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Sample records for nanocrystals fundamentals materials

  1. Nonthermal Plasma Synthesis of Nanocrystals: Fundamental Principles, Materials, and Applications.

    PubMed

    Kortshagen, Uwe R; Sankaran, R Mohan; Pereira, Rui N; Girshick, Steven L; Wu, Jeslin J; Aydil, Eray S

    2016-09-28

    Nonthermal plasmas have emerged as a viable synthesis technique for nanocrystal materials. Inherently solvent and ligand-free, nonthermal plasmas offer the ability to synthesize high purity nanocrystals of materials that require high synthesis temperatures. The nonequilibrium environment in nonthermal plasmas has a number of attractive attributes: energetic surface reactions selectively heat the nanoparticles to temperatures that can strongly exceed the gas temperature; charging of nanoparticles through plasma electrons reduces or eliminates nanoparticle agglomeration; and the large difference between the chemical potentials of the gaseous growth species and the species bound to the nanoparticle surfaces facilitates nanocrystal doping. This paper reviews the state of the art in nonthermal plasma synthesis of nanocrystals. It discusses the fundamentals of nanocrystal formation in plasmas, reviews practical implementations of plasma reactors, surveys the materials that have been produced with nonthermal plasmas and surface chemistries that have been developed, and provides an overview of applications of plasma-synthesized nanocrystals.

  2. Fundamental studies of chalcogenide nanocrystals, carbonaceous nanoparticles, and chromatographic materials

    NASA Astrophysics Data System (ADS)

    Baker, Jared Scott

    2011-12-01

    The development of novel nanomaterials and the understanding of their fundamental physical and chemical properties represent an exciting area of research. These materials are continuously being sought for ever-increasing applications; finding their way into uses that influence mankind on a daily basis. Combining elements from traditional nanoparticle characterization with electrophoretic-based techniques, this dissertation presents the analysis of carbon nanoparticles (CNPs) generated from a novel source (candle soot) as well as a unique perspective on the reactivity and degradation process of magic-sized cadmium chalcogenide nanocrystals. One potential application of CNPs is their use as an alternative fluorophore in a separation-based sensor system. Laser-induced-fluorescence (LIF) is a commonly used manner of detection in this type of platform, but is limited in many cases by problems associated with the fluorophore. Carbon-based nanoparticles have the potential to improve upon traditional fluorophores in applications that make use of LIF as the detection scheme. CNPs were extracted from the carbonaceous material produced by the incomplete combustion of a candle. The soot was submitted to an oxidizing treatment and extraction/filtration procedures rendering watersoluble luminescent species. Electron microscopy was used to identify globular, amorphous structures in the nanometer size-range. An aqueous suspension of CNPs demonstrated excellent stability in terms of its electronic properties, showing little change in absorption and emission spectra upon storage under ambient conditions over a two-year period. Capitalizing on the strengths of capillary electrophoresis (CE) as a characterization technique, we have analyzed the negatively-charged CNPs in terms of charge and size by studying the influence of variable CE conditions on the resulting separation. Separations at different pH revealed a highly complex mixture of CNPs, containing species with large

  3. Synthesis of new nanocrystal materials

    NASA Astrophysics Data System (ADS)

    Hassan, Yasser Hassan Abd El-Fattah

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

  4. 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

  5. Designer Nanocrystal Materials for Photovoltaics

    NASA Astrophysics Data System (ADS)

    Kagan, Cherie

    Advances in synthetic methods allow a wide range of semiconductor nanocrystals (NCs) to be tailored in size and shape and to be used as building blocks in the design of NC solids. However, the long, insulating ligands commonly employed in the synthesis of colloidal NCs inhibit strong interparticle coupling and charge transport once NCs are assembled into the solids state as NC arrays. We will describe the range of short, compact ligand chemistries we employ to exchange the long, insulating ligands used in synthesis and to increase interparticle coupling. These ligand exchange processes can have a dramatic influence on NC surface chemistry as well as NC organization in the solids, showing examples of short-range order. Synergistically, we use 1) thermal evaporation and diffusion and 2) wet-chemical methods to introduce extrinsic impurities and non-stoichiometry to passivate surface traps and dope NC solids. NC coupling and doping provide control over the density of states and the carrier type, concentration, mobility, and lifetime, which we characterize by a range of electronic and spectroscopic techniques. We will describe the importance of engineering device interfaces to design NC materials for solar photovoltaics.

  6. Comparison of Silicon Nanocrystals Prepared by Two Fundamentally Different Methods

    NASA Astrophysics Data System (ADS)

    Cibulka, Ondřej; Vorkötter, Christoph; Purkrt, Adam; Holovský, Jakub; Benedikt, Jan; Herynková, Kateřina

    2016-10-01

    This work compares structural and optical properties of silicon nanocrystals prepared by two fundamentally different methods, namely, electrochemical etching of Si wafers and low-pressure plasma synthesis, completed with a mechano-photo-chemical treatment. This treatment leads to surface passivation of the nanoparticles by methyl groups. Plasma synthesis unlike electrochemical etching allows selecting of the particle sizes. Measured sizes of the nanoparticles by dynamic light scattering show 3 and 20 nm for electrochemically etched and plasma-synthetized samples, respectively. Plasma-synthetized 20-nm particles do not exhibit photoluminescence due to absence of quantum confinement effect, and freshly appeared photoluminescence after surface passivation could indicate presence of organic molecules on the nanoparticle surface, luminescing instead of nanocrystal core. Electrochemically etched sample exhibits dramatic changes in photoluminescence during the mechano-photo-chemical treatment while no photoluminescence is observed for the plasma-synthetized one. We also used the Fourier transform infrared spectroscopy for comparison of the chemical changes happened during the treatment.

  7. Fundamentals of polymeric materials

    SciTech Connect

    Shilling, M.S.

    1998-12-31

    The polymer industry is a young industry that has undergone tremendous growth and change over the last sixty years. Many important discoveries in polymer science have been accidental. Most of the learning has been by trial and error and most of the understanding is still basically empirical--make a polymer material or compound and then put it to the test to study what it is and how it performs. This article provides an overview of what polymers and polymer compounds are, why they behave as they do, and it discusses several examples of failures of rubber and plastic components.

  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. Supersonic Nanocrystal Deposition for Nanostructured Materials

    DTIC Science & Technology

    2001-11-01

    element. Previous work has characterized the nanoerystals produced by ablation of silver microparticles. In addition to silver and cadmium selenide , several...silver and cadmium selenide in argon the kinetic energy per atom is limited to 0.03 eV/atom while for helium it is up to 0.3 cV/atom. Therefore materials...2. Cadmium Selenide nanocrystals deposited at low kinetic energy in argon carrier gas. The main TEM micrograph shows the overall size distribution and

  11. Hybrid polymer-nanocrystal materials for photovoltaic applications.

    PubMed

    Zhou, Renjia; Xue, Jiangeng

    2012-07-16

    Hybrid polymer-nanocrystal photovoltaic (PV) cells have received much attention during the past decade as promising low-cost solar energy harvesting devices, and showed significant progress with power conversion efficiency reaching 5% recently. This review starts from the introduction of hybrid materials to their application in electronic devices, with particular focus on bulk-heterojunction hybrid polymer-nanocrystal PV devices. The synthesis, surface chemistry, and electronic properties of colloidal inorganic nanocrystals are described. The recent development of hybrid PV devices will be discussed from the perspective of tailoring both inorganic nanocrystals and conjugated polymers, controlling polymer-nanocrystal hybrid morphology, engineering polymer-nanocrystal interface, and optimizing device architecture. Finally, future directions for further advancing hybrid PV technology to potential commercialization are also discussed.

  12. Strength weakening by nanocrystals in ceramic materials.

    PubMed

    Wang, Yuejian; Zhang, Jianzhong; Zhao, Yusheng

    2007-10-01

    A key question in nanomechanics concerns the grain size effects on materials' strength. Correct solution to this question is critical to design and tailor the properties of materials for particular applications. The full map of grain sizes-hardness/yield stress relationship in metals has been built. However, for ceramic materials, the similar studies and understandings are really lacking. Here we employed a novel technique to comparatively study the mechanical features of titanium dioxide (TiO(2)) with different crystallite sizes. On the basis of peak profile analysis of the X-ray diffraction data, we determined yield strength for nanocrystalline and bulk TiO(2). Our results reveal a remarkable reduction in yield strength as the grain size decreases from 30-40 microm to approximately 10 nm, providing the only evidence of a strength weakening by nanocrystals relative to their bulk counterparts. This finding infers an inverse Hall-Petch effect, the first of its kind for ceramic materials, and a dramatic strength weakening after the breakdown of classic Hall-Petch relation below a characteristic grain size.

  13. 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.

  14. Cobalt Nanocrystals as Starting Materials for Shape Modificationand Assembly Formation

    SciTech Connect

    Erdonmez, Can Kerem

    2005-01-01

    Surfactant-coated cobalt nanocrystals can be prepared with areasonable degree of control over particle size and shape using athermolytic route. The small crystallite size, enhanced reactivity andtunable interparticle interactions enable use of this material asstarting material for demonstration of achievement of novel structuresusing extremely simple solution-based approaches. In particular,formation of hollow cobalt sulfide nanocrystals upon chemicalmodification and emergence of long-range orientational order upondrying-mediated assembly of cobalt nanocrystals is reportedhere.Colloidal preparation of Co nanocrystals has been well-studied.Here, we emphasize general principles and crystallographic/morphologicalcharacterization of disk-shaped hcp-Co nanocrystals. Use of surfactantmolecules enables achievement of multiple morphologies in one syntheticsystem.Formation of hollow structures upon in-solution sulfidation of Conanocrystals is presented and discussed. A Kirkendall-type effect,involving dominant outward mass transport during formation of the ionicshell material explains the results naturally. It is expected that thisphenomenon will generalize extensively to formation of hollow structuresof an enormous variety of compositions. Detailed study of particlemorphology as a function of reaction conditions suggest phenomena likelyto be generally relevant to use of this approach. A short report ofcrystallographic co-alignment into vortex-like structures is alsoprovided. Our current best picture of this process involves an interplayof packing and magnetic interactions between facetedparticles.

  15. Interactions and Assemblies of Polymeric Materials and Colloidal Nanocrystals

    NASA Astrophysics Data System (ADS)

    Williams, Teresa Elaine

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

  16. Methods of use of semiconductor nanocrystal probes for treating a material

    DOEpatents

    Weiss, Shimon; Bruchez, Marcel; Alivisatos, Paul

    2007-04-27

    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 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.

  17. DOE fundamentals handbook: Material science. Volume 1

    SciTech Connect

    Not Available

    1993-01-01

    This handbook was developed to assist nuclear facility operating contractors in providing operators, maintenance personnel, and the technical staff with the necessary fundamentals training to ensure a basic understanding of the structure and properties of metals. This volume contains the two modules: structure of metals (bonding, common lattic types, grain structure/boundary, polymorphis, alloys, imperfections in metals) and properties of metals (stress, strain, Young modulus, stress-strain relation, physical properties, working of metals, corrosion, hydrogen embrittlement, tritium/material compatibility).

  18. Fundamentals of materials accounting for nuclear safeguards

    SciTech Connect

    Pillay, K.K.S.

    1989-04-01

    Materials accounting is essential to providing the necessary assurance for verifying the effectiveness of a safeguards system. The use of measurements, analyses, records, and reports to maintain knowledge of the quantities of nuclear material present in a defined area of a facility and the use of physical inventories and materials balances to verify the presence of special nuclear materials are collectively known as materials accounting for nuclear safeguards. This manual, prepared as part of the resource materials for the Safeguards Technology Training Program of the US Department of Energy, addresses fundamental aspects of materials accounting, enriching and complementing them with the first-hand experiences of authors from varied disciplines. The topics range from highly technical subjects to site-specific system designs and policy discussions. This collection of papers is prepared by more than 25 professionals from the nuclear safeguards field. Representing research institutions, industries, and regulatory agencies, the authors create a unique resource for the annual course titled ''Materials Accounting for Nuclear Safeguards,'' which is offered at the Los Alamos National Laboratory.

  19. Coupling single giant nanocrystal quantum dots to the fundamental mode of patch nanoantennas through fringe field

    DOE PAGES

    Wang, Feng; Karan, Niladri S.; Minh Nguyen, Hue; ...

    2015-09-23

    Through single dot spectroscopy and numerical simulation studies, we demonstrate that the fundamental mode of gold patch nanoantennas have fringe-field resonance capable of enhancing the nano-emitters coupled around the edge of the patch antenna. This fringe-field coupling is used to enhance the radiative rates of core/thick-shell nanocrystal quantum dots (g-NQDs) that cannot be embedded into the ultra-thin dielectric gap of patch nanoantennas due to their large sizes. We attain 14 and 3 times enhancements in single exciton radiative decay rate and bi-exciton emission efficiencies of g-NQDs respectively, with no detectable metal quenching. Our numerical studies confirmed our experimental results andmore » further reveal that patch nanoantennas can provide strong emission enhancement for dipoles lying not only in radial direction of the circular patches but also in the direction normal to the antennas surface. Finally, this provides a distinct advantage over the parallel gap-bar antennas that can provide enhancement only for the dipoles oriented across the gap.« less

  20. Coupling single giant nanocrystal quantum dots to the fundamental mode of patch nanoantennas through fringe field

    SciTech Connect

    Wang, Feng; Karan, Niladri S.; Minh Nguyen, Hue; Ghosh, Yagnaseni; Hollingsworth, Jennifer A.; Htoon, Han

    2015-09-23

    Through single dot spectroscopy and numerical simulation studies, we demonstrate that the fundamental mode of gold patch nanoantennas have fringe-field resonance capable of enhancing the nano-emitters coupled around the edge of the patch antenna. This fringe-field coupling is used to enhance the radiative rates of core/thick-shell nanocrystal quantum dots (g-NQDs) that cannot be embedded into the ultra-thin dielectric gap of patch nanoantennas due to their large sizes. We attain 14 and 3 times enhancements in single exciton radiative decay rate and bi-exciton emission efficiencies of g-NQDs respectively, with no detectable metal quenching. Our numerical studies confirmed our experimental results and further reveal that patch nanoantennas can provide strong emission enhancement for dipoles lying not only in radial direction of the circular patches but also in the direction normal to the antennas surface. Finally, this provides a distinct advantage over the parallel gap-bar antennas that can provide enhancement only for the dipoles oriented across the gap.

  1. Coupling Single Giant Nanocrystal Quantum Dots to the Fundamental Mode of Patch Nanoantennas through Fringe Field

    PubMed Central

    Wang, Feng; Karan, Niladri S.; Minh Nguyen, Hue; Ghosh, Yagnaseni; Hollingsworth, Jennifer A.; Htoon, Han

    2015-01-01

    Through single dot spectroscopy and numerical simulation studies, we demonstrate that the fundamental mode of gold patch nanoantennas have fringe-field resonance capable of enhancing the nano-emitters coupled around the edge of the patch antenna. This fringe-field coupling is used to enhance the radiative rates of core/thick-shell nanocrystal quantum dots (g-NQDs) that cannot be embedded into the ultra-thin dielectric gap of patch nanoantennas due to their large sizes. We attain 14 and 3 times enhancements in single exciton radiative decay rate and bi-exciton emission efficiencies of g-NQDs respectively, with no detectable metal quenching. Our numerical studies confirmed our experimental results and further reveal that patch nanoantennas can provide strong emission enhancement for dipoles lying not only in radial direction of the circular patches but also in the direction normal to the antennas surface. This provides a distinct advantage over the parallel gap-bar antennas that can provide enhancement only for the dipoles oriented across the gap. PMID:26394763

  2. Coupling Single Giant Nanocrystal Quantum Dots to the Fundamental Mode of Patch Nanoantennas through Fringe Field.

    PubMed

    Wang, Feng; Karan, Niladri S; Minh Nguyen, Hue; Ghosh, Yagnaseni; Hollingsworth, Jennifer A; Htoon, Han

    2015-09-23

    Through single dot spectroscopy and numerical simulation studies, we demonstrate that the fundamental mode of gold patch nanoantennas have fringe-field resonance capable of enhancing the nano-emitters coupled around the edge of the patch antenna. This fringe-field coupling is used to enhance the radiative rates of core/thick-shell nanocrystal quantum dots (g-NQDs) that cannot be embedded into the ultra-thin dielectric gap of patch nanoantennas due to their large sizes. We attain 14 and 3 times enhancements in single exciton radiative decay rate and bi-exciton emission efficiencies of g-NQDs respectively, with no detectable metal quenching. Our numerical studies confirmed our experimental results and further reveal that patch nanoantennas can provide strong emission enhancement for dipoles lying not only in radial direction of the circular patches but also in the direction normal to the antennas surface. This provides a distinct advantage over the parallel gap-bar antennas that can provide enhancement only for the dipoles oriented across the gap.

  3. 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.

  4. Constructing functional mesostructured materials from colloidal nanocrystal building blocks.

    PubMed

    Milliron, Delia J; Buonsanti, Raffaella; Llordes, Anna; Helms, Brett A

    2014-01-21

    Through synthesizing colloidal nanocrystals (NCs) in the organic phase, chemists gain fine control over their composition, size, and shape. Strategies for arranging them into ordered superlattices have followed closely behind synthetic advances. Nonetheless, the same hydrophobic ligands that help their assembly also severely limit interactions between adjacent nanocrystals. As a result, examples of nanocrystal-based materials whose functionality derives from their mesoscale structure have lagged well behind advances in synthesis and assembly. In this Account, we describe how recent insights into NC surface chemistry have fueled dramatic progress in functional mesostructures. In these constructs, intimate contact between NCs as well as with heterogeneous components is key in determining macroscopic behavior. The simplest mesoscale assemblies we consider are networks of NCs constructed by in situ replacement of their bulky, insulating surface ligands with small molecules. Transistors are a test bed for understanding conductivity, setting the stage for new functionality. For instance, we demonstrated that by electrochemically charging and discharging networks of plasmonic metal oxide NCs, the transmittance of near infrared light can be strongly and reversibly modulated. When we assemble NCs with heterogeneous components, there is an even greater potential for generating complex functionality. Nanocomposites can exhibit favorable characteristics of their component materials, yet the interaction between components can also have a strong influence. Realizing such opportunities requires an intimate linking of embedded NCs to the surrounding matrix phase. We accomplish this link by coordinating inorganic anionic clusters directly to NC surfaces. By exploiting this connection, we found enhanced ionic conductivity in Ag2S-in-GeS2 nanocrystal-in-glass electrodes. In another example, we also found enhanced optical contrast when linking electrochromic niobium oxide to embedded

  5. Fundamental Characterization Studies of Advanced Photocatalytic Materials

    NASA Astrophysics Data System (ADS)

    Phivilay, Somphonh Peter

    Solar powered photocatalytic water splitting has been proposed as a method for the production of sustainable, non-carbon hydrogen fuel. Although much technological progress has been achieved in recent years in the discovery of advanced photocatalytic materials, the progress in the fundamental scientific understanding of such novel, complex mixed oxide and oxynitride photocatalysts has significantly lagged. One of the major reasons for this slow scientific progress is the limited number of reported surface characterization studies of the complex bulk mixed oxide and oxynitride photocatalyst systems. Although photocatalytic splitting of water by bulk mixed oxide and oxynitride materials involves both bulk (generation of excited electrons and holes) and surface phenomena (reaction of H2O with excited electrons and holes at the surface), the photocatalysis community has almost completely ignored the surface characteristics of such complex bulk photocatalysts and correlates the photocatalytic properties with bulk properties. Some of the most promising photocatalyst systems (NaTaO3, GaN, (Ga1-xZnx)(N1-xOx) and TaON) were investigated to establish fundamental bulk/surface structure photoactivity relationships. The bulk molecular and electronic structures of the photocatalysts were determined with Raman and UV-vis spectroscopy. Photoluminescence (PL) and transient PL spectroscopy were provided insight into how recombination of photogenerated electrons is related to the photocatalysis activity. The chemical states and atomic compositions of the surface region of the photocatalysts were determined with high resolution X-ray photoelectron spectroscopy (˜1-3 nm) and high sensitivity-low energy ion scattering spectroscopy (˜0.3 nm). The new insights obtained from surface characterization clarified the role of La and Ni promoters species for the NaTaO3 photocatalyst system. The La2O3 additive was found to be a structural promoter that stabilizes small NaTaO3 nanoparticles (NPs

  6. Tuning optoelectronic properties and understanding charge transport in nanocrystal thin films of earth abundant semiconducting materials

    NASA Astrophysics Data System (ADS)

    Riha, Shannon C.

    2011-12-01

    With the capability of producing nearly 600 TW annually, solar power is one renewable energy source with the potential to meet a large fraction of the world's burgeoning energy demand. To make solar technology cost-competitive with carbon-based fuels, cheaper devices need to be realized. Solution-processed solar cells from nanocrystal inks of earth abundant materials satisfy this requirement. Nonetheless, a major hurdle in commercializing such devices is poor charge transport through nanocrystal thin films. The efficiency of charge transport through nanocrystal thin films is strongly dependent on the quality of the nanocrystals, as well as their optoelectronic properties. Therefore, the first part of this dissertation is focused on synthesizing high quality nanocrystals of Cu2ZnSnS4, a promising earth abundant photovoltaic absorber material. The optoelectronic properties of the nanocrystals were tuned by altering the copper to zinc ratio, as well as by introducing selenium to create Cu2ZnSn(S1-xSe x)4 solid solutions. Photoelectrochemical characterization was used to test the Cu2ZnSnS4 and Cu2ZnSn(S 1-xSex)4 nanocrystal thin films. The results identify minority carrier diffusion and recombination via the redox shuttle as the major loss mechanisms hindering efficient charge transport through the nanocrystal thin films. One way to solve this issue is to sinter the nanocrystals together, creating large grains for efficient charge transport. Although this may be quick and effective, it can lead to the formation of structural defects, among other issues. To this end, using a different copper-based material, namely Cu2Se, and simple surface chemistry treatments, an alternative route to enhance charge transport through nanocrystals thin films is proposed.

  7. Semiconductor Nanocrystals Hybridized with Functional Ligands: New Composite Materials with Tunable Properties

    PubMed Central

    McDowell, Matthew; Wright, Ashley E.; Hammer, Nathan I.

    2010-01-01

    Semiconductor nanocrystals hybridized with functional ligands represent an important new class of composite nanomaterials. The development of these new nanoscale building blocks has intensified over the past few years and offer significant advantages in a wide array of applications. Functional ligands allow for incorporation of nanocrystals into areas where their unique photophysics can be exploited. Energy and charge transfer between the ligands and the nanocrystal also result in enhanced physical properties that can be tuned by the choice of ligand architecture. Here, progress in the development and applications involving this new class of composite materials will be discussed.

  8. DOE fundamentals handbook: Material science. Volume 1

    SciTech Connect

    Not Available

    1993-01-01

    The Mechanical Science Handbook was developed to assist nuclear facility operating contractors in providing operators, maintenance personnel, and the technical staff with the necessary fundamentals training to ensure a basic understanding of mechanical components and mechanical science. The handbook includes information on diesel engines, heat exchangers, pumps, valves, and miscellaneous mechanical components. This information will provide personnel with a foundation for understanding the construction and operation of mechanical components that are associated with various DOE nuclear facility operations and maintenance.

  9. EDITORIAL: Tribocorrosion: fundamentals, materials and applications

    NASA Astrophysics Data System (ADS)

    MORE ADDRESSES--> Alfons Fischer,

  1. Nanostructured electrochromic smart windows: traditional materials and NIR-selective plasmonic nanocrystals.

    PubMed

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

    2014-09-21

    Electrochromic devices, which dynamically change colour under applied potential, are widely studied for use in energy-efficient smart windows. To improve the viability of smart windows, many researchers are utilizing nanomaterials, which can provide electrochromic devices with improved colouration efficiencies, faster switching times, longer cycle lives, and potentially reduced costs. In an effort to demonstrate a new type of electrochromic device that goes beyond the capabilities of commonly used electrochromic materials, researchers have turned to plasmonic transparent conductive oxide (TCO) nanocrystals. Electrochemical injection of electrons into plasmonic TCO nanocrystal films induces a shift in the plasmon frequency and gives rise to the new functionality of selective optical modulation in the near-infrared region of the solar spectrum. These nanocrystals can be used as building blocks to enable creation of advanced electrochromic devices containing mesoporous electrodes or nanocrystal-in-glass composites. Such devices have been important in advancing the field towards achieving the ideal smart window with independent control over visible and NIR transmittance.

  2. Nanostructured electrochromic smart windows: traditional materials and NIR-selective plasmonic nanocrystals

    SciTech Connect

    Runnerstrom, EL; Llordes, A; Lounis, SD; Milliron, DJ

    2014-06-04

    Electrochromic devices, which dynamically change colour under applied potential, are widely studied for use in energy-efficient smart windows. To improve the viability of smart windows, many researchers are utilizing nanomaterials, which can provide electrochromic devices with improved colouration efficiencies, faster switching times, longer cycle lives, and potentially reduced costs. In an effort to demonstrate a new type of electrochromic device that goes beyond the capabilities of commonly used electrochromic materials, researchers have turned to plasmonic transparent conductive oxide (TCO) nanocrystals. Electrochemical injection of electrons into plasmonic TCO nanocrystal films induces a shift in the plasmon frequency and gives rise to the new functionality of selective optical modulation in the near-infrared region of the solar spectrum. These nanocrystals can be used as building blocks to enable creation of advanced electrochromic devices containing mesoporous electrodes or nanocrystal-in-glass composites. Such devices have been important in advancing the field towards achieving the ideal smart window with independent control over visible and NIR transmittance.

  3. Sol-gel derived precursors to Group 14 semiconductor nanocrystals - Convenient materials for enabling nanocrystal-based applications

    NASA Astrophysics Data System (ADS)

    Veinot, Jonathan G. C.; Henderson, Eric J.; Hessel, Colin M.

    2009-11-01

    Semiconductor nanocrystals are intriguing because of their electronic, optical, and chemical characteristics. Silicon nanocrystals (Si-NCs) of sub-5 nm dimension are of particular interest due to their intense photoluminescent response and the promise of linking silicon photonics and electronics. Other related nanomaterials of technological importance include SiC and Ge. The following contribution describes key experimental findings pertaining to synthetic methodology, investigation of nanodomain formation and growth, as determined by X-ray powder diffraction (XRD) and photoluminescence (PL) spectroscopy for a series of sol-gel derived prepolymers suitable for preparing Group 14 based nanocrystal containing composites.

  4. Urokinase immobilized on medical polymeric materials: fundamental and clinical studies.

    PubMed

    Ohshiro, T; Kosaki, G

    1980-02-01

    One of the methods of preparing an antithrombogenic material is to immobilize a fibrinolytic enzyme on the surface of a carrier. The clinical trial of such a material must be subject to not only a basic study on the quality of a carrier, the technique of immobilization, and the method of disinfection, but also an in vivo study on its antithrombotic effect. Reported herein is the evaluation of the fibrinolytic ability, at fundamental and clinical levels, of the urokinase that was immobilized on the surface of various polymeric materials. The results were favorable.

  5. Prediction and Design of Materials from Crystal Structures to Nanocrystal Morphology and Assembly

    NASA Astrophysics Data System (ADS)

    Hennig, Richard

    2012-02-01

    Predictions of structure formation by computational methods have the potential to accelerate materials discovery and design. Here we present two computational approaches for the prediction of crystal structures and the morphology of nanoparticles. Many materials properties are controlled by composition and crystal structure. We show that evolutionary algorithms coupled to ab-initio relaxations can accurately predict the crystal structure and composition of compounds without any prior information about the system. We will discuss results for various systems including the prediction of unexpected quasi-1D and 2D electronic structures in Li-Be compounds under pressure [1] and of the crystal structure of the superconducting high-pressure phase of Eu [2]. The self-assembly of nanocrystals into mesoscale superlattices provides a path to the design of materials with tunable electronic, physical and chemical properties for various applications. The self-assembly is controlled by the nanocrystal shape and by ligand-mediated interactions between them. To understand this, it is necessary to know the effect of the ligands on the surface energies (which tune the nanocrystal shape), as well as the relative coverage of the different facets (which control the interactions). Density functional calculations for the binding energy of oleic acid-based ligands on PbSe nanocrystals determine the surface energies as a function of ligand coverage. The Wulff construction predicts the thermodynamic equilibrium shape of the PbSe nanocrystals as a function of the ligand coverage. We show that the different ligand binding energies on the 100 and 111 facets results in different ligand coverages on the facets and predict a transition in the equilibrium shape from octahedral to cubic when increasing the ligand concentration during synthesis. Our results furthermore suggest that the experimentally observed transformation of the nanocrystal superlattice structure from fcc to bcc is caused by the

  6. Modeling the antireflective properties of composite materials based on semiconductor filamentary nanocrystals

    NASA Astrophysics Data System (ADS)

    Gorai, L. I.; Buravlev, A. D.; Ponyaev, S. A.

    2015-07-01

    The feasibility of application of films of composite materials based on semiconductor filamentary nanocrystals (FNCs) to suppress the reflection of electromagnetic radiation in the radiofrequency range is demonstrated for the first time with the use of the effective medium theory (EMT). It is shown that the reflec- tion coefficients of single- and double-layer models may be reduced several-fold and by as much as two orders of magnitude, respectively, in a wide range of parameters. The agreement of the EMT data with the results of rigorous calculations allows one to apply the zeroth-order EMT in the analysis and synthesis of antireflective composite materials based on FNCs.

  7. Fundamentals of lateral and vertical heterojunctions of atomically thin materials

    NASA Astrophysics Data System (ADS)

    Pant, Anupum; Mutlu, Zafer; Wickramaratne, Darshana; Cai, Hui; Lake, Roger K.; Ozkan, Cengiz; Tongay, Sefaattin

    2016-02-01

    At the turn of this century, Herbert Kroemer, the 2000 Nobel Prize winner in Physics, famously commented that ``the interface is the device''. This statement has since opened up unparalleled opportunities at the interface of conventional three-dimensional (3D) materials (H. Kroemer, Quasi-Electric and Quasi-Magnetic Fields in Non-Uniform Semiconductors, RCA Rev., 1957, 18, 332-342). More than a decade later, Sir Andre Geim and Irina Grigorieva presented their views on 2D heterojunctions which further cultivated broad interests in the 2D materials field. Currently, advances in two-dimensional (2D) materials enable us to deposit layered materials that are only one or few unit-cells in thickness to construct sharp in-plane and out-of-plane interfaces between dissimilar materials, and to be able to fabricate novel devices using these cutting-edge techniques. The interface alone, which traditionally dominated overall device performance, thus has now become the device itself. Fueled by recent progress in atomically thin materials, we are now at the ultimate limit of interface physics, which brings to us new and exciting opportunities, with equally demanding challenges. This paper endeavors to provide stalwarts and newcomers a perspective on recent advances in synthesis, fundamentals, applications, and future prospects of a large variety of heterojunctions of atomically thin materials.

  8. Fundamentals of lateral and vertical heterojunctions of atomically thin materials.

    PubMed

    Pant, Anupum; Mutlu, Zafer; Wickramaratne, Darshana; Cai, Hui; Lake, Roger K; Ozkan, Cengiz; Tongay, Sefaattin

    2016-02-21

    At the turn of this century, Herbert Kroemer, the 2000 Nobel Prize winner in Physics, famously commented that "the interface is the device". This statement has since opened up unparalleled opportunities at the interface of conventional three-dimensional (3D) materials (H. Kroemer, Quasi-Electric and Quasi-Magnetic Fields in Non-Uniform Semiconductors, RCA Rev., 1957, 18, 332-342). More than a decade later, Sir Andre Geim and Irina Grigorieva presented their views on 2D heterojunctions which further cultivated broad interests in the 2D materials field. Currently, advances in two-dimensional (2D) materials enable us to deposit layered materials that are only one or few unit-cells in thickness to construct sharp in-plane and out-of-plane interfaces between dissimilar materials, and to be able to fabricate novel devices using these cutting-edge techniques. The interface alone, which traditionally dominated overall device performance, thus has now become the device itself. Fueled by recent progress in atomically thin materials, we are now at the ultimate limit of interface physics, which brings to us new and exciting opportunities, with equally demanding challenges. This paper endeavors to provide stalwarts and newcomers a perspective on recent advances in synthesis, fundamentals, applications, and future prospects of a large variety of heterojunctions of atomically thin materials.

  9. Carrier multiplication in semiconductor nanocrystals: theoretical screening of candidate materials based on band-structure effects.

    PubMed

    Luo, Jun-Wei; Franceschetti, Alberto; Zunger, Alex

    2008-10-01

    Direct carrier multiplication (DCM) occurs when a highly excited electron-hole pair decays by transferring its excess energy to the electrons rather than to the lattice, possibly exciting additional electron-hole pairs. Atomistic electronic structure calculations have shown that DCM can be induced by electron-hole Coulomb interactions, in an impact-ionization-like process whose rate is proportional to the density of biexciton states rho XX. Here we introduce a DCM "figure of merit" R2(E) which is proportional to the ratio between the biexciton density of states rhoXX and the single-exciton density of states rhoX, restricted to single-exciton and biexciton states that are coupled by Coulomb interactions. Using R2(E), we consider GaAs, InAs, InP, GaSb, InSb, CdSe, Ge, Si, and PbSe nanocrystals of different sizes. Although DCM can be affected by both quantum-confinement effects (reflecting the underly electronic structure of the confined dot-interior states) and surface effects, here we are interested to isolate the former. To this end the nanocrystal energy levels are obtained from the corresponding bulk band structure via the truncated crystal approximation. We find that PbSe, Si, GaAs, CdSe, and InP nanocrystals have larger DCM figure of merit than the other nanocrystals. Our calculations suggest that high DCM efficiency requires high degeneracy of the corresponding bulk band-edge states. Interestingly, by considering band structure effects we find that as the dot size increases the DCM critical energy E0 (the energy at which R2(E) becomes >or=1) is reduced, suggesting improved DCM. However, whether the normalized E0/epsilong increases or decreases as the dot size increases depends on dot material.

  10. Core/Shell semiconductor nanocrystals.

    PubMed

    Reiss, Peter; Protière, Myriam; Li, Liang

    2009-02-01

    Colloidal core/shell nanocrystals contain at least two semiconductor materials in an onionlike structure. The possibility to tune the basic optical properties of the core nanocrystals, for example, their fluorescence wavelength, quantum yield, and lifetime, by growing an epitaxial-type shell of another semiconductor has fueled significant progress on the chemical synthesis of these systems. In such core/shell nanocrystals, the shell provides a physical barrier between the optically active core and the surrounding medium, thus making the nanocrystals less sensitive to environmental changes, surface chemistry, and photo-oxidation. The shell further provides an efficient passivation of the surface trap states, giving rise to a strongly enhanced fluorescence quantum yield. This effect is a fundamental prerequisite for the use of nanocrystals in applications such as biological labeling and light-emitting devices, which rely on their emission properties. Focusing on recent advances, this Review discusses the fundamental properties and synthesis methods of core/shell and core/multiple shell structures of II-VI, IV-VI, and III-V semiconductors.

  11. Oxide Nanocrystal Model Catalysts.

    PubMed

    Huang, Weixin

    2016-03-15

    Model catalysts with uniform and well-defined surface structures have been extensively employed to explore structure-property relationships of powder catalysts. Traditional oxide model catalysts are based on oxide single crystals and single crystal thin films, and the surface chemistry and catalysis are studied under ultrahigh-vacuum conditions. However, the acquired fundamental understandings often suffer from the "materials gap" and "pressure gap" when they are extended to the real world of powder catalysts working at atmospheric or higher pressures. Recent advances in colloidal synthesis have realized controlled synthesis of catalytic oxide nanocrystals with uniform and well-defined morphologies. These oxide nanocrystals consist of a novel type of oxide model catalyst whose surface chemistry and catalysis can be studied under the same conditions as working oxide catalysts. In this Account, the emerging concept of oxide nanocrystal model catalysts is demonstrated using our investigations of surface chemistry and catalysis of uniform and well-defined cuprous oxide nanocrystals and ceria nanocrystals. Cu2O cubes enclosed with the {100} crystal planes, Cu2O octahedra enclosed with the {111} crystal planes, and Cu2O rhombic dodecahedra enclosed with the {110} crystal planes exhibit distinct morphology-dependent surface reactivities and catalytic properties that can be well correlated with the surface compositions and structures of exposed crystal planes. Among these types of Cu2O nanocrystals, the octahedra are most reactive and catalytically active due to the presence of coordination-unsaturated (1-fold-coordinated) Cu on the exposed {111} crystal planes. The crystal-plane-controlled surface restructuring and catalytic activity of Cu2O nanocrystals were observed in CO oxidation with excess oxygen. In the propylene oxidation reaction with O2, 1-fold-coordinated Cu on Cu2O(111), 3-fold-coordinated O on Cu2O(110), and 2-fold-coordinated O on Cu2O(100) were identified

  12. Copper Selenide Nanocrystals as a High Performance, Solution Processed Thermoelectric Material

    NASA Astrophysics Data System (ADS)

    Forster, Jason; Lynch, Jared; Coates, Nelson; Sahu, Ayaskanta; Liu, Jun; Cahill, David; Urban, Jeff

    Nano-structuring a thermoelectric material often results in enhanced performance due to a decrease in the materials' thermal conductivity. Traditional nano-structuring techniques involve ball milling a bulk material followed by spark plasma sintering, a very energy intensive process. In this talk, we will describe the development of a self-assembled, high-performing, nano-structured thin film based on copper selenide nanocrystals. Mild thermal annealing of these films results in concurrent increases in the Seebeck coefficient and electrical conductivity. We are able to achieve power factors at room temperature that are as high as the best spark plasma sintered materials. These solution-processed films have potential applications as conformal, flexible materials for thermoelectric power generation.

  13. Radiative sky cooling: fundamental physics, materials, structures, and applications

    NASA Astrophysics Data System (ADS)

    Sun, Xingshu; Sun, Yubo; Zhou, Zhiguang; Alam, Muhammad Ashraful; Bermel, Peter

    2017-08-01

    Radiative sky cooling reduces the temperature of a system by promoting heat exchange with the sky; its key advantage is that no input energy is required. We will review the origins of radiative sky cooling from ancient times to the modern day, and illustrate how the fundamental physics of radiative cooling calls for a combination of properties that may not occur in bulk materials. A detailed comparison with recent modeling and experiments on nanophotonic structures will then illustrate the advantages of this recently emerging approach. Potential applications of these radiative cooling materials to a variety of temperature-sensitive optoelectronic devices, such as photovoltaics, thermophotovoltaics, rectennas, and infrared detectors, will then be discussed. This review will conclude by forecasting the prospects for the field as a whole in both terrestrial and space-based systems.

  14. The fundamental mechanisms of material removal by fluidjet machining

    SciTech Connect

    Kang, Sang-Wook; Reitter, T.; Carlson, G.

    1994-06-01

    The fundamental mechanisms of material removal by fluidjet machining have been theoretically and experimentally investigated as a potential method for dismantling nuclear weapons with efficiency and safety. Preliminary experiments and analyses have revealed that at small standoff distances between the nozzle exit and the target workpiece there is no mass removal from the workpiece, but that far from the nozzle there exists an optimum standoff distance at which the jet impact removes mass from the workpiece at a maximum rate. Such results suggest a mass-removal process due to the droplets and ligaments impinging on the material that cause sudden pressure increases in the impact regions. This proposed material-removal mechanism has been addressed theoretically by considering a series of multiple droplet impacts on a material. The calculated results display a series of pressure peaks at the target surface as each of these droplets strikes the material, supporting the plausibility of the proposed mass-removal scenario at the optimum standoff distance. Although plausible further experiments and analyses are needed to verify the proposed jet-induced mass removal mechanism.

  15. Advanced materials for magnetic cooling: Fundamentals and practical aspects

    NASA Astrophysics Data System (ADS)

    Balli, M.; Jandl, S.; Fournier, P.; Kedous-Lebouc, A.

    2017-06-01

    Over the last two decades, the research activities on magnetocalorics have been exponentially increased, leading to the discovery of a wide category of materials including intermetallics and oxides. Even though the reported materials were found to show excellent magnetocaloric properties on a laboratory scale, only a restricted family among them could be upscaled toward industrial levels and implemented as refrigerants in magnetic cooling devices. On the other hand, in the most of the reported reviews, the magnetocaloric materials are usually discussed in terms of their adiabatic temperature and entropy changes (ΔTad and ΔS), which is not enough to get more insight about their large scale applicability. In this review, not only the fundamental properties of the recently reported magnetocaloric materials but also their thermodynamic performance in functional devices are discussed. The reviewed families particularly include Gd1-xRx alloys, LaFe13-xSix, MnFeP1-xAsx, and R1-xAxMnO3 (R = lanthanide and A = divalent alkaline earth)-based compounds. Other relevant practical aspects such as mechanical stability, synthesis, and corrosion issues are discussed. In addition, the intrinsic and extrinsic parameters that play a crucial role in the control of magnetic and magnetocaloric properties are regarded. In order to reproduce the needed magnetocaloric parameters, some practical models are proposed. Finally, the concepts of the rotating magnetocaloric effect and multilayered magnetocalorics are introduced.

  16. Colloidal Inorganic Nanocrystal Based Nanocomposites: Functional Materials for Micro and Nanofabrication

    PubMed Central

    Ingrosso, Chiara; Panniello, AnnaMaria; Comparelli, Roberto; Curri, Maria Lucia; Striccoli, Marinella

    2010-01-01

    The unique size- and shape-dependent electronic properties of nanocrystals (NCs) make them extremely attractive as novel structural building blocks for constructing a new generation of innovative materials and solid-state devices. Recent advances in material chemistry has allowed the synthesis of colloidal NCs with a wide range of compositions, with a precise control on size, shape and uniformity as well as specific surface chemistry. By incorporating such nanostructures in polymers, mesoscopic materials can be achieved and their properties engineered by choosing NCs differing in size and/or composition, properly tuning the interaction between NCs and surrounding environment. In this contribution, different approaches will be presented as effective opportunities for conveying colloidal NC properties to nanocomposite materials for micro and nanofabrication. Patterning of such nanocomposites either by conventional lithographic techniques and emerging patterning tools, such as ink jet printing and nanoimprint lithography, will be illustrated, pointing out their technological impact on developing new optoelectronic and sensing devices.

  17. Ligand coupling symmetry correlates with thermopower enhancement in small-molecule/nanocrystal hybrid materials.

    PubMed

    Lynch, Jared; Kotiuga, Michele; Doan-Nguyen, Vicky V T; Queen, Wendy L; Forster, Jason D; Schlitz, Ruth A; Murray, Christopher B; Neaton, Jeffrey B; Chabinyc, Michael L; Urban, Jeffrey J

    2014-10-28

    We investigate the impact of the coupling symmetry and chemical nature of organic-inorganic interfaces on thermoelectric transport in Cu2-xSe nanocrystal thin films. By coupling ligand-exchange techniques with layer-by-layer assembly methods, we are able to systematically vary nanocrystal-organic linker interfaces, demonstrating how the functionality of the polar headgroup and the coupling symmetry of the organic linkers can change the power factor (S(2)σ) by nearly 2 orders of magnitude. Remarkably, we observe that ligand-coupling symmetry has a profound effect on thermoelectric transport in these hybrid materials. We shed light on these results using intuition from a simplified model for interparticle charge transport via tunneling through the frontier orbital of a bound ligand. Our analysis indicates that ligand-coupling symmetry and binding mechanisms correlate with enhanced conductivity approaching 2000 S/cm, and we employ this concept to demonstrate among the highest power factors measured for quantum-dot based thermoelectric inorganic-organic composite materials of ∼ 30 μW/m · K(2).

  18. Hierarchical Materials Design by Pattern Transfer Printing of Self-Assembled Binary Nanocrystal Superlattices.

    PubMed

    Paik, Taejong; Yun, Hongseok; Fleury, Blaise; Hong, Sung-Hoon; Jo, Pil Sung; Wu, Yaoting; Oh, Soong-Ju; Cargnello, Matteo; Yang, Haoran; Murray, Christopher B; Kagan, Cherie R

    2017-03-08

    We demonstrate the fabrication of hierarchical materials by controlling the structure of highly ordered binary nanocrystal superlattices (BNSLs) on multiple length scales. Combinations of magnetic, plasmonic, semiconducting, and insulating colloidal nanocrystal (NC) building blocks are self-assembled into BNSL membranes via the liquid-interfacial assembly technique. Free-standing BNSL membranes are transferred onto topographically structured poly(dimethylsiloxane) molds via the Langmuir-Schaefer technique and then deposited in patterns onto substrates via transfer printing. BNSLs with different structural motifs are successfully patterned into various meso- and microstructures such as lines, circles, and even three-dimensional grids across large-area substrates. A combination of electron microscopy and grazing incidence small-angle X-ray scattering (GISAXS) measurements confirm the ordering of NC building blocks in meso- and micropatterned BNSLs. This technique demonstrates structural diversity in the design of hierarchical materials by assembling BNSLs from NC building blocks of different composition and size by patterning BNSLs into various size and shape superstructures of interest for a broad range of applications.

  19. Fundamental Studies of Crystal Growth of Microporous Materials

    NASA Technical Reports Server (NTRS)

    Dutta, P.; George, M.; Ramachandran, N.; Schoeman, B.; Curreri, Peter A. (Technical Monitor)

    2002-01-01

    Microporous materials are framework structures with well-defined porosity, often of molecular dimensions. Zeolites contain aluminum and silicon atoms in their framework and are the most extensively studied amongst all microporous materials. Framework structures with P, Ga, Fe, Co, Zn, B, Ti and a host of other elements have also been made. Typical synthesis of microporous materials involve mixing the framework elements (or compounds, thereof) in a basic solution, followed by aging in some cases and then heating at elevated temperatures. This process is termed hydrothermal synthesis, and involves complex chemical and physical changes. Because of a limited understanding of this process, most synthesis advancements happen by a trial and error approach. There is considerable interest in understanding the synthesis process at a molecular level with the expectation that eventually new framework structures will be built by design. The basic issues in the microporous materials crystallization process include: (1) Nature of the molecular units responsible for the crystal nuclei formation; (2) Nature of the nuclei and nucleation process; (3) Growth process of the nuclei into crystal; (4) Morphological control and size of the resulting crystal; (5) Surface structure of the resulting crystals; (6) Transformation of frameworks into other frameworks or condensed structures. The NASA-funded research described in this report focuses to varying degrees on all of the above issues and has been described in several publications. Following is the presentation of the highlights of our current research program. The report is divided into five sections: (1) Fundamental aspects of the crystal growth process; (2) Morphological and Surface properties of crystals; (3) Crystal dissolution and transformations; (4) Modeling of Crystal Growth; (5) Relevant Microgravity Experiments.

  20. Fundamental Studies of Crystal Growth of Microporous Materials

    NASA Technical Reports Server (NTRS)

    Dutta, P.; George, M.; Ramachandran, N.; Schoeman, B.; Curreri, Peter A. (Technical Monitor)

    2002-01-01

    Microporous materials are framework structures with well-defined porosity, often of molecular dimensions. Zeolites contain aluminum and silicon atoms in their framework and are the most extensively studied amongst all microporous materials. Framework structures with P, Ga, Fe, Co, Zn, B, Ti and a host of other elements have also been made. Typical synthesis of microporous materials involve mixing the framework elements (or compounds, thereof) in a basic solution, followed by aging in some cases and then heating at elevated temperatures. This process is termed hydrothermal synthesis, and involves complex chemical and physical changes. Because of a limited understanding of this process, most synthesis advancements happen by a trial and error approach. There is considerable interest in understanding the synthesis process at a molecular level with the expectation that eventually new framework structures will be built by design. The basic issues in the microporous materials crystallization process include: (1) Nature of the molecular units responsible for the crystal nuclei formation; (2) Nature of the nuclei and nucleation process; (3) Growth process of the nuclei into crystal; (4) Morphological control and size of the resulting crystal; (5) Surface structure of the resulting crystals; (6) Transformation of frameworks into other frameworks or condensed structures. The NASA-funded research described in this report focuses to varying degrees on all of the above issues and has been described in several publications. Following is the presentation of the highlights of our current research program. The report is divided into five sections: (1) Fundamental aspects of the crystal growth process; (2) Morphological and Surface properties of crystals; (3) Crystal dissolution and transformations; (4) Modeling of Crystal Growth; (5) Relevant Microgravity Experiments.

  1. Tunable PhoXonic Band Gap Materials from Self-Assembly of Block Copoliymers and Colloidal Nanocrystals (NBIT Phase II)

    DTIC Science & Technology

    2011-05-06

    interaction with photons and phonons. Concerning this, we seek to develop methods and understanding to create both periodically structured materials ...this, we seek to develop methods and understanding to create both periodically structured materials (Bragg gap materials ) and non-periodically...Final Report for AOARD Grant 1014069 “Tunable PhoXonic Band Gap Materials from Self-Assembly of Block Copoliymers and Colloidal Nanocrystals

  2. Building robust carbon nanotube-interweaved-nanocrystal architecture for high-performance anode materials.

    PubMed

    Jia, Xilai; Cheng, Yanhua; Lu, Yunfeng; Wei, Fei

    2014-09-23

    Rational design of electrode materials is essential but still a challenge for lithium-ion batteries. Herein, we report the design and fabrication of a class of nanocomposite architecture featured by hierarchically structured composite particles that are built from iron oxide nanocrystals and carbon nanotubes. An aerosol spray drying process was used to synthesize this architecture. Such nanoarchitecture enhanced the ion transport and conductivity that are required for high-power anodes. The large volume changes of the anodes during lithium insertion and extraction are accommodated by the particle's resilience and internal porosity. High reversible capacities, excellent rate capability, and stable performance are attained. The synthesis process is simple and broadly applicable, providing a general approach toward high-performance energy storage materials.

  3. Interconnected MoO2 nanocrystals with carbon nanocoating as high-capacity anode materials for lithium-ion batteries.

    PubMed

    Zhou, Liang; Wu, Hao Bin; Wang, Zhiyu; Lou, Xiong Wen David

    2011-12-01

    A facile one-pot hydrothermal method has been developed for the preparation of carbon-coated MoO(2) nanocrystals. The annealed MoO(2)-C nanocomposite consists of interconnected MoO(2)@C nanocrystals. When evaluated for lithium storage capabilities, these MoO(2)@C nanocrystals exhibit high specific capacities (~640 mA h g(-1) at 200 mA g(-1) and ~575 mA h g(-1) at 400 mA g(-1)) and excellent cycling stability. In view of the excellent lithium storage properties and the ease in large-scale preparation, the as-synthesized MoO(2)-C nanocomposite might be used as promising anode materials for high-performance lithium-ion batteries. © 2011 American Chemical Society

  4. Fundamentals of polycrystalline thin film materials and devices

    SciTech Connect

    Baron, B.N.; Birkmire, R.W.; Phillips, J.E.; Shafarman, W.N.; Hegedus, S.S.; McCandless, B.E. . Inst. of Energy Conversion)

    1991-01-01

    This report presents the results of a one-year research program on polycrystalline thin-film solar cells. The research was conducted to better understand the limitations and potential of solar cells using CuInSe{sub 2} and CdTe by systematically investigating the fundamental relationships linking material processing, material properties, and device behavior. By selenizing Cu and In layers, we fabricated device-quality CuInSe{sub 2} thin films and demonstrated a CuInSe{sub 2} solar cell with 7% efficiency. We added Ga, to increase the band gap of CuInSe{sub 2} devices to increase the open-circuit voltage to 0.55 V. We fabricated and analyzed Cu(InGa)Se{sub 2}/CuInSe{sub 2} devices to demonstrate the potential for combining the benefits of higher V{sub oc} while retaining the current-generating capacity of CuInSe{sub 2}. We fabricated an innovative superstrate device design with more than 5% efficiency, as well as a bifacial spectral-response technique for determining the electron diffusion length and optical absorption coefficient of CuInSe{sub 2} in an operational cell. The diffusion length was found to be greater than 1 {mu}m. We qualitatively modeled the effect of reducing heat treatments in hydrogen and oxidizing treatments in air on the I-V behavior of CuInSe{sub 2} devices. We also investigated post-deposition heat treatments and chemical processing and used them to fabricate a 9.6%-efficient CdTe/CdS solar cell using physical vapor deposition.

  5. Fundamental Formation of Material Particles at All Velocities

    NASA Astrophysics Data System (ADS)

    Zheng-Johansson, J. X.; Johansson, P.-I.

    2003-04-01

    A systematic survey of relevant pivotal experiments leads us to arrive at (I) vacuum comprises substantial entities called aethers and (II) the velocities of light as measured in vacuum c and by a moving observer c', and the observer's velocity v obey the law of vector addition. (I)-(II) facilitate a General Scheme, which leads to (A) from Newton Mechanics solution for vacuum the fundamental formation of basic material particles having a mass, size, charge, etc. and being a de Broglie wave obeying Quantum Mechanics (B) augmentation in the mass, de Broglie wavevector, etc of a moving particle by a factor γ = 1/[1-(v/c)^2]^1/2 (C) length and time contractions of a moving body as measured in the frame in which the body resides (D) coordinate transformation between an inertial frame at rest and one relatively moving, called Galileo-Lorentz transformation (GLT) (E) using GLT the prediction of null-fringe shift of the Michelson-Morley experiment and the Doppler effect of light etc (F) inference of various contemporary empirical rules, incl Uncertainty relation; etc.

  6. Material instability in granular assemblies from fundamentally different models

    NASA Astrophysics Data System (ADS)

    Sibille, L.; Nicot, F.; Donzé, F. V.; Darve, F.

    2007-03-01

    Three fundamentally different models: a phenomenological constitutive relation, a micro-mechanical model and direct numerical simulations by Distinct Element Method (DEM) are compared in this paper. In addition, the local form of Hill's sufficient condition of stability (i.e. the vanishing of the second-order work d2W) is considered to describe material instabilities in granular assemblies. Stress probes in the axisymmetric plane of stress increments are achieved with all three models to check whether d2W vanishes at different stress-strain states. For all the models, cones of unstable stress directions (cones of stress probe directions for which d2W = 0) are found and they appear for stress states strictly inside the plastic limit condition. Thus, independently of the model, a bifurcation domain exists inside the plastic limit condition which can describe the sudden collapses of sand samples observed in laboratory tests before reaching the Mohr-Coulomb criterion. Taking advantage of the different models considered, the vanishing of the second-order work is linked to the existence of non-associated plastic strains and to micro-mechanical bases. Copyright

  7. Nanocrystals Research for Energy Efficient and Clean Energy Technologies:

    SciTech Connect

    Rosenthal, Sandra J

    2013-12-17

    Efforts centered on: nanocrystal photovoltaic fabrication, ultrafast dynamics and aberration-corrected STEM characterization of II-VI core, core/shell and alloyed nanocrystals, and fundamental investigation and applications of ultrasmall white light-emitting CdSe nanocrystal.

  8. 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

  9. 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.

  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. Superior pseudocapacitive behavior of confined lignin nanocrystals for renewable energy-storage materials.

    PubMed

    Kim, Sung-Kon; Kim, Yun Ki; Lee, Hyunjoo; Lee, Sang Bok; Park, Ho Seok

    2014-04-01

    Strong demand for high-performance energy-storage devices has currently motivated the development of emerging capacitive materials that can resolve their critical challenge (i.e., low energy density) and that are renewable and inexpensive energy-storage materials from both environmental and economic viewpoints. Herein, the pseudocapacitive behavior of lignin nanocrystals confined on reduced graphene oxides (RGOs) used for renewable energy-storage materials is demonstrated. The excellent capacitive characteristics of the renewable hybrid electrodes were achieved by synergizing the fast and reversible redox charge transfer of surface-confined quinone and the interplay with electron-conducting RGOs. Accordingly, pseudocapacitors with remarkable rate and cyclic performances (~96 % retention after 3000 cycles) showed a maximum capacitance of 432 F g(-1), which was close to the theoretical capacitance of 482 F g(-1) and sixfold higher than that of RGO (93 F g(-1)). The chemical strategy delineated herein paves the way to develop advanced renewable electrodes for energy-storage applications and understand the redox chemistry of electroactive biomaterials. © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  12. Dual-Size Silicon Nanocrystal-Embedded SiO(x) Nanocomposite as a High-Capacity Lithium Storage Material.

    PubMed

    Park, Eunjun; Yoo, Hyundong; Lee, Jaewoo; Park, Min-Sik; Kim, Young-Jun; Kim, Hansu

    2015-07-28

    SiOx-based materials attracted a great deal of attention as high-capacity Li(+) storage materials for lithium-ion batteries due to their high reversible capacity and good cycle performance. However, these materials still suffer from low initial Coulombic efficiency as well as high production cost, which are associated with the complicated synthesis process. Here, we propose a dual-size Si nanocrystal-embedded SiOx nanocomposite as a high-capacity Li(+) storage material prepared via cost-effective sol-gel reaction of triethoxysilane with commercially available Si nanoparticles. In the proposed nanocomposite, dual-size Si nanocrystals are incorporated into the amorphous SiOx matrix, providing a high capacity (1914 mAh g(-1)) with a notably improved initial efficiency (73.6%) and stable cycle performance over 100 cycles. The highly robust electrochemical and mechanical properties of the dual-size Si nanocrystal-embedded SiOx nanocomposite presented here are mainly attributed to its peculiar nanoarchitecture. This study represents one of the most promising routes for advancing SiOx-based Li(+) storage materials for practical use.

  13. Hybrid fundamental-solution-based FEM for piezoelectric materials

    NASA Astrophysics Data System (ADS)

    Cao, Changyong; Qin, Qing-Hua; Yu, Aibing

    2012-10-01

    In this paper, a new type of hybrid finite element method (FEM), hybrid fundamental-solution-based FEM (HFS-FEM), is developed for analyzing plane piezoelectric problems by employing fundamental solutions (Green's functions) as internal interpolation functions. A modified variational functional used in the proposed model is first constructed, and then the assumed intra-element displacement fields satisfying a priori the governing equations of the problem are constructed by using a linear combination of fundamental solutions at a number of source points located outside the element domain. To ensure continuity of fields over inter-element boundaries, conventional shape functions are employed to construct the independent element frame displacement fields defined over the element boundary. The proposed methodology is assessed by several examples with different boundary conditions and is also used to investigate the phenomenon of stress concentration in infinite piezoelectric medium containing a hole under remote loading. The numerical results show that the proposed algorithm has good performance in numerical accuracy and mesh distortion insensitivity compared with analytical solutions and those from ABAQUS. In addition, some new insights on the stress concentration have been clarified and presented in the paper.

  14. Exciton Dynamics in Alternative Solar Cell Materials: Polymers, Nanocrystals, and Small Molecules

    NASA Astrophysics Data System (ADS)

    Pundsack, Thomas J.

    To keep fossil fuel usage in 2040 even with 2010 usage, 50% of global energy will need to come from alternative sources such as solar cells. While the photovoltaic market is currently dominated by crystalline silicon, there are many low-cost solar cell materials such as conjugated polymers, semiconductor nanocrystals, and organic small molecules which could compete with fossil fuels. To create cost-competitive devices, understanding the excited state dynamics of these materials is necessary. The first section of this thesis looks at aggregation in poly(3-hexylthiophene) (P3HT) which is commonly used in organic photovoltaics. The amount of aggregation in P3HT thin films was controlled by using a mixture of regioregular and regiorandom P3HT. Even with few aggregates present, excited states were found to transfer from amorphous to aggregate domains in <50 fs which could indicate efficient long-range energy transfer. To further study P3HT aggregation, a triblock consisting of two P3HT chains with a coil polymer between them was investigated. By changing solvents, aggregation was induced in a stable and reversible manner allowing for spectroscopic studies of P3HT aggregates in solution. The polarity of the solvent was adjusted, and no change in excited state dynamics was observed implying the excited state has little charge-transfer character. Next, the conduction band density of states for copper zinc tin sulfide nanocrystals (CZTS NCs) was measured using pump-probe spectroscopy and found to be in agreement with theoretical results. The density of states shifted and dilated for smaller NCs indicative of quantum confinement. The excited state lifetime was found to be short (<20 ps) and independent of NC size which could limit the efficiency of CZTS photovoltaic devices. Finally, triplet-triplet annihilation (TTA) was studied in platinum octaethylporphyrin (PtOEP) thin films. By analyzing pump-probe spectra, the product of TTA in PtOEP thin films was assigned to a long

  15. 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.

  16. Luminescent Colloidal Semiconductor Nanocrystals Containing Copper: Synthesis, Photophysics, and Applications.

    PubMed

    Knowles, Kathryn E; Hartstein, Kimberly H; Kilburn, Troy B; Marchioro, Arianna; Nelson, Heidi D; Whitham, Patrick J; Gamelin, Daniel R

    2016-09-28

    Copper-doped semiconductors are classic phosphor materials that have been used in a variety of applications for many decades. Colloidal copper-doped semiconductor nanocrystals have recently attracted a great deal of interest because they combine the solution processability and spectral tunability of colloidal nanocrystals with the unique photoluminescence properties of copper-doped semiconductor phosphors. Although ternary and quaternary semiconductors containing copper, such as CuInS2 and Cu2ZnSnS4, have been studied primarily in the context of their photovoltaic applications, when synthesized as colloidal nanocrystals, these materials have photoluminescence properties that are remarkably similar to those of copper-doped semiconductor nanocrystals. This review focuses on the luminescent properties of colloidal copper-doped, copper-based, and related copper-containing semiconductor nanocrystals. Fundamental investigations into the luminescence of copper-containing colloidal nanocrystals are reviewed in the context of the well-established luminescence mechanisms of bulk copper-doped semiconductors and copper(I) molecular coordination complexes. The use of colloidal copper-containing nanocrystals in applications that take advantage of their luminescent properties, such as bioimaging, solid-state lighting, and luminescent solar concentrators, is also discussed.

  17. Synthesis of Semiconductor Nanocrystals, Focusing on Nontoxic and Earth-Abundant Materials.

    PubMed

    Reiss, Peter; Carrière, Marie; Lincheneau, Christophe; Vaure, Louis; Tamang, Sudarsan

    2016-09-28

    We review the synthesis of semiconductor nanocrystals/colloidal quantum dots in organic solvents with special emphasis on earth-abundant and toxic heavy metal free compounds. Following the Introduction, section 2 defines the terms related to the toxicity of nanocrystals and gives a comprehensive overview on toxicity studies concerning all types of quantum dots. Section 3 aims at providing the reader with the basic concepts of nanocrystal synthesis. It starts with the concepts currently used to describe the nucleation and growth of monodisperse particles and next takes a closer look at the chemistry of the inorganic core and its interactions with surface ligands. Section 4 reviews in more detail the synthesis of different families of semiconductor nanocrystals, namely elemental group IV compounds (carbon nanodots, Si, Ge), III-V compounds (e.g., InP, InAs), and binary and multinary metal chalcogenides. Finally, the authors' view on the perspectives in this field is given.

  18. A Review: Fundamental Aspects of Silicate Mesoporous Materials

    PubMed Central

    ALOthman, Zeid A.

    2012-01-01

    Silicate mesoporous materials have received widespread interest because of their potential applications as supports for catalysis, separation, selective adsorption, novel functional materials, and use as hosts to confine guest molecules, due to their extremely high surface areas combined with large and uniform pore sizes. Over time a constant demand has developed for larger pores with well-defined pore structures. Silicate materials, with well-defined pore sizes of about 2.0–10.0 nm, surpass the pore-size constraint (<2.0 nm) of microporous zeolites. They also possess extremely high surface areas (>700 m2 g−1) and narrow pore size distributions. Instead of using small organic molecules as templating compounds, as in the case of zeolites, long chain surfactant molecules were employed as the structure-directing agent during the synthesis of these highly ordered materials. The structure, composition, and pore size of these materials can be tailored during synthesis by variation of the reactant stoichiometry, the nature of the surfactant molecule, the auxiliary chemicals, the reaction conditions, or by post-synthesis functionalization techniques. This review focuses mainly on a concise overview of silicate mesoporous materials together with their applications. Perusal of the review will enable researchers to obtain succinct information about microporous and mesoporous materials.

  19. Photoactive hybrid material based on pyrene functionalized PbS nanocrystals decorating CVD monolayer graphene.

    PubMed

    Ingrosso, Chiara; Bianco, Giuseppe V; Corricelli, Michela; Comparelli, Roberto; Altamura, Davide; Agostiano, Angela; Striccoli, Marinella; Losurdo, Maria; Curri, M Lucia; Bruno, Giovanni

    2015-02-25

    A simple and facile solution-based procedure is implemented for decorating a large area, monolayer graphene film, grown by chemical vapor deposition, with size-tunable light absorbing colloidal PbS nanocrystals (NCs). The hybrid is obtained by exposing a large area graphene film to a solution of 1-pyrene butyric acid surface coated PbS NCs, obtained by a capping exchange procedure onto presynthesized organic-capped NCs. The results demonstrate that at the interface, multiple and cooperative π-π stacking interactions promoted by the pyrene ligand coordinating the NC surface lead to a successful anchoring of the nano-objects on the graphene platform which concomitantly preserves its aromatic structure. Interligand interactions provide organization of the nano-objects in highly interconnected nanostructured multilayer coatings, where the NCs retain geometry and composition. The resulting hybrid exhibits a sheet resistance lower than that of bare graphene, which is explained in terms of electronic communication in the hybrid, due to the interconnection of the NC film and to a hole transfer from photoexcited PbS NCs to graphene, channelled at the interface by pyrene. Such a direct electron coupling makes the manufactured hybrid material an interesting component for optoelectronics, sensors and for optical communication and information technology.

  20. Fundamental Study of Material Flow in Friction Stir Welds

    NASA Technical Reports Server (NTRS)

    Reynolds, Anthony P.

    1999-01-01

    The presented research project consists of two major parts. First, the material flow in solid-state, friction stir, butt-welds as been investigated using a marker insert technique. Changes in material flow due to welding parameter as well as tool geometry variations have been examined for different materials. The method provides a semi-quantitative, three-dimensional view of the material transport in the welded zone. Second, a FSW process model has been developed. The fully coupled model is based on fluid mechanics; the solid-state material transport during welding is treated as a laminar, viscous flow of a non-Newtonian fluid past a rotating circular cylinder. The heat necessary for the material softening is generated by deformation of the material. As a first step, a two-dimensional model, which contains only the pin of the FSW tool, has been created to test the suitability of the modeling approach and to perform parametric studies of the boundary conditions. The material flow visualization experiments agree very well with the predicted flow field. Accordingly, material within the pin diameter is transported only in the rotation direction around the pin. Due to the simplifying assumptions inherent in the 2-D model, other experimental data such as forces on the pin, torque, and weld energy cannot be directly used for validation. However, the 2-D model predicts the same trends as shown in the experiments. The model also predicts a deviation from the "normal" material flow at certain combinations of welding parameters, suggesting a possible mechanism for the occurrence of some typical FSW defects. The next step has been the development of a three-dimensional process model. The simplified FSW tool has been designed as a flat shoulder rotating on the top of the workpiece and a rotating, cylindrical pin, which extends throughout the total height of the flow domain. The thermal boundary conditions at the tool and at the contact area to the backing plate have been varied

  1. "Diffuse Scattering and the Fundamental Properties of materials"

    SciTech Connect

    Barabash, Rozaliya; Ice, Gene E; Turchi, Dr. Patrice E.A.

    2009-01-01

    This book highlights emerging research areas that exploit the ability of diffuse scattering to characterize local structures in materials. An emphasis is placed on the coming renaissance in diffuse scattering driven by new sources, better instrumentation, novel new materials, and advanced theories and methods. This book will provide an overview of some of the most exciting recent advances in diffuse scattering and provides guidance for students and researchers interested in new methods to characterize their samples.

  2. A Fundamental Investigation into the Joining of Advanced Light Materials

    DTIC Science & Technology

    1991-11-25

    materials to replace conventional elevated-temperature aluminum alloys (eg., 2XXX series alloys) and titanium alloys. The effective utilization of...effective utilization of Al-Fe-V-Si al- loys in structural applications as potential replacements for conventional elevated- temperature aluminum ...Fo-V- Si alloys are currently being considered as a strong candidate material to replace titanium alloys and conventional high- strength aluminum

  3. Fundamental Understanding and Theoretical Design of Novel Nanostructured Semiconductor Materials

    DTIC Science & Technology

    2012-01-04

    approach, and transport properties including electrical conductivity and Seebeck coefficients using our newly developed transport codes. Specific...photovoltaic materials and transparent conducting oxides. Electronic structure and volume effect on thermoelectric transport in p-type Bi and Sb...technologies. The efficiency of TE materials is represented by the figure of merit, ZT=SlaT/ (Ke+K/.), where S is the Seebeck coefficient, a is the electrical

  4. Biomineralization: Nanocrystals by design

    NASA Astrophysics Data System (ADS)

    Shang, Li; Nienhaus, Gerd Ulrich

    2015-10-01

    Nanocrystals with precisely defined structures offer promise as components of advanced materials yet they are challenging to create. Now, a nanocrystal made up of seven cadmium and twelve chloride ions has been synthesized via a biotemplating approach that uses a de novo designed protein.

  5. Fundamental Studies of Crystal Growth of Microporous Materials

    NASA Technical Reports Server (NTRS)

    Singh, Ramsharan; Doolittle, John, Jr.; Payra, Pramatha; Dutta, Prabir K.; George, Michael A.; Ramachandran, Narayanan; Schoeman, Brian J.

    2003-01-01

    Microporous materials are framework structures with well-defined porosity, often of molecular dimensions. Zeolites contain aluminum and silicon atoms in their framework and are the most extensively studied amongst all microporous materials. Framework structures with P, Ga, Fe, Co, Zn, B, Ti and a host of other elements have also been made. Typical synthesis of microporous materials involve mixing the framework elements (or compounds, thereof) in a basic solution, followed by aging in some cases and then heating at elevated temperatures. This process is termed hydrothermal synthesis, and involves complex chemical and physical changes. Because of a limited understanding of this process, most synthesis advancements happen by a trial and error approach. There is considerable interest in understanding the synthesis process at a molecular level with the expectation that eventually new framework structures will be built by design. The basic issues in the microporous materials crystallization process include: (a) Nature of the molecular units responsible for the crystal nuclei formation; (b) Nature of the nuclei and nucleation process; (c) Growth process of the nuclei into crystal; (d) Morphological control and size of the resulting crystal; (e) Surface structure of the resulting crystals; and (f) Transformation of frameworks into other frameworks or condensed structures.

  6. Charge-tunable quantum plasmons in colloidal semiconductor nanocrystals.

    PubMed

    Schimpf, Alina M; Thakkar, Niket; Gunthardt, Carolyn E; Masiello, David J; Gamelin, Daniel R

    2014-01-28

    Nanomaterials exhibiting plasmonic optical responses are impacting sensing, information processing, catalysis, solar, and photonics technologies. Recent advances have expanded the portfolio of plasmonic nanostructures into doped semiconductor nanocrystals, which allow dynamic manipulation of carrier densities. Once interpreted as intraband single-electron transitions, the infrared absorption of doped semiconductor nanocrystals is now commonly attributed to localized surface plasmon resonances and analyzed using the classical Drude model to determine carrier densities. Here, we show that the experimental plasmon resonance energies of photodoped ZnO nanocrystals with controlled sizes and carrier densities diverge from classical Drude model predictions at small sizes, revealing quantum plasmons in these nanocrystals. A Lorentz oscillator model more adequately describes the data and illustrates a closer link between plasmon resonances and single-electron transitions in semiconductors than in metals, highlighting a fundamental contrast between these two classes of plasmonic materials.

  7. Ultrafast laser diagnostics to investigate initiation fundamentals in energetic materials.

    SciTech Connect

    Farrow, Darcie; Jilek, Brook Anton; Kohl, Ian Thomas; Kearney, Sean Patrick

    2013-08-01

    We present the results of a two year early career LDRD project, which has focused on the development of ultrafast diagnostics to measure temperature, pressure and chemical change during the shock initiation of energetic materials. We compare two single-shot versions of femtosecond rotational CARS to measure nitrogen temperature: chirped-probe-pulse and ps/fs hybrid CARS thermometry. The applicability of measurements to the combustion of energetic materials will be discussed. We have also demonstrated laser shock and particle velocity measurements in thin film explosives using stretched femtosecond laser pulses. We will discuss preliminary results from Al and PETN thin films. Agreement between our results and previous work will be discussed.

  8. Fundamental ignition study for material fire safety improvement, part 2

    NASA Technical Reports Server (NTRS)

    Paciorek, K. L.; Kratzer, R. H.; Kaufman, J.

    1971-01-01

    The autoignition behavior of polymeric compositions in oxidizing media was investigated as well as the nature and relative concentration of the volatiles produced during oxidative decomposition culminating in combustion. The materials investigated were Teflon, Fluorel KF-2140 raw gum and its compounded versions Refset and Ladicote, 45B3 intumenscent paint, and Ames isocyanurate foam. The majority of the tests were conducted using a stagnation burner arrangement which provided a laminar gas flow and allowed the sample block and gas temperatures to be varied independently. The oxidizing atmospheres were essentially air and oxygen, although in the case of the Fluorel family of materials, due to partial blockage of the gas inlet system, some tests were performed unintentionally in enriched air (not oxygen). The 45B3 paint was not amenable to sampling in a dynamic system, due to its highly intumescent nature. Consequently, selected experiments were conducted using a sealed tube technique both in air and oxygen media.

  9. Materials Properties at Internal Interfaces: Fundamental Atomic Issues

    SciTech Connect

    Browning, Nigel D.

    2014-09-12

    During the course of this research, the microscopy methods were applied to many different systems (see publication list). However, the work can be broadly classified into three main areas: the statistical distribution of grain boundary structures under different doping conditions, the identification of individual dopant atoms in oxide materials, and the evaluation of nucleation and growth processes in liquid and more recently. The main results from each of these efforts will be discussed in the final report.

  10. Silicon Nanocrystal Laser

    SciTech Connect

    Yu, J

    2005-03-09

    The purpose of this feasibility study project was to attempt to demonstrate the silicon-nanocrystal-based laser. Such a silicon laser (made using conventional silicon-manufacturing technologies) would provide the crucial missing link that would enable a completely-silicon-based photonic system. We prepared thin layers of silicon nanocrystal material by ion-implanting Si in fused silica substrates, followed by a high temperature anneal process. These Si nanocrystals produced intense photoluminescence when optically pumped with ultraviolet light. Laser structures based on Fabry-Perot cavity and distributed feedback (DFB) designs were fabricated using the Si nanocrystals as the ''lasing'' medium. We optically pumped the samples with CW lasers at 413nm wavelength to quickly assess the feasibility of making lasers out of the Nanocrystal Si material and to verify the gain coefficients reported by other research groups.

  11. 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.

  12. 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.

  13. Cellulose nanocrystals in nanocomposite approach: Green and high-performance materials for industrial, biomedical and agricultural applications

    NASA Astrophysics Data System (ADS)

    Fortunati, E.; Torre, L.

    2016-05-01

    The need to both avoid wastes and find new renewable resources has led to a new and promising research based on the possibility to revalorize the biomass producing sustainable chemicals and/or materials which may play a major role in replacing systems traditionally obtained from non-renewable sources. Most of the low-value biomass is termed lignocellulosic, referring to its main constituent biopolymers: cellulose, hemicelluloses and lignin. In this context, nanocellulose, and in particular cellulose nanocrystals (CNC), have gain considerable attention as nanoreinforcement for polymer matrices, mainly biodegradable. Derived from the most abundant polymeric resource in nature and with inherent biodegradability, nanocellulose is an interesting nanofiller for the development of nanocomposites for industrial, biomedical and agricultural applications. Due to the high amount of hydroxyl groups on their surface, cellulose nanocrystals are easy to functionalize. Well dispersed CNC are able, in fact, to enhance several properties of polymers, i.e.: thermal, mechanical, barrier, surface wettability, controlled of active compound and/or drug release. The main objective here is to give a general overview of CNC applications, summarizing our recent developments of bio-based nanocomposite formulations reinforced with cellulose nanocrystals extracted from different natural sources and/or wastes for food packaging, medical and agricultural sectors.

  14. Fundamental problems in porous materials: Experiments & computer simulation

    NASA Astrophysics Data System (ADS)

    Xu, Zhanping

    Porous materials have attracted massive scientific and technological interest because of their extremely high surface-to-volume ratio, molecular tunability in construction, and surface-based applications. Through my PhD work, porous materials were engineered to meet the design in selective binding, self-healing, and energy damping. For example, crystalline MOFs with pore size spanning from a few angstroms to a couple of nanometers were chemically engineered to show 120 times more efficiency in binding of large molecules. In addition, we found building blocks released from those crystals can be further patched back through a healing process at ambient and low temperatures down to -56 °C. When building blocks are replaced with graphenes, ultra-flyweight aerogels with pore size larger than 100 nm were made to delay shock waves. More stable rigid porous metal with larger pores (~um) was also fabricated, and its performance and survivability are under investigation. Aside from experimental studies, we also successfully applied numerical simulations to study the mutual interaction between the nonplanar liquid-solid interface and colloidal particles during the freezing of the colloidal suspensions. Colloidal particles can be either rejected or engulfed by the evolving interface depending on the freezing speed and strength of interface-particle interaction. Our interactive simulation was achieved by programming both simulation module and visualization module on high performance GPU devices.

  15. High surface area silicon materials: fundamentals and new technology.

    PubMed

    Buriak, Jillian M

    2006-01-15

    Crystalline silicon forms the basis of just about all computing technologies on the planet, in the form of microelectronics. An enormous amount of research infrastructure and knowledge has been developed over the past half-century to construct complex functional microelectronic structures in silicon. As a result, it is highly probable that silicon will remain central to computing and related technologies as a platform for integration of, for instance, molecular electronics, sensing elements and micro- and nanoelectromechanical systems. Porous nanocrystalline silicon is a fascinating variant of the same single crystal silicon wafers used to make computer chips. Its synthesis, a straightforward electrochemical, chemical or photochemical etch, is compatible with existing silicon-based fabrication techniques. Porous silicon literally adds an entirely new dimension to the realm of silicon-based technologies as it has a complex, three-dimensional architecture made up of silicon nanoparticles, nanowires, and channel structures. The intrinsic material is photoluminescent at room temperature in the visible region due to quantum confinement effects, and thus provides an optical element to electronic applications. Our group has been developing new organic surface reactions on porous and nanocrystalline silicon to tailor it for a myriad of applications, including molecular electronics and sensing. Integration of organic and biological molecules with porous silicon is critical to harness the properties of this material. The construction and use of complex, hierarchical molecular synthetic strategies on porous silicon will be described.

  16. Fundamental Materials Studies for Advanced High Power Microwave and Terahertz Vacuum Electronic Radiation Sources

    DTIC Science & Technology

    2014-12-10

    AFRL-OSR-VA-TR-2014-0359 Fundamental Materials Studies for Advanced High Power Microwave and Terahertz John Booske UNIVERSITY OF WISCONSIN SYSTEM...12-2014 Final Technical Performance Report October 1, 2011 - September 30, 2014 Fundamental Materials Studies for Advanced High Power Microwave and...based upon the perovskite structure that have potential to provide superior high power microwave (vacuum electronic) device cathodes (thermionic or

  17. Fundamental Study of Interactions Between Pulsed High-Density Plasmas and Materials for Space Propulsion

    DTIC Science & Technology

    2016-05-23

    AFRL-AFOSR-VA-TR-2016-0199 FUNDAMENTAL STUDY OF INTERACTIONS BETWEEN PULSED HIGH-DENSITY PLASMAS AND MATERIALS FOR SPACE PROPULSION LAXAMIRIAN RAJA...CONTRACT NUMBER FA9550-11-1-0062 FUNDAMENTAL STUDY OF INTERACTIONS BETWEEN PULSED HIGH-DENSITY LASMAS AND MATERIALS FOR SPACE PROPULSION 5b. GRANT... SPACE PROPULSION Principal Investigators: L. L. Raja, I. McNab, F. Stefani, R. D. Bengtson, G. Henkelman, F. Stefani The University of Texas at

  18. Reversible solvent vapor-mediated phase changes in nanocrystal superlattices.

    PubMed

    Goodfellow, Brian W; Korgel, Brian A

    2011-04-26

    Colloidal nanocrystals are being explored for use in a variety of applications, from solar cells to transistors to medical diagnostics and therapy. Ordered assemblies of nanocrystals, or superlattices, are one particularly interesting class of these materials, in which the nanocrystals serve as modular building blocks to construct nanostructures by self-assembly with spatial and temporal complexity and unique properties. From a fundamental perspective, the nanocrystals are simple molecular models that can be manipulated and studied to test statistical mechanical and thermodynamic models of crystallization and disorder. An article by Bian et al. in this issue of ACS Nano reports surprising new phase behavior in semiconductor nanocrystal superlattices: reversible transitions between non-close-packed body-centered cubic (bcc) and body-centered tetragonal (bct) structures, and close-packed face-centered cubic (fcc) structures, observed by real-time in situ grazing incidence small-angle X-ray scattering (GISAXS) measurements, upon solvent vapor exposure and increased interparticle separation. These studies offer new insight and raise new questions about superlattice structure and the forces that control self-assembly. Accompanying computer simulations show that ligand-ligand interactions are important. Furthermore, it appears that ligand-coated nanocrystals have more in common with soft microphase-separated materials, like diblock copolymers and surfactant assemblies, than previously realized.

  19. 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.

  20. On Ultrasmall Nanocrystals

    PubMed Central

    McBride, James R.; Dukes, Albert D.; Schreuder, Michael A.; Rosenthal, Sandra J.

    2010-01-01

    Ultrasmall nanocrystals are a growing sub-class of traditional nanocrystals that exhibit new properties at diameters typically below 2 nm. In this review, we define what constitutes an ultrasmall nanoparticle while distinguishing between ultrasmall and magic-size nanoparticles. After a brief overview of ultrasmall nanoparticles, including ultrasmall gold clusters, our recent work is presented covering the optical properties, structure, and application of ultrasmall CdSe nanocrystals. This unique material has potential application in solid state lighting due to its balanced white emission. This section is followed by a discussion on the blurring boundary between what can be considered a nanoparticle and a molecule. PMID:21132106

  1. Biomolecularly capped uniformly sized nanocrystalline materials: glutathione-capped ZnS nanocrystals

    NASA Astrophysics Data System (ADS)

    Torres-Martínez, Claudia L.; Nguyen, Liem; Kho, Richard; Bae, Weon; Bozhilov, Krassimir; Klimov, Victor; Mehra, Rajesh K.

    1999-09-01

    Micro-organisms such as bacteria and yeasts form CdS to detoxify toxic cadmium ions. Frequently, CdS particles formed in yeasts and bacteria were found to be associated with specific biomolecules. It was later determined that these biomolecules were present at the surface of CdS. This coating caused a restriction in the growth of CdS particles and resulted in the formation of nanometre-sized semiconductors (NCs) that exhibited typical quantum confinement properties. Glutathione and related phytochelatin peptides were shown to be the biomolecules that capped CdS nanocrystallites synthesized by yeasts Candida glabrata and Schizosaccharomyces pombe. Although early studies showed the existence of specific biochemical pathways for the synthesis of biomolecularly capped CdS NCs, these NCs could be formed in vitro under appropriate conditions. We have recently shown that cysteine and cysteine-containing peptides such as glutathione and phytochelatins can be used in vitro to dictate the formation of discrete sizes of CdS and ZnS nanocrystals. We have evolved protocols for the synthesis of ZnS or CdS nanocrystals within a narrow size distribution range. These procedures involve three steps: (1) formation of metallo-complexes of cysteine or cysteine-containing peptides, (2) introduction of stoichiometric amounts of inorganic sulfide into the metallo-complexes to initiate the formation of nanocrystallites and finally (3) size-selective precipitation of NCs with ethanol in the presence of Na+. The resulting NCs were characterized by optical spectroscopy, high-resolution transmission electron microscopy (HRTEM), x-ray diffraction and electron diffraction. HRTEM showed that the diameter of the ZnS-glutathione nanocrystals was 3.45+/-0.5 nm. X-ray diffraction and electron diffraction analyses indicated ZnS-glutathione to be hexagonal. Photocatalytic studies suggest that glutathione-capped ZnS nanocrystals prepared by our procedure are highly efficient in degrading a test model

  2. Ultrafine and well dispersed silver nanocrystals on 2D nanosheets: synthesis and application as a multifunctional material for electrochemical catalysis and biosensing.

    PubMed

    Gao, Tao; Yang, Dawei; Ning, Limin; Lei, Lin; Ye, Zonghuang; Li, Genxi

    2014-12-21

    The strong coupling of inorganic nanocrystals with 2D nanosheets to produce function-enhanced nano-materials with uniform size, dispersion, and high coverage density has long been of interest to scientists from various research fields. Here, a simple and effective method has been described to fabricate ultrafine and well dispersed silver nanocrystals (AgNCs) on graphene oxide (GO), based on a facial-induced co-reduction strategy. The synthesized nanohybrid has shown uniform and well dispersed AgNCs (2.9 ± 1.4 nm), individually separated GO sheets, as well as highly covered surface (5250 nanocrystals per square micrometer), indicating the formation of a high-quality GO-based nanohybrid. Moreover, this material shows excellent catalytic activity for oxygen reduction reactions (ORRs) and exhibits enhanced signal readout for molecular sensing, demonstrating the potential application of this newly synthesized inorganic hybrid with strong synergistic coupling effects on advanced functional systems.

  3. The 12-3-12 cationic gemini surfactant as a novel gastrointestinal bioadhesive material for improving the oral bioavailability of coenzyme Q10 naked nanocrystals.

    PubMed

    Song, Yanzhi; Han, Jie; Feng, Rui; Wang, Mengjing; Tian, Qingjing; Zhang, Ting; Liu, Xinrong; Cheng, Xiaobo; Deng, Yihui

    2016-12-01

    To improve the oral bioavailability of nanocrystalline drug preparations, the cationic 12-3-12 quaternary ammonium surfactant gemini was introduced into nanocrystals as a novel gastrointestinal bioadhesive material. Coenzyme Q10 (CoQ10), a typical Biopharmaceutics Classification System (BCS) class II drug, was used as a model drug. The 12-3-12 gemini surfactant was added to the preparation at a low concentration and imbued the particles with abundant positive charges. In vitro and in vivo gastrointestinal adhesion tests confirmed that the gemini-modified nanocrystals were prone to adhere to the upper gastrointestinal tract (GIT), thereby prolonging retention time in the GIT and enhancing absorption. In the distribution study in rats, the use of nanocrystals modified with gemini led to greater drug distribution to the heart and the liver than that achieved with the naked nanocrystals. A pharmacokinetic study in beagle dogs showed that the gemini-modified CoQ10 nanocrystals improved the oral bioavailability of CoQ10 in a dose-dependent manner, and the smaller size produced a much better effect with the same gemini modification. These results demonstrate that the cationic surfactant gemini is a promising oral bioadhesive material with applications in nanoscale drug delivery systems.

  4. Ultrafine and well dispersed silver nanocrystals on 2D nanosheets: synthesis and application as a multifunctional material for electrochemical catalysis and biosensing

    NASA Astrophysics Data System (ADS)

    Gao, Tao; Yang, Dawei; Ning, Limin; Lei, Lin; Ye, Zonghuang; Li, Genxi

    2014-11-01

    The strong coupling of inorganic nanocrystals with 2D nanosheets to produce function-enhanced nano-materials with uniform size, dispersion, and high coverage density has long been of interest to scientists from various research fields. Here, a simple and effective method has been described to fabricate ultrafine and well dispersed silver nanocrystals (AgNCs) on graphene oxide (GO), based on a facial-induced co-reduction strategy. The synthesized nanohybrid has shown uniform and well dispersed AgNCs (2.9 +/- 1.4 nm), individually separated GO sheets, as well as highly covered surface (5250 nanocrystals per square micrometer), indicating the formation of a high-quality GO-based nanohybrid. Moreover, this material shows excellent catalytic activity for oxygen reduction reactions (ORRs) and exhibits enhanced signal readout for molecular sensing, demonstrating the potential application of this newly synthesized inorganic hybrid with strong synergistic coupling effects on advanced functional systems.The strong coupling of inorganic nanocrystals with 2D nanosheets to produce function-enhanced nano-materials with uniform size, dispersion, and high coverage density has long been of interest to scientists from various research fields. Here, a simple and effective method has been described to fabricate ultrafine and well dispersed silver nanocrystals (AgNCs) on graphene oxide (GO), based on a facial-induced co-reduction strategy. The synthesized nanohybrid has shown uniform and well dispersed AgNCs (2.9 +/- 1.4 nm), individually separated GO sheets, as well as highly covered surface (5250 nanocrystals per square micrometer), indicating the formation of a high-quality GO-based nanohybrid. Moreover, this material shows excellent catalytic activity for oxygen reduction reactions (ORRs) and exhibits enhanced signal readout for molecular sensing, demonstrating the potential application of this newly synthesized inorganic hybrid with strong synergistic coupling effects on advanced

  5. Substitutional doping in nanocrystal superlattices

    NASA Astrophysics Data System (ADS)

    Cargnello, Matteo; Johnston-Peck, Aaron C.; Diroll, Benjamin T.; Wong, Eric; Datta, Bianca; Damodhar, Divij; Doan-Nguyen, Vicky V. T.; Herzing, Andrew A.; Kagan, Cherie R.; Murray, Christopher B.

    2015-08-01

    Doping is a process in which atomic impurities are intentionally added to a host material to modify its properties. It has had a revolutionary impact in altering or introducing electronic, magnetic, luminescent, and catalytic properties for several applications, for example in semiconductors. Here we explore and demonstrate the extension of the concept of substitutional atomic doping to nanometre-scale crystal doping, in which one nanocrystal is used to replace another to form doped self-assembled superlattices. Towards this goal, we show that gold nanocrystals act as substitutional dopants in superlattices of cadmium selenide or lead selenide nanocrystals when the size of the gold nanocrystal is very close to that of the host. The gold nanocrystals occupy random positions in the superlattice and their density is readily and widely controllable, analogous to the case of atomic doping, but here through nanocrystal self-assembly. We also show that the electronic properties of the superlattices are highly tunable and strongly affected by the presence and density of the gold nanocrystal dopants. The conductivity of lead selenide films, for example, can be manipulated over at least six orders of magnitude by the addition of gold nanocrystals and is explained by a percolation model. As this process relies on the self-assembly of uniform nanocrystals, it can be generally applied to assemble a wide variety of nanocrystal-doped structures for electronic, optical, magnetic, and catalytic materials.

  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. 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.

  8. Nanomechanics of silk: the fundamentals of a strong, tough and versatile material

    NASA Astrophysics Data System (ADS)

    Su, Isabelle; Buehler, Markus J.

    2016-07-01

    Spider silk is a remarkable material that provides a template for upscaling molecular properties to the macroscale. In this article we review fundamental aspects of the mechanisms behind these behaviors, discuss the molecular makeup, chemical designs, and how these integrate in a complex arrangement to form webs, cocoons and other material architectures. Moreover, this review paper explores the unique ability of silk to tolerate various kinds of defects, in a way enabling this material platform to serve as one of the most resilient materials in nature. We conclude the discussion with a summary of key scaling laws, an attempt model and define hierarchical length-scales, and the translation to synthetic materials.

  9. Synthesis and Characterization of Microencapsulated Phase Change Materials with Poly(urea-urethane) Shells Containing Cellulose Nanocrystals.

    PubMed

    Yoo, Youngman; Martinez, Carlos; Youngblood, Jeffrey P

    2017-09-20

    The main objective of this study is to develop microencapsulation technology for thermal energy storage incorporating a phase change material (PCM) in a composite wall shell, which can be used to create a stable environment and allow the PCM to undergo phase change without any outside influence. Surface modification of cellulose nanocrystals (CNCs) was conducted by grafting poly(lactic acid) oligomers and oleic acid to improve the dispersion of nanoparticles in a polymeric shell. A microencapsulated phase change material (methyl laurate) with poly(urea-urethane) (PU) composite shells containing the hydrophobized cellulose nanocrystals (hCNCs) was fabricated using an in situ emulsion interfacial polymerization process. The encapsulation process of the PCMs with subsequent interfacial hCNC-PU to form composite microcapsules as well as their morphology, composition, thermal properties, and release rates was examined in this study. Oil soluble Sudan II dye solution in methyl laurate was used as a model hydrophobic fill, representing other latent fills with low partition coefficients, and their encapsulation efficiency as well as dye release rates were measured spectroscopically in a water medium. The influence of polyol content in the PU polymer matrix of microcapsules was investigated. An increase in polyol contents leads to an increase in the mean size of microcapsules but a decrease in the gel content (degree of cross-linking density) and permeability of their shell structure. The encapsulated PCMs for thermal energy storage demonstrated here exhibited promising performance for possible use in building or paving materials in terms of released heat, desired phase transformation temperature, chemical and physical stability, and concrete durability during placement.

  10. Fundamentals of Materials Science and Engineering: An Integrated Approach, 2nd Edition

    NASA Astrophysics Data System (ADS)

    Callister, William D., Jr.

    2004-04-01

    This Second Edition of Fundamentals of Materials Science and Engineering continues to take an integrated approach to the topic organization. One specific structure, characteristic, or property type at a time is discussed for all three basic material types--metals, ceramics, and polymeric materials. This order of presentation allows for early introduction of non-metals and supports the engineer's role of choosing a material based on its characteristics. New copies of this text include a CD at no additional charge. The CD is an integral part of the text package and features animated software modules and the last five text chapters in .pdf format.

  11. Structural Transformation of Li-Excess Cathode Materials via Facile Preparation and Assembly of Sonication-Induced Colloidal Nanocrystals for Enhanced Lithium Storage Performance.

    PubMed

    Zhao, Jianqing; Huang, Ruiming; Ramos, Pablo; Yue, Yiying; Wu, Qinglin; Pavanello, Michele; Zhou, Jieyu; Kuai, Xiaoxiao; Gao, Lijun; He, Huixin; Wang, Ying

    2017-09-13

    A surfactant-free sonication-induced route is developed to facilely prepare colloidal nanocrystals of Li-excess layered Li1.2Mn0.54Ni0.13Co0.13O2 (marked as LMNCO) material. The sonication process plays a critical role in forming LMNCO nanocrystals in ethanol (ethanol molecules marked as EtOHs) and inducing the interaction between LMNCO and solvent molecules. The formation mechanism of LMNCO-EtOH supramolecules in the colloidal dispersion system is proposed and examined by the theoretical simulation and light scattering technique. It is suggested that the as-formed supramolecule is composed of numerous ethanol molecules capping the surface of the LMNCO nanocrystal core via hydrogen bonding. Such chemisorption gives rise to dielectric polarization of the absorbed ethanol molecules, resulting in a negative surface charge of LMNCO colloids. The self-assembly behaviors of colloidal LMNCO nanocrystals are then tentatively investigated by tuning the solvent evaporation condition, which results in diverse superstructures of LMNCO materials after the evaporation of ethanol. The reassembled LMNCO architectures exhibit remarkably improved capacity and cyclability in comparison with the original LMNCO particles, demonstrating a very promising cathode material for high-energy lithium-ion batteries. This work thus provides new insights into the formation and self-assembly of multiple-element complex inorganic colloids in common and surfactant-free solvents for enhanced performance in device applications.

  12. Military Curriculum Materials for Vocational and Technical Education. Fundamentals of Electricity, 3-7.

    ERIC Educational Resources Information Center

    Ohio State Univ., Columbus. National Center for Research in Vocational Education.

    This self-paced correspondence course for independent study in electricity was adapted from military curriculum materials for use in vocational education. This basic course is designed to provide the student with some fundamentals of electricity--not with specific job skills. The seven lessons of the course each have a lesson assignment sheet with…

  13. Ultra-small photoluminescent silicon-carbide nanocrystals by atmospheric-pressure plasmas.

    PubMed

    Askari, Sadegh; Ul Haq, Atta; Macias-Montero, Manuel; Levchenko, Igor; Yu, Fengjiao; Zhou, Wuzong; Ostrikov, Kostya Ken; Maguire, Paul; Svrcek, Vladimir; Mariotti, Davide

    2016-10-06

    Highly size-controllable synthesis of free-standing perfectly crystalline silicon carbide nanocrystals has been achieved for the first time through a plasma-based bottom-up process. This low-cost, scalable, ligand-free atmospheric pressure technique allows fabrication of ultra-small (down to 1.5 nm) nanocrystals with very low level of surface contamination, leading to fundamental insights into optical properties of the nanocrystals. This is also confirmed by their exceptional photoluminescence emission yield enhanced by more than 5 times by reducing the nanocrystals sizes in the range of 1-5 nm, which is attributed to quantum confinement in ultra-small nanocrystals. This method is potentially scalable and readily extendable to a wide range of other classes of materials. Moreover, this ligand-free process can produce colloidal nanocrystals by direct deposition into liquid, onto biological materials or onto the substrate of choice to form nanocrystal films. Our simple but efficient approach based on non-equilibrium plasma environment is a response to the need of most efficient bottom-up processes in nanosynthesis and nanotechnology.

  14. 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

  15. Photocatalytic Active Nanoporous Carbon/ZnO Hybrid Materials from Block Copolymer Tethered ZnO Nanocrystals.

    PubMed

    Wang, Zongyu; Liu, Siyuan; Zhang, Jianan; Yan, Jiajun; Zhao, Yepin; Mahoney, Clare; Ferebee, Rachel; Luo, Danli; Pietrasik, Joanna; Bockstaller, Michael R; Matyjaszewski, Krzysztof

    2017-10-10

    Severe water pollution issues present an important contemporary challenge that drives the development and advancement of efficient and environmentally benign photocatalysts that enable the degradation of pollutants upon visible light irradiation. One example are zinc oxide/carbon (ZnO/C) hybrid materials that have been shown to be effective photocatalysts. To maximize the effectiveness of ZnO/C hybrids, materials with high accessible surface area of ZnO are required. Here, a novel strategy is presented to enable the synthesis of fine dispersions of ZnO nanoparticles within a porous carbon matrix. The synthesis entails the grafting of ZnO nanparticles with polystyrene-b-poly(styrene-co-acrylonitrile) (PS-b-PSAN) block copolymer and subsequent pyrolysis of the material under inert gas (N2) atmosphere. During the pyrolysis process, the PS block effectively prevents agglomeration of ZnO particles, thus resulting in a fine dispersion of ZnO nanocrystals within a prorous C matrix. Materials are found to exhibit a dye adsorption capacity of 125 mg g-1 (from a methylene blue aqueous solution with a concentration of 305 mg L-1) and dye degradation rate constant of 0.012 min-1. The significant increase of effective surface area and degradation efficacy (as compared to ZnO/C synthesized by the pyrolysis of binary PSAN/ZnO blends) is rationalized as a consequence of the increased porosity that promotes dye adsorption and transport within the hybrid material.

  16. Atomic Diffusion within Individual Gold Nanocrystal

    PubMed Central

    Xiong, Gang; Clark, Jesse N.; Nicklin, Chris; Rawle, Jonathan; Robinson, Ian K.

    2014-01-01

    Due to their excess surface free energy and structural instabilities, nanoparticles exhibit interesting physical and chemical properties. There has been an ever-growing interest in investigating these properties, driven by the desire to further miniaturize electronic devices, develop new functional materials and catalysts. Here, the intriguing question of how diffusion evolves in a single nanoparticle is investigated by measuring the spatial and temporal variations of the diffracted coherent X-ray intensity during copper diffusion into a gold nanocrystal. Dislocation loops formed from the insertion of single layer of extra atoms between neighbouring gold host lattice planes are detected. Au-Cu alloy channels are found to penetrate the nanocrystal due to the differential diffusion rate along different directions. With the advent of higher brilliance sources and free-electron-lasers, Bragg Coherent X-ray Diffraction Imaging can play an important role in unveiling atomic behaviours in three dimensions for nanomaterials during various fundamental processes. PMID:25341377

  17. Deformation twinning of a silver nanocrystal under high pressure. Supplementary materials

    SciTech Connect

    Huang, X. J.; Yang, W. G.; Harder, R.; Sun, Y.; Lu, M.; Chu, Y. S.; Robinson, I. K.; Mao, H. K.

    2015-10-20

    Within a high-pressure environment, crystal deformation is controlled by complex processes such as dislocation motion, twinning, and phase transitions, which change materials’ microscopic morphology and alter their properties. Likewise, understanding a crystal’s response to external stress provides a unique opportunity for rational tailoring of its functionalities. It is very challenging to track the strain evolution and physical deformation from a single nanoscale crystal under high-pressure stress. Here, we report an in situ three-dimensional mapping of morphology and strain evolutions in a single-crystal silver nanocube within a high-pressure environment using the Bragg Coherent Diffractive Imaging (CDI) method. We also observed a continuous lattice distortion, followed by a deformation twining process at a constant pressure. The ability to visualize stress-introduced deformation of nanocrystals with high spatial resolution and prominent strain sensitivity provides an important route for interpreting and engineering novel properties of nanomaterials.

  18. Hf-based high-k materials for Si nanocrystal floating gate memories

    PubMed Central

    2011-01-01

    Pure and Si-rich HfO2 layers fabricated by radio frequency sputtering were utilized as alternative tunnel oxide layers for high-k/Si-nanocrystals-SiO2/SiO2 memory structures. The effect of Si incorporation on the properties of Hf-based tunnel layer was investigated. The Si-rich SiO2 active layers were used as charge storage layers, and their properties were studied versus deposition conditions and annealing treatment. The capacitance-voltage measurements were performed to study the charge trapping characteristics of these structures. It was shown that with specific deposition conditions and annealing treatment, a large memory window of about 6.8 V is achievable at a sweeping voltage of ± 6 V, indicating the utility of these stack structures for low-operating-voltage nonvolatile memory devices. PMID:21711676

  19. Hf-based high-k materials for Si nanocrystal floating gate memories.

    PubMed

    Khomenkova, Larysa; Sahu, Bhabani S; Slaoui, Abdelilah; Gourbilleau, Fabrice

    2011-02-24

    Pure and Si-rich HfO2 layers fabricated by radio frequency sputtering were utilized as alternative tunnel oxide layers for high-k/Si-nanocrystals-SiO2/SiO2 memory structures. The effect of Si incorporation on the properties of Hf-based tunnel layer was investigated. The Si-rich SiO2 active layers were used as charge storage layers, and their properties were studied versus deposition conditions and annealing treatment. The capacitance-voltage measurements were performed to study the charge trapping characteristics of these structures. It was shown that with specific deposition conditions and annealing treatment, a large memory window of about 6.8 V is achievable at a sweeping voltage of ± 6 V, indicating the utility of these stack structures for low-operating-voltage nonvolatile memory devices.

  20. Deformation twinning of a silver nanocrystal under high pressure. Supplementary materials

    DOE PAGES

    Huang, X. J.; Yang, W. G.; Harder, R.; ...

    2015-10-20

    Within a high-pressure environment, crystal deformation is controlled by complex processes such as dislocation motion, twinning, and phase transitions, which change materials’ microscopic morphology and alter their properties. Likewise, understanding a crystal’s response to external stress provides a unique opportunity for rational tailoring of its functionalities. It is very challenging to track the strain evolution and physical deformation from a single nanoscale crystal under high-pressure stress. Here, we report an in situ three-dimensional mapping of morphology and strain evolutions in a single-crystal silver nanocube within a high-pressure environment using the Bragg Coherent Diffractive Imaging (CDI) method. We also observed amore » continuous lattice distortion, followed by a deformation twining process at a constant pressure. The ability to visualize stress-introduced deformation of nanocrystals with high spatial resolution and prominent strain sensitivity provides an important route for interpreting and engineering novel properties of nanomaterials.« less

  1. Workshop on Fundamental Research Needs in Organic Electronic Materials (May 23-25, 2003)

    SciTech Connect

    Prof. Zeev Valentine Vardeny

    2007-05-26

    The workshop, Fundamental Research Needs in Organic Electronic Materials, jointly sponsored by DOE Basic Energy Sciences (BES) and EERE/BT was held on May 23-25, 2003 at the University of Utah Campus in Salt Lake City, Utah for the purpose of identifying key scientific issues enabling the technological success of these materials. Approximately thirty key experts and world leaders in organic materials chemistry, transport physics, time-resolved and steady stated optical processes, organic spintronics, and device technology, gathered to stimulate new and revolutionary sciences.

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

    PubMed

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

    2015-10-05

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

  3. All-inorganic nanocrystals as a glue for BiSbTe grains: design of interfaces in mesostructured thermoelectric materials.

    PubMed

    Son, Jae Sung; Zhang, Hao; Jang, Jaeyoung; Poudel, Bed; Waring, Al; Nally, Luke; Talapin, Dmitri V

    2014-07-14

    Nano- and mesostructuring is widely used in thermoelectric (TE) materials. It introduces numerous interfaces and grain boundaries that scatter phonons and decrease thermal conductivity. A new approach has been developed for the rational design of the interfaces in TE materials by using all-inorganic nanocrystals (NCs) that serve as a "glue" for mesoscopic grains. For example, circa 10 nm Bi NCs capped with (N2H5)4Sb2Te7 chalcogenidometallate ligands can be used as an additive to BiSbTe particles. During heat treatment, NCs fill up the voids between particles and act as a "glue", joining grains in hot-pressed pellets or solution-processed films. The chemical design of NC glue allowed the selective enhancement or decrease of the majority-carrier concentration near the grain boundaries, and thus resulted in doped or de-doped interfaces in granular TE material. Chemically engineered interfaces can be used as to optimize power factor and thermal conductivity.

  4. Fundamental investigation of the tribological and mechanical responses of materials and nanostructures

    NASA Astrophysics Data System (ADS)

    Bucholz, Eric W.

    In the field of tribology, the ability to predict, and ultimately control, frictional performance is of critical importance for the optimization of tribological systems. As such, understanding the specific mechanisms involved in the lubrication processes for different materials is a fundamental step in tribological system design. In this work, a combination of computational and experimental methods that include classical molecular dynamics (MD) simulations, atomic force microscopy (AFM) experiments, and multivariate statistical analyses provides fundamental insight into the tribological and mechanical properties of carbon-based and inorganic nanostructures, lamellar materials, and inorganic ceramic compounds. One class of materials of modern interest for tribological applications is nanoparticles, which can be employed either as solid lubricating films or as lubricant additives. In experimental systems, however, it is often challenging to attain the in situ observation of tribological interfaces necessary to identify the atomic-level mechanisms involved during lubrication and response to mechanical deformation. Here, classical MD simulations establish the mechanisms occurring during the friction and compression of several types of nanoparticles including carbon nano-onions, amorphous carbon nanoparticles, and inorganic fullerene-like MoS2 nanoparticles. Specifically, the effect of a nanoparticle's structural properties on the lubrication mechanisms of rolling, sliding, and lamellar exfoliation is indicated; the findings quantify the relative impact of each mechanism on the tribological and mechanical properties of these nanoparticles. Beyond identifying the lubrication mechanisms of known lubricating materials, the continual advancement of modern technology necessitates the identification of new candidate materials for use in tribological applications. To this effect, atomic-scale AFM friction experiments on the aluminosilicate mineral pyrophyllite demonstrate that

  5. Fundamentals and Catalytic Applications of CeO2-Based Materials.

    PubMed

    Montini, Tiziano; Melchionna, Michele; Monai, Matteo; Fornasiero, Paolo

    2016-05-25

    Cerium dioxide (CeO2, ceria) is becoming an ubiquitous constituent in catalytic systems for a variety of applications. 2016 sees the 40(th) anniversary since ceria was first employed by Ford Motor Company as an oxygen storage component in car converters, to become in the years since its inception an irreplaceable component in three-way catalysts (TWCs). Apart from this well-established use, ceria is looming as a catalyst component for a wide range of catalytic applications. For some of these, such as fuel cells, CeO2-based materials have almost reached the market stage, while for some other catalytic reactions, such as reforming processes, photocatalysis, water-gas shift reaction, thermochemical water splitting, and organic reactions, ceria is emerging as a unique material, holding great promise for future market breakthroughs. While much knowledge about the fundamental characteristics of CeO2-based materials has already been acquired, new characterization techniques and powerful theoretical methods are deepening our understanding of these materials, helping us to predict their behavior and application potential. This review has a wide view on all those aspects related to ceria which promise to produce an important impact on our life, encompassing fundamental knowledge of CeO2 and its properties, characterization toolbox, emerging features, theoretical studies, and all the catalytic applications, organized by their degree of establishment on the market.

  6. Mechanical Properties of Nanocrystal Supercrystals

    SciTech Connect

    Tam, Enrico; Podsiadlo, Paul; Shevchenko, Elena; Ogletree, D. Frank; Delplancke-Ogletree, Marie-Paule; Ashby, Paul D.

    2009-12-30

    Colloidal nanocrystals attract significant interest due to their potential applications in electronic, magnetic, and optical devices. Nanocrystal supercrystals (NCSCs) are particularly appealing for their well ordered structure and homogeneity. The interactions between organic ligands that passivate the inorganic nanocrystal cores critically influence their self-organization into supercrystals, By investigating the mechanical properties of supercrystals, we can directly characterize the particle-particle interactions in a well-defined geometry, and gain insight into both the self-assembly process and the potential applications of nanocrystal supercrystals. Here we report nanoindentation studies of well ordered lead-sulfide (Pbs) nanocrystal supercrystals. Their modulus and hardness were found to be similar to soft polymers at 1.7 GPa and 70 MPa respectively and the fractures toughness was 39 KPa/m1/2, revealing the extremely brittle nature of these materials.

  7. 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.

  8. Highly stable sub-5 nm Sn₆O₄(OH)₄ nanocrystals with ultrahigh activity as advanced photocatalytic materials for photodegradation of methyl orange.

    PubMed

    Xiao, J; Wu, Q L; Liu, P; Liang, Y; Li, H B; Wu, M M; Yang, G W

    2014-04-04

    Among numerous active photocatalytic materials, Sn-based oxide nanomaterials are promising photocatalytic materials in environmental protection measures such as water remediation due to their excellent physicochemical property. Research on photocatalytic nanomaterials for photodegradation of methyl orange (MO) so far has focused on TiO₂-based nanostructures; e.g., TiO₂-P25 is recognized to be the best commercial photocatalyst to date, rather than Sn-based oxide nanomaterials, in spite of their impressive acid- and alkali-resistant properties and high stability. Here, we demonstrate very high photocatalytic activity of highly stable sub-5 nm hydromarchite (Sn₆O₄(OH)₄) nanocrystals synthesized by a simple and environmentally friendly laser-based technique. These Sn₆O₄(OH)₄ nanocrystals exhibit ultrahigh photocatalytic performance for photodegradation of MO and their degradation efficiency is far superior to that of TiO₂-P25. The detailed investigations demonstrated that the great photocatalytic activity results from the ultrafine size and unique surface activity induced by the laser-based technique. Mass production of reactive species of hydroxyl radicals was detected in the experiments due to the appropriate bandgap of Sn₆O₄(OH)₄ nanocrystals. These findings actually open a door to applications of Sn-based oxide nanomaterials as advanced photocatalytic materials.

  9. Formation of pure Cu nanocrystals upon post-growth annealing of Cu-C material obtained from focused electron beam induced deposition: comparison of different methods.

    PubMed

    Szkudlarek, Aleksandra; Rodrigues Vaz, Alfredo; Zhang, Yucheng; Rudkowski, Andrzej; Kapusta, Czesław; Erni, Rolf; Moshkalev, Stanislav; Utke, Ivo

    2015-01-01

    In this paper we study in detail the post-growth annealing of a copper-containing material deposited with focused electron beam induced deposition (FEBID). The organometallic precursor Cu(II)(hfac)2 was used for deposition and the results were compared to that of compared to earlier experiments with (hfac)Cu(I)(VTMS) and (hfac)Cu(I)(DMB). Transmission electron microscopy revealed the deposition of amorphous material from Cu(II)(hfac)2. In contrast, as-deposited material from (hfac)Cu(I)(VTMS) and (hfac)Cu(I)(DMB) was nano-composite with Cu nanocrystals dispersed in a carbonaceous matrix. After annealing at around 150-200 °C all deposits showed the formation of pure Cu nanocrystals at the outer surface of the initial deposit due to the migration of Cu atoms from the carbonaceous matrix containing the elements carbon, oxygen, and fluorine. Post-irradiation of deposits with 200 keV electrons in a transmission electron microscope favored the formation of Cu nanocrystals within the carbonaceous matrix of freestanding rods and suppressed the formation on their surface. Electrical four-point measurements on FEBID lines from Cu(hfac)2 showed five orders of magnitude improvement in conductivity when being annealed conventionally and by laser-induced heating in the scanning electron microscope chamber.

  10. Formation of pure Cu nanocrystals upon post-growth annealing of Cu–C material obtained from focused electron beam induced deposition: comparison of different methods

    PubMed Central

    Szkudlarek, Aleksandra; Rodrigues Vaz, Alfredo; Zhang, Yucheng; Rudkowski, Andrzej; Kapusta, Czesław; Erni, Rolf; Moshkalev, Stanislav

    2015-01-01

    Summary In this paper we study in detail the post-growth annealing of a copper-containing material deposited with focused electron beam induced deposition (FEBID). The organometallic precursor Cu(II)(hfac)2 was used for deposition and the results were compared to that of compared to earlier experiments with (hfac)Cu(I)(VTMS) and (hfac)Cu(I)(DMB). Transmission electron microscopy revealed the deposition of amorphous material from Cu(II)(hfac)2. In contrast, as-deposited material from (hfac)Cu(I)(VTMS) and (hfac)Cu(I)(DMB) was nano-composite with Cu nanocrystals dispersed in a carbonaceous matrix. After annealing at around 150–200 °C all deposits showed the formation of pure Cu nanocrystals at the outer surface of the initial deposit due to the migration of Cu atoms from the carbonaceous matrix containing the elements carbon, oxygen, and fluorine. Post-irradiation of deposits with 200 keV electrons in a transmission electron microscope favored the formation of Cu nanocrystals within the carbonaceous matrix of freestanding rods and suppressed the formation on their surface. Electrical four-point measurements on FEBID lines from Cu(hfac)2 showed five orders of magnitude improvement in conductivity when being annealed conventionally and by laser-induced heating in the scanning electron microscope chamber. PMID:26425404

  11. Fluorine-Doped Tin Oxide Nanocrystal/Reduced Graphene Oxide Composites as Lithium Ion Battery Anode Material with High Capacity and Cycling Stability.

    PubMed

    Xu, Haiping; Shi, Liyi; Wang, Zhuyi; Liu, Jia; Zhu, Jiefang; Zhao, Yin; Zhang, Meihong; Yuan, Shuai

    2015-12-16

    Tin oxide (SnO2) is a kind of anode material with high theoretical capacity. However, the volume expansion and fast capability fading during cycling have prevented its practical application in lithium ion batteries. Herein, we report that the nanocomposite of fluorine-doped tin oxide (FTO) and reduced graphene oxide (RGO) is an ideal anode material with high capacity, high rate capability, and high stability. The FTO conductive nanocrystals were successfully anchored on RGO nanosheets from an FTO nanocrystals colloid and RGO suspension by hydrothermal treatment. As the anode material, the FTO/RGO composite showed high structural stability during the lithiation and delithiation processes. The conductive FTO nanocrystals favor the formation of stable and thin solid electrolyte interface films. Significantly, the FTO/RGO composite retains a discharge capacity as high as 1439 mAhg(-1) after 200 cycles at a current density of 100 mAg(-1). Moreover, its rate capacity displays 1148 mAhg(-1) at a current density of 1000 mAg(-1).

  12. Center for Fundamental and Applied Research in Nanostructured and Lightweight Materials. Final Technical Summary

    SciTech Connect

    Mullins, Michael; Rogers, Tony; King, Julia; Keith, Jason; Cornilsen, Bahne; Allen, Jeffrey; Gilbert, Ryan; Holles, Joseph

    2010-09-28

    The core projects for this DOE-sponsored Center at Michigan Tech have focused on several of the materials problems identified by the NAS. These include: new electrode materials, enhanced PEM materials, lighter and more effective bipolar plates, and improvement of the carbon used as a current carrier. This project involved fundamental and applied research in the development and testing of lightweight and nanostructured materials to be used in fuel cell applications and for chemical synthesis. The advent of new classes of materials engineered at the nanometer level can produce materials that are lightweight and have unique physical and chemical properties. The grant was used to obtain and improve the equipment infrastructure to support this research and also served to fund seven research projects. These included: 1. Development of lightweight, thermally conductive bipolar plates for improved thermal management in fuel cells; 2. Exploration of pseudomorphic nanoscale overlayer bimetallic catalysts for fuel cells; 3. Development of hybrid inorganic/organic polymer nanocomposites with improved ionic and electronic properties; 4. Development of oriented polymeric materials for membrane applications; 5. Preparation of a graphitic carbon foam current collectors; 6. The development of lightweight carbon electrodes using graphitic carbon foams for battery and fuel cell applications; and 7. Movement of water in fuel cell electrodes.

  13. Bioinspired Interfacial Materials with Enhanced Drop Mobility: From Fundamentals to Multifunctional Applications.

    PubMed

    Hao, Chonglei; Liu, Yahua; Chen, Xuemei; Li, Jing; Zhang, Mei; Zhao, Yanhua; Wang, Zuankai

    2016-04-13

    The development of bioinspired interfacial materials with enhanced drop mobility that mimic the innate functionalities of nature will have a significant impact on the energy, environment and global healthcare. Despite extensive progress, state of the art interfacial materials have not reached the level of maturity sufficient for industrial applications in terms of scalability, stability, and reliability. These are complicated by their operating environments and lack of facile approaches to control the local structural texture and chemical composition at multiple length scales. The recent advances in the fundamental understanding are reviewed, as well as practical applications of bioinspired interfacial materials, with an emphasis on the drop bouncing and coalescence-induced jumping behaviors. Perspectives on how to catalyze new discoveries and to foster technological adoption to move this exciting area forward are also suggested. © 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  14. Exploiting the colloidal nanocrystal library to construct electronic devices

    NASA Astrophysics Data System (ADS)

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

    2016-04-01

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

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

    SciTech Connect

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

    2008-07-15

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

  16. Inexpensive Antimony Nanocrystals and Their Composites with Red Phosphorus as High-Performance Anode Materials for Na-ion Batteries

    PubMed Central

    Walter, Marc; Erni, Rolf; Kovalenko, Maksym V.

    2015-01-01

    Sodium-ion batteries increasingly become of immense research interest as a potential inexpensive alternative to Lithium-ion batteries. Development of high-energy-density negative electrodes (anodes) remains to be a great challenge, especially because of significant differences between lithium and sodium chemistries. Two Na-ion anode materials – antimony (Sb) and phosphorus (P) – have been recently shown to offer excellent cycling stability (Sb) and highest known Na-ion charge storage capacity (P). In this work we report on the synergistic Na-ion storage in a P/Sb/Cu-nanocomposite, produced by mixing inexpensive colloidal Sb nanocrystals with red P and with copper (Cu) nanowires. In comparison to electrodes composed of only phosphorus, such P/Sb/Cu-composite shows much greater cycling stability providing a capacity of above 1100 mAh g−1 after 50 charge/discharge cycles at a current density of 125 mA g−1. Furthermore, P/Sb/Cu-composite also exhibits excellent rate-capability, with capacity of more than 900 mAh g−1 at a high charge/discharge current density of 2000 mA g−1. PMID:25673146

  17. Cu3-xP Nanocrystals as a Material Platform for Near-Infrared Plasmonics and Cation Exchange Reactions

    PubMed Central

    2015-01-01

    Synthesis approaches to colloidal Cu3P nanocrystals (NCs) have been recently developed, and their optical absorption features in the near-infrared (NIR) have been interpreted as arising from a localized surface plasmon resonance (LSPR). Our pump–probe measurements on platelet-shaped Cu3-xP NCs corroborate the plasmonic character of this absorption. In accordance with studies on crystal structure analysis of Cu3P dating back to the 1970s, our density functional calculations indicate that this material is substoichiometric in copper, since the energy of formation of Cu vacancies in certain crystallographic sites is negative, that is, they are thermodynamically favored. Also, thermoelectric measurements point to a p-type behavior of the majority carriers from films of Cu3-xP NCs. It is likely that both the LSPR and the p-type character of our Cu3-xP NCs arise from the presence of a large number of Cu vacancies in such NCs. Motivated by the presence of Cu vacancies that facilitate the ion diffusion, we have additionally exploited Cu3-xP NCs as a starting material on which to probe cation exchange reactions. We demonstrate here that Cu3-xP NCs can be easily cation-exchanged to hexagonal wurtzite InP NCs, with preservation of the anion framework (the anion framework in Cu3-xP is very close to that of wurtzite InP). Intermediate steps in this reaction are represented by Cu3-xP/InP heterostructures, as a consequence of the fact that the exchange between Cu+ and In3+ ions starts from the peripheral corners of each NC and gradually evolves toward the center. The feasibility of this transformation makes Cu3-xP NCs an interesting material platform from which to access other metal phosphides by cation exchange. PMID:25960605

  18. Cu3-x P Nanocrystals as a Material Platform for Near-Infrared Plasmonics and Cation Exchange Reactions.

    PubMed

    De Trizio, Luca; Gaspari, Roberto; Bertoni, Giovanni; Kriegel, Ilka; Moretti, Luca; Scotognella, Francesco; Maserati, Lorenzo; Zhang, Yang; Messina, Gabriele C; Prato, Mirko; Marras, Sergio; Cavalli, Andrea; Manna, Liberato

    2015-02-10

    Synthesis approaches to colloidal Cu3P nanocrystals (NCs) have been recently developed, and their optical absorption features in the near-infrared (NIR) have been interpreted as arising from a localized surface plasmon resonance (LSPR). Our pump-probe measurements on platelet-shaped Cu3-x P NCs corroborate the plasmonic character of this absorption. In accordance with studies on crystal structure analysis of Cu3P dating back to the 1970s, our density functional calculations indicate that this material is substoichiometric in copper, since the energy of formation of Cu vacancies in certain crystallographic sites is negative, that is, they are thermodynamically favored. Also, thermoelectric measurements point to a p-type behavior of the majority carriers from films of Cu3-x P NCs. It is likely that both the LSPR and the p-type character of our Cu3-x P NCs arise from the presence of a large number of Cu vacancies in such NCs. Motivated by the presence of Cu vacancies that facilitate the ion diffusion, we have additionally exploited Cu3-x P NCs as a starting material on which to probe cation exchange reactions. We demonstrate here that Cu3-x P NCs can be easily cation-exchanged to hexagonal wurtzite InP NCs, with preservation of the anion framework (the anion framework in Cu3-x P is very close to that of wurtzite InP). Intermediate steps in this reaction are represented by Cu3-x P/InP heterostructures, as a consequence of the fact that the exchange between Cu(+) and In(3+) ions starts from the peripheral corners of each NC and gradually evolves toward the center. The feasibility of this transformation makes Cu3-x P NCs an interesting material platform from which to access other metal phosphides by cation exchange.

  19. Nanocrystal synthesis

    SciTech Connect

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

    2016-11-01

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

  20. Injected nanocrystals for targeted drug delivery

    PubMed Central

    Lu, Yi; Li, Ye; Wu, Wei

    2016-01-01

    Nanocrystals are pure drug crystals with sizes in the nanometer range. Due to the advantages of high drug loading, platform stability, and ease of scaling-up, nanocrystals have been widely used to deliver poorly water-soluble drugs. Nanocrystals in the blood stream can be recognized and sequestered as exogenous materials by mononuclear phagocytic system (MPS) cells, leading to passive accumulation in MPS-rich organs, such as liver, spleen and lung. Particle size, morphology and surface modification affect the biodistribution of nanocrystals. Ligand conjugation and stimuli-responsive polymers can also be used to target nanocrystals to specific pathogenic sites. In this review, the progress on injected nanocrystals for targeted drug delivery is discussed following a brief introduction to nanocrystal preparation methods, i.e., top-down and bottom-up technologies. PMID:27006893

  1. Extracting hot carriers from photoexcited semiconductor nanocrystals

    SciTech Connect

    Zhu, Xiaoyang

    2014-12-10

    This research program addresses a fundamental question related to the use of nanomaterials in solar energy -- namely, whether semiconductor nanocrystals (NCs) can help surpass the efficiency limits, the so-called “Shockley-Queisser” limit, in conventional solar cells. In these cells, absorption of photons with energies above the semiconductor bandgap generates “hot” charge carriers that quickly “cool” to the band edges before they can be utilized to do work; this sets the solar cell efficiency at a limit of ~31%. If instead, all of the energy of the hot carriers could be captured, solar-to-electric power conversion efficiencies could be increased, theoretically, to as high as 66%. A potential route to capture this energy is to utilize semiconductor nanocrystals. In these materials, the quasi-continuous conduction and valence bands of the bulk semiconductor become discretized due to confinement of the charge carriers. Consequently, the energy spacing between the electronic levels can be much larger than the highest phonon frequency of the lattice, creating a “phonon bottleneck” wherein hot-carrier relaxation is possible via slower multiphonon emission. For example, hot-electron lifetimes as long as ~1 ns have been observed in NCs grown by molecular beam epitaxy. In colloidal NCs, long lifetimes have been demonstrated through careful design of the nanocrystal interfaces. Due to their ability to slow electronic relaxation, semiconductor NCs can in principle enable extraction of hot carriers before they cool to the band edges, leading to more efficient solar cells.

  2. Fundamental studies to develop certified reference material to calibrate spectrophotometer in the ultraviolet region

    NASA Astrophysics Data System (ADS)

    da Conceição, F. C.; Borges, P. P.; Gomes, J. F. S.

    2016-07-01

    Spectrophotometry is the technique used in a great number of laboratories around the world. Quantitative determination of a high number of inorganic, organic and biological species can be made by spectrophotometry using calibrated spectrophotometers. International standards require the use of optical filters to perform the calibration of spectrophotometers. One of the recommended materials is the crystalline potassium dichromate (K2Cr2O7), which is used to prepare solutions in specific concentrations for calibration or verification of spectrophotometers in the ultraviolet (UV) spectral regions. This paper presents the results concerning the fundamental studies for developing a certified reference material (CRM) of crystalline potassium dichromate to be used as standard of spectrophotometers in order to contribute to reliable quantitative analyses.

  3. Material nature versus structural nurture: the embodied carbon of fundamental structural elements.

    PubMed

    Purnell, P

    2012-01-03

    The construction industry is under considerable legislative pressure to reduce its CO(2) emissions. The current focus is on operational CO(2) emissions, but as these are compulsorily reduced, the embodied CO(2) of structural components, overwhelmingly attributable to the material from which they are manufactured, will become of greater interest. Choice of structural materials for minimal embodied CO(2) is currently based either on subjective narrative arguments, or values of embodied CO(2) per unit volume or mass. Here we show that such arguments are invalid. We found that structural design parameters (dimensions, section choice, and load capacity) for fundamental structural components (simple beams and columns) are at least as important as material choice with regard to their effect on embodied CO(2) per unit load capacity per unit dimension, which can vary over several decades within and between material choices. This result demonstrates that relying on apparently objective analyses based on embodied CO(2) per unit volume or mass will not lead to minimum carbon solutions; a formal definition of the correct functional unit for embodied CO(2) must be used. In short, there is no such thing as a green structural material.

  4. Unified analytical expressions of the three-dimensional fundamental solutions and their derivatives for linear elastic anisotropic materials

    PubMed Central

    Xie, Longtao; Zhang, Chuanzeng; Sladek, Jan; Sladek, Vladimir

    2016-01-01

    Novel unified analytical displacement and stress fundamental solutions as well as the higher order derivatives of the displacement fundamental solutions for three-dimensional, generally anisotropic and linear elastic materials are presented in this paper. Adequate integral expressions for the displacement and stress fundamental solutions as well as the higher order derivatives of the displacement fundamental solutions are evaluated analytically by using the Cauchy residue theorem. The resulting explicit displacement fundamental solutions and their first and second derivatives are recast into convenient analytical forms which are valid for non-degenerate, partially degenerate, fully degenerate and nearly degenerate cases. The correctness and the accuracy of the novel unified and closed-form three-dimensional anisotropic fundamental solutions are verified by using some available analytical expressions for both transversely isotropic (non-degenerate or partially degenerate) and isotropic (fully degenerate) linear elastic materials. PMID:27118881

  5. Unified analytical expressions of the three-dimensional fundamental solutions and their derivatives for linear elastic anisotropic materials.

    PubMed

    Xie, Longtao; Zhang, Chuanzeng; Sladek, Jan; Sladek, Vladimir

    2016-02-01

    Novel unified analytical displacement and stress fundamental solutions as well as the higher order derivatives of the displacement fundamental solutions for three-dimensional, generally anisotropic and linear elastic materials are presented in this paper. Adequate integral expressions for the displacement and stress fundamental solutions as well as the higher order derivatives of the displacement fundamental solutions are evaluated analytically by using the Cauchy residue theorem. The resulting explicit displacement fundamental solutions and their first and second derivatives are recast into convenient analytical forms which are valid for non-degenerate, partially degenerate, fully degenerate and nearly degenerate cases. The correctness and the accuracy of the novel unified and closed-form three-dimensional anisotropic fundamental solutions are verified by using some available analytical expressions for both transversely isotropic (non-degenerate or partially degenerate) and isotropic (fully degenerate) linear elastic materials.

  6. Synthesis of hybrid organic-inorganic nanocomposite materials based on CdS nanocrystals for energy conversion applications

    NASA Astrophysics Data System (ADS)

    Laera, A. M.; Resta, V.; Ferrara, M. C.; Schioppa, M.; Piscopiello, E.; Tapfer, L.

    2011-11-01

    Efficient solar energy conversion is strongly related to the development of new materials with enhanced functional properties. In this context, a wide variety of inorganic, organic, or hybrid nanostructured materials have been investigated. In particular, in hybrid organic-inorganic nanocomposites are combined the convenient properties of organic polymers, such as easy manipulation and mechanical flexibility, and the unique size-dependent properties of nanocrystals (NCs). However, applications of hybrid nanocomposites in photovoltaic devices require a homogeneous and highly dense dispersion of NCs in polymer in order to guarantee not only an efficient charge separation, but also an efficient transport of the carriers to the electrodes without recombination. In previous works, we demonstrated that cadmium thiolate complexes are suitable precursors for the in situ synthesis of nanocrystalline CdS. Here, we show that the soluble [Cd(SBz)2]2·(1-methyl imidazole) complex can be efficiently annealed in a conjugated polymer obtaining a nanocomposite with a regular and compact network of NCs. The proposed synthetic strategies require annealing temperatures well below 200 °C and short time for the thermal treatment, i.e., less than 30 min. We also show that the same complex can be used to synthesize CdS NCs in mesoporous TiO2. The adsorption of cadmium thiolate molecule in TiO2 matrix can be obtained by using chemical bath deposition technique and subsequent thermal annealing. The use of NCs, quantum dots, as sensitizers of TiO2 matrices represents a very promising alternative to common dye-sensitized solar cells and an interesting solution for heterogeneous photocatalysis.

  7. Understanding Fundamental Material Degradation Processes in High Temperature Aggressive Chemomechanical Environments

    SciTech Connect

    Stubbins, James; Gewirth, Andrew; Sehitoglu, Huseyin; Sofronis, Petros; Robertson, Ian

    2014-01-16

    The objective of this project is to develop a fundamental understanding of the mechanisms that limit materials durability for very high-temperature applications. Current design limitations are based on material strength and corrosion resistance. This project will characterize the interactions of high-temperature creep, fatigue, and environmental attack in structural metallic alloys of interest for the very high-temperature gas-cooled reactor (VHTR) or Next–Generation Nuclear Plant (NGNP) and for the associated thermo-chemical processing systems for hydrogen generation. Each of these degradation processes presents a major materials design challenge on its own, but in combination, they can act synergistically to rapidly degrade materials and limit component lives. This research and development effort will provide experimental results to characterize creep-fatigue-environment interactions and develop predictive models to define operation limits for high-temperature structural material applications. Researchers will study individually and in combination creep-fatigue-environmental attack processes in Alloys 617, 230, and 800H, as well as in an advanced Ni-Cr oxide dispersion strengthened steel (ODS) system. For comparison, the study will also examine basic degradation processes in nichrome (Ni-20Cr), which is a basis for most high-temperature structural materials, as well as many of the superalloys. These materials are selected to represent primary candidate alloys, one advanced developmental alloy that may have superior high-temperature durability, and one model system on which basic performance and modeling efforts can be based. The research program is presented in four parts, which all complement each other. The first three are primarily experimental in nature, and the last will tie the work together in a coordinated modeling effort. The sections are (1) dynamic creep-fatigue-environment process, (2) subcritical crack processes, (3) dynamic corrosion – crack

  8. Fundamentals of Materials, Techniques, and Instrumentation for OSL and FNTD Dosimetry

    NASA Astrophysics Data System (ADS)

    Akselrod, M. S.

    2011-05-01

    The optically stimulated luminescence (OSL) technique has already become a successful commercial tool in personal radiation dosimetry, medical dosimetry, diagnostic imaging, geological and archeological dating. This review briefly describes the history and fundamental principles of OSL materials, methods and instrumentation. The advantages of OSL technology and instrumentation in comparison with thermoluminescent technique are analyzed. Progress in material and detector engineering has allowed new and promising developments regarding OSL applications in the medical field. Special attention is dedicated to Al2O3:C as a material of choice for many dosimetric applications. Different aspects of OSL theory, materials optical and dosimetric properties, instrumentation, and data processing algorithms are described. The next technological breakthrough was done with Fluorescent Nuclear Track Detectors (FNTD) that have some important advantages in measuring fast neutron and high energy heavy charge particles that have become the latest tool in radiation therapy. New Mg-doped aluminum oxide crystals and novel type of imaging instrumentation for FNTD technology are discussed with regard to application in mixed neutron-gamma fields, medical dosimetry and radiobiological research.

  9. NaNaX 4--4th event of the international conference series "Nanoscience with Nanocrystals".

    PubMed

    Reiss, Peter

    2010-07-27

    The conference "NaNaX 4--Nanoscience with Nanocrystals" held near Munich (April 11-15, 2010) brought together a wide range of scientists discussing the most important current issues in the field of colloidal nanoparticles. Chemical synthesis gives access to nanocrystals of controlled size, shape, composition, and surface functionalization. Past research mainly concentrated on cadmium and lead chalcogenide nanocrystals as well as on gold and iron oxide nanoparticles. Today, there is a trend toward the development of nanoscale heterostructures, which combine different classes of materials and exhibit unique optical, magnetic, and electronic properties. Beside their interest for fundamental science, colloidal nanoparticles hold great promise for a wide range of applications. To this end, speakers and poster presenters showed routes for designing and using nanocrystals in biological imaging and sensing, in energy-related applications, and in catalysis. This report gives a nonexhaustive overview of selected "hot topics" in nanoparticle research discussed at NaNaX 4.

  10. In situ Transmission Electron Microscopy observation of Ag nanocrystal evolution by surfactant free electron-driven synthesis

    PubMed Central

    Longo, Elson; Avansi, Waldir; Bettini, Jefferson; Andrés, Juan; Gracia, Lourdes

    2016-01-01

    The study of the interaction of electron irradiation with matter and the response of the material to the passage of electrons is a very challenging problem. However, the growth mechanism observed during nanostructural evolution appears to be a broad and promising scientific field in nanotechnology. We report the in situ TEM study of nanostructural evolution of electron-driven silver (Ag) nanocrystals through an additive-free synthetic procedure. Observations revealed the direct effect of the electron beam on the morphological evolution of Ag nanocrystals through different mechanisms, such as mass transport, site-selective coalescence, and an appropriate structural configuration after coalescence leading to a more stable configuration. A fundamental understanding of the growth and formation mechanisms of Ag nanocrystals, which interact with the electron beam, is essential to improve the nanocrystal shape-control mechanisms as well as the future design and study of nanomaterials. PMID:26979671

  11. Gram-scale synthesis of catalytic Co9S8 nanocrystal ink as a cathode material for spray-deposited, large-area dye-sensitized solar cells.

    PubMed

    Chang, Shu-Hao; Lu, Ming-De; Tung, Yung-Liang; Tuan, Hsing-Yu

    2013-10-22

    We report the development of Co9S8 nanocrystals as a cost-effective cathode material that can be readily combined with spraying techniques to fabricate large-area dye-sensitized solar cell (DSSC) devices and can be further connected with series or parallel cell architectures to obtain a relatively high output voltage or current. A gram-scale synthesis of Co9S8 nanocrystal is carried out via a noninjection reaction by mixing anhydrous CoCl2 with trioctylphosphine (TOP), dodecanethiol and oleylamine (OLA) at 250 °C. The Co9S8 nanocrystals possess excellent catalytic ability with respect to I(-)/I3(-) redox reactions. The Co9S8 nanocrystals are prepared as nanoinks to fabricate uniform, crack-free Co9S8 thin films on different substrates by using a spray deposition technique. These Co9S8 films are used as counter electrodes assembled with dye-adsorbed TiO2 photoanodes to fabricate DSSC devices having a working area of 2 cm(2) and an average power conversion efficiency (PCE) of 7.02 ± 0.18% under AM 1.5 solar illumination, which is comparable with the PCE of 7.2 ± 0.12% obtained using a Pt cathode. Furthermore, six 2 cm(2)-sized DSSC devices connected in series output an open-circuit voltage of 4.2 V that can power a wide range of electronic devices such as LED arrays and can charge commercial lithium ion batteries.

  12. Thin films and assemblies of photosensitive membrane proteins and colloidal nanocrystals for engineering of hybrid materials with advanced properties.

    PubMed

    Zaitsev, Sergei Yu; Solovyeva, Daria O; Nabiev, Igor

    2012-11-15

    Langmuir-Schaefer methods < self-assembly and layer-by-layer methods. The key advances in the techniques of preparation of the assemblies or complexes of colloidal nanocrystals with bR, purple membranes, or photosynthetic reaction centres are also reviewed. Approaches to the fabrication of the prototype photosensitive nano-bio hybrid materials with advanced photovoltaic, energy transfer, and optical switching properties and future prospects in this field are analyzed in the concluding part of the review. Copyright © 2012 Elsevier B.V. All rights reserved.

  13. 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.

  14. Tunable infrared absorption and visible transparency of colloidal aluminum-doped zinc oxide nanocrystals.

    PubMed

    Buonsanti, Raffaella; Llordes, Anna; Aloni, Shaul; Helms, Brett A; Milliron, Delia J

    2011-11-09

    Plasmonic nanocrystals have been attracting a lot of attention both for fundamental studies and different applications, from sensing to imaging and optoelectronic devices. Transparent conductive oxides represent an interesting class of plasmonic materials in addition to metals and vacancy-doped semiconductor quantum dots. Herein, we report a rational synthetic strategy of high-quality colloidal aluminum-doped zinc oxide nanocrystals. The presence of substitutional aluminum in the zinc oxide lattice accompanied by the generation of free electrons is proved for the first time by tunable surface plasmon absorption in the infrared region both in solution and in thin films.

  15. 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

  16. Fundamentals of materials, techniques and instrumentation for OSL and FNTD dosimetry

    NASA Astrophysics Data System (ADS)

    Akselrod, M. S.

    2013-02-01

    The optically stimulated luminescence (OSL) technique has already become a successful commercial tool in personal radiation dosimetry, medical dosimetry, diagnostic imaging, geological and archeological dating. This review briefly describes the history and fundamental principles of OSL materials, methods and instrumentation. The advantages of OSL technology and instrumentation in comparison with thermoluminescent technique are analyzed. Progress in material and detector engineering has allowed new and promising developments regarding OSL applications in the medical field. Special attention is dedicated to Al2O3:C as a material of choice for many dosimetric applications including fiberoptic OSL/RL sensors with diameters as small as 300 μm. A new RL/OSL fiberoptic system has a high potential for in vivo and in vitro dosimetry in both radiation therapy and diagnostic mammography. Different aspects of instrumentation, data processing algorithms, post-irradiation and real-time measurements are described. The next technological breakthrough was done with Fluorescent Nuclear Track detectors (FNTD) that has some important advantages in measuring fast neutron and high energy heavy charge particles that became the latest tool in radiation therapy. New Mg-doped aluminum oxide crystals and novel type of imaging instrumentation for FNTD technology were engineered and successfully demonstrated for occupational and accident dosimetry, for medical dosimetry and radiobiological research.

  17. Ubiquitous trisulfur radical anion: fundamentals and applications in materials science, electrochemistry, analytical chemistry and geochemistry.

    PubMed

    Chivers, Tristram; Elder, Philip J W

    2013-07-21

    The trisulfur radical anion [S3]˙(-) is well-known from inorganic chemistry textbooks as the blue chromophore in ultramarine blues in which this highly reactive species is trapped in a zeolitic framework. Recent findings have revealed that [S3]˙(-) has a multi-faceted role in a variety of media, including alkali metal-sulfur batteries, aqueous solutions at high temperatures and pressures, and ionic liquids; it has also been used to detect trace amounts of water in organic solvents. This tutorial review illustrates how various physical techniques are used to identify a reactive species in solution and shows how elucidation of electronic structures can be used to explain spectroscopic and structural properties. Examples of the function of [S3]˙(-) in materials science, electrochemistry, analytical chemistry and geochemistry are used to illustrate the widespread influence of this fundamentally important triatomic sulfur species.

  18. 2009 Clusters, Nanocrystals & Nanostructures GRC

    SciTech Connect

    Lai-Sheng Wang

    2009-07-19

    For over thirty years, this Gordon Conference has been the premiere meeting for the field of cluster science, which studies the phenomena that arise when matter becomes small. During its history, participants have witnessed the discovery and development of many novel materials, including C60, carbon nanotubes, semiconductor and metal nanocrystals, and nanowires. In addition to addressing fundamental scientific questions related to these materials, the meeting has always included a discussion of their potential applications. Consequently, this conference has played a critical role in the birth and growth of nanoscience and engineering. The goal of the 2009 Gordon Conference is to continue the forward-looking tradition of this meeting and discuss the most recent advances in the field of clusters, nanocrystals, and nanostructures. As in past meetings, this will include new topics that broaden the field. In particular, a special emphasis will be placed on nanomaterials related to the efficient use, generation, or conversion of energy. For example, we anticipate presentations related to batteries, catalysts, photovoltaics, and thermoelectrics. In addition, we expect to address the controversy surrounding carrier multiplication with a session in which recent results addressing this phenomenon will be discussed and debated. The atmosphere of the conference, which emphasizes the presentation of unpublished results and lengthy discussion periods, ensures that attendees will enjoy a valuable and stimulating experience. Because only a limited number of participants are allowed to attend this conference, and oversubscription is anticipated, we encourage all interested researchers from academia, industry, and government institutions to apply as early as possible. An invitation is not required. We also encourage all attendees to submit their latest results for presentation at the poster sessions. We anticipate that several posters will be selected for 'hot topic' oral

  19. Biomolecular Assembly of Gold Nanocrystals

    SciTech Connect

    Micheel, Christine Marya

    2005-05-20

    Over the past ten years, methods have been developed to construct discrete nanostructures using nanocrystals and biomolecules. While these frequently consist of gold nanocrystals and DNA, semiconductor nanocrystals as well as antibodies and enzymes have also been used. One example of discrete nanostructures is dimers of gold nanocrystals linked together with complementary DNA. This type of nanostructure is also known as a nanocrystal molecule. Discrete nanostructures of this kind have a number of potential applications, from highly parallel self-assembly of electronics components and rapid read-out of DNA computations to biological imaging and a variety of bioassays. My research focused in three main areas. The first area, the refinement of electrophoresis as a purification and characterization method, included application of agarose gel electrophoresis to the purification of discrete gold nanocrystal/DNA conjugates and nanocrystal molecules, as well as development of a more detailed understanding of the hydrodynamic behavior of these materials in gels. The second area, the development of methods for quantitative analysis of transmission electron microscope data, used computer programs written to find pair correlations as well as higher order correlations. With these programs, it is possible to reliably locate and measure nanocrystal molecules in TEM images. The final area of research explored the use of DNA ligase in the formation of nanocrystal molecules. Synthesis of dimers of gold particles linked with a single strand of DNA possible through the use of DNA ligase opens the possibility for amplification of nanostructures in a manner similar to polymerase chain reaction. These three areas are discussed in the context of the work in the Alivisatos group, as well as the field as a whole.

  20. Cellulose nanocrystals as a reinforcing material for electrospun poly(methyl methacrylate) fibers: formation, properties and nanomechanical characterization

    Treesearch

    Hong Dong; Kenneth E. Strawhecker; James A. Snyder; Joshua A. Orlicki; Richard S. Reiner; Alan W. Rudie

    2012-01-01

    Uniform fibers composed of poly(methyl methacrylate) (PMMA) reinforced with progressively increasing contents of cellulose nanocrystals (CNCs), up to 41 wt% CNCs, have been successfully produced by electrospinning. The morphological, thermal and nanomechanical properties of the composite sub-micron fibers were investigated. The CNCs derived from wood pulp by sulfuric...

  1. Ultrafine SnO{sub 2} nanocrystals anchored graphene composites as anode material for lithium-ion batteries

    SciTech Connect

    Zhang, Jun Chang, Ling; Wang, Fengxian; Xie, Dong; Su, Qingmei; Du, Gaohui

    2015-08-15

    Highlights: • Ultrafine SnO{sub 2}@graphene composite is synthesized by a simple hydrothermal method. • SnO{sub 2} nanocrystals with size of ∼5 nm are distributed on the graphene sheets uniformly. • A reversible capacity of 808 mAh g{sup −1} is retained after 100 cycles at 200 mA g{sup −1}. • The capacity recovers to 1290 mAh g{sup −1} after being cycled at various rates for 60 cycles. - Abstract: Ultrafine tin dioxide (SnO{sub 2}) nanocrystals anchored graphene composite is synthesized by a simple hydrothermal method. Well-defined SnO{sub 2} nanocrystals with size of ∼5 nm are uniformly anchored on the graphene sheets. The two-dimensional nanostructure inherits the advantages of graphene, which possesses high electrical conductivity and large surface area. Furthermore, the ultrafine SnO{sub 2} nanocrystals anchoring on graphene sheets facilitate fast ion transportation and prevent aggregation. As a result, the produced nanocomposite exhibits an excellent cycling stability and rate capability for lithium storage (808 mAh g{sup −1} after 100 cycles at 200 mA g{sup −1}, 1290 mAh g{sup −1} at the current of 50 mA g{sup −1} after being cycled at various current densities for 60 cycles)

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

    DOEpatents

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

    2014-12-16

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

  3. 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

  4. Prospects of nanoscience with nanocrystals

    DOE PAGES

    Kovalenko, Maksym V.; Manna, Liberato; Cabot, Andreu; ...

    2015-01-22

    Colloidal nanocrystals (NCs, i.e., crystalline nanoparticles) have become an important class of materials with great potential for applications ranging from medicine to electronic and optoelectronic devices. Today’s strong research focus on NCs has been prompted by the tremendous progress in their synthesis. Impressively narrow size distributions of just a few percent, rational shape-engineering, compositional modulation, electronic doping, and tailored surface chemistries are now feasible for a broad range of inorganic compounds. The performance of inorganic NC-based photovoltaic and light-emitting devices has become competitive to other state-of-the-art materials. Semiconductor NCs hold unique promise for near- and mid-infrared technologies, where very fewmore » semiconductor materials are available. On a purely fundamental side, new insights into NC growth, chemical transformations, and self-organization can be gained from rapidly progressing in situ characterization and direct imaging techniques. In addition, new phenomena are constantly being discovered in the photophysics of NCs and in the electronic properties of NC solids. In this Nano Focus, we review the state of the art in research on colloidal NCs focusing on the most recent works published in the last 2 years.« less

  5. Prospects of nanoscience with nanocrystals

    SciTech Connect

    Kovalenko, Maksym V.; Manna, Liberato; Cabot, Andreu; Hens, Zeger; Talapin, Dmitri V.; Kagan, Cherie R.; Klimov, Victor I.; Rogach, Andrey L.; Reiss, Peter; Milliron, Delia J.; Guyot-Sionnnest, Philippe; Konstantatos, Gerasimos; Parak, Wolfgang J.; Hyeon, Taeghwan; Korgel, Brian A.; Murray, Christopher B.; Heiss, Wolfgang

    2015-01-22

    Colloidal nanocrystals (NCs, i.e., crystalline nanoparticles) have become an important class of materials with great potential for applications ranging from medicine to electronic and optoelectronic devices. Today’s strong research focus on NCs has been prompted by the tremendous progress in their synthesis. Impressively narrow size distributions of just a few percent, rational shape-engineering, compositional modulation, electronic doping, and tailored surface chemistries are now feasible for a broad range of inorganic compounds. The performance of inorganic NC-based photovoltaic and light-emitting devices has become competitive to other state-of-the-art materials. Semiconductor NCs hold unique promise for near- and mid-infrared technologies, where very few semiconductor materials are available. On a purely fundamental side, new insights into NC growth, chemical transformations, and self-organization can be gained from rapidly progressing in situ characterization and direct imaging techniques. In addition, new phenomena are constantly being discovered in the photophysics of NCs and in the electronic properties of NC solids. In this Nano Focus, we review the state of the art in research on colloidal NCs focusing on the most recent works published in the last 2 years.

  6. Prospects of nanoscience with nanocrystals.

    PubMed

    Kovalenko, Maksym V; Manna, Liberato; Cabot, Andreu; Hens, Zeger; Talapin, Dmitri V; Kagan, Cherie R; Klimov, Victor I; Rogach, Andrey L; Reiss, Peter; Milliron, Delia J; Guyot-Sionnnest, Philippe; Konstantatos, Gerasimos; Parak, Wolfgang J; Hyeon, Taeghwan; Korgel, Brian A; Murray, Christopher B; Heiss, Wolfgang

    2015-02-24

    Colloidal nanocrystals (NCs, i.e., crystalline nanoparticles) have become an important class of materials with great potential for applications ranging from medicine to electronic and optoelectronic devices. Today's strong research focus on NCs has been prompted by the tremendous progress in their synthesis. Impressively narrow size distributions of just a few percent, rational shape-engineering, compositional modulation, electronic doping, and tailored surface chemistries are now feasible for a broad range of inorganic compounds. The performance of inorganic NC-based photovoltaic and light-emitting devices has become competitive to other state-of-the-art materials. Semiconductor NCs hold unique promise for near- and mid-infrared technologies, where very few semiconductor materials are available. On a purely fundamental side, new insights into NC growth, chemical transformations, and self-organization can be gained from rapidly progressing in situ characterization and direct imaging techniques. New phenomena are constantly being discovered in the photophysics of NCs and in the electronic properties of NC solids. In this Nano Focus, we review the state of the art in research on colloidal NCs focusing on the most recent works published in the last 2 years.

  7. Influence of Dopant Distribution on the Plasmonic Properties of Indium Tin Oxide Nanocrystals

    SciTech Connect

    Lounis, SD; Runnerstrom, EL; Bergerud, A; Nordlund, D; Milliron, DJ

    2014-05-14

    Doped metal oxide nanocrystals represent an exciting frontier for colloidal synthesis of plasmonic materials, displaying unique optoelectronic properties and showing promise for a variety of applications. However, fundamental questions about the nature of doping in these materials remain. In this article, the strong influence of radial dopant distribution on the optoelectronic properties of colloidal indium tin oxide nanocrystals is reported. Comparing elemental depth-profiling by X-ray photoelectron spectroscopy (XPS) with detailed modeling and simulation of the optical extinction of these nanocrystals using the Drude model for free electrons, a correlation between surface segregation of tin ions and the average activation of dopants is observed. A strong influence of surface segregation of tin on the line shape of the localized surface plasmon resonance (LSPR) is also reported. Samples with tin segregated near the surface show a symmetric line shape that suggests weak or no damping of the plasmon by ionized impurities. It is suggested that segregation of tin near the surface facilitates compensation of the dopant ions by electronic defects and oxygen interstitials, thus reducing activation. A core shell model is proposed to explain the observed differences in line shape. These results demonstrate the nuanced role of dopant distribution in determining the optoelectronic properties of semiconductor nanocrystals and suggest that more detailed study of the distribution and structure of defects in plasmonic colloidal nanocrystals is warranted.

  8. Doped Sodium Aluminum Hydride: Fundamental Studies and Practical Development of a Promising New Hydrogen Storage Material

    NASA Astrophysics Data System (ADS)

    Jensen, Craig

    2004-03-01

    In 1997, Bogdanovic and Schwickardi reported that the elimination of hydrogen from solid NaAlH4 is markedly accelerated and rendered reversible under moderate conditions upon mixing the hydride with a few mole percent of selected transition metal complexes. We found that doping the hydride through an alternative, mechanical milling method leads to considerable improvements in the practical hydrogen cycling performance of the hydride. It now appears that a variation of the doped hydride could possibly be developed as a viable means for the onboard storage of hydrogen. However, no dopant precursors have been found that give a greater kinetic enhancement than those cataloged in Bogdanovic's original, 1995 patent. Similarly, only the sodium and mixed sodium, lithium salts of the alanates have been found undergo largely reversible dehydrogenation under moderate conditions upon doping. This lack of progress is surprising in view of the recent "gold rush" flurry of activity that has been direct towards the development of alanates as practical onboard hydrogen carriers. Clearly, these efforts have been handicapped by a lack of understanding of the nature and mechanism of action the dopants. We have therefore initiated efforts to elucidate the fundamental basis of the remarkable hydrogen storage properties of this material. Our efforts have pointed to a model of the material in which the dopants are substituted into the bulk hydride lattice. A detailed version of this model has emerged from our recent infra red, Raman, and electron paramagnetic resonance spectroscopic studies as well as neutron diffraction, inelastic neutron scattering, and kinetic investigations of the doped hydride. The results of these studies will be presented and discussed in terms of their relationship to our "substitutional" model of the doped hydride.

  9. Material fundamentals and clinical performance of plasma-sprayed hydroxyapatite coatings: a review.

    PubMed

    Sun, L; Berndt, C C; Gross, K A; Kucuk, A

    2001-01-01

    The clinical use of plasma-sprayed hydroxyapatite (HA) coatings on metal implants has aroused as many controversies as interests over the last decade. Although faster and stronger fixation and more bone growth have been revealed, the performance of HA-coated implants has been doubted. This article will initially address the fundamentals of the material selection, design, and processing of the HA coating and show how the coating microstructure and properties can be a good predictor of the expected behavior in the body. Further discussion will clarify the major concerns with the clinical use of HA coatings and introduce a comprehensive review concerning the outcomes experienced with respect to clinical practice over the past 5 years. A reflection on the results indicates that HA coatings can promote earlier and stronger fixation but exhibit a durability that can be related to the coating quality. Specific relationships between coating quality and clinical performance are being established as characterization methods disclose more information about the coating.

  10. The high-temperature vaporization/decomposition of actinide materials: Fundamental and technological aspects

    NASA Astrophysics Data System (ADS)

    Haire, R. G.

    1997-08-01

    The unique and variable chemistry exhibited across the actinide series offers a scientifically challenging group of elements. Investigations of their high-temperature materials science and thermodynamics can provide important insights into fundamental actinide science and generate critical information for technological applications. The wide variations in the physicochemical properties and the availability of the various actinide elements necessitates special experimental techniques be employed, even when investigating a single property (e.g., the enthalpy of vaporization). Experimental approaches range can from classical to novel methods to permit studies of the rarer and the more intensely radioactive members. We have developed special equipment and techniques to investigate the high-temperature, physicochemical properties of several actinides through Md, as well as the precursor elements, radium and actinium. These experimental approaches employed both alloys and solid solutions of compounds, in addition to the pure elements themselves. The vaporization/decomposition of compounds and the sublimation of the elements, together with the associated thermodynamics, are the main issues. Results for several of the actinide elements, some of the techniques employed and systematic comparisons of the thermochemical aspects of bonding are discussed to give a fuller understanding of the series as a whole.

  11. Nanocrystals of Cesium Lead Halide Perovskites (CsPbX₃, X = Cl, Br, and I): Novel Optoelectronic Materials Showing Bright Emission with Wide Color Gamut.

    PubMed

    Protesescu, Loredana; Yakunin, Sergii; Bodnarchuk, Maryna I; Krieg, Franziska; Caputo, Riccarda; Hendon, Christopher H; Yang, Ruo Xi; Walsh, Aron; Kovalenko, Maksym V

    2015-06-10

    Metal halides perovskites, such as hybrid organic-inorganic CH3NH3PbI3, are newcomer optoelectronic materials that have attracted enormous attention as solution-deposited absorbing layers in solar cells with power conversion efficiencies reaching 20%. Herein we demonstrate a new avenue for halide perovskites by designing highly luminescent perovskite-based colloidal quantum dot materials. We have synthesized monodisperse colloidal nanocubes (4-15 nm edge lengths) of fully inorganic cesium lead halide perovskites (CsPbX3, X = Cl, Br, and I or mixed halide systems Cl/Br and Br/I) using inexpensive commercial precursors. Through compositional modulations and quantum size-effects, the bandgap energies and emission spectra are readily tunable over the entire visible spectral region of 410-700 nm. The photoluminescence of CsPbX3 nanocrystals is characterized by narrow emission line-widths of 12-42 nm, wide color gamut covering up to 140% of the NTSC color standard, high quantum yields of up to 90%, and radiative lifetimes in the range of 1-29 ns. The compelling combination of enhanced optical properties and chemical robustness makes CsPbX3 nanocrystals appealing for optoelectronic applications, particularly for blue and green spectral regions (410-530 nm), where typical metal chalcogenide-based quantum dots suffer from photodegradation.

  12. Nanocrystals of Cesium Lead Halide Perovskites (CsPbX3, X = Cl, Br, and I): Novel Optoelectronic Materials Showing Bright Emission with Wide Color Gamut

    PubMed Central

    2015-01-01

    Metal halides perovskites, such as hybrid organic–inorganic CH3NH3PbI3, are newcomer optoelectronic materials that have attracted enormous attention as solution-deposited absorbing layers in solar cells with power conversion efficiencies reaching 20%. Herein we demonstrate a new avenue for halide perovskites by designing highly luminescent perovskite-based colloidal quantum dot materials. We have synthesized monodisperse colloidal nanocubes (4–15 nm edge lengths) of fully inorganic cesium lead halide perovskites (CsPbX3, X = Cl, Br, and I or mixed halide systems Cl/Br and Br/I) using inexpensive commercial precursors. Through compositional modulations and quantum size-effects, the bandgap energies and emission spectra are readily tunable over the entire visible spectral region of 410–700 nm. The photoluminescence of CsPbX3 nanocrystals is characterized by narrow emission line-widths of 12–42 nm, wide color gamut covering up to 140% of the NTSC color standard, high quantum yields of up to 90%, and radiative lifetimes in the range of 1–29 ns. The compelling combination of enhanced optical properties and chemical robustness makes CsPbX3 nanocrystals appealing for optoelectronic applications, particularly for blue and green spectral regions (410–530 nm), where typical metal chalcogenide-based quantum dots suffer from photodegradation. PMID:25633588

  13. The size control of silver nanocrystals with different polyols and its application to low-reflection coating materials

    NASA Astrophysics Data System (ADS)

    Park, Keum Hwan; Im, Sang Hyuk; Park, O. Ok

    2011-01-01

    The size of silver nanocrystals in polyol synthesis can be simply controlled by tuning the viscosity of the reaction medium such as ethylene glycol, 1,2-propanediol, 1,4-butanediol and 1,5-pentanediol. We found that a higher viscose medium (1,5-pentanediol) led to monodispersed smaller particles thanks to the slow addition of silver atoms into the nuclei. Size-controlled silver nanocrystals of 30 nm were obtained in a viscosity controlled medium of 1,5-pentanediol to synthesize a low refractive index filler by coating with silica and subsequent etching of the silver core. The coated low-reflection layer from the hollow silica nanoparticles on polyethylene terephthalate (PET) film can greatly reduce the reflection of the PET film from 10% to 2% over the entire visible region.

  14. A fundamental discussion of what triggers localized deformation in geological materials

    NASA Astrophysics Data System (ADS)

    Peters, Max; Paesold, Martin; Poulet, Thomas; Herwegh, Marco; Regenauer-Lieb, Klaus; Veveakis, Manolis

    2015-04-01

    critical amount of dissipative work translated into heat over the diffusive capacity of the system by an instability study designed for such materials (Gruntfest, 1963). With respect to our numerical experiments, this critical parameter determines the timing when the entire amount of deformation energy translated into heat cannot be diffusively transported out of the system anymore. The resulting local temperature rise then induces strain localization. In contrast to classical shear heating scenarios with (catastrophic) thermal runaways, temperature variations of less than 1 K are sufficient for this localization mode to occur due to the balance between heat producing (e.g. dislocation creep) and consuming (grain growth) processes in the present setup. We demonstrate that this rise in latent heat is sufficient to provoke grain growth, operating as an endothermic reaction, stabilizing the simulated localized structure in turn. Various localized ductile structures, such as folded or boudinaged layers, can therefore be placed at the same material failure mode due to fundamental energy bifurcations triggered by dissipative work out of homogeneous state. Finally, we will discuss situations, in which structural heterogeneities are considered negligible and where the energy theory described here plays an underlying role by means of a comparison between numerical experiments and natural examples. REFERENCES Austin, N. and Evans, B. (2007). Paleowattmeters: A scaling relation for dynamically recrystallized grain size. Geology, 35. Gruntfest, I.J. (1963). Thermal feedback in liquid flow, plane shear at constant stress. Transactions of the Society of Rheology, 7. Hansen, L.N. and Zimmermann, M.E. and Dillman, A.M. and Kohlstedt, D.L (2012). Strain localization in olivine aggregates at high temperature: a laboratory comparison of constant-strain-rate and constant-stress boundary conditions. Earth and Planetary Science Letters, 333-334. Herwegh, M., Poulet, T., Karrech, A. and

  15. OLED Fundamentals: Materials, Devices, and Processing of Organic Light-Emitting Diodes

    SciTech Connect

    Blochwitz-Nimoth, Jan; Bhandari, Abhinav; Boesch, Damien; Fincher, Curtis R.; Gaspar, Daniel J.; Gotthold, David W.; Greiner, Mark T.; Kido, Junji; Kondakov, Denis; Korotkov, Roman; Krylova, Valentina A.; Loeser, Falk; Lu, Min-Hao; Lu, Zheng-Hong; Lussem, Bjorn; Moro, Lorenza; Padmaperuma, Asanga B.; Polikarpov, Evgueni; Rostovtsev, Vsevolod V.; Sasabe, Hisahiro; Silverman, Gary; Thompson, Mark E.; Tietze, Max; Tyan, Yuan-Sheng; Weaver, Michael; Xin , Xu; Zeng, Xianghui

    2015-05-26

    -efficiency OLED demonstrated in 1987. Thus, we expect to see exciting advances in the science, technology and commercialization in the coming years. We hope that this book helps to advance the field in some small way. Contributors to this monograph are experts from top academic institutions, industry and national laboratories who provide comprehensive and up-to-date coverage of the rapidly evolving field of OLEDs. Furthermore, this monograph collects in one place, for the first time, key topics across the field of OLEDs, from fundamental chemistry and physics, to practical materials science and engineering topics, to aspects of design and manufacturing. The monograph synthesizes and puts into context information scattered throughout the literature for easy review in one book. The scope of the monograph reflects the necessity to focus on new technological challenges brought about by the transition to manufacturing. In the Section 1, all materials of construction of the OLED device are covered, from substrate to encapsulation. In Section 2, for the first time, additional challenges in devices and processing are addressed. This book is geared towards a broad audience, including materials scientists, device physicists, synthetic chemists and electrical engineers. Furthermore, this book makes a great introduction to scientists in industry and academia, as well as graduate students interested in applied aspects of photophysics and electrochemistry in organic thin films. This book is a comprehensive source for OLED R&D professionals from all backgrounds and institutions.

  16. Advanced biomaterials from renewable resources: An investigation on cellulose nanocrystal composites and carbon dioxide extraction of rendered materials

    NASA Astrophysics Data System (ADS)

    Orellana, Jose Luis

    The annual global consumption of petroleum-based plastics is approximately 280 million tons and is impacting the sustainability of our planet and prosperity of future generations. One solution is the development of bio-based polymer materials with advanced properties for commercial applications. Therefore, the ultimate goal of this dissertation is to investigate the properties of new bio-based materials for broader applications. This dissertation includes two research areas: cellulose nanocomposites, and CO2 extractions of rendered fat. In the first half, cellulose nanocrystals (CNCs), which exhibit excellent mechanical and optical properties, were investigated for the reinforcement of a biodegradable polymer. The properties of these nanocomposites were studied to intellectually contribute to the understanding of the reinforcement mechanisms of CNC nanocomposites. In the second half, a more efficient and greener extraction of fat from rendered materials (RMs) was explored to broaden their potential applications, which include protein-based polymers and biofuels. Since CNCs are hydrophilic, surface modification with various surfactants was first accomplished in this research, increasing the dispersion stability in non-polar solvents by at least a month. Only 1 wt.% of surfactant with respect to CNCs was needed to afford a significant increase in the CNC stability, representing a much lower percentage than the values reported in the literature. Moreover, these CNCs showed the ability to selfassemble into local liquid crystal structures, a potential advantage for polymer reinforcement. CNCs were subsequently investigated as an additive for polylactic acid (PLA), which is the most widely used synthetic biopolymer in the market. CNC addition yielded a 61% increase in toughness at 1 wt.% CNC load. The tensile strength and modulus were not affected by the CNC addition, addressing one of the most frequent issues in the toughening of polymers. In addition, polarized

  17. Porous networks of CdSe nanocrystal chains from ultrafine Cd(OH)2 nanowires and their composite materials.

    PubMed

    Ko, Sungwook; Kim, Jeong Won; Moon, Geon Dae; Shim, Hee-Sang; Kim, Won Bae; Jeong, Unyong

    2010-03-16

    Long ultrathin Cd(OH)(2) nanowires have been selectively grown on silica colloids in a basic aqueous condition. The Cd(OH)(2) nanowires could be detached from the surface of the silica colloids by simply applying ultrasonication and then transformed into isolated CdSe nanocrystal chains. When the transformation into CdSe was conducted without detaching the Cd(OH)(2) nanowires, nanoporous CdSe shells composed of wire-like nanocrystal chains were produced. The good solubility of the Cd(OH)(2) nanowires in both hydrophilic and hydrophobic solvents facilitated the formation of composites with quantum dots, magnetic particles, organic molecules, and polymers. Embedding premade quantum dots possessed broad light absorption range and enhanced photoluminescence. Large amount of superparamagnetic particles endowed a fast magnetic response in addition to the fluorescence. Composites of organic/nanocrystal chains were readily fabricated by employing the electrostatic attraction between the positively charged Cd(OH)(2) nanowires and negatively charged polymers or small molecules.

  18. Silicon Nanocrystal Synthesis in Microplasma Reactor

    NASA Astrophysics Data System (ADS)

    Nozaki, Tomohiro; Sasaki, Kenji; Ogino, Tomohisa; Asahi, Daisuke; Okazaki, Ken

    Nanocrystalline silicon particles with grains smaller than 5 nm are widely recognized as a key material in optoelectronic devices, lithium battery electrodes, and bio-medical labels. Another important characteristic is that silicon is an environmentally safe material that is used in numerous silicon technologies. To date, several synthesis methods such as sputtering, laser ablation, and plasma-enhanced chemical vapor deposition (PECVD) based on low-pressure silane chemistry (SiH4) have been developed for precise control of size and density distributions of silicon nanocrystals. In this study, we explore the possibility of microplasma technologies for efficient production of mono-dispersed nanocrystalline silicon particles on a micrometer-scale, continuous-flow plasma reactor operated at atmospheric pressure. Mixtures of argon, hydrogen, and silicon tetrachloride were activated using a very-high-frequency (144 MHz) power source in a capillary glass tube with volume of less than 1 μl. Fundamental plasma parameters of the microplasma were characterized using optical emission spectroscopy, which respectively indicated electron density of 1015 cm-3, argon excitation temperature of 5000 K, and rotational temperature of 1500 K. Such high-density non-thermal reactive plasma can decompose silicon tetrachloride into atomic silicon to produce supersaturated silicon vapor, followed by gas-phase nucleation via three-body collision: particle synthesis in high-density plasma media is beneficial for promoting nucleation processes. In addition, further growth of silicon nuclei can be terminated in a short-residence-time reactor. Micro-Raman scattering spectra showed that as-deposited particles are mostly amorphous silicon with a small fraction of silicon nanocrystals. Transmission electron micrography confirmed individual 3-15 nm silicon nanocrystals. Although particles were not mono-dispersed, they were well separated and not coagulated.

  19. Synthesis of Silicon Nanocrystals in Microplasma Reactor

    NASA Astrophysics Data System (ADS)

    Nozaki, Tomohiro; Sasaki, Kenji; Ogino, Tomohisa; Asahi, Daisuke; Okazaki, Ken

    Nanocrystalline silicon particles with a grain size of at least less than 10 nm are widely recognized as one of the key materials in optoelectronic devices, electrodes of lithium battery, bio-medical labels. There is also important character that silicon is safe material to the environment and easily gets involved in existing silicon technologies. To date, several synthesis methods such as sputtering, laser ablation, and plasma enhanced chemical vapor deposition (PECVD) based on low-pressure silane chemistry (SiH4) have been developed for precise control of size and density distributions of silicon nanocrystals. We explore the possibility of microplasma technologies for the efficient production of mono-dispersed nanocrystalline silicon particles in a micrometer-scale, continuous-flow plasma reactor operated at atmospheric pressure. Mixtures of argon, hydrogen, and silicon tetrachloride were activated using very high frequency (VHF = 144 MHz) power source in a capillary glass tube with a volume of less than 1 μ-liter. Fundamental plasma parameters of VHF capacitively coupled microplasma were characterized by optical emission spectroscopy, showing electron density of approximately 1015 cm-3 and rotational temperature of 1500 K, respectively. Such high-density non-thermal reactive plasma has a capability of decomposing silicon tetrachloride into atomic silicon to produce supersaturated atomic silicon vapor, followed by gas phase nucleation via three-body collision. The particle synthesis in high-density plasma media is beneficial for promoting nucleation process. In addition, further growth of silicon nuclei was able to be favorably terminated in a short-residence time reactor. Micro Raman scattering spectrum showed that as-deposited particles were mostly amorphous silicon with small fraction of silicon nanocrystals. Transmission electron micrograph confirmed individual silicon nanocrystals of 3-15 nm size. Although those particles were not mono-dispersed, they were

  20. 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.

  1. Controlling upconversion nanocrystals for emerging applications.

    PubMed

    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.

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

    NASA Astrophysics Data System (ADS)

    Kramer, Nicolaas Johannes

    materials which is very interesting for certain applications. Finally the boron atoms were used to form a Lewis acidic nanocrystal surface chemistry allowing for the creation of ligand-less silicon nanocrystal solutions. This represents an immense step towards an abundant, non-toxic alternative to Pb and Cd-based nanocrystal technologies. The lack of long ligand chains enables the production of dense films with excellent electrical conductivity. This was demonstrated by forming uniform nanocrystal thin-films using simple and inexpensive spray coating techniques.

  3. Influence of fundamental material properties and air void structure on moisture damage of asphalt mixes

    NASA Astrophysics Data System (ADS)

    Arambula Mercado, Edith

    2007-12-01

    Moisture damage in asphalt mixes refers to the loss of serviceability due to the presence of moisture. The extent of moisture damage, also called moisture susceptibility, depends on internal and external factors. The internal factors relate to the properties of the materials and the microstructure distribution, while the external factors include the environmental conditions, production and construction practices, pavement design, and traffic level. The majority of the research on moisture damage is based on the hypothesis that infiltration of surface water is the main source of moisture. Of the two other principal mechanisms of water transport, permeation of water vapor and capillary rise of subsurface water, the latter has been least explored. A laboratory test and analysis methods based on X-ray computed tomography (CT) were established to assess the capillary rise of water. The amount and size of air voids filled with water were used in the capillary rise equation to estimate the distribution of the contact angles between the water and the mastic. The results were able to show the influence of air void size on capillary rise and contact angles. The relationship between air void structure and moisture susceptibility was evaluated using a fundamental fracture model based on dissipated energy of viscoelastic materials. Detailed description is provided in this dissertation on the deduction of the model equation, the selection of the model parameters, and the required testing protocols. The model parameters were obtained using mechanical tests and surface energy measurements. The microstructure of asphalt mixes prepared in the laboratory having different air void structures was captured using X-ray CT, and image analysis techniques were used to quantify the air void structure and air void connectivity. The air void structure was found to influence the mix resistance to moisture damage. To validate the fracture model, asphalt mixes with known field performance were

  4. Fundamental Studies of the Durability of Materials for Interconnects in Solid Oxide Fuel Cells

    SciTech Connect

    Frederick S. Pettit; Gerald H. Meier

    2006-06-30

    Ferritic stainless steels are a leading candidate material for use as an SOFC interconnect, but have the problem of forming volatile chromia species that lead to cathode poisoning. This project has focused both on optimization of ferritic alloys for SOFC applications and evaluating the possibility of using alternative materials. The initial efforts involved studying the oxidation behavior of a variety of chromia-forming ferritic stainless steels in the temperature range 700-900 C in atmospheres relevant to solid oxide fuel cell operation. The alloys exhibited a wide variety of oxidation behavior based on composition. A method for reducing the vaporization is to add alloying elements that lead to the formation of a thermally grown oxide layer over the protective chromia. Several commercial steels form manganese chromate on the surface. This same approach, combined with observations of TiO{sub 2} overlayer formation on the chromia forming, Ni-based superalloy IN 738, has resulted in the development of a series of Fe-22 Cr-X Ti alloys (X=0-4 wt%). Oxidation testing has indicated that this approach results in significant reduction in chromia evaporation. Unfortunately, the Ti also results in accelerated chromia scale growth. Fundamental thermo-mechanical aspects of the durability of solid oxide fuel cell (SOFC) interconnect alloys have also been investigated. A key failure mechanism for interconnects is the spallation of the chromia scale that forms on the alloy, as it is exposed to fuel cell environments. Indentation testing methods to measure the critical energy release rate (Gc) associated with the spallation of chromia scale/alloy systems have been evaluated. This approach has been used to evaluate the thermomechanical stability of chromia films as a function of oxidation exposure. The oxidation of pure nickel in SOFC environments was evaluated using thermogravimetric analysis (TGA) to determine the NiO scaling kinetics and a four-point probe was used to measure

  5. Metastability in pressure-induced structural transformations of CdSe/ZnS core/shell nanocrystals.

    PubMed

    Grünwald, Michael; Lutker, Katie; Alivisatos, A Paul; Rabani, Eran; Geissler, Phillip L

    2013-04-10

    The kinetics and thermodynamics of structural transformations under pressure depend strongly on particle size due to the influence of surface free energy. By suitable design of surface structure, composition, and passivation it is possible, in principle, to prepare nanocrystals in structures inaccessible to bulk materials. However, few realizations of such extreme size-dependent behavior exist. Here, we show with molecular dynamics computer simulation that in a model of CdSe/ZnS core/shell nanocrystals the core high-pressure structure can be made metastable under ambient conditions by tuning the thickness of the shell. In nanocrystals with thick shells, we furthermore observe a wurtzite to NiAs transformation, which does not occur in the pure bulk materials. These phenomena are linked to a fundamental change in the atomistic transformation mechanism from heterogeneous nucleation at the surface to homogeneous nucleation in the crystal core.

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

    PubMed

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

    2017-08-22

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

  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. Pyrite (FeS2) nanocrystals as inexpensive high-performance lithium-ion cathode and sodium-ion anode materials.

    PubMed

    Walter, Marc; Zünd, Tanja; Kovalenko, Maksym V

    2015-05-28

    In light of the impeding depletion of fossil fuels and necessity to lower carbon dioxide emissions, economically viable high-performance batteries are urgently needed for numerous applications ranging from electric cars to stationary large-scale electricity storage. Due to its low raw material cost, non-toxicity and potentially high charge-storage capacity pyrite (FeS2) is a highly promising material for such next-generation batteries. In this work we present the electrochemical performance of FeS2 nanocrystals (NCs) as lithium-ion and sodium-ion storage materials. First, we show that nanoscopic FeS2 is a promising lithium-ion cathode material, delivering a capacity of 715 mA h g(-1) and average energy density of 1237 Wh kg(-1) for 100 cycles, twice higher than for commonly used LiCoO2 cathodes. Then we demonstrate, for the first time, that FeS2 NCs can serve as highly reversible sodium-ion anode material with long cycling life. As sodium-ion anode material, FeS2 NCs provide capacities above 500 mA h g(-1) for 400 cycles at a current rate of 1000 mA g(-1). In all our tests and control experiments, the performance of chemically synthesized nanoscale FeS2 clearly surpasses bulk FeS2 as well as large number of other nanostructured metal sulfides.

  9. Nanocrystal technology, drug delivery and clinical applications

    PubMed Central

    Junghanns, Jens-Uwe A H; Müller, Rainer H

    2008-01-01

    Nanotechnology will affect our lives tremendously over the next decade in very different fields, including medicine and pharmacy. Transfer of materials into the nanodimension changes their physical properties which were used in pharmaceutics to develop a new innovative formulation principle for poorly soluble drugs: the drug nanocrystals. The drug nanocrystals do not belong to the future; the first products are already on the market. The industrially relevant production technologies, pearl milling and high pressure homogenization, are reviewed. The physics behind the drug nanocrystals and changes of their physical properties are discussed. The marketed products are presented and the special physical effects of nanocrystals explained which are utilized in each market product. Examples of products in the development pipelines (clinical phases) are presented and the benefits for in vivo administration of drug nanocrystals are summarized in an overview. PMID:18990939

  10. Semiconductor Nanocrystals for Biological Imaging

    SciTech Connect

    Fu, Aihua; Gu, Weiwei; Larabell, Carolyn; Alivisatos, A. Paul

    2005-06-28

    Conventional organic fluorophores suffer from poor photo stability, narrow absorption spectra and broad emission feature. Semiconductor nanocrystals, on the other hand, are highly photo-stable with broad absorption spectra and narrow size-tunable emission spectra. Recent advances in the synthesis of these materials have resulted in bright, sensitive, extremely photo-stable and biocompatible semiconductor fluorophores. Commercial availability facilitates their application in a variety of unprecedented biological experiments, including multiplexed cellular imaging, long-term in vitro and in vivo labeling, deep tissue structure mapping and single particle investigation of dynamic cellular processes. Semiconductor nanocrystals are one of the first examples of nanotechnology enabling a new class of biomedical applications.

  11. Patterning nanocrystals using DNA

    SciTech Connect

    Williams, Shara Carol

    2003-01-01

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

  12. Fundamentals of Composite Materials for Undergraduate Engineering--A Filmed Presentation. Final Report.

    ERIC Educational Resources Information Center

    Busching, Herbert W.

    Curricula in undergraduate engineering have not adequately reflected present usage and knowledge of composite materials (types of rock and organic matter in which structurally dissimilar materials are combined). Wide usage of composites is expected to increase the importance of this class of materials and the need for more substantive exposure to…

  13. 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.

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

    PubMed

    Fu, Huiying; Tsang, Sai-Wing

    2012-04-07

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

  15. Mesoporous carbon-coated LiFePO4 nanocrystals co-modified with graphene and Mg2+ doping as superior cathode materials for lithium ion batteries

    NASA Astrophysics Data System (ADS)

    Wang, Bo; Xu, Binghui; Liu, Tiefeng; Liu, Peng; Guo, Chenfeng; Wang, Shuo; Wang, Qiuming; Xiong, Zhigang; Wang, Dianlong; Zhao, X. S.

    2013-12-01

    In this work, mesoporous carbon-coated LiFePO4 nanocrystals further co-modified with graphene and Mg2+ doping (G/LFMP) were synthesized by a modified rheological phase method to improve the speed of lithium storage as well as cycling stability. The mesoporous structure of LiFePO4 nanocrystals was designed and realized by introducing the bead milling technique, which assisted in forming sucrose-pyrolytic carbon nanoparticles as the template for generating mesopores. For comparison purposes, samples modified only with graphene (G/LFP) or Mg2+ doping (LFMP) as well as pure LiFePO4 (LFP) were also prepared and investigated. Microscopic observation and nitrogen sorption analysis have revealed the mesoporous morphologies of the as-prepared composites. X-ray diffraction (XRD) and Rietveld refinement data demonstrated that the Mg-doped LiFePO4 is a single olivine-type phase and well crystallized with shortened Fe-O and P-O bonds and a lengthened Li-O bond, resulting in an enhanced Li+ diffusion velocity. Electrochemical properties have also been investigated after assembling coin cells with the as-prepared composites as the cathode active materials. Remarkably, the G/LFMP composite has exhibited the best electrochemical properties, including fast lithium storage performance and excellent cycle stability. That is because the modification of graphene provided active sites for nuclei, restricted the in situ crystallite growth, increased the electronic conductivity and reduced the interface reaction current density, while, Mg2+ doping improved the intrinsically electronic and ionic transfer properties of LFP crystals. Moreover, in the G/LFMP composite, the graphene component plays the role of ``cushion'' as it could quickly realize capacity response, buffering the impact to LFMP under the conditions of high-rate charging or discharging, which results in a pre-eminent rate capability and cycling stability.In this work, mesoporous carbon-coated LiFePO4 nanocrystals further co

  16. Tunable and responsive plasmonic properties of metal oxide nanocrystals

    NASA Astrophysics Data System (ADS)

    Milliron, Delia

    2015-03-01

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

  17. Mesoporous carbon-coated LiFePO4 nanocrystals co-modified with graphene and Mg2+ doping as superior cathode materials for lithium ion batteries.

    PubMed

    Wang, Bo; Xu, Binghui; Liu, Tiefeng; Liu, Peng; Guo, Chenfeng; Wang, Shuo; Wang, Qiuming; Xiong, Zhigang; Wang, Dianlong; Zhao, X S

    2014-01-21

    In this work, mesoporous carbon-coated LiFePO4 nanocrystals further co-modified with graphene and Mg(2+) doping (G/LFMP) were synthesized by a modified rheological phase method to improve the speed of lithium storage as well as cycling stability. The mesoporous structure of LiFePO4 nanocrystals was designed and realized by introducing the bead milling technique, which assisted in forming sucrose-pyrolytic carbon nanoparticles as the template for generating mesopores. For comparison purposes, samples modified only with graphene (G/LFP) or Mg(2+) doping (LFMP) as well as pure LiFePO4 (LFP) were also prepared and investigated. Microscopic observation and nitrogen sorption analysis have revealed the mesoporous morphologies of the as-prepared composites. X-ray diffraction (XRD) and Rietveld refinement data demonstrated that the Mg-doped LiFePO4 is a single olivine-type phase and well crystallized with shortened Fe-O and P-O bonds and a lengthened Li-O bond, resulting in an enhanced Li(+) diffusion velocity. Electrochemical properties have also been investigated after assembling coin cells with the as-prepared composites as the cathode active materials. Remarkably, the G/LFMP composite has exhibited the best electrochemical properties, including fast lithium storage performance and excellent cycle stability. That is because the modification of graphene provided active sites for nuclei, restricted the in situ crystallite growth, increased the electronic conductivity and reduced the interface reaction current density, while, Mg(2+) doping improved the intrinsically electronic and ionic transfer properties of LFP crystals. Moreover, in the G/LFMP composite, the graphene component plays the role of "cushion" as it could quickly realize capacity response, buffering the impact to LFMP under the conditions of high-rate charging or discharging, which results in a pre-eminent rate capability and cycling stability.

  18. 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

  19. Nonlinear optical properties of semiconductor nanocrystals

    NASA Astrophysics Data System (ADS)

    Ricard, Gianpiero Banfi Vittorio Degiorgio Daniel

    1998-05-01

    nanocrystals can be tailored by controlling the temperature or time of the treatment. The major problem is the size dispersion of the crystallites, which is intrinsic to the diffusion process. At present, this is the major source of the undesired inhomogeneous broadening of the optical transition lines of the SDGs. Efforts are at present being made to fabricate materials, SDGs included, which embed nanocrystals with a reduced spread of sizes. The interest in the nonlinear optical properties is due not only to fundamental reasons but also to possible applications for optical devices. Generally speaking, resonant nonlinearities are much larger than non-resonant nonlinearities, but they are not necessarily the most interesting for applications because materials at resonance absorb the incident radiation and also present long response times. The studies below the bandgap seem to indicate that the values of the intrinsic nonlinearities of nanocrystals in the structures which are at present available are similar to those of the bulk. New and better controlled structures are now under development and have to be tested from the viewpoint of optical nonlinearities. In several situations SDGs cannot be modelled as an ensemble of freely standing nanocrystals, with the glass matrix playing the role of an inert support. Phenomena such as trapping and darkening, which are very probably connected with electronic states at the glasssemiconductor interface, may play a role in determining the optical response. They might give rise to an extrinsic optical nonlinearity which can be even larger than the intrinsic nonlinearity. The physical processes which are involved in these extrinsic nonlinearities are poorly understood and at present being investigated.

  20. Aviation Maintenance Technology. General. G102 Fundamentals of Aircraft Maintenance. Instructor Material.

    ERIC Educational Resources Information Center

    Oklahoma State Board of Vocational and Technical Education, Stillwater. Curriculum and Instructional Materials Center.

    These instructor materials for an aviation maintenance technology course contain four instructional modules. The modules cover the following topics: identifying basic components of aircraft, performing aircraft cleaning and corrosion control, interpreting blueprints and drawing sketches, identifying structural materials, and performing basic…

  1. Aviation Maintenance Technology. General. G102 Fundamentals of Aircraft Maintenance. Instructor Material.

    ERIC Educational Resources Information Center

    Oklahoma State Board of Vocational and Technical Education, Stillwater. Curriculum and Instructional Materials Center.

    These instructor materials for an aviation maintenance technology course contain four instructional modules. The modules cover the following topics: identifying basic components of aircraft, performing aircraft cleaning and corrosion control, interpreting blueprints and drawing sketches, identifying structural materials, and performing basic…

  2. Ultra-large-scale syntheses of monodisperse nanocrystals

    NASA Astrophysics Data System (ADS)

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

    2004-12-01

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

  3. FUNDAMENTAL STUDIES OF THE DURABILITY OF MATERIALS FOR INTERCONNECTS IN SOLID OXIDE FUEL CELLS

    SciTech Connect

    Frederick S. Pettit; Gerald H. Meier

    2003-06-30

    This report describes the result of the first eight months of effort on a project directed at improving metallic interconnect materials for solid oxide fuel cells (SOFCs). The results include cyclic oxidation studies of a group of ferritic alloys, which are candidate interconnect materials. The exposures have been carried out in simulated fuel cell atmospheres. The oxidation morphologies have been characterized and the ASR has been measured for the oxide scales. The effect of fuel cell electric current density on chromia growth rates has been considered The thermomechanical behavior of the scales has been investigated by stress measurements using x-ray diffraction and interfacial fracture toughness measurements using indentation. The ultimate goal of this thrust is to use knowledge of changes in oxide thickness, stress and adhesion to develop accelerated testing methods for evaluating SOFC interconnect alloys. Finally a theoretical assessment of the potential for use of ''new'' metallic materials as interconnect materials has been conducted and is presented in this report. Alloys being considered include materials based on pure nickel, materials based on the ''Invar'' concept, and coated materials to optimize properties in both the anode and cathode gases.

  4. Pyrite (FeS2) nanocrystals as inexpensive high-performance lithium-ion cathode and sodium-ion anode materials

    NASA Astrophysics Data System (ADS)

    Walter, Marc; Zünd, Tanja; Kovalenko, Maksym V.

    2015-05-01

    In light of the impeding depletion of fossil fuels and necessity to lower carbon dioxide emissions, economically viable high-performance batteries are urgently needed for numerous applications ranging from electric cars to stationary large-scale electricity storage. Due to its low raw material cost, non-toxicity and potentially high charge-storage capacity pyrite (FeS2) is a highly promising material for such next-generation batteries. In this work we present the electrochemical performance of FeS2 nanocrystals (NCs) as lithium-ion and sodium-ion storage materials. First, we show that nanoscopic FeS2 is a promising lithium-ion cathode material, delivering a capacity of 715 mA h g-1 and average energy density of 1237 Wh kg-1 for 100 cycles, twice higher than for commonly used LiCoO2 cathodes. Then we demonstrate, for the first time, that FeS2 NCs can serve as highly reversible sodium-ion anode material with long cycling life. As sodium-ion anode material, FeS2 NCs provide capacities above 500 mA h g-1 for 400 cycles at a current rate of 1000 mA g-1. In all our tests and control experiments, the performance of chemically synthesized nanoscale FeS2 clearly surpasses bulk FeS2 as well as large number of other nanostructured metal sulfides.In light of the impeding depletion of fossil fuels and necessity to lower carbon dioxide emissions, economically viable high-performance batteries are urgently needed for numerous applications ranging from electric cars to stationary large-scale electricity storage. Due to its low raw material cost, non-toxicity and potentially high charge-storage capacity pyrite (FeS2) is a highly promising material for such next-generation batteries. In this work we present the electrochemical performance of FeS2 nanocrystals (NCs) as lithium-ion and sodium-ion storage materials. First, we show that nanoscopic FeS2 is a promising lithium-ion cathode material, delivering a capacity of 715 mA h g-1 and average energy density of 1237 Wh kg-1 for 100

  5. Growth of platinum nanocrystals

    SciTech Connect

    2009-01-01

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

  6. FUNDAMENTAL SAFETY TESTING AND ANALYSIS OF HYDROGEN STORAGE MATERIALS AND SYSTEMS

    SciTech Connect

    Anton, D

    2007-05-01

    Hydrogen is seen as the future automobile energy storage media due to its inherent cleanliness upon oxidation and its ready utilization in fuel cell applications. Its physical storage in light weight, low volume systems is a key technical requirement. In searching for ever higher gravimetric and volumetric density hydrogen storage materials and systems, it is inevitable that higher energy density materials will be studied and used. To make safe and commercially acceptable systems, it is important to understand quantitatively, the risks involved in using and handling these materials and to develop appropriate risk mitigation strategies to handle unforeseen accidental events. To evaluate these materials and systems, an IPHE sanctioned program was initiated in 2006 partnering laboratories from Europe, North America and Japan. The objective of this international program is to understanding the physical risks involved in synthesis, handling and utilization of solid state hydrogen storage materials and to develop methods to mitigate these risks. This understanding will support ultimate acceptance of commercially high density hydrogen storage system designs. An overview of the approaches to be taken to achieve this objective will be given. Initial experimental results will be presented on environmental exposure of NaAlH{sub 4}, a candidate high density hydrogen storage compound. The tests to be shown are based on United Nations recommendations for the transport of hazardous materials and include air and water exposure of the hydride at three hydrogen charge levels in various physical configurations. Additional tests developed by the American Society for Testing and Materials were used to quantify the dust cloud ignition characteristics of this material which may result from accidental high energy impacts and system breach. Results of these tests are shown along with necessary risk mitigation techniques used in the synthesis and fabrication of a prototype hydrogen storage

  7. An evaluation of complementary approaches to elucidate fundamental interfacial phenomena driving adhesion of energetic materials

    SciTech Connect

    Hoss, Darby J.; Knepper, Robert; Hotchkiss, Peter J.; Tappan, Alexander S.; Boudouris, Bryan W.; Beaudoin, Stephen P.

    2016-03-23

    In this study, cohesive Hamaker constants of solid materials are measured via optical and dielectric properties (i.e., Lifshitz theory), inverse gas chromatography (IGC), and contact angle measurements. To date, however, a comparison across these measurement techniques for common energetic materials has not been reported. This has been due to the inability of the community to produce samples of energetic materials that are readily compatible with contact angle measurements. Here we overcome this limitation by using physical vapor deposition to produce thin films of five common energetic materials, and the contact angle measurement approach is applied to estimate the cohesive Hamaker constants and surface energy components of the materials. The cohesive Hamaker constants range from 85 zJ to 135 zJ across the different films. When these Hamaker constants are compared to prior work using Lifshitz theory and nonpolar probe IGC, the relative magnitudes can be ordered as follows: contact angle > Lifshitz > IGC. Furthermore, the dispersive surface energy components estimated here are in good agreement with those estimated by IGC. Due to these results, researchers and technologists will now have access to a comprehensive database of adhesion constants which describe the behavior of these energetic materials over a range of settings.

  8. An evaluation of complementary approaches to elucidate fundamental interfacial phenomena driving adhesion of energetic materials.

    PubMed

    Hoss, Darby J; Knepper, Robert; Hotchkiss, Peter J; Tappan, Alexander S; Boudouris, Bryan W; Beaudoin, Stephen P

    2016-07-01

    Cohesive Hamaker constants of solid materials are measured via optical and dielectric properties (i.e., Lifshitz theory), inverse gas chromatography (IGC), and contact angle measurements. To date, however, a comparison across these measurement techniques for common energetic materials has not been reported. This has been due to the inability of the community to produce samples of energetic materials that are readily compatible with contact angle measurements. Here we overcome this limitation by using physical vapor deposition to produce thin films of five common energetic materials, and the contact angle measurement approach is applied to estimate the cohesive Hamaker constants and surface energy components of the materials. The cohesive Hamaker constants range from 85zJ to 135zJ across the different films. When these Hamaker constants are compared to prior work using Lifshitz theory and nonpolar probe IGC, the relative magnitudes can be ordered as follows: contact angle>Lifshitz>IGC. Furthermore, the dispersive surface energy components estimated here are in good agreement with those estimated by IGC. Due to these results, researchers and technologists will now have access to a comprehensive database of adhesion constants which describe the behavior of these energetic materials over a range of settings. Copyright © 2016 Elsevier Inc. All rights reserved.

  9. An evaluation of complementary approaches to elucidate fundamental interfacial phenomena driving adhesion of energetic materials

    DOE PAGES

    Hoss, Darby J.; Knepper, Robert; Hotchkiss, Peter J.; ...

    2016-03-23

    In this study, cohesive Hamaker constants of solid materials are measured via optical and dielectric properties (i.e., Lifshitz theory), inverse gas chromatography (IGC), and contact angle measurements. To date, however, a comparison across these measurement techniques for common energetic materials has not been reported. This has been due to the inability of the community to produce samples of energetic materials that are readily compatible with contact angle measurements. Here we overcome this limitation by using physical vapor deposition to produce thin films of five common energetic materials, and the contact angle measurement approach is applied to estimate the cohesive Hamakermore » constants and surface energy components of the materials. The cohesive Hamaker constants range from 85 zJ to 135 zJ across the different films. When these Hamaker constants are compared to prior work using Lifshitz theory and nonpolar probe IGC, the relative magnitudes can be ordered as follows: contact angle > Lifshitz > IGC. Furthermore, the dispersive surface energy components estimated here are in good agreement with those estimated by IGC. Due to these results, researchers and technologists will now have access to a comprehensive database of adhesion constants which describe the behavior of these energetic materials over a range of settings.« less

  10. Fundamental Studies of the Role of Grain Boundaries on Uniform Corrosion of Advanced Nuclear Reactor Materials

    SciTech Connect

    Taheri, Mitra; Motta, Arthur; Marquis, Emmanuelle

    2016-05-20

    The main objective of this proposal is to develop fundamental understanding of the role of grain boundaries in stable oxide growth. To understand the process of oxide layer destabilization, it is necessary to observe the early stages of corrosion. During conventional studies in which a sample is exposed and examined after removal from the autoclave, the destabilization process will normally have already taken place, and is only examined post facto. To capture the instants of oxide destabilization, it is necessary to observe it in situ; however, significant questions always arise as to the influence of the corrosion geometry and conditions on the corrosion process. Thus, a combination of post facto examinations and in situ studies is proposed, which also combines state-of-the-art characterization techniques to derive a complete understanding of the destabilization process and the role of grain boundaries.

  11. Advanced Small Rocket Chambers. Basic Program and Option 2: Fundamental Processes and Material Evaluation

    NASA Technical Reports Server (NTRS)

    Jassowski, Donald M.

    1993-01-01

    Propellants, chamber materials, and processes for fabrication of small high performance radiation cooled liquid rocket engines were evaluated to determine candidates for eventual demonstration in flight-type thrusters. Both storable and cryogenic propellant systems were considered. The storable propellant systems chosen for further study were nitrogen tetroxide oxidizer with either hydrazine or monomethylhydrazine as fuel. The cryogenic propellants chosen were oxygen with either hydrogen or methane as fuel. Chamber material candidates were chemical vapor deposition (CVD) rhenium protected from oxidation by CVD iridium for the chamber hot section, and film cooled wrought platinum-rhodium or regeneratively cooled stainless steel for the front end section exposed to partially reacted propellants. Laser diagnostics of the combustion products near the hot chamber surface and measurements at the surface layer were performed in a collaborative program at Sandia National Laboratories, Livermore, CA. The Material Sample Test Apparatus, a laboratory system to simulate the combustion environment in terms of gas and material temperature, composition, and pressure up to 6 Atm, was developed for these studies. Rocket engine simulator studies were conducted to evaluate the materials under simulated combustor flow conditions, in the diagnostic test chamber. These tests used the exhaust species measurement system, a device developed to monitor optically species composition and concentration in the chamber and exhaust by emission and absorption measurements.

  12. Fundamental mass transfer modeling of emission of volatile organic compounds from building materials

    NASA Astrophysics Data System (ADS)

    Bodalal, Awad Saad

    In this study, a mass transfer theory based model is presented for characterizing the VOC emissions from building materials. A 3-D diffusion model is developed to describe the emissions of volatile organic compounds (VOCs) from individual sources. Then the formulation is extended to include the emissions from composite sources (system comprising an assemblage of individual sources). The key parameters for the model (The diffusion coefficient of the VOC in the source material D, and the equilibrium partition coefficient k e) were determined independently (model parameters are determined without the use of chamber emission data). This procedure eliminated to a large extent the need for emission testing using environmental chambers, which is costly, time consuming, and may be subject to confounding sink effects. An experimental method is developed and implemented to measure directly the internal diffusion (D) and partition coefficients ( ke). The use of the method is illustrated for three types of VOC's: (i) Aliphatic Hydrocarbons, (ii) Aromatic Hydrocarbons and ( iii) Aldehydes, through typical dry building materials (carpet, plywood, particleboard, vinyl floor tile, gypsum board, sub-floor tile and OSB). Then correlations for predicting D and ke based solely on commonly available properties such as molecular weight and vapour pressure were proposed for each product and type of VOC. These correlations can be used to estimate the D and ke when direct measurement data are not available, and thus facilitate the prediction of VOC emissions from the building materials using mass transfer theory. The VOC emissions from a sub-floor material (made of the recycled automobile tires), and a particleboard are measured and predicted. Finally, a mathematical model to predict the diffusion coefficient through complex sources (floor adhesive) as a function of time was developed. Then this model (for diffusion coefficient in complex sources) was used to predict the emission rate from

  13. Fundamental investigation of ultraviolet radiation effects in polymeric film-forming materials

    NASA Technical Reports Server (NTRS)

    Giori, C.; Yamauchi, T.; Llewellen, P.; Gilligan, J.

    1974-01-01

    A literature search from 1958 to present was conducted on the effect of ultraviolet radiation on polymeric materials, with particular emphasis on vacuum photolysis, mechanisms of degradation, and energy transfer phenomena. The literature from 1958 to 1968 was searched manually, while the literature from 1968 to present was searched by using a computerized keyword system. The primary objective was to provide the necessary background information for the design of new or modified materials with improved stability to the vacuum-radiation environment of space.

  14. Aviation Maintenance Technology. General. G103 Fundamentals of Regulations, Publications, and Records. Instructor Material.

    ERIC Educational Resources Information Center

    Oklahoma State Board of Vocational and Technical Education, Stillwater. Curriculum and Instructional Materials Center.

    These instructor materials for an aviation maintenance technology course contain three instructional modules. The modules cover the following topics: selecting and using regulations, publications, and records; documenting aircraft records; and exercising mechanic's privileges and limitations. Each module contains some or all of these nine basic…

  15. Fundamentals of Digital Logic, 7-1. Military Curriculum Materials for Vocational and Technical Education.

    ERIC Educational Resources Information Center

    Marine Corps, Washington, DC.

    Targeted for grades 10 through adult, these military-developed curriculum materials consist of a student lesson book with text readings and review exercises designed to prepare electronic personnel for further training in digital techniques. Covered in the five lessons are binary arithmetic (number systems, decimal systems, the mathematical form…

  16. Aviation Maintenance Technology. General. G103 Fundamentals of Regulations, Publications, and Records. Instructor Material.

    ERIC Educational Resources Information Center

    Oklahoma State Board of Vocational and Technical Education, Stillwater. Curriculum and Instructional Materials Center.

    These instructor materials for an aviation maintenance technology course contain three instructional modules. The modules cover the following topics: selecting and using regulations, publications, and records; documenting aircraft records; and exercising mechanic's privileges and limitations. Each module contains some or all of these nine basic…

  17. Fundamental Analysis of Piezocatalysis Process on the Surfaces of Strained Piezoelectric Materials

    PubMed Central

    Starr, Matthew B.; Wang, Xudong

    2013-01-01

    Recently, the strain state of a piezoelectric electrode has been found to impact the electrochemical activity taking place between the piezoelectric material and its solution environment. This effect, dubbed piezocatalysis, is prominent in piezoelectric materials because the strain state and electronic state of these materials are strongly coupled. Herein we develop a general theoretical analysis of the piezocatalysis process utilizing well-established piezoelectric, semiconductor, molecular orbital and electrochemistry frameworks. The analysis shows good agreement with experimental results, reproducing the time-dependent voltage drop and H2 production behaviors of an oscillating piezoelectric Pb(Mg1/3Nb2/3)O3-32PbTiO3 (PMN-PT) cantilever in deionized water environment. This study provides general guidance for future experiments utilizing different piezoelectric materials, such as ZnO, BaTiO3, PbTiO3, and PMN-PT. Our analysis indicates a high piezoelectric coupling coefficient and a low electrical conductivity are desired for enabling high electrochemical activity; whereas electrical permittivity must be optimized to balance piezoelectric and capacitive effects. PMID:23831736

  18. Fundamental analysis of piezocatalysis process on the surfaces of strained piezoelectric materials.

    PubMed

    Starr, Matthew B; Wang, Xudong

    2013-01-01

    Recently, the strain state of a piezoelectric electrode has been found to impact the electrochemical activity taking place between the piezoelectric material and its solution environment. This effect, dubbed piezocatalysis, is prominent in piezoelectric materials because the strain state and electronic state of these materials are strongly coupled. Herein we develop a general theoretical analysis of the piezocatalysis process utilizing well-established piezoelectric, semiconductor, molecular orbital and electrochemistry frameworks. The analysis shows good agreement with experimental results, reproducing the time-dependent voltage drop and H₂ production behaviors of an oscillating piezoelectric Pb(Mg₁/₃Nb₂/₃)O₃-32PbTiO₃ (PMN-PT) cantilever in deionized water environment. This study provides general guidance for future experiments utilizing different piezoelectric materials, such as ZnO, BaTiO₃, PbTiO₃, and PMN-PT. Our analysis indicates a high piezoelectric coupling coefficient and a low electrical conductivity are desired for enabling high electrochemical activity; whereas electrical permittivity must be optimized to balance piezoelectric and capacitive effects.

  19. Military Curriculum Materials for Vocational and Technical Education. Fundamentals of Electricity 3-3.

    ERIC Educational Resources Information Center

    Ohio State Univ., Columbus. National Center for Research in Vocational Education.

    This independent self-study course on electricity was developed from military sources for use in vocational education. The course provides a source of study materials on the principles of electricity. The five lessons are divided into two parts, each of which contains criterion objectives and self-tests. The course provides basic coverage of…

  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

    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.

  1. 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.

  2. A Focused Fundamental Study of Predicting Materials Degradation & Fatigue. Volume 1

    DTIC Science & Technology

    1997-05-31

    viscosity of the lubricant can be predicted with the Einstein relationship for particulate suspensions once the concentration of sludge particles is...bearing balls while as-polished surfaces (Ra=0.08 gim) resulted in fatigue life determined by either the metal ball failing or test suspension at 100...mechanical-type wear process with the load (P), indenter geometry , elastic modulus (E), hardness (H), and fracture toughness (Kc) of the materials as the

  3. Hydrogel microparticles from lithographic processes: novel materials for fundamental and applied colloid science

    PubMed Central

    Helgeson, Matthew E.; Chapin, Stephen C.; Doyle, Patrick S.

    2011-01-01

    In recent years there has been a surge in methods to synthesize geometrically and chemically complex microparticles. Analogous to atoms, the concept of a “periodic table” of particles has emerged and continues to be expanded upon. Complementing the natural intellectual curiosity that drives the creation of increasingly intricate particles is the pull from applications that take advantage of such high-value materials. Complex particles are now being used in fields ranging from diagnostics and catalysis to self-assembly and rheology, where material composition and microstructure are closely linked with particle function. This is especially true of polymer hydrogels, which offer an attractive and broad class of base materials for synthesis. Lithography affords the ability to engineer particle properties a priori and leads to the production of homogenous ensembles of particles. This review summarizes recent advances in synthesizing hydrogel microparticles using lithographic processes and highlight a number of emerging applications. We discuss advantages and limitations of current strategies, and conclude with an outlook on future trends in the field. PMID:21516212

  4. Hydrogel microparticles from lithographic processes: novel materials for fundamental and applied colloid science.

    PubMed

    Helgeson, Matthew E; Chapin, Stephen C; Doyle, Patrick S

    2011-04-01

    In recent years there has been a surge in methods to synthesize geometrically and chemically complex microparticles. Analogous to atoms, the concept of a "periodic table" of particles has emerged and continues to be expanded upon. Complementing the natural intellectual curiosity that drives the creation of increasingly intricate particles is the pull from applications that take advantage of such high-value materials. Complex particles are now being used in fields ranging from diagnostics and catalysis to self-assembly and rheology, where material composition and microstructure are closely linked with particle function. This is especially true of polymer hydrogels, which offer an attractive and broad class of base materials for synthesis. Lithography affords the ability to engineer particle properties a priori and leads to the production of homogenous ensembles of particles. This review summarizes recent advances in synthesizing hydrogel microparticles using lithographic processes and highlight a number of emerging applications. We discuss advantages and limitations of current strategies, and conclude with an outlook on future trends in the field.

  5. Lattice Symmetry and Identification-The Fundamental Role of Reduced Cells in Materials Characterization.

    PubMed

    Mighell, A D

    2001-01-01

    In theory, physical crystals can be represented by idealized mathematical lattices. Under appropriate conditions, these representations can be used for a variety of purposes such as identifying, classifying, and understanding the physical properties of materials. Critical to these applications is the ability to construct a unique representation of the lattice. The vital link that enabled this theory to be realized in practice was provided by the 1970 paper on the determination of reduced cells. This seminal paper led to a mathematical approach to lattice analysis initially based on systematic reduction procedures and the use of standard cells. Subsequently, the process evolved to a matrix approach based on group theory and linear algebra that offered a more abstract and powerful way to look at lattices and their properties. Application of the reduced cell to both database work and laboratory research at NIST was immediately successful. Currently, this cell and/or procedures based on reduction are widely and routinely used by the general scientific community: (i) for calculating standard cells for the reporting of crystalline materials, (ii) for classifying materials, (iii) in crystallographic database work (iv) in routine x-ray and neutron diffractometry, and (v) in general crystallographic research. Especially important is its use in symmetry determination and in identification. The focus herein is on the role of the reduced cell in lattice symmetry determination.

  6. Surface chemical modification of nanocrystals

    DOEpatents

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

    2017-03-14

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

  7. Exciton polarizability in semiconductor nanocrystals.

    PubMed

    Wang, Feng; Shan, Jie; Islam, Mohammad A; Herman, Irving P; Bonn, Mischa; Heinz, Tony F

    2006-11-01

    The response of charge to externally applied electric fields is an important basic property of any material system, as well as one critical for many applications. Here, we examine the behaviour and dynamics of charges fully confined on the nanometre length scale. This is accomplished using CdSe nanocrystals of controlled radius (1-2.5 nm) as prototype quantum systems. Individual electron-hole pairs are created at room temperature within these structures by photoexcitation and are probed by terahertz (THz) electromagnetic pulses. The electronic response is found to be instantaneous even for THz frequencies, in contrast to the behaviour reported in related measurements for larger nanocrystals and nanocrystal assemblies. The measured polarizability of an electron-hole pair (exciton) amounts to approximately 10(4) A(3) and scales approximately as the fourth power of the nanocrystal radius. This size dependence and the instantaneous response reflect the presence of well-separated electronic energy levels induced in the system by strong quantum-confinement effects.

  8. Fundamental Studies of the Mechanical Behavior of Microelectronic Thin Film Materials

    DTIC Science & Technology

    1991-01-01

    Si I-xGex Strained Layers (D.B.Noble) ................................................ 55 I. Oral Presentations Resulting from AFOSR Grants No. 89-0185...120 8 7 0 100 6 4 60 80 , E 60 0 F. ac sorption D - 21 - A desorption ( Vih ) Q 1 I - I - - a- 1 -10 0 10 20 30 40 annealing time (min) Fig. 8 D...III. ORAL PRESENTATIONS RESULTING FROM AFOSR GRANTS NO. 86- 0051 AND 86-0051 1. W.DhjX, "Mechanical Properties of Microelectronic Thin Film Materials

  9. FUNDAMENTAL ENVIRONMENTAL REACTIVITY TESTING AND ANALYSIS OF THE HYDROGEN STORAGE MATERIAL 2LIBH4 MGH2

    SciTech Connect

    James, C.; Anton, D.; Cortes-Concepcion, J.; Brinkman, K.; Gray, J.

    2012-01-10

    While the storage of hydrogen for portable and stationary applications is regarded as critical in bringing PEM fuel cells to commercial acceptance, little is known of the environmental exposure risks posed in utilizing condensed phase chemical storage options as in complex hydrides. It is thus important to understand the effect of environmental exposure of metal hydrides in the case of accident scenarios. Simulated tests were performed following the United Nations standards to test for flammability and water reactivity in air for a destabilized lithium borohydride and magnesium hydride system in a 2 to 1 molar ratio respectively. It was determined that the mixture acted similarly to the parent, lithium borohydride, but at slower rate of reaction seen in magnesium hydride. To quantify environmental exposure kinetics, isothermal calorimetry was utilized to measure the enthalpy of reaction as a function of exposure time to dry and humid air, and liquid water. The reaction with liquid water was found to increase the heat flow significantly during exposure compared to exposure in dry or humid air environments. Calorimetric results showed the maximum normalized heat flow the fully charged material was 6 mW/mg under liquid phase hydrolysis; and 14 mW/mg for the fully discharged material also occurring under liquid phase hydrolysis conditions.

  10. Silicon and germanium nanocrystals: properties and characterization

    PubMed Central

    Carvalho, Alexandra; Coutinho, José

    2014-01-01

    Summary Group-IV nanocrystals have emerged as a promising group of materials that extends the realm of application of bulk diamond, silicon, germanium and related materials beyond their traditional boundaries. Over the last two decades of research, their potential for application in areas such as optoelectronic applications and memory devices has been progressively unraveled. Nevertheless, new challenges with no parallel in the respective bulk material counterparts have arisen. In this review, we consider what has been achieved and what are the current limitations with regard to growth, characterization and modeling of silicon and germanium nanocrystals and related materials. PMID:25383290

  11. Multifunctional nanocrystals

    DOEpatents

    Klimov, Victor I.; Hollingsworth, Jennifer A.; Crooker, Scott A.; Kim, Hyungrak

    2010-06-22

    Multifunctional nanocomposites are provided including a core of either a magnetic material or an inorganic semiconductor, and, a shell of either a magnetic material or an inorganic semiconductor, wherein the core and the shell are of differing materials, such multifunctional nanocomposites having multifunctional properties including magnetic properties from the magnetic material and optical properties from the inorganic semiconductor material. Various applications of such multifunctional nanocomposites are also provided.

  12. Multifunctional nanocrystals

    DOEpatents

    Klimov, Victor I.; Hollingsworth, Jennifer A.; Crooker, Scott A.; Kim, Hyungrak

    2007-08-28

    Multifunctional nanocomposites are provided including a core of either a magnetic material or an inorganic semiconductor, and, a shell of either a magnetic material or an inorganic semiconductor, wherein the core and the shell are of differing materials, such multifunctional nanocomposites having multifunctional properties including magnetic properties from the magnetic material and optical properties from the inorganic semiconductor material. Various applications of such multifunctional nanocomposites are also provided.

  13. Investigation of fundamental growth mechanisms in pulsed laser deposition synthesis of nanostructured materials

    NASA Astrophysics Data System (ADS)

    Mozet, William Thomas

    Studies are conducted to better understand growth mechanisms in pulsed laser deposition (PLD) synthesis of nanostructured materials, namely graphene and bismuth telluride (Bi2Te3). For graphene, as the substrate temperature increases, the order of the film increases, from an amorphous carbon film to nanocrystalline graphite and few-layer graphene (FLG). By using a high energy laser, the size and type of ablated species can be controlled to create films with smaller nanocrystalline domains. PLD allows the thickness of the films to be directly controlled by the deposition duration. Films can be grown on arbitrary substrates, unlike other methods which utilize surface chemistry. Substrate morphology also affects the samples, with higher surface roughness leading to larger D/G and 2D/G ratios. Polishing substrates prior to deposition can decrease these ratios by up to 15%. Here, the type of carbon source has little impact on sample growth, except in atmospheric growth of graphene, which may not be an optimal condition because of energy loss of the carbon species. In-situ plasma plume analysis is conducted to analyze the species being ablated from the target. Ablated species consist primarily of C+ ions, with some neutral C and C2 species. Ablated C+ ions are at temperatures as high as 12,000 K in vacuum and 10,000 K in 0.1 torr argon. For bismuth telluride, optimal growth conditions are found for the stoichiometric transfer of Bi2Te3, which can vary from system to system. In general, a deposition temperature of 200°C and a deposition pressure of 0.1 to 1.0 torr argon are required for stoichiometric transfer. Using a high energy laser for ablation leads to smaller grain sizes in the nanostructured films. In addition, using a nitrogen atmosphere instead of argon leads to increased gas-phase condensation prior to deposition, resulting in a highly featured surface. When outside of the ideal pressure range, the substrate material can significantly affect the surface

  14. Atmospheric-Pressure Plasma Interaction with Soft Materials as Fundamental Processes in Plasma Medicine.

    PubMed

    Takenaka, Kosuke; Miyazaki, Atsushi; Uchida, Giichiro; Setsuhara, Yuichi

    2015-03-01

    Molecular-structure variation of organic materials irradiated with atmospheric pressure He plasma jet have been investigated. Optical emission spectrum in the atmospheric-pressure He plasma jet has been measured. The spectrum shows considerable emissions of He lines, and the emission of O and N radicals attributed to air. Variation in molecular structure of Polyethylene terephthalate (PET) film surface irradiated with the atmospheric-pressure He plasma jet has been observed via X-ray photoelectron spectroscopy (XPS) and Fourier transform infrared spectroscopy (FT-IR). These results via XPS and FT-IR indicate that the PET surface irradiated with the atmospheric-pressure He plasma jet was oxidized by chemical and/or physical effect due to irradiation of active species.

  15. Fundamental Understanding of Ambient and High-Temperature Plasticity Phenomena in Structural Materials in Advanced Reactors

    SciTech Connect

    Deo, Chaitanya; Zhu, Ting; McDowell, David

    2013-11-17

    The goal of this research project is to develop the methods and tools necessary to link unit processes analyzed using atomistic simulations involving interaction of vacancies and interstitials with dislocations, as well as dislocation mediation at sessile junctions and interfaces as affected by radiation, with cooperative influence on higher-length scale behavior of polycrystals. These tools and methods are necessary to design and enhance radiation-induced damage-tolerant alloys. The project will achieve this goal by applying atomistic simulations to characterize unit processes of: 1. Dislocation nucleation, absorption, and desorption at interfaces 2. Vacancy production, radiation-induced segregation of substitutional Cr at defect clusters (point defect sinks) in BCC Fe-Cr ferritic/martensitic steels 3. Investigation of interaction of interstitials and vacancies with impurities (V, Nb, Ta, Mo, W, Al, Si, P, S) 4. Time evolution of swelling (cluster growth) phenomena of irradiated materials 5. Energetics and kinetics of dislocation bypass of defects formed by interstitial clustering and formation of prismatic loops, informing statistical models of continuum character with regard to processes of dislocation glide, vacancy agglomeration and swelling, climb and cross slip This project will consider the Fe, Fe-C, and Fe-Cr ferritic/martensitic material system, accounting for magnetism by choosing appropriate interatomic potentials and validating with first principles calculations. For these alloys, the rate of swelling and creep enhancement is considerably lower than that of face-centered cubic (FCC) alloys and of austenitic Fe-Cr-Mo alloys. The team will confirm mechanisms, validate simulations at various time and length scales, and improve the veracity of computational models. The proposed research?s feasibility is supported by recent modeling of radiation effects in metals and alloys, interfacial dislocation transfer reactions in nano-twinned copper, and dislocation

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

    NASA Astrophysics Data System (ADS)

    Vezmar, Igor

    1998-09-01

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

  17. CdTe Nanocrystal Hetero-Junction Solar Cells with High Open Circuit Voltage Based on Sb-doped TiO2 Electron Acceptor Materials

    PubMed Central

    Li, Miaozi; Liu, Xinyan; Wen, Shiya; Liu, Songwei; Heng, Jingxuan; Qin, Donghuan; Hou, Lintao; Wu, Hongbin; Xu, Wei; Huang, Wenbo

    2017-01-01

    We propose Sb-doped TiO2 as electron acceptor material for depleted CdTe nanocrystal (NC) hetero-junction solar cells. Novel devices with the architecture of FTO/ZnO/Sb:TiO2/CdTe/Au based on CdTe NC and TiO2 precursor are fabricated by rational ambient solution process. By introducing TiO2 with dopant concentration, we are able to tailor the optoelectronic properties of NC solar cells. Our novel devices demonstrate a very high open circuit voltage of 0.74 V, which is the highest Voc reported for any CdTe NC based solar cells. The power conversion efficiency (PCE) of solar cells increases with the increase of Sb-doped content from 1% to 3%, then decreases almost linearly with further increase of Sb content due to the recombination effect. The champion device shows Jsc, Voc, FF, and PCE of 14.65 mA/cm2, 0.70 V, 34.44, and 3.53% respectively, which is prospective for solution processed NC solar cells with high Voc. PMID:28467347

  18. Solution-Processed Cu(In, Ga)(S, Se)2 Nanocrystal as Inorganic Hole-Transporting Material for Efficient and Stable Perovskite Solar Cells.

    PubMed

    Xu, Lu; Deng, Lin-Long; Cao, Jing; Wang, Xin; Chen, Wei-Yi; Jiang, Zhiyuan

    2017-12-01

    Perovskite solar cells are emerging as one of the most promising candidates for solar energy harvesting. To date, most of the high-performance perovskite solar cells have exclusively employed organic hole-transporting materials (HTMs) such as 2,2',7,7'-tetrakis-(N,N-di-p-methoxyphenylamine)-9,9'-spirobifluorene (spiro-OMeTAD) or polytriarylamine (PTAA) which are often expensive and have low hole mobility. Almost all these HTMs reported needed lithium salt, e.g., lithium bis(trifluoromethylsulfonyl)imide (Li-TFSI) doping, to improve hole mobility and performance. However, the use of Li-TFSI should be avoided because the hygroscopic nature of Li-TFSI could cause decomposition of perovskite and reduce device stability. Herein, we employed solution-processed CuIn0.1Ga0.9(S0.9Se0.1)2 (CIGSSe) nanocrystals as a novel inorganic HTM in perovskite solar cells. A power conversion efficiency of 9.15% was obtained for CIGSSe-based devices with improved stability, compared to devices using spiro-OMeTAD as HTM. This work offers a promising candidate of Cu-based inorganic HTM for efficient and stable perovskite solar cells.

  19. CdTe Nanocrystal Hetero-Junction Solar Cells with High Open Circuit Voltage Based on Sb-doped TiO₂ Electron Acceptor Materials.

    PubMed

    Li, Miaozi; Liu, Xinyan; Wen, Shiya; Liu, Songwei; Heng, Jingxuan; Qin, Donghuan; Hou, Lintao; Wu, Hongbin; Xu, Wei; Huang, Wenbo

    2017-05-03

    We propose Sb-doped TiO₂ as electron acceptor material for depleted CdTe nanocrystal (NC) hetero-junction solar cells. Novel devices with the architecture of FTO/ZnO/Sb:TiO₂/CdTe/Au based on CdTe NC and TiO₂ precursor are fabricated by rational ambient solution process. By introducing TiO₂ with dopant concentration, we are able to tailor the optoelectronic properties of NC solar cells. Our novel devices demonstrate a very high open circuit voltage of 0.74 V, which is the highest Voc reported for any CdTe NC based solar cells. The power conversion efficiency (PCE) of solar cells increases with the increase of Sb-doped content from 1% to 3%, then decreases almost linearly with further increase of Sb content due to the recombination effect. The champion device shows Jsc, Voc, FF, and PCE of 14.65 mA/cm², 0.70 V, 34.44, and 3.53% respectively, which is prospective for solution processed NC solar cells with high Voc.

  20. Solution-Processed Cu(In, Ga)(S, Se)2 Nanocrystal as Inorganic Hole-Transporting Material for Efficient and Stable Perovskite Solar Cells

    NASA Astrophysics Data System (ADS)

    Xu, Lu; Deng, Lin-Long; Cao, Jing; Wang, Xin; Chen, Wei-Yi; Jiang, Zhiyuan

    2017-02-01

    Perovskite solar cells are emerging as one of the most promising candidates for solar energy harvesting. To date, most of the high-performance perovskite solar cells have exclusively employed organic hole-transporting materials (HTMs) such as 2,2',7,7'-tetrakis-( N, N-di- p-methoxyphenylamine)-9,9'-spirobifluorene (spiro-OMeTAD) or polytriarylamine (PTAA) which are often expensive and have low hole mobility. Almost all these HTMs reported needed lithium salt, e.g., lithium bis(trifluoromethylsulfonyl)imide (Li-TFSI) doping, to improve hole mobility and performance. However, the use of Li-TFSI should be avoided because the hygroscopic nature of Li-TFSI could cause decomposition of perovskite and reduce device stability. Herein, we employed solution-processed CuIn0.1Ga0.9(S0.9Se0.1)2 (CIGSSe) nanocrystals as a novel inorganic HTM in perovskite solar cells. A power conversion efficiency of 9.15% was obtained for CIGSSe-based devices with improved stability, compared to devices using spiro-OMeTAD as HTM. This work offers a promising candidate of Cu-based inorganic HTM for efficient and stable perovskite solar cells.

  1. Cyclotron Splittings in the Plasmon Resonances of Electronically Doped Semiconductor Nanocrystals Probed by Magnetic Circular Dichroism Spectroscopy.

    PubMed

    Hartstein, Kimberly H; Schimpf, Alina M; Salvador, Michael; Gamelin, Daniel R

    2017-04-10

    A fundamental understanding of the rich electronic structures of electronically doped semiconductor nanocrystals is vital for assessing the utility of these materials for future applications from solar cells to redox catalysis. Here, we examine the use of magnetic circular dichroism (MCD) spectroscopy to probe the infrared localized surface plasmon resonances of p-Cu2-xSe, n-ZnO, and tin-doped In2O3 (n-ITO) nanocrystals. We demonstrate that the MCD spectra of these nanocrystals can be analyzed by invoking classical cyclotron motions of their excess charge carriers, with experimental MCD signs conveying the carrier types (n or p) and experimental MCD intensities conveying the cyclotron splitting magnitudes. The experimental cyclotron splittings can then be used to quantify carrier effective masses (m*), with results that agree with bulk in most cases. MCD spectroscopy thus offers a unique measure of m* in free-standing colloidal semiconductor nanocrystals, raising new opportunities to investigate the influence of various other synthetic or environmental parameters on this fundamentally important electronic property.

  2. 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

  3. Enhancement of open-circuit voltage and the fill factor in CdTe nanocrystal solar cells by using interface materials

    NASA Astrophysics Data System (ADS)

    Zhu, Jiaoyan; Yang, Yuehua; Gao, Yuping; Qin, Donghuan; Wu, Hongbin; Hou, Lintao; Huang, Wenbo

    2014-09-01

    Interface states influence the operation of nanocrystal (NC) solar cell carrier transport, recombination and energetic mechanisms. In a typical CdTe NC solar cell with a normal structure of a ITO/p-CdTe NCs/n-acceptor (or without)/Al configuration, the contact between the ITO and CdTe is a non-ohm contact due to a different work function (for an ITO, the value is ˜4.7 eV, while for CdTe NCs, the value is ˜5.3 eV), which results in an energetic barrier at the ITO/CdTe interface and decreases the performance of the NC solar cells. This work investigates how interface materials (including Au, MoOx and C60) affect the performance of NC solar cells. It is found that devices with interface materials have shown higher Voc than those without interface materials. For the case in which we used Au as an interface, we obtained a high open-circuit voltage of 0.65 V, coupled with a high fill factor (62%); this resulted in a higher energy conversion efficiency (ECE) of 5.3%, which showed a 30% increase in the ECE compared with those without the interlayer. The capacitance measurements indicate that the increased Voc in the case in which Au was used as the interface is likely due to good ohm contact between the Au’s and the CdTe NCs’ thin film, which decreases the energetic barrier at the ITO/CdTe interface.

  4. Enhancement of open-circuit voltage and the fill factor in CdTe nanocrystal solar cells by using interface materials.

    PubMed

    Zhu, Jiaoyan; Yang, Yuehua; Gao, Yuping; Qin, Donghuan; Wu, Hongbin; Hou, Lintao; Huang, Wenbo

    2014-09-12

    Interface states influence the operation of nanocrystal (NC) solar cell carrier transport, recombination and energetic mechanisms. In a typical CdTe NC solar cell with a normal structure of a ITO/p-CdTe NCs/n-acceptor (or without)/Al configuration, the contact between the ITO and CdTe is a non-ohm contact due to a different work function (for an ITO, the value is ~4.7 eV, while for CdTe NCs, the value is ~5.3 eV), which results in an energetic barrier at the ITO/CdTe interface and decreases the performance of the NC solar cells. This work investigates how interface materials (including Au, MoO(x) and C₆₀) affect the performance of NC solar cells. It is found that devices with interface materials have shown higher V(oc) than those without interface materials. For the case in which we used Au as an interface, we obtained a high open-circuit voltage of 0.65 V, coupled with a high fill factor (62%); this resulted in a higher energy conversion efficiency (ECE) of 5.3%, which showed a 30% increase in the ECE compared with those without the interlayer. The capacitance measurements indicate that the increased V(oc) in the case in which Au was used as the interface is likely due to good ohm contact between the Au's and the CdTe NCs' thin film, which decreases the energetic barrier at the ITO/CdTe interface.

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

    PubMed

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

    2012-09-06

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

  6. High-Performance Doped Silver Films: Overcoming Fundamental Material Limits for Nanophotonic Applications.

    PubMed

    Zhang, Cheng; Kinsey, Nathaniel; Chen, Long; Ji, Chengang; Xu, Mingjie; Ferrera, Marcello; Pan, Xiaoqing; Shalaev, Vladimir M; Boltasseva, Alexandra; Guo, L Jay

    2017-03-20

    The field of nanophotonics has ushered in a new paradigm of light manipulation by enabling deep subdiffraction confinement assisted by metallic nanostructures. However, a key limitation which has stunted a full development of high-performance nanophotonic devices is the typical large losses associated with the constituent metals. Although silver has long been known as the highest quality plasmonic material for visible and near infrared applications, its usage has been limited due to practical issues of continuous thin film formation, stability, adhesion, and surface roughness. Recently, a solution is proposed to the above issues by doping a proper amount of aluminum during silver deposition. In this work, the potential of doped silver for nanophotonic applications is presented by demonstrating several high-performance key nanophotonic devices. First, long-range surface plasmon polariton waveguides show propagation distances of a few centimeters. Second, hyperbolic metamaterials consisting of ultrathin Al-doped Ag films are attained having a homogeneous and low-loss response, and supporting a broad range of high-k modes. Finally, transparent conductors based on Al-doped Ag possess both a high and flat transmittance over the visible and near-IR range.

  7. Fundamental ecology is fundamental.

    PubMed

    Courchamp, Franck; Dunne, Jennifer A; Le Maho, Yvon; May, Robert M; Thébaud, Christophe; Hochberg, Michael E

    2015-01-01

    The primary reasons for conducting fundamental research are satisfying curiosity, acquiring knowledge, and achieving understanding. Here we develop why we believe it is essential to promote basic ecological research, despite increased impetus for ecologists to conduct and present their research in the light of potential applications. This includes the understanding of our environment, for intellectual, economical, social, and political reasons, and as a major source of innovation. We contend that we should focus less on short-term, objective-driven research and more on creativity and exploratory analyses, quantitatively estimate the benefits of fundamental research for society, and better explain the nature and importance of fundamental ecology to students, politicians, decision makers, and the general public. Our perspective and underlying arguments should also apply to evolutionary biology and to many of the other biological and physical sciences. Copyright © 2014 The Authors. Published by Elsevier Ltd.. All rights reserved.

  8. Fundamental Processes of Coupled Radiation Damage and Mechanical Behavior in Nuclear Fuel Materials for High Temperature Reactors

    SciTech Connect

    Phillpot, Simon; Tulenko, James

    2011-09-08

    The objective of this work has been to elucidate the relationship among microstructure, radiation damage and mechanical properties for nuclear fuel materials. As representative nuclear materials, we have taken an hcp metal (Mg as a generic metal, and Ti alloys for fast reactors) and UO2 (representing fuel). The degradation of the thermo-mechanical behavior of nuclear fuels under irradiation, both the fissionable material itself and its cladding, is a longstanding issue of critical importance to the nuclear industry. There are experimental indications that nanocrystalline metals and ceramics may be more resistant to radiation damage than their coarse-grained counterparts. The objective of this project look at the effect of microstructure on radiation damage and mechanical behavior in these materials. The approach to be taken was state-of-the-art, large-scale atomic-level simulation. This systematic simulation program of the effects of irradiation on the structure and mechanical properties of polycrystalline Ti and UO2 identified radiation damage mechanisms. Moreover, it will provided important insights into behavior that can be expected in nanocrystalline microstructures and, by extension, nanocomposites. The fundamental insights from this work can be expected to help in the design microstructures that are less susceptible to radiation damage and thermomechanical degradation.

  9. Collaborative Research. Fundamental Science of Low Temperature Plasma-Biological Material Interactions

    SciTech Connect

    Graves, David Barry; Oehrlein, Gottlieb

    2014-09-01

    atmospheric pressure using several types of low temperature plasma sources, for which radical induced interactions generally dominate due to short mean free paths of ions and VUV photons. For these conditions we demonstrated the importance of environmental interactions when atmospheric pressure plasma sources are used to modify biomolecules. This is evident from both gas phase characterization data and in-situ surface characterization of treated biomolecules. Environmental interactions can produce unexpected outcomes due to the complexity of reactions of reactive species with the atmosphere which determines the composition of reactive fluxes and atomistic changes of biomolecules. Overall, this work clarified a richer spectrum of scientific opportunities and challenges for the field of low temperature plasma-biomolecule surface interactions than initially anticipated, in particular for plasma sources operating at atmospheric pressure. The insights produced in this work, e.g. demonstration of the importance of environmental interactions, are generally important for applications of APP to materials modifications. Thus one major contributions of this research has been the establishment of methodologies to more systematically study the interaction of plasma with bio-molecules. In particular, our studies of atmospheric pressure plasma sources using very well-defined experimental conditions enabled to combine atomistic surface modifications of biomolecules with changes in their biological function. The clarification of the role of ions, VUV photons and radicals in deactivation of biomolecules during low pressure and atmospheric pressure plasma-biomolecule interaction has broad implications, e.g. for the emerging field of plasma medicine. The development of methods to detect the effects of plasma treatment on immune-active biomolecules will be helpful in many future studies.

  10. The 2013 Clusters, Nanocrystals & Nanostructures Gordon Research Conference/Gordon Research Seminar

    SciTech Connect

    Krauss, Todd D.

    2014-11-25

    The fundamental properties of small particles and their potential for groundbreaking applications are among the most exciting areas of study in modern physics, chemistry, and materials science. The Clusters, Nanocrystals & Nanostructures Gordon ResearchConference and Gordon Research Seminar synthesize contributions from these inter-related fields that reflect the pivotal role of nano-particles at the interface between these disciplines. Size-dependent optical, electronic, magnetic and catalytic properties offer prospects for applications in many fields, and possible solutions for many of the grand challenges facing energy generation, consumption, delivery, and storage in the 21st century. The goal of the 2013 Clusters, Nanocrystals & Nanostructures Gordon Research Conference and Gordon Research Seminar is to continue the historical interdisciplinary tradition of this series and discuss the most recent advances, basic scientific questions, and emerging applications of clusters, nanocrystals, and nanostructures. The Clusters, Nanocrystals & Nanostructures GRC/GRS traditionally brings together the leading scientific groups that have made significant recent advances in one or more fundamental nanoscience or nanotechnology areas. Broad interests of the DOE BES and Solar Photochemistry Program addressed by this meeting include the areas of solar energy to fuels conversion, new photovoltaic systems, fundamental characterization of nanomaterials, magnetism, catalysis, and quantum physics. The vast majority of speakers and attendees will address either directly the topic of nanotechnology for photoinduced charge transfer, charge transport, and catalysis, or will have made significant contributions to related areas that will impact these fields indirectly. These topics have direct relevance to the mission of the DOE BES since it is this cutting-edge basic science that underpins our energy future.

  11. Mesoporous TiO2 Nanocrystals/Graphene as an Efficient Sulfur Host Material for High-Performance Lithium-Sulfur Batteries.

    PubMed

    Li, Yuanyuan; Cai, Qifa; Wang, Lei; Li, Qingwei; Peng, Xiang; Gao, Biao; Huo, Kaifu; Chu, Paul K

    2016-09-14

    Rechargeable lithium-sulfur (Li-S) batteries are promising in high-energy storage due to the large specific energy density of about 2600 W h kg(-1). However, the low conductivity of sulfur and discharge products as well as polysulfide-shuttle effect between the cathode and anode hamper applications of Li-S batteries. Herein, we describe a novel and efficient S host material consisting of mesoporous TiO2 nanocrystals (NCs) fabricated in situ on reduced graphene oxide (rGO) for Li-S batteries. The TiO2@rGO hybrid can be loaded with 72 wt % sulfur. The strong chemisorption ability of the TiO2 NCs toward polysulfide combined with high electrical conductivity of rGO effectively localize the soluble polysulfide species within the cathode and facilitate electron and Li ions transport to/from the cathode materials. The sulfur-incorporated TiO2@rGO hybrid (S/TiO2@rGO) shows large capacities of 1116 and 917 mA h g(-1) at the current densities of 0.2 and 1 C (1 C = 1675 mA g(-1)) after 100 cycles, respectively. When the current density is increased 20 times from 0.2 to 4 C, 60% capacity is retained, thereby demonstrating good cycling stability and rate capability. The synergistic effects of TiO2 NCs toward effective chemisorption of polysulfides and conductive rGO with high electron mobility make a promising application of S/TiO2@rGO hybrid in high-performance Li-S batteries.

  12. Atomistic understanding of diffusion kinetics in nanocrystals from molecular dynamics simulations

    NASA Astrophysics Data System (ADS)

    Wang, Yun-Jiang; Gao, Guo-Jie J.; Ogata, Shigenobu

    2013-09-01

    Understanding the grain size effect on diffusion in nanocrystals has been hampered by the difficulty of measuring diffusion directly in experiments. Here large-scale atomistic modeling is applied to understand the diffusion kinetics in nanocrystals. Enhanced short-circuit diffusivity is revealed to be controlled by the rule of mixtures for grain-boundary diffusion and lattice diffusion, which can be accurately described by the Maxwell-Garnett equation instead of the commonly thought Hart equation, and the thermodynamics of pure grain-boundary self-diffusion is not remarkably affected by varying grain size. Experimentally comparable Arrhenius parameters with atomic detail validate our results. We also propose a free-volume diffusion mechanism considering negative activation entropy and small activation volume. These help provide a fundamental understanding of how the activation parameters depend on size and the structure-property relationship of nanostructured materials from a physical viewpoint.

  13. Charge transport in semiconductor nanocrystal quantum dots

    NASA Astrophysics Data System (ADS)

    Mentzel, Tamar Shoshana

    In this thesis, we study charge transport in arrays of semiconductor nanocrystal quantum dots. Nanocrystals are synthesized in solution, and an organic ligand on the surface of the nanocrystal creates a potential barrier that confines charges in the nanocrystal. Optical absorption measurements reveal discrete electronic energy levels in the nanocrystals resulting from quantum confinement. When nanocrystals are deposited on a surface, they self-assemble into a close-packed array forming a nanocrystal solid. We report electrical transport measurements of a PbSe nanocrystal solid that serves as the channel of an inverted field-effect transistor. We measure the conductance as a function of temperature, source-drain bias and. gate voltage. The data indicates that holes are the majority carriers; the Fermi energy lies in impurity states in the bandgap of the nanocrystal; and charges hop between the highest occupied valence state in the nanocrystals (the 1S h states). At low source-drain voltages, the activation energy for hopping is given by the energy required to generate holes in the 1Sh state plus activation over barriers resulting from site disorder. The barriers from site disorder are eliminated with a sufficiently high source-drain bias. From the gate effect, we extract the Thomas-Fermi screening length and a density of states that is consistent with the estimated value. We consider variable-range hopping as an alternative model, and find no self-consistent evidence for it. Next, we employ charge sensing as an alternative to current measurements for studying transport in materials with localized sites. A narrow-channel MOSFET serves as a charge sensor because its conductance is sensitive to potential fluctuations in the nearby environment caused by the motion of charge. In particular, it is sensitive to the fluctuation of single electrons at the silicon-oxide interface within the MOSFET. We pattern a strip of amorphous germanium within 100 nm of the transistor. The

  14. Electronic Structure of Germanium Nanocrystal Films Probed with Synchrotron Radiation

    SciTech Connect

    Bostedt, C

    2002-05-01

    The fundamental structure--property relationship of semiconductor quantum dots has been investigated. For deposited germanium nanocrystals strong quantum confinement effects have been determined with synchrotron radiation based x-ray absorption and photoemission techniques. The nanocrystals are condensed out of the gas phase with a narrow size distribution and subsequently deposited in situ onto various substrates. The particles are crystalline in the cubic phase with a structurally disordered surface shell and the resulting film morphology depends strongly on the substrate material and condition. The disordered surface region has an impact on the overall electronic structure of the particles. In a size-dependent study, the conduction and valence band edge of germanium nanocrystals have been measured for the first time and compared to the bulk crystal. The band edges move to higher energies as the particle size is decreased, consistent with quantum confinement theory. To obtain a more accurate analysis of confinement effects in the empty states, a novel analysis method utilizing an effective particle size for the x-ray absorption experiment, which allows a deconvolution of absorption edge broadening effects, has been introduced. Comparison of the present study to earlier studies on silicon reveals that germanium exhibits stronger quantum confinement effects than silicon. Below a critical particle size of 2.3 {+-} 0.7 nm, the band gap of germanium becomes larger than that of silicon--even if it is the opposite for bulk materials. This result agrees phenomenologically with effective mass and tight binding theories but contradicts the findings of recent pseudopotential calculations. The discrepancy between theory and experiments is attributed to the differences in the theoretical models and experimental systems. The experimentally observed structural disorder of the particle surface has to be included in the theoretical models.

  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. Colloidal synthesis and characterizations of wittichenite copper bismuth sulphide nanocrystals

    NASA Astrophysics Data System (ADS)

    Yan, Chang; Gu, Ening; Liu, Fangyang; Lai, Yanqing; Li, Jie; Liu, Yexiang

    2013-02-01

    Wittichenite (Cu3BiS3) nanocrystals have been synthesized utilizing a hot-injection method. They have been characterized in detail. Cu3BiS3 nanocrystals possessed a band gap of 1.56 eV, and the corresponding nanocrystal-film shows a clear photoresponse in I-V measurements. Our work illustrates that Cu3BiS3 nanocrystals have potential in the application of solar cells.Wittichenite (Cu3BiS3) nanocrystals have been synthesized utilizing a hot-injection method. They have been characterized in detail. Cu3BiS3 nanocrystals possessed a band gap of 1.56 eV, and the corresponding nanocrystal-film shows a clear photoresponse in I-V measurements. Our work illustrates that Cu3BiS3 nanocrystals have potential in the application of solar cells. Electronic supplementary information (ESI) available: Experimental details. Materials characterization. Additional TEM images, Fast Fourier Transform (FFT) pattern of as-synthesized Cu3BiS3. Simulated Cu3BiS3 single crystal electron diffraction data. EDX data of as-synthesized Cu3BiS3 nanocrystals. Additional XRD patterns and TEM images for the product at different reaction conditions. See DOI: 10.1039/c3nr33268c

  17. Quantitative tunneling spectroscopy of nanocrystals

    SciTech Connect

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

    2007-05-25

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

  18. Lead sulphide nanocrystal photodetector technologies

    NASA Astrophysics Data System (ADS)

    Saran, Rinku; Curry, Richard J.

    2016-02-01

    Light detection is the underlying principle of many optoelectronic systems. For decades, semiconductors including silicon carbide, silicon, indium gallium arsenide and germanium have dominated the photodetector industry. They can show excellent photosensitivity but are limited by one or more aspects, such as high production cost, high-temperature processing, flexible substrate incompatibility, limited spectral range or a requirement for cryogenic cooling for efficient operation. Recently lead sulphide (PbS) nanocrystals have emerged as one of the most promising new materials for photodetector fabrication. They offer several advantages including low-cost manufacturing, solution processability, size-tunable spectral sensitivity and flexible substrate compatibility, and they have achieved figures of merit outperforming conventional photodetectors. We review the underlying concepts, breakthroughs and remaining challenges in photodetector technologies based on PbS nanocrystals.

  19. Atomic force microscopy characterization of cellulose nanocrystals

    Treesearch

    Roya R. Lahiji; Xin Xu; Ronald Reifenberger; Arvind Raman; Alan Rudie; Robert J. Moon

    2010-01-01

    Cellulose nanocrystals (CNCs) are gaining interest as a “green” nanomaterial with superior mechanical and chemical properties for high-performance nanocomposite materials; however, there is a lack of accurate material property characterization of individual CNCs. Here, a detailed study of the topography, elastic and adhesive properties of individual wood-derived CNCs...

  20. Multistep nucleation of nanocrystals in aqueous solution

    NASA Astrophysics Data System (ADS)

    Loh, N. Duane; Sen, Soumyo; Bosman, Michel; Tan, Shu Fen; Zhong, Jun; Nijhuis, Christian A.; Král, Petr; Matsudaira, Paul; Mirsaidov, Utkur

    2017-01-01

    The nucleation and growth of solids from solutions impacts many natural processes and is fundamental to applications in materials engineering and medicine. For a crystalline solid, the nucleus is a nanoscale cluster of ordered atoms that forms through mechanisms still poorly understood. In particular, it is unclear whether a nucleus forms spontaneously from solution via a single- or multiple-step process. Here, using in situ electron microscopy, we show how gold and silver nanocrystals nucleate from supersaturated aqueous solutions in three distinct steps: spinodal decomposition into solute-rich and solute-poor liquid phases, nucleation of amorphous nanoclusters within the metal-rich liquid phase, followed by crystallization of these amorphous clusters. Our ab initio calculations on gold nucleation suggest that these steps might be associated with strong gold-gold atom coupling and water-mediated metastable gold complexes. The understanding of intermediate steps in nuclei formation has important implications for the formation and growth of both crystalline and amorphous materials.

  1. Fundamentally updating fundamentals.

    PubMed

    Armstrong, Gail; Barton, Amy

    2013-01-01

    Recent educational research indicates that the six competencies of the Quality and Safety Education for Nurses initiative are best introduced in early prelicensure clinical courses. Content specific to quality and safety has traditionally been covered in senior level courses. This article illustrates an effective approach to using quality and safety as an organizing framework for any prelicensure fundamentals of nursing course. Providing prelicensure students a strong foundation in quality and safety in an introductory clinical course facilitates early adoption of quality and safety competencies as core practice values. Copyright © 2013 Elsevier Inc. All rights reserved.

  2. Shaping metal nanocrystals through epitaxial seeded growth

    SciTech Connect

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

    2008-02-17

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

  3. Antioxidant properties of cerium oxide nanocrystals as a function of nanocrystal diameter and surface coating.

    PubMed

    Lee, Seung Soo; Song, Wensi; Cho, Minjung; Puppala, Hema L; Nguyen, Phuc; Zhu, Huiguang; Segatori, Laura; Colvin, Vicki L

    2013-11-26

    This work examines the effect of nanocrystal diameter and surface coating on the reactivity of cerium oxide nanocrystals with H2O2 both in chemical solutions and in cells. Monodisperse nanocrystals were formed in organic solvents from the decomposition of cerium precursors, and subsequently phase transferred into water using amphiphiles as nanoparticle coatings. Quantitative analysis of the antioxidant capacity of CeO2-x using gas chromatography and a luminol test revealed that 2 mol of H2O2 reacted with every mole of cerium(III), suggesting that the reaction proceeds via a Fenton-type mechanism. Smaller diameter nanocrystals containing more cerium(III) were found to be more reactive toward H2O2. Additionally, the presence of a surface coating did not preclude the reaction between the nanocrystal surface cerium(III) and hydrogen peroxide. Taken together, the most reactive nanoparticles were the smallest (e.g., 3.8 nm diameter) with the thinnest surface coating (e.g., oleic acid). Moreover, a benchmark test of their antioxidant capacity revealed these materials were 9 times more reactive than commercial antioxidants such as Trolox. A unique feature of these antioxidant nanocrystals is that they can be applied multiple times: over weeks, cerium(IV) rich particles slowly return to their starting cerium(III) content. In nearly all cases, the particles remain colloidally stable (e.g., nonaggregated) and could be applied multiple times as antioxidants. These chemical properties were also observed in cell culture, where the materials were able to reduce oxidative stress in human dermal fibroblasts exposed to H2O2 with efficiency comparable to their solution phase reactivity. These data suggest that organic coatings on cerium oxide nanocrystals do not limit the antioxidant behavior of the nanocrystals, and that their redox cycling behavior can be preserved even when stabilized.

  4. Germanium nanocrystals: Synthesis, characterization, and applications

    NASA Astrophysics Data System (ADS)

    Gerung, Henry

    superlattice of Ge nanocrystals within a SiO2 matrix, the real-time monitoring of ordered mesoporous SiO 2 structure formation via evaporation induced self assembly was also conducted to understand the structural ordering inside the silica matrix. The mesoporous film was then used for in situ and real-time study of profile evolution during plasma etching using attenuated total reflection Fourier transform infrared spectroscopy. We envision that the patterned 3-D superlattice of Ge nanocrystals will lead to advanced materials applications, such as coherent phonon generator and high-sensitivity biosensor.

  5. 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.

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

    SciTech Connect

    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 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.

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

    SciTech Connect

    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.

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

    DOEpatents

    Weiss, Shimon; Bruchez, Marcel; Alivisatos, Paul

    2011-12-06

    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.

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

    DOEpatents

    Weiss, Shimon; Bruchez, Marcel; Alivisatos, Paul

    2012-10-16

    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.

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

    DOEpatents

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

    2011-12-06

    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.

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

    SciTech Connect

    Weiss, Shimon; Bruchez, Marcel; Alivisatos, Paul

    2012-10-16

    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.

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

    DOEpatents

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

    2011-12-20

    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.

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

    SciTech Connect

    Claridge, Shelley A.

    2008-05-01

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

  14. Fabrication and electronic transport studies of single nanocrystal systems

    SciTech Connect

    Klein, David Louis

    1997-05-01

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

  15. Shape-anisotropy driven symmetry transformations in nanocrystal superlattice polymorphs.

    PubMed

    Bian, Kaifu; Choi, Joshua J; Kaushik, Ananth; Clancy, Paulette; Smilgies, Detlef-M; Hanrath, Tobias

    2011-04-26

    Despite intense research efforts by research groups worldwide, the potential of self-assembled nanocrystal superlattices (NCSLs) has not been realized due to an incomplete understanding of the fundamental molecular interactions governing the self-assembly process. Because NCSLs reside naturally at length-scales between atomic crystals and colloidal assemblies, synthetic control over the properties of constituent nanocrystal (NC) building blocks and their coupling in ordered assemblies is expected to yield a new class of materials with remarkable optical, electronic, and vibrational characteristics. Progress toward the formation of suitable test structures and subsequent development of NCSL-based technologies has been held back by the limited control over superlattice spacing and symmetry. Here we show that NCSL symmetry can be controlled by manipulating molecular interactions between ligands bound to the NC surface and the surrounding solvent. Specifically, we demonstrate solvent vapor-mediated NCSL symmetry transformations that are driven by the orientational ordering of NCs within the lattice. The assembly of various superlattice polymorphs, including face-centered cubic (fcc), body-centered cubic (bcc), and body-centered tetragonal (bct) structures, is studied in real time using in situ grazing incidence small-angle X-ray scattering (GISAXS) under controlled solvent vapor exposure. This approach provides quantitative insights into the molecular level physics that controls solvent-ligand interactions and assembly of NCSLs. Computer simulations based on all-atom molecular dynamics techniques confirm several key insights gained from experiment.

  16. Nanocrystal diffusion doping.

    PubMed

    Vlaskin, Vladimir A; Barrows, Charles J; Erickson, Christian S; Gamelin, Daniel R

    2013-09-25

    A diffusion-based synthesis of doped colloidal semiconductor nanocrystals is demonstrated. This approach involves thermodynamically controlled addition of both impurity cations and host anions to preformed seed nanocrystals under equilibrium conditions, rather than kinetically controlled doping during growth. This chemistry allows thermodynamic crystal compositions to be prepared without sacrificing other kinetically trapped properties such as shape, size, or crystallographic phase. This doping chemistry thus shares some similarities with cation-exchange reactions, but proceeds without the loss of host cations and excels at the introduction of relatively unreactive impurity ions that have not been previously accessible using cation exchange. Specifically, we demonstrate the preparation of Cd(1-x)Mn(x)Se (0 ≤ x ≤ ∼0.2) nanocrystals with narrow size distribution, unprecedentedly high Mn(2+) content, and very large magneto-optical effects by diffusion of Mn(2+) into seed CdSe nanocrystals grown by hot injection. Controlling the solution and lattice chemical potentials of Cd(2+) and Mn(2+) allows Mn(2+) diffusion into the internal volumes of the CdSe nanocrystals with negligible Ostwald ripening, while retaining the crystallographic phase (wurtzite or zinc blende), shape anisotropy, and ensemble size uniformity of the seed nanocrystals. Experimental results for diffusion doping of other nanocrystals with other cations are also presented that indicate this method may be generalized, providing access to a variety of new doped semiconductor nanostructures not previously attainable by kinetic routes or cation exchange.

  17. Octahedral Tin Dioxide Nanocrystals Anchored on Vertically Aligned Carbon Aerogels as High Capacity Anode Materials for Lithium-Ion Batteries

    NASA Astrophysics Data System (ADS)

    Liu, Mingkai; Liu, Yuqing; Zhang, Yuting; Li, Yiliao; Zhang, Peng; Yan, Yan; Liu, Tianxi

    2016-08-01

    A novel binder-free graphene - carbon nanotubes - SnO2 (GCNT-SnO2) aerogel with vertically aligned pores was prepared via a simple and efficient directional freezing method. SnO2 octahedrons exposed of {221} high energy facets were uniformly distributed and tightly anchored on multidimensional graphene/carbon nanotube (GCNT) composites. Vertically aligned pores can effectively prevent the emersion of “closed” pores which cannot load the active SnO2 nanoparticles, further ensure quick immersion of electrolyte throughout the aerogel, and can largely shorten the transport distance between lithium ions and active sites of SnO2. Especially, excellent electrical conductivity of GCNT-SnO2 aerogel was achieved as a result of good interconnected networks of graphene and CNTs. Furthermore, meso- and macroporous structures with large surface area created by the vertically aligned pores can provide great benefit to the favorable transport kinetics for both lithium ion and electrons and afford sufficient space for volume expansion of SnO2. Due to the well-designed architecture of GCNT-SnO2 aerogel, a high specific capacity of 1190 mAh/g with good long-term cycling stability up to 1000 times was achieved. This work provides a promising strategy for preparing free-standing and binder-free active electrode materials with high performance for lithium ion batteries and other energy storage devices.

  18. All-solid-state high performance asymmetric supercapacitors based on novel MnS nanocrystal and activated carbon materials

    NASA Astrophysics Data System (ADS)

    Chen, Teng; Tang, Yongfu; Qiao, Yuqing; Liu, Zhangyu; Guo, Wenfeng; Song, Jianzheng; Mu, Shichun; Yu, Shengxue; Zhao, Yufeng; Gao, Faming

    2016-03-01

    All-solid-state high-performance asymmetric supercapacitors (ASCs) are fabricated using γ-MnS as positive electrode and porous eggplant derived activated carbon (EDAC) as negative electrode with saturated potassium hydroxide agar gel as the solid electrolyte. The laminar wurtzite nanostructure of γ-MnS facilitates the insertion of hydroxyl ions into the interlayer space, and the manganese sulfide nanowire offers electronic transportation channels. The size-uniform porous nanostructure of EDAC provides a continuous electron pathway as well as facilitates short ionic transportation pathways. Due to these special nanostructures of both the MnS and the EDAC, they exhibited a specific capacitance of 573.9 and 396 F g‑1 at 0.5 A g‑1, respectively. The optimized MnS//EDAC asymmetric supercapacitor shows a superior performance with specific capacitance of 110.4 F g‑1 and 89.87% capacitance retention after 5000 cycles, a high energy density of 37.6 Wh kg‑1 at a power density of 181.2 W kg‑1 and remains 24.9 Wh kg‑1 even at 5976 W kg‑1. Impressively, such two assembled all-solid-state cells in series can light up a red LED indicator for 15 minutes after fully charged. These impressive results make these pollution-free materials promising for practical applications in solid aqueous electrolyte-based ASCs.

  19. Octahedral Tin Dioxide Nanocrystals Anchored on Vertically Aligned Carbon Aerogels as High Capacity Anode Materials for Lithium-Ion Batteries

    PubMed Central

    Liu, Mingkai; Liu, Yuqing; Zhang, Yuting; Li, Yiliao; Zhang, Peng; Yan, Yan; Liu, Tianxi

    2016-01-01

    A novel binder-free graphene - carbon nanotubes - SnO2 (GCNT-SnO2) aerogel with vertically aligned pores was prepared via a simple and efficient directional freezing method. SnO2 octahedrons exposed of {221} high energy facets were uniformly distributed and tightly anchored on multidimensional graphene/carbon nanotube (GCNT) composites. Vertically aligned pores can effectively prevent the emersion of “closed” pores which cannot load the active SnO2 nanoparticles, further ensure quick immersion of electrolyte throughout the aerogel, and can largely shorten the transport distance between lithium ions and active sites of SnO2. Especially, excellent electrical conductivity of GCNT-SnO2 aerogel was achieved as a result of good interconnected networks of graphene and CNTs. Furthermore, meso- and macroporous structures with large surface area created by the vertically aligned pores can provide great benefit to the favorable transport kinetics for both lithium ion and electrons and afford sufficient space for volume expansion of SnO2. Due to the well-designed architecture of GCNT-SnO2 aerogel, a high specific capacity of 1190 mAh/g with good long-term cycling stability up to 1000 times was achieved. This work provides a promising strategy for preparing free-standing and binder-free active electrode materials with high performance for lithium ion batteries and other energy storage devices. PMID:27510357

  20. All-solid-state high performance asymmetric supercapacitors based on novel MnS nanocrystal and activated carbon materials.

    PubMed

    Chen, Teng; Tang, Yongfu; Qiao, Yuqing; Liu, Zhangyu; Guo, Wenfeng; Song, Jianzheng; Mu, Shichun; Yu, Shengxue; Zhao, Yufeng; Gao, Faming

    2016-03-29

    All-solid-state high-performance asymmetric supercapacitors (ASCs) are fabricated using γ-MnS as positive electrode and porous eggplant derived activated carbon (EDAC) as negative electrode with saturated potassium hydroxide agar gel as the solid electrolyte. The laminar wurtzite nanostructure of γ-MnS facilitates the insertion of hydroxyl ions into the interlayer space, and the manganese sulfide nanowire offers electronic transportation channels. The size-uniform porous nanostructure of EDAC provides a continuous electron pathway as well as facilitates short ionic transportation pathways. Due to these special nanostructures of both the MnS and the EDAC, they exhibited a specific capacitance of 573.9 and 396 F g(-1) at 0.5 A g(-1), respectively. The optimized MnS//EDAC asymmetric supercapacitor shows a superior performance with specific capacitance of 110.4 F g(-1) and 89.87% capacitance retention after 5000 cycles, a high energy density of 37.6 Wh kg(-1) at a power density of 181.2 W kg(-1) and remains 24.9 Wh kg(-1) even at 5976 W kg(-1). Impressively, such two assembled all-solid-state cells in series can light up a red LED indicator for 15 minutes after fully charged. These impressive results make these pollution-free materials promising for practical applications in solid aqueous electrolyte-based ASCs.

  1. Octahedral Tin Dioxide Nanocrystals Anchored on Vertically Aligned Carbon Aerogels as High Capacity Anode Materials for Lithium-Ion Batteries.

    PubMed

    Liu, Mingkai; Liu, Yuqing; Zhang, Yuting; Li, Yiliao; Zhang, Peng; Yan, Yan; Liu, Tianxi

    2016-08-11

    A novel binder-free graphene - carbon nanotubes - SnO2 (GCNT-SnO2) aerogel with vertically aligned pores was prepared via a simple and efficient directional freezing method. SnO2 octahedrons exposed of {221} high energy facets were uniformly distributed and tightly anchored on multidimensional graphene/carbon nanotube (GCNT) composites. Vertically aligned pores can effectively prevent the emersion of "closed" pores which cannot load the active SnO2 nanoparticles, further ensure quick immersion of electrolyte throughout the aerogel, and can largely shorten the transport distance between lithium ions and active sites of SnO2. Especially, excellent electrical conductivity of GCNT-SnO2 aerogel was achieved as a result of good interconnected networks of graphene and CNTs. Furthermore, meso- and macroporous structures with large surface area created by the vertically aligned pores can provide great benefit to the favorable transport kinetics for both lithium ion and electrons and afford sufficient space for volume expansion of SnO2. Due to the well-designed architecture of GCNT-SnO2 aerogel, a high specific capacity of 1190 mAh/g with good long-term cycling stability up to 1000 times was achieved. This work provides a promising strategy for preparing free-standing and binder-free active electrode materials with high performance for lithium ion batteries and other energy storage devices.

  2. Iron-oxide colloidal nanoclusters: from fundamental physical properties to diagnosis and therapy

    NASA Astrophysics Data System (ADS)

    Kostopoulou, Athanasia; Brintakis, Konstantinos; Lascialfari, Alessandro; Angelakeris, Mavroeidis; Vasilakaki, Marianna; Trohidou, Kalliopi; Douvalis, Alexios P.; Psycharakis, Stylianos; Ranella, Anthi; Manna, Liberato; Lappas, Alexandros

    2014-03-01

    Research on magnetic nanocrystals attracts wide-spread interest because of their challenging fundamental properties, but it is also driven by problems of practical importance to the society, ranging from electronics (e.g. magnetic recording) to biomedicine. In that respect, iron oxides are model functional materials as they adopt a variety of oxidation states and coordinations that facilitate their use. We show that a promising way to engineer further their technological potential in diagnosis and therapy is the assembly of primary nanocrystals into larger colloidal entities, possibly with increased structural complexity. In this context, elevated-temperature nanochemistry (c.f. based on a polyol approach) permitted us to develop size-tunable, low-cytotoxicity iron-oxide nanoclusters, entailing iso-oriented nanocrystals, with enhanced magnetization. Experimental (magnetometry, electron microscopy, Mössbauer and NMR spectroscopies) results supported by Monte Carlo simulations are reviewed to show that such assemblies of surface-functionalized iron oxide nanocrystals have a strong potential for innovation. The clusters' optimized magnetic anisotropy (including microscopic surface spin disorder) and weak ferrimagnetism at room temperature, while they do not undermine colloidal stability, endow them a profound advantage as efficient MRI contrast agents and hyperthermic mediators with important biomedical potential.

  3. Thermoplastic starch-waxy maize starch nanocrystals nanocomposites.

    PubMed

    Angellier, Hélène; Molina-Boisseau, Sonia; Dole, Patrice; Dufresne, Alain

    2006-02-01

    Waxy maize starch nanocrystals obtained by hydrolysis of native granules were used as a reinforcing agent in a thermoplastic waxy maize starch matrix plasticized with glycerol. Compared to our previous studies on starch nanocrystals reinforced natural rubber (NR) [Macromolecules 2005, 38, 3783; 2005, 38, 9161], the present system presents two particularities: (i) thermoplastic starch is a polar matrix, contrarily to NR, and (ii) the chemical structures of the matrix and the filler are similar. The influence of the glycerol content, filler content, and aging on the reinforcing properties of waxy maize starch nanocrystals (tensile tests, DMA) and crystalline structure (X-ray diffraction) of materials were studied. It was shown that the reinforcing effect of starch nanocrystals can be attributed to strong filler/filler and filler/matrix interactions due to the establishment of hydrogen bonding. The presence of starch nanocrystals leads to a slowing down of the recrystallization of the matrix during aging in humid atmosphere.

  4. 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

  5. Synthesis, Deposition, and Microstructure Development of Thin Films Formed by Sulfidation and Selenization of Copper Zinc Tin Sulfide Nanocrystals

    NASA Astrophysics Data System (ADS)

    Chernomordik, Boris David

    Significant reduction in greenhouse gas emission and pollution associated with the global power demand can be accomplished by supplying tens-of-terawatts of power with solar cell technologies. No one solar cell material currently on the market is poised to meet this challenge due to issues such as manufacturing cost, material shortage, or material toxicity. For this reason, there is increasing interest in efficient light-absorbing materials that are comprised of abundant and non-toxic elements for thin film solar cell. Among these materials are copper zinc tin sulfide (Cu2ZnSnS4, or CZTS), copper zinc tin selenide (Cu2ZnSnSe4, or CZTSe), and copper zinc tin sulfoselenide alloys [Cu2ZnSn(SxSe1-x )4, or CZTSSe]. Laboratory power conversion efficiencies of CZTSSe-based solar cells have risen to almost 13% in less than three decades of research. Meeting the terawatt challenge will also require low cost fabrication. CZTSSe thin films from annealed colloidal nanocrystal coatings is an example of solution-based methods that can reduce manufacturing costs through advantages such as high throughput, high material utilization, and low capital expenses. The film microstructure and grain size affects the solar cell performance. To realize low cost commercial production and high efficiencies of CZTSSe-based solar cells, it is necessary to understand the fundamental factors that affect crystal growth and microstructure evolution during CZTSSe annealing. Cu2ZnSnS4 (CZTS) nanocrystals were synthesized via thermolysis of single-source cation and sulfur precursors copper, zinc and tin diethyldithiocarbamates. The average nanocrystal size could be tuned between 2 nm and 40 nm, by varying the synthesis temperature between 150 °C and 340 °C. The synthesis is rapid and is completed in less than 10 minutes. Characterization by X-ray diffraction, Raman spectroscopy, transmission electron microscopy and energy dispersive X-ray spectroscopy confirm that the nanocrystals are nominally

  6. Fundamentals of Marketing. Marketing Education Teacher's Resource Guide. Expected Student Learning Outcomes and Cross-Referenced Instructional Materials by Competencies.

    ERIC Educational Resources Information Center

    Smith, Clifton L.

    This guide, developed by a project to revise the minimum core competencies for the Fundamentals of Marketing course in secondary marketing education in Missouri, contains four sections. The first section explains competency-based marketing education, including its mission, nature, curriculum, and the fundamentals of competency-based instruction.…

  7. Atomic-scale modeling of cellulose nanocrystals

    NASA Astrophysics Data System (ADS)

    Wu, Xiawa

    Cellulose nanocrystals (CNCs), the most abundant nanomaterials in nature, are recognized as one of the most promising candidates to meet the growing demand of green, bio-degradable and sustainable nanomaterials for future applications. CNCs draw significant interest due to their high axial elasticity and low density-elasticity ratio, both of which are extensively researched over the years. In spite of the great potential of CNCs as functional nanoparticles for nanocomposite materials, a fundamental understanding of CNC properties and their role in composite property enhancement is not available. In this work, CNCs are studied using molecular dynamics simulation method to predict their material' behaviors in the nanoscale. (a) Mechanical properties include tensile deformation in the elastic and plastic regions using molecular mechanics, molecular dynamics and nanoindentation methods. This allows comparisons between the methods and closer connectivity to experimental measurement techniques. The elastic moduli in the axial and transverse directions are obtained and the results are found to be in good agreement with previous research. The ultimate properties in plastic deformation are reported for the first time and failure mechanism are analyzed in details. (b) The thermal expansion of CNC crystals and films are studied. It is proposed that CNC film thermal expansion is due primarily to single crystal expansion and CNC-CNC interfacial motion. The relative contributions of inter- and intra-crystal responses to heating are explored. (c) Friction at cellulose-CNCs and diamond-CNCs interfaces is studied. The effects of sliding velocity, normal load, and relative angle between sliding surfaces are predicted. The Cellulose-CNC model is analyzed in terms of hydrogen bonding effect, and the diamond-CNC model compliments some of the discussion of the previous model. In summary, CNC's material properties and molecular models are both studied in this research, contributing to

  8. Ellipsometric characterization of nanocrystals in porous silicon

    NASA Astrophysics Data System (ADS)

    Petrik, P.; Fried, M.; Vázsonyi, É.; Lohner, T.; Horváth, E.; Polgár, O.; Basa, P.; Bársony, I.; Gyulai, J.

    2006-10-01

    Porous silicon layers (PSLs) were prepared by electrochemical etching of p-type single-crystalline silicon (c-Si) wafers having different dopant concentrations to obtain systematically changing sizes of nanocrystals (walls). The microstructure of the porous material was characterized using spectroscopic ellipsometry with multi-layer effective medium approximation (EMA) models. The dielectric function of PSL is conventionally calculated using EMA mixtures of c-Si and voids. The porosity is described by the concentration of voids. Some PSL structures can be described only by adding fine-grained polycrystalline silicon (nc-Si) reference material to the EMA model. Modified model dielectric functions (MDF) of c-Si have been shown to fit composite materials containing nanocrystalline regions, either by fitting only the broadening parameter or also other parameters of the parametric oscillator in MDF. The broadening parameter correlates with the long-range order in the crystalline material, and, as a consequence, with the size of nanocrystals. EMA and MDF models were used to describe systematically changing nanostructure of PSLs. Volume fraction of nc-Si in EMA and broadening parameter in MDF provide information on the nanocrystal size. The longer-term goal of this work is to provide a method for the quantitative characterization of nanocrystal size using quick, sensitive and non-destructive optical techniques.

  9. Emission efficiency limit of Si nanocrystals.

    PubMed

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

    2016-01-20

    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 × 10(12) cm(12), 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.

  10. Polymer grafting onto starch nanocrystals.

    PubMed

    Labet, Marianne; Thielemans, Wim; Dufresne, Alain

    2007-09-01

    Monocrystalline starch nanoparticles were successfully grafted with poly(tetrahydrofuran), poly(caprolactone), and poly(ethylene glycol) monobutyl ether chains using toluene 2,4-diisocyanate as a linking agent. Surface grafting was confirmed using Fourier transform infrared and X-ray photoelectron spectroscopies, differential scanning calorimetry, elemental analysis, and contact angle measurements. Transmission electron microscopy observations of modified starch nanocrystals showed either the individualization of nanoparticles or the formation of a film, depending on the polymer used. It was shown that grafting efficiency decreased with the length of the polymeric chains, as expected. The resulting modified nanoparticles can find applications in the field of co-continuous nanocomposite materials.

  11. Nanocrystal-Powered Nanomotor

    SciTech Connect

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

    2005-07-05

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

  12. 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.

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

    DOEpatents

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

    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.

  14. 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.

  15. 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.

  16. Solution synthesis of germanium nanocrystals

    DOEpatents

    Gerung, Henry [Albuquerque, NM; Boyle, Timothy J [Kensington, MD; Bunge, Scott D [Cuyahoga Falls, OH

    2009-09-22

    A method for providing a route for the synthesis of a Ge(0) nanometer-sized material from. A Ge(II) precursor is dissolved in a ligand heated to a temperature, generally between approximately 100.degree. C. and 400.degree. C., sufficient to thermally reduce the Ge(II) to Ge(0), where the ligand is a compound that can bond to the surface of the germanium nanomaterials to subsequently prevent agglomeration of the nanomaterials. The ligand encapsulates the surface of the Ge(0) material to prevent agglomeration. The resulting solution is cooled for handling, with the cooling characteristics useful in controlling the size and size distribution of the Ge(0) materials. The characteristics of the Ge(II) precursor determine whether the Ge(0) materials that result will be nanocrystals or nanowires.

  17. Composition-tunable alloyed semiconductor nanocrystals.

    PubMed

    Regulacio, Michelle D; Han, Ming-Yong

    2010-05-18

    The ability to engineer the band gap energy of semiconductor nanocrystals has led to the development of nanomaterials with many new exciting properties and applications. Band gap engineering has thus proven to be an effective tool in the design of new nanocrystal-based semiconductor devices. As reported in numerous publications over the last three decades, tuning the size of nanocrystalline semiconductors is one way of adjusting the band gap energy. On the other hand, research on band gap engineering via control of nanocrystal composition, which is achieved by adjusting the constituent stoichiometries of alloyed semiconductors, is still in its infancy. In this Account, we summarize recent research on colloidal alloyed semiconductor nanocrystals that exhibit novel composition-tunable properties. Alloying of two semiconductors at the nanometer scale produces materials that display properties distinct not only from the properties of their bulk counterparts but also from those of their parent semiconductors. As a result, alloyed nanocrystals possess additional properties that are composition-dependent aside from the properties that emerge due to quantum confinement effects. For example, although the size-dependent emission wavelength of the widely studied CdSe nanocrystals can be continuously tuned to cover almost the entire visible spectrum, the near-infrared (NIR) region is far outside its spectral range. By contrast, certain alloy compositions of nanocrystalline CdSe(x)Te(1-x), an alloy of CdSe and CdTe, can efficiently emit light in the NIR spectral window. These NIR-emitting nanocrystals are potentially useful in several biomedical applications. In addition, highly stable nanocrystals formed by alloying CdSe with ZnSe (i.e., Zn(x)Cd(1-x)Se) emit blue light with excellent efficiency, a property seldom achieved by the parent binary systems. As a result, these materials can be used in short-wavelength optoelectronic devices. In the future, we foresee new discoveries

  18. Fundamental investigations related to the mitigation of volume changes in cement-based materials at early ages

    NASA Astrophysics Data System (ADS)

    Sant, Gaurav Niteen

    additional Sodium Hydroxide. Further, to quantify the influence of temperature on volume changes in SRA containing materials, deformation measurements are performed at different temperatures. The results indicate maturity transformations are incapable of simulating volume changes over any temperature regime due to the influence of temperature on salt solubility and pore solution composition, crystallization stresses and self-desiccation. The performance of a CaO-based expansive additive is evaluated over a range of additive concentrations and curing conditions to quantify the reduction in restrained and unrestrained volume changes effected in low w/c cement pastes. The results suggest, under unrestrained sealed conditions the additive generates an expansion and reduces the magnitude of total shrinkage experienced by the material. However, the extent of drying shrinkage developed is noted to be similar in all systems and independent of the additive dosage. Under restrained sealed conditions, the additive induces a significant compressive stress which delays tensile stress development in the system. However, a critical additive concentration (around four percent) needs to be exceeded to appreciably reduce the risk of cracking at early-ages. The influence of shrinkage reducing admixtures (SRAs) is quantified in terms of the effects of SRA addition on fluid transport in cement-based materials. The change in the cement paste's pore solution properties, i.e., the surface tension and fluid-viscosity, induced by the addition of a SRA is observed to depress the fluid-sorption and wetting moisture diffusion coefficients, with the depression being a function of the SRA concentration. The experimental results are compared to analytical descriptions of water sorption and a good correlation is observed. These results allow for the change in pore-solution and fluid-transport properties to be incorporated from a fundamental perspective in models which aim to describe the service-life of

  19. Colloidal nanocrystal synthesis and the organic-inorganicinterface

    SciTech Connect

    Yin, Yadong; Alivisatos, A. Paul

    2005-05-12

    Colloidal nanocrystals are nanometer-sized, solution-grown inorganic particles stabilized by a layer of surfactants attached to their surface. The inorganic cores exhibit useful properties controlled by composition as well as size and shape, while the surfactant coating ensures that these structures are easy to fabricate and process. It is this combination of features that makes colloidal nanocrystals attractive and promising building blocks for advanced materials and devices. But their full potential can only be exploited if we achieve exquisite control over their composition, size, shape, crystal structure and surface properties. Here we review what is known about nanocrystal growth and outline strategies for controlling it.

  20. Controlled Chemical Doping of Semiconductor Nanocrystals Using Redox Buffers

    SciTech Connect

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

    2013-07-20

    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 concentration in porous semiconductor thin films.

  1. Study of the fundamental units of novel semiconductor materials: structures, energetics, and thermodynamics of the Ge-Sn and Si-Ge-Sn molecular systems.

    PubMed

    Ciccioli, A; Gigli, G

    2012-07-05

    The binary Ge(y)Sn(z) and ternary Si(x)Ge(y)Sn(z) molecular systems containing up to five atoms were investigated by means of density functional theory and coupled cluster calculations. The minimum energy structures were calculated and higher energy isomers are also proposed. The atomization energies of the ground state isomers were calculated by the CCSD(T) method with correlation consistent basis sets up to quadruple-ζ quality. The resulting values were extrapolated to the complete basis set limit and corrected by an approximate evaluation of the spin-orbit effect. Energetic properties such as binding, fragmentation and mixing energies, and HOMO-LUMO gap were analyzed as a function of the cluster size and composition. By using empirically adjusted atomization energies and DFT harmonic frequencies, the thermal functions were evaluated, and a thermodynamic database for the Si-Ge-Sn system was built, containing data for 55 gaseous species. On this basis, equilibrium calculations were performed in the temperature interval 1600-2200 K aimed at predicting the composition of the gas phase under various conditions. The results presented here can be of interest to improve the microscopic knowledge of Ge-Sn and Si-Ge-Sn materials, which are among the most promising candidates for advanced applications in the field of electronic and optoelectronic components, both as epitaxially grown layers and as nanocrystal quantum dots.

  2. 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.

  3. Silicon nanowires, carbon nanotubes, and magnetic nanocrystals: Synthesis, properties, and applications

    NASA Astrophysics Data System (ADS)

    Lee, Doh Chang

    Central to the practical use of nanoscale materials is the controlled growth in technologically meaningful quantities. Many of the proposed applications of the nanomaterials potentially require inexpensive production of the building blocks. Solution-based synthetic approach offers controllability, high throughput, and scalability, which make the process attractive for the potential scale-up. Growth kinetics could be readily influenced by chemical interactions between the precursor and the solvent. In order to fully utilize its benefits, it is therefore pivotal to understand the decomposition chemistry of the precursors used in the reactions. Supercritical fluids were used as solvent in which high temperature reactions could take place. Silicon nanowires with diameters of 20˜30 nm was synthesized in supercritical fluids with metal nanocrystals as seeds for the nanowire growth. To unravel the effect of silicon precursors, several silicon precursors were reacted and the resulting products were investigated. The scalability of the system is discussed based on the experimental data. The nanowires were characterized with various characterization tools, including high-resolution transmission electron microscopy and electron energy loss spectroscopy. The crystallographic signatures were analyzed through the transmission electron microscopic study, and fundamental electrical and optical properties were probed by electron energy loss spectroscopy. Carbon nanotubes were prepared by reacting carbon-containing chemicals in supercritical fluids with organometallic compounds that form metal seed particles in-situ. A batch reaction, in which the temperature control was relatively poor, yielded a mixture of multiwall nanotubes and amorphous carbon nanofilaments with a low selectivity of nanotubes in the product. When reaction parameters were translated into a continuous flow-through reaction, nanotube selectivity as well as the throughput of the total product significantly

  4. Radiative decay rates of impurity states in semiconductor nanocrystals

    NASA Astrophysics Data System (ADS)

    Turkov, Vadim K.; Baranov, Alexander V.; Fedorov, Anatoly V.; Rukhlenko, Ivan D.

    2015-10-01

    Doped semiconductor nanocrystals is a versatile material base for contemporary photonics and optoelectronics devices. Here, for the first time to the best of our knowledge, we theoretically calculate the radiative decay rates of the lowest-energy states of donor impurity in spherical nanocrystals made of four widely used semiconductors: ZnS, CdSe, Ge, and GaAs. The decay rates were shown to vary significantly with the nanocrystal radius, increasing by almost three orders of magnitude when the radius is reduced from 15 to 5 nm. Our results suggest that spontaneous emission may dominate the decay of impurity states at low temperatures, and should be taken into account in the design of advanced materials and devices based on doped semiconductor nanocrystals.

  5. Radiative decay rates of impurity states in semiconductor nanocrystals

    SciTech Connect

    Turkov, Vadim K.; Baranov, Alexander V.; Fedorov, Anatoly V.; Rukhlenko, Ivan D.

    2015-10-15

    Doped semiconductor nanocrystals is a versatile material base for contemporary photonics and optoelectronics devices. Here, for the first time to the best of our knowledge, we theoretically calculate the radiative decay rates of the lowest-energy states of donor impurity in spherical nanocrystals made of four widely used semiconductors: ZnS, CdSe, Ge, and GaAs. The decay rates were shown to vary significantly with the nanocrystal radius, increasing by almost three orders of magnitude when the radius is reduced from 15 to 5 nm. Our results suggest that spontaneous emission may dominate the decay of impurity states at low temperatures, and should be taken into account in the design of advanced materials and devices based on doped semiconductor nanocrystals.

  6. Ternary Silver Halide Nanocrystals.

    PubMed

    Abeyweera, Sasitha C; Rasamani, Kowsalya D; Sun, Yugang

    2017-07-18

    Nanocrystalline silver halides (AgX) such as AgCl, AgBr, and AgI, a class of semiconductor materials with characteristics of both direct and indirect band gaps, represent the most crucial components in traditional photographic processing. The nanocrystal surfaces provide sensitivity specks that can turn into metallic silver, forming an invisible latent image, upon exposure to light. The photographic processing implies that the AgX nanoparticles possess unique properties. First, pristine AgX nanoparticles absorb light only at low efficiency to convert surface AgX into tiny clusters of silver atoms. Second, AgX nanoparticles represent an excellent class of materials to capture electrons efficiently. Third, small metallic silver clusters can catalyze the reduction of AgX nanoparticles to Ag nanoparticles in the presence of mild reducing reagents, known as self-catalytic reduction. These properties indicate that AgX nanoparticles can be partially converted to metallic silver with high precision, leading to the formation of hybrid AgX/Ag nanoparticles. The nanosized metallic Ag usually exhibit intense absorption bands in the visible spectral region due to their strong surface plasmon resonances, which make the AgX/Ag nanoparticles a class of promising visible-light-driven photocatalysts for environmental remediation and CO2 reduction. Despite the less attention paid to their ability of capturing electrons, AgX nanoparticles might be a class of ideal electron shuttle materials to bridge light absorbers and catalysts on which electrons can drive chemical transformations. In this Account, we focus on ternary silver halide alloy (TSHA) nanoparticles, containing two types of halide ions, which increase the composition complexity of the silver halide nanoparticles. Interdiffusion of halide ions between two types of AgX at elevated temperatures has been developed for fabricating ternary silver halide alloy crystals, such as silver chlorobromide optical fibers for infrared

  7. Three-dimensional mapping of a deformation field inside a nanocrystal

    NASA Astrophysics Data System (ADS)

    Pfeifer, Mark A.; Williams, Garth J.; Vartanyants, Ivan A.; Harder, Ross; Robinson, Ian K.

    2006-07-01

    Coherent X-ray diffraction imaging is a rapidly advancing form of microscopy: diffraction patterns, measured using the latest third-generation synchrotron radiation sources, can be inverted to obtain full three-dimensional images of the interior density within nanocrystals. Diffraction from an ideal crystal lattice results in an identical copy of this continuous diffraction pattern at every Bragg peak. This symmetry is broken by the presence of strain fields, which arise from the epitaxial contact forces that are inevitable whenever nanocrystals are prepared on a substrate. When strain is present, the diffraction copies at different Bragg peaks are no longer identical and contain additional information, appearing as broken local inversion symmetry about each Bragg point. Here we show that one such pattern can nevertheless be inverted to obtain a `complex' crystal density, whose phase encodes a projection of the lattice deformation. A lead nanocrystal was crystallized in ultrahigh vacuum from a droplet on a silica substrate and equilibrated close to its melting point. A three-dimensional image of the density, obtained by inversion of the coherent X-ray diffraction, shows the expected facetted morphology, but in addition reveals a real-space phase that is consistent with the three-dimensional evolution of a deformation field arising from interfacial contact forces. Quantitative three-dimensional imaging of lattice strain on the nanometre scale will have profound consequences for our fundamental understanding of grain interactions and defects in crystalline materials. Our method of measuring and inverting diffraction patterns from nanocrystals represents a vital step towards the ultimate goal of atomic resolution single-molecule imaging that is a prominent justification for development of X-ray free-electron lasers.

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

    NASA Astrophysics Data System (ADS)

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

    2016-09-01

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

  9. Mn-Doped Multinary CIZS and AIZS Nanocrystals.

    PubMed

    Manna, Goutam; Jana, Santanu; Bose, Riya; Pradhan, Narayan

    2012-09-20

    Multinary nanocrystals (CuInS2, CIS, and AgInS2, AIS) are widely known for their strong defect state emission. On alloying with Zn (CIZS and AIZS), stable and intense emission tunable in visible and NIR windows has already been achieved. In these nanocrystals, the photogenerated hole efficiently moves to the defect-induced state and recombines with the electron in the conduction band. As a result, the defect state emission is predominantly observed without any band edge excitonic emission. Herein, we report the doping of the transition-metal ion Mn in these nanocrystals, which in certain compositions of the host nanocrystals quenches this strong defect state emission and predominantly shows the spin-flip Mn emission. Though several Mn-doped semiconductor nanocrystals are reported in the literature, these nanocrystals are of its first kind that can be excited in the visible window, do not contain the toxic element Cd, and provide efficient emission. Hence, when Mn emission is required, these multinary nanocrystals can be the ideal versatile materials for widespread technological applications.

  10. Synthesis of TiO2 nanocrystals with a high affinity for amine organic compounds.

    PubMed

    Gonçalves, Ricardo H; Schreiner, Wido Herwig; Leite, Edson R

    2010-07-20

    This article describes a different approach to the colloidal synthesis of TiO(2) nanocrystals using a polymer melt as a solvent. This approach allowed us to obtain a colloidal dispersion with a high degree of stability in a polymeric solvent, resulting in a transparent colloid. Using this method, it was possible to obtain the TiO(2) nanocrystal with Brønsted acid sites and polymer chains chemically anchored on the nanocrystal surface. The acid surface of those nanocrystals has the chemical property to react in the presence of amine organic compounds and to maintain the colloidal stability. In this way, TiO(2) nanocrystals were combined with a molecular probe containing amine functional groups such as polyaniline. Through the combination of the molecular probe and inorganic nanocrystals, we obtained a hybrid material with interesting chemical, optical, and electronic behavior, making it a promising material for photovoltaic, photochromic, and sensor devices.

  11. Optics-free lithography on colloidal nanocrystal assemblies

    NASA Astrophysics Data System (ADS)

    Shaw, Santosh; Miller, Kyle J.; Colaux, Julien L.; Cademartiri, Ludovico

    2016-03-01

    We describe a lithographic approach - Nanocrystal Plasma Polymerization (NPP)-based lithography (Figure 1) - where colloidal nanocrystal assemblies (CNAs) are used as the resist and, potentially, the active material. The patterning process is based on a change in the dispersibility of the CNAs in solvents as a result of the exposure to plasmas. Plasmas can etch the capping ligands from the exposed area. During the development step, the unexposed area of CNAs are redispersed leaving behind the patterned area.

  12. Fundamental Physics

    NASA Image and Video Library

    2003-01-22

    Still photographs taken over 16 hours on Nov. 13, 2001, on the International Space Station have been condensed into a few seconds to show the de-mixing -- or phase separation -- process studied by the Experiment on Physics of Colloids in Space. Commanded from the ground, dozens of similar tests have been conducted since the experiment arrived on ISS in 2000. The sample is a mix of polymethylmethacrylate (PMMA or acrylic) colloids, polystyrene polymers and solvents. The circular area is 2 cm (0.8 in.) in diameter. The phase separation process occurs spontaneously after the sample is mechanically mixed. The evolving lighter regions are rich in colloid and have the structure of a liquid. The dark regions are poor in colloids and have the structure of a gas. This behavior carnot be observed on Earth because gravity causes the particles to fall out of solution faster than the phase separation can occur. While similar to a gas-liquid phase transition, the growth rate observed in this test is different from any atomic gas-liquid or liquid-liquid phase transition ever measured experimentally. Ultimately, the sample separates into colloid-poor and colloid-rich areas, just as oil and vinegar separate. The fundamental science of de-mixing in this colloid-polymer sample is the same found in the annealing of metal alloys and plastic polymer blends. Improving the understanding of this process may lead to improving processing of these materials on Earth.

  13. Origin and chemical composition of the amorphous material from the intergrain pores of self-assembled cubic ZnS:Mn nanocrystals

    NASA Astrophysics Data System (ADS)

    Stefan, Mariana; Vlaicu, Ioana Dorina; Nistor, Leona Cristina; Ghica, Daniela; Nistor, Sergiu Vasile

    2017-12-01

    We have shown in previous investigations that the low temperature collective magnetism observed in mesoporous cubic ZnS:Mn nanocrystalline powders prepared by colloidal synthesis, with nominal doping concentrations above 0.2 at.%, is due to the formation of Mn2+ clusters with distributed antiferromagnetic coupling localized in an amorphous phase found between the cubic ZnS:Mn nanocrystals. Here we investigate the composition, origin and thermal annealing behavior of this amorphous phase in such a mesoporous ZnS:Mn sample doped with 5 at.% Mn nominal concentration. Correlated analytical transmission electron microscopy, multifrequency electron paramagnetic resonance and Fourier transform infrared spectroscopy data show that the amorphous nanomaterial consists of unreacted precursor hydrated zinc and manganese acetates trapped inside the pores and on the surface of the cubic ZnS nanocrystals. The decomposition of the acetates under isochronal annealing up to 270 °C, where the mesoporous structure is still preserved, lead to changes in the nature and strength of the magnetic interactions between the aggregated Mn2+ ions. These results strongly suggest the possibility to modulate the magnetic properties of such transition metal ions doped II-VI mesoporous structures by varying the synthesis conditions and/or by post-synthesis thermochemical treatments.

  14. Synthesis of Doped Semiconductor Nanocrystals and Conductive Coatings

    NASA Astrophysics Data System (ADS)

    Wills, Andrew Wilke

    Semiconductor nanocrystals are an intriguing class of materials because of their size-tunable properties. This makes them promising for future optoelectronic devices such as solar cells and light emitting diodes. Realization of these devices, however, requires precise control of the flow of electricity through the particles. In bulk semiconductors, this is achieved by using materials with few unintentional defects, then intentionally adding particular defects or dopants to alter the semiconductor's electronic properties. In contrast, the addition of electrically active dopants has scarcely been demonstrated in semiconductor nanocrystals, and charge transport is hindered by the barrier of electron hopping between particles. The goal of this thesis, therefore, is to discover new methods to control charge transport in nanocrystals. It divides into three major thrusts: 1) the investigation of the doping process in semiconductor nanocrystals, 2) the invention of new synthetic methods to incorporate electrically active dopants into semiconductor nanocrystals, and 3) the invention of a new nanocrystal surface coating that aids processing of nanocrystals into devices but can be removed to enhance charge transport between particles. The first objective is achieved by the comparison of four different precursors that have been used to dope Mn into nanocrystals. Experiments show that dimethylmanganese incorporates efficiently into ZnSe nanocrystals while other precursors are less efficient and sometimes lower the quality of the nanocrystals produced. The second goal is met by the application of a core-shell synthetic strategy to the incorporation of non-isovalent impurities (Al and In) into CdSe nanocrystals. By separating the three steps of nucleation, dopant binding, and growth, each step can be optimized so that doping is achieved and high quality particles are produced. Detailed characterization shows dopant incorporation and local environment, while transistor

  15. Self-Assembled Epitaxial Core-Shell Nanocrystals with Tunable Magnetic Anisotropy.

    PubMed

    Liao, Sheng-Chieh; Chen, Yong-Lun; Kuo, Wei-Cheng; Cheung, Jeffrey; Wang, Wei-Cheng; Cheng, Xuan; Chin, Yi-Ying; Chen, Yu-Ze; Liu, Heng-Jui; Lin, Hong-Ji; Chen, Chien-Te; Juang, Jeng-Yih; Chueh, Yu-Lun; Nagarajan, Valanoor; Chu, Ying-Hao; Lai, Chih-Huang

    2015-09-02

    Epitaxial core-shell CoO-CoFe2 O4 nanocrystals are fabricated by using pulsed laser deposition with the aid of melted material (Bi2 O3 ) addition and suitable lattice mismatch provided by substrates (SrTiO3 ). Well aligned orientations among nanocrystals and reversible core-shell sequence reveal tunable magnetic anisotropy. The interfacial coupling between core and shell further engineers the nanocrystal functionality.

  16. High-Performance Low-Cost Portable Radiological and Nuclear Detectors Based on Colloidal Nanocrystals (TOPIC 07-B)

    DTIC Science & Technology

    2016-07-01

    September 2015 Prepared by: MAREK OSIŃ SKI Center for High Technology Materials University of New Mexico 1313 Goddard SE Albuquerque...OF ABBREVIATIONS 2D – two-dimensional 3D – three-dimensional CHTM - Center for High Technology Materials CNC – colloidal nanocrystal CWO...nanocrystals was to be compared with nanocrystals containing activating dopants, such as Ce. For neutron detection, the host materials was to contain neutron

  17. A luminescent nanocrystal stress gauge

    SciTech Connect

    Choi, Charina; Koski, Kristie; Olson, Andrew; Alivisatos, Paul

    2010-10-25

    Microscale mechanical forces can determine important outcomes ranging from the site of material fracture to stem cell fate. However, local stresses in a vast majority of systems cannot be measured due to the limitations of current techniques. In this work, we present the design and implementation of the CdSe/CdS core/shell tetrapod nanocrystal, a local stress sensor with bright luminescence readout. We calibrate the tetrapod luminescence response to stress, and use the luminescence signal to report the spatial distribution of local stresses in single polyester fibers under uniaxial strain. The bright stress-dependent emission of the tetrapod, its nanoscale size, and its colloidal nature provide a unique tool that may be incorporated into a variety of micromechanical systems including materials and biological samples to quantify local stresses with high spatial resolution.

  18. Solvothermal synthesis and characterization of CZTS nanocrystals

    NASA Astrophysics Data System (ADS)

    Dumasiya, Ajay; Shah, N. M.

    2017-05-01

    Cu2ZnSnS4 (CZTS) is a promising thin film absorber material for low cost solar cell applications. CZTS nanoparticle ink synthesized using solvothermal route is an attractive option to deposit absorber layer using screen printing or spin coating method in CZTS thin film solar cell. In this study we have synthesized CZTS nanocrystals using solvothermal method from aqueous solution of Copper nitrate [Cu(NO3)2], Zinc nitrate [Zn(NO3)2], tin chloride [SnCl4] and thiourea with varying concentration of Cu(NO3)2 (viz 0.82 mmol,1.4 mmol, 1.7 mmol) keeping concentrations of rest of solutions constant. As synthesized CZTS nanocrystals are characterized using Energy Dispersive Analysis of X-rays (EDAX) to verify stoichiometry of elements. Analysis of EDAX data suggests that CZTS nanocrystals having Copper nitrate [Cu (NO3)2] concentration of 1.4 m mole is near stoichiometric. X-ray diffraction analysis study of CZTS nanocrystals having Copper nitrate [Cu (NO3)2] concentration of 1.4 m mole reveals the preferred orientation of the grains in (112), (220) and (312) direction confirming Kesterite structure of CZTS.

  19. 3D lattice distortions and defect structures in ion-implanted nano-crystals

    DOE PAGES

    Hofmann, Felix; Robinson, Ian K.; Tarleton, Edmund; ...

    2017-04-06

    The ability of Focused Ion Beam (FIB) techniques to cut solid matter at the nano-scale revolutionized the study of material structure across the life-, earth- and material sciences. But a detailed understanding of the damage caused by the ion beam and its effect on material properties remains elusive. We examine this damage in 3D using coherent X-ray diffraction to measure the full lattice strain tensor in FIB-milled gold nano-crystals. We also found that even very low ion doses, previously thought to be negligible, cause substantial lattice distortions. At higher doses, extended self-organized defect structures appear. Combined with detailed numerical calculations,more » these observations allow fundamental insight into the nature of the damage created and the structural instabilities that lead to a surprisingly inhomogeneous morphology.« less

  20. Tether fundamentals

    NASA Technical Reports Server (NTRS)

    Carroll, J. A.

    1986-01-01

    Some fundamental aspects of tethers are presented and briefly discussed. The effects of gravity gradients, dumbbell libration in circular orbits, tether control strategies and impact hazards for tethers are among those fundamentals. Also considered are aerodynamic drag, constraints in momentum transfer applications and constraints with permanently deployed tethers. The theoretical feasibility of these concepts are reviewed.

  1. Stiffness, compliance, resilience, and creep deformation: understanding implant-soft tissue dynamics in the augmented breast: fundamentals based on materials science.

    PubMed

    Vegas, Manuel R; Martin del Yerro, Jose L

    2013-10-01

    Postoperative tissue stretch deformities are among the possible complications in breast augmentation. These deformities are responsible for many potential risks such as bottoming-out deformity, breakdown of the inframammary fold, permanent tissue atrophy, sensory loss, and breast distortion (visible implant edges and traction rippling), among others. Although the elastic properties of the breast are a major concern for plastic surgeons, concepts such as stiffness, compliance, elasticity, and resilience have not been sufficiently defined or explored in the plastic surgery literature. Similar to any other material, living tissues are subject to the fundamentals of the mechanics of materials. Based on their experience with more than 5,000 breast augmentations, the authors explored the basic fundamentals of the mechanics of materials in search of a rational explanation for long-term results in breast augmentation and augmentation-mastopexy. A basic law of the mechanics of materials determines that when a material (e.g., breast) is loaded with a force (e.g., implant), it produces a stress that causes the material to deform (e.g., breast augmentation), and this behavior might be graphed in a theoretical material's stress-stress curve. This deformation will increase with time although the load (implant) remains constant, a concept termed "creep deformation." Because the breast, like all human tissues, is a viscoelastic material, the application of concepts such as elastic and plastic deformation, stiffness, compliance, resilience, and creep deformation can and should be applied to breast augmentation surgery. The authors have found that the principles of the mechanics of materials can provide plastic surgeons with some clues for a predictable, long-lasting good result in breast augmentation and augmentation-mastopexy. Future studies are needed to develop these concepts and evaluate how they might individually determine the mid- and long-term outcomes of augmented breasts.

  2. Shape-Controlled Metal Nanocrystals for Heterogeneous Catalysis.

    PubMed

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

    2016-06-07

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

  3. Plasmonic engineering of spontaneous emission from silicon nanocrystals

    PubMed Central

    Goffard, Julie; Gérard, Davy; Miska, Patrice; Baudrion, Anne-Laure; Deturche, Régis; Plain, Jérôme

    2013-01-01

    Silicon nanocrystals offer huge advantages compared to other semi-conductor quantum dots as they are made from an abundant, non-toxic material and are compatible with silicon devices. Besides, among a wealth of extraordinary properties ranging from catalysis to nanomedicine, metal nanoparticles are known to increase the radiative emission rate of semiconductor quantum dots. Here, we use gold nanoparticles to accelerate the emission of silicon nanocrystals. The resulting integrated hybrid emitter is 5-fold brighter than bare silicon nanocrystals. We also propose an in-depth analysis highlighting the role of the different physical parameters in the photoluminescence enhancement phenomenon. This result has important implications for the practical use of silicon nanocrystals in optoelectronic devices, for instance for the design of efficient down-shifting devices that could be integrated within future silicon solar cells. PMID:24037020

  4. Highly Emissive Transition Metal Ion Doped Semiconducting Nanocrystals

    NASA Astrophysics Data System (ADS)

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

    2011-07-01

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

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

    PubMed

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

    2016-03-01

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

  6. Structural Characterization of Bimetallic Nanocrystal Electrocatalysts

    SciTech Connect

    Cullen, David A

    2016-01-01

    Late transition metal nanocrystals find applications in heterogeneous catalysis such as plasmon-enhanced catalysis and as electrode materials for fuel cells, a zero-emission and sustainable energy technology. Their commercial viability for automotive transportation has steadily increased in recent years, almost exclusively due to the discovery of more efficient bimetallic nanocatalysts for the oxygen reduction reaction (ORR) at the cathode. Despite improvements to catalyst design, achieving high activity while maintaining durability is essential to further enhance their performance for this and other important applications in catalysis. Electronic effects arising from the generation of metal-metal interfaces, from plasmonic metals, and from lattice distortions, can vastly improve sorption properties at catalytic surfaces, while increasing durability.[1] Multimetallic lattice-strained nanoparticles are thus an interesting opportunity for fundamental research.[2,3] A colloidal synthesis approach is demonstrated to produce AuPd alloy and Pd@Au core-shell nanoicosahedra as catalysts for electro-oxidations. The nanoparticles are characterized using aberration-corrected scanning transmission electron microscopy (ac-STEM) and large solid angle energy dispersive X-ray spectroscopy (EDS) on an FEI Talos 4-detector STEM/EDS system. Figure 1 shows bright-field (BF) and high-angle annular dark-field (HAADF) ac-STEM images of the alloy and core-shell nanoicosahedra together with EDS line-scans and elemental maps. These structures are unique in that the presence of twin boundaries, alloying, and core-shell morphology could create highly strained surfaces and interfaces. The shell thickness of the core-shell structures observed in HAADF-STEM images is tuned by adjusting the ratio between metal precursors (Figure 2a-f) to produce shells ranging from a few to several monolayers. Specific activity was measured in ethanol electro-oxidation to examine the effect of shell thickness on

  7. Entropy-driven formation of binary semiconductor-nanocrystal superlattices.

    PubMed

    Evers, Wiel H; De Nijs, Bart; Filion, Laura; Castillo, Sonja; Dijkstra, Marjolein; Vanmaekelbergh, Daniel

    2010-10-13

    One of the main reasons for the current interest in colloidal nanocrystals is their propensity to form superlattices, systems in which (different) nanocrystals are in close contact in a well-ordered three-dimensional (3D) geometry resulting in novel material properties. However, the principles underlying the formation of binary nanocrystal superlattices are not well understood. Here, we present a study of the driving forces for the formation of binary nanocrystal superlattices by comparing the formed structures with full free energy calculations. The nature (metallic or semiconducting) and the size-ratio of the two nanocrystals are varied systematically. With semiconductor nanocrystals, self-organization at high temperature leads to superlattices (AlB(2), NaZn(13), MgZn(2)) in accordance with the phase diagrams for binary hard-sphere mixtures; hence entropy increase is the dominant driving force. A slight change of the conditions results in structures that are energetically stabilized. This study provides rules for the rational design of 3D nanostructured binary semiconductors, materials with promises in thermoelectrics and photovoltaics and which cannot be reached by any other technology.

  8. Cellulose nanocrystals from acacia bark-Influence of solvent extraction.

    PubMed

    Taflick, Ticiane; Schwendler, Luana A; Rosa, Simone M L; Bica, Clara I D; Nachtigall, Sônia M B

    2017-08-01

    The isolation of cellulose nanocrystals from different lignocellulosic materials has shown increased interest in academic and technological research. These materials have excellent mechanical properties and can be used as nanofillers for polymer composites as well as transparent films for various applications. In this work, cellulose isolation was performed following an environmental friendly procedure without chlorine. Cellulose nanocrystals were isolated from the exhausted acacia bark (after the industrial process of extracting tannin) with the objective of evaluating the effect of the solvent extraction steps on the characteristics of cellulose and cellulose nanocrystals. It was also assessed the effect of acid hydrolysis time on the thermal stability, morphology and size of the nanocrystals, through TGA, TEM and light scattering analyses. It was concluded that the extraction step with solvents was important in the isolation of cellulose, but irrelevant in the isolation of cellulose nanocrystals. Light scattering experiments indicated that 30min of hydrolysis was long enough for the isolation of cellulose nanocrystals. Copyright © 2017 Elsevier B.V. All rights reserved.

  9. Nanocrystal superlattices: No need to wait

    NASA Astrophysics Data System (ADS)

    Liu, Kun; Kumacheva, Eugenia

    2017-09-01

    In contrast with protocols reporting self-assembly of nanocrystals after synthesis, Pd nanocrystals rapidly form 3D micrometre-size superlattices during growth. The nanocrystals keep growing after assembly, tuning the size of the lattice.

  10. 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.

  11. [A study of preparation and infrared absorbency of La2O3 nanocrystals].

    PubMed

    Wang, Chun-Xiu; Li, Fu-Li

    2006-05-01

    Nanocrystals were prepared by stearic acid gel method. The structure and morphology of nanocrystals were characterized by X-ray powder diffraction (XRD), transmission electron microscope (TEM) and infrared spectra. Experimental results show that the absorption peaks of La2O3 extendwith their blue shift or red shift. The absorption of La2O3 nanocrystals is good in the wavelength range of 1 000 to 1 700 nm, where La2O3 nanocrystals may serve as a kind of absorbent of laser camouflage material.

  12. White-light emission from magic-sized cadmium selenide nanocrystals.

    PubMed

    Bowers, Michael J; McBride, James R; Rosenthal, Sandra J

    2005-11-09

    Magic-sized cadmium selenide (CdSe) nanocrystals have been pyrolytically synthesized. These ultra-small nanocrystals exhibit broadband emission (420-710 nm) that covers most of the visible spectrum while not suffering from self absorption. This behavior is a direct result of the extremely narrow size distribution and unusually large Stokes shift (40-50 nm). The intrinsic properties of these ultra-small nanocrystals make them an ideal material for applications in solid state lighting and also the perfect platform to study the molecule-to-nanocrystal transition.

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

    PubMed

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

    2017-04-24

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

  14. Surface-Driven Magnetotransport in Perovskite Nanocrystals.

    PubMed

    Thi N'Goc, Ha Le; Mouafo, Louis Donald Notemgnou; Etrillard, Céline; Torres-Pardo, Almudena; Dayen, Jean-François; Rano, Simon; Rousse, Gwenaëlle; Laberty-Robert, Christel; Calbet, Jose Gonzales; Drillon, Marc; Sanchez, Clément; Doudin, Bernard; Portehault, David

    2017-03-01

    Unique insights into magnetotransport in 20 nm ligand-free La0.67 Sr0.33 MnO3 perovskite nanocrystals of nearly perfect crystalline quality reveal a chemically altered 0.8 nm thick surface layer that triggers exceptionally large magnetoresistance at low temperature, independently of the spin polarization of the ferromagnetic core. This discovery shows how the nanoscale impacts magnetotransport in a material widely spread as electrode in hybrid spintronic devices.

  15. 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.

  16. 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.

  17. 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

  18. An Accurate Quartic Force Field, Fundamental Frequencies, and Binding Energy for the High Energy Density Material T(d)N4

    NASA Technical Reports Server (NTRS)

    Lee, Timothy J.; Martin, Jan M. L.; Kwak, Dochan (Technical Monitor)

    2002-01-01

    The CCSD(T) method has been used to compute a highly accurate quartic force field and fundamental frequencies for all N-14 and N-15 isotopomers of the high energy density material T(sub d)N(sub 4). The computed fundamental frequencies show beyond doubt that the bands observed in a matrix isolation experiment by Radziszewski and coworkers are not due to different isotopomers of T(sub d)N(sub 4). The most sophisticated thermochemical calculations to date yield a N(sub 4) -> 2N(sub 2) heat of reaction of 182.22 +/- 0.5 kcal/mol at 0 K (180.64 +/- 0.5 at 298 K). It is hoped that the data reported herein will aid in the ultimate detection of T(sub d)N(sub 4).

  19. Sorting fluorescent nanocrystals with DNA

    SciTech Connect

    Gerion, Daniele; Parak, Wolfgang J.; Williams, Shara C.; Zanchet, Daniela; Micheel, Christine M.; Alivisatos, A. Paul

    2001-12-10

    Semiconductor nanocrystals with narrow and tunable fluorescence are covalently linked to oligonucleotides. These biocompounds retain the properties of both nanocrystals and DNA. Therefore, different sequences of DNA can be coded with nanocrystals and still preserve their ability to hybridize to their complements. We report the case where four different sequences of DNA are linked to four nanocrystal samples having different colors of emission in the range of 530-640 nm. When the DNA-nanocrystal conjugates are mixed together, it is possible to sort each type of nanoparticle using hybridization on a defined micrometer -size surface containing the complementary oligonucleotide. Detection of sorting requires only a single excitation source and an epifluorescence microscope. The possibility of directing fluorescent nanocrystals towards specific biological targets and detecting them, combined with their superior photo-stability compared to organic dyes, opens the way to improved biolabeling experiments, such as gene mapping on a nanometer scale or multicolor microarray analysis.

  20. Polyimide Cellulose Nanocrystal Composite Aerogels

    NASA Technical Reports Server (NTRS)

    Nguyen, Baochau N.; Meador, Mary Ann; Rowan, Stuart; Cudjoe, Elvis; Sandberg, Anna

    2014-01-01

    Polyimide (PI) aerogels are highly porous solids having low density, high porosity and low thermal conductivity with good mechanical properties. They are ideal for various applications including use in antenna and insulation such as inflatable decelerators used in entry, decent and landing operations. Recently, attention has been focused on stimuli responsive materials such as cellulose nano crystals (CNCs). CNCs are environmentally friendly, bio-renewable, commonly found in plants and the dermis of sea tunicates, and potentially low cost. This study is to examine the effects of CNC on the polyimide aerogels. The CNC used in this project are extracted from mantle of a sea creature called tunicates. A series of polyimide cellulose nanocrystal composite aerogels has been fabricated having 0-13 wt of CNC. Results will be discussed.

  1. 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.

  2. Surfactant-Assisted Hydrothermal Synthesis of Single Phase Pyrite FeS2 Nanocrystals

    SciTech Connect

    Wadia, Cyrus; Wu, Yue; Gul, Sheraz; Volkman, Steven; Guo, Jinghua; Alivisatos, Paul

    2009-03-27

    Iron pyrite nanocrystals with high purity have been synthesized through a surfactant-assisted hydrothermal reaction under optimum pH value. These pyrite nanocrystals represent a new group of well-defined nanoscale structures for high-performance photovoltaic solar cells based on non-toxic and earth abundant materials.

  3. Size control and quantum confinement in Cu2ZnSnS4 nanocrystals.

    PubMed

    Khare, Ankur; Wills, Andrew W; Ammerman, Lauren M; Norris, David J; Aydil, Eray S

    2011-11-14

    Starting with metal dithiocarbamate complexes, we synthesize colloidal Cu(2)ZnSnS(4) (CZTS) nanocrystals with diameters ranging from 2 to 7 nm. Structural and Raman scattering data confirm that CZTS is obtained rather than other possible material phases. The optical absorption spectra of nanocrystals with diameters less than 3 nm show a shift to higher energy due to quantum confinement.

  4. Chemical design of nanocrystal solids.

    PubMed

    Kovalenko, Maksym V

    2013-01-01

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

  5. Aircraft Environmental System Mechanic, 2-9. Block I--Fundamentals. Military Curriculum Materials for Vocational and Technical Education.

    ERIC Educational Resources Information Center

    Ohio State Univ., Columbus. National Center for Research in Vocational Education.

    This publication contains a teaching guide and student instructional materials for conducting a high school or adult vocational education course to train persons to perform duties as an aircraft environmental systems mechanic. Course content has been adapted from a military course. The instructional design for this course is self-paced and/or…

  6. Development of nanostructured magnetic materials based on high-purity rare-earth metals and study of their fundamental characteristics

    NASA Astrophysics Data System (ADS)

    Pelevin, I. A.; Tereshina, I. S.; Burkhanov, G. S.; Dobatkin, S. V.; Kaminskaya, T. P.; Karpenkov, D. Yu.; Zaleski, A.; Tereshina, E. A.

    2014-09-01

    The effect of the structural state on magnetic and hysteretic properties of compounds with high contents of a 3 d transition metal, i.e., R 2Fe14 - x Co x B and RFe11 - x Co x Ti (where R = Y, Sm; 0 ≤ x ≤ 8), was studied. Alloys were prepared using high-purity rare-earth metals by two different methods: induction melting and argon-arc melting. Severe plastic deformation and rapid melt-quenching allowed preparation of nanostructured samples. Structural studies of the samples were performed by X-ray powder diffraction and atomic-force microscopy methods. Magnetic hysteretic properties were studied using a PPMS magnetometer in the temperature range of 4.2-300 K in fields to 20 kOe. It was shown that the dependences of fundamental magnetic parameters (Curie temperature, saturation magnetization, and magnetocrystalline anisotropy constant) on the cobalt content exhibit a similarity for both systems. It was found that, depending on sample treatment, the grain size varies from 30 to 70 nm after severe plastic deformation and in wider ranges (from 10 to 100 nm) after rapid quenching, not exceeding the single-domain size. The interrelation between the microstructure and magnetic characteristics was investigated. It was revealed that the concentration dependence of the coercivity for both systems has a maximum at the same cobalt content, i.e., x = 2.

  7. CaO-based CO2 sorbents: from fundamentals to the development of new, highly effective materials.

    PubMed

    Kierzkowska, Agnieszka M; Pacciani, Roberta; Müller, Christoph R

    2013-07-01

    The enormous anthropogenic emission of the greenhouse gas CO2 is most likely the main reason for climate change. Considering the continuing and indeed growing utilisation of fossil fuels for electricity generation and transportation purposes, development and implementation of processes that avoid the associated emissions of CO2 are urgently needed. CO2 capture and storage, commonly termed CCS, would be a possible mid-term solution to reduce the emissions of CO2 into the atmosphere. However, the costs associated with the currently available CO2 capture technology, that is, amine scrubbing, are prohibitively high, thus making the development of new CO2 sorbents a highly important research challenge. Indeed, CaO, readily obtained through the calcination of naturally occurring limestone, has been proposed as an alternative CO2 sorbent that could substantially reduce the costs of CO2 capture. However, one of the major drawbacks of using CaO derived from natural sources is its rapidly decreasing CO2 uptake capacity with repeated carbonation-calcination reactions. Here, we review the current understanding of fundamental aspects of the cyclic carbonation-calcination reactions of CaO such as its reversibility and kinetics. Subsequently, recent attempts to develop synthetic, CaO-based sorbents that possess high and cyclically stable CO2 uptakes are presented.

  8. Atomically precise gold nanocrystal molecules with surface plasmon resonance.

    PubMed

    Qian, Huifeng; Zhu, Yan; Jin, Rongchao

    2012-01-17

    Since Faraday's pioneering work on gold colloids, tremendous scientific research on plasmonic gold nanoparticles has been carried out, but no atomically precise Au nanocrystals have been achieved. This work reports the first example of gold nanocrystal molecules. Mass spectrometry analysis has determined its formula to be Au(333)(SR)(79) (R = CH(2)CH(2)Ph). This magic sized nanocrystal molecule exhibits fcc-crystallinity and surface plasmon resonance at approximately 520 nm, hence, a metallic nanomolecule. Simulations have revealed that atomic shell closing largely contributes to the particular robustness of Au(333)(SR)(79), albeit the number of free electrons (i.e., 333 - 79 = 254) is also consistent with electron shell closing based on calculations using a confined free electron model. Guided by the atomic shell closing growth mode, we have also found the next larger size of extraordinarily stability to be Au(~530)(SR)(~100) after a size-focusing selection--which selects the robust size available in the starting polydisperse nanoparticles. This work clearly demonstrates that atomically precise nanocrystal molecules are achievable and that the factor of atomic shell closing contributes to their extraordinary stability compared to other sizes. Overall, this work opens up new opportunities for investigating many fundamental issues of nanocrystals, such as the formation of metallic state, and will have potential impact on condensed matter physics, nanochemistry, and catalysis as well.

  9. 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.

  10. Fundamental and exploratory studies of catalytic steam gasification of carbonaceous materials. Final report, fiscal years 1985--1994

    SciTech Connect

    Heinemann, H.; Somorjai, G.A.

    1994-03-01

    The major purpose of this project was to find catalysts which will permit steam gasification of carbonaceous material at reasonable rates and at lower temperatures than currently practiced. Rapid catalyst deactivation must be avoided. An understanding of the catalytic mechanism is necessary to provide leads towards this aim. This report describes the gasification of graphite studies and the gasification of coals, chars, and petroleum cokes.

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

    PubMed

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

    2017-04-12

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

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

    NASA Astrophysics Data System (ADS)

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

    2015-08-01

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

  13. Mapping the Atomistic Structure of Graded Core/Shell Colloidal Nanocrystals.

    PubMed

    Yarema, Maksym; Xing, Yunhua; Lechner, Rainer T; Ludescher, Lukas; Dordevic, Nikola; Lin, Weyde M M; Yarema, Olesya; Wood, Vanessa

    2017-09-15

    Engineering the compositional gradient for core/shell semiconductor nanocrystals improves their optical properties. To date, however, the structure of graded core/shell nanocrystal emitters has only been qualitatively described. In this paper, we demonstrate an approach to quantify nanocrystal structure, selecting graded Ag-In-Se/ZnSe core/shell nanocrystals as a proof-of-concept material. A combination of multi-energy small-angle X-ray scattering and electron microscopy techniques enables us to establish the radial distribution of ZnSe with sub-nanometer resolution. Using ab initio shape-retrieval analysis of X-ray scattering spectra, we further determine the average shape of nanocrystals. These results allow us to generate three-dimensional, atomistic reconstructions of graded core/shell nanocrystals. We use these reconstructions to calculate solid-state Zn diffusion in the Ag-In-Se nanocrystals and the lattice mismatch between nanocrystal monolayers. Finally, we apply these findings to propose design rules for optimal shell structure and record-luminescent core/shell nanocrystals.

  14. Tunable plasmonic lattices of silver nanocrystals

    SciTech Connect

    Tao, Andrea; Sinsermsuksakul, Prasert; Yang, Peidong

    2008-02-18

    Silver nanocrystals are ideal building blocks for plasmonicmaterials that exhibit a wide range of unique and potentially usefuloptical phenomena. Individual nanocrystals display distinct opticalscattering spectra and can be assembled into hierarchical structures thatcouple strongly to external electromagnetic fields. This coupling, whichis mediated by surface plasmons, depends on their shape and arrangement.Here we demonstrate the bottom-up assembly of polyhedral silvernanocrystals into macroscopic two-dimensional superlattices using theLangmuir-Blodgett technique. Our ability to control interparticlespacing, density, and packing symmetry allows for tunability of theoptical response over the entire visible range. This assembly strategyoffers a new, practical approach to making novel plasmonic materials forapplication in spectroscopic sensors, sub-wavelength optics, andintegrated devices that utilize field enhancement effects.

  15. Structure and electronic properties of lead-selenide nanocrystal solids

    NASA Astrophysics Data System (ADS)

    Whitham, Kevin

    Recent advances in the controlled formation of nanocrystal superlattices have potential for creating materials with properties by design. The ability to tune nanocrystal size, shape and composition as well as symmetry of the superlattice opens routes to new materials. Calculations of such materials predict interesting electronic phenomena including topological states and Dirac cones, however experimental support is lacking. We have investigated electron localization in nanocrystal superlattices using a combination of advanced structural characterization techniques and charge transport measurements. Recent experimental efforts to improve the electronic properties of nanocrystal solids have focused on increasing inter-dot coupling. However, this approach only leads to electronic bands if the coupling energy can overcome energetic and translational disorder. We have investigated oriented-attachment as a method to create nanocrystal superlattices with increased coupling and translational order. We show that epitaxially connected superlattices form by a coherent phase transformation that is sensitive to structural defects and ligand length. In order to measure intrinsic electronic properties we demonstrate control over electronic defects by tailoring surface chemistry and device architecture. To probe charge transport in these structures we performed variable temperature field-effect measurements. By integrating structure analysis, surface chemistry, and transport measurements we find that carriers are localized to a few superlattice constants due to disorder. Importantly, our analysis shows that greater delocalization is possible by optimizing dot-to-dot bonding, thus providing a path forward to create quantum dot solids in which theoretically predicted properties can be realized.

  16. The prospects of phosphorene as an anode material for high-performance lithium-ion batteries: a fundamental study

    NASA Astrophysics Data System (ADS)

    Zhang, Congyan; Yu, Ming; Anderson, George; Ravinath Dharmasena, Ruchira; Sumanasekera, Gamini

    2017-02-01

    To completely understand lithium adsorption, diffusion, and capacity on the surface of phosphorene and, therefore, the prospects of phosphorene as an anode material for high-performance lithium-ion batteries (LIBs), we carried out density-functional-theory calculations and studied the lithium adsorption energy landscape, the lithium diffusion mobility, the lithium intercalation, and the lithium capacity of phosphorene. We also carried out, for the very first time, experimental measurement of the lithium capacity of phosphorene. Our calculations show that the lithium diffusion mobility along the zigzag direction in the valley of phosphorene was about 7 to 11 orders of magnitude faster than that along the other directions, indicating its ultrafast and anisotropic diffusivity. The lithium intercalation in phosphorene was studied by considering various Li n P16 configurations (n = 1-16) including single-side and double-side adsorptions. We found that phosphorene could accommodate up to a ratio of one Li per P atom (i.e. Li16P16). In particular, we found that, even at a high Li concentration (e.g. x = 1 in Li x P), there was no lithium clustering, and the structure of phosphorene (when fractured) is reversible during lithium intercalation. The theoretical value of the lithium capacity for a monolayer phosphorene is predicted to be above 433 mAh g-1, depending on whether Li atoms are adsorbed on the single side or the double side of phosphorene. Our experimental measurement of the lithium capacity for few-layer phosphorene networks shows a reversible stable value of ˜453 mAh g-1 even after 50 cycles. Our results clearly show that phosphorene, compared to graphene and other two-dimensional materials, has great promise as a novel anode material for high-performance LIBs.

  17. Fundamentals and application of materials integration for low-power piezoelectrically actuated ultra-nanocrystalline diamond MEMS/NEMS.

    SciTech Connect

    Auciello, O.; Srinivasan, S.; Hiller, J.; Kabius, B.

    2009-01-01

    Most current micro/nanoelectromechanical systems (MEMS/NEMS) are based on silicon. However, silicon exhibits relatively poor mechanical/tribological properties, compromising applications to several projected MEMS/NEMS devices, particularly those that require materials with high Young's modulus for MEMS resonators or low surface adhesion forces for MEMS/NEMS working in conditions with extensive surface contact. Diamond films with superior mechanical/tribological properties provide an excellent alternative platform material. Ultrananocrystalline diamond (UNCD{cflx W}) in film form with 2-5 nm grains exhibits excellent properties for high-performance MEMS/NEMS devices. Concurrently, piezoelectric Pb(Zr{sub x}Ti{sub 1-x})O{sub 3} (PZT) films provide high sensitivity/low electrical noise for sensing/high-force actuation at relatively low voltages. Therefore, integration of PZT and UNCD films provides a high-performance platform for advanced MEMS/NEMS devices. This paper describes the bases of such integration and demonstration of low voltage piezoactuated hybrid PZT/UNCD cantilevers.

  18. Fabrication of Supported AuPt Alloy Nanocrystals with Enhanced Electrocatalytic Activity for Formic Acid Oxidation through Conversion Chemistry of Layer-Deposited Pt(2+) on Au Nanocrystals.

    PubMed

    Kim, Seong Hyeon; Jeong, Hwakyeung; Kim, Jongwon; Lee, In Su

    2015-10-07

    The exploitation of nanoconfined conversion of Au- and Pt-containing binary nanocrystals for developing a controllable synthesis of surfactant-free AuPt nanocrystals with enhanced formic acid oxidation (FAO) activity is reported, which can be stably and evenly immobilized on various support materials to diversify and optimize their electrocatalytic performance. In this study, an atomic layer of Pt(2+) species is discovered to be spontaneously deposited in situ on the Au nanocrystal generated from a reverse-microemulsion solution. The resulting Au/Pt(2+) nanocrystal thermally transforms into a reduced AuPt alloy nanocrystal during the subsequent solid-state conversion process within the SiO2 nanosphere. The alloy nanocrystals can be isolated from SiO2 in a surfactant-free form and then dispersedly loaded on the carbon sphere surface, allowing for the production of a supported electrocatalyst that exhibits much higher FAO activity than commercial Pt/C catalysts. Furthermore, by involving Fe3O4 nanocrystals in the conversion process, the AuPt alloy nanocrystals can be grown on the oxide surface, improving the durability of supported metal catalysts, and then uniformly loaded on a reduced graphene oxide (RGO) layer with high electroconductivity. This produces electrocatalytic AuPt/Fe3O4/RGO nanocomposites whose catalyst-oxide-graphene triple-junction structure provides improved electrocatalytic properties in terms of both activity and durability in catalyzing FAO. © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  19. FUNDAMENTAL AREAS OF PHENOMENOLOGY (INCLUDING APPLICATIONS): Measurement of Refractive Index for High Reflectance Materials with Terahertz Time Domain Reflection Spectroscopy

    NASA Astrophysics Data System (ADS)

    Sun, Wen-Feng; Wang, Xin-Ke; Zhang, Yan

    2009-11-01

    A method to measure the refractive index for high reflectance materials in the terahertz range with terahertz time domain reflection spectroscopy is proposed. In this method, the THz waveforms reflected by a silicon wafer and high reflectance sample are measured respectively. The refractive index of the silicon wafer, measured with the THz time domain transmission spectroscopy, is used as a reference in the THz time domain reflective spectroscopy. Therefore, the complex refractive index of the sample can be obtained by resorting to the known reflective index of the silicon and the Fresnel law. To improve the accuracy of the phase shift, the Kramers-Kronig transform is adopted. This method is also verified by the index of the silicon in THz reflection spectroscopy. The bulk metal plates have been taken as the sample, and the experimentally obtained metallic refractive indexes are compared with the simple Drude model.

  20. Photoemission studies of semiconductor nanocrystals

    SciTech Connect

    Hamad, K. S.; Roth, R.; Alivisatos, A. P.

    1997-04-01

    Semiconductor nanocrystals have been the focus of much attention in the last ten years due predominantly to their size dependent optical properties. Namely, the band gap of nanocrystals exhibits a shift to higher energy with decreasing size due to quantum confinement effects. Research in this field has employed primarily optical techniques to study nanocrystals, and in this respect this system has been investigated extensively. In addition, one is able to synthesize monodisperse, crystalline particles of CdS, CdSe, Si, InP, InAs, as well as CdS/HgS/CdS and CdSe/CdS composites. However, optical spectroscopies have proven ambiguous in determining the degree to which electronic excitations are interior or surface admixtures or giving a complete picture of the density of states. Photoemission is a useful technique for understanding the electronic structure of nanocrystals and the effects of quantum confinement, chemical environments of the nanocrystals, and surface coverages. Of particular interest to the authors is the surface composition and structure of these particles, for they have found that much of the behavior of nanocrystals is governed by their surface. Previously, the authors had performed x-ray photoelectron spectroscopy (XPS) on CdSe nanocrystals. XPS has proven to be a powerful tool in that it allows one to determine the composition of the nanocrystal surface.

  1. 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

  2. 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.

  3. Electronic spectra of semiconductor nanocrystals

    SciTech Connect

    Alivisatos, A.P.

    1993-12-31

    Semiconductor nanocrystals smaller than the bulk exciton show substantial quantum confinement effects. Recent experiments including Stark effect, resonance Raman, valence band photoemission, and near edge X-ray adsorption will be used to put together a picture of the nanocrystal electronic states.

  4. 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.

  5. 25th anniversary article: Ion exchange in colloidal nanocrystals.

    PubMed

    Gupta, Shuchi; Kershaw, Stephen V; Rogach, Andrey L

    2013-12-23

    We review the progress in ion exchange in a variety of nanocrystal structures from the earliest accounts dating back over two decades ago to the present day. In recent years the number of groups using this method to form otherwise difficult or inaccessible nanoparticle shapes and morphologies has increased considerably and the field has experienced a resurgence of interest. Whilst most of the early work on cation exchange centered on II-VI materials, the methodology has been expanded to cover a far broader range of semiconductor nanocrystals including low toxicity I-III-VI materials and the much less facile III-V materials. The extent of exchange can be controlled leading to lightly doped nanoparticles, alloys, core-shells, segmented rods and dots-in-rods. Progress has been driven by a better understanding of the underlying principles of the exchange process - from thermodynamic factors (differences in cation solubilities); the interactions between ions and transfer agents (solvents, ligands, anions, co-dopants); ionic in-diffusion mechanisms and kinetics. More recent availability of very detailed electron microscopy coupled with image reconstruction techniques has been a valuable tool to investigate the resulting heterostructures and internal interfaces. We start by surveying the range of synthetic approaches most often used to carry out ion exchange, mainly focusing on cation replacement strategies, and then describe the rich variety of nanostructures these techniques can bring forth. We also describe some of the principles that are used to establish the relative ease of exchange and to systematically improve the process where the basic energetics are less favorable. To help further the understanding of the underlying fundamentals we have gathered together useful data from the literature on solubilities, cation and anion hardness, ligand and solvent Lewis acid or base strengths for a wide range of chemical species generally used. We offer a perspective on the

  6. Development and properties of surfactant-free water-dispersible Cu2ZnSnS4 nanocrystals: a material for low-cost photovoltaics.

    PubMed

    Kush, Priya; Ujjain, Sanjeev Kumar; Mehra, Navin Chand; Jha, Pika; Sharma, Raj Kishore; Deka, Sasanka

    2013-08-26

    A simple, yet novel hydrothermal method has been developed to synthesize surfactant-free Cu2ZnSnS4 nanocrystal ink in water. The environmentally friendly, 2-4 nm ultrafine particles are stable in water for several weeks. Detailed X-ray diffraction (XRD) and high-resolution transmission electron microscopy revealed the formation of single-crystalline-kesterite-phase Cu2ZnSnS4. Elemental mapping by scanning electron microscopy/energy dispersive spectrometry corroborated the presence of all four elements in a stoichiometric ratio with minor sulfur deficiency. Finally, Raman spectroscopy ruled out the possible presence of impurities of ZnS, Cu2SnS3, SnS, SnS2, Cu(2-x)S, or Sn2S3, which often interfere with the XRD and optical spectra of Cu2ZnSnS4. X-ray photoelectron spectroscopic studies of the as-synthesized samples confirmed that the oxidation states of the four elements match those of the bulk sample. Optical absorption analyses of thin film and solution samples showed high absorption efficiency (>10(4) cm(-1)) across the visible and near-infrared spectral regions and a band gap E(g) of 1.75 eV for the as-synthesized sample. A non-ohmic asymmetric rectifying response was observed in the I-V measurement at room temperature. The nonlinearity was more pronounced for this p-type semiconductor when the resistance was measured against temperature in the range 180-400 K, which was detected in the hot-point probe measurement.

  7. Structure and Magnetic Properties of Lanthanide Nanocrystals

    SciTech Connect

    Dickerson, James Henry

    2014-06-01

    We have had considerable success on this project, particularly in the understanding of the relationship between nanostructure and magnetic properties in lanthanide nanocrystals. We also have successfully facilitated the doctoral degrees of Dr. Suseela Somarajan, in the Department of Physics and Astronomy, and Dr. Melissa Harrison, in the Materials Science Program. The following passages summarize the various accomplishments that were featured in 9 publications that were generated based on support from this grant. We thank the Department of Energy for their generous support of our research efforts in this area of materials science, magnetism, and electron microscopy.

  8. 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.

  9. 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.

  10. 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.

  11. Synthesis of nanocrystals and nanocrystal self-assembly

    NASA Astrophysics Data System (ADS)

    Chen, Zhuoying

    Chapter 1. A general introduction is presented on nanomaterials and nanoscience. Nanoparticles are discussed with respect to their structure and properties. Ferroelectric materials and nanoparticles in particular are highlighted, especially in the case of the barium titanate, and their potential applications are discussed. Different nanocrystal synthetic techniques are discussed. Nanoparticle superlattices, the novel "meta-materials" built from self-assembly at the nanoscale, are introduced. The formation of nanoparticle superlattices and the importance and interest of synthesizing these nanostructures is discussed. Chapter 2. 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. The first part of this chapter presents the synthesis, processing, and electrical characterization of nanostructured thin films (thickness ˜100 nm) of barium titanate BaTiO3 built from uniform nanoparticles (<20 nm in diameter) in diameter. Essential to our 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. We observe the BaTiO3 nanocrystals crystallize with evidence of tetragonality. Electric field dependent polarization measurements show spontaneous polarization and hysteresis, indicating ferroelectric behavior for the BaTiO 3 nanocrystalline films with grain sizes in the range of 10--30 nm. Dielectric measurements of the films show dielectic constants in the range of 85--90 over the 1 kHz--100 kHz, with low loss. We present nanocrystals as initial building blocks for the preparation of thin films which exhibit uniform nanostructured morphologies and grain sizes. In the second part of this chapter, a nonhydrolytic alcoholysis route to study the preparation of well-crystallized size-tunable BaTiO3

  12. Germanium Nanocrystal Solar Cells

    NASA Astrophysics Data System (ADS)

    Holman, Zachary Charles

    Greenhouse gas concentrations in the atmosphere are approaching historically unprecedented levels from burning fossil fuels to meet the ever-increasing world energy demand. A rapid transition to clean energy sources is necessary to avoid the potentially catastrophic consequences of global warming. The sun provides more than enough energy to power the world, and solar cells that convert sunlight to electricity are commercially available. However, the high cost and low efficiency of current solar cells prevent their widespread implementation, and grid parity is not anticipated to be reached for at least 15 years without breakthrough technologies. Semiconductor nanocrystals (NCs) show promise for cheap multi-junction photovoltaic devices. To compete with photovoltaic materials that are currently commercially available, NCs need to be inexpensively cast into dense thin films with bulk-like electrical mobilities and absorption spectra that can be tuned by altering the NC size. The Group II-VI and IV-VI NC communities have had some success in achieving this goal by drying and then chemically treating colloidal particles, but the more abundant and less toxic Group IV NCs have proven more challenging. This thesis reports thin films of plasma-synthesized Ge NCs deposited using three different techniques, and preliminary solar cells based on these films. Germanium tetrachloride is dissociated in the presence of hydrogen in a nonthermal plasma to nucleate Ge NCs. Transmission electron microscopy and X-ray diffraction indicate that the particles are nearly monodisperse (standard deviations of 10-15% the mean particle diameter) and the mean diameter can be tuned from 4-15 nm by changing the residence time of the Ge NCs in the plasma. In the first deposition scheme, a Ge NC colloid is formed by reacting nanocrystalline powder with 1-dodecene and dispersing the functionalized NCs in a solvent. Films are then formed on substrates by drop-casting the colloid and allowing it to dry

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

    SciTech Connect

    Owen, Jonathan; Park, Jungwon; Trudeau, Paul-Emile; Alivisatos, A. Paul

    2008-12-02

    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, and 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.

  14. Marketing fundamentals.

    PubMed

    Redmond, W H

    2001-01-01

    This chapter outlines current marketing practice from a managerial perspective. The role of marketing within an organization is discussed in relation to efficiency and adaptation to changing environments. Fundamental terms and concepts are presented in an applied context. The implementation of marketing plans is organized around the four P's of marketing: product (or service), promotion (including advertising), place of delivery, and pricing. These are the tools with which marketers seek to better serve their clients and form the basis for competing with other organizations. Basic concepts of strategic relationship management are outlined. Lastly, alternate viewpoints on the role of advertising in healthcare markets are examined.

  15. Cooling the motion of diamond nanocrystals in a magneto-gravitational trap in high vacuum

    SciTech Connect

    Hsu, Jen -Feng; Ji, Peng; Lewandowski, Charles W.; D’Urso, Brian

    2016-07-22

    Levitated diamond nanocrystals with nitrogen-vacancy (NV) centres in high vacuum have been proposed as a unique system for experiments in fundamental quantum mechanics, including the generation of large quantum superposition states and tests of quantum gravity. This system promises extreme isolation from its environment while providing quantum control and sensing through the NV centre spin. While optical trapping has been the most explored method of levitation, recent results indicate that excessive optical heating of the nanodiamonds under vacuum may make the method impractical with currently available materials. Here, we study an alternative magneto-gravitational trap for diamagnetic particles, such as diamond nanocrystals, with stable levitation from atmospheric pressure to high vacuum. Magnetic field gradients from permanent magnets confine the particle in two dimensions, while confinement in the third dimension is gravitational. Furthermore, we demonstrate that feedback cooling of the centre-of-mass motion of a trapped nanodiamond cluster results in cooling of one degree of freedom to less than 1 K.

  16. Cooling the motion of diamond nanocrystals in a magneto-gravitational trap in high vacuum

    DOE PAGES

    Hsu, Jen -Feng; Ji, Peng; Lewandowski, Charles W.; ...

    2016-07-22

    Levitated diamond nanocrystals with nitrogen-vacancy (NV) centres in high vacuum have been proposed as a unique system for experiments in fundamental quantum mechanics, including the generation of large quantum superposition states and tests of quantum gravity. This system promises extreme isolation from its environment while providing quantum control and sensing through the NV centre spin. While optical trapping has been the most explored method of levitation, recent results indicate that excessive optical heating of the nanodiamonds under vacuum may make the method impractical with currently available materials. Here, we study an alternative magneto-gravitational trap for diamagnetic particles, such as diamondmore » nanocrystals, with stable levitation from atmospheric pressure to high vacuum. Magnetic field gradients from permanent magnets confine the particle in two dimensions, while confinement in the third dimension is gravitational. Furthermore, we demonstrate that feedback cooling of the centre-of-mass motion of a trapped nanodiamond cluster results in cooling of one degree of freedom to less than 1 K.« less

  17. Cooling the Motion of Diamond Nanocrystals in a Magneto-Gravitational Trap in High Vacuum.

    PubMed

    Hsu, Jen-Feng; Ji, Peng; Lewandowski, Charles W; D'Urso, Brian

    2016-07-22

    Levitated diamond nanocrystals with nitrogen-vacancy (NV) centres in high vacuum have been proposed as a unique system for experiments in fundamental quantum mechanics, including the generation of large quantum superposition states and tests of quantum gravity. This system promises extreme isolation from its environment while providing quantum control and sensing through the NV centre spin. While optical trapping has been the most explored method of levitation, recent results indicate that excessive optical heating of the nanodiamonds under vacuum may make the method impractical with currently available materials. Here, we study an alternative magneto-gravitational trap for diamagnetic particles, such as diamond nanocrystals, with stable levitation from atmospheric pressure to high vacuum. Magnetic field gradients from permanent magnets confine the particle in two dimensions, while confinement in the third dimension is gravitational. We demonstrate that feedback cooling of the centre-of-mass motion of a trapped nanodiamond cluster results in cooling of one degree of freedom to less than 1 K.

  18. Cooling the Motion of Diamond Nanocrystals in a Magneto-Gravitational Trap in High Vacuum

    PubMed Central

    Hsu, Jen-Feng; Ji, Peng; Lewandowski, Charles W.; D’Urso, Brian

    2016-01-01

    Levitated diamond nanocrystals with nitrogen-vacancy (NV) centres in high vacuum have been proposed as a unique system for experiments in fundamental quantum mechanics, including the generation of large quantum superposition states and tests of quantum gravity. This system promises extreme isolation from its environment while providing quantum control and sensing through the NV centre spin. While optical trapping has been the most explored method of levitation, recent results indicate that excessive optical heating of the nanodiamonds under vacuum may make the method impractical with currently available materials. Here, we study an alternative magneto-gravitational trap for diamagnetic particles, such as diamond nanocrystals, with stable levitation from atmospheric pressure to high vacuum. Magnetic field gradients from permanent magnets confine the particle in two dimensions, while confinement in the third dimension is gravitational. We demonstrate that feedback cooling of the centre-of-mass motion of a trapped nanodiamond cluster results in cooling of one degree of freedom to less than 1 K. PMID:27444654

  19. Recommendations to the NRC on acceptable standard format and content for the Fundamental Nuclear Material Control (FNMC) Plan required for low-enriched uranium enrichment facilities

    SciTech Connect

    Moran, B.W.; Belew, W.L. ); Hammond, G.A.; Brenner, L.M. )

    1991-11-01

    A new section, 10 CFR 74.33, has been added to the material control and accounting (MC A) requirements of 10 CFR Part 74. This new section pertains to US Nuclear Regulatory Commission (NRC)-licensed uranium enrichment facilities that are authorized to produce and to possess more than one effective kilogram of special nuclear material (SNM) of low strategic significance. The new section is patterned after 10 CFR 74.31, which pertains to NRC licensees (other than production or utilization facilities licensed pursuant to 10 CFR Part 50 and 70 and waste disposal facilities) that are authorized to possess and use more than one effective kilogram of unencapsulated SNM of low strategic significance. Because enrichment facilities have the potential capability of producing SNM of moderate strategic significance and also strategic SNM, certain performance objectives and MC A system capabilities are required in 10 CFR 74.33 that are not contained in 10 CFR 74.31. This document recommends to the NRC information that the licensee or applicant should provide in the fundamental nuclear material control (FNMC) plan. This document also describes methods that should be acceptable for compliance with the general performance objectives. While this document is intended to cover various uranium enrichment technologies, the primary focus at this time is gas centrifuge and gaseous diffusion.

  20. 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.

  1. Towards depleted heterojunction solar cells with CuInS2 and ZnO nanocrystals

    NASA Astrophysics Data System (ADS)

    Scheunemann, Dorothea; Wilken, Sebastian; Parisi, Jürgen; Borchert, Holger

    2013-09-01

    Colloidal quantum dot solar cells have shown remarkable improvements in performance during the last few years. Until now, mostly Pb- or Cd-based nanocrystals were used as absorber material, which might limit the potential application of nanocrystal solar cells due to toxicity issues. A promising, potentially less-toxic alternative are CuInS2 (CIS) nanocrystals. Here, we report about the realization of solar cells based on a heterojunction formed by solution-producible layers of colloidal CIS and ZnO nanocrystals. Device performance was found to be sensitive to illumination conditions, i.e., the presence of UV light. Although, power conversion efficiencies remain limited in this work, we modeled the possible photocurrents and show that the CIS nanocrystals have a high potential for light-harvesting in quantum dot solar cells.

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

    SciTech Connect

    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 molecule bonds are of particular interest. We discuss synthetic approaches, predicted and observed physical properties, and prospects and challenges toward this new class of materials.

  3. 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

  4. Thermal and mechanical properties of bio-nanocomposites reinforced by Luffa cylindrica cellulose nanocrystals.

    PubMed

    Siqueira, Gilberto; Bras, Julien; Follain, Nadège; Belbekhouche, Sabrina; Marais, Stéphane; Dufresne, Alain

    2013-01-16

    Cellulose nanocrystals have been prepared by acid hydrolysis of Luffa cylindrica fibers. The acid-resistant residue consisted of rod-like nanoparticles with an average length an diameter around 242 and 5.2nm, respectively (aspect ratio around 46). These cellulose nanocrystals have been used as a reinforcing phase for the processing of bio-nanocomposites using polycaprolactone (PCL) as matrix. To promote interfacial filler/matrix interactions the surface of cellulose nanocrystals was chemically modified with n-octadecyl isocyanate (C(18)H(37)NCO). Evidence of the grafting was supported by infrared spectroscopy and elemental analysis. X-ray diffraction analysis was used to confirm the integrity of cellulose nanocrystals after chemical modification. Both unmodified and chemically modified nanocrystals were used to prepare nanocomposites. The thermal properties of these materials were determined from differential scanning calorimetry and their mechanical behavior was evaluated in both the linear and non-linear range. Copyright © 2012 Elsevier Ltd. All rights reserved.

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

    PubMed

    Yao, En-Ping; Yang, Zhanlue; Meng, Lei; Sun, Pengyu; Dong, Shiqi; Yang, Ye; Yang, Yang

    2017-04-10

    Inorganic metal halide perovskite nanocrystals (NCs) have been employed universally in light-emitting applications during the past two years. Here, blue-emission (≈470 nm) Cs-based perovskite NCs are derived by directly mixing synthesized bromide and chloride nanocrystals with a weight ratio of 2:1. High-brightness blue perovskite light-emitting diodes (PeLEDs) are obtained by controlling the grain size of the perovskite films. Moreover, a white PeLED is demonstrated for the first time by blending orange polymer materials with the blue perovskite nanocrystals as the active layer. Exciton transfer from the blue nanocrystals to the orange polymers via Förster or Dexter energy transfer is analyzed through time resolved photoluminescence. By tuning the ratio between the perovskite nanocrystals and polymers, pure white light is achieved with the a CIE coordinate at (0.33,0.34).

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

    PubMed

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

    2013-02-20

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

  7. Ion beam synthesis and optical properties of semiconductor nanocrystals and quantum dots

    SciTech Connect

    Zhu, J.G.; White, C.W.; Withrow, S.P.

    1996-11-01

    Nanocrystals of semiconductor materials have been fabricated in SiO{sub 2} by ion implantation and subsequent thermal annealing. Strong red photoluminescence (PL) peaked around 750 nm has been observed in samples containing Si nanocrystals in SiO{sub 2}. The Si nanocrystals in the samples with optimized PL intensities are a few nanometers in diameter. Difference in the absorption bandgap energies and the PL peak energies are discussed. Significant influence of implantation sequence on the formation of compound semiconductor nanocrystals are demonstrated with the GaAs in the SiO{sub 2} system. Optical absorption measurements show that Ga particles have already formed in the as-implanted stage if Ga is implanted first. A single surface phonon mode has been observed in the infrared reflectance measurement from samples containing GaAs nanocrystals.

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

    NASA Astrophysics Data System (ADS)

    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.

  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. 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.

  11. 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.

  12. Some modification of cellulose nanocrystals for functional Pickering emulsions

    PubMed Central

    Saidane, Dorra; Perrin, Emilie; Cherhal, Fanch; Guellec, Florian

    2016-01-01

    Cellulose nanocrystals (CNCs) are negatively charged colloidal particles well known to form highly stable surfactant-free Pickering emulsions. These particles can vary in surface charge density depending on their preparation by acid hydrolysis or applying post-treatments. CNCs with three different surface charge densities were prepared corresponding to 0.08, 0.16 and 0.64 e nm−2, respectively. Post-treatment might also increase the surface charge density. The well-known TEMPO-mediated oxidation substitutes C6-hydroxyl groups by C6-carboxyl groups on the surface. We report that these different modified CNCs lead to stable oil-in-water emulsions. TEMPO-oxidized CNC might be the basis of further modifications. It is shown that they can, for example, lead to hydrophobic CNCs with a simple method using quaternary ammonium salts that allow producing inverse water-in-oil emulsions. Different from CNC modification before emulsification, modification can be carried out on the droplets after emulsification. This way allows preparing functional capsules according to the layer-by-layer process. As a result, it is demonstrated here the large range of use of these biobased rod-like nanoparticles, extending therefore their potential use to highly sophisticated formulations. This article is part of the themed issue ‘Soft interfacial materials: from fundamentals to formulation’. PMID:27298429

  13. A quantitative model for charge carrier transport, trapping and recombination in nanocrystal-based solar cells

    PubMed Central

    Bozyigit, Deniz; Lin, Weyde M. M.; Yazdani, Nuri; Yarema, Olesya; Wood, Vanessa

    2015-01-01

    Improving devices incorporating solution-processed nanocrystal-based semiconductors requires a better understanding of charge transport in these complex, inorganic–organic materials. Here we perform a systematic study on PbS nanocrystal-based diodes using temperature-dependent current–voltage characterization and thermal admittance spectroscopy to develop a model for charge transport that is applicable to different nanocrystal-solids and device architectures. Our analysis confirms that charge transport occurs in states that derive from the quantum-confined electronic levels of the individual nanocrystals and is governed by diffusion-controlled trap-assisted recombination. The current is limited not by the Schottky effect, but by Fermi-level pinning because of trap states that is independent of the electrode–nanocrystal interface. Our model successfully explains the non-trivial trends in charge transport as a function of nanocrystal size and the origins of the trade-offs facing the optimization of nanocrystal-based solar cells. We use the insights from our charge transport model to formulate design guidelines for engineering higher-performance nanocrystal-based devices. PMID:25625647

  14. Nanocrystals encapsulated in SiO2 particles: silanization and homogenous coating for bio applications.

    PubMed

    Yang, Ping; Li, Xiaoyu; Zhang, Ruili; Liu, Ning; Zhang, Yulan

    2013-03-01

    Sol-gel procedures have been developed to encapsulate inorganic nanocrystals including metallic Au and II-VI semiconductor materials (CdSe/Cd(1-x)Zn(x)S) in SiO2 particles by using tetraethyl orthosilicate. The key strategy was the control of a sol-gel procedure. The anisotropic deposition of SiO2 monomers occurs because well-developed crystal facets having different affinity to SiO2 monomers. SiO2 monomers were not homogeneously deposited on nonspherical Au and CdSe/Cd(1-x)Zn(x)S nanocrystals. A surface silanization process, partly hydrolyzed tetraethyl orthosilicate were attached to the nanocrystals instead of initial ligands, plays an important role for the nanocrystals coated homogeneously with a SiO2 layer. Furthermore, CdSe/Cd(1-x)Zn(x)S nanocrystals were homogeneously coated with a thin SiO2 layer by the surface silanization process and a subsequent reverse micelle route. Colloidal Au nanocrystals were homogeneously coated with a SiO2 shell by the surface silanization process and subsequent Stöber synthesis without using a silane coupling agent or bulk polymer as the surface primer to render the Au surface vitreophilic. These results indicated partly hydrolyzed tetraethyl orthosilicate has an ability to replace the ligand on nanocrystals. After surface modification, the SiO2 particles with nanocrystals were conjugated with antibody for bioapplications.

  15. A quantitative model for charge carrier transport, trapping and recombination in nanocrystal-based solar cells

    NASA Astrophysics Data System (ADS)

    Bozyigit, Deniz; Lin, Weyde M. M.; Yazdani, Nuri; Yarema, Olesya; Wood, Vanessa

    2015-01-01

    Improving devices incorporating solution-processed nanocrystal-based semiconductors requires a better understanding of charge transport in these complex, inorganic-organic materials. Here we perform a systematic study on PbS nanocrystal-based diodes using temperature-dependent current-voltage characterization and thermal admittance spectroscopy to develop a model for charge transport that is applicable to different nanocrystal-solids and device architectures. Our analysis confirms that charge transport occurs in states that derive from the quantum-confined electronic levels of the individual nanocrystals and is governed by diffusion-controlled trap-assisted recombination. The current is limited not by the Schottky effect, but by Fermi-level pinning because of trap states that is independent of the electrode-nanocrystal interface. Our model successfully explains the non-trivial trends in charge transport as a function of nanocrystal size and the origins of the trade-offs facing the optimization of nanocrystal-based solar cells. We use the insights from our charge transport model to formulate design guidelines for engineering higher-performance nanocrystal-based devices.

  16. Magnetic Fluorescent Delivery Vehicle using Uniform Mesoporous Silica Spheres Embedded with Monodisperse Magnetic and Semiconductor Nanocrystals

    SciTech Connect

    Kim, Jaeyun; Lee, Ji Eun; Lee, Jinwoo; Yu, Jung Ho; Kim, Byoung Chan; An, Kwangjin; Hwang, Yosun; Shin, Chae-Ho; Park, Je-Geun; Kim, Jungbae; Hyeon, Taeghwan

    2006-01-25

    Uniform sized colloidal nanocrystals have attracted much attention, because of their unique magnetic and optical properties, as compared with those of their bulk counterparts. Especially magnetic nanocrystals and quantum dots have been intensively pursued for biomedical applications such as contrast enhancement agents in magnetic resonance imaging, magnetic carriers for drug delivery system, biological labeling and diagnostics. Due to their large pore sizes and high surface areas, mesoporous materials and its composites with nanocrystals have attracted considerable attention. In order to use the nanocrystals as functional delivery carriers and catalytic supports, nanocrystals coated with porous silica shells are desirable. Herein, we report a synthetic procedure for the fabrication of monodisperse nanocrystals embedded in uniform pore-sized mesoporous silica spheres. As a representative example, we synthesized monodisperse magnetite (Fe3O4) nanocrystals embedded in mesoporous silica spheres and both magnetite nanocrystals and CdSe/ZnS quantum dots embedded in mesoporous silica spheres. Furthermore, these mesoporous silica spheres were applied to the uptake and controlled release of drugs.

  17. Fundamentals of Monte Carlo

    SciTech Connect

    Wollaber, Allan Benton

    2016-06-16

    This is a powerpoint presentation which serves as lecture material for the Parallel Computing summer school. It goes over the fundamentals of the Monte Carlo calculation method. The material is presented according to the following outline: Introduction (background, a simple example: estimating π), Why does this even work? (The Law of Large Numbers, The Central Limit Theorem), How to sample (inverse transform sampling, rejection), and An example from particle transport.

  18. Food Service Fundamentals.

    ERIC Educational Resources Information Center

    Marine Corps Inst., Washington, DC.

    Developed as part of the Marine Corps Institute (MCI) correspondence training program, this course on food service fundamentals is designed to provide a general background in the basic aspects of the food service program in the Marine Corps; it is adaptable for nonmilitary instruction. Introductory materials include specific information for MCI…

  19. Cellulose nanocrystal submonolayers by spin coating.

    PubMed

    Kontturi, Eero; Johansson, Leena-Sisko; Kontturi, Katri S; Ahonen, Päivi; Thüne, Peter C; Laine, Janne

    2007-09-11

    Dilute concentrations of cellulose nanocrystal solutions were spin coated onto different substrates to investigate the effect of the substrate on the nanocrystal submonolayers. Three substrates were probed: silica, titania, and amorphous cellulose. According to atomic force microscopy (AFM) images, anionic cellulose nanocrystals formed small aggregates on the anionic silica substrate, whereas a uniform two-dimensional distribution of nanocrystals was achieved on the cationic titania substrate. The uniform distribution of cellulose nanocrystal submonolayers on titania is an important factor when dimensional analysis of the nanocrystals is desired. Furthermore, the amount of nanocrystals deposited on titania was multifold in comparison to the amounts on silica, as revealed by AFM image analysis and X-ray photoelectron spectroscopy. Amorphous cellulose, the third substrate, resulted in a somewhat homogeneous distribution of the nanocrystal submonolayers, but the amounts were as low as those on the silica substrate. These differences in the cellulose nanocrystal deposition were attributed to electrostatic effects: anionic cellulose nanocrystals are adsorbed on cationic titania in addition to the normal spin coating deposition. The anionic silica surface, on the other hand, causes aggregation of the weakly anionic cellulose nanocrystals which are forced on the repulsive substrate by spin coating. The electrostatically driven adsorption also influences the film thickness of continuous ultrathin films of cellulose nanocrystals. The thicker films of charged nanocrystals on a substrate of opposite charge means that the film thickness is not independent of the substrate when spin coating cellulose nanocrystals in the ultrathin regime (<100 nm).

  20. Starch nanocrystals based hydrogel: Construction, characterizations and transdermal application.

    PubMed

    Bakrudeen, Haja Bava; Sudarvizhi, C; Reddy, B S R

    2016-11-01

    Bio-based nanocomposites were prepared using starch nanocrystals obtained by acid hydrolysis of native starches using different acid sources. In recent times, focuses on starch nanocrystals (SNCs) have been increasing in number of research works dedicated to the development of bio-nanocomposites by blending with different biopolymeric matrices. The work mainly deals with the preparation of starch nanocrystals using different native starches by acid hydrolysis using hydrochloric acid and trifluroacetic acid. The as-prepared starch nanocrystals are having high crystallinity and more platelet morphologies, and used as a drug carrying filler material in the hydrogel formulations with the care of different polymer matrices. The condensed work also concentrates on the dispersion of antiviral drug in the hydrogels, which are applied onto biocompatible bio-membrane to be formulating a complete transdermal patch. The acid hydrolysed starch nanocrystals were thoroughly characterized using TEM, SEM, particle size analysis and zeta potential. Their thermal stability and the crystalline properties were also characterized using TG-DSC and XRD respectively. The physiochemical interaction and compatibility between the drug and the SNCs filler in the polymeric hydrogels were evaluated using FT-IR analysis. The formulated hydrogels were subjected to evaluation of in vitro permeation studies using Franz diffusion studies. The in vitro study was indicated substantial guarantee for the fabrication of drug dispersed in polymeric hydrogels using SNCs as filler matrices for a successful transdermal drug delivery. Copyright © 2016 Elsevier B.V. All rights reserved.

  1. Biocomposites reinforced with cellulose nanocrystals derived from potato peel waste.

    PubMed

    Chen, D; Lawton, D; Thompson, M R; Liu, Q

    2012-09-01

    This study investigated the effectiveness of cellulose nanocrystals derived from potato peel waste as a reinforcement and vapor barrier additive. The nanocrystals were derived from cellulosic material in the potato peel by alkali treatment and subsequently acid hydrolysis. TEM images revealed the average fiber length of the nanocrystals was 410 nm with an aspect ratio of 41; its aspect ratio being considerably larger than cotton-derived nanocrystals prepared using similar reaction conditions. Cellulose nanocrystals (CNC)-filled polyvinyl alcohol (PVA) and thermoplastic starch (TPS) films were prepared by solution casting method to maintain uniform dispersion of the 1-2% (w/w) filler content. An increase of 19% and 33% (starch composite) and 38% and 49% (PVA composite) in tensile modulus was observed for the 1% and 2% CNC-reinforced composites, respectively. Water vapor transmission measurements showed a marginal reduction of water permeability for the PVA composite, whereas no effect was observed for the thermoplastic starch composite. Copyright © 2012 Elsevier Ltd. All rights reserved.

  2. Stabilizing Agents for Drug Nanocrystals: Effect on Bioavailability

    PubMed Central

    Tuomela, Annika; Hirvonen, Jouni; Peltonen, Leena

    2016-01-01

    Drug nanocrystals are a versatile option for drug delivery purposes, and while the number of poorly soluble drug materials is all the time increasing, more research in this area is performed. Drug nanocrystals have a simple structure—a solid drug core is surrounded by a layer of stabilizing agent. However, despite the considerably simple structure, the selection of an appropriate stabilizer for a certain drug can be challenging. Mostly, the stabilizer selection is based purely on the requirement of physical stability, e.g., maintaining the nanosized particle size as long as possible after the formation of drug nanocrystals. However, it is also worth taking into account that stabilizer can affect the bioavailability in the final formulation via interactions with cells and cell layers. In addition, formation of nanocrystals is only one process step, and for the final formulation, more excipients are often added to the composition. The role of the stabilizers in the final formulation can be more than only stabilizing the nanocrystal particle size. A good example is the stabilizer’s role as cryoprotectant during freeze drying. In this review, the stabilizing effect, role of stabilizers in final nanocrystalline formulations, challenges in reaching in vitro–in vivo correlation with nanocrystalline products, and stabilizers’ effect on higher bioavailability are discussed. PMID:27213435

  3. Synthesis and preservation of graphene-supported uranium dioxide nanocrystals

    NASA Astrophysics Data System (ADS)

    Ma, Hanyu; Wang, Haitao; Burns, Peter C.; McNamara, Bruce K.; Buck, Edgar C.; Na, Chongzheng

    2016-07-01

    Graphene-supported uranium dioxide (UO2) nanocrystals are potentially important fuel materials. Here, we investigate the possibility of synthesizing graphene-supported UO2 nanocrystals in polar ethylene glycol compounds by the polyol reduction of uranyl acetylacetone under boiling reflux, thereby enabling the use of an inexpensive graphene precursor graphene oxide into a one-pot process. We show that triethylene glycol is the most suitable solvent with an appropriate reduction potential for producing nanometer-sized UO2 crystals compared to monoethylene glycol, diethylene glycol, and polyethylene glycol. Graphene-supported UO2 nanocrystals synthesized with triethylene glycol show evidence of heteroepitaxy, which can be beneficial for facilitating heat transfer in nuclear fuel particles. Furthermore, we show that graphene-supported UO2 nanocrystals synthesized by polyol reduction can be readily stored in alcohols, impeding oxidation from the prevalent oxygen in air. Together, these methods provide a facile approach for preparing and storing graphene-supported UO2 nanocrystals for further investigation and development under ambient conditions.

  4. Selectivity on Etching: Creation of High-Energy Facets on Copper Nanocrystals for CO2 Electrochemical Reduction.

    PubMed

    Wang, Zhenni; Yang, Guang; Zhang, Zhaorui; Jin, Mingshang; Yin, Yadong

    2016-04-26

    Creating high-energy facets on the surface of catalyst nanocrystals represents a promising method for enhancing their catalytic activity. Herein we show that crystal etching as the reverse process of crystal growth can directly endow nanocrystal surfaces with high-energy facets. The key is to avoid significant modification of the surface energies of the nanocrystal facets by capping effects from solvents, ions, and ligands. Using Cu nanocubes as the starting material, we have successfully demonstrated the creation of high-energy facets in metal nanocrystals by controlled chemical etching. The etched Cu nanocrystals with enriched high-energy {110} facets showed significantly enhanced activity toward CO2 reduction. We believe the etching-based strategy could be extended to the synthesis of nanocrystals of many other catalysts with more active high-energy facets.

  5. Sol-gel precursors for group 14 nanocrystals.

    PubMed

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

    2010-12-14

    The synthesis of Group 14 nanocrystals with controlled size dispersity and composition is an area of considerable interest due to their size-dependent optical and electronic properties, thought to enable their use in a wide range of applications such as fluorophores for biological imaging and photovoltaics. In this review, the use of sol-gel derived polymers as precursors for oxide-embedded Group 14 nanocrystals is presented. This versatile approach can yield tangible quantities of both oxide-embedded and freestanding materials with controllable size, narrow size distributions, and tailorable composition.

  6. Quantitative analysis of cadmium selenide nanocrystal concentration by comparative techniques.

    PubMed

    Kuçur, Erol; Boldt, Frank M; Cavaliere-Jaricot, Sara; Ziegler, Jan; Nann, Thomas

    2007-12-01

    In this paper, we compared atomic absorption spectroscopy (AAS), anodic stripping voltammetry (ASV), and UV-vis spectroscopy for the determination of the concentration of CdSe nanocrystal (NC) solutions. The experimental results were combined with crystallographic calculations of the NC size, which led to a very accurate determination of the nanocrystal concentration--a crucial parameter for bioanalytical applications. Furthermore, such a combined approach can be extended to the determination of shell thickness of core/shell materials (e.g., CdSe/ZnS).

  7. Cellulose nanocrystals the next big nano-thing?

    Treesearch

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

    2008-01-01

    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...

  8. Adsorption of vitamin E on mesoporous titania nanocrystals

    SciTech Connect

    Shih, C.J.; 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 to 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.

  9. Preparation and Evaluation of Two Apatites with Spherical Nanocrystal Morphology.

    PubMed

    Zhang, Yali; Li, Qihong; Li, Xiaojie; Li, Yong; Wang, Chunhui; Zhao, Yantao; Song, Yingliang; Liu, Yanpu

    2016-03-01

    Spherical nanocrystal of apatite has been proved to be beneficial for osteoblast growth. Two apatites with spherical nanocrystal morphology were prepared in this study by chemical wet method and further sintering process. SEM exhibited that both apatites had spherical nanocrystal morphology. The crystal morphology and size was approaching to each other. XRD showed the apatites separately were hydroxyapatite and tricalcium phosphate phases. The cellular biocompatibility was evaluated by osteoblasts for these two spherical nanocrstal apatites. The MTT result indicated a higher cell proliferation rate for spherical tricalcium phosphate group. The ALP activity assay also strongly favored the tricalcium phosphate group. RT-PCR results indicated that Collagen I had a higher transcription level on the spherical tricalcium phosphate group. SEM results showed robust cell growth on the materials. It was concluded that the spherical nanophase tricalcium phosphate was superior to the cellular biocompatibility of spherical nanophase hydroxyapatite and the results were helpful in the manufacture of more suitable tissue engineering scaffolds.

  10. 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.

  11. Alexa Fluor-labeled Fluorescent Cellulose Nanocrystals for Bioimaging Solid Cellulose in Spatially Structured Microenvironments

    SciTech Connect

    Grate, Jay W.; Mo, Kai-For; Shin, Yongsoon; Vasdekis, Andreas; Warner, Marvin G.; Kelly, Ryan T.; Orr, Galya; Hu, Dehong; Dehoff, Karl J.; Brockman, Fred J.; Wilkins, Michael J.

    2015-03-18

    Cellulose nanocrystal materials have been labeled with modern Alexa Fluor dyes in a process that first links the dye to a cyanuric chloride molecule. Subsequent reaction with cellulose nanocrystals provides dyed solid microcrystalline cellulose material that can be used for bioimaging and suitable for deposition in films and spatially structured microenvironments. It is demonstrated with single molecular fluorescence microscopy that these films are subject to hydrolysis by cellulose enzymes.

  12. Early stage of nanocrystal growth

    SciTech Connect

    2012-01-01

    Berkeley Lab researchers at the Molecular Foundry have elucidated important mechanisms behind oriented attachment, the phenomenon that drives biomineralization and the growth of nanocrystals. This electron microscopy movie shows the early stage of nanocrystal growth. Nanoparticles make transient contact at many points and orientations until their lattices are perfectly matched. The particles then make a sudden jump-to-contact to form attached aggregates. (Movie courtesy of Jim DeYoreo)

  13. Healthcare fundamentals.

    PubMed

    Kauk, Justin; Hill, Austin D; Althausen, Peter L

    2014-07-01

    In order for a trauma surgeon to have an intelligent discussion with hospital administrators, healthcare plans, policymakers, or any other physicians, a basic understanding of the fundamentals of healthcare is paramount. It is truly shocking how many surgeons are unable to describe the difference between Medicare and Medicaid or describe how hospitals and physicians get paid. These topics may seem burdensome but they are vital to all business decision making in the healthcare field. The following chapter provides further insight about what we call "the basics" of providing medical care today. Most of the topics presented can be applied to all specialties of medicine. It is broken down into 5 sections. The first section is a brief overview of government programs, their influence on care delivery and reimbursement, and past and future legislation. Section 2 focuses on the compliance, care provision, and privacy statutes that regulate physicians who care for Medicare/Medicaid patient populations. With a better understanding of these obligations, section 3 discusses avenues by which physicians can stay informed of current and pending health policy and provides ways that they can become involved in shaping future legislation. The fourth section changes gears slightly by explaining how the concepts of trade restraint, libel, antitrust legislation, and indemnity relate to physician practice. The fifth, and final, section ties all of components together by describing how physician-hospital alignment can be mutually beneficial in providing patient care under current healthcare policy legislation.

  14. Fundamentals of fluid sealing

    NASA Technical Reports Server (NTRS)

    Zuk, J.

    1976-01-01

    The fundamentals of fluid sealing, including seal operating regimes, are discussed and the general fluid-flow equations for fluid sealing are developed. Seal performance parameters such as leakage and power loss are presented. Included in the discussion are the effects of geometry, surface deformations, rotation, and both laminar and turbulent flows. The concept of pressure balancing is presented, as are differences between liquid and gas sealing. Mechanisms of seal surface separation, fundamental friction and wear concepts applicable to seals, seal materials, and pressure-velocity (PV) criteria are discussed.

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

    NASA Astrophysics Data System (ADS)

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

    2016-05-01

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

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

    PubMed Central

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

    2016-01-01

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

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

    DOE PAGES

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

    2016-05-13

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

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

    SciTech Connect

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

    2016-05-13

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

  19. Fundamental Physics

    NASA Image and Video Library

    2003-01-22

    Clues to the formation of planets and planetary rings -- like Saturn's dazzling ring system -- may be found by studying how dust grains interact as they collide at low speeds. To study the question of low-speed dust collisions, NASA sponsored the COLLisions Into Dust Experiment (COLLIDE) at the University of Colorado. It was designed to spring-launch marble-size projectiles into trays of powder similar to space or lunar dust. COLLIDE-1 (1998) discovered that collisions below a certain energy threshold eject no material. COLLIDE-2 was designed to identify where the threshold is. In COLLIDE-2, scientists nudged small projectiles into dust beds and recorded how the dust splashed outward (video frame at top; artist's rendering at bottom). The slowest impactor ejected no material and stuck in the target. The faster impactors produced ejecta; some rebounded while others stuck in the target.

  20. Tuning Equilibrium Compositions in Colloidal Cd1-xMnxSe Nanocrystals Using Diffusion Doping and Cation Exchange.

    PubMed

    Barrows, Charles J; Chakraborty, Pradip; Kornowske, Lindsey M; Gamelin, Daniel R

    2016-01-26

    The physical properties of semiconductor nanocrystals can be tuned dramatically via composition control. Here, we report a detailed investigation of the synthesis of high-quality colloidal Cd1-xMnxSe nanocrystals by diffusion doping of preformed CdSe nanocrystals. Until recently, Cd1-xMnxSe nanocrystals proved elusive because of kinetic incompatibilities between Mn(2+) and Cd(2+) chemistries. Diffusion doping allows Cd1-xMnxSe nanocrystals to be prepared under thermodynamic rather than kinetic control, allowing access to broader composition ranges. We now investigate this chemistry as a model system for understanding the characteristics of nanocrystal diffusion doping more deeply. From the present work, a Se(2-)-limited reaction regime is identified, in which Mn(2+) diffusion into CdSe nanocrystals is gated by added Se(2-), and equilibrium compositions are proportional to the amount of added Se(2-). At large added Se(2-) concentrations, a solubility-limited regime is also identified, in which x = xmax = ∼0.31, independent of the amount of added Se(2-). We further demonstrate that Mn(2+) in-diffusion can be reversed by cation exchange with Cd(2+) under exactly the same reaction conditions, purifying Cd1-xMnxSe nanocrystals back to CdSe nanocrystals with fine tunability. These chemistries offer exceptional composition control in Cd1-xMnxSe NCs, providing opportunities for fundamental studies of impurity diffusion in nanocrystals and for development of compositionally tuned nanocrystals with diverse applications ranging from solar energy conversion to spin-based photonics.

  1. 2nd International Symposium on Fundamental Aspects of Rare-earth Elements Mining and Separation and Modern Materials Engineering (REES-2015)

    NASA Astrophysics Data System (ADS)

    Tavadyan, Levon, Prof; Sachkov, Viktor, Prof; Godymchuk, Anna, Dr.; Bogdan, Anna

    2016-01-01

    The 2nd International Symposium «Fundamental Aspects of Rare-earth Elements Mining and Separation and Modern Materials Engineering» (REES2015) was jointly organized by Tomsk State University (Russia), National Academy of Science (Armenia), Shenyang Polytechnic University (China), Moscow Institute of Physics and Engineering (Russia), Siberian Physical-technical Institute (Russia), and Tomsk Polytechnic University (Russia) in September, 7-15, 2015, Belokuriha, Russia. The Symposium provided a high quality of presentations and gathered engineers, scientists, academicians, and young researchers working in the field of rare and rare earth elements mining, modification, separation, elaboration and application, in order to facilitate aggregation and sharing interests and results for a better collaboration and activity visibility. The goal of the REES2015 was to bring researchers and practitioners together to share the latest knowledge on rare and rare earth elements technologies. The Symposium was aimed at presenting new trends in rare and rare earth elements mining, research and separation and recent achievements in advanced materials elaboration and developments for different purposes, as well as strengthening the already existing contacts between manufactures, highly-qualified specialists and young scientists. The topics of the REES2015 were: (1) Problems of extraction and separation of rare and rare earth elements; (2) Methods and approaches to the separation and isolation of rare and rare earth elements with ultra-high purity; (3) Industrial technologies of production and separation of rare and rare earth elements; (4) Economic aspects in technology of rare and rare earth elements; and (5) Rare and rare earth based materials (application in metallurgy, catalysis, medicine, optoelectronics, etc.). We want to thank the Organizing Committee, the Universities and Sponsors supporting the Symposium, and everyone who contributed to the organization of the event and to

  2. Assemblies of Cellulose Nanocrystals

    NASA Astrophysics Data System (ADS)

    Kumacheva, Eugenia

    The entropically driven coassembly of nanorods (cellulose nanocrystals, CNCs) and different types of nanoparticles (NPs), including dye-labeled latex NPs, carbon dots and plasmonic NPs was experimentally studied in aqueous suspensions and in solid films. In mixed CNC-NP suspensions, phase separation into an isotropic NP-rich and a chiral nematic CNC-rich phase took place; the latter contained a significant amount of NPs. Drying the mixed suspension resulted in CNC-NP films with planar disordered layers of NPs, which alternated with chiral nematic CNC-rich regions. In addition, NPs were embedded in the chiral nematic domains. The stratified morphology of the films, together with a random distribution of NPs in the anisotropic phase, led to the films having close-to-uniform fluorescence, birefringence, and circular dichroism properties.

  3. Functionalization of cellulose nanocrystals for advanced applications.

    PubMed

    Tang, Juntao; Sisler, Jared; Grishkewich, Nathan; Tam, Kam Chiu

    2017-05-15

    Replacing the widespread use of petroleum-derived non-biodegradable materials with green and sustainable materials is a pressing challenge that is gaining increasing attention by the scientific community. One such system is cellulose nanocrystal (CNC) derived from acid hydrolysis of cellulosic materials, such as plants, tunicates and agriculture biomass. The utilization of colloidal CNCs can aid in the reduction of carbon dioxide that is responsible for global warming and climate change. CNCs are excellent candidates for the design and development of functional nanomaterials in many applications due to several attractive features, such as high surface area, hydroxyl groups for functionalization, colloidal stability, low toxicity, chirality and mechanical strength. Several large scale manufacturing facilities have been commissioned to produce CNCs of up to 1000kg/day, and this has generated increasing interests in both academic and industrial laboratories. In this feature article, we will describe the recent development of functionalized cellulose nanocrystals for several important applications in ours and other laboratories. We will highlight some challenges and offer perspectives on the potentials of these sustainable nanomaterials. Copyright © 2017 Elsevier Inc. All rights reserved.

  4. Spectroscopic and Device Aspects of Nanocrystal Quantum Dots.

    PubMed

    Pietryga, Jeffrey M; Park, Young-Shin; Lim, Jaehoon; Fidler, Andrew F; Bae, Wan Ki; Brovelli, Sergio; Klimov, Victor I

    2016-09-28

    The field of nanocrystal quantum dots (QDs) is already more than 30 years old, and yet continuing interest in these structures is driven by both the fascinating physics emerging from strong quantum confinement of electronic excitations, as well as a large number of prospective applications that could benefit from the tunable properties and amenability toward solution-based processing of these materials. The focus of this review is on recent advances in nanocrystal research related to applications of QD materials in lasing, light-emitting diodes (LEDs), and solar energy conversion. A specific underlying theme is innovative concepts for tuning the properties of QDs beyond what is possible via traditional size manipulation, particularly through heterostructuring. Examples of such advanced control of nanocrystal functionalities include the following: interface engineering for suppressing Auger recombination in the context of QD LEDs and lasers; Stokes-shift engineering for applications in large-area luminescent solar concentrators; and control of intraband relaxation for enhanced carrier multiplication in advanced QD photovoltaics. We examine the considerable recent progress on these multiple fronts of nanocrystal research, which has resulted in the first commercialized QD technologies. These successes explain the continuing appeal of this field to a broad community of scientists and engineers, which in turn ensures even more exciting results to come from future exploration of this fascinating class of materials.

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

    SciTech Connect

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

    2016-11-28

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

  6. Controllable Synthesis of Monodisperse Er3+-Doped Lanthanide Oxyfluorides Nanocrystals with Intense Mid-Infrared Emission

    PubMed Central

    He, Huilin; Liu, Qiang; Yang, Dandan; Pan, Qiwen; Qiu, Jianrong; Dong, Guoping

    2016-01-01

    Monodisperse lanthanide oxyfluorides LnOF (Ln = Gd, Y) with mid-infrared emissions were controllably synthesized via a mild co-precipitation route and a subsequent heat-treatment. The detailed composition and morphology were characterized by X-ray diffraction (XRD), scanning electron microscope (SEM) and high resolution transmission electron microscopy (HRTEM). The results showed that monodisperse GdOF:Er3+ were nano-riced shape with length about 350 nm and width about 120 nm, while the quasi-spherical YOF:Er3+ were uniform nanocrystals with an average size around 100 nm. The influence of calcination temperature on the size and phase transition of LnOF nanocrystals was also investigated. The photoluminescence (PL) spectra indicated that the 2.7 μm emission of Er3+ had achieved in both GdOF and YOF nanocrystals, which were calcined at different temperatures. In addition, the decay time of both 4I13/2 and 4I13/2 energy levels corresponding to Er3+ in YOF nanocrystals were also studied in detail. The results suggested that both rice-shaped GdOF nanocrystals and YOF nanocrystals could provide suitable candidate materials for nanocrystals-glass composites, which could be a step forward to the realization of mid-infrared laser materials. PMID:27748411

  7. Controllable Synthesis of Monodisperse Er3+-Doped Lanthanide Oxyfluorides Nanocrystals with Intense Mid-Infrared Emission

    NASA Astrophysics Data System (ADS)

    He, Huilin; Liu, Qiang; Yang, Dandan; Pan, Qiwen; Qiu, Jianrong; Dong, Guoping

    2016-10-01

    Monodisperse lanthanide oxyfluorides LnOF (Ln = Gd, Y) with mid-infrared emissions were controllably synthesized via a mild co-precipitation route and a subsequent heat-treatment. The detailed composition and morphology were characterized by X-ray diffraction (XRD), scanning electron microscope (SEM) and high resolution transmission electron microscopy (HRTEM). The results showed that monodisperse GdOF:Er3+ were nano-riced shape with length about 350 nm and width about 120 nm, while the quasi-spherical YOF:Er3+ were uniform nanocrystals with an average size around 100 nm. The influence of calcination temperature on the size and phase transition of LnOF nanocrystals was also investigated. The photoluminescence (PL) spectra indicated that the 2.7 μm emission of Er3+ had achieved in both GdOF and YOF nanocrystals, which were calcined at different temperatures. In addition, the decay time of both 4I13/2 and 4I13/2 energy levels corresponding to Er3+ in YOF nanocrystals were also studied in detail. The results suggested that both rice-shaped GdOF nanocrystals and YOF nanocrystals could provide suitable candidate materials for nanocrystals-glass composites, which could be a step forward to the realization of mid-infrared laser materials.

  8. Nonlinear Absorption and Low-Threshold Multiphoton Pumped Stimulated Emission from All-Inorganic Perovskite Nanocrystals.

    PubMed

    Wang, Yue; Li, Xiaoming; Zhao, Xin; Xiao, Lian; Zeng, Haibo; Sun, Handong

    2016-01-13

    Halide perovskite materials have attracted intense research interest due to the striking performance in photoharvesting photovoltaics as well as photoemitting applications. Very recently, the emerging CsPbX3 (X = Cl, Br, I) perovskite nanocrystals have been demonstrated to be efficient emitters with photoluminescence quantum yield as high as ∼90%, room temperature single photon sources, and favorable lasing materials. Herein, the nonlinear optical properties, in particular, the multiphoton absorption and resultant photoluminescence of the CsPbBr3 nanocrystals, were investigated. Notably, a large two-photon absorption cross-section of up to ∼1.2 × 10(5) GM is determined for 9 nm sized CsPbBr3 nanocrystals. Moreover, low-threshold frequency-upconverted stimulated emission by two-photon absorption was observed from the thin film of close-packed CsPbBr3 nanocrystals. The stimulated emission is found to be photostable and wavelength-tunable. We further realize the three-photon pumped stimulated emission in green spectra range from colloidal nanocrystals for the first time. Our results reveal the strong nonlinear absorption in the emerging CsPbX3 perovskite nanocrystals and suggest these nanocrystals as attractive multiphoton pumped optical gain media, which would offer new opportunities in nonlinear photonics and revive the nonlinear optical devices.

  9. 2011 Clusters, Nanocrystals & Nanostructures Gordon Research Conference

    SciTech Connect

    Lai-Sheng Wang

    2011-07-29

    Small particles have been at the heart of nanoscience since the birth of the field and now stand ready to make significant contributions to the big challenges of energy, health and sustainability. Atomic clusters show exquisite size-dependent electronic and magnetic properties and offer a new level of control in catalyses, sensors and biochips; functionalised nanocrystals offer remarkable optical properties and diverse applications in electronic devices, solar energy, and therapy. Both areas are complemented by a raft of recent advances in fabrication, characterization, and performance of a diversity of nanomaterials from the single atom level to nanowires, nanodevices, and biologically-inspired nanosystems. The goal of the 2011 Gordon Conference is thus to continue and enhance the interdisciplinary tradition of this series and discuss the most recent advances, fundamental scientific questions, and emerging applications of clusters, nanocrystals, and nanostructures. A single conference covering all aspects of nanoscience from fundamental issues to applications has the potential to create new ideas and stimulate cross fertilization. The meeting will therefore provide a balance among the three sub-components of the conference, true to its title, with a selection of new topics added to reflect rapid advances in the field. The open atmosphere of a Gordon conference, emphasizing the presentation of unpublished results and extensive discussions, is an ideal home for this rapidly developing field and will allow all participants to enjoy a valuable and stimulating experience. Historically, this Gordon conference has been oversubscribed, so we encourage all interested researchers from academia, industry, and government institutions to apply as early as possible. We also encourage all attendees to submit their latest results for presentation at the poster sessions. We anticipate that several posters will be selected for 'hot topic' oral presentations. Given the important

  10. Facet effects of palladium nanocrystals for oxygen reduction in ionic liquids and for sensing applications

    NASA Astrophysics Data System (ADS)

    Tang, Yongan; Chi, Xiaowei; Zou, Shouzhong; Zeng, Xiangqun

    2016-03-01

    Palladium nanocrystals enclosed by {100} and {110} crystal facets, were successfully synthesized through an aqueous one-pot synthesis method. A new thermal annealing approach was developed for fabricating these palladium nanocrystals as a working electrode on a gas permeable membrane to study the facet effects of the oxygen reduction process in an ionic liquid, 1-butyl-1-methylpyrrolidinium bis(trifluoromethylsulfonyl)imide ([Bmpy][NTf2]). Results were compared with the same processes at a conventional platinum electrode. Our study shows that the structural difference between the two facets of Pd nanocrystals has little effect on the oxygen reduction process but significantly affects the oxidation process of the superoxide. It is found that the Pd{110}/IL interface can better stabilize superoxide radicals revealed by a more positive oxidation potential compared to that of Pd{100}. In addition, the analytical characteristic of utilizing both palladium nanocrystals as electrodes for oxygen sensing is comparable with a polycrystal platinum oxygen sensor, in which Pd{110} presents the best sensitivity and lowest detection limit. Our results demonstrate the facet-dependence of oxygen reduction in an ionic liquid medium and provide the fundamental information needed to guide the applications of palladium nanocrystals in electrochemical gas sensor and fuel cell research.Palladium nanocrystals enclosed by {100} and {110} crystal facets, were successfully synthesized through an aqueous one-pot synthesis method. A new thermal annealing approach was developed for fabricating these palladium nanocrystals as a working electrode on a gas permeable membrane to study the facet effects of the oxygen reduction process in an ionic liquid, 1-butyl-1-methylpyrrolidinium bis(trifluoromethylsulfonyl)imide ([Bmpy][NTf2]). Results were compared with the same processes at a conventional platinum electrode. Our study shows that the structural difference between the two facets of Pd

  11. Periodic mesoporous hydridosilica--synthesis of an "impossible" material and its thermal transformation into brightly photoluminescent periodic mesoporous nanocrystal silicon-silica composite.

    PubMed

    Xie, Zhuoying; Henderson, Eric J; Dag, Ömer; Wang, Wendong; Lofgreen, Jennifer E; Kübel, Christian; Scherer, Torsten; Brodersen, Peter M; Gu, Zhong-Ze; Ozin, Geoffrey A

    2011-04-06

    There has always been a fascination with "impossible" compounds, ones that do not break any rules of chemical bonding or valence but whose structures are unstable and do not exist. This instability can usually be rationalized in terms of chemical or physical restrictions associated with valence electron shells, multiple bonding, oxidation states, catenation, and the inert pair effect. In the pursuit of these "impossible" materials, appropriate conditions have sometimes been found to overcome these instabilities and synthesize missing compounds, yet for others these tricks have yet to be uncovered and the materials remain elusive. In the scientifically and technologically important field of periodic mesoporous silicas (PMS), one such "impossible" material is periodic mesoporous hydridosilica (meso-HSiO(1.5)). It is the archetype of a completely interrupted silica open framework material: its pore walls are comprised of a three-connected three-dimensional network that should be so thermodynamically unstable that any mesopores present would immediately collapse upon removal of the mesopore template. In this study we show that meso-HSiO(1.5) can be synthesized by template-directed self-assembly of HSi(OEt)(3) under aqueous acid-catalyzed conditions and after template extraction remains stable to 300 °C. Above this temperature, bond redistribution reactions initiate a metamorphic transformation which eventually yields periodic mesoporous nanocrystalline silicon-silica, meso-ncSi/SiO(2), a nanocomposite material in which brightly photoluminescent silicon nanocrystallites are embedded within a silica matrix throughout the mesostructure. The integration of the properties of silicon nanocrystallinity with silica mesoporosity provides a wealth of new opportunities for emerging nanotechnologies.

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

    PubMed

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

    2017-07-01

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

  13. Effects of Gamma Irradiation on Optical Properties of Colloidal Nano-crystals

    SciTech Connect

    Withers, Nathan J.; Sankar, Krishnaprasad; Akins, Brian A.; Memon, Tosifa A.; Smolyakov, Gennady A.; Osinski, Marek; Gu, Jiangjiang; Gu, Tingyi; Bowers, Shin T. |; Greenberg, Melisa R. |; Busch, Robert D.

    2008-07-01

    The effects of {sup 137}Cs gamma irradiation on photoluminescence properties, such as spectra, light output, and lifetime, of several types of colloidal nano-crystals have been investigated. Irradiation-induced damage testing was performed on CdSe/ZnS, LaF{sub 3}:Eu, LaF{sub 3}:Ce, ZnO, and PbI{sub 2} nano-crystals synthesized on a Schlenk line using appropriate solvents and precursors. Optical degradation of the nano-crystals was evaluated based on the measured dependence of their photoluminescence intensity on the irradiation dose. Radiation hardness varies significantly between various nano-crystalline material systems. (authors)

  14. Photosensitizer methylene blue-semiconductor nanocrystals hybrid system for photodynamic therapy.

    PubMed

    Rakovich, Aliaksandra; Rakovich, Tatsiana; Kelly, Vincent; Lesnyak, Vladimir; Eychmüller, Alexander; Rakovich, Yury P; Donegan, John F

    2010-04-01

    In this work we report on the development of novel hybrid material with enhanced photodynamic properties based on methylene blue and CdTe nanocrystals. Absorption spectroscopy, visible photoluminescence spectroscopy and fluorescence lifetime imaging of this system reveal efficient charge transfer between nanocrystals and the methylene blue dye. Near infra-red photoluminescence measurements provide evidence for an increased efficiency of singlet oxygen production by the methylene blue dye. In vitro studies on the growth of HepG2 and HeLa cancerous cells were also performed, they point towards an improvement in the cell kill efficiency for the methylene blue-semiconductor nanocrystals hybrid system.

  15. 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.

  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. Fundamental DSC investigations of alpha-keratinous materials as basis for the interpretation of specific effects of chemical, cosmetic treatments on human hair.

    PubMed

    Wortmann, F-J; Sendelbach, G; Popescu, C

    2007-01-01

    Alpha-keratinous materials can be considered as two-phase, filament/matrix composites, in which partly crystalline, alpha-helical intermediate filaments (if) are embedded in an amorphous matrix of IF-associated proteins (IFAP). Differential Scanning Calorimetry (DSC) of keratins in water was found to be especially suited to analyze various aspects of the thermal stability of these main morphological components. Results and considerations are reviewed, which were gained by applying the principles derived from fundamental investigations to the specific effects of oxidation (bleaching) and reduction (perm-waving). Properties and interactions of the main morphological components of human hair are considered that are specifically related to the various aspects of their thermal stability. The overall view of the results shows that the course of the thermal unfolding of the alpha-helix in the IFs is independent of the chemical history of hair. The matrix properties are the primary factor controlling the kinetics of the onset of the denaturation process in the IF/IFAP-composite.

  18. Photovoltaic fundamentals

    SciTech Connect

    Pitchford, P.; Jones, J.; Glenn, B.; Cook, G.; Billman, L.; Adcock, R.

    1991-09-01

    This booklet describes how PV devices and systems work. It also describes the specific materials and devices that are most widely used commercially as of 1990 and those that have the brightest prospects. Students, engineers, scientists, and others needing an introduction to basic PV technology, and manufacturers and consumers who want more information about PV systems should find this booklet helpful. We begin with an overview and then explain the rudimentary physical process of the technology, the photovoltaic effect. Next, we consider how scientists and engineers have harnessed this process to generate electricity in silicon solar cells, thin-film devices, and high-efficiency cells. We then look at how these devices are incorporated into modules, arrays, and power-producing systems. We have written and designed this book so that the reader may approach the subject on three different levels. First, for the person who is in a hurry or needs a very cursory overview, in the margins of each page we generalize the important points of that page. Second, for a somewhat deeper understanding, we have provided ample illustrations, photographs, and captions. And third, for a thorough introduction to the subject, the reader can resort to reading the text.

  19. Single-particle mapping of nonequilibrium nanocrystal transformations

    NASA Astrophysics Data System (ADS)

    Ye, Xingchen; Jones, Matthew R.; Frechette, Layne B.; Chen, Qian; Powers, Alexander S.; Ercius, Peter; Dunn, Gabriel; Rotskoff, Grant M.; Nguyen, Son C.; Adiga, Vivekananda P.; Zettl, Alex; Rabani, Eran; Geissler, Phillip L.; Alivisatos, A. Paul

    2016-11-01

    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. 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 the importance of developing tools capable of probing short-lived nanoscale species at the single-particle level.

  20. Single-particle mapping of nonequilibrium nanocrystal transformations.

    PubMed

    Ye, Xingchen; Jones, Matthew R; Frechette, Layne B; Chen, Qian; Powers, Alexander S; Ercius, Peter; Dunn, Gabriel; Rotskoff, Grant M; Nguyen, Son C; Adiga, Vivekananda P; Zettl, Alex; Rabani, Eran; Geissler, Phillip L; Alivisatos, A Paul

    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. 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 the importance of developing tools capable of probing short-lived nanoscale species at the single-particle level.

  1. 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

  2. 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

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

    PubMed

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

    2013-02-13

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

  4. Pyramidal and Chiral Groupings of Gold Nanocrystals Assembled Using DNA Scaffolds

    PubMed Central

    Mastroianni, Alexander; Claridge, Shelley; Alivisatos, A. Paul

    2009-01-01

    Nanostructures constructed from metal and semiconductor nanocrystals conjugated to, and organized by DNA are an emerging class of material with collective optical properties. We created discrete pyramids of DNA with gold nanocrystals at the tips. By taking small angle X-ray scattering (SAXS) measurments from solutions of these pyramids we confirmed that this pyramidal geometry creates structures which are more rigid in solution than linear DNA. We then took advantage of the tetrahedral symmetry to demonstrate construction of chiral nanostructures. PMID:19331419

  5. Pyramidal and Chiral Groupings of Gold Nanocrystals Assembled Using DNA Scaffolds

    SciTech Connect

    Mastroianni, Alexander; Claridge, Shelley; Alivisatos, A. Paul

    2009-03-30

    Nanostructures constructed from metal and semiconductor nanocrystals conjugated to, and organized by DNA are an emerging class of material with collective optical properties. We created discrete pyramids of DNA with gold nanocrystals at the tips. By taking small angle X-ray scattering (SAXS) measurments from solutions of these pyramids we confirmed that this pyramidal geometry creates structures which are more rigid in solution than linear DNA. We then took advantage of the tetrahedral symmetry to demonstrate construction of chiral nanostructures.

  6. Convenient Molecular Approach of Size and Shape Controlled ZnSe and ZnTe Nanocrystals

    DTIC Science & Technology

    2001-01-01

    Materials Research Society Symposium Proceedings Volume 635. Anisotropic Nanoparticles - Synthesis , Characterization and Applications To order the...diffraction patterns were measured on a Rigaku Miniflex instrument (0.5 kW) operating with a Cu K,(X, 0.1541 nm) X-ray source. ZnSc Nanocrystals. Zn ...one-pot synthesis of size and shape controlled zinc chalcogenide nanocrystals using a monomeric molecular precursor, [ Zn (EPh)2][TMEDA]. By varying

  7. Building Structural Complexity in Semiconductor Nanocrystals through Chemical Transformations

    SciTech Connect

    Sadtler, Bryce F

    2009-05-01

    Methods are presented for synthesizing nanocrystal heterostructures comprised of two semiconductor materials epitaxially attached within individual nanostructures. The chemical transformation of cation exchange, where the cations within the lattice of an ionic nanocrystal are replaced with a different metal ion species, is used to alter the chemical composition at specific regions ofa nanocrystal. Partial cation exchange was performed in cadmium sulfide (CdS) nanorods of well-defined size and shape to examine the spatial organization of materials within the resulting nanocrystal heterostructures. The selectivity for cation exchange to take place at different facets of the nanocrystal plays an important role in determining the resulting morphology of the binary heterostructure. The exchange of copper (I) (Cu+) cations in CdS nanorods occurs preferentially at the ends of the nanorods. Theoretical modeling of epitaxial attachments between different facets of CdS and Cu2S indicate that the selectivity for cation exchange at the ends of the nanorods is a result of the low formation energy of the interfaces produced. During silver (I) (Ag+) cation exchange in CdS nanorods, non-selective nucleation of silver sulfide (Ag2S), followed by partial phase segregation leads to significant changes in the spatial arrangement of CdS and Ag2S regions at the exchange reaction proceeds through the nanocrystal. A well-ordered striped pattern of alternating CdS and Ag2S segments is found at intermediate fractions of exchange. The forces mediating this spontaneous process are a combination of Ostwald ripening to reduce the interfacial area along with a strain-induced repulsive interaction between Ag2S segments. To elucidate why Cu+ and Ag+ cation exchange with CdS nanorods produce different morphologies, models for epitaxial attachments between various facets of CdS with Cu2S or

  8. Oxygen transport in unreduced, reduced and Rh(III)-doped CeO2 nanocrystals.

    PubMed

    Sayle, Thi X T; Parker, Stephen C; Sayle, Dean C

    2007-01-01

    Ceria, CeO2, based materials are a major (active) component of exhaust catalysts and promising candidates for solid oxide fuel cells. In this capacity, oxygen transport through the material is pivotal. Here, we explore whether oxygen transport is influenced (desirably increased) compared with transport within the bulk parent material by traversing to the nanoscale. In particular, atomistic models for ceria nanocrystals, including perfect: CeO2; reduced: CeO1.95 and doped: Rh0.1Ce0.9O1.95, have been generated. The nanocrystals were about 8 nm in diameter and each comprised about 16,000 atoms. Oxygen transport can also be influenced, sometimes profoundly, by microstructural features such as dislocations and grain-boundaries. However, these are difficult to generate within an atomistic model using, for example, symmetry operations. Accordingly, we crystallised the nanocrystals from an amorphous precursor, which facilitated the evolution of a variety of microstructures including: twin-boundaries and more general grain-boundaries and grain-junctions, dislocations and epitaxy, isolated and associated point defects. The shapes of the nanocrystals are in accord with HRTEM data and comprise octahedral morphologies with {111} surfaces, truncated by (dipolar) {100} surfaces together with a complex array of steps, edges and corners. Oxygen transport data was then calculated using these models and compared with data calculated previously for CeO1.97/ YSZ thin films and the (bulk) parent material, CeO197. Oxygen transport was calculated to increase in the order: CeO2 nanocrystal < (reduced) CeO1.95 nanocrystal approximately Rh0.1Ce0.9O1.95 nanocrystal < CeO1.97/YSZ thin film < (reduced) CeO1.97 (bulk) parent material; the mechanism was determined to be primarily vacancy driven. Our findings indicate that reducing one- (thin film) or especially three- (nanocrystal) dimensions to the nanoscale may prove deleterious to oxygen transport. Conversely, we observed dynamic evolution and

  9. Ablative Thermal Protection System Fundamentals

    NASA Technical Reports Server (NTRS)

    Beck, Robin A. S.

    2013-01-01

    This is the presentation for a short course on the fundamentals of ablative thermal protection systems. It covers the definition of ablation, description of ablative materials, how they work, how to analyze them and how to model them.

  10. Station for X-ray structural analysis of materials and single crystals (including nanocrystals) on a synchrotron radiation beam from the wiggler at the Siberia-2 storage ring

    SciTech Connect

    Kheiker, D. M. Kovalchuk, M. V.; Korchuganov, V. N.; Shilin, Yu. N.; Shishkov, V. A.; Sulyanov, S. N.; Dorovatovskii, P. V.; Rubinsky, S. V.; Rusakov, A. A.

    2007-11-15

    The design of the station for structural analysis of polycrystalline materials and single crystals (including nanoobjects and macromolecular crystals) on a synchrotron radiation beam from the superconducting wiggler of the Siberia-2 storage ring is described. The wiggler is constructed at the Budker Institute of Nuclear Physics of the Siberian Division of the Russian Academy of Sciences. The X-ray optical scheme of the station involves a (1, -1) double-crystal monochromator with a fixed position of the monochromatic beam and a sagittal bending of the second crystal, segmented mirrors bent by piezoelectric motors, and a (2{theta}, {omega}, {phi}) three-circle goniometer with a fixed tilt angle. Almost all devices of the station are designed and fabricated at the Shubnikov Institute of Crystallography of the Russian Academy of Sciences. The Bruker APEX11 two-dimensional CCD detector will serve as a detector in the station.

  11. Nanocrystal powered nanomotor

    DOEpatents

    Regan, Brian C [Los Angeles, CA; Zettl, Alexander K [Kensington, CA; Aloni, Shaul [Albany, CA

    2011-01-04

    A nanoscale nanocrystal which may be used as a reciprocating motor is provided, comprising a substrate having an energy differential across it, e.g. an electrical connection to a voltage source at a proximal end; an atom reservoir on the substrate distal to the electrical connection; a nanoparticle ram on the substrate distal to the atom reservoir; a nanolever contacting the nanoparticle ram and having an electrical connection to a voltage source, whereby a voltage applied between the electrical connections on the substrate and the nanolever causes movement of atoms between the reservoir and the ram. Movement of the ram causes movement of the nanolever relative to the substrate. The substrate and nanolever preferably comprise multiwalled carbon nanotubes (MWNTs) and the atom reservoir and nanoparticle ram are preferably metal (e.g. indium) deposited as small particles on the MWNTs. The substrate may comprise a silicon chip that has been fabricated to provide the necessary electrodes and other electromechanical structures, and further supports an atomic track, which may comprise an MWNT.

  12. Nanocrystals for luminescent solar concentrators.

    PubMed

    Bradshaw, Liam R; Knowles, Kathryn E; McDowall, Stephen; Gamelin, Daniel R

    2015-02-11

    Luminescent solar concentrators (LSCs) harvest sunlight over large areas and concentrate this energy onto photovoltaics or for other uses by transporting photons through macroscopic waveguides. Although attractive for lowering solar energy costs, LSCs remain severely limited by luminophore reabsorption losses. Here, we report a quantitative comparison of four types of nanocrystal (NC) phosphors recently proposed to minimize reabsorption in large-scale LSCs: two nanocrystal heterostructures and two doped nanocrystals. Experimental and numerical analyses both show that even the small core absorption of the leading NC heterostructures causes major reabsorption losses at relatively short transport lengths. Doped NCs outperform the heterostructures substantially in this critical property. A new LSC phosphor is introduced, nanocrystalline Cd(1-x)Cu(x)Se, that outperforms all other leading NCs by a significant margin in both small- and large-scale LSCs under full-spectrum conditions.

  13. 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.

  14. Synthesis of epitaxially grown core/shell nanocrystals with nonthermal plasmas

    NASA Astrophysics Data System (ADS)

    Hunter, Katharine; Held, Jacob; Mkhoyan, Andre; Kortshagen, Uwe

    2016-09-01

    Nonthermal plasmas have gained increasing adoption as capable sources of nanocrystal materials that are challenging to grow in solution due to the high synthesis temperatures required. To date, little progress has been made to grow core/shell nanocrystals with nonthermal plasmas. In colloidal synthesis, core/shell structures have proven to be indispensable to improve the optical properties of nanocrystal materials. The epitaxially grown shells terminate surface states on the nanocrystal cores and can be selected to form heterojunctions that confine charge carriers in the core region. Here, we present the nonthermal plasma synthesis of germanium (Ge) nanocrystals with epitaxially grown silicon (Si) shells. Core/shell growth is achieved in a single flow-through plasma reactor by first injecting the core precursor and, after its depletion, injecting the shell precursor further downstream. Electron microscopy studies confirm epitaxial shell growth with minimal intermixing of core and shell material. Due to the lattice mismatch between core and shell, we find that Ge cores are compressively strained, which enables tuning of the Ge band structure via shell thickness. This demonstration of core/shell nanocrystals can be extended to an exciting array of heterostructures. This work was supported by the MRSEC program of the U.S. National Science Foundation under grant DMR-1420013.

  15. 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

    Ge1–xSnx alloy nanocrystals and Ge1–xSnx/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 Ge1–xSnx 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 Ge1–xSnx nanocrystals does enhance the photoluminescence up to 15-fold versus that of Ge/CdS nanocrystals with a pure Gemore » 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 Ge1–xSnx/CdS materials. With enhanced photoluminescence in the near-infrared region, Ge1–xSnx core/shell nanocrystals might be useful alternatives to other materials for energy capture and conversion applications and as imaging probes.« less

  16. Memory and coupling in nanocrystal optoelectronic devices

    NASA Astrophysics Data System (ADS)

    Fairfield, Jessamyn A.

    Optoelectronic devices incorporating semiconducting nanocrystals are promising for many potential applications. Nanocrystals whose size is below the exciton Bohr radius have optical absorption and emission that is tunable with size, due to the quantum confinement of the charge carriers. However, the same confinement that yields these optical properties also makes electrical conduction in a film of nanocrystals occur via tunneling, due to the high energy barrier between nanocrystals. Hence, the extraction of photo-generated charge carriers presents a significant challenge. Several approaches to optimizing the reliability and efficiency of optoelectronic devices using semiconducting nanocrystals are explored herein. Force microscopy is used to investigate charge behavior in nanocrystal films. Plasmonic structures are lithographically defined to enhance electric field and thus charge collection efficiency in two-electrode nanocrystal devices illuminated at plasmonically resonant wavelengths. Graphene substrates are shown to couple electronically with nanocrystal films, improving device conduction while maintaining carrier quantum confinement within the nanocrystal. And finally, the occupancy of charge carrier traps is shown to both directly impact the temperature-dependent photocurrent behavior, and be tunable using a combination of illumination and electric field treatments. Trap population manipulation is robustly demonstrated and verified using a variety of wavelength, intensity, and time-dependent measurements of photocurrent in nanogap nanocrystal devices, emphasizing the importance of measurement history and the possibility of advanced device behavior tuning based on desired operating conditions. Each of these experiments reveals a path toward understanding and optimizing semiconducting nanocrystal optoelectronic devices.

  17. The potential of cellulose nanocrystals in tissue engineering strategies.

    PubMed

    Domingues, Rui M A; Gomes, Manuela E; Reis, Rui L

    2014-07-14

    Cellulose nanocrystals (CNCs) are a renewable nanosized raw material that is drawing a tremendous level of attention from the materials community. These rod-shaped nanocrystals that can be produced from a variety of highly available and renewable cellulose-rich sources are endowed with exceptional physicochemical properties which have promoted their intensive exploration as building blocks for the design of a broad range of new materials in the past few decades. However, only recently have these nanosized substrates been considered for bioapplications following the knowledge on their low toxicity and ecotoxicological risk. This Review provides an overview on the recent developments on CNC-based functional biomaterials with potential for tissue engineering (TE) applications, focusing on nanocomposites obtained through different processing technologies usually employed in the fabrication of TE scaffolds into various formats, namely, dense films and membranes, hierarchical three-dimensional (3D) porous constructs (micro/nanofibers mats, foams and sponges), and hydrogels. Finally, while highlighting the major achievements and potential of the reviewed work on cellulose nanocrystals, alternative applications for some of the developed materials are provided, and topics for future research to extend the use of CNCs-based materials in the scope of the TE field are identified.

  18. Gas-phase synthesis of semiconductor nanocrystals and its applications

    NASA Astrophysics Data System (ADS)

    Mandal, Rajib

    Luminescent nanomaterials is a newly emerging field that provides challenges not only to fundamental research but also to innovative technology in several areas such as electronics, photonics, nanotechnology, display, lighting, biomedical engineering and environmental control. These nanomaterials come in various forms, shapes and comprises of semiconductors, metals, oxides, and inorganic and organic polymers. Most importantly, these luminescent nanomaterials can have different properties owing to their size as compared to their bulk counterparts. Here we describe the use of plasmas in synthesis, modification, and deposition of semiconductor nanomaterials for luminescence applications. Nanocrystalline silicon is widely known as an efficient and tunable optical emitter and is attracting great interest for applications in several areas. To date, however, luminescent silicon nanocrystals (NCs) have been used exclusively in traditional rigid devices. For the field to advance towards new and versatile applications for nanocrystal-based devices, there is a need to investigate whether these NCs can be used in flexible and stretchable devices. We show how the optical and structural/morphological properties of plasma-synthesized silicon nanocrystals (Si NCs) change when they are deposited on stretchable substrates made of polydimethylsiloxane (PDMS). Synthesis of these NCs was performed in a nonthermal, low-pressure gas phase plasma reactor. To our knowledge, this is the first demonstration of direct deposition of NCs onto stretchable substrates. Additionally, in order to prevent oxidation and enhance the luminescence properties, a silicon nitride shell was grown around Si NCs. We have demonstrated surface nitridation of Si NCs in a single step process using non?thermal plasma in several schemes including a novel dual-plasma synthesis/shell growth process. These coated NCs exhibit SiNx shells with composition depending on process parameters. While measurements including

  19. Binary superlattices from colloidal nanocrystals and giant polyoxometalate clusters.

    PubMed

    Bodnarchuk, Maryna I; Erni, Rolf; Krumeich, Frank; Kovalenko, Maksym V

    2013-04-10

    We report a new kind of long-range ordered binary superlattices comprising atomically defined inorganic clusters and colloidally synthesized nanocrystals. In a model system, we combined surfactant-encapsulated, nearly spherical giant polyoxometalate clusters containing 2.9 nm polyoxomolybdate or 2.5 nm polyoxovanadomolybdate cores with monodisperse colloidal semiconductor nanocrystals (PbS, CdSe, PbS/CdS; 4-11 nm). The results are rationalized on the basis of dense packing principles of sterically stabilized particles with predominantly hard-spherelike interparticle interactions. By varying the size-ratios and relative concentrations of constituents, we obtained known thermodynamically stable binary packings of hard-spheres such as NaCl, AlB2, and NaZn13 lattices and also CaCu5-type lattice and aperiodic quasicrystals with 12-fold symmetry. These results suggest that other kinds of cluster materials such as fullerenes and magic-sized metallic and semiconductor clusters can also be integrated into supramolecular assemblies with nanocrystals. Furthermore, synergistic effects are expected from the combination of redox and catalytic properties of polyoxometalates with excitonic and plasmonic properties of inorganic nanocrystals.

  20. Temperature effect on elastic modulus of thin films and nanocrystals

    NASA Astrophysics Data System (ADS)

    Liang, Lihong; Li, Meizhi; Qin, Fuqi; Wei, Yueguang

    2013-02-01

    The stability of nanoscale devices is directly related to elasticity and the effect of temperature on the elasticity of thin films and nanocrystals. The elastic instability induced by rising temperature will cause the failure of integrated circuits and other microelectronic devices in service. The temperature effect on the elastic modulus of thin films and nanocrystals is unclear although the temperature dependence of the modulus of bulk materials has been studied for over half a century. In this paper, a theoretical model of the temperature-dependent elastic modulus of thin films and nanocrystals is developed based on the physical definition of the modulus by considering the size effect of the related cohesive energy and the thermal expansion coefficient. Moreover, the temperature effect on the modulus of Cu thin films is simulated by the molecular dynamics method. The results indicate that the elastic modulus decreases with increasing temperature and the rate of the modulus decrease increases with reducing thickness of thin films. The theoretical predictions based on the model are consistent with the results of computational simulations, semi-continuum calculations and the experimental measurements for Cu, Si thin films and Pd nanocrystals.

  1. Two-Photon-Pumped Perovskite Semiconductor Nanocrystal Lasers.

    PubMed

    Xu, Yanqing; Chen, Qi; Zhang, Chunfeng; Wang, Rui; Wu, Hua; Zhang, Xiaoyu; Xing, Guichuan; Yu, William W; Wang, Xiaoyong; Zhang, Yu; Xiao, Min

    2016-03-23

    Two-photon-pumped lasers have been regarded as a promising strategy to achieve frequency up-conversion for situations where the condition of phase matching required by conventional approaches cannot be fulfilled. However, their practical applications have been hindered by the lack of materials holding both efficient two-photon absorption and ease of achieving population inversion. Here, we show that this challenge can be tackled by employing colloidal nanocrystals of perovskite semiconductors. We observe highly efficient two-photon absorption (with a cross section of 2.7 × 10(6) GM) in toluene solutions of CsPbBr3 nanocrystals that can excite large optical gain (>500 cm(-1)) in thin films. We have succeeded in demonstrating stable two-photon-pumped lasing at a remarkable low threshold by coupling CsPbBr3 nanocrystals with microtubule resonators. Our findings suggest perovskite nanocrystals can be used as excellent gain medium for high-performance frequency-up-conversion lasers toward practical applications.

  2. 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

  3. The Size and Shape dependence of the Surface Free Energy of Nanocrystals

    NASA Astrophysics Data System (ADS)

    Abdul-Hafidh, Esam

    Based on many recent reports, it became possible to control the synthesis of nanomaterials with certain sizes and shapes. A theoretical model to investigate the effect of size and shape on the surface free energy of nanocrystals is worked out in this research. The model is applied to a general shape and size nanocrsytal designated by a shape factor. The model considers all nanocrystals with different morphologies (but with the same shape factor) to be the same. The results were tested for gold and silver. The surface free energy was found to decrease with size for spherical nanocrystals. On the other hand, the surface free energy is enhanced for non-spherical nanocrystals. These findings are in qualitative agreement with previous experimental and theoretical predictions. The results pave the road to manufacture controlled- mechanical properties materials.

  4. Identification and dynamics of polyglycine II nanocrystals in Argiope trifasciata flagelliform silk.

    PubMed

    Perea, G B; Riekel, C; Guinea, G V; Madurga, R; Daza, R; Burghammer, M; Hayashi, C; Elices, M; Plaza, G R; Pérez-Rigueiro, J

    2013-10-28

    Spider silks combine a significant number of desirable characteristics in one material, including large tensile strength and strain at breaking, biocompatibility, and the possibility of tailoring their properties. Major ampullate gland silk (MAS) is the most studied silk and their properties are explained by a double lattice of hydrogen bonds and elastomeric protein chains linked to polyalanine β-nanocrystals. However, many basic details regarding the relationship between composition, microstructure and properties in silks are still lacking. Here we show that this relationship can be traced in flagelliform silk (Flag) spun by Argiope trifasciata spiders after identifying a phase consisting of polyglycine II nanocrystals. The presence of this phase is consistent with the dominant presence of the -GGX- and -GPG- motifs in its sequence. In contrast to the passive role assigned to polyalanine nanocrystals in MAS, polyglycine II nanocrystals can undergo growing/collapse processes that contribute to increase toughness and justify the ability of Flag to supercontract.

  5. Identification and dynamics of polyglycine II nanocrystals in Argiope trifasciata flagelliform silk

    NASA Astrophysics Data System (ADS)

    Perea, G. B.; Riekel, C.; Guinea, G. V.; Madurga, R.; Daza, R.; Burghammer, M.; Hayashi, C.; Elices, M.; Plaza, G. R.; Pérez-Rigueiro, J.

    2013-10-01

    Spider silks combine a significant number of desirable characteristics in one material, including large tensile strength and strain at breaking, biocompatibility, and the possibility of tailoring their properties. Major ampullate gland silk (MAS) is the most studied silk and their properties are explained by a double lattice of hydrogen bonds and elastomeric protein chains linked to polyalanine β-nanocrystals. However, many basic details regarding the relationship between composition, microstructure and properties in silks are still lacking. Here we show that this relationship can be traced in flagelliform silk (Flag) spun by Argiope trifasciata spiders after identifying a phase consisting of polyglycine II nanocrystals. The presence of this phase is consistent with the dominant presence of the -GGX- and -GPG- motifs in its sequence. In contrast to the passive role assigned to polyalanine nanocrystals in MAS, polyglycine II nanocrystals can undergo growing/collapse processes that contribute to increase toughness and justify the ability of Flag to supercontract.

  6. 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.

  7. "Nanocrystal bilayer for tandem catalysis"

    SciTech Connect

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

    2011-01-24

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

  8. Origin of asymmetric broadening of Raman peak profiles in Si nanocrystals

    PubMed Central

    Gao, Yukun; Yin, Penggang

    2017-01-01

    The asymmetric peak broadening towards the low-frequency side of the Raman-active mode of Si nanocrystals with the decreasing size has been extensively reported in the literatures. In this study, an atomic coordination model is developed to study the origin of the ubiquitous asymmetric peak on the optical phonon fundamental in the Raman spectra of Si nanocrystals. Our calculation results accurately replicate the line shape of the experimentally measured optical Raman curves. More importantly, it is revealed that the observed asymmetric broadening is mainly caused by the surface bond contraction and the quantum confinement. PMID:28240325

  9. Origin of asymmetric broadening of Raman peak profiles in Si nanocrystals

    NASA Astrophysics Data System (ADS)

    Gao, Yukun; Yin, Penggang

    2017-02-01

    The asymmetric peak broadening towards the low-frequency side of the Raman-active mode of Si nanocrystals with the decreasing size has been extensively reported in the literatures. In this study, an atomic coordination model is developed to study the origin of the ubiquitous asymmetric peak on the optical phonon fundamental in the Raman spectra of Si nanocrystals. Our calculation results accurately replicate the line shape of the experimentally measured optical Raman curves. More importantly, it is revealed that the observed asymmetric broadening is mainly caused by the surface bond contraction and the quantum confinement.

  10. Highly efficient (infra)red conversion of InGaN light emitting diodes by nanocrystals, enhanced by colour selective mirrors.

    PubMed

    Roither, Jürgen; Kovalenko, Maksym V; Heiss, Wolfgang

    2008-09-03

    Colloidal nanocrystal layers deposited onto the enclosure of InGaN light emitting diodes are demonstrated to operate as nano-phosphors for colour conversion with high colour stability. Depending on the choice of the nanocrystal material (either CdSe/ZnS or PbS nanocrystals are applied), the diode emission at 470 nm is converted to red or to infrared light, with similar quantum efficiencies. The colour conversion is further improved by dielectric mirrors with high reflectivity at the emission band of the nanocrystals, resulting in an almost doubling of the nanocrystal light extraction from the devices, which increases the nanocrystal device efficiency up to 19.1%.

  11. Effect of ligand exchange of Cu2ZnSnS4 nanocrystals on the charge transport and photovoltaic performance of nanostructured depleted bulk heterojunction solar cell

    NASA Astrophysics Data System (ADS)

    Zhang, Zhuo-Xi; Zhou, Zheng-Ji; Bai, Bing; Liu, Ming-Hua; Zhou, Wen-Hui; Kou, Dong-Xing; Wu, Si-Xin

    2015-12-01

    Cu2ZnSnS4 (CZTS) nanocrystals combining the advantage of feasible solution-phase synthesis and processing are perceived as promising materials for application in efficient, low-cost photovoltaic technology. Herein, we have got surfactant-free CZTS nanocrystals by a novel ligand exchange method, and the obtained CZTS nanocrystals were deposited onto ZnO nanorod arrays to construct depleted bulk heterojunction solar cell. The all-inorganic CZTS nanocrystal solar cells demonstrated a remarkable improvement in J sc (from 8.14 to 13.97 mA/cm2) and power conversion efficiency (from 1.83 to 3.34 %) compared with surfactant-capped CZTS nanocrystals. Using surface photovoltage spectrum, the influence of ligand exchange of CZTS nanocrystals on the charge transport and photovoltaic performance of the nanostructured CZTS solar cells was discussed.

  12. Selective epitaxial growth of zinc blende-derivative on wurtzite-derivative: the case of polytypic Cu2CdSn(S1-xSex)4 nanocrystals

    NASA Astrophysics Data System (ADS)

    Wu, Liang; Fan, Feng-Jia; Gong, Ming; Ge, Jin; Yu, Shu-Hong

    2014-02-01

    Polytypic nanocrystals with zinc blende (ZB) cores and wurtzite (WZ) arms, such as tetrapod and octopod nanocrystals, have been widely reported. However, polytypic nanocrystals with WZ cores and ZB arms or ends have been rarely reported. Here, we report a facile, solution-based approach to the synthesis of polytypic Cu2CdSn(S1-xSex)4 (CCTSSe) nanocrystals with ZB-derivative selectively engineered on (000+/-2)WZ facets of WZ-derived cores. Accordingly, two typical morphologies, i.e., bullet-like nanocrystals with a WZ-derivative core and one ZB-derivative end, and rugby ball-like nanocrystals with a WZ-derivative core and two ZB-derivative ends, can be selectively prepared. The epitaxial growth mechanism is confirmed by the time-dependent experiments. The ratio of rugby ball-like and bullet-like polytypic CCTSSe nanocrystals can be tuned through changing the amount of Cd precursor to adjust the reactivity difference between (0002)WZ and (000-2)WZ facets. These unique polytypic CCTSSe nanocrystals may find applications in energetic semiconducting materials for energy conversion in the future.Polytypic nanocrystals with zinc blende (ZB) cores and wurtzite (WZ) arms, such as tetrapod and octopod nanocrystals, have been widely reported. However, polytypic nanocrystals with WZ cores and ZB arms or ends have been rarely reported. Here, we report a facile, solution-based approach to the synthesis of polytypic Cu2CdSn(S1-xSex)4 (CCTSSe) nanocrystals with ZB-derivative selectively engineered on (000+/-2)WZ facets of WZ-derived cores. Accordingly, two typical morphologies, i.e., bullet-like nanocrystals with a WZ-derivative core and one ZB-derivative end, and rugby ball-like nanocrystals with a WZ-derivative core and two ZB-derivative ends, can be selectively prepared. The epitaxial growth mechanism is confirmed by the time-dependent experiments. The ratio of rugby ball-like and bullet-like polytypic CCTSSe nanocrystals can be tuned through changing the amount of Cd precursor

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

    PubMed

    Pileni, Marie-Paule

    2017-08-15

    The spontaneous assembly of uniform-sized globular entities into ordered arrays is a universal phenomenon observed for objects with diameters spanning a broad range of length scales. These extend from the atomic scale (10(-8) cm), through molecular and macromolecular scales with proteins, synthetic low polymers, and colloidal crystals (∼10(-6) cm), to the wavelength of visible light (∼10(-5) cm). The associated concepts of sphere packing have had an influence in diverse fields ranging from pure geometrical analysis to architectural models or ideals. Self-assembly of atoms, supramolecules, or nanocrystals into ordered functional superstructures is a universal process and prevalent topic in science. About five billion years ago in the early solar system, highly uniform magnetite particles of a few hundred nanometers in size were assembled in 3D arrays.1 Thirty million years ago, silicate particles with submicrometer size were self-organized in the form of opal.2 Opal is colorless when composed of disordered silicate microparticles whereas it shows specific reflectivity when particles order in arrays. Nowadays, nanocrystals, characterized by a narrow size distribution and coated with alkyl chains to maintain their integrity, self-assemble to form crystallographic orders called supracrystals. Nanocrystals and supracrystals are arrangements of highly ordered atoms and nanocrystals, respectively. The morphologies of nanocrystals, supracrystals, and minerals are similar at various scales from nanometer to millimeter scale.3,4 Such suprastructures, which enable the design of novel materials, are expected to become one of the main driving forces in material research for the 21st century.5,6 Nanocrystals vibrate coherently in a supracrystal as atoms in a nanocrystal. Longitudinal acoustic phonons are detected in supracrystals as with atomic crystals, where longitudinal acoustic phonons propagate through coherent movements of atoms of the lattice out of their equilibrium

  14. Fundamentals of Welding. Teacher Edition.

    ERIC Educational Resources Information Center

    Fortney, Clarence; And Others

    These instructional materials assist teachers in improving instruction on the fundamentals of welding. The following introductory information is included: use of this publication; competency profile; instructional/task analysis; related academic and workplace skills list; tools, materials, and equipment list; and 27 references. Seven units of…

  15. Fundamentals of Welding. Teacher Edition.

    ERIC Educational Resources Information Center

    Fortney, Clarence; And Others

    These instructional materials assist teachers in improving instruction on the fundamentals of welding. The following introductory information is included: use of this publication; competency profile; instructional/task analysis; related academic and workplace skills list; tools, materials, and equipment list; and 27 references. Seven units of…

  16. The study of oriented aggregation: A non-classical nanocrystal growth mechanism

    NASA Astrophysics Data System (ADS)

    Burrows, Nathan Dennis

    Oriented aggregation is a nonclassical crystal growth mechanism resulting in new secondary nanoparticles composed of crystallographically aligned primary crystallites. These secondary crystals often have unique and symmetry-defying morphologies, can be twinned, and can contain stacking faults and other significant defects. A wide range of important materials, such as titanium dioxide, iron oxides, selenides and sulfides, and metal oxyhydroxides, are known to grow by oriented aggregation under certain conditions. Evidence for oriented aggregation also has been observed in natural materials. However questions remain about what conditions are the most importing in facilitating purposeful control over nanoparticle size, size distribution, and morphology. Kinetic models for oriented aggregation point to important variables such as ionic strength, pH, temperature, and choice of dispersing solvent as being the key or keys to gaining control of this natural phenomenon and moving it towards a tool to be used in designing novel nanomaterials. The main technique used in this research is transmission electron microscopy with temporal resolution to characterize the population of growing nanocrystals. Cryogenic transmission electron microscopy is employed to observe the various stages of crystal growth. With extensive image analysis, it is possible to determine the kinetics of growth and the effects of systematically changing these key growth conditions. Additional complimentary techniques are employed, such as dynamic light scattering as well as various methods of characterization, such as powder X-ray diffraction. As our fundamental understanding of oriented aggregation improves, novel and complex functional materials are expected to emerge.

  17. Fundamentals of Structural Geology

    NASA Astrophysics Data System (ADS)

    Pollard, David D.; Fletcher, Raymond C.

    2005-09-01

    Fundamentals of Structural Geology provides a new framework for the investigation of geological structures by integrating field mapping and mechanical analysis. Assuming a basic knowledge of physical geology, introductory calculus and physics, it emphasizes the observational data, modern mapping technology, principles of continuum mechanics, and the mathematical and computational skills, necessary to quantitatively map, describe, model, and explain deformation in Earth's lithosphere. By starting from the fundamental conservation laws of mass and momentum, the constitutive laws of material behavior, and the kinematic relationships for strain and rate of deformation, the authors demonstrate the relevance of solid and fluid mechanics to structural geology. This book offers a modern quantitative approach to structural geology for advanced students and researchers in structural geology and tectonics. It is supported by a website hosting images from the book, additional colour images, student exercises and MATLAB scripts. Solutions to the exercises are available to instructors. The book integrates field mapping using modern technology with the analysis of structures based on a complete mechanics MATLAB is used to visualize physical fields and analytical results and MATLAB scripts can be downloaded from the website to recreate textbook graphics and enable students to explore their choice of parameters and boundary conditions The supplementary website hosts color images of outcrop photographs used in the text, supplementary color images, and images of textbook figures for classroom presentations The textbook website also includes student exercises designed to instill the fundamental relationships, and to encourage the visualization of the evolution of geological structures; solutions are available to instructors

  18. Intermetallic Nanocrystals: Syntheses and Catalytic Applications.

    PubMed

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

    2017-02-24

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

  19. 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.

  20. Terahertz Properties of Cellulose Nanocrystals and Films

    NASA Astrophysics Data System (ADS)

    Carnio, B. N.; Ahvazi, B.; Elezzabi, A. Y.

    2016-03-01

    Terahertz (THz) radiation properties of cellulose nanocrystal (CNC) films, a CNC powder, and a dissolving pulp film are examined using THz time-domain spectroscopy. The relative permittivity (real component) of the CNC samples are found to vary between 1.78 and 3.81, over the frequency range of 0.2-1.5 THz, despite the fact that they are made from the same linear chain of glucose monomers. The results show that the permittivity is strongly dependent on the source from which the CNC glucose monomers are extracted, as well as on the drying process used. The THz loss tangent (0.043 < tan( δ) < 0.145), absorption coefficient (3.5 cm-1 < α < 63.7 cm-1), and growth-varying permittivity, combined with other appealing thermal and mechanical characteristic of CNC, make such material attractive for use in both passive and potential THz bandwidth electronic components.

  1. Hydrothermal Gelation of Aqueous Cellulose Nanocrystal Suspensions.

    PubMed

    Lewis, Lev; Derakhshandeh, Maziar; Hatzikiriakos, Savvas G; Hamad, Wadood Y; MacLachlan, Mark J

    2016-08-08

    We report the facile preparation of gels from the hydrothermal treatment of suspensions of cellulose nanocrystals (CNCs). The properties of the hydrogels have been investigated by rheology, electron microscopy, and spectroscopy with respect to variation in the temperature, time, and CNC concentration used in preparation. Desulfation of the CNCs at high temperature appears to be responsible for the gelation of the CNCs, giving highly porous networks. The viscosity and storage modulus of the gels was shown to increase when samples were prepared at higher treatment temperature. Considering the wide natural abundance and biocompatibility of CNCs, this simple, green approach to CNC-based hydrogels is attractive for producing materials that can be used in drug delivery, insulation, and as tissue scaffolds.

  2. Cellulose nanocrystals reinforced foamed nitrile rubber nanocomposites.

    PubMed

    Chen, Yukun; Zhang, Yuanbing; Xu, Chuanhui; Cao, Xiaodong

    2015-10-05

    Research on foamed nitrile rubber (NBR)/cellulose nanocrystals (CNs) nanocomposites is rarely found in the literatures. In this paper, CNs suspension and NBR latex was mixed to prepared the foamed NBR/CNs nanocomposites. We found that the CNs mainly located in the cell walls, effectively reinforcing the foamed NBR. The strong interaction between the CNs and NBR matrix restricted the mobility of NBR chains surrounding the CNs, hence increasing the crosslink density of the NBR matrix. CNs exhibited excellent reinforcement on the foamed NBR: a remarkable increase nearly 76% in the tensile strength of the foamed nanocomposites was achieved with a load of only 15 phr CNs. Enhanced mechanical properties make the foamed NBR/CNs nanocomposites a promising damping material for industrial applications with a potential to reduce the petroleum consumption.

  3. Unique Challenges Accompany Thick-Shell CdSe/nCdS (n > 10) Nanocrystal Synthesis

    SciTech Connect

    Guo, Y; Marchuk, K; Abraham, R; Sampat, S; Abraham, R.; Fang, N; Malko, AV; Vela, J

    2011-12-23

    Thick-shell CdSe/nCdS (n {ge} 10) nanocrystals were recently reported that show remarkably suppressed fluorescence intermittency or 'blinking' at the single-particle level as well as slow rates of Auger decay. Unfortunately, whereas CdSe/nCdS nanocrystal synthesis is well-developed up to n {le} 6 CdS monolayers (MLs), reproducible syntheses for n {ge} 10 MLs are less understood. Known procedures sometimes result in homogeneous CdS nucleation instead of heterogeneous, epitaxial CdS nucleation on CdSe, leading to broad and multimodal particle size distributions. Critically, obtained core/shell sizes are often below those desired. This article describes synthetic conditions specific to thick-shell growth (n {ge} 10 and n {ge} 20 MLs) on both small (sub2 nm) and large (>4.5 nm) CdSe cores. We find added secondary amine and low concentration of CdSe cores and molecular precursors give desired core/shell sizes. Amine-induced, partial etching of CdSe cores results in apparent shell-thicknesses slightly beyond those desired, especially for very-thick shells (n {ge} 20 MLs). Thermal ripening and fast precursor injection lead to undesired homogeneous CdS nucleation and incomplete shell growth. Core/shells derived from small CdSe (1.9 nm) have longer PL lifetimes and more pronounced blinking at single-particle level compared with those derived from large CdSe (4.7 nm). We expect our new synthetic approach will lead to a larger throughput of these materials, increasing their availability for fundamental studies and applications.

  4. Formation of Organic Molecular Nanocrystals under Rigid Confinement with Analysis by Solid State NMR.

    PubMed

    Yang, X; Ong, T C; Michaelis, V K; Heng, S; Huang, J; Griffin, R G; Myerson, A S

    2014-10-21

    Crystallization in rigid confinement is a promising method to obtain organic molecular nanocrystals. However, the crystallization behavior and the related characterization methods are not well studied. Here we present a systematic study of the nucleation of organic molecular nanocrystals in rigid pores. Four different compounds were studied, ibuprofen, fenofibrate, griseofulvin, and indomethacin, which range from simple to complex molecules. Solid-state Nuclear Magnetic Resonance (NMR) was employed to analyse the structure of these compounds inside pores which are difficult to characterize by other analytical methods. We successfully demonstrated the production of nano-crystalline ibuprofen, fenofibrate and griseofulvin in porous silica particles with ~ 40 nm pores. These nanocrystals showed significant enhancement in dissolution rates. These results help advance the fundamental understanding of nucleation under rigid confinement and may lead to potential applications in developing new formulations in the pharmaceutical industry.

  5. Formation of Organic Molecular Nanocrystals under Rigid Confinement with Analysis by Solid State NMR

    PubMed Central

    Yang, X.; Ong, T. C.; Michaelis, V. K.; Heng, S.; Huang, J.; Griffin, R. G.; Myerson, A. S.

    2014-01-01

    Crystallization in rigid confinement is a promising method to obtain organic molecular nanocrystals. However, the crystallization behavior and the related characterization methods are not well studied. Here we present a systematic study of the nucleation of organic molecular nanocrystals in rigid pores. Four different compounds were studied, ibuprofen, fenofibrate, griseofulvin, and indomethacin, which range from simple to complex molecules. Solid-state Nuclear Magnetic Resonance (NMR) was employed to analyse the structure of these compounds inside pores which are difficult to characterize by other analytical methods. We successfully demonstrated the production of nano-crystalline ibuprofen, fenofibrate and griseofulvin in porous silica particles with ~ 40 nm pores. These nanocrystals showed significant enhancement in dissolution rates. These results help advance the fundamental understanding of nucleation under rigid confinement and may lead to potential applications in developing new formulations in the pharmaceutical industry. PMID:25258590

  6. Invictus: Five Advocacy Presentations on Educational Fiscal Policy in Illinois Including Material Relating to the Attempt To Establish Education as a Fundamental Constitutional Right in 1992.

    ERIC Educational Resources Information Center

    Hickrod, George Alan Karnes Wallis; Pruyne, Gwen, Ed.

    This monograph contains five presentations delivered during the course of an attempt made in November 1992 to amend the state constitution of Illinois in such a way as to make education a fundamental constitutional right. The effort failed to garner the 60 percent of the vote required to pass the amendment. These presentations made a strong…

  7. Incorporation of organic crystals into the interspace of oriented nanocrystals: morphologies and properties.

    PubMed

    Munekawa, Yurika; Oaki, Yuya; Sato, Kosuke; Imai, Hiroaki

    2015-02-28

    Oriented nanocrystals, as seen in biominerals, have both the macroscopic hierarchical morphologies and the nanoscale interspace among the unit crystals. Here we studied the incorporation effects of the specific interspace in the oriented nanocrystals on the morphologies, properties, and applications of organic crystals. Organic crystals, such as 9-vinylcarbazole (VCz), azobenzene (AB), and pyrene (PY), were introduced into the specific interspace of oriented nanocrystals from the melts. The morphologies and properties of the incorporated organic crystals were systematically studied in these model cases. The incorporation of the organic crystals provided the composites with the original oriented nanocrystals. The incorporated organic crystals formed the single-crystalline structures even in the nanoscale interspace. The melts of the organic compounds were crystallized and grown in the interspace of the original materials. The incorporated organic crystals showed the specific phase transition behavior. The freezing points of the organic crystals were raised by the incorporation into the nanospace while the melting points were not changed. The hierarchical morphologies of the organic crystals were obtained after the dissolution of the original materials. The hierarchical morphologies of the original materials were replicated to the organic crystals. The incorporated organic crystal was polymerized without deformation of the hierarchical morphologies. The hierarchical polymer can be applied to the donor material for the generation of a larger amount of the charge-transfer complex with the acceptor molecule than the commercial polymer microparticles. The present work shows the potential use of the nanoscale interspace generated in the oriented nanocrystals.

  8. Final Report of “Collaborative research: Fundamental science of low temperature plasma-biological material interactions” (Award# DE-SC0005105)

    SciTech Connect

    Oehrlein, Gottlieb S.; Seog, Joonil; Graves, David; Chu, J. -W.

    2014-09-24

    temperature plasma sources with modified geometry where radical induced interactions generally dominate due to short mean free paths of ions and VUV photons. In these conditions we demonstrated the importance of environmental interactions of plasma species when APP sources are used to modify biomolecules. This is evident from both gas phase characterization data and in-situ surface characterization of treated biomolecules. Environmental interactions can produce unexpected outcomes due to the complex reactions of reactive species with the atmosphere which determine the composition of reactive fluxes and atomistic changes in biomolecules. Overall, this work elucidated a richer spectrum of scientific opportunities and challenges for the field of low temperature plasma-biomolecule surface interactions than initially anticipated, in particular, for plasma sources operating at atmospheric pressure. The insights produced in this work, e.g. demonstration of the importance of environmental interactions, are generally important for applications of APP to materials modifications. Thus one major contributions of this research has been the establishment of methodologies to study the interaction of plasma with bio-molecules in a systemic and rigorous manner. In particular, our studies of atmospheric pressure plasma sources using very well-defined experimental conditions enabled us to correlate atomistic surface modifications of biomolecules with changes in their biological function. The clarification of the role of ions, VUV photons and radicals in deactivation of biomolecules during low pressure and atmospheric pressure plasma-biomolecule interaction has broad implications, e.g. for the emerging field of plasma medicine. The development of methods to detect the effects of plasma treatment on immune-active biomolecules will lay a fundamental foundation to enhance our understanding of the effect of plasma on biological systems. be helpful in many future studies.

  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. 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.

  11. Hydrothermal Synthesis of Yttria-Stabilized Zirconia Nanocrystals with Controlled Yttria Content.

    PubMed

    Sato, Kazuyoshi; Horiguchi, Kazuya; Nishikawa, Taku; Yagishita, Sadahiro; Kuruma, Kazuo; Murakami, Takeshi; Abe, Hiroya

    2015-08-17

    In this study, we demonstrate for the first time the hydrothermal synthesis of yttria-stabilized zirconia (YSZ) nanocrystals with controlled yttria content (x = 3-12 mol %; xYSZ) with negligible aggregation from aqueous solution. The nanocrystals were grown via the hydrothermal treatment of basic Zr(IV) and Y(III) carbonate complex aqueous solutions in the presence of a cationic ligand, N(CH3)4(+). The nanocrystals were characterized in detail by dynamic light scattering, ζ-potential measurement, X-ray diffraction, specific surface area measurement based on the Brunauer-Emmett-Teller theory, transmission electron microscopy, energy dispersive X-ray spectroscopy, and Raman spectroscopy. Shorter reaction times and higher Y2O3 content produce aqueous solutions with higher transparencies containing nanocrystals with sizes of 10 nm or less. Nanocrystals with the target composition were obtained by hydrothermal reaction for longer than 3 h, regardless of the Y2O3 content. The main phase is tetragonal for (3-6)YSZ and cubic with disordered oxygen vacancies for (8-12)YSZ. The characteristics of the nanocrystalline material synthesized are consistent with those of bulk YSZ crystals, indicating the growth of high-quality nanocrystals.

  12. Self-assembly of PbTe quantum dots into nanocrystal superlattices and glassy films.

    PubMed

    Urban, Jeffrey J; Talapin, Dmitri V; Shevchenko, Elena V; Murray, Christopher B

    2006-03-15

    Monodisperse lead telluride (PbTe) nanocrystals ranging from approximately 4 to 10 nm in diameter are synthesized to provide quantum dot building blocks for the design of novel materials for electronic applications. Two complementary synthetic approaches are developed that enable either (1) isolation of small quantities of nanocrystals of many different sizes or (2) the production of up to 10 g of a single nanocrystal size. PbTe nanocrystals are characterized by transmission electron microscopy (TEM), X-ray diffraction (XRD), and optical absorption. Assembly of PbTe nanocrystals is directed to prepare nanocrystal solids that display either short-range (glassy solids) or long-range (superlattices) packing order by varying deposition conditions. Film order and average interparticle spacing are analyzed with grazing-incidence small-angle X-ray scattering (GISAXS) and high-resolution scanning electron microscopy (HRSEM). We perform the first optical and electronic studies of PbTe solids and demonstrate that chemical activation of these films enhances conductivity by approximately 9-10 orders of magnitude while preserving their quantum dot nature.

  13. Binary nanocrystal superlattice membranes self-assembled at the liquid-air interface.

    PubMed

    Dong, Angang; Chen, Jun; Vora, Patrick M; Kikkawa, James M; Murray, Christopher B

    2010-07-22

    The spontaneous organization of multicomponent micrometre-sized colloids or nanocrystals into superlattices is of scientific importance for understanding the assembly process on the nanometre scale and is of great interest for bottom-up fabrication of functional devices. In particular, co-assembly of two types of nanocrystal into binary nanocrystal superlattices (BNSLs) has recently attracted significant attention, as this provides a low-cost, programmable way to design metamaterials with precisely controlled properties that arise from the organization and interactions of the constituent nanocrystal components. Although challenging, the ability to grow and manipulate large-scale BNSLs is critical for extensive exploration of this new class of material. Here we report a general method of growing centimetre-scale, uniform membranes of BNSLs that can readily be transferred to arbitrary substrates. Our method is based on the liquid-air interfacial assembly of multicomponent nanocrystals and circumvents the limitations associated with the current assembly strategies, allowing integration of BNSLs on any substrate for the fabrication of nanocrystal-based devices. We demonstrate the construction of magnetoresistive devices by incorporating large-area (1.5 mm x 2.5 mm) BNSL membranes; their magnetotransport measurements clearly show that device magnetoresistance is dependent on the structure (stoichiometry) of the BNSLs. The ability to transfer BNSLs also allows the construction of free-standing membranes and other complex architectures that have not been accessible previously.

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

    PubMed

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

    2017-02-28

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

  15. Nanocrystal and surface alloy properties of bimetallic Gold-Platinum nanoparticles

    PubMed Central

    Mott, Derrick; Luo, Jin; Smith, Andrew; Njoki, Peter N; Wang, Lingyan

    2007-01-01

    We report on the correlation between the nanocrystal and surface alloy properties with the bimetallic composition of gold-platinum(AuPt) nanoparticles. The fundamental understanding of whether the AuPt nanocrystal core is alloyed or phase-segregated and how the surface binding properties are correlated with the nanoscale bimetallic properties is important not only for the exploitation of catalytic activity of the nanoscale bimetallic catalysts, but also to the general exploration of the surface or interfacial reactivities of bimetallic or multimetallic nanoparticles. The AuPt nanoparticles are shown to exhibit not only single-phase alloy character in the nanocrystal, but also bimetallic alloy property on the surface. The nanocrystal and surface alloy properties are directly correlated with the bimetallic composition. The FTIR probing of CO adsorption on the bimetallic nanoparticles supported on silica reveals that the surface binding sites are dependent on the bimetallic composition. The analysis of this dependence further led to the conclusion that the relative Au-atop and Pt-atop sites for the linear CO adsorption on the nanoparticle surface are not only correlated with the bimetallic composition, but also with the electronic effect as a result of the d-band shift of Pt in the bimetallic nanocrystals, which is the first demonstration of the nanoscale core-surface property correlation for the bimetallic nanoparticles over a wide range of bimetallic composition.

  16. Grain boundary and lattice diffusion in nanocrystal α-iron: An atomistic simulation study

    NASA Astrophysics Data System (ADS)

    Mohammadzadeh, Roghayeh; Mohammadzadeh, Mina

    2017-09-01

    To obtain fundamental understanding on the effect of grain boundaries on the diffusion kinetics, molecular dynamics simulations (MD) were carried out on single crystal and nanocrystal (with a mean grain size of 2.5 nm) bcc iron using the second nearest-neighbor modified embedded atom method (2NN-MEAM) interatomic potential. Self-diffusion coefficient in single crystal and nanocrystal samples were calculated in the temperature range from 350 K to 1000 K. A temperature-dependence of the diffusion coefficient according to the Arrhenius law was obtained for both lattice and grain boundary diffusion. By doing so, activation energies as well as pre-exponential factors were derived from the diffusion coefficients and compared to experimental data. MD simulation results show that diffusion rate of iron atoms in nanocrystal sample is 6 to 28 orders of magnitude greater than single crystal. The trajectory of iron atoms during diffusion process verified that diffusion occurs mostly in the grain boundaries of nanocrystal iron; suggesting that grain boundary diffusion is dominant in nanocrystal iron. Based on the obtained results pure grain boundary diffusion coefficient was calculated.

  17. Influence of Binders and Solvents on Stability of Ru/RuOx Nanoparticles on ITO Nanocrystals as Li-O2 Battery Cathodes.

    PubMed

    Vankova, Svetoslava; Francia, Carlotta; Amici, Julia; Zeng, Juqin; Bodoardo, Silvia; Penazzi, Nerino; Collins, Gillian; Geaney, Hugh; O'Dwyer, Colm

    2017-02-08

    Fundamental research on Li-O2 batteries remains critical, and the nature of the reactions and stability are paramount for realising the promise of the Li-O2 system. We report that indium tin oxide (ITO) nanocrystals with supported 1-2 nm oxygen evolution reaction (OER) catalyst Ru/RuOx nanoparticles (NPs) demonstrate efficient OER processes, reduce the recharge overpotential of the cell significantly and maintain catalytic activity to promote a consistent cycling discharge potential in Li-O2 cells even when the ITO support nanocrystals deteriorate from the very first cycle. The Ru/RuOx nanoparticles lower the charge overpotential compared with those for ITO and carbon-only cathodes and have the greatest effect in DMSO electrolytes with a solution-processable F-free carboxymethyl cellulose (CMC) binder (<3.5 V) instead of polyvinylidene fluoride (PVDF). The Ru/RuOx /ITO nanocrystalline materials in DMSO provide efficient Li2 O2 decomposition from within the cathode during cycling. We demonstrate that the ITO is actually unstable from the first cycle and is modified by chemical etching, but the Ru/RuOx NPs remain effective OER catalysts for Li2 O2 during cycling. The CMC binders avoid PVDF-based side-reactions and improve the cyclability. The deterioration of the ITO nanocrystals is mitigated significantly in cathodes with a CMC binder, and the cells show good cycle life. In mixed DMSO-EMITFSI [EMITFSI=1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide] ionic liquid electrolytes, the Ru/RuOx /ITO materials in Li-O2 cells cycle very well and maintain a consistently very low charge overpotential of 0.5-0.8 V. © 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

  18. Direct Observation of Room-Temperature Polar Ordering in Colloidal GeTe Nanocrystals

    SciTech Connect

    Polking, Mark J.; Zheng, Haimei; Urban, Jeffrey J.; Milliron, Delia J.; Chan, Emory; Caldwell, Marissa A.; Raoux, Simone; Kisielowski, Christian F.; Ager III, Joel W.; Ramesh, Ramamoorthy; Alivisatos, A.P.

    2009-12-07