulations allow us to extract both rates and length scales for exciton diffusion in PDTC-treated films. These simulations reproduce dynamics observed in transient absorption measurements over a range of temperatures and confirm excitons hop via a Miller-Abrahams mechanism. Importantly, our experiments and simulations show PDTC treatment increases the exciton hopping rate to 200 fs, an improvement of 5 orders of magnitude relative to oleate-capped films. This exciton hopping rate stands as one of the fastest determined for CdSe solids. The facile, room-temperature processing and improved transport properties offered by the solid-state exchange of exciton-delocalizing ligands show they offer promise for the construction of strongly coupled nanocrystal arrays.

  13. Asymmetry and coherence weight of quantum states

    NASA Astrophysics Data System (ADS)

    Bu, Kaifeng; Anand, Namit; Singh, Uttam

    2018-03-01

    The asymmetry of quantum states is an important resource in quantum information processing tasks such as quantum metrology and quantum communication. In this paper, we introduce the notion of asymmetry weight—an operationally motivated asymmetry quantifier in the resource theory of asymmetry. We study the convexity and monotonicity properties of asymmetry weight and focus on its interplay with the corresponding semidefinite programming (SDP) forms along with its connection to other asymmetry measures. Since the SDP form of asymmetry weight is closely related to asymmetry witnesses, we find that the asymmetry weight can be regarded as a (state-dependent) asymmetry witness. Moreover, some specific entanglement witnesses can be viewed as a special case of an asymmetry witness—which indicates a potential connection between asymmetry and entanglement. We also provide an operationally meaningful coherence measure, which we term coherence weight, and investigate its relationship to other coherence measures like the robustness of coherence and the l1 norm of coherence. In particular, we show that for Werner states in any dimension d all three coherence quantifiers, namely, the coherence weight, the robustness of coherence, and the l1 norm of coherence, are equal and are given by a single letter formula.

  14. Organo luminescent semiconductor nanocrystal probes for biological applications and process for making and using such probes

    DOEpatents

    Weiss, Shimon [Pinole, CA; Bruchez, Jr., Marcel; Alivisatos, Paul [Oakland, CA

    2008-01-01

    A semiconductor nanocrystal compound is described capable of linking to an affinity molecule. The compound comprises (1) a semiconductor nanocrystal capable of emitting electromagnetic radiation and/or absorbing energy, and/or scattering or diffracting electromagnetic radiation--when excited by an electromagnetic radiation source or a particle beam; and (2) an affinity molecule linked to the semiconductor nanocrystal. The semiconductor nanocrystal is linked to an affinity molecule to form a semiconductor nanocrystal probe capable of bonding with a detectable substance. Exposure of the semiconductor nanocrystal to excitation energy will excite the semiconductor nanocrystal causing the emission of electromagnetic radiation. Further described are processes for respectively: making the luminescent semiconductor nanocrystal compound; making the semiconductor nanocrystal probe; and using the probe to determine the presence of a detectable substance in a material.

  15. A wearable multiplexed silicon nonvolatile memory array using nanocrystal charge confinement.

    PubMed

    Kim, Jaemin; Son, Donghee; Lee, Mincheol; Song, Changyeong; Song, Jun-Kyul; Koo, Ja Hoon; Lee, Dong Jun; Shim, Hyung Joon; Kim, Ji Hoon; Lee, Minbaek; Hyeon, Taeghwan; Kim, Dae-Hyeong

    2016-01-01

    Strategies for efficient charge confinement in nanocrystal floating gates to realize high-performance memory devices have been investigated intensively. However, few studies have reported nanoscale experimental validations of charge confinement in closely packed uniform nanocrystals and related device performance characterization. Furthermore, the system-level integration of the resulting devices with wearable silicon electronics has not yet been realized. We introduce a wearable, fully multiplexed silicon nonvolatile memory array with nanocrystal floating gates. The nanocrystal monolayer is assembled over a large area using the Langmuir-Blodgett method. Efficient particle-level charge confinement is verified with the modified atomic force microscopy technique. Uniform nanocrystal charge traps evidently improve the memory window margin and retention performance. Furthermore, the multiplexing of memory devices in conjunction with the amplification of sensor signals based on ultrathin silicon nanomembrane circuits in stretchable layouts enables wearable healthcare applications such as long-term data storage of monitored heart rates.

  16. 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

  17. 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

  18. Optical properties of an indium doped CdSe nanocrystal: A density functional approach

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Salini, K.; Mathew, Vincent, E-mail: vincent@cukerala.ac.in; Mathew, Thomas

    2016-05-06

    We have studied the electronic and optical properties of a CdSe nanocrystal doped with n-type impurity atom. First principle calculations of the CdSe nanocrystal based on the density functional theory (DFT), as implemented in the Vienna Ab Initio Simulation Package (VASP) was used in the calculations. We have introduced a single Indium impurity atom into CdSe nanocrystal with 1.3 nm diameter. Nanocrystal surface dangling bonds are passivated with hydrogen atom. The band-structure, density of states and absorption spectra of the doped and undopted nanocrystals were discussed. Inclusion of the n-type impurity atom introduces an additional electron in conduction band, and significantlymore » alters the electronic and optical properties of undoped CdSe nanocrystal. Indium doped CdSe nannocrystal have potential applications in optoelectronic devices.« less

  19. Single step synthesis of high-purity CoO nanocrystals.

    PubMed

    Yang, Huaming; Ouyang, Jing; Tang, Aidong

    2007-07-19

    Both octahedral and slice-shaped cubic cobalt monoxide (CoO) nanocrystals with narrow size distributions have been successfully synthesized by a simple solvothermal route. It was found that conditions of the solvothermal treatment showed obvious effects on the formation and purity of the as-synthesized CoO nanocrystals, only when cobalt acetate was used as the cobalt source and when temperature reached 190 degrees C could CoO be produced; also, freeze-drying was necessary for obtaining pure CoO. Size of the CoO nanocrystals varied from 30 to 130 nm. Morphology of the products could be controlled by simply changing the type of surfactant in solvent, and the octahedral CoO nanocrystals showed rounded turns. Purity of the products was detected by intensive X-ray photoelectron spectroscopy (XPS) investigation and Fourier transform infrared spectroscopy (FTIR) combined with differential scanning calorimetry/thermal gravity (DSC/TG). The results indicated an absence of unexpected trivalence cobalt series on surface of the samples, thanks to the protection of the surface by trace amount of carbonate ions, adsorbed hydroxylation, and surfactant with a maximum thickness of 2 nm, which were proved by high-resolution transmission electron microscopy (HRTEM). The as-synthesized CoO nanoparticles were added into positive electrode of Ni/MH batteries, and discharge/charge cycling tests were performed under different rates from 0.1C to 5.0C. The results indicated that the specific capacities of batteries with addition of 5% octahedral or slice CoO nanocrystals at 0.1C were 393.3 and 318.1 mAh/g, respectively, which were higher than that without CoO (269.2mAh/g). Specific capacity of battery with addition of 5% octahedral CoO nanocrystals was 40% higher than that without CoO at 5.0C. Octahedral CoO nanocrystals show better electrochemical activity than slice CoO and indicate interesting potential in the field of electrochemical application.

  20. Group IV nanocrystals with ion-exchangeable surface ligands and methods of making the same

    DOE Office of Scientific and Technical Information (OSTI.GOV)

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

    Methods are described that include reacting a starting nanocrystal that includes a starting nanocrystal core and a covalently bound surface species to create an ion-exchangeable (IE) nanocrystal that includes a surface charge and a first ion-exchangeable (IE) surface ligand ionically bound to the surface charge, where the starting nanocrystal core includes a group IV element.

  1. Semiconductor nanocrystal probes for biological applications and process for making and using such probes

    DOEpatents

    Weiss, Shimon; Bruchez, Marcel; Alivisatos, Paul

    2014-01-28

    A semiconductor nanocrystal compound and probe are described. The compound is capable of linking to one or more affinity molecules. The compound comprises (1) one or more semiconductor nanocrystals capable of, in response to exposure to a first energy, providing a second energy, and (2) one or more linking agents, having a first portion linked to the one or more semiconductor nanocrystals and a second portion capable of linking to one or more affinity molecules. One or more semiconductor nanocrystal compounds are linked to one or more affinity molecules to form a semiconductor nanocrystal probe capable of bonding with one or more detectable substances in a material being analyzed, and capable of, in response to exposure to a first energy, providing a second energy. Also described are processes for respectively: making the semiconductor nanocrystal compound; making the semiconductor nanocrystal probe; and treating materials with the probe.

  2. Semiconductor nanocrystal probes for biological applications and process for making and using such probes

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Weiss, Shimon; Bruchez, Marcel; Alivisatos, Paul A.

    2016-12-27

    A semiconductor nanocrystal compound and probe are described. The compound is capable of linking to one or more affinity molecules. The compound comprises (1) one or more semiconductor nanocrystals capable of, in response to exposure to a first energy, providing a second energy, and (2) one or more linking agents, having a first portion linked to the one or more semiconductor nanocrystals and a second portion capable of linking to one or more affinity molecules. One or more semiconductor nanocrystal compounds are linked to one or more affinity molecules to form a semiconductor nanocrystal probe capable of bonding with onemore » or more detectable substances in a material being analyzed, and capable of, in response to exposure to a first energy, providing a second energy. Also described are processes for respectively: making the semiconductor nanocrystal compound; making the semiconductor nanocrystal probe; and treating materials with the probe.« less

  3. Cobalt ferrite nanocrystals: out-performing magnetotactic bacteria.

    PubMed

    Prozorov, Tanya; Palo, Pierre; Wang, Lijun; Nilsen-Hamilton, Marit; Jones, DeAnna; Orr, Daniel; Mallapragada, Surya K; Narasimhan, Balaji; Canfield, Paul C; Prozorov, Ruslan

    2007-10-01

    Magnetotactic bacteria produce exquisitely ordered chains of uniform magnetite (Fe(3)O(4)) nanocrystals, and the use of the bacterial mms6 protein allows for the shape-selective synthesis of Fe(3)O(4) nanocrystals. Cobalt ferrite (CoFe(2)O(4)) nanoparticles, on the other hand, are not known to occur in living organisms. Here we report on the use of the recombinant mms6 protein in a templated synthesis of CoFe(2)O(4) nanocrystals in vitro. We have covalently attached the full-length mms6 protein and a synthetic C-terminal domain of mms6 protein to self-assembling polymers in order to template hierarchical CoFe(2)O(4) nanostructures. This new synthesis pathway enables facile room-temperature shape-specific synthesis of complex magnetic crystalline nanomaterials with particle sizes in the range of 40-100 nm that are difficult to produce using conventional techniques.

  4. A dual-colored bio-marker made of doped ZnO nanocrystals

    NASA Astrophysics Data System (ADS)

    Wu, Y. L.; Fu, S.; Tok, A. I. Y.; Zeng, X. T.; Lim, C. S.; Kwek, L. C.; Boey, F. C. Y.

    2008-08-01

    Bio-compatible ZnO nanocrystals doped with Co, Cu and Ni cations, surface capped with two types of aminosilanes and titania are synthesized by a soft chemical process. Due to the small particle size (2-5 nm), surface functional groups and the high photoluminescence emissions at the UV and blue-violet wavelength ranges, bio-imaging on human osteosarcoma (Mg-63) cells and histiocytic lymphoma U-937 monocyte cells showed blue emission at the nucleus and bright turquoise emission at the cytoplasm simultaneously. This is the first report on dual-color bio-images labeled by one semiconductor nanocrystal colloidal solution. Bright green emission was detected on mung bean seedlings labeled by all the synthesized ZnO nanocrystals. Cytotoxicity tests showed that the aminosilanes capped nanoparticles are non-toxic. Quantum yields of the nanocrystals varied from 79% to 95%. The results showed the potential of the pure ZnO and Co-doped ZnO nanocrystals for live imaging of both human cells and plant systems.

  5. A wearable multiplexed silicon nonvolatile memory array using nanocrystal charge confinement

    PubMed Central

    Kim, Jaemin; Son, Donghee; Lee, Mincheol; Song, Changyeong; Song, Jun-Kyul; Koo, Ja Hoon; Lee, Dong Jun; Shim, Hyung Joon; Kim, Ji Hoon; Lee, Minbaek; Hyeon, Taeghwan; Kim, Dae-Hyeong

    2016-01-01

    Strategies for efficient charge confinement in nanocrystal floating gates to realize high-performance memory devices have been investigated intensively. However, few studies have reported nanoscale experimental validations of charge confinement in closely packed uniform nanocrystals and related device performance characterization. Furthermore, the system-level integration of the resulting devices with wearable silicon electronics has not yet been realized. We introduce a wearable, fully multiplexed silicon nonvolatile memory array with nanocrystal floating gates. The nanocrystal monolayer is assembled over a large area using the Langmuir-Blodgett method. Efficient particle-level charge confinement is verified with the modified atomic force microscopy technique. Uniform nanocrystal charge traps evidently improve the memory window margin and retention performance. Furthermore, the multiplexing of memory devices in conjunction with the amplification of sensor signals based on ultrathin silicon nanomembrane circuits in stretchable layouts enables wearable healthcare applications such as long-term data storage of monitored heart rates. PMID:26763827

  6. Hypervalent surface interactions for colloidal stability and doping of silicon nanocrystals

    PubMed Central

    Wheeler, Lance M.; Neale, Nathan R.; Chen, Ting; Kortshagen, Uwe R.

    2013-01-01

    Colloidal semiconductor nanocrystals have attracted attention for cost-effective, solution-based deposition of quantum-confined thin films for optoelectronics. However, two significant challenges must be addressed before practical nanocrystal-based devices can be realized. The first is coping with the ligands that terminate the nanocrystal surfaces. Though ligands provide the colloidal stability needed to cast thin films from solution, these ligands dramatically hinder charge carrier transport in the resulting film. Second, after a conductive film is achieved, doping has proven difficult for further control of the optoelectronic properties of the film. Here we report the ability to confront both of these challenges by exploiting the ability of silicon to engage in hypervalent interactions with hard donor molecules. For the first time, we demonstrate the significant potential of applying the interaction to the nanocrystal surface. In this study, hypervalent interactions are shown to provide colloidal stability as well as doping of silicon nanocrystals. PMID:23893292

  7. Structure refinement for tantalum nitrides nanocrystals with various morphologies

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Liu, Lianyun; School of Science, Beijing Jiaotong University, 3 Shang Yuan Cun, Haidian District, Beijing 100044; Huang, Kai

    2012-07-15

    Graphical abstract: Tantalum nitrides nanocrystals with various phases and morphologies for the first time have been synthesized through homogenous sodium reduction under low temperature with the subsequent annealing process under high vacuum. Highlights: ► The spherical TaN, cuboidal TaN{sub 0.83} and TaN{sub 0.5} nanocrystals have been synthesized through homogenous sodium reduction under low temperature with the subsequent annealing process under high vacuum. ► The crystal structures of different tantalum nitrides were determined by Rietveld refinement on the X-ray diffraction data and the examinations of electron microcopies. ► The specific surface area of the tantalum nitrides powders was around 10 m{supmore » 2} g{sup −1}. ► Tantalum nitrides powders could be suitable for capacitor with high specific capacitance. -- Abstract: Tantalum nitrides (TaN{sub x}) nanocrystals with different phase and morphology have been synthesized through homogenous sodium reduction under low temperature with the subsequent annealing process under high vacuum. The crystal structures of tantalum nitrides were determined by Rietveld refinement based on the X-ray diffraction data. The morphologies of various tantalum nitrides nanocrystals in high quality were analyzed through the electron microcopies examinations. The spherical TaN nanoparticles, cuboidal TaN{sub 0.83} and TaN{sub 0.5} nanocrystals have been selectively prepared at different annealing temperatures. In addition, the specific surface areas of the tantalum nitrides nanocrystals measured by BET method were around 9.87–11.64 m{sup 2} g{sup −1}, indicating that such nano-sized tantalum nitrides could be suitable for capacitor with high specific capacitance.« less

  8. Size-tunable phosphorescence in colloidal metastable gamma-Ga2O3 nanocrystals.

    PubMed

    Wang, Ting; Farvid, Shokouh S; Abulikemu, Mutalifu; Radovanovic, Pavle V

    2010-07-14

    We report a colloidal synthesis of gallium oxide (Ga(2)O(3)) nanocrystals having metastable cubic crystal structure (gamma phase) and uniform size distribution. Using the synthesized nanocrystal size series we demonstrate for the first time a size-tunable photoluminescence in Ga(2)O(3) from ultraviolet to blue, with the emission shifting to lower energies with increasing nanocrystal size. The observed photoluminescence is dominated by defect-based donor-acceptor pair recombination and has a lifetime of several milliseconds. Importantly, the decay of this phosphorescence is also size dependent. The phosphorescence energy and the decay rate increase with decreasing nanocrystal size, owing to a reduced donor-acceptor separation. These results allow for a rational and predictable tuning of the optical properties of this technologically important material and demonstrate the possibility of manipulating the localized defect interactions via nanocrystal size. Furthermore, the same defect states, particularly donors, are also implicated in electrical conductivity rendering monodispersed Ga(2)O(3) nanocrystals a promising material for multifunctional optoelectronic structures and devices.

  9. 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

  10. Colloidal chemical synthesis and formation kinetics of uniformly sized nanocrystals of metals, oxides, and chalcogenides.

    PubMed

    Kwon, Soon Gu; Hyeon, Taeghwan

    2008-12-01

    Nanocrystals exhibit interesting electrical, optical, magnetic, and chemical properties not achieved by their bulk counterparts. Consequently, to fully exploit the potential of nanocrystals, the synthesis of nanocrystals must focus on producing materials with uniform size and shape. Top-down physical processes can produce large quantities of nanocrystals, but controlling the size is difficult with these methods. On the other hand, colloidal chemical synthetic methods can produce uniform nanocrystals with a controlled particle size. In this Account, we present our synthesis of uniform nanocrystals of various shapes and materials, and we discuss the kinetics of nanocrystal formation. We employed four different synthetic approaches including thermal decomposition, nonhydrolytic sol-gel reactions, thermal reduction, and use of reactive chalcogen reagents. We synthesized uniform oxide nanocrystals via heat-up methods. This method involved slowly heat-up reaction mixtures composed of metal precursors, surfactants, and solvents from room temperature to high temperature. We then held reaction mixtures at an aging temperature for a few minutes to a few hours. Kinetics studies revealed a three-step mechanism for the synthesis of nanocrystals through the heat-up method with size distribution control. First, as metal precursors thermally decompose, monomers accumulate. At the aging temperature, burst nucleation occurs rapidly; at the end of this second phase, nucleation stops, but continued diffusion-controlled growth leads to size focusing to produce uniform nanocrystals. We used nonhydrolytic sol-gel reactions to synthesize various transition metal oxide nanocrystals. We employed ester elimination reactions for the synthesis of ZnO and TiO(2) nanocrystals. Uniform Pd nanoparticles were synthesized via a thermal reduction reaction induced by heating up a mixture of Pd(acac)(2), tri-n-octylphosphine, and oleylamine to the aging temperature. Similarly, we synthesized

  11. Controlled Chemical Doping of Semiconductor Nanocrystals Using Redox Buffers

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Engel, Jesse H.; Surendranath, Yogesh; Alivisatos, Paul

    Semiconductor nanocrystal solids are attractive materials for active layers in next-generation optoelectronic devices; however, their efficient implementation has been impeded by the lack of precise control over dopant concentrations. Herein we demonstrate a chemical strategy for the controlled doping of nanocrystal solids under equilibrium conditions. Exposing lead selenide nanocrystal thin films to solutions containing varying proportions of decamethylferrocene and decamethylferrocenium incrementally and reversibly increased the carrier concentration in the solid by 2 orders of magnitude from their native values. This application of redox buffers for controlled doping provides a new method for the precise control of the majority carrier concentrationmore » in porous semiconductor thin films.« less

  12. Supramolecular Assembly of Single-Source Metal-Chalcogenide Nanocrystal Precursors.

    PubMed

    Smith, Stephanie C; Bryks, Whitney; Tao, Andrea R

    2018-05-28

    In this Feature Article, we discuss our recent work in the synthesis of novel supramolecular precursors for semiconductor nanocrystals. Metal chalcogenolates that adopt liquid crystalline phases are employed as single-source precursors that template the growth of shaped solid-state nanocrystals. Supramolecular assembly is programmed by both precursor chemical composition and molecular parameters such alkyl chain length, steric bulk, and the intercalation of halide ions. Here, we explore the various design principles that enable the rational synthesis of these single-source precursors, their liquid crystalline phases, and the various semiconductor nanocrystal products that can be generated by thermolysis, ranging from highly anisotropic two-dimensional nanosheets and nanodisks to spheres.

  13. Cloning nanocrystal morphology with soft templates

    NASA Astrophysics Data System (ADS)

    Thapa, Dev Kumar; Pandey, Anshu

    2016-08-01

    In most template directed preparative methods, while the template decides the nanostructure morphology, the structure of the template itself is a non-general outcome of its peculiar chemistry. Here we demonstrate a template mediated synthesis that overcomes this deficiency. This synthesis involves overgrowth of silica template onto a sacrificial nanocrystal. Such templates are used to copy the morphologies of gold nanorods. After template overgrowth, gold is removed and silver is regrown in the template cavity to produce a single crystal silver nanorod. This technique allows for duplicating existing nanocrystals, while also providing a quantifiable breakdown of the structure - shape interdependence.

  14. Electron tomography and 3D molecular simulations of platinum nanocrystals

    NASA Astrophysics Data System (ADS)

    Florea, Ileana; Demortière, Arnaud; Petit, Christophe; Bulou, Hervé; Hirlimann, Charles; Ersen, Ovidiu

    2012-07-01

    This work reports on the morphology of individual platinum nanocrystals with sizes of about 5 nm. By using the electron tomography technique that gives 3D spatial selectivity, access to quantitative information in the real space was obtained. The morphology of individual nanoparticles was characterized using HAADF-STEM tomography and it was shown to be close to a truncated octahedron. Using molecular dynamics simulations, this geometrical shape was found to be the one minimizing the nanocrystal energy. Starting from the tomographic reconstruction, 3D crystallographic representations of the studied Pt nanocrystals were obtained at the nanometer scale, allowing the quantification of the relative amount of the crystallographic facets present on the particle surface.This work reports on the morphology of individual platinum nanocrystals with sizes of about 5 nm. By using the electron tomography technique that gives 3D spatial selectivity, access to quantitative information in the real space was obtained. The morphology of individual nanoparticles was characterized using HAADF-STEM tomography and it was shown to be close to a truncated octahedron. Using molecular dynamics simulations, this geometrical shape was found to be the one minimizing the nanocrystal energy. Starting from the tomographic reconstruction, 3D crystallographic representations of the studied Pt nanocrystals were obtained at the nanometer scale, allowing the quantification of the relative amount of the crystallographic facets present on the particle surface. Electronic supplementary information (ESI) available. See DOI: 10.1039/c2nr30990d

  15. Preparation and characterization of potato starch nanocrystal reinforced natural rubber nanocomposites.

    PubMed

    Rajisha, K R; Maria, H J; Pothan, L A; Ahmad, Zakiah; Thomas, S

    2014-06-01

    Potato starch nanocrystals were found to serve as an effective reinforcing agent for natural rubber (NR). Starch nanocrystals were obtained by the sulfuric acid hydrolysis of potato starch granules. After mixing the latex and the starch nanocrystals, the resulting aqueous suspension was cast into film by solvent evaporation method. The composite samples were successfully prepared by varying filler loadings, using a colloidal suspension of starch nanocrystals and NR latex. The morphology of the nanocomposite prepared was analyzed by field emission scanning electron microscopy (FESEM) and transmission electron microscopy (TEM). FESEM analysis revealed the size and shape of the crystal and their homogeneous dispersion in the composites. The crystallinity of the nanocomposites was studied using XRD analysis which indicated an overall increase in crystallinity with filler content. The mechanical properties of the nanocomposites such as stress-strain behavior, tensile strength, tensile modulus and elongation at break were measured according to ASTM standards. The tensile strength and modulus of the composites were found to improve tremendously with increasing nanocrystal content. This dramatic increase observed can be attributed to the formation of starch nanocrystal network. This network immobilizes the polymer chains leading to an increase in the modulus and other mechanical properties. Copyright © 2014 Elsevier B.V. All rights reserved.

  16. Enhanced Luminescent Stability through Particle Interactions in Silicon Nanocrystal Aggregates

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Miller, Joseph B.; Dandu, Naveen; Velizhanin, Kirill A.

    2015-10-27

    Close-packed assemblies of ligand-passivated colloidal nanocrystals can exhibit enhanced photoluminescent stability, but the origin of this effect is unclear. Here, we use experiment, simulation, and ab initio computation to examine the influence of interparticle interactions on the photoluminescent stability of silicon nanocrystal aggregates. The time-dependent photoluminescence emitted by structures ranging in size from a single quantum dot to agglomerates of more than a thousand is compared with Monte Carlo simulations of noninteracting ensembles using measured single-particle blinking data as input. In contrast to the behavior typically exhibited by the metal chalcogenides, the measured photoluminescent stability shows an enhancement with respectmore » to the noninteracting scenario with increasing aggregate size. We model this behavior using time-dependent density functional theory calculations of energy transfer between neighboring nanocrystals as a function of nanocrystal size, separation, and the presence of charge and/or surface-passivation defects. Our results suggest that rapid exciton transfer from “bright” nanocrystals to surface trap states in nearest-neighbors can efficiently fill such traps and enhance the stability of emission by promoting the radiative recombination of slowly diffusing excited electrons.« less

  17. Crystallization Methods for Preparation of Nanocrystals for Drug Delivery System.

    PubMed

    Gao, Yuan; Wang, Jingkang; Wang, Yongli; Yin, Qiuxiang; Glennon, Brian; Zhong, Jian; Ouyang, Jinbo; Huang, Xin; Hao, Hongxun

    2015-01-01

    Low water solubility of drug products causes delivery problems such as low bioavailability. The reduced particle size and increased surface area of nanocrystals lead to the increasing of the dissolution rate. The formulation of drug nanocrystals is a robust approach and has been widely applied to drug delivery system (DDS) due to the significant development of nanoscience and nanotechnology. It can be used to improve drug efficacy, provide targeted delivery and minimize side-effects. Crystallization is the main and efficient unit operation to produce nanocrystals. Both traditional crystallization methods such as reactive crystallization, anti-solvent crystallization and new crystallization methods such as supercritical fluid crystallization, high-gravity controlled precipitation can be used to produce nanocrystals. The current mini-review outlines the main crystallization methods addressed in literature. The advantages and disadvantages of each method were summarized and compared.

  18. Ligand exchange in quaternary alloyed nanocrystals--a spectroscopic study.

    PubMed

    Gabka, Grzegorz; Bujak, Piotr; Giedyk, Kamila; Kotwica, Kamil; Ostrowski, Andrzej; Malinowska, Karolina; Lisowski, Wojciech; Sobczak, Janusz W; Pron, Adam

    2014-11-14

    Exchange of initial, predominantly stearate ligands for pyridine in the first step and butylamine (BA) or 11-mercaptoundecanoic acid (MUA) in the second one was studied for alloyed quaternary Cu-In-Zn-S nanocrystals. The NMR results enabled us to demonstrate, for the first time, direct binding of the pyridine labile ligand to the nanocrystal surface as evidenced by paramagnetic shifts of the three signals attributed to its protons to 7.58, 7.95 and 8.75 ppm. XPS investigations indicated, in turn, a significant change in the composition of the nanocrystal surface upon the exchange of initial ligands for pyridine, which being enriched in indium in the 'as prepared' form became enriched in zinc after pyridine binding. This finding indicated that the first step of ligand exchange had to involve the removal of the surface layer enriched in indium with simultaneous exposure of a new, zinc-enriched layer. In the second ligand exchange step (replacement of pyridine with BA or MUA) the changes in the nanocrystal surface compositions were much less significant. The presence of zinc in the nanocrystal surface layer turned out necessary for effective binding of pyridine as shown by a comparative study of ligand exchange in Cu-In-Zn-S, Ag-In-Zn-S and CuInS2, carried out by complementary XPS and NMR investigations.

  19. 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.

  20. Fundamental absorption edge of NiO nanocrystals

    NASA Astrophysics Data System (ADS)

    Sokolov, V. I.; Druzhinin, A. V.; Kim, G. A.; Gruzdev, N. B.; Yermakov, A. Ye.; Uimin, M. A.; Byzov, I. V.; Shchegoleva, N. N.; Vykhodets, V. B.; Kurennykh, T. E.

    2013-12-01

    NiO nanocrystals with the average size of 5, 10 and 25 nm were synthesized by gas-condensation method. The well-defined increase of the optical density D near the fundamental absorption edge of NiO nanocrystals in the range of 3.5-4.0 eV observed after the annealing in air is caused by the oxygen content growth. It is the direct experimental evidence of the fact that p-d charge transfer transitions form the fundamental absorption edge.

  1. Surface states in the photoionization of high-quality CdSe core/shell nanocrystals.

    PubMed

    Li, Shu; Steigerwald, Michael L; Brus, Louis E

    2009-05-26

    We use electric force microscopy (EFM) to study single nanocrystal photoionization in two classes of high-quality nanocrystals whose exciton luminescence quantum yields approach unity in solution. The CdSe/CdS/ZnS core/shell nanocrystals do not photoionize, while the CdSe/CdS nanocrystals do show substantial photoionization. This verifies the theoretical prediction that the ZnS shell confines the excited electron within the nanocrystal. Despite the high luminescence quantum yield, photoionization varies substantially among the CdSe/CdS nanocrystals. We have studied the nanocrystal photoionization with both UV (396 nm) and green (532 nm) light, and we have found that the magnitude of the charge due to photoionization per absorbed photon is greater for UV excitation than for green excitation. A fraction of the photoionization occurs directly via a "hot electron" process, using trap states that are either on the particle surface, within the ligand sphere, or within the silicon oxide layer. This must occur without relaxation to the thermalized, lowest-energy, emitting exciton. We discuss the occurrence of hot carrier processes that are common to photoionization, luminescence blinking, and the fast transient optical absorption that is associated with multiple exciton generation MEG studies.

  2. Synthesis and characterization of luminescent aluminium selenide nanocrystals

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Balitskii, O.A., E-mail: balitskii@electronics.wups.lviv.ua; Demchenko, P.Yu.; Mijowska, E.

    Highlights: ► Synthesis procedure of size and sharp controlled Al{sub 2}Se{sub 3} nanocrystals is introduced. ► Obtained nanoparticles are highly crystalline of hexagonal wurtzite type. ► Colloidal Al{sub 2}Se{sub 3} nanocrystals are highly luminescent in the near UV spectral region. ► They can be implemented in light emitters/collectors, concurring with II–VI nanodots. -- Abstract: We propose the synthesis and characterization of colloidal aluminium selenide nanocrystals using trioctylphosphine as a solvent. The nanoparticles have several absorption bands in the spectral region 330–410 nm and are bright UV-blue luminescent, which is well demanded in light collecting and emitting devices, e.g. for tuningmore » their spectral characteristics to higher energy solar photons.« less

  3. Effects of PEGylated paclitaxel nanocrystals on breast cancer and its lung metastasis

    NASA Astrophysics Data System (ADS)

    Zhang, Hua; Hu, Hongxiang; Zhang, Haoran; Dai, Wenbing; Wang, Xinglin; Wang, Xueqing; Zhang, Qiang

    2015-06-01

    As an attractive strategy developed rapidly in recent years, nanocrystals are used to deliver insoluble drugs. PEGylation may further prolong the circulation time of nanoparticles and improve the therapeutic outcome of drugs. In this study, paclitaxel (PTX) nanocrystals (PTX-NCs) and PEGylated PTX nanocrystals (PEG-PTX-NCs) were prepared using antisolvent precipitation augmented by probe sonication. The characteristics and antitumor efficacy of nanocrystals were investigated. The results indicated that the nanocrystals showed rod-like morphology, and the average particle size was 240 nm and 330 nm for PTX-NCs and PEG-PTX-NCs, respectively. The PEG molecules covered the surface of nanocrystals with an 11.54 nm fixed aqueous layer thickness (FALT), much higher than that of PTX-NCs (0.2 nm). PEG-PTX-NCs showed higher stability than PTX-NCs under both storage and physiological conditions. In breast cancer xenografted mice, PEG-PTX-NCs showed significantly better tumor inhibition compared to saline (p < 0.001) and PTX-NC groups (p < 0.05) after intravenous administration. In a model of lung tumor metastasis quantified by the luciferase activity, the PEG-PTX-NCs group showed higher anticancer efficacy not only than saline and PTX-NCs groups, but also than Taxol®, achieving an 82% reduction at the end of the experiment. These studies suggested the potential advantages of PEGylated PTX nanocrystals as alternative drug delivery systems for anticancer therapy.

  4. Structural phase transitions in niobium oxide nanocrystals

    NASA Astrophysics Data System (ADS)

    Yuvakkumar, R.; Hong, Sun Ig

    2015-09-01

    Niobium oxide nanocrystals were successfully synthesized employing the green synthesis method. Phase formation, microstructure and compositional properties of 1, 4 and 7 days incubation treated samples after calcinations at 450 °C were examined using X-ray diffraction, Raman, photoluminescence (PL), infrared, X-ray photoelectron spectra and transmission electron microscopic characterizations. It was observed that phase formation of Nb2O5 nanocrystals was dependent upon the incubation period required to form stable metal oxides. The characteristic results clearly revealed that with increasing incubation and aging, the transformation of cubic, orthorhombic and monoclinic phases were observed. The uniform heating at room temperature (32 °C) and the ligation of niobium atoms due to higher phenolic constituents of utilized rambutan during aging processing plays a vital role in structural phase transitions in niobium oxide nanocrystals. The defects over a period of incubation and the intensities of the PL spectra changing over a period of aging were related to the amount of the defects induced by the phase transition.

  5. Morphology evolution of single-crystalline hematite nanocrystals: magnetically recoverable nanocatalysts for enhanced facet-driven photoredox activity

    NASA Astrophysics Data System (ADS)

    Patra, Astam K.; Kundu, Sudipta K.; Bhaumik, Asim; Kim, Dukjoon

    2015-12-01

    We have developed a new green chemical approach for the shape-controlled synthesis of single-crystalline hematite nanocrystals in aqueous medium. FESEM, HRTEM and SAED techniques were used to determine the morphology and crystallographic orientations of each nanocrystal and its exposed facets. PXRD and HRTEM techniques revealed that the nanocrystals are single crystalline in nature; twins and stacking faults were not detected in these nanocrystals. The structural, vibrational, and electronic spectra of these nanocrystals were highly dependent on their shape. Different shaped hematite nanocrystals with distinct crystallographic planes have been synthesized under similar reaction conditions, which can be desired as a model for the purpose of properties comparison with the nanocrystals prepared under different reaction conditions. Here we investigated the photocatalytic performance of these different shaped-nanocrystals for methyl orange degradation in the presence of white light (λ > 420 nm). In this study, we found that the density of surface Fe3+ ions in particular facets was the key factor for the photocatalytic activity and was higher on the bitruncated-dodecahedron shape nanocrystals by coexposed {104}, {100} and {001} facets, attributing to higher catalytic activity. The catalytic activity of different exposed facet nanocrystals were as follows: {104} + {100} + {001} (bitruncated-dodecahedron) > {101} + {001} (bitruncated-octahedron) > {001} + {110} (nanorods) > {012} (nanocuboid) which provided the direct evidence of exposed facet-driven photocatalytic activity. The nanocrystals were easily recoverable using an external magnet and reused at least six times without significant loss of its catalytic activity.We have developed a new green chemical approach for the shape-controlled synthesis of single-crystalline hematite nanocrystals in aqueous medium. FESEM, HRTEM and SAED techniques were used to determine the morphology and crystallographic orientations of

  6. Synthesis and characterization of some metal oxide nanocrystals by microwave irradiation

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Rashad, M.; Gaber, A.; Abdelrahim, M. A.

    2013-12-16

    Copper oxide and cobalt oxide (CuO, Co3O4) nanocrystals (NCs) have been successfully prepared in a short time using microwave irradiation. The resulted powders of nanocrystals (NCs) were characterized by X-ray diffraction (XRD) and transmission electron microscopy (TEM). Thermogravimetric analysis (TGA) measurements are also studied. Fourier-transform infrared (FT-IR) and UV–visible absorption spectroscopy of both kind of nanoparticels are illustrated. Optical absorption analysis indicated the direct band gap for both kinds of nanocrystals.

  7. Charge injection and discharging of Si nanocrystals and arrays by atomic force microscopy

    NASA Technical Reports Server (NTRS)

    Boer, E.; Ostraat, M.; Brongersma, M. L.; Flagan, R. C.; Atwater, H. A.

    2000-01-01

    Charge injection and storage in dense arrays of silicon nanocrystals in SiO(sub 2) 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.

  8. The interplay of shape and crystalline anisotropies in plasmonic semiconductor nanocrystals

    DOE PAGES

    Kim, Jongwook; Agrawal, Ankit; Krieg, Franziska; ...

    2016-05-16

    Doped semiconductor nanocrystals are an emerging class of materials hosting localized surface plasmon resonance (LSPR) over a wide optical range. Studies so far have focused on tuning LSPR frequency by controlling the dopant and carrier concentrations in diverse semiconductor materials. However, the influence of anisotropic nanocrystal shape and of intrinsic crystal structure on LSPR remain poorly explored. Here, we illustrate how these two factors collaborate to determine LSPR characteristics in hexagonal cesium-doped tungsten oxide nanocrystals. The effect of shape anisotropy is systematically analyzed via synthetic control of nanocrystal aspect ratio (AR), from disks to nanorods. We demonstrate the dominant influencemore » of crystalline anisotropy, which uniquely causes strong LSPR band-splitting into two distinct peaks with comparable intensities. Modeling typically used to rationalize particle shape effects is refined by taking into account the anisotropic dielectric function due to crystalline anisotropy, thus fully accounting for the AR-dependent evolution of multiband LSPR spectra. Furthermore, this new insight into LSPR of semiconductor nanocrystals provides a novel strategy for an exquisite tuning of LSPR line shape.« less

  9. Structural diversity in binary superlattices self-assembled from polymer-grafted nanocrystals

    DOE PAGES

    Ye, Xingchen; Zhu, Chenhui; Ercius, Peter; ...

    2015-12-02

    Multicomponent nanocrystal superlattices represent an interesting class of material that derives emergent properties from mesoscale structure, yet their programmability can be limited by the alkyl-chain-based ligands decorating the surfaces of the constituent nanocrystals. Polymeric ligands offer distinct advantages, as they allow for more precise tuning of the effective size and ‘interaction softness’ through changes to the polymer’s molecular weight, chemical nature, architecture, persistence length and surrounding solvent. Here we show the formation of 10 different binary nanocrystal superlattices (BNSLs) with both two- and three-dimensional order through independent adjustment of the core size of spherical nanocrystals and the molecular weight ofmore » densely grafted polystyrene ligands. These polymer-brush-based ligands introduce new energetic contributions to the interparticle potential that stabilizes various BNSL phases across a range of length scales and interparticle spacings. In conclusion, our study opens the door for nanocrystals to become modular elements in the design of functional particle brush solids with controlled nanoscale interfaces and mesostructures.« less

  10. Intrachromosomal karyotype asymmetry in Orchidaceae.

    PubMed

    Medeiros-Neto, Enoque; Nollet, Felipe; Moraes, Ana Paula; Felix, Leonardo P

    2017-01-01

    The asymmetry indexes have helped cytotaxonomists to interpret and classify plant karyotypes for species delimitation efforts. However, there is no consensus about the best method to calculate the intrachromosomal asymmetry. The present study aimed to compare different intrachromosomal asymmetry indexes in order to indicate which are more efficient for the estimation of asymmetry in different groups of orchids. Besides, we aimed to compare our results with the Orchidaceae phylogenetic proposal to test the hypothesis of Stebbins (1971). Through a literature review, karyotypes were selected and analyzed comparatively with ideal karyotypes in a cluster analysis. All karyotypes showed some level of interchromosomal asymmetry, ranging from slightly asymmetric to moderately asymmetric. The five tested intrachromosomal asymmetry indexes indicated Sarcoglottis grandiflora as the species with the most symmetrical karyotype and Christensonella pachyphylla with the most asymmetrical karyotype. In the cluster analysis, the largest number of species were grouped with the intermediary ideal karyotypes B or C. Considering our results, we recommend the combined use of at least two indexes, especially Ask% or A1 with Syi, for cytotaxonomic analysis in groups of orchids. In an evolutionary perspective, our results support Stebbins' hypothesis that asymmetric karyotypes derive from a symmetric karyotypes.

  11. In situ bioinspired synthesis of silver chloride nanocrystals on silk fibroin fibers

    NASA Astrophysics Data System (ADS)

    Su, Huilan; Han, Jie; Dong, Qun; Xu, Jia; Chen, Ying; Gu, Yu; Song, Weiqiang; Zhang, Di

    2011-02-01

    Silver chloride (AgCl) nanocrystals were formed and grown on silk fibroin fibers (SFFs) by a room-temperature process. Practically, the degummed SFFs were immersed into silver nitrate solution and sodium chloride solution in turn. The amino acids on the SFF surface were negatively charged in alkaline impregnant, providing locations to immobilize silver ions and form silver chloride seeds. AgCl nanocrystals can further grow into cubic AgCl nanocrystals with an edge of about 100 nm. The morphologies of the AgCl nanocrystals were mostly influenced by the concentration of sodium chloride solution and the special configurations of the SFFs. The target AgCl/SFF nanocomposites constructed by AgCl nanocrystals and substrate SFFs could be used as photocatalysts in water splitting and antibacterial agents. This work provides an important example in the introduction of natural biofibers to the synthesis of functional hybrid nanocomposites by a green and mild technique.

  12. [Diagnosis of facial and craniofacial asymmetry].

    PubMed

    Arnaud, E; Marchac, D; Renier, D

    2001-10-01

    Craniofacial asymmetry is caused by various aetiologies but clinical examination remains the most important criteria since minor asymmetry is always present. The diagnosis can be confirmed by anthropometric measurements and radiological examinations but only severe asymmetries or asymmetries with an associated functional impairment should be treated. The treatment depends on the cause, and on the time of appearance. Congenital asymmetries might be treated early, during the first year of life if a craniosynostosis is present. Hemifacial microsomia are treated later if there is no breathing impairment. Since the pediatricians have recommended the dorsal position for infant sleeping, an increasing number of posterior flattening of the skull has been appearing, and could be prevented by adequate nursing. Other causes of craniofacial asymmetries are rare and should be adapted to the cause (tumors, atrophies, neurological paralysis, hypertrophies) by a specialized multidisciplinar team.

  13. 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.

  14. 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.

  15. Assessing and conceptualizing frontal EEG asymmetry: An updated primer on recording, processing, analyzing, and interpreting frontal alpha asymmetry.

    PubMed

    Smith, Ezra E; Reznik, Samantha J; Stewart, Jennifer L; Allen, John J B

    2017-01-01

    Frontal electroencephalographic (EEG) alpha asymmetry is widely researched in studies of emotion, motivation, and psychopathology, yet it is a metric that has been quantified and analyzed using diverse procedures, and diversity in procedures muddles cross-study interpretation. The aim of this article is to provide an updated tutorial for EEG alpha asymmetry recording, processing, analysis, and interpretation, with an eye towards improving consistency of results across studies. First, a brief background in alpha asymmetry findings is provided. Then, some guidelines for recording, processing, and analyzing alpha asymmetry are presented with an emphasis on the creation of asymmetry scores, referencing choices, and artifact removal. Processing steps are explained in detail, and references to MATLAB-based toolboxes that are helpful for creating and investigating alpha asymmetry are noted. Then, conceptual challenges and interpretative issues are reviewed, including a discussion of alpha asymmetry as a mediator/moderator of emotion and psychopathology. Finally, the effects of two automated component-based artifact correction algorithms-MARA and ADJUST-on frontal alpha asymmetry are evaluated. Copyright © 2016 Elsevier B.V. All rights reserved.

  16. Photoelectron spectroscopy of color centers in negatively charged cesium iodide nanocrystals

    NASA Astrophysics Data System (ADS)

    Sarkas, Harry W.; Kidder, Linda H.; Bowen, Kit H.

    1995-01-01

    We present the photoelectron spectra of negatively charged cesium iodide nanocrystals recorded using 2.540 eV photons. The species examined were produced using an inert gas condensation cluster ion source, and they ranged in size from (CsI)-n=13 to nanocrystal anions comprised of 330 atoms. Nanocrystals showing two distinct types of photoemission behavior were observed. For (CsI)-n=13 and (CsI)-n=36-165, a plot of cluster anion photodetachment threshold energies vs n-1/3 gives a straight line extrapolating (at n-1/3=0, i.e., n=∞) to 2.2 eV, the photoelectric threshold energy for F centers in bulk cesium iodide. The linear extrapolation of the cluster anion data to the corresponding bulk property implies that the electron localization in these gas-phase nanocrystals is qualitatively similar to that of F centers in extended alkali halide crystals. These negatively charged cesium iodide nanocrystals are thus shown to support embryonic forms of F centers, which mature with increasing cluster size toward condensed phase impurity centers. Under an alternative set of source conditions, nanocrystals were produced which showed significantly lower photodetachment thresholds than the aforementioned F-center cluster anions. For these species, containing 83-131 atoms, a plot of their cluster anion photodetachment threshold energies versus n-1/3 gives a straight line which extrapolates to 1.4 eV. This value is in accord with the expected photoelectric threshold energy for F' centers in bulk cesium iodide, i.e., color centers with two excess electrons in a single defect site. These nanocrystals are interpreted to be the embryonic F'-center containing species, Cs(CsI)-n=41-65.

  17. Stoichiometric control of lead chalcogenide nanocrystal solids to enhance their electronic and optoelectronic device performance.

    PubMed

    Oh, Soong Ju; Berry, Nathaniel E; Choi, Ji-Hyuk; Gaulding, E Ashley; Paik, Taejong; Hong, Sung-Hoon; Murray, Christopher B; Kagan, Cherie R

    2013-03-26

    We investigate the effects of stoichiometric imbalance on the electronic properties of lead chalcogenide nanocrystal films by introducing excess lead (Pb) or selenium (Se) through thermal evaporation. Hall-effect and capacitance-voltage measurements show that the carrier type, concentration, and Fermi level in nanocrystal solids may be precisely controlled through their stoichiometry. By manipulating only the stoichiometry of the nanocrystal solids, we engineer the characteristics of electronic and optoelectronic devices. Lead chalcogenide nanocrystal field-effect transistors (FETs) are fabricated at room temperature to form ambipolar, unipolar n-type, and unipolar p-type semiconducting channels as-prepared and with excess Pb and Se, respectively. Introducing excess Pb forms nanocrystal FETs with electron mobilities of 10 cm(2)/(V s), which is an order of magnitude higher than previously reported in lead chalcogenide nanocrystal devices. Adding excess Se to semiconductor nanocrystal solids in PbSe Schottky solar cells enhances the power conversion efficiency.

  18. Nanocrystal-mediated charge screening effects in nanowire field-effect transistors

    NASA Astrophysics Data System (ADS)

    Yoon, C. J.; Yeom, D. H.; Jeong, D. Y.; Lee, M. G.; Moon, B. M.; Kim, S. S.; Choi, C. Y.; Koo, S. M.

    2009-03-01

    ZnO nanowire field-effect transistors having an omega-shaped floating gate (OSFG) have been successfully fabricated by directly coating CdTe nanocrystals (˜6±2.5 nm) at room temperature, and compared to simultaneously prepared control devices without nanocrystals. Herein, we demonstrate that channel punchthrough may occur when the depletion from the OSFG takes place due to the trapped charges in the nanocrystals. Electrical measurements on the OSFG nanowire devices showed static-induction transistorlike behavior in the drain output IDS-VDS characteristics and a hysteresis window as large as ˜3.1 V in the gate transfer IDS-VGS characteristics. This behavior is ascribed to the presence of the CdTe nanocrystals, and is indicative of the trapping and emission of electrons in the nanocrystals. The numerical simulations clearly show qualitatively the same characteristics as the experimental data and confirm the effect, showing that the change in the potential distribution across the channel, induced by both the wrapping-around gate and the drain, affects the transport characteristics of the device. The cross-sectional energy band and potential profile of the OSFG channel corresponding to the "programed (noncharged)" and "erased (charged)" operations for the device are also discussed on the basis of the numerical capacitance-voltage simulations.

  19. Dichotic listening in patients with situs inversus: brain asymmetry and situs asymmetry.

    PubMed

    Tanaka, S; Kanzaki, R; Yoshibayashi, M; Kamiya, T; Sugishita, M

    1999-06-01

    In order to investigate the relation between situs asymmetry and functional asymmetry of the human brain, a consonant-vowel syllable dichotic listening test known as the Standard Dichotic Listening Test (SDLT) was administered to nine subjects with situs inversus (SI) that ranged in age from 6 to 46 years old (mean of 21.8 years old, S.D. = 15.6); the four males and five females all exhibited strong right-handedness. The SDLT was also used to study twenty four age-matched normal subjects that were from 6 to 48 years old (mean 21.7 years old, S.D. = 15.3); the twelve males and twelve females were all strongly right-handed and served as a control group. Eight out of the nine subjects (88.9%) with SI more often reproduced the sounds from the right ear than sounds from the left ear; this is called right ear advantage (REA). The ratio of REA in the control group was almost the same, i.e., nineteen out of the twenty-four subjects (79.1%) showed REA. Results of the present study suggest that the left-right reversal in situs inversus does not involve functional asymmetry of the brain. As such, the system that produces functional asymmetry in the human brain must independently recognize laterality from situs asymmetry.

  20. Seeded Growth Route to Noble Calcium Carbonate Nanocrystal.

    PubMed

    Islam, Aminul; Teo, Siow Hwa; Rahman, M Aminur; Taufiq-Yap, Yun Hin

    2015-01-01

    A solution-phase route has been considered as the most promising route to synthesize noble nanostructures. A majority of their synthesis approaches of calcium carbonate (CaCO3) are based on either using fungi or the CO2 bubbling methods. Here, we approached the preparation of nano-precipitated calcium carbonate single crystal from salmacis sphaeroides in the presence of zwitterionic or cationic biosurfactants without external source of CO2. The calcium carbonate crystals were rhombohedron structure and regularly shaped with side dimension ranging from 33-41 nm. The high degree of morphological control of CaCO3 nanocrystals suggested that surfactants are capable of strongly interacting with the CaCO3 surface and control the nucleation and growth direction of calcium carbonate nanocrystals. Finally, the mechanism of formation of nanocrystals in light of proposed routes was also discussed.

  1. Seeded Growth Route to Noble Calcium Carbonate Nanocrystal

    PubMed Central

    Islam, Aminul; Teo, Siow Hwa; Rahman, M. Aminur; Taufiq-Yap, Yun Hin

    2015-01-01

    A solution-phase route has been considered as the most promising route to synthesize noble nanostructures. A majority of their synthesis approaches of calcium carbonate (CaCO3) are based on either using fungi or the CO2 bubbling methods. Here, we approached the preparation of nano-precipitated calcium carbonate single crystal from salmacis sphaeroides in the presence of zwitterionic or cationic biosurfactants without external source of CO2. The calcium carbonate crystals were rhombohedron structure and regularly shaped with side dimension ranging from 33–41 nm. The high degree of morphological control of CaCO3 nanocrystals suggested that surfactants are capable of strongly interacting with the CaCO3 surface and control the nucleation and growth direction of calcium carbonate nanocrystals. Finally, the mechanism of formation of nanocrystals in light of proposed routes was also discussed. PMID:26700479

  2. Adsorption of vitamin E on mesoporous titania nanocrystals

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Shih, C.J., E-mail: cjshih@kmu.edu.tw; Lin, C.T.; Wu, S.M.

    2010-07-15

    Tri-block nonionic surfactant and titanium chloride were used as starting materials for the synthesis of mesoporous titania nanocrystallite powders. The main objective of the present study was to examine the synthesis of mesoporous titania nanocrystals and the adsorption of vitamin E on those nanocrystals using X-ray diffraction (XRD), transmission electron microscopy, and nitrogen adsorption and desorption isotherms. When the calcination temperature was increased to 300 {sup o}C, the reflection peaks in the XRD pattern indicated the presence of an anatase phase. The crystallinity of the nanocrystallites increased from 80% to 98.6% with increasing calcination temperature from 465 {sup o}C tomore » 500 {sup o}C. The N{sub 2} adsorption data and XRD data taken after vitamin E adsorption revealed that the vitamin E molecules were adsorbed in the mesopores of the titania nanocrystals.« less

  3. Nanocrystal synthesis in microfluidic reactors: where next?

    PubMed

    Phillips, Thomas W; Lignos, Ioannis G; Maceiczyk, Richard M; deMello, Andrew J; deMello, John C

    2014-09-07

    The past decade has seen a steady rise in the use of microfluidic reactors for nanocrystal synthesis, with numerous studies reporting improved reaction control relative to conventional batch chemistry. However, flow synthesis procedures continue to lag behind batch methods in terms of chemical sophistication and the range of accessible materials, with most reports having involved simple one- or two-step chemical procedures directly adapted from proven batch protocols. Here we examine the current status of microscale methods for nanocrystal synthesis, and consider what role microreactors might ultimately play in laboratory-scale research and industrial production.

  4. From Artificial Atoms to Nanocrystal Molecules: Preparation and Properties of More Complex Nanostructures

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Choi, Charina L; Alivisatos, A Paul

    2009-10-20

    Quantum dots, which have found widespread use in fields such as biomedicine, photovoltaics, and electronics, are often called artificial atoms due to their size-dependent physical properties. Here this analogy is extended to consider artificial nanocrystal molecules, formed from well-defined groupings of plasmonically or electronically coupled single nanocrystals. Just as a hydrogen molecule has properties distinct from two uncoupled hydrogen atoms, a key feature of nanocrystal molecules is that they exhibit properties altered from those of the component nanoparticles due to coupling. The nature of the coupling between nanocrystal atoms and its response to vibrations and deformations of the nanocrystal moleculemore » bonds are of particular interest. We discuss synthetic approaches, predicted and observed physical properties, and prospects and challenges toward this new class of materials.« less

  5. 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.

  6. Intrinsic behavior of face-centered-cubic supra-crystals of nanocrystals self-organized on mesoscopic scale

    NASA Astrophysics Data System (ADS)

    Pileni, M. P.

    2005-12-01

    We describe intrinsic behavior due to the high ordering of nanocrystals at the mesoscopic scale. The first example shows well-defined columns in the formation of cobalt nanocrystals when an applied magnetic field is applied during the evaporation process. Collective breathing properties between nanocrystals are demonstrated. In both cases, these features are observed when the nanocrystals are highly ordered in fcc supra-crystals.

  7. Quantitative tunneling spectroscopy of nanocrystals

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    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]).more » Funding from this DOE grant was critical for the initial development of epitaxial graphene for nanoelectronics« less

  8. Low-frequency (1/f) noise in nanocrystal field-effect transistors.

    PubMed

    Lai, Yuming; Li, Haipeng; Kim, David K; Diroll, Benjamin T; Murray, Christopher B; Kagan, Cherie R

    2014-09-23

    We investigate the origins and magnitude of low-frequency noise in high-mobility nanocrystal field-effect transistors and show the noise is of 1/f-type. Sub-band gap states, in particular, those introduced by nanocrystal surfaces, have a significant influence on the 1/f noise. By engineering the device geometry and passivating nanocrystal surfaces, we show that in the linear and saturation regimes the 1/f noise obeys Hooge's model of mobility fluctuations, consistent with transport of a high density of accumulated carriers in extended electronic states of the NC thin films. In the subthreshold regime, the Fermi energy moves deeper into the mobility gap and sub-band gap trap states give rise to a transition to noise dominated by carrier number fluctuations as described in McWhorter's model. CdSe nanocrystal field-effect transistors have a Hooge parameter of 3 × 10(-2), comparable to other solution-deposited, thin-film devices, promising high-performance, low-cost, low-noise integrated circuitry.

  9. In situ microscopy of the self-assembly of branched nanocrystals in solution

    DOE PAGES

    Sutter, Eli; Tkachenko, Alexei V.; Sutter, Peter; ...

    2016-04-04

    Here, solution-phase self-assembly of nanocrystals into mesoscale structures is a promising strategy for constructing functional materials from nanoscale components. Liquid environments are key to self-assembly since they allow suspended nanocrystals to diffuse and interact freely, but they also complicate experiments. Real-time observations with single-particle resolution could have transformative impact on our understanding of nanocrystal self-assembly. Here we use real-time in situ imaging by liquid-cell electron microscopy to elucidate the nucleation and growth mechanism and properties of linear chains of octapod-shaped nanocrystals in their native solution environment. Statistical mechanics modelling based on these observations and using the measured chain-length distribution clarifiesmore » the relative importance of dipolar and entropic forces in the assembly process and gives direct access to the interparticle interaction. Our results suggest that monomer-resolved in situ imaging combined with modelling can provide unprecedented quantitative insight into the microscopic processes and interactions that govern nanocrystal self-assembly in solution.« less

  10. Polycatenar Ligand Control of the Synthesis and Self-Assembly of Colloidal Nanocrystals.

    PubMed

    Diroll, Benjamin T; Jishkariani, Davit; Cargnello, Matteo; Murray, Christopher B; Donnio, Bertrand

    2016-08-24

    Hydrophobic colloidal nanocrystals are typically synthesized and manipulated with commercially available ligands, and surface functionalization is therefore typically limited to a small number of molecules. Here, we report the use of polycatenar ligands derived from polyalkylbenzoates for the direct synthesis of metallic, chalcogenide, pnictide, and oxide nanocrystals. Polycatenar molecules, branched structures bearing diverging chains in which the terminal substitution pattern, functionality, and binding group can be independently modified, offer a modular platform for the development of ligands with targeted properties. Not only are these ligands used for the direct synthesis of monodisperse nanocrystals, but nanocrystals coated with polycatenar ligands self-assemble into softer bcc superlattices that deviate from conventional harder close-packed structures (fcc or hcp) formed by the same nanocrystals coated with commercial ligands. Self-assembly experiments demonstrate that the molecular structure of polycatenar ligands encodes interparticle spacings and attractions, engineering self-assembly, which is tunable from hard sphere to soft sphere behavior.

  11. In situ microscopy of the self-assembly of branched nanocrystals in solution

    NASA Astrophysics Data System (ADS)

    Sutter, Eli; Sutter, Peter; Tkachenko, Alexei V.; Krahne, Roman; de Graaf, Joost; Arciniegas, Milena; Manna, Liberato

    2016-04-01

    Solution-phase self-assembly of nanocrystals into mesoscale structures is a promising strategy for constructing functional materials from nanoscale components. Liquid environments are key to self-assembly since they allow suspended nanocrystals to diffuse and interact freely, but they also complicate experiments. Real-time observations with single-particle resolution could have transformative impact on our understanding of nanocrystal self-assembly. Here we use real-time in situ imaging by liquid-cell electron microscopy to elucidate the nucleation and growth mechanism and properties of linear chains of octapod-shaped nanocrystals in their native solution environment. Statistical mechanics modelling based on these observations and using the measured chain-length distribution clarifies the relative importance of dipolar and entropic forces in the assembly process and gives direct access to the interparticle interaction. Our results suggest that monomer-resolved in situ imaging combined with modelling can provide unprecedented quantitative insight into the microscopic processes and interactions that govern nanocrystal self-assembly in solution.

  12. Slow cooling and highly efficient extraction of hot carriers in colloidal perovskite nanocrystals

    PubMed Central

    Li, Mingjie; Bhaumik, Saikat; Goh, Teck Wee; Kumar, Muduli Subas; Yantara, Natalia; Grätzel, Michael; Mhaisalkar, Subodh; Mathews, Nripan; Sum, Tze Chien

    2017-01-01

    Hot-carrier solar cells can overcome the Shockley-Queisser limit by harvesting excess energy from hot carriers. Inorganic semiconductor nanocrystals are considered prime candidates. However, hot-carrier harvesting is compromised by competitive relaxation pathways (for example, intraband Auger process and defects) that overwhelm their phonon bottlenecks. Here we show colloidal halide perovskite nanocrystals transcend these limitations and exhibit around two orders slower hot-carrier cooling times and around four times larger hot-carrier temperatures than their bulk-film counterparts. Under low pump excitation, hot-carrier cooling mediated by a phonon bottleneck is surprisingly slower in smaller nanocrystals (contrasting with conventional nanocrystals). At high pump fluence, Auger heating dominates hot-carrier cooling, which is slower in larger nanocrystals (hitherto unobserved in conventional nanocrystals). Importantly, we demonstrate efficient room temperature hot-electrons extraction (up to ∼83%) by an energy-selective electron acceptor layer within 1 ps from surface-treated perovskite NCs thin films. These insights enable fresh approaches for extremely thin absorber and concentrator-type hot-carrier solar cells. PMID:28176882

  13. Slow cooling and highly efficient extraction of hot carriers in colloidal perovskite nanocrystals.

    PubMed

    Li, Mingjie; Bhaumik, Saikat; Goh, Teck Wee; Kumar, Muduli Subas; Yantara, Natalia; Grätzel, Michael; Mhaisalkar, Subodh; Mathews, Nripan; Sum, Tze Chien

    2017-02-08

    Hot-carrier solar cells can overcome the Schottky-Queisser limit by harvesting excess energy from hot carriers. Inorganic semiconductor nanocrystals are considered prime candidates. However, hot-carrier harvesting is compromised by competitive relaxation pathways (for example, intraband Auger process and defects) that overwhelm their phonon bottlenecks. Here we show colloidal halide perovskite nanocrystals transcend these limitations and exhibit around two orders slower hot-carrier cooling times and around four times larger hot-carrier temperatures than their bulk-film counterparts. Under low pump excitation, hot-carrier cooling mediated by a phonon bottleneck is surprisingly slower in smaller nanocrystals (contrasting with conventional nanocrystals). At high pump fluence, Auger heating dominates hot-carrier cooling, which is slower in larger nanocrystals (hitherto unobserved in conventional nanocrystals). Importantly, we demonstrate efficient room temperature hot-electrons extraction (up to ∼83%) by an energy-selective electron acceptor layer within 1 ps from surface-treated perovskite NCs thin films. These insights enable fresh approaches for extremely thin absorber and concentrator-type hot-carrier solar cells.

  14. Pseudo-direct bandgap transitions in silicon nanocrystals: effects on optoelectronics and thermoelectrics

    NASA Astrophysics Data System (ADS)

    Singh, Vivek; Yu, Yixuan; Sun, Qi-C.; Korgel, Brian; Nagpal, Prashant

    2014-11-01

    While silicon nanostructures are extensively used in electronics, the indirect bandgap of silicon poses challenges for optoelectronic applications like photovoltaics and light emitting diodes (LEDs). Here, we show that size-dependent pseudo-direct bandgap transitions in silicon nanocrystals dominate the interactions between (photoexcited) charge carriers and phonons, and hence the optoelectronic properties of silicon nanocrystals. Direct measurements of the electronic density of states (DOS) for different sized silicon nanocrystals reveal that these pseudo-direct transitions, likely arising from the nanocrystal surface, can couple with the quantum-confined silicon states. Moreover, we demonstrate that since these transitions determine the interactions of charge carriers with phonons, they change the light emission, absorption, charge carrier diffusion and phonon drag (Seebeck coefficient) in nanoscaled silicon semiconductors. Therefore, these results can have important implications for the design of optoelectronics and thermoelectric devices based on nanostructured silicon.While silicon nanostructures are extensively used in electronics, the indirect bandgap of silicon poses challenges for optoelectronic applications like photovoltaics and light emitting diodes (LEDs). Here, we show that size-dependent pseudo-direct bandgap transitions in silicon nanocrystals dominate the interactions between (photoexcited) charge carriers and phonons, and hence the optoelectronic properties of silicon nanocrystals. Direct measurements of the electronic density of states (DOS) for different sized silicon nanocrystals reveal that these pseudo-direct transitions, likely arising from the nanocrystal surface, can couple with the quantum-confined silicon states. Moreover, we demonstrate that since these transitions determine the interactions of charge carriers with phonons, they change the light emission, absorption, charge carrier diffusion and phonon drag (Seebeck coefficient) in

  15. Black–white asymmetry in visual perception

    PubMed Central

    Lu, Zhong-Lin; Sperling, George

    2012-01-01

    With eleven different types of stimuli that exercise a wide gamut of spatial and temporal visual processes, negative perturbations from mean luminance are found to be typically 25% more effective visually than positive perturbations of the same magnitude (range 8–67%). In Experiment 12, the magnitude of the black–white asymmetry is shown to be a saturating function of stimulus contrast. Experiment 13 shows black–white asymmetry primarily involves a nonlinearity in the visual representation of decrements. Black–white asymmetry in early visual processing produces even-harmonic distortion frequencies in all ordinary stimuli and in illusions such as the perceived asymmetry of optically perfect sine wave gratings. In stimuli intended to stimulate exclusively second-order processing in which motion or shape are defined not by luminance differences but by differences in texture contrast, the black–white asymmetry typically generates artifactual luminance (first-order) motion and shape components. Because black–white asymmetry pervades psychophysical and neurophysiological procedures that utilize spatial or temporal variations of luminance, it frequently needs to be considered in the design and evaluation of experiments that involve visual stimuli. Simple procedures to compensate for black–white asymmetry are proposed. PMID:22984221

  16. A pH-Sensitive, Biobased Calcium Carbonate Aragonite Nanocrystal as a Novel Anticancer Delivery System

    PubMed Central

    Ismail, Maznah; Tengku Ibrahim, Tengku Azmi; Zakaria, Zuki Abu Bakar

    2013-01-01

    The synthesised biobased calcium carbonate nanocrystals had demonstrated to be an effective carrier for delivery of anticancer drug doxorubicin (DOX). The use of these nanocrystals displayed high levels of selectivity and specificity in achieving effective cancer cell death without nonspecific toxicity. These results confirmed that DOX was intercalated into calcium carbonate nanocrystals at high loading and encapsulation efficiency (4.8 and 96%, resp.). The CaCO3/DOX nanocrystals are relatively stable at neutral pH (7.4), resulting in slow release, but the nanocrystals progressively dissociated in acidic pH (4.8) regimes, triggering faster release of DOX. The CaCO3/DOX nanocrystals exhibited high uptake by MDA MB231 breast cancer cells and a promising potential delivery of DOX to target cells. In vitro chemosensitivity using MTT, modified neutral red/trypan blue assay, and LDH on MDA MB231 breast cancer cells revealed that CaCO3/DOX nanocrystals are more sensitive and gave a greater reduction in cell growth than free DOX. Our findings suggest that CaCO3 nanocrystals hold tremendous promise in the areas of controlled drug delivery and targeted cancer therapy. PMID:24324966

  17. Intrachromosomal karyotype asymmetry in Orchidaceae

    PubMed Central

    Medeiros-Neto, Enoque; Nollet, Felipe; Moraes, Ana Paula; Felix, Leonardo P.

    2017-01-01

    Abstract The asymmetry indexes have helped cytotaxonomists to interpret and classify plant karyotypes for species delimitation efforts. However, there is no consensus about the best method to calculate the intrachromosomal asymmetry. The present study aimed to compare different intrachromosomal asymmetry indexes in order to indicate which are more efficient for the estimation of asymmetry in different groups of orchids. Besides, we aimed to compare our results with the Orchidaceae phylogenetic proposal to test the hypothesis of Stebbins (1971). Through a literature review, karyotypes were selected and analyzed comparatively with ideal karyotypes in a cluster analysis. All karyotypes showed some level of interchromosomal asymmetry, ranging from slightly asymmetric to moderately asymmetric. The five tested intrachromosomal asymmetry indexes indicated Sarcoglottis grandiflora as the species with the most symmetrical karyotype and Christensonella pachyphylla with the most asymmetrical karyotype. In the cluster analysis, the largest number of species were grouped with the intermediary ideal karyotypes B or C. Considering our results, we recommend the combined use of at least two indexes, especially Ask% or A1 with Syi, for cytotaxonomic analysis in groups of orchids. In an evolutionary perspective, our results support Stebbins’ hypothesis that asymmetric karyotypes derive from a symmetric karyotypes. PMID:28644507

  18. Bilateral asymmetry prediction.

    PubMed

    Kostoff, Ronald Neil

    2003-08-01

    This study predicts asymmetries in lateral organ cancer incidence from text mining of the Medline database. Lung, kidney, teste, and ovary cancers were examined. For each cancer, Medline case report articles focused solely on (1) cancer of the right organ and (2) cancer of the left organ were retrieved. The ratio of right organ to left organ articles was compared to actual patient incidence data obtained from the National Cancer Institute's (NCI) SEER database for the period 1979-1998. The agreement between the Medline record ratios and the NCI's patient incidence data ratios ranged from within 3% for lung cancer to within 1% for teste and ovary cancer. This is the first known study to generate cancer lateral incidence asymmetries from the Medline database. The technique should be applicable to other diseases and other types of system asymmetries.

  19. Dermal miconazole nitrate nanocrystals - formulation development, increased antifungal efficacy & skin penetration.

    PubMed

    Pyo, Sung Min; Hespeler, David; Keck, Cornelia M; Müller, Rainer H

    2017-10-05

    Miconazole nitrate nanosuspension was developed to increase its antifungal activity and dermal penetration. In addition, the nanosuspension was combined with the synergistic additive chlorhexidine digluconate. The production was performed by wet bead milling and both production and formulation parameters were optimized. A stabilizer screening revealed poloxamer 407 and Tween 80 both at 0.15% as the most effective stabilizers for miconazole nanosuspensions at 1.0%. The nanocrystals were incorporated into a hydroxypropyl cellulose gel base. Short-term stability (3months) of the nanocrystal bulk population could be shown at room temperature and fridge. Besides the stable bulk nanocrystals, some longitudinal crystal growth to needle like crystals occurred. The addition of ionic compounds as the chlorhexidine digluconate often destabilizes suspensions. Surprisingly here, the addition minimized the crystal growth. An underlying mechanism is proposed. An inhibition zone assay was performed using Candida albicans (ATCC ® 10231™). When comparing the nanocrystals in suspension and in gel to μm-sized miconazole nitrate formulations and two market products, the increase in inhibition zone diameter for the nanosuspension formulations was most pronounced in the chlorhexidine digluconate free formulations. These nanocrystal formulations were closely or similarly effective as the microsuspensions and the market products containing the synergistic chlorhexidine digluconate, showing the potential of the nanosuspension formulation. Nanosuspension performance was even further increased when chlorhexidine digluconate was added. Ex-vivo skin penetration studies on porcine ears revealed distinctly less remaining miconazole nitrate on the skin surface for nanocrystals (e.g., 76-86%) compared to market products (e.g. 94%). Also, penetration was increased e.g. in skin depth of 5-10μm from <1.0/1.7% to e.g. 3.3-6.2% for nanocrystals. Copyright © 2017 Elsevier B.V. All rights reserved.

  20. NanoCrySP technology for generation of drug nanocrystals: translational aspects and business potential.

    PubMed

    Shete, Ganesh; Bansal, Arvind Kumar

    2016-08-01

    Drug nanocrystals have rapidly evolved into a mature drug delivery strategy in the last decade, with almost 16 products currently on the market. Several "top-down" technologies are available in the market for generation of nanocrystals. Despite several advantages, very few bottom-up technologies have been explored for commercial purpose. This short communication highlights a novel, bottom-up, spray drying based technology-NanoCrySP-to generate drug nanocrystals. Nanocrystals are generated in the presence of non-polymeric excipients that act as crystallization inducer for the drug. Excipients encourage crystallization of drug by plasticization, primary heterogeneous nucleation, and imparting physical barrier to crystal growth. Nanocrystals have shown significant improvement in dissolution and thereby oral bioavailability. NanoCrySP technology is protected through patents in India, the USA, and the European Union. NanoCrySP can be utilized for (i) pharmaceutical development of new chemical entities, (ii) differentiated products of existing molecules, and (iii) generic drug products. The aggregation of drug nanocrystals generated using NanoCrySP poses significant challenges in the nanocrystal-based product development. Addition of stabilizers either during spray drying or during dissolution has shown beneficial effects.

  1. Singlet Oxygen Generation Mediated By Silicon Nanocrystal Assemblies

    DTIC Science & Technology

    2011-01-01

    Lattice fringes in Fig.3 d correspond to the (111) atomic planes of Si nanocrystals. Length scales are indicated. Downscaling of the stain etched PSi...intensity of 1W/cm2 in a time scale of a few hours a monolayer of oxygen is formed on the surface of Si nanocrystals. Fig. 8. Infrared absorption...solution. Fig. 10. PL intensity as a function of continuously prolonged etching of Si powder. Inset: PL suppression level (can be scaled as singlet

  2. Doped and codoped silicon nanocrystals: The role of surfaces and interfaces

    NASA Astrophysics Data System (ADS)

    Marri, Ivan; Degoli, Elena; Ossicini, Stefano

    2017-12-01

    Si nanocrystals have been extensively studied because of their novel properties and their potential applications in electronic, optoelectronic, photovoltaic, thermoelectric and biological devices. These new properties are achieved through the combination of the quantum confinement of carriers and the strong influence of surface chemistry. As in the case of bulk Si the tuning of the electronic, optical and transport properties is related to the possibility of doping, in a controlled way, the nanocrystals. This is a big challenge since several studies have revealed that doping in Si nanocrystals differs from the one of the bulk. Theory and experiments have underlined that doping and codoping are influenced by a large number of parameters such as size, shape, passivation and chemical environment of the silicon nanocrystals. However, the connection between these parameters and dopant localization as well as the occurrence of self-purification effects are still not clear. In this review we summarize the latest progress in this fascinating research field considering free-standing and matrix-embedded Si nanocrystals both from the theoretical and experimental point of view, with special attention given to the results obtained by ab-initio calculations and to size-, surface- and interface-induced effects.

  3. Magnesium ferrite nanocrystal clusters for magnetorheological fluid with enhanced sedimentation stability

    NASA Astrophysics Data System (ADS)

    Wang, Guangshuo; Ma, Yingying; Li, Meixia; Cui, Guohua; Che, Hongwei; Mu, Jingbo; Zhang, Xiaoliang; Tong, Yu; Dong, Xufeng

    2017-01-01

    In this study, magnesium ferrite (MgFe2O4) nanocrystal clusters were synthesized using an ascorbic acid-assistant solvothermal method and evaluated as a candidate for magnetorheological (MR) fluid. The morphology, microstructure and magnetic properties of the MgFe2O4 nanocrystal clusters were investigated in detail by field emission scanning electron microscopy (FESEM), transmission electron microscope (TEM), thermogravimetric analyzer (TGA), X-ray diffraction (XRD) and superconducting quantum interference device (SQUID). The MgFe2O4 nanocrystal clusters were suspended in silicone oil to prepare MR fluid and the MR properties were tested using a Physica MCR301 rheometer fitted with a magneto-rheological module. The prepared MR fluid showed typical Bingham plastic behavior, changing from a liquid-like to a solid-like structure under an external magnetic field. Compared with the conventional carbonyl iron particles, MgFe2O4 nanocrystal clusters-based MR fluid demonstrated enhanced sedimentation stability due to the reduced mismatch in density between the particles and the carrier medium. In summary, the as-prepared MgFe2O4 nanocrystal clusters are regarded as a promising candidate for MR fluid with enhanced sedimentation stability.

  4. Light-Harvesting Organic Nanocrystals Capable of Photon Upconversion.

    PubMed

    Li, Li; Zeng, Yi; Yu, Tianjun; Chen, Jinping; Yang, Guoqiang; Li, Yi

    2017-11-23

    Harvesting and converting low energy photons into higher ones through upconversion have great potential in solar energy conversion. A light-harvesting nanocrystal assembled from 9,10-distyrylanthracene and palladium(II) meso-tetraphenyltetrabenzoporphyrin as the acceptor and the sensitizer, respectively effects red-to-green upconversion under incoherent excitation of low power density. An upconversion quantum yield of 0.29±0.02 % is obtained upon excitation with 640 nm laser of 120 mW cm -2 . The well-organized packing of acceptor molecules with aggregation-induced emission in the nanocrystals dramatically reduces the nonradiative decay of the excited acceptor, benefits the triplet-triplet annihilation (TTA) upconversion and guides the consequent upconverted emission. This work provides a straightforward strategy to develop light-harvesting nanocrystals based on TTA upconversion, which is attractive for energy conversion and photonic applications. © 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

  5. Synthesis and characterization of colloidal CdTe nanocrystals

    NASA Astrophysics Data System (ADS)

    Semendy, Fred; Jaganathan, Gomatam; Dhar, Nibir; Trivedi, Sudhir; Bhat, Ishwara; Chen, Yuanping

    2008-08-01

    We synthesized CdTe nano crystals (NCs) in uniform sizes and in good quality as characterized by photoluminescence (PL), AFM, and X-ray diffraction. In this growth procedure, CdTe nano-crystal band gap is strongly dependent on the growth time and not on the injection temperature or organic ligand concentration. This is very attractive because of nano-crystal size can be easily controlled by the growth time only and is very attractive for large scale synthesis. The color of the solution changes from greenish yellow to light orange then to deep orange and finally grayish black to black over a period of one hour. This is a clear indication of the gradual growth of different size (and different band gap) of CdTe nano-crystals as a function of the growth time. In other words, the size of the nano-crystal and its band gap can be controlled by adjusting the growth time after injection of the tellurium. The prepared CdTe NCs were characterized by absorption spectra, photoluminescence (PL), AFM and X-ray diffraction. Measured absorption maxima are at 521, 560, 600 and 603 nm corresponding to band gaps of 2.38, 2.21,2,07 and 2.04 eV respectively for growth times of 15, 30, 45 and 60 minutes. From the absorption data nano-crystal growth size saturates out after 45 minutes. AFM scanning of these materials indicate that the size of these particles is between 4 - 10 nm in diameter for growth time of 45 minutes. XD-ray diffraction indicates that these nano crystals are of cubic zinc blende phase. This paper will present growth and characterization data on CdTe nano crystals for various growth times.

  6. Photochemical versus Thermal Synthesis of Cobalt Oxyhydroxide Nanocrystals

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Alvarado, Samuel R.; Guo, Yijun; Ruberu, T. Purnima A.

    2012-04-18

    Photochemical methods facilitate the generation, isolation, and study of metastable nanomaterials having unusual size, composition, and morphology. These harder-to-isolate and highly reactive phases, inaccessible using conventional high-temperature pyrolysis, are likely to possess enhanced and unprecedented chemical, electromagnetic, and catalytic properties. We report a fast, low-temperature and scalable photochemical route to synthesize very small (3 nm) monodisperse cobalt oxyhydroxide (Co(O)OH) nanocrystals. This method uses readily and commercially available pentaamminechlorocobalt(III) chloride, [Co(NH3)5Cl]Cl2, under acidic or neutral pH and proceeds under either near-UV (350 nm) or Vis (575 nm) illumination. Control experiments showed that the reaction proceeds at competent rates only in themore » presence of light, does not involve a free radical mechanism, is insensitive to O2, and proceeds in two steps: (1) Aquation of [Co(NH3)5Cl]2+ to yield [Co(NH3)5(H2O)]3+, followed by (2) slow photoinduced release of NH3 from the aqua complex. This reaction is slow enough for Co(O)OH to form but fast enough so that nanocrystals are small (ca. 3 nm). The alternative dark thermal reaction proceeds much more slowly and produces much larger (250 nm) polydisperse Co(O)OH aggregates. UV–Vis absorption measurements and ab initio calculations yield a Co(O)OH band gap of 1.7 eV. Fast thermal annealing of Co(O)OH nanocrystals leads to Co3O4 nanocrystals with overall retention of nanoparticle size and morphology. Thermogravimetric analysis shows that oxyhydroxide to mixed-oxide phase transition occurs at significantly lower temperatures (up to ΔT = 64 °C) for small nanocrystals compared with the bulk.« less

  7. Electron Irradiation Effects on Nanocrystal Quantum Dots Used in Bio-Sensing Applications

    NASA Technical Reports Server (NTRS)

    Leon, R.; Nadeau, J.; Evans, K.; Paskova, T.; Monemar, B.

    2004-01-01

    Effects of electron irradiation on some of the optical properties in organic CdSe nanocrystals coated in trioctylphosphine oxide (TOPO) and biologically compatible CdSe nanocrystals coated in mercaptoacetic acid, as CdSe as CdSe nanocrystals conjugated with the protein are investigated using the technique of cathodoluminescence. Effects of varying the beam energy and temperatures were examined and faster degradation at cryogenic temperatures and higher beam energies was found under some conditions.

  8. Nanocrystal Core Lipoprotein Biomimetics for Imaging of Lipoproteins and Associated Diseases.

    PubMed

    Fay, Francois; Sanchez-Gaytan, Brenda L; Cormode, David P; Skajaa, Torjus; Fisher, Edward A; Fayad, Zahi A; Mulder, Willem J M

    2013-02-01

    Lipoproteins are natural nanoparticles composed of phospholipids and apolipoproteins that transport lipids throughout the body. As key effectors of lipid homeostasis, the functions of lipoproteins have been demonstrated to be crucial during the development of cardiovascular diseases. Therefore various strategies have been used to study their biology and detect them in vivo. A recent approach has been the production of lipoprotein biomimetic particles loaded with diagnostically active nanocrystals in their core. These include, but are not limited to: quantum dots, iron oxide or gold nanocrystals. Inclusion of these nanocrystals enables the utilization of lipoproteins as probes for a variety of imaging modalities (computed tomography, magnetic resonance imaging, fluorescence) while preserving their biological activity. Furthermore as some lipoproteins naturally accumulate in atherosclerotic plaque or specific tumor tissues, nanocrystal core lipoprotein biomimetics have been developed as contrast agents for early diagnosis of these diseases.

  9. Copper indium gallium selenide (CIGS) photovoltaic devices made using multistep selenization of nanocrystal films.

    PubMed

    Harvey, Taylor B; Mori, Isao; Stolle, C Jackson; Bogart, Timothy D; Ostrowski, David P; Glaz, Micah S; Du, Jiang; Pernik, Douglas R; Akhavan, Vahid A; Kesrouani, Hady; Vanden Bout, David A; Korgel, Brian A

    2013-09-25

    The power conversion efficiency of photovoltaic devices made with ink-deposited Cu(InxGa1-x)Se2 (CIGS) nanocrystal layers can be enhanced by sintering the nanocrystals with a high temperature selenization process. This process, however, can be challenging to control. Here, we report that ink deposition followed by annealing under inert gas and then selenization can provide better control over CIGS nanocrystal sintering and yield generally improved device efficiency. Annealing under argon at 525 °C removes organic ligands and diffuses sodium from the underlying soda lime glass into the Mo back contact to improve the rate and quality of nanocrystal sintering during selenization at 500 °C. Shorter selenization time alleviates excessive MoSe2 formation at the Mo back contact that leads to film delamination, which in turn enables multiple cycles of nanocrystal deposition and selenization to create thicker, more uniform absorber films. Devices with power conversion efficiency greater than 7% are fabricated using the multiple step nanocrystal deposition and sintering process.

  10. Self-bonded composite films based on cellulose nanofibers and chitin nanocrystals as antifungal materials.

    PubMed

    Robles, Eduardo; Salaberria, Asier M; Herrera, Rene; Fernandes, Susana C M; Labidi, Jalel

    2016-06-25

    Cellulose nanofibers and chitin nanocrystals, two main components of agricultural and aquacultural by-products, were obtained from blue agave and yellow squat lobster industrial residues. Cellulose nanofibers were obtained using high pressure homogenization, while chitin nanocrystals were obtained by hydrolysis in acid medium. Cellulose nanofibers and chitin nanocrystals were characterized by X-ray diffraction, Atomic Force Microscopy and Infrared spectroscopy. Self-bonded composite films with different composition were fabricated by hot pressing and their properties were evaluated. Antifungal activity of chitin nanocrystals was studied using a Cellometer(®) cell count device, mechanical properties at tension were measured with a universal testing machine, water vapor permeability was evaluated with a thermohygrometer and surface tension with sessile drop contact angle method. The addition of chitin nanocrystals reduced slightly the mechanical properties of the composite. Presence of chitin nanocrystals influenced the growth of Aspergillus sp fungus in the surface of the composites as expected. Copyright © 2016 Elsevier Ltd. All rights reserved.

  11. Fluctuating Asymmetry and Intelligence

    ERIC Educational Resources Information Center

    Bates, Timothy C.

    2007-01-01

    The general factor of mental ability ("g") may reflect general biological fitness. If so, "g"-loaded measures such as Raven's progressive matrices should be related to morphological measures of fitness such as fluctuating asymmetry (FA: left-right asymmetry of a set of typically left-right symmetrical body traits such as finger…

  12. Biomedical Nanocrystal Agents: Design, Synthesis, and Applications

    NASA Astrophysics Data System (ADS)

    Cho, Minjung

    In these days, nanomaterials are applied in a variety of biomedical applications including magnetic resonance imaging (MRI), cell imaging, drug delivery, and cell separation. Most MRI contrast agents affect the longitudinal relaxation time (T1) and transverse relaxation time (T2 ) of water protons in the tissue and result in increased positive or negative contrast. Here, we report the optimization of r1 (1/T 1) or r2 (1/T2) relaxivity dynamics with diameter controlled gadolinium oxide nanocrystals (2˜22 nm) and iron based magnetic nanocrystals (4 ˜33 nm). The r1 and r2 MR relaxivity values of hydrated nanocrystals were optimized and examined depending on their core diameter, surface coating, and compositions; the high r1 value of gadolinium oxide was 40-60 S-1mM-1, which is 10-15 fold higher than that of commercial Gd (III) chelates (4.3˜4.6 S-1mM-1). Moreover, in vitro toxicological studies revealed that polymer coated nanocrystals suspensions had no significant effect on human dermal fibroblast (HDF) cells even at high concentration. Towards multimodal imaging or multifunctional ability, we developed the iron oxide/QDs complexes, which consist of cores of iron oxide that act as nucleation sites for fluorescent QDs. The choice of variable QDs helped to visualize and remove large iron oxide materials in a magnetic separation. Additionally, diluted materials concentrated on the magnet could be fluorescently detected even at very low concentration. The designed MRI or multifunctional nanomaterials will give great and powerful uses in biomedical applications.

  13. Direct printing of microstructures by femtosecond laser excitation of nanocrystals in solution

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Shou, Wan; Pan, Heng, E-mail: hp5c7@mst.edu

    2016-05-23

    We report direct printing of micro/sub-micron structures by femtosecond laser excitation of semiconductor nanocrystals (NCs) in solution. Laser excitation with moderate intensity (10{sup 11}–10{sup 12} W/cm{sup 2}) induces 2D and 3D deposition of CdTe nanocrystals in aqueous solution, which can be applied for direct printing of microstructures. It is believed that laser irradiation induces charge formation on nanocrystals leading to deposition. Furthermore, it is demonstrated that the charged nanocrystals can respond to external electrical bias, enabling a printing approach based on selective laser induced electrophoretic deposition. Finally, energy dispersive X-ray analysis of deposited structures shows oxidation occurs and deposited structure mainlymore » consists of Cd{sub x}O.« less

  14. Electromagnetic and microwave-absorbing properties of magnetic nickel ferrite nanocrystals.

    PubMed

    Zhu, Weimo; Wang, Lei; Zhao, Rui; Ren, Jiawen; Lu, Guanzhong; Wang, Yanqin

    2011-07-01

    The electromagnetic and microwave absorbing properties of nickel ferrite nanocrystals were investigated for the first time. There were two frequencies corresponding to the maximum reflection loss in a wide thickness range from 3.0 to 5.0 mm, which may be bought by the nanosize effect and the good crystallization of the nanocrystals.

  15. Acceptors in ZnO nanocrystals: A reinterpretation

    NASA Astrophysics Data System (ADS)

    Gehlhoff, W.; Hoffmann, A.

    2012-12-01

    In a recent article, Teklemichael et al. reported on the identification of an uncompensated acceptor in ZnO nanocrystals using infrared spectroscopy and electron paramagnetic resonance (EPR) in the dark and under illumination. Most of their conclusions, interpretations, and suggestions turned out to be erroneous. The observed EPR signals were interpreted to originate from axial and nonaxial VZn-H defects. We show that the given interpretation of the EPR results is based on misinterpretations of EPR spectra arising from defects in nanocrystals. The explanation of the infrared absorption lines is in conflict with recent results of valence band ordering and valence band splitting.

  16. Dense Ge nanocrystals embedded in TiO2 with exponentially increased photoconduction by field effect.

    PubMed

    Lepadatu, A-M; Slav, A; Palade, C; Dascalescu, I; Enculescu, M; Iftimie, S; Lazanu, S; Teodorescu, V S; Ciurea, M L; Stoica, T

    2018-03-20

    Si and Ge nanocrystals in oxides are of a large interest for photo-effect applications due to the fine-tuning of the optical bandgap by quantum confinement in nanocrystals. In this work, dense Ge nanocrystals suitable for enhanced photoconduction were fabricated from 60% Ge in TiO 2 amorphous layers by low temperature rapid thermal annealing at 550 °C. An exponential increase of the photocurrent with the applied voltage was observed in coplanar structure of Ge nanocrystals composite films deposited on oxidized Si wafers. The behaviour was explained by field effect control of the Fermi level at the Ge nanocrystals-TiO 2 layer/substrate interfaces. The blue-shift of the absorption gap from bulk Ge value to 1.14 eV was evidenced in both photocurrent spectra and optical reflection-transmission experiments, in good agreement with quantum confinement induced bandgap broadening in Ge nanocrystal with sizes of about 5 nm as found from HRTEM and XRD investigations. A nonmonotonic spectral dependence of the refractive index is associated to the Ge nanocrystals formation. The nanocrystal morphology is also in good agreement with the Coulomb gap hopping mechanism of T -1/2 -type explaining the temperature dependence of the dark conduction.

  17. Nanomagnetism study of highly-ordered iron oxide nanocrystal assemblies fabricated by the Langmuir-Blodgett technique.

    PubMed

    Zhang, HaiTao; Bao, NiNa; Yuan, Du; Ding, Jun

    2013-09-21

    Iron oxide nanocrystals are ideal building blocks for the construction of flexible nanodevices whose performance can be modulated by controlling the morphology of isolated particles and their organizational form. This work demonstrates the fabrication of high quality Langmuir-Blodgett (LB) nanocrystal assemblies with limited overlapping and higher coverage by systemically and combinatorially optimizing the parameters of compression pressure and quantity of spread nanocrystals. Monodispersed iron oxide nanocrystals with a diameter of 11.8 nm were synthesized by thermal decomposition of Fe(CO)5 in trioctylamine with the presence of oleic acid. Multilayer nanocrystal assemblies were obtained through a layer-by-layer (LBL) process by repeating the transfer procedure after their hydrophilicity had been improved via treatment in a UV-ozone oven. The quality of nanocrystal assemblies was investigated by UV-vis spectrometry and scanning electron microscopy. The nanomagnetism for the nanostructures of different combination manners was studied systemically by a superconducting quantum interference device (SQUID). A lower superparamagnetic blocking temperature was found in the monolayer Fe3O4 nanocrystal assembly. The superparamagnetic blocking temperature in magnetic nanocrystal assemblies could be tuned through modifying the interparticle interactions among the interlayer and intralayers by controlling the layer number of the assemblies.

  18. Nanocrystals in compression: unexpected structural phase transition and amorphization due to surface impurities.

    PubMed

    Liu, Gang; Kong, Lingping; Yan, Jinyuan; Liu, Zhenxian; Zhang, Hengzhong; Lei, Pei; Xu, Tao; Mao, Ho-Kwang; Chen, Bin

    2016-06-09

    We report an unprecedented surface doping-driven anomaly in the compression behaviors of nanocrystals demonstrating that the change of surface chemistry can lead to an interior bulk structure change in nanoparticles. In the synchrotron-based X-ray diffraction experiments, titania nanocrystals with low concentration yttrium dopants at the surface are found to be less compressible than undoped titania nanocrystals. More surprisingly, an unexpected TiO2(ii) phase (α-PbO2 type) is induced and obvious anisotropy is observed in the compression of yttrium-doped TiO2, in sharp contrast to the compression behavior of undoped TiO2. In addition, the undoped brookite nanocrystals remain with the same structure up to 30 GPa, whereas the yttrium-doped brookite amorphizes above 20 GPa. The abnormal structural evolution observed in yttrium-doped TiO2 does not agree with the reported phase stability of nano titania polymorphs, thus suggesting that the physical properties of the interior of nanocrystals can be controlled by the surface, providing an unconventional and new degree of freedom in search for nanocrystals with novel tunable properties that can trigger applications in multiple areas of industry and provoke more related basic science research.

  19. Ferromagnetic cobalt nanocrystals achieved by soft annealing approach—From individual behavior to mesoscopic organized properties

    NASA Astrophysics Data System (ADS)

    Petit, C.; Wang, Z. L.; Pileni, M. P.

    2007-05-01

    By gentle annealing, 7 nm cobalt nanoparticles synthesized by soft chemistry, are transformed to hard magnetic hexagonal close packed (HCP) cobalt nanocrystals without changing the size, size distribution and passivating layer. This method permits to recover the nanocrystals isolated in solution after the annealing process and then to study the magnetic properties of the HCP cobalt nanocrystals at isolated status or in a self-organized film. Monolayer self-assembly of the HCP cobalt nanocrystals is obtained, and due to the dipolar interaction, ferromagnetic behavior close to room temperature has been observed. The magnetic properties differ significantly due to the influence of the substrate on the annealing process. This different approach of the annealing process of nanocrystals is compared to the classical approach of annealing in which the nanocrystals are first deposited on a substrate and then annealed.

  20. Organo luminescent semiconductor nanocrystal probes for biological applications and process for making and using such probes

    DOEpatents

    Weiss, Shimon; Bruchez, Jr., Marcel; Alivisatos, Paul

    2006-09-05

    A semiconductor nanocrystal compound is described capable of linking to an affinity molecule. The compound comprises (1) a semiconductor nanocrystal capable of emitting electromagnetic radiation and/or absorbing energy, and/or scattering or diffracting electromagnetic radiation--when excited by an electromagnetic radiation source or a particle beam; and (2) at least one linking agent, having a first portion linked to the semiconductor nanocrystal and a second portion capable of linking to an affinity molecule. The compound is linked to an affinity molecule to form a semiconductor nanocrystal probe capable of bonding with a detectable substance. subsequent exposure to excitation energy will excite the semiconductor nanocrystal in the probe causing the emission of electromagnetic radiation. Further described are processes for respectively: making the luminescent semiconductor nanocrystal compound; making the semiconductor nanocrystal probe; and using the probe to determine the presence of a detectable substance in a material.

  1. Organo luminescent semiconductor nanocrystal probes for biological applications and process for making and using such probes

    DOEpatents

    Weiss, Shimon [Pinole, CA; Bruchez, Jr., Marcel; Alivisatos, Paul [Oakland, CA

    2004-03-02

    A semiconductor nanocrystal compound is described capable of linking to an affinity molecule. The compound comprises (1) a semiconductor nanocrystal capable of emitting electromagnetic radiation and/or absorbing energy, and/or scattering or diffracting electromagnetic radiation--when excited by an electromagnetic radiation source or a particle beam; and (2) at least one linking agent, having a first portion linked to the semiconductor nanocrystal and a second portion capable of linking to an affinity molecule. The compound is linked to an affinity molecule to form a semiconductor nanocrystal probe capable of bonding with a detectable substance. Subsequent exposure to excitation energy will excite the semiconductor nanocrystal in the probe, causing the emission of electromagnetic radiation. Further described are processes for respectively: making the semiconductor nanocrystal compound; making the semiconductor nanocrystal probe; and using the probe to determine the presence of a detectable substance in a material.

  2. Organo luminescent semiconductor nanocrystal probes for biological applications and process for making and using such probes

    DOEpatents

    Weiss, Shimon; Bruchez, Jr., Marcel; Alivisatos, Paul

    2005-08-09

    A semiconductor nanocrystal compound is described capable of linking to an affinity molecule. The compound comprises (1) a semiconductor nanocrystal capable of emitting electromagnetic radiation and/or absorbing energy, and/or scattering or diffracting electromagnetic radiation--when excited by an electromagnetic radiation source or a particle beam; and (2) at least one linking agent, having a first portion linked to the semiconductor nanocrystal and a second portion capable of linking to an affinity molecule. The compound is linked to an affinity molecule to form a semiconductor nanocrystal probe capable of bonding with a detectable substance. Subsequent exposure to excitation energy will excite the semiconductor nanocrystal in the probe causing the emission of electromagnetic radiation. Further described are processes for respectively: making the luminescent semiconductor nanocrystal compound; making the semiconductor nanocrystal probe; and using the probe to determine the presence of a detectable substance in a material.

  3. Organo luminescent semiconductor nanocrystal probes for biological applications and process for making and using such probes

    DOEpatents

    Weiss, Shimon; Bruchez, Jr., Marcel; Alivisatos, Paul

    2002-01-01

    A semiconductor nanocrystal compound is described capable of linking to an affinity molecule. The compound comprises (1) a semiconductor nanocrystal capable of emitting electromagnetic radiation and/or absorbing energy, and/or scattering or diffracting electromagnetic radiation--when excited by an electromagnetic radiation source or a particle beam; and (2) at least one linking agent, having a first portion linked to the semiconductor nanocrystal and a second portion capable of linking to an affity molecule. The compound is linked to an affinity molecule to form a semiconductor nanocrystal probe capable of bonding with a detectable substance. Subsequent exposure to excitation energy will excite the semiconductor nanocrystal in he probe, causing the emission of electromagnetic radiation. Further described are processes for respectively: making the semiconductor nanocrystal compound; making the semiconductor nanocrystal probe; and using the probe to determine the presence of a detectable substance in a material.

  4. 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.

  5. Asymmetries of solar oscillation line profiles

    NASA Technical Reports Server (NTRS)

    Duvall, T. L., Jr.; Jefferies, S. M.; Harvey, J. W.; Osaki, Y.; Pomerantz, M. A.

    1993-01-01

    Asymmetries of the power spectral line profiles of solar global p-modes are detected in full-disk intensity observations of the Ca II K Fraunhofer line. The asymmetry is a strong function of temporal frequency being strongest at the lowest frequencies observed and vanishing near the peak of the power distribution. The variation with spherical harmonic degree is small. The asymmetry is interpreted in terms of a model in which the solar oscillation cavity is compared to a Fabry-Perot interferometer with the source slightly outside the cavity. A phase difference between an outward direct wave and a corresponding inward wave that passes through the cavity gives rise to the asymmetry. The asymmetry is different in velocity and intensity observations. Neglecting the asymmetry when modeling the power spectrum can lead to systematic errors in the measurement of mode frequencies of as much as 10 exp -4 of the mode frequency. The present observations and interpretation locate the source of the oscillations to be approximately 60 km beneath the photosphere, the shallowest position suggested to date.

  6. ``Green's function'' approach & low-mode asymmetries

    NASA Astrophysics Data System (ADS)

    Masse, Laurent; Clark, Dan; Salmonson, Jay; MacLaren, Steve; Ma, Tammy; Khan, Shahab; Pino, Jesse; Ralph, Jo; Czajka, C.; Tipton, Robert; Landen, Otto; Kyrala, Georges; 2 Team; 1 Team

    2017-10-01

    Long wavelength, low mode asymmetries are believed to play a leading role in limiting the performance of current ICF implosions on NIF. These long wavelength modes are initiated and driven by asymmetries in the x-ray flux from the hohlraum; however, the underlying hydrodynamics of the implosion also act to amplify these asymmetries. The work presented here aim to deepen our understanding of the interplay of the drive asymmetries and the underlying implosion hydrodynamics in determining the final imploded configuration. This is accomplished through a synthesis of numerical modeling, analytic theory, and experimental data. In detail, we use a Green's function approach to connect the drive asymmetry seen by the capsule to the measured inflight and hot spot symmetries. The approach has been validated against a suite of numerical simulations. Ultimately, we hope this work will identify additional measurements to further constrain the asymmetries and increase hohlraum illumination design flexibility on the NIF. The technique and derivation of associated error bars will be presented. LLC, (LLNS) Contract No. DE-AC52-07NA27344.

  7. Donor ionization in size controlled silicon nanocrystals: The transition from defect passivation to free electron generation

    NASA Astrophysics Data System (ADS)

    Crowe, I. F.; Papachristodoulou, N.; Halsall, M. P.; Hylton, N. P.; Hulko, O.; Knights, A. P.; Yang, P.; Gwilliam, R. M.; Shah, M.; Kenyon, A. J.

    2013-01-01

    We studied the photoluminescence spectra of silicon and phosphorus co-implanted silica thin films on (100) silicon substrates as a function of isothermal annealing time. The rapid phase segregation, formation, and growth dynamics of intrinsic silicon nanocrystals are observed, in the first 600 s of rapid thermal processing, using dark field mode X-TEM. For short annealing times, when the nanocrystal size distribution exhibits a relatively small mean diameter, formation in the presence of phosphorus yields an increase in the luminescence intensity and a blue shift in the emission peak compared with intrinsic nanocrystals. As the mean size increases with annealing time, this enhancement rapidly diminishes and the peak energy shifts further to the red than the intrinsic nanocrystals. These results indicate the existence of competing pathways for the donor electron, which depends strongly on the nanocrystal size. In samples containing a large density of relatively small nanocrystals, the tendency of phosphorus to accumulate at the nanocrystal-oxide interface means that ionization results in a passivation of dangling bond (Pb-centre) type defects, through a charge compensation mechanism. As the size distribution evolves with isothermal annealing, the density of large nanocrystals increases at the expense of smaller nanocrystals, through an Ostwald ripening mechanism, and the majority of phosphorus atoms occupy substitutional lattice sites within the nanocrystals. As a consequence of the smaller band-gap, ionization of phosphorus donors at these sites increases the free carrier concentration and opens up an efficient, non-radiative de-excitation route for photo-generated electrons via Auger recombination. This effect is exacerbated by an enhanced diffusion in phosphorus doped glasses, which accelerates silicon nanocrystal growth.

  8. Nanocrystal Core Lipoprotein Biomimetics for Imaging of Lipoproteins and Associated Diseases

    PubMed Central

    Fay, Francois; Sanchez-Gaytan, Brenda L.; Cormode, David P.; Skajaa, Torjus; Fisher, Edward A.; Fayad, Zahi A.

    2013-01-01

    Lipoproteins are natural nanoparticles composed of phospholipids and apolipoproteins that transport lipids throughout the body. As key effectors of lipid homeostasis, the functions of lipoproteins have been demonstrated to be crucial during the development of cardiovascular diseases. Therefore various strategies have been used to study their biology and detect them in vivo. A recent approach has been the production of lipoprotein biomimetic particles loaded with diagnostically active nanocrystals in their core. These include, but are not limited to: quantum dots, iron oxide or gold nanocrystals. Inclusion of these nanocrystals enables the utilization of lipoproteins as probes for a variety of imaging modalities (computed tomography, magnetic resonance imaging, fluorescence) while preserving their biological activity. Furthermore as some lipoproteins naturally accumulate in atherosclerotic plaque or specific tumor tissues, nanocrystal core lipoprotein biomimetics have been developed as contrast agents for early diagnosis of these diseases. PMID:23687557

  9. Chalcogenide and pnictide nanocrystals from the silylative deoxygenation of metal oxides

    DOE PAGES

    Lin, Chia-Cheng; Tan, Shannon J.; Vela, Javier

    2017-09-11

    Transition metal chalcogenide and pnictide nanocrystals are of interest for optoelectronic and catalytic applications. In this paper, we present a generalized route to the synthesis of these materials from the silylative deoxygenation of metal oxides with trimethylsilyl reagents. Specific nanophases produced in this way include Ni 3S 2, Ni 5Se 5, Ni 2P, Co 9S 8, Co 3Se 4, CoP, Co 2P, and heterobimetallic (Ni/Co) 9S 8. The resulting chalcogenide nanocrystals are hollow, likely due to differential rates of ion diffusion during the interfacial phase transformation reaction (Kirkendall-type effect). In contrast, the phosphide nanocrystals are solid, likely because they formmore » at higher reaction temperatures. Finally, in all cases, simultaneous partial decomposition of the deoxygenating silyl reagent produces a coating of amorphous silica around the newly formed nanocrystals, which could impact their stability and recyclability.« less

  10. Reaction chemistry and ligand exchange at cadmium selenide nanocrystal surfaces

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Owen, Jonathan; Park, Jungwon; Trudeau, Paul-Emile

    Chemical modification of nanocrystal surfaces is fundamentally important to their assembly, their implementation in biology and medicine, and greatly impacts their electrical and optical properties. However, it remains a major challenge owing to a lack of analytical tools to directly determine nanoparticle surface structure. Early nuclear magnetic resonance (NMR) and X-ray photoelectron spectroscopy (XPS) studies of CdSe nanocrystals prepared in tri-n-octylphosphine oxide (1) and tri-n-octylphosphine (2), suggested these coordinating solvents are datively bound to the particle surface. However, assigning the broad NMR resonances of surface-bound ligands is complicated by significant concentrations of phosphorus-containing impurities in commercial sources of 1, andmore » XPS provides only limited information about the nature of the phosphorus containing molecules in the sample. More recent reports have shown the surface ligands of CdSe nanocrystals prepared in technical grade 1, and in the presence of alkylphosphonic acids, include phosphonic and phosphinic acids. These studies do not, however, distinguish whether these ligands are bound datively, as neutral, L-type ligands, or by X-type interaction of an anionic phosphonate/phosphinate moiety with a surface Cd{sup 2+} ion. Answering this question would help clarify why ligand exchange with such particles does not proceed generally as expected based on a L-type ligand model. By using reagents with reactive silicon-chalcogen and silicon-chlorine bonds to cleave the ligands from the nanocrystal surface, we show that our CdSe and CdSe/ZnS core-shell nanocrystal surfaces are likely terminated by X-type binding of alkylphosphonate ligands to a layer of Cd{sup 2+}/Zn{sup 2+} ions, rather than by dative interactions. Further, we provide spectroscopic evidence that 1 and 2 are not coordinated to our purified nanocrystals.« less

  11. Recent progress in cellulose nanocrystals: sources and production.

    PubMed

    Trache, Djalal; Hussin, M Hazwan; Haafiz, M K Mohamad; Thakur, Vijay Kumar

    2017-02-02

    Cellulose nanocrystals, a class of fascinating bio-based nanoscale materials, have received a tremendous amount of interest both in industry and academia owing to its unique structural features and impressive physicochemical properties such as biocompatibility, biodegradability, renewability, low density, adaptable surface chemistry, optical transparency, and improved mechanical properties. This nanomaterial is a promising candidate for applications in fields such as biomedical, pharmaceuticals, electronics, barrier films, nanocomposites, membranes, supercapacitors, etc. New resources, new extraction procedures, and new treatments are currently under development to satisfy the increasing demand of manufacturing new types of cellulose nanocrystals-based materials on an industrial scale. Therefore, this review addresses the recent progress in the production methodologies of cellulose nanocrystals, covering principal cellulose resources and the main processes used for its isolation. A critical and analytical examination of the shortcomings of various approaches employed so far is made. Additionally, structural organization of cellulose and nomenclature of cellulose nanomaterials have also been discussed for beginners in this field.

  12. Williamson-Hall analysis and optical properties of small sized ZnO nanocrystals

    NASA Astrophysics Data System (ADS)

    Kalita, Amarjyoti; Kalita, Manos P. C.

    2017-08-01

    We apply Williamson-Hall (WH) method of X-ray diffraction (XRD) line profile analysis for lattice strain estimation of small sized ZnO nanocrystals (crystallite size≈4 nm). The ZnO nanocrystals are synthesized by room temperature chemical co-precipitation followed by heating at 40 °C. Zinc acetate, sodium hydroxide and 2-mercaptoethanol (ME) are used for the synthesis of the nanocrystals. {100}, {002}, {101} and {200}, {112}, {201} line profiles in the XRD pattern are significantly merged, therefore determination of the full width at half maximum values and peak positions of the line profiles required for WH analysis has been carried out by executing Rietveld refinement of the XRD pattern. Lattice strain of the 4 nm sized ZnO nanocrystals is found to be 5.8×10-3 which is significantly higher as compared to the literature reported values for larger ones (crystallite size≈17-47 nm). Role of ME as capping agent is confirmed by Fourier transform infrared spectroscopy. The band gap of the nanocrystals is determined from the UV-Visible absorption spectrum and is found to be 3.68 eV. The photoluminescence spectrum exhibits emissions in the visible (408 nm-violet, 467 nm-blue and 538 nm-green) regions showing presence of zinc interstitial and oxygen vacancy in the ZnO nanocrystals.

  13. Germanium–Tin/Cadmium Sulfide Core/Shell Nanocrystals with Enhanced Near-Infrared Photoluminescence

    DOE PAGES

    Boote, Brett W.; Men, Long; Andaraarachchi, Himashi P.; ...

    2017-06-27

    Ge 1–xSn x alloy nanocrystals and Ge 1–xSn x/CdS core/shell nanocrystals were prepared via solution phase synthesis, and their size, composition, and optical properties were characterized. We found that the diameter of the nanocrystal samples ranged from 6 to 13 nm. Furthermore, the crystal structure of the Ge 1–xSn x materials was consistent with a cubic diamond phase, while the CdS shell was consistent with the zinc blende polytype. Inclusion of Sn alone does not result in enhanced photoluminescence intensity; however, adding an epitaxial CdS shell onto the Ge 1–xSn x nanocrystals does enhance the photoluminescence up to 15-fold versusmore » that of Ge/CdS nanocrystals with a pure Ge core. There is more effective passivation of surface defects, and a consequent decrease in the level of surface oxidation, by the CdS shell as a result of improved epitaxy (smaller lattice mismatch) is the most likely explanation for the increased photoluminescence observed for the Ge 1–xSn x/CdS materials. With enhanced photoluminescence in the near-infrared region, Ge 1–xSn x core/shell nanocrystals might be useful alternatives to other materials for energy capture and conversion applications and as imaging probes.« less

  14. Magnetic and upconverted luminescent properties of multifunctional lanthanide doped cubic KGdF4 nanocrystals.

    PubMed

    Yang, L W; Zhang, Y Y; Li, J J; Li, Y; Zhong, J X; Chu, Paul K

    2010-12-01

    Lanthanide (Ln3+) doped KGdF4 (Ln=Yb3+, Er3+, Ho3+, Tm3+) nanocrystals with a mean diameter of approximately 12 nm were synthesized by a hydrothermal method using oleic acid as a stabilizing agent at 180 °C. The nanocrystals crystallize in the cubic phase as α-NaGdF4. When excited by a 980 nm laser, these Ln3+ doped nanocrystals exhibit multicolor up-conversion (UC) emissions in red, yellow, blue and white. The calculated color coordinates demonstrate that white UC emission (CIE-X=0.352, CIE-Y=0.347) can be obtained by varying the dopant concentrations in the Yb3+/Ho3+/Tm3+ triply-doped nanocrystals to yield different RGB emission intensities. The measured field dependence of magnetization (M-H curves) of the KGdF4 nanocrystals shows their paramagnetic characteristics that can be ascribed to the non-interacting localized nature of the magnetic moment of Gd3+ ions. Moreover, low temperature thermal treatment can enhance UC properties, magnetization and magnetic mass susceptibility of Ln3+ doped KGdF4 nanocrystals. The multifunctional Ln3+ doped KGdF4 nanocrystals have potential applications in color displays, bioseparation, and optical-magnetic dual modal nanoprobes in biomedical imaging.

  15. Magnetic and upconverted luminescent properties of multifunctional lanthanide doped cubic KGdF4nanocrystals

    NASA Astrophysics Data System (ADS)

    Yang, L. W.; Zhang, Y. Y.; Li, J. J.; Li, Y.; Zhong, J. X.; Chu, Paul K.

    2010-12-01

    Lanthanide (Ln3+) doped KGdF4 (Ln = Yb3+, Er3+, Ho3+, Tm3+) nanocrystals with a mean diameter of approximately 12 nm were synthesized by a hydrothermal method using oleic acid as a stabilizing agent at 180 °C. The nanocrystals crystallize in the cubic phase as α-NaGdF4. When excited by a 980 nm laser, these Ln3+ doped nanocrystals exhibit multicolor up-conversion (UC) emissions in red, yellow, blue and white. The calculated color coordinates demonstrate that white UC emission (CIE-X = 0.352, CIE-Y = 0.347) can be obtained by varying the dopant concentrations in the Yb3+/Ho3+/Tm3+ triply-doped nanocrystals to yield different RGB emission intensities. The measured field dependence of magnetization (M-H curves) of the KGdF4nanocrystals shows their paramagnetic characteristics that can be ascribed to the non-interacting localized nature of the magnetic moment of Gd3+ ions. Moreover, low temperature thermal treatment can enhance UC properties, magnetization and magnetic mass susceptibility of Ln3+ doped KGdF4nanocrystals. The multifunctional Ln3+ doped KGdF4nanocrystals have potential applications in color displays, bioseparation, and optical-magnetic dual modal nanoprobes in biomedical imaging.

  16. Photosensitivity enhancement with TiO2 in semitransparent light-sensitive skins of nanocrystal monolayers.

    PubMed

    Akhavan, Shahab; Yeltik, Aydan; Demir, Hilmi Volkan

    2014-06-25

    We propose and demonstrate light-sensitive nanocrystal skins that exhibit broadband sensitivity enhancement based on electron transfer to a thin TiO2 film grown by atomic layer deposition. In these photosensors, which operate with no external bias, photogenerated electrons remain trapped inside the nanocrystals. These electrons generally recombine with the photogenerated holes that accumulate at the top interfacing contact, which leads to lower photovoltage buildup. Because favorable conduction band offset aids in transferring photoelectrons from CdTe nanocrystals to the TiO2 layer, which decreases the exciton recombination probability, TiO2 has been utilized as the electron-accepting material in these light-sensitive nanocrystal skins. A controlled interface thickness between the TiO2 layer and the monolayer of CdTe nanocrystals enables a photovoltage buildup enhancement in the proposed nanostructure platform. With TiO2 serving as the electron acceptor, we observed broadband sensitivity improvement across 350-475 nm, with an approximately 22% enhancement. Furthermore, time-resolved fluorescence measurements verified the electron transfer from the CdTe nanocrystals to the TiO2 layer in light-sensitive skins. These results could pave the way for engineering nanocrystal-based light-sensing platforms, such as smart transparent windows, light-sensitive walls, and large-area optical detection systems.

  17. Bilateral Asymmetry in the Human Pelvis.

    PubMed

    Kurki, Helen K

    2017-04-01

    Asymmetry of the human axial skeleton has received much less attention that of the limb skeleton. Pelvic morphology is subject to multiple selective factors, including bipedal locomotion and obstetrics, among others, as well as environmental factors such as biomechanical loading. How these various factors influence or restrict asymmetry of the pelvis is unknown and few studies have investigated levels and patterns of pelvic asymmetry. This study examines percentage directional (%DA) and absolute (%AA) asymmetry in 14 bilaterally paired dimensions of the pelvic canal, non-canal pelvis, and femur in female (n = 111) and male (n = 126) skeletons from nine geographically dispersed skeletal samples. Directional asymmetries were uniformly low for all measures and lacked any consistent patterning across the variables, while %AA was highest in the pelvic canal, particularly the posterior aspects. Few sex differences and no population differences were found for %DA and %AA; however the latter was correlated with coefficients of variation across the 14 variables in both sexes. While sample mean %DA were low, standard deviations of the canal variables were high and the majority of individuals in both sexes displayed %DA values >±0.5, suggesting asymmetry is common, if not directionally consistent. Biomechanical loading of the pelvic girdle may influence asymmetry of both the canal and non-canal aspects of the pelvis; however it is unlikely that these asymmetries negatively affect obstetric function, given the prevalence for %DA found in this study. Anat Rec, 300:653-665, 2017. © 2017 Wiley Periodicals, Inc. © 2017 Wiley Periodicals, Inc.

  18. Enhancement of photoluminescence intensity of erbium doped silica containing Ge nanocrystals: distance dependent interactions

    NASA Astrophysics Data System (ADS)

    Manna, S.; Aluguri, R.; Bar, R.; Das, S.; Prtljaga, N.; Pavesi, L.; Ray, S. K.

    2015-01-01

    Photo-physical processes in Er-doped silica glass matrix containing Ge nanocrystals prepared by the sol-gel method are presented in this article. Strong photoluminescence at 1.54 μm, important for fiber optics telecommunication systems, is observed from the different sol-gel derived glasses at room temperature. We demonstrate that Ge nanocrystals act as strong sensitizers for Er3+ ions emission and the effective Er excitation cross section increases by almost four orders of magnitude with respect to the one without Ge nanocrystals. Rate equations are considered to demonstrate the sensitization of erbium luminescence by Ge nanocrystals. Analyzing the erbium effective excitation cross section, extracted from the flux dependent rise and decay times, a Dexter type of short range energy transfer from a Ge nanocrystal to erbium ion is established.

  19. Characterization of memory and measurement history in photoconductivity of nanocrystal arrays

    NASA Astrophysics Data System (ADS)

    Fairfield, Jessamyn A.; Dadosh, Tali; Drndic, Marija

    2010-10-01

    Photoconductivity in nanocrystal films has been previously characterized, but memory effects have received little attention despite their importance for device applications. We show that the magnitude and temperature dependence of the photocurrent in CdSe/ZnS core-shell nanocrystal arrays depends on the illumination and electric field history. Changes in photoconductivity occur on a few-hour timescale, and subband gap illumination of nanocrystals prior to measurements modifies the photocurrent more than band gap illumination. The observed effects can be explained by charge traps within the band gap that are filled or emptied, which may alter nonradiative recombination processes and affect photocurrent.

  20. Controlled synthesis of bright and compatible lanthanide-doped upconverting nanocrystals

    DOEpatents

    Cohen, Bruce E.; Ostrowski, Alexis D.; Chan, Emory M.; Gargas, Daniel J.; Katz, Elan M.; Schuck, P. James; Milliron, Delia J.

    2017-01-31

    Certain nanocrystals possess exceptional optical properties that may make them valuable probes for biological imaging, but rendering these nanoparticles biocompatible requires that they be small enough not to perturb cellular systems. This invention describes a phosphorescent upconverting sub-10 nm nanoparticle comprising a lanthanide-doped hexagonal .beta.-phase NaYF.sub.4 nanocrystal and methods for making the same.

  1. In vivo investigation of hybrid Paclitaxel nanocrystals with dual fluorescent probes for cancer theranostics.

    PubMed

    Hollis, Christin P; Weiss, Heidi L; Evers, B Mark; Gemeinhart, Richard A; Li, Tonglei

    2014-06-01

    To develop novel hybrid paclitaxel (PTX) nanocrystals, in which bioactivatable (MMPSense® 750 FAST) and near infrared (Flamma Fluor® FPR-648) fluorophores are physically incorporated, and to evaluate their anticancer efficacy and diagnostic properties in breast cancer xenograft murine model. The pure and hybrid paclitaxel nanocrystals were prepared by an anti-solvent method, and their physical properties were characterized. The tumor volume change and body weight change were evaluated to assess the treatment efficacy and toxicity. Bioimaging of treated mice was obtained non-invasively in vivo. The released MMPSense molecules from the hybrid nanocrystals were activated by matrix metalloproteinases (MMPs) in vivo, similarly to the free MMPSense, demonstrating its ability to monitor cancer progression. Concurrently, the entrapped FPR-648 was imaged at a different wavelength. Furthermore, when administered at 20 mg/kg, the nanocrystal formulations exerted comparable efficacy as Taxol®, but with decreased toxicity. Hybrid nanocrystals that physically integrated two fluorophores were successfully prepared from solution. Hybrid nanocrystals were shown not only exerting antitumor activity, but also demonstrating the potential of multi-modular bioimaging for diagnostics.

  2. Novel silica stabilization method for the analysis of fine nanocrystals using coherent X-ray diffraction imaging

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Monteforte, Marianne; Estandarte, Ana K.; Chen, Bo

    2016-06-23

    High-energy X-ray Bragg coherent diffraction imaging (BCDI) is a well established synchrotron-based technique used to quantitatively reconstruct the three-dimensional morphology and strain distribution in nanocrystals. The BCDI technique has become a powerful analytical tool for quantitative investigations of nanocrystals, nanotubes, nanorods and more recently biological systems. BCDI has however typically failed for fine nanocrystals in sub-100?nm size regimes ? a size routinely achievable by chemical synthesis ? despite the spatial resolution of the BCDI technique being 20?30?nm. The limitations of this technique arise from the movement of nanocrystals under illumination by the highly coherent beam, which prevents full diffraction datamore » sets from being acquired. A solution is provided here to overcome this problem and extend the size limit of the BCDI technique, through the design of a novel stabilization method by embedding the fine nanocrystals into a silica matrix. Chemically synthesized FePt nanocrystals of maximum dimension 20?nm and AuPd nanocrystals in the size range 60?65?nm were investigated with BCDI measurement at beamline 34-ID-C of the APS, Argonne National Laboratory. Novel experimental methodologies to elucidate the presence of strain in fine nanocrystals are a necessary pre-requisite in order to better understand strain profiles in engineered nanocrystals for novel device development.« less

  3. Novel silica stabilization method for the analysis of fine nanocrystals using coherent X-ray diffraction imaging.

    PubMed

    Monteforte, Marianne; Estandarte, Ana K; Chen, Bo; Harder, Ross; Huang, Michael H; Robinson, Ian K

    2016-07-01

    High-energy X-ray Bragg coherent diffraction imaging (BCDI) is a well established synchrotron-based technique used to quantitatively reconstruct the three-dimensional morphology and strain distribution in nanocrystals. The BCDI technique has become a powerful analytical tool for quantitative investigations of nanocrystals, nanotubes, nanorods and more recently biological systems. BCDI has however typically failed for fine nanocrystals in sub-100 nm size regimes - a size routinely achievable by chemical synthesis - despite the spatial resolution of the BCDI technique being 20-30 nm. The limitations of this technique arise from the movement of nanocrystals under illumination by the highly coherent beam, which prevents full diffraction data sets from being acquired. A solution is provided here to overcome this problem and extend the size limit of the BCDI technique, through the design of a novel stabilization method by embedding the fine nanocrystals into a silica matrix. Chemically synthesized FePt nanocrystals of maximum dimension 20 nm and AuPd nanocrystals in the size range 60-65 nm were investigated with BCDI measurement at beamline 34-ID-C of the APS, Argonne National Laboratory. Novel experimental methodologies to elucidate the presence of strain in fine nanocrystals are a necessary pre-requisite in order to better understand strain profiles in engineered nanocrystals for novel device development.

  4. Improved oral bioavailability for lutein by nanocrystal technology: formulation development, in vitro and in vivo evaluation.

    PubMed

    Chang, Daoxiao; Ma, Yanni; Cao, Guoyu; Wang, Jianhuan; Zhang, Xia; Feng, Jun; Wang, Wenping

    2018-08-01

    Lutein is a kind of natural carotenoids possessing many pharmacological effects. The application of lutein was limited mainly due to its low oral bioavailability caused by poor aqueous solubility. Nanocrystal formulation of lutein was developed to improve the oral bioavailability in this study. The nanosuspension was prepared by the anti-solvent precipitation-ultrasonication method and optimized by Box-Behnken design, followed by freeze-drying to obtain lutein nanocrystals. The nanocrystals were characterized on their physical properties, in vitro dissolution and in vivo absorption performance. Lutein nanocrystals showed as tiny spheres with an average particle size of 110.7 nm. The result of diffractograms indicated that the percent crystallinity of lutein was 89.4% in coarse powder and then declined in nanocrystal formulation. The saturated solubility of lutein in water increased from 7.3 μg/ml for coarse powder up to 215.7 μg/ml for lutein nanocrystals. The dissolution rate of lutein nanocrystals was significantly higher than that of coarse powder or the physical mixture. The C max and AUC 0-24 h of lutein nanocrystals after oral administration in rats was 3.24 and 2.28 times higher than those of lutein suspension, respectively. These results indicated that the nanocrystal formulation could significantly enhance the dissolution and absorption of lutein and might be a promising approach for improving its oral bioavailability.

  5. Surface oxidation of tin chalcogenide nanocrystals revealed by 119Sn-Mössbauer spectroscopy.

    PubMed

    de Kergommeaux, Antoine; Faure-Vincent, Jérôme; Pron, Adam; de Bettignies, Rémi; Malaman, Bernard; Reiss, Peter

    2012-07-18

    Narrow band gap tin(II) chalcogenide (SnS, SnSe, SnTe) nanocrystals are of high interest for optoelectronic applications such as thin film solar cells or photodetectors. However, charge transfer and charge transport processes strongly depend on nanocrystals' surface quality. Using (119)Sn-Mössbauer spectroscopy, which is the most sensitive tool for probing the Sn oxidation state, we show that SnS nanocrystals exhibit a Sn((IV))/Sn((II)) ratio of around 20:80 before and 40:60 after five minutes exposure to air. Regardless of the tin or sulfur precursors used, similar results are obtained using six different synthesis protocols. The Sn((IV)) content before air exposure arises from surface related SnS(2) and Sn(2)S(3) species as well as from surface Sn atoms bound to oleic acid ligands. The increase of the Sn((IV)) content upon air exposure results from surface oxidation. Full oxidation of the SnS nanocrystals without size change is achieved by annealing at 500 °C in air. With the goal to prevent surface oxidation, SnS nanocrystals are capped with a cadmium-phosphonate complex. A broad photoluminescence signal centered at 600 nm indicates successful capping, which however does not reduce the air sensitivity. Finally we demonstrate that SnSe nanocrystals exhibit a very similar behavior with a Sn((IV))/Sn((II)) ratio of 43:57 after air exposure. In the case of SnTe nanocrystals, the ratio of 55:45 is evidence of a more pronounced tendency for oxidation. These results demonstrate that prior to their use in optoelectronics further surface engineering of tin chalcogenide nanocrystals is required, which otherwise have to be stored and processed under inert atmosphere.

  6. Low capping group surface density on zinc oxide nanocrystals.

    PubMed

    Valdez, Carolyn N; Schimpf, Alina M; Gamelin, Daniel R; Mayer, James M

    2014-09-23

    The ligand shell of colloidal nanocrystals can dramatically affect their stability and reaction chemistry. We present a methodology to quantify the dodecylamine (DDA) capping shell of colloidal zinc oxide nanocrystals in a nonpolar solvent. Using NMR spectroscopy, three different binding regimes are observed: strongly bound, weakly associated, and free in solution. The surface density of bound DDA is constant over a range of nanocrystal sizes, and is low compared to both predictions of the number of surface cations and maximum coverages of self-assembled monolayers. The density of strongly bound DDA ligands on the as-prepared ZnO NCs is 25% of the most conservative estimate of the maximum surface DDA density. Thus, these NCs do not resemble the common picture of a densely capped surface ligand layer. Annealing the ZnO NCs in molten DDA for 12 h at 160 °C, which is thought to remove surface hydroxide groups, resulted in a decrease of the weakly associated DDA and an increase in the density of strongly bound DDA, to ca. 80% of the estimated density of a self-assembled monolayer on a flat ZnO surface. These findings suggest that as-prepared nanocrystal surfaces contain hydroxide groups (protons on the ZnO surfaces) that inhibit strong binding of DDA.

  7. The evolution and genetics of cerebral asymmetry

    PubMed Central

    Corballis, Michael C.

    2008-01-01

    Handedness and cerebral asymmetry are commonly assumed to be uniquely human, and even defining characteristics of our species. This is increasingly refuted by the evidence of behavioural asymmetries in non-human species. Although complex manual skill and language are indeed unique to our species and are represented asymmetrically in the brain, some non-human asymmetries appear to be precursors, and others are shared between humans and non-humans. In all behavioural and cerebral asymmetries so far investigated, a minority of individuals reverse or negate the dominant asymmetry, suggesting that such asymmetries are best understood in the context of the overriding bilateral symmetry of the brain and body, and a trade-off between the relative advantages and disadvantages of symmetry and asymmetry. Genetic models of handedness, for example, typically postulate a gene with two alleles, one disposing towards right-handedness and the other imposing no directional influence. There is as yet no convincing evidence as to the location of this putative gene, suggesting that several genes may be involved, or that the gene may be monomorphic with variations due to environmental or epigenetic influences. Nevertheless, it is suggested that, in behavioural, neurological and evolutionary terms, it may be more profitable to examine the degree rather than the direction of asymmetry. PMID:19064358

  8. Ensemble brightening and enhanced quantum yield in size-purified silicon nanocrystals

    DOE PAGES

    Miller, Joseph B.; Van Sickle, Austin R.; Anthony, Rebecca J.; ...

    2012-07-18

    Here, we report on the quantum yield, photoluminescence (PL) lifetime and ensemble photoluminescent stability of highly monodisperse plasma-synthesized silicon nanocrystals (SiNCs) prepared though density-gradient ultracentrifugation in mixed organic solvents. Improved size uniformity leads to a reduction in PL line width and the emergence of entropic order in dry nanocrystal films. We find excellent agreement with the anticipated trends of quantum confinement in nanocrystalline silicon, with a solution quantum yield that is independent of nanocrystal size for the larger fractions but decreases dramatically with size for the smaller fractions. We also find a significant PL enhancement in films assembled from themore » fractions, and we use a combination of measurement, simulation and modeling to link this ‘brightening’ to a temporally enhanced quantum yield arising from SiNC interactions in ordered ensembles of monodisperse nanocrystals. Using an appropriate excitation scheme, we exploit this enhancement to achieve photostable emission.« less

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

    DOE Office of Scientific and Technical Information (OSTI.GOV)

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

    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 poremore » 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.« less

  10. 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.

  11. 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.

  12. Zero-reabsorption doped-nanocrystal luminescent solar concentrators.

    PubMed

    Erickson, Christian S; Bradshaw, Liam R; McDowall, Stephen; Gilbertson, John D; Gamelin, Daniel R; Patrick, David L

    2014-04-22

    Optical concentration can lower the cost of solar energy conversion by reducing photovoltaic cell area and increasing photovoltaic efficiency. Luminescent solar concentrators offer an attractive approach to combined spectral and spatial concentration of both specular and diffuse light without tracking, but they have been plagued by luminophore self-absorption losses when employed on practical size scales. Here, we introduce doped semiconductor nanocrystals as a new class of phosphors for use in luminescent solar concentrators. In proof-of-concept experiments, visibly transparent, ultraviolet-selective luminescent solar concentrators have been prepared using colloidal Mn(2+)-doped ZnSe nanocrystals that show no luminescence reabsorption. Optical quantum efficiencies of 37% are measured, yielding a maximum projected energy concentration of ∼6× and flux gain for a-Si photovoltaics of 15.6 in the large-area limit, for the first time bounded not by luminophore self-absorption but by the transparency of the waveguide itself. Future directions in the use of colloidal doped nanocrystals as robust, processable spectrum-shifting phosphors for luminescent solar concentration on the large scales required for practical application of this technology are discussed.

  13. Fragmentation, rings and coarsening: structure and transformations of nanocrystal aggregate networks on a liquid surface

    NASA Astrophysics Data System (ADS)

    Yang, Bo; Scheidtmann, Jens; Mayer, Joachim; Wuttig, Matthias; Michely, Thomas

    2002-01-01

    Deposition of Ag on a silicon oil surface leads to the formation of nm-sized Ag crystals floating on the oil surface. These nanocrystals mutually attract each other, forming strongly branched nanocrystal aggregates and continuous aggregate networks. Transformation processes of such nanocrystal aggregate networks are imaged in situ by optical microscopy. The observations are explained on the basis of a simple model involving diffusion of nanocrystals along aggregate edges and the rupture of branches resulting from branch width fluctuations due to edge diffusion.

  14. Compensation procedures for facial asymmetries.

    PubMed

    Kozol, F

    1995-01-01

    Why would a patient complain of "fuzzy and uncomfortable" vision with a variety of glasses? Perhaps because the practitioner has failed to take facial asymmetry into account. Methods of measuring facial asymmetry and optically correcting for it are discussed.

  15. Mesoporous Colloidal Superparticles of Platinum-Group Nanocrystals with Surfactant-Free Surfaces and Enhanced Heterogeneous Catalysis

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Hu, Yongxing; Liu, Yuzi; Sun, Yugang

    2015-01-23

    Synthesis of colloidal superparticles (CSPs) of nanocrystals, a class of assembled nanocrystals in the form of colloidal particles, has been emerging as a new frontier in the field of nanotechnology because of their potential novel properties originated from coupling of individual nanocrystals in CSPs. Here, a facile approach is reported for the controlled synthesis of mesoporous CSPs made of various platinum-group nanocrystals that exhibit high colloidal stability and ligand-free surfaces to significantly benefit their applications in solution-phase heterogeneous catalysis. The synthesis relies on self-limiting growth of composite particles through coprecipitation of both Pt-group nanocrystals (or their precursor compounds) and silvermore » halides on sacrificial substrates of colloidal silver particles. The intermediate silver halides in the composite particles play the critical role in limiting the continuous growth (and/or coalescence) of individual Pt-group nanocrystals and they can be selectively dissolved to create nanoscale pores in the resulting CSPs.« less

  16. Improving polymer/nanocrystal hybrid solar cell performance via tuning ligand orientation at CdSe quantum dot surface.

    PubMed

    Fu, Weifei; Wang, Ling; Zhang, Yanfang; Ma, Ruisong; Zuo, Lijian; Mai, Jiangquan; Lau, Tsz-Ki; Du, Shixuan; Lu, Xinhui; Shi, Minmin; Li, Hanying; Chen, Hongzheng

    2014-11-12

    Achieving superior solar cell performance based on the colloidal nanocrystals remains challenging due to their complex surface composition. Much attention has been devoted to the development of effective surface modification strategies to enhance electronic coupling between the nanocrystals to promote charge carrier transport. Herein, we aim to attach benzenedithiol ligands onto the surface of CdSe nanocrystals in the "face-on" geometry to minimize the nanocrystal-nanocrystal or polymer-nanocrystal distance. Furthermore, the "electroactive" π-orbitals of the benzenedithiol are expected to further enhance the electronic coupling, which facilitates charge carrier dissociation and transport. The electron mobility of CdSe QD films was improved 20 times by tuning the ligand orientation, and high performance poly[2,6-(4,4-bis(2-ethylhexyl)-4H-cyclopenta[2,1-b;3,4-b']-dithiophene)-alt-4,7-(2,1,3-benzothiadiazole)] (PCPDTBT):CdSe nanocrystal hybrid solar cells were also achieved, showing a highest power conversion efficiency of 4.18%. This research could open up a new pathway to improve further the performance of colloidal nanocrystal based solar cells.

  17. A Safer, Easier, Faster Synthesis for CdSe Quantum Dot Nanocrystals

    ERIC Educational Resources Information Center

    Boatman, Elizabeth M.; Lisensky, George C.; Nordell, Karen J.

    2005-01-01

    The synthesis for CdSe quantum dot nanocrystals that vary in color and are a visually engaging way to demonstrate quantum effects in chemistry is presented. CdSe nanocrystals are synthesized from CdO and elemental Se using a kinetic growth method where particle size depends on reaction time.

  18. Nanocrystals of medium soluble actives--novel concept for improved dermal delivery and production strategy.

    PubMed

    Zhai, Xuezhen; Lademann, Jürgen; Keck, Cornelia M; Müller, Rainer H

    2014-08-15

    After use in oral pharmaceutical products, nanocrystals are meanwhile applied to improve the dermal penetration of cosmetic actives (e.g. rutin, hesperidin) and of drugs. By now, nanocrystals are only dermally applied made from poorly soluble actives. The novel concept is to formulate nanocrystals also from medium soluble actives, and to apply a dermal formulation containing additionally nanocrystals. The nanocrystals should act as fast dissolving depot, increase saturation solubility and especially accumulate in the hair follicles, to further increase skin penetration. Caffeine was used as model compound with relevance to market products, and a particular process was developed for the production of caffeine nanocrystals to overcome the supersaturation related effect of crystal growth and fiber formation - typical with medium soluble compounds. It is based on low energy milling (pearl milling) in combination with low dielectric constant dispersion media (water-ethanol or ethanol-propylene glycol mixtures) and optimal stabilizers. Most successful was Carbopol(®) 981 (e.g. 20% caffeine in ethanol-propylene glycol 3:7 with 2% Carbopol, w/w). Nanocrystals with varied sizes can now be produced in a controlled process e.g. 660 nm (optimal for hair follicle accumulation) to 250 nm (optimal for fast dissolution). The short term test proved stability over 2 months of the present formulation being sufficient to perform in vivo testing of the novel concept. Copyright © 2014 Elsevier B.V. All rights reserved.

  19. Analytical modeling of localized surface plasmon resonance in heterostructure copper sulfide nanocrystals

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Caldwell, Andrew H.; Ha, Don-Hyung; Ding, Xiaoyue

    2014-10-28

    Localized surface plasmon resonance (LSPR) in semiconductor nanocrystals is a relatively new field of investigation that promises greater tunability of plasmonic properties compared to metal nanoparticles. A novel process by which the LSPR in semiconductor nanocrystals can be altered is through heterostructure formation arising from solution-based cation exchange. Herein, we describe the development of an analytical model of LSPR in heterostructure copper sulfide-zinc sulfide nanocrystals synthesized via a cation exchange reaction between copper sulfide (Cu 1.81S) nanocrystals and Zn ions. The cation exchange reaction produces dual-interface, heterostructure nanocrystals in which the geometry of the copper sulfide phase can be tunedmore » from a sphere to a thin disk separating symmetrically-grown sulfide (ZnS) grains. Drude model electronic conduction and Mie-Gans theory are applied to describe how the LSPR wavelength changes during cation exchange, taking into account the morphology evolution and changes to the local permittivity. The results of the modeling indicate that the presence of the ZnS grains has a significant effect on the out-of-plane LSPR mode. By comparing the results of the model to previous studies on solid-solid phase transformations of copper sulfide in these nanocrystals during cation exchange, we show that the carrier concentration is independent of the copper vacancy concentration dictated by its atomic phase. The evolution of the effective carrier concentration calculated from the model suggests that the out-of-plane resonance mode is dominant. The classical model was compared to a simplified quantum mechanical model which suggested that quantum mechanical effects become significant when the characteristic size is less than ~8 nm. Overall, we find that the analytical models are not accurate for these heterostructured semiconductor nanocrystals, indicating the need for new model development for this emerging field.« less

  20. Analytical modeling of localized surface plasmon resonance in heterostructure copper sulfide nanocrystals

    NASA Astrophysics Data System (ADS)

    Caldwell, Andrew H.; Ha, Don-Hyung; Ding, Xiaoyue; Robinson, Richard D.

    2014-10-01

    Localized surface plasmon resonance (LSPR) in semiconductor nanocrystals is a relatively new field of investigation that promises greater tunability of plasmonic properties compared to metal nanoparticles. A novel process by which the LSPR in semiconductor nanocrystals can be altered is through heterostructure formation arising from solution-based cation exchange. Herein, we describe the development of an analytical model of LSPR in heterostructure copper sulfide-zinc sulfide nanocrystals synthesized via a cation exchange reaction between copper sulfide (Cu1.81S) nanocrystals and Zn ions. The cation exchange reaction produces dual-interface, heterostructure nanocrystals in which the geometry of the copper sulfide phase can be tuned from a sphere to a thin disk separating symmetrically-grown sulfide (ZnS) grains. Drude model electronic conduction and Mie-Gans theory are applied to describe how the LSPR wavelength changes during cation exchange, taking into account the morphology evolution and changes to the local permittivity. The results of the modeling indicate that the presence of the ZnS grains has a significant effect on the out-of-plane LSPR mode. By comparing the results of the model to previous studies on solid-solid phase transformations of copper sulfide in these nanocrystals during cation exchange, we show that the carrier concentration is independent of the copper vacancy concentration dictated by its atomic phase. The evolution of the effective carrier concentration calculated from the model suggests that the out-of-plane resonance mode is dominant. The classical model was compared to a simplified quantum mechanical model which suggested that quantum mechanical effects become significant when the characteristic size is less than ˜8 nm. Overall, we find that the analytical models are not accurate for these heterostructured semiconductor nanocrystals, indicating the need for new model development for this emerging field.

  1. Analytical modeling of localized surface plasmon resonance in heterostructure copper sulfide nanocrystals

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Caldwell, Andrew H.; Ha, Don-Hyung; Robinson, Richard D., E-mail: rdr82@cornell.edu

    2014-10-28

    Localized surface plasmon resonance (LSPR) in semiconductor nanocrystals is a relatively new field of investigation that promises greater tunability of plasmonic properties compared to metal nanoparticles. A novel process by which the LSPR in semiconductor nanocrystals can be altered is through heterostructure formation arising from solution-based cation exchange. Herein, we describe the development of an analytical model of LSPR in heterostructure copper sulfide-zinc sulfide nanocrystals synthesized via a cation exchange reaction between copper sulfide (Cu{sub 1.81}S) nanocrystals and Zn ions. The cation exchange reaction produces dual-interface, heterostructure nanocrystals in which the geometry of the copper sulfide phase can be tunedmore » from a sphere to a thin disk separating symmetrically-grown sulfide (ZnS) grains. Drude model electronic conduction and Mie-Gans theory are applied to describe how the LSPR wavelength changes during cation exchange, taking into account the morphology evolution and changes to the local permittivity. The results of the modeling indicate that the presence of the ZnS grains has a significant effect on the out-of-plane LSPR mode. By comparing the results of the model to previous studies on solid-solid phase transformations of copper sulfide in these nanocrystals during cation exchange, we show that the carrier concentration is independent of the copper vacancy concentration dictated by its atomic phase. The evolution of the effective carrier concentration calculated from the model suggests that the out-of-plane resonance mode is dominant. The classical model was compared to a simplified quantum mechanical model which suggested that quantum mechanical effects become significant when the characteristic size is less than ∼8 nm. Overall, we find that the analytical models are not accurate for these heterostructured semiconductor nanocrystals, indicating the need for new model development for this emerging field.« less

  2. Analytical formulation of lunar cratering asymmetries

    NASA Astrophysics Data System (ADS)

    Wang, Nan; Zhou, Ji-Lin

    2016-10-01

    Context. The cratering asymmetry of a bombarded satellite is related to both its orbit and impactors. The inner solar system impactor populations, that is, the main-belt asteroids (MBAs) and the near-Earth objects (NEOs), have dominated during the late heavy bombardment (LHB) and ever since, respectively. Aims: We formulate the lunar cratering distribution and verify the cratering asymmetries generated by the MBAs as well as the NEOs. Methods: Based on a planar model that excludes the terrestrial and lunar gravitations on the impactors and assuming the impactor encounter speed with Earth venc is higher than the lunar orbital speed vM, we rigorously integrated the lunar cratering distribution, and derived its approximation to the first order of vM/venc. Numerical simulations of lunar bombardment by the MBAs during the LHB were performed with an Earth-Moon distance aM = 20-60 Earth radii in five cases. Results: The analytical model directly proves the existence of a leading/trailing asymmetry and the absence of near/far asymmetry. The approximate form of the leading/trailing asymmetry is (1 + A1cosβ), which decreases as the apex distance β increases. The numerical simulations show evidence of a pole/equator asymmetry as well as the leading/trailing asymmetry, and the former is empirically described as (1 + A2cos2ϕ), which decreases as the latitude modulus | ϕ | increases. The amplitudes A1,2 are reliable measurements of asymmetries. Our analysis explicitly indicates the quantitative relations between cratering distribution and bombardment conditions (impactor properties and the lunar orbital status) like A1 ∝ vM/venc, resulting in a method for reproducing the bombardment conditions through measuring the asymmetry. Mutual confirmation between analytical model and numerical simulations is found in terms of the cratering distribution and its variation with aM. Estimates of A1 for crater density distributions generated by the MBAs and the NEOs are 0.101-0.159 and 0

  3. Preparation of plasmonic vesicles from amphiphilic gold nanocrystals grafted with polymer brushes

    PubMed Central

    Song, Jibin; Huang, Peng; Chen, Xiaoyuan

    2016-01-01

    Gold nanovesicles contain multiple nanocrystals within a polymeric coating. The strong plasmonic coupling between adjacent nanoparticles in their vesicular shell makes ultrasensitive biosensing and bioimaging possible. In our laboratory, multifunctional plasmonic vesicles are assembled from amphiphilic gold nanocrystals (such as gold nanoparticles and gold nanorods) coated with mixed hydrophilic and hydrophobic polymer brushes or amphiphilic diblock co-polymer brushes. To fulfill the different requirements of biomedical applications, different polymers that are either pH=responsive, photoactive or biodegradable can be used to form the hydrophobic brush, while the hydrophilicity is maintained by polyethylene glycol (PEG). This protocol covers the preparation, surface functionalization and self-assembly of amphiphilic gold nanocrystals grafted covalently with polymer brushes. The protocol can be completed within 2 d. The preparation of amphiphilic gold nanocrystals, coated with amphiphilic diblock polymer brushes using a ‘grafting to’ method or mixed hydrophilic and hydrophobic polymer brushes using tandem ‘grafting to’ and ‘grafting from’ methods, is described. We also provide detailed procedures for the preparation and characterization of pH-responsive plasmonic gold nanovesicles from amphiphilic gold nanocrystals using a film-rehydration method that can be completed within ~3 d. PMID:27763624

  4. Pseudo-direct bandgap transitions in silicon nanocrystals: effects on optoelectronics and thermoelectrics.

    PubMed

    Singh, Vivek; Yu, Yixuan; Sun, Qi-C; Korgel, Brian; Nagpal, Prashant

    2014-12-21

    While silicon nanostructures are extensively used in electronics, the indirect bandgap of silicon poses challenges for optoelectronic applications like photovoltaics and light emitting diodes (LEDs). Here, we show that size-dependent pseudo-direct bandgap transitions in silicon nanocrystals dominate the interactions between (photoexcited) charge carriers and phonons, and hence the optoelectronic properties of silicon nanocrystals. Direct measurements of the electronic density of states (DOS) for different sized silicon nanocrystals reveal that these pseudo-direct transitions, likely arising from the nanocrystal surface, can couple with the quantum-confined silicon states. Moreover, we demonstrate that since these transitions determine the interactions of charge carriers with phonons, they change the light emission, absorption, charge carrier diffusion and phonon drag (Seebeck coefficient) in nanoscaled silicon semiconductors. Therefore, these results can have important implications for the design of optoelectronics and thermoelectric devices based on nanostructured silicon.

  5. White light emission and optical gains from a Si nanocrystal thin film

    NASA Astrophysics Data System (ADS)

    Wang, Dong-Chen; Hao, Hong-Chen; Chen, Jia-Rong; Zhang, Chi; Zhou, Jing; Sun, Jian; Lu, Ming

    2015-11-01

    We report a Si nanocrystal thin film consisting of free-standing Si nanocrystals, which can emit white light and show positive optical gains for its red, green and blue (RGB) components under ultraviolet excitation. Si nanocrystals with ϕ = 2.31 ± 0.35 nm were prepared by chemical etching of Si powder, followed by filtering. After being mixed with SiO2 sol-gel and thermally annealed, a broadband photoluminescence (PL) from the thin film was observed. The RGB ratio of the PL can be tuned by changing the annealing temperature or atmosphere, which is 1.00/3.26/4.59 for the pure white light emission. The origins of the PL components could be due to differences in oxygen-passivation degree for Si nanocrystals. The results may find applications in white-light Si lasing and Si lighting.

  6. A facile and green preparation of high-quality CdTe semiconductor nanocrystals at room temperature

    NASA Astrophysics Data System (ADS)

    Liu, Yan; Shen, Qihui; Yu, Dongdong; Shi, Weiguang; Li, Jixue; Zhou, Jianguang; Liu, Xiaoyang

    2008-06-01

    One chemical reagent, hydrazine hydrate, was discovered to accelerate the growth of semiconductor nanocrystals (cadmium telluride) instead of additional energy, which was applied to the synthesis of high-quality CdTe nanocrystals at room temperature and ambient conditions within several hours. Under this mild condition the mercapto stabilizers were not destroyed, and they guaranteed CdTe nanocrystal particle sizes with narrow and uniform distribution over the largest possible range. The CdTe nanocrystals (photoluminescence emission range of 530-660 nm) synthesized in this way had very good spectral properties; for instance, they showed high photoluminescence quantum yield of up to 60%. Furthermore, we have succeeded in detecting the living Borrelia burgdorferi of Lyme disease by its photoluminescence image using CdTe nanocrystals.

  7. Aqueous based synthesis of N-acetyl-L-cysteine capped ZnSe nanocrystals with intense blue emission

    NASA Astrophysics Data System (ADS)

    Soheyli, Ehsan; Sahraei, Reza; Nabiyouni, Gholamreza

    2016-10-01

    In this work a very simple reflux route for preparation of ZnSe nanocrystals with minor modification and faster preparation over conventional ones is introduced. X-ray diffraction analysis indicated that the ZnSe nanocrystals have a cubic structure. The complete disappearance of the S-H band in FT-IR spectrum of N-acetyl-L-cysteine capped ZnSe nanocrystals was an indication over formation of Zn-thiol covalent bonds at the surface of the nanocrystals which results in passivation of small nanocrystals. The strong size-quantization regime was responsible of significant blue shift in absorption/emission spectra. Using the well-known calculations, band gap and Urbach energy of the ZnSe nanocrystals were measured and their average size was estimated optically to be around 4.6 nm along with the TEM image. A dark blue emission with higher relative intensity of excitonic to trap emissions (compared to conventional method), very narrow excitonic emission peak of about 16 nm and remarkable stability was obtained from the ZnSe nanocrystals.

  8. Predicting kinetic nanocrystal shapes through multi-scale theory and simulation: Polyvinylpyrrolidone-mediated growth of Ag nanocrystals

    NASA Astrophysics Data System (ADS)

    Balankura, Tonnam; Qi, Xin; Zhou, Ya; Fichthorn, Kristen A.

    2016-10-01

    In the shape-controlled synthesis of colloidal Ag nanocrystals, structure-directing agents, particularly polyvinylpyrrolidone (PVP), are known to be a key additive in making nanostructures with well-defined shapes. Although many Ag nanocrystals have been successfully synthesized using PVP, the mechanism by which PVP actuates shape control remains elusive. Here, we present a multi-scale theoretical framework for kinetic Wulff shape predictions that accounts for the chemical environment, which we used to probe the kinetic influence of the adsorbed PVP film. Within this framework, we use umbrella-sampling molecular dynamics simulations to calculate the potential of mean force and diffusion coefficient profiles of Ag atom deposition onto Ag(100) and Ag(111) in ethylene glycol solution with surface-adsorbed PVP. We use these profiles to calculate the mean-first passage times and implement extensive Brownian dynamics simulations, which allows the kinetic effects to be quantitatively evaluated. Our results show that PVP films can regulate the flux of Ag atoms to be greater towards Ag(111) than Ag(100). PVP's preferential binding towards Ag(100) over Ag(111) gives PVP its flux-regulating capabilities through the lower free-energy barrier of Ag atoms to cross the lower-density PVP film on Ag(111) and enhanced Ag trapping by the extended PVP film on Ag(111). Under kinetic control, {100}-faceted nanocrystals will be formed when the Ag flux is greater towards Ag(111). The predicted kinetic Wulff shapes are in agreement with the analogous experimental system.

  9. Toroidal current asymmetry in tokamak disruptions

    NASA Astrophysics Data System (ADS)

    Strauss, H. R.

    2014-10-01

    It was discovered on JET that disruptions were accompanied by toroidal asymmetry of the toroidal plasma current I ϕ. It was found that the toroidal current asymmetry was proportional to the vertical current moment asymmetry with positive sign for an upward vertical displacement event (VDE) and negative sign for a downward VDE. It was observed that greater displacement leads to greater measured I ϕ asymmetry. Here, it is shown that this is essentially a kinematic effect produced by a VDE interacting with three dimensional MHD perturbations. The relation of toroidal current asymmetry and vertical current moment is calculated analytically and is verified by numerical simulations. It is shown analytically that the toroidal variation of the toroidal plasma current is accompanied by an equal and opposite variation of the toroidal current flowing in a thin wall surrounding the plasma. These currents are connected by 3D halo current, which is π/2 radians out of phase with the n = 1 toroidal current variations.

  10. Stochastic left-right neuronal asymmetry in Caenorhabditis elegans.

    PubMed

    Alqadah, Amel; Hsieh, Yi-Wen; Xiong, Rui; Chuang, Chiou-Fen

    2016-12-19

    Left-right asymmetry in the nervous system is observed across species. Defects in left-right cerebral asymmetry are linked to several neurological diseases, but the molecular mechanisms underlying brain asymmetry in vertebrates are still not very well understood. The Caenorhabditis elegans left and right amphid wing 'C' (AWC) olfactory neurons communicate through intercellular calcium signalling in a transient embryonic gap junction neural network to specify two asymmetric subtypes, AWC OFF (default) and AWC ON (induced), in a stochastic manner. Here, we highlight the molecular mechanisms that establish and maintain stochastic AWC asymmetry. As the components of the AWC asymmetry pathway are highly conserved, insights from the model organism C. elegans may provide a window onto how brain asymmetry develops in humans.This article is part of the themed issue 'Provocative questions in left-right asymmetry'. © 2016 The Author(s).

  11. Semiconductor-nanocrystal/conjugated polymer thin films

    DOEpatents

    Alivisatos, A. Paul; Dittmer, Janke J.; Huynh, Wendy U.; Milliron, Delia

    2014-06-17

    The invention described herein provides for thin films and methods of making comprising inorganic semiconductor-nanocrystals dispersed in semiconducting-polymers in high loading amounts. The invention also describes photovoltaic devices incorporating the thin films.

  12. Semiconductor-nanocrystal/conjugated polymer thin films

    DOEpatents

    Alivisatos, A. Paul; Dittmer, Janke J.; Huynh, Wendy U.; Milliron, Delia

    2010-08-17

    The invention described herein provides for thin films and methods of making comprising inorganic semiconductor-nanocrystals dispersed in semiconducting-polymers in high loading amounts. The invention also describes photovoltaic devices incorporating the thin films.

  13. Synthesis of germanium nanocrystals in high temperature supercritical CO2

    NASA Astrophysics Data System (ADS)

    Lu, Xianmao; Korgel, Brian A.; Johnston, Keith P.

    2005-07-01

    Germanium nanocrystals were synthesized in supercritical (sc) CO2 by thermolysis of diphenylgermane (DPG) or tetraethylgermane (TEG) with octanol as a capping ligand at 500 °C and 27.6 MPa. The Ge nanocrystals were characterized with high resolution transmission electron microscopy (HRTEM), energy-dispersive x-ray spectroscopy (EDS), and x-ray diffraction (XRD). On the basis of TEM, the mean diameters of the nanocrystals made from DPG and TEG were 10.1 and 5.6 nm, respectively. The synthesis in sc-CO2 produced much less organic contamination compared with similar reactions in organic supercritical fluids. When the same reaction of DPG with octanol was performed in the gas phase without CO2 present, bulk Ge crystals were formed instead of nanocrystals. Thus, the solvation of the hydrocarbon ligands by CO2 was sufficient to provide steric stabilization. The presence of steric stabilization in CO2 at a reduced temperature of 2.5, with a reduced solvent density of only 0.4, may be attributed to a reduction in the differences between ligand-ligand interactions and ligand-CO2 interactions relative to thermal energy.

  14. Size-dependent characterization of embedded Ge nanocrystals: Structural and thermal properties

    NASA Astrophysics Data System (ADS)

    Araujo, L. L.; Giulian, R.; Sprouster, D. J.; Schnohr, C. S.; Llewellyn, D. J.; Kluth, P.; Cookson, D. J.; Foran, G. J.; Ridgway, M. C.

    2008-09-01

    A combination of conventional and synchrotron-based techniques has been used to characterize the size-dependent structural and thermal properties of Ge nanocrystals (NCs) embedded in a silica (a-SiO2) matrix. Ge NC size distributions with four different diameters ranging from 4.0 to 9.0 nm were produced by ion implantation and thermal annealing as characterized with small-angle x-ray scattering and transmission electron microscopy. The NCs were well represented by the superposition of bulklike crystalline and amorphous environments, suggesting the formation of an amorphous layer separating the crystalline NC core and the a-SiO2 matrix. The amorphous fraction was quantified with x-ray-absorption near-edge spectroscopy and increased as the NC diameter decreased, consistent with the increase in surface-to-volume ratio. The structural parameters of the first three nearest-neighbor shells were determined with extended x-ray-absorption fine-structure (EXAFS) spectroscopy and evolved linearly with inverse NC diameter. Specifically, increases in total disorder, interatomic distance, and the asymmetry in the distribution of distances were observed as the NC size decreased, demonstrating that finite-size effects govern the structural properties of embedded Ge NCs. Temperature-dependent EXAFS measurements in the range of 15-300 K were employed to probe the mean vibrational frequency and the variation of the interatomic distance distribution (mean value, variance, and asymmetry) with temperature for all NC distributions. A clear trend of increased stiffness (higher vibrational frequency) and decreased thermal expansion with decreasing NC size was evident, confirming the close relationship between the variation of structural and thermal/vibrational properties with size for embedded Ge NCs. The increase in surface-to-volume ratio and the presence of an amorphous Ge layer separating the matrix and crystalline NC core are identified as the main factors responsible for the observed

  15. Stability study of PbSe semiconductor nanocrystals over concentration, size, atmosphere, and light exposure.

    PubMed

    Dai, Quanqin; Wang, Yingnan; Zhang, Yu; Li, Xinbi; Li, Ruowang; Zou, Bo; Seo, JaeTae; Wang, Yiding; Liu, Manhong; Yu, William W

    2009-10-20

    Infrared-emitting PbSe nanocrystals are of increasing interest in both fundamental research and technical application. However, the practical applications are greatly limited by their poor stability. In this work, absorption and photoluminescence spectra of PbSe nanocrystals were utilized to observe the stability of PbSe nanocrystals over several conventional factors, that is, particle concentration, particle size, temperature, light exposure, contacting atmosphere, and storage forms (solution or solid powder). Both absorption and luminescence spectra of PbSe nanocrystals exposed to air showed dependence on particle concentration, size, and light exposure, which caused large and quick blue-shifts in the optical spectra. This air-contacted instability arising from the destructive oxidation and subsequent collision-induced decomposition was kinetically dominated and differed from the traditional thought that smaller particles with lower concentrations shrank fast. The photoluminescence emission intensity of the PbSe nanocrystal solution under ultraviolet (UV) exposure in air increased first and then decreased slowly; without UV irradiation, the emission intensity monotonously decreased over time. However, if stored under nitrogen, no obvious changes in absorption and photoluminescence spectra of the PbSe nanocrystals were observed even under UV exposure or upon being heated up to 100 degrees C.

  16. Fabrication of multilayered Ge nanocrystals embedded in SiO xGeN y films

    NASA Astrophysics Data System (ADS)

    Gao, Fei; Green, Martin A.; Conibeer, Gavin; Cho, Eun-Chel; Huang, Yidan; Perez-Wurfl, Ivan; Flynn, Chris

    2008-09-01

    Multilayered Ge nanocrystals embedded in SiO xGeN y films have been fabricated on Si substrate by a (Ge + SiO 2)/SiO xGeN y superlattice approach, using a rf magnetron sputtering technique with a Ge + SiO 2 composite target and subsequent thermal annealing in N 2 ambient at 750 °C for 30 min. X-ray diffraction (XRD) measurement indicated the formation of Ge nanocrystals with an average size estimated to be 5.4 nm. Raman scattering spectra showed a peak of the Ge-Ge vibrational mode downward shifted to 299.4 cm -1, which was caused by quantum confinement of phonons in the Ge nanocrystals. Transmission electron microscopy (TEM) revealed that Ge nanocrystals were confined in (Ge + SiO 2) layers. This superlattice approach significantly improved both the size uniformity of Ge nanocrystals and their uniformity of spacing on the 'Z' growth direction.

  17. 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

  18. High-Brightness Blue and White LEDs based on Inorganic Perovskite Nanocrystals and their Composites

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Yao, En -Ping; Yang, Zhanlue; Meng, Lei

    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

  19. 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. Copyright © 2016 Elsevier Ltd. All rights reserved.

  20. Multicolor tuning of manganese-doped ZnS colloidal nanocrystals.

    PubMed

    Quan, Zewei; Yang, Dongmei; Li, Chunxia; Kong, Deyan; Yang, Piaoping; Cheng, Ziyong; Lin, Jun

    2009-09-01

    In this paper, we report a facile route which is based on tuning doping concentration of Mn(2+) ions in ZnS nanocrystals, to achieve deliberate color modulation from blue to orange-yellow under single-wavelength excitation. X-ray diffraction (XRD), transmission electron microscopy (TEM), as well as photoluminescence (PL) spectra were employed to characterize the obtained samples. In this process, the relative emission intensities of both ZnS host (blue) and Mn(2+) dopant (orange-yellow) are sensitive to the Mn(2+) doping concentration, due to the energy transfer from ZnS host to Mn(2+) dopant. As a result of fine-tuning of these two emission components, white emission can be realized for Mn(2+)-doped ZnS nanocrystals. Furthermore, the as-synthesized doped nanocrystals possess extremely narrow size distribution and can be readily transferred into aqueous solution for the next potential applications.

  1. Preparation and optical characteristics of ZnSe nanocrystals doped glass by sol gel in situ crystallization method

    NASA Astrophysics Data System (ADS)

    Hao, Haiyan; Yao, Xi; Wang, Minqiang

    2007-01-01

    Homogeneous ZnSe nanocrystals doped SiO 2 glass was successfully prepared by sol-gel in situ crystallization method. The structure of the doped ZnSe nanocrystals was studied by X-ray diffraction (XRD). ZnSe nanocrystals in silica were about 4-10 nm analysed by transmission electron microscopy (TEM), which was consistent with the results of XRD estimated using Scherrer's formular. The quantum size effect in ZnSe nanocrystals was evidenced from the blue-shifts of the optical absorption edge, and the average size of ZnSe nanocrystals was estimated by the magnitude of blue shift according to the L.E. Brus' effective mass model. The size of ZnSe nanocrystals depending on annealing time and temperature was further discussed using XRF.

  2. Expansion and melting of Xe nanocrystals in Si

    NASA Astrophysics Data System (ADS)

    Faraci, Giuseppe; Pennisi, Agata R.; Zontone, Federico; Li, Boquan; Petrov, Ivan

    2006-12-01

    Xe agglomerates confined in a Si matrix by ion implantation were synthesized with different size depending on the implantation process and/or the thermal treatment. At low temperature Xe nanocrystals are formed, whose expansion and melting were studied in the range 15- 300K . Previous high resolution x-ray diffraction spectra were corroborated with complementary techniques such as two-dimensional imaging plate patterns and transmission electron microscopy. We detected fcc Xe nanocrystals whose properties were size dependent. The experiments showed that in annealed samples epitaxial condensation of small Xe clusters, on the cavities of the Si matrix, gave in fact expanded and oriented Xe, suggesting a possible preferential growth of Xe(311) planes oriented orthogonally to the Si[02-2] direction. On the contrary, small Xe clusters in an amorphous Si matrix have a fcc lattice contracted as a consequence of surface tension. Furthermore, a solid-to-liquid phase transition size dependent was found. Expansion of fcc Xe lattice was accurately determined as a function of the temperature. Overpressurized nanocrystals and/or binary size distributions were disproved.

  3. Size-Tunable Photothermal Germanium Nanocrystals.

    PubMed

    Sun, Wei; Zhong, Grace; Kübel, Christian; Jelle, Abdinoor A; Qian, Chenxi; Wang, Lu; Ebrahimi, Manuchehr; Reyes, Laura M; Helmy, Amr S; Ozin, Geoffrey A

    2017-05-22

    Germanium nanocrystals (ncGe) have not received as much attention as silicon nanocrystals (ncSi). However, Ge has demonstrated superiority over Si nanomaterials in some applications. Examples include, high charge-discharge rate lithium-ion batteries, small band-gap opto-electronic devices, and photo-therapeutics. When stabilized in an oxide matrix (ncGe/GeO x ), its high charge-retention has enabled non-volatile memories. It has also found utility as a high-capacity anode material for Li-ion batteries with impressive stability. Herein, we report an organic-free synthesis of size-controlled ncGe in a GeO x matrix as well as freestanding ncGe, via the thermal disproportionation of GeO prepared from thermally induced dehydration of Ge(OH) 2 . The photothermal effect of ncGe, quantified by Raman spectroscopy, is found to be size dependent and superior to ncSi. This advance suggests applications of ncGe in photothermal therapy, desalination, and catalysis. © 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

  4. Role of Halides in the Ordered Structure Transitions of Heated Gold Nanocrystal Superlattices

    PubMed Central

    2015-01-01

    Dodecanethiol-capped gold (Au) nanocrystal superlattices can undergo a surprisingly diverse series of ordered structure transitions when heated (Goodfellow, B. W.; Rasch, M. R.; Hessel, C. M.; Patel, R. N.; Smilgies, D.-M.; Korgel, B. A. Nano Lett.2013, 13, 5710–5714). These are the result of highly uniform changes in nanocrystal size, which subsequently force a spontaneous rearrangement of superlattice structure. Here, we show that halide-containing surfactants play an essential role in these transitions. In the absence of any halide-containing surfactant, superlattices of dodecanethiol-capped (1.9-nm-diameter) Au nanocrystals do not change size until reaching about 190–205 °C, at which point the gold cores coalesce. In the presence of halide-containing surfactant, such as tetraoctylphosphonium bromide (TOPB) or tetraoctylammounium bromide (TOAB), the nanocrystals ripen at much lower temperature and superlattices undergo various ordered structure transitions upon heating. Chloride- and iodide-containing surfactants induce similar behavior, destabilizing the Au–thiol bond and reducing the thermal stability of the nanocrystals. PMID:26013597

  5. Size and ligand effects on the electrochemical and spectroelectrochemical responses of CdSe nanocrystals.

    PubMed

    Querner, Claudia; Reiss, Peter; Sadki, Said; Zagorska, Malgorzata; Pron, Adam

    2005-09-07

    The electrochemical properties of CdSe quantum dots with electrochemically inactive surface ligands (TOPO) have been investigated in comparison with the analogous nanocrystals containing electrochemically active oligoaniline ligands. The TOPO-capped nanocrystals have been studied in a wide size range (from 3 to 6.5 nm) with the goal to amplify the influence of the quantum confinement effect on the electrochemical response. The determined HOMO and LUMO levels have been found in good agreement with the ones obtained from photoluminescence studies and those predicted theoretically. Ligand exchange with aniline tetramer significantly influences the voltammetric peaks associated with the HOMO oxidation and the LUMO reduction of the quantum dots, which are shifted to higher and lower potentials, respectively. These shifts are interpreted in terms of the positive ligand charging which precedes the oxidation of the nanocrystals and the insulating nature of the ligand in the case of the nanocrystal reduction. The ligand-nanocrystal interactions have also been studied by UV-Vis-NIR and Raman spectroelectrochemistry in comparison with a specially prepared model compound which, apart from the anchoring function is identical to the grafted oligoaniline ligand. Both spectroelectrochemical techniques clearly indicate the same nature of the oxidation/reduction pathway for both the model compound and the grafted ligand. The influence of the grafting is manifested by a shift in the onset of the ligand oxidation as compared to the case of the "free" model compound. Since both components (ligands and nanocrystals) mutually influence their electrochemical and spectroelectrochemical properties, the newly developed system can be considered as a true molecular hybrid. Such hybrids are of interest because the potential zone of the ligand electroactivity is well separated from that of the nanocrystals and, as a result, the organic part can be electrochemically switched between the

  6. A voxel-based asymmetry study of the relationship between hemispheric asymmetry and language dominance in Wada tested patients.

    PubMed

    Keller, Simon S; Roberts, Neil; Baker, Gus; Sluming, Vanessa; Cezayirli, Enis; Mayes, Andrew; Eldridge, Paul; Marson, Anthony G; Wieshmann, Udo C

    2018-03-23

    Determining the anatomical basis of hemispheric language dominance (HLD) remains an important scientific endeavor. The Wada test remains the gold standard test for HLD and provides a unique opportunity to determine the relationship between HLD and hemispheric structural asymmetries on MRI. In this study, we applied a whole-brain voxel-based asymmetry (VBA) approach to determine the relationship between interhemispheric structural asymmetries and HLD in a large consecutive sample of Wada tested patients. Of 135 patients, 114 (84.4%) had left HLD, 10 (7.4%) right HLD, and 11 (8.2%) bilateral language representation. Fifty-four controls were also studied. Right-handed controls and right-handed patients with left HLD had comparable structural brain asymmetries in cortical, subcortical, and cerebellar regions that have previously been documented in healthy people. However, these patients and controls differed in structural asymmetry of the mesial temporal lobe and a circumscribed region in the superior temporal gyrus, suggesting that only asymmetries of these regions were due to brain alterations caused by epilepsy. Additional comparisons between patients with left and right HLD, matched for type and location of epilepsy, revealed that structural asymmetries of insula, pars triangularis, inferior temporal gyrus, orbitofrontal cortex, ventral temporo-occipital cortex, mesial somatosensory cortex, and mesial cerebellum were significantly associated with the side of HLD. Patients with right HLD and bilateral language representation were significantly less right-handed. These results suggest that structural asymmetries of an insular-fronto-temporal network may be related to HLD. © 2018 The Authors Human Brain Mapping Published by Wiley Periodicals, Inc.

  7. Cellulose nanocrystals the next big nano-thing?

    NASA Astrophysics Data System (ADS)

    Postek, Michael T.; Vladar, Andras; Dagata, John; Farkas, Natalia; Ming, Bin; Sabo, Ronald; Wegner, Theodore H.; Beecher, James

    2008-08-01

    Biomass surrounds us from the smallest alga to the largest redwood tree. Even the largest trees owe their strength to a newly-appreciated class of nanomaterials known as cellulose nanocrystals (CNC). Cellulose, the world's most abundant natural, renewable, biodegradable polymer, occurs as whisker like microfibrils that are biosynthesized and deposited in plant material in a continuous fashion. Therefore, the basic raw materials for a future of new nanomaterials breakthroughs already abound in the environment and are available to be utilized in an array of future materials once the manufacturing processes and nanometrology are fully developed. This presentation will discuss some of the instrumentation, metrology and standards issues associated with nanomanufacturing of cellulose nanocrystals. The use of lignocellulosic fibers derived from sustainable, annually renewable resources as a reinforcing phase in polymeric matrix composites provides positive environmental benefits with respect to ultimate disposability and raw material use. Today we lack the essential metrology infrastructure that would enable the manufacture of nanotechnology-based products based on CNCs (or other new nanomaterial) to significantly impact the U.S. economy. The basic processes common to manufacturing - qualification of raw materials, continuous synthesis methods, process monitoring and control, in-line and off-line characterization of product for quality control purposes, validation by standard reference materials - are not generally in place for nanotechnology based products, and thus are barriers to innovation. One advantage presented by the study of CNCs is that, unlike other nanomaterials, at least, cellulose nanocrystal manufacturing is already a sustainable and viable bulk process. Literally tons of cellulose nanocrystals can be generated each day, producing other viable byproducts such as glucose (for alternative fuel) and gypsum (for buildings).There is an immediate need for the

  8. Reproducible, high-throughput synthesis of colloidal nanocrystals for optimization in multidimensional parameter space.

    PubMed

    Chan, Emory M; Xu, Chenxu; Mao, Alvin W; Han, Gang; Owen, Jonathan S; Cohen, Bruce E; Milliron, Delia J

    2010-05-12

    While colloidal nanocrystals hold tremendous potential for both enhancing fundamental understanding of materials scaling and enabling advanced technologies, progress in both realms can be inhibited by the limited reproducibility of traditional synthetic methods and by the difficulty of optimizing syntheses over a large number of synthetic parameters. Here, we describe an automated platform for the reproducible synthesis of colloidal nanocrystals and for the high-throughput optimization of physical properties relevant to emerging applications of nanomaterials. This robotic platform enables precise control over reaction conditions while performing workflows analogous to those of traditional flask syntheses. We demonstrate control over the size, size distribution, kinetics, and concentration of reactions by synthesizing CdSe nanocrystals with 0.2% coefficient of variation in the mean diameters across an array of batch reactors and over multiple runs. Leveraging this precise control along with high-throughput optical and diffraction characterization, we effectively map multidimensional parameter space to tune the size and polydispersity of CdSe nanocrystals, to maximize the photoluminescence efficiency of CdTe nanocrystals, and to control the crystal phase and maximize the upconverted luminescence of lanthanide-doped NaYF(4) nanocrystals. On the basis of these demonstrative examples, we conclude that this automated synthesis approach will be of great utility for the development of diverse colloidal nanomaterials for electronic assemblies, luminescent biological labels, electroluminescent devices, and other emerging applications.

  9. Quantitative Analysis of Charge Injection and Discharging of Si Nanocrystals and Arrays by Electrostatic Force Microscopy

    NASA Technical Reports Server (NTRS)

    Bell, L. D.; Boer, E.; Ostraat, M.; Brongersma, M. L.; Flagan, R. C.; Atwater, H. A.

    2000-01-01

    NASA requirements for computing and memory for microspacecraft emphasize high density, low power, small size, and radiation hardness. The distributed nature of storage elements in nanocrystal floating-gate memories leads to intrinsic fault tolerance and radiation hardness. Conventional floating-gate non-volatile memories are more susceptible to radiation damage. Nanocrystal-based memories also offer the possibility of faster, lower power operation. In the pursuit of filling these requirements, the following tasks have been accomplished: (1) Si nanocrystal charging has been accomplished with conducting-tip AFM; (2) Both individual nanocrystals on an oxide surface and nanocrystals formed by implantation have been charged; (3) Discharging is consistent with tunneling through a field-lowered oxide barrier; (4) Modeling of the response of the AFM to trapped charge has allowed estimation of the quantity of trapped charge; and (5) Initial attempts to fabricate competitive nanocrystal non-volatile memories have been extremely successful.

  10. Asymmetry in search.

    PubMed

    Kaindl, H; Kainz, G; Radda, K

    2001-01-01

    Most of the work on search in artificial intelligence (AI) deals with one search direction only-mostly forward search-although it is known that a structural asymmetry of the search graph causes differences in the efficiency of searching in the forward or the backward direction, respectively. In the case of symmetrical graph structure, however, current theory would not predict such differences in efficiency. In several classes of job sequencing problems, we observed a phenomenon of asymmetry in search that relates to the distribution of the are costs in the search graph. This phenomenon can be utilized for improving the search efficiency by a new algorithm that automatically selects the search direction. We demonstrate fur a class of job sequencing problems that, through the utilization of this phenomenon, much more difficult problems can be solved-according to our best knowledge-than by the best published approach, and on the same problems, the running time is much reduced. As a consequence, we propose to check given problems for asymmetrical distribution of are costs that may cause asymmetry in search.

  11. Hydrogen-Bonded Organic Semiconductor Micro- And Nanocrystals: From Colloidal Syntheses to (Opto-)Electronic Devices

    PubMed Central

    2014-01-01

    Organic pigments such as indigos, quinacridones, and phthalocyanines are widely produced industrially as colorants for everyday products as various as cosmetics and printing inks. Herein we introduce a general procedure to transform commercially available insoluble microcrystalline pigment powders into colloidal solutions of variously sized and shaped semiconductor micro- and nanocrystals. The synthesis is based on the transformation of the pigments into soluble dyes by introducing transient protecting groups on the secondary amine moieties, followed by controlled deprotection in solution. Three deprotection methods are demonstrated: thermal cleavage, acid-catalyzed deprotection, and amine-induced deprotection. During these processes, ligands are introduced to afford colloidal stability and to provide dedicated surface functionality and for size and shape control. The resulting micro- and nanocrystals exhibit a wide range of optical absorption and photoluminescence over spectral regions from the visible to the near-infrared. Due to excellent colloidal solubility offered by the ligands, the achieved organic nanocrystals are suitable for solution processing of (opto)electronic devices. As examples, phthalocyanine nanowire transistors as well as quinacridone nanocrystal photodetectors, with photoresponsivity values by far outperforming those of vacuum deposited reference samples, are demonstrated. The high responsivity is enabled by photoinduced charge transfer between the nanocrystals and the directly attached electron-accepting vitamin B2 ligands. The semiconducting nanocrystals described here offer a cheap, nontoxic, and environmentally friendly alternative to inorganic nanocrystals as well as a new paradigm for obtaining organic semiconductor materials from commercial colorants. PMID:25253644

  12. Mapping hemispheric symmetries, relative asymmetries, and absolute asymmetries underlying the auditory laterality effect.

    PubMed

    Westerhausen, René; Kompus, Kristiina; Hugdahl, Kenneth

    2014-01-01

    Functional hemispheric differences for speech and language processing have been traditionally studied by using verbal dichotic-listening paradigms. The commonly observed right-ear preference for the report of dichotically presented syllables is taken to reflect the left hemispheric dominance for speech processing. However, the results of recent functional imaging studies also show that both hemispheres - not only the left - are engaged by dichotic listening, suggesting a more complex relationship between behavioral laterality and functional hemispheric activation asymmetries. In order to more closely examine the hemispheric differences underlying dichotic-listening performance, we report an analysis of functional magnetic resonance imaging (fMRI) data of 104 right-handed subjects, for the first time combining an interhemispheric difference and conjunction analysis. This approach allowed for a distinction of homotopic brain regions which showed symmetrical (i.e., brain region significantly activated in both hemispheres and no activation difference between the hemispheres), relative asymmetrical (i.e., activated in both hemispheres but significantly stronger in one than the other hemisphere), and absolute asymmetrical activation patterns (i.e., activated only in one hemisphere and this activation is significantly stronger than in the other hemisphere). Symmetrical activation was found in large clusters encompassing temporal, parietal, inferior frontal, and medial superior frontal regions. Relative and absolute left-ward asymmetries were found in the posterior superior temporal gyrus, located adjacent to symmetrically activated areas, and creating a lateral-medial gradient from symmetrical towards absolute asymmetrical activation within the peri-Sylvian region. Absolute leftward asymmetry was also found in the post-central and medial superior frontal gyri, while rightward asymmetries were found in middle temporal and middle frontal gyri. We conclude that dichotic

  13. Movement asymmetry in working polo horses.

    PubMed

    Pfau, T; Parkes, R S; Burden, E R; Bell, N; Fairhurst, H; Witte, T H

    2016-07-01

    The high, repetitive demands imposed on polo horses in training and competition may predispose them to musculoskeletal injuries and lameness. To quantify movement symmetry and lameness in a population of polo horses, and to investigate the existence of a relationship with age. Convenience sampled cross-sectional study. Sixty polo horses were equipped with inertial measurement units (IMUs) attached to the poll, and between the tubera sacrale. Six movement symmetry measures were calculated for vertical head and pelvic displacement during in-hand trot and compared with values for perfect symmetry, compared between left and right limb lame horses, and compared with published thresholds for lameness. Regression lines were calculated as a function of age of horse. Based on 2 different sets of published asymmetry thresholds 52-53% of the horses were quantified with head movement asymmetry and 27-50% with pelvic movement asymmetry resulting in 60-67% of horses being classified with movement asymmetry outside published guideline values for either the forelimbs, hindlimbs or both. Neither forelimb nor hindlimb asymmetries were preferentially left or right sided, with directional asymmetry values across all horses not different from perfect symmetry and absolute values not different between left and right lame horses (P values >0.6 for all forelimb symmetry measures and >0.2 for all hindlimb symmetry measures). None of the symmetry parameters increased or decreased significantly with age. A large proportion of polo horses show gait asymmetries consistent with previously defined thresholds for lameness. These do not appear to be lateralised or associated with age. © 2015 EVJ Ltd.

  14. Magnetic Cobalt Ferrite Nanocrystals For an Energy Storage Concentration Cell.

    PubMed

    Dai, Qilin; Patel, Ketan; Donatelli, Greg; Ren, Shenqiang

    2016-08-22

    Energy-storage concentration cells are based on the concentration gradient of redox-active reactants; the increased entropy is transformed into electric energy as the concentration gradient reaches equilibrium between two half cells. A recyclable and flow-controlled magnetic electrolyte concentration cell is now presented. The hybrid inorganic-organic nanocrystal-based electrolyte, consisting of molecular redox-active ligands adsorbed on the surface of magnetic nanocrystals, leads to a magnetic-field-driven concentration gradient of redox molecules. The energy storage performance of concentration cells is dictated by magnetic characteristics of cobalt ferrite nanocrystal carriers. The enhanced conductivity and kinetics of redox-active electrolytes could further induce a sharp concentration gradient to improve the energy density and voltage switching of magnetic electrolyte concentration cells. © 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  15. Microfluidic Technology: Uncovering the Mechanisms of Nanocrystal Nucleation and Growth.

    PubMed

    Lignos, Ioannis; Maceiczyk, Richard; deMello, Andrew J

    2017-05-16

    The controlled and reproducible formation of colloidal semiconductor nanocrystals (or quantum dots) is of central importance in nanoscale science and technology. The tunable size- and shape-dependent properties of such materials make them ideal candidates for the development of efficient and low-cost displays, solar cells, light-emitting devices, and catalysts. The formidable difficulties associated with the macroscale preparation of semiconductor nanocrystals (possessing bespoke optical and chemical properties) result from the fact that underlying reaction mechanisms are complex and that the reactive environment is difficult to control. Automated microfluidic reactors coupled with monitoring systems and optimization algorithms aim to elucidate complex reaction mechanisms that govern both nucleation and growth of nanocrystals. Such platforms are ideally suited for the efficient optimization of reaction parameters, assuring the reproducible synthesis of nanocrystals with user-defined properties. This Account aims to inform the nanomaterials community about how microfluidic technologies can supplement flask experimentation for the ensemble investigation of formation mechanisms and design of semiconductor nanocrystals. We present selected studies outlining the preparation of quantum dots using microfluidic systems with integrated analytics. Such microfluidic reaction systems leverage the ability to extract real-time information regarding optical, structural, and compositional characteristics of quantum dots during nucleation and growth stages. The Account further highlights our recent research activities focused on the development and application of droplet-based microfluidics with integrated optical detection systems for the efficient and rapid screening of reaction conditions and a better understanding of the mechanisms of quantum dot synthesis. We describe the features and operation of fully automated microfluidic reactors and their subsequent application to high

  16. [Orthodontic treatment of Class III patients with mandibular asymmetry].

    PubMed

    Duan, Yin-Zhong; Huo, Na; Chen, Lei; Chen, Xue-Peng; Lin, Yang

    2008-12-01

    To investigate the treatment outcome of Class III patients with dental, functional and mild skeletal mandibular asymmetry. Thirty-five patients (14 males and 21 females) with dental, functional and mild skeletal mandibular asymmetry were selected. The age range of the patients was 7 - 22 years with a mean age of 16.5 years. Dental mandibular asymmetry was treated with expansion of maxillary arch to help the mandible returning to normal position. Functional mandibular asymmetry was treated with activator or asymmetrical protraction and Class III elastics. Mild skeletal mandibular asymmetry was treated with camouflage treatment. Good occlusal relationships were achieved and facial esthetics was greatly improved after orthodontic treatment in patients with dental and functional mandibular asymmetry. However, patients with skeletal mandibular asymmetry should be treated with both extraction and genioplasty. Orthodontic treatment was suitable for patients with dental and functional mandibular asymmetry, while combined orthodontics and surgery could get good results in patients with skeletal mandibular asymmetry.

  17. Organo Luminescent semiconductor nanocrystal probes for biological applications and process for making and using such probes

    DOEpatents

    Weiss, Shimon; Bruchez, Jr., Marcel; Alivisatos, Paul

    1999-01-01

    A luminescent semiconductor nanocrystal compound is described which is capable of linking to an affinity molecule. The compound comprises (1) a semiconductor nanocrystal capable of emitting electromagnetic radiation (luminescing) in a narrow wavelength band and/or absorbing energy, and/or scattering or diffracting electromagnetic radiation--when excited by an electromagnetic radiation source (of narrow or broad bandwidth) or a particle beam; and (2) at least one linking agent, having a first portion linked to the semiconductor nanocrystal and a second portion capable of linking to an affinity molecule. The luminescent semiconductor nanocrystal compound is linked to an affinity molecule to form an organo luminescent semiconductor nanocrystal probe capable of bonding with a detectable substance in a material being analyzed, and capable of emitting electromagnetic radiation in a narrow wavelength band and/or absorbing, scattering, or diffracting energy when excited by an electromagnetic radiation source (of narrow or broad bandwidth) or a particle beam. The probe is stable to repeated exposure to light in the presence of oxygen and/or other radicals. Further described is a process for making the luminescent semiconductor nanocrystal compound and for making the organo luminescent semiconductor nanocrystal probe comprising the luminescent semiconductor nanocrystal compound linked to an affinity molecule capable of bonding to a detectable substance. A process is also described for using the probe to determine the presence of a detectable substance in a material.

  18. Controllable synthesis of nickel bicarbonate nanocrystals with high homogeneity for a high-performance supercapacitor

    NASA Astrophysics Data System (ADS)

    Gu, Jianmin; Liu, Xin; Wang, Zhuang; Bian, Zhenpan; Jin, Cuihong; Sun, Xiao; Yin, Baipeng; Wu, Tianhui; Wang, Lin; Tang, Shoufeng; Wang, Hongchao; Gao, Faming

    2017-08-01

    The electrochemical performance of supercapacitors might be associated with the homogeneous structure of the electrode materials. However, the relationship between the degree of uniformity for the electrode materials and the electrochemical performance of the supercapacitor is not clear. Herein, we synthesize two types of nickel bicarbonate nanocrystals with different degrees of uniformity to investigate this relationship. As the electroactive material, the nickel bicarbonate nanocrystals with a homogeneous structure could provide a larger space and offer more exposed atoms for the electrochemical reaction than the nanocrystals with a heterogeneous structure. The homogeneous nickel bicarbonate nanocrystals exhibit better electrochemical performance and show excellent specific capacitance (1596 F g-1 at 2 A g-1 and 1260 F g-1 at 30 A g-1), which is approximately twice that of the heterogeneous nickel bicarbonate nanocrystals. The cycling stability for the homogeneity (˜80%) is higher than the inhomogeneity (˜61%) at a high current density of 5 A g-1.

  19. Nanocrystal grain growth and device architectures for high-efficiency CdTe ink-based photovoltaics.

    PubMed

    Crisp, Ryan W; Panthani, Matthew G; Rance, William L; Duenow, Joel N; Parilla, Philip A; Callahan, Rebecca; Dabney, Matthew S; Berry, Joseph J; Talapin, Dmitri V; Luther, Joseph M

    2014-09-23

    We study the use of cadmium telluride (CdTe) nanocrystal colloids as a solution-processable "ink" for large-grain CdTe absorber layers in solar cells. The resulting grain structure and solar cell performance depend on the initial nanocrystal size, shape, and crystal structure. We find that inks of predominantly wurtzite tetrapod-shaped nanocrystals with arms ∼5.6 nm in diameter exhibit better device performance compared to inks composed of smaller tetrapods, irregular faceted nanocrystals, or spherical zincblende nanocrystals despite the fact that the final sintered film has a zincblende crystal structure. Five different working device architectures were investigated. The indium tin oxide (ITO)/CdTe/zinc oxide structure leads to our best performing device architecture (with efficiency >11%) compared to others including two structures with a cadmium sulfide (CdS) n-type layer typically used in high efficiency sublimation-grown CdTe solar cells. Moreover, devices without CdS have improved response at short wavelengths.

  20. Temperature dependent recombination dynamics in InP/ZnS colloidal nanocrystals

    NASA Astrophysics Data System (ADS)

    Shirazi, R.; Kopylov, O.; Kovacs, A.; Kardynał, B. E.

    2012-08-01

    In this letter, we investigate exciton recombination in InP/ZnS core-shell colloidal nanocrystals over a wide temperature range. Over the entire range between room temperature and liquid helium temperature, multi-exponential exciton decay curves are observed and well explained by the presence of bright and dark exciton states, as well as defect states. Two different types of defect are present: one located at the core-shell interface and the other on the surface of the nanocrystal. Based on the temperature dependent contributions of all four states to the total photoluminescence signal, we estimate that the four states are distributed within a 20 meV energy band in nanocrystals that emit at 1.82 eV.

  1. Photoluminescence studies on Cd(1-x)Zn(x)S:Mn2+ nanocrystals.

    PubMed

    Sethi, Ruchi; Kumar, Lokendra; Pandey, A C

    2009-09-01

    Highly monodispersed, undoped and doped with Mn2+, binary and ternary (CdS, ZnS, Cd(1-x)Zn(x)S) compound semiconductor nanocrystals have been synthesized by co-precipitation method using citric acid as a stabilizer. As prepared sample are characterized by X-ray diffraction, Small angle X-ray scattering, Transmission electron microscope, Optical absorption and Photoluminescence spectroscopy, for their optical and structural properties. X-ray diffraction, Small angle X-ray scattering and Transmission electron microscope results confirm the preparation of monodispersed nanocrystals. Photoluminescence studies show a significant blue shift in the wavelength with an increasing concentration of Zn in alloy nanocrystals.

  2. Femtosecond transient absorption dynamics of close-packed gold nanocrystal monolayer arrays*1

    NASA Astrophysics Data System (ADS)

    Eah, Sang-Kee; Jaeger, Heinrich M.; Scherer, Norbert F.; Lin, Xiao-Min; Wiederrecht, Gary P.

    2004-03-01

    Femtosecond transient absorption spectroscopy is used to investigate hot electron dynamics of close-packed 6 nm gold nanocrystal monolayers. Morphology changes of the monolayer caused by the laser pump pulse are monitored by transmission electron microscopy. At low pump power, the monolayer maintains its structural integrity. Hot electrons induced by the pump pulse decay through electron-phonon (e-ph) coupling inside the nanocrystals with a decay constant that is similar to the value for bulk films. At high pump power, irreversible particle aggregation and sintering occur in the nanocrystal monolayer, which cause damping and peak shifting of the transient bleach signal.

  3. Simple eco-friendly synthesis of the surfactant free SnS nanocrystal toward the photoelectrochemical cell application.

    PubMed

    Huang, Xiaoguang; Woo, Heechul; Wu, Peinian; Hong, Hyo Jin; Jung, Wan Gil; Kim, Bong-Joong; Vanel, Jean-Charles; Choi, Jin Woo

    2017-11-28

    A simple, low cost, non-toxic and eco-friendly pathway for synthesizing efficient sunlight-driven tin sulfide photocatalyst was studied. SnS nanocrystals were prepared by using mechanical method. The bulk SnS was obtained by evaporation of SnS nanocrystal solution. The synthesized samples were characterized by using XRD, SEM, TEM, UV-vis, and Raman analyses. Well crystallized SnS nanocrystals were verified and the electrochemical characterization was also performed under visible light irradiation. The SnS nanocrystals have shown remarkable photocurrent density of 7.6 mA cm -2 under 100 mW cm -2 which is about 10 times larger than that of the bulk SnS under notably stable operation conditions. Furthermore, the SnS nanocrystals presented higher stability than the bulk form. The IPCE(Incident photon to current conversion efficiency) of 9.3% at 420 nm was obtained for SnS nanocrystal photoanode which is strikingly higher than that of bulk SnS, 0.78%. This work suggests that the enhancement of reacting area by using SnS nanocrystal absorbers could give rise to the improvement of photoelectrochemical cell efficiency.

  4. Tailoring indium oxide nanocrystal synthesis conditions for air-stable high-performance solution-processed thin-film transistors.

    PubMed

    Swisher, Sarah L; Volkman, Steven K; Subramanian, Vivek

    2015-05-20

    Semiconducting metal oxides (ZnO, SnO2, In2O3, and combinations thereof) are a uniquely interesting family of materials because of their high carrier mobilities in the amorphous and generally disordered states, and solution-processed routes to these materials are of particular interest to the printed electronics community. Colloidal nanocrystal routes to these materials are particularly interesting, because nanocrystals may be formulated with tunable surface properties into stable inks, and printed to form devices in an additive manner. We report our investigation of an In2O3 nanocrystal synthesis for high-performance solution-deposited semiconductor layers for thin-film transistors (TFTs). We studied the effects of various synthesis parameters on the nanocrystals themselves, and how those changes ultimately impacted the performance of TFTs. Using a sintered film of solution-deposited In2O3 nanocrystals as the TFT channel material, we fabricated devices that exhibit field effect mobility of 10 cm(2)/(V s) and an on/off current ratio greater than 1 × 10(6). These results outperform previous air-stable nanocrystal TFTs, and demonstrate the suitability of colloidal nanocrystal inks for high-performance printed electronics.

  5. Electronic Properties of Free-Standing Surfactant-Capped Lead Halide Perovskite Nanocrystals Isolated in Vacuo.

    PubMed

    Milosavljevic, Aleksandar R; Bozanic, Dusan; Sadhu, Subha; Vukmirovic, Nenad; Dojcilovic, Radovan; Sapkota, Pitambar; Huang, Weixin; Bozek, John D; Nicolas, Christophe; Nahon, Laurent; Ptasinska, Sylwia

    2018-06-14

    We report an investigation of lead halide perovskite CH3NH3PbBr3 nanocrystals and associated ligand molecules, by combining several different state-of-the-art experimental techniques, including synchrotron radiation based XPS and VUV PES of free-standing nanocrystals isolated in vacuum. By using this novel approach for perovskite materials we could directly obtain a complete band alignment to vacuum of both CH3NH3PbBr3 nanocrystals and the ligands widely used in their preparation. We discuss possible influence of the ligand molecules to apparent perovskite properties, and we compare the electronic properties of nanocrystals to that of bulk material. The experimental results were supported by DFT calculations.

  6. Synthesis, screening, and nanocrystals preparation of rhein amide derivatives.

    PubMed

    Chen, Lijiang; Zhang, Jinfeng; Rong, Jinghong; Liu, Yu; Zhao, Jinhua; Cui, Qingguo; Wang, Xin; Liang, Xiao; Pan, Hao; Liu, Hongsheng

    2018-04-23

    Rhein (RH) have many bioactivities, but the application was limited of its poor solubility. The present study aimed to establish an efficient method for the synthesis of rhein amide derivatives (RAD) to increase the solubility and anti-tumor activity. RAD exhibited stronger anti-tumor activity than RH in MTT assay. The solubility and oil/water partition coefficient results indicated that rhein-phenylalanine and rhein-isoleucine have better absorption effect, which was consolidated in pharmacokinetic study. Then, rhein-phenylalanine and rhein-isoleucine were prepared into nanocrystals via the precipitation-high pressure homogenization method. Additionally, the nanocrystals both displayed much higher dissolution profiles than the bulk drugs. Pharmacokinetics study indicated that the AUC 0-∞ and C max of nanocrystals increased markedly (p < 0.01). However, the concentration of RH-Phe-NC was far less than RH-Ile-NC in plasma. Consequently, RH-Ile-NC was validated to be an applicable way to improve the bioavailability of RH, which owns a promising future in clinical application.

  7. Microstructure, thermal properties and crystallinity of amadumbe starch nanocrystals.

    PubMed

    Mukurumbira, Agnes; Mariano, Marcos; Dufresne, Alain; Mellem, John J; Amonsou, Eric O

    2017-09-01

    Amadumbe (Colocasia esculenta), commonly known as taro is a tropical tuber that produces starch-rich underground corms. In this study, the physicochemical properties of starch nanocrystals (SNC) prepared by acid hydrolysis of amadumbe starches were investigated. Two varieties of amadumbe corms were used for starch extraction. Amadumbe starches produced substantially high yield (25%) of SNC's. These nanocrystals appeared as aggregated and individual particles and possessed square-like platelet morphology with size: 50-100nm. FTIR revealed high peak intensities corresponding to OH stretch, CH stretch and H 2 O bending vibrations for SNCs compared to their native starch counterparts. Both the native starch and SNC exhibited the A-type crystalline pattern. However, amadumbe SNCs showed higher degree of crystallinity and slightly reduced melting temperatures than their native starches. Amadumbe SNCs presented similar thermal decomposition property as their native starches. Amadumbe starch nanocrystals may have potential application in biocomposite films due to their square-like platelet morphology. Copyright © 2017 Elsevier B.V. All rights reserved.

  8. Volumetric flame synthesis of well-defined molybdenum oxide nanocrystals.

    PubMed

    Merchan-Merchan, Wilson; Saveliev, Alexei V; Desai, Milind

    2009-11-25

    Well-defined faceted inorganic Mo oxide nanocrystals are synthesized in the gas phase using a solid-fed-precursor flame synthesis method. The solid crystals have rectangular cross-section with characteristic size of 10-20 nm and with lengths ranging from 50 nm to a few hundred nanometres. A 1 mm diameter high purity Mo probe introduced in the oxygen-rich part of the flame serves as the material source. A combination of the strong temperature gradient and varying chemical species concentrations within the flame volume provides the ideal conditions for the rapid and direct formation of these unique nanocrystals. Oxidation and evaporation of MoO3 in the oxygen-rich zone are followed by reduction to MoO2 in the lower temperature, more fuel-rich zone. The MoO3 vapours formed are pushed in the direction of the gas flow and transformed into mature well-defined convex polyhedron nanocrystals bounded with six faces resembling rectangular parallelepipeds.

  9. Bioinspired greigite magnetic nanocrystals: chemical synthesis and biomedicine applications

    PubMed Central

    Feng, Mei; Lu, Yang; Yang, Yuan; Zhang, Meng; Xu, Yun-Jun; Gao, Huai-Ling; Dong, Liang; Xu, Wei-Ping; Yu, Shu-Hong

    2013-01-01

    Large scale greigite with uniform dimensions has stimulated significant demands for applications such as hyperthermia, photovoltaics, medicine and cell separation, etc. However, the inhomogeneity and hydrophobicity for most of the as prepared greigite crystals has limited their applications in biomedicine. Herein, we report a green chemical method utilizing β-cyclodextrin (β-CD) and polyethylene glycol (PEG) to synthesize bioinspired greigite (Fe3S4) magnetic nanocrystals (GMNCs) with similar structure and magnetic property of magnetosome in a large scale. β-CD and PEG is responsible to control the crystal phase and morphology, as well as to bound onto the surface of nanocrystals and form polymer layers. The GMNCs exhibit a transverse relaxivity of 94.8 mM−1s−1 which is as high as iron oxide nanocrystals, and an entrapment efficiency of 58.7% for magnetic guided delivery of chemotherapeutic drug doxorubicin. Moreover, enhanced chemotherapeutic treatment of mice tumor was obtained via intravenous injection of doxorubicin loaded GMNCs. PMID:24141204

  10. The Inherent Asymmetry of DNA Replication.

    PubMed

    Snedeker, Jonathan; Wooten, Matthew; Chen, Xin

    2017-10-06

    Semiconservative DNA replication has provided an elegant solution to the fundamental problem of how life is able to proliferate in a way that allows cells, organisms, and populations to survive and replicate many times over. Somewhat lost, however, in our admiration for this mechanism is an appreciation for the asymmetries that occur in the process of DNA replication. As we discuss in this review, these asymmetries arise as a consequence of the structure of the DNA molecule and the enzymatic mechanism of DNA synthesis. Increasing evidence suggests that asymmetries in DNA replication are able to play a central role in the processes of adaptation and evolution by shaping the mutagenic landscape of cells. Additionally, in eukaryotes, recent work has demonstrated that the inherent asymmetries in DNA replication may play an important role in the process of chromatin replication. As chromatin plays an essential role in defining cell identity, asymmetries generated during the process of DNA replication may play critical roles in cell fate decisions related to patterning and development.

  11. Poloidal asymmetries in edge transport barriersa)

    NASA Astrophysics Data System (ADS)

    Churchill, R. M.; Theiler, C.; Lipschultz, B.; Hutchinson, I. H.; Reinke, M. L.; Whyte, D.; Hughes, J. W.; Catto, P.; Landreman, M.; Ernst, D.; Chang, C. S.; Hager, R.; Hubbard, A.; Ennever, P.; Walk, J. R.

    2015-05-01

    Measurements of impurities in Alcator C-Mod indicate that in the pedestal region, significant poloidal asymmetries can exist in the impurity density, ion temperature, and main ion density. In light of the observation that ion temperature and electrostatic potential are not constant on a flux surface [Theiler et al., Nucl. Fusion 54, 083017 (2014)], a technique based on total pressure conservation to align profiles measured at separate poloidal locations is presented and applied. Gyrokinetic neoclassical simulations with XGCa support the observed large poloidal variations in ion temperature and density, and that the total pressure is approximately constant on a flux surface. With the updated alignment technique, the observed in-out asymmetry in impurity density is reduced from previous publishing [Churchill et al., Nucl. Fusion 53, 122002 (2013)], but remains substantial ( n z , H / n z , L ˜ 6 ). Candidate asymmetry drivers are explored, showing that neither non-uniform impurity sources nor localized fluctuation-driven transport are able to explain satisfactorily the impurity density asymmetry. Since impurity density asymmetries are only present in plasmas with strong electron density gradients, and radial transport timescales become comparable to parallel transport timescales in the pedestal region, it is suggested that global transport effects relating to the strong electron density gradients in the pedestal are the main driver for the pedestal in-out impurity density asymmetry.

  12. TMD evolution of the Sivers asymmetry

    NASA Astrophysics Data System (ADS)

    Boer, Daniël

    2013-09-01

    The energy scale dependence of the Sivers asymmetry in semi-inclusive deep inelastic scattering is studied numerically within the framework of TMD factorization that was put forward in 2011. The comparison to previous results in the literature shows that the treatment of next-to-leading logarithmic effects is important for the fall-off of the Sivers asymmetry with energy in the measurable regime. The TMD factorization based approach indicates that the peak of the Sivers asymmetry falls off with energy scale Q to good approximation as 1/Q0.7, somewhat faster than found previously based on the first TMD factorization expressions by Collins and Soper in 1981. It is found that the peak of the asymmetry moves rather slowly towards higher transverse momentum values as Q increases, which may be due to the absence of perturbative tails of the TMDs in the presented treatments. We conclude that the behavior of the peak of the asymmetry as a function of energy and transverse momentum allows for valuable tests of the TMD formalism and the considered approximations. To confront the TMD approach with experiment, high energy experimental data from an Electron-Ion Collider is required. Note that in B01/B09 the Gaussian width of the Sivers TMD appears in the asymmetry expressions, because of the derivative in f1T⊥ ' a(x;Q0).

  13. Multifunctional superparamagnetic nanocrystals for imaging and targeted drug delivery to the lung

    NASA Astrophysics Data System (ADS)

    Armijo, Leisha M.; Brandt, Yekaterina I.; Withers, Nathan J.; Plumley, John B.; Cook, Nathaniel C.; Rivera, Antonio C.; Yadav, Surabhi; Smolyakov, Gennady A.; Monson, Todd; Huber, Dale L.; Smyth, Hugh D. C.; Osiński, Marek

    2012-03-01

    Iron oxide colloidal nanocrystals (ferrofluids) are investigated for application in the treatment of cystic fibrosis lung infections, the leading cause of mortality in cystic fibrosis patients. We investigate the use of iron oxide nanocrystals to increase the effectiveness of inhalation aerosol antibiotics therapy through two mechanisms: directed particle movement in the presence of a static external magnetic field and magnetic hyperthermia. Magnetic hyperthermia is an effective method for decreasing the viscosity of the mucus and biofilm thereby increasing drug, immune cell, and antibody penetration to the affected area. Iron oxide nanocrystals of various sizes and morphologies were synthesized and tested for specific losses (heating power) using frequencies of 111.1 kHz and 629.2 kHz, and corresponding magnetic field strengths of 9 and 25 mT. Nanocrystals in the superparamagnetic to ferromagnetic size range exhibited excellent heating power. Additionally, iron oxide-zinc selenide core-shell nanoparticles were prepared in parallel in order to allow imaging of the iron oxide nanoparticles.

  14. Plasmon induced modification of silicon nanocrystals photoluminescence in presence of gold nanostripes

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Dyakov, S. A.; Zhigunov, D. M.; Marinins, A.

    Here, we report on the results of theoretical and experimental studies of photoluminescense of silicon nanocrystals in the proximity to plasmonic modes of different types. In the studied samples, the type of plasmonic mode is determined by the filling ratio of a one-dimensional array of gold stripes which covers the thin film with silicon nanocrystals on a quartz substrate. We analyze the extinction, photoluminesce spectra and decay kinetics of silicon nanocrystals and show that the incident and emitted light is coupled to the corresponding plasmonic mode. We demonstrate the modification of the extinction and photoluminesce spectra under the transition frommore » wide to narrow gold stripes. The experimental extinction and photoluminescense spectra are in good agreement with theoretical calculations performed by the rigorous coupled wave analysis. Finally, we study the contribution of individual silicon nanocrystals to the overall photoluminescense intensity, depending on their spacial position inside the structure.« less

  15. Off-Resonance Photosensitization of a Photorefractive Polymer Composite Using PbS Nanocrystals

    DOE PAGES

    Moon, Jong-Sik; Liang, Yichen; Stevens, Tyler E.; ...

    2015-05-26

    The photosensitization of photorefractive polymeric composites for operation at 633 nm is accomplished through the inclusion of narrow band gap semiconductor nanocrystals composed of PbS. Unlike previous studies involving photosensitization of photorefractive polymer composites with inorganic nanocrystals, we employ an off-resonance approach where the first excitonic transition associated with the PbS nanocrystals lies at ~1220 nm and not the wavelength of operation. Using this methodology, internal diffraction efficiencies exceeding 82%, two-beam-coupling gain coefficients of 211 cm –1, and response times of 34 ms have been observed, representing some of the best figures of merit reported for this class of materials.more » Furthermore, these data demonstrate the ability of semiconductor nanocrystals to compete effectively with traditional organic photosensitizers. In addition to superior performance, this approach also offers an inexpensive and easy means by which to photosensitize composite materials. Additionally, the photoconductive characteristics of the composites used for this study will also be considered.« less

  16. Plasmon induced modification of silicon nanocrystals photoluminescence in presence of gold nanostripes

    DOE PAGES

    Dyakov, S. A.; Zhigunov, D. M.; Marinins, A.; ...

    2018-03-20

    Here, we report on the results of theoretical and experimental studies of photoluminescense of silicon nanocrystals in the proximity to plasmonic modes of different types. In the studied samples, the type of plasmonic mode is determined by the filling ratio of a one-dimensional array of gold stripes which covers the thin film with silicon nanocrystals on a quartz substrate. We analyze the extinction, photoluminesce spectra and decay kinetics of silicon nanocrystals and show that the incident and emitted light is coupled to the corresponding plasmonic mode. We demonstrate the modification of the extinction and photoluminesce spectra under the transition frommore » wide to narrow gold stripes. The experimental extinction and photoluminescense spectra are in good agreement with theoretical calculations performed by the rigorous coupled wave analysis. Finally, we study the contribution of individual silicon nanocrystals to the overall photoluminescense intensity, depending on their spacial position inside the structure.« less

  17. Exciton Energy Transfer from Halide Terminated Nanocrystals to Graphene in Solar Photovoltaics

    NASA Astrophysics Data System (ADS)

    Ajayi, Obafunso; Abramson, Justin; Anderson, Nicholas; Owen, Jonathan; Zhao, Yue; Kim, Phillip; Gesuele, Felice; Wong, Chee Wei

    2011-03-01

    Graphene, a zero-gap semiconductor, has been identified as an ideal electrode for nanocrystal solar cell photovoltaic applications due to its high carrier mobility. Further advances in efficient current extraction are required towards this end. We investigate the resonant energy transfer dynamics between photoexcited nanocrystals and graphene, where the energy transfer rate is characterized by the fluorescent quenching of the quantum dots in the presence of graphene. Energy transfer has been shown to have a d -4 dependence on the nanocrystal distance from the graphene surface, with a correction due to blinking statistics. We investigate this relationship with single and few layer graphene. We study halide-terminated CdSe quantum dots; where the absence of the insulating outershell improves the electronic coupling of the donor-acceptor system leads to improved electron transfer. We observe quenching of the halide terminated nanocrystals on graphene, with the quenching factor ρ defined as IQ /IG (the relative intensities on quartz and graphene).

  18. Designing lanthanide-doped nanocrystals with both up- and down-conversion luminescence for anti-counterfeiting

    NASA Astrophysics Data System (ADS)

    Liu, Yanlan; Ai, Kelong; Lu, Lehui

    2011-11-01

    The widespread forgery in all kinds of paper documents and certificates has become a real threat to society. Traditional fluorescent anti-counterfeiting materials generally exhibit unicolor display and suffer greatly from substitution, thus leading to a poor anti-counterfeiting effect. In this work, unseen but significant enhanced blue down-conversion emission from oleic acid-stabilized lanthanide-doped fluoride nanocrystals is first present and the mechanism is proposed and validated. This not only endows these nanocrystals with dual-mode fluorescence, but also offers a simplified synthesis approach for dual-mode fluorescent nanocrystals involving no further complicated assembly or coating procedures, unlike the traditional methods. Furthermore, by changing the host/dopant combination or the content of dopant, these nanocrystals can exhibit simultaneously multicolor up-conversion emission under excitation at near-infrared light and unalterable blue down-conversion emission under ultraviolet light. A preliminary investigation of their anti-counterfeiting performance has been made, and the results indicate that this color tuning capability and high concealment makes these nanocrystals behave in a similar way to chameleons and can provide a strengthened and more reliable anti-counterfeiting effect.The widespread forgery in all kinds of paper documents and certificates has become a real threat to society. Traditional fluorescent anti-counterfeiting materials generally exhibit unicolor display and suffer greatly from substitution, thus leading to a poor anti-counterfeiting effect. In this work, unseen but significant enhanced blue down-conversion emission from oleic acid-stabilized lanthanide-doped fluoride nanocrystals is first present and the mechanism is proposed and validated. This not only endows these nanocrystals with dual-mode fluorescence, but also offers a simplified synthesis approach for dual-mode fluorescent nanocrystals involving no further complicated

  19. Mechanisms of oriented attachment of TiO2 nanocrystals in vacuum and humid environments: reactive molecular dynamics.

    PubMed

    Raju, Muralikrishna; van Duin, Adri C T; Fichthorn, Kristen A

    2014-01-01

    Oriented attachment (OA) of nanocrystals is now widely recognized as a key process in the solution-phase growth of hierarchical nanostructures. However, the microscopic origins of OA remain unclear. We perform molecular dynamics simulations using a recently developed ReaxFF reactive force field to study the aggregation of various titanium dioxide (anatase) nanocrystals in vacuum and humid environments. In vacuum, the nanocrystals merge along their direction of approach, resulting in a polycrystalline material. By contrast, in the presence of water vapor the nanocrystals reorient themselves and aggregate via the OA mechanism to form a single or twinned crystal. They accomplish this by creating a dynamic network of hydrogen bonds between surface hydroxyls and surface oxygens of aggregating nanocrystals. We determine that OA is dominant on surfaces that have the greatest propensity to dissociate water. Our results are consistent with experiment, are likely to be general for aqueous oxide systems, and demonstrate the critical role of solvent in nanocrystal aggregation. This work opens up new possibilities for directing nanocrystal growth to fabricate nanomaterials with desired shapes and sizes.

  20. New crystal structures in hexagonal CuInS2 nanocrystals

    NASA Astrophysics Data System (ADS)

    Shen, Xiao; Hernández-Pagan, Emil A.; Zhou, Wu; Puzyrev, Yevgeniy S.; Idrobo, Juan C.; MacDonald, Janet E.; Pennycook, Stephen J.; Pantelides, Sokrates T.

    2013-03-01

    CuInS2 is one of the best candidate materials for solar energy harvesting. Its nanocrystals with a hexagonal lattice structure that is different from the bulk chalcopyrite phase have been synthesized by many groups. The structure of these CuInS2 nanocrystals has been previously identified as the wurtzite structure in which the copper and indium atoms randomly occupy the cation sites. Using first-principles total energy and electronic structure calculations based on density functional theory, UV-vis absorption spectroscopy, X-ray diffraction, and atomic resolution Z-contrast images obtained in an aberration-corrected scanning transmission electron microscope, we show that CuInS2 nanocrystals do not form random wurtzite structure. Instead, the CuInS2 nanocrystals consist of several wurtzite- related crystal structures with ordered cation sublattices, some of which are reported for the first time here. This work is supported by the NSF TN-SCORE (JEM), by NSF (WZ), by ORNL's Shared Research Equipment User Program (JCI) sponsored by DOE BES, by DOE BES Materials Sciences and Engineering Division (SJP, STP), and used resources of the National Energy Research Scientific Computing Center, supported by the DOE Office of Science under Contract No. DE-AC02-05CH11231.

  1. Terbium-Aspartic Acid Nanocrystals with Chirality-Dependent Tunable Fluorescent Properties.

    PubMed

    Ma, Baojin; Wu, Yu; Zhang, Shan; Wang, Shicai; Qiu, Jichuan; Zhao, Lili; Guo, Daidong; Duan, Jiazhi; Sang, Yuanhua; Li, Linlin; Jiang, Huaidong; Liu, Hong

    2017-02-28

    Terbium-aspartic acid (Tb-Asp) nanocrystals with chirality-dependent tunable fluorescent properties can be synthesized through a facile synthesis method through the coordination between Tb and Asp. Asp with different chirality (dextrorotation/d and levogyration/l) changes the stability of the coordination center following fluorescent absorption/emission ability differences. Compared with l-Asp, d-Asp can coordinate Tb to form a more stable center, following the higher quantum yield and longer fluorescence life. Fluorescence intensity of Tb-Asp linearly increases with increase ratio of d-Asp in the mixed chirality Tb-Asp system, and the fluorescent properties of Tb-Asp nanocrystals can be tuned by adjusting the chirality ratio. Tb-Asp nanocrystals possess many advantage, such as high biocompatibility, without any color in visible light irradiation, monodispersion with very small size, and long fluorescent life. Those characteristics will give them great potential in many application fields, such as low-cost antifake markers and advertisements using inkjet printers or for molds when dispersed in polydimethylsiloxane. In addition, europium can also be used to synthesize Eu-Asp nanoparticles. Importantly, the facile, low-cost, high-yield, mass-productive "green" process provides enormous advantages for synthesis and application of fluorescent nanocrystals, which will have great impact in nanomaterial technology.

  2. Large Transient Optical Modulation of Epsilon-Near-Zero Colloidal Nanocrystals

    DOE PAGES

    Diroll, Benjamin T.; Guo, Peijun; Chang, Robert P. H.; ...

    2016-10-18

    Here, epsilon-near-zero materials may be synthesized as colloidal nanocrystals which display large magnitude subpicosecond switching of infrared localized surface plasmon resonances. Such nanocrystals offer a solution-processable, scalable source of tunable metamaterials compatible with arbitrary substrates. Under intraband excitation, these nanocrystals display a red-shift of the plasmon feature arising from the low electron heat capacities and conduction band nonparabolicity of the oxide. Under interband pumping, they show in an ultrafast blueshift of the plasmon resonance due to transient increases in the carrier density. Combined with their high-quality factor, large changes in relative transmittance (+86%) and index of refraction (+85%) at modestmore » control fluences (<5 mJ/cm 2) suggest that these materials offer great promise for all-optical switching, wavefront engineering, and beam steering operating at terahertz switching frequencies.« less

  3. Cellulose nanocrystals, nanofibers, and their composites as renewable smart materials

    NASA Astrophysics Data System (ADS)

    Kim, Jaehwan; Zhai, Lindong; Mun, Seongcheol; Ko, Hyun-U.; Yun, Young-Min

    2015-04-01

    Cellulose is one of abundant renewable biomaterials in the world. Over 1.5 trillion tons of cellulose is produced per year in nature by biosynthesis, forming microfibrils which in turn aggregate to form cellulose fibers. Using new effective methods these microfibrils can be disintegrated from the fibers to nanosized materials, so called cellulose nanocrystal (CNC) and cellulose nanofiber (CNF). The CNC and CNF have extremely good strength properties, dimensional stability, thermal stability and good optical properties on top of their renewable behavior, which can be a building block of new materials. This paper represents recent advancement of cellulose nanocrystals and cellulose nanofibers, followed by their possibility for smart materials. Natural behaviors, extraction, modification of cellulose nanocrystals and fibers are explained and their synthesis with nanomaterials is introduced, which is necessary to meet the technological requirements for smart materials. Also, its challenges are addressed.

  4. 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.

  5. Visualizing Current Flow at the Mesoscale in Disordered Assemblies of Touching Semiconductor Nanocrystals

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Chen, Qinyi; Guest, Jeffrey R.; Thimsen, Elijah

    2017-07-12

    The transport of electrons through assemblies of nanocrystals is important to performance in optoelectronic applications for these materials. Previous work has primarily focused on single nanocrystals or transitions between pairs of nanocrystals. There is a gap in knowledge of how large numbers of nanocrystals in an assembly behave collectively, and how this collective behavior manifests at the mesoscale. In this work, the variable range hopping (VRH) transport of electrons in disordered assemblies of touching, heavily doped ZnO nanocrystals was visualized at the mesoscale as a function of temperature both theoretically, using the model of Skinner, Chen and Shklovskii (SCS), andmore » experimentally, with conductive atomic force microscopy on ultrathin films only a few particle layers thick. Agreement was obtained between the model and experiments, with a few notable exceptions. The SCS model predicts that a single network within the nanocrystal assembly, comprised of sites connected by small resistances, dominates conduction - namely the optimum band from variable range hopping theory. However, our experiments revealed that in addition to the optimum band, there are subnetworks that appear as additional peaks in the resistance histogram of conductive atomic force microscopy (CAFM) maps. Furthermore, the connections of these subnetworks to the optimum band change in time, such that some subnetworks become connected to the optimum band while others become disconnected and isolated from the optimum band; this observation appears to be an experimental manifestation of the ‘blinking’ phenomenon in our images of mesoscale transport.« less

  6. Nonvolatile memory with Co-SiO2 core-shell nanocrystals as charge storage nodes in floating gate

    NASA Astrophysics Data System (ADS)

    Liu, Hai; Ferrer, Domingo A.; Ferdousi, Fahmida; Banerjee, Sanjay K.

    2009-11-01

    In this letter, we reported nanocrystal floating gate memory with Co-SiO2 core-shell nanocrystal charge storage nodes. By using a water-in-oil microemulsion scheme, Co-SiO2 core-shell nanocrystals were synthesized and closely packed to achieve high density matrix in the floating gate without aggregation. The insulator shell also can help to increase the thermal stability of the nanocrystal metal core during the fabrication process to improve memory performance.

  7. Nanocrystal: a novel approach to overcome skin barriers for improved topical drug delivery.

    PubMed

    Patel, Viral; Sharma, Om Prakash; Mehta, Tejal

    2018-04-01

    Skin is an important route of drug delivery for the treatment of various dermatological conditions. The advent of nanotechnology is paving the roadmaps for topical drug delivery by providing sustained release as well as maintaining a localized effect, outweighing the toxicity concern. Area covered: This review highlighted the morphology of skin, its barrier nature as well as drug penetration pathways after topical application of formulations. The existing methods to improve topical drug delivery, by infringing or permeating the skin barriers, are discussed. This context concretes the foundation to accentuate the need for the development of nanocrystal-based topical formulation. The mechanism of drug release, immediate as well as sustained release, after topical administration of drug nanocrystals is also elaborated. The special emphasis is given on the breakthrough achieved, in topical drug delivery using drug nanocrystals, so far in the plethora of literature, patents, and products, under clinical trial as well as in the market. Expert opinion: The current research on nanocrystals for topical drug delivery is highlighting the breakthroughs achieved so far. The output of these research envisages that topical nanocrystals based formulations can be a novel strategy for the drugs which are facing solubility, bioavailability and toxicity concerns.

  8. Structural, optical, and electrical properties of PbSe nanocrystal solids treated thermally or with simple amines.

    PubMed

    Law, Matt; Luther, Joseph M; Song, Qing; Hughes, Barbara K; Perkins, Craig L; Nozik, Arthur J

    2008-05-07

    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 approximately 200 degrees 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.

  9. Precipitation-lyophilization-homogenization (PLH) for preparation of clarithromycin nanocrystals: influencing factors on physicochemical properties and stability.

    PubMed

    Morakul, Boontida; Suksiriworapong, Jiraphong; Leanpolchareanchai, Jiraporn; Junyaprasert, Varaporn Buraphacheep

    2013-11-30

    Nanocrystals is one of effective technologies used to improve solubility and dissolution behavior of poorly soluble drugs. Clarithromycin is classified in BCS class II having low bioavailability due to very low dissolution behavior. The main purpose of this study was to investigate an efficiency of clarithromycin nanocrystals preparation by precipitation-lyophilization-homogenization (PLH) combination method in comparison with high pressure homogenization (HPH) method. The factors influencing particle size reduction and physical stability were assessed. The results showed that the PLH technique provided an effective and rapid reduction of particle size of nanocrystals to 460 ± 10 nm with homogeneity size distribution after only the fifth cycle of homogenization, whereas the same size was attained after 30 cycles by the HPH method. The smallest nanocrystals were achieved by using the combination of poloxamer 407 (2%, w/v) and SLS (0.1%, w/v) as stabilizers. This combination could prevent the particle aggregation over 3-month storage at 4 °C. The results from SEM showed that the clarithromycin nanocrystals were in cubic-shaped similar to its initial particle morphology. The DSC thermogram and X-ray diffraction pattern of nanocrystals were not different from the original drug except for intensity of peaks which indicated the presenting of nanocrystals in the crystalline state and/or partial amorphous form. In addition, the dissolution of the clarithromycin nanocrystals was dramatically increased as compared to the coarse clarithromycin. Copyright © 2013 Elsevier B.V. All rights reserved.

  10. 14N NQR lineshape in nanocrystals: An ab initio investigation of urea

    PubMed Central

    Gregorovič, Alan

    2017-01-01

    14N nuclear quadrupole resonance (NQR) lineshapes mostly contain information of low interest, although in nanocrystals they may display some unexpected behaviour. In this work, we present an ab initio computational study of the 14N NQR lineshapes in urea nanocrystals as a function of the nanocrystal size and geometry, focusing on the surface induced broadening of the lineshapes. The lineshapes were obtained through a calculation of the electric field gradient for each nitrogen site in the nanocrystal separately, taking into account the individual crystal field by embedding the molecule of interest in a suitable lattice of point multipoles representing other urea molecules in the nanocrystal. The small influence of distant molecules is found with a series expansion, using the in-crystal Sternheimer shieldings which we also calculated ab initio. We have considered nanocrystals with two geometries: a sphere and a cube, with characteristic sizes between 5 and 100 nm. Our calculations suggest that there is a dramatic difference between the linewidths for the two geometries. For spheres, we find a steep drop in linewidths at ∼10 nm; at 5 nm the linewidth is ∼11 kHz, whereas for sizes above 20 nm the linewidth is practically negligible (<100 Hz). For cubes, on the other hand, we find a steady 1/size decrease, from 12 kHz at 10 nm to 1.2 kHz at 100 nm. This analysis is important for 14N NQR spectroscopy of crystalline pharmaceuticals, where nanoparticles are increasingly more often embedded in some sort of matrix. Although this is only a theoretical analysis, we believe that this work can serve as a guidance for the forthcoming experimental analysis. PMID:28527464

  11. Paramagnetic behavior of Co doped TiO{sub 2} nanocrystals controlled by self-purification mechanism

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Anitha, B.; Khadar, M. Abdul, E-mail: mabdulkhadar@rediffmail.com; Banerjee, Alok

    Doping in nanocrystals is a challenging process because of the self- purification mechanism which tends to segregate out the dopants resulting in a greater dopant concentration near the surface than at the interior of nanocrystals. In the present work nanocrystals of TiO{sub 2} doped with different atom % of Co were synthesized by peroxide gel method. XRD analysis confirmed the tetragonal anatase structure and HRTEM images showed the rod-like morphology of the samples. Raman modes of anatase phase of TiO{sub 2} along with weak intensity peaks of Co{sub 3}O{sub 4} for higher Co dopant concentrations were observed for the samples.more » EPR measurements revealed the presence of cobalt in +2 oxidation state in the TiO{sub 2} matrix. SQUID measurements indicated paramagnetic behavior of the Co doped TiO{sub 2} nanocrystals. The paramagnetic behavior is attributed to an increased concentration of Co{sup 2+} ions and an increased presence of Co{sub 3}O{sub 4} phase near the surface of the TiO{sub 2} nanocrystals due to self-purification mechanism. - Graphical abstract: Variation of the intensity ratios of XRD peaks as a function of atomic ratio of Co. Inset: variation of structure factor for (101) reflection as a function of atomic ratio of Co. Display Omitted - Highlights: • Co doped TiO{sub 2} nanocrystals were synthesized by peroxide gel method. • HRTEM images showed Co doped TiO{sub 2} nanocrystals to be rod-like. • EPR spectra showed +2 oxidation states for Co in the samples. • Co doped TiO{sub 2} nanocrystals showed paramagnetic behavior.« less

  12. Exchange asymmetry in experimental settings

    Treesearch

    Thomas C. Brown; Mark D. Morrison; Jacob A. Benfield; Gretchen Nurse Rainbolt; Paul A. Bell

    2015-01-01

    We review past trading experiments and present 11 new experiments designed to show how the trading rate responds to alterations of the experimental procedure. In agreement with earlier studies, results show that if the trade decision is converted to one resembling a choice between goods the exchange asymmetry disappears, but otherwise the asymmetry is...

  13. Nodal signalling and asymmetry of the nervous system

    PubMed Central

    Signore, Iskra A.; Palma, Karina

    2016-01-01

    The role of Nodal signalling in nervous system asymmetry is still poorly understood. Here, we review and discuss how asymmetric Nodal signalling controls the ontogeny of nervous system asymmetry using a comparative developmental perspective. A detailed analysis of asymmetry in ascidians and fishes reveals a critical context-dependency of Nodal function and emphasizes that bilaterally paired and midline-unpaired structures/organs behave as different entities. We propose a conceptual framework to dissect the developmental function of Nodal as asymmetry inducer and laterality modulator in the nervous system, which can be used to study other types of body and visceral organ asymmetries. Using insights from developmental biology, we also present novel evolutionary hypotheses on how Nodal led the evolution of directional asymmetry in the brain, with a particular focus on the epithalamus. We intend this paper to provide a synthesis on how Nodal signalling controls left–right asymmetry of the nervous system. This article is part of the themed issue ‘Provocative questions in left–right asymmetry’. PMID:27821531

  14. Silver nanocrystal-decorated polyoxometalate single-walled nanotubes as nanoreactors for desulfurization catalysis at room temperature.

    PubMed

    Zhang, Hao; Xu, Xiaobin; Lin, Haifeng; Ud Din, Muhammad Aizaz; Wang, Haiqing; Wang, Xun

    2017-09-14

    Ultrathin nanocrystals generally provide a remarkable catalytic performance due to their high specific surface area and exposure of certain active sites. However, deactivation caused by growth and gathering limits the catalytic application of ultrathin nanocrystals. Here we report Ag nanocrystal-decorated polyoxometalate (Ag-POM) single-walled nanotubes assembled via a concise, surfactant-free soaking method as a new kind of well-defined core-sheath nanoreactor. The diameter of Ag nanocrystals inside polyoxometalate nanotubes can be controlled via simply adjusting the reactant concentration. Ag-POM provided outstanding oxidative desulfurization (ODS) catalytic performance for aromatic sulfocompounds at room temperature. It was suggested that Ag nanocrystals decorated on the inner surface played a key role in adjusting the electronic distribution and enhancing the catalytic activity. The as-prepared Ag-POM nanotubes are promising candidate catalysts with enhanced performance for practical catalytic applications in the gasoline desulfurization industry.

  15. Stochastic left–right neuronal asymmetry in Caenorhabditis elegans

    PubMed Central

    Alqadah, Amel; Hsieh, Yi-Wen; Xiong, Rui

    2016-01-01

    Left–right asymmetry in the nervous system is observed across species. Defects in left–right cerebral asymmetry are linked to several neurological diseases, but the molecular mechanisms underlying brain asymmetry in vertebrates are still not very well understood. The Caenorhabditis elegans left and right amphid wing ‘C’ (AWC) olfactory neurons communicate through intercellular calcium signalling in a transient embryonic gap junction neural network to specify two asymmetric subtypes, AWCOFF (default) and AWCON (induced), in a stochastic manner. Here, we highlight the molecular mechanisms that establish and maintain stochastic AWC asymmetry. As the components of the AWC asymmetry pathway are highly conserved, insights from the model organism C. elegans may provide a window onto how brain asymmetry develops in humans. This article is part of the themed issue ‘Provocative questions in left–right asymmetry’. PMID:27821536

  16. In situ functionalization and PEO coating of iron oxide nanocrystals using seeded emulsion polymerization.

    PubMed

    Kloust, Hauke; Schmidtke, Christian; Feld, Artur; Schotten, Theo; Eggers, Robin; Fittschen, Ursula E A; Schulz, Florian; Pöselt, Elmar; Ostermann, Johannes; Bastús, Neus G; Weller, Horst

    2013-04-16

    Herein we demonstrate that seeded emulsion polymerization is a powerful tool to produce multiply functionalized PEO coated iron oxide nanocrystals. Advantageously, by simple addition of functional surfactants, functional monomers, or functional polymerizable linkers-solely or in combinations thereof-during the seeded emulsion polymerization process, a broad range of in situ functionalized polymer-coated iron oxide nanocrystals were obtained. This was demonstrated by purposeful modulation of the zeta potential of encapsulated iron oxide nanocrystals and conjugation of a dyestuff. Successful functionalization was unequivocally proven by TXRF. Furthermore, the spatial position of the functional groups can be controlled by choosing the appropriate spacers. In conclusion, this methodology is highly amenable for combinatorial strategies and will spur rapid expedited synthesis and purposeful optimization of a broad scope of nanocrystals.

  17. Automated microfluidic platform for systematic studies of colloidal perovskite nanocrystals: towards continuous nano-manufacturing.

    PubMed

    Epps, Robert W; Felton, Kobi C; Coley, Connor W; Abolhasani, Milad

    2017-11-21

    Colloidal organic/inorganic metal-halide perovskite nanocrystals have recently emerged as a potential low-cost replacement for the semiconductor materials in commercial photovoltaics and light emitting diodes. However, unlike III-V and IV-VI semiconductor nanocrystals, studies of colloidal perovskite nanocrystals have yet to develop a fundamental and comprehensive understanding of nucleation and growth kinetics. Here, we introduce a modular and automated microfluidic platform for the systematic studies of room-temperature synthesized cesium-lead halide perovskite nanocrystals. With abundant data collection across the entirety of four orders of magnitude reaction time span, we comprehensively characterize nanocrystal growth within a modular microfluidic reactor. The developed high-throughput screening platform features a custom-designed three-port flow cell with translational capability for in situ spectral characterization of the in-flow synthesized perovskite nanocrystals along a tubular microreactor with an adjustable length, ranging from 3 cm to 196 cm. The translational flow cell allows for sampling of twenty unique residence times at a single equilibrated flow rate. The developed technique requires an average total liquid consumption of 20 μL per spectra and as little as 2 μL at the time of sampling. It may continuously sample up to 30 000 unique spectra per day in both single and multi-phase flow formats. Using the developed plug-and-play microfluidic platform, we study the growth of cesium lead trihalide perovskite nanocrystals through in situ monitoring of their absorption and emission band-gaps at residence times ranging from 100 ms to 17 min. The automated microfluidic platform enables a systematic study of the effect of mixing enhancement on the quality of the synthesized nanocrystals through a direct comparison between single- and multi-phase flow systems at similar reaction time scales. The improved mixing characteristics of the multi-phase flow

  18. Transition‐Metal‐Doped NIR‐Emitting Silicon Nanocrystals

    PubMed Central

    Chandra, Sourov; Masuda, Yoshitake

    2017-01-01

    Abstract Impurity‐doping in nanocrystals significantly affects their electronic properties and diversifies their applications. Herein, we report the synthesis of transition metal (Mn, Ni, Co, Cu)‐doped oleophilic silicon nanocrystals (SiNCs) through hydrolysis/polymerization of triethoxysilane with acidic aqueous metal salt solutions, followed by thermal disproportionation of the resulting gel into a doped‐Si/SiO2 composite that, upon HF etching and hydrosilylation with 1‐n‐octadecene, produces free‐standing octadecyl‐capped doped SiNCs (diameter≈3 to 8 nm; dopant <0.2 atom %). Metal‐doping triggers a red‐shift of the SiNC photoluminescence (PL) of up to 270 nm, while maintaining high PL quantum yield (26 % for Co doping). PMID:28374522

  19. Single-particle mapping of nonequilibrium nanocrystal transformations

    DOE PAGES

    Ye, Xingchen; Jones, Matthew R.; Frechette, Layne B.; ...

    2016-11-18

    Chemists have developed mechanistic insight into numerous chemical reactions by thoroughly characterizing nonequilibrium species. Although methods to probe these processes are well established for molecules, analogous techniques for understanding intermediate structures in nanomaterials have been lacking. For this study, we monitor the shape evolution of individual anisotropic gold nanostructures as they are oxidatively etched in a graphene liquid cell with a controlled redox environment. Short-lived, nonequilibrium nanocrystals are observed, structurally analyzed, and rationalized through Monte Carlo simulations. Understanding these reaction trajectories provides important fundamental insight connecting high-energy nanocrystal morphologies to the development of kinetically stabilized surface features and demonstrates themore » importance of developing tools capable of probing short-lived nanoscale species at the single-particle level.« less

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

    NASA Astrophysics Data System (ADS)

    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.

    2017-04-01

    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.

  1. A New Method for Delivering a Hydrophobic Drug for Photodynamic Therapy Using Pure Nanocrystal Form of the Drug

    PubMed Central

    Baba, Koichi; Pudavar, Haridas E.; Roy, Indrajit; Ohulchanskyy, Tymish Y.; Chen, Yihui; Pandey, Ravindra; Prasad, Paras N.

    2008-01-01

    A carrier free method for delivery of a hydrophobic drug in its pure form, using nanocrystals (nano sized crystals) is proposed. To demonstrate this technique, nanocrystals of a hydrophobic photosensitizing anticancer drug 2-devinyl-2-(1-hexyloxyethyl)pyropheophorbide (HPPH), have been synthesized using re-precipitation method. The resulting drug nanocrystals were monodispersed and stable in aqueous dispersion, without the necessity of an additional stabilizer (surfactant). As shown by confocal microscopy, these pure drug nanocrystals were taken-up by the cancer cells with high avidity. Though the fluorescence and photodynamic activity of the drug were substantially quenched in the form of nanocrystals in aqueous suspension, both these characteristics were recovered under in vitro and in vivo conditions. This recovery of drug activity and fluorescence is possibly due to the interaction of nanocrystals with serum albumin, resulting in conversion of the drug nanocrystals into the molecular form. This was confirmed by demonstrating similar recovery in presence of Fetal Bovine Serum (FBS) or Bovine Serum Albumin (BSA). Under similar treatment conditions, the HPPH in nanocrystal form or in 1% Tween 80/water formulation showed comparable in vitro and in vivo efficacy. PMID:17266331

  2. Permeability Asymmetry in Composite Porous Ceramic Membranes

    NASA Astrophysics Data System (ADS)

    Kurcharov, I. M.; Laguntsov, N. I.; Uvarov, V. I.; Kurchatova, O. V.

    The results from the investigation of transport characteristics and gas transport asymmetry in bilayer composite membranes are submitted. These membranes are produced by SHS method. Asymmetric effect and hysteresis of permeability in nanoporous membranes are detected. It's shown, that permeability ratio (asymmetry value of permeability) increases up to several times. The asymmetry of permeability usually decreases monotonically with the pressure decrease.

  3. Bessel Weighted Asymmetries

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Avakian, Harut; Gamberg, Leonard; Rossi, Patrizia

    We review the concept of Bessel weighted asymmetries for semi-inclusive deep inelastic scattering and focus on the cross section in Fourier space, conjugate to the outgoing hadron’s transverse momentum, where convolutions of transverse momentum dependent parton distribution functions and fragmentation functions become simple products. Individual asymmetric terms in the cross section can be projected out by means of a generalized set of weights involving Bessel functions. The procedure is applied to studies of the double longitudinal spin asymmetry in semi-inclusive deep inelastic scattering using a new dedicated Monte Carlo generator which includes quark intrinsic transverse momentum within the generalized partonmore » model. We observe a few percent systematic offset of the Bessel-weighted asymmetry obtained from Monte Carlo extraction compared to input model calculations, which is due to the limitations imposed by the energy and momentum conservation at the given energy and hard scale Q2. We find that the Bessel weighting technique provides a powerful and reliable tool to study the Fourier transform of TMDs with controlled systematics due to experimental acceptances and resolutions with different TMD model inputs.« less

  4. Validity and sensitivity of the longitudinal asymmetry index to detect gait asymmetry using Microsoft Kinect data.

    PubMed

    Auvinet, E; Multon, F; Manning, V; Meunier, J; Cobb, J P

    2017-01-01

    Gait asymmetry information is a key point in disease screening and follow-up. Constant Relative Phase (CRP) has been used to quantify within-stride asymmetry index, which requires noise-free and accurate motion capture, which is difficult to obtain in clinical settings. This study explores a new index, the Longitudinal Asymmetry Index (ILong) which is derived using data from a low-cost depth camera (Kinect). ILong is based on depth images averaged over several gait cycles, rather than derived joint positions or angles. This study aims to evaluate (1) the validity of CRP computed with Kinect, (2) the validity and sensitivity of ILong for measuring gait asymmetry based solely on data provided by a depth camera, (3) the clinical applicability of a posteriorly mounted camera system to avoid occlusion caused by the standard front-fitted treadmill consoles and (4) the number of strides needed to reliably calculate ILong. The gait of 15 subjects was recorded concurrently with a marker-based system (MBS) and Kinect, and asymmetry was artificially reproduced by introducing a 5cm sole attached to one foot. CRP computed with Kinect was not reliable. ILong detected this disturbed gait reliably and could be computed from a posteriorly placed Kinect without loss of validity. A minimum of five strides was needed to achieve a correlation coefficient of 0.9 between standard MBS and low-cost depth camera based ILong. ILong provides a clinically pragmatic method for measuring gait asymmetry, with application for improved patient care through enhanced disease, screening, diagnosis and monitoring. Copyright © 2016. Published by Elsevier B.V.

  5. Optically coded nanocrystal taggants and optical frequency IDs

    NASA Astrophysics Data System (ADS)

    Williams, George M., Jr.; Allen, Thomas; Dupuy, Charles; Novet, Thomas; Schut, David

    2010-04-01

    A series of nanocrystal and nanocrystal quantum dot taggant technologies were developed for covertly tagging and tracking objects of interest. Homogeneous and heterogeneous nanocrystal taggant designs were developed and optimized for ultraviolet through infrared emissions, utilizing either Dexter energy transfer or Förster resonant energy transfer (FRET) between specific absorbing and emitting functionalities. The conversion efficiency, target-specific identification, and adhesion properties of the taggants were engineered by means of various surface ligand chemistries. The ability to engineer poly-functional ligands was shown effective in the detection of a biological agent simulant, detected through a NC photoluminescence that is altered in the presence of the agent of interest; the technique has broad potential applicability to chemical, biological, and explosive (CBE) agent detection. The NC photoluminescence can be detected by a remote LIDAR system; the performance of a taggant system has been modeled and subsequently verified in a series of controlled field tests. LIDAR detection of visible-emitting taggants was shown to exceed 2.8 km in calibrated field tests, and from these field data and calibrated laboratory measurements we predict >5 km range in the covert shortwavelength infrared (SWIR) spectral region.

  6. Soluble Supercapacitors: Large and Reversible Charge Storage in Colloidal Iron-Doped ZnO Nanocrystals.

    PubMed

    Brozek, Carl K; Zhou, Dongming; Liu, Hongbin; Li, Xiaosong; Kittilstved, Kevin R; Gamelin, Daniel R

    2018-05-09

    Colloidal ZnO semiconductor nanocrystals have previously been shown to accumulate multiple delocalized conduction-band electrons under chemical, electrochemical, or photochemical reducing conditions, leading to emergent semimetallic characteristics such as quantum plasmon resonances and raising prospects for application in multielectron redox transformations. Here, we demonstrate a dramatic enhancement in the capacitance of colloidal ZnO nanocrystals through aliovalent Fe 3+ -doping. Very high areal and volumetric capacitances (33 μF cm -2 , 233 F cm -3 ) are achieved in Zn 0.99 Fe 0.01 O nanocrystals that rival those of the best supercapacitors used in commercial energy-storage devices. The redox properties of these nanocrystals are probed by potentiometric titration and optical spectroscopy. These data indicate an equilibrium between electron localization by Fe 3+ dopants and electron delocalization within the ZnO conduction band, allowing facile reversible charge storage and removal. As "soluble supercapacitors", colloidal iron-doped ZnO nanocrystals constitute a promising class of solution-processable electronic materials with large charge-storage capacity attractive for future energy-storage applications.

  7. Facial Asymmetry: Brow and Ear Position.

    PubMed

    Perumal, Balaji; Meyer, Dale R

    2018-04-01

    The purpose of the current study was to analyze brow and ear position, and examine the relationship between these structures in patients presenting for blepharoplasty evaluation. A retrospective chart review was performed, which included all patients presenting to one oculoplastic physician for a blepharoplasty evaluation from November, 2012 to March, 2014. The prevalence of brow ptosis and brow and ear asymmetry was calculated; the proportional distribution was determined, and chi-square analysis and the z-test of proportions were used to calculate the significance. Institutional Review Board approval was obtained for this study. A total of 133 patients met the inclusion criteria. Some degree of brow ptosis was noted in 83% of patients. Brow asymmetry was found in 88% of patients, and ear asymmetry in 77%. Of those patients who had asymmetry, 61% had the right brow lower and 75% had the right ear lower; 73% of all patients had the brow and ear lower on the same side ( p  < 0.001). In this study, brow ptosis and asymmetry were quite common. In addition, the side of the lower brow correlated strongly with the side of the lower ear, and the right side structures were lower more often than the left. Patients presenting for blepharoplasty evaluation may have an element of generalized facial asymmetry which includes the brows and ears. These observations can be important for preoperative planning and patient counseling. Thieme Medical Publishers 333 Seventh Avenue, New York, NY 10001, USA.

  8. Asymmetry identification in rigid rotating bodies—Theory and experiment

    NASA Astrophysics Data System (ADS)

    Bucher, Izhak; Shomer, Ofer

    2013-12-01

    Asymmetry and anisotropy are important parameters in rotating devices that can cause instability; indicate a manufacturing defect or a developing fault. The present paper discusses an identification method capable of detecting minute levels of asymmetry by exploiting the unique dynamics of parametric excitation caused by asymmetry and rotation. The detection relies on rigid body dynamics without resorting to nonlinear vibration analysis, and the natural dynamics of elastically supported systems is exploited in order to increase the sensitivity to asymmetry. It is possible to isolate asymmetry from other rotation-induced phenomena like unbalance. An asymmetry detection machine which was built in the laboratory demonstrates the method alongside theoretical analysis.

  9. Charging-induced asymmetry in molecular conductors

    NASA Astrophysics Data System (ADS)

    Zahid, F.; Ghosh, A. W.; Paulsson, M.; Polizzi, E.; Datta, S.

    2004-12-01

    We investigate the origin of asymmetry in various measured current-voltage (I-V) characteristics of molecules with no inherent spatial asymmetry, with particular focus on a recent break junction measurement. We argue that such asymmetry arises due to unequal coupling with the contacts and a consequent difference in charging effects, which can only be captured in a self-consistent model for molecular conduction. The direction of the asymmetry depends on the sign of the majority carriers in the molecule. For conduction through highest occupied molecular orbitals (i.e., HOMO or p -type conduction), the current is smaller for positive voltage on the stronger contact, while for conduction through lowest unoccupied molecular orbitals (i.e., LUMO or n -type conduction), the sense of the asymmetry is reversed. Within an extended Hückel description of the molecular chemistry and the contact microstructure (with two adjustable parameters, the position of the Fermi energy and the sulphur-gold bond length), an appropriate description of Poisson’s equation, and a self-consistently coupled nonequilibrium Green’s function description of transport, we achieve good agreement between theoretical and experimental I-V characteristics, both in shape as well as overall magnitude.

  10. 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 CH 3 NH 3 PbI 3 and CH 3 NH 3 PbBr 3 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 CH 3 NH 3 PbI 3 red/near-infrared LEDs and CH 3 NH 3 PbBr 3 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.

  11. Optical properties and ensemble characteristics of size purified Silicon nanocrystals

    NASA Astrophysics Data System (ADS)

    Miller, Joseph Bradley

    Nanotechnology is at the forefront of current scientific research and nanocrystals are being hailed as the 'artificial' atoms of the 21st century. Semiconducting silicon nanocrystals (SiNCs) are prime candidates for potential commercial applications because of silicon's already ubiquitous presence in the semiconductor industry, nontoxicity and abundance in nature. For realization of these potential applications, the properties and behavior of SiNCs need to be understood and enhanced. In this report, some of the main SiNC synthesis schemes are discussed, including those we are currently experimenting with to create our own SiNCs and the one utilized to create the SiNCs used in this study. The underlying physics that governs the unique behavior of SiNCs is then presented. The properties of the as-produced SiNCs are determined to depend strongly on surface passivation and environment. Size purification, an important aspect of nanomaterial utilization, was successfully performed on our SiNCs though density gradient ultracentrifugation. We demonstrate that the size-purified fractions exhibit an enhanced ability for colloidal self-assembly, with better aligned nanocrystal energy levels which promotes greater photostability in close-packed films and produces a slight increase in photoluminescence (PL) quantum yield. The qualities displayed by the fractions are exploited to form SiNC clusters that exhibit photostable PL. An analysis of SiNC cluster (from individual nanocrystals to collections of more than one thousand) blinking and PL shows an improvement in their PL emitting 'on' times. Pure SiNC films and SiNC-polymer nanocomposites are created and the dependence of their PL on temperature is measured. For such nanocomposites, the coupling between the 'coffee-ring' effect and liquid-liquid phase separation is also examined for ternary mixtures of solvent, polymer and semiconducting nanocrystal. We discover that with the right SiNC-polymer concentration and polymer

  12. Synthesis and Manipulation of Semiconductor Nanocrystals inMicrofluidic Reactors

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Chan, Emory Ming-Yue

    2006-01-01

    Microfluidic reactors are investigated as a mechanism tocontrol the growth of semiconductor nanocrystals and characterize thestructural evolution of colloidal quantum dots. Due to their shortdiffusion lengths, low thermal masses, and predictable fluid dynamics,microfluidic devices can be used to quickly and reproducibly alterreaction conditions such as concentration, temperature, and reactiontime, while allowing for rapid reagent mixing and productcharacterization. These features are particularly useful for colloidalnanocrystal reactions, which scale poorly and are difficult to controland characterize in bulk fluids. To demonstrate the capabilities ofnanoparticle microreactors, a size series of spherical CdSe nanocrystalswas synthesized at high temperature in a continuous-flow, microfabricatedglass reactor. Nanocrystalmore » diameters are reproducibly controlled bysystematically altering reaction parameters such as the temperature,concentration, and reaction time. Microreactors with finer control overtemperature and reagent mixing were designed to synthesize nanoparticlesof different shapes, such as rods, tetrapods, and hollow shells. The twomajor challenges observed with continuous flow reactors are thedeposition of particles on channel walls and the broad distribution ofresidence times that result from laminar flow. To alleviate theseproblems, I designed and fabricated liquid-liquid segmented flowmicroreactors in which the reaction precursors are encapsulated inflowing droplets suspended in an immiscible carrier fluid. The synthesisof CdSe nanocrystals in such microreactors exhibited reduced depositionand residence time distributions while enabling the rapid screening aseries of samples isolated in nL droplets. Microfluidic reactors werealso designed to modify the composition of existing nanocrystals andcharacterize the kinetics of such reactions. The millisecond kinetics ofthe CdSe-to-Ag 2Se nanocrystal cation exchange reaction are measured insitu with micro

  13. Light-induced changes in silicon nanocrystal based solar cells: Modification of silicon-hydrogen bonding on silicon nanocrystal surface under illumination

    NASA Astrophysics Data System (ADS)

    Kim, Ka-Hyun; Johnson, Erik V.; Cabarrocas, Pere Roca i.

    2016-07-01

    Hydrogenated polymorphous silicon (pm-Si:H) is a material consisting of a small volume fraction of nanocrystals embedded in an amorphous matrix. pm-Si:H solar cells demonstrate interesting initial degradation behaviors such as rapid initial change in photovoltaic parameters and self-healing after degradation during light-soaking. The precise dynamics of the light-induced degradation was studied in a series of light-soaking experiments under various illumination conditions such as AM1.5G and filtered 570 nm yellow light. Hydrogen effusion experiment before and after light-soaking further revealed that the initial degradation of pm-Si:H solar cells originate from the modification of silicon-hydrogen bonding on the surface of silicon nanocrystals in pm-Si:H.

  14. Shape-Controlled Synthesis of Colloidal Metal Nanocrystals: Thermodynamic versus Kinetic Products.

    PubMed

    Xia, Younan; Xia, Xiaohu; Peng, Hsin-Chieh

    2015-07-01

    This Perspective provides a contemporary understanding of the shape evolution of colloidal metal nanocrystals under thermodynamically and kinetically controlled conditions. It has been extremely challenging to investigate this subject in the setting of one-pot synthesis because both the type and number of seeds involved would be changed whenever the experimental conditions are altered, making it essentially impossible to draw conclusions when comparing the outcomes of two syntheses conducted under different conditions. Because of the uncertainty about seeds, most of the mechanistic insights reported in literature for one-pot syntheses of metal nanocrystals with different shapes are either incomplete or ambiguous, and some of them might be misleading or even wrong. Recently, with the use of well-defined seeds for such syntheses, it became possible to separate growth from nucleation and therefore investigate the explicit role(s) played by a specific thermodynamic or kinetic parameter in directing the evolution of colloidal metal nanocrystals into a specific shape. Starting from single-crystal seeds enclosed by a mix of {100}, {111}, and {110} facets, for example, one can obtain colloidal nanocrystals with diversified shapes by adjusting various thermodynamic or kinetic parameters. The mechanistic insights learnt from these studies can also be extended to account for the products of conventional one-pot syntheses that involve self-nucleation only. The knowledge can be further applied to many other types of seeds with twin defects or stacking faults, making it an exciting time to design and synthesize colloidal metal nanocrystals with the shapes sought for a variety of fundamental studies and technologically important applications.

  15. Bionanocomposite films based on plasticized PLA-PHB/cellulose nanocrystal blends.

    PubMed

    Arrieta, M P; Fortunati, E; Dominici, F; López, J; Kenny, J M

    2015-05-05

    Optically transparent plasticized poly(lactic acid) (PLA) based bionanocomposite films intended for food packaging were prepared by melt blending. Materials were plasticized with 15wt% of acetyl(tributyl citrate) (ATBC) to improve the material processability and to obtain flexibile films. Poly(hydroxybutyrate) (PHB) was used to increase PLA crystallinity. The thermal stability of the PLA-PHB blends was improved by the addition of 5 wt% of cellulose nanocrystals (CNC) or modified cellulose nanocrystals (CNCs) synthesized from microcrystalline cellulose. The combination of ATBC and cellulose nanocrystals, mainly the better dispersed CNCs, improved the interaction between PLA and PHB. Thus, an improvement on the oxygen barrier and stretchability was achieved in PLA-PHB-CNCs-ATBC which also displayed somewhat UV light blocking effect. All bionanocomposite films presented appropriate disintegration in compost suggesting their possible applications as biodegradable packaging materials. Copyright © 2014 Elsevier Ltd. All rights reserved.

  16. Nanocrystals-Related Synthesis, Assembly, and Energy Applications

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Zou, Bo; Yu, Williams; Seo, Jaetae

    2012-01-01

    During the past decades, nanocrystals have attracted broad attention due to their unique shape- and size-dependent physical and chemical properties that differ drastically from their bulk counterparts. Hitherto, much effort has been dedicated to achieving rational controlling over the morphology, assembly, and related energy applications of the nanomaterials. Therefore, the ability to manipulate the morphology, size, and size distribution of inorganic nanomaterials is still an important goal in modern materials physics and chemistry. Especially, the world s demand for energy supply is causing a dramatic escalation of social and political unrest. Likewise, the environmental impact of the global climate changemore » due to the combustion of fossil fuel is becoming increasingly alarming. These problems compel us to search for effective routes to build devices that can supply sustainable energy, with not only high efficiency but also environmental friendship. One of ways to relieve the energy crisis is to exploit devices based on renewable energy sources, such as solar energy and water power. Aiming at this exploration, the primary stage requires the design of appropriate strategies for the synthesis of high-quality nanocrystals with respect to size uniformity and superior electrochemical performances. As a consequence, we organize the current special issue for Journal of Nanomaterials to provide the authors with a platform and readers with the latest achievements of nanocrystals-related synthesis, assembly, and energy applications.« less

  17. Plasmon-induced carrier polarization in semiconductor nanocrystals.

    PubMed

    Yin, Penghui; Tan, Yi; Fang, Hanbing; Hegde, Manu; Radovanovic, Pavle V

    2018-06-01

    Spintronics 1 and valleytronics 2 are emerging quantum electronic technologies that rely on using electron spin and multiple extrema of the band structure (valleys), respectively, as additional degrees of freedom. There are also collective properties of electrons in semiconductor nanostructures that potentially could be exploited in multifunctional quantum devices. Specifically, plasmonic semiconductor nanocrystals 3-10 offer an opportunity for interface-free coupling between a plasmon and an exciton. However, plasmon-exciton coupling in single-phase semiconductor nanocrystals remains challenging because confined plasmon oscillations are generally not resonant with excitonic transitions. Here, we demonstrate a robust electron polarization in degenerately doped In 2 O 3 nanocrystals, enabled by non-resonant coupling of cyclotron magnetoplasmonic modes 11 with the exciton at the Fermi level. Using magnetic circular dichroism spectroscopy, we show that intrinsic plasmon-exciton coupling allows for the indirect excitation of the magnetoplasmonic modes, and subsequent Zeeman splitting of the excitonic states. Splitting of the band states and selective carrier polarization can be manipulated further by spin-orbit coupling. Our results effectively open up the field of plasmontronics, which involves the phenomena that arise from intrinsic plasmon-exciton and plasmon-spin interactions. Furthermore, the dynamic control of carrier polarization is readily achieved at room temperature, which allows us to harness the magnetoplasmonic mode as a new degree of freedom in practical photonic, optoelectronic and quantum-information processing devices.

  18. Plasmon-induced carrier polarization in semiconductor nanocrystals

    NASA Astrophysics Data System (ADS)

    Yin, Penghui; Tan, Yi; Fang, Hanbing; Hegde, Manu; Radovanovic, Pavle V.

    2018-06-01

    Spintronics1 and valleytronics2 are emerging quantum electronic technologies that rely on using electron spin and multiple extrema of the band structure (valleys), respectively, as additional degrees of freedom. There are also collective properties of electrons in semiconductor nanostructures that potentially could be exploited in multifunctional quantum devices. Specifically, plasmonic semiconductor nanocrystals3-10 offer an opportunity for interface-free coupling between a plasmon and an exciton. However, plasmon-exciton coupling in single-phase semiconductor nanocrystals remains challenging because confined plasmon oscillations are generally not resonant with excitonic transitions. Here, we demonstrate a robust electron polarization in degenerately doped In2O3 nanocrystals, enabled by non-resonant coupling of cyclotron magnetoplasmonic modes11 with the exciton at the Fermi level. Using magnetic circular dichroism spectroscopy, we show that intrinsic plasmon-exciton coupling allows for the indirect excitation of the magnetoplasmonic modes, and subsequent Zeeman splitting of the excitonic states. Splitting of the band states and selective carrier polarization can be manipulated further by spin-orbit coupling. Our results effectively open up the field of plasmontronics, which involves the phenomena that arise from intrinsic plasmon-exciton and plasmon-spin interactions. Furthermore, the dynamic control of carrier polarization is readily achieved at room temperature, which allows us to harness the magnetoplasmonic mode as a new degree of freedom in practical photonic, optoelectronic and quantum-information processing devices.

  19. Induced static asymmetry of the pelvis is associated with functional asymmetry of the lumbo-pelvo-hip complex.

    PubMed

    Gnat, Rafał; Saulicz, Edward

    2008-03-01

    This study evaluates the hypothesis that triggering and eliminating induced static pelvic asymmetry (SPA) may be followed by immediate change in functional asymmetry of the lumbo-pelvo-hip complex. Repeated measures experimental design with 2 levels of independent variable, that is, induced SPA triggered and induced SPA eliminated, was implemented. Three series of measurements were performed, that is, baseline, after triggering SPA, and after eliminating SPA. A group of 84 subjects with no initial symptoms of SPA was studied. Different forms of mechanical stimulation were applied aiming to induce SPA, and the 2 manual stretching-manipulating techniques were performed aiming to eliminate it. A hand inclinometer was used to measure SPA in standing posture. Selected ranges of motion of the hip joints and lumbar spine were used to depict functional asymmetry of the lumbo-pelvo-hip complex. The functional asymmetry indices for individual movements were calculated. Repeated measures design of analysis of variance, dependent data Student t test, and linear Pearson's correlation test were used. Assessment of the SPA showed its significant increase between baseline and series 2 measurements, with a subsequent significant decrease between series 2 and series 3 measurements. Values of the functional asymmetry indices changed accordingly, that is, they increased significantly between series 1 and series 2 and had returned to their initial level in series 3 measurements. Induced SPA shows considerable association with functional asymmetry of the lumbo-pelvo-hip complex.

  20. Cellular internalization of LiNbO3 nanocrystals for second harmonic imaging and the effects on stem cell differentiation

    NASA Astrophysics Data System (ADS)

    Li, Jianhua; Qiu, Jichuan; Guo, Weibo; Wang, Shu; Ma, Baojin; Mou, Xiaoning; Tanes, Michael; Jiang, Huaidong; Liu, Hong

    2016-03-01

    Second harmonic generation (SHG) nanocrystals have recently been reported to label cancer cells and other functional cell lines due to their unique double-frequency property. In this paper, we report for the first time the use of lithium niobate (LiNbO3, LN) nanocrystals as SHG labels for imaging stem cells. Rat mesenchymal stem cells (rMSCs) were labeled with LN nanocrystals in order to study the cellular internalization of the nanocrystals and the influence on stem cell differentiation. The results showed that LN nanocrystals were endocytosed by the rMSCs and the distribution of the internalized nanoparticles demonstrated a high consistency with the orientation of the actin filaments. Besides, LN-labeled rMSCs showed a concentration-dependent viability. Most importantly, rMSCs labeled with 50 μg per mL of LN nanocrystals retained their ability to differentiate into both osteogenic and adipogenic lineages. The results prove that LN nanocrystals can be used as a cytocompatible, near-infrared (NIR) light driven cell label for long-term imaging, without hindering stem cell differentiation. This work will promote the use of LN nanocrystals to broader applications like deep-tissue tracking, remote drug delivery and stem cell therapy.Second harmonic generation (SHG) nanocrystals have recently been reported to label cancer cells and other functional cell lines due to their unique double-frequency property. In this paper, we report for the first time the use of lithium niobate (LiNbO3, LN) nanocrystals as SHG labels for imaging stem cells. Rat mesenchymal stem cells (rMSCs) were labeled with LN nanocrystals in order to study the cellular internalization of the nanocrystals and the influence on stem cell differentiation. The results showed that LN nanocrystals were endocytosed by the rMSCs and the distribution of the internalized nanoparticles demonstrated a high consistency with the orientation of the actin filaments. Besides, LN-labeled rMSCs showed a concentration

  1. Autophoretic locomotion from geometric asymmetry.

    PubMed

    Michelin, Sébastien; Lauga, Eric

    2015-02-01

    Among the few methods which have been proposed to create small-scale swimmers, those relying on self-phoretic mechanisms present an interesting design challenge in that chemical gradients are required to generate net propulsion. Building on recent work, we propose that asymmetries in geometry are sufficient to induce chemical gradients and swimming. We illustrate this idea using two different calculations. We first calculate exactly the self-propulsion speed of a system composed of two spheres of unequal sizes but identically chemically homogeneous. We then consider arbitrary, small-amplitude, shape deformations of a chemically homogeneous sphere, and calculate asymptotically the self-propulsion velocity induced by the shape asymmetries. Our results demonstrate how geometric asymmetries can be tuned to induce large locomotion speeds without the need of chemical patterning.

  2. Radiation damage and nanocrystal formation in uranium-niobium titanates

    NASA Astrophysics Data System (ADS)

    Lian, J.; Wang, S. X.; Wang, L. M.; Ewing, R. C.

    2001-07-01

    Two uranium-niobium titanates, U 2.25Nb 1.90Ti 0.32O 9.8 and Nb 2.75U 1.20Ti 0.36O 10, formed during the synthesis of brannnerite (UTi 2O 6), a minor phase in titanate-based ceramics investigated for plutonium immobilization. These uranium titanates were subjected to 800 keV Kr 2+ irradiation from 30 to 973 K. The critical amorphization dose of the U-rich and Nb-rich titanates at room temperature were 4.72×10 17 and 5×10 17 ions/ m2, respectively. At elevated temperature, the critical amorphization dose increases due to dynamic thermal annealing. The critical amorphization temperature for both Nb-rich and U-rich titanates is ˜933 K under a 800 keV Kr 2+ irradiation. Above the critical amorphization temperature, nanocrystals with an average size of ˜15 nm were observed. The formation of nanocrystals is due to epitaxial recrystallization. At higher temperatures, an ion irradiation-induced nucleation-growth mechanism also contributes to the formation of nanocrystals.

  3. Noscapinoids bearing silver nanocrystals augmented drug delivery, cytotoxicity, apoptosis and cellular uptake in B16F1, mouse melanoma skin cancer cells.

    PubMed

    Soni, Naina; Jyoti, Kiran; Jain, Upendra Kumar; Katyal, Anju; Chandra, Ramesh; Madan, Jitender

    2017-06-01

    Noscapine (Nos) and reduced brominated analogue of noscapine (Red-Br-Nos) prevent cellular proliferation and induce apoptosis in cancer cells either alone or in combination with other chemotherapeutic drugs. However, owing to poor physicochemical properties, Nos and Red-Br-Nos have demonstrated their anticancer activity at higher and multiple doses. Therefore, in present investigation, silver nanocrystals of noscapinoids (Nos-Ag 2+ nanocrystals and Red-Br-Nos-Ag 2+ nanocrystals) were customized to augment drug delivery, cytotoxicity, apoptosis and cellular uptake in B16F1 mouse melanoma cancer cells. Nos-Ag 2+ nanocrystals and Red-Br-Nos-Ag 2+ nanocrystals were prepared separately by precipitation method. The mean particle size of Nos-Ag 2+ nanocrystals was measured to be 25.33±3.52nm, insignificantly (P>0.05) different from 27.43±4.51nm of Red-Br-Nos-Ag 2+ nanocrystals. Furthermore, zeta-potential of Nos-Ag 2+ nanocrystals was determined to be -25.3±3.11mV significantly (P<0.05) different from -15.2±3.33mV of Red-Br-Nos-Ag 2+ nanocrystals. The shape of tailored nanocrystals was slightly spherical and or irregular in shape. The architecture of Nos-Ag 2+ nanocrystals and Red-Br-Nos-Ag 2+ nanocrystals was crystalline in nature. FT-IR spectroscopy evinced the successful interaction of Ag 2+ nanocrystals with Nos and Red-Br-Nos, respectively. The superior therapeutic efficacy of tailored nanocrystals was measured in terms of enhanced cytotoxicity, apoptosis and cellular uptake. The Nos-Ag 2+ nanocrystals and Red-Br-Nos-Ag 2+ nanocrystals exhibited an IC 50 of 16.6μM and 6.5μM, significantly (P<0.05) lower than 38.5μM of Nos and 10.3μM of Red-Br-Nos, respectively. Finally, cellular morphological alterations in B16F1 cells upon internalization of Nos-Ag 2+ nanocrystals and Red-Br-Nos-Ag 2+ nanocrystals provided the evidences for accumulation within membrane-bound cytoplasmic vacuoles and in enlarged lysosomes and thus triggered mitochondria mediated apoptosis via

  4. 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

  5. Semiconductor nanocrystals covalently bound to solid inorganic surfaces using self-assembled monolayers

    DOEpatents

    Alivisatos, A.P.; Colvin, V.L.

    1998-05-12

    Methods are described for attaching semiconductor nanocrystals to solid inorganic surfaces, using self-assembled bifunctional organic monolayers as bridge compounds. Two different techniques are presented. One relies on the formation of self-assembled monolayers on these surfaces. When exposed to solutions of nanocrystals, these bridge compounds bind the crystals and anchor them to the surface. The second technique attaches nanocrystals already coated with bridge compounds to the surfaces. Analyses indicate the presence of quantum confined clusters on the surfaces at the nanolayer level. These materials allow electron spectroscopies to be completed on condensed phase clusters, and represent a first step towards synthesis of an organized assembly of clusters. These new products are also disclosed. 10 figs.

  6. Semiconductor nanocrystals covalently bound to solid inorganic surfaces using self-assembled monolayers

    DOEpatents

    Alivisatos, A. Paul; Colvin, Vicki L.

    1998-01-01

    Methods are described for attaching semiconductor nanocrystals to solid inorganic surfaces, using self-assembled bifunctional organic monolayers as bridge compounds. Two different techniques are presented. One relies on the formation of self-assembled monolayers on these surfaces. When exposed to solutions of nanocrystals, these bridge compounds bind the crystals and anchor them to the surface. The second technique attaches nanocrystals already coated with bridge compounds to the surfaces. Analyses indicate the presence of quantum confined clusters on the surfaces at the nanolayer level. These materials allow electron spectroscopies to be completed on condensed phase clusters, and represent a first step towards synthesis of an organized assembly of clusters. These new products are also disclosed.

  7. Shape-Controlled Synthesis of Isotopic Yttrium-90-Labeled Rare Earth Fluoride Nanocrystals for Multimodal Imaging.

    PubMed

    Paik, Taejong; Chacko, Ann-Marie; Mikitsh, John L; Friedberg, Joseph S; Pryma, Daniel A; Murray, Christopher B

    2015-09-22

    Isotopically labeled nanomaterials have recently attracted much attention in biomedical research, environmental health studies, and clinical medicine because radioactive probes allow the elucidation of in vitro and in vivo cellular transport mechanisms, as well as the unambiguous distribution and localization of nanomaterials in vivo. In addition, nanocrystal-based inorganic materials have a unique capability of customizing size, shape, and composition; with the potential to be designed as multimodal imaging probes. Size and shape of nanocrystals can directly influence interactions with biological systems, hence it is important to develop synthetic methods to design radiolabeled nanocrystals with precise control of size and shape. Here, we report size- and shape-controlled synthesis of rare earth fluoride nanocrystals doped with the β-emitting radioisotope yttrium-90 ((90)Y). Size and shape of nanocrystals are tailored via tight control of reaction parameters and the type of rare earth hosts (e.g., Gd or Y) employed. Radiolabeled nanocrystals are synthesized in high radiochemical yield and purity as well as excellent radiolabel stability in the face of surface modification with different polymeric ligands. We demonstrate the Cerenkov radioluminescence imaging and magnetic resonance imaging capabilities of (90)Y-doped GdF3 nanoplates, which offer unique opportunities as a promising platform for multimodal imaging and targeted therapy.

  8. Prevalence of arytenoid asymmetry in relation to vocal symptoms.

    PubMed

    Hamdan, A-L; Nassar, J; Ashkar, J; Sibai, A

    2011-03-01

    (1) To assess the prevalence of arytenoid asymmetry during adduction, and (2) to correlate arytenoid asymmetry with vocal symptoms. The medical records and video recordings of 116 patients who presented to the voice clinic were reviewed for the presence of arytenoid asymmetry, as regards sharpening of the aryepiglottic fold angle and altered positioning of the cuneiform and corniculate cartilages. There were 61 males and 55 females, with a mean age of 39 years and a standard deviation of 15 years. Almost one-third had a history of reflux, 25 per cent had a history of smoking and 9.6 per cent had a history of allergy. Hoarseness was the most common symptom, occurring in 42.2 per cent of patients, followed by vocal fatigue (25 per cent) and inability to project the voice. The most common type of asymmetry was corniculate asymmetry, present in 27.6 per cent of the cases and accounting for 74.39 per cent of cases. This was followed by cuneiform cartilage asymmetry, present in 15.5 per cent of cases. There was no correlation between arytenoid asymmetry and vocal symptoms, except for vocal fatigue (p = 0.038). The prevalence of arytenoid asymmetry during adduction is common. The presence of vocal symptoms such as hoarseness, breathiness, inability to project the voice and straining does not generally seem to correlate with the prevalence of arytenoid asymmetry. However, subjects with vocal fatigue are more likely to have cuneiform asymmetry.

  9. Au/ZnS core/shell nanocrystals as an efficient anode photocatalyst in direct methanol fuel cells.

    PubMed

    Chen, Wei-Ta; Lin, Yin-Kai; Yang, Ting-Ting; Pu, Ying-Chih; Hsu, Yung-Jung

    2013-10-04

    Au/ZnS core/shell nanocrystals with controllable shell thicknesses were synthesized using a cysteine-assisted hydrothermal method. Incorporating Au/ZnS nanocrystals into the traditional Pt-catalyzed half-cell reaction led to a 43.3% increase in methanol oxidation current under light illumination, demonstrating their promising potential for metal/semiconductor hybrid nanocrystals as the anode photocatalyst in direct methanol fuel cells.

  10. High symmetric 18-facet polyhedron nanocrystals of Cu7S4 with a hollow nanocage.

    PubMed

    Cao, Hongliang; Qian, Xuefeng; Wang, Cheng; Ma, Xiaodong; Yin, Jie; Zhu, Zikang

    2005-11-23

    On the basis of Kirkendall Effect, high symmetric 18-facet polyhedral nanocrystals of Cu7S4 with a hollow nanocage could be converted from cubic nanocrystals of Cu2O in an aqueous media. The presence of organic additives makes the surface energy of {110} smaller than those of {100} and {111}. The growth of nanocrystals along the normal direction of highest energy surface {100} leads to the formation of a 18-facet polyhedron.

  11. Phase Stability and Transformations in Vanadium Oxide Nanocrystals

    NASA Astrophysics Data System (ADS)

    Bergerud, Amy Jo

    Vanadium oxides are both fascinating and complex, due in part to the many compounds and phases that can be stabilized as well as the phase transformations which occur between them. The metal to insulator transitions (MITs) that take place in vanadium oxides are particularly interesting for both fundamental and applied study as they can be induced by a variety of stimuli ( i.e., temperature, pressure, doping) and utilized in many applications (i.e., smart windows, sensors, phase change memory). Nanocrystals also tend to demonstrate interesting phase behavior, due in part to the enhanced influence of surface energy on material thermodynamics. Vanadium oxide nanocrystals are thus expected to demonstrate very interesting properties in regard to phase stability and phase transformations, although synthesizing vanadium oxides in nanocrystal form remains a challenge. Vanadium sesquioxide (V2O3) is an example of a material that undergoes a MIT. For decades, the low temperature monoclinic phase and high temperature corundum phase were the only known crystal structures of V2O3. However, in 2011, a new metastable polymorph of V2O3 was reported with a cubic, bixbyite crystal structure. In Chapter 2, a colloidal route to bixbyite V2O 3 nanocrystals is presented. In addition to being one of the first reported observations of the bixbyite phase in V2O3, it is also one of the first successful colloidal syntheses of any of the vanadium oxides. The nanocrystals possess a flower-like morphology, the size and shape of which are dependent on synthesis time and temperature, respectively. An aminolysis reaction mechanism is determined from Fourier transform infrared spectroscopy data and the bixbyite crystal structure is confirmed by Rietveld refinement of X-ray diffraction (XRD) data. Phase stability is assessed in both air and inert environments, confirming the metastable nature of the material. Upon heating in an inert atmosphere above 700°C, the nanocrystals irreversibly transform

  12. 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

  13. Transparent 'solution' of ultrathin magnesium hydroxide nanocrystals for flexible and transparent nanocomposite films.

    PubMed

    Wang, Jie-Xin; Sun, Qian; Chen, Bo; Wu, Xi; Zeng, Xiao-Fei; Zhang, Cong; Zou, Hai-Kui; Chen, Jian-Feng

    2015-05-15

    Transparent solutions of nanocrystals exhibit many unique properties, and are thus attractive materials for numerous applications. However, the synthesis of transparent nanocrystal solutions of magnesium hydroxide (MH) with wide applications is yet to be realized. Here, we report a facile two-step process, which includes a direct reactive precipitation in alcohol phase instead of aqueous phase combined with a successive surface modification, to prepare transparent alcohol solutions containing lamellar MH nanocrystals with an average size of 52 nm and an ultrathin thickness of 1-2 nm, which is the thinnest MH nanoplatelet reported in the literatures. Further, highly flexible and transparent nanocomposite films are fabricated with a solution mixing method by adding the transparent MH nanocrystal solutions into PVB solution. Considering the simplicity of the fabrication process, high transparency and good flexibility, this MH/polymer nanocomposite film is promising for flame-resistant applications in plastic electronics and optical devices with high transparency, such as flexible displays, optical filters, and flexible solar cells.

  14. Atomistic understanding of cation exchange in PbS nanocrystals using simulations with pseudoligands

    PubMed Central

    Fan, Zhaochuan; Lin, Li-Chiang; Buijs, Wim; Vlugt, Thijs J. H.; van Huis, Marijn A.

    2016-01-01

    Cation exchange is a powerful tool for the synthesis of nanostructures such as core–shell nanocrystals, however, the underlying mechanism is poorly understood. Interactions of cations with ligands and solvent molecules are systematically ignored in simulations. Here, we introduce the concept of pseudoligands to incorporate cation-ligand-solvent interactions in molecular dynamics. This leads to excellent agreement with experimental data on cation exchange of PbS nanocrystals, whereby Pb ions are partially replaced by Cd ions from solution. The temperature and the ligand-type control the exchange rate and equilibrium composition of cations in the nanocrystal. Our simulations reveal that Pb ions are kicked out by exchanged Cd interstitials and migrate through interstitial sites, aided by local relaxations at core–shell interfaces and point defects. We also predict that high-pressure conditions facilitate strongly enhanced cation exchange reactions at elevated temperatures. Our approach is easily extendable to other semiconductor compounds and to other families of nanocrystals. PMID:27160371

  15. Cellulose nanocrystal from pomelo (C. Grandis osbeck) albedo: Chemical, morphology and crystallinity evaluation

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Zain, Nor Fazelin Mat; Yusop, Salma Mohamad; Ahmad, Ishak

    Citrus peel is one of the under-utilized waste materials that have potential in producing a valuable fibre, which are cellulose and cellulose nanocrystal. Cellulose was first isolated from pomelo (C. Grandis Osbeck) albedo by combination of alkali treatment and bleaching process, followed by acid hydrolysis (65% H{sub 2}SO{sub 4}, 45 °C, 45min) to produce cellulose nanocrystal. The crystalline, structural, morphological and chemical properties of both materials were studied. Result reveals the crystallinity index obtained from X-ray diffraction for cellulose nanocrystal was found higher than extracted cellulose with the value of 60.27% and 57.47%, respectively. Fourier transform infrared showed that themore » chemical treatments removed most of the hemicellulose and lignin from the pomelo albedo fibre. This has been confirmed further by SEM and TEM for their morphological studies. These results showed that cellulose and cellulose nanocrystal were successfully obtained from pomelo albedo and might be potentially used in producing functional fibres for food application.« less

  16. Quantum asymmetry between time and space

    PubMed Central

    2016-01-01

    An asymmetry exists between time and space in the sense that physical systems inevitably evolve over time, whereas there is no corresponding ubiquitous translation over space. The asymmetry, which is presumed to be elemental, is represented by equations of motion and conservation laws that operate differently over time and space. If, however, the asymmetry was found to be due to deeper causes, this conventional view of time evolution would need reworking. Here we show, using a sum-over-paths formalism, that a violation of time reversal (T) symmetry might be such a cause. If T symmetry is obeyed, then the formalism treats time and space symmetrically such that states of matter are localized both in space and in time. In this case, equations of motion and conservation laws are undefined or inapplicable. However, if T symmetry is violated, then the same sum over paths formalism yields states that are localized in space and distributed without bound over time, creating an asymmetry between time and space. Moreover, the states satisfy an equation of motion (the Schrödinger equation) and conservation laws apply. This suggests that the time–space asymmetry is not elemental as currently presumed, and that T violation may have a deep connection with time evolution. PMID:26997899

  17. Anomalies and asymmetries in quark-gluon matter

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Teryaev, O. V., E-mail: teryaev@theor.jinr.ru

    The manifestations of axial anomaly and related effects in heavy-ion collisions are considered. Special role is played by various asymmetries. The azimuthal correlational asymmetries of neutron pairs at NICA/FAIR energy range may probe the global rotation of strongly interacting matter. The conductivity is related to the angular asymmetries of dilepton pairs. The strong magnetic field generated in heavy-ion collisions leads to the excess of soft dileptons flying predominantly in the scattering plane.

  18. Hybrid nanocomposites of CdSe nanocrystals distributed in complexing thiophene-based copolymers.

    PubMed

    Aldakov, Dmitry; Jiu, Tonggang; Zagorska, Malgorzata; de Bettignies, Rémi; Jouneau, Pierre-Henri; Pron, Adam; Chandezon, Frédéric

    2010-07-21

    Two types of conjugated polymers were prepared with the goal to blend them with rod-like CdSe nanocrystals. The polymers of the first type were synthesized through copolymerization of 3-octylthiophene and 3-methylene-ethylcarboxylate-thiophene to give polythiophene with solubilizing alkyl groups and methylene ester functional groups (PE series). Post-polymerization hydrolysis of the ester type polymers yielded acid-type ones (PA series). Photoluminescence (PL) quenching in these polymers induced by their titration with nanocrystals solution was chosen as a measure of the polymer-nanocrystal interactions. PL of polyacids turned out to be more efficiently quenched as compared to the case of polymers with ester groups which was interpreted as an indication of better electronic communication between the hybrid components. Infrared (IR) spectroscopy confirmed efficient coordination of the carboxylic groups to CdSe. Voltammetric studies combined with UV-vis spectroelectrochemistry enabled the determination of energy levels alignment of the molecular composite components which turned out to be of staggered type-appropriate for photovoltaic applications. The obtained blends of polyacids with CdSe nanocrystals, when studied by transmission electron microscopy (TEM), revealed the presence of an interpenetrating network in which nanorods were homogeneously distributed within the polymer matrix without any indication of agglomerates formation both on the film surface and in the cross-section. Blends with polymers containing ester groups were less homogeneous which could be explained by weaker polymer-nanocrystals interactions. Photovoltaic cells based on these hybrid materials are also discussed.

  19. 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.

  20. Chronotherapeutically Modulated Pulsatile System of Valsartan Nanocrystals-an In Vitro and In Vivo Evaluation.

    PubMed

    Biswas, Nikhil; Kuotsu, Ketousetuo

    2017-02-01

    The objective was to improve the dissolution of valsartan by developing valsartan nanocrystals and design a pulsed release system for the chronotherapy of hypertension. Valsartan nanocrystals were prepared by sonication-anti-solvent precipitation method and lyophilized to obtain dry powder. Nanocrystals were directly compressed to minitablets and coated to achieve pulsatile valsartan release. Pharmacokinetic profiles of optimized and commercial formulations were compared in rabbit model. The mean particle size and PDI of the optimized nanocrystal batch V4 was reported as 211 nm and 0.117, respectively. DSC and PXRD analysis confirmed the crystalline nature of valsartan in nanocrystals. The dissolution extent of valsartan was markedly enhanced with both nanocrystals and minitablets as compared to pure valsartan irrespective of pH of the medium. Core minitablet V4F containing 5% w/w polyplasdone XL showed quickest release of valsartan, over 90% within 15 min. Coated formulation CV4F showed two spikes in release profile after successive lag times of 235 and 390 min. The pharmacokinetic study revealed that the bioavailability of optimized formulation (72.90%) was significantly higher than the commercial Diovan tablet (30.18%). The accelerated stability studies showed no significant changes in physicochemical properties, release behavior, and bioavialability of CV4F formulation. The formulation was successfully designed to achieve enhanced bioavailability and dual pulsatile release. Bedtime dosing will more efficiently control the circadian spikes of hypertension in the morning.

  1. Ultrafast exciton fine structure relaxation dynamics in lead chalcogenide nanocrystals.

    PubMed

    Johnson, Justin C; Gerth, Kathrine A; Song, Qing; Murphy, James E; Nozik, Arthur J; Scholes, Gregory D

    2008-05-01

    The rates of fine structure relaxation in PbS, PbSe, and PbTe nanocrystals were measured on a femtosecond time scale as a function of temperature with no applied magnetic field by cross-polarized transient grating spectroscopy (CPTG) and circularly polarized pump-probe spectroscopy. The relaxation rates among exciton fine structure states follow trends with nanocrystal composition and size that are consistent with the expected influence of material dependent spin-orbit coupling, confinement enhanced electron-hole exchange interaction, and splitting between L valleys that are degenerate in the bulk. The size dependence of the fine structure relaxation rate is considerably different from what is observed for small CdSe nanocrystals, which appears to result from the unique material properties of the highly confined lead chalcogenide quantum dots. Modeling and qualitative considerations lead to conclusions about the fine structure of the lowest exciton absorption band, which has a potentially significant bearing on photophysical processes that make these materials attractive for practical purposes.

  2. 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.

  3. Nanocrystal synthesis and thin film formation for earth abundant photovoltaics

    NASA Astrophysics Data System (ADS)

    Carter, Nathaniel J.

    Providing access to on-demand energy at the global scale is a grand challenge of our time. The fabrication of solar cells from nanocrystal inks comprising earth abundant elements represents a scalable and sustainable photovoltaic technology with the potential to meet the global demand for electricity. Solar cells with Cu2ZnSn(S,Se)4 (CZTSSe) absorber layers are of particular interest due to the high absorption coefficient of CZTSSe, its band gap in the ideal range for efficient photovoltaic power conversion, and the relative abundance of its constituent elements in the earth's crust. Despite the promise of this material system, CZTSSe solar cell efficiencies reported throughout literature have failed to exceed 12.6%, principally due to the low open-circuit voltage (VOC) achieved in these devices compared to the absorber band gap. The work presented herein primarily aims to address the low VOC problem. First, the fundamental cause for such low VOC's is investigated. Interparticle compositional inhomogeneities identified in the synthesized CZTS nanocrystals and their effect on the absorber layer formation and device performance are characterized. Real-time energy-dispersive x-ray diffraction (EDXRD) elucidates the role of these inhomogeneities in the mechanism by which a film of CZTS nanocrystals converts into a dense absorber layer comprising micron-sized CZTSSe grains upon annealing in a selenium atmosphere (selenization). Additionally, a direct correlation between the nanocrystal inhomogeneities and the VOC in completed devices is observed. Detailed characterization of CZTSSe solar cells identifies electrical potential fluctuations in the CZTSSe absorber - due to spatial composition variations not unlike those observed in the nanocrystals - as a primary V OC inhibitor. Additional causes for low VOC's in CZTSSe solar cells proposed in the literature involve recombination at the interface between the CZTSSe absorber and: (1) the n-type, CdS buffer layer, or (2) the

  4. Geometric asymmetry driven Janus micromotors

    NASA Astrophysics Data System (ADS)

    Zhao, Guanjia; Pumera, Martin

    2014-09-01

    The production and application of nano-/micromotors is of great importance. In order for the motors to work, asymmetry in their chemical composition or physical geometry must be present if no external asymmetric field is applied. In this paper, we present a ``coconut'' micromotor made of platinum through the partial or complete etching of the silica templates. It was shown that although both the inner and outer surfaces are made of the same material (Pt), motion of the structure can be observed as the convex surface is capable of generating oxygen bubbles. This finding shows that not only the chemical asymmetry of the micromotor, but also its geometric asymmetry can lead to fast propulsion of the motor. Moreover, a considerably higher velocity can be seen for partially etched coconut structures than the velocities of Janus or fully etched, shell-like motors. These findings will have great importance on the design of future micromotors.The production and application of nano-/micromotors is of great importance. In order for the motors to work, asymmetry in their chemical composition or physical geometry must be present if no external asymmetric field is applied. In this paper, we present a ``coconut'' micromotor made of platinum through the partial or complete etching of the silica templates. It was shown that although both the inner and outer surfaces are made of the same material (Pt), motion of the structure can be observed as the convex surface is capable of generating oxygen bubbles. This finding shows that not only the chemical asymmetry of the micromotor, but also its geometric asymmetry can lead to fast propulsion of the motor. Moreover, a considerably higher velocity can be seen for partially etched coconut structures than the velocities of Janus or fully etched, shell-like motors. These findings will have great importance on the design of future micromotors. Electronic supplementary information (ESI) available: Additional SEM images, data analysis, Videos S

  5. Spectral Selectivity of Plasmonic Interactions between Individual Up-Converting Nanocrystals and Spherical Gold Nanoparticles.

    PubMed

    Piątkowski, Dawid; Schmidt, Mikołaj K; Twardowska, Magdalena; Nyk, Marcin; Aizpurua, Javier; Maćkowski, Sebastian

    2017-08-04

    We experimentally demonstrate strong spectral selectivity of plasmonic interaction that occurs between α-NaYF₄:Er 3+ /Yb 3+ nanocrystals, which feature two emission bands, and spherical gold nanoparticles, with plasmon frequency resonant with one of the emission bands. Spatially-resolved luminescence intensity maps acquired for individual nanocrystals, together with microsecond luminescence lifetime images, show two qualitatively different effects that result from the coupling between plasmon excitations in metallic nanoparticles and emitting states of the nanocrystals. On the one hand, we observe nanocrystals, whose emission intensity is strongly enhanced for both resonant and non-resonant bands with respect to the plasmon resonance. Importantly, this increase is accompanied with shortening of luminescence decays times. In contrast, a significant number of nanocrystals exhibits almost complete quenching of the emission resonant with the plasmon resonance of gold nanoparticles. Theoretical analysis indicates that such an effect can occur for emitters placed at distances of about 5 nm from gold nanoparticles. While under these conditions, both transitions experience significant increases of the radiative emission rates due to the Purcell effect, the non-radiative energy transfer between resonant bands results in strong quenching, which in that situation nullifies the enhancement.

  6. Solvent-like ligand-coated ultrasmall cadmium selenide nanocrystals: strong electronic coupling in a self-organized assembly.

    PubMed

    Lawrence, Katie N; Johnson, Merrell A; Dolai, Sukanta; Kumbhar, Amar; Sardar, Rajesh

    2015-07-21

    Strong inter-nanocrystal electronic coupling is a prerequisite for delocalization of exciton wave functions and high conductivity. We report 170 meV electronic coupling energy of short chain poly(ethylene glycol) thiolate-coated ultrasmall (<2.5 nm in diameter) CdSe semiconductor nanocrystals (SNCs) in solution. Cryo-transmission electron microscopy analysis showed the formation of a pearl-necklace assembly of nanocrystals in solution with regular inter-nanocrystal spacing. The electronic coupling was studied as a function of CdSe nanocrystal size where the smallest nanocrystals exhibited the largest coupling energy. The electronic coupling in spin-cast thin-film (<200 nm in thickness) of poly(ethylene glycol) thiolate-coated CdSe SNCs was studied as a function of annealing temperature, where an unprecedentedly large, ∼400 meV coupling energy was observed for 1.6 nm diameter SNCs, which were coated with a thin layer of poly(ethylene glycol) thiolates. Small-angle X-ray scattering measurements showed that CdSe SNCs maintained an order array inside the films. The strong electronic coupling of SNCs in a self-organized film could facilitate the large-scale production of highly efficient electronic materials for advanced optoelectronic device application.

  7. Tolerance to structural disorder and tunable mechanical behavior in self-assembled superlattices of polymer-grafted nanocrystals

    DOE PAGES

    Gu, X. Wendy; Ye, Xingchen; Koshy, David M.; ...

    2017-02-27

    Large, freestanding membranes with remarkably high elastic modulus ( > 10 GPa) have been fabricated through the self-Assembly of ligand-stabilized inorganic nanocrystals, even though these nanocrystals are connected only by soft organic ligands (e.g., dodecanethiol or DNA) that are not cross-linked or entangled. Recent developments in the synthesis of polymer-grafted nanocrystals have greatly expanded the library of accessible superlattice architectures,which allows superlattice mechanical behavior to be linked to specific structural features. Here, colloidal self-Assembly is used to organize polystyrene-grafted Au nanocrystals at a fluid interface to form ordered solids with sub-10-nm periodic features. We used thin-film buckling and nanoindentation tomore » evaluate the mechanical behavior of polymer-grafted nanocrystal superlattices while exploring the role of polymer structural conformation, nanocrystal packing, and superlattice dimensions. Superlattices containing 3-20 vol % Au are found to have an elastic modulus of ~6-19 GPa, and hardness of ~120-170 MPa. We also found that rapidly self-Assembled superlattices have the highest elastic modulus, despite containing significant structural defects. Polymer extension, interdigitation, and grafting density are determined to be critical parameters that govern superlattice elastic and plastic deformation.« less

  8. Tolerance to structural disorder and tunable mechanical behavior in self-assembled superlattices of polymer-grafted nanocrystals

    NASA Astrophysics Data System (ADS)

    Gu, X. Wendy; Ye, Xingchen; Koshy, David M.; Vachhani, Shraddha; Hosemann, Peter; Alivisatos, A. Paul

    2017-03-01

    Large, freestanding membranes with remarkably high elastic modulus (>10 GPa) have been fabricated through the self-assembly of ligand-stabilized inorganic nanocrystals, even though these nanocrystals are connected only by soft organic ligands (e.g., dodecanethiol or DNA) that are not cross-linked or entangled. Recent developments in the synthesis of polymer-grafted nanocrystals have greatly expanded the library of accessible superlattice architectures, which allows superlattice mechanical behavior to be linked to specific structural features. Here, colloidal self-assembly is used to organize polystyrene-grafted Au nanocrystals at a fluid interface to form ordered solids with sub-10-nm periodic features. Thin-film buckling and nanoindentation are used to evaluate the mechanical behavior of polymer-grafted nanocrystal superlattices while exploring the role of polymer structural conformation, nanocrystal packing, and superlattice dimensions. Superlattices containing 3-20 vol % Au are found to have an elastic modulus of ˜6-19 GPa, and hardness of ˜120-170 MPa. We find that rapidly self-assembled superlattices have the highest elastic modulus, despite containing significant structural defects. Polymer extension, interdigitation, and grafting density are determined to be critical parameters that govern superlattice elastic and plastic deformation.

  9. Novel green synthetic strategy to prepare ZnO nanocrystals using rambutan (Nephelium lappaceum L.) peel extract and its antibacterial applications.

    PubMed

    Yuvakkumar, R; Suresh, J; Nathanael, A Joseph; Sundrarajan, M; Hong, S I

    2014-08-01

    In the present investigation, we report a sustainable novel green synthetic strategy to synthesis zinc oxide nanocrystals. This is the first report on sustainable biosynthesis of zinc oxide nanocrystals employing Nephelium lappaceum L., peel extract as a natural ligation agent. Green synthesis of zinc oxide nanocrystals was carried out via zinc-ellagate complex formation using rambutan peel wastes. The successful formation of zinc oxide nanocrystals was confirmed employing standard characterisation studies. A possible mechanism for the formation of ZnO nanocrystals with rambutan peel extract was also proposed. The prepared ZnO nanocrystals were coated on the cotton fabric and their antibacterial activity were analyzed. ZnO nanocrystals coated cotton showed good antibacterial activity towards Escherichia coli (E. coli), gram negative bacteria and Staphylococcus aureus (S. aureus), gram positive bacteria. Copyright © 2014 Elsevier B.V. All rights reserved.

  10. Size and shape dependence of electronic and optical excitations in TiO2 nanocrystals

    NASA Astrophysics Data System (ADS)

    Baishya, Kopinjol; Ogut, Serdar

    2013-03-01

    We present results for the electronic structures, quasi-particle gaps, and the absorption spectra of TiO2 nanocrystals of both rutile and anatase phases with various shapes, sizes, and surfaces exposed. We study the size and shape dependences of these electronic and optical properties, computed both within time-dependent density functional theory and many-body perturbation methods such as the GW-BSE, using appropriately passivated nanocrystals to mimic bulk termination. Surface effects are examined by using nanocrystals of various sizes with particular surfaces, such as (110) in rutile and (101) in anatase phases, exposed. We interpret the resulting optical absorption spectra of these nanocrystals in terms of the bulk spectra and compare them with predictions from classical Mie-Gans theory. This work was supported by the DOE Grant No. DE-FG02-09ER16072.

  11. Composition-Dependent Energy Splitting between Bright and Dark Excitons in Lead Halide Perovskite Nanocrystals.

    PubMed

    Chen, Lan; Li, Bin; Zhang, Chunfeng; Huang, Xinyu; Wang, Xiaoyong; Xiao, Min

    2018-03-14

    Perovskite semiconductor nanocrystals with different compositions have shown promise for applications in light-emitting devices. Dark excitonic states may suppress light emission from such nanocrystals by providing an additional nonradiative recombination channel. Here, we study the composition dependence of dark exciton dynamics in nanocrystals of lead halides by time-resolved photoluminescence spectroscopy at cryogenic temperatures. The presence of a spin-related dark state is revealed by magneto-optical spectroscopy. The energy splitting between bright and dark states is found to be highly sensitive to both halide elements and organic cations, which is explained by considering the effects of size confinement and charge screening, respectively, on the exchange interaction. These findings suggest the possibility of manipulating dark exciton dynamics in perovskite semiconductor nanocrystals by composition engineering, which will be instrumental in the design of highly efficient light-emitting devices.

  12. Introduction to provocative questions in left-right asymmetry.

    PubMed

    Levin, Michael; Klar, Amar J S; Ramsdell, Ann F

    2016-12-19

    Left-right asymmetry is a phenomenon that has a broad appeal-to anatomists, developmental biologists and evolutionary biologists-because it is a morphological feature of organisms that spans scales of size and levels of organization, from unicellular protists, to vertebrate organs, to social behaviour. Here, we highlight a number of important aspects of asymmetry that encompass several areas of biology-cell-level, physiological, genetic, anatomical and evolutionary components-and that are based on research conducted in diverse model systems, ranging from single cells to invertebrates to human developmental disorders. Together, the contributions in this issue reveal a heretofore-unsuspected variety in asymmetry mechanisms, including ancient chirality elements that could underlie a much more universal basis to asymmetry development, and provide much fodder for thought with far reaching implications in biomedical, developmental, evolutionary and synthetic biology. The new emerging theme of binary cell-fate choice, promoted by asymmetric cell division of a deterministic cell, has focused on investigating asymmetry mechanisms functioning at the single cell level. These include cytoskeleton and DNA chain asymmetry-mechanisms that are amplified and coordinated with those employed for the determination of the anterior-posterior and dorsal-ventral axes of the embryo.This article is part of the themed issue 'Provocative questions in left-right asymmetry'. © 2016 The Author(s).

  13. [Spectroscopic Research on Slag Nanocrystal Glass Ceramics Containing Rare Earth Elements].

    PubMed

    Ouyang, Shun-li; Li, Bao-wei; Zhang, Xue-feng; Jia, Xiao-lin; Zhao, Ming; Deng, Lei-bo

    2015-08-01

    The research group prepared the high-performance slag nanocrystal glass ceramics by utilizing the valuable elements of the wastes in the Chinese Bayan Obo which are characterized by their symbiotic or associated existence. In this paper, inductively coupled plasma emission spectroscopy (ICP), X-ray diffraction (XRD), Raman spectroscopy (Raman) and scanning electron microscopy (SEM) are all used in the depth analysis for the composition and structure of the samples. The experiment results of ICP, XRD and SEM showed that the principal crystalline phase of the slag nanocrystal glass ceramics containing rare earth elements is diopside, its grain size ranges from 45 to 100 nm, the elements showed in the SEM scan are basically in consistent with the component analysis of ICP. Raman analysis indicated that its amorphous phase is a three-dimensional network structure composed by the structural unit of silicon-oxy tetrahedron with different non-bridging oxygen bonds. According to the further analysis, we found that the rare earth microelement has significant effect on the network structure. Compared the nanocrystal slag glass ceramic with the glass ceramics of similar ingredients, we found that generally, the Raman band wavenumber for the former is lower than the later. The composition difference between the glass ceramics and the slag nanocrystal with the similar ingredients mainly lies on the rare earth elements and other trace elements. Therefore, we think that the rare earth elements and other trace elements remains in the slag nanocrystal glass ceramics have a significant effect on the network structure of amorphous phase. The research method of this study provides an approach for the relationship among the composition, structure and performance of the glass ceramics.

  14. Preparation of core-shell Ti-Nb oxide nanocrystals

    NASA Astrophysics Data System (ADS)

    Simakov, David S. A.; Tsur, Yoed

    2008-01-01

    Nanosized powders of Ti-Nb oxide core-shell nanocrystals with atomic ratios of Nb/Ti = 0.11, 0.25, and 0.38 have been prepared by two preparation routes. The first route was co-precipitation, followed by␣annealing, using NbCl5 as a source of Nb. The second route was coating of pure TiO2 nanocrystals by Nb-isopropoxide in liquid medium, followed by impregnation of the Nb into the nanoparticles by annealing. Both methods yielded anatase nanocrystals with a Nb-rich shell and a core, which had much lower Nb loadings. The anatase structure solid solution (with Nb incorporated) was stable under annealing up to 760°C. The particle size remained within the nanometric scale ( <50 nm) under heat-treatment up to 760°C. It has been shown that the fabricated powders can be redispersed in aqueous media by simple ultrasound treatment, resulting in nanosized dispersions. Using a variety of analytical techniques, including depth profiling of single nanocrystallites by AES combined with sputtering by Ar ions, the mechanism of the core-shell structure creation was studied. It is proposed that the formation of the core-shell structure is governed by solubility limitations in the co-precipitation route and by solubility and diffusion limitations in the coating-incorporation route.

  15. 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.

  16. Three-dimensional assessment of facial asymmetry: A systematic review.

    PubMed

    Akhil, Gopi; Senthil Kumar, Kullampalayam Palanisamy; Raja, Subramani; Janardhanan, Kumaresan

    2015-08-01

    For patients with facial asymmetry, complete and precise diagnosis, and surgical treatments to correct the underlying cause of the asymmetry are significant. Conventional diagnostic radiographs (submento-vertex projections, posteroanterior radiography) have limitations in asymmetry diagnosis due to two-dimensional assessments of three-dimensional (3D) images. The advent of 3D images has greatly reduced the magnification and projection errors that are common in conventional radiographs making it as a precise diagnostic aid for assessment of facial asymmetry. Thus, this article attempts to review the newly introduced 3D tools in the diagnosis of more complex facial asymmetries.

  17. Thick-shell nanocrystal quantum dots

    DOEpatents

    Hollingsworth, Jennifer A [Los Alamos, NM; Chen, Yongfen [Eugene, OR; Klimov, Victor I [Los Alamos, NM; Htoon, Han [Los Alamos, NM; Vela, Javier [Los Alamos, NM

    2011-05-03

    Colloidal nanocrystal quantum dots comprising an inner core having an average diameter of at least 1.5 nm and an outer shell, where said outer shell comprises multiple monolayers, wherein at least 30% of the quantum dots have an on-time fraction of 0.80 or greater under continuous excitation conditions for a period of time of at least 10 minutes.

  18. Synthesis of Mn doped ZnS nanocrystals: Crystallographic and morphological study

    NASA Astrophysics Data System (ADS)

    Shaikh, Azharuddin Z.; Shirsath, Narendra B.; Sonawane, Prabhakar S.

    2018-05-01

    The influence of doping concentration on the physical properties of ZnS nanocrystals synthesized using coprecipitation method at room temperature is reported in this paper. In particular, we have studied the structural properties of Zn1-xMnxS where (x=0.01, 0.03, 0.05) by X-ray diffraction. X-ray peak broadening analysis used to calculate the crystalline sizes, lattice parameters, number of unit cell per particle and volume of unit cell. Crystalline ZnS with a cubic structure is confirmed by XRD results. The grain size of pure and Mn doped samples were found in the range of 7nm to 9nm. All the physical parameters of cubic ZnS nanocrystals were calculated are similar with standard values. The scanning electron microscope (SEM) which revealed that the synthesized nanocrystals are well-crystalline and possessing cubic phase.

  19. Entanglement asymmetry for boosted black branes and the bound

    NASA Astrophysics Data System (ADS)

    Mishra, Rohit; Singh, Harvendra

    2017-06-01

    We study the effects of asymmetry in the entanglement thermodynamics of CFT subsystems. It is found that “boosted” Dp-brane backgrounds give rise to the first law of the entanglement thermodynamics where the CFT pressure asymmetry plays a decisive role in the entanglement. Two different strip like subsystems, one parallel to the boost and the other perpendicular, are studied in the perturbative regime Tthermal ≪ TE. We mainly seek to quantify this entanglement asymmetry as a ratio of the first-order entanglement entropies of the excitations. We discuss the AdS-wave backgrounds at zero temperature having maximum asymmetry from where a bound on entanglement asymmetry is obtained. The entanglement asymmetry reduces as we switch on finite temperature in the CFT while it is maximum at zero temperature.

  20. Replication-associated mutational asymmetry in the human genome.

    PubMed

    Chen, Chun-Long; Duquenne, Lauranne; Audit, Benjamin; Guilbaud, Guillaume; Rappailles, Aurélien; Baker, Antoine; Huvet, Maxime; d'Aubenton-Carafa, Yves; Hyrien, Olivier; Arneodo, Alain; Thermes, Claude

    2011-08-01

    During evolution, mutations occur at rates that can differ between the two DNA strands. In the human genome, nucleotide substitutions occur at different rates on the transcribed and non-transcribed strands that may result from transcription-coupled repair. These mutational asymmetries generate transcription-associated compositional skews. To date, the existence of such asymmetries associated with replication has not yet been established. Here, we compute the nucleotide substitution matrices around replication initiation zones identified as sharp peaks in replication timing profiles and associated with abrupt jumps in the compositional skew profile. We show that the substitution matrices computed in these regions fully explain the jumps in the compositional skew profile when crossing initiation zones. In intergenic regions, we observe mutational asymmetries measured as differences between complementary substitution rates; their sign changes when crossing initiation zones. These mutational asymmetries are unlikely to result from cryptic transcription but can be explained by a model based on replication errors and strand-biased repair. In transcribed regions, mutational asymmetries associated with replication superimpose on the previously described mutational asymmetries associated with transcription. We separate the substitution asymmetries associated with both mechanisms, which allows us to determine for the first time in eukaryotes, the mutational asymmetries associated with replication and to reevaluate those associated with transcription. Replication-associated mutational asymmetry may result from unequal rates of complementary base misincorporation by the DNA polymerases coupled with DNA mismatch repair (MMR) acting with different efficiencies on the leading and lagging strands. Replication, acting in germ line cells during long evolutionary times, contributed equally with transcription to produce the present abrupt jumps in the compositional skew. These results

  1. Regional facial asymmetries and attractiveness of the face.

    PubMed

    Kaipainen, Anu E; Sieber, Kevin R; Nada, Rania M; Maal, Thomas J; Katsaros, Christos; Fudalej, Piotr S

    2016-12-01

    Facial attractiveness is an important factor in our social interactions. It is still not entirely clear which factors influence the attractiveness of a face and facial asymmetry appears to play a certain role. The aim of the present study was to assess the association between facial attractiveness and regional facial asymmetries evaluated on three-dimensional (3D) images. 3D facial images of 59 (23 male, 36 female) young adult patients (age 16-25 years) before orthodontic treatment were evaluated for asymmetry. The same 3D images were presented to 12 lay judges who rated the attractiveness of each subject on a 100mm visual analogue scale. Reliability of the method was assessed with Bland-Altman plots and Cronbach's alpha coefficient. All subjects showed a certain amount of asymmetry in all regions of the face; most asymmetry was found in the chin and cheek areas and less in the lip, nose and forehead areas. No statistically significant differences in regional facial asymmetries were found between male and female subjects (P > 0.05). Regression analyses demonstrated that the judgement of facial attractiveness was not influenced by absolute regional facial asymmetries when gender, facial width-to-height ratio and type of malocclusion were controlled (P > 0.05). A potential limitation of the study could be that other biologic and cultural factors influencing the perception of facial attractiveness were not controlled for. A small amount of asymmetry was present in all subjects assessed in this study, and asymmetry of this magnitude may not influence the assessment of facial attractiveness. © The Author 2015. Published by Oxford University Press on behalf of the European Orthodontic Society. All rights reserved. For permissions, please email: journals.permissions@oup.com.

  2. Measurement of parity-violating asymmetry in electron-deuteron inelastic scattering

    DOE PAGES

    Wang, D.; Pan, K.; Subedi, R.; ...

    2015-04-01

    The parity-violating asymmetries between a longitudinally-polarized electron beam and an unpolarized deuterium target have been measured recently. The measurement covered two kinematic points in the deep inelastic scattering region and five in the nucleon resonance region. We provide here details of the experimental setup, data analysis, and results on all asymmetry measurements including parity-violating electron asymmetries and those of inclusive pion production and beam-normal asymmetries. The parity-violating deep-inelastic asymmetries were used to extract the electron-quark weak effective couplings, and the resonance asymmetries provided the first evidence for quark-hadron duality in electroweak observables. These electron asymmetries and their interpretation were publishedmore » earlier, but are presented here in more detail.« less

  3. Mercury exposure may influence fluctuating asymmetry in waterbirds

    USGS Publications Warehouse

    Herring, Garth; Eagles-Smith, Collin A.; Ackerman, Joshua T.

    2017-01-01

    Variation in avian bilateral symmetry can be an indicator of developmental instability in response to a variety of stressors, including environmental contaminants. The authors used composite measures of fluctuating asymmetry to examine the influence of mercury concentrations in 2 tissues on fluctuating asymmetry within 4 waterbird species. Fluctuating asymmetry increased with mercury concentrations in whole blood and breast feathers of Forster's terns (Sterna forsteri), a species with elevated mercury concentrations. Specifically, fluctuating asymmetry in rectrix feather 1 was the most strongly correlated structural variable of those tested (wing chord, tarsus, primary feather 10, rectrix feather 6) with mercury concentrations in Forster's terns. However, for American avocets (Recurvirostra americana), black-necked stilts (Himantopus mexicanus), and Caspian terns (Hydroprogne caspia), the authors found no relationship between fluctuating asymmetry and either whole-blood or breast feather mercury concentrations, even though these species had moderate to elevated mercury exposure. The results indicate that mercury contamination may act as an environmental stressor during development and feather growth and contribute to fluctuating asymmetry of some species of highly contaminated waterbirds.

  4. Asymmetry of the Brain: Development and Implications.

    PubMed

    Duboc, Véronique; Dufourcq, Pascale; Blader, Patrick; Roussigné, Myriam

    2015-01-01

    Although the left and right hemispheres of our brains develop with a high degree of symmetry at both the anatomical and functional levels, it has become clear that subtle structural differences exist between the two sides and that each is dominant in processing specific cognitive tasks. As the result of evolutionary conservation or convergence, lateralization of the brain is found in both vertebrates and invertebrates, suggesting that it provides significant fitness for animal life. This widespread feature of hemispheric specialization has allowed the emergence of model systems to study its development and, in some cases, to link anatomical asymmetries to brain function and behavior. Here, we present some of what is known about brain asymmetry in humans and model organisms as well as what is known about the impact of environmental and genetic factors on brain asymmetry development. We specifically highlight the progress made in understanding the development of epithalamic asymmetries in zebrafish and how this model provides an exciting opportunity to address brain asymmetry at different levels of complexity.

  5. Semiconductor nanocrystals for novel optical applications

    NASA Astrophysics Data System (ADS)

    Moon, Jong-Sik

    Inspired by the promise of enhanced spectral response, photorefractive polymeric composites photosensitized with semiconductor nanocrystals have emerged as an important class of materials. Here, we report on the photosensitization of photorefractive polymeric composites at visible wavelengths through the inclusion of narrow band-gap semiconductor nanocrystals composed of PbS. Through this approach, internal diffraction efficiencies in excess of 82%, two-beam-coupling gain coefficients in excess of 211 cm-1, and response times 34 ms have been observed, representing some of the best figures-of-merit reported on this class of materials. In addition to providing efficient photosensitization, however, extensive studies of these hybrid composites have indicated that the inclusion of nanocrystals also provides an enhancement in the charge-carrier mobility and subsequent reduction in the photorefractive response time. Through this approach with PbS as charge-carrier, unprecedented response times of 399 micros were observed, opening the door for video and other high-speed applications. It is further demonstrated that this improvement in response time occurs with little sacrifice in photorefractive efficiency and with internal diffraction efficiencies of 72% and two- beam-coupling gain coefficients of 500 cm-1 being measured. A thorough analysis of the experimental data is presented, supporting the hypothesized mechanism of the enhanced charge mobility without the accompaniment of superfluous traps. Finally, water soluble InP/ZnS and CdSe/ZnS quantum dots interacted with CPP and Herceptin to apply them as a bio-maker. Both of quantum dots showed the excellent potential for use in biomedical imaging and drug delivery applications. It is anticipated that these approaches can play a significant role in the eventual commercialization of these classes of materials.

  6. Ferritin-based nanocrystals for solar energy harvesting

    NASA Astrophysics Data System (ADS)

    Colton, John; Erickson, Stephen; Olsen, Cameron; Embley, Jacob; Smith, Trevor; Watt, Richard

    2015-03-01

    Ferritin is a 12 nm diameter hollow protein with an 8 nm cavity that can be filled with a variety of nanocrystals (ferrihydrite being native). We report on several experiments with ferritin-based nanocrystals designed to utilize ferritin for solar energy harvesting. First, we have shown that the native band gap can be altered by controlling nanocrystal size, by replacing the native iron oxide core with other metal oxides, and by depositing halides and oxo-anions with the iron oxide core. This gives available band gaps of 1.6 to 2.3 eV. Theoretical efficiency calculations based on these band gaps show that the efficiency of a multi-junction solar cell based on layered structures of ferritin can be as high as 44.9 %, and up to 63.1 % if a ferritin-based material with band gap of 1.1 eV can be developed. For the latter case, the efficiencies remain quite high even in a current-matched configuration, namely 50.0 %. We have also demonstrated that photo-excitation of these materials can produce charge separation and give rise to usable electrons; we have used photo-excited electrons to reduce gold in solution and thereby produce gold nanoparticles on the surface of the ferritin. This technique can potentially be extended to platinum, whose nanoparticles catalyze water splitting. This research was partially supported by the Utah Office of Energy Development, Governor's Energy Leadership Scholars Program.

  7. Exciton-to-Dopant Energy Transfer in Mn-Doped Cesium Lead Halide Perovskite Nanocrystals.

    PubMed

    Parobek, David; Roman, Benjamin J; Dong, Yitong; Jin, Ho; Lee, Elbert; Sheldon, Matthew; Son, Dong Hee

    2016-12-14

    We report the one-pot synthesis of colloidal Mn-doped cesium lead halide (CsPbX 3 ) perovskite nanocrystals and efficient intraparticle energy transfer between the exciton and dopant ions resulting in intense sensitized Mn luminescence. Mn-doped CsPbCl 3 and CsPb(Cl/Br) 3 nanocrystals maintained the same lattice structure and crystallinity as their undoped counterparts with nearly identical lattice parameters at ∼0.2% doping concentrations and no signature of phase separation. The strong sensitized luminescence from d-d transition of Mn 2+ ions upon band-edge excitation of the CsPbX 3 host is indicative of sufficiently strong exchange coupling between the charge carriers of the host and dopant d electrons mediating the energy transfer, essential for obtaining unique properties of magnetically doped quantum dots. Highly homogeneous spectral characteristics of Mn luminescence from an ensemble of Mn-doped CsPbX 3 nanocrystals and well-defined electron paramagnetic resonance spectra of Mn 2+ in host CsPbX 3 nanocrystal lattices suggest relatively uniform doping sites, likely from substitutional doping at Pb 2+ . These observations indicate that CsPbX 3 nanocrystals, possessing many superior optical and electronic characteristics, can be utilized as a new platform for magnetically doped quantum dots expanding the range of optical, electronic, and magnetic functionality.

  8. Density functional theory study of atomic and electronic properties of defects in reduced anatase TiO2 nanocrystals

    NASA Astrophysics Data System (ADS)

    Morita, Kazuki; Yasuoka, Kenji

    2018-03-01

    Anatase TiO2 nanocrystals have received considerable attention owing to their promising applications in photocatalysis, photovoltaics, and fuel cells. Although experimental evidence has shown that the performance of nanocrystals can be significantly improved through reduction, the mechanistic basis of this enhancement remains unclear. To shed a light on the chemistry of reduced anatase TiO2 nanocrystals, density functional theory were used to investigate the properties of defects and excess electrons. We demonstrated that oxygen vacancies are stable both on the surface and at the sub-surface of the nanocrystal, while titanium interstitials prefer sub-surface sites. Different defect locations possessed different excess electron structures, which contributed to deep and shallow states in the band gap of the nanocrystals. Furthermore, valence band tailing was observed, resulting in band gap narrowing. The theoretical results presented here deepen our understanding, and show the potential of defects to considerably change the macroscopic properties of anatase TiO2 nanocrystals.

  9. Near white light emission of silicon nanocrystals

    NASA Astrophysics Data System (ADS)

    Lee, Soojin; Han, Il-Ki; Cho, Woon-Jo

    2003-11-01

    Silicon nanoparticles in the range from 2 nm to 5 nm was prepared from Zintl salt, soldium silicide (NaSi) by sonochemical method. This synthesis permits the reaction completed as fast as in a few hours and the easy alkyl-modification of nanocrystals surface at room temperature and ambient pressure. The average size of nanoparticles measured by the dynamic light scattering analysis was 2.7 nm. The high-resolution transmission electron micrograph cofirmed the material identity of nanoparticles as crystalline silicon. FT-IR spectra are consistent with the surface states of nanocrystals that is chlorine- or butyl-capped. The emission peak center moved to longer wavelength (up to 430 nm) with the reaction time, under a 325 nm excitation. The luminescence of silicon colloids looks bright bluish-white under excitation using a commercial low-intensity UV lamp.

  10. Electron coherent diffraction tomography of a nanocrystal

    NASA Astrophysics Data System (ADS)

    Dronyak, Roman; Liang, Keng S.; Tsai, Jin-Sheng; Stetsko, Yuri P.; Lee, Ting-Kuo; Chen, Fu-Rong

    2010-05-01

    Coherent diffractive imaging (CDI) with electron or x-ray sources is a promising technique for investigating the structure of nanoparticles down to the atomic scale. In electron CDI, a two-dimensional reconstruction is demonstrated using highly coherent illumination from a field-emission gun as a source of electrons. In a three-dimensional (3D) electron CDI, we experimentally determine the morphology of a single MgO nanocrystal using the Bragg diffraction geometry. An iterative algorithm is applied to invert the 3D diffraction pattern about a (200) reflection of the nanoparticle measured at an angular range of 1.8°. The results reveal a 3D image of the sample at ˜8 nm resolution, and agree with a simulation. Our work demonstrates an alternative approach to obtain the 3D structure of nanocrystals with an electron microscope.

  11. Hydrothermal Synthesis of PbTiO3 Nanocrystals with a pH-Adjusting Agent of Ammonia Solution

    NASA Astrophysics Data System (ADS)

    Li, Xinyi; Huang, Zhixiong; Zhang, Lianmeng; Guo, Dongyun

    2018-05-01

    The PbTiO3 nanocrystals were synthesized by a hydrothermal method, and ammonia solution was firstly used as a pH-adjusting agent. The effect of ammonia concentration on formation and morphologies of PbTiO3 nanocrystals was investigated. At low ammonia concentration (0-2.2 mol/L), no perovskite PbTiO3 phase was formed. When the ammonia concentration was 4.4 mol/L, the rod-like PbTiO3 nanocrystals with highly crystalline were successfully synthesized. As the ammonia concentration further increased to 13.2 mol/L, the flake-like PbTiO3 nanocrystals were formed.

  12. Fluctuating asymmetry and stress in a medieval Nubian population.

    PubMed

    Deleon, Valerie B

    2007-04-01

    Fluctuating asymmetry is commonly used as a bioindicator of developmental stress. This study addresses asymmetry under nutritional/systemic stress in the human craniofacial skeleton and its utility as an indicator of developmental instability. Crania from the diachronic Christian cemeteries at Kulubnarti (Sudanese Nubia) were chosen as a model for nutrition/systemic stress. Previous studies indicate that individuals from the Early Christian cemetery were subjected to greater developmental stress when compared with individuals from the Late Christian cemetery. Therefore, crania from the Early Christian cemetery should display a greater magnitude of fluctuating asymmetry than crania from the Late Christian cemetery. Thirty adult crania of comparable age and sex were selected from each population. Landmark coordinates were digitized in two separate trials and averaged to minimize error. Euclidean distance matrix analysis (EDMA) was used to measure and compare the magnitude of fluctuating asymmetry in each sample. Results indicate that crania from the Early Christian cemetery display greater amounts of fluctuating asymmetry than those from the Late Christian cemetery, as predicted. The degree of fluctuating asymmetry for each linear distance is highly correlated between the cemeteries, suggesting that all humans may share common patterns of fluctuating asymmetry in the skull. In contrast, there is little correlation between magnitude of fluctuating asymmetry and length of linear distance, between-subject variability, or measurement error. These results support the hypothesis that poor nutrition/systemic stress increases developmental instability in the human skull and that increased fluctuating asymmetry constitutes morphological evidence of this stress.

  13. Generalized syntheses of nanocrystal-graphene hybrids in high-boiling-point organic solvents.

    PubMed

    Pang, Danny Wei-Ping; Yuan, Fang-Wei; Chang, Yan-Cheng; Li, Guo-An; Tuan, Hsing-Yu

    2012-08-07

    Nanocrystal-graphene have been proposed as a new kind of promising hybrid for a wide range of application areas including catalysts, electronics, sensors, biomedicine, and energy storage, etc. Although a variety of methods have been developed for the preparation of hybrids, a facile and general synthetic approach is still highly required. In this study, nanocrystal-graphene hybrids were successfully synthesized in high-boiling-point organic solvents. Graphene oxide (GO) nanosheets were modified by oleylamine (OLA) to form a OLA-GO complex in order to be readily incorporated into hydrophobic synthesis. A rich library of highly crystalline nanocrystals, with types including noble metal, metal oxide, magnetic material and semiconductor were successfully grown on chemically converted graphene (CCG), which is simultaneously reduced from GO during the synthesis. High boiling-point solvents afford sufficient thermal energy to assure the high-quality crystalline nature of NCs, therefore the post-annealing process is obviated. Controlled experiments revealed that OLA-GO triggers heterogeneous nucleation and serves as excellent nuclei anchorage media. The protocol developed here brings one step closer to achieve "unity in diversity" on the preparation of nanocrystal-graphene hybrids.

  14. Direct Single-Enzyme Biomineralization of Catalytically Active Ceria and Ceria–Zirconia Nanocrystals

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Curran, Christopher D.; Lu, Li; Jia, Yue

    Biomineralization is an intriguing approach to the synthesis of functional inorganic materials for energy applications whereby biological systems are engineered to mineralize inorganic materials and control their structure over multiple length scales under mild reaction conditions. Herein we demonstrate a single-enzyme-mediated biomineralization route to synthesize crystalline, catalytically active, quantum-confined ceria (CeO2–x) and ceria–zirconia (Ce1–yZryO2–x) nanocrystals for application as environmental catalysts. In contrast to typical anthropogenic synthesis routes, the crystalline oxide nanoparticles are formed at room temperature from an otherwise inert aqueous solution without the addition of a precipitant or additional reactant. An engineered form of silicatein, rCeSi, as a singlemore » enzyme not only catalyzes the direct biomineralization of the nanocrystalline oxides but also serves as a templating agent to control their morphological structure. The biomineralized nanocrystals of less than 3 nm in diameter are catalytically active toward carbon monoxide oxidation following an oxidative annealing step to remove carbonaceous residue. The introduction of zirconia into the nanocrystals leads to an increase in Ce(III) concentration, associated catalytic activity, and the thermal stability of the nanocrystals.« less

  15. Transverse single-spin asymmetries: Challenges and recent progress

    DOE PAGES

    Metz, Andreas; Pitonyak, Daniel; Schafer, Andreas; ...

    2014-11-25

    In this study, transverse single-spin asymmetries are among the most intriguing observables in hadronic physics. Though such asymmetries were already measured for the first time about four decades ago, their origin is still under debate. Here we consider transverse single-spin asymmetries in semi-inclusive lepton–nucleon scattering, in nucleon–nucleon scattering, and in inclusive lepton–nucleon scattering. It is argued that, according to recent work, the single-spin asymmetries for those three processes may be simultaneously described in perturbative QCD, where the re-scattering of the active partons plays a crucial role. A comparison of single-spin asymmetries in different reactions can also shed light on themore » universality of transverse momentum dependent parton correlation functions. In particular, we discuss what existing data may tell us about the predicted process dependence of the Sivers function.« less

  16. Optimizing non-radiative energy transfer in hybrid colloidal-nanocrystal/silicon structures by controlled nanopillar architectures for future photovoltaic cells

    NASA Astrophysics Data System (ADS)

    Seitz, O.; Caillard, L.; Nguyen, H. M.; Chiles, C.; Chabal, Y. J.; Malko, A. V.

    2012-01-01

    To optimize colloidal nanocrystals/Si hybrid structures, nanopillars are prepared and organized via microparticle patterning and Si etching. A monolayer of CdSe nanocrystals is then grafted on the passivated oxide-free nanopillar surfaces, functionalized with carboxy-alkyl chain linkers. This process results to a negligible number of non-radiative surface state defects with a tightly controlled separation between the nanocrystals and Si. Steady-state and time-resolved photoluminescence measurements confirm the close-packing nanocrystal arrangement and the dominance of non-radiative energy transfer from nanocrystals to Si. We suggest that radially doped p-n junction devices based on energy transfer offer a viable approach for thin film photovoltaic devices.

  17. TheE Dynamics of Formation and Evaporation of Mixed Alkali halide Nanocrystals: A Case of Comparable Lattice Energies

    DTIC Science & Technology

    1994-09-21

    nI131+ mixed nanocrystals containing a " magic " number of 14 metal cations and 13 iodide anions is examined. These nanocrystals were generated through...RbnK14-nl13J+ mixed nanocrystals containing a " magic " number of 14 metal cations and 13 iodide anions is examined. These nanocrystals were generated...deviations or "local maxima" occur at n= 14, 23, 38, and 63 . These n values are called the " magic numbers" and are attributed to the formation of relatively

  18. Effects of longitudinal asymmetry in heavy-ion collisions

    NASA Astrophysics Data System (ADS)

    Raniwala, Rashmi; Raniwala, Sudhir; Loizides, Constantin

    2018-02-01

    In collisions of identical nuclei at a given impact parameter, the number of nucleons participating in the overlap region of each nucleus can be unequal due to nuclear density fluctuations. The asymmetry due to the unequal number of participating nucleons, referred to as longitudinal asymmetry, causes a shift in the center-of-mass rapidity of the participant zone. The information of the event asymmetry allows us to isolate and study the effect of longitudinal asymmetry on rapidity distribution of final state particles. In a Monte Carlo Glauber model the average rapidity shift is found to be almost linearly related to the asymmetry. Using toy models, as well as Monte Carlo data for Pb-Pb collisions at 2.76 TeV generated with hijing, two different versions of ampt and dpmjet models, we demonstrate that the effect of asymmetry on final state rapidity distribution can be quantitatively related to the average rapidity shift via a third-order polynomial with a dominantly linear term. The coefficients of the polynomial are proportional to the rapidity shift with the dependence being sensitive to the details of the rapidity distribution. Experimental estimates of the spectator asymmetry through the measurement of spectator nucleons in a zero-degree calorimeter may hence be used to further constrain the initial conditions in ultra-relativistic heavy-ion collisions.

  19. Self-assembled pit arrays as templates for the integration of Au nanocrystals in oxide surfaces.

    PubMed

    Konstantinović, Z; Sandiumenge, F; Santiso, J; Balcells, Ll; Martínez, B

    2013-02-07

    We report on the fabrication of long-range ordered arrays of Au nanocrystals (sub-50 nm range) on top of manganite (La(2/3)Sr(1/3)MnO(3)) thin films achieving area densities around 2 × 10(10) gold nanocrystals per cm(2), well above the densities achievable by using conventional nanofabrication techniques. The gold-manganite interface exhibits excellent conduction properties. Long-range order is achieved by a guided self-assembling process of Au nanocrystals on self-organized pit-arrays acting as a template for the nucleation of gold nanocrystals. Self-organization of pits on the manganite film surface promoted by the underlying stepped SrTiO(3) substrate is achieved by a fine tuning of the growth kinetic pathway, taking advantage of the unusual misfit strain relaxation behaviour of manganite films.

  20. Thermic conversion of benzene into 6-phenylfulvene with high yield mediated by GaP nanocrystals.

    PubMed

    Gao, Shanmin; Lu, Jun; Zhao, Yan; Chen, Nan; Xie, Yi

    2002-12-07

    With GaP nanocrystals being used in a close reaction system, 6-phenylfulvene is successfully obtained via a high yield thermic conversion from benzene, which provides the possibility of applying nanocrystals to mediate organic reactions.

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

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Hu, Michael Z.; Easterly, Clay E

    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 moleculesmore » 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.« less

  2. Eco-friendly approach towards green synthesis of zinc oxide nanocrystals and its potential applications.

    PubMed

    Velmurugan, Palanivel; Park, Jung-Hee; Lee, Sang-Myeong; Yi, Young-Joo; Cho, Min; Jang, Jum-Suk; Myung, Hyun; Bang, Keuk-Soo; Oh, Byung-Taek

    2016-09-01

    In the present study, we investigated a novel green route for synthesis of zinc oxide (ZnO) nanocrystals using Prunus × yedoensis Matsumura leaf extract as a reducing agent without using any surfactant or external energy. Standard characterization studies were carried out to confirm the obtained product using UV-Vis spectra, SEM-EDS, FTIR, TEM, and XRD. In addition, the synthesized ZnO nanocrystals were coated onto fabric and leather samples to study their bacteriostatic effect against odor-causing bacteria Brevibacterium linens and Staphylococcus epidermidis. Zinc oxide nanocrystal-coated fabric and leather showed good activity against both bacteria.

  3. Phase diagrams of ferroelectric nanocrystals strained by an elastic matrix

    NASA Astrophysics Data System (ADS)

    Nikitchenko, A. I.; Azovtsev, A. V.; Pertsev, N. A.

    2018-01-01

    Ferroelectric crystallites embedded into a dielectric matrix experience temperature-dependent elastic strains caused by differences in the thermal expansion of the crystallites and the matrix. Owing to the electrostriction, these lattice strains may affect polarization states of ferroelectric inclusions significantly, making them different from those of a stress-free bulk crystal. Here, using a nonlinear thermodynamic theory, we study the mechanical effect of elastic matrix on the phase states of embedded single-domain ferroelectric nanocrystals. Their equilibrium polarization states are determined by minimizing a special thermodynamic potential that describes the energetics of an ellipsoidal ferroelectric inclusion surrounded by a linear elastic medium. To demonstrate the stability ranges of such states for a given material combination, we construct a phase diagram, where the inclusion’s shape anisotropy and temperature are used as two parameters. The ‘shape-temperature’ phase diagrams are calculated numerically for PbTiO3 and BaTiO3 nanocrystals embedded into representative dielectric matrices generating tensile (silica glass) or compressive (potassium silicate glass) thermal stresses inside ferroelectric inclusions. The developed phase maps demonstrate that the joint effect of thermal stresses and matrix-induced elastic clamping of ferroelectric inclusions gives rise to several important features in the polarization behavior of PbTiO3 and BaTiO3 nanocrystals. In particular, the Curie temperature displays a nonmonotonic variation with the ellipsoid’s aspect ratio, being minimal for spherical inclusions. Furthermore, the diagrams show that the polarization orientation with respect to the ellipsoid’s symmetry axis is controlled by the shape anisotropy and the sign of thermal stresses. Under certain conditions, the mechanical inclusion-matrix interaction qualitatively alters the evolution of ferroelectric states on cooling, inducing a structural transition

  4. Organic-Inorganic Composites of Semiconductor Nanocrystals for Efficient Excitonics.

    PubMed

    Guzelturk, Burak; Demir, Hilmi Volkan

    2015-06-18

    Nanocomposites of colloidal semiconductor nanocrystals integrated into conjugated polymers are the key to soft-material hybrid optoelectronics, combining advantages of both plastics and particles. Synergic combination of the favorable properties in the hybrids of colloidal nanocrystals and conjugated polymers offers enhanced performance and new functionalities in light-generation and light-harvesting applications, where controlling and mastering the excitonic interactions at the nanoscale are essential. In this Perspective, we highlight and critically consider the excitonic interactions in the organic-inorganic nanocomposites to achieve highly efficient exciton transfer through rational design of the nanocomposites. The use of strong excitonic interactions in optoelectronic devices can trigger efficiency breakthroughs in hybrid optoelectronics.

  5. Solvent-Assisted Surface Engineering for High-Performance All-Inorganic Perovskite Nanocrystal Light-Emitting Diodes.

    PubMed

    Wang, Lin; Liu, Baiquan; Zhao, Xin; Demir, Hilmi Volkan; Gu, Haoshuang; Sun, Handong

    2018-06-13

    All-inorganic cesium halide perovskite nanocrystals have attracted much interest in optoelectronic applications for the sake of the readily adjustable band gaps, high photoluminescence quantum yield, pure color emission, and affordable cost. However, because of the ineluctable utilization of organic surfactants during the synthesis, the structural and optical properties of CsPbBr 3 nanocrystals degrade upon transforming from colloidal solutions to solid thin films, which plagues the device operation. Here, we develop a novel solvent-assisted surface engineering strategy, producing high-quality CsPbBr 3 thin films for device applications. A good solvent is first introduced as an assembly trigger to conduct assembly in a one-dimensional direction, which is then interrupted by adding a nonsolvent. The nonsolvent drives the adjacent nanoparticles connecting in a two-dimensional direction. Assembled CsPbBr 3 nanocrystal thin films are densely packed and very smooth with a surface roughness of ∼4.8 nm, which is highly desirable for carrier transport in a light-emitting diode (LED) device. Meanwhile, the film stability is apparently improved. Benefiting from this facile and reliable strategy, we have achieved remarkably improved performance of CsPbBr 3 nanocrystal-based LEDs. Our results not only enrich the methods of nanocrystal surface engineering but also shed light on developing high-performance LEDs.

  6. [Fluorescence spectra and quantum yield of TiO2 nanocrystals synthesized by alcohothermal method].

    PubMed

    Song, Cui-Hong; Li, Yan-Ting; Li, Jing; Wei, Yong-Ju; Hu, Yu-Zhu; Wei, Yu

    2008-01-01

    Fluorescence spectra and fluorescence quantum yield of TiO2 nanocrystals were studied. Using tetra n-butyl titanate as a starting material, a facile alcohothermal technique was used to synthesize TiO2 nanocrystals. As can be seen from the transmittance electron microscopy (TEM) image, TiO2 nanocrystals with a relatively uniform particle size distribution of < 10 nm are present in the transparent sol. The transparent sol presents a strong stable fluorescence emission with a maximum at 450 nm, which is greatly dependent on the size quantization effects, defect energy level and the surface state of TiO2 nanocrystals. The quantum yield (gamma) of TiO2 was determined by the relative comparison procedure, using freshly prepared analytical purity quinine sulfate in 0.05 mol x L(-1) H2SO4 as a relative quantum yield standard. The emission quantum yield of TiO2 nanocrystals prepared in alcoholic media was calculated to be about 0.20 at wavelengths ranging from 330 to 370 nm, which was much higher than the values reported in previous works. So, it is supposed that nano-TiO2 will be applied as a potential quantum dots fluorescence probe in biological analysis.

  7. Nanocrystals embedded in hafnium dioxide-based dielectrics as charge storage nodes of nano-floating gate memory

    NASA Astrophysics Data System (ADS)

    Lee, Pui Fai

    2007-12-01

    Nanocrystals (NC) embedded in dielectrics have attracted a great deal of attention recently because they can potentially be applied in nonvolatile, high-speed, high-density and low-power memory devices. This device benefits from a relatively low operating voltage, high endurance, fast write-erase speeds and better immunity to soft errors. The nanocrystal materials suitable for such an application can be either metals or semiconductors. Recent studies have shown that high-k dielectrics, instead of SiO2 , for the tunneling layer in nanocrystal floating gate memory can improve the trade-off between data retention and program efficiency due to the unique band alignment of high-k dielectrics in the programming and retention modes. In this project, HfAlO has been selected as the high- k dielectric for the nanocrystal floating gate memory structure. The trilayer structure (HfAlO/Ge-NC/HfAlO) on Si was fabricated by PLD. Results revealed that relatively low substrate temperature and growth rate are favourable for the formation of smaller-size Ge nanocrystals. Effects of size/density of the Ge nanocrystal, the tunneling and control oxide layer thicknesses and the oxygen partial pressure during their growth on the charge storage and charge retention characteristics have also been studied. The island structure of the Ge nanocrystal suggests that the growth is based on the Volmer-Webber mode. The self-organized Ge nanocrystals so formed were uniform in size (5--20 nm diameter) and distribution with a density approaching 1012--1013cm-2. Flat-band voltage shift (DeltaVFB) of about 3.6 V and good retention property have been achieved. By varying aggregation distance, sputtering gas pressure and ionization power of the nanocluster source, nanoclusters of Ge with different sizes can be formed. The memory effect of the trilayer structure so formed with 10 nm Ge nanoclusters are manifested by the counter-clockwise hysteresis loop in the C-V curves and a maximum flat-band voltage

  8. Solvothermal synthesis and controlled self-assembly of monodisperse titanium-based perovskite colloidal nanocrystals

    NASA Astrophysics Data System (ADS)

    Caruntu, Daniela; Rostamzadeh, Taha; Costanzo, Tommaso; Salemizadeh Parizi, Saman; Caruntu, Gabriel

    2015-07-01

    The rational design of monodisperse ferroelectric nanocrystals with controlled size and shape and their organization into hierarchical structures has been a critical step for understanding the polar ordering in nanoscale ferroelectrics, as well as the design of nanocrystal-based functional materials which harness the properties of individual nanoparticles and the collective interactions between them. We report here on the synthesis and self-assembly of aggregate-free, single-crystalline titanium-based perovskite nanoparticles with controlled morphology and surface composition by using a simple, easily scalable and highly versatile colloidal route. Single-crystalline, non-aggregated BaTiO3 colloidal nanocrystals, used as a model system, have been prepared under solvothermal conditions at temperatures as low as 180 °C. The shape of the nanocrystals was tuned from spheroidal to cubic upon changing the polarity of the solvent, whereas their size was varied from 16 to 30 nm for spheres and 5 to 78 nm for cubes by changing the concentration of the precursors and the reaction time, respectively. The hydrophobic, oleic acid-passivated nanoparticles exhibit very good solubility in non-polar solvents and can be rendered dispersible in polar solvents by a simple process involving the oxidative cleavage of the double bond upon treating the nanopowders with the Lemieux-von Rudloff reagent. Lattice dynamic analysis indicated that regardless of their size, BaTiO3 nanocrystals present local disorder within the perovskite unit cell, associated with the existence of polar ordering. We also demonstrate for the first time that, in addition to being used for fabricating large area, crack-free, highly uniform films, BaTiO3 nanocubes can serve as building blocks for the design of 2D and 3D mesoscale structures, such as superlattices and superparticles. Interestingly, the type of superlattice structure (simple cubic or face centered cubic) appears to be determined by the type of solvent

  9. Nanocomposites Based on Luminescent Colloidal Nanocrystals and Polymeric Ionic Liquids towards Optoelectronic Applications

    PubMed Central

    Panniello, Annamaria; Ingrosso, Chiara; Coupillaud, Paul; Tamborra, Michela; Binetti, Enrico; Curri, Maria Lucia; Agostiano, Angela; Taton, Daniel; Striccoli, Marinella

    2014-01-01

    Polymeric ionic liquids (PILs) are an interesting class of polyelectrolytes, merging peculiar physical-chemical features of ionic liquids with the flexibility, mechanical stability and processability typical of polymers. The combination of PILs with colloidal semiconducting nanocrystals leads to novel nanocomposite materials with high potential for batteries and solar cells. We report the synthesis and properties of a hybrid nanocomposite made of colloidal luminescent CdSe nanocrystals incorporated in a novel ex situ synthesized imidazolium-based PIL, namely, either a poly(N-vinyl-3-butylimidazolium hexafluorophosphate) or a homologous PIL functionalized with a thiol end-group exhibiting a chemical affinity with the nanocrystal surface. A capping exchange procedure has been implemented for replacing the pristine organic capping molecules of the colloidal CdSe nanocrystals with inorganic chalcogenide ions, aiming to disperse the nano-objects in the PILs, by using a common polar solvent. The as-prepared nanocomposites have been studied by TEM investigation, UV-Vis, steady-state and time resolved photoluminescence spectroscopy for elucidating the effects of the PIL functionalization on the morphological and optical properties of the nanocomposites. PMID:28788477

  10. Gait asymmetry: composite scores for mechanical analyses of sprint running.

    PubMed

    Exell, T A; Gittoes, M J R; Irwin, G; Kerwin, D G

    2012-04-05

    Gait asymmetry analyses are beneficial from clinical, coaching and technology perspectives. Quantifying overall athlete asymmetry would be useful in allowing comparisons between participants, or between asymmetry and other factors, such as sprint running performance. The aim of this study was to develop composite kinematic and kinetic asymmetry scores to quantify athlete asymmetry during maximal speed sprint running. Eight male sprint trained athletes (age 22±5 years, mass 74.0±8.7 kg and stature 1.79±0.07 m) participated in this study. Synchronised sagittal plane kinematic and kinetic data were collected via a CODA motion analysis system, synchronised to two Kistler force plates. Bilateral, lower limb data were collected during the maximal velocity phase of sprint running (velocity=9.05±0.37 ms(-1)). Kinematic and kinetic composite asymmetry scores were developed using the previously established symmetry angle for discrete variables associated with successful sprint performance and comparisons of continuous joint power data. Unlike previous studies quantifying gait asymmetry, the scores incorporated intra-limb variability by excluding variables from the composite scores that did not display significantly larger (p<0.05) asymmetry than intra-limb variability. The variables that contributed to the composite scores and the magnitude of asymmetry observed for each measure varied on an individual participant basis. The new composite scores indicated the inter-participant differences that exist in asymmetry during sprint running and may serve to allow comparisons between overall athlete asymmetry with other important factors such as performance. Copyright © 2012 Elsevier Ltd. All rights reserved.

  11. Precise discussion of time-reversal asymmetries in B-meson decays

    DOE PAGES

    Morozumi, Takuya; Okane, Hideaki; Umeeda, Hiroyuki

    2015-02-26

    BaBar collaboration announced that they observed time reversal (T) asymmetry through B meson system. In the experiment, time dependencies of two distinctive processes, B_ →B¯ 0 and B¯ 0 → B_ (– expresses CP value) are compared with each other. In our study, we examine event number difference of these two processes. In contrast to the BaBar asymmetry, the asymmetry of events number includes the overall normalization difference for rates. Time dependence of the asymmetry is more general and it includes terms absent in one used by BaBar collaboration. Both of the BaBar asymmetry and ours are naively thought tomore » be T-odd since two processes compared are related with flipping time direction. We investigate the time reversal transformation property of our asymmetry. Using our notation, one can see that the asymmetry is not precisely a T-odd quantity, taking into account indirect CP and CPT violation of K meson systems. The effect of ϵK is extracted and gives rise to O(10 –3) contribution. The introduced parameters are invariant under rephasing of quarks so that the coefficients of our asymmetry are expressed as phase convention independent quantities. Some combinations of the asymmetry enable us to extract parameters for wrong sign decays of B d meson, CPT violation, etc. As a result, we also study the reason why the T-even terms are allowed to contribute to the asymmetry, and find that several conditions are needed for the asymmetry to be a T-odd quantity.« less

  12. 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.

  13. A voxel-based approach to gray matter asymmetries.

    PubMed

    Luders, E; Gaser, C; Jancke, L; Schlaug, G

    2004-06-01

    Voxel-based morphometry (VBM) was used to analyze gray matter (GM) asymmetries in a large sample (n = 60) of male and female professional musicians with and without absolute pitch (AP). We chose to examine these particular groups because previous studies using traditional region-of-interest (ROI) analyses have shown differences in hemispheric asymmetry related to AP and gender. Voxel-based methods may have advantages over traditional ROI-based methods since the analysis can be performed across the whole brain with minimal user bias. After determining that the VBM method was sufficiently sensitive for the detection of differences in GM asymmetries between groups, we found that male AP musicians were more leftward lateralized in the anterior region of the planum temporale (PT) than male non-AP musicians. This confirmed the results of previous studies using ROI-based methods that showed an association between PT asymmetry and the AP phenotype. We further observed that male non-AP musicians revealed an increased leftward GM asymmetry in the postcentral gyrus compared to female non-AP musicians, again corroborating results of a previously published study using ROI-based methods. By analyzing hemispheric GM differences across our entire sample, we were able to partially confirm findings of previous studies using traditional morphometric techniques, as well as more recent, voxel-based analyses. In addition, we found some unusually pronounced GM asymmetries in our musician sample not previously detected in subjects unselected for musical training. Since we were able to validate gender- and AP-related brain asymmetries previously described using traditional ROI-based morphometric techniques, the results of our analyses support the use of VBM for examinations of GM asymmetries.

  14. Biocompatibility of bio based calcium carbonate nanocrystals aragonite polymorph on NIH 3T3 fibroblast cell line.

    PubMed

    Kamba, Abdullahi Shafiu; Ismail, Maznah; Ibrahim, Tengku Azmi Tengku; Zakaria, Zuki Abu Bakar

    2014-01-01

    Currently, there has been extensive research interest for inorganic nanocrystals such as calcium phosphate, iron oxide, silicone, carbon nanotube and layered double hydroxide as a drug delivery system especially in cancer therapy. However, toxicological screening of such particles is paramount importance before use as delivery carrier. In this study we examine the biocompatibility of CaCO3 nanocrystal on NIH 3T3 cell line. Transmission and field emission scanning electron microscopy (TEM and FESEM) were used for the characterisation of CaCO3 nanocrystals. Cytotoxicity and genotoxic effect of calcium carbonate nanocrystals in cultured mouse embryonic fibroblast NIH 3T3 cell line using various bioassays including MTT, and Neutral red/Trypan blue double-staining assays. LDH, BrdU and reactive oxygen species were used for toxicity analysis. Cellular morphology was examined by scanning electron microscopy (SEM) and confocal fluorescence microscope. The outcome of the analyses revealed a clear rod-shaped aragonite polymorph of calcium carbonate nanocrystal. The analysed cytotoxic and genotoxicity of CaCO3 nanocrystal on NIH 3T3 cells using different bioassays revealed no significance differences as compared to control. A slight decrease in cell viability was noticed when the cells were exposed to higher concentrations of 200 to 400 µg/ml, while increase in ROS generation and LDH released at 200 and 400 µg/ml was observed. The study has shown that CaCO3 nanocrystal is biocompatible and non toxic to NIH 3T3 fibroblast cells. The analysed results offer a promising potential of CaCO3 nanocrystal for the development of intracellular drugs, genes and other macromolecule delivery systems.

  15. Asymmetry in power-law magnitude correlations.

    PubMed

    Podobnik, Boris; Horvatić, Davor; Tenenbaum, Joel N; Stanley, H Eugene

    2009-07-01

    Time series of increments can be created in a number of different ways from a variety of physical phenomena. For example, in the phenomenon of volatility clustering-well-known in finance-magnitudes of adjacent increments are correlated. Moreover, in some time series, magnitude correlations display asymmetry with respect to an increment's sign: the magnitude of |x_{i}| depends on the sign of the previous increment x_{i-1} . Here we define a model-independent test to measure the statistical significance of any observed asymmetry. We propose a simple stochastic process characterized by a an asymmetry parameter lambda and a method for estimating lambda . We illustrate both the test and process by analyzing physiological data.

  16. Facial asymmetry quantitative evaluation in oculoauriculovertebral spectrum.

    PubMed

    Manara, Renzo; Schifano, Giovanni; Brotto, Davide; Mardari, Rodica; Ghiselli, Sara; Gerunda, Antonio; Ghirotto, Cristina; Fusetti, Stefano; Piacentile, Katherine; Scienza, Renato; Ermani, Mario; Martini, Alessandro

    2016-03-01

    Facial asymmetries in oculoauriculovertebral spectrum (OAVS) patients might require surgical corrections that are mostly based on qualitative approach and surgeon's experience. The present study aimed to develop a quantitative 3D CT imaging-based procedure suitable for maxillo-facial surgery planning in OAVS patients. Thirteen OAVS patients (mean age 3.5 ± 4.0 years; range 0.2-14.2, 6 females) and 13 controls (mean age 7.1 ± 5.3 years; range 0.6-15.7, 5 females) who underwent head CT examination were retrospectively enrolled. Eight bilateral anatomical facial landmarks were defined on 3D CT images (porion, orbitale, most anterior point of frontozygomatic suture, most superior point of temporozygomatic suture, most posterior-lateral point of the maxilla, gonion, condylion, mental foramen) and distance from orthogonal planes (in millimeters) was used to evaluate the asymmetry on each axis and to calculate a global asymmetry index of each anatomical landmark. Mean asymmetry values and relative confidence intervals were obtained from the control group. OAVS patients showed 2.5 ± 1.8 landmarks above the confidence interval while considering the global asymmetry values; 12 patients (92%) showed at least one pathologically asymmetric landmark. Considering each axis, the mean number of pathologically asymmetric landmarks increased to 5.5 ± 2.6 (p = 0.002) and all patients presented at least one significant landmark asymmetry. Modern CT-based 3D reconstructions allow accurate assessment of facial bone asymmetries in patients affected by OAVS. The evaluation as a global score and in different orthogonal axes provides precise quantitative data suitable for maxillo-facial surgical planning. CT-based 3D reconstruction might allow a quantitative approach for planning and following-up maxillo-facial surgery in OAVS patients.

  17. Tuning the morphology, stability and photocatalytic activity of TiO{sub 2} nanocrystal colloids by tungsten doping

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Xu, Haiping; Liao, Jianhua; School of Pharmaceutical Sciences, Gannan Medical University, Ganzhou, Jiangxi 341000

    2014-03-01

    Graphical abstract: - Highlights: • W{sup 6+}-doped TiO{sub 2} nanocrystal colloids were prepared by hydrothermal methods. • The properties of TiO{sub 2} nanocrystal colloids can be tuned by tungsten doping. • W{sup 6+}-doped TiO{sub 2} nanocrystal colloids show higher stability and dispersity. • W{sup 6+}-doped TiO{sub 2} nanocrystal colloids show higher photocatalytic activity. - Abstract: The effects of tungsten doping on the morphology, stability and photocatalytic activity of TiO{sub 2} nanocrystal colloids were investigated. The nanostructure, chemical state of Ti, W, O, and the properties of tungsten doped TiO{sub 2} samples were investigated carefully by TEM, XRD, XPS, UV–vis, PLmore » and photocatalytic degradation experiments. And the structure–activity relationship was discussed according to the analysis and measurement results. The analysis results reveal that the morphology, zeta potential and photocatalytic activity of TiO{sub 2} nanocrystals can be easily tuned by changing the tungsten doping concentration. The tungsten doped TiO{sub 2} colloid combines the characters of high dispersity and high photocatalytic activity.« less

  18. What determines direction of asymmetry: genes, environment or chance?

    PubMed Central

    2016-01-01

    Conspicuous asymmetries seen in many animals and plants offer diverse opportunities to test how the development of a similar morphological feature has evolved in wildly different types of organisms. One key question is: do common rules govern how direction of asymmetry is determined (symmetry is broken) during ontogeny to yield an asymmetrical individual? Examples from numerous organisms illustrate how diverse this process is. These examples also provide some surprising answers to related questions. Is direction of asymmetry in an individual determined by genes, environment or chance? Is direction of asymmetry determined locally (structure by structure) or globally (at the level of the whole body)? Does direction of asymmetry persist when an asymmetrical structure regenerates following autotomy? The answers vary greatly for asymmetries as diverse as gastropod coiling direction, flatfish eye side, crossbill finch bill crossing, asymmetrical claws in shrimp, lobsters and crabs, katydid sound-producing structures, earwig penises and various plant asymmetries. Several examples also reveal how stochastic asymmetry in mollusc and crustacean early cleavage, in Drosophila oogenesis, and in Caenorhabditis elegans epidermal blast cell movement, is a normal component of deterministic development. Collectively, these examples shed light on the role of genes as leaders or followers in evolution. This article is part of the themed issue ‘Provocative questions in left–right asymmetry’. PMID:27821528

  19. Chemical composition of matrix-embedded ternary II-VI nanocrystals derived from first- and second-order Raman spectra

    NASA Astrophysics Data System (ADS)

    Azhniuk, Yu. M.; Hutych, Yu. I.; Lopushansky, V. V.; Prymak, M. V.; Gomonnai, A. V.; Zahn, D. R. T.

    2016-12-01

    A one- and multiphonon Raman scattering study is performed for an extensive set of CdS1-xSex, Cd1-yZnyS, Cd1-yZnySe, and CdSe1-xTex nanocrystals to investigate the applicability of first- and second-order Raman spectra for the determination of the matrix-embedded ternary nanocrystal composition. For one-mode ternary systems both the LO and 2LO phonon frequencies in the Raman spectra are shown to be a good measure of the nanocrystal composition. For two-mode systems, the approaches based on the difference of the LO phonon frequencies (first-order Raman spectra) or double LO overtone and combination tone frequencies (second-order Raman spectra) as well as on the LO phonon band intensity ratios are analysed. The weak electron-phonon coupling in the II-VI nanocrystals and the polaron constant values for the nanocrystal sublattices are discussed.

  20. Fabrication and characterization of morphology-tuned single-crystal monodisperse Fe3O4 nanocrystals

    NASA Astrophysics Data System (ADS)

    Yu, Xuegang; Shan, Yan; Chen, Kezheng

    2018-05-01

    Monodisperse Fe3O4 nanocrystals with different size and morphology have been successfully fabricated by a facile high temperature reflow method. The presented materials were characterized by X-ray diffraction (XRD), fourier transform infrared (FTIR) spectroscopy, transmission electron microscope (TEM), selection area electron diffraction (SAED) and magnetic property measurement system (MPMS). The results showed that the as-prepared materials have face-centered cubic structures. Oleic acid plays a key role in the dispersion of Fe3O4 nanocrystals. The cubic and octahedral nanocrystals are enclosed by {1 0 0} and {1 1 1} lattice planes. The MPMS measurements show that magnetic properties are closely related to the sizes of the materials, and there is a stronger dipolar interaction between Fe3O4 nanocrystals with larger sizes. The controllable magnetic property and good dispersion endow the as-synthesized materials with great potential applications in magnetic fluid fields including sealing, medical equipment, mineral processing and other aspects.

  1. Colloidal synthesis of Cu-ZnO and Cu@CuNi-ZnO hybrid nanocrystals with controlled morphologies and multifunctional properties

    NASA Astrophysics Data System (ADS)

    Zeng, Deqian; Gong, Pingyun; Chen, Yuanzhi; Zhang, Qinfu; Xie, Qingshui; Peng, Dong-Liang

    2016-06-01

    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.Metal-semiconductor hybrid nanocrystals have received extensive attention owing to their multiple functionalities which can find wide technological applications

  2. Observation of Quantum Confinement in Monodisperse Methylammonium Lead Halide Perovskite Nanocrystals Embedded in Mesoporous Silica.

    PubMed

    Malgras, Victor; Tominaka, Satoshi; Ryan, James W; Henzie, Joel; Takei, Toshiaki; Ohara, Koji; Yamauchi, Yusuke

    2016-10-13

    Hybrid organic-inorganic metal halide perovskites have fascinating electronic properties and have already been implemented in various devices. Although the behavior of bulk metal halide perovskites has been widely studied, the properties of perovskite nanocrystals are less well-understood because synthesizing them is still very challenging, in part because of stability. Here we demonstrate a simple and versatile method to grow monodisperse CH 3 NH 3 PbBr x I x-3 perovskite nanocrystals inside mesoporous silica templates. The size of the nanocrystal is governed by the pore size of the templates (3.3, 3.7, 4.2, 6.2, and 7.1 nm). In-depth structural analysis shows that the nanocrystals maintain the perovskite crystal structure, but it is slightly distorted. Quantum confinement was observed by tuning the size of the particles via the template. This approach provides an additional route to tune the optical bandgap of the nanocrystal. The level of quantum confinement was modeled taking into account the dimensions of the rod-shaped nanocrystals and their close packing inside the channels of the template. Photoluminescence measurements on CH 3 NH 3 PbBr clearly show a shift from green to blue as the pore size is decreased. Synthesizing perovskite nanostructures in templates improves their stability and enables tunable electronic properties via quantum confinement. These structures may be useful as reference materials for comparison with other perovskites, or as functional materials in all solid-state light-emitting diodes.

  3. Tuning light emission of PbS nanocrystals from infrared to visible range by cation exchange

    PubMed Central

    Binetti, Enrico; Striccoli, Marinella; Sibillano, Teresa; Giannini, Cinzia; Brescia, Rosaria; Falqui, Andrea; Comparelli, Roberto; Corricelli, Michela; Tommasi, Raffaele; Agostiano, Angela; Curri, M Lucia

    2015-01-01

    Colloidal semiconductor nanocrystals, with intense and sharp-line emission between red and near-infrared spectral regions, are of great interest for optoelectronic and bio-imaging applications. The growth of an inorganic passivation layer on nanocrystal surfaces is a common strategy to improve their chemical and optical stability and their photoluminescence quantum yield. In particular, cation exchange is a suitable approach for shell growth at the expense of the nanocrystal core size. Here, the cation exchange process is used to promote the formation of a CdS passivation layer on the surface of very small PbS nanocrystals (2.3 nm in diameter), blue shifting their optical spectra and yielding luminescent and stable nanostructures emitting in the range of 700–850 nm. Structural, morphological and compositional investigation confirms the nanocrystal size contraction after the cation-exchange process, while the PbS rock-salt crystalline phase is retained. Absorption and photoluminescence spectroscopy demonstrate the growth of a passivation layer with a decrease of the PbS core size, as inferred by the blue-shift of the excitonic peaks. The surface passivation strongly increases the photoluminescence intensity and the excited state lifetime. In addition, the nanocrystals reveal increased stability against oxidation over time. Thanks to their absorption and emission spectral range and the slow recombination dynamics, such highly luminescent nano-objects can find interesting applications in sensitized photovoltaic cells and light-emitting devices. PMID:27877842

  4. Magnetic properties and photovoltaic applications of ZnO:Mn nanocrystals.

    PubMed

    Zhang, Ying; Han, Fengxiang; Dai, Qilin; Tang, Jinke

    2018-05-01

    A simple and large-scale synthetic method of Mn doped ZnO (ZnO:Mn) was developed in this work. ZnO:Mn nanocrystals with hexagonal structure were prepared by thermal decomposition of zinc acetate and manganese acetate in the presence of oleylamine and oleic acid with different temperatures, ligand ratios, and Mn doping concentrations. The particle size (47-375 nm) and morphology (hexagonal nanopyramid, hexagonal nanodisk and irregular nanospheres) of ZnO:Mn nanocrystals can be controlled by the ratio of capping ligand, reaction temperature, reaction time and Mn doping concentration. The corresponding optical and magnetic properties were systemically studied and compared. All samples were found to be paramagnetic with antiferromagnetic (AFM) exchange interactions between the Mn moments in the ZnO lattice, which can be affected by the reaction conditions. The quantum dot sensitized solar cells (QDSSCs) were fabricated based on ZnO:Mn nanocrystals and CdS quantum dots, and the device performance affected by Mn doping concentration was also studied and compared. Copyright © 2018 Elsevier Inc. All rights reserved.

  5. Non-injection synthesis of monodisperse Cu-Fe-S nanocrystals and their size dependent properties.

    PubMed

    Gabka, Grzegorz; Bujak, Piotr; Żukrowski, Jan; Zabost, Damian; Kotwica, Kamil; Malinowska, Karolina; Ostrowski, Andrzej; Wielgus, Ireneusz; Lisowski, Wojciech; Sobczak, Janusz W; Przybylski, Marek; Pron, Adam

    2016-06-01

    It is demonstrated that ternary Cu-Fe-S nanocrystals differing in composition (from Cu-rich to Fe-rich), structure (chalcopyrite or high bornite) and size can be obtained from a mixture of CuCl, FeCl3, thiourea and oleic acid (OA) in oleylamine (OLA) using the heating up procedure. This new preparation method yields the smallest Cu-Fe-S nanocrystals ever reported to date (1.5 nm for the high bornite structure and 2.7 nm for the chalcopyrite structure). A comparative study of nanocrystals of the same composition (Cu1.6Fe1.0S2.0) but different in size (2.7 nm and 9.3 nm) revealed a pronounced quantum confinement effect, confirmed by three different techniques: UV-vis spectroscopy, cyclic voltammetry and Mössbauer spectroscopy. The optical band gap increased from 0.60 eV in the bulk material to 0.69 eV in the nanocrystals of 9.3 nm size and to 1.39 eV in nanocrystals of 2.7 nm size. The same trend was observed in the electrochemical band gaps, derived from cyclic voltammetry studies (band gaps of 0.74 eV and 1.54 eV). The quantum effect was also manifested in Mössbauer spectroscopy by an abrupt change in the spectrum from a quadrupole doublet to a Zeeman sextet below 10 K, which could be interpreted in terms of the well defined energy states in these nanoparticles, resulting from quantum confinement. The Mössbauer spectroscopic data confirmed, in addition to the results of XPS spectroscopy, the co-existence of Fe(iii) and Fe(ii) in the synthesized nanocrystals. The organic shell composition was investigated by NMR (after dissolution of the inorganic core) and IR spectroscopy. Both methods identified oleylamine (OLA) and 1-octadecene (ODE) as surfacial ligands, the latter being formed in situ via an elimination-hydrogenation reaction occurring between OLA and the nanocrystal surface.

  6. Serotonin-Labeled CdSe Nanocrystals: Applications for Neuroscience

    NASA Astrophysics Data System (ADS)

    Kippeny, Tadd; Adkins, Erika; Adams, Scott; Thomlinson, Ian; Schroeter, Sally; Defelice, Louis; Blakely, Randy; Rosenthal, Sandra

    2000-03-01

    Serotonin (5-hydroxytryptamine, 5-HT) is an important neurotransmitter which has been linked to the regulation of critical behaviors including sleep, appetite, and mood. The serotonin transporter (SERT) is a 12-transmembrane domain protein responsible for clearance of serotonin from extracellular spaces following release. In order to assess the potential for use of ligand-conjugated nanocrystals to target cell surface receptors, ion channels, and transporters we have measured the ability of serotonin-labeled CdSe nanocrystals (SNACs) to block the uptake of tritiated serotonin by the human and Drosophila serotonin transporters (hSERT and dSERT). Estimated Ki values, the SNAC concentration at which half of the serotonin transport activity is blocked, were determined by nonlinear regression to be Ki (hSERT ) = 74uM and Ki (dSERT ) = 29uM. These values and our inability to detect free serotonin indicate that SNACs selectively interact with the serotonin recognition site of the transporter. We have also exposed the SNACs to cells containing ionotropic serotonin receptors and have measured the electrical response of the cell using a two microelectrode voltage clamp. We find that serotonin receptors do respond to the SNACs and we measure currents similar to the free serotonin response. These results indicate that ligand-conjugated nanocrystals can be used to label both receptor and transporter proteins. Initial fluorescence labeling experiments will be discussed.

  7. Brilliant molecular nanocrystals emerging from sol-gel thin films: towards a new generation of fluorescent biochips.

    PubMed

    Dubuisson, E; Monnier, V; Sanz-Menez, N; Boury, B; Usson, Y; Pansu, R B; Ibanez, A

    2009-08-05

    To develop highly sensitive biosensors, we made directly available to biological aqueous solutions organic nanocrystals previously grown in the pores of sol-gel films. Through the controlled dissolution of the sol-gel surface, we obtained emerging nanocrystals that remained strongly anchored to the sol-gel coating for good mechanical stability of the final sensing device. We demonstrated that in the presence of a solution of DNA functionalized with a molecular probe, the nanocrystal fluorescence is strongly quenched by Förster resonance energy transfer thus opening the way towards very sensitive fluorescent biosensors through biomolecules grafted onto fluorescent nanocrystals. Finally, this controlled dissolution, involving weak concentrated NaOH solution, is a generic process that can be used for the thinning of any kind of sol-gel layer.

  8. Discriminating different Z{sup '}'s via asymmetries at the LHC

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Zhou Zhongqiu; Xiao Bo; Wang Youkai

    2011-05-01

    In practice the asymmetry, which is defined based on the angular distribution of the final states in scattering or decay processes, can be utilized to scrutinize underlying dynamics in and/or beyond the standard model (BSM). As one of the possible BSM physics which might be discovered early at the LHC, extra neutral gauge bosons Z{sup '}'s are theoretically well motivated. Once Z{sup '}'s are discovered at the LHC, it is crucial to discriminate different Z{sup '}'s in various BSM. In principle such a task can be accomplished by measuring the angular distribution of the final states which are produced viamore » Z{sup '}-mediated processes. In the real data analysis, asymmetry is always adopted. In the literature several asymmetries have been proposed at the LHC. Based on these works, we stepped further on to study how to optimize the asymmetries in the left-right model and the sequential standard model, as the examples of BSM. In this paper, we examined four kinds of asymmetries, namely, rapidity-dependent forward-backward asymmetry, oneside forward-backward asymmetry, central charge asymmetry, and edge charge asymmetry (see text for details), with l{sup +}l{sup -} (l=e, {mu}), bb, and tt as the final states. In the calculations with bb and tt final states, the QCD-induced higher-order contributions to the asymmetric cross section were also included. For each kind of final state, we estimated the four kinds of asymmetries and especially the optimal cut usually associated with the definition of the asymmetry. Our numerical results indicated that the capacity to discriminate Z{sup '} models can be improved by imposing the optimal cuts.« less

  9. Forward-backward asymmetry in top quark-antiquark production

    DOE PAGES

    Abazov, Victor Mukhamedovich

    2011-12-12

    We present a measurement of forward-backward asymmetry in top quark-antiquark production in proton-antiproton collisions in the final state containing a lepton and at least four jets. Using a dataset corresponding to an integrated luminosity of 5.4 fb -1, collected by the D0 experiment at the Fermilab Tevatron Collider, we measure the t{bar t} forward-backward asymmetry to be (9.2 ± 3.7)% at the reconstruction level. When corrected for detector acceptance and resolution, the asymmetry is found to be (19.6 ± 6.5)%. We also measure a corrected asymmetry based on the lepton from a top quark decay, found to be (15.2 ±more » 4.0)%. The results are compared to predictions based on the next-to-leading-order QCD generator mc@nlo. The sensitivity of the measured and predicted asymmetries to the modeling of gluon radiation is discussed.« less

  10. Infant Positioning, Baby Gear Use, and Cranial Asymmetry.

    PubMed

    Zachry, Anne H; Nolan, Vikki G; Hand, Sarah B; Klemm, Susan A

    2017-12-01

    Objectives This study aimed to identify predictors of cranial asymmetry. We hypothesize that among infants diagnosed with cranial asymmetry in the sampled region, there is an association between exposure to more time in baby gear and less awake time in prone and side-lying than in infants who do not present with this condition. Methods The study employed a cross sectional survey of caregivers of typically developing infants and infants diagnosed with cranial asymmetry. Results A mutivariable model reveals that caregivers of children who are diagnosed with cranial asymmetry report their children spending significantly less time in prone play than those children without a diagnosis of cranial asymmetry. Side-lying and time spent in baby gear did not attain statistical significance. Conclusions for Practice Occupational therapists, physical therapists, pediatricians, nurses and other health care professionals must provide parents with early education about the importance of varying positions and prone play in infancy and address fears and concerns that may serve as barriers to providing prone playtime.

  11. Optical activity of chirally distorted nanocrystals

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Tepliakov, Nikita V.; Baimuratov, Anvar S.; Baranov, Alexander V.

    2016-05-21

    We develop a general theory of optical activity of semiconductor nanocrystals whose chirality is induced by a small perturbation of their otherwise achiral electronic subsystems. The optical activity is described using the quantum-mechanical expressions for the rotatory strengths and dissymmetry factors introduced by Rosenfeld. We show that the rotatory strengths of optically active transitions are decomposed on electric dipole and magnetic dipole contributions, which correspond to the electric dipole and magnetic dipole transitions between the unperturbed quantum states. Remarkably, while the two kinds of rotatory strengths are of the same order of magnitude, the corresponding dissymmetry factors can differ bymore » a factor of 10{sup 5}. By maximizing the dissymmetry of magnetic dipole absorption one can significantly enhance the enantioselectivity in the interaction of semiconductor nanocrystals with circularly polarized light. This feature may advance chiral and analytical methods, which will benefit biophysics, chemistry, and pharmaceutical science. The developed theory is illustrated by an example of intraband transitions inside a semiconductor nanocuboid, whose rotatory strengths and dissymmetry factors are calculated analytically.« less

  12. Optical activity of chirally distorted nanocrystals

    NASA Astrophysics Data System (ADS)

    Tepliakov, Nikita V.; Baimuratov, Anvar S.; Baranov, Alexander V.; Fedorov, Anatoly V.; Rukhlenko, Ivan D.

    2016-05-01

    We develop a general theory of optical activity of semiconductor nanocrystals whose chirality is induced by a small perturbation of their otherwise achiral electronic subsystems. The optical activity is described using the quantum-mechanical expressions for the rotatory strengths and dissymmetry factors introduced by Rosenfeld. We show that the rotatory strengths of optically active transitions are decomposed on electric dipole and magnetic dipole contributions, which correspond to the electric dipole and magnetic dipole transitions between the unperturbed quantum states. Remarkably, while the two kinds of rotatory strengths are of the same order of magnitude, the corresponding dissymmetry factors can differ by a factor of 105. By maximizing the dissymmetry of magnetic dipole absorption one can significantly enhance the enantioselectivity in the interaction of semiconductor nanocrystals with circularly polarized light. This feature may advance chiral and analytical methods, which will benefit biophysics, chemistry, and pharmaceutical science. The developed theory is illustrated by an example of intraband transitions inside a semiconductor nanocuboid, whose rotatory strengths and dissymmetry factors are calculated analytically.

  13. Bottom-quark forward-backward asymmetry in the standard model and beyond.

    PubMed

    Grinstein, Benjamín; Murphy, Christopher W

    2013-08-09

    We computed the bottom-quark forward-backward asymmetry at the Tevatron in the standard model (SM) and for several new physics scenarios. Near the Z pole, the SM bottom asymmetry is dominated by tree level exchanges of electroweak gauge bosons. While above the Z pole, next-to-leading order QCD dominates the SM asymmetry as was the case with the top-quark forward-backward asymmetry. Light new physics, M(NP)≲150  GeV, can cause significant deviations from the SM prediction for the bottom asymmetry. The bottom asymmetry can be used to distinguish between competing new physics (NP) explanations of the top asymmetry based on how the NP interferes with s-channel gluon and Z exchange.

  14. Photo-thermoelectric properties of SnS nanocrystals with orthorhombic layered structure

    NASA Astrophysics Data System (ADS)

    Hyun, Cheol-Min; Choi, Jeong-Hun; Lee, Myoung-Jae; Ahn, Ji-Hoon

    2017-07-01

    The photo-thermoelectric properties of SnS nanocrystals, two-dimensional materials with an orthorhombic symmetry, were investigated using a focused laser scanning method. The SnS nanocrystals were synthesized by a vapor transport method, and their fundamental material and electrical properties were investigated. Upon shining a laser onto the SnS channel region under a positive source-drain bias, a positive photocurrent was observed due to photo-excited electron-hole pairs. On the other hand, when this external electric field was not applied, a strong photocurrent was observed within the metal electrode region rather than at the metal-semiconductor interface, which indicated that the major mechanism for the photocurrent under zero external bias was a photo-induced thermoelectric effect rather than a photovoltaic effect. Moreover, the Seebeck coefficient of the SnS nanocrystal device was approximately 1735 μV/K, which is 3.5 times larger than that of its bulk counterpart.

  15. Sulvanite (Cu 3VS 4) nanocrystals for printable thin film photovoltaics

    DOE PAGES

    Chen, Ching -Chin; Stone, Kevin H.; Lai, Cheng -Yu; ...

    2017-09-21

    Copper Vanadium Sulfide (Cu 3VS 4), also known as sulvanite, has recently emerged as a suitable absorber material for thin film photovoltaics. The synthesis of Cu 3VS 4 nanocrystals via a rapid solvothermal route is reported for the first time. The phase purity of the Cu 3VS 4 nanocrystals has been confirmed by X-ray powder diffraction (XRD) and Raman spectroscopy, while the nanoparticle size, of about 10 nm, was evaluated by transmission electron microscopy (TEM). Successful ligand exchange with sulfide, an inorganic ligand, demonstrated that the nanoparticles are amenable to surface modifications, key element in solution processing. Further annealing ofmore » as-synthesized nanocrystals under a sulfur/argon atmosphere at 600 °C, rendered highly crystalline Cu 3VS 4 powders exhibiting an impurity that could be potentially mitigated by annealing temperature optimization. Furthermore, Cu 3VS 4, formed solely from Earth-abundant elements, could provide an inexpensive, reliable approach to fabricating solution processed thin film photovoltaic absorbers.« less

  16. Sulvanite (Cu 3VS 4) nanocrystals for printable thin film photovoltaics

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Chen, Ching -Chin; Stone, Kevin H.; Lai, Cheng -Yu

    Copper Vanadium Sulfide (Cu 3VS 4), also known as sulvanite, has recently emerged as a suitable absorber material for thin film photovoltaics. The synthesis of Cu 3VS 4 nanocrystals via a rapid solvothermal route is reported for the first time. The phase purity of the Cu 3VS 4 nanocrystals has been confirmed by X-ray powder diffraction (XRD) and Raman spectroscopy, while the nanoparticle size, of about 10 nm, was evaluated by transmission electron microscopy (TEM). Successful ligand exchange with sulfide, an inorganic ligand, demonstrated that the nanoparticles are amenable to surface modifications, key element in solution processing. Further annealing ofmore » as-synthesized nanocrystals under a sulfur/argon atmosphere at 600 °C, rendered highly crystalline Cu 3VS 4 powders exhibiting an impurity that could be potentially mitigated by annealing temperature optimization. Furthermore, Cu 3VS 4, formed solely from Earth-abundant elements, could provide an inexpensive, reliable approach to fabricating solution processed thin film photovoltaic absorbers.« less

  17. Angular rheology study of colloidal nanocrystals using Coherent X-ray Diffraction

    NASA Astrophysics Data System (ADS)

    Liang, Mengning; Harder, Ross; Robinson, Ian

    2007-03-01

    A new method using coherent x-ray diffraction provides a way to investigate the rotational motion of a colloidal suspension of crystals in real time. Coherent x-ray diffraction uses the long coherence lengths of synchrotron sources to illuminate a nanoscale particle coherently over its spatial dimensions. The penetration of high energy x-rays into various media allows for in-situ measurements making it ideal for suspensions. This technique has been used to image the structure of nanocrystals for some time but also has the capability of providing information about the orientation and dynamics of crystals. The particles are imaged in a specific diffraction condition allowing us to determine their orientation and observe how they rotate in real time with exceptional resolution. Such sensitivity allows for the study of rotational Brownian motion of nanocrystals in various suspensions and conditions. We present a study of the angular rheology of alumina and TiO2 colloidal nanocrystals in media using coherent x-ray diffraction.

  18. Atomic level characterization of cadmium selenide nanocrystal systems using atomic number contrast scanning transmission electron microscopy and Rutherford backscattering spectroscopy

    NASA Astrophysics Data System (ADS)

    McBride, James R.

    This project involved the characterization of CdSe nanocrystals. Through the use of Atomic Number Contrast Scanning Transmission Electron Microscopy (Z-STEM) and Rutherford Backscattering Spectroscopy (RBS), atomic level structure and chemical information was obtained. Specifically, CdSe nanocrystals produced using a mixture of hexadecylamine (HDA) and trioctylphosphine oxide (TOPO) were determined to be spherical compared to nanocrystals produced in TOPO only, which had elongated (101) facets. Additionally, the first Z-STEM images of CdSe/ZnS core/shell nanocrystals were obtained. From these images, the growth mechanism of the ZnS shell was determined and the existence of non-fluorescent ZnS particles was confirmed. Through collaboration with Quantum Dot Corp., core/shell nanocrystals with near unity quantum yield were developed. These core/shell nanocrystals included a US intermediate layer to improve shell coverage.

  19. Birth order and fluctuating asymmetry: a first look.

    PubMed Central

    Lalumière, M L; Harris, G T; Rice, M E

    1999-01-01

    We investigated the hypothesis that maternal immunoreactivity to male-specific features of the foetus can increase developmental instability. We predicted that the participants' number of older brothers would be positively related to the fluctuating asymmetry of ten bilateral morphological traits. The participants were 40 adult male psychiatric patients and 31 adult male hospital employees. Consistent with the hypothesis, the participants' number of older brothers--but not number of older sisters, younger brothers or younger sisters--was positively associated with fluctuating asymmetry. The patients had significantly larger fluctuating asymmetry scores and tended to have more older brothers than the employees, but the positive relationship between the number of older brothers and fluctuating asymmetry was observed in both groups. PMID:10643079

  20. Cerebral blood flow asymmetries in headache-free migraineurs

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Levine, S.R.; Welch, K.M.; Ewing, J.R.

    1987-11-01

    Regional cerebral blood flow (rCBF) asymmetries were studied in controls and patients with common and classic/complicated migraine using /sup 133/Xe inhalation with 8 homologously situated external collimators over each cerebral hemisphere. Migraine patients as a group more frequently had posterior rCBF asymmetries than controls (p less than 0.03). Although there were no differences in the number of anterior rCBF asymmetries, migraine patients had 2 or more asymmetric probe pairs more often than controls (p less than 0.02). The posterior rCBF asymmetries, consistent with the site of activation of many migraine attacks, may be related to more labile control of themore » cerebral circulation.« less